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/-
Copyright (c) 2020 Kevin Kappelmann. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kevin Kappelmann
-/
import Mathlib.Algebra.ContinuedFractions.ContinuantsRecurrence
import Mathlib.Algebra.ContinuedFractions.TerminatedStable
import Mathlib.Tactic.FieldSimp
import Mathlib.Tactic.Ring
/-!
# Equivalence of Recursive and Direct Computations of Convergents of Generalized Continued Fractions
## Summary
We show the equivalence of two computations of convergents (recurrence relation (`convs`) vs.
direct evaluation (`convs'`)) for generalized continued fractions
(`GenContFract`s) on linear ordered fields. We follow the proof from
[hardy2008introduction], Chapter 10. Here's a sketch:
Let `c` be a continued fraction `[h; (a₀, b₀), (a₁, b₁), (a₂, b₂),...]`, visually:
$$
c = h + \dfrac{a_0}
{b_0 + \dfrac{a_1}
{b_1 + \dfrac{a_2}
{b_2 + \dfrac{a_3}
{b_3 + \dots}}}}
$$
One can compute the convergents of `c` in two ways:
1. Directly evaluating the fraction described by `c` up to a given `n` (`convs'`)
2. Using the recurrence (`convs`):
- `A₋₁ = 1, A₀ = h, Aₙ = bₙ₋₁ * Aₙ₋₁ + aₙ₋₁ * Aₙ₋₂`, and
- `B₋₁ = 0, B₀ = 1, Bₙ = bₙ₋₁ * Bₙ₋₁ + aₙ₋₁ * Bₙ₋₂`.
To show the equivalence of the computations in the main theorem of this file
`convs_eq_convs'`, we proceed by induction. The case `n = 0` is trivial.
For `n + 1`, we first "squash" the `n + 1`th position of `c` into the `n`th position to obtain
another continued fraction
`c' := [h; (a₀, b₀),..., (aₙ-₁, bₙ-₁), (aₙ, bₙ + aₙ₊₁ / bₙ₊₁), (aₙ₊₁, bₙ₊₁),...]`.
This squashing process is formalised in section `Squash`. Note that directly evaluating `c` up to
position `n + 1` is equal to evaluating `c'` up to `n`. This is shown in lemma
`succ_nth_conv'_eq_squashGCF_nth_conv'`.
By the inductive hypothesis, the two computations for the `n`th convergent of `c` coincide.
So all that is left to show is that the recurrence relation for `c` at `n + 1` and `c'` at
`n` coincide. This can be shown by another induction.
The corresponding lemma in this file is `succ_nth_conv_eq_squashGCF_nth_conv`.
## Main Theorems
- `GenContFract.convs_eq_convs'` shows the equivalence under a strict positivity restriction
on the sequence.
- `ContFract.convs_eq_convs'` shows the equivalence for regular continued fractions.
## References
- https://en.wikipedia.org/wiki/Generalized_continued_fraction
- [*Hardy, GH and Wright, EM and Heath-Brown, Roger and Silverman, Joseph*][hardy2008introduction]
## Tags
fractions, recurrence, equivalence
-/
variable {K : Type*} {n : ℕ}
namespace GenContFract
variable {g : GenContFract K} {s : Stream'.Seq <| Pair K}
section Squash
/-!
We will show the equivalence of the computations by induction. To make the induction work, we need
to be able to *squash* the nth and (n + 1)th value of a sequence. This squashing itself and the
lemmas about it are not very interesting. As a reader, you hence might want to skip this section.
-/
section WithDivisionRing
variable [DivisionRing K]
/-- Given a sequence of `GenContFract.Pair`s `s = [(a₀, bₒ), (a₁, b₁), ...]`, `squashSeq s n`
combines `⟨aₙ, bₙ⟩` and `⟨aₙ₊₁, bₙ₊₁⟩` at position `n` to `⟨aₙ, bₙ + aₙ₊₁ / bₙ₊₁⟩`. For example,
`squashSeq s 0 = [(a₀, bₒ + a₁ / b₁), (a₁, b₁),...]`.
If `s.TerminatedAt (n + 1)`, then `squashSeq s n = s`.
-/
def squashSeq (s : Stream'.Seq <| Pair K) (n : ℕ) : Stream'.Seq (Pair K) :=
match Prod.mk (s.get? n) (s.get? (n + 1)) with
| ⟨some gp_n, some gp_succ_n⟩ =>
Stream'.Seq.nats.zipWith
-- return the squashed value at position `n`; otherwise, do nothing.
(fun n' gp => if n' = n then ⟨gp_n.a, gp_n.b + gp_succ_n.a / gp_succ_n.b⟩ else gp) s
| _ => s
/-! We now prove some simple lemmas about the squashed sequence -/
/-- If the sequence already terminated at position `n + 1`, nothing gets squashed. -/
theorem squashSeq_eq_self_of_terminated (terminatedAt_succ_n : s.TerminatedAt (n + 1)) :
squashSeq s n = s := by
change s.get? (n + 1) = none at terminatedAt_succ_n
cases s_nth_eq : s.get? n <;> simp only [*, squashSeq]
/-- If the sequence has not terminated before position `n + 1`, the value at `n + 1` gets
squashed into position `n`. -/
theorem squashSeq_nth_of_not_terminated {gp_n gp_succ_n : Pair K} (s_nth_eq : s.get? n = some gp_n)
(s_succ_nth_eq : s.get? (n + 1) = some gp_succ_n) :
(squashSeq s n).get? n = some ⟨gp_n.a, gp_n.b + gp_succ_n.a / gp_succ_n.b⟩ := by
simp [*, squashSeq]
/-- The values before the squashed position stay the same. -/
theorem squashSeq_nth_of_lt {m : ℕ} (m_lt_n : m < n) : (squashSeq s n).get? m = s.get? m := by
cases s_succ_nth_eq : s.get? (n + 1) with
| none => rw [squashSeq_eq_self_of_terminated s_succ_nth_eq]
| some =>
obtain ⟨gp_n, s_nth_eq⟩ : ∃ gp_n, s.get? n = some gp_n :=
s.ge_stable n.le_succ s_succ_nth_eq
obtain ⟨gp_m, s_mth_eq⟩ : ∃ gp_m, s.get? m = some gp_m :=
s.ge_stable (le_of_lt m_lt_n) s_nth_eq
simp [*, squashSeq, m_lt_n.ne]
/-- Squashing at position `n + 1` and taking the tail is the same as squashing the tail of the
sequence at position `n`. -/
theorem squashSeq_succ_n_tail_eq_squashSeq_tail_n :
(squashSeq s (n + 1)).tail = squashSeq s.tail n := by
cases s_succ_succ_nth_eq : s.get? (n + 2) with
| none =>
cases s_succ_nth_eq : s.get? (n + 1) <;>
simp only [squashSeq, Stream'.Seq.get?_tail, s_succ_nth_eq, s_succ_succ_nth_eq]
| some gp_succ_succ_n =>
obtain ⟨gp_succ_n, s_succ_nth_eq⟩ : ∃ gp_succ_n, s.get? (n + 1) = some gp_succ_n :=
s.ge_stable (n + 1).le_succ s_succ_succ_nth_eq
-- apply extensionality with `m` and continue by cases `m = n`.
ext1 m
rcases Decidable.em (m = n) with m_eq_n | m_ne_n
· simp [*, squashSeq]
· cases s_succ_mth_eq : s.get? (m + 1)
· simp only [*, squashSeq, Stream'.Seq.get?_tail, Stream'.Seq.get?_zipWith,
Option.map₂_none_right]
· simp [*, squashSeq]
/-- The auxiliary function `convs'Aux` returns the same value for a sequence and the
corresponding squashed sequence at the squashed position. -/
theorem succ_succ_nth_conv'Aux_eq_succ_nth_conv'Aux_squashSeq :
convs'Aux s (n + 2) = convs'Aux (squashSeq s n) (n + 1) := by
cases s_succ_nth_eq : s.get? <| n + 1 with
| none =>
rw [squashSeq_eq_self_of_terminated s_succ_nth_eq,
convs'Aux_stable_step_of_terminated s_succ_nth_eq]
| some gp_succ_n =>
induction n generalizing s gp_succ_n with
| zero =>
obtain ⟨gp_head, s_head_eq⟩ : ∃ gp_head, s.head = some gp_head :=
s.ge_stable zero_le_one s_succ_nth_eq
have : (squashSeq s 0).head = some ⟨gp_head.a, gp_head.b + gp_succ_n.a / gp_succ_n.b⟩ :=
squashSeq_nth_of_not_terminated s_head_eq s_succ_nth_eq
simp_all [convs'Aux, Stream'.Seq.head, Stream'.Seq.get?_tail]
| succ m IH =>
obtain ⟨gp_head, s_head_eq⟩ : ∃ gp_head, s.head = some gp_head :=
s.ge_stable (m + 2).zero_le s_succ_nth_eq
suffices
gp_head.a / (gp_head.b + convs'Aux s.tail (m + 2)) =
convs'Aux (squashSeq s (m + 1)) (m + 2)
by simpa only [convs'Aux, s_head_eq]
have : (squashSeq s (m + 1)).head = some gp_head :=
(squashSeq_nth_of_lt m.succ_pos).trans s_head_eq
simp_all [convs'Aux, squashSeq_succ_n_tail_eq_squashSeq_tail_n]
/-! Let us now lift the squashing operation to gcfs. -/
/-- Given a gcf `g = [h; (a₀, bₒ), (a₁, b₁), ...]`, we have
- `squashGCF g 0 = [h + a₀ / b₀); (a₀, bₒ), ...]`,
- `squashGCF g (n + 1) = ⟨g.h, squashSeq g.s n⟩`
-/
def squashGCF (g : GenContFract K) : ℕ → GenContFract K
| 0 =>
match g.s.get? 0 with
| none => g
| some gp => ⟨g.h + gp.a / gp.b, g.s⟩
| n + 1 => ⟨g.h, squashSeq g.s n⟩
/-! Again, we derive some simple lemmas that are not really of interest. This time for the
squashed gcf. -/
/-- If the gcf already terminated at position `n`, nothing gets squashed. -/
theorem squashGCF_eq_self_of_terminated (terminatedAt_n : TerminatedAt g n) :
squashGCF g n = g := by
cases n with
| zero =>
change g.s.get? 0 = none at terminatedAt_n
simp only [convs', squashGCF, convs'Aux, terminatedAt_n]
| succ =>
cases g
simp only [squashGCF, mk.injEq, true_and]
exact squashSeq_eq_self_of_terminated terminatedAt_n
/-- The values before the squashed position stay the same. -/
theorem squashGCF_nth_of_lt {m : ℕ} (m_lt_n : m < n) :
(squashGCF g (n + 1)).s.get? m = g.s.get? m := by
simp only [squashGCF, squashSeq_nth_of_lt m_lt_n, Nat.add_eq, add_zero]
/-- `convs'` returns the same value for a gcf and the corresponding squashed gcf at the
squashed position. -/
theorem succ_nth_conv'_eq_squashGCF_nth_conv' :
g.convs' (n + 1) = (squashGCF g n).convs' n := by
cases n with
| zero =>
cases g_s_head_eq : g.s.get? 0 <;>
simp [g_s_head_eq, squashGCF, convs', convs'Aux, Stream'.Seq.head]
| succ =>
simp only [succ_succ_nth_conv'Aux_eq_succ_nth_conv'Aux_squashSeq, convs',
squashGCF]
/-- The auxiliary continuants before the squashed position stay the same. -/
theorem contsAux_eq_contsAux_squashGCF_of_le {m : ℕ} :
m ≤ n → contsAux g m = (squashGCF g n).contsAux m :=
Nat.strong_induction_on m
(by
clear m
intro m IH m_le_n
rcases m with - | m'
· rfl
· rcases n with - | n'
· exact (m'.not_succ_le_zero m_le_n).elim
-- 1 ≰ 0
· rcases m' with - | m''
· rfl
· -- get some inequalities to instantiate the IH for m'' and m'' + 1
have m'_lt_n : m'' + 1 < n' + 1 := m_le_n
have succ_m''th_contsAux_eq := IH (m'' + 1) (lt_add_one (m'' + 1)) m'_lt_n.le
have : m'' < m'' + 2 := lt_add_of_pos_right m'' zero_lt_two
have m''th_contsAux_eq := IH m'' this (le_trans this.le m_le_n)
have : (squashGCF g (n' + 1)).s.get? m'' = g.s.get? m'' :=
squashGCF_nth_of_lt (Nat.succ_lt_succ_iff.mp m'_lt_n)
simp [contsAux, succ_m''th_contsAux_eq, m''th_contsAux_eq, this])
end WithDivisionRing
/-- The convergents coincide in the expected way at the squashed position if the partial denominator
at the squashed position is not zero. -/
theorem succ_nth_conv_eq_squashGCF_nth_conv [Field K]
(nth_partDen_ne_zero : ∀ {b : K}, g.partDens.get? n = some b → b ≠ 0) :
g.convs (n + 1) = (squashGCF g n).convs n := by
rcases Decidable.em (g.TerminatedAt n) with terminatedAt_n | not_terminatedAt_n
· have : squashGCF g n = g := squashGCF_eq_self_of_terminated terminatedAt_n
simp only [this, convs_stable_of_terminated n.le_succ terminatedAt_n]
· obtain ⟨⟨a, b⟩, s_nth_eq⟩ : ∃ gp_n, g.s.get? n = some gp_n :=
Option.ne_none_iff_exists'.mp not_terminatedAt_n
have b_ne_zero : b ≠ 0 := nth_partDen_ne_zero (partDen_eq_s_b s_nth_eq)
cases n with
| zero =>
suffices (b * g.h + a) / b = g.h + a / b by
simpa [squashGCF, s_nth_eq, conv_eq_conts_a_div_conts_b,
conts_recurrenceAux s_nth_eq zeroth_contAux_eq_one_zero first_contAux_eq_h_one]
calc
(b * g.h + a) / b = b * g.h / b + a / b := by ring
-- requires `Field`, not `DivisionRing`
_ = g.h + a / b := by rw [mul_div_cancel_left₀ _ b_ne_zero]
| succ n' =>
obtain ⟨⟨pa, pb⟩, s_n'th_eq⟩ : ∃ gp_n', g.s.get? n' = some gp_n' :=
g.s.ge_stable n'.le_succ s_nth_eq
-- Notations
let g' := squashGCF g (n' + 1)
set pred_conts := g.contsAux (n' + 1) with succ_n'th_contsAux_eq
set ppred_conts := g.contsAux n' with n'th_contsAux_eq
let pA := pred_conts.a
let pB := pred_conts.b
let ppA := ppred_conts.a
let ppB := ppred_conts.b
set pred_conts' := g'.contsAux (n' + 1) with succ_n'th_contsAux_eq'
set ppred_conts' := g'.contsAux n' with n'th_contsAux_eq'
let pA' := pred_conts'.a
let pB' := pred_conts'.b
let ppA' := ppred_conts'.a
let ppB' := ppred_conts'.b
-- first compute the convergent of the squashed gcf
have : g'.convs (n' + 1) =
((pb + a / b) * pA' + pa * ppA') / ((pb + a / b) * pB' + pa * ppB') := by
have : g'.s.get? n' = some ⟨pa, pb + a / b⟩ :=
squashSeq_nth_of_not_terminated s_n'th_eq s_nth_eq
rw [conv_eq_conts_a_div_conts_b,
conts_recurrenceAux this n'th_contsAux_eq'.symm succ_n'th_contsAux_eq'.symm]
rw [this]
-- then compute the convergent of the original gcf by recursively unfolding the continuants
-- computation twice
have : g.convs (n' + 2) =
(b * (pb * pA + pa * ppA) + a * pA) / (b * (pb * pB + pa * ppB) + a * pB) := by
-- use the recurrence once
have : g.contsAux (n' + 2) = ⟨pb * pA + pa * ppA, pb * pB + pa * ppB⟩ :=
contsAux_recurrence s_n'th_eq n'th_contsAux_eq.symm succ_n'th_contsAux_eq.symm
-- and a second time
rw [conv_eq_conts_a_div_conts_b,
conts_recurrenceAux s_nth_eq succ_n'th_contsAux_eq.symm this]
rw [this]
suffices
((pb + a / b) * pA + pa * ppA) / ((pb + a / b) * pB + pa * ppB) =
(b * (pb * pA + pa * ppA) + a * pA) / (b * (pb * pB + pa * ppB) + a * pB) by
obtain ⟨eq1, eq2, eq3, eq4⟩ : pA' = pA ∧ pB' = pB ∧ ppA' = ppA ∧ ppB' = ppB := by
simp [*, g', pA, pB, ppA, ppB, pA', pB', ppA', ppB',
(contsAux_eq_contsAux_squashGCF_of_le <| le_refl <| n' + 1).symm,
(contsAux_eq_contsAux_squashGCF_of_le n'.le_succ).symm]
symm
simpa only [eq1, eq2, eq3, eq4, mul_div_cancel_right₀ _ b_ne_zero]
field_simp
congr 1 <;> ring
end Squash
/-- Shows that the recurrence relation (`convs`) and direct evaluation (`convs'`) of the
generalized continued fraction coincide at position `n` if the sequence of fractions contains
strictly positive values only.
Requiring positivity of all values is just one possible condition to obtain this result.
For example, the dual - sequences with strictly negative values only - would also work.
In practice, one most commonly deals with regular continued fractions, which satisfy the
positivity criterion required here. The analogous result for them
(see `ContFract.convs_eq_convs`) hence follows directly from this theorem.
-/
theorem convs_eq_convs' [Field K] [LinearOrder K] [IsStrictOrderedRing K]
(s_pos : ∀ {gp : Pair K} {m : ℕ}, m < n → g.s.get? m = some gp → 0 < gp.a ∧ 0 < gp.b) :
g.convs n = g.convs' n := by
induction n generalizing g with
| zero => simp
| succ n IH =>
let g' := squashGCF g n
-- first replace the rhs with the squashed computation
suffices g.convs (n + 1) = g'.convs' n by
rwa [succ_nth_conv'_eq_squashGCF_nth_conv']
rcases Decidable.em (TerminatedAt g n) with terminatedAt_n | not_terminatedAt_n
· have g'_eq_g : g' = g := squashGCF_eq_self_of_terminated terminatedAt_n
rw [convs_stable_of_terminated n.le_succ terminatedAt_n, g'_eq_g, IH _]
intro _ _ m_lt_n s_mth_eq
exact s_pos (Nat.lt.step m_lt_n) s_mth_eq
· suffices g.convs (n + 1) = g'.convs n by
-- invoke the IH for the squashed gcf
rwa [← IH]
intro gp' m m_lt_n s_mth_eq'
-- case distinction on m + 1 = n or m + 1 < n
rcases m_lt_n with n | succ_m_lt_n
· -- the difficult case at the squashed position: we first obtain the values from
-- the sequence
obtain ⟨gp_succ_m, s_succ_mth_eq⟩ : ∃ gp_succ_m, g.s.get? (m + 1) = some gp_succ_m :=
Option.ne_none_iff_exists'.mp not_terminatedAt_n
obtain ⟨gp_m, mth_s_eq⟩ : ∃ gp_m, g.s.get? m = some gp_m :=
g.s.ge_stable m.le_succ s_succ_mth_eq
-- we then plug them into the recurrence
suffices 0 < gp_m.a ∧ 0 < gp_m.b + gp_succ_m.a / gp_succ_m.b by
have ot : g'.s.get? m = some ⟨gp_m.a, gp_m.b + gp_succ_m.a / gp_succ_m.b⟩ :=
squashSeq_nth_of_not_terminated mth_s_eq s_succ_mth_eq
have : gp' = ⟨gp_m.a, gp_m.b + gp_succ_m.a / gp_succ_m.b⟩ := by
simp_all only [Option.some.injEq]
rwa [this]
have m_lt_n : m < m.succ := Nat.lt_succ_self m
refine ⟨(s_pos (Nat.lt.step m_lt_n) mth_s_eq).left, ?_⟩
refine add_pos (s_pos (Nat.lt.step m_lt_n) mth_s_eq).right ?_
have : 0 < gp_succ_m.a ∧ 0 < gp_succ_m.b := s_pos (lt_add_one <| m + 1) s_succ_mth_eq
exact div_pos this.left this.right
· -- the easy case: before the squashed position, nothing changes
refine s_pos (Nat.lt.step <| Nat.lt.step succ_m_lt_n) ?_
exact Eq.trans (squashGCF_nth_of_lt succ_m_lt_n).symm s_mth_eq'
-- now the result follows from the fact that the convergents coincide at the squashed position
-- as established in `succ_nth_conv_eq_squashGCF_nth_conv`.
have : ∀ ⦃b⦄, g.partDens.get? n = some b → b ≠ 0 := by
intro b nth_partDen_eq
obtain ⟨gp, s_nth_eq, ⟨refl⟩⟩ : ∃ gp, g.s.get? n = some gp ∧ gp.b = b :=
exists_s_b_of_partDen nth_partDen_eq
exact (ne_of_lt (s_pos (lt_add_one n) s_nth_eq).right).symm
exact succ_nth_conv_eq_squashGCF_nth_conv @this
end GenContFract
open GenContFract
namespace ContFract
/-- Shows that the recurrence relation (`convs`) and direct evaluation (`convs'`) of a
(regular) continued fraction coincide. -/
nonrec theorem convs_eq_convs' [Field K] [LinearOrder K] [IsStrictOrderedRing K]
{c : ContFract K} :
(↑c : GenContFract K).convs = (↑c : GenContFract K).convs' := by
ext n
apply convs_eq_convs'
intro gp m _ s_nth_eq
exact ⟨zero_lt_one.trans_le ((c : SimpContFract K).property m gp.a
(partNum_eq_s_a s_nth_eq)).symm.le, c.property m gp.b <| partDen_eq_s_b s_nth_eq⟩
end ContFract
| Mathlib/Algebra/ContinuedFractions/ConvergentsEquiv.lean | 402 | 409 | |
/-
Copyright (c) 2014 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Data.Int.Cast.Defs
import Mathlib.Logic.Basic
/-!
# Characteristic zero
A ring `R` is called of characteristic zero if every natural number `n` is non-zero when considered
as an element of `R`. Since this definition doesn't mention the multiplicative structure of `R`
except for the existence of `1` in this file characteristic zero is defined for additive monoids
with `1`.
## Main definition
`CharZero` is the typeclass of an additive monoid with one such that the natural homomorphism
from the natural numbers into it is injective.
## TODO
* Unify with `CharP` (possibly using an out-parameter)
-/
/-- Typeclass for monoids with characteristic zero.
(This is usually stated on fields but it makes sense for any additive monoid with 1.)
*Warning*: for a semiring `R`, `CharZero R` and `CharP R 0` need not coincide.
* `CharZero R` requires an injection `ℕ ↪ R`;
* `CharP R 0` asks that only `0 : ℕ` maps to `0 : R` under the map `ℕ → R`.
For instance, endowing `{0, 1}` with addition given by `max` (i.e. `1` is absorbing), shows that
`CharZero {0, 1}` does not hold and yet `CharP {0, 1} 0` does.
This example is formalized in `Counterexamples/CharPZeroNeCharZero.lean`.
-/
class CharZero (R) [AddMonoidWithOne R] : Prop where
/-- An additive monoid with one has characteristic zero if the canonical map `ℕ → R` is
injective. -/
cast_injective : Function.Injective (Nat.cast : ℕ → R)
variable {R : Type*}
theorem charZero_of_inj_zero [AddGroupWithOne R] (H : ∀ n : ℕ, (n : R) = 0 → n = 0) :
CharZero R :=
⟨@fun m n h => by
induction m generalizing n with
| zero => rw [H n]; rw [← h, Nat.cast_zero]
| succ m ih =>
cases n
· apply H; rw [h, Nat.cast_zero]
· simp only [Nat.cast_succ, add_right_cancel_iff] at h; rwa [ih]⟩
namespace Nat
variable [AddMonoidWithOne R] [CharZero R]
theorem cast_injective : Function.Injective (Nat.cast : ℕ → R) :=
CharZero.cast_injective
@[simp, norm_cast]
theorem cast_inj {m n : ℕ} : (m : R) = n ↔ m = n :=
cast_injective.eq_iff
@[simp, norm_cast]
theorem cast_eq_zero {n : ℕ} : (n : R) = 0 ↔ n = 0 := by rw [← cast_zero, cast_inj]
@[norm_cast]
theorem cast_ne_zero {n : ℕ} : (n : R) ≠ 0 ↔ n ≠ 0 :=
not_congr cast_eq_zero
theorem cast_add_one_ne_zero (n : ℕ) : (n + 1 : R) ≠ 0 :=
mod_cast n.succ_ne_zero
@[simp, norm_cast]
theorem cast_eq_one {n : ℕ} : (n : R) = 1 ↔ n = 1 := by rw [← cast_one, cast_inj]
@[norm_cast]
theorem cast_ne_one {n : ℕ} : (n : R) ≠ 1 ↔ n ≠ 1 :=
cast_eq_one.not
instance (priority := 100) AtLeastTwo.toNeZero (n : ℕ) [n.AtLeastTwo] : NeZero n :=
⟨Nat.ne_of_gt (Nat.le_of_lt one_lt)⟩
end Nat
namespace OfNat
variable [AddMonoidWithOne R] [CharZero R]
| @[simp] lemma ofNat_ne_zero (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : R) ≠ 0 :=
| Mathlib/Algebra/CharZero/Defs.lean | 92 | 92 |
/-
Copyright (c) 2022 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies
-/
import Mathlib.Data.Set.Lattice.Image
import Mathlib.Order.Hom.BoundedLattice
/-!
# Complete lattice homomorphisms
This file defines frame homomorphisms and complete lattice homomorphisms.
We use the `DFunLike` design, so each type of morphisms has a companion typeclass which is meant to
be satisfied by itself and all stricter types.
## Types of morphisms
* `sSupHom`: Maps which preserve `⨆`.
* `sInfHom`: Maps which preserve `⨅`.
* `FrameHom`: Frame homomorphisms. Maps which preserve `⨆`, `⊓` and `⊤`.
* `CompleteLatticeHom`: Complete lattice homomorphisms. Maps which preserve `⨆` and `⨅`.
## Typeclasses
* `sSupHomClass`
* `sInfHomClass`
* `FrameHomClass`
* `CompleteLatticeHomClass`
## Concrete homs
* `CompleteLatticeHom.setPreimage`: `Set.preimage` as a complete lattice homomorphism.
## TODO
Frame homs are Heyting homs.
-/
assert_not_exists Monoid
open Function OrderDual Set
variable {F α β γ δ : Type*} {ι : Sort*} {κ : ι → Sort*}
/-- The type of `⨆`-preserving functions from `α` to `β`. -/
structure sSupHom (α β : Type*) [SupSet α] [SupSet β] where
/-- The underlying function of a sSupHom. -/
toFun : α → β
/-- The proposition that a `sSupHom` commutes with arbitrary suprema/joins. -/
map_sSup' (s : Set α) : toFun (sSup s) = sSup (toFun '' s)
/-- The type of `⨅`-preserving functions from `α` to `β`. -/
structure sInfHom (α β : Type*) [InfSet α] [InfSet β] where
/-- The underlying function of an `sInfHom`. -/
toFun : α → β
/-- The proposition that a `sInfHom` commutes with arbitrary infima/meets -/
map_sInf' (s : Set α) : toFun (sInf s) = sInf (toFun '' s)
/-- The type of frame homomorphisms from `α` to `β`. They preserve finite meets and arbitrary joins.
-/
structure FrameHom (α β : Type*) [CompleteLattice α] [CompleteLattice β] extends
InfTopHom α β where
/-- The proposition that frame homomorphisms commute with arbitrary suprema/joins. -/
map_sSup' (s : Set α) : toFun (sSup s) = sSup (toFun '' s)
/-- The type of complete lattice homomorphisms from `α` to `β`. -/
structure CompleteLatticeHom (α β : Type*) [CompleteLattice α] [CompleteLattice β] extends
sInfHom α β where
/-- The proposition that complete lattice homomorphism commutes with arbitrary suprema/joins. -/
map_sSup' (s : Set α) : toFun (sSup s) = sSup (toFun '' s)
section
/-- `sSupHomClass F α β` states that `F` is a type of `⨆`-preserving morphisms.
You should extend this class when you extend `sSupHom`. -/
class sSupHomClass (F α β : Type*) [SupSet α] [SupSet β] [FunLike F α β] : Prop where
/-- The proposition that members of `sSupHomClass`s commute with arbitrary suprema/joins. -/
map_sSup (f : F) (s : Set α) : f (sSup s) = sSup (f '' s)
/-- `sInfHomClass F α β` states that `F` is a type of `⨅`-preserving morphisms.
You should extend this class when you extend `sInfHom`. -/
class sInfHomClass (F α β : Type*) [InfSet α] [InfSet β] [FunLike F α β] : Prop where
/-- The proposition that members of `sInfHomClass`s commute with arbitrary infima/meets. -/
map_sInf (f : F) (s : Set α) : f (sInf s) = sInf (f '' s)
/-- `FrameHomClass F α β` states that `F` is a type of frame morphisms. They preserve `⊓` and `⨆`.
You should extend this class when you extend `FrameHom`. -/
class FrameHomClass (F α β : Type*) [CompleteLattice α] [CompleteLattice β] [FunLike F α β] : Prop
extends InfTopHomClass F α β where
/-- The proposition that members of `FrameHomClass` commute with arbitrary suprema/joins. -/
map_sSup (f : F) (s : Set α) : f (sSup s) = sSup (f '' s)
/-- `CompleteLatticeHomClass F α β` states that `F` is a type of complete lattice morphisms.
You should extend this class when you extend `CompleteLatticeHom`. -/
class CompleteLatticeHomClass (F α β : Type*) [CompleteLattice α] [CompleteLattice β]
[FunLike F α β] : Prop
extends sInfHomClass F α β where
/-- The proposition that members of `CompleteLatticeHomClass` commute with arbitrary
suprema/joins. -/
map_sSup (f : F) (s : Set α) : f (sSup s) = sSup (f '' s)
end
export sSupHomClass (map_sSup)
export sInfHomClass (map_sInf)
attribute [simp] map_sSup map_sInf
section Hom
variable [FunLike F α β]
@[simp] theorem map_iSup [SupSet α] [SupSet β] [sSupHomClass F α β] (f : F) (g : ι → α) :
f (⨆ i, g i) = ⨆ i, f (g i) := by simp [iSup, ← Set.range_comp, Function.comp_def]
theorem map_iSup₂ [SupSet α] [SupSet β] [sSupHomClass F α β] (f : F) (g : ∀ i, κ i → α) :
f (⨆ (i) (j), g i j) = ⨆ (i) (j), f (g i j) := by simp_rw [map_iSup]
@[simp] theorem map_iInf [InfSet α] [InfSet β] [sInfHomClass F α β] (f : F) (g : ι → α) :
f (⨅ i, g i) = ⨅ i, f (g i) := by simp [iInf, ← Set.range_comp, Function.comp_def]
theorem map_iInf₂ [InfSet α] [InfSet β] [sInfHomClass F α β] (f : F) (g : ∀ i, κ i → α) :
f (⨅ (i) (j), g i j) = ⨅ (i) (j), f (g i j) := by simp_rw [map_iInf]
-- See note [lower instance priority]
instance (priority := 100) sSupHomClass.toSupBotHomClass [CompleteLattice α]
[CompleteLattice β] [sSupHomClass F α β] : SupBotHomClass F α β :=
{ ‹sSupHomClass F α β› with
map_sup := fun f a b => by
rw [← sSup_pair, map_sSup]
simp only [Set.image_pair, sSup_insert, sSup_singleton]
map_bot := fun f => by
rw [← sSup_empty, map_sSup, Set.image_empty, sSup_empty] }
-- See note [lower instance priority]
instance (priority := 100) sInfHomClass.toInfTopHomClass [CompleteLattice α]
[CompleteLattice β] [sInfHomClass F α β] : InfTopHomClass F α β :=
{ ‹sInfHomClass F α β› with
map_inf := fun f a b => by
rw [← sInf_pair, map_sInf, Set.image_pair]
simp only [Set.image_pair, sInf_insert, sInf_singleton]
map_top := fun f => by
rw [← sInf_empty, map_sInf, Set.image_empty, sInf_empty] }
-- See note [lower instance priority]
instance (priority := 100) FrameHomClass.tosSupHomClass [CompleteLattice α]
[CompleteLattice β] [FrameHomClass F α β] : sSupHomClass F α β :=
{ ‹FrameHomClass F α β› with }
-- See note [lower instance priority]
instance (priority := 100) FrameHomClass.toBoundedLatticeHomClass [CompleteLattice α]
[CompleteLattice β] [FrameHomClass F α β] : BoundedLatticeHomClass F α β :=
{ ‹FrameHomClass F α β›, sSupHomClass.toSupBotHomClass with }
-- See note [lower instance priority]
instance (priority := 100) CompleteLatticeHomClass.toFrameHomClass [CompleteLattice α]
[CompleteLattice β] [CompleteLatticeHomClass F α β] : FrameHomClass F α β :=
{ ‹CompleteLatticeHomClass F α β›, sInfHomClass.toInfTopHomClass with }
-- See note [lower instance priority]
instance (priority := 100) CompleteLatticeHomClass.toBoundedLatticeHomClass [CompleteLattice α]
[CompleteLattice β] [CompleteLatticeHomClass F α β] : BoundedLatticeHomClass F α β :=
{ sSupHomClass.toSupBotHomClass, sInfHomClass.toInfTopHomClass with }
end Hom
section Equiv
variable [EquivLike F α β]
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.tosSupHomClass [CompleteLattice α]
[CompleteLattice β] [OrderIsoClass F α β] : sSupHomClass F α β :=
{ show OrderHomClass F α β from inferInstance with
map_sSup := fun f s =>
eq_of_forall_ge_iff fun c => by
simp only [← le_map_inv_iff, sSup_le_iff, Set.forall_mem_image] }
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.tosInfHomClass [CompleteLattice α]
[CompleteLattice β] [OrderIsoClass F α β] : sInfHomClass F α β :=
{ show OrderHomClass F α β from inferInstance with
map_sInf := fun f s =>
eq_of_forall_le_iff fun c => by
simp only [← map_inv_le_iff, le_sInf_iff, Set.forall_mem_image] }
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.toCompleteLatticeHomClass [CompleteLattice α]
[CompleteLattice β] [OrderIsoClass F α β] : CompleteLatticeHomClass F α β :=
{ OrderIsoClass.tosSupHomClass, OrderIsoClass.tosInfHomClass with }
end Equiv
variable [FunLike F α β]
/-- Reinterpret an order isomorphism as a morphism of complete lattices. -/
@[simps] def OrderIso.toCompleteLatticeHom [CompleteLattice α] [CompleteLattice β]
(f : OrderIso α β) : CompleteLatticeHom α β where
toFun := f
map_sInf' := sInfHomClass.map_sInf f
map_sSup' := sSupHomClass.map_sSup f
instance [SupSet α] [SupSet β] [sSupHomClass F α β] : CoeTC F (sSupHom α β) :=
⟨fun f => ⟨f, map_sSup f⟩⟩
instance [InfSet α] [InfSet β] [sInfHomClass F α β] : CoeTC F (sInfHom α β) :=
⟨fun f => ⟨f, map_sInf f⟩⟩
instance [CompleteLattice α] [CompleteLattice β] [FrameHomClass F α β] : CoeTC F (FrameHom α β) :=
⟨fun f => ⟨f, map_sSup f⟩⟩
instance [CompleteLattice α] [CompleteLattice β] [CompleteLatticeHomClass F α β] :
CoeTC F (CompleteLatticeHom α β) :=
⟨fun f => ⟨f, map_sSup f⟩⟩
/-! ### Supremum homomorphisms -/
namespace sSupHom
variable [SupSet α]
section SupSet
variable [SupSet β] [SupSet γ] [SupSet δ]
instance : FunLike (sSupHom α β) α β where
coe := sSupHom.toFun
coe_injective' f g h := by cases f; cases g; congr
instance : sSupHomClass (sSupHom α β) α β where
map_sSup := sSupHom.map_sSup'
@[simp] lemma toFun_eq_coe (f : sSupHom α β) : f.toFun = f := rfl
@[simp, norm_cast] lemma coe_mk (f : α → β) (hf) : ⇑(mk f hf) = f := rfl
@[ext]
theorem ext {f g : sSupHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
/-- Copy of a `sSupHom` with a new `toFun` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (f : sSupHom α β) (f' : α → β) (h : f' = f) : sSupHom α β where
toFun := f'
map_sSup' := h.symm ▸ f.map_sSup'
@[simp]
theorem coe_copy (f : sSupHom α β) (f' : α → β) (h : f' = f) : ⇑(f.copy f' h) = f' :=
rfl
theorem copy_eq (f : sSupHom α β) (f' : α → β) (h : f' = f) : f.copy f' h = f :=
DFunLike.ext' h
variable (α)
/-- `id` as a `sSupHom`. -/
protected def id : sSupHom α α :=
⟨id, fun s => by rw [id, Set.image_id]⟩
instance : Inhabited (sSupHom α α) :=
⟨sSupHom.id α⟩
@[simp, norm_cast]
theorem coe_id : ⇑(sSupHom.id α) = id :=
rfl
variable {α}
@[simp]
theorem id_apply (a : α) : sSupHom.id α a = a :=
rfl
/-- Composition of `sSupHom`s as a `sSupHom`. -/
def comp (f : sSupHom β γ) (g : sSupHom α β) : sSupHom α γ where
toFun := f ∘ g
map_sSup' s := by rw [comp_apply, map_sSup, map_sSup, Set.image_image]; simp only [Function.comp]
@[simp]
theorem coe_comp (f : sSupHom β γ) (g : sSupHom α β) : ⇑(f.comp g) = f ∘ g :=
rfl
@[simp]
theorem comp_apply (f : sSupHom β γ) (g : sSupHom α β) (a : α) : (f.comp g) a = f (g a) :=
rfl
@[simp]
theorem comp_assoc (f : sSupHom γ δ) (g : sSupHom β γ) (h : sSupHom α β) :
(f.comp g).comp h = f.comp (g.comp h) :=
rfl
@[simp]
theorem comp_id (f : sSupHom α β) : f.comp (sSupHom.id α) = f :=
ext fun _ => rfl
@[simp]
theorem id_comp (f : sSupHom α β) : (sSupHom.id β).comp f = f :=
ext fun _ => rfl
@[simp]
theorem cancel_right {g₁ g₂ : sSupHom β γ} {f : sSupHom α β} (hf : Surjective f) :
g₁.comp f = g₂.comp f ↔ g₁ = g₂ :=
⟨fun h => ext <| hf.forall.2 <| DFunLike.ext_iff.1 h, congr_arg (fun a ↦ comp a f)⟩
@[simp]
theorem cancel_left {g : sSupHom β γ} {f₁ f₂ : sSupHom α β} (hg : Injective g) :
g.comp f₁ = g.comp f₂ ↔ f₁ = f₂ :=
⟨fun h => ext fun a => hg <| by rw [← comp_apply, h, comp_apply], congr_arg _⟩
end SupSet
variable {_ : CompleteLattice β}
instance : PartialOrder (sSupHom α β) :=
PartialOrder.lift _ DFunLike.coe_injective
instance : Bot (sSupHom α β) :=
⟨⟨fun _ => ⊥, fun s => by
obtain rfl | hs := s.eq_empty_or_nonempty
· rw [Set.image_empty, sSup_empty]
· rw [hs.image_const, sSup_singleton]⟩⟩
instance : OrderBot (sSupHom α β) where
bot := ⊥
bot_le := fun _ _ ↦ CompleteLattice.bot_le _
@[simp]
theorem coe_bot : ⇑(⊥ : sSupHom α β) = ⊥ :=
rfl
@[simp]
theorem bot_apply (a : α) : (⊥ : sSupHom α β) a = ⊥ :=
rfl
end sSupHom
/-! ### Infimum homomorphisms -/
namespace sInfHom
variable [InfSet α]
section InfSet
variable [InfSet β] [InfSet γ] [InfSet δ]
instance : FunLike (sInfHom α β) α β where
coe := sInfHom.toFun
coe_injective' f g h := by cases f; cases g; congr
instance : sInfHomClass (sInfHom α β) α β where
map_sInf := sInfHom.map_sInf'
@[simp] lemma toFun_eq_coe (f : sInfHom α β) : f.toFun = f := rfl
@[simp] lemma coe_mk (f : α → β) (hf) : ⇑(mk f hf) = f := rfl
@[ext]
theorem ext {f g : sInfHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
/-- Copy of a `sInfHom` with a new `toFun` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (f : sInfHom α β) (f' : α → β) (h : f' = f) : sInfHom α β where
toFun := f'
map_sInf' := h.symm ▸ f.map_sInf'
@[simp]
theorem coe_copy (f : sInfHom α β) (f' : α → β) (h : f' = f) : ⇑(f.copy f' h) = f' :=
rfl
theorem copy_eq (f : sInfHom α β) (f' : α → β) (h : f' = f) : f.copy f' h = f :=
DFunLike.ext' h
variable (α)
/-- `id` as an `sInfHom`. -/
protected def id : sInfHom α α :=
⟨id, fun s => by rw [id, Set.image_id]⟩
instance : Inhabited (sInfHom α α) :=
⟨sInfHom.id α⟩
@[simp, norm_cast]
theorem coe_id : ⇑(sInfHom.id α) = id :=
rfl
variable {α}
@[simp]
theorem id_apply (a : α) : sInfHom.id α a = a :=
rfl
/-- Composition of `sInfHom`s as a `sInfHom`. -/
def comp (f : sInfHom β γ) (g : sInfHom α β) : sInfHom α γ where
toFun := f ∘ g
map_sInf' s := by rw [comp_apply, map_sInf, map_sInf, Set.image_image]; simp only [Function.comp]
@[simp]
theorem coe_comp (f : sInfHom β γ) (g : sInfHom α β) : ⇑(f.comp g) = f ∘ g :=
rfl
@[simp]
theorem comp_apply (f : sInfHom β γ) (g : sInfHom α β) (a : α) : (f.comp g) a = f (g a) :=
rfl
@[simp]
theorem comp_assoc (f : sInfHom γ δ) (g : sInfHom β γ) (h : sInfHom α β) :
(f.comp g).comp h = f.comp (g.comp h) :=
rfl
@[simp]
theorem comp_id (f : sInfHom α β) : f.comp (sInfHom.id α) = f :=
ext fun _ => rfl
@[simp]
theorem id_comp (f : sInfHom α β) : (sInfHom.id β).comp f = f :=
ext fun _ => rfl
@[simp]
theorem cancel_right {g₁ g₂ : sInfHom β γ} {f : sInfHom α β} (hf : Surjective f) :
g₁.comp f = g₂.comp f ↔ g₁ = g₂ :=
⟨fun h => ext <| hf.forall.2 <| DFunLike.ext_iff.1 h, congr_arg (fun a ↦ comp a f)⟩
@[simp]
theorem cancel_left {g : sInfHom β γ} {f₁ f₂ : sInfHom α β} (hg : Injective g) :
g.comp f₁ = g.comp f₂ ↔ f₁ = f₂ :=
⟨fun h => ext fun a => hg <| by rw [← comp_apply, h, comp_apply], congr_arg _⟩
end InfSet
variable [CompleteLattice β]
instance : PartialOrder (sInfHom α β) :=
PartialOrder.lift _ DFunLike.coe_injective
instance : Top (sInfHom α β) :=
⟨⟨fun _ => ⊤, fun s => by
obtain rfl | hs := s.eq_empty_or_nonempty
· rw [Set.image_empty, sInf_empty]
· rw [hs.image_const, sInf_singleton]⟩⟩
instance : OrderTop (sInfHom α β) where
top := ⊤
le_top := fun _ _ => CompleteLattice.le_top _
@[simp]
theorem coe_top : ⇑(⊤ : sInfHom α β) = ⊤ :=
rfl
@[simp]
theorem top_apply (a : α) : (⊤ : sInfHom α β) a = ⊤ :=
rfl
end sInfHom
/-! ### Frame homomorphisms -/
namespace FrameHom
variable [CompleteLattice α] [CompleteLattice β] [CompleteLattice γ] [CompleteLattice δ]
instance : FunLike (FrameHom α β) α β where
coe f := f.toFun
coe_injective' f g h := by
obtain ⟨⟨⟨_, _⟩, _⟩, _⟩ := f
obtain ⟨⟨⟨_, _⟩, _⟩, _⟩ := g
congr
instance : FrameHomClass (FrameHom α β) α β where
map_sSup f := f.map_sSup'
map_inf f := f.map_inf'
map_top f := f.map_top'
/-- Reinterpret a `FrameHom` as a `LatticeHom`. -/
def toLatticeHom (f : FrameHom α β) : LatticeHom α β :=
f
lemma toFun_eq_coe (f : FrameHom α β) : f.toFun = f := rfl
@[simp] lemma coe_toInfTopHom (f : FrameHom α β) : ⇑f.toInfTopHom = f := rfl
@[simp] lemma coe_toLatticeHom (f : FrameHom α β) : ⇑f.toLatticeHom = f := rfl
@[simp] lemma coe_mk (f : InfTopHom α β) (hf) : ⇑(mk f hf) = f := rfl
| @[ext]
theorem ext {f g : FrameHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
| Mathlib/Order/Hom/CompleteLattice.lean | 493 | 495 |
/-
Copyright (c) 2020 Johan Commelin, Robert Y. Lewis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johan Commelin, Robert Y. Lewis
-/
import Mathlib.Algebra.Field.ZMod
import Mathlib.NumberTheory.Padics.PadicIntegers
import Mathlib.RingTheory.LocalRing.ResidueField.Defs
import Mathlib.RingTheory.ZMod
/-!
# Relating `ℤ_[p]` to `ZMod (p ^ n)`, aka `ℤ/p^nℤ`.
In this file we establish connections between the `p`-adic integers `ℤ_[p]`
and the integers modulo powers of `p`, `ℤ/p^nℤ`, implemented as `ZMod (p^n)`.
## Main declarations
We show that `ℤ_[p]` has a ring homomorphism to `ℤ/p^nℤ` for each `n`.
The case for `n = 1` is handled separately, since it is used in the general construction
and we may want to use it without the `^1` getting in the way.
* `PadicInt.toZMod`: ring homomorphism to `ℤ/pℤ`, implemented as `ZMod p`.
* `PadicInt.toZModPow`: ring homomorphism to `ℤ/p^nℤ`, implemented as `ZMod (p^n)`.
* `PadicInt.ker_toZMod` / `PadicInt.ker_toZModPow`: the kernels of these maps are the ideals
generated by `p^n`
* `PadicInt.residueField` shows that the residue field of `ℤ_[p]` is isomorhic to ``ℤ/pℤ`.
We also establish the universal property of `ℤ_[p]` as a projective limit.
Given a family of compatible ring homomorphisms `f_k : R → ℤ/p^nℤ`,
there is a unique limit `R → ℤ_[p]`
* `PadicInt.lift`: the limit function
* `PadicInt.lift_spec` / `PadicInt.lift_unique`: the universal property
## Implementation notes
The constructions of the ring homomorphisms go through an auxiliary constructor
`PadicInt.toZModHom`, which removes some boilerplate code.
-/
noncomputable section
open Nat IsLocalRing Padic
namespace PadicInt
variable {p : ℕ} [hp_prime : Fact p.Prime]
section RingHoms
/-! ### Ring homomorphisms to `ZMod p` and `ZMod (p ^ n)` -/
variable (p) (r : ℚ)
/-- `modPart p r` is an integer that satisfies
`‖(r - modPart p r : ℚ_[p])‖ < 1` when `‖(r : ℚ_[p])‖ ≤ 1`,
see `PadicInt.norm_sub_modPart`.
It is the unique non-negative integer that is `< p` with this property.
(Note that this definition assumes `r : ℚ`.
See `PadicInt.zmodRepr` for a version that takes values in `ℕ`
and works for arbitrary `x : ℤ_[p]`.) -/
def modPart : ℤ :=
r.num * gcdA r.den p % p
variable {p}
theorem modPart_lt_p : modPart p r < p := by
convert Int.emod_lt_abs _ _
· simp
· exact mod_cast hp_prime.1.ne_zero
theorem modPart_nonneg : 0 ≤ modPart p r :=
Int.emod_nonneg _ <| mod_cast hp_prime.1.ne_zero
theorem isUnit_den (r : ℚ) (h : ‖(r : ℚ_[p])‖ ≤ 1) : IsUnit (r.den : ℤ_[p]) := by
rw [isUnit_iff]
apply le_antisymm (r.den : ℤ_[p]).2
rw [← not_lt, coe_natCast]
intro norm_denom_lt
have hr : ‖(r * r.den : ℚ_[p])‖ = ‖(r.num : ℚ_[p])‖ := by
congr
rw_mod_cast [@Rat.mul_den_eq_num r]
rw [padicNormE.mul] at hr
have key : ‖(r.num : ℚ_[p])‖ < 1 := by
calc
_ = _ := hr.symm
_ < 1 * 1 := mul_lt_mul' h norm_denom_lt (norm_nonneg _) zero_lt_one
_ = 1 := mul_one 1
have : ↑p ∣ r.num ∧ (p : ℤ) ∣ r.den := by
simp only [← norm_int_lt_one_iff_dvd, ← padic_norm_e_of_padicInt]
exact ⟨key, norm_denom_lt⟩
apply hp_prime.1.not_dvd_one
rwa [← r.reduced.gcd_eq_one, Nat.dvd_gcd_iff, ← Int.natCast_dvd, ← Int.natCast_dvd_natCast]
theorem norm_sub_modPart_aux (r : ℚ) (h : ‖(r : ℚ_[p])‖ ≤ 1) :
↑p ∣ r.num - r.num * r.den.gcdA p % p * ↑r.den := by
rw [← ZMod.intCast_zmod_eq_zero_iff_dvd]
simp only [Int.cast_natCast, ZMod.natCast_mod, Int.cast_mul, Int.cast_sub]
have := congr_arg (fun x => x % p : ℤ → ZMod p) (gcd_eq_gcd_ab r.den p)
simp only [Int.cast_natCast, CharP.cast_eq_zero, EuclideanDomain.mod_zero, Int.cast_add,
Int.cast_mul, zero_mul, add_zero] at this
push_cast
rw [mul_right_comm, mul_assoc, ← this]
suffices rdcp : r.den.Coprime p by
rw [rdcp.gcd_eq_one]
simp only [mul_one, cast_one, sub_self]
apply Coprime.symm
apply (coprime_or_dvd_of_prime hp_prime.1 _).resolve_right
rw [← Int.natCast_dvd_natCast, ← norm_int_lt_one_iff_dvd, not_lt]
apply ge_of_eq
rw [← isUnit_iff]
exact isUnit_den r h
theorem norm_sub_modPart (h : ‖(r : ℚ_[p])‖ ≤ 1) : ‖(⟨r, h⟩ - modPart p r : ℤ_[p])‖ < 1 := by
let n := modPart p r
rw [norm_lt_one_iff_dvd, ← (isUnit_den r h).dvd_mul_right]
suffices ↑p ∣ r.num - n * r.den by
convert (Int.castRingHom ℤ_[p]).map_dvd this
simp only [n, sub_mul, Int.cast_natCast, eq_intCast, Int.cast_mul, sub_left_inj,
Int.cast_sub]
apply Subtype.coe_injective
simp only [coe_mul, Subtype.coe_mk, coe_natCast]
rw_mod_cast [@Rat.mul_den_eq_num r]
rfl
exact norm_sub_modPart_aux r h
theorem exists_mem_range_of_norm_rat_le_one (h : ‖(r : ℚ_[p])‖ ≤ 1) :
∃ n : ℤ, 0 ≤ n ∧ n < p ∧ ‖(⟨r, h⟩ - n : ℤ_[p])‖ < 1 :=
⟨modPart p r, modPart_nonneg _, modPart_lt_p _, norm_sub_modPart _ h⟩
theorem zmod_congr_of_sub_mem_span_aux (n : ℕ) (x : ℤ_[p]) (a b : ℤ)
(ha : x - a ∈ (Ideal.span {(p : ℤ_[p]) ^ n}))
(hb : x - b ∈ (Ideal.span {(p : ℤ_[p]) ^ n})) : (a : ZMod (p ^ n)) = b := by
rw [Ideal.mem_span_singleton] at ha hb
rw [← sub_eq_zero, ← Int.cast_sub, ZMod.intCast_zmod_eq_zero_iff_dvd, Int.natCast_pow]
rw [← dvd_neg, neg_sub] at ha
have := dvd_add ha hb
rwa [sub_eq_add_neg, sub_eq_add_neg, add_assoc, neg_add_cancel_left, ← sub_eq_add_neg, ←
Int.cast_sub, pow_p_dvd_int_iff] at this
theorem zmod_congr_of_sub_mem_span (n : ℕ) (x : ℤ_[p]) (a b : ℕ)
(ha : x - a ∈ (Ideal.span {(p : ℤ_[p]) ^ n}))
(hb : x - b ∈ (Ideal.span {(p : ℤ_[p]) ^ n})) : (a : ZMod (p ^ n)) = b := by
simpa using zmod_congr_of_sub_mem_span_aux n x a b ha hb
theorem zmod_congr_of_sub_mem_max_ideal (x : ℤ_[p]) (m n : ℕ) (hm : x - m ∈ maximalIdeal ℤ_[p])
(hn : x - n ∈ maximalIdeal ℤ_[p]) : (m : ZMod p) = n := by
rw [maximalIdeal_eq_span_p] at hm hn
have := zmod_congr_of_sub_mem_span_aux 1 x m n
simp only [pow_one] at this
specialize this hm hn
apply_fun ZMod.castHom (show p ∣ p ^ 1 by rw [pow_one]) (ZMod p) at this
simp only [map_intCast] at this
simpa only [Int.cast_natCast] using this
variable (x : ℤ_[p])
theorem exists_mem_range : ∃ n : ℕ, n < p ∧ x - n ∈ maximalIdeal ℤ_[p] := by
simp only [maximalIdeal_eq_span_p, Ideal.mem_span_singleton, ← norm_lt_one_iff_dvd]
obtain ⟨r, hr⟩ := rat_dense p (x : ℚ_[p]) zero_lt_one
have H : ‖(r : ℚ_[p])‖ ≤ 1 := by
rw [norm_sub_rev] at hr
calc
_ = ‖(r : ℚ_[p]) - x + x‖ := by ring_nf
_ ≤ _ := padicNormE.nonarchimedean _ _
_ ≤ _ := max_le (le_of_lt hr) x.2
obtain ⟨n, hzn, hnp, hn⟩ := exists_mem_range_of_norm_rat_le_one r H
lift n to ℕ using hzn
use n
constructor
· exact mod_cast hnp
simp only [norm_def, coe_sub, Subtype.coe_mk, coe_natCast] at hn ⊢
rw [show (x - n : ℚ_[p]) = x - r + (r - n) by ring]
apply lt_of_le_of_lt (padicNormE.nonarchimedean _ _)
apply max_lt hr
simpa using hn
theorem existsUnique_mem_range : ∃! n : ℕ, n < p ∧ x - n ∈ maximalIdeal ℤ_[p] := by
obtain ⟨n, hn₁, hn₂⟩ := exists_mem_range x
use n, ⟨hn₁, hn₂⟩, fun m ⟨hm₁, hm₂⟩ ↦ ?_
have := (zmod_congr_of_sub_mem_max_ideal x n m hn₂ hm₂).symm
rwa [ZMod.natCast_eq_natCast_iff, ModEq, mod_eq_of_lt hn₁, mod_eq_of_lt hm₁] at this
@[deprecated (since := "2024-12-17")] alias exists_unique_mem_range := existsUnique_mem_range
/-- `zmodRepr x` is the unique natural number smaller than `p`
satisfying `‖(x - zmodRepr x : ℤ_[p])‖ < 1`.
-/
def zmodRepr : ℕ :=
Classical.choose (existsUnique_mem_range x).exists
theorem zmodRepr_spec : zmodRepr x < p ∧ x - zmodRepr x ∈ maximalIdeal ℤ_[p] :=
Classical.choose_spec (existsUnique_mem_range x).exists
theorem zmodRepr_unique (y : ℕ) (hy₁ : y < p) (hy₂ : x - y ∈ maximalIdeal ℤ_[p]) : y = zmodRepr x :=
have h := (Classical.choose_spec (existsUnique_mem_range x)).right
(h y ⟨hy₁, hy₂⟩).trans (h (zmodRepr x) (zmodRepr_spec x)).symm
theorem zmodRepr_lt_p : zmodRepr x < p :=
(zmodRepr_spec _).1
theorem sub_zmodRepr_mem : x - zmodRepr x ∈ maximalIdeal ℤ_[p] :=
(zmodRepr_spec _).2
/-- `toZModHom` is an auxiliary constructor for creating ring homs from `ℤ_[p]` to `ZMod v`.
-/
def toZModHom (v : ℕ) (f : ℤ_[p] → ℕ) (f_spec : ∀ x, x - f x ∈ (Ideal.span {↑v} : Ideal ℤ_[p]))
(f_congr :
∀ (x : ℤ_[p]) (a b : ℕ),
x - a ∈ (Ideal.span {↑v} : Ideal ℤ_[p]) →
x - b ∈ (Ideal.span {↑v} : Ideal ℤ_[p]) → (a : ZMod v) = b) :
ℤ_[p] →+* ZMod v where
toFun x := f x
map_zero' := by
rw [f_congr (0 : ℤ_[p]) _ 0, cast_zero]
· exact f_spec _
· simp only [sub_zero, cast_zero, Submodule.zero_mem]
map_one' := by
rw [f_congr (1 : ℤ_[p]) _ 1, cast_one]
· exact f_spec _
· simp only [sub_self, cast_one, Submodule.zero_mem]
map_add' := by
intro x y
rw [f_congr (x + y) _ (f x + f y), cast_add]
· exact f_spec _
· convert Ideal.add_mem _ (f_spec x) (f_spec y) using 1
rw [cast_add]
ring
map_mul' := by
intro x y
rw [f_congr (x * y) _ (f x * f y), cast_mul]
· exact f_spec _
· let I : Ideal ℤ_[p] := Ideal.span {↑v}
convert I.add_mem (I.mul_mem_left x (f_spec y)) (I.mul_mem_right ↑(f y) (f_spec x)) using 1
rw [cast_mul]
ring
/-- `toZMod` is a ring hom from `ℤ_[p]` to `ZMod p`,
with the equality `toZMod x = (zmodRepr x : ZMod p)`.
-/
def toZMod : ℤ_[p] →+* ZMod p :=
toZModHom p zmodRepr
(by
rw [← maximalIdeal_eq_span_p]
exact sub_zmodRepr_mem)
(by
rw [← maximalIdeal_eq_span_p]
exact zmod_congr_of_sub_mem_max_ideal)
/-- `z - (toZMod z : ℤ_[p])` is contained in the maximal ideal of `ℤ_[p]`, for every `z : ℤ_[p]`.
The coercion from `ZMod p` to `ℤ_[p]` is `ZMod.cast`,
which coerces `ZMod p` into arbitrary rings.
This is unfortunate, but a consequence of the fact that we allow `ZMod p`
to coerce to rings of arbitrary characteristic, instead of only rings of characteristic `p`.
This coercion is only a ring homomorphism if it coerces into a ring whose characteristic divides
`p`. While this is not the case here we can still make use of the coercion.
-/
theorem toZMod_spec : x - (ZMod.cast (toZMod x) : ℤ_[p]) ∈ maximalIdeal ℤ_[p] := by
convert sub_zmodRepr_mem x using 2
dsimp [toZMod, toZModHom]
rcases Nat.exists_eq_add_of_lt hp_prime.1.pos with ⟨p', rfl⟩
change ↑((_ : ZMod (0 + p' + 1)).val) = (_ : ℤ_[0 + p' + 1])
rw [Nat.cast_inj]
apply mod_eq_of_lt
simpa only [zero_add] using zmodRepr_lt_p x
theorem ker_toZMod : RingHom.ker (toZMod : ℤ_[p] →+* ZMod p) = maximalIdeal ℤ_[p] := by
ext x
rw [RingHom.mem_ker]
constructor
· intro h
simpa only [h, ZMod.cast_zero, sub_zero] using toZMod_spec x
· intro h
rw [← sub_zero x] at h
dsimp [toZMod, toZModHom]
convert zmod_congr_of_sub_mem_max_ideal x _ 0 _ h
· norm_cast
· apply sub_zmodRepr_mem
/-- The equivalence between the residue field of the `p`-adic integers and `ℤ/pℤ` -/
def residueField : IsLocalRing.ResidueField ℤ_[p] ≃+* ZMod p :=
(Ideal.quotEquivOfEq PadicInt.ker_toZMod.symm).trans <|
RingHom.quotientKerEquivOfSurjective (ZMod.ringHom_surjective PadicInt.toZMod)
open scoped Classical in
/-- `appr n x` gives a value `v : ℕ` such that `x` and `↑v : ℤ_p` are congruent mod `p^n`.
See `appr_spec`. -/
noncomputable def appr : ℤ_[p] → ℕ → ℕ
| _x, 0 => 0
| x, n + 1 =>
let y := x - appr x n
if hy : y = 0 then appr x n
else
let u := (unitCoeff hy : ℤ_[p])
appr x n + p ^ n * (toZMod ((u * (p : ℤ_[p]) ^ (y.valuation - n : ℤ).natAbs) : ℤ_[p])).val
theorem appr_lt (x : ℤ_[p]) (n : ℕ) : x.appr n < p ^ n := by
induction n generalizing x with
| zero => simp only [appr, zero_eq, _root_.pow_zero, zero_lt_one]
| succ n ih =>
simp only [appr, map_natCast, ZMod.natCast_self, RingHom.map_pow, Int.natAbs, RingHom.map_mul]
have hp : p ^ n < p ^ (n + 1) := by apply Nat.pow_lt_pow_right hp_prime.1.one_lt n.lt_add_one
split_ifs with h
· apply lt_trans (ih _) hp
· calc
_ < p ^ n + p ^ n * (p - 1) := ?_
_ = p ^ (n + 1) := ?_
· apply add_lt_add_of_lt_of_le (ih _)
apply Nat.mul_le_mul_left
apply le_pred_of_lt
apply ZMod.val_lt
· rw [mul_tsub, mul_one, ← _root_.pow_succ]
apply add_tsub_cancel_of_le (le_of_lt hp)
theorem appr_mono (x : ℤ_[p]) : Monotone x.appr := by
apply monotone_nat_of_le_succ
intro n
dsimp [appr]
split_ifs; · rfl
apply Nat.le_add_right
|
theorem dvd_appr_sub_appr (x : ℤ_[p]) (m n : ℕ) (h : m ≤ n) : p ^ m ∣ x.appr n - x.appr m := by
obtain ⟨k, rfl⟩ := Nat.exists_eq_add_of_le h; clear h
induction k with
| zero =>
simp only [zero_eq, add_zero, le_refl, tsub_eq_zero_of_le, ne_eq, Nat.isUnit_iff, dvd_zero]
| Mathlib/NumberTheory/Padics/RingHoms.lean | 329 | 334 |
/-
Copyright (c) 2020 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Algebra.Star.SelfAdjoint
import Mathlib.LinearAlgebra.Dimension.StrongRankCondition
import Mathlib.LinearAlgebra.FreeModule.Finite.Basic
/-!
# Quaternions
In this file we define quaternions `ℍ[R]` over a commutative ring `R`, and define some
algebraic structures on `ℍ[R]`.
## Main definitions
* `QuaternionAlgebra R a b c`, `ℍ[R, a, b, c]` :
[Bourbaki, *Algebra I*][bourbaki1989] with coefficients `a`, `b`, `c`
(Many other references such as Wikipedia assume $\operatorname{char} R ≠ 2$ therefore one can
complete the square and WLOG assume $b = 0$.)
* `Quaternion R`, `ℍ[R]` : the space of quaternions, a.k.a.
`QuaternionAlgebra R (-1) (0) (-1)`;
* `Quaternion.normSq` : square of the norm of a quaternion;
We also define the following algebraic structures on `ℍ[R]`:
* `Ring ℍ[R, a, b, c]`, `StarRing ℍ[R, a, b, c]`, and `Algebra R ℍ[R, a, b, c]` :
for any commutative ring `R`;
* `Ring ℍ[R]`, `StarRing ℍ[R]`, and `Algebra R ℍ[R]` : for any commutative ring `R`;
* `IsDomain ℍ[R]` : for a linear ordered commutative ring `R`;
* `DivisionRing ℍ[R]` : for a linear ordered field `R`.
## Notation
The following notation is available with `open Quaternion` or `open scoped Quaternion`.
* `ℍ[R, c₁, c₂, c₃]` : `QuaternionAlgebra R c₁ c₂ c₃`
* `ℍ[R, c₁, c₂]` : `QuaternionAlgebra R c₁ 0 c₂`
* `ℍ[R]` : quaternions over `R`.
## Implementation notes
We define quaternions over any ring `R`, not just `ℝ` to be able to deal with, e.g., integer
or rational quaternions without using real numbers. In particular, all definitions in this file
are computable.
## Tags
quaternion
-/
/-- Quaternion algebra over a type with fixed coefficients where $i^2 = a + bi$ and $j^2 = c$,
denoted as `ℍ[R,a,b]`.
Implemented as a structure with four fields: `re`, `imI`, `imJ`, and `imK`. -/
@[ext]
structure QuaternionAlgebra (R : Type*) (a b c : R) where
/-- Real part of a quaternion. -/
re : R
/-- First imaginary part (i) of a quaternion. -/
imI : R
/-- Second imaginary part (j) of a quaternion. -/
imJ : R
/-- Third imaginary part (k) of a quaternion. -/
imK : R
@[inherit_doc]
scoped[Quaternion] notation "ℍ[" R "," a "," b "," c "]" =>
QuaternionAlgebra R a b c
@[inherit_doc]
scoped[Quaternion] notation "ℍ[" R "," a "," b "]" => QuaternionAlgebra R a 0 b
namespace QuaternionAlgebra
open Quaternion
/-- The equivalence between a quaternion algebra over `R` and `R × R × R × R`. -/
@[simps]
def equivProd {R : Type*} (c₁ c₂ c₃ : R) : ℍ[R,c₁,c₂,c₃] ≃ R × R × R × R where
toFun a := ⟨a.1, a.2, a.3, a.4⟩
invFun a := ⟨a.1, a.2.1, a.2.2.1, a.2.2.2⟩
left_inv _ := rfl
right_inv _ := rfl
/-- The equivalence between a quaternion algebra over `R` and `Fin 4 → R`. -/
@[simps symm_apply]
def equivTuple {R : Type*} (c₁ c₂ c₃ : R) : ℍ[R,c₁,c₂,c₃] ≃ (Fin 4 → R) where
toFun a := ![a.1, a.2, a.3, a.4]
invFun a := ⟨a 0, a 1, a 2, a 3⟩
left_inv _ := rfl
right_inv f := by ext ⟨_, _ | _ | _ | _ | _ | ⟨⟩⟩ <;> rfl
@[simp]
theorem equivTuple_apply {R : Type*} (c₁ c₂ c₃ : R) (x : ℍ[R,c₁,c₂,c₃]) :
equivTuple c₁ c₂ c₃ x = ![x.re, x.imI, x.imJ, x.imK] :=
rfl
@[simp]
theorem mk.eta {R : Type*} {c₁ c₂ c₃} (a : ℍ[R,c₁,c₂,c₃]) : mk a.1 a.2 a.3 a.4 = a := rfl
variable {S T R : Type*} {c₁ c₂ c₃ : R} (r x y : R) (a b : ℍ[R,c₁,c₂,c₃])
instance [Subsingleton R] : Subsingleton ℍ[R, c₁, c₂, c₃] := (equivTuple c₁ c₂ c₃).subsingleton
instance [Nontrivial R] : Nontrivial ℍ[R, c₁, c₂, c₃] := (equivTuple c₁ c₂ c₃).surjective.nontrivial
section Zero
variable [Zero R]
/-- The imaginary part of a quaternion.
Note that unless `c₂ = 0`, this definition is not particularly well-behaved;
for instance, `QuaternionAlgebra.star_im` only says that the star of an imaginary quaternion
is imaginary under this condition. -/
def im (x : ℍ[R,c₁,c₂,c₃]) : ℍ[R,c₁,c₂,c₃] :=
⟨0, x.imI, x.imJ, x.imK⟩
@[simp]
theorem im_re : a.im.re = 0 :=
rfl
@[simp]
theorem im_imI : a.im.imI = a.imI :=
rfl
@[simp]
theorem im_imJ : a.im.imJ = a.imJ :=
rfl
@[simp]
theorem im_imK : a.im.imK = a.imK :=
rfl
@[simp]
theorem im_idem : a.im.im = a.im :=
rfl
/-- Coercion `R → ℍ[R,c₁,c₂,c₃]`. -/
@[coe] def coe (x : R) : ℍ[R,c₁,c₂,c₃] := ⟨x, 0, 0, 0⟩
instance : CoeTC R ℍ[R,c₁,c₂,c₃] := ⟨coe⟩
@[simp, norm_cast]
theorem coe_re : (x : ℍ[R,c₁,c₂,c₃]).re = x := rfl
@[simp, norm_cast]
theorem coe_imI : (x : ℍ[R,c₁,c₂,c₃]).imI = 0 := rfl
@[simp, norm_cast]
theorem coe_imJ : (x : ℍ[R,c₁,c₂,c₃]).imJ = 0 := rfl
@[simp, norm_cast]
theorem coe_imK : (x : ℍ[R,c₁,c₂,c₃]).imK = 0 := rfl
theorem coe_injective : Function.Injective (coe : R → ℍ[R,c₁,c₂,c₃]) := fun _ _ h => congr_arg re h
@[simp]
theorem coe_inj {x y : R} : (x : ℍ[R,c₁,c₂,c₃]) = y ↔ x = y :=
coe_injective.eq_iff
-- Porting note: removed `simps`, added simp lemmas manually.
-- Should adjust `simps` to name properly, i.e. as `zero_re` rather than `instZero_zero_re`.
instance : Zero ℍ[R,c₁,c₂,c₃] := ⟨⟨0, 0, 0, 0⟩⟩
@[scoped simp] theorem zero_re : (0 : ℍ[R,c₁,c₂,c₃]).re = 0 := rfl
@[scoped simp] theorem zero_imI : (0 : ℍ[R,c₁,c₂,c₃]).imI = 0 := rfl
@[scoped simp] theorem zero_imJ : (0 : ℍ[R,c₁,c₂,c₃]).imJ = 0 := rfl
@[scoped simp] theorem zero_imK : (0 : ℍ[R,c₁,c₂,c₃]).imK = 0 := rfl
@[scoped simp] theorem zero_im : (0 : ℍ[R,c₁,c₂,c₃]).im = 0 := rfl
@[simp, norm_cast]
theorem coe_zero : ((0 : R) : ℍ[R,c₁,c₂,c₃]) = 0 := rfl
instance : Inhabited ℍ[R,c₁,c₂,c₃] := ⟨0⟩
section One
variable [One R]
-- Porting note: removed `simps`, added simp lemmas manually. Should adjust `simps` to name properly
instance : One ℍ[R,c₁,c₂,c₃] := ⟨⟨1, 0, 0, 0⟩⟩
@[scoped simp] theorem one_re : (1 : ℍ[R,c₁,c₂,c₃]).re = 1 := rfl
@[scoped simp] theorem one_imI : (1 : ℍ[R,c₁,c₂,c₃]).imI = 0 := rfl
@[scoped simp] theorem one_imJ : (1 : ℍ[R,c₁,c₂,c₃]).imJ = 0 := rfl
@[scoped simp] theorem one_imK : (1 : ℍ[R,c₁,c₂,c₃]).imK = 0 := rfl
@[scoped simp] theorem one_im : (1 : ℍ[R,c₁,c₂,c₃]).im = 0 := rfl
@[simp, norm_cast]
theorem coe_one : ((1 : R) : ℍ[R,c₁,c₂,c₃]) = 1 := rfl
end One
end Zero
section Add
variable [Add R]
-- Porting note: removed `simps`, added simp lemmas manually. Should adjust `simps` to name properly
instance : Add ℍ[R,c₁,c₂,c₃] :=
⟨fun a b => ⟨a.1 + b.1, a.2 + b.2, a.3 + b.3, a.4 + b.4⟩⟩
@[simp] theorem add_re : (a + b).re = a.re + b.re := rfl
@[simp] theorem add_imI : (a + b).imI = a.imI + b.imI := rfl
@[simp] theorem add_imJ : (a + b).imJ = a.imJ + b.imJ := rfl
@[simp] theorem add_imK : (a + b).imK = a.imK + b.imK := rfl
@[simp]
theorem mk_add_mk (a₁ a₂ a₃ a₄ b₁ b₂ b₃ b₄ : R) :
(mk a₁ a₂ a₃ a₄ : ℍ[R,c₁,c₂,c₃]) + mk b₁ b₂ b₃ b₄ =
mk (a₁ + b₁) (a₂ + b₂) (a₃ + b₃) (a₄ + b₄) :=
rfl
end Add
section AddZeroClass
variable [AddZeroClass R]
@[simp] theorem add_im : (a + b).im = a.im + b.im :=
QuaternionAlgebra.ext (zero_add _).symm rfl rfl rfl
@[simp, norm_cast]
theorem coe_add : ((x + y : R) : ℍ[R,c₁,c₂,c₃]) = x + y := by ext <;> simp
end AddZeroClass
section Neg
variable [Neg R]
-- Porting note: removed `simps`, added simp lemmas manually. Should adjust `simps` to name properly
instance : Neg ℍ[R,c₁,c₂,c₃] := ⟨fun a => ⟨-a.1, -a.2, -a.3, -a.4⟩⟩
@[simp] theorem neg_re : (-a).re = -a.re := rfl
@[simp] theorem neg_imI : (-a).imI = -a.imI := rfl
@[simp] theorem neg_imJ : (-a).imJ = -a.imJ := rfl
@[simp] theorem neg_imK : (-a).imK = -a.imK := rfl
@[simp]
theorem neg_mk (a₁ a₂ a₃ a₄ : R) : -(mk a₁ a₂ a₃ a₄ : ℍ[R,c₁,c₂,c₃]) = ⟨-a₁, -a₂, -a₃, -a₄⟩ :=
rfl
end Neg
section AddGroup
variable [AddGroup R]
@[simp] theorem neg_im : (-a).im = -a.im :=
QuaternionAlgebra.ext neg_zero.symm rfl rfl rfl
@[simp, norm_cast]
theorem coe_neg : ((-x : R) : ℍ[R,c₁,c₂,c₃]) = -x := by ext <;> simp
instance : Sub ℍ[R,c₁,c₂,c₃] :=
⟨fun a b => ⟨a.1 - b.1, a.2 - b.2, a.3 - b.3, a.4 - b.4⟩⟩
@[simp] theorem sub_re : (a - b).re = a.re - b.re := rfl
@[simp] theorem sub_imI : (a - b).imI = a.imI - b.imI := rfl
@[simp] theorem sub_imJ : (a - b).imJ = a.imJ - b.imJ := rfl
@[simp] theorem sub_imK : (a - b).imK = a.imK - b.imK := rfl
@[simp] theorem sub_im : (a - b).im = a.im - b.im :=
QuaternionAlgebra.ext (sub_zero _).symm rfl rfl rfl
@[simp]
theorem mk_sub_mk (a₁ a₂ a₃ a₄ b₁ b₂ b₃ b₄ : R) :
(mk a₁ a₂ a₃ a₄ : ℍ[R,c₁,c₂,c₃]) - mk b₁ b₂ b₃ b₄ =
mk (a₁ - b₁) (a₂ - b₂) (a₃ - b₃) (a₄ - b₄) :=
rfl
@[simp, norm_cast]
theorem coe_im : (x : ℍ[R,c₁,c₂,c₃]).im = 0 :=
rfl
@[simp]
theorem re_add_im : ↑a.re + a.im = a :=
QuaternionAlgebra.ext (add_zero _) (zero_add _) (zero_add _) (zero_add _)
@[simp]
theorem sub_self_im : a - a.im = a.re :=
QuaternionAlgebra.ext (sub_zero _) (sub_self _) (sub_self _) (sub_self _)
@[simp]
theorem sub_self_re : a - a.re = a.im :=
QuaternionAlgebra.ext (sub_self _) (sub_zero _) (sub_zero _) (sub_zero _)
end AddGroup
section Ring
variable [Ring R]
/-- Multiplication is given by
* `1 * x = x * 1 = x`;
* `i * i = c₁ + c₂ * i`;
* `j * j = c₃`;
* `i * j = k`, `j * i = c₂ * j - k`;
* `k * k = - c₁ * c₃`;
* `i * k = c₁ * j + c₂ * k`, `k * i = -c₁ * j`;
* `j * k = c₂ * c₃ - c₃ * i`, `k * j = c₃ * i`. -/
instance : Mul ℍ[R,c₁,c₂,c₃] :=
⟨fun a b =>
⟨a.1 * b.1 + c₁ * a.2 * b.2 + c₃ * a.3 * b.3 + c₂ * c₃ * a.3 * b.4 - c₁ * c₃ * a.4 * b.4,
a.1 * b.2 + a.2 * b.1 + c₂ * a.2 * b.2 - c₃ * a.3 * b.4 + c₃ * a.4 * b.3,
a.1 * b.3 + c₁ * a.2 * b.4 + a.3 * b.1 + c₂ * a.3 * b.2 - c₁ * a.4 * b.2,
a.1 * b.4 + a.2 * b.3 + c₂ * a.2 * b.4 - a.3 * b.2 + a.4 * b.1⟩⟩
@[simp]
theorem mul_re : (a * b).re = a.1 * b.1 + c₁ * a.2 * b.2 + c₃ * a.3 * b.3 +
c₂ * c₃ * a.3 * b.4 - c₁ * c₃ * a.4 * b.4 := rfl
@[simp]
theorem mul_imI : (a * b).imI = a.1 * b.2 + a.2 * b.1 +
c₂ * a.2 * b.2 - c₃ * a.3 * b.4 + c₃ * a.4 * b.3 := rfl
@[simp]
theorem mul_imJ : (a * b).imJ = a.1 * b.3 + c₁ * a.2 * b.4 + a.3 * b.1 +
c₂ * a.3 * b.2 - c₁ * a.4 * b.2 := rfl
@[simp]
theorem mul_imK : (a * b).imK = a.1 * b.4 + a.2 * b.3 +
c₂ * a.2 * b.4 - a.3 * b.2 + a.4 * b.1 := rfl
@[simp]
theorem mk_mul_mk (a₁ a₂ a₃ a₄ b₁ b₂ b₃ b₄ : R) :
(mk a₁ a₂ a₃ a₄ : ℍ[R,c₁,c₂,c₃]) * mk b₁ b₂ b₃ b₄ =
mk
(a₁ * b₁ + c₁ * a₂ * b₂ + c₃ * a₃ * b₃ + c₂ * c₃ * a₃ * b₄ - c₁ * c₃ * a₄ * b₄)
(a₁ * b₂ + a₂ * b₁ + c₂ * a₂ * b₂ - c₃ * a₃ * b₄ + c₃ * a₄ * b₃)
(a₁ * b₃ + c₁ * a₂ * b₄ + a₃ * b₁ + c₂ * a₃ * b₂ - c₁ * a₄ * b₂)
(a₁ * b₄ + a₂ * b₃ + c₂ * a₂ * b₄ - a₃ * b₂ + a₄ * b₁) :=
rfl
end Ring
section SMul
variable [SMul S R] [SMul T R] (s : S)
instance : SMul S ℍ[R,c₁,c₂,c₃] where smul s a := ⟨s • a.1, s • a.2, s • a.3, s • a.4⟩
instance [SMul S T] [IsScalarTower S T R] : IsScalarTower S T ℍ[R,c₁,c₂,c₃] where
smul_assoc s t x := by ext <;> exact smul_assoc _ _ _
instance [SMulCommClass S T R] : SMulCommClass S T ℍ[R,c₁,c₂,c₃] where
smul_comm s t x := by ext <;> exact smul_comm _ _ _
@[simp] theorem smul_re : (s • a).re = s • a.re := rfl
@[simp] theorem smul_imI : (s • a).imI = s • a.imI := rfl
@[simp] theorem smul_imJ : (s • a).imJ = s • a.imJ := rfl
@[simp] theorem smul_imK : (s • a).imK = s • a.imK := rfl
@[simp] theorem smul_im {S} [CommRing R] [SMulZeroClass S R] (s : S) : (s • a).im = s • a.im :=
QuaternionAlgebra.ext (smul_zero s).symm rfl rfl rfl
@[simp]
theorem smul_mk (re im_i im_j im_k : R) :
s • (⟨re, im_i, im_j, im_k⟩ : ℍ[R,c₁,c₂,c₃]) = ⟨s • re, s • im_i, s • im_j, s • im_k⟩ :=
rfl
end SMul
@[simp, norm_cast]
theorem coe_smul [Zero R] [SMulZeroClass S R] (s : S) (r : R) :
(↑(s • r) : ℍ[R,c₁,c₂,c₃]) = s • (r : ℍ[R,c₁,c₂,c₃]) :=
QuaternionAlgebra.ext rfl (smul_zero _).symm (smul_zero _).symm (smul_zero _).symm
instance [AddCommGroup R] : AddCommGroup ℍ[R,c₁,c₂,c₃] :=
(equivProd c₁ c₂ c₃).injective.addCommGroup _ rfl (fun _ _ ↦ rfl) (fun _ ↦ rfl) (fun _ _ ↦ rfl)
(fun _ _ ↦ rfl) (fun _ _ ↦ rfl)
section AddCommGroupWithOne
variable [AddCommGroupWithOne R]
instance : AddCommGroupWithOne ℍ[R,c₁,c₂,c₃] where
natCast n := ((n : R) : ℍ[R,c₁,c₂,c₃])
natCast_zero := by simp
natCast_succ := by simp
intCast n := ((n : R) : ℍ[R,c₁,c₂,c₃])
intCast_ofNat _ := congr_arg coe (Int.cast_natCast _)
intCast_negSucc n := by
change coe _ = -coe _
rw [Int.cast_negSucc, coe_neg]
@[simp, norm_cast]
theorem natCast_re (n : ℕ) : (n : ℍ[R,c₁,c₂,c₃]).re = n :=
rfl
@[simp, norm_cast]
theorem natCast_imI (n : ℕ) : (n : ℍ[R,c₁,c₂,c₃]).imI = 0 :=
rfl
@[simp, norm_cast]
theorem natCast_imJ (n : ℕ) : (n : ℍ[R,c₁,c₂,c₃]).imJ = 0 :=
rfl
@[simp, norm_cast]
theorem natCast_imK (n : ℕ) : (n : ℍ[R,c₁,c₂,c₃]).imK = 0 :=
rfl
@[simp, norm_cast]
theorem natCast_im (n : ℕ) : (n : ℍ[R,c₁,c₂,c₃]).im = 0 :=
rfl
@[norm_cast]
theorem coe_natCast (n : ℕ) : ↑(n : R) = (n : ℍ[R,c₁,c₂,c₃]) :=
rfl
@[simp, norm_cast]
theorem intCast_re (z : ℤ) : (z : ℍ[R,c₁,c₂,c₃]).re = z :=
rfl
@[scoped simp]
theorem ofNat_re (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℍ[R,c₁,c₂,c₃]).re = ofNat(n) := rfl
@[scoped simp]
theorem ofNat_imI (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℍ[R,c₁,c₂,c₃]).imI = 0 := rfl
@[scoped simp]
theorem ofNat_imJ (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℍ[R,c₁,c₂,c₃]).imJ = 0 := rfl
@[scoped simp]
theorem ofNat_imK (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℍ[R,c₁,c₂,c₃]).imK = 0 := rfl
@[scoped simp]
theorem ofNat_im (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℍ[R,c₁,c₂,c₃]).im = 0 := rfl
@[simp, norm_cast]
theorem intCast_imI (z : ℤ) : (z : ℍ[R,c₁,c₂,c₃]).imI = 0 :=
rfl
@[simp, norm_cast]
theorem intCast_imJ (z : ℤ) : (z : ℍ[R,c₁,c₂,c₃]).imJ = 0 :=
rfl
@[simp, norm_cast]
theorem intCast_imK (z : ℤ) : (z : ℍ[R,c₁,c₂,c₃]).imK = 0 :=
rfl
@[simp, norm_cast]
theorem intCast_im (z : ℤ) : (z : ℍ[R,c₁,c₂,c₃]).im = 0 :=
rfl
@[norm_cast]
theorem coe_intCast (z : ℤ) : ↑(z : R) = (z : ℍ[R,c₁,c₂,c₃]) :=
rfl
end AddCommGroupWithOne
-- For the remainder of the file we assume `CommRing R`.
variable [CommRing R]
instance instRing : Ring ℍ[R,c₁,c₂,c₃] where
__ := inferInstanceAs (AddCommGroupWithOne ℍ[R,c₁,c₂,c₃])
left_distrib _ _ _ := by ext <;> simp <;> ring
right_distrib _ _ _ := by ext <;> simp <;> ring
zero_mul _ := by ext <;> simp
mul_zero _ := by ext <;> simp
mul_assoc _ _ _ := by ext <;> simp <;> ring
one_mul _ := by ext <;> simp
mul_one _ := by ext <;> simp
@[norm_cast, simp]
theorem coe_mul : ((x * y : R) : ℍ[R,c₁,c₂,c₃]) = x * y := by ext <;> simp
@[norm_cast, simp]
lemma coe_ofNat {n : ℕ} [n.AtLeastTwo]:
((ofNat(n) : R) : ℍ[R,c₁,c₂,c₃]) = (ofNat(n) : ℍ[R,c₁,c₂,c₃]) := by
rfl
-- TODO: add weaker `MulAction`, `DistribMulAction`, and `Module` instances (and repeat them
-- for `ℍ[R]`)
instance [CommSemiring S] [Algebra S R] : Algebra S ℍ[R,c₁,c₂,c₃] where
smul := (· • ·)
algebraMap :=
{ toFun s := coe (algebraMap S R s)
map_one' := by simp only [map_one, coe_one]
map_zero' := by simp only [map_zero, coe_zero]
map_mul' x y := by simp only [map_mul, coe_mul]
map_add' x y := by simp only [map_add, coe_add] }
smul_def' s x := by ext <;> simp [Algebra.smul_def]
commutes' s x := by ext <;> simp [Algebra.commutes]
theorem algebraMap_eq (r : R) : algebraMap R ℍ[R,c₁,c₂,c₃] r = ⟨r, 0, 0, 0⟩ :=
rfl
theorem algebraMap_injective : (algebraMap R ℍ[R,c₁,c₂,c₃] : _ → _).Injective :=
fun _ _ ↦ by simp [algebraMap_eq]
instance [NoZeroDivisors R] : NoZeroSMulDivisors R ℍ[R,c₁,c₂,c₃] := ⟨by
rintro t ⟨a, b, c, d⟩ h
rw [or_iff_not_imp_left]
intro ht
simpa [QuaternionAlgebra.ext_iff, ht] using h⟩
section
variable (c₁ c₂ c₃)
/-- `QuaternionAlgebra.re` as a `LinearMap` -/
@[simps]
def reₗ : ℍ[R,c₁,c₂,c₃] →ₗ[R] R where
toFun := re
map_add' _ _ := rfl
map_smul' _ _ := rfl
/-- `QuaternionAlgebra.imI` as a `LinearMap` -/
@[simps]
def imIₗ : ℍ[R,c₁,c₂,c₃] →ₗ[R] R where
toFun := imI
map_add' _ _ := rfl
map_smul' _ _ := rfl
/-- `QuaternionAlgebra.imJ` as a `LinearMap` -/
@[simps]
def imJₗ : ℍ[R,c₁,c₂,c₃] →ₗ[R] R where
toFun := imJ
map_add' _ _ := rfl
map_smul' _ _ := rfl
/-- `QuaternionAlgebra.imK` as a `LinearMap` -/
@[simps]
def imKₗ : ℍ[R,c₁,c₂,c₃] →ₗ[R] R where
toFun := imK
map_add' _ _ := rfl
map_smul' _ _ := rfl
/-- `QuaternionAlgebra.equivTuple` as a linear equivalence. -/
def linearEquivTuple : ℍ[R,c₁,c₂,c₃] ≃ₗ[R] Fin 4 → R :=
LinearEquiv.symm -- proofs are not `rfl` in the forward direction
{ (equivTuple c₁ c₂ c₃).symm with
toFun := (equivTuple c₁ c₂ c₃).symm
invFun := equivTuple c₁ c₂ c₃
map_add' := fun _ _ => rfl
map_smul' := fun _ _ => rfl }
@[simp]
theorem coe_linearEquivTuple :
⇑(linearEquivTuple c₁ c₂ c₃) = equivTuple c₁ c₂ c₃ := rfl
@[simp]
theorem coe_linearEquivTuple_symm :
⇑(linearEquivTuple c₁ c₂ c₃).symm = (equivTuple c₁ c₂ c₃).symm := rfl
/-- `ℍ[R, c₁, c₂, c₃]` has a basis over `R` given by `1`, `i`, `j`, and `k`. -/
noncomputable def basisOneIJK : Basis (Fin 4) R ℍ[R,c₁,c₂,c₃] :=
.ofEquivFun <| linearEquivTuple c₁ c₂ c₃
@[simp]
theorem coe_basisOneIJK_repr (q : ℍ[R,c₁,c₂,c₃]) :
((basisOneIJK c₁ c₂ c₃).repr q) = ![q.re, q.imI, q.imJ, q.imK] :=
rfl
instance : Module.Finite R ℍ[R,c₁,c₂,c₃] := .of_basis (basisOneIJK c₁ c₂ c₃)
instance : Module.Free R ℍ[R,c₁,c₂,c₃] := .of_basis (basisOneIJK c₁ c₂ c₃)
theorem rank_eq_four [StrongRankCondition R] : Module.rank R ℍ[R,c₁,c₂,c₃] = 4 := by
rw [rank_eq_card_basis (basisOneIJK c₁ c₂ c₃), Fintype.card_fin]
norm_num
theorem finrank_eq_four [StrongRankCondition R] : Module.finrank R ℍ[R,c₁,c₂,c₃] = 4 := by
rw [Module.finrank, rank_eq_four, Cardinal.toNat_ofNat]
/-- There is a natural equivalence when swapping the first and third coefficients of a
quaternion algebra if `c₂` is 0. -/
@[simps]
def swapEquiv : ℍ[R,c₁,0,c₃] ≃ₐ[R] ℍ[R,c₃,0,c₁] where
toFun t := ⟨t.1, t.3, t.2, -t.4⟩
invFun t := ⟨t.1, t.3, t.2, -t.4⟩
left_inv _ := by simp
right_inv _ := by simp
map_mul' _ _ := by ext <;> simp <;> ring
map_add' _ _ := by ext <;> simp [add_comm]
commutes' _ := by simp [algebraMap_eq]
end
@[norm_cast, simp]
theorem coe_sub : ((x - y : R) : ℍ[R,c₁,c₂,c₃]) = x - y :=
(algebraMap R ℍ[R,c₁,c₂,c₃]).map_sub x y
@[norm_cast, simp]
theorem coe_pow (n : ℕ) : (↑(x ^ n) : ℍ[R,c₁,c₂,c₃]) = (x : ℍ[R,c₁,c₂,c₃]) ^ n :=
(algebraMap R ℍ[R,c₁,c₂,c₃]).map_pow x n
theorem coe_commutes : ↑r * a = a * r :=
Algebra.commutes r a
theorem coe_commute : Commute (↑r) a :=
coe_commutes r a
theorem coe_mul_eq_smul : ↑r * a = r • a :=
(Algebra.smul_def r a).symm
theorem mul_coe_eq_smul : a * r = r • a := by rw [← coe_commutes, coe_mul_eq_smul]
@[norm_cast, simp]
theorem coe_algebraMap : ⇑(algebraMap R ℍ[R,c₁,c₂,c₃]) = coe :=
rfl
theorem smul_coe : x • (y : ℍ[R,c₁,c₂,c₃]) = ↑(x * y) := by rw [coe_mul, coe_mul_eq_smul]
/-- Quaternion conjugate. -/
instance instStarQuaternionAlgebra : Star ℍ[R,c₁,c₂,c₃] where star a :=
⟨a.1 + c₂ * a.2, -a.2, -a.3, -a.4⟩
@[simp] theorem re_star : (star a).re = a.re + c₂ * a.imI := rfl
@[simp]
theorem imI_star : (star a).imI = -a.imI :=
rfl
@[simp]
theorem imJ_star : (star a).imJ = -a.imJ :=
rfl
@[simp]
theorem imK_star : (star a).imK = -a.imK :=
rfl
@[simp]
theorem im_star : (star a).im = -a.im :=
QuaternionAlgebra.ext neg_zero.symm rfl rfl rfl
@[simp]
theorem star_mk (a₁ a₂ a₃ a₄ : R) : star (mk a₁ a₂ a₃ a₄ : ℍ[R,c₁,c₂,c₃]) =
⟨a₁ + c₂ * a₂, -a₂, -a₃, -a₄⟩ := rfl
instance instStarRing : StarRing ℍ[R,c₁,c₂,c₃] where
star_involutive x := by simp [Star.star]
star_add a b := by ext <;> simp [add_comm] ; ring
star_mul a b := by ext <;> simp <;> ring
theorem self_add_star' : a + star a = ↑(2 * a.re + c₂ * a.imI) := by ext <;> simp [two_mul]; ring
theorem self_add_star : a + star a = 2 * a.re + c₂ * a.imI := by simp [self_add_star']
theorem star_add_self' : star a + a = ↑(2 * a.re + c₂ * a.imI) := by rw [add_comm, self_add_star']
theorem star_add_self : star a + a = 2 * a.re + c₂ * a.imI := by rw [add_comm, self_add_star]
theorem star_eq_two_re_sub : star a = ↑(2 * a.re + c₂ * a.imI) - a :=
eq_sub_iff_add_eq.2 a.star_add_self'
lemma comm (r : R) (x : ℍ[R, c₁, c₂, c₃]) : r * x = x * r := by
ext <;> simp [mul_comm]
instance : IsStarNormal a :=
⟨by
rw [commute_iff_eq, a.star_eq_two_re_sub];
ext <;> simp <;> ring⟩
@[simp, norm_cast]
theorem star_coe : star (x : ℍ[R,c₁,c₂,c₃]) = x := by ext <;> simp
@[simp] theorem star_im : star a.im = -a.im + c₂ * a.imI := by ext <;> simp
@[simp]
theorem star_smul [Monoid S] [DistribMulAction S R] [SMulCommClass S R R]
(s : S) (a : ℍ[R,c₁,c₂,c₃]) :
star (s • a) = s • star a :=
QuaternionAlgebra.ext
(by simp [mul_smul_comm]) (smul_neg _ _).symm (smul_neg _ _).symm (smul_neg _ _).symm
/-- A version of `star_smul` for the special case when `c₂ = 0`, without `SMulCommClass S R R`. -/
theorem star_smul' [Monoid S] [DistribMulAction S R] (s : S) (a : ℍ[R,c₁,0,c₃]) :
star (s • a) = s • star a :=
QuaternionAlgebra.ext (by simp) (smul_neg _ _).symm (smul_neg _ _).symm (smul_neg _ _).symm
theorem eq_re_of_eq_coe {a : ℍ[R,c₁,c₂,c₃]} {x : R} (h : a = x) : a = a.re := by rw [h, coe_re]
theorem eq_re_iff_mem_range_coe {a : ℍ[R,c₁,c₂,c₃]} :
a = a.re ↔ a ∈ Set.range (coe : R → ℍ[R,c₁,c₂,c₃]) :=
⟨fun h => ⟨a.re, h.symm⟩, fun ⟨_, h⟩ => eq_re_of_eq_coe h.symm⟩
section CharZero
variable [NoZeroDivisors R] [CharZero R]
@[simp]
theorem star_eq_self {c₁ c₂ : R} {a : ℍ[R,c₁,c₂,c₃]} : star a = a ↔ a = a.re := by
simp_all [QuaternionAlgebra.ext_iff, neg_eq_iff_add_eq_zero, add_self_eq_zero]
theorem star_eq_neg {c₁ : R} {a : ℍ[R,c₁,0,c₃]} : star a = -a ↔ a.re = 0 := by
simp [QuaternionAlgebra.ext_iff, eq_neg_iff_add_eq_zero]
end CharZero
-- Can't use `rw ← star_eq_self` in the proof without additional assumptions
theorem star_mul_eq_coe : star a * a = (star a * a).re := by ext <;> simp <;> ring
theorem mul_star_eq_coe : a * star a = (a * star a).re := by
rw [← star_comm_self']
exact a.star_mul_eq_coe
open MulOpposite
/-- Quaternion conjugate as an `AlgEquiv` to the opposite ring. -/
def starAe : ℍ[R,c₁,c₂,c₃] ≃ₐ[R] ℍ[R,c₁,c₂,c₃]ᵐᵒᵖ :=
{ starAddEquiv.trans opAddEquiv with
toFun := op ∘ star
invFun := star ∘ unop
map_mul' := fun x y => by simp
commutes' := fun r => by simp }
@[simp]
theorem coe_starAe : ⇑(starAe : ℍ[R,c₁,c₂,c₃] ≃ₐ[R] _) = op ∘ star :=
rfl
end QuaternionAlgebra
/-- Space of quaternions over a type, denoted as `ℍ[R]`.
Implemented as a structure with four fields: `re`, `im_i`, `im_j`, and `im_k`. -/
def Quaternion (R : Type*) [Zero R] [One R] [Neg R] :=
QuaternionAlgebra R (-1) (0) (-1)
@[inherit_doc]
scoped[Quaternion] notation "ℍ[" R "]" => Quaternion R
open Quaternion
/-- The equivalence between the quaternions over `R` and `R × R × R × R`. -/
@[simps!]
def Quaternion.equivProd (R : Type*) [Zero R] [One R] [Neg R] : ℍ[R] ≃ R × R × R × R :=
QuaternionAlgebra.equivProd _ _ _
/-- The equivalence between the quaternions over `R` and `Fin 4 → R`. -/
@[simps! symm_apply]
def Quaternion.equivTuple (R : Type*) [Zero R] [One R] [Neg R] : ℍ[R] ≃ (Fin 4 → R) :=
QuaternionAlgebra.equivTuple _ _ _
@[simp]
theorem Quaternion.equivTuple_apply (R : Type*) [Zero R] [One R] [Neg R] (x : ℍ[R]) :
Quaternion.equivTuple R x = ![x.re, x.imI, x.imJ, x.imK] :=
rfl
instance {R : Type*} [Zero R] [One R] [Neg R] [Subsingleton R] : Subsingleton ℍ[R] :=
inferInstanceAs (Subsingleton <| ℍ[R, -1, 0, -1])
instance {R : Type*} [Zero R] [One R] [Neg R] [Nontrivial R] : Nontrivial ℍ[R] :=
inferInstanceAs (Nontrivial <| ℍ[R, -1, 0, -1])
namespace Quaternion
variable {S T R : Type*} [CommRing R] (r x y : R) (a b : ℍ[R])
/-- Coercion `R → ℍ[R]`. -/
@[coe] def coe : R → ℍ[R] := QuaternionAlgebra.coe
instance : CoeTC R ℍ[R] := ⟨coe⟩
instance instRing : Ring ℍ[R] := QuaternionAlgebra.instRing
instance : Inhabited ℍ[R] := inferInstanceAs <| Inhabited ℍ[R,-1, 0, -1]
instance [SMul S R] : SMul S ℍ[R] := inferInstanceAs <| SMul S ℍ[R,-1, 0, -1]
instance [SMul S T] [SMul S R] [SMul T R] [IsScalarTower S T R] : IsScalarTower S T ℍ[R] :=
inferInstanceAs <| IsScalarTower S T ℍ[R,-1,0,-1]
instance [SMul S R] [SMul T R] [SMulCommClass S T R] : SMulCommClass S T ℍ[R] :=
inferInstanceAs <| SMulCommClass S T ℍ[R,-1,0,-1]
protected instance algebra [CommSemiring S] [Algebra S R] : Algebra S ℍ[R] :=
inferInstanceAs <| Algebra S ℍ[R,-1,0,-1]
instance : Star ℍ[R] := QuaternionAlgebra.instStarQuaternionAlgebra
instance : StarRing ℍ[R] := QuaternionAlgebra.instStarRing
instance : IsStarNormal a := inferInstanceAs <| IsStarNormal (R := ℍ[R,-1,0,-1]) a
@[ext]
theorem ext : a.re = b.re → a.imI = b.imI → a.imJ = b.imJ → a.imK = b.imK → a = b :=
QuaternionAlgebra.ext
/-- The imaginary part of a quaternion. -/
nonrec def im (x : ℍ[R]) : ℍ[R] := x.im
@[simp] theorem im_re : a.im.re = 0 := rfl
@[simp] theorem im_imI : a.im.imI = a.imI := rfl
@[simp] theorem im_imJ : a.im.imJ = a.imJ := rfl
@[simp] theorem im_imK : a.im.imK = a.imK := rfl
@[simp] theorem im_idem : a.im.im = a.im := rfl
@[simp] nonrec theorem re_add_im : ↑a.re + a.im = a := a.re_add_im
@[simp] nonrec theorem sub_self_im : a - a.im = a.re := a.sub_self_im
@[simp] nonrec theorem sub_self_re : a - ↑a.re = a.im := a.sub_self_re
@[simp, norm_cast]
theorem coe_re : (x : ℍ[R]).re = x := rfl
@[simp, norm_cast]
theorem coe_imI : (x : ℍ[R]).imI = 0 := rfl
@[simp, norm_cast]
theorem coe_imJ : (x : ℍ[R]).imJ = 0 := rfl
@[simp, norm_cast]
theorem coe_imK : (x : ℍ[R]).imK = 0 := rfl
@[simp, norm_cast]
theorem coe_im : (x : ℍ[R]).im = 0 := rfl
@[scoped simp] theorem zero_re : (0 : ℍ[R]).re = 0 := rfl
@[scoped simp] theorem zero_imI : (0 : ℍ[R]).imI = 0 := rfl
@[scoped simp] theorem zero_imJ : (0 : ℍ[R]).imJ = 0 := rfl
@[scoped simp] theorem zero_imK : (0 : ℍ[R]).imK = 0 := rfl
@[scoped simp] theorem zero_im : (0 : ℍ[R]).im = 0 := rfl
@[simp, norm_cast]
theorem coe_zero : ((0 : R) : ℍ[R]) = 0 := rfl
@[scoped simp] theorem one_re : (1 : ℍ[R]).re = 1 := rfl
@[scoped simp] theorem one_imI : (1 : ℍ[R]).imI = 0 := rfl
@[scoped simp] theorem one_imJ : (1 : ℍ[R]).imJ = 0 := rfl
@[scoped simp] theorem one_imK : (1 : ℍ[R]).imK = 0 := rfl
@[scoped simp] theorem one_im : (1 : ℍ[R]).im = 0 := rfl
@[simp, norm_cast]
theorem coe_one : ((1 : R) : ℍ[R]) = 1 := rfl
@[simp] theorem add_re : (a + b).re = a.re + b.re := rfl
@[simp] theorem add_imI : (a + b).imI = a.imI + b.imI := rfl
@[simp] theorem add_imJ : (a + b).imJ = a.imJ + b.imJ := rfl
@[simp] theorem add_imK : (a + b).imK = a.imK + b.imK := rfl
@[simp] nonrec theorem add_im : (a + b).im = a.im + b.im := a.add_im b
@[simp, norm_cast]
theorem coe_add : ((x + y : R) : ℍ[R]) = x + y :=
QuaternionAlgebra.coe_add x y
@[simp] theorem neg_re : (-a).re = -a.re := rfl
@[simp] theorem neg_imI : (-a).imI = -a.imI := rfl
@[simp] theorem neg_imJ : (-a).imJ = -a.imJ := rfl
@[simp] theorem neg_imK : (-a).imK = -a.imK := rfl
@[simp] nonrec theorem neg_im : (-a).im = -a.im := a.neg_im
@[simp, norm_cast]
theorem coe_neg : ((-x : R) : ℍ[R]) = -x :=
QuaternionAlgebra.coe_neg x
@[simp] theorem sub_re : (a - b).re = a.re - b.re := rfl
@[simp] theorem sub_imI : (a - b).imI = a.imI - b.imI := rfl
@[simp] theorem sub_imJ : (a - b).imJ = a.imJ - b.imJ := rfl
@[simp] theorem sub_imK : (a - b).imK = a.imK - b.imK := rfl
@[simp] nonrec theorem sub_im : (a - b).im = a.im - b.im := a.sub_im b
@[simp, norm_cast]
theorem coe_sub : ((x - y : R) : ℍ[R]) = x - y :=
QuaternionAlgebra.coe_sub x y
@[simp]
theorem mul_re : (a * b).re = a.re * b.re - a.imI * b.imI - a.imJ * b.imJ - a.imK * b.imK :=
(QuaternionAlgebra.mul_re a b).trans <| by simp [one_mul, neg_mul, sub_eq_add_neg, neg_neg]
@[simp]
theorem mul_imI : (a * b).imI = a.re * b.imI + a.imI * b.re + a.imJ * b.imK - a.imK * b.imJ :=
(QuaternionAlgebra.mul_imI a b).trans <| by ring
@[simp]
theorem mul_imJ : (a * b).imJ = a.re * b.imJ - a.imI * b.imK + a.imJ * b.re + a.imK * b.imI :=
(QuaternionAlgebra.mul_imJ a b).trans <| by ring
@[simp]
theorem mul_imK : (a * b).imK = a.re * b.imK + a.imI * b.imJ - a.imJ * b.imI + a.imK * b.re :=
(QuaternionAlgebra.mul_imK a b).trans <| by ring
@[simp, norm_cast]
theorem coe_mul : ((x * y : R) : ℍ[R]) = x * y := QuaternionAlgebra.coe_mul x y
@[norm_cast, simp]
theorem coe_pow (n : ℕ) : (↑(x ^ n) : ℍ[R]) = (x : ℍ[R]) ^ n :=
QuaternionAlgebra.coe_pow x n
@[simp, norm_cast]
theorem natCast_re (n : ℕ) : (n : ℍ[R]).re = n := rfl
@[simp, norm_cast]
theorem natCast_imI (n : ℕ) : (n : ℍ[R]).imI = 0 := rfl
@[simp, norm_cast]
theorem natCast_imJ (n : ℕ) : (n : ℍ[R]).imJ = 0 := rfl
@[simp, norm_cast]
theorem natCast_imK (n : ℕ) : (n : ℍ[R]).imK = 0 := rfl
@[simp, norm_cast]
theorem natCast_im (n : ℕ) : (n : ℍ[R]).im = 0 := rfl
@[norm_cast]
theorem coe_natCast (n : ℕ) : ↑(n : R) = (n : ℍ[R]) := rfl
@[simp, norm_cast]
theorem intCast_re (z : ℤ) : (z : ℍ[R]).re = z := rfl
@[simp, norm_cast]
theorem intCast_imI (z : ℤ) : (z : ℍ[R]).imI = 0 := rfl
@[simp, norm_cast]
theorem intCast_imJ (z : ℤ) : (z : ℍ[R]).imJ = 0 := rfl
@[simp, norm_cast]
theorem intCast_imK (z : ℤ) : (z : ℍ[R]).imK = 0 := rfl
@[simp, norm_cast]
theorem intCast_im (z : ℤ) : (z : ℍ[R]).im = 0 := rfl
@[norm_cast]
theorem coe_intCast (z : ℤ) : ↑(z : R) = (z : ℍ[R]) := rfl
theorem coe_injective : Function.Injective (coe : R → ℍ[R]) :=
QuaternionAlgebra.coe_injective
@[simp]
theorem coe_inj {x y : R} : (x : ℍ[R]) = y ↔ x = y :=
coe_injective.eq_iff
@[simp]
theorem smul_re [SMul S R] (s : S) : (s • a).re = s • a.re :=
rfl
@[simp] theorem smul_imI [SMul S R] (s : S) : (s • a).imI = s • a.imI := rfl
@[simp] theorem smul_imJ [SMul S R] (s : S) : (s • a).imJ = s • a.imJ := rfl
@[simp] theorem smul_imK [SMul S R] (s : S) : (s • a).imK = s • a.imK := rfl
@[simp]
nonrec theorem smul_im [SMulZeroClass S R] (s : S) : (s • a).im = s • a.im :=
a.smul_im s
@[simp, norm_cast]
theorem coe_smul [SMulZeroClass S R] (s : S) (r : R) : (↑(s • r) : ℍ[R]) = s • (r : ℍ[R]) :=
QuaternionAlgebra.coe_smul _ _
theorem coe_commutes : ↑r * a = a * r :=
QuaternionAlgebra.coe_commutes r a
theorem coe_commute : Commute (↑r) a :=
QuaternionAlgebra.coe_commute r a
theorem coe_mul_eq_smul : ↑r * a = r • a :=
QuaternionAlgebra.coe_mul_eq_smul r a
theorem mul_coe_eq_smul : a * r = r • a :=
QuaternionAlgebra.mul_coe_eq_smul r a
@[simp]
theorem algebraMap_def : ⇑(algebraMap R ℍ[R]) = coe :=
rfl
theorem algebraMap_injective : (algebraMap R ℍ[R] : _ → _).Injective :=
QuaternionAlgebra.algebraMap_injective
theorem smul_coe : x • (y : ℍ[R]) = ↑(x * y) :=
QuaternionAlgebra.smul_coe x y
instance : Module.Finite R ℍ[R] := inferInstanceAs <| Module.Finite R ℍ[R,-1,0,-1]
instance : Module.Free R ℍ[R] := inferInstanceAs <| Module.Free R ℍ[R,-1,0,-1]
theorem rank_eq_four [StrongRankCondition R] : Module.rank R ℍ[R] = 4 :=
QuaternionAlgebra.rank_eq_four _ _ _
theorem finrank_eq_four [StrongRankCondition R] : Module.finrank R ℍ[R] = 4 :=
QuaternionAlgebra.finrank_eq_four _ _ _
@[simp] theorem star_re : (star a).re = a.re := by
rw [QuaternionAlgebra.re_star, zero_mul, add_zero]
@[simp] theorem star_imI : (star a).imI = -a.imI := rfl
@[simp] theorem star_imJ : (star a).imJ = -a.imJ := rfl
@[simp] theorem star_imK : (star a).imK = -a.imK := rfl
@[simp] theorem star_im : (star a).im = -a.im := a.im_star
nonrec theorem self_add_star' : a + star a = ↑(2 * a.re) := by
simp [a.self_add_star', Quaternion.coe]
nonrec theorem self_add_star : a + star a = 2 * a.re := by
simp [a.self_add_star, Quaternion.coe]
nonrec theorem star_add_self' : star a + a = ↑(2 * a.re) := by
simp [a.star_add_self', Quaternion.coe]
nonrec theorem star_add_self : star a + a = 2 * a.re := by
simp [a.star_add_self, Quaternion.coe]
nonrec theorem star_eq_two_re_sub : star a = ↑(2 * a.re) - a := by
simp [a.star_eq_two_re_sub, Quaternion.coe]
@[simp, norm_cast]
theorem star_coe : star (x : ℍ[R]) = x :=
QuaternionAlgebra.star_coe x
@[simp]
theorem im_star : star a.im = -a.im := by ext <;> simp
@[simp]
theorem star_smul [Monoid S] [DistribMulAction S R] (s : S) (a : ℍ[R]) :
star (s • a) = s • star a := QuaternionAlgebra.star_smul' s a
theorem eq_re_of_eq_coe {a : ℍ[R]} {x : R} (h : a = x) : a = a.re :=
QuaternionAlgebra.eq_re_of_eq_coe h
theorem eq_re_iff_mem_range_coe {a : ℍ[R]} : a = a.re ↔ a ∈ Set.range (coe : R → ℍ[R]) :=
QuaternionAlgebra.eq_re_iff_mem_range_coe
section CharZero
variable [NoZeroDivisors R] [CharZero R]
@[simp]
theorem star_eq_self {a : ℍ[R]} : star a = a ↔ a = a.re :=
QuaternionAlgebra.star_eq_self
@[simp]
theorem star_eq_neg {a : ℍ[R]} : star a = -a ↔ a.re = 0 :=
QuaternionAlgebra.star_eq_neg
end CharZero
nonrec theorem star_mul_eq_coe : star a * a = (star a * a).re :=
a.star_mul_eq_coe
nonrec theorem mul_star_eq_coe : a * star a = (a * star a).re :=
a.mul_star_eq_coe
open MulOpposite
/-- Quaternion conjugate as an `AlgEquiv` to the opposite ring. -/
def starAe : ℍ[R] ≃ₐ[R] ℍ[R]ᵐᵒᵖ :=
QuaternionAlgebra.starAe
@[simp]
theorem coe_starAe : ⇑(starAe : ℍ[R] ≃ₐ[R] ℍ[R]ᵐᵒᵖ) = op ∘ star :=
rfl
/-- Square of the norm. -/
def normSq : ℍ[R] →*₀ R where
toFun a := (a * star a).re
map_zero' := by simp only [star_zero, zero_mul, zero_re]
map_one' := by simp only [star_one, one_mul, one_re]
map_mul' x y := coe_injective <| by
conv_lhs => rw [← mul_star_eq_coe, star_mul, mul_assoc, ← mul_assoc y, y.mul_star_eq_coe,
coe_commutes, ← mul_assoc, x.mul_star_eq_coe, ← coe_mul]
theorem normSq_def : normSq a = (a * star a).re := rfl
theorem normSq_def' : normSq a = a.1 ^ 2 + a.2 ^ 2 + a.3 ^ 2 + a.4 ^ 2 := by
simp only [normSq_def, sq, mul_neg, sub_neg_eq_add, mul_re, star_re, star_imI, star_imJ,
star_imK]
theorem normSq_coe : normSq (x : ℍ[R]) = x ^ 2 := by
rw [normSq_def, star_coe, ← coe_mul, coe_re, sq]
@[simp]
theorem normSq_star : normSq (star a) = normSq a := by simp [normSq_def']
@[norm_cast]
theorem normSq_natCast (n : ℕ) : normSq (n : ℍ[R]) = (n : R) ^ 2 := by
rw [← coe_natCast, normSq_coe]
@[norm_cast]
theorem normSq_intCast (z : ℤ) : normSq (z : ℍ[R]) = (z : R) ^ 2 := by
rw [← coe_intCast, normSq_coe]
@[simp]
theorem normSq_neg : normSq (-a) = normSq a := by simp only [normSq_def, star_neg, neg_mul_neg]
theorem self_mul_star : a * star a = normSq a := by rw [mul_star_eq_coe, normSq_def]
theorem star_mul_self : star a * a = normSq a := by rw [star_comm_self, self_mul_star]
theorem im_sq : a.im ^ 2 = -normSq a.im := by
simp_rw [sq, ← star_mul_self, im_star, neg_mul, neg_neg]
theorem coe_normSq_add : normSq (a + b) = normSq a + a * star b + b * star a + normSq b := by
simp only [star_add, ← self_mul_star, mul_add, add_mul, add_assoc, add_left_comm]
theorem normSq_smul (r : R) (q : ℍ[R]) : normSq (r • q) = r ^ 2 * normSq q := by
simp only [normSq_def', smul_re, smul_imI, smul_imJ, smul_imK, mul_pow, mul_add, smul_eq_mul]
theorem normSq_add (a b : ℍ[R]) : normSq (a + b) = normSq a + normSq b + 2 * (a * star b).re :=
calc
normSq (a + b) = normSq a + (a * star b).re + ((b * star a).re + normSq b) := by
simp_rw [normSq_def, star_add, add_mul, mul_add, add_re]
_ = normSq a + normSq b + ((a * star b).re + (b * star a).re) := by abel
_ = normSq a + normSq b + 2 * (a * star b).re := by
rw [← add_re, ← star_mul_star a b, self_add_star', coe_re]
end Quaternion
namespace Quaternion
variable {R : Type*}
section LinearOrderedCommRing
variable [CommRing R] [LinearOrder R] [IsStrictOrderedRing R] {a : ℍ[R]}
@[simp]
theorem normSq_eq_zero : normSq a = 0 ↔ a = 0 := by
refine ⟨fun h => ?_, fun h => h.symm ▸ normSq.map_zero⟩
rw [normSq_def', add_eq_zero_iff_of_nonneg, add_eq_zero_iff_of_nonneg, add_eq_zero_iff_of_nonneg]
at h
· exact ext a 0 (pow_eq_zero h.1.1.1) (pow_eq_zero h.1.1.2) (pow_eq_zero h.1.2) (pow_eq_zero h.2)
all_goals apply_rules [sq_nonneg, add_nonneg]
theorem normSq_ne_zero : normSq a ≠ 0 ↔ a ≠ 0 := normSq_eq_zero.not
@[simp]
theorem normSq_nonneg : 0 ≤ normSq a := by
rw [normSq_def']
apply_rules [sq_nonneg, add_nonneg]
@[simp]
theorem normSq_le_zero : normSq a ≤ 0 ↔ a = 0 :=
normSq_nonneg.le_iff_eq.trans normSq_eq_zero
instance instNontrivial : Nontrivial ℍ[R] where
exists_pair_ne := ⟨0, 1, mt (congr_arg QuaternionAlgebra.re) zero_ne_one⟩
instance : NoZeroDivisors ℍ[R] where
eq_zero_or_eq_zero_of_mul_eq_zero {a b} hab :=
have : normSq a * normSq b = 0 := by rwa [← map_mul, normSq_eq_zero]
(eq_zero_or_eq_zero_of_mul_eq_zero this).imp normSq_eq_zero.1 normSq_eq_zero.1
instance : IsDomain ℍ[R] := NoZeroDivisors.to_isDomain _
theorem sq_eq_normSq : a ^ 2 = normSq a ↔ a = a.re := by
rw [← star_eq_self, ← star_mul_self, sq, mul_eq_mul_right_iff, eq_comm]
exact or_iff_left_of_imp fun ha ↦ ha.symm ▸ star_zero _
theorem sq_eq_neg_normSq : a ^ 2 = -normSq a ↔ a.re = 0 := by
simp_rw [← star_eq_neg]
obtain rfl | hq0 := eq_or_ne a 0
· simp
· rw [← star_mul_self, ← mul_neg, ← neg_sq, sq, mul_left_inj' (neg_ne_zero.mpr hq0), eq_comm]
end LinearOrderedCommRing
section Field
variable [Field R] (a b : ℍ[R])
instance instNNRatCast : NNRatCast ℍ[R] where nnratCast q := (q : R)
instance instRatCast : RatCast ℍ[R] where ratCast q := (q : R)
@[simp, norm_cast] lemma re_nnratCast (q : ℚ≥0) : (q : ℍ[R]).re = q := rfl
@[simp, norm_cast] lemma im_nnratCast (q : ℚ≥0) : (q : ℍ[R]).im = 0 := rfl
@[simp, norm_cast] lemma imI_nnratCast (q : ℚ≥0) : (q : ℍ[R]).imI = 0 := rfl
@[simp, norm_cast] lemma imJ_nnratCast (q : ℚ≥0) : (q : ℍ[R]).imJ = 0 := rfl
@[simp, norm_cast] lemma imK_nnratCast (q : ℚ≥0) : (q : ℍ[R]).imK = 0 := rfl
@[simp, norm_cast] lemma ratCast_re (q : ℚ) : (q : ℍ[R]).re = q := rfl
@[simp, norm_cast] lemma ratCast_im (q : ℚ) : (q : ℍ[R]).im = 0 := rfl
@[simp, norm_cast] lemma ratCast_imI (q : ℚ) : (q : ℍ[R]).imI = 0 := rfl
@[simp, norm_cast] lemma ratCast_imJ (q : ℚ) : (q : ℍ[R]).imJ = 0 := rfl
@[simp, norm_cast] lemma ratCast_imK (q : ℚ) : (q : ℍ[R]).imK = 0 := rfl
@[norm_cast] lemma coe_nnratCast (q : ℚ≥0) : ↑(q : R) = (q : ℍ[R]) := rfl
@[norm_cast] lemma coe_ratCast (q : ℚ) : ↑(q : R) = (q : ℍ[R]) := rfl
variable [LinearOrder R] [IsStrictOrderedRing R] (a b : ℍ[R])
@[simps -isSimp]
instance instInv : Inv ℍ[R] :=
⟨fun a => (normSq a)⁻¹ • star a⟩
instance instGroupWithZero : GroupWithZero ℍ[R] :=
{ Quaternion.instNontrivial with
inv := Inv.inv
inv_zero := by rw [instInv_inv, star_zero, smul_zero]
mul_inv_cancel := fun a ha => by
rw [instInv_inv, Algebra.mul_smul_comm (normSq a)⁻¹ a (star a), self_mul_star, smul_coe,
inv_mul_cancel₀ (normSq_ne_zero.2 ha), coe_one] }
@[norm_cast, simp]
theorem coe_inv (x : R) : ((x⁻¹ : R) : ℍ[R]) = (↑x)⁻¹ :=
map_inv₀ (algebraMap R ℍ[R]) _
@[norm_cast, simp]
theorem coe_div (x y : R) : ((x / y : R) : ℍ[R]) = x / y :=
map_div₀ (algebraMap R ℍ[R]) x y
@[norm_cast, simp]
theorem coe_zpow (x : R) (z : ℤ) : ((x ^ z : R) : ℍ[R]) = (x : ℍ[R]) ^ z :=
map_zpow₀ (algebraMap R ℍ[R]) x z
instance instDivisionRing : DivisionRing ℍ[R] where
__ := Quaternion.instRing
__ := Quaternion.instGroupWithZero
nnqsmul := (· • ·)
qsmul := (· • ·)
nnratCast_def _ := by rw [← coe_nnratCast, NNRat.cast_def, coe_div, coe_natCast, coe_natCast]
ratCast_def _ := by rw [← coe_ratCast, Rat.cast_def, coe_div, coe_intCast, coe_natCast]
nnqsmul_def _ _ := by rw [← coe_nnratCast, coe_mul_eq_smul]; ext <;> exact NNRat.smul_def ..
qsmul_def _ _ := by rw [← coe_ratCast, coe_mul_eq_smul]; ext <;> exact Rat.smul_def ..
theorem normSq_inv : normSq a⁻¹ = (normSq a)⁻¹ :=
map_inv₀ normSq _
theorem normSq_div : normSq (a / b) = normSq a / normSq b :=
map_div₀ normSq a b
theorem normSq_zpow (z : ℤ) : normSq (a ^ z) = normSq a ^ z :=
map_zpow₀ normSq a z
@[norm_cast]
theorem normSq_ratCast (q : ℚ) : normSq (q : ℍ[R]) = (q : ℍ[R]) ^ 2 := by
rw [← coe_ratCast, normSq_coe, coe_pow]
end Field
end Quaternion
namespace Cardinal
open Quaternion
section QuaternionAlgebra
variable {R : Type*} (c₁ c₂ c₃ : R)
private theorem pow_four [Infinite R] : #R ^ 4 = #R :=
power_nat_eq (aleph0_le_mk R) <| by decide
/-- The cardinality of a quaternion algebra, as a type. -/
theorem mk_quaternionAlgebra : #(ℍ[R,c₁,c₂,c₃]) = #R ^ 4 := by
rw [mk_congr (QuaternionAlgebra.equivProd c₁ c₂ c₃)]
simp only [mk_prod, lift_id]
ring
@[simp]
theorem mk_quaternionAlgebra_of_infinite [Infinite R] : #(ℍ[R,c₁,c₂,c₃]) = #R := by
rw [mk_quaternionAlgebra, pow_four]
/-- The cardinality of a quaternion algebra, as a set. -/
theorem mk_univ_quaternionAlgebra : #(Set.univ : Set ℍ[R,c₁,c₂,c₃]) = #R ^ 4 := by
rw [mk_univ, mk_quaternionAlgebra]
theorem mk_univ_quaternionAlgebra_of_infinite [Infinite R] :
#(Set.univ : Set ℍ[R,c₁,c₂,c₃]) = #R := by rw [mk_univ_quaternionAlgebra, pow_four]
/-- Show the quaternion ⟨w, x, y, z⟩ as a string "{ re := w, imI := x, imJ := y, imK := z }".
For the typical case of quaternions over ℝ, each component will show as a Cauchy sequence due to
the way Real numbers are represented.
-/
instance [Repr R] {a b c : R} : Repr ℍ[R, a, b, c] where
reprPrec q _ :=
s!"\{ re := {repr q.re}, imI := {repr q.imI}, imJ := {repr q.imJ}, imK := {repr q.imK} }"
end QuaternionAlgebra
section Quaternion
variable (R : Type*) [Zero R] [One R] [Neg R]
/-- The cardinality of the quaternions, as a type. -/
@[simp]
theorem mk_quaternion : #(ℍ[R]) = #R ^ 4 :=
mk_quaternionAlgebra _ _ _
theorem mk_quaternion_of_infinite [Infinite R] : #(ℍ[R]) = #R :=
mk_quaternionAlgebra_of_infinite _ _ _
/-- The cardinality of the quaternions, as a set. -/
theorem mk_univ_quaternion : #(Set.univ : Set ℍ[R]) = #R ^ 4 :=
mk_univ_quaternionAlgebra _ _ _
theorem mk_univ_quaternion_of_infinite [Infinite R] : #(Set.univ : Set ℍ[R]) = #R :=
mk_univ_quaternionAlgebra_of_infinite _ _ _
end Quaternion
end Cardinal
| Mathlib/Algebra/Quaternion.lean | 1,386 | 1,388 | |
/-
Copyright (c) 2022 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov, Heather Macbeth
-/
import Mathlib.Analysis.Normed.Field.Lemmas
import Mathlib.Analysis.Normed.Group.BallSphere
/-!
# Algebraic structures on unit balls and spheres
In this file we define algebraic structures (`Semigroup`, `CommSemigroup`, `Monoid`, `CommMonoid`,
`Group`, `CommGroup`) on `Metric.ball (0 : 𝕜) 1`, `Metric.closedBall (0 : 𝕜) 1`, and
`Metric.sphere (0 : 𝕜) 1`. In each case we use the weakest possible typeclass assumption on `𝕜`,
from `NonUnitalSeminormedRing` to `NormedField`.
-/
open Set Metric
variable {𝕜 : Type*}
/-!
### Algebraic structures on `Metric.ball 0 1`
-/
/-- Unit ball in a non-unital seminormed ring as a bundled `Subsemigroup`. -/
def Subsemigroup.unitBall (𝕜 : Type*) [NonUnitalSeminormedRing 𝕜] : Subsemigroup 𝕜 where
carrier := ball (0 : 𝕜) 1
mul_mem' hx hy := by
rw [mem_ball_zero_iff] at *
exact (norm_mul_le _ _).trans_lt (mul_lt_one_of_nonneg_of_lt_one_left (norm_nonneg _) hx hy.le)
instance Metric.unitBall.instSemigroup [NonUnitalSeminormedRing 𝕜] : Semigroup (ball (0 : 𝕜) 1) :=
MulMemClass.toSemigroup (Subsemigroup.unitBall 𝕜)
instance Metric.unitBall.instContinuousMul [NonUnitalSeminormedRing 𝕜] :
ContinuousMul (ball (0 : 𝕜) 1) :=
(Subsemigroup.unitBall 𝕜).continuousMul
instance Metric.unitBall.instCommSemigroup [SeminormedCommRing 𝕜] :
CommSemigroup (ball (0 : 𝕜) 1) :=
MulMemClass.toCommSemigroup (Subsemigroup.unitBall 𝕜)
instance Metric.unitBall.instHasDistribNeg [NonUnitalSeminormedRing 𝕜] :
HasDistribNeg (ball (0 : 𝕜) 1) :=
Subtype.coe_injective.hasDistribNeg ((↑) : ball (0 : 𝕜) 1 → 𝕜) (fun _ => rfl) fun _ _ => rfl
@[simp, norm_cast]
protected theorem Metric.unitBall.coe_mul [NonUnitalSeminormedRing 𝕜] (x y : ball (0 : 𝕜) 1) :
↑(x * y) = (x * y : 𝕜) :=
rfl
@[deprecated (since := "2025-04-18")]
alias coe_mul_unitBall := Metric.unitBall.coe_mul
instance Metric.unitBall.instZero [Zero 𝕜] [PseudoMetricSpace 𝕜] : Zero (ball (0 : 𝕜) 1) :=
⟨⟨0, by simp⟩⟩
@[simp, norm_cast]
protected theorem Metric.unitBall.coe_zero [Zero 𝕜] [PseudoMetricSpace 𝕜] :
((0 : ball (0 : 𝕜) 1) : 𝕜) = 0 :=
rfl
@[simp, norm_cast]
protected theorem Metric.unitBall.coe_eq_zero [Zero 𝕜] [PseudoMetricSpace 𝕜] {a : ball (0 : 𝕜) 1} :
(a : 𝕜) = 0 ↔ a = 0 :=
Subtype.val_injective.eq_iff' unitBall.coe_zero
instance Metric.unitBall.instSemigroupWithZero [NonUnitalSeminormedRing 𝕜] :
SemigroupWithZero (ball (0 : 𝕜) 1) where
zero_mul _ := Subtype.eq <| zero_mul _
mul_zero _ := Subtype.eq <| mul_zero _
instance Metric.unitBall.instIsLeftCancelMulZero [NonUnitalSeminormedRing 𝕜]
[IsLeftCancelMulZero 𝕜] : IsLeftCancelMulZero (ball (0 : 𝕜) 1) :=
Subtype.val_injective.isLeftCancelMulZero _ rfl fun _ _ ↦ rfl
instance Metric.unitBall.instIsRightCancelMulZero [NonUnitalSeminormedRing 𝕜]
[IsRightCancelMulZero 𝕜] : IsRightCancelMulZero (ball (0 : 𝕜) 1) :=
Subtype.val_injective.isRightCancelMulZero _ rfl fun _ _ ↦ rfl
instance Metric.unitBall.instIsCancelMulZero [NonUnitalSeminormedRing 𝕜]
[IsCancelMulZero 𝕜] : IsCancelMulZero (ball (0 : 𝕜) 1) where
/-!
### Algebraic instances for `Metric.closedBall 0 1`
-/
/-- Closed unit ball in a non-unital seminormed ring as a bundled `Subsemigroup`. -/
def Subsemigroup.unitClosedBall (𝕜 : Type*) [NonUnitalSeminormedRing 𝕜] : Subsemigroup 𝕜 where
carrier := closedBall 0 1
mul_mem' hx hy := by
rw [mem_closedBall_zero_iff] at *
exact (norm_mul_le _ _).trans (mul_le_one₀ hx (norm_nonneg _) hy)
instance Metric.unitClosedBall.instSemigroup [NonUnitalSeminormedRing 𝕜] :
Semigroup (closedBall (0 : 𝕜) 1) :=
MulMemClass.toSemigroup (Subsemigroup.unitClosedBall 𝕜)
instance Metric.unitClosedBall.instHasDistribNeg [NonUnitalSeminormedRing 𝕜] :
HasDistribNeg (closedBall (0 : 𝕜) 1) :=
Subtype.coe_injective.hasDistribNeg ((↑) : closedBall (0 : 𝕜) 1 → 𝕜) (fun _ => rfl) fun _ _ => rfl
instance Metric.unitClosedBall.instContinuousMul [NonUnitalSeminormedRing 𝕜] :
ContinuousMul (closedBall (0 : 𝕜) 1) :=
(Subsemigroup.unitClosedBall 𝕜).continuousMul
@[simp, norm_cast]
protected theorem Metric.unitClosedBall.coe_mul [NonUnitalSeminormedRing 𝕜]
(x y : closedBall (0 : 𝕜) 1) : ↑(x * y) = (x * y : 𝕜) :=
rfl
@[deprecated (since := "2025-04-18")]
alias coe_mul_unitClosedBall := Metric.unitClosedBall.coe_mul
instance Metric.unitClosedBall.instZero [Zero 𝕜] [PseudoMetricSpace 𝕜] :
Zero (closedBall (0 : 𝕜) 1) where
zero := ⟨0, by simp⟩
@[simp, norm_cast]
protected lemma Metric.unitClosedBall.coe_zero [Zero 𝕜] [PseudoMetricSpace 𝕜] :
((0 : closedBall (0 : 𝕜) 1) : 𝕜) = 0 :=
rfl
@[simp, norm_cast]
protected lemma Metric.unitClosedBall.coe_eq_zero [Zero 𝕜] [PseudoMetricSpace 𝕜]
{a : closedBall (0 : 𝕜) 1} : (a : 𝕜) = 0 ↔ a = 0 :=
Subtype.val_injective.eq_iff' unitClosedBall.coe_zero
instance Metric.unitClosedBall.instSemigroupWithZero [NonUnitalSeminormedRing 𝕜] :
SemigroupWithZero (closedBall (0 : 𝕜) 1) where
zero_mul _ := Subtype.eq <| zero_mul _
mul_zero _ := Subtype.eq <| mul_zero _
/-- Closed unit ball in a seminormed ring as a bundled `Submonoid`. -/
def Submonoid.unitClosedBall (𝕜 : Type*) [SeminormedRing 𝕜] [NormOneClass 𝕜] : Submonoid 𝕜 :=
{ Subsemigroup.unitClosedBall 𝕜 with
carrier := closedBall 0 1
one_mem' := mem_closedBall_zero_iff.2 norm_one.le }
instance Metric.unitClosedBall.instMonoid [SeminormedRing 𝕜] [NormOneClass 𝕜] :
Monoid (closedBall (0 : 𝕜) 1) :=
SubmonoidClass.toMonoid (Submonoid.unitClosedBall 𝕜)
instance Metric.unitClosedBall.instCommMonoid [SeminormedCommRing 𝕜] [NormOneClass 𝕜] :
CommMonoid (closedBall (0 : 𝕜) 1) :=
SubmonoidClass.toCommMonoid (Submonoid.unitClosedBall 𝕜)
@[simp, norm_cast]
protected theorem Metric.unitClosedBall.coe_one [SeminormedRing 𝕜] [NormOneClass 𝕜] :
((1 : closedBall (0 : 𝕜) 1) : 𝕜) = 1 :=
rfl
@[deprecated (since := "2025-04-18")]
alias coe_one_unitClosedBall := Metric.unitClosedBall.coe_one
@[simp, norm_cast]
protected theorem Metric.unitClosedBall.coe_eq_one [SeminormedRing 𝕜] [NormOneClass 𝕜]
{a : closedBall (0 : 𝕜) 1} : (a : 𝕜) = 1 ↔ a = 1 :=
Subtype.val_injective.eq_iff' unitClosedBall.coe_one
@[simp, norm_cast]
protected theorem Metric.unitClosedBall.coe_pow [SeminormedRing 𝕜] [NormOneClass 𝕜]
(x : closedBall (0 : 𝕜) 1) (n : ℕ) : ↑(x ^ n) = (x : 𝕜) ^ n :=
rfl
@[deprecated (since := "2025-04-18")]
alias coe_pow_unitClosedBall := Metric.unitClosedBall.coe_pow
instance Metric.unitClosedBall.instMonoidWithZero [SeminormedRing 𝕜] [NormOneClass 𝕜] :
MonoidWithZero (closedBall (0 : 𝕜) 1) where
instance Metric.unitClosedBall.instCancelMonoidWithZero [SeminormedRing 𝕜] [IsCancelMulZero 𝕜]
[NormOneClass 𝕜] : CancelMonoidWithZero (closedBall (0 : 𝕜) 1) where
toIsCancelMulZero := Subtype.val_injective.isCancelMulZero _ rfl fun _ _ ↦ rfl
/-!
### Algebraic instances on the unit sphere
-/
| /-- Unit sphere in a seminormed ring (with strictly multiplicative norm) as a bundled
`Submonoid`. -/
@[simps]
| Mathlib/Analysis/Normed/Field/UnitBall.lean | 182 | 184 |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Antoine Chambert-Loir
-/
import Mathlib.Algebra.DirectSum.Finsupp
import Mathlib.LinearAlgebra.DirectSum.TensorProduct
import Mathlib.LinearAlgebra.Finsupp.SumProd
/-!
# Results on finitely supported functions.
* `TensorProduct.finsuppLeft`, the tensor product of `ι →₀ M` and `N`
is linearly equivalent to `ι →₀ M ⊗[R] N`
* `TensorProduct.finsuppScalarLeft`, the tensor product of `ι →₀ R` and `N`
is linearly equivalent to `ι →₀ N`
* `TensorProduct.finsuppRight`, the tensor product of `M` and `ι →₀ N`
is linearly equivalent to `ι →₀ M ⊗[R] N`
* `TensorProduct.finsuppScalarRight`, the tensor product of `M` and `ι →₀ R`
is linearly equivalent to `ι →₀ N`
* `TensorProduct.finsuppLeft'`, if `M` is an `S`-module,
then the tensor product of `ι →₀ M` and `N` is `S`-linearly equivalent
to `ι →₀ M ⊗[R] N`
* `finsuppTensorFinsupp`, the tensor product of `ι →₀ M` and `κ →₀ N`
is linearly equivalent to `(ι × κ) →₀ (M ⊗ N)`.
## Case of MvPolynomial
These functions apply to `MvPolynomial`, one can define
```
noncomputable def MvPolynomial.rTensor' :
MvPolynomial σ S ⊗[R] N ≃ₗ[S] (σ →₀ ℕ) →₀ (S ⊗[R] N) :=
TensorProduct.finsuppLeft'
noncomputable def MvPolynomial.rTensor :
MvPolynomial σ R ⊗[R] N ≃ₗ[R] (σ →₀ ℕ) →₀ N :=
TensorProduct.finsuppScalarLeft
```
However, to be actually usable, these definitions need lemmas to be given in companion PR.
## Case of `Polynomial`
`Polynomial` is a structure containing a `Finsupp`, so these functions
can't be applied directly to `Polynomial`.
Some linear equivs need to be added to mathlib for that.
This belongs to a companion PR.
## TODO
* generalize to `MonoidAlgebra`, `AlgHom `
* reprove `TensorProduct.finsuppLeft'` using existing heterobasic version of `TensorProduct.congr`
-/
noncomputable section
open DirectSum TensorProduct
open Set LinearMap Submodule
section TensorProduct
variable (R : Type*) [CommSemiring R]
(M : Type*) [AddCommMonoid M] [Module R M]
(N : Type*) [AddCommMonoid N] [Module R N]
namespace TensorProduct
variable (ι : Type*) [DecidableEq ι]
/-- The tensor product of `ι →₀ M` and `N` is linearly equivalent to `ι →₀ M ⊗[R] N` -/
noncomputable def finsuppLeft :
(ι →₀ M) ⊗[R] N ≃ₗ[R] ι →₀ M ⊗[R] N :=
congr (finsuppLEquivDirectSum R M ι) (.refl R N) ≪≫ₗ
directSumLeft R (fun _ ↦ M) N ≪≫ₗ (finsuppLEquivDirectSum R _ ι).symm
variable {R M N ι}
lemma finsuppLeft_apply_tmul (p : ι →₀ M) (n : N) :
finsuppLeft R M N ι (p ⊗ₜ[R] n) = p.sum fun i m ↦ Finsupp.single i (m ⊗ₜ[R] n) := by
induction p using Finsupp.induction_linear with
| zero => simp
| add f g hf hg => simp [add_tmul, map_add, hf, hg, Finsupp.sum_add_index]
| single => simp [finsuppLeft]
@[simp]
lemma finsuppLeft_apply_tmul_apply (p : ι →₀ M) (n : N) (i : ι) :
finsuppLeft R M N ι (p ⊗ₜ[R] n) i = p i ⊗ₜ[R] n := by
rw [finsuppLeft_apply_tmul, Finsupp.sum_apply,
Finsupp.sum_eq_single i (fun _ _ ↦ Finsupp.single_eq_of_ne) (by simp), Finsupp.single_eq_same]
theorem finsuppLeft_apply (t : (ι →₀ M) ⊗[R] N) (i : ι) :
finsuppLeft R M N ι t i = rTensor N (Finsupp.lapply i) t := by
induction t with
| zero => simp
| tmul f n => simp only [finsuppLeft_apply_tmul_apply, rTensor_tmul, Finsupp.lapply_apply]
| add x y hx hy => simp [map_add, hx, hy]
@[simp]
lemma finsuppLeft_symm_apply_single (i : ι) (m : M) (n : N) :
(finsuppLeft R M N ι).symm (Finsupp.single i (m ⊗ₜ[R] n)) =
Finsupp.single i m ⊗ₜ[R] n := by
simp [finsuppLeft, Finsupp.lsum]
variable (R M N ι)
/-- The tensor product of `M` and `ι →₀ N` is linearly equivalent to `ι →₀ M ⊗[R] N` -/
noncomputable def finsuppRight :
M ⊗[R] (ι →₀ N) ≃ₗ[R] ι →₀ M ⊗[R] N :=
congr (.refl R M) (finsuppLEquivDirectSum R N ι) ≪≫ₗ
directSumRight R M (fun _ : ι ↦ N) ≪≫ₗ (finsuppLEquivDirectSum R _ ι).symm
variable {R M N ι}
lemma finsuppRight_apply_tmul (m : M) (p : ι →₀ N) :
finsuppRight R M N ι (m ⊗ₜ[R] p) = p.sum fun i n ↦ Finsupp.single i (m ⊗ₜ[R] n) := by
induction p using Finsupp.induction_linear with
| zero => simp
| add f g hf hg => simp [tmul_add, map_add, hf, hg, Finsupp.sum_add_index]
| single => simp [finsuppRight]
@[simp]
lemma finsuppRight_apply_tmul_apply (m : M) (p : ι →₀ N) (i : ι) :
finsuppRight R M N ι (m ⊗ₜ[R] p) i = m ⊗ₜ[R] p i := by
rw [finsuppRight_apply_tmul, Finsupp.sum_apply,
Finsupp.sum_eq_single i (fun _ _ ↦ Finsupp.single_eq_of_ne) (by simp), Finsupp.single_eq_same]
theorem finsuppRight_apply (t : M ⊗[R] (ι →₀ N)) (i : ι) :
finsuppRight R M N ι t i = lTensor M (Finsupp.lapply i) t := by
induction t with
| zero => simp
| tmul m f => simp [finsuppRight_apply_tmul_apply]
| add x y hx hy => simp [map_add, hx, hy]
@[simp]
lemma finsuppRight_symm_apply_single (i : ι) (m : M) (n : N) :
(finsuppRight R M N ι).symm (Finsupp.single i (m ⊗ₜ[R] n)) =
m ⊗ₜ[R] Finsupp.single i n := by
simp [finsuppRight, Finsupp.lsum]
variable {S : Type*} [CommSemiring S] [Algebra R S]
[Module S M] [IsScalarTower R S M]
lemma finsuppLeft_smul' (s : S) (t : (ι →₀ M) ⊗[R] N) :
finsuppLeft R M N ι (s • t) = s • finsuppLeft R M N ι t := by
induction t with
| zero => simp
| add x y hx hy => simp [hx, hy]
| tmul p n => ext; simp [smul_tmul', finsuppLeft_apply_tmul_apply]
variable (R M N ι S)
/-- When `M` is also an `S`-module, then `TensorProduct.finsuppLeft R M N``
is an `S`-linear equiv -/
noncomputable def finsuppLeft' :
(ι →₀ M) ⊗[R] N ≃ₗ[S] ι →₀ M ⊗[R] N where
__ := finsuppLeft R M N ι
map_smul' := finsuppLeft_smul'
variable {R M N ι S}
lemma finsuppLeft'_apply (x : (ι →₀ M) ⊗[R] N) :
finsuppLeft' R M N ι S x = finsuppLeft R M N ι x := rfl
/- -- TODO : reprove using the existing heterobasic lemmas
noncomputable example :
(ι →₀ M) ⊗[R] N ≃ₗ[S] ι →₀ (M ⊗[R] N) := by
have f : (⨁ (i₁ : ι), M) ⊗[R] N ≃ₗ[S] ⨁ (i : ι), M ⊗[R] N := sorry
exact (AlgebraTensorModule.congr
(finsuppLEquivDirectSum S M ι) (.refl R N)).trans
(f.trans (finsuppLEquivDirectSum S (M ⊗[R] N) ι).symm) -/
variable (R M N ι)
/-- The tensor product of `ι →₀ R` and `N` is linearly equivalent to `ι →₀ N` -/
noncomputable def finsuppScalarLeft :
(ι →₀ R) ⊗[R] N ≃ₗ[R] ι →₀ N :=
finsuppLeft R R N ι ≪≫ₗ (Finsupp.mapRange.linearEquiv (TensorProduct.lid R N))
variable {R M N ι}
@[simp]
lemma finsuppScalarLeft_apply_tmul_apply (p : ι →₀ R) (n : N) (i : ι) :
| finsuppScalarLeft R N ι (p ⊗ₜ[R] n) i = p i • n := by
simp [finsuppScalarLeft]
lemma finsuppScalarLeft_apply_tmul (p : ι →₀ R) (n : N) :
| Mathlib/LinearAlgebra/DirectSum/Finsupp.lean | 187 | 190 |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Algebra.Order.Group.Unbundled.Int
import Mathlib.Algebra.Ring.Nat
import Mathlib.Data.Int.GCD
/-!
# Congruences modulo a natural number
This file defines the equivalence relation `a ≡ b [MOD n]` on the natural numbers,
and proves basic properties about it such as the Chinese Remainder Theorem
`modEq_and_modEq_iff_modEq_mul`.
## Notations
`a ≡ b [MOD n]` is notation for `nat.ModEq n a b`, which is defined to mean `a % n = b % n`.
## Tags
ModEq, congruence, mod, MOD, modulo
-/
assert_not_exists OrderedAddCommMonoid Function.support
namespace Nat
/-- Modular equality. `n.ModEq a b`, or `a ≡ b [MOD n]`, means that `a - b` is a multiple of `n`. -/
def ModEq (n a b : ℕ) :=
a % n = b % n
@[inherit_doc]
notation:50 a " ≡ " b " [MOD " n "]" => ModEq n a b
variable {m n a b c d : ℕ}
-- Since `ModEq` is semi-reducible, we need to provide the decidable instance manually
instance : Decidable (ModEq n a b) := inferInstanceAs <| Decidable (a % n = b % n)
namespace ModEq
@[refl]
protected theorem refl (a : ℕ) : a ≡ a [MOD n] := rfl
protected theorem rfl : a ≡ a [MOD n] :=
ModEq.refl _
instance : IsRefl _ (ModEq n) :=
⟨ModEq.refl⟩
@[symm]
protected theorem symm : a ≡ b [MOD n] → b ≡ a [MOD n] :=
Eq.symm
@[trans]
protected theorem trans : a ≡ b [MOD n] → b ≡ c [MOD n] → a ≡ c [MOD n] :=
Eq.trans
instance : Trans (ModEq n) (ModEq n) (ModEq n) where
trans := Nat.ModEq.trans
protected theorem comm : a ≡ b [MOD n] ↔ b ≡ a [MOD n] :=
⟨ModEq.symm, ModEq.symm⟩
end ModEq
theorem modEq_zero_iff_dvd : a ≡ 0 [MOD n] ↔ n ∣ a := by rw [ModEq, zero_mod, dvd_iff_mod_eq_zero]
theorem _root_.Dvd.dvd.modEq_zero_nat (h : n ∣ a) : a ≡ 0 [MOD n] :=
modEq_zero_iff_dvd.2 h
theorem _root_.Dvd.dvd.zero_modEq_nat (h : n ∣ a) : 0 ≡ a [MOD n] :=
h.modEq_zero_nat.symm
theorem modEq_iff_dvd : a ≡ b [MOD n] ↔ (n : ℤ) ∣ b - a := by
| rw [ModEq, eq_comm, ← Int.natCast_inj, Int.natCast_mod, Int.natCast_mod,
| Mathlib/Data/Nat/ModEq.lean | 78 | 78 |
/-
Copyright (c) 2020 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Computability.Halting
import Mathlib.Computability.TuringMachine
import Mathlib.Data.Num.Lemmas
import Mathlib.Tactic.DeriveFintype
import Mathlib.Computability.TMConfig
/-!
# Modelling partial recursive functions using Turing machines
The files `TMConfig` and `TMToPartrec` define a simplified basis for partial recursive functions,
and a `Turing.TM2` model
Turing machine for evaluating these functions. This amounts to a constructive proof that every
`Partrec` function can be evaluated by a Turing machine.
## Main definitions
* `PartrecToTM2.tr`: A TM2 turing machine which can evaluate `code` programs
-/
open List (Vector)
open Function (update)
open Relation
namespace Turing
/-!
## Simulating sequentialized partial recursive functions in TM2
At this point we have a sequential model of partial recursive functions: the `Cfg` type and
`step : Cfg → Option Cfg` function from `TMConfig.lean`. The key feature of this model is that
it does a finite amount of computation (in fact, an amount which is statically bounded by the size
of the program) between each step, and no individual step can diverge (unlike the compositional
semantics, where every sub-part of the computation is potentially divergent). So we can utilize the
same techniques as in the other TM simulations in `Computability.TuringMachine` to prove that
each step corresponds to a finite number of steps in a lower level model. (We don't prove it here,
but in anticipation of the complexity class P, the simulation is actually polynomial-time as well.)
The target model is `Turing.TM2`, which has a fixed finite set of stacks, a bit of local storage,
with programs selected from a potentially infinite (but finitely accessible) set of program
positions, or labels `Λ`, each of which executes a finite sequence of basic stack commands.
For this program we will need four stacks, each on an alphabet `Γ'` like so:
inductive Γ' | consₗ | cons | bit0 | bit1
We represent a number as a bit sequence, lists of numbers by putting `cons` after each element, and
lists of lists of natural numbers by putting `consₗ` after each list. For example:
0 ~> []
1 ~> [bit1]
6 ~> [bit0, bit1, bit1]
[1, 2] ~> [bit1, cons, bit0, bit1, cons]
[[], [1, 2]] ~> [consₗ, bit1, cons, bit0, bit1, cons, consₗ]
The four stacks are `main`, `rev`, `aux`, `stack`. In normal mode, `main` contains the input to the
current program (a `List ℕ`) and `stack` contains data (a `List (List ℕ)`) associated to the
current continuation, and in `ret` mode `main` contains the value that is being passed to the
continuation and `stack` contains the data for the continuation. The `rev` and `aux` stacks are
usually empty; `rev` is used to store reversed data when e.g. moving a value from one stack to
another, while `aux` is used as a temporary for a `main`/`stack` swap that happens during `cons₁`
evaluation.
The only local store we need is `Option Γ'`, which stores the result of the last pop
operation. (Most of our working data are natural numbers, which are too large to fit in the local
store.)
The continuations from the previous section are data-carrying, containing all the values that have
been computed and are awaiting other arguments. In order to have only a finite number of
continuations appear in the program so that they can be used in machine states, we separate the
data part (anything with type `List ℕ`) from the `Cont` type, producing a `Cont'` type that lacks
this information. The data is kept on the `stack` stack.
Because we want to have subroutines for e.g. moving an entire stack to another place, we use an
infinite inductive type `Λ'` so that we can execute a program and then return to do something else
without having to define too many different kinds of intermediate states. (We must nevertheless
prove that only finitely many labels are accessible.) The labels are:
* `move p k₁ k₂ q`: move elements from stack `k₁` to `k₂` while `p` holds of the value being moved.
The last element, that fails `p`, is placed in neither stack but left in the local store.
At the end of the operation, `k₂` will have the elements of `k₁` in reverse order. Then do `q`.
* `clear p k q`: delete elements from stack `k` until `p` is true. Like `move`, the last element is
left in the local storage. Then do `q`.
* `copy q`: Move all elements from `rev` to both `main` and `stack` (in reverse order),
then do `q`. That is, it takes `(a, b, c, d)` to `(b.reverse ++ a, [], c, b.reverse ++ d)`.
* `push k f q`: push `f s`, where `s` is the local store, to stack `k`, then do `q`. This is a
duplicate of the `push` instruction that is part of the TM2 model, but by having a subroutine
just for this purpose we can build up programs to execute inside a `goto` statement, where we
have the flexibility to be general recursive.
* `read (f : Option Γ' → Λ')`: go to state `f s` where `s` is the local store. Again this is only
here for convenience.
* `succ q`: perform a successor operation. Assuming `[n]` is encoded on `main` before,
`[n+1]` will be on main after. This implements successor for binary natural numbers.
* `pred q₁ q₂`: perform a predecessor operation or `case` statement. If `[]` is encoded on
`main` before, then we transition to `q₁` with `[]` on main; if `(0 :: v)` is on `main` before
then `v` will be on `main` after and we transition to `q₁`; and if `(n+1 :: v)` is on `main`
before then `n :: v` will be on `main` after and we transition to `q₂`.
* `ret k`: call continuation `k`. Each continuation has its own interpretation of the data in
`stack` and sets up the data for the next continuation.
* `ret (cons₁ fs k)`: `v :: KData` on `stack` and `ns` on `main`, and the next step expects
`v` on `main` and `ns :: KData` on `stack`. So we have to do a little dance here with six
reverse-moves using the `aux` stack to perform a three-point swap, each of which involves two
reversals.
* `ret (cons₂ k)`: `ns :: KData` is on `stack` and `v` is on `main`, and we have to put
`ns.headI :: v` on `main` and `KData` on `stack`. This is done using the `head` subroutine.
* `ret (fix f k)`: This stores no data, so we just check if `main` starts with `0` and
if so, remove it and call `k`, otherwise `clear` the first value and call `f`.
* `ret halt`: the stack is empty, and `main` has the output. Do nothing and halt.
In addition to these basic states, we define some additional subroutines that are used in the
above:
* `push'`, `peek'`, `pop'` are special versions of the builtins that use the local store to supply
inputs and outputs.
* `unrev`: special case `move false rev main` to move everything from `rev` back to `main`. Used as
a cleanup operation in several functions.
* `moveExcl p k₁ k₂ q`: same as `move` but pushes the last value read back onto the source stack.
* `move₂ p k₁ k₂ q`: double `move`, so that the result comes out in the right order at the target
stack. Implemented as `moveExcl p k rev; move false rev k₂`. Assumes that neither `k₁` nor `k₂`
is `rev` and `rev` is initially empty.
* `head k q`: get the first natural number from stack `k` and reverse-move it to `rev`, then clear
the rest of the list at `k` and then `unrev` to reverse-move the head value to `main`. This is
used with `k = main` to implement regular `head`, i.e. if `v` is on `main` before then `[v.headI]`
will be on `main` after; and also with `k = stack` for the `cons` operation, which has `v` on
`main` and `ns :: KData` on `stack`, and results in `KData` on `stack` and `ns.headI :: v` on
`main`.
* `trNormal` is the main entry point, defining states that perform a given `code` computation.
It mostly just dispatches to functions written above.
The main theorem of this section is `tr_eval`, which asserts that for each that for each code `c`,
the state `init c v` steps to `halt v'` in finitely many steps if and only if
`Code.eval c v = some v'`.
-/
namespace PartrecToTM2
section
open ToPartrec
/-- The alphabet for the stacks in the program. `bit0` and `bit1` are used to represent `ℕ` values
as lists of binary digits, `cons` is used to separate `List ℕ` values, and `consₗ` is used to
separate `List (List ℕ)` values. See the section documentation. -/
inductive Γ'
| consₗ
| cons
| bit0
| bit1
deriving DecidableEq, Inhabited, Fintype
/-- The four stacks used by the program. `main` is used to store the input value in `trNormal`
mode and the output value in `Λ'.ret` mode, while `stack` is used to keep all the data for the
continuations. `rev` is used to store reversed lists when transferring values between stacks, and
`aux` is only used once in `cons₁`. See the section documentation. -/
inductive K'
| main
| rev
| aux
| stack
deriving DecidableEq, Inhabited
open K'
/-- Continuations as in `ToPartrec.Cont` but with the data removed. This is done because we want
the set of all continuations in the program to be finite (so that it can ultimately be encoded into
the finite state machine of a Turing machine), but a continuation can handle a potentially infinite
number of data values during execution. -/
inductive Cont'
| halt
| cons₁ : Code → Cont' → Cont'
| cons₂ : Cont' → Cont'
| comp : Code → Cont' → Cont'
| fix : Code → Cont' → Cont'
deriving DecidableEq, Inhabited
/-- The set of program positions. We make extensive use of inductive types here to let us describe
"subroutines"; for example `clear p k q` is a program that clears stack `k`, then does `q` where
`q` is another label. In order to prevent this from resulting in an infinite number of distinct
accessible states, we are careful to be non-recursive (although loops are okay). See the section
documentation for a description of all the programs. -/
inductive Λ'
| move (p : Γ' → Bool) (k₁ k₂ : K') (q : Λ')
| clear (p : Γ' → Bool) (k : K') (q : Λ')
| copy (q : Λ')
| push (k : K') (s : Option Γ' → Option Γ') (q : Λ')
| read (f : Option Γ' → Λ')
| succ (q : Λ')
| pred (q₁ q₂ : Λ')
| ret (k : Cont')
compile_inductive% Code
compile_inductive% Cont'
compile_inductive% K'
compile_inductive% Λ'
instance Λ'.instInhabited : Inhabited Λ' :=
⟨Λ'.ret Cont'.halt⟩
instance Λ'.instDecidableEq : DecidableEq Λ' := fun a b => by
induction a generalizing b <;> cases b <;> first
| apply Decidable.isFalse; rintro ⟨⟨⟩⟩; done
| exact decidable_of_iff' _ (by simp [funext_iff]; rfl)
/-- The type of TM2 statements used by this machine. -/
def Stmt' :=
TM2.Stmt (fun _ : K' => Γ') Λ' (Option Γ') deriving Inhabited
/-- The type of TM2 configurations used by this machine. -/
def Cfg' :=
TM2.Cfg (fun _ : K' => Γ') Λ' (Option Γ') deriving Inhabited
open TM2.Stmt
/-- A predicate that detects the end of a natural number, either `Γ'.cons` or `Γ'.consₗ` (or
implicitly the end of the list), for use in predicate-taking functions like `move` and `clear`. -/
@[simp]
def natEnd : Γ' → Bool
| Γ'.consₗ => true
| Γ'.cons => true
| _ => false
attribute [nolint simpNF] natEnd.eq_3
/-- Pop a value from the stack and place the result in local store. -/
@[simp]
def pop' (k : K') : Stmt' → Stmt' :=
pop k fun _ v => v
/-- Peek a value from the stack and place the result in local store. -/
@[simp]
def peek' (k : K') : Stmt' → Stmt' :=
peek k fun _ v => v
/-- Push the value in the local store to the given stack. -/
@[simp]
def push' (k : K') : Stmt' → Stmt' :=
push k fun x => x.iget
/-- Move everything from the `rev` stack to the `main` stack (reversed). -/
def unrev :=
Λ'.move (fun _ => false) rev main
/-- Move elements from `k₁` to `k₂` while `p` holds, with the last element being left on `k₁`. -/
def moveExcl (p k₁ k₂ q) :=
Λ'.move p k₁ k₂ <| Λ'.push k₁ id q
/-- Move elements from `k₁` to `k₂` without reversion, by performing a double move via the `rev`
stack. -/
def move₂ (p k₁ k₂ q) :=
moveExcl p k₁ rev <| Λ'.move (fun _ => false) rev k₂ q
/-- Assuming `trList v` is on the front of stack `k`, remove it, and push `v.headI` onto `main`.
See the section documentation. -/
def head (k : K') (q : Λ') : Λ' :=
Λ'.move natEnd k rev <|
(Λ'.push rev fun _ => some Γ'.cons) <|
Λ'.read fun s =>
(if s = some Γ'.consₗ then id else Λ'.clear (fun x => x = Γ'.consₗ) k) <| unrev q
/-- The program that evaluates code `c` with continuation `k`. This expects an initial state where
`trList v` is on `main`, `trContStack k` is on `stack`, and `aux` and `rev` are empty.
See the section documentation for details. -/
@[simp]
def trNormal : Code → Cont' → Λ'
| Code.zero', k => (Λ'.push main fun _ => some Γ'.cons) <| Λ'.ret k
| Code.succ, k => head main <| Λ'.succ <| Λ'.ret k
| Code.tail, k => Λ'.clear natEnd main <| Λ'.ret k
| Code.cons f fs, k =>
(Λ'.push stack fun _ => some Γ'.consₗ) <|
Λ'.move (fun _ => false) main rev <| Λ'.copy <| trNormal f (Cont'.cons₁ fs k)
| Code.comp f g, k => trNormal g (Cont'.comp f k)
| Code.case f g, k => Λ'.pred (trNormal f k) (trNormal g k)
| Code.fix f, k => trNormal f (Cont'.fix f k)
/-- The main program. See the section documentation for details. -/
def tr : Λ' → Stmt'
| Λ'.move p k₁ k₂ q =>
pop' k₁ <|
branch (fun s => s.elim true p) (goto fun _ => q)
(push' k₂ <| goto fun _ => Λ'.move p k₁ k₂ q)
| Λ'.push k f q =>
branch (fun s => (f s).isSome) ((push k fun s => (f s).iget) <| goto fun _ => q)
(goto fun _ => q)
| Λ'.read q => goto q
| Λ'.clear p k q =>
pop' k <| branch (fun s => s.elim true p) (goto fun _ => q) (goto fun _ => Λ'.clear p k q)
| Λ'.copy q =>
pop' rev <|
branch Option.isSome (push' main <| push' stack <| goto fun _ => Λ'.copy q) (goto fun _ => q)
| Λ'.succ q =>
pop' main <|
branch (fun s => s = some Γ'.bit1) ((push rev fun _ => Γ'.bit0) <| goto fun _ => Λ'.succ q) <|
branch (fun s => s = some Γ'.cons)
((push main fun _ => Γ'.cons) <| (push main fun _ => Γ'.bit1) <| goto fun _ => unrev q)
((push main fun _ => Γ'.bit1) <| goto fun _ => unrev q)
| Λ'.pred q₁ q₂ =>
pop' main <|
branch (fun s => s = some Γ'.bit0)
((push rev fun _ => Γ'.bit1) <| goto fun _ => Λ'.pred q₁ q₂) <|
branch (fun s => natEnd s.iget) (goto fun _ => q₁)
(peek' main <|
branch (fun s => natEnd s.iget) (goto fun _ => unrev q₂)
((push rev fun _ => Γ'.bit0) <| goto fun _ => unrev q₂))
| Λ'.ret (Cont'.cons₁ fs k) =>
goto fun _ =>
move₂ (fun _ => false) main aux <|
move₂ (fun s => s = Γ'.consₗ) stack main <|
move₂ (fun _ => false) aux stack <| trNormal fs (Cont'.cons₂ k)
| Λ'.ret (Cont'.cons₂ k) => goto fun _ => head stack <| Λ'.ret k
| Λ'.ret (Cont'.comp f k) => goto fun _ => trNormal f k
| Λ'.ret (Cont'.fix f k) =>
pop' main <|
goto fun s =>
cond (natEnd s.iget) (Λ'.ret k) <| Λ'.clear natEnd main <| trNormal f (Cont'.fix f k)
| Λ'.ret Cont'.halt => (load fun _ => none) <| halt
@[simp]
theorem tr_move (p k₁ k₂ q) : tr (Λ'.move p k₁ k₂ q) =
pop' k₁ (branch (fun s => s.elim true p) (goto fun _ => q)
(push' k₂ <| goto fun _ => Λ'.move p k₁ k₂ q)) := rfl
@[simp]
theorem tr_push (k f q) : tr (Λ'.push k f q) = branch (fun s => (f s).isSome)
((push k fun s => (f s).iget) <| goto fun _ => q) (goto fun _ => q) := rfl
@[simp]
theorem tr_read (q) : tr (Λ'.read q) = goto q := rfl
@[simp]
theorem tr_clear (p k q) : tr (Λ'.clear p k q) = pop' k (branch
(fun s => s.elim true p) (goto fun _ => q) (goto fun _ => Λ'.clear p k q)) := rfl
@[simp]
theorem tr_copy (q) : tr (Λ'.copy q) = pop' rev (branch Option.isSome
(push' main <| push' stack <| goto fun _ => Λ'.copy q) (goto fun _ => q)) := rfl
@[simp]
theorem tr_succ (q) : tr (Λ'.succ q) = pop' main (branch (fun s => s = some Γ'.bit1)
((push rev fun _ => Γ'.bit0) <| goto fun _ => Λ'.succ q) <|
branch (fun s => s = some Γ'.cons)
((push main fun _ => Γ'.cons) <| (push main fun _ => Γ'.bit1) <| goto fun _ => unrev q)
((push main fun _ => Γ'.bit1) <| goto fun _ => unrev q)) := rfl
@[simp]
theorem tr_pred (q₁ q₂) : tr (Λ'.pred q₁ q₂) = pop' main (branch (fun s => s = some Γ'.bit0)
((push rev fun _ => Γ'.bit1) <| goto fun _ => Λ'.pred q₁ q₂) <|
branch (fun s => natEnd s.iget) (goto fun _ => q₁)
(peek' main <|
branch (fun s => natEnd s.iget) (goto fun _ => unrev q₂)
((push rev fun _ => Γ'.bit0) <| goto fun _ => unrev q₂))) := rfl
@[simp]
theorem tr_ret_cons₁ (fs k) : tr (Λ'.ret (Cont'.cons₁ fs k)) = goto fun _ =>
move₂ (fun _ => false) main aux <|
move₂ (fun s => s = Γ'.consₗ) stack main <|
move₂ (fun _ => false) aux stack <| trNormal fs (Cont'.cons₂ k) := rfl
@[simp]
theorem tr_ret_cons₂ (k) : tr (Λ'.ret (Cont'.cons₂ k)) =
goto fun _ => head stack <| Λ'.ret k := rfl
@[simp]
theorem tr_ret_comp (f k) : tr (Λ'.ret (Cont'.comp f k)) = goto fun _ => trNormal f k := rfl
@[simp]
theorem tr_ret_fix (f k) : tr (Λ'.ret (Cont'.fix f k)) = pop' main (goto fun s =>
cond (natEnd s.iget) (Λ'.ret k) <| Λ'.clear natEnd main <| trNormal f (Cont'.fix f k)) := rfl
@[simp]
theorem tr_ret_halt : tr (Λ'.ret Cont'.halt) = (load fun _ => none) halt := rfl
/-- Translating a `Cont` continuation to a `Cont'` continuation simply entails dropping all the
data. This data is instead encoded in `trContStack` in the configuration. -/
def trCont : Cont → Cont'
| Cont.halt => Cont'.halt
| Cont.cons₁ c _ k => Cont'.cons₁ c (trCont k)
| Cont.cons₂ _ k => Cont'.cons₂ (trCont k)
| Cont.comp c k => Cont'.comp c (trCont k)
| Cont.fix c k => Cont'.fix c (trCont k)
/-- We use `PosNum` to define the translation of binary natural numbers. A natural number is
represented as a little-endian list of `bit0` and `bit1` elements:
1 = [bit1]
2 = [bit0, bit1]
3 = [bit1, bit1]
4 = [bit0, bit0, bit1]
In particular, this representation guarantees no trailing `bit0`'s at the end of the list. -/
def trPosNum : PosNum → List Γ'
| PosNum.one => [Γ'.bit1]
| PosNum.bit0 n => Γ'.bit0 :: trPosNum n
| PosNum.bit1 n => Γ'.bit1 :: trPosNum n
/-- We use `Num` to define the translation of binary natural numbers. Positive numbers are
translated using `trPosNum`, and `trNum 0 = []`. So there are never any trailing `bit0`'s in
a translated `Num`.
0 = []
1 = [bit1]
2 = [bit0, bit1]
3 = [bit1, bit1]
4 = [bit0, bit0, bit1]
-/
def trNum : Num → List Γ'
| Num.zero => []
| Num.pos n => trPosNum n
/-- Because we use binary encoding, we define `trNat` in terms of `trNum`, using `Num`, which are
binary natural numbers. (We could also use `Nat.binaryRecOn`, but `Num` and `PosNum` make for
easy inductions.) -/
def trNat (n : ℕ) : List Γ' :=
trNum n
@[simp]
theorem trNat_zero : trNat 0 = [] := by rw [trNat, Nat.cast_zero]; rfl
theorem trNat_default : trNat default = [] :=
trNat_zero
/-- Lists are translated with a `cons` after each encoded number.
For example:
[] = []
[0] = [cons]
[1] = [bit1, cons]
[6, 0] = [bit0, bit1, bit1, cons, cons]
-/
@[simp]
def trList : List ℕ → List Γ'
| [] => []
| n::ns => trNat n ++ Γ'.cons :: trList ns
/-- Lists of lists are translated with a `consₗ` after each encoded list.
For example:
[] = []
[[]] = [consₗ]
[[], []] = [consₗ, consₗ]
[[0]] = [cons, consₗ]
[[1, 2], [0]] = [bit1, cons, bit0, bit1, cons, consₗ, cons, consₗ]
-/
@[simp]
def trLList : List (List ℕ) → List Γ'
| [] => []
| l::ls => trList l ++ Γ'.consₗ :: trLList ls
/-- The data part of a continuation is a list of lists, which is encoded on the `stack` stack
using `trLList`. -/
@[simp]
def contStack : Cont → List (List ℕ)
| Cont.halt => []
| Cont.cons₁ _ ns k => ns :: contStack k
| Cont.cons₂ ns k => ns :: contStack k
| Cont.comp _ k => contStack k
| Cont.fix _ k => contStack k
/-- The data part of a continuation is a list of lists, which is encoded on the `stack` stack
using `trLList`. -/
def trContStack (k : Cont) :=
trLList (contStack k)
/-- This is the nondependent eliminator for `K'`, but we use it specifically here in order to
represent the stack data as four lists rather than as a function `K' → List Γ'`, because this makes
rewrites easier. The theorems `K'.elim_update_main` et. al. show how such a function is updated
after an `update` to one of the components. -/
def K'.elim (a b c d : List Γ') : K' → List Γ'
| K'.main => a
| K'.rev => b
| K'.aux => c
| K'.stack => d
-- The equation lemma of `elim` simplifies to `match` structures.
theorem K'.elim_main (a b c d) : K'.elim a b c d K'.main = a := rfl
theorem K'.elim_rev (a b c d) : K'.elim a b c d K'.rev = b := rfl
theorem K'.elim_aux (a b c d) : K'.elim a b c d K'.aux = c := rfl
theorem K'.elim_stack (a b c d) : K'.elim a b c d K'.stack = d := rfl
attribute [simp] K'.elim
@[simp]
theorem K'.elim_update_main {a b c d a'} : update (K'.elim a b c d) main a' = K'.elim a' b c d := by
funext x; cases x <;> rfl
@[simp]
theorem K'.elim_update_rev {a b c d b'} : update (K'.elim a b c d) rev b' = K'.elim a b' c d := by
funext x; cases x <;> rfl
@[simp]
theorem K'.elim_update_aux {a b c d c'} : update (K'.elim a b c d) aux c' = K'.elim a b c' d := by
funext x; cases x <;> rfl
@[simp]
theorem K'.elim_update_stack {a b c d d'} :
update (K'.elim a b c d) stack d' = K'.elim a b c d' := by funext x; cases x <;> rfl
/-- The halting state corresponding to a `List ℕ` output value. -/
def halt (v : List ℕ) : Cfg' :=
⟨none, none, K'.elim (trList v) [] [] []⟩
/-- The `Cfg` states map to `Cfg'` states almost one to one, except that in normal operation the
local store contains an arbitrary garbage value. To make the final theorem cleaner we explicitly
clear it in the halt state so that there is exactly one configuration corresponding to output `v`.
-/
def TrCfg : Cfg → Cfg' → Prop
| Cfg.ret k v, c' =>
∃ s, c' = ⟨some (Λ'.ret (trCont k)), s, K'.elim (trList v) [] [] (trContStack k)⟩
| Cfg.halt v, c' => c' = halt v
/-- This could be a general list definition, but it is also somewhat specialized to this
application. `splitAtPred p L` will search `L` for the first element satisfying `p`.
If it is found, say `L = l₁ ++ a :: l₂` where `a` satisfies `p` but `l₁` does not, then it returns
`(l₁, some a, l₂)`. Otherwise, if there is no such element, it returns `(L, none, [])`. -/
def splitAtPred {α} (p : α → Bool) : List α → List α × Option α × List α
| [] => ([], none, [])
| a :: as =>
cond (p a) ([], some a, as) <|
let ⟨l₁, o, l₂⟩ := splitAtPred p as
⟨a::l₁, o, l₂⟩
theorem splitAtPred_eq {α} (p : α → Bool) :
∀ L l₁ o l₂,
(∀ x ∈ l₁, p x = false) →
Option.elim' (L = l₁ ∧ l₂ = []) (fun a => p a = true ∧ L = l₁ ++ a::l₂) o →
splitAtPred p L = (l₁, o, l₂)
| [], _, none, _, _, ⟨rfl, rfl⟩ => rfl
| [], l₁, some o, l₂, _, ⟨_, h₃⟩ => by simp at h₃
| a :: L, l₁, o, l₂, h₁, h₂ => by
rw [splitAtPred]
have IH := splitAtPred_eq p L
rcases o with - | o
· rcases l₁ with - | ⟨a', l₁⟩ <;> rcases h₂ with ⟨⟨⟩, rfl⟩
rw [h₁ a (List.Mem.head _), cond, IH L none [] _ ⟨rfl, rfl⟩]
exact fun x h => h₁ x (List.Mem.tail _ h)
· rcases l₁ with - | ⟨a', l₁⟩ <;> rcases h₂ with ⟨h₂, ⟨⟩⟩
· rw [h₂, cond]
rw [h₁ a (List.Mem.head _), cond, IH l₁ (some o) l₂ _ ⟨h₂, _⟩] <;> try rfl
exact fun x h => h₁ x (List.Mem.tail _ h)
theorem splitAtPred_false {α} (L : List α) : splitAtPred (fun _ => false) L = (L, none, []) :=
splitAtPred_eq _ _ _ _ _ (fun _ _ => rfl) ⟨rfl, rfl⟩
theorem move_ok {p k₁ k₂ q s L₁ o L₂} {S : K' → List Γ'} (h₁ : k₁ ≠ k₂)
(e : splitAtPred p (S k₁) = (L₁, o, L₂)) :
Reaches₁ (TM2.step tr) ⟨some (Λ'.move p k₁ k₂ q), s, S⟩
⟨some q, o, update (update S k₁ L₂) k₂ (L₁.reverseAux (S k₂))⟩ := by
induction' L₁ with a L₁ IH generalizing S s
· rw [(_ : [].reverseAux _ = _), Function.update_eq_self]
swap
· rw [Function.update_of_ne h₁.symm, List.reverseAux_nil]
refine TransGen.head' rfl ?_
rw [tr]; simp only [pop', TM2.stepAux]
revert e; rcases S k₁ with - | ⟨a, Sk⟩ <;> intro e
· cases e
rfl
simp only [splitAtPred, Option.elim, List.head?, List.tail_cons, Option.iget_some] at e ⊢
revert e; cases p a <;> intro e <;>
simp only [cond_false, cond_true, Prod.mk.injEq, true_and, false_and, reduceCtorEq] at e ⊢
simp only [e]
rfl
· refine TransGen.head rfl ?_
rw [tr]; simp only [pop', Option.elim, TM2.stepAux, push']
rcases e₁ : S k₁ with - | ⟨a', Sk⟩ <;> rw [e₁, splitAtPred] at e
· cases e
cases e₂ : p a' <;> simp only [e₂, cond] at e
swap
· cases e
rcases e₃ : splitAtPred p Sk with ⟨_, _, _⟩
rw [e₃] at e
cases e
simp only [List.head?_cons, e₂, List.tail_cons, ne_eq, cond_false]
convert @IH _ (update (update S k₁ Sk) k₂ (a :: S k₂)) _ using 2 <;>
simp [Function.update_of_ne, h₁, h₁.symm, e₃, List.reverseAux]
simp [Function.update_comm h₁.symm]
theorem unrev_ok {q s} {S : K' → List Γ'} :
Reaches₁ (TM2.step tr) ⟨some (unrev q), s, S⟩
⟨some q, none, update (update S rev []) main (List.reverseAux (S rev) (S main))⟩ :=
move_ok (by decide) <| splitAtPred_false _
theorem move₂_ok {p k₁ k₂ q s L₁ o L₂} {S : K' → List Γ'} (h₁ : k₁ ≠ rev ∧ k₂ ≠ rev ∧ k₁ ≠ k₂)
(h₂ : S rev = []) (e : splitAtPred p (S k₁) = (L₁, o, L₂)) :
Reaches₁ (TM2.step tr) ⟨some (move₂ p k₁ k₂ q), s, S⟩
⟨some q, none, update (update S k₁ (o.elim id List.cons L₂)) k₂ (L₁ ++ S k₂)⟩ := by
refine (move_ok h₁.1 e).trans (TransGen.head rfl ?_)
simp only [TM2.step, Option.mem_def, TM2.stepAux, id_eq, ne_eq, Option.elim]
cases o <;> simp only [Option.elim] <;> rw [tr]
<;> simp only [id, TM2.stepAux, Option.isSome, cond_true, cond_false]
· convert move_ok h₁.2.1.symm (splitAtPred_false _) using 2
simp only [Function.update_comm h₁.1, Function.update_idem]
rw [show update S rev [] = S by rw [← h₂, Function.update_eq_self]]
simp only [Function.update_of_ne h₁.2.2.symm, Function.update_of_ne h₁.2.1,
Function.update_of_ne h₁.1.symm, List.reverseAux_eq, h₂, Function.update_self,
List.append_nil, List.reverse_reverse]
· convert move_ok h₁.2.1.symm (splitAtPred_false _) using 2
simp only [h₂, Function.update_comm h₁.1, List.reverseAux_eq, Function.update_self,
List.append_nil, Function.update_idem]
rw [show update S rev [] = S by rw [← h₂, Function.update_eq_self]]
simp only [Function.update_of_ne h₁.1.symm, Function.update_of_ne h₁.2.2.symm,
Function.update_of_ne h₁.2.1, Function.update_self, List.reverse_reverse]
theorem clear_ok {p k q s L₁ o L₂} {S : K' → List Γ'} (e : splitAtPred p (S k) = (L₁, o, L₂)) :
Reaches₁ (TM2.step tr) ⟨some (Λ'.clear p k q), s, S⟩ ⟨some q, o, update S k L₂⟩ := by
induction' L₁ with a L₁ IH generalizing S s
· refine TransGen.head' rfl ?_
rw [tr]; simp only [pop', TM2.step, Option.mem_def, TM2.stepAux, Option.elim]
revert e; rcases S k with - | ⟨a, Sk⟩ <;> intro e
· cases e
rfl
simp only [splitAtPred, Option.elim, List.head?, List.tail_cons] at e ⊢
revert e; cases p a <;> intro e <;>
simp only [cond_false, cond_true, Prod.mk.injEq, true_and, false_and, reduceCtorEq] at e ⊢
rcases e with ⟨e₁, e₂⟩
rw [e₁, e₂]
· refine TransGen.head rfl ?_
rw [tr]; simp only [pop', TM2.step, Option.mem_def, TM2.stepAux, Option.elim]
rcases e₁ : S k with - | ⟨a', Sk⟩ <;> rw [e₁, splitAtPred] at e
· cases e
cases e₂ : p a' <;> simp only [e₂, cond] at e
swap
· cases e
rcases e₃ : splitAtPred p Sk with ⟨_, _, _⟩
rw [e₃] at e
cases e
simp only [List.head?_cons, e₂, List.tail_cons, cond_false]
convert @IH _ (update S k Sk) _ using 2 <;> simp [e₃]
theorem copy_ok (q s a b c d) :
Reaches₁ (TM2.step tr) ⟨some (Λ'.copy q), s, K'.elim a b c d⟩
⟨some q, none, K'.elim (List.reverseAux b a) [] c (List.reverseAux b d)⟩ := by
induction' b with x b IH generalizing a d s
· refine TransGen.single ?_
simp
refine TransGen.head rfl ?_
rw [tr]
simp only [TM2.step, Option.mem_def, TM2.stepAux, elim_rev, List.head?_cons, Option.isSome_some,
List.tail_cons, elim_update_rev, ne_eq, Function.update_of_ne, elim_main, elim_update_main,
elim_stack, elim_update_stack, cond_true, List.reverseAux_cons, pop', push']
exact IH _ _ _
theorem trPosNum_natEnd : ∀ (n), ∀ x ∈ trPosNum n, natEnd x = false
| PosNum.one, _, List.Mem.head _ => rfl
| PosNum.bit0 _, _, List.Mem.head _ => rfl
| PosNum.bit0 n, _, List.Mem.tail _ h => trPosNum_natEnd n _ h
| PosNum.bit1 _, _, List.Mem.head _ => rfl
| PosNum.bit1 n, _, List.Mem.tail _ h => trPosNum_natEnd n _ h
theorem trNum_natEnd : ∀ (n), ∀ x ∈ trNum n, natEnd x = false
| Num.pos n, x, h => trPosNum_natEnd n x h
theorem trNat_natEnd (n) : ∀ x ∈ trNat n, natEnd x = false :=
trNum_natEnd _
theorem trList_ne_consₗ : ∀ (l), ∀ x ∈ trList l, x ≠ Γ'.consₗ
| a :: l, x, h => by
simp only [trList, List.mem_append, List.mem_cons] at h
obtain h | rfl | h := h
· rintro rfl
cases trNat_natEnd _ _ h
· rintro ⟨⟩
· exact trList_ne_consₗ l _ h
theorem head_main_ok {q s L} {c d : List Γ'} :
Reaches₁ (TM2.step tr) ⟨some (head main q), s, K'.elim (trList L) [] c d⟩
⟨some q, none, K'.elim (trList [L.headI]) [] c d⟩ := by
let o : Option Γ' := List.casesOn L none fun _ _ => some Γ'.cons
refine
(move_ok (by decide)
(splitAtPred_eq _ _ (trNat L.headI) o (trList L.tail) (trNat_natEnd _) ?_)).trans
(TransGen.head rfl (TransGen.head rfl ?_))
· cases L <;> simp [o]
rw [tr]
simp only [TM2.step, Option.mem_def, TM2.stepAux, elim_update_main, elim_rev, elim_update_rev,
Function.update_self, trList]
rw [if_neg (show o ≠ some Γ'.consₗ by cases L <;> simp [o])]
refine (clear_ok (splitAtPred_eq _ _ _ none [] ?_ ⟨rfl, rfl⟩)).trans ?_
· exact fun x h => Bool.decide_false (trList_ne_consₗ _ _ h)
convert unrev_ok using 2; simp [List.reverseAux_eq]
theorem head_stack_ok {q s L₁ L₂ L₃} :
Reaches₁ (TM2.step tr)
⟨some (head stack q), s, K'.elim (trList L₁) [] [] (trList L₂ ++ Γ'.consₗ :: L₃)⟩
⟨some q, none, K'.elim (trList (L₂.headI :: L₁)) [] [] L₃⟩ := by
rcases L₂ with - | ⟨a, L₂⟩
· refine
TransGen.trans
(move_ok (by decide)
(splitAtPred_eq _ _ [] (some Γ'.consₗ) L₃ (by rintro _ ⟨⟩) ⟨rfl, rfl⟩))
(TransGen.head rfl (TransGen.head rfl ?_))
rw [tr]
simp only [TM2.step, Option.mem_def, TM2.stepAux, ite_true, id_eq, trList, List.nil_append,
elim_update_stack, elim_rev, List.reverseAux_nil, elim_update_rev, Function.update_self,
List.headI_nil, trNat_default]
convert unrev_ok using 2
simp
· refine
TransGen.trans
(move_ok (by decide)
(splitAtPred_eq _ _ (trNat a) (some Γ'.cons) (trList L₂ ++ Γ'.consₗ :: L₃)
(trNat_natEnd _) ⟨rfl, by simp⟩))
(TransGen.head rfl (TransGen.head rfl ?_))
simp only [TM2.step, Option.mem_def, TM2.stepAux, ite_false, trList, List.append_assoc,
List.cons_append, elim_update_stack, elim_rev, elim_update_rev, Function.update_self,
List.headI_cons]
refine
TransGen.trans
(clear_ok
(splitAtPred_eq _ _ (trList L₂) (some Γ'.consₗ) L₃
(fun x h => Bool.decide_false (trList_ne_consₗ _ _ h)) ⟨rfl, by simp⟩))
?_
convert unrev_ok using 2
simp [List.reverseAux_eq]
theorem succ_ok {q s n} {c d : List Γ'} :
Reaches₁ (TM2.step tr) ⟨some (Λ'.succ q), s, K'.elim (trList [n]) [] c d⟩
⟨some q, none, K'.elim (trList [n.succ]) [] c d⟩ := by
simp only [TM2.step, trList, trNat.eq_1, Nat.cast_succ, Num.add_one]
rcases (n : Num) with - | a
· refine TransGen.head rfl ?_
simp only [Option.mem_def, TM2.stepAux, elim_main, decide_false, elim_update_main, ne_eq,
Function.update_of_ne, elim_rev, elim_update_rev, decide_true, Function.update_self,
cond_true, cond_false]
convert unrev_ok using 1
simp only [elim_update_rev, elim_rev, elim_main, List.reverseAux_nil, elim_update_main]
rfl
simp only [trNum, Num.succ, Num.succ']
suffices ∀ l₁, ∃ l₁' l₂' s',
List.reverseAux l₁ (trPosNum a.succ) = List.reverseAux l₁' l₂' ∧
Reaches₁ (TM2.step tr) ⟨some q.succ, s, K'.elim (trPosNum a ++ [Γ'.cons]) l₁ c d⟩
⟨some (unrev q), s', K'.elim (l₂' ++ [Γ'.cons]) l₁' c d⟩ by
obtain ⟨l₁', l₂', s', e, h⟩ := this []
simp? [List.reverseAux] at e says simp only [List.reverseAux, List.reverseAux_eq] at e
refine h.trans ?_
convert unrev_ok using 2
simp [e, List.reverseAux_eq]
induction' a with m IH m _ generalizing s <;> intro l₁
· refine ⟨Γ'.bit0 :: l₁, [Γ'.bit1], some Γ'.cons, rfl, TransGen.head rfl (TransGen.single ?_)⟩
simp [trPosNum]
· obtain ⟨l₁', l₂', s', e, h⟩ := IH (Γ'.bit0 :: l₁)
refine ⟨l₁', l₂', s', e, TransGen.head ?_ h⟩
simp [PosNum.succ, trPosNum]
rfl
· refine ⟨l₁, _, some Γ'.bit0, rfl, TransGen.single ?_⟩
simp only [TM2.step]; rw [tr]
simp only [TM2.stepAux, pop', elim_main, elim_update_main, ne_eq, Function.update_of_ne,
elim_rev, elim_update_rev, Function.update_self, Option.mem_def, Option.some.injEq]
rfl
theorem pred_ok (q₁ q₂ s v) (c d : List Γ') : ∃ s',
Reaches₁ (TM2.step tr) ⟨some (Λ'.pred q₁ q₂), s, K'.elim (trList v) [] c d⟩
(v.headI.rec ⟨some q₁, s', K'.elim (trList v.tail) [] c d⟩ fun n _ =>
⟨some q₂, s', K'.elim (trList (n::v.tail)) [] c d⟩) := by
rcases v with (_ | ⟨_ | n, v⟩)
· refine ⟨none, TransGen.single ?_⟩
simp
· refine ⟨some Γ'.cons, TransGen.single ?_⟩
simp
refine ⟨none, ?_⟩
simp only [TM2.step, trList, trNat.eq_1, trNum, Nat.cast_succ, Num.add_one, Num.succ,
List.tail_cons, List.headI_cons]
rcases (n : Num) with - | a
· simp only [trPosNum, Num.succ', List.singleton_append, List.nil_append]
refine TransGen.head rfl ?_
rw [tr]; simp only [pop', TM2.stepAux, cond_false]
convert unrev_ok using 2
simp
simp only [Num.succ']
suffices ∀ l₁, ∃ l₁' l₂' s',
List.reverseAux l₁ (trPosNum a) = List.reverseAux l₁' l₂' ∧
Reaches₁ (TM2.step tr)
⟨some (q₁.pred q₂), s, K'.elim (trPosNum a.succ ++ Γ'.cons :: trList v) l₁ c d⟩
⟨some (unrev q₂), s', K'.elim (l₂' ++ Γ'.cons :: trList v) l₁' c d⟩ by
obtain ⟨l₁', l₂', s', e, h⟩ := this []
simp only [List.reverseAux] at e
refine h.trans ?_
convert unrev_ok using 2
simp [e, List.reverseAux_eq]
induction' a with m IH m IH generalizing s <;> intro l₁
· refine ⟨Γ'.bit1::l₁, [], some Γ'.cons, rfl, TransGen.head rfl (TransGen.single ?_)⟩
simp [trPosNum, show PosNum.one.succ = PosNum.one.bit0 from rfl]
· obtain ⟨l₁', l₂', s', e, h⟩ := IH (some Γ'.bit0) (Γ'.bit1 :: l₁)
refine ⟨l₁', l₂', s', e, TransGen.head ?_ h⟩
simp
rfl
· obtain ⟨a, l, e, h⟩ : ∃ a l, (trPosNum m = a::l) ∧ natEnd a = false := by
cases m <;> refine ⟨_, _, rfl, rfl⟩
refine ⟨Γ'.bit0 :: l₁, _, some a, rfl, TransGen.single ?_⟩
simp [trPosNum, PosNum.succ, e, h, show some Γ'.bit1 ≠ some Γ'.bit0 by decide,
Option.iget, -natEnd]
rfl
theorem trNormal_respects (c k v s) :
∃ b₂,
TrCfg (stepNormal c k v) b₂ ∧
Reaches₁ (TM2.step tr)
⟨some (trNormal c (trCont k)), s, K'.elim (trList v) [] [] (trContStack k)⟩ b₂ := by
induction c generalizing k v s with
| zero' => refine ⟨_, ⟨s, rfl⟩, TransGen.single ?_⟩; simp
| succ => refine ⟨_, ⟨none, rfl⟩, head_main_ok.trans succ_ok⟩
| tail =>
let o : Option Γ' := List.casesOn v none fun _ _ => some Γ'.cons
refine ⟨_, ⟨o, rfl⟩, ?_⟩; convert clear_ok _ using 2
· simp; rfl
swap
refine splitAtPred_eq _ _ (trNat v.headI) _ _ (trNat_natEnd _) ?_
cases v <;> simp [o]
| cons f fs IHf _ =>
obtain ⟨c, h₁, h₂⟩ := IHf (Cont.cons₁ fs v k) v none
refine ⟨c, h₁, TransGen.head rfl <| (move_ok (by decide) (splitAtPred_false _)).trans ?_⟩
simp only [TM2.step, Option.mem_def, elim_stack, elim_update_stack, elim_update_main, ne_eq,
Function.update_of_ne, elim_main, elim_rev, elim_update_rev]
refine (copy_ok _ none [] (trList v).reverse _ _).trans ?_
convert h₂ using 2
simp [List.reverseAux_eq, trContStack]
| comp f _ _ IHg => exact IHg (Cont.comp f k) v s
| case f g IHf IHg =>
rw [stepNormal]
simp only
obtain ⟨s', h⟩ := pred_ok _ _ s v _ _
revert h; rcases v.headI with - | n <;> intro h
· obtain ⟨c, h₁, h₂⟩ := IHf k _ s'
exact ⟨_, h₁, h.trans h₂⟩
· obtain ⟨c, h₁, h₂⟩ := IHg k _ s'
exact ⟨_, h₁, h.trans h₂⟩
| fix f IH => apply IH
theorem tr_ret_respects (k v s) : ∃ b₂,
TrCfg (stepRet k v) b₂ ∧
Reaches₁ (TM2.step tr)
⟨some (Λ'.ret (trCont k)), s, K'.elim (trList v) [] [] (trContStack k)⟩ b₂ := by
induction k generalizing v s with
| halt => exact ⟨_, rfl, TransGen.single rfl⟩
| cons₁ fs as k _ =>
obtain ⟨s', h₁, h₂⟩ := trNormal_respects fs (Cont.cons₂ v k) as none
refine ⟨s', h₁, TransGen.head rfl ?_⟩; simp
refine (move₂_ok (by decide) ?_ (splitAtPred_false _)).trans ?_; · rfl
simp only [TM2.step, Option.mem_def, Option.elim, id_eq, elim_update_main, elim_main, elim_aux,
List.append_nil, elim_update_aux]
refine (move₂_ok (L₁ := ?_) (o := ?_) (L₂ := ?_) (by decide) rfl ?_).trans ?_
pick_goal 4
· exact splitAtPred_eq _ _ _ (some Γ'.consₗ) _
(fun x h => Bool.decide_false (trList_ne_consₗ _ _ h)) ⟨rfl, rfl⟩
refine (move₂_ok (by decide) ?_ (splitAtPred_false _)).trans ?_; · rfl
simp only [TM2.step, Option.mem_def, Option.elim, elim_update_stack, elim_main,
List.append_nil, elim_update_main, id_eq, elim_update_aux, ne_eq, Function.update_of_ne,
elim_aux, elim_stack]
exact h₂
| cons₂ ns k IH =>
obtain ⟨c, h₁, h₂⟩ := IH (ns.headI :: v) none
exact ⟨c, h₁, TransGen.head rfl <| head_stack_ok.trans h₂⟩
| comp f k _ =>
obtain ⟨s', h₁, h₂⟩ := trNormal_respects f k v s
exact ⟨_, h₁, TransGen.head rfl h₂⟩
| fix f k IH =>
rw [stepRet]
have :
if v.headI = 0 then natEnd (trList v).head?.iget = true ∧ (trList v).tail = trList v.tail
else
natEnd (trList v).head?.iget = false ∧
(trList v).tail = (trNat v.headI).tail ++ Γ'.cons :: trList v.tail := by
obtain - | n := v
· exact ⟨rfl, rfl⟩
rcases n with - | n
· simp
rw [trList, List.headI, trNat, Nat.cast_succ, Num.add_one, Num.succ, List.tail]
cases (n : Num).succ' <;> exact ⟨rfl, rfl⟩
by_cases h : v.headI = 0 <;> simp only [h, ite_true, ite_false] at this ⊢
· obtain ⟨c, h₁, h₂⟩ := IH v.tail (trList v).head?
refine ⟨c, h₁, TransGen.head rfl ?_⟩
rw [trCont, tr]; simp only [pop', TM2.stepAux, elim_main, this, elim_update_main]
exact h₂
· obtain ⟨s', h₁, h₂⟩ := trNormal_respects f (Cont.fix f k) v.tail (some Γ'.cons)
refine ⟨_, h₁, TransGen.head rfl <| TransGen.trans ?_ h₂⟩
rw [trCont, tr]; simp only [pop', TM2.stepAux, elim_main, this.1]
convert clear_ok (splitAtPred_eq _ _ (trNat v.headI).tail (some Γ'.cons) _ _ _) using 2
· simp
convert rfl
· exact fun x h => trNat_natEnd _ _ (List.tail_subset _ h)
· exact ⟨rfl, this.2⟩
theorem tr_respects : Respects step (TM2.step tr) TrCfg
| Cfg.ret _ _, _, ⟨_, rfl⟩ => tr_ret_respects _ _ _
| Cfg.halt _, _, rfl => rfl
/-- The initial state, evaluating function `c` on input `v`. -/
def init (c : Code) (v : List ℕ) : Cfg' :=
⟨some (trNormal c Cont'.halt), none, K'.elim (trList v) [] [] []⟩
theorem tr_init (c v) :
∃ b, TrCfg (stepNormal c Cont.halt v) b ∧ Reaches₁ (TM2.step tr) (init c v) b :=
trNormal_respects _ _ _ _
theorem tr_eval (c v) : eval (TM2.step tr) (init c v) = halt <$> Code.eval c v := by
obtain ⟨i, h₁, h₂⟩ := tr_init c v
refine Part.ext fun x => ?_
rw [reaches_eval h₂.to_reflTransGen]; simp only [Part.map_eq_map, Part.mem_map_iff]
refine ⟨fun h => ?_, ?_⟩
· obtain ⟨c, hc₁, hc₂⟩ := tr_eval_rev tr_respects h₁ h
simp [stepNormal_eval] at hc₂
obtain ⟨v', hv, rfl⟩ := hc₂
exact ⟨_, hv, hc₁.symm⟩
· rintro ⟨v', hv, rfl⟩
have := Turing.tr_eval (b₁ := Cfg.halt v') tr_respects h₁
simp only [stepNormal_eval, Part.map_eq_map, Part.mem_map_iff, Cfg.halt.injEq,
exists_eq_right] at this
obtain ⟨_, ⟨⟩, h⟩ := this hv
exact h
/-- The set of machine states reachable via downward label jumps, discounting jumps via `ret`. -/
def trStmts₁ : Λ' → Finset Λ'
| Q@(Λ'.move _ _ _ q) => insert Q <| trStmts₁ q
| Q@(Λ'.push _ _ q) => insert Q <| trStmts₁ q
| Q@(Λ'.read q) => insert Q <| Finset.univ.biUnion fun s => trStmts₁ (q s)
| Q@(Λ'.clear _ _ q) => insert Q <| trStmts₁ q
| Q@(Λ'.copy q) => insert Q <| trStmts₁ q
| Q@(Λ'.succ q) => insert Q <| insert (unrev q) <| trStmts₁ q
| Q@(Λ'.pred q₁ q₂) => insert Q <| trStmts₁ q₁ ∪ insert (unrev q₂) (trStmts₁ q₂)
| Q@(Λ'.ret _) => {Q}
theorem trStmts₁_trans {q q'} : q' ∈ trStmts₁ q → trStmts₁ q' ⊆ trStmts₁ q := by
induction q with
| move _ _ _ q q_ih => _ | clear _ _ q q_ih => _ | copy q q_ih => _ | push _ _ q q_ih => _
| read q q_ih => _ | succ q q_ih => _ | pred q₁ q₂ q₁_ih q₂_ih => _ | ret => _ <;>
all_goals
simp +contextual only [trStmts₁, Finset.mem_insert, Finset.mem_union,
or_imp, Finset.mem_singleton, Finset.Subset.refl, imp_true_iff, true_and]
repeat exact fun h => Finset.Subset.trans (q_ih h) (Finset.subset_insert _ _)
· simp
intro s h x h'
simp only [Finset.mem_biUnion, Finset.mem_univ, true_and, Finset.mem_insert]
exact Or.inr ⟨_, q_ih s h h'⟩
· constructor
· rintro rfl
apply Finset.subset_insert
· intro h x h'
simp only [Finset.mem_insert]
exact Or.inr (Or.inr <| q_ih h h')
· refine ⟨fun h x h' => ?_, fun _ x h' => ?_, fun h x h' => ?_⟩ <;> simp
· exact Or.inr (Or.inr <| Or.inl <| q₁_ih h h')
· rcases Finset.mem_insert.1 h' with h' | h' <;> simp [h', unrev]
· exact Or.inr (Or.inr <| Or.inr <| q₂_ih h h')
theorem trStmts₁_self (q) : q ∈ trStmts₁ q := by
induction q <;> · first |apply Finset.mem_singleton_self|apply Finset.mem_insert_self
/-- The (finite!) set of machine states visited during the course of evaluation of `c`,
including the state `ret k` but not any states after that (that is, the states visited while
evaluating `k`). -/
def codeSupp' : Code → Cont' → Finset Λ'
| c@Code.zero', k => trStmts₁ (trNormal c k)
| c@Code.succ, k => trStmts₁ (trNormal c k)
| c@Code.tail, k => trStmts₁ (trNormal c k)
| c@(Code.cons f fs), k =>
trStmts₁ (trNormal c k) ∪
(codeSupp' f (Cont'.cons₁ fs k) ∪
(trStmts₁
(move₂ (fun _ => false) main aux <|
move₂ (fun s => s = Γ'.consₗ) stack main <|
move₂ (fun _ => false) aux stack <| trNormal fs (Cont'.cons₂ k)) ∪
(codeSupp' fs (Cont'.cons₂ k) ∪ trStmts₁ (head stack <| Λ'.ret k))))
| c@(Code.comp f g), k =>
trStmts₁ (trNormal c k) ∪
(codeSupp' g (Cont'.comp f k) ∪ (trStmts₁ (trNormal f k) ∪ codeSupp' f k))
| c@(Code.case f g), k => trStmts₁ (trNormal c k) ∪ (codeSupp' f k ∪ codeSupp' g k)
| c@(Code.fix f), k =>
trStmts₁ (trNormal c k) ∪
(codeSupp' f (Cont'.fix f k) ∪
(trStmts₁ (Λ'.clear natEnd main <| trNormal f (Cont'.fix f k)) ∪ {Λ'.ret k}))
@[simp]
theorem codeSupp'_self (c k) : trStmts₁ (trNormal c k) ⊆ codeSupp' c k := by
cases c <;> first | rfl | exact Finset.union_subset_left (fun _ a ↦ a)
/-- The (finite!) set of machine states visited during the course of evaluation of a continuation
`k`, not including the initial state `ret k`. -/
def contSupp : Cont' → Finset Λ'
| Cont'.cons₁ fs k =>
trStmts₁
(move₂ (fun _ => false) main aux <|
move₂ (fun s => s = Γ'.consₗ) stack main <|
move₂ (fun _ => false) aux stack <| trNormal fs (Cont'.cons₂ k)) ∪
(codeSupp' fs (Cont'.cons₂ k) ∪ (trStmts₁ (head stack <| Λ'.ret k) ∪ contSupp k))
| Cont'.cons₂ k => trStmts₁ (head stack <| Λ'.ret k) ∪ contSupp k
| Cont'.comp f k => codeSupp' f k ∪ contSupp k
| Cont'.fix f k => codeSupp' (Code.fix f) k ∪ contSupp k
| Cont'.halt => ∅
/-- The (finite!) set of machine states visited during the course of evaluation of `c` in
continuation `k`. This is actually closed under forward simulation (see `tr_supports`), and the
existence of this set means that the machine constructed in this section is in fact a proper
Turing machine, with a finite set of states. -/
def codeSupp (c : Code) (k : Cont') : Finset Λ' :=
codeSupp' c k ∪ contSupp k
@[simp]
theorem codeSupp_self (c k) : trStmts₁ (trNormal c k) ⊆ codeSupp c k :=
Finset.Subset.trans (codeSupp'_self _ _) (Finset.union_subset_left fun _ a ↦ a)
@[simp]
theorem codeSupp_zero (k) : codeSupp Code.zero' k = trStmts₁ (trNormal Code.zero' k) ∪ contSupp k :=
rfl
@[simp]
theorem codeSupp_succ (k) : codeSupp Code.succ k = trStmts₁ (trNormal Code.succ k) ∪ contSupp k :=
rfl
@[simp]
theorem codeSupp_tail (k) : codeSupp Code.tail k = trStmts₁ (trNormal Code.tail k) ∪ contSupp k :=
rfl
@[simp]
theorem codeSupp_cons (f fs k) :
codeSupp (Code.cons f fs) k =
trStmts₁ (trNormal (Code.cons f fs) k) ∪ codeSupp f (Cont'.cons₁ fs k) := by
simp [codeSupp, codeSupp', contSupp, Finset.union_assoc]
@[simp]
theorem codeSupp_comp (f g k) :
codeSupp (Code.comp f g) k =
trStmts₁ (trNormal (Code.comp f g) k) ∪ codeSupp g (Cont'.comp f k) := by
simp only [codeSupp, codeSupp', trNormal, Finset.union_assoc, contSupp]
rw [← Finset.union_assoc _ _ (contSupp k),
Finset.union_eq_right.2 (codeSupp'_self _ _)]
@[simp]
theorem codeSupp_case (f g k) :
codeSupp (Code.case f g) k =
trStmts₁ (trNormal (Code.case f g) k) ∪ (codeSupp f k ∪ codeSupp g k) := by
simp [codeSupp, codeSupp', contSupp, Finset.union_assoc, Finset.union_left_comm]
@[simp]
theorem codeSupp_fix (f k) :
codeSupp (Code.fix f) k = trStmts₁ (trNormal (Code.fix f) k) ∪ codeSupp f (Cont'.fix f k) := by
simp [codeSupp, codeSupp', contSupp, Finset.union_assoc, Finset.union_left_comm,
Finset.union_left_idem]
@[simp]
theorem contSupp_cons₁ (fs k) :
contSupp (Cont'.cons₁ fs k) =
trStmts₁
(move₂ (fun _ => false) main aux <|
move₂ (fun s => s = Γ'.consₗ) stack main <|
move₂ (fun _ => false) aux stack <| trNormal fs (Cont'.cons₂ k)) ∪
codeSupp fs (Cont'.cons₂ k) := by
simp [codeSupp, codeSupp', contSupp, Finset.union_assoc]
@[simp]
theorem contSupp_cons₂ (k) :
contSupp (Cont'.cons₂ k) = trStmts₁ (head stack <| Λ'.ret k) ∪ contSupp k :=
rfl
@[simp]
theorem contSupp_comp (f k) : contSupp (Cont'.comp f k) = codeSupp f k :=
rfl
theorem contSupp_fix (f k) : contSupp (Cont'.fix f k) = codeSupp f (Cont'.fix f k) := by
simp +contextual [codeSupp, codeSupp', contSupp, Finset.union_assoc,
Finset.subset_iff]
@[simp]
theorem contSupp_halt : contSupp Cont'.halt = ∅ :=
rfl
/-- The statement `Λ'.Supports S q` means that `contSupp k ⊆ S` for any `ret k`
reachable from `q`.
(This is a technical condition used in the proof that the machine is supported.) -/
def Λ'.Supports (S : Finset Λ') : Λ' → Prop
| Λ'.move _ _ _ q => Λ'.Supports S q
| Λ'.push _ _ q => Λ'.Supports S q
| Λ'.read q => ∀ s, Λ'.Supports S (q s)
| Λ'.clear _ _ q => Λ'.Supports S q
| Λ'.copy q => Λ'.Supports S q
| Λ'.succ q => Λ'.Supports S q
| Λ'.pred q₁ q₂ => Λ'.Supports S q₁ ∧ Λ'.Supports S q₂
| Λ'.ret k => contSupp k ⊆ S
/-- A shorthand for the predicate that we are proving in the main theorems `trStmts₁_supports`,
`codeSupp'_supports`, `contSupp_supports`, `codeSupp_supports`. The set `S` is fixed throughout
the proof, and denotes the full set of states in the machine, while `K` is a subset that we are
currently proving a property about. The predicate asserts that every state in `K` is closed in `S`
under forward simulation, i.e. stepping forward through evaluation starting from any state in `K`
stays entirely within `S`. -/
def Supports (K S : Finset Λ') :=
∀ q ∈ K, TM2.SupportsStmt S (tr q)
theorem supports_insert {K S q} :
Supports (insert q K) S ↔ TM2.SupportsStmt S (tr q) ∧ Supports K S := by simp [Supports]
theorem supports_singleton {S q} : Supports {q} S ↔ TM2.SupportsStmt S (tr q) := by simp [Supports]
theorem supports_union {K₁ K₂ S} : Supports (K₁ ∪ K₂) S ↔ Supports K₁ S ∧ Supports K₂ S := by
simp [Supports, or_imp, forall_and]
theorem supports_biUnion {K : Option Γ' → Finset Λ'} {S} :
Supports (Finset.univ.biUnion K) S ↔ ∀ a, Supports (K a) S := by
simpa [Supports] using forall_swap
theorem head_supports {S k q} (H : (q : Λ').Supports S) : (head k q).Supports S := fun _ => by
dsimp only; split_ifs <;> exact H
theorem ret_supports {S k} (H₁ : contSupp k ⊆ S) : TM2.SupportsStmt S (tr (Λ'.ret k)) := by
have W := fun {q} => trStmts₁_self q
cases k with
| halt => trivial
| cons₁ => rw [contSupp_cons₁, Finset.union_subset_iff] at H₁; exact fun _ => H₁.1 W
| cons₂ => rw [contSupp_cons₂, Finset.union_subset_iff] at H₁; exact fun _ => H₁.1 W
| comp => rw [contSupp_comp] at H₁; exact fun _ => H₁ (codeSupp_self _ _ W)
| fix =>
rw [contSupp_fix] at H₁
have L := @Finset.mem_union_left; have R := @Finset.mem_union_right
intro s; dsimp only; cases natEnd s.iget
· refine H₁ (R _ <| L _ <| R _ <| R _ <| L _ W)
· exact H₁ (R _ <| L _ <| R _ <| R _ <| R _ <| Finset.mem_singleton_self _)
theorem trStmts₁_supports {S q} (H₁ : (q : Λ').Supports S) (HS₁ : trStmts₁ q ⊆ S) :
Supports (trStmts₁ q) S := by
have W := fun {q} => trStmts₁_self q
induction q with
| move _ _ _ q q_ih => _ | clear _ _ q q_ih => _ | copy q q_ih => _ | push _ _ q q_ih => _
| read q q_ih => _ | succ q q_ih => _ | pred q₁ q₂ q₁_ih q₂_ih => _ | ret => _ <;>
simp [trStmts₁, -Finset.singleton_subset_iff] at HS₁ ⊢
any_goals
obtain ⟨h₁, h₂⟩ := Finset.insert_subset_iff.1 HS₁
first | have h₃ := h₂ W | try simp [Finset.subset_iff] at h₂
· exact supports_insert.2 ⟨⟨fun _ => h₃, fun _ => h₁⟩, q_ih H₁ h₂⟩ -- move
· exact supports_insert.2 ⟨⟨fun _ => h₃, fun _ => h₁⟩, q_ih H₁ h₂⟩ -- clear
· exact supports_insert.2 ⟨⟨fun _ => h₁, fun _ => h₃⟩, q_ih H₁ h₂⟩ -- copy
· exact supports_insert.2 ⟨⟨fun _ => h₃, fun _ => h₃⟩, q_ih H₁ h₂⟩ -- push
· refine supports_insert.2 ⟨fun _ => h₂ _ W, ?_⟩ -- read
exact supports_biUnion.2 fun _ => q_ih _ (H₁ _) fun _ h => h₂ _ h
· refine supports_insert.2 ⟨⟨fun _ => h₁, fun _ => h₂.1, fun _ => h₂.1⟩, ?_⟩ -- succ
exact supports_insert.2 ⟨⟨fun _ => h₂.2 _ W, fun _ => h₂.1⟩, q_ih H₁ h₂.2⟩
· refine -- pred
supports_insert.2 ⟨⟨fun _ => h₁, fun _ => h₂.2 _ (Or.inl W),
fun _ => h₂.1, fun _ => h₂.1⟩, ?_⟩
refine supports_insert.2 ⟨⟨fun _ => h₂.2 _ (Or.inr W), fun _ => h₂.1⟩, ?_⟩
refine supports_union.2 ⟨?_, ?_⟩
· exact q₁_ih H₁.1 fun _ h => h₂.2 _ (Or.inl h)
· exact q₂_ih H₁.2 fun _ h => h₂.2 _ (Or.inr h)
· exact supports_singleton.2 (ret_supports H₁) -- ret
theorem trStmts₁_supports' {S q K} (H₁ : (q : Λ').Supports S) (H₂ : trStmts₁ q ∪ K ⊆ S)
(H₃ : K ⊆ S → Supports K S) : Supports (trStmts₁ q ∪ K) S := by
simp only [Finset.union_subset_iff] at H₂
exact supports_union.2 ⟨trStmts₁_supports H₁ H₂.1, H₃ H₂.2⟩
theorem trNormal_supports {S c k} (Hk : codeSupp c k ⊆ S) : (trNormal c k).Supports S := by
induction c generalizing k with simp [Λ'.Supports, head]
| zero' => exact Finset.union_subset_right Hk
| succ => intro; split_ifs <;> exact Finset.union_subset_right Hk
| tail => exact Finset.union_subset_right Hk
| cons f fs IHf _ =>
apply IHf
rw [codeSupp_cons] at Hk
exact Finset.union_subset_right Hk
| comp f g _ IHg => apply IHg; rw [codeSupp_comp] at Hk; exact Finset.union_subset_right Hk
| case f g IHf IHg =>
simp only [codeSupp_case, Finset.union_subset_iff] at Hk
exact ⟨IHf Hk.2.1, IHg Hk.2.2⟩
| fix f IHf => apply IHf; rw [codeSupp_fix] at Hk; exact Finset.union_subset_right Hk
theorem codeSupp'_supports {S c k} (H : codeSupp c k ⊆ S) : Supports (codeSupp' c k) S := by
induction c generalizing k with
| cons f fs IHf IHfs =>
have H' := H; simp only [codeSupp_cons, Finset.union_subset_iff] at H'
refine trStmts₁_supports' (trNormal_supports H) (Finset.union_subset_left H) fun h => ?_
refine supports_union.2 ⟨IHf H'.2, ?_⟩
refine trStmts₁_supports' (trNormal_supports ?_) (Finset.union_subset_right h) fun h => ?_
· simp only [codeSupp, Finset.union_subset_iff, contSupp] at h H ⊢
exact ⟨h.2.2.1, h.2.2.2, H.2⟩
refine supports_union.2 ⟨IHfs ?_, ?_⟩
· rw [codeSupp, contSupp_cons₁] at H'
exact Finset.union_subset_right (Finset.union_subset_right H'.2)
exact
trStmts₁_supports (head_supports <| Finset.union_subset_right H)
(Finset.union_subset_right h)
| comp f g IHf IHg =>
have H' := H; rw [codeSupp_comp] at H'; have H' := Finset.union_subset_right H'
refine trStmts₁_supports' (trNormal_supports H) (Finset.union_subset_left H) fun h => ?_
refine supports_union.2 ⟨IHg H', ?_⟩
refine trStmts₁_supports' (trNormal_supports ?_) (Finset.union_subset_right h) fun _ => ?_
· simp only [codeSupp', codeSupp, Finset.union_subset_iff, contSupp] at h H ⊢
exact ⟨h.2.2, H.2⟩
exact IHf (Finset.union_subset_right H')
| case f g IHf IHg =>
have H' := H; simp only [codeSupp_case, Finset.union_subset_iff] at H'
refine trStmts₁_supports' (trNormal_supports H) (Finset.union_subset_left H) fun _ => ?_
exact supports_union.2 ⟨IHf H'.2.1, IHg H'.2.2⟩
| fix f IHf =>
have H' := H; simp only [codeSupp_fix, Finset.union_subset_iff] at H'
refine trStmts₁_supports' (trNormal_supports H) (Finset.union_subset_left H) fun h => ?_
refine supports_union.2 ⟨IHf H'.2, ?_⟩
refine trStmts₁_supports' (trNormal_supports ?_) (Finset.union_subset_right h) fun _ => ?_
· simp only [codeSupp', codeSupp, Finset.union_subset_iff, contSupp, trStmts₁,
Finset.insert_subset_iff] at h H ⊢
exact ⟨h.1, ⟨H.1.1, h⟩, H.2⟩
exact supports_singleton.2 (ret_supports <| Finset.union_subset_right H)
| _ => exact trStmts₁_supports (trNormal_supports H) (Finset.Subset.trans (codeSupp_self _ _) H)
theorem contSupp_supports {S k} (H : contSupp k ⊆ S) : Supports (contSupp k) S := by
induction k with
| halt => simp [contSupp_halt, Supports]
| cons₁ f k IH =>
have H₁ := H; rw [contSupp_cons₁] at H₁; have H₂ := Finset.union_subset_right H₁
refine trStmts₁_supports' (trNormal_supports H₂) H₁ fun h => ?_
refine supports_union.2 ⟨codeSupp'_supports H₂, ?_⟩
simp only [codeSupp, contSupp_cons₂, Finset.union_subset_iff] at H₂
exact trStmts₁_supports' (head_supports H₂.2.2) (Finset.union_subset_right h) IH
| cons₂ k IH =>
have H' := H; rw [contSupp_cons₂] at H'
exact trStmts₁_supports' (head_supports <| Finset.union_subset_right H') H' IH
| comp f k IH =>
have H' := H; rw [contSupp_comp] at H'; have H₂ := Finset.union_subset_right H'
exact supports_union.2 ⟨codeSupp'_supports H', IH H₂⟩
| fix f k IH =>
rw [contSupp] at H
exact supports_union.2 ⟨codeSupp'_supports H, IH (Finset.union_subset_right H)⟩
theorem codeSupp_supports {S c k} (H : codeSupp c k ⊆ S) : Supports (codeSupp c k) S :=
supports_union.2 ⟨codeSupp'_supports H, contSupp_supports (Finset.union_subset_right H)⟩
/-- The set `codeSupp c k` is a finite set that witnesses the effective finiteness of the `tr`
Turing machine. Starting from the initial state `trNormal c k`, forward simulation uses only
states in `codeSupp c k`, so this is a finite state machine. Even though the underlying type of
state labels `Λ'` is infinite, for a given partial recursive function `c` and continuation `k`,
only finitely many states are accessed, corresponding roughly to subterms of `c`. -/
theorem tr_supports (c k) : @TM2.Supports _ _ _ _ ⟨trNormal c k⟩ tr (codeSupp c k) :=
⟨codeSupp_self _ _ (trStmts₁_self _), fun _ => codeSupp_supports (Finset.Subset.refl _) _⟩
end
end PartrecToTM2
end Turing
| Mathlib/Computability/TMToPartrec.lean | 1,476 | 1,507 | |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Johannes Hölzl, Patrick Massot
-/
import Mathlib.Data.Set.Image
import Mathlib.Data.SProd
/-!
# Sets in product and pi types
This file proves basic properties of product of sets in `α × β` and in `Π i, α i`, and of the
diagonal of a type.
## Main declarations
This file contains basic results on the following notions, which are defined in `Set.Operations`.
* `Set.prod`: Binary product of sets. For `s : Set α`, `t : Set β`, we have
`s.prod t : Set (α × β)`. Denoted by `s ×ˢ t`.
* `Set.diagonal`: Diagonal of a type. `Set.diagonal α = {(x, x) | x : α}`.
* `Set.offDiag`: Off-diagonal. `s ×ˢ s` without the diagonal.
* `Set.pi`: Arbitrary product of sets.
-/
open Function
namespace Set
/-! ### Cartesian binary product of sets -/
section Prod
variable {α β γ δ : Type*} {s s₁ s₂ : Set α} {t t₁ t₂ : Set β} {a : α} {b : β}
theorem Subsingleton.prod (hs : s.Subsingleton) (ht : t.Subsingleton) :
(s ×ˢ t).Subsingleton := fun _x hx _y hy ↦
Prod.ext (hs hx.1 hy.1) (ht hx.2 hy.2)
noncomputable instance decidableMemProd [DecidablePred (· ∈ s)] [DecidablePred (· ∈ t)] :
DecidablePred (· ∈ s ×ˢ t) := fun x => inferInstanceAs (Decidable (x.1 ∈ s ∧ x.2 ∈ t))
@[gcongr]
theorem prod_mono (hs : s₁ ⊆ s₂) (ht : t₁ ⊆ t₂) : s₁ ×ˢ t₁ ⊆ s₂ ×ˢ t₂ :=
fun _ ⟨h₁, h₂⟩ => ⟨hs h₁, ht h₂⟩
@[gcongr]
theorem prod_mono_left (hs : s₁ ⊆ s₂) : s₁ ×ˢ t ⊆ s₂ ×ˢ t :=
prod_mono hs Subset.rfl
@[gcongr]
theorem prod_mono_right (ht : t₁ ⊆ t₂) : s ×ˢ t₁ ⊆ s ×ˢ t₂ :=
prod_mono Subset.rfl ht
@[simp]
theorem prod_self_subset_prod_self : s₁ ×ˢ s₁ ⊆ s₂ ×ˢ s₂ ↔ s₁ ⊆ s₂ :=
⟨fun h _ hx => (h (mk_mem_prod hx hx)).1, fun h _ hx => ⟨h hx.1, h hx.2⟩⟩
@[simp]
theorem prod_self_ssubset_prod_self : s₁ ×ˢ s₁ ⊂ s₂ ×ˢ s₂ ↔ s₁ ⊂ s₂ :=
and_congr prod_self_subset_prod_self <| not_congr prod_self_subset_prod_self
theorem prod_subset_iff {P : Set (α × β)} : s ×ˢ t ⊆ P ↔ ∀ x ∈ s, ∀ y ∈ t, (x, y) ∈ P :=
⟨fun h _ hx _ hy => h (mk_mem_prod hx hy), fun h ⟨_, _⟩ hp => h _ hp.1 _ hp.2⟩
theorem forall_prod_set {p : α × β → Prop} : (∀ x ∈ s ×ˢ t, p x) ↔ ∀ x ∈ s, ∀ y ∈ t, p (x, y) :=
prod_subset_iff
theorem exists_prod_set {p : α × β → Prop} : (∃ x ∈ s ×ˢ t, p x) ↔ ∃ x ∈ s, ∃ y ∈ t, p (x, y) := by
simp [and_assoc]
@[simp]
theorem prod_empty : s ×ˢ (∅ : Set β) = ∅ := by
ext
exact iff_of_eq (and_false _)
@[simp]
theorem empty_prod : (∅ : Set α) ×ˢ t = ∅ := by
ext
exact iff_of_eq (false_and _)
@[simp, mfld_simps]
theorem univ_prod_univ : @univ α ×ˢ @univ β = univ := by
ext
exact iff_of_eq (true_and _)
theorem univ_prod {t : Set β} : (univ : Set α) ×ˢ t = Prod.snd ⁻¹' t := by simp [prod_eq]
theorem prod_univ {s : Set α} : s ×ˢ (univ : Set β) = Prod.fst ⁻¹' s := by simp [prod_eq]
@[simp] lemma prod_eq_univ [Nonempty α] [Nonempty β] : s ×ˢ t = univ ↔ s = univ ∧ t = univ := by
simp [eq_univ_iff_forall, forall_and]
theorem singleton_prod : ({a} : Set α) ×ˢ t = Prod.mk a '' t := by
ext ⟨x, y⟩
simp [and_left_comm, eq_comm]
theorem prod_singleton : s ×ˢ ({b} : Set β) = (fun a => (a, b)) '' s := by
ext ⟨x, y⟩
simp [and_left_comm, eq_comm]
@[simp]
theorem singleton_prod_singleton : ({a} : Set α) ×ˢ ({b} : Set β) = {(a, b)} := by ext ⟨c, d⟩; simp
@[simp]
theorem union_prod : (s₁ ∪ s₂) ×ˢ t = s₁ ×ˢ t ∪ s₂ ×ˢ t := by
ext ⟨x, y⟩
simp [or_and_right]
@[simp]
theorem prod_union : s ×ˢ (t₁ ∪ t₂) = s ×ˢ t₁ ∪ s ×ˢ t₂ := by
ext ⟨x, y⟩
simp [and_or_left]
theorem inter_prod : (s₁ ∩ s₂) ×ˢ t = s₁ ×ˢ t ∩ s₂ ×ˢ t := by
ext ⟨x, y⟩
simp only [← and_and_right, mem_inter_iff, mem_prod]
theorem prod_inter : s ×ˢ (t₁ ∩ t₂) = s ×ˢ t₁ ∩ s ×ˢ t₂ := by
ext ⟨x, y⟩
simp only [← and_and_left, mem_inter_iff, mem_prod]
@[mfld_simps]
theorem prod_inter_prod : s₁ ×ˢ t₁ ∩ s₂ ×ˢ t₂ = (s₁ ∩ s₂) ×ˢ (t₁ ∩ t₂) := by
ext ⟨x, y⟩
simp [and_assoc, and_left_comm]
lemma compl_prod_eq_union {α β : Type*} (s : Set α) (t : Set β) :
(s ×ˢ t)ᶜ = (sᶜ ×ˢ univ) ∪ (univ ×ˢ tᶜ) := by
ext p
simp only [mem_compl_iff, mem_prod, not_and, mem_union, mem_univ, and_true, true_and]
constructor <;> intro h
· by_cases fst_in_s : p.fst ∈ s
· exact Or.inr (h fst_in_s)
· exact Or.inl fst_in_s
· intro fst_in_s
simpa only [fst_in_s, not_true, false_or] using h
@[simp]
theorem disjoint_prod : Disjoint (s₁ ×ˢ t₁) (s₂ ×ˢ t₂) ↔ Disjoint s₁ s₂ ∨ Disjoint t₁ t₂ := by
simp_rw [disjoint_left, mem_prod, not_and_or, Prod.forall, and_imp, ← @forall_or_right α, ←
@forall_or_left β, ← @forall_or_right (_ ∈ s₁), ← @forall_or_left (_ ∈ t₁)]
theorem Disjoint.set_prod_left (hs : Disjoint s₁ s₂) (t₁ t₂ : Set β) :
Disjoint (s₁ ×ˢ t₁) (s₂ ×ˢ t₂) :=
disjoint_left.2 fun ⟨_a, _b⟩ ⟨ha₁, _⟩ ⟨ha₂, _⟩ => disjoint_left.1 hs ha₁ ha₂
theorem Disjoint.set_prod_right (ht : Disjoint t₁ t₂) (s₁ s₂ : Set α) :
Disjoint (s₁ ×ˢ t₁) (s₂ ×ˢ t₂) :=
disjoint_left.2 fun ⟨_a, _b⟩ ⟨_, hb₁⟩ ⟨_, hb₂⟩ => disjoint_left.1 ht hb₁ hb₂
theorem prodMap_image_prod (f : α → β) (g : γ → δ) (s : Set α) (t : Set γ) :
(Prod.map f g) '' (s ×ˢ t) = (f '' s) ×ˢ (g '' t) := by
ext
aesop
theorem insert_prod : insert a s ×ˢ t = Prod.mk a '' t ∪ s ×ˢ t := by
simp only [insert_eq, union_prod, singleton_prod]
theorem prod_insert : s ×ˢ insert b t = (fun a => (a, b)) '' s ∪ s ×ˢ t := by
simp only [insert_eq, prod_union, prod_singleton]
theorem prod_preimage_eq {f : γ → α} {g : δ → β} :
(f ⁻¹' s) ×ˢ (g ⁻¹' t) = (fun p : γ × δ => (f p.1, g p.2)) ⁻¹' s ×ˢ t :=
rfl
theorem prod_preimage_left {f : γ → α} :
(f ⁻¹' s) ×ˢ t = (fun p : γ × β => (f p.1, p.2)) ⁻¹' s ×ˢ t :=
rfl
theorem prod_preimage_right {g : δ → β} :
s ×ˢ (g ⁻¹' t) = (fun p : α × δ => (p.1, g p.2)) ⁻¹' s ×ˢ t :=
rfl
theorem preimage_prod_map_prod (f : α → β) (g : γ → δ) (s : Set β) (t : Set δ) :
Prod.map f g ⁻¹' s ×ˢ t = (f ⁻¹' s) ×ˢ (g ⁻¹' t) :=
rfl
theorem mk_preimage_prod (f : γ → α) (g : γ → β) :
(fun x => (f x, g x)) ⁻¹' s ×ˢ t = f ⁻¹' s ∩ g ⁻¹' t :=
rfl
@[simp]
theorem mk_preimage_prod_left (hb : b ∈ t) : (fun a => (a, b)) ⁻¹' s ×ˢ t = s := by
ext a
simp [hb]
@[simp]
theorem mk_preimage_prod_right (ha : a ∈ s) : Prod.mk a ⁻¹' s ×ˢ t = t := by
ext b
simp [ha]
@[simp]
theorem mk_preimage_prod_left_eq_empty (hb : b ∉ t) : (fun a => (a, b)) ⁻¹' s ×ˢ t = ∅ := by
ext a
simp [hb]
@[simp]
theorem mk_preimage_prod_right_eq_empty (ha : a ∉ s) : Prod.mk a ⁻¹' s ×ˢ t = ∅ := by
ext b
simp [ha]
theorem mk_preimage_prod_left_eq_if [DecidablePred (· ∈ t)] :
(fun a => (a, b)) ⁻¹' s ×ˢ t = if b ∈ t then s else ∅ := by split_ifs with h <;> simp [h]
theorem mk_preimage_prod_right_eq_if [DecidablePred (· ∈ s)] :
Prod.mk a ⁻¹' s ×ˢ t = if a ∈ s then t else ∅ := by split_ifs with h <;> simp [h]
theorem mk_preimage_prod_left_fn_eq_if [DecidablePred (· ∈ t)] (f : γ → α) :
(fun a => (f a, b)) ⁻¹' s ×ˢ t = if b ∈ t then f ⁻¹' s else ∅ := by
rw [← mk_preimage_prod_left_eq_if, prod_preimage_left, preimage_preimage]
theorem mk_preimage_prod_right_fn_eq_if [DecidablePred (· ∈ s)] (g : δ → β) :
(fun b => (a, g b)) ⁻¹' s ×ˢ t = if a ∈ s then g ⁻¹' t else ∅ := by
rw [← mk_preimage_prod_right_eq_if, prod_preimage_right, preimage_preimage]
@[simp]
theorem preimage_swap_prod (s : Set α) (t : Set β) : Prod.swap ⁻¹' s ×ˢ t = t ×ˢ s := by
ext ⟨x, y⟩
simp [and_comm]
@[simp]
theorem image_swap_prod (s : Set α) (t : Set β) : Prod.swap '' s ×ˢ t = t ×ˢ s := by
rw [image_swap_eq_preimage_swap, preimage_swap_prod]
theorem mapsTo_swap_prod (s : Set α) (t : Set β) : MapsTo Prod.swap (s ×ˢ t) (t ×ˢ s) :=
fun _ ⟨hx, hy⟩ ↦ ⟨hy, hx⟩
theorem prod_image_image_eq {m₁ : α → γ} {m₂ : β → δ} :
(m₁ '' s) ×ˢ (m₂ '' t) = (fun p : α × β => (m₁ p.1, m₂ p.2)) '' s ×ˢ t :=
ext <| by
simp [-exists_and_right, exists_and_right.symm, and_left_comm, and_assoc, and_comm]
theorem prod_range_range_eq {m₁ : α → γ} {m₂ : β → δ} :
range m₁ ×ˢ range m₂ = range fun p : α × β => (m₁ p.1, m₂ p.2) :=
ext <| by simp [range]
@[simp, mfld_simps]
theorem range_prodMap {m₁ : α → γ} {m₂ : β → δ} : range (Prod.map m₁ m₂) = range m₁ ×ˢ range m₂ :=
prod_range_range_eq.symm
@[deprecated (since := "2025-04-10")] alias range_prod_map := range_prodMap
theorem prod_range_univ_eq {m₁ : α → γ} :
range m₁ ×ˢ (univ : Set β) = range fun p : α × β => (m₁ p.1, p.2) :=
ext <| by simp [range]
theorem prod_univ_range_eq {m₂ : β → δ} :
(univ : Set α) ×ˢ range m₂ = range fun p : α × β => (p.1, m₂ p.2) :=
ext <| by simp [range]
theorem range_pair_subset (f : α → β) (g : α → γ) :
(range fun x => (f x, g x)) ⊆ range f ×ˢ range g := by
have : (fun x => (f x, g x)) = Prod.map f g ∘ fun x => (x, x) := funext fun x => rfl
rw [this, ← range_prodMap]
apply range_comp_subset_range
theorem Nonempty.prod : s.Nonempty → t.Nonempty → (s ×ˢ t).Nonempty := fun ⟨x, hx⟩ ⟨y, hy⟩ =>
⟨(x, y), ⟨hx, hy⟩⟩
theorem Nonempty.fst : (s ×ˢ t).Nonempty → s.Nonempty := fun ⟨x, hx⟩ => ⟨x.1, hx.1⟩
theorem Nonempty.snd : (s ×ˢ t).Nonempty → t.Nonempty := fun ⟨x, hx⟩ => ⟨x.2, hx.2⟩
@[simp]
theorem prod_nonempty_iff : (s ×ˢ t).Nonempty ↔ s.Nonempty ∧ t.Nonempty :=
⟨fun h => ⟨h.fst, h.snd⟩, fun h => h.1.prod h.2⟩
@[simp]
theorem prod_eq_empty_iff : s ×ˢ t = ∅ ↔ s = ∅ ∨ t = ∅ := by
simp only [not_nonempty_iff_eq_empty.symm, prod_nonempty_iff, not_and_or]
theorem prod_sub_preimage_iff {W : Set γ} {f : α × β → γ} :
s ×ˢ t ⊆ f ⁻¹' W ↔ ∀ a b, a ∈ s → b ∈ t → f (a, b) ∈ W := by simp [subset_def]
theorem image_prodMk_subset_prod {f : α → β} {g : α → γ} {s : Set α} :
(fun x => (f x, g x)) '' s ⊆ (f '' s) ×ˢ (g '' s) := by
rintro _ ⟨x, hx, rfl⟩
exact mk_mem_prod (mem_image_of_mem f hx) (mem_image_of_mem g hx)
@[deprecated (since := "2025-02-22")]
alias image_prod_mk_subset_prod := image_prodMk_subset_prod
theorem image_prodMk_subset_prod_left (hb : b ∈ t) : (fun a => (a, b)) '' s ⊆ s ×ˢ t := by
rintro _ ⟨a, ha, rfl⟩
exact ⟨ha, hb⟩
@[deprecated (since := "2025-02-22")]
alias image_prod_mk_subset_prod_left := image_prodMk_subset_prod_left
theorem image_prodMk_subset_prod_right (ha : a ∈ s) : Prod.mk a '' t ⊆ s ×ˢ t := by
rintro _ ⟨b, hb, rfl⟩
exact ⟨ha, hb⟩
@[deprecated (since := "2025-02-22")]
alias image_prod_mk_subset_prod_right := image_prodMk_subset_prod_right
theorem prod_subset_preimage_fst (s : Set α) (t : Set β) : s ×ˢ t ⊆ Prod.fst ⁻¹' s :=
inter_subset_left
theorem fst_image_prod_subset (s : Set α) (t : Set β) : Prod.fst '' s ×ˢ t ⊆ s :=
image_subset_iff.2 <| prod_subset_preimage_fst s t
theorem fst_image_prod (s : Set β) {t : Set α} (ht : t.Nonempty) : Prod.fst '' s ×ˢ t = s :=
(fst_image_prod_subset _ _).antisymm fun y hy =>
let ⟨x, hx⟩ := ht
⟨(y, x), ⟨hy, hx⟩, rfl⟩
lemma mapsTo_fst_prod {s : Set α} {t : Set β} : MapsTo Prod.fst (s ×ˢ t) s :=
fun _ hx ↦ (mem_prod.1 hx).1
theorem prod_subset_preimage_snd (s : Set α) (t : Set β) : s ×ˢ t ⊆ Prod.snd ⁻¹' t :=
inter_subset_right
theorem snd_image_prod_subset (s : Set α) (t : Set β) : Prod.snd '' s ×ˢ t ⊆ t :=
image_subset_iff.2 <| prod_subset_preimage_snd s t
theorem snd_image_prod {s : Set α} (hs : s.Nonempty) (t : Set β) : Prod.snd '' s ×ˢ t = t :=
(snd_image_prod_subset _ _).antisymm fun y y_in =>
let ⟨x, x_in⟩ := hs
⟨(x, y), ⟨x_in, y_in⟩, rfl⟩
lemma mapsTo_snd_prod {s : Set α} {t : Set β} : MapsTo Prod.snd (s ×ˢ t) t :=
fun _ hx ↦ (mem_prod.1 hx).2
theorem prod_diff_prod : s ×ˢ t \ s₁ ×ˢ t₁ = s ×ˢ (t \ t₁) ∪ (s \ s₁) ×ˢ t := by
ext x
by_cases h₁ : x.1 ∈ s₁ <;> by_cases h₂ : x.2 ∈ t₁ <;> simp [*]
/-- A product set is included in a product set if and only factors are included, or a factor of the
first set is empty. -/
theorem prod_subset_prod_iff : s ×ˢ t ⊆ s₁ ×ˢ t₁ ↔ s ⊆ s₁ ∧ t ⊆ t₁ ∨ s = ∅ ∨ t = ∅ := by
rcases (s ×ˢ t).eq_empty_or_nonempty with h | h
· simp [h, prod_eq_empty_iff.1 h]
have st : s.Nonempty ∧ t.Nonempty := by rwa [prod_nonempty_iff] at h
refine ⟨fun H => Or.inl ⟨?_, ?_⟩, ?_⟩
· have := image_subset (Prod.fst : α × β → α) H
rwa [fst_image_prod _ st.2, fst_image_prod _ (h.mono H).snd] at this
· have := image_subset (Prod.snd : α × β → β) H
rwa [snd_image_prod st.1, snd_image_prod (h.mono H).fst] at this
· intro H
simp only [st.1.ne_empty, st.2.ne_empty, or_false] at H
exact prod_mono H.1 H.2
theorem prod_eq_prod_iff_of_nonempty (h : (s ×ˢ t).Nonempty) :
s ×ˢ t = s₁ ×ˢ t₁ ↔ s = s₁ ∧ t = t₁ := by
constructor
· intro heq
have h₁ : (s₁ ×ˢ t₁ : Set _).Nonempty := by rwa [← heq]
rw [prod_nonempty_iff] at h h₁
rw [← fst_image_prod s h.2, ← fst_image_prod s₁ h₁.2, heq, eq_self_iff_true, true_and, ←
snd_image_prod h.1 t, ← snd_image_prod h₁.1 t₁, heq]
· rintro ⟨rfl, rfl⟩
rfl
theorem prod_eq_prod_iff :
s ×ˢ t = s₁ ×ˢ t₁ ↔ s = s₁ ∧ t = t₁ ∨ (s = ∅ ∨ t = ∅) ∧ (s₁ = ∅ ∨ t₁ = ∅) := by
symm
rcases eq_empty_or_nonempty (s ×ˢ t) with h | h
· simp_rw [h, @eq_comm _ ∅, prod_eq_empty_iff, prod_eq_empty_iff.mp h, true_and,
or_iff_right_iff_imp]
rintro ⟨rfl, rfl⟩
exact prod_eq_empty_iff.mp h
rw [prod_eq_prod_iff_of_nonempty h]
rw [nonempty_iff_ne_empty, Ne, prod_eq_empty_iff] at h
simp_rw [h, false_and, or_false]
@[simp]
theorem prod_eq_iff_eq (ht : t.Nonempty) : s ×ˢ t = s₁ ×ˢ t ↔ s = s₁ := by
simp_rw [prod_eq_prod_iff, ht.ne_empty, and_true, or_iff_left_iff_imp, or_false]
rintro ⟨rfl, rfl⟩
rfl
theorem subset_prod {s : Set (α × β)} : s ⊆ (Prod.fst '' s) ×ˢ (Prod.snd '' s) :=
fun _ hp ↦ mem_prod.2 ⟨mem_image_of_mem _ hp, mem_image_of_mem _ hp⟩
section Mono
variable [Preorder α] {f : α → Set β} {g : α → Set γ}
theorem _root_.Monotone.set_prod (hf : Monotone f) (hg : Monotone g) :
Monotone fun x => f x ×ˢ g x :=
fun _ _ h => prod_mono (hf h) (hg h)
theorem _root_.Antitone.set_prod (hf : Antitone f) (hg : Antitone g) :
Antitone fun x => f x ×ˢ g x :=
fun _ _ h => prod_mono (hf h) (hg h)
theorem _root_.MonotoneOn.set_prod (hf : MonotoneOn f s) (hg : MonotoneOn g s) :
MonotoneOn (fun x => f x ×ˢ g x) s := fun _ ha _ hb h => prod_mono (hf ha hb h) (hg ha hb h)
theorem _root_.AntitoneOn.set_prod (hf : AntitoneOn f s) (hg : AntitoneOn g s) :
AntitoneOn (fun x => f x ×ˢ g x) s := fun _ ha _ hb h => prod_mono (hf ha hb h) (hg ha hb h)
end Mono
end Prod
/-! ### Diagonal
In this section we prove some lemmas about the diagonal set `{p | p.1 = p.2}` and the diagonal map
`fun x ↦ (x, x)`.
-/
section Diagonal
variable {α : Type*} {s t : Set α}
lemma diagonal_nonempty [Nonempty α] : (diagonal α).Nonempty :=
Nonempty.elim ‹_› fun x => ⟨_, mem_diagonal x⟩
instance decidableMemDiagonal [h : DecidableEq α] (x : α × α) : Decidable (x ∈ diagonal α) :=
h x.1 x.2
theorem preimage_coe_coe_diagonal (s : Set α) :
Prod.map (fun x : s => (x : α)) (fun x : s => (x : α)) ⁻¹' diagonal α = diagonal s := by
ext ⟨⟨x, hx⟩, ⟨y, hy⟩⟩
simp [Set.diagonal]
@[simp]
theorem range_diag : (range fun x => (x, x)) = diagonal α := by
ext ⟨x, y⟩
simp [diagonal, eq_comm]
theorem diagonal_subset_iff {s} : diagonal α ⊆ s ↔ ∀ x, (x, x) ∈ s := by
rw [← range_diag, range_subset_iff]
@[simp]
theorem prod_subset_compl_diagonal_iff_disjoint : s ×ˢ t ⊆ (diagonal α)ᶜ ↔ Disjoint s t :=
prod_subset_iff.trans disjoint_iff_forall_ne.symm
@[simp]
theorem diag_preimage_prod (s t : Set α) : (fun x => (x, x)) ⁻¹' s ×ˢ t = s ∩ t :=
rfl
theorem diag_preimage_prod_self (s : Set α) : (fun x => (x, x)) ⁻¹' s ×ˢ s = s :=
inter_self s
theorem diag_image (s : Set α) : (fun x => (x, x)) '' s = diagonal α ∩ s ×ˢ s := by
rw [← range_diag, ← image_preimage_eq_range_inter, diag_preimage_prod_self]
theorem diagonal_eq_univ_iff : diagonal α = univ ↔ Subsingleton α := by
simp only [subsingleton_iff, eq_univ_iff_forall, Prod.forall, mem_diagonal_iff]
theorem diagonal_eq_univ [Subsingleton α] : diagonal α = univ := diagonal_eq_univ_iff.2 ‹_›
end Diagonal
/-- A function is `Function.const α a` for some `a` if and only if `∀ x y, f x = f y`. -/
theorem range_const_eq_diagonal {α β : Type*} [hβ : Nonempty β] :
range (const α) = {f : α → β | ∀ x y, f x = f y} := by
refine (range_eq_iff _ _).mpr ⟨fun _ _ _ ↦ rfl, fun f hf ↦ ?_⟩
rcases isEmpty_or_nonempty α with h|⟨⟨a⟩⟩
· exact hβ.elim fun b ↦ ⟨b, Subsingleton.elim _ _⟩
· exact ⟨f a, funext fun x ↦ hf _ _⟩
end Set
section Pullback
open Set
variable {X Y Z}
/-- The fiber product $X \times_Y Z$. -/
abbrev Function.Pullback (f : X → Y) (g : Z → Y) := {p : X × Z // f p.1 = g p.2}
/-- The fiber product $X \times_Y X$. -/
abbrev Function.PullbackSelf (f : X → Y) := f.Pullback f
/-- The projection from the fiber product to the first factor. -/
def Function.Pullback.fst {f : X → Y} {g : Z → Y} (p : f.Pullback g) : X := p.val.1
/-- The projection from the fiber product to the second factor. -/
def Function.Pullback.snd {f : X → Y} {g : Z → Y} (p : f.Pullback g) : Z := p.val.2
open Function.Pullback in
lemma Function.pullback_comm_sq (f : X → Y) (g : Z → Y) :
f ∘ @fst X Y Z f g = g ∘ @snd X Y Z f g := funext fun p ↦ p.2
/-- The diagonal map $\Delta: X \to X \times_Y X$. -/
@[simps]
def toPullbackDiag (f : X → Y) (x : X) : f.Pullback f := ⟨(x, x), rfl⟩
/-- The diagonal $\Delta(X) \subseteq X \times_Y X$. -/
def Function.pullbackDiagonal (f : X → Y) : Set (f.Pullback f) := {p | p.fst = p.snd}
/-- Three functions between the three pairs of spaces $X_i, Y_i, Z_i$ that are compatible
induce a function $X_1 \times_{Y_1} Z_1 \to X_2 \times_{Y_2} Z_2$. -/
def Function.mapPullback {X₁ X₂ Y₁ Y₂ Z₁ Z₂}
{f₁ : X₁ → Y₁} {g₁ : Z₁ → Y₁} {f₂ : X₂ → Y₂} {g₂ : Z₂ → Y₂}
(mapX : X₁ → X₂) (mapY : Y₁ → Y₂) (mapZ : Z₁ → Z₂)
(commX : f₂ ∘ mapX = mapY ∘ f₁) (commZ : g₂ ∘ mapZ = mapY ∘ g₁)
(p : f₁.Pullback g₁) : f₂.Pullback g₂ :=
⟨(mapX p.fst, mapZ p.snd),
(congr_fun commX _).trans <| (congr_arg mapY p.2).trans <| congr_fun commZ.symm _⟩
open Function.Pullback in
/-- The projection $(X \times_Y Z) \times_Z (X \times_Y Z) \to X \times_Y X$. -/
def Function.PullbackSelf.map_fst {f : X → Y} {g : Z → Y} :
(@snd X Y Z f g).PullbackSelf → f.PullbackSelf :=
mapPullback fst g fst (pullback_comm_sq f g) (pullback_comm_sq f g)
open Function.Pullback in
/-- The projection $(X \times_Y Z) \times_X (X \times_Y Z) \to Z \times_Y Z$. -/
def Function.PullbackSelf.map_snd {f : X → Y} {g : Z → Y} :
(@fst X Y Z f g).PullbackSelf → g.PullbackSelf :=
mapPullback snd f snd (pullback_comm_sq f g).symm (pullback_comm_sq f g).symm
open Function.PullbackSelf Function.Pullback
theorem preimage_map_fst_pullbackDiagonal {f : X → Y} {g : Z → Y} :
@map_fst X Y Z f g ⁻¹' pullbackDiagonal f = pullbackDiagonal (@snd X Y Z f g) := by
ext ⟨⟨p₁, p₂⟩, he⟩
simp_rw [pullbackDiagonal, mem_setOf, Subtype.ext_iff, Prod.ext_iff]
exact (and_iff_left he).symm
theorem Function.Injective.preimage_pullbackDiagonal {f : X → Y} {g : Z → X} (inj : g.Injective) :
mapPullback g id g (by rfl) (by rfl) ⁻¹' pullbackDiagonal f = pullbackDiagonal (f ∘ g) :=
ext fun _ ↦ inj.eq_iff
theorem image_toPullbackDiag (f : X → Y) (s : Set X) :
toPullbackDiag f '' s = pullbackDiagonal f ∩ Subtype.val ⁻¹' s ×ˢ s := by
ext x
constructor
· rintro ⟨x, hx, rfl⟩
exact ⟨rfl, hx, hx⟩
· obtain ⟨⟨x, y⟩, h⟩ := x
rintro ⟨rfl : x = y, h2x⟩
exact mem_image_of_mem _ h2x.1
theorem range_toPullbackDiag (f : X → Y) : range (toPullbackDiag f) = pullbackDiagonal f := by
rw [← image_univ, image_toPullbackDiag, univ_prod_univ, preimage_univ, inter_univ]
theorem injective_toPullbackDiag (f : X → Y) : (toPullbackDiag f).Injective :=
fun _ _ h ↦ congr_arg Prod.fst (congr_arg Subtype.val h)
end Pullback
namespace Set
section OffDiag
variable {α : Type*} {s t : Set α} {a : α}
theorem offDiag_mono : Monotone (offDiag : Set α → Set (α × α)) := fun _ _ h _ =>
And.imp (@h _) <| And.imp_left <| @h _
@[simp]
theorem offDiag_nonempty : s.offDiag.Nonempty ↔ s.Nontrivial := by
simp [offDiag, Set.Nonempty, Set.Nontrivial]
@[simp]
theorem offDiag_eq_empty : s.offDiag = ∅ ↔ s.Subsingleton := by
rw [← not_nonempty_iff_eq_empty, ← not_nontrivial_iff, offDiag_nonempty.not]
alias ⟨_, Nontrivial.offDiag_nonempty⟩ := offDiag_nonempty
alias ⟨_, Subsingleton.offDiag_eq_empty⟩ := offDiag_nonempty
variable (s t)
theorem offDiag_subset_prod : s.offDiag ⊆ s ×ˢ s := fun _ hx => ⟨hx.1, hx.2.1⟩
theorem offDiag_eq_sep_prod : s.offDiag = { x ∈ s ×ˢ s | x.1 ≠ x.2 } :=
ext fun _ => and_assoc.symm
@[simp]
theorem offDiag_empty : (∅ : Set α).offDiag = ∅ := by simp
@[simp]
theorem offDiag_singleton (a : α) : ({a} : Set α).offDiag = ∅ := by simp
@[simp]
theorem offDiag_univ : (univ : Set α).offDiag = (diagonal α)ᶜ :=
ext <| by simp
@[simp]
theorem prod_sdiff_diagonal : s ×ˢ s \ diagonal α = s.offDiag :=
ext fun _ => and_assoc
@[simp]
| theorem disjoint_diagonal_offDiag : Disjoint (diagonal α) s.offDiag :=
disjoint_left.mpr fun _ hd ho => ho.2.2 hd
| Mathlib/Data/Set/Prod.lean | 585 | 587 |
/-
Copyright (c) 2023 Peter Nelson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Peter Nelson
-/
import Mathlib.SetTheory.Cardinal.Finite
import Mathlib.Data.Set.Finite.Powerset
/-!
# Noncomputable Set Cardinality
We define the cardinality of set `s` as a term `Set.encard s : ℕ∞` and a term `Set.ncard s : ℕ`.
The latter takes the junk value of zero if `s` is infinite. Both functions are noncomputable, and
are defined in terms of `ENat.card` (which takes a type as its argument); this file can be seen
as an API for the same function in the special case where the type is a coercion of a `Set`,
allowing for smoother interactions with the `Set` API.
`Set.encard` never takes junk values, so is more mathematically natural than `Set.ncard`, even
though it takes values in a less convenient type. It is probably the right choice in settings where
one is concerned with the cardinalities of sets that may or may not be infinite.
`Set.ncard` has a nicer codomain, but when using it, `Set.Finite` hypotheses are normally needed to
make sure its values are meaningful. More generally, `Set.ncard` is intended to be used over the
obvious alternative `Finset.card` when finiteness is 'propositional' rather than 'structural'.
When working with sets that are finite by virtue of their definition, then `Finset.card` probably
makes more sense. One setting where `Set.ncard` works nicely is in a type `α` with `[Finite α]`,
where every set is automatically finite. In this setting, we use default arguments and a simple
tactic so that finiteness goals are discharged automatically in `Set.ncard` theorems.
## Main Definitions
* `Set.encard s` is the cardinality of the set `s` as an extended natural number, with value `⊤` if
`s` is infinite.
* `Set.ncard s` is the cardinality of the set `s` as a natural number, provided `s` is Finite.
If `s` is Infinite, then `Set.ncard s = 0`.
* `toFinite_tac` is a tactic that tries to synthesize a `Set.Finite s` argument with
`Set.toFinite`. This will work for `s : Set α` where there is a `Finite α` instance.
## Implementation Notes
The theorems in this file are very similar to those in `Data.Finset.Card`, but with `Set` operations
instead of `Finset`. We first prove all the theorems for `Set.encard`, and then derive most of the
`Set.ncard` results as a consequence. Things are done this way to avoid reliance on the `Finset` API
for theorems about infinite sets, and to allow for a refactor that removes or modifies `Set.ncard`
in the future.
Nearly all the theorems for `Set.ncard` require finiteness of one or more of their arguments. We
provide this assumption with a default argument of the form `(hs : s.Finite := by toFinite_tac)`,
where `toFinite_tac` will find an `s.Finite` term in the cases where `s` is a set in a `Finite`
type.
Often, where there are two set arguments `s` and `t`, the finiteness of one follows from the other
in the context of the theorem, in which case we only include the ones that are needed, and derive
the other inside the proof. A few of the theorems, such as `ncard_union_le` do not require
finiteness arguments; they are true by coincidence due to junk values.
-/
namespace Set
variable {α β : Type*} {s t : Set α}
/-- The cardinality of a set as a term in `ℕ∞` -/
noncomputable def encard (s : Set α) : ℕ∞ := ENat.card s
@[simp] theorem encard_univ_coe (s : Set α) : encard (univ : Set s) = encard s := by
rw [encard, encard, ENat.card_congr (Equiv.Set.univ ↑s)]
theorem encard_univ (α : Type*) :
encard (univ : Set α) = ENat.card α := by
rw [encard, ENat.card_congr (Equiv.Set.univ α)]
theorem Finite.encard_eq_coe_toFinset_card (h : s.Finite) : s.encard = h.toFinset.card := by
have := h.fintype
rw [encard, ENat.card_eq_coe_fintype_card, toFinite_toFinset, toFinset_card]
theorem encard_eq_coe_toFinset_card (s : Set α) [Fintype s] : encard s = s.toFinset.card := by
have h := toFinite s
rw [h.encard_eq_coe_toFinset_card, toFinite_toFinset]
@[simp] theorem toENat_cardinalMk (s : Set α) : (Cardinal.mk s).toENat = s.encard := rfl
theorem toENat_cardinalMk_subtype (P : α → Prop) :
(Cardinal.mk {x // P x}).toENat = {x | P x}.encard :=
rfl
@[simp] theorem coe_fintypeCard (s : Set α) [Fintype s] : Fintype.card s = s.encard := by
simp [encard_eq_coe_toFinset_card]
@[simp, norm_cast] theorem encard_coe_eq_coe_finsetCard (s : Finset α) :
encard (s : Set α) = s.card := by
rw [Finite.encard_eq_coe_toFinset_card (Finset.finite_toSet s)]; simp
@[simp] theorem Infinite.encard_eq {s : Set α} (h : s.Infinite) : s.encard = ⊤ := by
have := h.to_subtype
rw [encard, ENat.card_eq_top_of_infinite]
@[simp] theorem encard_eq_zero : s.encard = 0 ↔ s = ∅ := by
rw [encard, ENat.card_eq_zero_iff_empty, isEmpty_subtype, eq_empty_iff_forall_not_mem]
@[simp] theorem encard_empty : (∅ : Set α).encard = 0 := by
rw [encard_eq_zero]
theorem nonempty_of_encard_ne_zero (h : s.encard ≠ 0) : s.Nonempty := by
rwa [nonempty_iff_ne_empty, Ne, ← encard_eq_zero]
theorem encard_ne_zero : s.encard ≠ 0 ↔ s.Nonempty := by
rw [ne_eq, encard_eq_zero, nonempty_iff_ne_empty]
@[simp] theorem encard_pos : 0 < s.encard ↔ s.Nonempty := by
rw [pos_iff_ne_zero, encard_ne_zero]
protected alias ⟨_, Nonempty.encard_pos⟩ := encard_pos
@[simp] theorem encard_singleton (e : α) : ({e} : Set α).encard = 1 := by
rw [encard, ENat.card_eq_coe_fintype_card, Fintype.card_ofSubsingleton, Nat.cast_one]
theorem encard_union_eq (h : Disjoint s t) : (s ∪ t).encard = s.encard + t.encard := by
classical
simp [encard, ENat.card_congr (Equiv.Set.union h)]
theorem encard_insert_of_not_mem {a : α} (has : a ∉ s) : (insert a s).encard = s.encard + 1 := by
rw [← union_singleton, encard_union_eq (by simpa), encard_singleton]
theorem Finite.encard_lt_top (h : s.Finite) : s.encard < ⊤ := by
induction s, h using Set.Finite.induction_on with
| empty => simp
| insert hat _ ht' =>
rw [encard_insert_of_not_mem hat]
exact lt_tsub_iff_right.1 ht'
theorem Finite.encard_eq_coe (h : s.Finite) : s.encard = ENat.toNat s.encard :=
(ENat.coe_toNat h.encard_lt_top.ne).symm
theorem Finite.exists_encard_eq_coe (h : s.Finite) : ∃ (n : ℕ), s.encard = n :=
⟨_, h.encard_eq_coe⟩
@[simp] theorem encard_lt_top_iff : s.encard < ⊤ ↔ s.Finite :=
⟨fun h ↦ by_contra fun h' ↦ h.ne (Infinite.encard_eq h'), Finite.encard_lt_top⟩
@[simp] theorem encard_eq_top_iff : s.encard = ⊤ ↔ s.Infinite := by
rw [← not_iff_not, ← Ne, ← lt_top_iff_ne_top, encard_lt_top_iff, not_infinite]
alias ⟨_, encard_eq_top⟩ := encard_eq_top_iff
theorem encard_ne_top_iff : s.encard ≠ ⊤ ↔ s.Finite := by
simp
theorem finite_of_encard_le_coe {k : ℕ} (h : s.encard ≤ k) : s.Finite := by
rw [← encard_lt_top_iff]; exact h.trans_lt (WithTop.coe_lt_top _)
theorem finite_of_encard_eq_coe {k : ℕ} (h : s.encard = k) : s.Finite :=
finite_of_encard_le_coe h.le
theorem encard_le_coe_iff {k : ℕ} : s.encard ≤ k ↔ s.Finite ∧ ∃ (n₀ : ℕ), s.encard = n₀ ∧ n₀ ≤ k :=
⟨fun h ↦ ⟨finite_of_encard_le_coe h, by rwa [ENat.le_coe_iff] at h⟩,
fun ⟨_,⟨n₀,hs, hle⟩⟩ ↦ by rwa [hs, Nat.cast_le]⟩
@[simp]
theorem encard_prod : (s ×ˢ t).encard = s.encard * t.encard := by
simp [Set.encard, ENat.card_congr (Equiv.Set.prod ..)]
section Lattice
theorem encard_le_encard (h : s ⊆ t) : s.encard ≤ t.encard := by
rw [← union_diff_cancel h, encard_union_eq disjoint_sdiff_right]; exact le_self_add
@[deprecated (since := "2025-01-05")] alias encard_le_card := encard_le_encard
theorem encard_mono {α : Type*} : Monotone (encard : Set α → ℕ∞) :=
fun _ _ ↦ encard_le_encard
theorem encard_diff_add_encard_of_subset (h : s ⊆ t) : (t \ s).encard + s.encard = t.encard := by
rw [← encard_union_eq disjoint_sdiff_left, diff_union_self, union_eq_self_of_subset_right h]
@[simp] theorem one_le_encard_iff_nonempty : 1 ≤ s.encard ↔ s.Nonempty := by
rw [nonempty_iff_ne_empty, Ne, ← encard_eq_zero, ENat.one_le_iff_ne_zero]
theorem encard_diff_add_encard_inter (s t : Set α) :
(s \ t).encard + (s ∩ t).encard = s.encard := by
rw [← encard_union_eq (disjoint_of_subset_right inter_subset_right disjoint_sdiff_left),
diff_union_inter]
theorem encard_union_add_encard_inter (s t : Set α) :
(s ∪ t).encard + (s ∩ t).encard = s.encard + t.encard := by
rw [← diff_union_self, encard_union_eq disjoint_sdiff_left, add_right_comm,
encard_diff_add_encard_inter]
theorem encard_eq_encard_iff_encard_diff_eq_encard_diff (h : (s ∩ t).Finite) :
s.encard = t.encard ↔ (s \ t).encard = (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_right_inj h.encard_lt_top.ne]
theorem encard_le_encard_iff_encard_diff_le_encard_diff (h : (s ∩ t).Finite) :
s.encard ≤ t.encard ↔ (s \ t).encard ≤ (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_le_add_iff_right h.encard_lt_top.ne]
theorem encard_lt_encard_iff_encard_diff_lt_encard_diff (h : (s ∩ t).Finite) :
s.encard < t.encard ↔ (s \ t).encard < (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_lt_add_iff_right h.encard_lt_top.ne]
theorem encard_union_le (s t : Set α) : (s ∪ t).encard ≤ s.encard + t.encard := by
rw [← encard_union_add_encard_inter]; exact le_self_add
theorem finite_iff_finite_of_encard_eq_encard (h : s.encard = t.encard) : s.Finite ↔ t.Finite := by
rw [← encard_lt_top_iff, ← encard_lt_top_iff, h]
theorem infinite_iff_infinite_of_encard_eq_encard (h : s.encard = t.encard) :
s.Infinite ↔ t.Infinite := by rw [← encard_eq_top_iff, h, encard_eq_top_iff]
theorem Finite.finite_of_encard_le {s : Set α} {t : Set β} (hs : s.Finite)
(h : t.encard ≤ s.encard) : t.Finite :=
encard_lt_top_iff.1 (h.trans_lt hs.encard_lt_top)
lemma Finite.eq_of_subset_of_encard_le' (ht : t.Finite) (hst : s ⊆ t) (hts : t.encard ≤ s.encard) :
s = t := by
rw [← zero_add (a := encard s), ← encard_diff_add_encard_of_subset hst] at hts
have hdiff := WithTop.le_of_add_le_add_right (ht.subset hst).encard_lt_top.ne hts
rw [nonpos_iff_eq_zero, encard_eq_zero, diff_eq_empty] at hdiff
exact hst.antisymm hdiff
theorem Finite.eq_of_subset_of_encard_le (hs : s.Finite) (hst : s ⊆ t)
(hts : t.encard ≤ s.encard) : s = t :=
(hs.finite_of_encard_le hts).eq_of_subset_of_encard_le' hst hts
theorem Finite.encard_lt_encard (hs : s.Finite) (h : s ⊂ t) : s.encard < t.encard :=
(encard_mono h.subset).lt_of_ne fun he ↦ h.ne (hs.eq_of_subset_of_encard_le h.subset he.symm.le)
theorem encard_strictMono [Finite α] : StrictMono (encard : Set α → ℕ∞) :=
fun _ _ h ↦ (toFinite _).encard_lt_encard h
theorem encard_diff_add_encard (s t : Set α) : (s \ t).encard + t.encard = (s ∪ t).encard := by
rw [← encard_union_eq disjoint_sdiff_left, diff_union_self]
theorem encard_le_encard_diff_add_encard (s t : Set α) : s.encard ≤ (s \ t).encard + t.encard :=
(encard_mono subset_union_left).trans_eq (encard_diff_add_encard _ _).symm
theorem tsub_encard_le_encard_diff (s t : Set α) : s.encard - t.encard ≤ (s \ t).encard := by
rw [tsub_le_iff_left, add_comm]; apply encard_le_encard_diff_add_encard
theorem encard_add_encard_compl (s : Set α) : s.encard + sᶜ.encard = (univ : Set α).encard := by
rw [← encard_union_eq disjoint_compl_right, union_compl_self]
end Lattice
section InsertErase
variable {a b : α}
theorem encard_insert_le (s : Set α) (x : α) : (insert x s).encard ≤ s.encard + 1 := by
rw [← union_singleton, ← encard_singleton x]; apply encard_union_le
theorem encard_singleton_inter (s : Set α) (x : α) : ({x} ∩ s).encard ≤ 1 := by
rw [← encard_singleton x]; exact encard_le_encard inter_subset_left
theorem encard_diff_singleton_add_one (h : a ∈ s) :
(s \ {a}).encard + 1 = s.encard := by
rw [← encard_insert_of_not_mem (fun h ↦ h.2 rfl), insert_diff_singleton, insert_eq_of_mem h]
theorem encard_diff_singleton_of_mem (h : a ∈ s) :
(s \ {a}).encard = s.encard - 1 := by
rw [← encard_diff_singleton_add_one h, ← WithTop.add_right_inj WithTop.one_ne_top,
tsub_add_cancel_of_le (self_le_add_left _ _)]
theorem encard_tsub_one_le_encard_diff_singleton (s : Set α) (x : α) :
s.encard - 1 ≤ (s \ {x}).encard := by
rw [← encard_singleton x]; apply tsub_encard_le_encard_diff
theorem encard_exchange (ha : a ∉ s) (hb : b ∈ s) : (insert a (s \ {b})).encard = s.encard := by
rw [encard_insert_of_not_mem, encard_diff_singleton_add_one hb]
simp_all only [not_true, mem_diff, mem_singleton_iff, false_and, not_false_eq_true]
theorem encard_exchange' (ha : a ∉ s) (hb : b ∈ s) : (insert a s \ {b}).encard = s.encard := by
rw [← insert_diff_singleton_comm (by rintro rfl; exact ha hb), encard_exchange ha hb]
theorem encard_eq_add_one_iff {k : ℕ∞} :
s.encard = k + 1 ↔ (∃ a t, ¬a ∈ t ∧ insert a t = s ∧ t.encard = k) := by
refine ⟨fun h ↦ ?_, ?_⟩
· obtain ⟨a, ha⟩ := nonempty_of_encard_ne_zero (s := s) (by simp [h])
refine ⟨a, s \ {a}, fun h ↦ h.2 rfl, by rwa [insert_diff_singleton, insert_eq_of_mem], ?_⟩
rw [← WithTop.add_right_inj WithTop.one_ne_top, ← h,
encard_diff_singleton_add_one ha]
rintro ⟨a, t, h, rfl, rfl⟩
rw [encard_insert_of_not_mem h]
/-- Every set is either empty, infinite, or can have its `encard` reduced by a removal. Intended
for well-founded induction on the value of `encard`. -/
theorem eq_empty_or_encard_eq_top_or_encard_diff_singleton_lt (s : Set α) :
s = ∅ ∨ s.encard = ⊤ ∨ ∃ a ∈ s, (s \ {a}).encard < s.encard := by
refine s.eq_empty_or_nonempty.elim Or.inl (Or.inr ∘ fun ⟨a,ha⟩ ↦
(s.finite_or_infinite.elim (fun hfin ↦ Or.inr ⟨a, ha, ?_⟩) (Or.inl ∘ Infinite.encard_eq)))
rw [← encard_diff_singleton_add_one ha]; nth_rw 1 [← add_zero (encard _)]
exact WithTop.add_lt_add_left hfin.diff.encard_lt_top.ne zero_lt_one
end InsertErase
section SmallSets
theorem encard_pair {x y : α} (hne : x ≠ y) : ({x, y} : Set α).encard = 2 := by
rw [encard_insert_of_not_mem (by simpa), ← one_add_one_eq_two,
WithTop.add_right_inj WithTop.one_ne_top, encard_singleton]
theorem encard_eq_one : s.encard = 1 ↔ ∃ x, s = {x} := by
refine ⟨fun h ↦ ?_, fun ⟨x, hx⟩ ↦ by rw [hx, encard_singleton]⟩
obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
exact ⟨x, ((finite_singleton x).eq_of_subset_of_encard_le (by simpa) (by simp [h])).symm⟩
theorem encard_le_one_iff_eq : s.encard ≤ 1 ↔ s = ∅ ∨ ∃ x, s = {x} := by
rw [le_iff_lt_or_eq, lt_iff_not_le, ENat.one_le_iff_ne_zero, not_not, encard_eq_zero,
encard_eq_one]
theorem encard_le_one_iff : s.encard ≤ 1 ↔ ∀ a b, a ∈ s → b ∈ s → a = b := by
rw [encard_le_one_iff_eq, or_iff_not_imp_left, ← Ne, ← nonempty_iff_ne_empty]
refine ⟨fun h a b has hbs ↦ ?_,
fun h ⟨x, hx⟩ ↦ ⟨x, ((singleton_subset_iff.2 hx).antisymm' (fun y hy ↦ h _ _ hy hx))⟩⟩
obtain ⟨x, rfl⟩ := h ⟨_, has⟩
rw [(has : a = x), (hbs : b = x)]
theorem encard_le_one_iff_subsingleton : s.encard ≤ 1 ↔ s.Subsingleton := by
rw [encard_le_one_iff, Set.Subsingleton]
tauto
theorem one_lt_encard_iff_nontrivial : 1 < s.encard ↔ s.Nontrivial := by
rw [← not_iff_not, not_lt, Set.not_nontrivial_iff, ← encard_le_one_iff_subsingleton]
theorem one_lt_encard_iff : 1 < s.encard ↔ ∃ a b, a ∈ s ∧ b ∈ s ∧ a ≠ b := by
rw [← not_iff_not, not_exists, not_lt, encard_le_one_iff]; aesop
theorem exists_ne_of_one_lt_encard (h : 1 < s.encard) (a : α) : ∃ b ∈ s, b ≠ a := by
by_contra! h'
obtain ⟨b, b', hb, hb', hne⟩ := one_lt_encard_iff.1 h
apply hne
rw [h' b hb, h' b' hb']
theorem encard_eq_two : s.encard = 2 ↔ ∃ x y, x ≠ y ∧ s = {x, y} := by
refine ⟨fun h ↦ ?_, fun ⟨x, y, hne, hs⟩ ↦ by rw [hs, encard_pair hne]⟩
obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
rw [← insert_eq_of_mem hx, ← insert_diff_singleton, encard_insert_of_not_mem (fun h ↦ h.2 rfl),
← one_add_one_eq_two, WithTop.add_right_inj (WithTop.one_ne_top), encard_eq_one] at h
obtain ⟨y, h⟩ := h
refine ⟨x, y, by rintro rfl; exact (h.symm.subset rfl).2 rfl, ?_⟩
rw [← h, insert_diff_singleton, insert_eq_of_mem hx]
theorem encard_eq_three {α : Type u_1} {s : Set α} :
encard s = 3 ↔ ∃ x y z, x ≠ y ∧ x ≠ z ∧ y ≠ z ∧ s = {x, y, z} := by
refine ⟨fun h ↦ ?_, fun ⟨x, y, z, hxy, hyz, hxz, hs⟩ ↦ ?_⟩
· obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
rw [← insert_eq_of_mem hx, ← insert_diff_singleton,
encard_insert_of_not_mem (fun h ↦ h.2 rfl), (by exact rfl : (3 : ℕ∞) = 2 + 1),
WithTop.add_right_inj WithTop.one_ne_top, encard_eq_two] at h
obtain ⟨y, z, hne, hs⟩ := h
refine ⟨x, y, z, ?_, ?_, hne, ?_⟩
· rintro rfl; exact (hs.symm.subset (Or.inl rfl)).2 rfl
· rintro rfl; exact (hs.symm.subset (Or.inr rfl)).2 rfl
rw [← hs, insert_diff_singleton, insert_eq_of_mem hx]
rw [hs, encard_insert_of_not_mem, encard_insert_of_not_mem, encard_singleton] <;> aesop
theorem Nat.encard_range (k : ℕ) : {i | i < k}.encard = k := by
convert encard_coe_eq_coe_finsetCard (Finset.range k) using 1
· rw [Finset.coe_range, Iio_def]
rw [Finset.card_range]
end SmallSets
theorem Finite.eq_insert_of_subset_of_encard_eq_succ (hs : s.Finite) (h : s ⊆ t)
(hst : t.encard = s.encard + 1) : ∃ a, t = insert a s := by
rw [← encard_diff_add_encard_of_subset h, add_comm, WithTop.add_left_inj hs.encard_lt_top.ne,
encard_eq_one] at hst
obtain ⟨x, hx⟩ := hst; use x; rw [← diff_union_of_subset h, hx, singleton_union]
theorem exists_subset_encard_eq {k : ℕ∞} (hk : k ≤ s.encard) : ∃ t, t ⊆ s ∧ t.encard = k := by
revert hk
refine ENat.nat_induction k (fun _ ↦ ⟨∅, empty_subset _, by simp⟩) (fun n IH hle ↦ ?_) ?_
· obtain ⟨t₀, ht₀s, ht₀⟩ := IH (le_trans (by simp) hle)
simp only [Nat.cast_succ] at *
have hne : t₀ ≠ s := by
rintro rfl; rw [ht₀, ← Nat.cast_one, ← Nat.cast_add, Nat.cast_le] at hle; simp at hle
obtain ⟨x, hx⟩ := exists_of_ssubset (ht₀s.ssubset_of_ne hne)
exact ⟨insert x t₀, insert_subset hx.1 ht₀s, by rw [encard_insert_of_not_mem hx.2, ht₀]⟩
simp only [top_le_iff, encard_eq_top_iff]
exact fun _ hi ↦ ⟨s, Subset.rfl, hi⟩
theorem exists_superset_subset_encard_eq {k : ℕ∞}
(hst : s ⊆ t) (hsk : s.encard ≤ k) (hkt : k ≤ t.encard) :
∃ r, s ⊆ r ∧ r ⊆ t ∧ r.encard = k := by
obtain (hs | hs) := eq_or_ne s.encard ⊤
· rw [hs, top_le_iff] at hsk; subst hsk; exact ⟨s, Subset.rfl, hst, hs⟩
obtain ⟨k, rfl⟩ := exists_add_of_le hsk
obtain ⟨k', hk'⟩ := exists_add_of_le hkt
have hk : k ≤ encard (t \ s) := by
rw [← encard_diff_add_encard_of_subset hst, add_comm] at hkt
exact WithTop.le_of_add_le_add_right hs hkt
obtain ⟨r', hr', rfl⟩ := exists_subset_encard_eq hk
refine ⟨s ∪ r', subset_union_left, union_subset hst (hr'.trans diff_subset), ?_⟩
rw [encard_union_eq (disjoint_of_subset_right hr' disjoint_sdiff_right)]
section Function
variable {s : Set α} {t : Set β} {f : α → β}
theorem InjOn.encard_image (h : InjOn f s) : (f '' s).encard = s.encard := by
rw [encard, ENat.card_image_of_injOn h, encard]
theorem encard_congr (e : s ≃ t) : s.encard = t.encard := by
rw [← encard_univ_coe, ← encard_univ_coe t, encard_univ, encard_univ, ENat.card_congr e]
theorem _root_.Function.Injective.encard_image (hf : f.Injective) (s : Set α) :
(f '' s).encard = s.encard :=
hf.injOn.encard_image
theorem _root_.Function.Embedding.encard_le (e : s ↪ t) : s.encard ≤ t.encard := by
rw [← encard_univ_coe, ← e.injective.encard_image, ← Subtype.coe_injective.encard_image]
exact encard_mono (by simp)
theorem encard_image_le (f : α → β) (s : Set α) : (f '' s).encard ≤ s.encard := by
obtain (h | h) := isEmpty_or_nonempty α
· rw [s.eq_empty_of_isEmpty]; simp
rw [← (f.invFunOn_injOn_image s).encard_image]
apply encard_le_encard
exact f.invFunOn_image_image_subset s
theorem Finite.injOn_of_encard_image_eq (hs : s.Finite) (h : (f '' s).encard = s.encard) :
InjOn f s := by
obtain (h' | hne) := isEmpty_or_nonempty α
· rw [s.eq_empty_of_isEmpty]; simp
rw [← (f.invFunOn_injOn_image s).encard_image] at h
rw [injOn_iff_invFunOn_image_image_eq_self]
exact hs.eq_of_subset_of_encard_le' (f.invFunOn_image_image_subset s) h.symm.le
theorem encard_preimage_of_injective_subset_range (hf : f.Injective) (ht : t ⊆ range f) :
(f ⁻¹' t).encard = t.encard := by
rw [← hf.encard_image, image_preimage_eq_inter_range, inter_eq_self_of_subset_left ht]
lemma encard_preimage_of_bijective (hf : f.Bijective) (t : Set β) : (f ⁻¹' t).encard = t.encard :=
encard_preimage_of_injective_subset_range hf.injective (by simp [hf.surjective.range_eq])
theorem encard_le_encard_of_injOn (hf : MapsTo f s t) (f_inj : InjOn f s) :
s.encard ≤ t.encard := by
rw [← f_inj.encard_image]; apply encard_le_encard; rintro _ ⟨x, hx, rfl⟩; exact hf hx
theorem Finite.exists_injOn_of_encard_le [Nonempty β] {s : Set α} {t : Set β} (hs : s.Finite)
(hle : s.encard ≤ t.encard) : ∃ (f : α → β), s ⊆ f ⁻¹' t ∧ InjOn f s := by
classical
obtain (rfl | h | ⟨a, has, -⟩) := s.eq_empty_or_encard_eq_top_or_encard_diff_singleton_lt
· simp
· exact (encard_ne_top_iff.mpr hs h).elim
obtain ⟨b, hbt⟩ := encard_pos.1 ((encard_pos.2 ⟨_, has⟩).trans_le hle)
have hle' : (s \ {a}).encard ≤ (t \ {b}).encard := by
rwa [← WithTop.add_le_add_iff_right WithTop.one_ne_top,
encard_diff_singleton_add_one has, encard_diff_singleton_add_one hbt]
obtain ⟨f₀, hf₀s, hinj⟩ := exists_injOn_of_encard_le hs.diff hle'
simp only [preimage_diff, subset_def, mem_diff, mem_singleton_iff, mem_preimage, and_imp] at hf₀s
use Function.update f₀ a b
rw [← insert_eq_of_mem has, ← insert_diff_singleton, injOn_insert (fun h ↦ h.2 rfl)]
simp only [mem_diff, mem_singleton_iff, not_true, and_false, insert_diff_singleton, subset_def,
mem_insert_iff, mem_preimage, ne_eq, Function.update_apply, forall_eq_or_imp, ite_true, and_imp,
mem_image, ite_eq_left_iff, not_exists, not_and, not_forall, exists_prop, and_iff_right hbt]
refine ⟨?_, ?_, fun x hxs hxa ↦ ⟨hxa, (hf₀s x hxs hxa).2⟩⟩
· rintro x hx; split_ifs with h
· assumption
· exact (hf₀s x hx h).1
exact InjOn.congr hinj (fun x ⟨_, hxa⟩ ↦ by rwa [Function.update_of_ne])
termination_by encard s
theorem Finite.exists_bijOn_of_encard_eq [Nonempty β] (hs : s.Finite) (h : s.encard = t.encard) :
∃ (f : α → β), BijOn f s t := by
obtain ⟨f, hf, hinj⟩ := hs.exists_injOn_of_encard_le h.le; use f
convert hinj.bijOn_image
rw [(hs.image f).eq_of_subset_of_encard_le (image_subset_iff.mpr hf)
(h.symm.trans hinj.encard_image.symm).le]
end Function
section ncard
open Nat
/-- A tactic (for use in default params) that applies `Set.toFinite` to synthesize a `Set.Finite`
term. -/
syntax "toFinite_tac" : tactic
macro_rules
| `(tactic| toFinite_tac) => `(tactic| apply Set.toFinite)
/-- A tactic useful for transferring proofs for `encard` to their corresponding `card` statements -/
syntax "to_encard_tac" : tactic
macro_rules
| `(tactic| to_encard_tac) => `(tactic|
simp only [← Nat.cast_le (α := ℕ∞), ← Nat.cast_inj (R := ℕ∞), Nat.cast_add, Nat.cast_one])
/-- The cardinality of `s : Set α` . Has the junk value `0` if `s` is infinite -/
noncomputable def ncard (s : Set α) : ℕ := ENat.toNat s.encard
theorem ncard_def (s : Set α) : s.ncard = ENat.toNat s.encard := rfl
theorem Finite.cast_ncard_eq (hs : s.Finite) : s.ncard = s.encard := by
rwa [ncard, ENat.coe_toNat_eq_self, ne_eq, encard_eq_top_iff, Set.Infinite, not_not]
lemma ncard_le_encard (s : Set α) : s.ncard ≤ s.encard := ENat.coe_toNat_le_self _
theorem Nat.card_coe_set_eq (s : Set α) : Nat.card s = s.ncard := by
obtain (h | h) := s.finite_or_infinite
· have := h.fintype
rw [ncard, h.encard_eq_coe_toFinset_card, Nat.card_eq_fintype_card,
toFinite_toFinset, toFinset_card, ENat.toNat_coe]
have := infinite_coe_iff.2 h
rw [ncard, h.encard_eq, Nat.card_eq_zero_of_infinite, ENat.toNat_top]
theorem ncard_eq_toFinset_card (s : Set α) (hs : s.Finite := by toFinite_tac) :
s.ncard = hs.toFinset.card := by
rw [← Nat.card_coe_set_eq, @Nat.card_eq_fintype_card _ hs.fintype,
@Finite.card_toFinset _ _ hs.fintype hs]
theorem ncard_eq_toFinset_card' (s : Set α) [Fintype s] :
s.ncard = s.toFinset.card := by
simp [← Nat.card_coe_set_eq, Nat.card_eq_fintype_card]
lemma cast_ncard {s : Set α} (hs : s.Finite) :
(s.ncard : Cardinal) = Cardinal.mk s := @Nat.cast_card _ hs
theorem encard_le_coe_iff_finite_ncard_le {k : ℕ} : s.encard ≤ k ↔ s.Finite ∧ s.ncard ≤ k := by
rw [encard_le_coe_iff, and_congr_right_iff]
exact fun hfin ↦ ⟨fun ⟨n₀, hn₀, hle⟩ ↦ by rwa [ncard_def, hn₀, ENat.toNat_coe],
fun h ↦ ⟨s.ncard, by rw [hfin.cast_ncard_eq], h⟩⟩
theorem Infinite.ncard (hs : s.Infinite) : s.ncard = 0 := by
rw [← Nat.card_coe_set_eq, @Nat.card_eq_zero_of_infinite _ hs.to_subtype]
@[gcongr]
theorem ncard_le_ncard (hst : s ⊆ t) (ht : t.Finite := by toFinite_tac) :
s.ncard ≤ t.ncard := by
rw [← Nat.cast_le (α := ℕ∞), ht.cast_ncard_eq, (ht.subset hst).cast_ncard_eq]
exact encard_mono hst
theorem ncard_mono [Finite α] : @Monotone (Set α) _ _ _ ncard := fun _ _ ↦ ncard_le_ncard
@[simp] theorem ncard_eq_zero (hs : s.Finite := by toFinite_tac) :
s.ncard = 0 ↔ s = ∅ := by
rw [← Nat.cast_inj (R := ℕ∞), hs.cast_ncard_eq, Nat.cast_zero, encard_eq_zero]
@[simp, norm_cast] theorem ncard_coe_Finset (s : Finset α) : (s : Set α).ncard = s.card := by
rw [ncard_eq_toFinset_card _, Finset.finite_toSet_toFinset]
theorem ncard_univ (α : Type*) : (univ : Set α).ncard = Nat.card α := by
rcases finite_or_infinite α with h | h
· have hft := Fintype.ofFinite α
rw [ncard_eq_toFinset_card, Finite.toFinset_univ, Finset.card_univ, Nat.card_eq_fintype_card]
rw [Nat.card_eq_zero_of_infinite, Infinite.ncard]
exact infinite_univ
@[simp] theorem ncard_empty (α : Type*) : (∅ : Set α).ncard = 0 := by
rw [ncard_eq_zero]
theorem ncard_pos (hs : s.Finite := by toFinite_tac) : 0 < s.ncard ↔ s.Nonempty := by
rw [pos_iff_ne_zero, Ne, ncard_eq_zero hs, nonempty_iff_ne_empty]
protected alias ⟨_, Nonempty.ncard_pos⟩ := ncard_pos
theorem ncard_ne_zero_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) : s.ncard ≠ 0 :=
((ncard_pos hs).mpr ⟨a, h⟩).ne.symm
theorem finite_of_ncard_ne_zero (hs : s.ncard ≠ 0) : s.Finite :=
s.finite_or_infinite.elim id fun h ↦ (hs h.ncard).elim
theorem finite_of_ncard_pos (hs : 0 < s.ncard) : s.Finite :=
finite_of_ncard_ne_zero hs.ne.symm
theorem nonempty_of_ncard_ne_zero (hs : s.ncard ≠ 0) : s.Nonempty := by
rw [nonempty_iff_ne_empty]; rintro rfl; simp at hs
@[simp] theorem ncard_singleton (a : α) : ({a} : Set α).ncard = 1 := by
simp [ncard]
theorem ncard_singleton_inter (a : α) (s : Set α) : ({a} ∩ s).ncard ≤ 1 := by
rw [← Nat.cast_le (α := ℕ∞), (toFinite _).cast_ncard_eq, Nat.cast_one]
apply encard_singleton_inter
@[simp]
theorem ncard_prod : (s ×ˢ t).ncard = s.ncard * t.ncard := by
simp [ncard, ENat.toNat_mul]
@[simp]
theorem ncard_powerset (s : Set α) (hs : s.Finite := by toFinite_tac) :
(𝒫 s).ncard = 2 ^ s.ncard := by
have h := Cardinal.mk_powerset s
rw [← cast_ncard hs.powerset, ← cast_ncard hs] at h
norm_cast at h
section InsertErase
@[simp] theorem ncard_insert_of_not_mem {a : α} (h : a ∉ s) (hs : s.Finite := by toFinite_tac) :
(insert a s).ncard = s.ncard + 1 := by
rw [← Nat.cast_inj (R := ℕ∞), (hs.insert a).cast_ncard_eq, Nat.cast_add, Nat.cast_one,
hs.cast_ncard_eq, encard_insert_of_not_mem h]
theorem ncard_insert_of_mem {a : α} (h : a ∈ s) : ncard (insert a s) = s.ncard := by
rw [insert_eq_of_mem h]
theorem ncard_insert_le (a : α) (s : Set α) : (insert a s).ncard ≤ s.ncard + 1 := by
obtain hs | hs := s.finite_or_infinite
· to_encard_tac; rw [hs.cast_ncard_eq, (hs.insert _).cast_ncard_eq]; apply encard_insert_le
rw [(hs.mono (subset_insert a s)).ncard]
exact Nat.zero_le _
theorem ncard_insert_eq_ite {a : α} [Decidable (a ∈ s)] (hs : s.Finite := by toFinite_tac) :
ncard (insert a s) = if a ∈ s then s.ncard else s.ncard + 1 := by
by_cases h : a ∈ s
· rw [ncard_insert_of_mem h, if_pos h]
· rw [ncard_insert_of_not_mem h hs, if_neg h]
theorem ncard_le_ncard_insert (a : α) (s : Set α) : s.ncard ≤ (insert a s).ncard := by
classical
refine
s.finite_or_infinite.elim (fun h ↦ ?_) (fun h ↦ by (rw [h.ncard]; exact Nat.zero_le _))
rw [ncard_insert_eq_ite h]; split_ifs <;> simp
@[simp] theorem ncard_pair {a b : α} (h : a ≠ b) : ({a, b} : Set α).ncard = 2 := by
rw [ncard_insert_of_not_mem, ncard_singleton]; simpa
@[simp] theorem ncard_diff_singleton_add_one {a : α} (h : a ∈ s)
(hs : s.Finite := by toFinite_tac) : (s \ {a}).ncard + 1 = s.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, hs.diff.cast_ncard_eq,
encard_diff_singleton_add_one h]
@[simp] theorem ncard_diff_singleton_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) :
(s \ {a}).ncard = s.ncard - 1 :=
eq_tsub_of_add_eq (ncard_diff_singleton_add_one h hs)
theorem ncard_diff_singleton_lt_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) :
(s \ {a}).ncard < s.ncard := by
rw [← ncard_diff_singleton_add_one h hs]; apply lt_add_one
theorem ncard_diff_singleton_le (s : Set α) (a : α) : (s \ {a}).ncard ≤ s.ncard := by
obtain hs | hs := s.finite_or_infinite
· apply ncard_le_ncard diff_subset hs
convert zero_le (α := ℕ) _
exact (hs.diff (by simp : Set.Finite {a})).ncard
theorem pred_ncard_le_ncard_diff_singleton (s : Set α) (a : α) : s.ncard - 1 ≤ (s \ {a}).ncard := by
rcases s.finite_or_infinite with hs | hs
· by_cases h : a ∈ s
· rw [ncard_diff_singleton_of_mem h hs]
rw [diff_singleton_eq_self h]
apply Nat.pred_le
convert Nat.zero_le _
rw [hs.ncard]
theorem ncard_exchange {a b : α} (ha : a ∉ s) (hb : b ∈ s) : (insert a (s \ {b})).ncard = s.ncard :=
congr_arg ENat.toNat <| encard_exchange ha hb
theorem ncard_exchange' {a b : α} (ha : a ∉ s) (hb : b ∈ s) :
(insert a s \ {b}).ncard = s.ncard := by
rw [← ncard_exchange ha hb, ← singleton_union, ← singleton_union, union_diff_distrib,
@diff_singleton_eq_self _ b {a} fun h ↦ ha (by rwa [← mem_singleton_iff.mp h])]
lemma odd_card_insert_iff {a : α} (ha : a ∉ s) (hs : s.Finite := by toFinite_tac) :
Odd (insert a s).ncard ↔ Even s.ncard := by
rw [ncard_insert_of_not_mem ha hs, Nat.odd_add]
simp only [Nat.odd_add, ← Nat.not_even_iff_odd, Nat.not_even_one, iff_false, Decidable.not_not]
lemma even_card_insert_iff {a : α} (ha : a ∉ s) (hs : s.Finite := by toFinite_tac) :
Even (insert a s).ncard ↔ Odd s.ncard := by
rw [ncard_insert_of_not_mem ha hs, Nat.even_add_one, Nat.not_even_iff_odd]
end InsertErase
variable {f : α → β}
theorem ncard_image_le (hs : s.Finite := by toFinite_tac) : (f '' s).ncard ≤ s.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, (hs.image _).cast_ncard_eq]; apply encard_image_le
theorem ncard_image_of_injOn (H : Set.InjOn f s) : (f '' s).ncard = s.ncard :=
congr_arg ENat.toNat <| H.encard_image
theorem injOn_of_ncard_image_eq (h : (f '' s).ncard = s.ncard) (hs : s.Finite := by toFinite_tac) :
Set.InjOn f s := by
rw [← Nat.cast_inj (R := ℕ∞), hs.cast_ncard_eq, (hs.image _).cast_ncard_eq] at h
exact hs.injOn_of_encard_image_eq h
theorem ncard_image_iff (hs : s.Finite := by toFinite_tac) :
(f '' s).ncard = s.ncard ↔ Set.InjOn f s :=
⟨fun h ↦ injOn_of_ncard_image_eq h hs, ncard_image_of_injOn⟩
theorem ncard_image_of_injective (s : Set α) (H : f.Injective) : (f '' s).ncard = s.ncard :=
ncard_image_of_injOn fun _ _ _ _ h ↦ H h
theorem ncard_preimage_of_injective_subset_range {s : Set β} (H : f.Injective)
(hs : s ⊆ Set.range f) :
(f ⁻¹' s).ncard = s.ncard := by
rw [← ncard_image_of_injective _ H, image_preimage_eq_iff.mpr hs]
theorem fiber_ncard_ne_zero_iff_mem_image {y : β} (hs : s.Finite := by toFinite_tac) :
{ x ∈ s | f x = y }.ncard ≠ 0 ↔ y ∈ f '' s := by
refine ⟨nonempty_of_ncard_ne_zero, ?_⟩
rintro ⟨z, hz, rfl⟩
exact @ncard_ne_zero_of_mem _ ({ x ∈ s | f x = f z }) z (mem_sep hz rfl)
(hs.subset (sep_subset _ _))
@[simp] theorem ncard_map (f : α ↪ β) : (f '' s).ncard = s.ncard :=
ncard_image_of_injective _ f.inj'
@[simp] theorem ncard_subtype (P : α → Prop) (s : Set α) :
{ x : Subtype P | (x : α) ∈ s }.ncard = (s ∩ setOf P).ncard := by
convert (ncard_image_of_injective _ (@Subtype.coe_injective _ P)).symm
ext x
simp [← and_assoc, exists_eq_right]
theorem ncard_inter_le_ncard_left (s t : Set α) (hs : s.Finite := by toFinite_tac) :
(s ∩ t).ncard ≤ s.ncard :=
ncard_le_ncard inter_subset_left hs
theorem ncard_inter_le_ncard_right (s t : Set α) (ht : t.Finite := by toFinite_tac) :
(s ∩ t).ncard ≤ t.ncard :=
ncard_le_ncard inter_subset_right ht
theorem eq_of_subset_of_ncard_le (h : s ⊆ t) (h' : t.ncard ≤ s.ncard)
(ht : t.Finite := by toFinite_tac) : s = t :=
ht.eq_of_subset_of_encard_le' h
(by rwa [← Nat.cast_le (α := ℕ∞), ht.cast_ncard_eq, (ht.subset h).cast_ncard_eq] at h')
theorem subset_iff_eq_of_ncard_le (h : t.ncard ≤ s.ncard) (ht : t.Finite := by toFinite_tac) :
s ⊆ t ↔ s = t :=
⟨fun hst ↦ eq_of_subset_of_ncard_le hst h ht, Eq.subset'⟩
theorem map_eq_of_subset {f : α ↪ α} (h : f '' s ⊆ s) (hs : s.Finite := by toFinite_tac) :
f '' s = s :=
eq_of_subset_of_ncard_le h (ncard_map _).ge hs
theorem sep_of_ncard_eq {a : α} {P : α → Prop} (h : { x ∈ s | P x }.ncard = s.ncard) (ha : a ∈ s)
(hs : s.Finite := by toFinite_tac) : P a :=
sep_eq_self_iff_mem_true.mp (eq_of_subset_of_ncard_le (by simp) h.symm.le hs) _ ha
theorem ncard_lt_ncard (h : s ⊂ t) (ht : t.Finite := by toFinite_tac) :
s.ncard < t.ncard := by
rw [← Nat.cast_lt (α := ℕ∞), ht.cast_ncard_eq, (ht.subset h.subset).cast_ncard_eq]
exact (ht.subset h.subset).encard_lt_encard h
theorem ncard_strictMono [Finite α] : @StrictMono (Set α) _ _ _ ncard :=
fun _ _ h ↦ ncard_lt_ncard h
theorem ncard_eq_of_bijective {n : ℕ} (f : ∀ i, i < n → α)
(hf : ∀ a ∈ s, ∃ i, ∃ h : i < n, f i h = a) (hf' : ∀ (i) (h : i < n), f i h ∈ s)
(f_inj : ∀ (i j) (hi : i < n) (hj : j < n), f i hi = f j hj → i = j) : s.ncard = n := by
let f' : Fin n → α := fun i ↦ f i.val i.is_lt
suffices himage : s = f' '' Set.univ by
rw [← Fintype.card_fin n, ← Nat.card_eq_fintype_card, ← Set.ncard_univ, himage]
exact ncard_image_of_injOn <| fun i _hi j _hj h ↦ Fin.ext <| f_inj i.val j.val i.is_lt j.is_lt h
ext x
simp only [image_univ, mem_range]
refine ⟨fun hx ↦ ?_, fun ⟨⟨i, hi⟩, hx⟩ ↦ hx ▸ hf' i hi⟩
obtain ⟨i, hi, rfl⟩ := hf x hx
use ⟨i, hi⟩
theorem ncard_congr {t : Set β} (f : ∀ a ∈ s, β) (h₁ : ∀ a ha, f a ha ∈ t)
(h₂ : ∀ a b ha hb, f a ha = f b hb → a = b) (h₃ : ∀ b ∈ t, ∃ a ha, f a ha = b) :
s.ncard = t.ncard := by
set f' : s → t := fun x ↦ ⟨f x.1 x.2, h₁ _ _⟩
have hbij : f'.Bijective := by
constructor
· rintro ⟨x, hx⟩ ⟨y, hy⟩ hxy
simp only [f', Subtype.mk.injEq] at hxy ⊢
exact h₂ _ _ hx hy hxy
rintro ⟨y, hy⟩
obtain ⟨a, ha, rfl⟩ := h₃ y hy
simp only [Subtype.mk.injEq, Subtype.exists]
exact ⟨_, ha, rfl⟩
simp_rw [← Nat.card_coe_set_eq]
exact Nat.card_congr (Equiv.ofBijective f' hbij)
theorem ncard_le_ncard_of_injOn {t : Set β} (f : α → β) (hf : ∀ a ∈ s, f a ∈ t) (f_inj : InjOn f s)
(ht : t.Finite := by toFinite_tac) :
s.ncard ≤ t.ncard := by
have hle := encard_le_encard_of_injOn hf f_inj
to_encard_tac; rwa [ht.cast_ncard_eq, (ht.finite_of_encard_le hle).cast_ncard_eq]
theorem exists_ne_map_eq_of_ncard_lt_of_maps_to {t : Set β} (hc : t.ncard < s.ncard) {f : α → β}
(hf : ∀ a ∈ s, f a ∈ t) (ht : t.Finite := by toFinite_tac) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ f x = f y := by
by_contra h'
simp only [Ne, exists_prop, not_exists, not_and, not_imp_not] at h'
exact (ncard_le_ncard_of_injOn f hf h' ht).not_lt hc
theorem le_ncard_of_inj_on_range {n : ℕ} (f : ℕ → α) (hf : ∀ i < n, f i ∈ s)
(f_inj : ∀ i < n, ∀ j < n, f i = f j → i = j) (hs : s.Finite := by toFinite_tac) :
n ≤ s.ncard := by
rw [ncard_eq_toFinset_card _ hs]
apply Finset.le_card_of_inj_on_range <;> simpa
theorem surj_on_of_inj_on_of_ncard_le {t : Set β} (f : ∀ a ∈ s, β) (hf : ∀ a ha, f a ha ∈ t)
(hinj : ∀ a₁ a₂ ha₁ ha₂, f a₁ ha₁ = f a₂ ha₂ → a₁ = a₂) (hst : t.ncard ≤ s.ncard)
(ht : t.Finite := by toFinite_tac) :
∀ b ∈ t, ∃ a ha, b = f a ha := by
intro b hb
set f' : s → t := fun x ↦ ⟨f x.1 x.2, hf _ _⟩
have finj : f'.Injective := by
rintro ⟨x, hx⟩ ⟨y, hy⟩ hxy
simp only [f', Subtype.mk.injEq] at hxy ⊢
apply hinj _ _ hx hy hxy
have hft := ht.fintype
have hft' := Fintype.ofInjective f' finj
set f'' : ∀ a, a ∈ s.toFinset → β := fun a h ↦ f a (by simpa using h)
convert @Finset.surj_on_of_inj_on_of_card_le _ _ _ t.toFinset f'' _ _ _ _ (by simpa) using 1
· simp [f'']
· simp [f'', hf]
· intros a₁ a₂ ha₁ ha₂ h
rw [mem_toFinset] at ha₁ ha₂
exact hinj _ _ ha₁ ha₂ h
rwa [← ncard_eq_toFinset_card', ← ncard_eq_toFinset_card']
theorem inj_on_of_surj_on_of_ncard_le {t : Set β} (f : ∀ a ∈ s, β) (hf : ∀ a ha, f a ha ∈ t)
(hsurj : ∀ b ∈ t, ∃ a ha, f a ha = b) (hst : s.ncard ≤ t.ncard) ⦃a₁⦄ (ha₁ : a₁ ∈ s) ⦃a₂⦄
(ha₂ : a₂ ∈ s) (ha₁a₂ : f a₁ ha₁ = f a₂ ha₂) (hs : s.Finite := by toFinite_tac) :
a₁ = a₂ := by
classical
set f' : s → t := fun x ↦ ⟨f x.1 x.2, hf _ _⟩
have hsurj : f'.Surjective := by
rintro ⟨y, hy⟩
obtain ⟨a, ha, rfl⟩ := hsurj y hy
simp only [Subtype.mk.injEq, Subtype.exists]
exact ⟨_, ha, rfl⟩
haveI := hs.fintype
haveI := Fintype.ofSurjective _ hsurj
set f'' : ∀ a, a ∈ s.toFinset → β := fun a h ↦ f a (by simpa using h)
exact
@Finset.inj_on_of_surj_on_of_card_le _ _ _ t.toFinset f''
(fun a ha ↦ by { rw [mem_toFinset] at ha ⊢; exact hf a ha }) (by simpa)
(by { rwa [← ncard_eq_toFinset_card', ← ncard_eq_toFinset_card'] }) a₁
(by simpa) a₂ (by simpa) (by simpa)
@[simp] theorem ncard_coe {α : Type*} (s : Set α) :
Set.ncard (Set.univ : Set (Set.Elem s)) = s.ncard :=
Set.ncard_congr (fun a ha ↦ ↑a) (fun a ha ↦ a.prop) (by simp) (by simp)
@[simp] lemma ncard_graphOn (s : Set α) (f : α → β) : (s.graphOn f).ncard = s.ncard := by
rw [← ncard_image_of_injOn fst_injOn_graph, image_fst_graphOn]
section Lattice
theorem ncard_union_add_ncard_inter (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∪ t).ncard + (s ∩ t).ncard = s.ncard + t.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, ht.cast_ncard_eq, (hs.union ht).cast_ncard_eq,
(hs.subset inter_subset_left).cast_ncard_eq, encard_union_add_encard_inter]
theorem ncard_inter_add_ncard_union (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∩ t).ncard + (s ∪ t).ncard = s.ncard + t.ncard := by
rw [add_comm, ncard_union_add_ncard_inter _ _ hs ht]
theorem ncard_union_le (s t : Set α) : (s ∪ t).ncard ≤ s.ncard + t.ncard := by
obtain (h | h) := (s ∪ t).finite_or_infinite
· to_encard_tac
rw [h.cast_ncard_eq, (h.subset subset_union_left).cast_ncard_eq,
(h.subset subset_union_right).cast_ncard_eq]
apply encard_union_le
rw [h.ncard]
apply zero_le
theorem ncard_union_eq (h : Disjoint s t) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∪ t).ncard = s.ncard + t.ncard := by
to_encard_tac
rw [hs.cast_ncard_eq, ht.cast_ncard_eq, (hs.union ht).cast_ncard_eq, encard_union_eq h]
theorem ncard_diff_add_ncard_of_subset (h : s ⊆ t) (ht : t.Finite := by toFinite_tac) :
(t \ s).ncard + s.ncard = t.ncard := by
to_encard_tac
rw [ht.cast_ncard_eq, (ht.subset h).cast_ncard_eq, ht.diff.cast_ncard_eq,
encard_diff_add_encard_of_subset h]
theorem ncard_diff (hst : s ⊆ t) (hs : s.Finite := by toFinite_tac) :
(t \ s).ncard = t.ncard - s.ncard := by
obtain ht | ht := t.finite_or_infinite
· rw [← ncard_diff_add_ncard_of_subset hst ht, add_tsub_cancel_right]
· rw [ht.ncard, Nat.zero_sub, (ht.diff hs).ncard]
lemma cast_ncard_sdiff {R : Type*} [AddGroupWithOne R] (hst : s ⊆ t) (ht : t.Finite) :
((t \ s).ncard : R) = t.ncard - s.ncard := by
rw [ncard_diff hst (ht.subset hst), Nat.cast_sub (ncard_le_ncard hst ht)]
theorem ncard_le_ncard_diff_add_ncard (s t : Set α) (ht : t.Finite := by toFinite_tac) :
s.ncard ≤ (s \ t).ncard + t.ncard := by
rcases s.finite_or_infinite with hs | hs
· to_encard_tac
rw [ht.cast_ncard_eq, hs.cast_ncard_eq, hs.diff.cast_ncard_eq]
apply encard_le_encard_diff_add_encard
convert Nat.zero_le _
rw [hs.ncard]
theorem le_ncard_diff (s t : Set α) (hs : s.Finite := by toFinite_tac) :
t.ncard - s.ncard ≤ (t \ s).ncard :=
tsub_le_iff_left.mpr (by rw [add_comm]; apply ncard_le_ncard_diff_add_ncard _ _ hs)
theorem ncard_diff_add_ncard (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) :
(s \ t).ncard + t.ncard = (s ∪ t).ncard := by
rw [← ncard_union_eq disjoint_sdiff_left hs.diff ht, diff_union_self]
theorem diff_nonempty_of_ncard_lt_ncard (h : s.ncard < t.ncard) (hs : s.Finite := by toFinite_tac) :
(t \ s).Nonempty := by
rw [Set.nonempty_iff_ne_empty, Ne, diff_eq_empty]
exact fun h' ↦ h.not_le (ncard_le_ncard h' hs)
theorem exists_mem_not_mem_of_ncard_lt_ncard (h : s.ncard < t.ncard)
(hs : s.Finite := by toFinite_tac) : ∃ e, e ∈ t ∧ e ∉ s :=
diff_nonempty_of_ncard_lt_ncard h hs
@[simp] theorem ncard_inter_add_ncard_diff_eq_ncard (s t : Set α)
(hs : s.Finite := by toFinite_tac) : (s ∩ t).ncard + (s \ t).ncard = s.ncard := by
rw [← ncard_union_eq (disjoint_of_subset_left inter_subset_right disjoint_sdiff_right)
(hs.inter_of_left _) hs.diff, union_comm, diff_union_inter]
theorem ncard_eq_ncard_iff_ncard_diff_eq_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard = t.ncard ↔ (s \ t).ncard = (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_right_inj]
theorem ncard_le_ncard_iff_ncard_diff_le_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard ≤ t.ncard ↔ (s \ t).ncard ≤ (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_le_add_iff_left]
theorem ncard_lt_ncard_iff_ncard_diff_lt_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard < t.ncard ↔ (s \ t).ncard < (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_lt_add_iff_left]
theorem ncard_add_ncard_compl (s : Set α) (hs : s.Finite := by toFinite_tac)
(hsc : sᶜ.Finite := by toFinite_tac) : s.ncard + sᶜ.ncard = Nat.card α := by
rw [← ncard_univ, ← ncard_union_eq (@disjoint_compl_right _ _ s) hs hsc, union_compl_self]
theorem eq_univ_iff_ncard [Finite α] (s : Set α) :
s = univ ↔ ncard s = Nat.card α := by
rw [← compl_empty_iff, ← ncard_eq_zero, ← ncard_add_ncard_compl s, left_eq_add]
lemma even_ncard_compl_iff [Finite α] (heven : Even (Nat.card α)) (s : Set α) :
Even sᶜ.ncard ↔ Even s.ncard := by
simp [compl_eq_univ_diff, ncard_diff (subset_univ _ : s ⊆ Set.univ),
Nat.even_sub (ncard_le_ncard (subset_univ _ : s ⊆ Set.univ)),
(ncard_univ _).symm ▸ heven]
lemma odd_ncard_compl_iff [Finite α] (heven : Even (Nat.card α)) (s : Set α) :
Odd sᶜ.ncard ↔ Odd s.ncard := by
rw [← Nat.not_even_iff_odd, even_ncard_compl_iff heven, Nat.not_even_iff_odd]
end Lattice
/-- Given a subset `s` of a set `t`, of sizes at most and at least `n` respectively, there exists a
set `u` of size `n` which is both a superset of `s` and a subset of `t`. -/
lemma exists_subsuperset_card_eq {n : ℕ} (hst : s ⊆ t) (hsn : s.ncard ≤ n) (hnt : n ≤ t.ncard) :
∃ u, s ⊆ u ∧ u ⊆ t ∧ u.ncard = n := by
obtain ht | ht := t.infinite_or_finite
· rw [ht.ncard, Nat.le_zero, ← ht.ncard] at hnt
exact ⟨t, hst, Subset.rfl, hnt.symm⟩
lift s to Finset α using ht.subset hst
lift t to Finset α using ht
obtain ⟨u, hsu, hut, hu⟩ := Finset.exists_subsuperset_card_eq (mod_cast hst) (by simpa using hsn)
(mod_cast hnt)
exact ⟨u, mod_cast hsu, mod_cast hut, mod_cast hu⟩
/-- We can shrink a set to any smaller size. -/
lemma exists_subset_card_eq {n : ℕ} (hns : n ≤ s.ncard) : ∃ t ⊆ s, t.ncard = n := by
simpa using exists_subsuperset_card_eq s.empty_subset (by simp) hns
theorem Infinite.exists_subset_ncard_eq {s : Set α} (hs : s.Infinite) (k : ℕ) :
∃ t, t ⊆ s ∧ t.Finite ∧ t.ncard = k := by
have := hs.to_subtype
obtain ⟨t', -, rfl⟩ := @Infinite.exists_subset_card_eq s univ infinite_univ k
refine ⟨Subtype.val '' (t' : Set s), by simp, Finite.image _ (by simp), ?_⟩
rw [ncard_image_of_injective _ Subtype.coe_injective]
simp
theorem Infinite.exists_superset_ncard_eq {s t : Set α} (ht : t.Infinite) (hst : s ⊆ t)
(hs : s.Finite) {k : ℕ} (hsk : s.ncard ≤ k) : ∃ s', s ⊆ s' ∧ s' ⊆ t ∧ s'.ncard = k := by
obtain ⟨s₁, hs₁, hs₁fin, hs₁card⟩ := (ht.diff hs).exists_subset_ncard_eq (k - s.ncard)
refine ⟨s ∪ s₁, subset_union_left, union_subset hst (hs₁.trans diff_subset), ?_⟩
rwa [ncard_union_eq (disjoint_of_subset_right hs₁ disjoint_sdiff_right) hs hs₁fin, hs₁card,
add_tsub_cancel_of_le]
theorem exists_subset_or_subset_of_two_mul_lt_ncard {n : ℕ} (hst : 2 * n < (s ∪ t).ncard) :
∃ r : Set α, n < r.ncard ∧ (r ⊆ s ∨ r ⊆ t) := by
classical
have hu := finite_of_ncard_ne_zero ((Nat.zero_le _).trans_lt hst).ne.symm
rw [ncard_eq_toFinset_card _ hu,
Finite.toFinset_union (hu.subset subset_union_left)
(hu.subset subset_union_right)] at hst
obtain ⟨r', hnr', hr'⟩ := Finset.exists_subset_or_subset_of_two_mul_lt_card hst
exact ⟨r', by simpa, by simpa using hr'⟩
/-! ### Explicit description of a set from its cardinality -/
@[simp] theorem ncard_eq_one : s.ncard = 1 ↔ ∃ a, s = {a} := by
refine ⟨fun h ↦ ?_, by rintro ⟨a, rfl⟩; rw [ncard_singleton]⟩
have hft := (finite_of_ncard_ne_zero (ne_zero_of_eq_one h)).fintype
simp_rw [ncard_eq_toFinset_card', @Finset.card_eq_one _ (toFinset s)] at h
refine h.imp fun a ha ↦ ?_
simp_rw [Set.ext_iff, mem_singleton_iff]
simp only [Finset.ext_iff, mem_toFinset, Finset.mem_singleton] at ha
exact ha
theorem exists_eq_insert_iff_ncard (hs : s.Finite := by toFinite_tac) :
(∃ a ∉ s, insert a s = t) ↔ s ⊆ t ∧ s.ncard + 1 = t.ncard := by
classical
rcases t.finite_or_infinite with ht | ht
· rw [ncard_eq_toFinset_card _ hs, ncard_eq_toFinset_card _ ht,
← @Finite.toFinset_subset_toFinset _ _ _ hs ht, ← Finset.exists_eq_insert_iff]
convert Iff.rfl using 2; simp only [Finite.mem_toFinset]
ext x
simp [Finset.ext_iff, Set.ext_iff]
simp only [ht.ncard, exists_prop, add_eq_zero, and_false, iff_false, not_exists, not_and,
reduceCtorEq]
rintro x - rfl
exact ht (hs.insert x)
theorem ncard_le_one (hs : s.Finite := by toFinite_tac) :
s.ncard ≤ 1 ↔ ∀ a ∈ s, ∀ b ∈ s, a = b := by
simp_rw [ncard_eq_toFinset_card _ hs, Finset.card_le_one, Finite.mem_toFinset]
@[simp] theorem ncard_le_one_iff_subsingleton [Finite s] :
s.ncard ≤ 1 ↔ s.Subsingleton :=
ncard_le_one <| inferInstanceAs (Finite s)
theorem ncard_le_one_iff (hs : s.Finite := by toFinite_tac) :
s.ncard ≤ 1 ↔ ∀ {a b}, a ∈ s → b ∈ s → a = b := by
rw [ncard_le_one hs]
tauto
theorem ncard_le_one_iff_eq (hs : s.Finite := by toFinite_tac) :
s.ncard ≤ 1 ↔ s = ∅ ∨ ∃ a, s = {a} := by
obtain rfl | ⟨x, hx⟩ := s.eq_empty_or_nonempty
· exact iff_of_true (by simp) (Or.inl rfl)
rw [ncard_le_one_iff hs]
refine ⟨fun h ↦ Or.inr ⟨x, (singleton_subset_iff.mpr hx).antisymm' fun y hy ↦ h hy hx⟩, ?_⟩
rintro (rfl | ⟨a, rfl⟩)
· exact (not_mem_empty _ hx).elim
simp_rw [mem_singleton_iff] at hx ⊢; subst hx
simp only [forall_eq_apply_imp_iff, imp_self, implies_true]
| theorem ncard_le_one_iff_subset_singleton [Nonempty α]
(hs : s.Finite := by toFinite_tac) :
s.ncard ≤ 1 ↔ ∃ x : α, s ⊆ {x} := by
simp_rw [ncard_eq_toFinset_card _ hs, Finset.card_le_one_iff_subset_singleton,
Finite.toFinset_subset, Finset.coe_singleton]
/-- A `Set` of a subsingleton type has cardinality at most one. -/
theorem ncard_le_one_of_subsingleton [Subsingleton α] (s : Set α) : s.ncard ≤ 1 := by
rw [ncard_eq_toFinset_card]
exact Finset.card_le_one_of_subsingleton _
| Mathlib/Data/Set/Card.lean | 1,042 | 1,051 |
/-
Copyright (c) 2022. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Yuma Mizuno, Oleksandr Manzyuk
-/
import Mathlib.CategoryTheory.Monoidal.Free.Coherence
import Mathlib.Lean.Meta
import Mathlib.Tactic.CategoryTheory.BicategoryCoherence
import Mathlib.Tactic.CategoryTheory.MonoidalComp
/-!
# A `coherence` tactic for monoidal categories
We provide a `coherence` tactic,
which proves equations where the two sides differ by replacing
strings of monoidal structural morphisms with other such strings.
(The replacements are always equalities by the monoidal coherence theorem.)
A simpler version of this tactic is `pure_coherence`,
which proves that any two morphisms (with the same source and target)
in a monoidal category which are built out of associators and unitors
are equal.
-/
universe v u
open CategoryTheory FreeMonoidalCategory
-- As the lemmas and typeclasses in this file are not intended for use outside of the tactic,
-- we put everything inside a namespace.
namespace Mathlib.Tactic.Coherence
variable {C : Type u} [Category.{v} C]
open scoped MonoidalCategory
noncomputable section lifting
variable [MonoidalCategory C]
/-- A typeclass carrying a choice of lift of an object from `C` to `FreeMonoidalCategory C`.
It must be the case that `projectObj id (LiftObj.lift x) = x` by defeq. -/
class LiftObj (X : C) where
protected lift : FreeMonoidalCategory C
instance LiftObj_unit : LiftObj (𝟙_ C) := ⟨unit⟩
instance LiftObj_tensor (X Y : C) [LiftObj X] [LiftObj Y] : LiftObj (X ⊗ Y) where
lift := LiftObj.lift X ⊗ LiftObj.lift Y
instance (priority := 100) LiftObj_of (X : C) : LiftObj X := ⟨of X⟩
/-- A typeclass carrying a choice of lift of a morphism from `C` to `FreeMonoidalCategory C`.
It must be the case that `projectMap id _ _ (LiftHom.lift f) = f` by defeq. -/
class LiftHom {X Y : C} [LiftObj X] [LiftObj Y] (f : X ⟶ Y) where
protected lift : LiftObj.lift X ⟶ LiftObj.lift Y
instance LiftHom_id (X : C) [LiftObj X] : LiftHom (𝟙 X) := ⟨𝟙 _⟩
instance LiftHom_left_unitor_hom (X : C) [LiftObj X] : LiftHom (λ_ X).hom where
lift := (λ_ (LiftObj.lift X)).hom
instance LiftHom_left_unitor_inv (X : C) [LiftObj X] : LiftHom (λ_ X).inv where
lift := (λ_ (LiftObj.lift X)).inv
instance LiftHom_right_unitor_hom (X : C) [LiftObj X] : LiftHom (ρ_ X).hom where
lift := (ρ_ (LiftObj.lift X)).hom
instance LiftHom_right_unitor_inv (X : C) [LiftObj X] : LiftHom (ρ_ X).inv where
lift := (ρ_ (LiftObj.lift X)).inv
instance LiftHom_associator_hom (X Y Z : C) [LiftObj X] [LiftObj Y] [LiftObj Z] :
LiftHom (α_ X Y Z).hom where
lift := (α_ (LiftObj.lift X) (LiftObj.lift Y) (LiftObj.lift Z)).hom
instance LiftHom_associator_inv (X Y Z : C) [LiftObj X] [LiftObj Y] [LiftObj Z] :
LiftHom (α_ X Y Z).inv where
lift := (α_ (LiftObj.lift X) (LiftObj.lift Y) (LiftObj.lift Z)).inv
instance LiftHom_comp {X Y Z : C} [LiftObj X] [LiftObj Y] [LiftObj Z] (f : X ⟶ Y) (g : Y ⟶ Z)
[LiftHom f] [LiftHom g] : LiftHom (f ≫ g) where
lift := LiftHom.lift f ≫ LiftHom.lift g
instance liftHom_WhiskerLeft (X : C) [LiftObj X] {Y Z : C} [LiftObj Y] [LiftObj Z]
(f : Y ⟶ Z) [LiftHom f] : LiftHom (X ◁ f) where
lift := LiftObj.lift X ◁ LiftHom.lift f
instance liftHom_WhiskerRight {X Y : C} (f : X ⟶ Y) [LiftObj X] [LiftObj Y] [LiftHom f]
{Z : C} [LiftObj Z] : LiftHom (f ▷ Z) where
lift := LiftHom.lift f ▷ LiftObj.lift Z
instance LiftHom_tensor {W X Y Z : C} [LiftObj W] [LiftObj X] [LiftObj Y] [LiftObj Z]
(f : W ⟶ X) (g : Y ⟶ Z) [LiftHom f] [LiftHom g] : LiftHom (f ⊗ g) where
lift := LiftHom.lift f ⊗ LiftHom.lift g
end lifting
open Lean Meta Elab Tactic
/-- Helper function for throwing exceptions. -/
def exception {α : Type} (g : MVarId) (msg : MessageData) : MetaM α :=
throwTacticEx `monoidal_coherence g msg
/-- Helper function for throwing exceptions with respect to the main goal. -/
def exception' (msg : MessageData) : TacticM Unit := do
try
liftMetaTactic (exception (msg := msg))
catch _ =>
-- There might not be any goals
throwError msg
/-- Auxiliary definition for `monoidal_coherence`. -/
-- We could construct this expression directly without using `elabTerm`,
-- but it would require preparing many implicit arguments by hand.
def mkProjectMapExpr (e : Expr) : TermElabM Expr := do
Term.elabTerm
(← ``(FreeMonoidalCategory.projectMap _root_.id _ _ (LiftHom.lift $(← Term.exprToSyntax e))))
none
/-- Coherence tactic for monoidal categories. -/
def monoidal_coherence (g : MVarId) : TermElabM Unit := g.withContext do
withOptions (fun opts => synthInstance.maxSize.set opts
(max 512 (synthInstance.maxSize.get opts))) do
let thms := [``MonoidalCoherence.iso, ``Iso.trans, ``Iso.symm, ``Iso.refl,
``MonoidalCategory.whiskerRightIso, ``MonoidalCategory.whiskerLeftIso].foldl
(·.addDeclToUnfoldCore ·) {}
let (ty, _) ← dsimp (← g.getType) (← Simp.mkContext (simpTheorems := #[thms]))
let some (_, lhs, rhs) := (← whnfR ty).eq? | exception g "Not an equation of morphisms."
let projectMap_lhs ← mkProjectMapExpr lhs
let projectMap_rhs ← mkProjectMapExpr rhs
-- This new equation is defeq to the original by assumption
-- on the `LiftObj` and `LiftHom` instances.
let g₁ ← g.change (← mkEq projectMap_lhs projectMap_rhs)
let [g₂] ← g₁.applyConst ``congrArg
| exception g "congrArg failed in coherence"
let [] ← g₂.applyConst ``Subsingleton.elim
| exception g "This shouldn't happen; Subsingleton.elim does not create goals."
/-- Coherence tactic for monoidal categories.
Use `pure_coherence` instead, which is a frontend to this one. -/
elab "monoidal_coherence" : tactic => do monoidal_coherence (← getMainGoal)
open Mathlib.Tactic.BicategoryCoherence
/--
`pure_coherence` uses the coherence theorem for monoidal categories to prove the goal.
It can prove any equality made up only of associators, unitors, and identities.
```lean
example {C : Type} [Category C] [MonoidalCategory C] :
(λ_ (𝟙_ C)).hom = (ρ_ (𝟙_ C)).hom := by
pure_coherence
```
Users will typically just use the `coherence` tactic,
which can also cope with identities of the form
`a ≫ f ≫ b ≫ g ≫ c = a' ≫ f ≫ b' ≫ g ≫ c'`
where `a = a'`, `b = b'`, and `c = c'` can be proved using `pure_coherence`
-/
elab (name := pure_coherence) "pure_coherence" : tactic => do
let g ← getMainGoal
monoidal_coherence g <|> bicategory_coherence g
/--
Auxiliary simp lemma for the `coherence` tactic:
this moves brackets to the left in order to expose a maximal prefix
built out of unitors and associators.
-/
-- We have unused typeclass arguments here.
-- They are intentional, to ensure that `simp only [assoc_LiftHom]` only left associates
-- monoidal structural morphisms.
@[nolint unusedArguments]
lemma assoc_liftHom {W X Y Z : C} [LiftObj W] [LiftObj X] [LiftObj Y]
(f : W ⟶ X) (g : X ⟶ Y) (h : Y ⟶ Z) [LiftHom f] [LiftHom g] :
f ≫ (g ≫ h) = (f ≫ g) ≫ h :=
(Category.assoc _ _ _).symm
/--
Internal tactic used in `coherence`.
Rewrites an equation `f = g` as `f₀ ≫ f₁ = g₀ ≫ g₁`,
where `f₀` and `g₀` are maximal prefixes of `f` and `g` (possibly after reassociating)
which are "liftable" (i.e. expressible as compositions of unitors and associators).
-/
elab (name := liftable_prefixes) "liftable_prefixes" : tactic => do
withOptions (fun opts => synthInstance.maxSize.set opts
(max 256 (synthInstance.maxSize.get opts))) do
evalTactic (← `(tactic|
(simp -failIfUnchanged only
[monoidalComp, bicategoricalComp, Category.assoc, BicategoricalCoherence.iso,
MonoidalCoherence.iso, Iso.trans, Iso.symm, Iso.refl,
MonoidalCategory.whiskerRightIso, MonoidalCategory.whiskerLeftIso,
Bicategory.whiskerRightIso, Bicategory.whiskerLeftIso]) <;>
(apply (cancel_epi (𝟙 _)).1 <;> try infer_instance) <;>
(simp -failIfUnchanged only
[assoc_liftHom, Mathlib.Tactic.BicategoryCoherence.assoc_liftHom₂])))
lemma insert_id_lhs {C : Type*} [Category C] {X Y : C} (f g : X ⟶ Y) (w : f ≫ 𝟙 _ = g) :
f = g := by
simpa using w
|
lemma insert_id_rhs {C : Type*} [Category C] {X Y : C} (f g : X ⟶ Y) (w : f = g ≫ 𝟙 _) :
f = g := by
| Mathlib/Tactic/CategoryTheory/Coherence.lean | 200 | 202 |
/-
Copyright (c) 2024 Joël Riou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joël Riou
-/
import Mathlib.Algebra.Category.ModuleCat.Sheaf.ChangeOfRings
import Mathlib.CategoryTheory.Sites.LocallySurjective
/-!
# The associated sheaf of a presheaf of modules
In this file, given a presheaf of modules `M₀` over a presheaf of rings `R₀`,
we construct the associated sheaf of `M₀`. More precisely, if `R` is a sheaf of
rings and `α : R₀ ⟶ R.val` is locally bijective, and `A` is the sheafification
of the underlying presheaf of abelian groups of `M₀`, i.e. we have a locally bijective
map `φ : M₀.presheaf ⟶ A.val`, then we endow `A` with the structure of a
sheaf of modules over `R`: this is `PresheafOfModules.sheafify α φ`.
In many applications, the morphism `α` shall be the identity, but this more
general construction allows the sheafification of both the presheaf of rings
and the presheaf of modules.
-/
universe w v v₁ u₁ u
open CategoryTheory
variable {C : Type u₁} [Category.{v₁} C] {J : GrothendieckTopology C}
namespace CategoryTheory
namespace Presieve.FamilyOfElements
section smul
variable {R : Cᵒᵖ ⥤ RingCat.{u}} {M : PresheafOfModules.{v} R} {X : C} {P : Presieve X}
(r : FamilyOfElements (R ⋙ forget _) P) (m : FamilyOfElements (M.presheaf ⋙ forget _) P)
/-- The scalar multiplication of family of elements of a presheaf of modules `M` over `R`
by a family of elements of `R`. -/
def smul : FamilyOfElements (M.presheaf ⋙ forget _) P := fun Y f hf =>
HSMul.hSMul (α := R.obj (Opposite.op Y)) (β := M.obj (Opposite.op Y)) (r f hf) (m f hf)
end smul
section
variable {R₀ R : Cᵒᵖ ⥤ RingCat.{u}} (α : R₀ ⟶ R) [Presheaf.IsLocallyInjective J α]
{M₀ : PresheafOfModules.{v} R₀} {A : Cᵒᵖ ⥤ AddCommGrp.{v}} (φ : M₀.presheaf ⟶ A)
[Presheaf.IsLocallyInjective J φ] (hA : Presheaf.IsSeparated J A)
{X : C} (r : R.obj (Opposite.op X)) (m : A.obj (Opposite.op X)) {P : Presieve X}
(r₀ : FamilyOfElements (R₀ ⋙ forget _) P) (m₀ : FamilyOfElements (M₀.presheaf ⋙ forget _) P)
include hA
lemma _root_.PresheafOfModules.Sheafify.app_eq_of_isLocallyInjective
{Y : C} (r₀ r₀' : R₀.obj (Opposite.op Y))
(m₀ m₀' : M₀.obj (Opposite.op Y))
(hr₀ : α.app _ r₀ = α.app _ r₀')
(hm₀ : φ.app _ m₀ = φ.app _ m₀') :
φ.app _ (r₀ • m₀) = φ.app _ (r₀' • m₀') := by
apply hA _ (Presheaf.equalizerSieve r₀ r₀' ⊓
Presheaf.equalizerSieve (F := M₀.presheaf) m₀ m₀')
· apply J.intersection_covering
· exact Presheaf.equalizerSieve_mem J α _ _ hr₀
· exact Presheaf.equalizerSieve_mem J φ _ _ hm₀
· intro Z g hg
rw [← NatTrans.naturality_apply (D := Ab), ← NatTrans.naturality_apply (D := Ab)]
erw [M₀.map_smul, M₀.map_smul, hg.1, hg.2]
rfl
lemma isCompatible_map_smul_aux {Y Z : C} (f : Y ⟶ X) (g : Z ⟶ Y)
(r₀ : R₀.obj (Opposite.op Y)) (r₀' : R₀.obj (Opposite.op Z))
| (m₀ : M₀.obj (Opposite.op Y)) (m₀' : M₀.obj (Opposite.op Z))
(hr₀ : α.app _ r₀ = R.map f.op r) (hr₀' : α.app _ r₀' = R.map (f.op ≫ g.op) r)
(hm₀ : φ.app _ m₀ = A.map f.op m) (hm₀' : φ.app _ m₀' = A.map (f.op ≫ g.op) m) :
φ.app _ (M₀.map g.op (r₀ • m₀)) = φ.app _ (r₀' • m₀') := by
rw [← PresheafOfModules.Sheafify.app_eq_of_isLocallyInjective α φ hA (R₀.map g.op r₀) r₀'
(M₀.map g.op m₀) m₀', M₀.map_smul]
· rw [hr₀', R.map_comp, RingCat.comp_apply, ← hr₀, ← RingCat.comp_apply, NatTrans.naturality,
RingCat.comp_apply]
· rw [hm₀', A.map_comp, AddCommGrp.coe_comp, Function.comp_apply, ← hm₀]
erw [NatTrans.naturality_apply φ]
variable (hr₀ : (r₀.map (whiskerRight α (forget _))).IsAmalgamation r)
| Mathlib/Algebra/Category/ModuleCat/Presheaf/Sheafify.lean | 74 | 85 |
/-
Copyright (c) 2018 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Floris van Doorn
-/
import Mathlib.Algebra.Order.Archimedean.Basic
import Mathlib.Algebra.Order.Group.Pointwise.Bounds
import Mathlib.Data.Real.Basic
import Mathlib.Order.ConditionallyCompleteLattice.Indexed
import Mathlib.Order.Interval.Set.Disjoint
/-!
# The real numbers are an Archimedean floor ring, and a conditionally complete linear order.
-/
assert_not_exists Finset
open Pointwise CauSeq
namespace Real
variable {ι : Sort*} {f : ι → ℝ} {s : Set ℝ} {a : ℝ}
instance instArchimedean : Archimedean ℝ :=
archimedean_iff_rat_le.2 fun x =>
Real.ind_mk x fun f =>
let ⟨M, _, H⟩ := f.bounded' 0
⟨M, mk_le_of_forall_le ⟨0, fun i _ => Rat.cast_le.2 <| le_of_lt (abs_lt.1 (H i)).2⟩⟩
noncomputable instance : FloorRing ℝ :=
Archimedean.floorRing _
theorem isCauSeq_iff_lift {f : ℕ → ℚ} : IsCauSeq abs f ↔ IsCauSeq abs fun i => (f i : ℝ) where
mp H ε ε0 :=
let ⟨δ, δ0, δε⟩ := exists_pos_rat_lt ε0
(H _ δ0).imp fun i hi j ij => by dsimp; exact lt_trans (mod_cast hi _ ij) δε
mpr H ε ε0 :=
(H _ (Rat.cast_pos.2 ε0)).imp fun i hi j ij => by dsimp at hi; exact mod_cast hi _ ij
theorem of_near (f : ℕ → ℚ) (x : ℝ) (h : ∀ ε > 0, ∃ i, ∀ j ≥ i, |(f j : ℝ) - x| < ε) :
∃ h', Real.mk ⟨f, h'⟩ = x :=
⟨isCauSeq_iff_lift.2 (CauSeq.of_near _ (const abs x) h),
sub_eq_zero.1 <|
abs_eq_zero.1 <|
(eq_of_le_of_forall_lt_imp_le_of_dense (abs_nonneg _)) fun _ε ε0 =>
mk_near_of_forall_near <| (h _ ε0).imp fun _i h j ij => le_of_lt (h j ij)⟩
theorem exists_floor (x : ℝ) : ∃ ub : ℤ, (ub : ℝ) ≤ x ∧ ∀ z : ℤ, (z : ℝ) ≤ x → z ≤ ub :=
Int.exists_greatest_of_bdd
(let ⟨n, hn⟩ := exists_int_gt x
⟨n, fun _ h' => Int.cast_le.1 <| le_trans h' <| le_of_lt hn⟩)
(let ⟨n, hn⟩ := exists_int_lt x
⟨n, le_of_lt hn⟩)
theorem exists_isLUB (hne : s.Nonempty) (hbdd : BddAbove s) : ∃ x, IsLUB s x := by
rcases hne, hbdd with ⟨⟨L, hL⟩, ⟨U, hU⟩⟩
have : ∀ d : ℕ, BddAbove { m : ℤ | ∃ y ∈ s, (m : ℝ) ≤ y * d } := by
obtain ⟨k, hk⟩ := exists_int_gt U
refine fun d => ⟨k * d, fun z h => ?_⟩
rcases h with ⟨y, yS, hy⟩
refine Int.cast_le.1 (hy.trans ?_)
push_cast
exact mul_le_mul_of_nonneg_right ((hU yS).trans hk.le) d.cast_nonneg
choose f hf using fun d : ℕ =>
Int.exists_greatest_of_bdd (this d) ⟨⌊L * d⌋, L, hL, Int.floor_le _⟩
have hf₁ : ∀ n > 0, ∃ y ∈ s, ((f n / n : ℚ) : ℝ) ≤ y := fun n n0 =>
let ⟨y, yS, hy⟩ := (hf n).1
⟨y, yS, by simpa using (div_le_iff₀ (Nat.cast_pos.2 n0 : (_ : ℝ) < _)).2 hy⟩
have hf₂ : ∀ n > 0, ∀ y ∈ s, (y - ((n : ℕ) : ℝ)⁻¹) < (f n / n : ℚ) := by
intro n n0 y yS
have := (Int.sub_one_lt_floor _).trans_le (Int.cast_le.2 <| (hf n).2 _ ⟨y, yS, Int.floor_le _⟩)
simp only [Rat.cast_div, Rat.cast_intCast, Rat.cast_natCast, gt_iff_lt]
rwa [lt_div_iff₀ (Nat.cast_pos.2 n0 : (_ : ℝ) < _), sub_mul, inv_mul_cancel₀]
exact ne_of_gt (Nat.cast_pos.2 n0)
have hg : IsCauSeq abs (fun n => f n / n : ℕ → ℚ) := by
intro ε ε0
suffices ∀ j ≥ ⌈ε⁻¹⌉₊, ∀ k ≥ ⌈ε⁻¹⌉₊, (f j / j - f k / k : ℚ) < ε by
refine ⟨_, fun j ij => abs_lt.2 ⟨?_, this _ ij _ le_rfl⟩⟩
rw [neg_lt, neg_sub]
exact this _ le_rfl _ ij
intro j ij k ik
replace ij := le_trans (Nat.le_ceil _) (Nat.cast_le.2 ij)
replace ik := le_trans (Nat.le_ceil _) (Nat.cast_le.2 ik)
have j0 := Nat.cast_pos.1 ((inv_pos.2 ε0).trans_le ij)
have k0 := Nat.cast_pos.1 ((inv_pos.2 ε0).trans_le ik)
rcases hf₁ _ j0 with ⟨y, yS, hy⟩
refine lt_of_lt_of_le ((Rat.cast_lt (K := ℝ)).1 ?_) ((inv_le_comm₀ ε0 (Nat.cast_pos.2 k0)).1 ik)
simpa using sub_lt_iff_lt_add'.2 (lt_of_le_of_lt hy <| sub_lt_iff_lt_add.1 <| hf₂ _ k0 _ yS)
let g : CauSeq ℚ abs := ⟨fun n => f n / n, hg⟩
refine ⟨mk g, ⟨fun x xS => ?_, fun y h => ?_⟩⟩
· refine le_of_forall_lt_imp_le_of_dense fun z xz => ?_
obtain ⟨K, hK⟩ := exists_nat_gt (x - z)⁻¹
refine le_mk_of_forall_le ⟨K, fun n nK => ?_⟩
replace xz := sub_pos.2 xz
replace hK := hK.le.trans (Nat.cast_le.2 nK)
have n0 : 0 < n := Nat.cast_pos.1 ((inv_pos.2 xz).trans_le hK)
refine le_trans ?_ (hf₂ _ n0 _ xS).le
rwa [le_sub_comm, inv_le_comm₀ (Nat.cast_pos.2 n0 : (_ : ℝ) < _) xz]
· exact
mk_le_of_forall_le
⟨1, fun n n1 =>
let ⟨x, xS, hx⟩ := hf₁ _ n1
le_trans hx (h xS)⟩
/-- A nonempty, bounded below set of real numbers has a greatest lower bound. -/
theorem exists_isGLB (hne : s.Nonempty) (hbdd : BddBelow s) : ∃ x, IsGLB s x := by
have hne' : (-s).Nonempty := Set.nonempty_neg.mpr hne
have hbdd' : BddAbove (-s) := bddAbove_neg.mpr hbdd
use -Classical.choose (Real.exists_isLUB hne' hbdd')
rw [← isLUB_neg]
exact Classical.choose_spec (Real.exists_isLUB hne' hbdd')
open scoped Classical in
noncomputable instance : SupSet ℝ :=
⟨fun s => if h : s.Nonempty ∧ BddAbove s then Classical.choose (exists_isLUB h.1 h.2) else 0⟩
open scoped Classical in
theorem sSup_def (s : Set ℝ) :
sSup s = if h : s.Nonempty ∧ BddAbove s then Classical.choose (exists_isLUB h.1 h.2) else 0 :=
rfl
protected theorem isLUB_sSup (h₁ : s.Nonempty) (h₂ : BddAbove s) : IsLUB s (sSup s) := by
simp only [sSup_def, dif_pos (And.intro h₁ h₂)]
apply Classical.choose_spec
noncomputable instance : InfSet ℝ :=
⟨fun s => -sSup (-s)⟩
theorem sInf_def (s : Set ℝ) : sInf s = -sSup (-s) := rfl
protected theorem isGLB_sInf (h₁ : s.Nonempty) (h₂ : BddBelow s) : IsGLB s (sInf s) := by
rw [sInf_def, ← isLUB_neg', neg_neg]
exact Real.isLUB_sSup h₁.neg h₂.neg
noncomputable instance : ConditionallyCompleteLinearOrder ℝ where
__ := Real.linearOrder
__ := Real.lattice
le_csSup s a hs ha := (Real.isLUB_sSup ⟨a, ha⟩ hs).1 ha
csSup_le s a hs ha := (Real.isLUB_sSup hs ⟨a, ha⟩).2 ha
csInf_le s a hs ha := (Real.isGLB_sInf ⟨a, ha⟩ hs).1 ha
le_csInf s a hs ha := (Real.isGLB_sInf hs ⟨a, ha⟩).2 ha
csSup_of_not_bddAbove s hs := by simp [hs, sSup_def]
csInf_of_not_bddBelow s hs := by simp [hs, sInf_def, sSup_def]
theorem lt_sInf_add_pos (h : s.Nonempty) {ε : ℝ} (hε : 0 < ε) : ∃ a ∈ s, a < sInf s + ε :=
exists_lt_of_csInf_lt h <| lt_add_of_pos_right _ hε
theorem add_neg_lt_sSup (h : s.Nonempty) {ε : ℝ} (hε : ε < 0) : ∃ a ∈ s, sSup s + ε < a :=
exists_lt_of_lt_csSup h <| add_lt_iff_neg_left.2 hε
theorem sInf_le_iff (h : BddBelow s) (h' : s.Nonempty) :
sInf s ≤ a ↔ ∀ ε, 0 < ε → ∃ x ∈ s, x < a + ε := by
rw [le_iff_forall_pos_lt_add]
constructor <;> intro H ε ε_pos
· exact exists_lt_of_csInf_lt h' (H ε ε_pos)
· rcases H ε ε_pos with ⟨x, x_in, hx⟩
exact csInf_lt_of_lt h x_in hx
theorem le_sSup_iff (h : BddAbove s) (h' : s.Nonempty) :
a ≤ sSup s ↔ ∀ ε, ε < 0 → ∃ x ∈ s, a + ε < x := by
rw [le_iff_forall_pos_lt_add]
refine ⟨fun H ε ε_neg => ?_, fun H ε ε_pos => ?_⟩
· exact exists_lt_of_lt_csSup h' (lt_sub_iff_add_lt.mp (H _ (neg_pos.mpr ε_neg)))
· rcases H _ (neg_lt_zero.mpr ε_pos) with ⟨x, x_in, hx⟩
exact sub_lt_iff_lt_add.mp (lt_csSup_of_lt h x_in hx)
@[simp]
theorem sSup_empty : sSup (∅ : Set ℝ) = 0 :=
dif_neg <| by simp
@[simp] lemma iSup_of_isEmpty [IsEmpty ι] (f : ι → ℝ) : ⨆ i, f i = 0 := by
dsimp [iSup]
convert Real.sSup_empty
rw [Set.range_eq_empty_iff]
infer_instance
@[simp]
theorem iSup_const_zero : ⨆ _ : ι, (0 : ℝ) = 0 := by
cases isEmpty_or_nonempty ι
· exact Real.iSup_of_isEmpty _
· exact ciSup_const
lemma sSup_of_not_bddAbove (hs : ¬BddAbove s) : sSup s = 0 := dif_neg fun h => hs h.2
lemma iSup_of_not_bddAbove (hf : ¬BddAbove (Set.range f)) : ⨆ i, f i = 0 := sSup_of_not_bddAbove hf
theorem sSup_univ : sSup (@Set.univ ℝ) = 0 := Real.sSup_of_not_bddAbove not_bddAbove_univ
@[simp]
theorem sInf_empty : sInf (∅ : Set ℝ) = 0 := by simp [sInf_def, sSup_empty]
@[simp] nonrec lemma iInf_of_isEmpty [IsEmpty ι] (f : ι → ℝ) : ⨅ i, f i = 0 := by
rw [iInf_of_isEmpty, sInf_empty]
@[simp]
theorem iInf_const_zero : ⨅ _ : ι, (0 : ℝ) = 0 := by
cases isEmpty_or_nonempty ι
· exact Real.iInf_of_isEmpty _
· exact ciInf_const
theorem sInf_of_not_bddBelow (hs : ¬BddBelow s) : sInf s = 0 :=
neg_eq_zero.2 <| sSup_of_not_bddAbove <| mt bddAbove_neg.1 hs
theorem iInf_of_not_bddBelow (hf : ¬BddBelow (Set.range f)) : ⨅ i, f i = 0 :=
sInf_of_not_bddBelow hf
/-- As `sSup s = 0` when `s` is an empty set of reals, it suffices to show that all elements of `s`
are at most some nonnegative number `a` to show that `sSup s ≤ a`.
See also `csSup_le`. -/
protected lemma sSup_le (hs : ∀ x ∈ s, x ≤ a) (ha : 0 ≤ a) : sSup s ≤ a := by
obtain rfl | hs' := s.eq_empty_or_nonempty
exacts [sSup_empty.trans_le ha, csSup_le hs' hs]
/-- As `⨆ i, f i = 0` when the domain of the real-valued function `f` is empty, it suffices to show
that all values of `f` are at most some nonnegative number `a` to show that `⨆ i, f i ≤ a`.
See also `ciSup_le`. -/
protected lemma iSup_le (hf : ∀ i, f i ≤ a) (ha : 0 ≤ a) : ⨆ i, f i ≤ a :=
Real.sSup_le (Set.forall_mem_range.2 hf) ha
/-- As `sInf s = 0` when `s` is an empty set of reals, it suffices to show that all elements of `s`
are at least some nonpositive number `a` to show that `a ≤ sInf s`.
See also `le_csInf`. -/
protected lemma le_sInf (hs : ∀ x ∈ s, a ≤ x) (ha : a ≤ 0) : a ≤ sInf s := by
obtain rfl | hs' := s.eq_empty_or_nonempty
exacts [ha.trans_eq sInf_empty.symm, le_csInf hs' hs]
/-- As `⨅ i, f i = 0` when the domain of the real-valued function `f` is empty, it suffices to show
that all values of `f` are at least some nonpositive number `a` to show that `a ≤ ⨅ i, f i`.
See also `le_ciInf`. -/
protected lemma le_iInf (hf : ∀ i, a ≤ f i) (ha : a ≤ 0) : a ≤ ⨅ i, f i :=
Real.le_sInf (Set.forall_mem_range.2 hf) ha
/-- As `sSup s = 0` when `s` is an empty set of reals, it suffices to show that all elements of `s`
are nonpositive to show that `sSup s ≤ 0`. -/
lemma sSup_nonpos (hs : ∀ x ∈ s, x ≤ 0) : sSup s ≤ 0 := Real.sSup_le hs le_rfl
/-- As `⨆ i, f i = 0` when the domain of the real-valued function `f` is empty,
it suffices to show that all values of `f` are nonpositive to show that `⨆ i, f i ≤ 0`. -/
lemma iSup_nonpos (hf : ∀ i, f i ≤ 0) : ⨆ i, f i ≤ 0 := Real.iSup_le hf le_rfl
/-- As `sInf s = 0` when `s` is an empty set of reals, it suffices to show that all elements of `s`
are nonnegative to show that `0 ≤ sInf s`. -/
lemma sInf_nonneg (hs : ∀ x ∈ s, 0 ≤ x) : 0 ≤ sInf s := Real.le_sInf hs le_rfl
/-- As `⨅ i, f i = 0` when the domain of the real-valued function `f` is empty,
it suffices to show that all values of `f` are nonnegative to show that `0 ≤ ⨅ i, f i`. -/
lemma iInf_nonneg (hf : ∀ i, 0 ≤ f i) : 0 ≤ iInf f := Real.le_iInf hf le_rfl
/-- As `sSup s = 0` when `s` is a set of reals that's unbounded above, it suffices to show that `s`
contains a nonnegative element to show that `0 ≤ sSup s`. -/
lemma sSup_nonneg' (hs : ∃ x ∈ s, 0 ≤ x) : 0 ≤ sSup s := by
classical
obtain ⟨x, hxs, hx⟩ := hs
exact dite _ (fun h ↦ le_csSup_of_le h hxs hx) fun h ↦ (sSup_of_not_bddAbove h).ge
/-- As `⨆ i, f i = 0` when the real-valued function `f` is unbounded above,
it suffices to show that `f` takes a nonnegative value to show that `0 ≤ ⨆ i, f i`. -/
lemma iSup_nonneg' (hf : ∃ i, 0 ≤ f i) : 0 ≤ ⨆ i, f i := sSup_nonneg' <| Set.exists_range_iff.2 hf
/-- As `sInf s = 0` when `s` is a set of reals that's unbounded below, it suffices to show that `s`
contains a nonpositive element to show that `sInf s ≤ 0`. -/
lemma sInf_nonpos' (hs : ∃ x ∈ s, x ≤ 0) : sInf s ≤ 0 := by
classical
obtain ⟨x, hxs, hx⟩ := hs
exact dite _ (fun h ↦ csInf_le_of_le h hxs hx) fun h ↦ (sInf_of_not_bddBelow h).le
/-- As `⨅ i, f i = 0` when the real-valued function `f` is unbounded below,
it suffices to show that `f` takes a nonpositive value to show that `0 ≤ ⨅ i, f i`. -/
lemma iInf_nonpos' (hf : ∃ i, f i ≤ 0) : ⨅ i, f i ≤ 0 := sInf_nonpos' <| Set.exists_range_iff.2 hf
/-- As `sSup s = 0` when `s` is a set of reals that's either empty or unbounded above,
it suffices to show that all elements of `s` are nonnegative to show that `0 ≤ sSup s`. -/
lemma sSup_nonneg (hs : ∀ x ∈ s, 0 ≤ x) : 0 ≤ sSup s := by
obtain rfl | ⟨x, hx⟩ := s.eq_empty_or_nonempty
· exact sSup_empty.ge
· exact sSup_nonneg' ⟨x, hx, hs _ hx⟩
/-- As `⨆ i, f i = 0` when the domain of the real-valued function `f` is empty or unbounded above,
it suffices to show that all values of `f` are nonnegative to show that `0 ≤ ⨆ i, f i`. -/
lemma iSup_nonneg (hf : ∀ i, 0 ≤ f i) : 0 ≤ ⨆ i, f i := sSup_nonneg <| Set.forall_mem_range.2 hf
/-- As `sInf s = 0` when `s` is a set of reals that's either empty or unbounded below,
it suffices to show that all elements of `s` are nonpositive to show that `sInf s ≤ 0`. -/
lemma sInf_nonpos (hs : ∀ x ∈ s, x ≤ 0) : sInf s ≤ 0 := by
obtain rfl | ⟨x, hx⟩ := s.eq_empty_or_nonempty
· exact sInf_empty.le
· exact sInf_nonpos' ⟨x, hx, hs _ hx⟩
/-- As `⨅ i, f i = 0` when the domain of the real-valued function `f` is empty or unbounded below,
it suffices to show that all values of `f` are nonpositive to show that `0 ≤ ⨅ i, f i`. -/
lemma iInf_nonpos (hf : ∀ i, f i ≤ 0) : ⨅ i, f i ≤ 0 := sInf_nonpos <| Set.forall_mem_range.2 hf
theorem sInf_le_sSup (s : Set ℝ) (h₁ : BddBelow s) (h₂ : BddAbove s) : sInf s ≤ sSup s := by
rcases s.eq_empty_or_nonempty with (rfl | hne)
· rw [sInf_empty, sSup_empty]
· exact csInf_le_csSup h₁ h₂ hne
theorem cauSeq_converges (f : CauSeq ℝ abs) : ∃ x, f ≈ const abs x := by
let s := {x : ℝ | const abs x < f}
have lb : ∃ x, x ∈ s := exists_lt f
have ub' : ∀ x, f < const abs x → ∀ y ∈ s, y ≤ x := fun x h y yS =>
le_of_lt <| const_lt.1 <| CauSeq.lt_trans yS h
have ub : ∃ x, ∀ y ∈ s, y ≤ x := (exists_gt f).imp ub'
refine ⟨sSup s, ((lt_total _ _).resolve_left fun h => ?_).resolve_right fun h => ?_⟩
· rcases h with ⟨ε, ε0, i, ih⟩
refine (csSup_le lb (ub' _ ?_)).not_lt (sub_lt_self _ (half_pos ε0))
refine ⟨_, half_pos ε0, i, fun j ij => ?_⟩
rw [sub_apply, const_apply, sub_right_comm, le_sub_iff_add_le, add_halves]
exact ih _ ij
· rcases h with ⟨ε, ε0, i, ih⟩
refine (le_csSup ub ?_).not_lt ((lt_add_iff_pos_left _).2 (half_pos ε0))
refine ⟨_, half_pos ε0, i, fun j ij => ?_⟩
rw [sub_apply, const_apply, add_comm, ← sub_sub, le_sub_iff_add_le, add_halves]
exact ih _ ij
instance : CauSeq.IsComplete ℝ abs :=
⟨cauSeq_converges⟩
open Set
theorem iInf_Ioi_eq_iInf_rat_gt {f : ℝ → ℝ} (x : ℝ) (hf : BddBelow (f '' Ioi x))
(hf_mono : Monotone f) : ⨅ r : Ioi x, f r = ⨅ q : { q' : ℚ // x < q' }, f q := by
refine le_antisymm ?_ ?_
· have : Nonempty { r' : ℚ // x < ↑r' } := by
obtain ⟨r, hrx⟩ := exists_rat_gt x
exact ⟨⟨r, hrx⟩⟩
refine le_ciInf fun r => ?_
obtain ⟨y, hxy, hyr⟩ := exists_rat_btwn r.prop
refine ciInf_set_le hf (hxy.trans ?_)
exact_mod_cast hyr
· refine le_ciInf fun q => ?_
have hq := q.prop
rw [mem_Ioi] at hq
obtain ⟨y, hxy, hyq⟩ := exists_rat_btwn hq
refine (ciInf_le ?_ ?_).trans ?_
· refine ⟨hf.some, fun z => ?_⟩
rintro ⟨u, rfl⟩
suffices hfu : f u ∈ f '' Ioi x from hf.choose_spec hfu
exact ⟨u, u.prop, rfl⟩
· exact ⟨y, hxy⟩
· refine hf_mono (le_trans ?_ hyq.le)
norm_cast
theorem not_bddAbove_coe : ¬ (BddAbove <| range (fun (x : ℚ) ↦ (x : ℝ))) := by
dsimp only [BddAbove, upperBounds]
rw [Set.not_nonempty_iff_eq_empty]
ext
simpa using exists_rat_gt _
theorem not_bddBelow_coe : ¬ (BddBelow <| range (fun (x : ℚ) ↦ (x : ℝ))) := by
dsimp only [BddBelow, lowerBounds]
rw [Set.not_nonempty_iff_eq_empty]
| ext
simpa using exists_rat_lt _
theorem iUnion_Iic_rat : ⋃ r : ℚ, Iic (r : ℝ) = univ := by
exact iUnion_Iic_of_not_bddAbove_range not_bddAbove_coe
| Mathlib/Data/Real/Archimedean.lean | 356 | 360 |
/-
Copyright (c) 2018 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Johannes Hölzl
-/
import Mathlib.Algebra.Order.Pi
import Mathlib.MeasureTheory.Constructions.BorelSpace.Order
/-!
# Simple functions
A function `f` from a measurable space to any type is called *simple*, if every preimage `f ⁻¹' {x}`
is measurable, and the range is finite. In this file, we define simple functions and establish their
basic properties; and we construct a sequence of simple functions approximating an arbitrary Borel
measurable function `f : α → ℝ≥0∞`.
The theorem `Measurable.ennreal_induction` shows that in order to prove something for an arbitrary
measurable function into `ℝ≥0∞`, it is sufficient to show that the property holds for (multiples of)
characteristic functions and is closed under addition and supremum of increasing sequences of
functions.
-/
noncomputable section
open Set hiding restrict restrict_apply
open Filter ENNReal
open Function (support)
open Topology NNReal ENNReal MeasureTheory
namespace MeasureTheory
variable {α β γ δ : Type*}
/-- A function `f` from a measurable space to any type is called *simple*,
if every preimage `f ⁻¹' {x}` is measurable, and the range is finite. This structure bundles
a function with these properties. -/
structure SimpleFunc.{u, v} (α : Type u) [MeasurableSpace α] (β : Type v) where
/-- The underlying function -/
toFun : α → β
measurableSet_fiber' : ∀ x, MeasurableSet (toFun ⁻¹' {x})
finite_range' : (Set.range toFun).Finite
local infixr:25 " →ₛ " => SimpleFunc
namespace SimpleFunc
section Measurable
variable [MeasurableSpace α]
instance instFunLike : FunLike (α →ₛ β) α β where
coe := toFun
coe_injective' | ⟨_, _, _⟩, ⟨_, _, _⟩, rfl => rfl
theorem coe_injective ⦃f g : α →ₛ β⦄ (H : (f : α → β) = g) : f = g := DFunLike.ext' H
@[ext]
theorem ext {f g : α →ₛ β} (H : ∀ a, f a = g a) : f = g := DFunLike.ext _ _ H
theorem finite_range (f : α →ₛ β) : (Set.range f).Finite :=
f.finite_range'
theorem measurableSet_fiber (f : α →ₛ β) (x : β) : MeasurableSet (f ⁻¹' {x}) :=
f.measurableSet_fiber' x
@[simp] theorem coe_mk (f : α → β) (h h') : ⇑(mk f h h') = f := rfl
theorem apply_mk (f : α → β) (h h') (x : α) : SimpleFunc.mk f h h' x = f x :=
rfl
/-- Simple function defined on a finite type. -/
def ofFinite [Finite α] [MeasurableSingletonClass α] (f : α → β) : α →ₛ β where
toFun := f
measurableSet_fiber' x := (toFinite (f ⁻¹' {x})).measurableSet
finite_range' := Set.finite_range f
/-- Simple function defined on the empty type. -/
def ofIsEmpty [IsEmpty α] : α →ₛ β := ofFinite isEmptyElim
/-- Range of a simple function `α →ₛ β` as a `Finset β`. -/
protected def range (f : α →ₛ β) : Finset β :=
f.finite_range.toFinset
@[simp]
theorem mem_range {f : α →ₛ β} {b} : b ∈ f.range ↔ b ∈ range f :=
Finite.mem_toFinset _
theorem mem_range_self (f : α →ₛ β) (x : α) : f x ∈ f.range :=
mem_range.2 ⟨x, rfl⟩
@[simp]
theorem coe_range (f : α →ₛ β) : (↑f.range : Set β) = Set.range f :=
f.finite_range.coe_toFinset
theorem mem_range_of_measure_ne_zero {f : α →ₛ β} {x : β} {μ : Measure α} (H : μ (f ⁻¹' {x}) ≠ 0) :
x ∈ f.range :=
let ⟨a, ha⟩ := nonempty_of_measure_ne_zero H
mem_range.2 ⟨a, ha⟩
theorem forall_mem_range {f : α →ₛ β} {p : β → Prop} : (∀ y ∈ f.range, p y) ↔ ∀ x, p (f x) := by
simp only [mem_range, Set.forall_mem_range]
theorem exists_range_iff {f : α →ₛ β} {p : β → Prop} : (∃ y ∈ f.range, p y) ↔ ∃ x, p (f x) := by
simpa only [mem_range, exists_prop] using Set.exists_range_iff
theorem preimage_eq_empty_iff (f : α →ₛ β) (b : β) : f ⁻¹' {b} = ∅ ↔ b ∉ f.range :=
preimage_singleton_eq_empty.trans <| not_congr mem_range.symm
theorem exists_forall_le [Nonempty β] [Preorder β] [IsDirected β (· ≤ ·)] (f : α →ₛ β) :
∃ C, ∀ x, f x ≤ C :=
f.range.exists_le.imp fun _ => forall_mem_range.1
/-- Constant function as a `SimpleFunc`. -/
def const (α) {β} [MeasurableSpace α] (b : β) : α →ₛ β :=
⟨fun _ => b, fun _ => MeasurableSet.const _, finite_range_const⟩
instance instInhabited [Inhabited β] : Inhabited (α →ₛ β) :=
⟨const _ default⟩
theorem const_apply (a : α) (b : β) : (const α b) a = b :=
rfl
@[simp]
theorem coe_const (b : β) : ⇑(const α b) = Function.const α b :=
rfl
@[simp]
theorem range_const (α) [MeasurableSpace α] [Nonempty α] (b : β) : (const α b).range = {b} :=
Finset.coe_injective <| by simp +unfoldPartialApp [Function.const]
theorem range_const_subset (α) [MeasurableSpace α] (b : β) : (const α b).range ⊆ {b} :=
Finset.coe_subset.1 <| by simp
theorem simpleFunc_bot {α} (f : @SimpleFunc α ⊥ β) [Nonempty β] : ∃ c, ∀ x, f x = c := by
have hf_meas := @SimpleFunc.measurableSet_fiber α _ ⊥ f
simp_rw [MeasurableSpace.measurableSet_bot_iff] at hf_meas
exact (exists_eq_const_of_preimage_singleton hf_meas).imp fun c hc ↦ congr_fun hc
theorem simpleFunc_bot' {α} [Nonempty β] (f : @SimpleFunc α ⊥ β) :
∃ c, f = @SimpleFunc.const α _ ⊥ c :=
letI : MeasurableSpace α := ⊥; (simpleFunc_bot f).imp fun _ ↦ ext
theorem measurableSet_cut (r : α → β → Prop) (f : α →ₛ β) (h : ∀ b, MeasurableSet { a | r a b }) :
MeasurableSet { a | r a (f a) } := by
have : { a | r a (f a) } = ⋃ b ∈ range f, { a | r a b } ∩ f ⁻¹' {b} := by
ext a
suffices r a (f a) ↔ ∃ i, r a (f i) ∧ f a = f i by simpa
exact ⟨fun h => ⟨a, ⟨h, rfl⟩⟩, fun ⟨a', ⟨h', e⟩⟩ => e.symm ▸ h'⟩
rw [this]
exact
MeasurableSet.biUnion f.finite_range.countable fun b _ =>
MeasurableSet.inter (h b) (f.measurableSet_fiber _)
@[measurability]
theorem measurableSet_preimage (f : α →ₛ β) (s) : MeasurableSet (f ⁻¹' s) :=
measurableSet_cut (fun _ b => b ∈ s) f fun b => MeasurableSet.const (b ∈ s)
/-- A simple function is measurable -/
@[measurability, fun_prop]
protected theorem measurable [MeasurableSpace β] (f : α →ₛ β) : Measurable f := fun s _ =>
measurableSet_preimage f s
@[measurability]
protected theorem aemeasurable [MeasurableSpace β] {μ : Measure α} (f : α →ₛ β) :
AEMeasurable f μ :=
f.measurable.aemeasurable
protected theorem sum_measure_preimage_singleton (f : α →ₛ β) {μ : Measure α} (s : Finset β) :
(∑ y ∈ s, μ (f ⁻¹' {y})) = μ (f ⁻¹' ↑s) :=
sum_measure_preimage_singleton _ fun _ _ => f.measurableSet_fiber _
theorem sum_range_measure_preimage_singleton (f : α →ₛ β) (μ : Measure α) :
(∑ y ∈ f.range, μ (f ⁻¹' {y})) = μ univ := by
rw [f.sum_measure_preimage_singleton, coe_range, preimage_range]
open scoped Classical in
/-- If-then-else as a `SimpleFunc`. -/
def piecewise (s : Set α) (hs : MeasurableSet s) (f g : α →ₛ β) : α →ₛ β :=
⟨s.piecewise f g, fun _ =>
letI : MeasurableSpace β := ⊤
f.measurable.piecewise hs g.measurable trivial,
(f.finite_range.union g.finite_range).subset range_ite_subset⟩
open scoped Classical in
@[simp]
theorem coe_piecewise {s : Set α} (hs : MeasurableSet s) (f g : α →ₛ β) :
⇑(piecewise s hs f g) = s.piecewise f g :=
rfl
open scoped Classical in
theorem piecewise_apply {s : Set α} (hs : MeasurableSet s) (f g : α →ₛ β) (a) :
piecewise s hs f g a = if a ∈ s then f a else g a :=
rfl
open scoped Classical in
@[simp]
theorem piecewise_compl {s : Set α} (hs : MeasurableSet sᶜ) (f g : α →ₛ β) :
piecewise sᶜ hs f g = piecewise s hs.of_compl g f :=
coe_injective <| by simp [hs]
@[simp]
theorem piecewise_univ (f g : α →ₛ β) : piecewise univ MeasurableSet.univ f g = f :=
coe_injective <| by simp
@[simp]
theorem piecewise_empty (f g : α →ₛ β) : piecewise ∅ MeasurableSet.empty f g = g :=
coe_injective <| by simp
open scoped Classical in
@[simp]
theorem piecewise_same (f : α →ₛ β) {s : Set α} (hs : MeasurableSet s) :
piecewise s hs f f = f :=
coe_injective <| Set.piecewise_same _ _
theorem support_indicator [Zero β] {s : Set α} (hs : MeasurableSet s) (f : α →ₛ β) :
Function.support (f.piecewise s hs (SimpleFunc.const α 0)) = s ∩ Function.support f :=
Set.support_indicator
open scoped Classical in
theorem range_indicator {s : Set α} (hs : MeasurableSet s) (hs_nonempty : s.Nonempty)
(hs_ne_univ : s ≠ univ) (x y : β) :
(piecewise s hs (const α x) (const α y)).range = {x, y} := by
simp only [← Finset.coe_inj, coe_range, coe_piecewise, range_piecewise, coe_const,
Finset.coe_insert, Finset.coe_singleton, hs_nonempty.image_const,
(nonempty_compl.2 hs_ne_univ).image_const, singleton_union, Function.const]
theorem measurable_bind [MeasurableSpace γ] (f : α →ₛ β) (g : β → α → γ)
(hg : ∀ b, Measurable (g b)) : Measurable fun a => g (f a) a := fun s hs =>
f.measurableSet_cut (fun a b => g b a ∈ s) fun b => hg b hs
/-- If `f : α →ₛ β` is a simple function and `g : β → α →ₛ γ` is a family of simple functions,
then `f.bind g` binds the first argument of `g` to `f`. In other words, `f.bind g a = g (f a) a`. -/
def bind (f : α →ₛ β) (g : β → α →ₛ γ) : α →ₛ γ :=
⟨fun a => g (f a) a, fun c =>
f.measurableSet_cut (fun a b => g b a = c) fun b => (g b).measurableSet_preimage {c},
(f.finite_range.biUnion fun b _ => (g b).finite_range).subset <| by
rintro _ ⟨a, rfl⟩; simp⟩
@[simp]
theorem bind_apply (f : α →ₛ β) (g : β → α →ₛ γ) (a) : f.bind g a = g (f a) a :=
rfl
/-- Given a function `g : β → γ` and a simple function `f : α →ₛ β`, `f.map g` return the simple
function `g ∘ f : α →ₛ γ` -/
def map (g : β → γ) (f : α →ₛ β) : α →ₛ γ :=
bind f (const α ∘ g)
theorem map_apply (g : β → γ) (f : α →ₛ β) (a) : f.map g a = g (f a) :=
rfl
theorem map_map (g : β → γ) (h : γ → δ) (f : α →ₛ β) : (f.map g).map h = f.map (h ∘ g) :=
rfl
@[simp]
theorem coe_map (g : β → γ) (f : α →ₛ β) : (f.map g : α → γ) = g ∘ f :=
rfl
@[simp]
theorem range_map [DecidableEq γ] (g : β → γ) (f : α →ₛ β) : (f.map g).range = f.range.image g :=
Finset.coe_injective <| by simp only [coe_range, coe_map, Finset.coe_image, range_comp]
@[simp]
theorem map_const (g : β → γ) (b : β) : (const α b).map g = const α (g b) :=
rfl
open scoped Classical in
theorem map_preimage (f : α →ₛ β) (g : β → γ) (s : Set γ) :
f.map g ⁻¹' s = f ⁻¹' ↑{b ∈ f.range | g b ∈ s} := by
simp only [coe_range, sep_mem_eq, coe_map, Finset.coe_filter,
← mem_preimage, inter_comm, preimage_inter_range, ← Finset.mem_coe]
exact preimage_comp
open scoped Classical in
theorem map_preimage_singleton (f : α →ₛ β) (g : β → γ) (c : γ) :
f.map g ⁻¹' {c} = f ⁻¹' ↑{b ∈ f.range | g b = c} :=
map_preimage _ _ _
/-- Composition of a `SimpleFun` and a measurable function is a `SimpleFunc`. -/
def comp [MeasurableSpace β] (f : β →ₛ γ) (g : α → β) (hgm : Measurable g) : α →ₛ γ where
toFun := f ∘ g
finite_range' := f.finite_range.subset <| Set.range_comp_subset_range _ _
measurableSet_fiber' z := hgm (f.measurableSet_fiber z)
@[simp]
theorem coe_comp [MeasurableSpace β] (f : β →ₛ γ) {g : α → β} (hgm : Measurable g) :
⇑(f.comp g hgm) = f ∘ g :=
rfl
theorem range_comp_subset_range [MeasurableSpace β] (f : β →ₛ γ) {g : α → β} (hgm : Measurable g) :
(f.comp g hgm).range ⊆ f.range :=
Finset.coe_subset.1 <| by simp only [coe_range, coe_comp, Set.range_comp_subset_range]
/-- Extend a `SimpleFunc` along a measurable embedding: `f₁.extend g hg f₂` is the function
`F : β →ₛ γ` such that `F ∘ g = f₁` and `F y = f₂ y` whenever `y ∉ range g`. -/
def extend [MeasurableSpace β] (f₁ : α →ₛ γ) (g : α → β) (hg : MeasurableEmbedding g)
(f₂ : β →ₛ γ) : β →ₛ γ where
toFun := Function.extend g f₁ f₂
finite_range' :=
(f₁.finite_range.union <| f₂.finite_range.subset (image_subset_range _ _)).subset
(range_extend_subset _ _ _)
measurableSet_fiber' := by
letI : MeasurableSpace γ := ⊤; haveI : MeasurableSingletonClass γ := ⟨fun _ => trivial⟩
exact fun x => hg.measurable_extend f₁.measurable f₂.measurable (measurableSet_singleton _)
@[simp]
theorem extend_apply [MeasurableSpace β] (f₁ : α →ₛ γ) {g : α → β} (hg : MeasurableEmbedding g)
(f₂ : β →ₛ γ) (x : α) : (f₁.extend g hg f₂) (g x) = f₁ x :=
hg.injective.extend_apply _ _ _
@[simp]
theorem extend_apply' [MeasurableSpace β] (f₁ : α →ₛ γ) {g : α → β} (hg : MeasurableEmbedding g)
(f₂ : β →ₛ γ) {y : β} (h : ¬∃ x, g x = y) : (f₁.extend g hg f₂) y = f₂ y :=
Function.extend_apply' _ _ _ h
@[simp]
theorem extend_comp_eq' [MeasurableSpace β] (f₁ : α →ₛ γ) {g : α → β} (hg : MeasurableEmbedding g)
(f₂ : β →ₛ γ) : f₁.extend g hg f₂ ∘ g = f₁ :=
funext fun _ => extend_apply _ _ _ _
@[simp]
theorem extend_comp_eq [MeasurableSpace β] (f₁ : α →ₛ γ) {g : α → β} (hg : MeasurableEmbedding g)
(f₂ : β →ₛ γ) : (f₁.extend g hg f₂).comp g hg.measurable = f₁ :=
coe_injective <| extend_comp_eq' _ hg _
/-- If `f` is a simple function taking values in `β → γ` and `g` is another simple function
with the same domain and codomain `β`, then `f.seq g = f a (g a)`. -/
def seq (f : α →ₛ β → γ) (g : α →ₛ β) : α →ₛ γ :=
f.bind fun f => g.map f
@[simp]
theorem seq_apply (f : α →ₛ β → γ) (g : α →ₛ β) (a : α) : f.seq g a = f a (g a) :=
rfl
/-- Combine two simple functions `f : α →ₛ β` and `g : α →ₛ β`
into `fun a => (f a, g a)`. -/
def pair (f : α →ₛ β) (g : α →ₛ γ) : α →ₛ β × γ :=
(f.map Prod.mk).seq g
@[simp]
theorem pair_apply (f : α →ₛ β) (g : α →ₛ γ) (a) : pair f g a = (f a, g a) :=
rfl
theorem pair_preimage (f : α →ₛ β) (g : α →ₛ γ) (s : Set β) (t : Set γ) :
pair f g ⁻¹' s ×ˢ t = f ⁻¹' s ∩ g ⁻¹' t :=
rfl
-- A special form of `pair_preimage`
theorem pair_preimage_singleton (f : α →ₛ β) (g : α →ₛ γ) (b : β) (c : γ) :
pair f g ⁻¹' {(b, c)} = f ⁻¹' {b} ∩ g ⁻¹' {c} := by
rw [← singleton_prod_singleton]
exact pair_preimage _ _ _ _
@[simp] theorem map_fst_pair (f : α →ₛ β) (g : α →ₛ γ) : (f.pair g).map Prod.fst = f := rfl
@[simp] theorem map_snd_pair (f : α →ₛ β) (g : α →ₛ γ) : (f.pair g).map Prod.snd = g := rfl
@[simp]
theorem bind_const (f : α →ₛ β) : f.bind (const α) = f := by ext; simp
@[to_additive]
instance instOne [One β] : One (α →ₛ β) :=
⟨const α 1⟩
@[to_additive]
instance instMul [Mul β] : Mul (α →ₛ β) :=
⟨fun f g => (f.map (· * ·)).seq g⟩
@[to_additive]
instance instDiv [Div β] : Div (α →ₛ β) :=
⟨fun f g => (f.map (· / ·)).seq g⟩
@[to_additive]
instance instInv [Inv β] : Inv (α →ₛ β) :=
⟨fun f => f.map Inv.inv⟩
instance instSup [Max β] : Max (α →ₛ β) :=
⟨fun f g => (f.map (· ⊔ ·)).seq g⟩
instance instInf [Min β] : Min (α →ₛ β) :=
⟨fun f g => (f.map (· ⊓ ·)).seq g⟩
instance instLE [LE β] : LE (α →ₛ β) :=
⟨fun f g => ∀ a, f a ≤ g a⟩
@[to_additive (attr := simp)]
theorem const_one [One β] : const α (1 : β) = 1 :=
rfl
@[to_additive (attr := simp, norm_cast)]
theorem coe_one [One β] : ⇑(1 : α →ₛ β) = 1 :=
rfl
@[to_additive (attr := simp, norm_cast)]
theorem coe_mul [Mul β] (f g : α →ₛ β) : ⇑(f * g) = ⇑f * ⇑g :=
rfl
@[to_additive (attr := simp, norm_cast)]
theorem coe_inv [Inv β] (f : α →ₛ β) : ⇑(f⁻¹) = (⇑f)⁻¹ :=
rfl
@[to_additive (attr := simp, norm_cast)]
theorem coe_div [Div β] (f g : α →ₛ β) : ⇑(f / g) = ⇑f / ⇑g :=
rfl
@[simp, norm_cast]
theorem coe_le [LE β] {f g : α →ₛ β} : (f : α → β) ≤ g ↔ f ≤ g :=
Iff.rfl
@[simp, norm_cast]
theorem coe_sup [Max β] (f g : α →ₛ β) : ⇑(f ⊔ g) = ⇑f ⊔ ⇑g :=
rfl
@[simp, norm_cast]
theorem coe_inf [Min β] (f g : α →ₛ β) : ⇑(f ⊓ g) = ⇑f ⊓ ⇑g :=
rfl
@[to_additive]
theorem mul_apply [Mul β] (f g : α →ₛ β) (a : α) : (f * g) a = f a * g a :=
rfl
@[to_additive]
theorem div_apply [Div β] (f g : α →ₛ β) (x : α) : (f / g) x = f x / g x :=
rfl
@[to_additive]
theorem inv_apply [Inv β] (f : α →ₛ β) (x : α) : f⁻¹ x = (f x)⁻¹ :=
rfl
theorem sup_apply [Max β] (f g : α →ₛ β) (a : α) : (f ⊔ g) a = f a ⊔ g a :=
rfl
theorem inf_apply [Min β] (f g : α →ₛ β) (a : α) : (f ⊓ g) a = f a ⊓ g a :=
rfl
@[to_additive (attr := simp)]
theorem range_one [Nonempty α] [One β] : (1 : α →ₛ β).range = {1} :=
Finset.ext fun x => by simp [eq_comm]
@[simp]
theorem range_eq_empty_of_isEmpty {β} [hα : IsEmpty α] (f : α →ₛ β) : f.range = ∅ := by
rw [← Finset.not_nonempty_iff_eq_empty]
by_contra h
obtain ⟨y, hy_mem⟩ := h
rw [SimpleFunc.mem_range, Set.mem_range] at hy_mem
obtain ⟨x, hxy⟩ := hy_mem
rw [isEmpty_iff] at hα
exact hα x
theorem eq_zero_of_mem_range_zero [Zero β] : ∀ {y : β}, y ∈ (0 : α →ₛ β).range → y = 0 :=
@(forall_mem_range.2 fun _ => rfl)
@[to_additive]
theorem mul_eq_map₂ [Mul β] (f g : α →ₛ β) : f * g = (pair f g).map fun p : β × β => p.1 * p.2 :=
rfl
theorem sup_eq_map₂ [Max β] (f g : α →ₛ β) : f ⊔ g = (pair f g).map fun p : β × β => p.1 ⊔ p.2 :=
rfl
@[to_additive]
theorem const_mul_eq_map [Mul β] (f : α →ₛ β) (b : β) : const α b * f = f.map fun a => b * a :=
rfl
@[to_additive]
theorem map_mul [Mul β] [Mul γ] {g : β → γ} (hg : ∀ x y, g (x * y) = g x * g y) (f₁ f₂ : α →ₛ β) :
(f₁ * f₂).map g = f₁.map g * f₂.map g :=
ext fun _ => hg _ _
variable {K : Type*}
@[to_additive]
instance instSMul [SMul K β] : SMul K (α →ₛ β) :=
⟨fun k f => f.map (k • ·)⟩
@[to_additive (attr := simp)]
theorem coe_smul [SMul K β] (c : K) (f : α →ₛ β) : ⇑(c • f) = c • ⇑f :=
rfl
@[to_additive (attr := simp)]
theorem smul_apply [SMul K β] (k : K) (f : α →ₛ β) (a : α) : (k • f) a = k • f a :=
rfl
instance hasNatSMul [AddMonoid β] : SMul ℕ (α →ₛ β) := inferInstance
@[to_additive existing hasNatSMul]
instance hasNatPow [Monoid β] : Pow (α →ₛ β) ℕ :=
⟨fun f n => f.map (· ^ n)⟩
@[simp]
theorem coe_pow [Monoid β] (f : α →ₛ β) (n : ℕ) : ⇑(f ^ n) = (⇑f) ^ n :=
rfl
theorem pow_apply [Monoid β] (n : ℕ) (f : α →ₛ β) (a : α) : (f ^ n) a = f a ^ n :=
rfl
instance hasIntPow [DivInvMonoid β] : Pow (α →ₛ β) ℤ :=
⟨fun f n => f.map (· ^ n)⟩
@[simp]
theorem coe_zpow [DivInvMonoid β] (f : α →ₛ β) (z : ℤ) : ⇑(f ^ z) = (⇑f) ^ z :=
rfl
theorem zpow_apply [DivInvMonoid β] (z : ℤ) (f : α →ₛ β) (a : α) : (f ^ z) a = f a ^ z :=
rfl
-- TODO: work out how to generate these instances with `to_additive`, which gets confused by the
-- argument order swap between `coe_smul` and `coe_pow`.
section Additive
instance instAddMonoid [AddMonoid β] : AddMonoid (α →ₛ β) :=
Function.Injective.addMonoid (fun f => show α → β from f) coe_injective coe_zero coe_add
fun _ _ => coe_smul _ _
instance instAddCommMonoid [AddCommMonoid β] : AddCommMonoid (α →ₛ β) :=
Function.Injective.addCommMonoid (fun f => show α → β from f) coe_injective coe_zero coe_add
fun _ _ => coe_smul _ _
instance instAddGroup [AddGroup β] : AddGroup (α →ₛ β) :=
Function.Injective.addGroup (fun f => show α → β from f) coe_injective coe_zero coe_add coe_neg
coe_sub (fun _ _ => coe_smul _ _) fun _ _ => coe_smul _ _
instance instAddCommGroup [AddCommGroup β] : AddCommGroup (α →ₛ β) :=
Function.Injective.addCommGroup (fun f => show α → β from f) coe_injective coe_zero coe_add
coe_neg coe_sub (fun _ _ => coe_smul _ _) fun _ _ => coe_smul _ _
end Additive
@[to_additive existing]
instance instMonoid [Monoid β] : Monoid (α →ₛ β) :=
Function.Injective.monoid (fun f => show α → β from f) coe_injective coe_one coe_mul coe_pow
@[to_additive existing]
instance instCommMonoid [CommMonoid β] : CommMonoid (α →ₛ β) :=
Function.Injective.commMonoid (fun f => show α → β from f) coe_injective coe_one coe_mul coe_pow
@[to_additive existing]
instance instGroup [Group β] : Group (α →ₛ β) :=
Function.Injective.group (fun f => show α → β from f) coe_injective coe_one coe_mul coe_inv
coe_div coe_pow coe_zpow
@[to_additive existing]
instance instCommGroup [CommGroup β] : CommGroup (α →ₛ β) :=
Function.Injective.commGroup (fun f => show α → β from f) coe_injective coe_one coe_mul coe_inv
coe_div coe_pow coe_zpow
instance instModule [Semiring K] [AddCommMonoid β] [Module K β] : Module K (α →ₛ β) :=
Function.Injective.module K ⟨⟨fun f => show α → β from f, coe_zero⟩, coe_add⟩
coe_injective coe_smul
theorem smul_eq_map [SMul K β] (k : K) (f : α →ₛ β) : k • f = f.map (k • ·) :=
rfl
section Preorder
variable [Preorder β] {s : Set α} {f f₁ f₂ g g₁ g₂ : α →ₛ β} {hs : MeasurableSet s}
instance instPreorder : Preorder (α →ₛ β) := Preorder.lift (⇑)
@[norm_cast] lemma coe_le_coe : ⇑f ≤ g ↔ f ≤ g := .rfl
@[simp, norm_cast] lemma coe_lt_coe : ⇑f < g ↔ f < g := .rfl
@[simp] lemma mk_le_mk {f g : α → β} {hf hg hf' hg'} : mk f hf hf' ≤ mk g hg hg' ↔ f ≤ g := Iff.rfl
@[simp] lemma mk_lt_mk {f g : α → β} {hf hg hf' hg'} : mk f hf hf' < mk g hg hg' ↔ f < g := Iff.rfl
@[gcongr] protected alias ⟨_, GCongr.mk_le_mk⟩ := mk_le_mk
@[gcongr] protected alias ⟨_, GCongr.mk_lt_mk⟩ := mk_lt_mk
@[gcongr] protected alias ⟨_, GCongr.coe_le_coe⟩ := coe_le_coe
@[gcongr] protected alias ⟨_, GCongr.coe_lt_coe⟩ := coe_lt_coe
open scoped Classical in
@[gcongr]
lemma piecewise_mono (hf : ∀ a ∈ s, f₁ a ≤ f₂ a) (hg : ∀ a ∉ s, g₁ a ≤ g₂ a) :
piecewise s hs f₁ g₁ ≤ piecewise s hs f₂ g₂ := Set.piecewise_mono hf hg
end Preorder
instance instPartialOrder [PartialOrder β] : PartialOrder (α →ₛ β) :=
{ SimpleFunc.instPreorder with
le_antisymm := fun _f _g hfg hgf => ext fun a => le_antisymm (hfg a) (hgf a) }
instance instOrderBot [LE β] [OrderBot β] : OrderBot (α →ₛ β) where
bot := const α ⊥
bot_le _ _ := bot_le
instance instOrderTop [LE β] [OrderTop β] : OrderTop (α →ₛ β) where
top := const α ⊤
le_top _ _ := le_top
@[to_additive]
instance [CommMonoid β] [PartialOrder β] [IsOrderedMonoid β] :
IsOrderedMonoid (α →ₛ β) where
mul_le_mul_left _ _ h _ _ := mul_le_mul_left' (h _) _
instance instSemilatticeInf [SemilatticeInf β] : SemilatticeInf (α →ₛ β) :=
{ SimpleFunc.instPartialOrder with
inf := (· ⊓ ·)
inf_le_left := fun _ _ _ => inf_le_left
inf_le_right := fun _ _ _ => inf_le_right
le_inf := fun _f _g _h hfh hgh a => le_inf (hfh a) (hgh a) }
instance instSemilatticeSup [SemilatticeSup β] : SemilatticeSup (α →ₛ β) :=
{ SimpleFunc.instPartialOrder with
sup := (· ⊔ ·)
le_sup_left := fun _ _ _ => le_sup_left
le_sup_right := fun _ _ _ => le_sup_right
sup_le := fun _f _g _h hfh hgh a => sup_le (hfh a) (hgh a) }
instance instLattice [Lattice β] : Lattice (α →ₛ β) :=
{ SimpleFunc.instSemilatticeSup, SimpleFunc.instSemilatticeInf with }
instance instBoundedOrder [LE β] [BoundedOrder β] : BoundedOrder (α →ₛ β) :=
{ SimpleFunc.instOrderBot, SimpleFunc.instOrderTop with }
theorem finset_sup_apply [SemilatticeSup β] [OrderBot β] {f : γ → α →ₛ β} (s : Finset γ) (a : α) :
s.sup f a = s.sup fun c => f c a := by
classical
refine Finset.induction_on s rfl ?_
intro a s _ ih
rw [Finset.sup_insert, Finset.sup_insert, sup_apply, ih]
section Restrict
variable [Zero β]
open scoped Classical in
/-- Restrict a simple function `f : α →ₛ β` to a set `s`. If `s` is measurable,
then `f.restrict s a = if a ∈ s then f a else 0`, otherwise `f.restrict s = const α 0`. -/
def restrict (f : α →ₛ β) (s : Set α) : α →ₛ β :=
if hs : MeasurableSet s then piecewise s hs f 0 else 0
theorem restrict_of_not_measurable {f : α →ₛ β} {s : Set α} (hs : ¬MeasurableSet s) :
restrict f s = 0 :=
dif_neg hs
@[simp]
theorem coe_restrict (f : α →ₛ β) {s : Set α} (hs : MeasurableSet s) :
⇑(restrict f s) = indicator s f := by
classical
rw [restrict, dif_pos hs, coe_piecewise, coe_zero, piecewise_eq_indicator]
@[simp]
theorem restrict_univ (f : α →ₛ β) : restrict f univ = f := by simp [restrict]
@[simp]
theorem restrict_empty (f : α →ₛ β) : restrict f ∅ = 0 := by simp [restrict]
open scoped Classical in
theorem map_restrict_of_zero [Zero γ] {g : β → γ} (hg : g 0 = 0) (f : α →ₛ β) (s : Set α) :
(f.restrict s).map g = (f.map g).restrict s :=
ext fun x =>
if hs : MeasurableSet s then by simp [hs, Set.indicator_comp_of_zero hg]
else by simp [restrict_of_not_measurable hs, hg]
theorem map_coe_ennreal_restrict (f : α →ₛ ℝ≥0) (s : Set α) :
(f.restrict s).map ((↑) : ℝ≥0 → ℝ≥0∞) = (f.map (↑)).restrict s :=
map_restrict_of_zero ENNReal.coe_zero _ _
theorem map_coe_nnreal_restrict (f : α →ₛ ℝ≥0) (s : Set α) :
(f.restrict s).map ((↑) : ℝ≥0 → ℝ) = (f.map (↑)).restrict s :=
map_restrict_of_zero NNReal.coe_zero _ _
theorem restrict_apply (f : α →ₛ β) {s : Set α} (hs : MeasurableSet s) (a) :
restrict f s a = indicator s f a := by simp only [f.coe_restrict hs]
theorem restrict_preimage (f : α →ₛ β) {s : Set α} (hs : MeasurableSet s) {t : Set β}
(ht : (0 : β) ∉ t) : restrict f s ⁻¹' t = s ∩ f ⁻¹' t := by
simp [hs, indicator_preimage_of_not_mem _ _ ht, inter_comm]
theorem restrict_preimage_singleton (f : α →ₛ β) {s : Set α} (hs : MeasurableSet s) {r : β}
(hr : r ≠ 0) : restrict f s ⁻¹' {r} = s ∩ f ⁻¹' {r} :=
f.restrict_preimage hs hr.symm
theorem mem_restrict_range {r : β} {s : Set α} {f : α →ₛ β} (hs : MeasurableSet s) :
r ∈ (restrict f s).range ↔ r = 0 ∧ s ≠ univ ∨ r ∈ f '' s := by
rw [← Finset.mem_coe, coe_range, coe_restrict _ hs, mem_range_indicator]
open scoped Classical in
theorem mem_image_of_mem_range_restrict {r : β} {s : Set α} {f : α →ₛ β}
(hr : r ∈ (restrict f s).range) (h0 : r ≠ 0) : r ∈ f '' s :=
if hs : MeasurableSet s then by simpa [mem_restrict_range hs, h0, -mem_range] using hr
else by
rw [restrict_of_not_measurable hs] at hr
exact (h0 <| eq_zero_of_mem_range_zero hr).elim
open scoped Classical in
@[gcongr, mono]
theorem restrict_mono [Preorder β] (s : Set α) {f g : α →ₛ β} (H : f ≤ g) :
f.restrict s ≤ g.restrict s :=
if hs : MeasurableSet s then fun x => by
simp only [coe_restrict _ hs, indicator_le_indicator (H x)]
else by simp only [restrict_of_not_measurable hs, le_refl]
end Restrict
section Approx
section
variable [SemilatticeSup β] [OrderBot β] [Zero β]
/-- Fix a sequence `i : ℕ → β`. Given a function `α → β`, its `n`-th approximation
by simple functions is defined so that in case `β = ℝ≥0∞` it sends each `a` to the supremum
of the set `{i k | k ≤ n ∧ i k ≤ f a}`, see `approx_apply` and `iSup_approx_apply` for details. -/
def approx (i : ℕ → β) (f : α → β) (n : ℕ) : α →ₛ β :=
(Finset.range n).sup fun k => restrict (const α (i k)) { a : α | i k ≤ f a }
open scoped Classical in
theorem approx_apply [TopologicalSpace β] [OrderClosedTopology β] [MeasurableSpace β]
[OpensMeasurableSpace β] {i : ℕ → β} {f : α → β} {n : ℕ} (a : α) (hf : Measurable f) :
(approx i f n : α →ₛ β) a = (Finset.range n).sup fun k => if i k ≤ f a then i k else 0 := by
dsimp only [approx]
rw [finset_sup_apply]
congr
funext k
rw [restrict_apply]
· simp only [coe_const, mem_setOf_eq, indicator_apply, Function.const_apply]
· exact hf measurableSet_Ici
theorem monotone_approx (i : ℕ → β) (f : α → β) : Monotone (approx i f) := fun _ _ h =>
Finset.sup_mono <| Finset.range_subset.2 h
theorem approx_comp [TopologicalSpace β] [OrderClosedTopology β] [MeasurableSpace β]
[OpensMeasurableSpace β] [MeasurableSpace γ] {i : ℕ → β} {f : γ → β} {g : α → γ} {n : ℕ} (a : α)
(hf : Measurable f) (hg : Measurable g) :
(approx i (f ∘ g) n : α →ₛ β) a = (approx i f n : γ →ₛ β) (g a) := by
rw [approx_apply _ hf, approx_apply _ (hf.comp hg), Function.comp_apply]
end
theorem iSup_approx_apply [TopologicalSpace β] [CompleteLattice β] [OrderClosedTopology β] [Zero β]
[MeasurableSpace β] [OpensMeasurableSpace β] (i : ℕ → β) (f : α → β) (a : α) (hf : Measurable f)
(h_zero : (0 : β) = ⊥) : ⨆ n, (approx i f n : α →ₛ β) a = ⨆ (k) (_ : i k ≤ f a), i k := by
refine le_antisymm (iSup_le fun n => ?_) (iSup_le fun k => iSup_le fun hk => ?_)
· rw [approx_apply a hf, h_zero]
refine Finset.sup_le fun k _ => ?_
split_ifs with h
· exact le_iSup_of_le k (le_iSup (fun _ : i k ≤ f a => i k) h)
· exact bot_le
· refine le_iSup_of_le (k + 1) ?_
rw [approx_apply a hf]
have : k ∈ Finset.range (k + 1) := Finset.mem_range.2 (Nat.lt_succ_self _)
refine le_trans (le_of_eq ?_) (Finset.le_sup this)
rw [if_pos hk]
end Approx
section EApprox
variable {f : α → ℝ≥0∞}
/-- A sequence of `ℝ≥0∞`s such that its range is the set of non-negative rational numbers. -/
def ennrealRatEmbed (n : ℕ) : ℝ≥0∞ :=
ENNReal.ofReal ((Encodable.decode (α := ℚ) n).getD (0 : ℚ))
theorem ennrealRatEmbed_encode (q : ℚ) :
ennrealRatEmbed (Encodable.encode q) = Real.toNNReal q := by
rw [ennrealRatEmbed, Encodable.encodek]; rfl
/-- Approximate a function `α → ℝ≥0∞` by a sequence of simple functions. -/
def eapprox : (α → ℝ≥0∞) → ℕ → α →ₛ ℝ≥0∞ :=
approx ennrealRatEmbed
theorem eapprox_lt_top (f : α → ℝ≥0∞) (n : ℕ) (a : α) : eapprox f n a < ∞ := by
simp only [eapprox, approx, finset_sup_apply, Finset.mem_range, ENNReal.bot_eq_zero, restrict]
rw [Finset.sup_lt_iff (α := ℝ≥0∞) WithTop.top_pos]
intro b _
split_ifs
· simp only [coe_zero, coe_piecewise, piecewise_eq_indicator, coe_const]
calc
{ a : α | ennrealRatEmbed b ≤ f a }.indicator (fun _ => ennrealRatEmbed b) a ≤
ennrealRatEmbed b :=
indicator_le_self _ _ a
_ < ⊤ := ENNReal.coe_lt_top
· exact WithTop.top_pos
@[mono]
theorem monotone_eapprox (f : α → ℝ≥0∞) : Monotone (eapprox f) :=
monotone_approx _ f
@[gcongr]
lemma eapprox_mono {m n : ℕ} (hmn : m ≤ n) : eapprox f m ≤ eapprox f n := monotone_eapprox _ hmn
lemma iSup_eapprox_apply (hf : Measurable f) (a : α) : ⨆ n, (eapprox f n : α →ₛ ℝ≥0∞) a = f a := by
rw [eapprox, iSup_approx_apply ennrealRatEmbed f a hf rfl]
refine le_antisymm (iSup_le fun i => iSup_le fun hi => hi) (le_of_not_gt ?_)
intro h
rcases ENNReal.lt_iff_exists_rat_btwn.1 h with ⟨q, _, lt_q, q_lt⟩
have :
(Real.toNNReal q : ℝ≥0∞) ≤ ⨆ (k : ℕ) (_ : ennrealRatEmbed k ≤ f a), ennrealRatEmbed k := by
refine le_iSup_of_le (Encodable.encode q) ?_
rw [ennrealRatEmbed_encode q]
exact le_iSup_of_le (le_of_lt q_lt) le_rfl
exact lt_irrefl _ (lt_of_le_of_lt this lt_q)
lemma iSup_coe_eapprox (hf : Measurable f) : ⨆ n, ⇑(eapprox f n) = f := by
simpa [funext_iff] using iSup_eapprox_apply hf
theorem eapprox_comp [MeasurableSpace γ] {f : γ → ℝ≥0∞} {g : α → γ} {n : ℕ} (hf : Measurable f)
(hg : Measurable g) : (eapprox (f ∘ g) n : α → ℝ≥0∞) = (eapprox f n : γ →ₛ ℝ≥0∞) ∘ g :=
funext fun a => approx_comp a hf hg
lemma tendsto_eapprox {f : α → ℝ≥0∞} (hf_meas : Measurable f) (a : α) :
Tendsto (fun n ↦ eapprox f n a) atTop (𝓝 (f a)) := by
nth_rw 2 [← iSup_coe_eapprox hf_meas]
rw [iSup_apply]
exact tendsto_atTop_iSup fun _ _ hnm ↦ monotone_eapprox f hnm a
/-- Approximate a function `α → ℝ≥0∞` by a series of simple functions taking their values
in `ℝ≥0`. -/
def eapproxDiff (f : α → ℝ≥0∞) : ℕ → α →ₛ ℝ≥0
| 0 => (eapprox f 0).map ENNReal.toNNReal
| n + 1 => (eapprox f (n + 1) - eapprox f n).map ENNReal.toNNReal
theorem sum_eapproxDiff (f : α → ℝ≥0∞) (n : ℕ) (a : α) :
(∑ k ∈ Finset.range (n + 1), (eapproxDiff f k a : ℝ≥0∞)) = eapprox f n a := by
induction' n with n IH
· simp only [Nat.zero_add, Finset.sum_singleton, Finset.range_one]
rfl
· rw [Finset.sum_range_succ, IH, eapproxDiff, coe_map, Function.comp_apply,
coe_sub, Pi.sub_apply, ENNReal.coe_toNNReal,
add_tsub_cancel_of_le (monotone_eapprox f (Nat.le_succ _) _)]
apply (lt_of_le_of_lt _ (eapprox_lt_top f (n + 1) a)).ne
rw [tsub_le_iff_right]
exact le_self_add
theorem tsum_eapproxDiff (f : α → ℝ≥0∞) (hf : Measurable f) (a : α) :
(∑' n, (eapproxDiff f n a : ℝ≥0∞)) = f a := by
simp_rw [ENNReal.tsum_eq_iSup_nat' (tendsto_add_atTop_nat 1), sum_eapproxDiff,
iSup_eapprox_apply hf a]
end EApprox
end Measurable
section Measure
variable {m : MeasurableSpace α} {μ ν : Measure α}
/-- Integral of a simple function whose codomain is `ℝ≥0∞`. -/
def lintegral {_m : MeasurableSpace α} (f : α →ₛ ℝ≥0∞) (μ : Measure α) : ℝ≥0∞ :=
∑ x ∈ f.range, x * μ (f ⁻¹' {x})
theorem lintegral_eq_of_subset (f : α →ₛ ℝ≥0∞) {s : Finset ℝ≥0∞}
(hs : ∀ x, f x ≠ 0 → μ (f ⁻¹' {f x}) ≠ 0 → f x ∈ s) :
f.lintegral μ = ∑ x ∈ s, x * μ (f ⁻¹' {x}) := by
refine Finset.sum_bij_ne_zero (fun r _ _ => r) ?_ ?_ ?_ ?_
· simpa only [forall_mem_range, mul_ne_zero_iff, and_imp]
· intros
assumption
· intro b _ hb
refine ⟨b, ?_, hb, rfl⟩
rw [mem_range, ← preimage_singleton_nonempty]
exact nonempty_of_measure_ne_zero (mul_ne_zero_iff.1 hb).2
· intros
rfl
theorem lintegral_eq_of_subset' (f : α →ₛ ℝ≥0∞) {s : Finset ℝ≥0∞} (hs : f.range \ {0} ⊆ s) :
f.lintegral μ = ∑ x ∈ s, x * μ (f ⁻¹' {x}) :=
f.lintegral_eq_of_subset fun x hfx _ =>
hs <| Finset.mem_sdiff.2 ⟨f.mem_range_self x, mt Finset.mem_singleton.1 hfx⟩
/-- Calculate the integral of `(g ∘ f)`, where `g : β → ℝ≥0∞` and `f : α →ₛ β`. -/
theorem map_lintegral (g : β → ℝ≥0∞) (f : α →ₛ β) :
(f.map g).lintegral μ = ∑ x ∈ f.range, g x * μ (f ⁻¹' {x}) := by
simp only [lintegral, range_map]
refine Finset.sum_image' _ fun b hb => ?_
rcases mem_range.1 hb with ⟨a, rfl⟩
rw [map_preimage_singleton, ← f.sum_measure_preimage_singleton, Finset.mul_sum]
refine Finset.sum_congr ?_ ?_
· congr
· intro x
simp only [Finset.mem_filter]
rintro ⟨_, h⟩
rw [h]
theorem add_lintegral (f g : α →ₛ ℝ≥0∞) : (f + g).lintegral μ = f.lintegral μ + g.lintegral μ :=
calc
(f + g).lintegral μ =
∑ x ∈ (pair f g).range, (x.1 * μ (pair f g ⁻¹' {x}) + x.2 * μ (pair f g ⁻¹' {x})) := by
rw [add_eq_map₂, map_lintegral]; exact Finset.sum_congr rfl fun a _ => add_mul _ _ _
_ = (∑ x ∈ (pair f g).range, x.1 * μ (pair f g ⁻¹' {x})) +
∑ x ∈ (pair f g).range, x.2 * μ (pair f g ⁻¹' {x}) := by
rw [Finset.sum_add_distrib]
_ = ((pair f g).map Prod.fst).lintegral μ + ((pair f g).map Prod.snd).lintegral μ := by
rw [map_lintegral, map_lintegral]
_ = lintegral f μ + lintegral g μ := rfl
theorem const_mul_lintegral (f : α →ₛ ℝ≥0∞) (x : ℝ≥0∞) :
(const α x * f).lintegral μ = x * f.lintegral μ :=
calc
(f.map fun a => x * a).lintegral μ = ∑ r ∈ f.range, x * r * μ (f ⁻¹' {r}) := map_lintegral _ _
_ = x * ∑ r ∈ f.range, r * μ (f ⁻¹' {r}) := by simp_rw [Finset.mul_sum, mul_assoc]
/-- Integral of a simple function `α →ₛ ℝ≥0∞` as a bilinear map. -/
def lintegralₗ {m : MeasurableSpace α} : (α →ₛ ℝ≥0∞) →ₗ[ℝ≥0∞] Measure α →ₗ[ℝ≥0∞] ℝ≥0∞ where
toFun f :=
{ toFun := lintegral f
map_add' := by simp [lintegral, mul_add, Finset.sum_add_distrib]
map_smul' := fun c μ => by
simp [lintegral, mul_left_comm _ c, Finset.mul_sum, Measure.smul_apply c] }
map_add' f g := LinearMap.ext fun _ => add_lintegral f g
map_smul' c f := LinearMap.ext fun _ => const_mul_lintegral f c
@[simp]
theorem zero_lintegral : (0 : α →ₛ ℝ≥0∞).lintegral μ = 0 :=
LinearMap.ext_iff.1 lintegralₗ.map_zero μ
theorem lintegral_add {ν} (f : α →ₛ ℝ≥0∞) : f.lintegral (μ + ν) = f.lintegral μ + f.lintegral ν :=
(lintegralₗ f).map_add μ ν
theorem lintegral_smul {R : Type*} [SMul R ℝ≥0∞] [IsScalarTower R ℝ≥0∞ ℝ≥0∞]
(f : α →ₛ ℝ≥0∞) (c : R) : f.lintegral (c • μ) = c • f.lintegral μ := by
simpa only [smul_one_smul] using (lintegralₗ f).map_smul (c • 1) μ
@[simp]
theorem lintegral_zero [MeasurableSpace α] (f : α →ₛ ℝ≥0∞) : f.lintegral 0 = 0 :=
(lintegralₗ f).map_zero
theorem lintegral_finset_sum {ι} (f : α →ₛ ℝ≥0∞) (μ : ι → Measure α) (s : Finset ι) :
f.lintegral (∑ i ∈ s, μ i) = ∑ i ∈ s, f.lintegral (μ i) :=
map_sum (lintegralₗ f) ..
theorem lintegral_sum {m : MeasurableSpace α} {ι} (f : α →ₛ ℝ≥0∞) (μ : ι → Measure α) :
f.lintegral (Measure.sum μ) = ∑' i, f.lintegral (μ i) := by
simp only [lintegral, Measure.sum_apply, f.measurableSet_preimage, ← Finset.tsum_subtype, ←
ENNReal.tsum_mul_left]
apply ENNReal.tsum_comm
open scoped Classical in
theorem restrict_lintegral (f : α →ₛ ℝ≥0∞) {s : Set α} (hs : MeasurableSet s) :
(restrict f s).lintegral μ = ∑ r ∈ f.range, r * μ (f ⁻¹' {r} ∩ s) :=
calc
(restrict f s).lintegral μ = ∑ r ∈ f.range, r * μ (restrict f s ⁻¹' {r}) :=
lintegral_eq_of_subset _ fun x hx =>
if hxs : x ∈ s then fun _ => by
simp only [f.restrict_apply hs, indicator_of_mem hxs, mem_range_self]
else False.elim <| hx <| by simp [*]
_ = ∑ r ∈ f.range, r * μ (f ⁻¹' {r} ∩ s) :=
Finset.sum_congr rfl <|
forall_mem_range.2 fun b =>
if hb : f b = 0 then by simp only [hb, zero_mul]
else by rw [restrict_preimage_singleton _ hs hb, inter_comm]
theorem lintegral_restrict {m : MeasurableSpace α} (f : α →ₛ ℝ≥0∞) (s : Set α) (μ : Measure α) :
f.lintegral (μ.restrict s) = ∑ y ∈ f.range, y * μ (f ⁻¹' {y} ∩ s) := by
simp only [lintegral, Measure.restrict_apply, f.measurableSet_preimage]
theorem restrict_lintegral_eq_lintegral_restrict (f : α →ₛ ℝ≥0∞) {s : Set α}
(hs : MeasurableSet s) : (restrict f s).lintegral μ = f.lintegral (μ.restrict s) := by
rw [f.restrict_lintegral hs, lintegral_restrict]
theorem lintegral_restrict_iUnion_of_directed {ι : Type*} [Countable ι]
(f : α →ₛ ℝ≥0∞) {s : ι → Set α} (hd : Directed (· ⊆ ·) s) (μ : Measure α) :
f.lintegral (μ.restrict (⋃ i, s i)) = ⨆ i, f.lintegral (μ.restrict (s i)) := by
simp only [lintegral, Measure.restrict_iUnion_apply_eq_iSup hd (measurableSet_preimage ..),
ENNReal.mul_iSup]
refine finsetSum_iSup fun i j ↦ (hd i j).imp fun k ⟨hik, hjk⟩ ↦ fun a ↦ ?_
-- TODO https://github.com/leanprover-community/mathlib4/pull/14739 make `gcongr` close this goal
constructor <;> · gcongr; refine Measure.restrict_mono ?_ le_rfl _; assumption
theorem const_lintegral (c : ℝ≥0∞) : (const α c).lintegral μ = c * μ univ := by
rw [lintegral]
cases isEmpty_or_nonempty α
· simp [μ.eq_zero_of_isEmpty]
· simp only [range_const, coe_const, Finset.sum_singleton]
unfold Function.const; rw [preimage_const_of_mem (mem_singleton c)]
| theorem const_lintegral_restrict (c : ℝ≥0∞) (s : Set α) :
(const α c).lintegral (μ.restrict s) = c * μ s := by
rw [const_lintegral, Measure.restrict_apply MeasurableSet.univ, univ_inter]
theorem restrict_const_lintegral (c : ℝ≥0∞) {s : Set α} (hs : MeasurableSet s) :
((const α c).restrict s).lintegral μ = c * μ s := by
rw [restrict_lintegral_eq_lintegral_restrict _ hs, const_lintegral_restrict]
@[gcongr]
theorem lintegral_mono_fun {f g : α →ₛ ℝ≥0∞} (h : f ≤ g) : f.lintegral μ ≤ g.lintegral μ := by
refine Monotone.of_left_le_map_sup (f := (lintegral · μ)) (fun f g ↦ ?_) h
calc
f.lintegral μ = ((pair f g).map Prod.fst).lintegral μ := by rw [map_fst_pair]
| Mathlib/MeasureTheory/Function/SimpleFunc.lean | 969 | 981 |
/-
Copyright (c) 2022 Damiano Testa. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Damiano Testa
-/
import Mathlib.Data.Finsupp.Defs
/-!
# Locus of unequal values of finitely supported functions
Let `α N` be two Types, assume that `N` has a `0` and let `f g : α →₀ N` be finitely supported
functions.
## Main definition
* `Finsupp.neLocus f g : Finset α`, the finite subset of `α` where `f` and `g` differ.
In the case in which `N` is an additive group, `Finsupp.neLocus f g` coincides with
`Finsupp.support (f - g)`.
-/
variable {α M N P : Type*}
namespace Finsupp
variable [DecidableEq α]
section NHasZero
variable [DecidableEq N] [Zero N] (f g : α →₀ N)
/-- Given two finitely supported functions `f g : α →₀ N`, `Finsupp.neLocus f g` is the `Finset`
where `f` and `g` differ. This generalizes `(f - g).support` to situations without subtraction. -/
def neLocus (f g : α →₀ N) : Finset α :=
(f.support ∪ g.support).filter fun x => f x ≠ g x
@[simp]
theorem mem_neLocus {f g : α →₀ N} {a : α} : a ∈ f.neLocus g ↔ f a ≠ g a := by
simpa only [neLocus, Finset.mem_filter, Finset.mem_union, mem_support_iff,
and_iff_right_iff_imp] using Ne.ne_or_ne _
theorem not_mem_neLocus {f g : α →₀ N} {a : α} : a ∉ f.neLocus g ↔ f a = g a :=
mem_neLocus.not.trans not_ne_iff
@[simp]
theorem coe_neLocus : ↑(f.neLocus g) = { x | f x ≠ g x } := by
ext
exact mem_neLocus
@[simp]
theorem neLocus_eq_empty {f g : α →₀ N} : f.neLocus g = ∅ ↔ f = g :=
⟨fun h =>
ext fun a => not_not.mp (mem_neLocus.not.mp (Finset.eq_empty_iff_forall_not_mem.mp h a)),
fun h => h ▸ by simp only [neLocus, Ne, eq_self_iff_true, not_true, Finset.filter_False]⟩
@[simp]
theorem nonempty_neLocus_iff {f g : α →₀ N} : (f.neLocus g).Nonempty ↔ f ≠ g :=
Finset.nonempty_iff_ne_empty.trans neLocus_eq_empty.not
theorem neLocus_comm : f.neLocus g = g.neLocus f := by
simp_rw [neLocus, Finset.union_comm, ne_comm]
@[simp]
theorem neLocus_zero_right : f.neLocus 0 = f.support := by
ext
rw [mem_neLocus, mem_support_iff, coe_zero, Pi.zero_apply]
@[simp]
theorem neLocus_zero_left : (0 : α →₀ N).neLocus f = f.support :=
(neLocus_comm _ _).trans (neLocus_zero_right _)
end NHasZero
section NeLocusAndMaps
theorem subset_mapRange_neLocus [DecidableEq N] [Zero N] [DecidableEq M] [Zero M] (f g : α →₀ N)
{F : N → M} (F0 : F 0 = 0) : (f.mapRange F F0).neLocus (g.mapRange F F0) ⊆ f.neLocus g :=
fun x => by simpa only [mem_neLocus, mapRange_apply, not_imp_not] using congr_arg F
theorem zipWith_neLocus_eq_left [DecidableEq N] [Zero M] [DecidableEq P] [Zero P] [Zero N]
{F : M → N → P} (F0 : F 0 0 = 0) (f : α →₀ M) (g₁ g₂ : α →₀ N)
(hF : ∀ f, Function.Injective fun g => F f g) :
(zipWith F F0 f g₁).neLocus (zipWith F F0 f g₂) = g₁.neLocus g₂ := by
ext
simpa only [mem_neLocus] using (hF _).ne_iff
theorem zipWith_neLocus_eq_right [DecidableEq M] [Zero M] [DecidableEq P] [Zero P] [Zero N]
{F : M → N → P} (F0 : F 0 0 = 0) (f₁ f₂ : α →₀ M) (g : α →₀ N)
(hF : ∀ g, Function.Injective fun f => F f g) :
(zipWith F F0 f₁ g).neLocus (zipWith F F0 f₂ g) = f₁.neLocus f₂ := by
ext
simpa only [mem_neLocus] using (hF _).ne_iff
theorem mapRange_neLocus_eq [DecidableEq N] [DecidableEq M] [Zero M] [Zero N] (f g : α →₀ N)
{F : N → M} (F0 : F 0 = 0) (hF : Function.Injective F) :
(f.mapRange F F0).neLocus (g.mapRange F F0) = f.neLocus g := by
ext
simpa only [mem_neLocus] using hF.ne_iff
end NeLocusAndMaps
variable [DecidableEq N]
@[simp]
theorem neLocus_add_left [AddLeftCancelMonoid N] (f g h : α →₀ N) :
(f + g).neLocus (f + h) = g.neLocus h :=
zipWith_neLocus_eq_left _ _ _ _ add_right_injective
@[simp]
theorem neLocus_add_right [AddRightCancelMonoid N] (f g h : α →₀ N) :
(f + h).neLocus (g + h) = f.neLocus g :=
zipWith_neLocus_eq_right _ _ _ _ add_left_injective
section AddGroup
variable [AddGroup N] (f f₁ f₂ g g₁ g₂ : α →₀ N)
@[simp]
theorem neLocus_neg_neg : neLocus (-f) (-g) = f.neLocus g :=
mapRange_neLocus_eq _ _ neg_zero neg_injective
theorem neLocus_neg : neLocus (-f) g = f.neLocus (-g) := by rw [← neLocus_neg_neg, neg_neg]
theorem neLocus_eq_support_sub : f.neLocus g = (f - g).support := by
rw [← neLocus_add_right _ _ (-g), add_neg_cancel, neLocus_zero_right, sub_eq_add_neg]
@[simp]
theorem neLocus_sub_left : neLocus (f - g₁) (f - g₂) = neLocus g₁ g₂ := by
simp only [sub_eq_add_neg, neLocus_add_left, neLocus_neg_neg]
@[simp]
theorem neLocus_sub_right : neLocus (f₁ - g) (f₂ - g) = neLocus f₁ f₂ := by
simpa only [sub_eq_add_neg] using neLocus_add_right _ _ _
@[simp]
theorem neLocus_self_add_right : neLocus f (f + g) = g.support := by
rw [← neLocus_zero_left, ← neLocus_add_left f 0 g, add_zero]
@[simp]
theorem neLocus_self_add_left : neLocus (f + g) f = g.support := by
rw [neLocus_comm, neLocus_self_add_right]
@[simp]
theorem neLocus_self_sub_right : neLocus f (f - g) = g.support := by
rw [sub_eq_add_neg, neLocus_self_add_right, support_neg]
@[simp]
| theorem neLocus_self_sub_left : neLocus (f - g) f = g.support := by
rw [neLocus_comm, neLocus_self_sub_right]
| Mathlib/Data/Finsupp/NeLocus.lean | 149 | 150 |
/-
Copyright (c) 2022 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Algebra.Group.Support
import Mathlib.Algebra.GroupWithZero.Action.Pointwise.Set
/-!
# Support of a function composed with a scalar action
We show that the support of `x ↦ f (c⁻¹ • x)` is equal to `c • support f`.
-/
open Pointwise
open Function Set
section Group
variable {α β γ : Type*} [Group α] [MulAction α β]
theorem mulSupport_comp_inv_smul [One γ] (c : α) (f : β → γ) :
(mulSupport fun x ↦ f (c⁻¹ • x)) = c • mulSupport f := by
ext x
simp only [mem_smul_set_iff_inv_smul_mem, mem_mulSupport]
/- Note: to_additive also automatically translates `SMul` to `VAdd`, so we give the additive version
manually. -/
theorem support_comp_inv_smul [Zero γ] (c : α) (f : β → γ) :
(support fun x ↦ f (c⁻¹ • x)) = c • support f := by
ext x
simp only [mem_smul_set_iff_inv_smul_mem, mem_support]
attribute [to_additive existing support_comp_inv_smul] mulSupport_comp_inv_smul
end Group
section GroupWithZero
variable {α β γ : Type*} [GroupWithZero α] [MulAction α β]
theorem mulSupport_comp_inv_smul₀ [One γ] {c : α} (hc : c ≠ 0) (f : β → γ) :
(mulSupport fun x ↦ f (c⁻¹ • x)) = c • mulSupport f := by
ext x
simp only [mem_smul_set_iff_inv_smul_mem₀ hc, mem_mulSupport]
|
/- Note: to_additive also automatically translates `SMul` to `VAdd`, so we give the additive version
manually. -/
theorem support_comp_inv_smul₀ [Zero γ] {c : α} (hc : c ≠ 0) (f : β → γ) :
| Mathlib/Data/Set/Pointwise/Support.lean | 48 | 51 |
/-
Copyright (c) 2022 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Yury Kudryashov
-/
import Mathlib.Analysis.Normed.Module.Convex
import Mathlib.Analysis.Normed.Module.Ray
import Mathlib.Analysis.NormedSpace.Pointwise
/-!
# Strictly convex spaces
This file defines strictly convex spaces. A normed space is strictly convex if all closed balls are
strictly convex. This does **not** mean that the norm is strictly convex (in fact, it never is).
## Main definitions
`StrictConvexSpace`: a typeclass saying that a given normed space over a normed linear ordered
field (e.g., `ℝ` or `ℚ`) is strictly convex. The definition requires strict convexity of a closed
ball of positive radius with center at the origin; strict convexity of any other closed ball follows
from this assumption.
## Main results
In a strictly convex space, we prove
- `strictConvex_closedBall`: a closed ball is strictly convex.
- `combo_mem_ball_of_ne`, `openSegment_subset_ball_of_ne`, `norm_combo_lt_of_ne`:
a nontrivial convex combination of two points in a closed ball belong to the corresponding open
ball;
- `norm_add_lt_of_not_sameRay`, `sameRay_iff_norm_add`, `dist_add_dist_eq_iff`:
the triangle inequality `dist x y + dist y z ≤ dist x z` is a strict inequality unless `y` belongs
to the segment `[x -[ℝ] z]`.
- `Isometry.affineIsometryOfStrictConvexSpace`: an isometry of `NormedAddTorsor`s for real
normed spaces, strictly convex in the case of the codomain, is an affine isometry.
We also provide several lemmas that can be used as alternative constructors for `StrictConvex ℝ E`:
- `StrictConvexSpace.of_strictConvex_unitClosedBall`: if `closed_ball (0 : E) 1` is strictly
convex, then `E` is a strictly convex space;
- `StrictConvexSpace.of_norm_add`: if `‖x + y‖ = ‖x‖ + ‖y‖` implies `SameRay ℝ x y` for all
nonzero `x y : E`, then `E` is a strictly convex space.
## Implementation notes
While the definition is formulated for any normed linear ordered field, most of the lemmas are
formulated only for the case `𝕜 = ℝ`.
## Tags
convex, strictly convex
-/
open Convex Pointwise Set Metric
/-- A *strictly convex space* is a normed space where the closed balls are strictly convex. We only
require balls of positive radius with center at the origin to be strictly convex in the definition,
then prove that any closed ball is strictly convex in `strictConvex_closedBall` below.
See also `StrictConvexSpace.of_strictConvex_unitClosedBall`. -/
@[mk_iff]
class StrictConvexSpace (𝕜 E : Type*) [NormedField 𝕜] [PartialOrder 𝕜]
[NormedAddCommGroup E] [NormedSpace 𝕜 E] : Prop where
strictConvex_closedBall : ∀ r : ℝ, 0 < r → StrictConvex 𝕜 (closedBall (0 : E) r)
variable (𝕜 : Type*) {E : Type*} [NormedField 𝕜] [PartialOrder 𝕜]
[NormedAddCommGroup E] [NormedSpace 𝕜 E]
/-- A closed ball in a strictly convex space is strictly convex. -/
theorem strictConvex_closedBall [StrictConvexSpace 𝕜 E] (x : E) (r : ℝ) :
StrictConvex 𝕜 (closedBall x r) := by
rcases le_or_lt r 0 with hr | hr
· exact (subsingleton_closedBall x hr).strictConvex
rw [← vadd_closedBall_zero]
exact (StrictConvexSpace.strictConvex_closedBall r hr).vadd _
variable [NormedSpace ℝ E]
/-- A real normed vector space is strictly convex provided that the unit ball is strictly convex. -/
theorem StrictConvexSpace.of_strictConvex_unitClosedBall [LinearMap.CompatibleSMul E E 𝕜 ℝ]
(h : StrictConvex 𝕜 (closedBall (0 : E) 1)) : StrictConvexSpace 𝕜 E :=
⟨fun r hr => by simpa only [smul_unitClosedBall_of_nonneg hr.le] using h.smul r⟩
@[deprecated (since := "2024-12-01")]
alias StrictConvexSpace.of_strictConvex_closed_unit_ball :=
StrictConvexSpace.of_strictConvex_unitClosedBall
/-- Strict convexity is equivalent to `‖a • x + b • y‖ < 1` for all `x` and `y` of norm at most `1`
and all strictly positive `a` and `b` such that `a + b = 1`. This lemma shows that it suffices to
check this for points of norm one and some `a`, `b` such that `a + b = 1`. -/
theorem StrictConvexSpace.of_norm_combo_lt_one
(h : ∀ x y : E, ‖x‖ = 1 → ‖y‖ = 1 → x ≠ y → ∃ a b : ℝ, a + b = 1 ∧ ‖a • x + b • y‖ < 1) :
StrictConvexSpace ℝ E := by
refine
StrictConvexSpace.of_strictConvex_unitClosedBall ℝ
((convex_closedBall _ _).strictConvex' fun x hx y hy hne => ?_)
rw [interior_closedBall (0 : E) one_ne_zero, closedBall_diff_ball,
mem_sphere_zero_iff_norm] at hx hy
rcases h x y hx hy hne with ⟨a, b, hab, hlt⟩
use b
rwa [AffineMap.lineMap_apply_module, interior_closedBall (0 : E) one_ne_zero, mem_ball_zero_iff,
sub_eq_iff_eq_add.2 hab.symm]
theorem StrictConvexSpace.of_norm_combo_ne_one
(h :
∀ x y : E,
‖x‖ = 1 → ‖y‖ = 1 → x ≠ y → ∃ a b : ℝ, 0 ≤ a ∧ 0 ≤ b ∧ a + b = 1 ∧ ‖a • x + b • y‖ ≠ 1) :
StrictConvexSpace ℝ E := by
refine StrictConvexSpace.of_strictConvex_unitClosedBall ℝ
((convex_closedBall _ _).strictConvex ?_)
simp only [interior_closedBall _ one_ne_zero, closedBall_diff_ball, Set.Pairwise,
frontier_closedBall _ one_ne_zero, mem_sphere_zero_iff_norm]
intro x hx y hy hne
rcases h x y hx hy hne with ⟨a, b, ha, hb, hab, hne'⟩
exact ⟨_, ⟨a, b, ha, hb, hab, rfl⟩, mt mem_sphere_zero_iff_norm.1 hne'⟩
theorem StrictConvexSpace.of_norm_add_ne_two
(h : ∀ ⦃x y : E⦄, ‖x‖ = 1 → ‖y‖ = 1 → x ≠ y → ‖x + y‖ ≠ 2) : StrictConvexSpace ℝ E := by
refine
StrictConvexSpace.of_norm_combo_ne_one fun x y hx hy hne =>
⟨1 / 2, 1 / 2, one_half_pos.le, one_half_pos.le, add_halves _, ?_⟩
rw [← smul_add, norm_smul, Real.norm_of_nonneg one_half_pos.le, one_div, ← div_eq_inv_mul, Ne,
div_eq_one_iff_eq (two_ne_zero' ℝ)]
exact h hx hy hne
theorem StrictConvexSpace.of_pairwise_sphere_norm_ne_two
(h : (sphere (0 : E) 1).Pairwise fun x y => ‖x + y‖ ≠ 2) : StrictConvexSpace ℝ E :=
StrictConvexSpace.of_norm_add_ne_two fun _ _ hx hy =>
h (mem_sphere_zero_iff_norm.2 hx) (mem_sphere_zero_iff_norm.2 hy)
/-- If `‖x + y‖ = ‖x‖ + ‖y‖` implies that `x y : E` are in the same ray, then `E` is a strictly
convex space. See also a more -/
theorem StrictConvexSpace.of_norm_add
(h : ∀ x y : E, ‖x‖ = 1 → ‖y‖ = 1 → ‖x + y‖ = 2 → SameRay ℝ x y) : StrictConvexSpace ℝ E := by
refine StrictConvexSpace.of_pairwise_sphere_norm_ne_two fun x hx y hy => mt fun h₂ => ?_
rw [mem_sphere_zero_iff_norm] at hx hy
exact (sameRay_iff_of_norm_eq (hx.trans hy.symm)).1 (h x y hx hy h₂)
variable [StrictConvexSpace ℝ E] {x y z : E} {a b r : ℝ}
/-- If `x ≠ y` belong to the same closed ball, then a convex combination of `x` and `y` with
positive coefficients belongs to the corresponding open ball. -/
theorem combo_mem_ball_of_ne (hx : x ∈ closedBall z r) (hy : y ∈ closedBall z r) (hne : x ≠ y)
(ha : 0 < a) (hb : 0 < b) (hab : a + b = 1) : a • x + b • y ∈ ball z r := by
rcases eq_or_ne r 0 with (rfl | hr)
· rw [closedBall_zero, mem_singleton_iff] at hx hy
exact (hne (hx.trans hy.symm)).elim
· simp only [← interior_closedBall _ hr] at hx hy ⊢
exact strictConvex_closedBall ℝ z r hx hy hne ha hb hab
/-- If `x ≠ y` belong to the same closed ball, then the open segment with endpoints `x` and `y` is
included in the corresponding open ball. -/
theorem openSegment_subset_ball_of_ne (hx : x ∈ closedBall z r) (hy : y ∈ closedBall z r)
(hne : x ≠ y) : openSegment ℝ x y ⊆ ball z r :=
(openSegment_subset_iff _).2 fun _ _ => combo_mem_ball_of_ne hx hy hne
/-- If `x` and `y` are two distinct vectors of norm at most `r`, then a convex combination of `x`
and `y` with positive coefficients has norm strictly less than `r`. -/
theorem norm_combo_lt_of_ne (hx : ‖x‖ ≤ r) (hy : ‖y‖ ≤ r) (hne : x ≠ y) (ha : 0 < a) (hb : 0 < b)
(hab : a + b = 1) : ‖a • x + b • y‖ < r := by
simp only [← mem_ball_zero_iff, ← mem_closedBall_zero_iff] at hx hy ⊢
exact combo_mem_ball_of_ne hx hy hne ha hb hab
/-- In a strictly convex space, if `x` and `y` are not in the same ray, then `‖x + y‖ < ‖x‖ + ‖y‖`.
-/
theorem norm_add_lt_of_not_sameRay (h : ¬SameRay ℝ x y) : ‖x + y‖ < ‖x‖ + ‖y‖ := by
simp only [sameRay_iff_inv_norm_smul_eq, not_or, ← Ne.eq_def] at h
rcases h with ⟨hx, hy, hne⟩
rw [← norm_pos_iff] at hx hy
have hxy : 0 < ‖x‖ + ‖y‖ := add_pos hx hy
have :=
combo_mem_ball_of_ne (inv_norm_smul_mem_unitClosedBall x)
(inv_norm_smul_mem_unitClosedBall y) hne (div_pos hx hxy) (div_pos hy hxy)
(by rw [← add_div, div_self hxy.ne'])
rwa [mem_ball_zero_iff, div_eq_inv_mul, div_eq_inv_mul, mul_smul, mul_smul, smul_inv_smul₀ hx.ne',
smul_inv_smul₀ hy.ne', ← smul_add, norm_smul, Real.norm_of_nonneg (inv_pos.2 hxy).le, ←
div_eq_inv_mul, div_lt_one hxy] at this
theorem lt_norm_sub_of_not_sameRay (h : ¬SameRay ℝ x y) : ‖x‖ - ‖y‖ < ‖x - y‖ := by
nth_rw 1 [← sub_add_cancel x y] at h ⊢
exact sub_lt_iff_lt_add.2 (norm_add_lt_of_not_sameRay fun H' => h <| H'.add_left SameRay.rfl)
theorem abs_lt_norm_sub_of_not_sameRay (h : ¬SameRay ℝ x y) : |‖x‖ - ‖y‖| < ‖x - y‖ := by
refine abs_sub_lt_iff.2 ⟨lt_norm_sub_of_not_sameRay h, ?_⟩
rw [norm_sub_rev]
exact lt_norm_sub_of_not_sameRay (mt SameRay.symm h)
/-- In a strictly convex space, two vectors `x`, `y` are in the same ray if and only if the triangle
inequality for `x` and `y` becomes an equality. -/
theorem sameRay_iff_norm_add : SameRay ℝ x y ↔ ‖x + y‖ = ‖x‖ + ‖y‖ :=
| ⟨SameRay.norm_add, fun h => Classical.not_not.1 fun h' => (norm_add_lt_of_not_sameRay h').ne h⟩
/-- If `x` and `y` are two vectors in a strictly convex space have the same norm and the norm of
| Mathlib/Analysis/Convex/StrictConvexSpace.lean | 192 | 194 |
/-
Copyright (c) 2020 Alexander Bentkamp, Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Alexander Bentkamp, Sébastien Gouëzel, Eric Wieser
-/
import Mathlib.Algebra.Algebra.RestrictScalars
import Mathlib.Algebra.CharP.Invertible
import Mathlib.Data.Complex.Basic
import Mathlib.LinearAlgebra.Matrix.ToLin
import Mathlib.Data.Real.Star
import Mathlib.Data.ZMod.Defs
/-!
# Complex number as a vector space over `ℝ`
This file contains the following instances:
* Any `•`-structure (`SMul`, `MulAction`, `DistribMulAction`, `Module`, `Algebra`) on
`ℝ` imbues a corresponding structure on `ℂ`. This includes the statement that `ℂ` is an `ℝ`
algebra.
* any complex vector space is a real vector space;
* any finite dimensional complex vector space is a finite dimensional real vector space;
* the space of `ℝ`-linear maps from a real vector space to a complex vector space is a complex
vector space.
It also defines bundled versions of four standard maps (respectively, the real part, the imaginary
part, the embedding of `ℝ` in `ℂ`, and the complex conjugate):
* `Complex.reLm` (`ℝ`-linear map);
* `Complex.imLm` (`ℝ`-linear map);
* `Complex.ofRealAm` (`ℝ`-algebra (homo)morphism);
* `Complex.conjAe` (`ℝ`-algebra equivalence).
It also provides a universal property of the complex numbers `Complex.lift`, which constructs a
`ℂ →ₐ[ℝ] A` into any `ℝ`-algebra `A` given a square root of `-1`.
In addition, this file provides a decomposition into `realPart` and `imaginaryPart` for any
element of a `StarModule` over `ℂ`.
## Notation
* `ℜ` and `ℑ` for the `realPart` and `imaginaryPart`, respectively, in the locale
`ComplexStarModule`.
-/
assert_not_exists NNReal
namespace Complex
open ComplexConjugate
open scoped SMul
variable {R : Type*} {S : Type*}
attribute [local ext] Complex.ext
/- The priority of the following instances has been manually lowered, as when they don't apply
they lead Lean to a very costly path, and most often they don't apply (most actions on `ℂ` don't
come from actions on `ℝ`). See https://github.com/leanprover-community/mathlib4/pull/11980 -/
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) [SMul R ℝ] [SMul S ℝ] [SMulCommClass R S ℝ] : SMulCommClass R S ℂ where
smul_comm r s x := by ext <;> simp [smul_re, smul_im, smul_comm]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) [SMul R S] [SMul R ℝ] [SMul S ℝ] [IsScalarTower R S ℝ] :
IsScalarTower R S ℂ where
smul_assoc r s x := by ext <;> simp [smul_re, smul_im, smul_assoc]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) [SMul R ℝ] [SMul Rᵐᵒᵖ ℝ] [IsCentralScalar R ℝ] :
IsCentralScalar R ℂ where
op_smul_eq_smul r x := by ext <;> simp [smul_re, smul_im, op_smul_eq_smul]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) mulAction [Monoid R] [MulAction R ℝ] : MulAction R ℂ where
one_smul x := by ext <;> simp [smul_re, smul_im, one_smul]
mul_smul r s x := by ext <;> simp [smul_re, smul_im, mul_smul]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) distribSMul [DistribSMul R ℝ] : DistribSMul R ℂ where
smul_add r x y := by ext <;> simp [smul_re, smul_im, smul_add]
smul_zero r := by ext <;> simp [smul_re, smul_im, smul_zero]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 90) [Semiring R] [DistribMulAction R ℝ] : DistribMulAction R ℂ :=
{ Complex.distribSMul, Complex.mulAction with }
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 100) instModule [Semiring R] [Module R ℝ] : Module R ℂ where
add_smul r s x := by ext <;> simp [smul_re, smul_im, add_smul]
zero_smul r := by ext <;> simp [smul_re, smul_im, zero_smul]
-- priority manually adjusted in https://github.com/leanprover-community/mathlib4/pull/11980
instance (priority := 95) instAlgebraOfReal [CommSemiring R] [Algebra R ℝ] : Algebra R ℂ where
algebraMap := Complex.ofRealHom.comp (algebraMap R ℝ)
smul := (· • ·)
smul_def' := fun r x => by ext <;> simp [smul_re, smul_im, Algebra.smul_def]
commutes' := fun r ⟨xr, xi⟩ => by ext <;> simp [smul_re, smul_im, Algebra.commutes]
instance : StarModule ℝ ℂ :=
⟨fun r x => by simp only [star_def, star_trivial, real_smul, map_mul, conj_ofReal]⟩
@[simp]
theorem coe_algebraMap : (algebraMap ℝ ℂ : ℝ → ℂ) = ((↑) : ℝ → ℂ) :=
rfl
section
variable {A : Type*} [Semiring A] [Algebra ℝ A]
/-- We need this lemma since `Complex.coe_algebraMap` diverts the simp-normal form away from
`AlgHom.commutes`. -/
@[simp]
theorem _root_.AlgHom.map_coe_real_complex (f : ℂ →ₐ[ℝ] A) (x : ℝ) : f x = algebraMap ℝ A x :=
f.commutes x
/-- Two `ℝ`-algebra homomorphisms from `ℂ` are equal if they agree on `Complex.I`. -/
@[ext]
theorem algHom_ext ⦃f g : ℂ →ₐ[ℝ] A⦄ (h : f I = g I) : f = g := by
ext ⟨x, y⟩
simp only [mk_eq_add_mul_I, map_add, AlgHom.map_coe_real_complex, map_mul, h]
end
open Submodule
/-- `ℂ` has a basis over `ℝ` given by `1` and `I`. -/
noncomputable def basisOneI : Basis (Fin 2) ℝ ℂ :=
Basis.ofEquivFun
{ toFun := fun z => ![z.re, z.im]
invFun := fun c => c 0 + c 1 • I
left_inv := fun z => by simp
right_inv := fun c => by
ext i
fin_cases i <;> simp
map_add' := fun z z' => by simp
map_smul' := fun c z => by simp }
@[simp]
theorem coe_basisOneI_repr (z : ℂ) : ⇑(basisOneI.repr z) = ![z.re, z.im] :=
rfl
@[simp]
theorem coe_basisOneI : ⇑basisOneI = ![1, I] :=
funext fun i =>
Basis.apply_eq_iff.mpr <|
Finsupp.ext fun j => by
fin_cases i <;> fin_cases j <;> simp
end Complex
/- Register as an instance (with low priority) the fact that a complex vector space is also a real
vector space. -/
instance (priority := 900) Module.complexToReal (E : Type*) [AddCommGroup E] [Module ℂ E] :
| Module ℝ E :=
RestrictScalars.module ℝ ℂ E
/- Register as an instance (with low priority) the fact that a complex algebra is also a real
algebra. -/
instance (priority := 900) Algebra.complexToReal {A : Type*} [Semiring A] [Algebra ℂ A] :
Algebra ℝ A :=
RestrictScalars.algebra ℝ ℂ A
| Mathlib/Data/Complex/Module.lean | 156 | 164 |
/-
Copyright (c) 2021 Aaron Anderson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Aaron Anderson
-/
import Mathlib.Data.Prod.Lex
import Mathlib.Data.Sigma.Lex
import Mathlib.Order.RelIso.Set
import Mathlib.Order.WellQuasiOrder
import Mathlib.Tactic.TFAE
/-!
# Well-founded sets
This file introduces versions of `WellFounded` and `WellQuasiOrdered` for sets.
## Main Definitions
* `Set.WellFoundedOn s r` indicates that the relation `r` is
well-founded when restricted to the set `s`.
* `Set.IsWF s` indicates that `<` is well-founded when restricted to `s`.
* `Set.PartiallyWellOrderedOn s r` indicates that the relation `r` is
partially well-ordered (also known as well quasi-ordered) when restricted to the set `s`.
* `Set.IsPWO s` indicates that any infinite sequence of elements in `s` contains an infinite
monotone subsequence. Note that this is equivalent to containing only two comparable elements.
## Main Results
* Higman's Lemma, `Set.PartiallyWellOrderedOn.partiallyWellOrderedOn_sublistForall₂`,
shows that if `r` is partially well-ordered on `s`, then `List.SublistForall₂` is partially
well-ordered on the set of lists of elements of `s`. The result was originally published by
Higman, but this proof more closely follows Nash-Williams.
* `Set.wellFoundedOn_iff` relates `well_founded_on` to the well-foundedness of a relation on the
original type, to avoid dealing with subtypes.
* `Set.IsWF.mono` shows that a subset of a well-founded subset is well-founded.
* `Set.IsWF.union` shows that the union of two well-founded subsets is well-founded.
* `Finset.isWF` shows that all `Finset`s are well-founded.
## TODO
* Prove that `s` is partial well ordered iff it has no infinite descending chain or antichain.
* Rename `Set.PartiallyWellOrderedOn` to `Set.WellQuasiOrderedOn` and `Set.IsPWO` to `Set.IsWQO`.
## References
* [Higman, *Ordering by Divisibility in Abstract Algebras*][Higman52]
* [Nash-Williams, *On Well-Quasi-Ordering Finite Trees*][Nash-Williams63]
-/
assert_not_exists OrderedSemiring
open scoped Function -- required for scoped `on` notation
variable {ι α β γ : Type*} {π : ι → Type*}
namespace Set
/-! ### Relations well-founded on sets -/
/-- `s.WellFoundedOn r` indicates that the relation `r` is `WellFounded` when restricted to `s`. -/
def WellFoundedOn (s : Set α) (r : α → α → Prop) : Prop :=
WellFounded (Subrel r (· ∈ s))
@[simp]
theorem wellFoundedOn_empty (r : α → α → Prop) : WellFoundedOn ∅ r :=
wellFounded_of_isEmpty _
section WellFoundedOn
variable {r r' : α → α → Prop}
section AnyRel
variable {f : β → α} {s t : Set α} {x y : α}
theorem wellFoundedOn_iff :
s.WellFoundedOn r ↔ WellFounded fun a b : α => r a b ∧ a ∈ s ∧ b ∈ s := by
have f : RelEmbedding (Subrel r (· ∈ s)) fun a b : α => r a b ∧ a ∈ s ∧ b ∈ s :=
⟨⟨(↑), Subtype.coe_injective⟩, by simp⟩
refine ⟨fun h => ?_, f.wellFounded⟩
rw [WellFounded.wellFounded_iff_has_min]
intro t ht
by_cases hst : (s ∩ t).Nonempty
· rw [← Subtype.preimage_coe_nonempty] at hst
rcases h.has_min (Subtype.val ⁻¹' t) hst with ⟨⟨m, ms⟩, mt, hm⟩
exact ⟨m, mt, fun x xt ⟨xm, xs, _⟩ => hm ⟨x, xs⟩ xt xm⟩
· rcases ht with ⟨m, mt⟩
exact ⟨m, mt, fun x _ ⟨_, _, ms⟩ => hst ⟨m, ⟨ms, mt⟩⟩⟩
@[simp]
theorem wellFoundedOn_univ : (univ : Set α).WellFoundedOn r ↔ WellFounded r := by
simp [wellFoundedOn_iff]
theorem _root_.WellFounded.wellFoundedOn : WellFounded r → s.WellFoundedOn r :=
InvImage.wf _
@[simp]
theorem wellFoundedOn_range : (range f).WellFoundedOn r ↔ WellFounded (r on f) := by
let f' : β → range f := fun c => ⟨f c, c, rfl⟩
refine ⟨fun h => (InvImage.wf f' h).mono fun c c' => id, fun h => ⟨?_⟩⟩
rintro ⟨_, c, rfl⟩
refine Acc.of_downward_closed f' ?_ _ ?_
· rintro _ ⟨_, c', rfl⟩ -
exact ⟨c', rfl⟩
· exact h.apply _
@[simp]
theorem wellFoundedOn_image {s : Set β} : (f '' s).WellFoundedOn r ↔ s.WellFoundedOn (r on f) := by
rw [image_eq_range]; exact wellFoundedOn_range
namespace WellFoundedOn
protected theorem induction (hs : s.WellFoundedOn r) (hx : x ∈ s) {P : α → Prop}
(hP : ∀ y ∈ s, (∀ z ∈ s, r z y → P z) → P y) : P x := by
let Q : s → Prop := fun y => P y
change Q ⟨x, hx⟩
refine WellFounded.induction hs ⟨x, hx⟩ ?_
simpa only [Subtype.forall]
protected theorem mono (h : t.WellFoundedOn r') (hle : r ≤ r') (hst : s ⊆ t) :
s.WellFoundedOn r := by
rw [wellFoundedOn_iff] at *
exact Subrelation.wf (fun xy => ⟨hle _ _ xy.1, hst xy.2.1, hst xy.2.2⟩) h
theorem mono' (h : ∀ (a) (_ : a ∈ s) (b) (_ : b ∈ s), r' a b → r a b) :
s.WellFoundedOn r → s.WellFoundedOn r' :=
Subrelation.wf @fun a b => h _ a.2 _ b.2
theorem subset (h : t.WellFoundedOn r) (hst : s ⊆ t) : s.WellFoundedOn r :=
h.mono le_rfl hst
open Relation
open List in
/-- `a` is accessible under the relation `r` iff `r` is well-founded on the downward transitive
closure of `a` under `r` (including `a` or not). -/
theorem acc_iff_wellFoundedOn {α} {r : α → α → Prop} {a : α} :
TFAE [Acc r a,
WellFoundedOn { b | ReflTransGen r b a } r,
WellFoundedOn { b | TransGen r b a } r] := by
tfae_have 1 → 2 := by
refine fun h => ⟨fun b => InvImage.accessible Subtype.val ?_⟩
rw [← acc_transGen_iff] at h ⊢
obtain h' | h' := reflTransGen_iff_eq_or_transGen.1 b.2
· rwa [h'] at h
· exact h.inv h'
tfae_have 2 → 3 := fun h => h.subset fun _ => TransGen.to_reflTransGen
tfae_have 3 → 1 := by
refine fun h => Acc.intro _ (fun b hb => (h.apply ⟨b, .single hb⟩).of_fibration Subtype.val ?_)
exact fun ⟨c, hc⟩ d h => ⟨⟨d, .head h hc⟩, h, rfl⟩
tfae_finish
end WellFoundedOn
end AnyRel
section IsStrictOrder
variable [IsStrictOrder α r] {s t : Set α}
instance IsStrictOrder.subset : IsStrictOrder α fun a b : α => r a b ∧ a ∈ s ∧ b ∈ s where
toIsIrrefl := ⟨fun a con => irrefl_of r a con.1⟩
toIsTrans := ⟨fun _ _ _ ab bc => ⟨trans_of r ab.1 bc.1, ab.2.1, bc.2.2⟩⟩
theorem wellFoundedOn_iff_no_descending_seq :
s.WellFoundedOn r ↔ ∀ f : ((· > ·) : ℕ → ℕ → Prop) ↪r r, ¬∀ n, f n ∈ s := by
simp only [wellFoundedOn_iff, RelEmbedding.wellFounded_iff_no_descending_seq, ← not_exists, ←
not_nonempty_iff, not_iff_not]
constructor
· rintro ⟨⟨f, hf⟩⟩
have H : ∀ n, f n ∈ s := fun n => (hf.2 n.lt_succ_self).2.2
refine ⟨⟨f, ?_⟩, H⟩
simpa only [H, and_true] using @hf
· rintro ⟨⟨f, hf⟩, hfs : ∀ n, f n ∈ s⟩
refine ⟨⟨f, ?_⟩⟩
simpa only [hfs, and_true] using @hf
theorem WellFoundedOn.union (hs : s.WellFoundedOn r) (ht : t.WellFoundedOn r) :
(s ∪ t).WellFoundedOn r := by
rw [wellFoundedOn_iff_no_descending_seq] at *
rintro f hf
rcases Nat.exists_subseq_of_forall_mem_union f hf with ⟨g, hg | hg⟩
exacts [hs (g.dual.ltEmbedding.trans f) hg, ht (g.dual.ltEmbedding.trans f) hg]
@[simp]
theorem wellFoundedOn_union : (s ∪ t).WellFoundedOn r ↔ s.WellFoundedOn r ∧ t.WellFoundedOn r :=
⟨fun h => ⟨h.subset subset_union_left, h.subset subset_union_right⟩, fun h =>
h.1.union h.2⟩
end IsStrictOrder
end WellFoundedOn
/-! ### Sets well-founded w.r.t. the strict inequality -/
section LT
variable [LT α] {s t : Set α}
/-- `s.IsWF` indicates that `<` is well-founded when restricted to `s`. -/
def IsWF (s : Set α) : Prop :=
WellFoundedOn s (· < ·)
@[simp]
theorem isWF_empty : IsWF (∅ : Set α) :=
wellFounded_of_isEmpty _
theorem IsWF.mono (h : IsWF t) (st : s ⊆ t) : IsWF s := h.subset st
theorem isWF_univ_iff : IsWF (univ : Set α) ↔ WellFoundedLT α := by
simp [IsWF, wellFoundedOn_iff, isWellFounded_iff]
theorem IsWF.of_wellFoundedLT [h : WellFoundedLT α] (s : Set α) : s.IsWF :=
(Set.isWF_univ_iff.2 h).mono s.subset_univ
@[deprecated IsWF.of_wellFoundedLT (since := "2025-01-16")]
theorem _root_.WellFounded.isWF (h : WellFounded ((· < ·) : α → α → Prop)) (s : Set α) : s.IsWF :=
have : WellFoundedLT α := ⟨h⟩
.of_wellFoundedLT s
end LT
section Preorder
variable [Preorder α] {s t : Set α} {a : α}
protected nonrec theorem IsWF.union (hs : IsWF s) (ht : IsWF t) : IsWF (s ∪ t) := hs.union ht
@[simp] theorem isWF_union : IsWF (s ∪ t) ↔ IsWF s ∧ IsWF t := wellFoundedOn_union
end Preorder
section Preorder
variable [Preorder α] {s t : Set α} {a : α}
theorem isWF_iff_no_descending_seq :
IsWF s ↔ ∀ f : ℕ → α, StrictAnti f → ¬∀ n, f (OrderDual.toDual n) ∈ s :=
wellFoundedOn_iff_no_descending_seq.trans
⟨fun H f hf => H ⟨⟨f, hf.injective⟩, hf.lt_iff_lt⟩, fun H f => H f fun _ _ => f.map_rel_iff.2⟩
end Preorder
/-! ### Partially well-ordered sets -/
/-- `s.PartiallyWellOrderedOn r` indicates that the relation `r` is `WellQuasiOrdered` when
restricted to `s`.
A set is partially well-ordered by a relation `r` when any infinite sequence contains two elements
where the first is related to the second by `r`. Equivalently, any antichain (see `IsAntichain`) is
finite, see `Set.partiallyWellOrderedOn_iff_finite_antichains`.
TODO: rename this to `WellQuasiOrderedOn` to match `WellQuasiOrdered`. -/
def PartiallyWellOrderedOn (s : Set α) (r : α → α → Prop) : Prop :=
WellQuasiOrdered (Subrel r (· ∈ s))
section PartiallyWellOrderedOn
variable {r : α → α → Prop} {r' : β → β → Prop} {f : α → β} {s : Set α} {t : Set α} {a : α}
theorem PartiallyWellOrderedOn.exists_lt (hs : s.PartiallyWellOrderedOn r) {f : ℕ → α}
(hf : ∀ n, f n ∈ s) : ∃ m n, m < n ∧ r (f m) (f n) :=
hs fun n ↦ ⟨_, hf n⟩
theorem partiallyWellOrderedOn_iff_exists_lt : s.PartiallyWellOrderedOn r ↔
∀ f : ℕ → α, (∀ n, f n ∈ s) → ∃ m n, m < n ∧ r (f m) (f n) :=
⟨PartiallyWellOrderedOn.exists_lt, fun hf f ↦ hf _ fun n ↦ (f n).2⟩
theorem PartiallyWellOrderedOn.mono (ht : t.PartiallyWellOrderedOn r) (h : s ⊆ t) :
s.PartiallyWellOrderedOn r :=
fun f ↦ ht (Set.inclusion h ∘ f)
@[simp]
theorem partiallyWellOrderedOn_empty (r : α → α → Prop) : PartiallyWellOrderedOn ∅ r :=
wellQuasiOrdered_of_isEmpty _
theorem PartiallyWellOrderedOn.union (hs : s.PartiallyWellOrderedOn r)
(ht : t.PartiallyWellOrderedOn r) : (s ∪ t).PartiallyWellOrderedOn r := by
intro f
obtain ⟨g, hgs | hgt⟩ := Nat.exists_subseq_of_forall_mem_union _ fun x ↦ (f x).2
· rcases hs.exists_lt hgs with ⟨m, n, hlt, hr⟩
exact ⟨g m, g n, g.strictMono hlt, hr⟩
· rcases ht.exists_lt hgt with ⟨m, n, hlt, hr⟩
exact ⟨g m, g n, g.strictMono hlt, hr⟩
@[simp]
theorem partiallyWellOrderedOn_union :
(s ∪ t).PartiallyWellOrderedOn r ↔ s.PartiallyWellOrderedOn r ∧ t.PartiallyWellOrderedOn r :=
⟨fun h ↦ ⟨h.mono subset_union_left, h.mono subset_union_right⟩, fun h ↦ h.1.union h.2⟩
theorem PartiallyWellOrderedOn.image_of_monotone_on (hs : s.PartiallyWellOrderedOn r)
(hf : ∀ a₁ ∈ s, ∀ a₂ ∈ s, r a₁ a₂ → r' (f a₁) (f a₂)) : (f '' s).PartiallyWellOrderedOn r' := by
rw [partiallyWellOrderedOn_iff_exists_lt] at *
intro g' hg'
choose g hgs heq using hg'
obtain rfl : f ∘ g = g' := funext heq
obtain ⟨m, n, hlt, hmn⟩ := hs g hgs
exact ⟨m, n, hlt, hf _ (hgs m) _ (hgs n) hmn⟩
-- TODO: prove this in terms of `IsAntichain.finite_of_wellQuasiOrdered`
theorem _root_.IsAntichain.finite_of_partiallyWellOrderedOn (ha : IsAntichain r s)
(hp : s.PartiallyWellOrderedOn r) : s.Finite := by
refine not_infinite.1 fun hi => ?_
obtain ⟨m, n, hmn, h⟩ := hp (hi.natEmbedding _)
exact hmn.ne ((hi.natEmbedding _).injective <| Subtype.val_injective <|
ha.eq (hi.natEmbedding _ m).2 (hi.natEmbedding _ n).2 h)
section IsRefl
variable [IsRefl α r]
protected theorem Finite.partiallyWellOrderedOn (hs : s.Finite) : s.PartiallyWellOrderedOn r :=
hs.to_subtype.wellQuasiOrdered _
theorem _root_.IsAntichain.partiallyWellOrderedOn_iff (hs : IsAntichain r s) :
s.PartiallyWellOrderedOn r ↔ s.Finite :=
⟨hs.finite_of_partiallyWellOrderedOn, Finite.partiallyWellOrderedOn⟩
@[simp]
theorem partiallyWellOrderedOn_singleton (a : α) : PartiallyWellOrderedOn {a} r :=
(finite_singleton a).partiallyWellOrderedOn
@[nontriviality]
theorem Subsingleton.partiallyWellOrderedOn (hs : s.Subsingleton) : PartiallyWellOrderedOn s r :=
hs.finite.partiallyWellOrderedOn
@[simp]
theorem partiallyWellOrderedOn_insert :
PartiallyWellOrderedOn (insert a s) r ↔ PartiallyWellOrderedOn s r := by
simp only [← singleton_union, partiallyWellOrderedOn_union,
partiallyWellOrderedOn_singleton, true_and]
protected theorem PartiallyWellOrderedOn.insert (h : PartiallyWellOrderedOn s r) (a : α) :
PartiallyWellOrderedOn (insert a s) r :=
partiallyWellOrderedOn_insert.2 h
theorem partiallyWellOrderedOn_iff_finite_antichains [IsSymm α r] :
s.PartiallyWellOrderedOn r ↔ ∀ t, t ⊆ s → IsAntichain r t → t.Finite := by
refine ⟨fun h t ht hrt => hrt.finite_of_partiallyWellOrderedOn (h.mono ht), ?_⟩
rw [partiallyWellOrderedOn_iff_exists_lt]
intro hs f hf
by_contra! H
refine infinite_range_of_injective (fun m n hmn => ?_) (hs _ (range_subset_iff.2 hf) ?_)
· obtain h | h | h := lt_trichotomy m n
· refine (H _ _ h ?_).elim
rw [hmn]
exact refl _
· exact h
· refine (H _ _ h ?_).elim
rw [hmn]
exact refl _
rintro _ ⟨m, hm, rfl⟩ _ ⟨n, hn, rfl⟩ hmn
obtain h | h := (ne_of_apply_ne _ hmn).lt_or_lt
· exact H _ _ h
· exact mt symm (H _ _ h)
end IsRefl
section IsPreorder
variable [IsPreorder α r]
theorem PartiallyWellOrderedOn.exists_monotone_subseq (h : s.PartiallyWellOrderedOn r) {f : ℕ → α}
(hf : ∀ n, f n ∈ s) : ∃ g : ℕ ↪o ℕ, ∀ m n : ℕ, m ≤ n → r (f (g m)) (f (g n)) :=
WellQuasiOrdered.exists_monotone_subseq h fun n ↦ ⟨_, hf n⟩
theorem partiallyWellOrderedOn_iff_exists_monotone_subseq :
s.PartiallyWellOrderedOn r ↔
∀ f : ℕ → α, (∀ n, f n ∈ s) → ∃ g : ℕ ↪o ℕ, ∀ m n : ℕ, m ≤ n → r (f (g m)) (f (g n)) := by
use PartiallyWellOrderedOn.exists_monotone_subseq
rw [PartiallyWellOrderedOn, wellQuasiOrdered_iff_exists_monotone_subseq]
exact fun H f ↦ H _ fun n ↦ (f n).2
protected theorem PartiallyWellOrderedOn.prod {t : Set β} (hs : PartiallyWellOrderedOn s r)
(ht : PartiallyWellOrderedOn t r') :
PartiallyWellOrderedOn (s ×ˢ t) fun x y : α × β => r x.1 y.1 ∧ r' x.2 y.2 := by
rw [partiallyWellOrderedOn_iff_exists_lt]
intro f hf
obtain ⟨g₁, h₁⟩ := hs.exists_monotone_subseq fun n => (hf n).1
obtain ⟨m, n, hlt, hle⟩ := ht.exists_lt fun n => (hf _).2
exact ⟨g₁ m, g₁ n, g₁.strictMono hlt, h₁ _ _ hlt.le, hle⟩
theorem PartiallyWellOrderedOn.wellFoundedOn (h : s.PartiallyWellOrderedOn r) :
s.WellFoundedOn fun a b => r a b ∧ ¬ r b a :=
h.wellFounded
end IsPreorder
end PartiallyWellOrderedOn
section IsPWO
variable [Preorder α] [Preorder β] {s t : Set α}
/-- A subset of a preorder is partially well-ordered when any infinite sequence contains
a monotone subsequence of length 2 (or equivalently, an infinite monotone subsequence). -/
def IsPWO (s : Set α) : Prop :=
PartiallyWellOrderedOn s (· ≤ ·)
nonrec theorem IsPWO.mono (ht : t.IsPWO) : s ⊆ t → s.IsPWO := ht.mono
nonrec theorem IsPWO.exists_monotone_subseq (h : s.IsPWO) {f : ℕ → α} (hf : ∀ n, f n ∈ s) :
∃ g : ℕ ↪o ℕ, Monotone (f ∘ g) :=
h.exists_monotone_subseq hf
theorem isPWO_iff_exists_monotone_subseq :
s.IsPWO ↔ ∀ f : ℕ → α, (∀ n, f n ∈ s) → ∃ g : ℕ ↪o ℕ, Monotone (f ∘ g) :=
partiallyWellOrderedOn_iff_exists_monotone_subseq
protected theorem IsPWO.isWF (h : s.IsPWO) : s.IsWF := by
simpa only [← lt_iff_le_not_le] using h.wellFoundedOn
nonrec theorem IsPWO.prod {t : Set β} (hs : s.IsPWO) (ht : t.IsPWO) : IsPWO (s ×ˢ t) :=
hs.prod ht
theorem IsPWO.image_of_monotoneOn (hs : s.IsPWO) {f : α → β} (hf : MonotoneOn f s) :
IsPWO (f '' s) :=
hs.image_of_monotone_on hf
theorem IsPWO.image_of_monotone (hs : s.IsPWO) {f : α → β} (hf : Monotone f) : IsPWO (f '' s) :=
hs.image_of_monotone_on (hf.monotoneOn _)
protected nonrec theorem IsPWO.union (hs : IsPWO s) (ht : IsPWO t) : IsPWO (s ∪ t) :=
hs.union ht
@[simp]
theorem isPWO_union : IsPWO (s ∪ t) ↔ IsPWO s ∧ IsPWO t :=
partiallyWellOrderedOn_union
protected theorem Finite.isPWO (hs : s.Finite) : IsPWO s := hs.partiallyWellOrderedOn
@[simp] theorem isPWO_of_finite [Finite α] : s.IsPWO := s.toFinite.isPWO
@[simp] theorem isPWO_singleton (a : α) : IsPWO ({a} : Set α) := (finite_singleton a).isPWO
@[simp] theorem isPWO_empty : IsPWO (∅ : Set α) := finite_empty.isPWO
protected theorem Subsingleton.isPWO (hs : s.Subsingleton) : IsPWO s := hs.finite.isPWO
@[simp]
theorem isPWO_insert {a} : IsPWO (insert a s) ↔ IsPWO s := by
simp only [← singleton_union, isPWO_union, isPWO_singleton, true_and]
protected theorem IsPWO.insert (h : IsPWO s) (a : α) : IsPWO (insert a s) :=
isPWO_insert.2 h
protected theorem Finite.isWF (hs : s.Finite) : IsWF s := hs.isPWO.isWF
@[simp] theorem isWF_singleton {a : α} : IsWF ({a} : Set α) := (finite_singleton a).isWF
protected theorem Subsingleton.isWF (hs : s.Subsingleton) : IsWF s := hs.isPWO.isWF
@[simp]
theorem isWF_insert {a} : IsWF (insert a s) ↔ IsWF s := by
simp only [← singleton_union, isWF_union, isWF_singleton, true_and]
protected theorem IsWF.insert (h : IsWF s) (a : α) : IsWF (insert a s) :=
isWF_insert.2 h
end IsPWO
section WellFoundedOn
variable {r : α → α → Prop} [IsStrictOrder α r] {s : Set α} {a : α}
protected theorem Finite.wellFoundedOn (hs : s.Finite) : s.WellFoundedOn r :=
letI := partialOrderOfSO r
hs.isWF
@[simp]
theorem wellFoundedOn_singleton : WellFoundedOn ({a} : Set α) r :=
(finite_singleton a).wellFoundedOn
protected theorem Subsingleton.wellFoundedOn (hs : s.Subsingleton) : s.WellFoundedOn r :=
hs.finite.wellFoundedOn
@[simp]
theorem wellFoundedOn_insert : WellFoundedOn (insert a s) r ↔ WellFoundedOn s r := by
simp only [← singleton_union, wellFoundedOn_union, wellFoundedOn_singleton, true_and]
@[simp]
theorem wellFoundedOn_sdiff_singleton : WellFoundedOn (s \ {a}) r ↔ WellFoundedOn s r := by
simp only [← wellFoundedOn_insert (a := a), insert_diff_singleton, mem_insert_iff, true_or,
insert_eq_of_mem]
protected theorem WellFoundedOn.insert (h : WellFoundedOn s r) (a : α) :
WellFoundedOn (insert a s) r :=
wellFoundedOn_insert.2 h
protected theorem WellFoundedOn.sdiff_singleton (h : WellFoundedOn s r) (a : α) :
WellFoundedOn (s \ {a}) r :=
wellFoundedOn_sdiff_singleton.2 h
lemma WellFoundedOn.mapsTo {α β : Type*} {r : α → α → Prop} (f : β → α)
{s : Set α} {t : Set β} (h : MapsTo f t s) (hw : s.WellFoundedOn r) :
t.WellFoundedOn (r on f) := by
exact InvImage.wf (fun x : t ↦ ⟨f x, h x.prop⟩) hw
end WellFoundedOn
section LinearOrder
variable [LinearOrder α] {s : Set α}
/-- In a linear order, the predicates `Set.IsPWO` and `Set.IsWF` are equivalent. -/
theorem isPWO_iff_isWF : s.IsPWO ↔ s.IsWF := by
change WellQuasiOrdered (· ≤ ·) ↔ WellFounded (· < ·)
rw [← wellQuasiOrderedLE_def, ← isWellFounded_iff, wellQuasiOrderedLE_iff_wellFoundedLT]
alias ⟨_, IsWF.isPWO⟩ := isPWO_iff_isWF
@[deprecated isPWO_iff_isWF (since := "2025-01-21")]
theorem isWF_iff_isPWO : s.IsWF ↔ s.IsPWO :=
isPWO_iff_isWF.symm
/--
If `α` is a linear order with well-founded `<`, then any set in it is a partially well-ordered set.
Note this does not hold without the linearity assumption.
-/
lemma IsPWO.of_linearOrder [WellFoundedLT α] (s : Set α) : s.IsPWO :=
(IsWF.of_wellFoundedLT s).isPWO
end LinearOrder
end Set
namespace Finset
variable {r : α → α → Prop}
@[simp]
protected theorem partiallyWellOrderedOn [IsRefl α r] (s : Finset α) :
(s : Set α).PartiallyWellOrderedOn r :=
s.finite_toSet.partiallyWellOrderedOn
@[simp]
protected theorem isPWO [Preorder α] (s : Finset α) : Set.IsPWO (↑s : Set α) :=
s.partiallyWellOrderedOn
@[simp]
protected theorem isWF [Preorder α] (s : Finset α) : Set.IsWF (↑s : Set α) :=
s.finite_toSet.isWF
@[simp]
protected theorem wellFoundedOn [IsStrictOrder α r] (s : Finset α) :
Set.WellFoundedOn (↑s : Set α) r :=
letI := partialOrderOfSO r
s.isWF
theorem wellFoundedOn_sup [IsStrictOrder α r] (s : Finset ι) {f : ι → Set α} :
(s.sup f).WellFoundedOn r ↔ ∀ i ∈ s, (f i).WellFoundedOn r :=
Finset.cons_induction_on s (by simp) fun a s ha hs => by simp [-sup_set_eq_biUnion, hs]
theorem partiallyWellOrderedOn_sup (s : Finset ι) {f : ι → Set α} :
(s.sup f).PartiallyWellOrderedOn r ↔ ∀ i ∈ s, (f i).PartiallyWellOrderedOn r :=
Finset.cons_induction_on s (by simp) fun a s ha hs => by simp [-sup_set_eq_biUnion, hs]
theorem isWF_sup [Preorder α] (s : Finset ι) {f : ι → Set α} :
(s.sup f).IsWF ↔ ∀ i ∈ s, (f i).IsWF :=
s.wellFoundedOn_sup
theorem isPWO_sup [Preorder α] (s : Finset ι) {f : ι → Set α} :
(s.sup f).IsPWO ↔ ∀ i ∈ s, (f i).IsPWO :=
s.partiallyWellOrderedOn_sup
@[simp]
theorem wellFoundedOn_bUnion [IsStrictOrder α r] (s : Finset ι) {f : ι → Set α} :
(⋃ i ∈ s, f i).WellFoundedOn r ↔ ∀ i ∈ s, (f i).WellFoundedOn r := by
simpa only [Finset.sup_eq_iSup] using s.wellFoundedOn_sup
@[simp]
theorem partiallyWellOrderedOn_bUnion (s : Finset ι) {f : ι → Set α} :
(⋃ i ∈ s, f i).PartiallyWellOrderedOn r ↔ ∀ i ∈ s, (f i).PartiallyWellOrderedOn r := by
simpa only [Finset.sup_eq_iSup] using s.partiallyWellOrderedOn_sup
@[simp]
theorem isWF_bUnion [Preorder α] (s : Finset ι) {f : ι → Set α} :
(⋃ i ∈ s, f i).IsWF ↔ ∀ i ∈ s, (f i).IsWF :=
s.wellFoundedOn_bUnion
@[simp]
theorem isPWO_bUnion [Preorder α] (s : Finset ι) {f : ι → Set α} :
(⋃ i ∈ s, f i).IsPWO ↔ ∀ i ∈ s, (f i).IsPWO :=
s.partiallyWellOrderedOn_bUnion
end Finset
namespace Set
section Preorder
variable [Preorder α] {s t : Set α} {a : α}
/-- `Set.IsWF.min` returns a minimal element of a nonempty well-founded set. -/
noncomputable nonrec def IsWF.min (hs : IsWF s) (hn : s.Nonempty) : α :=
hs.min univ (nonempty_iff_univ_nonempty.1 hn.to_subtype)
theorem IsWF.min_mem (hs : IsWF s) (hn : s.Nonempty) : hs.min hn ∈ s :=
(WellFounded.min hs univ (nonempty_iff_univ_nonempty.1 hn.to_subtype)).2
nonrec theorem IsWF.not_lt_min (hs : IsWF s) (hn : s.Nonempty) (ha : a ∈ s) : ¬a < hs.min hn :=
hs.not_lt_min univ (nonempty_iff_univ_nonempty.1 hn.to_subtype) (mem_univ (⟨a, ha⟩ : s))
theorem IsWF.min_of_subset_not_lt_min {hs : s.IsWF} {hsn : s.Nonempty} {ht : t.IsWF}
{htn : t.Nonempty} (hst : s ⊆ t) : ¬hs.min hsn < ht.min htn :=
ht.not_lt_min htn (hst (min_mem hs hsn))
@[simp]
theorem isWF_min_singleton (a) {hs : IsWF ({a} : Set α)} {hn : ({a} : Set α).Nonempty} :
hs.min hn = a :=
eq_of_mem_singleton (IsWF.min_mem hs hn)
theorem IsWF.min_eq_of_lt (hs : s.IsWF) (ha : a ∈ s) (hlt : ∀ b ∈ s, b ≠ a → a < b) :
hs.min (nonempty_of_mem ha) = a := by
by_contra h
exact (hs.not_lt_min (nonempty_of_mem ha) ha) (hlt (hs.min (nonempty_of_mem ha))
(hs.min_mem (nonempty_of_mem ha)) h)
end Preorder
section PartialOrder
variable [PartialOrder α] {s : Set α} {a : α}
theorem IsWF.min_eq_of_le (hs : s.IsWF) (ha : a ∈ s) (hle : ∀ b ∈ s, a ≤ b) :
hs.min (nonempty_of_mem ha) = a :=
(eq_of_le_of_not_lt (hle (hs.min (nonempty_of_mem ha))
(hs.min_mem (nonempty_of_mem ha))) (hs.not_lt_min (nonempty_of_mem ha) ha)).symm
end PartialOrder
section LinearOrder
variable [LinearOrder α] {s t : Set α} {a : α}
theorem IsWF.min_le (hs : s.IsWF) (hn : s.Nonempty) (ha : a ∈ s) : hs.min hn ≤ a :=
le_of_not_lt (hs.not_lt_min hn ha)
theorem IsWF.le_min_iff (hs : s.IsWF) (hn : s.Nonempty) : a ≤ hs.min hn ↔ ∀ b, b ∈ s → a ≤ b :=
⟨fun ha _b hb => le_trans ha (hs.min_le hn hb), fun h => h _ (hs.min_mem _)⟩
theorem IsWF.min_le_min_of_subset {hs : s.IsWF} {hsn : s.Nonempty} {ht : t.IsWF} {htn : t.Nonempty}
(hst : s ⊆ t) : ht.min htn ≤ hs.min hsn :=
(IsWF.le_min_iff _ _).2 fun _b hb => ht.min_le htn (hst hb)
theorem IsWF.min_union (hs : s.IsWF) (hsn : s.Nonempty) (ht : t.IsWF) (htn : t.Nonempty) :
(hs.union ht).min (union_nonempty.2 (Or.intro_left _ hsn)) =
Min.min (hs.min hsn) (ht.min htn) := by
refine le_antisymm (le_min (IsWF.min_le_min_of_subset subset_union_left)
(IsWF.min_le_min_of_subset subset_union_right)) ?_
rw [min_le_iff]
exact ((mem_union _ _ _).1 ((hs.union ht).min_mem (union_nonempty.2 (.inl hsn)))).imp
(hs.min_le _) (ht.min_le _)
end LinearOrder
end Set
open Set
section LocallyFiniteOrder
variable {s : Set α} [Preorder α] [LocallyFiniteOrder α]
theorem BddBelow.wellFoundedOn_lt : BddBelow s → s.WellFoundedOn (· < ·) := by
rw [wellFoundedOn_iff_no_descending_seq]
rintro ⟨a, ha⟩ f hf
refine infinite_range_of_injective f.injective ?_
exact (finite_Icc a <| f 0).subset <| range_subset_iff.2 <| fun n =>
⟨ha <| hf _,
antitone_iff_forall_lt.2 (fun a b hab => (f.map_rel_iff.2 hab).le) <| Nat.zero_le _⟩
theorem BddAbove.wellFoundedOn_gt : BddAbove s → s.WellFoundedOn (· > ·) :=
fun h => h.dual.wellFoundedOn_lt
theorem BddBelow.isWF : BddBelow s → IsWF s :=
BddBelow.wellFoundedOn_lt
end LocallyFiniteOrder
namespace Set.PartiallyWellOrderedOn
variable {r : α → α → Prop}
-- TODO: move this material to the main file on WQOs.
/-- In the context of partial well-orderings, a bad sequence is a nonincreasing sequence
whose range is contained in a particular set `s`. One exists if and only if `s` is not
partially well-ordered. -/
def IsBadSeq (r : α → α → Prop) (s : Set α) (f : ℕ → α) : Prop :=
(∀ n, f n ∈ s) ∧ ∀ m n : ℕ, m < n → ¬r (f m) (f n)
theorem iff_forall_not_isBadSeq (r : α → α → Prop) (s : Set α) :
s.PartiallyWellOrderedOn r ↔ ∀ f, ¬IsBadSeq r s f := by
rw [partiallyWellOrderedOn_iff_exists_lt]
exact forall_congr' fun f => by simp [IsBadSeq]
/-- This indicates that every bad sequence `g` that agrees with `f` on the first `n`
terms has `rk (f n) ≤ rk (g n)`. -/
def IsMinBadSeq (r : α → α → Prop) (rk : α → ℕ) (s : Set α) (n : ℕ) (f : ℕ → α) : Prop :=
∀ g : ℕ → α, (∀ m : ℕ, m < n → f m = g m) → rk (g n) < rk (f n) → ¬IsBadSeq r s g
/-- Given a bad sequence `f`, this constructs a bad sequence that agrees with `f` on the first `n`
terms and is minimal at `n`.
-/
noncomputable def minBadSeqOfBadSeq (r : α → α → Prop) (rk : α → ℕ) (s : Set α) (n : ℕ) (f : ℕ → α)
(hf : IsBadSeq r s f) :
{ g : ℕ → α // (∀ m : ℕ, m < n → f m = g m) ∧ IsBadSeq r s g ∧ IsMinBadSeq r rk s n g } := by
classical
have h : ∃ (k : ℕ) (g : ℕ → α), (∀ m, m < n → f m = g m) ∧ IsBadSeq r s g ∧ rk (g n) = k :=
⟨_, f, fun _ _ => rfl, hf, rfl⟩
obtain ⟨h1, h2, h3⟩ := Classical.choose_spec (Nat.find_spec h)
refine ⟨Classical.choose (Nat.find_spec h), h1, by convert h2, fun g hg1 hg2 con => ?_⟩
refine Nat.find_min h ?_ ⟨g, fun m mn => (h1 m mn).trans (hg1 m mn), con, rfl⟩
rwa [← h3]
theorem exists_min_bad_of_exists_bad (r : α → α → Prop) (rk : α → ℕ) (s : Set α) :
(∃ f, IsBadSeq r s f) → ∃ f, IsBadSeq r s f ∧ ∀ n, IsMinBadSeq r rk s n f := by
rintro ⟨f0, hf0 : IsBadSeq r s f0⟩
let fs : ∀ n : ℕ, { f : ℕ → α // IsBadSeq r s f ∧ IsMinBadSeq r rk s n f } := by
refine Nat.rec ?_ fun n fn => ?_
· exact ⟨(minBadSeqOfBadSeq r rk s 0 f0 hf0).1, (minBadSeqOfBadSeq r rk s 0 f0 hf0).2.2⟩
· exact ⟨(minBadSeqOfBadSeq r rk s (n + 1) fn.1 fn.2.1).1,
(minBadSeqOfBadSeq r rk s (n + 1) fn.1 fn.2.1).2.2⟩
have h : ∀ m n, m ≤ n → (fs m).1 m = (fs n).1 m := fun m n mn => by
obtain ⟨k, rfl⟩ := Nat.exists_eq_add_of_le mn; clear mn
induction' k with k ih
· rfl
· rw [ih, (minBadSeqOfBadSeq r rk s (m + k + 1) (fs (m + k)).1 (fs (m + k)).2.1).2.1 m
(Nat.lt_succ_iff.2 (Nat.add_le_add_left k.zero_le m))]
rfl
refine ⟨fun n => (fs n).1 n, ⟨fun n => (fs n).2.1.1 n, fun m n mn => ?_⟩, fun n g hg1 hg2 => ?_⟩
· dsimp
rw [h m n mn.le]
exact (fs n).2.1.2 m n mn
· refine (fs n).2.2 g (fun m mn => ?_) hg2
rw [← h m n mn.le, ← hg1 m mn]
theorem iff_not_exists_isMinBadSeq (rk : α → ℕ) {s : Set α} :
s.PartiallyWellOrderedOn r ↔ ¬∃ f, IsBadSeq r s f ∧ ∀ n, IsMinBadSeq r rk s n f := by
rw [iff_forall_not_isBadSeq, ← not_exists, not_congr]
constructor
· apply exists_min_bad_of_exists_bad
· rintro ⟨f, hf1, -⟩
exact ⟨f, hf1⟩
/-- Higman's Lemma, which states that for any reflexive, transitive relation `r` which is
partially well-ordered on a set `s`, the relation `List.SublistForall₂ r` is partially
well-ordered on the set of lists of elements of `s`. That relation is defined so that
`List.SublistForall₂ r l₁ l₂` whenever `l₁` related pointwise by `r` to a sublist of `l₂`. -/
theorem partiallyWellOrderedOn_sublistForall₂ (r : α → α → Prop) [IsPreorder α r]
{s : Set α} (h : s.PartiallyWellOrderedOn r) :
{ l : List α | ∀ x, x ∈ l → x ∈ s }.PartiallyWellOrderedOn (List.SublistForall₂ r) := by
rcases isEmpty_or_nonempty α
· exact subsingleton_of_subsingleton.partiallyWellOrderedOn
inhabit α
rw [iff_not_exists_isMinBadSeq List.length]
rintro ⟨f, hf1, hf2⟩
have hnil : ∀ n, f n ≠ List.nil := fun n con =>
hf1.2 n n.succ n.lt_succ_self (con.symm ▸ List.SublistForall₂.nil)
obtain ⟨g, hg⟩ := h.exists_monotone_subseq fun n => hf1.1 n _ (List.head!_mem_self (hnil n))
have hf' :=
hf2 (g 0) (fun n => if n < g 0 then f n else List.tail (f (g (n - g 0))))
(fun m hm => (if_pos hm).symm) ?_
swap
· simp only [if_neg (lt_irrefl (g 0)), Nat.sub_self]
rw [List.length_tail, ← Nat.pred_eq_sub_one]
exact Nat.pred_lt fun con => hnil _ (List.length_eq_zero_iff.1 con)
rw [IsBadSeq] at hf'
push_neg at hf'
obtain ⟨m, n, mn, hmn⟩ := hf' fun n x hx => by
split_ifs at hx with hn
exacts [hf1.1 _ _ hx, hf1.1 _ _ (List.tail_subset _ hx)]
by_cases hn : n < g 0
· apply hf1.2 m n mn
rwa [if_pos hn, if_pos (mn.trans hn)] at hmn
· obtain ⟨n', rfl⟩ := Nat.exists_eq_add_of_le (not_lt.1 hn)
rw [if_neg hn, add_comm (g 0) n', Nat.add_sub_cancel_right] at hmn
split_ifs at hmn with hm
· apply hf1.2 m (g n') (lt_of_lt_of_le hm (g.monotone n'.zero_le))
exact _root_.trans hmn (List.tail_sublistForall₂_self _)
· rw [← Nat.sub_lt_iff_lt_add' (le_of_not_lt hm)] at mn
apply hf1.2 _ _ (g.lt_iff_lt.2 mn)
rw [← List.cons_head!_tail (hnil (g (m - g 0))), ← List.cons_head!_tail (hnil (g n'))]
exact List.SublistForall₂.cons (hg _ _ (le_of_lt mn)) hmn
theorem subsetProdLex [PartialOrder α] [Preorder β] {s : Set (α ×ₗ β)}
(hα : ((fun (x : α ×ₗ β) => (ofLex x).1) '' s).IsPWO)
(hβ : ∀ a, {y | toLex (a, y) ∈ s}.IsPWO) : s.IsPWO := by
rw [IsPWO, partiallyWellOrderedOn_iff_exists_lt]
intro f hf
rw [isPWO_iff_exists_monotone_subseq] at hα
obtain ⟨g, hg⟩ : ∃ (g : (ℕ ↪o ℕ)), Monotone fun n => (ofLex f (g n)).1 :=
hα (fun n => (ofLex f n).1) (fun k => mem_image_of_mem (fun x => (ofLex x).1) (hf k))
have hhg : ∀ n, (ofLex f (g 0)).1 ≤ (ofLex f (g n)).1 := fun n => hg n.zero_le
by_cases hc : ∃ n, (ofLex f (g 0)).1 < (ofLex f (g n)).1
· obtain ⟨n, hn⟩ := hc
use (g 0), (g n)
constructor
· by_contra hx
simp_all
· exact Prod.Lex.toLex_le_toLex.mpr <| .inl hn
· have hhc : ∀ n, (ofLex f (g 0)).1 = (ofLex f (g n)).1 := by
intro n
rw [not_exists] at hc
exact (hhg n).eq_of_not_lt (hc n)
obtain ⟨g', hg'⟩ : ∃ g' : ℕ ↪o ℕ, Monotone ((fun n ↦ (ofLex f (g (g' n))).2)) := by
simp_rw [isPWO_iff_exists_monotone_subseq] at hβ
apply hβ (ofLex f (g 0)).1 fun n ↦ (ofLex f (g n)).2
intro n
rw [hhc n]
simpa using hf _
use (g (g' 0)), (g (g' 1))
suffices (f (g (g' 0))) ≤ (f (g (g' 1))) by simpa
· refine Prod.Lex.toLex_le_toLex.mpr <| .inr ⟨?_, ?_⟩
· exact (hhc (g' 0)).symm.trans (hhc (g' 1))
· exact hg' (Nat.zero_le 1)
theorem imageProdLex [Preorder α] [Preorder β] {s : Set (α ×ₗ β)}
(hαβ : s.IsPWO) : ((fun (x : α ×ₗ β) => (ofLex x).1)'' s).IsPWO :=
IsPWO.image_of_monotone hαβ Prod.Lex.monotone_fst
theorem fiberProdLex [Preorder α] [Preorder β] {s : Set (α ×ₗ β)}
(hαβ : s.IsPWO) (a : α) : {y | toLex (a, y) ∈ s}.IsPWO := by
let f : α ×ₗ β → β := fun x => (ofLex x).2
have h : {y | toLex (a, y) ∈ s} = f '' (s ∩ (fun x ↦ (ofLex x).1) ⁻¹' {a}) := by
ext x
simp [f]
rw [h]
apply IsPWO.image_of_monotoneOn (hαβ.mono inter_subset_left)
rintro b ⟨-, hb⟩ c ⟨-, hc⟩ hbc
simp only [mem_preimage, mem_singleton_iff] at hb hc
have : (ofLex b).1 < (ofLex c).1 ∨ (ofLex b).1 = (ofLex c).1 ∧ f b ≤ f c :=
Prod.Lex.toLex_le_toLex.mp hbc
simp_all only [lt_self_iff_false, true_and, false_or]
theorem ProdLex_iff [PartialOrder α] [Preorder β] {s : Set (α ×ₗ β)} :
s.IsPWO ↔
((fun (x : α ×ₗ β) ↦ (ofLex x).1) '' s).IsPWO ∧ ∀ a, {y | toLex (a, y) ∈ s}.IsPWO :=
⟨fun h ↦ ⟨imageProdLex h, fiberProdLex h⟩, fun h ↦ subsetProdLex h.1 h.2⟩
end Set.PartiallyWellOrderedOn
/-- A version of **Dickson's lemma** any subset of functions `Π s : σ, α s` is partially well
ordered, when `σ` is a `Fintype` and each `α s` is a linear well order.
This includes the classical case of Dickson's lemma that `ℕ ^ n` is a well partial order.
Some generalizations would be possible based on this proof, to include cases where the target is
partially well ordered, and also to consider the case of `Set.PartiallyWellOrderedOn` instead of
`Set.IsPWO`. -/
theorem Pi.isPWO {α : ι → Type*} [∀ i, LinearOrder (α i)] [∀ i, IsWellOrder (α i) (· < ·)]
[Finite ι] (s : Set (∀ i, α i)) : s.IsPWO := by
cases nonempty_fintype ι
suffices ∀ (s : Finset ι) (f : ℕ → ∀ s, α s),
∃ g : ℕ ↪o ℕ, ∀ ⦃a b : ℕ⦄, a ≤ b → ∀ x, x ∈ s → (f ∘ g) a x ≤ (f ∘ g) b x by
refine isPWO_iff_exists_monotone_subseq.2 fun f _ => ?_
simpa only [Finset.mem_univ, true_imp_iff] using this Finset.univ f
refine Finset.cons_induction ?_ ?_
· intro f
exists RelEmbedding.refl (· ≤ ·)
simp only [IsEmpty.forall_iff, imp_true_iff, forall_const, Finset.not_mem_empty]
· intro x s hx ih f
obtain ⟨g, hg⟩ := (IsPWO.of_linearOrder univ).exists_monotone_subseq (f := (f · x)) mem_univ
obtain ⟨g', hg'⟩ := ih (f ∘ g)
refine ⟨g'.trans g, fun a b hab => (Finset.forall_mem_cons _ _).2 ?_⟩
exact ⟨hg (OrderHomClass.mono g' hab), hg' hab⟩
section ProdLex
variable {rα : α → α → Prop} {rβ : β → β → Prop} {f : γ → α} {g : γ → β} {s : Set γ}
/-- Stronger version of `WellFounded.prod_lex`. Instead of requiring `rβ on g` to be well-founded,
we only require it to be well-founded on fibers of `f`. -/
theorem WellFounded.prod_lex_of_wellFoundedOn_fiber (hα : WellFounded (rα on f))
(hβ : ∀ a, (f ⁻¹' {a}).WellFoundedOn (rβ on g)) :
WellFounded (Prod.Lex rα rβ on fun c => (f c, g c)) := by
refine ((psigma_lex (wellFoundedOn_range.2 hα) fun a => hβ a).onFun
| (f := fun c => ⟨⟨_, c, rfl⟩, c, rfl⟩)).mono fun c c' h => ?_
obtain h' | h' := Prod.lex_iff.1 h
· exact PSigma.Lex.left _ _ h'
· dsimp only [InvImage, (· on ·)] at h' ⊢
convert PSigma.Lex.right (⟨_, c', rfl⟩ : range f) _ using 1; swap
exacts [⟨c, h'.1⟩, PSigma.subtype_ext (Subtype.ext h'.1) rfl, h'.2]
theorem Set.WellFoundedOn.prod_lex_of_wellFoundedOn_fiber (hα : s.WellFoundedOn (rα on f))
(hβ : ∀ a, (s ∩ f ⁻¹' {a}).WellFoundedOn (rβ on g)) :
s.WellFoundedOn (Prod.Lex rα rβ on fun c => (f c, g c)) :=
WellFounded.prod_lex_of_wellFoundedOn_fiber hα
fun a ↦ ((hβ a).onFun (f := fun x => ⟨x, x.1.2, x.2⟩)).mono (fun _ _ h ↦ ‹_›)
| Mathlib/Order/WellFoundedSet.lean | 873 | 885 |
/-
Copyright (c) 2019 Reid Barton. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Reid Barton, Johan Commelin, Bhavik Mehta
-/
import Mathlib.CategoryTheory.Equivalence
import Mathlib.CategoryTheory.Yoneda
/-!
# Adjunctions between functors
`F ⊣ G` represents the data of an adjunction between two functors
`F : C ⥤ D` and `G : D ⥤ C`. `F` is the left adjoint and `G` is the right adjoint.
We provide various useful constructors:
* `mkOfHomEquiv`
* `mk'`: construct an adjunction from the data of a hom set equivalence, unit and counit natural
transformations together with proofs of the equalities `homEquiv_unit` and `homEquiv_counit`
relating them to each other.
* `leftAdjointOfEquiv` / `rightAdjointOfEquiv`
construct a left/right adjoint of a given functor given the action on objects and
the relevant equivalence of morphism spaces.
* `adjunctionOfEquivLeft` / `adjunctionOfEquivRight` witness that these constructions
give adjunctions.
There are also typeclasses `IsLeftAdjoint` / `IsRightAdjoint`, which asserts the
existence of a adjoint functor. Given `[F.IsLeftAdjoint]`, a chosen right
adjoint can be obtained as `F.rightAdjoint`.
`Adjunction.comp` composes adjunctions.
`toEquivalence` upgrades an adjunction to an equivalence,
given witnesses that the unit and counit are pointwise isomorphisms.
Conversely `Equivalence.toAdjunction` recovers the underlying adjunction from an equivalence.
## Overview of the directory `CategoryTheory.Adjunction`
* Adjoint lifting theorems are in the directory `Lifting`.
* The file `AdjointFunctorTheorems` proves the adjoint functor theorems.
* The file `Comma` shows that for a functor `G : D ⥤ C` the data of an initial object in each
`StructuredArrow` category on `G` is equivalent to a left adjoint to `G`, as well as the dual.
* The file `Evaluation` shows that products and coproducts are adjoint to evaluation of functors.
* The file `FullyFaithful` characterizes when adjoints are full or faithful in terms of the unit
and counit.
* The file `Limits` proves that left adjoints preserve colimits and right adjoints preserve limits.
* The file `Mates` establishes the bijection between the 2-cells
```
L₁ R₁
C --→ D C ←-- D
G ↓ ↗ ↓ H G ↓ ↘ ↓ H
E --→ F E ←-- F
L₂ R₂
```
where `L₁ ⊣ R₁` and `L₂ ⊣ R₂`. Specializing to a pair of adjoints `L₁ L₂ : C ⥤ D`,
`R₁ R₂ : D ⥤ C`, it provides equivalences `(L₂ ⟶ L₁) ≃ (R₁ ⟶ R₂)` and `(L₂ ≅ L₁) ≃ (R₁ ≅ R₂)`.
* The file `Opposites` contains constructions to relate adjunctions of functors to adjunctions of
their opposites.
* The file `Reflective` defines reflective functors, i.e. fully faithful right adjoints. Note that
many facts about reflective functors are proved in the earlier file `FullyFaithful`.
* The file `Restrict` defines the restriction of an adjunction along fully faithful functors.
* The file `Triple` proves that in an adjoint triple, the left adjoint is fully faithful if and
only if the right adjoint is.
* The file `Unique` proves uniqueness of adjoints.
* The file `Whiskering` proves that functors `F : D ⥤ E` and `G : E ⥤ D` with an adjunction
`F ⊣ G`, induce adjunctions between the functor categories `C ⥤ D` and `C ⥤ E`,
and the functor categories `E ⥤ C` and `D ⥤ C`.
## Other files related to adjunctions
* The file `CategoryTheory.Monad.Adjunction` develops the basic relationship between adjunctions
and (co)monads. There it is also shown that given an adjunction `L ⊣ R` and an isomorphism
`L ⋙ R ≅ 𝟭 C`, the unit is an isomorphism, and similarly for the counit.
-/
namespace CategoryTheory
open Category
-- declare the `v`'s first; see `CategoryTheory.Category` for an explanation
universe v₁ v₂ v₃ u₁ u₂ u₃
variable {C : Type u₁} [Category.{v₁} C] {D : Type u₂} [Category.{v₂} D]
/-- `F ⊣ G` represents the data of an adjunction between two functors
`F : C ⥤ D` and `G : D ⥤ C`. `F` is the left adjoint and `G` is the right adjoint.
We use the unit-counit definition of an adjunction. There is a constructor `Adjunction.mk'`
which constructs an adjunction from the data of a hom set equivalence, a unit, and a counit,
together with proofs of the equalities `homEquiv_unit` and `homEquiv_counit` relating them to each
other.
There is also a constructor `Adjunction.mkOfHomEquiv` which constructs an adjunction from a natural
hom set equivalence.
To construct adjoints to a given functor, there are constructors `leftAdjointOfEquiv` and
`adjunctionOfEquivLeft` (as well as their duals). -/
@[stacks 0037]
structure Adjunction (F : C ⥤ D) (G : D ⥤ C) where
/-- The unit of an adjunction -/
unit : 𝟭 C ⟶ F.comp G
/-- The counit of an adjunction -/
counit : G.comp F ⟶ 𝟭 D
/-- Equality of the composition of the unit and counit with the identity `F ⟶ FGF ⟶ F = 𝟙` -/
left_triangle_components (X : C) :
F.map (unit.app X) ≫ counit.app (F.obj X) = 𝟙 (F.obj X) := by aesop_cat
/-- Equality of the composition of the unit and counit with the identity `G ⟶ GFG ⟶ G = 𝟙` -/
right_triangle_components (Y : D) :
unit.app (G.obj Y) ≫ G.map (counit.app Y) = 𝟙 (G.obj Y) := by aesop_cat
/-- The notation `F ⊣ G` stands for `Adjunction F G` representing that `F` is left adjoint to `G` -/
infixl:15 " ⊣ " => Adjunction
namespace Functor
/-- A class asserting the existence of a right adjoint. -/
class IsLeftAdjoint (left : C ⥤ D) : Prop where
exists_rightAdjoint : ∃ (right : D ⥤ C), Nonempty (left ⊣ right)
/-- A class asserting the existence of a left adjoint. -/
class IsRightAdjoint (right : D ⥤ C) : Prop where
exists_leftAdjoint : ∃ (left : C ⥤ D), Nonempty (left ⊣ right)
/-- A chosen left adjoint to a functor that is a right adjoint. -/
noncomputable def leftAdjoint (R : D ⥤ C) [IsRightAdjoint R] : C ⥤ D :=
(IsRightAdjoint.exists_leftAdjoint (right := R)).choose
/-- A chosen right adjoint to a functor that is a left adjoint. -/
noncomputable def rightAdjoint (L : C ⥤ D) [IsLeftAdjoint L] : D ⥤ C :=
(IsLeftAdjoint.exists_rightAdjoint (left := L)).choose
end Functor
/-- The adjunction associated to a functor known to be a left adjoint. -/
noncomputable def Adjunction.ofIsLeftAdjoint (left : C ⥤ D) [left.IsLeftAdjoint] :
left ⊣ left.rightAdjoint :=
Functor.IsLeftAdjoint.exists_rightAdjoint.choose_spec.some
/-- The adjunction associated to a functor known to be a right adjoint. -/
noncomputable def Adjunction.ofIsRightAdjoint (right : C ⥤ D) [right.IsRightAdjoint] :
right.leftAdjoint ⊣ right :=
Functor.IsRightAdjoint.exists_leftAdjoint.choose_spec.some
namespace Adjunction
attribute [reassoc (attr := simp)] left_triangle_components right_triangle_components
/-- The hom set equivalence associated to an adjunction. -/
@[simps -isSimp]
def homEquiv {F : C ⥤ D} {G : D ⥤ C} (adj : F ⊣ G) (X : C) (Y : D) :
(F.obj X ⟶ Y) ≃ (X ⟶ G.obj Y) where
toFun := fun f => adj.unit.app X ≫ G.map f
invFun := fun g => F.map g ≫ adj.counit.app Y
left_inv := fun f => by
dsimp
rw [F.map_comp, assoc, ← Functor.comp_map, adj.counit.naturality, ← assoc]
simp
right_inv := fun g => by
simp only [Functor.comp_obj, Functor.map_comp]
rw [← assoc, ← Functor.comp_map, ← adj.unit.naturality]
simp
alias homEquiv_unit := homEquiv_apply
alias homEquiv_counit := homEquiv_symm_apply
end Adjunction
-- These lemmas are not global simp lemmas because certain adjunctions
-- are constructed using `Adjunction.mkOfHomEquiv`, and we certainly
-- do not want `dsimp` to apply `homEquiv_unit` or `homEquiv_counit`
-- in that case. However, when proving general API results about adjunctions,
-- it may be advisable to add a local simp attribute to these lemmas.
attribute [local simp] Adjunction.homEquiv_unit Adjunction.homEquiv_counit
namespace Adjunction
@[ext]
lemma ext {F : C ⥤ D} {G : D ⥤ C} {adj adj' : F ⊣ G}
(h : adj.unit = adj'.unit) : adj = adj' := by
suffices h' : adj.counit = adj'.counit by cases adj; cases adj'; aesop
ext X
apply (adj.homEquiv _ _).injective
rw [Adjunction.homEquiv_unit, Adjunction.homEquiv_unit,
Adjunction.right_triangle_components, h, Adjunction.right_triangle_components]
section
variable {F : C ⥤ D} {G : D ⥤ C} (adj : F ⊣ G)
lemma isLeftAdjoint (adj : F ⊣ G) : F.IsLeftAdjoint := ⟨_, ⟨adj⟩⟩
| lemma isRightAdjoint (adj : F ⊣ G) : G.IsRightAdjoint := ⟨_, ⟨adj⟩⟩
instance (R : D ⥤ C) [R.IsRightAdjoint] : R.leftAdjoint.IsLeftAdjoint :=
(ofIsRightAdjoint R).isLeftAdjoint
| Mathlib/CategoryTheory/Adjunction/Basic.lean | 192 | 195 |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Patrick Massot, Casper Putz, Anne Baanen
-/
import Mathlib.LinearAlgebra.FreeModule.StrongRankCondition
import Mathlib.LinearAlgebra.GeneralLinearGroup
import Mathlib.LinearAlgebra.Matrix.Reindex
import Mathlib.Tactic.FieldSimp
import Mathlib.LinearAlgebra.Matrix.NonsingularInverse
import Mathlib.LinearAlgebra.Matrix.Basis
/-!
# Determinant of families of vectors
This file defines the determinant of an endomorphism, and of a family of vectors
with respect to some basis. For the determinant of a matrix, see the file
`LinearAlgebra.Matrix.Determinant`.
## Main definitions
In the list below, and in all this file, `R` is a commutative ring (semiring
is sometimes enough), `M` and its variations are `R`-modules, `ι`, `κ`, `n` and `m` are finite
types used for indexing.
* `Basis.det`: the determinant of a family of vectors with respect to a basis,
as a multilinear map
* `LinearMap.det`: the determinant of an endomorphism `f : End R M` as a
multiplicative homomorphism (if `M` does not have a finite `R`-basis, the
result is `1` instead)
* `LinearEquiv.det`: the determinant of an isomorphism `f : M ≃ₗ[R] M` as a
multiplicative homomorphism (if `M` does not have a finite `R`-basis, the
result is `1` instead)
## Tags
basis, det, determinant
-/
noncomputable section
open Matrix LinearMap Submodule Set Function
universe u v w
variable {R : Type*} [CommRing R]
variable {M : Type*} [AddCommGroup M] [Module R M]
variable {M' : Type*} [AddCommGroup M'] [Module R M']
variable {ι : Type*} [DecidableEq ι] [Fintype ι]
variable (e : Basis ι R M)
section Conjugate
variable {A : Type*} [CommRing A]
variable {m n : Type*}
/-- If `R^m` and `R^n` are linearly equivalent, then `m` and `n` are also equivalent. -/
def equivOfPiLEquivPi {R : Type*} [Finite m] [Finite n] [CommRing R] [Nontrivial R]
(e : (m → R) ≃ₗ[R] n → R) : m ≃ n :=
Basis.indexEquiv (Basis.ofEquivFun e.symm) (Pi.basisFun _ _)
namespace Matrix
variable [Fintype m] [Fintype n]
/-- If `M` and `M'` are each other's inverse matrices, they are square matrices up to
equivalence of types. -/
def indexEquivOfInv [Nontrivial A] [DecidableEq m] [DecidableEq n] {M : Matrix m n A}
{M' : Matrix n m A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) : m ≃ n :=
equivOfPiLEquivPi (toLin'OfInv hMM' hM'M)
theorem det_comm [DecidableEq n] (M N : Matrix n n A) : det (M * N) = det (N * M) := by
rw [det_mul, det_mul, mul_comm]
/-- If there exists a two-sided inverse `M'` for `M` (indexed differently),
then `det (N * M) = det (M * N)`. -/
theorem det_comm' [DecidableEq m] [DecidableEq n] {M : Matrix n m A} {N : Matrix m n A}
{M' : Matrix m n A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) : det (M * N) = det (N * M) := by
nontriviality A
-- Although `m` and `n` are different a priori, we will show they have the same cardinality.
-- This turns the problem into one for square matrices, which is easy.
let e := indexEquivOfInv hMM' hM'M
rw [← det_submatrix_equiv_self e, ← submatrix_mul_equiv _ _ _ (Equiv.refl n) _, det_comm,
submatrix_mul_equiv, Equiv.coe_refl, submatrix_id_id]
/-- If `M'` is a two-sided inverse for `M` (indexed differently), `det (M * N * M') = det N`.
See `Matrix.det_conj` and `Matrix.det_conj'` for the case when `M' = M⁻¹` or vice versa. -/
theorem det_conj_of_mul_eq_one [DecidableEq m] [DecidableEq n] {M : Matrix m n A}
{M' : Matrix n m A} {N : Matrix n n A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) :
det (M * N * M') = det N := by
rw [← det_comm' hM'M hMM', ← Matrix.mul_assoc, hM'M, Matrix.one_mul]
end Matrix
end Conjugate
namespace LinearMap
/-! ### Determinant of a linear map -/
variable {A : Type*} [CommRing A] [Module A M]
variable {κ : Type*} [Fintype κ]
/-- The determinant of `LinearMap.toMatrix` does not depend on the choice of basis. -/
theorem det_toMatrix_eq_det_toMatrix [DecidableEq κ] (b : Basis ι A M) (c : Basis κ A M)
(f : M →ₗ[A] M) : det (LinearMap.toMatrix b b f) = det (LinearMap.toMatrix c c f) := by
rw [← linearMap_toMatrix_mul_basis_toMatrix c b c, ← basis_toMatrix_mul_linearMap_toMatrix b c b,
Matrix.det_conj_of_mul_eq_one] <;>
rw [Basis.toMatrix_mul_toMatrix, Basis.toMatrix_self]
/-- The determinant of an endomorphism given a basis.
See `LinearMap.det` for a version that populates the basis non-computably.
Although the `Trunc (Basis ι A M)` parameter makes it slightly more convenient to switch bases,
there is no good way to generalize over universe parameters, so we can't fully state in `detAux`'s
type that it does not depend on the choice of basis. Instead you can use the `detAux_def''` lemma,
or avoid mentioning a basis at all using `LinearMap.det`.
-/
irreducible_def detAux : Trunc (Basis ι A M) → (M →ₗ[A] M) →* A :=
Trunc.lift
(fun b : Basis ι A M => detMonoidHom.comp (toMatrixAlgEquiv b : (M →ₗ[A] M) →* Matrix ι ι A))
fun b c => MonoidHom.ext <| det_toMatrix_eq_det_toMatrix b c
/-- Unfold lemma for `detAux`.
See also `detAux_def''` which allows you to vary the basis.
-/
theorem detAux_def' (b : Basis ι A M) (f : M →ₗ[A] M) :
LinearMap.detAux (Trunc.mk b) f = Matrix.det (LinearMap.toMatrix b b f) := by
rw [detAux]
rfl
theorem detAux_def'' {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (tb : Trunc <| Basis ι A M)
(b' : Basis ι' A M) (f : M →ₗ[A] M) :
LinearMap.detAux tb f = Matrix.det (LinearMap.toMatrix b' b' f) := by
induction tb using Trunc.induction_on with
| h b => rw [detAux_def', det_toMatrix_eq_det_toMatrix b b']
@[simp]
theorem detAux_id (b : Trunc <| Basis ι A M) : LinearMap.detAux b LinearMap.id = 1 :=
(LinearMap.detAux b).map_one
@[simp]
theorem detAux_comp (b : Trunc <| Basis ι A M) (f g : M →ₗ[A] M) :
LinearMap.detAux b (f.comp g) = LinearMap.detAux b f * LinearMap.detAux b g :=
(LinearMap.detAux b).map_mul f g
section
open scoped Classical in
-- Discourage the elaborator from unfolding `det` and producing a huge term by marking it
-- as irreducible.
/-- The determinant of an endomorphism independent of basis.
If there is no finite basis on `M`, the result is `1` instead.
-/
protected irreducible_def det : (M →ₗ[A] M) →* A :=
if H : ∃ s : Finset M, Nonempty (Basis s A M) then LinearMap.detAux (Trunc.mk H.choose_spec.some)
else 1
open scoped Classical in
theorem coe_det [DecidableEq M] :
⇑(LinearMap.det : (M →ₗ[A] M) →* A) =
if H : ∃ s : Finset M, Nonempty (Basis s A M) then
LinearMap.detAux (Trunc.mk H.choose_spec.some)
else 1 := by
ext
rw [LinearMap.det_def]
split_ifs
· congr -- use the correct `DecidableEq` instance
rfl
end
-- Auxiliary lemma, the `simp` normal form goes in the other direction
-- (using `LinearMap.det_toMatrix`)
theorem det_eq_det_toMatrix_of_finset [DecidableEq M] {s : Finset M} (b : Basis s A M)
(f : M →ₗ[A] M) : LinearMap.det f = Matrix.det (LinearMap.toMatrix b b f) := by
have : ∃ s : Finset M, Nonempty (Basis s A M) := ⟨s, ⟨b⟩⟩
rw [LinearMap.coe_det, dif_pos, detAux_def'' _ b] <;> assumption
@[simp]
theorem det_toMatrix (b : Basis ι A M) (f : M →ₗ[A] M) :
Matrix.det (toMatrix b b f) = LinearMap.det f := by
haveI := Classical.decEq M
rw [det_eq_det_toMatrix_of_finset b.reindexFinsetRange,
det_toMatrix_eq_det_toMatrix b b.reindexFinsetRange]
@[simp]
theorem det_toMatrix' {ι : Type*} [Fintype ι] [DecidableEq ι] (f : (ι → A) →ₗ[A] ι → A) :
Matrix.det (LinearMap.toMatrix' f) = LinearMap.det f := by simp [← toMatrix_eq_toMatrix']
@[simp]
theorem det_toLin (b : Basis ι R M) (f : Matrix ι ι R) :
LinearMap.det (Matrix.toLin b b f) = f.det := by
rw [← LinearMap.det_toMatrix b, LinearMap.toMatrix_toLin]
@[simp]
theorem det_toLin' (f : Matrix ι ι R) : LinearMap.det (Matrix.toLin' f) = Matrix.det f := by
simp only [← toLin_eq_toLin', det_toLin]
/-- To show `P (LinearMap.det f)` it suffices to consider `P (Matrix.det (toMatrix _ _ f))` and
`P 1`. -/
@[elab_as_elim]
theorem det_cases [DecidableEq M] {P : A → Prop} (f : M →ₗ[A] M)
(hb : ∀ (s : Finset M) (b : Basis s A M), P (Matrix.det (toMatrix b b f))) (h1 : P 1) :
P (LinearMap.det f) := by
classical
if H : ∃ s : Finset M, Nonempty (Basis s A M) then
obtain ⟨s, ⟨b⟩⟩ := H
rw [← det_toMatrix b]
exact hb s b
else
rwa [LinearMap.det_def, dif_neg H]
@[simp]
theorem det_comp (f g : M →ₗ[A] M) :
LinearMap.det (f.comp g) = LinearMap.det f * LinearMap.det g :=
LinearMap.det.map_mul f g
@[simp]
theorem det_id : LinearMap.det (LinearMap.id : M →ₗ[A] M) = 1 :=
LinearMap.det.map_one
/-- Multiplying a map by a scalar `c` multiplies its determinant by `c ^ dim M`. -/
@[simp]
theorem det_smul [Module.Free A M] (c : A) (f : M →ₗ[A] M) :
LinearMap.det (c • f) = c ^ Module.finrank A M * LinearMap.det f := by
nontriviality A
by_cases H : ∃ s : Finset M, Nonempty (Basis s A M)
· have : Module.Finite A M := by
rcases H with ⟨s, ⟨hs⟩⟩
exact Module.Finite.of_basis hs
simp only [← det_toMatrix (Module.finBasis A M), LinearEquiv.map_smul,
Fintype.card_fin, Matrix.det_smul]
· classical
have : Module.finrank A M = 0 := finrank_eq_zero_of_not_exists_basis H
simp [coe_det, H, this]
theorem det_zero' {ι : Type*} [Finite ι] [Nonempty ι] (b : Basis ι A M) :
LinearMap.det (0 : M →ₗ[A] M) = 0 := by
haveI := Classical.decEq ι
cases nonempty_fintype ι
rwa [← det_toMatrix b, LinearEquiv.map_zero, det_zero]
/-- In a finite-dimensional vector space, the zero map has determinant `1` in dimension `0`,
and `0` otherwise. We give a formula that also works in infinite dimension, where we define
the determinant to be `1`. -/
@[simp]
theorem det_zero [Module.Free A M] :
LinearMap.det (0 : M →ₗ[A] M) = (0 : A) ^ Module.finrank A M := by
simp only [← zero_smul A (1 : M →ₗ[A] M), det_smul, mul_one, MonoidHom.map_one]
theorem det_eq_one_of_not_module_finite (h : ¬Module.Finite R M) (f : M →ₗ[R] M) : f.det = 1 := by
rw [LinearMap.det, dif_neg, MonoidHom.one_apply]
exact fun ⟨_, ⟨b⟩⟩ ↦ h (Module.Finite.of_basis b)
theorem det_eq_one_of_subsingleton [Subsingleton M] (f : M →ₗ[R] M) :
LinearMap.det (f : M →ₗ[R] M) = 1 := by
have b : Basis (Fin 0) R M := Basis.empty M
rw [← f.det_toMatrix b]
exact Matrix.det_isEmpty
theorem det_eq_one_of_finrank_eq_zero {𝕜 : Type*} [Field 𝕜] {M : Type*} [AddCommGroup M]
[Module 𝕜 M] (h : Module.finrank 𝕜 M = 0) (f : M →ₗ[𝕜] M) :
LinearMap.det (f : M →ₗ[𝕜] M) = 1 := by
classical
refine @LinearMap.det_cases M _ 𝕜 _ _ _ (fun t => t = 1) f ?_ rfl
intro s b
have : IsEmpty s := by
rw [← Fintype.card_eq_zero_iff]
exact (Module.finrank_eq_card_basis b).symm.trans h
exact Matrix.det_isEmpty
/-- Conjugating a linear map by a linear equiv does not change its determinant. -/
@[simp]
theorem det_conj {N : Type*} [AddCommGroup N] [Module A N] (f : M →ₗ[A] M) (e : M ≃ₗ[A] N) :
LinearMap.det ((e : M →ₗ[A] N) ∘ₗ f ∘ₗ (e.symm : N →ₗ[A] M)) = LinearMap.det f := by
classical
by_cases H : ∃ s : Finset M, Nonempty (Basis s A M)
· rcases H with ⟨s, ⟨b⟩⟩
rw [← det_toMatrix b f, ← det_toMatrix (b.map e), toMatrix_comp (b.map e) b (b.map e),
toMatrix_comp (b.map e) b b, ← Matrix.mul_assoc, Matrix.det_conj_of_mul_eq_one]
· rw [← toMatrix_comp, LinearEquiv.comp_coe, e.symm_trans_self, LinearEquiv.refl_toLinearMap,
toMatrix_id]
· rw [← toMatrix_comp, LinearEquiv.comp_coe, e.self_trans_symm, LinearEquiv.refl_toLinearMap,
toMatrix_id]
· have H' : ¬∃ t : Finset N, Nonempty (Basis t A N) := by
contrapose! H
rcases H with ⟨s, ⟨b⟩⟩
exact ⟨_, ⟨(b.map e.symm).reindexFinsetRange⟩⟩
simp only [coe_det, H, H', MonoidHom.one_apply, dif_neg, not_false_eq_true]
/-- If a linear map is invertible, so is its determinant. -/
theorem isUnit_det {A : Type*} [CommRing A] [Module A M] (f : M →ₗ[A] M) (hf : IsUnit f) :
IsUnit (LinearMap.det f) := by
obtain ⟨g, hg⟩ : ∃ g, f.comp g = 1 := hf.exists_right_inv
have : LinearMap.det f * LinearMap.det g = 1 := by
simp only [← LinearMap.det_comp, hg, MonoidHom.map_one]
exact isUnit_of_mul_eq_one _ _ this
/-- If a linear map has determinant different from `1`, then the space is finite-dimensional. -/
theorem finiteDimensional_of_det_ne_one {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] (f : M →ₗ[𝕜] M)
(hf : LinearMap.det f ≠ 1) : FiniteDimensional 𝕜 M := by
by_cases H : ∃ s : Finset M, Nonempty (Basis s 𝕜 M)
· rcases H with ⟨s, ⟨hs⟩⟩
exact FiniteDimensional.of_fintype_basis hs
· classical simp [LinearMap.coe_det, H] at hf
/-- If the determinant of a map vanishes, then the map is not onto. -/
theorem range_lt_top_of_det_eq_zero {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] {f : M →ₗ[𝕜] M}
(hf : LinearMap.det f = 0) : LinearMap.range f < ⊤ := by
have : FiniteDimensional 𝕜 M := by simp [f.finiteDimensional_of_det_ne_one, hf]
contrapose hf
simp only [lt_top_iff_ne_top, Classical.not_not, ← isUnit_iff_range_eq_top] at hf
exact isUnit_iff_ne_zero.1 (f.isUnit_det hf)
/-- If the determinant of a map vanishes, then the map is not injective. -/
theorem bot_lt_ker_of_det_eq_zero {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] {f : M →ₗ[𝕜] M}
(hf : LinearMap.det f = 0) : ⊥ < LinearMap.ker f := by
have : FiniteDimensional 𝕜 M := by simp [f.finiteDimensional_of_det_ne_one, hf]
contrapose hf
simp only [bot_lt_iff_ne_bot, Classical.not_not, ← isUnit_iff_ker_eq_bot] at hf
exact isUnit_iff_ne_zero.1 (f.isUnit_det hf)
/-- When the function is over the base ring, the determinant is the evaluation at `1`. -/
@[simp] lemma det_ring (f : R →ₗ[R] R) : f.det = f 1 := by
simp [← det_toMatrix (Basis.singleton Unit R)]
lemma det_mulLeft (a : R) : (mulLeft R a).det = a := by simp
lemma det_mulRight (a : R) : (mulRight R a).det = a := by simp
theorem det_prodMap [Module.Free R M] [Module.Free R M'] [Module.Finite R M] [Module.Finite R M']
(f : Module.End R M) (f' : Module.End R M') :
(prodMap f f').det = f.det * f'.det := by
let b := Module.Free.chooseBasis R M
let b' := Module.Free.chooseBasis R M'
rw [← det_toMatrix (b.prod b'), ← det_toMatrix b, ← det_toMatrix b', toMatrix_prodMap,
det_fromBlocks_zero₂₁, det_toMatrix]
omit [DecidableEq ι] in
theorem det_pi [Module.Free R M] [Module.Finite R M] (f : ι → M →ₗ[R] M) :
(LinearMap.pi (fun i ↦ (f i).comp (LinearMap.proj i))).det = ∏ i, (f i).det := by
classical
let b := Module.Free.chooseBasis R M
let B := (Pi.basis (fun _ : ι ↦ b)).reindex <|
(Equiv.sigmaEquivProd _ _).trans (Equiv.prodComm _ _)
simp_rw [← LinearMap.det_toMatrix B, ← LinearMap.det_toMatrix b]
have : ((LinearMap.toMatrix B B) (LinearMap.pi fun i ↦ f i ∘ₗ LinearMap.proj i)) =
Matrix.blockDiagonal (fun i ↦ LinearMap.toMatrix b b (f i)) := by
ext ⟨i₁, i₂⟩ ⟨j₁, j₂⟩
unfold B
simp_rw [LinearMap.toMatrix_apply', Matrix.blockDiagonal_apply, Basis.coe_reindex,
Function.comp_apply, Basis.repr_reindex_apply, Equiv.symm_trans_apply, Equiv.prodComm_symm,
Equiv.prodComm_apply, Equiv.sigmaEquivProd_symm_apply, Prod.swap_prod_mk, Pi.basis_apply,
Pi.basis_repr, LinearMap.pi_apply, LinearMap.coe_comp, Function.comp_apply,
LinearMap.toMatrix_apply', LinearMap.coe_proj, Function.eval, Pi.single_apply]
split_ifs with h
· rw [h]
· simp only [map_zero, Finsupp.coe_zero, Pi.zero_apply]
rw [this, Matrix.det_blockDiagonal]
end LinearMap
namespace LinearEquiv
/-- On a `LinearEquiv`, the domain of `LinearMap.det` can be promoted to `Rˣ`. -/
protected def det : (M ≃ₗ[R] M) →* Rˣ :=
(Units.map (LinearMap.det : (M →ₗ[R] M) →* R)).comp
(LinearMap.GeneralLinearGroup.generalLinearEquiv R M).symm.toMonoidHom
@[simp]
theorem coe_det (f : M ≃ₗ[R] M) : ↑(LinearEquiv.det f) = LinearMap.det (f : M →ₗ[R] M) :=
rfl
@[simp]
theorem coe_inv_det (f : M ≃ₗ[R] M) : ↑(LinearEquiv.det f)⁻¹ = LinearMap.det (f.symm : M →ₗ[R] M) :=
rfl
@[simp]
theorem det_refl : LinearEquiv.det (LinearEquiv.refl R M) = 1 :=
Units.ext <| LinearMap.det_id
@[simp]
theorem det_trans (f g : M ≃ₗ[R] M) :
LinearEquiv.det (f.trans g) = LinearEquiv.det g * LinearEquiv.det f :=
map_mul _ g f
@[simp]
theorem det_symm (f : M ≃ₗ[R] M) : LinearEquiv.det f.symm = LinearEquiv.det f⁻¹ :=
map_inv _ f
/-- Conjugating a linear equiv by a linear equiv does not change its determinant. -/
@[simp]
theorem det_conj (f : M ≃ₗ[R] M) (e : M ≃ₗ[R] M') :
LinearEquiv.det ((e.symm.trans f).trans e) = LinearEquiv.det f := by
rw [← Units.eq_iff, coe_det, coe_det, ← comp_coe, ← comp_coe, LinearMap.det_conj]
attribute [irreducible] LinearEquiv.det
end LinearEquiv
/-- The determinants of a `LinearEquiv` and its inverse multiply to 1. -/
@[simp]
theorem LinearEquiv.det_mul_det_symm {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
LinearMap.det (f : M →ₗ[A] M) * LinearMap.det (f.symm : M →ₗ[A] M) = 1 := by
simp [← LinearMap.det_comp]
/-- The determinants of a `LinearEquiv` and its inverse multiply to 1. -/
@[simp]
theorem LinearEquiv.det_symm_mul_det {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
LinearMap.det (f.symm : M →ₗ[A] M) * LinearMap.det (f : M →ₗ[A] M) = 1 := by
simp [← LinearMap.det_comp]
-- Cannot be stated using `LinearMap.det` because `f` is not an endomorphism.
theorem LinearEquiv.isUnit_det (f : M ≃ₗ[R] M') (v : Basis ι R M) (v' : Basis ι R M') :
IsUnit (LinearMap.toMatrix v v' f).det := by
apply isUnit_det_of_left_inverse
simpa using (LinearMap.toMatrix_comp v v' v f.symm f).symm
/-- Specialization of `LinearEquiv.isUnit_det` -/
theorem LinearEquiv.isUnit_det' {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
IsUnit (LinearMap.det (f : M →ₗ[A] M)) :=
isUnit_of_mul_eq_one _ _ f.det_mul_det_symm
/-- The determinant of `f.symm` is the inverse of that of `f` when `f` is a linear equiv. -/
theorem LinearEquiv.det_coe_symm {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] (f : M ≃ₗ[𝕜] M) :
LinearMap.det (f.symm : M →ₗ[𝕜] M) = (LinearMap.det (f : M →ₗ[𝕜] M))⁻¹ := by
field_simp [IsUnit.ne_zero f.isUnit_det']
/-- Builds a linear equivalence from a linear map whose determinant in some bases is a unit. -/
@[simps]
def LinearEquiv.ofIsUnitDet {f : M →ₗ[R] M'} {v : Basis ι R M} {v' : Basis ι R M'}
(h : IsUnit (LinearMap.toMatrix v v' f).det) : M ≃ₗ[R] M' where
toFun := f
map_add' := f.map_add
map_smul' := f.map_smul
invFun := toLin v' v (toMatrix v v' f)⁻¹
left_inv x :=
calc toLin v' v (toMatrix v v' f)⁻¹ (f x)
_ = toLin v v ((toMatrix v v' f)⁻¹ * toMatrix v v' f) x := by
rw [toLin_mul v v' v, toLin_toMatrix, LinearMap.comp_apply]
_ = x := by simp [h]
right_inv x :=
calc f (toLin v' v (toMatrix v v' f)⁻¹ x)
_ = toLin v' v' (toMatrix v v' f * (toMatrix v v' f)⁻¹) x := by
rw [toLin_mul v' v v', LinearMap.comp_apply, toLin_toMatrix v v']
_ = x := by simp [h]
@[simp]
theorem LinearEquiv.coe_ofIsUnitDet {f : M →ₗ[R] M'} {v : Basis ι R M} {v' : Basis ι R M'}
(h : IsUnit (LinearMap.toMatrix v v' f).det) :
(LinearEquiv.ofIsUnitDet h : M →ₗ[R] M') = f := by
ext x
rfl
/-- Builds a linear equivalence from a linear map on a finite-dimensional vector space whose
determinant is nonzero. -/
abbrev LinearMap.equivOfDetNeZero {𝕜 : Type*} [Field 𝕜] {M : Type*} [AddCommGroup M] [Module 𝕜 M]
[FiniteDimensional 𝕜 M] (f : M →ₗ[𝕜] M) (hf : LinearMap.det f ≠ 0) : M ≃ₗ[𝕜] M :=
have : IsUnit (LinearMap.toMatrix (Module.finBasis 𝕜 M)
(Module.finBasis 𝕜 M) f).det := by
rw [LinearMap.det_toMatrix]
exact isUnit_iff_ne_zero.2 hf
LinearEquiv.ofIsUnitDet this
theorem LinearMap.associated_det_of_eq_comp (e : M ≃ₗ[R] M) (f f' : M →ₗ[R] M)
(h : ∀ x, f x = f' (e x)) : Associated (LinearMap.det f) (LinearMap.det f') := by
suffices Associated (LinearMap.det (f' ∘ₗ ↑e)) (LinearMap.det f') by
convert this using 2
ext x
exact h x
rw [← mul_one (LinearMap.det f'), LinearMap.det_comp]
exact Associated.mul_left _ (associated_one_iff_isUnit.mpr e.isUnit_det')
theorem LinearMap.associated_det_comp_equiv {N : Type*} [AddCommGroup N] [Module R N]
(f : N →ₗ[R] M) (e e' : M ≃ₗ[R] N) :
Associated (LinearMap.det (f ∘ₗ ↑e)) (LinearMap.det (f ∘ₗ ↑e')) := by
refine LinearMap.associated_det_of_eq_comp (e.trans e'.symm) _ _ ?_
intro x
simp only [LinearMap.comp_apply, LinearEquiv.coe_coe, LinearEquiv.trans_apply,
LinearEquiv.apply_symm_apply]
/-- The determinant of a family of vectors with respect to some basis, as an alternating
multilinear map. -/
nonrec def Basis.det : M [⋀^ι]→ₗ[R] R where
toMultilinearMap :=
MultilinearMap.mk' (fun v ↦ det (e.toMatrix v))
(fun v i x y ↦ by
simp only [e.toMatrix_update, map_add, Finsupp.coe_add, det_updateCol_add])
(fun u i c x ↦ by
simp only [e.toMatrix_update, Algebra.id.smul_eq_mul, LinearEquiv.map_smul]
apply det_updateCol_smul)
map_eq_zero_of_eq' := by
intro v i j h hij
dsimp
rw [← Function.update_eq_self i v, h, ← det_transpose, e.toMatrix_update, ← updateRow_transpose,
← e.toMatrix_transpose_apply]
apply det_zero_of_row_eq hij
rw [updateRow_ne hij.symm, updateRow_self]
theorem Basis.det_apply (v : ι → M) : e.det v = Matrix.det (e.toMatrix v) :=
rfl
theorem Basis.det_self : e.det e = 1 := by simp [e.det_apply]
@[simp]
theorem Basis.det_isEmpty [IsEmpty ι] : e.det = AlternatingMap.constOfIsEmpty R M ι 1 := by
ext v
exact Matrix.det_isEmpty
/-- `Basis.det` is not the zero map. -/
theorem Basis.det_ne_zero [Nontrivial R] : e.det ≠ 0 := fun h => by simpa [h] using e.det_self
theorem Basis.smul_det {G} [Group G] [DistribMulAction G M] [SMulCommClass G R M]
(g : G) (v : ι → M) :
(g • e).det v = e.det (g⁻¹ • v) := by
simp_rw [det_apply, toMatrix_smul_left]
theorem is_basis_iff_det {v : ι → M} :
LinearIndependent R v ∧ span R (Set.range v) = ⊤ ↔ IsUnit (e.det v) := by
constructor
· rintro ⟨hli, hspan⟩
set v' := Basis.mk hli hspan.ge
rw [e.det_apply]
convert LinearEquiv.isUnit_det (LinearEquiv.refl R M) v' e using 2
ext i j
simp [v']
· intro h
rw [Basis.det_apply, Basis.toMatrix_eq_toMatrix_constr] at h
set v' := Basis.map e (LinearEquiv.ofIsUnitDet h) with v'_def
have : ⇑v' = v := by
ext i
rw [v'_def, Basis.map_apply, LinearEquiv.ofIsUnitDet_apply, e.constr_basis]
rw [← this]
exact ⟨v'.linearIndependent, v'.span_eq⟩
theorem Basis.isUnit_det (e' : Basis ι R M) : IsUnit (e.det e') :=
(is_basis_iff_det e).mp ⟨e'.linearIndependent, e'.span_eq⟩
/-- Any alternating map to `R` where `ι` has the cardinality of a basis equals the determinant
map with respect to that basis, multiplied by the value of that alternating map on that basis. -/
theorem AlternatingMap.eq_smul_basis_det (f : M [⋀^ι]→ₗ[R] R) : f = f e • e.det := by
refine Basis.ext_alternating e fun i h => ?_
let σ : Equiv.Perm ι := Equiv.ofBijective i (Finite.injective_iff_bijective.1 h)
change f (e ∘ σ) = (f e • e.det) (e ∘ σ)
simp [AlternatingMap.map_perm, Basis.det_self]
@[simp]
theorem AlternatingMap.map_basis_eq_zero_iff {ι : Type*} [Finite ι] (e : Basis ι R M)
(f : M [⋀^ι]→ₗ[R] R) : f e = 0 ↔ f = 0 :=
⟨fun h => by
cases nonempty_fintype ι
letI := Classical.decEq ι
simpa [h] using f.eq_smul_basis_det e,
fun h => h.symm ▸ AlternatingMap.zero_apply _⟩
theorem AlternatingMap.map_basis_ne_zero_iff {ι : Type*} [Finite ι] (e : Basis ι R M)
(f : M [⋀^ι]→ₗ[R] R) : f e ≠ 0 ↔ f ≠ 0 :=
not_congr <| f.map_basis_eq_zero_iff e
variable {A : Type*} [CommRing A] [Module A M]
@[simp]
theorem Basis.det_comp (e : Basis ι A M) (f : M →ₗ[A] M) (v : ι → M) :
e.det (f ∘ v) = (LinearMap.det f) * e.det v := by
rw [Basis.det_apply, Basis.det_apply, ← f.det_toMatrix e, ← Matrix.det_mul,
e.toMatrix_eq_toMatrix_constr (f ∘ v), e.toMatrix_eq_toMatrix_constr v, ← toMatrix_comp,
e.constr_comp]
@[simp]
theorem Basis.det_comp_basis [Module A M'] (b : Basis ι A M) (b' : Basis ι A M') (f : M →ₗ[A] M') :
b'.det (f ∘ b) = LinearMap.det (f ∘ₗ (b'.equiv b (Equiv.refl ι) : M' →ₗ[A] M)) := by
rw [Basis.det_apply, ← LinearMap.det_toMatrix b', LinearMap.toMatrix_comp _ b, Matrix.det_mul,
LinearMap.toMatrix_basis_equiv, Matrix.det_one, mul_one]
congr 1; ext i j
rw [Basis.toMatrix_apply, LinearMap.toMatrix_apply, Function.comp_apply]
@[simp]
theorem Basis.det_basis (b : Basis ι A M) (b' : Basis ι A M) :
LinearMap.det (b'.equiv b (Equiv.refl ι)).toLinearMap = b'.det b :=
(b.det_comp_basis b' (LinearMap.id)).symm
theorem Basis.det_inv (b : Basis ι A M) (b' : Basis ι A M) :
(b.isUnit_det b').unit⁻¹ = b'.det b := by
rw [← Units.mul_eq_one_iff_inv_eq, IsUnit.unit_spec, ← Basis.det_basis, ← Basis.det_basis]
exact LinearEquiv.det_mul_det_symm _
theorem Basis.det_reindex {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M) (v : ι' → M)
(e : ι ≃ ι') : (b.reindex e).det v = b.det (v ∘ e) := by
rw [Basis.det_apply, Basis.toMatrix_reindex', det_reindexAlgEquiv, Basis.det_apply]
theorem Basis.det_reindex' {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M)
(e : ι ≃ ι') : (b.reindex e).det = b.det.domDomCongr e :=
AlternatingMap.ext fun _ => Basis.det_reindex _ _ _
theorem Basis.det_reindex_symm {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M)
(v : ι → M) (e : ι' ≃ ι) : (b.reindex e.symm).det (v ∘ e) = b.det v := by
rw [Basis.det_reindex, Function.comp_assoc, e.self_comp_symm, Function.comp_id]
@[simp]
theorem Basis.det_map (b : Basis ι R M) (f : M ≃ₗ[R] M') (v : ι → M') :
(b.map f).det v = b.det (f.symm ∘ v) := by
rw [Basis.det_apply, Basis.toMatrix_map, Basis.det_apply]
theorem Basis.det_map' (b : Basis ι R M) (f : M ≃ₗ[R] M') :
(b.map f).det = b.det.compLinearMap f.symm :=
AlternatingMap.ext <| b.det_map f
@[simp]
theorem Pi.basisFun_det : (Pi.basisFun R ι).det = Matrix.detRowAlternating := by
ext M
rw [Basis.det_apply, Basis.coePiBasisFun.toMatrix_eq_transpose, det_transpose]
theorem Pi.basisFun_det_apply (v : ι → ι → R) :
(Pi.basisFun R ι).det v = (Matrix.of v).det := by
rw [Pi.basisFun_det]
rfl
/-- If we fix a background basis `e`, then for any other basis `v`, we can characterise the
coordinates provided by `v` in terms of determinants relative to `e`. -/
theorem Basis.det_smul_mk_coord_eq_det_update {v : ι → M} (hli : LinearIndependent R v)
(hsp : ⊤ ≤ span R (range v)) (i : ι) :
e.det v • (Basis.mk hli hsp).coord i = e.det.toMultilinearMap.toLinearMap v i := by
apply (Basis.mk hli hsp).ext
intro k
rcases eq_or_ne k i with (rfl | hik) <;>
simp only [Algebra.id.smul_eq_mul, Basis.coe_mk, LinearMap.smul_apply, LinearMap.coe_mk,
MultilinearMap.toLinearMap_apply]
· rw [Basis.mk_coord_apply_eq, mul_one, update_eq_self]
congr
· rw [Basis.mk_coord_apply_ne hik, mul_zero, eq_comm]
exact e.det.map_eq_zero_of_eq _ (by simp [hik, Function.update_apply]) hik
/-- If a basis is multiplied columnwise by scalars `w : ι → Rˣ`, then the determinant with respect
to this basis is multiplied by the product of the inverse of these scalars. -/
theorem Basis.det_unitsSMul (e : Basis ι R M) (w : ι → Rˣ) :
(e.unitsSMul w).det = (↑(∏ i, w i)⁻¹ : R) • e.det := by
ext f
change
(Matrix.det fun i j => (e.unitsSMul w).repr (f j) i) =
(↑(∏ i, w i)⁻¹ : R) • Matrix.det fun i j => e.repr (f j) i
simp only [e.repr_unitsSMul]
convert Matrix.det_mul_column (fun i => (↑(w i)⁻¹ : R)) fun i j => e.repr (f j) i
simp [← Finset.prod_inv_distrib]
/-- The determinant of a basis constructed by `unitsSMul` is the product of the given units. -/
@[simp]
theorem Basis.det_unitsSMul_self (w : ι → Rˣ) : e.det (e.unitsSMul w) = ∏ i, (w i : R) := by
simp [Basis.det_apply]
/-- The determinant of a basis constructed by `isUnitSMul` is the product of the given units. -/
| @[simp]
theorem Basis.det_isUnitSMul {w : ι → R} (hw : ∀ i, IsUnit (w i)) :
e.det (e.isUnitSMul hw) = ∏ i, w i :=
e.det_unitsSMul_self _
| Mathlib/LinearAlgebra/Determinant.lean | 659 | 669 |
/-
Copyright (c) 2021 Aaron Anderson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Aaron Anderson
-/
import Mathlib.RingTheory.HahnSeries.Multiplication
/-!
# Summable families of Hahn Series
We introduce a notion of formal summability for families of Hahn series, and define a formal sum
function. This theory is applied to characterize invertible Hahn series whose coefficients are in a
commutative domain.
## Main Definitions
* A `HahnSeries.SummableFamily` is a family of Hahn series such that the union of the supports
is partially well-ordered and only finitely many are nonzero at any given coefficient. Note that
this is different from `Summable` in the valuation topology, because there are topologically
summable families that do not satisfy the axioms of `HahnSeries.SummableFamily`, and formally
summable families whose sums do not converge topologically.
* The formal sum, `HahnSeries.SummableFamily.hsum` can be bundled as a `LinearMap` via
`HahnSeries.SummableFamily.lsum`.
## Main results
* If `R` is a commutative domain, and `Γ` is a linearly ordered additive commutative group, then
a Hahn series is a unit if and only if its leading term is a unit in `R`.
## TODO
* Remove unnecessary domain hypotheses.
* More general summable families, e.g., define the evaluation homomorphism from a power series
ring taking `X` to a positive order element.
## References
- [J. van der Hoeven, *Operators on Generalized Power Series*][van_der_hoeven]
-/
open Finset Function
open Pointwise
noncomputable section
variable {Γ Γ' R V α β : Type*}
namespace HahnSeries
section
/-- A family of Hahn series whose formal coefficient-wise sum is a Hahn series. For each
coefficient of the sum to be well-defined, we require that only finitely many series are nonzero at
any given coefficient. For the formal sum to be a Hahn series, we require that the union of the
supports of the constituent series is partially well-ordered. -/
structure SummableFamily (Γ) (R) [PartialOrder Γ] [AddCommMonoid R] (α : Type*) where
/-- A parametrized family of Hahn series. -/
toFun : α → HahnSeries Γ R
isPWO_iUnion_support' : Set.IsPWO (⋃ a : α, (toFun a).support)
finite_co_support' : ∀ g : Γ, { a | (toFun a).coeff g ≠ 0 }.Finite
end
namespace SummableFamily
section AddCommMonoid
variable [PartialOrder Γ] [AddCommMonoid R]
instance : FunLike (SummableFamily Γ R α) α (HahnSeries Γ R) where
coe := toFun
coe_injective' | ⟨_, _, _⟩, ⟨_, _, _⟩, rfl => rfl
theorem isPWO_iUnion_support (s : SummableFamily Γ R α) : Set.IsPWO (⋃ a : α, (s a).support) :=
s.isPWO_iUnion_support'
theorem finite_co_support (s : SummableFamily Γ R α) (g : Γ) :
(Function.support fun a => (s a).coeff g).Finite :=
s.finite_co_support' g
theorem coe_injective : @Function.Injective (SummableFamily Γ R α) (α → HahnSeries Γ R) (⇑) :=
DFunLike.coe_injective
@[ext]
theorem ext {s t : SummableFamily Γ R α} (h : ∀ a : α, s a = t a) : s = t :=
DFunLike.ext s t h
instance : Add (SummableFamily Γ R α) :=
⟨fun x y =>
{ toFun := x + y
isPWO_iUnion_support' :=
(x.isPWO_iUnion_support.union y.isPWO_iUnion_support).mono
(by
rw [← Set.iUnion_union_distrib]
exact Set.iUnion_mono fun a => support_add_subset)
finite_co_support' := fun g =>
((x.finite_co_support g).union (y.finite_co_support g)).subset
(by
intro a ha
change (x a).coeff g + (y a).coeff g ≠ 0 at ha
rw [Set.mem_union, Function.mem_support, Function.mem_support]
contrapose! ha
rw [ha.1, ha.2, add_zero]) }⟩
instance : Zero (SummableFamily Γ R α) :=
⟨⟨0, by simp, by simp⟩⟩
instance : Inhabited (SummableFamily Γ R α) :=
⟨0⟩
@[simp]
theorem coe_add {s t : SummableFamily Γ R α} : ⇑(s + t) = s + t :=
rfl
theorem add_apply {s t : SummableFamily Γ R α} {a : α} : (s + t) a = s a + t a :=
rfl
@[simp]
theorem coe_zero : ((0 : SummableFamily Γ R α) : α → HahnSeries Γ R) = 0 :=
rfl
theorem zero_apply {a : α} : (0 : SummableFamily Γ R α) a = 0 :=
rfl
instance : AddCommMonoid (SummableFamily Γ R α) where
zero := 0
nsmul := nsmulRec
zero_add s := by
ext
apply zero_add
add_zero s := by
ext
apply add_zero
add_comm s t := by
ext
apply add_comm
add_assoc r s t := by
ext
apply add_assoc
/-- The coefficient function of a summable family, as a finsupp on the parameter type. -/
@[simps]
def coeff (s : SummableFamily Γ R α) (g : Γ) : α →₀ R where
support := (s.finite_co_support g).toFinset
toFun a := (s a).coeff g
mem_support_toFun a := by simp
@[simp]
theorem coeff_def (s : SummableFamily Γ R α) (a : α) (g : Γ) : s.coeff g a = (s a).coeff g :=
rfl
/-- The infinite sum of a `SummableFamily` of Hahn series. -/
def hsum (s : SummableFamily Γ R α) : HahnSeries Γ R where
coeff g := ∑ᶠ i, (s i).coeff g
isPWO_support' :=
s.isPWO_iUnion_support.mono fun g => by
contrapose
rw [Set.mem_iUnion, not_exists, Function.mem_support, Classical.not_not]
simp_rw [mem_support, Classical.not_not]
intro h
rw [finsum_congr h, finsum_zero]
@[simp]
theorem coeff_hsum {s : SummableFamily Γ R α} {g : Γ} : s.hsum.coeff g = ∑ᶠ i, (s i).coeff g :=
rfl
@[deprecated (since := "2025-01-31")] alias hsum_coeff := coeff_hsum
theorem support_hsum_subset {s : SummableFamily Γ R α} : s.hsum.support ⊆ ⋃ a : α, (s a).support :=
fun g hg => by
rw [mem_support, coeff_hsum, finsum_eq_sum _ (s.finite_co_support _)] at hg
obtain ⟨a, _, h2⟩ := exists_ne_zero_of_sum_ne_zero hg
rw [Set.mem_iUnion]
exact ⟨a, h2⟩
@[simp]
theorem hsum_add {s t : SummableFamily Γ R α} : (s + t).hsum = s.hsum + t.hsum := by
ext g
simp only [coeff_hsum, coeff_add, add_apply]
exact finsum_add_distrib (s.finite_co_support _) (t.finite_co_support _)
theorem coeff_hsum_eq_sum_of_subset {s : SummableFamily Γ R α} {g : Γ} {t : Finset α}
(h : { a | (s a).coeff g ≠ 0 } ⊆ t) : s.hsum.coeff g = ∑ i ∈ t, (s i).coeff g := by
simp only [coeff_hsum, finsum_eq_sum _ (s.finite_co_support _)]
exact sum_subset (Set.Finite.toFinset_subset.mpr h) (by simp)
@[deprecated (since := "2025-01-31")] alias hsum_coeff_eq_sum_of_subset :=
coeff_hsum_eq_sum_of_subset
theorem coeff_hsum_eq_sum {s : SummableFamily Γ R α} {g : Γ} :
s.hsum.coeff g = ∑ i ∈ (s.coeff g).support, (s i).coeff g := by
simp only [coeff_hsum, finsum_eq_sum _ (s.finite_co_support _), coeff_support]
@[deprecated (since := "2025-01-31")] alias hsum_coeff_eq_sum := coeff_hsum_eq_sum
/-- The summable family made of a single Hahn series. -/
@[simps]
def single (x : HahnSeries Γ R) : SummableFamily Γ R Unit where
toFun _ := x
isPWO_iUnion_support' :=
Eq.mpr (congrArg (fun s ↦ s.IsPWO) (Set.iUnion_const x.support)) x.isPWO_support
finite_co_support' g := Set.toFinite {a | ((fun _ ↦ x) a).coeff g ≠ 0}
@[simp]
theorem hsum_single (x : HahnSeries Γ R) : (single x).hsum = x := by
ext g
simp only [coeff_hsum, single_toFun, finsum_unique]
/-- A summable family induced by an equivalence of the parametrizing type. -/
@[simps]
def Equiv (e : α ≃ β) (s : SummableFamily Γ R α) : SummableFamily Γ R β where
toFun b := s (e.symm b)
isPWO_iUnion_support' := by
refine Set.IsPWO.mono s.isPWO_iUnion_support fun g => ?_
simp only [Set.mem_iUnion, mem_support, ne_eq, forall_exists_index]
exact fun b hg => Exists.intro (e.symm b) hg
finite_co_support' g :=
(Equiv.set_finite_iff e.subtypeEquivOfSubtype').mp <| s.finite_co_support' g
@[simp]
theorem hsum_equiv (e : α ≃ β) (s : SummableFamily Γ R α) : (Equiv e s).hsum = s.hsum := by
ext g
simp only [coeff_hsum, Equiv_toFun]
exact finsum_eq_of_bijective e.symm (Equiv.bijective e.symm) fun x => rfl
/-- The summable family given by multiplying every series in a summable family by a scalar. -/
@[simps]
def smulFamily [AddCommMonoid V] [SMulWithZero R V] (f : α → R) (s : SummableFamily Γ V α) :
SummableFamily Γ V α where
toFun a := (f a) • s a
isPWO_iUnion_support' := by
refine Set.IsPWO.mono s.isPWO_iUnion_support fun g hg => ?_
simp_all only [Set.mem_iUnion, mem_support, coeff_smul, ne_eq]
obtain ⟨i, hi⟩ := hg
exact Exists.intro i <| right_ne_zero_of_smul hi
finite_co_support' g := by
refine Set.Finite.subset (s.finite_co_support g) fun i hi => ?_
simp_all only [coeff_smul, ne_eq, Set.mem_setOf_eq, Function.mem_support]
exact right_ne_zero_of_smul hi
theorem hsum_smulFamily [AddCommMonoid V] [SMulWithZero R V] (f : α → R)
(s : SummableFamily Γ V α) (g : Γ) :
(smulFamily f s).hsum.coeff g = ∑ᶠ i, (f i) • ((s i).coeff g) :=
rfl
end AddCommMonoid
section AddCommGroup
variable [PartialOrder Γ] [AddCommGroup R] {s t : SummableFamily Γ R α} {a : α}
instance : Neg (SummableFamily Γ R α) :=
⟨fun s =>
{ toFun := fun a => -s a
isPWO_iUnion_support' := by
simp_rw [support_neg]
exact s.isPWO_iUnion_support
finite_co_support' := fun g => by
simp only [coeff_neg', Pi.neg_apply, Ne, neg_eq_zero]
exact s.finite_co_support g }⟩
instance : AddCommGroup (SummableFamily Γ R α) :=
{ inferInstanceAs (AddCommMonoid (SummableFamily Γ R α)) with
zsmul := zsmulRec
neg_add_cancel := fun a => by
ext
apply neg_add_cancel }
@[simp]
theorem coe_neg : ⇑(-s) = -s :=
rfl
theorem neg_apply : (-s) a = -s a :=
rfl
@[simp]
theorem coe_sub : ⇑(s - t) = s - t :=
rfl
theorem sub_apply : (s - t) a = s a - t a :=
rfl
end AddCommGroup
section SMul
variable [PartialOrder Γ] [PartialOrder Γ'] [AddCommMonoid V]
instance [Zero R] [SMulWithZero R V] : SMul R (SummableFamily Γ' V β) :=
⟨fun r t =>
{ toFun := r • t
isPWO_iUnion_support' := t.isPWO_iUnion_support.mono (Set.iUnion_mono fun i =>
Pi.smul_apply r t i ▸ Function.support_const_smul_subset r _)
finite_co_support' := by
intro g
refine (t.finite_co_support g).subset ?_
intro i hi
simp only [Pi.smul_apply, coeff_smul, ne_eq, Set.mem_setOf_eq] at hi
simp only [Function.mem_support, ne_eq]
exact right_ne_zero_of_smul hi } ⟩
variable [AddCommMonoid R] [SMulWithZero R V]
theorem smul_support_subset_prod (s : SummableFamily Γ R α)
(t : SummableFamily Γ' V β) (gh : Γ × Γ') :
(Function.support fun (i : α × β) ↦ (s i.1).coeff gh.1 • (t i.2).coeff gh.2) ⊆
((s.finite_co_support' gh.1).prod (t.finite_co_support' gh.2)).toFinset := by
intro _ hab
simp_all only [Function.mem_support, ne_eq, Set.Finite.coe_toFinset, Set.mem_prod,
Set.mem_setOf_eq]
exact ⟨left_ne_zero_of_smul hab, right_ne_zero_of_smul hab⟩
theorem smul_support_finite (s : SummableFamily Γ R α)
(t : SummableFamily Γ' V β) (gh : Γ × Γ') :
(Function.support fun (i : α × β) ↦ (s i.1).coeff gh.1 • (t i.2).coeff gh.2).Finite :=
Set.Finite.subset (Set.toFinite ((s.finite_co_support' gh.1).prod
(t.finite_co_support' gh.2)).toFinset) (smul_support_subset_prod s t gh)
variable [VAdd Γ Γ'] [IsOrderedCancelVAdd Γ Γ']
open HahnModule
theorem isPWO_iUnion_support_prod_smul {s : α → HahnSeries Γ R} {t : β → HahnSeries Γ' V}
(hs : (⋃ a, (s a).support).IsPWO) (ht : (⋃ b, (t b).support).IsPWO) :
(⋃ (a : α × β), ((fun a ↦ (of R).symm
((s a.1) • (of R) (t a.2))) a).support).IsPWO := by
apply (hs.vadd ht).mono
have hsupp : ∀ ab : α × β, support ((fun ab ↦ (of R).symm (s ab.1 • (of R) (t ab.2))) ab) ⊆
(s ab.1).support +ᵥ (t ab.2).support := by
intro ab
refine Set.Subset.trans (fun x hx => ?_) (support_vaddAntidiagonal_subset_vadd
(hs := (s ab.1).isPWO_support) (ht := (t ab.2).isPWO_support))
contrapose! hx
simp only [Set.mem_setOf_eq, not_nonempty_iff_eq_empty] at hx
rw [mem_support, not_not, HahnModule.coeff_smul, hx, sum_empty]
refine Set.Subset.trans (Set.iUnion_mono fun a => (hsupp a)) ?_
simp_all only [Set.iUnion_subset_iff, Prod.forall]
exact fun a b => Set.vadd_subset_vadd (Set.subset_iUnion_of_subset a fun x y ↦ y)
(Set.subset_iUnion_of_subset b fun x y ↦ y)
theorem finite_co_support_prod_smul (s : SummableFamily Γ R α)
(t : SummableFamily Γ' V β) (g : Γ') :
Finite {(ab : α × β) |
((fun (ab : α × β) ↦ (of R).symm (s ab.1 • (of R) (t ab.2))) ab).coeff g ≠ 0} := by
apply ((VAddAntidiagonal s.isPWO_iUnion_support t.isPWO_iUnion_support g).finite_toSet.biUnion'
(fun gh _ => smul_support_finite s t gh)).subset _
exact fun ab hab => by
simp only [coeff_smul, ne_eq, Set.mem_setOf_eq] at hab
obtain ⟨ij, hij⟩ := Finset.exists_ne_zero_of_sum_ne_zero hab
simp only [mem_coe, mem_vaddAntidiagonal, Set.mem_iUnion, mem_support, ne_eq,
Function.mem_support, exists_prop, Prod.exists]
exact ⟨ij.1, ij.2, ⟨⟨ab.1, left_ne_zero_of_smul hij.2⟩, ⟨ab.2, right_ne_zero_of_smul hij.2⟩,
((mem_vaddAntidiagonal _ _ _).mp hij.1).2.2⟩, hij.2⟩
/-- An elementwise scalar multiplication of one summable family on another. -/
@[simps]
def smul (s : SummableFamily Γ R α) (t : SummableFamily Γ' V β) : SummableFamily Γ' V (α × β) where
toFun ab := (of R).symm (s (ab.1) • ((of R) (t (ab.2))))
isPWO_iUnion_support' :=
isPWO_iUnion_support_prod_smul s.isPWO_iUnion_support t.isPWO_iUnion_support
finite_co_support' g := finite_co_support_prod_smul s t g
@[deprecated (since := "2024-11-17")] noncomputable alias FamilySMul := smul
theorem sum_vAddAntidiagonal_eq (s : SummableFamily Γ R α) (t : SummableFamily Γ' V β) (g : Γ')
(a : α × β) :
∑ x ∈ VAddAntidiagonal (s a.1).isPWO_support' (t a.2).isPWO_support' g, (s a.1).coeff x.1 •
(t a.2).coeff x.2 = ∑ x ∈ VAddAntidiagonal s.isPWO_iUnion_support' t.isPWO_iUnion_support' g,
(s a.1).coeff x.1 • (t a.2).coeff x.2 := by
refine sum_subset (fun gh hgh => ?_) fun gh hgh h => ?_
· simp_all only [mem_vaddAntidiagonal, Function.mem_support, Set.mem_iUnion, mem_support]
exact ⟨Exists.intro a.1 hgh.1, Exists.intro a.2 hgh.2.1, trivial⟩
· by_cases hs : (s a.1).coeff gh.1 = 0
· exact smul_eq_zero_of_left hs ((t a.2).coeff gh.2)
· simp_all
theorem coeff_smul {R} {V} [Semiring R] [AddCommMonoid V] [Module R V]
(s : SummableFamily Γ R α) (t : SummableFamily Γ' V β) (g : Γ') :
(smul s t).hsum.coeff g = ∑ gh ∈ VAddAntidiagonal s.isPWO_iUnion_support
t.isPWO_iUnion_support g, (s.hsum.coeff gh.1) • (t.hsum.coeff gh.2) := by
rw [coeff_hsum]
simp only [coeff_hsum_eq_sum, smul_toFun, HahnModule.coeff_smul, Equiv.symm_apply_apply]
simp_rw [sum_vAddAntidiagonal_eq, Finset.smul_sum, Finset.sum_smul]
rw [← sum_finsum_comm _ _ <| fun gh _ => smul_support_finite s t gh]
refine sum_congr rfl fun gh _ => ?_
rw [finsum_eq_sum _ (smul_support_finite s t gh), ← sum_product_right']
refine sum_subset (fun ab hab => ?_) (fun ab _ hab => by simp_all)
have hsupp := smul_support_subset_prod s t gh
simp_all only [mem_vaddAntidiagonal, Set.mem_iUnion, mem_support, ne_eq, Set.Finite.mem_toFinset,
Function.mem_support, Set.Finite.coe_toFinset, support_subset_iff, Set.mem_prod,
Set.mem_setOf_eq, Prod.forall, coeff_support, mem_product]
exact hsupp ab.1 ab.2 hab
@[deprecated (since := "2024-11-17")] alias family_smul_coeff := coeff_smul
theorem smul_hsum {R} {V} [Semiring R] [AddCommMonoid V] [Module R V]
(s : SummableFamily Γ R α) (t : SummableFamily Γ' V β) :
(smul s t).hsum = (of R).symm (s.hsum • (of R) (t.hsum)) := by
ext g
rw [coeff_smul s t g, HahnModule.coeff_smul, Equiv.symm_apply_apply]
refine Eq.symm (sum_of_injOn (fun a ↦ a) (fun _ _ _ _ h ↦ h) (fun _ hgh => ?_)
(fun gh _ hgh => ?_) fun _ _ => by simp)
· simp_all only [mem_coe, mem_vaddAntidiagonal, mem_support, ne_eq, Set.mem_iUnion, and_true]
constructor
· rw [coeff_hsum_eq_sum] at hgh
have h' := Finset.exists_ne_zero_of_sum_ne_zero hgh.1
simpa using h'
· by_contra hi
simp_all
· simp only [Set.image_id', mem_coe, mem_vaddAntidiagonal, mem_support, ne_eq, not_and] at hgh
by_cases h : s.hsum.coeff gh.1 = 0
· exact smul_eq_zero_of_left h (t.hsum.coeff gh.2)
· simp_all
@[deprecated (since := "2024-11-17")] alias hsum_family_smul := smul_hsum
instance [AddCommMonoid R] [SMulWithZero R V] : SMul (HahnSeries Γ R) (SummableFamily Γ' V β) where
smul x t := Equiv (Equiv.punitProd β) <| smul (single x) t
theorem smul_eq {x : HahnSeries Γ R} {t : SummableFamily Γ' V β} :
x • t = Equiv (Equiv.punitProd β) (smul (single x) t) :=
rfl
@[simp]
theorem smul_apply {x : HahnSeries Γ R} {s : SummableFamily Γ' V α} {a : α} :
(x • s) a = (of R).symm (x • of R (s a)) :=
rfl
@[simp]
theorem hsum_smul_module {R} {V} [Semiring R] [AddCommMonoid V] [Module R V] {x : HahnSeries Γ R}
{s : SummableFamily Γ' V α} :
(x • s).hsum = (of R).symm (x • of R s.hsum) := by
rw [smul_eq, hsum_equiv, smul_hsum, hsum_single]
end SMul
section Semiring
variable [AddCommMonoid Γ] [PartialOrder Γ] [IsOrderedCancelAddMonoid Γ]
[PartialOrder Γ'] [AddAction Γ Γ'] [IsOrderedCancelVAdd Γ Γ'] [Semiring R]
instance [AddCommMonoid V] [Module R V] : Module (HahnSeries Γ R) (SummableFamily Γ' V α) where
smul := (· • ·)
smul_zero _ := ext fun _ => by simp
zero_smul _ := ext fun _ => by simp
one_smul _ := ext fun _ => by rw [smul_apply, HahnModule.one_smul', Equiv.symm_apply_apply]
add_smul _ _ _ := ext fun _ => by simp [add_smul]
smul_add _ _ _ := ext fun _ => by simp
mul_smul _ _ _ := ext fun _ => by simp [HahnModule.instModule.mul_smul]
theorem hsum_smul {x : HahnSeries Γ R} {s : SummableFamily Γ R α} :
(x • s).hsum = x * s.hsum := by
rw [hsum_smul_module, of_symm_smul_of_eq_mul]
/-- The summation of a `summable_family` as a `LinearMap`. -/
@[simps]
def lsum : SummableFamily Γ R α →ₗ[HahnSeries Γ R] HahnSeries Γ R where
toFun := hsum
map_add' _ _ := hsum_add
map_smul' _ _ := hsum_smul
@[simp]
theorem hsum_sub {R : Type*} [Ring R] {s t : SummableFamily Γ R α} :
(s - t).hsum = s.hsum - t.hsum := by
rw [← lsum_apply, LinearMap.map_sub, lsum_apply, lsum_apply]
theorem isPWO_iUnion_support_prod_mul {s : α → HahnSeries Γ R} {t : β → HahnSeries Γ R}
(hs : (⋃ a, (s a).support).IsPWO) (ht : (⋃ b, (t b).support).IsPWO) :
(⋃ (a : α × β), ((fun a ↦ ((s a.1) * (t a.2))) a).support).IsPWO :=
isPWO_iUnion_support_prod_smul hs ht
theorem finite_co_support_prod_mul (s : SummableFamily Γ R α)
(t : SummableFamily Γ R β) (g : Γ) :
Finite {(a : α × β) | ((fun (a : α × β) ↦ (s a.1 * t a.2)) a).coeff g ≠ 0} :=
finite_co_support_prod_smul s t g
/-- A summable family given by pointwise multiplication of a pair of summable families. -/
@[simps]
def mul (s : SummableFamily Γ R α) (t : SummableFamily Γ R β) :
(SummableFamily Γ R (α × β)) where
toFun a := s (a.1) * t (a.2)
isPWO_iUnion_support' :=
isPWO_iUnion_support_prod_mul s.isPWO_iUnion_support t.isPWO_iUnion_support
finite_co_support' g := finite_co_support_prod_mul s t g
theorem mul_eq_smul {β : Type*} (s : SummableFamily Γ R α) (t : SummableFamily Γ R β) :
mul s t = smul s t :=
rfl
theorem coeff_hsum_mul {β : Type*} (s : SummableFamily Γ R α) (t : SummableFamily Γ R β) (g : Γ) :
(mul s t).hsum.coeff g = ∑ gh ∈ addAntidiagonal s.isPWO_iUnion_support
t.isPWO_iUnion_support g, (s.hsum.coeff gh.1) * (t.hsum.coeff gh.2) := by
simp_rw [← smul_eq_mul, mul_eq_smul]
exact coeff_smul s t g
@[deprecated (since := "2025-01-31")] alias mul_coeff := coeff_hsum_mul
theorem hsum_mul {β : Type*} (s : SummableFamily Γ R α) (t : SummableFamily Γ R β) :
(mul s t).hsum = s.hsum * t.hsum := by
rw [← smul_eq_mul, mul_eq_smul]
exact smul_hsum s t
end Semiring
section OfFinsupp
variable [PartialOrder Γ] [AddCommMonoid R] {α : Type*}
/-- A family with only finitely many nonzero elements is summable. -/
def ofFinsupp (f : α →₀ HahnSeries Γ R) : SummableFamily Γ R α where
toFun := f
isPWO_iUnion_support' := by
apply (f.support.isPWO_bUnion.2 fun a _ => (f a).isPWO_support).mono
refine Set.iUnion_subset_iff.2 fun a g hg => ?_
have haf : a ∈ f.support := by
rw [Finsupp.mem_support_iff, ← support_nonempty_iff]
exact ⟨g, hg⟩
exact Set.mem_biUnion haf hg
finite_co_support' g := by
refine f.support.finite_toSet.subset fun a ha => ?_
simp only [coeff.addMonoidHom_apply, mem_coe, Finsupp.mem_support_iff, Ne,
Function.mem_support]
contrapose! ha
simp [ha]
@[simp]
theorem coe_ofFinsupp {f : α →₀ HahnSeries Γ R} : ⇑(SummableFamily.ofFinsupp f) = f :=
rfl
@[simp]
theorem hsum_ofFinsupp {f : α →₀ HahnSeries Γ R} : (ofFinsupp f).hsum = f.sum fun _ => id := by
ext g
simp only [coeff_hsum, coe_ofFinsupp, Finsupp.sum, Ne]
simp_rw [← coeff.addMonoidHom_apply, id]
rw [map_sum, finsum_eq_sum_of_support_subset]
intro x h
simp only [coeff.addMonoidHom_apply, mem_coe, Finsupp.mem_support_iff, Ne]
contrapose! h
simp [h]
end OfFinsupp
section EmbDomain
variable [PartialOrder Γ] [AddCommMonoid R] {α β : Type*}
open Classical in
/-- A summable family can be reindexed by an embedding without changing its sum. -/
def embDomain (s : SummableFamily Γ R α) (f : α ↪ β) : SummableFamily Γ R β where
toFun b := if h : b ∈ Set.range f then s (Classical.choose h) else 0
isPWO_iUnion_support' := by
refine s.isPWO_iUnion_support.mono (Set.iUnion_subset fun b g h => ?_)
by_cases hb : b ∈ Set.range f
· rw [dif_pos hb] at h
exact Set.mem_iUnion.2 ⟨Classical.choose hb, h⟩
· simp [-Set.mem_range, dif_neg hb] at h
finite_co_support' g :=
((s.finite_co_support g).image f).subset
| (by
intro b h
by_cases hb : b ∈ Set.range f
· simp only [Ne, Set.mem_setOf_eq, dif_pos hb] at h
exact ⟨Classical.choose hb, h, Classical.choose_spec hb⟩
· simp only [Ne, Set.mem_setOf_eq, dif_neg hb, coeff_zero, not_true_eq_false] at h)
variable (s : SummableFamily Γ R α) (f : α ↪ β) {a : α} {b : β}
open Classical in
theorem embDomain_apply :
s.embDomain f b = if h : b ∈ Set.range f then s (Classical.choose h) else 0 :=
rfl
| Mathlib/RingTheory/HahnSeries/Summable.lean | 556 | 569 |
/-
Copyright (c) 2020 Floris van Doorn. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Floris van Doorn
-/
import Mathlib.Data.Set.Prod
/-!
# N-ary images of sets
This file defines `Set.image2`, the binary image of sets.
This is mostly useful to define pointwise operations and `Set.seq`.
## Notes
This file is very similar to `Data.Finset.NAry`, to `Order.Filter.NAry`, and to
`Data.Option.NAry`. Please keep them in sync.
-/
open Function
namespace Set
variable {α α' β β' γ γ' δ δ' ε ε' ζ ζ' ν : Type*} {f f' : α → β → γ}
variable {s s' : Set α} {t t' : Set β} {u : Set γ} {v : Set δ} {a : α} {b : β}
theorem mem_image2_iff (hf : Injective2 f) : f a b ∈ image2 f s t ↔ a ∈ s ∧ b ∈ t :=
⟨by
rintro ⟨a', ha', b', hb', h⟩
rcases hf h with ⟨rfl, rfl⟩
exact ⟨ha', hb'⟩, fun ⟨ha, hb⟩ => mem_image2_of_mem ha hb⟩
/-- image2 is monotone with respect to `⊆`. -/
@[gcongr]
theorem image2_subset (hs : s ⊆ s') (ht : t ⊆ t') : image2 f s t ⊆ image2 f s' t' := by
rintro _ ⟨a, ha, b, hb, rfl⟩
exact mem_image2_of_mem (hs ha) (ht hb)
@[gcongr]
theorem image2_subset_left (ht : t ⊆ t') : image2 f s t ⊆ image2 f s t' :=
image2_subset Subset.rfl ht
@[gcongr]
theorem image2_subset_right (hs : s ⊆ s') : image2 f s t ⊆ image2 f s' t :=
image2_subset hs Subset.rfl
theorem image_subset_image2_left (hb : b ∈ t) : (fun a => f a b) '' s ⊆ image2 f s t :=
forall_mem_image.2 fun _ ha => mem_image2_of_mem ha hb
theorem image_subset_image2_right (ha : a ∈ s) : f a '' t ⊆ image2 f s t :=
forall_mem_image.2 fun _ => mem_image2_of_mem ha
lemma forall_mem_image2 {p : γ → Prop} :
(∀ z ∈ image2 f s t, p z) ↔ ∀ x ∈ s, ∀ y ∈ t, p (f x y) := by aesop
lemma exists_mem_image2 {p : γ → Prop} :
(∃ z ∈ image2 f s t, p z) ↔ ∃ x ∈ s, ∃ y ∈ t, p (f x y) := by aesop
@[deprecated (since := "2024-11-23")] alias forall_image2_iff := forall_mem_image2
@[simp]
theorem image2_subset_iff {u : Set γ} : image2 f s t ⊆ u ↔ ∀ x ∈ s, ∀ y ∈ t, f x y ∈ u :=
forall_mem_image2
theorem image2_subset_iff_left : image2 f s t ⊆ u ↔ ∀ a ∈ s, (fun b => f a b) '' t ⊆ u := by
simp_rw [image2_subset_iff, image_subset_iff, subset_def, mem_preimage]
theorem image2_subset_iff_right : image2 f s t ⊆ u ↔ ∀ b ∈ t, (fun a => f a b) '' s ⊆ u := by
simp_rw [image2_subset_iff, image_subset_iff, subset_def, mem_preimage, @forall₂_swap α]
variable (f)
@[simp]
lemma image_prod : (fun x : α × β ↦ f x.1 x.2) '' s ×ˢ t = image2 f s t :=
ext fun _ ↦ by simp [and_assoc]
@[simp] lemma image_uncurry_prod (s : Set α) (t : Set β) : uncurry f '' s ×ˢ t = image2 f s t :=
image_prod _
@[simp] lemma image2_mk_eq_prod : image2 Prod.mk s t = s ×ˢ t := ext <| by simp
@[simp]
lemma image2_curry (f : α × β → γ) (s : Set α) (t : Set β) :
image2 (fun a b ↦ f (a, b)) s t = f '' s ×ˢ t := by
simp [← image_uncurry_prod, uncurry]
theorem image2_swap (s : Set α) (t : Set β) : image2 f s t = image2 (fun a b => f b a) t s := by
ext
constructor <;> rintro ⟨a, ha, b, hb, rfl⟩ <;> exact ⟨b, hb, a, ha, rfl⟩
variable {f}
theorem image2_union_left : image2 f (s ∪ s') t = image2 f s t ∪ image2 f s' t := by
simp_rw [← image_prod, union_prod, image_union]
theorem image2_union_right : image2 f s (t ∪ t') = image2 f s t ∪ image2 f s t' := by
rw [← image2_swap, image2_union_left, image2_swap f, image2_swap f]
lemma image2_inter_left (hf : Injective2 f) :
image2 f (s ∩ s') t = image2 f s t ∩ image2 f s' t := by
simp_rw [← image_uncurry_prod, inter_prod, image_inter hf.uncurry]
lemma image2_inter_right (hf : Injective2 f) :
image2 f s (t ∩ t') = image2 f s t ∩ image2 f s t' := by
simp_rw [← image_uncurry_prod, prod_inter, image_inter hf.uncurry]
@[simp]
theorem image2_empty_left : image2 f ∅ t = ∅ :=
ext <| by simp
@[simp]
theorem image2_empty_right : image2 f s ∅ = ∅ :=
ext <| by simp
theorem Nonempty.image2 : s.Nonempty → t.Nonempty → (image2 f s t).Nonempty :=
fun ⟨_, ha⟩ ⟨_, hb⟩ => ⟨_, mem_image2_of_mem ha hb⟩
@[simp]
theorem image2_nonempty_iff : (image2 f s t).Nonempty ↔ s.Nonempty ∧ t.Nonempty :=
⟨fun ⟨_, a, ha, b, hb, _⟩ => ⟨⟨a, ha⟩, b, hb⟩, fun h => h.1.image2 h.2⟩
theorem Nonempty.of_image2_left (h : (Set.image2 f s t).Nonempty) : s.Nonempty :=
(image2_nonempty_iff.1 h).1
theorem Nonempty.of_image2_right (h : (Set.image2 f s t).Nonempty) : t.Nonempty :=
(image2_nonempty_iff.1 h).2
@[simp]
theorem image2_eq_empty_iff : image2 f s t = ∅ ↔ s = ∅ ∨ t = ∅ := by
rw [← not_nonempty_iff_eq_empty, image2_nonempty_iff, not_and_or]
simp [not_nonempty_iff_eq_empty]
theorem Subsingleton.image2 (hs : s.Subsingleton) (ht : t.Subsingleton) (f : α → β → γ) :
(image2 f s t).Subsingleton := by
rw [← image_prod]
apply (hs.prod ht).image
theorem image2_inter_subset_left : image2 f (s ∩ s') t ⊆ image2 f s t ∩ image2 f s' t :=
Monotone.map_inf_le (fun _ _ ↦ image2_subset_right) s s'
theorem image2_inter_subset_right : image2 f s (t ∩ t') ⊆ image2 f s t ∩ image2 f s t' :=
Monotone.map_inf_le (fun _ _ ↦ image2_subset_left) t t'
@[simp]
theorem image2_singleton_left : image2 f {a} t = f a '' t :=
ext fun x => by simp
@[simp]
theorem image2_singleton_right : image2 f s {b} = (fun a => f a b) '' s :=
ext fun x => by simp
theorem image2_singleton : image2 f {a} {b} = {f a b} := by simp
@[simp]
theorem image2_insert_left : image2 f (insert a s) t = (fun b => f a b) '' t ∪ image2 f s t := by
rw [insert_eq, image2_union_left, image2_singleton_left]
@[simp]
theorem image2_insert_right : image2 f s (insert b t) = (fun a => f a b) '' s ∪ image2 f s t := by
rw [insert_eq, image2_union_right, image2_singleton_right]
@[congr]
theorem image2_congr (h : ∀ a ∈ s, ∀ b ∈ t, f a b = f' a b) : image2 f s t = image2 f' s t := by
ext
constructor <;> rintro ⟨a, ha, b, hb, rfl⟩ <;> exact ⟨a, ha, b, hb, by rw [h a ha b hb]⟩
/-- A common special case of `image2_congr` -/
theorem image2_congr' (h : ∀ a b, f a b = f' a b) : image2 f s t = image2 f' s t :=
image2_congr fun a _ b _ => h a b
theorem image_image2 (f : α → β → γ) (g : γ → δ) :
g '' image2 f s t = image2 (fun a b => g (f a b)) s t := by
simp only [← image_prod, image_image]
theorem image2_image_left (f : γ → β → δ) (g : α → γ) :
image2 f (g '' s) t = image2 (fun a b => f (g a) b) s t := by
ext; simp
theorem image2_image_right (f : α → γ → δ) (g : β → γ) :
image2 f s (g '' t) = image2 (fun a b => f a (g b)) s t := by
ext; simp
@[simp]
theorem image2_left (h : t.Nonempty) : image2 (fun x _ => x) s t = s := by
simp [nonempty_def.mp h, Set.ext_iff]
@[simp]
theorem image2_right (h : s.Nonempty) : image2 (fun _ y => y) s t = t := by
simp [nonempty_def.mp h, Set.ext_iff]
lemma image2_range (f : α' → β' → γ) (g : α → α') (h : β → β') :
image2 f (range g) (range h) = range fun x : α × β ↦ f (g x.1) (h x.2) := by
simp_rw [← image_univ, image2_image_left, image2_image_right, ← image_prod, univ_prod_univ]
theorem image2_assoc {f : δ → γ → ε} {g : α → β → δ} {f' : α → ε' → ε} {g' : β → γ → ε'}
(h_assoc : ∀ a b c, f (g a b) c = f' a (g' b c)) :
image2 f (image2 g s t) u = image2 f' s (image2 g' t u) :=
eq_of_forall_subset_iff fun _ ↦ by simp only [image2_subset_iff, forall_mem_image2, h_assoc]
theorem image2_comm {g : β → α → γ} (h_comm : ∀ a b, f a b = g b a) : image2 f s t = image2 g t s :=
(image2_swap _ _ _).trans <| by simp_rw [h_comm]
theorem image2_left_comm {f : α → δ → ε} {g : β → γ → δ} {f' : α → γ → δ'} {g' : β → δ' → ε}
(h_left_comm : ∀ a b c, f a (g b c) = g' b (f' a c)) :
image2 f s (image2 g t u) = image2 g' t (image2 f' s u) := by
rw [image2_swap f', image2_swap f]
exact image2_assoc fun _ _ _ => h_left_comm _ _ _
theorem image2_right_comm {f : δ → γ → ε} {g : α → β → δ} {f' : α → γ → δ'} {g' : δ' → β → ε}
(h_right_comm : ∀ a b c, f (g a b) c = g' (f' a c) b) :
image2 f (image2 g s t) u = image2 g' (image2 f' s u) t := by
rw [image2_swap g, image2_swap g']
exact image2_assoc fun _ _ _ => h_right_comm _ _ _
| theorem image2_image2_image2_comm {f : ε → ζ → ν} {g : α → β → ε} {h : γ → δ → ζ} {f' : ε' → ζ' → ν}
{g' : α → γ → ε'} {h' : β → δ → ζ'}
(h_comm : ∀ a b c d, f (g a b) (h c d) = f' (g' a c) (h' b d)) :
| Mathlib/Data/Set/NAry.lean | 214 | 216 |
/-
Copyright (c) 2019 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel, Floris van Doorn, Heather Macbeth
-/
import Mathlib.Topology.FiberBundle.Trivialization
import Mathlib.Topology.Order.LeftRightNhds
/-!
# Fiber bundles
Mathematically, a (topological) fiber bundle with fiber `F` over a base `B` is a space projecting on
`B` for which the fibers are all homeomorphic to `F`, such that the local situation around each
point is a direct product.
In our formalism, a fiber bundle is by definition the type `Bundle.TotalSpace F E` where
`E : B → Type*` is a function associating to `x : B` the fiber over `x`. This type
`Bundle.TotalSpace F E` is a type of pairs `⟨proj : B, snd : E proj⟩`.
To have a fiber bundle structure on `Bundle.TotalSpace F E`, one should
additionally have the following data:
* `F` should be a topological space;
* There should be a topology on `Bundle.TotalSpace F E`, for which the projection to `B` is
a fiber bundle with fiber `F` (in particular, each fiber `E x` is homeomorphic to `F`);
* For each `x`, the fiber `E x` should be a topological space, and the injection
from `E x` to `Bundle.TotalSpace F E` should be an embedding;
* There should be a distinguished set of bundle trivializations, the "trivialization atlas"
* There should be a choice of bundle trivialization at each point, which belongs to this atlas.
If all these conditions are satisfied, we register the typeclass `FiberBundle F E`.
It is in general nontrivial to construct a fiber bundle. A way is to start from the knowledge of
how changes of local trivializations act on the fiber. From this, one can construct the total space
of the bundle and its topology by a suitable gluing construction. The main content of this file is
an implementation of this construction: starting from an object of type
`FiberBundleCore` registering the trivialization changes, one gets the corresponding
fiber bundle and projection.
Similarly we implement the object `FiberPrebundle` which allows to define a topological
fiber bundle from trivializations given as partial equivalences with minimum additional properties.
## Main definitions
### Basic definitions
* `FiberBundle F E` : Structure saying that `E : B → Type*` is a fiber bundle with fiber `F`.
### Construction of a bundle from trivializations
* `Bundle.TotalSpace F E` is the type of pairs `(proj : B, snd : E proj)`. We can use the extra
argument `F` to construct topology on the total space.
* `FiberBundleCore ι B F` : structure registering how changes of coordinates act
on the fiber `F` above open subsets of `B`, where local trivializations are indexed by `ι`.
Let `Z : FiberBundleCore ι B F`. Then we define
* `Z.Fiber x` : the fiber above `x`, homeomorphic to `F` (and defeq to `F` as a type).
* `Z.TotalSpace` : the total space of `Z`, defined as `Bundle.TotalSpace F Z.Fiber` with a custom
topology.
* `Z.proj` : projection from `Z.TotalSpace` to `B`. It is continuous.
* `Z.localTriv i` : for `i : ι`, bundle trivialization above the set `Z.baseSet i`, which is an
open set in `B`.
* `FiberPrebundle F E` : structure registering a cover of prebundle trivializations
and requiring that the relative transition maps are partial homeomorphisms.
* `FiberPrebundle.totalSpaceTopology a` : natural topology of the total space, making
the prebundle into a bundle.
## Implementation notes
### Data vs mixins
For both fiber and vector bundles, one faces a choice: should the definition state the *existence*
of local trivializations (a propositional typeclass), or specify a fixed atlas of trivializations (a
typeclass containing data)?
In their initial mathlib implementations, both fiber and vector bundles were defined
propositionally. For vector bundles, this turns out to be mathematically wrong: in infinite
dimension, the transition function between two trivializations is not automatically continuous as a
map from the base `B` to the endomorphisms `F →L[R] F` of the fiber (considered with the
operator-norm topology), and so the definition needs to be modified by restricting consideration to
a family of trivializations (constituting the data) which are all mutually-compatible in this sense.
The PRs https://github.com/leanprover-community/mathlib4/pull/13052 and https://github.com/leanprover-community/mathlib4/pull/13175 implemented this change.
There is still the choice about whether to hold this data at the level of fiber bundles or of vector
bundles. As of PR https://github.com/leanprover-community/mathlib4/pull/17505, the data is all held in `FiberBundle`, with `VectorBundle` a
(propositional) mixin stating fiberwise-linearity.
This allows bundles to carry instances of typeclasses in which the scalar field, `R`, does not
appear as a parameter. Notably, we would like a vector bundle over `R` with fiber `F` over base `B`
to be a `ChartedSpace (B × F)`, with the trivializations providing the charts. This would be a
dangerous instance for typeclass inference, because `R` does not appear as a parameter in
`ChartedSpace (B × F)`. But if the data of the trivializations is held in `FiberBundle`, then a
fiber bundle with fiber `F` over base `B` can be a `ChartedSpace (B × F)`, and this is safe for
typeclass inference.
We expect that this choice of definition will also streamline constructions of fiber bundles with
similar underlying structure (e.g., the same bundle being both a real and complex vector bundle).
### Core construction
A fiber bundle with fiber `F` over a base `B` is a family of spaces isomorphic to `F`,
indexed by `B`, which is locally trivial in the following sense: there is a covering of `B` by open
sets such that, on each such open set `s`, the bundle is isomorphic to `s × F`.
To construct a fiber bundle formally, the main data is what happens when one changes trivializations
from `s × F` to `s' × F` on `s ∩ s'`: one should get a family of homeomorphisms of `F`, depending
continuously on the base point, satisfying basic compatibility conditions (cocycle property).
Useful classes of bundles can then be specified by requiring that these homeomorphisms of `F`
belong to some subgroup, preserving some structure (the "structure group of the bundle"): then
these structures are inherited by the fibers of the bundle.
Given such trivialization change data (encoded below in a structure called
`FiberBundleCore`), one can construct the fiber bundle. The intrinsic canonical
mathematical construction is the following.
The fiber above `x` is the disjoint union of `F` over all trivializations, modulo the gluing
identifications: one gets a fiber which is isomorphic to `F`, but non-canonically
(each choice of one of the trivializations around `x` gives such an isomorphism). Given a
trivialization over a set `s`, one gets an isomorphism between `s × F` and `proj^{-1} s`, by using
the identification corresponding to this trivialization. One chooses the topology on the bundle that
makes all of these into homeomorphisms.
For the practical implementation, it turns out to be more convenient to avoid completely the
gluing and quotienting construction above, and to declare above each `x` that the fiber is `F`,
but thinking that it corresponds to the `F` coming from the choice of one trivialization around `x`.
This has several practical advantages:
* without any work, one gets a topological space structure on the fiber. And if `F` has more
structure it is inherited for free by the fiber.
* In the case of the tangent bundle of manifolds, this implies that on vector spaces the derivative
(from `F` to `F`) and the manifold derivative (from `TangentSpace I x` to `TangentSpace I' (f x)`)
are equal.
A drawback is that some silly constructions will typecheck: in the case of the tangent bundle, one
can add two vectors in different tangent spaces (as they both are elements of `F` from the point of
view of Lean). To solve this, one could mark the tangent space as irreducible, but then one would
lose the identification of the tangent space to `F` with `F`. There is however a big advantage of
this situation: even if Lean can not check that two basepoints are defeq, it will accept the fact
that the tangent spaces are the same. For instance, if two maps `f` and `g` are locally inverse to
each other, one can express that the composition of their derivatives is the identity of
`TangentSpace I x`. One could fear issues as this composition goes from `TangentSpace I x` to
`TangentSpace I (g (f x))` (which should be the same, but should not be obvious to Lean
as it does not know that `g (f x) = x`). As these types are the same to Lean (equal to `F`), there
are in fact no dependent type difficulties here!
For this construction of a fiber bundle from a `FiberBundleCore`, we should thus
choose for each `x` one specific trivialization around it. We include this choice in the definition
of the `FiberBundleCore`, as it makes some constructions more
functorial and it is a nice way to say that the trivializations cover the whole space `B`.
With this definition, the type of the fiber bundle space constructed from the core data is
`Bundle.TotalSpace F (fun b : B ↦ F)`, but the topology is not the product one, in general.
We also take the indexing type (indexing all the trivializations) as a parameter to the fiber bundle
core: it could always be taken as a subtype of all the maps from open subsets of `B` to continuous
maps of `F`, but in practice it will sometimes be something else. For instance, on a manifold, one
will use the set of charts as a good parameterization for the trivializations of the tangent bundle.
Or for the pullback of a `FiberBundleCore`, the indexing type will be the same as
for the initial bundle.
## Tags
Fiber bundle, topological bundle, structure group
-/
variable {ι B F X : Type*} [TopologicalSpace X]
open TopologicalSpace Filter Set Bundle Topology
/-! ### General definition of fiber bundles -/
section FiberBundle
variable (F)
variable [TopologicalSpace B] [TopologicalSpace F] (E : B → Type*)
[TopologicalSpace (TotalSpace F E)] [∀ b, TopologicalSpace (E b)]
/-- A (topological) fiber bundle with fiber `F` over a base `B` is a space projecting on `B`
for which the fibers are all homeomorphic to `F`, such that the local situation around each point
is a direct product. -/
class FiberBundle where
totalSpaceMk_isInducing' : ∀ b : B, IsInducing (@TotalSpace.mk B F E b)
trivializationAtlas' : Set (Trivialization F (π F E))
trivializationAt' : B → Trivialization F (π F E)
mem_baseSet_trivializationAt' : ∀ b : B, b ∈ (trivializationAt' b).baseSet
trivialization_mem_atlas' : ∀ b : B, trivializationAt' b ∈ trivializationAtlas'
namespace FiberBundle
variable [FiberBundle F E] (b : B)
theorem totalSpaceMk_isInducing : IsInducing (@TotalSpace.mk B F E b) := totalSpaceMk_isInducing' b
@[deprecated (since := "2024-10-28")] alias totalSpaceMk_inducing := totalSpaceMk_isInducing
/-- Atlas of a fiber bundle. -/
abbrev trivializationAtlas : Set (Trivialization F (π F E)) := trivializationAtlas'
/-- Trivialization of a fiber bundle at a point. -/
abbrev trivializationAt : Trivialization F (π F E) := trivializationAt' b
theorem mem_baseSet_trivializationAt : b ∈ (trivializationAt F E b).baseSet :=
mem_baseSet_trivializationAt' b
theorem trivialization_mem_atlas : trivializationAt F E b ∈ trivializationAtlas F E :=
trivialization_mem_atlas' b
end FiberBundle
export FiberBundle (totalSpaceMk_isInducing trivializationAtlas trivializationAt
mem_baseSet_trivializationAt trivialization_mem_atlas)
variable {F}
variable {E}
/-- Given a type `E` equipped with a fiber bundle structure, this is a `Prop` typeclass
for trivializations of `E`, expressing that a trivialization is in the designated atlas for the
bundle. This is needed because lemmas about the linearity of trivializations or the continuity (as
functions to `F →L[R] F`, where `F` is the model fiber) of the transition functions are only
expected to hold for trivializations in the designated atlas. -/
@[mk_iff]
class MemTrivializationAtlas [FiberBundle F E] (e : Trivialization F (π F E)) : Prop where
out : e ∈ trivializationAtlas F E
instance [FiberBundle F E] (b : B) : MemTrivializationAtlas (trivializationAt F E b) where
out := trivialization_mem_atlas F E b
namespace FiberBundle
variable (F)
variable [FiberBundle F E]
theorem map_proj_nhds (x : TotalSpace F E) : map (π F E) (𝓝 x) = 𝓝 x.proj :=
(trivializationAt F E x.proj).map_proj_nhds <|
(trivializationAt F E x.proj).mem_source.2 <| mem_baseSet_trivializationAt F E x.proj
variable (E)
/-- The projection from a fiber bundle to its base is continuous. -/
@[continuity]
theorem continuous_proj : Continuous (π F E) :=
continuous_iff_continuousAt.2 fun x => (map_proj_nhds F x).le
/-- The projection from a fiber bundle to its base is an open map. -/
theorem isOpenMap_proj : IsOpenMap (π F E) :=
IsOpenMap.of_nhds_le fun x => (map_proj_nhds F x).ge
/-- The projection from a fiber bundle with a nonempty fiber to its base is a surjective
map. -/
theorem surjective_proj [Nonempty F] : Function.Surjective (π F E) := fun b =>
let ⟨p, _, hpb⟩ :=
(trivializationAt F E b).proj_surjOn_baseSet (mem_baseSet_trivializationAt F E b)
⟨p, hpb⟩
/-- The projection from a fiber bundle with a nonempty fiber to its base is a quotient
map. -/
theorem isQuotientMap_proj [Nonempty F] : IsQuotientMap (π F E) :=
(isOpenMap_proj F E).isQuotientMap (continuous_proj F E) (surjective_proj F E)
@[deprecated (since := "2024-10-22")]
alias quotientMap_proj := isQuotientMap_proj
theorem continuous_totalSpaceMk (x : B) : Continuous (@TotalSpace.mk B F E x) :=
(totalSpaceMk_isInducing F E x).continuous
theorem totalSpaceMk_isEmbedding (x : B) : IsEmbedding (@TotalSpace.mk B F E x) :=
⟨totalSpaceMk_isInducing F E x, TotalSpace.mk_injective x⟩
@[deprecated (since := "2024-10-26")]
alias totalSpaceMk_embedding := totalSpaceMk_isEmbedding
theorem totalSpaceMk_isClosedEmbedding [T1Space B] (x : B) :
IsClosedEmbedding (@TotalSpace.mk B F E x) :=
⟨totalSpaceMk_isEmbedding F E x, by
rw [TotalSpace.range_mk]
exact isClosed_singleton.preimage <| continuous_proj F E⟩
variable {E F}
@[simp, mfld_simps]
theorem mem_trivializationAt_proj_source {x : TotalSpace F E} :
x ∈ (trivializationAt F E x.proj).source :=
(Trivialization.mem_source _).mpr <| mem_baseSet_trivializationAt F E x.proj
theorem trivializationAt_proj_fst {x : TotalSpace F E} :
((trivializationAt F E x.proj) x).1 = x.proj :=
Trivialization.coe_fst' _ <| mem_baseSet_trivializationAt F E x.proj
variable (F)
open Trivialization
/-- Characterization of continuous functions (at a point, within a set) into a fiber bundle. -/
theorem continuousWithinAt_totalSpace (f : X → TotalSpace F E) {s : Set X} {x₀ : X} :
ContinuousWithinAt f s x₀ ↔
ContinuousWithinAt (fun x => (f x).proj) s x₀ ∧
ContinuousWithinAt (fun x => ((trivializationAt F E (f x₀).proj) (f x)).2) s x₀ :=
(trivializationAt F E (f x₀).proj).tendsto_nhds_iff mem_trivializationAt_proj_source
/-- Characterization of continuous functions (at a point) into a fiber bundle. -/
theorem continuousAt_totalSpace (f : X → TotalSpace F E) {x₀ : X} :
ContinuousAt f x₀ ↔
ContinuousAt (fun x => (f x).proj) x₀ ∧
ContinuousAt (fun x => ((trivializationAt F E (f x₀).proj) (f x)).2) x₀ :=
(trivializationAt F E (f x₀).proj).tendsto_nhds_iff mem_trivializationAt_proj_source
end FiberBundle
variable (F)
variable (E)
/-- If `E` is a fiber bundle over a conditionally complete linear order,
then it is trivial over any closed interval. -/
theorem FiberBundle.exists_trivialization_Icc_subset [ConditionallyCompleteLinearOrder B]
[OrderTopology B] [FiberBundle F E] (a b : B) :
∃ e : Trivialization F (π F E), Icc a b ⊆ e.baseSet := by
obtain ⟨ea, hea⟩ : ∃ ea : Trivialization F (π F E), a ∈ ea.baseSet :=
⟨trivializationAt F E a, mem_baseSet_trivializationAt F E a⟩
-- If `a < b`, then `[a, b] = ∅`, and the statement is trivial
rcases lt_or_le b a with _ | hab
· exact ⟨ea, by simp [*]⟩
/- Let `s` be the set of points `x ∈ [a, b]` such that `E` is trivializable over `[a, x]`.
We need to show that `b ∈ s`. Let `c = Sup s`. We will show that `c ∈ s` and `c = b`. -/
set s : Set B := { x ∈ Icc a b | ∃ e : Trivialization F (π F E), Icc a x ⊆ e.baseSet }
have ha : a ∈ s := ⟨left_mem_Icc.2 hab, ea, by simp [hea]⟩
have sne : s.Nonempty := ⟨a, ha⟩
have hsb : b ∈ upperBounds s := fun x hx => hx.1.2
have sbd : BddAbove s := ⟨b, hsb⟩
set c := sSup s
have hsc : IsLUB s c := isLUB_csSup sne sbd
have hc : c ∈ Icc a b := ⟨hsc.1 ha, hsc.2 hsb⟩
obtain ⟨-, ec : Trivialization F (π F E), hec : Icc a c ⊆ ec.baseSet⟩ : c ∈ s := by
rcases hc.1.eq_or_lt with heq | hlt
· rwa [← heq]
refine ⟨hc, ?_⟩
/- In order to show that `c ∈ s`, consider a trivialization `ec` of `proj` over a neighborhood
of `c`. Its base set includes `(c', c]` for some `c' ∈ [a, c)`. -/
obtain ⟨ec, hc⟩ : ∃ ec : Trivialization F (π F E), c ∈ ec.baseSet :=
⟨trivializationAt F E c, mem_baseSet_trivializationAt F E c⟩
obtain ⟨c', hc', hc'e⟩ : ∃ c' ∈ Ico a c, Ioc c' c ⊆ ec.baseSet :=
(mem_nhdsLE_iff_exists_mem_Ico_Ioc_subset hlt).1
(mem_nhdsWithin_of_mem_nhds <| IsOpen.mem_nhds ec.open_baseSet hc)
/- Since `c' < c = Sup s`, there exists `d ∈ s ∩ (c', c]`. Let `ead` be a trivialization of
`proj` over `[a, d]`. Then we can glue `ead` and `ec` into a trivialization over `[a, c]`. -/
obtain ⟨d, ⟨hdab, ead, had⟩, hd⟩ : ∃ d ∈ s, d ∈ Ioc c' c := hsc.exists_between hc'.2
refine ⟨ead.piecewiseLe ec d (had ⟨hdab.1, le_rfl⟩) (hc'e hd), subset_ite.2 ?_⟩
exact ⟨fun x hx => had ⟨hx.1.1, hx.2⟩, fun x hx => hc'e ⟨hd.1.trans (not_le.1 hx.2), hx.1.2⟩⟩
/- So, `c ∈ s`. Let `ec` be a trivialization of `proj` over `[a, c]`. If `c = b`, then we are
done. Otherwise we show that `proj` can be trivialized over a larger interval `[a, d]`,
`d ∈ (c, b]`, hence `c` is not an upper bound of `s`. -/
rcases hc.2.eq_or_lt with heq | hlt
· exact ⟨ec, heq ▸ hec⟩
rsuffices ⟨d, hdcb, hd⟩ : ∃ d ∈ Ioc c b, ∃ e : Trivialization F (π F E), Icc a d ⊆ e.baseSet
· exact ((hsc.1 ⟨⟨hc.1.trans hdcb.1.le, hdcb.2⟩, hd⟩).not_lt hdcb.1).elim
/- Since the base set of `ec` is open, it includes `[c, d)` (hence, `[a, d)`) for some
`d ∈ (c, b]`. -/
obtain ⟨d, hdcb, hd⟩ : ∃ d ∈ Ioc c b, Ico c d ⊆ ec.baseSet :=
(mem_nhdsGE_iff_exists_mem_Ioc_Ico_subset hlt).1
(mem_nhdsWithin_of_mem_nhds <| IsOpen.mem_nhds ec.open_baseSet (hec ⟨hc.1, le_rfl⟩))
have had : Ico a d ⊆ ec.baseSet := Ico_subset_Icc_union_Ico.trans (union_subset hec hd)
by_cases he : Disjoint (Iio d) (Ioi c)
· /- If `(c, d) = ∅`, then let `ed` be a trivialization of `proj` over a neighborhood of `d`.
Then the disjoint union of `ec` restricted to `(-∞, d)` and `ed` restricted to `(c, ∞)` is
a trivialization over `[a, d]`. -/
obtain ⟨ed, hed⟩ : ∃ ed : Trivialization F (π F E), d ∈ ed.baseSet :=
⟨trivializationAt F E d, mem_baseSet_trivializationAt F E d⟩
refine ⟨d, hdcb,
(ec.restrOpen (Iio d) isOpen_Iio).disjointUnion (ed.restrOpen (Ioi c) isOpen_Ioi)
(he.mono inter_subset_right inter_subset_right), fun x hx => ?_⟩
rcases hx.2.eq_or_lt with (rfl | hxd)
exacts [Or.inr ⟨hed, hdcb.1⟩, Or.inl ⟨had ⟨hx.1, hxd⟩, hxd⟩]
· /- If `(c, d)` is nonempty, then take `d' ∈ (c, d)`. Since the base set of `ec` includes
`[a, d)`, it includes `[a, d'] ⊆ [a, d)` as well. -/
rw [disjoint_left] at he
push_neg at he
rcases he with ⟨d', hdd' : d' < d, hd'c⟩
exact ⟨d', ⟨hd'c, hdd'.le.trans hdcb.2⟩, ec, (Icc_subset_Ico_right hdd').trans had⟩
end FiberBundle
/-! ### Core construction for constructing fiber bundles -/
/-- Core data defining a locally trivial bundle with fiber `F` over a topological
space `B`. Note that "bundle" is used in its mathematical sense. This is the (computer science)
bundled version, i.e., all the relevant data is contained in the following structure. A family of
local trivializations is indexed by a type `ι`, on open subsets `baseSet i` for each `i : ι`.
Trivialization changes from `i` to `j` are given by continuous maps `coordChange i j` from
`baseSet i ∩ baseSet j` to the set of homeomorphisms of `F`, but we express them as maps
`B → F → F` and require continuity on `(baseSet i ∩ baseSet j) × F` to avoid the topology on the
space of continuous maps on `F`. -/
structure FiberBundleCore (ι : Type*) (B : Type*) [TopologicalSpace B] (F : Type*)
[TopologicalSpace F] where
baseSet : ι → Set B
isOpen_baseSet : ∀ i, IsOpen (baseSet i)
indexAt : B → ι
mem_baseSet_at : ∀ x, x ∈ baseSet (indexAt x)
coordChange : ι → ι → B → F → F
coordChange_self : ∀ i, ∀ x ∈ baseSet i, ∀ v, coordChange i i x v = v
continuousOn_coordChange : ∀ i j,
ContinuousOn (fun p : B × F => coordChange i j p.1 p.2) ((baseSet i ∩ baseSet j) ×ˢ univ)
coordChange_comp : ∀ i j k, ∀ x ∈ baseSet i ∩ baseSet j ∩ baseSet k, ∀ v,
(coordChange j k x) (coordChange i j x v) = coordChange i k x v
namespace FiberBundleCore
variable [TopologicalSpace B] [TopologicalSpace F] (Z : FiberBundleCore ι B F)
/-- The index set of a fiber bundle core, as a convenience function for dot notation -/
@[nolint unusedArguments]
def Index (_Z : FiberBundleCore ι B F) := ι
/-- The base space of a fiber bundle core, as a convenience function for dot notation -/
@[nolint unusedArguments, reducible]
def Base (_Z : FiberBundleCore ι B F) := B
/-- The fiber of a fiber bundle core, as a convenience function for dot notation and
typeclass inference -/
@[nolint unusedArguments]
def Fiber (_ : FiberBundleCore ι B F) (_x : B) := F
instance topologicalSpaceFiber (x : B) : TopologicalSpace (Z.Fiber x) := ‹_›
/-- The total space of the fiber bundle, as a convenience function for dot notation.
It is by definition equal to `Bundle.TotalSpace F Z.Fiber`. -/
abbrev TotalSpace := Bundle.TotalSpace F Z.Fiber
/-- The projection from the total space of a fiber bundle core, on its base. -/
@[reducible, simp, mfld_simps]
def proj : Z.TotalSpace → B :=
Bundle.TotalSpace.proj
/-- Local homeomorphism version of the trivialization change. -/
def trivChange (i j : ι) : PartialHomeomorph (B × F) (B × F) where
source := (Z.baseSet i ∩ Z.baseSet j) ×ˢ univ
target := (Z.baseSet i ∩ Z.baseSet j) ×ˢ univ
toFun p := ⟨p.1, Z.coordChange i j p.1 p.2⟩
invFun p := ⟨p.1, Z.coordChange j i p.1 p.2⟩
map_source' p hp := by simpa using hp
map_target' p hp := by simpa using hp
left_inv' := by
rintro ⟨x, v⟩ hx
simp only [prodMk_mem_set_prod_eq, mem_inter_iff, and_true, mem_univ] at hx
dsimp only
rw [coordChange_comp, Z.coordChange_self]
exacts [hx.1, ⟨⟨hx.1, hx.2⟩, hx.1⟩]
right_inv' := by
rintro ⟨x, v⟩ hx
simp only [prodMk_mem_set_prod_eq, mem_inter_iff, and_true, mem_univ] at hx
dsimp only
rw [Z.coordChange_comp, Z.coordChange_self]
· exact hx.2
· simp [hx]
open_source := ((Z.isOpen_baseSet i).inter (Z.isOpen_baseSet j)).prod isOpen_univ
open_target := ((Z.isOpen_baseSet i).inter (Z.isOpen_baseSet j)).prod isOpen_univ
continuousOn_toFun := continuous_fst.continuousOn.prodMk (Z.continuousOn_coordChange i j)
continuousOn_invFun := by
simpa [inter_comm] using continuous_fst.continuousOn.prodMk (Z.continuousOn_coordChange j i)
@[simp, mfld_simps]
theorem mem_trivChange_source (i j : ι) (p : B × F) :
p ∈ (Z.trivChange i j).source ↔ p.1 ∈ Z.baseSet i ∩ Z.baseSet j := by
rw [trivChange, mem_prod]
simp
/-- Associate to a trivialization index `i : ι` the corresponding trivialization, i.e., a bijection
between `proj ⁻¹ (baseSet i)` and `baseSet i × F`. As the fiber above `x` is `F` but read in the
chart with index `index_at x`, the trivialization in the fiber above x is by definition the
coordinate change from i to `index_at x`, so it depends on `x`.
The local trivialization will ultimately be a partial homeomorphism. For now, we only introduce the
partial equivalence version, denoted with a prime.
In further developments, avoid this auxiliary version, and use `Z.local_triv` instead. -/
def localTrivAsPartialEquiv (i : ι) : PartialEquiv Z.TotalSpace (B × F) where
source := Z.proj ⁻¹' Z.baseSet i
target := Z.baseSet i ×ˢ univ
invFun p := ⟨p.1, Z.coordChange i (Z.indexAt p.1) p.1 p.2⟩
toFun p := ⟨p.1, Z.coordChange (Z.indexAt p.1) i p.1 p.2⟩
map_source' p hp := by
simpa only [Set.mem_preimage, and_true, Set.mem_univ, Set.prodMk_mem_set_prod_eq] using hp
map_target' p hp := by
simpa only [Set.mem_preimage, and_true, Set.mem_univ, Set.mem_prod] using hp
left_inv' := by
rintro ⟨x, v⟩ hx
replace hx : x ∈ Z.baseSet i := hx
dsimp only
rw [Z.coordChange_comp, Z.coordChange_self] <;> apply_rules [mem_baseSet_at, mem_inter]
right_inv' := by
rintro ⟨x, v⟩ hx
simp only [prodMk_mem_set_prod_eq, and_true, mem_univ] at hx
dsimp only
rw [Z.coordChange_comp, Z.coordChange_self]
exacts [hx, ⟨⟨hx, Z.mem_baseSet_at _⟩, hx⟩]
variable (i : ι)
theorem mem_localTrivAsPartialEquiv_source (p : Z.TotalSpace) :
p ∈ (Z.localTrivAsPartialEquiv i).source ↔ p.1 ∈ Z.baseSet i :=
Iff.rfl
theorem mem_localTrivAsPartialEquiv_target (p : B × F) :
p ∈ (Z.localTrivAsPartialEquiv i).target ↔ p.1 ∈ Z.baseSet i := by
rw [localTrivAsPartialEquiv, mem_prod]
simp only [and_true, mem_univ]
theorem localTrivAsPartialEquiv_apply (p : Z.TotalSpace) :
(Z.localTrivAsPartialEquiv i) p = ⟨p.1, Z.coordChange (Z.indexAt p.1) i p.1 p.2⟩ :=
rfl
/-- The composition of two local trivializations is the trivialization change Z.triv_change i j. -/
theorem localTrivAsPartialEquiv_trans (i j : ι) :
(Z.localTrivAsPartialEquiv i).symm.trans (Z.localTrivAsPartialEquiv j) ≈
(Z.trivChange i j).toPartialEquiv := by
constructor
· ext x
simp only [mem_localTrivAsPartialEquiv_target, mfld_simps]
rfl
· rintro ⟨x, v⟩ hx
simp only [trivChange, localTrivAsPartialEquiv, PartialEquiv.symm,
Prod.mk_inj, prodMk_mem_set_prod_eq, PartialEquiv.trans_source, mem_inter_iff,
mem_preimage, proj, mem_univ, eq_self_iff_true, (· ∘ ·),
PartialEquiv.coe_trans, TotalSpace.proj] at hx ⊢
simp only [Z.coordChange_comp, hx, mem_inter_iff, and_self_iff, mem_baseSet_at]
/-- Topological structure on the total space of a fiber bundle created from core, designed so
that all the local trivialization are continuous. -/
instance toTopologicalSpace : TopologicalSpace (Bundle.TotalSpace F Z.Fiber) :=
TopologicalSpace.generateFrom <| ⋃ (i : ι) (s : Set (B × F)) (_ : IsOpen s),
{(Z.localTrivAsPartialEquiv i).source ∩ Z.localTrivAsPartialEquiv i ⁻¹' s}
variable (b : B) (a : F)
theorem open_source' (i : ι) : IsOpen (Z.localTrivAsPartialEquiv i).source := by
apply TopologicalSpace.GenerateOpen.basic
simp only [exists_prop, mem_iUnion, mem_singleton_iff]
refine ⟨i, Z.baseSet i ×ˢ univ, (Z.isOpen_baseSet i).prod isOpen_univ, ?_⟩
ext p
simp only [localTrivAsPartialEquiv_apply, prodMk_mem_set_prod_eq, mem_inter_iff, and_self_iff,
mem_localTrivAsPartialEquiv_source, and_true, mem_univ, mem_preimage]
/-- Extended version of the local trivialization of a fiber bundle constructed from core,
registering additionally in its type that it is a local bundle trivialization. -/
def localTriv (i : ι) : Trivialization F Z.proj where
baseSet := Z.baseSet i
open_baseSet := Z.isOpen_baseSet i
source_eq := rfl
target_eq := rfl
proj_toFun p _ := by
simp only [mfld_simps]
rfl
open_source := Z.open_source' i
open_target := (Z.isOpen_baseSet i).prod isOpen_univ
continuousOn_toFun := by
rw [continuousOn_open_iff (Z.open_source' i)]
intro s s_open
apply TopologicalSpace.GenerateOpen.basic
simp only [exists_prop, mem_iUnion, mem_singleton_iff]
exact ⟨i, s, s_open, rfl⟩
continuousOn_invFun := by
refine continuousOn_isOpen_of_generateFrom fun t ht ↦ ?_
simp only [exists_prop, mem_iUnion, mem_singleton_iff] at ht
obtain ⟨j, s, s_open, ts⟩ : ∃ j s, IsOpen s ∧
t = (localTrivAsPartialEquiv Z j).source ∩ localTrivAsPartialEquiv Z j ⁻¹' s := ht
rw [ts]
simp only [PartialEquiv.right_inv, preimage_inter, PartialEquiv.left_inv]
let e := Z.localTrivAsPartialEquiv i
let e' := Z.localTrivAsPartialEquiv j
let f := e.symm.trans e'
have : IsOpen (f.source ∩ f ⁻¹' s) := by
rw [PartialEquiv.EqOnSource.source_inter_preimage_eq (Z.localTrivAsPartialEquiv_trans i j)]
exact (continuousOn_open_iff (Z.trivChange i j).open_source).1
(Z.trivChange i j).continuousOn _ s_open
convert this using 1
dsimp [f, PartialEquiv.trans_source]
rw [← preimage_comp, inter_assoc]
toPartialEquiv := Z.localTrivAsPartialEquiv i
/-- Preferred local trivialization of a fiber bundle constructed from core, at a given point, as
a bundle trivialization -/
def localTrivAt (b : B) : Trivialization F (π F Z.Fiber) :=
Z.localTriv (Z.indexAt b)
@[simp, mfld_simps]
theorem localTrivAt_def (b : B) : Z.localTriv (Z.indexAt b) = Z.localTrivAt b :=
rfl
theorem localTrivAt_snd (b : B) (p) :
(Z.localTrivAt b p).2 = Z.coordChange (Z.indexAt p.1) (Z.indexAt b) p.1 p.2 :=
rfl
/-- If an element of `F` is invariant under all coordinate changes, then one can define a
corresponding section of the fiber bundle, which is continuous. This applies in particular to the
zero section of a vector bundle. Another example (not yet defined) would be the identity
section of the endomorphism bundle of a vector bundle. -/
theorem continuous_const_section (v : F)
(h : ∀ i j, ∀ x ∈ Z.baseSet i ∩ Z.baseSet j, Z.coordChange i j x v = v) :
Continuous (show B → Z.TotalSpace from fun x => ⟨x, v⟩) := by
refine continuous_iff_continuousAt.2 fun x => ?_
have A : Z.baseSet (Z.indexAt x) ∈ 𝓝 x :=
IsOpen.mem_nhds (Z.isOpen_baseSet (Z.indexAt x)) (Z.mem_baseSet_at x)
refine ((Z.localTrivAt x).toPartialHomeomorph.continuousAt_iff_continuousAt_comp_left ?_).2 ?_
· exact A
· apply continuousAt_id.prodMk
simp only [(· ∘ ·), mfld_simps, localTrivAt_snd]
have : ContinuousOn (fun _ : B => v) (Z.baseSet (Z.indexAt x)) := continuousOn_const
refine (this.congr fun y hy ↦ ?_).continuousAt A
exact h _ _ _ ⟨mem_baseSet_at _ _, hy⟩
@[simp, mfld_simps]
theorem localTrivAsPartialEquiv_coe : ⇑(Z.localTrivAsPartialEquiv i) = Z.localTriv i :=
rfl
@[simp, mfld_simps]
theorem localTrivAsPartialEquiv_source :
(Z.localTrivAsPartialEquiv i).source = (Z.localTriv i).source :=
rfl
@[simp, mfld_simps]
theorem localTrivAsPartialEquiv_target :
(Z.localTrivAsPartialEquiv i).target = (Z.localTriv i).target :=
rfl
@[simp, mfld_simps]
theorem localTrivAsPartialEquiv_symm :
(Z.localTrivAsPartialEquiv i).symm = (Z.localTriv i).toPartialEquiv.symm :=
rfl
@[simp, mfld_simps]
theorem baseSet_at : Z.baseSet i = (Z.localTriv i).baseSet :=
rfl
@[simp, mfld_simps]
theorem localTriv_apply (p : Z.TotalSpace) :
(Z.localTriv i) p = ⟨p.1, Z.coordChange (Z.indexAt p.1) i p.1 p.2⟩ :=
rfl
@[simp, mfld_simps]
theorem localTrivAt_apply (p : Z.TotalSpace) : (Z.localTrivAt p.1) p = ⟨p.1, p.2⟩ := by
rw [localTrivAt, localTriv_apply, coordChange_self]
exact Z.mem_baseSet_at p.1
@[simp, mfld_simps]
theorem localTrivAt_apply_mk (b : B) (a : F) : (Z.localTrivAt b) ⟨b, a⟩ = ⟨b, a⟩ :=
Z.localTrivAt_apply _
@[simp, mfld_simps]
theorem mem_localTriv_source (p : Z.TotalSpace) :
p ∈ (Z.localTriv i).source ↔ p.1 ∈ (Z.localTriv i).baseSet :=
Iff.rfl
@[simp, mfld_simps]
theorem mem_localTrivAt_source (p : Z.TotalSpace) (b : B) :
p ∈ (Z.localTrivAt b).source ↔ p.1 ∈ (Z.localTrivAt b).baseSet :=
Iff.rfl
@[simp, mfld_simps]
theorem mem_localTriv_target (p : B × F) :
p ∈ (Z.localTriv i).target ↔ p.1 ∈ (Z.localTriv i).baseSet :=
Trivialization.mem_target _
@[simp, mfld_simps]
theorem mem_localTrivAt_target (p : B × F) (b : B) :
p ∈ (Z.localTrivAt b).target ↔ p.1 ∈ (Z.localTrivAt b).baseSet :=
Trivialization.mem_target _
@[simp, mfld_simps]
theorem localTriv_symm_apply (p : B × F) :
(Z.localTriv i).toPartialHomeomorph.symm p = ⟨p.1, Z.coordChange i (Z.indexAt p.1) p.1 p.2⟩ :=
rfl
@[simp, mfld_simps]
theorem mem_localTrivAt_baseSet (b : B) : b ∈ (Z.localTrivAt b).baseSet := by
rw [localTrivAt, ← baseSet_at]
exact Z.mem_baseSet_at b
theorem mk_mem_localTrivAt_source : (⟨b, a⟩ : Z.TotalSpace) ∈ (Z.localTrivAt b).source := by
simp only [mfld_simps]
/-- A fiber bundle constructed from core is indeed a fiber bundle. -/
instance fiberBundle : FiberBundle F Z.Fiber where
totalSpaceMk_isInducing' b := isInducing_iff_nhds.2 fun x ↦ by
rw [(Z.localTrivAt b).nhds_eq_comap_inf_principal (mk_mem_localTrivAt_source _ _ _), comap_inf,
comap_principal, comap_comap]
simp only [Function.comp_def, localTrivAt_apply_mk, Trivialization.coe_coe,
← (isEmbedding_prodMk b).nhds_eq_comap]
convert_to 𝓝 x = 𝓝 x ⊓ 𝓟 univ
· congr
exact eq_univ_of_forall (mk_mem_localTrivAt_source Z _)
· rw [principal_univ, inf_top_eq]
trivializationAtlas' := Set.range Z.localTriv
trivializationAt' := Z.localTrivAt
mem_baseSet_trivializationAt' := Z.mem_baseSet_at
trivialization_mem_atlas' b := ⟨Z.indexAt b, rfl⟩
/-- The inclusion of a fiber into the total space is a continuous map. -/
@[continuity]
theorem continuous_totalSpaceMk (b : B) :
Continuous (TotalSpace.mk b : Z.Fiber b → Bundle.TotalSpace F Z.Fiber) :=
FiberBundle.continuous_totalSpaceMk F Z.Fiber b
/-- The projection on the base of a fiber bundle created from core is continuous -/
nonrec theorem continuous_proj : Continuous Z.proj :=
FiberBundle.continuous_proj F Z.Fiber
/-- The projection on the base of a fiber bundle created from core is an open map -/
nonrec theorem isOpenMap_proj : IsOpenMap Z.proj :=
FiberBundle.isOpenMap_proj F Z.Fiber
end FiberBundleCore
/-! ### Prebundle construction for constructing fiber bundles -/
variable (F)
variable (E : B → Type*) [TopologicalSpace B] [TopologicalSpace F]
[∀ x, TopologicalSpace (E x)]
/-- This structure permits to define a fiber bundle when trivializations are given as local
equivalences but there is not yet a topology on the total space. The total space is hence given a
topology in such a way that there is a fiber bundle structure for which the partial equivalences
are also partial homeomorphisms and hence local trivializations. -/
structure FiberPrebundle where
pretrivializationAtlas : Set (Pretrivialization F (π F E))
pretrivializationAt : B → Pretrivialization F (π F E)
mem_base_pretrivializationAt : ∀ x : B, x ∈ (pretrivializationAt x).baseSet
pretrivialization_mem_atlas : ∀ x : B, pretrivializationAt x ∈ pretrivializationAtlas
continuous_trivChange : ∀ e, e ∈ pretrivializationAtlas → ∀ e', e' ∈ pretrivializationAtlas →
ContinuousOn (e ∘ e'.toPartialEquiv.symm) (e'.target ∩ e'.toPartialEquiv.symm ⁻¹' e.source)
totalSpaceMk_isInducing : ∀ b : B, IsInducing (pretrivializationAt b ∘ TotalSpace.mk b)
namespace FiberPrebundle
variable {F E}
variable (a : FiberPrebundle F E) {e : Pretrivialization F (π F E)}
/-- Topology on the total space that will make the prebundle into a bundle. -/
def totalSpaceTopology (a : FiberPrebundle F E) : TopologicalSpace (TotalSpace F E) :=
⨆ (e : Pretrivialization F (π F E)) (_ : e ∈ a.pretrivializationAtlas),
coinduced e.setSymm instTopologicalSpaceSubtype
theorem continuous_symm_of_mem_pretrivializationAtlas (he : e ∈ a.pretrivializationAtlas) :
@ContinuousOn _ _ _ a.totalSpaceTopology e.toPartialEquiv.symm e.target := by
refine fun z H U h => preimage_nhdsWithin_coinduced' H (le_def.1 (nhds_mono ?_) U h)
exact le_iSup₂ (α := TopologicalSpace (TotalSpace F E)) e he
theorem isOpen_source (e : Pretrivialization F (π F E)) :
IsOpen[a.totalSpaceTopology] e.source := by
refine isOpen_iSup_iff.mpr fun e' => isOpen_iSup_iff.mpr fun _ => ?_
refine isOpen_coinduced.mpr (isOpen_induced_iff.mpr ⟨e.target, e.open_target, ?_⟩)
ext ⟨x, hx⟩
simp only [mem_preimage, Pretrivialization.setSymm, restrict, e.mem_target, e.mem_source,
e'.proj_symm_apply hx]
theorem isOpen_target_of_mem_pretrivializationAtlas_inter (e e' : Pretrivialization F (π F E))
(he' : e' ∈ a.pretrivializationAtlas) :
IsOpen (e'.toPartialEquiv.target ∩ e'.toPartialEquiv.symm ⁻¹' e.source) := by
letI := a.totalSpaceTopology
obtain ⟨u, hu1, hu2⟩ := continuousOn_iff'.mp (a.continuous_symm_of_mem_pretrivializationAtlas he')
e.source (a.isOpen_source e)
rw [inter_comm, hu2]
exact hu1.inter e'.open_target
/-- Promotion from a `Pretrivialization` to a `Trivialization`. -/
def trivializationOfMemPretrivializationAtlas (he : e ∈ a.pretrivializationAtlas) :
@Trivialization B F _ _ _ a.totalSpaceTopology (π F E) :=
let _ := a.totalSpaceTopology
{ e with
open_source := a.isOpen_source e,
continuousOn_toFun := by
refine continuousOn_iff'.mpr fun s hs => ⟨e ⁻¹' s ∩ e.source,
isOpen_iSup_iff.mpr fun e' => ?_, by rw [inter_assoc, inter_self]; rfl⟩
refine isOpen_iSup_iff.mpr fun he' => ?_
rw [isOpen_coinduced, isOpen_induced_iff]
obtain ⟨u, hu1, hu2⟩ := continuousOn_iff'.mp (a.continuous_trivChange _ he _ he') s hs
have hu3 := congr_arg (fun s => (fun x : e'.target => (x : B × F)) ⁻¹' s) hu2
simp only [Subtype.coe_preimage_self, preimage_inter, univ_inter] at hu3
refine ⟨u ∩ e'.toPartialEquiv.target ∩ e'.toPartialEquiv.symm ⁻¹' e.source, ?_, by
simp only [preimage_inter, inter_univ, Subtype.coe_preimage_self, hu3.symm]; rfl⟩
rw [inter_assoc]
exact hu1.inter (a.isOpen_target_of_mem_pretrivializationAtlas_inter e e' he')
continuousOn_invFun := a.continuous_symm_of_mem_pretrivializationAtlas he }
theorem mem_pretrivializationAt_source (b : B) (x : E b) :
⟨b, x⟩ ∈ (a.pretrivializationAt b).source := by
simp only [(a.pretrivializationAt b).source_eq, mem_preimage, TotalSpace.proj]
exact a.mem_base_pretrivializationAt b
@[simp]
theorem totalSpaceMk_preimage_source (b : B) :
TotalSpace.mk b ⁻¹' (a.pretrivializationAt b).source = univ :=
eq_univ_of_forall (a.mem_pretrivializationAt_source b)
@[continuity]
theorem continuous_totalSpaceMk (b : B) :
Continuous[_, a.totalSpaceTopology] (TotalSpace.mk b) := by
letI := a.totalSpaceTopology
let e := a.trivializationOfMemPretrivializationAtlas (a.pretrivialization_mem_atlas b)
rw [e.toPartialHomeomorph.continuous_iff_continuous_comp_left
(a.totalSpaceMk_preimage_source b)]
exact continuous_iff_le_induced.2 (a.totalSpaceMk_isInducing b).eq_induced.le
theorem inducing_totalSpaceMk_of_inducing_comp (b : B)
(h : IsInducing (a.pretrivializationAt b ∘ TotalSpace.mk b)) :
| @IsInducing _ _ _ a.totalSpaceTopology (TotalSpace.mk b) := by
letI := a.totalSpaceTopology
rw [← restrict_comp_codRestrict (a.mem_pretrivializationAt_source b)] at h
apply IsInducing.of_codRestrict (a.mem_pretrivializationAt_source b)
refine h.of_comp ?_ (continuousOn_iff_continuous_restrict.mp
(a.trivializationOfMemPretrivializationAtlas (a.pretrivialization_mem_atlas b)).continuousOn)
exact (a.continuous_totalSpaceMk b).codRestrict (a.mem_pretrivializationAt_source b)
| Mathlib/Topology/FiberBundle/Basic.lean | 801 | 808 |
/-
Copyright (c) 2019 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Markus Himmel
-/
import Mathlib.CategoryTheory.Limits.Preserves.Shapes.Zero
/-!
# Kernels and cokernels
In a category with zero morphisms, the kernel of a morphism `f : X ⟶ Y` is
the equalizer of `f` and `0 : X ⟶ Y`. (Similarly the cokernel is the coequalizer.)
The basic definitions are
* `kernel : (X ⟶ Y) → C`
* `kernel.ι : kernel f ⟶ X`
* `kernel.condition : kernel.ι f ≫ f = 0` and
* `kernel.lift (k : W ⟶ X) (h : k ≫ f = 0) : W ⟶ kernel f` (as well as the dual versions)
## Main statements
Besides the definition and lifts, we prove
* `kernel.ιZeroIsIso`: a kernel map of a zero morphism is an isomorphism
* `kernel.eq_zero_of_epi_kernel`: if `kernel.ι f` is an epimorphism, then `f = 0`
* `kernel.ofMono`: the kernel of a monomorphism is the zero object
* `kernel.liftMono`: the lift of a monomorphism `k : W ⟶ X` such that `k ≫ f = 0`
is still a monomorphism
* `kernel.isLimitConeZeroCone`: if our category has a zero object, then the map from the zero
object is a kernel map of any monomorphism
* `kernel.ιOfZero`: `kernel.ι (0 : X ⟶ Y)` is an isomorphism
and the corresponding dual statements.
## Future work
* TODO: connect this with existing work in the group theory and ring theory libraries.
## Implementation notes
As with the other special shapes in the limits library, all the definitions here are given as
`abbreviation`s of the general statements for limits, so all the `simp` lemmas and theorems about
general limits can be used.
## References
* [F. Borceux, *Handbook of Categorical Algebra 2*][borceux-vol2]
-/
noncomputable section
universe v v₂ u u' u₂
open CategoryTheory
open CategoryTheory.Limits.WalkingParallelPair
namespace CategoryTheory.Limits
variable {C : Type u} [Category.{v} C]
variable [HasZeroMorphisms C]
/-- A morphism `f` has a kernel if the functor `ParallelPair f 0` has a limit. -/
abbrev HasKernel {X Y : C} (f : X ⟶ Y) : Prop :=
HasLimit (parallelPair f 0)
/-- A morphism `f` has a cokernel if the functor `ParallelPair f 0` has a colimit. -/
abbrev HasCokernel {X Y : C} (f : X ⟶ Y) : Prop :=
HasColimit (parallelPair f 0)
variable {X Y : C} (f : X ⟶ Y)
section
/-- A kernel fork is just a fork where the second morphism is a zero morphism. -/
abbrev KernelFork :=
Fork f 0
variable {f}
@[reassoc (attr := simp)]
theorem KernelFork.condition (s : KernelFork f) : Fork.ι s ≫ f = 0 := by
rw [Fork.condition, HasZeroMorphisms.comp_zero]
theorem KernelFork.app_one (s : KernelFork f) : s.π.app one = 0 := by
simp [Fork.app_one_eq_ι_comp_right]
|
/-- A morphism `ι` satisfying `ι ≫ f = 0` determines a kernel fork over `f`. -/
| Mathlib/CategoryTheory/Limits/Shapes/Kernels.lean | 86 | 87 |
/-
Copyright (c) 2022 Floris van Doorn, Heather Macbeth. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Floris van Doorn, Heather Macbeth
-/
import Mathlib.Geometry.Manifold.ContMDiff.Atlas
import Mathlib.Geometry.Manifold.VectorBundle.FiberwiseLinear
import Mathlib.Topology.VectorBundle.Constructions
/-! # `C^n` vector bundles
This file defines `C^n` vector bundles over a manifold.
Let `E` be a topological vector bundle, with model fiber `F` and base space `B`. We consider `E` as
carrying a charted space structure given by its trivializations -- these are charts to `B × F`.
Then, by "composition", if `B` is itself a charted space over `H` (e.g. a smooth manifold), then `E`
is also a charted space over `H × F`.
Now, we define `ContMDiffVectorBundle` as the `Prop` of having `C^n` transition functions.
Recall the structure groupoid `contMDiffFiberwiseLinear` on `B × F` consisting of `C^n`, fiberwise
linear partial homeomorphisms. We show that our definition of "`C^n` vector bundle" implies
`HasGroupoid` for this groupoid, and show (by a "composition" of `HasGroupoid` instances) that
this means that a `C^n` vector bundle is a `C^n` manifold.
Since `ContMDiffVectorBundle` is a mixin, it should be easy to make variants and for many such
variants to coexist -- vector bundles can be `C^n` vector bundles over several different base
fields, etc.
## Main definitions and constructions
* `FiberBundle.chartedSpace`: A fiber bundle `E` over a base `B` with model fiber `F` is naturally
a charted space modelled on `B × F`.
* `FiberBundle.chartedSpace'`: Let `B` be a charted space modelled on `HB`. Then a fiber bundle
`E` over a base `B` with model fiber `F` is naturally a charted space modelled on `HB.prod F`.
* `ContMDiffVectorBundle`: Mixin class stating that a (topological) `VectorBundle` is `C^n`, in the
sense of having `C^n` transition functions, where the smoothness index `n`
belongs to `WithTop ℕ∞`.
* `ContMDiffFiberwiseLinear.hasGroupoid`: For a `C^n` vector bundle `E` over `B` with fiber
modelled on `F`, the change-of-co-ordinates between two trivializations `e`, `e'` for `E`,
considered as charts to `B × F`, is `C^n` and fiberwise linear, in the sense of belonging to the
structure groupoid `contMDiffFiberwiseLinear`.
* `Bundle.TotalSpace.isManifold`: A `C^n` vector bundle is naturally a `C^n` manifold.
* `VectorBundleCore.instContMDiffVectorBundle`: If a (topological) `VectorBundleCore` is `C^n`,
in the sense of having `C^n` transition functions (cf. `VectorBundleCore.IsContMDiff`),
then the vector bundle constructed from it is a `C^n` vector bundle.
* `VectorPrebundle.contMDiffVectorBundle`: If a `VectorPrebundle` is `C^n`,
in the sense of having `C^n` transition functions (cf. `VectorPrebundle.IsContMDiff`),
then the vector bundle constructed from it is a `C^n` vector bundle.
* `Bundle.Prod.contMDiffVectorBundle`: The direct sum of two `C^n` vector bundles is a `C^n`
vector bundle.
-/
assert_not_exists mfderiv
open Bundle Set PartialHomeomorph
open Function (id_def)
open Filter
open scoped Manifold Bundle Topology ContDiff
variable {n : WithTop ℕ∞} {𝕜 B B' F M : Type*} {E : B → Type*}
/-! ### Charted space structure on a fiber bundle -/
section
variable [TopologicalSpace F] [TopologicalSpace (TotalSpace F E)] [∀ x, TopologicalSpace (E x)]
{HB : Type*} [TopologicalSpace HB] [TopologicalSpace B] [ChartedSpace HB B] [FiberBundle F E]
/-- A fiber bundle `E` over a base `B` with model fiber `F` is naturally a charted space modelled on
`B × F`. -/
instance FiberBundle.chartedSpace' : ChartedSpace (B × F) (TotalSpace F E) where
atlas := (fun e : Trivialization F (π F E) => e.toPartialHomeomorph) '' trivializationAtlas F E
chartAt x := (trivializationAt F E x.proj).toPartialHomeomorph
mem_chart_source x :=
(trivializationAt F E x.proj).mem_source.mpr (mem_baseSet_trivializationAt F E x.proj)
chart_mem_atlas _ := mem_image_of_mem _ (trivialization_mem_atlas F E _)
theorem FiberBundle.chartedSpace'_chartAt (x : TotalSpace F E) :
chartAt (B × F) x = (trivializationAt F E x.proj).toPartialHomeomorph :=
rfl
/- Porting note: In Lean 3, the next instance was inside a section with locally reducible
`ModelProd` and it used `ModelProd B F` as the intermediate space. Using `B × F` in the middle
gives the same instance.
-/
--attribute [local reducible] ModelProd
/-- Let `B` be a charted space modelled on `HB`. Then a fiber bundle `E` over a base `B` with model
fiber `F` is naturally a charted space modelled on `HB.prod F`. -/
instance FiberBundle.chartedSpace : ChartedSpace (ModelProd HB F) (TotalSpace F E) :=
ChartedSpace.comp _ (B × F) _
theorem FiberBundle.chartedSpace_chartAt (x : TotalSpace F E) :
chartAt (ModelProd HB F) x =
(trivializationAt F E x.proj).toPartialHomeomorph ≫ₕ
(chartAt HB x.proj).prod (PartialHomeomorph.refl F) := by
dsimp only [chartAt_comp, prodChartedSpace_chartAt, FiberBundle.chartedSpace'_chartAt,
chartAt_self_eq]
rw [Trivialization.coe_coe, Trivialization.coe_fst' _ (mem_baseSet_trivializationAt F E x.proj)]
theorem FiberBundle.chartedSpace_chartAt_symm_fst (x : TotalSpace F E) (y : ModelProd HB F)
(hy : y ∈ (chartAt (ModelProd HB F) x).target) :
((chartAt (ModelProd HB F) x).symm y).proj = (chartAt HB x.proj).symm y.1 := by
simp only [FiberBundle.chartedSpace_chartAt, mfld_simps] at hy ⊢
exact (trivializationAt F E x.proj).proj_symm_apply hy.2
end
section
variable [NontriviallyNormedField 𝕜] [NormedAddCommGroup F] [NormedSpace 𝕜 F]
[TopologicalSpace (TotalSpace F E)] [∀ x, TopologicalSpace (E x)] {EB : Type*}
[NormedAddCommGroup EB] [NormedSpace 𝕜 EB] {HB : Type*} [TopologicalSpace HB]
{IB : ModelWithCorners 𝕜 EB HB} (E' : B → Type*) [∀ x, Zero (E' x)] {EM : Type*}
[NormedAddCommGroup EM] [NormedSpace 𝕜 EM] {HM : Type*} [TopologicalSpace HM]
{IM : ModelWithCorners 𝕜 EM HM} [TopologicalSpace M] [ChartedSpace HM M]
variable [TopologicalSpace B] [ChartedSpace HB B] [FiberBundle F E]
protected theorem FiberBundle.extChartAt (x : TotalSpace F E) :
extChartAt (IB.prod 𝓘(𝕜, F)) x =
(trivializationAt F E x.proj).toPartialEquiv ≫
(extChartAt IB x.proj).prod (PartialEquiv.refl F) := by
simp_rw [extChartAt, FiberBundle.chartedSpace_chartAt, extend]
simp only [PartialEquiv.trans_assoc, mfld_simps]
-- Porting note: should not be needed
rw [PartialEquiv.prod_trans, PartialEquiv.refl_trans]
protected theorem FiberBundle.extChartAt_target (x : TotalSpace F E) :
(extChartAt (IB.prod 𝓘(𝕜, F)) x).target =
((extChartAt IB x.proj).target ∩
(extChartAt IB x.proj).symm ⁻¹' (trivializationAt F E x.proj).baseSet) ×ˢ univ := by
rw [FiberBundle.extChartAt, PartialEquiv.trans_target, Trivialization.target_eq, inter_prod]
rfl
theorem FiberBundle.writtenInExtChartAt_trivializationAt {x : TotalSpace F E} {y}
(hy : y ∈ (extChartAt (IB.prod 𝓘(𝕜, F)) x).target) :
writtenInExtChartAt (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) x
(trivializationAt F E x.proj) y = y :=
writtenInExtChartAt_chartAt_comp _ hy
theorem FiberBundle.writtenInExtChartAt_trivializationAt_symm {x : TotalSpace F E} {y}
(hy : y ∈ (extChartAt (IB.prod 𝓘(𝕜, F)) x).target) :
writtenInExtChartAt (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) (trivializationAt F E x.proj x)
(trivializationAt F E x.proj).toPartialHomeomorph.symm y = y :=
writtenInExtChartAt_chartAt_symm_comp _ hy
/-! ### Regularity of maps in/out fiber bundles
Note: For these results we don't need that the bundle is a `C^n` vector bundle, or even a vector
bundle at all, just that it is a fiber bundle over a charted base space.
-/
namespace Bundle
/-- Characterization of `C^n` functions into a vector bundle. -/
theorem contMDiffWithinAt_totalSpace (f : M → TotalSpace F E) {s : Set M} {x₀ : M} :
ContMDiffWithinAt IM (IB.prod 𝓘(𝕜, F)) n f s x₀ ↔
ContMDiffWithinAt IM IB n (fun x => (f x).proj) s x₀ ∧
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun x ↦ (trivializationAt F E (f x₀).proj (f x)).2) s x₀ := by
simp +singlePass only [contMDiffWithinAt_iff_target]
rw [and_and_and_comm, ← FiberBundle.continuousWithinAt_totalSpace, and_congr_right_iff]
intro hf
simp_rw [modelWithCornersSelf_prod, FiberBundle.extChartAt, Function.comp_def,
PartialEquiv.trans_apply, PartialEquiv.prod_coe, PartialEquiv.refl_coe,
extChartAt_self_apply, modelWithCornersSelf_coe, Function.id_def, ← chartedSpaceSelf_prod]
refine (contMDiffWithinAt_prod_iff _).trans (and_congr ?_ Iff.rfl)
have h1 : (fun x => (f x).proj) ⁻¹' (trivializationAt F E (f x₀).proj).baseSet ∈ 𝓝[s] x₀ :=
((FiberBundle.continuous_proj F E).continuousWithinAt.comp hf (mapsTo_image f s))
((Trivialization.open_baseSet _).mem_nhds (mem_baseSet_trivializationAt F E _))
refine EventuallyEq.contMDiffWithinAt_iff (eventually_of_mem h1 fun x hx => ?_) ?_
· simp_rw [Function.comp, PartialHomeomorph.coe_coe, Trivialization.coe_coe]
rw [Trivialization.coe_fst']
exact hx
· simp only [mfld_simps]
/-- Characterization of `C^n` functions into a vector bundle. -/
theorem contMDiffAt_totalSpace (f : M → TotalSpace F E) (x₀ : M) :
ContMDiffAt IM (IB.prod 𝓘(𝕜, F)) n f x₀ ↔
ContMDiffAt IM IB n (fun x => (f x).proj) x₀ ∧
ContMDiffAt IM 𝓘(𝕜, F) n (fun x => (trivializationAt F E (f x₀).proj (f x)).2) x₀ := by
simp_rw [← contMDiffWithinAt_univ]; exact contMDiffWithinAt_totalSpace f
/-- Characterization of `C^n` sections within a set at a point of a vector bundle. -/
theorem contMDiffWithinAt_section (s : ∀ x, E x) (a : Set B) (x₀ : B) :
ContMDiffWithinAt IB (IB.prod 𝓘(𝕜, F)) n (fun x => TotalSpace.mk' F x (s x)) a x₀ ↔
ContMDiffWithinAt IB 𝓘(𝕜, F) n (fun x ↦ (trivializationAt F E x₀ ⟨x, s x⟩).2) a x₀ := by
simp_rw [contMDiffWithinAt_totalSpace, and_iff_right_iff_imp]; intro; exact contMDiffWithinAt_id
/-- Characterization of `C^n` sections of a vector bundle. -/
theorem contMDiffAt_section (s : ∀ x, E x) (x₀ : B) :
ContMDiffAt IB (IB.prod 𝓘(𝕜, F)) n (fun x => TotalSpace.mk' F x (s x)) x₀ ↔
ContMDiffAt IB 𝓘(𝕜, F) n (fun x ↦ (trivializationAt F E x₀ ⟨x, s x⟩).2) x₀ := by
simp_rw [contMDiffAt_totalSpace, and_iff_right_iff_imp]; intro; exact contMDiffAt_id
variable (E)
theorem contMDiff_proj : ContMDiff (IB.prod 𝓘(𝕜, F)) IB n (π F E) := fun x ↦ by
have : ContMDiffAt (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) n id x := contMDiffAt_id
rw [contMDiffAt_totalSpace] at this
exact this.1
@[deprecated (since := "2024-11-21")] alias smooth_proj := contMDiff_proj
theorem contMDiffOn_proj {s : Set (TotalSpace F E)} :
ContMDiffOn (IB.prod 𝓘(𝕜, F)) IB n (π F E) s :=
(Bundle.contMDiff_proj E).contMDiffOn
@[deprecated (since := "2024-11-21")] alias smoothOn_proj := contMDiffOn_proj
theorem contMDiffAt_proj {p : TotalSpace F E} : ContMDiffAt (IB.prod 𝓘(𝕜, F)) IB n (π F E) p :=
(Bundle.contMDiff_proj E).contMDiffAt
@[deprecated (since := "2024-11-21")] alias smoothAt_proj := contMDiffAt_proj
theorem contMDiffWithinAt_proj {s : Set (TotalSpace F E)} {p : TotalSpace F E} :
ContMDiffWithinAt (IB.prod 𝓘(𝕜, F)) IB n (π F E) s p :=
(Bundle.contMDiffAt_proj E).contMDiffWithinAt
@[deprecated (since := "2024-11-21")] alias smoothWithinAt_proj := contMDiffWithinAt_proj
variable (𝕜) [∀ x, AddCommMonoid (E x)]
variable [∀ x, Module 𝕜 (E x)] [VectorBundle 𝕜 F E]
theorem contMDiff_zeroSection : ContMDiff IB (IB.prod 𝓘(𝕜, F)) n (zeroSection F E) := fun x ↦ by
unfold zeroSection
rw [Bundle.contMDiffAt_section]
apply (contMDiffAt_const (c := 0)).congr_of_eventuallyEq
filter_upwards [(trivializationAt F E x).open_baseSet.mem_nhds
(mem_baseSet_trivializationAt F E x)] with y hy
using congr_arg Prod.snd <| (trivializationAt F E x).zeroSection 𝕜 hy
@[deprecated (since := "2024-11-21")] alias smooth_zeroSection := contMDiff_zeroSection
end Bundle
end
/-! ### `C^n` vector bundles -/
variable [NontriviallyNormedField 𝕜] {EB : Type*} [NormedAddCommGroup EB] [NormedSpace 𝕜 EB]
{HB : Type*} [TopologicalSpace HB] {IB : ModelWithCorners 𝕜 EB HB} [TopologicalSpace B]
[ChartedSpace HB B] {EM : Type*} [NormedAddCommGroup EM]
[NormedSpace 𝕜 EM] {HM : Type*} [TopologicalSpace HM] {IM : ModelWithCorners 𝕜 EM HM}
[TopologicalSpace M] [ChartedSpace HM M]
[∀ x, AddCommMonoid (E x)] [∀ x, Module 𝕜 (E x)] [NormedAddCommGroup F] [NormedSpace 𝕜 F]
section WithTopology
variable [TopologicalSpace (TotalSpace F E)] [∀ x, TopologicalSpace (E x)] (F E)
variable [FiberBundle F E] [VectorBundle 𝕜 F E]
variable (n IB) in
/-- When `B` is a manifold with respect to a model `IB` and `E` is a
topological vector bundle over `B` with fibers isomorphic to `F`,
then `ContMDiffVectorBundle n F E IB` registers that the bundle is `C^n`, in the sense of having
`C^n` transition functions. This is a mixin, not carrying any new data. -/
class ContMDiffVectorBundle : Prop where
protected contMDiffOn_coordChangeL :
∀ (e e' : Trivialization F (π F E)) [MemTrivializationAtlas e] [MemTrivializationAtlas e'],
ContMDiffOn IB 𝓘(𝕜, F →L[𝕜] F) n (fun b : B => (e.coordChangeL 𝕜 e' b : F →L[𝕜] F))
(e.baseSet ∩ e'.baseSet)
@[deprecated (since := "2025-01-09")] alias SmoothVectorBundle := ContMDiffVectorBundle
variable {F E} in
protected theorem ContMDiffVectorBundle.of_le {m n : WithTop ℕ∞} (hmn : m ≤ n)
[h : ContMDiffVectorBundle n F E IB] : ContMDiffVectorBundle m F E IB :=
⟨fun e e' _ _ ↦ (h.contMDiffOn_coordChangeL e e').of_le hmn⟩
instance {a : WithTop ℕ∞} [ContMDiffVectorBundle ∞ F E IB] [h : ENat.LEInfty a] :
ContMDiffVectorBundle a F E IB :=
ContMDiffVectorBundle.of_le h.out
instance {a : WithTop ℕ∞} [ContMDiffVectorBundle ω F E IB] : ContMDiffVectorBundle a F E IB :=
ContMDiffVectorBundle.of_le le_top
instance [ContMDiffVectorBundle 2 F E IB] : ContMDiffVectorBundle 1 F E IB :=
ContMDiffVectorBundle.of_le one_le_two
instance : ContMDiffVectorBundle 0 F E IB := by
constructor
intro e e' he he'
rw [contMDiffOn_zero_iff]
exact VectorBundle.continuousOn_coordChange' e e'
variable [ContMDiffVectorBundle n F E IB]
section ContMDiffCoordChange
variable {F E}
variable (e e' : Trivialization F (π F E)) [MemTrivializationAtlas e] [MemTrivializationAtlas e']
theorem contMDiffOn_coordChangeL :
ContMDiffOn IB 𝓘(𝕜, F →L[𝕜] F) n (fun b : B => (e.coordChangeL 𝕜 e' b : F →L[𝕜] F))
(e.baseSet ∩ e'.baseSet) :=
ContMDiffVectorBundle.contMDiffOn_coordChangeL e e'
theorem contMDiffOn_symm_coordChangeL :
ContMDiffOn IB 𝓘(𝕜, F →L[𝕜] F) n (fun b : B => ((e.coordChangeL 𝕜 e' b).symm : F →L[𝕜] F))
(e.baseSet ∩ e'.baseSet) := by
rw [inter_comm]
refine (ContMDiffVectorBundle.contMDiffOn_coordChangeL e' e).congr fun b hb ↦ ?_
rw [e.symm_coordChangeL e' hb]
@[deprecated (since := "2024-11-21")] alias smoothOn_coordChangeL := contMDiffOn_coordChangeL
@[deprecated (since := "2024-11-21")]
alias smoothOn_symm_coordChangeL := contMDiffOn_symm_coordChangeL
variable {e e'}
theorem contMDiffAt_coordChangeL {x : B} (h : x ∈ e.baseSet) (h' : x ∈ e'.baseSet) :
ContMDiffAt IB 𝓘(𝕜, F →L[𝕜] F) n (fun b : B => (e.coordChangeL 𝕜 e' b : F →L[𝕜] F)) x :=
(contMDiffOn_coordChangeL e e').contMDiffAt <|
(e.open_baseSet.inter e'.open_baseSet).mem_nhds ⟨h, h'⟩
@[deprecated (since := "2024-11-21")] alias smoothAt_coordChangeL := contMDiffAt_coordChangeL
variable {s : Set M} {f : M → B} {g : M → F} {x : M}
protected theorem ContMDiffWithinAt.coordChangeL
(hf : ContMDiffWithinAt IM IB n f s x) (he : f x ∈ e.baseSet) (he' : f x ∈ e'.baseSet) :
ContMDiffWithinAt IM 𝓘(𝕜, F →L[𝕜] F) n (fun y ↦ (e.coordChangeL 𝕜 e' (f y) : F →L[𝕜] F)) s x :=
(contMDiffAt_coordChangeL he he').comp_contMDiffWithinAt _ hf
protected nonrec theorem ContMDiffAt.coordChangeL
(hf : ContMDiffAt IM IB n f x) (he : f x ∈ e.baseSet) (he' : f x ∈ e'.baseSet) :
ContMDiffAt IM 𝓘(𝕜, F →L[𝕜] F) n (fun y ↦ (e.coordChangeL 𝕜 e' (f y) : F →L[𝕜] F)) x :=
hf.coordChangeL he he'
protected theorem ContMDiffOn.coordChangeL
(hf : ContMDiffOn IM IB n f s) (he : MapsTo f s e.baseSet) (he' : MapsTo f s e'.baseSet) :
ContMDiffOn IM 𝓘(𝕜, F →L[𝕜] F) n (fun y ↦ (e.coordChangeL 𝕜 e' (f y) : F →L[𝕜] F)) s :=
fun x hx ↦ (hf x hx).coordChangeL (he hx) (he' hx)
protected theorem ContMDiff.coordChangeL
(hf : ContMDiff IM IB n f) (he : ∀ x, f x ∈ e.baseSet) (he' : ∀ x, f x ∈ e'.baseSet) :
ContMDiff IM 𝓘(𝕜, F →L[𝕜] F) n (fun y ↦ (e.coordChangeL 𝕜 e' (f y) : F →L[𝕜] F)) := fun x ↦
(hf x).coordChangeL (he x) (he' x)
@[deprecated (since := "2024-11-21")]
alias SmoothWithinAt.coordChangeL := ContMDiffWithinAt.coordChangeL
@[deprecated (since := "2024-11-21")]
alias SmoothAt.coordChangeL := ContMDiffAt.coordChangeL
@[deprecated (since := "2024-11-21")]
alias SmoothOn.coordChangeL := ContMDiffOn.coordChangeL
@[deprecated (since := "2024-11-21")]
alias Smooth.coordChangeL := ContMDiff.coordChangeL
protected theorem ContMDiffWithinAt.coordChange
(hf : ContMDiffWithinAt IM IB n f s x) (hg : ContMDiffWithinAt IM 𝓘(𝕜, F) n g s x)
(he : f x ∈ e.baseSet) (he' : f x ∈ e'.baseSet) :
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun y ↦ e.coordChange e' (f y) (g y)) s x := by
refine ((hf.coordChangeL he he').clm_apply hg).congr_of_eventuallyEq ?_ ?_
· have : e.baseSet ∩ e'.baseSet ∈ 𝓝 (f x) :=
(e.open_baseSet.inter e'.open_baseSet).mem_nhds ⟨he, he'⟩
filter_upwards [hf.continuousWithinAt this] with y hy
exact (Trivialization.coordChangeL_apply' e e' hy (g y)).symm
· exact (Trivialization.coordChangeL_apply' e e' ⟨he, he'⟩ (g x)).symm
protected nonrec theorem ContMDiffAt.coordChange
(hf : ContMDiffAt IM IB n f x) (hg : ContMDiffAt IM 𝓘(𝕜, F) n g x) (he : f x ∈ e.baseSet)
(he' : f x ∈ e'.baseSet) :
ContMDiffAt IM 𝓘(𝕜, F) n (fun y ↦ e.coordChange e' (f y) (g y)) x :=
hf.coordChange hg he he'
protected theorem ContMDiffOn.coordChange (hf : ContMDiffOn IM IB n f s)
(hg : ContMDiffOn IM 𝓘(𝕜, F) n g s) (he : MapsTo f s e.baseSet) (he' : MapsTo f s e'.baseSet) :
ContMDiffOn IM 𝓘(𝕜, F) n (fun y ↦ e.coordChange e' (f y) (g y)) s := fun x hx ↦
(hf x hx).coordChange (hg x hx) (he hx) (he' hx)
protected theorem ContMDiff.coordChange (hf : ContMDiff IM IB n f)
(hg : ContMDiff IM 𝓘(𝕜, F) n g) (he : ∀ x, f x ∈ e.baseSet) (he' : ∀ x, f x ∈ e'.baseSet) :
ContMDiff IM 𝓘(𝕜, F) n (fun y ↦ e.coordChange e' (f y) (g y)) := fun x ↦
(hf x).coordChange (hg x) (he x) (he' x)
@[deprecated (since := "2024-11-21")]
alias SmoothWithinAt.coordChange := ContMDiffWithinAt.coordChange
@[deprecated (since := "2024-11-21")]
alias SmoothAt.coordChange := ContMDiffAt.coordChange
@[deprecated (since := "2024-11-21")]
alias SmoothOn.coordChange := ContMDiffOn.coordChange
@[deprecated (since := "2024-11-21")]
alias Smooth.coordChange := ContMDiff.coordChange
variable (e e')
variable (IB) in
theorem Trivialization.contMDiffOn_symm_trans :
ContMDiffOn (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) n
(e.toPartialHomeomorph.symm ≫ₕ e'.toPartialHomeomorph) (e.target ∩ e'.target) := by
have Hmaps : MapsTo Prod.fst (e.target ∩ e'.target) (e.baseSet ∩ e'.baseSet) := fun x hx ↦
⟨e.mem_target.1 hx.1, e'.mem_target.1 hx.2⟩
rw [mapsTo_inter] at Hmaps
-- TODO: drop `congr` https://github.com/leanprover-community/mathlib4/issues/5473
refine (contMDiffOn_fst.prodMk
(contMDiffOn_fst.coordChange contMDiffOn_snd Hmaps.1 Hmaps.2)).congr ?_
rintro ⟨b, x⟩ hb
refine Prod.ext ?_ rfl
have : (e.toPartialHomeomorph.symm (b, x)).1 ∈ e'.baseSet := by
simp_all only [Trivialization.mem_target, mfld_simps]
exact (e'.coe_fst' this).trans (e.proj_symm_apply hb.1)
variable {e e'}
theorem ContMDiffWithinAt.change_section_trivialization {f : M → TotalSpace F E}
(hp : ContMDiffWithinAt IM IB n (π F E ∘ f) s x)
(hf : ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun y ↦ (e (f y)).2) s x)
(he : f x ∈ e.source) (he' : f x ∈ e'.source) :
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun y ↦ (e' (f y)).2) s x := by
rw [Trivialization.mem_source] at he he'
refine (hp.coordChange hf he he').congr_of_eventuallyEq ?_ ?_
· filter_upwards [hp.continuousWithinAt (e.open_baseSet.mem_nhds he)] with y hy
rw [Function.comp_apply, e.coordChange_apply_snd _ hy]
· rw [Function.comp_apply, e.coordChange_apply_snd _ he]
theorem Trivialization.contMDiffWithinAt_snd_comp_iff₂ {f : M → TotalSpace F E}
(hp : ContMDiffWithinAt IM IB n (π F E ∘ f) s x)
(he : f x ∈ e.source) (he' : f x ∈ e'.source) :
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun y ↦ (e (f y)).2) s x ↔
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun y ↦ (e' (f y)).2) s x :=
⟨(hp.change_section_trivialization · he he'), (hp.change_section_trivialization · he' he)⟩
end ContMDiffCoordChange
variable [IsManifold IB n B] in
/-- For a `C^n` vector bundle `E` over `B` with fiber modelled on `F`, the change-of-co-ordinates
between two trivializations `e`, `e'` for `E`, considered as charts to `B × F`, is `C^n` and
fiberwise linear. -/
instance ContMDiffFiberwiseLinear.hasGroupoid :
HasGroupoid (TotalSpace F E) (contMDiffFiberwiseLinear B F IB n) where
compatible := by
rintro _ _ ⟨e, he, rfl⟩ ⟨e', he', rfl⟩
haveI : MemTrivializationAtlas e := ⟨he⟩
haveI : MemTrivializationAtlas e' := ⟨he'⟩
rw [mem_contMDiffFiberwiseLinear_iff]
refine ⟨_, _, e.open_baseSet.inter e'.open_baseSet, contMDiffOn_coordChangeL e e',
contMDiffOn_symm_coordChangeL e e', ?_⟩
refine PartialHomeomorph.eqOnSourceSetoid.symm ⟨?_, ?_⟩
· simp only [e.symm_trans_source_eq e', FiberwiseLinear.partialHomeomorph, trans_toPartialEquiv,
symm_toPartialEquiv]
· rintro ⟨b, v⟩ hb
exact (e.apply_symm_apply_eq_coordChangeL e' hb.1 v).symm
variable [IsManifold IB n B] in
/-- A `C^n` vector bundle `E` is naturally a `C^n` manifold. -/
instance Bundle.TotalSpace.isManifold :
IsManifold (IB.prod 𝓘(𝕜, F)) n (TotalSpace F E) := by
refine { StructureGroupoid.HasGroupoid.comp (contMDiffFiberwiseLinear B F IB n) ?_ with }
intro e he
rw [mem_contMDiffFiberwiseLinear_iff] at he
obtain ⟨φ, U, hU, hφ, h2φ, heφ⟩ := he
rw [isLocalStructomorphOn_contDiffGroupoid_iff]
refine ⟨ContMDiffOn.congr ?_ (EqOnSource.eqOn heφ),
ContMDiffOn.congr ?_ (EqOnSource.eqOn (EqOnSource.symm' heφ))⟩
· rw [EqOnSource.source_eq heφ]
apply contMDiffOn_fst.prodMk
exact (hφ.comp contMDiffOn_fst <| prod_subset_preimage_fst _ _).clm_apply contMDiffOn_snd
· rw [EqOnSource.target_eq heφ]
apply contMDiffOn_fst.prodMk
exact (h2φ.comp contMDiffOn_fst <| prod_subset_preimage_fst _ _).clm_apply contMDiffOn_snd
section
variable {F E}
variable {e e' : Trivialization F (π F E)} [MemTrivializationAtlas e] [MemTrivializationAtlas e']
theorem Trivialization.contMDiffWithinAt_iff {f : M → TotalSpace F E} {s : Set M} {x₀ : M}
(he : f x₀ ∈ e.source) :
ContMDiffWithinAt IM (IB.prod 𝓘(𝕜, F)) n f s x₀ ↔
ContMDiffWithinAt IM IB n (fun x => (f x).proj) s x₀ ∧
ContMDiffWithinAt IM 𝓘(𝕜, F) n (fun x ↦ (e (f x)).2) s x₀ :=
(contMDiffWithinAt_totalSpace _).trans <| and_congr_right fun h ↦
Trivialization.contMDiffWithinAt_snd_comp_iff₂ h FiberBundle.mem_trivializationAt_proj_source he
theorem Trivialization.contMDiffAt_iff {f : M → TotalSpace F E} {x₀ : M} (he : f x₀ ∈ e.source) :
ContMDiffAt IM (IB.prod 𝓘(𝕜, F)) n f x₀ ↔
ContMDiffAt IM IB n (fun x => (f x).proj) x₀ ∧
ContMDiffAt IM 𝓘(𝕜, F) n (fun x ↦ (e (f x)).2) x₀ :=
e.contMDiffWithinAt_iff he
theorem Trivialization.contMDiffOn_iff {f : M → TotalSpace F E} {s : Set M}
(he : MapsTo f s e.source) :
ContMDiffOn IM (IB.prod 𝓘(𝕜, F)) n f s ↔
ContMDiffOn IM IB n (fun x => (f x).proj) s ∧
ContMDiffOn IM 𝓘(𝕜, F) n (fun x ↦ (e (f x)).2) s := by
simp only [ContMDiffOn, ← forall_and]
exact forall₂_congr fun x hx ↦ e.contMDiffWithinAt_iff (he hx)
theorem Trivialization.contMDiff_iff {f : M → TotalSpace F E} (he : ∀ x, f x ∈ e.source) :
ContMDiff IM (IB.prod 𝓘(𝕜, F)) n f ↔
ContMDiff IM IB n (fun x => (f x).proj) ∧
ContMDiff IM 𝓘(𝕜, F) n (fun x ↦ (e (f x)).2) :=
(forall_congr' fun x ↦ e.contMDiffAt_iff (he x)).trans forall_and
@[deprecated (since := "2024-11-21")]
alias Trivialization.smoothWithinAt_iff := Trivialization.contMDiffWithinAt_iff
@[deprecated (since := "2024-11-21")]
alias Trivialization.smoothAt_iff := Trivialization.contMDiffAt_iff
@[deprecated (since := "2024-11-21")]
alias Trivialization.smoothOn_iff := Trivialization.contMDiffOn_iff
@[deprecated (since := "2024-11-21")]
alias Trivialization.smooth_iff := Trivialization.contMDiff_iff
theorem Trivialization.contMDiffOn (e : Trivialization F (π F E)) [MemTrivializationAtlas e] :
ContMDiffOn (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) n e e.source := by
have : ContMDiffOn (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) n id e.source := contMDiffOn_id
rw [e.contMDiffOn_iff (mapsTo_id _)] at this
exact (this.1.prodMk this.2).congr fun x hx ↦ (e.mk_proj_snd hx).symm
theorem Trivialization.contMDiffOn_symm (e : Trivialization F (π F E)) [MemTrivializationAtlas e] :
ContMDiffOn (IB.prod 𝓘(𝕜, F)) (IB.prod 𝓘(𝕜, F)) n e.toPartialHomeomorph.symm e.target := by
rw [e.contMDiffOn_iff e.toPartialHomeomorph.symm_mapsTo]
refine ⟨contMDiffOn_fst.congr fun x hx ↦ e.proj_symm_apply hx,
contMDiffOn_snd.congr fun x hx ↦ ?_⟩
rw [e.apply_symm_apply hx]
@[deprecated (since := "2024-11-21")] alias Trivialization.smoothOn := Trivialization.contMDiffOn
@[deprecated (since := "2024-11-21")]
alias Trivialization.smoothOn_symm := Trivialization.contMDiffOn_symm
end
/-! ### Core construction for `C^n` vector bundles -/
namespace VectorBundleCore
variable {F}
variable {ι : Type*} (Z : VectorBundleCore 𝕜 B F ι)
/-- Mixin for a `VectorBundleCore` stating that transition functions are `C^n`. -/
class IsContMDiff (IB : ModelWithCorners 𝕜 EB HB) (n : WithTop ℕ∞) : Prop where
contMDiffOn_coordChange :
∀ i j, ContMDiffOn IB 𝓘(𝕜, F →L[𝕜] F) n (Z.coordChange i j) (Z.baseSet i ∩ Z.baseSet j)
| @[deprecated (since := "2025-01-09")] alias IsSmooth := IsContMDiff
theorem contMDiffOn_coordChange (IB : ModelWithCorners 𝕜 EB HB) [h : Z.IsContMDiff IB n] (i j : ι) :
ContMDiffOn IB 𝓘(𝕜, F →L[𝕜] F) n (Z.coordChange i j) (Z.baseSet i ∩ Z.baseSet j) :=
h.1 i j
| Mathlib/Geometry/Manifold/VectorBundle/Basic.lean | 559 | 563 |
/-
Copyright (c) 2019 Johan Commelin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johan Commelin, Kenny Lau, María Inés de Frutos-Fernández, Filippo A. E. Nuccio
-/
import Mathlib.Algebra.Polynomial.FieldDivision
import Mathlib.RingTheory.DiscreteValuationRing.Basic
import Mathlib.RingTheory.MvPowerSeries.Inverse
import Mathlib.RingTheory.PowerSeries.NoZeroDivisors
import Mathlib.RingTheory.LocalRing.ResidueField.Defs
import Mathlib.RingTheory.UniqueFactorizationDomain.Multiplicity
import Mathlib.Data.ENat.Lattice
/-! # Formal power series - Inverses
If the constant coefficient of a formal (univariate) power series is invertible,
then this formal power series is invertible.
(See the discussion in `Mathlib.RingTheory.MvPowerSeries.Inverse` for
the construction.)
Formal (univariate) power series over a local ring form a local ring.
Formal (univariate) power series over a field form a discrete valuation ring, and a normalization
monoid. The definition `residueFieldOfPowerSeries` provides the isomorphism between the residue
field of `k⟦X⟧` and `k`, when `k` is a field.
-/
noncomputable section
open Polynomial
open Finset (antidiagonal mem_antidiagonal)
namespace PowerSeries
open Finsupp (single)
variable {R : Type*}
section Ring
variable [Ring R]
/-- Auxiliary function used for computing inverse of a power series -/
protected def inv.aux : R → R⟦X⟧ → R⟦X⟧ :=
MvPowerSeries.inv.aux
theorem coeff_inv_aux (n : ℕ) (a : R) (φ : R⟦X⟧) :
coeff R n (inv.aux a φ) =
if n = 0 then a
else
-a *
∑ x ∈ antidiagonal n,
if x.2 < n then coeff R x.1 φ * coeff R x.2 (inv.aux a φ) else 0 := by
rw [coeff, inv.aux, MvPowerSeries.coeff_inv_aux]
simp only [Finsupp.single_eq_zero]
split_ifs; · rfl
congr 1
symm
apply Finset.sum_nbij' (fun (a, b) ↦ (single () a, single () b))
fun (f, g) ↦ (f (), g ())
· aesop
· aesop
· aesop
· aesop
· rintro ⟨i, j⟩ _hij
obtain H | H := le_or_lt n j
· aesop
rw [if_pos H, if_pos]
· rfl
refine ⟨?_, fun hh ↦ H.not_le ?_⟩
· rintro ⟨⟩
simpa [Finsupp.single_eq_same] using le_of_lt H
· simpa [Finsupp.single_eq_same] using hh ()
/-- A formal power series is invertible if the constant coefficient is invertible. -/
def invOfUnit (φ : R⟦X⟧) (u : Rˣ) : R⟦X⟧ :=
MvPowerSeries.invOfUnit φ u
theorem coeff_invOfUnit (n : ℕ) (φ : R⟦X⟧) (u : Rˣ) :
coeff R n (invOfUnit φ u) =
if n = 0 then ↑u⁻¹
else
-↑u⁻¹ *
∑ x ∈ antidiagonal n,
if x.2 < n then coeff R x.1 φ * coeff R x.2 (invOfUnit φ u) else 0 :=
coeff_inv_aux n (↑u⁻¹ : R) φ
@[simp]
theorem constantCoeff_invOfUnit (φ : R⟦X⟧) (u : Rˣ) :
constantCoeff R (invOfUnit φ u) = ↑u⁻¹ := by
rw [← coeff_zero_eq_constantCoeff_apply, coeff_invOfUnit, if_pos rfl]
@[simp]
theorem mul_invOfUnit (φ : R⟦X⟧) (u : Rˣ) (h : constantCoeff R φ = u) :
| φ * invOfUnit φ u = 1 :=
MvPowerSeries.mul_invOfUnit φ u <| h
| Mathlib/RingTheory/PowerSeries/Inverse.lean | 100 | 102 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Abhimanyu Pallavi Sudhir, Jean Lo, Calle Sönne, Benjamin Davidson
-/
import Mathlib.Analysis.Calculus.InverseFunctionTheorem.Deriv
import Mathlib.Analysis.Calculus.LogDeriv
import Mathlib.Analysis.SpecialFunctions.Complex.Log
import Mathlib.Analysis.SpecialFunctions.ExpDeriv
/-!
# Differentiability of the complex `log` function
-/
assert_not_exists IsConformalMap Conformal
open Set Filter
open scoped Real Topology
namespace Complex
theorem isOpenMap_exp : IsOpenMap exp :=
isOpenMap_of_hasStrictDerivAt hasStrictDerivAt_exp exp_ne_zero
/-- `Complex.exp` as a `PartialHomeomorph` with `source = {z | -π < im z < π}` and
`target = {z | 0 < re z} ∪ {z | im z ≠ 0}`. This definition is used to prove that `Complex.log`
is complex differentiable at all points but the negative real semi-axis. -/
noncomputable def expPartialHomeomorph : PartialHomeomorph ℂ ℂ :=
PartialHomeomorph.ofContinuousOpen
{ toFun := exp
invFun := log
source := {z : ℂ | z.im ∈ Ioo (-π) π}
target := slitPlane
map_source' := by
rintro ⟨x, y⟩ ⟨h₁ : -π < y, h₂ : y < π⟩
refine (not_or_of_imp fun hz => ?_).symm
obtain rfl : y = 0 := by
rw [exp_im] at hz
simpa [(Real.exp_pos _).ne', Real.sin_eq_zero_iff_of_lt_of_lt h₁ h₂] using hz
rw [← ofReal_def, exp_ofReal_re]
exact Real.exp_pos x
map_target' := fun z h => by
simp only [mem_setOf, log_im, mem_Ioo, neg_pi_lt_arg, arg_lt_pi_iff, true_and]
exact h.imp_left le_of_lt
left_inv' := fun _ hx => log_exp hx.1 (le_of_lt hx.2)
right_inv' := fun _ hx => exp_log <| slitPlane_ne_zero hx }
continuous_exp.continuousOn isOpenMap_exp (isOpen_Ioo.preimage continuous_im)
theorem hasStrictDerivAt_log {x : ℂ} (h : x ∈ slitPlane) : HasStrictDerivAt log x⁻¹ x :=
have h0 : x ≠ 0 := slitPlane_ne_zero h
| expPartialHomeomorph.hasStrictDerivAt_symm h h0 <| by
simpa [exp_log h0] using hasStrictDerivAt_exp (log x)
lemma hasDerivAt_log {z : ℂ} (hz : z ∈ slitPlane) : HasDerivAt log z⁻¹ z :=
| Mathlib/Analysis/SpecialFunctions/Complex/LogDeriv.lean | 53 | 56 |
/-
Copyright (c) 2020 Kenny Lau. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kenny Lau, Wrenna Robson
-/
import Mathlib.Algebra.BigOperators.Group.Finset.Pi
import Mathlib.Algebra.Polynomial.FieldDivision
import Mathlib.LinearAlgebra.Vandermonde
import Mathlib.RingTheory.Polynomial.Basic
/-!
# Lagrange interpolation
## Main definitions
* In everything that follows, `s : Finset ι` is a finite set of indexes, with `v : ι → F` an
indexing of the field over some type. We call the image of v on s the interpolation nodes,
though strictly unique nodes are only defined when v is injective on s.
* `Lagrange.basisDivisor x y`, with `x y : F`. These are the normalised irreducible factors of
the Lagrange basis polynomials. They evaluate to `1` at `x` and `0` at `y` when `x` and `y`
are distinct.
* `Lagrange.basis v i` with `i : ι`: the Lagrange basis polynomial that evaluates to `1` at `v i`
and `0` at `v j` for `i ≠ j`.
* `Lagrange.interpolate v r` where `r : ι → F` is a function from the fintype to the field: the
Lagrange interpolant that evaluates to `r i` at `x i` for all `i : ι`. The `r i` are the _values_
associated with the _nodes_`x i`.
-/
open Polynomial
section PolynomialDetermination
namespace Polynomial
variable {R : Type*} [CommRing R] [IsDomain R] {f g : R[X]}
section Finset
open Function Fintype
open scoped Finset
variable (s : Finset R)
theorem eq_zero_of_degree_lt_of_eval_finset_eq_zero (degree_f_lt : f.degree < #s)
(eval_f : ∀ x ∈ s, f.eval x = 0) : f = 0 := by
rw [← mem_degreeLT] at degree_f_lt
simp_rw [eval_eq_sum_degreeLTEquiv degree_f_lt] at eval_f
rw [← degreeLTEquiv_eq_zero_iff_eq_zero degree_f_lt]
exact
Matrix.eq_zero_of_forall_index_sum_mul_pow_eq_zero
(Injective.comp (Embedding.subtype _).inj' (equivFinOfCardEq (card_coe _)).symm.injective)
fun _ => eval_f _ (Finset.coe_mem _)
theorem eq_of_degree_sub_lt_of_eval_finset_eq (degree_fg_lt : (f - g).degree < #s)
(eval_fg : ∀ x ∈ s, f.eval x = g.eval x) : f = g := by
rw [← sub_eq_zero]
refine eq_zero_of_degree_lt_of_eval_finset_eq_zero _ degree_fg_lt ?_
simp_rw [eval_sub, sub_eq_zero]
exact eval_fg
theorem eq_of_degrees_lt_of_eval_finset_eq (degree_f_lt : f.degree < #s)
(degree_g_lt : g.degree < #s) (eval_fg : ∀ x ∈ s, f.eval x = g.eval x) : f = g := by
rw [← mem_degreeLT] at degree_f_lt degree_g_lt
refine eq_of_degree_sub_lt_of_eval_finset_eq _ ?_ eval_fg
rw [← mem_degreeLT]; exact Submodule.sub_mem _ degree_f_lt degree_g_lt
/--
Two polynomials, with the same degree and leading coefficient, which have the same evaluation
on a set of distinct values with cardinality equal to the degree, are equal.
-/
theorem eq_of_degree_le_of_eval_finset_eq
(h_deg_le : f.degree ≤ #s)
(h_deg_eq : f.degree = g.degree)
(hlc : f.leadingCoeff = g.leadingCoeff)
(h_eval : ∀ x ∈ s, f.eval x = g.eval x) :
f = g := by
rcases eq_or_ne f 0 with rfl | hf
· rwa [degree_zero, eq_comm, degree_eq_bot, eq_comm] at h_deg_eq
· exact eq_of_degree_sub_lt_of_eval_finset_eq s
(lt_of_lt_of_le (degree_sub_lt h_deg_eq hf hlc) h_deg_le) h_eval
end Finset
section Indexed
open Finset
variable {ι : Type*} {v : ι → R} (s : Finset ι)
theorem eq_zero_of_degree_lt_of_eval_index_eq_zero (hvs : Set.InjOn v s)
(degree_f_lt : f.degree < #s) (eval_f : ∀ i ∈ s, f.eval (v i) = 0) : f = 0 := by
classical
rw [← card_image_of_injOn hvs] at degree_f_lt
refine eq_zero_of_degree_lt_of_eval_finset_eq_zero _ degree_f_lt ?_
intro x hx
rcases mem_image.mp hx with ⟨_, hj, rfl⟩
exact eval_f _ hj
theorem eq_of_degree_sub_lt_of_eval_index_eq (hvs : Set.InjOn v s)
(degree_fg_lt : (f - g).degree < #s) (eval_fg : ∀ i ∈ s, f.eval (v i) = g.eval (v i)) :
f = g := by
rw [← sub_eq_zero]
refine eq_zero_of_degree_lt_of_eval_index_eq_zero _ hvs degree_fg_lt ?_
simp_rw [eval_sub, sub_eq_zero]
exact eval_fg
theorem eq_of_degrees_lt_of_eval_index_eq (hvs : Set.InjOn v s) (degree_f_lt : f.degree < #s)
(degree_g_lt : g.degree < #s) (eval_fg : ∀ i ∈ s, f.eval (v i) = g.eval (v i)) : f = g := by
refine eq_of_degree_sub_lt_of_eval_index_eq _ hvs ?_ eval_fg
rw [← mem_degreeLT] at degree_f_lt degree_g_lt ⊢
exact Submodule.sub_mem _ degree_f_lt degree_g_lt
theorem eq_of_degree_le_of_eval_index_eq (hvs : Set.InjOn v s)
(h_deg_le : f.degree ≤ #s)
(h_deg_eq : f.degree = g.degree)
(hlc : f.leadingCoeff = g.leadingCoeff)
(h_eval : ∀ i ∈ s, f.eval (v i) = g.eval (v i)) : f = g := by
rcases eq_or_ne f 0 with rfl | hf
· rwa [degree_zero, eq_comm, degree_eq_bot, eq_comm] at h_deg_eq
· exact eq_of_degree_sub_lt_of_eval_index_eq s hvs
(lt_of_lt_of_le (degree_sub_lt h_deg_eq hf hlc) h_deg_le)
h_eval
end Indexed
end Polynomial
end PolynomialDetermination
noncomputable section
namespace Lagrange
open Polynomial
section BasisDivisor
variable {F : Type*} [Field F]
variable {x y : F}
/-- `basisDivisor x y` is the unique linear or constant polynomial such that
when evaluated at `x` it gives `1` and `y` it gives `0` (where when `x = y` it is identically `0`).
Such polynomials are the building blocks for the Lagrange interpolants. -/
def basisDivisor (x y : F) : F[X] :=
C (x - y)⁻¹ * (X - C y)
theorem basisDivisor_self : basisDivisor x x = 0 := by
simp only [basisDivisor, sub_self, inv_zero, map_zero, zero_mul]
theorem basisDivisor_inj (hxy : basisDivisor x y = 0) : x = y := by
simp_rw [basisDivisor, mul_eq_zero, X_sub_C_ne_zero, or_false, C_eq_zero, inv_eq_zero,
sub_eq_zero] at hxy
exact hxy
@[simp]
theorem basisDivisor_eq_zero_iff : basisDivisor x y = 0 ↔ x = y :=
⟨basisDivisor_inj, fun H => H ▸ basisDivisor_self⟩
theorem basisDivisor_ne_zero_iff : basisDivisor x y ≠ 0 ↔ x ≠ y := by
rw [Ne, basisDivisor_eq_zero_iff]
theorem degree_basisDivisor_of_ne (hxy : x ≠ y) : (basisDivisor x y).degree = 1 := by
rw [basisDivisor, degree_mul, degree_X_sub_C, degree_C, zero_add]
exact inv_ne_zero (sub_ne_zero_of_ne hxy)
@[simp]
theorem degree_basisDivisor_self : (basisDivisor x x).degree = ⊥ := by
rw [basisDivisor_self, degree_zero]
theorem natDegree_basisDivisor_self : (basisDivisor x x).natDegree = 0 := by
rw [basisDivisor_self, natDegree_zero]
theorem natDegree_basisDivisor_of_ne (hxy : x ≠ y) : (basisDivisor x y).natDegree = 1 :=
natDegree_eq_of_degree_eq_some (degree_basisDivisor_of_ne hxy)
@[simp]
theorem eval_basisDivisor_right : eval y (basisDivisor x y) = 0 := by
simp only [basisDivisor, eval_mul, eval_C, eval_sub, eval_X, sub_self, mul_zero]
theorem eval_basisDivisor_left_of_ne (hxy : x ≠ y) : eval x (basisDivisor x y) = 1 := by
simp only [basisDivisor, eval_mul, eval_C, eval_sub, eval_X]
exact inv_mul_cancel₀ (sub_ne_zero_of_ne hxy)
end BasisDivisor
section Basis
variable {F : Type*} [Field F] {ι : Type*} [DecidableEq ι]
variable {s : Finset ι} {v : ι → F} {i j : ι}
open Finset
/-- Lagrange basis polynomials indexed by `s : Finset ι`, defined at nodes `v i` for a
map `v : ι → F`. For `i, j ∈ s`, `basis s v i` evaluates to 0 at `v j` for `i ≠ j`. When
`v` is injective on `s`, `basis s v i` evaluates to 1 at `v i`. -/
protected def basis (s : Finset ι) (v : ι → F) (i : ι) : F[X] :=
∏ j ∈ s.erase i, basisDivisor (v i) (v j)
@[simp]
theorem basis_empty : Lagrange.basis ∅ v i = 1 :=
rfl
@[simp]
theorem basis_singleton (i : ι) : Lagrange.basis {i} v i = 1 := by
rw [Lagrange.basis, erase_singleton, prod_empty]
@[simp]
theorem basis_pair_left (hij : i ≠ j) : Lagrange.basis {i, j} v i = basisDivisor (v i) (v j) := by
simp only [Lagrange.basis, hij, erase_insert_eq_erase, erase_eq_of_not_mem, mem_singleton,
not_false_iff, prod_singleton]
@[simp]
theorem basis_pair_right (hij : i ≠ j) : Lagrange.basis {i, j} v j = basisDivisor (v j) (v i) := by
rw [pair_comm]
exact basis_pair_left hij.symm
theorem basis_ne_zero (hvs : Set.InjOn v s) (hi : i ∈ s) : Lagrange.basis s v i ≠ 0 := by
simp_rw [Lagrange.basis, prod_ne_zero_iff, Ne, mem_erase]
rintro j ⟨hij, hj⟩
rw [basisDivisor_eq_zero_iff, hvs.eq_iff hi hj]
exact hij.symm
@[simp]
theorem eval_basis_self (hvs : Set.InjOn v s) (hi : i ∈ s) :
(Lagrange.basis s v i).eval (v i) = 1 := by
rw [Lagrange.basis, eval_prod]
refine prod_eq_one fun j H => ?_
rw [eval_basisDivisor_left_of_ne]
rcases mem_erase.mp H with ⟨hij, hj⟩
exact mt (hvs hi hj) hij.symm
@[simp]
theorem eval_basis_of_ne (hij : i ≠ j) (hj : j ∈ s) : (Lagrange.basis s v i).eval (v j) = 0 := by
simp_rw [Lagrange.basis, eval_prod, prod_eq_zero_iff]
exact ⟨j, ⟨mem_erase.mpr ⟨hij.symm, hj⟩, eval_basisDivisor_right⟩⟩
@[simp]
theorem natDegree_basis (hvs : Set.InjOn v s) (hi : i ∈ s) :
(Lagrange.basis s v i).natDegree = #s - 1 := by
have H : ∀ j, j ∈ s.erase i → basisDivisor (v i) (v j) ≠ 0 := by
simp_rw [Ne, mem_erase, basisDivisor_eq_zero_iff]
exact fun j ⟨hij₁, hj⟩ hij₂ => hij₁ (hvs hj hi hij₂.symm)
rw [← card_erase_of_mem hi, card_eq_sum_ones]
convert natDegree_prod _ _ H using 1
refine sum_congr rfl fun j hj => (natDegree_basisDivisor_of_ne ?_).symm
rw [Ne, ← basisDivisor_eq_zero_iff]
exact H _ hj
theorem degree_basis (hvs : Set.InjOn v s) (hi : i ∈ s) :
(Lagrange.basis s v i).degree = ↑(#s - 1) := by
rw [degree_eq_natDegree (basis_ne_zero hvs hi), natDegree_basis hvs hi]
theorem sum_basis (hvs : Set.InjOn v s) (hs : s.Nonempty) :
∑ j ∈ s, Lagrange.basis s v j = 1 := by
refine eq_of_degrees_lt_of_eval_index_eq s hvs (lt_of_le_of_lt (degree_sum_le _ _) ?_) ?_ ?_
· rw [Nat.cast_withBot, Finset.sup_lt_iff (WithBot.bot_lt_coe #s)]
intro i hi
rw [degree_basis hvs hi, Nat.cast_withBot, WithBot.coe_lt_coe]
exact Nat.pred_lt (card_ne_zero_of_mem hi)
· rw [degree_one, ← WithBot.coe_zero, Nat.cast_withBot, WithBot.coe_lt_coe]
exact Nonempty.card_pos hs
· intro i hi
rw [eval_finset_sum, eval_one, ← add_sum_erase _ _ hi, eval_basis_self hvs hi,
add_eq_left]
refine sum_eq_zero fun j hj => ?_
rcases mem_erase.mp hj with ⟨hij, _⟩
rw [eval_basis_of_ne hij hi]
theorem basisDivisor_add_symm {x y : F} (hxy : x ≠ y) :
basisDivisor x y + basisDivisor y x = 1 := by
classical
rw [← sum_basis Function.injective_id.injOn ⟨x, mem_insert_self _ {y}⟩,
sum_insert (not_mem_singleton.mpr hxy), sum_singleton, basis_pair_left hxy,
basis_pair_right hxy, id, id]
end Basis
section Interpolate
variable {F : Type*} [Field F] {ι : Type*} [DecidableEq ι]
variable {s t : Finset ι} {i j : ι} {v : ι → F} (r r' : ι → F)
open Finset
/-- Lagrange interpolation: given a finset `s : Finset ι`, a nodal map `v : ι → F` injective on
`s` and a value function `r : ι → F`, `interpolate s v r` is the unique
polynomial of degree `< #s` that takes value `r i` on `v i` for all `i` in `s`. -/
@[simps]
def interpolate (s : Finset ι) (v : ι → F) : (ι → F) →ₗ[F] F[X] where
toFun r := ∑ i ∈ s, C (r i) * Lagrange.basis s v i
map_add' f g := by
simp_rw [← Finset.sum_add_distrib]
have h : (fun x => C (f x) * Lagrange.basis s v x + C (g x) * Lagrange.basis s v x) =
(fun x => C ((f + g) x) * Lagrange.basis s v x) := by
simp_rw [← add_mul, ← C_add, Pi.add_apply]
rw [h]
map_smul' c f := by
simp_rw [Finset.smul_sum, C_mul', smul_smul, Pi.smul_apply, RingHom.id_apply, smul_eq_mul]
theorem interpolate_empty : interpolate ∅ v r = 0 := by rw [interpolate_apply, sum_empty]
theorem interpolate_singleton : interpolate {i} v r = C (r i) := by
rw [interpolate_apply, sum_singleton, basis_singleton, mul_one]
theorem interpolate_one (hvs : Set.InjOn v s) (hs : s.Nonempty) : interpolate s v 1 = 1 := by
simp_rw [interpolate_apply, Pi.one_apply, map_one, one_mul]
exact sum_basis hvs hs
theorem eval_interpolate_at_node (hvs : Set.InjOn v s) (hi : i ∈ s) :
eval (v i) (interpolate s v r) = r i := by
rw [interpolate_apply, eval_finset_sum, ← add_sum_erase _ _ hi]
simp_rw [eval_mul, eval_C, eval_basis_self hvs hi, mul_one, add_eq_left]
refine sum_eq_zero fun j H => ?_
rw [eval_basis_of_ne (mem_erase.mp H).1 hi, mul_zero]
theorem degree_interpolate_le (hvs : Set.InjOn v s) :
(interpolate s v r).degree ≤ ↑(#s - 1) := by
refine (degree_sum_le _ _).trans ?_
rw [Finset.sup_le_iff]
intro i hi
rw [degree_mul, degree_basis hvs hi]
by_cases hr : r i = 0
· simpa only [hr, map_zero, degree_zero, WithBot.bot_add] using bot_le
· rw [degree_C hr, zero_add]
theorem degree_interpolate_lt (hvs : Set.InjOn v s) : (interpolate s v r).degree < #s := by
rw [Nat.cast_withBot]
rcases eq_empty_or_nonempty s with (rfl | h)
· rw [interpolate_empty, degree_zero, card_empty]
exact WithBot.bot_lt_coe _
· refine lt_of_le_of_lt (degree_interpolate_le _ hvs) ?_
rw [Nat.cast_withBot, WithBot.coe_lt_coe]
exact Nat.sub_lt (Nonempty.card_pos h) zero_lt_one
theorem degree_interpolate_erase_lt (hvs : Set.InjOn v s) (hi : i ∈ s) :
(interpolate (s.erase i) v r).degree < ↑(#s - 1) := by
rw [← Finset.card_erase_of_mem hi]
exact degree_interpolate_lt _ (Set.InjOn.mono (coe_subset.mpr (erase_subset _ _)) hvs)
theorem values_eq_on_of_interpolate_eq (hvs : Set.InjOn v s)
(hrr' : interpolate s v r = interpolate s v r') : ∀ i ∈ s, r i = r' i := fun _ hi => by
rw [← eval_interpolate_at_node r hvs hi, hrr', eval_interpolate_at_node r' hvs hi]
theorem interpolate_eq_of_values_eq_on (hrr' : ∀ i ∈ s, r i = r' i) :
interpolate s v r = interpolate s v r' :=
sum_congr rfl fun i hi => by rw [hrr' _ hi]
theorem interpolate_eq_iff_values_eq_on (hvs : Set.InjOn v s) :
interpolate s v r = interpolate s v r' ↔ ∀ i ∈ s, r i = r' i :=
⟨values_eq_on_of_interpolate_eq _ _ hvs, interpolate_eq_of_values_eq_on _ _⟩
theorem eq_interpolate {f : F[X]} (hvs : Set.InjOn v s) (degree_f_lt : f.degree < #s) :
f = interpolate s v fun i => f.eval (v i) :=
eq_of_degrees_lt_of_eval_index_eq _ hvs degree_f_lt (degree_interpolate_lt _ hvs) fun _ hi =>
(eval_interpolate_at_node (fun x ↦ eval (v x) f) hvs hi).symm
theorem eq_interpolate_of_eval_eq {f : F[X]} (hvs : Set.InjOn v s) (degree_f_lt : f.degree < #s)
(eval_f : ∀ i ∈ s, f.eval (v i) = r i) : f = interpolate s v r := by
rw [eq_interpolate hvs degree_f_lt]
exact interpolate_eq_of_values_eq_on _ _ eval_f
/-- This is the characteristic property of the interpolation: the interpolation is the
unique polynomial of `degree < Fintype.card ι` which takes the value of the `r i` on the `v i`.
-/
theorem eq_interpolate_iff {f : F[X]} (hvs : Set.InjOn v s) :
(f.degree < #s ∧ ∀ i ∈ s, eval (v i) f = r i) ↔ f = interpolate s v r := by
constructor <;> intro h
· exact eq_interpolate_of_eval_eq _ hvs h.1 h.2
· rw [h]
exact ⟨degree_interpolate_lt _ hvs, fun _ hi => eval_interpolate_at_node _ hvs hi⟩
/-- Lagrange interpolation induces isomorphism between functions from `s`
and polynomials of degree less than `Fintype.card ι`. -/
def funEquivDegreeLT (hvs : Set.InjOn v s) : degreeLT F #s ≃ₗ[F] s → F where
toFun f i := f.1.eval (v i)
map_add' _ _ := funext fun _ => eval_add
map_smul' c f := funext <| by simp
invFun r :=
⟨interpolate s v fun x => if hx : x ∈ s then r ⟨x, hx⟩ else 0,
mem_degreeLT.2 <| degree_interpolate_lt _ hvs⟩
left_inv := by
rintro ⟨f, hf⟩
simp only [Subtype.mk_eq_mk, Subtype.coe_mk, dite_eq_ite]
rw [mem_degreeLT] at hf
conv => rhs; rw [eq_interpolate hvs hf]
exact interpolate_eq_of_values_eq_on _ _ fun _ hi => if_pos hi
right_inv := by
intro f
ext ⟨i, hi⟩
simp only [Subtype.coe_mk, eval_interpolate_at_node _ hvs hi]
exact dif_pos hi
theorem interpolate_eq_sum_interpolate_insert_sdiff (hvt : Set.InjOn v t) (hs : s.Nonempty)
(hst : s ⊆ t) :
interpolate t v r = ∑ i ∈ s, interpolate (insert i (t \ s)) v r * Lagrange.basis s v i := by
symm
refine eq_interpolate_of_eval_eq _ hvt (lt_of_le_of_lt (degree_sum_le _ _) ?_) fun i hi => ?_
· simp_rw [Nat.cast_withBot, Finset.sup_lt_iff (WithBot.bot_lt_coe #t), degree_mul]
intro i hi
have hs : 1 ≤ #s := Nonempty.card_pos ⟨_, hi⟩
have hst' : #s ≤ #t := card_le_card hst
have H : #t = 1 + (#t - #s) + (#s - 1) := by
rw [add_assoc, tsub_add_tsub_cancel hst' hs, ← add_tsub_assoc_of_le (hs.trans hst'),
Nat.succ_add_sub_one, zero_add]
rw [degree_basis (Set.InjOn.mono hst hvt) hi, H, WithBot.coe_add, Nat.cast_withBot,
WithBot.add_lt_add_iff_right (@WithBot.coe_ne_bot _ (#s - 1))]
convert degree_interpolate_lt _
(hvt.mono (coe_subset.mpr (insert_subset_iff.mpr ⟨hst hi, sdiff_subset⟩)))
rw [card_insert_of_not_mem (not_mem_sdiff_of_mem_right hi), card_sdiff hst, add_comm]
· simp_rw [eval_finset_sum, eval_mul]
by_cases hi' : i ∈ s
· rw [← add_sum_erase _ _ hi', eval_basis_self (hvt.mono hst) hi',
eval_interpolate_at_node _
(hvt.mono (coe_subset.mpr (insert_subset_iff.mpr ⟨hi, sdiff_subset⟩)))
(mem_insert_self _ _),
mul_one, add_eq_left]
refine sum_eq_zero fun j hj => ?_
rcases mem_erase.mp hj with ⟨hij, _⟩
rw [eval_basis_of_ne hij hi', mul_zero]
· have H : (∑ j ∈ s, eval (v i) (Lagrange.basis s v j)) = 1 := by
rw [← eval_finset_sum, sum_basis (hvt.mono hst) hs, eval_one]
rw [← mul_one (r i), ← H, mul_sum]
refine sum_congr rfl fun j hj => ?_
congr
exact
eval_interpolate_at_node _ (hvt.mono (insert_subset_iff.mpr ⟨hst hj, sdiff_subset⟩))
(mem_insert.mpr (Or.inr (mem_sdiff.mpr ⟨hi, hi'⟩)))
theorem interpolate_eq_add_interpolate_erase (hvs : Set.InjOn v s) (hi : i ∈ s) (hj : j ∈ s)
(hij : i ≠ j) :
interpolate s v r =
interpolate (s.erase j) v r * basisDivisor (v i) (v j) +
interpolate (s.erase i) v r * basisDivisor (v j) (v i) := by
rw [interpolate_eq_sum_interpolate_insert_sdiff _ hvs ⟨i, mem_insert_self i {j}⟩ _,
sum_insert (not_mem_singleton.mpr hij), sum_singleton, basis_pair_left hij,
basis_pair_right hij, sdiff_insert_insert_of_mem_of_not_mem hi (not_mem_singleton.mpr hij),
sdiff_singleton_eq_erase, pair_comm,
sdiff_insert_insert_of_mem_of_not_mem hj (not_mem_singleton.mpr hij.symm),
sdiff_singleton_eq_erase]
exact insert_subset_iff.mpr ⟨hi, singleton_subset_iff.mpr hj⟩
end Interpolate
section Nodal
variable {R : Type*} [CommRing R] {ι : Type*}
variable {s : Finset ι} {v : ι → R}
open Finset Polynomial
/-- `nodal s v` is the unique monic polynomial whose roots are the nodes defined by `v` and `s`.
That is, the roots of `nodal s v` are exactly the image of `v` on `s`,
with appropriate multiplicity.
We can use `nodal` to define the barycentric forms of the evaluated interpolant.
-/
def nodal (s : Finset ι) (v : ι → R) : R[X] :=
∏ i ∈ s, (X - C (v i))
theorem nodal_eq (s : Finset ι) (v : ι → R) : nodal s v = ∏ i ∈ s, (X - C (v i)) :=
rfl
@[simp]
theorem nodal_empty : nodal ∅ v = 1 := by
rfl
@[simp]
theorem natDegree_nodal [Nontrivial R] : (nodal s v).natDegree = #s := by
simp_rw [nodal, natDegree_prod_of_monic (h := fun i _ => monic_X_sub_C (v i)),
natDegree_X_sub_C, sum_const, smul_eq_mul, mul_one]
theorem nodal_ne_zero [Nontrivial R] : nodal s v ≠ 0 := by
rcases s.eq_empty_or_nonempty with (rfl | h)
· exact one_ne_zero
· apply ne_zero_of_natDegree_gt (n := 0)
simp only [natDegree_nodal, h.card_pos]
@[simp]
theorem degree_nodal [Nontrivial R] : (nodal s v).degree = #s := by
simp_rw [degree_eq_natDegree nodal_ne_zero, natDegree_nodal]
theorem nodal_monic : (nodal s v).Monic :=
monic_prod_of_monic s (fun i ↦ X - C (v i)) fun i _ ↦ monic_X_sub_C (v i)
theorem eval_nodal {x : R} : (nodal s v).eval x = ∏ i ∈ s, (x - v i) := by
simp_rw [nodal, eval_prod, eval_sub, eval_X, eval_C]
theorem eval_nodal_at_node {i : ι} (hi : i ∈ s) : eval (v i) (nodal s v) = 0 := by
rw [eval_nodal]
exact s.prod_eq_zero hi (sub_self (v i))
theorem eval_nodal_not_at_node [Nontrivial R] [NoZeroDivisors R] {x : R}
(hx : ∀ i ∈ s, x ≠ v i) : eval x (nodal s v) ≠ 0 := by
simp_rw [nodal, eval_prod, prod_ne_zero_iff, eval_sub, eval_X, eval_C, sub_ne_zero]
exact hx
theorem nodal_eq_mul_nodal_erase [DecidableEq ι] {i : ι} (hi : i ∈ s) :
nodal s v = (X - C (v i)) * nodal (s.erase i) v := by
simp_rw [nodal, Finset.mul_prod_erase _ (fun x => X - C (v x)) hi]
theorem X_sub_C_dvd_nodal (v : ι → R) {i : ι} (hi : i ∈ s) : X - C (v i) ∣ nodal s v := by
classical
exact ⟨nodal (s.erase i) v, nodal_eq_mul_nodal_erase hi⟩
theorem nodal_insert_eq_nodal [DecidableEq ι] {i : ι} (hi : i ∉ s) :
nodal (insert i s) v = (X - C (v i)) * nodal s v := by
simp_rw [nodal, prod_insert hi]
theorem derivative_nodal [DecidableEq ι] :
derivative (nodal s v) = ∑ i ∈ s, nodal (s.erase i) v := by
refine s.induction_on ?_ fun i t hit IH => ?_
· rw [nodal_empty, derivative_one, sum_empty]
· rw [nodal_insert_eq_nodal hit, derivative_mul, IH, derivative_sub, derivative_X, derivative_C,
sub_zero, one_mul, sum_insert hit, mul_sum, erase_insert hit, add_right_inj]
refine sum_congr rfl fun j hjt => ?_
rw [t.erase_insert_of_ne (ne_of_mem_of_not_mem hjt hit).symm,
nodal_insert_eq_nodal (mem_of_mem_erase.mt hit)]
theorem eval_nodal_derivative_eval_node_eq [DecidableEq ι] {i : ι} (hi : i ∈ s) :
eval (v i) (derivative (nodal s v)) = eval (v i) (nodal (s.erase i) v) := by
rw [derivative_nodal, eval_finset_sum, ← add_sum_erase _ _ hi, add_eq_left]
exact sum_eq_zero fun j hj => (eval_nodal_at_node (mem_erase.mpr ⟨(mem_erase.mp hj).1.symm, hi⟩))
/-- The vanishing polynomial on a multiplicative subgroup is of the form X ^ n - 1. -/
@[simp] theorem nodal_subgroup_eq_X_pow_card_sub_one [IsDomain R]
(G : Subgroup Rˣ) [Fintype G] :
nodal (G : Set Rˣ).toFinset ((↑) : Rˣ → R) = X ^ (Fintype.card G) - 1 := by
have h : degree (1 : R[X]) < degree ((X : R[X]) ^ Fintype.card G) := by simp [Fintype.card_pos]
apply eq_of_degree_le_of_eval_index_eq (v := ((↑) : Rˣ → R)) (G : Set Rˣ).toFinset
· exact Set.injOn_of_injective Units.ext
· simp
· rw [degree_sub_eq_left_of_degree_lt h, degree_nodal, Set.toFinset_card, degree_pow, degree_X,
nsmul_eq_mul, mul_one, Nat.cast_inj]
exact rfl
· rw [nodal_monic, leadingCoeff_sub_of_degree_lt h, monic_X_pow]
· intros i hi
rw [eval_nodal_at_node hi]
replace hi : i ∈ G := by simpa using hi
obtain ⟨g, rfl⟩ : ∃ g : G, g.val = i := ⟨⟨i, hi⟩, rfl⟩
simp [← Units.val_pow_eq_pow_val, ← Subgroup.coe_pow G]
end Nodal
section NodalWeight
variable {F : Type*} [Field F] {ι : Type*} [DecidableEq ι]
variable {s : Finset ι} {v : ι → F} {i : ι}
open Finset
/-- This defines the nodal weight for a given set of node indexes and node mapping function `v`. -/
def nodalWeight (s : Finset ι) (v : ι → F) (i : ι) :=
∏ j ∈ s.erase i, (v i - v j)⁻¹
theorem nodalWeight_eq_eval_nodal_erase_inv :
nodalWeight s v i = (eval (v i) (nodal (s.erase i) v))⁻¹ := by
rw [eval_nodal, nodalWeight, prod_inv_distrib]
theorem nodal_erase_eq_nodal_div (hi : i ∈ s) :
nodal (s.erase i) v = nodal s v / (X - C (v i)) := by
rw [nodal_eq_mul_nodal_erase hi, mul_div_cancel_left₀]
exact X_sub_C_ne_zero _
theorem nodalWeight_eq_eval_nodal_derative (hi : i ∈ s) :
nodalWeight s v i = (eval (v i) (Polynomial.derivative (nodal s v)))⁻¹ := by
rw [eval_nodal_derivative_eval_node_eq hi, nodalWeight_eq_eval_nodal_erase_inv]
theorem nodalWeight_ne_zero (hvs : Set.InjOn v s) (hi : i ∈ s) : nodalWeight s v i ≠ 0 := by
rw [nodalWeight, prod_ne_zero_iff]
intro j hj
rcases mem_erase.mp hj with ⟨hij, hj⟩
exact inv_ne_zero (sub_ne_zero_of_ne (mt (hvs.eq_iff hi hj).mp hij.symm))
end NodalWeight
section LagrangeBarycentric
variable {F : Type*} [Field F] {ι : Type*} [DecidableEq ι]
variable {s : Finset ι} {v : ι → F} (r : ι → F) {i : ι} {x : F}
open Finset
theorem basis_eq_prod_sub_inv_mul_nodal_div (hi : i ∈ s) :
Lagrange.basis s v i = C (nodalWeight s v i) * (nodal s v / (X - C (v i))) := by
simp_rw [Lagrange.basis, basisDivisor, nodalWeight, prod_mul_distrib, map_prod, ←
nodal_erase_eq_nodal_div hi, nodal]
theorem eval_basis_not_at_node (hi : i ∈ s) (hxi : x ≠ v i) :
eval x (Lagrange.basis s v i) = eval x (nodal s v) * (nodalWeight s v i * (x - v i)⁻¹) := by
rw [mul_comm, basis_eq_prod_sub_inv_mul_nodal_div hi, eval_mul, eval_C, ←
| nodal_erase_eq_nodal_div hi, eval_nodal, eval_nodal, mul_assoc, ← mul_prod_erase _ _ hi, ←
mul_assoc (x - v i)⁻¹, inv_mul_cancel₀ (sub_ne_zero_of_ne hxi), one_mul]
theorem interpolate_eq_nodalWeight_mul_nodal_div_X_sub_C :
interpolate s v r = ∑ i ∈ s, C (nodalWeight s v i) * (nodal s v / (X - C (v i))) * C (r i) :=
sum_congr rfl fun j hj => by rw [mul_comm, basis_eq_prod_sub_inv_mul_nodal_div hj]
/-- This is the first barycentric form of the Lagrange interpolant. -/
theorem eval_interpolate_not_at_node (hx : ∀ i ∈ s, x ≠ v i) :
eval x (interpolate s v r) =
eval x (nodal s v) * ∑ i ∈ s, nodalWeight s v i * (x - v i)⁻¹ * r i := by
simp_rw [interpolate_apply, mul_sum, eval_finset_sum, eval_mul, eval_C]
refine sum_congr rfl fun i hi => ?_
rw [← mul_assoc, mul_comm, eval_basis_not_at_node hi (hx _ hi)]
theorem sum_nodalWeight_mul_inv_sub_ne_zero (hvs : Set.InjOn v s) (hx : ∀ i ∈ s, x ≠ v i)
| Mathlib/LinearAlgebra/Lagrange.lean | 592 | 607 |
/-
Copyright (c) 2020 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Analysis.Analytic.Basic
import Mathlib.Analysis.SpecialFunctions.Pow.NNReal
/-!
# Representation of `FormalMultilinearSeries.radius` as a `liminf`
In this file we prove that the radius of convergence of a `FormalMultilinearSeries` is equal to
$\liminf_{n\to\infty} \frac{1}{\sqrt[n]{‖p n‖}}$. This lemma can't go to `Analysis.Analytic.Basic`
because this would create a circular dependency once we redefine `exp` using
`FormalMultilinearSeries`.
-/
variable {𝕜 : Type*} [NontriviallyNormedField 𝕜] {E : Type*} [NormedAddCommGroup E]
[NormedSpace 𝕜 E] {F : Type*} [NormedAddCommGroup F] [NormedSpace 𝕜 F]
open scoped Topology NNReal ENNReal
open Filter Asymptotics
namespace FormalMultilinearSeries
variable (p : FormalMultilinearSeries 𝕜 E F)
/-- The radius of a formal multilinear series is equal to
$\liminf_{n\to\infty} \frac{1}{\sqrt[n]{‖p n‖}}$. The actual statement uses `ℝ≥0` and some
coercions. -/
theorem radius_eq_liminf :
p.radius = liminf (fun n => (1 / (‖p n‖₊ ^ (1 / (n : ℝ)) : ℝ≥0) : ℝ≥0∞)) atTop := by
| have :
∀ (r : ℝ≥0) {n},
0 < n → ((r : ℝ≥0∞) ≤ 1 / ↑(‖p n‖₊ ^ (1 / (n : ℝ))) ↔ ‖p n‖₊ * r ^ n ≤ 1) := by
intro r n hn
have : 0 < (n : ℝ) := Nat.cast_pos.2 hn
conv_lhs =>
rw [one_div, ENNReal.le_inv_iff_mul_le, ← ENNReal.coe_mul, ENNReal.coe_le_one_iff, one_div, ←
NNReal.rpow_one r, ← mul_inv_cancel₀ this.ne', NNReal.rpow_mul, ← NNReal.mul_rpow, ←
NNReal.one_rpow n⁻¹, NNReal.rpow_le_rpow_iff (inv_pos.2 this), mul_comm,
NNReal.rpow_natCast]
apply le_antisymm <;> refine ENNReal.le_of_forall_nnreal_lt fun r hr => ?_
· have := ((TFAE_exists_lt_isLittleO_pow (fun n => ‖p n‖ * r ^ n) 1).out 1 7).1
(p.isLittleO_of_lt_radius hr)
obtain ⟨a, ha, H⟩ := this
apply le_liminf_of_le
· infer_param
· rw [← eventually_map]
refine
H.mp ((eventually_gt_atTop 0).mono fun n hn₀ hn => (this _ hn₀).2 (NNReal.coe_le_coe.1 ?_))
push_cast
exact (le_abs_self _).trans (hn.trans (pow_le_one₀ ha.1.le ha.2.le))
· refine p.le_radius_of_isBigO <| .of_norm_eventuallyLE ?_
filter_upwards [eventually_lt_of_lt_liminf hr, eventually_gt_atTop 0] with n hn hn₀
simpa using NNReal.coe_le_coe.2 ((this _ hn₀).1 hn.le)
end FormalMultilinearSeries
| Mathlib/Analysis/Analytic/RadiusLiminf.lean | 35 | 61 |
/-
Copyright (c) 2021 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov, Alistair Tucker, Wen Yang
-/
import Mathlib.Order.Interval.Set.Image
import Mathlib.Order.CompleteLatticeIntervals
import Mathlib.Topology.Order.DenselyOrdered
import Mathlib.Topology.Order.Monotone
import Mathlib.Topology.Connected.TotallyDisconnected
/-!
# Intermediate Value Theorem
In this file we prove the Intermediate Value Theorem: if `f : α → β` is a function defined on a
connected set `s` that takes both values `≤ a` and values `≥ a` on `s`, then it is equal to `a` at
some point of `s`. We also prove that intervals in a dense conditionally complete order are
preconnected and any preconnected set is an interval. Then we specialize IVT to functions continuous
on intervals.
## Main results
* `IsPreconnected_I??` : all intervals `I??` are preconnected,
* `IsPreconnected.intermediate_value`, `intermediate_value_univ` : Intermediate Value Theorem for
connected sets and connected spaces, respectively;
* `intermediate_value_Icc`, `intermediate_value_Icc'`: Intermediate Value Theorem for functions
on closed intervals.
### Miscellaneous facts
* `IsClosed.Icc_subset_of_forall_mem_nhdsWithin` : “Continuous induction” principle;
if `s ∩ [a, b]` is closed, `a ∈ s`, and for each `x ∈ [a, b) ∩ s` some of its right neighborhoods
is included `s`, then `[a, b] ⊆ s`.
* `IsClosed.Icc_subset_of_forall_exists_gt`, `IsClosed.mem_of_ge_of_forall_exists_gt` : two
other versions of the “continuous induction” principle.
* `ContinuousOn.StrictMonoOn_of_InjOn_Ioo` :
Every continuous injective `f : (a, b) → δ` is strictly monotone
or antitone (increasing or decreasing).
## Tags
intermediate value theorem, connected space, connected set
-/
open Filter OrderDual TopologicalSpace Function Set
open scoped Topology Filter Interval
universe u v
/-!
### Intermediate value theorem on a (pre)connected space
In this section we prove the following theorem (see `IsPreconnected.intermediate_value₂`): if `f`
and `g` are two functions continuous on a preconnected set `s`, `f a ≤ g a` at some `a ∈ s` and
`g b ≤ f b` at some `b ∈ s`, then `f c = g c` at some `c ∈ s`. We prove several versions of this
statement, including the classical IVT that corresponds to a constant function `g`.
-/
section
variable {X : Type u} {α : Type v} [TopologicalSpace X] [LinearOrder α] [TopologicalSpace α]
[OrderClosedTopology α]
/-- Intermediate value theorem for two functions: if `f` and `g` are two continuous functions
on a preconnected space and `f a ≤ g a` and `g b ≤ f b`, then for some `x` we have `f x = g x`. -/
theorem intermediate_value_univ₂ [PreconnectedSpace X] {a b : X} {f g : X → α} (hf : Continuous f)
(hg : Continuous g) (ha : f a ≤ g a) (hb : g b ≤ f b) : ∃ x, f x = g x := by
obtain ⟨x, _, hfg, hgf⟩ : (univ ∩ { x | f x ≤ g x ∧ g x ≤ f x }).Nonempty :=
isPreconnected_closed_iff.1 PreconnectedSpace.isPreconnected_univ _ _ (isClosed_le hf hg)
(isClosed_le hg hf) (fun _ _ => le_total _ _) ⟨a, trivial, ha⟩ ⟨b, trivial, hb⟩
exact ⟨x, le_antisymm hfg hgf⟩
theorem intermediate_value_univ₂_eventually₁ [PreconnectedSpace X] {a : X} {l : Filter X} [NeBot l]
{f g : X → α} (hf : Continuous f) (hg : Continuous g) (ha : f a ≤ g a) (he : g ≤ᶠ[l] f) :
∃ x, f x = g x :=
let ⟨_, h⟩ := he.exists; intermediate_value_univ₂ hf hg ha h
theorem intermediate_value_univ₂_eventually₂ [PreconnectedSpace X] {l₁ l₂ : Filter X} [NeBot l₁]
[NeBot l₂] {f g : X → α} (hf : Continuous f) (hg : Continuous g) (he₁ : f ≤ᶠ[l₁] g)
(he₂ : g ≤ᶠ[l₂] f) : ∃ x, f x = g x :=
let ⟨_, h₁⟩ := he₁.exists
let ⟨_, h₂⟩ := he₂.exists
intermediate_value_univ₂ hf hg h₁ h₂
/-- Intermediate value theorem for two functions: if `f` and `g` are two functions continuous
on a preconnected set `s` and for some `a b ∈ s` we have `f a ≤ g a` and `g b ≤ f b`,
then for some `x ∈ s` we have `f x = g x`. -/
theorem IsPreconnected.intermediate_value₂ {s : Set X} (hs : IsPreconnected s) {a b : X}
(ha : a ∈ s) (hb : b ∈ s) {f g : X → α} (hf : ContinuousOn f s) (hg : ContinuousOn g s)
(ha' : f a ≤ g a) (hb' : g b ≤ f b) : ∃ x ∈ s, f x = g x :=
let ⟨x, hx⟩ :=
@intermediate_value_univ₂ s α _ _ _ _ (Subtype.preconnectedSpace hs) ⟨a, ha⟩ ⟨b, hb⟩ _ _
(continuousOn_iff_continuous_restrict.1 hf) (continuousOn_iff_continuous_restrict.1 hg) ha'
hb'
⟨x, x.2, hx⟩
theorem IsPreconnected.intermediate_value₂_eventually₁ {s : Set X} (hs : IsPreconnected s) {a : X}
{l : Filter X} (ha : a ∈ s) [NeBot l] (hl : l ≤ 𝓟 s) {f g : X → α} (hf : ContinuousOn f s)
(hg : ContinuousOn g s) (ha' : f a ≤ g a) (he : g ≤ᶠ[l] f) : ∃ x ∈ s, f x = g x := by
rw [continuousOn_iff_continuous_restrict] at hf hg
obtain ⟨b, h⟩ :=
@intermediate_value_univ₂_eventually₁ _ _ _ _ _ _ (Subtype.preconnectedSpace hs) ⟨a, ha⟩ _
(comap_coe_neBot_of_le_principal hl) _ _ hf hg ha' (he.comap _)
exact ⟨b, b.prop, h⟩
theorem IsPreconnected.intermediate_value₂_eventually₂ {s : Set X} (hs : IsPreconnected s)
{l₁ l₂ : Filter X} [NeBot l₁] [NeBot l₂] (hl₁ : l₁ ≤ 𝓟 s) (hl₂ : l₂ ≤ 𝓟 s) {f g : X → α}
(hf : ContinuousOn f s) (hg : ContinuousOn g s) (he₁ : f ≤ᶠ[l₁] g) (he₂ : g ≤ᶠ[l₂] f) :
∃ x ∈ s, f x = g x := by
rw [continuousOn_iff_continuous_restrict] at hf hg
obtain ⟨b, h⟩ :=
@intermediate_value_univ₂_eventually₂ _ _ _ _ _ _ (Subtype.preconnectedSpace hs) _ _
(comap_coe_neBot_of_le_principal hl₁) (comap_coe_neBot_of_le_principal hl₂) _ _ hf hg
(he₁.comap _) (he₂.comap _)
exact ⟨b, b.prop, h⟩
/-- **Intermediate Value Theorem** for continuous functions on connected sets. -/
theorem IsPreconnected.intermediate_value {s : Set X} (hs : IsPreconnected s) {a b : X} (ha : a ∈ s)
(hb : b ∈ s) {f : X → α} (hf : ContinuousOn f s) : Icc (f a) (f b) ⊆ f '' s := fun _x hx =>
hs.intermediate_value₂ ha hb hf continuousOn_const hx.1 hx.2
theorem IsPreconnected.intermediate_value_Ico {s : Set X} (hs : IsPreconnected s) {a : X}
{l : Filter X} (ha : a ∈ s) [NeBot l] (hl : l ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s) {v : α}
(ht : Tendsto f l (𝓝 v)) : Ico (f a) v ⊆ f '' s := fun _ h =>
hs.intermediate_value₂_eventually₁ ha hl hf continuousOn_const h.1 (ht.eventually_const_le h.2)
theorem IsPreconnected.intermediate_value_Ioc {s : Set X} (hs : IsPreconnected s) {a : X}
{l : Filter X} (ha : a ∈ s) [NeBot l] (hl : l ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s) {v : α}
(ht : Tendsto f l (𝓝 v)) : Ioc v (f a) ⊆ f '' s := fun _ h =>
(hs.intermediate_value₂_eventually₁ ha hl continuousOn_const hf h.2
(ht.eventually_le_const h.1)).imp fun _ h => h.imp_right Eq.symm
theorem IsPreconnected.intermediate_value_Ioo {s : Set X} (hs : IsPreconnected s) {l₁ l₂ : Filter X}
[NeBot l₁] [NeBot l₂] (hl₁ : l₁ ≤ 𝓟 s) (hl₂ : l₂ ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
{v₁ v₂ : α} (ht₁ : Tendsto f l₁ (𝓝 v₁)) (ht₂ : Tendsto f l₂ (𝓝 v₂)) :
Ioo v₁ v₂ ⊆ f '' s := fun _ h =>
hs.intermediate_value₂_eventually₂ hl₁ hl₂ hf continuousOn_const
(ht₁.eventually_le_const h.1) (ht₂.eventually_const_le h.2)
theorem IsPreconnected.intermediate_value_Ici {s : Set X} (hs : IsPreconnected s) {a : X}
{l : Filter X} (ha : a ∈ s) [NeBot l] (hl : l ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
(ht : Tendsto f l atTop) : Ici (f a) ⊆ f '' s := fun y h =>
hs.intermediate_value₂_eventually₁ ha hl hf continuousOn_const h (tendsto_atTop.1 ht y)
theorem IsPreconnected.intermediate_value_Iic {s : Set X} (hs : IsPreconnected s) {a : X}
{l : Filter X} (ha : a ∈ s) [NeBot l] (hl : l ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
(ht : Tendsto f l atBot) : Iic (f a) ⊆ f '' s := fun y h =>
(hs.intermediate_value₂_eventually₁ ha hl continuousOn_const hf h (tendsto_atBot.1 ht y)).imp
fun _ h => h.imp_right Eq.symm
theorem IsPreconnected.intermediate_value_Ioi {s : Set X} (hs : IsPreconnected s) {l₁ l₂ : Filter X}
[NeBot l₁] [NeBot l₂] (hl₁ : l₁ ≤ 𝓟 s) (hl₂ : l₂ ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
{v : α} (ht₁ : Tendsto f l₁ (𝓝 v)) (ht₂ : Tendsto f l₂ atTop) : Ioi v ⊆ f '' s := fun y h =>
hs.intermediate_value₂_eventually₂ hl₁ hl₂ hf continuousOn_const
(ht₁.eventually_le_const h) (ht₂.eventually_ge_atTop y)
theorem IsPreconnected.intermediate_value_Iio {s : Set X} (hs : IsPreconnected s) {l₁ l₂ : Filter X}
[NeBot l₁] [NeBot l₂] (hl₁ : l₁ ≤ 𝓟 s) (hl₂ : l₂ ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
{v : α} (ht₁ : Tendsto f l₁ atBot) (ht₂ : Tendsto f l₂ (𝓝 v)) : Iio v ⊆ f '' s := fun y h =>
hs.intermediate_value₂_eventually₂ hl₁ hl₂ hf continuousOn_const (ht₁.eventually_le_atBot y)
(ht₂.eventually_const_le h)
theorem IsPreconnected.intermediate_value_Iii {s : Set X} (hs : IsPreconnected s) {l₁ l₂ : Filter X}
[NeBot l₁] [NeBot l₂] (hl₁ : l₁ ≤ 𝓟 s) (hl₂ : l₂ ≤ 𝓟 s) {f : X → α} (hf : ContinuousOn f s)
(ht₁ : Tendsto f l₁ atBot) (ht₂ : Tendsto f l₂ atTop) : univ ⊆ f '' s := fun y _ =>
hs.intermediate_value₂_eventually₂ hl₁ hl₂ hf continuousOn_const (ht₁.eventually_le_atBot y)
(ht₂.eventually_ge_atTop y)
/-- **Intermediate Value Theorem** for continuous functions on connected spaces. -/
theorem intermediate_value_univ [PreconnectedSpace X] (a b : X) {f : X → α} (hf : Continuous f) :
Icc (f a) (f b) ⊆ range f := fun _ hx => intermediate_value_univ₂ hf continuous_const hx.1 hx.2
/-- **Intermediate Value Theorem** for continuous functions on connected spaces. -/
theorem mem_range_of_exists_le_of_exists_ge [PreconnectedSpace X] {c : α} {f : X → α}
(hf : Continuous f) (h₁ : ∃ a, f a ≤ c) (h₂ : ∃ b, c ≤ f b) : c ∈ range f :=
let ⟨a, ha⟩ := h₁; let ⟨b, hb⟩ := h₂; intermediate_value_univ a b hf ⟨ha, hb⟩
/-!
### (Pre)connected sets in a linear order
In this section we prove the following results:
* `IsPreconnected.ordConnected`: any preconnected set `s` in a linear order is `OrdConnected`,
i.e. `a ∈ s` and `b ∈ s` imply `Icc a b ⊆ s`;
* `IsPreconnected.mem_intervals`: any preconnected set `s` in a conditionally complete linear order
is one of the intervals `Set.Icc`, `set.`Ico`, `set.Ioc`, `set.Ioo`, ``Set.Ici`, `Set.Iic`,
`Set.Ioi`, `Set.Iio`; note that this is false for non-complete orders: e.g., in `ℝ \ {0}`, the set
of positive numbers cannot be represented as `Set.Ioi _`.
-/
/-- If a preconnected set contains endpoints of an interval, then it includes the whole interval. -/
theorem IsPreconnected.Icc_subset {s : Set α} (hs : IsPreconnected s) {a b : α} (ha : a ∈ s)
(hb : b ∈ s) : Icc a b ⊆ s := by
simpa only [image_id] using hs.intermediate_value ha hb continuousOn_id
theorem IsPreconnected.ordConnected {s : Set α} (h : IsPreconnected s) : OrdConnected s :=
⟨fun _ hx _ hy => h.Icc_subset hx hy⟩
/-- If a preconnected set contains endpoints of an interval, then it includes the whole interval. -/
theorem IsConnected.Icc_subset {s : Set α} (hs : IsConnected s) {a b : α} (ha : a ∈ s)
(hb : b ∈ s) : Icc a b ⊆ s :=
hs.2.Icc_subset ha hb
/-- If preconnected set in a linear order space is unbounded below and above, then it is the whole
space. -/
theorem IsPreconnected.eq_univ_of_unbounded {s : Set α} (hs : IsPreconnected s) (hb : ¬BddBelow s)
(ha : ¬BddAbove s) : s = univ := by
refine eq_univ_of_forall fun x => ?_
obtain ⟨y, ys, hy⟩ : ∃ y ∈ s, y < x := not_bddBelow_iff.1 hb x
obtain ⟨z, zs, hz⟩ : ∃ z ∈ s, x < z := not_bddAbove_iff.1 ha x
exact hs.Icc_subset ys zs ⟨le_of_lt hy, le_of_lt hz⟩
end
variable {α : Type u} [ConditionallyCompleteLinearOrder α] [TopologicalSpace α] [OrderTopology α]
/-- A bounded connected subset of a conditionally complete linear order includes the open interval
`(Inf s, Sup s)`. -/
theorem IsConnected.Ioo_csInf_csSup_subset {s : Set α} (hs : IsConnected s) (hb : BddBelow s)
(ha : BddAbove s) : Ioo (sInf s) (sSup s) ⊆ s := fun _x hx =>
let ⟨_y, ys, hy⟩ := (isGLB_lt_iff (isGLB_csInf hs.nonempty hb)).1 hx.1
let ⟨_z, zs, hz⟩ := (lt_isLUB_iff (isLUB_csSup hs.nonempty ha)).1 hx.2
hs.Icc_subset ys zs ⟨hy.le, hz.le⟩
theorem eq_Icc_csInf_csSup_of_connected_bdd_closed {s : Set α} (hc : IsConnected s)
(hb : BddBelow s) (ha : BddAbove s) (hcl : IsClosed s) : s = Icc (sInf s) (sSup s) :=
(subset_Icc_csInf_csSup hb ha).antisymm <|
hc.Icc_subset (hcl.csInf_mem hc.nonempty hb) (hcl.csSup_mem hc.nonempty ha)
theorem IsPreconnected.Ioi_csInf_subset {s : Set α} (hs : IsPreconnected s) (hb : BddBelow s)
| (ha : ¬BddAbove s) : Ioi (sInf s) ⊆ s := fun x hx =>
have sne : s.Nonempty := nonempty_of_not_bddAbove ha
let ⟨_y, ys, hy⟩ : ∃ y ∈ s, y < x := (isGLB_lt_iff (isGLB_csInf sne hb)).1 hx
let ⟨_z, zs, hz⟩ : ∃ z ∈ s, x < z := not_bddAbove_iff.1 ha x
hs.Icc_subset ys zs ⟨hy.le, hz.le⟩
| Mathlib/Topology/Order/IntermediateValue.lean | 235 | 240 |
/-
Copyright (c) 2020 Kenny Lau. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kenny Lau, Antoine Chambert-Loir
-/
import Mathlib.Algebra.Group.Hom.CompTypeclasses
import Mathlib.Algebra.Module.Defs
import Mathlib.Algebra.Notation.Prod
import Mathlib.Algebra.Ring.Action.Basic
/-!
# Equivariant homomorphisms
## Main definitions
* `MulActionHom φ X Y`, the type of equivariant functions from `X` to `Y`,
where `φ : M → N` is a map, `M` acting on the type `X` and `N` acting on the type of `Y`.
`AddActionHom φ X Y` is its additive version.
* `DistribMulActionHom φ A B`,
the type of equivariant additive monoid homomorphisms from `A` to `B`,
where `φ : M → N` is a morphism of monoids,
`M` acting on the additive monoid `A` and `N` acting on the additive monoid of `B`
* `SMulSemiringHom φ R S`, the type of equivariant ring homomorphisms
from `R` to `S`, where `φ : M → N` is a morphism of monoids,
`M` acting on the ring `R` and `N` acting on the ring `S`.
The above types have corresponding classes:
* `MulActionHomClass F φ X Y` states that `F` is a type of bundled `X → Y` homs
which are `φ`-equivariant;
`AddActionHomClass F φ X Y` is its additive version.
* `DistribMulActionHomClass F φ A B` states that `F` is a type of bundled `A → B` homs
preserving the additive monoid structure and `φ`-equivariant
* `SMulSemiringHomClass F φ R S` states that `F` is a type of bundled `R → S` homs
preserving the ring structure and `φ`-equivariant
## Notation
We introduce the following notation to code equivariant maps
(the subscript index `ₑ` is for *equivariant*) :
* `X →ₑ[φ] Y` is `MulActionHom φ X Y` and `AddActionHom φ X Y`
* `A →ₑ+[φ] B` is `DistribMulActionHom φ A B`.
* `R →ₑ+*[φ] S` is `MulSemiringActionHom φ R S`.
When `M = N` and `φ = MonoidHom.id M`, we provide the backward compatible notation :
* `X →[M] Y` is `MulActionHom (@id M) X Y` and `AddActionHom (@id M) X Y`
* `A →+[M] B` is `DistribMulActionHom (MonoidHom.id M) A B`
* `R →+*[M] S` is `MulSemiringActionHom (MonoidHom.id M) R S`
The notation for `MulActionHom` and `AddActionHom` is the same, because it is unlikely
that it could lead to confusion — unless one needs types `M` and `X` with simultaneous
instances of `Mul M`, `Add M`, `SMul M X` and `VAdd M X`…
-/
assert_not_exists Submonoid
section MulActionHom
variable {M' : Type*}
variable {M : Type*} {N : Type*} {P : Type*}
variable (φ : M → N) (ψ : N → P) (χ : M → P)
variable (X : Type*) [SMul M X] [SMul M' X]
variable (Y : Type*) [SMul N Y] [SMul M' Y]
variable (Z : Type*) [SMul P Z]
/-- Equivariant functions :
When `φ : M → N` is a function, and types `X` and `Y` are endowed with additive actions
of `M` and `N`, a function `f : X → Y` is `φ`-equivariant if `f (m +ᵥ x) = (φ m) +ᵥ (f x)`. -/
structure AddActionHom {M N : Type*} (φ: M → N) (X : Type*) [VAdd M X] (Y : Type*) [VAdd N Y] where
/-- The underlying function. -/
protected toFun : X → Y
/-- The proposition that the function commutes with the additive actions. -/
protected map_vadd' : ∀ (m : M) (x : X), toFun (m +ᵥ x) = (φ m) +ᵥ toFun x
/-- Equivariant functions :
When `φ : M → N` is a function, and types `X` and `Y` are endowed with actions of `M` and `N`,
a function `f : X → Y` is `φ`-equivariant if `f (m • x) = (φ m) • (f x)`. -/
@[to_additive]
structure MulActionHom where
/-- The underlying function. -/
protected toFun : X → Y
/-- The proposition that the function commutes with the actions. -/
protected map_smul' : ∀ (m : M) (x : X), toFun (m • x) = (φ m) • toFun x
/- Porting note: local notation given a name, conflict with Algebra.Hom.GroupAction
see https://github.com/leanprover/lean4/issues/2000 -/
/-- `φ`-equivariant functions `X → Y`,
where `φ : M → N`, where `M` and `N` act on `X` and `Y` respectively. -/
notation:25 (name := «MulActionHomLocal≺») X " →ₑ[" φ:25 "] " Y:0 => MulActionHom φ X Y
/-- `M`-equivariant functions `X → Y` with respect to the action of `M`.
This is the same as `X →ₑ[@id M] Y`. -/
notation:25 (name := «MulActionHomIdLocal≺») X " →[" M:25 "] " Y:0 => MulActionHom (@id M) X Y
/-- `φ`-equivariant functions `X → Y`,
where `φ : M → N`, where `M` and `N` act additively on `X` and `Y` respectively
We use the same notation as for multiplicative actions, as conflicts are unlikely. -/
notation:25 (name := «AddActionHomLocal≺») X " →ₑ[" φ:25 "] " Y:0 => AddActionHom φ X Y
/-- `M`-equivariant functions `X → Y` with respect to the additive action of `M`.
This is the same as `X →ₑ[@id M] Y`.
We use the same notation as for multiplicative actions, as conflicts are unlikely. -/
notation:25 (name := «AddActionHomIdLocal≺») X " →[" M:25 "] " Y:0 => AddActionHom (@id M) X Y
/-- `AddActionSemiHomClass F φ X Y` states that
`F` is a type of morphisms which are `φ`-equivariant.
You should extend this class when you extend `AddActionHom`. -/
class AddActionSemiHomClass (F : Type*)
{M N : outParam Type*} (φ : outParam (M → N))
(X Y : outParam Type*) [VAdd M X] [VAdd N Y] [FunLike F X Y] : Prop where
/-- The proposition that the function preserves the action. -/
map_vaddₛₗ : ∀ (f : F) (c : M) (x : X), f (c +ᵥ x) = (φ c) +ᵥ (f x)
/-- `MulActionSemiHomClass F φ X Y` states that
`F` is a type of morphisms which are `φ`-equivariant.
You should extend this class when you extend `MulActionHom`. -/
@[to_additive]
class MulActionSemiHomClass (F : Type*)
{M N : outParam Type*} (φ : outParam (M → N))
(X Y : outParam Type*) [SMul M X] [SMul N Y] [FunLike F X Y] : Prop where
/-- The proposition that the function preserves the action. -/
map_smulₛₗ : ∀ (f : F) (c : M) (x : X), f (c • x) = (φ c) • (f x)
export MulActionSemiHomClass (map_smulₛₗ)
export AddActionSemiHomClass (map_vaddₛₗ)
/-- `MulActionHomClass F M X Y` states that `F` is a type of
morphisms which are equivariant with respect to actions of `M`
This is an abbreviation of `MulActionSemiHomClass`. -/
@[to_additive "`MulActionHomClass F M X Y` states that `F` is a type of
morphisms which are equivariant with respect to actions of `M`
This is an abbreviation of `MulActionSemiHomClass`."]
abbrev MulActionHomClass (F : Type*) (M : outParam Type*)
(X Y : outParam Type*) [SMul M X] [SMul M Y] [FunLike F X Y] :=
MulActionSemiHomClass F (@id M) X Y
@[to_additive] instance : FunLike (MulActionHom φ X Y) X Y where
coe := MulActionHom.toFun
coe_injective' f g h := by cases f; cases g; congr
@[to_additive (attr := simp)]
theorem map_smul {F M X Y : Type*} [SMul M X] [SMul M Y]
[FunLike F X Y] [MulActionHomClass F M X Y]
(f : F) (c : M) (x : X) : f (c • x) = c • f x :=
map_smulₛₗ f c x
@[to_additive]
instance : MulActionSemiHomClass (X →ₑ[φ] Y) φ X Y where
map_smulₛₗ := MulActionHom.map_smul'
initialize_simps_projections MulActionHom (toFun → apply)
initialize_simps_projections AddActionHom (toFun → apply)
namespace MulActionHom
variable {φ X Y}
variable {F : Type*} [FunLike F X Y]
/-- Turn an element of a type `F` satisfying `MulActionSemiHomClass F φ X Y`
into an actual `MulActionHom`.
This is declared as the default coercion from `F` to `MulActionSemiHom φ X Y`. -/
@[to_additive (attr := coe)
"Turn an element of a type `F` satisfying `AddActionSemiHomClass F φ X Y`
into an actual `AddActionHom`.
This is declared as the default coercion from `F` to `AddActionSemiHom φ X Y`."]
def _root_.MulActionSemiHomClass.toMulActionHom [MulActionSemiHomClass F φ X Y] (f : F) :
X →ₑ[φ] Y where
toFun := DFunLike.coe f
map_smul' := map_smulₛₗ f
/-- Any type satisfying `MulActionSemiHomClass` can be cast into `MulActionHom` via
`MulActionHomSemiClass.toMulActionHom`. -/
@[to_additive]
instance [MulActionSemiHomClass F φ X Y] : CoeTC F (X →ₑ[φ] Y) :=
⟨MulActionSemiHomClass.toMulActionHom⟩
variable (M' X Y F) in
/-- If Y/X/M forms a scalar tower, any map X → Y preserving X-action also preserves M-action. -/
@[to_additive]
theorem _root_.IsScalarTower.smulHomClass [MulOneClass X] [SMul X Y] [IsScalarTower M' X Y]
[MulActionHomClass F X X Y] : MulActionHomClass F M' X Y where
map_smulₛₗ f m x := by
rw [← mul_one (m • x), ← smul_eq_mul, map_smul, smul_assoc, ← map_smul,
smul_eq_mul, mul_one, id_eq]
@[to_additive]
protected theorem map_smul (f : X →[M'] Y) (m : M') (x : X) : f (m • x) = m • f x :=
map_smul f m x
@[to_additive (attr := ext)]
theorem ext {f g : X →ₑ[φ] Y} :
(∀ x, f x = g x) → f = g :=
DFunLike.ext f g
@[to_additive]
protected theorem congr_fun {f g : X →ₑ[φ] Y} (h : f = g) (x : X) :
f x = g x :=
DFunLike.congr_fun h _
/-- Two equal maps on scalars give rise to an equivariant map for identity -/
@[to_additive "Two equal maps on scalars give rise to an equivariant map for identity"]
def ofEq {φ' : M → N} (h : φ = φ') (f : X →ₑ[φ] Y) : X →ₑ[φ'] Y where
toFun := f.toFun
map_smul' m a := h ▸ f.map_smul' m a
@[to_additive (attr := simp)]
theorem ofEq_coe {φ' : M → N} (h : φ = φ') (f : X →ₑ[φ] Y) :
(f.ofEq h).toFun = f.toFun := rfl
@[to_additive (attr := simp)]
theorem ofEq_apply {φ' : M → N} (h : φ = φ') (f : X →ₑ[φ] Y) (a : X) :
(f.ofEq h) a = f a :=
rfl
lemma _root_.FaithfulSMul.of_injective
[FaithfulSMul M' X] [MulActionHomClass F M' X Y] (f : F)
(hf : Function.Injective f) :
FaithfulSMul M' Y where
eq_of_smul_eq_smul {_ _} h := eq_of_smul_eq_smul fun m ↦ hf <| by simp_rw [map_smul, h]
variable {ψ χ} (M N)
/-- The identity map as an equivariant map. -/
@[to_additive "The identity map as an equivariant map."]
protected def id : X →[M] X :=
⟨id, fun _ _ => rfl⟩
variable {M N Z}
@[to_additive (attr := simp)]
theorem id_apply (x : X) :
MulActionHom.id M x = x :=
rfl
end MulActionHom
namespace MulActionHom
open MulActionHom
variable {φ ψ χ X Y Z}
-- attribute [instance] CompTriple.id_comp CompTriple.comp_id
/-- Composition of two equivariant maps. -/
@[to_additive "Composition of two equivariant maps."]
def comp (g : Y →ₑ[ψ] Z) (f : X →ₑ[φ] Y) [κ : CompTriple φ ψ χ] :
X →ₑ[χ] Z :=
⟨g ∘ f, fun m x =>
calc
g (f (m • x)) = g (φ m • f x) := by rw [map_smulₛₗ]
_ = ψ (φ m) • g (f x) := by rw [map_smulₛₗ]
_ = (ψ ∘ φ) m • g (f x) := rfl
_ = χ m • g (f x) := by rw [κ.comp_eq] ⟩
@[to_additive (attr := simp)]
theorem comp_apply
(g : Y →ₑ[ψ] Z) (f : X →ₑ[φ] Y) [CompTriple φ ψ χ] (x : X) :
g.comp f x = g (f x) := rfl
@[to_additive (attr := simp)]
theorem id_comp (f : X →ₑ[φ] Y) :
(MulActionHom.id N).comp f = f :=
ext fun x => by rw [comp_apply, id_apply]
@[to_additive (attr := simp)]
theorem comp_id (f : X →ₑ[φ] Y) :
f.comp (MulActionHom.id M) = f :=
ext fun x => by rw [comp_apply, id_apply]
@[to_additive (attr := simp)]
theorem comp_assoc {Q T : Type*} [SMul Q T]
{η : P → Q} {θ : M → Q} {ζ : N → Q}
(h : Z →ₑ[η] T) (g : Y →ₑ[ψ] Z) (f : X →ₑ[φ] Y)
[CompTriple φ ψ χ] [CompTriple χ η θ]
[CompTriple ψ η ζ] [CompTriple φ ζ θ] :
h.comp (g.comp f) = (h.comp g).comp f :=
ext fun _ => rfl
variable {φ' : N → M}
variable {Y₁ : Type*} [SMul M Y₁]
/-- The inverse of a bijective equivariant map is equivariant. -/
@[to_additive (attr := simps) "The inverse of a bijective equivariant map is equivariant."]
def inverse (f : X →[M] Y₁) (g : Y₁ → X)
(h₁ : Function.LeftInverse g f) (h₂ : Function.RightInverse g f) : Y₁ →[M] X where
toFun := g
map_smul' m x :=
calc
g (m • x) = g (m • f (g x)) := by rw [h₂]
_ = g (f (m • g x)) := by simp only [map_smul, id_eq]
_ = m • g x := by rw [h₁]
/-- The inverse of a bijective equivariant map is equivariant. -/
@[to_additive (attr := simps) "The inverse of a bijective equivariant map is equivariant."]
def inverse' (f : X →ₑ[φ] Y) (g : Y → X) (k : Function.RightInverse φ' φ)
(h₁ : Function.LeftInverse g f) (h₂ : Function.RightInverse g f) :
Y →ₑ[φ'] X where
toFun := g
map_smul' m x :=
calc
g (m • x) = g (m • f (g x)) := by rw [h₂]
_ = g ((φ (φ' m)) • f (g x)) := by rw [k]
_ = g (f (φ' m • g x)) := by rw [map_smulₛₗ]
_ = φ' m • g x := by rw [h₁]
@[to_additive]
lemma inverse_eq_inverse' (f : X →[M] Y₁) (g : Y₁ → X)
(h₁ : Function.LeftInverse g f) (h₂ : Function.RightInverse g f) :
inverse f g h₁ h₂ = inverse' f g (congrFun rfl) h₁ h₂ := by
rfl
@[to_additive]
theorem inverse'_inverse'
{f : X →ₑ[φ] Y} {g : Y → X}
{k₁ : Function.LeftInverse φ' φ} {k₂ : Function.RightInverse φ' φ}
{h₁ : Function.LeftInverse g f} {h₂ : Function.RightInverse g f} :
inverse' (inverse' f g k₂ h₁ h₂) f k₁ h₂ h₁ = f :=
ext fun _ => rfl
@[to_additive]
theorem comp_inverse' {f : X →ₑ[φ] Y} {g : Y → X}
{k₁ : Function.LeftInverse φ' φ} {k₂ : Function.RightInverse φ' φ}
{h₁ : Function.LeftInverse g f} {h₂ : Function.RightInverse g f} :
(inverse' f g k₂ h₁ h₂).comp f (κ := CompTriple.comp_inv k₁)
= MulActionHom.id M := by
rw [MulActionHom.ext_iff]
intro x
simp only [comp_apply, inverse_apply, id_apply]
exact h₁ x
@[to_additive]
theorem inverse'_comp {f : X →ₑ[φ] Y} {g : Y → X}
{k₂ : Function.RightInverse φ' φ}
{h₁ : Function.LeftInverse g f} {h₂ : Function.RightInverse g f} :
f.comp (inverse' f g k₂ h₁ h₂) (κ := CompTriple.comp_inv k₂) = MulActionHom.id N := by
rw [MulActionHom.ext_iff]
intro x
simp only [comp_apply, inverse_apply, id_apply]
exact h₂ x
/-- If actions of `M` and `N` on `α` commute,
then for `c : M`, `(c • · : α → α)` is an `N`-action homomorphism. -/
@[to_additive (attr := simps) "If additive actions of `M` and `N` on `α` commute,
then for `c : M`, `(c • · : α → α)` is an `N`-additive action homomorphism."]
def _root_.SMulCommClass.toMulActionHom {M} (N α : Type*)
[SMul M α] [SMul N α] [SMulCommClass M N α] (c : M) :
α →[N] α where
toFun := (c • ·)
map_smul' := smul_comm _
end MulActionHom
end MulActionHom
/-- Evaluation at a point as a `MulActionHom`. -/
@[to_additive (attr := simps) "Evaluation at a point as an `AddActionHom`."]
def Pi.evalMulActionHom {ι M : Type*} {X : ι → Type*} [∀ i, SMul M (X i)] (i : ι) :
(∀ i, X i) →[M] X i where
toFun := Function.eval i
map_smul' _ _ := rfl
namespace MulActionHom
section FstSnd
variable {M α β : Type*} [SMul M α] [SMul M β]
variable (M α β) in
/-- `Prod.fst` as a bundled `MulActionHom`. -/
@[to_additive (attr := simps -fullyApplied) "`Prod.fst` as a bundled `AddActionHom`."]
def fst : α × β →[M] α where
toFun := Prod.fst
map_smul' _ _ := rfl
variable (M α β) in
/-- `Prod.snd` as a bundled `MulActionHom`. -/
@[to_additive (attr := simps -fullyApplied) "`Prod.snd` as a bundled `AddActionHom`."]
def snd : α × β →[M] β where
toFun := Prod.snd
map_smul' _ _ := rfl
end FstSnd
variable {M N α β γ δ : Type*} [SMul M α] [SMul M β] [SMul N γ] [SMul N δ] {σ : M → N}
/-- If `f` and `g` are equivariant maps, then so is `x ↦ (f x, g x)`. -/
@[to_additive (attr := simps -fullyApplied) prod
"If `f` and `g` are equivariant maps, then so is `x ↦ (f x, g x)`."]
def prod (f : α →ₑ[σ] γ) (g : α →ₑ[σ] δ) : α →ₑ[σ] γ × δ where
toFun x := (f x, g x)
map_smul' _ _ := Prod.ext (map_smulₛₗ f _ _) (map_smulₛₗ g _ _)
@[to_additive (attr := simp) fst_comp_prod]
lemma fst_comp_prod (f : α →ₑ[σ] γ) (g : α →ₑ[σ] δ) : (fst _ _ _).comp (prod f g) = f := rfl
@[to_additive (attr := simp) snd_comp_prod]
lemma snd_comp_prod (f : α →ₑ[σ] γ) (g : α →ₑ[σ] δ) : (snd _ _ _).comp (prod f g) = g := rfl
@[to_additive (attr := simp) prod_fst_snd]
lemma prod_fst_snd : prod (fst M α β) (snd M α β) = .id .. := rfl
/-- If `f` and `g` are equivariant maps, then so is `(x, y) ↦ (f x, g y)`. -/
@[to_additive (attr := simps -fullyApplied) prodMap
"If `f` and `g` are equivariant maps, then so is `(x, y) ↦ (f x, g y)`."]
def prodMap (f : α →ₑ[σ] γ) (g : β →ₑ[σ] δ) : α × β →ₑ[σ] γ × δ where
toFun := Prod.map f g
__ := (f.comp (fst ..)).prod (g.comp (snd ..))
end MulActionHom
section DistribMulAction
variable {M : Type*} [Monoid M]
variable {N : Type*} [Monoid N]
variable {P : Type*} [Monoid P]
variable (φ : M →* N) (φ' : N →* M) (ψ : N →* P) (χ : M →* P)
variable (A : Type*) [AddMonoid A] [DistribMulAction M A]
variable (B : Type*) [AddMonoid B] [DistribMulAction N B]
variable (B₁ : Type*) [AddMonoid B₁] [DistribMulAction M B₁]
variable (C : Type*) [AddMonoid C] [DistribMulAction P C]
variable (A' : Type*) [AddGroup A'] [DistribMulAction M A']
variable (B' : Type*) [AddGroup B'] [DistribMulAction N B']
/-- Equivariant additive monoid homomorphisms. -/
structure DistribMulActionHom extends A →ₑ[φ] B, A →+ B
/-- Reinterpret an equivariant additive monoid homomorphism as an additive monoid homomorphism. -/
add_decl_doc DistribMulActionHom.toAddMonoidHom
/-- Reinterpret an equivariant additive monoid homomorphism as an equivariant function. -/
add_decl_doc DistribMulActionHom.toMulActionHom
/- Porting note: local notation given a name, conflict with Algebra.Hom.Freiman
see https://github.com/leanprover/lean4/issues/2000 -/
@[inherit_doc]
notation:25 (name := «DistribMulActionHomLocal≺»)
A " →ₑ+[" φ:25 "] " B:0 => DistribMulActionHom φ A B
@[inherit_doc]
notation:25 (name := «DistribMulActionHomIdLocal≺»)
A " →+[" M:25 "] " B:0 => DistribMulActionHom (MonoidHom.id M) A B
-- QUESTION/TODO : Impose that `φ` is a morphism of monoids?
/-- `DistribMulActionSemiHomClass F φ A B` states that `F` is a type of morphisms
preserving the additive monoid structure and equivariant with respect to `φ`.
You should extend this class when you extend `DistribMulActionSemiHom`. -/
class DistribMulActionSemiHomClass (F : Type*)
{M N : outParam Type*} (φ : outParam (M → N))
(A B : outParam Type*)
[Monoid M] [Monoid N]
[AddMonoid A] [AddMonoid B] [DistribMulAction M A] [DistribMulAction N B]
[FunLike F A B] : Prop
extends MulActionSemiHomClass F φ A B, AddMonoidHomClass F A B
/-- `DistribMulActionHomClass F M A B` states that `F` is a type of morphisms preserving
the additive monoid structure and equivariant with respect to the action of `M`.
It is an abbreviation to `DistribMulActionHomClass F (MonoidHom.id M) A B`
You should extend this class when you extend `DistribMulActionHom`. -/
abbrev DistribMulActionHomClass (F : Type*) (M : outParam Type*)
(A B : outParam Type*) [Monoid M] [AddMonoid A] [AddMonoid B]
[DistribMulAction M A] [DistribMulAction M B] [FunLike F A B] :=
DistribMulActionSemiHomClass F (MonoidHom.id M) A B
namespace DistribMulActionHom
instance : FunLike (A →ₑ+[φ] B) A B where
coe m := m.toFun
coe_injective' f g h := by
rcases f with ⟨tF, _, _⟩; rcases g with ⟨tG, _, _⟩
cases tF; cases tG; congr
instance : DistribMulActionSemiHomClass (A →ₑ+[φ] B) φ A B where
map_smulₛₗ m := m.map_smul'
map_zero := DistribMulActionHom.map_zero'
map_add := DistribMulActionHom.map_add'
variable {φ φ' A B B₁}
variable {F : Type*} [FunLike F A B]
/-- Turn an element of a type `F` satisfying `MulActionHomClass F M X Y` into an actual
`MulActionHom`. This is declared as the default coercion from `F` to `MulActionHom M X Y`. -/
@[coe]
def _root_.DistribMulActionSemiHomClass.toDistribMulActionHom
[DistribMulActionSemiHomClass F φ A B]
(f : F) : A →ₑ+[φ] B :=
{ (f : A →+ B), (f : A →ₑ[φ] B) with }
/-- Any type satisfying `MulActionHomClass` can be cast into `MulActionHom`
via `MulActionHomClass.toMulActionHom`. -/
instance [DistribMulActionSemiHomClass F φ A B] :
CoeTC F (A →ₑ+[φ] B) :=
⟨DistribMulActionSemiHomClass.toDistribMulActionHom⟩
/-- If `DistribMulAction` of `M` and `N` on `A` commute,
then for each `c : M`, `(c • ·)` is an `N`-action additive homomorphism. -/
@[simps]
def _root_.SMulCommClass.toDistribMulActionHom {M} (N A : Type*) [Monoid N] [AddMonoid A]
[DistribSMul M A] [DistribMulAction N A] [SMulCommClass M N A] (c : M) : A →+[N] A :=
{ SMulCommClass.toMulActionHom N A c,
DistribSMul.toAddMonoidHom _ c with
toFun := (c • ·) }
@[simp]
theorem toFun_eq_coe (f : A →ₑ+[φ] B) : f.toFun = f := rfl
@[norm_cast]
theorem coe_fn_coe (f : A →ₑ+[φ] B) : ⇑(f : A →+ B) = f :=
rfl
@[norm_cast]
theorem coe_fn_coe' (f : A →ₑ+[φ] B) : ⇑(f : A →ₑ[φ] B) = f :=
rfl
@[ext]
theorem ext {f g : A →ₑ+[φ] B} : (∀ x, f x = g x) → f = g :=
DFunLike.ext f g
protected theorem congr_fun {f g : A →ₑ+[φ] B} (h : f = g) (x : A) : f x = g x :=
DFunLike.congr_fun h _
theorem toMulActionHom_injective {f g : A →ₑ+[φ] B} (h : (f : A →ₑ[φ] B) = (g : A →ₑ[φ] B)) :
f = g := by
ext a
exact MulActionHom.congr_fun h a
theorem toAddMonoidHom_injective {f g : A →ₑ+[φ] B} (h : (f : A →+ B) = (g : A →+ B)) : f = g := by
ext a
exact DFunLike.congr_fun h a
protected theorem map_zero (f : A →ₑ+[φ] B) : f 0 = 0 :=
map_zero f
protected theorem map_add (f : A →ₑ+[φ] B) (x y : A) : f (x + y) = f x + f y :=
map_add f x y
protected theorem map_neg (f : A' →ₑ+[φ] B') (x : A') : f (-x) = -f x :=
map_neg f x
protected theorem map_sub (f : A' →ₑ+[φ] B') (x y : A') : f (x - y) = f x - f y :=
map_sub f x y
protected theorem map_smulₑ (f : A →ₑ+[φ] B) (m : M) (x : A) : f (m • x) = (φ m) • f x :=
map_smulₛₗ f m x
variable (M)
/-- The identity map as an equivariant additive monoid homomorphism. -/
protected def id : A →+[M] A :=
⟨MulActionHom.id _, rfl, fun _ _ => rfl⟩
@[simp]
theorem id_apply (x : A) : DistribMulActionHom.id M x = x := by
rfl
variable {M C ψ χ}
| instance : Zero (A →ₑ+[φ] B) :=
⟨{ (0 : A →+ B) with map_smul' := fun m _ => by simp }⟩
| Mathlib/GroupTheory/GroupAction/Hom.lean | 565 | 566 |
/-
Copyright (c) 2014 Robert Y. Lewis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Robert Y. Lewis, Leonardo de Moura, Mario Carneiro, Floris van Doorn
-/
import Mathlib.Algebra.Field.Basic
import Mathlib.Algebra.GroupWithZero.Units.Lemmas
import Mathlib.Algebra.Order.Ring.Abs
import Mathlib.Order.Bounds.Basic
import Mathlib.Order.Bounds.OrderIso
import Mathlib.Tactic.Positivity.Core
/-!
# Lemmas about linear ordered (semi)fields
-/
open Function OrderDual
variable {ι α β : Type*}
section LinearOrderedSemifield
variable [Semifield α] [LinearOrder α] [IsStrictOrderedRing α] {a b c d e : α} {m n : ℤ}
/-!
### Relating two divisions.
-/
@[deprecated div_le_div_iff_of_pos_right (since := "2024-11-12")]
theorem div_le_div_right (hc : 0 < c) : a / c ≤ b / c ↔ a ≤ b := div_le_div_iff_of_pos_right hc
@[deprecated div_lt_div_iff_of_pos_right (since := "2024-11-12")]
theorem div_lt_div_right (hc : 0 < c) : a / c < b / c ↔ a < b := div_lt_div_iff_of_pos_right hc
@[deprecated div_lt_div_iff_of_pos_left (since := "2024-11-13")]
theorem div_lt_div_left (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : a / b < a / c ↔ c < b :=
div_lt_div_iff_of_pos_left ha hb hc
@[deprecated div_le_div_iff_of_pos_left (since := "2024-11-12")]
theorem div_le_div_left (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : a / b ≤ a / c ↔ c ≤ b :=
div_le_div_iff_of_pos_left ha hb hc
@[deprecated div_lt_div_iff₀ (since := "2024-11-12")]
theorem div_lt_div_iff (b0 : 0 < b) (d0 : 0 < d) : a / b < c / d ↔ a * d < c * b :=
div_lt_div_iff₀ b0 d0
@[deprecated div_le_div_iff₀ (since := "2024-11-12")]
theorem div_le_div_iff (b0 : 0 < b) (d0 : 0 < d) : a / b ≤ c / d ↔ a * d ≤ c * b :=
div_le_div_iff₀ b0 d0
@[deprecated div_le_div₀ (since := "2024-11-12")]
theorem div_le_div (hc : 0 ≤ c) (hac : a ≤ c) (hd : 0 < d) (hbd : d ≤ b) : a / b ≤ c / d :=
div_le_div₀ hc hac hd hbd
@[deprecated div_lt_div₀ (since := "2024-11-12")]
theorem div_lt_div (hac : a < c) (hbd : d ≤ b) (c0 : 0 ≤ c) (d0 : 0 < d) : a / b < c / d :=
div_lt_div₀ hac hbd c0 d0
@[deprecated div_lt_div₀' (since := "2024-11-12")]
theorem div_lt_div' (hac : a ≤ c) (hbd : d < b) (c0 : 0 < c) (d0 : 0 < d) : a / b < c / d :=
div_lt_div₀' hac hbd c0 d0
/-!
### Relating one division and involving `1`
-/
@[bound]
theorem div_le_self (ha : 0 ≤ a) (hb : 1 ≤ b) : a / b ≤ a := by
simpa only [div_one] using div_le_div_of_nonneg_left ha zero_lt_one hb
@[bound]
theorem div_lt_self (ha : 0 < a) (hb : 1 < b) : a / b < a := by
simpa only [div_one] using div_lt_div_of_pos_left ha zero_lt_one hb
@[bound]
theorem le_div_self (ha : 0 ≤ a) (hb₀ : 0 < b) (hb₁ : b ≤ 1) : a ≤ a / b := by
simpa only [div_one] using div_le_div_of_nonneg_left ha hb₀ hb₁
theorem one_le_div (hb : 0 < b) : 1 ≤ a / b ↔ b ≤ a := by rw [le_div_iff₀ hb, one_mul]
theorem div_le_one (hb : 0 < b) : a / b ≤ 1 ↔ a ≤ b := by rw [div_le_iff₀ hb, one_mul]
theorem one_lt_div (hb : 0 < b) : 1 < a / b ↔ b < a := by rw [lt_div_iff₀ hb, one_mul]
theorem div_lt_one (hb : 0 < b) : a / b < 1 ↔ a < b := by rw [div_lt_iff₀ hb, one_mul]
theorem one_div_le (ha : 0 < a) (hb : 0 < b) : 1 / a ≤ b ↔ 1 / b ≤ a := by
simpa using inv_le_comm₀ ha hb
theorem one_div_lt (ha : 0 < a) (hb : 0 < b) : 1 / a < b ↔ 1 / b < a := by
simpa using inv_lt_comm₀ ha hb
theorem le_one_div (ha : 0 < a) (hb : 0 < b) : a ≤ 1 / b ↔ b ≤ 1 / a := by
simpa using le_inv_comm₀ ha hb
theorem lt_one_div (ha : 0 < a) (hb : 0 < b) : a < 1 / b ↔ b < 1 / a := by
simpa using lt_inv_comm₀ ha hb
@[bound] lemma Bound.one_lt_div_of_pos_of_lt (b0 : 0 < b) : b < a → 1 < a / b := (one_lt_div b0).mpr
@[bound] lemma Bound.div_lt_one_of_pos_of_lt (b0 : 0 < b) : a < b → a / b < 1 := (div_lt_one b0).mpr
/-!
### Relating two divisions, involving `1`
-/
theorem one_div_le_one_div_of_le (ha : 0 < a) (h : a ≤ b) : 1 / b ≤ 1 / a := by
simpa using inv_anti₀ ha h
theorem one_div_lt_one_div_of_lt (ha : 0 < a) (h : a < b) : 1 / b < 1 / a := by
rwa [lt_div_iff₀' ha, ← div_eq_mul_one_div, div_lt_one (ha.trans h)]
theorem le_of_one_div_le_one_div (ha : 0 < a) (h : 1 / a ≤ 1 / b) : b ≤ a :=
le_imp_le_of_lt_imp_lt (one_div_lt_one_div_of_lt ha) h
theorem lt_of_one_div_lt_one_div (ha : 0 < a) (h : 1 / a < 1 / b) : b < a :=
lt_imp_lt_of_le_imp_le (one_div_le_one_div_of_le ha) h
/-- For the single implications with fewer assumptions, see `one_div_le_one_div_of_le` and
`le_of_one_div_le_one_div` -/
theorem one_div_le_one_div (ha : 0 < a) (hb : 0 < b) : 1 / a ≤ 1 / b ↔ b ≤ a :=
div_le_div_iff_of_pos_left zero_lt_one ha hb
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_lt_one_div (ha : 0 < a) (hb : 0 < b) : 1 / a < 1 / b ↔ b < a :=
div_lt_div_iff_of_pos_left zero_lt_one ha hb
theorem one_lt_one_div (h1 : 0 < a) (h2 : a < 1) : 1 < 1 / a := by
rwa [lt_one_div (@zero_lt_one α _ _ _ _ _) h1, one_div_one]
theorem one_le_one_div (h1 : 0 < a) (h2 : a ≤ 1) : 1 ≤ 1 / a := by
rwa [le_one_div (@zero_lt_one α _ _ _ _ _) h1, one_div_one]
/-!
### Results about halving.
The equalities also hold in semifields of characteristic `0`.
-/
theorem half_pos (h : 0 < a) : 0 < a / 2 :=
div_pos h zero_lt_two
theorem one_half_pos : (0 : α) < 1 / 2 :=
half_pos zero_lt_one
@[simp]
theorem half_le_self_iff : a / 2 ≤ a ↔ 0 ≤ a := by
rw [div_le_iff₀ (zero_lt_two' α), mul_two, le_add_iff_nonneg_left]
@[simp]
theorem half_lt_self_iff : a / 2 < a ↔ 0 < a := by
rw [div_lt_iff₀ (zero_lt_two' α), mul_two, lt_add_iff_pos_left]
alias ⟨_, half_le_self⟩ := half_le_self_iff
alias ⟨_, half_lt_self⟩ := half_lt_self_iff
alias div_two_lt_of_pos := half_lt_self
theorem one_half_lt_one : (1 / 2 : α) < 1 :=
half_lt_self zero_lt_one
theorem two_inv_lt_one : (2⁻¹ : α) < 1 :=
(one_div _).symm.trans_lt one_half_lt_one
theorem left_lt_add_div_two : a < (a + b) / 2 ↔ a < b := by simp [lt_div_iff₀, mul_two]
theorem add_div_two_lt_right : (a + b) / 2 < b ↔ a < b := by simp [div_lt_iff₀, mul_two]
theorem add_thirds (a : α) : a / 3 + a / 3 + a / 3 = a := by
rw [div_add_div_same, div_add_div_same, ← two_mul, ← add_one_mul 2 a, two_add_one_eq_three,
mul_div_cancel_left₀ a three_ne_zero]
/-!
### Miscellaneous lemmas
-/
@[simp] lemma div_pos_iff_of_pos_left (ha : 0 < a) : 0 < a / b ↔ 0 < b := by
simp only [div_eq_mul_inv, mul_pos_iff_of_pos_left ha, inv_pos]
@[simp] lemma div_pos_iff_of_pos_right (hb : 0 < b) : 0 < a / b ↔ 0 < a := by
simp only [div_eq_mul_inv, mul_pos_iff_of_pos_right (inv_pos.2 hb)]
theorem mul_le_mul_of_mul_div_le (h : a * (b / c) ≤ d) (hc : 0 < c) : b * a ≤ d * c := by
rw [← mul_div_assoc] at h
rwa [mul_comm b, ← div_le_iff₀ hc]
theorem div_mul_le_div_mul_of_div_le_div (h : a / b ≤ c / d) (he : 0 ≤ e) :
a / (b * e) ≤ c / (d * e) := by
rw [div_mul_eq_div_mul_one_div, div_mul_eq_div_mul_one_div]
exact mul_le_mul_of_nonneg_right h (one_div_nonneg.2 he)
theorem exists_pos_mul_lt {a : α} (h : 0 < a) (b : α) : ∃ c : α, 0 < c ∧ b * c < a := by
have : 0 < a / max (b + 1) 1 := div_pos h (lt_max_iff.2 (Or.inr zero_lt_one))
refine ⟨a / max (b + 1) 1, this, ?_⟩
rw [← lt_div_iff₀ this, div_div_cancel₀ h.ne']
exact lt_max_iff.2 (Or.inl <| lt_add_one _)
theorem exists_pos_lt_mul {a : α} (h : 0 < a) (b : α) : ∃ c : α, 0 < c ∧ b < c * a :=
let ⟨c, hc₀, hc⟩ := exists_pos_mul_lt h b;
⟨c⁻¹, inv_pos.2 hc₀, by rwa [← div_eq_inv_mul, lt_div_iff₀ hc₀]⟩
lemma monotone_div_right_of_nonneg (ha : 0 ≤ a) : Monotone (· / a) :=
fun _b _c hbc ↦ div_le_div_of_nonneg_right hbc ha
lemma strictMono_div_right_of_pos (ha : 0 < a) : StrictMono (· / a) :=
fun _b _c hbc ↦ div_lt_div_of_pos_right hbc ha
theorem Monotone.div_const {β : Type*} [Preorder β] {f : β → α} (hf : Monotone f) {c : α}
(hc : 0 ≤ c) : Monotone fun x => f x / c := (monotone_div_right_of_nonneg hc).comp hf
theorem StrictMono.div_const {β : Type*} [Preorder β] {f : β → α} (hf : StrictMono f) {c : α}
(hc : 0 < c) : StrictMono fun x => f x / c := by
simpa only [div_eq_mul_inv] using hf.mul_const (inv_pos.2 hc)
-- see Note [lower instance priority]
instance (priority := 100) LinearOrderedSemiField.toDenselyOrdered : DenselyOrdered α where
dense a₁ a₂ h :=
⟨(a₁ + a₂) / 2,
calc
a₁ = (a₁ + a₁) / 2 := (add_self_div_two a₁).symm
_ < (a₁ + a₂) / 2 := div_lt_div_of_pos_right (add_lt_add_left h _) zero_lt_two
,
calc
(a₁ + a₂) / 2 < (a₂ + a₂) / 2 := div_lt_div_of_pos_right (add_lt_add_right h _) zero_lt_two
_ = a₂ := add_self_div_two a₂
⟩
theorem min_div_div_right {c : α} (hc : 0 ≤ c) (a b : α) : min (a / c) (b / c) = min a b / c :=
(monotone_div_right_of_nonneg hc).map_min.symm
theorem max_div_div_right {c : α} (hc : 0 ≤ c) (a b : α) : max (a / c) (b / c) = max a b / c :=
(monotone_div_right_of_nonneg hc).map_max.symm
theorem one_div_strictAntiOn : StrictAntiOn (fun x : α => 1 / x) (Set.Ioi 0) :=
fun _ x1 _ y1 xy => (one_div_lt_one_div (Set.mem_Ioi.mp y1) (Set.mem_Ioi.mp x1)).mpr xy
theorem one_div_pow_le_one_div_pow_of_le (a1 : 1 ≤ a) {m n : ℕ} (mn : m ≤ n) :
1 / a ^ n ≤ 1 / a ^ m := by
refine (one_div_le_one_div ?_ ?_).mpr (pow_right_mono₀ a1 mn) <;>
exact pow_pos (zero_lt_one.trans_le a1) _
theorem one_div_pow_lt_one_div_pow_of_lt (a1 : 1 < a) {m n : ℕ} (mn : m < n) :
1 / a ^ n < 1 / a ^ m := by
refine (one_div_lt_one_div ?_ ?_).2 (pow_lt_pow_right₀ a1 mn) <;>
exact pow_pos (zero_lt_one.trans a1) _
theorem one_div_pow_anti (a1 : 1 ≤ a) : Antitone fun n : ℕ => 1 / a ^ n := fun _ _ =>
one_div_pow_le_one_div_pow_of_le a1
theorem one_div_pow_strictAnti (a1 : 1 < a) : StrictAnti fun n : ℕ => 1 / a ^ n := fun _ _ =>
one_div_pow_lt_one_div_pow_of_lt a1
theorem inv_strictAntiOn : StrictAntiOn (fun x : α => x⁻¹) (Set.Ioi 0) := fun _ hx _ hy xy =>
(inv_lt_inv₀ hy hx).2 xy
theorem inv_pow_le_inv_pow_of_le (a1 : 1 ≤ a) {m n : ℕ} (mn : m ≤ n) : (a ^ n)⁻¹ ≤ (a ^ m)⁻¹ := by
convert one_div_pow_le_one_div_pow_of_le a1 mn using 1 <;> simp
theorem inv_pow_lt_inv_pow_of_lt (a1 : 1 < a) {m n : ℕ} (mn : m < n) : (a ^ n)⁻¹ < (a ^ m)⁻¹ := by
convert one_div_pow_lt_one_div_pow_of_lt a1 mn using 1 <;> simp
theorem inv_pow_anti (a1 : 1 ≤ a) : Antitone fun n : ℕ => (a ^ n)⁻¹ := fun _ _ =>
inv_pow_le_inv_pow_of_le a1
theorem inv_pow_strictAnti (a1 : 1 < a) : StrictAnti fun n : ℕ => (a ^ n)⁻¹ := fun _ _ =>
inv_pow_lt_inv_pow_of_lt a1
theorem le_iff_forall_one_lt_le_mul₀ {α : Type*}
[Semifield α] [LinearOrder α] [IsStrictOrderedRing α]
{a b : α} (hb : 0 ≤ b) : a ≤ b ↔ ∀ ε, 1 < ε → a ≤ b * ε := by
refine ⟨fun h _ hε ↦ h.trans <| le_mul_of_one_le_right hb hε.le, fun h ↦ ?_⟩
obtain rfl|hb := hb.eq_or_lt
· simp_rw [zero_mul] at h
exact h 2 one_lt_two
refine le_of_forall_gt_imp_ge_of_dense fun x hbx => ?_
convert h (x / b) ((one_lt_div hb).mpr hbx)
rw [mul_div_cancel₀ _ hb.ne']
/-! ### Results about `IsGLB` -/
theorem IsGLB.mul_left {s : Set α} (ha : 0 ≤ a) (hs : IsGLB s b) :
IsGLB ((fun b => a * b) '' s) (a * b) := by
rcases lt_or_eq_of_le ha with (ha | rfl)
· exact (OrderIso.mulLeft₀ _ ha).isGLB_image'.2 hs
· simp_rw [zero_mul]
rw [hs.nonempty.image_const]
exact isGLB_singleton
theorem IsGLB.mul_right {s : Set α} (ha : 0 ≤ a) (hs : IsGLB s b) :
IsGLB ((fun b => b * a) '' s) (b * a) := by simpa [mul_comm] using hs.mul_left ha
end LinearOrderedSemifield
section
variable [Field α] [LinearOrder α] [IsStrictOrderedRing α] {a b c d : α} {n : ℤ}
/-! ### Lemmas about pos, nonneg, nonpos, neg -/
theorem div_pos_iff : 0 < a / b ↔ 0 < a ∧ 0 < b ∨ a < 0 ∧ b < 0 := by
simp only [division_def, mul_pos_iff, inv_pos, inv_lt_zero]
theorem div_neg_iff : a / b < 0 ↔ 0 < a ∧ b < 0 ∨ a < 0 ∧ 0 < b := by
simp [division_def, mul_neg_iff]
theorem div_nonneg_iff : 0 ≤ a / b ↔ 0 ≤ a ∧ 0 ≤ b ∨ a ≤ 0 ∧ b ≤ 0 := by
simp [division_def, mul_nonneg_iff]
theorem div_nonpos_iff : a / b ≤ 0 ↔ 0 ≤ a ∧ b ≤ 0 ∨ a ≤ 0 ∧ 0 ≤ b := by
simp [division_def, mul_nonpos_iff]
theorem div_nonneg_of_nonpos (ha : a ≤ 0) (hb : b ≤ 0) : 0 ≤ a / b :=
div_nonneg_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_pos_of_neg_of_neg (ha : a < 0) (hb : b < 0) : 0 < a / b :=
div_pos_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_neg_of_neg_of_pos (ha : a < 0) (hb : 0 < b) : a / b < 0 :=
div_neg_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_neg_of_pos_of_neg (ha : 0 < a) (hb : b < 0) : a / b < 0 :=
div_neg_iff.2 <| Or.inl ⟨ha, hb⟩
/-! ### Relating one division with another term -/
theorem div_le_iff_of_neg (hc : c < 0) : b / c ≤ a ↔ a * c ≤ b :=
⟨fun h => div_mul_cancel₀ b (ne_of_lt hc) ▸ mul_le_mul_of_nonpos_right h hc.le, fun h =>
calc
a = a * c * (1 / c) := mul_mul_div a (ne_of_lt hc)
_ ≥ b * (1 / c) := mul_le_mul_of_nonpos_right h (one_div_neg.2 hc).le
_ = b / c := (div_eq_mul_one_div b c).symm
⟩
theorem div_le_iff_of_neg' (hc : c < 0) : b / c ≤ a ↔ c * a ≤ b := by
rw [mul_comm, div_le_iff_of_neg hc]
theorem le_div_iff_of_neg (hc : c < 0) : a ≤ b / c ↔ b ≤ a * c := by
rw [← neg_neg c, mul_neg, div_neg, le_neg, div_le_iff₀ (neg_pos.2 hc), neg_mul]
theorem le_div_iff_of_neg' (hc : c < 0) : a ≤ b / c ↔ b ≤ c * a := by
rw [mul_comm, le_div_iff_of_neg hc]
theorem div_lt_iff_of_neg (hc : c < 0) : b / c < a ↔ a * c < b :=
lt_iff_lt_of_le_iff_le <| le_div_iff_of_neg hc
theorem div_lt_iff_of_neg' (hc : c < 0) : b / c < a ↔ c * a < b := by
rw [mul_comm, div_lt_iff_of_neg hc]
theorem lt_div_iff_of_neg (hc : c < 0) : a < b / c ↔ b < a * c :=
lt_iff_lt_of_le_iff_le <| div_le_iff_of_neg hc
theorem lt_div_iff_of_neg' (hc : c < 0) : a < b / c ↔ b < c * a := by
rw [mul_comm, lt_div_iff_of_neg hc]
theorem div_le_one_of_ge (h : b ≤ a) (hb : b ≤ 0) : a / b ≤ 1 := by
simpa only [neg_div_neg_eq] using div_le_one_of_le₀ (neg_le_neg h) (neg_nonneg_of_nonpos hb)
/-! ### Bi-implications of inequalities using inversions -/
theorem inv_le_inv_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ ≤ b⁻¹ ↔ b ≤ a := by
rw [← one_div, div_le_iff_of_neg ha, ← div_eq_inv_mul, div_le_iff_of_neg hb, one_mul]
theorem inv_le_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ ≤ b ↔ b⁻¹ ≤ a := by
rw [← inv_le_inv_of_neg hb (inv_lt_zero.2 ha), inv_inv]
theorem le_inv_of_neg (ha : a < 0) (hb : b < 0) : a ≤ b⁻¹ ↔ b ≤ a⁻¹ := by
rw [← inv_le_inv_of_neg (inv_lt_zero.2 hb) ha, inv_inv]
theorem inv_lt_inv_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ < b⁻¹ ↔ b < a :=
lt_iff_lt_of_le_iff_le (inv_le_inv_of_neg hb ha)
theorem inv_lt_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ < b ↔ b⁻¹ < a :=
lt_iff_lt_of_le_iff_le (le_inv_of_neg hb ha)
theorem lt_inv_of_neg (ha : a < 0) (hb : b < 0) : a < b⁻¹ ↔ b < a⁻¹ :=
lt_iff_lt_of_le_iff_le (inv_le_of_neg hb ha)
/-!
### Monotonicity results involving inversion
-/
theorem sub_inv_antitoneOn_Ioi :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Ioi c) :=
antitoneOn_iff_forall_lt.mpr fun _ ha _ hb hab ↦
inv_le_inv₀ (sub_pos.mpr hb) (sub_pos.mpr ha) |>.mpr <| sub_le_sub (le_of_lt hab) le_rfl
theorem sub_inv_antitoneOn_Iio :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Iio c) :=
antitoneOn_iff_forall_lt.mpr fun _ ha _ hb hab ↦
inv_le_inv_of_neg (sub_neg.mpr hb) (sub_neg.mpr ha) |>.mpr <| sub_le_sub (le_of_lt hab) le_rfl
theorem sub_inv_antitoneOn_Icc_right (ha : c < a) :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Icc a b) := by
by_cases hab : a ≤ b
· exact sub_inv_antitoneOn_Ioi.mono <| (Set.Icc_subset_Ioi_iff hab).mpr ha
· simp [hab, Set.Subsingleton.antitoneOn]
theorem sub_inv_antitoneOn_Icc_left (ha : b < c) :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Icc a b) := by
by_cases hab : a ≤ b
· exact sub_inv_antitoneOn_Iio.mono <| (Set.Icc_subset_Iio_iff hab).mpr ha
· simp [hab, Set.Subsingleton.antitoneOn]
theorem inv_antitoneOn_Ioi :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Ioi 0) := by
convert sub_inv_antitoneOn_Ioi (α := α)
exact (sub_zero _).symm
theorem inv_antitoneOn_Iio :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Iio 0) := by
convert sub_inv_antitoneOn_Iio (α := α)
exact (sub_zero _).symm
theorem inv_antitoneOn_Icc_right (ha : 0 < a) :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Icc a b) := by
convert sub_inv_antitoneOn_Icc_right ha
exact (sub_zero _).symm
theorem inv_antitoneOn_Icc_left (hb : b < 0) :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Icc a b) := by
convert sub_inv_antitoneOn_Icc_left hb
exact (sub_zero _).symm
/-! ### Relating two divisions -/
theorem div_le_div_of_nonpos_of_le (hc : c ≤ 0) (h : b ≤ a) : a / c ≤ b / c := by
rw [div_eq_mul_one_div a c, div_eq_mul_one_div b c]
exact mul_le_mul_of_nonpos_right h (one_div_nonpos.2 hc)
theorem div_lt_div_of_neg_of_lt (hc : c < 0) (h : b < a) : a / c < b / c := by
rw [div_eq_mul_one_div a c, div_eq_mul_one_div b c]
exact mul_lt_mul_of_neg_right h (one_div_neg.2 hc)
theorem div_le_div_right_of_neg (hc : c < 0) : a / c ≤ b / c ↔ b ≤ a :=
⟨le_imp_le_of_lt_imp_lt <| div_lt_div_of_neg_of_lt hc, div_le_div_of_nonpos_of_le <| hc.le⟩
theorem div_lt_div_right_of_neg (hc : c < 0) : a / c < b / c ↔ b < a :=
lt_iff_lt_of_le_iff_le <| div_le_div_right_of_neg hc
/-! ### Relating one division and involving `1` -/
theorem one_le_div_of_neg (hb : b < 0) : 1 ≤ a / b ↔ a ≤ b := by rw [le_div_iff_of_neg hb, one_mul]
theorem div_le_one_of_neg (hb : b < 0) : a / b ≤ 1 ↔ b ≤ a := by rw [div_le_iff_of_neg hb, one_mul]
theorem one_lt_div_of_neg (hb : b < 0) : 1 < a / b ↔ a < b := by rw [lt_div_iff_of_neg hb, one_mul]
theorem div_lt_one_of_neg (hb : b < 0) : a / b < 1 ↔ b < a := by rw [div_lt_iff_of_neg hb, one_mul]
theorem one_div_le_of_neg (ha : a < 0) (hb : b < 0) : 1 / a ≤ b ↔ 1 / b ≤ a := by
simpa using inv_le_of_neg ha hb
theorem one_div_lt_of_neg (ha : a < 0) (hb : b < 0) : 1 / a < b ↔ 1 / b < a := by
simpa using inv_lt_of_neg ha hb
theorem le_one_div_of_neg (ha : a < 0) (hb : b < 0) : a ≤ 1 / b ↔ b ≤ 1 / a := by
simpa using le_inv_of_neg ha hb
theorem lt_one_div_of_neg (ha : a < 0) (hb : b < 0) : a < 1 / b ↔ b < 1 / a := by
simpa using lt_inv_of_neg ha hb
theorem one_lt_div_iff : 1 < a / b ↔ 0 < b ∧ b < a ∨ b < 0 ∧ a < b := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, one_lt_div_of_neg]
· simp [lt_irrefl, zero_le_one]
· simp [hb, hb.not_lt, one_lt_div]
theorem one_le_div_iff : 1 ≤ a / b ↔ 0 < b ∧ b ≤ a ∨ b < 0 ∧ a ≤ b := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, one_le_div_of_neg]
· simp [lt_irrefl, zero_lt_one.not_le, zero_lt_one]
· simp [hb, hb.not_lt, one_le_div]
theorem div_lt_one_iff : a / b < 1 ↔ 0 < b ∧ a < b ∨ b = 0 ∨ b < 0 ∧ b < a := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, hb.ne, div_lt_one_of_neg]
· simp [zero_lt_one]
· simp [hb, hb.not_lt, div_lt_one, hb.ne.symm]
theorem div_le_one_iff : a / b ≤ 1 ↔ 0 < b ∧ a ≤ b ∨ b = 0 ∨ b < 0 ∧ b ≤ a := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, hb.ne, div_le_one_of_neg]
· simp [zero_le_one]
· simp [hb, hb.not_lt, div_le_one, hb.ne.symm]
/-! ### Relating two divisions, involving `1` -/
theorem one_div_le_one_div_of_neg_of_le (hb : b < 0) (h : a ≤ b) : 1 / b ≤ 1 / a := by
rwa [div_le_iff_of_neg' hb, ← div_eq_mul_one_div, div_le_one_of_neg (h.trans_lt hb)]
theorem one_div_lt_one_div_of_neg_of_lt (hb : b < 0) (h : a < b) : 1 / b < 1 / a := by
rwa [div_lt_iff_of_neg' hb, ← div_eq_mul_one_div, div_lt_one_of_neg (h.trans hb)]
theorem le_of_neg_of_one_div_le_one_div (hb : b < 0) (h : 1 / a ≤ 1 / b) : b ≤ a :=
le_imp_le_of_lt_imp_lt (one_div_lt_one_div_of_neg_of_lt hb) h
theorem lt_of_neg_of_one_div_lt_one_div (hb : b < 0) (h : 1 / a < 1 / b) : b < a :=
lt_imp_lt_of_le_imp_le (one_div_le_one_div_of_neg_of_le hb) h
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_neg_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_le_one_div_of_neg (ha : a < 0) (hb : b < 0) : 1 / a ≤ 1 / b ↔ b ≤ a := by
simpa [one_div] using inv_le_inv_of_neg ha hb
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_lt_one_div_of_neg (ha : a < 0) (hb : b < 0) : 1 / a < 1 / b ↔ b < a :=
lt_iff_lt_of_le_iff_le (one_div_le_one_div_of_neg hb ha)
theorem one_div_lt_neg_one (h1 : a < 0) (h2 : -1 < a) : 1 / a < -1 :=
suffices 1 / a < 1 / -1 by rwa [one_div_neg_one_eq_neg_one] at this
one_div_lt_one_div_of_neg_of_lt h1 h2
theorem one_div_le_neg_one (h1 : a < 0) (h2 : -1 ≤ a) : 1 / a ≤ -1 :=
suffices 1 / a ≤ 1 / -1 by rwa [one_div_neg_one_eq_neg_one] at this
one_div_le_one_div_of_neg_of_le h1 h2
/-! ### Results about halving -/
theorem sub_self_div_two (a : α) : a - a / 2 = a / 2 := by
suffices a / 2 + a / 2 - a / 2 = a / 2 by rwa [add_halves] at this
rw [add_sub_cancel_right]
theorem div_two_sub_self (a : α) : a / 2 - a = -(a / 2) := by
suffices a / 2 - (a / 2 + a / 2) = -(a / 2) by rwa [add_halves] at this
rw [sub_add_eq_sub_sub, sub_self, zero_sub]
theorem add_sub_div_two_lt (h : a < b) : a + (b - a) / 2 < b := by
rwa [← div_sub_div_same, sub_eq_add_neg, add_comm (b / 2), ← add_assoc, ← sub_eq_add_neg, ←
lt_sub_iff_add_lt, sub_self_div_two, sub_self_div_two,
div_lt_div_iff_of_pos_right (zero_lt_two' α)]
/-- An inequality involving `2`. -/
theorem sub_one_div_inv_le_two (a2 : 2 ≤ a) : (1 - 1 / a)⁻¹ ≤ 2 := by
-- Take inverses on both sides to obtain `2⁻¹ ≤ 1 - 1 / a`
refine (inv_anti₀ (inv_pos.2 <| zero_lt_two' α) ?_).trans_eq (inv_inv (2 : α))
-- move `1 / a` to the left and `2⁻¹` to the right.
rw [le_sub_iff_add_le, add_comm, ← le_sub_iff_add_le]
-- take inverses on both sides and use the assumption `2 ≤ a`.
convert (one_div a).le.trans (inv_anti₀ zero_lt_two a2) using 1
-- show `1 - 1 / 2 = 1 / 2`.
rw [sub_eq_iff_eq_add, ← two_mul, mul_inv_cancel₀ two_ne_zero]
/-! ### Results about `IsLUB` -/
-- TODO: Generalize to `LinearOrderedSemifield`
theorem IsLUB.mul_left {s : Set α} (ha : 0 ≤ a) (hs : IsLUB s b) :
IsLUB ((fun b => a * b) '' s) (a * b) := by
rcases lt_or_eq_of_le ha with (ha | rfl)
· exact (OrderIso.mulLeft₀ _ ha).isLUB_image'.2 hs
· simp_rw [zero_mul]
rw [hs.nonempty.image_const]
exact isLUB_singleton
-- TODO: Generalize to `LinearOrderedSemifield`
theorem IsLUB.mul_right {s : Set α} (ha : 0 ≤ a) (hs : IsLUB s b) :
IsLUB ((fun b => b * a) '' s) (b * a) := by simpa [mul_comm] using hs.mul_left ha
/-! ### Miscellaneous lemmas -/
theorem mul_sub_mul_div_mul_neg_iff (hc : c ≠ 0) (hd : d ≠ 0) :
(a * d - b * c) / (c * d) < 0 ↔ a / c < b / d := by
rw [mul_comm b c, ← div_sub_div _ _ hc hd, sub_lt_zero]
theorem mul_sub_mul_div_mul_nonpos_iff (hc : c ≠ 0) (hd : d ≠ 0) :
(a * d - b * c) / (c * d) ≤ 0 ↔ a / c ≤ b / d := by
rw [mul_comm b c, ← div_sub_div _ _ hc hd, sub_nonpos]
alias ⟨div_lt_div_of_mul_sub_mul_div_neg, mul_sub_mul_div_mul_neg⟩ := mul_sub_mul_div_mul_neg_iff
alias ⟨div_le_div_of_mul_sub_mul_div_nonpos, mul_sub_mul_div_mul_nonpos⟩ :=
mul_sub_mul_div_mul_nonpos_iff
theorem exists_add_lt_and_pos_of_lt (h : b < a) : ∃ c, b + c < a ∧ 0 < c :=
⟨(a - b) / 2, add_sub_div_two_lt h, div_pos (sub_pos_of_lt h) zero_lt_two⟩
theorem le_of_forall_sub_le (h : ∀ ε > 0, b - ε ≤ a) : b ≤ a := by
contrapose! h
simpa only [@and_comm ((0 : α) < _), lt_sub_iff_add_lt, gt_iff_lt] using
exists_add_lt_and_pos_of_lt h
private lemma exists_lt_mul_left_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c) (h : c < a * b) :
∃ a' ∈ Set.Ico 0 a, c < a' * b := by
have hb : 0 < b := pos_of_mul_pos_right (hc.trans_lt h) ha
obtain ⟨a', ha', a_a'⟩ := exists_between ((div_lt_iff₀ hb).2 h)
exact ⟨a', ⟨(div_nonneg hc hb.le).trans ha'.le, a_a'⟩, (div_lt_iff₀ hb).1 ha'⟩
private lemma exists_lt_mul_right_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c) (h : c < a * b) :
∃ b' ∈ Set.Ico 0 b, c < a * b' := by
have hb : 0 < b := pos_of_mul_pos_right (hc.trans_lt h) ha
simp_rw [mul_comm a] at h ⊢
exact exists_lt_mul_left_of_nonneg hb.le hc h
private lemma exists_mul_left_lt₀ {a b c : α} (hc : a * b < c) : ∃ a' > a, a' * b < c := by
rcases le_or_lt b 0 with hb | hb
· obtain ⟨a', ha'⟩ := exists_gt a
exact ⟨a', ha', hc.trans_le' (antitone_mul_right hb ha'.le)⟩
· obtain ⟨a', ha', hc'⟩ := exists_between ((lt_div_iff₀ hb).2 hc)
exact ⟨a', ha', (lt_div_iff₀ hb).1 hc'⟩
private lemma exists_mul_right_lt₀ {a b c : α} (hc : a * b < c) : ∃ b' > b, a * b' < c := by
simp_rw [mul_comm a] at hc ⊢; exact exists_mul_left_lt₀ hc
lemma le_mul_of_forall_lt₀ {a b c : α} (h : ∀ a' > a, ∀ b' > b, c ≤ a' * b') : c ≤ a * b := by
refine le_of_forall_gt_imp_ge_of_dense fun d hd ↦ ?_
obtain ⟨a', ha', hd⟩ := exists_mul_left_lt₀ hd
obtain ⟨b', hb', hd⟩ := exists_mul_right_lt₀ hd
exact (h a' ha' b' hb').trans hd.le
lemma mul_le_of_forall_lt_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c)
(h : ∀ a' ≥ 0, a' < a → ∀ b' ≥ 0, b' < b → a' * b' ≤ c) : a * b ≤ c := by
refine le_of_forall_lt_imp_le_of_dense fun d d_ab ↦ ?_
rcases lt_or_le d 0 with hd | hd
· exact hd.le.trans hc
obtain ⟨a', ha', d_ab⟩ := exists_lt_mul_left_of_nonneg ha hd d_ab
obtain ⟨b', hb', d_ab⟩ := exists_lt_mul_right_of_nonneg ha'.1 hd d_ab
exact d_ab.le.trans (h a' ha'.1 ha'.2 b' hb'.1 hb'.2)
theorem mul_self_inj_of_nonneg (a0 : 0 ≤ a) (b0 : 0 ≤ b) : a * a = b * b ↔ a = b :=
mul_self_eq_mul_self_iff.trans <|
or_iff_left_of_imp fun h => by
subst a
have : b = 0 := le_antisymm (neg_nonneg.1 a0) b0
rw [this, neg_zero]
theorem min_div_div_right_of_nonpos (hc : c ≤ 0) (a b : α) : min (a / c) (b / c) = max a b / c :=
Eq.symm <| Antitone.map_max fun _ _ => div_le_div_of_nonpos_of_le hc
theorem max_div_div_right_of_nonpos (hc : c ≤ 0) (a b : α) : max (a / c) (b / c) = min a b / c :=
Eq.symm <| Antitone.map_min fun _ _ => div_le_div_of_nonpos_of_le hc
theorem abs_inv (a : α) : |a⁻¹| = |a|⁻¹ :=
map_inv₀ (absHom : α →*₀ α) a
theorem abs_div (a b : α) : |a / b| = |a| / |b| :=
map_div₀ (absHom : α →*₀ α) a b
theorem abs_one_div (a : α) : |1 / a| = 1 / |a| := by rw [abs_div, abs_one]
theorem uniform_continuous_npow_on_bounded (B : α) {ε : α} (hε : 0 < ε) (n : ℕ) :
∃ δ > 0, ∀ q r : α, |r| ≤ B → |q - r| ≤ δ → |q ^ n - r ^ n| < ε := by
wlog B_pos : 0 < B generalizing B
· have ⟨δ, δ_pos, cont⟩ := this 1 zero_lt_one
exact ⟨δ, δ_pos, fun q r hr ↦ cont q r (hr.trans ((le_of_not_lt B_pos).trans zero_le_one))⟩
have pos : 0 < 1 + ↑n * (B + 1) ^ (n - 1) := zero_lt_one.trans_le <| le_add_of_nonneg_right <|
mul_nonneg n.cast_nonneg <| (pow_pos (B_pos.trans <| lt_add_of_pos_right _ zero_lt_one) _).le
refine ⟨min 1 (ε / (1 + n * (B + 1) ^ (n - 1))), lt_min zero_lt_one (div_pos hε pos),
fun q r hr hqr ↦ (abs_pow_sub_pow_le ..).trans_lt ?_⟩
rw [le_inf_iff, le_div_iff₀ pos, mul_one_add, ← mul_assoc] at hqr
obtain h | h := (abs_nonneg (q - r)).eq_or_lt
· simpa only [← h, zero_mul] using hε
refine (lt_of_le_of_lt ?_ <| lt_add_of_pos_left _ h).trans_le hqr.2
refine mul_le_mul_of_nonneg_left (pow_le_pow_left₀ ((abs_nonneg _).trans le_sup_left) ?_ _)
(mul_nonneg (abs_nonneg _) n.cast_nonneg)
refine max_le ?_ (hr.trans <| le_add_of_nonneg_right zero_le_one)
exact add_sub_cancel r q ▸ (abs_add_le ..).trans (add_le_add hr hqr.1)
end
namespace Mathlib.Meta.Positivity
open Lean Meta Qq Function
section LinearOrderedSemifield
variable {α : Type*} [Semifield α] [LinearOrder α] [IsStrictOrderedRing α] {a b : α}
private lemma div_nonneg_of_pos_of_nonneg (ha : 0 < a) (hb : 0 ≤ b) : 0 ≤ a / b :=
div_nonneg ha.le hb
private lemma div_nonneg_of_nonneg_of_pos (ha : 0 ≤ a) (hb : 0 < b) : 0 ≤ a / b :=
div_nonneg ha hb.le
omit [IsStrictOrderedRing α] in
private lemma div_ne_zero_of_pos_of_ne_zero (ha : 0 < a) (hb : b ≠ 0) : a / b ≠ 0 :=
div_ne_zero ha.ne' hb
omit [IsStrictOrderedRing α] in
private lemma div_ne_zero_of_ne_zero_of_pos (ha : a ≠ 0) (hb : 0 < b) : a / b ≠ 0 :=
div_ne_zero ha hb.ne'
private lemma zpow_zero_pos (a : α) : 0 < a ^ (0 : ℤ) := zero_lt_one.trans_eq (zpow_zero a).symm
end LinearOrderedSemifield
/-- The `positivity` extension which identifies expressions of the form `a / b`,
such that `positivity` successfully recognises both `a` and `b`. -/
@[positivity _ / _] def evalDiv : PositivityExt where eval {u α} zα pα e := do
let .app (.app (f : Q($α → $α → $α)) (a : Q($α))) (b : Q($α)) ← withReducible (whnf e)
| throwError "not /"
let _e_eq : $e =Q $f $a $b := ⟨⟩
let _a ← synthInstanceQ q(Semifield $α)
let _a ← synthInstanceQ q(LinearOrder $α)
let _a ← synthInstanceQ q(IsStrictOrderedRing $α)
assumeInstancesCommute
let ⟨_f_eq⟩ ← withDefault <| withNewMCtxDepth <| assertDefEqQ q($f) q(HDiv.hDiv)
let ra ← core zα pα a; let rb ← core zα pα b
match ra, rb with
| .positive pa, .positive pb => pure (.positive q(div_pos $pa $pb))
| .positive pa, .nonnegative pb => pure (.nonnegative q(div_nonneg_of_pos_of_nonneg $pa $pb))
| .nonnegative pa, .positive pb => pure (.nonnegative q(div_nonneg_of_nonneg_of_pos $pa $pb))
| .nonnegative pa, .nonnegative pb => pure (.nonnegative q(div_nonneg $pa $pb))
| .positive pa, .nonzero pb => pure (.nonzero q(div_ne_zero_of_pos_of_ne_zero $pa $pb))
| .nonzero pa, .positive pb => pure (.nonzero q(div_ne_zero_of_ne_zero_of_pos $pa $pb))
| .nonzero pa, .nonzero pb => pure (.nonzero q(div_ne_zero $pa $pb))
| _, _ => pure .none
/-- The `positivity` extension which identifies expressions of the form `a⁻¹`,
such that `positivity` successfully recognises `a`. -/
@[positivity _⁻¹]
def evalInv : PositivityExt where eval {u α} zα pα e := do
let .app (f : Q($α → $α)) (a : Q($α)) ← withReducible (whnf e) | throwError "not ⁻¹"
let _e_eq : $e =Q $f $a := ⟨⟩
let _a ← synthInstanceQ q(Semifield $α)
let _a ← synthInstanceQ q(LinearOrder $α)
let _a ← synthInstanceQ q(IsStrictOrderedRing $α)
assumeInstancesCommute
let ⟨_f_eq⟩ ← withDefault <| withNewMCtxDepth <| assertDefEqQ q($f) q(Inv.inv)
let ra ← core zα pα a
match ra with
| .positive pa => pure (.positive q(inv_pos_of_pos $pa))
| .nonnegative pa => pure (.nonnegative q(inv_nonneg_of_nonneg $pa))
| .nonzero pa => pure (.nonzero q(inv_ne_zero $pa))
| .none => pure .none
/-- The `positivity` extension which identifies expressions of the form `a ^ (0:ℤ)`. -/
@[positivity _ ^ (0 : ℤ), Pow.pow _ (0 : ℤ)]
def evalPowZeroInt : PositivityExt where eval {u α} _zα _pα e := do
let .app (.app _ (a : Q($α))) _ ← withReducible (whnf e) | throwError "not ^"
let _a ← synthInstanceQ q(Semifield $α)
let _a ← synthInstanceQ q(LinearOrder $α)
let _a ← synthInstanceQ q(IsStrictOrderedRing $α)
assumeInstancesCommute
let ⟨_a⟩ ← Qq.assertDefEqQ q($e) q($a ^ (0 : ℤ))
pure (.positive q(zpow_zero_pos $a))
end Mathlib.Meta.Positivity
| Mathlib/Algebra/Order/Field/Basic.lean | 845 | 849 | |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Data.Ordmap.Invariants
/-!
# Verification of `Ordnode`
This file uses the invariants defined in `Mathlib.Data.Ordmap.Invariants` to construct `Ordset α`,
a wrapper around `Ordnode α` which includes the correctness invariant of the type. It exposes
parallel operations like `insert` as functions on `Ordset` that do the same thing but bundle the
correctness proofs.
The advantage is that it is possible to, for example, prove that the result of `find` on `insert`
will actually find the element, while `Ordnode` cannot guarantee this if the input tree did not
satisfy the type invariants.
## Main definitions
* `Ordnode.Valid`: The validity predicate for an `Ordnode` subtree.
* `Ordset α`: A well formed set of values of type `α`.
## Implementation notes
Because the `Ordnode` file was ported from Haskell, the correctness invariants of some
of the functions have not been spelled out, and some theorems like
`Ordnode.Valid'.balanceL_aux` show very intricate assumptions on the sizes,
which may need to be revised if it turns out some operations violate these assumptions,
because there is a decent amount of slop in the actual data structure invariants, so the
theorem will go through with multiple choices of assumption.
-/
variable {α : Type*}
namespace Ordnode
section Valid
variable [Preorder α]
/-- The validity predicate for an `Ordnode` subtree. This asserts that the `size` fields are
correct, the tree is balanced, and the elements of the tree are organized according to the
ordering. This version of `Valid` also puts all elements in the tree in the interval `(lo, hi)`. -/
structure Valid' (lo : WithBot α) (t : Ordnode α) (hi : WithTop α) : Prop where
ord : t.Bounded lo hi
sz : t.Sized
bal : t.Balanced
/-- The validity predicate for an `Ordnode` subtree. This asserts that the `size` fields are
correct, the tree is balanced, and the elements of the tree are organized according to the
ordering. -/
def Valid (t : Ordnode α) : Prop :=
Valid' ⊥ t ⊤
theorem Valid'.mono_left {x y : α} (xy : x ≤ y) {t : Ordnode α} {o} (h : Valid' y t o) :
Valid' x t o :=
⟨h.1.mono_left xy, h.2, h.3⟩
theorem Valid'.mono_right {x y : α} (xy : x ≤ y) {t : Ordnode α} {o} (h : Valid' o t x) :
Valid' o t y :=
⟨h.1.mono_right xy, h.2, h.3⟩
theorem Valid'.trans_left {t₁ t₂ : Ordnode α} {x : α} {o₁ o₂} (h : Bounded t₁ o₁ x)
(H : Valid' x t₂ o₂) : Valid' o₁ t₂ o₂ :=
⟨h.trans_left H.1, H.2, H.3⟩
theorem Valid'.trans_right {t₁ t₂ : Ordnode α} {x : α} {o₁ o₂} (H : Valid' o₁ t₁ x)
(h : Bounded t₂ x o₂) : Valid' o₁ t₁ o₂ :=
⟨H.1.trans_right h, H.2, H.3⟩
theorem Valid'.of_lt {t : Ordnode α} {x : α} {o₁ o₂} (H : Valid' o₁ t o₂) (h₁ : Bounded nil o₁ x)
(h₂ : All (· < x) t) : Valid' o₁ t x :=
⟨H.1.of_lt h₁ h₂, H.2, H.3⟩
theorem Valid'.of_gt {t : Ordnode α} {x : α} {o₁ o₂} (H : Valid' o₁ t o₂) (h₁ : Bounded nil x o₂)
(h₂ : All (· > x) t) : Valid' x t o₂ :=
⟨H.1.of_gt h₁ h₂, H.2, H.3⟩
theorem Valid'.valid {t o₁ o₂} (h : @Valid' α _ o₁ t o₂) : Valid t :=
⟨h.1.weak, h.2, h.3⟩
theorem valid'_nil {o₁ o₂} (h : Bounded nil o₁ o₂) : Valid' o₁ (@nil α) o₂ :=
⟨h, ⟨⟩, ⟨⟩⟩
theorem valid_nil : Valid (@nil α) :=
valid'_nil ⟨⟩
theorem Valid'.node {s l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : BalancedSz (size l) (size r)) (hs : s = size l + size r + 1) :
Valid' o₁ (@node α s l x r) o₂ :=
⟨⟨hl.1, hr.1⟩, ⟨hs, hl.2, hr.2⟩, ⟨H, hl.3, hr.3⟩⟩
theorem Valid'.dual : ∀ {t : Ordnode α} {o₁ o₂}, Valid' o₁ t o₂ → @Valid' αᵒᵈ _ o₂ (dual t) o₁
| .nil, _, _, h => valid'_nil h.1.dual
| .node _ l _ r, _, _, ⟨⟨ol, Or⟩, ⟨rfl, sl, sr⟩, ⟨b, bl, br⟩⟩ =>
let ⟨ol', sl', bl'⟩ := Valid'.dual ⟨ol, sl, bl⟩
let ⟨or', sr', br'⟩ := Valid'.dual ⟨Or, sr, br⟩
⟨⟨or', ol'⟩, ⟨by simp [size_dual, add_comm], sr', sl'⟩,
⟨by rw [size_dual, size_dual]; exact b.symm, br', bl'⟩⟩
theorem Valid'.dual_iff {t : Ordnode α} {o₁ o₂} : Valid' o₁ t o₂ ↔ @Valid' αᵒᵈ _ o₂ (.dual t) o₁ :=
⟨Valid'.dual, fun h => by
have := Valid'.dual h; rwa [dual_dual, OrderDual.Preorder.dual_dual] at this⟩
theorem Valid.dual {t : Ordnode α} : Valid t → @Valid αᵒᵈ _ (.dual t) :=
Valid'.dual
theorem Valid.dual_iff {t : Ordnode α} : Valid t ↔ @Valid αᵒᵈ _ (.dual t) :=
Valid'.dual_iff
theorem Valid'.left {s l x r o₁ o₂} (H : Valid' o₁ (@Ordnode.node α s l x r) o₂) : Valid' o₁ l x :=
⟨H.1.1, H.2.2.1, H.3.2.1⟩
theorem Valid'.right {s l x r o₁ o₂} (H : Valid' o₁ (@Ordnode.node α s l x r) o₂) : Valid' x r o₂ :=
⟨H.1.2, H.2.2.2, H.3.2.2⟩
nonrec theorem Valid.left {s l x r} (H : Valid (@node α s l x r)) : Valid l :=
H.left.valid
nonrec theorem Valid.right {s l x r} (H : Valid (@node α s l x r)) : Valid r :=
H.right.valid
theorem Valid.size_eq {s l x r} (H : Valid (@node α s l x r)) :
size (@node α s l x r) = size l + size r + 1 :=
H.2.1
theorem Valid'.node' {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : BalancedSz (size l) (size r)) : Valid' o₁ (@node' α l x r) o₂ :=
hl.node hr H rfl
theorem valid'_singleton {x : α} {o₁ o₂} (h₁ : Bounded nil o₁ x) (h₂ : Bounded nil x o₂) :
Valid' o₁ (singleton x : Ordnode α) o₂ :=
(valid'_nil h₁).node (valid'_nil h₂) (Or.inl zero_le_one) rfl
theorem valid_singleton {x : α} : Valid (singleton x : Ordnode α) :=
valid'_singleton ⟨⟩ ⟨⟩
theorem Valid'.node3L {l} {x : α} {m} {y : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hm : Valid' x m y)
(hr : Valid' y r o₂) (H1 : BalancedSz (size l) (size m))
(H2 : BalancedSz (size l + size m + 1) (size r)) : Valid' o₁ (@node3L α l x m y r) o₂ :=
(hl.node' hm H1).node' hr H2
theorem Valid'.node3R {l} {x : α} {m} {y : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hm : Valid' x m y)
(hr : Valid' y r o₂) (H1 : BalancedSz (size l) (size m + size r + 1))
(H2 : BalancedSz (size m) (size r)) : Valid' o₁ (@node3R α l x m y r) o₂ :=
hl.node' (hm.node' hr H2) H1
theorem Valid'.node4L_lemma₁ {a b c d : ℕ} (lr₂ : 3 * (b + c + 1 + d) ≤ 16 * a + 9)
(mr₂ : b + c + 1 ≤ 3 * d) (mm₁ : b ≤ 3 * c) : b < 3 * a + 1 := by omega
theorem Valid'.node4L_lemma₂ {b c d : ℕ} (mr₂ : b + c + 1 ≤ 3 * d) : c ≤ 3 * d := by omega
theorem Valid'.node4L_lemma₃ {b c d : ℕ} (mr₁ : 2 * d ≤ b + c + 1) (mm₁ : b ≤ 3 * c) :
d ≤ 3 * c := by omega
theorem Valid'.node4L_lemma₄ {a b c d : ℕ} (lr₁ : 3 * a ≤ b + c + 1 + d) (mr₂ : b + c + 1 ≤ 3 * d)
(mm₁ : b ≤ 3 * c) : a + b + 1 ≤ 3 * (c + d + 1) := by omega
theorem Valid'.node4L_lemma₅ {a b c d : ℕ} (lr₂ : 3 * (b + c + 1 + d) ≤ 16 * a + 9)
(mr₁ : 2 * d ≤ b + c + 1) (mm₂ : c ≤ 3 * b) : c + d + 1 ≤ 3 * (a + b + 1) := by omega
theorem Valid'.node4L {l} {x : α} {m} {y : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hm : Valid' x m y)
(hr : Valid' (↑y) r o₂) (Hm : 0 < size m)
(H : size l = 0 ∧ size m = 1 ∧ size r ≤ 1 ∨
0 < size l ∧
ratio * size r ≤ size m ∧
delta * size l ≤ size m + size r ∧
3 * (size m + size r) ≤ 16 * size l + 9 ∧ size m ≤ delta * size r) :
Valid' o₁ (@node4L α l x m y r) o₂ := by
obtain - | ⟨s, ml, z, mr⟩ := m; · cases Hm
suffices
BalancedSz (size l) (size ml) ∧
BalancedSz (size mr) (size r) ∧ BalancedSz (size l + size ml + 1) (size mr + size r + 1) from
Valid'.node' (hl.node' hm.left this.1) (hm.right.node' hr this.2.1) this.2.2
rcases H with (⟨l0, m1, r0⟩ | ⟨l0, mr₁, lr₁, lr₂, mr₂⟩)
· rw [hm.2.size_eq, Nat.succ_inj, add_eq_zero] at m1
rw [l0, m1.1, m1.2]; revert r0; rcases size r with (_ | _ | _) <;>
[decide; decide; (intro r0; unfold BalancedSz delta; omega)]
· rcases Nat.eq_zero_or_pos (size r) with r0 | r0
· rw [r0] at mr₂; cases not_le_of_lt Hm mr₂
rw [hm.2.size_eq] at lr₁ lr₂ mr₁ mr₂
by_cases mm : size ml + size mr ≤ 1
· have r1 :=
le_antisymm
((mul_le_mul_left (by decide)).1 (le_trans mr₁ (Nat.succ_le_succ mm) : _ ≤ ratio * 1)) r0
rw [r1, add_assoc] at lr₁
have l1 :=
le_antisymm
((mul_le_mul_left (by decide)).1 (le_trans lr₁ (add_le_add_right mm 2) : _ ≤ delta * 1))
l0
rw [l1, r1]
revert mm; cases size ml <;> cases size mr <;> intro mm
· decide
· rw [zero_add] at mm; rcases mm with (_ | ⟨⟨⟩⟩)
decide
· rcases mm with (_ | ⟨⟨⟩⟩); decide
· rw [Nat.succ_add] at mm; rcases mm with (_ | ⟨⟨⟩⟩)
rcases hm.3.1.resolve_left mm with ⟨mm₁, mm₂⟩
rcases Nat.eq_zero_or_pos (size ml) with ml0 | ml0
· rw [ml0, mul_zero, Nat.le_zero] at mm₂
rw [ml0, mm₂] at mm; cases mm (by decide)
have : 2 * size l ≤ size ml + size mr + 1 := by
have := Nat.mul_le_mul_left ratio lr₁
rw [mul_left_comm, mul_add] at this
have := le_trans this (add_le_add_left mr₁ _)
rw [← Nat.succ_mul] at this
exact (mul_le_mul_left (by decide)).1 this
refine ⟨Or.inr ⟨?_, ?_⟩, Or.inr ⟨?_, ?_⟩, Or.inr ⟨?_, ?_⟩⟩
· refine (mul_le_mul_left (by decide)).1 (le_trans this ?_)
rw [two_mul, Nat.succ_le_iff]
refine add_lt_add_of_lt_of_le ?_ mm₂
simpa using (mul_lt_mul_right ml0).2 (by decide : 1 < 3)
· exact Nat.le_of_lt_succ (Valid'.node4L_lemma₁ lr₂ mr₂ mm₁)
· exact Valid'.node4L_lemma₂ mr₂
· exact Valid'.node4L_lemma₃ mr₁ mm₁
· exact Valid'.node4L_lemma₄ lr₁ mr₂ mm₁
· exact Valid'.node4L_lemma₅ lr₂ mr₁ mm₂
theorem Valid'.rotateL_lemma₁ {a b c : ℕ} (H2 : 3 * a ≤ b + c) (hb₂ : c ≤ 3 * b) : a ≤ 3 * b := by
omega
theorem Valid'.rotateL_lemma₂ {a b c : ℕ} (H3 : 2 * (b + c) ≤ 9 * a + 3) (h : b < 2 * c) :
b < 3 * a + 1 := by omega
theorem Valid'.rotateL_lemma₃ {a b c : ℕ} (H2 : 3 * a ≤ b + c) (h : b < 2 * c) : a + b < 3 * c := by
omega
theorem Valid'.rotateL_lemma₄ {a b : ℕ} (H3 : 2 * b ≤ 9 * a + 3) : 3 * b ≤ 16 * a + 9 := by
omega
theorem Valid'.rotateL {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H1 : ¬size l + size r ≤ 1) (H2 : delta * size l < size r)
(H3 : 2 * size r ≤ 9 * size l + 5 ∨ size r ≤ 3) : Valid' o₁ (@rotateL α l x r) o₂ := by
obtain - | ⟨rs, rl, rx, rr⟩ := r; · cases H2
rw [hr.2.size_eq, Nat.lt_succ_iff] at H2
rw [hr.2.size_eq] at H3
replace H3 : 2 * (size rl + size rr) ≤ 9 * size l + 3 ∨ size rl + size rr ≤ 2 :=
H3.imp (@Nat.le_of_add_le_add_right _ 2 _) Nat.le_of_succ_le_succ
have H3_0 : size l = 0 → size rl + size rr ≤ 2 := by
intro l0; rw [l0] at H3
exact
(or_iff_right_of_imp fun h => (mul_le_mul_left (by decide)).1 (le_trans h (by decide))).1 H3
have H3p : size l > 0 → 2 * (size rl + size rr) ≤ 9 * size l + 3 := fun l0 : 1 ≤ size l =>
(or_iff_left_of_imp <| by omega).1 H3
have ablem : ∀ {a b : ℕ}, 1 ≤ a → a + b ≤ 2 → b ≤ 1 := by omega
have hlp : size l > 0 → ¬size rl + size rr ≤ 1 := fun l0 hb =>
absurd (le_trans (le_trans (Nat.mul_le_mul_left _ l0) H2) hb) (by decide)
rw [Ordnode.rotateL_node]; split_ifs with h
· have rr0 : size rr > 0 :=
(mul_lt_mul_left (by decide)).1 (lt_of_le_of_lt (Nat.zero_le _) h : ratio * 0 < _)
suffices BalancedSz (size l) (size rl) ∧ BalancedSz (size l + size rl + 1) (size rr) by
exact hl.node3L hr.left hr.right this.1 this.2
rcases Nat.eq_zero_or_pos (size l) with l0 | l0
· rw [l0]; replace H3 := H3_0 l0
have := hr.3.1
rcases Nat.eq_zero_or_pos (size rl) with rl0 | rl0
· rw [rl0] at this ⊢
rw [le_antisymm (balancedSz_zero.1 this.symm) rr0]
decide
have rr1 : size rr = 1 := le_antisymm (ablem rl0 H3) rr0
rw [add_comm] at H3
rw [rr1, show size rl = 1 from le_antisymm (ablem rr0 H3) rl0]
decide
replace H3 := H3p l0
rcases hr.3.1.resolve_left (hlp l0) with ⟨_, hb₂⟩
refine ⟨Or.inr ⟨?_, ?_⟩, Or.inr ⟨?_, ?_⟩⟩
· exact Valid'.rotateL_lemma₁ H2 hb₂
· exact Nat.le_of_lt_succ (Valid'.rotateL_lemma₂ H3 h)
· exact Valid'.rotateL_lemma₃ H2 h
· exact
le_trans hb₂
(Nat.mul_le_mul_left _ <| le_trans (Nat.le_add_left _ _) (Nat.le_add_right _ _))
· rcases Nat.eq_zero_or_pos (size rl) with rl0 | rl0
· rw [rl0, not_lt, Nat.le_zero, Nat.mul_eq_zero] at h
replace h := h.resolve_left (by decide)
rw [rl0, h, Nat.le_zero, Nat.mul_eq_zero] at H2
rw [hr.2.size_eq, rl0, h, H2.resolve_left (by decide)] at H1
cases H1 (by decide)
refine hl.node4L hr.left hr.right rl0 ?_
rcases Nat.eq_zero_or_pos (size l) with l0 | l0
· replace H3 := H3_0 l0
rcases Nat.eq_zero_or_pos (size rr) with rr0 | rr0
· have := hr.3.1
rw [rr0] at this
exact Or.inl ⟨l0, le_antisymm (balancedSz_zero.1 this) rl0, rr0.symm ▸ zero_le_one⟩
exact Or.inl ⟨l0, le_antisymm (ablem rr0 <| by rwa [add_comm]) rl0, ablem rl0 H3⟩
exact
Or.inr ⟨l0, not_lt.1 h, H2, Valid'.rotateL_lemma₄ (H3p l0), (hr.3.1.resolve_left (hlp l0)).1⟩
theorem Valid'.rotateR {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H1 : ¬size l + size r ≤ 1) (H2 : delta * size r < size l)
(H3 : 2 * size l ≤ 9 * size r + 5 ∨ size l ≤ 3) : Valid' o₁ (@rotateR α l x r) o₂ := by
refine Valid'.dual_iff.2 ?_
rw [dual_rotateR]
refine hr.dual.rotateL hl.dual ?_ ?_ ?_
· rwa [size_dual, size_dual, add_comm]
· rwa [size_dual, size_dual]
· rwa [size_dual, size_dual]
theorem Valid'.balance'_aux {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H₁ : 2 * @size α r ≤ 9 * size l + 5 ∨ size r ≤ 3)
(H₂ : 2 * @size α l ≤ 9 * size r + 5 ∨ size l ≤ 3) : Valid' o₁ (@balance' α l x r) o₂ := by
rw [balance']; split_ifs with h h_1 h_2
· exact hl.node' hr (Or.inl h)
· exact hl.rotateL hr h h_1 H₁
· exact hl.rotateR hr h h_2 H₂
· exact hl.node' hr (Or.inr ⟨not_lt.1 h_2, not_lt.1 h_1⟩)
theorem Valid'.balance'_lemma {α l l' r r'} (H1 : BalancedSz l' r')
(H2 : Nat.dist (@size α l) l' ≤ 1 ∧ size r = r' ∨ Nat.dist (size r) r' ≤ 1 ∧ size l = l') :
2 * @size α r ≤ 9 * size l + 5 ∨ size r ≤ 3 := by
suffices @size α r ≤ 3 * (size l + 1) by omega
rcases H2 with (⟨hl, rfl⟩ | ⟨hr, rfl⟩) <;> rcases H1 with (h | ⟨_, h₂⟩)
· exact le_trans (Nat.le_add_left _ _) (le_trans h (Nat.le_add_left _ _))
· exact
le_trans h₂
(Nat.mul_le_mul_left _ <| le_trans (Nat.dist_tri_right _ _) (Nat.add_le_add_left hl _))
· exact
le_trans (Nat.dist_tri_left' _ _)
(le_trans (add_le_add hr (le_trans (Nat.le_add_left _ _) h)) (by omega))
· rw [Nat.mul_succ]
exact le_trans (Nat.dist_tri_right' _ _) (add_le_add h₂ (le_trans hr (by decide)))
theorem Valid'.balance' {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : ∃ l' r', BalancedSz l' r' ∧
(Nat.dist (size l) l' ≤ 1 ∧ size r = r' ∨ Nat.dist (size r) r' ≤ 1 ∧ size l = l')) :
Valid' o₁ (@balance' α l x r) o₂ :=
let ⟨_, _, H1, H2⟩ := H
Valid'.balance'_aux hl hr (Valid'.balance'_lemma H1 H2) (Valid'.balance'_lemma H1.symm H2.symm)
theorem Valid'.balance {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : ∃ l' r', BalancedSz l' r' ∧
(Nat.dist (size l) l' ≤ 1 ∧ size r = r' ∨ Nat.dist (size r) r' ≤ 1 ∧ size l = l')) :
Valid' o₁ (@balance α l x r) o₂ := by
rw [balance_eq_balance' hl.3 hr.3 hl.2 hr.2]; exact hl.balance' hr H
theorem Valid'.balanceL_aux {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H₁ : size l = 0 → size r ≤ 1) (H₂ : 1 ≤ size l → 1 ≤ size r → size r ≤ delta * size l)
(H₃ : 2 * @size α l ≤ 9 * size r + 5 ∨ size l ≤ 3) : Valid' o₁ (@balanceL α l x r) o₂ := by
rw [balanceL_eq_balance hl.2 hr.2 H₁ H₂, balance_eq_balance' hl.3 hr.3 hl.2 hr.2]
refine hl.balance'_aux hr (Or.inl ?_) H₃
rcases Nat.eq_zero_or_pos (size r) with r0 | r0
· rw [r0]; exact Nat.zero_le _
rcases Nat.eq_zero_or_pos (size l) with l0 | l0
· rw [l0]; exact le_trans (Nat.mul_le_mul_left _ (H₁ l0)) (by decide)
replace H₂ : _ ≤ 3 * _ := H₂ l0 r0; omega
theorem Valid'.balanceL {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : (∃ l', Raised l' (size l) ∧ BalancedSz l' (size r)) ∨
∃ r', Raised (size r) r' ∧ BalancedSz (size l) r') :
Valid' o₁ (@balanceL α l x r) o₂ := by
rw [balanceL_eq_balance' hl.3 hr.3 hl.2 hr.2 H]
refine hl.balance' hr ?_
rcases H with (⟨l', e, H⟩ | ⟨r', e, H⟩)
· exact ⟨_, _, H, Or.inl ⟨e.dist_le', rfl⟩⟩
· exact ⟨_, _, H, Or.inr ⟨e.dist_le, rfl⟩⟩
theorem Valid'.balanceR_aux {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H₁ : size r = 0 → size l ≤ 1) (H₂ : 1 ≤ size r → 1 ≤ size l → size l ≤ delta * size r)
(H₃ : 2 * @size α r ≤ 9 * size l + 5 ∨ size r ≤ 3) : Valid' o₁ (@balanceR α l x r) o₂ := by
rw [Valid'.dual_iff, dual_balanceR]
have := hr.dual.balanceL_aux hl.dual
rw [size_dual, size_dual] at this
exact this H₁ H₂ H₃
theorem Valid'.balanceR {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂)
(H : (∃ l', Raised (size l) l' ∧ BalancedSz l' (size r)) ∨
∃ r', Raised r' (size r) ∧ BalancedSz (size l) r') :
Valid' o₁ (@balanceR α l x r) o₂ := by
rw [Valid'.dual_iff, dual_balanceR]; exact hr.dual.balanceL hl.dual (balance_sz_dual H)
theorem Valid'.eraseMax_aux {s l x r o₁ o₂} (H : Valid' o₁ (.node s l x r) o₂) :
Valid' o₁ (@eraseMax α (.node' l x r)) ↑(findMax' x r) ∧
size (.node' l x r) = size (eraseMax (.node' l x r)) + 1 := by
have := H.2.eq_node'; rw [this] at H; clear this
induction r generalizing l x o₁ with
| nil => exact ⟨H.left, rfl⟩
| node rs rl rx rr _ IHrr =>
have := H.2.2.2.eq_node'; rw [this] at H ⊢
rcases IHrr H.right with ⟨h, e⟩
refine ⟨Valid'.balanceL H.left h (Or.inr ⟨_, Or.inr e, H.3.1⟩), ?_⟩
rw [eraseMax, size_balanceL H.3.2.1 h.3 H.2.2.1 h.2 (Or.inr ⟨_, Or.inr e, H.3.1⟩)]
rw [size_node, e]; rfl
theorem Valid'.eraseMin_aux {s l} {x : α} {r o₁ o₂} (H : Valid' o₁ (.node s l x r) o₂) :
Valid' ↑(findMin' l x) (@eraseMin α (.node' l x r)) o₂ ∧
size (.node' l x r) = size (eraseMin (.node' l x r)) + 1 := by
have := H.dual.eraseMax_aux
rwa [← dual_node', size_dual, ← dual_eraseMin, size_dual, ← Valid'.dual_iff, findMax'_dual]
at this
theorem eraseMin.valid : ∀ {t}, @Valid α _ t → Valid (eraseMin t)
| nil, _ => valid_nil
| node _ l x r, h => by rw [h.2.eq_node']; exact h.eraseMin_aux.1.valid
theorem eraseMax.valid {t} (h : @Valid α _ t) : Valid (eraseMax t) := by
rw [Valid.dual_iff, dual_eraseMax]; exact eraseMin.valid h.dual
theorem Valid'.glue_aux {l r o₁ o₂} (hl : Valid' o₁ l o₂) (hr : Valid' o₁ r o₂)
(sep : l.All fun x => r.All fun y => x < y) (bal : BalancedSz (size l) (size r)) :
Valid' o₁ (@glue α l r) o₂ ∧ size (glue l r) = size l + size r := by
obtain - | ⟨ls, ll, lx, lr⟩ := l; · exact ⟨hr, (zero_add _).symm⟩
obtain - | ⟨rs, rl, rx, rr⟩ := r; · exact ⟨hl, rfl⟩
dsimp [glue]; split_ifs
· rw [splitMax_eq]
· obtain ⟨v, e⟩ := Valid'.eraseMax_aux hl
suffices H : _ by
refine ⟨Valid'.balanceR v (hr.of_gt ?_ ?_) H, ?_⟩
· refine findMax'_all (P := fun a : α => Bounded nil (a : WithTop α) o₂)
lx lr hl.1.2.to_nil (sep.2.2.imp ?_)
exact fun x h => hr.1.2.to_nil.mono_left (le_of_lt h.2.1)
· exact @findMax'_all _ (fun a => All (· > a) (.node rs rl rx rr)) lx lr sep.2.1 sep.2.2
· rw [size_balanceR v.3 hr.3 v.2 hr.2 H, add_right_comm, ← e, hl.2.1]; rfl
refine Or.inl ⟨_, Or.inr e, ?_⟩
rwa [hl.2.eq_node'] at bal
· rw [splitMin_eq]
· obtain ⟨v, e⟩ := Valid'.eraseMin_aux hr
suffices H : _ by
refine ⟨Valid'.balanceL (hl.of_lt ?_ ?_) v H, ?_⟩
· refine @findMin'_all (P := fun a : α => Bounded nil o₁ (a : WithBot α))
_ rl rx (sep.2.1.1.imp ?_) hr.1.1.to_nil
exact fun y h => hl.1.1.to_nil.mono_right (le_of_lt h)
· exact
@findMin'_all _ (fun a => All (· < a) (.node ls ll lx lr)) rl rx
(all_iff_forall.2 fun x hx => sep.imp fun y hy => all_iff_forall.1 hy.1 _ hx)
(sep.imp fun y hy => hy.2.1)
· rw [size_balanceL hl.3 v.3 hl.2 v.2 H, add_assoc, ← e, hr.2.1]; rfl
refine Or.inr ⟨_, Or.inr e, ?_⟩
rwa [hr.2.eq_node'] at bal
theorem Valid'.glue {l} {x : α} {r o₁ o₂} (hl : Valid' o₁ l x) (hr : Valid' x r o₂) :
BalancedSz (size l) (size r) →
Valid' o₁ (@glue α l r) o₂ ∧ size (@glue α l r) = size l + size r :=
Valid'.glue_aux (hl.trans_right hr.1) (hr.trans_left hl.1) (hl.1.to_sep hr.1)
theorem Valid'.merge_lemma {a b c : ℕ} (h₁ : 3 * a < b + c + 1) (h₂ : b ≤ 3 * c) :
2 * (a + b) ≤ 9 * c + 5 := by omega
theorem Valid'.merge_aux₁ {o₁ o₂ ls ll lx lr rs rl rx rr t}
(hl : Valid' o₁ (@Ordnode.node α ls ll lx lr) o₂) (hr : Valid' o₁ (.node rs rl rx rr) o₂)
(h : delta * ls < rs) (v : Valid' o₁ t rx) (e : size t = ls + size rl) :
Valid' o₁ (.balanceL t rx rr) o₂ ∧ size (.balanceL t rx rr) = ls + rs := by
rw [hl.2.1] at e
rw [hl.2.1, hr.2.1, delta] at h
rcases hr.3.1 with (H | ⟨hr₁, hr₂⟩); · omega
suffices H₂ : _ by
suffices H₁ : _ by
refine ⟨Valid'.balanceL_aux v hr.right H₁ H₂ ?_, ?_⟩
· rw [e]; exact Or.inl (Valid'.merge_lemma h hr₁)
· rw [balanceL_eq_balance v.2 hr.2.2.2 H₁ H₂, balance_eq_balance' v.3 hr.3.2.2 v.2 hr.2.2.2,
size_balance' v.2 hr.2.2.2, e, hl.2.1, hr.2.1]
abel
· rw [e, add_right_comm]; rintro ⟨⟩
intro _ _; rw [e]; unfold delta at hr₂ ⊢; omega
theorem Valid'.merge_aux {l r o₁ o₂} (hl : Valid' o₁ l o₂) (hr : Valid' o₁ r o₂)
(sep : l.All fun x => r.All fun y => x < y) :
Valid' o₁ (@merge α l r) o₂ ∧ size (merge l r) = size l + size r := by
induction l generalizing o₁ o₂ r with
| nil => exact ⟨hr, (zero_add _).symm⟩
| node ls ll lx lr _ IHlr => ?_
induction r generalizing o₁ o₂ with
| nil => exact ⟨hl, rfl⟩
| node rs rl rx rr IHrl _ => ?_
rw [merge_node]; split_ifs with h h_1
· obtain ⟨v, e⟩ := IHrl (hl.of_lt hr.1.1.to_nil <| sep.imp fun x h => h.2.1) hr.left
(sep.imp fun x h => h.1)
exact Valid'.merge_aux₁ hl hr h v e
· obtain ⟨v, e⟩ := IHlr hl.right (hr.of_gt hl.1.2.to_nil sep.2.1) sep.2.2
have := Valid'.merge_aux₁ hr.dual hl.dual h_1 v.dual
rw [size_dual, add_comm, size_dual, ← dual_balanceR, ← Valid'.dual_iff, size_dual,
add_comm rs] at this
exact this e
· refine Valid'.glue_aux hl hr sep (Or.inr ⟨not_lt.1 h_1, not_lt.1 h⟩)
theorem Valid.merge {l r} (hl : Valid l) (hr : Valid r)
(sep : l.All fun x => r.All fun y => x < y) : Valid (@merge α l r) :=
(Valid'.merge_aux hl hr sep).1
theorem insertWith.valid_aux [IsTotal α (· ≤ ·)] [DecidableLE α] (f : α → α) (x : α)
(hf : ∀ y, x ≤ y ∧ y ≤ x → x ≤ f y ∧ f y ≤ x) :
∀ {t o₁ o₂},
Valid' o₁ t o₂ →
Bounded nil o₁ x →
Bounded nil x o₂ →
Valid' o₁ (insertWith f x t) o₂ ∧ Raised (size t) (size (insertWith f x t))
| nil, _, _, _, bl, br => ⟨valid'_singleton bl br, Or.inr rfl⟩
| node sz l y r, o₁, o₂, h, bl, br => by
rw [insertWith, cmpLE]
split_ifs with h_1 h_2 <;> dsimp only
· rcases h with ⟨⟨lx, xr⟩, hs, hb⟩
rcases hf _ ⟨h_1, h_2⟩ with ⟨xf, fx⟩
refine
⟨⟨⟨lx.mono_right (le_trans h_2 xf), xr.mono_left (le_trans fx h_1)⟩, hs, hb⟩, Or.inl rfl⟩
· rcases insertWith.valid_aux f x hf h.left bl (lt_of_le_not_le h_1 h_2) with ⟨vl, e⟩
suffices H : _ by
refine ⟨vl.balanceL h.right H, ?_⟩
rw [size_balanceL vl.3 h.3.2.2 vl.2 h.2.2.2 H, h.2.size_eq]
exact (e.add_right _).add_right _
exact Or.inl ⟨_, e, h.3.1⟩
· have : y < x := lt_of_le_not_le ((total_of (· ≤ ·) _ _).resolve_left h_1) h_1
rcases insertWith.valid_aux f x hf h.right this br with ⟨vr, e⟩
suffices H : _ by
refine ⟨h.left.balanceR vr H, ?_⟩
rw [size_balanceR h.3.2.1 vr.3 h.2.2.1 vr.2 H, h.2.size_eq]
exact (e.add_left _).add_right _
exact Or.inr ⟨_, e, h.3.1⟩
theorem insertWith.valid [IsTotal α (· ≤ ·)] [DecidableLE α] (f : α → α) (x : α)
(hf : ∀ y, x ≤ y ∧ y ≤ x → x ≤ f y ∧ f y ≤ x) {t} (h : Valid t) : Valid (insertWith f x t) :=
(insertWith.valid_aux _ _ hf h ⟨⟩ ⟨⟩).1
theorem insert_eq_insertWith [DecidableLE α] (x : α) :
∀ t, Ordnode.insert x t = insertWith (fun _ => x) x t
| nil => rfl
| node _ l y r => by
unfold Ordnode.insert insertWith; cases cmpLE x y <;> simp [insert_eq_insertWith]
theorem insert.valid [IsTotal α (· ≤ ·)] [DecidableLE α] (x : α) {t} (h : Valid t) :
Valid (Ordnode.insert x t) := by
rw [insert_eq_insertWith]; exact insertWith.valid _ _ (fun _ _ => ⟨le_rfl, le_rfl⟩) h
theorem insert'_eq_insertWith [DecidableLE α] (x : α) :
∀ t, insert' x t = insertWith id x t
| nil => rfl
| node _ l y r => by
unfold insert' insertWith; cases cmpLE x y <;> simp [insert'_eq_insertWith]
theorem insert'.valid [IsTotal α (· ≤ ·)] [DecidableLE α]
(x : α) {t} (h : Valid t) : Valid (insert' x t) := by
rw [insert'_eq_insertWith]; exact insertWith.valid _ _ (fun _ => id) h
theorem Valid'.map_aux {β} [Preorder β] {f : α → β} (f_strict_mono : StrictMono f) {t a₁ a₂}
(h : Valid' a₁ t a₂) :
Valid' (Option.map f a₁) (map f t) (Option.map f a₂) ∧ (map f t).size = t.size := by
induction t generalizing a₁ a₂ with
| nil =>
simp only [map, size_nil, and_true]; apply valid'_nil
cases a₁; · trivial
cases a₂; · trivial
simp only [Option.map, Bounded]
exact f_strict_mono h.ord
| node _ _ _ _ t_ih_l t_ih_r =>
have t_ih_l' := t_ih_l h.left
have t_ih_r' := t_ih_r h.right
clear t_ih_l t_ih_r
obtain ⟨t_l_valid, t_l_size⟩ := t_ih_l'
obtain ⟨t_r_valid, t_r_size⟩ := t_ih_r'
simp only [map, size_node, and_true]
constructor
· exact And.intro t_l_valid.ord t_r_valid.ord
· constructor
· rw [t_l_size, t_r_size]; exact h.sz.1
· constructor
· exact t_l_valid.sz
· exact t_r_valid.sz
· constructor
· rw [t_l_size, t_r_size]; exact h.bal.1
· constructor
· exact t_l_valid.bal
· exact t_r_valid.bal
theorem map.valid {β} [Preorder β] {f : α → β} (f_strict_mono : StrictMono f) {t} (h : Valid t) :
Valid (map f t) :=
(Valid'.map_aux f_strict_mono h).1
theorem Valid'.erase_aux [DecidableLE α] (x : α) {t a₁ a₂} (h : Valid' a₁ t a₂) :
Valid' a₁ (erase x t) a₂ ∧ Raised (erase x t).size t.size := by
induction t generalizing a₁ a₂ with
| nil =>
simpa [erase, Raised]
| node _ t_l t_x t_r t_ih_l t_ih_r =>
simp only [erase, size_node]
have t_ih_l' := t_ih_l h.left
have t_ih_r' := t_ih_r h.right
clear t_ih_l t_ih_r
obtain ⟨t_l_valid, t_l_size⟩ := t_ih_l'
obtain ⟨t_r_valid, t_r_size⟩ := t_ih_r'
cases cmpLE x t_x <;> rw [h.sz.1]
· suffices h_balanceable : _ by
constructor
· exact Valid'.balanceR t_l_valid h.right h_balanceable
· rw [size_balanceR t_l_valid.bal h.right.bal t_l_valid.sz h.right.sz h_balanceable]
repeat apply Raised.add_right
exact t_l_size
left; exists t_l.size; exact And.intro t_l_size h.bal.1
· have h_glue := Valid'.glue h.left h.right h.bal.1
obtain ⟨h_glue_valid, h_glue_sized⟩ := h_glue
constructor
· exact h_glue_valid
· right; rw [h_glue_sized]
· suffices h_balanceable : _ by
constructor
· exact Valid'.balanceL h.left t_r_valid h_balanceable
· rw [size_balanceL h.left.bal t_r_valid.bal h.left.sz t_r_valid.sz h_balanceable]
apply Raised.add_right
apply Raised.add_left
exact t_r_size
right; exists t_r.size; exact And.intro t_r_size h.bal.1
theorem erase.valid [DecidableLE α] (x : α) {t} (h : Valid t) : Valid (erase x t) :=
(Valid'.erase_aux x h).1
theorem size_erase_of_mem [DecidableLE α] {x : α} {t a₁ a₂} (h : Valid' a₁ t a₂)
(h_mem : x ∈ t) : size (erase x t) = size t - 1 := by
induction t generalizing a₁ a₂ with
| nil =>
contradiction
| node _ t_l t_x t_r t_ih_l t_ih_r =>
have t_ih_l' := t_ih_l h.left
have t_ih_r' := t_ih_r h.right
clear t_ih_l t_ih_r
dsimp only [Membership.mem, mem] at h_mem
unfold erase
revert h_mem; cases cmpLE x t_x <;> intro h_mem <;> dsimp only at h_mem ⊢
· have t_ih_l := t_ih_l' h_mem
clear t_ih_l' t_ih_r'
have t_l_h := Valid'.erase_aux x h.left
obtain ⟨t_l_valid, t_l_size⟩ := t_l_h
rw [size_balanceR t_l_valid.bal h.right.bal t_l_valid.sz h.right.sz
(Or.inl (Exists.intro t_l.size (And.intro t_l_size h.bal.1)))]
rw [t_ih_l, h.sz.1]
have h_pos_t_l_size := pos_size_of_mem h.left.sz h_mem
revert h_pos_t_l_size; rcases t_l.size with - | t_l_size <;> intro h_pos_t_l_size
· cases h_pos_t_l_size
· simp [Nat.add_right_comm]
· rw [(Valid'.glue h.left h.right h.bal.1).2, h.sz.1]; rfl
· have t_ih_r := t_ih_r' h_mem
clear t_ih_l' t_ih_r'
have t_r_h := Valid'.erase_aux x h.right
obtain ⟨t_r_valid, t_r_size⟩ := t_r_h
rw [size_balanceL h.left.bal t_r_valid.bal h.left.sz t_r_valid.sz
(Or.inr (Exists.intro t_r.size (And.intro t_r_size h.bal.1)))]
rw [t_ih_r, h.sz.1]
have h_pos_t_r_size := pos_size_of_mem h.right.sz h_mem
revert h_pos_t_r_size; rcases t_r.size with - | t_r_size <;> intro h_pos_t_r_size
· cases h_pos_t_r_size
· simp [Nat.add_assoc]
end Valid
end Ordnode
/-- An `Ordset α` is a finite set of values, represented as a tree. The operations on this type
maintain that the tree is balanced and correctly stores subtree sizes at each level. The
correctness property of the tree is baked into the type, so all operations on this type are correct
by construction. -/
def Ordset (α : Type*) [Preorder α] :=
{ t : Ordnode α // t.Valid }
namespace Ordset
open Ordnode
variable [Preorder α]
/-- O(1). The empty set. -/
nonrec def nil : Ordset α :=
⟨nil, ⟨⟩, ⟨⟩, ⟨⟩⟩
/-- O(1). Get the size of the set. -/
def size (s : Ordset α) : ℕ :=
s.1.size
/-- O(1). Construct a singleton set containing value `a`. -/
protected def singleton (a : α) : Ordset α :=
⟨singleton a, valid_singleton⟩
instance instEmptyCollection : EmptyCollection (Ordset α) :=
⟨nil⟩
instance instInhabited : Inhabited (Ordset α) :=
⟨nil⟩
instance instSingleton : Singleton α (Ordset α) :=
⟨Ordset.singleton⟩
/-- O(1). Is the set empty? -/
def Empty (s : Ordset α) : Prop :=
s = ∅
theorem empty_iff {s : Ordset α} : s = ∅ ↔ s.1.empty :=
⟨fun h => by cases h; exact rfl,
fun h => by cases s with | mk s_val _ => cases s_val <;> [rfl; cases h]⟩
instance Empty.instDecidablePred : DecidablePred (@Empty α _) :=
fun _ => decidable_of_iff' _ empty_iff
/-- O(log n). Insert an element into the set, preserving balance and the BST property.
If an equivalent element is already in the set, this replaces it. -/
protected def insert [IsTotal α (· ≤ ·)] [DecidableLE α] (x : α) (s : Ordset α) :
Ordset α :=
⟨Ordnode.insert x s.1, insert.valid _ s.2⟩
instance instInsert [IsTotal α (· ≤ ·)] [DecidableLE α] : Insert α (Ordset α) :=
⟨Ordset.insert⟩
/-- O(log n). Insert an element into the set, preserving balance and the BST property.
If an equivalent element is already in the set, the set is returned as is. -/
nonrec def insert' [IsTotal α (· ≤ ·)] [DecidableLE α] (x : α) (s : Ordset α) :
Ordset α :=
⟨insert' x s.1, insert'.valid _ s.2⟩
section
variable [DecidableLE α]
/-- O(log n). Does the set contain the element `x`? That is,
is there an element that is equivalent to `x` in the order? -/
def mem (x : α) (s : Ordset α) : Bool :=
x ∈ s.val
/-- O(log n). Retrieve an element in the set that is equivalent to `x` in the order,
if it exists. -/
def find (x : α) (s : Ordset α) : Option α :=
Ordnode.find x s.val
instance instMembership : Membership α (Ordset α) :=
⟨fun s x => mem x s⟩
instance mem.decidable (x : α) (s : Ordset α) : Decidable (x ∈ s) :=
instDecidableEqBool _ _
theorem pos_size_of_mem {x : α} {t : Ordset α} (h_mem : x ∈ t) : 0 < size t := by
simp? [Membership.mem, mem] at h_mem says
simp only [Membership.mem, mem, Bool.decide_eq_true] at h_mem
apply Ordnode.pos_size_of_mem t.property.sz h_mem
end
/-- O(log n). Remove an element from the set equivalent to `x`. Does nothing if there
is no such element. -/
def erase [DecidableLE α] (x : α) (s : Ordset α) : Ordset α :=
⟨Ordnode.erase x s.val, Ordnode.erase.valid x s.property⟩
/-- O(n). Map a function across a tree, without changing the structure. -/
def map {β} [Preorder β] (f : α → β) (f_strict_mono : StrictMono f) (s : Ordset α) : Ordset β :=
⟨Ordnode.map f s.val, Ordnode.map.valid f_strict_mono s.property⟩
end Ordset
| Mathlib/Data/Ordmap/Ordset.lean | 1,561 | 1,563 | |
/-
Copyright (c) 2018 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl
-/
import Mathlib.Logic.Relator
import Mathlib.Tactic.Use
import Mathlib.Tactic.MkIffOfInductiveProp
import Mathlib.Tactic.SimpRw
import Mathlib.Logic.Basic
import Mathlib.Order.Defs.Unbundled
/-!
# Relation closures
This file defines the reflexive, transitive, reflexive transitive and equivalence closures
of relations and proves some basic results on them.
Note that this is about unbundled relations, that is terms of types of the form `α → β → Prop`. For
the bundled version, see `Rel`.
## Definitions
* `Relation.ReflGen`: Reflexive closure. `ReflGen r` relates everything `r` related, plus for all
`a` it relates `a` with itself. So `ReflGen r a b ↔ r a b ∨ a = b`.
* `Relation.TransGen`: Transitive closure. `TransGen r` relates everything `r` related
transitively. So `TransGen r a b ↔ ∃ x₀ ... xₙ, r a x₀ ∧ r x₀ x₁ ∧ ... ∧ r xₙ b`.
* `Relation.ReflTransGen`: Reflexive transitive closure. `ReflTransGen r` relates everything
`r` related transitively, plus for all `a` it relates `a` with itself. So
`ReflTransGen r a b ↔ (∃ x₀ ... xₙ, r a x₀ ∧ r x₀ x₁ ∧ ... ∧ r xₙ b) ∨ a = b`. It is the same as
the reflexive closure of the transitive closure, or the transitive closure of the reflexive
closure. In terms of rewriting systems, this means that `a` can be rewritten to `b` in a number of
rewrites.
* `Relation.EqvGen`: Equivalence closure. `EqvGen r` relates everything `ReflTransGen r` relates,
plus for all related pairs it relates them in the opposite order.
* `Relation.Comp`: Relation composition. We provide notation `∘r`. For `r : α → β → Prop` and
`s : β → γ → Prop`, `r ∘r s`relates `a : α` and `c : γ` iff there exists `b : β` that's related to
both.
* `Relation.Map`: Image of a relation under a pair of maps. For `r : α → β → Prop`, `f : α → γ`,
`g : β → δ`, `Map r f g` is the relation `γ → δ → Prop` relating `f a` and `g b` for all `a`, `b`
related by `r`.
* `Relation.Join`: Join of a relation. For `r : α → α → Prop`, `Join r a b ↔ ∃ c, r a c ∧ r b c`. In
terms of rewriting systems, this means that `a` and `b` can be rewritten to the same term.
-/
open Function
variable {α β γ δ ε ζ : Type*}
section NeImp
variable {r : α → α → Prop}
theorem IsRefl.reflexive [IsRefl α r] : Reflexive r := fun x ↦ IsRefl.refl x
/-- To show a reflexive relation `r : α → α → Prop` holds over `x y : α`,
it suffices to show it holds when `x ≠ y`. -/
theorem Reflexive.rel_of_ne_imp (h : Reflexive r) {x y : α} (hr : x ≠ y → r x y) : r x y := by
by_cases hxy : x = y
· exact hxy ▸ h x
· exact hr hxy
/-- If a reflexive relation `r : α → α → Prop` holds over `x y : α`,
then it holds whether or not `x ≠ y`. -/
theorem Reflexive.ne_imp_iff (h : Reflexive r) {x y : α} : x ≠ y → r x y ↔ r x y :=
⟨h.rel_of_ne_imp, fun hr _ ↦ hr⟩
/-- If a reflexive relation `r : α → α → Prop` holds over `x y : α`,
then it holds whether or not `x ≠ y`. Unlike `Reflexive.ne_imp_iff`, this uses `[IsRefl α r]`. -/
theorem reflexive_ne_imp_iff [IsRefl α r] {x y : α} : x ≠ y → r x y ↔ r x y :=
IsRefl.reflexive.ne_imp_iff
protected theorem Symmetric.iff (H : Symmetric r) (x y : α) : r x y ↔ r y x :=
⟨fun h ↦ H h, fun h ↦ H h⟩
theorem Symmetric.flip_eq (h : Symmetric r) : flip r = r :=
funext₂ fun _ _ ↦ propext <| h.iff _ _
theorem Symmetric.swap_eq : Symmetric r → swap r = r :=
Symmetric.flip_eq
theorem flip_eq_iff : flip r = r ↔ Symmetric r :=
⟨fun h _ _ ↦ (congr_fun₂ h _ _).mp, Symmetric.flip_eq⟩
theorem swap_eq_iff : swap r = r ↔ Symmetric r :=
flip_eq_iff
end NeImp
section Comap
variable {r : β → β → Prop}
theorem Reflexive.comap (h : Reflexive r) (f : α → β) : Reflexive (r on f) := fun a ↦ h (f a)
theorem Symmetric.comap (h : Symmetric r) (f : α → β) : Symmetric (r on f) := fun _ _ hab ↦ h hab
theorem Transitive.comap (h : Transitive r) (f : α → β) : Transitive (r on f) :=
fun _ _ _ hab hbc ↦ h hab hbc
theorem Equivalence.comap (h : Equivalence r) (f : α → β) : Equivalence (r on f) :=
⟨fun a ↦ h.refl (f a), h.symm, h.trans⟩
end Comap
namespace Relation
section Comp
variable {r : α → β → Prop} {p : β → γ → Prop} {q : γ → δ → Prop}
/-- The composition of two relations, yielding a new relation. The result
relates a term of `α` and a term of `γ` if there is an intermediate
term of `β` related to both.
-/
def Comp (r : α → β → Prop) (p : β → γ → Prop) (a : α) (c : γ) : Prop :=
∃ b, r a b ∧ p b c
@[inherit_doc]
local infixr:80 " ∘r " => Relation.Comp
@[simp]
theorem comp_eq_fun (f : γ → β) : r ∘r (· = f ·) = (r · <| f ·) := by
ext x y
simp [Comp]
@[simp]
theorem comp_eq : r ∘r (· = ·) = r := comp_eq_fun ..
@[simp]
theorem fun_eq_comp (f : γ → α) : (f · = ·) ∘r r = (r <| f ·) := by
ext x y
simp [Comp]
@[simp]
theorem eq_comp : (· = ·) ∘r r = r := fun_eq_comp ..
@[simp]
theorem iff_comp {r : Prop → α → Prop} : (· ↔ ·) ∘r r = r := by
have : (· ↔ ·) = (· = ·) := by funext a b; exact iff_eq_eq
rw [this, eq_comp]
@[simp]
theorem comp_iff {r : α → Prop → Prop} : r ∘r (· ↔ ·) = r := by
have : (· ↔ ·) = (· = ·) := by funext a b; exact iff_eq_eq
rw [this, comp_eq]
theorem comp_assoc : (r ∘r p) ∘r q = r ∘r p ∘r q := by
funext a d
apply propext
constructor
· exact fun ⟨c, ⟨b, hab, hbc⟩, hcd⟩ ↦ ⟨b, hab, c, hbc, hcd⟩
· exact fun ⟨b, hab, c, hbc, hcd⟩ ↦ ⟨c, ⟨b, hab, hbc⟩, hcd⟩
theorem flip_comp : flip (r ∘r p) = flip p ∘r flip r := by
funext c a
apply propext
constructor
· exact fun ⟨b, hab, hbc⟩ ↦ ⟨b, hbc, hab⟩
· exact fun ⟨b, hbc, hab⟩ ↦ ⟨b, hab, hbc⟩
end Comp
section Fibration
variable (rα : α → α → Prop) (rβ : β → β → Prop) (f : α → β)
/-- A function `f : α → β` is a fibration between the relation `rα` and `rβ` if for all
`a : α` and `b : β`, whenever `b : β` and `f a` are related by `rβ`, `b` is the image
of some `a' : α` under `f`, and `a'` and `a` are related by `rα`. -/
def Fibration :=
∀ ⦃a b⦄, rβ b (f a) → ∃ a', rα a' a ∧ f a' = b
variable {rα rβ}
/-- If `f : α → β` is a fibration between relations `rα` and `rβ`, and `a : α` is
accessible under `rα`, then `f a` is accessible under `rβ`. -/
theorem _root_.Acc.of_fibration (fib : Fibration rα rβ f) {a} (ha : Acc rα a) : Acc rβ (f a) := by
induction ha with | intro a _ ih => ?_
refine Acc.intro (f a) fun b hr ↦ ?_
obtain ⟨a', hr', rfl⟩ := fib hr
exact ih a' hr'
theorem _root_.Acc.of_downward_closed (dc : ∀ {a b}, rβ b (f a) → ∃ c, f c = b) (a : α)
(ha : Acc (InvImage rβ f) a) : Acc rβ (f a) :=
ha.of_fibration f fun a _ h ↦
let ⟨a', he⟩ := dc h
⟨a', by simp_all [InvImage], he⟩
| end Fibration
section Map
variable {r : α → β → Prop} {f : α → γ} {g : β → δ} {c : γ} {d : δ}
| Mathlib/Logic/Relation.lean | 192 | 196 |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Patrick Massot, Casper Putz, Anne Baanen
-/
import Mathlib.Algebra.Algebra.Subalgebra.Tower
import Mathlib.Data.Finite.Sum
import Mathlib.Data.Matrix.Block
import Mathlib.Data.Matrix.Notation
import Mathlib.LinearAlgebra.Basis.Basic
import Mathlib.LinearAlgebra.Basis.Fin
import Mathlib.LinearAlgebra.Basis.Prod
import Mathlib.LinearAlgebra.Basis.SMul
import Mathlib.LinearAlgebra.Matrix.StdBasis
import Mathlib.RingTheory.AlgebraTower
import Mathlib.RingTheory.Ideal.Span
/-!
# Linear maps and matrices
This file defines the maps to send matrices to a linear map,
and to send linear maps between modules with a finite bases
to matrices. This defines a linear equivalence between linear maps
between finite-dimensional vector spaces and matrices indexed by
the respective bases.
## Main definitions
In the list below, and in all this file, `R` is a commutative ring (semiring
is sometimes enough), `M` and its variations are `R`-modules, `ι`, `κ`, `n` and `m` are finite
types used for indexing.
* `LinearMap.toMatrix`: given bases `v₁ : ι → M₁` and `v₂ : κ → M₂`,
the `R`-linear equivalence from `M₁ →ₗ[R] M₂` to `Matrix κ ι R`
* `Matrix.toLin`: the inverse of `LinearMap.toMatrix`
* `LinearMap.toMatrix'`: the `R`-linear equivalence from `(m → R) →ₗ[R] (n → R)`
to `Matrix m n R` (with the standard basis on `m → R` and `n → R`)
* `Matrix.toLin'`: the inverse of `LinearMap.toMatrix'`
* `algEquivMatrix`: given a basis indexed by `n`, the `R`-algebra equivalence between
`R`-endomorphisms of `M` and `Matrix n n R`
## Issues
This file was originally written without attention to non-commutative rings,
and so mostly only works in the commutative setting. This should be fixed.
In particular, `Matrix.mulVec` gives us a linear equivalence
`Matrix m n R ≃ₗ[R] (n → R) →ₗ[Rᵐᵒᵖ] (m → R)`
while `Matrix.vecMul` gives us a linear equivalence
`Matrix m n R ≃ₗ[Rᵐᵒᵖ] (m → R) →ₗ[R] (n → R)`.
At present, the first equivalence is developed in detail but only for commutative rings
(and we omit the distinction between `Rᵐᵒᵖ` and `R`),
while the second equivalence is developed only in brief, but for not-necessarily-commutative rings.
Naming is slightly inconsistent between the two developments.
In the original (commutative) development `linear` is abbreviated to `lin`,
although this is not consistent with the rest of mathlib.
In the new (non-commutative) development `linear` is not abbreviated, and declarations use `_right`
to indicate they use the right action of matrices on vectors (via `Matrix.vecMul`).
When the two developments are made uniform, the names should be made uniform, too,
by choosing between `linear` and `lin` consistently,
and (presumably) adding `_left` where necessary.
## Tags
linear_map, matrix, linear_equiv, diagonal, det, trace
-/
noncomputable section
open LinearMap Matrix Set Submodule
section ToMatrixRight
variable {R : Type*} [Semiring R]
variable {l m n : Type*}
/-- `Matrix.vecMul M` is a linear map. -/
def Matrix.vecMulLinear [Fintype m] (M : Matrix m n R) : (m → R) →ₗ[R] n → R where
toFun x := x ᵥ* M
map_add' _ _ := funext fun _ ↦ add_dotProduct _ _ _
map_smul' _ _ := funext fun _ ↦ smul_dotProduct _ _ _
@[simp] theorem Matrix.vecMulLinear_apply [Fintype m] (M : Matrix m n R) (x : m → R) :
M.vecMulLinear x = x ᵥ* M := rfl
theorem Matrix.coe_vecMulLinear [Fintype m] (M : Matrix m n R) :
(M.vecMulLinear : _ → _) = M.vecMul := rfl
variable [Fintype m]
theorem range_vecMulLinear (M : Matrix m n R) :
LinearMap.range M.vecMulLinear = span R (range M.row) := by
letI := Classical.decEq m
simp_rw [range_eq_map, ← iSup_range_single, Submodule.map_iSup, range_eq_map, ←
Ideal.span_singleton_one, Ideal.span, Submodule.map_span, image_image, image_singleton,
Matrix.vecMulLinear_apply, iSup_span, range_eq_iUnion, iUnion_singleton_eq_range,
LinearMap.single, LinearMap.coe_mk, AddHom.coe_mk, row_def]
unfold vecMul
simp_rw [single_dotProduct, one_mul]
theorem Matrix.vecMul_injective_iff {R : Type*} [Ring R] {M : Matrix m n R} :
Function.Injective M.vecMul ↔ LinearIndependent R M.row := by
rw [← coe_vecMulLinear]
simp only [← LinearMap.ker_eq_bot, Fintype.linearIndependent_iff, Submodule.eq_bot_iff,
LinearMap.mem_ker, vecMulLinear_apply, row_def]
refine ⟨fun h c h0 ↦ congr_fun <| h c ?_, fun h c h0 ↦ funext <| h c ?_⟩
· rw [← h0]
ext i
simp [vecMul, dotProduct]
· rw [← h0]
ext j
simp [vecMul, dotProduct]
lemma Matrix.linearIndependent_rows_of_isUnit {R : Type*} [Ring R] {A : Matrix m m R}
[DecidableEq m] (ha : IsUnit A) : LinearIndependent R A.row := by
rw [← Matrix.vecMul_injective_iff]
exact Matrix.vecMul_injective_of_isUnit ha
section
variable [DecidableEq m]
/-- Linear maps `(m → R) →ₗ[R] (n → R)` are linearly equivalent over `Rᵐᵒᵖ` to `Matrix m n R`,
by having matrices act by right multiplication.
-/
def LinearMap.toMatrixRight' : ((m → R) →ₗ[R] n → R) ≃ₗ[Rᵐᵒᵖ] Matrix m n R where
toFun f i j := f (single R (fun _ ↦ R) i 1) j
invFun := Matrix.vecMulLinear
right_inv M := by
ext i j
simp
left_inv f := by
apply (Pi.basisFun R m).ext
intro j; ext i
simp
map_add' f g := by
ext i j
simp only [Pi.add_apply, LinearMap.add_apply, Matrix.add_apply]
map_smul' c f := by
ext i j
simp only [Pi.smul_apply, LinearMap.smul_apply, RingHom.id_apply, Matrix.smul_apply]
/-- A `Matrix m n R` is linearly equivalent over `Rᵐᵒᵖ` to a linear map `(m → R) →ₗ[R] (n → R)`,
by having matrices act by right multiplication. -/
abbrev Matrix.toLinearMapRight' [DecidableEq m] : Matrix m n R ≃ₗ[Rᵐᵒᵖ] (m → R) →ₗ[R] n → R :=
LinearEquiv.symm LinearMap.toMatrixRight'
@[simp]
theorem Matrix.toLinearMapRight'_apply (M : Matrix m n R) (v : m → R) :
(Matrix.toLinearMapRight') M v = v ᵥ* M := rfl
@[simp]
theorem Matrix.toLinearMapRight'_mul [Fintype l] [DecidableEq l] (M : Matrix l m R)
(N : Matrix m n R) :
Matrix.toLinearMapRight' (M * N) =
(Matrix.toLinearMapRight' N).comp (Matrix.toLinearMapRight' M) :=
LinearMap.ext fun _x ↦ (vecMul_vecMul _ M N).symm
theorem Matrix.toLinearMapRight'_mul_apply [Fintype l] [DecidableEq l] (M : Matrix l m R)
(N : Matrix m n R) (x) :
Matrix.toLinearMapRight' (M * N) x =
Matrix.toLinearMapRight' N (Matrix.toLinearMapRight' M x) :=
(vecMul_vecMul _ M N).symm
@[simp]
theorem Matrix.toLinearMapRight'_one :
Matrix.toLinearMapRight' (1 : Matrix m m R) = LinearMap.id := by
ext
simp [Module.End.one_apply]
/-- If `M` and `M'` are each other's inverse matrices, they provide an equivalence between `n → A`
and `m → A` corresponding to `M.vecMul` and `M'.vecMul`. -/
@[simps]
def Matrix.toLinearEquivRight'OfInv [Fintype n] [DecidableEq n] {M : Matrix m n R}
{M' : Matrix n m R} (hMM' : M * M' = 1) (hM'M : M' * M = 1) : (n → R) ≃ₗ[R] m → R :=
{ LinearMap.toMatrixRight'.symm M' with
toFun := Matrix.toLinearMapRight' M'
invFun := Matrix.toLinearMapRight' M
left_inv := fun x ↦ by
rw [← Matrix.toLinearMapRight'_mul_apply, hM'M, Matrix.toLinearMapRight'_one, id_apply]
right_inv := fun x ↦ by
rw [← Matrix.toLinearMapRight'_mul_apply, hMM', Matrix.toLinearMapRight'_one, id_apply] }
end
end ToMatrixRight
/-!
From this point on, we only work with commutative rings,
and fail to distinguish between `Rᵐᵒᵖ` and `R`.
This should eventually be remedied.
-/
section mulVec
variable {R : Type*} [CommSemiring R]
variable {k l m n : Type*}
/-- `Matrix.mulVec M` is a linear map. -/
def Matrix.mulVecLin [Fintype n] (M : Matrix m n R) : (n → R) →ₗ[R] m → R where
toFun := M.mulVec
map_add' _ _ := funext fun _ ↦ dotProduct_add _ _ _
map_smul' _ _ := funext fun _ ↦ dotProduct_smul _ _ _
theorem Matrix.coe_mulVecLin [Fintype n] (M : Matrix m n R) :
(M.mulVecLin : _ → _) = M.mulVec := rfl
@[simp]
theorem Matrix.mulVecLin_apply [Fintype n] (M : Matrix m n R) (v : n → R) :
M.mulVecLin v = M *ᵥ v :=
rfl
@[simp]
theorem Matrix.mulVecLin_zero [Fintype n] : Matrix.mulVecLin (0 : Matrix m n R) = 0 :=
LinearMap.ext zero_mulVec
@[simp]
theorem Matrix.mulVecLin_add [Fintype n] (M N : Matrix m n R) :
(M + N).mulVecLin = M.mulVecLin + N.mulVecLin :=
LinearMap.ext fun _ ↦ add_mulVec _ _ _
@[simp] theorem Matrix.mulVecLin_transpose [Fintype m] (M : Matrix m n R) :
Mᵀ.mulVecLin = M.vecMulLinear := by
ext; simp [mulVec_transpose]
@[simp] theorem Matrix.vecMulLinear_transpose [Fintype n] (M : Matrix m n R) :
Mᵀ.vecMulLinear = M.mulVecLin := by
ext; simp [vecMul_transpose]
theorem Matrix.mulVecLin_submatrix [Fintype n] [Fintype l] (f₁ : m → k) (e₂ : n ≃ l)
(M : Matrix k l R) :
(M.submatrix f₁ e₂).mulVecLin = funLeft R R f₁ ∘ₗ M.mulVecLin ∘ₗ funLeft _ _ e₂.symm :=
LinearMap.ext fun _ ↦ submatrix_mulVec_equiv _ _ _ _
/-- A variant of `Matrix.mulVecLin_submatrix` that keeps around `LinearEquiv`s. -/
theorem Matrix.mulVecLin_reindex [Fintype n] [Fintype l] (e₁ : k ≃ m) (e₂ : l ≃ n)
(M : Matrix k l R) :
(reindex e₁ e₂ M).mulVecLin =
↑(LinearEquiv.funCongrLeft R R e₁.symm) ∘ₗ
M.mulVecLin ∘ₗ ↑(LinearEquiv.funCongrLeft R R e₂) :=
Matrix.mulVecLin_submatrix _ _ _
variable [Fintype n]
@[simp]
theorem Matrix.mulVecLin_one [DecidableEq n] :
Matrix.mulVecLin (1 : Matrix n n R) = LinearMap.id := by
ext; simp [Matrix.one_apply, Pi.single_apply, eq_comm]
@[simp]
theorem Matrix.mulVecLin_mul [Fintype m] (M : Matrix l m R) (N : Matrix m n R) :
Matrix.mulVecLin (M * N) = (Matrix.mulVecLin M).comp (Matrix.mulVecLin N) :=
LinearMap.ext fun _ ↦ (mulVec_mulVec _ _ _).symm
theorem Matrix.ker_mulVecLin_eq_bot_iff {M : Matrix m n R} :
(LinearMap.ker M.mulVecLin) = ⊥ ↔ ∀ v, M *ᵥ v = 0 → v = 0 := by
simp only [Submodule.eq_bot_iff, LinearMap.mem_ker, Matrix.mulVecLin_apply]
theorem Matrix.range_mulVecLin (M : Matrix m n R) :
LinearMap.range M.mulVecLin = span R (range M.col) := by
rw [← vecMulLinear_transpose, range_vecMulLinear, row_transpose]
theorem Matrix.mulVec_injective_iff {R : Type*} [CommRing R] {M : Matrix m n R} :
Function.Injective M.mulVec ↔ LinearIndependent R M.col := by
change Function.Injective (fun x ↦ _) ↔ _
simp_rw [← M.vecMul_transpose, vecMul_injective_iff, row_transpose]
lemma Matrix.linearIndependent_cols_of_isUnit {R : Type*} [CommRing R] [Fintype m]
{A : Matrix m m R} [DecidableEq m] (ha : IsUnit A) :
LinearIndependent R A.col := by
rw [← Matrix.mulVec_injective_iff]
exact Matrix.mulVec_injective_of_isUnit ha
end mulVec
section ToMatrix'
variable {R : Type*} [CommSemiring R]
variable {k l m n : Type*} [DecidableEq n] [Fintype n]
/-- Linear maps `(n → R) →ₗ[R] (m → R)` are linearly equivalent to `Matrix m n R`. -/
def LinearMap.toMatrix' : ((n → R) →ₗ[R] m → R) ≃ₗ[R] Matrix m n R where
toFun f := of fun i j ↦ f (Pi.single j 1) i
invFun := Matrix.mulVecLin
right_inv M := by
ext i j
simp only [Matrix.mulVec_single_one, Matrix.mulVecLin_apply, of_apply, transpose_apply]
left_inv f := by
apply (Pi.basisFun R n).ext
intro j; ext i
simp only [Pi.basisFun_apply, Matrix.mulVec_single_one,
Matrix.mulVecLin_apply, of_apply, transpose_apply]
map_add' f g := by
ext i j
simp only [Pi.add_apply, LinearMap.add_apply, of_apply, Matrix.add_apply]
map_smul' c f := by
ext i j
simp only [Pi.smul_apply, LinearMap.smul_apply, RingHom.id_apply, of_apply, Matrix.smul_apply]
/-- A `Matrix m n R` is linearly equivalent to a linear map `(n → R) →ₗ[R] (m → R)`.
Note that the forward-direction does not require `DecidableEq` and is `Matrix.vecMulLin`. -/
def Matrix.toLin' : Matrix m n R ≃ₗ[R] (n → R) →ₗ[R] m → R :=
LinearMap.toMatrix'.symm
theorem Matrix.toLin'_apply' (M : Matrix m n R) : Matrix.toLin' M = M.mulVecLin :=
rfl
@[simp]
theorem LinearMap.toMatrix'_symm :
(LinearMap.toMatrix'.symm : Matrix m n R ≃ₗ[R] _) = Matrix.toLin' :=
rfl
@[simp]
theorem Matrix.toLin'_symm :
(Matrix.toLin'.symm : ((n → R) →ₗ[R] m → R) ≃ₗ[R] _) = LinearMap.toMatrix' :=
rfl
@[simp]
theorem LinearMap.toMatrix'_toLin' (M : Matrix m n R) : LinearMap.toMatrix' (Matrix.toLin' M) = M :=
LinearMap.toMatrix'.apply_symm_apply M
@[simp]
theorem Matrix.toLin'_toMatrix' (f : (n → R) →ₗ[R] m → R) :
Matrix.toLin' (LinearMap.toMatrix' f) = f :=
Matrix.toLin'.apply_symm_apply f
@[simp]
theorem LinearMap.toMatrix'_apply (f : (n → R) →ₗ[R] m → R) (i j) :
LinearMap.toMatrix' f i j = f (fun j' ↦ if j' = j then 1 else 0) i := by
simp only [LinearMap.toMatrix', LinearEquiv.coe_mk, of_apply]
congr! with i
split_ifs with h
· rw [h, Pi.single_eq_same]
apply Pi.single_eq_of_ne h
@[simp]
theorem Matrix.toLin'_apply (M : Matrix m n R) (v : n → R) : Matrix.toLin' M v = M *ᵥ v :=
rfl
@[simp]
theorem Matrix.toLin'_one : Matrix.toLin' (1 : Matrix n n R) = LinearMap.id :=
Matrix.mulVecLin_one
@[simp]
theorem LinearMap.toMatrix'_id : LinearMap.toMatrix' (LinearMap.id : (n → R) →ₗ[R] n → R) = 1 := by
ext
rw [Matrix.one_apply, LinearMap.toMatrix'_apply, id_apply]
@[simp]
theorem LinearMap.toMatrix'_one : LinearMap.toMatrix' (1 : (n → R) →ₗ[R] n → R) = 1 :=
LinearMap.toMatrix'_id
@[simp]
theorem Matrix.toLin'_mul [Fintype m] [DecidableEq m] (M : Matrix l m R) (N : Matrix m n R) :
Matrix.toLin' (M * N) = (Matrix.toLin' M).comp (Matrix.toLin' N) :=
Matrix.mulVecLin_mul _ _
@[simp]
theorem Matrix.toLin'_submatrix [Fintype l] [DecidableEq l] (f₁ : m → k) (e₂ : n ≃ l)
(M : Matrix k l R) :
Matrix.toLin' (M.submatrix f₁ e₂) =
funLeft R R f₁ ∘ₗ (Matrix.toLin' M) ∘ₗ funLeft _ _ e₂.symm :=
Matrix.mulVecLin_submatrix _ _ _
/-- A variant of `Matrix.toLin'_submatrix` that keeps around `LinearEquiv`s. -/
theorem Matrix.toLin'_reindex [Fintype l] [DecidableEq l] (e₁ : k ≃ m) (e₂ : l ≃ n)
(M : Matrix k l R) :
Matrix.toLin' (reindex e₁ e₂ M) =
↑(LinearEquiv.funCongrLeft R R e₁.symm) ∘ₗ (Matrix.toLin' M) ∘ₗ
↑(LinearEquiv.funCongrLeft R R e₂) :=
Matrix.mulVecLin_reindex _ _ _
/-- Shortcut lemma for `Matrix.toLin'_mul` and `LinearMap.comp_apply` -/
theorem Matrix.toLin'_mul_apply [Fintype m] [DecidableEq m] (M : Matrix l m R) (N : Matrix m n R)
(x) : Matrix.toLin' (M * N) x = Matrix.toLin' M (Matrix.toLin' N x) := by
rw [Matrix.toLin'_mul, LinearMap.comp_apply]
theorem LinearMap.toMatrix'_comp [Fintype l] [DecidableEq l] (f : (n → R) →ₗ[R] m → R)
(g : (l → R) →ₗ[R] n → R) :
LinearMap.toMatrix' (f.comp g) = LinearMap.toMatrix' f * LinearMap.toMatrix' g := by
suffices f.comp g = Matrix.toLin' (LinearMap.toMatrix' f * LinearMap.toMatrix' g) by
rw [this, LinearMap.toMatrix'_toLin']
rw [Matrix.toLin'_mul, Matrix.toLin'_toMatrix', Matrix.toLin'_toMatrix']
theorem LinearMap.toMatrix'_mul [Fintype m] [DecidableEq m] (f g : (m → R) →ₗ[R] m → R) :
LinearMap.toMatrix' (f * g) = LinearMap.toMatrix' f * LinearMap.toMatrix' g :=
LinearMap.toMatrix'_comp f g
@[simp]
theorem LinearMap.toMatrix'_algebraMap (x : R) :
LinearMap.toMatrix' (algebraMap R (Module.End R (n → R)) x) = scalar n x := by
simp [Module.algebraMap_end_eq_smul_id, smul_eq_diagonal_mul]
theorem Matrix.ker_toLin'_eq_bot_iff {M : Matrix n n R} :
LinearMap.ker (Matrix.toLin' M) = ⊥ ↔ ∀ v, M *ᵥ v = 0 → v = 0 :=
Matrix.ker_mulVecLin_eq_bot_iff
theorem Matrix.range_toLin' (M : Matrix m n R) :
LinearMap.range (Matrix.toLin' M) = span R (range M.col) :=
Matrix.range_mulVecLin _
/-- If `M` and `M'` are each other's inverse matrices, they provide an equivalence between `m → A`
and `n → A` corresponding to `M.mulVec` and `M'.mulVec`. -/
@[simps]
def Matrix.toLin'OfInv [Fintype m] [DecidableEq m] {M : Matrix m n R} {M' : Matrix n m R}
(hMM' : M * M' = 1) (hM'M : M' * M = 1) : (m → R) ≃ₗ[R] n → R :=
{ Matrix.toLin' M' with
toFun := Matrix.toLin' M'
invFun := Matrix.toLin' M
left_inv := fun x ↦ by rw [← Matrix.toLin'_mul_apply, hMM', Matrix.toLin'_one, id_apply]
right_inv := fun x ↦ by
rw [← Matrix.toLin'_mul_apply, hM'M, Matrix.toLin'_one, id_apply] }
/-- Linear maps `(n → R) →ₗ[R] (n → R)` are algebra equivalent to `Matrix n n R`. -/
def LinearMap.toMatrixAlgEquiv' : ((n → R) →ₗ[R] n → R) ≃ₐ[R] Matrix n n R :=
AlgEquiv.ofLinearEquiv LinearMap.toMatrix' LinearMap.toMatrix'_one LinearMap.toMatrix'_mul
/-- A `Matrix n n R` is algebra equivalent to a linear map `(n → R) →ₗ[R] (n → R)`. -/
def Matrix.toLinAlgEquiv' : Matrix n n R ≃ₐ[R] (n → R) →ₗ[R] n → R :=
LinearMap.toMatrixAlgEquiv'.symm
@[simp]
theorem LinearMap.toMatrixAlgEquiv'_symm :
(LinearMap.toMatrixAlgEquiv'.symm : Matrix n n R ≃ₐ[R] _) = Matrix.toLinAlgEquiv' :=
rfl
@[simp]
theorem Matrix.toLinAlgEquiv'_symm :
(Matrix.toLinAlgEquiv'.symm : ((n → R) →ₗ[R] n → R) ≃ₐ[R] _) = LinearMap.toMatrixAlgEquiv' :=
rfl
@[simp]
theorem LinearMap.toMatrixAlgEquiv'_toLinAlgEquiv' (M : Matrix n n R) :
LinearMap.toMatrixAlgEquiv' (Matrix.toLinAlgEquiv' M) = M :=
LinearMap.toMatrixAlgEquiv'.apply_symm_apply M
@[simp]
theorem Matrix.toLinAlgEquiv'_toMatrixAlgEquiv' (f : (n → R) →ₗ[R] n → R) :
Matrix.toLinAlgEquiv' (LinearMap.toMatrixAlgEquiv' f) = f :=
Matrix.toLinAlgEquiv'.apply_symm_apply f
@[simp]
theorem LinearMap.toMatrixAlgEquiv'_apply (f : (n → R) →ₗ[R] n → R) (i j) :
LinearMap.toMatrixAlgEquiv' f i j = f (fun j' ↦ if j' = j then 1 else 0) i := by
simp [LinearMap.toMatrixAlgEquiv']
@[simp]
theorem Matrix.toLinAlgEquiv'_apply (M : Matrix n n R) (v : n → R) :
Matrix.toLinAlgEquiv' M v = M *ᵥ v :=
rfl
theorem Matrix.toLinAlgEquiv'_one : Matrix.toLinAlgEquiv' (1 : Matrix n n R) = LinearMap.id :=
Matrix.toLin'_one
@[simp]
theorem LinearMap.toMatrixAlgEquiv'_id :
LinearMap.toMatrixAlgEquiv' (LinearMap.id : (n → R) →ₗ[R] n → R) = 1 :=
LinearMap.toMatrix'_id
theorem LinearMap.toMatrixAlgEquiv'_comp (f g : (n → R) →ₗ[R] n → R) :
LinearMap.toMatrixAlgEquiv' (f.comp g) =
LinearMap.toMatrixAlgEquiv' f * LinearMap.toMatrixAlgEquiv' g :=
LinearMap.toMatrix'_comp _ _
theorem LinearMap.toMatrixAlgEquiv'_mul (f g : (n → R) →ₗ[R] n → R) :
LinearMap.toMatrixAlgEquiv' (f * g) =
LinearMap.toMatrixAlgEquiv' f * LinearMap.toMatrixAlgEquiv' g :=
LinearMap.toMatrixAlgEquiv'_comp f g
end ToMatrix'
section ToMatrix
section Finite
variable {R : Type*} [CommSemiring R]
variable {l m n : Type*} [Fintype n] [Finite m] [DecidableEq n]
variable {M₁ M₂ : Type*} [AddCommMonoid M₁] [AddCommMonoid M₂] [Module R M₁] [Module R M₂]
variable (v₁ : Basis n R M₁) (v₂ : Basis m R M₂)
/-- Given bases of two modules `M₁` and `M₂` over a commutative ring `R`, we get a linear
equivalence between linear maps `M₁ →ₗ M₂` and matrices over `R` indexed by the bases. -/
def LinearMap.toMatrix : (M₁ →ₗ[R] M₂) ≃ₗ[R] Matrix m n R :=
LinearEquiv.trans (LinearEquiv.arrowCongr v₁.equivFun v₂.equivFun) LinearMap.toMatrix'
/-- `LinearMap.toMatrix'` is a particular case of `LinearMap.toMatrix`, for the standard basis
`Pi.basisFun R n`. -/
theorem LinearMap.toMatrix_eq_toMatrix' :
LinearMap.toMatrix (Pi.basisFun R n) (Pi.basisFun R n) = LinearMap.toMatrix' :=
rfl
/-- Given bases of two modules `M₁` and `M₂` over a commutative ring `R`, we get a linear
equivalence between matrices over `R` indexed by the bases and linear maps `M₁ →ₗ M₂`. -/
def Matrix.toLin : Matrix m n R ≃ₗ[R] M₁ →ₗ[R] M₂ :=
(LinearMap.toMatrix v₁ v₂).symm
/-- `Matrix.toLin'` is a particular case of `Matrix.toLin`, for the standard basis
`Pi.basisFun R n`. -/
theorem Matrix.toLin_eq_toLin' : Matrix.toLin (Pi.basisFun R n) (Pi.basisFun R m) = Matrix.toLin' :=
rfl
@[simp]
theorem LinearMap.toMatrix_symm : (LinearMap.toMatrix v₁ v₂).symm = Matrix.toLin v₁ v₂ :=
rfl
@[simp]
theorem Matrix.toLin_symm : (Matrix.toLin v₁ v₂).symm = LinearMap.toMatrix v₁ v₂ :=
rfl
@[simp]
theorem Matrix.toLin_toMatrix (f : M₁ →ₗ[R] M₂) :
Matrix.toLin v₁ v₂ (LinearMap.toMatrix v₁ v₂ f) = f := by
rw [← Matrix.toLin_symm, LinearEquiv.apply_symm_apply]
@[simp]
theorem LinearMap.toMatrix_toLin (M : Matrix m n R) :
LinearMap.toMatrix v₁ v₂ (Matrix.toLin v₁ v₂ M) = M := by
rw [← Matrix.toLin_symm, LinearEquiv.symm_apply_apply]
theorem LinearMap.toMatrix_apply (f : M₁ →ₗ[R] M₂) (i : m) (j : n) :
LinearMap.toMatrix v₁ v₂ f i j = v₂.repr (f (v₁ j)) i := by
rw [LinearMap.toMatrix, LinearEquiv.trans_apply, LinearMap.toMatrix'_apply,
LinearEquiv.arrowCongr_apply, Basis.equivFun_symm_apply, Finset.sum_eq_single j, if_pos rfl,
one_smul, Basis.equivFun_apply]
· intro j' _ hj'
rw [if_neg hj', zero_smul]
· intro hj
have := Finset.mem_univ j
contradiction
theorem LinearMap.toMatrix_transpose_apply (f : M₁ →ₗ[R] M₂) (j : n) :
(LinearMap.toMatrix v₁ v₂ f)ᵀ j = v₂.repr (f (v₁ j)) :=
funext fun i ↦ f.toMatrix_apply _ _ i j
theorem LinearMap.toMatrix_apply' (f : M₁ →ₗ[R] M₂) (i : m) (j : n) :
LinearMap.toMatrix v₁ v₂ f i j = v₂.repr (f (v₁ j)) i :=
LinearMap.toMatrix_apply v₁ v₂ f i j
theorem LinearMap.toMatrix_transpose_apply' (f : M₁ →ₗ[R] M₂) (j : n) :
(LinearMap.toMatrix v₁ v₂ f)ᵀ j = v₂.repr (f (v₁ j)) :=
LinearMap.toMatrix_transpose_apply v₁ v₂ f j
/-- This will be a special case of `LinearMap.toMatrix_id_eq_basis_toMatrix`. -/
theorem LinearMap.toMatrix_id : LinearMap.toMatrix v₁ v₁ id = 1 := by
ext i j
simp [LinearMap.toMatrix_apply, Matrix.one_apply, Finsupp.single_apply, eq_comm]
@[simp]
theorem LinearMap.toMatrix_one : LinearMap.toMatrix v₁ v₁ 1 = 1 :=
LinearMap.toMatrix_id v₁
@[simp]
lemma LinearMap.toMatrix_singleton {ι : Type*} [Unique ι] (f : R →ₗ[R] R) (i j : ι) :
f.toMatrix (.singleton ι R) (.singleton ι R) i j = f 1 := by
simp [toMatrix, Subsingleton.elim j default]
@[simp]
theorem Matrix.toLin_one : Matrix.toLin v₁ v₁ 1 = LinearMap.id := by
rw [← LinearMap.toMatrix_id v₁, Matrix.toLin_toMatrix]
theorem LinearMap.toMatrix_reindexRange [DecidableEq M₁] (f : M₁ →ₗ[R] M₂) (k : m) (i : n) :
LinearMap.toMatrix v₁.reindexRange v₂.reindexRange f ⟨v₂ k, Set.mem_range_self k⟩
⟨v₁ i, Set.mem_range_self i⟩ =
LinearMap.toMatrix v₁ v₂ f k i := by
simp_rw [LinearMap.toMatrix_apply, Basis.reindexRange_self, Basis.reindexRange_repr]
@[simp]
theorem LinearMap.toMatrix_algebraMap (x : R) :
LinearMap.toMatrix v₁ v₁ (algebraMap R (Module.End R M₁) x) = scalar n x := by
simp [Module.algebraMap_end_eq_smul_id, LinearMap.toMatrix_id, smul_eq_diagonal_mul]
theorem LinearMap.toMatrix_mulVec_repr (f : M₁ →ₗ[R] M₂) (x : M₁) :
LinearMap.toMatrix v₁ v₂ f *ᵥ v₁.repr x = v₂.repr (f x) := by
ext i
rw [← Matrix.toLin'_apply, LinearMap.toMatrix, LinearEquiv.trans_apply, Matrix.toLin'_toMatrix',
LinearEquiv.arrowCongr_apply, v₂.equivFun_apply]
congr
exact v₁.equivFun.symm_apply_apply x
@[simp]
theorem LinearMap.toMatrix_basis_equiv [Fintype l] [DecidableEq l] (b : Basis l R M₁)
(b' : Basis l R M₂) :
LinearMap.toMatrix b' b (b'.equiv b (Equiv.refl l) : M₂ →ₗ[R] M₁) = 1 := by
ext i j
simp [LinearMap.toMatrix_apply, Matrix.one_apply, Finsupp.single_apply, eq_comm]
theorem LinearMap.toMatrix_smulBasis_left {G} [Group G] [DistribMulAction G M₁]
[SMulCommClass G R M₁] (g : G) (f : M₁ →ₗ[R] M₂) :
LinearMap.toMatrix (g • v₁) v₂ f =
LinearMap.toMatrix v₁ v₂ (f ∘ₗ DistribMulAction.toLinearMap _ _ g) := by
ext
rw [LinearMap.toMatrix_apply, LinearMap.toMatrix_apply]
dsimp
theorem LinearMap.toMatrix_smulBasis_right {G} [Group G] [DistribMulAction G M₂]
[SMulCommClass G R M₂] (g : G) (f : M₁ →ₗ[R] M₂) :
LinearMap.toMatrix v₁ (g • v₂) f =
LinearMap.toMatrix v₁ v₂ (DistribMulAction.toLinearMap _ _ g⁻¹ ∘ₗ f) := by
ext
rw [LinearMap.toMatrix_apply, LinearMap.toMatrix_apply]
dsimp
end Finite
variable {R : Type*} [CommSemiring R]
variable {l m n : Type*} [Fintype n] [Fintype m] [DecidableEq n]
variable {M₁ M₂ : Type*} [AddCommMonoid M₁] [AddCommMonoid M₂] [Module R M₁] [Module R M₂]
variable (v₁ : Basis n R M₁) (v₂ : Basis m R M₂)
theorem Matrix.toLin_apply (M : Matrix m n R) (v : M₁) :
Matrix.toLin v₁ v₂ M v = ∑ j, (M *ᵥ v₁.repr v) j • v₂ j :=
show v₂.equivFun.symm (Matrix.toLin' M (v₁.repr v)) = _ by
rw [Matrix.toLin'_apply, v₂.equivFun_symm_apply]
@[simp]
theorem Matrix.toLin_self (M : Matrix m n R) (i : n) :
Matrix.toLin v₁ v₂ M (v₁ i) = ∑ j, M j i • v₂ j := by
rw [Matrix.toLin_apply, Finset.sum_congr rfl fun j _hj ↦ ?_]
rw [Basis.repr_self, Matrix.mulVec, dotProduct, Finset.sum_eq_single i, Finsupp.single_eq_same,
mul_one]
· intro i' _ i'_ne
rw [Finsupp.single_eq_of_ne i'_ne.symm, mul_zero]
· intros
have := Finset.mem_univ i
contradiction
variable {M₃ : Type*} [AddCommMonoid M₃] [Module R M₃] (v₃ : Basis l R M₃)
theorem LinearMap.toMatrix_comp [Finite l] [DecidableEq m] (f : M₂ →ₗ[R] M₃) (g : M₁ →ₗ[R] M₂) :
LinearMap.toMatrix v₁ v₃ (f.comp g) =
LinearMap.toMatrix v₂ v₃ f * LinearMap.toMatrix v₁ v₂ g := by
simp_rw [LinearMap.toMatrix, LinearEquiv.trans_apply, LinearEquiv.arrowCongr_comp _ v₂.equivFun,
LinearMap.toMatrix'_comp]
theorem LinearMap.toMatrix_mul (f g : M₁ →ₗ[R] M₁) :
LinearMap.toMatrix v₁ v₁ (f * g) = LinearMap.toMatrix v₁ v₁ f * LinearMap.toMatrix v₁ v₁ g := by
rw [Module.End.mul_eq_comp, LinearMap.toMatrix_comp v₁ v₁ v₁ f g]
lemma LinearMap.toMatrix_pow (f : M₁ →ₗ[R] M₁) (k : ℕ) :
(toMatrix v₁ v₁ f) ^ k = toMatrix v₁ v₁ (f ^ k) := by
induction k with
| zero => simp
| succ k ih => rw [pow_succ, pow_succ, ih, ← toMatrix_mul]
theorem Matrix.toLin_mul [Finite l] [DecidableEq m] (A : Matrix l m R) (B : Matrix m n R) :
Matrix.toLin v₁ v₃ (A * B) = (Matrix.toLin v₂ v₃ A).comp (Matrix.toLin v₁ v₂ B) := by
apply (LinearMap.toMatrix v₁ v₃).injective
haveI : DecidableEq l := fun _ _ ↦ Classical.propDecidable _
rw [LinearMap.toMatrix_comp v₁ v₂ v₃]
repeat' rw [LinearMap.toMatrix_toLin]
/-- Shortcut lemma for `Matrix.toLin_mul` and `LinearMap.comp_apply`. -/
theorem Matrix.toLin_mul_apply [Finite l] [DecidableEq m] (A : Matrix l m R) (B : Matrix m n R)
(x) : Matrix.toLin v₁ v₃ (A * B) x = (Matrix.toLin v₂ v₃ A) (Matrix.toLin v₁ v₂ B x) := by
rw [Matrix.toLin_mul v₁ v₂, LinearMap.comp_apply]
/-- If `M` and `M` are each other's inverse matrices, `Matrix.toLin M` and `Matrix.toLin M'`
form a linear equivalence. -/
@[simps]
def Matrix.toLinOfInv [DecidableEq m] {M : Matrix m n R} {M' : Matrix n m R} (hMM' : M * M' = 1)
(hM'M : M' * M = 1) : M₁ ≃ₗ[R] M₂ :=
{ Matrix.toLin v₁ v₂ M with
toFun := Matrix.toLin v₁ v₂ M
invFun := Matrix.toLin v₂ v₁ M'
left_inv := fun x ↦ by rw [← Matrix.toLin_mul_apply, hM'M, Matrix.toLin_one, id_apply]
right_inv := fun x ↦ by
rw [← Matrix.toLin_mul_apply, hMM', Matrix.toLin_one, id_apply] }
/-- Given a basis of a module `M₁` over a commutative ring `R`, we get an algebra
equivalence between linear maps `M₁ →ₗ M₁` and square matrices over `R` indexed by the basis. -/
def LinearMap.toMatrixAlgEquiv : (M₁ →ₗ[R] M₁) ≃ₐ[R] Matrix n n R :=
AlgEquiv.ofLinearEquiv
(LinearMap.toMatrix v₁ v₁) (LinearMap.toMatrix_one v₁) (LinearMap.toMatrix_mul v₁)
/-- Given a basis of a module `M₁` over a commutative ring `R`, we get an algebra
equivalence between square matrices over `R` indexed by the basis and linear maps `M₁ →ₗ M₁`. -/
def Matrix.toLinAlgEquiv : Matrix n n R ≃ₐ[R] M₁ →ₗ[R] M₁ :=
(LinearMap.toMatrixAlgEquiv v₁).symm
@[simp]
theorem LinearMap.toMatrixAlgEquiv_symm :
(LinearMap.toMatrixAlgEquiv v₁).symm = Matrix.toLinAlgEquiv v₁ :=
rfl
@[simp]
theorem Matrix.toLinAlgEquiv_symm :
(Matrix.toLinAlgEquiv v₁).symm = LinearMap.toMatrixAlgEquiv v₁ :=
rfl
@[simp]
theorem Matrix.toLinAlgEquiv_toMatrixAlgEquiv (f : M₁ →ₗ[R] M₁) :
Matrix.toLinAlgEquiv v₁ (LinearMap.toMatrixAlgEquiv v₁ f) = f := by
rw [← Matrix.toLinAlgEquiv_symm, AlgEquiv.apply_symm_apply]
@[simp]
theorem LinearMap.toMatrixAlgEquiv_toLinAlgEquiv (M : Matrix n n R) :
LinearMap.toMatrixAlgEquiv v₁ (Matrix.toLinAlgEquiv v₁ M) = M := by
rw [← Matrix.toLinAlgEquiv_symm, AlgEquiv.symm_apply_apply]
theorem LinearMap.toMatrixAlgEquiv_apply (f : M₁ →ₗ[R] M₁) (i j : n) :
LinearMap.toMatrixAlgEquiv v₁ f i j = v₁.repr (f (v₁ j)) i := by
simp [LinearMap.toMatrixAlgEquiv, LinearMap.toMatrix_apply]
theorem LinearMap.toMatrixAlgEquiv_transpose_apply (f : M₁ →ₗ[R] M₁) (j : n) :
(LinearMap.toMatrixAlgEquiv v₁ f)ᵀ j = v₁.repr (f (v₁ j)) :=
funext fun i ↦ f.toMatrix_apply _ _ i j
theorem LinearMap.toMatrixAlgEquiv_apply' (f : M₁ →ₗ[R] M₁) (i j : n) :
LinearMap.toMatrixAlgEquiv v₁ f i j = v₁.repr (f (v₁ j)) i :=
LinearMap.toMatrixAlgEquiv_apply v₁ f i j
theorem LinearMap.toMatrixAlgEquiv_transpose_apply' (f : M₁ →ₗ[R] M₁) (j : n) :
(LinearMap.toMatrixAlgEquiv v₁ f)ᵀ j = v₁.repr (f (v₁ j)) :=
LinearMap.toMatrixAlgEquiv_transpose_apply v₁ f j
theorem Matrix.toLinAlgEquiv_apply (M : Matrix n n R) (v : M₁) :
Matrix.toLinAlgEquiv v₁ M v = ∑ j, (M *ᵥ v₁.repr v) j • v₁ j :=
show v₁.equivFun.symm (Matrix.toLinAlgEquiv' M (v₁.repr v)) = _ by
rw [Matrix.toLinAlgEquiv'_apply, v₁.equivFun_symm_apply]
@[simp]
theorem Matrix.toLinAlgEquiv_self (M : Matrix n n R) (i : n) :
Matrix.toLinAlgEquiv v₁ M (v₁ i) = ∑ j, M j i • v₁ j :=
Matrix.toLin_self _ _ _ _
theorem LinearMap.toMatrixAlgEquiv_id : LinearMap.toMatrixAlgEquiv v₁ id = 1 := by
simp_rw [LinearMap.toMatrixAlgEquiv, AlgEquiv.ofLinearEquiv_apply, LinearMap.toMatrix_id]
theorem Matrix.toLinAlgEquiv_one : Matrix.toLinAlgEquiv v₁ 1 = LinearMap.id := by
rw [← LinearMap.toMatrixAlgEquiv_id v₁, Matrix.toLinAlgEquiv_toMatrixAlgEquiv]
theorem LinearMap.toMatrixAlgEquiv_reindexRange [DecidableEq M₁] (f : M₁ →ₗ[R] M₁) (k i : n) :
LinearMap.toMatrixAlgEquiv v₁.reindexRange f
⟨v₁ k, Set.mem_range_self k⟩ ⟨v₁ i, Set.mem_range_self i⟩ =
LinearMap.toMatrixAlgEquiv v₁ f k i := by
simp_rw [LinearMap.toMatrixAlgEquiv_apply, Basis.reindexRange_self, Basis.reindexRange_repr]
theorem LinearMap.toMatrixAlgEquiv_comp (f g : M₁ →ₗ[R] M₁) :
LinearMap.toMatrixAlgEquiv v₁ (f.comp g) =
LinearMap.toMatrixAlgEquiv v₁ f * LinearMap.toMatrixAlgEquiv v₁ g := by
simp [LinearMap.toMatrixAlgEquiv, LinearMap.toMatrix_comp v₁ v₁ v₁ f g]
theorem LinearMap.toMatrixAlgEquiv_mul (f g : M₁ →ₗ[R] M₁) :
LinearMap.toMatrixAlgEquiv v₁ (f * g) =
LinearMap.toMatrixAlgEquiv v₁ f * LinearMap.toMatrixAlgEquiv v₁ g := by
rw [Module.End.mul_eq_comp, LinearMap.toMatrixAlgEquiv_comp v₁ f g]
theorem Matrix.toLinAlgEquiv_mul (A B : Matrix n n R) :
Matrix.toLinAlgEquiv v₁ (A * B) =
(Matrix.toLinAlgEquiv v₁ A).comp (Matrix.toLinAlgEquiv v₁ B) := by
convert Matrix.toLin_mul v₁ v₁ v₁ A B
@[simp]
theorem Matrix.toLin_finTwoProd_apply (a b c d : R) (x : R × R) :
Matrix.toLin (Basis.finTwoProd R) (Basis.finTwoProd R) !![a, b; c, d] x =
(a * x.fst + b * x.snd, c * x.fst + d * x.snd) := by
simp [Matrix.toLin_apply, Matrix.mulVec, dotProduct]
theorem Matrix.toLin_finTwoProd (a b c d : R) :
Matrix.toLin (Basis.finTwoProd R) (Basis.finTwoProd R) !![a, b; c, d] =
(a • LinearMap.fst R R R + b • LinearMap.snd R R R).prod
(c • LinearMap.fst R R R + d • LinearMap.snd R R R) :=
LinearMap.ext <| Matrix.toLin_finTwoProd_apply _ _ _ _
@[simp]
theorem toMatrix_distrib_mul_action_toLinearMap (x : R) :
LinearMap.toMatrix v₁ v₁ (DistribMulAction.toLinearMap R M₁ x) =
Matrix.diagonal fun _ ↦ x := by
ext
rw [LinearMap.toMatrix_apply, DistribMulAction.toLinearMap_apply, LinearEquiv.map_smul,
Basis.repr_self, Finsupp.smul_single_one, Finsupp.single_eq_pi_single, Matrix.diagonal_apply,
Pi.single_apply]
lemma LinearMap.toMatrix_prodMap [DecidableEq m] [DecidableEq (n ⊕ m)]
(φ₁ : Module.End R M₁) (φ₂ : Module.End R M₂) :
toMatrix (v₁.prod v₂) (v₁.prod v₂) (φ₁.prodMap φ₂) =
Matrix.fromBlocks (toMatrix v₁ v₁ φ₁) 0 0 (toMatrix v₂ v₂ φ₂) := by
ext (i|i) (j|j) <;> simp [toMatrix]
end ToMatrix
namespace Algebra
section Lmul
variable {R S : Type*} [CommSemiring R] [Semiring S] [Algebra R S]
variable {m : Type*} [Fintype m] [DecidableEq m] (b : Basis m R S)
theorem toMatrix_lmul' (x : S) (i j) :
LinearMap.toMatrix b b (lmul R S x) i j = b.repr (x * b j) i := by
simp only [LinearMap.toMatrix_apply', coe_lmul_eq_mul, LinearMap.mul_apply']
@[simp]
theorem toMatrix_lsmul (x : R) :
LinearMap.toMatrix b b (Algebra.lsmul R R S x) = Matrix.diagonal fun _ ↦ x :=
toMatrix_distrib_mul_action_toLinearMap b x
/-- `leftMulMatrix b x` is the matrix corresponding to the linear map `fun y ↦ x * y`.
`leftMulMatrix_eq_repr_mul` gives a formula for the entries of `leftMulMatrix`.
This definition is useful for doing (more) explicit computations with `LinearMap.mulLeft`,
such as the trace form or norm map for algebras.
-/
noncomputable def leftMulMatrix : S →ₐ[R] Matrix m m R where
toFun x := LinearMap.toMatrix b b (Algebra.lmul R S x)
map_zero' := by
rw [map_zero, LinearEquiv.map_zero]
map_one' := by
rw [map_one, LinearMap.toMatrix_one]
map_add' x y := by
rw [map_add, LinearEquiv.map_add]
map_mul' x y := by
rw [map_mul, LinearMap.toMatrix_mul]
commutes' r := by
ext
rw [lmul_algebraMap, toMatrix_lsmul, algebraMap_eq_diagonal, Pi.algebraMap_def,
Algebra.id.map_eq_self]
theorem leftMulMatrix_apply (x : S) : leftMulMatrix b x = LinearMap.toMatrix b b (lmul R S x) :=
rfl
theorem leftMulMatrix_eq_repr_mul (x : S) (i j) : leftMulMatrix b x i j = b.repr (x * b j) i := by
-- This is defeq to just `toMatrix_lmul' b x i j`,
-- but the unfolding goes a lot faster with this explicit `rw`.
rw [leftMulMatrix_apply, toMatrix_lmul' b x i j]
theorem leftMulMatrix_mulVec_repr (x y : S) :
leftMulMatrix b x *ᵥ b.repr y = b.repr (x * y) :=
(LinearMap.mulLeft R x).toMatrix_mulVec_repr b b y
@[simp]
theorem toMatrix_lmul_eq (x : S) :
LinearMap.toMatrix b b (LinearMap.mulLeft R x) = leftMulMatrix b x :=
rfl
theorem leftMulMatrix_injective : Function.Injective (leftMulMatrix b) := fun x x' h ↦
calc
x = Algebra.lmul R S x 1 := (mul_one x).symm
_ = Algebra.lmul R S x' 1 := by rw [(LinearMap.toMatrix b b).injective h]
_ = x' := mul_one x'
@[simp]
theorem smul_leftMulMatrix {G} [Group G] [DistribMulAction G S]
[SMulCommClass G R S] [SMulCommClass G S S] (g : G) (x) :
leftMulMatrix (g • b) x = leftMulMatrix b x := by
ext
simp_rw [leftMulMatrix_apply, LinearMap.toMatrix_apply, coe_lmul_eq_mul, LinearMap.mul_apply',
Basis.repr_smul, Basis.smul_apply, LinearEquiv.trans_apply,
DistribMulAction.toLinearEquiv_symm_apply, mul_smul_comm, inv_smul_smul]
variable {A M n : Type*} [Fintype n] [DecidableEq n]
[CommSemiring A] [AddCommMonoid M] [Module R M] [Module A M] [Algebra R A] [IsScalarTower R A M]
(bA : Basis m R A) (bM : Basis n A M)
lemma _root_.LinearMap.restrictScalars_toMatrix (f : M →ₗ[A] M) :
(f.restrictScalars R).toMatrix (bA.smulTower' bM) (bA.smulTower' bM) =
((f.toMatrix bM bM).map (leftMulMatrix bA)).comp _ _ _ _ _ := by
ext; simp [toMatrix, Basis.repr, Algebra.leftMulMatrix_apply,
Basis.smulTower'_repr, Basis.smulTower'_apply, mul_comm]
end Lmul
section LmulTower
variable {R S T : Type*} [CommSemiring R] [CommSemiring S] [Semiring T]
variable [Algebra R S] [Algebra S T] [Algebra R T] [IsScalarTower R S T]
variable {m n : Type*} [Fintype m] [Fintype n] [DecidableEq m] [DecidableEq n]
variable (b : Basis m R S) (c : Basis n S T)
theorem smulTower_leftMulMatrix (x) (ik jk) :
leftMulMatrix (b.smulTower c) x ik jk =
leftMulMatrix b (leftMulMatrix c x ik.2 jk.2) ik.1 jk.1 := by
simp only [leftMulMatrix_apply, LinearMap.toMatrix_apply, mul_comm, Basis.smulTower_apply,
Basis.smulTower_repr, Finsupp.smul_apply, id.smul_eq_mul, LinearEquiv.map_smul, mul_smul_comm,
coe_lmul_eq_mul, LinearMap.mul_apply']
theorem smulTower_leftMulMatrix_algebraMap (x : S) :
leftMulMatrix (b.smulTower c) (algebraMap _ _ x) = blockDiagonal fun _ ↦ leftMulMatrix b x := by
ext ⟨i, k⟩ ⟨j, k'⟩
rw [smulTower_leftMulMatrix, AlgHom.commutes, blockDiagonal_apply, algebraMap_matrix_apply]
split_ifs with h <;> simp only at h <;> simp [h]
theorem smulTower_leftMulMatrix_algebraMap_eq (x : S) (i j k) :
leftMulMatrix (b.smulTower c) (algebraMap _ _ x) (i, k) (j, k) = leftMulMatrix b x i j := by
rw [smulTower_leftMulMatrix_algebraMap, blockDiagonal_apply_eq]
theorem smulTower_leftMulMatrix_algebraMap_ne (x : S) (i j) {k k'} (h : k ≠ k') :
leftMulMatrix (b.smulTower c) (algebraMap _ _ x) (i, k) (j, k') = 0 := by
rw [smulTower_leftMulMatrix_algebraMap, blockDiagonal_apply_ne _ _ _ h]
end LmulTower
end Algebra
section
variable {R S : Type*} [CommSemiring R] {n : Type*} [DecidableEq n]
variable {M M₁ M₂ : Type*} [AddCommMonoid M] [Module R M]
variable [AddCommMonoid M₁] [Module R M₁] [AddCommMonoid M₂] [Module R M₂]
variable [Semiring S] [Module S M₁] [Module S M₂] [SMulCommClass S R M₁] [SMulCommClass S R M₂]
variable [SMul R S] [IsScalarTower R S M₁] [IsScalarTower R S M₂]
/-- The natural equivalence between linear endomorphisms of finite free modules and square matrices
is compatible with the algebra structures. -/
def algEquivMatrix' [Fintype n] : Module.End R (n → R) ≃ₐ[R] Matrix n n R :=
{ LinearMap.toMatrix' with
map_mul' := LinearMap.toMatrix'_comp
commutes' := LinearMap.toMatrix'_algebraMap }
variable (R) in
/-- A linear equivalence of two modules induces an equivalence of algebras of their
endomorphisms. -/
@[simps!] def LinearEquiv.algConj (e : M₁ ≃ₗ[S] M₂) : Module.End S M₁ ≃ₐ[R] Module.End S M₂ where
__ := e.conjRingEquiv
commutes' := fun _ ↦ by ext; show e.restrictScalars R _ = _; simp
/-- A basis of a module induces an equivalence of algebras from the endomorphisms of the module to
square matrices. -/
def algEquivMatrix [Fintype n] (h : Basis n R M) : Module.End R M ≃ₐ[R] Matrix n n R :=
(h.equivFun.algConj R).trans algEquivMatrix'
end
namespace Basis
|
variable {R M M₁ M₂ ι ι₁ ι₂ : Type*} [CommSemiring R]
variable [AddCommMonoid M] [AddCommMonoid M₁] [AddCommMonoid M₂]
variable [Module R M] [Module R M₁] [Module R M₂]
| Mathlib/LinearAlgebra/Matrix/ToLin.lean | 927 | 930 |
/-
Copyright (c) 2021 Thomas Browning. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Thomas Browning
-/
import Mathlib.Algebra.BigOperators.GroupWithZero.Finset
import Mathlib.Algebra.GroupWithZero.Subgroup
import Mathlib.Data.Finite.Card
import Mathlib.Data.Finite.Prod
import Mathlib.Data.Set.Card
import Mathlib.GroupTheory.Coset.Card
import Mathlib.GroupTheory.GroupAction.Quotient
import Mathlib.GroupTheory.QuotientGroup.Basic
/-!
# Index of a Subgroup
In this file we define the index of a subgroup, and prove several divisibility properties.
Several theorems proved in this file are known as Lagrange's theorem.
## Main definitions
- `H.index` : the index of `H : Subgroup G` as a natural number,
and returns 0 if the index is infinite.
- `H.relindex K` : the relative index of `H : Subgroup G` in `K : Subgroup G` as a natural number,
and returns 0 if the relative index is infinite.
# Main results
- `card_mul_index` : `Nat.card H * H.index = Nat.card G`
- `index_mul_card` : `H.index * Fintype.card H = Fintype.card G`
- `index_dvd_card` : `H.index ∣ Fintype.card G`
- `relindex_mul_index` : If `H ≤ K`, then `H.relindex K * K.index = H.index`
- `index_dvd_of_le` : If `H ≤ K`, then `K.index ∣ H.index`
- `relindex_mul_relindex` : `relindex` is multiplicative in towers
- `MulAction.index_stabilizer`: the index of the stabilizer is the cardinality of the orbit
-/
assert_not_exists Field
open scoped Pointwise
namespace Subgroup
open Cardinal Function
variable {G G' : Type*} [Group G] [Group G'] (H K L : Subgroup G)
/-- The index of a subgroup as a natural number. Returns `0` if the index is infinite. -/
@[to_additive "The index of an additive subgroup as a natural number.
Returns 0 if the index is infinite."]
noncomputable def index : ℕ :=
Nat.card (G ⧸ H)
/-- If `H` and `K` are subgroups of a group `G`, then `relindex H K : ℕ` is the index
of `H ∩ K` in `K`. The function returns `0` if the index is infinite. -/
@[to_additive "If `H` and `K` are subgroups of an additive group `G`, then `relindex H K : ℕ`
is the index of `H ∩ K` in `K`. The function returns `0` if the index is infinite."]
noncomputable def relindex : ℕ :=
(H.subgroupOf K).index
@[to_additive]
theorem index_comap_of_surjective {f : G' →* G} (hf : Function.Surjective f) :
(H.comap f).index = H.index := by
have key : ∀ x y : G',
QuotientGroup.leftRel (H.comap f) x y ↔ QuotientGroup.leftRel H (f x) (f y) := by
simp only [QuotientGroup.leftRel_apply]
exact fun x y => iff_of_eq (congr_arg (· ∈ H) (by rw [f.map_mul, f.map_inv]))
refine Cardinal.toNat_congr (Equiv.ofBijective (Quotient.map' f fun x y => (key x y).mp) ⟨?_, ?_⟩)
· simp_rw [← Quotient.eq''] at key
refine Quotient.ind' fun x => ?_
refine Quotient.ind' fun y => ?_
exact (key x y).mpr
· refine Quotient.ind' fun x => ?_
obtain ⟨y, hy⟩ := hf x
exact ⟨y, (Quotient.map'_mk'' f _ y).trans (congr_arg Quotient.mk'' hy)⟩
@[to_additive]
theorem index_comap (f : G' →* G) :
(H.comap f).index = H.relindex f.range :=
Eq.trans (congr_arg index (by rfl))
((H.subgroupOf f.range).index_comap_of_surjective f.rangeRestrict_surjective)
@[to_additive]
theorem relindex_comap (f : G' →* G) (K : Subgroup G') :
relindex (comap f H) K = relindex H (map f K) := by
rw [relindex, subgroupOf, comap_comap, index_comap, ← f.map_range, K.range_subtype]
variable {H K L}
@[to_additive relindex_mul_index]
theorem relindex_mul_index (h : H ≤ K) : H.relindex K * K.index = H.index :=
((mul_comm _ _).trans (Cardinal.toNat_mul _ _).symm).trans
(congr_arg Cardinal.toNat (Equiv.cardinal_eq (quotientEquivProdOfLE h))).symm
@[to_additive]
theorem index_dvd_of_le (h : H ≤ K) : K.index ∣ H.index :=
dvd_of_mul_left_eq (H.relindex K) (relindex_mul_index h)
@[to_additive]
theorem relindex_dvd_index_of_le (h : H ≤ K) : H.relindex K ∣ H.index :=
dvd_of_mul_right_eq K.index (relindex_mul_index h)
@[to_additive]
theorem relindex_subgroupOf (hKL : K ≤ L) :
(H.subgroupOf L).relindex (K.subgroupOf L) = H.relindex K :=
((index_comap (H.subgroupOf L) (inclusion hKL)).trans (congr_arg _ (inclusion_range hKL))).symm
variable (H K L)
@[to_additive relindex_mul_relindex]
theorem relindex_mul_relindex (hHK : H ≤ K) (hKL : K ≤ L) :
H.relindex K * K.relindex L = H.relindex L := by
rw [← relindex_subgroupOf hKL]
exact relindex_mul_index fun x hx => hHK hx
@[to_additive]
theorem inf_relindex_right : (H ⊓ K).relindex K = H.relindex K := by
rw [relindex, relindex, inf_subgroupOf_right]
@[to_additive]
theorem inf_relindex_left : (H ⊓ K).relindex H = K.relindex H := by
rw [inf_comm, inf_relindex_right]
@[to_additive relindex_inf_mul_relindex]
theorem relindex_inf_mul_relindex : H.relindex (K ⊓ L) * K.relindex L = (H ⊓ K).relindex L := by
rw [← inf_relindex_right H (K ⊓ L), ← inf_relindex_right K L, ← inf_relindex_right (H ⊓ K) L,
inf_assoc, relindex_mul_relindex (H ⊓ (K ⊓ L)) (K ⊓ L) L inf_le_right inf_le_right]
@[to_additive (attr := simp)]
theorem relindex_sup_right [K.Normal] : K.relindex (H ⊔ K) = K.relindex H :=
Nat.card_congr (QuotientGroup.quotientInfEquivProdNormalQuotient H K).toEquiv.symm
@[to_additive (attr := simp)]
theorem relindex_sup_left [K.Normal] : K.relindex (K ⊔ H) = K.relindex H := by
rw [sup_comm, relindex_sup_right]
@[to_additive]
theorem relindex_dvd_index_of_normal [H.Normal] : H.relindex K ∣ H.index :=
relindex_sup_right K H ▸ relindex_dvd_index_of_le le_sup_right
variable {H K}
@[to_additive]
theorem relindex_dvd_of_le_left (hHK : H ≤ K) : K.relindex L ∣ H.relindex L :=
inf_of_le_left hHK ▸ dvd_of_mul_left_eq _ (relindex_inf_mul_relindex _ _ _)
/-- A subgroup has index two if and only if there exists `a` such that for all `b`, exactly one
of `b * a` and `b` belong to `H`. -/
@[to_additive "An additive subgroup has index two if and only if there exists `a` such that
for all `b`, exactly one of `b + a` and `b` belong to `H`."]
theorem index_eq_two_iff : H.index = 2 ↔ ∃ a, ∀ b, Xor' (b * a ∈ H) (b ∈ H) := by
simp only [index, Nat.card_eq_two_iff' ((1 : G) : G ⧸ H), ExistsUnique, inv_mem_iff,
QuotientGroup.exists_mk, QuotientGroup.forall_mk, Ne, QuotientGroup.eq, mul_one,
xor_iff_iff_not]
refine exists_congr fun a =>
⟨fun ha b => ⟨fun hba hb => ?_, fun hb => ?_⟩, fun ha => ⟨?_, fun b hb => ?_⟩⟩
· exact ha.1 ((mul_mem_cancel_left hb).1 hba)
· exact inv_inv b ▸ ha.2 _ (mt (inv_mem_iff (x := b)).1 hb)
· rw [← inv_mem_iff (x := a), ← ha, inv_mul_cancel]
exact one_mem _
· rwa [ha, inv_mem_iff (x := b)]
@[to_additive]
theorem mul_mem_iff_of_index_two (h : H.index = 2) {a b : G} : a * b ∈ H ↔ (a ∈ H ↔ b ∈ H) := by
by_cases ha : a ∈ H; · simp only [ha, true_iff, mul_mem_cancel_left ha]
by_cases hb : b ∈ H; · simp only [hb, iff_true, mul_mem_cancel_right hb]
simp only [ha, hb, iff_true]
rcases index_eq_two_iff.1 h with ⟨c, hc⟩
refine (hc _).or.resolve_left ?_
rwa [mul_assoc, mul_mem_cancel_right ((hc _).or.resolve_right hb)]
@[to_additive]
theorem mul_self_mem_of_index_two (h : H.index = 2) (a : G) : a * a ∈ H := by
rw [mul_mem_iff_of_index_two h]
@[to_additive two_smul_mem_of_index_two]
theorem sq_mem_of_index_two (h : H.index = 2) (a : G) : a ^ 2 ∈ H :=
(pow_two a).symm ▸ mul_self_mem_of_index_two h a
variable (H K) {f : G →* G'}
@[to_additive (attr := simp)]
theorem index_top : (⊤ : Subgroup G).index = 1 :=
Nat.card_eq_one_iff_unique.mpr ⟨QuotientGroup.subsingleton_quotient_top, ⟨1⟩⟩
@[to_additive (attr := simp)]
theorem index_bot : (⊥ : Subgroup G).index = Nat.card G :=
Cardinal.toNat_congr QuotientGroup.quotientBot.toEquiv
@[to_additive (attr := simp)]
theorem relindex_top_left : (⊤ : Subgroup G).relindex H = 1 :=
index_top
@[to_additive (attr := simp)]
theorem relindex_top_right : H.relindex ⊤ = H.index := by
rw [← relindex_mul_index (show H ≤ ⊤ from le_top), index_top, mul_one]
@[to_additive (attr := simp)]
theorem relindex_bot_left : (⊥ : Subgroup G).relindex H = Nat.card H := by
rw [relindex, bot_subgroupOf, index_bot]
@[to_additive (attr := simp)]
theorem relindex_bot_right : H.relindex ⊥ = 1 := by rw [relindex, subgroupOf_bot_eq_top, index_top]
@[to_additive (attr := simp)]
theorem relindex_self : H.relindex H = 1 := by rw [relindex, subgroupOf_self, index_top]
@[to_additive]
theorem index_ker (f : G →* G') : f.ker.index = Nat.card f.range := by
rw [← MonoidHom.comap_bot, index_comap, relindex_bot_left]
@[to_additive]
theorem relindex_ker (f : G →* G') : f.ker.relindex K = Nat.card (K.map f) := by
rw [← MonoidHom.comap_bot, relindex_comap, relindex_bot_left]
@[to_additive (attr := simp) card_mul_index]
theorem card_mul_index : Nat.card H * H.index = Nat.card G := by
rw [← relindex_bot_left, ← index_bot]
exact relindex_mul_index bot_le
@[to_additive]
theorem card_dvd_of_surjective (f : G →* G') (hf : Function.Surjective f) :
Nat.card G' ∣ Nat.card G := by
rw [← Nat.card_congr (QuotientGroup.quotientKerEquivOfSurjective f hf).toEquiv]
exact Dvd.intro_left (Nat.card f.ker) f.ker.card_mul_index
@[to_additive]
theorem card_range_dvd (f : G →* G') : Nat.card f.range ∣ Nat.card G :=
card_dvd_of_surjective f.rangeRestrict f.rangeRestrict_surjective
@[to_additive]
theorem card_map_dvd (f : G →* G') : Nat.card (H.map f) ∣ Nat.card H :=
card_dvd_of_surjective (f.subgroupMap H) (f.subgroupMap_surjective H)
@[to_additive]
theorem index_map (f : G →* G') :
(H.map f).index = (H ⊔ f.ker).index * f.range.index := by
rw [← comap_map_eq, index_comap, relindex_mul_index (H.map_le_range f)]
@[to_additive]
theorem index_map_dvd {f : G →* G'} (hf : Function.Surjective f) :
(H.map f).index ∣ H.index := by
rw [index_map, f.range_eq_top_of_surjective hf, index_top, mul_one]
exact index_dvd_of_le le_sup_left
@[to_additive]
theorem dvd_index_map {f : G →* G'} (hf : f.ker ≤ H) :
H.index ∣ (H.map f).index := by
rw [index_map, sup_of_le_left hf]
apply dvd_mul_right
@[to_additive]
theorem index_map_eq (hf1 : Surjective f) (hf2 : f.ker ≤ H) : (H.map f).index = H.index :=
Nat.dvd_antisymm (H.index_map_dvd hf1) (H.dvd_index_map hf2)
@[to_additive]
lemma index_map_of_bijective (hf : Bijective f) (H : Subgroup G) : (H.map f).index = H.index :=
index_map_eq _ hf.2 (by rw [f.ker_eq_bot_iff.2 hf.1]; exact bot_le)
@[to_additive]
theorem index_map_of_injective {f : G →* G'} (hf : Function.Injective f) :
(H.map f).index = H.index * f.range.index := by
rw [H.index_map, f.ker_eq_bot_iff.mpr hf, sup_bot_eq]
@[to_additive]
theorem index_map_subtype {H : Subgroup G} (K : Subgroup H) :
(K.map H.subtype).index = K.index * H.index := by
rw [K.index_map_of_injective H.subtype_injective, H.range_subtype]
@[to_additive]
theorem index_eq_card : H.index = Nat.card (G ⧸ H) :=
rfl
@[to_additive index_mul_card]
theorem index_mul_card : H.index * Nat.card H = Nat.card G := by
rw [mul_comm, card_mul_index]
@[to_additive]
theorem index_dvd_card : H.index ∣ Nat.card G :=
⟨Nat.card H, H.index_mul_card.symm⟩
@[to_additive]
theorem relindex_dvd_card : H.relindex K ∣ Nat.card K :=
(H.subgroupOf K).index_dvd_card
variable {H K L}
@[to_additive]
theorem relindex_eq_zero_of_le_left (hHK : H ≤ K) (hKL : K.relindex L = 0) : H.relindex L = 0 :=
eq_zero_of_zero_dvd (hKL ▸ relindex_dvd_of_le_left L hHK)
@[to_additive]
theorem relindex_eq_zero_of_le_right (hKL : K ≤ L) (hHK : H.relindex K = 0) : H.relindex L = 0 :=
Finite.card_eq_zero_of_embedding (quotientSubgroupOfEmbeddingOfLE H hKL) hHK
@[to_additive]
theorem index_eq_zero_of_relindex_eq_zero (h : H.relindex K = 0) : H.index = 0 :=
H.relindex_top_right.symm.trans (relindex_eq_zero_of_le_right le_top h)
@[to_additive]
theorem relindex_le_of_le_left (hHK : H ≤ K) (hHL : H.relindex L ≠ 0) :
K.relindex L ≤ H.relindex L :=
Nat.le_of_dvd (Nat.pos_of_ne_zero hHL) (relindex_dvd_of_le_left L hHK)
@[to_additive]
theorem relindex_le_of_le_right (hKL : K ≤ L) (hHL : H.relindex L ≠ 0) :
H.relindex K ≤ H.relindex L :=
Finite.card_le_of_embedding' (quotientSubgroupOfEmbeddingOfLE H hKL) fun h => (hHL h).elim
@[to_additive]
theorem relindex_ne_zero_trans (hHK : H.relindex K ≠ 0) (hKL : K.relindex L ≠ 0) :
H.relindex L ≠ 0 := fun h =>
mul_ne_zero (mt (relindex_eq_zero_of_le_right (show K ⊓ L ≤ K from inf_le_left)) hHK) hKL
((relindex_inf_mul_relindex H K L).trans (relindex_eq_zero_of_le_left inf_le_left h))
@[to_additive]
theorem relindex_inf_ne_zero (hH : H.relindex L ≠ 0) (hK : K.relindex L ≠ 0) :
(H ⊓ K).relindex L ≠ 0 := by
replace hH : H.relindex (K ⊓ L) ≠ 0 := mt (relindex_eq_zero_of_le_right inf_le_right) hH
rw [← inf_relindex_right] at hH hK ⊢
rw [inf_assoc]
exact relindex_ne_zero_trans hH hK
@[to_additive]
theorem index_inf_ne_zero (hH : H.index ≠ 0) (hK : K.index ≠ 0) : (H ⊓ K).index ≠ 0 := by
rw [← relindex_top_right] at hH hK ⊢
exact relindex_inf_ne_zero hH hK
@[to_additive]
theorem relindex_inf_le : (H ⊓ K).relindex L ≤ H.relindex L * K.relindex L := by
by_cases h : H.relindex L = 0
· exact (le_of_eq (relindex_eq_zero_of_le_left inf_le_left h)).trans (zero_le _)
rw [← inf_relindex_right, inf_assoc, ← relindex_mul_relindex _ _ L inf_le_right inf_le_right,
inf_relindex_right, inf_relindex_right]
exact mul_le_mul_right' (relindex_le_of_le_right inf_le_right h) (K.relindex L)
@[to_additive]
theorem index_inf_le : (H ⊓ K).index ≤ H.index * K.index := by
simp_rw [← relindex_top_right, relindex_inf_le]
@[to_additive]
theorem relindex_iInf_ne_zero {ι : Type*} [_hι : Finite ι] {f : ι → Subgroup G}
(hf : ∀ i, (f i).relindex L ≠ 0) : (⨅ i, f i).relindex L ≠ 0 :=
haveI := Fintype.ofFinite ι
(Finset.prod_ne_zero_iff.mpr fun i _hi => hf i) ∘
Nat.card_pi.symm.trans ∘
Finite.card_eq_zero_of_embedding (quotientiInfSubgroupOfEmbedding f L)
@[to_additive]
theorem relindex_iInf_le {ι : Type*} [Fintype ι] (f : ι → Subgroup G) :
(⨅ i, f i).relindex L ≤ ∏ i, (f i).relindex L :=
le_of_le_of_eq
(Finite.card_le_of_embedding' (quotientiInfSubgroupOfEmbedding f L) fun h =>
let ⟨i, _hi, h⟩ := Finset.prod_eq_zero_iff.mp (Nat.card_pi.symm.trans h)
relindex_eq_zero_of_le_left (iInf_le f i) h)
Nat.card_pi
@[to_additive]
theorem index_iInf_ne_zero {ι : Type*} [Finite ι] {f : ι → Subgroup G}
(hf : ∀ i, (f i).index ≠ 0) : (⨅ i, f i).index ≠ 0 := by
simp_rw [← relindex_top_right] at hf ⊢
exact relindex_iInf_ne_zero hf
@[to_additive]
theorem index_iInf_le {ι : Type*} [Fintype ι] (f : ι → Subgroup G) :
(⨅ i, f i).index ≤ ∏ i, (f i).index := by simp_rw [← relindex_top_right, relindex_iInf_le]
@[to_additive (attr := simp) index_eq_one]
theorem index_eq_one : H.index = 1 ↔ H = ⊤ :=
⟨fun h =>
QuotientGroup.subgroup_eq_top_of_subsingleton H (Nat.card_eq_one_iff_unique.mp h).1,
fun h => (congr_arg index h).trans index_top⟩
@[to_additive (attr := simp) relindex_eq_one]
theorem relindex_eq_one : H.relindex K = 1 ↔ K ≤ H :=
index_eq_one.trans subgroupOf_eq_top
@[to_additive (attr := simp) card_eq_one]
theorem card_eq_one : Nat.card H = 1 ↔ H = ⊥ :=
H.relindex_bot_left ▸ relindex_eq_one.trans le_bot_iff
@[to_additive]
lemma inf_eq_bot_of_coprime (h : Nat.Coprime (Nat.card H) (Nat.card K)) : H ⊓ K = ⊥ :=
card_eq_one.1 <| Nat.eq_one_of_dvd_coprimes h
(card_dvd_of_le inf_le_left) (card_dvd_of_le inf_le_right)
@[deprecated (since := "2024-12-18")]
alias _root_.add_inf_eq_bot_of_coprime := AddSubgroup.inf_eq_bot_of_coprime
@[to_additive]
theorem index_ne_zero_of_finite [hH : Finite (G ⧸ H)] : H.index ≠ 0 := by
cases nonempty_fintype (G ⧸ H)
rw [index_eq_card]
exact Nat.card_pos.ne'
/-- Finite index implies finite quotient. -/
@[to_additive "Finite index implies finite quotient."]
noncomputable def fintypeOfIndexNeZero (hH : H.index ≠ 0) : Fintype (G ⧸ H) :=
@Fintype.ofFinite _ (Nat.finite_of_card_ne_zero hH)
@[to_additive]
lemma index_eq_zero_iff_infinite : H.index = 0 ↔ Infinite (G ⧸ H) := by
simp [index_eq_card, Nat.card_eq_zero]
@[to_additive one_lt_index_of_ne_top]
theorem one_lt_index_of_ne_top [Finite (G ⧸ H)] (hH : H ≠ ⊤) : 1 < H.index :=
Nat.one_lt_iff_ne_zero_and_ne_one.mpr ⟨index_ne_zero_of_finite, mt index_eq_one.mp hH⟩
@[to_additive]
lemma finite_quotient_of_finite_quotient_of_index_ne_zero {X : Type*} [MulAction G X]
[Finite <| MulAction.orbitRel.Quotient G X] (hi : H.index ≠ 0) :
Finite <| MulAction.orbitRel.Quotient H X := by
have := fintypeOfIndexNeZero hi
exact MulAction.finite_quotient_of_finite_quotient_of_finite_quotient
@[to_additive]
lemma finite_quotient_of_pretransitive_of_index_ne_zero {X : Type*} [MulAction G X]
[MulAction.IsPretransitive G X] (hi : H.index ≠ 0) :
Finite <| MulAction.orbitRel.Quotient H X := by
have := (MulAction.pretransitive_iff_subsingleton_quotient G X).1 inferInstance
exact finite_quotient_of_finite_quotient_of_index_ne_zero hi
@[to_additive]
lemma exists_pow_mem_of_index_ne_zero (h : H.index ≠ 0) (a : G) :
∃ n, 0 < n ∧ n ≤ H.index ∧ a ^ n ∈ H := by
suffices ∃ n₁ n₂, n₁ < n₂ ∧ n₂ ≤ H.index ∧ ((a ^ n₂ : G) : G ⧸ H) = ((a ^ n₁ : G) : G ⧸ H) by
rcases this with ⟨n₁, n₂, hlt, hle, he⟩
refine ⟨n₂ - n₁, by omega, by omega, ?_⟩
rw [eq_comm, QuotientGroup.eq, ← zpow_natCast, ← zpow_natCast, ← zpow_neg, ← zpow_add,
add_comm] at he
rw [← zpow_natCast]
convert he
omega
suffices ∃ n₁ n₂, n₁ ≠ n₂ ∧ n₁ ≤ H.index ∧ n₂ ≤ H.index ∧
((a ^ n₂ : G) : G ⧸ H) = ((a ^ n₁ : G) : G ⧸ H) by
rcases this with ⟨n₁, n₂, hne, hle₁, hle₂, he⟩
rcases hne.lt_or_lt with hlt | hlt
· exact ⟨n₁, n₂, hlt, hle₂, he⟩
· exact ⟨n₂, n₁, hlt, hle₁, he.symm⟩
by_contra hc
simp_rw [not_exists] at hc
let f : (Set.Icc 0 H.index) → G ⧸ H := fun n ↦ (a ^ (n : ℕ) : G)
have hf : Function.Injective f := by
rintro ⟨n₁, h₁, hle₁⟩ ⟨n₂, h₂, hle₂⟩ he
have hc' := hc n₁ n₂
dsimp only [f] at he
simpa [hle₁, hle₂, he] using hc'
have := (fintypeOfIndexNeZero h).finite
have hcard := Finite.card_le_of_injective f hf
simp [← index_eq_card] at hcard
@[to_additive]
lemma exists_pow_mem_of_relindex_ne_zero (h : H.relindex K ≠ 0) {a : G} (ha : a ∈ K) :
∃ n, 0 < n ∧ n ≤ H.relindex K ∧ a ^ n ∈ H ⊓ K := by
rcases exists_pow_mem_of_index_ne_zero h ⟨a, ha⟩ with ⟨n, hlt, hle, he⟩
refine ⟨n, hlt, hle, ?_⟩
simpa [pow_mem ha, mem_subgroupOf] using he
@[to_additive]
lemma pow_mem_of_index_ne_zero_of_dvd (h : H.index ≠ 0) (a : G) {n : ℕ}
(hn : ∀ m, 0 < m → m ≤ H.index → m ∣ n) : a ^ n ∈ H := by
rcases exists_pow_mem_of_index_ne_zero h a with ⟨m, hlt, hle, he⟩
rcases hn m hlt hle with ⟨k, rfl⟩
rw [pow_mul]
exact pow_mem he _
@[to_additive]
lemma pow_mem_of_relindex_ne_zero_of_dvd (h : H.relindex K ≠ 0) {a : G} (ha : a ∈ K) {n : ℕ}
(hn : ∀ m, 0 < m → m ≤ H.relindex K → m ∣ n) : a ^ n ∈ H ⊓ K := by
convert pow_mem_of_index_ne_zero_of_dvd h ⟨a, ha⟩ hn
| simp [pow_mem ha, mem_subgroupOf]
@[to_additive (attr := simp) index_prod]
lemma index_prod (H : Subgroup G) (K : Subgroup G') : (H.prod K).index = H.index * K.index := by
| Mathlib/GroupTheory/Index.lean | 472 | 475 |
/-
Copyright (c) 2019 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Sébastien Gouëzel, Yury Kudryashov
-/
import Mathlib.Analysis.Calculus.TangentCone
import Mathlib.Analysis.NormedSpace.OperatorNorm.Asymptotics
import Mathlib.Analysis.Asymptotics.TVS
import Mathlib.Analysis.Asymptotics.Lemmas
/-!
# The Fréchet derivative
Let `E` and `F` be normed spaces, `f : E → F`, and `f' : E →L[𝕜] F` a
continuous 𝕜-linear map, where `𝕜` is a non-discrete normed field. Then
`HasFDerivWithinAt f f' s x`
says that `f` has derivative `f'` at `x`, where the domain of interest
is restricted to `s`. We also have
`HasFDerivAt f f' x := HasFDerivWithinAt f f' x univ`
Finally,
`HasStrictFDerivAt f f' x`
means that `f : E → F` has derivative `f' : E →L[𝕜] F` in the sense of strict differentiability,
i.e., `f y - f z - f'(y - z) = o(y - z)` as `y, z → x`. This notion is used in the inverse
function theorem, and is defined here only to avoid proving theorems like
`IsBoundedBilinearMap.hasFDerivAt` twice: first for `HasFDerivAt`, then for
`HasStrictFDerivAt`.
## Main results
In addition to the definition and basic properties of the derivative,
the folder `Analysis/Calculus/FDeriv/` contains the usual formulas
(and existence assertions) for the derivative of
* constants
* the identity
* bounded linear maps (`Linear.lean`)
* bounded bilinear maps (`Bilinear.lean`)
* sum of two functions (`Add.lean`)
* sum of finitely many functions (`Add.lean`)
* multiplication of a function by a scalar constant (`Add.lean`)
* negative of a function (`Add.lean`)
* subtraction of two functions (`Add.lean`)
* multiplication of a function by a scalar function (`Mul.lean`)
* multiplication of two scalar functions (`Mul.lean`)
* composition of functions (the chain rule) (`Comp.lean`)
* inverse function (`Mul.lean`)
(assuming that it exists; the inverse function theorem is in `../Inverse.lean`)
For most binary operations we also define `const_op` and `op_const` theorems for the cases when
the first or second argument is a constant. This makes writing chains of `HasDerivAt`'s easier,
and they more frequently lead to the desired result.
One can also interpret the derivative of a function `f : 𝕜 → E` as an element of `E` (by identifying
a linear function from `𝕜` to `E` with its value at `1`). Results on the Fréchet derivative are
translated to this more elementary point of view on the derivative in the file `Deriv.lean`. The
derivative of polynomials is handled there, as it is naturally one-dimensional.
The simplifier is set up to prove automatically that some functions are differentiable, or
differentiable at a point (but not differentiable on a set or within a set at a point, as checking
automatically that the good domains are mapped one to the other when using composition is not
something the simplifier can easily do). This means that one can write
`example (x : ℝ) : Differentiable ℝ (fun x ↦ sin (exp (3 + x^2)) - 5 * cos x) := by simp`.
If there are divisions, one needs to supply to the simplifier proofs that the denominators do
not vanish, as in
```lean
example (x : ℝ) (h : 1 + sin x ≠ 0) : DifferentiableAt ℝ (fun x ↦ exp x / (1 + sin x)) x := by
simp [h]
```
Of course, these examples only work once `exp`, `cos` and `sin` have been shown to be
differentiable, in `Mathlib.Analysis.SpecialFunctions.Trigonometric.Deriv`.
The simplifier is not set up to compute the Fréchet derivative of maps (as these are in general
complicated multidimensional linear maps), but it will compute one-dimensional derivatives,
see `Deriv.lean`.
## Implementation details
The derivative is defined in terms of the `IsLittleOTVS` relation to ensure the definition does not
ingrain a choice of norm, and is then quickly translated to the more convenient `IsLittleO` in the
subsequent theorems.
It is also characterized in terms of the `Tendsto` relation.
We also introduce predicates `DifferentiableWithinAt 𝕜 f s x` (where `𝕜` is the base field,
`f` the function to be differentiated, `x` the point at which the derivative is asserted to exist,
and `s` the set along which the derivative is defined), as well as `DifferentiableAt 𝕜 f x`,
`DifferentiableOn 𝕜 f s` and `Differentiable 𝕜 f` to express the existence of a derivative.
To be able to compute with derivatives, we write `fderivWithin 𝕜 f s x` and `fderiv 𝕜 f x`
for some choice of a derivative if it exists, and the zero function otherwise. This choice only
behaves well along sets for which the derivative is unique, i.e., those for which the tangent
directions span a dense subset of the whole space. The predicates `UniqueDiffWithinAt s x` and
`UniqueDiffOn s`, defined in `TangentCone.lean` express this property. We prove that indeed
they imply the uniqueness of the derivative. This is satisfied for open subsets, and in particular
for `univ`. This uniqueness only holds when the field is non-discrete, which we request at the very
beginning: otherwise, a derivative can be defined, but it has no interesting properties whatsoever.
To make sure that the simplifier can prove automatically that functions are differentiable, we tag
many lemmas with the `simp` attribute, for instance those saying that the sum of differentiable
functions is differentiable, as well as their product, their cartesian product, and so on. A notable
exception is the chain rule: we do not mark as a simp lemma the fact that, if `f` and `g` are
differentiable, then their composition also is: `simp` would always be able to match this lemma,
by taking `f` or `g` to be the identity. Instead, for every reasonable function (say, `exp`),
we add a lemma that if `f` is differentiable then so is `(fun x ↦ exp (f x))`. This means adding
some boilerplate lemmas, but these can also be useful in their own right.
Tests for this ability of the simplifier (with more examples) are provided in
`Tests/Differentiable.lean`.
## TODO
Generalize more results to topological vector spaces.
## Tags
derivative, differentiable, Fréchet, calculus
-/
open Filter Asymptotics ContinuousLinearMap Set Metric Topology NNReal ENNReal
noncomputable section
section TVS
variable {𝕜 : Type*} [NontriviallyNormedField 𝕜]
variable {E : Type*} [AddCommGroup E] [Module 𝕜 E] [TopologicalSpace E]
variable {F : Type*} [AddCommGroup F] [Module 𝕜 F] [TopologicalSpace F]
/-- A function `f` has the continuous linear map `f'` as derivative along the filter `L` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` converges along the filter `L`. This definition
is designed to be specialized for `L = 𝓝 x` (in `HasFDerivAt`), giving rise to the usual notion
of Fréchet derivative, and for `L = 𝓝[s] x` (in `HasFDerivWithinAt`), giving rise to
the notion of Fréchet derivative along the set `s`. -/
@[mk_iff hasFDerivAtFilter_iff_isLittleOTVS]
structure HasFDerivAtFilter (f : E → F) (f' : E →L[𝕜] F) (x : E) (L : Filter E) : Prop where
of_isLittleOTVS ::
isLittleOTVS : (fun x' => f x' - f x - f' (x' - x)) =o[𝕜; L] (fun x' => x' - x)
/-- A function `f` has the continuous linear map `f'` as derivative at `x` within a set `s` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` tends to `x` inside `s`. -/
@[fun_prop]
def HasFDerivWithinAt (f : E → F) (f' : E →L[𝕜] F) (s : Set E) (x : E) :=
HasFDerivAtFilter f f' x (𝓝[s] x)
/-- A function `f` has the continuous linear map `f'` as derivative at `x` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` tends to `x`. -/
@[fun_prop]
def HasFDerivAt (f : E → F) (f' : E →L[𝕜] F) (x : E) :=
HasFDerivAtFilter f f' x (𝓝 x)
/-- A function `f` has derivative `f'` at `a` in the sense of *strict differentiability*
if `f x - f y - f' (x - y) = o(x - y)` as `x, y → a`. This form of differentiability is required,
e.g., by the inverse function theorem. Any `C^1` function on a vector space over `ℝ` is strictly
differentiable but this definition works, e.g., for vector spaces over `p`-adic numbers. -/
@[fun_prop, mk_iff hasStrictFDerivAt_iff_isLittleOTVS]
structure HasStrictFDerivAt (f : E → F) (f' : E →L[𝕜] F) (x : E) where
of_isLittleOTVS ::
isLittleOTVS :
(fun p : E × E => f p.1 - f p.2 - f' (p.1 - p.2))
=o[𝕜; 𝓝 (x, x)] (fun p : E × E => p.1 - p.2)
variable (𝕜)
/-- A function `f` is differentiable at a point `x` within a set `s` if it admits a derivative
there (possibly non-unique). -/
@[fun_prop]
def DifferentiableWithinAt (f : E → F) (s : Set E) (x : E) :=
∃ f' : E →L[𝕜] F, HasFDerivWithinAt f f' s x
/-- A function `f` is differentiable at a point `x` if it admits a derivative there (possibly
non-unique). -/
@[fun_prop]
def DifferentiableAt (f : E → F) (x : E) :=
∃ f' : E →L[𝕜] F, HasFDerivAt f f' x
open scoped Classical in
/-- If `f` has a derivative at `x` within `s`, then `fderivWithin 𝕜 f s x` is such a derivative.
Otherwise, it is set to `0`. We also set it to be zero, if zero is one of possible derivatives. -/
irreducible_def fderivWithin (f : E → F) (s : Set E) (x : E) : E →L[𝕜] F :=
if HasFDerivWithinAt f (0 : E →L[𝕜] F) s x
then 0
else if h : DifferentiableWithinAt 𝕜 f s x
then Classical.choose h
else 0
/-- If `f` has a derivative at `x`, then `fderiv 𝕜 f x` is such a derivative. Otherwise, it is
set to `0`. -/
irreducible_def fderiv (f : E → F) (x : E) : E →L[𝕜] F :=
fderivWithin 𝕜 f univ x
/-- `DifferentiableOn 𝕜 f s` means that `f` is differentiable within `s` at any point of `s`. -/
@[fun_prop]
def DifferentiableOn (f : E → F) (s : Set E) :=
∀ x ∈ s, DifferentiableWithinAt 𝕜 f s x
/-- `Differentiable 𝕜 f` means that `f` is differentiable at any point. -/
@[fun_prop]
def Differentiable (f : E → F) :=
∀ x, DifferentiableAt 𝕜 f x
variable {𝕜}
variable {f f₀ f₁ g : E → F}
variable {f' f₀' f₁' g' : E →L[𝕜] F}
variable {x : E}
variable {s t : Set E}
variable {L L₁ L₂ : Filter E}
theorem fderivWithin_zero_of_not_differentiableWithinAt (h : ¬DifferentiableWithinAt 𝕜 f s x) :
fderivWithin 𝕜 f s x = 0 := by
simp [fderivWithin, h]
@[simp]
theorem fderivWithin_univ : fderivWithin 𝕜 f univ = fderiv 𝕜 f := by
ext
rw [fderiv]
end TVS
section
variable {𝕜 : Type*} [NontriviallyNormedField 𝕜]
variable {E : Type*} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
variable {F : Type*} [NormedAddCommGroup F] [NormedSpace 𝕜 F]
variable {f f₀ f₁ g : E → F}
variable {f' f₀' f₁' g' : E →L[𝕜] F}
variable {x : E}
variable {s t : Set E}
variable {L L₁ L₂ : Filter E}
theorem hasFDerivAtFilter_iff_isLittleO :
HasFDerivAtFilter f f' x L ↔ (fun x' => f x' - f x - f' (x' - x)) =o[L] fun x' => x' - x :=
(hasFDerivAtFilter_iff_isLittleOTVS ..).trans isLittleOTVS_iff_isLittleO
alias ⟨HasFDerivAtFilter.isLittleO, HasFDerivAtFilter.of_isLittleO⟩ :=
hasFDerivAtFilter_iff_isLittleO
theorem hasStrictFDerivAt_iff_isLittleO :
HasStrictFDerivAt f f' x ↔
(fun p : E × E => f p.1 - f p.2 - f' (p.1 - p.2)) =o[𝓝 (x, x)] fun p : E × E => p.1 - p.2 :=
(hasStrictFDerivAt_iff_isLittleOTVS ..).trans isLittleOTVS_iff_isLittleO
alias ⟨HasStrictFDerivAt.isLittleO, HasStrictFDerivAt.of_isLittleO⟩ :=
hasStrictFDerivAt_iff_isLittleO
section DerivativeUniqueness
/- In this section, we discuss the uniqueness of the derivative.
We prove that the definitions `UniqueDiffWithinAt` and `UniqueDiffOn` indeed imply the
uniqueness of the derivative. -/
/-- If a function f has a derivative f' at x, a rescaled version of f around x converges to f',
i.e., `n (f (x + (1/n) v) - f x)` converges to `f' v`. More generally, if `c n` tends to infinity
and `c n * d n` tends to `v`, then `c n * (f (x + d n) - f x)` tends to `f' v`. This lemma expresses
this fact, for functions having a derivative within a set. Its specific formulation is useful for
tangent cone related discussions. -/
theorem HasFDerivWithinAt.lim (h : HasFDerivWithinAt f f' s x) {α : Type*} (l : Filter α)
{c : α → 𝕜} {d : α → E} {v : E} (dtop : ∀ᶠ n in l, x + d n ∈ s)
(clim : Tendsto (fun n => ‖c n‖) l atTop) (cdlim : Tendsto (fun n => c n • d n) l (𝓝 v)) :
Tendsto (fun n => c n • (f (x + d n) - f x)) l (𝓝 (f' v)) := by
have tendsto_arg : Tendsto (fun n => x + d n) l (𝓝[s] x) := by
conv in 𝓝[s] x => rw [← add_zero x]
rw [nhdsWithin, tendsto_inf]
constructor
· apply tendsto_const_nhds.add (tangentConeAt.lim_zero l clim cdlim)
· rwa [tendsto_principal]
have : (fun y => f y - f x - f' (y - x)) =o[𝓝[s] x] fun y => y - x := h.isLittleO
have : (fun n => f (x + d n) - f x - f' (x + d n - x)) =o[l] fun n => x + d n - x :=
this.comp_tendsto tendsto_arg
have : (fun n => f (x + d n) - f x - f' (d n)) =o[l] d := by simpa only [add_sub_cancel_left]
have : (fun n => c n • (f (x + d n) - f x - f' (d n))) =o[l] fun n => c n • d n :=
(isBigO_refl c l).smul_isLittleO this
have : (fun n => c n • (f (x + d n) - f x - f' (d n))) =o[l] fun _ => (1 : ℝ) :=
this.trans_isBigO (cdlim.isBigO_one ℝ)
have L1 : Tendsto (fun n => c n • (f (x + d n) - f x - f' (d n))) l (𝓝 0) :=
(isLittleO_one_iff ℝ).1 this
have L2 : Tendsto (fun n => f' (c n • d n)) l (𝓝 (f' v)) :=
Tendsto.comp f'.cont.continuousAt cdlim
have L3 :
Tendsto (fun n => c n • (f (x + d n) - f x - f' (d n)) + f' (c n • d n)) l (𝓝 (0 + f' v)) :=
L1.add L2
have :
(fun n => c n • (f (x + d n) - f x - f' (d n)) + f' (c n • d n)) = fun n =>
c n • (f (x + d n) - f x) := by
ext n
simp [smul_add, smul_sub]
rwa [this, zero_add] at L3
/-- If `f'` and `f₁'` are two derivatives of `f` within `s` at `x`, then they are equal on the
tangent cone to `s` at `x` -/
theorem HasFDerivWithinAt.unique_on (hf : HasFDerivWithinAt f f' s x)
(hg : HasFDerivWithinAt f f₁' s x) : EqOn f' f₁' (tangentConeAt 𝕜 s x) :=
fun _ ⟨_, _, dtop, clim, cdlim⟩ =>
tendsto_nhds_unique (hf.lim atTop dtop clim cdlim) (hg.lim atTop dtop clim cdlim)
/-- `UniqueDiffWithinAt` achieves its goal: it implies the uniqueness of the derivative. -/
theorem UniqueDiffWithinAt.eq (H : UniqueDiffWithinAt 𝕜 s x) (hf : HasFDerivWithinAt f f' s x)
(hg : HasFDerivWithinAt f f₁' s x) : f' = f₁' :=
ContinuousLinearMap.ext_on H.1 (hf.unique_on hg)
theorem UniqueDiffOn.eq (H : UniqueDiffOn 𝕜 s) (hx : x ∈ s) (h : HasFDerivWithinAt f f' s x)
(h₁ : HasFDerivWithinAt f f₁' s x) : f' = f₁' :=
(H x hx).eq h h₁
end DerivativeUniqueness
section FDerivProperties
/-! ### Basic properties of the derivative -/
theorem hasFDerivAtFilter_iff_tendsto :
HasFDerivAtFilter f f' x L ↔
Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) L (𝓝 0) := by
have h : ∀ x', ‖x' - x‖ = 0 → ‖f x' - f x - f' (x' - x)‖ = 0 := fun x' hx' => by
rw [sub_eq_zero.1 (norm_eq_zero.1 hx')]
simp
rw [hasFDerivAtFilter_iff_isLittleO, ← isLittleO_norm_left, ← isLittleO_norm_right,
isLittleO_iff_tendsto h]
exact tendsto_congr fun _ => div_eq_inv_mul _ _
theorem hasFDerivWithinAt_iff_tendsto :
HasFDerivWithinAt f f' s x ↔
Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) (𝓝[s] x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasFDerivAt_iff_tendsto :
HasFDerivAt f f' x ↔ Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) (𝓝 x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasFDerivAt_iff_isLittleO_nhds_zero :
HasFDerivAt f f' x ↔ (fun h : E => f (x + h) - f x - f' h) =o[𝓝 0] fun h => h := by
rw [HasFDerivAt, hasFDerivAtFilter_iff_isLittleO, ← map_add_left_nhds_zero x, isLittleO_map]
simp [Function.comp_def]
nonrec theorem HasFDerivAtFilter.mono (h : HasFDerivAtFilter f f' x L₂) (hst : L₁ ≤ L₂) :
HasFDerivAtFilter f f' x L₁ :=
.of_isLittleOTVS <| h.isLittleOTVS.mono hst
theorem HasFDerivWithinAt.mono_of_mem_nhdsWithin
(h : HasFDerivWithinAt f f' t x) (hst : t ∈ 𝓝[s] x) :
HasFDerivWithinAt f f' s x :=
h.mono <| nhdsWithin_le_iff.mpr hst
@[deprecated (since := "2024-10-31")]
alias HasFDerivWithinAt.mono_of_mem := HasFDerivWithinAt.mono_of_mem_nhdsWithin
nonrec theorem HasFDerivWithinAt.mono (h : HasFDerivWithinAt f f' t x) (hst : s ⊆ t) :
HasFDerivWithinAt f f' s x :=
h.mono <| nhdsWithin_mono _ hst
theorem HasFDerivAt.hasFDerivAtFilter (h : HasFDerivAt f f' x) (hL : L ≤ 𝓝 x) :
HasFDerivAtFilter f f' x L :=
h.mono hL
@[fun_prop]
theorem HasFDerivAt.hasFDerivWithinAt (h : HasFDerivAt f f' x) : HasFDerivWithinAt f f' s x :=
h.hasFDerivAtFilter inf_le_left
@[fun_prop]
theorem HasFDerivWithinAt.differentiableWithinAt (h : HasFDerivWithinAt f f' s x) :
DifferentiableWithinAt 𝕜 f s x :=
⟨f', h⟩
@[fun_prop]
theorem HasFDerivAt.differentiableAt (h : HasFDerivAt f f' x) : DifferentiableAt 𝕜 f x :=
⟨f', h⟩
@[simp]
theorem hasFDerivWithinAt_univ : HasFDerivWithinAt f f' univ x ↔ HasFDerivAt f f' x := by
simp only [HasFDerivWithinAt, nhdsWithin_univ, HasFDerivAt]
alias ⟨HasFDerivWithinAt.hasFDerivAt_of_univ, _⟩ := hasFDerivWithinAt_univ
theorem differentiableWithinAt_univ :
DifferentiableWithinAt 𝕜 f univ x ↔ DifferentiableAt 𝕜 f x := by
simp only [DifferentiableWithinAt, hasFDerivWithinAt_univ, DifferentiableAt]
theorem fderiv_zero_of_not_differentiableAt (h : ¬DifferentiableAt 𝕜 f x) : fderiv 𝕜 f x = 0 := by
rw [fderiv, fderivWithin_zero_of_not_differentiableWithinAt]
rwa [differentiableWithinAt_univ]
theorem hasFDerivWithinAt_of_mem_nhds (h : s ∈ 𝓝 x) :
HasFDerivWithinAt f f' s x ↔ HasFDerivAt f f' x := by
rw [HasFDerivAt, HasFDerivWithinAt, nhdsWithin_eq_nhds.mpr h]
lemma hasFDerivWithinAt_of_isOpen (h : IsOpen s) (hx : x ∈ s) :
HasFDerivWithinAt f f' s x ↔ HasFDerivAt f f' x :=
hasFDerivWithinAt_of_mem_nhds (h.mem_nhds hx)
@[simp]
theorem hasFDerivWithinAt_insert {y : E} :
HasFDerivWithinAt f f' (insert y s) x ↔ HasFDerivWithinAt f f' s x := by
rcases eq_or_ne x y with (rfl | h)
· simp_rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleOTVS]
apply isLittleOTVS_insert
simp only [sub_self, map_zero]
refine ⟨fun h => h.mono <| subset_insert y s, fun hf => hf.mono_of_mem_nhdsWithin ?_⟩
simp_rw [nhdsWithin_insert_of_ne h, self_mem_nhdsWithin]
alias ⟨HasFDerivWithinAt.of_insert, HasFDerivWithinAt.insert'⟩ := hasFDerivWithinAt_insert
protected theorem HasFDerivWithinAt.insert (h : HasFDerivWithinAt g g' s x) :
HasFDerivWithinAt g g' (insert x s) x :=
h.insert'
@[simp]
theorem hasFDerivWithinAt_diff_singleton (y : E) :
HasFDerivWithinAt f f' (s \ {y}) x ↔ HasFDerivWithinAt f f' s x := by
rw [← hasFDerivWithinAt_insert, insert_diff_singleton, hasFDerivWithinAt_insert]
@[simp]
protected theorem HasFDerivWithinAt.empty : HasFDerivWithinAt f f' ∅ x := by
simp [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleOTVS]
@[simp]
protected theorem DifferentiableWithinAt.empty : DifferentiableWithinAt 𝕜 f ∅ x :=
⟨0, .empty⟩
theorem HasFDerivWithinAt.of_finite (h : s.Finite) : HasFDerivWithinAt f f' s x := by
induction s, h using Set.Finite.induction_on with
| empty => exact .empty
| insert _ _ ih => exact ih.insert'
theorem DifferentiableWithinAt.of_finite (h : s.Finite) : DifferentiableWithinAt 𝕜 f s x :=
⟨0, .of_finite h⟩
@[simp]
protected theorem HasFDerivWithinAt.singleton {y} : HasFDerivWithinAt f f' {x} y :=
.of_finite <| finite_singleton _
@[simp]
protected theorem DifferentiableWithinAt.singleton {y} : DifferentiableWithinAt 𝕜 f {x} y :=
⟨0, .singleton⟩
theorem HasFDerivWithinAt.of_subsingleton (h : s.Subsingleton) : HasFDerivWithinAt f f' s x :=
.of_finite h.finite
theorem DifferentiableWithinAt.of_subsingleton (h : s.Subsingleton) :
DifferentiableWithinAt 𝕜 f s x :=
.of_finite h.finite
theorem HasStrictFDerivAt.isBigO_sub (hf : HasStrictFDerivAt f f' x) :
(fun p : E × E => f p.1 - f p.2) =O[𝓝 (x, x)] fun p : E × E => p.1 - p.2 :=
hf.isLittleO.isBigO.congr_of_sub.2 (f'.isBigO_comp _ _)
theorem HasFDerivAtFilter.isBigO_sub (h : HasFDerivAtFilter f f' x L) :
(fun x' => f x' - f x) =O[L] fun x' => x' - x :=
h.isLittleO.isBigO.congr_of_sub.2 (f'.isBigO_sub _ _)
@[fun_prop]
protected theorem HasStrictFDerivAt.hasFDerivAt (hf : HasStrictFDerivAt f f' x) :
HasFDerivAt f f' x :=
.of_isLittleOTVS <| by
simpa only using hf.isLittleOTVS.comp_tendsto (tendsto_id.prodMk_nhds tendsto_const_nhds)
protected theorem HasStrictFDerivAt.differentiableAt (hf : HasStrictFDerivAt f f' x) :
DifferentiableAt 𝕜 f x :=
hf.hasFDerivAt.differentiableAt
/-- If `f` is strictly differentiable at `x` with derivative `f'` and `K > ‖f'‖₊`, then `f` is
`K`-Lipschitz in a neighborhood of `x`. -/
theorem HasStrictFDerivAt.exists_lipschitzOnWith_of_nnnorm_lt (hf : HasStrictFDerivAt f f' x)
(K : ℝ≥0) (hK : ‖f'‖₊ < K) : ∃ s ∈ 𝓝 x, LipschitzOnWith K f s := by
have := hf.isLittleO.add_isBigOWith (f'.isBigOWith_comp _ _) hK
simp only [sub_add_cancel, IsBigOWith] at this
rcases exists_nhds_square this with ⟨U, Uo, xU, hU⟩
exact
⟨U, Uo.mem_nhds xU, lipschitzOnWith_iff_norm_sub_le.2 fun x hx y hy => hU (mk_mem_prod hx hy)⟩
/-- If `f` is strictly differentiable at `x` with derivative `f'`, then `f` is Lipschitz in a
neighborhood of `x`. See also `HasStrictFDerivAt.exists_lipschitzOnWith_of_nnnorm_lt` for a
more precise statement. -/
theorem HasStrictFDerivAt.exists_lipschitzOnWith (hf : HasStrictFDerivAt f f' x) :
∃ K, ∃ s ∈ 𝓝 x, LipschitzOnWith K f s :=
(exists_gt _).imp hf.exists_lipschitzOnWith_of_nnnorm_lt
/-- Directional derivative agrees with `HasFDeriv`. -/
theorem HasFDerivAt.lim (hf : HasFDerivAt f f' x) (v : E) {α : Type*} {c : α → 𝕜} {l : Filter α}
(hc : Tendsto (fun n => ‖c n‖) l atTop) :
Tendsto (fun n => c n • (f (x + (c n)⁻¹ • v) - f x)) l (𝓝 (f' v)) := by
refine (hasFDerivWithinAt_univ.2 hf).lim _ univ_mem hc ?_
intro U hU
refine (eventually_ne_of_tendsto_norm_atTop hc (0 : 𝕜)).mono fun y hy => ?_
convert mem_of_mem_nhds hU
dsimp only
rw [← mul_smul, mul_inv_cancel₀ hy, one_smul]
theorem HasFDerivAt.unique (h₀ : HasFDerivAt f f₀' x) (h₁ : HasFDerivAt f f₁' x) : f₀' = f₁' := by
rw [← hasFDerivWithinAt_univ] at h₀ h₁
exact uniqueDiffWithinAt_univ.eq h₀ h₁
theorem hasFDerivWithinAt_inter' (h : t ∈ 𝓝[s] x) :
HasFDerivWithinAt f f' (s ∩ t) x ↔ HasFDerivWithinAt f f' s x := by
simp [HasFDerivWithinAt, nhdsWithin_restrict'' s h]
theorem hasFDerivWithinAt_inter (h : t ∈ 𝓝 x) :
HasFDerivWithinAt f f' (s ∩ t) x ↔ HasFDerivWithinAt f f' s x := by
simp [HasFDerivWithinAt, nhdsWithin_restrict' s h]
theorem HasFDerivWithinAt.union (hs : HasFDerivWithinAt f f' s x)
(ht : HasFDerivWithinAt f f' t x) : HasFDerivWithinAt f f' (s ∪ t) x := by
simp only [HasFDerivWithinAt, nhdsWithin_union]
exact .of_isLittleOTVS <| hs.isLittleOTVS.sup ht.isLittleOTVS
theorem HasFDerivWithinAt.hasFDerivAt (h : HasFDerivWithinAt f f' s x) (hs : s ∈ 𝓝 x) :
HasFDerivAt f f' x := by
rwa [← univ_inter s, hasFDerivWithinAt_inter hs, hasFDerivWithinAt_univ] at h
theorem DifferentiableWithinAt.differentiableAt (h : DifferentiableWithinAt 𝕜 f s x)
| (hs : s ∈ 𝓝 x) : DifferentiableAt 𝕜 f x :=
h.imp fun _ hf' => hf'.hasFDerivAt hs
/-- If `x` is isolated in `s`, then `f` has any derivative at `x` within `s`,
| Mathlib/Analysis/Calculus/FDeriv/Basic.lean | 513 | 516 |
/-
Copyright (c) 2020 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Shing Tak Lam, Mario Carneiro
-/
import Mathlib.Algebra.BigOperators.Intervals
import Mathlib.Algebra.BigOperators.Ring.List
import Mathlib.Data.Int.ModEq
import Mathlib.Data.Nat.Bits
import Mathlib.Data.Nat.Log
import Mathlib.Data.List.Palindrome
import Mathlib.Tactic.IntervalCases
import Mathlib.Tactic.Linarith
import Mathlib.Tactic.Ring
/-!
# Digits of a natural number
This provides a basic API for extracting the digits of a natural number in a given base,
and reconstructing numbers from their digits.
We also prove some divisibility tests based on digits, in particular completing
Theorem #85 from https://www.cs.ru.nl/~freek/100/.
Also included is a bound on the length of `Nat.toDigits` from core.
## TODO
A basic `norm_digits` tactic for proving goals of the form `Nat.digits a b = l` where `a` and `b`
are numerals is not yet ported.
-/
namespace Nat
variable {n : ℕ}
/-- (Impl.) An auxiliary definition for `digits`, to help get the desired definitional unfolding. -/
def digitsAux0 : ℕ → List ℕ
| 0 => []
| n + 1 => [n + 1]
/-- (Impl.) An auxiliary definition for `digits`, to help get the desired definitional unfolding. -/
def digitsAux1 (n : ℕ) : List ℕ :=
List.replicate n 1
/-- (Impl.) An auxiliary definition for `digits`, to help get the desired definitional unfolding. -/
def digitsAux (b : ℕ) (h : 2 ≤ b) : ℕ → List ℕ
| 0 => []
| n + 1 =>
((n + 1) % b) :: digitsAux b h ((n + 1) / b)
decreasing_by exact Nat.div_lt_self (Nat.succ_pos _) h
@[simp]
theorem digitsAux_zero (b : ℕ) (h : 2 ≤ b) : digitsAux b h 0 = [] := by rw [digitsAux]
theorem digitsAux_def (b : ℕ) (h : 2 ≤ b) (n : ℕ) (w : 0 < n) :
digitsAux b h n = (n % b) :: digitsAux b h (n / b) := by
cases n
· cases w
· rw [digitsAux]
/-- `digits b n` gives the digits, in little-endian order,
of a natural number `n` in a specified base `b`.
In any base, we have `ofDigits b L = L.foldr (fun x y ↦ x + b * y) 0`.
* For any `2 ≤ b`, we have `l < b` for any `l ∈ digits b n`,
and the last digit is not zero.
This uniquely specifies the behaviour of `digits b`.
* For `b = 1`, we define `digits 1 n = List.replicate n 1`.
* For `b = 0`, we define `digits 0 n = [n]`, except `digits 0 0 = []`.
Note this differs from the existing `Nat.toDigits` in core, which is used for printing numerals.
In particular, `Nat.toDigits b 0 = ['0']`, while `digits b 0 = []`.
-/
def digits : ℕ → ℕ → List ℕ
| 0 => digitsAux0
| 1 => digitsAux1
| b + 2 => digitsAux (b + 2) (by norm_num)
@[simp]
theorem digits_zero (b : ℕ) : digits b 0 = [] := by
rcases b with (_ | ⟨_ | ⟨_⟩⟩) <;> simp [digits, digitsAux0, digitsAux1]
theorem digits_zero_zero : digits 0 0 = [] :=
rfl
@[simp]
theorem digits_zero_succ (n : ℕ) : digits 0 n.succ = [n + 1] :=
rfl
theorem digits_zero_succ' : ∀ {n : ℕ}, n ≠ 0 → digits 0 n = [n]
| 0, h => (h rfl).elim
| _ + 1, _ => rfl
@[simp]
theorem digits_one (n : ℕ) : digits 1 n = List.replicate n 1 :=
rfl
-- no `@[simp]`: dsimp can prove this
theorem digits_one_succ (n : ℕ) : digits 1 (n + 1) = 1 :: digits 1 n :=
rfl
theorem digits_add_two_add_one (b n : ℕ) :
digits (b + 2) (n + 1) = ((n + 1) % (b + 2)) :: digits (b + 2) ((n + 1) / (b + 2)) := by
simp [digits, digitsAux_def]
@[simp]
lemma digits_of_two_le_of_pos {b : ℕ} (hb : 2 ≤ b) (hn : 0 < n) :
Nat.digits b n = n % b :: Nat.digits b (n / b) := by
rw [Nat.eq_add_of_sub_eq hb rfl, Nat.eq_add_of_sub_eq hn rfl, Nat.digits_add_two_add_one]
theorem digits_def' :
∀ {b : ℕ} (_ : 1 < b) {n : ℕ} (_ : 0 < n), digits b n = (n % b) :: digits b (n / b)
| 0, h => absurd h (by decide)
| 1, h => absurd h (by decide)
| b + 2, _ => digitsAux_def _ (by simp) _
@[simp]
theorem digits_of_lt (b x : ℕ) (hx : x ≠ 0) (hxb : x < b) : digits b x = [x] := by
rcases exists_eq_succ_of_ne_zero hx with ⟨x, rfl⟩
rcases Nat.exists_eq_add_of_le' ((Nat.le_add_left 1 x).trans_lt hxb) with ⟨b, rfl⟩
rw [digits_add_two_add_one, div_eq_of_lt hxb, digits_zero, mod_eq_of_lt hxb]
theorem digits_add (b : ℕ) (h : 1 < b) (x y : ℕ) (hxb : x < b) (hxy : x ≠ 0 ∨ y ≠ 0) :
digits b (x + b * y) = x :: digits b y := by
rcases Nat.exists_eq_add_of_le' h with ⟨b, rfl : _ = _ + 2⟩
cases y
· simp [hxb, hxy.resolve_right (absurd rfl)]
dsimp [digits]
rw [digitsAux_def]
· congr
· simp [Nat.add_mod, mod_eq_of_lt hxb]
· simp [add_mul_div_left, div_eq_of_lt hxb]
· apply Nat.succ_pos
-- If we had a function converting a list into a polynomial,
-- and appropriate lemmas about that function,
-- we could rewrite this in terms of that.
/-- `ofDigits b L` takes a list `L` of natural numbers, and interprets them
as a number in semiring, as the little-endian digits in base `b`.
-/
def ofDigits {α : Type*} [Semiring α] (b : α) : List ℕ → α
| [] => 0
| h :: t => h + b * ofDigits b t
theorem ofDigits_eq_foldr {α : Type*} [Semiring α] (b : α) (L : List ℕ) :
ofDigits b L = List.foldr (fun x y => ↑x + b * y) 0 L := by
induction' L with d L ih
· rfl
· dsimp [ofDigits]
rw [ih]
theorem ofDigits_eq_sum_mapIdx_aux (b : ℕ) (l : List ℕ) :
(l.zipWith ((fun a i : ℕ => a * b ^ (i + 1))) (List.range l.length)).sum =
b * (l.zipWith (fun a i => a * b ^ i) (List.range l.length)).sum := by
suffices
l.zipWith (fun a i : ℕ => a * b ^ (i + 1)) (List.range l.length) =
l.zipWith (fun a i=> b * (a * b ^ i)) (List.range l.length)
by simp [this]
congr; ext; simp [pow_succ]; ring
theorem ofDigits_eq_sum_mapIdx (b : ℕ) (L : List ℕ) :
ofDigits b L = (L.mapIdx fun i a => a * b ^ i).sum := by
rw [List.mapIdx_eq_zipIdx_map, List.zipIdx_eq_zip_range', List.map_zip_eq_zipWith,
ofDigits_eq_foldr, ← List.range_eq_range']
induction' L with hd tl hl
· simp
· simpa [List.range_succ_eq_map, List.zipWith_map_right, ofDigits_eq_sum_mapIdx_aux] using
Or.inl hl
@[simp]
theorem ofDigits_nil {b : ℕ} : ofDigits b [] = 0 := rfl
@[simp]
theorem ofDigits_singleton {b n : ℕ} : ofDigits b [n] = n := by simp [ofDigits]
@[simp]
theorem ofDigits_one_cons {α : Type*} [Semiring α] (h : ℕ) (L : List ℕ) :
ofDigits (1 : α) (h :: L) = h + ofDigits 1 L := by simp [ofDigits]
theorem ofDigits_cons {b hd} {tl : List ℕ} :
ofDigits b (hd :: tl) = hd + b * ofDigits b tl := rfl
theorem ofDigits_append {b : ℕ} {l1 l2 : List ℕ} :
ofDigits b (l1 ++ l2) = ofDigits b l1 + b ^ l1.length * ofDigits b l2 := by
induction' l1 with hd tl IH
· simp [ofDigits]
· rw [ofDigits, List.cons_append, ofDigits, IH, List.length_cons, pow_succ']
ring
@[norm_cast]
theorem coe_ofDigits (α : Type*) [Semiring α] (b : ℕ) (L : List ℕ) :
((ofDigits b L : ℕ) : α) = ofDigits (b : α) L := by
induction' L with d L ih
· simp [ofDigits]
· dsimp [ofDigits]; push_cast; rw [ih]
@[norm_cast]
theorem coe_int_ofDigits (b : ℕ) (L : List ℕ) : ((ofDigits b L : ℕ) : ℤ) = ofDigits (b : ℤ) L := by
induction' L with d L _
· rfl
· dsimp [ofDigits]; push_cast; simp only
theorem digits_zero_of_eq_zero {b : ℕ} (h : b ≠ 0) :
∀ {L : List ℕ} (_ : ofDigits b L = 0), ∀ l ∈ L, l = 0
| _ :: _, h0, _, List.Mem.head .. => Nat.eq_zero_of_add_eq_zero_right h0
| _ :: _, h0, _, List.Mem.tail _ hL =>
digits_zero_of_eq_zero h (mul_right_injective₀ h (Nat.eq_zero_of_add_eq_zero_left h0)) _ hL
theorem digits_ofDigits (b : ℕ) (h : 1 < b) (L : List ℕ) (w₁ : ∀ l ∈ L, l < b)
(w₂ : ∀ h : L ≠ [], L.getLast h ≠ 0) : digits b (ofDigits b L) = L := by
induction' L with d L ih
· dsimp [ofDigits]
simp
· dsimp [ofDigits]
replace w₂ := w₂ (by simp)
rw [digits_add b h]
· rw [ih]
· intro l m
apply w₁
exact List.mem_cons_of_mem _ m
· intro h
rw [List.getLast_cons h] at w₂
convert w₂
· exact w₁ d List.mem_cons_self
· by_cases h' : L = []
· rcases h' with rfl
left
simpa using w₂
· right
contrapose! w₂
refine digits_zero_of_eq_zero h.ne_bot w₂ _ ?_
rw [List.getLast_cons h']
exact List.getLast_mem h'
theorem ofDigits_digits (b n : ℕ) : ofDigits b (digits b n) = n := by
rcases b with - | b
· rcases n with - | n
· rfl
· simp
· rcases b with - | b
· induction' n with n ih
· rfl
· rw [Nat.zero_add] at ih ⊢
simp only [ih, add_comm 1, ofDigits_one_cons, Nat.cast_id, digits_one_succ]
· induction n using Nat.strongRecOn with | ind n h => ?_
cases n
· rw [digits_zero]
rfl
· simp only [Nat.succ_eq_add_one, digits_add_two_add_one]
dsimp [ofDigits]
rw [h _ (Nat.div_lt_self' _ b)]
rw [Nat.mod_add_div]
theorem ofDigits_one (L : List ℕ) : ofDigits 1 L = L.sum := by
induction L with
| nil => rfl
| cons _ _ ih => simp [ofDigits, List.sum_cons, ih]
/-!
### Properties
This section contains various lemmas of properties relating to `digits` and `ofDigits`.
-/
theorem digits_eq_nil_iff_eq_zero {b n : ℕ} : digits b n = [] ↔ n = 0 := by
constructor
· intro h
have : ofDigits b (digits b n) = ofDigits b [] := by rw [h]
convert this
rw [ofDigits_digits]
· rintro rfl
simp
theorem digits_ne_nil_iff_ne_zero {b n : ℕ} : digits b n ≠ [] ↔ n ≠ 0 :=
not_congr digits_eq_nil_iff_eq_zero
theorem digits_eq_cons_digits_div {b n : ℕ} (h : 1 < b) (w : n ≠ 0) :
digits b n = (n % b) :: digits b (n / b) := by
rcases b with (_ | _ | b)
· rw [digits_zero_succ' w, Nat.mod_zero, Nat.div_zero, Nat.digits_zero_zero]
· norm_num at h
rcases n with (_ | n)
· norm_num at w
· simp only [digits_add_two_add_one, ne_eq]
theorem digits_getLast {b : ℕ} (m : ℕ) (h : 1 < b) (p q) :
(digits b m).getLast p = (digits b (m / b)).getLast q := by
by_cases hm : m = 0
· simp [hm]
simp only [digits_eq_cons_digits_div h hm]
rw [List.getLast_cons]
theorem digits.injective (b : ℕ) : Function.Injective b.digits :=
Function.LeftInverse.injective (ofDigits_digits b)
@[simp]
theorem digits_inj_iff {b n m : ℕ} : b.digits n = b.digits m ↔ n = m :=
(digits.injective b).eq_iff
theorem digits_len (b n : ℕ) (hb : 1 < b) (hn : n ≠ 0) : (b.digits n).length = b.log n + 1 := by
induction' n using Nat.strong_induction_on with n IH
rw [digits_eq_cons_digits_div hb hn, List.length]
by_cases h : n / b = 0
· simp [IH, h]
aesop
· have : n / b < n := div_lt_self (Nat.pos_of_ne_zero hn) hb
rw [IH _ this h, log_div_base, tsub_add_cancel_of_le]
refine Nat.succ_le_of_lt (log_pos hb ?_)
contrapose! h
exact div_eq_of_lt h
theorem getLast_digit_ne_zero (b : ℕ) {m : ℕ} (hm : m ≠ 0) :
(digits b m).getLast (digits_ne_nil_iff_ne_zero.mpr hm) ≠ 0 := by
rcases b with (_ | _ | b)
· cases m
· cases hm rfl
· simp
· cases m
· cases hm rfl
rename ℕ => m
simp only [zero_add, digits_one, List.getLast_replicate_succ m 1]
exact Nat.one_ne_zero
revert hm
induction m using Nat.strongRecOn with | ind n IH => ?_
intro hn
by_cases hnb : n < b + 2
· simpa only [digits_of_lt (b + 2) n hn hnb]
· rw [digits_getLast n (le_add_left 2 b)]
refine IH _ (Nat.div_lt_self hn.bot_lt (one_lt_succ_succ b)) ?_
rw [← pos_iff_ne_zero]
exact Nat.div_pos (le_of_not_lt hnb) (zero_lt_succ (succ b))
theorem mul_ofDigits (n : ℕ) {b : ℕ} {l : List ℕ} :
n * ofDigits b l = ofDigits b (l.map (n * ·)) := by
induction l with
| nil => rfl
| cons hd tl ih =>
rw [List.map_cons, ofDigits_cons, ofDigits_cons, ← ih]
ring
lemma ofDigits_inj_of_len_eq {b : ℕ} (hb : 1 < b) {L1 L2 : List ℕ}
(len : L1.length = L2.length) (w1 : ∀ l ∈ L1, l < b) (w2 : ∀ l ∈ L2, l < b)
(h : ofDigits b L1 = ofDigits b L2) : L1 = L2 := by
induction' L1 with D L ih generalizing L2
· simp only [List.length_nil] at len
exact (List.length_eq_zero_iff.mp len.symm).symm
obtain ⟨d, l, rfl⟩ := List.exists_cons_of_length_eq_add_one len.symm
simp only [List.length_cons, add_left_inj] at len
simp only [ofDigits_cons] at h
have eqd : D = d := by
have H : (D + b * ofDigits b L) % b = (d + b * ofDigits b l) % b := by rw [h]
simpa [mod_eq_of_lt (w2 d List.mem_cons_self),
mod_eq_of_lt (w1 D List.mem_cons_self)] using H
simp only [eqd, add_right_inj, mul_left_cancel_iff_of_pos (zero_lt_of_lt hb)] at h
have := ih len (fun a ha ↦ w1 a <| List.mem_cons_of_mem D ha)
(fun a ha ↦ w2 a <| List.mem_cons_of_mem d ha) h
rw [eqd, this]
/-- The addition of ofDigits of two lists is equal to ofDigits of digit-wise addition of them -/
theorem ofDigits_add_ofDigits_eq_ofDigits_zipWith_of_length_eq {b : ℕ} {l1 l2 : List ℕ}
(h : l1.length = l2.length) :
ofDigits b l1 + ofDigits b l2 = ofDigits b (l1.zipWith (· + ·) l2) := by
induction l1 generalizing l2 with
| nil => simp_all [eq_comm, List.length_eq_zero_iff, ofDigits]
| cons hd₁ tl₁ ih₁ =>
induction l2 generalizing tl₁ with
| nil => simp_all
| cons hd₂ tl₂ ih₂ =>
simp_all only [List.length_cons, succ_eq_add_one, ofDigits_cons, add_left_inj,
eq_comm, List.zipWith_cons_cons, add_eq]
rw [← ih₁ h.symm, mul_add]
ac_rfl
/-- The digits in the base b+2 expansion of n are all less than b+2 -/
theorem digits_lt_base' {b m : ℕ} : ∀ {d}, d ∈ digits (b + 2) m → d < b + 2 := by
induction m using Nat.strongRecOn with | ind n IH => ?_
intro d hd
rcases n with - | n
· rw [digits_zero] at hd
cases hd
-- base b+2 expansion of 0 has no digits
rw [digits_add_two_add_one] at hd
cases hd
· exact n.succ.mod_lt (by linarith)
· apply IH ((n + 1) / (b + 2))
· apply Nat.div_lt_self <;> omega
· assumption
/-- The digits in the base b expansion of n are all less than b, if b ≥ 2 -/
theorem digits_lt_base {b m d : ℕ} (hb : 1 < b) (hd : d ∈ digits b m) : d < b := by
rcases b with (_ | _ | b) <;> try simp_all
exact digits_lt_base' hd
/-- an n-digit number in base b + 2 is less than (b + 2)^n -/
theorem ofDigits_lt_base_pow_length' {b : ℕ} {l : List ℕ} (hl : ∀ x ∈ l, x < b + 2) :
ofDigits (b + 2) l < (b + 2) ^ l.length := by
induction' l with hd tl IH
· simp [ofDigits]
· rw [ofDigits, List.length_cons, pow_succ]
have : (ofDigits (b + 2) tl + 1) * (b + 2) ≤ (b + 2) ^ tl.length * (b + 2) :=
| mul_le_mul (IH fun x hx => hl _ (List.mem_cons_of_mem _ hx)) (by rfl) (by simp only [zero_le])
(Nat.zero_le _)
suffices ↑hd < b + 2 by linarith
exact hl hd List.mem_cons_self
/-- an n-digit number in base b is less than b^n if b > 1 -/
theorem ofDigits_lt_base_pow_length {b : ℕ} {l : List ℕ} (hb : 1 < b) (hl : ∀ x ∈ l, x < b) :
ofDigits b l < b ^ l.length := by
rcases b with (_ | _ | b) <;> try simp_all
exact ofDigits_lt_base_pow_length' hl
/-- Any number m is less than (b+2)^(number of digits in the base b + 2 representation of m) -/
theorem lt_base_pow_length_digits' {b m : ℕ} : m < (b + 2) ^ (digits (b + 2) m).length := by
convert @ofDigits_lt_base_pow_length' b (digits (b + 2) m) fun _ => digits_lt_base'
rw [ofDigits_digits (b + 2) m]
| Mathlib/Data/Nat/Digits.lean | 403 | 417 |
/-
Copyright (c) 2024 Joël Riou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joël Riou
-/
import Mathlib.CategoryTheory.CatCommSq
import Mathlib.CategoryTheory.GuitartExact.Basic
/-!
# Vertical composition of Guitart exact squares
In this file, we show that the vertical composition of Guitart exact squares
is Guitart exact.
-/
namespace CategoryTheory
open Category
variable {C₁ C₂ C₃ D₁ D₂ D₃ : Type*} [Category C₁] [Category C₂] [Category C₃]
[Category D₁] [Category D₂] [Category D₃]
namespace TwoSquare
section WhiskerVertical
variable {T : C₁ ⥤ D₁} {L : C₁ ⥤ C₂} {R : D₁ ⥤ D₂} {B : C₂ ⥤ D₂} (w : TwoSquare T L R B)
{L' : C₁ ⥤ C₂} {R' : D₁ ⥤ D₂}
/-- Given `w : TwoSquare T L R B`, one may obtain a 2-square `TwoSquare T L' R' B` if we
provide natural transformations `α : L ⟶ L'` and `β : R' ⟶ R`. -/
@[simps!]
def whiskerVertical (α : L ⟶ L') (β : R' ⟶ R) :
TwoSquare T L' R' B :=
(w.whiskerLeft α).whiskerRight β
namespace GuitartExact
/-- A 2-square stays Guitart exact if we replace the left and right functors
by isomorphic functors. See also `whiskerVertical_iff`. -/
lemma whiskerVertical [w.GuitartExact] (α : L ≅ L') (β : R ≅ R') :
(w.whiskerVertical α.hom β.inv).GuitartExact := by
rw [guitartExact_iff_initial]
intro X₂
let e : structuredArrowDownwards (w.whiskerVertical α.hom β.inv) X₂ ≅
w.structuredArrowDownwards X₂ ⋙ (StructuredArrow.mapIso (β.app X₂) ).functor :=
NatIso.ofComponents (fun f => StructuredArrow.isoMk (α.symm.app f.right) (by
dsimp
simp only [NatTrans.naturality_assoc, assoc, NatIso.cancel_natIso_inv_left, ← B.map_comp,
Iso.hom_inv_id_app, B.map_id, comp_id]))
rw [Functor.initial_natIso_iff e]
infer_instance
/-- A 2-square is Guitart exact iff it is so after replacing the left and right functors by
isomorphic functors. -/
@[simp]
lemma whiskerVertical_iff (α : L ≅ L') (β : R ≅ R') :
(w.whiskerVertical α.hom β.inv).GuitartExact ↔ w.GuitartExact := by
constructor
· intro h
have : w = (w.whiskerVertical α.hom β.inv).whiskerVertical α.inv β.hom := by
ext X₁
simp only [Functor.comp_obj, whiskerVertical_app, assoc, Iso.hom_inv_id_app_assoc,
← B.map_comp, Iso.hom_inv_id_app, B.map_id, comp_id]
rw [this]
exact whiskerVertical (w.whiskerVertical α.hom β.inv) α.symm β.symm
· intro h
exact whiskerVertical w α β
instance [w.GuitartExact] (α : L ⟶ L') (β : R' ⟶ R)
[IsIso α] [IsIso β] : (w.whiskerVertical α β).GuitartExact :=
whiskerVertical w (asIso α) (asIso β).symm
end GuitartExact
end WhiskerVertical
section VerticalComposition
variable {H₁ : C₁ ⥤ D₁} {L₁ : C₁ ⥤ C₂} {R₁ : D₁ ⥤ D₂} {H₂ : C₂ ⥤ D₂}
(w : TwoSquare H₁ L₁ R₁ H₂)
{L₂ : C₂ ⥤ C₃} {R₂ : D₂ ⥤ D₃} {H₃ : C₃ ⥤ D₃}
(w' : TwoSquare H₂ L₂ R₂ H₃)
/-- The canonical isomorphism between
`w.structuredArrowDownwards Y₁ ⋙ w'.structuredArrowDownwards (R₁.obj Y₁)` and
`(w ≫ᵥ w').structuredArrowDownwards Y₁.` -/
def structuredArrowDownwardsComp (Y₁ : D₁) :
w.structuredArrowDownwards Y₁ ⋙ w'.structuredArrowDownwards (R₁.obj Y₁) ≅
(w ≫ᵥ w').structuredArrowDownwards Y₁ :=
NatIso.ofComponents (fun _ => StructuredArrow.isoMk (Iso.refl _))
/-- The vertical composition of 2-squares. (Variant where we allow the replacement of
the vertical compositions by isomorphic functors.) -/
@[simps!]
def vComp' {L₁₂ : C₁ ⥤ C₃} {R₁₂ : D₁ ⥤ D₃} (eL : L₁ ⋙ L₂ ≅ L₁₂)
(eR : R₁ ⋙ R₂ ≅ R₁₂) : TwoSquare H₁ L₁₂ R₁₂ H₃ :=
(w ≫ᵥ w').whiskerVertical eL.hom eR.inv
namespace GuitartExact
instance vComp [hw : w.GuitartExact] [hw' : w'.GuitartExact] :
(w ≫ᵥ w').GuitartExact := by
simp only [TwoSquare.guitartExact_iff_initial]
intro Y₁
rw [← Functor.initial_natIso_iff (structuredArrowDownwardsComp w w' Y₁)]
infer_instance
instance vComp' [GuitartExact w] [GuitartExact w'] {L₁₂ : C₁ ⥤ C₃}
{R₁₂ : D₁ ⥤ D₃} (eL : L₁ ⋙ L₂ ≅ L₁₂)
(eR : R₁ ⋙ R₂ ≅ R₁₂) : (w.vComp' w' eL eR).GuitartExact := by
dsimp only [TwoSquare.vComp']
infer_instance
lemma vComp_iff_of_equivalences (eL : C₂ ≌ C₃) (eR : D₂ ≌ D₃)
(w' : H₂ ⋙ eR.functor ≅ eL.functor ⋙ H₃) :
(w ≫ᵥ w'.hom).GuitartExact ↔ w.GuitartExact := by
constructor
· intro hww'
letI : CatCommSq H₂ eL.functor eR.functor H₃ := ⟨w'⟩
have hw' : CatCommSq.iso H₂ eL.functor eR.functor H₃ = w' := rfl
letI : CatCommSq H₃ eL.inverse eR.inverse H₂ := CatCommSq.vInvEquiv _ _ _ _ inferInstance
let w'' := CatCommSq.iso H₃ eL.inverse eR.inverse H₂
let α : (L₁ ⋙ eL.functor) ⋙ eL.inverse ≅ L₁ :=
Functor.associator _ _ _ ≪≫ isoWhiskerLeft L₁ eL.unitIso.symm ≪≫ L₁.rightUnitor
let β : (R₁ ⋙ eR.functor) ⋙ eR.inverse ≅ R₁ :=
Functor.associator _ _ _ ≪≫ isoWhiskerLeft R₁ eR.unitIso.symm ≪≫ R₁.rightUnitor
have : w = (w ≫ᵥ w'.hom).vComp' w''.hom α β := by
ext X₁
dsimp
simp? [w'', α, β] says
simp only [vComp'_app, Functor.comp_obj, Iso.trans_inv, isoWhiskerLeft_inv, Iso.symm_inv,
assoc, NatTrans.comp_app, Functor.id_obj, Functor.rightUnitor_inv_app,
CategoryTheory.whiskerLeft_app, Functor.associator_inv_app, comp_id, id_comp, vComp_app,
Functor.map_comp, Equivalence.inv_fun_map, CatCommSq.vInv_iso'_hom_app, Iso.trans_hom,
isoWhiskerLeft_hom, Iso.symm_hom, Functor.associator_hom_app, Functor.rightUnitor_hom_app,
Iso.hom_inv_id_app_assoc, w'', α, β, this]
simp only [hw', ← eR.inverse.map_comp_assoc, w'', this, β, α]
rw [Equivalence.counitInv_app_functor, ← Functor.comp_map, ← NatTrans.naturality_assoc]
simp [← H₂.map_comp]
rw [this]
infer_instance
· intro
exact vComp w w'.hom
lemma vComp'_iff_of_equivalences (E : C₂ ≌ C₃) (E' : D₂ ≌ D₃)
(w' : H₂ ⋙ E'.functor ≅ E.functor ⋙ H₃) {L₁₂ : C₁ ⥤ C₃}
{R₁₂ : D₁ ⥤ D₃} (eL : L₁ ⋙ E.functor ≅ L₁₂)
(eR : R₁ ⋙ E'.functor ≅ R₁₂) :
(w.vComp' w'.hom eL eR).GuitartExact ↔ w.GuitartExact := by
rw [← vComp_iff_of_equivalences w E E' w', TwoSquare.vComp', whiskerVertical_iff]
end GuitartExact
| end VerticalComposition
end TwoSquare
end CategoryTheory
| Mathlib/CategoryTheory/GuitartExact/VerticalComposition.lean | 156 | 161 |
/-
Copyright (c) 2022 Andrew Yang. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Andrew Yang
-/
import Mathlib.Algebra.Polynomial.Module.AEval
/-!
# Polynomial module
In this file, we define the polynomial module for an `R`-module `M`, i.e. the `R[X]`-module `M[X]`.
This is defined as a type alias `PolynomialModule R M := ℕ →₀ M`, since there might be different
module structures on `ℕ →₀ M` of interest. See the docstring of `PolynomialModule` for details.
-/
universe u v
open Polynomial
/-- The `R[X]`-module `M[X]` for an `R`-module `M`.
This is isomorphic (as an `R`-module) to `M[X]` when `M` is a ring.
We require all the module instances `Module S (PolynomialModule R M)` to factor through `R` except
`Module R[X] (PolynomialModule R M)`.
In this constraint, we have the following instances for example :
- `R` acts on `PolynomialModule R R[X]`
- `R[X]` acts on `PolynomialModule R R[X]` as `R[Y]` acting on `R[X][Y]`
- `R` acts on `PolynomialModule R[X] R[X]`
- `R[X]` acts on `PolynomialModule R[X] R[X]` as `R[X]` acting on `R[X][Y]`
- `R[X][X]` acts on `PolynomialModule R[X] R[X]` as `R[X][Y]` acting on itself
This is also the reason why `R` is included in the alias, or else there will be two different
instances of `Module R[X] (PolynomialModule R[X])`.
See https://leanprover.zulipchat.com/#narrow/stream/144837-PR-reviews/topic/.2315065.20polynomial.20modules
for the full discussion.
-/
@[nolint unusedArguments]
def PolynomialModule (R M : Type*) [CommRing R] [AddCommGroup M] [Module R M] := ℕ →₀ M
variable (R M : Type*) [CommRing R] [AddCommGroup M] [Module R M] (I : Ideal R)
-- The `Inhabited, AddCommGroup` instances should be constructed by a deriving handler.
-- https://github.com/leanprover-community/mathlib4/issues/380
noncomputable instance : Inhabited (PolynomialModule R M) := Finsupp.instInhabited
noncomputable instance : AddCommGroup (PolynomialModule R M) := Finsupp.instAddCommGroup
variable {M}
variable {S : Type*} [CommSemiring S] [Algebra S R] [Module S M] [IsScalarTower S R M]
namespace PolynomialModule
/-- This is required to have the `IsScalarTower S R M` instance to avoid diamonds. -/
@[nolint unusedArguments]
noncomputable instance : Module S (PolynomialModule R M) :=
Finsupp.module ℕ M
instance instFunLike : FunLike (PolynomialModule R M) ℕ M :=
Finsupp.instFunLike
instance : CoeFun (PolynomialModule R M) fun _ => ℕ → M :=
inferInstanceAs <| CoeFun (_ →₀ _) _
theorem zero_apply (i : ℕ) : (0 : PolynomialModule R M) i = 0 :=
Finsupp.zero_apply
theorem add_apply (g₁ g₂ : PolynomialModule R M) (a : ℕ) : (g₁ + g₂) a = g₁ a + g₂ a :=
Finsupp.add_apply g₁ g₂ a
/-- The monomial `m * x ^ i`. This is defeq to `Finsupp.singleAddHom`, and is redefined here
so that it has the desired type signature. -/
noncomputable def single (i : ℕ) : M →+ PolynomialModule R M :=
Finsupp.singleAddHom i
theorem single_apply (i : ℕ) (m : M) (n : ℕ) : single R i m n = ite (i = n) m 0 :=
Finsupp.single_apply
/-- `PolynomialModule.single` as a linear map. -/
noncomputable def lsingle (i : ℕ) : M →ₗ[R] PolynomialModule R M :=
Finsupp.lsingle i
theorem lsingle_apply (i : ℕ) (m : M) (n : ℕ) : lsingle R i m n = ite (i = n) m 0 :=
Finsupp.single_apply
theorem single_smul (i : ℕ) (r : R) (m : M) : single R i (r • m) = r • single R i m :=
(lsingle R i).map_smul r m
variable {R}
@[elab_as_elim]
theorem induction_linear {motive : PolynomialModule R M → Prop} (f : PolynomialModule R M)
(zero : motive 0) (add : ∀ f g, motive f → motive g → motive (f + g))
(single : ∀ a b, motive (single R a b)) : motive f :=
Finsupp.induction_linear f zero add single
noncomputable instance polynomialModule : Module R[X] (PolynomialModule R M) :=
inferInstanceAs (Module R[X] (Module.AEval' (Finsupp.lmapDomain M R Nat.succ)))
lemma smul_def (f : R[X]) (m : PolynomialModule R M) :
f • m = aeval (Finsupp.lmapDomain M R Nat.succ) f m := by
rfl
instance (M : Type u) [AddCommGroup M] [Module R M] [Module S M] [IsScalarTower S R M] :
IsScalarTower S R (PolynomialModule R M) :=
Finsupp.isScalarTower _ _
instance isScalarTower' (M : Type u) [AddCommGroup M] [Module R M] [Module S M]
[IsScalarTower S R M] : IsScalarTower S R[X] (PolynomialModule R M) := by
haveI : IsScalarTower R R[X] (PolynomialModule R M) :=
inferInstanceAs <| IsScalarTower R R[X] <| Module.AEval' <| Finsupp.lmapDomain M R Nat.succ
constructor
intro x y z
rw [← @IsScalarTower.algebraMap_smul S R, ← @IsScalarTower.algebraMap_smul S R, smul_assoc]
@[simp]
theorem monomial_smul_single (i : ℕ) (r : R) (j : ℕ) (m : M) :
monomial i r • single R j m = single R (i + j) (r • m) := by
simp only [Module.End.mul_apply, Polynomial.aeval_monomial, Module.End.pow_apply,
Module.algebraMap_end_apply, smul_def]
induction i generalizing r j m with
| zero =>
rw [Function.iterate_zero, zero_add]
exact Finsupp.smul_single r j m
| succ n hn =>
rw [Function.iterate_succ, Function.comp_apply, add_assoc, ← hn]
congr 2
rw [Nat.one_add]
exact Finsupp.mapDomain_single
@[simp]
theorem monomial_smul_apply (i : ℕ) (r : R) (g : PolynomialModule R M) (n : ℕ) :
(monomial i r • g) n = ite (i ≤ n) (r • g (n - i)) 0 := by
induction' g using PolynomialModule.induction_linear with p q hp hq
· simp only [smul_zero, zero_apply, ite_self]
· simp only [smul_add, add_apply, hp, hq]
split_ifs
exacts [rfl, zero_add 0]
· rw [monomial_smul_single, single_apply, single_apply, smul_ite, smul_zero, ← ite_and]
congr
rw [eq_iff_iff]
constructor
· rintro rfl
simp
· rintro ⟨e, rfl⟩
rw [add_comm, tsub_add_cancel_of_le e]
@[simp]
theorem smul_single_apply (i : ℕ) (f : R[X]) (m : M) (n : ℕ) :
(f • single R i m) n = ite (i ≤ n) (f.coeff (n - i) • m) 0 := by
induction' f using Polynomial.induction_on' with p q hp hq
· rw [add_smul, Finsupp.add_apply, hp, hq, coeff_add, add_smul]
split_ifs
exacts [rfl, zero_add 0]
· rw [monomial_smul_single, single_apply, coeff_monomial, ite_smul, zero_smul]
by_cases h : i ≤ n
· simp_rw [eq_tsub_iff_add_eq_of_le h, if_pos h]
· rw [if_neg h, if_neg]
omega
theorem smul_apply (f : R[X]) (g : PolynomialModule R M) (n : ℕ) :
(f • g) n = ∑ x ∈ Finset.antidiagonal n, f.coeff x.1 • g x.2 := by
induction f using Polynomial.induction_on' with
| add p q hp hq =>
rw [add_smul, Finsupp.add_apply, hp, hq, ← Finset.sum_add_distrib]
congr
ext
rw [coeff_add, add_smul]
| monomial f_n f_a =>
rw [Finset.Nat.sum_antidiagonal_eq_sum_range_succ fun i j => (monomial f_n f_a).coeff i • g j,
monomial_smul_apply]
simp_rw [Polynomial.coeff_monomial, ← Finset.mem_range_succ_iff]
rw [← Finset.sum_ite_eq (Finset.range (Nat.succ n)) f_n (fun x => f_a • g (n - x))]
| congr
ext x
split_ifs
exacts [rfl, (zero_smul R _).symm]
/-- `PolynomialModule R R` is isomorphic to `R[X]` as an `R[X]` module. -/
noncomputable def equivPolynomialSelf : PolynomialModule R R ≃ₗ[R[X]] R[X] :=
{ (Polynomial.toFinsuppIso R).symm with
map_smul' := fun r x => by
dsimp
rw [← RingEquiv.coe_toEquiv_symm, RingEquiv.coe_toEquiv]
induction x using induction_linear with
| zero => rw [smul_zero, map_zero, mul_zero]
| add _ _ hp hq => rw [smul_add, map_add, map_add, mul_add, hp, hq]
| single n a =>
| Mathlib/Algebra/Polynomial/Module/Basic.lean | 172 | 186 |
/-
Copyright (c) 2014 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Leonardo de Moura
-/
import Mathlib.Data.Set.Operations
import Mathlib.Order.Basic
import Mathlib.Order.BooleanAlgebra
import Mathlib.Tactic.Tauto
import Mathlib.Tactic.ByContra
import Mathlib.Util.Delaborators
import Mathlib.Tactic.Lift
/-!
# Basic properties of sets
Sets in Lean are homogeneous; all their elements have the same type. Sets whose elements
have type `X` are thus defined as `Set X := X → Prop`. Note that this function need not
be decidable. The definition is in the module `Mathlib.Data.Set.Defs`.
This file provides some basic definitions related to sets and functions not present in the
definitions file, as well as extra lemmas for functions defined in the definitions file and
`Mathlib.Data.Set.Operations` (empty set, univ, union, intersection, insert, singleton,
set-theoretic difference, complement, and powerset).
Note that a set is a term, not a type. There is a coercion from `Set α` to `Type*` sending
`s` to the corresponding subtype `↥s`.
See also the file `SetTheory/ZFC.lean`, which contains an encoding of ZFC set theory in Lean.
## Main definitions
Notation used here:
- `f : α → β` is a function,
- `s : Set α` and `s₁ s₂ : Set α` are subsets of `α`
- `t : Set β` is a subset of `β`.
Definitions in the file:
* `Nonempty s : Prop` : the predicate `s ≠ ∅`. Note that this is the preferred way to express the
fact that `s` has an element (see the Implementation Notes).
* `inclusion s₁ s₂ : ↥s₁ → ↥s₂` : the map `↥s₁ → ↥s₂` induced by an inclusion `s₁ ⊆ s₂`.
## Notation
* `sᶜ` for the complement of `s`
## Implementation notes
* `s.Nonempty` is to be preferred to `s ≠ ∅` or `∃ x, x ∈ s`. It has the advantage that
the `s.Nonempty` dot notation can be used.
* For `s : Set α`, do not use `Subtype s`. Instead use `↥s` or `(s : Type*)` or `s`.
## Tags
set, sets, subset, subsets, union, intersection, insert, singleton, complement, powerset
-/
assert_not_exists RelIso
/-! ### Set coercion to a type -/
open Function
universe u v
namespace Set
variable {α : Type u} {s t : Set α}
instance instBooleanAlgebra : BooleanAlgebra (Set α) :=
{ (inferInstance : BooleanAlgebra (α → Prop)) with
sup := (· ∪ ·),
le := (· ≤ ·),
lt := fun s t => s ⊆ t ∧ ¬t ⊆ s,
inf := (· ∩ ·),
bot := ∅,
compl := (·ᶜ),
top := univ,
sdiff := (· \ ·) }
instance : HasSSubset (Set α) :=
⟨(· < ·)⟩
@[simp]
theorem top_eq_univ : (⊤ : Set α) = univ :=
rfl
@[simp]
theorem bot_eq_empty : (⊥ : Set α) = ∅ :=
rfl
@[simp]
theorem sup_eq_union : ((· ⊔ ·) : Set α → Set α → Set α) = (· ∪ ·) :=
rfl
@[simp]
theorem inf_eq_inter : ((· ⊓ ·) : Set α → Set α → Set α) = (· ∩ ·) :=
rfl
@[simp]
theorem le_eq_subset : ((· ≤ ·) : Set α → Set α → Prop) = (· ⊆ ·) :=
rfl
@[simp]
theorem lt_eq_ssubset : ((· < ·) : Set α → Set α → Prop) = (· ⊂ ·) :=
rfl
theorem le_iff_subset : s ≤ t ↔ s ⊆ t :=
Iff.rfl
theorem lt_iff_ssubset : s < t ↔ s ⊂ t :=
Iff.rfl
alias ⟨_root_.LE.le.subset, _root_.HasSubset.Subset.le⟩ := le_iff_subset
alias ⟨_root_.LT.lt.ssubset, _root_.HasSSubset.SSubset.lt⟩ := lt_iff_ssubset
instance PiSetCoe.canLift (ι : Type u) (α : ι → Type v) [∀ i, Nonempty (α i)] (s : Set ι) :
CanLift (∀ i : s, α i) (∀ i, α i) (fun f i => f i) fun _ => True :=
PiSubtype.canLift ι α s
instance PiSetCoe.canLift' (ι : Type u) (α : Type v) [Nonempty α] (s : Set ι) :
CanLift (s → α) (ι → α) (fun f i => f i) fun _ => True :=
PiSetCoe.canLift ι (fun _ => α) s
end Set
section SetCoe
variable {α : Type u}
instance (s : Set α) : CoeTC s α := ⟨fun x => x.1⟩
theorem Set.coe_eq_subtype (s : Set α) : ↥s = { x // x ∈ s } :=
rfl
@[simp]
theorem Set.coe_setOf (p : α → Prop) : ↥{ x | p x } = { x // p x } :=
rfl
theorem SetCoe.forall {s : Set α} {p : s → Prop} : (∀ x : s, p x) ↔ ∀ (x) (h : x ∈ s), p ⟨x, h⟩ :=
Subtype.forall
theorem SetCoe.exists {s : Set α} {p : s → Prop} :
(∃ x : s, p x) ↔ ∃ (x : _) (h : x ∈ s), p ⟨x, h⟩ :=
Subtype.exists
theorem SetCoe.exists' {s : Set α} {p : ∀ x, x ∈ s → Prop} :
(∃ (x : _) (h : x ∈ s), p x h) ↔ ∃ x : s, p x.1 x.2 :=
(@SetCoe.exists _ _ fun x => p x.1 x.2).symm
theorem SetCoe.forall' {s : Set α} {p : ∀ x, x ∈ s → Prop} :
(∀ (x) (h : x ∈ s), p x h) ↔ ∀ x : s, p x.1 x.2 :=
(@SetCoe.forall _ _ fun x => p x.1 x.2).symm
@[simp]
theorem set_coe_cast :
∀ {s t : Set α} (H' : s = t) (H : ↥s = ↥t) (x : s), cast H x = ⟨x.1, H' ▸ x.2⟩
| _, _, rfl, _, _ => rfl
theorem SetCoe.ext {s : Set α} {a b : s} : (a : α) = b → a = b :=
Subtype.eq
theorem SetCoe.ext_iff {s : Set α} {a b : s} : (↑a : α) = ↑b ↔ a = b :=
Iff.intro SetCoe.ext fun h => h ▸ rfl
end SetCoe
/-- See also `Subtype.prop` -/
theorem Subtype.mem {α : Type*} {s : Set α} (p : s) : (p : α) ∈ s :=
p.prop
/-- Duplicate of `Eq.subset'`, which currently has elaboration problems. -/
theorem Eq.subset {α} {s t : Set α} : s = t → s ⊆ t :=
fun h₁ _ h₂ => by rw [← h₁]; exact h₂
namespace Set
variable {α : Type u} {β : Type v} {a b : α} {s s₁ s₂ t t₁ t₂ u : Set α}
instance : Inhabited (Set α) :=
⟨∅⟩
@[trans]
theorem mem_of_mem_of_subset {x : α} {s t : Set α} (hx : x ∈ s) (h : s ⊆ t) : x ∈ t :=
h hx
theorem forall_in_swap {p : α → β → Prop} : (∀ a ∈ s, ∀ (b), p a b) ↔ ∀ (b), ∀ a ∈ s, p a b := by
tauto
theorem setOf_injective : Function.Injective (@setOf α) := injective_id
theorem setOf_inj {p q : α → Prop} : { x | p x } = { x | q x } ↔ p = q := Iff.rfl
/-! ### Lemmas about `mem` and `setOf` -/
theorem mem_setOf {a : α} {p : α → Prop} : a ∈ { x | p x } ↔ p a :=
Iff.rfl
/-- This lemma is intended for use with `rw` where a membership predicate is needed,
hence the explicit argument and the equality in the reverse direction from normal.
See also `Set.mem_setOf_eq` for the reverse direction applied to an argument. -/
theorem eq_mem_setOf (p : α → Prop) : p = (· ∈ {a | p a}) := rfl
/-- If `h : a ∈ {x | p x}` then `h.out : p x`. These are definitionally equal, but this can
nevertheless be useful for various reasons, e.g. to apply further projection notation or in an
argument to `simp`. -/
theorem _root_.Membership.mem.out {p : α → Prop} {a : α} (h : a ∈ { x | p x }) : p a :=
h
theorem nmem_setOf_iff {a : α} {p : α → Prop} : a ∉ { x | p x } ↔ ¬p a :=
Iff.rfl
@[simp]
theorem setOf_mem_eq {s : Set α} : { x | x ∈ s } = s :=
rfl
theorem setOf_set {s : Set α} : setOf s = s :=
rfl
theorem setOf_app_iff {p : α → Prop} {x : α} : { x | p x } x ↔ p x :=
Iff.rfl
theorem mem_def {a : α} {s : Set α} : a ∈ s ↔ s a :=
Iff.rfl
theorem setOf_bijective : Bijective (setOf : (α → Prop) → Set α) :=
bijective_id
theorem subset_setOf {p : α → Prop} {s : Set α} : s ⊆ setOf p ↔ ∀ x, x ∈ s → p x :=
Iff.rfl
theorem setOf_subset {p : α → Prop} {s : Set α} : setOf p ⊆ s ↔ ∀ x, p x → x ∈ s :=
Iff.rfl
@[simp]
theorem setOf_subset_setOf {p q : α → Prop} : { a | p a } ⊆ { a | q a } ↔ ∀ a, p a → q a :=
Iff.rfl
theorem setOf_and {p q : α → Prop} : { a | p a ∧ q a } = { a | p a } ∩ { a | q a } :=
rfl
theorem setOf_or {p q : α → Prop} : { a | p a ∨ q a } = { a | p a } ∪ { a | q a } :=
rfl
/-! ### Subset and strict subset relations -/
instance : IsRefl (Set α) (· ⊆ ·) :=
show IsRefl (Set α) (· ≤ ·) by infer_instance
instance : IsTrans (Set α) (· ⊆ ·) :=
show IsTrans (Set α) (· ≤ ·) by infer_instance
instance : Trans ((· ⊆ ·) : Set α → Set α → Prop) (· ⊆ ·) (· ⊆ ·) :=
show Trans (· ≤ ·) (· ≤ ·) (· ≤ ·) by infer_instance
instance : IsAntisymm (Set α) (· ⊆ ·) :=
show IsAntisymm (Set α) (· ≤ ·) by infer_instance
instance : IsIrrefl (Set α) (· ⊂ ·) :=
show IsIrrefl (Set α) (· < ·) by infer_instance
instance : IsTrans (Set α) (· ⊂ ·) :=
show IsTrans (Set α) (· < ·) by infer_instance
instance : Trans ((· ⊂ ·) : Set α → Set α → Prop) (· ⊂ ·) (· ⊂ ·) :=
show Trans (· < ·) (· < ·) (· < ·) by infer_instance
instance : Trans ((· ⊂ ·) : Set α → Set α → Prop) (· ⊆ ·) (· ⊂ ·) :=
show Trans (· < ·) (· ≤ ·) (· < ·) by infer_instance
instance : Trans ((· ⊆ ·) : Set α → Set α → Prop) (· ⊂ ·) (· ⊂ ·) :=
show Trans (· ≤ ·) (· < ·) (· < ·) by infer_instance
instance : IsAsymm (Set α) (· ⊂ ·) :=
show IsAsymm (Set α) (· < ·) by infer_instance
instance : IsNonstrictStrictOrder (Set α) (· ⊆ ·) (· ⊂ ·) :=
⟨fun _ _ => Iff.rfl⟩
-- TODO(Jeremy): write a tactic to unfold specific instances of generic notation?
theorem subset_def : (s ⊆ t) = ∀ x, x ∈ s → x ∈ t :=
rfl
theorem ssubset_def : (s ⊂ t) = (s ⊆ t ∧ ¬t ⊆ s) :=
rfl
@[refl]
theorem Subset.refl (a : Set α) : a ⊆ a := fun _ => id
theorem Subset.rfl {s : Set α} : s ⊆ s :=
Subset.refl s
@[trans]
theorem Subset.trans {a b c : Set α} (ab : a ⊆ b) (bc : b ⊆ c) : a ⊆ c := fun _ h => bc <| ab h
@[trans]
theorem mem_of_eq_of_mem {x y : α} {s : Set α} (hx : x = y) (h : y ∈ s) : x ∈ s :=
hx.symm ▸ h
theorem Subset.antisymm {a b : Set α} (h₁ : a ⊆ b) (h₂ : b ⊆ a) : a = b :=
Set.ext fun _ => ⟨@h₁ _, @h₂ _⟩
theorem Subset.antisymm_iff {a b : Set α} : a = b ↔ a ⊆ b ∧ b ⊆ a :=
⟨fun e => ⟨e.subset, e.symm.subset⟩, fun ⟨h₁, h₂⟩ => Subset.antisymm h₁ h₂⟩
-- an alternative name
theorem eq_of_subset_of_subset {a b : Set α} : a ⊆ b → b ⊆ a → a = b :=
Subset.antisymm
theorem mem_of_subset_of_mem {s₁ s₂ : Set α} {a : α} (h : s₁ ⊆ s₂) : a ∈ s₁ → a ∈ s₂ :=
@h _
theorem not_mem_subset (h : s ⊆ t) : a ∉ t → a ∉ s :=
mt <| mem_of_subset_of_mem h
theorem not_subset : ¬s ⊆ t ↔ ∃ a ∈ s, a ∉ t := by
simp only [subset_def, not_forall, exists_prop]
theorem not_top_subset : ¬⊤ ⊆ s ↔ ∃ a, a ∉ s := by
simp [not_subset]
lemma eq_of_forall_subset_iff (h : ∀ u, s ⊆ u ↔ t ⊆ u) : s = t := eq_of_forall_ge_iff h
/-! ### Definition of strict subsets `s ⊂ t` and basic properties. -/
protected theorem eq_or_ssubset_of_subset (h : s ⊆ t) : s = t ∨ s ⊂ t :=
eq_or_lt_of_le h
theorem exists_of_ssubset {s t : Set α} (h : s ⊂ t) : ∃ x ∈ t, x ∉ s :=
not_subset.1 h.2
protected theorem ssubset_iff_subset_ne {s t : Set α} : s ⊂ t ↔ s ⊆ t ∧ s ≠ t :=
@lt_iff_le_and_ne (Set α) _ s t
theorem ssubset_iff_of_subset {s t : Set α} (h : s ⊆ t) : s ⊂ t ↔ ∃ x ∈ t, x ∉ s :=
⟨exists_of_ssubset, fun ⟨_, hxt, hxs⟩ => ⟨h, fun h => hxs <| h hxt⟩⟩
theorem ssubset_iff_exists {s t : Set α} : s ⊂ t ↔ s ⊆ t ∧ ∃ x ∈ t, x ∉ s :=
⟨fun h ↦ ⟨h.le, Set.exists_of_ssubset h⟩, fun ⟨h1, h2⟩ ↦ (Set.ssubset_iff_of_subset h1).mpr h2⟩
protected theorem ssubset_of_ssubset_of_subset {s₁ s₂ s₃ : Set α} (hs₁s₂ : s₁ ⊂ s₂)
(hs₂s₃ : s₂ ⊆ s₃) : s₁ ⊂ s₃ :=
⟨Subset.trans hs₁s₂.1 hs₂s₃, fun hs₃s₁ => hs₁s₂.2 (Subset.trans hs₂s₃ hs₃s₁)⟩
protected theorem ssubset_of_subset_of_ssubset {s₁ s₂ s₃ : Set α} (hs₁s₂ : s₁ ⊆ s₂)
(hs₂s₃ : s₂ ⊂ s₃) : s₁ ⊂ s₃ :=
⟨Subset.trans hs₁s₂ hs₂s₃.1, fun hs₃s₁ => hs₂s₃.2 (Subset.trans hs₃s₁ hs₁s₂)⟩
theorem not_mem_empty (x : α) : ¬x ∈ (∅ : Set α) :=
id
theorem not_not_mem : ¬a ∉ s ↔ a ∈ s :=
not_not
/-! ### Non-empty sets -/
theorem nonempty_coe_sort {s : Set α} : Nonempty ↥s ↔ s.Nonempty :=
nonempty_subtype
alias ⟨_, Nonempty.coe_sort⟩ := nonempty_coe_sort
theorem nonempty_def : s.Nonempty ↔ ∃ x, x ∈ s :=
Iff.rfl
theorem nonempty_of_mem {x} (h : x ∈ s) : s.Nonempty :=
⟨x, h⟩
theorem Nonempty.not_subset_empty : s.Nonempty → ¬s ⊆ ∅
| ⟨_, hx⟩, hs => hs hx
/-- Extract a witness from `s.Nonempty`. This function might be used instead of case analysis
on the argument. Note that it makes a proof depend on the `Classical.choice` axiom. -/
protected noncomputable def Nonempty.some (h : s.Nonempty) : α :=
Classical.choose h
protected theorem Nonempty.some_mem (h : s.Nonempty) : h.some ∈ s :=
Classical.choose_spec h
theorem Nonempty.mono (ht : s ⊆ t) (hs : s.Nonempty) : t.Nonempty :=
hs.imp ht
theorem nonempty_of_not_subset (h : ¬s ⊆ t) : (s \ t).Nonempty :=
let ⟨x, xs, xt⟩ := not_subset.1 h
⟨x, xs, xt⟩
theorem nonempty_of_ssubset (ht : s ⊂ t) : (t \ s).Nonempty :=
nonempty_of_not_subset ht.2
theorem Nonempty.of_diff (h : (s \ t).Nonempty) : s.Nonempty :=
h.imp fun _ => And.left
theorem nonempty_of_ssubset' (ht : s ⊂ t) : t.Nonempty :=
(nonempty_of_ssubset ht).of_diff
theorem Nonempty.inl (hs : s.Nonempty) : (s ∪ t).Nonempty :=
hs.imp fun _ => Or.inl
theorem Nonempty.inr (ht : t.Nonempty) : (s ∪ t).Nonempty :=
ht.imp fun _ => Or.inr
@[simp]
theorem union_nonempty : (s ∪ t).Nonempty ↔ s.Nonempty ∨ t.Nonempty :=
exists_or
theorem Nonempty.left (h : (s ∩ t).Nonempty) : s.Nonempty :=
h.imp fun _ => And.left
theorem Nonempty.right (h : (s ∩ t).Nonempty) : t.Nonempty :=
h.imp fun _ => And.right
theorem inter_nonempty : (s ∩ t).Nonempty ↔ ∃ x, x ∈ s ∧ x ∈ t :=
Iff.rfl
theorem inter_nonempty_iff_exists_left : (s ∩ t).Nonempty ↔ ∃ x ∈ s, x ∈ t := by
simp_rw [inter_nonempty]
theorem inter_nonempty_iff_exists_right : (s ∩ t).Nonempty ↔ ∃ x ∈ t, x ∈ s := by
simp_rw [inter_nonempty, and_comm]
theorem nonempty_iff_univ_nonempty : Nonempty α ↔ (univ : Set α).Nonempty :=
⟨fun ⟨x⟩ => ⟨x, trivial⟩, fun ⟨x, _⟩ => ⟨x⟩⟩
@[simp]
theorem univ_nonempty : ∀ [Nonempty α], (univ : Set α).Nonempty
| ⟨x⟩ => ⟨x, trivial⟩
theorem Nonempty.to_subtype : s.Nonempty → Nonempty (↥s) :=
nonempty_subtype.2
theorem Nonempty.to_type : s.Nonempty → Nonempty α := fun ⟨x, _⟩ => ⟨x⟩
instance univ.nonempty [Nonempty α] : Nonempty (↥(Set.univ : Set α)) :=
Set.univ_nonempty.to_subtype
-- Redeclare for refined keys
-- `Nonempty (@Subtype _ (@Membership.mem _ (Set _) _ (@Top.top (Set _) _)))`
instance instNonemptyTop [Nonempty α] : Nonempty (⊤ : Set α) :=
inferInstanceAs (Nonempty (univ : Set α))
theorem Nonempty.of_subtype [Nonempty (↥s)] : s.Nonempty := nonempty_subtype.mp ‹_›
@[deprecated (since := "2024-11-23")] alias nonempty_of_nonempty_subtype := Nonempty.of_subtype
/-! ### Lemmas about the empty set -/
theorem empty_def : (∅ : Set α) = { _x : α | False } :=
rfl
@[simp]
theorem mem_empty_iff_false (x : α) : x ∈ (∅ : Set α) ↔ False :=
Iff.rfl
@[simp]
theorem setOf_false : { _a : α | False } = ∅ :=
rfl
@[simp] theorem setOf_bot : { _x : α | ⊥ } = ∅ := rfl
@[simp]
theorem empty_subset (s : Set α) : ∅ ⊆ s :=
nofun
@[simp]
theorem subset_empty_iff {s : Set α} : s ⊆ ∅ ↔ s = ∅ :=
(Subset.antisymm_iff.trans <| and_iff_left (empty_subset _)).symm
theorem eq_empty_iff_forall_not_mem {s : Set α} : s = ∅ ↔ ∀ x, x ∉ s :=
subset_empty_iff.symm
theorem eq_empty_of_forall_not_mem (h : ∀ x, x ∉ s) : s = ∅ :=
subset_empty_iff.1 h
theorem eq_empty_of_subset_empty {s : Set α} : s ⊆ ∅ → s = ∅ :=
subset_empty_iff.1
theorem eq_empty_of_isEmpty [IsEmpty α] (s : Set α) : s = ∅ :=
eq_empty_of_subset_empty fun x _ => isEmptyElim x
/-- There is exactly one set of a type that is empty. -/
instance uniqueEmpty [IsEmpty α] : Unique (Set α) where
default := ∅
uniq := eq_empty_of_isEmpty
/-- See also `Set.nonempty_iff_ne_empty`. -/
theorem not_nonempty_iff_eq_empty {s : Set α} : ¬s.Nonempty ↔ s = ∅ := by
simp only [Set.Nonempty, not_exists, eq_empty_iff_forall_not_mem]
/-- See also `Set.not_nonempty_iff_eq_empty`. -/
theorem nonempty_iff_ne_empty : s.Nonempty ↔ s ≠ ∅ :=
not_nonempty_iff_eq_empty.not_right
/-- See also `nonempty_iff_ne_empty'`. -/
theorem not_nonempty_iff_eq_empty' : ¬Nonempty s ↔ s = ∅ := by
rw [nonempty_subtype, not_exists, eq_empty_iff_forall_not_mem]
/-- See also `not_nonempty_iff_eq_empty'`. -/
theorem nonempty_iff_ne_empty' : Nonempty s ↔ s ≠ ∅ :=
not_nonempty_iff_eq_empty'.not_right
alias ⟨Nonempty.ne_empty, _⟩ := nonempty_iff_ne_empty
@[simp]
theorem not_nonempty_empty : ¬(∅ : Set α).Nonempty := fun ⟨_, hx⟩ => hx
@[simp]
theorem isEmpty_coe_sort {s : Set α} : IsEmpty (↥s) ↔ s = ∅ :=
not_iff_not.1 <| by simpa using nonempty_iff_ne_empty
theorem eq_empty_or_nonempty (s : Set α) : s = ∅ ∨ s.Nonempty :=
or_iff_not_imp_left.2 nonempty_iff_ne_empty.2
theorem subset_eq_empty {s t : Set α} (h : t ⊆ s) (e : s = ∅) : t = ∅ :=
subset_empty_iff.1 <| e ▸ h
theorem forall_mem_empty {p : α → Prop} : (∀ x ∈ (∅ : Set α), p x) ↔ True :=
iff_true_intro fun _ => False.elim
instance (α : Type u) : IsEmpty.{u + 1} (↥(∅ : Set α)) :=
⟨fun x => x.2⟩
@[simp]
theorem empty_ssubset : ∅ ⊂ s ↔ s.Nonempty :=
(@bot_lt_iff_ne_bot (Set α) _ _ _).trans nonempty_iff_ne_empty.symm
alias ⟨_, Nonempty.empty_ssubset⟩ := empty_ssubset
/-!
### Universal set.
In Lean `@univ α` (or `univ : Set α`) is the set that contains all elements of type `α`.
Mathematically it is the same as `α` but it has a different type.
-/
@[simp]
theorem setOf_true : { _x : α | True } = univ :=
rfl
@[simp] theorem setOf_top : { _x : α | ⊤ } = univ := rfl
@[simp]
theorem univ_eq_empty_iff : (univ : Set α) = ∅ ↔ IsEmpty α :=
eq_empty_iff_forall_not_mem.trans
⟨fun H => ⟨fun x => H x trivial⟩, fun H x _ => @IsEmpty.false α H x⟩
theorem empty_ne_univ [Nonempty α] : (∅ : Set α) ≠ univ := fun e =>
not_isEmpty_of_nonempty α <| univ_eq_empty_iff.1 e.symm
@[simp]
theorem subset_univ (s : Set α) : s ⊆ univ := fun _ _ => trivial
@[simp]
theorem univ_subset_iff {s : Set α} : univ ⊆ s ↔ s = univ :=
@top_le_iff _ _ _ s
alias ⟨eq_univ_of_univ_subset, _⟩ := univ_subset_iff
theorem eq_univ_iff_forall {s : Set α} : s = univ ↔ ∀ x, x ∈ s :=
univ_subset_iff.symm.trans <| forall_congr' fun _ => imp_iff_right trivial
theorem eq_univ_of_forall {s : Set α} : (∀ x, x ∈ s) → s = univ :=
eq_univ_iff_forall.2
theorem Nonempty.eq_univ [Subsingleton α] : s.Nonempty → s = univ := by
rintro ⟨x, hx⟩
exact eq_univ_of_forall fun y => by rwa [Subsingleton.elim y x]
theorem eq_univ_of_subset {s t : Set α} (h : s ⊆ t) (hs : s = univ) : t = univ :=
eq_univ_of_univ_subset <| (hs ▸ h : univ ⊆ t)
theorem exists_mem_of_nonempty (α) : ∀ [Nonempty α], ∃ x : α, x ∈ (univ : Set α)
| ⟨x⟩ => ⟨x, trivial⟩
theorem ne_univ_iff_exists_not_mem {α : Type*} (s : Set α) : s ≠ univ ↔ ∃ a, a ∉ s := by
rw [← not_forall, ← eq_univ_iff_forall]
theorem not_subset_iff_exists_mem_not_mem {α : Type*} {s t : Set α} :
¬s ⊆ t ↔ ∃ x, x ∈ s ∧ x ∉ t := by simp [subset_def]
theorem univ_unique [Unique α] : @Set.univ α = {default} :=
Set.ext fun x => iff_of_true trivial <| Subsingleton.elim x default
theorem ssubset_univ_iff : s ⊂ univ ↔ s ≠ univ :=
lt_top_iff_ne_top
instance nontrivial_of_nonempty [Nonempty α] : Nontrivial (Set α) :=
⟨⟨∅, univ, empty_ne_univ⟩⟩
/-! ### Lemmas about union -/
theorem union_def {s₁ s₂ : Set α} : s₁ ∪ s₂ = { a | a ∈ s₁ ∨ a ∈ s₂ } :=
rfl
theorem mem_union_left {x : α} {a : Set α} (b : Set α) : x ∈ a → x ∈ a ∪ b :=
Or.inl
theorem mem_union_right {x : α} {b : Set α} (a : Set α) : x ∈ b → x ∈ a ∪ b :=
Or.inr
theorem mem_or_mem_of_mem_union {x : α} {a b : Set α} (H : x ∈ a ∪ b) : x ∈ a ∨ x ∈ b :=
H
theorem MemUnion.elim {x : α} {a b : Set α} {P : Prop} (H₁ : x ∈ a ∪ b) (H₂ : x ∈ a → P)
(H₃ : x ∈ b → P) : P :=
Or.elim H₁ H₂ H₃
@[simp]
theorem mem_union (x : α) (a b : Set α) : x ∈ a ∪ b ↔ x ∈ a ∨ x ∈ b :=
Iff.rfl
@[simp]
theorem union_self (a : Set α) : a ∪ a = a :=
ext fun _ => or_self_iff
@[simp]
theorem union_empty (a : Set α) : a ∪ ∅ = a :=
ext fun _ => iff_of_eq (or_false _)
@[simp]
theorem empty_union (a : Set α) : ∅ ∪ a = a :=
ext fun _ => iff_of_eq (false_or _)
theorem union_comm (a b : Set α) : a ∪ b = b ∪ a :=
ext fun _ => or_comm
theorem union_assoc (a b c : Set α) : a ∪ b ∪ c = a ∪ (b ∪ c) :=
ext fun _ => or_assoc
instance union_isAssoc : Std.Associative (α := Set α) (· ∪ ·) :=
⟨union_assoc⟩
instance union_isComm : Std.Commutative (α := Set α) (· ∪ ·) :=
⟨union_comm⟩
theorem union_left_comm (s₁ s₂ s₃ : Set α) : s₁ ∪ (s₂ ∪ s₃) = s₂ ∪ (s₁ ∪ s₃) :=
ext fun _ => or_left_comm
theorem union_right_comm (s₁ s₂ s₃ : Set α) : s₁ ∪ s₂ ∪ s₃ = s₁ ∪ s₃ ∪ s₂ :=
ext fun _ => or_right_comm
@[simp]
theorem union_eq_left {s t : Set α} : s ∪ t = s ↔ t ⊆ s :=
sup_eq_left
@[simp]
theorem union_eq_right {s t : Set α} : s ∪ t = t ↔ s ⊆ t :=
sup_eq_right
theorem union_eq_self_of_subset_left {s t : Set α} (h : s ⊆ t) : s ∪ t = t :=
union_eq_right.mpr h
theorem union_eq_self_of_subset_right {s t : Set α} (h : t ⊆ s) : s ∪ t = s :=
union_eq_left.mpr h
@[simp]
theorem subset_union_left {s t : Set α} : s ⊆ s ∪ t := fun _ => Or.inl
@[simp]
theorem subset_union_right {s t : Set α} : t ⊆ s ∪ t := fun _ => Or.inr
theorem union_subset {s t r : Set α} (sr : s ⊆ r) (tr : t ⊆ r) : s ∪ t ⊆ r := fun _ =>
Or.rec (@sr _) (@tr _)
@[simp]
theorem union_subset_iff {s t u : Set α} : s ∪ t ⊆ u ↔ s ⊆ u ∧ t ⊆ u :=
(forall_congr' fun _ => or_imp).trans forall_and
@[gcongr]
theorem union_subset_union {s₁ s₂ t₁ t₂ : Set α} (h₁ : s₁ ⊆ s₂) (h₂ : t₁ ⊆ t₂) :
s₁ ∪ t₁ ⊆ s₂ ∪ t₂ := fun _ => Or.imp (@h₁ _) (@h₂ _)
@[gcongr]
theorem union_subset_union_left {s₁ s₂ : Set α} (t) (h : s₁ ⊆ s₂) : s₁ ∪ t ⊆ s₂ ∪ t :=
union_subset_union h Subset.rfl
@[gcongr]
theorem union_subset_union_right (s) {t₁ t₂ : Set α} (h : t₁ ⊆ t₂) : s ∪ t₁ ⊆ s ∪ t₂ :=
union_subset_union Subset.rfl h
theorem subset_union_of_subset_left {s t : Set α} (h : s ⊆ t) (u : Set α) : s ⊆ t ∪ u :=
h.trans subset_union_left
theorem subset_union_of_subset_right {s u : Set α} (h : s ⊆ u) (t : Set α) : s ⊆ t ∪ u :=
h.trans subset_union_right
theorem union_congr_left (ht : t ⊆ s ∪ u) (hu : u ⊆ s ∪ t) : s ∪ t = s ∪ u :=
sup_congr_left ht hu
theorem union_congr_right (hs : s ⊆ t ∪ u) (ht : t ⊆ s ∪ u) : s ∪ u = t ∪ u :=
sup_congr_right hs ht
theorem union_eq_union_iff_left : s ∪ t = s ∪ u ↔ t ⊆ s ∪ u ∧ u ⊆ s ∪ t :=
sup_eq_sup_iff_left
theorem union_eq_union_iff_right : s ∪ u = t ∪ u ↔ s ⊆ t ∪ u ∧ t ⊆ s ∪ u :=
sup_eq_sup_iff_right
@[simp]
theorem union_empty_iff {s t : Set α} : s ∪ t = ∅ ↔ s = ∅ ∧ t = ∅ := by
simp only [← subset_empty_iff]
exact union_subset_iff
@[simp]
theorem union_univ (s : Set α) : s ∪ univ = univ := sup_top_eq _
@[simp]
theorem univ_union (s : Set α) : univ ∪ s = univ := top_sup_eq _
@[simp]
theorem ssubset_union_left_iff : s ⊂ s ∪ t ↔ ¬ t ⊆ s :=
left_lt_sup
@[simp]
theorem ssubset_union_right_iff : t ⊂ s ∪ t ↔ ¬ s ⊆ t :=
right_lt_sup
/-! ### Lemmas about intersection -/
theorem inter_def {s₁ s₂ : Set α} : s₁ ∩ s₂ = { a | a ∈ s₁ ∧ a ∈ s₂ } :=
rfl
@[simp, mfld_simps]
theorem mem_inter_iff (x : α) (a b : Set α) : x ∈ a ∩ b ↔ x ∈ a ∧ x ∈ b :=
Iff.rfl
theorem mem_inter {x : α} {a b : Set α} (ha : x ∈ a) (hb : x ∈ b) : x ∈ a ∩ b :=
⟨ha, hb⟩
theorem mem_of_mem_inter_left {x : α} {a b : Set α} (h : x ∈ a ∩ b) : x ∈ a :=
h.left
theorem mem_of_mem_inter_right {x : α} {a b : Set α} (h : x ∈ a ∩ b) : x ∈ b :=
h.right
@[simp]
theorem inter_self (a : Set α) : a ∩ a = a :=
ext fun _ => and_self_iff
@[simp]
theorem inter_empty (a : Set α) : a ∩ ∅ = ∅ :=
ext fun _ => iff_of_eq (and_false _)
@[simp]
theorem empty_inter (a : Set α) : ∅ ∩ a = ∅ :=
ext fun _ => iff_of_eq (false_and _)
theorem inter_comm (a b : Set α) : a ∩ b = b ∩ a :=
ext fun _ => and_comm
theorem inter_assoc (a b c : Set α) : a ∩ b ∩ c = a ∩ (b ∩ c) :=
ext fun _ => and_assoc
instance inter_isAssoc : Std.Associative (α := Set α) (· ∩ ·) :=
⟨inter_assoc⟩
instance inter_isComm : Std.Commutative (α := Set α) (· ∩ ·) :=
⟨inter_comm⟩
theorem inter_left_comm (s₁ s₂ s₃ : Set α) : s₁ ∩ (s₂ ∩ s₃) = s₂ ∩ (s₁ ∩ s₃) :=
ext fun _ => and_left_comm
theorem inter_right_comm (s₁ s₂ s₃ : Set α) : s₁ ∩ s₂ ∩ s₃ = s₁ ∩ s₃ ∩ s₂ :=
ext fun _ => and_right_comm
@[simp, mfld_simps]
theorem inter_subset_left {s t : Set α} : s ∩ t ⊆ s := fun _ => And.left
@[simp]
theorem inter_subset_right {s t : Set α} : s ∩ t ⊆ t := fun _ => And.right
theorem subset_inter {s t r : Set α} (rs : r ⊆ s) (rt : r ⊆ t) : r ⊆ s ∩ t := fun _ h =>
⟨rs h, rt h⟩
@[simp]
theorem subset_inter_iff {s t r : Set α} : r ⊆ s ∩ t ↔ r ⊆ s ∧ r ⊆ t :=
(forall_congr' fun _ => imp_and).trans forall_and
@[simp] lemma inter_eq_left : s ∩ t = s ↔ s ⊆ t := inf_eq_left
@[simp] lemma inter_eq_right : s ∩ t = t ↔ t ⊆ s := inf_eq_right
@[simp] lemma left_eq_inter : s = s ∩ t ↔ s ⊆ t := left_eq_inf
@[simp] lemma right_eq_inter : t = s ∩ t ↔ t ⊆ s := right_eq_inf
theorem inter_eq_self_of_subset_left {s t : Set α} : s ⊆ t → s ∩ t = s :=
inter_eq_left.mpr
theorem inter_eq_self_of_subset_right {s t : Set α} : t ⊆ s → s ∩ t = t :=
inter_eq_right.mpr
theorem inter_congr_left (ht : s ∩ u ⊆ t) (hu : s ∩ t ⊆ u) : s ∩ t = s ∩ u :=
inf_congr_left ht hu
theorem inter_congr_right (hs : t ∩ u ⊆ s) (ht : s ∩ u ⊆ t) : s ∩ u = t ∩ u :=
inf_congr_right hs ht
theorem inter_eq_inter_iff_left : s ∩ t = s ∩ u ↔ s ∩ u ⊆ t ∧ s ∩ t ⊆ u :=
inf_eq_inf_iff_left
theorem inter_eq_inter_iff_right : s ∩ u = t ∩ u ↔ t ∩ u ⊆ s ∧ s ∩ u ⊆ t :=
inf_eq_inf_iff_right
@[simp, mfld_simps]
theorem inter_univ (a : Set α) : a ∩ univ = a := inf_top_eq _
@[simp, mfld_simps]
theorem univ_inter (a : Set α) : univ ∩ a = a := top_inf_eq _
@[gcongr]
theorem inter_subset_inter {s₁ s₂ t₁ t₂ : Set α} (h₁ : s₁ ⊆ t₁) (h₂ : s₂ ⊆ t₂) :
s₁ ∩ s₂ ⊆ t₁ ∩ t₂ := fun _ => And.imp (@h₁ _) (@h₂ _)
@[gcongr]
theorem inter_subset_inter_left {s t : Set α} (u : Set α) (H : s ⊆ t) : s ∩ u ⊆ t ∩ u :=
inter_subset_inter H Subset.rfl
@[gcongr]
theorem inter_subset_inter_right {s t : Set α} (u : Set α) (H : s ⊆ t) : u ∩ s ⊆ u ∩ t :=
inter_subset_inter Subset.rfl H
theorem union_inter_cancel_left {s t : Set α} : (s ∪ t) ∩ s = s :=
inter_eq_self_of_subset_right subset_union_left
theorem union_inter_cancel_right {s t : Set α} : (s ∪ t) ∩ t = t :=
inter_eq_self_of_subset_right subset_union_right
theorem inter_setOf_eq_sep (s : Set α) (p : α → Prop) : s ∩ {a | p a} = {a ∈ s | p a} :=
rfl
theorem setOf_inter_eq_sep (p : α → Prop) (s : Set α) : {a | p a} ∩ s = {a ∈ s | p a} :=
inter_comm _ _
@[simp]
theorem inter_ssubset_right_iff : s ∩ t ⊂ t ↔ ¬ t ⊆ s :=
inf_lt_right
@[simp]
theorem inter_ssubset_left_iff : s ∩ t ⊂ s ↔ ¬ s ⊆ t :=
inf_lt_left
/-! ### Distributivity laws -/
theorem inter_union_distrib_left (s t u : Set α) : s ∩ (t ∪ u) = s ∩ t ∪ s ∩ u :=
inf_sup_left _ _ _
theorem union_inter_distrib_right (s t u : Set α) : (s ∪ t) ∩ u = s ∩ u ∪ t ∩ u :=
inf_sup_right _ _ _
theorem union_inter_distrib_left (s t u : Set α) : s ∪ t ∩ u = (s ∪ t) ∩ (s ∪ u) :=
sup_inf_left _ _ _
theorem inter_union_distrib_right (s t u : Set α) : s ∩ t ∪ u = (s ∪ u) ∩ (t ∪ u) :=
sup_inf_right _ _ _
theorem union_union_distrib_left (s t u : Set α) : s ∪ (t ∪ u) = s ∪ t ∪ (s ∪ u) :=
sup_sup_distrib_left _ _ _
theorem union_union_distrib_right (s t u : Set α) : s ∪ t ∪ u = s ∪ u ∪ (t ∪ u) :=
sup_sup_distrib_right _ _ _
theorem inter_inter_distrib_left (s t u : Set α) : s ∩ (t ∩ u) = s ∩ t ∩ (s ∩ u) :=
inf_inf_distrib_left _ _ _
theorem inter_inter_distrib_right (s t u : Set α) : s ∩ t ∩ u = s ∩ u ∩ (t ∩ u) :=
inf_inf_distrib_right _ _ _
theorem union_union_union_comm (s t u v : Set α) : s ∪ t ∪ (u ∪ v) = s ∪ u ∪ (t ∪ v) :=
sup_sup_sup_comm _ _ _ _
theorem inter_inter_inter_comm (s t u v : Set α) : s ∩ t ∩ (u ∩ v) = s ∩ u ∩ (t ∩ v) :=
inf_inf_inf_comm _ _ _ _
/-! ### Lemmas about sets defined as `{x ∈ s | p x}`. -/
section Sep
variable {p q : α → Prop} {x : α}
theorem mem_sep (xs : x ∈ s) (px : p x) : x ∈ { x ∈ s | p x } :=
⟨xs, px⟩
@[simp]
theorem sep_mem_eq : { x ∈ s | x ∈ t } = s ∩ t :=
rfl
@[simp]
theorem mem_sep_iff : x ∈ { x ∈ s | p x } ↔ x ∈ s ∧ p x :=
Iff.rfl
theorem sep_ext_iff : { x ∈ s | p x } = { x ∈ s | q x } ↔ ∀ x ∈ s, p x ↔ q x := by
simp_rw [Set.ext_iff, mem_sep_iff, and_congr_right_iff]
theorem sep_eq_of_subset (h : s ⊆ t) : { x ∈ t | x ∈ s } = s :=
inter_eq_self_of_subset_right h
@[simp]
theorem sep_subset (s : Set α) (p : α → Prop) : { x ∈ s | p x } ⊆ s := fun _ => And.left
@[simp]
theorem sep_eq_self_iff_mem_true : { x ∈ s | p x } = s ↔ ∀ x ∈ s, p x := by
simp_rw [Set.ext_iff, mem_sep_iff, and_iff_left_iff_imp]
@[simp]
theorem sep_eq_empty_iff_mem_false : { x ∈ s | p x } = ∅ ↔ ∀ x ∈ s, ¬p x := by
simp_rw [Set.ext_iff, mem_sep_iff, mem_empty_iff_false, iff_false, not_and]
theorem sep_true : { x ∈ s | True } = s :=
inter_univ s
theorem sep_false : { x ∈ s | False } = ∅ :=
inter_empty s
theorem sep_empty (p : α → Prop) : { x ∈ (∅ : Set α) | p x } = ∅ :=
empty_inter {x | p x}
theorem sep_univ : { x ∈ (univ : Set α) | p x } = { x | p x } :=
univ_inter {x | p x}
@[simp]
theorem sep_union : { x | (x ∈ s ∨ x ∈ t) ∧ p x } = { x ∈ s | p x } ∪ { x ∈ t | p x } :=
union_inter_distrib_right { x | x ∈ s } { x | x ∈ t } p
@[simp]
theorem sep_inter : { x | (x ∈ s ∧ x ∈ t) ∧ p x } = { x ∈ s | p x } ∩ { x ∈ t | p x } :=
inter_inter_distrib_right s t {x | p x}
@[simp]
theorem sep_and : { x ∈ s | p x ∧ q x } = { x ∈ s | p x } ∩ { x ∈ s | q x } :=
inter_inter_distrib_left s {x | p x} {x | q x}
@[simp]
theorem sep_or : { x ∈ s | p x ∨ q x } = { x ∈ s | p x } ∪ { x ∈ s | q x } :=
inter_union_distrib_left s p q
@[simp]
theorem sep_setOf : { x ∈ { y | p y } | q x } = { x | p x ∧ q x } :=
rfl
end Sep
/-- See also `Set.sdiff_inter_right_comm`. -/
lemma inter_diff_assoc (a b c : Set α) : (a ∩ b) \ c = a ∩ (b \ c) := inf_sdiff_assoc ..
/-- See also `Set.inter_diff_assoc`. -/
lemma sdiff_inter_right_comm (s t u : Set α) : s \ t ∩ u = (s ∩ u) \ t := sdiff_inf_right_comm ..
lemma inter_sdiff_left_comm (s t u : Set α) : s ∩ (t \ u) = t ∩ (s \ u) := inf_sdiff_left_comm ..
theorem diff_union_diff_cancel (hts : t ⊆ s) (hut : u ⊆ t) : s \ t ∪ t \ u = s \ u :=
sdiff_sup_sdiff_cancel hts hut
/-- A version of `diff_union_diff_cancel` with more general hypotheses. -/
theorem diff_union_diff_cancel' (hi : s ∩ u ⊆ t) (hu : t ⊆ s ∪ u) : (s \ t) ∪ (t \ u) = s \ u :=
sdiff_sup_sdiff_cancel' hi hu
theorem diff_diff_eq_sdiff_union (h : u ⊆ s) : s \ (t \ u) = s \ t ∪ u := sdiff_sdiff_eq_sdiff_sup h
theorem inter_diff_distrib_left (s t u : Set α) : s ∩ (t \ u) = (s ∩ t) \ (s ∩ u) :=
inf_sdiff_distrib_left _ _ _
theorem inter_diff_distrib_right (s t u : Set α) : (s \ t) ∩ u = (s ∩ u) \ (t ∩ u) :=
inf_sdiff_distrib_right _ _ _
theorem diff_inter_distrib_right (s t r : Set α) : (t ∩ r) \ s = (t \ s) ∩ (r \ s) :=
inf_sdiff
/-! ### Lemmas about complement -/
theorem compl_def (s : Set α) : sᶜ = { x | x ∉ s } :=
rfl
theorem mem_compl {s : Set α} {x : α} (h : x ∉ s) : x ∈ sᶜ :=
h
theorem compl_setOf {α} (p : α → Prop) : { a | p a }ᶜ = { a | ¬p a } :=
rfl
theorem not_mem_of_mem_compl {s : Set α} {x : α} (h : x ∈ sᶜ) : x ∉ s :=
h
theorem not_mem_compl_iff {x : α} : x ∉ sᶜ ↔ x ∈ s :=
not_not
@[simp]
theorem inter_compl_self (s : Set α) : s ∩ sᶜ = ∅ :=
inf_compl_eq_bot
@[simp]
theorem compl_inter_self (s : Set α) : sᶜ ∩ s = ∅ :=
compl_inf_eq_bot
@[simp]
theorem compl_empty : (∅ : Set α)ᶜ = univ :=
compl_bot
@[simp]
theorem compl_union (s t : Set α) : (s ∪ t)ᶜ = sᶜ ∩ tᶜ :=
compl_sup
theorem compl_inter (s t : Set α) : (s ∩ t)ᶜ = sᶜ ∪ tᶜ :=
compl_inf
@[simp]
theorem compl_univ : (univ : Set α)ᶜ = ∅ :=
compl_top
@[simp]
theorem compl_empty_iff {s : Set α} : sᶜ = ∅ ↔ s = univ :=
compl_eq_bot
@[simp]
theorem compl_univ_iff {s : Set α} : sᶜ = univ ↔ s = ∅ :=
compl_eq_top
theorem compl_ne_univ : sᶜ ≠ univ ↔ s.Nonempty :=
compl_univ_iff.not.trans nonempty_iff_ne_empty.symm
lemma inl_compl_union_inr_compl {α β : Type*} {s : Set α} {t : Set β} :
Sum.inl '' sᶜ ∪ Sum.inr '' tᶜ = (Sum.inl '' s ∪ Sum.inr '' t)ᶜ := by
rw [compl_union]
aesop
theorem nonempty_compl : sᶜ.Nonempty ↔ s ≠ univ :=
(ne_univ_iff_exists_not_mem s).symm
theorem union_eq_compl_compl_inter_compl (s t : Set α) : s ∪ t = (sᶜ ∩ tᶜ)ᶜ :=
ext fun _ => or_iff_not_and_not
theorem inter_eq_compl_compl_union_compl (s t : Set α) : s ∩ t = (sᶜ ∪ tᶜ)ᶜ :=
ext fun _ => and_iff_not_or_not
@[simp]
theorem union_compl_self (s : Set α) : s ∪ sᶜ = univ :=
eq_univ_iff_forall.2 fun _ => em _
@[simp]
theorem compl_union_self (s : Set α) : sᶜ ∪ s = univ := by rw [union_comm, union_compl_self]
theorem compl_subset_comm : sᶜ ⊆ t ↔ tᶜ ⊆ s :=
@compl_le_iff_compl_le _ s _ _
theorem subset_compl_comm : s ⊆ tᶜ ↔ t ⊆ sᶜ :=
@le_compl_iff_le_compl _ _ _ t
@[simp]
theorem compl_subset_compl : sᶜ ⊆ tᶜ ↔ t ⊆ s :=
@compl_le_compl_iff_le (Set α) _ _ _
@[gcongr] theorem compl_subset_compl_of_subset (h : t ⊆ s) : sᶜ ⊆ tᶜ := compl_subset_compl.2 h
theorem subset_union_compl_iff_inter_subset {s t u : Set α} : s ⊆ t ∪ uᶜ ↔ s ∩ u ⊆ t :=
(@isCompl_compl _ u _).le_sup_right_iff_inf_left_le
theorem compl_subset_iff_union {s t : Set α} : sᶜ ⊆ t ↔ s ∪ t = univ :=
Iff.symm <| eq_univ_iff_forall.trans <| forall_congr' fun _ => or_iff_not_imp_left
theorem inter_subset (a b c : Set α) : a ∩ b ⊆ c ↔ a ⊆ bᶜ ∪ c :=
forall_congr' fun _ => and_imp.trans <| imp_congr_right fun _ => imp_iff_not_or
theorem inter_compl_nonempty_iff {s t : Set α} : (s ∩ tᶜ).Nonempty ↔ ¬s ⊆ t :=
(not_subset.trans <| exists_congr fun x => by simp [mem_compl]).symm
/-! ### Lemmas about set difference -/
theorem not_mem_diff_of_mem {s t : Set α} {x : α} (hx : x ∈ t) : x ∉ s \ t := fun h => h.2 hx
theorem mem_of_mem_diff {s t : Set α} {x : α} (h : x ∈ s \ t) : x ∈ s :=
h.left
theorem not_mem_of_mem_diff {s t : Set α} {x : α} (h : x ∈ s \ t) : x ∉ t :=
h.right
theorem diff_eq_compl_inter {s t : Set α} : s \ t = tᶜ ∩ s := by rw [diff_eq, inter_comm]
theorem diff_nonempty {s t : Set α} : (s \ t).Nonempty ↔ ¬s ⊆ t :=
inter_compl_nonempty_iff
theorem diff_subset {s t : Set α} : s \ t ⊆ s := show s \ t ≤ s from sdiff_le
theorem diff_subset_compl (s t : Set α) : s \ t ⊆ tᶜ :=
diff_eq_compl_inter ▸ inter_subset_left
theorem union_diff_cancel' {s t u : Set α} (h₁ : s ⊆ t) (h₂ : t ⊆ u) : t ∪ u \ s = u :=
sup_sdiff_cancel' h₁ h₂
theorem union_diff_cancel {s t : Set α} (h : s ⊆ t) : s ∪ t \ s = t :=
sup_sdiff_cancel_right h
theorem union_diff_cancel_left {s t : Set α} (h : s ∩ t ⊆ ∅) : (s ∪ t) \ s = t :=
Disjoint.sup_sdiff_cancel_left <| disjoint_iff_inf_le.2 h
theorem union_diff_cancel_right {s t : Set α} (h : s ∩ t ⊆ ∅) : (s ∪ t) \ t = s :=
Disjoint.sup_sdiff_cancel_right <| disjoint_iff_inf_le.2 h
@[simp]
theorem union_diff_left {s t : Set α} : (s ∪ t) \ s = t \ s :=
sup_sdiff_left_self
@[simp]
theorem union_diff_right {s t : Set α} : (s ∪ t) \ t = s \ t :=
sup_sdiff_right_self
theorem union_diff_distrib {s t u : Set α} : (s ∪ t) \ u = s \ u ∪ t \ u :=
sup_sdiff
@[simp]
theorem inter_diff_self (a b : Set α) : a ∩ (b \ a) = ∅ :=
inf_sdiff_self_right
@[simp]
theorem inter_union_diff (s t : Set α) : s ∩ t ∪ s \ t = s :=
sup_inf_sdiff s t
@[simp]
theorem diff_union_inter (s t : Set α) : s \ t ∪ s ∩ t = s := by
rw [union_comm]
exact sup_inf_sdiff _ _
@[simp]
theorem inter_union_compl (s t : Set α) : s ∩ t ∪ s ∩ tᶜ = s :=
inter_union_diff _ _
@[gcongr]
theorem diff_subset_diff {s₁ s₂ t₁ t₂ : Set α} : s₁ ⊆ s₂ → t₂ ⊆ t₁ → s₁ \ t₁ ⊆ s₂ \ t₂ :=
show s₁ ≤ s₂ → t₂ ≤ t₁ → s₁ \ t₁ ≤ s₂ \ t₂ from sdiff_le_sdiff
@[gcongr]
theorem diff_subset_diff_left {s₁ s₂ t : Set α} (h : s₁ ⊆ s₂) : s₁ \ t ⊆ s₂ \ t :=
sdiff_le_sdiff_right ‹s₁ ≤ s₂›
@[gcongr]
theorem diff_subset_diff_right {s t u : Set α} (h : t ⊆ u) : s \ u ⊆ s \ t :=
sdiff_le_sdiff_left ‹t ≤ u›
theorem diff_subset_diff_iff_subset {r : Set α} (hs : s ⊆ r) (ht : t ⊆ r) :
r \ s ⊆ r \ t ↔ t ⊆ s :=
sdiff_le_sdiff_iff_le hs ht
theorem compl_eq_univ_diff (s : Set α) : sᶜ = univ \ s :=
top_sdiff.symm
@[simp]
theorem empty_diff (s : Set α) : (∅ \ s : Set α) = ∅ :=
bot_sdiff
theorem diff_eq_empty {s t : Set α} : s \ t = ∅ ↔ s ⊆ t :=
sdiff_eq_bot_iff
@[simp]
theorem diff_empty {s : Set α} : s \ ∅ = s :=
sdiff_bot
@[simp]
theorem diff_univ (s : Set α) : s \ univ = ∅ :=
diff_eq_empty.2 (subset_univ s)
theorem diff_diff {u : Set α} : (s \ t) \ u = s \ (t ∪ u) :=
sdiff_sdiff_left
-- the following statement contains parentheses to help the reader
theorem diff_diff_comm {s t u : Set α} : (s \ t) \ u = (s \ u) \ t :=
sdiff_sdiff_comm
theorem diff_subset_iff {s t u : Set α} : s \ t ⊆ u ↔ s ⊆ t ∪ u :=
show s \ t ≤ u ↔ s ≤ t ∪ u from sdiff_le_iff
theorem subset_diff_union (s t : Set α) : s ⊆ s \ t ∪ t :=
show s ≤ s \ t ∪ t from le_sdiff_sup
theorem diff_union_of_subset {s t : Set α} (h : t ⊆ s) : s \ t ∪ t = s :=
Subset.antisymm (union_subset diff_subset h) (subset_diff_union _ _)
theorem diff_subset_comm {s t u : Set α} : s \ t ⊆ u ↔ s \ u ⊆ t :=
show s \ t ≤ u ↔ s \ u ≤ t from sdiff_le_comm
theorem diff_inter {s t u : Set α} : s \ (t ∩ u) = s \ t ∪ s \ u :=
sdiff_inf
theorem diff_inter_diff : s \ t ∩ (s \ u) = s \ (t ∪ u) :=
sdiff_sup.symm
theorem diff_compl : s \ tᶜ = s ∩ t :=
sdiff_compl
theorem compl_diff : (t \ s)ᶜ = s ∪ tᶜ :=
Eq.trans compl_sdiff himp_eq
theorem diff_diff_right {s t u : Set α} : s \ (t \ u) = s \ t ∪ s ∩ u :=
sdiff_sdiff_right'
theorem inter_diff_right_comm : (s ∩ t) \ u = s \ u ∩ t := by
rw [diff_eq, diff_eq, inter_right_comm]
theorem diff_inter_right_comm : (s \ u) ∩ t = (s ∩ t) \ u := by
rw [diff_eq, diff_eq, inter_right_comm]
@[simp]
theorem union_diff_self {s t : Set α} : s ∪ t \ s = s ∪ t :=
sup_sdiff_self _ _
@[simp]
theorem diff_union_self {s t : Set α} : s \ t ∪ t = s ∪ t :=
sdiff_sup_self _ _
@[simp]
theorem diff_inter_self {a b : Set α} : b \ a ∩ a = ∅ :=
inf_sdiff_self_left
@[simp]
theorem diff_inter_self_eq_diff {s t : Set α} : s \ (t ∩ s) = s \ t :=
sdiff_inf_self_right _ _
@[simp]
theorem diff_self_inter {s t : Set α} : s \ (s ∩ t) = s \ t :=
sdiff_inf_self_left _ _
theorem diff_self {s : Set α} : s \ s = ∅ :=
sdiff_self
theorem diff_diff_right_self (s t : Set α) : s \ (s \ t) = s ∩ t :=
sdiff_sdiff_right_self
theorem diff_diff_cancel_left {s t : Set α} (h : s ⊆ t) : t \ (t \ s) = s :=
sdiff_sdiff_eq_self h
theorem union_eq_diff_union_diff_union_inter (s t : Set α) : s ∪ t = s \ t ∪ t \ s ∪ s ∩ t :=
sup_eq_sdiff_sup_sdiff_sup_inf
/-! ### Powerset -/
theorem mem_powerset {x s : Set α} (h : x ⊆ s) : x ∈ 𝒫 s := @h
theorem subset_of_mem_powerset {x s : Set α} (h : x ∈ 𝒫 s) : x ⊆ s := @h
@[simp]
theorem mem_powerset_iff (x s : Set α) : x ∈ 𝒫 s ↔ x ⊆ s :=
Iff.rfl
theorem powerset_inter (s t : Set α) : 𝒫(s ∩ t) = 𝒫 s ∩ 𝒫 t :=
ext fun _ => subset_inter_iff
@[simp]
theorem powerset_mono : 𝒫 s ⊆ 𝒫 t ↔ s ⊆ t :=
⟨fun h => @h _ (fun _ h => h), fun h _ hu _ ha => h (hu ha)⟩
theorem monotone_powerset : Monotone (powerset : Set α → Set (Set α)) := fun _ _ => powerset_mono.2
@[simp]
theorem powerset_nonempty : (𝒫 s).Nonempty :=
⟨∅, fun _ h => empty_subset s h⟩
@[simp]
theorem powerset_empty : 𝒫(∅ : Set α) = {∅} :=
ext fun _ => subset_empty_iff
@[simp]
theorem powerset_univ : 𝒫(univ : Set α) = univ :=
eq_univ_of_forall subset_univ
/-! ### Sets defined as an if-then-else -/
@[deprecated _root_.mem_dite (since := "2025-01-30")]
protected theorem mem_dite (p : Prop) [Decidable p] (s : p → Set α) (t : ¬ p → Set α) (x : α) :
(x ∈ if h : p then s h else t h) ↔ (∀ h : p, x ∈ s h) ∧ ∀ h : ¬p, x ∈ t h :=
_root_.mem_dite
theorem mem_dite_univ_right (p : Prop) [Decidable p] (t : p → Set α) (x : α) :
(x ∈ if h : p then t h else univ) ↔ ∀ h : p, x ∈ t h := by
simp [mem_dite]
@[simp]
theorem mem_ite_univ_right (p : Prop) [Decidable p] (t : Set α) (x : α) :
x ∈ ite p t Set.univ ↔ p → x ∈ t :=
mem_dite_univ_right p (fun _ => t) x
theorem mem_dite_univ_left (p : Prop) [Decidable p] (t : ¬p → Set α) (x : α) :
(x ∈ if h : p then univ else t h) ↔ ∀ h : ¬p, x ∈ t h := by
split_ifs <;> simp_all
@[simp]
theorem mem_ite_univ_left (p : Prop) [Decidable p] (t : Set α) (x : α) :
x ∈ ite p Set.univ t ↔ ¬p → x ∈ t :=
mem_dite_univ_left p (fun _ => t) x
theorem mem_dite_empty_right (p : Prop) [Decidable p] (t : p → Set α) (x : α) :
(x ∈ if h : p then t h else ∅) ↔ ∃ h : p, x ∈ t h := by
simp only [mem_dite, mem_empty_iff_false, imp_false, not_not]
exact ⟨fun h => ⟨h.2, h.1 h.2⟩, fun ⟨h₁, h₂⟩ => ⟨fun _ => h₂, h₁⟩⟩
@[simp]
theorem mem_ite_empty_right (p : Prop) [Decidable p] (t : Set α) (x : α) :
x ∈ ite p t ∅ ↔ p ∧ x ∈ t :=
(mem_dite_empty_right p (fun _ => t) x).trans (by simp)
theorem mem_dite_empty_left (p : Prop) [Decidable p] (t : ¬p → Set α) (x : α) :
(x ∈ if h : p then ∅ else t h) ↔ ∃ h : ¬p, x ∈ t h := by
simp only [mem_dite, mem_empty_iff_false, imp_false]
exact ⟨fun h => ⟨h.1, h.2 h.1⟩, fun ⟨h₁, h₂⟩ => ⟨fun h => h₁ h, fun _ => h₂⟩⟩
@[simp]
theorem mem_ite_empty_left (p : Prop) [Decidable p] (t : Set α) (x : α) :
x ∈ ite p ∅ t ↔ ¬p ∧ x ∈ t :=
(mem_dite_empty_left p (fun _ => t) x).trans (by simp)
/-! ### If-then-else for sets -/
/-- `ite` for sets: `Set.ite t s s' ∩ t = s ∩ t`, `Set.ite t s s' ∩ tᶜ = s' ∩ tᶜ`.
Defined as `s ∩ t ∪ s' \ t`. -/
protected def ite (t s s' : Set α) : Set α :=
s ∩ t ∪ s' \ t
@[simp]
theorem ite_inter_self (t s s' : Set α) : t.ite s s' ∩ t = s ∩ t := by
rw [Set.ite, union_inter_distrib_right, diff_inter_self, inter_assoc, inter_self, union_empty]
@[simp]
theorem ite_compl (t s s' : Set α) : tᶜ.ite s s' = t.ite s' s := by
rw [Set.ite, Set.ite, diff_compl, union_comm, diff_eq]
@[simp]
theorem ite_inter_compl_self (t s s' : Set α) : t.ite s s' ∩ tᶜ = s' ∩ tᶜ := by
rw [← ite_compl, ite_inter_self]
@[simp]
theorem ite_diff_self (t s s' : Set α) : t.ite s s' \ t = s' \ t :=
ite_inter_compl_self t s s'
@[simp]
theorem ite_same (t s : Set α) : t.ite s s = s :=
inter_union_diff _ _
@[simp]
theorem ite_left (s t : Set α) : s.ite s t = s ∪ t := by simp [Set.ite]
@[simp]
theorem ite_right (s t : Set α) : s.ite t s = t ∩ s := by simp [Set.ite]
@[simp]
theorem ite_empty (s s' : Set α) : Set.ite ∅ s s' = s' := by simp [Set.ite]
@[simp]
theorem ite_univ (s s' : Set α) : Set.ite univ s s' = s := by simp [Set.ite]
@[simp]
theorem ite_empty_left (t s : Set α) : t.ite ∅ s = s \ t := by simp [Set.ite]
@[simp]
theorem ite_empty_right (t s : Set α) : t.ite s ∅ = s ∩ t := by simp [Set.ite]
theorem ite_mono (t : Set α) {s₁ s₁' s₂ s₂' : Set α} (h : s₁ ⊆ s₂) (h' : s₁' ⊆ s₂') :
t.ite s₁ s₁' ⊆ t.ite s₂ s₂' :=
union_subset_union (inter_subset_inter_left _ h) (inter_subset_inter_left _ h')
theorem ite_subset_union (t s s' : Set α) : t.ite s s' ⊆ s ∪ s' :=
union_subset_union inter_subset_left diff_subset
theorem inter_subset_ite (t s s' : Set α) : s ∩ s' ⊆ t.ite s s' :=
ite_same t (s ∩ s') ▸ ite_mono _ inter_subset_left inter_subset_right
theorem ite_inter_inter (t s₁ s₂ s₁' s₂' : Set α) :
t.ite (s₁ ∩ s₂) (s₁' ∩ s₂') = t.ite s₁ s₁' ∩ t.ite s₂ s₂' := by
ext x
simp only [Set.ite, Set.mem_inter_iff, Set.mem_diff, Set.mem_union]
tauto
theorem ite_inter (t s₁ s₂ s : Set α) : t.ite (s₁ ∩ s) (s₂ ∩ s) = t.ite s₁ s₂ ∩ s := by
rw [ite_inter_inter, ite_same]
theorem ite_inter_of_inter_eq (t : Set α) {s₁ s₂ s : Set α} (h : s₁ ∩ s = s₂ ∩ s) :
t.ite s₁ s₂ ∩ s = s₁ ∩ s := by rw [← ite_inter, ← h, ite_same]
theorem subset_ite {t s s' u : Set α} : u ⊆ t.ite s s' ↔ u ∩ t ⊆ s ∧ u \ t ⊆ s' := by
simp only [subset_def, ← forall_and]
refine forall_congr' fun x => ?_
by_cases hx : x ∈ t <;> simp [*, Set.ite]
theorem ite_eq_of_subset_left (t : Set α) {s₁ s₂ : Set α} (h : s₁ ⊆ s₂) :
t.ite s₁ s₂ = s₁ ∪ (s₂ \ t) := by
ext x
by_cases hx : x ∈ t <;> simp [*, Set.ite, or_iff_right_of_imp (@h x)]
theorem ite_eq_of_subset_right (t : Set α) {s₁ s₂ : Set α} (h : s₂ ⊆ s₁) :
t.ite s₁ s₂ = (s₁ ∩ t) ∪ s₂ := by
ext x
by_cases hx : x ∈ t <;> simp [*, Set.ite, or_iff_left_of_imp (@h x)]
end Set
open Set
namespace Function
variable {α : Type*} {β : Type*}
theorem Injective.nonempty_apply_iff {f : Set α → Set β} (hf : Injective f) (h2 : f ∅ = ∅)
{s : Set α} : (f s).Nonempty ↔ s.Nonempty := by
rw [nonempty_iff_ne_empty, ← h2, nonempty_iff_ne_empty, hf.ne_iff]
end Function
namespace Subsingleton
variable {α : Type*} [Subsingleton α]
theorem eq_univ_of_nonempty {s : Set α} : s.Nonempty → s = univ := fun ⟨x, hx⟩ =>
eq_univ_of_forall fun y => Subsingleton.elim x y ▸ hx
@[elab_as_elim]
theorem set_cases {p : Set α → Prop} (h0 : p ∅) (h1 : p univ) (s) : p s :=
(s.eq_empty_or_nonempty.elim fun h => h.symm ▸ h0) fun h => (eq_univ_of_nonempty h).symm ▸ h1
theorem mem_iff_nonempty {α : Type*} [Subsingleton α] {s : Set α} {x : α} : x ∈ s ↔ s.Nonempty :=
⟨fun hx => ⟨x, hx⟩, fun ⟨y, hy⟩ => Subsingleton.elim y x ▸ hy⟩
end Subsingleton
/-! ### Decidability instances for sets -/
namespace Set
variable {α : Type u} (s t : Set α) (a b : α)
instance decidableSdiff [Decidable (a ∈ s)] [Decidable (a ∈ t)] : Decidable (a ∈ s \ t) :=
inferInstanceAs (Decidable (a ∈ s ∧ a ∉ t))
instance decidableInter [Decidable (a ∈ s)] [Decidable (a ∈ t)] : Decidable (a ∈ s ∩ t) :=
inferInstanceAs (Decidable (a ∈ s ∧ a ∈ t))
instance decidableUnion [Decidable (a ∈ s)] [Decidable (a ∈ t)] : Decidable (a ∈ s ∪ t) :=
inferInstanceAs (Decidable (a ∈ s ∨ a ∈ t))
instance decidableCompl [Decidable (a ∈ s)] : Decidable (a ∈ sᶜ) :=
inferInstanceAs (Decidable (a ∉ s))
instance decidableEmptyset : Decidable (a ∈ (∅ : Set α)) := Decidable.isFalse (by simp)
instance decidableUniv : Decidable (a ∈ univ) := Decidable.isTrue (by simp)
instance decidableInsert [Decidable (a = b)] [Decidable (a ∈ s)] : Decidable (a ∈ insert b s) :=
inferInstanceAs (Decidable (_ ∨ _))
instance decidableSetOf (p : α → Prop) [Decidable (p a)] : Decidable (a ∈ { a | p a }) := by
assumption
end Set
variable {α : Type*} {s t u : Set α}
namespace Equiv
/-- Given a predicate `p : α → Prop`, produces an equivalence between
`Set {a : α // p a}` and `{s : Set α // ∀ a ∈ s, p a}`. -/
protected def setSubtypeComm (p : α → Prop) :
Set {a : α // p a} ≃ {s : Set α // ∀ a ∈ s, p a} where
toFun s := ⟨{a | ∃ h : p a, s ⟨a, h⟩}, fun _ h ↦ h.1⟩
invFun s := {a | a.val ∈ s.val}
left_inv s := by ext a; exact ⟨fun h ↦ h.2, fun h ↦ ⟨a.property, h⟩⟩
right_inv s := by ext; exact ⟨fun h ↦ h.2, fun h ↦ ⟨s.property _ h, h⟩⟩
@[simp]
protected lemma setSubtypeComm_apply (p : α → Prop) (s : Set {a // p a}) :
(Equiv.setSubtypeComm p) s = ⟨{a | ∃ h : p a, ⟨a, h⟩ ∈ s}, fun _ h ↦ h.1⟩ :=
rfl
@[simp]
protected lemma setSubtypeComm_symm_apply (p : α → Prop) (s : {s // ∀ a ∈ s, p a}) :
(Equiv.setSubtypeComm p).symm s = {a | a.val ∈ s.val} :=
rfl
end Equiv
| Mathlib/Data/Set/Basic.lean | 2,090 | 2,091 | |
/-
Copyright (c) 2022 Markus Himmel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Markus Himmel
-/
import Mathlib.Data.Opposite
import Mathlib.Data.Set.Operations
/-!
# The opposite of a set
The opposite of a set `s` is simply the set obtained by taking the opposite of each member of `s`.
-/
variable {α : Type*}
open Opposite
namespace Set
/-- The opposite of a set `s` is the set obtained by taking the opposite of each member of `s`. -/
protected def op (s : Set α) : Set αᵒᵖ :=
unop ⁻¹' s
/-- The unop of a set `s` is the set obtained by taking the unop of each member of `s`. -/
protected def unop (s : Set αᵒᵖ) : Set α :=
op ⁻¹' s
@[simp]
theorem mem_op {s : Set α} {a : αᵒᵖ} : a ∈ s.op ↔ unop a ∈ s :=
Iff.rfl
@[simp 1100]
theorem op_mem_op {s : Set α} {a : α} : op a ∈ s.op ↔ a ∈ s := by rfl
@[simp]
theorem mem_unop {s : Set αᵒᵖ} {a : α} : a ∈ s.unop ↔ op a ∈ s :=
Iff.rfl
@[simp 1100]
theorem unop_mem_unop {s : Set αᵒᵖ} {a : αᵒᵖ} : unop a ∈ s.unop ↔ a ∈ s := by rfl
@[simp]
theorem op_unop (s : Set α) : s.op.unop = s := rfl
@[simp]
theorem unop_op (s : Set αᵒᵖ) : s.unop.op = s := rfl
| Mathlib/Data/Set/Opposite.lean | 48 | 48 | |
/-
Copyright (c) 2019 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Algebra.Order.BigOperators.Ring.Finset
import Mathlib.Analysis.Convex.Hull
import Mathlib.LinearAlgebra.AffineSpace.Basis
/-!
# Convex combinations
This file defines convex combinations of points in a vector space.
## Main declarations
* `Finset.centerMass`: Center of mass of a finite family of points.
## Implementation notes
We divide by the sum of the weights in the definition of `Finset.centerMass` because of the way
mathematical arguments go: one doesn't change weights, but merely adds some. This also makes a few
lemmas unconditional on the sum of the weights being `1`.
-/
open Set Function Pointwise
universe u u'
section
variable {R R' E F ι ι' α : Type*} [Field R] [Field R'] [AddCommGroup E] [AddCommGroup F]
[AddCommGroup α] [LinearOrder α] [Module R E] [Module R F] [Module R α] {s : Set E}
/-- Center of mass of a finite collection of points with prescribed weights.
Note that we require neither `0 ≤ w i` nor `∑ w = 1`. -/
def Finset.centerMass (t : Finset ι) (w : ι → R) (z : ι → E) : E :=
(∑ i ∈ t, w i)⁻¹ • ∑ i ∈ t, w i • z i
variable (i j : ι) (c : R) (t : Finset ι) (w : ι → R) (z : ι → E)
open Finset
theorem Finset.centerMass_empty : (∅ : Finset ι).centerMass w z = 0 := by
simp only [centerMass, sum_empty, smul_zero]
theorem Finset.centerMass_pair [DecidableEq ι] (hne : i ≠ j) :
({i, j} : Finset ι).centerMass w z = (w i / (w i + w j)) • z i + (w j / (w i + w j)) • z j := by
simp only [centerMass, sum_pair hne]
module
variable {w}
theorem Finset.centerMass_insert [DecidableEq ι] (ha : i ∉ t) (hw : ∑ j ∈ t, w j ≠ 0) :
(insert i t).centerMass w z =
(w i / (w i + ∑ j ∈ t, w j)) • z i +
((∑ j ∈ t, w j) / (w i + ∑ j ∈ t, w j)) • t.centerMass w z := by
simp only [centerMass, sum_insert ha, smul_add, (mul_smul _ _ _).symm, ← div_eq_inv_mul]
congr 2
rw [div_mul_eq_mul_div, mul_inv_cancel₀ hw, one_div]
theorem Finset.centerMass_singleton (hw : w i ≠ 0) : ({i} : Finset ι).centerMass w z = z i := by
rw [centerMass, sum_singleton, sum_singleton]
match_scalars
field_simp
@[simp] lemma Finset.centerMass_neg_left : t.centerMass (-w) z = t.centerMass w z := by
simp [centerMass, inv_neg]
lemma Finset.centerMass_smul_left {c : R'} [Module R' R] [Module R' E] [SMulCommClass R' R R]
[IsScalarTower R' R R] [SMulCommClass R R' E] [IsScalarTower R' R E] (hc : c ≠ 0) :
t.centerMass (c • w) z = t.centerMass w z := by
simp [centerMass, -smul_assoc, smul_assoc c, ← smul_sum, smul_inv₀, smul_smul_smul_comm, hc]
theorem Finset.centerMass_eq_of_sum_1 (hw : ∑ i ∈ t, w i = 1) :
t.centerMass w z = ∑ i ∈ t, w i • z i := by
simp only [Finset.centerMass, hw, inv_one, one_smul]
theorem Finset.centerMass_smul : (t.centerMass w fun i => c • z i) = c • t.centerMass w z := by
simp only [Finset.centerMass, Finset.smul_sum, (mul_smul _ _ _).symm, mul_comm c, mul_assoc]
/-- A convex combination of two centers of mass is a center of mass as well. This version
deals with two different index types. -/
theorem Finset.centerMass_segment' (s : Finset ι) (t : Finset ι') (ws : ι → R) (zs : ι → E)
(wt : ι' → R) (zt : ι' → E) (hws : ∑ i ∈ s, ws i = 1) (hwt : ∑ i ∈ t, wt i = 1) (a b : R)
(hab : a + b = 1) : a • s.centerMass ws zs + b • t.centerMass wt zt = (s.disjSum t).centerMass
(Sum.elim (fun i => a * ws i) fun j => b * wt j) (Sum.elim zs zt) := by
rw [s.centerMass_eq_of_sum_1 _ hws, t.centerMass_eq_of_sum_1 _ hwt, smul_sum, smul_sum, ←
Finset.sum_sumElim, Finset.centerMass_eq_of_sum_1]
· congr with ⟨⟩ <;> simp only [Sum.elim_inl, Sum.elim_inr, mul_smul]
· rw [sum_sumElim, ← mul_sum, ← mul_sum, hws, hwt, mul_one, mul_one, hab]
/-- A convex combination of two centers of mass is a center of mass as well. This version
works if two centers of mass share the set of original points. -/
theorem Finset.centerMass_segment (s : Finset ι) (w₁ w₂ : ι → R) (z : ι → E)
(hw₁ : ∑ i ∈ s, w₁ i = 1) (hw₂ : ∑ i ∈ s, w₂ i = 1) (a b : R) (hab : a + b = 1) :
a • s.centerMass w₁ z + b • s.centerMass w₂ z =
s.centerMass (fun i => a * w₁ i + b * w₂ i) z := by
have hw : (∑ i ∈ s, (a * w₁ i + b * w₂ i)) = 1 := by
simp only [← mul_sum, sum_add_distrib, mul_one, *]
simp only [Finset.centerMass_eq_of_sum_1, Finset.centerMass_eq_of_sum_1 _ _ hw,
smul_sum, sum_add_distrib, add_smul, mul_smul, *]
theorem Finset.centerMass_ite_eq [DecidableEq ι] (hi : i ∈ t) :
t.centerMass (fun j => if i = j then (1 : R) else 0) z = z i := by
rw [Finset.centerMass_eq_of_sum_1]
· trans ∑ j ∈ t, if i = j then z i else 0
· congr with i
split_ifs with h
exacts [h ▸ one_smul _ _, zero_smul _ _]
· rw [sum_ite_eq, if_pos hi]
· rw [sum_ite_eq, if_pos hi]
variable {t}
theorem Finset.centerMass_subset {t' : Finset ι} (ht : t ⊆ t') (h : ∀ i ∈ t', i ∉ t → w i = 0) :
t.centerMass w z = t'.centerMass w z := by
rw [centerMass, sum_subset ht h, smul_sum, centerMass, smul_sum]
apply sum_subset ht
intro i hit' hit
rw [h i hit' hit, zero_smul, smul_zero]
theorem Finset.centerMass_filter_ne_zero [∀ i, Decidable (w i ≠ 0)] :
{i ∈ t | w i ≠ 0}.centerMass w z = t.centerMass w z :=
Finset.centerMass_subset z (filter_subset _ _) fun i hit hit' => by
simpa only [hit, mem_filter, true_and, Ne, Classical.not_not] using hit'
namespace Finset
variable [LinearOrder R] [IsStrictOrderedRing R] [IsOrderedAddMonoid α] [OrderedSMul R α]
theorem centerMass_le_sup {s : Finset ι} {f : ι → α} {w : ι → R} (hw₀ : ∀ i ∈ s, 0 ≤ w i)
(hw₁ : 0 < ∑ i ∈ s, w i) :
s.centerMass w f ≤ s.sup' (nonempty_of_ne_empty <| by rintro rfl; simp at hw₁) f := by
rw [centerMass, inv_smul_le_iff_of_pos hw₁, sum_smul]
| exact sum_le_sum fun i hi => smul_le_smul_of_nonneg_left (le_sup' _ hi) <| hw₀ i hi
theorem inf_le_centerMass {s : Finset ι} {f : ι → α} {w : ι → R} (hw₀ : ∀ i ∈ s, 0 ≤ w i)
(hw₁ : 0 < ∑ i ∈ s, w i) :
| Mathlib/Analysis/Convex/Combination.lean | 136 | 139 |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Patrick Massot, Casper Putz, Anne Baanen
-/
import Mathlib.LinearAlgebra.FreeModule.StrongRankCondition
import Mathlib.LinearAlgebra.GeneralLinearGroup
import Mathlib.LinearAlgebra.Matrix.Reindex
import Mathlib.Tactic.FieldSimp
import Mathlib.LinearAlgebra.Matrix.NonsingularInverse
import Mathlib.LinearAlgebra.Matrix.Basis
/-!
# Determinant of families of vectors
This file defines the determinant of an endomorphism, and of a family of vectors
with respect to some basis. For the determinant of a matrix, see the file
`LinearAlgebra.Matrix.Determinant`.
## Main definitions
In the list below, and in all this file, `R` is a commutative ring (semiring
is sometimes enough), `M` and its variations are `R`-modules, `ι`, `κ`, `n` and `m` are finite
types used for indexing.
* `Basis.det`: the determinant of a family of vectors with respect to a basis,
as a multilinear map
* `LinearMap.det`: the determinant of an endomorphism `f : End R M` as a
multiplicative homomorphism (if `M` does not have a finite `R`-basis, the
result is `1` instead)
* `LinearEquiv.det`: the determinant of an isomorphism `f : M ≃ₗ[R] M` as a
multiplicative homomorphism (if `M` does not have a finite `R`-basis, the
result is `1` instead)
## Tags
basis, det, determinant
-/
noncomputable section
open Matrix LinearMap Submodule Set Function
universe u v w
variable {R : Type*} [CommRing R]
variable {M : Type*} [AddCommGroup M] [Module R M]
variable {M' : Type*} [AddCommGroup M'] [Module R M']
variable {ι : Type*} [DecidableEq ι] [Fintype ι]
variable (e : Basis ι R M)
section Conjugate
variable {A : Type*} [CommRing A]
variable {m n : Type*}
/-- If `R^m` and `R^n` are linearly equivalent, then `m` and `n` are also equivalent. -/
def equivOfPiLEquivPi {R : Type*} [Finite m] [Finite n] [CommRing R] [Nontrivial R]
(e : (m → R) ≃ₗ[R] n → R) : m ≃ n :=
Basis.indexEquiv (Basis.ofEquivFun e.symm) (Pi.basisFun _ _)
namespace Matrix
variable [Fintype m] [Fintype n]
/-- If `M` and `M'` are each other's inverse matrices, they are square matrices up to
equivalence of types. -/
def indexEquivOfInv [Nontrivial A] [DecidableEq m] [DecidableEq n] {M : Matrix m n A}
{M' : Matrix n m A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) : m ≃ n :=
equivOfPiLEquivPi (toLin'OfInv hMM' hM'M)
theorem det_comm [DecidableEq n] (M N : Matrix n n A) : det (M * N) = det (N * M) := by
rw [det_mul, det_mul, mul_comm]
/-- If there exists a two-sided inverse `M'` for `M` (indexed differently),
then `det (N * M) = det (M * N)`. -/
theorem det_comm' [DecidableEq m] [DecidableEq n] {M : Matrix n m A} {N : Matrix m n A}
{M' : Matrix m n A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) : det (M * N) = det (N * M) := by
nontriviality A
-- Although `m` and `n` are different a priori, we will show they have the same cardinality.
-- This turns the problem into one for square matrices, which is easy.
let e := indexEquivOfInv hMM' hM'M
rw [← det_submatrix_equiv_self e, ← submatrix_mul_equiv _ _ _ (Equiv.refl n) _, det_comm,
submatrix_mul_equiv, Equiv.coe_refl, submatrix_id_id]
/-- If `M'` is a two-sided inverse for `M` (indexed differently), `det (M * N * M') = det N`.
See `Matrix.det_conj` and `Matrix.det_conj'` for the case when `M' = M⁻¹` or vice versa. -/
theorem det_conj_of_mul_eq_one [DecidableEq m] [DecidableEq n] {M : Matrix m n A}
{M' : Matrix n m A} {N : Matrix n n A} (hMM' : M * M' = 1) (hM'M : M' * M = 1) :
det (M * N * M') = det N := by
rw [← det_comm' hM'M hMM', ← Matrix.mul_assoc, hM'M, Matrix.one_mul]
end Matrix
end Conjugate
namespace LinearMap
/-! ### Determinant of a linear map -/
variable {A : Type*} [CommRing A] [Module A M]
variable {κ : Type*} [Fintype κ]
/-- The determinant of `LinearMap.toMatrix` does not depend on the choice of basis. -/
theorem det_toMatrix_eq_det_toMatrix [DecidableEq κ] (b : Basis ι A M) (c : Basis κ A M)
(f : M →ₗ[A] M) : det (LinearMap.toMatrix b b f) = det (LinearMap.toMatrix c c f) := by
rw [← linearMap_toMatrix_mul_basis_toMatrix c b c, ← basis_toMatrix_mul_linearMap_toMatrix b c b,
Matrix.det_conj_of_mul_eq_one] <;>
rw [Basis.toMatrix_mul_toMatrix, Basis.toMatrix_self]
/-- The determinant of an endomorphism given a basis.
See `LinearMap.det` for a version that populates the basis non-computably.
Although the `Trunc (Basis ι A M)` parameter makes it slightly more convenient to switch bases,
there is no good way to generalize over universe parameters, so we can't fully state in `detAux`'s
type that it does not depend on the choice of basis. Instead you can use the `detAux_def''` lemma,
or avoid mentioning a basis at all using `LinearMap.det`.
-/
irreducible_def detAux : Trunc (Basis ι A M) → (M →ₗ[A] M) →* A :=
Trunc.lift
(fun b : Basis ι A M => detMonoidHom.comp (toMatrixAlgEquiv b : (M →ₗ[A] M) →* Matrix ι ι A))
fun b c => MonoidHom.ext <| det_toMatrix_eq_det_toMatrix b c
/-- Unfold lemma for `detAux`.
See also `detAux_def''` which allows you to vary the basis.
-/
theorem detAux_def' (b : Basis ι A M) (f : M →ₗ[A] M) :
LinearMap.detAux (Trunc.mk b) f = Matrix.det (LinearMap.toMatrix b b f) := by
rw [detAux]
rfl
theorem detAux_def'' {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (tb : Trunc <| Basis ι A M)
(b' : Basis ι' A M) (f : M →ₗ[A] M) :
LinearMap.detAux tb f = Matrix.det (LinearMap.toMatrix b' b' f) := by
induction tb using Trunc.induction_on with
| h b => rw [detAux_def', det_toMatrix_eq_det_toMatrix b b']
@[simp]
theorem detAux_id (b : Trunc <| Basis ι A M) : LinearMap.detAux b LinearMap.id = 1 :=
(LinearMap.detAux b).map_one
@[simp]
theorem detAux_comp (b : Trunc <| Basis ι A M) (f g : M →ₗ[A] M) :
LinearMap.detAux b (f.comp g) = LinearMap.detAux b f * LinearMap.detAux b g :=
(LinearMap.detAux b).map_mul f g
section
open scoped Classical in
-- Discourage the elaborator from unfolding `det` and producing a huge term by marking it
-- as irreducible.
/-- The determinant of an endomorphism independent of basis.
If there is no finite basis on `M`, the result is `1` instead.
-/
protected irreducible_def det : (M →ₗ[A] M) →* A :=
if H : ∃ s : Finset M, Nonempty (Basis s A M) then LinearMap.detAux (Trunc.mk H.choose_spec.some)
else 1
open scoped Classical in
theorem coe_det [DecidableEq M] :
⇑(LinearMap.det : (M →ₗ[A] M) →* A) =
if H : ∃ s : Finset M, Nonempty (Basis s A M) then
LinearMap.detAux (Trunc.mk H.choose_spec.some)
else 1 := by
ext
rw [LinearMap.det_def]
split_ifs
· congr -- use the correct `DecidableEq` instance
rfl
end
-- Auxiliary lemma, the `simp` normal form goes in the other direction
-- (using `LinearMap.det_toMatrix`)
theorem det_eq_det_toMatrix_of_finset [DecidableEq M] {s : Finset M} (b : Basis s A M)
(f : M →ₗ[A] M) : LinearMap.det f = Matrix.det (LinearMap.toMatrix b b f) := by
have : ∃ s : Finset M, Nonempty (Basis s A M) := ⟨s, ⟨b⟩⟩
rw [LinearMap.coe_det, dif_pos, detAux_def'' _ b] <;> assumption
@[simp]
theorem det_toMatrix (b : Basis ι A M) (f : M →ₗ[A] M) :
Matrix.det (toMatrix b b f) = LinearMap.det f := by
haveI := Classical.decEq M
rw [det_eq_det_toMatrix_of_finset b.reindexFinsetRange,
det_toMatrix_eq_det_toMatrix b b.reindexFinsetRange]
@[simp]
theorem det_toMatrix' {ι : Type*} [Fintype ι] [DecidableEq ι] (f : (ι → A) →ₗ[A] ι → A) :
Matrix.det (LinearMap.toMatrix' f) = LinearMap.det f := by simp [← toMatrix_eq_toMatrix']
@[simp]
theorem det_toLin (b : Basis ι R M) (f : Matrix ι ι R) :
LinearMap.det (Matrix.toLin b b f) = f.det := by
rw [← LinearMap.det_toMatrix b, LinearMap.toMatrix_toLin]
@[simp]
theorem det_toLin' (f : Matrix ι ι R) : LinearMap.det (Matrix.toLin' f) = Matrix.det f := by
simp only [← toLin_eq_toLin', det_toLin]
/-- To show `P (LinearMap.det f)` it suffices to consider `P (Matrix.det (toMatrix _ _ f))` and
`P 1`. -/
@[elab_as_elim]
theorem det_cases [DecidableEq M] {P : A → Prop} (f : M →ₗ[A] M)
(hb : ∀ (s : Finset M) (b : Basis s A M), P (Matrix.det (toMatrix b b f))) (h1 : P 1) :
P (LinearMap.det f) := by
classical
if H : ∃ s : Finset M, Nonempty (Basis s A M) then
obtain ⟨s, ⟨b⟩⟩ := H
rw [← det_toMatrix b]
exact hb s b
else
rwa [LinearMap.det_def, dif_neg H]
@[simp]
theorem det_comp (f g : M →ₗ[A] M) :
LinearMap.det (f.comp g) = LinearMap.det f * LinearMap.det g :=
LinearMap.det.map_mul f g
@[simp]
theorem det_id : LinearMap.det (LinearMap.id : M →ₗ[A] M) = 1 :=
LinearMap.det.map_one
/-- Multiplying a map by a scalar `c` multiplies its determinant by `c ^ dim M`. -/
@[simp]
theorem det_smul [Module.Free A M] (c : A) (f : M →ₗ[A] M) :
LinearMap.det (c • f) = c ^ Module.finrank A M * LinearMap.det f := by
nontriviality A
by_cases H : ∃ s : Finset M, Nonempty (Basis s A M)
· have : Module.Finite A M := by
rcases H with ⟨s, ⟨hs⟩⟩
exact Module.Finite.of_basis hs
simp only [← det_toMatrix (Module.finBasis A M), LinearEquiv.map_smul,
Fintype.card_fin, Matrix.det_smul]
· classical
have : Module.finrank A M = 0 := finrank_eq_zero_of_not_exists_basis H
simp [coe_det, H, this]
theorem det_zero' {ι : Type*} [Finite ι] [Nonempty ι] (b : Basis ι A M) :
LinearMap.det (0 : M →ₗ[A] M) = 0 := by
haveI := Classical.decEq ι
cases nonempty_fintype ι
rwa [← det_toMatrix b, LinearEquiv.map_zero, det_zero]
/-- In a finite-dimensional vector space, the zero map has determinant `1` in dimension `0`,
and `0` otherwise. We give a formula that also works in infinite dimension, where we define
the determinant to be `1`. -/
@[simp]
theorem det_zero [Module.Free A M] :
LinearMap.det (0 : M →ₗ[A] M) = (0 : A) ^ Module.finrank A M := by
simp only [← zero_smul A (1 : M →ₗ[A] M), det_smul, mul_one, MonoidHom.map_one]
theorem det_eq_one_of_not_module_finite (h : ¬Module.Finite R M) (f : M →ₗ[R] M) : f.det = 1 := by
rw [LinearMap.det, dif_neg, MonoidHom.one_apply]
exact fun ⟨_, ⟨b⟩⟩ ↦ h (Module.Finite.of_basis b)
theorem det_eq_one_of_subsingleton [Subsingleton M] (f : M →ₗ[R] M) :
LinearMap.det (f : M →ₗ[R] M) = 1 := by
have b : Basis (Fin 0) R M := Basis.empty M
rw [← f.det_toMatrix b]
exact Matrix.det_isEmpty
theorem det_eq_one_of_finrank_eq_zero {𝕜 : Type*} [Field 𝕜] {M : Type*} [AddCommGroup M]
[Module 𝕜 M] (h : Module.finrank 𝕜 M = 0) (f : M →ₗ[𝕜] M) :
LinearMap.det (f : M →ₗ[𝕜] M) = 1 := by
classical
refine @LinearMap.det_cases M _ 𝕜 _ _ _ (fun t => t = 1) f ?_ rfl
intro s b
have : IsEmpty s := by
rw [← Fintype.card_eq_zero_iff]
exact (Module.finrank_eq_card_basis b).symm.trans h
exact Matrix.det_isEmpty
/-- Conjugating a linear map by a linear equiv does not change its determinant. -/
@[simp]
theorem det_conj {N : Type*} [AddCommGroup N] [Module A N] (f : M →ₗ[A] M) (e : M ≃ₗ[A] N) :
LinearMap.det ((e : M →ₗ[A] N) ∘ₗ f ∘ₗ (e.symm : N →ₗ[A] M)) = LinearMap.det f := by
classical
by_cases H : ∃ s : Finset M, Nonempty (Basis s A M)
· rcases H with ⟨s, ⟨b⟩⟩
rw [← det_toMatrix b f, ← det_toMatrix (b.map e), toMatrix_comp (b.map e) b (b.map e),
toMatrix_comp (b.map e) b b, ← Matrix.mul_assoc, Matrix.det_conj_of_mul_eq_one]
· rw [← toMatrix_comp, LinearEquiv.comp_coe, e.symm_trans_self, LinearEquiv.refl_toLinearMap,
toMatrix_id]
· rw [← toMatrix_comp, LinearEquiv.comp_coe, e.self_trans_symm, LinearEquiv.refl_toLinearMap,
toMatrix_id]
· have H' : ¬∃ t : Finset N, Nonempty (Basis t A N) := by
contrapose! H
rcases H with ⟨s, ⟨b⟩⟩
exact ⟨_, ⟨(b.map e.symm).reindexFinsetRange⟩⟩
simp only [coe_det, H, H', MonoidHom.one_apply, dif_neg, not_false_eq_true]
/-- If a linear map is invertible, so is its determinant. -/
theorem isUnit_det {A : Type*} [CommRing A] [Module A M] (f : M →ₗ[A] M) (hf : IsUnit f) :
IsUnit (LinearMap.det f) := by
obtain ⟨g, hg⟩ : ∃ g, f.comp g = 1 := hf.exists_right_inv
have : LinearMap.det f * LinearMap.det g = 1 := by
simp only [← LinearMap.det_comp, hg, MonoidHom.map_one]
exact isUnit_of_mul_eq_one _ _ this
/-- If a linear map has determinant different from `1`, then the space is finite-dimensional. -/
theorem finiteDimensional_of_det_ne_one {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] (f : M →ₗ[𝕜] M)
(hf : LinearMap.det f ≠ 1) : FiniteDimensional 𝕜 M := by
by_cases H : ∃ s : Finset M, Nonempty (Basis s 𝕜 M)
· rcases H with ⟨s, ⟨hs⟩⟩
exact FiniteDimensional.of_fintype_basis hs
· classical simp [LinearMap.coe_det, H] at hf
/-- If the determinant of a map vanishes, then the map is not onto. -/
theorem range_lt_top_of_det_eq_zero {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] {f : M →ₗ[𝕜] M}
(hf : LinearMap.det f = 0) : LinearMap.range f < ⊤ := by
have : FiniteDimensional 𝕜 M := by simp [f.finiteDimensional_of_det_ne_one, hf]
contrapose hf
simp only [lt_top_iff_ne_top, Classical.not_not, ← isUnit_iff_range_eq_top] at hf
exact isUnit_iff_ne_zero.1 (f.isUnit_det hf)
/-- If the determinant of a map vanishes, then the map is not injective. -/
theorem bot_lt_ker_of_det_eq_zero {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] {f : M →ₗ[𝕜] M}
(hf : LinearMap.det f = 0) : ⊥ < LinearMap.ker f := by
have : FiniteDimensional 𝕜 M := by simp [f.finiteDimensional_of_det_ne_one, hf]
contrapose hf
simp only [bot_lt_iff_ne_bot, Classical.not_not, ← isUnit_iff_ker_eq_bot] at hf
exact isUnit_iff_ne_zero.1 (f.isUnit_det hf)
/-- When the function is over the base ring, the determinant is the evaluation at `1`. -/
@[simp] lemma det_ring (f : R →ₗ[R] R) : f.det = f 1 := by
simp [← det_toMatrix (Basis.singleton Unit R)]
lemma det_mulLeft (a : R) : (mulLeft R a).det = a := by simp
lemma det_mulRight (a : R) : (mulRight R a).det = a := by simp
theorem det_prodMap [Module.Free R M] [Module.Free R M'] [Module.Finite R M] [Module.Finite R M']
(f : Module.End R M) (f' : Module.End R M') :
(prodMap f f').det = f.det * f'.det := by
let b := Module.Free.chooseBasis R M
let b' := Module.Free.chooseBasis R M'
rw [← det_toMatrix (b.prod b'), ← det_toMatrix b, ← det_toMatrix b', toMatrix_prodMap,
det_fromBlocks_zero₂₁, det_toMatrix]
omit [DecidableEq ι] in
theorem det_pi [Module.Free R M] [Module.Finite R M] (f : ι → M →ₗ[R] M) :
(LinearMap.pi (fun i ↦ (f i).comp (LinearMap.proj i))).det = ∏ i, (f i).det := by
classical
let b := Module.Free.chooseBasis R M
let B := (Pi.basis (fun _ : ι ↦ b)).reindex <|
(Equiv.sigmaEquivProd _ _).trans (Equiv.prodComm _ _)
simp_rw [← LinearMap.det_toMatrix B, ← LinearMap.det_toMatrix b]
have : ((LinearMap.toMatrix B B) (LinearMap.pi fun i ↦ f i ∘ₗ LinearMap.proj i)) =
Matrix.blockDiagonal (fun i ↦ LinearMap.toMatrix b b (f i)) := by
ext ⟨i₁, i₂⟩ ⟨j₁, j₂⟩
unfold B
simp_rw [LinearMap.toMatrix_apply', Matrix.blockDiagonal_apply, Basis.coe_reindex,
Function.comp_apply, Basis.repr_reindex_apply, Equiv.symm_trans_apply, Equiv.prodComm_symm,
Equiv.prodComm_apply, Equiv.sigmaEquivProd_symm_apply, Prod.swap_prod_mk, Pi.basis_apply,
Pi.basis_repr, LinearMap.pi_apply, LinearMap.coe_comp, Function.comp_apply,
LinearMap.toMatrix_apply', LinearMap.coe_proj, Function.eval, Pi.single_apply]
split_ifs with h
· rw [h]
· simp only [map_zero, Finsupp.coe_zero, Pi.zero_apply]
rw [this, Matrix.det_blockDiagonal]
end LinearMap
namespace LinearEquiv
/-- On a `LinearEquiv`, the domain of `LinearMap.det` can be promoted to `Rˣ`. -/
protected def det : (M ≃ₗ[R] M) →* Rˣ :=
(Units.map (LinearMap.det : (M →ₗ[R] M) →* R)).comp
(LinearMap.GeneralLinearGroup.generalLinearEquiv R M).symm.toMonoidHom
@[simp]
theorem coe_det (f : M ≃ₗ[R] M) : ↑(LinearEquiv.det f) = LinearMap.det (f : M →ₗ[R] M) :=
rfl
@[simp]
theorem coe_inv_det (f : M ≃ₗ[R] M) : ↑(LinearEquiv.det f)⁻¹ = LinearMap.det (f.symm : M →ₗ[R] M) :=
rfl
@[simp]
theorem det_refl : LinearEquiv.det (LinearEquiv.refl R M) = 1 :=
Units.ext <| LinearMap.det_id
@[simp]
theorem det_trans (f g : M ≃ₗ[R] M) :
LinearEquiv.det (f.trans g) = LinearEquiv.det g * LinearEquiv.det f :=
map_mul _ g f
@[simp]
theorem det_symm (f : M ≃ₗ[R] M) : LinearEquiv.det f.symm = LinearEquiv.det f⁻¹ :=
map_inv _ f
/-- Conjugating a linear equiv by a linear equiv does not change its determinant. -/
@[simp]
theorem det_conj (f : M ≃ₗ[R] M) (e : M ≃ₗ[R] M') :
LinearEquiv.det ((e.symm.trans f).trans e) = LinearEquiv.det f := by
rw [← Units.eq_iff, coe_det, coe_det, ← comp_coe, ← comp_coe, LinearMap.det_conj]
attribute [irreducible] LinearEquiv.det
end LinearEquiv
/-- The determinants of a `LinearEquiv` and its inverse multiply to 1. -/
@[simp]
theorem LinearEquiv.det_mul_det_symm {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
LinearMap.det (f : M →ₗ[A] M) * LinearMap.det (f.symm : M →ₗ[A] M) = 1 := by
simp [← LinearMap.det_comp]
/-- The determinants of a `LinearEquiv` and its inverse multiply to 1. -/
@[simp]
theorem LinearEquiv.det_symm_mul_det {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
LinearMap.det (f.symm : M →ₗ[A] M) * LinearMap.det (f : M →ₗ[A] M) = 1 := by
simp [← LinearMap.det_comp]
-- Cannot be stated using `LinearMap.det` because `f` is not an endomorphism.
theorem LinearEquiv.isUnit_det (f : M ≃ₗ[R] M') (v : Basis ι R M) (v' : Basis ι R M') :
IsUnit (LinearMap.toMatrix v v' f).det := by
apply isUnit_det_of_left_inverse
simpa using (LinearMap.toMatrix_comp v v' v f.symm f).symm
/-- Specialization of `LinearEquiv.isUnit_det` -/
theorem LinearEquiv.isUnit_det' {A : Type*} [CommRing A] [Module A M] (f : M ≃ₗ[A] M) :
IsUnit (LinearMap.det (f : M →ₗ[A] M)) :=
isUnit_of_mul_eq_one _ _ f.det_mul_det_symm
/-- The determinant of `f.symm` is the inverse of that of `f` when `f` is a linear equiv. -/
theorem LinearEquiv.det_coe_symm {𝕜 : Type*} [Field 𝕜] [Module 𝕜 M] (f : M ≃ₗ[𝕜] M) :
LinearMap.det (f.symm : M →ₗ[𝕜] M) = (LinearMap.det (f : M →ₗ[𝕜] M))⁻¹ := by
field_simp [IsUnit.ne_zero f.isUnit_det']
/-- Builds a linear equivalence from a linear map whose determinant in some bases is a unit. -/
@[simps]
def LinearEquiv.ofIsUnitDet {f : M →ₗ[R] M'} {v : Basis ι R M} {v' : Basis ι R M'}
(h : IsUnit (LinearMap.toMatrix v v' f).det) : M ≃ₗ[R] M' where
toFun := f
map_add' := f.map_add
map_smul' := f.map_smul
invFun := toLin v' v (toMatrix v v' f)⁻¹
left_inv x :=
calc toLin v' v (toMatrix v v' f)⁻¹ (f x)
_ = toLin v v ((toMatrix v v' f)⁻¹ * toMatrix v v' f) x := by
rw [toLin_mul v v' v, toLin_toMatrix, LinearMap.comp_apply]
_ = x := by simp [h]
right_inv x :=
calc f (toLin v' v (toMatrix v v' f)⁻¹ x)
_ = toLin v' v' (toMatrix v v' f * (toMatrix v v' f)⁻¹) x := by
rw [toLin_mul v' v v', LinearMap.comp_apply, toLin_toMatrix v v']
_ = x := by simp [h]
@[simp]
theorem LinearEquiv.coe_ofIsUnitDet {f : M →ₗ[R] M'} {v : Basis ι R M} {v' : Basis ι R M'}
(h : IsUnit (LinearMap.toMatrix v v' f).det) :
(LinearEquiv.ofIsUnitDet h : M →ₗ[R] M') = f := by
ext x
rfl
/-- Builds a linear equivalence from a linear map on a finite-dimensional vector space whose
determinant is nonzero. -/
abbrev LinearMap.equivOfDetNeZero {𝕜 : Type*} [Field 𝕜] {M : Type*} [AddCommGroup M] [Module 𝕜 M]
[FiniteDimensional 𝕜 M] (f : M →ₗ[𝕜] M) (hf : LinearMap.det f ≠ 0) : M ≃ₗ[𝕜] M :=
have : IsUnit (LinearMap.toMatrix (Module.finBasis 𝕜 M)
(Module.finBasis 𝕜 M) f).det := by
rw [LinearMap.det_toMatrix]
exact isUnit_iff_ne_zero.2 hf
LinearEquiv.ofIsUnitDet this
theorem LinearMap.associated_det_of_eq_comp (e : M ≃ₗ[R] M) (f f' : M →ₗ[R] M)
(h : ∀ x, f x = f' (e x)) : Associated (LinearMap.det f) (LinearMap.det f') := by
suffices Associated (LinearMap.det (f' ∘ₗ ↑e)) (LinearMap.det f') by
convert this using 2
ext x
exact h x
rw [← mul_one (LinearMap.det f'), LinearMap.det_comp]
exact Associated.mul_left _ (associated_one_iff_isUnit.mpr e.isUnit_det')
theorem LinearMap.associated_det_comp_equiv {N : Type*} [AddCommGroup N] [Module R N]
(f : N →ₗ[R] M) (e e' : M ≃ₗ[R] N) :
Associated (LinearMap.det (f ∘ₗ ↑e)) (LinearMap.det (f ∘ₗ ↑e')) := by
refine LinearMap.associated_det_of_eq_comp (e.trans e'.symm) _ _ ?_
intro x
simp only [LinearMap.comp_apply, LinearEquiv.coe_coe, LinearEquiv.trans_apply,
LinearEquiv.apply_symm_apply]
/-- The determinant of a family of vectors with respect to some basis, as an alternating
multilinear map. -/
nonrec def Basis.det : M [⋀^ι]→ₗ[R] R where
toMultilinearMap :=
MultilinearMap.mk' (fun v ↦ det (e.toMatrix v))
(fun v i x y ↦ by
simp only [e.toMatrix_update, map_add, Finsupp.coe_add, det_updateCol_add])
(fun u i c x ↦ by
simp only [e.toMatrix_update, Algebra.id.smul_eq_mul, LinearEquiv.map_smul]
apply det_updateCol_smul)
map_eq_zero_of_eq' := by
intro v i j h hij
dsimp
rw [← Function.update_eq_self i v, h, ← det_transpose, e.toMatrix_update, ← updateRow_transpose,
← e.toMatrix_transpose_apply]
apply det_zero_of_row_eq hij
rw [updateRow_ne hij.symm, updateRow_self]
theorem Basis.det_apply (v : ι → M) : e.det v = Matrix.det (e.toMatrix v) :=
rfl
theorem Basis.det_self : e.det e = 1 := by simp [e.det_apply]
@[simp]
theorem Basis.det_isEmpty [IsEmpty ι] : e.det = AlternatingMap.constOfIsEmpty R M ι 1 := by
ext v
exact Matrix.det_isEmpty
/-- `Basis.det` is not the zero map. -/
theorem Basis.det_ne_zero [Nontrivial R] : e.det ≠ 0 := fun h => by simpa [h] using e.det_self
theorem Basis.smul_det {G} [Group G] [DistribMulAction G M] [SMulCommClass G R M]
(g : G) (v : ι → M) :
(g • e).det v = e.det (g⁻¹ • v) := by
simp_rw [det_apply, toMatrix_smul_left]
theorem is_basis_iff_det {v : ι → M} :
LinearIndependent R v ∧ span R (Set.range v) = ⊤ ↔ IsUnit (e.det v) := by
constructor
· rintro ⟨hli, hspan⟩
set v' := Basis.mk hli hspan.ge
rw [e.det_apply]
convert LinearEquiv.isUnit_det (LinearEquiv.refl R M) v' e using 2
ext i j
simp [v']
· intro h
rw [Basis.det_apply, Basis.toMatrix_eq_toMatrix_constr] at h
set v' := Basis.map e (LinearEquiv.ofIsUnitDet h) with v'_def
have : ⇑v' = v := by
ext i
rw [v'_def, Basis.map_apply, LinearEquiv.ofIsUnitDet_apply, e.constr_basis]
rw [← this]
exact ⟨v'.linearIndependent, v'.span_eq⟩
theorem Basis.isUnit_det (e' : Basis ι R M) : IsUnit (e.det e') :=
(is_basis_iff_det e).mp ⟨e'.linearIndependent, e'.span_eq⟩
/-- Any alternating map to `R` where `ι` has the cardinality of a basis equals the determinant
map with respect to that basis, multiplied by the value of that alternating map on that basis. -/
theorem AlternatingMap.eq_smul_basis_det (f : M [⋀^ι]→ₗ[R] R) : f = f e • e.det := by
refine Basis.ext_alternating e fun i h => ?_
let σ : Equiv.Perm ι := Equiv.ofBijective i (Finite.injective_iff_bijective.1 h)
change f (e ∘ σ) = (f e • e.det) (e ∘ σ)
simp [AlternatingMap.map_perm, Basis.det_self]
@[simp]
theorem AlternatingMap.map_basis_eq_zero_iff {ι : Type*} [Finite ι] (e : Basis ι R M)
(f : M [⋀^ι]→ₗ[R] R) : f e = 0 ↔ f = 0 :=
⟨fun h => by
cases nonempty_fintype ι
letI := Classical.decEq ι
simpa [h] using f.eq_smul_basis_det e,
fun h => h.symm ▸ AlternatingMap.zero_apply _⟩
theorem AlternatingMap.map_basis_ne_zero_iff {ι : Type*} [Finite ι] (e : Basis ι R M)
(f : M [⋀^ι]→ₗ[R] R) : f e ≠ 0 ↔ f ≠ 0 :=
not_congr <| f.map_basis_eq_zero_iff e
variable {A : Type*} [CommRing A] [Module A M]
@[simp]
theorem Basis.det_comp (e : Basis ι A M) (f : M →ₗ[A] M) (v : ι → M) :
e.det (f ∘ v) = (LinearMap.det f) * e.det v := by
rw [Basis.det_apply, Basis.det_apply, ← f.det_toMatrix e, ← Matrix.det_mul,
e.toMatrix_eq_toMatrix_constr (f ∘ v), e.toMatrix_eq_toMatrix_constr v, ← toMatrix_comp,
e.constr_comp]
@[simp]
theorem Basis.det_comp_basis [Module A M'] (b : Basis ι A M) (b' : Basis ι A M') (f : M →ₗ[A] M') :
b'.det (f ∘ b) = LinearMap.det (f ∘ₗ (b'.equiv b (Equiv.refl ι) : M' →ₗ[A] M)) := by
rw [Basis.det_apply, ← LinearMap.det_toMatrix b', LinearMap.toMatrix_comp _ b, Matrix.det_mul,
LinearMap.toMatrix_basis_equiv, Matrix.det_one, mul_one]
congr 1; ext i j
rw [Basis.toMatrix_apply, LinearMap.toMatrix_apply, Function.comp_apply]
@[simp]
theorem Basis.det_basis (b : Basis ι A M) (b' : Basis ι A M) :
LinearMap.det (b'.equiv b (Equiv.refl ι)).toLinearMap = b'.det b :=
(b.det_comp_basis b' (LinearMap.id)).symm
theorem Basis.det_inv (b : Basis ι A M) (b' : Basis ι A M) :
(b.isUnit_det b').unit⁻¹ = b'.det b := by
rw [← Units.mul_eq_one_iff_inv_eq, IsUnit.unit_spec, ← Basis.det_basis, ← Basis.det_basis]
exact LinearEquiv.det_mul_det_symm _
theorem Basis.det_reindex {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M) (v : ι' → M)
(e : ι ≃ ι') : (b.reindex e).det v = b.det (v ∘ e) := by
rw [Basis.det_apply, Basis.toMatrix_reindex', det_reindexAlgEquiv, Basis.det_apply]
theorem Basis.det_reindex' {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M)
(e : ι ≃ ι') : (b.reindex e).det = b.det.domDomCongr e :=
AlternatingMap.ext fun _ => Basis.det_reindex _ _ _
theorem Basis.det_reindex_symm {ι' : Type*} [Fintype ι'] [DecidableEq ι'] (b : Basis ι R M)
(v : ι → M) (e : ι' ≃ ι) : (b.reindex e.symm).det (v ∘ e) = b.det v := by
rw [Basis.det_reindex, Function.comp_assoc, e.self_comp_symm, Function.comp_id]
@[simp]
theorem Basis.det_map (b : Basis ι R M) (f : M ≃ₗ[R] M') (v : ι → M') :
(b.map f).det v = b.det (f.symm ∘ v) := by
rw [Basis.det_apply, Basis.toMatrix_map, Basis.det_apply]
theorem Basis.det_map' (b : Basis ι R M) (f : M ≃ₗ[R] M') :
(b.map f).det = b.det.compLinearMap f.symm :=
AlternatingMap.ext <| b.det_map f
@[simp]
theorem Pi.basisFun_det : (Pi.basisFun R ι).det = Matrix.detRowAlternating := by
ext M
rw [Basis.det_apply, Basis.coePiBasisFun.toMatrix_eq_transpose, det_transpose]
theorem Pi.basisFun_det_apply (v : ι → ι → R) :
(Pi.basisFun R ι).det v = (Matrix.of v).det := by
rw [Pi.basisFun_det]
rfl
/-- If we fix a background basis `e`, then for any other basis `v`, we can characterise the
coordinates provided by `v` in terms of determinants relative to `e`. -/
theorem Basis.det_smul_mk_coord_eq_det_update {v : ι → M} (hli : LinearIndependent R v)
(hsp : ⊤ ≤ span R (range v)) (i : ι) :
e.det v • (Basis.mk hli hsp).coord i = e.det.toMultilinearMap.toLinearMap v i := by
apply (Basis.mk hli hsp).ext
intro k
rcases eq_or_ne k i with (rfl | hik) <;>
simp only [Algebra.id.smul_eq_mul, Basis.coe_mk, LinearMap.smul_apply, LinearMap.coe_mk,
MultilinearMap.toLinearMap_apply]
· rw [Basis.mk_coord_apply_eq, mul_one, update_eq_self]
congr
· rw [Basis.mk_coord_apply_ne hik, mul_zero, eq_comm]
exact e.det.map_eq_zero_of_eq _ (by simp [hik, Function.update_apply]) hik
/-- If a basis is multiplied columnwise by scalars `w : ι → Rˣ`, then the determinant with respect
to this basis is multiplied by the product of the inverse of these scalars. -/
| theorem Basis.det_unitsSMul (e : Basis ι R M) (w : ι → Rˣ) :
(e.unitsSMul w).det = (↑(∏ i, w i)⁻¹ : R) • e.det := by
ext f
change
(Matrix.det fun i j => (e.unitsSMul w).repr (f j) i) =
(↑(∏ i, w i)⁻¹ : R) • Matrix.det fun i j => e.repr (f j) i
simp only [e.repr_unitsSMul]
convert Matrix.det_mul_column (fun i => (↑(w i)⁻¹ : R)) fun i j => e.repr (f j) i
simp [← Finset.prod_inv_distrib]
/-- The determinant of a basis constructed by `unitsSMul` is the product of the given units. -/
@[simp]
| Mathlib/LinearAlgebra/Determinant.lean | 643 | 654 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Abhimanyu Pallavi Sudhir
-/
import Mathlib.Algebra.CharP.Defs
import Mathlib.Algebra.Order.CauSeq.BigOperators
import Mathlib.Algebra.Order.Star.Basic
import Mathlib.Data.Complex.BigOperators
import Mathlib.Data.Complex.Norm
import Mathlib.Data.Nat.Choose.Sum
/-!
# Exponential Function
This file contains the definitions of the real and complex exponential function.
## Main definitions
* `Complex.exp`: The complex exponential function, defined via its Taylor series
* `Real.exp`: The real exponential function, defined as the real part of the complex exponential
-/
open CauSeq Finset IsAbsoluteValue
open scoped ComplexConjugate
namespace Complex
theorem isCauSeq_norm_exp (z : ℂ) :
IsCauSeq abs fun n => ∑ m ∈ range n, ‖z ^ m / m.factorial‖ :=
let ⟨n, hn⟩ := exists_nat_gt ‖z‖
have hn0 : (0 : ℝ) < n := lt_of_le_of_lt (norm_nonneg _) hn
IsCauSeq.series_ratio_test n (‖z‖ / n) (div_nonneg (norm_nonneg _) (le_of_lt hn0))
(by rwa [div_lt_iff₀ hn0, one_mul]) fun m hm => by
rw [abs_norm, abs_norm, Nat.factorial_succ, pow_succ', mul_comm m.succ, Nat.cast_mul,
← div_div, mul_div_assoc, mul_div_right_comm, Complex.norm_mul, Complex.norm_div,
norm_natCast]
gcongr
exact le_trans hm (Nat.le_succ _)
@[deprecated (since := "2025-02-16")] alias isCauSeq_abs_exp := isCauSeq_norm_exp
noncomputable section
theorem isCauSeq_exp (z : ℂ) : IsCauSeq (‖·‖) fun n => ∑ m ∈ range n, z ^ m / m.factorial :=
(isCauSeq_norm_exp z).of_abv
/-- The Cauchy sequence consisting of partial sums of the Taylor series of
the complex exponential function -/
@[pp_nodot]
def exp' (z : ℂ) : CauSeq ℂ (‖·‖) :=
⟨fun n => ∑ m ∈ range n, z ^ m / m.factorial, isCauSeq_exp z⟩
/-- The complex exponential function, defined via its Taylor series -/
@[pp_nodot]
def exp (z : ℂ) : ℂ :=
CauSeq.lim (exp' z)
/-- scoped notation for the complex exponential function -/
scoped notation "cexp" => Complex.exp
end
end Complex
namespace Real
open Complex
noncomputable section
/-- The real exponential function, defined as the real part of the complex exponential -/
@[pp_nodot]
nonrec def exp (x : ℝ) : ℝ :=
(exp x).re
/-- scoped notation for the real exponential function -/
scoped notation "rexp" => Real.exp
end
end Real
namespace Complex
variable (x y : ℂ)
@[simp]
theorem exp_zero : exp 0 = 1 := by
rw [exp]
refine lim_eq_of_equiv_const fun ε ε0 => ⟨1, fun j hj => ?_⟩
convert (config := .unfoldSameFun) ε0 -- ε0 : ε > 0 but goal is _ < ε
rcases j with - | j
· exact absurd hj (not_le_of_gt zero_lt_one)
· dsimp [exp']
induction' j with j ih
· dsimp [exp']; simp [show Nat.succ 0 = 1 from rfl]
· rw [← ih (by simp [Nat.succ_le_succ])]
simp only [sum_range_succ, pow_succ]
simp
theorem exp_add : exp (x + y) = exp x * exp y := by
have hj : ∀ j : ℕ, (∑ m ∈ range j, (x + y) ^ m / m.factorial) =
∑ i ∈ range j, ∑ k ∈ range (i + 1), x ^ k / k.factorial *
(y ^ (i - k) / (i - k).factorial) := by
intro j
refine Finset.sum_congr rfl fun m _ => ?_
rw [add_pow, div_eq_mul_inv, sum_mul]
refine Finset.sum_congr rfl fun I hi => ?_
have h₁ : (m.choose I : ℂ) ≠ 0 :=
Nat.cast_ne_zero.2 (pos_iff_ne_zero.1 (Nat.choose_pos (Nat.le_of_lt_succ (mem_range.1 hi))))
have h₂ := Nat.choose_mul_factorial_mul_factorial (Nat.le_of_lt_succ <| Finset.mem_range.1 hi)
rw [← h₂, Nat.cast_mul, Nat.cast_mul, mul_inv, mul_inv]
simp only [mul_left_comm (m.choose I : ℂ), mul_assoc, mul_left_comm (m.choose I : ℂ)⁻¹,
mul_comm (m.choose I : ℂ)]
rw [inv_mul_cancel₀ h₁]
simp [div_eq_mul_inv, mul_comm, mul_assoc, mul_left_comm]
simp_rw [exp, exp', lim_mul_lim]
apply (lim_eq_lim_of_equiv _).symm
simp only [hj]
exact cauchy_product (isCauSeq_norm_exp x) (isCauSeq_exp y)
/-- the exponential function as a monoid hom from `Multiplicative ℂ` to `ℂ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℂ) ℂ :=
{ toFun := fun z => exp z.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℂ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℂ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℂ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℂ) ℂ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℂ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℂ) expMonoidHom f s
lemma exp_nsmul (x : ℂ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℂ) ℂ _ _ expMonoidHom _ _
theorem exp_nat_mul (x : ℂ) : ∀ n : ℕ, exp (n * x) = exp x ^ n
| 0 => by rw [Nat.cast_zero, zero_mul, exp_zero, pow_zero]
| Nat.succ n => by rw [pow_succ, Nat.cast_add_one, add_mul, exp_add, ← exp_nat_mul _ n, one_mul]
@[simp]
theorem exp_ne_zero : exp x ≠ 0 := fun h =>
zero_ne_one (α := ℂ) <| by rw [← exp_zero, ← add_neg_cancel x, exp_add, h]; simp
theorem exp_neg : exp (-x) = (exp x)⁻¹ := by
rw [← mul_right_inj' (exp_ne_zero x), ← exp_add]; simp [mul_inv_cancel₀ (exp_ne_zero x)]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
theorem exp_int_mul (z : ℂ) (n : ℤ) : Complex.exp (n * z) = Complex.exp z ^ n := by
cases n
· simp [exp_nat_mul]
· simp [exp_add, add_mul, pow_add, exp_neg, exp_nat_mul]
@[simp]
theorem exp_conj : exp (conj x) = conj (exp x) := by
dsimp [exp]
rw [← lim_conj]
refine congr_arg CauSeq.lim (CauSeq.ext fun _ => ?_)
dsimp [exp', Function.comp_def, cauSeqConj]
rw [map_sum (starRingEnd _)]
refine sum_congr rfl fun n _ => ?_
rw [map_div₀, map_pow, ← ofReal_natCast, conj_ofReal]
@[simp]
theorem ofReal_exp_ofReal_re (x : ℝ) : ((exp x).re : ℂ) = exp x :=
conj_eq_iff_re.1 <| by rw [← exp_conj, conj_ofReal]
@[simp, norm_cast]
theorem ofReal_exp (x : ℝ) : (Real.exp x : ℂ) = exp x :=
ofReal_exp_ofReal_re _
@[simp]
theorem exp_ofReal_im (x : ℝ) : (exp x).im = 0 := by rw [← ofReal_exp_ofReal_re, ofReal_im]
theorem exp_ofReal_re (x : ℝ) : (exp x).re = Real.exp x :=
rfl
end Complex
namespace Real
open Complex
variable (x y : ℝ)
@[simp]
theorem exp_zero : exp 0 = 1 := by simp [Real.exp]
nonrec theorem exp_add : exp (x + y) = exp x * exp y := by simp [exp_add, exp]
/-- the exponential function as a monoid hom from `Multiplicative ℝ` to `ℝ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℝ) ℝ :=
{ toFun := fun x => exp x.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℝ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℝ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℝ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℝ) ℝ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℝ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℝ) expMonoidHom f s
lemma exp_nsmul (x : ℝ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℝ) ℝ _ _ expMonoidHom _ _
nonrec theorem exp_nat_mul (x : ℝ) (n : ℕ) : exp (n * x) = exp x ^ n :=
ofReal_injective (by simp [exp_nat_mul])
@[simp]
nonrec theorem exp_ne_zero : exp x ≠ 0 := fun h =>
exp_ne_zero x <| by rw [exp, ← ofReal_inj] at h; simp_all
nonrec theorem exp_neg : exp (-x) = (exp x)⁻¹ :=
ofReal_injective <| by simp [exp_neg]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
open IsAbsoluteValue Nat
theorem sum_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) (n : ℕ) : ∑ i ∈ range n, x ^ i / i ! ≤ exp x :=
calc
∑ i ∈ range n, x ^ i / i ! ≤ lim (⟨_, isCauSeq_re (exp' x)⟩ : CauSeq ℝ abs) := by
refine le_lim (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp only [exp', const_apply, re_sum]
norm_cast
refine sum_le_sum_of_subset_of_nonneg (range_mono hj) fun _ _ _ ↦ ?_
positivity
_ = exp x := by rw [exp, Complex.exp, ← cauSeqRe, lim_re]
lemma pow_div_factorial_le_exp (hx : 0 ≤ x) (n : ℕ) : x ^ n / n ! ≤ exp x :=
calc
x ^ n / n ! ≤ ∑ k ∈ range (n + 1), x ^ k / k ! :=
single_le_sum (f := fun k ↦ x ^ k / k !) (fun k _ ↦ by positivity) (self_mem_range_succ n)
_ ≤ exp x := sum_le_exp_of_nonneg hx _
theorem quadratic_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : 1 + x + x ^ 2 / 2 ≤ exp x :=
calc
1 + x + x ^ 2 / 2 = ∑ i ∈ range 3, x ^ i / i ! := by
simp only [sum_range_succ, range_one, sum_singleton, _root_.pow_zero, factorial, cast_one,
ne_eq, one_ne_zero, not_false_eq_true, div_self, pow_one, mul_one, div_one, Nat.mul_one,
cast_succ, add_right_inj]
ring_nf
_ ≤ exp x := sum_le_exp_of_nonneg hx 3
private theorem add_one_lt_exp_of_pos {x : ℝ} (hx : 0 < x) : x + 1 < exp x :=
(by nlinarith : x + 1 < 1 + x + x ^ 2 / 2).trans_le (quadratic_le_exp_of_nonneg hx.le)
private theorem add_one_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : x + 1 ≤ exp x := by
rcases eq_or_lt_of_le hx with (rfl | h)
· simp
exact (add_one_lt_exp_of_pos h).le
theorem one_le_exp {x : ℝ} (hx : 0 ≤ x) : 1 ≤ exp x := by linarith [add_one_le_exp_of_nonneg hx]
@[bound]
theorem exp_pos (x : ℝ) : 0 < exp x :=
(le_total 0 x).elim (lt_of_lt_of_le zero_lt_one ∘ one_le_exp) fun h => by
rw [← neg_neg x, Real.exp_neg]
exact inv_pos.2 (lt_of_lt_of_le zero_lt_one (one_le_exp (neg_nonneg.2 h)))
@[bound]
lemma exp_nonneg (x : ℝ) : 0 ≤ exp x := x.exp_pos.le
@[simp]
theorem abs_exp (x : ℝ) : |exp x| = exp x :=
abs_of_pos (exp_pos _)
lemma exp_abs_le (x : ℝ) : exp |x| ≤ exp x + exp (-x) := by
cases le_total x 0 <;> simp [abs_of_nonpos, abs_of_nonneg, exp_nonneg, *]
@[mono]
theorem exp_strictMono : StrictMono exp := fun x y h => by
rw [← sub_add_cancel y x, Real.exp_add]
exact (lt_mul_iff_one_lt_left (exp_pos _)).2
(lt_of_lt_of_le (by linarith) (add_one_le_exp_of_nonneg (by linarith)))
@[gcongr]
theorem exp_lt_exp_of_lt {x y : ℝ} (h : x < y) : exp x < exp y := exp_strictMono h
@[mono]
theorem exp_monotone : Monotone exp :=
exp_strictMono.monotone
@[gcongr, bound]
theorem exp_le_exp_of_le {x y : ℝ} (h : x ≤ y) : exp x ≤ exp y := exp_monotone h
@[simp]
theorem exp_lt_exp {x y : ℝ} : exp x < exp y ↔ x < y :=
exp_strictMono.lt_iff_lt
@[simp]
theorem exp_le_exp {x y : ℝ} : exp x ≤ exp y ↔ x ≤ y :=
exp_strictMono.le_iff_le
theorem exp_injective : Function.Injective exp :=
exp_strictMono.injective
@[simp]
theorem exp_eq_exp {x y : ℝ} : exp x = exp y ↔ x = y :=
exp_injective.eq_iff
@[simp]
theorem exp_eq_one_iff : exp x = 1 ↔ x = 0 :=
exp_injective.eq_iff' exp_zero
@[simp]
theorem one_lt_exp_iff {x : ℝ} : 1 < exp x ↔ 0 < x := by rw [← exp_zero, exp_lt_exp]
@[bound] private alias ⟨_, Bound.one_lt_exp_of_pos⟩ := one_lt_exp_iff
@[simp]
theorem exp_lt_one_iff {x : ℝ} : exp x < 1 ↔ x < 0 := by rw [← exp_zero, exp_lt_exp]
@[simp]
theorem exp_le_one_iff {x : ℝ} : exp x ≤ 1 ↔ x ≤ 0 :=
exp_zero ▸ exp_le_exp
@[simp]
theorem one_le_exp_iff {x : ℝ} : 1 ≤ exp x ↔ 0 ≤ x :=
exp_zero ▸ exp_le_exp
end Real
namespace Complex
theorem sum_div_factorial_le {α : Type*} [Field α] [LinearOrder α] [IsStrictOrderedRing α]
(n j : ℕ) (hn : 0 < n) :
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) ≤ n.succ / (n.factorial * n) :=
calc
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) =
∑ m ∈ range (j - n), (1 / ((m + n).factorial : α)) := by
refine sum_nbij' (· - n) (· + n) ?_ ?_ ?_ ?_ ?_ <;>
simp +contextual [lt_tsub_iff_right, tsub_add_cancel_of_le]
_ ≤ ∑ m ∈ range (j - n), ((n.factorial : α) * (n.succ : α) ^ m)⁻¹ := by
simp_rw [one_div]
gcongr
rw [← Nat.cast_pow, ← Nat.cast_mul, Nat.cast_le, add_comm]
exact Nat.factorial_mul_pow_le_factorial
_ = (n.factorial : α)⁻¹ * ∑ m ∈ range (j - n), (n.succ : α)⁻¹ ^ m := by
simp [mul_inv, ← mul_sum, ← sum_mul, mul_comm, inv_pow]
_ = ((n.succ : α) - n.succ * (n.succ : α)⁻¹ ^ (j - n)) / (n.factorial * n) := by
have h₁ : (n.succ : α) ≠ 1 :=
@Nat.cast_one α _ ▸ mt Nat.cast_inj.1 (mt Nat.succ.inj (pos_iff_ne_zero.1 hn))
have h₂ : (n.succ : α) ≠ 0 := by positivity
have h₃ : (n.factorial * n : α) ≠ 0 := by positivity
have h₄ : (n.succ - 1 : α) = n := by simp
rw [geom_sum_inv h₁ h₂, eq_div_iff_mul_eq h₃, mul_comm _ (n.factorial * n : α),
← mul_assoc (n.factorial⁻¹ : α), ← mul_inv_rev, h₄, ← mul_assoc (n.factorial * n : α),
mul_comm (n : α) n.factorial, mul_inv_cancel₀ h₃, one_mul, mul_comm]
_ ≤ n.succ / (n.factorial * n : α) := by gcongr; apply sub_le_self; positivity
theorem exp_bound {x : ℂ} (hx : ‖x‖ ≤ 1) {n : ℕ} (hn : 0 < n) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹) := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _), exp, sub_eq_add_neg,
← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show
‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹)
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (1 / m.factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr
rw [Complex.norm_pow]
exact pow_le_one₀ (norm_nonneg _) hx
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (1 / m.factorial : ℝ) := by
simp [abs_mul, abv_pow abs, abs_div, ← mul_sum]
_ ≤ ‖x‖ ^ n * (n.succ * (n.factorial * n : ℝ)⁻¹) := by
gcongr
exact sum_div_factorial_le _ _ hn
theorem exp_bound' {x : ℂ} {n : ℕ} (hx : ‖x‖ / n.succ ≤ 1 / 2) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n / n.factorial * 2 := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _),
exp, sub_eq_add_neg, ← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n / n.factorial * 2
let k := j - n
have hj : j = n + k := (add_tsub_cancel_of_le hj).symm
rw [hj, sum_range_add_sub_sum_range]
calc
‖∑ i ∈ range k, x ^ (n + i) / ((n + i).factorial : ℂ)‖ ≤
∑ i ∈ range k, ‖x ^ (n + i) / ((n + i).factorial : ℂ)‖ :=
IsAbsoluteValue.abv_sum _ _ _
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / (n + i).factorial := by
simp [norm_natCast, Complex.norm_pow]
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / ((n.factorial : ℝ) * (n.succ : ℝ) ^ i) := ?_
_ = ∑ i ∈ range k, ‖x‖ ^ n / n.factorial * (‖x‖ ^ i / (n.succ : ℝ) ^ i) := ?_
_ ≤ ‖x‖ ^ n / ↑n.factorial * 2 := ?_
· gcongr
exact mod_cast Nat.factorial_mul_pow_le_factorial
· refine Finset.sum_congr rfl fun _ _ => ?_
simp only [pow_add, div_eq_inv_mul, mul_inv, mul_left_comm, mul_assoc]
· rw [← mul_sum]
gcongr
simp_rw [← div_pow]
rw [geom_sum_eq, div_le_iff_of_neg]
· trans (-1 : ℝ)
· linarith
· simp only [neg_le_sub_iff_le_add, div_pow, Nat.cast_succ, le_add_iff_nonneg_left]
positivity
· linarith
· linarith
theorem norm_exp_sub_one_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1‖ ≤ 2 * ‖x‖ :=
calc
‖exp x - 1‖ = ‖exp x - ∑ m ∈ range 1, x ^ m / m.factorial‖ := by simp [sum_range_succ]
_ ≤ ‖x‖ ^ 1 * ((Nat.succ 1 : ℝ) * ((Nat.factorial 1) * (1 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ = 2 * ‖x‖ := by simp [two_mul, mul_two, mul_add, mul_comm, add_mul, Nat.factorial]
theorem norm_exp_sub_one_sub_id_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1 - x‖ ≤ ‖x‖ ^ 2 :=
calc
‖exp x - 1 - x‖ = ‖exp x - ∑ m ∈ range 2, x ^ m / m.factorial‖ := by
simp [sub_eq_add_neg, sum_range_succ_comm, add_assoc, Nat.factorial]
_ ≤ ‖x‖ ^ 2 * ((Nat.succ 2 : ℝ) * (Nat.factorial 2 * (2 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ ≤ ‖x‖ ^ 2 * 1 := by gcongr; norm_num [Nat.factorial]
_ = ‖x‖ ^ 2 := by rw [mul_one]
lemma norm_exp_sub_sum_le_exp_norm_sub_sum (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖
≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
calc ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖
_ ≤ (∑ m ∈ range j, ‖x‖ ^ m / m.factorial) - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [sum_range_sub_sum_range hj, sum_range_sub_sum_range hj]
refine (IsAbsoluteValue.abv_sum norm ..).trans_eq ?_
congr with i
simp [Complex.norm_pow]
_ ≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
gcongr
exact Real.sum_le_exp_of_nonneg (norm_nonneg _) _
lemma norm_exp_le_exp_norm (x : ℂ) : ‖exp x‖ ≤ Real.exp ‖x‖ := by
convert norm_exp_sub_sum_le_exp_norm_sub_sum x 0 using 1 <;> simp
lemma norm_exp_sub_sum_le_norm_mul_exp (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ _
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (‖x‖ ^ (m - n) / (m - n).factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr with i hi
· rw [Complex.norm_pow]
· simp
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (‖x‖ ^ (m - n) / (m - n).factorial) := by
rw [← mul_sum]
_ = ‖x‖ ^ n * ∑ m ∈ range (j - n), (‖x‖ ^ m / m.factorial) := by
congr 1
refine (sum_bij (fun m hm ↦ m + n) ?_ ?_ ?_ ?_).symm
· intro a ha
simp only [mem_filter, mem_range, le_add_iff_nonneg_left, zero_le, and_true]
simp only [mem_range] at ha
rwa [← lt_tsub_iff_right]
· intro a ha b hb hab
simpa using hab
· intro b hb
simp only [mem_range, exists_prop]
simp only [mem_filter, mem_range] at hb
refine ⟨b - n, ?_, ?_⟩
· rw [tsub_lt_tsub_iff_right hb.2]
exact hb.1
· rw [tsub_add_cancel_of_le hb.2]
· simp
_ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
gcongr
refine Real.sum_le_exp_of_nonneg ?_ _
exact norm_nonneg _
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_le := norm_exp_sub_one_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_sub_id_le := norm_exp_sub_one_sub_id_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_exp_abs_sub_sum :=
norm_exp_sub_sum_le_exp_norm_sub_sum
@[deprecated (since := "2025-02-16")] alias abs_exp_le_exp_abs := norm_exp_le_exp_norm
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_abs_mul_exp :=
norm_exp_sub_sum_le_norm_mul_exp
end Complex
namespace Real
open Complex Finset
nonrec theorem exp_bound {x : ℝ} (hx : |x| ≤ 1) {n : ℕ} (hn : 0 < n) :
|exp x - ∑ m ∈ range n, x ^ m / m.factorial| ≤ |x| ^ n * (n.succ / (n.factorial * n)) := by
have hxc : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
convert exp_bound hxc hn using 2 <;>
norm_cast
theorem exp_bound' {x : ℝ} (h1 : 0 ≤ x) (h2 : x ≤ 1) {n : ℕ} (hn : 0 < n) :
Real.exp x ≤ (∑ m ∈ Finset.range n, x ^ m / m.factorial) +
x ^ n * (n + 1) / (n.factorial * n) := by
have h3 : |x| = x := by simpa
have h4 : |x| ≤ 1 := by rwa [h3]
have h' := Real.exp_bound h4 hn
rw [h3] at h'
have h'' := (abs_sub_le_iff.1 h').1
have t := sub_le_iff_le_add'.1 h''
simpa [mul_div_assoc] using t
theorem abs_exp_sub_one_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1| ≤ 2 * |x| := by
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_le (x := x) this
theorem abs_exp_sub_one_sub_id_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1 - x| ≤ x ^ 2 := by
rw [← sq_abs]
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_sub_id_le this
/-- A finite initial segment of the exponential series, followed by an arbitrary tail.
For fixed `n` this is just a linear map wrt `r`, and each map is a simple linear function
of the previous (see `expNear_succ`), with `expNear n x r ⟶ exp x` as `n ⟶ ∞`,
for any `r`. -/
noncomputable def expNear (n : ℕ) (x r : ℝ) : ℝ :=
(∑ m ∈ range n, x ^ m / m.factorial) + x ^ n / n.factorial * r
@[simp]
theorem expNear_zero (x r) : expNear 0 x r = r := by simp [expNear]
@[simp]
theorem expNear_succ (n x r) : expNear (n + 1) x r = expNear n x (1 + x / (n + 1) * r) := by
simp [expNear, range_succ, mul_add, add_left_comm, add_assoc, pow_succ, div_eq_mul_inv,
mul_inv, Nat.factorial]
ac_rfl
theorem expNear_sub (n x r₁ r₂) : expNear n x r₁ -
expNear n x r₂ = x ^ n / n.factorial * (r₁ - r₂) := by
simp [expNear, mul_sub]
theorem exp_approx_end (n m : ℕ) (x : ℝ) (e₁ : n + 1 = m) (h : |x| ≤ 1) :
|exp x - expNear m x 0| ≤ |x| ^ m / m.factorial * ((m + 1) / m) := by
simp only [expNear, mul_zero, add_zero]
convert exp_bound (n := m) h ?_ using 1
· field_simp [mul_comm]
· omega
theorem exp_approx_succ {n} {x a₁ b₁ : ℝ} (m : ℕ) (e₁ : n + 1 = m) (a₂ b₂ : ℝ)
(e : |1 + x / m * a₂ - a₁| ≤ b₁ - |x| / m * b₂)
(h : |exp x - expNear m x a₂| ≤ |x| ^ m / m.factorial * b₂) :
|exp x - expNear n x a₁| ≤ |x| ^ n / n.factorial * b₁ := by
refine (abs_sub_le _ _ _).trans ((add_le_add_right h _).trans ?_)
subst e₁; rw [expNear_succ, expNear_sub, abs_mul]
convert mul_le_mul_of_nonneg_left (a := |x| ^ n / ↑(Nat.factorial n))
(le_sub_iff_add_le'.1 e) ?_ using 1
· simp [mul_add, pow_succ', div_eq_mul_inv, abs_mul, abs_inv, ← pow_abs, mul_inv, Nat.factorial]
ac_rfl
· simp [div_nonneg, abs_nonneg]
theorem exp_approx_end' {n} {x a b : ℝ} (m : ℕ) (e₁ : n + 1 = m) (rm : ℝ) (er : ↑m = rm)
(h : |x| ≤ 1) (e : |1 - a| ≤ b - |x| / rm * ((rm + 1) / rm)) :
|exp x - expNear n x a| ≤ |x| ^ n / n.factorial * b := by
subst er
exact exp_approx_succ _ e₁ _ _ (by simpa using e) (exp_approx_end _ _ _ e₁ h)
theorem exp_1_approx_succ_eq {n} {a₁ b₁ : ℝ} {m : ℕ} (en : n + 1 = m) {rm : ℝ} (er : ↑m = rm)
(h : |exp 1 - expNear m 1 ((a₁ - 1) * rm)| ≤ |1| ^ m / m.factorial * (b₁ * rm)) :
|exp 1 - expNear n 1 a₁| ≤ |1| ^ n / n.factorial * b₁ := by
subst er
refine exp_approx_succ _ en _ _ ?_ h
field_simp [show (m : ℝ) ≠ 0 by norm_cast; omega]
theorem exp_approx_start (x a b : ℝ) (h : |exp x - expNear 0 x a| ≤ |x| ^ 0 / Nat.factorial 0 * b) :
|exp x - a| ≤ b := by simpa using h
theorem exp_bound_div_one_sub_of_interval' {x : ℝ} (h1 : 0 < x) (h2 : x < 1) :
Real.exp x < 1 / (1 - x) := by
have H : 0 < 1 - (1 + x + x ^ 2) * (1 - x) := calc
0 < x ^ 3 := by positivity
_ = 1 - (1 + x + x ^ 2) * (1 - x) := by ring
calc
exp x ≤ _ := exp_bound' h1.le h2.le zero_lt_three
_ ≤ 1 + x + x ^ 2 := by
-- Porting note: was `norm_num [Finset.sum] <;> nlinarith`
-- This proof should be restored after the norm_num plugin for big operators is ported.
-- (It may also need the positivity extensions in https://github.com/leanprover-community/mathlib4/pull/3907.)
rw [show 3 = 1 + 1 + 1 from rfl]
repeat rw [Finset.sum_range_succ]
norm_num [Nat.factorial]
nlinarith
_ < 1 / (1 - x) := by rw [lt_div_iff₀] <;> nlinarith
theorem exp_bound_div_one_sub_of_interval {x : ℝ} (h1 : 0 ≤ x) (h2 : x < 1) :
Real.exp x ≤ 1 / (1 - x) := by
rcases eq_or_lt_of_le h1 with (rfl | h1)
· simp
· exact (exp_bound_div_one_sub_of_interval' h1 h2).le
theorem add_one_lt_exp {x : ℝ} (hx : x ≠ 0) : x + 1 < Real.exp x := by
obtain hx | hx := hx.symm.lt_or_lt
· exact add_one_lt_exp_of_pos hx
obtain h' | h' := le_or_lt 1 (-x)
· linarith [x.exp_pos]
have hx' : 0 < x + 1 := by linarith
simpa [add_comm, exp_neg, inv_lt_inv₀ (exp_pos _) hx']
using exp_bound_div_one_sub_of_interval' (neg_pos.2 hx) h'
theorem add_one_le_exp (x : ℝ) : x + 1 ≤ Real.exp x := by
obtain rfl | hx := eq_or_ne x 0
· simp
· exact (add_one_lt_exp hx).le
lemma one_sub_lt_exp_neg {x : ℝ} (hx : x ≠ 0) : 1 - x < exp (-x) :=
(sub_eq_neg_add _ _).trans_lt <| add_one_lt_exp <| neg_ne_zero.2 hx
lemma one_sub_le_exp_neg (x : ℝ) : 1 - x ≤ exp (-x) :=
(sub_eq_neg_add _ _).trans_le <| add_one_le_exp _
theorem one_sub_div_pow_le_exp_neg {n : ℕ} {t : ℝ} (ht' : t ≤ n) : (1 - t / n) ^ n ≤ exp (-t) := by
rcases eq_or_ne n 0 with (rfl | hn)
· simp
rwa [Nat.cast_zero] at ht'
calc
(1 - t / n) ^ n ≤ rexp (-(t / n)) ^ n := by
gcongr
· exact sub_nonneg.2 <| div_le_one_of_le₀ ht' n.cast_nonneg
· exact one_sub_le_exp_neg _
_ = rexp (-t) := by rw [← Real.exp_nat_mul, mul_neg, mul_comm, div_mul_cancel₀]; positivity
lemma le_inv_mul_exp (x : ℝ) {c : ℝ} (hc : 0 < c) : x ≤ c⁻¹ * exp (c * x) := by
rw [le_inv_mul_iff₀ hc]
calc c * x
_ ≤ c * x + 1 := le_add_of_nonneg_right zero_le_one
_ ≤ _ := Real.add_one_le_exp (c * x)
end Real
namespace Mathlib.Meta.Positivity
open Lean.Meta Qq
/-- Extension for the `positivity` tactic: `Real.exp` is always positive. -/
@[positivity Real.exp _]
def evalExp : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q(Real.exp $a) =>
assertInstancesCommute
pure (.positive q(Real.exp_pos $a))
| _, _, _ => throwError "not Real.exp"
end Mathlib.Meta.Positivity
namespace Complex
@[simp]
theorem norm_exp_ofReal (x : ℝ) : ‖exp x‖ = Real.exp x := by
rw [← ofReal_exp]
exact Complex.norm_of_nonneg (le_of_lt (Real.exp_pos _))
@[deprecated (since := "2025-02-16")] alias abs_exp_ofReal := norm_exp_ofReal
end Complex
| Mathlib/Data/Complex/Exponential.lean | 911 | 912 | |
/-
Copyright (c) 2021 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Oliver Nash
-/
import Mathlib.Algebra.Lie.Solvable
import Mathlib.Algebra.Lie.Quotient
import Mathlib.Algebra.Lie.Normalizer
import Mathlib.Algebra.Order.Archimedean.Basic
import Mathlib.LinearAlgebra.Eigenspace.Basic
import Mathlib.RingTheory.Artinian.Module
import Mathlib.RingTheory.Nilpotent.Lemmas
/-!
# Nilpotent Lie algebras
Like groups, Lie algebras admit a natural concept of nilpotency. More generally, any Lie module
carries a natural concept of nilpotency. We define these here via the lower central series.
## Main definitions
* `LieModule.lowerCentralSeries`
* `LieModule.IsNilpotent`
* `LieModule.maxNilpotentSubmodule`
* `LieAlgebra.maxNilpotentIdeal`
## Tags
lie algebra, lower central series, nilpotent, max nilpotent ideal
-/
universe u v w w₁ w₂
section NilpotentModules
variable {R : Type u} {L : Type v} {M : Type w}
variable [CommRing R] [LieRing L] [LieAlgebra R L] [AddCommGroup M] [Module R M]
variable [LieRingModule L M]
variable (k : ℕ) (N : LieSubmodule R L M)
namespace LieSubmodule
/-- A generalisation of the lower central series. The zeroth term is a specified Lie submodule of
a Lie module. In the case when we specify the top ideal `⊤` of the Lie algebra, regarded as a Lie
module over itself, we get the usual lower central series of a Lie algebra.
It can be more convenient to work with this generalisation when considering the lower central series
of a Lie submodule, regarded as a Lie module in its own right, since it provides a type-theoretic
expression of the fact that the terms of the Lie submodule's lower central series are also Lie
submodules of the enclosing Lie module.
See also `LieSubmodule.lowerCentralSeries_eq_lcs_comap` and
`LieSubmodule.lowerCentralSeries_map_eq_lcs` below, as well as `LieSubmodule.ucs`. -/
def lcs : LieSubmodule R L M → LieSubmodule R L M :=
(fun N => ⁅(⊤ : LieIdeal R L), N⁆)^[k]
@[simp]
theorem lcs_zero (N : LieSubmodule R L M) : N.lcs 0 = N :=
rfl
@[simp]
theorem lcs_succ : N.lcs (k + 1) = ⁅(⊤ : LieIdeal R L), N.lcs k⁆ :=
Function.iterate_succ_apply' (fun N' => ⁅⊤, N'⁆) k N
@[simp]
lemma lcs_sup {N₁ N₂ : LieSubmodule R L M} {k : ℕ} :
(N₁ ⊔ N₂).lcs k = N₁.lcs k ⊔ N₂.lcs k := by
induction k with
| zero => simp
| succ k ih => simp only [LieSubmodule.lcs_succ, ih, LieSubmodule.lie_sup]
end LieSubmodule
namespace LieModule
variable (R L M)
/-- The lower central series of Lie submodules of a Lie module. -/
def lowerCentralSeries : LieSubmodule R L M :=
(⊤ : LieSubmodule R L M).lcs k
@[simp]
theorem lowerCentralSeries_zero : lowerCentralSeries R L M 0 = ⊤ :=
rfl
@[simp]
theorem lowerCentralSeries_succ :
lowerCentralSeries R L M (k + 1) = ⁅(⊤ : LieIdeal R L), lowerCentralSeries R L M k⁆ :=
(⊤ : LieSubmodule R L M).lcs_succ k
private theorem coe_lowerCentralSeries_eq_int_aux (R₁ R₂ L M : Type*)
[CommRing R₁] [CommRing R₂] [AddCommGroup M]
[LieRing L] [LieAlgebra R₁ L] [LieAlgebra R₂ L] [Module R₁ M] [Module R₂ M] [LieRingModule L M]
[LieModule R₁ L M] (k : ℕ) :
let I := lowerCentralSeries R₂ L M k; let S : Set M := {⁅a, b⁆ | (a : L) (b ∈ I)}
(Submodule.span R₁ S : Set M) ≤ (Submodule.span R₂ S : Set M) := by
intro I S x hx
simp only [SetLike.mem_coe] at hx ⊢
induction hx using Submodule.closure_induction with
| zero => exact Submodule.zero_mem _
| add y z hy₁ hz₁ hy₂ hz₂ => exact Submodule.add_mem _ hy₂ hz₂
| smul_mem c y hy =>
obtain ⟨a, b, hb, rfl⟩ := hy
rw [← smul_lie]
exact Submodule.subset_span ⟨c • a, b, hb, rfl⟩
theorem coe_lowerCentralSeries_eq_int [LieModule R L M] (k : ℕ) :
(lowerCentralSeries R L M k : Set M) = (lowerCentralSeries ℤ L M k : Set M) := by
rw [← LieSubmodule.coe_toSubmodule, ← LieSubmodule.coe_toSubmodule]
induction k with
| zero => rfl
| succ k ih =>
rw [lowerCentralSeries_succ, lowerCentralSeries_succ]
rw [LieSubmodule.lieIdeal_oper_eq_linear_span', LieSubmodule.lieIdeal_oper_eq_linear_span']
rw [Set.ext_iff] at ih
simp only [SetLike.mem_coe, LieSubmodule.mem_toSubmodule] at ih
simp only [LieSubmodule.mem_top, ih, true_and]
apply le_antisymm
· exact coe_lowerCentralSeries_eq_int_aux _ _ L M k
· simp only [← ih]
exact coe_lowerCentralSeries_eq_int_aux _ _ L M k
end LieModule
namespace LieSubmodule
open LieModule
theorem lcs_le_self : N.lcs k ≤ N := by
induction k with
| zero => simp
| succ k ih =>
simp only [lcs_succ]
exact (LieSubmodule.mono_lie_right ⊤ ih).trans (N.lie_le_right ⊤)
variable [LieModule R L M]
theorem lowerCentralSeries_eq_lcs_comap : lowerCentralSeries R L N k = (N.lcs k).comap N.incl := by
induction k with
| zero => simp
| succ k ih =>
simp only [lcs_succ, lowerCentralSeries_succ] at ih ⊢
have : N.lcs k ≤ N.incl.range := by
rw [N.range_incl]
apply lcs_le_self
rw [ih, LieSubmodule.comap_bracket_eq _ N.incl _ N.ker_incl this]
theorem lowerCentralSeries_map_eq_lcs : (lowerCentralSeries R L N k).map N.incl = N.lcs k := by
rw [lowerCentralSeries_eq_lcs_comap, LieSubmodule.map_comap_incl, inf_eq_right]
apply lcs_le_self
theorem lowerCentralSeries_eq_bot_iff_lcs_eq_bot:
lowerCentralSeries R L N k = ⊥ ↔ lcs k N = ⊥ := by
refine ⟨fun h ↦ ?_, fun h ↦ ?_⟩
· rw [← N.lowerCentralSeries_map_eq_lcs, ← LieModuleHom.le_ker_iff_map]
simpa
· rw [N.lowerCentralSeries_eq_lcs_comap, comap_incl_eq_bot]
simp [h]
end LieSubmodule
namespace LieModule
variable {M₂ : Type w₁} [AddCommGroup M₂] [Module R M₂] [LieRingModule L M₂] [LieModule R L M₂]
variable (R L M)
theorem antitone_lowerCentralSeries : Antitone <| lowerCentralSeries R L M := by
intro l k
induction k generalizing l with
| zero => exact fun h ↦ (Nat.le_zero.mp h).symm ▸ le_rfl
| succ k ih =>
intro h
rcases Nat.of_le_succ h with (hk | hk)
· rw [lowerCentralSeries_succ]
exact (LieSubmodule.mono_lie_right ⊤ (ih hk)).trans (LieSubmodule.lie_le_right _ _)
· exact hk.symm ▸ le_rfl
theorem eventually_iInf_lowerCentralSeries_eq [IsArtinian R M] :
∀ᶠ l in Filter.atTop, ⨅ k, lowerCentralSeries R L M k = lowerCentralSeries R L M l := by
have h_wf : WellFoundedGT (LieSubmodule R L M)ᵒᵈ :=
LieSubmodule.wellFoundedLT_of_isArtinian R L M
obtain ⟨n, hn : ∀ m, n ≤ m → lowerCentralSeries R L M n = lowerCentralSeries R L M m⟩ :=
h_wf.monotone_chain_condition ⟨_, antitone_lowerCentralSeries R L M⟩
refine Filter.eventually_atTop.mpr ⟨n, fun l hl ↦ le_antisymm (iInf_le _ _) (le_iInf fun m ↦ ?_)⟩
rcases le_or_lt l m with h | h
· rw [← hn _ hl, ← hn _ (hl.trans h)]
· exact antitone_lowerCentralSeries R L M (le_of_lt h)
theorem trivial_iff_lower_central_eq_bot : IsTrivial L M ↔ lowerCentralSeries R L M 1 = ⊥ := by
constructor <;> intro h
· simp
· rw [LieSubmodule.eq_bot_iff] at h; apply IsTrivial.mk; intro x m; apply h
apply LieSubmodule.subset_lieSpan
simp only [LieSubmodule.top_coe, Subtype.exists, LieSubmodule.mem_top, exists_prop, true_and,
Set.mem_setOf]
exact ⟨x, m, rfl⟩
section
variable [LieModule R L M]
theorem iterate_toEnd_mem_lowerCentralSeries (x : L) (m : M) (k : ℕ) :
(toEnd R L M x)^[k] m ∈ lowerCentralSeries R L M k := by
induction k with
| zero => simp only [Function.iterate_zero, lowerCentralSeries_zero, LieSubmodule.mem_top]
| succ k ih =>
simp only [lowerCentralSeries_succ, Function.comp_apply, Function.iterate_succ',
toEnd_apply_apply]
exact LieSubmodule.lie_mem_lie (LieSubmodule.mem_top x) ih
theorem iterate_toEnd_mem_lowerCentralSeries₂ (x y : L) (m : M) (k : ℕ) :
(toEnd R L M x ∘ₗ toEnd R L M y)^[k] m ∈
lowerCentralSeries R L M (2 * k) := by
induction k with
| zero => simp
| succ k ih =>
have hk : 2 * k.succ = (2 * k + 1) + 1 := rfl
simp only [lowerCentralSeries_succ, Function.comp_apply, Function.iterate_succ', hk,
toEnd_apply_apply, LinearMap.coe_comp, toEnd_apply_apply]
refine LieSubmodule.lie_mem_lie (LieSubmodule.mem_top x) ?_
exact LieSubmodule.lie_mem_lie (LieSubmodule.mem_top y) ih
variable {R L M}
theorem map_lowerCentralSeries_le (f : M →ₗ⁅R,L⁆ M₂) :
(lowerCentralSeries R L M k).map f ≤ lowerCentralSeries R L M₂ k := by
induction k with
| zero => simp only [lowerCentralSeries_zero, le_top]
| succ k ih =>
simp only [LieModule.lowerCentralSeries_succ, LieSubmodule.map_bracket_eq]
exact LieSubmodule.mono_lie_right ⊤ ih
lemma map_lowerCentralSeries_eq {f : M →ₗ⁅R,L⁆ M₂} (hf : Function.Surjective f) :
(lowerCentralSeries R L M k).map f = lowerCentralSeries R L M₂ k := by
apply le_antisymm (map_lowerCentralSeries_le k f)
induction k with
| zero =>
rwa [lowerCentralSeries_zero, lowerCentralSeries_zero, top_le_iff, f.map_top,
f.range_eq_top]
| succ =>
simp only [lowerCentralSeries_succ, LieSubmodule.map_bracket_eq]
apply LieSubmodule.mono_lie_right
assumption
end
open LieAlgebra
theorem derivedSeries_le_lowerCentralSeries (k : ℕ) :
derivedSeries R L k ≤ lowerCentralSeries R L L k := by
induction k with
| zero => rw [derivedSeries_def, derivedSeriesOfIdeal_zero, lowerCentralSeries_zero]
| succ k h =>
have h' : derivedSeries R L k ≤ ⊤ := by simp only [le_top]
rw [derivedSeries_def, derivedSeriesOfIdeal_succ, lowerCentralSeries_succ]
exact LieSubmodule.mono_lie h' h
/-- A Lie module is nilpotent if its lower central series reaches 0 (in a finite number of
steps). -/
@[mk_iff isNilpotent_iff_int]
class IsNilpotent : Prop where
mk_int ::
nilpotent_int : ∃ k, lowerCentralSeries ℤ L M k = ⊥
section
variable [LieModule R L M]
/-- See also `LieModule.isNilpotent_iff_exists_ucs_eq_top`. -/
lemma isNilpotent_iff :
IsNilpotent L M ↔ ∃ k, lowerCentralSeries R L M k = ⊥ := by
simp [isNilpotent_iff_int, SetLike.ext'_iff, coe_lowerCentralSeries_eq_int R L M]
lemma IsNilpotent.nilpotent [IsNilpotent L M] : ∃ k, lowerCentralSeries R L M k = ⊥ :=
(isNilpotent_iff R L M).mp ‹_›
variable {R L} in
lemma IsNilpotent.mk {k : ℕ} (h : lowerCentralSeries R L M k = ⊥) : IsNilpotent L M :=
(isNilpotent_iff R L M).mpr ⟨k, h⟩
@[deprecated IsNilpotent.nilpotent (since := "2025-01-07")]
theorem exists_lowerCentralSeries_eq_bot_of_isNilpotent [IsNilpotent L M] :
∃ k, lowerCentralSeries R L M k = ⊥ :=
IsNilpotent.nilpotent R L M
@[simp] lemma iInf_lowerCentralSeries_eq_bot_of_isNilpotent [IsNilpotent L M] :
⨅ k, lowerCentralSeries R L M k = ⊥ := by
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent R L M
rw [eq_bot_iff, ← hk]
exact iInf_le _ _
end
section
variable {R L M}
variable [LieModule R L M]
theorem _root_.LieSubmodule.isNilpotent_iff_exists_lcs_eq_bot (N : LieSubmodule R L M) :
LieModule.IsNilpotent L N ↔ ∃ k, N.lcs k = ⊥ := by
rw [isNilpotent_iff R L N]
refine exists_congr fun k => ?_
rw [N.lowerCentralSeries_eq_lcs_comap k, LieSubmodule.comap_incl_eq_bot,
inf_eq_right.mpr (N.lcs_le_self k)]
variable (R L M)
instance (priority := 100) trivialIsNilpotent [IsTrivial L M] : IsNilpotent L M :=
⟨by use 1; simp⟩
instance instIsNilpotentSup (M₁ M₂ : LieSubmodule R L M) [IsNilpotent L M₁] [IsNilpotent L M₂] :
IsNilpotent L (M₁ ⊔ M₂ : LieSubmodule R L M) := by
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent R L M₁
obtain ⟨l, hl⟩ := IsNilpotent.nilpotent R L M₂
let lcs_eq_bot {m n} (N : LieSubmodule R L M) (le : m ≤ n) (hn : lowerCentralSeries R L N m = ⊥) :
lowerCentralSeries R L N n = ⊥ := by
simpa [hn] using antitone_lowerCentralSeries R L N le
have h₁ : lowerCentralSeries R L M₁ (k ⊔ l) = ⊥ := lcs_eq_bot M₁ (Nat.le_max_left k l) hk
have h₂ : lowerCentralSeries R L M₂ (k ⊔ l) = ⊥ := lcs_eq_bot M₂ (Nat.le_max_right k l) hl
refine (isNilpotent_iff R L (M₁ + M₂)).mpr ⟨k ⊔ l, ?_⟩
simp [LieSubmodule.add_eq_sup, (M₁ ⊔ M₂).lowerCentralSeries_eq_lcs_comap, LieSubmodule.lcs_sup,
(M₁.lowerCentralSeries_eq_bot_iff_lcs_eq_bot (k ⊔ l)).1 h₁,
(M₂.lowerCentralSeries_eq_bot_iff_lcs_eq_bot (k ⊔ l)).1 h₂, LieSubmodule.comap_incl_eq_bot]
theorem exists_forall_pow_toEnd_eq_zero [IsNilpotent L M] :
∃ k : ℕ, ∀ x : L, toEnd R L M x ^ k = 0 := by
obtain ⟨k, hM⟩ := IsNilpotent.nilpotent R L M
use k
intro x; ext m
rw [Module.End.pow_apply, LinearMap.zero_apply, ← @LieSubmodule.mem_bot R L M, ← hM]
exact iterate_toEnd_mem_lowerCentralSeries R L M x m k
theorem isNilpotent_toEnd_of_isNilpotent [IsNilpotent L M] (x : L) :
_root_.IsNilpotent (toEnd R L M x) := by
change ∃ k, toEnd R L M x ^ k = 0
have := exists_forall_pow_toEnd_eq_zero R L M
tauto
theorem isNilpotent_toEnd_of_isNilpotent₂ [IsNilpotent L M] (x y : L) :
_root_.IsNilpotent (toEnd R L M x ∘ₗ toEnd R L M y) := by
obtain ⟨k, hM⟩ := IsNilpotent.nilpotent R L M
replace hM : lowerCentralSeries R L M (2 * k) = ⊥ := by
rw [eq_bot_iff, ← hM]; exact antitone_lowerCentralSeries R L M (by omega)
use k
ext m
rw [Module.End.pow_apply, LinearMap.zero_apply, ← LieSubmodule.mem_bot (R := R) (L := L), ← hM]
exact iterate_toEnd_mem_lowerCentralSeries₂ R L M x y m k
@[simp] lemma maxGenEigenSpace_toEnd_eq_top [IsNilpotent L M] (x : L) :
((toEnd R L M x).maxGenEigenspace 0) = ⊤ := by
ext m
simp only [Module.End.mem_maxGenEigenspace, zero_smul, sub_zero, Submodule.mem_top,
iff_true]
obtain ⟨k, hk⟩ := exists_forall_pow_toEnd_eq_zero R L M
exact ⟨k, by simp [hk x]⟩
/-- If the quotient of a Lie module `M` by a Lie submodule on which the Lie algebra acts trivially
is nilpotent then `M` is nilpotent.
This is essentially the Lie module equivalent of the fact that a central
extension of nilpotent Lie algebras is nilpotent. See `LieAlgebra.nilpotent_of_nilpotent_quotient`
below for the corresponding result for Lie algebras. -/
theorem nilpotentOfNilpotentQuotient {N : LieSubmodule R L M} (h₁ : N ≤ maxTrivSubmodule R L M)
(h₂ : IsNilpotent L (M ⧸ N)) : IsNilpotent L M := by
rw [isNilpotent_iff R L] at h₂ ⊢
obtain ⟨k, hk⟩ := h₂
use k + 1
simp only [lowerCentralSeries_succ]
suffices lowerCentralSeries R L M k ≤ N by
replace this := LieSubmodule.mono_lie_right ⊤ (le_trans this h₁)
rwa [ideal_oper_maxTrivSubmodule_eq_bot, le_bot_iff] at this
rw [← LieSubmodule.Quotient.map_mk'_eq_bot_le, ← le_bot_iff, ← hk]
exact map_lowerCentralSeries_le k (LieSubmodule.Quotient.mk' N)
theorem isNilpotent_quotient_iff :
IsNilpotent L (M ⧸ N) ↔ ∃ k, lowerCentralSeries R L M k ≤ N := by
rw [isNilpotent_iff R L]
refine exists_congr fun k ↦ ?_
rw [← LieSubmodule.Quotient.map_mk'_eq_bot_le, map_lowerCentralSeries_eq k
(LieSubmodule.Quotient.surjective_mk' N)]
theorem iInf_lcs_le_of_isNilpotent_quot (h : IsNilpotent L (M ⧸ N)) :
⨅ k, lowerCentralSeries R L M k ≤ N := by
obtain ⟨k, hk⟩ := (isNilpotent_quotient_iff R L M N).mp h
exact iInf_le_of_le k hk
end
/-- Given a nilpotent Lie module `M` with lower central series `M = C₀ ≥ C₁ ≥ ⋯ ≥ Cₖ = ⊥`, this is
the natural number `k` (the number of inclusions).
For a non-nilpotent module, we use the junk value 0. -/
noncomputable def nilpotencyLength : ℕ :=
sInf {k | lowerCentralSeries ℤ L M k = ⊥}
@[simp]
theorem nilpotencyLength_eq_zero_iff [IsNilpotent L M] :
nilpotencyLength L M = 0 ↔ Subsingleton M := by
let s := {k | lowerCentralSeries ℤ L M k = ⊥}
have hs : s.Nonempty := by
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent ℤ L M
exact ⟨k, hk⟩
change sInf s = 0 ↔ _
rw [← LieSubmodule.subsingleton_iff ℤ L M, ← subsingleton_iff_bot_eq_top, ←
lowerCentralSeries_zero, @eq_comm (LieSubmodule ℤ L M)]
refine ⟨fun h => h ▸ Nat.sInf_mem hs, fun h => ?_⟩
rw [Nat.sInf_eq_zero]
exact Or.inl h
section
variable [LieModule R L M]
theorem nilpotencyLength_eq_succ_iff (k : ℕ) :
nilpotencyLength L M = k + 1 ↔
lowerCentralSeries R L M (k + 1) = ⊥ ∧ lowerCentralSeries R L M k ≠ ⊥ := by
have aux (k : ℕ) : lowerCentralSeries R L M k = ⊥ ↔ lowerCentralSeries ℤ L M k = ⊥ := by
simp [SetLike.ext'_iff, coe_lowerCentralSeries_eq_int R L M]
let s := {k | lowerCentralSeries ℤ L M k = ⊥}
rw [aux, ne_eq, aux]
change sInf s = k + 1 ↔ k + 1 ∈ s ∧ k ∉ s
have hs : ∀ k₁ k₂, k₁ ≤ k₂ → k₁ ∈ s → k₂ ∈ s := by
rintro k₁ k₂ h₁₂ (h₁ : lowerCentralSeries ℤ L M k₁ = ⊥)
exact eq_bot_iff.mpr (h₁ ▸ antitone_lowerCentralSeries ℤ L M h₁₂)
exact Nat.sInf_upward_closed_eq_succ_iff hs k
@[simp]
theorem nilpotencyLength_eq_one_iff [Nontrivial M] :
nilpotencyLength L M = 1 ↔ IsTrivial L M := by
rw [nilpotencyLength_eq_succ_iff ℤ, ← trivial_iff_lower_central_eq_bot]
simp
theorem isTrivial_of_nilpotencyLength_le_one [IsNilpotent L M] (h : nilpotencyLength L M ≤ 1) :
IsTrivial L M := by
nontriviality M
rcases Nat.le_one_iff_eq_zero_or_eq_one.mp h with h | h
· rw [nilpotencyLength_eq_zero_iff] at h; infer_instance
· rwa [nilpotencyLength_eq_one_iff] at h
end
/-- Given a non-trivial nilpotent Lie module `M` with lower central series
`M = C₀ ≥ C₁ ≥ ⋯ ≥ Cₖ = ⊥`, this is the `k-1`th term in the lower central series (the last
non-trivial term).
For a trivial or non-nilpotent module, this is the bottom submodule, `⊥`. -/
noncomputable def lowerCentralSeriesLast : LieSubmodule R L M :=
match nilpotencyLength L M with
| 0 => ⊥
| k + 1 => lowerCentralSeries R L M k
theorem lowerCentralSeriesLast_le_max_triv [LieModule R L M] :
lowerCentralSeriesLast R L M ≤ maxTrivSubmodule R L M := by
rw [lowerCentralSeriesLast]
rcases h : nilpotencyLength L M with - | k
· exact bot_le
· rw [le_max_triv_iff_bracket_eq_bot]
rw [nilpotencyLength_eq_succ_iff R, lowerCentralSeries_succ] at h
exact h.1
theorem nontrivial_lowerCentralSeriesLast [LieModule R L M] [Nontrivial M] [IsNilpotent L M] :
Nontrivial (lowerCentralSeriesLast R L M) := by
rw [LieSubmodule.nontrivial_iff_ne_bot, lowerCentralSeriesLast]
cases h : nilpotencyLength L M
· rw [nilpotencyLength_eq_zero_iff, ← not_nontrivial_iff_subsingleton] at h
contradiction
· rw [nilpotencyLength_eq_succ_iff R] at h
exact h.2
theorem lowerCentralSeriesLast_le_of_not_isTrivial [IsNilpotent L M] (h : ¬ IsTrivial L M) :
lowerCentralSeriesLast R L M ≤ lowerCentralSeries R L M 1 := by
rw [lowerCentralSeriesLast]
replace h : 1 < nilpotencyLength L M := by
by_contra contra
have := isTrivial_of_nilpotencyLength_le_one L M (not_lt.mp contra)
contradiction
rcases hk : nilpotencyLength L M with - | k <;> rw [hk] at h
· contradiction
· exact antitone_lowerCentralSeries _ _ _ (Nat.lt_succ.mp h)
variable [LieModule R L M]
/-- For a nilpotent Lie module `M` of a Lie algebra `L`, the first term in the lower central series
of `M` contains a non-zero element on which `L` acts trivially unless the entire action is trivial.
Taking `M = L`, this provides a useful characterisation of Abelian-ness for nilpotent Lie
algebras. -/
lemma disjoint_lowerCentralSeries_maxTrivSubmodule_iff [IsNilpotent L M] :
Disjoint (lowerCentralSeries R L M 1) (maxTrivSubmodule R L M) ↔ IsTrivial L M := by
refine ⟨fun h ↦ ?_, fun h ↦ by simp⟩
nontriviality M
by_contra contra
have : lowerCentralSeriesLast R L M ≤ lowerCentralSeries R L M 1 ⊓ maxTrivSubmodule R L M :=
le_inf_iff.mpr ⟨lowerCentralSeriesLast_le_of_not_isTrivial R L M contra,
lowerCentralSeriesLast_le_max_triv R L M⟩
suffices ¬ Nontrivial (lowerCentralSeriesLast R L M) by
exact this (nontrivial_lowerCentralSeriesLast R L M)
rw [h.eq_bot, le_bot_iff] at this
exact this ▸ not_nontrivial _
theorem nontrivial_max_triv_of_isNilpotent [Nontrivial M] [IsNilpotent L M] :
Nontrivial (maxTrivSubmodule R L M) :=
Set.nontrivial_mono (lowerCentralSeriesLast_le_max_triv R L M)
(nontrivial_lowerCentralSeriesLast R L M)
@[simp]
theorem coe_lcs_range_toEnd_eq (k : ℕ) :
(lowerCentralSeries R (toEnd R L M).range M k : Submodule R M) =
lowerCentralSeries R L M k := by
induction k with
| zero => simp
| succ k ih =>
simp only [lowerCentralSeries_succ, LieSubmodule.lieIdeal_oper_eq_linear_span', ←
(lowerCentralSeries R (toEnd R L M).range M k).mem_toSubmodule, ih]
congr
ext m
constructor
· rintro ⟨⟨-, ⟨y, rfl⟩⟩, -, n, hn, rfl⟩
exact ⟨y, LieSubmodule.mem_top _, n, hn, rfl⟩
· rintro ⟨x, -, n, hn, rfl⟩
exact
⟨⟨toEnd R L M x, LieHom.mem_range_self _ x⟩, LieSubmodule.mem_top _, n, hn, rfl⟩
@[simp]
theorem isNilpotent_range_toEnd_iff :
IsNilpotent (toEnd R L M).range M ↔ IsNilpotent L M := by
simp only [isNilpotent_iff R _ M]
constructor <;> rintro ⟨k, hk⟩ <;> use k <;>
rw [← LieSubmodule.toSubmodule_inj] at hk ⊢ <;>
simpa using hk
end LieModule
namespace LieSubmodule
variable {N₁ N₂ : LieSubmodule R L M}
variable [LieModule R L M]
/-- The upper (aka ascending) central series.
See also `LieSubmodule.lcs`. -/
def ucs (k : ℕ) : LieSubmodule R L M → LieSubmodule R L M :=
normalizer^[k]
@[simp]
theorem ucs_zero : N.ucs 0 = N :=
rfl
@[simp]
theorem ucs_succ (k : ℕ) : N.ucs (k + 1) = (N.ucs k).normalizer :=
Function.iterate_succ_apply' normalizer k N
theorem ucs_add (k l : ℕ) : N.ucs (k + l) = (N.ucs l).ucs k :=
Function.iterate_add_apply normalizer k l N
@[gcongr, mono]
theorem ucs_mono (k : ℕ) (h : N₁ ≤ N₂) : N₁.ucs k ≤ N₂.ucs k := by
induction k with
| zero => simpa
| succ k ih =>
simp only [ucs_succ]
gcongr
theorem ucs_eq_self_of_normalizer_eq_self (h : N₁.normalizer = N₁) (k : ℕ) : N₁.ucs k = N₁ := by
induction k with
| zero => simp
| succ k ih => rwa [ucs_succ, ih]
/-- If a Lie module `M` contains a self-normalizing Lie submodule `N`, then all terms of the upper
central series of `M` are contained in `N`.
An important instance of this situation arises from a Cartan subalgebra `H ⊆ L` with the roles of
`L`, `M`, `N` played by `H`, `L`, `H`, respectively. -/
theorem ucs_le_of_normalizer_eq_self (h : N₁.normalizer = N₁) (k : ℕ) :
(⊥ : LieSubmodule R L M).ucs k ≤ N₁ := by
rw [← ucs_eq_self_of_normalizer_eq_self h k]
gcongr
simp
theorem lcs_add_le_iff (l k : ℕ) : N₁.lcs (l + k) ≤ N₂ ↔ N₁.lcs l ≤ N₂.ucs k := by
induction k generalizing l with
| zero => simp
| succ k ih =>
rw [(by abel : l + (k + 1) = l + 1 + k), ih, ucs_succ, lcs_succ, top_lie_le_iff_le_normalizer]
theorem lcs_le_iff (k : ℕ) : N₁.lcs k ≤ N₂ ↔ N₁ ≤ N₂.ucs k := by
convert lcs_add_le_iff (R := R) (L := L) (M := M) 0 k
rw [zero_add]
theorem gc_lcs_ucs (k : ℕ) :
GaloisConnection (fun N : LieSubmodule R L M => N.lcs k) fun N : LieSubmodule R L M =>
N.ucs k :=
fun _ _ => lcs_le_iff k
theorem ucs_eq_top_iff (k : ℕ) : N.ucs k = ⊤ ↔ LieModule.lowerCentralSeries R L M k ≤ N := by
rw [eq_top_iff, ← lcs_le_iff]; rfl
variable (R) in
theorem _root_.LieModule.isNilpotent_iff_exists_ucs_eq_top :
LieModule.IsNilpotent L M ↔ ∃ k, (⊥ : LieSubmodule R L M).ucs k = ⊤ := by
rw [LieModule.isNilpotent_iff R]; exact exists_congr fun k => by simp [ucs_eq_top_iff]
theorem ucs_comap_incl (k : ℕ) :
((⊥ : LieSubmodule R L M).ucs k).comap N.incl = (⊥ : LieSubmodule R L N).ucs k := by
induction k with
| zero => exact N.ker_incl
| succ k ih => simp [← ih]
theorem isNilpotent_iff_exists_self_le_ucs :
LieModule.IsNilpotent L N ↔ ∃ k, N ≤ (⊥ : LieSubmodule R L M).ucs k := by
simp_rw [LieModule.isNilpotent_iff_exists_ucs_eq_top R, ← ucs_comap_incl, comap_incl_eq_top]
theorem ucs_bot_one : (⊥ : LieSubmodule R L M).ucs 1 = LieModule.maxTrivSubmodule R L M := by
simp [LieSubmodule.normalizer_bot_eq_maxTrivSubmodule]
end LieSubmodule
section Morphisms
open LieModule Function
variable [LieModule R L M]
variable {L₂ M₂ : Type*} [LieRing L₂] [LieAlgebra R L₂]
variable [AddCommGroup M₂] [Module R M₂] [LieRingModule L₂ M₂]
variable {f : L →ₗ⁅R⁆ L₂} {g : M →ₗ[R] M₂}
variable (hfg : ∀ x m, ⁅f x, g m⁆ = g ⁅x, m⁆)
include hfg in
theorem lieModule_lcs_map_le (k : ℕ) :
(lowerCentralSeries R L M k : Submodule R M).map g ≤ lowerCentralSeries R L₂ M₂ k := by
induction k with
| zero =>
simp [LinearMap.range_eq_top, Submodule.map_top]
| succ k ih =>
rw [lowerCentralSeries_succ, LieSubmodule.lieIdeal_oper_eq_linear_span', Submodule.map_span,
Submodule.span_le]
rintro m₂ ⟨m, ⟨x, n, m_n, ⟨h₁, h₂⟩⟩, rfl⟩
simp only [lowerCentralSeries_succ, SetLike.mem_coe, LieSubmodule.mem_toSubmodule]
have : ∃ y : L₂, ∃ n : lowerCentralSeries R L₂ M₂ k, ⁅y, n⁆ = g m := by
use f x, ⟨g m_n, ih (Submodule.mem_map_of_mem h₁)⟩
simp [hfg x m_n, h₂]
obtain ⟨y, n, hn⟩ := this
rw [← hn]
apply LieSubmodule.lie_mem_lie
· simp
· exact SetLike.coe_mem n
variable [LieModule R L₂ M₂] (hg_inj : Injective g)
include hg_inj hfg in
theorem Function.Injective.lieModuleIsNilpotent [IsNilpotent L₂ M₂] : IsNilpotent L M := by
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent R L₂ M₂
rw [isNilpotent_iff R]
use k
rw [← LieSubmodule.toSubmodule_inj] at hk ⊢
apply Submodule.map_injective_of_injective hg_inj
simpa [hk] using lieModule_lcs_map_le hfg k
variable (hf_surj : Surjective f) (hg_surj : Surjective g)
include hf_surj hg_surj hfg in
theorem Function.Surjective.lieModule_lcs_map_eq (k : ℕ) :
(lowerCentralSeries R L M k : Submodule R M).map g = lowerCentralSeries R L₂ M₂ k := by
refine le_antisymm (lieModule_lcs_map_le hfg k) ?_
induction k with
| zero => simpa [LinearMap.range_eq_top]
| succ k ih =>
suffices
{m | ∃ (x : L₂) (n : _), n ∈ lowerCentralSeries R L M k ∧ ⁅x, g n⁆ = m} ⊆
g '' {m | ∃ (x : L) (n : _), n ∈ lowerCentralSeries R L M k ∧ ⁅x, n⁆ = m} by
simp only [← LieSubmodule.mem_toSubmodule] at this
simp_rw [lowerCentralSeries_succ, LieSubmodule.lieIdeal_oper_eq_linear_span',
Submodule.map_span, LieSubmodule.mem_top, true_and, ← LieSubmodule.mem_toSubmodule]
refine Submodule.span_mono (Set.Subset.trans ?_ this)
rintro m₁ ⟨x, n, hn, rfl⟩
obtain ⟨n', hn', rfl⟩ := ih hn
exact ⟨x, n', hn', rfl⟩
rintro m₂ ⟨x, n, hn, rfl⟩
obtain ⟨y, rfl⟩ := hf_surj x
exact ⟨⁅y, n⁆, ⟨y, n, hn, rfl⟩, (hfg y n).symm⟩
include hf_surj hg_surj hfg in
theorem Function.Surjective.lieModuleIsNilpotent [IsNilpotent L M] : IsNilpotent L₂ M₂ := by
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent R L M
rw [isNilpotent_iff R]
use k
rw [← LieSubmodule.toSubmodule_inj] at hk ⊢
simp [← hf_surj.lieModule_lcs_map_eq hfg hg_surj k, hk]
theorem Equiv.lieModule_isNilpotent_iff (f : L ≃ₗ⁅R⁆ L₂) (g : M ≃ₗ[R] M₂)
(hfg : ∀ x m, ⁅f x, g m⁆ = g ⁅x, m⁆) : IsNilpotent L M ↔ IsNilpotent L₂ M₂ := by
constructor <;> intro h
· have hg : Surjective (g : M →ₗ[R] M₂) := g.surjective
exact f.surjective.lieModuleIsNilpotent hfg hg
· have hg : Surjective (g.symm : M₂ →ₗ[R] M) := g.symm.surjective
refine f.symm.surjective.lieModuleIsNilpotent (fun x m => ?_) hg
rw [LinearEquiv.coe_coe, LieEquiv.coe_toLieHom, ← g.symm_apply_apply ⁅f.symm x, g.symm m⁆, ←
hfg, f.apply_symm_apply, g.apply_symm_apply]
@[simp]
theorem LieModule.isNilpotent_of_top_iff :
IsNilpotent (⊤ : LieSubalgebra R L) M ↔ IsNilpotent L M :=
Equiv.lieModule_isNilpotent_iff LieSubalgebra.topEquiv (1 : M ≃ₗ[R] M) fun _ _ => rfl
@[simp] lemma LieModule.isNilpotent_of_top_iff' :
IsNilpotent L {x // x ∈ (⊤ : LieSubmodule R L M)} ↔ IsNilpotent L M :=
Equiv.lieModule_isNilpotent_iff 1 (LinearEquiv.ofTop ⊤ rfl) fun _ _ ↦ rfl
end Morphisms
namespace LieModule
variable (R L M)
variable [LieModule R L M]
theorem isNilpotent_of_le (M₁ M₂ : LieSubmodule R L M) (h₁ : M₁ ≤ M₂) [IsNilpotent L M₂] :
IsNilpotent L M₁ := by
let f : L →ₗ⁅R⁆ L := LieHom.id
let g : M₁ →ₗ[R] M₂ := Submodule.inclusion h₁
have hfg : ∀ x m, ⁅f x, g m⁆ = g ⁅x, m⁆ := by aesop
exact (Submodule.inclusion_injective h₁).lieModuleIsNilpotent hfg
| /-- The max nilpotent submodule is the `sSup` of all nilpotent submodules. -/
def maxNilpotentSubmodule :=
sSup { N : LieSubmodule R L M | IsNilpotent L N }
instance instMaxNilpotentSubmoduleIsNilpotent [IsNoetherian R M] :
IsNilpotent L (maxNilpotentSubmodule R L M) := by
have hwf := CompleteLattice.WellFoundedGT.isSupClosedCompact (LieSubmodule R L M) inferInstance
| Mathlib/Algebra/Lie/Nilpotent.lean | 721 | 727 |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl
-/
import Mathlib.Order.Filter.Prod
import Mathlib.Order.ConditionallyCompleteLattice.Basic
import Mathlib.Order.Filter.Finite
import Mathlib.Order.Filter.Bases.Basic
/-!
# Lift filters along filter and set functions
-/
open Set Filter Function
namespace Filter
variable {α β γ : Type*} {ι : Sort*}
section lift
variable {f f₁ f₂ : Filter α} {g g₁ g₂ : Set α → Filter β}
@[simp]
theorem lift_top (g : Set α → Filter β) : (⊤ : Filter α).lift g = g univ := by simp [Filter.lift]
/-- If `(p : ι → Prop, s : ι → Set α)` is a basis of a filter `f`, `g` is a monotone function
`Set α → Filter γ`, and for each `i`, `(pg : β i → Prop, sg : β i → Set α)` is a basis
of the filter `g (s i)`, then
`(fun (i : ι) (x : β i) ↦ p i ∧ pg i x, fun (i : ι) (x : β i) ↦ sg i x)` is a basis
of the filter `f.lift g`.
This basis is parametrized by `i : ι` and `x : β i`, so in order to formulate this fact using
`Filter.HasBasis` one has to use `Σ i, β i` as the index type, see `Filter.HasBasis.lift`.
This lemma states the corresponding `mem_iff` statement without using a sigma type. -/
theorem HasBasis.mem_lift_iff {ι} {p : ι → Prop} {s : ι → Set α} {f : Filter α}
(hf : f.HasBasis p s) {β : ι → Type*} {pg : ∀ i, β i → Prop} {sg : ∀ i, β i → Set γ}
{g : Set α → Filter γ} (hg : ∀ i, (g <| s i).HasBasis (pg i) (sg i)) (gm : Monotone g)
{s : Set γ} : s ∈ f.lift g ↔ ∃ i, p i ∧ ∃ x, pg i x ∧ sg i x ⊆ s := by
refine (mem_biInf_of_directed ?_ ⟨univ, univ_sets _⟩).trans ?_
· intro t₁ ht₁ t₂ ht₂
exact ⟨t₁ ∩ t₂, inter_mem ht₁ ht₂, gm inter_subset_left, gm inter_subset_right⟩
· simp only [← (hg _).mem_iff]
exact hf.exists_iff fun t₁ t₂ ht H => gm ht H
/-- If `(p : ι → Prop, s : ι → Set α)` is a basis of a filter `f`, `g` is a monotone function
`Set α → Filter γ`, and for each `i`, `(pg : β i → Prop, sg : β i → Set α)` is a basis
of the filter `g (s i)`, then
`(fun (i : ι) (x : β i) ↦ p i ∧ pg i x, fun (i : ι) (x : β i) ↦ sg i x)`
is a basis of the filter `f.lift g`.
This basis is parametrized by `i : ι` and `x : β i`, so in order to formulate this fact using
`has_basis` one has to use `Σ i, β i` as the index type. See also `Filter.HasBasis.mem_lift_iff`
for the corresponding `mem_iff` statement formulated without using a sigma type. -/
theorem HasBasis.lift {ι} {p : ι → Prop} {s : ι → Set α} {f : Filter α} (hf : f.HasBasis p s)
{β : ι → Type*} {pg : ∀ i, β i → Prop} {sg : ∀ i, β i → Set γ} {g : Set α → Filter γ}
(hg : ∀ i, (g (s i)).HasBasis (pg i) (sg i)) (gm : Monotone g) :
(f.lift g).HasBasis (fun i : Σi, β i => p i.1 ∧ pg i.1 i.2) fun i : Σi, β i => sg i.1 i.2 := by
refine ⟨fun t => (hf.mem_lift_iff hg gm).trans ?_⟩
simp [Sigma.exists, and_assoc, exists_and_left]
theorem mem_lift_sets (hg : Monotone g) {s : Set β} : s ∈ f.lift g ↔ ∃ t ∈ f, s ∈ g t :=
(f.basis_sets.mem_lift_iff (fun s => (g s).basis_sets) hg).trans <| by
simp only [id, exists_mem_subset_iff]
theorem sInter_lift_sets (hg : Monotone g) :
⋂₀ { s | s ∈ f.lift g } = ⋂ s ∈ f, ⋂₀ { t | t ∈ g s } := by
simp only [sInter_eq_biInter, mem_setOf_eq, Filter.mem_sets, mem_lift_sets hg, iInter_exists,
iInter_and, @iInter_comm _ (Set β)]
theorem mem_lift {s : Set β} {t : Set α} (ht : t ∈ f) (hs : s ∈ g t) : s ∈ f.lift g :=
le_principal_iff.mp <|
show f.lift g ≤ 𝓟 s from iInf_le_of_le t <| iInf_le_of_le ht <| le_principal_iff.mpr hs
theorem lift_le {f : Filter α} {g : Set α → Filter β} {h : Filter β} {s : Set α} (hs : s ∈ f)
(hg : g s ≤ h) : f.lift g ≤ h :=
iInf₂_le_of_le s hs hg
theorem le_lift {f : Filter α} {g : Set α → Filter β} {h : Filter β} :
h ≤ f.lift g ↔ ∀ s ∈ f, h ≤ g s :=
le_iInf₂_iff
theorem lift_mono (hf : f₁ ≤ f₂) (hg : g₁ ≤ g₂) : f₁.lift g₁ ≤ f₂.lift g₂ :=
iInf_mono fun s => iInf_mono' fun hs => ⟨hf hs, hg s⟩
theorem lift_mono' (hg : ∀ s ∈ f, g₁ s ≤ g₂ s) : f.lift g₁ ≤ f.lift g₂ := iInf₂_mono hg
theorem tendsto_lift {m : γ → β} {l : Filter γ} :
Tendsto m l (f.lift g) ↔ ∀ s ∈ f, Tendsto m l (g s) := by
simp only [Filter.lift, tendsto_iInf]
theorem map_lift_eq {m : β → γ} (hg : Monotone g) : map m (f.lift g) = f.lift (map m ∘ g) :=
have : Monotone (map m ∘ g) := map_mono.comp hg
Filter.ext fun s => by
simp only [mem_lift_sets hg, mem_lift_sets this, exists_prop, mem_map, Function.comp_apply]
theorem comap_lift_eq {m : γ → β} : comap m (f.lift g) = f.lift (comap m ∘ g) := by
simp only [Filter.lift, comap_iInf]; rfl
theorem comap_lift_eq2 {m : β → α} {g : Set β → Filter γ} (hg : Monotone g) :
(comap m f).lift g = f.lift (g ∘ preimage m) :=
le_antisymm (le_iInf₂ fun s hs => iInf₂_le (m ⁻¹' s) ⟨s, hs, Subset.rfl⟩)
(le_iInf₂ fun _s ⟨s', hs', h_sub⟩ => iInf₂_le_of_le s' hs' <| hg h_sub)
theorem lift_map_le {g : Set β → Filter γ} {m : α → β} : (map m f).lift g ≤ f.lift (g ∘ image m) :=
le_lift.2 fun _s hs => lift_le (image_mem_map hs) le_rfl
theorem map_lift_eq2 {g : Set β → Filter γ} {m : α → β} (hg : Monotone g) :
(map m f).lift g = f.lift (g ∘ image m) :=
lift_map_le.antisymm <| le_lift.2 fun _s hs => lift_le hs <| hg <| image_preimage_subset _ _
theorem lift_comm {g : Filter β} {h : Set α → Set β → Filter γ} :
(f.lift fun s => g.lift (h s)) = g.lift fun t => f.lift fun s => h s t :=
le_antisymm
(le_iInf fun i => le_iInf fun hi => le_iInf fun j => le_iInf fun hj =>
iInf_le_of_le j <| iInf_le_of_le hj <| iInf_le_of_le i <| iInf_le _ hi)
(le_iInf fun i => le_iInf fun hi => le_iInf fun j => le_iInf fun hj =>
iInf_le_of_le j <| iInf_le_of_le hj <| iInf_le_of_le i <| iInf_le _ hi)
theorem lift_assoc {h : Set β → Filter γ} (hg : Monotone g) :
(f.lift g).lift h = f.lift fun s => (g s).lift h :=
le_antisymm
(le_iInf₂ fun _s hs => le_iInf₂ fun t ht =>
iInf_le_of_le t <| iInf_le _ <| (mem_lift_sets hg).mpr ⟨_, hs, ht⟩)
(le_iInf₂ fun t ht =>
let ⟨s, hs, h'⟩ := (mem_lift_sets hg).mp ht
iInf_le_of_le s <| iInf_le_of_le hs <| iInf_le_of_le t <| iInf_le _ h')
theorem lift_lift_same_le_lift {g : Set α → Set α → Filter β} :
(f.lift fun s => f.lift (g s)) ≤ f.lift fun s => g s s :=
le_lift.2 fun _s hs => lift_le hs <| lift_le hs le_rfl
theorem lift_lift_same_eq_lift {g : Set α → Set α → Filter β} (hg₁ : ∀ s, Monotone fun t => g s t)
(hg₂ : ∀ t, Monotone fun s => g s t) : (f.lift fun s => f.lift (g s)) = f.lift fun s => g s s :=
lift_lift_same_le_lift.antisymm <|
le_lift.2 fun s hs => le_lift.2 fun t ht => lift_le (inter_mem hs ht) <|
calc
g (s ∩ t) (s ∩ t) ≤ g s (s ∩ t) := hg₂ (s ∩ t) inter_subset_left
_ ≤ g s t := hg₁ s inter_subset_right
theorem lift_principal {s : Set α} (hg : Monotone g) : (𝓟 s).lift g = g s :=
(lift_le (mem_principal_self _) le_rfl).antisymm (le_lift.2 fun _t ht => hg ht)
theorem monotone_lift [Preorder γ] {f : γ → Filter α} {g : γ → Set α → Filter β} (hf : Monotone f)
(hg : Monotone g) : Monotone fun c => (f c).lift (g c) := fun _ _ h => lift_mono (hf h) (hg h)
theorem lift_neBot_iff (hm : Monotone g) : (NeBot (f.lift g)) ↔ ∀ s ∈ f, NeBot (g s) := by
simp only [neBot_iff, Ne, ← empty_mem_iff_bot, mem_lift_sets hm, not_exists, not_and]
@[simp]
theorem lift_const {f : Filter α} {g : Filter β} : (f.lift fun _ => g) = g :=
iInf_subtype'.trans iInf_const
@[simp]
theorem lift_inf {f : Filter α} {g h : Set α → Filter β} :
(f.lift fun x => g x ⊓ h x) = f.lift g ⊓ f.lift h := by simp only [Filter.lift, iInf_inf_eq]
@[simp]
theorem lift_principal2 {f : Filter α} : f.lift 𝓟 = f :=
le_antisymm (fun s hs => mem_lift hs (mem_principal_self s))
(le_iInf fun s => le_iInf fun hs => by simp only [hs, le_principal_iff])
theorem lift_iInf_le {f : ι → Filter α} {g : Set α → Filter β} :
(iInf f).lift g ≤ ⨅ i, (f i).lift g :=
le_iInf fun _ => lift_mono (iInf_le _ _) le_rfl
theorem lift_iInf [Nonempty ι] {f : ι → Filter α} {g : Set α → Filter β}
(hg : ∀ s t, g (s ∩ t) = g s ⊓ g t) : (iInf f).lift g = ⨅ i, (f i).lift g := by
refine lift_iInf_le.antisymm fun s => ?_
have H : ∀ t ∈ iInf f, ⨅ i, (f i).lift g ≤ g t := by
intro t ht
refine iInf_sets_induct ht ?_ fun hs ht => ?_
· inhabit ι
exact iInf₂_le_of_le default univ (iInf_le _ univ_mem)
· rw [hg]
exact le_inf (iInf₂_le_of_le _ _ <| iInf_le _ hs) ht
simp only [mem_lift_sets (Monotone.of_map_inf hg), exists_imp, and_imp]
exact fun t ht hs => H t ht hs
theorem lift_iInf_of_directed [Nonempty ι] {f : ι → Filter α} {g : Set α → Filter β}
(hf : Directed (· ≥ ·) f) (hg : Monotone g) : (iInf f).lift g = ⨅ i, (f i).lift g :=
lift_iInf_le.antisymm fun s => by
simp only [mem_lift_sets hg, exists_imp, and_imp, mem_iInf_of_directed hf]
exact fun t i ht hs => mem_iInf_of_mem i <| mem_lift ht hs
theorem lift_iInf_of_map_univ {f : ι → Filter α} {g : Set α → Filter β}
(hg : ∀ s t, g (s ∩ t) = g s ⊓ g t) (hg' : g univ = ⊤) :
(iInf f).lift g = ⨅ i, (f i).lift g := by
cases isEmpty_or_nonempty ι
· simp [iInf_of_empty, hg']
· exact lift_iInf hg
end lift
section Lift'
variable {f f₁ f₂ : Filter α} {h h₁ h₂ : Set α → Set β}
@[simp]
theorem lift'_top (h : Set α → Set β) : (⊤ : Filter α).lift' h = 𝓟 (h univ) :=
lift_top _
theorem mem_lift' {t : Set α} (ht : t ∈ f) : h t ∈ f.lift' h :=
le_principal_iff.mp <| show f.lift' h ≤ 𝓟 (h t) from iInf_le_of_le t <| iInf_le_of_le ht <| le_rfl
theorem tendsto_lift' {m : γ → β} {l : Filter γ} :
Tendsto m l (f.lift' h) ↔ ∀ s ∈ f, ∀ᶠ a in l, m a ∈ h s := by
simp only [Filter.lift', tendsto_lift, tendsto_principal, comp]
theorem HasBasis.lift' {ι} {p : ι → Prop} {s} (hf : f.HasBasis p s) (hh : Monotone h) :
(f.lift' h).HasBasis p (h ∘ s) :=
⟨fun t => (hf.mem_lift_iff (fun i => hasBasis_principal (h (s i)))
(monotone_principal.comp hh)).trans <| by simp only [exists_const, true_and, comp]⟩
theorem mem_lift'_sets (hh : Monotone h) {s : Set β} : s ∈ f.lift' h ↔ ∃ t ∈ f, h t ⊆ s :=
mem_lift_sets <| monotone_principal.comp hh
theorem eventually_lift'_iff (hh : Monotone h) {p : β → Prop} :
(∀ᶠ y in f.lift' h, p y) ↔ ∃ t ∈ f, ∀ y ∈ h t, p y :=
mem_lift'_sets hh
theorem sInter_lift'_sets (hh : Monotone h) : ⋂₀ { s | s ∈ f.lift' h } = ⋂ s ∈ f, h s :=
(sInter_lift_sets (monotone_principal.comp hh)).trans <| iInter₂_congr fun _ _ => csInf_Ici
theorem lift'_le {f : Filter α} {g : Set α → Set β} {h : Filter β} {s : Set α} (hs : s ∈ f)
(hg : 𝓟 (g s) ≤ h) : f.lift' g ≤ h :=
lift_le hs hg
theorem lift'_mono (hf : f₁ ≤ f₂) (hh : h₁ ≤ h₂) : f₁.lift' h₁ ≤ f₂.lift' h₂ :=
lift_mono hf fun s => principal_mono.mpr <| hh s
theorem lift'_mono' (hh : ∀ s ∈ f, h₁ s ⊆ h₂ s) : f.lift' h₁ ≤ f.lift' h₂ :=
iInf₂_mono fun s hs => principal_mono.mpr <| hh s hs
theorem lift'_cong (hh : ∀ s ∈ f, h₁ s = h₂ s) : f.lift' h₁ = f.lift' h₂ :=
le_antisymm (lift'_mono' fun s hs => le_of_eq <| hh s hs)
(lift'_mono' fun s hs => le_of_eq <| (hh s hs).symm)
theorem map_lift'_eq {m : β → γ} (hh : Monotone h) : map m (f.lift' h) = f.lift' (image m ∘ h) :=
calc
map m (f.lift' h) = f.lift (map m ∘ 𝓟 ∘ h) := map_lift_eq <| monotone_principal.comp hh
_ = f.lift' (image m ∘ h) := by simp only [comp_def, Filter.lift', map_principal]
theorem lift'_map_le {g : Set β → Set γ} {m : α → β} : (map m f).lift' g ≤ f.lift' (g ∘ image m) :=
lift_map_le
theorem map_lift'_eq2 {g : Set β → Set γ} {m : α → β} (hg : Monotone g) :
(map m f).lift' g = f.lift' (g ∘ image m) :=
map_lift_eq2 <| monotone_principal.comp hg
theorem comap_lift'_eq {m : γ → β} : comap m (f.lift' h) = f.lift' (preimage m ∘ h) := by
simp only [Filter.lift', comap_lift_eq, comp_def, comap_principal]
theorem comap_lift'_eq2 {m : β → α} {g : Set β → Set γ} (hg : Monotone g) :
(comap m f).lift' g = f.lift' (g ∘ preimage m) :=
comap_lift_eq2 <| monotone_principal.comp hg
theorem lift'_principal {s : Set α} (hh : Monotone h) : (𝓟 s).lift' h = 𝓟 (h s) :=
lift_principal <| monotone_principal.comp hh
theorem lift'_pure {a : α} (hh : Monotone h) : (pure a : Filter α).lift' h = 𝓟 (h {a}) := by
rw [← principal_singleton, lift'_principal hh]
theorem lift'_bot (hh : Monotone h) : (⊥ : Filter α).lift' h = 𝓟 (h ∅) := by
rw [← principal_empty, lift'_principal hh]
theorem le_lift' {f : Filter α} {h : Set α → Set β} {g : Filter β} :
g ≤ f.lift' h ↔ ∀ s ∈ f, h s ∈ g :=
le_lift.trans <| forall₂_congr fun _ _ => le_principal_iff
theorem principal_le_lift' {t : Set β} : 𝓟 t ≤ f.lift' h ↔ ∀ s ∈ f, t ⊆ h s :=
le_lift'
theorem monotone_lift' [Preorder γ] {f : γ → Filter α} {g : γ → Set α → Set β} (hf : Monotone f)
(hg : Monotone g) : Monotone fun c => (f c).lift' (g c) := fun _ _ h => lift'_mono (hf h) (hg h)
theorem lift_lift'_assoc {g : Set α → Set β} {h : Set β → Filter γ} (hg : Monotone g)
(hh : Monotone h) : (f.lift' g).lift h = f.lift fun s => h (g s) :=
calc
(f.lift' g).lift h = f.lift fun s => (𝓟 (g s)).lift h := lift_assoc (monotone_principal.comp hg)
_ = f.lift fun s => h (g s) := by simp only [lift_principal, hh, eq_self_iff_true]
theorem lift'_lift'_assoc {g : Set α → Set β} {h : Set β → Set γ} (hg : Monotone g)
(hh : Monotone h) : (f.lift' g).lift' h = f.lift' fun s => h (g s) :=
lift_lift'_assoc hg (monotone_principal.comp hh)
theorem lift'_lift_assoc {g : Set α → Filter β} {h : Set β → Set γ} (hg : Monotone g) :
(f.lift g).lift' h = f.lift fun s => (g s).lift' h :=
lift_assoc hg
theorem lift_lift'_same_le_lift' {g : Set α → Set α → Set β} :
(f.lift fun s => f.lift' (g s)) ≤ f.lift' fun s => g s s :=
lift_lift_same_le_lift
theorem lift_lift'_same_eq_lift' {g : Set α → Set α → Set β} (hg₁ : ∀ s, Monotone fun t => g s t)
(hg₂ : ∀ t, Monotone fun s => g s t) :
(f.lift fun s => f.lift' (g s)) = f.lift' fun s => g s s :=
lift_lift_same_eq_lift (fun s => monotone_principal.comp (hg₁ s)) fun t =>
monotone_principal.comp (hg₂ t)
theorem lift'_inf_principal_eq {h : Set α → Set β} {s : Set β} :
f.lift' h ⊓ 𝓟 s = f.lift' fun t => h t ∩ s := by
simp only [Filter.lift', Filter.lift, (· ∘ ·), ← inf_principal, iInf_subtype', ← iInf_inf]
theorem lift'_neBot_iff (hh : Monotone h) : NeBot (f.lift' h) ↔ ∀ s ∈ f, (h s).Nonempty :=
calc
NeBot (f.lift' h) ↔ ∀ s ∈ f, NeBot (𝓟 (h s)) := lift_neBot_iff (monotone_principal.comp hh)
_ ↔ ∀ s ∈ f, (h s).Nonempty := by simp only [principal_neBot_iff]
@[simp]
theorem lift'_id {f : Filter α} : f.lift' id = f :=
lift_principal2
theorem lift'_iInf [Nonempty ι] {f : ι → Filter α} {g : Set α → Set β}
(hg : ∀ s t, g (s ∩ t) = g s ∩ g t) : (iInf f).lift' g = ⨅ i, (f i).lift' g :=
lift_iInf fun s t => by simp only [inf_principal, comp, hg]
theorem lift'_iInf_of_map_univ {f : ι → Filter α} {g : Set α → Set β}
(hg : ∀ {s t}, g (s ∩ t) = g s ∩ g t) (hg' : g univ = univ) :
(iInf f).lift' g = ⨅ i, (f i).lift' g :=
lift_iInf_of_map_univ (fun s t => by simp only [inf_principal, comp, hg])
(by rw [Function.comp_apply, hg', principal_univ])
theorem lift'_inf (f g : Filter α) {s : Set α → Set β} (hs : ∀ t₁ t₂, s (t₁ ∩ t₂) = s t₁ ∩ s t₂) :
(f ⊓ g).lift' s = f.lift' s ⊓ g.lift' s := by
rw [inf_eq_iInf, inf_eq_iInf, lift'_iInf hs]
refine iInf_congr ?_
rintro (_|_) <;> rfl
theorem lift'_inf_le (f g : Filter α) (s : Set α → Set β) :
(f ⊓ g).lift' s ≤ f.lift' s ⊓ g.lift' s :=
le_inf (lift'_mono inf_le_left le_rfl) (lift'_mono inf_le_right le_rfl)
theorem comap_eq_lift' {f : Filter β} {m : α → β} : comap m f = f.lift' (preimage m) :=
Filter.ext fun _ => (mem_lift'_sets monotone_preimage).symm
end Lift'
section Prod
variable {f : Filter α}
theorem prod_def {f : Filter α} {g : Filter β} :
f ×ˢ g = f.lift fun s => g.lift' fun t => s ×ˢ t := by
simpa only [Filter.lift', Filter.lift, (f.basis_sets.prod g.basis_sets).eq_biInf,
iInf_prod, iInf_and] using iInf_congr fun i => iInf_comm
alias mem_prod_same_iff := mem_prod_self_iff
theorem prod_same_eq : f ×ˢ f = f.lift' fun t : Set α => t ×ˢ t :=
f.basis_sets.prod_self.eq_biInf
theorem tendsto_prod_self_iff {f : α × α → β} {x : Filter α} {y : Filter β} :
Filter.Tendsto f (x ×ˢ x) y ↔ ∀ W ∈ y, ∃ U ∈ x, ∀ x x' : α, x ∈ U → x' ∈ U → f (x, x') ∈ W := by
simp only [tendsto_def, mem_prod_same_iff, prod_sub_preimage_iff, exists_prop]
variable {α₁ : Type*} {α₂ : Type*} {β₁ : Type*} {β₂ : Type*}
theorem prod_lift_lift {f₁ : Filter α₁} {f₂ : Filter α₂} {g₁ : Set α₁ → Filter β₁}
{g₂ : Set α₂ → Filter β₂} (hg₁ : Monotone g₁) (hg₂ : Monotone g₂) :
f₁.lift g₁ ×ˢ f₂.lift g₂ = f₁.lift fun s => f₂.lift fun t => g₁ s ×ˢ g₂ t := by
simp only [prod_def, lift_assoc hg₁]
apply congr_arg; funext x
rw [lift_comm]
apply congr_arg; funext y
apply lift'_lift_assoc hg₂
theorem prod_lift'_lift' {f₁ : Filter α₁} {f₂ : Filter α₂} {g₁ : Set α₁ → Set β₁}
{g₂ : Set α₂ → Set β₂} (hg₁ : Monotone g₁) (hg₂ : Monotone g₂) :
f₁.lift' g₁ ×ˢ f₂.lift' g₂ = f₁.lift fun s => f₂.lift' fun t => g₁ s ×ˢ g₂ t :=
calc
f₁.lift' g₁ ×ˢ f₂.lift' g₂ = f₁.lift fun s => f₂.lift fun t => 𝓟 (g₁ s) ×ˢ 𝓟 (g₂ t) :=
prod_lift_lift (monotone_principal.comp hg₁) (monotone_principal.comp hg₂)
_ = f₁.lift fun s => f₂.lift fun t => 𝓟 (g₁ s ×ˢ g₂ t) := by
{ simp only [prod_principal_principal] }
|
end Prod
end Filter
| Mathlib/Order/Filter/Lift.lean | 377 | 380 |
/-
Copyright (c) 2020 Jean Lo. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jean Lo
-/
import Mathlib.Dynamics.Flow
import Mathlib.Tactic.Monotonicity
/-!
# ω-limits
For a function `ϕ : τ → α → β` where `β` is a topological space, we
define the ω-limit under `ϕ` of a set `s` in `α` with respect to
filter `f` on `τ`: an element `y : β` is in the ω-limit of `s` if the
forward images of `s` intersect arbitrarily small neighbourhoods of
`y` frequently "in the direction of `f`".
In practice `ϕ` is often a continuous monoid-act, but the definition
requires only that `ϕ` has a coercion to the appropriate function
type. In the case where `τ` is `ℕ` or `ℝ` and `f` is `atTop`, we
recover the usual definition of the ω-limit set as the set of all `y`
such that there exist sequences `(tₙ)`, `(xₙ)` such that `ϕ tₙ xₙ ⟶ y`
as `n ⟶ ∞`.
## Notations
The `omegaLimit` locale provides the localised notation `ω` for
`omegaLimit`, as well as `ω⁺` and `ω⁻` for `omegaLimit atTop` and
`omegaLimit atBot` respectively for when the acting monoid is
endowed with an order.
-/
open Set Function Filter Topology
/-!
### Definition and notation
-/
section omegaLimit
variable {τ : Type*} {α : Type*} {β : Type*} {ι : Type*}
/-- The ω-limit of a set `s` under `ϕ` with respect to a filter `f` is `⋂ u ∈ f, cl (ϕ u s)`. -/
def omegaLimit [TopologicalSpace β] (f : Filter τ) (ϕ : τ → α → β) (s : Set α) : Set β :=
⋂ u ∈ f, closure (image2 ϕ u s)
@[inherit_doc]
scoped[omegaLimit] notation "ω" => omegaLimit
/-- The ω-limit w.r.t. `Filter.atTop`. -/
scoped[omegaLimit] notation "ω⁺" => omegaLimit Filter.atTop
/-- The ω-limit w.r.t. `Filter.atBot`. -/
scoped[omegaLimit] notation "ω⁻" => omegaLimit Filter.atBot
variable [TopologicalSpace β]
variable (f : Filter τ) (ϕ : τ → α → β) (s s₁ s₂ : Set α)
/-!
### Elementary properties
-/
open omegaLimit
theorem omegaLimit_def : ω f ϕ s = ⋂ u ∈ f, closure (image2 ϕ u s) := rfl
theorem omegaLimit_subset_of_tendsto {m : τ → τ} {f₁ f₂ : Filter τ} (hf : Tendsto m f₁ f₂) :
ω f₁ (fun t x ↦ ϕ (m t) x) s ⊆ ω f₂ ϕ s := by
refine iInter₂_mono' fun u hu ↦ ⟨m ⁻¹' u, tendsto_def.mp hf _ hu, ?_⟩
rw [← image2_image_left]
exact closure_mono (image2_subset (image_preimage_subset _ _) Subset.rfl)
theorem omegaLimit_mono_left {f₁ f₂ : Filter τ} (hf : f₁ ≤ f₂) : ω f₁ ϕ s ⊆ ω f₂ ϕ s :=
omegaLimit_subset_of_tendsto ϕ s (tendsto_id'.2 hf)
theorem omegaLimit_mono_right {s₁ s₂ : Set α} (hs : s₁ ⊆ s₂) : ω f ϕ s₁ ⊆ ω f ϕ s₂ :=
iInter₂_mono fun _u _hu ↦ closure_mono (image2_subset Subset.rfl hs)
theorem isClosed_omegaLimit : IsClosed (ω f ϕ s) :=
isClosed_iInter fun _u ↦ isClosed_iInter fun _hu ↦ isClosed_closure
theorem mapsTo_omegaLimit' {α' β' : Type*} [TopologicalSpace β'] {f : Filter τ} {ϕ : τ → α → β}
{ϕ' : τ → α' → β'} {ga : α → α'} {s' : Set α'} (hs : MapsTo ga s s') {gb : β → β'}
(hg : ∀ᶠ t in f, EqOn (gb ∘ ϕ t) (ϕ' t ∘ ga) s) (hgc : Continuous gb) :
MapsTo gb (ω f ϕ s) (ω f ϕ' s') := by
simp only [omegaLimit_def, mem_iInter, MapsTo]
intro y hy u hu
refine map_mem_closure hgc (hy _ (inter_mem hu hg)) (forall_mem_image2.2 fun t ht x hx ↦ ?_)
calc
ϕ' t (ga x) ∈ image2 ϕ' u s' := mem_image2_of_mem ht.1 (hs hx)
_ = gb (ϕ t x) := ht.2 hx |>.symm
theorem mapsTo_omegaLimit {α' β' : Type*} [TopologicalSpace β'] {f : Filter τ} {ϕ : τ → α → β}
{ϕ' : τ → α' → β'} {ga : α → α'} {s' : Set α'} (hs : MapsTo ga s s') {gb : β → β'}
(hg : ∀ t x, gb (ϕ t x) = ϕ' t (ga x)) (hgc : Continuous gb) :
MapsTo gb (ω f ϕ s) (ω f ϕ' s') :=
mapsTo_omegaLimit' _ hs (Eventually.of_forall fun t x _hx ↦ hg t x) hgc
theorem omegaLimit_image_eq {α' : Type*} (ϕ : τ → α' → β) (f : Filter τ) (g : α → α') :
ω f ϕ (g '' s) = ω f (fun t x ↦ ϕ t (g x)) s := by simp only [omegaLimit, image2_image_right]
theorem omegaLimit_preimage_subset {α' : Type*} (ϕ : τ → α' → β) (s : Set α') (f : Filter τ)
(g : α → α') : ω f (fun t x ↦ ϕ t (g x)) (g ⁻¹' s) ⊆ ω f ϕ s :=
mapsTo_omegaLimit _ (mapsTo_preimage _ _) (fun _t _x ↦ rfl) continuous_id
/-!
### Equivalent definitions of the omega limit
The next few lemmas are various versions of the property
characterising ω-limits:
-/
/-- An element `y` is in the ω-limit set of `s` w.r.t. `f` if the
preimages of an arbitrary neighbourhood of `y` frequently
(w.r.t. `f`) intersects of `s`. -/
theorem mem_omegaLimit_iff_frequently (y : β) :
y ∈ ω f ϕ s ↔ ∀ n ∈ 𝓝 y, ∃ᶠ t in f, (s ∩ ϕ t ⁻¹' n).Nonempty := by
simp_rw [frequently_iff, omegaLimit_def, mem_iInter, mem_closure_iff_nhds]
constructor
· intro h _ hn _ hu
rcases h _ hu _ hn with ⟨_, _, _, ht, _, hx, rfl⟩
exact ⟨_, ht, _, hx, by rwa [mem_preimage]⟩
· intro h _ hu _ hn
rcases h _ hn hu with ⟨_, ht, _, hx, hϕtx⟩
exact ⟨_, hϕtx, _, ht, _, hx, rfl⟩
/-- An element `y` is in the ω-limit set of `s` w.r.t. `f` if the
forward images of `s` frequently (w.r.t. `f`) intersect arbitrary
neighbourhoods of `y`. -/
theorem mem_omegaLimit_iff_frequently₂ (y : β) :
y ∈ ω f ϕ s ↔ ∀ n ∈ 𝓝 y, ∃ᶠ t in f, (ϕ t '' s ∩ n).Nonempty := by
simp_rw [mem_omegaLimit_iff_frequently, image_inter_nonempty_iff]
/-- An element `y` is in the ω-limit of `x` w.r.t. `f` if the forward
images of `x` frequently (w.r.t. `f`) falls within an arbitrary
neighbourhood of `y`. -/
theorem mem_omegaLimit_singleton_iff_map_cluster_point (x : α) (y : β) :
y ∈ ω f ϕ {x} ↔ MapClusterPt y f fun t ↦ ϕ t x := by
simp_rw [mem_omegaLimit_iff_frequently, mapClusterPt_iff_frequently, singleton_inter_nonempty,
mem_preimage]
/-!
| ### Set operations and omega limits
-/
| Mathlib/Dynamics/OmegaLimit.lean | 142 | 144 |
/-
Copyright (c) 2022 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies
-/
import Mathlib.Analysis.Convex.Hull
/-!
# Convex join
This file defines the convex join of two sets. The convex join of `s` and `t` is the union of the
segments with one end in `s` and the other in `t`. This is notably a useful gadget to deal with
convex hulls of finite sets.
-/
open Set
variable {ι : Sort*} {𝕜 E : Type*}
section OrderedSemiring
variable (𝕜) [Semiring 𝕜] [PartialOrder 𝕜] [AddCommMonoid E] [Module 𝕜 E]
{s t s₁ s₂ t₁ t₂ u : Set E}
{x y : E}
/-- The join of two sets is the union of the segments joining them. This can be interpreted as the
topological join, but within the original space. -/
def convexJoin (s t : Set E) : Set E :=
⋃ (x ∈ s) (y ∈ t), segment 𝕜 x y
variable {𝕜}
theorem mem_convexJoin : x ∈ convexJoin 𝕜 s t ↔ ∃ a ∈ s, ∃ b ∈ t, x ∈ segment 𝕜 a b := by
simp [convexJoin]
theorem convexJoin_comm (s t : Set E) : convexJoin 𝕜 s t = convexJoin 𝕜 t s :=
(iUnion₂_comm _).trans <| by simp_rw [convexJoin, segment_symm]
theorem convexJoin_mono (hs : s₁ ⊆ s₂) (ht : t₁ ⊆ t₂) : convexJoin 𝕜 s₁ t₁ ⊆ convexJoin 𝕜 s₂ t₂ :=
biUnion_mono hs fun _ _ => biUnion_subset_biUnion_left ht
theorem convexJoin_mono_left (hs : s₁ ⊆ s₂) : convexJoin 𝕜 s₁ t ⊆ convexJoin 𝕜 s₂ t :=
convexJoin_mono hs Subset.rfl
theorem convexJoin_mono_right (ht : t₁ ⊆ t₂) : convexJoin 𝕜 s t₁ ⊆ convexJoin 𝕜 s t₂ :=
convexJoin_mono Subset.rfl ht
@[simp]
theorem convexJoin_empty_left (t : Set E) : convexJoin 𝕜 ∅ t = ∅ := by simp [convexJoin]
@[simp]
theorem convexJoin_empty_right (s : Set E) : convexJoin 𝕜 s ∅ = ∅ := by simp [convexJoin]
@[simp]
theorem convexJoin_singleton_left (t : Set E) (x : E) :
convexJoin 𝕜 {x} t = ⋃ y ∈ t, segment 𝕜 x y := by simp [convexJoin]
@[simp]
theorem convexJoin_singleton_right (s : Set E) (y : E) :
convexJoin 𝕜 s {y} = ⋃ x ∈ s, segment 𝕜 x y := by simp [convexJoin]
theorem convexJoin_singletons (x : E) : convexJoin 𝕜 {x} {y} = segment 𝕜 x y := by simp
@[simp]
theorem convexJoin_union_left (s₁ s₂ t : Set E) :
convexJoin 𝕜 (s₁ ∪ s₂) t = convexJoin 𝕜 s₁ t ∪ convexJoin 𝕜 s₂ t := by
simp_rw [convexJoin, mem_union, iUnion_or, iUnion_union_distrib]
@[simp]
theorem convexJoin_union_right (s t₁ t₂ : Set E) :
convexJoin 𝕜 s (t₁ ∪ t₂) = convexJoin 𝕜 s t₁ ∪ convexJoin 𝕜 s t₂ := by
simp_rw [convexJoin_comm s, convexJoin_union_left]
@[simp]
theorem convexJoin_iUnion_left (s : ι → Set E) (t : Set E) :
convexJoin 𝕜 (⋃ i, s i) t = ⋃ i, convexJoin 𝕜 (s i) t := by
simp_rw [convexJoin, mem_iUnion, iUnion_exists]
| exact iUnion_comm _
@[simp]
| Mathlib/Analysis/Convex/Join.lean | 79 | 81 |
/-
Copyright (c) 2021 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.MeasureTheory.Covering.Differentiation
/-!
# Besicovitch covering theorems
The topological Besicovitch covering theorem ensures that, in a nice metric space, there exists a
number `N` such that, from any family of balls with bounded radii, one can extract `N` families,
each made of disjoint balls, covering together all the centers of the initial family.
By "nice metric space", we mean a technical property stated as follows: there exists no satellite
configuration of `N + 1` points (with a given parameter `τ > 1`). Such a configuration is a family
of `N + 1` balls, where the first `N` balls all intersect the last one, but none of them contains
the center of another one and their radii are controlled. This property is for instance
satisfied by finite-dimensional real vector spaces.
In this file, we prove the topological Besicovitch covering theorem,
in `Besicovitch.exist_disjoint_covering_families`.
The measurable Besicovitch theorem ensures that, in the same class of metric spaces, if at every
point one considers a class of balls of arbitrarily small radii, called admissible balls, then
one can cover almost all the space by a family of disjoint admissible balls.
It is deduced from the topological Besicovitch theorem, and proved
in `Besicovitch.exists_disjoint_closedBall_covering_ae`.
This implies that balls of small radius form a Vitali family in such spaces. Therefore, theorems
on differentiation of measures hold as a consequence of general results. We restate them in this
context to make them more easily usable.
## Main definitions and results
* `SatelliteConfig α N τ` is the type of all satellite configurations of `N + 1` points
in the metric space `α`, with parameter `τ`.
* `HasBesicovitchCovering` is a class recording that there exist `N` and `τ > 1` such that
there is no satellite configuration of `N + 1` points with parameter `τ`.
* `exist_disjoint_covering_families` is the topological Besicovitch covering theorem: from any
family of balls one can extract finitely many disjoint subfamilies covering the same set.
* `exists_disjoint_closedBall_covering` is the measurable Besicovitch covering theorem: from any
family of balls with arbitrarily small radii at every point, one can extract countably many
disjoint balls covering almost all the space. While the value of `N` is relevant for the precise
statement of the topological Besicovitch theorem, it becomes irrelevant for the measurable one.
Therefore, this statement is expressed using the `Prop`-valued
typeclass `HasBesicovitchCovering`.
We also restate the following specialized versions of general theorems on differentiation of
measures:
* `Besicovitch.ae_tendsto_rnDeriv` ensures that `ρ (closedBall x r) / μ (closedBall x r)` tends
almost surely to the Radon-Nikodym derivative of `ρ` with respect to `μ` at `x`.
* `Besicovitch.ae_tendsto_measure_inter_div` states that almost every point in an arbitrary set `s`
is a Lebesgue density point, i.e., `μ (s ∩ closedBall x r) / μ (closedBall x r)` tends to `1` as
`r` tends to `0`. A stronger version for measurable sets is given in
`Besicovitch.ae_tendsto_measure_inter_div_of_measurableSet`.
## Implementation
#### Sketch of proof of the topological Besicovitch theorem:
We choose balls in a greedy way. First choose a ball with maximal radius (or rather, since there
is no guarantee the maximal radius is realized, a ball with radius within a factor `τ` of the
supremum). Then, remove all balls whose center is covered by the first ball, and choose among the
remaining ones a ball with radius close to maximum. Go on forever until there is no available
center (this is a transfinite induction in general).
Then define inductively a coloring of the balls. A ball will be of color `i` if it intersects
already chosen balls of color `0`, ..., `i - 1`, but none of color `i`. In this way, balls of the
same color form a disjoint family, and the space is covered by the families of the different colors.
The nontrivial part is to show that at most `N` colors are used. If one needs `N + 1` colors,
consider the first time this happens. Then the corresponding ball intersects `N` balls of the
different colors. Moreover, the inductive construction ensures that the radii of all the balls are
controlled: they form a satellite configuration with `N + 1` balls (essentially by definition of
satellite configurations). Since we assume that there are no such configurations, this is a
contradiction.
#### Sketch of proof of the measurable Besicovitch theorem:
From the topological Besicovitch theorem, one can find a disjoint countable family of balls
covering a proportion `> 1 / (N + 1)` of the space. Taking a large enough finite subset of these
balls, one gets the same property for finitely many balls. Their union is closed. Therefore, any
point in the complement has around it an admissible ball not intersecting these finitely many balls.
Applying again the topological Besicovitch theorem, one extracts from these a disjoint countable
subfamily covering a proportion `> 1 / (N + 1)` of the remaining points, and then even a disjoint
finite subfamily. Then one goes on again and again, covering at each step a positive proportion of
the remaining points, while remaining disjoint from the already chosen balls. The union of all these
balls is the desired almost everywhere covering.
-/
noncomputable section
universe u
open Metric Set Filter Fin MeasureTheory TopologicalSpace
open scoped Topology ENNReal MeasureTheory NNReal
/-!
### Satellite configurations
-/
/-- A satellite configuration is a configuration of `N+1` points that shows up in the inductive
construction for the Besicovitch covering theorem. It depends on some parameter `τ ≥ 1`.
This is a family of balls (indexed by `i : Fin N.succ`, with center `c i` and radius `r i`) such
that the last ball intersects all the other balls (condition `inter`),
and given any two balls there is an order between them, ensuring that the first ball does not
contain the center of the other one, and the radius of the second ball can not be larger than
the radius of the first ball (up to a factor `τ`). This order corresponds to the order of choice
in the inductive construction: otherwise, the second ball would have been chosen before.
This is the condition `h`.
Finally, the last ball is chosen after all the other ones, meaning that `h` can be strengthened
by keeping only one side of the alternative in `hlast`.
-/
structure Besicovitch.SatelliteConfig (α : Type*) [MetricSpace α] (N : ℕ) (τ : ℝ) where
/-- Centers of the balls -/
c : Fin N.succ → α
/-- Radii of the balls -/
r : Fin N.succ → ℝ
rpos : ∀ i, 0 < r i
h : Pairwise fun i j =>
r i ≤ dist (c i) (c j) ∧ r j ≤ τ * r i ∨ r j ≤ dist (c j) (c i) ∧ r i ≤ τ * r j
hlast : ∀ i < last N, r i ≤ dist (c i) (c (last N)) ∧ r (last N) ≤ τ * r i
inter : ∀ i < last N, dist (c i) (c (last N)) ≤ r i + r (last N)
namespace Mathlib.Meta.Positivity
open Lean Meta Qq
/-- Extension for the `positivity` tactic: `Besicovitch.SatelliteConfig.r`. -/
@[positivity Besicovitch.SatelliteConfig.r _ _]
def evalBesicovitchSatelliteConfigR : PositivityExt where eval {u α} _zα _pα e := do
match u, α, e with
| 0, ~q(ℝ), ~q(@Besicovitch.SatelliteConfig.r $β $inst $N $τ $self $i) =>
assertInstancesCommute
return .positive q(Besicovitch.SatelliteConfig.rpos $self $i)
| _, _, _ => throwError "not Besicovitch.SatelliteConfig.r"
end Mathlib.Meta.Positivity
/-- A metric space has the Besicovitch covering property if there exist `N` and `τ > 1` such that
there are no satellite configuration of parameter `τ` with `N+1` points. This is the condition that
guarantees that the measurable Besicovitch covering theorem holds. It is satisfied by
finite-dimensional real vector spaces. -/
class HasBesicovitchCovering (α : Type*) [MetricSpace α] : Prop where
no_satelliteConfig : ∃ (N : ℕ) (τ : ℝ), 1 < τ ∧ IsEmpty (Besicovitch.SatelliteConfig α N τ)
/-- There is always a satellite configuration with a single point. -/
instance Besicovitch.SatelliteConfig.instInhabited {α : Type*} {τ : ℝ}
[Inhabited α] [MetricSpace α] : Inhabited (Besicovitch.SatelliteConfig α 0 τ) :=
⟨{ c := default
r := fun _ => 1
rpos := fun _ => zero_lt_one
h := fun i j hij => (hij (Subsingleton.elim (α := Fin 1) i j)).elim
hlast := fun i hi => by
rw [Subsingleton.elim (α := Fin 1) i (last 0)] at hi; exact (lt_irrefl _ hi).elim
inter := fun i hi => by
rw [Subsingleton.elim (α := Fin 1) i (last 0)] at hi; exact (lt_irrefl _ hi).elim }⟩
namespace Besicovitch
namespace SatelliteConfig
variable {α : Type*} [MetricSpace α] {N : ℕ} {τ : ℝ} (a : SatelliteConfig α N τ)
theorem inter' (i : Fin N.succ) : dist (a.c i) (a.c (last N)) ≤ a.r i + a.r (last N) := by
rcases lt_or_le i (last N) with (H | H)
· exact a.inter i H
· have I : i = last N := top_le_iff.1 H
have := (a.rpos (last N)).le
simp only [I, add_nonneg this this, dist_self]
theorem hlast' (i : Fin N.succ) (h : 1 ≤ τ) : a.r (last N) ≤ τ * a.r i := by
rcases lt_or_le i (last N) with (H | H)
· exact (a.hlast i H).2
· have : i = last N := top_le_iff.1 H
rw [this]
exact le_mul_of_one_le_left (a.rpos _).le h
end SatelliteConfig
/-! ### Extracting disjoint subfamilies from a ball covering -/
/-- A ball package is a family of balls in a metric space with positive bounded radii. -/
structure BallPackage (β : Type*) (α : Type*) where
/-- Centers of the balls -/
c : β → α
/-- Radii of the balls -/
r : β → ℝ
rpos : ∀ b, 0 < r b
/-- Bound on the radii of the balls -/
r_bound : ℝ
r_le : ∀ b, r b ≤ r_bound
/-- The ball package made of unit balls. -/
def unitBallPackage (α : Type*) : BallPackage α α where
c := id
r _ := 1
rpos _ := zero_lt_one
r_bound := 1
r_le _ := le_rfl
instance BallPackage.instInhabited (α : Type*) : Inhabited (BallPackage α α) :=
⟨unitBallPackage α⟩
/-- A Besicovitch tau-package is a family of balls in a metric space with positive bounded radii,
together with enough data to proceed with the Besicovitch greedy algorithm. We register this in
a single structure to make sure that all our constructions in this algorithm only depend on
one variable. -/
structure TauPackage (β : Type*) (α : Type*) extends BallPackage β α where
/-- Parameter used by the Besicovitch greedy algorithm -/
τ : ℝ
one_lt_tau : 1 < τ
instance TauPackage.instInhabited (α : Type*) : Inhabited (TauPackage α α) :=
⟨{ unitBallPackage α with
τ := 2
one_lt_tau := one_lt_two }⟩
variable {α : Type*} [MetricSpace α] {β : Type u}
namespace TauPackage
variable [Nonempty β] (p : TauPackage β α)
/-- Choose inductively large balls with centers that are not contained in the union of already
chosen balls. This is a transfinite induction. -/
noncomputable def index : Ordinal.{u} → β
| i =>
-- `Z` is the set of points that are covered by already constructed balls
let Z := ⋃ j : { j // j < i }, ball (p.c (index j)) (p.r (index j))
-- `R` is the supremum of the radii of balls with centers not in `Z`
let R := iSup fun b : { b : β // p.c b ∉ Z } => p.r b
-- return an index `b` for which the center `c b` is not in `Z`, and the radius is at
-- least `R / τ`, if such an index exists (and garbage otherwise).
Classical.epsilon fun b : β => p.c b ∉ Z ∧ R ≤ p.τ * p.r b
termination_by i => i
decreasing_by exact j.2
/-- The set of points that are covered by the union of balls selected at steps `< i`. -/
def iUnionUpTo (i : Ordinal.{u}) : Set α :=
⋃ j : { j // j < i }, ball (p.c (p.index j)) (p.r (p.index j))
theorem monotone_iUnionUpTo : Monotone p.iUnionUpTo := by
intro i j hij
simp only [iUnionUpTo]
exact iUnion_mono' fun r => ⟨⟨r, r.2.trans_le hij⟩, Subset.rfl⟩
/-- Supremum of the radii of balls whose centers are not yet covered at step `i`. -/
def R (i : Ordinal.{u}) : ℝ :=
iSup fun b : { b : β // p.c b ∉ p.iUnionUpTo i } => p.r b
/-- Group the balls into disjoint families, by assigning to a ball the smallest color for which
it does not intersect any already chosen ball of this color. -/
noncomputable def color : Ordinal.{u} → ℕ
| i =>
let A : Set ℕ :=
⋃ (j : { j // j < i })
(_ : (closedBall (p.c (p.index j)) (p.r (p.index j)) ∩
closedBall (p.c (p.index i)) (p.r (p.index i))).Nonempty), {color j}
sInf (univ \ A)
termination_by i => i
decreasing_by exact j.2
/-- `p.lastStep` is the first ordinal where the construction stops making sense, i.e., `f` returns
garbage since there is no point left to be chosen. We will only use ordinals before this step. -/
def lastStep : Ordinal.{u} :=
sInf {i | ¬∃ b : β, p.c b ∉ p.iUnionUpTo i ∧ p.R i ≤ p.τ * p.r b}
theorem lastStep_nonempty :
{i | ¬∃ b : β, p.c b ∉ p.iUnionUpTo i ∧ p.R i ≤ p.τ * p.r b}.Nonempty := by
by_contra h
suffices H : Function.Injective p.index from not_injective_of_ordinal p.index H
intro x y hxy
wlog x_le_y : x ≤ y generalizing x y
· exact (this hxy.symm (le_of_not_le x_le_y)).symm
rcases eq_or_lt_of_le x_le_y with (rfl | H); · rfl
simp only [nonempty_def, not_exists, exists_prop, not_and, not_lt, not_le, mem_setOf_eq,
not_forall] at h
specialize h y
have A : p.c (p.index y) ∉ p.iUnionUpTo y := by
have :
p.index y =
Classical.epsilon fun b : β => p.c b ∉ p.iUnionUpTo y ∧ p.R y ≤ p.τ * p.r b := by
rw [TauPackage.index]; rfl
rw [this]
exact (Classical.epsilon_spec h).1
simp only [iUnionUpTo, not_exists, exists_prop, mem_iUnion, mem_closedBall, not_and, not_le,
Subtype.exists, Subtype.coe_mk] at A
specialize A x H
simp? [hxy] at A says simp only [hxy, mem_ball, dist_self, not_lt] at A
exact (lt_irrefl _ ((p.rpos (p.index y)).trans_le A)).elim
/-- Every point is covered by chosen balls, before `p.lastStep`. -/
theorem mem_iUnionUpTo_lastStep (x : β) : p.c x ∈ p.iUnionUpTo p.lastStep := by
have A : ∀ z : β, p.c z ∈ p.iUnionUpTo p.lastStep ∨ p.τ * p.r z < p.R p.lastStep := by
have : p.lastStep ∈ {i | ¬∃ b : β, p.c b ∉ p.iUnionUpTo i ∧ p.R i ≤ p.τ * p.r b} :=
csInf_mem p.lastStep_nonempty
simpa only [not_exists, mem_setOf_eq, not_and_or, not_le, not_not_mem]
by_contra h
rcases A x with (H | H); · exact h H
have Rpos : 0 < p.R p.lastStep := by
apply lt_trans (mul_pos (_root_.zero_lt_one.trans p.one_lt_tau) (p.rpos _)) H
have B : p.τ⁻¹ * p.R p.lastStep < p.R p.lastStep := by
conv_rhs => rw [← one_mul (p.R p.lastStep)]
exact mul_lt_mul (inv_lt_one_of_one_lt₀ p.one_lt_tau) le_rfl Rpos zero_le_one
obtain ⟨y, hy1, hy2⟩ : ∃ y, p.c y ∉ p.iUnionUpTo p.lastStep ∧ p.τ⁻¹ * p.R p.lastStep < p.r y := by
have := exists_lt_of_lt_csSup ?_ B
· simpa only [exists_prop, mem_range, exists_exists_and_eq_and, Subtype.exists,
Subtype.coe_mk]
rw [← image_univ, image_nonempty]
exact ⟨⟨_, h⟩, mem_univ _⟩
rcases A y with (Hy | Hy)
· exact hy1 Hy
· rw [← div_eq_inv_mul] at hy2
have := (div_le_iff₀' (_root_.zero_lt_one.trans p.one_lt_tau)).1 hy2.le
exact lt_irrefl _ (Hy.trans_le this)
/-- If there are no configurations of satellites with `N+1` points, one never uses more than `N`
distinct families in the Besicovitch inductive construction. -/
theorem color_lt {i : Ordinal.{u}} (hi : i < p.lastStep) {N : ℕ}
(hN : IsEmpty (SatelliteConfig α N p.τ)) : p.color i < N := by
/- By contradiction, consider the first ordinal `i` for which one would have `p.color i = N`.
Choose for each `k < N` a ball with color `k` that intersects the ball at color `i`
(there is such a ball, otherwise one would have used the color `k` and not `N`).
Then this family of `N+1` balls forms a satellite configuration, which is forbidden by
the assumption `hN`. -/
induction' i using Ordinal.induction with i IH
| let A : Set ℕ :=
⋃ (j : { j // j < i })
(_ : (closedBall (p.c (p.index j)) (p.r (p.index j)) ∩
closedBall (p.c (p.index i)) (p.r (p.index i))).Nonempty),
{p.color j}
have color_i : p.color i = sInf (univ \ A) := by rw [color]
rw [color_i]
have N_mem : N ∈ univ \ A := by
simp only [A, not_exists, true_and, exists_prop, mem_iUnion, mem_singleton_iff,
mem_closedBall, not_and, mem_univ, mem_diff, Subtype.exists, Subtype.coe_mk]
intro j ji _
exact (IH j ji (ji.trans hi)).ne'
suffices sInf (univ \ A) ≠ N by
rcases (csInf_le (OrderBot.bddBelow (univ \ A)) N_mem).lt_or_eq with (H | H)
· exact H
· exact (this H).elim
intro Inf_eq_N
have :
∀ k, k < N → ∃ j, j < i ∧
(closedBall (p.c (p.index j)) (p.r (p.index j)) ∩
closedBall (p.c (p.index i)) (p.r (p.index i))).Nonempty ∧ k = p.color j := by
intro k hk
rw [← Inf_eq_N] at hk
| Mathlib/MeasureTheory/Covering/Besicovitch.lean | 335 | 357 |
/-
Copyright (c) 2020 Bhavik Mehta. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Bhavik Mehta
-/
import Mathlib.CategoryTheory.Adjunction.FullyFaithful
import Mathlib.CategoryTheory.Functor.EpiMono
import Mathlib.CategoryTheory.HomCongr
/-!
# Reflective functors
Basic properties of reflective functors, especially those relating to their essential image.
Note properties of reflective functors relating to limits and colimits are included in
`Mathlib.CategoryTheory.Monad.Limits`.
-/
universe v₁ v₂ v₃ u₁ u₂ u₃
noncomputable section
namespace CategoryTheory
open Category Adjunction
variable {C : Type u₁} {D : Type u₂} {E : Type u₃}
variable [Category.{v₁} C] [Category.{v₂} D] [Category.{v₃} E]
/--
A functor is *reflective*, or *a reflective inclusion*, if it is fully faithful and right adjoint.
-/
class Reflective (R : D ⥤ C) extends R.Full, R.Faithful where
/-- a choice of a left adjoint to `R` -/
L : C ⥤ D
/-- `R` is a right adjoint -/
adj : L ⊣ R
variable (i : D ⥤ C)
/-- The reflector `C ⥤ D` when `R : D ⥤ C` is reflective. -/
def reflector [Reflective i] : C ⥤ D := Reflective.L (R := i)
/-- The adjunction `reflector i ⊣ i` when `i` is reflective. -/
def reflectorAdjunction [Reflective i] : reflector i ⊣ i := Reflective.adj
instance [Reflective i] : i.IsRightAdjoint := ⟨_, ⟨reflectorAdjunction i⟩⟩
instance [Reflective i] : (reflector i).IsLeftAdjoint := ⟨_, ⟨reflectorAdjunction i⟩⟩
/-- A reflective functor is fully faithful. -/
def Functor.fullyFaithfulOfReflective [Reflective i] : i.FullyFaithful :=
(reflectorAdjunction i).fullyFaithfulROfIsIsoCounit
-- TODO: This holds more generally for idempotent adjunctions, not just reflective adjunctions.
/-- For a reflective functor `i` (with left adjoint `L`), with unit `η`, we have `η_iL = iL η`.
-/
theorem unit_obj_eq_map_unit [Reflective i] (X : C) :
(reflectorAdjunction i).unit.app (i.obj ((reflector i).obj X)) =
i.map ((reflector i).map ((reflectorAdjunction i).unit.app X)) := by
rw [← cancel_mono (i.map ((reflectorAdjunction i).counit.app ((reflector i).obj X))),
← i.map_comp]
simp
/--
When restricted to objects in `D` given by `i : D ⥤ C`, the unit is an isomorphism. In other words,
`η_iX` is an isomorphism for any `X` in `D`.
More generally this applies to objects essentially in the reflective subcategory, see
`Functor.essImage.unit_isIso`.
-/
example [Reflective i] {B : D} : IsIso ((reflectorAdjunction i).unit.app (i.obj B)) :=
inferInstance
variable {i}
/-- If `A` is essentially in the image of a reflective functor `i`, then `η_A` is an isomorphism.
This gives that the "witness" for `A` being in the essential image can instead be given as the
reflection of `A`, with the isomorphism as `η_A`.
(For any `B` in the reflective subcategory, we automatically have that `ε_B` is an iso.)
-/
theorem Functor.essImage.unit_isIso [Reflective i] {A : C} (h : i.essImage A) :
IsIso ((reflectorAdjunction i).unit.app A) := by
rwa [isIso_unit_app_iff_mem_essImage]
| /-- If `η_A` is a split monomorphism, then `A` is in the reflective subcategory. -/
theorem mem_essImage_of_unit_isSplitMono [Reflective i] {A : C}
[IsSplitMono ((reflectorAdjunction i).unit.app A)] : i.essImage A := by
| Mathlib/CategoryTheory/Adjunction/Reflective.lean | 87 | 89 |
/-
Copyright (c) 2020 Frédéric Dupuis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Frédéric Dupuis, Eric Wieser
-/
import Mathlib.LinearAlgebra.Multilinear.TensorProduct
import Mathlib.Tactic.AdaptationNote
import Mathlib.LinearAlgebra.Multilinear.Curry
/-!
# Tensor product of an indexed family of modules over commutative semirings
We define the tensor product of an indexed family `s : ι → Type*` of modules over commutative
semirings. We denote this space by `⨂[R] i, s i` and define it as `FreeAddMonoid (R × Π i, s i)`
quotiented by the appropriate equivalence relation. The treatment follows very closely that of the
binary tensor product in `LinearAlgebra/TensorProduct.lean`.
## Main definitions
* `PiTensorProduct R s` with `R` a commutative semiring and `s : ι → Type*` is the tensor product
of all the `s i`'s. This is denoted by `⨂[R] i, s i`.
* `tprod R f` with `f : Π i, s i` is the tensor product of the vectors `f i` over all `i : ι`.
This is bundled as a multilinear map from `Π i, s i` to `⨂[R] i, s i`.
* `liftAddHom` constructs an `AddMonoidHom` from `(⨂[R] i, s i)` to some space `F` from a
function `φ : (R × Π i, s i) → F` with the appropriate properties.
* `lift φ` with `φ : MultilinearMap R s E` is the corresponding linear map
`(⨂[R] i, s i) →ₗ[R] E`. This is bundled as a linear equivalence.
* `PiTensorProduct.reindex e` re-indexes the components of `⨂[R] i : ι, M` along `e : ι ≃ ι₂`.
* `PiTensorProduct.tmulEquiv` equivalence between a `TensorProduct` of `PiTensorProduct`s and
a single `PiTensorProduct`.
## Notations
* `⨂[R] i, s i` is defined as localized notation in locale `TensorProduct`.
* `⨂ₜ[R] i, f i` with `f : ∀ i, s i` is defined globally as the tensor product of all the `f i`'s.
## Implementation notes
* We define it via `FreeAddMonoid (R × Π i, s i)` with the `R` representing a "hidden" tensor
factor, rather than `FreeAddMonoid (Π i, s i)` to ensure that, if `ι` is an empty type,
the space is isomorphic to the base ring `R`.
* We have not restricted the index type `ι` to be a `Fintype`, as nothing we do here strictly
requires it. However, problems may arise in the case where `ι` is infinite; use at your own
caution.
* Instead of requiring `DecidableEq ι` as an argument to `PiTensorProduct` itself, we include it
as an argument in the constructors of the relation. A decidability instance still has to come
from somewhere due to the use of `Function.update`, but this hides it from the downstream user.
See the implementation notes for `MultilinearMap` for an extended discussion of this choice.
## TODO
* Define tensor powers, symmetric subspace, etc.
* API for the various ways `ι` can be split into subsets; connect this with the binary
tensor product.
* Include connection with holors.
* Port more of the API from the binary tensor product over to this case.
## Tags
multilinear, tensor, tensor product
-/
suppress_compilation
open Function
section Semiring
variable {ι ι₂ ι₃ : Type*}
variable {R : Type*} [CommSemiring R]
variable {R₁ R₂ : Type*}
variable {s : ι → Type*} [∀ i, AddCommMonoid (s i)] [∀ i, Module R (s i)]
variable {M : Type*} [AddCommMonoid M] [Module R M]
variable {E : Type*} [AddCommMonoid E] [Module R E]
variable {F : Type*} [AddCommMonoid F]
namespace PiTensorProduct
variable (R) (s)
/-- The relation on `FreeAddMonoid (R × Π i, s i)` that generates a congruence whose quotient is
the tensor product. -/
inductive Eqv : FreeAddMonoid (R × Π i, s i) → FreeAddMonoid (R × Π i, s i) → Prop
| of_zero : ∀ (r : R) (f : Π i, s i) (i : ι) (_ : f i = 0), Eqv (FreeAddMonoid.of (r, f)) 0
| of_zero_scalar : ∀ f : Π i, s i, Eqv (FreeAddMonoid.of (0, f)) 0
| of_add : ∀ (_ : DecidableEq ι) (r : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i),
Eqv (FreeAddMonoid.of (r, update f i m₁) + FreeAddMonoid.of (r, update f i m₂))
(FreeAddMonoid.of (r, update f i (m₁ + m₂)))
| of_add_scalar : ∀ (r r' : R) (f : Π i, s i),
Eqv (FreeAddMonoid.of (r, f) + FreeAddMonoid.of (r', f)) (FreeAddMonoid.of (r + r', f))
| of_smul : ∀ (_ : DecidableEq ι) (r : R) (f : Π i, s i) (i : ι) (r' : R),
Eqv (FreeAddMonoid.of (r, update f i (r' • f i))) (FreeAddMonoid.of (r' * r, f))
| add_comm : ∀ x y, Eqv (x + y) (y + x)
end PiTensorProduct
variable (R) (s)
/-- `PiTensorProduct R s` with `R` a commutative semiring and `s : ι → Type*` is the tensor
product of all the `s i`'s. This is denoted by `⨂[R] i, s i`. -/
def PiTensorProduct : Type _ :=
(addConGen (PiTensorProduct.Eqv R s)).Quotient
variable {R}
unsuppress_compilation in
/-- This enables the notation `⨂[R] i : ι, s i` for the pi tensor product `PiTensorProduct`,
given an indexed family of types `s : ι → Type*`. -/
scoped[TensorProduct] notation3:100"⨂["R"] "(...)", "r:(scoped f => PiTensorProduct R f) => r
open TensorProduct
namespace PiTensorProduct
section Module
instance : AddCommMonoid (⨂[R] i, s i) :=
{ (addConGen (PiTensorProduct.Eqv R s)).addMonoid with
add_comm := fun x y ↦
AddCon.induction_on₂ x y fun _ _ ↦
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.add_comm _ _ }
instance : Inhabited (⨂[R] i, s i) := ⟨0⟩
variable (R) {s}
/-- `tprodCoeff R r f` with `r : R` and `f : Π i, s i` is the tensor product of the vectors `f i`
over all `i : ι`, multiplied by the coefficient `r`. Note that this is meant as an auxiliary
definition for this file alone, and that one should use `tprod` defined below for most purposes. -/
def tprodCoeff (r : R) (f : Π i, s i) : ⨂[R] i, s i :=
AddCon.mk' _ <| FreeAddMonoid.of (r, f)
variable {R}
theorem zero_tprodCoeff (f : Π i, s i) : tprodCoeff R 0 f = 0 :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_zero_scalar _
theorem zero_tprodCoeff' (z : R) (f : Π i, s i) (i : ι) (hf : f i = 0) : tprodCoeff R z f = 0 :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_zero _ _ i hf
theorem add_tprodCoeff [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i) :
tprodCoeff R z (update f i m₁) + tprodCoeff R z (update f i m₂) =
tprodCoeff R z (update f i (m₁ + m₂)) :=
Quotient.sound' <| AddConGen.Rel.of _ _ (Eqv.of_add _ z f i m₁ m₂)
theorem add_tprodCoeff' (z₁ z₂ : R) (f : Π i, s i) :
tprodCoeff R z₁ f + tprodCoeff R z₂ f = tprodCoeff R (z₁ + z₂) f :=
Quotient.sound' <| AddConGen.Rel.of _ _ (Eqv.of_add_scalar z₁ z₂ f)
theorem smul_tprodCoeff_aux [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (r : R) :
tprodCoeff R z (update f i (r • f i)) = tprodCoeff R (r * z) f :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_smul _ _ _ _ _
theorem smul_tprodCoeff [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (r : R₁) [SMul R₁ R]
[IsScalarTower R₁ R R] [SMul R₁ (s i)] [IsScalarTower R₁ R (s i)] :
tprodCoeff R z (update f i (r • f i)) = tprodCoeff R (r • z) f := by
have h₁ : r • z = r • (1 : R) * z := by rw [smul_mul_assoc, one_mul]
have h₂ : r • f i = (r • (1 : R)) • f i := (smul_one_smul _ _ _).symm
rw [h₁, h₂]
exact smul_tprodCoeff_aux z f i _
/-- Construct an `AddMonoidHom` from `(⨂[R] i, s i)` to some space `F` from a function
`φ : (R × Π i, s i) → F` with the appropriate properties. -/
def liftAddHom (φ : (R × Π i, s i) → F)
(C0 : ∀ (r : R) (f : Π i, s i) (i : ι) (_ : f i = 0), φ (r, f) = 0)
(C0' : ∀ f : Π i, s i, φ (0, f) = 0)
(C_add : ∀ [DecidableEq ι] (r : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i),
φ (r, update f i m₁) + φ (r, update f i m₂) = φ (r, update f i (m₁ + m₂)))
(C_add_scalar : ∀ (r r' : R) (f : Π i, s i), φ (r, f) + φ (r', f) = φ (r + r', f))
(C_smul : ∀ [DecidableEq ι] (r : R) (f : Π i, s i) (i : ι) (r' : R),
φ (r, update f i (r' • f i)) = φ (r' * r, f)) :
(⨂[R] i, s i) →+ F :=
(addConGen (PiTensorProduct.Eqv R s)).lift (FreeAddMonoid.lift φ) <|
AddCon.addConGen_le fun x y hxy ↦
match hxy with
| Eqv.of_zero r' f i hf =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C0 r' f i hf]
| Eqv.of_zero_scalar f =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C0']
| Eqv.of_add inst z f i m₁ m₂ =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, @C_add inst]
| Eqv.of_add_scalar z₁ z₂ f =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C_add_scalar]
| Eqv.of_smul inst z f i r' =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, @C_smul inst]
| Eqv.add_comm x y =>
(AddCon.ker_rel _).2 <| by simp_rw [AddMonoidHom.map_add, add_comm]
/-- Induct using `tprodCoeff` -/
@[elab_as_elim]
protected theorem induction_on' {motive : (⨂[R] i, s i) → Prop} (z : ⨂[R] i, s i)
(tprodCoeff : ∀ (r : R) (f : Π i, s i), motive (tprodCoeff R r f))
(add : ∀ x y, motive x → motive y → motive (x + y)) :
motive z := by
have C0 : motive 0 := by
have h₁ := tprodCoeff 0 0
rwa [zero_tprodCoeff] at h₁
refine AddCon.induction_on z fun x ↦ FreeAddMonoid.recOn x C0 ?_
simp_rw [AddCon.coe_add]
refine fun f y ih ↦ add _ _ ?_ ih
convert tprodCoeff f.1 f.2
section DistribMulAction
variable [Monoid R₁] [DistribMulAction R₁ R] [SMulCommClass R₁ R R]
variable [Monoid R₂] [DistribMulAction R₂ R] [SMulCommClass R₂ R R]
-- Most of the time we want the instance below this one, which is easier for typeclass resolution
-- to find.
instance hasSMul' : SMul R₁ (⨂[R] i, s i) :=
⟨fun r ↦
liftAddHom (fun f : R × Π i, s i ↦ tprodCoeff R (r • f.1) f.2)
(fun r' f i hf ↦ by simp_rw [zero_tprodCoeff' _ f i hf])
(fun f ↦ by simp [zero_tprodCoeff]) (fun r' f i m₁ m₂ ↦ by simp [add_tprodCoeff])
(fun r' r'' f ↦ by simp [add_tprodCoeff', mul_add]) fun z f i r' ↦ by
simp [smul_tprodCoeff, mul_smul_comm]⟩
instance : SMul R (⨂[R] i, s i) :=
PiTensorProduct.hasSMul'
theorem smul_tprodCoeff' (r : R₁) (z : R) (f : Π i, s i) :
r • tprodCoeff R z f = tprodCoeff R (r • z) f := rfl
protected theorem smul_add (r : R₁) (x y : ⨂[R] i, s i) : r • (x + y) = r • x + r • y :=
AddMonoidHom.map_add _ _ _
instance distribMulAction' : DistribMulAction R₁ (⨂[R] i, s i) where
smul := (· • ·)
smul_add _ _ _ := AddMonoidHom.map_add _ _ _
mul_smul r r' x :=
PiTensorProduct.induction_on' x (fun {r'' f} ↦ by simp [smul_tprodCoeff', smul_smul])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy]
one_smul x :=
PiTensorProduct.induction_on' x (fun {r f} ↦ by rw [smul_tprodCoeff', one_smul])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]
smul_zero _ := AddMonoidHom.map_zero _
instance smulCommClass' [SMulCommClass R₁ R₂ R] : SMulCommClass R₁ R₂ (⨂[R] i, s i) :=
⟨fun {r' r''} x ↦
PiTensorProduct.induction_on' x (fun {xr xf} ↦ by simp only [smul_tprodCoeff', smul_comm])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]⟩
instance isScalarTower' [SMul R₁ R₂] [IsScalarTower R₁ R₂ R] :
IsScalarTower R₁ R₂ (⨂[R] i, s i) :=
⟨fun {r' r''} x ↦
PiTensorProduct.induction_on' x (fun {xr xf} ↦ by simp only [smul_tprodCoeff', smul_assoc])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]⟩
end DistribMulAction
-- Most of the time we want the instance below this one, which is easier for typeclass resolution
-- to find.
instance module' [Semiring R₁] [Module R₁ R] [SMulCommClass R₁ R R] : Module R₁ (⨂[R] i, s i) :=
{ PiTensorProduct.distribMulAction' with
add_smul := fun r r' x ↦
PiTensorProduct.induction_on' x
(fun {r f} ↦ by simp_rw [smul_tprodCoeff', add_smul, add_tprodCoeff'])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy, add_add_add_comm]
zero_smul := fun x ↦
PiTensorProduct.induction_on' x
(fun {r f} ↦ by simp_rw [smul_tprodCoeff', zero_smul, zero_tprodCoeff])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy, add_zero] }
-- shortcut instances
instance : Module R (⨂[R] i, s i) :=
PiTensorProduct.module'
instance : SMulCommClass R R (⨂[R] i, s i) :=
PiTensorProduct.smulCommClass'
instance : IsScalarTower R R (⨂[R] i, s i) :=
PiTensorProduct.isScalarTower'
variable (R) in
/-- The canonical `MultilinearMap R s (⨂[R] i, s i)`.
`tprod R fun i => f i` has notation `⨂ₜ[R] i, f i`. -/
def tprod : MultilinearMap R s (⨂[R] i, s i) where
toFun := tprodCoeff R 1
map_update_add' {_ f} i x y := (add_tprodCoeff (1 : R) f i x y).symm
map_update_smul' {_ f} i r x := by
rw [smul_tprodCoeff', ← smul_tprodCoeff (1 : R) _ i, update_idem, update_self]
unsuppress_compilation in
@[inherit_doc tprod]
notation3:100 "⨂ₜ["R"] "(...)", "r:(scoped f => tprod R f) => r
theorem tprod_eq_tprodCoeff_one :
⇑(tprod R : MultilinearMap R s (⨂[R] i, s i)) = tprodCoeff R 1 := rfl
@[simp]
theorem tprodCoeff_eq_smul_tprod (z : R) (f : Π i, s i) : tprodCoeff R z f = z • tprod R f := by
have : z = z • (1 : R) := by simp only [mul_one, Algebra.id.smul_eq_mul]
conv_lhs => rw [this]
rfl
/-- The image of an element `p` of `FreeAddMonoid (R × Π i, s i)` in the `PiTensorProduct` is
equal to the sum of `a • ⨂ₜ[R] i, m i` over all the entries `(a, m)` of `p`.
-/
lemma _root_.FreeAddMonoid.toPiTensorProduct (p : FreeAddMonoid (R × Π i, s i)) :
AddCon.toQuotient (c := addConGen (PiTensorProduct.Eqv R s)) p =
List.sum (List.map (fun x ↦ x.1 • ⨂ₜ[R] i, x.2 i) p.toList) := by
-- TODO: this is defeq abuse: `p` is not a `List`.
match p with
| [] => rw [FreeAddMonoid.toList_nil, List.map_nil, List.sum_nil]; rfl
| x :: ps =>
rw [FreeAddMonoid.toList_cons, List.map_cons, List.sum_cons, ← List.singleton_append,
← toPiTensorProduct ps, ← tprodCoeff_eq_smul_tprod]
rfl
/-- The set of lifts of an element `x` of `⨂[R] i, s i` in `FreeAddMonoid (R × Π i, s i)`. -/
def lifts (x : ⨂[R] i, s i) : Set (FreeAddMonoid (R × Π i, s i)) :=
{p | AddCon.toQuotient (c := addConGen (PiTensorProduct.Eqv R s)) p = x}
/-- An element `p` of `FreeAddMonoid (R × Π i, s i)` lifts an element `x` of `⨂[R] i, s i`
if and only if `x` is equal to the sum of `a • ⨂ₜ[R] i, m i` over all the entries
`(a, m)` of `p`.
-/
lemma mem_lifts_iff (x : ⨂[R] i, s i) (p : FreeAddMonoid (R × Π i, s i)) :
p ∈ lifts x ↔ List.sum (List.map (fun x ↦ x.1 • ⨂ₜ[R] i, x.2 i) p.toList) = x := by
simp only [lifts, Set.mem_setOf_eq, FreeAddMonoid.toPiTensorProduct]
/-- Every element of `⨂[R] i, s i` has a lift in `FreeAddMonoid (R × Π i, s i)`.
-/
lemma nonempty_lifts (x : ⨂[R] i, s i) : Set.Nonempty (lifts x) := by
existsi @Quotient.out _ (addConGen (PiTensorProduct.Eqv R s)).toSetoid x
simp only [lifts, Set.mem_setOf_eq]
rw [← AddCon.quot_mk_eq_coe]
erw [Quot.out_eq]
/-- The empty list lifts the element `0` of `⨂[R] i, s i`.
-/
lemma lifts_zero : 0 ∈ lifts (0 : ⨂[R] i, s i) := by
rw [mem_lifts_iff]; erw [List.map_nil]; rw [List.sum_nil]
/-- If elements `p,q` of `FreeAddMonoid (R × Π i, s i)` lift elements `x,y` of `⨂[R] i, s i`
respectively, then `p + q` lifts `x + y`.
-/
lemma lifts_add {x y : ⨂[R] i, s i} {p q : FreeAddMonoid (R × Π i, s i)}
(hp : p ∈ lifts x) (hq : q ∈ lifts y) : p + q ∈ lifts (x + y) := by
simp only [lifts, Set.mem_setOf_eq, AddCon.coe_add]
rw [hp, hq]
/-- If an element `p` of `FreeAddMonoid (R × Π i, s i)` lifts an element `x` of `⨂[R] i, s i`,
| and if `a` is an element of `R`, then the list obtained by multiplying the first entry of each
element of `p` by `a` lifts `a • x`.
-/
lemma lifts_smul {x : ⨂[R] i, s i} {p : FreeAddMonoid (R × Π i, s i)} (h : p ∈ lifts x) (a : R) :
p.map (fun (y : R × Π i, s i) ↦ (a * y.1, y.2)) ∈ lifts (a • x) := by
rw [mem_lifts_iff] at h ⊢
rw [← h]
| Mathlib/LinearAlgebra/PiTensorProduct.lean | 345 | 351 |
/-
Copyright (c) 2024 David Loeffler. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: David Loeffler
-/
import Mathlib.NumberTheory.LSeries.AbstractFuncEq
import Mathlib.NumberTheory.ModularForms.JacobiTheta.Bounds
import Mathlib.NumberTheory.LSeries.MellinEqDirichlet
import Mathlib.NumberTheory.LSeries.Basic
/-!
# Odd Hurwitz zeta functions
In this file we study the functions on `ℂ` which are the analytic continuation of the following
series (convergent for `1 < re s`), where `a ∈ ℝ` is a parameter:
`hurwitzZetaOdd a s = 1 / 2 * ∑' n : ℤ, sgn (n + a) / |n + a| ^ s`
and
`sinZeta a s = ∑' n : ℕ, sin (2 * π * a * n) / n ^ s`.
The term for `n = -a` in the first sum is understood as 0 if `a` is an integer, as is the term for
`n = 0` in the second sum (for all `a`). Note that these functions are differentiable everywhere,
unlike their even counterparts which have poles.
Of course, we cannot *define* these functions by the above formulae (since existence of the
analytic continuation is not at all obvious); we in fact construct them as Mellin transforms of
various versions of the Jacobi theta function.
## Main definitions and theorems
* `completedHurwitzZetaOdd`: the completed Hurwitz zeta function
* `completedSinZeta`: the completed cosine zeta function
* `differentiable_completedHurwitzZetaOdd` and `differentiable_completedSinZeta`:
differentiability on `ℂ`
* `completedHurwitzZetaOdd_one_sub`: the functional equation
`completedHurwitzZetaOdd a (1 - s) = completedSinZeta a s`
* `hasSum_int_hurwitzZetaOdd` and `hasSum_nat_sinZeta`: relation between
the zeta functions and corresponding Dirichlet series for `1 < re s`
-/
noncomputable section
open Complex hiding abs_of_nonneg
open CharZero Filter Topology Asymptotics Real Set MeasureTheory
open scoped ComplexConjugate
namespace HurwitzZeta
section kernel_defs
/-!
## Definitions and elementary properties of kernels
-/
/-- Variant of `jacobiTheta₂'` which we introduce to simplify some formulae. -/
def jacobiTheta₂'' (z τ : ℂ) : ℂ :=
cexp (π * I * z ^ 2 * τ) * (jacobiTheta₂' (z * τ) τ / (2 * π * I) + z * jacobiTheta₂ (z * τ) τ)
lemma jacobiTheta₂''_conj (z τ : ℂ) :
conj (jacobiTheta₂'' z τ) = jacobiTheta₂'' (conj z) (-conj τ) := by
simp [jacobiTheta₂'', jacobiTheta₂'_conj, jacobiTheta₂_conj, ← exp_conj, map_ofNat, div_neg,
neg_div, jacobiTheta₂'_neg_left]
/-- Restatement of `jacobiTheta₂'_add_left'`: the function `jacobiTheta₂''` is 1-periodic in `z`. -/
lemma jacobiTheta₂''_add_left (z τ : ℂ) : jacobiTheta₂'' (z + 1) τ = jacobiTheta₂'' z τ := by
simp only [jacobiTheta₂'', add_mul z 1, one_mul, jacobiTheta₂'_add_left', jacobiTheta₂_add_left']
generalize jacobiTheta₂ (z * τ) τ = J
generalize jacobiTheta₂' (z * τ) τ = J'
-- clear denominator
simp_rw [div_add' _ _ _ two_pi_I_ne_zero, ← mul_div_assoc]
refine congr_arg (· / (2 * π * I)) ?_
-- get all exponential terms to left
rw [mul_left_comm _ (cexp _), ← mul_add, mul_assoc (cexp _), ← mul_add, ← mul_assoc (cexp _),
← Complex.exp_add]
congrm (cexp ?_ * ?_) <;> ring
lemma jacobiTheta₂''_neg_left (z τ : ℂ) : jacobiTheta₂'' (-z) τ = -jacobiTheta₂'' z τ := by
simp [jacobiTheta₂'', jacobiTheta₂'_neg_left, neg_div, -neg_add_rev, ← neg_add]
lemma jacobiTheta₂'_functional_equation' (z τ : ℂ) :
jacobiTheta₂' z τ = (-2 * π) / (-I * τ) ^ (3 / 2 : ℂ) * jacobiTheta₂'' z (-1 / τ) := by
rcases eq_or_ne τ 0 with rfl | hτ
· rw [jacobiTheta₂'_undef _ (by simp), mul_zero, zero_cpow (by norm_num), div_zero, zero_mul]
have aux1 : (-2 * π : ℂ) / (2 * π * I) = I := by
rw [div_eq_iff two_pi_I_ne_zero, mul_comm I, mul_assoc _ I I, I_mul_I, neg_mul, mul_neg,
mul_one]
rw [jacobiTheta₂'_functional_equation, ← mul_one_div _ τ, mul_right_comm _ (cexp _),
(by rw [cpow_one, ← div_div, div_self (neg_ne_zero.mpr I_ne_zero)] :
1 / τ = -I / (-I * τ) ^ (1 : ℂ)), div_mul_div_comm,
← cpow_add _ _ (mul_ne_zero (neg_ne_zero.mpr I_ne_zero) hτ), ← div_mul_eq_mul_div,
(by norm_num : (1 / 2 + 1 : ℂ) = 3 / 2), mul_assoc (1 / _), mul_assoc (1 / _),
← mul_one_div (-2 * π : ℂ), mul_comm _ (1 / _), mul_assoc (1 / _)]
congr 1
rw [jacobiTheta₂'', div_add' _ _ _ two_pi_I_ne_zero, ← mul_div_assoc, ← mul_div_assoc,
← div_mul_eq_mul_div (-2 * π : ℂ), mul_assoc, aux1, mul_div z (-1), mul_neg_one, neg_div τ z,
jacobiTheta₂_neg_left, jacobiTheta₂'_neg_left, neg_mul, ← mul_neg, ← mul_neg,
mul_div, mul_neg_one, neg_div, neg_mul, neg_mul, neg_div]
congr 2
rw [neg_sub, ← sub_eq_neg_add, mul_comm _ (_ * I), ← mul_assoc]
/-- Odd Hurwitz zeta kernel (function whose Mellin transform will be the odd part of the completed
Hurwitz zeta function). See `oddKernel_def` for the defining formula, and `hasSum_int_oddKernel`
for an expression as a sum over `ℤ`.
-/
@[irreducible] def oddKernel (a : UnitAddCircle) (x : ℝ) : ℝ :=
(show Function.Periodic (fun a : ℝ ↦ re (jacobiTheta₂'' a (I * x))) 1 by
intro a; simp [jacobiTheta₂''_add_left]).lift a
lemma oddKernel_def (a x : ℝ) : ↑(oddKernel a x) = jacobiTheta₂'' a (I * x) := by
simp [oddKernel, ← conj_eq_iff_re, jacobiTheta₂''_conj]
lemma oddKernel_def' (a x : ℝ) : ↑(oddKernel ↑a x) = cexp (-π * a ^ 2 * x) *
(jacobiTheta₂' (a * I * x) (I * x) / (2 * π * I) + a * jacobiTheta₂ (a * I * x) (I * x)) := by
rw [oddKernel_def, jacobiTheta₂'', ← mul_assoc ↑a I x,
(by ring : ↑π * I * ↑a ^ 2 * (I * ↑x) = I ^ 2 * ↑π * ↑a ^ 2 * x), I_sq, neg_one_mul]
lemma oddKernel_undef (a : UnitAddCircle) {x : ℝ} (hx : x ≤ 0) : oddKernel a x = 0 := by
induction a using QuotientAddGroup.induction_on with | H a' =>
rw [← ofReal_eq_zero, oddKernel_def', jacobiTheta₂_undef, jacobiTheta₂'_undef, zero_div, zero_add,
mul_zero, mul_zero] <;>
simpa
/-- Auxiliary function appearing in the functional equation for the odd Hurwitz zeta kernel, equal
to `∑ (n : ℕ), 2 * n * sin (2 * π * n * a) * exp (-π * n ^ 2 * x)`. See `hasSum_nat_sinKernel`
for the defining sum. -/
@[irreducible] def sinKernel (a : UnitAddCircle) (x : ℝ) : ℝ :=
(show Function.Periodic (fun ξ : ℝ ↦ re (jacobiTheta₂' ξ (I * x) / (-2 * π))) 1 by
intro ξ; simp [jacobiTheta₂'_add_left]).lift a
lemma sinKernel_def (a x : ℝ) : ↑(sinKernel ↑a x) = jacobiTheta₂' a (I * x) / (-2 * π) := by
simp [sinKernel, re_eq_add_conj, jacobiTheta₂'_conj, map_ofNat]
lemma sinKernel_undef (a : UnitAddCircle) {x : ℝ} (hx : x ≤ 0) : sinKernel a x = 0 := by
induction a using QuotientAddGroup.induction_on with
| H a => rw [← ofReal_eq_zero, sinKernel_def, jacobiTheta₂'_undef _ (by simpa), zero_div]
lemma oddKernel_neg (a : UnitAddCircle) (x : ℝ) : oddKernel (-a) x = -oddKernel a x := by
induction a using QuotientAddGroup.induction_on with
| H a => simp [← ofReal_inj, ← QuotientAddGroup.mk_neg, oddKernel_def, jacobiTheta₂''_neg_left]
@[simp] lemma oddKernel_zero (x : ℝ) : oddKernel 0 x = 0 := by
simpa using oddKernel_neg 0 x
lemma sinKernel_neg (a : UnitAddCircle) (x : ℝ) :
sinKernel (-a) x = -sinKernel a x := by
induction a using QuotientAddGroup.induction_on with
| H a => simp [← ofReal_inj, ← QuotientAddGroup.mk_neg, sinKernel_def, jacobiTheta₂'_neg_left,
neg_div]
@[simp] lemma sinKernel_zero (x : ℝ) : sinKernel 0 x = 0 := by
simpa using sinKernel_neg 0 x
/-- The odd kernel is continuous on `Ioi 0`. -/
lemma continuousOn_oddKernel (a : UnitAddCircle) : ContinuousOn (oddKernel a) (Ioi 0) := by
induction a using QuotientAddGroup.induction_on with | H a =>
suffices ContinuousOn (fun x ↦ (oddKernel a x : ℂ)) (Ioi 0) from
(continuous_re.comp_continuousOn this).congr fun a _ ↦ (ofReal_re _).symm
simp_rw [oddKernel_def' a]
refine fun x hx ↦ ((Continuous.continuousAt ?_).mul ?_).continuousWithinAt
· fun_prop
· have hf : Continuous fun u : ℝ ↦ (a * I * u, I * u) := by fun_prop
apply ContinuousAt.add
· exact ((continuousAt_jacobiTheta₂' (a * I * x) (by rwa [I_mul_im, ofReal_re])).comp
(f := fun u : ℝ ↦ (a * I * u, I * u)) hf.continuousAt).div_const _
· exact continuousAt_const.mul <| (continuousAt_jacobiTheta₂ (a * I * x)
(by rwa [I_mul_im, ofReal_re])).comp (f := fun u : ℝ ↦ (a * I * u, I * u)) hf.continuousAt
lemma continuousOn_sinKernel (a : UnitAddCircle) : ContinuousOn (sinKernel a) (Ioi 0) := by
induction a using QuotientAddGroup.induction_on with | H a =>
suffices ContinuousOn (fun x ↦ (sinKernel a x : ℂ)) (Ioi 0) from
(continuous_re.comp_continuousOn this).congr fun a _ ↦ (ofReal_re _).symm
simp_rw [sinKernel_def]
apply (continuousOn_of_forall_continuousAt (fun x hx ↦ ?_)).div_const
have h := continuousAt_jacobiTheta₂' a (by rwa [I_mul_im, ofReal_re])
fun_prop
lemma oddKernel_functional_equation (a : UnitAddCircle) (x : ℝ) :
oddKernel a x = 1 / x ^ (3 / 2 : ℝ) * sinKernel a (1 / x) := by
-- first reduce to `0 < x`
rcases le_or_lt x 0 with hx | hx
· rw [oddKernel_undef _ hx, sinKernel_undef _ (one_div_nonpos.mpr hx), mul_zero]
induction a using QuotientAddGroup.induction_on with | H a =>
have h1 : -1 / (I * ↑(1 / x)) = I * x := by rw [one_div, ofReal_inv, mul_comm, ← div_div,
div_inv_eq_mul, div_eq_mul_inv, inv_I, mul_neg, neg_one_mul, neg_mul, neg_neg, mul_comm]
have h2 : (-I * (I * ↑(1 / x))) = 1 / x := by
rw [← mul_assoc, neg_mul, I_mul_I, neg_neg, one_mul, ofReal_div, ofReal_one]
have h3 : (x : ℂ) ^ (3 / 2 : ℂ) ≠ 0 := by
simp only [Ne, cpow_eq_zero_iff, ofReal_eq_zero, hx.ne', false_and, not_false_eq_true]
have h4 : arg x ≠ π := by rw [arg_ofReal_of_nonneg hx.le]; exact pi_ne_zero.symm
rw [← ofReal_inj, oddKernel_def, ofReal_mul, sinKernel_def, jacobiTheta₂'_functional_equation',
h1, h2]
generalize jacobiTheta₂'' a (I * ↑x) = J
rw [one_div (x : ℂ), inv_cpow _ _ h4, div_inv_eq_mul, one_div, ofReal_inv, ofReal_cpow hx.le,
ofReal_div, ofReal_ofNat, ofReal_ofNat, ← mul_div_assoc _ _ (-2 * π : ℂ),
eq_div_iff <| mul_ne_zero (neg_ne_zero.mpr two_ne_zero) (ofReal_ne_zero.mpr pi_ne_zero),
← div_eq_inv_mul, eq_div_iff h3, mul_comm J _, mul_right_comm]
end kernel_defs
section sum_formulas
/-!
## Formulae for the kernels as sums
-/
lemma hasSum_int_oddKernel (a : ℝ) {x : ℝ} (hx : 0 < x) :
HasSum (fun n : ℤ ↦ (n + a) * rexp (-π * (n + a) ^ 2 * x)) (oddKernel ↑a x) := by
rw [← hasSum_ofReal, oddKernel_def' a x]
have h1 := hasSum_jacobiTheta₂_term (a * I * x) (by rwa [I_mul_im, ofReal_re])
have h2 := hasSum_jacobiTheta₂'_term (a * I * x) (by rwa [I_mul_im, ofReal_re])
refine (((h2.div_const (2 * π * I)).add (h1.mul_left ↑a)).mul_left
(cexp (-π * a ^ 2 * x))).congr_fun (fun n ↦ ?_)
rw [jacobiTheta₂'_term, mul_assoc (2 * π * I), mul_div_cancel_left₀ _ two_pi_I_ne_zero, ← add_mul,
mul_left_comm, jacobiTheta₂_term, ← Complex.exp_add]
push_cast
simp only [← mul_assoc, ← add_mul]
congrm _ * cexp (?_ * x)
simp only [mul_right_comm _ I, add_mul, mul_assoc _ I, I_mul_I]
ring_nf
lemma hasSum_int_sinKernel (a : ℝ) {t : ℝ} (ht : 0 < t) : HasSum
(fun n : ℤ ↦ -I * n * cexp (2 * π * I * a * n) * rexp (-π * n ^ 2 * t)) ↑(sinKernel a t) := by
have h : -2 * (π : ℂ) ≠ (0 : ℂ) := by
simp only [neg_mul, ne_eq, neg_eq_zero, mul_eq_zero,
OfNat.ofNat_ne_zero, ofReal_eq_zero, pi_ne_zero, or_self, not_false_eq_true]
rw [sinKernel_def]
refine ((hasSum_jacobiTheta₂'_term a
(by rwa [I_mul_im, ofReal_re])).div_const _).congr_fun fun n ↦ ?_
rw [jacobiTheta₂'_term, jacobiTheta₂_term, ofReal_exp, mul_assoc (-I * n), ← Complex.exp_add,
eq_div_iff h, ofReal_mul, ofReal_mul, ofReal_pow, ofReal_neg, ofReal_intCast,
mul_comm _ (-2 * π : ℂ), ← mul_assoc]
congrm ?_ * cexp (?_ + ?_)
· simp [mul_assoc]
· exact mul_right_comm (2 * π * I) a n
· simp [← mul_assoc, mul_comm _ I]
lemma hasSum_nat_sinKernel (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℕ ↦ 2 * n * Real.sin (2 * π * a * n) * rexp (-π * n ^ 2 * t))
(sinKernel ↑a t) := by
rw [← hasSum_ofReal]
have := (hasSum_int_sinKernel a ht).nat_add_neg
simp only [Int.cast_zero, sq (0 : ℂ), zero_mul, mul_zero, add_zero] at this
refine this.congr_fun fun n ↦ ?_
simp_rw [Int.cast_neg, neg_sq, mul_neg, ofReal_mul, Int.cast_natCast, ofReal_natCast,
ofReal_ofNat, ← add_mul, ofReal_sin, Complex.sin]
push_cast
congr 1
rw [← mul_div_assoc, ← div_mul_eq_mul_div, ← div_mul_eq_mul_div, div_self two_ne_zero, one_mul,
neg_mul, neg_mul, neg_neg, mul_comm _ I, ← mul_assoc, mul_comm _ I, neg_mul,
← sub_eq_neg_add, mul_sub]
congr 3 <;> ring
end sum_formulas
section asymp
/-!
## Asymptotics of the kernels as `t → ∞`
-/
/-- The function `oddKernel a` has exponential decay at `+∞`, for any `a`. -/
lemma isBigO_atTop_oddKernel (a : UnitAddCircle) :
∃ p, 0 < p ∧ IsBigO atTop (oddKernel a) (fun x ↦ Real.exp (-p * x)) := by
induction a using QuotientAddGroup.induction_on with | H b =>
obtain ⟨p, hp, hp'⟩ := HurwitzKernelBounds.isBigO_atTop_F_int_one b
refine ⟨p, hp, (Eventually.isBigO ?_).trans hp'⟩
filter_upwards [eventually_gt_atTop 0] with t ht
simpa [← (hasSum_int_oddKernel b ht).tsum_eq, HurwitzKernelBounds.F_int,
HurwitzKernelBounds.f_int, abs_of_nonneg (exp_pos _).le] using
norm_tsum_le_tsum_norm (hasSum_int_oddKernel b ht).summable.norm
/-- The function `sinKernel a` has exponential decay at `+∞`, for any `a`. -/
lemma isBigO_atTop_sinKernel (a : UnitAddCircle) :
∃ p, 0 < p ∧ IsBigO atTop (sinKernel a) (fun x ↦ Real.exp (-p * x)) := by
induction a using QuotientAddGroup.induction_on with | H a =>
obtain ⟨p, hp, hp'⟩ := HurwitzKernelBounds.isBigO_atTop_F_nat_one (le_refl 0)
refine ⟨p, hp, (Eventually.isBigO ?_).trans (hp'.const_mul_left 2)⟩
filter_upwards [eventually_gt_atTop 0] with t ht
rw [HurwitzKernelBounds.F_nat, ← (hasSum_nat_sinKernel a ht).tsum_eq]
apply tsum_of_norm_bounded (g := fun n ↦ 2 * HurwitzKernelBounds.f_nat 1 0 t n)
· exact (HurwitzKernelBounds.summable_f_nat 1 0 ht).hasSum.mul_left _
· intro n
rw [norm_mul, norm_mul, norm_mul, norm_two, mul_assoc, mul_assoc,
mul_le_mul_iff_of_pos_left two_pos, HurwitzKernelBounds.f_nat, pow_one, add_zero,
norm_of_nonneg (exp_pos _).le, Real.norm_eq_abs, Nat.abs_cast, ← mul_assoc,
mul_le_mul_iff_of_pos_right (exp_pos _)]
exact mul_le_of_le_one_right (Nat.cast_nonneg _) (abs_sin_le_one _)
end asymp
section FEPair
/-!
## Construction of an FE-pair
-/
/-- A `StrongFEPair` structure with `f = oddKernel a` and `g = sinKernel a`. -/
@[simps]
def hurwitzOddFEPair (a : UnitAddCircle) : StrongFEPair ℂ where
f := ofReal ∘ oddKernel a
g := ofReal ∘ sinKernel a
hf_int := (continuous_ofReal.comp_continuousOn (continuousOn_oddKernel a)).locallyIntegrableOn
measurableSet_Ioi
hg_int := (continuous_ofReal.comp_continuousOn (continuousOn_sinKernel a)).locallyIntegrableOn
measurableSet_Ioi
k := 3 / 2
hk := by norm_num
ε := 1
hε := one_ne_zero
f₀ := 0
hf₀ := rfl
g₀ := 0
hg₀ := rfl
hf_top r := by
let ⟨v, hv, hv'⟩ := isBigO_atTop_oddKernel a
rw [← isBigO_norm_left] at hv' ⊢
simpa using hv'.trans (isLittleO_exp_neg_mul_rpow_atTop hv _).isBigO
hg_top r := by
let ⟨v, hv, hv'⟩ := isBigO_atTop_sinKernel a
rw [← isBigO_norm_left] at hv' ⊢
simpa using hv'.trans (isLittleO_exp_neg_mul_rpow_atTop hv _).isBigO
h_feq x hx := by simp [← ofReal_mul, oddKernel_functional_equation a, inv_rpow (le_of_lt hx)]
end FEPair
/-!
## Definition of the completed odd Hurwitz zeta function
-/
/-- The entire function of `s` which agrees with
`1 / 2 * Gamma ((s + 1) / 2) * π ^ (-(s + 1) / 2) * ∑' (n : ℤ), sgn (n + a) / |n + a| ^ s`
for `1 < re s`.
-/
def completedHurwitzZetaOdd (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzOddFEPair a).Λ ((s + 1) / 2)) / 2
lemma differentiable_completedHurwitzZetaOdd (a : UnitAddCircle) :
Differentiable ℂ (completedHurwitzZetaOdd a) :=
((hurwitzOddFEPair a).differentiable_Λ.comp
((differentiable_id.add_const 1).div_const 2)).div_const 2
/-- The entire function of `s` which agrees with
` Gamma ((s + 1) / 2) * π ^ (-(s + 1) / 2) * ∑' (n : ℕ), sin (2 * π * a * n) / n ^ s`
for `1 < re s`.
-/
def completedSinZeta (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzOddFEPair a).symm.Λ ((s + 1) / 2)) / 2
lemma differentiable_completedSinZeta (a : UnitAddCircle) :
Differentiable ℂ (completedSinZeta a) :=
((hurwitzOddFEPair a).symm.differentiable_Λ.comp
((differentiable_id.add_const 1).div_const 2)).div_const 2
/-!
## Parity and functional equations
-/
lemma completedHurwitzZetaOdd_neg (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaOdd (-a) s = -completedHurwitzZetaOdd a s := by
simp [completedHurwitzZetaOdd, StrongFEPair.Λ, hurwitzOddFEPair, mellin, oddKernel_neg,
integral_neg, neg_div]
lemma completedSinZeta_neg (a : UnitAddCircle) (s : ℂ) :
completedSinZeta (-a) s = -completedSinZeta a s := by
simp [completedSinZeta, StrongFEPair.Λ, mellin, StrongFEPair.symm, WeakFEPair.symm,
hurwitzOddFEPair, sinKernel_neg, integral_neg, neg_div]
/-- Functional equation for the odd Hurwitz zeta function. -/
theorem completedHurwitzZetaOdd_one_sub (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaOdd a (1 - s) = completedSinZeta a s := by
rw [completedHurwitzZetaOdd, completedSinZeta,
(by { push_cast; ring } : (1 - s + 1) / 2 = ↑(3 / 2 : ℝ) - (s + 1) / 2),
← hurwitzOddFEPair_k, (hurwitzOddFEPair a).functional_equation ((s + 1) / 2),
hurwitzOddFEPair_ε, one_smul]
/-- Functional equation for the odd Hurwitz zeta function (alternative form). -/
lemma completedSinZeta_one_sub (a : UnitAddCircle) (s : ℂ) :
completedSinZeta a (1 - s) = completedHurwitzZetaOdd a s := by
simp [← completedHurwitzZetaOdd_one_sub]
/-!
## Relation to the Dirichlet series for `1 < re s`
-/
/-- Formula for `completedSinZeta` as a Dirichlet series in the convergence range
(first version, with sum over `ℤ`). -/
lemma hasSum_int_completedSinZeta (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ Gammaℝ (s + 1) * (-I) * Int.sign n *
cexp (2 * π * I * a * n) / (↑|n| : ℂ) ^ s / 2) (completedSinZeta a s) := by
let c (n : ℤ) : ℂ := -I * cexp (2 * π * I * a * n) / 2
have hc (n : ℤ) : ‖c n‖ = 1 / 2 := by
simp_rw [c, (by { push_cast; ring } : 2 * π * I * a * n = ↑(2 * π * a * n) * I), norm_div,
RCLike.norm_ofNat, norm_mul, norm_neg, norm_I, one_mul, norm_exp_ofReal_mul_I]
have hF t (ht : 0 < t) :
HasSum (fun n ↦ c n * n * rexp (-π * n ^ 2 * t)) (sinKernel a t / 2) := by
refine ((hasSum_int_sinKernel a ht).div_const 2).congr_fun fun n ↦ ?_
rw [div_mul_eq_mul_div, div_mul_eq_mul_div, mul_right_comm (-I)]
have h_sum : Summable fun i ↦ ‖c i‖ / |↑i| ^ s.re := by
simp_rw [hc, div_right_comm]
apply Summable.div_const
apply Summable.of_nat_of_neg <;>
simpa
refine (mellin_div_const .. ▸ hasSum_mellin_pi_mul_sq' (zero_lt_one.trans hs) hF h_sum).congr_fun
fun n ↦ ?_
simp [Int.sign_eq_sign, ← Int.cast_abs] -- non-terminal simp OK when `ring` follows
ring
/-- Formula for `completedSinZeta` as a Dirichlet series in the convergence range
(second version, with sum over `ℕ`). -/
lemma hasSum_nat_completedSinZeta (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℕ ↦ Gammaℝ (s + 1) * Real.sin (2 * π * a * n) / (n : ℂ) ^ s)
(completedSinZeta a s) := by
have := (hasSum_int_completedSinZeta a hs).nat_add_neg
simp_rw [Int.sign_zero, Int.cast_zero, mul_zero, zero_mul, zero_div, add_zero, abs_neg,
Int.sign_neg, Nat.abs_cast, Int.cast_neg, Int.cast_natCast, ← add_div] at this
refine this.congr_fun fun n ↦ ?_
rw [div_right_comm]
rcases eq_or_ne n 0 with rfl | h
· simp
simp_rw [Int.sign_natCast_of_ne_zero h, Int.cast_one, ofReal_sin, Complex.sin]
simp only [← mul_div_assoc, push_cast, mul_assoc (Gammaℝ _), ← mul_add]
congr 3
rw [mul_one, mul_neg_one, neg_neg, neg_mul I, ← sub_eq_neg_add, ← mul_sub, mul_comm,
mul_neg, neg_mul]
congr 3 <;> ring
/-- Formula for `completedHurwitzZetaOdd` as a Dirichlet series in the convergence range. -/
lemma hasSum_int_completedHurwitzZetaOdd (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ Gammaℝ (s + 1) * SignType.sign (n + a) / (↑|n + a| : ℂ) ^ s / 2)
(completedHurwitzZetaOdd a s) := by
let r (n : ℤ) : ℝ := n + a
let c (n : ℤ) : ℂ := 1 / 2
have hF t (ht : 0 < t) : HasSum (fun n ↦ c n * r n * rexp (-π * (r n) ^ 2 * t))
(oddKernel a t / 2) := by
refine ((hasSum_ofReal.mpr (hasSum_int_oddKernel a ht)).div_const 2).congr_fun fun n ↦ ?_
simp [r, c, push_cast, div_mul_eq_mul_div, -one_div]
have h_sum : Summable fun i ↦ ‖c i‖ / |r i| ^ s.re := by
simp_rw [c, ← mul_one_div ‖_‖]
apply Summable.mul_left
rwa [summable_one_div_int_add_rpow]
have := mellin_div_const .. ▸ hasSum_mellin_pi_mul_sq' (zero_lt_one.trans hs) hF h_sum
refine this.congr_fun fun n ↦ ?_
simp only [r, c, mul_one_div, div_mul_eq_mul_div, div_right_comm]
/-!
## Non-completed zeta functions
-/
/-- The odd part of the Hurwitz zeta function, i.e. the meromorphic function of `s` which agrees
with `1 / 2 * ∑' (n : ℤ), sign (n + a) / |n + a| ^ s` for `1 < re s` -/
noncomputable def hurwitzZetaOdd (a : UnitAddCircle) (s : ℂ) :=
completedHurwitzZetaOdd a s / Gammaℝ (s + 1)
lemma hurwitzZetaOdd_neg (a : UnitAddCircle) (s : ℂ) :
hurwitzZetaOdd (-a) s = -hurwitzZetaOdd a s := by
simp_rw [hurwitzZetaOdd, completedHurwitzZetaOdd_neg, neg_div]
/-- The odd Hurwitz zeta function is differentiable everywhere. -/
lemma differentiable_hurwitzZetaOdd (a : UnitAddCircle) :
Differentiable ℂ (hurwitzZetaOdd a) :=
(differentiable_completedHurwitzZetaOdd a).mul <| differentiable_Gammaℝ_inv.comp <|
differentiable_id.add <| differentiable_const _
/-- The sine zeta function, i.e. the meromorphic function of `s` which agrees
with `∑' (n : ℕ), sin (2 * π * a * n) / n ^ s` for `1 < re s`. -/
noncomputable def sinZeta (a : UnitAddCircle) (s : ℂ) :=
completedSinZeta a s / Gammaℝ (s + 1)
lemma sinZeta_neg (a : UnitAddCircle) (s : ℂ) :
sinZeta (-a) s = -sinZeta a s := by
simp_rw [sinZeta, completedSinZeta_neg, neg_div]
/-- The sine zeta function is differentiable everywhere. -/
lemma differentiableAt_sinZeta (a : UnitAddCircle) :
Differentiable ℂ (sinZeta a) :=
(differentiable_completedSinZeta a).mul <| differentiable_Gammaℝ_inv.comp <|
differentiable_id.add <| differentiable_const _
/-- Formula for `hurwitzZetaOdd` as a Dirichlet series in the convergence range (sum over `ℤ`). -/
theorem hasSum_int_hurwitzZetaOdd (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ SignType.sign (n + a) / (↑|n + a| : ℂ) ^ s / 2) (hurwitzZetaOdd a s) := by
refine ((hasSum_int_completedHurwitzZetaOdd a hs).div_const (Gammaℝ _)).congr_fun fun n ↦ ?_
| have : 0 < re (s + 1) := by rw [add_re, one_re]; positivity
simp [div_right_comm _ _ (Gammaℝ _), mul_div_cancel_left₀ _ (Gammaℝ_ne_zero_of_re_pos this)]
| Mathlib/NumberTheory/LSeries/HurwitzZetaOdd.lean | 482 | 484 |
/-
Copyright (c) 2017 Kevin Buzzard. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kevin Buzzard, Mario Carneiro
-/
import Mathlib.Algebra.Ring.CharZero
import Mathlib.Algebra.Star.Basic
import Mathlib.Data.Real.Basic
import Mathlib.Order.Interval.Set.UnorderedInterval
import Mathlib.Tactic.Ring
/-!
# The complex numbers
The complex numbers are modelled as ℝ^2 in the obvious way and it is shown that they form a field
of characteristic zero. The result that the complex numbers are algebraically closed, see
`FieldTheory.AlgebraicClosure`.
-/
assert_not_exists Multiset Algebra
open Set Function
/-! ### Definition and basic arithmetic -/
/-- Complex numbers consist of two `Real`s: a real part `re` and an imaginary part `im`. -/
structure Complex : Type where
/-- The real part of a complex number. -/
re : ℝ
/-- The imaginary part of a complex number. -/
im : ℝ
@[inherit_doc] notation "ℂ" => Complex
namespace Complex
open ComplexConjugate
noncomputable instance : DecidableEq ℂ :=
Classical.decEq _
/-- The equivalence between the complex numbers and `ℝ × ℝ`. -/
@[simps apply]
def equivRealProd : ℂ ≃ ℝ × ℝ where
toFun z := ⟨z.re, z.im⟩
invFun p := ⟨p.1, p.2⟩
left_inv := fun ⟨_, _⟩ => rfl
right_inv := fun ⟨_, _⟩ => rfl
@[simp]
theorem eta : ∀ z : ℂ, Complex.mk z.re z.im = z
| ⟨_, _⟩ => rfl
-- We only mark this lemma with `ext` *locally* to avoid it applying whenever terms of `ℂ` appear.
theorem ext : ∀ {z w : ℂ}, z.re = w.re → z.im = w.im → z = w
| ⟨_, _⟩, ⟨_, _⟩, rfl, rfl => rfl
attribute [local ext] Complex.ext
lemma «forall» {p : ℂ → Prop} : (∀ x, p x) ↔ ∀ a b, p ⟨a, b⟩ := by aesop
lemma «exists» {p : ℂ → Prop} : (∃ x, p x) ↔ ∃ a b, p ⟨a, b⟩ := by aesop
theorem re_surjective : Surjective re := fun x => ⟨⟨x, 0⟩, rfl⟩
theorem im_surjective : Surjective im := fun y => ⟨⟨0, y⟩, rfl⟩
@[simp]
theorem range_re : range re = univ :=
re_surjective.range_eq
@[simp]
theorem range_im : range im = univ :=
im_surjective.range_eq
/-- The natural inclusion of the real numbers into the complex numbers. -/
@[coe]
def ofReal (r : ℝ) : ℂ :=
⟨r, 0⟩
instance : Coe ℝ ℂ :=
⟨ofReal⟩
@[simp, norm_cast]
theorem ofReal_re (r : ℝ) : Complex.re (r : ℂ) = r :=
rfl
@[simp, norm_cast]
theorem ofReal_im (r : ℝ) : (r : ℂ).im = 0 :=
rfl
theorem ofReal_def (r : ℝ) : (r : ℂ) = ⟨r, 0⟩ :=
rfl
@[simp, norm_cast]
theorem ofReal_inj {z w : ℝ} : (z : ℂ) = w ↔ z = w :=
⟨congrArg re, by apply congrArg⟩
theorem ofReal_injective : Function.Injective ((↑) : ℝ → ℂ) := fun _ _ => congrArg re
instance canLift : CanLift ℂ ℝ (↑) fun z => z.im = 0 where
prf z hz := ⟨z.re, ext rfl hz.symm⟩
/-- The product of a set on the real axis and a set on the imaginary axis of the complex plane,
denoted by `s ×ℂ t`. -/
def reProdIm (s t : Set ℝ) : Set ℂ :=
re ⁻¹' s ∩ im ⁻¹' t
@[deprecated (since := "2024-12-03")] protected alias Set.reProdIm := reProdIm
@[inherit_doc]
infixl:72 " ×ℂ " => reProdIm
theorem mem_reProdIm {z : ℂ} {s t : Set ℝ} : z ∈ s ×ℂ t ↔ z.re ∈ s ∧ z.im ∈ t :=
Iff.rfl
instance : Zero ℂ :=
⟨(0 : ℝ)⟩
instance : Inhabited ℂ :=
⟨0⟩
@[simp]
theorem zero_re : (0 : ℂ).re = 0 :=
rfl
@[simp]
theorem zero_im : (0 : ℂ).im = 0 :=
rfl
@[simp, norm_cast]
theorem ofReal_zero : ((0 : ℝ) : ℂ) = 0 :=
rfl
@[simp]
theorem ofReal_eq_zero {z : ℝ} : (z : ℂ) = 0 ↔ z = 0 :=
ofReal_inj
theorem ofReal_ne_zero {z : ℝ} : (z : ℂ) ≠ 0 ↔ z ≠ 0 :=
not_congr ofReal_eq_zero
instance : One ℂ :=
⟨(1 : ℝ)⟩
@[simp]
theorem one_re : (1 : ℂ).re = 1 :=
rfl
@[simp]
theorem one_im : (1 : ℂ).im = 0 :=
rfl
@[simp, norm_cast]
theorem ofReal_one : ((1 : ℝ) : ℂ) = 1 :=
rfl
@[simp]
theorem ofReal_eq_one {z : ℝ} : (z : ℂ) = 1 ↔ z = 1 :=
ofReal_inj
theorem ofReal_ne_one {z : ℝ} : (z : ℂ) ≠ 1 ↔ z ≠ 1 :=
not_congr ofReal_eq_one
instance : Add ℂ :=
⟨fun z w => ⟨z.re + w.re, z.im + w.im⟩⟩
@[simp]
theorem add_re (z w : ℂ) : (z + w).re = z.re + w.re :=
rfl
@[simp]
theorem add_im (z w : ℂ) : (z + w).im = z.im + w.im :=
rfl
-- replaced by `re_ofNat`
-- replaced by `im_ofNat`
@[simp, norm_cast]
theorem ofReal_add (r s : ℝ) : ((r + s : ℝ) : ℂ) = r + s :=
Complex.ext_iff.2 <| by simp [ofReal]
-- replaced by `Complex.ofReal_ofNat`
instance : Neg ℂ :=
⟨fun z => ⟨-z.re, -z.im⟩⟩
@[simp]
theorem neg_re (z : ℂ) : (-z).re = -z.re :=
rfl
@[simp]
theorem neg_im (z : ℂ) : (-z).im = -z.im :=
rfl
@[simp, norm_cast]
theorem ofReal_neg (r : ℝ) : ((-r : ℝ) : ℂ) = -r :=
Complex.ext_iff.2 <| by simp [ofReal]
instance : Sub ℂ :=
⟨fun z w => ⟨z.re - w.re, z.im - w.im⟩⟩
instance : Mul ℂ :=
⟨fun z w => ⟨z.re * w.re - z.im * w.im, z.re * w.im + z.im * w.re⟩⟩
@[simp]
theorem mul_re (z w : ℂ) : (z * w).re = z.re * w.re - z.im * w.im :=
rfl
@[simp]
theorem mul_im (z w : ℂ) : (z * w).im = z.re * w.im + z.im * w.re :=
rfl
@[simp, norm_cast]
theorem ofReal_mul (r s : ℝ) : ((r * s : ℝ) : ℂ) = r * s :=
Complex.ext_iff.2 <| by simp [ofReal]
theorem re_ofReal_mul (r : ℝ) (z : ℂ) : (r * z).re = r * z.re := by simp [ofReal]
theorem im_ofReal_mul (r : ℝ) (z : ℂ) : (r * z).im = r * z.im := by simp [ofReal]
lemma re_mul_ofReal (z : ℂ) (r : ℝ) : (z * r).re = z.re * r := by simp [ofReal]
lemma im_mul_ofReal (z : ℂ) (r : ℝ) : (z * r).im = z.im * r := by simp [ofReal]
theorem ofReal_mul' (r : ℝ) (z : ℂ) : ↑r * z = ⟨r * z.re, r * z.im⟩ :=
ext (re_ofReal_mul _ _) (im_ofReal_mul _ _)
/-! ### The imaginary unit, `I` -/
/-- The imaginary unit. -/
def I : ℂ :=
⟨0, 1⟩
@[simp]
theorem I_re : I.re = 0 :=
rfl
@[simp]
theorem I_im : I.im = 1 :=
rfl
@[simp]
theorem I_mul_I : I * I = -1 :=
Complex.ext_iff.2 <| by simp
theorem I_mul (z : ℂ) : I * z = ⟨-z.im, z.re⟩ :=
Complex.ext_iff.2 <| by simp
@[simp] lemma I_ne_zero : (I : ℂ) ≠ 0 := mt (congr_arg im) zero_ne_one.symm
theorem mk_eq_add_mul_I (a b : ℝ) : Complex.mk a b = a + b * I :=
Complex.ext_iff.2 <| by simp [ofReal]
@[simp]
theorem re_add_im (z : ℂ) : (z.re : ℂ) + z.im * I = z :=
Complex.ext_iff.2 <| by simp [ofReal]
theorem mul_I_re (z : ℂ) : (z * I).re = -z.im := by simp
theorem mul_I_im (z : ℂ) : (z * I).im = z.re := by simp
theorem I_mul_re (z : ℂ) : (I * z).re = -z.im := by simp
theorem I_mul_im (z : ℂ) : (I * z).im = z.re := by simp
@[simp]
theorem equivRealProd_symm_apply (p : ℝ × ℝ) : equivRealProd.symm p = p.1 + p.2 * I := by
ext <;> simp [Complex.equivRealProd, ofReal]
/-- The natural `AddEquiv` from `ℂ` to `ℝ × ℝ`. -/
@[simps! +simpRhs apply symm_apply_re symm_apply_im]
def equivRealProdAddHom : ℂ ≃+ ℝ × ℝ :=
{ equivRealProd with map_add' := by simp }
theorem equivRealProdAddHom_symm_apply (p : ℝ × ℝ) :
equivRealProdAddHom.symm p = p.1 + p.2 * I := equivRealProd_symm_apply p
/-! ### Commutative ring instance and lemmas -/
/- We use a nonstandard formula for the `ℕ` and `ℤ` actions to make sure there is no
diamond from the other actions they inherit through the `ℝ`-action on `ℂ` and action transitivity
defined in `Data.Complex.Module`. -/
instance : Nontrivial ℂ :=
domain_nontrivial re rfl rfl
namespace SMul
-- The useless `0` multiplication in `smul` is to make sure that
-- `RestrictScalars.module ℝ ℂ ℂ = Complex.module` definitionally.
-- instance made scoped to avoid situations like instance synthesis
-- of `SMul ℂ ℂ` trying to proceed via `SMul ℂ ℝ`.
/-- Scalar multiplication by `R` on `ℝ` extends to `ℂ`. This is used here and in
`Matlib.Data.Complex.Module` to transfer instances from `ℝ` to `ℂ`, but is not
needed outside, so we make it scoped. -/
scoped instance instSMulRealComplex {R : Type*} [SMul R ℝ] : SMul R ℂ where
smul r x := ⟨r • x.re - 0 * x.im, r • x.im + 0 * x.re⟩
end SMul
open scoped SMul
section SMul
variable {R : Type*} [SMul R ℝ]
theorem smul_re (r : R) (z : ℂ) : (r • z).re = r • z.re := by simp [(· • ·), SMul.smul]
theorem smul_im (r : R) (z : ℂ) : (r • z).im = r • z.im := by simp [(· • ·), SMul.smul]
@[simp]
theorem real_smul {x : ℝ} {z : ℂ} : x • z = x * z :=
rfl
end SMul
instance addCommGroup : AddCommGroup ℂ :=
{ zero := (0 : ℂ)
add := (· + ·)
neg := Neg.neg
sub := Sub.sub
nsmul := fun n z => n • z
zsmul := fun n z => n • z
zsmul_zero' := by intros; ext <;> simp [smul_re, smul_im]
nsmul_zero := by intros; ext <;> simp [smul_re, smul_im]
nsmul_succ := by intros; ext <;> simp [smul_re, smul_im] <;> ring
zsmul_succ' := by intros; ext <;> simp [smul_re, smul_im] <;> ring
zsmul_neg' := by intros; ext <;> simp [smul_re, smul_im] <;> ring
add_assoc := by intros; ext <;> simp <;> ring
zero_add := by intros; ext <;> simp
add_zero := by intros; ext <;> simp
add_comm := by intros; ext <;> simp <;> ring
neg_add_cancel := by intros; ext <;> simp }
instance addGroupWithOne : AddGroupWithOne ℂ :=
{ Complex.addCommGroup with
natCast := fun n => ⟨n, 0⟩
natCast_zero := by
ext <;> simp [Nat.cast, AddMonoidWithOne.natCast_zero]
natCast_succ := fun _ => by ext <;> simp [Nat.cast, AddMonoidWithOne.natCast_succ]
intCast := fun n => ⟨n, 0⟩
intCast_ofNat := fun _ => by ext <;> rfl
intCast_negSucc := fun n => by
ext
· simp [AddGroupWithOne.intCast_negSucc]
show -(1 : ℝ) + (-n) = -(↑(n + 1))
simp [Nat.cast_add, add_comm]
· simp [AddGroupWithOne.intCast_negSucc]
show im ⟨n, 0⟩ = 0
rfl
one := 1 }
instance commRing : CommRing ℂ :=
{ addGroupWithOne with
mul := (· * ·)
npow := @npowRec _ ⟨(1 : ℂ)⟩ ⟨(· * ·)⟩
add_comm := by intros; ext <;> simp <;> ring
left_distrib := by intros; ext <;> simp [mul_re, mul_im] <;> ring
right_distrib := by intros; ext <;> simp [mul_re, mul_im] <;> ring
zero_mul := by intros; ext <;> simp
mul_zero := by intros; ext <;> simp
mul_assoc := by intros; ext <;> simp <;> ring
one_mul := by intros; ext <;> simp
mul_one := by intros; ext <;> simp
mul_comm := by intros; ext <;> simp <;> ring }
/-- This shortcut instance ensures we do not find `Ring` via the noncomputable `Complex.field`
instance. -/
instance : Ring ℂ := by infer_instance
/-- This shortcut instance ensures we do not find `CommSemiring` via the noncomputable
`Complex.field` instance. -/
instance : CommSemiring ℂ :=
inferInstance
/-- This shortcut instance ensures we do not find `Semiring` via the noncomputable
`Complex.field` instance. -/
instance : Semiring ℂ :=
inferInstance
/-- The "real part" map, considered as an additive group homomorphism. -/
def reAddGroupHom : ℂ →+ ℝ where
toFun := re
map_zero' := zero_re
map_add' := add_re
@[simp]
theorem coe_reAddGroupHom : (reAddGroupHom : ℂ → ℝ) = re :=
rfl
/-- The "imaginary part" map, considered as an additive group homomorphism. -/
def imAddGroupHom : ℂ →+ ℝ where
toFun := im
map_zero' := zero_im
map_add' := add_im
@[simp]
theorem coe_imAddGroupHom : (imAddGroupHom : ℂ → ℝ) = im :=
rfl
/-! ### Cast lemmas -/
instance instNNRatCast : NNRatCast ℂ where nnratCast q := ofReal q
instance instRatCast : RatCast ℂ where ratCast q := ofReal q
@[simp, norm_cast] lemma ofReal_ofNat (n : ℕ) [n.AtLeastTwo] : ofReal ofNat(n) = ofNat(n) := rfl
@[simp, norm_cast] lemma ofReal_natCast (n : ℕ) : ofReal n = n := rfl
@[simp, norm_cast] lemma ofReal_intCast (n : ℤ) : ofReal n = n := rfl
@[simp, norm_cast] lemma ofReal_nnratCast (q : ℚ≥0) : ofReal q = q := rfl
@[simp, norm_cast] lemma ofReal_ratCast (q : ℚ) : ofReal q = q := rfl
@[simp]
lemma re_ofNat (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℂ).re = ofNat(n) := rfl
@[simp] lemma im_ofNat (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℂ).im = 0 := rfl
@[simp, norm_cast] lemma natCast_re (n : ℕ) : (n : ℂ).re = n := rfl
@[simp, norm_cast] lemma natCast_im (n : ℕ) : (n : ℂ).im = 0 := rfl
@[simp, norm_cast] lemma intCast_re (n : ℤ) : (n : ℂ).re = n := rfl
@[simp, norm_cast] lemma intCast_im (n : ℤ) : (n : ℂ).im = 0 := rfl
@[simp, norm_cast] lemma re_nnratCast (q : ℚ≥0) : (q : ℂ).re = q := rfl
@[simp, norm_cast] lemma im_nnratCast (q : ℚ≥0) : (q : ℂ).im = 0 := rfl
@[simp, norm_cast] lemma ratCast_re (q : ℚ) : (q : ℂ).re = q := rfl
@[simp, norm_cast] lemma ratCast_im (q : ℚ) : (q : ℂ).im = 0 := rfl
lemma re_nsmul (n : ℕ) (z : ℂ) : (n • z).re = n • z.re := smul_re ..
lemma im_nsmul (n : ℕ) (z : ℂ) : (n • z).im = n • z.im := smul_im ..
lemma re_zsmul (n : ℤ) (z : ℂ) : (n • z).re = n • z.re := smul_re ..
lemma im_zsmul (n : ℤ) (z : ℂ) : (n • z).im = n • z.im := smul_im ..
@[simp] lemma re_nnqsmul (q : ℚ≥0) (z : ℂ) : (q • z).re = q • z.re := smul_re ..
@[simp] lemma im_nnqsmul (q : ℚ≥0) (z : ℂ) : (q • z).im = q • z.im := smul_im ..
@[simp] lemma re_qsmul (q : ℚ) (z : ℂ) : (q • z).re = q • z.re := smul_re ..
@[simp] lemma im_qsmul (q : ℚ) (z : ℂ) : (q • z).im = q • z.im := smul_im ..
@[norm_cast] lemma ofReal_nsmul (n : ℕ) (r : ℝ) : ↑(n • r) = n • (r : ℂ) := by simp
@[norm_cast] lemma ofReal_zsmul (n : ℤ) (r : ℝ) : ↑(n • r) = n • (r : ℂ) := by simp
/-! ### Complex conjugation -/
/-- This defines the complex conjugate as the `star` operation of the `StarRing ℂ`. It
is recommended to use the ring endomorphism version `starRingEnd`, available under the
notation `conj` in the locale `ComplexConjugate`. -/
instance : StarRing ℂ where
star z := ⟨z.re, -z.im⟩
star_involutive x := by simp only [eta, neg_neg]
star_mul a b := by ext <;> simp [add_comm] <;> ring
star_add a b := by ext <;> simp [add_comm]
@[simp]
theorem conj_re (z : ℂ) : (conj z).re = z.re :=
rfl
@[simp]
theorem conj_im (z : ℂ) : (conj z).im = -z.im :=
rfl
@[simp]
theorem conj_ofReal (r : ℝ) : conj (r : ℂ) = r :=
Complex.ext_iff.2 <| by simp [star]
@[simp]
theorem conj_I : conj I = -I :=
Complex.ext_iff.2 <| by simp
theorem conj_natCast (n : ℕ) : conj (n : ℂ) = n := map_natCast _ _
theorem conj_ofNat (n : ℕ) [n.AtLeastTwo] : conj (ofNat(n) : ℂ) = ofNat(n) :=
map_ofNat _ _
theorem conj_neg_I : conj (-I) = I := by simp
theorem conj_eq_iff_real {z : ℂ} : conj z = z ↔ ∃ r : ℝ, z = r :=
⟨fun h => ⟨z.re, ext rfl <| eq_zero_of_neg_eq (congr_arg im h)⟩, fun ⟨h, e⟩ => by
rw [e, conj_ofReal]⟩
theorem conj_eq_iff_re {z : ℂ} : conj z = z ↔ (z.re : ℂ) = z :=
conj_eq_iff_real.trans ⟨by rintro ⟨r, rfl⟩; simp [ofReal], fun h => ⟨_, h.symm⟩⟩
theorem conj_eq_iff_im {z : ℂ} : conj z = z ↔ z.im = 0 :=
⟨fun h => add_self_eq_zero.mp (neg_eq_iff_add_eq_zero.mp (congr_arg im h)), fun h =>
ext rfl (neg_eq_iff_add_eq_zero.mpr (add_self_eq_zero.mpr h))⟩
@[simp]
theorem star_def : (Star.star : ℂ → ℂ) = conj :=
rfl
/-! ### Norm squared -/
/-- The norm squared function. -/
@[pp_nodot]
def normSq : ℂ →*₀ ℝ where
toFun z := z.re * z.re + z.im * z.im
map_zero' := by simp
map_one' := by simp
map_mul' z w := by
dsimp
ring
theorem normSq_apply (z : ℂ) : normSq z = z.re * z.re + z.im * z.im :=
rfl
@[simp]
theorem normSq_ofReal (r : ℝ) : normSq r = r * r := by
simp [normSq, ofReal]
@[simp]
theorem normSq_natCast (n : ℕ) : normSq n = n * n := normSq_ofReal _
@[simp]
theorem normSq_intCast (z : ℤ) : normSq z = z * z := normSq_ofReal _
@[simp]
theorem normSq_ratCast (q : ℚ) : normSq q = q * q := normSq_ofReal _
@[simp]
theorem normSq_ofNat (n : ℕ) [n.AtLeastTwo] :
normSq (ofNat(n) : ℂ) = ofNat(n) * ofNat(n) :=
normSq_natCast _
@[simp]
theorem normSq_mk (x y : ℝ) : normSq ⟨x, y⟩ = x * x + y * y :=
rfl
theorem normSq_add_mul_I (x y : ℝ) : normSq (x + y * I) = x ^ 2 + y ^ 2 := by
rw [← mk_eq_add_mul_I, normSq_mk, sq, sq]
theorem normSq_eq_conj_mul_self {z : ℂ} : (normSq z : ℂ) = conj z * z := by
ext <;> simp [normSq, mul_comm, ofReal]
theorem normSq_zero : normSq 0 = 0 := by simp
theorem normSq_one : normSq 1 = 1 := by simp
@[simp]
theorem normSq_I : normSq I = 1 := by simp [normSq]
theorem normSq_nonneg (z : ℂ) : 0 ≤ normSq z :=
add_nonneg (mul_self_nonneg _) (mul_self_nonneg _)
theorem normSq_eq_zero {z : ℂ} : normSq z = 0 ↔ z = 0 :=
⟨fun h =>
ext (eq_zero_of_mul_self_add_mul_self_eq_zero h)
(eq_zero_of_mul_self_add_mul_self_eq_zero <| (add_comm _ _).trans h),
fun h => h.symm ▸ normSq_zero⟩
@[simp]
theorem normSq_pos {z : ℂ} : 0 < normSq z ↔ z ≠ 0 :=
(normSq_nonneg z).lt_iff_ne.trans <| not_congr (eq_comm.trans normSq_eq_zero)
@[simp]
theorem normSq_neg (z : ℂ) : normSq (-z) = normSq z := by simp [normSq]
@[simp]
theorem normSq_conj (z : ℂ) : normSq (conj z) = normSq z := by simp [normSq]
theorem normSq_mul (z w : ℂ) : normSq (z * w) = normSq z * normSq w :=
normSq.map_mul z w
theorem normSq_add (z w : ℂ) : normSq (z + w) = normSq z + normSq w + 2 * (z * conj w).re := by
dsimp [normSq]; ring
theorem re_sq_le_normSq (z : ℂ) : z.re * z.re ≤ normSq z :=
le_add_of_nonneg_right (mul_self_nonneg _)
theorem im_sq_le_normSq (z : ℂ) : z.im * z.im ≤ normSq z :=
le_add_of_nonneg_left (mul_self_nonneg _)
theorem mul_conj (z : ℂ) : z * conj z = normSq z :=
Complex.ext_iff.2 <| by simp [normSq, mul_comm, sub_eq_neg_add, add_comm, ofReal]
theorem add_conj (z : ℂ) : z + conj z = (2 * z.re : ℝ) :=
Complex.ext_iff.2 <| by simp [two_mul, ofReal]
/-- The coercion `ℝ → ℂ` as a `RingHom`. -/
def ofRealHom : ℝ →+* ℂ where
toFun x := (x : ℂ)
map_one' := ofReal_one
map_zero' := ofReal_zero
map_mul' := ofReal_mul
map_add' := ofReal_add
@[simp] lemma ofRealHom_eq_coe (r : ℝ) : ofRealHom r = r := rfl
variable {α : Type*}
@[simp] lemma ofReal_comp_add (f g : α → ℝ) : ofReal ∘ (f + g) = ofReal ∘ f + ofReal ∘ g :=
map_comp_add ofRealHom ..
@[simp] lemma ofReal_comp_sub (f g : α → ℝ) : ofReal ∘ (f - g) = ofReal ∘ f - ofReal ∘ g :=
map_comp_sub ofRealHom ..
@[simp] lemma ofReal_comp_neg (f : α → ℝ) : ofReal ∘ (-f) = -(ofReal ∘ f) :=
map_comp_neg ofRealHom _
lemma ofReal_comp_nsmul (n : ℕ) (f : α → ℝ) : ofReal ∘ (n • f) = n • (ofReal ∘ f) :=
map_comp_nsmul ofRealHom ..
lemma ofReal_comp_zsmul (n : ℤ) (f : α → ℝ) : ofReal ∘ (n • f) = n • (ofReal ∘ f) :=
map_comp_zsmul ofRealHom ..
@[simp] lemma ofReal_comp_mul (f g : α → ℝ) : ofReal ∘ (f * g) = ofReal ∘ f * ofReal ∘ g :=
map_comp_mul ofRealHom ..
@[simp] lemma ofReal_comp_pow (f : α → ℝ) (n : ℕ) : ofReal ∘ (f ^ n) = (ofReal ∘ f) ^ n :=
map_comp_pow ofRealHom ..
@[simp]
theorem I_sq : I ^ 2 = -1 := by rw [sq, I_mul_I]
@[simp]
lemma I_pow_three : I ^ 3 = -I := by rw [pow_succ, I_sq, neg_one_mul]
@[simp]
theorem I_pow_four : I ^ 4 = 1 := by rw [(by norm_num : 4 = 2 * 2), pow_mul, I_sq, neg_one_sq]
lemma I_pow_eq_pow_mod (n : ℕ) : I ^ n = I ^ (n % 4) := by
conv_lhs => rw [← Nat.div_add_mod n 4]
simp [pow_add, pow_mul, I_pow_four]
@[simp]
theorem sub_re (z w : ℂ) : (z - w).re = z.re - w.re :=
rfl
@[simp]
theorem sub_im (z w : ℂ) : (z - w).im = z.im - w.im :=
rfl
@[simp, norm_cast]
theorem ofReal_sub (r s : ℝ) : ((r - s : ℝ) : ℂ) = r - s :=
Complex.ext_iff.2 <| by simp [ofReal]
@[simp, norm_cast]
theorem ofReal_pow (r : ℝ) (n : ℕ) : ((r ^ n : ℝ) : ℂ) = (r : ℂ) ^ n := by
induction n <;> simp [*, ofReal_mul, pow_succ]
theorem sub_conj (z : ℂ) : z - conj z = (2 * z.im : ℝ) * I :=
Complex.ext_iff.2 <| by simp [two_mul, sub_eq_add_neg, ofReal]
theorem normSq_sub (z w : ℂ) : normSq (z - w) = normSq z + normSq w - 2 * (z * conj w).re := by
rw [sub_eq_add_neg, normSq_add]
simp only [RingHom.map_neg, mul_neg, neg_re, normSq_neg]
ring
/-! ### Inversion -/
noncomputable instance : Inv ℂ :=
⟨fun z => conj z * ((normSq z)⁻¹ : ℝ)⟩
theorem inv_def (z : ℂ) : z⁻¹ = conj z * ((normSq z)⁻¹ : ℝ) :=
rfl
@[simp]
theorem inv_re (z : ℂ) : z⁻¹.re = z.re / normSq z := by simp [inv_def, division_def, ofReal]
@[simp]
theorem inv_im (z : ℂ) : z⁻¹.im = -z.im / normSq z := by simp [inv_def, division_def, ofReal]
@[simp, norm_cast]
theorem ofReal_inv (r : ℝ) : ((r⁻¹ : ℝ) : ℂ) = (r : ℂ)⁻¹ :=
Complex.ext_iff.2 <| by simp [ofReal]
protected theorem inv_zero : (0⁻¹ : ℂ) = 0 := by
rw [← ofReal_zero, ← ofReal_inv, inv_zero]
protected theorem mul_inv_cancel {z : ℂ} (h : z ≠ 0) : z * z⁻¹ = 1 := by
rw [inv_def, ← mul_assoc, mul_conj, ← ofReal_mul, mul_inv_cancel₀ (mt normSq_eq_zero.1 h),
ofReal_one]
noncomputable instance instDivInvMonoid : DivInvMonoid ℂ where
lemma div_re (z w : ℂ) : (z / w).re = z.re * w.re / normSq w + z.im * w.im / normSq w := by
simp [div_eq_mul_inv, mul_assoc, sub_eq_add_neg]
lemma div_im (z w : ℂ) : (z / w).im = z.im * w.re / normSq w - z.re * w.im / normSq w := by
simp [div_eq_mul_inv, mul_assoc, sub_eq_add_neg, add_comm]
/-! ### Field instance and lemmas -/
noncomputable instance instField : Field ℂ where
mul_inv_cancel := @Complex.mul_inv_cancel
inv_zero := Complex.inv_zero
nnqsmul := (· • ·)
qsmul := (· • ·)
nnratCast_def q := by ext <;> simp [NNRat.cast_def, div_re, div_im, mul_div_mul_comm]
ratCast_def q := by ext <;> simp [Rat.cast_def, div_re, div_im, mul_div_mul_comm]
nnqsmul_def n z := Complex.ext_iff.2 <| by simp [NNRat.smul_def, smul_re, smul_im]
qsmul_def n z := Complex.ext_iff.2 <| by simp [Rat.smul_def, smul_re, smul_im]
@[simp, norm_cast]
lemma ofReal_nnqsmul (q : ℚ≥0) (r : ℝ) : ofReal (q • r) = q • r := by simp [NNRat.smul_def]
@[simp, norm_cast]
lemma ofReal_qsmul (q : ℚ) (r : ℝ) : ofReal (q • r) = q • r := by simp [Rat.smul_def]
theorem conj_inv (x : ℂ) : conj x⁻¹ = (conj x)⁻¹ :=
star_inv₀ _
@[simp, norm_cast]
theorem ofReal_div (r s : ℝ) : ((r / s : ℝ) : ℂ) = r / s := map_div₀ ofRealHom r s
@[simp, norm_cast]
theorem ofReal_zpow (r : ℝ) (n : ℤ) : ((r ^ n : ℝ) : ℂ) = (r : ℂ) ^ n := map_zpow₀ ofRealHom r n
@[simp]
theorem div_I (z : ℂ) : z / I = -(z * I) :=
(div_eq_iff_mul_eq I_ne_zero).2 <| by simp [mul_assoc]
@[simp]
theorem inv_I : I⁻¹ = -I := by
rw [inv_eq_one_div, div_I, one_mul]
theorem normSq_inv (z : ℂ) : normSq z⁻¹ = (normSq z)⁻¹ := by simp
theorem normSq_div (z w : ℂ) : normSq (z / w) = normSq z / normSq w := by simp
lemma div_ofReal (z : ℂ) (x : ℝ) : z / x = ⟨z.re / x, z.im / x⟩ := by
simp_rw [div_eq_inv_mul, ← ofReal_inv, ofReal_mul']
lemma div_natCast (z : ℂ) (n : ℕ) : z / n = ⟨z.re / n, z.im / n⟩ :=
mod_cast div_ofReal z n
lemma div_intCast (z : ℂ) (n : ℤ) : z / n = ⟨z.re / n, z.im / n⟩ :=
mod_cast div_ofReal z n
lemma div_ratCast (z : ℂ) (x : ℚ) : z / x = ⟨z.re / x, z.im / x⟩ :=
mod_cast div_ofReal z x
lemma div_ofNat (z : ℂ) (n : ℕ) [n.AtLeastTwo] :
z / ofNat(n) = ⟨z.re / ofNat(n), z.im / ofNat(n)⟩ :=
div_natCast z n
@[simp] lemma div_ofReal_re (z : ℂ) (x : ℝ) : (z / x).re = z.re / x := by rw [div_ofReal]
@[simp] lemma div_ofReal_im (z : ℂ) (x : ℝ) : (z / x).im = z.im / x := by rw [div_ofReal]
@[simp] lemma div_natCast_re (z : ℂ) (n : ℕ) : (z / n).re = z.re / n := by rw [div_natCast]
@[simp] lemma div_natCast_im (z : ℂ) (n : ℕ) : (z / n).im = z.im / n := by rw [div_natCast]
@[simp] lemma div_intCast_re (z : ℂ) (n : ℤ) : (z / n).re = z.re / n := by rw [div_intCast]
@[simp] lemma div_intCast_im (z : ℂ) (n : ℤ) : (z / n).im = z.im / n := by rw [div_intCast]
@[simp] lemma div_ratCast_re (z : ℂ) (x : ℚ) : (z / x).re = z.re / x := by rw [div_ratCast]
@[simp] lemma div_ratCast_im (z : ℂ) (x : ℚ) : (z / x).im = z.im / x := by rw [div_ratCast]
@[simp]
lemma div_ofNat_re (z : ℂ) (n : ℕ) [n.AtLeastTwo] :
(z / ofNat(n)).re = z.re / ofNat(n) := div_natCast_re z n
@[simp]
lemma div_ofNat_im (z : ℂ) (n : ℕ) [n.AtLeastTwo] :
(z / ofNat(n)).im = z.im / ofNat(n) := div_natCast_im z n
/-! ### Characteristic zero -/
instance instCharZero : CharZero ℂ :=
charZero_of_inj_zero fun n h => by rwa [← ofReal_natCast, ofReal_eq_zero, Nat.cast_eq_zero] at h
/-- A complex number `z` plus its conjugate `conj z` is `2` times its real part. -/
theorem re_eq_add_conj (z : ℂ) : (z.re : ℂ) = (z + conj z) / 2 := by
simp only [add_conj, ofReal_mul, ofReal_ofNat, mul_div_cancel_left₀ (z.re : ℂ) two_ne_zero]
/-- A complex number `z` minus its conjugate `conj z` is `2i` times its imaginary part. -/
theorem im_eq_sub_conj (z : ℂ) : (z.im : ℂ) = (z - conj z) / (2 * I) := by
simp only [sub_conj, ofReal_mul, ofReal_ofNat, mul_right_comm,
mul_div_cancel_left₀ _ (mul_ne_zero two_ne_zero I_ne_zero : 2 * I ≠ 0)]
/-- Show the imaginary number ⟨x, y⟩ as an "x + y*I" string
Note that the Real numbers used for x and y will show as cauchy sequences due to the way Real
numbers are represented.
-/
unsafe instance instRepr : Repr ℂ where
reprPrec f p :=
(if p > 65 then (Std.Format.bracket "(" · ")") else (·)) <|
reprPrec f.re 65 ++ " + " ++ reprPrec f.im 70 ++ "*I"
section reProdIm
/-- The preimage under `equivRealProd` of `s ×ˢ t` is `s ×ℂ t`. -/
lemma preimage_equivRealProd_prod (s t : Set ℝ) : equivRealProd ⁻¹' (s ×ˢ t) = s ×ℂ t := rfl
/-- The inequality `s × t ⊆ s₁ × t₁` holds in `ℂ` iff it holds in `ℝ × ℝ`. -/
lemma reProdIm_subset_iff {s s₁ t t₁ : Set ℝ} : s ×ℂ t ⊆ s₁ ×ℂ t₁ ↔ s ×ˢ t ⊆ s₁ ×ˢ t₁ := by
rw [← @preimage_equivRealProd_prod s t, ← @preimage_equivRealProd_prod s₁ t₁]
exact Equiv.preimage_subset equivRealProd _ _
/-- If `s ⊆ s₁ ⊆ ℝ` and `t ⊆ t₁ ⊆ ℝ`, then `s × t ⊆ s₁ × t₁` in `ℂ`. -/
lemma reProdIm_subset_iff' {s s₁ t t₁ : Set ℝ} :
s ×ℂ t ⊆ s₁ ×ℂ t₁ ↔ s ⊆ s₁ ∧ t ⊆ t₁ ∨ s = ∅ ∨ t = ∅ := by
convert prod_subset_prod_iff
exact reProdIm_subset_iff
variable {s t : Set ℝ}
@[simp] lemma reProdIm_nonempty : (s ×ℂ t).Nonempty ↔ s.Nonempty ∧ t.Nonempty := by
simp [Set.Nonempty, reProdIm, Complex.exists]
@[simp] lemma reProdIm_eq_empty : s ×ℂ t = ∅ ↔ s = ∅ ∨ t = ∅ := by
simp [← not_nonempty_iff_eq_empty, reProdIm_nonempty, -not_and, not_and_or]
end reProdIm
open scoped Interval
section Rectangle
/-- A `Rectangle` is an axis-parallel rectangle with corners `z` and `w`. -/
def Rectangle (z w : ℂ) : Set ℂ := [[z.re, w.re]] ×ℂ [[z.im, w.im]]
end Rectangle
section Segments
/-- A real segment `[a₁, a₂]` translated by `b * I` is the complex line segment. -/
lemma horizontalSegment_eq (a₁ a₂ b : ℝ) :
(fun (x : ℝ) ↦ x + b * I) '' [[a₁, a₂]] = [[a₁, a₂]] ×ℂ {b} := by
rw [← preimage_equivRealProd_prod]
ext x
constructor
· intro hx
obtain ⟨x₁, hx₁, hx₁'⟩ := hx
simp [← hx₁', mem_preimage, mem_prod, hx₁]
· intro hx
obtain ⟨x₁, hx₁, hx₁', hx₁''⟩ := hx
refine ⟨x.re, x₁, by simp⟩
/-- A vertical segment `[b₁, b₂]` translated by `a` is the complex line segment. -/
lemma verticalSegment_eq (a b₁ b₂ : ℝ) :
(fun (y : ℝ) ↦ a + y * I) '' [[b₁, b₂]] = {a} ×ℂ [[b₁, b₂]] := by
rw [← preimage_equivRealProd_prod]
ext x
constructor
· intro hx
obtain ⟨x₁, hx₁, hx₁'⟩ := hx
simp [← hx₁', mem_preimage, mem_prod, hx₁]
· intro hx
simp only [equivRealProd_apply, singleton_prod, mem_image, Prod.mk.injEq,
exists_eq_right_right, mem_preimage] at hx
obtain ⟨x₁, hx₁, hx₁', hx₁''⟩ := hx
refine ⟨x.im, x₁, by simp⟩
end Segments
end Complex
| Mathlib/Data/Complex/Basic.lean | 941 | 941 | |
/-
Copyright (c) 2024 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Oliver Nash
-/
import Mathlib.Algebra.Module.Torsion
import Mathlib.FieldTheory.Perfect
import Mathlib.LinearAlgebra.AnnihilatingPolynomial
import Mathlib.RingTheory.Artinian.Instances
import Mathlib.RingTheory.Ideal.Quotient.Nilpotent
import Mathlib.RingTheory.SimpleModule.Basic
/-!
# Semisimple linear endomorphisms
Given an `R`-module `M` together with an `R`-linear endomorphism `f : M → M`, the following two
conditions are equivalent:
1. Every `f`-invariant submodule of `M` has an `f`-invariant complement.
2. `M` is a semisimple `R[X]`-module, where the action of the polynomial ring is induced by `f`.
A linear endomorphism `f` satisfying these equivalent conditions is known as a *semisimple*
endomorphism. We provide basic definitions and results about such endomorphisms in this file.
## Main definitions / results:
* `Module.End.IsSemisimple`: the definition that a linear endomorphism is semisimple
* `Module.End.isSemisimple_iff`: the characterisation of semisimplicity in terms of invariant
submodules.
* `Module.End.eq_zero_of_isNilpotent_isSemisimple`: the zero endomorphism is the only endomorphism
that is both nilpotent and semisimple.
* `Module.End.isSemisimple_of_squarefree_aeval_eq_zero`: an endomorphism that is a root of a
square-free polynomial is semisimple (in finite dimensions over a field).
* `Module.End.IsSemisimple.minpoly_squarefree`: the minimal polynomial of a semisimple
endomorphism is squarefree.
* `IsSemisimple.of_mem_adjoin_pair`: every endomorphism in the subalgebra generated by two
commuting semisimple endomorphisms is semisimple, if the base field is perfect.
## TODO
In finite dimensions over a field:
* Triangularizable iff diagonalisable for semisimple endomorphisms
-/
open Set Function Polynomial
variable {R M : Type*} [CommRing R] [AddCommGroup M] [Module R M]
namespace Module.End
section CommRing
variable (f : End R M)
/-- A linear endomorphism of an `R`-module `M` is called *semisimple* if the induced `R[X]`-module
structure on `M` is semisimple. This is equivalent to saying that every `f`-invariant `R`-submodule
of `M` has an `f`-invariant complement: see `Module.End.isSemisimple_iff`. -/
def IsSemisimple := IsSemisimpleModule R[X] (AEval' f)
/-- A weaker version of semisimplicity that only prescribes behaviour on finitely-generated
submodules. -/
def IsFinitelySemisimple : Prop :=
∀ p (hp : p ∈ invtSubmodule f), Module.Finite R p → IsSemisimple (LinearMap.restrict f hp)
variable {f}
/-- A linear endomorphism is semisimple if every invariant submodule has in invariant complement.
See also `Module.End.isSemisimple_iff`. -/
lemma isSemisimple_iff' :
f.IsSemisimple ↔ ∀ p : invtSubmodule f, ∃ q : invtSubmodule f, IsCompl p q := by
rw [IsSemisimple, IsSemisimpleModule, (AEval.mapSubmodule R M f).symm.complementedLattice_iff,
complementedLattice_iff]
rfl
|
lemma isSemisimple_iff :
f.IsSemisimple ↔ ∀ p ∈ invtSubmodule f, ∃ q ∈ invtSubmodule f, IsCompl p q := by
| Mathlib/LinearAlgebra/Semisimple.lean | 73 | 75 |
/-
Copyright (c) 2024 Judith Ludwig, Christian Merten. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Judith Ludwig, Christian Merten
-/
import Mathlib.Algebra.Module.Torsion
import Mathlib.Algebra.Algebra.Pi
import Mathlib.RingTheory.AdicCompletion.Basic
/-!
# Algebra instance on adic completion
In this file we provide an algebra instance on the adic completion of a ring. Then the adic
completion of any module is a module over the adic completion of the ring.
## Implementation details
We do not make a separate adic completion type in algebra case, to not duplicate all module
theoretic results on adic completions. This choice does cause some trouble though,
since `I ^ n • ⊤` is not defeq to `I ^ n`. We try to work around most of the trouble by
providing as much API as possible.
-/
suppress_compilation
open Submodule
variable {R S : Type*} [CommRing R] [CommRing S] (I : Ideal R)
variable {M : Type*} [AddCommGroup M] [Module R M]
namespace AdicCompletion
attribute [-simp] smul_eq_mul Algebra.id.smul_eq_mul
@[local simp]
theorem transitionMap_ideal_mk {m n : ℕ} (hmn : m ≤ n) (x : R) :
transitionMap I R hmn (Ideal.Quotient.mk (I ^ n • ⊤ : Ideal R) x) =
Ideal.Quotient.mk (I ^ m • ⊤ : Ideal R) x :=
rfl
@[local simp]
theorem transitionMap_map_one {m n : ℕ} (hmn : m ≤ n) : transitionMap I R hmn 1 = 1 :=
rfl
@[local simp]
theorem transitionMap_map_mul {m n : ℕ} (hmn : m ≤ n) (x y : R ⧸ (I ^ n • ⊤ : Ideal R)) :
transitionMap I R hmn (x * y) = transitionMap I R hmn x * transitionMap I R hmn y :=
Quotient.inductionOn₂' x y (fun _ _ ↦ rfl)
@[local simp]
theorem transitionMap_map_pow {m n a : ℕ} (hmn : m ≤ n) (x : R ⧸ (I ^ n • ⊤ : Ideal R)) :
transitionMap I R hmn (x ^ a) = transitionMap I R hmn x ^ a :=
Quotient.inductionOn' x (fun _ ↦ rfl)
/-- `AdicCompletion.transitionMap` as an algebra homomorphism. -/
def transitionMapₐ {m n : ℕ} (hmn : m ≤ n) :
R ⧸ (I ^ n • ⊤ : Ideal R) →ₐ[R] R ⧸ (I ^ m • ⊤ : Ideal R) :=
AlgHom.ofLinearMap (transitionMap I R hmn) rfl (transitionMap_map_mul I hmn)
/-- `AdicCompletion I R` is an `R`-subalgebra of `∀ n, R ⧸ (I ^ n • ⊤ : Ideal R)`. -/
def subalgebra : Subalgebra R (∀ n, R ⧸ (I ^ n • ⊤ : Ideal R)) :=
Submodule.toSubalgebra (submodule I R) (fun _ ↦ by simp [transitionMap_map_one I])
(fun x y hx hy m n hmn ↦ by simp [hx hmn, hy hmn, transitionMap_map_mul I hmn])
/-- `AdicCompletion I R` is a subring of `∀ n, R ⧸ (I ^ n • ⊤ : Ideal R)`. -/
def subring : Subring (∀ n, R ⧸ (I ^ n • ⊤ : Ideal R)) :=
Subalgebra.toSubring (subalgebra I)
instance : Mul (AdicCompletion I R) where
mul x y := ⟨x.val * y.val, fun hmn ↦ by
simp [x.property, y.property, transitionMap_map_mul I hmn]⟩
instance : One (AdicCompletion I R) where
one := ⟨1, by simp [transitionMap_map_one I]⟩
instance : NatCast (AdicCompletion I R) where
natCast n := ⟨n, fun _ ↦ rfl⟩
instance : IntCast (AdicCompletion I R) where
intCast n := ⟨n, fun _ ↦ rfl⟩
instance : Pow (AdicCompletion I R) ℕ where
pow x n := ⟨x.val ^ n, fun hmn ↦ by simp [x.property, transitionMap_map_pow I hmn]⟩
instance : CommRing (AdicCompletion I R) :=
let f : AdicCompletion I R → ∀ n, R ⧸ (I ^ n • ⊤ : Ideal R) := Subtype.val
Subtype.val_injective.commRing f rfl rfl
(fun _ _ ↦ rfl) (fun _ _ ↦ rfl) (fun _ ↦ rfl) (fun _ _ ↦ rfl) (fun _ _ ↦ rfl)
(fun _ _ ↦ rfl) (fun _ _ ↦ rfl) (fun _ ↦ rfl) (fun _ ↦ rfl)
instance [Algebra S R] : Algebra S (AdicCompletion I R) where
algebraMap :=
{ toFun r := ⟨algebraMap S (∀ n, R ⧸ (I ^ n • ⊤ : Ideal R)) r, fun hmn ↦ by
simp only [Pi.algebraMap_apply,
IsScalarTower.algebraMap_apply S R (R ⧸ (I ^ _ • ⊤ : Ideal R)),
Ideal.Quotient.algebraMap_eq, mapQ_eq_factor]
rfl⟩
map_one' := Subtype.ext <| map_one _
map_mul' x y := Subtype.ext <| map_mul _ x y
map_zero' := Subtype.ext <| map_zero _
map_add' x y := Subtype.ext <| map_add _ x y }
commutes' r x := Subtype.ext <| Algebra.commutes' r x.val
smul_def' r x := Subtype.ext <| Algebra.smul_def' r x.val
@[simp]
theorem val_one (n : ℕ) : (1 : AdicCompletion I R).val n = 1 :=
rfl
@[simp]
theorem val_mul (n : ℕ) (x y : AdicCompletion I R) : (x * y).val n = x.val n * y.val n :=
rfl
/-- The canonical algebra map from the adic completion to `R ⧸ I ^ n`.
This is `AdicCompletion.eval` postcomposed with the algebra isomorphism
`R ⧸ (I ^ n • ⊤) ≃ₐ[R] R ⧸ I ^ n`. -/
def evalₐ (n : ℕ) : AdicCompletion I R →ₐ[R] R ⧸ I ^ n :=
have h : (I ^ n • ⊤ : Ideal R) = I ^ n := by ext x; simp
AlgHom.comp
(Ideal.quotientEquivAlgOfEq R h)
(AlgHom.ofLinearMap (eval I R n) rfl (fun _ _ ↦ rfl))
@[simp]
theorem evalₐ_mk (n : ℕ) (x : AdicCauchySequence I R) :
evalₐ I n (mk I R x) = Ideal.Quotient.mk (I ^ n) (x.val n) := by
| simp [evalₐ]
/-- `AdicCauchySequence I R` is an `R`-subalgebra of `ℕ → R`. -/
def AdicCauchySequence.subalgebra : Subalgebra R (ℕ → R) :=
Submodule.toSubalgebra (AdicCauchySequence.submodule I R)
| Mathlib/RingTheory/AdicCompletion/Algebra.lean | 127 | 131 |
/-
Copyright (c) 2022 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers, Heather Macbeth
-/
import Mathlib.Analysis.InnerProductSpace.TwoDim
import Mathlib.Geometry.Euclidean.Angle.Unoriented.Basic
/-!
# Oriented angles.
This file defines oriented angles in real inner product spaces.
## Main definitions
* `Orientation.oangle` is the oriented angle between two vectors with respect to an orientation.
## Implementation notes
The definitions here use the `Real.angle` type, angles modulo `2 * π`. For some purposes,
angles modulo `π` are more convenient, because results are true for such angles with less
configuration dependence. Results that are only equalities modulo `π` can be represented
modulo `2 * π` as equalities of `(2 : ℤ) • θ`.
## References
* Evan Chen, Euclidean Geometry in Mathematical Olympiads.
-/
noncomputable section
open Module Complex
open scoped Real RealInnerProductSpace ComplexConjugate
namespace Orientation
attribute [local instance] Complex.finrank_real_complex_fact
variable {V V' : Type*}
variable [NormedAddCommGroup V] [NormedAddCommGroup V']
variable [InnerProductSpace ℝ V] [InnerProductSpace ℝ V']
variable [Fact (finrank ℝ V = 2)] [Fact (finrank ℝ V' = 2)] (o : Orientation ℝ V (Fin 2))
local notation "ω" => o.areaForm
/-- The oriented angle from `x` to `y`, modulo `2 * π`. If either vector is 0, this is 0.
See `InnerProductGeometry.angle` for the corresponding unoriented angle definition. -/
def oangle (x y : V) : Real.Angle :=
Complex.arg (o.kahler x y)
/-- Oriented angles are continuous when the vectors involved are nonzero. -/
@[fun_prop]
theorem continuousAt_oangle {x : V × V} (hx1 : x.1 ≠ 0) (hx2 : x.2 ≠ 0) :
ContinuousAt (fun y : V × V => o.oangle y.1 y.2) x := by
refine (Complex.continuousAt_arg_coe_angle ?_).comp ?_
· exact o.kahler_ne_zero hx1 hx2
exact ((continuous_ofReal.comp continuous_inner).add
((continuous_ofReal.comp o.areaForm'.continuous₂).mul continuous_const)).continuousAt
/-- If the first vector passed to `oangle` is 0, the result is 0. -/
@[simp]
theorem oangle_zero_left (x : V) : o.oangle 0 x = 0 := by simp [oangle]
/-- If the second vector passed to `oangle` is 0, the result is 0. -/
@[simp]
theorem oangle_zero_right (x : V) : o.oangle x 0 = 0 := by simp [oangle]
/-- If the two vectors passed to `oangle` are the same, the result is 0. -/
@[simp]
theorem oangle_self (x : V) : o.oangle x x = 0 := by
rw [oangle, kahler_apply_self, ← ofReal_pow]
convert QuotientAddGroup.mk_zero (AddSubgroup.zmultiples (2 * π))
apply arg_ofReal_of_nonneg
positivity
/-- If the angle between two vectors is nonzero, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : x ≠ 0 := by
rintro rfl; simp at h
/-- If the angle between two vectors is nonzero, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : y ≠ 0 := by
rintro rfl; simp at h
/-- If the angle between two vectors is nonzero, the vectors are not equal. -/
theorem ne_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : x ≠ y := by
rintro rfl; simp at h
/-- If the angle between two vectors is `π`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π`, the vectors are not equal. -/
theorem ne_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the vectors are not equal. -/
theorem ne_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the vectors are not equal. -/
theorem ne_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the sign of the angle between two vectors is nonzero, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is nonzero, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is nonzero, the vectors are not equal. -/
theorem ne_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : x ≠ y :=
o.ne_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is positive, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : x ≠ 0 :=
o.left_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is positive, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : y ≠ 0 :=
o.right_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is positive, the vectors are not equal. -/
theorem ne_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : x ≠ y :=
o.ne_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : x ≠ 0 :=
o.left_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : y ≠ 0 :=
o.right_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the vectors are not equal. -/
theorem ne_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : x ≠ y :=
o.ne_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- Swapping the two vectors passed to `oangle` negates the angle. -/
theorem oangle_rev (x y : V) : o.oangle y x = -o.oangle x y := by
simp only [oangle, o.kahler_swap y x, Complex.arg_conj_coe_angle]
/-- Adding the angles between two vectors in each order results in 0. -/
@[simp]
theorem oangle_add_oangle_rev (x y : V) : o.oangle x y + o.oangle y x = 0 := by
simp [o.oangle_rev y x]
/-- Negating the first vector passed to `oangle` adds `π` to the angle. -/
theorem oangle_neg_left {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle (-x) y = o.oangle x y + π := by
simp only [oangle, map_neg]
convert Complex.arg_neg_coe_angle _
exact o.kahler_ne_zero hx hy
/-- Negating the second vector passed to `oangle` adds `π` to the angle. -/
theorem oangle_neg_right {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle x (-y) = o.oangle x y + π := by
simp only [oangle, map_neg]
convert Complex.arg_neg_coe_angle _
exact o.kahler_ne_zero hx hy
/-- Negating the first vector passed to `oangle` does not change twice the angle. -/
@[simp]
theorem two_zsmul_oangle_neg_left (x y : V) :
(2 : ℤ) • o.oangle (-x) y = (2 : ℤ) • o.oangle x y := by
by_cases hx : x = 0
· simp [hx]
· by_cases hy : y = 0
· simp [hy]
· simp [o.oangle_neg_left hx hy]
/-- Negating the second vector passed to `oangle` does not change twice the angle. -/
@[simp]
theorem two_zsmul_oangle_neg_right (x y : V) :
(2 : ℤ) • o.oangle x (-y) = (2 : ℤ) • o.oangle x y := by
by_cases hx : x = 0
· simp [hx]
· by_cases hy : y = 0
· simp [hy]
· simp [o.oangle_neg_right hx hy]
/-- Negating both vectors passed to `oangle` does not change the angle. -/
@[simp]
theorem oangle_neg_neg (x y : V) : o.oangle (-x) (-y) = o.oangle x y := by simp [oangle]
/-- Negating the first vector produces the same angle as negating the second vector. -/
theorem oangle_neg_left_eq_neg_right (x y : V) : o.oangle (-x) y = o.oangle x (-y) := by
rw [← neg_neg y, oangle_neg_neg, neg_neg]
/-- The angle between the negation of a nonzero vector and that vector is `π`. -/
@[simp]
theorem oangle_neg_self_left {x : V} (hx : x ≠ 0) : o.oangle (-x) x = π := by
simp [oangle_neg_left, hx]
/-- The angle between a nonzero vector and its negation is `π`. -/
@[simp]
theorem oangle_neg_self_right {x : V} (hx : x ≠ 0) : o.oangle x (-x) = π := by
simp [oangle_neg_right, hx]
/-- Twice the angle between the negation of a vector and that vector is 0. -/
theorem two_zsmul_oangle_neg_self_left (x : V) : (2 : ℤ) • o.oangle (-x) x = 0 := by
by_cases hx : x = 0 <;> simp [hx]
/-- Twice the angle between a vector and its negation is 0. -/
theorem two_zsmul_oangle_neg_self_right (x : V) : (2 : ℤ) • o.oangle x (-x) = 0 := by
by_cases hx : x = 0 <;> simp [hx]
/-- Adding the angles between two vectors in each order, with the first vector in each angle
negated, results in 0. -/
@[simp]
theorem oangle_add_oangle_rev_neg_left (x y : V) : o.oangle (-x) y + o.oangle (-y) x = 0 := by
rw [oangle_neg_left_eq_neg_right, oangle_rev, neg_add_cancel]
/-- Adding the angles between two vectors in each order, with the second vector in each angle
negated, results in 0. -/
@[simp]
theorem oangle_add_oangle_rev_neg_right (x y : V) : o.oangle x (-y) + o.oangle y (-x) = 0 := by
rw [o.oangle_rev (-x), oangle_neg_left_eq_neg_right, add_neg_cancel]
/-- Multiplying the first vector passed to `oangle` by a positive real does not change the
angle. -/
@[simp]
theorem oangle_smul_left_of_pos (x y : V) {r : ℝ} (hr : 0 < r) :
o.oangle (r • x) y = o.oangle x y := by simp [oangle, Complex.arg_real_mul _ hr]
/-- Multiplying the second vector passed to `oangle` by a positive real does not change the
angle. -/
@[simp]
theorem oangle_smul_right_of_pos (x y : V) {r : ℝ} (hr : 0 < r) :
o.oangle x (r • y) = o.oangle x y := by simp [oangle, Complex.arg_real_mul _ hr]
/-- Multiplying the first vector passed to `oangle` by a negative real produces the same angle
as negating that vector. -/
@[simp]
theorem oangle_smul_left_of_neg (x y : V) {r : ℝ} (hr : r < 0) :
o.oangle (r • x) y = o.oangle (-x) y := by
rw [← neg_neg r, neg_smul, ← smul_neg, o.oangle_smul_left_of_pos _ _ (neg_pos_of_neg hr)]
/-- Multiplying the second vector passed to `oangle` by a negative real produces the same angle
as negating that vector. -/
@[simp]
theorem oangle_smul_right_of_neg (x y : V) {r : ℝ} (hr : r < 0) :
o.oangle x (r • y) = o.oangle x (-y) := by
rw [← neg_neg r, neg_smul, ← smul_neg, o.oangle_smul_right_of_pos _ _ (neg_pos_of_neg hr)]
/-- The angle between a nonnegative multiple of a vector and that vector is 0. -/
@[simp]
theorem oangle_smul_left_self_of_nonneg (x : V) {r : ℝ} (hr : 0 ≤ r) : o.oangle (r • x) x = 0 := by
rcases hr.lt_or_eq with (h | h)
· simp [h]
· simp [h.symm]
/-- The angle between a vector and a nonnegative multiple of that vector is 0. -/
@[simp]
theorem oangle_smul_right_self_of_nonneg (x : V) {r : ℝ} (hr : 0 ≤ r) : o.oangle x (r • x) = 0 := by
rcases hr.lt_or_eq with (h | h)
· simp [h]
· simp [h.symm]
/-- The angle between two nonnegative multiples of the same vector is 0. -/
@[simp]
theorem oangle_smul_smul_self_of_nonneg (x : V) {r₁ r₂ : ℝ} (hr₁ : 0 ≤ r₁) (hr₂ : 0 ≤ r₂) :
o.oangle (r₁ • x) (r₂ • x) = 0 := by
rcases hr₁.lt_or_eq with (h | h)
· simp [h, hr₂]
· simp [h.symm]
/-- Multiplying the first vector passed to `oangle` by a nonzero real does not change twice the
angle. -/
@[simp]
theorem two_zsmul_oangle_smul_left_of_ne_zero (x y : V) {r : ℝ} (hr : r ≠ 0) :
(2 : ℤ) • o.oangle (r • x) y = (2 : ℤ) • o.oangle x y := by
rcases hr.lt_or_lt with (h | h) <;> simp [h]
/-- Multiplying the second vector passed to `oangle` by a nonzero real does not change twice the
angle. -/
@[simp]
theorem two_zsmul_oangle_smul_right_of_ne_zero (x y : V) {r : ℝ} (hr : r ≠ 0) :
(2 : ℤ) • o.oangle x (r • y) = (2 : ℤ) • o.oangle x y := by
rcases hr.lt_or_lt with (h | h) <;> simp [h]
/-- Twice the angle between a multiple of a vector and that vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_left_self (x : V) {r : ℝ} : (2 : ℤ) • o.oangle (r • x) x = 0 := by
rcases lt_or_le r 0 with (h | h) <;> simp [h]
/-- Twice the angle between a vector and a multiple of that vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_right_self (x : V) {r : ℝ} : (2 : ℤ) • o.oangle x (r • x) = 0 := by
rcases lt_or_le r 0 with (h | h) <;> simp [h]
/-- Twice the angle between two multiples of a vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_smul_self (x : V) {r₁ r₂ : ℝ} :
(2 : ℤ) • o.oangle (r₁ • x) (r₂ • x) = 0 := by by_cases h : r₁ = 0 <;> simp [h]
/-- If the spans of two vectors are equal, twice angles with those vectors on the left are
equal. -/
theorem two_zsmul_oangle_left_of_span_eq {x y : V} (z : V) (h : (ℝ ∙ x) = ℝ ∙ y) :
(2 : ℤ) • o.oangle x z = (2 : ℤ) • o.oangle y z := by
rw [Submodule.span_singleton_eq_span_singleton] at h
rcases h with ⟨r, rfl⟩
exact (o.two_zsmul_oangle_smul_left_of_ne_zero _ _ (Units.ne_zero _)).symm
/-- If the spans of two vectors are equal, twice angles with those vectors on the right are
equal. -/
theorem two_zsmul_oangle_right_of_span_eq (x : V) {y z : V} (h : (ℝ ∙ y) = ℝ ∙ z) :
(2 : ℤ) • o.oangle x y = (2 : ℤ) • o.oangle x z := by
rw [Submodule.span_singleton_eq_span_singleton] at h
rcases h with ⟨r, rfl⟩
exact (o.two_zsmul_oangle_smul_right_of_ne_zero _ _ (Units.ne_zero _)).symm
/-- If the spans of two pairs of vectors are equal, twice angles between those vectors are
equal. -/
theorem two_zsmul_oangle_of_span_eq_of_span_eq {w x y z : V} (hwx : (ℝ ∙ w) = ℝ ∙ x)
(hyz : (ℝ ∙ y) = ℝ ∙ z) : (2 : ℤ) • o.oangle w y = (2 : ℤ) • o.oangle x z := by
rw [o.two_zsmul_oangle_left_of_span_eq y hwx, o.two_zsmul_oangle_right_of_span_eq x hyz]
/-- The oriented angle between two vectors is zero if and only if the angle with the vectors
swapped is zero. -/
theorem oangle_eq_zero_iff_oangle_rev_eq_zero {x y : V} : o.oangle x y = 0 ↔ o.oangle y x = 0 := by
rw [oangle_rev, neg_eq_zero]
/-- The oriented angle between two vectors is zero if and only if they are on the same ray. -/
theorem oangle_eq_zero_iff_sameRay {x y : V} : o.oangle x y = 0 ↔ SameRay ℝ x y := by
rw [oangle, kahler_apply_apply, Complex.arg_coe_angle_eq_iff_eq_toReal, Real.Angle.toReal_zero,
Complex.arg_eq_zero_iff]
simpa using o.nonneg_inner_and_areaForm_eq_zero_iff_sameRay x y
/-- The oriented angle between two vectors is `π` if and only if the angle with the vectors
swapped is `π`. -/
theorem oangle_eq_pi_iff_oangle_rev_eq_pi {x y : V} : o.oangle x y = π ↔ o.oangle y x = π := by
rw [oangle_rev, neg_eq_iff_eq_neg, Real.Angle.neg_coe_pi]
/-- The oriented angle between two vectors is `π` if and only they are nonzero and the first is
on the same ray as the negation of the second. -/
theorem oangle_eq_pi_iff_sameRay_neg {x y : V} :
o.oangle x y = π ↔ x ≠ 0 ∧ y ≠ 0 ∧ SameRay ℝ x (-y) := by
rw [← o.oangle_eq_zero_iff_sameRay]
constructor
· intro h
by_cases hx : x = 0; · simp [hx, Real.Angle.pi_ne_zero.symm] at h
by_cases hy : y = 0; · simp [hy, Real.Angle.pi_ne_zero.symm] at h
refine ⟨hx, hy, ?_⟩
rw [o.oangle_neg_right hx hy, h, Real.Angle.coe_pi_add_coe_pi]
· rintro ⟨hx, hy, h⟩
rwa [o.oangle_neg_right hx hy, ← Real.Angle.sub_coe_pi_eq_add_coe_pi, sub_eq_zero] at h
/-- The oriented angle between two vectors is zero or `π` if and only if those two vectors are
not linearly independent. -/
theorem oangle_eq_zero_or_eq_pi_iff_not_linearIndependent {x y : V} :
o.oangle x y = 0 ∨ o.oangle x y = π ↔ ¬LinearIndependent ℝ ![x, y] := by
rw [oangle_eq_zero_iff_sameRay, oangle_eq_pi_iff_sameRay_neg,
sameRay_or_ne_zero_and_sameRay_neg_iff_not_linearIndependent]
/-- The oriented angle between two vectors is zero or `π` if and only if the first vector is zero
or the second is a multiple of the first. -/
theorem oangle_eq_zero_or_eq_pi_iff_right_eq_smul {x y : V} :
o.oangle x y = 0 ∨ o.oangle x y = π ↔ x = 0 ∨ ∃ r : ℝ, y = r • x := by
rw [oangle_eq_zero_iff_sameRay, oangle_eq_pi_iff_sameRay_neg]
refine ⟨fun h => ?_, fun h => ?_⟩
· rcases h with (h | ⟨-, -, h⟩)
· by_cases hx : x = 0; · simp [hx]
obtain ⟨r, -, rfl⟩ := h.exists_nonneg_left hx
exact Or.inr ⟨r, rfl⟩
· by_cases hx : x = 0; · simp [hx]
obtain ⟨r, -, hy⟩ := h.exists_nonneg_left hx
refine Or.inr ⟨-r, ?_⟩
simp [hy]
· rcases h with (rfl | ⟨r, rfl⟩); · simp
by_cases hx : x = 0; · simp [hx]
rcases lt_trichotomy r 0 with (hr | hr | hr)
· rw [← neg_smul]
exact Or.inr ⟨hx, smul_ne_zero hr.ne hx,
SameRay.sameRay_pos_smul_right x (Left.neg_pos_iff.2 hr)⟩
· simp [hr]
· exact Or.inl (SameRay.sameRay_pos_smul_right x hr)
/-- The oriented angle between two vectors is not zero or `π` if and only if those two vectors
are linearly independent. -/
theorem oangle_ne_zero_and_ne_pi_iff_linearIndependent {x y : V} :
o.oangle x y ≠ 0 ∧ o.oangle x y ≠ π ↔ LinearIndependent ℝ ![x, y] := by
rw [← not_or, ← not_iff_not, Classical.not_not,
oangle_eq_zero_or_eq_pi_iff_not_linearIndependent]
/-- Two vectors are equal if and only if they have equal norms and zero angle between them. -/
theorem eq_iff_norm_eq_and_oangle_eq_zero (x y : V) : x = y ↔ ‖x‖ = ‖y‖ ∧ o.oangle x y = 0 := by
rw [oangle_eq_zero_iff_sameRay]
constructor
· rintro rfl
simp; rfl
· rcases eq_or_ne y 0 with (rfl | hy)
· simp
rintro ⟨h₁, h₂⟩
obtain ⟨r, hr, rfl⟩ := h₂.exists_nonneg_right hy
have : ‖y‖ ≠ 0 := by simpa using hy
obtain rfl : r = 1 := by
apply mul_right_cancel₀ this
simpa [norm_smul, abs_of_nonneg hr] using h₁
simp
/-- Two vectors with equal norms are equal if and only if they have zero angle between them. -/
theorem eq_iff_oangle_eq_zero_of_norm_eq {x y : V} (h : ‖x‖ = ‖y‖) : x = y ↔ o.oangle x y = 0 :=
⟨fun he => ((o.eq_iff_norm_eq_and_oangle_eq_zero x y).1 he).2, fun ha =>
(o.eq_iff_norm_eq_and_oangle_eq_zero x y).2 ⟨h, ha⟩⟩
/-- Two vectors with zero angle between them are equal if and only if they have equal norms. -/
theorem eq_iff_norm_eq_of_oangle_eq_zero {x y : V} (h : o.oangle x y = 0) : x = y ↔ ‖x‖ = ‖y‖ :=
⟨fun he => ((o.eq_iff_norm_eq_and_oangle_eq_zero x y).1 he).1, fun hn =>
(o.eq_iff_norm_eq_and_oangle_eq_zero x y).2 ⟨hn, h⟩⟩
/-- Given three nonzero vectors, the angle between the first and the second plus the angle
between the second and the third equals the angle between the first and the third. -/
@[simp]
theorem oangle_add {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x y + o.oangle y z = o.oangle x z := by
simp_rw [oangle]
rw [← Complex.arg_mul_coe_angle, o.kahler_mul y x z]
· congr 1
exact mod_cast Complex.arg_real_mul _ (by positivity : 0 < ‖y‖ ^ 2)
· exact o.kahler_ne_zero hx hy
· exact o.kahler_ne_zero hy hz
/-- Given three nonzero vectors, the angle between the second and the third plus the angle
between the first and the second equals the angle between the first and the third. -/
@[simp]
theorem oangle_add_swap {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle y z + o.oangle x y = o.oangle x z := by rw [add_comm, o.oangle_add hx hy hz]
/-- Given three nonzero vectors, the angle between the first and the third minus the angle
between the first and the second equals the angle between the second and the third. -/
@[simp]
theorem oangle_sub_left {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x z - o.oangle x y = o.oangle y z := by
rw [sub_eq_iff_eq_add, o.oangle_add_swap hx hy hz]
/-- Given three nonzero vectors, the angle between the first and the third minus the angle
between the second and the third equals the angle between the first and the second. -/
@[simp]
theorem oangle_sub_right {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x z - o.oangle y z = o.oangle x y := by rw [sub_eq_iff_eq_add, o.oangle_add hx hy hz]
/-- Given three nonzero vectors, adding the angles between them in cyclic order results in 0. -/
@[simp]
theorem oangle_add_cyc3 {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x y + o.oangle y z + o.oangle z x = 0 := by simp [hx, hy, hz]
/-- Given three nonzero vectors, adding the angles between them in cyclic order, with the first
vector in each angle negated, results in π. If the vectors add to 0, this is a version of the
sum of the angles of a triangle. -/
@[simp]
theorem oangle_add_cyc3_neg_left {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle (-x) y + o.oangle (-y) z + o.oangle (-z) x = π := by
rw [o.oangle_neg_left hx hy, o.oangle_neg_left hy hz, o.oangle_neg_left hz hx,
show o.oangle x y + π + (o.oangle y z + π) + (o.oangle z x + π) =
o.oangle x y + o.oangle y z + o.oangle z x + (π + π + π : Real.Angle) by abel,
o.oangle_add_cyc3 hx hy hz, Real.Angle.coe_pi_add_coe_pi, zero_add, zero_add]
/-- Given three nonzero vectors, adding the angles between them in cyclic order, with the second
vector in each angle negated, results in π. If the vectors add to 0, this is a version of the
sum of the angles of a triangle. -/
@[simp]
theorem oangle_add_cyc3_neg_right {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x (-y) + o.oangle y (-z) + o.oangle z (-x) = π := by
simp_rw [← oangle_neg_left_eq_neg_right, o.oangle_add_cyc3_neg_left hx hy hz]
/-- Pons asinorum, oriented vector angle form. -/
theorem oangle_sub_eq_oangle_sub_rev_of_norm_eq {x y : V} (h : ‖x‖ = ‖y‖) :
o.oangle x (x - y) = o.oangle (y - x) y := by simp [oangle, h]
/-- The angle at the apex of an isosceles triangle is `π` minus twice a base angle, oriented
vector angle form. -/
theorem oangle_eq_pi_sub_two_zsmul_oangle_sub_of_norm_eq {x y : V} (hn : x ≠ y) (h : ‖x‖ = ‖y‖) :
o.oangle y x = π - (2 : ℤ) • o.oangle (y - x) y := by
rw [two_zsmul]
nth_rw 1 [← o.oangle_sub_eq_oangle_sub_rev_of_norm_eq h]
rw [eq_sub_iff_add_eq, ← oangle_neg_neg, ← add_assoc]
have hy : y ≠ 0 := by
rintro rfl
rw [norm_zero, norm_eq_zero] at h
exact hn h
have hx : x ≠ 0 := norm_ne_zero_iff.1 (h.symm ▸ norm_ne_zero_iff.2 hy)
convert o.oangle_add_cyc3_neg_right (neg_ne_zero.2 hy) hx (sub_ne_zero_of_ne hn.symm) using 1
simp
/-- The angle between two vectors, with respect to an orientation given by `Orientation.map`
with a linear isometric equivalence, equals the angle between those two vectors, transformed by
the inverse of that equivalence, with respect to the original orientation. -/
@[simp]
theorem oangle_map (x y : V') (f : V ≃ₗᵢ[ℝ] V') :
(Orientation.map (Fin 2) f.toLinearEquiv o).oangle x y = o.oangle (f.symm x) (f.symm y) := by
simp [oangle, o.kahler_map]
@[simp]
protected theorem _root_.Complex.oangle (w z : ℂ) :
Complex.orientation.oangle w z = Complex.arg (conj w * z) := by
simp [oangle, mul_comm z]
/-- The oriented angle on an oriented real inner product space of dimension 2 can be evaluated in
terms of a complex-number representation of the space. -/
theorem oangle_map_complex (f : V ≃ₗᵢ[ℝ] ℂ)
(hf : Orientation.map (Fin 2) f.toLinearEquiv o = Complex.orientation) (x y : V) :
o.oangle x y = Complex.arg (conj (f x) * f y) := by
rw [← Complex.oangle, ← hf, o.oangle_map]
iterate 2 rw [LinearIsometryEquiv.symm_apply_apply]
/-- Negating the orientation negates the value of `oangle`. -/
theorem oangle_neg_orientation_eq_neg (x y : V) : (-o).oangle x y = -o.oangle x y := by
simp [oangle]
/-- The inner product of two vectors is the product of the norms and the cosine of the oriented
angle between the vectors. -/
theorem inner_eq_norm_mul_norm_mul_cos_oangle (x y : V) :
⟪x, y⟫ = ‖x‖ * ‖y‖ * Real.Angle.cos (o.oangle x y) := by
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0; · simp [hy]
rw [oangle, Real.Angle.cos_coe, Complex.cos_arg, o.norm_kahler]
· simp only [kahler_apply_apply, real_smul, add_re, ofReal_re, mul_re, I_re, ofReal_im]
field_simp
· exact o.kahler_ne_zero hx hy
/-- The cosine of the oriented angle between two nonzero vectors is the inner product divided by
the product of the norms. -/
theorem cos_oangle_eq_inner_div_norm_mul_norm {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
Real.Angle.cos (o.oangle x y) = ⟪x, y⟫ / (‖x‖ * ‖y‖) := by
rw [o.inner_eq_norm_mul_norm_mul_cos_oangle]
field_simp [norm_ne_zero_iff.2 hx, norm_ne_zero_iff.2 hy]
/-- The cosine of the oriented angle between two nonzero vectors equals that of the unoriented
angle. -/
theorem cos_oangle_eq_cos_angle {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
Real.Angle.cos (o.oangle x y) = Real.cos (InnerProductGeometry.angle x y) := by
rw [o.cos_oangle_eq_inner_div_norm_mul_norm hx hy, InnerProductGeometry.cos_angle]
/-- The oriented angle between two nonzero vectors is plus or minus the unoriented angle. -/
theorem oangle_eq_angle_or_eq_neg_angle {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle x y = InnerProductGeometry.angle x y ∨
o.oangle x y = -InnerProductGeometry.angle x y :=
Real.Angle.cos_eq_real_cos_iff_eq_or_eq_neg.1 <| o.cos_oangle_eq_cos_angle hx hy
/-- The unoriented angle between two nonzero vectors is the absolute value of the oriented angle,
converted to a real. -/
theorem angle_eq_abs_oangle_toReal {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
InnerProductGeometry.angle x y = |(o.oangle x y).toReal| := by
have h0 := InnerProductGeometry.angle_nonneg x y
have hpi := InnerProductGeometry.angle_le_pi x y
rcases o.oangle_eq_angle_or_eq_neg_angle hx hy with (h | h)
· rw [h, eq_comm, Real.Angle.abs_toReal_coe_eq_self_iff]
exact ⟨h0, hpi⟩
· rw [h, eq_comm, Real.Angle.abs_toReal_neg_coe_eq_self_iff]
exact ⟨h0, hpi⟩
/-- If the sign of the oriented angle between two vectors is zero, either one of the vectors is
zero or the unoriented angle is 0 or π. -/
theorem eq_zero_or_angle_eq_zero_or_pi_of_sign_oangle_eq_zero {x y : V}
(h : (o.oangle x y).sign = 0) :
x = 0 ∨ y = 0 ∨ InnerProductGeometry.angle x y = 0 ∨ InnerProductGeometry.angle x y = π := by
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0; · simp [hy]
rw [o.angle_eq_abs_oangle_toReal hx hy]
rw [Real.Angle.sign_eq_zero_iff] at h
rcases h with (h | h) <;> simp [h, Real.pi_pos.le]
/-- If two unoriented angles are equal, and the signs of the corresponding oriented angles are
equal, then the oriented angles are equal (even in degenerate cases). -/
theorem oangle_eq_of_angle_eq_of_sign_eq {w x y z : V}
(h : InnerProductGeometry.angle w x = InnerProductGeometry.angle y z)
(hs : (o.oangle w x).sign = (o.oangle y z).sign) : o.oangle w x = o.oangle y z := by
by_cases h0 : (w = 0 ∨ x = 0) ∨ y = 0 ∨ z = 0
· have hs' : (o.oangle w x).sign = 0 ∧ (o.oangle y z).sign = 0 := by
rcases h0 with ((rfl | rfl) | rfl | rfl)
· simpa using hs.symm
· simpa using hs.symm
· simpa using hs
· simpa using hs
rcases hs' with ⟨hswx, hsyz⟩
have h' : InnerProductGeometry.angle w x = π / 2 ∧ InnerProductGeometry.angle y z = π / 2 := by
rcases h0 with ((rfl | rfl) | rfl | rfl)
· simpa using h.symm
· simpa using h.symm
· simpa using h
· simpa using h
rcases h' with ⟨hwx, hyz⟩
have hpi : π / 2 ≠ π := by
intro hpi
rw [div_eq_iff, eq_comm, ← sub_eq_zero, mul_two, add_sub_cancel_right] at hpi
· exact Real.pi_pos.ne.symm hpi
· exact two_ne_zero
have h0wx : w = 0 ∨ x = 0 := by
have h0' := o.eq_zero_or_angle_eq_zero_or_pi_of_sign_oangle_eq_zero hswx
simpa [hwx, Real.pi_pos.ne.symm, hpi] using h0'
have h0yz : y = 0 ∨ z = 0 := by
have h0' := o.eq_zero_or_angle_eq_zero_or_pi_of_sign_oangle_eq_zero hsyz
simpa [hyz, Real.pi_pos.ne.symm, hpi] using h0'
rcases h0wx with (h0wx | h0wx) <;> rcases h0yz with (h0yz | h0yz) <;> simp [h0wx, h0yz]
· push_neg at h0
rw [Real.Angle.eq_iff_abs_toReal_eq_of_sign_eq hs]
rwa [o.angle_eq_abs_oangle_toReal h0.1.1 h0.1.2,
o.angle_eq_abs_oangle_toReal h0.2.1 h0.2.2] at h
/-- If the signs of two oriented angles between nonzero vectors are equal, the oriented angles are
equal if and only if the unoriented angles are equal. -/
theorem angle_eq_iff_oangle_eq_of_sign_eq {w x y z : V} (hw : w ≠ 0) (hx : x ≠ 0) (hy : y ≠ 0)
(hz : z ≠ 0) (hs : (o.oangle w x).sign = (o.oangle y z).sign) :
InnerProductGeometry.angle w x = InnerProductGeometry.angle y z ↔
o.oangle w x = o.oangle y z := by
refine ⟨fun h => o.oangle_eq_of_angle_eq_of_sign_eq h hs, fun h => ?_⟩
rw [o.angle_eq_abs_oangle_toReal hw hx, o.angle_eq_abs_oangle_toReal hy hz, h]
/-- The oriented angle between two vectors equals the unoriented angle if the sign is positive. -/
theorem oangle_eq_angle_of_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) :
o.oangle x y = InnerProductGeometry.angle x y := by
by_cases hx : x = 0; · exfalso; simp [hx] at h
by_cases hy : y = 0; · exfalso; simp [hy] at h
refine (o.oangle_eq_angle_or_eq_neg_angle hx hy).resolve_right ?_
intro hxy
rw [hxy, Real.Angle.sign_neg, neg_eq_iff_eq_neg, ← SignType.neg_iff, ← not_le] at h
exact h (Real.Angle.sign_coe_nonneg_of_nonneg_of_le_pi (InnerProductGeometry.angle_nonneg _ _)
(InnerProductGeometry.angle_le_pi _ _))
/-- The oriented angle between two vectors equals minus the unoriented angle if the sign is
negative. -/
theorem oangle_eq_neg_angle_of_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) :
o.oangle x y = -InnerProductGeometry.angle x y := by
by_cases hx : x = 0; · exfalso; simp [hx] at h
by_cases hy : y = 0; · exfalso; simp [hy] at h
refine (o.oangle_eq_angle_or_eq_neg_angle hx hy).resolve_left ?_
intro hxy
rw [hxy, ← SignType.neg_iff, ← not_le] at h
exact h (Real.Angle.sign_coe_nonneg_of_nonneg_of_le_pi (InnerProductGeometry.angle_nonneg _ _)
(InnerProductGeometry.angle_le_pi _ _))
/-- The oriented angle between two nonzero vectors is zero if and only if the unoriented angle
is zero. -/
theorem oangle_eq_zero_iff_angle_eq_zero {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle x y = 0 ↔ InnerProductGeometry.angle x y = 0 := by
refine ⟨fun h => ?_, fun h => ?_⟩
· simpa [o.angle_eq_abs_oangle_toReal hx hy]
· have ha := o.oangle_eq_angle_or_eq_neg_angle hx hy
rw [h] at ha
simpa using ha
/-- The oriented angle between two vectors is `π` if and only if the unoriented angle is `π`. -/
theorem oangle_eq_pi_iff_angle_eq_pi {x y : V} :
o.oangle x y = π ↔ InnerProductGeometry.angle x y = π := by
by_cases hx : x = 0
· simp [hx, Real.Angle.pi_ne_zero.symm, div_eq_mul_inv, mul_right_eq_self₀, not_or,
Real.pi_ne_zero]
by_cases hy : y = 0
· simp [hy, Real.Angle.pi_ne_zero.symm, div_eq_mul_inv, mul_right_eq_self₀, not_or,
Real.pi_ne_zero]
refine ⟨fun h => ?_, fun h => ?_⟩
· rw [o.angle_eq_abs_oangle_toReal hx hy, h]
simp [Real.pi_pos.le]
· have ha := o.oangle_eq_angle_or_eq_neg_angle hx hy
rw [h] at ha
simpa using ha
/-- One of two vectors is zero or the oriented angle between them is plus or minus `π / 2` if
and only if the inner product of those vectors is zero. -/
theorem eq_zero_or_oangle_eq_iff_inner_eq_zero {x y : V} :
x = 0 ∨ y = 0 ∨ o.oangle x y = (π / 2 : ℝ) ∨ o.oangle x y = (-π / 2 : ℝ) ↔ ⟪x, y⟫ = 0 := by
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0; · simp [hy]
rw [InnerProductGeometry.inner_eq_zero_iff_angle_eq_pi_div_two, or_iff_right hx, or_iff_right hy]
refine ⟨fun h => ?_, fun h => ?_⟩
· rwa [o.angle_eq_abs_oangle_toReal hx hy, Real.Angle.abs_toReal_eq_pi_div_two_iff]
· convert o.oangle_eq_angle_or_eq_neg_angle hx hy using 2 <;> rw [h]
simp only [neg_div, Real.Angle.coe_neg]
/-- If the oriented angle between two vectors is `π / 2`, the inner product of those vectors
is zero. -/
theorem inner_eq_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) :
⟪x, y⟫ = 0 :=
o.eq_zero_or_oangle_eq_iff_inner_eq_zero.1 <| Or.inr <| Or.inr <| Or.inl h
/-- If the oriented angle between two vectors is `π / 2`, the inner product of those vectors
(reversed) is zero. -/
theorem inner_rev_eq_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) :
⟪y, x⟫ = 0 := by rw [real_inner_comm, o.inner_eq_zero_of_oangle_eq_pi_div_two h]
/-- If the oriented angle between two vectors is `-π / 2`, the inner product of those vectors
is zero. -/
theorem inner_eq_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
⟪x, y⟫ = 0 :=
o.eq_zero_or_oangle_eq_iff_inner_eq_zero.1 <| Or.inr <| Or.inr <| Or.inr h
/-- If the oriented angle between two vectors is `-π / 2`, the inner product of those vectors
(reversed) is zero. -/
theorem inner_rev_eq_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
⟪y, x⟫ = 0 := by rw [real_inner_comm, o.inner_eq_zero_of_oangle_eq_neg_pi_div_two h]
/-- Negating the first vector passed to `oangle` negates the sign of the angle. -/
@[simp]
theorem oangle_sign_neg_left (x y : V) : (o.oangle (-x) y).sign = -(o.oangle x y).sign := by
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0; · simp [hy]
rw [o.oangle_neg_left hx hy, Real.Angle.sign_add_pi]
/-- Negating the second vector passed to `oangle` negates the sign of the angle. -/
@[simp]
theorem oangle_sign_neg_right (x y : V) : (o.oangle x (-y)).sign = -(o.oangle x y).sign := by
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0; · simp [hy]
rw [o.oangle_neg_right hx hy, Real.Angle.sign_add_pi]
/-- Multiplying the first vector passed to `oangle` by a real multiplies the sign of the angle by
the sign of the real. -/
@[simp]
theorem oangle_sign_smul_left (x y : V) (r : ℝ) :
(o.oangle (r • x) y).sign = SignType.sign r * (o.oangle x y).sign := by
rcases lt_trichotomy r 0 with (h | h | h) <;> simp [h]
/-- Multiplying the second vector passed to `oangle` by a real multiplies the sign of the angle by
the sign of the real. -/
@[simp]
theorem oangle_sign_smul_right (x y : V) (r : ℝ) :
(o.oangle x (r • y)).sign = SignType.sign r * (o.oangle x y).sign := by
rcases lt_trichotomy r 0 with (h | h | h) <;> simp [h]
/-- Auxiliary lemma for the proof of `oangle_sign_smul_add_right`; not intended to be used
outside of that proof. -/
theorem oangle_smul_add_right_eq_zero_or_eq_pi_iff {x y : V} (r : ℝ) :
o.oangle x (r • x + y) = 0 ∨ o.oangle x (r • x + y) = π ↔
o.oangle x y = 0 ∨ o.oangle x y = π := by
simp_rw [oangle_eq_zero_or_eq_pi_iff_not_linearIndependent, Fintype.not_linearIndependent_iff,
Fin.sum_univ_two, Fin.exists_fin_two]
refine ⟨fun h => ?_, fun h => ?_⟩
· rcases h with ⟨m, h, hm⟩
change m 0 • x + m 1 • (r • x + y) = 0 at h
refine ⟨![m 0 + m 1 * r, m 1], ?_⟩
change (m 0 + m 1 * r) • x + m 1 • y = 0 ∧ (m 0 + m 1 * r ≠ 0 ∨ m 1 ≠ 0)
rw [smul_add, smul_smul, ← add_assoc, ← add_smul] at h
refine ⟨h, not_and_or.1 fun h0 => ?_⟩
obtain ⟨h0, h1⟩ := h0
rw [h1] at h0 hm
rw [zero_mul, add_zero] at h0
simp [h0] at hm
· rcases h with ⟨m, h, hm⟩
change m 0 • x + m 1 • y = 0 at h
refine ⟨![m 0 - m 1 * r, m 1], ?_⟩
change (m 0 - m 1 * r) • x + m 1 • (r • x + y) = 0 ∧ (m 0 - m 1 * r ≠ 0 ∨ m 1 ≠ 0)
rw [sub_smul, smul_add, smul_smul, ← add_assoc, sub_add_cancel]
refine ⟨h, not_and_or.1 fun h0 => ?_⟩
obtain ⟨h0, h1⟩ := h0
rw [h1] at h0 hm
rw [zero_mul, sub_zero] at h0
simp [h0] at hm
/-- Adding a multiple of the first vector passed to `oangle` to the second vector does not change
the sign of the angle. -/
@[simp]
theorem oangle_sign_smul_add_right (x y : V) (r : ℝ) :
(o.oangle x (r • x + y)).sign = (o.oangle x y).sign := by
by_cases h : o.oangle x y = 0 ∨ o.oangle x y = π
· rwa [Real.Angle.sign_eq_zero_iff.2 h, Real.Angle.sign_eq_zero_iff,
oangle_smul_add_right_eq_zero_or_eq_pi_iff]
have h' : ∀ r' : ℝ, o.oangle x (r' • x + y) ≠ 0 ∧ o.oangle x (r' • x + y) ≠ π := by
intro r'
rwa [← o.oangle_smul_add_right_eq_zero_or_eq_pi_iff r', not_or] at h
let s : Set (V × V) := (fun r' : ℝ => (x, r' • x + y)) '' Set.univ
have hc : IsConnected s := isConnected_univ.image _ (by fun_prop)
have hf : ContinuousOn (fun z : V × V => o.oangle z.1 z.2) s := by
refine continuousOn_of_forall_continuousAt fun z hz => o.continuousAt_oangle ?_ ?_
all_goals
simp_rw [s, Set.mem_image] at hz
obtain ⟨r', -, rfl⟩ := hz
simp only [Prod.fst, Prod.snd]
intro hz
· simpa [hz] using (h' 0).1
· simpa [hz] using (h' r').1
have hs : ∀ z : V × V, z ∈ s → o.oangle z.1 z.2 ≠ 0 ∧ o.oangle z.1 z.2 ≠ π := by
intro z hz
simp_rw [s, Set.mem_image] at hz
obtain ⟨r', -, rfl⟩ := hz
exact h' r'
have hx : (x, y) ∈ s := by
convert Set.mem_image_of_mem (fun r' : ℝ => (x, r' • x + y)) (Set.mem_univ 0)
simp
have hy : (x, r • x + y) ∈ s := Set.mem_image_of_mem _ (Set.mem_univ _)
convert Real.Angle.sign_eq_of_continuousOn hc hf hs hx hy
/-- Adding a multiple of the second vector passed to `oangle` to the first vector does not change
the sign of the angle. -/
@[simp]
theorem oangle_sign_add_smul_left (x y : V) (r : ℝ) :
(o.oangle (x + r • y) y).sign = (o.oangle x y).sign := by
simp_rw [o.oangle_rev y, Real.Angle.sign_neg, add_comm x, oangle_sign_smul_add_right]
/-- Subtracting a multiple of the first vector passed to `oangle` from the second vector does
not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_smul_right (x y : V) (r : ℝ) :
(o.oangle x (y - r • x)).sign = (o.oangle x y).sign := by
rw [sub_eq_add_neg, ← neg_smul, add_comm, oangle_sign_smul_add_right]
/-- Subtracting a multiple of the second vector passed to `oangle` from the first vector does
not change the sign of the angle. -/
@[simp]
theorem oangle_sign_sub_smul_left (x y : V) (r : ℝ) :
(o.oangle (x - r • y) y).sign = (o.oangle x y).sign := by
rw [sub_eq_add_neg, ← neg_smul, oangle_sign_add_smul_left]
/-- Adding the first vector passed to `oangle` to the second vector does not change the sign of
the angle. -/
@[simp]
theorem oangle_sign_add_right (x y : V) : (o.oangle x (x + y)).sign = (o.oangle x y).sign := by
rw [← o.oangle_sign_smul_add_right x y 1, one_smul]
/-- Adding the second vector passed to `oangle` to the first vector does not change the sign of
the angle. -/
@[simp]
theorem oangle_sign_add_left (x y : V) : (o.oangle (x + y) y).sign = (o.oangle x y).sign := by
| rw [← o.oangle_sign_add_smul_left x y 1, one_smul]
/-- Subtracting the first vector passed to `oangle` from the second vector does not change the
| Mathlib/Geometry/Euclidean/Angle/Oriented/Basic.lean | 840 | 842 |
/-
Copyright (c) 2023 Peter Nelson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Peter Nelson
-/
import Mathlib.SetTheory.Cardinal.Finite
import Mathlib.Data.Set.Finite.Powerset
/-!
# Noncomputable Set Cardinality
We define the cardinality of set `s` as a term `Set.encard s : ℕ∞` and a term `Set.ncard s : ℕ`.
The latter takes the junk value of zero if `s` is infinite. Both functions are noncomputable, and
are defined in terms of `ENat.card` (which takes a type as its argument); this file can be seen
as an API for the same function in the special case where the type is a coercion of a `Set`,
allowing for smoother interactions with the `Set` API.
`Set.encard` never takes junk values, so is more mathematically natural than `Set.ncard`, even
though it takes values in a less convenient type. It is probably the right choice in settings where
one is concerned with the cardinalities of sets that may or may not be infinite.
`Set.ncard` has a nicer codomain, but when using it, `Set.Finite` hypotheses are normally needed to
make sure its values are meaningful. More generally, `Set.ncard` is intended to be used over the
obvious alternative `Finset.card` when finiteness is 'propositional' rather than 'structural'.
When working with sets that are finite by virtue of their definition, then `Finset.card` probably
makes more sense. One setting where `Set.ncard` works nicely is in a type `α` with `[Finite α]`,
where every set is automatically finite. In this setting, we use default arguments and a simple
tactic so that finiteness goals are discharged automatically in `Set.ncard` theorems.
## Main Definitions
* `Set.encard s` is the cardinality of the set `s` as an extended natural number, with value `⊤` if
`s` is infinite.
* `Set.ncard s` is the cardinality of the set `s` as a natural number, provided `s` is Finite.
If `s` is Infinite, then `Set.ncard s = 0`.
* `toFinite_tac` is a tactic that tries to synthesize a `Set.Finite s` argument with
`Set.toFinite`. This will work for `s : Set α` where there is a `Finite α` instance.
## Implementation Notes
The theorems in this file are very similar to those in `Data.Finset.Card`, but with `Set` operations
instead of `Finset`. We first prove all the theorems for `Set.encard`, and then derive most of the
`Set.ncard` results as a consequence. Things are done this way to avoid reliance on the `Finset` API
for theorems about infinite sets, and to allow for a refactor that removes or modifies `Set.ncard`
in the future.
Nearly all the theorems for `Set.ncard` require finiteness of one or more of their arguments. We
provide this assumption with a default argument of the form `(hs : s.Finite := by toFinite_tac)`,
where `toFinite_tac` will find an `s.Finite` term in the cases where `s` is a set in a `Finite`
type.
Often, where there are two set arguments `s` and `t`, the finiteness of one follows from the other
in the context of the theorem, in which case we only include the ones that are needed, and derive
the other inside the proof. A few of the theorems, such as `ncard_union_le` do not require
finiteness arguments; they are true by coincidence due to junk values.
-/
namespace Set
variable {α β : Type*} {s t : Set α}
/-- The cardinality of a set as a term in `ℕ∞` -/
noncomputable def encard (s : Set α) : ℕ∞ := ENat.card s
@[simp] theorem encard_univ_coe (s : Set α) : encard (univ : Set s) = encard s := by
rw [encard, encard, ENat.card_congr (Equiv.Set.univ ↑s)]
theorem encard_univ (α : Type*) :
encard (univ : Set α) = ENat.card α := by
rw [encard, ENat.card_congr (Equiv.Set.univ α)]
theorem Finite.encard_eq_coe_toFinset_card (h : s.Finite) : s.encard = h.toFinset.card := by
have := h.fintype
rw [encard, ENat.card_eq_coe_fintype_card, toFinite_toFinset, toFinset_card]
theorem encard_eq_coe_toFinset_card (s : Set α) [Fintype s] : encard s = s.toFinset.card := by
have h := toFinite s
rw [h.encard_eq_coe_toFinset_card, toFinite_toFinset]
@[simp] theorem toENat_cardinalMk (s : Set α) : (Cardinal.mk s).toENat = s.encard := rfl
theorem toENat_cardinalMk_subtype (P : α → Prop) :
(Cardinal.mk {x // P x}).toENat = {x | P x}.encard :=
rfl
@[simp] theorem coe_fintypeCard (s : Set α) [Fintype s] : Fintype.card s = s.encard := by
simp [encard_eq_coe_toFinset_card]
@[simp, norm_cast] theorem encard_coe_eq_coe_finsetCard (s : Finset α) :
encard (s : Set α) = s.card := by
rw [Finite.encard_eq_coe_toFinset_card (Finset.finite_toSet s)]; simp
@[simp] theorem Infinite.encard_eq {s : Set α} (h : s.Infinite) : s.encard = ⊤ := by
have := h.to_subtype
rw [encard, ENat.card_eq_top_of_infinite]
@[simp] theorem encard_eq_zero : s.encard = 0 ↔ s = ∅ := by
rw [encard, ENat.card_eq_zero_iff_empty, isEmpty_subtype, eq_empty_iff_forall_not_mem]
@[simp] theorem encard_empty : (∅ : Set α).encard = 0 := by
rw [encard_eq_zero]
theorem nonempty_of_encard_ne_zero (h : s.encard ≠ 0) : s.Nonempty := by
rwa [nonempty_iff_ne_empty, Ne, ← encard_eq_zero]
theorem encard_ne_zero : s.encard ≠ 0 ↔ s.Nonempty := by
rw [ne_eq, encard_eq_zero, nonempty_iff_ne_empty]
@[simp] theorem encard_pos : 0 < s.encard ↔ s.Nonempty := by
rw [pos_iff_ne_zero, encard_ne_zero]
protected alias ⟨_, Nonempty.encard_pos⟩ := encard_pos
@[simp] theorem encard_singleton (e : α) : ({e} : Set α).encard = 1 := by
rw [encard, ENat.card_eq_coe_fintype_card, Fintype.card_ofSubsingleton, Nat.cast_one]
theorem encard_union_eq (h : Disjoint s t) : (s ∪ t).encard = s.encard + t.encard := by
classical
simp [encard, ENat.card_congr (Equiv.Set.union h)]
theorem encard_insert_of_not_mem {a : α} (has : a ∉ s) : (insert a s).encard = s.encard + 1 := by
rw [← union_singleton, encard_union_eq (by simpa), encard_singleton]
theorem Finite.encard_lt_top (h : s.Finite) : s.encard < ⊤ := by
induction s, h using Set.Finite.induction_on with
| empty => simp
| insert hat _ ht' =>
rw [encard_insert_of_not_mem hat]
exact lt_tsub_iff_right.1 ht'
theorem Finite.encard_eq_coe (h : s.Finite) : s.encard = ENat.toNat s.encard :=
(ENat.coe_toNat h.encard_lt_top.ne).symm
theorem Finite.exists_encard_eq_coe (h : s.Finite) : ∃ (n : ℕ), s.encard = n :=
⟨_, h.encard_eq_coe⟩
@[simp] theorem encard_lt_top_iff : s.encard < ⊤ ↔ s.Finite :=
⟨fun h ↦ by_contra fun h' ↦ h.ne (Infinite.encard_eq h'), Finite.encard_lt_top⟩
@[simp] theorem encard_eq_top_iff : s.encard = ⊤ ↔ s.Infinite := by
rw [← not_iff_not, ← Ne, ← lt_top_iff_ne_top, encard_lt_top_iff, not_infinite]
alias ⟨_, encard_eq_top⟩ := encard_eq_top_iff
theorem encard_ne_top_iff : s.encard ≠ ⊤ ↔ s.Finite := by
simp
theorem finite_of_encard_le_coe {k : ℕ} (h : s.encard ≤ k) : s.Finite := by
rw [← encard_lt_top_iff]; exact h.trans_lt (WithTop.coe_lt_top _)
theorem finite_of_encard_eq_coe {k : ℕ} (h : s.encard = k) : s.Finite :=
finite_of_encard_le_coe h.le
theorem encard_le_coe_iff {k : ℕ} : s.encard ≤ k ↔ s.Finite ∧ ∃ (n₀ : ℕ), s.encard = n₀ ∧ n₀ ≤ k :=
⟨fun h ↦ ⟨finite_of_encard_le_coe h, by rwa [ENat.le_coe_iff] at h⟩,
fun ⟨_,⟨n₀,hs, hle⟩⟩ ↦ by rwa [hs, Nat.cast_le]⟩
@[simp]
theorem encard_prod : (s ×ˢ t).encard = s.encard * t.encard := by
simp [Set.encard, ENat.card_congr (Equiv.Set.prod ..)]
section Lattice
theorem encard_le_encard (h : s ⊆ t) : s.encard ≤ t.encard := by
rw [← union_diff_cancel h, encard_union_eq disjoint_sdiff_right]; exact le_self_add
@[deprecated (since := "2025-01-05")] alias encard_le_card := encard_le_encard
theorem encard_mono {α : Type*} : Monotone (encard : Set α → ℕ∞) :=
fun _ _ ↦ encard_le_encard
theorem encard_diff_add_encard_of_subset (h : s ⊆ t) : (t \ s).encard + s.encard = t.encard := by
rw [← encard_union_eq disjoint_sdiff_left, diff_union_self, union_eq_self_of_subset_right h]
@[simp] theorem one_le_encard_iff_nonempty : 1 ≤ s.encard ↔ s.Nonempty := by
rw [nonempty_iff_ne_empty, Ne, ← encard_eq_zero, ENat.one_le_iff_ne_zero]
theorem encard_diff_add_encard_inter (s t : Set α) :
(s \ t).encard + (s ∩ t).encard = s.encard := by
rw [← encard_union_eq (disjoint_of_subset_right inter_subset_right disjoint_sdiff_left),
diff_union_inter]
theorem encard_union_add_encard_inter (s t : Set α) :
(s ∪ t).encard + (s ∩ t).encard = s.encard + t.encard := by
rw [← diff_union_self, encard_union_eq disjoint_sdiff_left, add_right_comm,
encard_diff_add_encard_inter]
theorem encard_eq_encard_iff_encard_diff_eq_encard_diff (h : (s ∩ t).Finite) :
s.encard = t.encard ↔ (s \ t).encard = (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_right_inj h.encard_lt_top.ne]
theorem encard_le_encard_iff_encard_diff_le_encard_diff (h : (s ∩ t).Finite) :
s.encard ≤ t.encard ↔ (s \ t).encard ≤ (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_le_add_iff_right h.encard_lt_top.ne]
theorem encard_lt_encard_iff_encard_diff_lt_encard_diff (h : (s ∩ t).Finite) :
s.encard < t.encard ↔ (s \ t).encard < (t \ s).encard := by
rw [← encard_diff_add_encard_inter s t, ← encard_diff_add_encard_inter t s, inter_comm t s,
WithTop.add_lt_add_iff_right h.encard_lt_top.ne]
theorem encard_union_le (s t : Set α) : (s ∪ t).encard ≤ s.encard + t.encard := by
rw [← encard_union_add_encard_inter]; exact le_self_add
theorem finite_iff_finite_of_encard_eq_encard (h : s.encard = t.encard) : s.Finite ↔ t.Finite := by
rw [← encard_lt_top_iff, ← encard_lt_top_iff, h]
theorem infinite_iff_infinite_of_encard_eq_encard (h : s.encard = t.encard) :
s.Infinite ↔ t.Infinite := by rw [← encard_eq_top_iff, h, encard_eq_top_iff]
theorem Finite.finite_of_encard_le {s : Set α} {t : Set β} (hs : s.Finite)
(h : t.encard ≤ s.encard) : t.Finite :=
encard_lt_top_iff.1 (h.trans_lt hs.encard_lt_top)
lemma Finite.eq_of_subset_of_encard_le' (ht : t.Finite) (hst : s ⊆ t) (hts : t.encard ≤ s.encard) :
s = t := by
rw [← zero_add (a := encard s), ← encard_diff_add_encard_of_subset hst] at hts
have hdiff := WithTop.le_of_add_le_add_right (ht.subset hst).encard_lt_top.ne hts
rw [nonpos_iff_eq_zero, encard_eq_zero, diff_eq_empty] at hdiff
exact hst.antisymm hdiff
theorem Finite.eq_of_subset_of_encard_le (hs : s.Finite) (hst : s ⊆ t)
(hts : t.encard ≤ s.encard) : s = t :=
(hs.finite_of_encard_le hts).eq_of_subset_of_encard_le' hst hts
theorem Finite.encard_lt_encard (hs : s.Finite) (h : s ⊂ t) : s.encard < t.encard :=
(encard_mono h.subset).lt_of_ne fun he ↦ h.ne (hs.eq_of_subset_of_encard_le h.subset he.symm.le)
theorem encard_strictMono [Finite α] : StrictMono (encard : Set α → ℕ∞) :=
fun _ _ h ↦ (toFinite _).encard_lt_encard h
theorem encard_diff_add_encard (s t : Set α) : (s \ t).encard + t.encard = (s ∪ t).encard := by
rw [← encard_union_eq disjoint_sdiff_left, diff_union_self]
theorem encard_le_encard_diff_add_encard (s t : Set α) : s.encard ≤ (s \ t).encard + t.encard :=
(encard_mono subset_union_left).trans_eq (encard_diff_add_encard _ _).symm
theorem tsub_encard_le_encard_diff (s t : Set α) : s.encard - t.encard ≤ (s \ t).encard := by
rw [tsub_le_iff_left, add_comm]; apply encard_le_encard_diff_add_encard
theorem encard_add_encard_compl (s : Set α) : s.encard + sᶜ.encard = (univ : Set α).encard := by
rw [← encard_union_eq disjoint_compl_right, union_compl_self]
end Lattice
section InsertErase
variable {a b : α}
theorem encard_insert_le (s : Set α) (x : α) : (insert x s).encard ≤ s.encard + 1 := by
rw [← union_singleton, ← encard_singleton x]; apply encard_union_le
theorem encard_singleton_inter (s : Set α) (x : α) : ({x} ∩ s).encard ≤ 1 := by
rw [← encard_singleton x]; exact encard_le_encard inter_subset_left
theorem encard_diff_singleton_add_one (h : a ∈ s) :
(s \ {a}).encard + 1 = s.encard := by
rw [← encard_insert_of_not_mem (fun h ↦ h.2 rfl), insert_diff_singleton, insert_eq_of_mem h]
theorem encard_diff_singleton_of_mem (h : a ∈ s) :
(s \ {a}).encard = s.encard - 1 := by
rw [← encard_diff_singleton_add_one h, ← WithTop.add_right_inj WithTop.one_ne_top,
tsub_add_cancel_of_le (self_le_add_left _ _)]
theorem encard_tsub_one_le_encard_diff_singleton (s : Set α) (x : α) :
s.encard - 1 ≤ (s \ {x}).encard := by
rw [← encard_singleton x]; apply tsub_encard_le_encard_diff
theorem encard_exchange (ha : a ∉ s) (hb : b ∈ s) : (insert a (s \ {b})).encard = s.encard := by
rw [encard_insert_of_not_mem, encard_diff_singleton_add_one hb]
simp_all only [not_true, mem_diff, mem_singleton_iff, false_and, not_false_eq_true]
theorem encard_exchange' (ha : a ∉ s) (hb : b ∈ s) : (insert a s \ {b}).encard = s.encard := by
rw [← insert_diff_singleton_comm (by rintro rfl; exact ha hb), encard_exchange ha hb]
theorem encard_eq_add_one_iff {k : ℕ∞} :
s.encard = k + 1 ↔ (∃ a t, ¬a ∈ t ∧ insert a t = s ∧ t.encard = k) := by
refine ⟨fun h ↦ ?_, ?_⟩
· obtain ⟨a, ha⟩ := nonempty_of_encard_ne_zero (s := s) (by simp [h])
refine ⟨a, s \ {a}, fun h ↦ h.2 rfl, by rwa [insert_diff_singleton, insert_eq_of_mem], ?_⟩
rw [← WithTop.add_right_inj WithTop.one_ne_top, ← h,
encard_diff_singleton_add_one ha]
rintro ⟨a, t, h, rfl, rfl⟩
rw [encard_insert_of_not_mem h]
/-- Every set is either empty, infinite, or can have its `encard` reduced by a removal. Intended
for well-founded induction on the value of `encard`. -/
theorem eq_empty_or_encard_eq_top_or_encard_diff_singleton_lt (s : Set α) :
s = ∅ ∨ s.encard = ⊤ ∨ ∃ a ∈ s, (s \ {a}).encard < s.encard := by
refine s.eq_empty_or_nonempty.elim Or.inl (Or.inr ∘ fun ⟨a,ha⟩ ↦
(s.finite_or_infinite.elim (fun hfin ↦ Or.inr ⟨a, ha, ?_⟩) (Or.inl ∘ Infinite.encard_eq)))
rw [← encard_diff_singleton_add_one ha]; nth_rw 1 [← add_zero (encard _)]
exact WithTop.add_lt_add_left hfin.diff.encard_lt_top.ne zero_lt_one
end InsertErase
section SmallSets
theorem encard_pair {x y : α} (hne : x ≠ y) : ({x, y} : Set α).encard = 2 := by
rw [encard_insert_of_not_mem (by simpa), ← one_add_one_eq_two,
WithTop.add_right_inj WithTop.one_ne_top, encard_singleton]
theorem encard_eq_one : s.encard = 1 ↔ ∃ x, s = {x} := by
refine ⟨fun h ↦ ?_, fun ⟨x, hx⟩ ↦ by rw [hx, encard_singleton]⟩
obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
exact ⟨x, ((finite_singleton x).eq_of_subset_of_encard_le (by simpa) (by simp [h])).symm⟩
theorem encard_le_one_iff_eq : s.encard ≤ 1 ↔ s = ∅ ∨ ∃ x, s = {x} := by
rw [le_iff_lt_or_eq, lt_iff_not_le, ENat.one_le_iff_ne_zero, not_not, encard_eq_zero,
encard_eq_one]
theorem encard_le_one_iff : s.encard ≤ 1 ↔ ∀ a b, a ∈ s → b ∈ s → a = b := by
rw [encard_le_one_iff_eq, or_iff_not_imp_left, ← Ne, ← nonempty_iff_ne_empty]
refine ⟨fun h a b has hbs ↦ ?_,
fun h ⟨x, hx⟩ ↦ ⟨x, ((singleton_subset_iff.2 hx).antisymm' (fun y hy ↦ h _ _ hy hx))⟩⟩
obtain ⟨x, rfl⟩ := h ⟨_, has⟩
rw [(has : a = x), (hbs : b = x)]
theorem encard_le_one_iff_subsingleton : s.encard ≤ 1 ↔ s.Subsingleton := by
rw [encard_le_one_iff, Set.Subsingleton]
tauto
theorem one_lt_encard_iff_nontrivial : 1 < s.encard ↔ s.Nontrivial := by
rw [← not_iff_not, not_lt, Set.not_nontrivial_iff, ← encard_le_one_iff_subsingleton]
theorem one_lt_encard_iff : 1 < s.encard ↔ ∃ a b, a ∈ s ∧ b ∈ s ∧ a ≠ b := by
rw [← not_iff_not, not_exists, not_lt, encard_le_one_iff]; aesop
theorem exists_ne_of_one_lt_encard (h : 1 < s.encard) (a : α) : ∃ b ∈ s, b ≠ a := by
by_contra! h'
obtain ⟨b, b', hb, hb', hne⟩ := one_lt_encard_iff.1 h
apply hne
rw [h' b hb, h' b' hb']
theorem encard_eq_two : s.encard = 2 ↔ ∃ x y, x ≠ y ∧ s = {x, y} := by
refine ⟨fun h ↦ ?_, fun ⟨x, y, hne, hs⟩ ↦ by rw [hs, encard_pair hne]⟩
obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
rw [← insert_eq_of_mem hx, ← insert_diff_singleton, encard_insert_of_not_mem (fun h ↦ h.2 rfl),
← one_add_one_eq_two, WithTop.add_right_inj (WithTop.one_ne_top), encard_eq_one] at h
obtain ⟨y, h⟩ := h
refine ⟨x, y, by rintro rfl; exact (h.symm.subset rfl).2 rfl, ?_⟩
rw [← h, insert_diff_singleton, insert_eq_of_mem hx]
theorem encard_eq_three {α : Type u_1} {s : Set α} :
encard s = 3 ↔ ∃ x y z, x ≠ y ∧ x ≠ z ∧ y ≠ z ∧ s = {x, y, z} := by
refine ⟨fun h ↦ ?_, fun ⟨x, y, z, hxy, hyz, hxz, hs⟩ ↦ ?_⟩
· obtain ⟨x, hx⟩ := nonempty_of_encard_ne_zero (s := s) (by rw [h]; simp)
rw [← insert_eq_of_mem hx, ← insert_diff_singleton,
encard_insert_of_not_mem (fun h ↦ h.2 rfl), (by exact rfl : (3 : ℕ∞) = 2 + 1),
WithTop.add_right_inj WithTop.one_ne_top, encard_eq_two] at h
obtain ⟨y, z, hne, hs⟩ := h
refine ⟨x, y, z, ?_, ?_, hne, ?_⟩
· rintro rfl; exact (hs.symm.subset (Or.inl rfl)).2 rfl
· rintro rfl; exact (hs.symm.subset (Or.inr rfl)).2 rfl
rw [← hs, insert_diff_singleton, insert_eq_of_mem hx]
rw [hs, encard_insert_of_not_mem, encard_insert_of_not_mem, encard_singleton] <;> aesop
theorem Nat.encard_range (k : ℕ) : {i | i < k}.encard = k := by
convert encard_coe_eq_coe_finsetCard (Finset.range k) using 1
· rw [Finset.coe_range, Iio_def]
rw [Finset.card_range]
end SmallSets
theorem Finite.eq_insert_of_subset_of_encard_eq_succ (hs : s.Finite) (h : s ⊆ t)
(hst : t.encard = s.encard + 1) : ∃ a, t = insert a s := by
rw [← encard_diff_add_encard_of_subset h, add_comm, WithTop.add_left_inj hs.encard_lt_top.ne,
encard_eq_one] at hst
obtain ⟨x, hx⟩ := hst; use x; rw [← diff_union_of_subset h, hx, singleton_union]
theorem exists_subset_encard_eq {k : ℕ∞} (hk : k ≤ s.encard) : ∃ t, t ⊆ s ∧ t.encard = k := by
revert hk
refine ENat.nat_induction k (fun _ ↦ ⟨∅, empty_subset _, by simp⟩) (fun n IH hle ↦ ?_) ?_
· obtain ⟨t₀, ht₀s, ht₀⟩ := IH (le_trans (by simp) hle)
simp only [Nat.cast_succ] at *
have hne : t₀ ≠ s := by
rintro rfl; rw [ht₀, ← Nat.cast_one, ← Nat.cast_add, Nat.cast_le] at hle; simp at hle
obtain ⟨x, hx⟩ := exists_of_ssubset (ht₀s.ssubset_of_ne hne)
exact ⟨insert x t₀, insert_subset hx.1 ht₀s, by rw [encard_insert_of_not_mem hx.2, ht₀]⟩
simp only [top_le_iff, encard_eq_top_iff]
exact fun _ hi ↦ ⟨s, Subset.rfl, hi⟩
theorem exists_superset_subset_encard_eq {k : ℕ∞}
(hst : s ⊆ t) (hsk : s.encard ≤ k) (hkt : k ≤ t.encard) :
∃ r, s ⊆ r ∧ r ⊆ t ∧ r.encard = k := by
obtain (hs | hs) := eq_or_ne s.encard ⊤
· rw [hs, top_le_iff] at hsk; subst hsk; exact ⟨s, Subset.rfl, hst, hs⟩
obtain ⟨k, rfl⟩ := exists_add_of_le hsk
obtain ⟨k', hk'⟩ := exists_add_of_le hkt
have hk : k ≤ encard (t \ s) := by
rw [← encard_diff_add_encard_of_subset hst, add_comm] at hkt
exact WithTop.le_of_add_le_add_right hs hkt
obtain ⟨r', hr', rfl⟩ := exists_subset_encard_eq hk
refine ⟨s ∪ r', subset_union_left, union_subset hst (hr'.trans diff_subset), ?_⟩
rw [encard_union_eq (disjoint_of_subset_right hr' disjoint_sdiff_right)]
section Function
variable {s : Set α} {t : Set β} {f : α → β}
theorem InjOn.encard_image (h : InjOn f s) : (f '' s).encard = s.encard := by
rw [encard, ENat.card_image_of_injOn h, encard]
theorem encard_congr (e : s ≃ t) : s.encard = t.encard := by
rw [← encard_univ_coe, ← encard_univ_coe t, encard_univ, encard_univ, ENat.card_congr e]
theorem _root_.Function.Injective.encard_image (hf : f.Injective) (s : Set α) :
(f '' s).encard = s.encard :=
hf.injOn.encard_image
theorem _root_.Function.Embedding.encard_le (e : s ↪ t) : s.encard ≤ t.encard := by
rw [← encard_univ_coe, ← e.injective.encard_image, ← Subtype.coe_injective.encard_image]
exact encard_mono (by simp)
theorem encard_image_le (f : α → β) (s : Set α) : (f '' s).encard ≤ s.encard := by
obtain (h | h) := isEmpty_or_nonempty α
· rw [s.eq_empty_of_isEmpty]; simp
rw [← (f.invFunOn_injOn_image s).encard_image]
apply encard_le_encard
exact f.invFunOn_image_image_subset s
theorem Finite.injOn_of_encard_image_eq (hs : s.Finite) (h : (f '' s).encard = s.encard) :
InjOn f s := by
obtain (h' | hne) := isEmpty_or_nonempty α
· rw [s.eq_empty_of_isEmpty]; simp
rw [← (f.invFunOn_injOn_image s).encard_image] at h
rw [injOn_iff_invFunOn_image_image_eq_self]
exact hs.eq_of_subset_of_encard_le' (f.invFunOn_image_image_subset s) h.symm.le
theorem encard_preimage_of_injective_subset_range (hf : f.Injective) (ht : t ⊆ range f) :
(f ⁻¹' t).encard = t.encard := by
rw [← hf.encard_image, image_preimage_eq_inter_range, inter_eq_self_of_subset_left ht]
lemma encard_preimage_of_bijective (hf : f.Bijective) (t : Set β) : (f ⁻¹' t).encard = t.encard :=
encard_preimage_of_injective_subset_range hf.injective (by simp [hf.surjective.range_eq])
theorem encard_le_encard_of_injOn (hf : MapsTo f s t) (f_inj : InjOn f s) :
s.encard ≤ t.encard := by
rw [← f_inj.encard_image]; apply encard_le_encard; rintro _ ⟨x, hx, rfl⟩; exact hf hx
theorem Finite.exists_injOn_of_encard_le [Nonempty β] {s : Set α} {t : Set β} (hs : s.Finite)
(hle : s.encard ≤ t.encard) : ∃ (f : α → β), s ⊆ f ⁻¹' t ∧ InjOn f s := by
classical
obtain (rfl | h | ⟨a, has, -⟩) := s.eq_empty_or_encard_eq_top_or_encard_diff_singleton_lt
· simp
· exact (encard_ne_top_iff.mpr hs h).elim
obtain ⟨b, hbt⟩ := encard_pos.1 ((encard_pos.2 ⟨_, has⟩).trans_le hle)
have hle' : (s \ {a}).encard ≤ (t \ {b}).encard := by
rwa [← WithTop.add_le_add_iff_right WithTop.one_ne_top,
encard_diff_singleton_add_one has, encard_diff_singleton_add_one hbt]
obtain ⟨f₀, hf₀s, hinj⟩ := exists_injOn_of_encard_le hs.diff hle'
simp only [preimage_diff, subset_def, mem_diff, mem_singleton_iff, mem_preimage, and_imp] at hf₀s
use Function.update f₀ a b
rw [← insert_eq_of_mem has, ← insert_diff_singleton, injOn_insert (fun h ↦ h.2 rfl)]
simp only [mem_diff, mem_singleton_iff, not_true, and_false, insert_diff_singleton, subset_def,
mem_insert_iff, mem_preimage, ne_eq, Function.update_apply, forall_eq_or_imp, ite_true, and_imp,
mem_image, ite_eq_left_iff, not_exists, not_and, not_forall, exists_prop, and_iff_right hbt]
refine ⟨?_, ?_, fun x hxs hxa ↦ ⟨hxa, (hf₀s x hxs hxa).2⟩⟩
· rintro x hx; split_ifs with h
· assumption
· exact (hf₀s x hx h).1
exact InjOn.congr hinj (fun x ⟨_, hxa⟩ ↦ by rwa [Function.update_of_ne])
termination_by encard s
theorem Finite.exists_bijOn_of_encard_eq [Nonempty β] (hs : s.Finite) (h : s.encard = t.encard) :
∃ (f : α → β), BijOn f s t := by
obtain ⟨f, hf, hinj⟩ := hs.exists_injOn_of_encard_le h.le; use f
convert hinj.bijOn_image
rw [(hs.image f).eq_of_subset_of_encard_le (image_subset_iff.mpr hf)
(h.symm.trans hinj.encard_image.symm).le]
end Function
section ncard
open Nat
/-- A tactic (for use in default params) that applies `Set.toFinite` to synthesize a `Set.Finite`
term. -/
syntax "toFinite_tac" : tactic
macro_rules
| `(tactic| toFinite_tac) => `(tactic| apply Set.toFinite)
/-- A tactic useful for transferring proofs for `encard` to their corresponding `card` statements -/
syntax "to_encard_tac" : tactic
macro_rules
| `(tactic| to_encard_tac) => `(tactic|
simp only [← Nat.cast_le (α := ℕ∞), ← Nat.cast_inj (R := ℕ∞), Nat.cast_add, Nat.cast_one])
/-- The cardinality of `s : Set α` . Has the junk value `0` if `s` is infinite -/
noncomputable def ncard (s : Set α) : ℕ := ENat.toNat s.encard
theorem ncard_def (s : Set α) : s.ncard = ENat.toNat s.encard := rfl
theorem Finite.cast_ncard_eq (hs : s.Finite) : s.ncard = s.encard := by
rwa [ncard, ENat.coe_toNat_eq_self, ne_eq, encard_eq_top_iff, Set.Infinite, not_not]
lemma ncard_le_encard (s : Set α) : s.ncard ≤ s.encard := ENat.coe_toNat_le_self _
theorem Nat.card_coe_set_eq (s : Set α) : Nat.card s = s.ncard := by
obtain (h | h) := s.finite_or_infinite
· have := h.fintype
rw [ncard, h.encard_eq_coe_toFinset_card, Nat.card_eq_fintype_card,
toFinite_toFinset, toFinset_card, ENat.toNat_coe]
have := infinite_coe_iff.2 h
rw [ncard, h.encard_eq, Nat.card_eq_zero_of_infinite, ENat.toNat_top]
theorem ncard_eq_toFinset_card (s : Set α) (hs : s.Finite := by toFinite_tac) :
s.ncard = hs.toFinset.card := by
rw [← Nat.card_coe_set_eq, @Nat.card_eq_fintype_card _ hs.fintype,
@Finite.card_toFinset _ _ hs.fintype hs]
theorem ncard_eq_toFinset_card' (s : Set α) [Fintype s] :
s.ncard = s.toFinset.card := by
simp [← Nat.card_coe_set_eq, Nat.card_eq_fintype_card]
lemma cast_ncard {s : Set α} (hs : s.Finite) :
(s.ncard : Cardinal) = Cardinal.mk s := @Nat.cast_card _ hs
theorem encard_le_coe_iff_finite_ncard_le {k : ℕ} : s.encard ≤ k ↔ s.Finite ∧ s.ncard ≤ k := by
rw [encard_le_coe_iff, and_congr_right_iff]
exact fun hfin ↦ ⟨fun ⟨n₀, hn₀, hle⟩ ↦ by rwa [ncard_def, hn₀, ENat.toNat_coe],
fun h ↦ ⟨s.ncard, by rw [hfin.cast_ncard_eq], h⟩⟩
theorem Infinite.ncard (hs : s.Infinite) : s.ncard = 0 := by
rw [← Nat.card_coe_set_eq, @Nat.card_eq_zero_of_infinite _ hs.to_subtype]
@[gcongr]
theorem ncard_le_ncard (hst : s ⊆ t) (ht : t.Finite := by toFinite_tac) :
s.ncard ≤ t.ncard := by
rw [← Nat.cast_le (α := ℕ∞), ht.cast_ncard_eq, (ht.subset hst).cast_ncard_eq]
exact encard_mono hst
theorem ncard_mono [Finite α] : @Monotone (Set α) _ _ _ ncard := fun _ _ ↦ ncard_le_ncard
@[simp] theorem ncard_eq_zero (hs : s.Finite := by toFinite_tac) :
s.ncard = 0 ↔ s = ∅ := by
rw [← Nat.cast_inj (R := ℕ∞), hs.cast_ncard_eq, Nat.cast_zero, encard_eq_zero]
@[simp, norm_cast] theorem ncard_coe_Finset (s : Finset α) : (s : Set α).ncard = s.card := by
rw [ncard_eq_toFinset_card _, Finset.finite_toSet_toFinset]
theorem ncard_univ (α : Type*) : (univ : Set α).ncard = Nat.card α := by
rcases finite_or_infinite α with h | h
· have hft := Fintype.ofFinite α
rw [ncard_eq_toFinset_card, Finite.toFinset_univ, Finset.card_univ, Nat.card_eq_fintype_card]
rw [Nat.card_eq_zero_of_infinite, Infinite.ncard]
exact infinite_univ
@[simp] theorem ncard_empty (α : Type*) : (∅ : Set α).ncard = 0 := by
rw [ncard_eq_zero]
theorem ncard_pos (hs : s.Finite := by toFinite_tac) : 0 < s.ncard ↔ s.Nonempty := by
rw [pos_iff_ne_zero, Ne, ncard_eq_zero hs, nonempty_iff_ne_empty]
protected alias ⟨_, Nonempty.ncard_pos⟩ := ncard_pos
theorem ncard_ne_zero_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) : s.ncard ≠ 0 :=
((ncard_pos hs).mpr ⟨a, h⟩).ne.symm
theorem finite_of_ncard_ne_zero (hs : s.ncard ≠ 0) : s.Finite :=
s.finite_or_infinite.elim id fun h ↦ (hs h.ncard).elim
theorem finite_of_ncard_pos (hs : 0 < s.ncard) : s.Finite :=
finite_of_ncard_ne_zero hs.ne.symm
theorem nonempty_of_ncard_ne_zero (hs : s.ncard ≠ 0) : s.Nonempty := by
rw [nonempty_iff_ne_empty]; rintro rfl; simp at hs
@[simp] theorem ncard_singleton (a : α) : ({a} : Set α).ncard = 1 := by
simp [ncard]
theorem ncard_singleton_inter (a : α) (s : Set α) : ({a} ∩ s).ncard ≤ 1 := by
rw [← Nat.cast_le (α := ℕ∞), (toFinite _).cast_ncard_eq, Nat.cast_one]
apply encard_singleton_inter
@[simp]
theorem ncard_prod : (s ×ˢ t).ncard = s.ncard * t.ncard := by
simp [ncard, ENat.toNat_mul]
@[simp]
theorem ncard_powerset (s : Set α) (hs : s.Finite := by toFinite_tac) :
(𝒫 s).ncard = 2 ^ s.ncard := by
have h := Cardinal.mk_powerset s
rw [← cast_ncard hs.powerset, ← cast_ncard hs] at h
norm_cast at h
section InsertErase
@[simp] theorem ncard_insert_of_not_mem {a : α} (h : a ∉ s) (hs : s.Finite := by toFinite_tac) :
(insert a s).ncard = s.ncard + 1 := by
rw [← Nat.cast_inj (R := ℕ∞), (hs.insert a).cast_ncard_eq, Nat.cast_add, Nat.cast_one,
hs.cast_ncard_eq, encard_insert_of_not_mem h]
theorem ncard_insert_of_mem {a : α} (h : a ∈ s) : ncard (insert a s) = s.ncard := by
rw [insert_eq_of_mem h]
theorem ncard_insert_le (a : α) (s : Set α) : (insert a s).ncard ≤ s.ncard + 1 := by
obtain hs | hs := s.finite_or_infinite
· to_encard_tac; rw [hs.cast_ncard_eq, (hs.insert _).cast_ncard_eq]; apply encard_insert_le
rw [(hs.mono (subset_insert a s)).ncard]
exact Nat.zero_le _
theorem ncard_insert_eq_ite {a : α} [Decidable (a ∈ s)] (hs : s.Finite := by toFinite_tac) :
ncard (insert a s) = if a ∈ s then s.ncard else s.ncard + 1 := by
by_cases h : a ∈ s
· rw [ncard_insert_of_mem h, if_pos h]
· rw [ncard_insert_of_not_mem h hs, if_neg h]
theorem ncard_le_ncard_insert (a : α) (s : Set α) : s.ncard ≤ (insert a s).ncard := by
classical
refine
s.finite_or_infinite.elim (fun h ↦ ?_) (fun h ↦ by (rw [h.ncard]; exact Nat.zero_le _))
rw [ncard_insert_eq_ite h]; split_ifs <;> simp
@[simp] theorem ncard_pair {a b : α} (h : a ≠ b) : ({a, b} : Set α).ncard = 2 := by
rw [ncard_insert_of_not_mem, ncard_singleton]; simpa
@[simp] theorem ncard_diff_singleton_add_one {a : α} (h : a ∈ s)
(hs : s.Finite := by toFinite_tac) : (s \ {a}).ncard + 1 = s.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, hs.diff.cast_ncard_eq,
encard_diff_singleton_add_one h]
@[simp] theorem ncard_diff_singleton_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) :
(s \ {a}).ncard = s.ncard - 1 :=
eq_tsub_of_add_eq (ncard_diff_singleton_add_one h hs)
theorem ncard_diff_singleton_lt_of_mem {a : α} (h : a ∈ s) (hs : s.Finite := by toFinite_tac) :
(s \ {a}).ncard < s.ncard := by
rw [← ncard_diff_singleton_add_one h hs]; apply lt_add_one
theorem ncard_diff_singleton_le (s : Set α) (a : α) : (s \ {a}).ncard ≤ s.ncard := by
obtain hs | hs := s.finite_or_infinite
· apply ncard_le_ncard diff_subset hs
convert zero_le (α := ℕ) _
exact (hs.diff (by simp : Set.Finite {a})).ncard
theorem pred_ncard_le_ncard_diff_singleton (s : Set α) (a : α) : s.ncard - 1 ≤ (s \ {a}).ncard := by
rcases s.finite_or_infinite with hs | hs
· by_cases h : a ∈ s
· rw [ncard_diff_singleton_of_mem h hs]
rw [diff_singleton_eq_self h]
apply Nat.pred_le
convert Nat.zero_le _
rw [hs.ncard]
theorem ncard_exchange {a b : α} (ha : a ∉ s) (hb : b ∈ s) : (insert a (s \ {b})).ncard = s.ncard :=
congr_arg ENat.toNat <| encard_exchange ha hb
theorem ncard_exchange' {a b : α} (ha : a ∉ s) (hb : b ∈ s) :
(insert a s \ {b}).ncard = s.ncard := by
rw [← ncard_exchange ha hb, ← singleton_union, ← singleton_union, union_diff_distrib,
@diff_singleton_eq_self _ b {a} fun h ↦ ha (by rwa [← mem_singleton_iff.mp h])]
lemma odd_card_insert_iff {a : α} (ha : a ∉ s) (hs : s.Finite := by toFinite_tac) :
Odd (insert a s).ncard ↔ Even s.ncard := by
rw [ncard_insert_of_not_mem ha hs, Nat.odd_add]
simp only [Nat.odd_add, ← Nat.not_even_iff_odd, Nat.not_even_one, iff_false, Decidable.not_not]
lemma even_card_insert_iff {a : α} (ha : a ∉ s) (hs : s.Finite := by toFinite_tac) :
Even (insert a s).ncard ↔ Odd s.ncard := by
rw [ncard_insert_of_not_mem ha hs, Nat.even_add_one, Nat.not_even_iff_odd]
end InsertErase
variable {f : α → β}
theorem ncard_image_le (hs : s.Finite := by toFinite_tac) : (f '' s).ncard ≤ s.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, (hs.image _).cast_ncard_eq]; apply encard_image_le
theorem ncard_image_of_injOn (H : Set.InjOn f s) : (f '' s).ncard = s.ncard :=
congr_arg ENat.toNat <| H.encard_image
theorem injOn_of_ncard_image_eq (h : (f '' s).ncard = s.ncard) (hs : s.Finite := by toFinite_tac) :
Set.InjOn f s := by
rw [← Nat.cast_inj (R := ℕ∞), hs.cast_ncard_eq, (hs.image _).cast_ncard_eq] at h
exact hs.injOn_of_encard_image_eq h
theorem ncard_image_iff (hs : s.Finite := by toFinite_tac) :
(f '' s).ncard = s.ncard ↔ Set.InjOn f s :=
⟨fun h ↦ injOn_of_ncard_image_eq h hs, ncard_image_of_injOn⟩
theorem ncard_image_of_injective (s : Set α) (H : f.Injective) : (f '' s).ncard = s.ncard :=
ncard_image_of_injOn fun _ _ _ _ h ↦ H h
theorem ncard_preimage_of_injective_subset_range {s : Set β} (H : f.Injective)
(hs : s ⊆ Set.range f) :
(f ⁻¹' s).ncard = s.ncard := by
rw [← ncard_image_of_injective _ H, image_preimage_eq_iff.mpr hs]
theorem fiber_ncard_ne_zero_iff_mem_image {y : β} (hs : s.Finite := by toFinite_tac) :
{ x ∈ s | f x = y }.ncard ≠ 0 ↔ y ∈ f '' s := by
refine ⟨nonempty_of_ncard_ne_zero, ?_⟩
rintro ⟨z, hz, rfl⟩
exact @ncard_ne_zero_of_mem _ ({ x ∈ s | f x = f z }) z (mem_sep hz rfl)
(hs.subset (sep_subset _ _))
@[simp] theorem ncard_map (f : α ↪ β) : (f '' s).ncard = s.ncard :=
ncard_image_of_injective _ f.inj'
@[simp] theorem ncard_subtype (P : α → Prop) (s : Set α) :
{ x : Subtype P | (x : α) ∈ s }.ncard = (s ∩ setOf P).ncard := by
convert (ncard_image_of_injective _ (@Subtype.coe_injective _ P)).symm
ext x
simp [← and_assoc, exists_eq_right]
theorem ncard_inter_le_ncard_left (s t : Set α) (hs : s.Finite := by toFinite_tac) :
(s ∩ t).ncard ≤ s.ncard :=
ncard_le_ncard inter_subset_left hs
theorem ncard_inter_le_ncard_right (s t : Set α) (ht : t.Finite := by toFinite_tac) :
(s ∩ t).ncard ≤ t.ncard :=
ncard_le_ncard inter_subset_right ht
theorem eq_of_subset_of_ncard_le (h : s ⊆ t) (h' : t.ncard ≤ s.ncard)
(ht : t.Finite := by toFinite_tac) : s = t :=
ht.eq_of_subset_of_encard_le' h
(by rwa [← Nat.cast_le (α := ℕ∞), ht.cast_ncard_eq, (ht.subset h).cast_ncard_eq] at h')
theorem subset_iff_eq_of_ncard_le (h : t.ncard ≤ s.ncard) (ht : t.Finite := by toFinite_tac) :
s ⊆ t ↔ s = t :=
⟨fun hst ↦ eq_of_subset_of_ncard_le hst h ht, Eq.subset'⟩
theorem map_eq_of_subset {f : α ↪ α} (h : f '' s ⊆ s) (hs : s.Finite := by toFinite_tac) :
f '' s = s :=
eq_of_subset_of_ncard_le h (ncard_map _).ge hs
theorem sep_of_ncard_eq {a : α} {P : α → Prop} (h : { x ∈ s | P x }.ncard = s.ncard) (ha : a ∈ s)
(hs : s.Finite := by toFinite_tac) : P a :=
sep_eq_self_iff_mem_true.mp (eq_of_subset_of_ncard_le (by simp) h.symm.le hs) _ ha
theorem ncard_lt_ncard (h : s ⊂ t) (ht : t.Finite := by toFinite_tac) :
s.ncard < t.ncard := by
rw [← Nat.cast_lt (α := ℕ∞), ht.cast_ncard_eq, (ht.subset h.subset).cast_ncard_eq]
exact (ht.subset h.subset).encard_lt_encard h
theorem ncard_strictMono [Finite α] : @StrictMono (Set α) _ _ _ ncard :=
fun _ _ h ↦ ncard_lt_ncard h
theorem ncard_eq_of_bijective {n : ℕ} (f : ∀ i, i < n → α)
(hf : ∀ a ∈ s, ∃ i, ∃ h : i < n, f i h = a) (hf' : ∀ (i) (h : i < n), f i h ∈ s)
(f_inj : ∀ (i j) (hi : i < n) (hj : j < n), f i hi = f j hj → i = j) : s.ncard = n := by
let f' : Fin n → α := fun i ↦ f i.val i.is_lt
suffices himage : s = f' '' Set.univ by
rw [← Fintype.card_fin n, ← Nat.card_eq_fintype_card, ← Set.ncard_univ, himage]
exact ncard_image_of_injOn <| fun i _hi j _hj h ↦ Fin.ext <| f_inj i.val j.val i.is_lt j.is_lt h
ext x
simp only [image_univ, mem_range]
refine ⟨fun hx ↦ ?_, fun ⟨⟨i, hi⟩, hx⟩ ↦ hx ▸ hf' i hi⟩
obtain ⟨i, hi, rfl⟩ := hf x hx
use ⟨i, hi⟩
theorem ncard_congr {t : Set β} (f : ∀ a ∈ s, β) (h₁ : ∀ a ha, f a ha ∈ t)
(h₂ : ∀ a b ha hb, f a ha = f b hb → a = b) (h₃ : ∀ b ∈ t, ∃ a ha, f a ha = b) :
s.ncard = t.ncard := by
set f' : s → t := fun x ↦ ⟨f x.1 x.2, h₁ _ _⟩
have hbij : f'.Bijective := by
constructor
· rintro ⟨x, hx⟩ ⟨y, hy⟩ hxy
simp only [f', Subtype.mk.injEq] at hxy ⊢
exact h₂ _ _ hx hy hxy
rintro ⟨y, hy⟩
obtain ⟨a, ha, rfl⟩ := h₃ y hy
simp only [Subtype.mk.injEq, Subtype.exists]
exact ⟨_, ha, rfl⟩
simp_rw [← Nat.card_coe_set_eq]
exact Nat.card_congr (Equiv.ofBijective f' hbij)
theorem ncard_le_ncard_of_injOn {t : Set β} (f : α → β) (hf : ∀ a ∈ s, f a ∈ t) (f_inj : InjOn f s)
(ht : t.Finite := by toFinite_tac) :
s.ncard ≤ t.ncard := by
have hle := encard_le_encard_of_injOn hf f_inj
to_encard_tac; rwa [ht.cast_ncard_eq, (ht.finite_of_encard_le hle).cast_ncard_eq]
theorem exists_ne_map_eq_of_ncard_lt_of_maps_to {t : Set β} (hc : t.ncard < s.ncard) {f : α → β}
(hf : ∀ a ∈ s, f a ∈ t) (ht : t.Finite := by toFinite_tac) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ f x = f y := by
by_contra h'
simp only [Ne, exists_prop, not_exists, not_and, not_imp_not] at h'
exact (ncard_le_ncard_of_injOn f hf h' ht).not_lt hc
theorem le_ncard_of_inj_on_range {n : ℕ} (f : ℕ → α) (hf : ∀ i < n, f i ∈ s)
(f_inj : ∀ i < n, ∀ j < n, f i = f j → i = j) (hs : s.Finite := by toFinite_tac) :
n ≤ s.ncard := by
rw [ncard_eq_toFinset_card _ hs]
apply Finset.le_card_of_inj_on_range <;> simpa
theorem surj_on_of_inj_on_of_ncard_le {t : Set β} (f : ∀ a ∈ s, β) (hf : ∀ a ha, f a ha ∈ t)
(hinj : ∀ a₁ a₂ ha₁ ha₂, f a₁ ha₁ = f a₂ ha₂ → a₁ = a₂) (hst : t.ncard ≤ s.ncard)
(ht : t.Finite := by toFinite_tac) :
∀ b ∈ t, ∃ a ha, b = f a ha := by
intro b hb
set f' : s → t := fun x ↦ ⟨f x.1 x.2, hf _ _⟩
have finj : f'.Injective := by
rintro ⟨x, hx⟩ ⟨y, hy⟩ hxy
simp only [f', Subtype.mk.injEq] at hxy ⊢
apply hinj _ _ hx hy hxy
have hft := ht.fintype
have hft' := Fintype.ofInjective f' finj
set f'' : ∀ a, a ∈ s.toFinset → β := fun a h ↦ f a (by simpa using h)
convert @Finset.surj_on_of_inj_on_of_card_le _ _ _ t.toFinset f'' _ _ _ _ (by simpa) using 1
· simp [f'']
· simp [f'', hf]
· intros a₁ a₂ ha₁ ha₂ h
rw [mem_toFinset] at ha₁ ha₂
exact hinj _ _ ha₁ ha₂ h
rwa [← ncard_eq_toFinset_card', ← ncard_eq_toFinset_card']
theorem inj_on_of_surj_on_of_ncard_le {t : Set β} (f : ∀ a ∈ s, β) (hf : ∀ a ha, f a ha ∈ t)
(hsurj : ∀ b ∈ t, ∃ a ha, f a ha = b) (hst : s.ncard ≤ t.ncard) ⦃a₁⦄ (ha₁ : a₁ ∈ s) ⦃a₂⦄
(ha₂ : a₂ ∈ s) (ha₁a₂ : f a₁ ha₁ = f a₂ ha₂) (hs : s.Finite := by toFinite_tac) :
a₁ = a₂ := by
classical
set f' : s → t := fun x ↦ ⟨f x.1 x.2, hf _ _⟩
have hsurj : f'.Surjective := by
rintro ⟨y, hy⟩
obtain ⟨a, ha, rfl⟩ := hsurj y hy
simp only [Subtype.mk.injEq, Subtype.exists]
exact ⟨_, ha, rfl⟩
haveI := hs.fintype
haveI := Fintype.ofSurjective _ hsurj
set f'' : ∀ a, a ∈ s.toFinset → β := fun a h ↦ f a (by simpa using h)
exact
@Finset.inj_on_of_surj_on_of_card_le _ _ _ t.toFinset f''
(fun a ha ↦ by { rw [mem_toFinset] at ha ⊢; exact hf a ha }) (by simpa)
(by { rwa [← ncard_eq_toFinset_card', ← ncard_eq_toFinset_card'] }) a₁
(by simpa) a₂ (by simpa) (by simpa)
@[simp] theorem ncard_coe {α : Type*} (s : Set α) :
Set.ncard (Set.univ : Set (Set.Elem s)) = s.ncard :=
Set.ncard_congr (fun a ha ↦ ↑a) (fun a ha ↦ a.prop) (by simp) (by simp)
@[simp] lemma ncard_graphOn (s : Set α) (f : α → β) : (s.graphOn f).ncard = s.ncard := by
rw [← ncard_image_of_injOn fst_injOn_graph, image_fst_graphOn]
section Lattice
theorem ncard_union_add_ncard_inter (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∪ t).ncard + (s ∩ t).ncard = s.ncard + t.ncard := by
to_encard_tac; rw [hs.cast_ncard_eq, ht.cast_ncard_eq, (hs.union ht).cast_ncard_eq,
(hs.subset inter_subset_left).cast_ncard_eq, encard_union_add_encard_inter]
theorem ncard_inter_add_ncard_union (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∩ t).ncard + (s ∪ t).ncard = s.ncard + t.ncard := by
rw [add_comm, ncard_union_add_ncard_inter _ _ hs ht]
theorem ncard_union_le (s t : Set α) : (s ∪ t).ncard ≤ s.ncard + t.ncard := by
obtain (h | h) := (s ∪ t).finite_or_infinite
· to_encard_tac
rw [h.cast_ncard_eq, (h.subset subset_union_left).cast_ncard_eq,
(h.subset subset_union_right).cast_ncard_eq]
apply encard_union_le
rw [h.ncard]
apply zero_le
theorem ncard_union_eq (h : Disjoint s t) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : (s ∪ t).ncard = s.ncard + t.ncard := by
to_encard_tac
rw [hs.cast_ncard_eq, ht.cast_ncard_eq, (hs.union ht).cast_ncard_eq, encard_union_eq h]
theorem ncard_diff_add_ncard_of_subset (h : s ⊆ t) (ht : t.Finite := by toFinite_tac) :
(t \ s).ncard + s.ncard = t.ncard := by
to_encard_tac
rw [ht.cast_ncard_eq, (ht.subset h).cast_ncard_eq, ht.diff.cast_ncard_eq,
encard_diff_add_encard_of_subset h]
theorem ncard_diff (hst : s ⊆ t) (hs : s.Finite := by toFinite_tac) :
(t \ s).ncard = t.ncard - s.ncard := by
obtain ht | ht := t.finite_or_infinite
· rw [← ncard_diff_add_ncard_of_subset hst ht, add_tsub_cancel_right]
· rw [ht.ncard, Nat.zero_sub, (ht.diff hs).ncard]
lemma cast_ncard_sdiff {R : Type*} [AddGroupWithOne R] (hst : s ⊆ t) (ht : t.Finite) :
((t \ s).ncard : R) = t.ncard - s.ncard := by
rw [ncard_diff hst (ht.subset hst), Nat.cast_sub (ncard_le_ncard hst ht)]
theorem ncard_le_ncard_diff_add_ncard (s t : Set α) (ht : t.Finite := by toFinite_tac) :
s.ncard ≤ (s \ t).ncard + t.ncard := by
rcases s.finite_or_infinite with hs | hs
· to_encard_tac
rw [ht.cast_ncard_eq, hs.cast_ncard_eq, hs.diff.cast_ncard_eq]
apply encard_le_encard_diff_add_encard
convert Nat.zero_le _
rw [hs.ncard]
theorem le_ncard_diff (s t : Set α) (hs : s.Finite := by toFinite_tac) :
t.ncard - s.ncard ≤ (t \ s).ncard :=
tsub_le_iff_left.mpr (by rw [add_comm]; apply ncard_le_ncard_diff_add_ncard _ _ hs)
theorem ncard_diff_add_ncard (s t : Set α) (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) :
(s \ t).ncard + t.ncard = (s ∪ t).ncard := by
rw [← ncard_union_eq disjoint_sdiff_left hs.diff ht, diff_union_self]
theorem diff_nonempty_of_ncard_lt_ncard (h : s.ncard < t.ncard) (hs : s.Finite := by toFinite_tac) :
(t \ s).Nonempty := by
rw [Set.nonempty_iff_ne_empty, Ne, diff_eq_empty]
exact fun h' ↦ h.not_le (ncard_le_ncard h' hs)
theorem exists_mem_not_mem_of_ncard_lt_ncard (h : s.ncard < t.ncard)
(hs : s.Finite := by toFinite_tac) : ∃ e, e ∈ t ∧ e ∉ s :=
diff_nonempty_of_ncard_lt_ncard h hs
@[simp] theorem ncard_inter_add_ncard_diff_eq_ncard (s t : Set α)
(hs : s.Finite := by toFinite_tac) : (s ∩ t).ncard + (s \ t).ncard = s.ncard := by
rw [← ncard_union_eq (disjoint_of_subset_left inter_subset_right disjoint_sdiff_right)
(hs.inter_of_left _) hs.diff, union_comm, diff_union_inter]
theorem ncard_eq_ncard_iff_ncard_diff_eq_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard = t.ncard ↔ (s \ t).ncard = (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_right_inj]
theorem ncard_le_ncard_iff_ncard_diff_le_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard ≤ t.ncard ↔ (s \ t).ncard ≤ (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_le_add_iff_left]
theorem ncard_lt_ncard_iff_ncard_diff_lt_ncard_diff (hs : s.Finite := by toFinite_tac)
(ht : t.Finite := by toFinite_tac) : s.ncard < t.ncard ↔ (s \ t).ncard < (t \ s).ncard := by
rw [← ncard_inter_add_ncard_diff_eq_ncard s t hs, ← ncard_inter_add_ncard_diff_eq_ncard t s ht,
inter_comm, add_lt_add_iff_left]
theorem ncard_add_ncard_compl (s : Set α) (hs : s.Finite := by toFinite_tac)
(hsc : sᶜ.Finite := by toFinite_tac) : s.ncard + sᶜ.ncard = Nat.card α := by
rw [← ncard_univ, ← ncard_union_eq (@disjoint_compl_right _ _ s) hs hsc, union_compl_self]
theorem eq_univ_iff_ncard [Finite α] (s : Set α) :
s = univ ↔ ncard s = Nat.card α := by
rw [← compl_empty_iff, ← ncard_eq_zero, ← ncard_add_ncard_compl s, left_eq_add]
lemma even_ncard_compl_iff [Finite α] (heven : Even (Nat.card α)) (s : Set α) :
Even sᶜ.ncard ↔ Even s.ncard := by
| simp [compl_eq_univ_diff, ncard_diff (subset_univ _ : s ⊆ Set.univ),
Nat.even_sub (ncard_le_ncard (subset_univ _ : s ⊆ Set.univ)),
(ncard_univ _).symm ▸ heven]
lemma odd_ncard_compl_iff [Finite α] (heven : Even (Nat.card α)) (s : Set α) :
Odd sᶜ.ncard ↔ Odd s.ncard := by
rw [← Nat.not_even_iff_odd, even_ncard_compl_iff heven, Nat.not_even_iff_odd]
end Lattice
/-- Given a subset `s` of a set `t`, of sizes at most and at least `n` respectively, there exists a
set `u` of size `n` which is both a superset of `s` and a subset of `t`. -/
| Mathlib/Data/Set/Card.lean | 941 | 952 |
/-
Copyright (c) 2022 Patrick Massot. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Patrick Massot, Floris van Doorn, Yury Kudryashov
-/
import Mathlib.Order.Filter.Lift
import Mathlib.Order.Filter.AtTopBot.Basic
/-!
# The filter of small sets
This file defines the filter of small sets w.r.t. a filter `f`, which is the largest filter
containing all powersets of members of `f`.
`g` converges to `f.smallSets` if for all `s ∈ f`, eventually we have `g x ⊆ s`.
An example usage is that if `f : ι → E → ℝ` is a family of nonnegative functions with integral 1,
then saying that `fun i ↦ support (f i)` tendsto `(𝓝 0).smallSets` is a way of saying that
`f` tends to the Dirac delta distribution.
-/
open Filter
open Filter Set
variable {α β : Type*} {ι : Sort*}
namespace Filter
variable {l l' la : Filter α} {lb : Filter β}
/-- The filter `l.smallSets` is the largest filter containing all powersets of members of `l`. -/
def smallSets (l : Filter α) : Filter (Set α) :=
l.lift' powerset
theorem smallSets_eq_generate {f : Filter α} : f.smallSets = generate (powerset '' f.sets) := by
simp_rw [generate_eq_biInf, smallSets, iInf_image, Filter.lift', Filter.lift, Function.comp_apply,
Filter.mem_sets]
-- TODO: get more properties from the adjunction?
-- TODO: is there a general way to get a lower adjoint for the lift of an upper adjoint?
theorem bind_smallSets_gc :
GaloisConnection (fun L : Filter (Set α) ↦ L.bind principal) smallSets := by
intro L l
simp_rw [smallSets_eq_generate, le_generate_iff, image_subset_iff]
rfl
protected theorem HasBasis.smallSets {p : ι → Prop} {s : ι → Set α} (h : HasBasis l p s) :
HasBasis l.smallSets p fun i => 𝒫 s i :=
h.lift' monotone_powerset
theorem hasBasis_smallSets (l : Filter α) :
HasBasis l.smallSets (fun t : Set α => t ∈ l) powerset :=
l.basis_sets.smallSets
theorem Eventually.exists_mem_basis_of_smallSets {p : ι → Prop} {s : ι → Set α} {P : Set α → Prop}
(h₁ : ∀ᶠ t in l.smallSets, P t) (h₂ : HasBasis l p s) : ∃ i, p i ∧ P (s i) :=
(h₂.smallSets.eventually_iff.mp h₁).imp fun _i ⟨hpi, hi⟩ ↦ ⟨hpi, hi Subset.rfl⟩
theorem Frequently.smallSets_of_forall_mem_basis {p : ι → Prop} {s : ι → Set α} {P : Set α → Prop}
(h₁ : ∀ i, p i → P (s i)) (h₂ : HasBasis l p s) : ∃ᶠ t in l.smallSets, P t :=
h₂.smallSets.frequently_iff.mpr fun _ hi => ⟨_, Subset.rfl, h₁ _ hi⟩
theorem Eventually.exists_mem_of_smallSets {p : Set α → Prop}
(h : ∀ᶠ t in l.smallSets, p t) : ∃ s ∈ l, p s :=
h.exists_mem_basis_of_smallSets l.basis_sets
/-! No `Frequently.smallSets_of_forall_mem (h : ∀ s ∈ l, p s) : ∃ᶠ t in l.smallSets, p t` as
`Filter.frequently_smallSets_mem : ∃ᶠ t in l.smallSets, t ∈ l` is preferred. -/
/-- `g` converges to `f.smallSets` if for all `s ∈ f`, eventually we have `g x ⊆ s`. -/
theorem tendsto_smallSets_iff {f : α → Set β} :
Tendsto f la lb.smallSets ↔ ∀ t ∈ lb, ∀ᶠ x in la, f x ⊆ t :=
(hasBasis_smallSets lb).tendsto_right_iff
theorem eventually_smallSets {p : Set α → Prop} :
(∀ᶠ s in l.smallSets, p s) ↔ ∃ s ∈ l, ∀ t, t ⊆ s → p t :=
eventually_lift'_iff monotone_powerset
theorem eventually_smallSets' {p : Set α → Prop} (hp : ∀ ⦃s t⦄, s ⊆ t → p t → p s) :
(∀ᶠ s in l.smallSets, p s) ↔ ∃ s ∈ l, p s :=
eventually_smallSets.trans <|
exists_congr fun s => Iff.rfl.and ⟨fun H => H s Subset.rfl, fun hs _t ht => hp ht hs⟩
theorem frequently_smallSets {p : Set α → Prop} :
(∃ᶠ s in l.smallSets, p s) ↔ ∀ t ∈ l, ∃ s, s ⊆ t ∧ p s :=
l.hasBasis_smallSets.frequently_iff
theorem frequently_smallSets_mem (l : Filter α) : ∃ᶠ s in l.smallSets, s ∈ l :=
frequently_smallSets.2 fun t ht => ⟨t, Subset.rfl, ht⟩
@[simp]
lemma tendsto_image_smallSets {f : α → β} :
Tendsto (f '' ·) la.smallSets lb.smallSets ↔ Tendsto f la lb := by
rw [tendsto_smallSets_iff]
refine forall₂_congr fun u hu ↦ ?_
rw [eventually_smallSets' fun s t hst ht ↦ (image_subset _ hst).trans ht]
simp only [image_subset_iff, exists_mem_subset_iff, mem_map]
alias ⟨_, Tendsto.image_smallSets⟩ := tendsto_image_smallSets
theorem HasAntitoneBasis.tendsto_smallSets {ι} [Preorder ι] {s : ι → Set α}
(hl : l.HasAntitoneBasis s) : Tendsto s atTop l.smallSets :=
tendsto_smallSets_iff.2 fun _t ht => hl.eventually_subset ht
@[mono]
theorem monotone_smallSets : Monotone (@smallSets α) :=
monotone_lift' monotone_id monotone_const
@[simp]
theorem smallSets_bot : (⊥ : Filter α).smallSets = pure ∅ := by
rw [smallSets, lift'_bot, powerset_empty, principal_singleton]
exact monotone_powerset
@[simp]
theorem smallSets_top : (⊤ : Filter α).smallSets = ⊤ := by
rw [smallSets, lift'_top, powerset_univ, principal_univ]
@[simp]
theorem smallSets_principal (s : Set α) : (𝓟 s).smallSets = 𝓟 (𝒫 s) :=
lift'_principal monotone_powerset
theorem smallSets_comap_eq_comap_image (l : Filter β) (f : α → β) :
(comap f l).smallSets = comap (image f) l.smallSets := by
refine (gc_map_comap _).u_comm_of_l_comm (gc_map_comap _) bind_smallSets_gc bind_smallSets_gc ?_
simp [Function.comp_def, map_bind, bind_map]
theorem smallSets_comap (l : Filter β) (f : α → β) :
(comap f l).smallSets = l.lift' (powerset ∘ preimage f) :=
comap_lift'_eq2 monotone_powerset
theorem comap_smallSets (l : Filter β) (f : α → Set β) :
comap f l.smallSets = l.lift' (preimage f ∘ powerset) :=
comap_lift'_eq
theorem smallSets_iInf {f : ι → Filter α} : (iInf f).smallSets = ⨅ i, (f i).smallSets :=
lift'_iInf_of_map_univ (powerset_inter _ _) powerset_univ
theorem smallSets_inf (l₁ l₂ : Filter α) : (l₁ ⊓ l₂).smallSets = l₁.smallSets ⊓ l₂.smallSets :=
lift'_inf _ _ powerset_inter
instance smallSets_neBot (l : Filter α) : NeBot l.smallSets := by
refine (lift'_neBot_iff ?_).2 fun _ _ => powerset_nonempty
exact monotone_powerset
theorem Tendsto.smallSets_mono {s t : α → Set β} (ht : Tendsto t la lb.smallSets)
(hst : ∀ᶠ x in la, s x ⊆ t x) : Tendsto s la lb.smallSets := by
rw [tendsto_smallSets_iff] at ht ⊢
exact fun u hu => (ht u hu).mp (hst.mono fun _ hst ht => hst.trans ht)
/-- Generalized **squeeze theorem** (also known as **sandwich theorem**). If `s : α → Set β` is a
family of sets that tends to `Filter.smallSets lb` along `la` and `f : α → β` is a function such
that `f x ∈ s x` eventually along `la`, then `f` tends to `lb` along `la`.
If `s x` is the closed interval `[g x, h x]` for some functions `g`, `h` that tend to the same limit
`𝓝 y`, then we obtain the standard squeeze theorem, see
`tendsto_of_tendsto_of_tendsto_of_le_of_le'`. -/
theorem Tendsto.of_smallSets {s : α → Set β} {f : α → β} (hs : Tendsto s la lb.smallSets)
(hf : ∀ᶠ x in la, f x ∈ s x) : Tendsto f la lb := fun t ht =>
hf.mp <| (tendsto_smallSets_iff.mp hs t ht).mono fun _ h₁ h₂ => h₁ h₂
@[simp]
theorem eventually_smallSets_eventually {p : α → Prop} :
(∀ᶠ s in l.smallSets, ∀ᶠ x in l', x ∈ s → p x) ↔ ∀ᶠ x in l ⊓ l', p x :=
calc
_ ↔ ∃ s ∈ l, ∀ᶠ x in l', x ∈ s → p x :=
eventually_smallSets' fun _ _ hst ht => ht.mono fun _ hx hs => hx (hst hs)
_ ↔ ∃ s ∈ l, ∃ t ∈ l', ∀ x, x ∈ t → x ∈ s → p x := by simp only [eventually_iff_exists_mem]
_ ↔ ∀ᶠ x in l ⊓ l', p x := by simp only [eventually_inf, and_comm, mem_inter_iff, ← and_imp]
| @[simp]
theorem eventually_smallSets_forall {p : α → Prop} :
(∀ᶠ s in l.smallSets, ∀ x ∈ s, p x) ↔ ∀ᶠ x in l, p x := by
simpa only [inf_top_eq, eventually_top] using @eventually_smallSets_eventually α l ⊤ p
alias ⟨Eventually.of_smallSets, Eventually.smallSets⟩ := eventually_smallSets_forall
| Mathlib/Order/Filter/SmallSets.lean | 172 | 178 |
/-
Copyright (c) 2021 Yaël Dillies, Bhavik Mehta. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Bhavik Mehta
-/
import Mathlib.Algebra.GroupWithZero.Action.Defs
import Mathlib.Algebra.Order.Interval.Finset.Basic
import Mathlib.Combinatorics.Additive.FreimanHom
import Mathlib.Order.Interval.Finset.Fin
import Mathlib.Algebra.Group.Pointwise.Set.Scalar
/-!
# Sets without arithmetic progressions of length three and Roth numbers
This file defines sets without arithmetic progressions of length three, aka 3AP-free sets, and the
Roth number of a set.
The corresponding notion, sets without geometric progressions of length three, are called 3GP-free
sets.
The Roth number of a finset is the size of its biggest 3AP-free subset. This is a more general
definition than the one often found in mathematical literature, where the `n`-th Roth number is
the size of the biggest 3AP-free subset of `{0, ..., n - 1}`.
## Main declarations
* `ThreeGPFree`: Predicate for a set to be 3GP-free.
* `ThreeAPFree`: Predicate for a set to be 3AP-free.
* `mulRothNumber`: The multiplicative Roth number of a finset.
* `addRothNumber`: The additive Roth number of a finset.
* `rothNumberNat`: The Roth number of a natural, namely `addRothNumber (Finset.range n)`.
## TODO
* Can `threeAPFree_iff_eq_right` be made more general?
* Generalize `ThreeGPFree.image` to Freiman homs
## References
* [Wikipedia, *Salem-Spencer set*](https://en.wikipedia.org/wiki/Salem–Spencer_set)
## Tags
3AP-free, Salem-Spencer, Roth, arithmetic progression, average, three-free
-/
assert_not_exists Field Ideal TwoSidedIdeal
open Finset Function
open scoped Pointwise
variable {F α β : Type*}
section ThreeAPFree
open Set
section Monoid
variable [Monoid α] [Monoid β] (s t : Set α)
/-- A set is **3GP-free** if it does not contain any non-trivial geometric progression of length
three. -/
@[to_additive "A set is **3AP-free** if it does not contain any non-trivial arithmetic progression
of length three.
This is also sometimes called a **non averaging set** or **Salem-Spencer set**."]
def ThreeGPFree : Prop := ∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → a * c = b * b → a = b
/-- Whether a given finset is 3GP-free is decidable. -/
@[to_additive "Whether a given finset is 3AP-free is decidable."]
instance ThreeGPFree.instDecidable [DecidableEq α] {s : Finset α} :
Decidable (ThreeGPFree (s : Set α)) :=
decidable_of_iff (∀ a ∈ s, ∀ b ∈ s, ∀ c ∈ s, a * c = b * b → a = b) Iff.rfl
variable {s t}
@[to_additive]
theorem ThreeGPFree.mono (h : t ⊆ s) (hs : ThreeGPFree s) : ThreeGPFree t :=
fun _ ha _ hb _ hc ↦ hs (h ha) (h hb) (h hc)
@[to_additive (attr := simp)]
theorem threeGPFree_empty : ThreeGPFree (∅ : Set α) := fun _ _ _ ha => ha.elim
@[to_additive]
theorem Set.Subsingleton.threeGPFree (hs : s.Subsingleton) : ThreeGPFree s :=
fun _ ha _ hb _ _ _ ↦ hs ha hb
@[to_additive (attr := simp)]
theorem threeGPFree_singleton (a : α) : ThreeGPFree ({a} : Set α) :=
subsingleton_singleton.threeGPFree
@[to_additive ThreeAPFree.prod]
theorem ThreeGPFree.prod {t : Set β} (hs : ThreeGPFree s) (ht : ThreeGPFree t) :
ThreeGPFree (s ×ˢ t) := fun _ ha _ hb _ hc h ↦
Prod.ext (hs ha.1 hb.1 hc.1 (Prod.ext_iff.1 h).1) (ht ha.2 hb.2 hc.2 (Prod.ext_iff.1 h).2)
@[to_additive]
theorem threeGPFree_pi {ι : Type*} {α : ι → Type*} [∀ i, Monoid (α i)] {s : ∀ i, Set (α i)}
(hs : ∀ i, ThreeGPFree (s i)) : ThreeGPFree ((univ : Set ι).pi s) :=
fun _ ha _ hb _ hc h ↦
funext fun i => hs i (ha i trivial) (hb i trivial) (hc i trivial) <| congr_fun h i
end Monoid
section CommMonoid
variable [CommMonoid α] [CommMonoid β] {s A : Set α} {t : Set β} {f : α → β}
/-- Geometric progressions of length three are reflected under `2`-Freiman homomorphisms. -/
@[to_additive
"Arithmetic progressions of length three are reflected under `2`-Freiman homomorphisms."]
lemma ThreeGPFree.of_image (hf : IsMulFreimanHom 2 s t f) (hf' : s.InjOn f) (hAs : A ⊆ s)
(hA : ThreeGPFree (f '' A)) : ThreeGPFree A :=
fun _ ha _ hb _ hc habc ↦ hf' (hAs ha) (hAs hb) <| hA (mem_image_of_mem _ ha)
(mem_image_of_mem _ hb) (mem_image_of_mem _ hc) <|
hf.mul_eq_mul (hAs ha) (hAs hc) (hAs hb) (hAs hb) habc
/-- Geometric progressions of length three are unchanged under `2`-Freiman isomorphisms. -/
@[to_additive
"Arithmetic progressions of length three are unchanged under `2`-Freiman isomorphisms."]
lemma threeGPFree_image (hf : IsMulFreimanIso 2 s t f) (hAs : A ⊆ s) :
ThreeGPFree (f '' A) ↔ ThreeGPFree A := by
rw [ThreeGPFree, ThreeGPFree]
have := (hf.bijOn.injOn.mono hAs).bijOn_image (f := f)
simp +contextual only
[((hf.bijOn.injOn.mono hAs).bijOn_image (f := f)).forall,
hf.mul_eq_mul (hAs _) (hAs _) (hAs _) (hAs _), this.injOn.eq_iff]
@[to_additive] alias ⟨_, ThreeGPFree.image⟩ := threeGPFree_image
/-- Geometric progressions of length three are reflected under `2`-Freiman homomorphisms. -/
@[to_additive
"Arithmetic progressions of length three are reflected under `2`-Freiman homomorphisms."]
lemma IsMulFreimanHom.threeGPFree (hf : IsMulFreimanHom 2 s t f) (hf' : s.InjOn f)
(ht : ThreeGPFree t) : ThreeGPFree s :=
(ht.mono hf.mapsTo.image_subset).of_image hf hf' subset_rfl
/-- Geometric progressions of length three are unchanged under `2`-Freiman isomorphisms. -/
@[to_additive
"Arithmetic progressions of length three are unchanged under `2`-Freiman isomorphisms."]
lemma IsMulFreimanIso.threeGPFree_congr (hf : IsMulFreimanIso 2 s t f) :
ThreeGPFree s ↔ ThreeGPFree t := by
rw [← threeGPFree_image hf subset_rfl, hf.bijOn.image_eq]
/-- Geometric progressions of length three are preserved under semigroup homomorphisms. -/
@[to_additive
"Arithmetic progressions of length three are preserved under semigroup homomorphisms."]
theorem ThreeGPFree.image' [FunLike F α β] [MulHomClass F α β] (f : F) (hf : (s * s).InjOn f)
(h : ThreeGPFree s) : ThreeGPFree (f '' s) := by
rintro _ ⟨a, ha, rfl⟩ _ ⟨b, hb, rfl⟩ _ ⟨c, hc, rfl⟩ habc
rw [h ha hb hc (hf (mul_mem_mul ha hc) (mul_mem_mul hb hb) <| by rwa [map_mul, map_mul])]
end CommMonoid
section CancelCommMonoid
variable [CommMonoid α] [IsCancelMul α] {s : Set α} {a : α}
@[to_additive] lemma ThreeGPFree.eq_right (hs : ThreeGPFree s) :
∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → a * c = b * b → b = c := by
rintro a ha b hb c hc habc
obtain rfl := hs ha hb hc habc
simpa using habc.symm
@[to_additive] lemma threeGPFree_insert :
ThreeGPFree (insert a s) ↔ ThreeGPFree s ∧
(∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → a * c = b * b → a = b) ∧
∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → b * c = a * a → b = a := by
refine ⟨fun hs ↦ ⟨hs.mono (subset_insert _ _),
fun b hb c hc ↦ hs (Or.inl rfl) (Or.inr hb) (Or.inr hc),
fun b hb c hc ↦ hs (Or.inr hb) (Or.inl rfl) (Or.inr hc)⟩, ?_⟩
rintro ⟨hs, ha, ha'⟩ b hb c hc d hd h
rw [mem_insert_iff] at hb hc hd
obtain rfl | hb := hb <;> obtain rfl | hc := hc
· rfl
all_goals obtain rfl | hd := hd
· exact (ha' hc hc h.symm).symm
· exact ha hc hd h
· exact mul_right_cancel h
· exact ha' hb hd h
· obtain rfl := ha hc hb ((mul_comm _ _).trans h)
exact ha' hb hc h
· exact hs hb hc hd h
@[to_additive]
theorem ThreeGPFree.smul_set (hs : ThreeGPFree s) : ThreeGPFree (a • s) := by
rintro _ ⟨b, hb, rfl⟩ _ ⟨c, hc, rfl⟩ _ ⟨d, hd, rfl⟩ h
exact congr_arg (a • ·) <| hs hb hc hd <| by simpa [mul_mul_mul_comm _ _ a] using h
@[to_additive] lemma threeGPFree_smul_set : ThreeGPFree (a • s) ↔ ThreeGPFree s where
mp hs b hb c hc d hd h := mul_left_cancel
(hs (mem_image_of_mem _ hb) (mem_image_of_mem _ hc) (mem_image_of_mem _ hd) <| by
rw [mul_mul_mul_comm, smul_eq_mul, smul_eq_mul, mul_mul_mul_comm, h])
mpr := ThreeGPFree.smul_set
end CancelCommMonoid
section OrderedCancelCommMonoid
variable [CommMonoid α] [PartialOrder α] [IsOrderedCancelMonoid α] {s : Set α} {a : α}
@[to_additive]
theorem threeGPFree_insert_of_lt (hs : ∀ i ∈ s, i < a) :
ThreeGPFree (insert a s) ↔
ThreeGPFree s ∧ ∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → a * c = b * b → a = b := by
refine threeGPFree_insert.trans ?_
rw [← and_assoc]
exact and_iff_left fun b hb c hc h => ((mul_lt_mul_of_lt_of_lt (hs _ hb) (hs _ hc)).ne h).elim
end OrderedCancelCommMonoid
section CancelCommMonoidWithZero
variable [CancelCommMonoidWithZero α] [NoZeroDivisors α] {s : Set α} {a : α}
lemma ThreeGPFree.smul_set₀ (hs : ThreeGPFree s) (ha : a ≠ 0) : ThreeGPFree (a • s) := by
rintro _ ⟨b, hb, rfl⟩ _ ⟨c, hc, rfl⟩ _ ⟨d, hd, rfl⟩ h
exact congr_arg (a • ·) <| hs hb hc hd <| by simpa [mul_mul_mul_comm _ _ a, ha] using h
theorem threeGPFree_smul_set₀ (ha : a ≠ 0) : ThreeGPFree (a • s) ↔ ThreeGPFree s :=
⟨fun hs b hb c hc d hd h ↦
mul_left_cancel₀ ha
(hs (Set.mem_image_of_mem _ hb) (Set.mem_image_of_mem _ hc) (Set.mem_image_of_mem _ hd) <| by
rw [smul_eq_mul, smul_eq_mul, mul_mul_mul_comm, h, mul_mul_mul_comm]),
fun hs => hs.smul_set₀ ha⟩
end CancelCommMonoidWithZero
section Nat
theorem threeAPFree_iff_eq_right {s : Set ℕ} :
ThreeAPFree s ↔ ∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → ∀ ⦃c⦄, c ∈ s → a + c = b + b → a = c := by
refine forall₄_congr fun a _ha b hb => forall₃_congr fun c hc habc => ⟨?_, ?_⟩
· rintro rfl
exact (add_left_cancel habc).symm
· rintro rfl
simp_rw [← two_mul] at habc
exact mul_left_cancel₀ two_ne_zero habc
end Nat
end ThreeAPFree
open Finset
section RothNumber
variable [DecidableEq α]
section Monoid
variable [Monoid α] [DecidableEq β] [Monoid β] (s t : Finset α)
/-- The multiplicative Roth number of a finset is the cardinality of its biggest 3GP-free subset. -/
@[to_additive "The additive Roth number of a finset is the cardinality of its biggest 3AP-free
subset.
The usual Roth number corresponds to `addRothNumber (Finset.range n)`, see `rothNumberNat`."]
def mulRothNumber : Finset α →o ℕ :=
⟨fun s ↦ Nat.findGreatest (fun m ↦ ∃ t ⊆ s, #t = m ∧ ThreeGPFree (t : Set α)) #s, by
rintro t u htu
refine Nat.findGreatest_mono (fun m => ?_) (card_le_card htu)
rintro ⟨v, hvt, hv⟩
exact ⟨v, hvt.trans htu, hv⟩⟩
@[to_additive]
theorem mulRothNumber_le : mulRothNumber s ≤ #s := Nat.findGreatest_le #s
@[to_additive]
theorem mulRothNumber_spec :
∃ t ⊆ s, #t = mulRothNumber s ∧ ThreeGPFree (t : Set α) :=
Nat.findGreatest_spec (P := fun m ↦ ∃ t ⊆ s, #t = m ∧ ThreeGPFree (t : Set α))
(Nat.zero_le _) ⟨∅, empty_subset _, card_empty, by norm_cast; exact threeGPFree_empty⟩
variable {s t} {n : ℕ}
@[to_additive]
theorem ThreeGPFree.le_mulRothNumber (hs : ThreeGPFree (s : Set α)) (h : s ⊆ t) :
#s ≤ mulRothNumber t :=
Nat.le_findGreatest (card_le_card h) ⟨s, h, rfl, hs⟩
@[to_additive]
theorem ThreeGPFree.mulRothNumber_eq (hs : ThreeGPFree (s : Set α)) :
mulRothNumber s = #s :=
(mulRothNumber_le _).antisymm <| hs.le_mulRothNumber <| Subset.refl _
@[to_additive (attr := simp)]
theorem mulRothNumber_empty : mulRothNumber (∅ : Finset α) = 0 :=
Nat.eq_zero_of_le_zero <| (mulRothNumber_le _).trans card_empty.le
@[to_additive (attr := simp)]
theorem mulRothNumber_singleton (a : α) : mulRothNumber ({a} : Finset α) = 1 := by
refine ThreeGPFree.mulRothNumber_eq ?_
rw [coe_singleton]
exact threeGPFree_singleton a
@[to_additive]
theorem mulRothNumber_union_le (s t : Finset α) :
mulRothNumber (s ∪ t) ≤ mulRothNumber s + mulRothNumber t :=
let ⟨u, hus, hcard, hu⟩ := mulRothNumber_spec (s ∪ t)
calc
mulRothNumber (s ∪ t) = #u := hcard.symm
_ = #(u ∩ s ∪ u ∩ t) := by rw [← inter_union_distrib_left, inter_eq_left.2 hus]
_ ≤ #(u ∩ s) + #(u ∩ t) := card_union_le _ _
_ ≤ mulRothNumber s + mulRothNumber t := _root_.add_le_add
((hu.mono inter_subset_left).le_mulRothNumber inter_subset_right)
((hu.mono inter_subset_left).le_mulRothNumber inter_subset_right)
@[to_additive]
theorem le_mulRothNumber_product (s : Finset α) (t : Finset β) :
mulRothNumber s * mulRothNumber t ≤ mulRothNumber (s ×ˢ t) := by
obtain ⟨u, hus, hucard, hu⟩ := mulRothNumber_spec s
obtain ⟨v, hvt, hvcard, hv⟩ := mulRothNumber_spec t
rw [← hucard, ← hvcard, ← card_product]
refine ThreeGPFree.le_mulRothNumber ?_ (product_subset_product hus hvt)
rw [coe_product]
exact hu.prod hv
@[to_additive]
theorem mulRothNumber_lt_of_forall_not_threeGPFree
(h : ∀ t ∈ powersetCard n s, ¬ThreeGPFree ((t : Finset α) : Set α)) :
mulRothNumber s < n := by
obtain ⟨t, hts, hcard, ht⟩ := mulRothNumber_spec s
rw [← hcard, ← not_le]
intro hn
obtain ⟨u, hut, rfl⟩ := exists_subset_card_eq hn
exact h _ (mem_powersetCard.2 ⟨hut.trans hts, rfl⟩) (ht.mono hut)
end Monoid
section CommMonoid
variable [CommMonoid α] [CommMonoid β] [DecidableEq β] {A : Finset α} {B : Finset β} {f : α → β}
/-- Arithmetic progressions can be pushed forward along bijective 2-Freiman homs. -/
@[to_additive "Arithmetic progressions can be pushed forward along bijective 2-Freiman homs."]
lemma IsMulFreimanHom.mulRothNumber_mono (hf : IsMulFreimanHom 2 A B f) (hf' : Set.BijOn f A B) :
mulRothNumber B ≤ mulRothNumber A := by
obtain ⟨s, hsB, hcard, hs⟩ := mulRothNumber_spec B
have hsA : invFunOn f A '' s ⊆ A :=
(hf'.surjOn.mapsTo_invFunOn.mono (coe_subset.2 hsB) Subset.rfl).image_subset
have hfsA : Set.SurjOn f A s := hf'.surjOn.mono Subset.rfl (coe_subset.2 hsB)
rw [← hcard, ← s.card_image_of_injOn ((invFunOn_injOn_image f _).mono hfsA)]
refine ThreeGPFree.le_mulRothNumber ?_ (mod_cast hsA)
rw [coe_image]
simpa using (hf.subset hsA hfsA.bijOn_subset.mapsTo).threeGPFree (hf'.injOn.mono hsA) hs
/-- Arithmetic progressions are preserved under 2-Freiman isos. -/
@[to_additive "Arithmetic progressions are preserved under 2-Freiman isos."]
lemma IsMulFreimanIso.mulRothNumber_congr (hf : IsMulFreimanIso 2 A B f) :
mulRothNumber A = mulRothNumber B := by
refine le_antisymm ?_ (hf.isMulFreimanHom.mulRothNumber_mono hf.bijOn)
obtain ⟨s, hsA, hcard, hs⟩ := mulRothNumber_spec A
rw [← coe_subset] at hsA
have hfs : Set.InjOn f s := hf.bijOn.injOn.mono hsA
have := (hf.subset hsA hfs.bijOn_image).threeGPFree_congr.1 hs
rw [← coe_image] at this
rw [← hcard, ← Finset.card_image_of_injOn hfs]
refine this.le_mulRothNumber ?_
rw [← coe_subset, coe_image]
exact (hf.bijOn.mapsTo.mono hsA Subset.rfl).image_subset
end CommMonoid
section CancelCommMonoid
variable [CancelCommMonoid α] (s : Finset α) (a : α)
@[to_additive (attr := simp)]
theorem mulRothNumber_map_mul_left :
mulRothNumber (s.map <| mulLeftEmbedding a) = mulRothNumber s := by
refine le_antisymm ?_ ?_
· obtain ⟨u, hus, hcard, hu⟩ := mulRothNumber_spec (s.map <| mulLeftEmbedding a)
rw [subset_map_iff] at hus
obtain ⟨u, hus, rfl⟩ := hus
rw [coe_map] at hu
rw [← hcard, card_map]
exact (threeGPFree_smul_set.1 hu).le_mulRothNumber hus
· obtain ⟨u, hus, hcard, hu⟩ := mulRothNumber_spec s
have h : ThreeGPFree (u.map <| mulLeftEmbedding a : Set α) := by rw [coe_map]; exact hu.smul_set
convert h.le_mulRothNumber (map_subset_map.2 hus) using 1
rw [card_map, hcard]
@[to_additive (attr := simp)]
theorem mulRothNumber_map_mul_right :
mulRothNumber (s.map <| mulRightEmbedding a) = mulRothNumber s := by
rw [← mulLeftEmbedding_eq_mulRightEmbedding, mulRothNumber_map_mul_left s a]
end CancelCommMonoid
end RothNumber
section rothNumberNat
variable {k n : ℕ}
/-- The Roth number of a natural `N` is the largest integer `m` for which there is a subset of
`range N` of size `m` with no arithmetic progression of length 3.
Trivially, `rothNumberNat N ≤ N`, but Roth's theorem (proved in 1953) shows that
`rothNumberNat N = o(N)` and the construction by Behrend gives a lower bound of the form
`N * exp(-C sqrt(log(N))) ≤ rothNumberNat N`.
A significant refinement of Roth's theorem by Bloom and Sisask announced in 2020 gives
`rothNumberNat N = O(N / (log N)^(1+c))` for an absolute constant `c`. -/
def rothNumberNat : ℕ →o ℕ :=
⟨fun n => addRothNumber (range n), addRothNumber.mono.comp range_mono⟩
theorem rothNumberNat_def (n : ℕ) : rothNumberNat n = addRothNumber (range n) :=
rfl
theorem rothNumberNat_le (N : ℕ) : rothNumberNat N ≤ N :=
(addRothNumber_le _).trans (card_range _).le
theorem rothNumberNat_spec (n : ℕ) :
∃ t ⊆ range n, #t = rothNumberNat n ∧ ThreeAPFree (t : Set ℕ) :=
addRothNumber_spec _
/-- A verbose specialization of `threeAPFree.le_addRothNumber`, sometimes convenient in
practice. -/
theorem ThreeAPFree.le_rothNumberNat (s : Finset ℕ) (hs : ThreeAPFree (s : Set ℕ))
(hsn : ∀ x ∈ s, x < n) (hsk : #s = k) : k ≤ rothNumberNat n :=
hsk.ge.trans <| hs.le_addRothNumber fun x hx => mem_range.2 <| hsn x hx
/-- The Roth number is a subadditive function. Note that by Fekete's lemma this shows that
the limit `rothNumberNat N / N` exists, but Roth's theorem gives the stronger result that this
limit is actually `0`. -/
theorem rothNumberNat_add_le (M N : ℕ) :
rothNumberNat (M + N) ≤ rothNumberNat M + rothNumberNat N := by
simp_rw [rothNumberNat_def]
rw [range_add_eq_union, ← addRothNumber_map_add_left (range N) M]
exact addRothNumber_union_le _ _
@[simp]
theorem rothNumberNat_zero : rothNumberNat 0 = 0 :=
rfl
theorem addRothNumber_Ico (a b : ℕ) : addRothNumber (Ico a b) = rothNumberNat (b - a) := by
obtain h | h := le_total b a
· rw [Nat.sub_eq_zero_of_le h, Ico_eq_empty_of_le h, rothNumberNat_zero, addRothNumber_empty]
convert addRothNumber_map_add_left _ a
rw [range_eq_Ico, map_eq_image]
convert (image_add_left_Ico 0 (b - a) _).symm
exact (add_tsub_cancel_of_le h).symm
lemma Fin.addRothNumber_eq_rothNumberNat (hkn : 2 * k ≤ n) :
addRothNumber (Iio k : Finset (Fin n.succ)) = rothNumberNat k :=
IsAddFreimanIso.addRothNumber_congr <| mod_cast isAddFreimanIso_Iio two_ne_zero hkn
lemma Fin.addRothNumber_le_rothNumberNat (k n : ℕ) (hkn : k ≤ n) :
addRothNumber (Iio k : Finset (Fin n.succ)) ≤ rothNumberNat k := by
suffices h : Set.BijOn (Nat.cast : ℕ → Fin n.succ) (range k) (Iio k : Finset (Fin n.succ)) by
exact (AddMonoidHomClass.isAddFreimanHom (Nat.castRingHom _) h.mapsTo).addRothNumber_mono h
refine ⟨?_, (CharP.natCast_injOn_Iio _ n.succ).mono (by simp; omega), ?_⟩
· simpa using fun x ↦ natCast_strictMono hkn
simp only [Set.SurjOn, coe_Iio, Set.subset_def, Set.mem_Iio, Set.mem_image, lt_iff_val_lt_val,
val_cast_of_lt, Nat.lt_succ_iff.2 hkn, coe_range]
exact fun x hx ↦ ⟨x, hx, by simp⟩
end rothNumberNat
| Mathlib/Combinatorics/Additive/AP/Three/Defs.lean | 519 | 527 | |
/-
Copyright (c) 2022 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies
-/
import Mathlib.Data.Finset.Lattice.Prod
import Mathlib.Data.Finite.Prod
import Mathlib.Data.Set.Lattice.Image
/-!
# N-ary images of finsets
This file defines `Finset.image₂`, the binary image of finsets. This is the finset version of
`Set.image2`. This is mostly useful to define pointwise operations.
## Notes
This file is very similar to `Data.Set.NAry`, `Order.Filter.NAry` and `Data.Option.NAry`. Please
keep them in sync.
We do not define `Finset.image₃` as its only purpose would be to prove properties of `Finset.image₂`
and `Set.image2` already fulfills this task.
-/
open Function Set
variable {α α' β β' γ γ' δ δ' ε ε' ζ ζ' ν : Type*}
namespace Finset
variable [DecidableEq α'] [DecidableEq β'] [DecidableEq γ] [DecidableEq γ']
[DecidableEq δ'] [DecidableEq ε] [DecidableEq ε'] {f f' : α → β → γ} {g g' : α → β → γ → δ}
{s s' : Finset α} {t t' : Finset β} {u u' : Finset γ} {a a' : α} {b b' : β} {c : γ}
/-- The image of a binary function `f : α → β → γ` as a function `Finset α → Finset β → Finset γ`.
Mathematically this should be thought of as the image of the corresponding function `α × β → γ`. -/
def image₂ (f : α → β → γ) (s : Finset α) (t : Finset β) : Finset γ :=
(s ×ˢ t).image <| uncurry f
@[simp]
theorem mem_image₂ : c ∈ image₂ f s t ↔ ∃ a ∈ s, ∃ b ∈ t, f a b = c := by
simp [image₂, and_assoc]
@[simp, norm_cast]
theorem coe_image₂ (f : α → β → γ) (s : Finset α) (t : Finset β) :
(image₂ f s t : Set γ) = Set.image2 f s t :=
Set.ext fun _ => mem_image₂
theorem card_image₂_le (f : α → β → γ) (s : Finset α) (t : Finset β) :
#(image₂ f s t) ≤ #s * #t :=
card_image_le.trans_eq <| card_product _ _
theorem card_image₂_iff :
#(image₂ f s t) = #s * #t ↔ (s ×ˢ t : Set (α × β)).InjOn fun x => f x.1 x.2 := by
rw [← card_product, ← coe_product]
exact card_image_iff
theorem card_image₂ (hf : Injective2 f) (s : Finset α) (t : Finset β) :
#(image₂ f s t) = #s * #t :=
(card_image_of_injective _ hf.uncurry).trans <| card_product _ _
theorem mem_image₂_of_mem (ha : a ∈ s) (hb : b ∈ t) : f a b ∈ image₂ f s t :=
mem_image₂.2 ⟨a, ha, b, hb, rfl⟩
theorem mem_image₂_iff (hf : Injective2 f) : f a b ∈ image₂ f s t ↔ a ∈ s ∧ b ∈ t := by
rw [← mem_coe, coe_image₂, mem_image2_iff hf, mem_coe, mem_coe]
@[gcongr]
theorem image₂_subset (hs : s ⊆ s') (ht : t ⊆ t') : image₂ f s t ⊆ image₂ f s' t' := by
rw [← coe_subset, coe_image₂, coe_image₂]
exact image2_subset hs ht
@[gcongr]
theorem image₂_subset_left (ht : t ⊆ t') : image₂ f s t ⊆ image₂ f s t' :=
image₂_subset Subset.rfl ht
@[gcongr]
theorem image₂_subset_right (hs : s ⊆ s') : image₂ f s t ⊆ image₂ f s' t :=
image₂_subset hs Subset.rfl
theorem image_subset_image₂_left (hb : b ∈ t) : s.image (fun a => f a b) ⊆ image₂ f s t :=
image_subset_iff.2 fun _ ha => mem_image₂_of_mem ha hb
theorem image_subset_image₂_right (ha : a ∈ s) : t.image (fun b => f a b) ⊆ image₂ f s t :=
image_subset_iff.2 fun _ => mem_image₂_of_mem ha
lemma forall_mem_image₂ {p : γ → Prop} :
(∀ z ∈ image₂ f s t, p z) ↔ ∀ x ∈ s, ∀ y ∈ t, p (f x y) := by
simp_rw [← mem_coe, coe_image₂, forall_mem_image2]
lemma exists_mem_image₂ {p : γ → Prop} :
(∃ z ∈ image₂ f s t, p z) ↔ ∃ x ∈ s, ∃ y ∈ t, p (f x y) := by
simp_rw [← mem_coe, coe_image₂, exists_mem_image2]
@[deprecated (since := "2024-11-23")] alias forall_image₂_iff := forall_mem_image₂
@[simp]
theorem image₂_subset_iff : image₂ f s t ⊆ u ↔ ∀ x ∈ s, ∀ y ∈ t, f x y ∈ u :=
forall_mem_image₂
theorem image₂_subset_iff_left : image₂ f s t ⊆ u ↔ ∀ a ∈ s, (t.image fun b => f a b) ⊆ u := by
simp_rw [image₂_subset_iff, image_subset_iff]
theorem image₂_subset_iff_right : image₂ f s t ⊆ u ↔ ∀ b ∈ t, (s.image fun a => f a b) ⊆ u := by
simp_rw [image₂_subset_iff, image_subset_iff, @forall₂_swap α]
@[simp]
theorem image₂_nonempty_iff : (image₂ f s t).Nonempty ↔ s.Nonempty ∧ t.Nonempty := by
rw [← coe_nonempty, coe_image₂]
exact image2_nonempty_iff
@[aesop safe apply (rule_sets := [finsetNonempty])]
theorem Nonempty.image₂ (hs : s.Nonempty) (ht : t.Nonempty) : (image₂ f s t).Nonempty :=
image₂_nonempty_iff.2 ⟨hs, ht⟩
theorem Nonempty.of_image₂_left (h : (s.image₂ f t).Nonempty) : s.Nonempty :=
(image₂_nonempty_iff.1 h).1
theorem Nonempty.of_image₂_right (h : (s.image₂ f t).Nonempty) : t.Nonempty :=
(image₂_nonempty_iff.1 h).2
@[simp]
theorem image₂_empty_left : image₂ f ∅ t = ∅ :=
coe_injective <| by simp
@[simp]
theorem image₂_empty_right : image₂ f s ∅ = ∅ :=
coe_injective <| by simp
@[simp]
theorem image₂_eq_empty_iff : image₂ f s t = ∅ ↔ s = ∅ ∨ t = ∅ := by
simp_rw [← not_nonempty_iff_eq_empty, image₂_nonempty_iff, not_and_or]
@[simp]
theorem image₂_singleton_left : image₂ f {a} t = t.image fun b => f a b :=
ext fun x => by simp
@[simp]
theorem image₂_singleton_right : image₂ f s {b} = s.image fun a => f a b :=
ext fun x => by simp
theorem image₂_singleton_left' : image₂ f {a} t = t.image (f a) :=
image₂_singleton_left
theorem image₂_singleton : image₂ f {a} {b} = {f a b} := by simp
theorem image₂_union_left [DecidableEq α] : image₂ f (s ∪ s') t = image₂ f s t ∪ image₂ f s' t :=
coe_injective <| by
push_cast
exact image2_union_left
theorem image₂_union_right [DecidableEq β] : image₂ f s (t ∪ t') = image₂ f s t ∪ image₂ f s t' :=
coe_injective <| by
push_cast
exact image2_union_right
@[simp]
theorem image₂_insert_left [DecidableEq α] :
image₂ f (insert a s) t = (t.image fun b => f a b) ∪ image₂ f s t :=
coe_injective <| by
push_cast
exact image2_insert_left
@[simp]
theorem image₂_insert_right [DecidableEq β] :
image₂ f s (insert b t) = (s.image fun a => f a b) ∪ image₂ f s t :=
coe_injective <| by
push_cast
exact image2_insert_right
theorem image₂_inter_left [DecidableEq α] (hf : Injective2 f) :
image₂ f (s ∩ s') t = image₂ f s t ∩ image₂ f s' t :=
coe_injective <| by
push_cast
exact image2_inter_left hf
theorem image₂_inter_right [DecidableEq β] (hf : Injective2 f) :
image₂ f s (t ∩ t') = image₂ f s t ∩ image₂ f s t' :=
coe_injective <| by
push_cast
exact image2_inter_right hf
theorem image₂_inter_subset_left [DecidableEq α] :
image₂ f (s ∩ s') t ⊆ image₂ f s t ∩ image₂ f s' t :=
coe_subset.1 <| by
push_cast
| exact image2_inter_subset_left
theorem image₂_inter_subset_right [DecidableEq β] :
image₂ f s (t ∩ t') ⊆ image₂ f s t ∩ image₂ f s t' :=
coe_subset.1 <| by
| Mathlib/Data/Finset/NAry.lean | 187 | 191 |
/-
Copyright (c) 2020 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Topology.UniformSpace.Cauchy
/-!
# Uniform convergence
A sequence of functions `Fₙ` (with values in a metric space) converges uniformly on a set `s` to a
function `f` if, for all `ε > 0`, for all large enough `n`, one has for all `y ∈ s` the inequality
`dist (f y, Fₙ y) < ε`. Under uniform convergence, many properties of the `Fₙ` pass to the limit,
most notably continuity. We prove this in the file, defining the notion of uniform convergence
in the more general setting of uniform spaces, and with respect to an arbitrary indexing set
endowed with a filter (instead of just `ℕ` with `atTop`).
## Main results
Let `α` be a topological space, `β` a uniform space, `Fₙ` and `f` be functions from `α` to `β`
(where the index `n` belongs to an indexing type `ι` endowed with a filter `p`).
* `TendstoUniformlyOn F f p s`: the fact that `Fₙ` converges uniformly to `f` on `s`. This means
that, for any entourage `u` of the diagonal, for large enough `n` (with respect to `p`), one has
`(f y, Fₙ y) ∈ u` for all `y ∈ s`.
* `TendstoUniformly F f p`: same notion with `s = univ`.
* `TendstoUniformlyOn.continuousOn`: a uniform limit on a set of functions which are continuous
on this set is itself continuous on this set.
* `TendstoUniformly.continuous`: a uniform limit of continuous functions is continuous.
* `TendstoUniformlyOn.tendsto_comp`: If `Fₙ` tends uniformly to `f` on a set `s`, and `gₙ` tends
to `x` within `s`, then `Fₙ gₙ` tends to `f x` if `f` is continuous at `x` within `s`.
* `TendstoUniformly.tendsto_comp`: If `Fₙ` tends uniformly to `f`, and `gₙ` tends to `x`, then
`Fₙ gₙ` tends to `f x`.
Finally, we introduce the notion of a uniform Cauchy sequence, which is to uniform
convergence what a Cauchy sequence is to the usual notion of convergence.
## Implementation notes
We derive most of our initial results from an auxiliary definition `TendstoUniformlyOnFilter`.
This definition in and of itself can sometimes be useful, e.g., when studying the local behavior
of the `Fₙ` near a point, which would typically look like `TendstoUniformlyOnFilter F f p (𝓝 x)`.
Still, while this may be the "correct" definition (see
`tendstoUniformlyOn_iff_tendstoUniformlyOnFilter`), it is somewhat unwieldy to work with in
practice. Thus, we provide the more traditional definition in `TendstoUniformlyOn`.
## Tags
Uniform limit, uniform convergence, tends uniformly to
-/
noncomputable section
open Topology Uniformity Filter Set Uniform
variable {α β γ ι : Type*} [UniformSpace β]
variable {F : ι → α → β} {f : α → β} {s s' : Set α} {x : α} {p : Filter ι} {p' : Filter α}
/-!
### Different notions of uniform convergence
We define uniform convergence, on a set or in the whole space.
-/
/-- A sequence of functions `Fₙ` converges uniformly on a filter `p'` to a limiting function `f`
with respect to the filter `p` if, for any entourage of the diagonal `u`, one has
`p ×ˢ p'`-eventually `(f x, Fₙ x) ∈ u`. -/
def TendstoUniformlyOnFilter (F : ι → α → β) (f : α → β) (p : Filter ι) (p' : Filter α) :=
∀ u ∈ 𝓤 β, ∀ᶠ n : ι × α in p ×ˢ p', (f n.snd, F n.fst n.snd) ∈ u
/--
A sequence of functions `Fₙ` converges uniformly on a filter `p'` to a limiting function `f` w.r.t.
filter `p` iff the function `(n, x) ↦ (f x, Fₙ x)` converges along `p ×ˢ p'` to the uniformity.
In other words: one knows nothing about the behavior of `x` in this limit besides it being in `p'`.
-/
theorem tendstoUniformlyOnFilter_iff_tendsto :
TendstoUniformlyOnFilter F f p p' ↔
Tendsto (fun q : ι × α => (f q.2, F q.1 q.2)) (p ×ˢ p') (𝓤 β) :=
Iff.rfl
/-- A sequence of functions `Fₙ` converges uniformly on a set `s` to a limiting function `f` with
respect to the filter `p` if, for any entourage of the diagonal `u`, one has `p`-eventually
`(f x, Fₙ x) ∈ u` for all `x ∈ s`. -/
def TendstoUniformlyOn (F : ι → α → β) (f : α → β) (p : Filter ι) (s : Set α) :=
∀ u ∈ 𝓤 β, ∀ᶠ n in p, ∀ x : α, x ∈ s → (f x, F n x) ∈ u
theorem tendstoUniformlyOn_iff_tendstoUniformlyOnFilter :
TendstoUniformlyOn F f p s ↔ TendstoUniformlyOnFilter F f p (𝓟 s) := by
simp only [TendstoUniformlyOn, TendstoUniformlyOnFilter]
apply forall₂_congr
simp_rw [eventually_prod_principal_iff]
simp
alias ⟨TendstoUniformlyOn.tendstoUniformlyOnFilter, TendstoUniformlyOnFilter.tendstoUniformlyOn⟩ :=
tendstoUniformlyOn_iff_tendstoUniformlyOnFilter
/-- A sequence of functions `Fₙ` converges uniformly on a set `s` to a limiting function `f` w.r.t.
filter `p` iff the function `(n, x) ↦ (f x, Fₙ x)` converges along `p ×ˢ 𝓟 s` to the uniformity.
In other words: one knows nothing about the behavior of `x` in this limit besides it being in `s`.
-/
theorem tendstoUniformlyOn_iff_tendsto :
TendstoUniformlyOn F f p s ↔
Tendsto (fun q : ι × α => (f q.2, F q.1 q.2)) (p ×ˢ 𝓟 s) (𝓤 β) := by
simp [tendstoUniformlyOn_iff_tendstoUniformlyOnFilter, tendstoUniformlyOnFilter_iff_tendsto]
/-- A sequence of functions `Fₙ` converges uniformly to a limiting function `f` with respect to a
filter `p` if, for any entourage of the diagonal `u`, one has `p`-eventually
`(f x, Fₙ x) ∈ u` for all `x`. -/
def TendstoUniformly (F : ι → α → β) (f : α → β) (p : Filter ι) :=
∀ u ∈ 𝓤 β, ∀ᶠ n in p, ∀ x : α, (f x, F n x) ∈ u
theorem tendstoUniformlyOn_univ : TendstoUniformlyOn F f p univ ↔ TendstoUniformly F f p := by
simp [TendstoUniformlyOn, TendstoUniformly]
theorem tendstoUniformly_iff_tendstoUniformlyOnFilter :
TendstoUniformly F f p ↔ TendstoUniformlyOnFilter F f p ⊤ := by
rw [← tendstoUniformlyOn_univ, tendstoUniformlyOn_iff_tendstoUniformlyOnFilter, principal_univ]
theorem TendstoUniformly.tendstoUniformlyOnFilter (h : TendstoUniformly F f p) :
TendstoUniformlyOnFilter F f p ⊤ := by rwa [← tendstoUniformly_iff_tendstoUniformlyOnFilter]
theorem tendstoUniformlyOn_iff_tendstoUniformly_comp_coe :
TendstoUniformlyOn F f p s ↔ TendstoUniformly (fun i (x : s) => F i x) (f ∘ (↑)) p :=
forall₂_congr fun u _ => by simp
/-- A sequence of functions `Fₙ` converges uniformly to a limiting function `f` w.r.t.
filter `p` iff the function `(n, x) ↦ (f x, Fₙ x)` converges along `p ×ˢ ⊤` to the uniformity.
In other words: one knows nothing about the behavior of `x` in this limit.
-/
theorem tendstoUniformly_iff_tendsto :
TendstoUniformly F f p ↔ Tendsto (fun q : ι × α => (f q.2, F q.1 q.2)) (p ×ˢ ⊤) (𝓤 β) := by
simp [tendstoUniformly_iff_tendstoUniformlyOnFilter, tendstoUniformlyOnFilter_iff_tendsto]
/-- Uniform convergence implies pointwise convergence. -/
theorem TendstoUniformlyOnFilter.tendsto_at (h : TendstoUniformlyOnFilter F f p p')
(hx : 𝓟 {x} ≤ p') : Tendsto (fun n => F n x) p <| 𝓝 (f x) := by
refine Uniform.tendsto_nhds_right.mpr fun u hu => mem_map.mpr ?_
filter_upwards [(h u hu).curry]
intro i h
simpa using h.filter_mono hx
/-- Uniform convergence implies pointwise convergence. -/
theorem TendstoUniformlyOn.tendsto_at (h : TendstoUniformlyOn F f p s) (hx : x ∈ s) :
Tendsto (fun n => F n x) p <| 𝓝 (f x) :=
h.tendstoUniformlyOnFilter.tendsto_at
(le_principal_iff.mpr <| mem_principal.mpr <| singleton_subset_iff.mpr <| hx)
/-- Uniform convergence implies pointwise convergence. -/
theorem TendstoUniformly.tendsto_at (h : TendstoUniformly F f p) (x : α) :
Tendsto (fun n => F n x) p <| 𝓝 (f x) :=
h.tendstoUniformlyOnFilter.tendsto_at le_top
theorem TendstoUniformlyOnFilter.mono_left {p'' : Filter ι} (h : TendstoUniformlyOnFilter F f p p')
(hp : p'' ≤ p) : TendstoUniformlyOnFilter F f p'' p' := fun u hu =>
(h u hu).filter_mono (p'.prod_mono_left hp)
theorem TendstoUniformlyOnFilter.mono_right {p'' : Filter α} (h : TendstoUniformlyOnFilter F f p p')
(hp : p'' ≤ p') : TendstoUniformlyOnFilter F f p p'' := fun u hu =>
(h u hu).filter_mono (p.prod_mono_right hp)
theorem TendstoUniformlyOn.mono (h : TendstoUniformlyOn F f p s) (h' : s' ⊆ s) :
TendstoUniformlyOn F f p s' :=
tendstoUniformlyOn_iff_tendstoUniformlyOnFilter.mpr
(h.tendstoUniformlyOnFilter.mono_right (le_principal_iff.mpr <| mem_principal.mpr h'))
theorem TendstoUniformlyOnFilter.congr {F' : ι → α → β} (hf : TendstoUniformlyOnFilter F f p p')
(hff' : ∀ᶠ n : ι × α in p ×ˢ p', F n.fst n.snd = F' n.fst n.snd) :
TendstoUniformlyOnFilter F' f p p' := by
refine fun u hu => ((hf u hu).and hff').mono fun n h => ?_
rw [← h.right]
exact h.left
theorem TendstoUniformlyOn.congr {F' : ι → α → β} (hf : TendstoUniformlyOn F f p s)
(hff' : ∀ᶠ n in p, Set.EqOn (F n) (F' n) s) : TendstoUniformlyOn F' f p s := by
rw [tendstoUniformlyOn_iff_tendstoUniformlyOnFilter] at hf ⊢
refine hf.congr ?_
rw [eventually_iff] at hff' ⊢
simp only [Set.EqOn] at hff'
simp only [mem_prod_principal, hff', mem_setOf_eq]
lemma tendstoUniformly_congr {F' : ι → α → β} (hF : F =ᶠ[p] F') :
TendstoUniformly F f p ↔ TendstoUniformly F' f p := by
simp_rw [← tendstoUniformlyOn_univ] at *
have HF := EventuallyEq.exists_mem hF
exact ⟨fun h => h.congr (by aesop), fun h => h.congr (by simp_rw [eqOn_comm]; aesop)⟩
theorem TendstoUniformlyOn.congr_right {g : α → β} (hf : TendstoUniformlyOn F f p s)
(hfg : EqOn f g s) : TendstoUniformlyOn F g p s := fun u hu => by
filter_upwards [hf u hu] with i hi a ha using hfg ha ▸ hi a ha
protected theorem TendstoUniformly.tendstoUniformlyOn (h : TendstoUniformly F f p) :
TendstoUniformlyOn F f p s :=
(tendstoUniformlyOn_univ.2 h).mono (subset_univ s)
/-- Composing on the right by a function preserves uniform convergence on a filter -/
theorem TendstoUniformlyOnFilter.comp (h : TendstoUniformlyOnFilter F f p p') (g : γ → α) :
TendstoUniformlyOnFilter (fun n => F n ∘ g) (f ∘ g) p (p'.comap g) := by
rw [tendstoUniformlyOnFilter_iff_tendsto] at h ⊢
exact h.comp (tendsto_id.prodMap tendsto_comap)
/-- Composing on the right by a function preserves uniform convergence on a set -/
theorem TendstoUniformlyOn.comp (h : TendstoUniformlyOn F f p s) (g : γ → α) :
TendstoUniformlyOn (fun n => F n ∘ g) (f ∘ g) p (g ⁻¹' s) := by
rw [tendstoUniformlyOn_iff_tendstoUniformlyOnFilter] at h ⊢
simpa [TendstoUniformlyOn, comap_principal] using TendstoUniformlyOnFilter.comp h g
/-- Composing on the right by a function preserves uniform convergence -/
theorem TendstoUniformly.comp (h : TendstoUniformly F f p) (g : γ → α) :
TendstoUniformly (fun n => F n ∘ g) (f ∘ g) p := by
rw [tendstoUniformly_iff_tendstoUniformlyOnFilter] at h ⊢
simpa [principal_univ, comap_principal] using h.comp g
/-- Composing on the left by a uniformly continuous function preserves
uniform convergence on a filter -/
theorem UniformContinuous.comp_tendstoUniformlyOnFilter [UniformSpace γ] {g : β → γ}
(hg : UniformContinuous g) (h : TendstoUniformlyOnFilter F f p p') :
TendstoUniformlyOnFilter (fun i => g ∘ F i) (g ∘ f) p p' := fun _u hu => h _ (hg hu)
/-- Composing on the left by a uniformly continuous function preserves
uniform convergence on a set -/
theorem UniformContinuous.comp_tendstoUniformlyOn [UniformSpace γ] {g : β → γ}
(hg : UniformContinuous g) (h : TendstoUniformlyOn F f p s) :
TendstoUniformlyOn (fun i => g ∘ F i) (g ∘ f) p s := fun _u hu => h _ (hg hu)
/-- Composing on the left by a uniformly continuous function preserves uniform convergence -/
theorem UniformContinuous.comp_tendstoUniformly [UniformSpace γ] {g : β → γ}
(hg : UniformContinuous g) (h : TendstoUniformly F f p) :
TendstoUniformly (fun i => g ∘ F i) (g ∘ f) p := fun _u hu => h _ (hg hu)
theorem TendstoUniformlyOnFilter.prodMap {ι' α' β' : Type*} [UniformSpace β'] {F' : ι' → α' → β'}
{f' : α' → β'} {q : Filter ι'} {q' : Filter α'} (h : TendstoUniformlyOnFilter F f p p')
(h' : TendstoUniformlyOnFilter F' f' q q') :
TendstoUniformlyOnFilter (fun i : ι × ι' => Prod.map (F i.1) (F' i.2)) (Prod.map f f') (p ×ˢ q)
(p' ×ˢ q') := by
rw [tendstoUniformlyOnFilter_iff_tendsto] at h h' ⊢
rw [uniformity_prod_eq_comap_prod, tendsto_comap_iff, ← map_swap4_prod, tendsto_map'_iff]
simpa using h.prodMap h'
@[deprecated (since := "2025-03-10")]
alias TendstoUniformlyOnFilter.prod_map := TendstoUniformlyOnFilter.prodMap
theorem TendstoUniformlyOn.prodMap {ι' α' β' : Type*} [UniformSpace β'] {F' : ι' → α' → β'}
{f' : α' → β'} {p' : Filter ι'} {s' : Set α'} (h : TendstoUniformlyOn F f p s)
(h' : TendstoUniformlyOn F' f' p' s') :
TendstoUniformlyOn (fun i : ι × ι' => Prod.map (F i.1) (F' i.2)) (Prod.map f f') (p ×ˢ p')
(s ×ˢ s') := by
rw [tendstoUniformlyOn_iff_tendstoUniformlyOnFilter] at h h' ⊢
simpa only [prod_principal_principal] using h.prodMap h'
@[deprecated (since := "2025-03-10")]
alias TendstoUniformlyOn.prod_map := TendstoUniformlyOn.prodMap
theorem TendstoUniformly.prodMap {ι' α' β' : Type*} [UniformSpace β'] {F' : ι' → α' → β'}
{f' : α' → β'} {p' : Filter ι'} (h : TendstoUniformly F f p) (h' : TendstoUniformly F' f' p') :
TendstoUniformly (fun i : ι × ι' => Prod.map (F i.1) (F' i.2)) (Prod.map f f') (p ×ˢ p') := by
rw [← tendstoUniformlyOn_univ, ← univ_prod_univ] at *
exact h.prodMap h'
@[deprecated (since := "2025-03-10")]
alias TendstoUniformly.prod_map := TendstoUniformly.prodMap
theorem TendstoUniformlyOnFilter.prodMk {ι' β' : Type*} [UniformSpace β'] {F' : ι' → α → β'}
{f' : α → β'} {q : Filter ι'} (h : TendstoUniformlyOnFilter F f p p')
(h' : TendstoUniformlyOnFilter F' f' q p') :
TendstoUniformlyOnFilter (fun (i : ι × ι') a => (F i.1 a, F' i.2 a)) (fun a => (f a, f' a))
(p ×ˢ q) p' :=
fun u hu => ((h.prodMap h') u hu).diag_of_prod_right
@[deprecated (since := "2025-03-10")]
alias TendstoUniformlyOnFilter.prod := TendstoUniformlyOnFilter.prodMk
protected theorem TendstoUniformlyOn.prodMk {ι' β' : Type*} [UniformSpace β'] {F' : ι' → α → β'}
{f' : α → β'} {p' : Filter ι'} (h : TendstoUniformlyOn F f p s)
(h' : TendstoUniformlyOn F' f' p' s) :
TendstoUniformlyOn (fun (i : ι × ι') a => (F i.1 a, F' i.2 a)) (fun a => (f a, f' a)) (p ×ˢ p')
s :=
(congr_arg _ s.inter_self).mp ((h.prodMap h').comp fun a => (a, a))
@[deprecated (since := "2025-03-10")]
alias TendstoUniformlyOn.prod := TendstoUniformlyOn.prodMk
theorem TendstoUniformly.prodMk {ι' β' : Type*} [UniformSpace β'] {F' : ι' → α → β'} {f' : α → β'}
{p' : Filter ι'} (h : TendstoUniformly F f p) (h' : TendstoUniformly F' f' p') :
TendstoUniformly (fun (i : ι × ι') a => (F i.1 a, F' i.2 a)) (fun a => (f a, f' a)) (p ×ˢ p') :=
(h.prodMap h').comp fun a => (a, a)
@[deprecated (since := "2025-03-10")]
alias TendstoUniformly.prod := TendstoUniformly.prodMk
/-- Uniform convergence on a filter `p'` to a constant function is equivalent to convergence in
`p ×ˢ p'`. -/
theorem tendsto_prod_filter_iff {c : β} :
Tendsto (↿F) (p ×ˢ p') (𝓝 c) ↔ TendstoUniformlyOnFilter F (fun _ => c) p p' := by
simp_rw [nhds_eq_comap_uniformity, tendsto_comap_iff]
rfl
/-- Uniform convergence on a set `s` to a constant function is equivalent to convergence in
`p ×ˢ 𝓟 s`. -/
theorem tendsto_prod_principal_iff {c : β} :
Tendsto (↿F) (p ×ˢ 𝓟 s) (𝓝 c) ↔ TendstoUniformlyOn F (fun _ => c) p s := by
rw [tendstoUniformlyOn_iff_tendstoUniformlyOnFilter]
exact tendsto_prod_filter_iff
/-- Uniform convergence to a constant function is equivalent to convergence in `p ×ˢ ⊤`. -/
theorem tendsto_prod_top_iff {c : β} :
Tendsto (↿F) (p ×ˢ ⊤) (𝓝 c) ↔ TendstoUniformly F (fun _ => c) p := by
rw [tendstoUniformly_iff_tendstoUniformlyOnFilter]
exact tendsto_prod_filter_iff
/-- Uniform convergence on the empty set is vacuously true -/
theorem tendstoUniformlyOn_empty : TendstoUniformlyOn F f p ∅ := fun u _ => by simp
/-- Uniform convergence on a singleton is equivalent to regular convergence -/
theorem tendstoUniformlyOn_singleton_iff_tendsto :
TendstoUniformlyOn F f p {x} ↔ Tendsto (fun n : ι => F n x) p (𝓝 (f x)) := by
simp_rw [tendstoUniformlyOn_iff_tendsto, Uniform.tendsto_nhds_right, tendsto_def]
exact forall₂_congr fun u _ => by simp [mem_prod_principal, preimage]
/-- If a sequence `g` converges to some `b`, then the sequence of constant functions
`fun n ↦ fun a ↦ g n` converges to the constant function `fun a ↦ b` on any set `s` -/
theorem Filter.Tendsto.tendstoUniformlyOnFilter_const {g : ι → β} {b : β} (hg : Tendsto g p (𝓝 b))
(p' : Filter α) :
TendstoUniformlyOnFilter (fun n : ι => fun _ : α => g n) (fun _ : α => b) p p' := by
simpa only [nhds_eq_comap_uniformity, tendsto_comap_iff] using hg.comp (tendsto_fst (g := p'))
/-- If a sequence `g` converges to some `b`, then the sequence of constant functions
`fun n ↦ fun a ↦ g n` converges to the constant function `fun a ↦ b` on any set `s` -/
theorem Filter.Tendsto.tendstoUniformlyOn_const {g : ι → β} {b : β} (hg : Tendsto g p (𝓝 b))
(s : Set α) : TendstoUniformlyOn (fun n : ι => fun _ : α => g n) (fun _ : α => b) p s :=
tendstoUniformlyOn_iff_tendstoUniformlyOnFilter.mpr (hg.tendstoUniformlyOnFilter_const (𝓟 s))
theorem UniformContinuousOn.tendstoUniformlyOn [UniformSpace α] [UniformSpace γ] {U : Set α}
{V : Set β} {F : α → β → γ} (hF : UniformContinuousOn (↿F) (U ×ˢ V)) (hU : x ∈ U) :
TendstoUniformlyOn F (F x) (𝓝[U] x) V := by
set φ := fun q : α × β => ((x, q.2), q)
rw [tendstoUniformlyOn_iff_tendsto]
change Tendsto (Prod.map (↿F) ↿F ∘ φ) (𝓝[U] x ×ˢ 𝓟 V) (𝓤 γ)
simp only [nhdsWithin, Filter.prod_eq_inf, comap_inf, inf_assoc, comap_principal, inf_principal]
refine hF.comp (Tendsto.inf ?_ <| tendsto_principal_principal.2 fun x hx => ⟨⟨hU, hx.2⟩, hx⟩)
simp only [uniformity_prod_eq_comap_prod, tendsto_comap_iff, (· ∘ ·),
nhds_eq_comap_uniformity, comap_comap]
exact tendsto_comap.prodMk (tendsto_diag_uniformity _ _)
theorem UniformContinuousOn.tendstoUniformly [UniformSpace α] [UniformSpace γ] {U : Set α}
(hU : U ∈ 𝓝 x) {F : α → β → γ} (hF : UniformContinuousOn (↿F) (U ×ˢ (univ : Set β))) :
TendstoUniformly F (F x) (𝓝 x) := by
simpa only [tendstoUniformlyOn_univ, nhdsWithin_eq_nhds.2 hU]
using hF.tendstoUniformlyOn (mem_of_mem_nhds hU)
theorem UniformContinuous₂.tendstoUniformly [UniformSpace α] [UniformSpace γ] {f : α → β → γ}
(h : UniformContinuous₂ f) : TendstoUniformly f (f x) (𝓝 x) :=
UniformContinuousOn.tendstoUniformly univ_mem <| by rwa [univ_prod_univ, uniformContinuousOn_univ]
/-- A sequence is uniformly Cauchy if eventually all of its pairwise differences are
uniformly bounded -/
def UniformCauchySeqOnFilter (F : ι → α → β) (p : Filter ι) (p' : Filter α) : Prop :=
∀ u ∈ 𝓤 β, ∀ᶠ m : (ι × ι) × α in (p ×ˢ p) ×ˢ p', (F m.fst.fst m.snd, F m.fst.snd m.snd) ∈ u
/-- A sequence is uniformly Cauchy if eventually all of its pairwise differences are
uniformly bounded -/
def UniformCauchySeqOn (F : ι → α → β) (p : Filter ι) (s : Set α) : Prop :=
∀ u ∈ 𝓤 β, ∀ᶠ m : ι × ι in p ×ˢ p, ∀ x : α, x ∈ s → (F m.fst x, F m.snd x) ∈ u
theorem uniformCauchySeqOn_iff_uniformCauchySeqOnFilter :
UniformCauchySeqOn F p s ↔ UniformCauchySeqOnFilter F p (𝓟 s) := by
simp only [UniformCauchySeqOn, UniformCauchySeqOnFilter]
refine forall₂_congr fun u hu => ?_
rw [eventually_prod_principal_iff]
theorem UniformCauchySeqOn.uniformCauchySeqOnFilter (hF : UniformCauchySeqOn F p s) :
UniformCauchySeqOnFilter F p (𝓟 s) := by rwa [← uniformCauchySeqOn_iff_uniformCauchySeqOnFilter]
/-- A sequence that converges uniformly is also uniformly Cauchy -/
theorem TendstoUniformlyOnFilter.uniformCauchySeqOnFilter (hF : TendstoUniformlyOnFilter F f p p') :
UniformCauchySeqOnFilter F p p' := by
intro u hu
rcases comp_symm_of_uniformity hu with ⟨t, ht, htsymm, htmem⟩
have := tendsto_swap4_prod.eventually ((hF t ht).prod_mk (hF t ht))
apply this.diag_of_prod_right.mono
simp only [and_imp, Prod.forall]
intro n1 n2 x hl hr
exact Set.mem_of_mem_of_subset (prodMk_mem_compRel (htsymm hl) hr) htmem
/-- A sequence that converges uniformly is also uniformly Cauchy -/
theorem TendstoUniformlyOn.uniformCauchySeqOn (hF : TendstoUniformlyOn F f p s) :
UniformCauchySeqOn F p s :=
uniformCauchySeqOn_iff_uniformCauchySeqOnFilter.mpr
hF.tendstoUniformlyOnFilter.uniformCauchySeqOnFilter
/-- A uniformly Cauchy sequence converges uniformly to its limit -/
theorem UniformCauchySeqOnFilter.tendstoUniformlyOnFilter_of_tendsto
(hF : UniformCauchySeqOnFilter F p p')
(hF' : ∀ᶠ x : α in p', Tendsto (fun n => F n x) p (𝓝 (f x))) :
TendstoUniformlyOnFilter F f p p' := by
rcases p.eq_or_neBot with rfl | _
· simp only [TendstoUniformlyOnFilter, bot_prod, eventually_bot, implies_true]
-- Proof idea: |f_n(x) - f(x)| ≤ |f_n(x) - f_m(x)| + |f_m(x) - f(x)|. We choose `n`
-- so that |f_n(x) - f_m(x)| is uniformly small across `s` whenever `m ≥ n`. Then for
-- a fixed `x`, we choose `m` sufficiently large such that |f_m(x) - f(x)| is small.
intro u hu
rcases comp_symm_of_uniformity hu with ⟨t, ht, htsymm, htmem⟩
-- We will choose n, x, and m simultaneously. n and x come from hF. m comes from hF'
-- But we need to promote hF' to the full product filter to use it
have hmc : ∀ᶠ x in (p ×ˢ p) ×ˢ p', Tendsto (fun n : ι => F n x.snd) p (𝓝 (f x.snd)) := by
rw [eventually_prod_iff]
exact ⟨fun _ => True, by simp, _, hF', by simp⟩
-- To apply filter operations we'll need to do some order manipulation
rw [Filter.eventually_swap_iff]
have := tendsto_prodAssoc.eventually (tendsto_prod_swap.eventually ((hF t ht).and hmc))
apply this.curry.mono
simp only [Equiv.prodAssoc_apply, eventually_and, eventually_const, Prod.snd_swap, Prod.fst_swap,
and_imp, Prod.forall]
-- Complete the proof
intro x n hx hm'
refine Set.mem_of_mem_of_subset (mem_compRel.mpr ?_) htmem
rw [Uniform.tendsto_nhds_right] at hm'
have := hx.and (hm' ht)
obtain ⟨m, hm⟩ := this.exists
exact ⟨F m x, ⟨hm.2, htsymm hm.1⟩⟩
/-- A uniformly Cauchy sequence converges uniformly to its limit -/
theorem UniformCauchySeqOn.tendstoUniformlyOn_of_tendsto (hF : UniformCauchySeqOn F p s)
(hF' : ∀ x : α, x ∈ s → Tendsto (fun n => F n x) p (𝓝 (f x))) : TendstoUniformlyOn F f p s :=
tendstoUniformlyOn_iff_tendstoUniformlyOnFilter.mpr
(hF.uniformCauchySeqOnFilter.tendstoUniformlyOnFilter_of_tendsto hF')
theorem UniformCauchySeqOnFilter.mono_left {p'' : Filter ι} (hf : UniformCauchySeqOnFilter F p p')
(hp : p'' ≤ p) : UniformCauchySeqOnFilter F p'' p' := by
intro u hu
have := (hf u hu).filter_mono (p'.prod_mono_left (Filter.prod_mono hp hp))
exact this.mono (by simp)
theorem UniformCauchySeqOnFilter.mono_right {p'' : Filter α} (hf : UniformCauchySeqOnFilter F p p')
(hp : p'' ≤ p') : UniformCauchySeqOnFilter F p p'' := fun u hu =>
have := (hf u hu).filter_mono ((p ×ˢ p).prod_mono_right hp)
this.mono (by simp)
theorem UniformCauchySeqOn.mono (hf : UniformCauchySeqOn F p s) (hss' : s' ⊆ s) :
UniformCauchySeqOn F p s' := by
rw [uniformCauchySeqOn_iff_uniformCauchySeqOnFilter] at hf ⊢
exact hf.mono_right (le_principal_iff.mpr <| mem_principal.mpr hss')
/-- Composing on the right by a function preserves uniform Cauchy sequences -/
theorem UniformCauchySeqOnFilter.comp {γ : Type*} (hf : UniformCauchySeqOnFilter F p p')
(g : γ → α) : UniformCauchySeqOnFilter (fun n => F n ∘ g) p (p'.comap g) := fun u hu => by
obtain ⟨pa, hpa, pb, hpb, hpapb⟩ := eventually_prod_iff.mp (hf u hu)
rw [eventually_prod_iff]
refine ⟨pa, hpa, pb ∘ g, ?_, fun hx _ hy => hpapb hx hy⟩
exact eventually_comap.mpr (hpb.mono fun x hx y hy => by simp only [hx, hy, Function.comp_apply])
/-- Composing on the right by a function preserves uniform Cauchy sequences -/
theorem UniformCauchySeqOn.comp {γ : Type*} (hf : UniformCauchySeqOn F p s) (g : γ → α) :
UniformCauchySeqOn (fun n => F n ∘ g) p (g ⁻¹' s) := by
rw [uniformCauchySeqOn_iff_uniformCauchySeqOnFilter] at hf ⊢
simpa only [UniformCauchySeqOn, comap_principal] using hf.comp g
/-- Composing on the left by a uniformly continuous function preserves
uniform Cauchy sequences -/
theorem UniformContinuous.comp_uniformCauchySeqOn [UniformSpace γ] {g : β → γ}
(hg : UniformContinuous g) (hf : UniformCauchySeqOn F p s) :
UniformCauchySeqOn (fun n => g ∘ F n) p s := fun _u hu => hf _ (hg hu)
theorem UniformCauchySeqOn.prodMap {ι' α' β' : Type*} [UniformSpace β'] {F' : ι' → α' → β'}
{p' : Filter ι'} {s' : Set α'} (h : UniformCauchySeqOn F p s)
(h' : UniformCauchySeqOn F' p' s') :
UniformCauchySeqOn (fun i : ι × ι' => Prod.map (F i.1) (F' i.2)) (p ×ˢ p') (s ×ˢ s') := by
intro u hu
rw [uniformity_prod_eq_prod, mem_map, mem_prod_iff] at hu
obtain ⟨v, hv, w, hw, hvw⟩ := hu
simp_rw [mem_prod, and_imp, Prod.forall, Prod.map_apply]
rw [← Set.image_subset_iff] at hvw
apply (tendsto_swap4_prod.eventually ((h v hv).prod_mk (h' w hw))).mono
intro x hx a b ha hb
| exact hvw ⟨_, mk_mem_prod (hx.1 a ha) (hx.2 b hb), rfl⟩
@[deprecated (since := "2025-03-10")]
alias UniformCauchySeqOn.prod_map := UniformCauchySeqOn.prodMap
| Mathlib/Topology/UniformSpace/UniformConvergence.lean | 474 | 478 |
/-
Copyright (c) 2024 Lean FRO. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison
-/
import Mathlib.Data.List.InsertIdx
/-!
This is a stub file for importing `Mathlib.Data.List.InsertNth`,
which has been renamed to `Mathlib.Data.List.InsertIdx`.
This file can be removed once the deprecation for `List.insertNth` is removed.
-/
| Mathlib/Data/List/InsertNth.lean | 205 | 209 | |
/-
Copyright (c) 2019 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johan Commelin
-/
import Mathlib.RingTheory.IntegralClosure.IsIntegral.Basic
/-!
# Minimal polynomials
This file defines the minimal polynomial of an element `x` of an `A`-algebra `B`,
under the assumption that x is integral over `A`, and derives some basic properties
such as irreducibility under the assumption `B` is a domain.
-/
open Polynomial Set Function
variable {A B B' : Type*}
section MinPolyDef
variable (A) [CommRing A] [Ring B] [Algebra A B]
open scoped Classical in
/-- Suppose `x : B`, where `B` is an `A`-algebra.
The minimal polynomial `minpoly A x` of `x`
is a monic polynomial with coefficients in `A` of smallest degree that has `x` as its root,
if such exists (`IsIntegral A x`) or zero otherwise.
For example, if `V` is a `𝕜`-vector space for some field `𝕜` and `f : V →ₗ[𝕜] V` then
the minimal polynomial of `f` is `minpoly 𝕜 f`.
-/
@[stacks 09GM]
noncomputable def minpoly (x : B) : A[X] :=
if hx : IsIntegral A x then degree_lt_wf.min _ hx else 0
end MinPolyDef
namespace minpoly
section Ring
variable [CommRing A] [Ring B] [Ring B'] [Algebra A B] [Algebra A B']
variable {x : B}
/-- A minimal polynomial is monic. -/
theorem monic (hx : IsIntegral A x) : Monic (minpoly A x) := by
delta minpoly
rw [dif_pos hx]
exact (degree_lt_wf.min_mem _ hx).1
/-- A minimal polynomial is nonzero. -/
theorem ne_zero [Nontrivial A] (hx : IsIntegral A x) : minpoly A x ≠ 0 :=
(monic hx).ne_zero
theorem eq_zero (hx : ¬IsIntegral A x) : minpoly A x = 0 :=
dif_neg hx
theorem ne_zero_iff [Nontrivial A] : minpoly A x ≠ 0 ↔ IsIntegral A x :=
⟨fun h => of_not_not <| eq_zero.mt h, ne_zero⟩
theorem algHom_eq (f : B →ₐ[A] B') (hf : Function.Injective f) (x : B) :
minpoly A (f x) = minpoly A x := by
classical
simp_rw [minpoly, isIntegral_algHom_iff _ hf, ← Polynomial.aeval_def, aeval_algHom,
AlgHom.comp_apply, _root_.map_eq_zero_iff f hf]
theorem algebraMap_eq {B} [CommRing B] [Algebra A B] [Algebra B B'] [IsScalarTower A B B']
(h : Function.Injective (algebraMap B B')) (x : B) :
minpoly A (algebraMap B B' x) = minpoly A x :=
algHom_eq (IsScalarTower.toAlgHom A B B') h x
@[simp]
theorem algEquiv_eq (f : B ≃ₐ[A] B') (x : B) : minpoly A (f x) = minpoly A x :=
algHom_eq (f : B →ₐ[A] B') f.injective x
variable (A x)
/-- An element is a root of its minimal polynomial. -/
@[simp]
theorem aeval : aeval x (minpoly A x) = 0 := by
delta minpoly
split_ifs with hx
· exact (degree_lt_wf.min_mem _ hx).2
· exact aeval_zero _
/-- Given any `f : B →ₐ[A] B'` and any `x : L`, the minimal polynomial of `x` vanishes at `f x`. -/
@[simp]
theorem aeval_algHom (f : B →ₐ[A] B') (x : B) : (Polynomial.aeval (f x)) (minpoly A x) = 0 := by
rw [Polynomial.aeval_algHom, AlgHom.coe_comp, comp_apply, aeval, map_zero]
/-- A minimal polynomial is not `1`. -/
theorem ne_one [Nontrivial B] : minpoly A x ≠ 1 := by
intro h
refine (one_ne_zero : (1 : B) ≠ 0) ?_
simpa using congr_arg (Polynomial.aeval x) h
theorem map_ne_one [Nontrivial B] {R : Type*} [Semiring R] [Nontrivial R] (f : A →+* R) :
(minpoly A x).map f ≠ 1 := by
by_cases hx : IsIntegral A x
· exact mt ((monic hx).eq_one_of_map_eq_one f) (ne_one A x)
· rw [eq_zero hx, Polynomial.map_zero]
exact zero_ne_one
/-- A minimal polynomial is not a unit. -/
theorem not_isUnit [Nontrivial B] : ¬IsUnit (minpoly A x) := by
haveI : Nontrivial A := (algebraMap A B).domain_nontrivial
by_cases hx : IsIntegral A x
· exact mt (monic hx).eq_one_of_isUnit (ne_one A x)
· rw [eq_zero hx]
exact not_isUnit_zero
theorem mem_range_of_degree_eq_one (hx : (minpoly A x).degree = 1) :
x ∈ (algebraMap A B).range := by
have h : IsIntegral A x := by
by_contra h
rw [eq_zero h, degree_zero, ← WithBot.coe_one] at hx
exact ne_of_lt (show ⊥ < ↑1 from WithBot.bot_lt_coe 1) hx
have key := minpoly.aeval A x
rw [eq_X_add_C_of_degree_eq_one hx, (minpoly.monic h).leadingCoeff, C_1, one_mul, aeval_add,
aeval_C, aeval_X, ← eq_neg_iff_add_eq_zero, ← RingHom.map_neg] at key
exact ⟨-(minpoly A x).coeff 0, key.symm⟩
/-- The defining property of the minimal polynomial of an element `x`:
it is the monic polynomial with smallest degree that has `x` as its root. -/
theorem min {p : A[X]} (pmonic : p.Monic) (hp : Polynomial.aeval x p = 0) :
degree (minpoly A x) ≤ degree p := by
delta minpoly; split_ifs with hx
· exact le_of_not_lt (degree_lt_wf.not_lt_min _ hx ⟨pmonic, hp⟩)
· simp only [degree_zero, bot_le]
theorem unique' {p : A[X]} (hm : p.Monic) (hp : Polynomial.aeval x p = 0)
(hl : ∀ q : A[X], degree q < degree p → q = 0 ∨ Polynomial.aeval x q ≠ 0) :
p = minpoly A x := by
nontriviality A
have hx : IsIntegral A x := ⟨p, hm, hp⟩
obtain h | h := hl _ ((minpoly A x).degree_modByMonic_lt hm)
swap
· exact (h <| (aeval_modByMonic_eq_self_of_root hm hp).trans <| aeval A x).elim
obtain ⟨r, hr⟩ := (modByMonic_eq_zero_iff_dvd hm).1 h
rw [hr]
have hlead := congr_arg leadingCoeff hr
rw [mul_comm, leadingCoeff_mul_monic hm, (monic hx).leadingCoeff] at hlead
have : natDegree r ≤ 0 := by
have hr0 : r ≠ 0 := by
rintro rfl
exact ne_zero hx (mul_zero p ▸ hr)
apply_fun natDegree at hr
rw [hm.natDegree_mul' hr0] at hr
apply Nat.le_of_add_le_add_left
rw [add_zero]
exact hr.symm.trans_le (natDegree_le_natDegree <| min A x hm hp)
rw [eq_C_of_natDegree_le_zero this, ← Nat.eq_zero_of_le_zero this, ← leadingCoeff, ← hlead, C_1,
mul_one]
@[nontriviality]
theorem subsingleton [Subsingleton B] : minpoly A x = 1 := by
nontriviality A
have := minpoly.min A x monic_one (Subsingleton.elim _ _)
rw [degree_one] at this
rcases le_or_lt (minpoly A x).degree 0 with h | h
· rwa [(monic ⟨1, monic_one, by simp [eq_iff_true_of_subsingleton]⟩ :
(minpoly A x).Monic).degree_le_zero_iff_eq_one] at h
· exact (this.not_lt h).elim
end Ring
section CommRing
variable [CommRing A]
section Ring
variable [Ring B] [Algebra A B]
variable {x : B}
/-- The degree of a minimal polynomial, as a natural number, is positive. -/
theorem natDegree_pos [Nontrivial B] (hx : IsIntegral A x) : 0 < natDegree (minpoly A x) := by
rw [pos_iff_ne_zero]
intro ndeg_eq_zero
have eq_one : minpoly A x = 1 := by
rw [eq_C_of_natDegree_eq_zero ndeg_eq_zero]
convert C_1 (R := A)
simpa only [ndeg_eq_zero.symm] using (monic hx).leadingCoeff
simpa only [eq_one, map_one, one_ne_zero] using aeval A x
/-- The degree of a minimal polynomial is positive. -/
theorem degree_pos [Nontrivial B] (hx : IsIntegral A x) : 0 < degree (minpoly A x) :=
| natDegree_pos_iff_degree_pos.mp (natDegree_pos hx)
section
variable [Nontrivial B]
open Polynomial in
theorem degree_eq_one_iff : (minpoly A x).degree = 1 ↔ x ∈ (algebraMap A B).range := by
refine ⟨minpoly.mem_range_of_degree_eq_one _ _, ?_⟩
| Mathlib/FieldTheory/Minpoly/Basic.lean | 192 | 199 |
/-
Copyright (c) 2022 Yaël Dillies, Bhavik Mehta. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Bhavik Mehta
-/
import Mathlib.Algebra.Order.Field.Basic
import Mathlib.Combinatorics.SimpleGraph.Basic
import Mathlib.Data.Rat.Cast.Order
import Mathlib.Order.Partition.Finpartition
import Mathlib.Tactic.GCongr
import Mathlib.Tactic.NormNum
import Mathlib.Tactic.Positivity
import Mathlib.Tactic.Ring
/-!
# Edge density
This file defines the number and density of edges of a relation/graph.
## Main declarations
Between two finsets of vertices,
* `Rel.interedges`: Finset of edges of a relation.
* `Rel.edgeDensity`: Edge density of a relation.
* `SimpleGraph.interedges`: Finset of edges of a graph.
* `SimpleGraph.edgeDensity`: Edge density of a graph.
-/
open Finset
variable {𝕜 ι κ α β : Type*}
/-! ### Density of a relation -/
namespace Rel
section Asymmetric
variable [Field 𝕜] [LinearOrder 𝕜] [IsStrictOrderedRing 𝕜]
(r : α → β → Prop) [∀ a, DecidablePred (r a)] {s s₁ s₂ : Finset α}
{t t₁ t₂ : Finset β} {a : α} {b : β} {δ : 𝕜}
/-- Finset of edges of a relation between two finsets of vertices. -/
def interedges (s : Finset α) (t : Finset β) : Finset (α × β) := {e ∈ s ×ˢ t | r e.1 e.2}
/-- Edge density of a relation between two finsets of vertices. -/
def edgeDensity (s : Finset α) (t : Finset β) : ℚ := #(interedges r s t) / (#s * #t)
variable {r}
theorem mem_interedges_iff {x : α × β} : x ∈ interedges r s t ↔ x.1 ∈ s ∧ x.2 ∈ t ∧ r x.1 x.2 := by
rw [interedges, mem_filter, Finset.mem_product, and_assoc]
theorem mk_mem_interedges_iff : (a, b) ∈ interedges r s t ↔ a ∈ s ∧ b ∈ t ∧ r a b :=
mem_interedges_iff
@[simp]
theorem interedges_empty_left (t : Finset β) : interedges r ∅ t = ∅ := by
rw [interedges, Finset.empty_product, filter_empty]
theorem interedges_mono (hs : s₂ ⊆ s₁) (ht : t₂ ⊆ t₁) : interedges r s₂ t₂ ⊆ interedges r s₁ t₁ :=
fun x ↦ by
simp_rw [mem_interedges_iff]
exact fun h ↦ ⟨hs h.1, ht h.2.1, h.2.2⟩
variable (r)
theorem card_interedges_add_card_interedges_compl (s : Finset α) (t : Finset β) :
| #(interedges r s t) + #(interedges (fun x y ↦ ¬r x y) s t) = #s * #t := by
classical
rw [← card_product, interedges, interedges, ← card_union_of_disjoint, filter_union_filter_neg_eq]
exact disjoint_filter.2 fun _ _ ↦ Classical.not_not.2
| Mathlib/Combinatorics/SimpleGraph/Density.lean | 70 | 73 |
/-
Copyright (c) 2020 Robert Y. Lewis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Robert Y. Lewis
-/
import Mathlib.Algebra.Field.Basic
import Mathlib.Algebra.Order.Ring.Defs
import Mathlib.Data.Tree.Basic
import Mathlib.Logic.Basic
import Mathlib.Tactic.NormNum.Core
import Mathlib.Util.SynthesizeUsing
import Mathlib.Util.Qq
/-!
# A tactic for canceling numeric denominators
This file defines tactics that cancel numeric denominators from field Expressions.
As an example, we want to transform a comparison `5*(a/3 + b/4) < c/3` into the equivalent
`5*(4*a + 3*b) < 4*c`.
## Implementation notes
The tooling here was originally written for `linarith`, not intended as an interactive tactic.
The interactive version has been split off because it is sometimes convenient to use on its own.
There are likely some rough edges to it.
Improving this tactic would be a good project for someone interested in learning tactic programming.
-/
open Lean Parser Tactic Mathlib Meta NormNum Qq
initialize registerTraceClass `CancelDenoms
namespace CancelDenoms
/-! ### Lemmas used in the procedure -/
theorem mul_subst {α} [CommRing α] {n1 n2 k e1 e2 t1 t2 : α}
(h1 : n1 * e1 = t1) (h2 : n2 * e2 = t2) (h3 : n1 * n2 = k) : k * (e1 * e2) = t1 * t2 := by
rw [← h3, mul_comm n1, mul_assoc n2, ← mul_assoc n1, h1,
← mul_assoc n2, mul_comm n2, mul_assoc, h2]
theorem div_subst {α} [Field α] {n1 n2 k e1 e2 t1 : α}
(h1 : n1 * e1 = t1) (h2 : n2 / e2 = 1) (h3 : n1 * n2 = k) : k * (e1 / e2) = t1 := by
rw [← h3, mul_assoc, mul_div_left_comm, h2, ← mul_assoc, h1, mul_comm, one_mul]
theorem cancel_factors_eq_div {α} [Field α] {n e e' : α}
(h : n * e = e') (h2 : n ≠ 0) : e = e' / n :=
eq_div_of_mul_eq h2 <| by rwa [mul_comm] at h
theorem add_subst {α} [Ring α] {n e1 e2 t1 t2 : α} (h1 : n * e1 = t1) (h2 : n * e2 = t2) :
n * (e1 + e2) = t1 + t2 := by simp [left_distrib, *]
theorem sub_subst {α} [Ring α] {n e1 e2 t1 t2 : α} (h1 : n * e1 = t1) (h2 : n * e2 = t2) :
n * (e1 - e2) = t1 - t2 := by simp [left_distrib, *, sub_eq_add_neg]
theorem neg_subst {α} [Ring α] {n e t : α} (h1 : n * e = t) : n * -e = -t := by simp [*]
|
theorem pow_subst {α} [CommRing α] {n e1 t1 k l : α} {e2 : ℕ}
| Mathlib/Tactic/CancelDenoms/Core.lean | 59 | 60 |
/-
Copyright (c) 2023 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies
-/
import Mathlib.Algebra.Order.Module.OrderedSMul
import Mathlib.Algebra.Order.Module.Synonym
import Mathlib.Algebra.Order.Monoid.Unbundled.MinMax
import Mathlib.Order.Monotone.Monovary
/-!
# Monovarying functions and algebraic operations
This file characterises the interaction of ordered algebraic structures with monovariance
of functions.
## See also
`Algebra.Order.Rearrangement` for the n-ary rearrangement inequality
-/
variable {ι α β : Type*}
/-! ### Algebraic operations on monovarying functions -/
section OrderedCommGroup
section
variable [CommGroup α] [PartialOrder α] [IsOrderedMonoid α] [PartialOrder β]
{s : Set ι} {f f₁ f₂ : ι → α} {g : ι → β}
|
@[to_additive (attr := simp)]
lemma monovaryOn_inv_left : MonovaryOn f⁻¹ g s ↔ AntivaryOn f g s := by
| Mathlib/Algebra/Order/Monovary.lean | 31 | 33 |
/-
Copyright (c) 2023 Yaël Dillies, Christopher Hoskin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Christopher Hoskin
-/
import Mathlib.Data.Finset.Lattice.Prod
import Mathlib.Data.Finset.Powerset
import Mathlib.Data.Set.Finite.Basic
import Mathlib.Order.Closure
import Mathlib.Order.ConditionallyCompleteLattice.Finset
/-!
# Sets closed under join/meet
This file defines predicates for sets closed under `⊔` and shows that each set in a join-semilattice
generates a join-closed set and that a semilattice where every directed set has a least upper bound
is automatically complete. All dually for `⊓`.
## Main declarations
* `SupClosed`: Predicate for a set to be closed under join (`a ∈ s` and `b ∈ s` imply `a ⊔ b ∈ s`).
* `InfClosed`: Predicate for a set to be closed under meet (`a ∈ s` and `b ∈ s` imply `a ⊓ b ∈ s`).
* `IsSublattice`: Predicate for a set to be closed under meet and join.
* `supClosure`: Sup-closure. Smallest sup-closed set containing a given set.
* `infClosure`: Inf-closure. Smallest inf-closed set containing a given set.
* `latticeClosure`: Smallest sublattice containing a given set.
* `SemilatticeSup.toCompleteSemilatticeSup`: A join-semilattice where every sup-closed set has a
least upper bound is automatically complete.
* `SemilatticeInf.toCompleteSemilatticeInf`: A meet-semilattice where every inf-closed set has a
greatest lower bound is automatically complete.
-/
variable {ι : Sort*} {F α β : Type*}
section SemilatticeSup
variable [SemilatticeSup α] [SemilatticeSup β]
section Set
variable {ι : Sort*} {S : Set (Set α)} {f : ι → Set α} {s t : Set α} {a : α}
open Set
/-- A set `s` is *sup-closed* if `a ⊔ b ∈ s` for all `a ∈ s`, `b ∈ s`. -/
def SupClosed (s : Set α) : Prop := ∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → a ⊔ b ∈ s
@[simp] lemma supClosed_empty : SupClosed (∅ : Set α) := by simp [SupClosed]
@[simp] lemma supClosed_singleton : SupClosed ({a} : Set α) := by simp [SupClosed]
@[simp] lemma supClosed_univ : SupClosed (univ : Set α) := by simp [SupClosed]
lemma SupClosed.inter (hs : SupClosed s) (ht : SupClosed t) : SupClosed (s ∩ t) :=
fun _a ha _b hb ↦ ⟨hs ha.1 hb.1, ht ha.2 hb.2⟩
lemma supClosed_sInter (hS : ∀ s ∈ S, SupClosed s) : SupClosed (⋂₀ S) :=
fun _a ha _b hb _s hs ↦ hS _ hs (ha _ hs) (hb _ hs)
lemma supClosed_iInter (hf : ∀ i, SupClosed (f i)) : SupClosed (⋂ i, f i) :=
supClosed_sInter <| forall_mem_range.2 hf
lemma SupClosed.directedOn (hs : SupClosed s) : DirectedOn (· ≤ ·) s :=
fun _a ha _b hb ↦ ⟨_, hs ha hb, le_sup_left, le_sup_right⟩
lemma IsUpperSet.supClosed (hs : IsUpperSet s) : SupClosed s := fun _a _ _b ↦ hs le_sup_right
lemma SupClosed.preimage [FunLike F β α] [SupHomClass F β α] (hs : SupClosed s) (f : F) :
SupClosed (f ⁻¹' s) :=
fun a ha b hb ↦ by simpa [map_sup] using hs ha hb
|
lemma SupClosed.image [FunLike F α β] [SupHomClass F α β] (hs : SupClosed s) (f : F) :
SupClosed (f '' s) := by
rintro _ ⟨a, ha, rfl⟩ _ ⟨b, hb, rfl⟩
rw [← map_sup]
| Mathlib/Order/SupClosed.lean | 66 | 70 |
/-
Copyright (c) 2021 Chris Birkbeck. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Birkbeck
-/
import Mathlib.Algebra.Group.Subgroup.Pointwise
import Mathlib.GroupTheory.Coset.Basic
/-!
# Double cosets
This file defines double cosets for two subgroups `H K` of a group `G` and the quotient of `G` by
the double coset relation, i.e. `H \ G / K`. We also prove that `G` can be written as a disjoint
union of the double cosets and that if one of `H` or `K` is the trivial group (i.e. `⊥` ) then
this is the usual left or right quotient of a group by a subgroup.
## Main definitions
* `rel`: The double coset relation defined by two subgroups `H K` of `G`.
* `Doset.quotient`: The quotient of `G` by the double coset relation, i.e, `H \ G / K`.
-/
assert_not_exists MonoidWithZero
variable {G : Type*} [Group G] {α : Type*} [Mul α]
open MulOpposite
open scoped Pointwise
namespace Doset
/-- The double coset as an element of `Set α` corresponding to `s a t` -/
def doset (a : α) (s t : Set α) : Set α :=
s * {a} * t
lemma doset_eq_image2 (a : α) (s t : Set α) : doset a s t = Set.image2 (· * a * ·) s t := by
simp_rw [doset, Set.mul_singleton, ← Set.image2_mul, Set.image2_image_left]
theorem mem_doset {s t : Set α} {a b : α} : b ∈ doset a s t ↔ ∃ x ∈ s, ∃ y ∈ t, b = x * a * y := by
simp only [doset_eq_image2, Set.mem_image2, eq_comm]
theorem mem_doset_self (H K : Subgroup G) (a : G) : a ∈ doset a H K :=
mem_doset.mpr ⟨1, H.one_mem, 1, K.one_mem, (one_mul a).symm.trans (mul_one (1 * a)).symm⟩
theorem doset_eq_of_mem {H K : Subgroup G} {a b : G} (hb : b ∈ doset a H K) :
doset b H K = doset a H K := by
obtain ⟨h, hh, k, hk, rfl⟩ := mem_doset.1 hb
rw [doset, doset, ← Set.singleton_mul_singleton, ← Set.singleton_mul_singleton, mul_assoc,
mul_assoc, Subgroup.singleton_mul_subgroup hk, ← mul_assoc, ← mul_assoc,
Subgroup.subgroup_mul_singleton hh]
| theorem mem_doset_of_not_disjoint {H K : Subgroup G} {a b : G}
(h : ¬Disjoint (doset a H K) (doset b H K)) : b ∈ doset a H K := by
rw [Set.not_disjoint_iff] at h
simp only [mem_doset] at *
obtain ⟨x, ⟨l, hl, r, hr, hrx⟩, y, hy, ⟨r', hr', rfl⟩⟩ := h
refine ⟨y⁻¹ * l, H.mul_mem (H.inv_mem hy) hl, r * r'⁻¹, K.mul_mem hr (K.inv_mem hr'), ?_⟩
| Mathlib/GroupTheory/DoubleCoset.lean | 52 | 57 |
/-
Copyright (c) 2021 Eric Wieser. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Eric Wieser
-/
import Mathlib.Control.EquivFunctor
import Mathlib.Data.Option.Basic
import Mathlib.Data.Subtype
import Mathlib.Logic.Equiv.Defs
/-!
# Equivalences for `Option α`
We define
* `Equiv.optionCongr`: the `Option α ≃ Option β` constructed from `e : α ≃ β` by sending `none` to
`none`, and applying `e` elsewhere.
* `Equiv.removeNone`: the `α ≃ β` constructed from `Option α ≃ Option β` by removing `none` from
both sides.
-/
universe u
namespace Equiv
open Option
variable {α β γ : Type*}
section OptionCongr
/-- A universe-polymorphic version of `EquivFunctor.mapEquiv Option e`. -/
@[simps apply]
def optionCongr (e : α ≃ β) : Option α ≃ Option β where
toFun := Option.map e
invFun := Option.map e.symm
left_inv x := (Option.map_map _ _ _).trans <| e.symm_comp_self.symm ▸ congr_fun Option.map_id x
right_inv x := (Option.map_map _ _ _).trans <| e.self_comp_symm.symm ▸ congr_fun Option.map_id x
@[simp]
theorem optionCongr_refl : optionCongr (Equiv.refl α) = Equiv.refl _ :=
ext <| congr_fun Option.map_id
@[simp]
theorem optionCongr_symm (e : α ≃ β) : (optionCongr e).symm = optionCongr e.symm :=
rfl
@[simp]
theorem optionCongr_trans (e₁ : α ≃ β) (e₂ : β ≃ γ) :
(optionCongr e₁).trans (optionCongr e₂) = optionCongr (e₁.trans e₂) :=
ext <| Option.map_map _ _
/-- When `α` and `β` are in the same universe, this is the same as the result of
`EquivFunctor.mapEquiv`. -/
theorem optionCongr_eq_equivFunctor_mapEquiv {α β : Type u} (e : α ≃ β) :
optionCongr e = EquivFunctor.mapEquiv Option e :=
rfl
end OptionCongr
section RemoveNone
variable (e : Option α ≃ Option β)
/-- If we have a value on one side of an `Equiv` of `Option`
we also have a value on the other side of the equivalence
-/
def removeNone_aux (x : α) : β :=
if h : (e (some x)).isSome then Option.get _ h
else
Option.get _ <|
show (e none).isSome by
rw [← Option.ne_none_iff_isSome]
intro hn
rw [Option.not_isSome_iff_eq_none, ← hn] at h
exact Option.some_ne_none _ (e.injective h)
theorem removeNone_aux_some {x : α} (h : ∃ x', e (some x) = some x') :
some (removeNone_aux e x) = e (some x) := by
simp [removeNone_aux, Option.isSome_iff_exists.mpr h]
theorem removeNone_aux_none {x : α} (h : e (some x) = none) :
some (removeNone_aux e x) = e none := by
simp [removeNone_aux, Option.not_isSome_iff_eq_none.mpr h]
theorem removeNone_aux_inv (x : α) : removeNone_aux e.symm (removeNone_aux e x) = x :=
Option.some_injective _
(by
cases h1 : e.symm (some (removeNone_aux e x)) <;> cases h2 : e (some x)
· rw [removeNone_aux_none _ h1]
exact (e.eq_symm_apply.mpr h2).symm
· rw [removeNone_aux_some _ ⟨_, h2⟩] at h1
simp at h1
|
· rw [removeNone_aux_none _ h2] at h1
simp at h1
| Mathlib/Logic/Equiv/Option.lean | 95 | 97 |
/-
Copyright (c) 2023 Jason Yuen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jason Yuen
-/
import Mathlib.Data.Real.ConjExponents
import Mathlib.Data.Real.Irrational
/-!
# Rayleigh's theorem on Beatty sequences
This file proves Rayleigh's theorem on Beatty sequences. We start by proving `compl_beattySeq`,
which is a generalization of Rayleigh's theorem, and eventually prove
`Irrational.beattySeq_symmDiff_beattySeq_pos`, which is Rayleigh's theorem.
## Main definitions
* `beattySeq`: In the Beatty sequence for real number `r`, the `k`th term is `⌊k * r⌋`.
* `beattySeq'`: In this variant of the Beatty sequence for `r`, the `k`th term is `⌈k * r⌉ - 1`.
## Main statements
Define the following Beatty sets, where `r` denotes a real number:
* `B_r := {⌊k * r⌋ | k ∈ ℤ}`
* `B'_r := {⌈k * r⌉ - 1 | k ∈ ℤ}`
* `B⁺_r := {⌊r⌋, ⌊2r⌋, ⌊3r⌋, ...}`
* `B⁺'_r := {⌈r⌉-1, ⌈2r⌉-1, ⌈3r⌉-1, ...}`
The main statements are:
* `compl_beattySeq`: Let `r` be a real number greater than 1, and `1/r + 1/s = 1`.
Then the complement of `B_r` is `B'_s`.
* `beattySeq_symmDiff_beattySeq'_pos`: Let `r` be a real number greater than 1, and `1/r + 1/s = 1`.
Then `B⁺_r` and `B⁺'_s` partition the positive integers.
* `Irrational.beattySeq_symmDiff_beattySeq_pos`: Let `r` be an irrational number greater than 1, and
`1/r + 1/s = 1`. Then `B⁺_r` and `B⁺_s` partition the positive integers.
## References
* [Wikipedia, *Beatty sequence*](https://en.wikipedia.org/wiki/Beatty_sequence)
## Tags
beatty, sequence, rayleigh, irrational, floor, positive
-/
/-- In the Beatty sequence for real number `r`, the `k`th term is `⌊k * r⌋`. -/
noncomputable def beattySeq (r : ℝ) : ℤ → ℤ :=
fun k ↦ ⌊k * r⌋
/-- In this variant of the Beatty sequence for `r`, the `k`th term is `⌈k * r⌉ - 1`. -/
noncomputable def beattySeq' (r : ℝ) : ℤ → ℤ :=
fun k ↦ ⌈k * r⌉ - 1
namespace Beatty
variable {r s : ℝ} {j : ℤ}
/-- Let `r > 1` and `1/r + 1/s = 1`. Then `B_r` and `B'_s` are disjoint (i.e. no collision exists).
-/
private theorem no_collision (hrs : r.HolderConjugate s) :
Disjoint {beattySeq r k | k} {beattySeq' s k | k} := by
rw [Set.disjoint_left]
intro j ⟨k, h₁⟩ ⟨m, h₂⟩
rw [beattySeq, Int.floor_eq_iff, ← div_le_iff₀ hrs.pos, ← lt_div_iff₀ hrs.pos] at h₁
rw [beattySeq', sub_eq_iff_eq_add, Int.ceil_eq_iff, Int.cast_add, Int.cast_one,
add_sub_cancel_right, ← div_lt_iff₀ hrs.symm.pos, ← le_div_iff₀ hrs.symm.pos] at h₂
have h₃ := add_lt_add_of_le_of_lt h₁.1 h₂.1
have h₄ := add_lt_add_of_lt_of_le h₁.2 h₂.2
simp_rw [div_eq_inv_mul, ← right_distrib, hrs.inv_add_inv_eq_one, one_mul] at h₃ h₄
rw [← Int.cast_one] at h₄
simp_rw [← Int.cast_add, Int.cast_lt, Int.lt_add_one_iff] at h₃ h₄
exact h₄.not_lt h₃
/-- Let `r > 1` and `1/r + 1/s = 1`. Suppose there is an integer `j` where `B_r` and `B'_s` both
jump over `j` (i.e. an anti-collision). Then this leads to a contradiction. -/
private theorem no_anticollision (hrs : r.HolderConjugate s) :
¬∃ j k m : ℤ, k < j / r ∧ (j + 1) / r ≤ k + 1 ∧ m ≤ j / s ∧ (j + 1) / s < m + 1 := by
intro ⟨j, k, m, h₁₁, h₁₂, h₂₁, h₂₂⟩
have h₃ := add_lt_add_of_lt_of_le h₁₁ h₂₁
have h₄ := add_lt_add_of_le_of_lt h₁₂ h₂₂
simp_rw [div_eq_inv_mul, ← right_distrib, hrs.inv_add_inv_eq_one, one_mul] at h₃ h₄
rw [← Int.cast_one, ← add_assoc, add_lt_add_iff_right, add_right_comm] at h₄
simp_rw [← Int.cast_add, Int.cast_lt, Int.lt_add_one_iff] at h₃ h₄
exact h₄.not_lt h₃
| /-- Let `0 < r ∈ ℝ` and `j ∈ ℤ`. Then either `j ∈ B_r` or `B_r` jumps over `j`. -/
private theorem hit_or_miss (h : r > 0) :
j ∈ {beattySeq r k | k} ∨ ∃ k : ℤ, k < j / r ∧ (j + 1) / r ≤ k + 1 := by
-- for both cases, the candidate is `k = ⌈(j + 1) / r⌉ - 1`
cases lt_or_ge ((⌈(j + 1) / r⌉ - 1) * r) j
· refine Or.inr ⟨⌈(j + 1) / r⌉ - 1, ?_⟩
rw [Int.cast_sub, Int.cast_one, lt_div_iff₀ h, sub_add_cancel]
exact ⟨‹_›, Int.le_ceil _⟩
· refine Or.inl ⟨⌈(j + 1) / r⌉ - 1, ?_⟩
rw [beattySeq, Int.floor_eq_iff, Int.cast_sub, Int.cast_one, ← lt_div_iff₀ h, sub_lt_iff_lt_add]
| Mathlib/NumberTheory/Rayleigh.lean | 88 | 97 |
/-
Copyright (c) 2020 Frédéric Dupuis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Frédéric Dupuis, Eric Wieser
-/
import Mathlib.LinearAlgebra.Multilinear.TensorProduct
import Mathlib.Tactic.AdaptationNote
import Mathlib.LinearAlgebra.Multilinear.Curry
/-!
# Tensor product of an indexed family of modules over commutative semirings
We define the tensor product of an indexed family `s : ι → Type*` of modules over commutative
semirings. We denote this space by `⨂[R] i, s i` and define it as `FreeAddMonoid (R × Π i, s i)`
quotiented by the appropriate equivalence relation. The treatment follows very closely that of the
binary tensor product in `LinearAlgebra/TensorProduct.lean`.
## Main definitions
* `PiTensorProduct R s` with `R` a commutative semiring and `s : ι → Type*` is the tensor product
of all the `s i`'s. This is denoted by `⨂[R] i, s i`.
* `tprod R f` with `f : Π i, s i` is the tensor product of the vectors `f i` over all `i : ι`.
This is bundled as a multilinear map from `Π i, s i` to `⨂[R] i, s i`.
* `liftAddHom` constructs an `AddMonoidHom` from `(⨂[R] i, s i)` to some space `F` from a
function `φ : (R × Π i, s i) → F` with the appropriate properties.
* `lift φ` with `φ : MultilinearMap R s E` is the corresponding linear map
`(⨂[R] i, s i) →ₗ[R] E`. This is bundled as a linear equivalence.
* `PiTensorProduct.reindex e` re-indexes the components of `⨂[R] i : ι, M` along `e : ι ≃ ι₂`.
* `PiTensorProduct.tmulEquiv` equivalence between a `TensorProduct` of `PiTensorProduct`s and
a single `PiTensorProduct`.
## Notations
* `⨂[R] i, s i` is defined as localized notation in locale `TensorProduct`.
* `⨂ₜ[R] i, f i` with `f : ∀ i, s i` is defined globally as the tensor product of all the `f i`'s.
## Implementation notes
* We define it via `FreeAddMonoid (R × Π i, s i)` with the `R` representing a "hidden" tensor
factor, rather than `FreeAddMonoid (Π i, s i)` to ensure that, if `ι` is an empty type,
the space is isomorphic to the base ring `R`.
* We have not restricted the index type `ι` to be a `Fintype`, as nothing we do here strictly
requires it. However, problems may arise in the case where `ι` is infinite; use at your own
caution.
* Instead of requiring `DecidableEq ι` as an argument to `PiTensorProduct` itself, we include it
as an argument in the constructors of the relation. A decidability instance still has to come
from somewhere due to the use of `Function.update`, but this hides it from the downstream user.
See the implementation notes for `MultilinearMap` for an extended discussion of this choice.
## TODO
* Define tensor powers, symmetric subspace, etc.
* API for the various ways `ι` can be split into subsets; connect this with the binary
tensor product.
* Include connection with holors.
* Port more of the API from the binary tensor product over to this case.
## Tags
multilinear, tensor, tensor product
-/
suppress_compilation
open Function
section Semiring
variable {ι ι₂ ι₃ : Type*}
variable {R : Type*} [CommSemiring R]
variable {R₁ R₂ : Type*}
variable {s : ι → Type*} [∀ i, AddCommMonoid (s i)] [∀ i, Module R (s i)]
variable {M : Type*} [AddCommMonoid M] [Module R M]
variable {E : Type*} [AddCommMonoid E] [Module R E]
variable {F : Type*} [AddCommMonoid F]
namespace PiTensorProduct
variable (R) (s)
/-- The relation on `FreeAddMonoid (R × Π i, s i)` that generates a congruence whose quotient is
the tensor product. -/
inductive Eqv : FreeAddMonoid (R × Π i, s i) → FreeAddMonoid (R × Π i, s i) → Prop
| of_zero : ∀ (r : R) (f : Π i, s i) (i : ι) (_ : f i = 0), Eqv (FreeAddMonoid.of (r, f)) 0
| of_zero_scalar : ∀ f : Π i, s i, Eqv (FreeAddMonoid.of (0, f)) 0
| of_add : ∀ (_ : DecidableEq ι) (r : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i),
Eqv (FreeAddMonoid.of (r, update f i m₁) + FreeAddMonoid.of (r, update f i m₂))
(FreeAddMonoid.of (r, update f i (m₁ + m₂)))
| of_add_scalar : ∀ (r r' : R) (f : Π i, s i),
Eqv (FreeAddMonoid.of (r, f) + FreeAddMonoid.of (r', f)) (FreeAddMonoid.of (r + r', f))
| of_smul : ∀ (_ : DecidableEq ι) (r : R) (f : Π i, s i) (i : ι) (r' : R),
Eqv (FreeAddMonoid.of (r, update f i (r' • f i))) (FreeAddMonoid.of (r' * r, f))
| add_comm : ∀ x y, Eqv (x + y) (y + x)
end PiTensorProduct
variable (R) (s)
/-- `PiTensorProduct R s` with `R` a commutative semiring and `s : ι → Type*` is the tensor
product of all the `s i`'s. This is denoted by `⨂[R] i, s i`. -/
def PiTensorProduct : Type _ :=
(addConGen (PiTensorProduct.Eqv R s)).Quotient
variable {R}
unsuppress_compilation in
/-- This enables the notation `⨂[R] i : ι, s i` for the pi tensor product `PiTensorProduct`,
given an indexed family of types `s : ι → Type*`. -/
scoped[TensorProduct] notation3:100"⨂["R"] "(...)", "r:(scoped f => PiTensorProduct R f) => r
open TensorProduct
namespace PiTensorProduct
section Module
instance : AddCommMonoid (⨂[R] i, s i) :=
{ (addConGen (PiTensorProduct.Eqv R s)).addMonoid with
add_comm := fun x y ↦
AddCon.induction_on₂ x y fun _ _ ↦
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.add_comm _ _ }
instance : Inhabited (⨂[R] i, s i) := ⟨0⟩
variable (R) {s}
/-- `tprodCoeff R r f` with `r : R` and `f : Π i, s i` is the tensor product of the vectors `f i`
over all `i : ι`, multiplied by the coefficient `r`. Note that this is meant as an auxiliary
definition for this file alone, and that one should use `tprod` defined below for most purposes. -/
def tprodCoeff (r : R) (f : Π i, s i) : ⨂[R] i, s i :=
AddCon.mk' _ <| FreeAddMonoid.of (r, f)
variable {R}
theorem zero_tprodCoeff (f : Π i, s i) : tprodCoeff R 0 f = 0 :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_zero_scalar _
theorem zero_tprodCoeff' (z : R) (f : Π i, s i) (i : ι) (hf : f i = 0) : tprodCoeff R z f = 0 :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_zero _ _ i hf
theorem add_tprodCoeff [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i) :
tprodCoeff R z (update f i m₁) + tprodCoeff R z (update f i m₂) =
tprodCoeff R z (update f i (m₁ + m₂)) :=
Quotient.sound' <| AddConGen.Rel.of _ _ (Eqv.of_add _ z f i m₁ m₂)
theorem add_tprodCoeff' (z₁ z₂ : R) (f : Π i, s i) :
tprodCoeff R z₁ f + tprodCoeff R z₂ f = tprodCoeff R (z₁ + z₂) f :=
Quotient.sound' <| AddConGen.Rel.of _ _ (Eqv.of_add_scalar z₁ z₂ f)
theorem smul_tprodCoeff_aux [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (r : R) :
tprodCoeff R z (update f i (r • f i)) = tprodCoeff R (r * z) f :=
Quotient.sound' <| AddConGen.Rel.of _ _ <| Eqv.of_smul _ _ _ _ _
theorem smul_tprodCoeff [DecidableEq ι] (z : R) (f : Π i, s i) (i : ι) (r : R₁) [SMul R₁ R]
[IsScalarTower R₁ R R] [SMul R₁ (s i)] [IsScalarTower R₁ R (s i)] :
tprodCoeff R z (update f i (r • f i)) = tprodCoeff R (r • z) f := by
have h₁ : r • z = r • (1 : R) * z := by rw [smul_mul_assoc, one_mul]
have h₂ : r • f i = (r • (1 : R)) • f i := (smul_one_smul _ _ _).symm
rw [h₁, h₂]
exact smul_tprodCoeff_aux z f i _
/-- Construct an `AddMonoidHom` from `(⨂[R] i, s i)` to some space `F` from a function
`φ : (R × Π i, s i) → F` with the appropriate properties. -/
def liftAddHom (φ : (R × Π i, s i) → F)
(C0 : ∀ (r : R) (f : Π i, s i) (i : ι) (_ : f i = 0), φ (r, f) = 0)
(C0' : ∀ f : Π i, s i, φ (0, f) = 0)
(C_add : ∀ [DecidableEq ι] (r : R) (f : Π i, s i) (i : ι) (m₁ m₂ : s i),
φ (r, update f i m₁) + φ (r, update f i m₂) = φ (r, update f i (m₁ + m₂)))
(C_add_scalar : ∀ (r r' : R) (f : Π i, s i), φ (r, f) + φ (r', f) = φ (r + r', f))
(C_smul : ∀ [DecidableEq ι] (r : R) (f : Π i, s i) (i : ι) (r' : R),
φ (r, update f i (r' • f i)) = φ (r' * r, f)) :
(⨂[R] i, s i) →+ F :=
(addConGen (PiTensorProduct.Eqv R s)).lift (FreeAddMonoid.lift φ) <|
AddCon.addConGen_le fun x y hxy ↦
match hxy with
| Eqv.of_zero r' f i hf =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C0 r' f i hf]
| Eqv.of_zero_scalar f =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C0']
| Eqv.of_add inst z f i m₁ m₂ =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, @C_add inst]
| Eqv.of_add_scalar z₁ z₂ f =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, C_add_scalar]
| Eqv.of_smul inst z f i r' =>
(AddCon.ker_rel _).2 <| by simp [FreeAddMonoid.lift_eval_of, @C_smul inst]
| Eqv.add_comm x y =>
(AddCon.ker_rel _).2 <| by simp_rw [AddMonoidHom.map_add, add_comm]
/-- Induct using `tprodCoeff` -/
@[elab_as_elim]
protected theorem induction_on' {motive : (⨂[R] i, s i) → Prop} (z : ⨂[R] i, s i)
(tprodCoeff : ∀ (r : R) (f : Π i, s i), motive (tprodCoeff R r f))
(add : ∀ x y, motive x → motive y → motive (x + y)) :
motive z := by
have C0 : motive 0 := by
have h₁ := tprodCoeff 0 0
rwa [zero_tprodCoeff] at h₁
refine AddCon.induction_on z fun x ↦ FreeAddMonoid.recOn x C0 ?_
simp_rw [AddCon.coe_add]
refine fun f y ih ↦ add _ _ ?_ ih
convert tprodCoeff f.1 f.2
section DistribMulAction
variable [Monoid R₁] [DistribMulAction R₁ R] [SMulCommClass R₁ R R]
variable [Monoid R₂] [DistribMulAction R₂ R] [SMulCommClass R₂ R R]
-- Most of the time we want the instance below this one, which is easier for typeclass resolution
-- to find.
instance hasSMul' : SMul R₁ (⨂[R] i, s i) :=
⟨fun r ↦
liftAddHom (fun f : R × Π i, s i ↦ tprodCoeff R (r • f.1) f.2)
(fun r' f i hf ↦ by simp_rw [zero_tprodCoeff' _ f i hf])
(fun f ↦ by simp [zero_tprodCoeff]) (fun r' f i m₁ m₂ ↦ by simp [add_tprodCoeff])
(fun r' r'' f ↦ by simp [add_tprodCoeff', mul_add]) fun z f i r' ↦ by
simp [smul_tprodCoeff, mul_smul_comm]⟩
instance : SMul R (⨂[R] i, s i) :=
PiTensorProduct.hasSMul'
theorem smul_tprodCoeff' (r : R₁) (z : R) (f : Π i, s i) :
r • tprodCoeff R z f = tprodCoeff R (r • z) f := rfl
protected theorem smul_add (r : R₁) (x y : ⨂[R] i, s i) : r • (x + y) = r • x + r • y :=
AddMonoidHom.map_add _ _ _
instance distribMulAction' : DistribMulAction R₁ (⨂[R] i, s i) where
smul := (· • ·)
smul_add _ _ _ := AddMonoidHom.map_add _ _ _
mul_smul r r' x :=
PiTensorProduct.induction_on' x (fun {r'' f} ↦ by simp [smul_tprodCoeff', smul_smul])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy]
one_smul x :=
PiTensorProduct.induction_on' x (fun {r f} ↦ by rw [smul_tprodCoeff', one_smul])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]
smul_zero _ := AddMonoidHom.map_zero _
instance smulCommClass' [SMulCommClass R₁ R₂ R] : SMulCommClass R₁ R₂ (⨂[R] i, s i) :=
⟨fun {r' r''} x ↦
PiTensorProduct.induction_on' x (fun {xr xf} ↦ by simp only [smul_tprodCoeff', smul_comm])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]⟩
instance isScalarTower' [SMul R₁ R₂] [IsScalarTower R₁ R₂ R] :
IsScalarTower R₁ R₂ (⨂[R] i, s i) :=
⟨fun {r' r''} x ↦
PiTensorProduct.induction_on' x (fun {xr xf} ↦ by simp only [smul_tprodCoeff', smul_assoc])
fun {z y} ihz ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihz, ihy]⟩
end DistribMulAction
-- Most of the time we want the instance below this one, which is easier for typeclass resolution
-- to find.
instance module' [Semiring R₁] [Module R₁ R] [SMulCommClass R₁ R R] : Module R₁ (⨂[R] i, s i) :=
{ PiTensorProduct.distribMulAction' with
add_smul := fun r r' x ↦
PiTensorProduct.induction_on' x
(fun {r f} ↦ by simp_rw [smul_tprodCoeff', add_smul, add_tprodCoeff'])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy, add_add_add_comm]
zero_smul := fun x ↦
PiTensorProduct.induction_on' x
(fun {r f} ↦ by simp_rw [smul_tprodCoeff', zero_smul, zero_tprodCoeff])
fun {x y} ihx ihy ↦ by simp_rw [PiTensorProduct.smul_add, ihx, ihy, add_zero] }
-- shortcut instances
instance : Module R (⨂[R] i, s i) :=
PiTensorProduct.module'
instance : SMulCommClass R R (⨂[R] i, s i) :=
PiTensorProduct.smulCommClass'
instance : IsScalarTower R R (⨂[R] i, s i) :=
PiTensorProduct.isScalarTower'
variable (R) in
/-- The canonical `MultilinearMap R s (⨂[R] i, s i)`.
`tprod R fun i => f i` has notation `⨂ₜ[R] i, f i`. -/
def tprod : MultilinearMap R s (⨂[R] i, s i) where
toFun := tprodCoeff R 1
map_update_add' {_ f} i x y := (add_tprodCoeff (1 : R) f i x y).symm
map_update_smul' {_ f} i r x := by
rw [smul_tprodCoeff', ← smul_tprodCoeff (1 : R) _ i, update_idem, update_self]
unsuppress_compilation in
@[inherit_doc tprod]
notation3:100 "⨂ₜ["R"] "(...)", "r:(scoped f => tprod R f) => r
theorem tprod_eq_tprodCoeff_one :
⇑(tprod R : MultilinearMap R s (⨂[R] i, s i)) = tprodCoeff R 1 := rfl
@[simp]
theorem tprodCoeff_eq_smul_tprod (z : R) (f : Π i, s i) : tprodCoeff R z f = z • tprod R f := by
have : z = z • (1 : R) := by simp only [mul_one, Algebra.id.smul_eq_mul]
conv_lhs => rw [this]
rfl
/-- The image of an element `p` of `FreeAddMonoid (R × Π i, s i)` in the `PiTensorProduct` is
equal to the sum of `a • ⨂ₜ[R] i, m i` over all the entries `(a, m)` of `p`.
-/
lemma _root_.FreeAddMonoid.toPiTensorProduct (p : FreeAddMonoid (R × Π i, s i)) :
AddCon.toQuotient (c := addConGen (PiTensorProduct.Eqv R s)) p =
List.sum (List.map (fun x ↦ x.1 • ⨂ₜ[R] i, x.2 i) p.toList) := by
-- TODO: this is defeq abuse: `p` is not a `List`.
match p with
| [] => rw [FreeAddMonoid.toList_nil, List.map_nil, List.sum_nil]; rfl
| x :: ps =>
rw [FreeAddMonoid.toList_cons, List.map_cons, List.sum_cons, ← List.singleton_append,
← toPiTensorProduct ps, ← tprodCoeff_eq_smul_tprod]
rfl
/-- The set of lifts of an element `x` of `⨂[R] i, s i` in `FreeAddMonoid (R × Π i, s i)`. -/
def lifts (x : ⨂[R] i, s i) : Set (FreeAddMonoid (R × Π i, s i)) :=
{p | AddCon.toQuotient (c := addConGen (PiTensorProduct.Eqv R s)) p = x}
/-- An element `p` of `FreeAddMonoid (R × Π i, s i)` lifts an element `x` of `⨂[R] i, s i`
if and only if `x` is equal to the sum of `a • ⨂ₜ[R] i, m i` over all the entries
`(a, m)` of `p`.
-/
lemma mem_lifts_iff (x : ⨂[R] i, s i) (p : FreeAddMonoid (R × Π i, s i)) :
p ∈ lifts x ↔ List.sum (List.map (fun x ↦ x.1 • ⨂ₜ[R] i, x.2 i) p.toList) = x := by
simp only [lifts, Set.mem_setOf_eq, FreeAddMonoid.toPiTensorProduct]
/-- Every element of `⨂[R] i, s i` has a lift in `FreeAddMonoid (R × Π i, s i)`.
-/
lemma nonempty_lifts (x : ⨂[R] i, s i) : Set.Nonempty (lifts x) := by
existsi @Quotient.out _ (addConGen (PiTensorProduct.Eqv R s)).toSetoid x
simp only [lifts, Set.mem_setOf_eq]
rw [← AddCon.quot_mk_eq_coe]
erw [Quot.out_eq]
/-- The empty list lifts the element `0` of `⨂[R] i, s i`.
-/
lemma lifts_zero : 0 ∈ lifts (0 : ⨂[R] i, s i) := by
rw [mem_lifts_iff]; erw [List.map_nil]; rw [List.sum_nil]
/-- If elements `p,q` of `FreeAddMonoid (R × Π i, s i)` lift elements `x,y` of `⨂[R] i, s i`
respectively, then `p + q` lifts `x + y`.
-/
lemma lifts_add {x y : ⨂[R] i, s i} {p q : FreeAddMonoid (R × Π i, s i)}
(hp : p ∈ lifts x) (hq : q ∈ lifts y) : p + q ∈ lifts (x + y) := by
simp only [lifts, Set.mem_setOf_eq, AddCon.coe_add]
rw [hp, hq]
/-- If an element `p` of `FreeAddMonoid (R × Π i, s i)` lifts an element `x` of `⨂[R] i, s i`,
and if `a` is an element of `R`, then the list obtained by multiplying the first entry of each
element of `p` by `a` lifts `a • x`.
-/
lemma lifts_smul {x : ⨂[R] i, s i} {p : FreeAddMonoid (R × Π i, s i)} (h : p ∈ lifts x) (a : R) :
p.map (fun (y : R × Π i, s i) ↦ (a * y.1, y.2)) ∈ lifts (a • x) := by
rw [mem_lifts_iff] at h ⊢
rw [← h]
simp [Function.comp_def, mul_smul, List.smul_sum]
/-- Induct using scaled versions of `PiTensorProduct.tprod`. -/
@[elab_as_elim]
protected theorem induction_on {motive : (⨂[R] i, s i) → Prop} (z : ⨂[R] i, s i)
(smul_tprod : ∀ (r : R) (f : Π i, s i), motive (r • tprod R f))
(add : ∀ x y, motive x → motive y → motive (x + y)) :
motive z := by
simp_rw [← tprodCoeff_eq_smul_tprod] at smul_tprod
exact PiTensorProduct.induction_on' z smul_tprod add
@[ext]
theorem ext {φ₁ φ₂ : (⨂[R] i, s i) →ₗ[R] E}
(H : φ₁.compMultilinearMap (tprod R) = φ₂.compMultilinearMap (tprod R)) : φ₁ = φ₂ := by
refine LinearMap.ext ?_
refine fun z ↦
PiTensorProduct.induction_on' z ?_ fun {x y} hx hy ↦ by rw [φ₁.map_add, φ₂.map_add, hx, hy]
· intro r f
rw [tprodCoeff_eq_smul_tprod, φ₁.map_smul, φ₂.map_smul]
apply congr_arg
exact MultilinearMap.congr_fun H f
/-- The pure tensors (i.e. the elements of the image of `PiTensorProduct.tprod`) span
the tensor product. -/
theorem span_tprod_eq_top :
Submodule.span R (Set.range (tprod R)) = (⊤ : Submodule R (⨂[R] i, s i)) :=
Submodule.eq_top_iff'.mpr fun t ↦ t.induction_on
(fun _ _ ↦ Submodule.smul_mem _ _
(Submodule.subset_span (by simp only [Set.mem_range, exists_apply_eq_apply])))
(fun _ _ hx hy ↦ Submodule.add_mem _ hx hy)
end Module
section Multilinear
open MultilinearMap
variable {s}
section lift
/-- Auxiliary function to constructing a linear map `(⨂[R] i, s i) → E` given a
`MultilinearMap R s E` with the property that its composition with the canonical
`MultilinearMap R s (⨂[R] i, s i)` is the given multilinear map. -/
def liftAux (φ : MultilinearMap R s E) : (⨂[R] i, s i) →+ E :=
liftAddHom (fun p : R × Π i, s i ↦ p.1 • φ p.2)
(fun z f i hf ↦ by simp_rw [map_coord_zero φ i hf, smul_zero])
(fun f ↦ by simp_rw [zero_smul])
(fun z f i m₁ m₂ ↦ by simp_rw [← smul_add, φ.map_update_add])
(fun z₁ z₂ f ↦ by rw [← add_smul])
fun z f i r ↦ by simp [φ.map_update_smul, smul_smul, mul_comm]
theorem liftAux_tprod (φ : MultilinearMap R s E) (f : Π i, s i) : liftAux φ (tprod R f) = φ f := by
simp only [liftAux, liftAddHom, tprod_eq_tprodCoeff_one, tprodCoeff, AddCon.coe_mk']
-- The end of this proof was very different before https://github.com/leanprover/lean4/pull/2644:
-- rw [FreeAddMonoid.of, FreeAddMonoid.ofList, Equiv.refl_apply, AddCon.lift_coe]
-- dsimp [FreeAddMonoid.lift, FreeAddMonoid.sumAux]
-- show _ • _ = _
-- rw [one_smul]
erw [AddCon.lift_coe]
rw [FreeAddMonoid.of]
dsimp [FreeAddMonoid.ofList]
rw [← one_smul R (φ f)]
erw [Equiv.refl_apply]
convert one_smul R (φ f)
simp
theorem liftAux_tprodCoeff (φ : MultilinearMap R s E) (z : R) (f : Π i, s i) :
liftAux φ (tprodCoeff R z f) = z • φ f := rfl
theorem liftAux.smul {φ : MultilinearMap R s E} (r : R) (x : ⨂[R] i, s i) :
liftAux φ (r • x) = r • liftAux φ x := by
refine PiTensorProduct.induction_on' x ?_ ?_
· intro z f
rw [smul_tprodCoeff' r z f, liftAux_tprodCoeff, liftAux_tprodCoeff, smul_assoc]
· intro z y ihz ihy
rw [smul_add, (liftAux φ).map_add, ihz, ihy, (liftAux φ).map_add, smul_add]
/-- Constructing a linear map `(⨂[R] i, s i) → E` given a `MultilinearMap R s E` with the
property that its composition with the canonical `MultilinearMap R s E` is
the given multilinear map `φ`. -/
def lift : MultilinearMap R s E ≃ₗ[R] (⨂[R] i, s i) →ₗ[R] E where
toFun φ := { liftAux φ with map_smul' := liftAux.smul }
invFun φ' := φ'.compMultilinearMap (tprod R)
left_inv φ := by
ext
simp [liftAux_tprod, LinearMap.compMultilinearMap]
right_inv φ := by
ext
simp [liftAux_tprod]
map_add' φ₁ φ₂ := by
ext
simp [liftAux_tprod]
map_smul' r φ₂ := by
ext
simp [liftAux_tprod]
variable {φ : MultilinearMap R s E}
@[simp]
theorem lift.tprod (f : Π i, s i) : lift φ (tprod R f) = φ f :=
liftAux_tprod φ f
theorem lift.unique' {φ' : (⨂[R] i, s i) →ₗ[R] E}
(H : φ'.compMultilinearMap (PiTensorProduct.tprod R) = φ) : φ' = lift φ :=
ext <| H.symm ▸ (lift.symm_apply_apply φ).symm
theorem lift.unique {φ' : (⨂[R] i, s i) →ₗ[R] E} (H : ∀ f, φ' (PiTensorProduct.tprod R f) = φ f) :
φ' = lift φ :=
lift.unique' (MultilinearMap.ext H)
@[simp]
theorem lift_symm (φ' : (⨂[R] i, s i) →ₗ[R] E) : lift.symm φ' = φ'.compMultilinearMap (tprod R) :=
rfl
@[simp]
theorem lift_tprod : lift (tprod R : MultilinearMap R s _) = LinearMap.id :=
Eq.symm <| lift.unique' rfl
end lift
section map
variable {t t' : ι → Type*}
variable [∀ i, AddCommMonoid (t i)] [∀ i, Module R (t i)]
variable [∀ i, AddCommMonoid (t' i)] [∀ i, Module R (t' i)]
variable (g : Π i, t i →ₗ[R] t' i) (f : Π i, s i →ₗ[R] t i)
/--
Let `sᵢ` and `tᵢ` be two families of `R`-modules.
Let `f` be a family of `R`-linear maps between `sᵢ` and `tᵢ`, i.e. `f : Πᵢ sᵢ → tᵢ`,
then there is an induced map `⨂ᵢ sᵢ → ⨂ᵢ tᵢ` by `⨂ aᵢ ↦ ⨂ fᵢ aᵢ`.
This is `TensorProduct.map` for an arbitrary family of modules.
-/
def map : (⨂[R] i, s i) →ₗ[R] ⨂[R] i, t i :=
lift <| (tprod R).compLinearMap f
@[simp] lemma map_tprod (x : Π i, s i) :
map f (tprod R x) = tprod R fun i ↦ f i (x i) :=
lift.tprod _
-- No lemmas about associativity, because we don't have associativity of `PiTensorProduct` yet.
theorem map_range_eq_span_tprod :
LinearMap.range (map f) =
Submodule.span R {t | ∃ (m : Π i, s i), tprod R (fun i ↦ f i (m i)) = t} := by
rw [← Submodule.map_top, ← span_tprod_eq_top, Submodule.map_span, ← Set.range_comp]
apply congrArg; ext x
simp only [Set.mem_range, comp_apply, map_tprod, Set.mem_setOf_eq]
/-- Given submodules `p i ⊆ s i`, this is the natural map: `⨂[R] i, p i → ⨂[R] i, s i`.
This is `TensorProduct.mapIncl` for an arbitrary family of modules.
-/
@[simp]
def mapIncl (p : Π i, Submodule R (s i)) : (⨂[R] i, p i) →ₗ[R] ⨂[R] i, s i :=
map fun (i : ι) ↦ (p i).subtype
theorem map_comp : map (fun (i : ι) ↦ g i ∘ₗ f i) = map g ∘ₗ map f := by
ext
simp only [LinearMap.compMultilinearMap_apply, map_tprod, LinearMap.coe_comp, Function.comp_apply]
theorem lift_comp_map (h : MultilinearMap R t E) :
lift h ∘ₗ map f = lift (h.compLinearMap f) := by
ext
simp only [LinearMap.compMultilinearMap_apply, LinearMap.coe_comp, Function.comp_apply,
map_tprod, lift.tprod, MultilinearMap.compLinearMap_apply]
attribute [local ext high] ext
@[simp]
theorem map_id : map (fun i ↦ (LinearMap.id : s i →ₗ[R] s i)) = .id := by
ext
simp only [LinearMap.compMultilinearMap_apply, map_tprod, LinearMap.id_coe, id_eq]
@[simp]
protected theorem map_one : map (fun (i : ι) ↦ (1 : s i →ₗ[R] s i)) = 1 :=
map_id
protected theorem map_mul (f₁ f₂ : Π i, s i →ₗ[R] s i) :
map (fun i ↦ f₁ i * f₂ i) = map f₁ * map f₂ :=
map_comp f₁ f₂
/-- Upgrading `PiTensorProduct.map` to a `MonoidHom` when `s = t`. -/
@[simps]
def mapMonoidHom : (Π i, s i →ₗ[R] s i) →* ((⨂[R] i, s i) →ₗ[R] ⨂[R] i, s i) where
toFun := map
map_one' := PiTensorProduct.map_one
map_mul' := PiTensorProduct.map_mul
@[simp]
protected theorem map_pow (f : Π i, s i →ₗ[R] s i) (n : ℕ) :
map (f ^ n) = map f ^ n := MonoidHom.map_pow mapMonoidHom _ _
open Function in
private theorem map_add_smul_aux [DecidableEq ι] (i : ι) (x : Π i, s i) (u : s i →ₗ[R] t i) :
(fun j ↦ update f i u j (x j)) = update (fun j ↦ (f j) (x j)) i (u (x i)) := by
ext j
exact apply_update (fun i F => F (x i)) f i u j
open Function in
protected theorem map_update_add [DecidableEq ι] (i : ι) (u v : s i →ₗ[R] t i) :
map (update f i (u + v)) = map (update f i u) + map (update f i v) := by
ext x
simp only [LinearMap.compMultilinearMap_apply, map_tprod, map_add_smul_aux, LinearMap.add_apply,
MultilinearMap.map_update_add]
@[deprecated (since := "2024-11-03")] protected alias map_add := PiTensorProduct.map_update_add
open Function in
protected theorem map_update_smul [DecidableEq ι] (i : ι) (c : R) (u : s i →ₗ[R] t i) :
map (update f i (c • u)) = c • map (update f i u) := by
ext x
simp only [LinearMap.compMultilinearMap_apply, map_tprod, map_add_smul_aux, LinearMap.smul_apply,
MultilinearMap.map_update_smul]
@[deprecated (since := "2024-11-03")] protected alias map_smul := PiTensorProduct.map_update_smul
variable (R s t)
/-- The tensor of a family of linear maps from `sᵢ` to `tᵢ`, as a multilinear map of
the family.
-/
@[simps]
noncomputable def mapMultilinear :
MultilinearMap R (fun (i : ι) ↦ s i →ₗ[R] t i) ((⨂[R] i, s i) →ₗ[R] ⨂[R] i, t i) where
toFun := map
map_update_smul' _ _ _ _ := PiTensorProduct.map_update_smul _ _ _ _
map_update_add' _ _ _ _ := PiTensorProduct.map_update_add _ _ _ _
variable {R s t}
/--
Let `sᵢ` and `tᵢ` be families of `R`-modules.
Then there is an `R`-linear map between `⨂ᵢ Hom(sᵢ, tᵢ)` and `Hom(⨂ᵢ sᵢ, ⨂ tᵢ)` defined by
`⨂ᵢ fᵢ ↦ ⨂ᵢ aᵢ ↦ ⨂ᵢ fᵢ aᵢ`.
This is `TensorProduct.homTensorHomMap` for an arbitrary family of modules.
Note that `PiTensorProduct.piTensorHomMap (tprod R f)` is equal to `PiTensorProduct.map f`.
-/
def piTensorHomMap : (⨂[R] i, s i →ₗ[R] t i) →ₗ[R] (⨂[R] i, s i) →ₗ[R] ⨂[R] i, t i :=
lift.toLinearMap ∘ₗ lift (MultilinearMap.piLinearMap <| tprod R)
@[simp] lemma piTensorHomMap_tprod_tprod (f : Π i, s i →ₗ[R] t i) (x : Π i, s i) :
piTensorHomMap (tprod R f) (tprod R x) = tprod R fun i ↦ f i (x i) := by
simp [piTensorHomMap]
lemma piTensorHomMap_tprod_eq_map (f : Π i, s i →ₗ[R] t i) :
piTensorHomMap (tprod R f) = map f := by
ext; simp
/-- If `s i` and `t i` are linearly equivalent for every `i` in `ι`, then `⨂[R] i, s i` and
`⨂[R] i, t i` are linearly equivalent.
This is the n-ary version of `TensorProduct.congr`
-/
noncomputable def congr (f : Π i, s i ≃ₗ[R] t i) :
(⨂[R] i, s i) ≃ₗ[R] ⨂[R] i, t i :=
.ofLinear
(map (fun i ↦ f i))
(map (fun i ↦ (f i).symm))
(by ext; simp)
(by ext; simp)
@[simp]
theorem congr_tprod (f : Π i, s i ≃ₗ[R] t i) (m : Π i, s i) :
congr f (tprod R m) = tprod R (fun (i : ι) ↦ (f i) (m i)) := by
simp only [congr, LinearEquiv.ofLinear_apply, map_tprod, LinearEquiv.coe_coe]
@[simp]
theorem congr_symm_tprod (f : Π i, s i ≃ₗ[R] t i) (p : Π i, t i) :
(congr f).symm (tprod R p) = tprod R (fun (i : ι) ↦ (f i).symm (p i)) := by
simp only [congr, LinearEquiv.ofLinear_symm_apply, map_tprod, LinearEquiv.coe_coe]
/--
Let `sᵢ`, `tᵢ` and `t'ᵢ` be families of `R`-modules, then `f : Πᵢ sᵢ → tᵢ → t'ᵢ` induces an
element of `Hom(⨂ᵢ sᵢ, Hom(⨂ tᵢ, ⨂ᵢ t'ᵢ))` defined by `⨂ᵢ aᵢ ↦ ⨂ᵢ bᵢ ↦ ⨂ᵢ fᵢ aᵢ bᵢ`.
This is `PiTensorProduct.map` for two arbitrary families of modules.
This is `TensorProduct.map₂` for families of modules.
-/
def map₂ (f : Π i, s i →ₗ[R] t i →ₗ[R] t' i) :
(⨂[R] i, s i) →ₗ[R] (⨂[R] i, t i) →ₗ[R] ⨂[R] i, t' i :=
lift <| LinearMap.compMultilinearMap piTensorHomMap <| (tprod R).compLinearMap f
lemma map₂_tprod_tprod (f : Π i, s i →ₗ[R] t i →ₗ[R] t' i) (x : Π i, s i) (y : Π i, t i) :
map₂ f (tprod R x) (tprod R y) = tprod R fun i ↦ f i (x i) (y i) := by
simp [map₂]
/--
Let `sᵢ`, `tᵢ` and `t'ᵢ` be families of `R`-modules.
Then there is a function from `⨂ᵢ Hom(sᵢ, Hom(tᵢ, t'ᵢ))` to `Hom(⨂ᵢ sᵢ, Hom(⨂ tᵢ, ⨂ᵢ t'ᵢ))`
defined by `⨂ᵢ fᵢ ↦ ⨂ᵢ aᵢ ↦ ⨂ᵢ bᵢ ↦ ⨂ᵢ fᵢ aᵢ bᵢ`. -/
def piTensorHomMapFun₂ : (⨂[R] i, s i →ₗ[R] t i →ₗ[R] t' i) →
(⨂[R] i, s i) →ₗ[R] (⨂[R] i, t i) →ₗ[R] (⨂[R] i, t' i) :=
fun φ => lift <| LinearMap.compMultilinearMap piTensorHomMap <|
(lift <| MultilinearMap.piLinearMap <| tprod R) φ
theorem piTensorHomMapFun₂_add (φ ψ : ⨂[R] i, s i →ₗ[R] t i →ₗ[R] t' i) :
piTensorHomMapFun₂ (φ + ψ) = piTensorHomMapFun₂ φ + piTensorHomMapFun₂ ψ := by
dsimp [piTensorHomMapFun₂]; ext; simp only [map_add, LinearMap.compMultilinearMap_apply,
lift.tprod, add_apply, LinearMap.add_apply]
theorem piTensorHomMapFun₂_smul (r : R) (φ : ⨂[R] i, s i →ₗ[R] t i →ₗ[R] t' i) :
piTensorHomMapFun₂ (r • φ) = r • piTensorHomMapFun₂ φ := by
dsimp [piTensorHomMapFun₂]; ext; simp only [map_smul, LinearMap.compMultilinearMap_apply,
lift.tprod, smul_apply, LinearMap.smul_apply]
/--
Let `sᵢ`, `tᵢ` and `t'ᵢ` be families of `R`-modules.
Then there is an linear map from `⨂ᵢ Hom(sᵢ, Hom(tᵢ, t'ᵢ))` to `Hom(⨂ᵢ sᵢ, Hom(⨂ tᵢ, ⨂ᵢ t'ᵢ))`
defined by `⨂ᵢ fᵢ ↦ ⨂ᵢ aᵢ ↦ ⨂ᵢ bᵢ ↦ ⨂ᵢ fᵢ aᵢ bᵢ`.
This is `TensorProduct.homTensorHomMap` for two arbitrary families of modules.
-/
def piTensorHomMap₂ : (⨂[R] i, s i →ₗ[R] t i →ₗ[R] t' i) →ₗ[R]
(⨂[R] i, s i) →ₗ[R] (⨂[R] i, t i) →ₗ[R] (⨂[R] i, t' i) where
toFun := piTensorHomMapFun₂
map_add' x y := piTensorHomMapFun₂_add x y
map_smul' x y := piTensorHomMapFun₂_smul x y
@[simp] lemma piTensorHomMap₂_tprod_tprod_tprod
(f : ∀ i, s i →ₗ[R] t i →ₗ[R] t' i) (a : ∀ i, s i) (b : ∀ i, t i) :
piTensorHomMap₂ (tprod R f) (tprod R a) (tprod R b) = tprod R (fun i ↦ f i (a i) (b i)) := by
simp [piTensorHomMapFun₂, piTensorHomMap₂]
end map
section
variable (R M)
variable (s) in
/-- Re-index the components of the tensor power by `e`. -/
def reindex (e : ι ≃ ι₂) : (⨂[R] i : ι, s i) ≃ₗ[R] ⨂[R] i : ι₂, s (e.symm i) :=
let f := domDomCongrLinearEquiv' R R s (⨂[R] (i : ι₂), s (e.symm i)) e
| let g := domDomCongrLinearEquiv' R R s (⨂[R] (i : ι), s i) e
#adaptation_note /-- v4.7.0-rc1
An alternative to the last two proofs would be `aesop (simp_config := {zetaDelta := true})`
or a wrapper macro to that effect. -/
| Mathlib/LinearAlgebra/PiTensorProduct.lean | 689 | 692 |
/-
Copyright (c) 2014 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Mario Carneiro
-/
import Mathlib.Data.Subtype
import Mathlib.Order.Defs.LinearOrder
import Mathlib.Order.Notation
import Mathlib.Tactic.GCongr.Core
import Mathlib.Tactic.Spread
import Mathlib.Tactic.Convert
import Mathlib.Tactic.Inhabit
import Mathlib.Tactic.SimpRw
/-!
# Basic definitions about `≤` and `<`
This file proves basic results about orders, provides extensive dot notation, defines useful order
classes and allows to transfer order instances.
## Type synonyms
* `OrderDual α` : A type synonym reversing the meaning of all inequalities, with notation `αᵒᵈ`.
* `AsLinearOrder α`: A type synonym to promote `PartialOrder α` to `LinearOrder α` using
`IsTotal α (≤)`.
### Transferring orders
- `Order.Preimage`, `Preorder.lift`: Transfers a (pre)order on `β` to an order on `α`
using a function `f : α → β`.
- `PartialOrder.lift`, `LinearOrder.lift`: Transfers a partial (resp., linear) order on `β` to a
partial (resp., linear) order on `α` using an injective function `f`.
### Extra class
* `DenselyOrdered`: An order with no gap, i.e. for any two elements `a < b` there exists `c` such
that `a < c < b`.
## Notes
`≤` and `<` are highly favored over `≥` and `>` in mathlib. The reason is that we can formulate all
lemmas using `≤`/`<`, and `rw` has trouble unifying `≤` and `≥`. Hence choosing one direction spares
us useless duplication. This is enforced by a linter. See Note [nolint_ge] for more infos.
Dot notation is particularly useful on `≤` (`LE.le`) and `<` (`LT.lt`). To that end, we
provide many aliases to dot notation-less lemmas. For example, `le_trans` is aliased with
`LE.le.trans` and can be used to construct `hab.trans hbc : a ≤ c` when `hab : a ≤ b`,
`hbc : b ≤ c`, `lt_of_le_of_lt` is aliased as `LE.le.trans_lt` and can be used to construct
`hab.trans hbc : a < c` when `hab : a ≤ b`, `hbc : b < c`.
## TODO
- expand module docs
- automatic construction of dual definitions / theorems
## Tags
preorder, order, partial order, poset, linear order, chain
-/
open Function
variable {ι α β : Type*} {π : ι → Type*}
/-! ### Bare relations -/
attribute [ext] LE
protected lemma LE.le.ge [LE α] {x y : α} (h : x ≤ y) : y ≥ x := h
protected lemma GE.ge.le [LE α] {x y : α} (h : x ≥ y) : y ≤ x := h
protected lemma LT.lt.gt [LT α] {x y : α} (h : x < y) : y > x := h
protected lemma GT.gt.lt [LT α] {x y : α} (h : x > y) : y < x := h
/-- Given a relation `R` on `β` and a function `f : α → β`, the preimage relation on `α` is defined
by `x ≤ y ↔ f x ≤ f y`. It is the unique relation on `α` making `f` a `RelEmbedding` (assuming `f`
is injective). -/
@[simp]
def Order.Preimage (f : α → β) (s : β → β → Prop) (x y : α) : Prop := s (f x) (f y)
@[inherit_doc] infixl:80 " ⁻¹'o " => Order.Preimage
/-- The preimage of a decidable order is decidable. -/
instance Order.Preimage.decidable (f : α → β) (s : β → β → Prop) [H : DecidableRel s] :
DecidableRel (f ⁻¹'o s) := fun _ _ ↦ H _ _
/-! ### Preorders -/
section Preorder
variable [Preorder α] {a b c d : α}
theorem le_trans' : b ≤ c → a ≤ b → a ≤ c :=
flip le_trans
theorem lt_trans' : b < c → a < b → a < c :=
flip lt_trans
theorem lt_of_le_of_lt' : b ≤ c → a < b → a < c :=
flip lt_of_lt_of_le
theorem lt_of_lt_of_le' : b < c → a ≤ b → a < c :=
flip lt_of_le_of_lt
theorem le_of_le_of_eq' : b ≤ c → a = b → a ≤ c :=
flip le_of_eq_of_le
theorem le_of_eq_of_le' : b = c → a ≤ b → a ≤ c :=
flip le_of_le_of_eq
theorem lt_of_lt_of_eq' : b < c → a = b → a < c :=
flip lt_of_eq_of_lt
theorem lt_of_eq_of_lt' : b = c → a < b → a < c :=
flip lt_of_lt_of_eq
theorem not_lt_iff_not_le_or_ge : ¬a < b ↔ ¬a ≤ b ∨ b ≤ a := by
rw [lt_iff_le_not_le, Classical.not_and_iff_not_or_not, Classical.not_not]
-- Unnecessary brackets are here for readability
lemma not_lt_iff_le_imp_le : ¬ a < b ↔ (a ≤ b → b ≤ a) := by
simp [not_lt_iff_not_le_or_ge, or_iff_not_imp_left]
/-- If `x = y` then `y ≤ x`. Note: this lemma uses `y ≤ x` instead of `x ≥ y`, because `le` is used
almost exclusively in mathlib. -/
lemma ge_of_eq (h : a = b) : b ≤ a := le_of_eq h.symm
@[simp] lemma lt_self_iff_false (x : α) : x < x ↔ False := ⟨lt_irrefl x, False.elim⟩
alias LE.le.trans := le_trans
alias LE.le.trans' := le_trans'
alias LT.lt.trans := lt_trans
alias LT.lt.trans' := lt_trans'
alias LE.le.trans_lt := lt_of_le_of_lt
alias LE.le.trans_lt' := lt_of_le_of_lt'
alias LT.lt.trans_le := lt_of_lt_of_le
alias LT.lt.trans_le' := lt_of_lt_of_le'
alias LE.le.trans_eq := le_of_le_of_eq
alias LE.le.trans_eq' := le_of_le_of_eq'
alias LT.lt.trans_eq := lt_of_lt_of_eq
alias LT.lt.trans_eq' := lt_of_lt_of_eq'
alias Eq.trans_le := le_of_eq_of_le
alias Eq.trans_ge := le_of_eq_of_le'
alias Eq.trans_lt := lt_of_eq_of_lt
alias Eq.trans_gt := lt_of_eq_of_lt'
alias LE.le.lt_of_not_le := lt_of_le_not_le
alias LE.le.lt_or_eq_dec := Decidable.lt_or_eq_of_le
alias LT.lt.le := le_of_lt
alias LT.lt.ne := ne_of_lt
alias Eq.le := le_of_eq
@[inherit_doc ge_of_eq] alias Eq.ge := ge_of_eq
alias LT.lt.asymm := lt_asymm
alias LT.lt.not_lt := lt_asymm
theorem ne_of_not_le (h : ¬a ≤ b) : a ≠ b := fun hab ↦ h (le_of_eq hab)
protected lemma Eq.not_lt (hab : a = b) : ¬a < b := fun h' ↦ h'.ne hab
protected lemma Eq.not_gt (hab : a = b) : ¬b < a := hab.symm.not_lt
@[simp] lemma le_of_subsingleton [Subsingleton α] : a ≤ b := (Subsingleton.elim a b).le
-- Making this a @[simp] lemma causes confluence problems downstream.
lemma not_lt_of_subsingleton [Subsingleton α] : ¬a < b := (Subsingleton.elim a b).not_lt
namespace LT.lt
protected theorem false : a < a → False := lt_irrefl a
theorem ne' (h : a < b) : b ≠ a := h.ne.symm
end LT.lt
theorem le_of_forall_le (H : ∀ c, c ≤ a → c ≤ b) : a ≤ b := H _ le_rfl
theorem le_of_forall_ge (H : ∀ c, a ≤ c → b ≤ c) : b ≤ a := H _ le_rfl
@[deprecated (since := "2025-01-30")] alias le_of_forall_le' := le_of_forall_ge
theorem forall_le_iff_le : (∀ ⦃c⦄, c ≤ a → c ≤ b) ↔ a ≤ b :=
⟨le_of_forall_le, fun h _ hca ↦ le_trans hca h⟩
theorem forall_le_iff_ge : (∀ ⦃c⦄, a ≤ c → b ≤ c) ↔ b ≤ a :=
⟨le_of_forall_ge, fun h _ hca ↦ le_trans h hca⟩
/-- monotonicity of `≤` with respect to `→` -/
theorem le_implies_le_of_le_of_le (hca : c ≤ a) (hbd : b ≤ d) : a ≤ b → c ≤ d :=
fun hab ↦ (hca.trans hab).trans hbd
end Preorder
/-! ### Partial order -/
section PartialOrder
variable [PartialOrder α] {a b : α}
theorem ge_antisymm : a ≤ b → b ≤ a → b = a :=
flip le_antisymm
theorem lt_of_le_of_ne' : a ≤ b → b ≠ a → a < b := fun h₁ h₂ ↦ lt_of_le_of_ne h₁ h₂.symm
theorem Ne.lt_of_le : a ≠ b → a ≤ b → a < b :=
flip lt_of_le_of_ne
theorem Ne.lt_of_le' : b ≠ a → a ≤ b → a < b :=
flip lt_of_le_of_ne'
alias LE.le.antisymm := le_antisymm
alias LE.le.antisymm' := ge_antisymm
alias LE.le.lt_of_ne := lt_of_le_of_ne
alias LE.le.lt_of_ne' := lt_of_le_of_ne'
alias LE.le.lt_or_eq := lt_or_eq_of_le
-- Unnecessary brackets are here for readability
lemma le_imp_eq_iff_le_imp_le : (a ≤ b → b = a) ↔ (a ≤ b → b ≤ a) where
mp h hab := (h hab).le
mpr h hab := (h hab).antisymm hab
-- Unnecessary brackets are here for readability
lemma ge_imp_eq_iff_le_imp_le : (a ≤ b → a = b) ↔ (a ≤ b → b ≤ a) where
mp h hab := (h hab).ge
mpr h hab := hab.antisymm (h hab)
namespace LE.le
theorem lt_iff_ne (h : a ≤ b) : a < b ↔ a ≠ b :=
⟨fun h ↦ h.ne, h.lt_of_ne⟩
theorem gt_iff_ne (h : a ≤ b) : a < b ↔ b ≠ a :=
⟨fun h ↦ h.ne.symm, h.lt_of_ne'⟩
theorem not_lt_iff_eq (h : a ≤ b) : ¬a < b ↔ a = b :=
h.lt_iff_ne.not_left
theorem not_gt_iff_eq (h : a ≤ b) : ¬a < b ↔ b = a :=
h.gt_iff_ne.not_left
theorem le_iff_eq (h : a ≤ b) : b ≤ a ↔ b = a :=
⟨fun h' ↦ h'.antisymm h, Eq.le⟩
theorem ge_iff_eq (h : a ≤ b) : b ≤ a ↔ a = b :=
⟨h.antisymm, Eq.ge⟩
end LE.le
-- See Note [decidable namespace]
protected theorem Decidable.le_iff_eq_or_lt [DecidableLE α] : a ≤ b ↔ a = b ∨ a < b :=
Decidable.le_iff_lt_or_eq.trans or_comm
theorem le_iff_eq_or_lt : a ≤ b ↔ a = b ∨ a < b := le_iff_lt_or_eq.trans or_comm
theorem lt_iff_le_and_ne : a < b ↔ a ≤ b ∧ a ≠ b :=
⟨fun h ↦ ⟨le_of_lt h, ne_of_lt h⟩, fun ⟨h1, h2⟩ ↦ h1.lt_of_ne h2⟩
lemma eq_iff_not_lt_of_le (hab : a ≤ b) : a = b ↔ ¬ a < b := by simp [hab, lt_iff_le_and_ne]
alias LE.le.eq_iff_not_lt := eq_iff_not_lt_of_le
-- See Note [decidable namespace]
protected theorem Decidable.eq_iff_le_not_lt [DecidableLE α] : a = b ↔ a ≤ b ∧ ¬a < b :=
⟨fun h ↦ ⟨h.le, h ▸ lt_irrefl _⟩, fun ⟨h₁, h₂⟩ ↦
h₁.antisymm <| Decidable.byContradiction fun h₃ ↦ h₂ (h₁.lt_of_not_le h₃)⟩
theorem eq_iff_le_not_lt : a = b ↔ a ≤ b ∧ ¬a < b :=
haveI := Classical.dec
Decidable.eq_iff_le_not_lt
theorem eq_or_lt_of_le (h : a ≤ b) : a = b ∨ a < b := h.lt_or_eq.symm
theorem eq_or_gt_of_le (h : a ≤ b) : b = a ∨ a < b := h.lt_or_eq.symm.imp Eq.symm id
theorem gt_or_eq_of_le (h : a ≤ b) : a < b ∨ b = a := (eq_or_gt_of_le h).symm
alias LE.le.eq_or_lt_dec := Decidable.eq_or_lt_of_le
alias LE.le.eq_or_lt := eq_or_lt_of_le
alias LE.le.eq_or_gt := eq_or_gt_of_le
alias LE.le.gt_or_eq := gt_or_eq_of_le
theorem eq_of_le_of_not_lt (hab : a ≤ b) (hba : ¬a < b) : a = b := hab.eq_or_lt.resolve_right hba
theorem eq_of_ge_of_not_gt (hab : a ≤ b) (hba : ¬a < b) : b = a := (eq_of_le_of_not_lt hab hba).symm
alias LE.le.eq_of_not_lt := eq_of_le_of_not_lt
alias LE.le.eq_of_not_gt := eq_of_ge_of_not_gt
theorem Ne.le_iff_lt (h : a ≠ b) : a ≤ b ↔ a < b := ⟨fun h' ↦ lt_of_le_of_ne h' h, fun h ↦ h.le⟩
theorem Ne.not_le_or_not_le (h : a ≠ b) : ¬a ≤ b ∨ ¬b ≤ a := not_and_or.1 <| le_antisymm_iff.not.1 h
-- See Note [decidable namespace]
protected theorem Decidable.ne_iff_lt_iff_le [DecidableEq α] : (a ≠ b ↔ a < b) ↔ a ≤ b :=
⟨fun h ↦ Decidable.byCases le_of_eq (le_of_lt ∘ h.mp), fun h ↦ ⟨lt_of_le_of_ne h, ne_of_lt⟩⟩
@[simp]
theorem ne_iff_lt_iff_le : (a ≠ b ↔ a < b) ↔ a ≤ b :=
haveI := Classical.dec
Decidable.ne_iff_lt_iff_le
lemma eq_of_forall_le_iff (H : ∀ c, c ≤ a ↔ c ≤ b) : a = b :=
((H _).1 le_rfl).antisymm ((H _).2 le_rfl)
lemma eq_of_forall_ge_iff (H : ∀ c, a ≤ c ↔ b ≤ c) : a = b :=
((H _).2 le_rfl).antisymm ((H _).1 le_rfl)
/-- To prove commutativity of a binary operation `○`, we only to check `a ○ b ≤ b ○ a` for all `a`,
`b`. -/
lemma commutative_of_le {f : β → β → α} (comm : ∀ a b, f a b ≤ f b a) : ∀ a b, f a b = f b a :=
fun _ _ ↦ (comm _ _).antisymm <| comm _ _
/-- To prove associativity of a commutative binary operation `○`, we only to check
`(a ○ b) ○ c ≤ a ○ (b ○ c)` for all `a`, `b`, `c`. -/
lemma associative_of_commutative_of_le {f : α → α → α} (comm : Std.Commutative f)
(assoc : ∀ a b c, f (f a b) c ≤ f a (f b c)) : Std.Associative f where
assoc a b c :=
le_antisymm (assoc _ _ _) <| by
rw [comm.comm, comm.comm b, comm.comm _ c, comm.comm a]
exact assoc ..
end PartialOrder
section LinearOrder
variable [LinearOrder α] {a b : α}
namespace LE.le
lemma lt_or_le (h : a ≤ b) (c : α) : a < c ∨ c ≤ b := (lt_or_ge a c).imp id h.trans'
lemma le_or_lt (h : a ≤ b) (c : α) : a ≤ c ∨ c < b := (le_or_gt a c).imp id h.trans_lt'
lemma le_or_le (h : a ≤ b) (c : α) : a ≤ c ∨ c ≤ b := (h.lt_or_le c).imp le_of_lt id
end LE.le
namespace LT.lt
lemma lt_or_lt (h : a < b) (c : α) : a < c ∨ c < b := (le_or_gt b c).imp h.trans_le id
end LT.lt
-- Variant of `min_def` with the branches reversed.
theorem min_def' (a b : α) : min a b = if b ≤ a then b else a := by
rw [min_def]
rcases lt_trichotomy a b with (lt | eq | gt)
· rw [if_pos lt.le, if_neg (not_le.mpr lt)]
· rw [if_pos eq.le, if_pos eq.ge, eq]
· rw [if_neg (not_le.mpr gt.gt), if_pos gt.le]
-- Variant of `min_def` with the branches reversed.
-- This is sometimes useful as it used to be the default.
theorem max_def' (a b : α) : max a b = if b ≤ a then a else b := by
rw [max_def]
rcases lt_trichotomy a b with (lt | eq | gt)
· rw [if_pos lt.le, if_neg (not_le.mpr lt)]
· rw [if_pos eq.le, if_pos eq.ge, eq]
· rw [if_neg (not_le.mpr gt.gt), if_pos gt.le]
theorem lt_of_not_le (h : ¬b ≤ a) : a < b :=
((le_total _ _).resolve_right h).lt_of_not_le h
theorem lt_iff_not_le : a < b ↔ ¬b ≤ a :=
⟨not_le_of_lt, lt_of_not_le⟩
theorem Ne.lt_or_lt (h : a ≠ b) : a < b ∨ b < a :=
lt_or_gt_of_ne h
/-- A version of `ne_iff_lt_or_gt` with LHS and RHS reversed. -/
@[simp]
theorem lt_or_lt_iff_ne : a < b ∨ b < a ↔ a ≠ b :=
ne_iff_lt_or_gt.symm
theorem not_lt_iff_eq_or_lt : ¬a < b ↔ a = b ∨ b < a :=
not_lt.trans <| Decidable.le_iff_eq_or_lt.trans <| or_congr eq_comm Iff.rfl
theorem exists_ge_of_linear (a b : α) : ∃ c, a ≤ c ∧ b ≤ c :=
match le_total a b with
| Or.inl h => ⟨_, h, le_rfl⟩
| Or.inr h => ⟨_, le_rfl, h⟩
lemma exists_forall_ge_and {p q : α → Prop} :
(∃ i, ∀ j ≥ i, p j) → (∃ i, ∀ j ≥ i, q j) → ∃ i, ∀ j ≥ i, p j ∧ q j
| ⟨a, ha⟩, ⟨b, hb⟩ =>
let ⟨c, hac, hbc⟩ := exists_ge_of_linear a b
⟨c, fun _d hcd ↦ ⟨ha _ <| hac.trans hcd, hb _ <| hbc.trans hcd⟩⟩
theorem le_of_forall_lt (H : ∀ c, c < a → c < b) : a ≤ b :=
le_of_not_lt fun h ↦ lt_irrefl _ (H _ h)
theorem forall_lt_iff_le : (∀ ⦃c⦄, c < a → c < b) ↔ a ≤ b :=
⟨le_of_forall_lt, fun h _ hca ↦ lt_of_lt_of_le hca h⟩
theorem le_of_forall_lt' (H : ∀ c, a < c → b < c) : b ≤ a :=
le_of_not_lt fun h ↦ lt_irrefl _ (H _ h)
theorem forall_lt_iff_le' : (∀ ⦃c⦄, a < c → b < c) ↔ b ≤ a :=
⟨le_of_forall_lt', fun h _ hac ↦ lt_of_le_of_lt h hac⟩
theorem eq_of_forall_lt_iff (h : ∀ c, c < a ↔ c < b) : a = b :=
(le_of_forall_lt fun _ ↦ (h _).1).antisymm <| le_of_forall_lt fun _ ↦ (h _).2
theorem eq_of_forall_gt_iff (h : ∀ c, a < c ↔ b < c) : a = b :=
(le_of_forall_lt' fun _ ↦ (h _).2).antisymm <| le_of_forall_lt' fun _ ↦ (h _).1
section ltByCases
variable {P : Sort*} {x y : α}
@[simp]
lemma ltByCases_lt (h : x < y) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P} :
ltByCases x y h₁ h₂ h₃ = h₁ h := dif_pos h
@[simp]
lemma ltByCases_gt (h : y < x) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P} :
ltByCases x y h₁ h₂ h₃ = h₃ h := (dif_neg h.not_lt).trans (dif_pos h)
@[simp]
lemma ltByCases_eq (h : x = y) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P} :
ltByCases x y h₁ h₂ h₃ = h₂ h := (dif_neg h.not_lt).trans (dif_neg h.not_gt)
lemma ltByCases_not_lt (h : ¬ x < y) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P}
(p : ¬ y < x → x = y := fun h' => (le_antisymm (le_of_not_gt h') (le_of_not_gt h))) :
ltByCases x y h₁ h₂ h₃ = if h' : y < x then h₃ h' else h₂ (p h') := dif_neg h
lemma ltByCases_not_gt (h : ¬ y < x) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P}
(p : ¬ x < y → x = y := fun h' => (le_antisymm (le_of_not_gt h) (le_of_not_gt h'))) :
ltByCases x y h₁ h₂ h₃ = if h' : x < y then h₁ h' else h₂ (p h') :=
dite_congr rfl (fun _ => rfl) (fun _ => dif_neg h)
lemma ltByCases_ne (h : x ≠ y) {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P}
(p : ¬ x < y → y < x := fun h' => h.lt_or_lt.resolve_left h') :
ltByCases x y h₁ h₂ h₃ = if h' : x < y then h₁ h' else h₃ (p h') :=
dite_congr rfl (fun _ => rfl) (fun _ => dif_pos _)
lemma ltByCases_comm {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P}
(p : y = x → x = y := fun h' => h'.symm) :
ltByCases x y h₁ h₂ h₃ = ltByCases y x h₃ (h₂ ∘ p) h₁ := by
refine ltByCases x y (fun h => ?_) (fun h => ?_) (fun h => ?_)
· rw [ltByCases_lt h, ltByCases_gt h]
· rw [ltByCases_eq h, ltByCases_eq h.symm, comp_apply]
· rw [ltByCases_lt h, ltByCases_gt h]
lemma eq_iff_eq_of_lt_iff_lt_of_gt_iff_gt {x' y' : α}
(ltc : (x < y) ↔ (x' < y')) (gtc : (y < x) ↔ (y' < x')) :
x = y ↔ x' = y' := by simp_rw [eq_iff_le_not_lt, ← not_lt, ltc, gtc]
lemma ltByCases_rec {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P} (p : P)
(hlt : (h : x < y) → h₁ h = p) (heq : (h : x = y) → h₂ h = p)
(hgt : (h : y < x) → h₃ h = p) :
ltByCases x y h₁ h₂ h₃ = p :=
ltByCases x y
(fun h => ltByCases_lt h ▸ hlt h)
(fun h => ltByCases_eq h ▸ heq h)
(fun h => ltByCases_gt h ▸ hgt h)
lemma ltByCases_eq_iff {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P} {p : P} :
ltByCases x y h₁ h₂ h₃ = p ↔ (∃ h, h₁ h = p) ∨ (∃ h, h₂ h = p) ∨ (∃ h, h₃ h = p) := by
refine ltByCases x y (fun h => ?_) (fun h => ?_) (fun h => ?_)
· simp only [ltByCases_lt, exists_prop_of_true, h, h.not_lt, not_false_eq_true,
exists_prop_of_false, or_false, h.ne]
· simp only [h, lt_self_iff_false, ltByCases_eq, not_false_eq_true,
exists_prop_of_false, exists_prop_of_true, or_false, false_or]
· simp only [ltByCases_gt, exists_prop_of_true, h, h.not_lt, not_false_eq_true,
exists_prop_of_false, false_or, h.ne']
lemma ltByCases_congr {x' y' : α} {h₁ : x < y → P} {h₂ : x = y → P} {h₃ : y < x → P}
{h₁' : x' < y' → P} {h₂' : x' = y' → P} {h₃' : y' < x' → P} (ltc : (x < y) ↔ (x' < y'))
(gtc : (y < x) ↔ (y' < x')) (hh'₁ : ∀ (h : x' < y'), h₁ (ltc.mpr h) = h₁' h)
(hh'₂ : ∀ (h : x' = y'), h₂ ((eq_iff_eq_of_lt_iff_lt_of_gt_iff_gt ltc gtc).mpr h) = h₂' h)
(hh'₃ : ∀ (h : y' < x'), h₃ (gtc.mpr h) = h₃' h) :
ltByCases x y h₁ h₂ h₃ = ltByCases x' y' h₁' h₂' h₃' := by
refine ltByCases_rec _ (fun h => ?_) (fun h => ?_) (fun h => ?_)
· rw [ltByCases_lt (ltc.mp h), hh'₁]
· rw [eq_iff_eq_of_lt_iff_lt_of_gt_iff_gt ltc gtc] at h
rw [ltByCases_eq h, hh'₂]
· rw [ltByCases_gt (gtc.mp h), hh'₃]
/-- Perform a case-split on the ordering of `x` and `y` in a decidable linear order,
non-dependently. -/
abbrev ltTrichotomy (x y : α) (p q r : P) := ltByCases x y (fun _ => p) (fun _ => q) (fun _ => r)
variable {p q r s : P}
@[simp]
lemma ltTrichotomy_lt (h : x < y) : ltTrichotomy x y p q r = p := ltByCases_lt h
@[simp]
lemma ltTrichotomy_gt (h : y < x) : ltTrichotomy x y p q r = r := ltByCases_gt h
@[simp]
lemma ltTrichotomy_eq (h : x = y) : ltTrichotomy x y p q r = q := ltByCases_eq h
lemma ltTrichotomy_not_lt (h : ¬ x < y) :
ltTrichotomy x y p q r = if y < x then r else q := ltByCases_not_lt h
lemma ltTrichotomy_not_gt (h : ¬ y < x) :
ltTrichotomy x y p q r = if x < y then p else q := ltByCases_not_gt h
lemma ltTrichotomy_ne (h : x ≠ y) :
ltTrichotomy x y p q r = if x < y then p else r := ltByCases_ne h
lemma ltTrichotomy_comm : ltTrichotomy x y p q r = ltTrichotomy y x r q p := ltByCases_comm
lemma ltTrichotomy_self {p : P} : ltTrichotomy x y p p p = p :=
ltByCases_rec p (fun _ => rfl) (fun _ => rfl) (fun _ => rfl)
lemma ltTrichotomy_eq_iff : ltTrichotomy x y p q r = s ↔
(x < y ∧ p = s) ∨ (x = y ∧ q = s) ∨ (y < x ∧ r = s) := by
refine ltByCases x y (fun h => ?_) (fun h => ?_) (fun h => ?_)
· simp only [ltTrichotomy_lt, false_and, true_and, or_false, h, h.not_lt, h.ne]
· simp only [ltTrichotomy_eq, false_and, true_and, or_false, false_or, h, lt_irrefl]
· simp only [ltTrichotomy_gt, false_and, true_and, false_or, h, h.not_lt, h.ne']
lemma ltTrichotomy_congr {x' y' : α} {p' q' r' : P} (ltc : (x < y) ↔ (x' < y'))
(gtc : (y < x) ↔ (y' < x')) (hh'₁ : x' < y' → p = p')
(hh'₂ : x' = y' → q = q') (hh'₃ : y' < x' → r = r') :
ltTrichotomy x y p q r = ltTrichotomy x' y' p' q' r' :=
ltByCases_congr ltc gtc hh'₁ hh'₂ hh'₃
end ltByCases
/-! #### `min`/`max` recursors -/
section MinMaxRec
variable {p : α → Prop}
lemma min_rec (ha : a ≤ b → p a) (hb : b ≤ a → p b) : p (min a b) := by
obtain hab | hba := le_total a b <;> simp [min_eq_left, min_eq_right, *]
lemma max_rec (ha : b ≤ a → p a) (hb : a ≤ b → p b) : p (max a b) := by
obtain hab | hba := le_total a b <;> simp [max_eq_left, max_eq_right, *]
lemma min_rec' (p : α → Prop) (ha : p a) (hb : p b) : p (min a b) :=
min_rec (fun _ ↦ ha) fun _ ↦ hb
lemma max_rec' (p : α → Prop) (ha : p a) (hb : p b) : p (max a b) :=
max_rec (fun _ ↦ ha) fun _ ↦ hb
lemma min_def_lt (a b : α) : min a b = if a < b then a else b := by
rw [min_comm, min_def, ← ite_not]; simp only [not_le]
lemma max_def_lt (a b : α) : max a b = if a < b then b else a := by
rw [max_comm, max_def, ← ite_not]; simp only [not_le]
end MinMaxRec
end LinearOrder
/-! ### Implications -/
lemma lt_imp_lt_of_le_imp_le {β} [LinearOrder α] [Preorder β] {a b : α} {c d : β}
(H : a ≤ b → c ≤ d) (h : d < c) : b < a :=
lt_of_not_le fun h' ↦ (H h').not_lt h
lemma le_imp_le_iff_lt_imp_lt {β} [LinearOrder α] [LinearOrder β] {a b : α} {c d : β} :
a ≤ b → c ≤ d ↔ d < c → b < a :=
⟨lt_imp_lt_of_le_imp_le, le_imp_le_of_lt_imp_lt⟩
lemma lt_iff_lt_of_le_iff_le' {β} [Preorder α] [Preorder β] {a b : α} {c d : β}
(H : a ≤ b ↔ c ≤ d) (H' : b ≤ a ↔ d ≤ c) : b < a ↔ d < c :=
lt_iff_le_not_le.trans <| (and_congr H' (not_congr H)).trans lt_iff_le_not_le.symm
lemma lt_iff_lt_of_le_iff_le {β} [LinearOrder α] [LinearOrder β] {a b : α} {c d : β}
(H : a ≤ b ↔ c ≤ d) : b < a ↔ d < c := not_le.symm.trans <| (not_congr H).trans <| not_le
lemma le_iff_le_iff_lt_iff_lt {β} [LinearOrder α] [LinearOrder β] {a b : α} {c d : β} :
(a ≤ b ↔ c ≤ d) ↔ (b < a ↔ d < c) :=
⟨lt_iff_lt_of_le_iff_le, fun H ↦ not_lt.symm.trans <| (not_congr H).trans <| not_lt⟩
/-- A symmetric relation implies two values are equal, when it implies they're less-equal. -/
lemma rel_imp_eq_of_rel_imp_le [PartialOrder β] (r : α → α → Prop) [IsSymm α r] {f : α → β}
(h : ∀ a b, r a b → f a ≤ f b) {a b : α} : r a b → f a = f b := fun hab ↦
le_antisymm (h a b hab) (h b a <| symm hab)
/-! ### Extensionality lemmas -/
@[ext]
lemma Preorder.toLE_injective : Function.Injective (@Preorder.toLE α) :=
fun
| { lt := A_lt, lt_iff_le_not_le := A_iff, .. },
{ lt := B_lt, lt_iff_le_not_le := B_iff, .. } => by
rintro ⟨⟩
have : A_lt = B_lt := by
funext a b
rw [A_iff, B_iff]
cases this
congr
@[ext]
lemma PartialOrder.toPreorder_injective : Function.Injective (@PartialOrder.toPreorder α) := by
rintro ⟨⟩ ⟨⟩ ⟨⟩; congr
@[ext]
lemma LinearOrder.toPartialOrder_injective : Function.Injective (@LinearOrder.toPartialOrder α) :=
fun
| { le := A_le, lt := A_lt,
toDecidableLE := A_decidableLE, toDecidableEq := A_decidableEq, toDecidableLT := A_decidableLT
min := A_min, max := A_max, min_def := A_min_def, max_def := A_max_def,
| compare := A_compare, compare_eq_compareOfLessAndEq := A_compare_canonical, .. },
{ le := B_le, lt := B_lt,
toDecidableLE := B_decidableLE, toDecidableEq := B_decidableEq, toDecidableLT := B_decidableLT
min := B_min, max := B_max, min_def := B_min_def, max_def := B_max_def,
compare := B_compare, compare_eq_compareOfLessAndEq := B_compare_canonical, .. } => by
rintro ⟨⟩
obtain rfl : A_decidableLE = B_decidableLE := Subsingleton.elim _ _
obtain rfl : A_decidableEq = B_decidableEq := Subsingleton.elim _ _
obtain rfl : A_decidableLT = B_decidableLT := Subsingleton.elim _ _
have : A_min = B_min := by
funext a b
| Mathlib/Order/Basic.lean | 589 | 599 |
/-
Copyright (c) 2018 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Kevin Kappelmann
-/
import Mathlib.Algebra.Order.Floor.Defs
import Mathlib.Algebra.Order.Floor.Ring
import Mathlib.Algebra.Order.Floor.Semiring
deprecated_module (since := "2025-04-13")
| Mathlib/Algebra/Order/Floor.lean | 767 | 769 | |
/-
Copyright (c) 2023 Dagur Asgeirsson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Dagur Asgeirsson
-/
import Mathlib.Topology.Category.Profinite.Nobeling.Basic
import Mathlib.Topology.Category.Profinite.Nobeling.Induction
import Mathlib.Topology.Category.Profinite.Nobeling.Span
import Mathlib.Topology.Category.Profinite.Nobeling.Successor
import Mathlib.Topology.Category.Profinite.Nobeling.ZeroLimit
deprecated_module (since := "2025-04-13")
| Mathlib/Topology/Category/Profinite/Nobeling.lean | 125 | 127 | |
/-
Copyright (c) 2022 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker, Yury Kudryashov
-/
import Mathlib.Topology.Algebra.Module.Equiv
import Mathlib.Topology.Algebra.Module.UniformConvergence
import Mathlib.Topology.Algebra.SeparationQuotient.Section
import Mathlib.Topology.Hom.ContinuousEvalConst
/-!
# Strong topologies on the space of continuous linear maps
In this file, we define the strong topologies on `E →L[𝕜] F` associated with a family
`𝔖 : Set (Set E)` to be the topology of uniform convergence on the elements of `𝔖` (also called
the topology of `𝔖`-convergence).
The lemma `UniformOnFun.continuousSMul_of_image_bounded` tells us that this is a
vector space topology if the continuous linear image of any element of `𝔖` is bounded (in the sense
of `Bornology.IsVonNBounded`).
We then declare an instance for the case where `𝔖` is exactly the set of all bounded subsets of
`E`, giving us the so-called "topology of uniform convergence on bounded sets" (or "topology of
bounded convergence"), which coincides with the operator norm topology in the case of
`NormedSpace`s.
Other useful examples include the weak-* topology (when `𝔖` is the set of finite sets or the set
of singletons) and the topology of compact convergence (when `𝔖` is the set of relatively compact
sets).
## Main definitions
* `UniformConvergenceCLM` is a type synonym for `E →SL[σ] F` equipped with the `𝔖`-topology.
* `UniformConvergenceCLM.instTopologicalSpace` is the topology mentioned above for an arbitrary `𝔖`.
* `ContinuousLinearMap.topologicalSpace` is the topology of bounded convergence. This is
declared as an instance.
## Main statements
* `UniformConvergenceCLM.instIsTopologicalAddGroup` and
`UniformConvergenceCLM.instContinuousSMul` show that the strong topology
makes `E →L[𝕜] F` a topological vector space, with the assumptions on `𝔖` mentioned above.
* `ContinuousLinearMap.topologicalAddGroup` and
`ContinuousLinearMap.continuousSMul` register these facts as instances for the special
case of bounded convergence.
## References
* [N. Bourbaki, *Topological Vector Spaces*][bourbaki1987]
## TODO
* Add convergence on compact subsets
## Tags
uniform convergence, bounded convergence
-/
open Bornology Filter Function Set Topology
open scoped UniformConvergence Uniformity
section General
/-! ### 𝔖-Topologies -/
variable {𝕜₁ 𝕜₂ : Type*} [NormedField 𝕜₁] [NormedField 𝕜₂] (σ : 𝕜₁ →+* 𝕜₂) {E F : Type*}
[AddCommGroup E] [Module 𝕜₁ E] [TopologicalSpace E]
[AddCommGroup F] [Module 𝕜₂ F]
variable (F)
/-- Given `E` and `F` two topological vector spaces and `𝔖 : Set (Set E)`, then
`UniformConvergenceCLM σ F 𝔖` is a type synonym of `E →SL[σ] F` equipped with the "topology of
uniform convergence on the elements of `𝔖`".
If the continuous linear image of any element of `𝔖` is bounded, this makes `E →SL[σ] F` a
topological vector space. -/
@[nolint unusedArguments]
def UniformConvergenceCLM [TopologicalSpace F] (_ : Set (Set E)) := E →SL[σ] F
namespace UniformConvergenceCLM
instance instFunLike [TopologicalSpace F] (𝔖 : Set (Set E)) :
FunLike (UniformConvergenceCLM σ F 𝔖) E F :=
ContinuousLinearMap.funLike
instance instContinuousSemilinearMapClass [TopologicalSpace F] (𝔖 : Set (Set E)) :
ContinuousSemilinearMapClass (UniformConvergenceCLM σ F 𝔖) σ E F :=
ContinuousLinearMap.continuousSemilinearMapClass
instance instTopologicalSpace [TopologicalSpace F] [IsTopologicalAddGroup F] (𝔖 : Set (Set E)) :
TopologicalSpace (UniformConvergenceCLM σ F 𝔖) :=
(@UniformOnFun.topologicalSpace E F (IsTopologicalAddGroup.toUniformSpace F) 𝔖).induced
(DFunLike.coe : (UniformConvergenceCLM σ F 𝔖) → (E →ᵤ[𝔖] F))
theorem topologicalSpace_eq [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
instTopologicalSpace σ F 𝔖 = TopologicalSpace.induced (UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe)
(UniformOnFun.topologicalSpace E F 𝔖) := by
rw [instTopologicalSpace]
congr
exact IsUniformAddGroup.toUniformSpace_eq
/-- The uniform structure associated with `ContinuousLinearMap.strongTopology`. We make sure
that this has nice definitional properties. -/
instance instUniformSpace [UniformSpace F] [IsUniformAddGroup F]
(𝔖 : Set (Set E)) : UniformSpace (UniformConvergenceCLM σ F 𝔖) :=
UniformSpace.replaceTopology
((UniformOnFun.uniformSpace E F 𝔖).comap (UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe))
(by rw [UniformConvergenceCLM.instTopologicalSpace, IsUniformAddGroup.toUniformSpace_eq]; rfl)
theorem uniformSpace_eq [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
instUniformSpace σ F 𝔖 =
UniformSpace.comap (UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe)
(UniformOnFun.uniformSpace E F 𝔖) := by
rw [instUniformSpace, UniformSpace.replaceTopology_eq]
@[simp]
theorem uniformity_toTopologicalSpace_eq [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
(UniformConvergenceCLM.instUniformSpace σ F 𝔖).toTopologicalSpace =
UniformConvergenceCLM.instTopologicalSpace σ F 𝔖 :=
rfl
theorem isUniformInducing_coeFn [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
IsUniformInducing (α := UniformConvergenceCLM σ F 𝔖) (UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe) :=
⟨rfl⟩
theorem isUniformEmbedding_coeFn [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
IsUniformEmbedding (α := UniformConvergenceCLM σ F 𝔖) (UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe) :=
⟨isUniformInducing_coeFn .., DFunLike.coe_injective⟩
theorem isEmbedding_coeFn [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
IsEmbedding (X := UniformConvergenceCLM σ F 𝔖) (Y := E →ᵤ[𝔖] F)
(UniformOnFun.ofFun 𝔖 ∘ DFunLike.coe) :=
IsUniformEmbedding.isEmbedding (isUniformEmbedding_coeFn _ _ _)
@[deprecated (since := "2024-10-26")]
alias embedding_coeFn := isEmbedding_coeFn
instance instAddCommGroup [TopologicalSpace F] [IsTopologicalAddGroup F] (𝔖 : Set (Set E)) :
AddCommGroup (UniformConvergenceCLM σ F 𝔖) := ContinuousLinearMap.addCommGroup
@[simp]
theorem coe_zero [TopologicalSpace F] [IsTopologicalAddGroup F] (𝔖 : Set (Set E)) :
⇑(0 : UniformConvergenceCLM σ F 𝔖) = 0 :=
rfl
instance instIsUniformAddGroup [UniformSpace F] [IsUniformAddGroup F] (𝔖 : Set (Set E)) :
IsUniformAddGroup (UniformConvergenceCLM σ F 𝔖) := by
let φ : (UniformConvergenceCLM σ F 𝔖) →+ E →ᵤ[𝔖] F :=
⟨⟨(DFunLike.coe : (UniformConvergenceCLM σ F 𝔖) → E →ᵤ[𝔖] F), rfl⟩, fun _ _ => rfl⟩
exact (isUniformEmbedding_coeFn _ _ _).isUniformAddGroup φ
instance instIsTopologicalAddGroup [TopologicalSpace F] [IsTopologicalAddGroup F]
(𝔖 : Set (Set E)) : IsTopologicalAddGroup (UniformConvergenceCLM σ F 𝔖) := by
letI : UniformSpace F := IsTopologicalAddGroup.toUniformSpace F
haveI : IsUniformAddGroup F := isUniformAddGroup_of_addCommGroup
infer_instance
theorem continuousEvalConst [TopologicalSpace F] [IsTopologicalAddGroup F]
(𝔖 : Set (Set E)) (h𝔖 : ⋃₀ 𝔖 = Set.univ) :
ContinuousEvalConst (UniformConvergenceCLM σ F 𝔖) E F where
continuous_eval_const x := by
letI : UniformSpace F := IsTopologicalAddGroup.toUniformSpace F
haveI : IsUniformAddGroup F := isUniformAddGroup_of_addCommGroup
exact (UniformOnFun.uniformContinuous_eval h𝔖 x).continuous.comp
(isEmbedding_coeFn σ F 𝔖).continuous
| theorem t2Space [TopologicalSpace F] [IsTopologicalAddGroup F] [T2Space F]
(𝔖 : Set (Set E)) (h𝔖 : ⋃₀ 𝔖 = univ) : T2Space (UniformConvergenceCLM σ F 𝔖) := by
letI : UniformSpace F := IsTopologicalAddGroup.toUniformSpace F
haveI : IsUniformAddGroup F := isUniformAddGroup_of_addCommGroup
haveI : T2Space (E →ᵤ[𝔖] F) := UniformOnFun.t2Space_of_covering h𝔖
exact (isEmbedding_coeFn σ F 𝔖).t2Space
instance instDistribMulAction (M : Type*) [Monoid M] [DistribMulAction M F] [SMulCommClass 𝕜₂ M F]
[TopologicalSpace F] [IsTopologicalAddGroup F] [ContinuousConstSMul M F] (𝔖 : Set (Set E)) :
DistribMulAction M (UniformConvergenceCLM σ F 𝔖) := ContinuousLinearMap.distribMulAction
| Mathlib/Topology/Algebra/Module/StrongTopology.lean | 168 | 177 |
/-
Copyright (c) 2018 Ellen Arlt. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Ellen Arlt, Blair Shi, Sean Leather, Mario Carneiro, Johan Commelin, Lu-Ming Zhang
-/
import Mathlib.Algebra.Algebra.Opposite
import Mathlib.Algebra.Algebra.Pi
import Mathlib.Algebra.BigOperators.RingEquiv
import Mathlib.Data.Finite.Prod
import Mathlib.Data.Matrix.Mul
import Mathlib.LinearAlgebra.Pi
/-!
# Matrices
This file contains basic results on matrices including bundled versions of matrix operators.
## Implementation notes
For convenience, `Matrix m n α` is defined as `m → n → α`, as this allows elements of the matrix
to be accessed with `A i j`. However, it is not advisable to _construct_ matrices using terms of the
form `fun i j ↦ _` or even `(fun i j ↦ _ : Matrix m n α)`, as these are not recognized by Lean
as having the right type. Instead, `Matrix.of` should be used.
## TODO
Under various conditions, multiplication of infinite matrices makes sense.
These have not yet been implemented.
-/
assert_not_exists Star
universe u u' v w
variable {l m n o : Type*} {m' : o → Type*} {n' : o → Type*}
variable {R : Type*} {S : Type*} {α : Type v} {β : Type w} {γ : Type*}
namespace Matrix
instance decidableEq [DecidableEq α] [Fintype m] [Fintype n] : DecidableEq (Matrix m n α) :=
Fintype.decidablePiFintype
instance {n m} [Fintype m] [DecidableEq m] [Fintype n] [DecidableEq n] (α) [Fintype α] :
Fintype (Matrix m n α) := inferInstanceAs (Fintype (m → n → α))
instance {n m} [Finite m] [Finite n] (α) [Finite α] :
Finite (Matrix m n α) := inferInstanceAs (Finite (m → n → α))
section
variable (R)
/-- This is `Matrix.of` bundled as a linear equivalence. -/
def ofLinearEquiv [Semiring R] [AddCommMonoid α] [Module R α] : (m → n → α) ≃ₗ[R] Matrix m n α where
__ := ofAddEquiv
map_smul' _ _ := rfl
@[simp] lemma coe_ofLinearEquiv [Semiring R] [AddCommMonoid α] [Module R α] :
⇑(ofLinearEquiv _ : (m → n → α) ≃ₗ[R] Matrix m n α) = of := rfl
@[simp] lemma coe_ofLinearEquiv_symm [Semiring R] [AddCommMonoid α] [Module R α] :
⇑((ofLinearEquiv _).symm : Matrix m n α ≃ₗ[R] (m → n → α)) = of.symm := rfl
end
theorem sum_apply [AddCommMonoid α] (i : m) (j : n) (s : Finset β) (g : β → Matrix m n α) :
(∑ c ∈ s, g c) i j = ∑ c ∈ s, g c i j :=
(congr_fun (s.sum_apply i g) j).trans (s.sum_apply j _)
end Matrix
open Matrix
namespace Matrix
section Diagonal
variable [DecidableEq n]
variable (n α)
/-- `Matrix.diagonal` as an `AddMonoidHom`. -/
@[simps]
def diagonalAddMonoidHom [AddZeroClass α] : (n → α) →+ Matrix n n α where
toFun := diagonal
map_zero' := diagonal_zero
map_add' x y := (diagonal_add x y).symm
variable (R)
/-- `Matrix.diagonal` as a `LinearMap`. -/
@[simps]
def diagonalLinearMap [Semiring R] [AddCommMonoid α] [Module R α] : (n → α) →ₗ[R] Matrix n n α :=
{ diagonalAddMonoidHom n α with map_smul' := diagonal_smul }
variable {n α R}
section One
variable [Zero α] [One α]
lemma zero_le_one_elem [Preorder α] [ZeroLEOneClass α] (i j : n) :
0 ≤ (1 : Matrix n n α) i j := by
by_cases hi : i = j
· subst hi
simp
· simp [hi]
lemma zero_le_one_row [Preorder α] [ZeroLEOneClass α] (i : n) :
0 ≤ (1 : Matrix n n α) i :=
zero_le_one_elem i
end One
end Diagonal
section Diag
variable (n α)
/-- `Matrix.diag` as an `AddMonoidHom`. -/
@[simps]
def diagAddMonoidHom [AddZeroClass α] : Matrix n n α →+ n → α where
toFun := diag
map_zero' := diag_zero
map_add' := diag_add
variable (R)
/-- `Matrix.diag` as a `LinearMap`. -/
@[simps]
def diagLinearMap [Semiring R] [AddCommMonoid α] [Module R α] : Matrix n n α →ₗ[R] n → α :=
{ diagAddMonoidHom n α with map_smul' := diag_smul }
variable {n α R}
@[simp]
theorem diag_list_sum [AddMonoid α] (l : List (Matrix n n α)) : diag l.sum = (l.map diag).sum :=
map_list_sum (diagAddMonoidHom n α) l
@[simp]
theorem diag_multiset_sum [AddCommMonoid α] (s : Multiset (Matrix n n α)) :
diag s.sum = (s.map diag).sum :=
map_multiset_sum (diagAddMonoidHom n α) s
@[simp]
theorem diag_sum {ι} [AddCommMonoid α] (s : Finset ι) (f : ι → Matrix n n α) :
diag (∑ i ∈ s, f i) = ∑ i ∈ s, diag (f i) :=
map_sum (diagAddMonoidHom n α) f s
end Diag
open Matrix
section AddCommMonoid
variable [AddCommMonoid α] [Mul α]
end AddCommMonoid
section NonAssocSemiring
variable [NonAssocSemiring α]
variable (α n)
/-- `Matrix.diagonal` as a `RingHom`. -/
@[simps]
def diagonalRingHom [Fintype n] [DecidableEq n] : (n → α) →+* Matrix n n α :=
{ diagonalAddMonoidHom n α with
toFun := diagonal
map_one' := diagonal_one
map_mul' := fun _ _ => (diagonal_mul_diagonal' _ _).symm }
end NonAssocSemiring
section Semiring
variable [Semiring α]
theorem diagonal_pow [Fintype n] [DecidableEq n] (v : n → α) (k : ℕ) :
diagonal v ^ k = diagonal (v ^ k) :=
(map_pow (diagonalRingHom n α) v k).symm
/-- The ring homomorphism `α →+* Matrix n n α`
sending `a` to the diagonal matrix with `a` on the diagonal.
-/
def scalar (n : Type u) [DecidableEq n] [Fintype n] : α →+* Matrix n n α :=
(diagonalRingHom n α).comp <| Pi.constRingHom n α
section Scalar
variable [DecidableEq n] [Fintype n]
@[simp]
theorem scalar_apply (a : α) : scalar n a = diagonal fun _ => a :=
rfl
theorem scalar_inj [Nonempty n] {r s : α} : scalar n r = scalar n s ↔ r = s :=
(diagonal_injective.comp Function.const_injective).eq_iff
theorem scalar_commute_iff {r : α} {M : Matrix n n α} :
Commute (scalar n r) M ↔ r • M = MulOpposite.op r • M := by
simp_rw [Commute, SemiconjBy, scalar_apply, ← smul_eq_diagonal_mul, ← op_smul_eq_mul_diagonal]
theorem scalar_commute (r : α) (hr : ∀ r', Commute r r') (M : Matrix n n α) :
Commute (scalar n r) M := scalar_commute_iff.2 <| ext fun _ _ => hr _
end Scalar
end Semiring
section Algebra
variable [Fintype n] [DecidableEq n]
variable [CommSemiring R] [Semiring α] [Semiring β] [Algebra R α] [Algebra R β]
instance instAlgebra : Algebra R (Matrix n n α) where
algebraMap := (Matrix.scalar n).comp (algebraMap R α)
commutes' _ _ := scalar_commute _ (fun _ => Algebra.commutes _ _) _
smul_def' r x := by ext; simp [Matrix.scalar, Algebra.smul_def r]
theorem algebraMap_matrix_apply {r : R} {i j : n} :
algebraMap R (Matrix n n α) r i j = if i = j then algebraMap R α r else 0 := by
dsimp [algebraMap, Algebra.algebraMap, Matrix.scalar]
split_ifs with h <;> simp [h, Matrix.one_apply_ne]
theorem algebraMap_eq_diagonal (r : R) :
algebraMap R (Matrix n n α) r = diagonal (algebraMap R (n → α) r) := rfl
theorem algebraMap_eq_diagonalRingHom :
algebraMap R (Matrix n n α) = (diagonalRingHom n α).comp (algebraMap R _) := rfl
@[simp]
theorem map_algebraMap (r : R) (f : α → β) (hf : f 0 = 0)
(hf₂ : f (algebraMap R α r) = algebraMap R β r) :
(algebraMap R (Matrix n n α) r).map f = algebraMap R (Matrix n n β) r := by
rw [algebraMap_eq_diagonal, algebraMap_eq_diagonal, diagonal_map hf]
simp [hf₂]
variable (R)
/-- `Matrix.diagonal` as an `AlgHom`. -/
@[simps]
def diagonalAlgHom : (n → α) →ₐ[R] Matrix n n α :=
{ diagonalRingHom n α with
toFun := diagonal
commutes' := fun r => (algebraMap_eq_diagonal r).symm }
end Algebra
section AddHom
variable [Add α]
variable (R α) in
/-- Extracting entries from a matrix as an additive homomorphism. -/
@[simps]
def entryAddHom (i : m) (j : n) : AddHom (Matrix m n α) α where
toFun M := M i j
map_add' _ _ := rfl
-- It is necessary to spell out the name of the coercion explicitly on the RHS
-- for unification to succeed
lemma entryAddHom_eq_comp {i : m} {j : n} :
entryAddHom α i j =
((Pi.evalAddHom (fun _ => α) j).comp (Pi.evalAddHom _ i)).comp
(AddHomClass.toAddHom ofAddEquiv.symm) :=
rfl
end AddHom
section AddMonoidHom
variable [AddZeroClass α]
variable (R α) in
/--
Extracting entries from a matrix as an additive monoid homomorphism. Note this cannot be upgraded to
a ring homomorphism, as it does not respect multiplication.
-/
@[simps]
def entryAddMonoidHom (i : m) (j : n) : Matrix m n α →+ α where
toFun M := M i j
map_add' _ _ := rfl
map_zero' := rfl
-- It is necessary to spell out the name of the coercion explicitly on the RHS
-- for unification to succeed
lemma entryAddMonoidHom_eq_comp {i : m} {j : n} :
entryAddMonoidHom α i j =
((Pi.evalAddMonoidHom (fun _ => α) j).comp (Pi.evalAddMonoidHom _ i)).comp
(AddMonoidHomClass.toAddMonoidHom ofAddEquiv.symm) := by
rfl
@[simp] lemma evalAddMonoidHom_comp_diagAddMonoidHom (i : m) :
(Pi.evalAddMonoidHom _ i).comp (diagAddMonoidHom m α) = entryAddMonoidHom α i i := by
simp [AddMonoidHom.ext_iff]
@[simp] lemma entryAddMonoidHom_toAddHom {i : m} {j : n} :
(entryAddMonoidHom α i j : AddHom _ _) = entryAddHom α i j := rfl
end AddMonoidHom
section LinearMap
variable [Semiring R] [AddCommMonoid α] [Module R α]
variable (R α) in
/--
Extracting entries from a matrix as a linear map. Note this cannot be upgraded to an algebra
homomorphism, as it does not respect multiplication.
-/
@[simps]
def entryLinearMap (i : m) (j : n) :
Matrix m n α →ₗ[R] α where
toFun M := M i j
map_add' _ _ := rfl
map_smul' _ _ := rfl
-- It is necessary to spell out the name of the coercion explicitly on the RHS
-- for unification to succeed
lemma entryLinearMap_eq_comp {i : m} {j : n} :
entryLinearMap R α i j =
LinearMap.proj j ∘ₗ LinearMap.proj i ∘ₗ (ofLinearEquiv R).symm.toLinearMap := by
rfl
@[simp] lemma proj_comp_diagLinearMap (i : m) :
LinearMap.proj i ∘ₗ diagLinearMap m R α = entryLinearMap R α i i := by
simp [LinearMap.ext_iff]
@[simp] lemma entryLinearMap_toAddMonoidHom {i : m} {j : n} :
(entryLinearMap R α i j : _ →+ _) = entryAddMonoidHom α i j := rfl
@[simp] lemma entryLinearMap_toAddHom {i : m} {j : n} :
(entryLinearMap R α i j : AddHom _ _) = entryAddHom α i j := rfl
end LinearMap
end Matrix
/-!
### Bundled versions of `Matrix.map`
-/
namespace Equiv
/-- The `Equiv` between spaces of matrices induced by an `Equiv` between their
coefficients. This is `Matrix.map` as an `Equiv`. -/
@[simps apply]
def mapMatrix (f : α ≃ β) : Matrix m n α ≃ Matrix m n β where
toFun M := M.map f
invFun M := M.map f.symm
left_inv _ := Matrix.ext fun _ _ => f.symm_apply_apply _
right_inv _ := Matrix.ext fun _ _ => f.apply_symm_apply _
@[simp]
theorem mapMatrix_refl : (Equiv.refl α).mapMatrix = Equiv.refl (Matrix m n α) :=
rfl
@[simp]
theorem mapMatrix_symm (f : α ≃ β) : f.mapMatrix.symm = (f.symm.mapMatrix : Matrix m n β ≃ _) :=
rfl
@[simp]
theorem mapMatrix_trans (f : α ≃ β) (g : β ≃ γ) :
f.mapMatrix.trans g.mapMatrix = ((f.trans g).mapMatrix : Matrix m n α ≃ _) :=
rfl
end Equiv
namespace AddMonoidHom
variable [AddZeroClass α] [AddZeroClass β] [AddZeroClass γ]
/-- The `AddMonoidHom` between spaces of matrices induced by an `AddMonoidHom` between their
coefficients. This is `Matrix.map` as an `AddMonoidHom`. -/
@[simps]
def mapMatrix (f : α →+ β) : Matrix m n α →+ Matrix m n β where
toFun M := M.map f
map_zero' := Matrix.map_zero f f.map_zero
map_add' := Matrix.map_add f f.map_add
@[simp]
theorem mapMatrix_id : (AddMonoidHom.id α).mapMatrix = AddMonoidHom.id (Matrix m n α) :=
rfl
@[simp]
theorem mapMatrix_comp (f : β →+ γ) (g : α →+ β) :
f.mapMatrix.comp g.mapMatrix = ((f.comp g).mapMatrix : Matrix m n α →+ _) :=
rfl
@[simp] lemma entryAddMonoidHom_comp_mapMatrix (f : α →+ β) (i : m) (j : n) :
(entryAddMonoidHom β i j).comp f.mapMatrix = f.comp (entryAddMonoidHom α i j) := rfl
end AddMonoidHom
namespace AddEquiv
variable [Add α] [Add β] [Add γ]
/-- The `AddEquiv` between spaces of matrices induced by an `AddEquiv` between their
coefficients. This is `Matrix.map` as an `AddEquiv`. -/
@[simps apply]
def mapMatrix (f : α ≃+ β) : Matrix m n α ≃+ Matrix m n β :=
{ f.toEquiv.mapMatrix with
toFun := fun M => M.map f
invFun := fun M => M.map f.symm
map_add' := Matrix.map_add f (map_add f) }
@[simp]
theorem mapMatrix_refl : (AddEquiv.refl α).mapMatrix = AddEquiv.refl (Matrix m n α) :=
rfl
@[simp]
theorem mapMatrix_symm (f : α ≃+ β) : f.mapMatrix.symm = (f.symm.mapMatrix : Matrix m n β ≃+ _) :=
rfl
|
@[simp]
| Mathlib/Data/Matrix/Basic.lean | 417 | 418 |
/-
Copyright (c) 2016 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Leonardo de Moura, Mario Carneiro, Johannes Hölzl
-/
import Mathlib.Algebra.Order.Group.Unbundled.Basic
import Mathlib.Algebra.Order.Monoid.Defs
import Mathlib.Algebra.Order.Sub.Defs
import Mathlib.Util.AssertExists
/-!
# Ordered groups
This file defines bundled ordered groups and develops a few basic results.
## Implementation details
Unfortunately, the number of `'` appended to lemmas in this file
may differ between the multiplicative and the additive version of a lemma.
The reason is that we did not want to change existing names in the library.
-/
/-
`NeZero` theory should not be needed at this point in the ordered algebraic hierarchy.
-/
assert_not_imported Mathlib.Algebra.NeZero
open Function
universe u
variable {α : Type u}
/-- An ordered additive commutative group is an additive commutative group
with a partial order in which addition is strictly monotone. -/
@[deprecated "Use `[AddCommGroup α] [PartialOrder α] [IsOrderedAddMonoid α]` instead."
(since := "2025-04-10")]
structure OrderedAddCommGroup (α : Type u) extends AddCommGroup α, PartialOrder α where
/-- Addition is monotone in an ordered additive commutative group. -/
protected add_le_add_left : ∀ a b : α, a ≤ b → ∀ c : α, c + a ≤ c + b
set_option linter.existingAttributeWarning false in
/-- An ordered commutative group is a commutative group
with a partial order in which multiplication is strictly monotone. -/
@[to_additive,
deprecated "Use `[CommGroup α] [PartialOrder α] [IsOrderedMonoid α]` instead."
(since := "2025-04-10")]
structure OrderedCommGroup (α : Type u) extends CommGroup α, PartialOrder α where
/-- Multiplication is monotone in an ordered commutative group. -/
protected mul_le_mul_left : ∀ a b : α, a ≤ b → ∀ c : α, c * a ≤ c * b
alias OrderedCommGroup.mul_lt_mul_left' := mul_lt_mul_left'
attribute [to_additive OrderedAddCommGroup.add_lt_add_left] OrderedCommGroup.mul_lt_mul_left'
alias OrderedCommGroup.le_of_mul_le_mul_left := le_of_mul_le_mul_left'
attribute [to_additive] OrderedCommGroup.le_of_mul_le_mul_left
alias OrderedCommGroup.lt_of_mul_lt_mul_left := lt_of_mul_lt_mul_left'
attribute [to_additive] OrderedCommGroup.lt_of_mul_lt_mul_left
-- See note [lower instance priority]
@[to_additive IsOrderedAddMonoid.toIsOrderedCancelAddMonoid]
instance (priority := 100) IsOrderedMonoid.toIsOrderedCancelMonoid
[CommGroup α] [PartialOrder α] [IsOrderedMonoid α] : IsOrderedCancelMonoid α where
le_of_mul_le_mul_left a b c bc := by simpa using mul_le_mul_left' bc a⁻¹
le_of_mul_le_mul_right a b c bc := by simpa using mul_le_mul_left' bc a⁻¹
/-!
### Linearly ordered commutative groups
-/
set_option linter.deprecated false in
/-- A linearly ordered additive commutative group is an
additive commutative group with a linear order in which
addition is monotone. -/
@[deprecated "Use `[AddCommGroup α] [LinearOrder α] [IsOrderedAddMonoid α]` instead."
(since := "2025-04-10")]
structure LinearOrderedAddCommGroup (α : Type u) extends OrderedAddCommGroup α, LinearOrder α
set_option linter.existingAttributeWarning false in
set_option linter.deprecated false in
/-- A linearly ordered commutative group is a
commutative group with a linear order in which
multiplication is monotone. -/
@[to_additive,
deprecated "Use `[CommGroup α] [LinearOrder α] [IsOrderedMonoid α]` instead."
(since := "2025-04-10")]
structure LinearOrderedCommGroup (α : Type u) extends OrderedCommGroup α, LinearOrder α
attribute [nolint docBlame]
LinearOrderedCommGroup.toLinearOrder LinearOrderedAddCommGroup.toLinearOrder
section LinearOrderedCommGroup
variable [CommGroup α] [LinearOrder α] [IsOrderedMonoid α] {a : α}
@[to_additive LinearOrderedAddCommGroup.add_lt_add_left]
theorem LinearOrderedCommGroup.mul_lt_mul_left' (a b : α) (h : a < b) (c : α) : c * a < c * b :=
_root_.mul_lt_mul_left' h c
@[to_additive eq_zero_of_neg_eq]
theorem eq_one_of_inv_eq' (h : a⁻¹ = a) : a = 1 :=
match lt_trichotomy a 1 with
| Or.inl h₁ =>
have : 1 < a := h ▸ one_lt_inv_of_inv h₁
absurd h₁ this.asymm
| Or.inr (Or.inl h₁) => h₁
| Or.inr (Or.inr h₁) =>
have : a < 1 := h ▸ inv_lt_one'.mpr h₁
absurd h₁ this.asymm
@[to_additive exists_zero_lt]
theorem exists_one_lt' [Nontrivial α] : ∃ a : α, 1 < a := by
obtain ⟨y, hy⟩ := Decidable.exists_ne (1 : α)
obtain h|h := hy.lt_or_lt
· exact ⟨y⁻¹, one_lt_inv'.mpr h⟩
· exact ⟨y, h⟩
-- see Note [lower instance priority]
@[to_additive]
instance (priority := 100) LinearOrderedCommGroup.to_noMaxOrder [Nontrivial α] : NoMaxOrder α :=
⟨by
obtain ⟨y, hy⟩ : ∃ a : α, 1 < a := exists_one_lt'
exact fun a => ⟨a * y, lt_mul_of_one_lt_right' a hy⟩⟩
-- see Note [lower instance priority]
@[to_additive]
instance (priority := 100) LinearOrderedCommGroup.to_noMinOrder [Nontrivial α] : NoMinOrder α :=
⟨by
obtain ⟨y, hy⟩ : ∃ a : α, 1 < a := exists_one_lt'
exact fun a => ⟨a / y, (div_lt_self_iff a).mpr hy⟩⟩
@[to_additive (attr := simp)]
theorem inv_le_self_iff : a⁻¹ ≤ a ↔ 1 ≤ a := by simp [inv_le_iff_one_le_mul']
@[to_additive (attr := simp)]
theorem inv_lt_self_iff : a⁻¹ < a ↔ 1 < a := by simp [inv_lt_iff_one_lt_mul]
@[to_additive (attr := simp)]
theorem le_inv_self_iff : a ≤ a⁻¹ ↔ a ≤ 1 := by simp [← not_iff_not]
@[to_additive (attr := simp)]
theorem lt_inv_self_iff : a < a⁻¹ ↔ a < 1 := by simp [← not_iff_not]
end LinearOrderedCommGroup
section NormNumLemmas
/- The following lemmas are stated so that the `norm_num` tactic can use them with the
expected signatures. -/
variable [CommGroup α] [PartialOrder α] [IsOrderedMonoid α] {a b : α}
@[to_additive (attr := gcongr) neg_le_neg]
theorem inv_le_inv' : a ≤ b → b⁻¹ ≤ a⁻¹ :=
inv_le_inv_iff.mpr
@[to_additive (attr := gcongr) neg_lt_neg]
theorem inv_lt_inv' : a < b → b⁻¹ < a⁻¹ :=
inv_lt_inv_iff.mpr
-- The additive version is also a `linarith` lemma.
@[to_additive]
theorem inv_lt_one_of_one_lt : 1 < a → a⁻¹ < 1 :=
inv_lt_one_iff_one_lt.mpr
-- The additive version is also a `linarith` lemma.
@[to_additive]
theorem inv_le_one_of_one_le : 1 ≤ a → a⁻¹ ≤ 1 :=
inv_le_one'.mpr
@[to_additive neg_nonneg_of_nonpos]
theorem one_le_inv_of_le_one : a ≤ 1 → 1 ≤ a⁻¹ :=
one_le_inv'.mpr
end NormNumLemmas
| Mathlib/Algebra/Order/Group/Defs.lean | 1,173 | 1,173 | |
/-
Copyright (c) 2016 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Leonardo de Moura, Mario Carneiro, Johannes Hölzl
-/
import Mathlib.Algebra.Order.Group.Defs
import Mathlib.Algebra.Order.Group.Unbundled.Abs
import Mathlib.Algebra.Order.Monoid.Unbundled.Pow
/-!
# Absolute values in ordered groups
The absolute value of an element in a group which is also a lattice is its supremum with its
negation. This generalizes the usual absolute value on real numbers (`|x| = max x (-x)`).
## Notations
- `|a|`: The *absolute value* of an element `a` of an additive lattice ordered group
- `|a|ₘ`: The *absolute value* of an element `a` of a multiplicative lattice ordered group
-/
open Function
variable {G : Type*}
section LinearOrderedCommGroup
variable [CommGroup G] [LinearOrder G] [IsOrderedMonoid G] {a b c : G}
@[to_additive] lemma mabs_pow (n : ℕ) (a : G) : |a ^ n|ₘ = |a|ₘ ^ n := by
obtain ha | ha := le_total a 1
· rw [mabs_of_le_one ha, ← mabs_inv, ← inv_pow, mabs_of_one_le]
exact one_le_pow_of_one_le' (one_le_inv'.2 ha) n
· rw [mabs_of_one_le ha, mabs_of_one_le (one_le_pow_of_one_le' ha n)]
@[to_additive] private lemma mabs_mul_eq_mul_mabs_le (hab : a ≤ b) :
|a * b|ₘ = |a|ₘ * |b|ₘ ↔ 1 ≤ a ∧ 1 ≤ b ∨ a ≤ 1 ∧ b ≤ 1 := by
obtain ha | ha := le_or_lt 1 a <;> obtain hb | hb := le_or_lt 1 b
· simp [ha, hb, mabs_of_one_le, one_le_mul ha hb]
· exact (lt_irrefl (1 : G) <| ha.trans_lt <| hab.trans_lt hb).elim
swap
· simp [ha.le, hb.le, mabs_of_le_one, mul_le_one', mul_comm]
have : (|a * b|ₘ = a⁻¹ * b ↔ b ≤ 1) ↔
(|a * b|ₘ = |a|ₘ * |b|ₘ ↔ 1 ≤ a ∧ 1 ≤ b ∨ a ≤ 1 ∧ b ≤ 1) := by
simp [ha.le, ha.not_le, hb, mabs_of_le_one, mabs_of_one_le]
refine this.mp ⟨fun h ↦ ?_, fun h ↦ by simp only [h.antisymm hb, mabs_of_lt_one ha, mul_one]⟩
obtain ab | ab := le_or_lt (a * b) 1
· refine (eq_one_of_inv_eq' ?_).le
rwa [mabs_of_le_one ab, mul_inv_rev, mul_comm, mul_right_inj] at h
· rw [mabs_of_one_lt ab, mul_left_inj] at h
rw [eq_one_of_inv_eq' h.symm] at ha
cases ha.false
@[to_additive] lemma mabs_mul_eq_mul_mabs_iff (a b : G) :
|a * b|ₘ = |a|ₘ * |b|ₘ ↔ 1 ≤ a ∧ 1 ≤ b ∨ a ≤ 1 ∧ b ≤ 1 := by
obtain ab | ab := le_total a b
· exact mabs_mul_eq_mul_mabs_le ab
· simpa only [mul_comm, and_comm] using mabs_mul_eq_mul_mabs_le ab
@[to_additive]
theorem mabs_le : |a|ₘ ≤ b ↔ b⁻¹ ≤ a ∧ a ≤ b := by rw [mabs_le', and_comm, inv_le']
@[to_additive]
theorem le_mabs' : a ≤ |b|ₘ ↔ b ≤ a⁻¹ ∨ a ≤ b := by rw [le_mabs, or_comm, le_inv']
@[to_additive]
theorem inv_le_of_mabs_le (h : |a|ₘ ≤ b) : b⁻¹ ≤ a :=
(mabs_le.mp h).1
@[to_additive]
theorem le_of_mabs_le (h : |a|ₘ ≤ b) : a ≤ b :=
(mabs_le.mp h).2
/-- The **triangle inequality** in `LinearOrderedCommGroup`s. -/
@[to_additive "The **triangle inequality** in `LinearOrderedAddCommGroup`s."]
theorem mabs_mul (a b : G) : |a * b|ₘ ≤ |a|ₘ * |b|ₘ := by
rw [mabs_le, mul_inv]
constructor <;> gcongr <;> apply_rules [inv_mabs_le, le_mabs_self]
@[to_additive]
theorem mabs_mul' (a b : G) : |a|ₘ ≤ |b|ₘ * |b * a|ₘ := by simpa using mabs_mul b⁻¹ (b * a)
@[to_additive]
theorem mabs_div (a b : G) : |a / b|ₘ ≤ |a|ₘ * |b|ₘ := by
rw [div_eq_mul_inv, ← mabs_inv b]
exact mabs_mul a _
@[to_additive]
theorem mabs_div_le_iff : |a / b|ₘ ≤ c ↔ a / b ≤ c ∧ b / a ≤ c := by
rw [mabs_le, inv_le_div_iff_le_mul, div_le_iff_le_mul', and_comm, div_le_iff_le_mul']
@[to_additive]
theorem mabs_div_lt_iff : |a / b|ₘ < c ↔ a / b < c ∧ b / a < c := by
rw [mabs_lt, inv_lt_div_iff_lt_mul', div_lt_iff_lt_mul', and_comm, div_lt_iff_lt_mul']
@[to_additive]
theorem div_le_of_mabs_div_le_left (h : |a / b|ₘ ≤ c) : b / c ≤ a :=
div_le_comm.1 <| (mabs_div_le_iff.1 h).2
@[to_additive]
theorem div_le_of_mabs_div_le_right (h : |a / b|ₘ ≤ c) : a / c ≤ b :=
div_le_of_mabs_div_le_left (mabs_div_comm a b ▸ h)
@[to_additive]
theorem div_lt_of_mabs_div_lt_left (h : |a / b|ₘ < c) : b / c < a :=
div_lt_comm.1 <| (mabs_div_lt_iff.1 h).2
@[to_additive]
theorem div_lt_of_mabs_div_lt_right (h : |a / b|ₘ < c) : a / c < b :=
div_lt_of_mabs_div_lt_left (mabs_div_comm a b ▸ h)
@[to_additive]
theorem mabs_div_mabs_le_mabs_div (a b : G) : |a|ₘ / |b|ₘ ≤ |a / b|ₘ :=
div_le_iff_le_mul.2 <|
calc
|a|ₘ = |a / b * b|ₘ := by rw [div_mul_cancel]
_ ≤ |a / b|ₘ * |b|ₘ := mabs_mul _ _
@[to_additive]
theorem mabs_mabs_div_mabs_le_mabs_div (a b : G) : |(|a|ₘ / |b|ₘ)|ₘ ≤ |a / b|ₘ :=
mabs_div_le_iff.2
⟨mabs_div_mabs_le_mabs_div _ _, by rw [mabs_div_comm]; apply mabs_div_mabs_le_mabs_div⟩
/-- `|a / b|ₘ ≤ n` if `1 ≤ a ≤ n` and `1 ≤ b ≤ n`. -/
@[to_additive "`|a - b| ≤ n` if `0 ≤ a ≤ n` and `0 ≤ b ≤ n`."]
theorem mabs_div_le_of_one_le_of_le {a b n : G} (one_le_a : 1 ≤ a) (a_le_n : a ≤ n)
(one_le_b : 1 ≤ b) (b_le_n : b ≤ n) : |a / b|ₘ ≤ n := by
rw [mabs_div_le_iff, div_le_iff_le_mul, div_le_iff_le_mul]
exact ⟨le_mul_of_le_of_one_le a_le_n one_le_b, le_mul_of_le_of_one_le b_le_n one_le_a⟩
/-- `|a - b| < n` if `0 ≤ a < n` and `0 ≤ b < n`. -/
@[to_additive "`|a / b|ₘ < n` if `1 ≤ a < n` and `1 ≤ b < n`."]
theorem mabs_div_lt_of_one_le_of_lt {a b n : G} (one_le_a : 1 ≤ a) (a_lt_n : a < n)
(one_le_b : 1 ≤ b) (b_lt_n : b < n) : |a / b|ₘ < n := by
rw [mabs_div_lt_iff, div_lt_iff_lt_mul, div_lt_iff_lt_mul]
exact ⟨lt_mul_of_lt_of_one_le a_lt_n one_le_b, lt_mul_of_lt_of_one_le b_lt_n one_le_a⟩
@[to_additive]
theorem mabs_eq (hb : 1 ≤ b) : |a|ₘ = b ↔ a = b ∨ a = b⁻¹ := by
refine ⟨eq_or_eq_inv_of_mabs_eq, ?_⟩
rintro (rfl | rfl) <;> simp only [mabs_inv, mabs_of_one_le hb]
@[to_additive]
theorem mabs_le_max_mabs_mabs (hab : a ≤ b) (hbc : b ≤ c) : |b|ₘ ≤ max |a|ₘ |c|ₘ :=
mabs_le'.2
⟨by simp [hbc.trans (le_mabs_self c)], by
simp [(inv_le_inv_iff.mpr hab).trans (inv_le_mabs a)]⟩
omit [IsOrderedMonoid G] in
@[to_additive]
theorem min_mabs_mabs_le_mabs_max : min |a|ₘ |b|ₘ ≤ |max a b|ₘ :=
(le_total a b).elim (fun h => (min_le_right _ _).trans_eq <| congr_arg _ (max_eq_right h).symm)
fun h => (min_le_left _ _).trans_eq <| congr_arg _ (max_eq_left h).symm
omit [IsOrderedMonoid G] in
@[to_additive]
theorem min_mabs_mabs_le_mabs_min : min |a|ₘ |b|ₘ ≤ |min a b|ₘ :=
(le_total a b).elim (fun h => (min_le_left _ _).trans_eq <| congr_arg _ (min_eq_left h).symm)
fun h => (min_le_right _ _).trans_eq <| congr_arg _ (min_eq_right h).symm
omit [IsOrderedMonoid G] in
@[to_additive]
theorem mabs_max_le_max_mabs_mabs : |max a b|ₘ ≤ max |a|ₘ |b|ₘ :=
(le_total a b).elim (fun h => (congr_arg _ <| max_eq_right h).trans_le <| le_max_right _ _)
fun h => (congr_arg _ <| max_eq_left h).trans_le <| le_max_left _ _
omit [IsOrderedMonoid G] in
@[to_additive]
theorem mabs_min_le_max_mabs_mabs : |min a b|ₘ ≤ max |a|ₘ |b|ₘ :=
(le_total a b).elim (fun h => (congr_arg _ <| min_eq_left h).trans_le <| le_max_left _ _) fun h =>
(congr_arg _ <| min_eq_right h).trans_le <| le_max_right _ _
@[to_additive]
theorem eq_of_mabs_div_eq_one {a b : G} (h : |a / b|ₘ = 1) : a = b :=
div_eq_one.1 <| mabs_eq_one.1 h
@[to_additive]
theorem mabs_div_le (a b c : G) : |a / c|ₘ ≤ |a / b|ₘ * |b / c|ₘ :=
calc
|a / c|ₘ = |a / b * (b / c)|ₘ := by rw [div_mul_div_cancel]
_ ≤ |a / b|ₘ * |b / c|ₘ := mabs_mul _ _
@[to_additive]
theorem mabs_mul_three (a b c : G) : |a * b * c|ₘ ≤ |a|ₘ * |b|ₘ * |c|ₘ :=
(mabs_mul _ _).trans (mul_le_mul_right' (mabs_mul _ _) _)
@[to_additive]
theorem mabs_div_le_of_le_of_le {a b lb ub : G} (hal : lb ≤ a) (hau : a ≤ ub) (hbl : lb ≤ b)
(hbu : b ≤ ub) : |a / b|ₘ ≤ ub / lb :=
mabs_div_le_iff.2 ⟨div_le_div'' hau hbl, div_le_div'' hbu hal⟩
@[deprecated (since := "2025-03-02")]
alias dist_bdd_within_interval := abs_sub_le_of_le_of_le
@[to_additive]
theorem eq_of_mabs_div_le_one (h : |a / b|ₘ ≤ 1) : a = b :=
eq_of_mabs_div_eq_one (le_antisymm h (one_le_mabs (a / b)))
@[to_additive]
lemma eq_of_mabs_div_lt_all {x y : G} (h : ∀ ε > 1, |x / y|ₘ < ε) : x = y :=
eq_of_mabs_div_le_one <| forall_lt_iff_le'.mp h
@[to_additive]
lemma eq_of_mabs_div_le_all [DenselyOrdered G] {x y : G} (h : ∀ ε > 1, |x / y|ₘ ≤ ε) : x = y :=
eq_of_mabs_div_le_one <| forall_gt_imp_ge_iff_le_of_dense.mp h
@[to_additive]
theorem mabs_div_le_one : |a / b|ₘ ≤ 1 ↔ a = b :=
⟨eq_of_mabs_div_le_one, by rintro rfl; rw [div_self', mabs_one]⟩
@[to_additive]
theorem mabs_div_pos : 1 < |a / b|ₘ ↔ a ≠ b :=
not_le.symm.trans mabs_div_le_one.not
@[to_additive (attr := simp)]
theorem mabs_eq_self : |a|ₘ = a ↔ 1 ≤ a := by
rw [mabs_eq_max_inv, max_eq_left_iff, inv_le_self_iff]
@[to_additive (attr := simp)]
theorem mabs_eq_inv_self : |a|ₘ = a⁻¹ ↔ a ≤ 1 := by
rw [mabs_eq_max_inv, max_eq_right_iff, le_inv_self_iff]
/-- For an element `a` of a multiplicative linear ordered group,
either `|a|ₘ = a` and `1 ≤ a`, or `|a|ₘ = a⁻¹` and `a < 1`. -/
@[to_additive
"For an element `a` of an additive linear ordered group,
either `|a| = a` and `0 ≤ a`, or `|a| = -a` and `a < 0`.
Use cases on this lemma to automate linarith in inequalities"]
theorem mabs_cases (a : G) : |a|ₘ = a ∧ 1 ≤ a ∨ |a|ₘ = a⁻¹ ∧ a < 1 := by
cases le_or_lt 1 a <;> simp [*, le_of_lt]
@[to_additive (attr := simp)]
theorem max_one_mul_max_inv_one_eq_mabs_self (a : G) : max a 1 * max a⁻¹ 1 = |a|ₘ := by
symm
rcases le_total 1 a with (ha | ha) <;> simp [ha]
end LinearOrderedCommGroup
section LinearOrderedAddCommGroup
variable [AddCommGroup G] [LinearOrder G] [IsOrderedAddMonoid G] {a b c : G}
@[to_additive]
theorem apply_abs_le_mul_of_one_le' {H : Type*} [MulOneClass H] [LE H]
[MulLeftMono H] [MulRightMono H] {f : G → H}
{a : G} (h₁ : 1 ≤ f a) (h₂ : 1 ≤ f (-a)) : f |a| ≤ f a * f (-a) :=
(le_total a 0).rec (fun ha => (abs_of_nonpos ha).symm ▸ le_mul_of_one_le_left' h₁) fun ha =>
(abs_of_nonneg ha).symm ▸ le_mul_of_one_le_right' h₂
@[to_additive]
theorem apply_abs_le_mul_of_one_le {H : Type*} [MulOneClass H] [LE H]
[MulLeftMono H] [MulRightMono H] {f : G → H}
(h : ∀ x, 1 ≤ f x) (a : G) : f |a| ≤ f a * f (-a) :=
apply_abs_le_mul_of_one_le' (h _) (h _)
end LinearOrderedAddCommGroup
| Mathlib/Algebra/Order/Group/Abs.lean | 543 | 544 | |
/-
Copyright (c) 2023 Joël Riou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joël Riou
-/
import Mathlib.Algebra.Homology.ShortComplex.LeftHomology
import Mathlib.CategoryTheory.Limits.Opposites
/-!
# Right Homology of short complexes
In this file, we define the dual notions to those defined in
`Algebra.Homology.ShortComplex.LeftHomology`. In particular, if `S : ShortComplex C` is
a short complex consisting of two composable maps `f : X₁ ⟶ X₂` and `g : X₂ ⟶ X₃` such
that `f ≫ g = 0`, we define `h : S.RightHomologyData` to be the datum of morphisms
`p : X₂ ⟶ Q` and `ι : H ⟶ Q` such that `Q` identifies to the cokernel of `f` and `H`
to the kernel of the induced map `g' : Q ⟶ X₃`.
When such a `S.RightHomologyData` exists, we shall say that `[S.HasRightHomology]`
and we define `S.rightHomology` to be the `H` field of a chosen right homology data.
Similarly, we define `S.opcycles` to be the `Q` field.
In `Homology.lean`, when `S` has two compatible left and right homology data
(i.e. they give the same `H` up to a canonical isomorphism), we shall define
`[S.HasHomology]` and `S.homology`.
-/
namespace CategoryTheory
open Category Limits
namespace ShortComplex
variable {C : Type*} [Category C] [HasZeroMorphisms C]
(S : ShortComplex C) {S₁ S₂ S₃ : ShortComplex C}
/-- A right homology data for a short complex `S` consists of morphisms `p : S.X₂ ⟶ Q` and
`ι : H ⟶ Q` such that `p` identifies `Q` to the kernel of `f : S.X₁ ⟶ S.X₂`,
and that `ι` identifies `H` to the kernel of the induced map `g' : Q ⟶ S.X₃` -/
structure RightHomologyData where
/-- a choice of cokernel of `S.f : S.X₁ ⟶ S.X₂` -/
Q : C
/-- a choice of kernel of the induced morphism `S.g' : S.Q ⟶ X₃` -/
H : C
/-- the projection from `S.X₂` -/
p : S.X₂ ⟶ Q
/-- the inclusion of the (right) homology in the chosen cokernel of `S.f` -/
ι : H ⟶ Q
/-- the cokernel condition for `p` -/
wp : S.f ≫ p = 0
/-- `p : S.X₂ ⟶ Q` is a cokernel of `S.f : S.X₁ ⟶ S.X₂` -/
hp : IsColimit (CokernelCofork.ofπ p wp)
/-- the kernel condition for `ι` -/
wι : ι ≫ hp.desc (CokernelCofork.ofπ _ S.zero) = 0
/-- `ι : H ⟶ Q` is a kernel of `S.g' : Q ⟶ S.X₃` -/
hι : IsLimit (KernelFork.ofι ι wι)
initialize_simps_projections RightHomologyData (-hp, -hι)
namespace RightHomologyData
/-- The chosen cokernels and kernels of the limits API give a `RightHomologyData` -/
@[simps]
noncomputable def ofHasCokernelOfHasKernel
[HasCokernel S.f] [HasKernel (cokernel.desc S.f S.g S.zero)] :
S.RightHomologyData :=
{ Q := cokernel S.f,
H := kernel (cokernel.desc S.f S.g S.zero),
p := cokernel.π _,
ι := kernel.ι _,
wp := cokernel.condition _,
hp := cokernelIsCokernel _,
wι := kernel.condition _,
hι := kernelIsKernel _, }
attribute [reassoc (attr := simp)] wp wι
variable {S}
variable (h : S.RightHomologyData) {A : C}
instance : Epi h.p := ⟨fun _ _ => Cofork.IsColimit.hom_ext h.hp⟩
instance : Mono h.ι := ⟨fun _ _ => Fork.IsLimit.hom_ext h.hι⟩
/-- Any morphism `k : S.X₂ ⟶ A` such that `S.f ≫ k = 0` descends
to a morphism `Q ⟶ A` -/
def descQ (k : S.X₂ ⟶ A) (hk : S.f ≫ k = 0) : h.Q ⟶ A :=
h.hp.desc (CokernelCofork.ofπ k hk)
@[reassoc (attr := simp)]
lemma p_descQ (k : S.X₂ ⟶ A) (hk : S.f ≫ k = 0) : h.p ≫ h.descQ k hk = k :=
h.hp.fac _ WalkingParallelPair.one
/-- The morphism from the (right) homology attached to a morphism
`k : S.X₂ ⟶ A` such that `S.f ≫ k = 0`. -/
@[simp]
def descH (k : S.X₂ ⟶ A) (hk : S.f ≫ k = 0) : h.H ⟶ A :=
h.ι ≫ h.descQ k hk
/-- The morphism `h.Q ⟶ S.X₃` induced by `S.g : S.X₂ ⟶ S.X₃` and the fact that
`h.Q` is a cokernel of `S.f : S.X₁ ⟶ S.X₂`. -/
def g' : h.Q ⟶ S.X₃ := h.descQ S.g S.zero
@[reassoc (attr := simp)] lemma p_g' : h.p ≫ h.g' = S.g := p_descQ _ _ _
@[reassoc (attr := simp)] lemma ι_g' : h.ι ≫ h.g' = 0 := h.wι
@[reassoc]
lemma ι_descQ_eq_zero_of_boundary (k : S.X₂ ⟶ A) (x : S.X₃ ⟶ A) (hx : k = S.g ≫ x) :
h.ι ≫ h.descQ k (by rw [hx, S.zero_assoc, zero_comp]) = 0 := by
rw [show 0 = h.ι ≫ h.g' ≫ x by simp]
congr 1
simp only [← cancel_epi h.p, hx, p_descQ, p_g'_assoc]
/-- For `h : S.RightHomologyData`, this is a restatement of `h.hι`, saying that
`ι : h.H ⟶ h.Q` is a kernel of `h.g' : h.Q ⟶ S.X₃`. -/
def hι' : IsLimit (KernelFork.ofι h.ι h.ι_g') := h.hι
/-- The morphism `A ⟶ H` induced by a morphism `k : A ⟶ Q` such that `k ≫ g' = 0` -/
def liftH (k : A ⟶ h.Q) (hk : k ≫ h.g' = 0) : A ⟶ h.H :=
h.hι.lift (KernelFork.ofι k hk)
@[reassoc (attr := simp)]
lemma liftH_ι (k : A ⟶ h.Q) (hk : k ≫ h.g' = 0) : h.liftH k hk ≫ h.ι = k :=
h.hι.fac (KernelFork.ofι k hk) WalkingParallelPair.zero
lemma isIso_p (hf : S.f = 0) : IsIso h.p :=
⟨h.descQ (𝟙 S.X₂) (by rw [hf, comp_id]), p_descQ _ _ _, by
simp only [← cancel_epi h.p, p_descQ_assoc, id_comp, comp_id]⟩
lemma isIso_ι (hg : S.g = 0) : IsIso h.ι := by
have ⟨φ, hφ⟩ := KernelFork.IsLimit.lift' h.hι' (𝟙 _)
(by rw [← cancel_epi h.p, id_comp, p_g', comp_zero, hg])
dsimp at hφ
exact ⟨φ, by rw [← cancel_mono h.ι, assoc, hφ, comp_id, id_comp], hφ⟩
variable (S)
/-- When the first map `S.f` is zero, this is the right homology data on `S` given
by any limit kernel fork of `S.g` -/
@[simps]
def ofIsLimitKernelFork (hf : S.f = 0) (c : KernelFork S.g) (hc : IsLimit c) :
S.RightHomologyData where
Q := S.X₂
H := c.pt
p := 𝟙 _
ι := c.ι
wp := by rw [comp_id, hf]
hp := CokernelCofork.IsColimit.ofId _ hf
wι := KernelFork.condition _
hι := IsLimit.ofIsoLimit hc (Fork.ext (Iso.refl _) (by simp))
@[simp] lemma ofIsLimitKernelFork_g' (hf : S.f = 0) (c : KernelFork S.g)
(hc : IsLimit c) : (ofIsLimitKernelFork S hf c hc).g' = S.g := by
rw [← cancel_epi (ofIsLimitKernelFork S hf c hc).p, p_g',
ofIsLimitKernelFork_p, id_comp]
/-- When the first map `S.f` is zero, this is the right homology data on `S` given by
the chosen `kernel S.g` -/
@[simps!]
noncomputable def ofHasKernel [HasKernel S.g] (hf : S.f = 0) : S.RightHomologyData :=
ofIsLimitKernelFork S hf _ (kernelIsKernel _)
/-- When the second map `S.g` is zero, this is the right homology data on `S` given
by any colimit cokernel cofork of `S.g` -/
@[simps]
def ofIsColimitCokernelCofork (hg : S.g = 0) (c : CokernelCofork S.f) (hc : IsColimit c) :
S.RightHomologyData where
Q := c.pt
H := c.pt
p := c.π
ι := 𝟙 _
wp := CokernelCofork.condition _
hp := IsColimit.ofIsoColimit hc (Cofork.ext (Iso.refl _) (by simp))
wι := Cofork.IsColimit.hom_ext hc (by simp [hg])
hι := KernelFork.IsLimit.ofId _ (Cofork.IsColimit.hom_ext hc (by simp [hg]))
@[simp] lemma ofIsColimitCokernelCofork_g' (hg : S.g = 0) (c : CokernelCofork S.f)
(hc : IsColimit c) : (ofIsColimitCokernelCofork S hg c hc).g' = 0 := by
rw [← cancel_epi (ofIsColimitCokernelCofork S hg c hc).p, p_g', hg, comp_zero]
/-- When the second map `S.g` is zero, this is the right homology data on `S` given
by the chosen `cokernel S.f` -/
@[simp]
noncomputable def ofHasCokernel [HasCokernel S.f] (hg : S.g = 0) : S.RightHomologyData :=
ofIsColimitCokernelCofork S hg _ (cokernelIsCokernel _)
/-- When both `S.f` and `S.g` are zero, the middle object `S.X₂`
gives a right homology data on S -/
@[simps]
def ofZeros (hf : S.f = 0) (hg : S.g = 0) : S.RightHomologyData where
Q := S.X₂
H := S.X₂
p := 𝟙 _
ι := 𝟙 _
wp := by rw [comp_id, hf]
hp := CokernelCofork.IsColimit.ofId _ hf
wι := by
change 𝟙 _ ≫ S.g = 0
simp only [hg, comp_zero]
hι := KernelFork.IsLimit.ofId _ hg
@[simp]
lemma ofZeros_g' (hf : S.f = 0) (hg : S.g = 0) :
(ofZeros S hf hg).g' = 0 := by
rw [← cancel_epi ((ofZeros S hf hg).p), comp_zero, p_g', hg]
end RightHomologyData
/-- A short complex `S` has right homology when there exists a `S.RightHomologyData` -/
class HasRightHomology : Prop where
condition : Nonempty S.RightHomologyData
/-- A chosen `S.RightHomologyData` for a short complex `S` that has right homology -/
noncomputable def rightHomologyData [HasRightHomology S] :
S.RightHomologyData := HasRightHomology.condition.some
variable {S}
namespace HasRightHomology
lemma mk' (h : S.RightHomologyData) : HasRightHomology S := ⟨Nonempty.intro h⟩
instance of_hasCokernel_of_hasKernel
[HasCokernel S.f] [HasKernel (cokernel.desc S.f S.g S.zero)] :
S.HasRightHomology := HasRightHomology.mk' (RightHomologyData.ofHasCokernelOfHasKernel S)
instance of_hasKernel {Y Z : C} (g : Y ⟶ Z) (X : C) [HasKernel g] :
(ShortComplex.mk (0 : X ⟶ Y) g zero_comp).HasRightHomology :=
HasRightHomology.mk' (RightHomologyData.ofHasKernel _ rfl)
instance of_hasCokernel {X Y : C} (f : X ⟶ Y) (Z : C) [HasCokernel f] :
(ShortComplex.mk f (0 : Y ⟶ Z) comp_zero).HasRightHomology :=
HasRightHomology.mk' (RightHomologyData.ofHasCokernel _ rfl)
instance of_zeros (X Y Z : C) :
(ShortComplex.mk (0 : X ⟶ Y) (0 : Y ⟶ Z) zero_comp).HasRightHomology :=
HasRightHomology.mk' (RightHomologyData.ofZeros _ rfl rfl)
end HasRightHomology
namespace RightHomologyData
/-- A right homology data for a short complex `S` induces a left homology data for `S.op`. -/
@[simps]
def op (h : S.RightHomologyData) : S.op.LeftHomologyData where
K := Opposite.op h.Q
H := Opposite.op h.H
i := h.p.op
π := h.ι.op
wi := Quiver.Hom.unop_inj h.wp
hi := CokernelCofork.IsColimit.ofπOp _ _ h.hp
wπ := Quiver.Hom.unop_inj h.wι
hπ := KernelFork.IsLimit.ofιOp _ _ h.hι
@[simp] lemma op_f' (h : S.RightHomologyData) :
h.op.f' = h.g'.op := rfl
/-- A right homology data for a short complex `S` in the opposite category
induces a left homology data for `S.unop`. -/
@[simps]
def unop {S : ShortComplex Cᵒᵖ} (h : S.RightHomologyData) : S.unop.LeftHomologyData where
K := Opposite.unop h.Q
H := Opposite.unop h.H
i := h.p.unop
π := h.ι.unop
wi := Quiver.Hom.op_inj h.wp
hi := CokernelCofork.IsColimit.ofπUnop _ _ h.hp
wπ := Quiver.Hom.op_inj h.wι
hπ := KernelFork.IsLimit.ofιUnop _ _ h.hι
@[simp] lemma unop_f' {S : ShortComplex Cᵒᵖ} (h : S.RightHomologyData) :
h.unop.f' = h.g'.unop := rfl
end RightHomologyData
namespace LeftHomologyData
/-- A left homology data for a short complex `S` induces a right homology data for `S.op`. -/
@[simps]
def op (h : S.LeftHomologyData) : S.op.RightHomologyData where
Q := Opposite.op h.K
H := Opposite.op h.H
p := h.i.op
ι := h.π.op
wp := Quiver.Hom.unop_inj h.wi
hp := KernelFork.IsLimit.ofιOp _ _ h.hi
wι := Quiver.Hom.unop_inj h.wπ
hι := CokernelCofork.IsColimit.ofπOp _ _ h.hπ
@[simp] lemma op_g' (h : S.LeftHomologyData) :
h.op.g' = h.f'.op := rfl
/-- A left homology data for a short complex `S` in the opposite category
induces a right homology data for `S.unop`. -/
@[simps]
def unop {S : ShortComplex Cᵒᵖ} (h : S.LeftHomologyData) : S.unop.RightHomologyData where
Q := Opposite.unop h.K
H := Opposite.unop h.H
p := h.i.unop
ι := h.π.unop
wp := Quiver.Hom.op_inj h.wi
hp := KernelFork.IsLimit.ofιUnop _ _ h.hi
wι := Quiver.Hom.op_inj h.wπ
hι := CokernelCofork.IsColimit.ofπUnop _ _ h.hπ
@[simp] lemma unop_g' {S : ShortComplex Cᵒᵖ} (h : S.LeftHomologyData) :
h.unop.g' = h.f'.unop := rfl
end LeftHomologyData
instance [S.HasLeftHomology] : HasRightHomology S.op :=
HasRightHomology.mk' S.leftHomologyData.op
instance [S.HasRightHomology] : HasLeftHomology S.op :=
HasLeftHomology.mk' S.rightHomologyData.op
lemma hasLeftHomology_iff_op (S : ShortComplex C) :
S.HasLeftHomology ↔ S.op.HasRightHomology :=
⟨fun _ => inferInstance, fun _ => HasLeftHomology.mk' S.op.rightHomologyData.unop⟩
lemma hasRightHomology_iff_op (S : ShortComplex C) :
S.HasRightHomology ↔ S.op.HasLeftHomology :=
⟨fun _ => inferInstance, fun _ => HasRightHomology.mk' S.op.leftHomologyData.unop⟩
lemma hasLeftHomology_iff_unop (S : ShortComplex Cᵒᵖ) :
S.HasLeftHomology ↔ S.unop.HasRightHomology :=
S.unop.hasRightHomology_iff_op.symm
lemma hasRightHomology_iff_unop (S : ShortComplex Cᵒᵖ) :
S.HasRightHomology ↔ S.unop.HasLeftHomology :=
S.unop.hasLeftHomology_iff_op.symm
section
variable (φ : S₁ ⟶ S₂) (h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData)
/-- Given right homology data `h₁` and `h₂` for two short complexes `S₁` and `S₂`,
a `RightHomologyMapData` for a morphism `φ : S₁ ⟶ S₂`
consists of a description of the induced morphisms on the `Q` (opcycles)
and `H` (right homology) fields of `h₁` and `h₂`. -/
structure RightHomologyMapData where
/-- the induced map on opcycles -/
φQ : h₁.Q ⟶ h₂.Q
/-- the induced map on right homology -/
φH : h₁.H ⟶ h₂.H
/-- commutation with `p` -/
commp : h₁.p ≫ φQ = φ.τ₂ ≫ h₂.p := by aesop_cat
/-- commutation with `g'` -/
commg' : φQ ≫ h₂.g' = h₁.g' ≫ φ.τ₃ := by aesop_cat
/-- commutation with `ι` -/
commι : φH ≫ h₂.ι = h₁.ι ≫ φQ := by aesop_cat
namespace RightHomologyMapData
attribute [reassoc (attr := simp)] commp commg' commι
/-- The right homology map data associated to the zero morphism between two short complexes. -/
@[simps]
def zero (h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) :
RightHomologyMapData 0 h₁ h₂ where
φQ := 0
φH := 0
/-- The right homology map data associated to the identity morphism of a short complex. -/
@[simps]
def id (h : S.RightHomologyData) : RightHomologyMapData (𝟙 S) h h where
φQ := 𝟙 _
φH := 𝟙 _
/-- The composition of right homology map data. -/
@[simps]
def comp {φ : S₁ ⟶ S₂} {φ' : S₂ ⟶ S₃} {h₁ : S₁.RightHomologyData}
{h₂ : S₂.RightHomologyData} {h₃ : S₃.RightHomologyData}
(ψ : RightHomologyMapData φ h₁ h₂) (ψ' : RightHomologyMapData φ' h₂ h₃) :
RightHomologyMapData (φ ≫ φ') h₁ h₃ where
φQ := ψ.φQ ≫ ψ'.φQ
φH := ψ.φH ≫ ψ'.φH
instance : Subsingleton (RightHomologyMapData φ h₁ h₂) :=
⟨fun ψ₁ ψ₂ => by
have hQ : ψ₁.φQ = ψ₂.φQ := by rw [← cancel_epi h₁.p, commp, commp]
have hH : ψ₁.φH = ψ₂.φH := by rw [← cancel_mono h₂.ι, commι, commι, hQ]
cases ψ₁
cases ψ₂
congr⟩
instance : Inhabited (RightHomologyMapData φ h₁ h₂) := ⟨by
let φQ : h₁.Q ⟶ h₂.Q := h₁.descQ (φ.τ₂ ≫ h₂.p) (by rw [← φ.comm₁₂_assoc, h₂.wp, comp_zero])
have commg' : φQ ≫ h₂.g' = h₁.g' ≫ φ.τ₃ := by
rw [← cancel_epi h₁.p, RightHomologyData.p_descQ_assoc, assoc,
RightHomologyData.p_g', φ.comm₂₃, RightHomologyData.p_g'_assoc]
let φH : h₁.H ⟶ h₂.H := h₂.liftH (h₁.ι ≫ φQ)
(by rw [assoc, commg', RightHomologyData.ι_g'_assoc, zero_comp])
exact ⟨φQ, φH, by simp [φQ], commg', by simp [φH]⟩⟩
instance : Unique (RightHomologyMapData φ h₁ h₂) := Unique.mk' _
variable {φ h₁ h₂}
lemma congr_φH {γ₁ γ₂ : RightHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) : γ₁.φH = γ₂.φH := by rw [eq]
lemma congr_φQ {γ₁ γ₂ : RightHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) : γ₁.φQ = γ₂.φQ := by rw [eq]
/-- When `S₁.f`, `S₁.g`, `S₂.f` and `S₂.g` are all zero, the action on right homology of a
morphism `φ : S₁ ⟶ S₂` is given by the action `φ.τ₂` on the middle objects. -/
@[simps]
def ofZeros (φ : S₁ ⟶ S₂) (hf₁ : S₁.f = 0) (hg₁ : S₁.g = 0) (hf₂ : S₂.f = 0) (hg₂ : S₂.g = 0) :
RightHomologyMapData φ (RightHomologyData.ofZeros S₁ hf₁ hg₁)
(RightHomologyData.ofZeros S₂ hf₂ hg₂) where
φQ := φ.τ₂
φH := φ.τ₂
/-- When `S₁.f` and `S₂.f` are zero and we have chosen limit kernel forks `c₁` and `c₂`
for `S₁.g` and `S₂.g` respectively, the action on right homology of a morphism `φ : S₁ ⟶ S₂` of
short complexes is given by the unique morphism `f : c₁.pt ⟶ c₂.pt` such that
`c₁.ι ≫ φ.τ₂ = f ≫ c₂.ι`. -/
@[simps]
def ofIsLimitKernelFork (φ : S₁ ⟶ S₂)
(hf₁ : S₁.f = 0) (c₁ : KernelFork S₁.g) (hc₁ : IsLimit c₁)
(hf₂ : S₂.f = 0) (c₂ : KernelFork S₂.g) (hc₂ : IsLimit c₂) (f : c₁.pt ⟶ c₂.pt)
(comm : c₁.ι ≫ φ.τ₂ = f ≫ c₂.ι) :
RightHomologyMapData φ (RightHomologyData.ofIsLimitKernelFork S₁ hf₁ c₁ hc₁)
(RightHomologyData.ofIsLimitKernelFork S₂ hf₂ c₂ hc₂) where
φQ := φ.τ₂
φH := f
commg' := by simp only [RightHomologyData.ofIsLimitKernelFork_g', φ.comm₂₃]
commι := comm.symm
/-- When `S₁.g` and `S₂.g` are zero and we have chosen colimit cokernel coforks `c₁` and `c₂`
for `S₁.f` and `S₂.f` respectively, the action on right homology of a morphism `φ : S₁ ⟶ S₂` of
short complexes is given by the unique morphism `f : c₁.pt ⟶ c₂.pt` such that
`φ.τ₂ ≫ c₂.π = c₁.π ≫ f`. -/
@[simps]
def ofIsColimitCokernelCofork (φ : S₁ ⟶ S₂)
(hg₁ : S₁.g = 0) (c₁ : CokernelCofork S₁.f) (hc₁ : IsColimit c₁)
(hg₂ : S₂.g = 0) (c₂ : CokernelCofork S₂.f) (hc₂ : IsColimit c₂) (f : c₁.pt ⟶ c₂.pt)
(comm : φ.τ₂ ≫ c₂.π = c₁.π ≫ f) :
RightHomologyMapData φ (RightHomologyData.ofIsColimitCokernelCofork S₁ hg₁ c₁ hc₁)
(RightHomologyData.ofIsColimitCokernelCofork S₂ hg₂ c₂ hc₂) where
φQ := f
φH := f
commp := comm.symm
variable (S)
/-- When both maps `S.f` and `S.g` of a short complex `S` are zero, this is the right homology map
data (for the identity of `S`) which relates the right homology data
`RightHomologyData.ofIsLimitKernelFork` and `ofZeros` . -/
@[simps]
def compatibilityOfZerosOfIsLimitKernelFork (hf : S.f = 0) (hg : S.g = 0)
(c : KernelFork S.g) (hc : IsLimit c) :
RightHomologyMapData (𝟙 S)
(RightHomologyData.ofIsLimitKernelFork S hf c hc)
(RightHomologyData.ofZeros S hf hg) where
φQ := 𝟙 _
φH := c.ι
/-- When both maps `S.f` and `S.g` of a short complex `S` are zero, this is the right homology map
data (for the identity of `S`) which relates the right homology data `ofZeros` and
`ofIsColimitCokernelCofork`. -/
@[simps]
def compatibilityOfZerosOfIsColimitCokernelCofork (hf : S.f = 0) (hg : S.g = 0)
(c : CokernelCofork S.f) (hc : IsColimit c) :
RightHomologyMapData (𝟙 S)
(RightHomologyData.ofZeros S hf hg)
(RightHomologyData.ofIsColimitCokernelCofork S hg c hc) where
φQ := c.π
φH := c.π
end RightHomologyMapData
end
section
variable (S)
variable [S.HasRightHomology]
/-- The right homology of a short complex,
given by the `H` field of a chosen right homology data. -/
noncomputable def rightHomology : C := S.rightHomologyData.H
-- `S.rightHomology` is the simp normal form.
@[simp] lemma rightHomologyData_H : S.rightHomologyData.H = S.rightHomology := rfl
/-- The "opcycles" of a short complex, given by the `Q` field of a chosen right homology data.
This is the dual notion to cycles. -/
noncomputable def opcycles : C := S.rightHomologyData.Q
/-- The canonical map `S.rightHomology ⟶ S.opcycles`. -/
noncomputable def rightHomologyι : S.rightHomology ⟶ S.opcycles :=
S.rightHomologyData.ι
/-- The projection `S.X₂ ⟶ S.opcycles`. -/
noncomputable def pOpcycles : S.X₂ ⟶ S.opcycles := S.rightHomologyData.p
/-- The canonical map `S.opcycles ⟶ X₃`. -/
noncomputable def fromOpcycles : S.opcycles ⟶ S.X₃ := S.rightHomologyData.g'
@[reassoc (attr := simp)]
lemma f_pOpcycles : S.f ≫ S.pOpcycles = 0 := S.rightHomologyData.wp
@[reassoc (attr := simp)]
lemma p_fromOpcycles : S.pOpcycles ≫ S.fromOpcycles = S.g := S.rightHomologyData.p_g'
instance : Epi S.pOpcycles := by
dsimp only [pOpcycles]
infer_instance
instance : Mono S.rightHomologyι := by
dsimp only [rightHomologyι]
infer_instance
lemma rightHomology_ext_iff {A : C} (f₁ f₂ : A ⟶ S.rightHomology) :
f₁ = f₂ ↔ f₁ ≫ S.rightHomologyι = f₂ ≫ S.rightHomologyι := by
rw [cancel_mono]
@[ext]
lemma rightHomology_ext {A : C} (f₁ f₂ : A ⟶ S.rightHomology)
(h : f₁ ≫ S.rightHomologyι = f₂ ≫ S.rightHomologyι) : f₁ = f₂ := by
simpa only [rightHomology_ext_iff]
lemma opcycles_ext_iff {A : C} (f₁ f₂ : S.opcycles ⟶ A) :
f₁ = f₂ ↔ S.pOpcycles ≫ f₁ = S.pOpcycles ≫ f₂ := by
rw [cancel_epi]
@[ext]
lemma opcycles_ext {A : C} (f₁ f₂ : S.opcycles ⟶ A)
(h : S.pOpcycles ≫ f₁ = S.pOpcycles ≫ f₂) : f₁ = f₂ := by
simpa only [opcycles_ext_iff]
lemma isIso_pOpcycles (hf : S.f = 0) : IsIso S.pOpcycles :=
RightHomologyData.isIso_p _ hf
/-- When `S.f = 0`, this is the canonical isomorphism `S.opcycles ≅ S.X₂`
induced by `S.pOpcycles`. -/
@[simps! inv]
noncomputable def opcyclesIsoX₂ (hf : S.f = 0) : S.opcycles ≅ S.X₂ := by
have := S.isIso_pOpcycles hf
exact (asIso S.pOpcycles).symm
@[reassoc (attr := simp)]
lemma opcyclesIsoX₂_inv_hom_id (hf : S.f = 0) :
S.pOpcycles ≫ (S.opcyclesIsoX₂ hf).hom = 𝟙 _ := (S.opcyclesIsoX₂ hf).inv_hom_id
@[reassoc (attr := simp)]
lemma opcyclesIsoX₂_hom_inv_id (hf : S.f = 0) :
(S.opcyclesIsoX₂ hf).hom ≫ S.pOpcycles = 𝟙 _ := (S.opcyclesIsoX₂ hf).hom_inv_id
lemma isIso_rightHomologyι (hg : S.g = 0) : IsIso S.rightHomologyι :=
RightHomologyData.isIso_ι _ hg
/-- When `S.g = 0`, this is the canonical isomorphism `S.opcycles ≅ S.rightHomology` induced
by `S.rightHomologyι`. -/
@[simps! inv]
noncomputable def opcyclesIsoRightHomology (hg : S.g = 0) : S.opcycles ≅ S.rightHomology := by
have := S.isIso_rightHomologyι hg
exact (asIso S.rightHomologyι).symm
@[reassoc (attr := simp)]
lemma opcyclesIsoRightHomology_inv_hom_id (hg : S.g = 0) :
S.rightHomologyι ≫ (S.opcyclesIsoRightHomology hg).hom = 𝟙 _ :=
(S.opcyclesIsoRightHomology hg).inv_hom_id
@[reassoc (attr := simp)]
lemma opcyclesIsoRightHomology_hom_inv_id (hg : S.g = 0) :
(S.opcyclesIsoRightHomology hg).hom ≫ S.rightHomologyι = 𝟙 _ :=
(S.opcyclesIsoRightHomology hg).hom_inv_id
end
section
variable (φ : S₁ ⟶ S₂) (h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData)
/-- The (unique) right homology map data associated to a morphism of short complexes that
are both equipped with right homology data. -/
def rightHomologyMapData : RightHomologyMapData φ h₁ h₂ := default
/-- Given a morphism `φ : S₁ ⟶ S₂` of short complexes and right homology data `h₁` and `h₂`
for `S₁` and `S₂` respectively, this is the induced right homology map `h₁.H ⟶ h₁.H`. -/
def rightHomologyMap' : h₁.H ⟶ h₂.H := (rightHomologyMapData φ _ _).φH
/-- Given a morphism `φ : S₁ ⟶ S₂` of short complexes and right homology data `h₁` and `h₂`
for `S₁` and `S₂` respectively, this is the induced morphism `h₁.K ⟶ h₁.K` on opcycles. -/
def opcyclesMap' : h₁.Q ⟶ h₂.Q := (rightHomologyMapData φ _ _).φQ
@[reassoc (attr := simp)]
lemma p_opcyclesMap' : h₁.p ≫ opcyclesMap' φ h₁ h₂ = φ.τ₂ ≫ h₂.p :=
RightHomologyMapData.commp _
@[reassoc (attr := simp)]
lemma opcyclesMap'_g' : opcyclesMap' φ h₁ h₂ ≫ h₂.g' = h₁.g' ≫ φ.τ₃ := by
simp only [← cancel_epi h₁.p, assoc, φ.comm₂₃, p_opcyclesMap'_assoc,
RightHomologyData.p_g'_assoc, RightHomologyData.p_g']
@[reassoc (attr := simp)]
lemma rightHomologyι_naturality' :
rightHomologyMap' φ h₁ h₂ ≫ h₂.ι = h₁.ι ≫ opcyclesMap' φ h₁ h₂ :=
RightHomologyMapData.commι _
end
section
variable [HasRightHomology S₁] [HasRightHomology S₂] (φ : S₁ ⟶ S₂)
/-- The (right) homology map `S₁.rightHomology ⟶ S₂.rightHomology` induced by a morphism
`S₁ ⟶ S₂` of short complexes. -/
noncomputable def rightHomologyMap : S₁.rightHomology ⟶ S₂.rightHomology :=
rightHomologyMap' φ _ _
/-- The morphism `S₁.opcycles ⟶ S₂.opcycles` induced by a morphism `S₁ ⟶ S₂` of short complexes. -/
noncomputable def opcyclesMap : S₁.opcycles ⟶ S₂.opcycles :=
opcyclesMap' φ _ _
@[reassoc (attr := simp)]
lemma p_opcyclesMap : S₁.pOpcycles ≫ opcyclesMap φ = φ.τ₂ ≫ S₂.pOpcycles :=
p_opcyclesMap' _ _ _
@[reassoc (attr := simp)]
lemma fromOpcycles_naturality : opcyclesMap φ ≫ S₂.fromOpcycles = S₁.fromOpcycles ≫ φ.τ₃ :=
opcyclesMap'_g' _ _ _
@[reassoc (attr := simp)]
lemma rightHomologyι_naturality :
rightHomologyMap φ ≫ S₂.rightHomologyι = S₁.rightHomologyι ≫ opcyclesMap φ :=
rightHomologyι_naturality' _ _ _
end
namespace RightHomologyMapData
variable {φ : S₁ ⟶ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData}
(γ : RightHomologyMapData φ h₁ h₂)
lemma rightHomologyMap'_eq : rightHomologyMap' φ h₁ h₂ = γ.φH :=
RightHomologyMapData.congr_φH (Subsingleton.elim _ _)
lemma opcyclesMap'_eq : opcyclesMap' φ h₁ h₂ = γ.φQ :=
RightHomologyMapData.congr_φQ (Subsingleton.elim _ _)
end RightHomologyMapData
@[simp]
lemma rightHomologyMap'_id (h : S.RightHomologyData) :
rightHomologyMap' (𝟙 S) h h = 𝟙 _ :=
(RightHomologyMapData.id h).rightHomologyMap'_eq
@[simp]
lemma opcyclesMap'_id (h : S.RightHomologyData) :
opcyclesMap' (𝟙 S) h h = 𝟙 _ :=
(RightHomologyMapData.id h).opcyclesMap'_eq
variable (S)
@[simp]
lemma rightHomologyMap_id [HasRightHomology S] :
rightHomologyMap (𝟙 S) = 𝟙 _ :=
rightHomologyMap'_id _
@[simp]
lemma opcyclesMap_id [HasRightHomology S] :
opcyclesMap (𝟙 S) = 𝟙 _ :=
opcyclesMap'_id _
@[simp]
lemma rightHomologyMap'_zero (h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) :
rightHomologyMap' 0 h₁ h₂ = 0 :=
(RightHomologyMapData.zero h₁ h₂).rightHomologyMap'_eq
@[simp]
lemma opcyclesMap'_zero (h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) :
opcyclesMap' 0 h₁ h₂ = 0 :=
(RightHomologyMapData.zero h₁ h₂).opcyclesMap'_eq
variable (S₁ S₂)
@[simp]
lemma rightHomologyMap_zero [HasRightHomology S₁] [HasRightHomology S₂] :
rightHomologyMap (0 : S₁ ⟶ S₂) = 0 :=
rightHomologyMap'_zero _ _
@[simp]
lemma opcyclesMap_zero [HasRightHomology S₁] [HasRightHomology S₂] :
opcyclesMap (0 : S₁ ⟶ S₂) = 0 :=
opcyclesMap'_zero _ _
variable {S₁ S₂}
@[reassoc]
lemma rightHomologyMap'_comp (φ₁ : S₁ ⟶ S₂) (φ₂ : S₂ ⟶ S₃)
(h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) (h₃ : S₃.RightHomologyData) :
rightHomologyMap' (φ₁ ≫ φ₂) h₁ h₃ = rightHomologyMap' φ₁ h₁ h₂ ≫
rightHomologyMap' φ₂ h₂ h₃ := by
let γ₁ := rightHomologyMapData φ₁ h₁ h₂
let γ₂ := rightHomologyMapData φ₂ h₂ h₃
rw [γ₁.rightHomologyMap'_eq, γ₂.rightHomologyMap'_eq, (γ₁.comp γ₂).rightHomologyMap'_eq,
RightHomologyMapData.comp_φH]
@[reassoc]
lemma opcyclesMap'_comp (φ₁ : S₁ ⟶ S₂) (φ₂ : S₂ ⟶ S₃)
(h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) (h₃ : S₃.RightHomologyData) :
opcyclesMap' (φ₁ ≫ φ₂) h₁ h₃ = opcyclesMap' φ₁ h₁ h₂ ≫ opcyclesMap' φ₂ h₂ h₃ := by
let γ₁ := rightHomologyMapData φ₁ h₁ h₂
let γ₂ := rightHomologyMapData φ₂ h₂ h₃
rw [γ₁.opcyclesMap'_eq, γ₂.opcyclesMap'_eq, (γ₁.comp γ₂).opcyclesMap'_eq,
RightHomologyMapData.comp_φQ]
@[simp]
lemma rightHomologyMap_comp [HasRightHomology S₁] [HasRightHomology S₂] [HasRightHomology S₃]
(φ₁ : S₁ ⟶ S₂) (φ₂ : S₂ ⟶ S₃) :
rightHomologyMap (φ₁ ≫ φ₂) = rightHomologyMap φ₁ ≫ rightHomologyMap φ₂ :=
rightHomologyMap'_comp _ _ _ _ _
@[simp]
lemma opcyclesMap_comp [HasRightHomology S₁] [HasRightHomology S₂] [HasRightHomology S₃]
(φ₁ : S₁ ⟶ S₂) (φ₂ : S₂ ⟶ S₃) :
opcyclesMap (φ₁ ≫ φ₂) = opcyclesMap φ₁ ≫ opcyclesMap φ₂ :=
opcyclesMap'_comp _ _ _ _ _
attribute [simp] rightHomologyMap_comp opcyclesMap_comp
/-- An isomorphism of short complexes `S₁ ≅ S₂` induces an isomorphism on the `H` fields
of right homology data of `S₁` and `S₂`. -/
@[simps]
def rightHomologyMapIso' (e : S₁ ≅ S₂) (h₁ : S₁.RightHomologyData)
(h₂ : S₂.RightHomologyData) : h₁.H ≅ h₂.H where
hom := rightHomologyMap' e.hom h₁ h₂
inv := rightHomologyMap' e.inv h₂ h₁
hom_inv_id := by rw [← rightHomologyMap'_comp, e.hom_inv_id, rightHomologyMap'_id]
inv_hom_id := by rw [← rightHomologyMap'_comp, e.inv_hom_id, rightHomologyMap'_id]
instance isIso_rightHomologyMap'_of_isIso (φ : S₁ ⟶ S₂) [IsIso φ]
(h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) :
IsIso (rightHomologyMap' φ h₁ h₂) :=
(inferInstance : IsIso (rightHomologyMapIso' (asIso φ) h₁ h₂).hom)
/-- An isomorphism of short complexes `S₁ ≅ S₂` induces an isomorphism on the `Q` fields
of right homology data of `S₁` and `S₂`. -/
@[simps]
def opcyclesMapIso' (e : S₁ ≅ S₂) (h₁ : S₁.RightHomologyData)
(h₂ : S₂.RightHomologyData) : h₁.Q ≅ h₂.Q where
hom := opcyclesMap' e.hom h₁ h₂
inv := opcyclesMap' e.inv h₂ h₁
hom_inv_id := by rw [← opcyclesMap'_comp, e.hom_inv_id, opcyclesMap'_id]
inv_hom_id := by rw [← opcyclesMap'_comp, e.inv_hom_id, opcyclesMap'_id]
instance isIso_opcyclesMap'_of_isIso (φ : S₁ ⟶ S₂) [IsIso φ]
(h₁ : S₁.RightHomologyData) (h₂ : S₂.RightHomologyData) :
IsIso (opcyclesMap' φ h₁ h₂) :=
(inferInstance : IsIso (opcyclesMapIso' (asIso φ) h₁ h₂).hom)
/-- The isomorphism `S₁.rightHomology ≅ S₂.rightHomology` induced by an isomorphism of
short complexes `S₁ ≅ S₂`. -/
@[simps]
noncomputable def rightHomologyMapIso (e : S₁ ≅ S₂) [S₁.HasRightHomology]
[S₂.HasRightHomology] : S₁.rightHomology ≅ S₂.rightHomology where
hom := rightHomologyMap e.hom
inv := rightHomologyMap e.inv
hom_inv_id := by rw [← rightHomologyMap_comp, e.hom_inv_id, rightHomologyMap_id]
inv_hom_id := by rw [← rightHomologyMap_comp, e.inv_hom_id, rightHomologyMap_id]
instance isIso_rightHomologyMap_of_iso (φ : S₁ ⟶ S₂) [IsIso φ] [S₁.HasRightHomology]
[S₂.HasRightHomology] :
IsIso (rightHomologyMap φ) :=
(inferInstance : IsIso (rightHomologyMapIso (asIso φ)).hom)
/-- The isomorphism `S₁.opcycles ≅ S₂.opcycles` induced by an isomorphism
of short complexes `S₁ ≅ S₂`. -/
@[simps]
noncomputable def opcyclesMapIso (e : S₁ ≅ S₂) [S₁.HasRightHomology]
[S₂.HasRightHomology] : S₁.opcycles ≅ S₂.opcycles where
hom := opcyclesMap e.hom
inv := opcyclesMap e.inv
hom_inv_id := by rw [← opcyclesMap_comp, e.hom_inv_id, opcyclesMap_id]
inv_hom_id := by rw [← opcyclesMap_comp, e.inv_hom_id, opcyclesMap_id]
instance isIso_opcyclesMap_of_iso (φ : S₁ ⟶ S₂) [IsIso φ] [S₁.HasRightHomology]
[S₂.HasRightHomology] : IsIso (opcyclesMap φ) :=
(inferInstance : IsIso (opcyclesMapIso (asIso φ)).hom)
variable {S}
namespace RightHomologyData
variable (h : S.RightHomologyData) [S.HasRightHomology]
/-- The isomorphism `S.rightHomology ≅ h.H` induced by a right homology data `h` for a
short complex `S`. -/
noncomputable def rightHomologyIso : S.rightHomology ≅ h.H :=
rightHomologyMapIso' (Iso.refl _) _ _
/-- The isomorphism `S.opcycles ≅ h.Q` induced by a right homology data `h` for a
short complex `S`. -/
noncomputable def opcyclesIso : S.opcycles ≅ h.Q :=
opcyclesMapIso' (Iso.refl _) _ _
@[reassoc (attr := simp)]
lemma p_comp_opcyclesIso_inv : h.p ≫ h.opcyclesIso.inv = S.pOpcycles := by
dsimp [pOpcycles, RightHomologyData.opcyclesIso]
simp only [p_opcyclesMap', id_τ₂, id_comp]
@[reassoc (attr := simp)]
lemma pOpcycles_comp_opcyclesIso_hom : S.pOpcycles ≫ h.opcyclesIso.hom = h.p := by
simp only [← h.p_comp_opcyclesIso_inv, assoc, Iso.inv_hom_id, comp_id]
@[reassoc (attr := simp)]
lemma rightHomologyIso_inv_comp_rightHomologyι :
h.rightHomologyIso.inv ≫ S.rightHomologyι = h.ι ≫ h.opcyclesIso.inv := by
dsimp only [rightHomologyι, rightHomologyIso, opcyclesIso, rightHomologyMapIso',
opcyclesMapIso', Iso.refl]
rw [rightHomologyι_naturality']
@[reassoc (attr := simp)]
lemma rightHomologyIso_hom_comp_ι :
h.rightHomologyIso.hom ≫ h.ι = S.rightHomologyι ≫ h.opcyclesIso.hom := by
simp only [← cancel_mono h.opcyclesIso.inv, ← cancel_epi h.rightHomologyIso.inv,
assoc, Iso.inv_hom_id_assoc, Iso.hom_inv_id, comp_id, rightHomologyIso_inv_comp_rightHomologyι]
end RightHomologyData
namespace RightHomologyMapData
variable {φ : S₁ ⟶ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData}
(γ : RightHomologyMapData φ h₁ h₂)
lemma rightHomologyMap_eq [S₁.HasRightHomology] [S₂.HasRightHomology] :
rightHomologyMap φ = h₁.rightHomologyIso.hom ≫ γ.φH ≫ h₂.rightHomologyIso.inv := by
dsimp [RightHomologyData.rightHomologyIso, rightHomologyMapIso']
rw [← γ.rightHomologyMap'_eq, ← rightHomologyMap'_comp,
← rightHomologyMap'_comp, id_comp, comp_id]
| rfl
lemma opcyclesMap_eq [S₁.HasRightHomology] [S₂.HasRightHomology] :
opcyclesMap φ = h₁.opcyclesIso.hom ≫ γ.φQ ≫ h₂.opcyclesIso.inv := by
dsimp [RightHomologyData.opcyclesIso, cyclesMapIso']
| Mathlib/Algebra/Homology/ShortComplex/RightHomology.lean | 835 | 839 |
/-
Copyright (c) 2022 Kexing Ying. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kexing Ying
-/
import Mathlib.MeasureTheory.Function.ConvergenceInMeasure
import Mathlib.MeasureTheory.Function.L1Space.Integrable
/-!
# Uniform integrability
This file contains the definitions for uniform integrability (both in the measure theory sense
as well as the probability theory sense). This file also contains the Vitali convergence theorem
which establishes a relation between uniform integrability, convergence in measure and
Lp convergence.
Uniform integrability plays a vital role in the theory of martingales most notably is used to
formulate the martingale convergence theorem.
## Main definitions
* `MeasureTheory.UnifIntegrable`: uniform integrability in the measure theory sense.
In particular, a sequence of functions `f` is uniformly integrable if for all `ε > 0`, there
exists some `δ > 0` such that for all sets `s` of smaller measure than `δ`, the Lp-norm of
`f i` restricted `s` is smaller than `ε` for all `i`.
* `MeasureTheory.UniformIntegrable`: uniform integrability in the probability theory sense.
In particular, a sequence of measurable functions `f` is uniformly integrable in the
probability theory sense if it is uniformly integrable in the measure theory sense and
has uniformly bounded Lp-norm.
# Main results
* `MeasureTheory.unifIntegrable_finite`: a finite sequence of Lp functions is uniformly
integrable.
* `MeasureTheory.tendsto_Lp_finite_of_tendsto_ae`: a sequence of Lp functions which is uniformly
integrable converges in Lp if they converge almost everywhere.
* `MeasureTheory.tendstoInMeasure_iff_tendsto_Lp_finite`: Vitali convergence theorem:
a sequence of Lp functions converges in Lp if and only if it is uniformly integrable
and converges in measure.
## Tags
uniform integrable, uniformly absolutely continuous integral, Vitali convergence theorem
-/
noncomputable section
open scoped MeasureTheory NNReal ENNReal Topology
namespace MeasureTheory
open Set Filter TopologicalSpace
variable {α β ι : Type*} {m : MeasurableSpace α} {μ : Measure α} [NormedAddCommGroup β]
/-- Uniform integrability in the measure theory sense.
A sequence of functions `f` is said to be uniformly integrable if for all `ε > 0`, there exists
some `δ > 0` such that for all sets `s` with measure less than `δ`, the Lp-norm of `f i`
restricted on `s` is less than `ε`.
Uniform integrability is also known as uniformly absolutely continuous integrals. -/
def UnifIntegrable {_ : MeasurableSpace α} (f : ι → α → β) (p : ℝ≥0∞) (μ : Measure α) : Prop :=
∀ ⦃ε : ℝ⦄ (_ : 0 < ε), ∃ (δ : ℝ) (_ : 0 < δ), ∀ i s,
MeasurableSet s → μ s ≤ ENNReal.ofReal δ → eLpNorm (s.indicator (f i)) p μ ≤ ENNReal.ofReal ε
/-- In probability theory, a family of measurable functions is uniformly integrable if it is
uniformly integrable in the measure theory sense and is uniformly bounded. -/
def UniformIntegrable {_ : MeasurableSpace α} (f : ι → α → β) (p : ℝ≥0∞) (μ : Measure α) : Prop :=
(∀ i, AEStronglyMeasurable (f i) μ) ∧ UnifIntegrable f p μ ∧ ∃ C : ℝ≥0, ∀ i, eLpNorm (f i) p μ ≤ C
namespace UniformIntegrable
protected theorem aestronglyMeasurable {f : ι → α → β} {p : ℝ≥0∞} (hf : UniformIntegrable f p μ)
(i : ι) : AEStronglyMeasurable (f i) μ :=
hf.1 i
@[deprecated (since := "2025-04-09")]
alias aeStronglyMeasurable := UniformIntegrable.aestronglyMeasurable
protected theorem unifIntegrable {f : ι → α → β} {p : ℝ≥0∞} (hf : UniformIntegrable f p μ) :
UnifIntegrable f p μ :=
hf.2.1
protected theorem memLp {f : ι → α → β} {p : ℝ≥0∞} (hf : UniformIntegrable f p μ) (i : ι) :
MemLp (f i) p μ :=
⟨hf.1 i,
let ⟨_, _, hC⟩ := hf.2
lt_of_le_of_lt (hC i) ENNReal.coe_lt_top⟩
end UniformIntegrable
section UnifIntegrable
/-! ### `UnifIntegrable`
This section deals with uniform integrability in the measure theory sense. -/
namespace UnifIntegrable
variable {f g : ι → α → β} {p : ℝ≥0∞}
protected theorem add (hf : UnifIntegrable f p μ) (hg : UnifIntegrable g p μ) (hp : 1 ≤ p)
(hf_meas : ∀ i, AEStronglyMeasurable (f i) μ) (hg_meas : ∀ i, AEStronglyMeasurable (g i) μ) :
UnifIntegrable (f + g) p μ := by
intro ε hε
have hε2 : 0 < ε / 2 := half_pos hε
obtain ⟨δ₁, hδ₁_pos, hfδ₁⟩ := hf hε2
obtain ⟨δ₂, hδ₂_pos, hgδ₂⟩ := hg hε2
refine ⟨min δ₁ δ₂, lt_min hδ₁_pos hδ₂_pos, fun i s hs hμs => ?_⟩
simp_rw [Pi.add_apply, Set.indicator_add']
refine (eLpNorm_add_le ((hf_meas i).indicator hs) ((hg_meas i).indicator hs) hp).trans ?_
have hε_halves : ENNReal.ofReal ε = ENNReal.ofReal (ε / 2) + ENNReal.ofReal (ε / 2) := by
rw [← ENNReal.ofReal_add hε2.le hε2.le, add_halves]
rw [hε_halves]
exact add_le_add (hfδ₁ i s hs (hμs.trans (ENNReal.ofReal_le_ofReal (min_le_left _ _))))
(hgδ₂ i s hs (hμs.trans (ENNReal.ofReal_le_ofReal (min_le_right _ _))))
protected theorem neg (hf : UnifIntegrable f p μ) : UnifIntegrable (-f) p μ := by
simp_rw [UnifIntegrable, Pi.neg_apply, Set.indicator_neg', eLpNorm_neg]
exact hf
protected theorem sub (hf : UnifIntegrable f p μ) (hg : UnifIntegrable g p μ) (hp : 1 ≤ p)
(hf_meas : ∀ i, AEStronglyMeasurable (f i) μ) (hg_meas : ∀ i, AEStronglyMeasurable (g i) μ) :
UnifIntegrable (f - g) p μ := by
rw [sub_eq_add_neg]
exact hf.add hg.neg hp hf_meas fun i => (hg_meas i).neg
protected theorem ae_eq (hf : UnifIntegrable f p μ) (hfg : ∀ n, f n =ᵐ[μ] g n) :
UnifIntegrable g p μ := by
classical
intro ε hε
obtain ⟨δ, hδ_pos, hfδ⟩ := hf hε
refine ⟨δ, hδ_pos, fun n s hs hμs => (le_of_eq <| eLpNorm_congr_ae ?_).trans (hfδ n s hs hμs)⟩
filter_upwards [hfg n] with x hx
simp_rw [Set.indicator_apply, hx]
/-- Uniform integrability is preserved by restriction of the functions to a set. -/
protected theorem indicator (hf : UnifIntegrable f p μ) (E : Set α) :
UnifIntegrable (fun i => E.indicator (f i)) p μ := fun ε hε ↦ by
obtain ⟨δ, hδ_pos, hε⟩ := hf hε
refine ⟨δ, hδ_pos, fun i s hs hμs ↦ ?_⟩
calc
eLpNorm (s.indicator (E.indicator (f i))) p μ
= eLpNorm (E.indicator (s.indicator (f i))) p μ := by
simp only [indicator_indicator, inter_comm]
_ ≤ eLpNorm (s.indicator (f i)) p μ := eLpNorm_indicator_le _
_ ≤ ENNReal.ofReal ε := hε _ _ hs hμs
/-- Uniform integrability is preserved by restriction of the measure to a set. -/
protected theorem restrict (hf : UnifIntegrable f p μ) (E : Set α) :
UnifIntegrable f p (μ.restrict E) := fun ε hε ↦ by
obtain ⟨δ, hδ_pos, hδε⟩ := hf hε
refine ⟨δ, hδ_pos, fun i s hs hμs ↦ ?_⟩
rw [μ.restrict_apply hs, ← measure_toMeasurable] at hμs
calc
eLpNorm (indicator s (f i)) p (μ.restrict E) = eLpNorm (f i) p (μ.restrict (s ∩ E)) := by
rw [eLpNorm_indicator_eq_eLpNorm_restrict hs, μ.restrict_restrict hs]
_ ≤ eLpNorm (f i) p (μ.restrict (toMeasurable μ (s ∩ E))) :=
eLpNorm_mono_measure _ <| Measure.restrict_mono (subset_toMeasurable _ _) le_rfl
_ = eLpNorm (indicator (toMeasurable μ (s ∩ E)) (f i)) p μ :=
(eLpNorm_indicator_eq_eLpNorm_restrict (measurableSet_toMeasurable _ _)).symm
_ ≤ ENNReal.ofReal ε := hδε i _ (measurableSet_toMeasurable _ _) hμs
end UnifIntegrable
theorem unifIntegrable_zero_meas [MeasurableSpace α] {p : ℝ≥0∞} {f : ι → α → β} :
UnifIntegrable f p (0 : Measure α) :=
fun ε _ => ⟨1, one_pos, fun i s _ _ => by simp⟩
theorem unifIntegrable_congr_ae {p : ℝ≥0∞} {f g : ι → α → β} (hfg : ∀ n, f n =ᵐ[μ] g n) :
UnifIntegrable f p μ ↔ UnifIntegrable g p μ :=
⟨fun hf => hf.ae_eq hfg, fun hg => hg.ae_eq fun n => (hfg n).symm⟩
theorem tendsto_indicator_ge (f : α → β) (x : α) :
Tendsto (fun M : ℕ => { x | (M : ℝ) ≤ ‖f x‖₊ }.indicator f x) atTop (𝓝 0) := by
refine tendsto_atTop_of_eventually_const (i₀ := Nat.ceil (‖f x‖₊ : ℝ) + 1) fun n hn => ?_
rw [Set.indicator_of_not_mem]
simp only [not_le, Set.mem_setOf_eq]
refine lt_of_le_of_lt (Nat.le_ceil _) ?_
refine lt_of_lt_of_le (lt_add_one _) ?_
norm_cast
variable {p : ℝ≥0∞}
section
variable {f : α → β}
/-- This lemma is weaker than `MeasureTheory.MemLp.integral_indicator_norm_ge_nonneg_le`
as the latter provides `0 ≤ M` and does not require the measurability of `f`. -/
theorem MemLp.integral_indicator_norm_ge_le (hf : MemLp f 1 μ) (hmeas : StronglyMeasurable f)
{ε : ℝ} (hε : 0 < ε) :
∃ M : ℝ, (∫⁻ x, ‖{ x | M ≤ ‖f x‖₊ }.indicator f x‖₊ ∂μ) ≤ ENNReal.ofReal ε := by
have htendsto :
∀ᵐ x ∂μ, Tendsto (fun M : ℕ => { x | (M : ℝ) ≤ ‖f x‖₊ }.indicator f x) atTop (𝓝 0) :=
univ_mem' (id fun x => tendsto_indicator_ge f x)
have hmeas : ∀ M : ℕ, AEStronglyMeasurable ({ x | (M : ℝ) ≤ ‖f x‖₊ }.indicator f) μ := by
intro M
apply hf.1.indicator
apply StronglyMeasurable.measurableSet_le stronglyMeasurable_const
hmeas.nnnorm.measurable.coe_nnreal_real.stronglyMeasurable
have hbound : HasFiniteIntegral (fun x => ‖f x‖) μ := by
rw [memLp_one_iff_integrable] at hf
exact hf.norm.2
have : Tendsto (fun n : ℕ ↦ ∫⁻ a, ENNReal.ofReal ‖{ x | n ≤ ‖f x‖₊ }.indicator f a - 0‖ ∂μ)
atTop (𝓝 0) := by
refine tendsto_lintegral_norm_of_dominated_convergence hmeas hbound ?_ htendsto
refine fun n => univ_mem' (id fun x => ?_)
by_cases hx : (n : ℝ) ≤ ‖f x‖
· dsimp
rwa [Set.indicator_of_mem]
· dsimp
rw [Set.indicator_of_not_mem, norm_zero]
· exact norm_nonneg _
· assumption
rw [ENNReal.tendsto_atTop_zero] at this
obtain ⟨M, hM⟩ := this (ENNReal.ofReal ε) (ENNReal.ofReal_pos.2 hε)
simp only [zero_tsub, zero_le, sub_zero, zero_add, coe_nnnorm,
Set.mem_Icc] at hM
refine ⟨M, ?_⟩
convert hM M le_rfl
simp only [coe_nnnorm, ENNReal.ofReal_eq_coe_nnreal (norm_nonneg _)]
rfl
/-- This lemma is superseded by `MeasureTheory.MemLp.integral_indicator_norm_ge_nonneg_le`
which does not require measurability. -/
theorem MemLp.integral_indicator_norm_ge_nonneg_le_of_meas (hf : MemLp f 1 μ)
(hmeas : StronglyMeasurable f) {ε : ℝ} (hε : 0 < ε) :
∃ M : ℝ, 0 ≤ M ∧ (∫⁻ x, ‖{ x | M ≤ ‖f x‖₊ }.indicator f x‖ₑ ∂μ) ≤ ENNReal.ofReal ε :=
let ⟨M, hM⟩ := hf.integral_indicator_norm_ge_le hmeas hε
⟨max M 0, le_max_right _ _, by simpa⟩
theorem MemLp.integral_indicator_norm_ge_nonneg_le (hf : MemLp f 1 μ) {ε : ℝ} (hε : 0 < ε) :
∃ M : ℝ, 0 ≤ M ∧ (∫⁻ x, ‖{ x | M ≤ ‖f x‖₊ }.indicator f x‖ₑ ∂μ) ≤ ENNReal.ofReal ε := by
have hf_mk : MemLp (hf.1.mk f) 1 μ := (memLp_congr_ae hf.1.ae_eq_mk).mp hf
obtain ⟨M, hM_pos, hfM⟩ :=
hf_mk.integral_indicator_norm_ge_nonneg_le_of_meas hf.1.stronglyMeasurable_mk hε
refine ⟨M, hM_pos, (le_of_eq ?_).trans hfM⟩
refine lintegral_congr_ae ?_
filter_upwards [hf.1.ae_eq_mk] with x hx
simp only [Set.indicator_apply, coe_nnnorm, Set.mem_setOf_eq, ENNReal.coe_inj, hx.symm]
theorem MemLp.eLpNormEssSup_indicator_norm_ge_eq_zero (hf : MemLp f ∞ μ)
(hmeas : StronglyMeasurable f) :
∃ M : ℝ, eLpNormEssSup ({ x | M ≤ ‖f x‖₊ }.indicator f) μ = 0 := by
have hbdd : eLpNormEssSup f μ < ∞ := hf.eLpNorm_lt_top
refine ⟨(eLpNorm f ∞ μ + 1).toReal, ?_⟩
rw [eLpNormEssSup_indicator_eq_eLpNormEssSup_restrict]
· have : μ.restrict { x : α | (eLpNorm f ⊤ μ + 1).toReal ≤ ‖f x‖₊ } = 0 := by
simp only [coe_nnnorm, eLpNorm_exponent_top, Measure.restrict_eq_zero]
have : { x : α | (eLpNormEssSup f μ + 1).toReal ≤ ‖f x‖ } ⊆
{ x : α | eLpNormEssSup f μ < ‖f x‖₊ } := by
intro x hx
rw [Set.mem_setOf_eq, ← ENNReal.toReal_lt_toReal hbdd.ne ENNReal.coe_lt_top.ne,
ENNReal.coe_toReal, coe_nnnorm]
refine lt_of_lt_of_le ?_ hx
rw [ENNReal.toReal_lt_toReal hbdd.ne]
· exact ENNReal.lt_add_right hbdd.ne one_ne_zero
· exact (ENNReal.add_lt_top.2 ⟨hbdd, ENNReal.one_lt_top⟩).ne
rw [← nonpos_iff_eq_zero]
refine (measure_mono this).trans ?_
have hle := enorm_ae_le_eLpNormEssSup f μ
simp_rw [ae_iff, not_le] at hle
exact nonpos_iff_eq_zero.2 hle
rw [this, eLpNormEssSup_measure_zero]
exact measurableSet_le measurable_const hmeas.nnnorm.measurable.subtype_coe
/- This lemma is slightly weaker than `MeasureTheory.MemLp.eLpNorm_indicator_norm_ge_pos_le` as the
latter provides `0 < M`. -/
theorem MemLp.eLpNorm_indicator_norm_ge_le (hf : MemLp f p μ) (hmeas : StronglyMeasurable f) {ε : ℝ}
(hε : 0 < ε) : ∃ M : ℝ, eLpNorm ({ x | M ≤ ‖f x‖₊ }.indicator f) p μ ≤ ENNReal.ofReal ε := by
by_cases hp_ne_zero : p = 0
· refine ⟨1, hp_ne_zero.symm ▸ ?_⟩
simp [eLpNorm_exponent_zero]
by_cases hp_ne_top : p = ∞
· subst hp_ne_top
obtain ⟨M, hM⟩ := hf.eLpNormEssSup_indicator_norm_ge_eq_zero hmeas
refine ⟨M, ?_⟩
simp only [eLpNorm_exponent_top, hM, zero_le]
obtain ⟨M, hM', hM⟩ := MemLp.integral_indicator_norm_ge_nonneg_le
(μ := μ) (hf.norm_rpow hp_ne_zero hp_ne_top) (Real.rpow_pos_of_pos hε p.toReal)
refine ⟨M ^ (1 / p.toReal), ?_⟩
rw [eLpNorm_eq_lintegral_rpow_enorm hp_ne_zero hp_ne_top, ← ENNReal.rpow_one (ENNReal.ofReal ε)]
conv_rhs => rw [← mul_one_div_cancel (ENNReal.toReal_pos hp_ne_zero hp_ne_top).ne.symm]
rw [ENNReal.rpow_mul,
ENNReal.rpow_le_rpow_iff (one_div_pos.2 <| ENNReal.toReal_pos hp_ne_zero hp_ne_top),
ENNReal.ofReal_rpow_of_pos hε]
convert hM using 3 with x
rw [enorm_indicator_eq_indicator_enorm, enorm_indicator_eq_indicator_enorm]
have hiff : M ^ (1 / p.toReal) ≤ ‖f x‖₊ ↔ M ≤ ‖‖f x‖ ^ p.toReal‖₊ := by
rw [coe_nnnorm, coe_nnnorm, Real.norm_rpow_of_nonneg (norm_nonneg _), norm_norm,
← Real.rpow_le_rpow_iff hM' (Real.rpow_nonneg (norm_nonneg _) _)
(one_div_pos.2 <| ENNReal.toReal_pos hp_ne_zero hp_ne_top), ← Real.rpow_mul (norm_nonneg _),
mul_one_div_cancel (ENNReal.toReal_pos hp_ne_zero hp_ne_top).ne.symm, Real.rpow_one]
by_cases hx : x ∈ { x : α | M ^ (1 / p.toReal) ≤ ‖f x‖₊ }
· rw [Set.indicator_of_mem hx, Set.indicator_of_mem, Real.enorm_of_nonneg (by positivity),
← ENNReal.ofReal_rpow_of_nonneg (norm_nonneg _) ENNReal.toReal_nonneg, ofReal_norm]
rw [Set.mem_setOf_eq]
rwa [← hiff]
· rw [Set.indicator_of_not_mem hx, Set.indicator_of_not_mem]
· simp [ENNReal.toReal_pos hp_ne_zero hp_ne_top]
· rw [Set.mem_setOf_eq]
rwa [← hiff]
/-- This lemma implies that a single function is uniformly integrable (in the probability sense). -/
theorem MemLp.eLpNorm_indicator_norm_ge_pos_le (hf : MemLp f p μ) (hmeas : StronglyMeasurable f)
{ε : ℝ} (hε : 0 < ε) :
∃ M : ℝ, 0 < M ∧ eLpNorm ({ x | M ≤ ‖f x‖₊ }.indicator f) p μ ≤ ENNReal.ofReal ε := by
obtain ⟨M, hM⟩ := hf.eLpNorm_indicator_norm_ge_le hmeas hε
refine
⟨max M 1, lt_of_lt_of_le zero_lt_one (le_max_right _ _), le_trans (eLpNorm_mono fun x => ?_) hM⟩
rw [norm_indicator_eq_indicator_norm, norm_indicator_eq_indicator_norm]
refine Set.indicator_le_indicator_of_subset (fun x hx => ?_) (fun x => norm_nonneg (f x)) x
rw [Set.mem_setOf_eq] at hx -- removing the `rw` breaks the proof!
exact (max_le_iff.1 hx).1
end
theorem eLpNorm_indicator_le_of_bound {f : α → β} (hp_top : p ≠ ∞) {ε : ℝ} (hε : 0 < ε) {M : ℝ}
(hf : ∀ x, ‖f x‖ < M) :
∃ (δ : ℝ) (_ : 0 < δ), ∀ s, MeasurableSet s →
μ s ≤ ENNReal.ofReal δ → eLpNorm (s.indicator f) p μ ≤ ENNReal.ofReal ε := by
by_cases hM : M ≤ 0
· refine ⟨1, zero_lt_one, fun s _ _ => ?_⟩
rw [(_ : f = 0)]
· simp [hε.le]
· ext x
rw [Pi.zero_apply, ← norm_le_zero_iff]
exact (lt_of_lt_of_le (hf x) hM).le
rw [not_le] at hM
refine ⟨(ε / M) ^ p.toReal, Real.rpow_pos_of_pos (div_pos hε hM) _, fun s hs hμ => ?_⟩
by_cases hp : p = 0
· simp [hp]
rw [eLpNorm_indicator_eq_eLpNorm_restrict hs]
have haebdd : ∀ᵐ x ∂μ.restrict s, ‖f x‖ ≤ M := by
filter_upwards
exact fun x => (hf x).le
refine le_trans (eLpNorm_le_of_ae_bound haebdd) ?_
rw [Measure.restrict_apply MeasurableSet.univ, Set.univ_inter,
← ENNReal.le_div_iff_mul_le (Or.inl _) (Or.inl ENNReal.ofReal_ne_top)]
· rw [ENNReal.rpow_inv_le_iff (ENNReal.toReal_pos hp hp_top)]
refine le_trans hμ ?_
rw [← ENNReal.ofReal_rpow_of_pos (div_pos hε hM),
ENNReal.rpow_le_rpow_iff (ENNReal.toReal_pos hp hp_top), ENNReal.ofReal_div_of_pos hM]
· simpa only [ENNReal.ofReal_eq_zero, not_le, Ne]
section
variable {f : α → β}
/-- Auxiliary lemma for `MeasureTheory.MemLp.eLpNorm_indicator_le`. -/
theorem MemLp.eLpNorm_indicator_le' (hp_one : 1 ≤ p) (hp_top : p ≠ ∞) (hf : MemLp f p μ)
(hmeas : StronglyMeasurable f) {ε : ℝ} (hε : 0 < ε) :
∃ (δ : ℝ) (_ : 0 < δ), ∀ s, MeasurableSet s → μ s ≤ ENNReal.ofReal δ →
eLpNorm (s.indicator f) p μ ≤ 2 * ENNReal.ofReal ε := by
obtain ⟨M, hMpos, hM⟩ := hf.eLpNorm_indicator_norm_ge_pos_le hmeas hε
obtain ⟨δ, hδpos, hδ⟩ :=
eLpNorm_indicator_le_of_bound (f := { x | ‖f x‖ < M }.indicator f) hp_top hε (by
intro x
rw [norm_indicator_eq_indicator_norm, Set.indicator_apply]
· split_ifs with h
exacts [h, hMpos])
refine ⟨δ, hδpos, fun s hs hμs => ?_⟩
rw [(_ : f = { x : α | M ≤ ‖f x‖₊ }.indicator f + { x : α | ‖f x‖ < M }.indicator f)]
· rw [eLpNorm_indicator_eq_eLpNorm_restrict hs]
refine le_trans (eLpNorm_add_le ?_ ?_ hp_one) ?_
· exact StronglyMeasurable.aestronglyMeasurable
(hmeas.indicator (measurableSet_le measurable_const hmeas.nnnorm.measurable.subtype_coe))
· exact StronglyMeasurable.aestronglyMeasurable
(hmeas.indicator (measurableSet_lt hmeas.nnnorm.measurable.subtype_coe measurable_const))
· rw [two_mul]
refine add_le_add (le_trans (eLpNorm_mono_measure _ Measure.restrict_le_self) hM) ?_
rw [← eLpNorm_indicator_eq_eLpNorm_restrict hs]
exact hδ s hs hμs
· ext x
by_cases hx : M ≤ ‖f x‖
· rw [Pi.add_apply, Set.indicator_of_mem, Set.indicator_of_not_mem, add_zero] <;> simpa
· rw [Pi.add_apply, Set.indicator_of_not_mem, Set.indicator_of_mem, zero_add] <;>
simpa using hx
/-- This lemma is superseded by `MeasureTheory.MemLp.eLpNorm_indicator_le` which does not require
measurability on `f`. -/
theorem MemLp.eLpNorm_indicator_le_of_meas (hp_one : 1 ≤ p) (hp_top : p ≠ ∞) (hf : MemLp f p μ)
(hmeas : StronglyMeasurable f) {ε : ℝ} (hε : 0 < ε) :
∃ (δ : ℝ) (_ : 0 < δ), ∀ s, MeasurableSet s → μ s ≤ ENNReal.ofReal δ →
eLpNorm (s.indicator f) p μ ≤ ENNReal.ofReal ε := by
| obtain ⟨δ, hδpos, hδ⟩ := hf.eLpNorm_indicator_le' hp_one hp_top hmeas (half_pos hε)
refine ⟨δ, hδpos, fun s hs hμs => le_trans (hδ s hs hμs) ?_⟩
rw [ENNReal.ofReal_div_of_pos zero_lt_two, (by norm_num : ENNReal.ofReal 2 = 2),
ENNReal.mul_div_cancel] <;>
norm_num
theorem MemLp.eLpNorm_indicator_le (hp_one : 1 ≤ p) (hp_top : p ≠ ∞) (hf : MemLp f p μ) {ε : ℝ}
(hε : 0 < ε) :
∃ (δ : ℝ) (_ : 0 < δ), ∀ s, MeasurableSet s → μ s ≤ ENNReal.ofReal δ →
eLpNorm (s.indicator f) p μ ≤ ENNReal.ofReal ε := by
have hℒp := hf
| Mathlib/MeasureTheory/Function/UniformIntegrable.lean | 389 | 399 |
/-
Copyright (c) 2019 Zhouhang Zhou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Zhouhang Zhou, Yury Kudryashov, Heather Macbeth
-/
import Mathlib.MeasureTheory.Function.SimpleFunc
import Mathlib.MeasureTheory.Constructions.BorelSpace.Metrizable
/-!
# Density of simple functions
Show that each Borel measurable function can be approximated pointwise
by a sequence of simple functions.
## Main definitions
* `MeasureTheory.SimpleFunc.nearestPt (e : ℕ → α) (N : ℕ) : α →ₛ ℕ`: the `SimpleFunc` sending
each `x : α` to the point `e k` which is the nearest to `x` among `e 0`, ..., `e N`.
* `MeasureTheory.SimpleFunc.approxOn (f : β → α) (hf : Measurable f) (s : Set α) (y₀ : α)
(h₀ : y₀ ∈ s) [SeparableSpace s] (n : ℕ) : β →ₛ α` : a simple function that takes values in `s`
and approximates `f`.
## Main results
* `tendsto_approxOn` (pointwise convergence): If `f x ∈ s`, then the sequence of simple
approximations `MeasureTheory.SimpleFunc.approxOn f hf s y₀ h₀ n`, evaluated at `x`,
tends to `f x` as `n` tends to `∞`.
## Notations
* `α →ₛ β` (local notation): the type of simple functions `α → β`.
-/
open Set Function Filter TopologicalSpace ENNReal EMetric Finset
open Topology ENNReal MeasureTheory
variable {α β ι E F 𝕜 : Type*}
noncomputable section
namespace MeasureTheory
local infixr:25 " →ₛ " => SimpleFunc
namespace SimpleFunc
/-! ### Pointwise approximation by simple functions -/
variable [MeasurableSpace α] [PseudoEMetricSpace α] [OpensMeasurableSpace α]
/-- `nearestPtInd e N x` is the index `k` such that `e k` is the nearest point to `x` among the
points `e 0`, ..., `e N`. If more than one point are at the same distance from `x`, then
`nearestPtInd e N x` returns the least of their indexes. -/
noncomputable def nearestPtInd (e : ℕ → α) : ℕ → α →ₛ ℕ
| 0 => const α 0
| N + 1 =>
piecewise (⋂ k ≤ N, { x | edist (e (N + 1)) x < edist (e k) x })
(MeasurableSet.iInter fun _ =>
MeasurableSet.iInter fun _ =>
measurableSet_lt measurable_edist_right measurable_edist_right)
(const α <| N + 1) (nearestPtInd e N)
/-- `nearestPt e N x` is the nearest point to `x` among the points `e 0`, ..., `e N`. If more than
one point are at the same distance from `x`, then `nearestPt e N x` returns the point with the
least possible index. -/
noncomputable def nearestPt (e : ℕ → α) (N : ℕ) : α →ₛ α :=
(nearestPtInd e N).map e
@[simp]
theorem nearestPtInd_zero (e : ℕ → α) : nearestPtInd e 0 = const α 0 :=
rfl
@[simp]
theorem nearestPt_zero (e : ℕ → α) : nearestPt e 0 = const α (e 0) :=
rfl
theorem nearestPtInd_succ (e : ℕ → α) (N : ℕ) (x : α) :
nearestPtInd e (N + 1) x =
if ∀ k ≤ N, edist (e (N + 1)) x < edist (e k) x then N + 1 else nearestPtInd e N x := by
simp only [nearestPtInd, coe_piecewise, Set.piecewise]
congr
simp
theorem nearestPtInd_le (e : ℕ → α) (N : ℕ) (x : α) : nearestPtInd e N x ≤ N := by
induction' N with N ihN; · simp
simp only [nearestPtInd_succ]
split_ifs
exacts [le_rfl, ihN.trans N.le_succ]
theorem edist_nearestPt_le (e : ℕ → α) (x : α) {k N : ℕ} (hk : k ≤ N) :
edist (nearestPt e N x) x ≤ edist (e k) x := by
induction' N with N ihN generalizing k
· simp [nonpos_iff_eq_zero.1 hk, le_refl]
· simp only [nearestPt, nearestPtInd_succ, map_apply]
split_ifs with h
· rcases hk.eq_or_lt with (rfl | hk)
exacts [le_rfl, (h k (Nat.lt_succ_iff.1 hk)).le]
· push_neg at h
rcases h with ⟨l, hlN, hxl⟩
rcases hk.eq_or_lt with (rfl | hk)
exacts [(ihN hlN).trans hxl, ihN (Nat.lt_succ_iff.1 hk)]
theorem tendsto_nearestPt {e : ℕ → α} {x : α} (hx : x ∈ closure (range e)) :
Tendsto (fun N => nearestPt e N x) atTop (𝓝 x) := by
refine (atTop_basis.tendsto_iff nhds_basis_eball).2 fun ε hε => ?_
rcases EMetric.mem_closure_iff.1 hx ε hε with ⟨_, ⟨N, rfl⟩, hN⟩
rw [edist_comm] at hN
exact ⟨N, trivial, fun n hn => (edist_nearestPt_le e x hn).trans_lt hN⟩
variable [MeasurableSpace β] {f : β → α}
/-- Approximate a measurable function by a sequence of simple functions `F n` such that
`F n x ∈ s`. -/
noncomputable def approxOn (f : β → α) (hf : Measurable f) (s : Set α) (y₀ : α) (h₀ : y₀ ∈ s)
[SeparableSpace s] (n : ℕ) : β →ₛ α :=
haveI : Nonempty s := ⟨⟨y₀, h₀⟩⟩
comp (nearestPt (fun k => Nat.casesOn k y₀ ((↑) ∘ denseSeq s) : ℕ → α) n) f hf
@[simp]
theorem approxOn_zero {f : β → α} (hf : Measurable f) {s : Set α} {y₀ : α} (h₀ : y₀ ∈ s)
[SeparableSpace s] (x : β) : approxOn f hf s y₀ h₀ 0 x = y₀ :=
rfl
theorem approxOn_mem {f : β → α} (hf : Measurable f) {s : Set α} {y₀ : α} (h₀ : y₀ ∈ s)
[SeparableSpace s] (n : ℕ) (x : β) : approxOn f hf s y₀ h₀ n x ∈ s := by
haveI : Nonempty s := ⟨⟨y₀, h₀⟩⟩
suffices ∀ n, (Nat.casesOn n y₀ ((↑) ∘ denseSeq s) : α) ∈ s by apply this
rintro (_ | n)
exacts [h₀, Subtype.mem _]
lemma approxOn_range_nonneg [Zero α] [Preorder α] {f : β → α}
(hf : 0 ≤ f) {hfm : Measurable f} [SeparableSpace (range f ∪ {0} : Set α)] (n : ℕ) :
0 ≤ approxOn f hfm (range f ∪ {0}) 0 (by simp) n := by
have : range f ∪ {0} ⊆ Set.Ici 0 := by
simp only [Set.union_singleton, Set.insert_subset_iff, Set.mem_Ici, le_refl, true_and]
rintro - ⟨x, rfl⟩
exact hf x
exact fun _ ↦ this <| approxOn_mem ..
@[simp, nolint simpNF] -- Porting note: LHS doesn't simplify.
-- It seems the side conditions `hf` and `hg` are not applied by `simpNF`.
theorem approxOn_comp {γ : Type*} [MeasurableSpace γ] {f : β → α} (hf : Measurable f) {g : γ → β}
(hg : Measurable g) {s : Set α} {y₀ : α} (h₀ : y₀ ∈ s) [SeparableSpace s] (n : ℕ) :
approxOn (f ∘ g) (hf.comp hg) s y₀ h₀ n = (approxOn f hf s y₀ h₀ n).comp g hg :=
rfl
theorem tendsto_approxOn {f : β → α} (hf : Measurable f) {s : Set α} {y₀ : α} (h₀ : y₀ ∈ s)
[SeparableSpace s] {x : β} (hx : f x ∈ closure s) :
Tendsto (fun n => approxOn f hf s y₀ h₀ n x) atTop (𝓝 <| f x) := by
haveI : Nonempty s := ⟨⟨y₀, h₀⟩⟩
rw [← @Subtype.range_coe _ s, ← image_univ, ← (denseRange_denseSeq s).closure_eq] at hx
| simp -iota only [approxOn, coe_comp]
refine tendsto_nearestPt (closure_minimal ?_ isClosed_closure hx)
simp -iota only [Nat.range_casesOn, closure_union, range_comp]
exact
Subset.trans (image_closure_subset_closure_image continuous_subtype_val)
subset_union_right
theorem edist_approxOn_mono {f : β → α} (hf : Measurable f) {s : Set α} {y₀ : α} (h₀ : y₀ ∈ s)
[SeparableSpace s] (x : β) {m n : ℕ} (h : m ≤ n) :
edist (approxOn f hf s y₀ h₀ n x) (f x) ≤ edist (approxOn f hf s y₀ h₀ m x) (f x) := by
dsimp only [approxOn, coe_comp, Function.comp_def]
| Mathlib/MeasureTheory/Function/SimpleFuncDense.lean | 155 | 165 |
/-
Copyright (c) 2022 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers
-/
import Mathlib.Geometry.Euclidean.Angle.Oriented.Affine
import Mathlib.Geometry.Euclidean.Angle.Unoriented.RightAngle
/-!
# Oriented angles in right-angled triangles.
This file proves basic geometrical results about distances and oriented angles in (possibly
degenerate) right-angled triangles in real inner product spaces and Euclidean affine spaces.
-/
noncomputable section
open scoped EuclideanGeometry
open scoped Real
open scoped RealInnerProductSpace
namespace Orientation
open Module
variable {V : Type*} [NormedAddCommGroup V] [InnerProductSpace ℝ V]
variable [hd2 : Fact (finrank ℝ V = 2)] (o : Orientation ℝ V (Fin 2))
/-- An angle in a right-angled triangle expressed using `arccos`. -/
theorem oangle_add_right_eq_arccos_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle x (x + y) = Real.arccos (‖x‖ / ‖x + y‖) := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_add_eq_arccos_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arccos`. -/
theorem oangle_add_left_eq_arccos_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x + y) y = Real.arccos (‖y‖ / ‖x + y‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).oangle_add_right_eq_arccos_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arcsin`. -/
theorem oangle_add_right_eq_arcsin_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle x (x + y) = Real.arcsin (‖y‖ / ‖x + y‖) := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_add_eq_arcsin_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- An angle in a right-angled triangle expressed using `arcsin`. -/
theorem oangle_add_left_eq_arcsin_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x + y) y = Real.arcsin (‖x‖ / ‖x + y‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).oangle_add_right_eq_arcsin_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arctan`. -/
theorem oangle_add_right_eq_arctan_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle x (x + y) = Real.arctan (‖y‖ / ‖x‖) := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_add_eq_arctan_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h) (o.left_ne_zero_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arctan`. -/
theorem oangle_add_left_eq_arctan_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x + y) y = Real.arctan (‖x‖ / ‖y‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).oangle_add_right_eq_arctan_of_oangle_eq_pi_div_two h
/-- The cosine of an angle in a right-angled triangle as a ratio of sides. -/
theorem cos_oangle_add_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.cos (o.oangle x (x + y)) = ‖x‖ / ‖x + y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.cos_angle_add_of_inner_eq_zero (o.inner_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle as a ratio of sides. -/
theorem cos_oangle_add_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.cos (o.oangle (x + y) y) = ‖y‖ / ‖x + y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).cos_oangle_add_right_of_oangle_eq_pi_div_two h
/-- The sine of an angle in a right-angled triangle as a ratio of sides. -/
theorem sin_oangle_add_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.sin (o.oangle x (x + y)) = ‖y‖ / ‖x + y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.sin_angle_add_of_inner_eq_zero (o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- The sine of an angle in a right-angled triangle as a ratio of sides. -/
theorem sin_oangle_add_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.sin (o.oangle (x + y) y) = ‖x‖ / ‖x + y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).sin_oangle_add_right_of_oangle_eq_pi_div_two h
/-- The tangent of an angle in a right-angled triangle as a ratio of sides. -/
theorem tan_oangle_add_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.tan (o.oangle x (x + y)) = ‖y‖ / ‖x‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.tan_angle_add_of_inner_eq_zero (o.inner_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The tangent of an angle in a right-angled triangle as a ratio of sides. -/
theorem tan_oangle_add_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.tan (o.oangle (x + y) y) = ‖x‖ / ‖y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).tan_oangle_add_right_of_oangle_eq_pi_div_two h
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side. -/
theorem cos_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.cos (o.oangle x (x + y)) * ‖x + y‖ = ‖x‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.cos_angle_add_mul_norm_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side. -/
theorem cos_oangle_add_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.cos (o.oangle (x + y) y) * ‖x + y‖ = ‖y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).cos_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two h
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side. -/
theorem sin_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.sin (o.oangle x (x + y)) * ‖x + y‖ = ‖y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.sin_angle_add_mul_norm_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side. -/
theorem sin_oangle_add_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.sin (o.oangle (x + y) y) * ‖x + y‖ = ‖x‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).sin_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two h
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side. -/
theorem tan_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.tan (o.oangle x (x + y)) * ‖x‖ = ‖y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.tan_angle_add_mul_norm_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side. -/
theorem tan_oangle_add_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.tan (o.oangle (x + y) y) * ‖y‖ = ‖x‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).tan_oangle_add_right_mul_norm_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse. -/
theorem norm_div_cos_oangle_add_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.cos (o.oangle x (x + y)) = ‖x + y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.norm_div_cos_angle_add_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse. -/
theorem norm_div_cos_oangle_add_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.cos (o.oangle (x + y) y) = ‖x + y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).norm_div_cos_oangle_add_right_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the sine of the opposite angle equals the
hypotenuse. -/
theorem norm_div_sin_oangle_add_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.sin (o.oangle x (x + y)) = ‖x + y‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.norm_div_sin_angle_add_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inr (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the sine of the opposite angle equals the
hypotenuse. -/
theorem norm_div_sin_oangle_add_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.sin (o.oangle (x + y) y) = ‖x + y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).norm_div_sin_oangle_add_right_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the tangent of the opposite angle equals the
adjacent side. -/
theorem norm_div_tan_oangle_add_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.tan (o.oangle x (x + y)) = ‖x‖ := by
have hs : (o.oangle x (x + y)).sign = 1 := by
rw [oangle_sign_add_right, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.norm_div_tan_angle_add_of_inner_eq_zero
(o.inner_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inr (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the tangent of the opposite angle equals the
adjacent side. -/
theorem norm_div_tan_oangle_add_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.tan (o.oangle (x + y) y) = ‖y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
rw [add_comm]
exact (-o).norm_div_tan_oangle_add_right_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arccos`, version subtracting vectors. -/
theorem oangle_sub_right_eq_arccos_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle y (y - x) = Real.arccos (‖y‖ / ‖y - x‖) := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_sub_eq_arccos_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arccos`, version subtracting vectors. -/
theorem oangle_sub_left_eq_arccos_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x - y) x = Real.arccos (‖x‖ / ‖x - y‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).oangle_sub_right_eq_arccos_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arcsin`, version subtracting vectors. -/
theorem oangle_sub_right_eq_arcsin_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle y (y - x) = Real.arcsin (‖x‖ / ‖y - x‖) := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_sub_eq_arcsin_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- An angle in a right-angled triangle expressed using `arcsin`, version subtracting vectors. -/
theorem oangle_sub_left_eq_arcsin_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x - y) x = Real.arcsin (‖y‖ / ‖x - y‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).oangle_sub_right_eq_arcsin_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arctan`, version subtracting vectors. -/
theorem oangle_sub_right_eq_arctan_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle y (y - x) = Real.arctan (‖x‖ / ‖y‖) := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs,
InnerProductGeometry.angle_sub_eq_arctan_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h) (o.right_ne_zero_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arctan`, version subtracting vectors. -/
theorem oangle_sub_left_eq_arctan_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
o.oangle (x - y) x = Real.arctan (‖y‖ / ‖x‖) := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).oangle_sub_right_eq_arctan_of_oangle_eq_pi_div_two h
/-- The cosine of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem cos_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.cos (o.oangle y (y - x)) = ‖y‖ / ‖y - x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.cos_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem cos_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.cos (o.oangle (x - y) x) = ‖x‖ / ‖x - y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).cos_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- The sine of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem sin_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.sin (o.oangle y (y - x)) = ‖x‖ / ‖y - x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.sin_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- The sine of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem sin_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.sin (o.oangle (x - y) x) = ‖y‖ / ‖x - y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).sin_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- The tangent of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem tan_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.tan (o.oangle y (y - x)) = ‖x‖ / ‖y‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.tan_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The tangent of an angle in a right-angled triangle as a ratio of sides, version subtracting
vectors. -/
theorem tan_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = ↑(π / 2)) :
Real.Angle.tan (o.oangle (x - y) x) = ‖y‖ / ‖x‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).tan_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side, version subtracting vectors. -/
theorem cos_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.cos (o.oangle y (y - x)) * ‖y - x‖ = ‖y‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.cos_angle_sub_mul_norm_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side, version subtracting vectors. -/
theorem cos_oangle_sub_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.cos (o.oangle (x - y) x) * ‖x - y‖ = ‖x‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).cos_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two h
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side, version subtracting vectors. -/
theorem sin_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.sin (o.oangle y (y - x)) * ‖y - x‖ = ‖x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.sin_angle_sub_mul_norm_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)]
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side, version subtracting vectors. -/
theorem sin_oangle_sub_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.sin (o.oangle (x - y) x) * ‖x - y‖ = ‖y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).sin_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two h
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side, version subtracting vectors. -/
theorem tan_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.tan (o.oangle y (y - x)) * ‖y‖ = ‖x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.tan_angle_sub_mul_norm_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side, version subtracting vectors. -/
theorem tan_oangle_sub_left_mul_norm_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : Real.Angle.tan (o.oangle (x - y) x) * ‖x‖ = ‖y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).tan_oangle_sub_right_mul_norm_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse, version subtracting vectors. -/
theorem norm_div_cos_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.cos (o.oangle y (y - x)) = ‖y - x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
InnerProductGeometry.norm_div_cos_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inl (o.right_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse, version subtracting vectors. -/
theorem norm_div_cos_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.cos (o.oangle (x - y) x) = ‖x - y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).norm_div_cos_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the sine of the opposite angle equals the
hypotenuse, version subtracting vectors. -/
theorem norm_div_sin_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.sin (o.oangle y (y - x)) = ‖y - x‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
InnerProductGeometry.norm_div_sin_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inr (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the sine of the opposite angle equals the
hypotenuse, version subtracting vectors. -/
theorem norm_div_sin_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.sin (o.oangle (x - y) x) = ‖x - y‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).norm_div_sin_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- A side of a right-angled triangle divided by the tangent of the opposite angle equals the
adjacent side, version subtracting vectors. -/
theorem norm_div_tan_oangle_sub_right_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖x‖ / Real.Angle.tan (o.oangle y (y - x)) = ‖y‖ := by
have hs : (o.oangle y (y - x)).sign = 1 := by
rw [oangle_sign_sub_right_swap, h, Real.Angle.sign_coe_pi_div_two]
rw [o.oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
InnerProductGeometry.norm_div_tan_angle_sub_of_inner_eq_zero
(o.inner_rev_eq_zero_of_oangle_eq_pi_div_two h)
(Or.inr (o.left_ne_zero_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the tangent of the opposite angle equals the
adjacent side, version subtracting vectors. -/
theorem norm_div_tan_oangle_sub_left_of_oangle_eq_pi_div_two {x y : V}
(h : o.oangle x y = ↑(π / 2)) : ‖y‖ / Real.Angle.tan (o.oangle (x - y) x) = ‖x‖ := by
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj] at h ⊢
exact (-o).norm_div_tan_oangle_sub_right_of_oangle_eq_pi_div_two h
/-- An angle in a right-angled triangle expressed using `arctan`, where one side is a multiple
of a rotation of another by `π / 2`. -/
theorem oangle_add_right_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
o.oangle x (x + r • o.rotation (π / 2 : ℝ) x) = Real.arctan r := by
rcases lt_trichotomy r 0 with (hr | rfl | hr)
· have ha : o.oangle x (r • o.rotation (π / 2 : ℝ) x) = -(π / 2 : ℝ) := by
rw [o.oangle_smul_right_of_neg _ _ hr, o.oangle_neg_right h, o.oangle_rotation_self_right h, ←
sub_eq_zero, add_comm, sub_neg_eq_add, ← Real.Angle.coe_add, ← Real.Angle.coe_add,
add_assoc, add_halves, ← two_mul, Real.Angle.coe_two_pi]
simpa using h
-- Porting note: if the type is not given in `neg_neg` then Lean "forgets" about the instance
-- `Neg (Orientation ℝ V (Fin 2))`
rw [← neg_inj, ← oangle_neg_orientation_eq_neg, @neg_neg Real.Angle] at ha
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj, oangle_rev,
(-o).oangle_add_right_eq_arctan_of_oangle_eq_pi_div_two ha, norm_smul,
LinearIsometryEquiv.norm_map, mul_div_assoc, div_self (norm_ne_zero_iff.2 h), mul_one,
Real.norm_eq_abs, abs_of_neg hr, Real.arctan_neg, Real.Angle.coe_neg, neg_neg]
· rw [zero_smul, add_zero, oangle_self, Real.arctan_zero, Real.Angle.coe_zero]
· have ha : o.oangle x (r • o.rotation (π / 2 : ℝ) x) = (π / 2 : ℝ) := by
rw [o.oangle_smul_right_of_pos _ _ hr, o.oangle_rotation_self_right h]
rw [o.oangle_add_right_eq_arctan_of_oangle_eq_pi_div_two ha, norm_smul,
LinearIsometryEquiv.norm_map, mul_div_assoc, div_self (norm_ne_zero_iff.2 h), mul_one,
Real.norm_eq_abs, abs_of_pos hr]
/-- An angle in a right-angled triangle expressed using `arctan`, where one side is a multiple
of a rotation of another by `π / 2`. -/
theorem oangle_add_left_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
o.oangle (x + r • o.rotation (π / 2 : ℝ) x) (r • o.rotation (π / 2 : ℝ) x)
= Real.arctan r⁻¹ := by
by_cases hr : r = 0; · simp [hr]
rw [← neg_inj, oangle_rev, ← oangle_neg_orientation_eq_neg, neg_inj, ←
neg_neg ((π / 2 : ℝ) : Real.Angle), ← rotation_neg_orientation_eq_neg, add_comm]
have hx : x = r⁻¹ • (-o).rotation (π / 2 : ℝ) (r • (-o).rotation (-(π / 2 : ℝ)) x) := by simp [hr]
nth_rw 3 [hx]
refine (-o).oangle_add_right_smul_rotation_pi_div_two ?_ _
simp [hr, h]
/-- The tangent of an angle in a right-angled triangle, where one side is a multiple of a
rotation of another by `π / 2`. -/
theorem tan_oangle_add_right_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
Real.Angle.tan (o.oangle x (x + r • o.rotation (π / 2 : ℝ) x)) = r := by
rw [o.oangle_add_right_smul_rotation_pi_div_two h, Real.Angle.tan_coe, Real.tan_arctan]
/-- The tangent of an angle in a right-angled triangle, where one side is a multiple of a
rotation of another by `π / 2`. -/
theorem tan_oangle_add_left_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
Real.Angle.tan (o.oangle (x + r • o.rotation (π / 2 : ℝ) x) (r • o.rotation (π / 2 : ℝ) x)) =
r⁻¹ := by
rw [o.oangle_add_left_smul_rotation_pi_div_two h, Real.Angle.tan_coe, Real.tan_arctan]
/-- An angle in a right-angled triangle expressed using `arctan`, where one side is a multiple
of a rotation of another by `π / 2`, version subtracting vectors. -/
theorem oangle_sub_right_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
o.oangle (r • o.rotation (π / 2 : ℝ) x) (r • o.rotation (π / 2 : ℝ) x - x)
= Real.arctan r⁻¹ := by
by_cases hr : r = 0; · simp [hr]
have hx : -x = r⁻¹ • o.rotation (π / 2 : ℝ) (r • o.rotation (π / 2 : ℝ) x) := by
simp [hr, ← Real.Angle.coe_add]
rw [sub_eq_add_neg, hx, o.oangle_add_right_smul_rotation_pi_div_two]
simpa [hr] using h
/-- An angle in a right-angled triangle expressed using `arctan`, where one side is a multiple
of a rotation of another by `π / 2`, version subtracting vectors. -/
theorem oangle_sub_left_smul_rotation_pi_div_two {x : V} (h : x ≠ 0) (r : ℝ) :
o.oangle (x - r • o.rotation (π / 2 : ℝ) x) x = Real.arctan r := by
by_cases hr : r = 0; · simp [hr]
have hx : x = r⁻¹ • o.rotation (π / 2 : ℝ) (-(r • o.rotation (π / 2 : ℝ) x)) := by
simp [hr, ← Real.Angle.coe_add]
rw [sub_eq_add_neg, add_comm]
nth_rw 3 [hx]
nth_rw 2 [hx]
rw [o.oangle_add_left_smul_rotation_pi_div_two, inv_inv]
simpa [hr] using h
end Orientation
namespace EuclideanGeometry
open Module
variable {V : Type*} {P : Type*} [NormedAddCommGroup V] [InnerProductSpace ℝ V] [MetricSpace P]
[NormedAddTorsor V P] [hd2 : Fact (finrank ℝ V = 2)] [Module.Oriented ℝ V (Fin 2)]
/-- An angle in a right-angled triangle expressed using `arccos`. -/
theorem oangle_right_eq_arccos_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₂ p₃ p₁ = Real.arccos (dist p₃ p₂ / dist p₁ p₃) := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs,
angle_eq_arccos_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arccos`. -/
theorem oangle_left_eq_arccos_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₃ p₁ p₂ = Real.arccos (dist p₁ p₂ / dist p₁ p₃) := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm,
angle_eq_arccos_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h),
dist_comm p₁ p₃]
/-- An angle in a right-angled triangle expressed using `arcsin`. -/
theorem oangle_right_eq_arcsin_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₂ p₃ p₁ = Real.arcsin (dist p₁ p₂ / dist p₁ p₃) := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs,
angle_eq_arcsin_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inl (left_ne_of_oangle_eq_pi_div_two h))]
/-- An angle in a right-angled triangle expressed using `arcsin`. -/
theorem oangle_left_eq_arcsin_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₃ p₁ p₂ = Real.arcsin (dist p₃ p₂ / dist p₁ p₃) := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm,
angle_eq_arcsin_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inr (left_ne_of_oangle_eq_pi_div_two h)),
dist_comm p₁ p₃]
/-- An angle in a right-angled triangle expressed using `arctan`. -/
theorem oangle_right_eq_arctan_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₂ p₃ p₁ = Real.arctan (dist p₁ p₂ / dist p₃ p₂) := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs,
angle_eq_arctan_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(right_ne_of_oangle_eq_pi_div_two h)]
/-- An angle in a right-angled triangle expressed using `arctan`. -/
theorem oangle_left_eq_arctan_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
∡ p₃ p₁ p₂ = Real.arctan (dist p₃ p₂ / dist p₁ p₂) := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm,
angle_eq_arctan_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(left_ne_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle as a ratio of sides. -/
theorem cos_oangle_right_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.cos (∡ p₂ p₃ p₁) = dist p₃ p₂ / dist p₁ p₃ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
cos_angle_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle as a ratio of sides. -/
theorem cos_oangle_left_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.cos (∡ p₃ p₁ p₂) = dist p₁ p₂ / dist p₁ p₃ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.cos_coe,
cos_angle_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h),
dist_comm p₁ p₃]
/-- The sine of an angle in a right-angled triangle as a ratio of sides. -/
theorem sin_oangle_right_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.sin (∡ p₂ p₃ p₁) = dist p₁ p₂ / dist p₁ p₃ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
sin_angle_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inl (left_ne_of_oangle_eq_pi_div_two h))]
/-- The sine of an angle in a right-angled triangle as a ratio of sides. -/
theorem sin_oangle_left_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.sin (∡ p₃ p₁ p₂) = dist p₃ p₂ / dist p₁ p₃ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.sin_coe,
sin_angle_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inr (left_ne_of_oangle_eq_pi_div_two h)),
dist_comm p₁ p₃]
/-- The tangent of an angle in a right-angled triangle as a ratio of sides. -/
theorem tan_oangle_right_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.tan (∡ p₂ p₃ p₁) = dist p₁ p₂ / dist p₃ p₂ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
tan_angle_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The tangent of an angle in a right-angled triangle as a ratio of sides. -/
theorem tan_oangle_left_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P} (h : ∡ p₁ p₂ p₃ = ↑(π / 2)) :
Real.Angle.tan (∡ p₃ p₁ p₂) = dist p₃ p₂ / dist p₁ p₂ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.tan_coe,
tan_angle_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side. -/
theorem cos_oangle_right_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.cos (∡ p₂ p₃ p₁) * dist p₁ p₃ = dist p₃ p₂ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
cos_angle_mul_dist_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The cosine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
adjacent side. -/
theorem cos_oangle_left_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.cos (∡ p₃ p₁ p₂) * dist p₁ p₃ = dist p₁ p₂ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.cos_coe, dist_comm p₁ p₃,
cos_angle_mul_dist_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side. -/
theorem sin_oangle_right_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.sin (∡ p₂ p₃ p₁) * dist p₁ p₃ = dist p₁ p₂ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.sin_coe,
sin_angle_mul_dist_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The sine of an angle in a right-angled triangle multiplied by the hypotenuse equals the
opposite side. -/
theorem sin_oangle_left_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.sin (∡ p₃ p₁ p₂) * dist p₁ p₃ = dist p₃ p₂ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.sin_coe, dist_comm p₁ p₃,
sin_angle_mul_dist_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)]
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side. -/
theorem tan_oangle_right_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.tan (∡ p₂ p₃ p₁) * dist p₃ p₂ = dist p₁ p₂ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.tan_coe,
tan_angle_mul_dist_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inr (right_ne_of_oangle_eq_pi_div_two h))]
/-- The tangent of an angle in a right-angled triangle multiplied by the adjacent side equals
the opposite side. -/
theorem tan_oangle_left_mul_dist_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : Real.Angle.tan (∡ p₃ p₁ p₂) * dist p₁ p₂ = dist p₃ p₂ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.tan_coe,
tan_angle_mul_dist_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inr (left_ne_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse. -/
theorem dist_div_cos_oangle_right_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : dist p₃ p₂ / Real.Angle.cos (∡ p₂ p₃ p₁) = dist p₁ p₃ := by
have hs : (∡ p₂ p₃ p₁).sign = 1 := by rw [oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, Real.Angle.cos_coe,
dist_div_cos_angle_of_angle_eq_pi_div_two (angle_eq_pi_div_two_of_oangle_eq_pi_div_two h)
(Or.inr (right_ne_of_oangle_eq_pi_div_two h))]
/-- A side of a right-angled triangle divided by the cosine of the adjacent angle equals the
hypotenuse. -/
| theorem dist_div_cos_oangle_left_of_oangle_eq_pi_div_two {p₁ p₂ p₃ : P}
(h : ∡ p₁ p₂ p₃ = ↑(π / 2)) : dist p₁ p₂ / Real.Angle.cos (∡ p₃ p₁ p₂) = dist p₁ p₃ := by
have hs : (∡ p₃ p₁ p₂).sign = 1 := by rw [← oangle_rotate_sign, h, Real.Angle.sign_coe_pi_div_two]
rw [oangle_eq_angle_of_sign_eq_one hs, angle_comm, Real.Angle.cos_coe, dist_comm p₁ p₃,
dist_div_cos_angle_of_angle_eq_pi_div_two (angle_rev_eq_pi_div_two_of_oangle_eq_pi_div_two h)
| Mathlib/Geometry/Euclidean/Angle/Oriented/RightAngle.lean | 682 | 686 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Abhimanyu Pallavi Sudhir, Jean Lo, Calle Sönne
-/
import Mathlib.Analysis.SpecialFunctions.Exp
import Mathlib.Data.Nat.Factorization.Defs
import Mathlib.Analysis.NormedSpace.Real
import Mathlib.Data.Rat.Cast.CharZero
/-!
# Real logarithm
In this file we define `Real.log` to be the logarithm of a real number. As usual, we extend it from
its domain `(0, +∞)` to a globally defined function. We choose to do it so that `log 0 = 0` and
`log (-x) = log x`.
We prove some basic properties of this function and show that it is continuous.
## Tags
logarithm, continuity
-/
open Set Filter Function
open Topology
noncomputable section
namespace Real
variable {x y : ℝ}
/-- The real logarithm function, equal to the inverse of the exponential for `x > 0`,
to `log |x|` for `x < 0`, and to `0` for `0`. We use this unconventional extension to
`(-∞, 0]` as it gives the formula `log (x * y) = log x + log y` for all nonzero `x` and `y`, and
the derivative of `log` is `1/x` away from `0`. -/
@[pp_nodot]
noncomputable def log (x : ℝ) : ℝ :=
if hx : x = 0 then 0 else expOrderIso.symm ⟨|x|, abs_pos.2 hx⟩
theorem log_of_ne_zero (hx : x ≠ 0) : log x = expOrderIso.symm ⟨|x|, abs_pos.2 hx⟩ :=
dif_neg hx
theorem log_of_pos (hx : 0 < x) : log x = expOrderIso.symm ⟨x, hx⟩ := by
rw [log_of_ne_zero hx.ne']
congr
exact abs_of_pos hx
theorem exp_log_eq_abs (hx : x ≠ 0) : exp (log x) = |x| := by
rw [log_of_ne_zero hx, ← coe_expOrderIso_apply, OrderIso.apply_symm_apply, Subtype.coe_mk]
theorem exp_log (hx : 0 < x) : exp (log x) = x := by
rw [exp_log_eq_abs hx.ne']
exact abs_of_pos hx
theorem exp_log_of_neg (hx : x < 0) : exp (log x) = -x := by
rw [exp_log_eq_abs (ne_of_lt hx)]
exact abs_of_neg hx
theorem le_exp_log (x : ℝ) : x ≤ exp (log x) := by
by_cases h_zero : x = 0
· rw [h_zero, log, dif_pos rfl, exp_zero]
exact zero_le_one
· rw [exp_log_eq_abs h_zero]
exact le_abs_self _
@[simp]
theorem log_exp (x : ℝ) : log (exp x) = x :=
exp_injective <| exp_log (exp_pos x)
theorem exp_one_mul_le_exp {x : ℝ} : exp 1 * x ≤ exp x := by
by_cases hx0 : x ≤ 0
· apply le_trans (mul_nonpos_of_nonneg_of_nonpos (exp_pos 1).le hx0) (exp_nonneg x)
· have h := add_one_le_exp (log x)
rwa [← exp_le_exp, exp_add, exp_log (lt_of_not_le hx0), mul_comm] at h
theorem two_mul_le_exp {x : ℝ} : 2 * x ≤ exp x := by
by_cases hx0 : x < 0
· exact le_trans (mul_nonpos_of_nonneg_of_nonpos (by simp only [Nat.ofNat_nonneg]) hx0.le)
(exp_nonneg x)
· apply le_trans (mul_le_mul_of_nonneg_right _ (le_of_not_lt hx0)) exp_one_mul_le_exp
have := Real.add_one_le_exp 1
rwa [one_add_one_eq_two] at this
theorem surjOn_log : SurjOn log (Ioi 0) univ := fun x _ => ⟨exp x, exp_pos x, log_exp x⟩
theorem log_surjective : Surjective log := fun x => ⟨exp x, log_exp x⟩
@[simp]
theorem range_log : range log = univ :=
log_surjective.range_eq
@[simp]
theorem log_zero : log 0 = 0 :=
dif_pos rfl
@[simp]
theorem log_one : log 1 = 0 :=
exp_injective <| by rw [exp_log zero_lt_one, exp_zero]
/-- This holds true for all `x : ℝ` because of the junk values `0 / 0 = 0` and `log 0 = 0`. -/
@[simp] lemma log_div_self (x : ℝ) : log (x / x) = 0 := by
obtain rfl | hx := eq_or_ne x 0 <;> simp [*]
@[simp]
theorem log_abs (x : ℝ) : log |x| = log x := by
by_cases h : x = 0
· simp [h]
| · rw [← exp_eq_exp, exp_log_eq_abs h, exp_log_eq_abs (abs_pos.2 h).ne', abs_abs]
| Mathlib/Analysis/SpecialFunctions/Log/Basic.lean | 111 | 111 |
/-
Copyright (c) 2019 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Data.Bundle
import Mathlib.Data.Set.Image
import Mathlib.Topology.CompactOpen
import Mathlib.Topology.PartialHomeomorph
import Mathlib.Topology.Order.Basic
/-!
# Trivializations
## Main definitions
### Basic definitions
* `Trivialization F p` : structure extending partial homeomorphisms, defining a local
trivialization of a topological space `Z` with projection `p` and fiber `F`.
* `Pretrivialization F proj` : trivialization as a partial equivalence, mainly used when the
topology on the total space has not yet been defined.
### Operations on bundles
We provide the following operations on `Trivialization`s.
* `Trivialization.compHomeomorph`: given a local trivialization `e` of a fiber bundle
`p : Z → B` and a homeomorphism `h : Z' ≃ₜ Z`, returns a local trivialization of the fiber bundle
`p ∘ h`.
## Implementation notes
Previously, in mathlib, there was a structure `topological_vector_bundle.trivialization` which
extended another structure `topological_fiber_bundle.trivialization` by a linearity hypothesis. As
of PR https://github.com/leanprover-community/mathlib3/pull/17359, we have changed this to a single structure
`Trivialization` (no namespace), together with a mixin class `Trivialization.IsLinear`.
This permits all the *data* of a vector bundle to be held at the level of fiber bundles, so that the
same trivializations can underlie an object's structure as (say) a vector bundle over `ℂ` and as a
vector bundle over `ℝ`, as well as its structure simply as a fiber bundle.
This might be a little surprising, given the general trend of the library to ever-increased
bundling. But in this case the typical motivation for more bundling does not apply: there is no
algebraic or order structure on the whole type of linear (say) trivializations of a bundle.
Indeed, since trivializations only have meaning on their base sets (taking junk values outside), the
type of linear trivializations is not even particularly well-behaved.
-/
open TopologicalSpace Filter Set Bundle Function
open scoped Topology
variable {B : Type*} (F : Type*) {E : B → Type*}
variable {Z : Type*} [TopologicalSpace B] [TopologicalSpace F] {proj : Z → B}
/-- This structure contains the information left for a local trivialization (which is implemented
below as `Trivialization F proj`) if the total space has not been given a topology, but we
have a topology on both the fiber and the base space. Through the construction
`topological_fiber_prebundle F proj` it will be possible to promote a
`Pretrivialization F proj` to a `Trivialization F proj`. -/
structure Pretrivialization (proj : Z → B) extends PartialEquiv Z (B × F) where
open_target : IsOpen target
baseSet : Set B
open_baseSet : IsOpen baseSet
source_eq : source = proj ⁻¹' baseSet
target_eq : target = baseSet ×ˢ univ
proj_toFun : ∀ p ∈ source, (toFun p).1 = proj p
namespace Pretrivialization
variable {F}
variable (e : Pretrivialization F proj) {x : Z}
/-- Coercion of a pretrivialization to a function. We don't use `e.toFun` in the `CoeFun` instance
because it is actually `e.toPartialEquiv.toFun`, so `simp` will apply lemmas about
`toPartialEquiv`. While we may want to switch to this behavior later, doing it mid-port will break a
lot of proofs. -/
@[coe] def toFun' : Z → (B × F) := e.toFun
instance : CoeFun (Pretrivialization F proj) fun _ => Z → B × F := ⟨toFun'⟩
@[ext]
lemma ext' (e e' : Pretrivialization F proj) (h₁ : e.toPartialEquiv = e'.toPartialEquiv)
(h₂ : e.baseSet = e'.baseSet) : e = e' := by
cases e; cases e'; congr
-- TODO: move `ext` here?
lemma ext {e e' : Pretrivialization F proj} (h₁ : ∀ x, e x = e' x)
(h₂ : ∀ x, e.toPartialEquiv.symm x = e'.toPartialEquiv.symm x) (h₃ : e.baseSet = e'.baseSet) :
e = e' := by
ext1 <;> [ext1; exact h₃]
· apply h₁
· apply h₂
· rw [e.source_eq, e'.source_eq, h₃]
/-- If the fiber is nonempty, then the projection also is. -/
lemma toPartialEquiv_injective [Nonempty F] :
Injective (toPartialEquiv : Pretrivialization F proj → PartialEquiv Z (B × F)) := by
refine fun e e' h ↦ ext' _ _ h ?_
simpa only [fst_image_prod, univ_nonempty, target_eq]
using congr_arg (Prod.fst '' PartialEquiv.target ·) h
@[simp, mfld_simps]
theorem coe_coe : ⇑e.toPartialEquiv = e :=
rfl
@[simp, mfld_simps]
theorem coe_fst (ex : x ∈ e.source) : (e x).1 = proj x :=
e.proj_toFun x ex
theorem mem_source : x ∈ e.source ↔ proj x ∈ e.baseSet := by rw [e.source_eq, mem_preimage]
theorem coe_fst' (ex : proj x ∈ e.baseSet) : (e x).1 = proj x :=
e.coe_fst (e.mem_source.2 ex)
protected theorem eqOn : EqOn (Prod.fst ∘ e) proj e.source := fun _ hx => e.coe_fst hx
theorem mk_proj_snd (ex : x ∈ e.source) : (proj x, (e x).2) = e x :=
Prod.ext (e.coe_fst ex).symm rfl
theorem mk_proj_snd' (ex : proj x ∈ e.baseSet) : (proj x, (e x).2) = e x :=
Prod.ext (e.coe_fst' ex).symm rfl
/-- Composition of inverse and coercion from the subtype of the target. -/
def setSymm : e.target → Z :=
e.target.restrict e.toPartialEquiv.symm
theorem mem_target {x : B × F} : x ∈ e.target ↔ x.1 ∈ e.baseSet := by
rw [e.target_eq, prod_univ, mem_preimage]
theorem proj_symm_apply {x : B × F} (hx : x ∈ e.target) : proj (e.toPartialEquiv.symm x) = x.1 := by
have := (e.coe_fst (e.map_target hx)).symm
rwa [← e.coe_coe, e.right_inv hx] at this
theorem proj_symm_apply' {b : B} {x : F} (hx : b ∈ e.baseSet) :
proj (e.toPartialEquiv.symm (b, x)) = b :=
e.proj_symm_apply (e.mem_target.2 hx)
theorem proj_surjOn_baseSet [Nonempty F] : Set.SurjOn proj e.source e.baseSet := fun b hb =>
let ⟨y⟩ := ‹Nonempty F›
⟨e.toPartialEquiv.symm (b, y), e.toPartialEquiv.map_target <| e.mem_target.2 hb,
e.proj_symm_apply' hb⟩
theorem apply_symm_apply {x : B × F} (hx : x ∈ e.target) : e (e.toPartialEquiv.symm x) = x :=
e.toPartialEquiv.right_inv hx
theorem apply_symm_apply' {b : B} {x : F} (hx : b ∈ e.baseSet) :
e (e.toPartialEquiv.symm (b, x)) = (b, x) :=
e.apply_symm_apply (e.mem_target.2 hx)
theorem symm_apply_apply {x : Z} (hx : x ∈ e.source) : e.toPartialEquiv.symm (e x) = x :=
e.toPartialEquiv.left_inv hx
@[simp, mfld_simps]
theorem symm_apply_mk_proj {x : Z} (ex : x ∈ e.source) :
e.toPartialEquiv.symm (proj x, (e x).2) = x := by
rw [← e.coe_fst ex, ← e.coe_coe, e.left_inv ex]
@[simp, mfld_simps]
theorem preimage_symm_proj_baseSet :
e.toPartialEquiv.symm ⁻¹' (proj ⁻¹' e.baseSet) ∩ e.target = e.target := by
refine inter_eq_right.mpr fun x hx => ?_
simp only [mem_preimage, PartialEquiv.invFun_as_coe, e.proj_symm_apply hx]
exact e.mem_target.mp hx
@[simp, mfld_simps]
theorem preimage_symm_proj_inter (s : Set B) :
e.toPartialEquiv.symm ⁻¹' (proj ⁻¹' s) ∩ e.baseSet ×ˢ univ = (s ∩ e.baseSet) ×ˢ univ := by
ext ⟨x, y⟩
suffices x ∈ e.baseSet → (proj (e.toPartialEquiv.symm (x, y)) ∈ s ↔ x ∈ s) by
simpa only [prodMk_mem_set_prod_eq, mem_inter_iff, and_true, mem_univ, and_congr_left_iff]
intro h
rw [e.proj_symm_apply' h]
theorem target_inter_preimage_symm_source_eq (e f : Pretrivialization F proj) :
f.target ∩ f.toPartialEquiv.symm ⁻¹' e.source = (e.baseSet ∩ f.baseSet) ×ˢ univ := by
rw [inter_comm, f.target_eq, e.source_eq, f.preimage_symm_proj_inter]
theorem trans_source (e f : Pretrivialization F proj) :
(f.toPartialEquiv.symm.trans e.toPartialEquiv).source = (e.baseSet ∩ f.baseSet) ×ˢ univ := by
rw [PartialEquiv.trans_source, PartialEquiv.symm_source, e.target_inter_preimage_symm_source_eq]
theorem symm_trans_symm (e e' : Pretrivialization F proj) :
(e.toPartialEquiv.symm.trans e'.toPartialEquiv).symm
= e'.toPartialEquiv.symm.trans e.toPartialEquiv := by
rw [PartialEquiv.trans_symm_eq_symm_trans_symm, PartialEquiv.symm_symm]
theorem symm_trans_source_eq (e e' : Pretrivialization F proj) :
(e.toPartialEquiv.symm.trans e'.toPartialEquiv).source = (e.baseSet ∩ e'.baseSet) ×ˢ univ := by
rw [PartialEquiv.trans_source, e'.source_eq, PartialEquiv.symm_source, e.target_eq, inter_comm,
e.preimage_symm_proj_inter, inter_comm]
theorem symm_trans_target_eq (e e' : Pretrivialization F proj) :
(e.toPartialEquiv.symm.trans e'.toPartialEquiv).target = (e.baseSet ∩ e'.baseSet) ×ˢ univ := by
rw [← PartialEquiv.symm_source, symm_trans_symm, symm_trans_source_eq, inter_comm]
variable (e' : Pretrivialization F (π F E)) {b : B} {y : E b}
@[simp]
theorem coe_mem_source : ↑y ∈ e'.source ↔ b ∈ e'.baseSet :=
e'.mem_source
@[simp, mfld_simps]
theorem coe_coe_fst (hb : b ∈ e'.baseSet) : (e' y).1 = b :=
e'.coe_fst (e'.mem_source.2 hb)
theorem mk_mem_target {x : B} {y : F} : (x, y) ∈ e'.target ↔ x ∈ e'.baseSet :=
e'.mem_target
theorem symm_coe_proj {x : B} {y : F} (e' : Pretrivialization F (π F E)) (h : x ∈ e'.baseSet) :
(e'.toPartialEquiv.symm (x, y)).1 = x :=
e'.proj_symm_apply' h
section Zero
variable [∀ x, Zero (E x)]
open Classical in
/-- A fiberwise inverse to `e`. This is the function `F → E b` that induces a local inverse
`B × F → TotalSpace F E` of `e` on `e.baseSet`. It is defined to be `0` outside `e.baseSet`. -/
protected noncomputable def symm (e : Pretrivialization F (π F E)) (b : B) (y : F) : E b :=
if hb : b ∈ e.baseSet then
cast (congr_arg E (e.proj_symm_apply' hb)) (e.toPartialEquiv.symm (b, y)).2
else 0
theorem symm_apply (e : Pretrivialization F (π F E)) {b : B} (hb : b ∈ e.baseSet) (y : F) :
e.symm b y = cast (congr_arg E (e.symm_coe_proj hb)) (e.toPartialEquiv.symm (b, y)).2 :=
dif_pos hb
theorem symm_apply_of_not_mem (e : Pretrivialization F (π F E)) {b : B} (hb : b ∉ e.baseSet)
(y : F) : e.symm b y = 0 :=
dif_neg hb
theorem coe_symm_of_not_mem (e : Pretrivialization F (π F E)) {b : B} (hb : b ∉ e.baseSet) :
(e.symm b : F → E b) = 0 :=
funext fun _ => dif_neg hb
theorem mk_symm (e : Pretrivialization F (π F E)) {b : B} (hb : b ∈ e.baseSet) (y : F) :
TotalSpace.mk b (e.symm b y) = e.toPartialEquiv.symm (b, y) := by
simp only [e.symm_apply hb, TotalSpace.mk_cast (e.proj_symm_apply' hb), TotalSpace.eta]
theorem symm_proj_apply (e : Pretrivialization F (π F E)) (z : TotalSpace F E)
(hz : z.proj ∈ e.baseSet) : e.symm z.proj (e z).2 = z.2 := by
rw [e.symm_apply hz, cast_eq_iff_heq, e.mk_proj_snd' hz, e.symm_apply_apply (e.mem_source.mpr hz)]
theorem symm_apply_apply_mk (e : Pretrivialization F (π F E)) {b : B} (hb : b ∈ e.baseSet)
(y : E b) : e.symm b (e ⟨b, y⟩).2 = y :=
e.symm_proj_apply ⟨b, y⟩ hb
theorem apply_mk_symm (e : Pretrivialization F (π F E)) {b : B} (hb : b ∈ e.baseSet) (y : F) :
e ⟨b, e.symm b y⟩ = (b, y) := by
rw [e.mk_symm hb, e.apply_symm_apply (e.mk_mem_target.mpr hb)]
end Zero
end Pretrivialization
variable [TopologicalSpace Z] [TopologicalSpace (TotalSpace F E)]
/-- A structure extending partial homeomorphisms, defining a local trivialization of a projection
`proj : Z → B` with fiber `F`, as a partial homeomorphism between `Z` and `B × F` defined between
two sets of the form `proj ⁻¹' baseSet` and `baseSet × F`, acting trivially on the first coordinate.
-/
structure Trivialization (proj : Z → B) extends PartialHomeomorph Z (B × F) where
baseSet : Set B
open_baseSet : IsOpen baseSet
source_eq : source = proj ⁻¹' baseSet
target_eq : target = baseSet ×ˢ univ
proj_toFun : ∀ p ∈ source, (toPartialHomeomorph p).1 = proj p
namespace Trivialization
variable {F}
variable (e : Trivialization F proj) {x : Z}
@[ext]
lemma ext' (e e' : Trivialization F proj) (h₁ : e.toPartialHomeomorph = e'.toPartialHomeomorph)
(h₂ : e.baseSet = e'.baseSet) : e = e' := by
cases e; cases e'; congr
/-- Coercion of a trivialization to a function. We don't use `e.toFun` in the `CoeFun` instance
because it is actually `e.toPartialEquiv.toFun`, so `simp` will apply lemmas about
`toPartialEquiv`. While we may want to switch to this behavior later, doing it mid-port will break a
lot of proofs. -/
@[coe] def toFun' : Z → (B × F) := e.toFun
/-- Natural identification as a `Pretrivialization`. -/
def toPretrivialization : Pretrivialization F proj :=
{ e with }
instance : CoeFun (Trivialization F proj) fun _ => Z → B × F := ⟨toFun'⟩
instance : Coe (Trivialization F proj) (Pretrivialization F proj) :=
⟨toPretrivialization⟩
theorem toPretrivialization_injective :
Function.Injective fun e : Trivialization F proj => e.toPretrivialization := fun e e' h => by
ext1
exacts [PartialHomeomorph.toPartialEquiv_injective (congr_arg Pretrivialization.toPartialEquiv h),
congr_arg Pretrivialization.baseSet h]
@[simp, mfld_simps]
theorem coe_coe : ⇑e.toPartialHomeomorph = e :=
rfl
@[simp, mfld_simps]
theorem coe_fst (ex : x ∈ e.source) : (e x).1 = proj x :=
e.proj_toFun x ex
protected theorem eqOn : EqOn (Prod.fst ∘ e) proj e.source := fun _x hx => e.coe_fst hx
theorem mem_source : x ∈ e.source ↔ proj x ∈ e.baseSet := by rw [e.source_eq, mem_preimage]
theorem coe_fst' (ex : proj x ∈ e.baseSet) : (e x).1 = proj x :=
e.coe_fst (e.mem_source.2 ex)
theorem mk_proj_snd (ex : x ∈ e.source) : (proj x, (e x).2) = e x :=
Prod.ext (e.coe_fst ex).symm rfl
theorem mk_proj_snd' (ex : proj x ∈ e.baseSet) : (proj x, (e x).2) = e x :=
Prod.ext (e.coe_fst' ex).symm rfl
theorem source_inter_preimage_target_inter (s : Set (B × F)) :
e.source ∩ e ⁻¹' (e.target ∩ s) = e.source ∩ e ⁻¹' s :=
e.toPartialHomeomorph.source_inter_preimage_target_inter s
@[simp, mfld_simps]
theorem coe_mk (e : PartialHomeomorph Z (B × F)) (i j k l m) (x : Z) :
(Trivialization.mk e i j k l m : Trivialization F proj) x = e x :=
rfl
theorem mem_target {x : B × F} : x ∈ e.target ↔ x.1 ∈ e.baseSet :=
e.toPretrivialization.mem_target
theorem map_target {x : B × F} (hx : x ∈ e.target) : e.toPartialHomeomorph.symm x ∈ e.source :=
e.toPartialHomeomorph.map_target hx
theorem proj_symm_apply {x : B × F} (hx : x ∈ e.target) :
proj (e.toPartialHomeomorph.symm x) = x.1 :=
e.toPretrivialization.proj_symm_apply hx
theorem proj_symm_apply' {b : B} {x : F} (hx : b ∈ e.baseSet) :
proj (e.toPartialHomeomorph.symm (b, x)) = b :=
e.toPretrivialization.proj_symm_apply' hx
theorem proj_surjOn_baseSet [Nonempty F] : Set.SurjOn proj e.source e.baseSet :=
e.toPretrivialization.proj_surjOn_baseSet
theorem apply_symm_apply {x : B × F} (hx : x ∈ e.target) : e (e.toPartialHomeomorph.symm x) = x :=
e.toPartialHomeomorph.right_inv hx
theorem apply_symm_apply' {b : B} {x : F} (hx : b ∈ e.baseSet) :
e (e.toPartialHomeomorph.symm (b, x)) = (b, x) :=
e.toPretrivialization.apply_symm_apply' hx
@[simp, mfld_simps]
theorem symm_apply_mk_proj (ex : x ∈ e.source) : e.toPartialHomeomorph.symm (proj x, (e x).2) = x :=
e.toPretrivialization.symm_apply_mk_proj ex
theorem symm_trans_source_eq (e e' : Trivialization F proj) :
(e.toPartialEquiv.symm.trans e'.toPartialEquiv).source = (e.baseSet ∩ e'.baseSet) ×ˢ univ :=
Pretrivialization.symm_trans_source_eq e.toPretrivialization e'
theorem symm_trans_target_eq (e e' : Trivialization F proj) :
(e.toPartialEquiv.symm.trans e'.toPartialEquiv).target = (e.baseSet ∩ e'.baseSet) ×ˢ univ :=
Pretrivialization.symm_trans_target_eq e.toPretrivialization e'
theorem coe_fst_eventuallyEq_proj (ex : x ∈ e.source) : Prod.fst ∘ e =ᶠ[𝓝 x] proj :=
mem_nhds_iff.2 ⟨e.source, fun _y hy => e.coe_fst hy, e.open_source, ex⟩
theorem coe_fst_eventuallyEq_proj' (ex : proj x ∈ e.baseSet) : Prod.fst ∘ e =ᶠ[𝓝 x] proj :=
e.coe_fst_eventuallyEq_proj (e.mem_source.2 ex)
theorem map_proj_nhds (ex : x ∈ e.source) : map proj (𝓝 x) = 𝓝 (proj x) := by
rw [← e.coe_fst ex, ← map_congr (e.coe_fst_eventuallyEq_proj ex), ← map_map, ← e.coe_coe,
e.map_nhds_eq ex, map_fst_nhds]
theorem preimage_subset_source {s : Set B} (hb : s ⊆ e.baseSet) : proj ⁻¹' s ⊆ e.source :=
fun _p hp => e.mem_source.mpr (hb hp)
theorem image_preimage_eq_prod_univ {s : Set B} (hb : s ⊆ e.baseSet) :
e '' (proj ⁻¹' s) = s ×ˢ univ :=
Subset.antisymm
(image_subset_iff.mpr fun p hp =>
⟨(e.proj_toFun p (e.preimage_subset_source hb hp)).symm ▸ hp, trivial⟩)
fun p hp =>
let hp' : p ∈ e.target := e.mem_target.mpr (hb hp.1)
⟨e.invFun p, mem_preimage.mpr ((e.proj_symm_apply hp').symm ▸ hp.1), e.apply_symm_apply hp'⟩
theorem tendsto_nhds_iff {α : Type*} {l : Filter α} {f : α → Z} {z : Z} (hz : z ∈ e.source) :
Tendsto f l (𝓝 z) ↔
Tendsto (proj ∘ f) l (𝓝 (proj z)) ∧ Tendsto (fun x ↦ (e (f x)).2) l (𝓝 (e z).2) := by
rw [e.nhds_eq_comap_inf_principal hz, tendsto_inf, tendsto_comap_iff, Prod.tendsto_iff, coe_coe,
tendsto_principal, coe_fst _ hz]
by_cases hl : ∀ᶠ x in l, f x ∈ e.source
· simp only [hl, and_true]
refine (tendsto_congr' ?_).and Iff.rfl
exact hl.mono fun x ↦ e.coe_fst
· simp only [hl, and_false, false_iff, not_and]
rw [e.source_eq] at hl hz
exact fun h _ ↦ hl <| h <| e.open_baseSet.mem_nhds hz
theorem nhds_eq_inf_comap {z : Z} (hz : z ∈ e.source) :
𝓝 z = comap proj (𝓝 (proj z)) ⊓ comap (Prod.snd ∘ e) (𝓝 (e z).2) := by
refine eq_of_forall_le_iff fun l ↦ ?_
rw [le_inf_iff, ← tendsto_iff_comap, ← tendsto_iff_comap]
exact e.tendsto_nhds_iff hz
/-- The preimage of a subset of the base set is homeomorphic to the product with the fiber. -/
def preimageHomeomorph {s : Set B} (hb : s ⊆ e.baseSet) : proj ⁻¹' s ≃ₜ s × F :=
(e.toPartialHomeomorph.homeomorphOfImageSubsetSource (e.preimage_subset_source hb)
(e.image_preimage_eq_prod_univ hb)).trans
((Homeomorph.Set.prod s univ).trans ((Homeomorph.refl s).prodCongr (Homeomorph.Set.univ F)))
@[simp]
theorem preimageHomeomorph_apply {s : Set B} (hb : s ⊆ e.baseSet) (p : proj ⁻¹' s) :
e.preimageHomeomorph hb p = (⟨proj p, p.2⟩, (e p).2) :=
Prod.ext (Subtype.ext (e.proj_toFun p (e.mem_source.mpr (hb p.2)))) rfl
/-- Auxiliary definition to avoid looping in `dsimp`
with `Trivialization.preimageHomeomorph_symm_apply`. -/
protected def preimageHomeomorph_symm_apply.aux {s : Set B} (hb : s ⊆ e.baseSet) :=
(e.preimageHomeomorph hb).symm
@[simp]
theorem preimageHomeomorph_symm_apply {s : Set B} (hb : s ⊆ e.baseSet) (p : s × F) :
(e.preimageHomeomorph hb).symm p =
⟨e.symm (p.1, p.2), ((preimageHomeomorph_symm_apply.aux e hb) p).2⟩ :=
rfl
/-- The source is homeomorphic to the product of the base set with the fiber. -/
def sourceHomeomorphBaseSetProd : e.source ≃ₜ e.baseSet × F :=
(Homeomorph.setCongr e.source_eq).trans (e.preimageHomeomorph subset_rfl)
@[simp]
theorem sourceHomeomorphBaseSetProd_apply (p : e.source) :
e.sourceHomeomorphBaseSetProd p = (⟨proj p, e.mem_source.mp p.2⟩, (e p).2) :=
e.preimageHomeomorph_apply subset_rfl ⟨p, e.mem_source.mp p.2⟩
/-- Auxiliary definition to avoid looping in `dsimp`
with `Trivialization.sourceHomeomorphBaseSetProd_symm_apply`. -/
protected def sourceHomeomorphBaseSetProd_symm_apply.aux := e.sourceHomeomorphBaseSetProd.symm
@[simp]
theorem sourceHomeomorphBaseSetProd_symm_apply (p : e.baseSet × F) :
e.sourceHomeomorphBaseSetProd.symm p =
⟨e.symm (p.1, p.2), (sourceHomeomorphBaseSetProd_symm_apply.aux e p).2⟩ :=
rfl
/-- Each fiber of a trivialization is homeomorphic to the specified fiber. -/
def preimageSingletonHomeomorph {b : B} (hb : b ∈ e.baseSet) : proj ⁻¹' {b} ≃ₜ F :=
.trans (e.preimageHomeomorph (Set.singleton_subset_iff.mpr hb)) <|
.trans (.prodCongr (Homeomorph.homeomorphOfUnique ({b} : Set B) PUnit.{1}) (Homeomorph.refl F))
(Homeomorph.punitProd F)
@[simp]
theorem preimageSingletonHomeomorph_apply {b : B} (hb : b ∈ e.baseSet) (p : proj ⁻¹' {b}) :
e.preimageSingletonHomeomorph hb p = (e p).2 :=
rfl
@[simp]
theorem preimageSingletonHomeomorph_symm_apply {b : B} (hb : b ∈ e.baseSet) (p : F) :
(e.preimageSingletonHomeomorph hb).symm p =
⟨e.symm (b, p), by rw [mem_preimage, e.proj_symm_apply' hb, mem_singleton_iff]⟩ :=
rfl
/-- In the domain of a bundle trivialization, the projection is continuous -/
theorem continuousAt_proj (ex : x ∈ e.source) : ContinuousAt proj x :=
(e.map_proj_nhds ex).le
|
/-- Composition of a `Trivialization` and a `Homeomorph`. -/
protected def compHomeomorph {Z' : Type*} [TopologicalSpace Z'] (h : Z' ≃ₜ Z) :
Trivialization F (proj ∘ h) where
toPartialHomeomorph := h.toPartialHomeomorph.trans e.toPartialHomeomorph
| Mathlib/Topology/FiberBundle/Trivialization.lean | 471 | 475 |
/-
Copyright (c) 2019 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Analysis.SpecificLimits.Basic
import Mathlib.Topology.MetricSpace.IsometricSMul
/-!
# Hausdorff distance
The Hausdorff distance on subsets of a metric (or emetric) space.
Given two subsets `s` and `t` of a metric space, their Hausdorff distance is the smallest `d`
such that any point `s` is within `d` of a point in `t`, and conversely. This quantity
is often infinite (think of `s` bounded and `t` unbounded), and therefore better
expressed in the setting of emetric spaces.
## Main definitions
This files introduces:
* `EMetric.infEdist x s`, the infimum edistance of a point `x` to a set `s` in an emetric space
* `EMetric.hausdorffEdist s t`, the Hausdorff edistance of two sets in an emetric space
* Versions of these notions on metric spaces, called respectively `Metric.infDist`
and `Metric.hausdorffDist`
## Main results
* `infEdist_closure`: the edistance to a set and its closure coincide
* `EMetric.mem_closure_iff_infEdist_zero`: a point `x` belongs to the closure of `s` iff
`infEdist x s = 0`
* `IsCompact.exists_infEdist_eq_edist`: if `s` is compact and non-empty, there exists a point `y`
which attains this edistance
* `IsOpen.exists_iUnion_isClosed`: every open set `U` can be written as the increasing union
of countably many closed subsets of `U`
* `hausdorffEdist_closure`: replacing a set by its closure does not change the Hausdorff edistance
* `hausdorffEdist_zero_iff_closure_eq_closure`: two sets have Hausdorff edistance zero
iff their closures coincide
* the Hausdorff edistance is symmetric and satisfies the triangle inequality
* in particular, closed sets in an emetric space are an emetric space
(this is shown in `EMetricSpace.closeds.emetricspace`)
* versions of these notions on metric spaces
* `hausdorffEdist_ne_top_of_nonempty_of_bounded`: if two sets in a metric space
are nonempty and bounded in a metric space, they are at finite Hausdorff edistance.
## Tags
metric space, Hausdorff distance
-/
noncomputable section
open NNReal ENNReal Topology Set Filter Pointwise Bornology
universe u v w
variable {ι : Sort*} {α : Type u} {β : Type v}
namespace EMetric
section InfEdist
variable [PseudoEMetricSpace α] [PseudoEMetricSpace β] {x y : α} {s t : Set α} {Φ : α → β}
/-! ### Distance of a point to a set as a function into `ℝ≥0∞`. -/
/-- The minimal edistance of a point to a set -/
def infEdist (x : α) (s : Set α) : ℝ≥0∞ :=
⨅ y ∈ s, edist x y
@[simp]
theorem infEdist_empty : infEdist x ∅ = ∞ :=
iInf_emptyset
theorem le_infEdist {d} : d ≤ infEdist x s ↔ ∀ y ∈ s, d ≤ edist x y := by
simp only [infEdist, le_iInf_iff]
/-- The edist to a union is the minimum of the edists -/
@[simp]
theorem infEdist_union : infEdist x (s ∪ t) = infEdist x s ⊓ infEdist x t :=
iInf_union
@[simp]
theorem infEdist_iUnion (f : ι → Set α) (x : α) : infEdist x (⋃ i, f i) = ⨅ i, infEdist x (f i) :=
iInf_iUnion f _
lemma infEdist_biUnion {ι : Type*} (f : ι → Set α) (I : Set ι) (x : α) :
infEdist x (⋃ i ∈ I, f i) = ⨅ i ∈ I, infEdist x (f i) := by simp only [infEdist_iUnion]
/-- The edist to a singleton is the edistance to the single point of this singleton -/
@[simp]
theorem infEdist_singleton : infEdist x {y} = edist x y :=
iInf_singleton
/-- The edist to a set is bounded above by the edist to any of its points -/
theorem infEdist_le_edist_of_mem (h : y ∈ s) : infEdist x s ≤ edist x y :=
iInf₂_le y h
/-- If a point `x` belongs to `s`, then its edist to `s` vanishes -/
theorem infEdist_zero_of_mem (h : x ∈ s) : infEdist x s = 0 :=
nonpos_iff_eq_zero.1 <| @edist_self _ _ x ▸ infEdist_le_edist_of_mem h
/-- The edist is antitone with respect to inclusion. -/
theorem infEdist_anti (h : s ⊆ t) : infEdist x t ≤ infEdist x s :=
iInf_le_iInf_of_subset h
/-- The edist to a set is `< r` iff there exists a point in the set at edistance `< r` -/
theorem infEdist_lt_iff {r : ℝ≥0∞} : infEdist x s < r ↔ ∃ y ∈ s, edist x y < r := by
simp_rw [infEdist, iInf_lt_iff, exists_prop]
/-- The edist of `x` to `s` is bounded by the sum of the edist of `y` to `s` and
the edist from `x` to `y` -/
theorem infEdist_le_infEdist_add_edist : infEdist x s ≤ infEdist y s + edist x y :=
calc
⨅ z ∈ s, edist x z ≤ ⨅ z ∈ s, edist y z + edist x y :=
iInf₂_mono fun _ _ => (edist_triangle _ _ _).trans_eq (add_comm _ _)
_ = (⨅ z ∈ s, edist y z) + edist x y := by simp only [ENNReal.iInf_add]
theorem infEdist_le_edist_add_infEdist : infEdist x s ≤ edist x y + infEdist y s := by
rw [add_comm]
exact infEdist_le_infEdist_add_edist
theorem edist_le_infEdist_add_ediam (hy : y ∈ s) : edist x y ≤ infEdist x s + diam s := by
simp_rw [infEdist, ENNReal.iInf_add]
refine le_iInf₂ fun i hi => ?_
calc
edist x y ≤ edist x i + edist i y := edist_triangle _ _ _
_ ≤ edist x i + diam s := add_le_add le_rfl (edist_le_diam_of_mem hi hy)
/-- The edist to a set depends continuously on the point -/
@[continuity]
theorem continuous_infEdist : Continuous fun x => infEdist x s :=
continuous_of_le_add_edist 1 (by simp) <| by
simp only [one_mul, infEdist_le_infEdist_add_edist, forall₂_true_iff]
/-- The edist to a set and to its closure coincide -/
theorem infEdist_closure : infEdist x (closure s) = infEdist x s := by
refine le_antisymm (infEdist_anti subset_closure) ?_
refine ENNReal.le_of_forall_pos_le_add fun ε εpos h => ?_
have ε0 : 0 < (ε / 2 : ℝ≥0∞) := by simpa [pos_iff_ne_zero] using εpos
have : infEdist x (closure s) < infEdist x (closure s) + ε / 2 :=
ENNReal.lt_add_right h.ne ε0.ne'
obtain ⟨y : α, ycs : y ∈ closure s, hy : edist x y < infEdist x (closure s) + ↑ε / 2⟩ :=
infEdist_lt_iff.mp this
obtain ⟨z : α, zs : z ∈ s, dyz : edist y z < ↑ε / 2⟩ := EMetric.mem_closure_iff.1 ycs (ε / 2) ε0
calc
infEdist x s ≤ edist x z := infEdist_le_edist_of_mem zs
_ ≤ edist x y + edist y z := edist_triangle _ _ _
_ ≤ infEdist x (closure s) + ε / 2 + ε / 2 := add_le_add (le_of_lt hy) (le_of_lt dyz)
_ = infEdist x (closure s) + ↑ε := by rw [add_assoc, ENNReal.add_halves]
/-- A point belongs to the closure of `s` iff its infimum edistance to this set vanishes -/
theorem mem_closure_iff_infEdist_zero : x ∈ closure s ↔ infEdist x s = 0 :=
⟨fun h => by
rw [← infEdist_closure]
exact infEdist_zero_of_mem h,
fun h =>
EMetric.mem_closure_iff.2 fun ε εpos => infEdist_lt_iff.mp <| by rwa [h]⟩
/-- Given a closed set `s`, a point belongs to `s` iff its infimum edistance to this set vanishes -/
theorem mem_iff_infEdist_zero_of_closed (h : IsClosed s) : x ∈ s ↔ infEdist x s = 0 := by
rw [← mem_closure_iff_infEdist_zero, h.closure_eq]
/-- The infimum edistance of a point to a set is positive if and only if the point is not in the
closure of the set. -/
theorem infEdist_pos_iff_not_mem_closure {x : α} {E : Set α} :
0 < infEdist x E ↔ x ∉ closure E := by
rw [mem_closure_iff_infEdist_zero, pos_iff_ne_zero]
theorem infEdist_closure_pos_iff_not_mem_closure {x : α} {E : Set α} :
0 < infEdist x (closure E) ↔ x ∉ closure E := by
rw [infEdist_closure, infEdist_pos_iff_not_mem_closure]
theorem exists_real_pos_lt_infEdist_of_not_mem_closure {x : α} {E : Set α} (h : x ∉ closure E) :
∃ ε : ℝ, 0 < ε ∧ ENNReal.ofReal ε < infEdist x E := by
rw [← infEdist_pos_iff_not_mem_closure, ENNReal.lt_iff_exists_real_btwn] at h
rcases h with ⟨ε, ⟨_, ⟨ε_pos, ε_lt⟩⟩⟩
exact ⟨ε, ⟨ENNReal.ofReal_pos.mp ε_pos, ε_lt⟩⟩
theorem disjoint_closedBall_of_lt_infEdist {r : ℝ≥0∞} (h : r < infEdist x s) :
Disjoint (closedBall x r) s := by
rw [disjoint_left]
intro y hy h'y
apply lt_irrefl (infEdist x s)
calc
infEdist x s ≤ edist x y := infEdist_le_edist_of_mem h'y
_ ≤ r := by rwa [mem_closedBall, edist_comm] at hy
_ < infEdist x s := h
/-- The infimum edistance is invariant under isometries -/
theorem infEdist_image (hΦ : Isometry Φ) : infEdist (Φ x) (Φ '' t) = infEdist x t := by
simp only [infEdist, iInf_image, hΦ.edist_eq]
@[to_additive (attr := simp)]
theorem infEdist_smul {M} [SMul M α] [IsIsometricSMul M α] (c : M) (x : α) (s : Set α) :
infEdist (c • x) (c • s) = infEdist x s :=
infEdist_image (isometry_smul _ _)
theorem _root_.IsOpen.exists_iUnion_isClosed {U : Set α} (hU : IsOpen U) :
∃ F : ℕ → Set α, (∀ n, IsClosed (F n)) ∧ (∀ n, F n ⊆ U) ∧ ⋃ n, F n = U ∧ Monotone F := by
obtain ⟨a, a_pos, a_lt_one⟩ : ∃ a : ℝ≥0∞, 0 < a ∧ a < 1 := exists_between zero_lt_one
let F := fun n : ℕ => (fun x => infEdist x Uᶜ) ⁻¹' Ici (a ^ n)
have F_subset : ∀ n, F n ⊆ U := fun n x hx ↦ by
by_contra h
have : infEdist x Uᶜ ≠ 0 := ((ENNReal.pow_pos a_pos _).trans_le hx).ne'
exact this (infEdist_zero_of_mem h)
refine ⟨F, fun n => IsClosed.preimage continuous_infEdist isClosed_Ici, F_subset, ?_, ?_⟩
· show ⋃ n, F n = U
refine Subset.antisymm (by simp only [iUnion_subset_iff, F_subset, forall_const]) fun x hx => ?_
have : ¬x ∈ Uᶜ := by simpa using hx
rw [mem_iff_infEdist_zero_of_closed hU.isClosed_compl] at this
have B : 0 < infEdist x Uᶜ := by simpa [pos_iff_ne_zero] using this
have : Filter.Tendsto (fun n => a ^ n) atTop (𝓝 0) :=
ENNReal.tendsto_pow_atTop_nhds_zero_of_lt_one a_lt_one
rcases ((tendsto_order.1 this).2 _ B).exists with ⟨n, hn⟩
simp only [mem_iUnion, mem_Ici, mem_preimage]
exact ⟨n, hn.le⟩
show Monotone F
intro m n hmn x hx
simp only [F, mem_Ici, mem_preimage] at hx ⊢
apply le_trans (pow_le_pow_right_of_le_one' a_lt_one.le hmn) hx
theorem _root_.IsCompact.exists_infEdist_eq_edist (hs : IsCompact s) (hne : s.Nonempty) (x : α) :
∃ y ∈ s, infEdist x s = edist x y := by
have A : Continuous fun y => edist x y := continuous_const.edist continuous_id
obtain ⟨y, ys, hy⟩ := hs.exists_isMinOn hne A.continuousOn
exact ⟨y, ys, le_antisymm (infEdist_le_edist_of_mem ys) (by rwa [le_infEdist])⟩
theorem exists_pos_forall_lt_edist (hs : IsCompact s) (ht : IsClosed t) (hst : Disjoint s t) :
∃ r : ℝ≥0, 0 < r ∧ ∀ x ∈ s, ∀ y ∈ t, (r : ℝ≥0∞) < edist x y := by
rcases s.eq_empty_or_nonempty with (rfl | hne)
· use 1
simp
obtain ⟨x, hx, h⟩ := hs.exists_isMinOn hne continuous_infEdist.continuousOn
have : 0 < infEdist x t :=
pos_iff_ne_zero.2 fun H => hst.le_bot ⟨hx, (mem_iff_infEdist_zero_of_closed ht).mpr H⟩
rcases ENNReal.lt_iff_exists_nnreal_btwn.1 this with ⟨r, h₀, hr⟩
exact ⟨r, ENNReal.coe_pos.mp h₀, fun y hy z hz => hr.trans_le <| le_infEdist.1 (h hy) z hz⟩
end InfEdist
/-! ### The Hausdorff distance as a function into `ℝ≥0∞`. -/
/-- The Hausdorff edistance between two sets is the smallest `r` such that each set
is contained in the `r`-neighborhood of the other one -/
irreducible_def hausdorffEdist {α : Type u} [PseudoEMetricSpace α] (s t : Set α) : ℝ≥0∞ :=
(⨆ x ∈ s, infEdist x t) ⊔ ⨆ y ∈ t, infEdist y s
section HausdorffEdist
variable [PseudoEMetricSpace α] [PseudoEMetricSpace β] {x : α} {s t u : Set α} {Φ : α → β}
/-- The Hausdorff edistance of a set to itself vanishes. -/
@[simp]
theorem hausdorffEdist_self : hausdorffEdist s s = 0 := by
simp only [hausdorffEdist_def, sup_idem, ENNReal.iSup_eq_zero]
exact fun x hx => infEdist_zero_of_mem hx
/-- The Haudorff edistances of `s` to `t` and of `t` to `s` coincide. -/
theorem hausdorffEdist_comm : hausdorffEdist s t = hausdorffEdist t s := by
simp only [hausdorffEdist_def]; apply sup_comm
/-- Bounding the Hausdorff edistance by bounding the edistance of any point
in each set to the other set -/
theorem hausdorffEdist_le_of_infEdist {r : ℝ≥0∞} (H1 : ∀ x ∈ s, infEdist x t ≤ r)
(H2 : ∀ x ∈ t, infEdist x s ≤ r) : hausdorffEdist s t ≤ r := by
simp only [hausdorffEdist_def, sup_le_iff, iSup_le_iff]
exact ⟨H1, H2⟩
/-- Bounding the Hausdorff edistance by exhibiting, for any point in each set,
another point in the other set at controlled distance -/
theorem hausdorffEdist_le_of_mem_edist {r : ℝ≥0∞} (H1 : ∀ x ∈ s, ∃ y ∈ t, edist x y ≤ r)
(H2 : ∀ x ∈ t, ∃ y ∈ s, edist x y ≤ r) : hausdorffEdist s t ≤ r := by
refine hausdorffEdist_le_of_infEdist (fun x xs ↦ ?_) (fun x xt ↦ ?_)
· rcases H1 x xs with ⟨y, yt, hy⟩
exact le_trans (infEdist_le_edist_of_mem yt) hy
· rcases H2 x xt with ⟨y, ys, hy⟩
exact le_trans (infEdist_le_edist_of_mem ys) hy
/-- The distance to a set is controlled by the Hausdorff distance. -/
theorem infEdist_le_hausdorffEdist_of_mem (h : x ∈ s) : infEdist x t ≤ hausdorffEdist s t := by
rw [hausdorffEdist_def]
refine le_trans ?_ le_sup_left
exact le_iSup₂ (α := ℝ≥0∞) x h
/-- If the Hausdorff distance is `< r`, then any point in one of the sets has
a corresponding point at distance `< r` in the other set. -/
theorem exists_edist_lt_of_hausdorffEdist_lt {r : ℝ≥0∞} (h : x ∈ s) (H : hausdorffEdist s t < r) :
∃ y ∈ t, edist x y < r :=
infEdist_lt_iff.mp <|
calc
infEdist x t ≤ hausdorffEdist s t := infEdist_le_hausdorffEdist_of_mem h
_ < r := H
/-- The distance from `x` to `s` or `t` is controlled in terms of the Hausdorff distance
between `s` and `t`. -/
theorem infEdist_le_infEdist_add_hausdorffEdist :
infEdist x t ≤ infEdist x s + hausdorffEdist s t :=
ENNReal.le_of_forall_pos_le_add fun ε εpos h => by
have ε0 : (ε / 2 : ℝ≥0∞) ≠ 0 := by simpa [pos_iff_ne_zero] using εpos
have : infEdist x s < infEdist x s + ε / 2 :=
ENNReal.lt_add_right (ENNReal.add_lt_top.1 h).1.ne ε0
obtain ⟨y : α, ys : y ∈ s, dxy : edist x y < infEdist x s + ↑ε / 2⟩ := infEdist_lt_iff.mp this
have : hausdorffEdist s t < hausdorffEdist s t + ε / 2 :=
ENNReal.lt_add_right (ENNReal.add_lt_top.1 h).2.ne ε0
obtain ⟨z : α, zt : z ∈ t, dyz : edist y z < hausdorffEdist s t + ↑ε / 2⟩ :=
exists_edist_lt_of_hausdorffEdist_lt ys this
calc
infEdist x t ≤ edist x z := infEdist_le_edist_of_mem zt
_ ≤ edist x y + edist y z := edist_triangle _ _ _
_ ≤ infEdist x s + ε / 2 + (hausdorffEdist s t + ε / 2) := add_le_add dxy.le dyz.le
_ = infEdist x s + hausdorffEdist s t + ε := by
simp [ENNReal.add_halves, add_comm, add_left_comm]
/-- The Hausdorff edistance is invariant under isometries. -/
theorem hausdorffEdist_image (h : Isometry Φ) :
hausdorffEdist (Φ '' s) (Φ '' t) = hausdorffEdist s t := by
simp only [hausdorffEdist_def, iSup_image, infEdist_image h]
/-- The Hausdorff distance is controlled by the diameter of the union. -/
theorem hausdorffEdist_le_ediam (hs : s.Nonempty) (ht : t.Nonempty) :
hausdorffEdist s t ≤ diam (s ∪ t) := by
rcases hs with ⟨x, xs⟩
rcases ht with ⟨y, yt⟩
refine hausdorffEdist_le_of_mem_edist ?_ ?_
· intro z hz
exact ⟨y, yt, edist_le_diam_of_mem (subset_union_left hz) (subset_union_right yt)⟩
· intro z hz
exact ⟨x, xs, edist_le_diam_of_mem (subset_union_right hz) (subset_union_left xs)⟩
/-- The Hausdorff distance satisfies the triangle inequality. -/
theorem hausdorffEdist_triangle : hausdorffEdist s u ≤ hausdorffEdist s t + hausdorffEdist t u := by
rw [hausdorffEdist_def]
simp only [sup_le_iff, iSup_le_iff]
constructor
· show ∀ x ∈ s, infEdist x u ≤ hausdorffEdist s t + hausdorffEdist t u
exact fun x xs =>
calc
infEdist x u ≤ infEdist x t + hausdorffEdist t u :=
infEdist_le_infEdist_add_hausdorffEdist
_ ≤ hausdorffEdist s t + hausdorffEdist t u :=
add_le_add_right (infEdist_le_hausdorffEdist_of_mem xs) _
· show ∀ x ∈ u, infEdist x s ≤ hausdorffEdist s t + hausdorffEdist t u
exact fun x xu =>
calc
infEdist x s ≤ infEdist x t + hausdorffEdist t s :=
infEdist_le_infEdist_add_hausdorffEdist
_ ≤ hausdorffEdist u t + hausdorffEdist t s :=
add_le_add_right (infEdist_le_hausdorffEdist_of_mem xu) _
_ = hausdorffEdist s t + hausdorffEdist t u := by simp [hausdorffEdist_comm, add_comm]
/-- Two sets are at zero Hausdorff edistance if and only if they have the same closure. -/
theorem hausdorffEdist_zero_iff_closure_eq_closure :
hausdorffEdist s t = 0 ↔ closure s = closure t := by
simp only [hausdorffEdist_def, ENNReal.sup_eq_zero, ENNReal.iSup_eq_zero, ← subset_def,
← mem_closure_iff_infEdist_zero, subset_antisymm_iff, isClosed_closure.closure_subset_iff]
/-- The Hausdorff edistance between a set and its closure vanishes. -/
@[simp]
theorem hausdorffEdist_self_closure : hausdorffEdist s (closure s) = 0 := by
rw [hausdorffEdist_zero_iff_closure_eq_closure, closure_closure]
/-- Replacing a set by its closure does not change the Hausdorff edistance. -/
@[simp]
theorem hausdorffEdist_closure₁ : hausdorffEdist (closure s) t = hausdorffEdist s t := by
refine le_antisymm ?_ ?_
· calc
_ ≤ hausdorffEdist (closure s) s + hausdorffEdist s t := hausdorffEdist_triangle
_ = hausdorffEdist s t := by simp [hausdorffEdist_comm]
· calc
_ ≤ hausdorffEdist s (closure s) + hausdorffEdist (closure s) t := hausdorffEdist_triangle
_ = hausdorffEdist (closure s) t := by simp
/-- Replacing a set by its closure does not change the Hausdorff edistance. -/
@[simp]
theorem hausdorffEdist_closure₂ : hausdorffEdist s (closure t) = hausdorffEdist s t := by
simp [@hausdorffEdist_comm _ _ s _]
/-- The Hausdorff edistance between sets or their closures is the same. -/
theorem hausdorffEdist_closure : hausdorffEdist (closure s) (closure t) = hausdorffEdist s t := by
simp
/-- Two closed sets are at zero Hausdorff edistance if and only if they coincide. -/
theorem hausdorffEdist_zero_iff_eq_of_closed (hs : IsClosed s) (ht : IsClosed t) :
hausdorffEdist s t = 0 ↔ s = t := by
rw [hausdorffEdist_zero_iff_closure_eq_closure, hs.closure_eq, ht.closure_eq]
/-- The Haudorff edistance to the empty set is infinite. -/
theorem hausdorffEdist_empty (ne : s.Nonempty) : hausdorffEdist s ∅ = ∞ := by
rcases ne with ⟨x, xs⟩
have : infEdist x ∅ ≤ hausdorffEdist s ∅ := infEdist_le_hausdorffEdist_of_mem xs
simpa using this
/-- If a set is at finite Hausdorff edistance of a nonempty set, it is nonempty. -/
theorem nonempty_of_hausdorffEdist_ne_top (hs : s.Nonempty) (fin : hausdorffEdist s t ≠ ⊤) :
t.Nonempty :=
t.eq_empty_or_nonempty.resolve_left fun ht ↦ fin (ht.symm ▸ hausdorffEdist_empty hs)
theorem empty_or_nonempty_of_hausdorffEdist_ne_top (fin : hausdorffEdist s t ≠ ⊤) :
(s = ∅ ∧ t = ∅) ∨ (s.Nonempty ∧ t.Nonempty) := by
rcases s.eq_empty_or_nonempty with hs | hs
· rcases t.eq_empty_or_nonempty with ht | ht
· exact Or.inl ⟨hs, ht⟩
· rw [hausdorffEdist_comm] at fin
exact Or.inr ⟨nonempty_of_hausdorffEdist_ne_top ht fin, ht⟩
· exact Or.inr ⟨hs, nonempty_of_hausdorffEdist_ne_top hs fin⟩
end HausdorffEdist
-- section
end EMetric
/-! Now, we turn to the same notions in metric spaces. To avoid the difficulties related to
`sInf` and `sSup` on `ℝ` (which is only conditionally complete), we use the notions in `ℝ≥0∞`
formulated in terms of the edistance, and coerce them to `ℝ`.
Then their properties follow readily from the corresponding properties in `ℝ≥0∞`,
modulo some tedious rewriting of inequalities from one to the other. -/
--namespace
namespace Metric
section
variable [PseudoMetricSpace α] [PseudoMetricSpace β] {s t u : Set α} {x y : α} {Φ : α → β}
open EMetric
/-! ### Distance of a point to a set as a function into `ℝ`. -/
/-- The minimal distance of a point to a set -/
def infDist (x : α) (s : Set α) : ℝ :=
ENNReal.toReal (infEdist x s)
theorem infDist_eq_iInf : infDist x s = ⨅ y : s, dist x y := by
rw [infDist, infEdist, iInf_subtype', ENNReal.toReal_iInf]
· simp only [dist_edist]
· exact fun _ ↦ edist_ne_top _ _
/-- The minimal distance is always nonnegative -/
theorem infDist_nonneg : 0 ≤ infDist x s := toReal_nonneg
/-- The minimal distance to the empty set is 0 (if you want to have the more reasonable
value `∞` instead, use `EMetric.infEdist`, which takes values in `ℝ≥0∞`) -/
@[simp]
theorem infDist_empty : infDist x ∅ = 0 := by simp [infDist]
lemma isGLB_infDist (hs : s.Nonempty) : IsGLB ((dist x ·) '' s) (infDist x s) := by
simpa [infDist_eq_iInf, sInf_image']
using isGLB_csInf (hs.image _) ⟨0, by simp [lowerBounds, dist_nonneg]⟩
/-- In a metric space, the minimal edistance to a nonempty set is finite. -/
theorem infEdist_ne_top (h : s.Nonempty) : infEdist x s ≠ ⊤ := by
rcases h with ⟨y, hy⟩
exact ne_top_of_le_ne_top (edist_ne_top _ _) (infEdist_le_edist_of_mem hy)
@[simp]
theorem infEdist_eq_top_iff : infEdist x s = ∞ ↔ s = ∅ := by
rcases s.eq_empty_or_nonempty with rfl | hs <;> simp [*, Nonempty.ne_empty, infEdist_ne_top]
/-- The minimal distance of a point to a set containing it vanishes. -/
theorem infDist_zero_of_mem (h : x ∈ s) : infDist x s = 0 := by
simp [infEdist_zero_of_mem h, infDist]
/-- The minimal distance to a singleton is the distance to the unique point in this singleton. -/
@[simp]
theorem infDist_singleton : infDist x {y} = dist x y := by simp [infDist, dist_edist]
/-- The minimal distance to a set is bounded by the distance to any point in this set. -/
theorem infDist_le_dist_of_mem (h : y ∈ s) : infDist x s ≤ dist x y := by
rw [dist_edist, infDist]
exact ENNReal.toReal_mono (edist_ne_top _ _) (infEdist_le_edist_of_mem h)
/-- The minimal distance is monotone with respect to inclusion. -/
theorem infDist_le_infDist_of_subset (h : s ⊆ t) (hs : s.Nonempty) : infDist x t ≤ infDist x s :=
ENNReal.toReal_mono (infEdist_ne_top hs) (infEdist_anti h)
lemma le_infDist {r : ℝ} (hs : s.Nonempty) : r ≤ infDist x s ↔ ∀ ⦃y⦄, y ∈ s → r ≤ dist x y := by
simp_rw [infDist, ← ENNReal.ofReal_le_iff_le_toReal (infEdist_ne_top hs), le_infEdist,
ENNReal.ofReal_le_iff_le_toReal (edist_ne_top _ _), ← dist_edist]
/-- The minimal distance to a set `s` is `< r` iff there exists a point in `s` at distance `< r`. -/
theorem infDist_lt_iff {r : ℝ} (hs : s.Nonempty) : infDist x s < r ↔ ∃ y ∈ s, dist x y < r := by
simp [← not_le, le_infDist hs]
/-- The minimal distance from `x` to `s` is bounded by the distance from `y` to `s`, modulo
the distance between `x` and `y`. -/
theorem infDist_le_infDist_add_dist : infDist x s ≤ infDist y s + dist x y := by
rw [infDist, infDist, dist_edist]
refine ENNReal.toReal_le_add' infEdist_le_infEdist_add_edist ?_ (flip absurd (edist_ne_top _ _))
simp only [infEdist_eq_top_iff, imp_self]
theorem not_mem_of_dist_lt_infDist (h : dist x y < infDist x s) : y ∉ s := fun hy =>
h.not_le <| infDist_le_dist_of_mem hy
theorem disjoint_ball_infDist : Disjoint (ball x (infDist x s)) s :=
disjoint_left.2 fun _y hy => not_mem_of_dist_lt_infDist <| mem_ball'.1 hy
theorem ball_infDist_subset_compl : ball x (infDist x s) ⊆ sᶜ :=
(disjoint_ball_infDist (s := s)).subset_compl_right
theorem ball_infDist_compl_subset : ball x (infDist x sᶜ) ⊆ s :=
ball_infDist_subset_compl.trans_eq (compl_compl s)
theorem disjoint_closedBall_of_lt_infDist {r : ℝ} (h : r < infDist x s) :
Disjoint (closedBall x r) s :=
disjoint_ball_infDist.mono_left <| closedBall_subset_ball h
theorem dist_le_infDist_add_diam (hs : IsBounded s) (hy : y ∈ s) :
dist x y ≤ infDist x s + diam s := by
rw [infDist, diam, dist_edist]
exact toReal_le_add (edist_le_infEdist_add_ediam hy) (infEdist_ne_top ⟨y, hy⟩) hs.ediam_ne_top
variable (s)
/-- The minimal distance to a set is Lipschitz in point with constant 1 -/
theorem lipschitz_infDist_pt : LipschitzWith 1 (infDist · s) :=
LipschitzWith.of_le_add fun _ _ => infDist_le_infDist_add_dist
/-- The minimal distance to a set is uniformly continuous in point -/
theorem uniformContinuous_infDist_pt : UniformContinuous (infDist · s) :=
(lipschitz_infDist_pt s).uniformContinuous
/-- The minimal distance to a set is continuous in point -/
@[continuity]
theorem continuous_infDist_pt : Continuous (infDist · s) :=
(uniformContinuous_infDist_pt s).continuous
variable {s}
/-- The minimal distances to a set and its closure coincide. -/
theorem infDist_closure : infDist x (closure s) = infDist x s := by
simp [infDist, infEdist_closure]
/-- If a point belongs to the closure of `s`, then its infimum distance to `s` equals zero.
The converse is true provided that `s` is nonempty, see `Metric.mem_closure_iff_infDist_zero`. -/
theorem infDist_zero_of_mem_closure (hx : x ∈ closure s) : infDist x s = 0 := by
rw [← infDist_closure]
exact infDist_zero_of_mem hx
/-- A point belongs to the closure of `s` iff its infimum distance to this set vanishes. -/
theorem mem_closure_iff_infDist_zero (h : s.Nonempty) : x ∈ closure s ↔ infDist x s = 0 := by
simp [mem_closure_iff_infEdist_zero, infDist, ENNReal.toReal_eq_zero_iff, infEdist_ne_top h]
theorem infDist_pos_iff_not_mem_closure (hs : s.Nonempty) :
x ∉ closure s ↔ 0 < infDist x s :=
(mem_closure_iff_infDist_zero hs).not.trans infDist_nonneg.gt_iff_ne.symm
/-- Given a closed set `s`, a point belongs to `s` iff its infimum distance to this set vanishes -/
theorem _root_.IsClosed.mem_iff_infDist_zero (h : IsClosed s) (hs : s.Nonempty) :
x ∈ s ↔ infDist x s = 0 := by rw [← mem_closure_iff_infDist_zero hs, h.closure_eq]
/-- Given a closed set `s`, a point belongs to `s` iff its infimum distance to this set vanishes. -/
theorem _root_.IsClosed.not_mem_iff_infDist_pos (h : IsClosed s) (hs : s.Nonempty) :
x ∉ s ↔ 0 < infDist x s := by
simp [h.mem_iff_infDist_zero hs, infDist_nonneg.gt_iff_ne]
theorem continuousAt_inv_infDist_pt (h : x ∉ closure s) :
ContinuousAt (fun x ↦ (infDist x s)⁻¹) x := by
rcases s.eq_empty_or_nonempty with (rfl | hs)
· simp only [infDist_empty, continuousAt_const]
· refine (continuous_infDist_pt s).continuousAt.inv₀ ?_
rwa [Ne, ← mem_closure_iff_infDist_zero hs]
/-- The infimum distance is invariant under isometries. -/
theorem infDist_image (hΦ : Isometry Φ) : infDist (Φ x) (Φ '' t) = infDist x t := by
simp [infDist, infEdist_image hΦ]
theorem infDist_inter_closedBall_of_mem (h : y ∈ s) :
infDist x (s ∩ closedBall x (dist y x)) = infDist x s := by
replace h : y ∈ s ∩ closedBall x (dist y x) := ⟨h, mem_closedBall.2 le_rfl⟩
refine le_antisymm ?_ (infDist_le_infDist_of_subset inter_subset_left ⟨y, h⟩)
refine not_lt.1 fun hlt => ?_
rcases (infDist_lt_iff ⟨y, h.1⟩).mp hlt with ⟨z, hzs, hz⟩
rcases le_or_lt (dist z x) (dist y x) with hle | hlt
· exact hz.not_le (infDist_le_dist_of_mem ⟨hzs, hle⟩)
· rw [dist_comm z, dist_comm y] at hlt
exact (hlt.trans hz).not_le (infDist_le_dist_of_mem h)
theorem _root_.IsCompact.exists_infDist_eq_dist (h : IsCompact s) (hne : s.Nonempty) (x : α) :
∃ y ∈ s, infDist x s = dist x y :=
let ⟨y, hys, hy⟩ := h.exists_infEdist_eq_edist hne x
⟨y, hys, by rw [infDist, dist_edist, hy]⟩
theorem _root_.IsClosed.exists_infDist_eq_dist [ProperSpace α] (h : IsClosed s) (hne : s.Nonempty)
(x : α) : ∃ y ∈ s, infDist x s = dist x y := by
rcases hne with ⟨z, hz⟩
rw [← infDist_inter_closedBall_of_mem hz]
set t := s ∩ closedBall x (dist z x)
have htc : IsCompact t := (isCompact_closedBall x (dist z x)).inter_left h
have htne : t.Nonempty := ⟨z, hz, mem_closedBall.2 le_rfl⟩
obtain ⟨y, ⟨hys, -⟩, hyd⟩ : ∃ y ∈ t, infDist x t = dist x y := htc.exists_infDist_eq_dist htne x
exact ⟨y, hys, hyd⟩
theorem exists_mem_closure_infDist_eq_dist [ProperSpace α] (hne : s.Nonempty) (x : α) :
∃ y ∈ closure s, infDist x s = dist x y := by
simpa only [infDist_closure] using isClosed_closure.exists_infDist_eq_dist hne.closure x
/-! ### Distance of a point to a set as a function into `ℝ≥0`. -/
/-- The minimal distance of a point to a set as a `ℝ≥0` -/
def infNndist (x : α) (s : Set α) : ℝ≥0 :=
ENNReal.toNNReal (infEdist x s)
@[simp]
theorem coe_infNndist : (infNndist x s : ℝ) = infDist x s :=
rfl
/-- The minimal distance to a set (as `ℝ≥0`) is Lipschitz in point with constant 1 -/
theorem lipschitz_infNndist_pt (s : Set α) : LipschitzWith 1 fun x => infNndist x s :=
LipschitzWith.of_le_add fun _ _ => infDist_le_infDist_add_dist
/-- The minimal distance to a set (as `ℝ≥0`) is uniformly continuous in point -/
theorem uniformContinuous_infNndist_pt (s : Set α) : UniformContinuous fun x => infNndist x s :=
(lipschitz_infNndist_pt s).uniformContinuous
/-- The minimal distance to a set (as `ℝ≥0`) is continuous in point -/
theorem continuous_infNndist_pt (s : Set α) : Continuous fun x => infNndist x s :=
(uniformContinuous_infNndist_pt s).continuous
/-! ### The Hausdorff distance as a function into `ℝ`. -/
/-- The Hausdorff distance between two sets is the smallest nonnegative `r` such that each set is
included in the `r`-neighborhood of the other. If there is no such `r`, it is defined to
be `0`, arbitrarily. -/
def hausdorffDist (s t : Set α) : ℝ :=
ENNReal.toReal (hausdorffEdist s t)
/-- The Hausdorff distance is nonnegative. -/
theorem hausdorffDist_nonneg : 0 ≤ hausdorffDist s t := by simp [hausdorffDist]
/-- If two sets are nonempty and bounded in a metric space, they are at finite Hausdorff
edistance. -/
theorem hausdorffEdist_ne_top_of_nonempty_of_bounded (hs : s.Nonempty) (ht : t.Nonempty)
(bs : IsBounded s) (bt : IsBounded t) : hausdorffEdist s t ≠ ⊤ := by
rcases hs with ⟨cs, hcs⟩
rcases ht with ⟨ct, hct⟩
rcases bs.subset_closedBall ct with ⟨rs, hrs⟩
rcases bt.subset_closedBall cs with ⟨rt, hrt⟩
have : hausdorffEdist s t ≤ ENNReal.ofReal (max rs rt) := by
apply hausdorffEdist_le_of_mem_edist
· intro x xs
exists ct, hct
have : dist x ct ≤ max rs rt := le_trans (hrs xs) (le_max_left _ _)
rwa [edist_dist, ENNReal.ofReal_le_ofReal_iff]
exact le_trans dist_nonneg this
· intro x xt
exists cs, hcs
have : dist x cs ≤ max rs rt := le_trans (hrt xt) (le_max_right _ _)
rwa [edist_dist, ENNReal.ofReal_le_ofReal_iff]
exact le_trans dist_nonneg this
exact ne_top_of_le_ne_top ENNReal.ofReal_ne_top this
| /-- The Hausdorff distance between a set and itself is zero. -/
@[simp]
theorem hausdorffDist_self_zero : hausdorffDist s s = 0 := by simp [hausdorffDist]
/-- The Hausdorff distances from `s` to `t` and from `t` to `s` coincide. -/
theorem hausdorffDist_comm : hausdorffDist s t = hausdorffDist t s := by
simp [hausdorffDist, hausdorffEdist_comm]
/-- The Hausdorff distance to the empty set vanishes (if you want to have the more reasonable
| Mathlib/Topology/MetricSpace/HausdorffDistance.lean | 654 | 662 |
/-
Copyright (c) 2019 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen
-/
import Mathlib.Algebra.Regular.Basic
import Mathlib.GroupTheory.MonoidLocalization.Basic
import Mathlib.LinearAlgebra.Matrix.MvPolynomial
import Mathlib.LinearAlgebra.Matrix.Polynomial
import Mathlib.RingTheory.Polynomial.Basic
/-!
# Cramer's rule and adjugate matrices
The adjugate matrix is the transpose of the cofactor matrix.
It is calculated with Cramer's rule, which we introduce first.
The vectors returned by Cramer's rule are given by the linear map `cramer`,
which sends a matrix `A` and vector `b` to the vector consisting of the
determinant of replacing the `i`th column of `A` with `b` at index `i`
(written as `(A.update_column i b).det`).
Using Cramer's rule, we can compute for each matrix `A` the matrix `adjugate A`.
The entries of the adjugate are the minors of `A`.
Instead of defining a minor by deleting row `i` and column `j` of `A`, we
replace the `i`th row of `A` with the `j`th basis vector; the resulting matrix
has the same determinant but more importantly equals Cramer's rule applied
to `A` and the `j`th basis vector, simplifying the subsequent proofs.
We prove the adjugate behaves like `det A • A⁻¹`.
## Main definitions
* `Matrix.cramer A b`: the vector output by Cramer's rule on `A` and `b`.
* `Matrix.adjugate A`: the adjugate (or classical adjoint) of the matrix `A`.
## References
* https://en.wikipedia.org/wiki/Cramer's_rule#Finding_inverse_matrix
## Tags
cramer, cramer's rule, adjugate
-/
namespace Matrix
universe u v w
variable {m : Type u} {n : Type v} {α : Type w}
variable [DecidableEq n] [Fintype n] [DecidableEq m] [Fintype m] [CommRing α]
open Matrix Polynomial Equiv Equiv.Perm Finset
section Cramer
/-!
### `cramer` section
Introduce the linear map `cramer` with values defined by `cramerMap`.
After defining `cramerMap` and showing it is linear,
we will restrict our proofs to using `cramer`.
-/
variable (A : Matrix n n α) (b : n → α)
/-- `cramerMap A b i` is the determinant of the matrix `A` with column `i` replaced with `b`,
and thus `cramerMap A b` is the vector output by Cramer's rule on `A` and `b`.
If `A * x = b` has a unique solution in `x`, `cramerMap A` sends the vector `b` to `A.det • x`.
Otherwise, the outcome of `cramerMap` is well-defined but not necessarily useful.
-/
def cramerMap (i : n) : α :=
(A.updateCol i b).det
theorem cramerMap_is_linear (i : n) : IsLinearMap α fun b => cramerMap A b i :=
{ map_add := det_updateCol_add _ _
map_smul := det_updateCol_smul _ _ }
theorem cramer_is_linear : IsLinearMap α (cramerMap A) := by
constructor <;> intros <;> ext i
· apply (cramerMap_is_linear A i).1
· apply (cramerMap_is_linear A i).2
/-- `cramer A b i` is the determinant of the matrix `A` with column `i` replaced with `b`,
and thus `cramer A b` is the vector output by Cramer's rule on `A` and `b`.
If `A * x = b` has a unique solution in `x`, `cramer A` sends the vector `b` to `A.det • x`.
Otherwise, the outcome of `cramer` is well-defined but not necessarily useful.
-/
def cramer (A : Matrix n n α) : (n → α) →ₗ[α] (n → α) :=
IsLinearMap.mk' (cramerMap A) (cramer_is_linear A)
theorem cramer_apply (i : n) : cramer A b i = (A.updateCol i b).det :=
rfl
theorem cramer_transpose_apply (i : n) : cramer Aᵀ b i = (A.updateRow i b).det := by
rw [cramer_apply, updateCol_transpose, det_transpose]
theorem cramer_transpose_row_self (i : n) : Aᵀ.cramer (A i) = Pi.single i A.det := by
ext j
rw [cramer_apply, Pi.single_apply]
split_ifs with h
· -- i = j: this entry should be `A.det`
subst h
simp only [updateCol_transpose, det_transpose, updateRow_eq_self]
· -- i ≠ j: this entry should be 0
rw [updateCol_transpose, det_transpose]
apply det_zero_of_row_eq h
rw [updateRow_self, updateRow_ne (Ne.symm h)]
theorem cramer_row_self (i : n) (h : ∀ j, b j = A j i) : A.cramer b = Pi.single i A.det := by
rw [← transpose_transpose A, det_transpose]
convert cramer_transpose_row_self Aᵀ i
exact funext h
@[simp]
theorem cramer_one : cramer (1 : Matrix n n α) = 1 := by
ext i j
convert congr_fun (cramer_row_self (1 : Matrix n n α) (Pi.single i 1) i _) j
· simp
· intro j
rw [Matrix.one_eq_pi_single, Pi.single_comm]
theorem cramer_smul (r : α) (A : Matrix n n α) :
cramer (r • A) = r ^ (Fintype.card n - 1) • cramer A :=
LinearMap.ext fun _ => funext fun _ => det_updateCol_smul_left _ _ _ _
@[simp]
theorem cramer_subsingleton_apply [Subsingleton n] (A : Matrix n n α) (b : n → α) (i : n) :
cramer A b i = b i := by rw [cramer_apply, det_eq_elem_of_subsingleton _ i, updateCol_self]
theorem cramer_zero [Nontrivial n] : cramer (0 : Matrix n n α) = 0 := by
ext i j
obtain ⟨j', hj'⟩ : ∃ j', j' ≠ j := exists_ne j
apply det_eq_zero_of_column_eq_zero j'
intro j''
simp [updateCol_ne hj']
/-- Use linearity of `cramer` to take it out of a summation. -/
theorem sum_cramer {β} (s : Finset β) (f : β → n → α) :
(∑ x ∈ s, cramer A (f x)) = cramer A (∑ x ∈ s, f x) :=
(map_sum (cramer A) ..).symm
/-- Use linearity of `cramer` and vector evaluation to take `cramer A _ i` out of a summation. -/
theorem sum_cramer_apply {β} (s : Finset β) (f : n → β → α) (i : n) :
(∑ x ∈ s, cramer A (fun j => f j x) i) = cramer A (fun j : n => ∑ x ∈ s, f j x) i :=
calc
(∑ x ∈ s, cramer A (fun j => f j x) i) = (∑ x ∈ s, cramer A fun j => f j x) i :=
(Finset.sum_apply i s _).symm
_ = cramer A (fun j : n => ∑ x ∈ s, f j x) i := by
rw [sum_cramer, cramer_apply, cramer_apply]
simp only [updateCol]
congr with j
congr
apply Finset.sum_apply
theorem cramer_submatrix_equiv (A : Matrix m m α) (e : n ≃ m) (b : n → α) :
cramer (A.submatrix e e) b = cramer A (b ∘ e.symm) ∘ e := by
ext i
simp_rw [Function.comp_apply, cramer_apply, updateCol_submatrix_equiv,
det_submatrix_equiv_self e, Function.comp_def]
theorem cramer_reindex (e : m ≃ n) (A : Matrix m m α) (b : n → α) :
cramer (reindex e e A) b = cramer A (b ∘ e) ∘ e.symm :=
cramer_submatrix_equiv _ _ _
end Cramer
section Adjugate
/-!
### `adjugate` section
Define the `adjugate` matrix and a few equations.
These will hold for any matrix over a commutative ring.
-/
/-- The adjugate matrix is the transpose of the cofactor matrix.
Typically, the cofactor matrix is defined by taking minors,
i.e. the determinant of the matrix with a row and column removed.
However, the proof of `mul_adjugate` becomes a lot easier if we use the
matrix replacing a column with a basis vector, since it allows us to use
facts about the `cramer` map.
-/
def adjugate (A : Matrix n n α) : Matrix n n α :=
of fun i => cramer Aᵀ (Pi.single i 1)
theorem adjugate_def (A : Matrix n n α) : adjugate A = of fun i => cramer Aᵀ (Pi.single i 1) :=
rfl
theorem adjugate_apply (A : Matrix n n α) (i j : n) :
adjugate A i j = (A.updateRow j (Pi.single i 1)).det := by
rw [adjugate_def, of_apply, cramer_apply, updateCol_transpose, det_transpose]
theorem adjugate_transpose (A : Matrix n n α) : (adjugate A)ᵀ = adjugate Aᵀ := by
ext i j
rw [transpose_apply, adjugate_apply, adjugate_apply, updateRow_transpose, det_transpose]
rw [det_apply', det_apply']
apply Finset.sum_congr rfl
intro σ _
congr 1
by_cases h : i = σ j
· -- Everything except `(i , j)` (= `(σ j , j)`) is given by A, and the rest is a single `1`.
congr
ext j'
subst h
have : σ j' = σ j ↔ j' = j := σ.injective.eq_iff
rw [updateRow_apply, updateCol_apply]
simp_rw [this]
rw [← dite_eq_ite, ← dite_eq_ite]
congr 1 with rfl
rw [Pi.single_eq_same, Pi.single_eq_same]
· -- Otherwise, we need to show that there is a `0` somewhere in the product.
have : (∏ j' : n, updateCol A j (Pi.single i 1) (σ j') j') = 0 := by
apply prod_eq_zero (mem_univ j)
| rw [updateCol_self, Pi.single_eq_of_ne' h]
rw [this]
apply prod_eq_zero (mem_univ (σ⁻¹ i))
erw [apply_symm_apply σ i, updateRow_self]
apply Pi.single_eq_of_ne
intro h'
exact h ((symm_apply_eq σ).mp h')
@[simp]
theorem adjugate_submatrix_equiv_self (e : n ≃ m) (A : Matrix m m α) :
adjugate (A.submatrix e e) = (adjugate A).submatrix e e := by
ext i j
have : (fun j ↦ Pi.single i 1 <| e.symm j) = Pi.single (e i) 1 :=
Function.update_comp_equiv (0 : n → α) e.symm i 1
rw [adjugate_apply, submatrix_apply, adjugate_apply, ← det_submatrix_equiv_self e,
updateRow_submatrix_equiv, this]
theorem adjugate_reindex (e : m ≃ n) (A : Matrix m m α) :
adjugate (reindex e e A) = reindex e e (adjugate A) :=
adjugate_submatrix_equiv_self _ _
/-- Since the map `b ↦ cramer A b` is linear in `b`, it must be multiplication by some matrix. This
matrix is `A.adjugate`. -/
theorem cramer_eq_adjugate_mulVec (A : Matrix n n α) (b : n → α) :
cramer A b = A.adjugate *ᵥ b := by
nth_rw 2 [← A.transpose_transpose]
rw [← adjugate_transpose, adjugate_def]
have : b = ∑ i, b i • (Pi.single i 1 : n → α) := by
| Mathlib/LinearAlgebra/Matrix/Adjugate.lean | 218 | 245 |
/-
Copyright (c) 2016 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Leonardo de Moura
-/
import Mathlib.Tactic.Attr.Register
import Mathlib.Tactic.Basic
import Batteries.Logic
import Batteries.Tactic.Trans
import Batteries.Util.LibraryNote
import Mathlib.Data.Nat.Notation
import Mathlib.Data.Int.Notation
/-!
# Basic logic properties
This file is one of the earliest imports in mathlib.
## Implementation notes
Theorems that require decidability hypotheses are in the namespace `Decidable`.
Classical versions are in the namespace `Classical`.
-/
open Function
section Miscellany
-- attribute [refl] HEq.refl -- FIXME This is still rejected after https://github.com/leanprover-community/mathlib4/pull/857
attribute [trans] Iff.trans HEq.trans heq_of_eq_of_heq
attribute [simp] cast_heq
/-- An identity function with its main argument implicit. This will be printed as `hidden` even
if it is applied to a large term, so it can be used for elision,
as done in the `elide` and `unelide` tactics. -/
abbrev hidden {α : Sort*} {a : α} := a
variable {α : Sort*}
instance (priority := 10) decidableEq_of_subsingleton [Subsingleton α] : DecidableEq α :=
fun a b ↦ isTrue (Subsingleton.elim a b)
instance [Subsingleton α] (p : α → Prop) : Subsingleton (Subtype p) :=
⟨fun ⟨x, _⟩ ⟨y, _⟩ ↦ by cases Subsingleton.elim x y; rfl⟩
theorem congr_heq {α β γ : Sort _} {f : α → γ} {g : β → γ} {x : α} {y : β}
(h₁ : HEq f g) (h₂ : HEq x y) : f x = g y := by
cases h₂; cases h₁; rfl
theorem congr_arg_heq {β : α → Sort*} (f : ∀ a, β a) :
∀ {a₁ a₂ : α}, a₁ = a₂ → HEq (f a₁) (f a₂)
| _, _, rfl => HEq.rfl
@[simp] theorem eq_iff_eq_cancel_left {b c : α} : (∀ {a}, a = b ↔ a = c) ↔ b = c :=
⟨fun h ↦ by rw [← h], fun h a ↦ by rw [h]⟩
@[simp] theorem eq_iff_eq_cancel_right {a b : α} : (∀ {c}, a = c ↔ b = c) ↔ a = b :=
⟨fun h ↦ by rw [h], fun h a ↦ by rw [h]⟩
lemma ne_and_eq_iff_right {a b c : α} (h : b ≠ c) : a ≠ b ∧ a = c ↔ a = c :=
and_iff_right_of_imp (fun h2 => h2.symm ▸ h.symm)
/-- Wrapper for adding elementary propositions to the type class systems.
Warning: this can easily be abused. See the rest of this docstring for details.
Certain propositions should not be treated as a class globally,
but sometimes it is very convenient to be able to use the type class system
in specific circumstances.
For example, `ZMod p` is a field if and only if `p` is a prime number.
In order to be able to find this field instance automatically by type class search,
we have to turn `p.prime` into an instance implicit assumption.
On the other hand, making `Nat.prime` a class would require a major refactoring of the library,
and it is questionable whether making `Nat.prime` a class is desirable at all.
The compromise is to add the assumption `[Fact p.prime]` to `ZMod.field`.
In particular, this class is not intended for turning the type class system
into an automated theorem prover for first order logic. -/
class Fact (p : Prop) : Prop where
/-- `Fact.out` contains the unwrapped witness for the fact represented by the instance of
`Fact p`. -/
out : p
library_note "fact non-instances"/--
In most cases, we should not have global instances of `Fact`; typeclass search only reads the head
symbol and then tries any instances, which means that adding any such instance will cause slowdowns
everywhere. We instead make them as lemmata and make them local instances as required.
-/
theorem Fact.elim {p : Prop} (h : Fact p) : p := h.1
theorem fact_iff {p : Prop} : Fact p ↔ p := ⟨fun h ↦ h.1, fun h ↦ ⟨h⟩⟩
instance {p : Prop} [Decidable p] : Decidable (Fact p) :=
decidable_of_iff _ fact_iff.symm
/-- Swaps two pairs of arguments to a function. -/
abbrev Function.swap₂ {ι₁ ι₂ : Sort*} {κ₁ : ι₁ → Sort*} {κ₂ : ι₂ → Sort*}
{φ : ∀ i₁, κ₁ i₁ → ∀ i₂, κ₂ i₂ → Sort*} (f : ∀ i₁ j₁ i₂ j₂, φ i₁ j₁ i₂ j₂)
(i₂ j₂ i₁ j₁) : φ i₁ j₁ i₂ j₂ := f i₁ j₁ i₂ j₂
end Miscellany
open Function
/-!
### Declarations about propositional connectives
-/
section Propositional
/-! ### Declarations about `implies` -/
alias Iff.imp := imp_congr
-- This is a duplicate of `Classical.imp_iff_right_iff`. Deprecate?
theorem imp_iff_right_iff {a b : Prop} : (a → b ↔ b) ↔ a ∨ b :=
open scoped Classical in Decidable.imp_iff_right_iff
-- This is a duplicate of `Classical.and_or_imp`. Deprecate?
theorem and_or_imp {a b c : Prop} : a ∧ b ∨ (a → c) ↔ a → b ∨ c :=
open scoped Classical in Decidable.and_or_imp
/-- Provide modus tollens (`mt`) as dot notation for implications. -/
protected theorem Function.mt {a b : Prop} : (a → b) → ¬b → ¬a := mt
/-! ### Declarations about `not` -/
alias dec_em := Decidable.em
theorem dec_em' (p : Prop) [Decidable p] : ¬p ∨ p := (dec_em p).symm
alias em := Classical.em
theorem em' (p : Prop) : ¬p ∨ p := (em p).symm
theorem or_not {p : Prop} : p ∨ ¬p := em _
theorem Decidable.eq_or_ne {α : Sort*} (x y : α) [Decidable (x = y)] : x = y ∨ x ≠ y :=
dec_em <| x = y
theorem Decidable.ne_or_eq {α : Sort*} (x y : α) [Decidable (x = y)] : x ≠ y ∨ x = y :=
dec_em' <| x = y
theorem eq_or_ne {α : Sort*} (x y : α) : x = y ∨ x ≠ y := em <| x = y
theorem ne_or_eq {α : Sort*} (x y : α) : x ≠ y ∨ x = y := em' <| x = y
theorem by_contradiction {p : Prop} : (¬p → False) → p :=
open scoped Classical in Decidable.byContradiction
theorem by_cases {p q : Prop} (hpq : p → q) (hnpq : ¬p → q) : q :=
open scoped Classical in if hp : p then hpq hp else hnpq hp
alias by_contra := by_contradiction
library_note "decidable namespace"/--
In most of mathlib, we use the law of excluded middle (LEM) and the axiom of choice (AC) freely.
The `Decidable` namespace contains versions of lemmas from the root namespace that explicitly
attempt to avoid the axiom of choice, usually by adding decidability assumptions on the inputs.
You can check if a lemma uses the axiom of choice by using `#print axioms foo` and seeing if
`Classical.choice` appears in the list.
-/
library_note "decidable arguments"/--
As mathlib is primarily classical,
if the type signature of a `def` or `lemma` does not require any `Decidable` instances to state,
it is preferable not to introduce any `Decidable` instances that are needed in the proof
as arguments, but rather to use the `classical` tactic as needed.
In the other direction, when `Decidable` instances do appear in the type signature,
it is better to use explicitly introduced ones rather than allowing Lean to automatically infer
classical ones, as these may cause instance mismatch errors later.
-/
export Classical (not_not)
attribute [simp] not_not
variable {a b : Prop}
theorem of_not_not {a : Prop} : ¬¬a → a := by_contra
theorem not_ne_iff {α : Sort*} {a b : α} : ¬a ≠ b ↔ a = b := not_not
theorem of_not_imp : ¬(a → b) → a := open scoped Classical in Decidable.of_not_imp
alias Not.decidable_imp_symm := Decidable.not_imp_symm
theorem Not.imp_symm : (¬a → b) → ¬b → a := open scoped Classical in Not.decidable_imp_symm
theorem not_imp_comm : ¬a → b ↔ ¬b → a := open scoped Classical in Decidable.not_imp_comm
@[simp] theorem not_imp_self : ¬a → a ↔ a := open scoped Classical in Decidable.not_imp_self
theorem Imp.swap {a b : Sort*} {c : Prop} : a → b → c ↔ b → a → c :=
⟨fun h x y ↦ h y x, fun h x y ↦ h y x⟩
alias Iff.not := not_congr
theorem Iff.not_left (h : a ↔ ¬b) : ¬a ↔ b := h.not.trans not_not
theorem Iff.not_right (h : ¬a ↔ b) : a ↔ ¬b := not_not.symm.trans h.not
protected lemma Iff.ne {α β : Sort*} {a b : α} {c d : β} : (a = b ↔ c = d) → (a ≠ b ↔ c ≠ d) :=
Iff.not
lemma Iff.ne_left {α β : Sort*} {a b : α} {c d : β} : (a = b ↔ c ≠ d) → (a ≠ b ↔ c = d) :=
Iff.not_left
lemma Iff.ne_right {α β : Sort*} {a b : α} {c d : β} : (a ≠ b ↔ c = d) → (a = b ↔ c ≠ d) :=
Iff.not_right
/-! ### Declarations about `Xor'` -/
/-- `Xor' a b` is the exclusive-or of propositions. -/
def Xor' (a b : Prop) := (a ∧ ¬b) ∨ (b ∧ ¬a)
instance [Decidable a] [Decidable b] : Decidable (Xor' a b) := inferInstanceAs (Decidable (Or ..))
@[simp] theorem xor_true : Xor' True = Not := by
simp +unfoldPartialApp [Xor']
@[simp] theorem xor_false : Xor' False = id := by ext; simp [Xor']
theorem xor_comm (a b : Prop) : Xor' a b = Xor' b a := by simp [Xor', and_comm, or_comm]
instance : Std.Commutative Xor' := ⟨xor_comm⟩
@[simp] theorem xor_self (a : Prop) : Xor' a a = False := by simp [Xor']
@[simp] theorem xor_not_left : Xor' (¬a) b ↔ (a ↔ b) := by by_cases a <;> simp [*]
@[simp] theorem xor_not_right : Xor' a (¬b) ↔ (a ↔ b) := by by_cases a <;> simp [*]
theorem xor_not_not : Xor' (¬a) (¬b) ↔ Xor' a b := by simp [Xor', or_comm, and_comm]
protected theorem Xor'.or (h : Xor' a b) : a ∨ b := h.imp And.left And.left
/-! ### Declarations about `and` -/
alias Iff.and := and_congr
alias ⟨And.rotate, _⟩ := and_rotate
theorem and_symm_right {α : Sort*} (a b : α) (p : Prop) : p ∧ a = b ↔ p ∧ b = a := by simp [eq_comm]
theorem and_symm_left {α : Sort*} (a b : α) (p : Prop) : a = b ∧ p ↔ b = a ∧ p := by simp [eq_comm]
/-! ### Declarations about `or` -/
alias Iff.or := or_congr
alias ⟨Or.rotate, _⟩ := or_rotate
theorem Or.elim3 {c d : Prop} (h : a ∨ b ∨ c) (ha : a → d) (hb : b → d) (hc : c → d) : d :=
Or.elim h ha fun h₂ ↦ Or.elim h₂ hb hc
theorem Or.imp3 {d e c f : Prop} (had : a → d) (hbe : b → e) (hcf : c → f) :
a ∨ b ∨ c → d ∨ e ∨ f :=
Or.imp had <| Or.imp hbe hcf
export Classical (or_iff_not_imp_left or_iff_not_imp_right)
theorem not_or_of_imp : (a → b) → ¬a ∨ b := open scoped Classical in Decidable.not_or_of_imp
-- See Note [decidable namespace]
protected theorem Decidable.or_not_of_imp [Decidable a] (h : a → b) : b ∨ ¬a :=
dite _ (Or.inl ∘ h) Or.inr
theorem or_not_of_imp : (a → b) → b ∨ ¬a := open scoped Classical in Decidable.or_not_of_imp
theorem imp_iff_not_or : a → b ↔ ¬a ∨ b := open scoped Classical in Decidable.imp_iff_not_or
theorem imp_iff_or_not {b a : Prop} : b → a ↔ a ∨ ¬b :=
open scoped Classical in Decidable.imp_iff_or_not
theorem not_imp_not : ¬a → ¬b ↔ b → a := open scoped Classical in Decidable.not_imp_not
theorem imp_and_neg_imp_iff (p q : Prop) : (p → q) ∧ (¬p → q) ↔ q := by simp
/-- Provide the reverse of modus tollens (`mt`) as dot notation for implications. -/
protected theorem Function.mtr : (¬a → ¬b) → b → a := not_imp_not.mp
theorem or_congr_left' {c a b : Prop} (h : ¬c → (a ↔ b)) : a ∨ c ↔ b ∨ c :=
open scoped Classical in Decidable.or_congr_left' h
theorem or_congr_right' {c : Prop} (h : ¬a → (b ↔ c)) : a ∨ b ↔ a ∨ c :=
open scoped Classical in Decidable.or_congr_right' h
/-! ### Declarations about distributivity -/
/-! Declarations about `iff` -/
alias Iff.iff := iff_congr
-- @[simp] -- FIXME simp ignores proof rewrites
theorem iff_mpr_iff_true_intro {P : Prop} (h : P) : Iff.mpr (iff_true_intro h) True.intro = h := rfl
theorem imp_or {a b c : Prop} : a → b ∨ c ↔ (a → b) ∨ (a → c) :=
open scoped Classical in Decidable.imp_or
theorem imp_or' {a : Sort*} {b c : Prop} : a → b ∨ c ↔ (a → b) ∨ (a → c) :=
open scoped Classical in Decidable.imp_or'
theorem not_imp : ¬(a → b) ↔ a ∧ ¬b := open scoped Classical in Decidable.not_imp_iff_and_not
theorem peirce (a b : Prop) : ((a → b) → a) → a := open scoped Classical in Decidable.peirce _ _
theorem not_iff_not : (¬a ↔ ¬b) ↔ (a ↔ b) := open scoped Classical in Decidable.not_iff_not
theorem not_iff_comm : (¬a ↔ b) ↔ (¬b ↔ a) := open scoped Classical in Decidable.not_iff_comm
theorem not_iff : ¬(a ↔ b) ↔ (¬a ↔ b) := open scoped Classical in Decidable.not_iff
theorem iff_not_comm : (a ↔ ¬b) ↔ (b ↔ ¬a) := open scoped Classical in Decidable.iff_not_comm
theorem iff_iff_and_or_not_and_not : (a ↔ b) ↔ a ∧ b ∨ ¬a ∧ ¬b :=
open scoped Classical in Decidable.iff_iff_and_or_not_and_not
theorem iff_iff_not_or_and_or_not : (a ↔ b) ↔ (¬a ∨ b) ∧ (a ∨ ¬b) :=
open scoped Classical in Decidable.iff_iff_not_or_and_or_not
theorem not_and_not_right : ¬(a ∧ ¬b) ↔ a → b :=
open scoped Classical in Decidable.not_and_not_right
/-! ### De Morgan's laws -/
/-- One of **de Morgan's laws**: the negation of a conjunction is logically equivalent to the
disjunction of the negations. -/
theorem not_and_or : ¬(a ∧ b) ↔ ¬a ∨ ¬b := open scoped Classical in Decidable.not_and_iff_not_or_not
theorem or_iff_not_and_not : a ∨ b ↔ ¬(¬a ∧ ¬b) :=
open scoped Classical in Decidable.or_iff_not_not_and_not
theorem and_iff_not_or_not : a ∧ b ↔ ¬(¬a ∨ ¬b) :=
open scoped Classical in Decidable.and_iff_not_not_or_not
@[simp] theorem not_xor (P Q : Prop) : ¬Xor' P Q ↔ (P ↔ Q) := by
simp only [not_and, Xor', not_or, not_not, ← iff_iff_implies_and_implies]
theorem xor_iff_not_iff (P Q : Prop) : Xor' P Q ↔ ¬ (P ↔ Q) := (not_xor P Q).not_right
theorem xor_iff_iff_not : Xor' a b ↔ (a ↔ ¬b) := by simp only [← @xor_not_right a, not_not]
theorem xor_iff_not_iff' : Xor' a b ↔ (¬a ↔ b) := by simp only [← @xor_not_left _ b, not_not]
theorem xor_iff_or_and_not_and (a b : Prop) : Xor' a b ↔ (a ∨ b) ∧ (¬ (a ∧ b)) := by
rw [Xor', or_and_right, not_and_or, and_or_left, and_not_self_iff, false_or,
and_or_left, and_not_self_iff, or_false]
end Propositional
/-! ### Membership -/
alias Membership.mem.ne_of_not_mem := ne_of_mem_of_not_mem
alias Membership.mem.ne_of_not_mem' := ne_of_mem_of_not_mem'
section Membership
variable {α β : Type*} [Membership α β] {p : Prop} [Decidable p]
theorem mem_dite {a : α} {s : p → β} {t : ¬p → β} :
(a ∈ if h : p then s h else t h) ↔ (∀ h, a ∈ s h) ∧ (∀ h, a ∈ t h) := by
by_cases h : p <;> simp [h]
theorem dite_mem {a : p → α} {b : ¬p → α} {s : β} :
(if h : p then a h else b h) ∈ s ↔ (∀ h, a h ∈ s) ∧ (∀ h, b h ∈ s) := by
by_cases h : p <;> simp [h]
theorem mem_ite {a : α} {s t : β} : (a ∈ if p then s else t) ↔ (p → a ∈ s) ∧ (¬p → a ∈ t) :=
mem_dite
theorem ite_mem {a b : α} {s : β} : (if p then a else b) ∈ s ↔ (p → a ∈ s) ∧ (¬p → b ∈ s) :=
dite_mem
end Membership
/-! ### Declarations about equality -/
section Equality
-- todo: change name
theorem forall_cond_comm {α} {s : α → Prop} {p : α → α → Prop} :
(∀ a, s a → ∀ b, s b → p a b) ↔ ∀ a b, s a → s b → p a b :=
⟨fun h a b ha hb ↦ h a ha b hb, fun h a ha b hb ↦ h a b ha hb⟩
theorem forall_mem_comm {α β} [Membership α β] {s : β} {p : α → α → Prop} :
(∀ a (_ : a ∈ s) b (_ : b ∈ s), p a b) ↔ ∀ a b, a ∈ s → b ∈ s → p a b :=
forall_cond_comm
lemma ne_of_eq_of_ne {α : Sort*} {a b c : α} (h₁ : a = b) (h₂ : b ≠ c) : a ≠ c := h₁.symm ▸ h₂
lemma ne_of_ne_of_eq {α : Sort*} {a b c : α} (h₁ : a ≠ b) (h₂ : b = c) : a ≠ c := h₂ ▸ h₁
alias Eq.trans_ne := ne_of_eq_of_ne
alias Ne.trans_eq := ne_of_ne_of_eq
theorem eq_equivalence {α : Sort*} : Equivalence (@Eq α) :=
⟨Eq.refl, @Eq.symm _, @Eq.trans _⟩
-- These were migrated to Batteries but the `@[simp]` attributes were (mysteriously?) removed.
attribute [simp] eq_mp_eq_cast eq_mpr_eq_cast
-- @[simp] -- FIXME simp ignores proof rewrites
theorem congr_refl_left {α β : Sort*} (f : α → β) {a b : α} (h : a = b) :
congr (Eq.refl f) h = congr_arg f h := rfl
-- @[simp] -- FIXME simp ignores proof rewrites
theorem congr_refl_right {α β : Sort*} {f g : α → β} (h : f = g) (a : α) :
congr h (Eq.refl a) = congr_fun h a := rfl
-- @[simp] -- FIXME simp ignores proof rewrites
theorem congr_arg_refl {α β : Sort*} (f : α → β) (a : α) :
congr_arg f (Eq.refl a) = Eq.refl (f a) :=
rfl
-- @[simp] -- FIXME simp ignores proof rewrites
theorem congr_fun_rfl {α β : Sort*} (f : α → β) (a : α) : congr_fun (Eq.refl f) a = Eq.refl (f a) :=
rfl
-- @[simp] -- FIXME simp ignores proof rewrites
theorem congr_fun_congr_arg {α β γ : Sort*} (f : α → β → γ) {a a' : α} (p : a = a') (b : β) :
congr_fun (congr_arg f p) b = congr_arg (fun a ↦ f a b) p := rfl
theorem Eq.rec_eq_cast {α : Sort _} {P : α → Sort _} {x y : α} (h : x = y) (z : P x) :
h ▸ z = cast (congr_arg P h) z := by induction h; rfl
theorem eqRec_heq' {α : Sort*} {a' : α} {motive : (a : α) → a' = a → Sort*}
(p : motive a' (rfl : a' = a')) {a : α} (t : a' = a) :
HEq (@Eq.rec α a' motive p a t) p := by
subst t; rfl
theorem rec_heq_of_heq {α β : Sort _} {a b : α} {C : α → Sort*} {x : C a} {y : β}
(e : a = b) (h : HEq x y) : HEq (e ▸ x) y := by subst e; exact h
theorem rec_heq_iff_heq {α β : Sort _} {a b : α} {C : α → Sort*} {x : C a} {y : β} {e : a = b} :
HEq (e ▸ x) y ↔ HEq x y := by subst e; rfl
theorem heq_rec_iff_heq {α β : Sort _} {a b : α} {C : α → Sort*} {x : β} {y : C a} {e : a = b} :
HEq x (e ▸ y) ↔ HEq x y := by subst e; rfl
@[simp]
theorem cast_heq_iff_heq {α β γ : Sort _} (e : α = β) (a : α) (c : γ) :
HEq (cast e a) c ↔ HEq a c := by subst e; rfl
@[simp]
theorem heq_cast_iff_heq {α β γ : Sort _} (e : β = γ) (a : α) (b : β) :
HEq a (cast e b) ↔ HEq a b := by subst e; rfl
universe u
variable {α β : Sort u} {e : β = α} {a : α} {b : β}
lemma heq_of_eq_cast (e : β = α) : a = cast e b → HEq a b := by rintro rfl; simp
lemma eq_cast_iff_heq : a = cast e b ↔ HEq a b := ⟨heq_of_eq_cast _, fun h ↦ by cases h; rfl⟩
end Equality
/-! ### Declarations about quantifiers -/
section Quantifiers
section Dependent
variable {α : Sort*} {β : α → Sort*} {γ : ∀ a, β a → Sort*}
theorem forall₂_imp {p q : ∀ a, β a → Prop} (h : ∀ a b, p a b → q a b) :
(∀ a b, p a b) → ∀ a b, q a b :=
forall_imp fun i ↦ forall_imp <| h i
theorem forall₃_imp {p q : ∀ a b, γ a b → Prop} (h : ∀ a b c, p a b c → q a b c) :
(∀ a b c, p a b c) → ∀ a b c, q a b c :=
forall_imp fun a ↦ forall₂_imp <| h a
theorem Exists₂.imp {p q : ∀ a, β a → Prop} (h : ∀ a b, p a b → q a b) :
(∃ a b, p a b) → ∃ a b, q a b :=
Exists.imp fun a ↦ Exists.imp <| h a
theorem Exists₃.imp {p q : ∀ a b, γ a b → Prop} (h : ∀ a b c, p a b c → q a b c) :
(∃ a b c, p a b c) → ∃ a b c, q a b c :=
Exists.imp fun a ↦ Exists₂.imp <| h a
end Dependent
variable {α β : Sort*} {p : α → Prop}
theorem forall_swap {p : α → β → Prop} : (∀ x y, p x y) ↔ ∀ y x, p x y :=
⟨fun f x y ↦ f y x, fun f x y ↦ f y x⟩
theorem forall₂_swap
{ι₁ ι₂ : Sort*} {κ₁ : ι₁ → Sort*} {κ₂ : ι₂ → Sort*} {p : ∀ i₁, κ₁ i₁ → ∀ i₂, κ₂ i₂ → Prop} :
(∀ i₁ j₁ i₂ j₂, p i₁ j₁ i₂ j₂) ↔ ∀ i₂ j₂ i₁ j₁, p i₁ j₁ i₂ j₂ := ⟨swap₂, swap₂⟩
/-- We intentionally restrict the type of `α` in this lemma so that this is a safer to use in simp
than `forall_swap`. -/
theorem imp_forall_iff {α : Type*} {p : Prop} {q : α → Prop} : (p → ∀ x, q x) ↔ ∀ x, p → q x :=
forall_swap
lemma imp_forall_iff_forall (A : Prop) (B : A → Prop) :
(A → ∀ h : A, B h) ↔ ∀ h : A, B h := by by_cases h : A <;> simp [h]
theorem exists_swap {p : α → β → Prop} : (∃ x y, p x y) ↔ ∃ y x, p x y :=
⟨fun ⟨x, y, h⟩ ↦ ⟨y, x, h⟩, fun ⟨y, x, h⟩ ↦ ⟨x, y, h⟩⟩
theorem exists_and_exists_comm {P : α → Prop} {Q : β → Prop} :
(∃ a, P a) ∧ (∃ b, Q b) ↔ ∃ a b, P a ∧ Q b :=
⟨fun ⟨⟨a, ha⟩, ⟨b, hb⟩⟩ ↦ ⟨a, b, ⟨ha, hb⟩⟩, fun ⟨a, b, ⟨ha, hb⟩⟩ ↦ ⟨⟨a, ha⟩, ⟨b, hb⟩⟩⟩
export Classical (not_forall)
theorem not_forall_not : (¬∀ x, ¬p x) ↔ ∃ x, p x :=
open scoped Classical in Decidable.not_forall_not
export Classical (not_exists_not)
lemma forall_or_exists_not (P : α → Prop) : (∀ a, P a) ∨ ∃ a, ¬ P a := by
rw [← not_forall]; exact em _
lemma exists_or_forall_not (P : α → Prop) : (∃ a, P a) ∨ ∀ a, ¬ P a := by
rw [← not_exists]; exact em _
theorem forall_imp_iff_exists_imp {α : Sort*} {p : α → Prop} {b : Prop} [ha : Nonempty α] :
(∀ x, p x) → b ↔ ∃ x, p x → b := by
classical
let ⟨a⟩ := ha
refine ⟨fun h ↦ not_forall_not.1 fun h' ↦ ?_, fun ⟨x, hx⟩ h ↦ hx (h x)⟩
exact if hb : b then h' a fun _ ↦ hb else hb <| h fun x ↦ (_root_.not_imp.1 (h' x)).1
@[mfld_simps]
theorem forall_true_iff : (α → True) ↔ True := imp_true_iff _
-- Unfortunately this causes simp to loop sometimes, so we
-- add the 2 and 3 cases as simp lemmas instead
theorem forall_true_iff' (h : ∀ a, p a ↔ True) : (∀ a, p a) ↔ True :=
iff_true_intro fun _ ↦ of_iff_true (h _)
-- This is not marked `@[simp]` because `implies_true : (α → True) = True` works
theorem forall₂_true_iff {β : α → Sort*} : (∀ a, β a → True) ↔ True := by simp
-- This is not marked `@[simp]` because `implies_true : (α → True) = True` works
theorem forall₃_true_iff {β : α → Sort*} {γ : ∀ a, β a → Sort*} :
(∀ (a) (b : β a), γ a b → True) ↔ True := by simp
theorem Decidable.and_forall_ne [DecidableEq α] (a : α) {p : α → Prop} :
(p a ∧ ∀ b, b ≠ a → p b) ↔ ∀ b, p b := by
simp only [← @forall_eq _ p a, ← forall_and, ← or_imp, Decidable.em, forall_const]
theorem and_forall_ne (a : α) : (p a ∧ ∀ b, b ≠ a → p b) ↔ ∀ b, p b :=
open scoped Classical in Decidable.and_forall_ne a
theorem Ne.ne_or_ne {x y : α} (z : α) (h : x ≠ y) : x ≠ z ∨ y ≠ z :=
not_and_or.1 <| mt (and_imp.2 (· ▸ ·)) h.symm
@[simp]
theorem exists_apply_eq_apply' (f : α → β) (a' : α) : ∃ a, f a' = f a := ⟨a', rfl⟩
@[simp]
lemma exists_apply_eq_apply2 {α β γ} {f : α → β → γ} {a : α} {b : β} : ∃ x y, f x y = f a b :=
⟨a, b, rfl⟩
@[simp]
lemma exists_apply_eq_apply2' {α β γ} {f : α → β → γ} {a : α} {b : β} : ∃ x y, f a b = f x y :=
⟨a, b, rfl⟩
@[simp]
lemma exists_apply_eq_apply3 {α β γ δ} {f : α → β → γ → δ} {a : α} {b : β} {c : γ} :
∃ x y z, f x y z = f a b c :=
⟨a, b, c, rfl⟩
@[simp]
lemma exists_apply_eq_apply3' {α β γ δ} {f : α → β → γ → δ} {a : α} {b : β} {c : γ} :
∃ x y z, f a b c = f x y z :=
⟨a, b, c, rfl⟩
/--
The constant function witnesses that
there exists a function sending a given term to a given term.
This is sometimes useful in `simp` to discharge side conditions.
-/
theorem exists_apply_eq (a : α) (b : β) : ∃ f : α → β, f a = b := ⟨fun _ ↦ b, rfl⟩
@[simp] theorem exists_exists_and_eq_and {f : α → β} {p : α → Prop} {q : β → Prop} :
(∃ b, (∃ a, p a ∧ f a = b) ∧ q b) ↔ ∃ a, p a ∧ q (f a) :=
⟨fun ⟨_, ⟨a, ha, hab⟩, hb⟩ ↦ ⟨a, ha, hab.symm ▸ hb⟩, fun ⟨a, hp, hq⟩ ↦ ⟨f a, ⟨a, hp, rfl⟩, hq⟩⟩
@[simp] theorem exists_exists_eq_and {f : α → β} {p : β → Prop} :
| (∃ b, (∃ a, f a = b) ∧ p b) ↔ ∃ a, p (f a) :=
⟨fun ⟨_, ⟨a, ha⟩, hb⟩ ↦ ⟨a, ha.symm ▸ hb⟩, fun ⟨a, ha⟩ ↦ ⟨f a, ⟨a, rfl⟩, ha⟩⟩
@[simp] theorem exists_exists_and_exists_and_eq_and {α β γ : Type*}
| Mathlib/Logic/Basic.lean | 584 | 587 |
/-
Copyright (c) 2020 Nicolò Cavalleri. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Nicolò Cavalleri, Andrew Yang
-/
import Mathlib.RingTheory.Derivation.ToSquareZero
import Mathlib.RingTheory.Ideal.Cotangent
import Mathlib.RingTheory.IsTensorProduct
import Mathlib.RingTheory.EssentialFiniteness
import Mathlib.Algebra.Exact
import Mathlib.LinearAlgebra.TensorProduct.RightExactness
/-!
# The module of kaehler differentials
## Main results
- `KaehlerDifferential`: The module of kaehler differentials. For an `R`-algebra `S`, we provide
the notation `Ω[S⁄R]` for `KaehlerDifferential R S`.
Note that the slash is `\textfractionsolidus`.
- `KaehlerDifferential.D`: The derivation into the module of kaehler differentials.
- `KaehlerDifferential.span_range_derivation`: The image of `D` spans `Ω[S⁄R]` as an `S`-module.
- `KaehlerDifferential.linearMapEquivDerivation`:
The isomorphism `Hom_R(Ω[S⁄R], M) ≃ₗ[S] Der_R(S, M)`.
- `KaehlerDifferential.quotKerTotalEquiv`: An alternative description of `Ω[S⁄R]` as `S` copies
of `S` with kernel (`KaehlerDifferential.kerTotal`) generated by the relations:
1. `dx + dy = d(x + y)`
2. `x dy + y dx = d(x * y)`
3. `dr = 0` for `r ∈ R`
- `KaehlerDifferential.map`: Given a map between the arrows `R →+* A` and `S →+* B`, we have an
`A`-linear map `Ω[A⁄R] → Ω[B⁄S]`.
- `KaehlerDifferential.map_surjective`:
The sequence `Ω[B⁄R] → Ω[B⁄A] → 0` is exact.
- `KaehlerDifferential.exact_mapBaseChange_map`:
The sequence `B ⊗[A] Ω[A⁄R] → Ω[B⁄R] → Ω[B⁄A]` is exact.
- `KaehlerDifferential.exact_kerCotangentToTensor_mapBaseChange`:
If `A → B` is surjective with kernel `I`, then
the sequence `I/I² → B ⊗[A] Ω[A⁄R] → Ω[B⁄R]` is exact.
- `KaehlerDifferential.mapBaseChange_surjective`:
If `A → B` is surjective, then the sequence `B ⊗[A] Ω[A⁄R] → Ω[B⁄R] → 0` is exact.
## Future project
- Define the `IsKaehlerDifferential` predicate.
-/
suppress_compilation
section KaehlerDifferential
open scoped TensorProduct
open Algebra Finsupp
universe u v
variable (R : Type u) (S : Type v) [CommRing R] [CommRing S] [Algebra R S]
/-- The kernel of the multiplication map `S ⊗[R] S →ₐ[R] S`. -/
abbrev KaehlerDifferential.ideal : Ideal (S ⊗[R] S) :=
RingHom.ker (TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S)
variable {S}
theorem KaehlerDifferential.one_smul_sub_smul_one_mem_ideal (a : S) :
(1 : S) ⊗ₜ[R] a - a ⊗ₜ[R] (1 : S) ∈ KaehlerDifferential.ideal R S := by simp [RingHom.mem_ker]
variable {R}
variable {M : Type*} [AddCommGroup M] [Module R M] [Module S M] [IsScalarTower R S M]
/-- For a `R`-derivation `S → M`, this is the map `S ⊗[R] S →ₗ[S] M` sending `s ⊗ₜ t ↦ s • D t`. -/
def Derivation.tensorProductTo (D : Derivation R S M) : S ⊗[R] S →ₗ[S] M :=
TensorProduct.AlgebraTensorModule.lift ((LinearMap.lsmul S (S →ₗ[R] M)).flip D.toLinearMap)
theorem Derivation.tensorProductTo_tmul (D : Derivation R S M) (s t : S) :
D.tensorProductTo (s ⊗ₜ t) = s • D t := rfl
theorem Derivation.tensorProductTo_mul (D : Derivation R S M) (x y : S ⊗[R] S) :
D.tensorProductTo (x * y) =
TensorProduct.lmul' (S := S) R x • D.tensorProductTo y +
TensorProduct.lmul' (S := S) R y • D.tensorProductTo x := by
refine TensorProduct.induction_on x ?_ ?_ ?_
· rw [zero_mul, map_zero, map_zero, zero_smul, smul_zero, add_zero]
swap
· intro x₁ y₁ h₁ h₂
rw [add_mul, map_add, map_add, map_add, add_smul, smul_add, h₁, h₂, add_add_add_comm]
intro x₁ x₂
refine TensorProduct.induction_on y ?_ ?_ ?_
· rw [mul_zero, map_zero, map_zero, zero_smul, smul_zero, add_zero]
swap
· intro x₁ y₁ h₁ h₂
rw [mul_add, map_add, map_add, map_add, add_smul, smul_add, h₁, h₂, add_add_add_comm]
intro x y
simp only [TensorProduct.tmul_mul_tmul, Derivation.tensorProductTo,
TensorProduct.AlgebraTensorModule.lift_apply, TensorProduct.lift.tmul',
TensorProduct.lmul'_apply_tmul]
dsimp
rw [D.leibniz]
simp only [smul_smul, smul_add, mul_comm (x * y) x₁, mul_right_comm x₁ x₂, ← mul_assoc]
variable (R S)
/-- The kernel of `S ⊗[R] S →ₐ[R] S` is generated by `1 ⊗ s - s ⊗ 1` as a `S`-module. -/
theorem KaehlerDifferential.submodule_span_range_eq_ideal :
Submodule.span S (Set.range fun s : S => (1 : S) ⊗ₜ[R] s - s ⊗ₜ[R] (1 : S)) =
(KaehlerDifferential.ideal R S).restrictScalars S := by
apply le_antisymm
· rw [Submodule.span_le]
rintro _ ⟨s, rfl⟩
exact KaehlerDifferential.one_smul_sub_smul_one_mem_ideal _ _
· rintro x (hx : _ = _)
have : x - TensorProduct.lmul' (S := S) R x ⊗ₜ[R] (1 : S) = x := by
rw [hx, TensorProduct.zero_tmul, sub_zero]
rw [← this]
clear this hx
refine TensorProduct.induction_on x ?_ ?_ ?_
· rw [map_zero, TensorProduct.zero_tmul, sub_zero]; exact zero_mem _
· intro x y
have : x ⊗ₜ[R] y - (x * y) ⊗ₜ[R] (1 : S) = x • ((1 : S) ⊗ₜ y - y ⊗ₜ (1 : S)) := by
simp_rw [smul_sub, TensorProduct.smul_tmul', smul_eq_mul, mul_one]
rw [TensorProduct.lmul'_apply_tmul, this]
refine Submodule.smul_mem _ x ?_
apply Submodule.subset_span
exact Set.mem_range_self y
· intro x y hx hy
rw [map_add, TensorProduct.add_tmul, ← sub_add_sub_comm]
exact add_mem hx hy
theorem KaehlerDifferential.span_range_eq_ideal :
Ideal.span (Set.range fun s : S => (1 : S) ⊗ₜ[R] s - s ⊗ₜ[R] (1 : S)) =
KaehlerDifferential.ideal R S := by
apply le_antisymm
· rw [Ideal.span_le]
rintro _ ⟨s, rfl⟩
exact KaehlerDifferential.one_smul_sub_smul_one_mem_ideal _ _
· change (KaehlerDifferential.ideal R S).restrictScalars S ≤ (Ideal.span _).restrictScalars S
rw [← KaehlerDifferential.submodule_span_range_eq_ideal, Ideal.span]
conv_rhs => rw [← Submodule.span_span_of_tower S]
exact Submodule.subset_span
/-- The module of Kähler differentials (Kahler differentials, Kaehler differentials).
This is implemented as `I / I ^ 2` with `I` the kernel of the multiplication map `S ⊗[R] S →ₐ[R] S`.
To view elements as a linear combination of the form `s • D s'`, use
`KaehlerDifferential.tensorProductTo_surjective` and `Derivation.tensorProductTo_tmul`.
We also provide the notation `Ω[S⁄R]` for `KaehlerDifferential R S`.
Note that the slash is `\textfractionsolidus`.
-/
def KaehlerDifferential : Type v :=
(KaehlerDifferential.ideal R S).Cotangent
instance : AddCommGroup (KaehlerDifferential R S) := inferInstanceAs <|
AddCommGroup (KaehlerDifferential.ideal R S).Cotangent
instance KaehlerDifferential.module : Module (S ⊗[R] S) (KaehlerDifferential R S) :=
Ideal.Cotangent.moduleOfTower _
@[inherit_doc KaehlerDifferential]
notation:100 "Ω[" S "⁄" R "]" => KaehlerDifferential R S
instance : Nonempty (Ω[S⁄R]) := ⟨0⟩
instance KaehlerDifferential.module' {R' : Type*} [CommRing R'] [Algebra R' S]
[SMulCommClass R R' S] :
Module R' (Ω[S⁄R]) :=
Submodule.Quotient.module' _
instance : IsScalarTower S (S ⊗[R] S) (Ω[S⁄R]) :=
Ideal.Cotangent.isScalarTower _
instance KaehlerDifferential.isScalarTower_of_tower {R₁ R₂ : Type*} [CommRing R₁] [CommRing R₂]
[Algebra R₁ S] [Algebra R₂ S] [SMul R₁ R₂]
[SMulCommClass R R₁ S] [SMulCommClass R R₂ S] [IsScalarTower R₁ R₂ S] :
IsScalarTower R₁ R₂ (Ω[S⁄R]) :=
Submodule.Quotient.isScalarTower _ _
instance KaehlerDifferential.isScalarTower' : IsScalarTower R (S ⊗[R] S) (Ω[S⁄R]) :=
Submodule.Quotient.isScalarTower _ _
/-- The quotient map `I → Ω[S⁄R]` with `I` being the kernel of `S ⊗[R] S → S`. -/
def KaehlerDifferential.fromIdeal : KaehlerDifferential.ideal R S →ₗ[S ⊗[R] S] Ω[S⁄R] :=
(KaehlerDifferential.ideal R S).toCotangent
/-- (Implementation) The underlying linear map of the derivation into `Ω[S⁄R]`. -/
def KaehlerDifferential.DLinearMap : S →ₗ[R] Ω[S⁄R] :=
((KaehlerDifferential.fromIdeal R S).restrictScalars R).comp
((TensorProduct.includeRight.toLinearMap - TensorProduct.includeLeft.toLinearMap :
S →ₗ[R] S ⊗[R] S).codRestrict
((KaehlerDifferential.ideal R S).restrictScalars R)
(KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R) :
_ →ₗ[R] _)
theorem KaehlerDifferential.DLinearMap_apply (s : S) :
KaehlerDifferential.DLinearMap R S s =
(KaehlerDifferential.ideal R S).toCotangent
⟨1 ⊗ₜ s - s ⊗ₜ 1, KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R s⟩ := rfl
/-- The universal derivation into `Ω[S⁄R]`. -/
def KaehlerDifferential.D : Derivation R S (Ω[S⁄R]) :=
{ toLinearMap := KaehlerDifferential.DLinearMap R S
map_one_eq_zero' := by
dsimp [KaehlerDifferential.DLinearMap_apply, Ideal.toCotangent_apply]
congr
rw [sub_self]
leibniz' := fun a b => by
have : LinearMap.CompatibleSMul { x // x ∈ ideal R S } (Ω[S⁄R]) S (S ⊗[R] S) := inferInstance
dsimp [KaehlerDifferential.DLinearMap_apply]
rw [← LinearMap.map_smul_of_tower (ideal R S).toCotangent,
← LinearMap.map_smul_of_tower (ideal R S).toCotangent,
← map_add (ideal R S).toCotangent, Ideal.toCotangent_eq, pow_two]
convert Submodule.mul_mem_mul (KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R a :)
(KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R b :) using 1
simp only [AddSubgroupClass.coe_sub, Submodule.coe_add, Submodule.coe_mk,
TensorProduct.tmul_mul_tmul, mul_sub, sub_mul, mul_comm b, Submodule.coe_smul_of_tower,
smul_sub, TensorProduct.smul_tmul', smul_eq_mul, mul_one]
ring_nf }
theorem KaehlerDifferential.D_apply (s : S) :
KaehlerDifferential.D R S s =
(KaehlerDifferential.ideal R S).toCotangent
⟨1 ⊗ₜ s - s ⊗ₜ 1, KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R s⟩ := rfl
theorem KaehlerDifferential.span_range_derivation :
Submodule.span S (Set.range <| KaehlerDifferential.D R S) = ⊤ := by
rw [_root_.eq_top_iff]
rintro x -
obtain ⟨⟨x, hx⟩, rfl⟩ := Ideal.toCotangent_surjective _ x
have : x ∈ (KaehlerDifferential.ideal R S).restrictScalars S := hx
rw [← KaehlerDifferential.submodule_span_range_eq_ideal] at this
suffices ∃ hx, (KaehlerDifferential.ideal R S).toCotangent ⟨x, hx⟩ ∈
Submodule.span S (Set.range <| KaehlerDifferential.D R S) by
exact this.choose_spec
refine Submodule.span_induction ?_ ?_ ?_ ?_ this
· rintro _ ⟨x, rfl⟩
refine ⟨KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R x, ?_⟩
apply Submodule.subset_span
exact ⟨x, KaehlerDifferential.DLinearMap_apply R S x⟩
· exact ⟨zero_mem _, Submodule.zero_mem _⟩
· rintro x y - - ⟨hx₁, hx₂⟩ ⟨hy₁, hy₂⟩; exact ⟨add_mem hx₁ hy₁, Submodule.add_mem _ hx₂ hy₂⟩
· rintro r x - ⟨hx₁, hx₂⟩
exact ⟨((KaehlerDifferential.ideal R S).restrictScalars S).smul_mem r hx₁,
Submodule.smul_mem _ r hx₂⟩
/-- `Ω[S⁄R]` is trivial if `R → S` is surjective.
Also see `Algebra.FormallyUnramified.iff_subsingleton_kaehlerDifferential`. -/
lemma KaehlerDifferential.subsingleton_of_surjective (h : Function.Surjective (algebraMap R S)) :
Subsingleton (Ω[S⁄R]) := by
suffices (⊤ : Submodule S (Ω[S⁄R])) ≤ ⊥ from
(subsingleton_iff_forall_eq 0).mpr fun y ↦ this trivial
rw [← KaehlerDifferential.span_range_derivation, Submodule.span_le]
rintro _ ⟨x, rfl⟩; obtain ⟨x, rfl⟩ := h x; simp
variable {R S}
/-- The linear map from `Ω[S⁄R]`, associated with a derivation. -/
def Derivation.liftKaehlerDifferential (D : Derivation R S M) : Ω[S⁄R] →ₗ[S] M := by
refine LinearMap.comp ((((KaehlerDifferential.ideal R S) •
(⊤ : Submodule (S ⊗[R] S) (KaehlerDifferential.ideal R S))).restrictScalars S).liftQ ?_ ?_)
(Submodule.Quotient.restrictScalarsEquiv S _).symm.toLinearMap
· exact D.tensorProductTo.comp ((KaehlerDifferential.ideal R S).subtype.restrictScalars S)
· intro x hx
rw [LinearMap.mem_ker]
refine Submodule.smul_induction_on ((Submodule.restrictScalars_mem _ _ _).mp hx) ?_ ?_
· rintro x hx y -
rw [RingHom.mem_ker] at hx
dsimp
rw [Derivation.tensorProductTo_mul, hx, y.prop, zero_smul, zero_smul, zero_add]
· intro x y ex ey; rw [map_add, ex, ey, zero_add]
theorem Derivation.liftKaehlerDifferential_apply (D : Derivation R S M) (x) :
D.liftKaehlerDifferential ((KaehlerDifferential.ideal R S).toCotangent x) =
D.tensorProductTo x := rfl
theorem Derivation.liftKaehlerDifferential_comp (D : Derivation R S M) :
D.liftKaehlerDifferential.compDer (KaehlerDifferential.D R S) = D := by
ext a
dsimp [KaehlerDifferential.D_apply]
refine (D.liftKaehlerDifferential_apply _).trans ?_
rw [Subtype.coe_mk, map_sub, Derivation.tensorProductTo_tmul, Derivation.tensorProductTo_tmul,
one_smul, D.map_one_eq_zero, smul_zero, sub_zero]
@[simp]
theorem Derivation.liftKaehlerDifferential_comp_D (D' : Derivation R S M) (x : S) :
D'.liftKaehlerDifferential (KaehlerDifferential.D R S x) = D' x :=
Derivation.congr_fun D'.liftKaehlerDifferential_comp x
@[ext]
theorem Derivation.liftKaehlerDifferential_unique (f f' : Ω[S⁄R] →ₗ[S] M)
(hf : f.compDer (KaehlerDifferential.D R S) = f'.compDer (KaehlerDifferential.D R S)) :
f = f' := by
apply LinearMap.ext
intro x
have : x ∈ Submodule.span S (Set.range <| KaehlerDifferential.D R S) := by
rw [KaehlerDifferential.span_range_derivation]; trivial
refine Submodule.span_induction ?_ ?_ ?_ ?_ this
· rintro _ ⟨x, rfl⟩; exact congr_arg (fun D : Derivation R S M => D x) hf
· rw [map_zero, map_zero]
· intro x y _ _ hx hy; rw [map_add, map_add, hx, hy]
· intro a x _ e; simp [e]
variable (R S)
theorem Derivation.liftKaehlerDifferential_D :
(KaehlerDifferential.D R S).liftKaehlerDifferential = LinearMap.id :=
Derivation.liftKaehlerDifferential_unique _ _
(KaehlerDifferential.D R S).liftKaehlerDifferential_comp
variable {R S}
theorem KaehlerDifferential.D_tensorProductTo (x : KaehlerDifferential.ideal R S) :
(KaehlerDifferential.D R S).tensorProductTo x =
(KaehlerDifferential.ideal R S).toCotangent x := by
rw [← Derivation.liftKaehlerDifferential_apply, Derivation.liftKaehlerDifferential_D]
rfl
variable (R S)
theorem KaehlerDifferential.tensorProductTo_surjective :
Function.Surjective (KaehlerDifferential.D R S).tensorProductTo := by
intro x; obtain ⟨x, rfl⟩ := (KaehlerDifferential.ideal R S).toCotangent_surjective x
exact ⟨x, KaehlerDifferential.D_tensorProductTo x⟩
/-- The `S`-linear maps from `Ω[S⁄R]` to `M` are (`S`-linearly) equivalent to `R`-derivations
from `S` to `M`. -/
@[simps! symm_apply apply_apply]
def KaehlerDifferential.linearMapEquivDerivation : (Ω[S⁄R] →ₗ[S] M) ≃ₗ[S] Derivation R S M :=
{ Derivation.llcomp.flip <| KaehlerDifferential.D R S with
invFun := Derivation.liftKaehlerDifferential
left_inv := fun _ =>
Derivation.liftKaehlerDifferential_unique _ _ (Derivation.liftKaehlerDifferential_comp _)
right_inv := Derivation.liftKaehlerDifferential_comp }
/-- The quotient ring of `S ⊗ S ⧸ J ^ 2` by `Ω[S⁄R]` is isomorphic to `S`. -/
def KaehlerDifferential.quotientCotangentIdealRingEquiv :
(S ⊗ S ⧸ KaehlerDifferential.ideal R S ^ 2) ⧸ (KaehlerDifferential.ideal R S).cotangentIdeal ≃+*
S := by
have : Function.RightInverse (TensorProduct.includeLeft (R := R) (S := R) (A := S) (B := S))
(↑(TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S) : S ⊗[R] S →+* S) := by
intro x; rw [AlgHom.coe_toRingHom, ← AlgHom.comp_apply, TensorProduct.lmul'_comp_includeLeft]
rfl
refine (Ideal.quotCotangent _).trans ?_
refine (Ideal.quotEquivOfEq ?_).trans (RingHom.quotientKerEquivOfRightInverse this)
ext; rfl
/-- The quotient ring of `S ⊗ S ⧸ J ^ 2` by `Ω[S⁄R]` is isomorphic to `S` as an `S`-algebra. -/
def KaehlerDifferential.quotientCotangentIdeal :
((S ⊗ S ⧸ KaehlerDifferential.ideal R S ^ 2) ⧸
(KaehlerDifferential.ideal R S).cotangentIdeal) ≃ₐ[S] S :=
{ KaehlerDifferential.quotientCotangentIdealRingEquiv R S with
commutes' := (KaehlerDifferential.quotientCotangentIdealRingEquiv R S).apply_symm_apply }
theorem KaehlerDifferential.End_equiv_aux (f : S →ₐ[R] S ⊗ S ⧸ KaehlerDifferential.ideal R S ^ 2) :
(Ideal.Quotient.mkₐ R (KaehlerDifferential.ideal R S).cotangentIdeal).comp f =
IsScalarTower.toAlgHom R S _ ↔
(TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S).kerSquareLift.comp f = AlgHom.id R S := by
rw [AlgHom.ext_iff, AlgHom.ext_iff]
apply forall_congr'
intro x
have e₁ : (TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S).kerSquareLift (f x) =
KaehlerDifferential.quotientCotangentIdealRingEquiv R S
(Ideal.Quotient.mk (KaehlerDifferential.ideal R S).cotangentIdeal <| f x) := by
generalize f x = y; obtain ⟨y, rfl⟩ := Ideal.Quotient.mk_surjective y; rfl
have e₂ :
x = KaehlerDifferential.quotientCotangentIdealRingEquiv R S (IsScalarTower.toAlgHom R S _ x) :=
(mul_one x).symm
constructor
· intro e
exact (e₁.trans (@RingEquiv.congr_arg _ _ _ _ _ _
(KaehlerDifferential.quotientCotangentIdealRingEquiv R S) _ _ e)).trans e₂.symm
· intro e; apply (KaehlerDifferential.quotientCotangentIdealRingEquiv R S).injective
exact e₁.symm.trans (e.trans e₂)
/- Note: Lean is slow to synthesize these instances (times out).
Without them the endEquivDerivation' and endEquivAuxEquiv both have significant timeouts.
In Mathlib 3, it was slow but not this slow. -/
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
local instance smul_SSmod_SSmod : SMul (S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2)
(S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2) := Mul.toSMul _
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
@[nolint defLemma]
local instance isScalarTower_S_right :
IsScalarTower S (S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2)
(S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2) := Ideal.Quotient.isScalarTower_right
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
@[nolint defLemma]
local instance isScalarTower_R_right :
IsScalarTower R (S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2)
(S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2) := Ideal.Quotient.isScalarTower_right
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
@[nolint defLemma]
local instance isScalarTower_SS_right : IsScalarTower (S ⊗[R] S)
(S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2) (S ⊗[R] S ⧸ KaehlerDifferential.ideal R S ^ 2) :=
Ideal.Quotient.isScalarTower_right
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
local instance instS : Module S (KaehlerDifferential.ideal R S).cotangentIdeal :=
Submodule.module' _
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
local instance instR : Module R (KaehlerDifferential.ideal R S).cotangentIdeal :=
Submodule.module' _
/-- A shortcut instance to prevent timing out. Hopefully to be removed in the future. -/
local instance instSS : Module (S ⊗[R] S) (KaehlerDifferential.ideal R S).cotangentIdeal :=
Submodule.module' _
/-- Derivations into `Ω[S⁄R]` is equivalent to derivations
into `(KaehlerDifferential.ideal R S).cotangentIdeal`. -/
noncomputable def KaehlerDifferential.endEquivDerivation' :
Derivation R S (Ω[S⁄R]) ≃ₗ[R] Derivation R S (ideal R S).cotangentIdeal :=
LinearEquiv.compDer ((KaehlerDifferential.ideal R S).cotangentEquivIdeal.restrictScalars S)
/-- (Implementation) An `Equiv` version of `KaehlerDifferential.End_equiv_aux`.
Used in `KaehlerDifferential.endEquiv`. -/
def KaehlerDifferential.endEquivAuxEquiv :
{ f //
(Ideal.Quotient.mkₐ R (KaehlerDifferential.ideal R S).cotangentIdeal).comp f =
IsScalarTower.toAlgHom R S _ } ≃
{ f // (TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S).kerSquareLift.comp f = AlgHom.id R S } :=
(Equiv.refl _).subtypeEquiv (KaehlerDifferential.End_equiv_aux R S)
/--
The endomorphisms of `Ω[S⁄R]` corresponds to sections of the surjection `S ⊗[R] S ⧸ J ^ 2 →ₐ[R] S`,
with `J` being the kernel of the multiplication map `S ⊗[R] S →ₐ[R] S`.
-/
noncomputable def KaehlerDifferential.endEquiv :
Module.End S (Ω[S⁄R]) ≃
{ f // (TensorProduct.lmul' R : S ⊗[R] S →ₐ[R] S).kerSquareLift.comp f = AlgHom.id R S } :=
(KaehlerDifferential.linearMapEquivDerivation R S).toEquiv.trans <|
(KaehlerDifferential.endEquivDerivation' R S).toEquiv.trans <|
(derivationToSquareZeroEquivLift (KaehlerDifferential.ideal R S).cotangentIdeal
(KaehlerDifferential.ideal R S).cotangentIdeal_square).trans <|
KaehlerDifferential.endEquivAuxEquiv R S
section Finiteness
theorem KaehlerDifferential.ideal_fg [EssFiniteType R S] :
(KaehlerDifferential.ideal R S).FG := by
classical
use (EssFiniteType.finset R S).image (fun s ↦ (1 : S) ⊗ₜ[R] s - s ⊗ₜ[R] (1 : S))
apply le_antisymm
· rw [Finset.coe_image, Ideal.span_le]
rintro _ ⟨x, _, rfl⟩
exact KaehlerDifferential.one_smul_sub_smul_one_mem_ideal R x
· rw [← KaehlerDifferential.span_range_eq_ideal, Ideal.span_le]
rintro _ ⟨x, rfl⟩
let I : Ideal (S ⊗[R] S) := Ideal.span
((EssFiniteType.finset R S).image (fun s ↦ (1 : S) ⊗ₜ[R] s - s ⊗ₜ[R] (1 : S)))
show _ - _ ∈ I
have : (IsScalarTower.toAlgHom R (S ⊗[R] S) (S ⊗[R] S ⧸ I)).comp TensorProduct.includeRight =
(IsScalarTower.toAlgHom R (S ⊗[R] S) (S ⊗[R] S ⧸ I)).comp TensorProduct.includeLeft := by
apply EssFiniteType.algHom_ext
intro a ha
simp only [AlgHom.coe_comp, IsScalarTower.coe_toAlgHom', Ideal.Quotient.algebraMap_eq,
Function.comp_apply, TensorProduct.includeLeft_apply, TensorProduct.includeRight_apply,
Ideal.Quotient.mk_eq_mk_iff_sub_mem]
refine Ideal.subset_span ?_
simp only [Finset.coe_image, Set.mem_image, Finset.mem_coe]
exact ⟨a, ha, rfl⟩
simpa [Ideal.Quotient.mk_eq_mk_iff_sub_mem] using AlgHom.congr_fun this x
instance KaehlerDifferential.finite [EssFiniteType R S] :
Module.Finite S (Ω[S⁄R]) := by
classical
let s := (EssFiniteType.finset R S).image (fun s ↦ D R S s)
refine ⟨⟨s, top_le_iff.mp ?_⟩⟩
rw [← span_range_derivation, Submodule.span_le]
rintro _ ⟨x, rfl⟩
have : ∀ x ∈ adjoin R (EssFiniteType.finset R S).toSet,
.D _ _ x ∈ Submodule.span S s.toSet := by
intro x hx
refine adjoin_induction ?_ ?_ ?_ ?_ hx
· exact fun x hx ↦ Submodule.subset_span (Finset.mem_image_of_mem _ hx)
· simp
· exact fun x y _ _ hx hy ↦ (D R S).map_add x y ▸ add_mem hx hy
· intro x y _ _ hx hy
simp only [Derivation.leibniz]
exact add_mem (Submodule.smul_mem _ _ hy) (Submodule.smul_mem _ _ hx)
obtain ⟨t, ht, ht', hxt⟩ := (essFiniteType_cond_iff R S (EssFiniteType.finset R S)).mp
EssFiniteType.cond.choose_spec x
rw [show D R S x =
ht'.unit⁻¹ • (D R S (x * t) - x • D R S t) by simp [smul_smul, Units.smul_def]]
exact Submodule.smul_mem _ _ (sub_mem (this _ hxt) (Submodule.smul_mem _ _ (this _ ht)))
end Finiteness
section Presentation
open KaehlerDifferential (D)
open Finsupp (single)
/-- The `S`-submodule of `S →₀ S` (the direct sum of copies of `S` indexed by `S`) generated by
the relations:
1. `dx + dy = d(x + y)`
2. `x dy + y dx = d(x * y)`
3. `dr = 0` for `r ∈ R`
where `db` is the unit in the copy of `S` with index `b`.
This is the kernel of the surjection
`Finsupp.linearCombination S Ω[S⁄R] S (KaehlerDifferential.D R S)`.
See `KaehlerDifferential.kerTotal_eq` and `KaehlerDifferential.linearCombination_surjective`.
-/
noncomputable def KaehlerDifferential.kerTotal : Submodule S (S →₀ S) :=
Submodule.span S
(((Set.range fun x : S × S => single x.1 1 + single x.2 1 - single (x.1 + x.2) 1) ∪
Set.range fun x : S × S => single x.2 x.1 + single x.1 x.2 - single (x.1 * x.2) 1) ∪
Set.range fun x : R => single (algebraMap R S x) 1)
unsuppress_compilation in
-- Porting note: was `local notation x "𝖣" y => (KaehlerDifferential.kerTotal R S).mkQ (single y x)`
-- but not having `DFunLike.coe` leads to `kerTotal_mkQ_single_smul` failing.
local notation3 x "𝖣" y => DFunLike.coe (KaehlerDifferential.kerTotal R S).mkQ (single y x)
theorem KaehlerDifferential.kerTotal_mkQ_single_add (x y z) : (z𝖣x + y) = (z𝖣x) + z𝖣y := by
rw [← map_add, eq_comm, ← sub_eq_zero, ← map_sub (Submodule.mkQ (kerTotal R S)),
Submodule.mkQ_apply, Submodule.Quotient.mk_eq_zero]
simp_rw [← Finsupp.smul_single_one _ z, ← smul_add, ← smul_sub]
exact Submodule.smul_mem _ _ (Submodule.subset_span (Or.inl <| Or.inl <| ⟨⟨_, _⟩, rfl⟩))
theorem KaehlerDifferential.kerTotal_mkQ_single_mul (x y z) :
(z𝖣x * y) = ((z * x)𝖣y) + (z * y)𝖣x := by
rw [← map_add, eq_comm, ← sub_eq_zero, ← map_sub (Submodule.mkQ (kerTotal R S)),
Submodule.mkQ_apply, Submodule.Quotient.mk_eq_zero]
simp_rw [← Finsupp.smul_single_one _ z, ← @smul_eq_mul _ _ z, ← Finsupp.smul_single, ← smul_add,
← smul_sub]
exact Submodule.smul_mem _ _ (Submodule.subset_span (Or.inl <| Or.inr <| ⟨⟨_, _⟩, rfl⟩))
theorem KaehlerDifferential.kerTotal_mkQ_single_algebraMap (x y) : (y𝖣algebraMap R S x) = 0 := by
rw [Submodule.mkQ_apply, Submodule.Quotient.mk_eq_zero, ← Finsupp.smul_single_one _ y]
exact Submodule.smul_mem _ _ (Submodule.subset_span (Or.inr <| ⟨_, rfl⟩))
theorem KaehlerDifferential.kerTotal_mkQ_single_algebraMap_one (x) : (x𝖣1) = 0 := by
rw [← (algebraMap R S).map_one, KaehlerDifferential.kerTotal_mkQ_single_algebraMap]
theorem KaehlerDifferential.kerTotal_mkQ_single_smul (r : R) (x y) : (y𝖣r • x) = r • y𝖣x := by
letI : SMulZeroClass R S := inferInstance
rw [Algebra.smul_def, KaehlerDifferential.kerTotal_mkQ_single_mul,
KaehlerDifferential.kerTotal_mkQ_single_algebraMap, add_zero, ← LinearMap.map_smul_of_tower,
Finsupp.smul_single, mul_comm, Algebra.smul_def]
/-- The (universal) derivation into `(S →₀ S) ⧸ KaehlerDifferential.kerTotal R S`. -/
noncomputable def KaehlerDifferential.derivationQuotKerTotal :
Derivation R S ((S →₀ S) ⧸ KaehlerDifferential.kerTotal R S) where
toFun x := 1𝖣x
map_add' _ _ := KaehlerDifferential.kerTotal_mkQ_single_add _ _ _ _ _
map_smul' _ _ := KaehlerDifferential.kerTotal_mkQ_single_smul _ _ _ _ _
map_one_eq_zero' := KaehlerDifferential.kerTotal_mkQ_single_algebraMap_one _ _ _
leibniz' a b :=
(KaehlerDifferential.kerTotal_mkQ_single_mul _ _ _ _ _).trans
(by simp_rw [← Finsupp.smul_single_one _ (1 * _ : S)]; dsimp; simp)
theorem KaehlerDifferential.derivationQuotKerTotal_apply (x) :
KaehlerDifferential.derivationQuotKerTotal R S x = 1𝖣x :=
rfl
theorem KaehlerDifferential.derivationQuotKerTotal_lift_comp_linearCombination :
(KaehlerDifferential.derivationQuotKerTotal R S).liftKaehlerDifferential.comp
(Finsupp.linearCombination S (KaehlerDifferential.D R S)) =
Submodule.mkQ _ := by
apply Finsupp.lhom_ext
intro a b
conv_rhs => rw [← Finsupp.smul_single_one a b, LinearMap.map_smul]
simp [KaehlerDifferential.derivationQuotKerTotal_apply]
theorem KaehlerDifferential.kerTotal_eq :
LinearMap.ker (Finsupp.linearCombination S (KaehlerDifferential.D R S)) =
KaehlerDifferential.kerTotal R S := by
apply le_antisymm
· conv_rhs => rw [← (KaehlerDifferential.kerTotal R S).ker_mkQ]
rw [← KaehlerDifferential.derivationQuotKerTotal_lift_comp_linearCombination]
exact LinearMap.ker_le_ker_comp _ _
· rw [KaehlerDifferential.kerTotal, Submodule.span_le]
rintro _ ((⟨⟨x, y⟩, rfl⟩ | ⟨⟨x, y⟩, rfl⟩) | ⟨x, rfl⟩) <;> dsimp <;> simp [LinearMap.mem_ker]
theorem KaehlerDifferential.linearCombination_surjective :
Function.Surjective (Finsupp.linearCombination S (KaehlerDifferential.D R S)) := by
rw [← LinearMap.range_eq_top, range_linearCombination, span_range_derivation]
/-- `Ω[S⁄R]` is isomorphic to `S` copies of `S` with kernel `KaehlerDifferential.kerTotal`. -/
@[simps!]
noncomputable def KaehlerDifferential.quotKerTotalEquiv :
((S →₀ S) ⧸ KaehlerDifferential.kerTotal R S) ≃ₗ[S] Ω[S⁄R] :=
{ (KaehlerDifferential.kerTotal R S).liftQ
(Finsupp.linearCombination S (KaehlerDifferential.D R S))
(KaehlerDifferential.kerTotal_eq R S).ge with
invFun := (KaehlerDifferential.derivationQuotKerTotal R S).liftKaehlerDifferential
left_inv := by
intro x
obtain ⟨x, rfl⟩ := Submodule.mkQ_surjective _ x
exact
LinearMap.congr_fun
(KaehlerDifferential.derivationQuotKerTotal_lift_comp_linearCombination R S :) x
right_inv := by
intro x
obtain ⟨x, rfl⟩ := KaehlerDifferential.linearCombination_surjective R S x
have := LinearMap.congr_fun
(KaehlerDifferential.derivationQuotKerTotal_lift_comp_linearCombination R S) x
rw [LinearMap.comp_apply] at this
rw [this]
rfl }
|
theorem KaehlerDifferential.quotKerTotalEquiv_symm_comp_D :
(KaehlerDifferential.quotKerTotalEquiv R S).symm.toLinearMap.compDer
(KaehlerDifferential.D R S) =
KaehlerDifferential.derivationQuotKerTotal R S := by
| Mathlib/RingTheory/Kaehler/Basic.lean | 604 | 608 |
/-
Copyright (c) 2019 Kevin Buzzard. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kevin Buzzard
-/
import Mathlib.Data.EReal.Basic
deprecated_module (since := "2025-04-13")
| Mathlib/Data/Real/EReal.lean | 533 | 537 | |
/-
Copyright (c) 2019 Reid Barton. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Topology.Constructions
/-!
# Neighborhoods and continuity relative to a subset
This file develops API on the relative versions
* `nhdsWithin` of `nhds`
* `ContinuousOn` of `Continuous`
* `ContinuousWithinAt` of `ContinuousAt`
related to continuity, which are defined in previous definition files.
Their basic properties studied in this file include the relationships between
these restricted notions and the corresponding notions for the subtype
equipped with the subspace topology.
## Notation
* `𝓝 x`: the filter of neighborhoods of a point `x`;
* `𝓟 s`: the principal filter of a set `s`;
* `𝓝[s] x`: the filter `nhdsWithin x s` of neighborhoods of a point `x` within a set `s`.
-/
open Set Filter Function Topology Filter
variable {α β γ δ : Type*}
variable [TopologicalSpace α]
/-!
## Properties of the neighborhood-within filter
-/
@[simp]
theorem nhds_bind_nhdsWithin {a : α} {s : Set α} : ((𝓝 a).bind fun x => 𝓝[s] x) = 𝓝[s] a :=
bind_inf_principal.trans <| congr_arg₂ _ nhds_bind_nhds rfl
@[simp]
theorem eventually_nhds_nhdsWithin {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ y in 𝓝 a, ∀ᶠ x in 𝓝[s] y, p x) ↔ ∀ᶠ x in 𝓝[s] a, p x :=
Filter.ext_iff.1 nhds_bind_nhdsWithin { x | p x }
theorem eventually_nhdsWithin_iff {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ x in 𝓝[s] a, p x) ↔ ∀ᶠ x in 𝓝 a, x ∈ s → p x :=
eventually_inf_principal
theorem frequently_nhdsWithin_iff {z : α} {s : Set α} {p : α → Prop} :
(∃ᶠ x in 𝓝[s] z, p x) ↔ ∃ᶠ x in 𝓝 z, p x ∧ x ∈ s :=
frequently_inf_principal.trans <| by simp only [and_comm]
theorem mem_closure_ne_iff_frequently_within {z : α} {s : Set α} :
z ∈ closure (s \ {z}) ↔ ∃ᶠ x in 𝓝[≠] z, x ∈ s := by
simp [mem_closure_iff_frequently, frequently_nhdsWithin_iff]
@[simp]
theorem eventually_eventually_nhdsWithin {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ y in 𝓝[s] a, ∀ᶠ x in 𝓝[s] y, p x) ↔ ∀ᶠ x in 𝓝[s] a, p x := by
refine ⟨fun h => ?_, fun h => (eventually_nhds_nhdsWithin.2 h).filter_mono inf_le_left⟩
simp only [eventually_nhdsWithin_iff] at h ⊢
exact h.mono fun x hx hxs => (hx hxs).self_of_nhds hxs
@[simp]
theorem eventually_mem_nhdsWithin_iff {x : α} {s t : Set α} :
(∀ᶠ x' in 𝓝[s] x, t ∈ 𝓝[s] x') ↔ t ∈ 𝓝[s] x :=
eventually_eventually_nhdsWithin
theorem nhdsWithin_eq (a : α) (s : Set α) :
𝓝[s] a = ⨅ t ∈ { t : Set α | a ∈ t ∧ IsOpen t }, 𝓟 (t ∩ s) :=
((nhds_basis_opens a).inf_principal s).eq_biInf
@[simp] lemma nhdsWithin_univ (a : α) : 𝓝[Set.univ] a = 𝓝 a := by
rw [nhdsWithin, principal_univ, inf_top_eq]
theorem nhdsWithin_hasBasis {ι : Sort*} {p : ι → Prop} {s : ι → Set α} {a : α}
(h : (𝓝 a).HasBasis p s) (t : Set α) : (𝓝[t] a).HasBasis p fun i => s i ∩ t :=
h.inf_principal t
theorem nhdsWithin_basis_open (a : α) (t : Set α) :
(𝓝[t] a).HasBasis (fun u => a ∈ u ∧ IsOpen u) fun u => u ∩ t :=
nhdsWithin_hasBasis (nhds_basis_opens a) t
theorem mem_nhdsWithin {t : Set α} {a : α} {s : Set α} :
t ∈ 𝓝[s] a ↔ ∃ u, IsOpen u ∧ a ∈ u ∧ u ∩ s ⊆ t := by
simpa only [and_assoc, and_left_comm] using (nhdsWithin_basis_open a s).mem_iff
theorem mem_nhdsWithin_iff_exists_mem_nhds_inter {t : Set α} {a : α} {s : Set α} :
t ∈ 𝓝[s] a ↔ ∃ u ∈ 𝓝 a, u ∩ s ⊆ t :=
(nhdsWithin_hasBasis (𝓝 a).basis_sets s).mem_iff
theorem diff_mem_nhdsWithin_compl {x : α} {s : Set α} (hs : s ∈ 𝓝 x) (t : Set α) :
s \ t ∈ 𝓝[tᶜ] x :=
diff_mem_inf_principal_compl hs t
theorem diff_mem_nhdsWithin_diff {x : α} {s t : Set α} (hs : s ∈ 𝓝[t] x) (t' : Set α) :
s \ t' ∈ 𝓝[t \ t'] x := by
rw [nhdsWithin, diff_eq, diff_eq, ← inf_principal, ← inf_assoc]
exact inter_mem_inf hs (mem_principal_self _)
theorem nhds_of_nhdsWithin_of_nhds {s t : Set α} {a : α} (h1 : s ∈ 𝓝 a) (h2 : t ∈ 𝓝[s] a) :
t ∈ 𝓝 a := by
rcases mem_nhdsWithin_iff_exists_mem_nhds_inter.mp h2 with ⟨_, Hw, hw⟩
exact (𝓝 a).sets_of_superset ((𝓝 a).inter_sets Hw h1) hw
theorem mem_nhdsWithin_iff_eventually {s t : Set α} {x : α} :
t ∈ 𝓝[s] x ↔ ∀ᶠ y in 𝓝 x, y ∈ s → y ∈ t :=
eventually_inf_principal
theorem mem_nhdsWithin_iff_eventuallyEq {s t : Set α} {x : α} :
t ∈ 𝓝[s] x ↔ s =ᶠ[𝓝 x] (s ∩ t : Set α) := by
simp_rw [mem_nhdsWithin_iff_eventually, eventuallyEq_set, mem_inter_iff, iff_self_and]
theorem nhdsWithin_eq_iff_eventuallyEq {s t : Set α} {x : α} : 𝓝[s] x = 𝓝[t] x ↔ s =ᶠ[𝓝 x] t :=
set_eventuallyEq_iff_inf_principal.symm
theorem nhdsWithin_le_iff {s t : Set α} {x : α} : 𝓝[s] x ≤ 𝓝[t] x ↔ t ∈ 𝓝[s] x :=
set_eventuallyLE_iff_inf_principal_le.symm.trans set_eventuallyLE_iff_mem_inf_principal
theorem preimage_nhdsWithin_coinduced' {π : α → β} {s : Set β} {t : Set α} {a : α} (h : a ∈ t)
(hs : s ∈ @nhds β (.coinduced (fun x : t => π x) inferInstance) (π a)) :
π ⁻¹' s ∈ 𝓝[t] a := by
lift a to t using h
replace hs : (fun x : t => π x) ⁻¹' s ∈ 𝓝 a := preimage_nhds_coinduced hs
rwa [← map_nhds_subtype_val, mem_map]
theorem mem_nhdsWithin_of_mem_nhds {s t : Set α} {a : α} (h : s ∈ 𝓝 a) : s ∈ 𝓝[t] a :=
mem_inf_of_left h
theorem self_mem_nhdsWithin {a : α} {s : Set α} : s ∈ 𝓝[s] a :=
mem_inf_of_right (mem_principal_self s)
theorem eventually_mem_nhdsWithin {a : α} {s : Set α} : ∀ᶠ x in 𝓝[s] a, x ∈ s :=
self_mem_nhdsWithin
theorem inter_mem_nhdsWithin (s : Set α) {t : Set α} {a : α} (h : t ∈ 𝓝 a) : s ∩ t ∈ 𝓝[s] a :=
inter_mem self_mem_nhdsWithin (mem_inf_of_left h)
theorem pure_le_nhdsWithin {a : α} {s : Set α} (ha : a ∈ s) : pure a ≤ 𝓝[s] a :=
le_inf (pure_le_nhds a) (le_principal_iff.2 ha)
theorem mem_of_mem_nhdsWithin {a : α} {s t : Set α} (ha : a ∈ s) (ht : t ∈ 𝓝[s] a) : a ∈ t :=
pure_le_nhdsWithin ha ht
theorem Filter.Eventually.self_of_nhdsWithin {p : α → Prop} {s : Set α} {x : α}
(h : ∀ᶠ y in 𝓝[s] x, p y) (hx : x ∈ s) : p x :=
mem_of_mem_nhdsWithin hx h
theorem tendsto_const_nhdsWithin {l : Filter β} {s : Set α} {a : α} (ha : a ∈ s) :
Tendsto (fun _ : β => a) l (𝓝[s] a) :=
tendsto_const_pure.mono_right <| pure_le_nhdsWithin ha
theorem nhdsWithin_restrict'' {a : α} (s : Set α) {t : Set α} (h : t ∈ 𝓝[s] a) :
𝓝[s] a = 𝓝[s ∩ t] a :=
le_antisymm (le_inf inf_le_left (le_principal_iff.mpr (inter_mem self_mem_nhdsWithin h)))
(inf_le_inf_left _ (principal_mono.mpr Set.inter_subset_left))
theorem nhdsWithin_restrict' {a : α} (s : Set α) {t : Set α} (h : t ∈ 𝓝 a) : 𝓝[s] a = 𝓝[s ∩ t] a :=
nhdsWithin_restrict'' s <| mem_inf_of_left h
theorem nhdsWithin_restrict {a : α} (s : Set α) {t : Set α} (h₀ : a ∈ t) (h₁ : IsOpen t) :
𝓝[s] a = 𝓝[s ∩ t] a :=
nhdsWithin_restrict' s (IsOpen.mem_nhds h₁ h₀)
theorem nhdsWithin_le_of_mem {a : α} {s t : Set α} (h : s ∈ 𝓝[t] a) : 𝓝[t] a ≤ 𝓝[s] a :=
nhdsWithin_le_iff.mpr h
theorem nhdsWithin_le_nhds {a : α} {s : Set α} : 𝓝[s] a ≤ 𝓝 a := by
rw [← nhdsWithin_univ]
apply nhdsWithin_le_of_mem
exact univ_mem
theorem nhdsWithin_eq_nhdsWithin' {a : α} {s t u : Set α} (hs : s ∈ 𝓝 a) (h₂ : t ∩ s = u ∩ s) :
𝓝[t] a = 𝓝[u] a := by rw [nhdsWithin_restrict' t hs, nhdsWithin_restrict' u hs, h₂]
theorem nhdsWithin_eq_nhdsWithin {a : α} {s t u : Set α} (h₀ : a ∈ s) (h₁ : IsOpen s)
(h₂ : t ∩ s = u ∩ s) : 𝓝[t] a = 𝓝[u] a := by
rw [nhdsWithin_restrict t h₀ h₁, nhdsWithin_restrict u h₀ h₁, h₂]
@[simp] theorem nhdsWithin_eq_nhds {a : α} {s : Set α} : 𝓝[s] a = 𝓝 a ↔ s ∈ 𝓝 a :=
inf_eq_left.trans le_principal_iff
theorem IsOpen.nhdsWithin_eq {a : α} {s : Set α} (h : IsOpen s) (ha : a ∈ s) : 𝓝[s] a = 𝓝 a :=
nhdsWithin_eq_nhds.2 <| h.mem_nhds ha
theorem preimage_nhds_within_coinduced {π : α → β} {s : Set β} {t : Set α} {a : α} (h : a ∈ t)
(ht : IsOpen t)
(hs : s ∈ @nhds β (.coinduced (fun x : t => π x) inferInstance) (π a)) :
π ⁻¹' s ∈ 𝓝 a := by
rw [← ht.nhdsWithin_eq h]
exact preimage_nhdsWithin_coinduced' h hs
@[simp]
theorem nhdsWithin_empty (a : α) : 𝓝[∅] a = ⊥ := by rw [nhdsWithin, principal_empty, inf_bot_eq]
theorem nhdsWithin_union (a : α) (s t : Set α) : 𝓝[s ∪ t] a = 𝓝[s] a ⊔ 𝓝[t] a := by
delta nhdsWithin
rw [← inf_sup_left, sup_principal]
theorem nhds_eq_nhdsWithin_sup_nhdsWithin (b : α) {I₁ I₂ : Set α} (hI : Set.univ = I₁ ∪ I₂) :
nhds b = nhdsWithin b I₁ ⊔ nhdsWithin b I₂ := by
rw [← nhdsWithin_univ b, hI, nhdsWithin_union]
/-- If `L` and `R` are neighborhoods of `b` within sets whose union is `Set.univ`, then
`L ∪ R` is a neighborhood of `b`. -/
theorem union_mem_nhds_of_mem_nhdsWithin {b : α}
{I₁ I₂ : Set α} (h : Set.univ = I₁ ∪ I₂)
{L : Set α} (hL : L ∈ nhdsWithin b I₁)
{R : Set α} (hR : R ∈ nhdsWithin b I₂) : L ∪ R ∈ nhds b := by
rw [← nhdsWithin_univ b, h, nhdsWithin_union]
exact ⟨mem_of_superset hL (by simp), mem_of_superset hR (by simp)⟩
/-- Writing a punctured neighborhood filter as a sup of left and right filters. -/
lemma punctured_nhds_eq_nhdsWithin_sup_nhdsWithin [LinearOrder α] {x : α} :
𝓝[≠] x = 𝓝[<] x ⊔ 𝓝[>] x := by
rw [← Iio_union_Ioi, nhdsWithin_union]
/-- Obtain a "predictably-sided" neighborhood of `b` from two one-sided neighborhoods. -/
theorem nhds_of_Ici_Iic [LinearOrder α] {b : α}
{L : Set α} (hL : L ∈ 𝓝[≤] b)
{R : Set α} (hR : R ∈ 𝓝[≥] b) : L ∩ Iic b ∪ R ∩ Ici b ∈ 𝓝 b :=
union_mem_nhds_of_mem_nhdsWithin Iic_union_Ici.symm
(inter_mem hL self_mem_nhdsWithin) (inter_mem hR self_mem_nhdsWithin)
theorem nhdsWithin_biUnion {ι} {I : Set ι} (hI : I.Finite) (s : ι → Set α) (a : α) :
𝓝[⋃ i ∈ I, s i] a = ⨆ i ∈ I, 𝓝[s i] a := by
induction I, hI using Set.Finite.induction_on with
| empty => simp
| insert _ _ hT => simp only [hT, nhdsWithin_union, iSup_insert, biUnion_insert]
theorem nhdsWithin_sUnion {S : Set (Set α)} (hS : S.Finite) (a : α) :
𝓝[⋃₀ S] a = ⨆ s ∈ S, 𝓝[s] a := by
rw [sUnion_eq_biUnion, nhdsWithin_biUnion hS]
theorem nhdsWithin_iUnion {ι} [Finite ι] (s : ι → Set α) (a : α) :
𝓝[⋃ i, s i] a = ⨆ i, 𝓝[s i] a := by
rw [← sUnion_range, nhdsWithin_sUnion (finite_range s), iSup_range]
theorem nhdsWithin_inter (a : α) (s t : Set α) : 𝓝[s ∩ t] a = 𝓝[s] a ⊓ 𝓝[t] a := by
delta nhdsWithin
rw [inf_left_comm, inf_assoc, inf_principal, ← inf_assoc, inf_idem]
theorem nhdsWithin_inter' (a : α) (s t : Set α) : 𝓝[s ∩ t] a = 𝓝[s] a ⊓ 𝓟 t := by
delta nhdsWithin
rw [← inf_principal, inf_assoc]
theorem nhdsWithin_inter_of_mem {a : α} {s t : Set α} (h : s ∈ 𝓝[t] a) : 𝓝[s ∩ t] a = 𝓝[t] a := by
rw [nhdsWithin_inter, inf_eq_right]
exact nhdsWithin_le_of_mem h
theorem nhdsWithin_inter_of_mem' {a : α} {s t : Set α} (h : t ∈ 𝓝[s] a) : 𝓝[s ∩ t] a = 𝓝[s] a := by
rw [inter_comm, nhdsWithin_inter_of_mem h]
@[simp]
theorem nhdsWithin_singleton (a : α) : 𝓝[{a}] a = pure a := by
rw [nhdsWithin, principal_singleton, inf_eq_right.2 (pure_le_nhds a)]
@[simp]
theorem nhdsWithin_insert (a : α) (s : Set α) : 𝓝[insert a s] a = pure a ⊔ 𝓝[s] a := by
rw [← singleton_union, nhdsWithin_union, nhdsWithin_singleton]
theorem mem_nhdsWithin_insert {a : α} {s t : Set α} : t ∈ 𝓝[insert a s] a ↔ a ∈ t ∧ t ∈ 𝓝[s] a := by
simp
theorem insert_mem_nhdsWithin_insert {a : α} {s t : Set α} (h : t ∈ 𝓝[s] a) :
insert a t ∈ 𝓝[insert a s] a := by simp [mem_of_superset h]
theorem insert_mem_nhds_iff {a : α} {s : Set α} : insert a s ∈ 𝓝 a ↔ s ∈ 𝓝[≠] a := by
simp only [nhdsWithin, mem_inf_principal, mem_compl_iff, mem_singleton_iff, or_iff_not_imp_left,
insert_def]
@[simp]
theorem nhdsNE_sup_pure (a : α) : 𝓝[≠] a ⊔ pure a = 𝓝 a := by
rw [← nhdsWithin_singleton, ← nhdsWithin_union, compl_union_self, nhdsWithin_univ]
@[deprecated (since := "2025-03-02")]
alias nhdsWithin_compl_singleton_sup_pure := nhdsNE_sup_pure
@[simp]
theorem pure_sup_nhdsNE (a : α) : pure a ⊔ 𝓝[≠] a = 𝓝 a := by rw [← sup_comm, nhdsNE_sup_pure]
theorem nhdsWithin_prod [TopologicalSpace β]
{s u : Set α} {t v : Set β} {a : α} {b : β} (hu : u ∈ 𝓝[s] a) (hv : v ∈ 𝓝[t] b) :
u ×ˢ v ∈ 𝓝[s ×ˢ t] (a, b) := by
rw [nhdsWithin_prod_eq]
exact prod_mem_prod hu hv
lemma Filter.EventuallyEq.mem_interior {x : α} {s t : Set α} (hst : s =ᶠ[𝓝 x] t)
(h : x ∈ interior s) : x ∈ interior t := by
rw [← nhdsWithin_eq_iff_eventuallyEq] at hst
simpa [mem_interior_iff_mem_nhds, ← nhdsWithin_eq_nhds, hst] using h
lemma Filter.EventuallyEq.mem_interior_iff {x : α} {s t : Set α} (hst : s =ᶠ[𝓝 x] t) :
x ∈ interior s ↔ x ∈ interior t :=
⟨fun h ↦ hst.mem_interior h, fun h ↦ hst.symm.mem_interior h⟩
@[deprecated (since := "2024-11-11")]
alias EventuallyEq.mem_interior_iff := Filter.EventuallyEq.mem_interior_iff
section Pi
variable {ι : Type*} {π : ι → Type*} [∀ i, TopologicalSpace (π i)]
theorem nhdsWithin_pi_eq' {I : Set ι} (hI : I.Finite) (s : ∀ i, Set (π i)) (x : ∀ i, π i) :
𝓝[pi I s] x = ⨅ i, comap (fun x => x i) (𝓝 (x i) ⊓ ⨅ (_ : i ∈ I), 𝓟 (s i)) := by
simp only [nhdsWithin, nhds_pi, Filter.pi, comap_inf, comap_iInf, pi_def, comap_principal, ←
iInf_principal_finite hI, ← iInf_inf_eq]
theorem nhdsWithin_pi_eq {I : Set ι} (hI : I.Finite) (s : ∀ i, Set (π i)) (x : ∀ i, π i) :
𝓝[pi I s] x =
(⨅ i ∈ I, comap (fun x => x i) (𝓝[s i] x i)) ⊓
⨅ (i) (_ : i ∉ I), comap (fun x => x i) (𝓝 (x i)) := by
simp only [nhdsWithin, nhds_pi, Filter.pi, pi_def, ← iInf_principal_finite hI, comap_inf,
comap_principal, eval]
rw [iInf_split _ fun i => i ∈ I, inf_right_comm]
simp only [iInf_inf_eq]
theorem nhdsWithin_pi_univ_eq [Finite ι] (s : ∀ i, Set (π i)) (x : ∀ i, π i) :
𝓝[pi univ s] x = ⨅ i, comap (fun x => x i) (𝓝[s i] x i) := by
simpa [nhdsWithin] using nhdsWithin_pi_eq finite_univ s x
theorem nhdsWithin_pi_eq_bot {I : Set ι} {s : ∀ i, Set (π i)} {x : ∀ i, π i} :
𝓝[pi I s] x = ⊥ ↔ ∃ i ∈ I, 𝓝[s i] x i = ⊥ := by
simp only [nhdsWithin, nhds_pi, pi_inf_principal_pi_eq_bot]
theorem nhdsWithin_pi_neBot {I : Set ι} {s : ∀ i, Set (π i)} {x : ∀ i, π i} :
(𝓝[pi I s] x).NeBot ↔ ∀ i ∈ I, (𝓝[s i] x i).NeBot := by
simp [neBot_iff, nhdsWithin_pi_eq_bot]
instance instNeBotNhdsWithinUnivPi {s : ∀ i, Set (π i)} {x : ∀ i, π i}
[∀ i, (𝓝[s i] x i).NeBot] : (𝓝[pi univ s] x).NeBot := by
simpa [nhdsWithin_pi_neBot]
instance Pi.instNeBotNhdsWithinIio [Nonempty ι] [∀ i, Preorder (π i)] {x : ∀ i, π i}
[∀ i, (𝓝[<] x i).NeBot] : (𝓝[<] x).NeBot :=
have : (𝓝[pi univ fun i ↦ Iio (x i)] x).NeBot := inferInstance
this.mono <| nhdsWithin_mono _ fun _y hy ↦ lt_of_strongLT fun i ↦ hy i trivial
instance Pi.instNeBotNhdsWithinIoi [Nonempty ι] [∀ i, Preorder (π i)] {x : ∀ i, π i}
[∀ i, (𝓝[>] x i).NeBot] : (𝓝[>] x).NeBot :=
Pi.instNeBotNhdsWithinIio (π := fun i ↦ (π i)ᵒᵈ) (x := fun i ↦ OrderDual.toDual (x i))
end Pi
theorem Filter.Tendsto.piecewise_nhdsWithin {f g : α → β} {t : Set α} [∀ x, Decidable (x ∈ t)]
{a : α} {s : Set α} {l : Filter β} (h₀ : Tendsto f (𝓝[s ∩ t] a) l)
(h₁ : Tendsto g (𝓝[s ∩ tᶜ] a) l) : Tendsto (piecewise t f g) (𝓝[s] a) l := by
apply Tendsto.piecewise <;> rwa [← nhdsWithin_inter']
theorem Filter.Tendsto.if_nhdsWithin {f g : α → β} {p : α → Prop} [DecidablePred p] {a : α}
{s : Set α} {l : Filter β} (h₀ : Tendsto f (𝓝[s ∩ { x | p x }] a) l)
(h₁ : Tendsto g (𝓝[s ∩ { x | ¬p x }] a) l) :
Tendsto (fun x => if p x then f x else g x) (𝓝[s] a) l :=
h₀.piecewise_nhdsWithin h₁
theorem map_nhdsWithin (f : α → β) (a : α) (s : Set α) :
map f (𝓝[s] a) = ⨅ t ∈ { t : Set α | a ∈ t ∧ IsOpen t }, 𝓟 (f '' (t ∩ s)) :=
((nhdsWithin_basis_open a s).map f).eq_biInf
theorem tendsto_nhdsWithin_mono_left {f : α → β} {a : α} {s t : Set α} {l : Filter β} (hst : s ⊆ t)
(h : Tendsto f (𝓝[t] a) l) : Tendsto f (𝓝[s] a) l :=
h.mono_left <| nhdsWithin_mono a hst
theorem tendsto_nhdsWithin_mono_right {f : β → α} {l : Filter β} {a : α} {s t : Set α} (hst : s ⊆ t)
(h : Tendsto f l (𝓝[s] a)) : Tendsto f l (𝓝[t] a) :=
h.mono_right (nhdsWithin_mono a hst)
theorem tendsto_nhdsWithin_of_tendsto_nhds {f : α → β} {a : α} {s : Set α} {l : Filter β}
(h : Tendsto f (𝓝 a) l) : Tendsto f (𝓝[s] a) l :=
h.mono_left inf_le_left
theorem eventually_mem_of_tendsto_nhdsWithin {f : β → α} {a : α} {s : Set α} {l : Filter β}
(h : Tendsto f l (𝓝[s] a)) : ∀ᶠ i in l, f i ∈ s := by
simp_rw [nhdsWithin_eq, tendsto_iInf, mem_setOf_eq, tendsto_principal, mem_inter_iff,
eventually_and] at h
exact (h univ ⟨mem_univ a, isOpen_univ⟩).2
theorem tendsto_nhds_of_tendsto_nhdsWithin {f : β → α} {a : α} {s : Set α} {l : Filter β}
(h : Tendsto f l (𝓝[s] a)) : Tendsto f l (𝓝 a) :=
h.mono_right nhdsWithin_le_nhds
theorem nhdsWithin_neBot_of_mem {s : Set α} {x : α} (hx : x ∈ s) : NeBot (𝓝[s] x) :=
mem_closure_iff_nhdsWithin_neBot.1 <| subset_closure hx
theorem IsClosed.mem_of_nhdsWithin_neBot {s : Set α} (hs : IsClosed s) {x : α}
(hx : NeBot <| 𝓝[s] x) : x ∈ s :=
hs.closure_eq ▸ mem_closure_iff_nhdsWithin_neBot.2 hx
theorem DenseRange.nhdsWithin_neBot {ι : Type*} {f : ι → α} (h : DenseRange f) (x : α) :
NeBot (𝓝[range f] x) :=
mem_closure_iff_clusterPt.1 (h x)
theorem mem_closure_pi {ι : Type*} {α : ι → Type*} [∀ i, TopologicalSpace (α i)] {I : Set ι}
{s : ∀ i, Set (α i)} {x : ∀ i, α i} : x ∈ closure (pi I s) ↔ ∀ i ∈ I, x i ∈ closure (s i) := by
simp only [mem_closure_iff_nhdsWithin_neBot, nhdsWithin_pi_neBot]
theorem closure_pi_set {ι : Type*} {α : ι → Type*} [∀ i, TopologicalSpace (α i)] (I : Set ι)
(s : ∀ i, Set (α i)) : closure (pi I s) = pi I fun i => closure (s i) :=
Set.ext fun _ => mem_closure_pi
theorem dense_pi {ι : Type*} {α : ι → Type*} [∀ i, TopologicalSpace (α i)] {s : ∀ i, Set (α i)}
(I : Set ι) (hs : ∀ i ∈ I, Dense (s i)) : Dense (pi I s) := by
simp only [dense_iff_closure_eq, closure_pi_set, pi_congr rfl fun i hi => (hs i hi).closure_eq,
pi_univ]
theorem DenseRange.piMap {ι : Type*} {X Y : ι → Type*} [∀ i, TopologicalSpace (Y i)]
{f : (i : ι) → (X i) → (Y i)} (hf : ∀ i, DenseRange (f i)):
DenseRange (Pi.map f) := by
rw [DenseRange, Set.range_piMap]
exact dense_pi Set.univ (fun i _ => hf i)
theorem eventuallyEq_nhdsWithin_iff {f g : α → β} {s : Set α} {a : α} :
f =ᶠ[𝓝[s] a] g ↔ ∀ᶠ x in 𝓝 a, x ∈ s → f x = g x :=
mem_inf_principal
/-- Two functions agree on a neighborhood of `x` if they agree at `x` and in a punctured
neighborhood. -/
theorem eventuallyEq_nhds_of_eventuallyEq_nhdsNE {f g : α → β} {a : α} (h₁ : f =ᶠ[𝓝[≠] a] g)
(h₂ : f a = g a) :
f =ᶠ[𝓝 a] g := by
filter_upwards [eventually_nhdsWithin_iff.1 h₁]
intro x hx
by_cases h₂x : x = a
· simp [h₂x, h₂]
· tauto
theorem eventuallyEq_nhdsWithin_of_eqOn {f g : α → β} {s : Set α} {a : α} (h : EqOn f g s) :
f =ᶠ[𝓝[s] a] g :=
mem_inf_of_right h
theorem Set.EqOn.eventuallyEq_nhdsWithin {f g : α → β} {s : Set α} {a : α} (h : EqOn f g s) :
f =ᶠ[𝓝[s] a] g :=
eventuallyEq_nhdsWithin_of_eqOn h
theorem tendsto_nhdsWithin_congr {f g : α → β} {s : Set α} {a : α} {l : Filter β}
(hfg : ∀ x ∈ s, f x = g x) (hf : Tendsto f (𝓝[s] a) l) : Tendsto g (𝓝[s] a) l :=
(tendsto_congr' <| eventuallyEq_nhdsWithin_of_eqOn hfg).1 hf
theorem eventually_nhdsWithin_of_forall {s : Set α} {a : α} {p : α → Prop} (h : ∀ x ∈ s, p x) :
∀ᶠ x in 𝓝[s] a, p x :=
mem_inf_of_right h
theorem tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within {a : α} {l : Filter β} {s : Set α}
(f : β → α) (h1 : Tendsto f l (𝓝 a)) (h2 : ∀ᶠ x in l, f x ∈ s) : Tendsto f l (𝓝[s] a) :=
tendsto_inf.2 ⟨h1, tendsto_principal.2 h2⟩
theorem tendsto_nhdsWithin_iff {a : α} {l : Filter β} {s : Set α} {f : β → α} :
Tendsto f l (𝓝[s] a) ↔ Tendsto f l (𝓝 a) ∧ ∀ᶠ n in l, f n ∈ s :=
⟨fun h => ⟨tendsto_nhds_of_tendsto_nhdsWithin h, eventually_mem_of_tendsto_nhdsWithin h⟩, fun h =>
tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _ h.1 h.2⟩
@[simp]
theorem tendsto_nhdsWithin_range {a : α} {l : Filter β} {f : β → α} :
Tendsto f l (𝓝[range f] a) ↔ Tendsto f l (𝓝 a) :=
⟨fun h => h.mono_right inf_le_left, fun h =>
tendsto_inf.2 ⟨h, tendsto_principal.2 <| Eventually.of_forall mem_range_self⟩⟩
theorem Filter.EventuallyEq.eq_of_nhdsWithin {s : Set α} {f g : α → β} {a : α} (h : f =ᶠ[𝓝[s] a] g)
(hmem : a ∈ s) : f a = g a :=
h.self_of_nhdsWithin hmem
theorem eventually_nhdsWithin_of_eventually_nhds {s : Set α}
{a : α} {p : α → Prop} (h : ∀ᶠ x in 𝓝 a, p x) : ∀ᶠ x in 𝓝[s] a, p x :=
mem_nhdsWithin_of_mem_nhds h
lemma Set.MapsTo.preimage_mem_nhdsWithin {f : α → β} {s : Set α} {t : Set β} {x : α}
(hst : MapsTo f s t) : f ⁻¹' t ∈ 𝓝[s] x :=
Filter.mem_of_superset self_mem_nhdsWithin hst
/-!
### `nhdsWithin` and subtypes
-/
theorem mem_nhdsWithin_subtype {s : Set α} {a : { x // x ∈ s }} {t u : Set { x // x ∈ s }} :
t ∈ 𝓝[u] a ↔ t ∈ comap ((↑) : s → α) (𝓝[(↑) '' u] a) := by
rw [nhdsWithin, nhds_subtype, principal_subtype, ← comap_inf, ← nhdsWithin]
theorem nhdsWithin_subtype (s : Set α) (a : { x // x ∈ s }) (t : Set { x // x ∈ s }) :
𝓝[t] a = comap ((↑) : s → α) (𝓝[(↑) '' t] a) :=
Filter.ext fun _ => mem_nhdsWithin_subtype
theorem nhdsWithin_eq_map_subtype_coe {s : Set α} {a : α} (h : a ∈ s) :
𝓝[s] a = map ((↑) : s → α) (𝓝 ⟨a, h⟩) :=
(map_nhds_subtype_val ⟨a, h⟩).symm
theorem mem_nhds_subtype_iff_nhdsWithin {s : Set α} {a : s} {t : Set s} :
t ∈ 𝓝 a ↔ (↑) '' t ∈ 𝓝[s] (a : α) := by
rw [← map_nhds_subtype_val, image_mem_map_iff Subtype.val_injective]
theorem preimage_coe_mem_nhds_subtype {s t : Set α} {a : s} : (↑) ⁻¹' t ∈ 𝓝 a ↔ t ∈ 𝓝[s] ↑a := by
rw [← map_nhds_subtype_val, mem_map]
theorem eventually_nhds_subtype_iff (s : Set α) (a : s) (P : α → Prop) :
(∀ᶠ x : s in 𝓝 a, P x) ↔ ∀ᶠ x in 𝓝[s] a, P x :=
preimage_coe_mem_nhds_subtype
|
theorem frequently_nhds_subtype_iff (s : Set α) (a : s) (P : α → Prop) :
(∃ᶠ x : s in 𝓝 a, P x) ↔ ∃ᶠ x in 𝓝[s] a, P x :=
| Mathlib/Topology/ContinuousOn.lean | 501 | 503 |
/-
Copyright (c) 2020 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison
-/
import Mathlib.Algebra.Group.PUnit
import Mathlib.CategoryTheory.Monoidal.Braided.Basic
import Mathlib.CategoryTheory.Monoidal.CoherenceLemmas
import Mathlib.CategoryTheory.Monoidal.Discrete
import Mathlib.CategoryTheory.Limits.Shapes.Terminal
/-!
# The category of monoids in a monoidal category.
We define monoids in a monoidal category `C` and show that the category of monoids is equivalent to
the category of lax monoidal functors from the unit monoidal category to `C`. We also show that if
`C` is braided, then the category of monoids is naturally monoidal.
-/
universe v₁ v₂ u₁ u₂ u
open CategoryTheory MonoidalCategory Functor.LaxMonoidal Functor.OplaxMonoidal
variable {C : Type u₁} [Category.{v₁} C] [MonoidalCategory.{v₁} C]
/-- A monoid object internal to a monoidal category.
When the monoidal category is preadditive, this is also sometimes called an "algebra object".
-/
class Mon_Class (X : C) where
/-- The unit morphism of a monoid object. -/
one : 𝟙_ C ⟶ X
/-- The multiplication morphism of a monoid object. -/
mul : X ⊗ X ⟶ X
/- For the names of the conditions below, the unprimed names are reserved for the version where
the argument `X` is explicit. -/
one_mul' : one ▷ X ≫ mul = (λ_ X).hom := by aesop_cat
mul_one' : X ◁ one ≫ mul = (ρ_ X).hom := by aesop_cat
-- Obviously there is some flexibility stating this axiom.
-- This one has left- and right-hand sides matching the statement of `Monoid.mul_assoc`,
-- and chooses to place the associator on the right-hand side.
-- The heuristic is that unitors and associators "don't have much weight".
mul_assoc' : (mul ▷ X) ≫ mul = (α_ X X X).hom ≫ (X ◁ mul) ≫ mul := by aesop_cat
namespace Mon_Class
@[inherit_doc] scoped notation "μ" => Mon_Class.mul
@[inherit_doc] scoped notation "μ["M"]" => Mon_Class.mul (X := M)
@[inherit_doc] scoped notation "η" => Mon_Class.one
@[inherit_doc] scoped notation "η["M"]" => Mon_Class.one (X := M)
/- The simp attribute is reserved for the unprimed versions. -/
attribute [reassoc] one_mul' mul_one' mul_assoc'
@[reassoc (attr := simp)]
theorem one_mul (X : C) [Mon_Class X] : η ▷ X ≫ μ = (λ_ X).hom := one_mul'
@[reassoc (attr := simp)]
theorem mul_one (X : C) [Mon_Class X] : X ◁ η ≫ μ = (ρ_ X).hom := mul_one'
@[reassoc (attr := simp)]
theorem mul_assoc (X : C) [Mon_Class X] : μ ▷ X ≫ μ = (α_ X X X).hom ≫ X ◁ μ ≫ μ := mul_assoc'
@[ext]
theorem ext {X : C} (h₁ h₂ : Mon_Class X) (H : h₁.mul = h₂.mul) : h₁ = h₂ := by
suffices h₁.one = h₂.one by cases h₁; cases h₂; subst H this; rfl
trans (λ_ _).inv ≫ (h₁.one ⊗ h₂.one) ≫ h₁.mul
· simp [tensorHom_def, H, ← unitors_equal]
· simp [tensorHom_def']
end Mon_Class
open scoped Mon_Class
variable {M N : C} [Mon_Class M] [Mon_Class N]
/-- The property that a morphism between monoid objects is a monoid morphism. -/
class IsMon_Hom (f : M ⟶ N) : Prop where
one_hom (f) : η ≫ f = η := by aesop_cat
mul_hom (f) : μ ≫ f = (f ⊗ f) ≫ μ := by aesop_cat
attribute [reassoc (attr := simp)] IsMon_Hom.one_hom IsMon_Hom.mul_hom
variable (C)
/-- A monoid object internal to a monoidal category.
When the monoidal category is preadditive, this is also sometimes called an "algebra object".
-/
structure Mon_ where
/-- The underlying object in the ambient monoidal category -/
X : C
/-- The unit morphism of the monoid object -/
one : 𝟙_ C ⟶ X
/-- The multiplication morphism of a monoid object -/
mul : X ⊗ X ⟶ X
one_mul : (one ▷ X) ≫ mul = (λ_ X).hom := by aesop_cat
mul_one : (X ◁ one) ≫ mul = (ρ_ X).hom := by aesop_cat
-- Obviously there is some flexibility stating this axiom.
-- This one has left- and right-hand sides matching the statement of `Monoid.mul_assoc`,
-- and chooses to place the associator on the right-hand side.
-- The heuristic is that unitors and associators "don't have much weight".
mul_assoc : (mul ▷ X) ≫ mul = (α_ X X X).hom ≫ (X ◁ mul) ≫ mul := by aesop_cat
attribute [reassoc] Mon_.one_mul Mon_.mul_one
attribute [simp] Mon_.one_mul Mon_.mul_one
-- We prove a more general `@[simp]` lemma below.
attribute [reassoc (attr := simp)] Mon_.mul_assoc
namespace Mon_
variable {C}
/-- Construct an object of `Mon_ C` from an object `X : C` and `Mon_Class X` instance. -/
@[simps]
def mk' (X : C) [Mon_Class X] : Mon_ C where
X := X
one := η
mul := μ
instance {M : Mon_ C} : Mon_Class M.X where
one := M.one
mul := M.mul
one_mul' := M.one_mul
mul_one' := M.mul_one
mul_assoc' := M.mul_assoc
variable (C)
/-- The trivial monoid object. We later show this is initial in `Mon_ C`.
-/
@[simps]
def trivial : Mon_ C where
X := 𝟙_ C
one := 𝟙 _
mul := (λ_ _).hom
mul_assoc := by monoidal_coherence
mul_one := by monoidal_coherence
instance : Inhabited (Mon_ C) :=
⟨trivial C⟩
variable {C}
variable {M : Mon_ C}
@[simp]
theorem one_mul_hom {Z : C} (f : Z ⟶ M.X) : (M.one ⊗ f) ≫ M.mul = (λ_ Z).hom ≫ f := by
rw [tensorHom_def'_assoc, M.one_mul, leftUnitor_naturality]
@[simp]
theorem mul_one_hom {Z : C} (f : Z ⟶ M.X) : (f ⊗ M.one) ≫ M.mul = (ρ_ Z).hom ≫ f := by
rw [tensorHom_def_assoc, M.mul_one, rightUnitor_naturality]
theorem mul_assoc_flip :
(M.X ◁ M.mul) ≫ M.mul = (α_ M.X M.X M.X).inv ≫ (M.mul ▷ M.X) ≫ M.mul := by simp
/-- A morphism of monoid objects. -/
@[ext]
structure Hom (M N : Mon_ C) where
/-- The underlying morphism -/
hom : M.X ⟶ N.X
one_hom : M.one ≫ hom = N.one := by aesop_cat
mul_hom : M.mul ≫ hom = (hom ⊗ hom) ≫ N.mul := by aesop_cat
/-- Construct a morphism `M ⟶ N` of `Mon_ C` from a map `f : M ⟶ N` and a `IsMon_Hom f` instance. -/
abbrev Hom.mk' {M N : C} [Mon_Class M] [Mon_Class N] (f : M ⟶ N) [IsMon_Hom f] :
Hom (.mk' M) (.mk' N) := .mk f
attribute [reassoc (attr := simp)] Hom.one_hom Hom.mul_hom
/-- The identity morphism on a monoid object. -/
@[simps]
def id (M : Mon_ C) : Hom M M where
hom := 𝟙 M.X
instance homInhabited (M : Mon_ C) : Inhabited (Hom M M) :=
⟨id M⟩
/-- Composition of morphisms of monoid objects. -/
@[simps]
def comp {M N O : Mon_ C} (f : Hom M N) (g : Hom N O) : Hom M O where
hom := f.hom ≫ g.hom
instance : Category (Mon_ C) where
Hom M N := Hom M N
id := id
comp f g := comp f g
instance {M N : Mon_ C} (f : M ⟶ N) : IsMon_Hom f.hom := ⟨f.2, f.3⟩
@[ext]
lemma ext {X Y : Mon_ C} {f g : X ⟶ Y} (w : f.hom = g.hom) : f = g :=
Hom.ext w
@[simp]
theorem id_hom' (M : Mon_ C) : (𝟙 M : Hom M M).hom = 𝟙 M.X :=
rfl
@[simp]
theorem comp_hom' {M N K : Mon_ C} (f : M ⟶ N) (g : N ⟶ K) :
(f ≫ g : Hom M K).hom = f.hom ≫ g.hom :=
rfl
section
variable (C)
/-- The forgetful functor from monoid objects to the ambient category. -/
@[simps]
def forget : Mon_ C ⥤ C where
obj A := A.X
map f := f.hom
end
instance forget_faithful : (forget C).Faithful where
instance {A B : Mon_ C} (f : A ⟶ B) [e : IsIso ((forget C).map f)] : IsIso f.hom :=
e
/-- The forgetful functor from monoid objects to the ambient category reflects isomorphisms. -/
instance : (forget C).ReflectsIsomorphisms where
reflects f e := ⟨⟨{ hom := inv f.hom }, by aesop_cat⟩⟩
/-- Construct an isomorphism of monoids by giving an isomorphism between the underlying objects
and checking compatibility with unit and multiplication only in the forward direction.
-/
@[simps]
def mkIso {M N : Mon_ C} (f : M.X ≅ N.X) (one_f : M.one ≫ f.hom = N.one := by aesop_cat)
(mul_f : M.mul ≫ f.hom = (f.hom ⊗ f.hom) ≫ N.mul := by aesop_cat) : M ≅ N where
hom := { hom := f.hom }
inv :=
{ hom := f.inv
one_hom := by rw [← one_f]; simp
mul_hom := by
rw [← cancel_mono f.hom]
slice_rhs 2 3 => rw [mul_f]
simp }
@[simps]
instance uniqueHomFromTrivial (A : Mon_ C) : Unique (trivial C ⟶ A) where
default :=
{ hom := A.one
mul_hom := by simp [A.one_mul, unitors_equal] }
uniq f := by
ext
simp only [trivial_X]
rw [← Category.id_comp f.hom]
erw [f.one_hom]
open CategoryTheory.Limits
instance : HasInitial (Mon_ C) :=
hasInitial_of_unique (trivial C)
end Mon_
namespace CategoryTheory.Functor
variable {C} {D : Type u₂} [Category.{v₂} D] [MonoidalCategory.{v₂} D] (F : C ⥤ D)
section LaxMonoidal
variable [F.LaxMonoidal] (X Y : C) [Mon_Class X] [Mon_Class Y] (f : X ⟶ Y) [IsMon_Hom f]
/-- The image of a monoid object under a lax monoidal functor is a monoid object. -/
abbrev obj.instMon_Class : Mon_Class (F.obj X) where
one := ε F ≫ F.map η
mul := LaxMonoidal.μ F X X ≫ F.map μ
one_mul' := by simp [← F.map_comp]
mul_one' := by simp [← F.map_comp]
mul_assoc' := by
simp_rw [comp_whiskerRight, Category.assoc, μ_natural_left_assoc,
MonoidalCategory.whiskerLeft_comp, Category.assoc, μ_natural_right_assoc]
slice_lhs 3 4 => rw [← F.map_comp, Mon_Class.mul_assoc]
simp
attribute [local instance] obj.instMon_Class
@[reassoc, simp] lemma obj.η_def : (η : 𝟙_ D ⟶ F.obj X) = ε F ≫ F.map η := rfl
@[reassoc, simp] lemma obj.μ_def : μ = LaxMonoidal.μ F X X ≫ F.map μ := rfl
instance map.instIsMon_Hom : IsMon_Hom (F.map f) where
one_hom := by simp [← map_comp]
mul_hom := by simp [← map_comp]
-- TODO: mapMod F A : Mod A ⥤ Mod (F.mapMon A)
/-- A lax monoidal functor takes monoid objects to monoid objects.
That is, a lax monoidal functor `F : C ⥤ D` induces a functor `Mon_ C ⥤ Mon_ D`.
-/
@[simps]
def mapMon (F : C ⥤ D) [F.LaxMonoidal] : Mon_ C ⥤ Mon_ D where
-- TODO: The following could be, but it leads to weird `erw`s later down the file
-- obj A := .mk' (F.obj A.X)
obj A :=
{ X := F.obj A.X
one := ε F ≫ F.map A.one
mul := «μ» F _ _ ≫ F.map A.mul
one_mul := by
simp_rw [comp_whiskerRight, Category.assoc, μ_natural_left_assoc,
LaxMonoidal.left_unitality]
slice_lhs 3 4 => rw [← F.map_comp, A.one_mul]
mul_one := by
simp_rw [MonoidalCategory.whiskerLeft_comp, Category.assoc, μ_natural_right_assoc,
LaxMonoidal.right_unitality]
slice_lhs 3 4 => rw [← F.map_comp, A.mul_one]
mul_assoc := by
simp_rw [comp_whiskerRight, Category.assoc, μ_natural_left_assoc,
MonoidalCategory.whiskerLeft_comp, Category.assoc, μ_natural_right_assoc]
slice_lhs 3 4 => rw [← F.map_comp, A.mul_assoc]
simp }
map f := .mk' (F.map f.hom)
protected instance Faithful.mapMon [F.Faithful] : F.mapMon.Faithful where
map_injective {_X _Y} _f _g hfg := Mon_.Hom.ext <| map_injective congr(($hfg).hom)
end LaxMonoidal
section Monoidal
variable [F.Monoidal]
attribute [local instance] obj.instMon_Class
protected instance Full.mapMon [F.Full] [F.Faithful] : F.mapMon.Full where
map_surjective {X Y} f :=
let ⟨g, hg⟩ := F.map_surjective f.hom
⟨{
hom := g
one_hom := F.map_injective <| by simpa [← hg, cancel_epi] using f.one_hom
mul_hom := F.map_injective <| by simpa [← hg, cancel_epi] using f.mul_hom
}, Mon_.Hom.ext hg⟩
instance FullyFaithful.isMon_Hom_preimage (hF : F.FullyFaithful) {X Y : C}
[Mon_Class X] [Mon_Class Y] (f : F.obj X ⟶ F.obj Y) [IsMon_Hom f] :
IsMon_Hom (hF.preimage f) where
one_hom := hF.map_injective <| by simp [← obj.η_def_assoc, ← obj.η_def, ← cancel_epi (ε F)]
mul_hom := hF.map_injective <| by
simp [← obj.μ_def_assoc, ← obj.μ_def, ← μ_natural_assoc, ← cancel_epi (LaxMonoidal.μ F ..)]
/-- If `F : C ⥤ D` is a fully faithful monoidal functor, then `Mon(F) : Mon C ⥤ Mon D` is fully
faithful too. -/
protected def FullyFaithful.mapMon (hF : F.FullyFaithful) : F.mapMon.FullyFaithful where
preimage {X Y} f := .mk' <| hF.preimage f.hom
end Monoidal
variable (C D)
/-- `mapMon` is functorial in the lax monoidal functor. -/
@[simps] -- Porting note: added this, not sure how it worked previously without.
def mapMonFunctor : LaxMonoidalFunctor C D ⥤ Mon_ C ⥤ Mon_ D where
obj F := F.mapMon
map α := { app := fun A => { hom := α.hom.app A.X } }
map_comp _ _ := rfl
end CategoryTheory.Functor
namespace Mon_
namespace EquivLaxMonoidalFunctorPUnit
/-- Implementation of `Mon_.equivLaxMonoidalFunctorPUnit`. -/
@[simps]
def laxMonoidalToMon : LaxMonoidalFunctor (Discrete PUnit.{u + 1}) C ⥤ Mon_ C where
obj F := (F.mapMon : Mon_ _ ⥤ Mon_ C).obj (trivial (Discrete PUnit))
map α := ((Functor.mapMonFunctor (Discrete PUnit) C).map α).app _
variable {C}
/-- Implementation of `Mon_.equivLaxMonoidalFunctorPUnit`. -/
@[simps!]
def monToLaxMonoidalObj (A : Mon_ C) :
Discrete PUnit.{u + 1} ⥤ C := (Functor.const _).obj A.X
instance (A : Mon_ C) : (monToLaxMonoidalObj A).LaxMonoidal where
ε' := A.one
μ' := fun _ _ => A.mul
@[simp]
lemma monToLaxMonoidalObj_ε (A : Mon_ C) :
ε (monToLaxMonoidalObj A) = A.one := rfl
@[simp]
lemma monToLaxMonoidalObj_μ (A : Mon_ C) (X Y) :
«μ» (monToLaxMonoidalObj A) X Y = A.mul := rfl
variable (C)
/-- Implementation of `Mon_.equivLaxMonoidalFunctorPUnit`. -/
@[simps]
def monToLaxMonoidal : Mon_ C ⥤ LaxMonoidalFunctor (Discrete PUnit.{u + 1}) C where
obj A := LaxMonoidalFunctor.of (monToLaxMonoidalObj A)
map f :=
{ hom := { app := fun _ => f.hom }
isMonoidal := { } }
attribute [local aesop safe tactic (rule_sets := [CategoryTheory])]
CategoryTheory.Discrete.discreteCases
/-- Implementation of `Mon_.equivLaxMonoidalFunctorPUnit`. -/
@[simps!]
def unitIso :
𝟭 (LaxMonoidalFunctor (Discrete PUnit.{u + 1}) C) ≅ laxMonoidalToMon C ⋙ monToLaxMonoidal C :=
NatIso.ofComponents
(fun F ↦ LaxMonoidalFunctor.isoOfComponents (fun _ ↦ F.mapIso (eqToIso (by ext))))
/-- Implementation of `Mon_.equivLaxMonoidalFunctorPUnit`. -/
@[simps!]
def counitIso : monToLaxMonoidal C ⋙ laxMonoidalToMon C ≅ 𝟭 (Mon_ C) :=
NatIso.ofComponents fun F ↦ mkIso (Iso.refl _)
end EquivLaxMonoidalFunctorPUnit
open EquivLaxMonoidalFunctorPUnit
attribute [local simp] eqToIso_map
/--
Monoid objects in `C` are "just" lax monoidal functors from the trivial monoidal category to `C`.
-/
@[simps]
def equivLaxMonoidalFunctorPUnit : LaxMonoidalFunctor (Discrete PUnit.{u + 1}) C ≌ Mon_ C where
functor := laxMonoidalToMon C
inverse := monToLaxMonoidal C
unitIso := unitIso C
counitIso := counitIso C
end Mon_
namespace Mon_
/-!
In this section, we prove that the category of monoids in a braided monoidal category is monoidal.
Given two monoids `M` and `N` in a braided monoidal category `C`,
the multiplication on the tensor product `M.X ⊗ N.X` is defined in the obvious way:
it is the tensor product of the multiplications on `M` and `N`,
except that the tensor factors in the source come in the wrong order,
which we fix by pre-composing with a permutation isomorphism constructed from the braiding.
(There is a subtlety here: in fact there are two ways to do these,
using either the positive or negative crossing.)
A more conceptual way of understanding this definition is the following:
The braiding on `C` gives rise to a monoidal structure on
the tensor product functor from `C × C` to `C`.
A pair of monoids in `C` gives rise to a monoid in `C × C`,
which the tensor product functor by being monoidal takes to a monoid in `C`.
The permutation isomorphism appearing in the definition of
the multiplication on the tensor product of two monoids is
an instance of a more general family of isomorphisms
which together form a strength that equips the tensor product functor with a monoidal structure,
and the monoid axioms for the tensor product follow from the monoid axioms for the tensor factors
plus the properties of the strength (i.e., monoidal functor axioms).
The strength `tensorμ` of the tensor product functor has been defined in
`Mathlib.CategoryTheory.Monoidal.Braided`.
Its properties, stated as independent lemmas in that module,
are used extensively in the proofs below.
Notice that we could have followed the above plan not only conceptually
but also as a possible implementation and
could have constructed the tensor product of monoids via `mapMon`,
but we chose to give a more explicit definition directly in terms of `tensorμ`.
To complete the definition of the monoidal category structure on the category of monoids,
we need to provide definitions of associator and unitors.
The obvious candidates are the associator and unitors from `C`,
but we need to prove that they are monoid morphisms, i.e., compatible with unit and multiplication.
These properties translate to the monoidality of the associator and unitors
(with respect to the monoidal structures on the functors they relate),
which have also been proved in `Mathlib.CategoryTheory.Monoidal.Braided`.
-/
variable {C}
-- The proofs that associators and unitors preserve monoid units don't require braiding.
theorem one_associator {M N P : Mon_ C} :
((λ_ (𝟙_ C)).inv ≫ ((λ_ (𝟙_ C)).inv ≫ (M.one ⊗ N.one) ⊗ P.one)) ≫ (α_ M.X N.X P.X).hom =
(λ_ (𝟙_ C)).inv ≫ (M.one ⊗ (λ_ (𝟙_ C)).inv ≫ (N.one ⊗ P.one)) := by
simp only [Category.assoc, Iso.cancel_iso_inv_left]
slice_lhs 1 3 => rw [← Category.id_comp P.one, tensor_comp]
slice_lhs 2 3 => rw [associator_naturality]
slice_rhs 1 2 => rw [← Category.id_comp M.one, tensor_comp]
slice_lhs 1 2 => rw [tensorHom_id, ← leftUnitor_tensor_inv]
rw [← cancel_epi (λ_ (𝟙_ C)).inv]
slice_lhs 1 2 => rw [leftUnitor_inv_naturality]
simp
theorem one_leftUnitor {M : Mon_ C} :
((λ_ (𝟙_ C)).inv ≫ (𝟙 (𝟙_ C) ⊗ M.one)) ≫ (λ_ M.X).hom = M.one := by
| simp
theorem one_rightUnitor {M : Mon_ C} :
| Mathlib/CategoryTheory/Monoidal/Mon_.lean | 496 | 498 |
/-
Copyright (c) 2021 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen
-/
import Mathlib.FieldTheory.RatFunc.Defs
import Mathlib.RingTheory.EuclideanDomain
import Mathlib.RingTheory.Localization.FractionRing
import Mathlib.RingTheory.Polynomial.Content
/-!
# The field structure of rational functions
## Main definitions
Working with rational functions as polynomials:
- `RatFunc.instField` provides a field structure
You can use `IsFractionRing` API to treat `RatFunc` as the field of fractions of polynomials:
* `algebraMap K[X] (RatFunc K)` maps polynomials to rational functions
* `IsFractionRing.algEquiv` maps other fields of fractions of `K[X]` to `RatFunc K`,
in particular:
* `FractionRing.algEquiv K[X] (RatFunc K)` maps the generic field of
fraction construction to `RatFunc K`. Combine this with `AlgEquiv.restrictScalars` to change
the `FractionRing K[X] ≃ₐ[K[X]] RatFunc K` to `FractionRing K[X] ≃ₐ[K] RatFunc K`.
Working with rational functions as fractions:
- `RatFunc.num` and `RatFunc.denom` give the numerator and denominator.
These values are chosen to be coprime and such that `RatFunc.denom` is monic.
Lifting homomorphisms of polynomials to other types, by mapping and dividing, as long
as the homomorphism retains the non-zero-divisor property:
- `RatFunc.liftMonoidWithZeroHom` lifts a `K[X] →*₀ G₀` to
a `RatFunc K →*₀ G₀`, where `[CommRing K] [CommGroupWithZero G₀]`
- `RatFunc.liftRingHom` lifts a `K[X] →+* L` to a `RatFunc K →+* L`,
where `[CommRing K] [Field L]`
- `RatFunc.liftAlgHom` lifts a `K[X] →ₐ[S] L` to a `RatFunc K →ₐ[S] L`,
where `[CommRing K] [Field L] [CommSemiring S] [Algebra S K[X]] [Algebra S L]`
This is satisfied by injective homs.
We also have lifting homomorphisms of polynomials to other polynomials,
with the same condition on retaining the non-zero-divisor property across the map:
- `RatFunc.map` lifts `K[X] →* R[X]` when `[CommRing K] [CommRing R]`
- `RatFunc.mapRingHom` lifts `K[X] →+* R[X]` when `[CommRing K] [CommRing R]`
- `RatFunc.mapAlgHom` lifts `K[X] →ₐ[S] R[X]` when
`[CommRing K] [IsDomain K] [CommRing R] [IsDomain R]`
-/
universe u v
noncomputable section
open scoped nonZeroDivisors Polynomial
variable {K : Type u}
namespace RatFunc
section Field
variable [CommRing K]
/-- The zero rational function. -/
protected irreducible_def zero : RatFunc K :=
⟨0⟩
instance : Zero (RatFunc K) :=
⟨RatFunc.zero⟩
theorem ofFractionRing_zero : (ofFractionRing 0 : RatFunc K) = 0 :=
zero_def.symm
/-- Addition of rational functions. -/
protected irreducible_def add : RatFunc K → RatFunc K → RatFunc K
| ⟨p⟩, ⟨q⟩ => ⟨p + q⟩
instance : Add (RatFunc K) :=
⟨RatFunc.add⟩
theorem ofFractionRing_add (p q : FractionRing K[X]) :
ofFractionRing (p + q) = ofFractionRing p + ofFractionRing q :=
(add_def _ _).symm
/-- Subtraction of rational functions. -/
protected irreducible_def sub : RatFunc K → RatFunc K → RatFunc K
| ⟨p⟩, ⟨q⟩ => ⟨p - q⟩
instance : Sub (RatFunc K) :=
⟨RatFunc.sub⟩
theorem ofFractionRing_sub (p q : FractionRing K[X]) :
ofFractionRing (p - q) = ofFractionRing p - ofFractionRing q :=
(sub_def _ _).symm
/-- Additive inverse of a rational function. -/
protected irreducible_def neg : RatFunc K → RatFunc K
| ⟨p⟩ => ⟨-p⟩
instance : Neg (RatFunc K) :=
⟨RatFunc.neg⟩
theorem ofFractionRing_neg (p : FractionRing K[X]) :
ofFractionRing (-p) = -ofFractionRing p :=
(neg_def _).symm
/-- The multiplicative unit of rational functions. -/
protected irreducible_def one : RatFunc K :=
⟨1⟩
instance : One (RatFunc K) :=
⟨RatFunc.one⟩
theorem ofFractionRing_one : (ofFractionRing 1 : RatFunc K) = 1 :=
one_def.symm
/-- Multiplication of rational functions. -/
protected irreducible_def mul : RatFunc K → RatFunc K → RatFunc K
| ⟨p⟩, ⟨q⟩ => ⟨p * q⟩
instance : Mul (RatFunc K) :=
⟨RatFunc.mul⟩
theorem ofFractionRing_mul (p q : FractionRing K[X]) :
ofFractionRing (p * q) = ofFractionRing p * ofFractionRing q :=
(mul_def _ _).symm
section IsDomain
variable [IsDomain K]
/-- Division of rational functions. -/
protected irreducible_def div : RatFunc K → RatFunc K → RatFunc K
| ⟨p⟩, ⟨q⟩ => ⟨p / q⟩
instance : Div (RatFunc K) :=
⟨RatFunc.div⟩
theorem ofFractionRing_div (p q : FractionRing K[X]) :
ofFractionRing (p / q) = ofFractionRing p / ofFractionRing q :=
(div_def _ _).symm
/-- Multiplicative inverse of a rational function. -/
protected irreducible_def inv : RatFunc K → RatFunc K
| ⟨p⟩ => ⟨p⁻¹⟩
instance : Inv (RatFunc K) :=
⟨RatFunc.inv⟩
theorem ofFractionRing_inv (p : FractionRing K[X]) :
ofFractionRing p⁻¹ = (ofFractionRing p)⁻¹ :=
(inv_def _).symm
-- Auxiliary lemma for the `Field` instance
theorem mul_inv_cancel : ∀ {p : RatFunc K}, p ≠ 0 → p * p⁻¹ = 1
| ⟨p⟩, h => by
have : p ≠ 0 := fun hp => h <| by rw [hp, ofFractionRing_zero]
simpa only [← ofFractionRing_inv, ← ofFractionRing_mul, ← ofFractionRing_one,
ofFractionRing.injEq] using
mul_inv_cancel₀ this
end IsDomain
section SMul
variable {R : Type*}
/-- Scalar multiplication of rational functions. -/
protected irreducible_def smul [SMul R (FractionRing K[X])] : R → RatFunc K → RatFunc K
| r, ⟨p⟩ => ⟨r • p⟩
instance [SMul R (FractionRing K[X])] : SMul R (RatFunc K) :=
⟨RatFunc.smul⟩
theorem ofFractionRing_smul [SMul R (FractionRing K[X])] (c : R) (p : FractionRing K[X]) :
ofFractionRing (c • p) = c • ofFractionRing p :=
(smul_def _ _).symm
theorem toFractionRing_smul [SMul R (FractionRing K[X])] (c : R) (p : RatFunc K) :
toFractionRing (c • p) = c • toFractionRing p := by
cases p
rw [← ofFractionRing_smul]
theorem smul_eq_C_smul (x : RatFunc K) (r : K) : r • x = Polynomial.C r • x := by
obtain ⟨x⟩ := x
induction x using Localization.induction_on
rw [← ofFractionRing_smul, ← ofFractionRing_smul, Localization.smul_mk,
Localization.smul_mk, smul_eq_mul, Polynomial.smul_eq_C_mul]
section IsDomain
variable [IsDomain K]
variable [Monoid R] [DistribMulAction R K[X]]
variable [IsScalarTower R K[X] K[X]]
theorem mk_smul (c : R) (p q : K[X]) : RatFunc.mk (c • p) q = c • RatFunc.mk p q := by
letI : SMulZeroClass R (FractionRing K[X]) := inferInstance
by_cases hq : q = 0
· rw [hq, mk_zero, mk_zero, ← ofFractionRing_smul, smul_zero]
· rw [mk_eq_localization_mk _ hq, mk_eq_localization_mk _ hq, ← Localization.smul_mk, ←
ofFractionRing_smul]
instance : IsScalarTower R K[X] (RatFunc K) :=
⟨fun c p q => q.induction_on' fun q r _ => by rw [← mk_smul, smul_assoc, mk_smul, mk_smul]⟩
end IsDomain
end SMul
variable (K)
instance [Subsingleton K] : Subsingleton (RatFunc K) :=
toFractionRing_injective.subsingleton
instance : Inhabited (RatFunc K) :=
⟨0⟩
instance instNontrivial [Nontrivial K] : Nontrivial (RatFunc K) :=
ofFractionRing_injective.nontrivial
/-- `RatFunc K` is isomorphic to the field of fractions of `K[X]`, as rings.
This is an auxiliary definition; `simp`-normal form is `IsLocalization.algEquiv`.
-/
@[simps apply]
def toFractionRingRingEquiv : RatFunc K ≃+* FractionRing K[X] where
toFun := toFractionRing
invFun := ofFractionRing
left_inv := fun ⟨_⟩ => rfl
right_inv _ := rfl
map_add' := fun ⟨_⟩ ⟨_⟩ => by simp [← ofFractionRing_add]
map_mul' := fun ⟨_⟩ ⟨_⟩ => by simp [← ofFractionRing_mul]
end Field
section TacticInterlude
/-- Solve equations for `RatFunc K` by working in `FractionRing K[X]`. -/
macro "frac_tac" : tactic => `(tactic|
· repeat (rintro (⟨⟩ : RatFunc _))
try simp only [← ofFractionRing_zero, ← ofFractionRing_add, ← ofFractionRing_sub,
← ofFractionRing_neg, ← ofFractionRing_one, ← ofFractionRing_mul, ← ofFractionRing_div,
← ofFractionRing_inv,
add_assoc, zero_add, add_zero, mul_assoc, mul_zero, mul_one, mul_add, inv_zero,
add_comm, add_left_comm, mul_comm, mul_left_comm, sub_eq_add_neg, div_eq_mul_inv,
add_mul, zero_mul, one_mul, neg_mul, mul_neg, add_neg_cancel])
/-- Solve equations for `RatFunc K` by applying `RatFunc.induction_on`. -/
macro "smul_tac" : tactic => `(tactic|
repeat
(first
| rintro (⟨⟩ : RatFunc _)
| intro) <;>
simp_rw [← ofFractionRing_smul] <;>
simp only [add_comm, mul_comm, zero_smul, succ_nsmul, zsmul_eq_mul, mul_add, mul_one, mul_zero,
neg_add, mul_neg,
Int.cast_zero, Int.cast_add, Int.cast_one,
Int.cast_negSucc, Int.cast_natCast, Nat.cast_succ,
Localization.mk_zero, Localization.add_mk_self, Localization.neg_mk,
ofFractionRing_zero, ← ofFractionRing_add, ← ofFractionRing_neg])
end TacticInterlude
section CommRing
variable (K) [CommRing K]
/-- `RatFunc K` is a commutative monoid.
This is an intermediate step on the way to the full instance `RatFunc.instCommRing`.
-/
def instCommMonoid : CommMonoid (RatFunc K) where
mul := (· * ·)
mul_assoc := by frac_tac
mul_comm := by frac_tac
one := 1
one_mul := by frac_tac
mul_one := by frac_tac
npow := npowRec
/-- `RatFunc K` is an additive commutative group.
This is an intermediate step on the way to the full instance `RatFunc.instCommRing`.
-/
def instAddCommGroup : AddCommGroup (RatFunc K) where
add := (· + ·)
add_assoc := by frac_tac
add_comm := by frac_tac
zero := 0
zero_add := by frac_tac
add_zero := by frac_tac
neg := Neg.neg
neg_add_cancel := by frac_tac
sub := Sub.sub
sub_eq_add_neg := by frac_tac
nsmul := (· • ·)
nsmul_zero := by smul_tac
nsmul_succ _ := by smul_tac
zsmul := (· • ·)
zsmul_zero' := by smul_tac
zsmul_succ' _ := by smul_tac
zsmul_neg' _ := by smul_tac
instance instCommRing : CommRing (RatFunc K) :=
{ instCommMonoid K, instAddCommGroup K with
zero := 0
sub := Sub.sub
zero_mul := by frac_tac
mul_zero := by frac_tac
left_distrib := by frac_tac
right_distrib := by frac_tac
one := 1
nsmul := (· • ·)
zsmul := (· • ·)
npow := npowRec }
variable {K}
section LiftHom
open RatFunc
variable {G₀ L R S F : Type*} [CommGroupWithZero G₀] [Field L] [CommRing R] [CommRing S]
variable [FunLike F R[X] S[X]]
open scoped Classical in
/-- Lift a monoid homomorphism that maps polynomials `φ : R[X] →* S[X]`
to a `RatFunc R →* RatFunc S`,
on the condition that `φ` maps non zero divisors to non zero divisors,
by mapping both the numerator and denominator and quotienting them. -/
def map [MonoidHomClass F R[X] S[X]] (φ : F) (hφ : R[X]⁰ ≤ S[X]⁰.comap φ) :
RatFunc R →* RatFunc S where
toFun f :=
RatFunc.liftOn f
(fun n d => if h : φ d ∈ S[X]⁰ then ofFractionRing (Localization.mk (φ n) ⟨φ d, h⟩) else 0)
fun {p q p' q'} hq hq' h => by
simp only [Submonoid.mem_comap.mp (hφ hq), Submonoid.mem_comap.mp (hφ hq'),
dif_pos, ofFractionRing.injEq, Localization.mk_eq_mk_iff]
refine Localization.r_of_eq ?_
simpa only [map_mul] using congr_arg φ h
map_one' := by
simp_rw [← ofFractionRing_one, ← Localization.mk_one, liftOn_ofFractionRing_mk,
OneMemClass.coe_one, map_one, OneMemClass.one_mem, dite_true, ofFractionRing.injEq,
Localization.mk_one, Localization.mk_eq_monoidOf_mk', Submonoid.LocalizationMap.mk'_self]
map_mul' x y := by
obtain ⟨x⟩ := x; obtain ⟨y⟩ := y
induction' x using Localization.induction_on with pq
induction' y using Localization.induction_on with p'q'
obtain ⟨p, q⟩ := pq
obtain ⟨p', q'⟩ := p'q'
have hq : φ q ∈ S[X]⁰ := hφ q.prop
have hq' : φ q' ∈ S[X]⁰ := hφ q'.prop
have hqq' : φ ↑(q * q') ∈ S[X]⁰ := by simpa using Submonoid.mul_mem _ hq hq'
simp_rw [← ofFractionRing_mul, Localization.mk_mul, liftOn_ofFractionRing_mk, dif_pos hq,
dif_pos hq', dif_pos hqq', ← ofFractionRing_mul, Submonoid.coe_mul, map_mul,
Localization.mk_mul, Submonoid.mk_mul_mk]
theorem map_apply_ofFractionRing_mk [MonoidHomClass F R[X] S[X]] (φ : F)
(hφ : R[X]⁰ ≤ S[X]⁰.comap φ) (n : R[X]) (d : R[X]⁰) :
map φ hφ (ofFractionRing (Localization.mk n d)) =
ofFractionRing (Localization.mk (φ n) ⟨φ d, hφ d.prop⟩) := by
simp only [map, MonoidHom.coe_mk, OneHom.coe_mk, liftOn_ofFractionRing_mk,
Submonoid.mem_comap.mp (hφ d.2), ↓reduceDIte]
theorem map_injective [MonoidHomClass F R[X] S[X]] (φ : F) (hφ : R[X]⁰ ≤ S[X]⁰.comap φ)
(hf : Function.Injective φ) : Function.Injective (map φ hφ) := by
rintro ⟨x⟩ ⟨y⟩ h
induction x using Localization.induction_on
induction y using Localization.induction_on
simpa only [map_apply_ofFractionRing_mk, ofFractionRing_injective.eq_iff,
Localization.mk_eq_mk_iff, Localization.r_iff_exists, mul_cancel_left_coe_nonZeroDivisors,
exists_const, ← map_mul, hf.eq_iff] using h
/-- Lift a ring homomorphism that maps polynomials `φ : R[X] →+* S[X]`
to a `RatFunc R →+* RatFunc S`,
on the condition that `φ` maps non zero divisors to non zero divisors,
by mapping both the numerator and denominator and quotienting them. -/
def mapRingHom [RingHomClass F R[X] S[X]] (φ : F) (hφ : R[X]⁰ ≤ S[X]⁰.comap φ) :
RatFunc R →+* RatFunc S :=
{ map φ hφ with
map_zero' := by
simp_rw [MonoidHom.toFun_eq_coe, ← ofFractionRing_zero, ← Localization.mk_zero (1 : R[X]⁰),
← Localization.mk_zero (1 : S[X]⁰), map_apply_ofFractionRing_mk, map_zero,
Localization.mk_eq_mk', IsLocalization.mk'_zero]
map_add' := by
rintro ⟨x⟩ ⟨y⟩
induction x using Localization.induction_on
induction y using Localization.induction_on
· simp only [← ofFractionRing_add, Localization.add_mk, map_add, map_mul,
MonoidHom.toFun_eq_coe, map_apply_ofFractionRing_mk, Submonoid.coe_mul,
-- We have to specify `S[X]⁰` to `mk_mul_mk`, otherwise it will try to rewrite
-- the wrong occurrence.
Submonoid.mk_mul_mk S[X]⁰] }
theorem coe_mapRingHom_eq_coe_map [RingHomClass F R[X] S[X]] (φ : F) (hφ : R[X]⁰ ≤ S[X]⁰.comap φ) :
(mapRingHom φ hφ : RatFunc R → RatFunc S) = map φ hφ :=
rfl
-- TODO: Generalize to `FunLike` classes,
/-- Lift a monoid with zero homomorphism `R[X] →*₀ G₀` to a `RatFunc R →*₀ G₀`
on the condition that `φ` maps non zero divisors to non zero divisors,
by mapping both the numerator and denominator and quotienting them. -/
def liftMonoidWithZeroHom (φ : R[X] →*₀ G₀) (hφ : R[X]⁰ ≤ G₀⁰.comap φ) : RatFunc R →*₀ G₀ where
toFun f :=
RatFunc.liftOn f (fun p q => φ p / φ q) fun {p q p' q'} hq hq' h => by
cases subsingleton_or_nontrivial R
· rw [Subsingleton.elim p q, Subsingleton.elim p' q, Subsingleton.elim q' q]
rw [div_eq_div_iff, ← map_mul, mul_comm p, h, map_mul, mul_comm] <;>
exact nonZeroDivisors.ne_zero (hφ ‹_›)
map_one' := by
simp_rw [← ofFractionRing_one, ← Localization.mk_one, liftOn_ofFractionRing_mk,
OneMemClass.coe_one, map_one, div_one]
map_mul' x y := by
obtain ⟨x⟩ := x
obtain ⟨y⟩ := y
induction' x using Localization.induction_on with p q
induction' y using Localization.induction_on with p' q'
rw [← ofFractionRing_mul, Localization.mk_mul]
simp only [liftOn_ofFractionRing_mk, div_mul_div_comm, map_mul, Submonoid.coe_mul]
map_zero' := by
simp_rw [← ofFractionRing_zero, ← Localization.mk_zero (1 : R[X]⁰), liftOn_ofFractionRing_mk,
map_zero, zero_div]
theorem liftMonoidWithZeroHom_apply_ofFractionRing_mk (φ : R[X] →*₀ G₀) (hφ : R[X]⁰ ≤ G₀⁰.comap φ)
(n : R[X]) (d : R[X]⁰) :
liftMonoidWithZeroHom φ hφ (ofFractionRing (Localization.mk n d)) = φ n / φ d :=
liftOn_ofFractionRing_mk _ _ _ _
theorem liftMonoidWithZeroHom_injective [Nontrivial R] (φ : R[X] →*₀ G₀) (hφ : Function.Injective φ)
(hφ' : R[X]⁰ ≤ G₀⁰.comap φ := nonZeroDivisors_le_comap_nonZeroDivisors_of_injective _ hφ) :
Function.Injective (liftMonoidWithZeroHom φ hφ') := by
rintro ⟨x⟩ ⟨y⟩
induction' x using Localization.induction_on with a
induction' y using Localization.induction_on with a'
simp_rw [liftMonoidWithZeroHom_apply_ofFractionRing_mk]
intro h
congr 1
refine Localization.mk_eq_mk_iff.mpr (Localization.r_of_eq (M := R[X]) ?_)
have := mul_eq_mul_of_div_eq_div _ _ ?_ ?_ h
· rwa [← map_mul, ← map_mul, hφ.eq_iff, mul_comm, mul_comm a'.fst] at this
all_goals exact map_ne_zero_of_mem_nonZeroDivisors _ hφ (SetLike.coe_mem _)
/-- Lift an injective ring homomorphism `R[X] →+* L` to a `RatFunc R →+* L`
by mapping both the numerator and denominator and quotienting them. -/
def liftRingHom (φ : R[X] →+* L) (hφ : R[X]⁰ ≤ L⁰.comap φ) : RatFunc R →+* L :=
{ liftMonoidWithZeroHom φ.toMonoidWithZeroHom hφ with
map_add' := fun x y => by
simp only [ZeroHom.toFun_eq_coe, MonoidWithZeroHom.toZeroHom_coe]
cases subsingleton_or_nontrivial R
· rw [Subsingleton.elim (x + y) y, Subsingleton.elim x 0, map_zero, zero_add]
obtain ⟨x⟩ := x
obtain ⟨y⟩ := y
induction' x using Localization.induction_on with pq
induction' y using Localization.induction_on with p'q'
obtain ⟨p, q⟩ := pq
obtain ⟨p', q'⟩ := p'q'
rw [← ofFractionRing_add, Localization.add_mk]
simp only [RingHom.toMonoidWithZeroHom_eq_coe,
liftMonoidWithZeroHom_apply_ofFractionRing_mk]
rw [div_add_div, div_eq_div_iff]
· rw [mul_comm _ p, mul_comm _ p', mul_comm _ (φ p'), add_comm]
simp only [map_add, map_mul, Submonoid.coe_mul]
all_goals
try simp only [← map_mul, ← Submonoid.coe_mul]
exact nonZeroDivisors.ne_zero (hφ (SetLike.coe_mem _)) }
theorem liftRingHom_apply_ofFractionRing_mk (φ : R[X] →+* L) (hφ : R[X]⁰ ≤ L⁰.comap φ) (n : R[X])
(d : R[X]⁰) : liftRingHom φ hφ (ofFractionRing (Localization.mk n d)) = φ n / φ d :=
liftMonoidWithZeroHom_apply_ofFractionRing_mk _ hφ _ _
theorem liftRingHom_injective [Nontrivial R] (φ : R[X] →+* L) (hφ : Function.Injective φ)
(hφ' : R[X]⁰ ≤ L⁰.comap φ := nonZeroDivisors_le_comap_nonZeroDivisors_of_injective _ hφ) :
Function.Injective (liftRingHom φ hφ') :=
liftMonoidWithZeroHom_injective _ hφ
end LiftHom
variable (K)
@[stacks 09FK]
instance instField [IsDomain K] : Field (RatFunc K) where
inv_zero := by frac_tac
div := (· / ·)
div_eq_mul_inv := by frac_tac
mul_inv_cancel _ := mul_inv_cancel
zpow := zpowRec
nnqsmul := _
nnqsmul_def := fun _ _ => rfl
qsmul := _
qsmul_def := fun _ _ => rfl
section IsFractionRing
/-! ### `RatFunc` as field of fractions of `Polynomial` -/
section IsDomain
variable [IsDomain K]
instance (R : Type*) [CommSemiring R] [Algebra R K[X]] : Algebra R (RatFunc K) where
algebraMap :=
{ toFun x := RatFunc.mk (algebraMap _ _ x) 1
map_add' x y := by simp only [mk_one', RingHom.map_add, ofFractionRing_add]
map_mul' x y := by simp only [mk_one', RingHom.map_mul, ofFractionRing_mul]
map_one' := by simp only [mk_one', RingHom.map_one, ofFractionRing_one]
map_zero' := by simp only [mk_one', RingHom.map_zero, ofFractionRing_zero] }
smul := (· • ·)
smul_def' c x := by
induction' x using RatFunc.induction_on' with p q hq
rw [RingHom.coe_mk, MonoidHom.coe_mk, OneHom.coe_mk, mk_one', ← mk_smul,
mk_def_of_ne (c • p) hq, mk_def_of_ne p hq, ← ofFractionRing_mul,
IsLocalization.mul_mk'_eq_mk'_of_mul, Algebra.smul_def]
commutes' _ _ := mul_comm _ _
variable {K}
/-- The coercion from polynomials to rational functions, implemented as the algebra map from a
domain to its field of fractions -/
@[coe]
def coePolynomial (P : Polynomial K) : RatFunc K := algebraMap _ _ P
instance : Coe (Polynomial K) (RatFunc K) := ⟨coePolynomial⟩
theorem mk_one (x : K[X]) : RatFunc.mk x 1 = algebraMap _ _ x :=
rfl
theorem ofFractionRing_algebraMap (x : K[X]) :
ofFractionRing (algebraMap _ (FractionRing K[X]) x) = algebraMap _ _ x := by
rw [← mk_one, mk_one']
@[simp]
theorem mk_eq_div (p q : K[X]) : RatFunc.mk p q = algebraMap _ _ p / algebraMap _ _ q := by
simp only [mk_eq_div', ofFractionRing_div, ofFractionRing_algebraMap]
@[simp]
theorem div_smul {R} [Monoid R] [DistribMulAction R K[X]] [IsScalarTower R K[X] K[X]] (c : R)
(p q : K[X]) :
algebraMap _ (RatFunc K) (c • p) / algebraMap _ _ q =
c • (algebraMap _ _ p / algebraMap _ _ q) := by
rw [← mk_eq_div, mk_smul, mk_eq_div]
theorem algebraMap_apply {R : Type*} [CommSemiring R] [Algebra R K[X]] (x : R) :
algebraMap R (RatFunc K) x = algebraMap _ _ (algebraMap R K[X] x) / algebraMap K[X] _ 1 := by
rw [← mk_eq_div]
rfl
theorem map_apply_div_ne_zero {R F : Type*} [CommRing R] [IsDomain R]
[FunLike F K[X] R[X]] [MonoidHomClass F K[X] R[X]]
(φ : F) (hφ : K[X]⁰ ≤ R[X]⁰.comap φ) (p q : K[X]) (hq : q ≠ 0) :
map φ hφ (algebraMap _ _ p / algebraMap _ _ q) =
algebraMap _ _ (φ p) / algebraMap _ _ (φ q) := by
have hq' : φ q ≠ 0 := nonZeroDivisors.ne_zero (hφ (mem_nonZeroDivisors_iff_ne_zero.mpr hq))
simp only [← mk_eq_div, mk_eq_localization_mk _ hq, map_apply_ofFractionRing_mk,
mk_eq_localization_mk _ hq']
@[simp]
theorem map_apply_div {R F : Type*} [CommRing R] [IsDomain R]
[FunLike F K[X] R[X]] [MonoidWithZeroHomClass F K[X] R[X]]
(φ : F) (hφ : K[X]⁰ ≤ R[X]⁰.comap φ) (p q : K[X]) :
map φ hφ (algebraMap _ _ p / algebraMap _ _ q) =
algebraMap _ _ (φ p) / algebraMap _ _ (φ q) := by
rcases eq_or_ne q 0 with (rfl | hq)
· have : (0 : RatFunc K) = algebraMap K[X] _ 0 / algebraMap K[X] _ 1 := by simp
rw [map_zero, map_zero, map_zero, div_zero, div_zero, this, map_apply_div_ne_zero, map_one,
map_one, div_one, map_zero, map_zero]
exact one_ne_zero
exact map_apply_div_ne_zero _ _ _ _ hq
theorem liftMonoidWithZeroHom_apply_div {L : Type*} [CommGroupWithZero L]
(φ : MonoidWithZeroHom K[X] L) (hφ : K[X]⁰ ≤ L⁰.comap φ) (p q : K[X]) :
liftMonoidWithZeroHom φ hφ (algebraMap _ _ p / algebraMap _ _ q) = φ p / φ q := by
rcases eq_or_ne q 0 with (rfl | hq)
· simp only [div_zero, map_zero]
simp only [← mk_eq_div, mk_eq_localization_mk _ hq,
liftMonoidWithZeroHom_apply_ofFractionRing_mk]
@[simp]
theorem liftMonoidWithZeroHom_apply_div' {L : Type*} [CommGroupWithZero L]
(φ : MonoidWithZeroHom K[X] L) (hφ : K[X]⁰ ≤ L⁰.comap φ) (p q : K[X]) :
liftMonoidWithZeroHom φ hφ (algebraMap _ _ p) / liftMonoidWithZeroHom φ hφ (algebraMap _ _ q) =
φ p / φ q := by
rw [← map_div₀, liftMonoidWithZeroHom_apply_div]
theorem liftRingHom_apply_div {L : Type*} [Field L] (φ : K[X] →+* L) (hφ : K[X]⁰ ≤ L⁰.comap φ)
(p q : K[X]) : liftRingHom φ hφ (algebraMap _ _ p / algebraMap _ _ q) = φ p / φ q :=
liftMonoidWithZeroHom_apply_div _ hφ _ _
@[simp]
theorem liftRingHom_apply_div' {L : Type*} [Field L] (φ : K[X] →+* L) (hφ : K[X]⁰ ≤ L⁰.comap φ)
(p q : K[X]) : liftRingHom φ hφ (algebraMap _ _ p) / liftRingHom φ hφ (algebraMap _ _ q) =
φ p / φ q :=
liftMonoidWithZeroHom_apply_div' _ hφ _ _
variable (K)
theorem ofFractionRing_comp_algebraMap :
ofFractionRing ∘ algebraMap K[X] (FractionRing K[X]) = algebraMap _ _ :=
funext ofFractionRing_algebraMap
theorem algebraMap_injective : Function.Injective (algebraMap K[X] (RatFunc K)) := by
rw [← ofFractionRing_comp_algebraMap]
exact ofFractionRing_injective.comp (IsFractionRing.injective _ _)
variable {K}
section LiftAlgHom
variable {L R S : Type*} [Field L] [CommRing R] [IsDomain R] [CommSemiring S] [Algebra S K[X]]
[Algebra S L] [Algebra S R[X]] (φ : K[X] →ₐ[S] L) (hφ : K[X]⁰ ≤ L⁰.comap φ)
/-- Lift an algebra homomorphism that maps polynomials `φ : K[X] →ₐ[S] R[X]`
to a `RatFunc K →ₐ[S] RatFunc R`,
on the condition that `φ` maps non zero divisors to non zero divisors,
by mapping both the numerator and denominator and quotienting them. -/
def mapAlgHom (φ : K[X] →ₐ[S] R[X]) (hφ : K[X]⁰ ≤ R[X]⁰.comap φ) : RatFunc K →ₐ[S] RatFunc R :=
{ mapRingHom φ hφ with
commutes' := fun r => by
simp_rw [RingHom.toFun_eq_coe, coe_mapRingHom_eq_coe_map, algebraMap_apply r, map_apply_div,
map_one, AlgHom.commutes] }
theorem coe_mapAlgHom_eq_coe_map (φ : K[X] →ₐ[S] R[X]) (hφ : K[X]⁰ ≤ R[X]⁰.comap φ) :
(mapAlgHom φ hφ : RatFunc K → RatFunc R) = map φ hφ :=
rfl
/-- Lift an injective algebra homomorphism `K[X] →ₐ[S] L` to a `RatFunc K →ₐ[S] L`
by mapping both the numerator and denominator and quotienting them. -/
def liftAlgHom : RatFunc K →ₐ[S] L :=
{ liftRingHom φ.toRingHom hφ with
commutes' := fun r => by
simp_rw [RingHom.toFun_eq_coe, AlgHom.toRingHom_eq_coe, algebraMap_apply r,
liftRingHom_apply_div, AlgHom.coe_toRingHom, map_one, div_one, AlgHom.commutes] }
theorem liftAlgHom_apply_ofFractionRing_mk (n : K[X]) (d : K[X]⁰) :
liftAlgHom φ hφ (ofFractionRing (Localization.mk n d)) = φ n / φ d :=
liftMonoidWithZeroHom_apply_ofFractionRing_mk _ hφ _ _
theorem liftAlgHom_injective (φ : K[X] →ₐ[S] L) (hφ : Function.Injective φ)
(hφ' : K[X]⁰ ≤ L⁰.comap φ := nonZeroDivisors_le_comap_nonZeroDivisors_of_injective _ hφ) :
Function.Injective (liftAlgHom φ hφ') :=
liftMonoidWithZeroHom_injective _ hφ
@[simp]
theorem liftAlgHom_apply_div' (p q : K[X]) :
liftAlgHom φ hφ (algebraMap _ _ p) / liftAlgHom φ hφ (algebraMap _ _ q) = φ p / φ q :=
liftMonoidWithZeroHom_apply_div' _ hφ _ _
theorem liftAlgHom_apply_div (p q : K[X]) :
liftAlgHom φ hφ (algebraMap _ _ p / algebraMap _ _ q) = φ p / φ q :=
liftMonoidWithZeroHom_apply_div _ hφ _ _
end LiftAlgHom
variable (K)
/-- `RatFunc K` is the field of fractions of the polynomials over `K`. -/
instance : IsFractionRing K[X] (RatFunc K) where
map_units' y := by
rw [← ofFractionRing_algebraMap]
exact (toFractionRingRingEquiv K).symm.toRingHom.isUnit_map (IsLocalization.map_units _ y)
exists_of_eq {x y} := by
rw [← ofFractionRing_algebraMap, ← ofFractionRing_algebraMap]
exact fun h ↦ IsLocalization.exists_of_eq ((toFractionRingRingEquiv K).symm.injective h)
surj' := by
rintro ⟨z⟩
convert IsLocalization.surj K[X]⁰ z
simp only [← ofFractionRing_algebraMap, Function.comp_apply, ← ofFractionRing_mul,
ofFractionRing.injEq]
variable {K}
theorem algebraMap_ne_zero {x : K[X]} (hx : x ≠ 0) : algebraMap K[X] (RatFunc K) x ≠ 0 := by
simpa
@[simp]
theorem liftOn_div {P : Sort v} (p q : K[X]) (f : K[X] → K[X] → P) (f0 : ∀ p, f p 0 = f 0 1)
(H' : ∀ {p q p' q'} (_hq : q ≠ 0) (_hq' : q' ≠ 0), q' * p = q * p' → f p q = f p' q')
(H : ∀ {p q p' q'} (_hq : q ∈ K[X]⁰) (_hq' : q' ∈ K[X]⁰), q' * p = q * p' → f p q = f p' q' :=
fun {_ _ _ _} hq hq' h => H' (nonZeroDivisors.ne_zero hq) (nonZeroDivisors.ne_zero hq') h) :
(RatFunc.liftOn (algebraMap _ (RatFunc K) p / algebraMap _ _ q)) f @H = f p q := by
rw [← mk_eq_div, liftOn_mk _ _ f f0 @H']
@[simp]
theorem liftOn'_div {P : Sort v} (p q : K[X]) (f : K[X] → K[X] → P) (f0 : ∀ p, f p 0 = f 0 1)
(H) :
(RatFunc.liftOn' (algebraMap _ (RatFunc K) p / algebraMap _ _ q)) f @H = f p q := by
rw [RatFunc.liftOn', liftOn_div _ _ _ f0]
apply liftOn_condition_of_liftOn'_condition H
/-- Induction principle for `RatFunc K`: if `f p q : P (p / q)` for all `p q : K[X]`,
then `P` holds on all elements of `RatFunc K`.
See also `induction_on'`, which is a recursion principle defined in terms of `RatFunc.mk`.
-/
protected theorem induction_on {P : RatFunc K → Prop} (x : RatFunc K)
(f : ∀ (p q : K[X]) (_ : q ≠ 0), P (algebraMap _ (RatFunc K) p / algebraMap _ _ q)) : P x :=
x.induction_on' fun p q hq => by simpa using f p q hq
theorem ofFractionRing_mk' (x : K[X]) (y : K[X]⁰) :
ofFractionRing (IsLocalization.mk' _ x y) =
IsLocalization.mk' (RatFunc K) x y := by
rw [IsFractionRing.mk'_eq_div, IsFractionRing.mk'_eq_div, ← mk_eq_div', ← mk_eq_div]
theorem mk_eq_mk' (f : Polynomial K) {g : Polynomial K} (hg : g ≠ 0) :
RatFunc.mk f g = IsLocalization.mk' (RatFunc K) f ⟨g, mem_nonZeroDivisors_iff_ne_zero.2 hg⟩ :=
by simp only [mk_eq_div, IsFractionRing.mk'_eq_div]
@[simp]
theorem ofFractionRing_eq :
(ofFractionRing : FractionRing K[X] → RatFunc K) = IsLocalization.algEquiv K[X]⁰ _ _ :=
funext fun x =>
Localization.induction_on x fun x => by
simp only [Localization.mk_eq_mk'_apply, ofFractionRing_mk', IsLocalization.algEquiv_apply,
IsLocalization.map_mk', RingHom.id_apply]
@[simp]
theorem toFractionRing_eq :
(toFractionRing : RatFunc K → FractionRing K[X]) = IsLocalization.algEquiv K[X]⁰ _ _ :=
funext fun ⟨x⟩ =>
Localization.induction_on x fun x => by
simp only [Localization.mk_eq_mk'_apply, ofFractionRing_mk', IsLocalization.algEquiv_apply,
IsLocalization.map_mk', RingHom.id_apply]
@[simp]
theorem toFractionRingRingEquiv_symm_eq :
(toFractionRingRingEquiv K).symm = (IsLocalization.algEquiv K[X]⁰ _ _).toRingEquiv := by
ext x
simp [toFractionRingRingEquiv, ofFractionRing_eq, AlgEquiv.coe_ringEquiv']
end IsDomain
end IsFractionRing
end CommRing
section NumDenom
/-! ### Numerator and denominator -/
open GCDMonoid Polynomial
variable [Field K]
open scoped Classical in
/-- `RatFunc.numDenom` are numerator and denominator of a rational function over a field,
normalized such that the denominator is monic. -/
def numDenom (x : RatFunc K) : K[X] × K[X] :=
x.liftOn'
(fun p q =>
if q = 0 then ⟨0, 1⟩
else
let r := gcd p q
⟨Polynomial.C (q / r).leadingCoeff⁻¹ * (p / r),
Polynomial.C (q / r).leadingCoeff⁻¹ * (q / r)⟩)
(by
intros p q a hq ha
dsimp
rw [if_neg hq, if_neg (mul_ne_zero ha hq)]
have ha' : a.leadingCoeff ≠ 0 := Polynomial.leadingCoeff_ne_zero.mpr ha
have hainv : a.leadingCoeff⁻¹ ≠ 0 := inv_ne_zero ha'
simp only [Prod.ext_iff, gcd_mul_left, normalize_apply a, Polynomial.coe_normUnit, mul_assoc,
CommGroupWithZero.coe_normUnit _ ha']
have hdeg : (gcd p q).degree ≤ q.degree := degree_gcd_le_right _ hq
have hdeg' : (Polynomial.C a.leadingCoeff⁻¹ * gcd p q).degree ≤ q.degree := by
rw [Polynomial.degree_mul, Polynomial.degree_C hainv, zero_add]
exact hdeg
have hdivp : Polynomial.C a.leadingCoeff⁻¹ * gcd p q ∣ p :=
(C_mul_dvd hainv).mpr (gcd_dvd_left p q)
have hdivq : Polynomial.C a.leadingCoeff⁻¹ * gcd p q ∣ q :=
(C_mul_dvd hainv).mpr (gcd_dvd_right p q)
rw [EuclideanDomain.mul_div_mul_cancel ha hdivp, EuclideanDomain.mul_div_mul_cancel ha hdivq,
leadingCoeff_div hdeg, leadingCoeff_div hdeg', Polynomial.leadingCoeff_mul,
Polynomial.leadingCoeff_C, div_C_mul, div_C_mul, ← mul_assoc, ← Polynomial.C_mul, ←
mul_assoc, ← Polynomial.C_mul]
constructor <;> congr <;>
rw [inv_div, mul_comm, mul_div_assoc, ← mul_assoc, inv_inv, mul_inv_cancel₀ ha',
one_mul, inv_div])
open scoped Classical in
@[simp]
theorem numDenom_div (p : K[X]) {q : K[X]} (hq : q ≠ 0) :
numDenom (algebraMap _ _ p / algebraMap _ _ q) =
(Polynomial.C (q / gcd p q).leadingCoeff⁻¹ * (p / gcd p q),
Polynomial.C (q / gcd p q).leadingCoeff⁻¹ * (q / gcd p q)) := by
rw [numDenom, liftOn'_div, if_neg hq]
| intro p
rw [if_pos rfl, if_neg (one_ne_zero' K[X])]
simp
/-- `RatFunc.num` is the numerator of a rational function,
| Mathlib/FieldTheory/RatFunc/Basic.lean | 782 | 786 |
/-
Copyright (c) 2023 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Oliver Nash
-/
import Mathlib.Algebra.Lie.CartanSubalgebra
import Mathlib.Algebra.Lie.Weights.Basic
/-!
# Weights and roots of Lie modules and Lie algebras with respect to Cartan subalgebras
Given a Lie algebra `L` which is not necessarily nilpotent, it may be useful to study its
representations by restricting them to a nilpotent subalgebra (e.g., a Cartan subalgebra). In the
particular case when we view `L` as a module over itself via the adjoint action, the weight spaces
of `L` restricted to a nilpotent subalgebra are known as root spaces.
Basic definitions and properties of the above ideas are provided in this file.
## Main definitions
* `LieAlgebra.rootSpace`
* `LieAlgebra.corootSpace`
* `LieAlgebra.rootSpaceWeightSpaceProduct`
* `LieAlgebra.rootSpaceProduct`
* `LieAlgebra.zeroRootSubalgebra_eq_iff_is_cartan`
-/
suppress_compilation
open Set
variable {R L : Type*} [CommRing R] [LieRing L] [LieAlgebra R L]
(H : LieSubalgebra R L) [LieRing.IsNilpotent H]
{M : Type*} [AddCommGroup M] [Module R M] [LieRingModule L M] [LieModule R L M]
namespace LieAlgebra
open scoped TensorProduct
open TensorProduct.LieModule LieModule
/-- Given a nilpotent Lie subalgebra `H ⊆ L`, the root space of a map `χ : H → R` is the weight
space of `L` regarded as a module of `H` via the adjoint action. -/
abbrev rootSpace (χ : H → R) : LieSubmodule R H L :=
genWeightSpace L χ
theorem zero_rootSpace_eq_top_of_nilpotent [LieRing.IsNilpotent L] :
rootSpace (⊤ : LieSubalgebra R L) 0 = ⊤ :=
zero_genWeightSpace_eq_top_of_nilpotent L
@[simp]
theorem rootSpace_comap_eq_genWeightSpace (χ : H → R) :
(rootSpace H χ).comap H.incl' = genWeightSpace H χ :=
comap_genWeightSpace_eq_of_injective Subtype.coe_injective
variable {H}
theorem lie_mem_genWeightSpace_of_mem_genWeightSpace {χ₁ χ₂ : H → R} {x : L} {m : M}
(hx : x ∈ rootSpace H χ₁) (hm : m ∈ genWeightSpace M χ₂) :
⁅x, m⁆ ∈ genWeightSpace M (χ₁ + χ₂) := by
rw [genWeightSpace, LieSubmodule.mem_iInf]
intro y
replace hx : x ∈ genWeightSpaceOf L (χ₁ y) y := by
rw [rootSpace, genWeightSpace, LieSubmodule.mem_iInf] at hx; exact hx y
replace hm : m ∈ genWeightSpaceOf M (χ₂ y) y := by
rw [genWeightSpace, LieSubmodule.mem_iInf] at hm; exact hm y
exact lie_mem_maxGenEigenspace_toEnd hx hm
lemma toEnd_pow_apply_mem {χ₁ χ₂ : H → R} {x : L} {m : M}
(hx : x ∈ rootSpace H χ₁) (hm : m ∈ genWeightSpace M χ₂) (n) :
(toEnd R L M x ^ n : Module.End R M) m ∈ genWeightSpace M (n • χ₁ + χ₂) := by
induction n with
| zero => simpa using hm
| succ n IH =>
simp only [pow_succ', Module.End.mul_apply, toEnd_apply_apply,
Nat.cast_add, Nat.cast_one, rootSpace]
convert lie_mem_genWeightSpace_of_mem_genWeightSpace hx IH using 2
rw [succ_nsmul, ← add_assoc, add_comm (n • _)]
variable (R L H M)
/-- Auxiliary definition for `rootSpaceWeightSpaceProduct`,
which is close to the deterministic timeout limit.
-/
def rootSpaceWeightSpaceProductAux {χ₁ χ₂ χ₃ : H → R} (hχ : χ₁ + χ₂ = χ₃) :
rootSpace H χ₁ →ₗ[R] genWeightSpace M χ₂ →ₗ[R] genWeightSpace M χ₃ where
toFun x :=
{ toFun := fun m =>
⟨⁅(x : L), (m : M)⁆,
hχ ▸ lie_mem_genWeightSpace_of_mem_genWeightSpace x.property m.property⟩
map_add' := fun m n => by simp only [LieSubmodule.coe_add, lie_add, AddMemClass.mk_add_mk]
map_smul' := fun t m => by
conv_lhs =>
congr
rw [LieSubmodule.coe_smul, lie_smul]
rfl }
map_add' x y := by
ext m
simp only [LieSubmodule.coe_add, add_lie, LinearMap.coe_mk, AddHom.coe_mk, LinearMap.add_apply,
AddMemClass.mk_add_mk]
map_smul' t x := by
simp only [RingHom.id_apply]
ext m
simp only [SetLike.val_smul, smul_lie, LinearMap.coe_mk, AddHom.coe_mk, LinearMap.smul_apply,
SetLike.mk_smul_mk]
/-- Given a nilpotent Lie subalgebra `H ⊆ L` together with `χ₁ χ₂ : H → R`, there is a natural
`R`-bilinear product of root vectors and weight vectors, compatible with the actions of `H`. -/
def rootSpaceWeightSpaceProduct (χ₁ χ₂ χ₃ : H → R) (hχ : χ₁ + χ₂ = χ₃) :
rootSpace H χ₁ ⊗[R] genWeightSpace M χ₂ →ₗ⁅R,H⁆ genWeightSpace M χ₃ :=
liftLie R H (rootSpace H χ₁) (genWeightSpace M χ₂) (genWeightSpace M χ₃)
{ toLinearMap := rootSpaceWeightSpaceProductAux R L H M hχ
map_lie' := fun {x y} => by
ext m
simp only [rootSpaceWeightSpaceProductAux]
dsimp
simp only [LieSubalgebra.coe_bracket_of_module, lie_lie] }
@[simp]
theorem coe_rootSpaceWeightSpaceProduct_tmul (χ₁ χ₂ χ₃ : H → R) (hχ : χ₁ + χ₂ = χ₃)
(x : rootSpace H χ₁) (m : genWeightSpace M χ₂) :
(rootSpaceWeightSpaceProduct R L H M χ₁ χ₂ χ₃ hχ (x ⊗ₜ m) : M) = ⁅(x : L), (m : M)⁆ := by
simp only [rootSpaceWeightSpaceProduct, rootSpaceWeightSpaceProductAux, coe_liftLie_eq_lift_coe,
AddHom.toFun_eq_coe, LinearMap.coe_toAddHom, lift_apply, LinearMap.coe_mk, AddHom.coe_mk,
Submodule.coe_mk]
theorem mapsTo_toEnd_genWeightSpace_add_of_mem_rootSpace (α χ : H → R)
{x : L} (hx : x ∈ rootSpace H α) :
MapsTo (toEnd R L M x) (genWeightSpace M χ) (genWeightSpace M (α + χ)) := by
intro m hm
let x' : rootSpace H α := ⟨x, hx⟩
let m' : genWeightSpace M χ := ⟨m, hm⟩
exact (rootSpaceWeightSpaceProduct R L H M α χ (α + χ) rfl (x' ⊗ₜ m')).property
/-- Given a nilpotent Lie subalgebra `H ⊆ L` together with `χ₁ χ₂ : H → R`, there is a natural
`R`-bilinear product of root vectors, compatible with the actions of `H`. -/
def rootSpaceProduct (χ₁ χ₂ χ₃ : H → R) (hχ : χ₁ + χ₂ = χ₃) :
rootSpace H χ₁ ⊗[R] rootSpace H χ₂ →ₗ⁅R,H⁆ rootSpace H χ₃ :=
rootSpaceWeightSpaceProduct R L H L χ₁ χ₂ χ₃ hχ
@[simp]
theorem rootSpaceProduct_def : rootSpaceProduct R L H = rootSpaceWeightSpaceProduct R L H L := rfl
theorem rootSpaceProduct_tmul
(χ₁ χ₂ χ₃ : H → R) (hχ : χ₁ + χ₂ = χ₃) (x : rootSpace H χ₁) (y : rootSpace H χ₂) :
(rootSpaceProduct R L H χ₁ χ₂ χ₃ hχ (x ⊗ₜ y) : L) = ⁅(x : L), (y : L)⁆ := by
simp only [rootSpaceProduct_def, coe_rootSpaceWeightSpaceProduct_tmul]
/-- Given a nilpotent Lie subalgebra `H ⊆ L`, the root space of the zero map `0 : H → R` is a Lie
subalgebra of `L`. -/
def zeroRootSubalgebra : LieSubalgebra R L :=
{ toSubmodule := (rootSpace H 0 : Submodule R L)
lie_mem' := fun {x y hx hy} => by
let xy : rootSpace H 0 ⊗[R] rootSpace H 0 := ⟨x, hx⟩ ⊗ₜ ⟨y, hy⟩
suffices (rootSpaceProduct R L H 0 0 0 (add_zero 0) xy : L) ∈ rootSpace H 0 by
rwa [rootSpaceProduct_tmul, Subtype.coe_mk, Subtype.coe_mk] at this
exact (rootSpaceProduct R L H 0 0 0 (add_zero 0) xy).property }
@[simp]
theorem coe_zeroRootSubalgebra : (zeroRootSubalgebra R L H : Submodule R L) = rootSpace H 0 := rfl
theorem mem_zeroRootSubalgebra (x : L) :
x ∈ zeroRootSubalgebra R L H ↔ ∀ y : H, ∃ k : ℕ, (toEnd R H L y ^ k) x = 0 := by
change x ∈ rootSpace H 0 ↔ _
simp only [mem_genWeightSpace, Pi.zero_apply, zero_smul, sub_zero]
theorem toLieSubmodule_le_rootSpace_zero : H.toLieSubmodule ≤ rootSpace H 0 := by
intro x hx
simp only [LieSubalgebra.mem_toLieSubmodule] at hx
simp only [mem_genWeightSpace, Pi.zero_apply, sub_zero, zero_smul]
intro y
obtain ⟨k, hk⟩ := IsNilpotent.nilpotent R H H
use k
let f : Module.End R H := toEnd R H H y
let g : Module.End R L := toEnd R H L y
have hfg : g.comp (H : Submodule R L).subtype = (H : Submodule R L).subtype.comp f := by
ext z
simp only [toEnd_apply_apply, Submodule.subtype_apply,
LieSubalgebra.coe_bracket_of_module, LieSubalgebra.coe_bracket, Function.comp_apply,
LinearMap.coe_comp]
rfl
change (g ^ k).comp (H : Submodule R L).subtype ⟨x, hx⟩ = 0
rw [Module.End.commute_pow_left_of_commute hfg k]
have h := iterate_toEnd_mem_lowerCentralSeries R H H y ⟨x, hx⟩ k
rw [hk, LieSubmodule.mem_bot] at h
simp only [Submodule.subtype_apply, Function.comp_apply, Module.End.pow_apply, LinearMap.coe_comp,
Submodule.coe_eq_zero]
exact h
/-- This enables the instance `Zero (Weight R H L)`. -/
instance [Nontrivial H] : Nontrivial (genWeightSpace L (0 : H → R)) := by
obtain ⟨⟨x, hx⟩, ⟨y, hy⟩, e⟩ := exists_pair_ne H
exact ⟨⟨x, toLieSubmodule_le_rootSpace_zero R L H hx⟩,
⟨y, toLieSubmodule_le_rootSpace_zero R L H hy⟩, by simpa using e⟩
theorem le_zeroRootSubalgebra : H ≤ zeroRootSubalgebra R L H := by
rw [← LieSubalgebra.toSubmodule_le_toSubmodule, ← H.coe_toLieSubmodule,
coe_zeroRootSubalgebra, LieSubmodule.toSubmodule_le_toSubmodule]
exact toLieSubmodule_le_rootSpace_zero R L H
@[simp]
theorem zeroRootSubalgebra_normalizer_eq_self :
(zeroRootSubalgebra R L H).normalizer = zeroRootSubalgebra R L H := by
refine le_antisymm ?_ (LieSubalgebra.le_normalizer _)
intro x hx
rw [LieSubalgebra.mem_normalizer_iff] at hx
rw [mem_zeroRootSubalgebra]
rintro ⟨y, hy⟩
specialize hx y (le_zeroRootSubalgebra R L H hy)
rw [mem_zeroRootSubalgebra] at hx
obtain ⟨k, hk⟩ := hx ⟨y, hy⟩
rw [← lie_skew, LinearMap.map_neg, neg_eq_zero] at hk
use k + 1
rw [Module.End.iterate_succ, LinearMap.coe_comp, Function.comp_apply, toEnd_apply_apply,
LieSubalgebra.coe_bracket_of_module, Submodule.coe_mk, hk]
/-- If the zero root subalgebra of a nilpotent Lie subalgebra `H` is just `H` then `H` is a Cartan
subalgebra.
When `L` is Noetherian, it follows from Engel's theorem that the converse holds. See
`LieAlgebra.zeroRootSubalgebra_eq_iff_is_cartan` -/
theorem is_cartan_of_zeroRootSubalgebra_eq (h : zeroRootSubalgebra R L H = H) :
H.IsCartanSubalgebra :=
{ nilpotent := inferInstance
self_normalizing := by rw [← h]; exact zeroRootSubalgebra_normalizer_eq_self R L H }
@[simp]
theorem zeroRootSubalgebra_eq_of_is_cartan (H : LieSubalgebra R L) [H.IsCartanSubalgebra]
[IsNoetherian R L] : zeroRootSubalgebra R L H = H := by
refine le_antisymm ?_ (le_zeroRootSubalgebra R L H)
suffices rootSpace H 0 ≤ H.toLieSubmodule by exact fun x hx => this hx
obtain ⟨k, hk⟩ := (rootSpace H 0).isNilpotent_iff_exists_self_le_ucs.mp (by infer_instance)
exact hk.trans (LieSubmodule.ucs_le_of_normalizer_eq_self (by simp) k)
theorem zeroRootSubalgebra_eq_iff_is_cartan [IsNoetherian R L] :
zeroRootSubalgebra R L H = H ↔ H.IsCartanSubalgebra :=
⟨is_cartan_of_zeroRootSubalgebra_eq R L H, by intros; simp⟩
@[simp]
theorem rootSpace_zero_eq (H : LieSubalgebra R L) [H.IsCartanSubalgebra] [IsNoetherian R L] :
rootSpace H 0 = H.toLieSubmodule := by
rw [← LieSubmodule.toSubmodule_inj, ← coe_zeroRootSubalgebra,
zeroRootSubalgebra_eq_of_is_cartan R L H, LieSubalgebra.coe_toLieSubmodule]
variable {R L H}
variable [H.IsCartanSubalgebra] [IsNoetherian R L] (α : H → R)
/-- Given a root `α` relative to a Cartan subalgebra `H`, this is the span of all products of
an element of the `α` root space and an element of the `-α` root space. Informally it is often
denoted `⁅H(α), H(-α)⁆`.
If the Killing form is non-degenerate and the coefficients are a perfect field, this space is
one-dimensional. See `LieAlgebra.IsKilling.coe_corootSpace_eq_span_singleton` and
`LieAlgebra.IsKilling.coe_corootSpace_eq_span_singleton'`.
Note that the name "coroot space" is not standard as this space does not seem to have a name in the
informal literature. -/
def corootSpace : LieIdeal R H :=
LieModuleHom.range <| ((rootSpace H 0).incl.comp <|
| rootSpaceProduct R L H α (-α) 0 (add_neg_cancel α)).codRestrict H.toLieSubmodule (by
rw [← rootSpace_zero_eq]
exact fun p ↦ (rootSpaceProduct R L H α (-α) 0 (add_neg_cancel α) p).property)
| Mathlib/Algebra/Lie/Weights/Cartan.lean | 260 | 263 |
/-
Copyright (c) 2021 Yourong Zang. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yourong Zang
-/
import Mathlib.Analysis.NormedSpace.ConformalLinearMap
import Mathlib.Analysis.Calculus.FDeriv.Add
/-!
# Conformal Maps
A continuous linear map between real normed spaces `X` and `Y` is `ConformalAt` some point `x`
if it is real differentiable at that point and its differential is a conformal linear map.
## Main definitions
* `ConformalAt`: the main definition of conformal maps
* `Conformal`: maps that are conformal at every point
## Main results
* The conformality of the composition of two conformal maps, the identity map
and multiplications by nonzero constants
* `conformalAt_iff_isConformalMap_fderiv`: an equivalent definition of the conformality of a map
In `Analysis.Calculus.Conformal.InnerProduct`:
* `conformalAt_iff`: an equivalent definition of the conformality of a map
In `Geometry.Euclidean.Angle.Unoriented.Conformal`:
* `ConformalAt.preserves_angle`: if a map is conformal at `x`, then its differential preserves
all angles at `x`
## Tags
conformal
## Warning
The definition of conformality in this file does NOT require the maps to be orientation-preserving.
Maps such as the complex conjugate are considered to be conformal.
-/
noncomputable section
variable {X Y Z : Type*} [NormedAddCommGroup X] [NormedAddCommGroup Y] [NormedAddCommGroup Z]
[NormedSpace ℝ X] [NormedSpace ℝ Y] [NormedSpace ℝ Z]
section LocConformality
open LinearIsometry ContinuousLinearMap
/-- A map `f` is said to be conformal if it has a conformal differential `f'`. -/
def ConformalAt (f : X → Y) (x : X) :=
∃ f' : X →L[ℝ] Y, HasFDerivAt f f' x ∧ IsConformalMap f'
theorem conformalAt_id (x : X) : ConformalAt _root_.id x :=
⟨id ℝ X, hasFDerivAt_id _, isConformalMap_id⟩
theorem conformalAt_const_smul {c : ℝ} (h : c ≠ 0) (x : X) : ConformalAt (fun x' : X => c • x') x :=
⟨c • ContinuousLinearMap.id ℝ X, (hasFDerivAt_id x).const_smul c, isConformalMap_const_smul h⟩
@[nontriviality]
theorem Subsingleton.conformalAt [Subsingleton X] (f : X → Y) (x : X) : ConformalAt f x :=
⟨0, hasFDerivAt_of_subsingleton _ _, isConformalMap_of_subsingleton _⟩
/-- A function is a conformal map if and only if its differential is a conformal linear map -/
theorem conformalAt_iff_isConformalMap_fderiv {f : X → Y} {x : X} :
ConformalAt f x ↔ IsConformalMap (fderiv ℝ f x) := by
constructor
· rintro ⟨f', hf, hf'⟩
rwa [hf.fderiv]
· intro H
by_cases h : DifferentiableAt ℝ f x
· exact ⟨fderiv ℝ f x, h.hasFDerivAt, H⟩
· nontriviality X
exact absurd (fderiv_zero_of_not_differentiableAt h) H.ne_zero
namespace ConformalAt
theorem differentiableAt {f : X → Y} {x : X} (h : ConformalAt f x) : DifferentiableAt ℝ f x :=
let ⟨_, h₁, _⟩ := h
h₁.differentiableAt
theorem congr {f g : X → Y} {x : X} {u : Set X} (hx : x ∈ u) (hu : IsOpen u) (hf : ConformalAt f x)
(h : ∀ x : X, x ∈ u → g x = f x) : ConformalAt g x :=
let ⟨f', hfderiv, hf'⟩ := hf
⟨f', hfderiv.congr_of_eventuallyEq ((hu.eventually_mem hx).mono h), hf'⟩
theorem comp {f : X → Y} {g : Y → Z} (x : X) (hg : ConformalAt g (f x)) (hf : ConformalAt f x) :
ConformalAt (g ∘ f) x := by
rcases hf with ⟨f', hf₁, cf⟩
rcases hg with ⟨g', hg₁, cg⟩
exact ⟨g'.comp f', hg₁.comp x hf₁, cg.comp cf⟩
theorem const_smul {f : X → Y} {x : X} {c : ℝ} (hc : c ≠ 0) (hf : ConformalAt f x) :
ConformalAt (c • f) x :=
(conformalAt_const_smul hc <| f x).comp x hf
|
end ConformalAt
end LocConformality
| Mathlib/Analysis/Calculus/Conformal/NormedSpace.lean | 98 | 102 |
/-
Copyright (c) 2020 Kexing Ying. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kexing Ying
-/
import Mathlib.Algebra.Group.Conj
import Mathlib.Algebra.Group.Pi.Lemmas
import Mathlib.Algebra.Group.Subgroup.Ker
/-!
# Basic results on subgroups
We prove basic results on the definitions of subgroups. The bundled subgroups use bundled monoid
homomorphisms.
Special thanks goes to Amelia Livingston and Yury Kudryashov for their help and inspiration.
## Main definitions
Notation used here:
- `G N` are `Group`s
- `A` is an `AddGroup`
- `H K` are `Subgroup`s of `G` or `AddSubgroup`s of `A`
- `x` is an element of type `G` or type `A`
- `f g : N →* G` are group homomorphisms
- `s k` are sets of elements of type `G`
Definitions in the file:
* `Subgroup.prod H K` : the product of subgroups `H`, `K` of groups `G`, `N` respectively, `H × K`
is a subgroup of `G × N`
## Implementation notes
Subgroup inclusion is denoted `≤` rather than `⊆`, although `∈` is defined as
membership of a subgroup's underlying set.
## Tags
subgroup, subgroups
-/
assert_not_exists OrderedAddCommMonoid Multiset Ring
open Function
open scoped Int
variable {G G' G'' : Type*} [Group G] [Group G'] [Group G'']
variable {A : Type*} [AddGroup A]
section SubgroupClass
variable {M S : Type*} [DivInvMonoid M] [SetLike S M] [hSM : SubgroupClass S M] {H K : S}
variable [SetLike S G] [SubgroupClass S G]
@[to_additive]
theorem div_mem_comm_iff {a b : G} : a / b ∈ H ↔ b / a ∈ H :=
inv_div b a ▸ inv_mem_iff
end SubgroupClass
namespace Subgroup
variable (H K : Subgroup G)
@[to_additive]
protected theorem div_mem_comm_iff {a b : G} : a / b ∈ H ↔ b / a ∈ H :=
div_mem_comm_iff
variable {k : Set G}
open Set
variable {N : Type*} [Group N] {P : Type*} [Group P]
/-- Given `Subgroup`s `H`, `K` of groups `G`, `N` respectively, `H × K` as a subgroup of `G × N`. -/
@[to_additive prod
"Given `AddSubgroup`s `H`, `K` of `AddGroup`s `A`, `B` respectively, `H × K`
as an `AddSubgroup` of `A × B`."]
def prod (H : Subgroup G) (K : Subgroup N) : Subgroup (G × N) :=
{ Submonoid.prod H.toSubmonoid K.toSubmonoid with
inv_mem' := fun hx => ⟨H.inv_mem' hx.1, K.inv_mem' hx.2⟩ }
@[to_additive coe_prod]
theorem coe_prod (H : Subgroup G) (K : Subgroup N) :
(H.prod K : Set (G × N)) = (H : Set G) ×ˢ (K : Set N) :=
rfl
@[to_additive mem_prod]
theorem mem_prod {H : Subgroup G} {K : Subgroup N} {p : G × N} : p ∈ H.prod K ↔ p.1 ∈ H ∧ p.2 ∈ K :=
Iff.rfl
open scoped Relator in
@[to_additive prod_mono]
theorem prod_mono : ((· ≤ ·) ⇒ (· ≤ ·) ⇒ (· ≤ ·)) (@prod G _ N _) (@prod G _ N _) :=
fun _s _s' hs _t _t' ht => Set.prod_mono hs ht
@[to_additive prod_mono_right]
theorem prod_mono_right (K : Subgroup G) : Monotone fun t : Subgroup N => K.prod t :=
prod_mono (le_refl K)
@[to_additive prod_mono_left]
theorem prod_mono_left (H : Subgroup N) : Monotone fun K : Subgroup G => K.prod H := fun _ _ hs =>
prod_mono hs (le_refl H)
@[to_additive prod_top]
theorem prod_top (K : Subgroup G) : K.prod (⊤ : Subgroup N) = K.comap (MonoidHom.fst G N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_fst]
@[to_additive top_prod]
theorem top_prod (H : Subgroup N) : (⊤ : Subgroup G).prod H = H.comap (MonoidHom.snd G N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_snd]
@[to_additive (attr := simp) top_prod_top]
theorem top_prod_top : (⊤ : Subgroup G).prod (⊤ : Subgroup N) = ⊤ :=
(top_prod _).trans <| comap_top _
@[to_additive (attr := simp) bot_prod_bot]
theorem bot_prod_bot : (⊥ : Subgroup G).prod (⊥ : Subgroup N) = ⊥ :=
SetLike.coe_injective <| by simp [coe_prod]
@[deprecated (since := "2025-03-11")]
alias _root_.AddSubgroup.bot_sum_bot := AddSubgroup.bot_prod_bot
@[to_additive le_prod_iff]
theorem le_prod_iff {H : Subgroup G} {K : Subgroup N} {J : Subgroup (G × N)} :
J ≤ H.prod K ↔ map (MonoidHom.fst G N) J ≤ H ∧ map (MonoidHom.snd G N) J ≤ K := by
simpa only [← Subgroup.toSubmonoid_le] using Submonoid.le_prod_iff
@[to_additive prod_le_iff]
theorem prod_le_iff {H : Subgroup G} {K : Subgroup N} {J : Subgroup (G × N)} :
H.prod K ≤ J ↔ map (MonoidHom.inl G N) H ≤ J ∧ map (MonoidHom.inr G N) K ≤ J := by
simpa only [← Subgroup.toSubmonoid_le] using Submonoid.prod_le_iff
@[to_additive (attr := simp) prod_eq_bot_iff]
theorem prod_eq_bot_iff {H : Subgroup G} {K : Subgroup N} : H.prod K = ⊥ ↔ H = ⊥ ∧ K = ⊥ := by
simpa only [← Subgroup.toSubmonoid_inj] using Submonoid.prod_eq_bot_iff
@[to_additive closure_prod]
theorem closure_prod {s : Set G} {t : Set N} (hs : 1 ∈ s) (ht : 1 ∈ t) :
closure (s ×ˢ t) = (closure s).prod (closure t) :=
le_antisymm
(closure_le _ |>.2 <| Set.prod_subset_prod_iff.2 <| .inl ⟨subset_closure, subset_closure⟩)
(prod_le_iff.2 ⟨
map_le_iff_le_comap.2 <| closure_le _ |>.2 fun _x hx => subset_closure ⟨hx, ht⟩,
map_le_iff_le_comap.2 <| closure_le _ |>.2 fun _y hy => subset_closure ⟨hs, hy⟩⟩)
/-- Product of subgroups is isomorphic to their product as groups. -/
@[to_additive prodEquiv
"Product of additive subgroups is isomorphic to their product
as additive groups"]
def prodEquiv (H : Subgroup G) (K : Subgroup N) : H.prod K ≃* H × K :=
{ Equiv.Set.prod (H : Set G) (K : Set N) with map_mul' := fun _ _ => rfl }
section Pi
variable {η : Type*} {f : η → Type*}
-- defined here and not in Algebra.Group.Submonoid.Operations to have access to Algebra.Group.Pi
/-- A version of `Set.pi` for submonoids. Given an index set `I` and a family of submodules
`s : Π i, Submonoid f i`, `pi I s` is the submonoid of dependent functions `f : Π i, f i` such that
`f i` belongs to `Pi I s` whenever `i ∈ I`. -/
@[to_additive "A version of `Set.pi` for `AddSubmonoid`s. Given an index set `I` and a family
of submodules `s : Π i, AddSubmonoid f i`, `pi I s` is the `AddSubmonoid` of dependent functions
`f : Π i, f i` such that `f i` belongs to `pi I s` whenever `i ∈ I`."]
def _root_.Submonoid.pi [∀ i, MulOneClass (f i)] (I : Set η) (s : ∀ i, Submonoid (f i)) :
Submonoid (∀ i, f i) where
carrier := I.pi fun i => (s i).carrier
one_mem' i _ := (s i).one_mem
mul_mem' hp hq i hI := (s i).mul_mem (hp i hI) (hq i hI)
variable [∀ i, Group (f i)]
/-- A version of `Set.pi` for subgroups. Given an index set `I` and a family of submodules
`s : Π i, Subgroup f i`, `pi I s` is the subgroup of dependent functions `f : Π i, f i` such that
`f i` belongs to `pi I s` whenever `i ∈ I`. -/
@[to_additive
"A version of `Set.pi` for `AddSubgroup`s. Given an index set `I` and a family
of submodules `s : Π i, AddSubgroup f i`, `pi I s` is the `AddSubgroup` of dependent functions
`f : Π i, f i` such that `f i` belongs to `pi I s` whenever `i ∈ I`."]
def pi (I : Set η) (H : ∀ i, Subgroup (f i)) : Subgroup (∀ i, f i) :=
{ Submonoid.pi I fun i => (H i).toSubmonoid with
inv_mem' := fun hp i hI => (H i).inv_mem (hp i hI) }
@[to_additive]
theorem coe_pi (I : Set η) (H : ∀ i, Subgroup (f i)) :
(pi I H : Set (∀ i, f i)) = Set.pi I fun i => (H i : Set (f i)) :=
rfl
@[to_additive]
theorem mem_pi (I : Set η) {H : ∀ i, Subgroup (f i)} {p : ∀ i, f i} :
p ∈ pi I H ↔ ∀ i : η, i ∈ I → p i ∈ H i :=
Iff.rfl
@[to_additive]
theorem pi_top (I : Set η) : (pi I fun i => (⊤ : Subgroup (f i))) = ⊤ :=
ext fun x => by simp [mem_pi]
@[to_additive]
theorem pi_empty (H : ∀ i, Subgroup (f i)) : pi ∅ H = ⊤ :=
ext fun x => by simp [mem_pi]
@[to_additive]
theorem pi_bot : (pi Set.univ fun i => (⊥ : Subgroup (f i))) = ⊥ :=
(eq_bot_iff_forall _).mpr fun p hp => by
simp only [mem_pi, mem_bot] at *
ext j
exact hp j trivial
@[to_additive]
theorem le_pi_iff {I : Set η} {H : ∀ i, Subgroup (f i)} {J : Subgroup (∀ i, f i)} :
J ≤ pi I H ↔ ∀ i : η, i ∈ I → map (Pi.evalMonoidHom f i) J ≤ H i := by
constructor
· intro h i hi
rintro _ ⟨x, hx, rfl⟩
exact (h hx) _ hi
· intro h x hx i hi
exact h i hi ⟨_, hx, rfl⟩
@[to_additive (attr := simp)]
theorem mulSingle_mem_pi [DecidableEq η] {I : Set η} {H : ∀ i, Subgroup (f i)} (i : η) (x : f i) :
Pi.mulSingle i x ∈ pi I H ↔ i ∈ I → x ∈ H i := by
constructor
· intro h hi
simpa using h i hi
· intro h j hj
by_cases heq : j = i
· subst heq
simpa using h hj
· simp [heq, one_mem]
@[to_additive]
theorem pi_eq_bot_iff (H : ∀ i, Subgroup (f i)) : pi Set.univ H = ⊥ ↔ ∀ i, H i = ⊥ := by
classical
simp only [eq_bot_iff_forall]
constructor
· intro h i x hx
have : MonoidHom.mulSingle f i x = 1 :=
h (MonoidHom.mulSingle f i x) ((mulSingle_mem_pi i x).mpr fun _ => hx)
simpa using congr_fun this i
· exact fun h x hx => funext fun i => h _ _ (hx i trivial)
end Pi
end Subgroup
namespace Subgroup
variable {H K : Subgroup G}
variable (H)
/-- A subgroup is characteristic if it is fixed by all automorphisms.
Several equivalent conditions are provided by lemmas of the form `Characteristic.iff...` -/
structure Characteristic : Prop where
/-- `H` is fixed by all automorphisms -/
fixed : ∀ ϕ : G ≃* G, H.comap ϕ.toMonoidHom = H
attribute [class] Characteristic
instance (priority := 100) normal_of_characteristic [h : H.Characteristic] : H.Normal :=
⟨fun a ha b => (SetLike.ext_iff.mp (h.fixed (MulAut.conj b)) a).mpr ha⟩
end Subgroup
namespace AddSubgroup
variable (H : AddSubgroup A)
/-- An `AddSubgroup` is characteristic if it is fixed by all automorphisms.
Several equivalent conditions are provided by lemmas of the form `Characteristic.iff...` -/
structure Characteristic : Prop where
/-- `H` is fixed by all automorphisms -/
fixed : ∀ ϕ : A ≃+ A, H.comap ϕ.toAddMonoidHom = H
attribute [to_additive] Subgroup.Characteristic
attribute [class] Characteristic
instance (priority := 100) normal_of_characteristic [h : H.Characteristic] : H.Normal :=
⟨fun a ha b => (SetLike.ext_iff.mp (h.fixed (AddAut.conj b)) a).mpr ha⟩
end AddSubgroup
namespace Subgroup
variable {H K : Subgroup G}
@[to_additive]
theorem characteristic_iff_comap_eq : H.Characteristic ↔ ∀ ϕ : G ≃* G, H.comap ϕ.toMonoidHom = H :=
⟨Characteristic.fixed, Characteristic.mk⟩
@[to_additive]
theorem characteristic_iff_comap_le : H.Characteristic ↔ ∀ ϕ : G ≃* G, H.comap ϕ.toMonoidHom ≤ H :=
characteristic_iff_comap_eq.trans
⟨fun h ϕ => le_of_eq (h ϕ), fun h ϕ =>
le_antisymm (h ϕ) fun g hg => h ϕ.symm ((congr_arg (· ∈ H) (ϕ.symm_apply_apply g)).mpr hg)⟩
@[to_additive]
theorem characteristic_iff_le_comap : H.Characteristic ↔ ∀ ϕ : G ≃* G, H ≤ H.comap ϕ.toMonoidHom :=
characteristic_iff_comap_eq.trans
⟨fun h ϕ => ge_of_eq (h ϕ), fun h ϕ =>
le_antisymm (fun g hg => (congr_arg (· ∈ H) (ϕ.symm_apply_apply g)).mp (h ϕ.symm hg)) (h ϕ)⟩
@[to_additive]
theorem characteristic_iff_map_eq : H.Characteristic ↔ ∀ ϕ : G ≃* G, H.map ϕ.toMonoidHom = H := by
simp_rw [map_equiv_eq_comap_symm']
exact characteristic_iff_comap_eq.trans ⟨fun h ϕ => h ϕ.symm, fun h ϕ => h ϕ.symm⟩
@[to_additive]
theorem characteristic_iff_map_le : H.Characteristic ↔ ∀ ϕ : G ≃* G, H.map ϕ.toMonoidHom ≤ H := by
simp_rw [map_equiv_eq_comap_symm']
exact characteristic_iff_comap_le.trans ⟨fun h ϕ => h ϕ.symm, fun h ϕ => h ϕ.symm⟩
@[to_additive]
theorem characteristic_iff_le_map : H.Characteristic ↔ ∀ ϕ : G ≃* G, H ≤ H.map ϕ.toMonoidHom := by
simp_rw [map_equiv_eq_comap_symm']
exact characteristic_iff_le_comap.trans ⟨fun h ϕ => h ϕ.symm, fun h ϕ => h ϕ.symm⟩
@[to_additive]
instance botCharacteristic : Characteristic (⊥ : Subgroup G) :=
characteristic_iff_le_map.mpr fun _ϕ => bot_le
@[to_additive]
instance topCharacteristic : Characteristic (⊤ : Subgroup G) :=
characteristic_iff_map_le.mpr fun _ϕ => le_top
variable (H)
section Normalizer
variable {H}
@[to_additive]
theorem normalizer_eq_top_iff : H.normalizer = ⊤ ↔ H.Normal :=
eq_top_iff.trans
⟨fun h => ⟨fun a ha b => (h (mem_top b) a).mp ha⟩, fun h a _ha b =>
⟨fun hb => h.conj_mem b hb a, fun hb => by rwa [h.mem_comm_iff, inv_mul_cancel_left] at hb⟩⟩
variable (H) in
@[to_additive]
theorem normalizer_eq_top [h : H.Normal] : H.normalizer = ⊤ :=
normalizer_eq_top_iff.mpr h
variable {N : Type*} [Group N]
/-- The preimage of the normalizer is contained in the normalizer of the preimage. -/
@[to_additive "The preimage of the normalizer is contained in the normalizer of the preimage."]
theorem le_normalizer_comap (f : N →* G) :
H.normalizer.comap f ≤ (H.comap f).normalizer := fun x => by
simp only [mem_normalizer_iff, mem_comap]
intro h n
simp [h (f n)]
/-- The image of the normalizer is contained in the normalizer of the image. -/
@[to_additive "The image of the normalizer is contained in the normalizer of the image."]
theorem le_normalizer_map (f : G →* N) : H.normalizer.map f ≤ (H.map f).normalizer := fun _ => by
simp only [and_imp, exists_prop, mem_map, exists_imp, mem_normalizer_iff]
rintro x hx rfl n
constructor
· rintro ⟨y, hy, rfl⟩
use x * y * x⁻¹, (hx y).1 hy
simp
· rintro ⟨y, hyH, hy⟩
use x⁻¹ * y * x
rw [hx]
simp [hy, hyH, mul_assoc]
@[to_additive]
theorem comap_normalizer_eq_of_le_range {f : N →* G} (h : H ≤ f.range) :
comap f H.normalizer = (comap f H).normalizer := by
apply le_antisymm (le_normalizer_comap f)
rw [← map_le_iff_le_comap]
apply (le_normalizer_map f).trans
rw [map_comap_eq_self h]
@[to_additive]
theorem subgroupOf_normalizer_eq {H N : Subgroup G} (h : H ≤ N) :
H.normalizer.subgroupOf N = (H.subgroupOf N).normalizer :=
comap_normalizer_eq_of_le_range (h.trans_eq N.range_subtype.symm)
@[to_additive]
theorem normal_subgroupOf_iff_le_normalizer (h : H ≤ K) :
(H.subgroupOf K).Normal ↔ K ≤ H.normalizer := by
rw [← subgroupOf_eq_top, subgroupOf_normalizer_eq h, normalizer_eq_top_iff]
@[to_additive]
theorem normal_subgroupOf_iff_le_normalizer_inf :
(H.subgroupOf K).Normal ↔ K ≤ (H ⊓ K).normalizer :=
inf_subgroupOf_right H K ▸ normal_subgroupOf_iff_le_normalizer inf_le_right
@[to_additive]
instance (priority := 100) normal_in_normalizer : (H.subgroupOf H.normalizer).Normal :=
(normal_subgroupOf_iff_le_normalizer H.le_normalizer).mpr le_rfl
@[to_additive]
theorem le_normalizer_of_normal_subgroupOf [hK : (H.subgroupOf K).Normal] (HK : H ≤ K) :
K ≤ H.normalizer :=
(normal_subgroupOf_iff_le_normalizer HK).mp hK
@[to_additive]
theorem subset_normalizer_of_normal {S : Set G} [hH : H.Normal] : S ⊆ H.normalizer :=
(@normalizer_eq_top _ _ H hH) ▸ le_top
@[to_additive]
theorem le_normalizer_of_normal [H.Normal] : K ≤ H.normalizer := subset_normalizer_of_normal
@[to_additive]
theorem inf_normalizer_le_normalizer_inf : H.normalizer ⊓ K.normalizer ≤ (H ⊓ K).normalizer :=
fun _ h g ↦ and_congr (h.1 g) (h.2 g)
variable (G) in
/-- Every proper subgroup `H` of `G` is a proper normal subgroup of the normalizer of `H` in `G`. -/
def _root_.NormalizerCondition :=
∀ H : Subgroup G, H < ⊤ → H < normalizer H
/-- Alternative phrasing of the normalizer condition: Only the full group is self-normalizing.
This may be easier to work with, as it avoids inequalities and negations. -/
theorem _root_.normalizerCondition_iff_only_full_group_self_normalizing :
NormalizerCondition G ↔ ∀ H : Subgroup G, H.normalizer = H → H = ⊤ := by
apply forall_congr'; intro H
simp only [lt_iff_le_and_ne, le_normalizer, le_top, Ne]
tauto
variable (H)
end Normalizer
end Subgroup
namespace Group
variable {s : Set G}
/-- Given a set `s`, `conjugatesOfSet s` is the set of all conjugates of
the elements of `s`. -/
def conjugatesOfSet (s : Set G) : Set G :=
⋃ a ∈ s, conjugatesOf a
theorem mem_conjugatesOfSet_iff {x : G} : x ∈ conjugatesOfSet s ↔ ∃ a ∈ s, IsConj a x := by
rw [conjugatesOfSet, Set.mem_iUnion₂]
simp only [conjugatesOf, isConj_iff, Set.mem_setOf_eq, exists_prop]
theorem subset_conjugatesOfSet : s ⊆ conjugatesOfSet s := fun (x : G) (h : x ∈ s) =>
mem_conjugatesOfSet_iff.2 ⟨x, h, IsConj.refl _⟩
theorem conjugatesOfSet_mono {s t : Set G} (h : s ⊆ t) : conjugatesOfSet s ⊆ conjugatesOfSet t :=
Set.biUnion_subset_biUnion_left h
theorem conjugates_subset_normal {N : Subgroup G} [tn : N.Normal] {a : G} (h : a ∈ N) :
conjugatesOf a ⊆ N := by
rintro a hc
obtain ⟨c, rfl⟩ := isConj_iff.1 hc
exact tn.conj_mem a h c
theorem conjugatesOfSet_subset {s : Set G} {N : Subgroup G} [N.Normal] (h : s ⊆ N) :
conjugatesOfSet s ⊆ N :=
Set.iUnion₂_subset fun _x H => conjugates_subset_normal (h H)
/-- The set of conjugates of `s` is closed under conjugation. -/
theorem conj_mem_conjugatesOfSet {x c : G} :
x ∈ conjugatesOfSet s → c * x * c⁻¹ ∈ conjugatesOfSet s := fun H => by
rcases mem_conjugatesOfSet_iff.1 H with ⟨a, h₁, h₂⟩
exact mem_conjugatesOfSet_iff.2 ⟨a, h₁, h₂.trans (isConj_iff.2 ⟨c, rfl⟩)⟩
end Group
namespace Subgroup
open Group
variable {s : Set G}
/-- The normal closure of a set `s` is the subgroup closure of all the conjugates of
elements of `s`. It is the smallest normal subgroup containing `s`. -/
def normalClosure (s : Set G) : Subgroup G :=
closure (conjugatesOfSet s)
theorem conjugatesOfSet_subset_normalClosure : conjugatesOfSet s ⊆ normalClosure s :=
subset_closure
theorem subset_normalClosure : s ⊆ normalClosure s :=
Set.Subset.trans subset_conjugatesOfSet conjugatesOfSet_subset_normalClosure
theorem le_normalClosure {H : Subgroup G} : H ≤ normalClosure ↑H := fun _ h =>
subset_normalClosure h
/-- The normal closure of `s` is a normal subgroup. -/
instance normalClosure_normal : (normalClosure s).Normal :=
⟨fun n h g => by
refine Subgroup.closure_induction (fun x hx => ?_) ?_ (fun x y _ _ ihx ihy => ?_)
(fun x _ ihx => ?_) h
· exact conjugatesOfSet_subset_normalClosure (conj_mem_conjugatesOfSet hx)
· simpa using (normalClosure s).one_mem
· rw [← conj_mul]
exact mul_mem ihx ihy
· rw [← conj_inv]
exact inv_mem ihx⟩
/-- The normal closure of `s` is the smallest normal subgroup containing `s`. -/
theorem normalClosure_le_normal {N : Subgroup G} [N.Normal] (h : s ⊆ N) : normalClosure s ≤ N := by
intro a w
refine closure_induction (fun x hx => ?_) ?_ (fun x y _ _ ihx ihy => ?_) (fun x _ ihx => ?_) w
· exact conjugatesOfSet_subset h hx
· exact one_mem _
· exact mul_mem ihx ihy
· exact inv_mem ihx
theorem normalClosure_subset_iff {N : Subgroup G} [N.Normal] : s ⊆ N ↔ normalClosure s ≤ N :=
⟨normalClosure_le_normal, Set.Subset.trans subset_normalClosure⟩
@[gcongr]
theorem normalClosure_mono {s t : Set G} (h : s ⊆ t) : normalClosure s ≤ normalClosure t :=
normalClosure_le_normal (Set.Subset.trans h subset_normalClosure)
theorem normalClosure_eq_iInf :
normalClosure s = ⨅ (N : Subgroup G) (_ : Normal N) (_ : s ⊆ N), N :=
le_antisymm (le_iInf fun _ => le_iInf fun _ => le_iInf normalClosure_le_normal)
(iInf_le_of_le (normalClosure s)
(iInf_le_of_le (by infer_instance) (iInf_le_of_le subset_normalClosure le_rfl)))
@[simp]
theorem normalClosure_eq_self (H : Subgroup G) [H.Normal] : normalClosure ↑H = H :=
le_antisymm (normalClosure_le_normal rfl.subset) le_normalClosure
theorem normalClosure_idempotent : normalClosure ↑(normalClosure s) = normalClosure s :=
normalClosure_eq_self _
theorem closure_le_normalClosure {s : Set G} : closure s ≤ normalClosure s := by
simp only [subset_normalClosure, closure_le]
@[simp]
theorem normalClosure_closure_eq_normalClosure {s : Set G} :
normalClosure ↑(closure s) = normalClosure s :=
le_antisymm (normalClosure_le_normal closure_le_normalClosure) (normalClosure_mono subset_closure)
/-- The normal core of a subgroup `H` is the largest normal subgroup of `G` contained in `H`,
as shown by `Subgroup.normalCore_eq_iSup`. -/
def normalCore (H : Subgroup G) : Subgroup G where
carrier := { a : G | ∀ b : G, b * a * b⁻¹ ∈ H }
one_mem' a := by rw [mul_one, mul_inv_cancel]; exact H.one_mem
inv_mem' {_} h b := (congr_arg (· ∈ H) conj_inv).mp (H.inv_mem (h b))
mul_mem' {_ _} ha hb c := (congr_arg (· ∈ H) conj_mul).mp (H.mul_mem (ha c) (hb c))
theorem normalCore_le (H : Subgroup G) : H.normalCore ≤ H := fun a h => by
rw [← mul_one a, ← inv_one, ← one_mul a]
exact h 1
instance normalCore_normal (H : Subgroup G) : H.normalCore.Normal :=
⟨fun a h b c => by
rw [mul_assoc, mul_assoc, ← mul_inv_rev, ← mul_assoc, ← mul_assoc]; exact h (c * b)⟩
theorem normal_le_normalCore {H : Subgroup G} {N : Subgroup G} [hN : N.Normal] :
N ≤ H.normalCore ↔ N ≤ H :=
⟨ge_trans H.normalCore_le, fun h_le n hn g => h_le (hN.conj_mem n hn g)⟩
theorem normalCore_mono {H K : Subgroup G} (h : H ≤ K) : H.normalCore ≤ K.normalCore :=
normal_le_normalCore.mpr (H.normalCore_le.trans h)
theorem normalCore_eq_iSup (H : Subgroup G) :
H.normalCore = ⨆ (N : Subgroup G) (_ : Normal N) (_ : N ≤ H), N :=
le_antisymm
(le_iSup_of_le H.normalCore
(le_iSup_of_le H.normalCore_normal (le_iSup_of_le H.normalCore_le le_rfl)))
(iSup_le fun _ => iSup_le fun _ => iSup_le normal_le_normalCore.mpr)
@[simp]
theorem normalCore_eq_self (H : Subgroup G) [H.Normal] : H.normalCore = H :=
le_antisymm H.normalCore_le (normal_le_normalCore.mpr le_rfl)
theorem normalCore_idempotent (H : Subgroup G) : H.normalCore.normalCore = H.normalCore :=
H.normalCore.normalCore_eq_self
end Subgroup
namespace MonoidHom
variable {N : Type*} {P : Type*} [Group N] [Group P] (K : Subgroup G)
open Subgroup
section Ker
variable {M : Type*} [MulOneClass M]
@[to_additive prodMap_comap_prod]
theorem prodMap_comap_prod {G' : Type*} {N' : Type*} [Group G'] [Group N'] (f : G →* N)
(g : G' →* N') (S : Subgroup N) (S' : Subgroup N') :
(S.prod S').comap (prodMap f g) = (S.comap f).prod (S'.comap g) :=
SetLike.coe_injective <| Set.preimage_prod_map_prod f g _ _
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoidHom.sumMap_comap_sum := AddMonoidHom.prodMap_comap_prod
@[to_additive ker_prodMap]
theorem ker_prodMap {G' : Type*} {N' : Type*} [Group G'] [Group N'] (f : G →* N) (g : G' →* N') :
(prodMap f g).ker = f.ker.prod g.ker := by
rw [← comap_bot, ← comap_bot, ← comap_bot, ← prodMap_comap_prod, bot_prod_bot]
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoidHom.ker_sumMap := AddMonoidHom.ker_prodMap
@[to_additive (attr := simp)]
lemma ker_fst : ker (fst G G') = .prod ⊥ ⊤ := SetLike.ext fun _ => (iff_of_eq (and_true _)).symm
@[to_additive (attr := simp)]
lemma ker_snd : ker (snd G G') = .prod ⊤ ⊥ := SetLike.ext fun _ => (iff_of_eq (true_and _)).symm
end Ker
end MonoidHom
namespace Subgroup
variable {N : Type*} [Group N] (H : Subgroup G)
@[to_additive]
theorem Normal.map {H : Subgroup G} (h : H.Normal) (f : G →* N) (hf : Function.Surjective f) :
(H.map f).Normal := by
rw [← normalizer_eq_top_iff, ← top_le_iff, ← f.range_eq_top_of_surjective hf, f.range_eq_map,
← H.normalizer_eq_top]
exact le_normalizer_map _
end Subgroup
namespace Subgroup
open MonoidHom
variable {N : Type*} [Group N] (f : G →* N)
/-- The preimage of the normalizer is equal to the normalizer of the preimage of a surjective
function. -/
@[to_additive
"The preimage of the normalizer is equal to the normalizer of the preimage of
a surjective function."]
theorem comap_normalizer_eq_of_surjective (H : Subgroup G) {f : N →* G}
(hf : Function.Surjective f) : H.normalizer.comap f = (H.comap f).normalizer :=
comap_normalizer_eq_of_le_range fun x _ ↦ hf x
@[deprecated (since := "2025-03-13")]
alias comap_normalizer_eq_of_injective_of_le_range := comap_normalizer_eq_of_le_range
@[deprecated (since := "2025-03-13")]
alias _root_.AddSubgroup.comap_normalizer_eq_of_injective_of_le_range :=
AddSubgroup.comap_normalizer_eq_of_le_range
/-- The image of the normalizer is equal to the normalizer of the image of an isomorphism. -/
@[to_additive
"The image of the normalizer is equal to the normalizer of the image of an
isomorphism."]
theorem map_equiv_normalizer_eq (H : Subgroup G) (f : G ≃* N) :
H.normalizer.map f.toMonoidHom = (H.map f.toMonoidHom).normalizer := by
ext x
simp only [mem_normalizer_iff, mem_map_equiv]
rw [f.toEquiv.forall_congr]
intro
simp
/-- The image of the normalizer is equal to the normalizer of the image of a bijective
function. -/
@[to_additive
"The image of the normalizer is equal to the normalizer of the image of a bijective
function."]
theorem map_normalizer_eq_of_bijective (H : Subgroup G) {f : G →* N} (hf : Function.Bijective f) :
H.normalizer.map f = (H.map f).normalizer :=
map_equiv_normalizer_eq H (MulEquiv.ofBijective f hf)
end Subgroup
namespace MonoidHom
variable {G₁ G₂ G₃ : Type*} [Group G₁] [Group G₂] [Group G₃]
variable (f : G₁ →* G₂) (f_inv : G₂ → G₁)
/-- Auxiliary definition used to define `liftOfRightInverse` -/
@[to_additive "Auxiliary definition used to define `liftOfRightInverse`"]
def liftOfRightInverseAux (hf : Function.RightInverse f_inv f) (g : G₁ →* G₃) (hg : f.ker ≤ g.ker) :
G₂ →* G₃ where
toFun b := g (f_inv b)
map_one' := hg (hf 1)
map_mul' := by
intro x y
rw [← g.map_mul, ← mul_inv_eq_one, ← g.map_inv, ← g.map_mul, ← g.mem_ker]
apply hg
rw [f.mem_ker, f.map_mul, f.map_inv, mul_inv_eq_one, f.map_mul]
simp only [hf _]
@[to_additive (attr := simp)]
theorem liftOfRightInverseAux_comp_apply (hf : Function.RightInverse f_inv f) (g : G₁ →* G₃)
(hg : f.ker ≤ g.ker) (x : G₁) : (f.liftOfRightInverseAux f_inv hf g hg) (f x) = g x := by
dsimp [liftOfRightInverseAux]
rw [← mul_inv_eq_one, ← g.map_inv, ← g.map_mul, ← g.mem_ker]
apply hg
rw [f.mem_ker, f.map_mul, f.map_inv, mul_inv_eq_one]
simp only [hf _]
/-- `liftOfRightInverse f hf g hg` is the unique group homomorphism `φ`
* such that `φ.comp f = g` (`MonoidHom.liftOfRightInverse_comp`),
* where `f : G₁ →+* G₂` has a RightInverse `f_inv` (`hf`),
* and `g : G₂ →+* G₃` satisfies `hg : f.ker ≤ g.ker`.
See `MonoidHom.eq_liftOfRightInverse` for the uniqueness lemma.
```
G₁.
| \
f | \ g
| \
v \⌟
G₂----> G₃
∃!φ
```
-/
@[to_additive
"`liftOfRightInverse f f_inv hf g hg` is the unique additive group homomorphism `φ`
* such that `φ.comp f = g` (`AddMonoidHom.liftOfRightInverse_comp`),
* where `f : G₁ →+ G₂` has a RightInverse `f_inv` (`hf`),
* and `g : G₂ →+ G₃` satisfies `hg : f.ker ≤ g.ker`.
See `AddMonoidHom.eq_liftOfRightInverse` for the uniqueness lemma.
```
G₁.
| \\
f | \\ g
| \\
v \\⌟
G₂----> G₃
∃!φ
```"]
def liftOfRightInverse (hf : Function.RightInverse f_inv f) :
{ g : G₁ →* G₃ // f.ker ≤ g.ker } ≃ (G₂ →* G₃) where
toFun g := f.liftOfRightInverseAux f_inv hf g.1 g.2
invFun φ := ⟨φ.comp f, fun x hx ↦ mem_ker.mpr <| by simp [mem_ker.mp hx]⟩
left_inv g := by
ext
simp only [comp_apply, liftOfRightInverseAux_comp_apply, Subtype.coe_mk]
right_inv φ := by
ext b
simp [liftOfRightInverseAux, hf b]
/-- A non-computable version of `MonoidHom.liftOfRightInverse` for when no computable right
inverse is available, that uses `Function.surjInv`. -/
@[to_additive (attr := simp)
"A non-computable version of `AddMonoidHom.liftOfRightInverse` for when no
computable right inverse is available."]
noncomputable abbrev liftOfSurjective (hf : Function.Surjective f) :
{ g : G₁ →* G₃ // f.ker ≤ g.ker } ≃ (G₂ →* G₃) :=
f.liftOfRightInverse (Function.surjInv hf) (Function.rightInverse_surjInv hf)
@[to_additive (attr := simp)]
theorem liftOfRightInverse_comp_apply (hf : Function.RightInverse f_inv f)
(g : { g : G₁ →* G₃ // f.ker ≤ g.ker }) (x : G₁) :
(f.liftOfRightInverse f_inv hf g) (f x) = g.1 x :=
f.liftOfRightInverseAux_comp_apply f_inv hf g.1 g.2 x
@[to_additive (attr := simp)]
theorem liftOfRightInverse_comp (hf : Function.RightInverse f_inv f)
(g : { g : G₁ →* G₃ // f.ker ≤ g.ker }) : (f.liftOfRightInverse f_inv hf g).comp f = g :=
MonoidHom.ext <| f.liftOfRightInverse_comp_apply f_inv hf g
@[to_additive]
theorem eq_liftOfRightInverse (hf : Function.RightInverse f_inv f) (g : G₁ →* G₃)
(hg : f.ker ≤ g.ker) (h : G₂ →* G₃) (hh : h.comp f = g) :
h = f.liftOfRightInverse f_inv hf ⟨g, hg⟩ := by
simp_rw [← hh]
exact ((f.liftOfRightInverse f_inv hf).apply_symm_apply _).symm
end MonoidHom
variable {N : Type*} [Group N]
namespace Subgroup
-- Here `H.Normal` is an explicit argument so we can use dot notation with `comap`.
@[to_additive]
theorem Normal.comap {H : Subgroup N} (hH : H.Normal) (f : G →* N) : (H.comap f).Normal :=
⟨fun _ => by simp +contextual [Subgroup.mem_comap, hH.conj_mem]⟩
@[to_additive]
instance (priority := 100) normal_comap {H : Subgroup N} [nH : H.Normal] (f : G →* N) :
(H.comap f).Normal :=
nH.comap _
-- Here `H.Normal` is an explicit argument so we can use dot notation with `subgroupOf`.
@[to_additive]
theorem Normal.subgroupOf {H : Subgroup G} (hH : H.Normal) (K : Subgroup G) :
(H.subgroupOf K).Normal :=
hH.comap _
@[to_additive]
instance (priority := 100) normal_subgroupOf {H N : Subgroup G} [N.Normal] :
(N.subgroupOf H).Normal :=
Subgroup.normal_comap _
theorem map_normalClosure (s : Set G) (f : G →* N) (hf : Surjective f) :
(normalClosure s).map f = normalClosure (f '' s) := by
have : Normal (map f (normalClosure s)) := Normal.map inferInstance f hf
apply le_antisymm
· simp [map_le_iff_le_comap, normalClosure_le_normal, coe_comap,
← Set.image_subset_iff, subset_normalClosure]
· exact normalClosure_le_normal (Set.image_subset f subset_normalClosure)
theorem comap_normalClosure (s : Set N) (f : G ≃* N) :
normalClosure (f ⁻¹' s) = (normalClosure s).comap f := by
have := Set.preimage_equiv_eq_image_symm s f.toEquiv
simp_all [comap_equiv_eq_map_symm, map_normalClosure s (f.symm : N →* G) f.symm.surjective]
lemma Normal.of_map_injective {G H : Type*} [Group G] [Group H] {φ : G →* H}
(hφ : Function.Injective φ) {L : Subgroup G} (n : (L.map φ).Normal) : L.Normal :=
L.comap_map_eq_self_of_injective hφ ▸ n.comap φ
theorem Normal.of_map_subtype {K : Subgroup G} {L : Subgroup K}
(n : (Subgroup.map K.subtype L).Normal) : L.Normal :=
n.of_map_injective K.subtype_injective
end Subgroup
namespace Subgroup
section SubgroupNormal
@[to_additive]
theorem normal_subgroupOf_iff {H K : Subgroup G} (hHK : H ≤ K) :
(H.subgroupOf K).Normal ↔ ∀ h k, h ∈ H → k ∈ K → k * h * k⁻¹ ∈ H :=
⟨fun hN h k hH hK => hN.conj_mem ⟨h, hHK hH⟩ hH ⟨k, hK⟩, fun hN =>
{ conj_mem := fun h hm k => hN h.1 k.1 hm k.2 }⟩
@[to_additive prod_addSubgroupOf_prod_normal]
instance prod_subgroupOf_prod_normal {H₁ K₁ : Subgroup G} {H₂ K₂ : Subgroup N}
[h₁ : (H₁.subgroupOf K₁).Normal] [h₂ : (H₂.subgroupOf K₂).Normal] :
((H₁.prod H₂).subgroupOf (K₁.prod K₂)).Normal where
conj_mem n hgHK g :=
⟨h₁.conj_mem ⟨(n : G × N).fst, (mem_prod.mp n.2).1⟩ hgHK.1
⟨(g : G × N).fst, (mem_prod.mp g.2).1⟩,
h₂.conj_mem ⟨(n : G × N).snd, (mem_prod.mp n.2).2⟩ hgHK.2
⟨(g : G × N).snd, (mem_prod.mp g.2).2⟩⟩
@[deprecated (since := "2025-03-11")]
alias _root_.AddSubgroup.sum_addSubgroupOf_sum_normal := AddSubgroup.prod_addSubgroupOf_prod_normal
@[to_additive prod_normal]
instance prod_normal (H : Subgroup G) (K : Subgroup N) [hH : H.Normal] [hK : K.Normal] :
(H.prod K).Normal where
conj_mem n hg g :=
⟨hH.conj_mem n.fst (Subgroup.mem_prod.mp hg).1 g.fst,
hK.conj_mem n.snd (Subgroup.mem_prod.mp hg).2 g.snd⟩
@[deprecated (since := "2025-03-11")]
alias _root_.AddSubgroup.sum_normal := AddSubgroup.prod_normal
@[to_additive]
theorem inf_subgroupOf_inf_normal_of_right (A B' B : Subgroup G)
[hN : (B'.subgroupOf B).Normal] : ((A ⊓ B').subgroupOf (A ⊓ B)).Normal := by
rw [normal_subgroupOf_iff_le_normalizer_inf] at hN ⊢
rw [inf_inf_inf_comm, inf_idem]
exact le_trans (inf_le_inf A.le_normalizer hN) (inf_normalizer_le_normalizer_inf)
@[to_additive]
theorem inf_subgroupOf_inf_normal_of_left {A' A : Subgroup G} (B : Subgroup G)
[hN : (A'.subgroupOf A).Normal] : ((A' ⊓ B).subgroupOf (A ⊓ B)).Normal := by
rw [normal_subgroupOf_iff_le_normalizer_inf] at hN ⊢
rw [inf_inf_inf_comm, inf_idem]
exact le_trans (inf_le_inf hN B.le_normalizer) (inf_normalizer_le_normalizer_inf)
@[to_additive]
instance normal_inf_normal (H K : Subgroup G) [hH : H.Normal] [hK : K.Normal] : (H ⊓ K).Normal :=
⟨fun n hmem g => ⟨hH.conj_mem n hmem.1 g, hK.conj_mem n hmem.2 g⟩⟩
@[to_additive]
theorem normal_iInf_normal {ι : Type*} {a : ι → Subgroup G}
(norm : ∀ i : ι, (a i).Normal) : (iInf a).Normal := by
constructor
intro g g_in_iInf h
rw [Subgroup.mem_iInf] at g_in_iInf ⊢
intro i
exact (norm i).conj_mem g (g_in_iInf i) h
@[to_additive]
theorem SubgroupNormal.mem_comm {H K : Subgroup G} (hK : H ≤ K) [hN : (H.subgroupOf K).Normal]
{a b : G} (hb : b ∈ K) (h : a * b ∈ H) : b * a ∈ H := by
have := (normal_subgroupOf_iff hK).mp hN (a * b) b h hb
rwa [mul_assoc, mul_assoc, mul_inv_cancel, mul_one] at this
/-- Elements of disjoint, normal subgroups commute. -/
@[to_additive "Elements of disjoint, normal subgroups commute."]
| theorem commute_of_normal_of_disjoint (H₁ H₂ : Subgroup G) (hH₁ : H₁.Normal) (hH₂ : H₂.Normal)
(hdis : Disjoint H₁ H₂) (x y : G) (hx : x ∈ H₁) (hy : y ∈ H₂) : Commute x y := by
suffices x * y * x⁻¹ * y⁻¹ = 1 by
show x * y = y * x
· rw [mul_assoc, mul_eq_one_iff_eq_inv] at this
simpa
apply hdis.le_bot
| Mathlib/Algebra/Group/Subgroup/Basic.lean | 894 | 900 |
/-
Copyright (c) 2024 Joël Riou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joël Riou
-/
import Mathlib.CategoryTheory.Localization.LocalizerMorphism
import Mathlib.CategoryTheory.HomCongr
/-!
# Bijections between morphisms in two localized categories
Given two localization functors `L₁ : C ⥤ D₁` and `L₂ : C ⥤ D₂` for the same
class of morphisms `W : MorphismProperty C`, we define a bijection
`Localization.homEquiv W L₁ L₂ : (L₁.obj X ⟶ L₁.obj Y) ≃ (L₂.obj X ⟶ L₂.obj Y)`
between the types of morphisms in the two localized categories.
More generally, given a localizer morphism `Φ : LocalizerMorphism W₁ W₂`, we define a map
`Φ.homMap L₁ L₂ : (L₁.obj X ⟶ L₁.obj Y) ⟶ (L₂.obj (Φ.functor.obj X) ⟶ L₂.obj (Φ.functor.obj Y))`.
The definition `Localization.homEquiv` is obtained by applying the construction
to the identity localizer morphism.
-/
namespace CategoryTheory
open Category
variable {C C₁ C₂ C₃ D₁ D₂ D₃ : Type*} [Category C]
[Category C₁] [Category C₂] [Category C₃]
[Category D₁] [Category D₂] [Category D₃]
namespace LocalizerMorphism
variable {W₁ : MorphismProperty C₁} {W₂ : MorphismProperty C₂} {W₃ : MorphismProperty C₃}
(Φ : LocalizerMorphism W₁ W₂) (Ψ : LocalizerMorphism W₂ W₃)
(L₁ : C₁ ⥤ D₁) [L₁.IsLocalization W₁]
(L₂ : C₂ ⥤ D₂) [L₂.IsLocalization W₂]
(L₃ : C₃ ⥤ D₃) [L₃.IsLocalization W₃]
{X Y Z : C₁}
/-- If `Φ : LocalizerMorphism W₁ W₂` is a morphism of localizers, `L₁` and `L₂`
are localization functors for `W₁` and `W₂`, then this is the induced map
`(L₁.obj X ⟶ L₁.obj Y) ⟶ (L₂.obj (Φ.functor.obj X) ⟶ L₂.obj (Φ.functor.obj Y))`
for all objects `X` and `Y`. -/
noncomputable def homMap (f : L₁.obj X ⟶ L₁.obj Y) :
L₂.obj (Φ.functor.obj X) ⟶ L₂.obj (Φ.functor.obj Y) :=
Iso.homCongr ((CatCommSq.iso _ _ _ _).symm.app _) ((CatCommSq.iso _ _ _ _).symm.app _)
((Φ.localizedFunctor L₁ L₂).map f)
@[simp]
lemma homMap_map (f : X ⟶ Y) :
Φ.homMap L₁ L₂ (L₁.map f) = L₂.map (Φ.functor.map f) := by
dsimp [homMap]
erw [← NatTrans.naturality_assoc]
simp
variable (X) in
@[simp]
lemma homMap_id :
Φ.homMap L₁ L₂ (𝟙 (L₁.obj X)) = 𝟙 (L₂.obj (Φ.functor.obj X)) := by
simpa using Φ.homMap_map L₁ L₂ (𝟙 X)
@[reassoc]
lemma homMap_comp (f : L₁.obj X ⟶ L₁.obj Y) (g : L₁.obj Y ⟶ L₁.obj Z) :
Φ.homMap L₁ L₂ (f ≫ g) = Φ.homMap L₁ L₂ f ≫ Φ.homMap L₁ L₂ g := by
simp [homMap]
@[reassoc]
lemma homMap_apply (G : D₁ ⥤ D₂) (e : Φ.functor ⋙ L₂ ≅ L₁ ⋙ G) (f : L₁.obj X ⟶ L₁.obj Y) :
Φ.homMap L₁ L₂ f = e.hom.app X ≫ G.map f ≫ e.inv.app Y := by
let G' := Φ.localizedFunctor L₁ L₂
let e' := CatCommSq.iso Φ.functor L₁ L₂ G'
change e'.hom.app X ≫ G'.map f ≫ e'.inv.app Y = _
letI : Localization.Lifting L₁ W₁ (Φ.functor ⋙ L₂) G := ⟨e.symm⟩
let α : G' ≅ G := Localization.liftNatIso L₁ W₁ (L₁ ⋙ G') (Φ.functor ⋙ L₂) _ _ e'.symm
have : e = e' ≪≫ isoWhiskerLeft _ α := by
ext X
dsimp [α]
rw [Localization.liftNatTrans_app]
erw [id_comp]
rw [Iso.hom_inv_id_app_assoc]
rfl
simp [this]
@[simp]
lemma id_homMap (f : L₁.obj X ⟶ L₁.obj Y) :
(id W₁).homMap L₁ L₁ f = f := by
simpa using (id W₁).homMap_apply L₁ L₁ (𝟭 D₁) (Iso.refl _) f
@[simp]
lemma homMap_homMap (f : L₁.obj X ⟶ L₁.obj Y) :
Ψ.homMap L₂ L₃ (Φ.homMap L₁ L₂ f) = (Φ.comp Ψ).homMap L₁ L₃ f := by
let G := Φ.localizedFunctor L₁ L₂
let G' := Ψ.localizedFunctor L₂ L₃
let e : Φ.functor ⋙ L₂ ≅ L₁ ⋙ G := CatCommSq.iso _ _ _ _
let e' : Ψ.functor ⋙ L₃ ≅ L₂ ⋙ G' := CatCommSq.iso _ _ _ _
rw [Φ.homMap_apply L₁ L₂ G e, Ψ.homMap_apply L₂ L₃ G' e',
(Φ.comp Ψ).homMap_apply L₁ L₃ (G ⋙ G')
(Functor.associator _ _ _ ≪≫ isoWhiskerLeft _ e' ≪≫
(Functor.associator _ _ _).symm ≪≫ isoWhiskerRight e _ ≪≫
Functor.associator _ _ _)]
dsimp
simp only [Functor.map_comp, assoc, comp_id, id_comp]
end LocalizerMorphism
namespace Localization
variable (W : MorphismProperty C) (L₁ : C ⥤ D₁) [L₁.IsLocalization W]
(L₂ : C ⥤ D₂) [L₂.IsLocalization W] (L₃ : C ⥤ D₃) [L₃.IsLocalization W]
{X Y Z : C}
/-- Bijection between types of morphisms in two localized categories
for the same class of morphisms `W`. -/
@[simps -isSimp apply]
noncomputable def homEquiv :
(L₁.obj X ⟶ L₁.obj Y) ≃ (L₂.obj X ⟶ L₂.obj Y) where
toFun := (LocalizerMorphism.id W).homMap L₁ L₂
invFun := (LocalizerMorphism.id W).homMap L₂ L₁
left_inv f := by
rw [LocalizerMorphism.homMap_homMap]
apply LocalizerMorphism.id_homMap
right_inv g := by
rw [LocalizerMorphism.homMap_homMap]
apply LocalizerMorphism.id_homMap
@[simp]
lemma homEquiv_symm_apply (g : L₂.obj X ⟶ L₂.obj Y) :
(homEquiv W L₁ L₂).symm g = homEquiv W L₂ L₁ g := rfl
lemma homEquiv_eq (G : D₁ ⥤ D₂) (e : L₁ ⋙ G ≅ L₂) (f : L₁.obj X ⟶ L₁.obj Y) :
homEquiv W L₁ L₂ f = e.inv.app X ≫ G.map f ≫ e.hom.app Y := by
rw [homEquiv_apply, LocalizerMorphism.homMap_apply (LocalizerMorphism.id W) L₁ L₂ G e.symm,
Iso.symm_hom, Iso.symm_inv]
@[simp]
lemma homEquiv_refl (f : L₁.obj X ⟶ L₁.obj Y) :
homEquiv W L₁ L₁ f = f := by
apply LocalizerMorphism.id_homMap
lemma homEquiv_trans (f : L₁.obj X ⟶ L₁.obj Y) :
homEquiv W L₂ L₃ (homEquiv W L₁ L₂ f) = homEquiv W L₁ L₃ f := by
dsimp only [homEquiv_apply]
apply LocalizerMorphism.homMap_homMap
| lemma homEquiv_comp (f : L₁.obj X ⟶ L₁.obj Y) (g : L₁.obj Y ⟶ L₁.obj Z) :
homEquiv W L₁ L₂ (f ≫ g) = homEquiv W L₁ L₂ f ≫ homEquiv W L₁ L₂ g := by
apply LocalizerMorphism.homMap_comp
| Mathlib/CategoryTheory/Localization/HomEquiv.lean | 147 | 149 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Mario Carneiro, Jeremy Avigad
-/
import Mathlib.Data.Set.Finite.Basic
import Mathlib.Data.Set.Finite.Range
import Mathlib.Data.Set.Lattice
import Mathlib.Topology.Defs.Filter
/-!
# Openness and closedness of a set
This file provides lemmas relating to the predicates `IsOpen` and `IsClosed` of a set endowed with
a topology.
## Implementation notes
Topology in mathlib heavily uses filters (even more than in Bourbaki). See explanations in
<https://leanprover-community.github.io/theories/topology.html>.
## References
* [N. Bourbaki, *General Topology*][bourbaki1966]
* [I. M. James, *Topologies and Uniformities*][james1999]
## Tags
topological space
-/
open Set Filter Topology
universe u v
/-- A constructor for topologies by specifying the closed sets,
and showing that they satisfy the appropriate conditions. -/
def TopologicalSpace.ofClosed {X : Type u} (T : Set (Set X)) (empty_mem : ∅ ∈ T)
(sInter_mem : ∀ A, A ⊆ T → ⋂₀ A ∈ T)
(union_mem : ∀ A, A ∈ T → ∀ B, B ∈ T → A ∪ B ∈ T) : TopologicalSpace X where
IsOpen X := Xᶜ ∈ T
isOpen_univ := by simp [empty_mem]
isOpen_inter s t hs ht := by simpa only [compl_inter] using union_mem sᶜ hs tᶜ ht
isOpen_sUnion s hs := by
simp only [Set.compl_sUnion]
exact sInter_mem (compl '' s) fun z ⟨y, hy, hz⟩ => hz ▸ hs y hy
section TopologicalSpace
variable {X : Type u} {ι : Sort v} {α : Type*} {x : X} {s s₁ s₂ t : Set X} {p p₁ p₂ : X → Prop}
lemma isOpen_mk {p h₁ h₂ h₃} : IsOpen[⟨p, h₁, h₂, h₃⟩] s ↔ p s := Iff.rfl
@[ext (iff := false)]
protected theorem TopologicalSpace.ext :
∀ {f g : TopologicalSpace X}, IsOpen[f] = IsOpen[g] → f = g
| ⟨_, _, _, _⟩, ⟨_, _, _, _⟩, rfl => rfl
protected theorem TopologicalSpace.ext_iff {t t' : TopologicalSpace X} :
t = t' ↔ ∀ s, IsOpen[t] s ↔ IsOpen[t'] s :=
⟨fun h _ => h ▸ Iff.rfl, fun h => by ext; exact h _⟩
theorem isOpen_fold {t : TopologicalSpace X} : t.IsOpen s = IsOpen[t] s :=
rfl
variable [TopologicalSpace X]
theorem isOpen_iUnion {f : ι → Set X} (h : ∀ i, IsOpen (f i)) : IsOpen (⋃ i, f i) :=
isOpen_sUnion (forall_mem_range.2 h)
theorem isOpen_biUnion {s : Set α} {f : α → Set X} (h : ∀ i ∈ s, IsOpen (f i)) :
IsOpen (⋃ i ∈ s, f i) :=
isOpen_iUnion fun i => isOpen_iUnion fun hi => h i hi
theorem IsOpen.union (h₁ : IsOpen s₁) (h₂ : IsOpen s₂) : IsOpen (s₁ ∪ s₂) := by
rw [union_eq_iUnion]; exact isOpen_iUnion (Bool.forall_bool.2 ⟨h₂, h₁⟩)
lemma isOpen_iff_of_cover {f : α → Set X} (ho : ∀ i, IsOpen (f i)) (hU : (⋃ i, f i) = univ) :
IsOpen s ↔ ∀ i, IsOpen (f i ∩ s) := by
refine ⟨fun h i ↦ (ho i).inter h, fun h ↦ ?_⟩
rw [← s.inter_univ, inter_comm, ← hU, iUnion_inter]
exact isOpen_iUnion fun i ↦ h i
@[simp] theorem isOpen_empty : IsOpen (∅ : Set X) := by
rw [← sUnion_empty]; exact isOpen_sUnion fun a => False.elim
theorem Set.Finite.isOpen_sInter {s : Set (Set X)} (hs : s.Finite) (h : ∀ t ∈ s, IsOpen t) :
IsOpen (⋂₀ s) := by
induction s, hs using Set.Finite.induction_on with
| empty => rw [sInter_empty]; exact isOpen_univ
| insert _ _ ih =>
simp only [sInter_insert, forall_mem_insert] at h ⊢
exact h.1.inter (ih h.2)
theorem Set.Finite.isOpen_biInter {s : Set α} {f : α → Set X} (hs : s.Finite)
(h : ∀ i ∈ s, IsOpen (f i)) :
IsOpen (⋂ i ∈ s, f i) :=
sInter_image f s ▸ (hs.image _).isOpen_sInter (forall_mem_image.2 h)
theorem isOpen_iInter_of_finite [Finite ι] {s : ι → Set X} (h : ∀ i, IsOpen (s i)) :
IsOpen (⋂ i, s i) :=
(finite_range _).isOpen_sInter (forall_mem_range.2 h)
theorem isOpen_biInter_finset {s : Finset α} {f : α → Set X} (h : ∀ i ∈ s, IsOpen (f i)) :
IsOpen (⋂ i ∈ s, f i) :=
s.finite_toSet.isOpen_biInter h
@[simp]
theorem isOpen_const {p : Prop} : IsOpen { _x : X | p } := by by_cases p <;> simp [*]
theorem IsOpen.and : IsOpen { x | p₁ x } → IsOpen { x | p₂ x } → IsOpen { x | p₁ x ∧ p₂ x } :=
IsOpen.inter
@[simp] theorem isOpen_compl_iff : IsOpen sᶜ ↔ IsClosed s :=
⟨fun h => ⟨h⟩, fun h => h.isOpen_compl⟩
theorem TopologicalSpace.ext_iff_isClosed {X} {t₁ t₂ : TopologicalSpace X} :
t₁ = t₂ ↔ ∀ s, IsClosed[t₁] s ↔ IsClosed[t₂] s := by
rw [TopologicalSpace.ext_iff, compl_surjective.forall]
simp only [@isOpen_compl_iff _ _ t₁, @isOpen_compl_iff _ _ t₂]
alias ⟨_, TopologicalSpace.ext_isClosed⟩ := TopologicalSpace.ext_iff_isClosed
theorem isClosed_const {p : Prop} : IsClosed { _x : X | p } := ⟨isOpen_const (p := ¬p)⟩
@[simp] theorem isClosed_empty : IsClosed (∅ : Set X) := isClosed_const
@[simp] theorem isClosed_univ : IsClosed (univ : Set X) := isClosed_const
lemma IsOpen.isLocallyClosed (hs : IsOpen s) : IsLocallyClosed s :=
⟨_, _, hs, isClosed_univ, (inter_univ _).symm⟩
lemma IsClosed.isLocallyClosed (hs : IsClosed s) : IsLocallyClosed s :=
⟨_, _, isOpen_univ, hs, (univ_inter _).symm⟩
theorem IsClosed.union : IsClosed s₁ → IsClosed s₂ → IsClosed (s₁ ∪ s₂) := by
simpa only [← isOpen_compl_iff, compl_union] using IsOpen.inter
theorem isClosed_sInter {s : Set (Set X)} : (∀ t ∈ s, IsClosed t) → IsClosed (⋂₀ s) := by
simpa only [← isOpen_compl_iff, compl_sInter, sUnion_image] using isOpen_biUnion
theorem isClosed_iInter {f : ι → Set X} (h : ∀ i, IsClosed (f i)) : IsClosed (⋂ i, f i) :=
isClosed_sInter <| forall_mem_range.2 h
theorem isClosed_biInter {s : Set α} {f : α → Set X} (h : ∀ i ∈ s, IsClosed (f i)) :
IsClosed (⋂ i ∈ s, f i) :=
isClosed_iInter fun i => isClosed_iInter <| h i
@[simp]
theorem isClosed_compl_iff {s : Set X} : IsClosed sᶜ ↔ IsOpen s := by
rw [← isOpen_compl_iff, compl_compl]
alias ⟨_, IsOpen.isClosed_compl⟩ := isClosed_compl_iff
theorem IsOpen.sdiff (h₁ : IsOpen s) (h₂ : IsClosed t) : IsOpen (s \ t) :=
IsOpen.inter h₁ h₂.isOpen_compl
theorem IsClosed.inter (h₁ : IsClosed s₁) (h₂ : IsClosed s₂) : IsClosed (s₁ ∩ s₂) := by
rw [← isOpen_compl_iff] at *
rw [compl_inter]
exact IsOpen.union h₁ h₂
theorem IsClosed.sdiff (h₁ : IsClosed s) (h₂ : IsOpen t) : IsClosed (s \ t) :=
IsClosed.inter h₁ (isClosed_compl_iff.mpr h₂)
theorem Set.Finite.isClosed_biUnion {s : Set α} {f : α → Set X} (hs : s.Finite)
(h : ∀ i ∈ s, IsClosed (f i)) :
IsClosed (⋃ i ∈ s, f i) := by
simp only [← isOpen_compl_iff, compl_iUnion] at *
exact hs.isOpen_biInter h
lemma isClosed_biUnion_finset {s : Finset α} {f : α → Set X} (h : ∀ i ∈ s, IsClosed (f i)) :
IsClosed (⋃ i ∈ s, f i) :=
s.finite_toSet.isClosed_biUnion h
theorem isClosed_iUnion_of_finite [Finite ι] {s : ι → Set X} (h : ∀ i, IsClosed (s i)) :
IsClosed (⋃ i, s i) := by
simp only [← isOpen_compl_iff, compl_iUnion] at *
exact isOpen_iInter_of_finite h
theorem isClosed_imp {p q : X → Prop} (hp : IsOpen { x | p x }) (hq : IsClosed { x | q x }) :
IsClosed { x | p x → q x } := by
simpa only [imp_iff_not_or] using hp.isClosed_compl.union hq
theorem IsClosed.not : IsClosed { a | p a } → IsOpen { a | ¬p a } :=
isOpen_compl_iff.mpr
/-!
### Limits of filters in topological spaces
In this section we define functions that return a limit of a filter (or of a function along a
filter), if it exists, and a random point otherwise. These functions are rarely used in Mathlib,
most of the theorems are written using `Filter.Tendsto`. One of the reasons is that
`Filter.limUnder f g = x` is not equivalent to `Filter.Tendsto g f (𝓝 x)` unless the codomain is a
Hausdorff space and `g` has a limit along `f`.
-/
section lim
/-- If a filter `f` is majorated by some `𝓝 x`, then it is majorated by `𝓝 (Filter.lim f)`. We
formulate this lemma with a `[Nonempty X]` argument of `lim` derived from `h` to make it useful for
types without a `[Nonempty X]` instance. Because of the built-in proof irrelevance, Lean will unify
this instance with any other instance. -/
theorem le_nhds_lim {f : Filter X} (h : ∃ x, f ≤ 𝓝 x) : f ≤ 𝓝 (@lim _ _ (nonempty_of_exists h) f) :=
Classical.epsilon_spec h
/-- If `g` tends to some `𝓝 x` along `f`, then it tends to `𝓝 (Filter.limUnder f g)`. We formulate
this lemma with a `[Nonempty X]` argument of `lim` derived from `h` to make it useful for types
without a `[Nonempty X]` instance. Because of the built-in proof irrelevance, Lean will unify this
instance with any other instance. -/
theorem tendsto_nhds_limUnder {f : Filter α} {g : α → X} (h : ∃ x, Tendsto g f (𝓝 x)) :
Tendsto g f (𝓝 (@limUnder _ _ _ (nonempty_of_exists h) f g)) :=
le_nhds_lim h
theorem limUnder_of_not_tendsto [hX : Nonempty X] {f : Filter α} {g : α → X}
(h : ¬ ∃ x, Tendsto g f (𝓝 x)) :
limUnder f g = Classical.choice hX := by
simp_rw [Tendsto] at h
simp_rw [limUnder, lim, Classical.epsilon, Classical.strongIndefiniteDescription, dif_neg h]
end lim
end TopologicalSpace
| Mathlib/Topology/Basic.lean | 515 | 517 |
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