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/-
Copyright (c) 2020 Devon Tuma. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Devon Tuma
-/
import Mathlib.Probability.ProbabilityMassFunction.Basic
/-!
# Monad Operations for Probability Mass Functions
This file constructs two operations on `PMF` that give it a monad structure.
`pure a` is the distribution where a single value `a` has probability `1`.
`bind pa pb : PMF β` is the distribution given by sampling `a : α` from `pa : PMF α`,
and then sampling from `pb a : PMF β` to get a final result `b : β`.
`bindOnSupport` generalizes `bind` to allow binding to a partial function,
so that the second argument only needs to be defined on the support of the first argument.
-/
noncomputable section
variable {α β γ : Type*}
open NNReal ENNReal
open MeasureTheory
namespace PMF
section Pure
open scoped Classical in
/-- The pure `PMF` is the `PMF` where all the mass lies in one point.
The value of `pure a` is `1` at `a` and `0` elsewhere. -/
def pure (a : α) : PMF α :=
⟨fun a' => if a' = a then 1 else 0, hasSum_ite_eq _ _⟩
variable (a a' : α)
open scoped Classical in
@[simp]
theorem pure_apply : pure a a' = if a' = a then 1 else 0 := rfl
@[simp]
theorem support_pure : (pure a).support = {a} :=
Set.ext fun a' => by simp [mem_support_iff]
theorem mem_support_pure_iff : a' ∈ (pure a).support ↔ a' = a := by simp
theorem pure_apply_self : pure a a = 1 :=
if_pos rfl
theorem pure_apply_of_ne (h : a' ≠ a) : pure a a' = 0 :=
if_neg h
instance [Inhabited α] : Inhabited (PMF α) :=
⟨pure default⟩
section Measure
variable (s : Set α)
open scoped Classical in
@[simp]
theorem toOuterMeasure_pure_apply : (pure a).toOuterMeasure s = if a ∈ s then 1 else 0 := by
refine (toOuterMeasure_apply (pure a) s).trans ?_
split_ifs with ha
· refine (tsum_congr fun b => ?_).trans (tsum_ite_eq a 1)
exact ite_eq_left_iff.2 fun hb =>
symm (ite_eq_right_iff.2 fun h => (hb <| h.symm ▸ ha).elim)
· refine (tsum_congr fun b => ?_).trans tsum_zero
exact ite_eq_right_iff.2 fun hb =>
ite_eq_right_iff.2 fun h => (ha <| h ▸ hb).elim
variable [MeasurableSpace α]
open scoped Classical in
/-- The measure of a set under `pure a` is `1` for sets containing `a` and `0` otherwise. -/
@[simp]
theorem toMeasure_pure_apply (hs : MeasurableSet s) :
(pure a).toMeasure s = if a ∈ s then 1 else 0 :=
(toMeasure_apply_eq_toOuterMeasure_apply (pure a) s hs).trans (toOuterMeasure_pure_apply a s)
theorem toMeasure_pure : (pure a).toMeasure = Measure.dirac a :=
Measure.ext fun s hs => by rw [toMeasure_pure_apply a s hs, Measure.dirac_apply' a hs]; rfl
@[simp]
theorem toPMF_dirac [Countable α] [h : MeasurableSingletonClass α] :
(Measure.dirac a).toPMF = pure a := by
rw [toPMF_eq_iff_toMeasure_eq, toMeasure_pure]
end Measure
end Pure
section Bind
/-- The monadic bind operation for `PMF`. -/
def bind (p : PMF α) (f : α → PMF β) : PMF β :=
⟨fun b => ∑' a, p a * f a b,
ENNReal.summable.hasSum_iff.2
(ENNReal.tsum_comm.trans <| by simp only [ENNReal.tsum_mul_left, tsum_coe, mul_one])⟩
variable (p : PMF α) (f : α → PMF β) (g : β → PMF γ)
@[simp]
theorem bind_apply (b : β) : p.bind f b = ∑' a, p a * f a b := rfl
@[simp]
theorem support_bind : (p.bind f).support = ⋃ a ∈ p.support, (f a).support :=
Set.ext fun b => by simp [mem_support_iff, ENNReal.tsum_eq_zero, not_or]
theorem mem_support_bind_iff (b : β) :
b ∈ (p.bind f).support ↔ ∃ a ∈ p.support, b ∈ (f a).support := by
simp only [support_bind, Set.mem_iUnion, Set.mem_setOf_eq, exists_prop]
@[simp]
theorem pure_bind (a : α) (f : α → PMF β) : (pure a).bind f = f a := by
classical
have : ∀ b a', ite (a' = a) (f a' b) 0 = ite (a' = a) (f a b) 0 := fun b a' => by
split_ifs with h <;> simp [h]
ext b
simp [this]
@[simp]
theorem bind_pure : p.bind pure = p :=
PMF.ext fun x => (bind_apply _ _ _).trans (_root_.trans
(tsum_eq_single x fun y hy => by rw [pure_apply_of_ne _ _ hy.symm, mul_zero]) <|
by rw [pure_apply_self, mul_one])
@[simp]
theorem bind_const (p : PMF α) (q : PMF β) : (p.bind fun _ => q) = q :=
PMF.ext fun x => by rw [bind_apply, ENNReal.tsum_mul_right, tsum_coe, one_mul]
@[simp]
theorem bind_bind : (p.bind f).bind g = p.bind fun a => (f a).bind g :=
PMF.ext fun b => by
simpa only [ENNReal.coe_inj.symm, bind_apply, ENNReal.tsum_mul_left.symm,
ENNReal.tsum_mul_right.symm, mul_assoc, mul_left_comm, mul_comm] using ENNReal.tsum_comm
theorem bind_comm (p : PMF α) (q : PMF β) (f : α → β → PMF γ) :
(p.bind fun a => q.bind (f a)) = q.bind fun b => p.bind fun a => f a b :=
PMF.ext fun b => by
simpa only [ENNReal.coe_inj.symm, bind_apply, ENNReal.tsum_mul_left.symm,
| ENNReal.tsum_mul_right.symm, mul_assoc, mul_left_comm, mul_comm] using ENNReal.tsum_comm
| Mathlib/Probability/ProbabilityMassFunction/Monad.lean | 147 | 148 |
/-
Copyright (c) 2021 Julian Kuelshammer. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Julian Kuelshammer
-/
import Mathlib.GroupTheory.OrderOfElement
import Mathlib.Algebra.GCDMonoid.Finset
import Mathlib.Algebra.GCDMonoid.Nat
import Mathlib.Data.Nat.Factorization.Basic
import Mathlib.Tactic.Peel
import Mathlib.Algebra.Order.BigOperators.Ring.Finset
/-!
# Exponent of a group
This file defines the exponent of a group, or more generally a monoid. For a group `G` it is defined
to be the minimal `n≥1` such that `g ^ n = 1` for all `g ∈ G`. For a finite group `G`,
it is equal to the lowest common multiple of the order of all elements of the group `G`.
## Main definitions
* `Monoid.ExponentExists` is a predicate on a monoid `G` saying that there is some positive `n`
such that `g ^ n = 1` for all `g ∈ G`.
* `Monoid.exponent` defines the exponent of a monoid `G` as the minimal positive `n` such that
`g ^ n = 1` for all `g ∈ G`, by convention it is `0` if no such `n` exists.
* `AddMonoid.ExponentExists` the additive version of `Monoid.ExponentExists`.
* `AddMonoid.exponent` the additive version of `Monoid.exponent`.
## Main results
* `Monoid.lcm_order_eq_exponent`: For a finite left cancel monoid `G`, the exponent is equal to the
`Finset.lcm` of the order of its elements.
* `Monoid.exponent_eq_iSup_orderOf(')`: For a commutative cancel monoid, the exponent is
equal to `⨆ g : G, orderOf g` (or zero if it has any order-zero elements).
* `Monoid.exponent_pi` and `Monoid.exponent_prod`: The exponent of a finite product of monoids is
the least common multiple (`Finset.lcm` and `lcm`, respectively) of the exponents of the
constituent monoids.
* `MonoidHom.exponent_dvd`: If `f : M₁ →⋆ M₂` is surjective, then the exponent of `M₂` divides the
exponent of `M₁`.
## TODO
* Refactor the characteristic of a ring to be the exponent of its underlying additive group.
-/
universe u
variable {G : Type u}
namespace Monoid
section Monoid
variable (G) [Monoid G]
/-- A predicate on a monoid saying that there is a positive integer `n` such that `g ^ n = 1`
for all `g`. -/
@[to_additive
"A predicate on an additive monoid saying that there is a positive integer `n` such\n
that `n • g = 0` for all `g`."]
def ExponentExists :=
∃ n, 0 < n ∧ ∀ g : G, g ^ n = 1
open scoped Classical in
/-- The exponent of a group is the smallest positive integer `n` such that `g ^ n = 1` for all
`g ∈ G` if it exists, otherwise it is zero by convention. -/
@[to_additive
"The exponent of an additive group is the smallest positive integer `n` such that\n
`n • g = 0` for all `g ∈ G` if it exists, otherwise it is zero by convention."]
noncomputable def exponent :=
if h : ExponentExists G then Nat.find h else 0
variable {G}
@[simp]
theorem _root_.AddMonoid.exponent_additive :
AddMonoid.exponent (Additive G) = exponent G := rfl
@[simp]
theorem exponent_multiplicative {G : Type*} [AddMonoid G] :
exponent (Multiplicative G) = AddMonoid.exponent G := rfl
open MulOpposite in
@[to_additive (attr := simp)]
theorem _root_.MulOpposite.exponent : exponent (MulOpposite G) = exponent G := by
simp only [Monoid.exponent, ExponentExists]
congr!
all_goals exact ⟨(op_injective <| · <| op ·), (unop_injective <| · <| unop ·)⟩
@[to_additive]
theorem ExponentExists.isOfFinOrder (h : ExponentExists G) {g : G} : IsOfFinOrder g :=
isOfFinOrder_iff_pow_eq_one.mpr <| by peel 2 h; exact this g
@[to_additive]
theorem ExponentExists.orderOf_pos (h : ExponentExists G) (g : G) : 0 < orderOf g :=
h.isOfFinOrder.orderOf_pos
@[to_additive]
theorem exponent_ne_zero : exponent G ≠ 0 ↔ ExponentExists G := by
rw [exponent]
split_ifs with h
· simp [h, @not_lt_zero' ℕ]
--if this isn't done this way, `to_additive` freaks
· tauto
@[to_additive]
protected alias ⟨_, ExponentExists.exponent_ne_zero⟩ := exponent_ne_zero
@[to_additive]
theorem exponent_pos : 0 < exponent G ↔ ExponentExists G :=
pos_iff_ne_zero.trans exponent_ne_zero
@[to_additive]
protected alias ⟨_, ExponentExists.exponent_pos⟩ := exponent_pos
@[to_additive]
theorem exponent_eq_zero_iff : exponent G = 0 ↔ ¬ExponentExists G :=
exponent_ne_zero.not_right
@[to_additive exponent_eq_zero_addOrder_zero]
theorem exponent_eq_zero_of_order_zero {g : G} (hg : orderOf g = 0) : exponent G = 0 :=
exponent_eq_zero_iff.mpr fun h ↦ h.orderOf_pos g |>.ne' hg
/-- The exponent is zero iff for all nonzero `n`, one can find a `g` such that `g ^ n ≠ 1`. -/
@[to_additive "The exponent is zero iff for all nonzero `n`, one can find a `g` such that
`n • g ≠ 0`."]
theorem exponent_eq_zero_iff_forall : exponent G = 0 ↔ ∀ n > 0, ∃ g : G, g ^ n ≠ 1 := by
rw [exponent_eq_zero_iff, ExponentExists]
push_neg
rfl
@[to_additive exponent_nsmul_eq_zero]
theorem pow_exponent_eq_one (g : G) : g ^ exponent G = 1 := by
classical
by_cases h : ExponentExists G
· simp_rw [exponent, dif_pos h]
exact (Nat.find_spec h).2 g
· simp_rw [exponent, dif_neg h, pow_zero]
@[to_additive]
theorem pow_eq_mod_exponent {n : ℕ} (g : G) : g ^ n = g ^ (n % exponent G) :=
calc
g ^ n = g ^ (n % exponent G + exponent G * (n / exponent G)) := by rw [Nat.mod_add_div]
_ = g ^ (n % exponent G) := by simp [pow_add, pow_mul, pow_exponent_eq_one]
@[to_additive]
theorem exponent_pos_of_exists (n : ℕ) (hpos : 0 < n) (hG : ∀ g : G, g ^ n = 1) :
0 < exponent G :=
ExponentExists.exponent_pos ⟨n, hpos, hG⟩
@[to_additive]
theorem exponent_min' (n : ℕ) (hpos : 0 < n) (hG : ∀ g : G, g ^ n = 1) : exponent G ≤ n := by
classical
rw [exponent, dif_pos]
· apply Nat.find_min'
exact ⟨hpos, hG⟩
· exact ⟨n, hpos, hG⟩
@[to_additive]
theorem exponent_min (m : ℕ) (hpos : 0 < m) (hm : m < exponent G) : ∃ g : G, g ^ m ≠ 1 := by
by_contra! h
have hcon : exponent G ≤ m := exponent_min' m hpos h
omega
@[to_additive AddMonoid.exp_eq_one_iff]
theorem exp_eq_one_iff : exponent G = 1 ↔ Subsingleton G := by
refine ⟨fun eq_one => ⟨fun a b => ?a_eq_b⟩, fun h => le_antisymm ?le ?ge⟩
· rw [← pow_one a, ← pow_one b, ← eq_one, Monoid.pow_exponent_eq_one, Monoid.pow_exponent_eq_one]
· apply exponent_min' _ Nat.one_pos
simp [eq_iff_true_of_subsingleton]
· apply Nat.succ_le_of_lt
apply exponent_pos_of_exists 1 Nat.one_pos
simp [eq_iff_true_of_subsingleton]
@[to_additive (attr := simp) AddMonoid.exp_eq_one_of_subsingleton]
theorem exp_eq_one_of_subsingleton [hs : Subsingleton G] : exponent G = 1 :=
exp_eq_one_iff.mpr hs
@[to_additive addOrder_dvd_exponent]
theorem order_dvd_exponent (g : G) : orderOf g ∣ exponent G :=
orderOf_dvd_of_pow_eq_one <| pow_exponent_eq_one g
@[to_additive]
theorem orderOf_le_exponent (h : ExponentExists G) (g : G) : orderOf g ≤ exponent G :=
Nat.le_of_dvd h.exponent_pos (order_dvd_exponent g)
@[to_additive]
theorem exponent_dvd_iff_forall_pow_eq_one {n : ℕ} : exponent G ∣ n ↔ ∀ g : G, g ^ n = 1 := by
rcases n.eq_zero_or_pos with (rfl | hpos)
· simp
constructor
· intro h g
rw [Nat.dvd_iff_mod_eq_zero] at h
rw [pow_eq_mod_exponent, h, pow_zero]
· intro hG
by_contra h
rw [Nat.dvd_iff_mod_eq_zero, ← Ne, ← pos_iff_ne_zero] at h
have h₂ : n % exponent G < exponent G := Nat.mod_lt _ (exponent_pos_of_exists n hpos hG)
have h₃ : exponent G ≤ n % exponent G := by
apply exponent_min' _ h
simp_rw [← pow_eq_mod_exponent]
exact hG
exact h₂.not_le h₃
@[to_additive]
alias ⟨_, exponent_dvd_of_forall_pow_eq_one⟩ := exponent_dvd_iff_forall_pow_eq_one
@[to_additive]
theorem exponent_dvd {n : ℕ} : exponent G ∣ n ↔ ∀ g : G, orderOf g ∣ n := by
simp_rw [exponent_dvd_iff_forall_pow_eq_one, orderOf_dvd_iff_pow_eq_one]
variable (G)
@[to_additive]
theorem lcm_orderOf_dvd_exponent [Fintype G] :
(Finset.univ : Finset G).lcm orderOf ∣ exponent G := by
apply Finset.lcm_dvd
intro g _
exact order_dvd_exponent g
@[to_additive exists_addOrderOf_eq_pow_padic_val_nat_add_exponent]
theorem _root_.Nat.Prime.exists_orderOf_eq_pow_factorization_exponent {p : ℕ} (hp : p.Prime) :
∃ g : G, orderOf g = p ^ (exponent G).factorization p := by
haveI := Fact.mk hp
rcases eq_or_ne ((exponent G).factorization p) 0 with (h | h)
· refine ⟨1, by rw [h, pow_zero, orderOf_one]⟩
have he : 0 < exponent G :=
Ne.bot_lt fun ht => by
rw [ht] at h
apply h
rw [bot_eq_zero, Nat.factorization_zero, Finsupp.zero_apply]
rw [← Finsupp.mem_support_iff] at h
obtain ⟨g, hg⟩ : ∃ g : G, g ^ (exponent G / p) ≠ 1 := by
suffices key : ¬exponent G ∣ exponent G / p by
rwa [exponent_dvd_iff_forall_pow_eq_one, not_forall] at key
exact fun hd =>
hp.one_lt.not_le
((mul_le_iff_le_one_left he).mp <|
Nat.le_of_dvd he <| Nat.mul_dvd_of_dvd_div (Nat.dvd_of_mem_primeFactors h) hd)
obtain ⟨k, hk : exponent G = p ^ _ * k⟩ := Nat.ordProj_dvd _ _
obtain ⟨t, ht⟩ := Nat.exists_eq_succ_of_ne_zero (Finsupp.mem_support_iff.mp h)
refine ⟨g ^ k, ?_⟩
rw [ht]
apply orderOf_eq_prime_pow
· rwa [hk, mul_comm, ht, pow_succ, ← mul_assoc, Nat.mul_div_cancel _ hp.pos, pow_mul] at hg
· rw [← Nat.succ_eq_add_one, ← ht, ← pow_mul, mul_comm, ← hk]
exact pow_exponent_eq_one g
variable {G} in
open Nat in
/-- If two commuting elements `x` and `y` of a monoid have order `n` and `m`, there is an element
of order `lcm n m`. The result actually gives an explicit (computable) element, written as the
product of a power of `x` and a power of `y`. See also the result below if you don't need the
explicit formula. -/
@[to_additive "If two commuting elements `x` and `y` of an additive monoid have order `n` and `m`,
there is an element of order `lcm n m`. The result actually gives an explicit (computable) element,
written as the sum of a multiple of `x` and a multiple of `y`. See also the result below if you
don't need the explicit formula."]
lemma _root_.Commute.orderOf_mul_pow_eq_lcm {x y : G} (h : Commute x y) (hx : orderOf x ≠ 0)
(hy : orderOf y ≠ 0) :
orderOf (x ^ (orderOf x / (factorizationLCMLeft (orderOf x) (orderOf y))) *
y ^ (orderOf y / factorizationLCMRight (orderOf x) (orderOf y))) =
Nat.lcm (orderOf x) (orderOf y) := by
rw [(h.pow_pow _ _).orderOf_mul_eq_mul_orderOf_of_coprime]
all_goals iterate 2 rw [orderOf_pow_orderOf_div]; try rw [Coprime]
all_goals simp [factorizationLCMLeft_mul_factorizationLCMRight, factorizationLCMLeft_dvd_left,
factorizationLCMRight_dvd_right, coprime_factorizationLCMLeft_factorizationLCMRight, hx, hy]
open Submonoid in
/-- If two commuting elements `x` and `y` of a monoid have order `n` and `m`, then there is an
element of order `lcm n m` that lies in the subgroup generated by `x` and `y`. -/
@[to_additive "If two commuting elements `x` and `y` of an additive monoid have order `n` and `m`,
then there is an element of order `lcm n m` that lies in the additive subgroup generated by `x`
and `y`."]
theorem _root_.Commute.exists_orderOf_eq_lcm {x y : G} (h : Commute x y) :
∃ z ∈ closure {x, y}, orderOf z = Nat.lcm (orderOf x) (orderOf y) := by
by_cases hx : orderOf x = 0 <;> by_cases hy : orderOf y = 0
· exact ⟨x, subset_closure (by simp), by simp [hx]⟩
· exact ⟨x, subset_closure (by simp), by simp [hx]⟩
· exact ⟨y, subset_closure (by simp), by simp [hy]⟩
· exact ⟨_, mul_mem (pow_mem (subset_closure (by simp)) _) (pow_mem (subset_closure (by simp)) _),
h.orderOf_mul_pow_eq_lcm hx hy⟩
/-- A nontrivial monoid has prime exponent `p` if and only if every non-identity element has
order `p`. -/
@[to_additive]
lemma exponent_eq_prime_iff {G : Type*} [Monoid G] [Nontrivial G] {p : ℕ} (hp : p.Prime) :
Monoid.exponent G = p ↔ ∀ g : G, g ≠ 1 → orderOf g = p := by
refine ⟨fun hG g hg ↦ ?_, fun h ↦ dvd_antisymm ?_ ?_⟩
· rw [Ne, ← orderOf_eq_one_iff] at hg
exact Eq.symm <| (hp.dvd_iff_eq hg).mp <| hG ▸ Monoid.order_dvd_exponent g
· rw [exponent_dvd]
intro g
by_cases hg : g = 1
· simp [hg]
· rw [h g hg]
· obtain ⟨g, hg⟩ := exists_ne (1 : G)
simpa [h g hg] using Monoid.order_dvd_exponent g
variable {G}
@[to_additive]
theorem exponent_ne_zero_iff_range_orderOf_finite (h : ∀ g : G, 0 < orderOf g) :
exponent G ≠ 0 ↔ (Set.range (orderOf : G → ℕ)).Finite := by
refine ⟨fun he => ?_, fun he => ?_⟩
· by_contra h
obtain ⟨m, ⟨t, rfl⟩, het⟩ := Set.Infinite.exists_gt h (exponent G)
exact pow_ne_one_of_lt_orderOf he het (pow_exponent_eq_one t)
· lift Set.range (orderOf (G := G)) to Finset ℕ using he with t ht
have htpos : 0 < t.prod id := by
refine Finset.prod_pos fun a ha => ?_
rw [← Finset.mem_coe, ht] at ha
obtain ⟨k, rfl⟩ := ha
exact h k
suffices exponent G ∣ t.prod id by
intro h
rw [h, zero_dvd_iff] at this
exact htpos.ne' this
rw [exponent_dvd]
intro g
apply Finset.dvd_prod_of_mem id (?_ : orderOf g ∈ _)
rw [← Finset.mem_coe, ht]
exact Set.mem_range_self g
@[to_additive]
theorem exponent_eq_zero_iff_range_orderOf_infinite (h : ∀ g : G, 0 < orderOf g) :
exponent G = 0 ↔ (Set.range (orderOf : G → ℕ)).Infinite := by
have := exponent_ne_zero_iff_range_orderOf_finite h
rwa [Ne, not_iff_comm, Iff.comm] at this
@[to_additive]
theorem lcm_orderOf_eq_exponent [Fintype G] : (Finset.univ : Finset G).lcm orderOf = exponent G :=
Nat.dvd_antisymm
(lcm_orderOf_dvd_exponent G)
(exponent_dvd.mpr fun g => Finset.dvd_lcm (Finset.mem_univ g))
variable {H : Type*} [Monoid H]
/--
If there exists an injective, multiplication-preserving map from `G` to `H`,
then the exponent of `G` divides the exponent of `H`.
-/
@[to_additive "If there exists an injective, addition-preserving map from `G` to `H`,
then the exponent of `G` divides the exponent of `H`."]
theorem exponent_dvd_of_monoidHom (e : G →* H) (e_inj : Function.Injective e) :
Monoid.exponent G ∣ Monoid.exponent H :=
exponent_dvd_of_forall_pow_eq_one fun g => e_inj (by
rw [map_pow, pow_exponent_eq_one, map_one])
/--
If there exists a multiplication-preserving equivalence between `G` and `H`,
then the exponent of `G` is equal to the exponent of `H`.
-/
@[to_additive "If there exists a addition-preserving equivalence between `G` and `H`,
then the exponent of `G` is equal to the exponent of `H`."]
theorem exponent_eq_of_mulEquiv (e : G ≃* H) : Monoid.exponent G = Monoid.exponent H :=
Nat.dvd_antisymm
(exponent_dvd_of_monoidHom e e.injective)
(exponent_dvd_of_monoidHom e.symm e.symm.injective)
end Monoid
section Submonoid
variable [Monoid G]
variable (G) in
@[to_additive (attr := simp)]
theorem _root_.Submonoid.exponent_top :
Monoid.exponent (⊤ : Submonoid G) = Monoid.exponent G :=
exponent_eq_of_mulEquiv Submonoid.topEquiv
@[to_additive]
theorem _root_.Submonoid.pow_exponent_eq_one {S : Submonoid G} {g : G} (g_in_s : g ∈ S) :
g ^ (Monoid.exponent S) = 1 := by
have := Monoid.pow_exponent_eq_one (⟨g, g_in_s⟩ : S)
rwa [SubmonoidClass.mk_pow, ← OneMemClass.coe_eq_one] at this
end Submonoid
section LeftCancelMonoid
variable [LeftCancelMonoid G] [Finite G]
@[to_additive]
theorem ExponentExists.of_finite : ExponentExists G := by
let _inst := Fintype.ofFinite G
simp only [Monoid.ExponentExists]
refine ⟨(Finset.univ : Finset G).lcm orderOf, ?_, fun g => ?_⟩
· simpa [pos_iff_ne_zero, Finset.lcm_eq_zero_iff] using fun x => (_root_.orderOf_pos x).ne'
· rw [← orderOf_dvd_iff_pow_eq_one, lcm_orderOf_eq_exponent]
exact order_dvd_exponent g
@[to_additive]
theorem exponent_ne_zero_of_finite : exponent G ≠ 0 :=
ExponentExists.of_finite.exponent_ne_zero
@[to_additive AddMonoid.one_lt_exponent]
lemma one_lt_exponent [Nontrivial G] : 1 < Monoid.exponent G := by
rw [Nat.one_lt_iff_ne_zero_and_ne_one]
exact ⟨exponent_ne_zero_of_finite, mt exp_eq_one_iff.mp (not_subsingleton G)⟩
@[to_additive]
instance neZero_exponent_of_finite : NeZero <| Monoid.exponent G :=
⟨Monoid.exponent_ne_zero_of_finite⟩
end LeftCancelMonoid
section CommMonoid
variable [CommMonoid G]
@[to_additive]
theorem exists_orderOf_eq_exponent (hG : ExponentExists G) : ∃ g : G, orderOf g = exponent G := by
have he := hG.exponent_ne_zero
have hne : (Set.range (orderOf : G → ℕ)).Nonempty := ⟨1, 1, orderOf_one⟩
have hfin : (Set.range (orderOf : G → ℕ)).Finite := by
rwa [← exponent_ne_zero_iff_range_orderOf_finite hG.orderOf_pos]
obtain ⟨t, ht⟩ := hne.csSup_mem hfin
use t
apply Nat.dvd_antisymm (order_dvd_exponent _)
refine Nat.dvd_of_primeFactorsList_subperm he ?_
rw [List.subperm_ext_iff]
by_contra! h
obtain ⟨p, hp, hpe⟩ := h
replace hp := Nat.prime_of_mem_primeFactorsList hp
simp only [Nat.primeFactorsList_count_eq] at hpe
set k := (orderOf t).factorization p with hk
obtain ⟨g, hg⟩ := hp.exists_orderOf_eq_pow_factorization_exponent G
suffices orderOf t < orderOf (t ^ p ^ k * g) by
rw [ht] at this
exact this.not_le (le_csSup hfin.bddAbove <| Set.mem_range_self _)
have hpk : p ^ k ∣ orderOf t := Nat.ordProj_dvd _ _
have hpk' : orderOf (t ^ p ^ k) = orderOf t / p ^ k := by
rw [orderOf_pow' t (pow_ne_zero k hp.ne_zero), Nat.gcd_eq_right hpk]
obtain ⟨a, ha⟩ := Nat.exists_eq_add_of_lt hpe
have hcoprime : (orderOf (t ^ p ^ k)).Coprime (orderOf g) := by
rw [hg, Nat.coprime_pow_right_iff (pos_of_gt hpe), Nat.coprime_comm]
apply Or.resolve_right (Nat.coprime_or_dvd_of_prime hp _)
nth_rw 1 [← pow_one p]
have : 1 = (Nat.factorization (orderOf (t ^ p ^ k))) p + 1 := by
rw [hpk', Nat.factorization_div hpk]
simp [k, hp]
rw [this]
-- Porting note: convert made to_additive complain
apply Nat.pow_succ_factorization_not_dvd (hG.orderOf_pos <| t ^ p ^ k).ne' hp
rw [(Commute.all _ g).orderOf_mul_eq_mul_orderOf_of_coprime hcoprime, hpk',
hg, ha, hk, pow_add, pow_add, pow_one, ← mul_assoc, ← mul_assoc,
Nat.div_mul_cancel, mul_assoc, lt_mul_iff_one_lt_right <| hG.orderOf_pos t, ← pow_succ]
· exact one_lt_pow₀ hp.one_lt a.succ_ne_zero
· exact hpk
@[to_additive]
theorem exponent_eq_iSup_orderOf (h : ∀ g : G, 0 < orderOf g) :
exponent G = ⨆ g : G, orderOf g := by
rw [iSup]
by_cases ExponentExists G
case neg he =>
rw [← exponent_eq_zero_iff] at he
rw [he, Set.Infinite.Nat.sSup_eq_zero <| (exponent_eq_zero_iff_range_orderOf_infinite h).1 he]
case pos he =>
rw [csSup_eq_of_forall_le_of_forall_lt_exists_gt (Set.range_nonempty _)]
· simp_rw [Set.mem_range, forall_exists_index, forall_apply_eq_imp_iff]
exact orderOf_le_exponent he
intro x hx
obtain ⟨g, hg⟩ := exists_orderOf_eq_exponent he
rw [← hg] at hx
simp_rw [Set.mem_range, exists_exists_eq_and]
exact ⟨g, hx⟩
open scoped Classical in
@[to_additive]
theorem exponent_eq_iSup_orderOf' :
exponent G = if ∃ g : G, orderOf g = 0 then 0 else ⨆ g : G, orderOf g := by
split_ifs with h
· obtain ⟨g, hg⟩ := h
exact exponent_eq_zero_of_order_zero hg
· have := not_exists.mp h
exact exponent_eq_iSup_orderOf fun g => Ne.bot_lt <| this g
end CommMonoid
section CancelCommMonoid
variable [CancelCommMonoid G]
@[to_additive]
theorem exponent_eq_max'_orderOf [Fintype G] :
exponent G = ((@Finset.univ G _).image orderOf).max' ⟨1, by simp⟩ := by
rw [← Finset.Nonempty.csSup_eq_max', Finset.coe_image, Finset.coe_univ, Set.image_univ, ← iSup]
exact exponent_eq_iSup_orderOf orderOf_pos
end CancelCommMonoid
end Monoid
section Group
variable [Group G] {n m : ℤ}
@[to_additive]
theorem Group.exponent_dvd_card [Fintype G] : Monoid.exponent G ∣ Fintype.card G :=
Monoid.exponent_dvd.mpr <| fun _ => orderOf_dvd_card
@[to_additive]
theorem Group.exponent_dvd_nat_card : Monoid.exponent G ∣ Nat.card G :=
Monoid.exponent_dvd.mpr orderOf_dvd_natCard
@[to_additive]
theorem Subgroup.exponent_toSubmonoid (H : Subgroup G) :
Monoid.exponent H.toSubmonoid = Monoid.exponent H :=
Monoid.exponent_eq_of_mulEquiv (MulEquiv.subgroupCongr rfl)
@[to_additive (attr := simp)]
theorem Subgroup.exponent_top : Monoid.exponent (⊤ : Subgroup G) = Monoid.exponent G :=
Monoid.exponent_eq_of_mulEquiv topEquiv
@[to_additive]
theorem Subgroup.pow_exponent_eq_one {H : Subgroup G} {g : G} (g_in_H : g ∈ H) :
g ^ Monoid.exponent H = 1 := exponent_toSubmonoid H ▸ Submonoid.pow_exponent_eq_one g_in_H
@[to_additive]
theorem Group.exponent_dvd_iff_forall_zpow_eq_one :
(Monoid.exponent G : ℤ) ∣ n ↔ ∀ g : G, g ^ n = 1 := by
simp_rw [Int.natCast_dvd, Monoid.exponent_dvd_iff_forall_pow_eq_one, pow_natAbs_eq_one]
@[to_additive]
theorem Group.exponent_dvd_sub_iff_zpow_eq_zpow :
(Monoid.exponent G : ℤ) ∣ n - m ↔ ∀ g : G, g ^ n = g ^ m := by
simp_rw [Group.exponent_dvd_iff_forall_zpow_eq_one, zpow_sub, mul_inv_eq_one]
end Group
section PiProd
open Finset Monoid
@[to_additive]
theorem Monoid.exponent_pi_eq_zero {ι : Type*} {M : ι → Type*} [∀ i, Monoid (M i)] {j : ι}
(hj : exponent (M j) = 0) : exponent ((i : ι) → M i) = 0 := by
classical
rw [@exponent_eq_zero_iff, ExponentExists] at hj ⊢
push_neg at hj ⊢
peel hj with n hn _
obtain ⟨m, hm⟩ := this
refine ⟨Pi.mulSingle j m, fun h ↦ hm ?_⟩
simpa using congr_fun h j
/-- If `f : M₁ →⋆ M₂` is surjective, then the exponent of `M₂` divides the exponent of `M₁`. -/
@[to_additive]
theorem MonoidHom.exponent_dvd {F M₁ M₂ : Type*} [Monoid M₁] [Monoid M₂]
[FunLike F M₁ M₂] [MonoidHomClass F M₁ M₂]
{f : F} (hf : Function.Surjective f) : exponent M₂ ∣ exponent M₁ := by
refine Monoid.exponent_dvd_of_forall_pow_eq_one fun m₂ ↦ ?_
obtain ⟨m₁, rfl⟩ := hf m₂
rw [← map_pow, pow_exponent_eq_one, map_one]
/-- The exponent of finite product of monoids is the `Finset.lcm` of the exponents of the
constituent monoids. -/
@[to_additive "The exponent of finite product of additive monoids is the `Finset.lcm` of the
exponents of the constituent additive monoids."]
theorem Monoid.exponent_pi {ι : Type*} [Fintype ι] {M : ι → Type*} [∀ i, Monoid (M i)] :
exponent ((i : ι) → M i) = lcm univ (exponent <| M ·) := by
refine dvd_antisymm ?_ ?_
· refine exponent_dvd_of_forall_pow_eq_one fun m ↦ ?_
ext i
rw [Pi.pow_apply, Pi.one_apply, ← orderOf_dvd_iff_pow_eq_one]
apply dvd_trans (Monoid.order_dvd_exponent (m i))
exact Finset.dvd_lcm (mem_univ i)
· apply Finset.lcm_dvd fun i _ ↦ ?_
exact MonoidHom.exponent_dvd (f := Pi.evalMonoidHom (M ·) i) (Function.surjective_eval i)
/-- The exponent of product of two monoids is the `lcm` of the exponents of the
individuaul monoids. -/
@[to_additive AddMonoid.exponent_prod "The exponent of product of two additive monoids is the `lcm`
of the exponents of the individuaul additive monoids."]
theorem Monoid.exponent_prod {M₁ M₂ : Type*} [Monoid M₁] [Monoid M₂] :
exponent (M₁ × M₂) = lcm (exponent M₁) (exponent M₂) := by
refine dvd_antisymm ?_ (lcm_dvd ?_ ?_)
· refine exponent_dvd_of_forall_pow_eq_one fun g ↦ ?_
ext1
· rw [Prod.pow_fst, Prod.fst_one, ← orderOf_dvd_iff_pow_eq_one]
exact dvd_trans (Monoid.order_dvd_exponent (g.1)) <| dvd_lcm_left _ _
· rw [Prod.pow_snd, Prod.snd_one, ← orderOf_dvd_iff_pow_eq_one]
exact dvd_trans (Monoid.order_dvd_exponent (g.2)) <| dvd_lcm_right _ _
· exact MonoidHom.exponent_dvd (f := MonoidHom.fst M₁ M₂) Prod.fst_surjective
· exact MonoidHom.exponent_dvd (f := MonoidHom.snd M₁ M₂) Prod.snd_surjective
end PiProd
/-! # Properties of monoids with exponent two -/
section ExponentTwo
|
section Monoid
variable [Monoid G]
@[to_additive]
| Mathlib/GroupTheory/Exponent.lean | 594 | 599 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes
-/
import Mathlib.Algebra.CharP.Basic
import Mathlib.Algebra.Module.End
import Mathlib.Algebra.Ring.Prod
import Mathlib.Data.Fintype.Units
import Mathlib.GroupTheory.GroupAction.SubMulAction
import Mathlib.GroupTheory.OrderOfElement
import Mathlib.Tactic.FinCases
/-!
# Integers mod `n`
Definition of the integers mod n, and the field structure on the integers mod p.
## Definitions
* `ZMod n`, which is for integers modulo a nat `n : ℕ`
* `val a` is defined as a natural number:
- for `a : ZMod 0` it is the absolute value of `a`
- for `a : ZMod n` with `0 < n` it is the least natural number in the equivalence class
* A coercion `cast` is defined from `ZMod n` into any ring.
This is a ring hom if the ring has characteristic dividing `n`
-/
assert_not_exists Field Submodule TwoSidedIdeal
open Function ZMod
namespace ZMod
/-- For non-zero `n : ℕ`, the ring `Fin n` is equivalent to `ZMod n`. -/
def finEquiv : ∀ (n : ℕ) [NeZero n], Fin n ≃+* ZMod n
| 0, h => (h.ne _ rfl).elim
| _ + 1, _ => .refl _
instance charZero : CharZero (ZMod 0) := inferInstanceAs (CharZero ℤ)
/-- `val a` is a natural number defined as:
- for `a : ZMod 0` it is the absolute value of `a`
- for `a : ZMod n` with `0 < n` it is the least natural number in the equivalence class
See `ZMod.valMinAbs` for a variant that takes values in the integers.
-/
def val : ∀ {n : ℕ}, ZMod n → ℕ
| 0 => Int.natAbs
| n + 1 => ((↑) : Fin (n + 1) → ℕ)
theorem val_lt {n : ℕ} [NeZero n] (a : ZMod n) : a.val < n := by
cases n
· cases NeZero.ne 0 rfl
exact Fin.is_lt a
theorem val_le {n : ℕ} [NeZero n] (a : ZMod n) : a.val ≤ n :=
a.val_lt.le
@[simp]
theorem val_zero : ∀ {n}, (0 : ZMod n).val = 0
| 0 => rfl
| _ + 1 => rfl
@[simp]
theorem val_one' : (1 : ZMod 0).val = 1 :=
rfl
@[simp]
theorem val_neg' {n : ZMod 0} : (-n).val = n.val :=
Int.natAbs_neg n
@[simp]
theorem val_mul' {m n : ZMod 0} : (m * n).val = m.val * n.val :=
Int.natAbs_mul m n
@[simp]
theorem val_natCast (n a : ℕ) : (a : ZMod n).val = a % n := by
cases n
· rw [Nat.mod_zero]
exact Int.natAbs_natCast a
· apply Fin.val_natCast
lemma val_natCast_of_lt {n a : ℕ} (h : a < n) : (a : ZMod n).val = a := by
rwa [val_natCast, Nat.mod_eq_of_lt]
lemma val_ofNat (n a : ℕ) [a.AtLeastTwo] : (ofNat(a) : ZMod n).val = ofNat(a) % n := val_natCast ..
lemma val_ofNat_of_lt {n a : ℕ} [a.AtLeastTwo] (han : a < n) : (ofNat(a) : ZMod n).val = ofNat(a) :=
val_natCast_of_lt han
theorem val_unit' {n : ZMod 0} : IsUnit n ↔ n.val = 1 := by
simp only [val]
rw [Int.isUnit_iff, Int.natAbs_eq_iff, Nat.cast_one]
lemma eq_one_of_isUnit_natCast {n : ℕ} (h : IsUnit (n : ZMod 0)) : n = 1 := by
rw [← Nat.mod_zero n, ← val_natCast, val_unit'.mp h]
instance charP (n : ℕ) : CharP (ZMod n) n where
cast_eq_zero_iff := by
intro k
rcases n with - | n
· simp [zero_dvd_iff, Int.natCast_eq_zero]
· exact Fin.natCast_eq_zero
@[simp]
theorem addOrderOf_one (n : ℕ) : addOrderOf (1 : ZMod n) = n :=
CharP.eq _ (CharP.addOrderOf_one _) (ZMod.charP n)
/-- This lemma works in the case in which `ZMod n` is not infinite, i.e. `n ≠ 0`. The version
where `a ≠ 0` is `addOrderOf_coe'`. -/
@[simp]
theorem addOrderOf_coe (a : ℕ) {n : ℕ} (n0 : n ≠ 0) : addOrderOf (a : ZMod n) = n / n.gcd a := by
rcases a with - | a
· simp only [Nat.cast_zero, addOrderOf_zero, Nat.gcd_zero_right,
Nat.pos_of_ne_zero n0, Nat.div_self]
rw [← Nat.smul_one_eq_cast, addOrderOf_nsmul' _ a.succ_ne_zero, ZMod.addOrderOf_one]
/-- This lemma works in the case in which `a ≠ 0`. The version where
`ZMod n` is not infinite, i.e. `n ≠ 0`, is `addOrderOf_coe`. -/
@[simp]
theorem addOrderOf_coe' {a : ℕ} (n : ℕ) (a0 : a ≠ 0) : addOrderOf (a : ZMod n) = n / n.gcd a := by
rw [← Nat.smul_one_eq_cast, addOrderOf_nsmul' _ a0, ZMod.addOrderOf_one]
/-- We have that `ringChar (ZMod n) = n`. -/
theorem ringChar_zmod_n (n : ℕ) : ringChar (ZMod n) = n := by
rw [ringChar.eq_iff]
exact ZMod.charP n
theorem natCast_self (n : ℕ) : (n : ZMod n) = 0 :=
CharP.cast_eq_zero (ZMod n) n
@[simp]
theorem natCast_self' (n : ℕ) : (n + 1 : ZMod (n + 1)) = 0 := by
rw [← Nat.cast_add_one, natCast_self (n + 1)]
section UniversalProperty
variable {n : ℕ} {R : Type*}
section
variable [AddGroupWithOne R]
/-- Cast an integer modulo `n` to another semiring.
This function is a morphism if the characteristic of `R` divides `n`.
See `ZMod.castHom` for a bundled version. -/
def cast : ∀ {n : ℕ}, ZMod n → R
| 0 => Int.cast
| _ + 1 => fun i => i.val
@[simp]
theorem cast_zero : (cast (0 : ZMod n) : R) = 0 := by
delta ZMod.cast
cases n
· exact Int.cast_zero
· simp
theorem cast_eq_val [NeZero n] (a : ZMod n) : (cast a : R) = a.val := by
cases n
· cases NeZero.ne 0 rfl
rfl
variable {S : Type*} [AddGroupWithOne S]
@[simp]
theorem _root_.Prod.fst_zmod_cast (a : ZMod n) : (cast a : R × S).fst = cast a := by
cases n
· rfl
· simp [ZMod.cast]
@[simp]
theorem _root_.Prod.snd_zmod_cast (a : ZMod n) : (cast a : R × S).snd = cast a := by
cases n
· rfl
· simp [ZMod.cast]
end
/-- So-named because the coercion is `Nat.cast` into `ZMod`. For `Nat.cast` into an arbitrary ring,
see `ZMod.natCast_val`. -/
theorem natCast_zmod_val {n : ℕ} [NeZero n] (a : ZMod n) : (a.val : ZMod n) = a := by
cases n
· cases NeZero.ne 0 rfl
· apply Fin.cast_val_eq_self
theorem natCast_rightInverse [NeZero n] : Function.RightInverse val ((↑) : ℕ → ZMod n) :=
natCast_zmod_val
theorem natCast_zmod_surjective [NeZero n] : Function.Surjective ((↑) : ℕ → ZMod n) :=
natCast_rightInverse.surjective
/-- So-named because the outer coercion is `Int.cast` into `ZMod`. For `Int.cast` into an arbitrary
ring, see `ZMod.intCast_cast`. -/
@[norm_cast]
theorem intCast_zmod_cast (a : ZMod n) : ((cast a : ℤ) : ZMod n) = a := by
cases n
· simp [ZMod.cast, ZMod]
· dsimp [ZMod.cast]
rw [Int.cast_natCast, natCast_zmod_val]
theorem intCast_rightInverse : Function.RightInverse (cast : ZMod n → ℤ) ((↑) : ℤ → ZMod n) :=
intCast_zmod_cast
theorem intCast_surjective : Function.Surjective ((↑) : ℤ → ZMod n) :=
intCast_rightInverse.surjective
lemma «forall» {P : ZMod n → Prop} : (∀ x, P x) ↔ ∀ x : ℤ, P x := intCast_surjective.forall
lemma «exists» {P : ZMod n → Prop} : (∃ x, P x) ↔ ∃ x : ℤ, P x := intCast_surjective.exists
theorem cast_id : ∀ (n) (i : ZMod n), (ZMod.cast i : ZMod n) = i
| 0, _ => Int.cast_id
| _ + 1, i => natCast_zmod_val i
@[simp]
theorem cast_id' : (ZMod.cast : ZMod n → ZMod n) = id :=
funext (cast_id n)
variable (R) [Ring R]
/-- The coercions are respectively `Nat.cast` and `ZMod.cast`. -/
@[simp]
theorem natCast_comp_val [NeZero n] : ((↑) : ℕ → R) ∘ (val : ZMod n → ℕ) = cast := by
cases n
· cases NeZero.ne 0 rfl
rfl
/-- The coercions are respectively `Int.cast`, `ZMod.cast`, and `ZMod.cast`. -/
@[simp]
theorem intCast_comp_cast : ((↑) : ℤ → R) ∘ (cast : ZMod n → ℤ) = cast := by
cases n
· exact congr_arg (Int.cast ∘ ·) ZMod.cast_id'
· ext
simp [ZMod, ZMod.cast]
variable {R}
@[simp]
theorem natCast_val [NeZero n] (i : ZMod n) : (i.val : R) = cast i :=
congr_fun (natCast_comp_val R) i
@[simp]
theorem intCast_cast (i : ZMod n) : ((cast i : ℤ) : R) = cast i :=
congr_fun (intCast_comp_cast R) i
theorem cast_add_eq_ite {n : ℕ} (a b : ZMod n) :
(cast (a + b) : ℤ) =
if (n : ℤ) ≤ cast a + cast b then (cast a + cast b - n : ℤ) else cast a + cast b := by
rcases n with - | n
· simp; rfl
change Fin (n + 1) at a b
change ((((a + b) : Fin (n + 1)) : ℕ) : ℤ) = if ((n + 1 : ℕ) : ℤ) ≤ (a : ℕ) + b then _ else _
simp only [Fin.val_add_eq_ite, Int.natCast_succ, Int.ofNat_le]
norm_cast
split_ifs with h
· rw [Nat.cast_sub h]
congr
· rfl
section CharDvd
/-! If the characteristic of `R` divides `n`, then `cast` is a homomorphism. -/
variable {m : ℕ} [CharP R m]
@[simp]
theorem cast_one (h : m ∣ n) : (cast (1 : ZMod n) : R) = 1 := by
rcases n with - | n
· exact Int.cast_one
show ((1 % (n + 1) : ℕ) : R) = 1
cases n
· rw [Nat.dvd_one] at h
subst m
subsingleton [CharP.CharOne.subsingleton]
rw [Nat.mod_eq_of_lt]
· exact Nat.cast_one
exact Nat.lt_of_sub_eq_succ rfl
theorem cast_add (h : m ∣ n) (a b : ZMod n) : (cast (a + b : ZMod n) : R) = cast a + cast b := by
cases n
· apply Int.cast_add
symm
dsimp [ZMod, ZMod.cast, ZMod.val]
rw [← Nat.cast_add, Fin.val_add, ← sub_eq_zero, ← Nat.cast_sub (Nat.mod_le _ _),
@CharP.cast_eq_zero_iff R _ m]
exact h.trans (Nat.dvd_sub_mod _)
theorem cast_mul (h : m ∣ n) (a b : ZMod n) : (cast (a * b : ZMod n) : R) = cast a * cast b := by
cases n
· apply Int.cast_mul
symm
dsimp [ZMod, ZMod.cast, ZMod.val]
rw [← Nat.cast_mul, Fin.val_mul, ← sub_eq_zero, ← Nat.cast_sub (Nat.mod_le _ _),
@CharP.cast_eq_zero_iff R _ m]
exact h.trans (Nat.dvd_sub_mod _)
/-- The canonical ring homomorphism from `ZMod n` to a ring of characteristic dividing `n`.
See also `ZMod.lift` for a generalized version working in `AddGroup`s.
-/
def castHom (h : m ∣ n) (R : Type*) [Ring R] [CharP R m] : ZMod n →+* R where
toFun := cast
map_zero' := cast_zero
map_one' := cast_one h
map_add' := cast_add h
map_mul' := cast_mul h
@[simp]
theorem castHom_apply {h : m ∣ n} (i : ZMod n) : castHom h R i = cast i :=
rfl
@[simp]
theorem cast_sub (h : m ∣ n) (a b : ZMod n) : (cast (a - b : ZMod n) : R) = cast a - cast b :=
(castHom h R).map_sub a b
@[simp]
theorem cast_neg (h : m ∣ n) (a : ZMod n) : (cast (-a : ZMod n) : R) = -(cast a) :=
(castHom h R).map_neg a
@[simp]
theorem cast_pow (h : m ∣ n) (a : ZMod n) (k : ℕ) : (cast (a ^ k : ZMod n) : R) = (cast a) ^ k :=
(castHom h R).map_pow a k
@[simp, norm_cast]
theorem cast_natCast (h : m ∣ n) (k : ℕ) : (cast (k : ZMod n) : R) = k :=
map_natCast (castHom h R) k
@[simp, norm_cast]
theorem cast_intCast (h : m ∣ n) (k : ℤ) : (cast (k : ZMod n) : R) = k :=
map_intCast (castHom h R) k
end CharDvd
section CharEq
/-! Some specialised simp lemmas which apply when `R` has characteristic `n`. -/
variable [CharP R n]
@[simp]
theorem cast_one' : (cast (1 : ZMod n) : R) = 1 :=
cast_one dvd_rfl
@[simp]
theorem cast_add' (a b : ZMod n) : (cast (a + b : ZMod n) : R) = cast a + cast b :=
cast_add dvd_rfl a b
@[simp]
theorem cast_mul' (a b : ZMod n) : (cast (a * b : ZMod n) : R) = cast a * cast b :=
cast_mul dvd_rfl a b
@[simp]
theorem cast_sub' (a b : ZMod n) : (cast (a - b : ZMod n) : R) = cast a - cast b :=
cast_sub dvd_rfl a b
@[simp]
theorem cast_pow' (a : ZMod n) (k : ℕ) : (cast (a ^ k : ZMod n) : R) = (cast a : R) ^ k :=
cast_pow dvd_rfl a k
@[simp, norm_cast]
theorem cast_natCast' (k : ℕ) : (cast (k : ZMod n) : R) = k :=
cast_natCast dvd_rfl k
@[simp, norm_cast]
theorem cast_intCast' (k : ℤ) : (cast (k : ZMod n) : R) = k :=
cast_intCast dvd_rfl k
variable (R)
theorem castHom_injective : Function.Injective (ZMod.castHom (dvd_refl n) R) := by
rw [injective_iff_map_eq_zero]
intro x
obtain ⟨k, rfl⟩ := ZMod.intCast_surjective x
rw [map_intCast, CharP.intCast_eq_zero_iff R n, CharP.intCast_eq_zero_iff (ZMod n) n]
exact id
theorem castHom_bijective [Fintype R] (h : Fintype.card R = n) :
Function.Bijective (ZMod.castHom (dvd_refl n) R) := by
haveI : NeZero n :=
⟨by
intro hn
rw [hn] at h
exact (Fintype.card_eq_zero_iff.mp h).elim' 0⟩
rw [Fintype.bijective_iff_injective_and_card, ZMod.card, h, eq_self_iff_true, and_true]
apply ZMod.castHom_injective
/-- The unique ring isomorphism between `ZMod n` and a ring `R`
of characteristic `n` and cardinality `n`. -/
noncomputable def ringEquiv [Fintype R] (h : Fintype.card R = n) : ZMod n ≃+* R :=
RingEquiv.ofBijective _ (ZMod.castHom_bijective R h)
/-- The unique ring isomorphism between `ZMod p` and a ring `R` of cardinality a prime `p`.
If you need any property of this isomorphism, first of all use `ringEquivOfPrime_eq_ringEquiv`
below (after `have : CharP R p := ...`) and deduce it by the results about `ZMod.ringEquiv`. -/
noncomputable def ringEquivOfPrime [Fintype R] {p : ℕ} (hp : p.Prime) (hR : Fintype.card R = p) :
ZMod p ≃+* R :=
have : Nontrivial R := Fintype.one_lt_card_iff_nontrivial.1 (hR ▸ hp.one_lt)
-- The following line exists as `charP_of_card_eq_prime` in `Mathlib.Algebra.CharP.CharAndCard`.
have : CharP R p := (CharP.charP_iff_prime_eq_zero hp).2 (hR ▸ Nat.cast_card_eq_zero R)
ZMod.ringEquiv R hR
@[simp]
lemma ringEquivOfPrime_eq_ringEquiv [Fintype R] {p : ℕ} [CharP R p] (hp : p.Prime)
(hR : Fintype.card R = p) : ringEquivOfPrime R hp hR = ringEquiv R hR := rfl
/-- The identity between `ZMod m` and `ZMod n` when `m = n`, as a ring isomorphism. -/
def ringEquivCongr {m n : ℕ} (h : m = n) : ZMod m ≃+* ZMod n := by
rcases m with - | m <;> rcases n with - | n
· exact RingEquiv.refl _
· exfalso
exact n.succ_ne_zero h.symm
· exfalso
exact m.succ_ne_zero h
· exact
{ finCongr h with
map_mul' := fun a b => by
dsimp [ZMod]
ext
rw [Fin.coe_cast, Fin.coe_mul, Fin.coe_mul, Fin.coe_cast, Fin.coe_cast, ← h]
map_add' := fun a b => by
dsimp [ZMod]
ext
rw [Fin.coe_cast, Fin.val_add, Fin.val_add, Fin.coe_cast, Fin.coe_cast, ← h] }
@[simp] lemma ringEquivCongr_refl (a : ℕ) : ringEquivCongr (rfl : a = a) = .refl _ := by
cases a <;> rfl
lemma ringEquivCongr_refl_apply {a : ℕ} (x : ZMod a) : ringEquivCongr rfl x = x := by
rw [ringEquivCongr_refl]
rfl
lemma ringEquivCongr_symm {a b : ℕ} (hab : a = b) :
(ringEquivCongr hab).symm = ringEquivCongr hab.symm := by
subst hab
cases a <;> rfl
lemma ringEquivCongr_trans {a b c : ℕ} (hab : a = b) (hbc : b = c) :
(ringEquivCongr hab).trans (ringEquivCongr hbc) = ringEquivCongr (hab.trans hbc) := by
subst hab hbc
cases a <;> rfl
lemma ringEquivCongr_ringEquivCongr_apply {a b c : ℕ} (hab : a = b) (hbc : b = c) (x : ZMod a) :
ringEquivCongr hbc (ringEquivCongr hab x) = ringEquivCongr (hab.trans hbc) x := by
rw [← ringEquivCongr_trans hab hbc]
rfl
lemma ringEquivCongr_val {a b : ℕ} (h : a = b) (x : ZMod a) :
ZMod.val ((ZMod.ringEquivCongr h) x) = ZMod.val x := by
subst h
cases a <;> rfl
lemma ringEquivCongr_intCast {a b : ℕ} (h : a = b) (z : ℤ) :
ZMod.ringEquivCongr h z = z := by
subst h
cases a <;> rfl
end CharEq
end UniversalProperty
variable {m n : ℕ}
@[simp]
theorem val_eq_zero : ∀ {n : ℕ} (a : ZMod n), a.val = 0 ↔ a = 0
| 0, _ => Int.natAbs_eq_zero
| n + 1, a => by
rw [Fin.ext_iff]
exact Iff.rfl
theorem intCast_eq_intCast_iff (a b : ℤ) (c : ℕ) : (a : ZMod c) = (b : ZMod c) ↔ a ≡ b [ZMOD c] :=
CharP.intCast_eq_intCast (ZMod c) c
theorem intCast_eq_intCast_iff' (a b : ℤ) (c : ℕ) : (a : ZMod c) = (b : ZMod c) ↔ a % c = b % c :=
ZMod.intCast_eq_intCast_iff a b c
theorem val_intCast {n : ℕ} (a : ℤ) [NeZero n] : ↑(a : ZMod n).val = a % n := by
have hle : (0 : ℤ) ≤ ↑(a : ZMod n).val := Int.natCast_nonneg _
have hlt : ↑(a : ZMod n).val < (n : ℤ) := Int.ofNat_lt.mpr (ZMod.val_lt a)
refine (Int.emod_eq_of_lt hle hlt).symm.trans ?_
rw [← ZMod.intCast_eq_intCast_iff', Int.cast_natCast, ZMod.natCast_val, ZMod.cast_id]
theorem natCast_eq_natCast_iff (a b c : ℕ) : (a : ZMod c) = (b : ZMod c) ↔ a ≡ b [MOD c] := by
simpa [Int.natCast_modEq_iff] using ZMod.intCast_eq_intCast_iff a b c
theorem natCast_eq_natCast_iff' (a b c : ℕ) : (a : ZMod c) = (b : ZMod c) ↔ a % c = b % c :=
ZMod.natCast_eq_natCast_iff a b c
theorem intCast_zmod_eq_zero_iff_dvd (a : ℤ) (b : ℕ) : (a : ZMod b) = 0 ↔ (b : ℤ) ∣ a := by
rw [← Int.cast_zero, ZMod.intCast_eq_intCast_iff, Int.modEq_zero_iff_dvd]
theorem intCast_eq_intCast_iff_dvd_sub (a b : ℤ) (c : ℕ) : (a : ZMod c) = ↑b ↔ ↑c ∣ b - a := by
rw [ZMod.intCast_eq_intCast_iff, Int.modEq_iff_dvd]
theorem natCast_zmod_eq_zero_iff_dvd (a b : ℕ) : (a : ZMod b) = 0 ↔ b ∣ a := by
rw [← Nat.cast_zero, ZMod.natCast_eq_natCast_iff, Nat.modEq_zero_iff_dvd]
theorem coe_intCast (a : ℤ) : cast (a : ZMod n) = a % n := by
cases n
· rw [Int.ofNat_zero, Int.emod_zero, Int.cast_id]; rfl
· rw [← val_intCast, val]; rfl
lemma intCast_cast_add (x y : ZMod n) : (cast (x + y) : ℤ) = (cast x + cast y) % n := by
rw [← ZMod.coe_intCast, Int.cast_add, ZMod.intCast_zmod_cast, ZMod.intCast_zmod_cast]
lemma intCast_cast_mul (x y : ZMod n) : (cast (x * y) : ℤ) = cast x * cast y % n := by
rw [← ZMod.coe_intCast, Int.cast_mul, ZMod.intCast_zmod_cast, ZMod.intCast_zmod_cast]
lemma intCast_cast_sub (x y : ZMod n) : (cast (x - y) : ℤ) = (cast x - cast y) % n := by
rw [← ZMod.coe_intCast, Int.cast_sub, ZMod.intCast_zmod_cast, ZMod.intCast_zmod_cast]
lemma intCast_cast_neg (x : ZMod n) : (cast (-x) : ℤ) = -cast x % n := by
rw [← ZMod.coe_intCast, Int.cast_neg, ZMod.intCast_zmod_cast]
@[simp]
theorem val_neg_one (n : ℕ) : (-1 : ZMod n.succ).val = n := by
dsimp [val, Fin.coe_neg]
cases n
· simp [Nat.mod_one]
· dsimp [ZMod, ZMod.cast]
rw [Fin.coe_neg_one]
/-- `-1 : ZMod n` lifts to `n - 1 : R`. This avoids the characteristic assumption in `cast_neg`. -/
theorem cast_neg_one {R : Type*} [Ring R] (n : ℕ) : cast (-1 : ZMod n) = (n - 1 : R) := by
rcases n with - | n
· dsimp [ZMod, ZMod.cast]; simp
· rw [← natCast_val, val_neg_one, Nat.cast_succ, add_sub_cancel_right]
theorem cast_sub_one {R : Type*} [Ring R] {n : ℕ} (k : ZMod n) :
(cast (k - 1 : ZMod n) : R) = (if k = 0 then (n : R) else cast k) - 1 := by
split_ifs with hk
· rw [hk, zero_sub, ZMod.cast_neg_one]
· cases n
· dsimp [ZMod, ZMod.cast]
rw [Int.cast_sub, Int.cast_one]
· dsimp [ZMod, ZMod.cast, ZMod.val]
rw [Fin.coe_sub_one, if_neg]
· rw [Nat.cast_sub, Nat.cast_one]
rwa [Fin.ext_iff, Fin.val_zero, ← Ne, ← Nat.one_le_iff_ne_zero] at hk
· exact hk
theorem natCast_eq_iff (p : ℕ) (n : ℕ) (z : ZMod p) [NeZero p] :
↑n = z ↔ ∃ k, n = z.val + p * k := by
constructor
· rintro rfl
refine ⟨n / p, ?_⟩
rw [val_natCast, Nat.mod_add_div]
· rintro ⟨k, rfl⟩
rw [Nat.cast_add, natCast_zmod_val, Nat.cast_mul, natCast_self, zero_mul,
add_zero]
theorem intCast_eq_iff (p : ℕ) (n : ℤ) (z : ZMod p) [NeZero p] :
↑n = z ↔ ∃ k, n = z.val + p * k := by
constructor
· rintro rfl
refine ⟨n / p, ?_⟩
rw [val_intCast, Int.emod_add_ediv]
· rintro ⟨k, rfl⟩
rw [Int.cast_add, Int.cast_mul, Int.cast_natCast, Int.cast_natCast, natCast_val,
ZMod.natCast_self, zero_mul, add_zero, cast_id]
@[push_cast, simp]
theorem intCast_mod (a : ℤ) (b : ℕ) : ((a % b : ℤ) : ZMod b) = (a : ZMod b) := by
rw [ZMod.intCast_eq_intCast_iff]
apply Int.mod_modEq
theorem ker_intCastAddHom (n : ℕ) :
(Int.castAddHom (ZMod n)).ker = AddSubgroup.zmultiples (n : ℤ) := by
ext
rw [Int.mem_zmultiples_iff, AddMonoidHom.mem_ker, Int.coe_castAddHom,
intCast_zmod_eq_zero_iff_dvd]
theorem cast_injective_of_le {m n : ℕ} [nzm : NeZero m] (h : m ≤ n) :
Function.Injective (@cast (ZMod n) _ m) := by
cases m with
| zero => cases nzm; simp_all
| succ m =>
rintro ⟨x, hx⟩ ⟨y, hy⟩ f
simp only [cast, val, natCast_eq_natCast_iff',
Nat.mod_eq_of_lt (hx.trans_le h), Nat.mod_eq_of_lt (hy.trans_le h)] at f
apply Fin.ext
exact f
theorem cast_zmod_eq_zero_iff_of_le {m n : ℕ} [NeZero m] (h : m ≤ n) (a : ZMod m) :
(cast a : ZMod n) = 0 ↔ a = 0 := by
rw [← ZMod.cast_zero (n := m)]
exact Injective.eq_iff' (cast_injective_of_le h) rfl
@[simp]
theorem natCast_toNat (p : ℕ) : ∀ {z : ℤ} (_h : 0 ≤ z), (z.toNat : ZMod p) = z
| (n : ℕ), _h => by simp only [Int.cast_natCast, Int.toNat_natCast]
| Int.negSucc n, h => by simp at h
theorem val_injective (n : ℕ) [NeZero n] : Function.Injective (val : ZMod n → ℕ) := by
cases n
· cases NeZero.ne 0 rfl
intro a b h
dsimp [ZMod]
ext
exact h
theorem val_one_eq_one_mod (n : ℕ) : (1 : ZMod n).val = 1 % n := by
rw [← Nat.cast_one, val_natCast]
theorem val_two_eq_two_mod (n : ℕ) : (2 : ZMod n).val = 2 % n := by
rw [← Nat.cast_two, val_natCast]
theorem val_one (n : ℕ) [Fact (1 < n)] : (1 : ZMod n).val = 1 := by
rw [val_one_eq_one_mod]
exact Nat.mod_eq_of_lt Fact.out
lemma val_one'' : ∀ {n}, n ≠ 1 → (1 : ZMod n).val = 1
| 0, _ => rfl
| 1, hn => by cases hn rfl
| n + 2, _ =>
haveI : Fact (1 < n + 2) := ⟨by simp⟩
ZMod.val_one _
theorem val_add {n : ℕ} [NeZero n] (a b : ZMod n) : (a + b).val = (a.val + b.val) % n := by
cases n
· cases NeZero.ne 0 rfl
· apply Fin.val_add
theorem val_add_of_lt {n : ℕ} {a b : ZMod n} (h : a.val + b.val < n) :
(a + b).val = a.val + b.val := by
have : NeZero n := by constructor; rintro rfl; simp at h
rw [ZMod.val_add, Nat.mod_eq_of_lt h]
theorem val_add_val_of_le {n : ℕ} [NeZero n] {a b : ZMod n} (h : n ≤ a.val + b.val) :
a.val + b.val = (a + b).val + n := by
rw [val_add, Nat.add_mod_add_of_le_add_mod, Nat.mod_eq_of_lt (val_lt _),
Nat.mod_eq_of_lt (val_lt _)]
rwa [Nat.mod_eq_of_lt (val_lt _), Nat.mod_eq_of_lt (val_lt _)]
theorem val_add_of_le {n : ℕ} [NeZero n] {a b : ZMod n} (h : n ≤ a.val + b.val) :
(a + b).val = a.val + b.val - n := by
rw [val_add_val_of_le h]
exact eq_tsub_of_add_eq rfl
theorem val_add_le {n : ℕ} (a b : ZMod n) : (a + b).val ≤ a.val + b.val := by
cases n
· simpa [ZMod.val] using Int.natAbs_add_le _ _
· simpa [ZMod.val_add] using Nat.mod_le _ _
theorem val_mul {n : ℕ} (a b : ZMod n) : (a * b).val = a.val * b.val % n := by
cases n
· rw [Nat.mod_zero]
apply Int.natAbs_mul
· apply Fin.val_mul
theorem val_mul_le {n : ℕ} (a b : ZMod n) : (a * b).val ≤ a.val * b.val := by
rw [val_mul]
apply Nat.mod_le
theorem val_mul_of_lt {n : ℕ} {a b : ZMod n} (h : a.val * b.val < n) :
(a * b).val = a.val * b.val := by
rw [val_mul]
apply Nat.mod_eq_of_lt h
theorem val_mul_iff_lt {n : ℕ} [NeZero n] (a b : ZMod n) :
(a * b).val = a.val * b.val ↔ a.val * b.val < n := by
constructor <;> intro h
· rw [← h]; apply ZMod.val_lt
· apply ZMod.val_mul_of_lt h
instance nontrivial (n : ℕ) [Fact (1 < n)] : Nontrivial (ZMod n) :=
⟨⟨0, 1, fun h =>
zero_ne_one <|
calc
0 = (0 : ZMod n).val := by rw [val_zero]
_ = (1 : ZMod n).val := congr_arg ZMod.val h
_ = 1 := val_one n
⟩⟩
instance nontrivial' : Nontrivial (ZMod 0) := by
delta ZMod; infer_instance
lemma one_eq_zero_iff {n : ℕ} : (1 : ZMod n) = 0 ↔ n = 1 := by
rw [← Nat.cast_one, natCast_zmod_eq_zero_iff_dvd, Nat.dvd_one]
/-- The inversion on `ZMod n`.
It is setup in such a way that `a * a⁻¹` is equal to `gcd a.val n`.
In particular, if `a` is coprime to `n`, and hence a unit, `a * a⁻¹ = 1`. -/
def inv : ∀ n : ℕ, ZMod n → ZMod n
| 0, i => Int.sign i
| n + 1, i => Nat.gcdA i.val (n + 1)
instance (n : ℕ) : Inv (ZMod n) :=
⟨inv n⟩
theorem inv_zero : ∀ n : ℕ, (0 : ZMod n)⁻¹ = 0
| 0 => Int.sign_zero
| n + 1 =>
show (Nat.gcdA _ (n + 1) : ZMod (n + 1)) = 0 by
rw [val_zero]
unfold Nat.gcdA Nat.xgcd Nat.xgcdAux
rfl
theorem mul_inv_eq_gcd {n : ℕ} (a : ZMod n) : a * a⁻¹ = Nat.gcd a.val n := by
rcases n with - | n
· dsimp [ZMod] at a ⊢
calc
_ = a * Int.sign a := rfl
_ = a.natAbs := by rw [Int.mul_sign_self]
_ = a.natAbs.gcd 0 := by rw [Nat.gcd_zero_right]
· calc
a * a⁻¹ = a * a⁻¹ + n.succ * Nat.gcdB (val a) n.succ := by
rw [natCast_self, zero_mul, add_zero]
_ = ↑(↑a.val * Nat.gcdA (val a) n.succ + n.succ * Nat.gcdB (val a) n.succ) := by
push_cast
rw [natCast_zmod_val]
rfl
_ = Nat.gcd a.val n.succ := by rw [← Nat.gcd_eq_gcd_ab a.val n.succ]; rfl
@[simp] protected lemma inv_one (n : ℕ) : (1⁻¹ : ZMod n) = 1 := by
obtain rfl | hn := eq_or_ne n 1
· exact Subsingleton.elim _ _
· simpa [ZMod.val_one'' hn] using mul_inv_eq_gcd (1 : ZMod n)
@[simp]
theorem natCast_mod (a : ℕ) (n : ℕ) : ((a % n : ℕ) : ZMod n) = a := by
conv =>
rhs
rw [← Nat.mod_add_div a n]
simp
theorem eq_iff_modEq_nat (n : ℕ) {a b : ℕ} : (a : ZMod n) = b ↔ a ≡ b [MOD n] := by
cases n
· simp [Nat.ModEq, Int.natCast_inj, Nat.mod_zero]
· rw [Fin.ext_iff, Nat.ModEq, ← val_natCast, ← val_natCast]
exact Iff.rfl
theorem eq_zero_iff_even {n : ℕ} : (n : ZMod 2) = 0 ↔ Even n :=
(CharP.cast_eq_zero_iff (ZMod 2) 2 n).trans even_iff_two_dvd.symm
theorem eq_one_iff_odd {n : ℕ} : (n : ZMod 2) = 1 ↔ Odd n := by
rw [← @Nat.cast_one (ZMod 2), ZMod.eq_iff_modEq_nat, Nat.odd_iff, Nat.ModEq]
theorem ne_zero_iff_odd {n : ℕ} : (n : ZMod 2) ≠ 0 ↔ Odd n := by
constructor <;>
· contrapose
simp [eq_zero_iff_even]
theorem coe_mul_inv_eq_one {n : ℕ} (x : ℕ) (h : Nat.Coprime x n) :
((x : ZMod n) * (x : ZMod n)⁻¹) = 1 := by
rw [Nat.Coprime, Nat.gcd_comm, Nat.gcd_rec] at h
rw [mul_inv_eq_gcd, val_natCast, h, Nat.cast_one]
lemma mul_val_inv (hmn : m.Coprime n) : (m * (m⁻¹ : ZMod n).val : ZMod n) = 1 := by
obtain rfl | hn := eq_or_ne n 0
· simp [m.coprime_zero_right.1 hmn]
haveI : NeZero n := ⟨hn⟩
rw [ZMod.natCast_zmod_val, ZMod.coe_mul_inv_eq_one _ hmn]
lemma val_inv_mul (hmn : m.Coprime n) : ((m⁻¹ : ZMod n).val * m : ZMod n) = 1 := by
rw [mul_comm, mul_val_inv hmn]
/-- `unitOfCoprime` makes an element of `(ZMod n)ˣ` given
a natural number `x` and a proof that `x` is coprime to `n` -/
def unitOfCoprime {n : ℕ} (x : ℕ) (h : Nat.Coprime x n) : (ZMod n)ˣ :=
⟨x, x⁻¹, coe_mul_inv_eq_one x h, by rw [mul_comm, coe_mul_inv_eq_one x h]⟩
@[simp]
theorem coe_unitOfCoprime {n : ℕ} (x : ℕ) (h : Nat.Coprime x n) :
(unitOfCoprime x h : ZMod n) = x :=
rfl
theorem val_coe_unit_coprime {n : ℕ} (u : (ZMod n)ˣ) : Nat.Coprime (u : ZMod n).val n := by
rcases n with - | n
· rcases Int.units_eq_one_or u with (rfl | rfl) <;> simp
apply Nat.coprime_of_mul_modEq_one ((u⁻¹ : Units (ZMod (n + 1))) : ZMod (n + 1)).val
have := Units.ext_iff.1 (mul_inv_cancel u)
rw [Units.val_one] at this
rw [← eq_iff_modEq_nat, Nat.cast_one, ← this]; clear this
rw [← natCast_zmod_val ((u * u⁻¹ : Units (ZMod (n + 1))) : ZMod (n + 1))]
rw [Units.val_mul, val_mul, natCast_mod]
lemma isUnit_iff_coprime (m n : ℕ) : IsUnit (m : ZMod n) ↔ m.Coprime n := by
refine ⟨fun H ↦ ?_, fun H ↦ (unitOfCoprime m H).isUnit⟩
have H' := val_coe_unit_coprime H.unit
rw [IsUnit.unit_spec, val_natCast, Nat.coprime_iff_gcd_eq_one] at H'
rw [Nat.coprime_iff_gcd_eq_one, Nat.gcd_comm, ← H']
exact Nat.gcd_rec n m
lemma isUnit_prime_iff_not_dvd {n p : ℕ} (hp : p.Prime) : IsUnit (p : ZMod n) ↔ ¬p ∣ n := by
rw [isUnit_iff_coprime, Nat.Prime.coprime_iff_not_dvd hp]
lemma isUnit_prime_of_not_dvd {n p : ℕ} (hp : p.Prime) (h : ¬ p ∣ n) : IsUnit (p : ZMod n) :=
(isUnit_prime_iff_not_dvd hp).mpr h
@[simp]
theorem inv_coe_unit {n : ℕ} (u : (ZMod n)ˣ) : (u : ZMod n)⁻¹ = (u⁻¹ : (ZMod n)ˣ) := by
have := congr_arg ((↑) : ℕ → ZMod n) (val_coe_unit_coprime u)
rw [← mul_inv_eq_gcd, Nat.cast_one] at this
let u' : (ZMod n)ˣ := ⟨u, (u : ZMod n)⁻¹, this, by rwa [mul_comm]⟩
have h : u = u' := by
apply Units.ext
rfl
rw [h]
rfl
theorem mul_inv_of_unit {n : ℕ} (a : ZMod n) (h : IsUnit a) : a * a⁻¹ = 1 := by
rcases h with ⟨u, rfl⟩
rw [inv_coe_unit, u.mul_inv]
theorem inv_mul_of_unit {n : ℕ} (a : ZMod n) (h : IsUnit a) : a⁻¹ * a = 1 := by
rw [mul_comm, mul_inv_of_unit a h]
-- TODO: If we changed `⁻¹` so that `ZMod n` is always a `DivisionMonoid`,
-- then we could use the general lemma `inv_eq_of_mul_eq_one`
protected theorem inv_eq_of_mul_eq_one (n : ℕ) (a b : ZMod n) (h : a * b = 1) : a⁻¹ = b :=
left_inv_eq_right_inv (inv_mul_of_unit a ⟨⟨a, b, h, mul_comm a b ▸ h⟩, rfl⟩) h
lemma inv_mul_eq_one_of_isUnit {n : ℕ} {a : ZMod n} (ha : IsUnit a) (b : ZMod n) :
a⁻¹ * b = 1 ↔ a = b := by
-- ideally, this would be `ha.inv_mul_eq_one`, but `ZMod n` is not a `DivisionMonoid`...
-- (see the "TODO" above)
refine ⟨fun H ↦ ?_, fun H ↦ H ▸ a.inv_mul_of_unit ha⟩
apply_fun (a * ·) at H
rwa [← mul_assoc, a.mul_inv_of_unit ha, one_mul, mul_one, eq_comm] at H
-- TODO: this equivalence is true for `ZMod 0 = ℤ`, but needs to use different functions.
/-- Equivalence between the units of `ZMod n` and
the subtype of terms `x : ZMod n` for which `x.val` is coprime to `n` -/
def unitsEquivCoprime {n : ℕ} [NeZero n] : (ZMod n)ˣ ≃ { x : ZMod n // Nat.Coprime x.val n } where
toFun x := ⟨x, val_coe_unit_coprime x⟩
invFun x := unitOfCoprime x.1.val x.2
left_inv := fun ⟨_, _, _, _⟩ => Units.ext (natCast_zmod_val _)
right_inv := fun ⟨_, _⟩ => by simp
/-- The **Chinese remainder theorem**. For a pair of coprime natural numbers, `m` and `n`,
the rings `ZMod (m * n)` and `ZMod m × ZMod n` are isomorphic.
See `Ideal.quotientInfRingEquivPiQuotient` for the Chinese remainder theorem for ideals in any
ring.
-/
def chineseRemainder {m n : ℕ} (h : m.Coprime n) : ZMod (m * n) ≃+* ZMod m × ZMod n :=
let to_fun : ZMod (m * n) → ZMod m × ZMod n :=
ZMod.castHom (show m.lcm n ∣ m * n by simp [Nat.lcm_dvd_iff]) (ZMod m × ZMod n)
let inv_fun : ZMod m × ZMod n → ZMod (m * n) := fun x =>
if m * n = 0 then
if m = 1 then cast (RingHom.snd _ (ZMod n) x) else cast (RingHom.fst (ZMod m) _ x)
else Nat.chineseRemainder h x.1.val x.2.val
have inv : Function.LeftInverse inv_fun to_fun ∧ Function.RightInverse inv_fun to_fun :=
if hmn0 : m * n = 0 then by
rcases h.eq_of_mul_eq_zero hmn0 with (⟨rfl, rfl⟩ | ⟨rfl, rfl⟩)
· constructor
· intro x; rfl
· rintro ⟨x, y⟩
fin_cases y
simp [to_fun, inv_fun, castHom, Prod.ext_iff, eq_iff_true_of_subsingleton]
· constructor
· intro x; rfl
· rintro ⟨x, y⟩
fin_cases x
simp [to_fun, inv_fun, castHom, Prod.ext_iff, eq_iff_true_of_subsingleton]
else by
haveI : NeZero (m * n) := ⟨hmn0⟩
haveI : NeZero m := ⟨left_ne_zero_of_mul hmn0⟩
haveI : NeZero n := ⟨right_ne_zero_of_mul hmn0⟩
have left_inv : Function.LeftInverse inv_fun to_fun := by
intro x
dsimp only [to_fun, inv_fun, ZMod.castHom_apply]
conv_rhs => rw [← ZMod.natCast_zmod_val x]
rw [if_neg hmn0, ZMod.eq_iff_modEq_nat, ← Nat.modEq_and_modEq_iff_modEq_mul h,
Prod.fst_zmod_cast, Prod.snd_zmod_cast]
refine
⟨(Nat.chineseRemainder h (cast x : ZMod m).val (cast x : ZMod n).val).2.left.trans ?_,
(Nat.chineseRemainder h (cast x : ZMod m).val (cast x : ZMod n).val).2.right.trans ?_⟩
· rw [← ZMod.eq_iff_modEq_nat, ZMod.natCast_zmod_val, ZMod.natCast_val]
· rw [← ZMod.eq_iff_modEq_nat, ZMod.natCast_zmod_val, ZMod.natCast_val]
exact ⟨left_inv, left_inv.rightInverse_of_card_le (by simp)⟩
{ toFun := to_fun,
invFun := inv_fun,
map_mul' := RingHom.map_mul _
map_add' := RingHom.map_add _
left_inv := inv.1
right_inv := inv.2 }
lemma subsingleton_iff {n : ℕ} : Subsingleton (ZMod n) ↔ n = 1 := by
constructor
· obtain (_ | _ | n) := n
· simpa [ZMod] using not_subsingleton _
· simp [ZMod]
· simpa [ZMod] using not_subsingleton _
· rintro rfl
infer_instance
lemma nontrivial_iff {n : ℕ} : Nontrivial (ZMod n) ↔ n ≠ 1 := by
rw [← not_subsingleton_iff_nontrivial, subsingleton_iff]
-- todo: this can be made a `Unique` instance.
instance subsingleton_units : Subsingleton (ZMod 2)ˣ :=
⟨by decide⟩
@[simp]
theorem add_self_eq_zero_iff_eq_zero {n : ℕ} (hn : Odd n) {a : ZMod n} :
a + a = 0 ↔ a = 0 := by
rw [Nat.odd_iff, ← Nat.two_dvd_ne_zero, ← Nat.prime_two.coprime_iff_not_dvd] at hn
rw [← mul_two, ← @Nat.cast_two (ZMod n), ← ZMod.coe_unitOfCoprime 2 hn, Units.mul_left_eq_zero]
theorem ne_neg_self {n : ℕ} (hn : Odd n) {a : ZMod n} (ha : a ≠ 0) : a ≠ -a := by
rwa [Ne, eq_neg_iff_add_eq_zero, add_self_eq_zero_iff_eq_zero hn]
theorem neg_one_ne_one {n : ℕ} [Fact (2 < n)] : (-1 : ZMod n) ≠ 1 :=
CharP.neg_one_ne_one (ZMod n) n
@[simp]
theorem neg_eq_self_mod_two (a : ZMod 2) : -a = a := by
fin_cases a <;> apply Fin.ext <;> simp [Fin.coe_neg, Int.natMod]; rfl
@[simp]
theorem natAbs_mod_two (a : ℤ) : (a.natAbs : ZMod 2) = a := by
cases a
· simp only [Int.natAbs_natCast, Int.cast_natCast, Int.ofNat_eq_coe]
· simp only [neg_eq_self_mod_two, Nat.cast_succ, Int.natAbs, Int.cast_negSucc]
theorem val_ne_zero {n : ℕ} (a : ZMod n) : a.val ≠ 0 ↔ a ≠ 0 :=
(val_eq_zero a).not
theorem val_pos {n : ℕ} {a : ZMod n} : 0 < a.val ↔ a ≠ 0 := by
simp [pos_iff_ne_zero]
theorem val_eq_one : ∀ {n : ℕ} (_ : 1 < n) (a : ZMod n), a.val = 1 ↔ a = 1
| 0, hn, _
| 1, hn, _ => by simp at hn
| n + 2, _, _ => by simp only [val, ZMod, Fin.ext_iff, Fin.val_one]
theorem neg_eq_self_iff {n : ℕ} (a : ZMod n) : -a = a ↔ a = 0 ∨ 2 * a.val = n := by
rw [neg_eq_iff_add_eq_zero, ← two_mul]
cases n
· rw [@mul_eq_zero ℤ, @mul_eq_zero ℕ, val_eq_zero]
exact
⟨fun h => h.elim (by simp) Or.inl, fun h =>
Or.inr (h.elim id fun h => h.elim (by simp) id)⟩
conv_lhs =>
rw [← a.natCast_zmod_val, ← Nat.cast_two, ← Nat.cast_mul, natCast_zmod_eq_zero_iff_dvd]
constructor
· rintro ⟨m, he⟩
rcases m with - | m
· rw [mul_zero, mul_eq_zero] at he
rcases he with (⟨⟨⟩⟩ | he)
exact Or.inl (a.val_eq_zero.1 he)
cases m
· right
rwa [show 0 + 1 = 1 from rfl, mul_one] at he
refine (a.val_lt.not_le <| Nat.le_of_mul_le_mul_left ?_ zero_lt_two).elim
rw [he, mul_comm]
apply Nat.mul_le_mul_left
simp
· rintro (rfl | h)
· rw [val_zero, mul_zero]
apply dvd_zero
· rw [h]
theorem val_cast_of_lt {n : ℕ} {a : ℕ} (h : a < n) : (a : ZMod n).val = a := by
rw [val_natCast, Nat.mod_eq_of_lt h]
theorem val_cast_zmod_lt {m : ℕ} [NeZero m] (n : ℕ) [NeZero n] (a : ZMod m) :
(a.cast : ZMod n).val < m := by
rcases m with (⟨⟩|⟨m⟩); · cases NeZero.ne 0 rfl
by_cases h : m < n
· rcases n with (⟨⟩|⟨n⟩); · simp at h
rw [← natCast_val, val_cast_of_lt]
· apply a.val_lt
apply lt_of_le_of_lt (Nat.le_of_lt_succ (ZMod.val_lt a)) h
· rw [not_lt] at h
apply lt_of_lt_of_le (ZMod.val_lt _) (le_trans h (Nat.le_succ m))
theorem neg_val' {n : ℕ} [NeZero n] (a : ZMod n) : (-a).val = (n - a.val) % n :=
calc
(-a).val = val (-a) % n := by rw [Nat.mod_eq_of_lt (-a).val_lt]
_ = (n - val a) % n :=
Nat.ModEq.add_right_cancel' (val a)
(by
rw [Nat.ModEq, ← val_add, neg_add_cancel, tsub_add_cancel_of_le a.val_le, Nat.mod_self,
val_zero])
theorem neg_val {n : ℕ} [NeZero n] (a : ZMod n) : (-a).val = if a = 0 then 0 else n - a.val := by
rw [neg_val']
by_cases h : a = 0; · rw [if_pos h, h, val_zero, tsub_zero, Nat.mod_self]
rw [if_neg h]
apply Nat.mod_eq_of_lt
apply Nat.sub_lt (NeZero.pos n)
contrapose! h
rwa [Nat.le_zero, val_eq_zero] at h
theorem val_neg_of_ne_zero {n : ℕ} [nz : NeZero n] (a : ZMod n) [na : NeZero a] :
(- a).val = n - a.val := by simp_all [neg_val a, na.out]
theorem val_sub {n : ℕ} [NeZero n] {a b : ZMod n} (h : b.val ≤ a.val) :
(a - b).val = a.val - b.val := by
by_cases hb : b = 0
· cases hb; simp
· have : NeZero b := ⟨hb⟩
rw [sub_eq_add_neg, val_add, val_neg_of_ne_zero, ← Nat.add_sub_assoc (le_of_lt (val_lt _)),
add_comm, Nat.add_sub_assoc h, Nat.add_mod_left]
apply Nat.mod_eq_of_lt (tsub_lt_of_lt (val_lt _))
theorem val_cast_eq_val_of_lt {m n : ℕ} [nzm : NeZero m] {a : ZMod m}
(h : a.val < n) : (a.cast : ZMod n).val = a.val := by
have nzn : NeZero n := by constructor; rintro rfl; simp at h
cases m with
| zero => cases nzm; simp_all
| succ m =>
cases n with
| zero => cases nzn; simp_all
| succ n => exact Fin.val_cast_of_lt h
theorem cast_cast_zmod_of_le {m n : ℕ} [hm : NeZero m] (h : m ≤ n) (a : ZMod m) :
(cast (cast a : ZMod n) : ZMod m) = a := by
have : NeZero n := ⟨((Nat.zero_lt_of_ne_zero hm.out).trans_le h).ne'⟩
rw [cast_eq_val, val_cast_eq_val_of_lt (a.val_lt.trans_le h), natCast_zmod_val]
theorem val_pow {m n : ℕ} {a : ZMod n} [ilt : Fact (1 < n)] (h : a.val ^ m < n) :
(a ^ m).val = a.val ^ m := by
induction m with
| zero => simp [ZMod.val_one]
| succ m ih =>
have : a.val ^ m < n := by
obtain rfl | ha := eq_or_ne a 0
· by_cases hm : m = 0
· cases hm; simp [ilt.out]
· simp only [val_zero, ne_eq, hm, not_false_eq_true, zero_pow, Nat.zero_lt_of_lt h]
· exact lt_of_le_of_lt
(Nat.pow_le_pow_right (by rwa [gt_iff_lt, ZMod.val_pos]) (Nat.le_succ m)) h
rw [pow_succ, ZMod.val_mul, ih this, ← pow_succ, Nat.mod_eq_of_lt h]
theorem val_pow_le {m n : ℕ} [Fact (1 < n)] {a : ZMod n} : (a ^ m).val ≤ a.val ^ m := by
induction m with
| zero => simp [ZMod.val_one]
| succ m ih =>
rw [pow_succ, pow_succ]
apply le_trans (ZMod.val_mul_le _ _)
apply Nat.mul_le_mul_right _ ih
theorem natAbs_min_of_le_div_two (n : ℕ) (x y : ℤ) (he : (x : ZMod n) = y) (hl : x.natAbs ≤ n / 2) :
x.natAbs ≤ y.natAbs := by
rw [intCast_eq_intCast_iff_dvd_sub] at he
obtain ⟨m, he⟩ := he
rw [sub_eq_iff_eq_add] at he
subst he
obtain rfl | hm := eq_or_ne m 0
· rw [mul_zero, zero_add]
apply hl.trans
rw [← add_le_add_iff_right x.natAbs]
refine le_trans (le_trans ((add_le_add_iff_left _).2 hl) ?_) (Int.natAbs_sub_le _ _)
rw [add_sub_cancel_right, Int.natAbs_mul, Int.natAbs_natCast]
refine le_trans ?_ (Nat.le_mul_of_pos_right _ <| Int.natAbs_pos.2 hm)
rw [← mul_two]; apply Nat.div_mul_le_self
end ZMod
theorem RingHom.ext_zmod {n : ℕ} {R : Type*} [NonAssocSemiring R] (f g : ZMod n →+* R) : f = g := by
ext a
obtain ⟨k, rfl⟩ := ZMod.intCast_surjective a
let φ : ℤ →+* R := f.comp (Int.castRingHom (ZMod n))
let ψ : ℤ →+* R := g.comp (Int.castRingHom (ZMod n))
show φ k = ψ k
rw [φ.ext_int ψ]
namespace ZMod
variable {n : ℕ} {R : Type*}
instance subsingleton_ringHom [Semiring R] : Subsingleton (ZMod n →+* R) :=
⟨RingHom.ext_zmod⟩
instance subsingleton_ringEquiv [Semiring R] : Subsingleton (ZMod n ≃+* R) :=
⟨fun f g => by
rw [RingEquiv.coe_ringHom_inj_iff]
apply RingHom.ext_zmod _ _⟩
@[simp]
theorem ringHom_map_cast [NonAssocRing R] (f : R →+* ZMod n) (k : ZMod n) : f (cast k) = k := by
cases n
· dsimp [ZMod, ZMod.cast] at f k ⊢; simp
· dsimp [ZMod.cast]
rw [map_natCast, natCast_zmod_val]
/-- Any ring homomorphism into `ZMod n` has a right inverse. -/
theorem ringHom_rightInverse [NonAssocRing R] (f : R →+* ZMod n) :
Function.RightInverse (cast : ZMod n → R) f :=
ringHom_map_cast f
/-- Any ring homomorphism into `ZMod n` is surjective. -/
theorem ringHom_surjective [NonAssocRing R] (f : R →+* ZMod n) : Function.Surjective f :=
(ringHom_rightInverse f).surjective
@[simp]
lemma castHom_self : ZMod.castHom dvd_rfl (ZMod n) = RingHom.id (ZMod n) :=
Subsingleton.elim _ _
@[simp]
lemma castHom_comp {m d : ℕ} (hm : n ∣ m) (hd : m ∣ d) :
(castHom hm (ZMod n)).comp (castHom hd (ZMod m)) = castHom (dvd_trans hm hd) (ZMod n) :=
RingHom.ext_zmod _ _
section lift
variable (n) {A : Type*} [AddGroup A]
/-- The map from `ZMod n` induced by `f : ℤ →+ A` that maps `n` to `0`. -/
def lift : { f : ℤ →+ A // f n = 0 } ≃ (ZMod n →+ A) :=
(Equiv.subtypeEquivRight <| by
intro f
rw [ker_intCastAddHom]
constructor
· rintro hf _ ⟨x, rfl⟩
simp only [f.map_zsmul, zsmul_zero, f.mem_ker, hf]
· intro h
exact h (AddSubgroup.mem_zmultiples _)).trans <|
(Int.castAddHom (ZMod n)).liftOfRightInverse cast intCast_zmod_cast
variable (f : { f : ℤ →+ A // f n = 0 })
@[simp]
theorem lift_coe (x : ℤ) : lift n f (x : ZMod n) = f.val x :=
AddMonoidHom.liftOfRightInverse_comp_apply _ _ (fun _ => intCast_zmod_cast _) _ _
theorem lift_castAddHom (x : ℤ) : lift n f (Int.castAddHom (ZMod n) x) = f.1 x :=
AddMonoidHom.liftOfRightInverse_comp_apply _ _ (fun _ => intCast_zmod_cast _) _ _
@[simp]
theorem lift_comp_coe : ZMod.lift n f ∘ ((↑) : ℤ → _) = f :=
funext <| lift_coe _ _
@[simp]
theorem lift_comp_castAddHom : (ZMod.lift n f).comp (Int.castAddHom (ZMod n)) = f :=
AddMonoidHom.ext <| lift_castAddHom _ _
lemma lift_injective {f : {f : ℤ →+ A // f n = 0}} :
Injective (lift n f) ↔ ∀ m, f.1 m = 0 → (m : ZMod n) = 0 := by
simp only [← AddMonoidHom.ker_eq_bot_iff, eq_bot_iff, SetLike.le_def,
ZMod.intCast_surjective.forall, ZMod.lift_coe, AddMonoidHom.mem_ker, AddSubgroup.mem_bot]
end lift
end ZMod
/-!
### Groups of bounded torsion
For `G` a group and `n` a natural number, `G` having torsion dividing `n`
(`∀ x : G, n • x = 0`) can be derived from `Module R G` where `R` has characteristic dividing `n`.
It is however painful to have the API for such groups `G` stated in this generality, as `R` does not
appear anywhere in the lemmas' return type. Instead of writing the API in terms of a general `R`, we
therefore specialise to the canonical ring of order `n`, namely `ZMod n`.
This spelling `Module (ZMod n) G` has the extra advantage of providing the canonical action by
`ZMod n`. It is however Type-valued, so we might want to acquire a Prop-valued version in the
future.
-/
section Module
variable {n : ℕ} {S G : Type*} [AddCommGroup G] [SetLike S G] [AddSubgroupClass S G] {K : S} {x : G}
section general
variable [Module (ZMod n) G] {x : G}
lemma zmod_smul_mem (hx : x ∈ K) : ∀ a : ZMod n, a • x ∈ K := by
simpa [ZMod.forall, Int.cast_smul_eq_zsmul] using zsmul_mem hx
/-- This cannot be made an instance because of the `[Module (ZMod n) G]` argument and the fact that
`n` only appears in the second argument of `SMulMemClass`, which is an `OutParam`. -/
lemma smulMemClass : SMulMemClass S (ZMod n) G where smul_mem _ _ {_x} hx := zmod_smul_mem hx _
namespace AddSubgroupClass
instance instZModSMul : SMul (ZMod n) K where smul a x := ⟨a • x, zmod_smul_mem x.2 _⟩
@[simp, norm_cast] lemma coe_zmod_smul (a : ZMod n) (x : K) : ↑(a • x) = (a • x : G) := rfl
instance instZModModule : Module (ZMod n) K :=
Subtype.coe_injective.module _ (AddSubmonoidClass.subtype K) coe_zmod_smul
end AddSubgroupClass
variable (n)
lemma ZModModule.char_nsmul_eq_zero (x : G) : n • x = 0 := by
simp [← Nat.cast_smul_eq_nsmul (ZMod n)]
variable (G) in
lemma ZModModule.char_ne_one [Nontrivial G] : n ≠ 1 := by
rintro rfl
obtain ⟨x, hx⟩ := exists_ne (0 : G)
exact hx <| by simpa using char_nsmul_eq_zero 1 x
variable (G) in
lemma ZModModule.two_le_char [NeZero n] [Nontrivial G] : 2 ≤ n := by
have := NeZero.ne n
have := char_ne_one n G
omega
lemma ZModModule.periodicPts_add_left [NeZero n] (x : G) : periodicPts (x + ·) = .univ :=
Set.eq_univ_of_forall fun y ↦ ⟨n, NeZero.pos n, by
simpa [char_nsmul_eq_zero, IsPeriodicPt] using isFixedPt_id _⟩
end general
section two
variable [Module (ZMod 2) G]
lemma ZModModule.add_self (x : G) : x + x = 0 := by
simpa [two_nsmul] using char_nsmul_eq_zero 2 x
lemma ZModModule.neg_eq_self (x : G) : -x = x := by simp [add_self, eq_comm, ← sub_eq_zero]
lemma ZModModule.sub_eq_add (x y : G) : x - y = x + y := by simp [neg_eq_self, sub_eq_add_neg]
lemma ZModModule.add_add_add_cancel (x y z : G) : (x + y) + (y + z) = x + z := by
simpa [sub_eq_add] using sub_add_sub_cancel x y z
end two
end Module
section AddGroup
variable {α : Type*} [AddGroup α] {n : ℕ}
@[simp]
lemma nsmul_zmod_val_inv_nsmul (hn : (Nat.card α).Coprime n) (a : α) :
n • (n⁻¹ : ZMod (Nat.card α)).val • a = a := by
rw [← mul_nsmul', ← mod_natCard_nsmul, ← ZMod.val_natCast, Nat.cast_mul,
ZMod.mul_val_inv hn.symm, ZMod.val_one_eq_one_mod, mod_natCard_nsmul, one_nsmul]
| @[simp]
lemma zmod_val_inv_nsmul_nsmul (hn : (Nat.card α).Coprime n) (a : α) :
(n⁻¹ : ZMod (Nat.card α)).val • n • a = a := by
rw [nsmul_left_comm, nsmul_zmod_val_inv_nsmul hn]
end AddGroup
section Group
variable {α : Type*} [Group α] {n : ℕ}
| Mathlib/Data/ZMod/Basic.lean | 1,235 | 1,244 |
/-
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, Sébastien Gouëzel,
Rémy Degenne, David Loeffler
-/
import Mathlib.Analysis.SpecialFunctions.Pow.Complex
import Qq
/-! # Power function on `ℝ`
We construct the power functions `x ^ y`, where `x` and `y` are real numbers.
-/
noncomputable section
open Real ComplexConjugate Finset Set
/-
## Definitions
-/
namespace Real
variable {x y z : ℝ}
/-- The real power function `x ^ y`, defined as the real part of the complex power function.
For `x > 0`, it is equal to `exp (y log x)`. For `x = 0`, one sets `0 ^ 0=1` and `0 ^ y=0` for
`y ≠ 0`. For `x < 0`, the definition is somewhat arbitrary as it depends on the choice of a complex
determination of the logarithm. With our conventions, it is equal to `exp (y log x) cos (π y)`. -/
noncomputable def rpow (x y : ℝ) :=
((x : ℂ) ^ (y : ℂ)).re
noncomputable instance : Pow ℝ ℝ := ⟨rpow⟩
@[simp]
theorem rpow_eq_pow (x y : ℝ) : rpow x y = x ^ y := rfl
theorem rpow_def (x y : ℝ) : x ^ y = ((x : ℂ) ^ (y : ℂ)).re := rfl
theorem rpow_def_of_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) := by
simp only [rpow_def, Complex.cpow_def]; split_ifs <;>
simp_all [(Complex.ofReal_log hx).symm, -Complex.ofReal_mul,
(Complex.ofReal_mul _ _).symm, Complex.exp_ofReal_re, Complex.ofReal_eq_zero]
theorem rpow_def_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : x ^ y = exp (log x * y) := by
rw [rpow_def_of_nonneg (le_of_lt hx), if_neg (ne_of_gt hx)]
theorem exp_mul (x y : ℝ) : exp (x * y) = exp x ^ y := by rw [rpow_def_of_pos (exp_pos _), log_exp]
@[simp, norm_cast]
theorem rpow_intCast (x : ℝ) (n : ℤ) : x ^ (n : ℝ) = x ^ n := by
simp only [rpow_def, ← Complex.ofReal_zpow, Complex.cpow_intCast, Complex.ofReal_intCast,
Complex.ofReal_re]
@[simp, norm_cast]
theorem rpow_natCast (x : ℝ) (n : ℕ) : x ^ (n : ℝ) = x ^ n := by simpa using rpow_intCast x n
@[simp]
theorem exp_one_rpow (x : ℝ) : exp 1 ^ x = exp x := by rw [← exp_mul, one_mul]
@[simp] lemma exp_one_pow (n : ℕ) : exp 1 ^ n = exp n := by rw [← rpow_natCast, exp_one_rpow]
theorem rpow_eq_zero_iff_of_nonneg (hx : 0 ≤ x) : x ^ y = 0 ↔ x = 0 ∧ y ≠ 0 := by
simp only [rpow_def_of_nonneg hx]
split_ifs <;> simp [*, exp_ne_zero]
@[simp]
lemma rpow_eq_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y = 0 ↔ x = 0 := by
simp [rpow_eq_zero_iff_of_nonneg, *]
@[simp]
lemma rpow_ne_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y ≠ 0 ↔ x ≠ 0 :=
Real.rpow_eq_zero hx hy |>.not
open Real
theorem rpow_def_of_neg {x : ℝ} (hx : x < 0) (y : ℝ) : x ^ y = exp (log x * y) * cos (y * π) := by
rw [rpow_def, Complex.cpow_def, if_neg]
· have : Complex.log x * y = ↑(log (-x) * y) + ↑(y * π) * Complex.I := by
simp only [Complex.log, Complex.norm_real, norm_eq_abs, abs_of_neg hx, log_neg_eq_log,
Complex.arg_ofReal_of_neg hx, Complex.ofReal_mul]
ring
rw [this, Complex.exp_add_mul_I, ← Complex.ofReal_exp, ← Complex.ofReal_cos, ←
Complex.ofReal_sin, mul_add, ← Complex.ofReal_mul, ← mul_assoc, ← Complex.ofReal_mul,
Complex.add_re, Complex.ofReal_re, Complex.mul_re, Complex.I_re, Complex.ofReal_im,
Real.log_neg_eq_log]
ring
· rw [Complex.ofReal_eq_zero]
exact ne_of_lt hx
theorem rpow_def_of_nonpos {x : ℝ} (hx : x ≤ 0) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) * cos (y * π) := by
split_ifs with h <;> simp [rpow_def, *]; exact rpow_def_of_neg (lt_of_le_of_ne hx h) _
@[bound]
theorem rpow_pos_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : 0 < x ^ y := by
rw [rpow_def_of_pos hx]; apply exp_pos
@[simp]
theorem rpow_zero (x : ℝ) : x ^ (0 : ℝ) = 1 := by simp [rpow_def]
theorem rpow_zero_pos (x : ℝ) : 0 < x ^ (0 : ℝ) := by simp
@[simp]
theorem zero_rpow {x : ℝ} (h : x ≠ 0) : (0 : ℝ) ^ x = 0 := by simp [rpow_def, *]
theorem zero_rpow_eq_iff {x : ℝ} {a : ℝ} : 0 ^ x = a ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
constructor
· intro hyp
simp only [rpow_def, Complex.ofReal_zero] at hyp
by_cases h : x = 0
· subst h
simp only [Complex.one_re, Complex.ofReal_zero, Complex.cpow_zero] at hyp
exact Or.inr ⟨rfl, hyp.symm⟩
· rw [Complex.zero_cpow (Complex.ofReal_ne_zero.mpr h)] at hyp
exact Or.inl ⟨h, hyp.symm⟩
· rintro (⟨h, rfl⟩ | ⟨rfl, rfl⟩)
· exact zero_rpow h
· exact rpow_zero _
theorem eq_zero_rpow_iff {x : ℝ} {a : ℝ} : a = 0 ^ x ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
rw [← zero_rpow_eq_iff, eq_comm]
@[simp]
theorem rpow_one (x : ℝ) : x ^ (1 : ℝ) = x := by simp [rpow_def]
| @[simp]
| Mathlib/Analysis/SpecialFunctions/Pow/Real.lean | 128 | 128 |
/-
Copyright (c) 2020 Johan Commelin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johan Commelin
-/
import Mathlib.RingTheory.WittVector.Frobenius
import Mathlib.RingTheory.WittVector.Verschiebung
import Mathlib.RingTheory.WittVector.MulP
/-!
## Identities between operations on the ring of Witt vectors
In this file we derive common identities between the Frobenius and Verschiebung operators.
## Main declarations
* `frobenius_verschiebung`: the composition of Frobenius and Verschiebung is multiplication by `p`
* `verschiebung_mul_frobenius`: the “projection formula”: `V(x * F y) = V x * y`
* `iterate_verschiebung_mul_coeff`: an identity from [Haze09] 6.2
## References
* [Hazewinkel, *Witt Vectors*][Haze09]
* [Commelin and Lewis, *Formalizing the Ring of Witt Vectors*][CL21]
-/
namespace WittVector
variable {p : ℕ} {R : Type*} [hp : Fact p.Prime] [CommRing R]
-- type as `\bbW`
local notation "𝕎" => WittVector p
noncomputable section
-- Porting note: `ghost_calc` failure: `simp only []` and the manual instances had to be added.
/-- The composition of Frobenius and Verschiebung is multiplication by `p`. -/
theorem frobenius_verschiebung (x : 𝕎 R) : frobenius (verschiebung x) = x * p := by
have : IsPoly p fun {R} [CommRing R] x ↦ frobenius (verschiebung x) :=
IsPoly.comp (hg := frobenius_isPoly p) (hf := verschiebung_isPoly)
have : IsPoly p fun {R} [CommRing R] x ↦ x * p := mulN_isPoly p p
ghost_calc x
ghost_simp [mul_comm]
/-- Verschiebung is the same as multiplication by `p` on the ring of Witt vectors of `ZMod p`. -/
theorem verschiebung_zmod (x : 𝕎 (ZMod p)) : verschiebung x = x * p := by
rw [← frobenius_verschiebung, frobenius_zmodp]
variable (p R)
theorem coeff_p_pow [CharP R p] (i : ℕ) : ((p : 𝕎 R) ^ i).coeff i = 1 := by
induction' i with i h
· simp only [one_coeff_zero, Ne, pow_zero]
· rw [pow_succ, ← frobenius_verschiebung, coeff_frobenius_charP,
verschiebung_coeff_succ, h, one_pow]
theorem coeff_p_pow_eq_zero [CharP R p] {i j : ℕ} (hj : j ≠ i) : ((p : 𝕎 R) ^ i).coeff j = 0 := by
induction' i with i hi generalizing j
· rw [pow_zero, one_coeff_eq_of_pos]
exact Nat.pos_of_ne_zero hj
· rw [pow_succ, ← frobenius_verschiebung, coeff_frobenius_charP]
cases j
· rw [verschiebung_coeff_zero, zero_pow hp.out.ne_zero]
· rw [verschiebung_coeff_succ, hi (ne_of_apply_ne _ hj), zero_pow hp.out.ne_zero]
theorem coeff_p [CharP R p] (i : ℕ) : (p : 𝕎 R).coeff i = if i = 1 then 1 else 0 := by
split_ifs with hi
· simpa only [hi, pow_one] using coeff_p_pow p R 1
· simpa only [pow_one] using coeff_p_pow_eq_zero p R hi
@[simp]
theorem coeff_p_zero [CharP R p] : (p : 𝕎 R).coeff 0 = 0 := by
rw [coeff_p, if_neg]
exact zero_ne_one
@[simp]
theorem coeff_p_one [CharP R p] : (p : 𝕎 R).coeff 1 = 1 := by rw [coeff_p, if_pos rfl]
theorem p_nonzero [Nontrivial R] [CharP R p] : (p : 𝕎 R) ≠ 0 := by
intro h
simpa only [h, zero_coeff, zero_ne_one] using coeff_p_one p R
theorem FractionRing.p_nonzero [Nontrivial R] [CharP R p] : (p : FractionRing (𝕎 R)) ≠ 0 := by
simpa using (IsFractionRing.injective (𝕎 R) (FractionRing (𝕎 R))).ne (WittVector.p_nonzero _ _)
variable {p R}
-- Porting note: `ghost_calc` failure: `simp only []` and the manual instances had to be added.
/-- The “projection formula” for Frobenius and Verschiebung. -/
theorem verschiebung_mul_frobenius (x y : 𝕎 R) :
verschiebung (x * frobenius y) = verschiebung x * y := by
have : IsPoly₂ p fun {R} [Rcr : CommRing R] x y ↦ verschiebung (x * frobenius y) :=
IsPoly.comp₂ (hg := verschiebung_isPoly)
(hf := IsPoly₂.comp (hh := mulIsPoly₂) (hf := idIsPolyI' p) (hg := frobenius_isPoly p))
have : IsPoly₂ p fun {R} [CommRing R] x y ↦ verschiebung x * y :=
IsPoly₂.comp (hh := mulIsPoly₂) (hf := verschiebung_isPoly) (hg := idIsPolyI' p)
ghost_calc x y
rintro ⟨⟩ <;> ghost_simp [mul_assoc]
theorem mul_charP_coeff_zero [CharP R p] (x : 𝕎 R) : (x * p).coeff 0 = 0 := by
rw [← frobenius_verschiebung, coeff_frobenius_charP, verschiebung_coeff_zero,
zero_pow hp.out.ne_zero]
theorem mul_charP_coeff_succ [CharP R p] (x : 𝕎 R) (i : ℕ) :
(x * p).coeff (i + 1) = x.coeff i ^ p := by
rw [← frobenius_verschiebung, coeff_frobenius_charP, verschiebung_coeff_succ]
theorem mul_pow_charP_coeff_zero [CharP R p] (x : 𝕎 R) {m n : ℕ} (h : m < n) :
(x * p ^ n).coeff m = 0 := by
induction' n with n ih generalizing m
· contradiction
· rw [pow_succ, ← mul_assoc]
cases m with
| zero => exact mul_charP_coeff_zero _
| succ m' =>
rw [mul_charP_coeff_succ, ih, zero_pow hp.out.ne_zero]
simpa using h
theorem mul_pow_charP_coeff_succ [CharP R p] (x : 𝕎 R) {m n : ℕ} :
(x * p ^ n).coeff (m + n) = x.coeff m ^ (p ^ n) := by
induction' n with n ih generalizing m
· simp
· rw [pow_succ, ← mul_assoc, ← add_assoc,mul_charP_coeff_succ, pow_succ, pow_mul]
congr
exact ih
theorem verschiebung_frobenius [CharP R p] (x : 𝕎 R) : verschiebung (frobenius x) = x * p := by
ext ⟨i⟩
· rw [mul_charP_coeff_zero, verschiebung_coeff_zero]
· rw [mul_charP_coeff_succ, verschiebung_coeff_succ, coeff_frobenius_charP]
theorem verschiebung_frobenius_comm [CharP R p] :
Function.Commute (verschiebung : 𝕎 R → 𝕎 R) frobenius := fun x => by
rw [verschiebung_frobenius, frobenius_verschiebung]
/-!
## Iteration lemmas
-/
|
open Function
theorem iterate_verschiebung_coeff_eq_zero (x : 𝕎 R) {n : ℕ} {m : ℕ} (h : m < n) :
(verschiebung^[n] x).coeff m = 0 := by
induction' n with n ih generalizing m
| Mathlib/RingTheory/WittVector/Identities.lean | 142 | 147 |
/-
Copyright (c) 2021 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes
-/
import Mathlib.RingTheory.Finiteness.Basic
import Mathlib.RingTheory.Finiteness.Nakayama
import Mathlib.RingTheory.Jacobson.Ideal
/-!
# Nakayama's lemma
This file contains some alternative statements of Nakayama's Lemma as found in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV).
## Main statements
* `Submodule.eq_smul_of_le_smul_of_le_jacobson` - A version of (2) in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV),
generalising to the Jacobson of any ideal.
* `Submodule.eq_bot_of_le_smul_of_le_jacobson_bot` - Statement (2) in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV).
* `Submodule.sup_smul_eq_sup_smul_of_le_smul_of_le_jacobson` - A version of (4) in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV),
generalising to the Jacobson of any ideal.
* `Submodule.smul_le_of_le_smul_of_le_jacobson_bot` - Statement (4) in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV).
Note that a version of Statement (1) in
[Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV) can be found in
`RingTheory.Finiteness` under the name
`Submodule.exists_sub_one_mem_and_smul_eq_zero_of_fg_of_le_smul`
## References
* [Stacks: Nakayama's Lemma](https://stacks.math.columbia.edu/tag/00DV)
## Tags
Nakayama, Jacobson
-/
variable {R M : Type*} [CommRing R] [AddCommGroup M] [Module R M]
open Ideal
namespace Submodule
/-- **Nakayama's Lemma** - A slightly more general version of (2) in
[Stacks 00DV](https://stacks.math.columbia.edu/tag/00DV).
See also `eq_bot_of_le_smul_of_le_jacobson_bot` for the special case when `J = ⊥`. -/
@[stacks 00DV "(2)"]
theorem eq_smul_of_le_smul_of_le_jacobson {I J : Ideal R} {N : Submodule R M} (hN : N.FG)
(hIN : N ≤ I • N) (hIjac : I ≤ jacobson J) : N = J • N := by
refine le_antisymm ?_ (Submodule.smul_le.2 fun _ _ _ => Submodule.smul_mem _ _)
intro n hn
obtain ⟨r, hr⟩ := Submodule.exists_sub_one_mem_and_smul_eq_zero_of_fg_of_le_smul I N hN hIN
obtain ⟨s, hs⟩ := exists_mul_sub_mem_of_sub_one_mem_jacobson r (hIjac hr.1)
have : n = -(s * r - 1) • n := by
rw [neg_sub, sub_smul, mul_smul, hr.2 n hn, one_smul, smul_zero, sub_zero]
rw [this]
exact Submodule.smul_mem_smul (Submodule.neg_mem _ hs) hn
lemma eq_bot_of_eq_ideal_smul_of_le_jacobson_annihilator {I : Ideal R}
{N : Submodule R M} (hN : FG N) (hIN : N = I • N)
(hIjac : I ≤ N.annihilator.jacobson) : N = ⊥ :=
(eq_smul_of_le_smul_of_le_jacobson hN hIN.le hIjac).trans N.annihilator_smul
open Pointwise in
lemma eq_bot_of_eq_pointwise_smul_of_mem_jacobson_annihilator {r : R}
{N : Submodule R M} (hN : FG N) (hrN : N = r • N)
(hrJac : r ∈ N.annihilator.jacobson) : N = ⊥ :=
eq_bot_of_eq_ideal_smul_of_le_jacobson_annihilator hN
(Eq.trans hrN (ideal_span_singleton_smul r N).symm)
((span_singleton_le_iff_mem r _).mpr hrJac)
open Pointwise in
lemma eq_bot_of_set_smul_eq_of_subset_jacobson_annihilator {s : Set R}
{N : Submodule R M} (hN : FG N) (hsN : N = s • N)
(hsJac : s ⊆ N.annihilator.jacobson) : N = ⊥ :=
eq_bot_of_eq_ideal_smul_of_le_jacobson_annihilator hN
(Eq.trans hsN (span_smul_eq s N).symm) (span_le.mpr hsJac)
lemma top_ne_ideal_smul_of_le_jacobson_annihilator [Nontrivial M]
[Module.Finite R M] {I} (h : I ≤ (Module.annihilator R M).jacobson) :
(⊤ : Submodule R M) ≠ I • ⊤ := fun H => top_ne_bot <|
eq_bot_of_eq_ideal_smul_of_le_jacobson_annihilator Module.Finite.fg_top H <|
(congrArg (I ≤ Ideal.jacobson ·) annihilator_top).mpr h
open Pointwise in
lemma top_ne_set_smul_of_subset_jacobson_annihilator [Nontrivial M]
[Module.Finite R M] {s : Set R}
(h : s ⊆ (Module.annihilator R M).jacobson) :
(⊤ : Submodule R M) ≠ s • ⊤ :=
ne_of_ne_of_eq (top_ne_ideal_smul_of_le_jacobson_annihilator (span_le.mpr h))
(span_smul_eq _ _)
open Pointwise in
lemma top_ne_pointwise_smul_of_mem_jacobson_annihilator [Nontrivial M]
[Module.Finite R M] {r} (h : r ∈ (Module.annihilator R M).jacobson) :
(⊤ : Submodule R M) ≠ r • ⊤ :=
ne_of_ne_of_eq (top_ne_set_smul_of_subset_jacobson_annihilator <|
Set.singleton_subset_iff.mpr h) (singleton_set_smul ⊤ r)
/-- **Nakayama's Lemma** - Statement (2) in
[Stacks 00DV](https://stacks.math.columbia.edu/tag/00DV).
See also `eq_smul_of_le_smul_of_le_jacobson` for a generalisation
to the `jacobson` of any ideal -/
@[stacks 00DV "(2)"]
theorem eq_bot_of_le_smul_of_le_jacobson_bot (I : Ideal R) (N : Submodule R M) (hN : N.FG)
(hIN : N ≤ I • N) (hIjac : I ≤ jacobson ⊥) : N = ⊥ := by
rw [eq_smul_of_le_smul_of_le_jacobson hN hIN hIjac, Submodule.bot_smul]
theorem sup_eq_sup_smul_of_le_smul_of_le_jacobson {I J : Ideal R} {N N' : Submodule R M}
(hN' : N'.FG) (hIJ : I ≤ jacobson J) (hNN : N' ≤ N ⊔ I • N') : N ⊔ N' = N ⊔ J • N' := by
have hNN' : N ⊔ N' = N ⊔ I • N' :=
le_antisymm (sup_le le_sup_left hNN)
(sup_le_sup_left (Submodule.smul_le.2 fun _ _ _ => Submodule.smul_mem _ _) _)
have h_comap :=
comap_injective_of_surjective (LinearMap.range_eq_top.1 N.range_mkQ)
have : (I • N').map N.mkQ = N'.map N.mkQ := by
simpa only [← h_comap.eq_iff, comap_map_mkQ, sup_comm, eq_comm] using hNN'
have :=
@Submodule.eq_smul_of_le_smul_of_le_jacobson _ _ _ _ _ I J (N'.map N.mkQ) (hN'.map _)
(by rw [← map_smul'', this]) hIJ
rwa [← map_smul'', ← h_comap.eq_iff, comap_map_eq, comap_map_eq, Submodule.ker_mkQ, sup_comm,
sup_comm (b := N)] at this
/-- **Nakayama's Lemma** - A slightly more general version of (4) in
[Stacks 00DV](https://stacks.math.columbia.edu/tag/00DV).
See also `smul_le_of_le_smul_of_le_jacobson_bot` for the special case when `J = ⊥`. -/
@[stacks 00DV "(4)"]
theorem sup_smul_eq_sup_smul_of_le_smul_of_le_jacobson {I J : Ideal R} {N N' : Submodule R M}
(hN' : N'.FG) (hIJ : I ≤ jacobson J) (hNN : N' ≤ N ⊔ I • N') : N ⊔ I • N' = N ⊔ J • N' :=
((sup_le_sup_left smul_le_right _).antisymm (sup_le le_sup_left hNN)).trans
(sup_eq_sup_smul_of_le_smul_of_le_jacobson hN' hIJ hNN)
|
theorem le_of_le_smul_of_le_jacobson_bot {R M} [CommRing R] [AddCommGroup M] [Module R M]
{I : Ideal R} {N N' : Submodule R M} (hN' : N'.FG)
(hIJ : I ≤ jacobson ⊥) (hNN : N' ≤ N ⊔ I • N') : N' ≤ N := by
| Mathlib/RingTheory/Nakayama.lean | 137 | 140 |
/-
Copyright (c) 2024 Jz Pan. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jz Pan
-/
import Mathlib.LinearAlgebra.Dimension.Free
import Mathlib.LinearAlgebra.Dimension.Finite
import Mathlib.LinearAlgebra.FreeModule.StrongRankCondition
/-!
# Some results on the ranks of subalgebras
This file contains some results on the ranks of subalgebras,
which are corollaries of `rank_mul_rank`.
Since their proof essentially depends on the fact that a non-trivial commutative ring
satisfies strong rank condition, we put them into a separate file.
-/
open Module
namespace Subalgebra
variable {R S : Type*} [CommRing R] [CommRing S] [Algebra R S]
(A B : Subalgebra R S)
section
variable [Module.Free R A] [Module.Free A (Algebra.adjoin A (B : Set S))]
theorem rank_sup_eq_rank_left_mul_rank_of_free :
Module.rank R ↥(A ⊔ B) = Module.rank R A * Module.rank A (Algebra.adjoin A (B : Set S)) := by
rcases subsingleton_or_nontrivial R with _ | _
· haveI := Module.subsingleton R S; simp
nontriviality S using rank_subsingleton'
letI : Algebra A (Algebra.adjoin A (B : Set S)) := Subalgebra.algebra _
letI : SMul A (Algebra.adjoin A (B : Set S)) := Algebra.toSMul
haveI : IsScalarTower R A (Algebra.adjoin A (B : Set S)) :=
IsScalarTower.of_algebraMap_eq (congrFun rfl)
rw [rank_mul_rank R A (Algebra.adjoin A (B : Set S))]
change _ = Module.rank R ((Algebra.adjoin A (B : Set S)).restrictScalars R)
rw [Algebra.restrictScalars_adjoin]; rfl
|
theorem finrank_sup_eq_finrank_left_mul_finrank_of_free :
finrank R ↥(A ⊔ B) = finrank R A * finrank A (Algebra.adjoin A (B : Set S)) := by
| Mathlib/Algebra/Algebra/Subalgebra/Rank.lean | 43 | 45 |
/-
Copyright (c) 2021 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Riccardo Brasca, Adam Topaz, Jujian Zhang, Joël Riou
-/
import Mathlib.Algebra.Homology.Additive
import Mathlib.CategoryTheory.Abelian.Projective.Resolution
/-!
# Left-derived functors
We define the left-derived functors `F.leftDerived n : C ⥤ D` for any additive functor `F`
out of a category with projective resolutions.
We first define a functor
`F.leftDerivedToHomotopyCategory : C ⥤ HomotopyCategory D (ComplexShape.down ℕ)` which is
`projectiveResolutions C ⋙ F.mapHomotopyCategory _`. We show that if `X : C` and
`P : ProjectiveResolution X`, then `F.leftDerivedToHomotopyCategory.obj X` identifies
to the image in the homotopy category of the functor `F` applied objectwise to `P.complex`
(this isomorphism is `P.isoLeftDerivedToHomotopyCategoryObj F`).
Then, the left-derived functors `F.leftDerived n : C ⥤ D` are obtained by composing
`F.leftDerivedToHomotopyCategory` with the homology functors on the homotopy category.
Similarly we define natural transformations between left-derived functors coming from
natural transformations between the original additive functors,
and show how to compute the components.
## Main results
* `Functor.isZero_leftDerived_obj_projective_succ`: projective objects have no higher
left derived functor.
* `NatTrans.leftDerived`: the natural isomorphism between left derived functors
induced by natural transformation.
* `Functor.fromLeftDerivedZero`: the natural transformation `F.leftDerived 0 ⟶ F`,
which is an isomorphism when `F` is right exact (i.e. preserves finite colimits),
see also `Functor.leftDerivedZeroIsoSelf`.
## TODO
* refactor `Functor.leftDerived` (and `Functor.rightDerived`) when the necessary
material enters mathlib: derived categories, injective/projective derivability
structures, existence of derived functors from derivability structures.
Eventually, we shall get a right derived functor
`F.leftDerivedFunctorMinus : DerivedCategory.Minus C ⥤ DerivedCategory.Minus D`,
and `F.leftDerived` shall be redefined using `F.leftDerivedFunctorMinus`.
-/
universe v u
namespace CategoryTheory
open Category Limits
variable {C : Type u} [Category.{v} C] {D : Type*} [Category D]
[Abelian C] [HasProjectiveResolutions C] [Abelian D]
/-- When `F : C ⥤ D` is an additive functor, this is
the functor `C ⥤ HomotopyCategory D (ComplexShape.down ℕ)` which
sends `X : C` to `F` applied to a projective resolution of `X`. -/
noncomputable def Functor.leftDerivedToHomotopyCategory (F : C ⥤ D) [F.Additive] :
C ⥤ HomotopyCategory D (ComplexShape.down ℕ) :=
projectiveResolutions C ⋙ F.mapHomotopyCategory _
/-- If `P : ProjectiveResolution Z` and `F : C ⥤ D` is an additive functor, this is
an isomorphism between `F.leftDerivedToHomotopyCategory.obj X` and the complex
obtained by applying `F` to `P.complex`. -/
noncomputable def ProjectiveResolution.isoLeftDerivedToHomotopyCategoryObj {X : C}
(P : ProjectiveResolution X) (F : C ⥤ D) [F.Additive] :
F.leftDerivedToHomotopyCategory.obj X ≅
(F.mapHomologicalComplex _ ⋙ HomotopyCategory.quotient _ _).obj P.complex :=
(F.mapHomotopyCategory _).mapIso P.iso ≪≫
(F.mapHomotopyCategoryFactors _).app P.complex
@[reassoc]
lemma ProjectiveResolution.isoLeftDerivedToHomotopyCategoryObj_inv_naturality
{X Y : C} (f : X ⟶ Y) (P : ProjectiveResolution X) (Q : ProjectiveResolution Y)
(φ : P.complex ⟶ Q.complex) (comm : φ.f 0 ≫ Q.π.f 0 = P.π.f 0 ≫ f)
(F : C ⥤ D) [F.Additive] :
(P.isoLeftDerivedToHomotopyCategoryObj F).inv ≫ F.leftDerivedToHomotopyCategory.map f =
(F.mapHomologicalComplex _ ⋙ HomotopyCategory.quotient _ _).map φ ≫
(Q.isoLeftDerivedToHomotopyCategoryObj F).inv := by
dsimp [Functor.leftDerivedToHomotopyCategory, isoLeftDerivedToHomotopyCategoryObj]
rw [assoc, ← Functor.map_comp, iso_inv_naturality f P Q φ comm, Functor.map_comp]
erw [(F.mapHomotopyCategoryFactors (ComplexShape.down ℕ)).inv.naturality_assoc]
rfl
@[reassoc]
lemma ProjectiveResolution.isoLeftDerivedToHomotopyCategoryObj_hom_naturality
{X Y : C} (f : X ⟶ Y) (P : ProjectiveResolution X) (Q : ProjectiveResolution Y)
(φ : P.complex ⟶ Q.complex) (comm : φ.f 0 ≫ Q.π.f 0 = P.π.f 0 ≫ f)
(F : C ⥤ D) [F.Additive] :
F.leftDerivedToHomotopyCategory.map f ≫ (Q.isoLeftDerivedToHomotopyCategoryObj F).hom =
(P.isoLeftDerivedToHomotopyCategoryObj F).hom ≫
(F.mapHomologicalComplex _ ⋙ HomotopyCategory.quotient _ _).map φ := by
dsimp
rw [← cancel_epi (P.isoLeftDerivedToHomotopyCategoryObj F).inv, Iso.inv_hom_id_assoc,
isoLeftDerivedToHomotopyCategoryObj_inv_naturality_assoc f P Q φ comm F,
Iso.inv_hom_id, comp_id]
/-- The left derived functors of an additive functor. -/
noncomputable def Functor.leftDerived (F : C ⥤ D) [F.Additive] (n : ℕ) : C ⥤ D :=
F.leftDerivedToHomotopyCategory ⋙ HomotopyCategory.homologyFunctor D _ n
/-- We can compute a left derived functor using a chosen projective resolution. -/
noncomputable def ProjectiveResolution.isoLeftDerivedObj {X : C} (P : ProjectiveResolution X)
(F : C ⥤ D) [F.Additive] (n : ℕ) :
(F.leftDerived n).obj X ≅
(HomologicalComplex.homologyFunctor D _ n).obj
((F.mapHomologicalComplex _).obj P.complex) :=
(HomotopyCategory.homologyFunctor D _ n).mapIso
(P.isoLeftDerivedToHomotopyCategoryObj F) ≪≫
(HomotopyCategory.homologyFunctorFactors D (ComplexShape.down ℕ) n).app _
@[reassoc]
lemma ProjectiveResolution.isoLeftDerivedObj_hom_naturality
{X Y : C} (f : X ⟶ Y) (P : ProjectiveResolution X) (Q : ProjectiveResolution Y)
(φ : P.complex ⟶ Q.complex) (comm : φ.f 0 ≫ Q.π.f 0 = P.π.f 0 ≫ f)
(F : C ⥤ D) [F.Additive] (n : ℕ) :
(F.leftDerived n).map f ≫ (Q.isoLeftDerivedObj F n).hom =
(P.isoLeftDerivedObj F n).hom ≫
(F.mapHomologicalComplex _ ⋙ HomologicalComplex.homologyFunctor _ _ n).map φ := by
dsimp [isoLeftDerivedObj, Functor.leftDerived]
rw [assoc, ← Functor.map_comp_assoc,
ProjectiveResolution.isoLeftDerivedToHomotopyCategoryObj_hom_naturality f P Q φ comm F,
Functor.map_comp, assoc]
erw [(HomotopyCategory.homologyFunctorFactors D (ComplexShape.down ℕ) n).hom.naturality]
rfl
@[reassoc]
lemma ProjectiveResolution.isoLeftDerivedObj_inv_naturality
{X Y : C} (f : X ⟶ Y) (P : ProjectiveResolution X) (Q : ProjectiveResolution Y)
(φ : P.complex ⟶ Q.complex) (comm : φ.f 0 ≫ Q.π.f 0 = P.π.f 0 ≫ f)
(F : C ⥤ D) [F.Additive] (n : ℕ) :
(P.isoLeftDerivedObj F n).inv ≫ (F.leftDerived n).map f =
(F.mapHomologicalComplex _ ⋙ HomologicalComplex.homologyFunctor _ _ n).map φ ≫
(Q.isoLeftDerivedObj F n).inv := by
rw [← cancel_mono (Q.isoLeftDerivedObj F n).hom, assoc, assoc,
ProjectiveResolution.isoLeftDerivedObj_hom_naturality f P Q φ comm F n,
Iso.inv_hom_id_assoc, Iso.inv_hom_id, comp_id]
/-- The higher derived functors vanish on projective objects. -/
lemma Functor.isZero_leftDerived_obj_projective_succ
(F : C ⥤ D) [F.Additive] (n : ℕ) (X : C) [Projective X] :
IsZero ((F.leftDerived (n + 1)).obj X) := by
refine IsZero.of_iso ?_ ((ProjectiveResolution.self X).isoLeftDerivedObj F (n + 1))
erw [← HomologicalComplex.exactAt_iff_isZero_homology]
exact ShortComplex.exact_of_isZero_X₂ _ (F.map_isZero (by apply isZero_zero))
/-- We can compute a left derived functor on a morphism using a descent of that morphism
to a chain map between chosen projective resolutions.
-/
theorem Functor.leftDerived_map_eq (F : C ⥤ D) [F.Additive] (n : ℕ) {X Y : C} (f : X ⟶ Y)
{P : ProjectiveResolution X} {Q : ProjectiveResolution Y} (g : P.complex ⟶ Q.complex)
(w : g ≫ Q.π = P.π ≫ (ChainComplex.single₀ C).map f) :
(F.leftDerived n).map f =
(P.isoLeftDerivedObj F n).hom ≫
(F.mapHomologicalComplex _ ⋙ HomologicalComplex.homologyFunctor _ _ n).map g ≫
(Q.isoLeftDerivedObj F n).inv := by
rw [← cancel_mono (Q.isoLeftDerivedObj F n).hom,
ProjectiveResolution.isoLeftDerivedObj_hom_naturality f P Q g _ F n,
assoc, assoc, Iso.inv_hom_id, comp_id]
rw [← HomologicalComplex.comp_f, w, HomologicalComplex.comp_f,
ChainComplex.single₀_map_f_zero]
/-- The natural transformation
`F.leftDerivedToHomotopyCategory ⟶ G.leftDerivedToHomotopyCategory` induced by
a natural transformation `F ⟶ G` between additive functors. -/
noncomputable def NatTrans.leftDerivedToHomotopyCategory
{F G : C ⥤ D} [F.Additive] [G.Additive] (α : F ⟶ G) :
F.leftDerivedToHomotopyCategory ⟶ G.leftDerivedToHomotopyCategory :=
whiskerLeft _ (NatTrans.mapHomotopyCategory α (ComplexShape.down ℕ))
lemma ProjectiveResolution.leftDerivedToHomotopyCategory_app_eq
{F G : C ⥤ D} [F.Additive] [G.Additive] (α : F ⟶ G) {X : C} (P : ProjectiveResolution X) :
(NatTrans.leftDerivedToHomotopyCategory α).app X =
(P.isoLeftDerivedToHomotopyCategoryObj F).hom ≫
(HomotopyCategory.quotient _ _).map
((NatTrans.mapHomologicalComplex α _).app P.complex) ≫
(P.isoLeftDerivedToHomotopyCategoryObj G).inv := by
rw [← cancel_mono (P.isoLeftDerivedToHomotopyCategoryObj G).hom, assoc, assoc,
Iso.inv_hom_id, comp_id]
dsimp [isoLeftDerivedToHomotopyCategoryObj, Functor.mapHomotopyCategoryFactors,
NatTrans.leftDerivedToHomotopyCategory]
rw [assoc]
erw [id_comp, comp_id]
obtain ⟨β, hβ⟩ := (HomotopyCategory.quotient _ _).map_surjective (iso P).hom
rw [← hβ]
dsimp
simp only [← Functor.map_comp, NatTrans.mapHomologicalComplex_naturality]
rfl
@[simp]
lemma NatTrans.leftDerivedToHomotopyCategory_id (F : C ⥤ D) [F.Additive] :
NatTrans.leftDerivedToHomotopyCategory (𝟙 F) = 𝟙 _ := rfl
@[simp, reassoc]
lemma NatTrans.leftDerivedToHomotopyCategory_comp {F G H : C ⥤ D} (α : F ⟶ G) (β : G ⟶ H)
[F.Additive] [G.Additive] [H.Additive] :
NatTrans.leftDerivedToHomotopyCategory (α ≫ β) =
NatTrans.leftDerivedToHomotopyCategory α ≫
NatTrans.leftDerivedToHomotopyCategory β := rfl
/-- The natural transformation between left-derived functors induced by a natural transformation. -/
noncomputable def NatTrans.leftDerived
{F G : C ⥤ D} [F.Additive] [G.Additive] (α : F ⟶ G) (n : ℕ) :
F.leftDerived n ⟶ G.leftDerived n :=
whiskerRight (NatTrans.leftDerivedToHomotopyCategory α) _
@[simp]
theorem NatTrans.leftDerived_id (F : C ⥤ D) [F.Additive] (n : ℕ) :
NatTrans.leftDerived (𝟙 F) n = 𝟙 (F.leftDerived n) := by
dsimp only [leftDerived]
simp only [leftDerivedToHomotopyCategory_id, whiskerRight_id']
rfl
@[simp, reassoc]
theorem NatTrans.leftDerived_comp {F G H : C ⥤ D} [F.Additive] [G.Additive] [H.Additive]
(α : F ⟶ G) (β : G ⟶ H) (n : ℕ) :
NatTrans.leftDerived (α ≫ β) n = NatTrans.leftDerived α n ≫ NatTrans.leftDerived β n := by
simp [NatTrans.leftDerived]
namespace ProjectiveResolution
/-- A component of the natural transformation between left-derived functors can be computed
using a chosen projective resolution. -/
lemma leftDerived_app_eq
{F G : C ⥤ D} [F.Additive] [G.Additive] (α : F ⟶ G) {X : C} (P : ProjectiveResolution X)
(n : ℕ) : (NatTrans.leftDerived α n).app X =
(P.isoLeftDerivedObj F n).hom ≫
(HomologicalComplex.homologyFunctor D (ComplexShape.down ℕ) n).map
((NatTrans.mapHomologicalComplex α _).app P.complex) ≫
| (P.isoLeftDerivedObj G n).inv := by
dsimp [NatTrans.leftDerived, isoLeftDerivedObj]
rw [ProjectiveResolution.leftDerivedToHomotopyCategory_app_eq α P,
Functor.map_comp, Functor.map_comp, assoc]
erw [← (HomotopyCategory.homologyFunctorFactors D (ComplexShape.down ℕ) n).hom.naturality_assoc
((NatTrans.mapHomologicalComplex α (ComplexShape.down ℕ)).app P.complex)]
simp only [Functor.comp_map, Iso.hom_inv_id_app_assoc]
/-- If `P : ProjectiveResolution X` and `F` is an additive functor, this is
the canonical morphism from the opcycles in degree `0` of
`(F.mapHomologicalComplex _).obj P.complex` to `F.obj X`. -/
noncomputable def fromLeftDerivedZero' {X : C}
(P : ProjectiveResolution X) (F : C ⥤ D) [F.Additive] :
((F.mapHomologicalComplex _).obj P.complex).opcycles 0 ⟶ F.obj X :=
HomologicalComplex.descOpcycles _ (F.map (P.π.f 0)) 1 (by simp) (by
| Mathlib/CategoryTheory/Abelian/LeftDerived.lean | 233 | 247 |
/-
Copyright (c) 2022 George Peter Banyard, Yaël Dillies, Kyle Miller. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: George Peter Banyard, Yaël Dillies, Kyle Miller
-/
import Mathlib.Combinatorics.SimpleGraph.Path
import Mathlib.Combinatorics.SimpleGraph.Metric
/-!
# Graph products
This file defines the box product of graphs and other product constructions. The box product of `G`
and `H` is the graph on the product of the vertices such that `x` and `y` are related iff they agree
on one component and the other one is related via either `G` or `H`. For example, the box product of
two edges is a square.
## Main declarations
* `SimpleGraph.boxProd`: The box product.
## Notation
* `G □ H`: The box product of `G` and `H`.
## TODO
Define all other graph products!
-/
variable {α β γ : Type*}
namespace SimpleGraph
variable {G : SimpleGraph α} {H : SimpleGraph β}
/-- Box product of simple graphs. It relates `(a₁, b)` and `(a₂, b)` if `G` relates `a₁` and `a₂`,
and `(a, b₁)` and `(a, b₂)` if `H` relates `b₁` and `b₂`. -/
def boxProd (G : SimpleGraph α) (H : SimpleGraph β) : SimpleGraph (α × β) where
Adj x y := G.Adj x.1 y.1 ∧ x.2 = y.2 ∨ H.Adj x.2 y.2 ∧ x.1 = y.1
symm x y := by simp [and_comm, or_comm, eq_comm, adj_comm]
loopless x := by simp
/-- Box product of simple graphs. It relates `(a₁, b)` and `(a₂, b)` if `G` relates `a₁` and `a₂`,
and `(a, b₁)` and `(a, b₂)` if `H` relates `b₁` and `b₂`. -/
infixl:70 " □ " => boxProd
@[simp]
theorem boxProd_adj {x y : α × β} :
(G □ H).Adj x y ↔ G.Adj x.1 y.1 ∧ x.2 = y.2 ∨ H.Adj x.2 y.2 ∧ x.1 = y.1 :=
Iff.rfl
theorem boxProd_adj_left {a₁ : α} {b : β} {a₂ : α} :
(G □ H).Adj (a₁, b) (a₂, b) ↔ G.Adj a₁ a₂ := by
simp only [boxProd_adj, and_true, SimpleGraph.irrefl, false_and, or_false]
theorem boxProd_adj_right {a : α} {b₁ b₂ : β} : (G □ H).Adj (a, b₁) (a, b₂) ↔ H.Adj b₁ b₂ := by
simp only [boxProd_adj, SimpleGraph.irrefl, false_and, and_true, false_or]
theorem boxProd_neighborSet (x : α × β) :
(G □ H).neighborSet x = G.neighborSet x.1 ×ˢ {x.2} ∪ {x.1} ×ˢ H.neighborSet x.2 := by
ext ⟨a', b'⟩
simp only [mem_neighborSet, Set.mem_union, boxProd_adj, Set.mem_prod, Set.mem_singleton_iff]
simp only [eq_comm, and_comm]
variable (G H)
/-- The box product is commutative up to isomorphism. `Equiv.prodComm` as a graph isomorphism. -/
@[simps!]
def boxProdComm : G □ H ≃g H □ G := ⟨Equiv.prodComm _ _, or_comm⟩
/-- The box product is associative up to isomorphism. `Equiv.prodAssoc` as a graph isomorphism. -/
@[simps!]
def boxProdAssoc (I : SimpleGraph γ) : G □ H □ I ≃g G □ (H □ I) :=
⟨Equiv.prodAssoc _ _ _, fun {x y} => by
simp only [boxProd_adj, Equiv.prodAssoc_apply, or_and_right, or_assoc, Prod.ext_iff,
and_assoc, @and_comm (x.fst.fst = _)]⟩
/-- The embedding of `G` into `G □ H` given by `b`. -/
@[simps]
def boxProdLeft (b : β) : G ↪g G □ H where
toFun a := (a, b)
inj' _ _ := congr_arg Prod.fst
map_rel_iff' {_ _} := boxProd_adj_left
/-- The embedding of `H` into `G □ H` given by `a`. -/
@[simps]
def boxProdRight (a : α) : H ↪g G □ H where
toFun := Prod.mk a
inj' _ _ := congr_arg Prod.snd
map_rel_iff' {_ _} := boxProd_adj_right
namespace Walk
variable {G}
/-- Turn a walk on `G` into a walk on `G □ H`. -/
protected def boxProdLeft {a₁ a₂ : α} (b : β) : G.Walk a₁ a₂ → (G □ H).Walk (a₁, b) (a₂, b) :=
Walk.map (G.boxProdLeft H b).toHom
variable (G) {H}
/-- Turn a walk on `H` into a walk on `G □ H`. -/
protected def boxProdRight {b₁ b₂ : β} (a : α) : H.Walk b₁ b₂ → (G □ H).Walk (a, b₁) (a, b₂) :=
Walk.map (G.boxProdRight H a).toHom
variable {G}
/-- Project a walk on `G □ H` to a walk on `G` by discarding the moves in the direction of `H`. -/
def ofBoxProdLeft [DecidableEq β] [DecidableRel G.Adj] {x y : α × β} :
(G □ H).Walk x y → G.Walk x.1 y.1
| nil => nil
| cons h w =>
Or.by_cases h
(fun hG => w.ofBoxProdLeft.cons hG.1)
(fun hH => hH.2 ▸ w.ofBoxProdLeft)
/-- Project a walk on `G □ H` to a walk on `H` by discarding the moves in the direction of `G`. -/
def ofBoxProdRight [DecidableEq α] [DecidableRel H.Adj] {x y : α × β} :
(G □ H).Walk x y → H.Walk x.2 y.2
| nil => nil
| cons h w =>
(Or.symm h).by_cases
(fun hH => w.ofBoxProdRight.cons hH.1)
(fun hG => hG.2 ▸ w.ofBoxProdRight)
@[simp]
theorem ofBoxProdLeft_boxProdLeft [DecidableEq β] [DecidableRel G.Adj] {a₁ a₂ : α} {b : β} :
∀ (w : G.Walk a₁ a₂), (w.boxProdLeft H b).ofBoxProdLeft = w
| nil => rfl
| cons' x y z h w => by
rw [Walk.boxProdLeft, map_cons, ofBoxProdLeft, Or.by_cases, dif_pos, ← Walk.boxProdLeft]
· simp [ofBoxProdLeft_boxProdLeft]
· exact ⟨h, rfl⟩
@[simp]
theorem ofBoxProdLeft_boxProdRight [DecidableEq α] [DecidableRel G.Adj] {a b₁ b₂ : α} :
∀ (w : G.Walk b₁ b₂), (w.boxProdRight G a).ofBoxProdRight = w
| nil => rfl
| cons' x y z h w => by
rw [Walk.boxProdRight, map_cons, ofBoxProdRight, Or.by_cases, dif_pos, ←
Walk.boxProdRight]
· simp [ofBoxProdLeft_boxProdRight]
· exact ⟨h, rfl⟩
lemma length_boxProd {a₁ a₂ : α} {b₁ b₂ : β} [DecidableEq α] [DecidableEq β]
[DecidableRel G.Adj] [DecidableRel H.Adj] (w : (G □ H).Walk (a₁, b₁) (a₂, b₂)) :
w.length = w.ofBoxProdLeft.length + w.ofBoxProdRight.length := by
match w with
| .nil => simp [ofBoxProdLeft, ofBoxProdRight]
| .cons x w' => next c =>
unfold ofBoxProdLeft ofBoxProdRight
rw [length_cons, length_boxProd w']
have disj : (G.Adj a₁ c.1 ∧ b₁ = c.2) ∨ (H.Adj b₁ c.2 ∧ a₁ = c.1) := by aesop
rcases disj with h₁ | h₂
· simp only [h₁, irrefl, false_and, and_self, ↓reduceDIte, length_cons, Or.by_cases]
rw [add_comm, add_comm w'.ofBoxProdLeft.length 1, add_assoc]
congr <;> simp [h₁.2.symm]
· simp only [h₂, irrefl, false_and, ↓reduceDIte, length_cons, add_assoc, Or.by_cases]
congr <;> simp [h₂.2.symm]
end Walk
variable {G H}
protected theorem Preconnected.boxProd (hG : G.Preconnected) (hH : H.Preconnected) :
(G □ H).Preconnected := by
rintro x y
obtain ⟨w₁⟩ := hG x.1 y.1
obtain ⟨w₂⟩ := hH x.2 y.2
exact ⟨(w₁.boxProdLeft _ _).append (w₂.boxProdRight _ _)⟩
protected theorem Preconnected.ofBoxProdLeft [Nonempty β] (h : (G □ H).Preconnected) :
G.Preconnected := by
classical
rintro a₁ a₂
obtain ⟨w⟩ := h (a₁, Classical.arbitrary _) (a₂, Classical.arbitrary _)
exact ⟨w.ofBoxProdLeft⟩
protected theorem Preconnected.ofBoxProdRight [Nonempty α] (h : (G □ H).Preconnected) :
H.Preconnected := by
classical
| rintro b₁ b₂
obtain ⟨w⟩ := h (Classical.arbitrary _, b₁) (Classical.arbitrary _, b₂)
exact ⟨w.ofBoxProdRight⟩
protected theorem Connected.boxProd (hG : G.Connected) (hH : H.Connected) : (G □ H).Connected := by
haveI := hG.nonempty
| Mathlib/Combinatorics/SimpleGraph/Prod.lean | 182 | 187 |
/-
Copyright (c) 2023 Rémy Degenne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Rémy Degenne
-/
import Mathlib.Probability.Independence.Kernel
import Mathlib.Probability.Kernel.Condexp
/-!
# Conditional Independence
We define conditional independence of sets/σ-algebras/functions with respect to a σ-algebra.
Two σ-algebras `m₁` and `m₂` are conditionally independent given a third σ-algebra `m'` if for all
`m₁`-measurable sets `t₁` and `m₂`-measurable sets `t₂`,
`μ⟦t₁ ∩ t₂ | m'⟧ =ᵐ[μ] μ⟦t₁ | m'⟧ * μ⟦t₂ | m'⟧`.
On standard Borel spaces, the conditional expectation with respect to `m'` defines a kernel
`ProbabilityTheory.condExpKernel`, and the definition above is equivalent to
`∀ᵐ ω ∂μ, condExpKernel μ m' ω (t₁ ∩ t₂) = condExpKernel μ m' ω t₁ * condExpKernel μ m' ω t₂`.
We use this property as the definition of conditional independence.
## Main definitions
We provide four definitions of conditional independence:
* `iCondIndepSets`: conditional independence of a family of sets of sets `pi : ι → Set (Set Ω)`.
This is meant to be used with π-systems.
* `iCondIndep`: conditional independence of a family of measurable space structures
`m : ι → MeasurableSpace Ω`,
* `iCondIndepSet`: conditional independence of a family of sets `s : ι → Set Ω`,
* `iCondIndepFun`: conditional independence of a family of functions. For measurable spaces
`m : Π (i : ι), MeasurableSpace (β i)`, we consider functions `f : Π (i : ι), Ω → β i`.
Additionally, we provide four corresponding statements for two measurable space structures (resp.
sets of sets, sets, functions) instead of a family. These properties are denoted by the same names
as for a family, but without the starting `i`, for example `CondIndepFun` is the version of
`iCondIndepFun` for two functions.
## Main statements
* `ProbabilityTheory.iCondIndepSets.iCondIndep`: if π-systems are conditionally independent as sets
of sets, then the measurable space structures they generate are conditionally independent.
* `ProbabilityTheory.condIndepSets.condIndep`: variant with two π-systems.
## Implementation notes
The definitions of conditional independence in this file are a particular case of independence with
respect to a kernel and a measure, as defined in the file `Probability/Independence/Kernel.lean`.
The kernel used is `ProbabilityTheory.condExpKernel`.
-/
open MeasureTheory MeasurableSpace
open scoped MeasureTheory ENNReal
namespace ProbabilityTheory
variable {Ω ι : Type*}
section Definitions
section
variable (m' : MeasurableSpace Ω) {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω] (hm' : m' ≤ mΩ)
/-- A family of sets of sets `π : ι → Set (Set Ω)` is conditionally independent given `m'` with
respect to a measure `μ` if for any finite set of indices `s = {i_1, ..., i_n}`, for any sets
`f i_1 ∈ π i_1, ..., f i_n ∈ π i_n`, then `μ⟦⋂ i in s, f i | m'⟧ =ᵐ[μ] ∏ i ∈ s, μ⟦f i | m'⟧`.
See `ProbabilityTheory.iCondIndepSets_iff`.
It will be used for families of pi_systems. -/
def iCondIndepSets (π : ι → Set (Set Ω)) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] :
Prop :=
Kernel.iIndepSets π (condExpKernel μ m') (μ.trim hm')
/-- Two sets of sets `s₁, s₂` are conditionally independent given `m'` with respect to a measure
`μ` if for any sets `t₁ ∈ s₁, t₂ ∈ s₂`, then `μ⟦t₁ ∩ t₂ | m'⟧ =ᵐ[μ] μ⟦t₁ | m'⟧ * μ⟦t₂ | m'⟧`.
See `ProbabilityTheory.condIndepSets_iff`. -/
def CondIndepSets (s1 s2 : Set (Set Ω)) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] :
Prop :=
Kernel.IndepSets s1 s2 (condExpKernel μ m') (μ.trim hm')
/-- A family of measurable space structures (i.e. of σ-algebras) is conditionally independent given
`m'` with respect to a measure `μ` (typically defined on a finer σ-algebra) if the family of sets of
measurable sets they define is independent. `m : ι → MeasurableSpace Ω` is conditionally independent
given `m'` with respect to measure `μ` if for any finite set of indices `s = {i_1, ..., i_n}`, for
any sets `f i_1 ∈ m i_1, ..., f i_n ∈ m i_n`, then
`μ⟦⋂ i in s, f i | m'⟧ =ᵐ[μ] ∏ i ∈ s, μ⟦f i | m'⟧ `.
See `ProbabilityTheory.iCondIndep_iff`. -/
def iCondIndep (m : ι → MeasurableSpace Ω)
(μ : @Measure Ω mΩ := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.iIndep m (condExpKernel (mΩ := mΩ) μ m') (μ.trim hm')
end
/-- Two measurable space structures (or σ-algebras) `m₁, m₂` are conditionally independent given
`m'` with respect to a measure `μ` (defined on a third σ-algebra) if for any sets
`t₁ ∈ m₁, t₂ ∈ m₂`, `μ⟦t₁ ∩ t₂ | m'⟧ =ᵐ[μ] μ⟦t₁ | m'⟧ * μ⟦t₂ | m'⟧`.
See `ProbabilityTheory.condIndep_iff`. -/
def CondIndep (m' m₁ m₂ : MeasurableSpace Ω)
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
(hm' : m' ≤ mΩ) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.Indep m₁ m₂ (condExpKernel μ m') (μ.trim hm')
section
variable (m' : MeasurableSpace Ω) {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
(hm' : m' ≤ mΩ)
/-- A family of sets is conditionally independent if the family of measurable space structures they
generate is conditionally independent. For a set `s`, the generated measurable space has measurable
sets `∅, s, sᶜ, univ`.
See `ProbabilityTheory.iCondIndepSet_iff`. -/
def iCondIndepSet (s : ι → Set Ω) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.iIndepSet s (condExpKernel μ m') (μ.trim hm')
/-- Two sets are conditionally independent if the two measurable space structures they generate are
conditionally independent. For a set `s`, the generated measurable space structure has measurable
sets `∅, s, sᶜ, univ`.
See `ProbabilityTheory.condIndepSet_iff`. -/
def CondIndepSet (s t : Set Ω) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.IndepSet s t (condExpKernel μ m') (μ.trim hm')
/-- A family of functions defined on the same space `Ω` and taking values in possibly different
spaces, each with a measurable space structure, is conditionally independent if the family of
measurable space structures they generate on `Ω` is conditionally independent. For a function `g`
with codomain having measurable space structure `m`, the generated measurable space structure is
`m.comap g`.
See `ProbabilityTheory.iCondIndepFun_iff`. -/
def iCondIndepFun {β : ι → Type*} [m : ∀ x : ι, MeasurableSpace (β x)]
(f : ∀ x : ι, Ω → β x) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.iIndepFun f (condExpKernel μ m') (μ.trim hm')
/-- Two functions are conditionally independent if the two measurable space structures they generate
are conditionally independent. For a function `f` with codomain having measurable space structure
`m`, the generated measurable space structure is `m.comap f`.
See `ProbabilityTheory.condIndepFun_iff`. -/
def CondIndepFun {β γ : Type*} [MeasurableSpace β] [MeasurableSpace γ]
(f : Ω → β) (g : Ω → γ) (μ : Measure Ω := by volume_tac) [IsFiniteMeasure μ] : Prop :=
Kernel.IndepFun f g (condExpKernel μ m') (μ.trim hm')
end
end Definitions
section DefinitionLemmas
section
variable (m' : MeasurableSpace Ω) {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω] (hm' : m' ≤ mΩ)
lemma iCondIndepSets_iff (π : ι → Set (Set Ω)) (hπ : ∀ i s (_hs : s ∈ π i), MeasurableSet s)
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepSets m' hm' π μ ↔ ∀ (s : Finset ι) {f : ι → Set Ω} (_H : ∀ i, i ∈ s → f i ∈ π i),
μ⟦⋂ i ∈ s, f i | m'⟧ =ᵐ[μ] ∏ i ∈ s, (μ⟦f i | m'⟧) := by
simp only [iCondIndepSets, Kernel.iIndepSets]
have h_eq' : ∀ (s : Finset ι) (f : ι → Set Ω) (_H : ∀ i, i ∈ s → f i ∈ π i) i (_hi : i ∈ s),
(fun ω ↦ ENNReal.toReal (condExpKernel μ m' ω (f i))) =ᵐ[μ] μ⟦f i | m'⟧ :=
fun s f H i hi ↦ condExpKernel_ae_eq_condExp hm' (hπ i (f i) (H i hi))
have h_eq : ∀ (s : Finset ι) (f : ι → Set Ω) (_H : ∀ i, i ∈ s → f i ∈ π i), ∀ᵐ ω ∂μ,
∀ i ∈ s, ENNReal.toReal (condExpKernel μ m' ω (f i)) = (μ⟦f i | m'⟧) ω := by
intros s f H
simp_rw [← Finset.mem_coe]
rw [ae_ball_iff (Finset.countable_toSet s)]
exact h_eq' s f H
have h_inter_eq : ∀ (s : Finset ι) (f : ι → Set Ω) (_H : ∀ i, i ∈ s → f i ∈ π i),
(fun ω ↦ ENNReal.toReal (condExpKernel μ m' ω (⋂ i ∈ s, f i)))
=ᵐ[μ] μ⟦⋂ i ∈ s, f i | m'⟧ := by
refine fun s f H ↦ condExpKernel_ae_eq_condExp hm' ?_
exact MeasurableSet.biInter (Finset.countable_toSet _) (fun i hi ↦ hπ i _ (H i hi))
refine ⟨fun h s f hf ↦ ?_, fun h s f hf ↦ ?_⟩ <;> specialize h s hf
· have h' := ae_eq_of_ae_eq_trim h
filter_upwards [h_eq s f hf, h_inter_eq s f hf, h'] with ω h_eq h_inter_eq h'
rw [← h_inter_eq, h', ENNReal.toReal_prod, Finset.prod_apply]
exact Finset.prod_congr rfl h_eq
· refine ((stronglyMeasurable_condExpKernel ?_).ae_eq_trim_iff hm' ?_).mpr ?_
· exact .biInter (Finset.countable_toSet _) (fun i hi ↦ hπ i _ (hf i hi))
· refine Measurable.stronglyMeasurable ?_
exact Finset.measurable_prod s (fun i hi ↦ measurable_condExpKernel (hπ i _ (hf i hi)))
filter_upwards [h_eq s f hf, h_inter_eq s f hf, h] with ω h_eq h_inter_eq h
have h_ne_top : condExpKernel μ m' ω (⋂ i ∈ s, f i) ≠ ∞ :=
(measure_ne_top (condExpKernel μ m' ω) _)
have : (∏ i ∈ s, condExpKernel μ m' ω (f i)) ≠ ∞ :=
ENNReal.prod_ne_top fun _ _ ↦ measure_ne_top (condExpKernel μ m' ω) _
rw [← ENNReal.ofReal_toReal h_ne_top, h_inter_eq, h, Finset.prod_apply,
← ENNReal.ofReal_toReal this, ENNReal.toReal_prod]
congr 1
exact Finset.prod_congr rfl (fun i hi ↦ (h_eq i hi).symm)
lemma condIndepSets_iff (s1 s2 : Set (Set Ω)) (hs1 : ∀ s ∈ s1, MeasurableSet s)
(hs2 : ∀ s ∈ s2, MeasurableSet s) (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepSets m' hm' s1 s2 μ ↔ ∀ (t1 t2 : Set Ω) (_ : t1 ∈ s1) (_ : t2 ∈ s2),
(μ⟦t1 ∩ t2 | m'⟧) =ᵐ[μ] (μ⟦t1 | m'⟧) * (μ⟦t2 | m'⟧) := by
simp only [CondIndepSets, Kernel.IndepSets]
have hs1_eq : ∀ s ∈ s1, (fun ω ↦ ENNReal.toReal (condExpKernel μ m' ω s)) =ᵐ[μ] μ⟦s | m'⟧ :=
fun s hs ↦ condExpKernel_ae_eq_condExp hm' (hs1 s hs)
have hs2_eq : ∀ s ∈ s2, (fun ω ↦ ENNReal.toReal (condExpKernel μ m' ω s)) =ᵐ[μ] μ⟦s | m'⟧ :=
fun s hs ↦ condExpKernel_ae_eq_condExp hm' (hs2 s hs)
have hs12_eq : ∀ s ∈ s1, ∀ t ∈ s2, (fun ω ↦ ENNReal.toReal (condExpKernel μ m' ω (s ∩ t)))
=ᵐ[μ] μ⟦s ∩ t | m'⟧ :=
fun s hs t ht ↦ condExpKernel_ae_eq_condExp hm' ((hs1 s hs).inter ((hs2 t ht)))
refine ⟨fun h s t hs ht ↦ ?_, fun h s t hs ht ↦ ?_⟩ <;> specialize h s t hs ht
· have h' := ae_eq_of_ae_eq_trim h
filter_upwards [hs1_eq s hs, hs2_eq t ht, hs12_eq s hs t ht, h'] with ω hs_eq ht_eq hst_eq h'
rw [← hst_eq, Pi.mul_apply, ← hs_eq, ← ht_eq, h', ENNReal.toReal_mul]
· refine ((stronglyMeasurable_condExpKernel ((hs1 s hs).inter (hs2 t ht))).ae_eq_trim_iff hm'
((measurable_condExpKernel (hs1 s hs)).mul
(measurable_condExpKernel (hs2 t ht))).stronglyMeasurable).mpr ?_
filter_upwards [hs1_eq s hs, hs2_eq t ht, hs12_eq s hs t ht, h] with ω hs_eq ht_eq hst_eq h
have h_ne_top : condExpKernel μ m' ω (s ∩ t) ≠ ∞ := measure_ne_top (condExpKernel μ m' ω) _
rw [← ENNReal.ofReal_toReal h_ne_top, hst_eq, h, Pi.mul_apply, ← hs_eq, ← ht_eq,
← ENNReal.toReal_mul, ENNReal.ofReal_toReal]
exact ENNReal.mul_ne_top (measure_ne_top (condExpKernel μ m' ω) s)
(measure_ne_top (condExpKernel μ m' ω) t)
lemma iCondIndepSets_singleton_iff (s : ι → Set Ω) (hπ : ∀ i, MeasurableSet (s i))
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepSets m' hm' (fun i ↦ {s i}) μ ↔ ∀ S : Finset ι,
μ⟦⋂ i ∈ S, s i | m'⟧ =ᵐ[μ] ∏ i ∈ S, (μ⟦s i | m'⟧) := by
rw [iCondIndepSets_iff]
· simp only [Set.mem_singleton_iff]
refine ⟨fun h S ↦ h S (fun i _ ↦ rfl), fun h S f hf ↦ ?_⟩
filter_upwards [h S] with a ha
refine Eq.trans ?_ (ha.trans ?_)
· congr
apply congr_arg₂
· exact Set.iInter₂_congr hf
· rfl
· simp_rw [Finset.prod_apply]
refine Finset.prod_congr rfl (fun i hi ↦ ?_)
rw [hf i hi]
· simpa only [Set.mem_singleton_iff, forall_eq]
theorem condIndepSets_singleton_iff {μ : Measure Ω} [IsFiniteMeasure μ]
{s t : Set Ω} (hs : MeasurableSet s) (ht : MeasurableSet t) :
CondIndepSets m' hm' {s} {t} μ ↔ (μ⟦s ∩ t | m'⟧) =ᵐ[μ] (μ⟦s | m'⟧) * (μ⟦t | m'⟧) := by
rw [condIndepSets_iff _ _ _ _ ?_ ?_]
· simp only [Set.mem_singleton_iff, forall_eq_apply_imp_iff, forall_eq]
· intros s' hs'
rw [Set.mem_singleton_iff] at hs'
rwa [hs']
· intros s' hs'
rw [Set.mem_singleton_iff] at hs'
rwa [hs']
lemma iCondIndep_iff_iCondIndepSets (m : ι → MeasurableSpace Ω)
(μ : @Measure Ω mΩ) [IsFiniteMeasure μ] :
iCondIndep m' hm' m μ ↔ iCondIndepSets m' hm' (fun x ↦ {s | MeasurableSet[m x] s}) μ := by
simp only [iCondIndep, iCondIndepSets, Kernel.iIndep]
lemma iCondIndep_iff (m : ι → MeasurableSpace Ω) (hm : ∀ i, m i ≤ mΩ)
(μ : @Measure Ω mΩ) [IsFiniteMeasure μ] :
iCondIndep m' hm' m μ
↔ ∀ (s : Finset ι) {f : ι → Set Ω} (_H : ∀ i, i ∈ s → MeasurableSet[m i] (f i)),
μ⟦⋂ i ∈ s, f i | m'⟧ =ᵐ[μ] ∏ i ∈ s, (μ⟦f i | m'⟧) := by
rw [iCondIndep_iff_iCondIndepSets, iCondIndepSets_iff]
· rfl
· exact hm
end
section CondIndep
lemma condIndep_iff_condIndepSets (m' m₁ m₂ : MeasurableSpace Ω) {mΩ : MeasurableSpace Ω}
[StandardBorelSpace Ω] (hm' : m' ≤ mΩ) (μ : Measure Ω ) [IsFiniteMeasure μ] :
CondIndep m' m₁ m₂ hm' μ
↔ CondIndepSets m' hm' {s | MeasurableSet[m₁] s} {s | MeasurableSet[m₂] s} μ := by
simp only [CondIndep, CondIndepSets, Kernel.Indep]
lemma condIndep_iff (m' m₁ m₂ : MeasurableSpace Ω)
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
(hm' : m' ≤ mΩ) (hm₁ : m₁ ≤ mΩ) (hm₂ : m₂ ≤ mΩ) (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndep m' m₁ m₂ hm' μ
↔ ∀ t1 t2, MeasurableSet[m₁] t1 → MeasurableSet[m₂] t2
→ (μ⟦t1 ∩ t2 | m'⟧) =ᵐ[μ] (μ⟦t1 | m'⟧) * (μ⟦t2 | m'⟧) := by
rw [condIndep_iff_condIndepSets, condIndepSets_iff]
· rfl
· exact hm₁
· exact hm₂
end CondIndep
variable (m' : MeasurableSpace Ω) {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
(hm' : m' ≤ mΩ)
lemma iCondIndepSet_iff_iCondIndep (s : ι → Set Ω) (μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepSet m' hm' s μ ↔ iCondIndep m' hm' (fun i ↦ generateFrom {s i}) μ := by
simp only [iCondIndepSet, iCondIndep, Kernel.iIndepSet]
theorem iCondIndepSet_iff_iCondIndepSets_singleton (s : ι → Set Ω) (hs : ∀ i, MeasurableSet (s i))
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepSet m' hm' s μ ↔ iCondIndepSets m' hm' (fun i ↦ {s i}) μ :=
Kernel.iIndepSet_iff_iIndepSets_singleton hs
lemma iCondIndepSet_iff (s : ι → Set Ω) (hs : ∀ i, MeasurableSet (s i))
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepSet m' hm' s μ ↔
∀ S : Finset ι, μ⟦⋂ i ∈ S, s i | m'⟧ =ᵐ[μ] ∏ i ∈ S, μ⟦s i | m'⟧ := by
rw [iCondIndepSet_iff_iCondIndepSets_singleton _ _ _ hs, iCondIndepSets_singleton_iff _ _ _ hs]
lemma condIndepSet_iff_condIndep (s t : Set Ω) (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepSet m' hm' s t μ ↔ CondIndep m' (generateFrom {s}) (generateFrom {t}) hm' μ := by
simp only [CondIndepSet, CondIndep, Kernel.IndepSet]
theorem condIndepSet_iff_condIndepSets_singleton {s t : Set Ω} (hs_meas : MeasurableSet s)
(ht_meas : MeasurableSet t) (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepSet m' hm' s t μ ↔ CondIndepSets m' hm' {s} {t} μ :=
Kernel.indepSet_iff_indepSets_singleton hs_meas ht_meas _ _
lemma condIndepSet_iff (s t : Set Ω) (hs : MeasurableSet s) (ht : MeasurableSet t)
(μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepSet m' hm' s t μ ↔ (μ⟦s ∩ t | m'⟧) =ᵐ[μ] (μ⟦s | m'⟧) * (μ⟦t | m'⟧) := by
rw [condIndepSet_iff_condIndepSets_singleton _ _ hs ht μ, condIndepSets_singleton_iff _ _ hs ht]
lemma iCondIndepFun_iff_iCondIndep {β : ι → Type*}
(m : ∀ x : ι, MeasurableSpace (β x)) (f : ∀ x : ι, Ω → β x)
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepFun m' hm' f μ
↔ iCondIndep m' hm' (fun x ↦ MeasurableSpace.comap (f x) (m x)) μ := by
simp only [iCondIndepFun, iCondIndep, Kernel.iIndepFun]
lemma iCondIndepFun_iff {β : ι → Type*}
(m : ∀ x : ι, MeasurableSpace (β x)) (f : ∀ x : ι, Ω → β x) (hf : ∀ i, Measurable (f i))
(μ : Measure Ω) [IsFiniteMeasure μ] :
iCondIndepFun m' hm' f μ
↔ ∀ (s : Finset ι) {g : ι → Set Ω} (_H : ∀ i, i ∈ s → MeasurableSet[(m i).comap (f i)] (g i)),
μ⟦⋂ i ∈ s, g i | m'⟧ =ᵐ[μ] ∏ i ∈ s, (μ⟦g i | m'⟧) := by
simp only [iCondIndepFun_iff_iCondIndep]
rw [iCondIndep_iff]
exact fun i ↦ (hf i).comap_le
lemma condIndepFun_iff_condIndep {β γ : Type*} [mβ : MeasurableSpace β]
[mγ : MeasurableSpace γ] (f : Ω → β) (g : Ω → γ) (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepFun m' hm' f g μ
↔ CondIndep m' (MeasurableSpace.comap f mβ) (MeasurableSpace.comap g mγ) hm' μ := by
simp only [CondIndepFun, CondIndep, Kernel.IndepFun]
lemma condIndepFun_iff {β γ : Type*} [mβ : MeasurableSpace β] [mγ : MeasurableSpace γ]
(f : Ω → β) (g : Ω → γ) (hf : Measurable f) (hg : Measurable g)
(μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndepFun m' hm' f g μ ↔ ∀ t1 t2, MeasurableSet[MeasurableSpace.comap f mβ] t1
→ MeasurableSet[MeasurableSpace.comap g mγ] t2
→ (μ⟦t1 ∩ t2 | m'⟧) =ᵐ[μ] (μ⟦t1 | m'⟧) * (μ⟦t2 | m'⟧) := by
rw [condIndepFun_iff_condIndep, condIndep_iff _ _ _ _ hf.comap_le hg.comap_le]
end DefinitionLemmas
section CondIndepSets
variable {m' : MeasurableSpace Ω} {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
@[symm]
theorem CondIndepSets.symm {s₁ s₂ : Set (Set Ω)}
(h : CondIndepSets m' hm' s₁ s₂ μ) : CondIndepSets m' hm' s₂ s₁ μ :=
Kernel.IndepSets.symm h
theorem condIndepSets_of_condIndepSets_of_le_left {s₁ s₂ s₃ : Set (Set Ω)}
(h_indep : CondIndepSets m' hm' s₁ s₂ μ) (h31 : s₃ ⊆ s₁) :
CondIndepSets m' hm' s₃ s₂ μ :=
Kernel.indepSets_of_indepSets_of_le_left h_indep h31
theorem condIndepSets_of_condIndepSets_of_le_right {s₁ s₂ s₃ : Set (Set Ω)}
(h_indep : CondIndepSets m' hm' s₁ s₂ μ) (h32 : s₃ ⊆ s₂) :
CondIndepSets m' hm' s₁ s₃ μ :=
Kernel.indepSets_of_indepSets_of_le_right h_indep h32
theorem CondIndepSets.union {s₁ s₂ s' : Set (Set Ω)}
(h₁ : CondIndepSets m' hm' s₁ s' μ) (h₂ : CondIndepSets m' hm' s₂ s' μ) :
CondIndepSets m' hm' (s₁ ∪ s₂) s' μ :=
Kernel.IndepSets.union h₁ h₂
@[simp]
theorem CondIndepSets.union_iff {s₁ s₂ s' : Set (Set Ω)} :
CondIndepSets m' hm' (s₁ ∪ s₂) s' μ
↔ CondIndepSets m' hm' s₁ s' μ ∧ CondIndepSets m' hm' s₂ s' μ :=
Kernel.IndepSets.union_iff
theorem CondIndepSets.iUnion {s : ι → Set (Set Ω)} {s' : Set (Set Ω)}
(hyp : ∀ n, CondIndepSets m' hm' (s n) s' μ) :
CondIndepSets m' hm' (⋃ n, s n) s' μ :=
Kernel.IndepSets.iUnion hyp
theorem CondIndepSets.bUnion {s : ι → Set (Set Ω)} {s' : Set (Set Ω)}
{u : Set ι} (hyp : ∀ n ∈ u, CondIndepSets m' hm' (s n) s' μ) :
CondIndepSets m' hm' (⋃ n ∈ u, s n) s' μ :=
Kernel.IndepSets.bUnion hyp
theorem CondIndepSets.inter {s₁ s' : Set (Set Ω)} (s₂ : Set (Set Ω))
(h₁ : CondIndepSets m' hm' s₁ s' μ) :
CondIndepSets m' hm' (s₁ ∩ s₂) s' μ :=
Kernel.IndepSets.inter s₂ h₁
theorem CondIndepSets.iInter {s : ι → Set (Set Ω)} {s' : Set (Set Ω)}
(h : ∃ n, CondIndepSets m' hm' (s n) s' μ) :
CondIndepSets m' hm' (⋂ n, s n) s' μ :=
Kernel.IndepSets.iInter h
theorem CondIndepSets.bInter {s : ι → Set (Set Ω)} {s' : Set (Set Ω)}
{u : Set ι} (h : ∃ n ∈ u, CondIndepSets m' hm' (s n) s' μ) :
CondIndepSets m' hm' (⋂ n ∈ u, s n) s' μ :=
Kernel.IndepSets.bInter h
end CondIndepSets
section CondIndepSet
variable {m' : MeasurableSpace Ω} {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
theorem condIndepSet_empty_right (s : Set Ω) : CondIndepSet m' hm' s ∅ μ :=
Kernel.indepSet_empty_right s
theorem condIndepSet_empty_left (s : Set Ω) : CondIndepSet m' hm' ∅ s μ :=
Kernel.indepSet_empty_left s
end CondIndepSet
section CondIndep
@[symm]
theorem CondIndep.symm {m' m₁ m₂ : MeasurableSpace Ω} {mΩ : MeasurableSpace Ω}
[StandardBorelSpace Ω] {hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
(h : CondIndep m' m₁ m₂ hm' μ) :
CondIndep m' m₂ m₁ hm' μ :=
CondIndepSets.symm h
theorem condIndep_bot_right (m₁ : MeasurableSpace Ω) {m' : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ] :
CondIndep m' m₁ ⊥ hm' μ :=
Kernel.indep_bot_right m₁
theorem condIndep_bot_left (m₁ : MeasurableSpace Ω) {m' : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ] :
CondIndep m' ⊥ m₁ hm' μ :=
(Kernel.indep_bot_right m₁).symm
theorem condIndep_of_condIndep_of_le_left {m' m₁ m₂ m₃ : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
(h_indep : CondIndep m' m₁ m₂ hm' μ) (h31 : m₃ ≤ m₁) :
CondIndep m' m₃ m₂ hm' μ :=
Kernel.indep_of_indep_of_le_left h_indep h31
theorem condIndep_of_condIndep_of_le_right {m' m₁ m₂ m₃ : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
(h_indep : CondIndep m' m₁ m₂ hm' μ) (h32 : m₃ ≤ m₂) :
CondIndep m' m₁ m₃ hm' μ :=
Kernel.indep_of_indep_of_le_right h_indep h32
end CondIndep
/-! ### Deducing `CondIndep` from `iCondIndep` -/
section FromiCondIndepToCondIndep
variable {m' : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
theorem iCondIndepSets.condIndepSets {s : ι → Set (Set Ω)}
(h_indep : iCondIndepSets m' hm' s μ) {i j : ι} (hij : i ≠ j) :
CondIndepSets m' hm' (s i) (s j) μ :=
Kernel.iIndepSets.indepSets h_indep hij
theorem iCondIndep.condIndep {m : ι → MeasurableSpace Ω}
(h_indep : iCondIndep m' hm' m μ) {i j : ι} (hij : i ≠ j) :
CondIndep m' (m i) (m j) hm' μ :=
Kernel.iIndep.indep h_indep hij
theorem iCondIndepFun.condIndepFun {β : ι → Type*}
{m : ∀ x, MeasurableSpace (β x)} {f : ∀ i, Ω → β i}
(hf_Indep : iCondIndepFun m' hm' f μ) {i j : ι} (hij : i ≠ j) :
CondIndepFun m' hm' (f i) (f j) μ :=
Kernel.iIndepFun.indepFun hf_Indep hij
end FromiCondIndepToCondIndep
/-!
## π-system lemma
Conditional independence of measurable spaces is equivalent to conditional independence of
generating π-systems.
-/
section FromMeasurableSpacesToSetsOfSets
/-! ### Conditional independence of σ-algebras implies conditional independence of
generating π-systems -/
variable {m' : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
theorem iCondIndep.iCondIndepSets {m : ι → MeasurableSpace Ω}
{s : ι → Set (Set Ω)} (hms : ∀ n, m n = generateFrom (s n))
(h_indep : iCondIndep m' hm' m μ) :
iCondIndepSets m' hm' s μ :=
Kernel.iIndep.iIndepSets hms h_indep
theorem CondIndep.condIndepSets {s1 s2 : Set (Set Ω)}
(h_indep : CondIndep m' (generateFrom s1) (generateFrom s2) hm' μ) :
CondIndepSets m' hm' s1 s2 μ :=
Kernel.Indep.indepSets h_indep
end FromMeasurableSpacesToSetsOfSets
section FromPiSystemsToMeasurableSpaces
/-! ### Conditional independence of generating π-systems implies conditional independence of
σ-algebras -/
variable {m' m₁ m₂ : MeasurableSpace Ω} {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
theorem CondIndepSets.condIndep
{p1 p2 : Set (Set Ω)} (h1 : m₁ ≤ mΩ) (h2 : m₂ ≤ mΩ)
(hp1 : IsPiSystem p1) (hp2 : IsPiSystem p2)
(hpm1 : m₁ = generateFrom p1) (hpm2 : m₂ = generateFrom p2)
(hyp : CondIndepSets m' hm' p1 p2 μ) :
CondIndep m' m₁ m₂ hm' μ :=
Kernel.IndepSets.indep h1 h2 hp1 hp2 hpm1 hpm2 hyp
theorem CondIndepSets.condIndep'
{p1 p2 : Set (Set Ω)} (hp1m : ∀ s ∈ p1, MeasurableSet s) (hp2m : ∀ s ∈ p2, MeasurableSet s)
(hp1 : IsPiSystem p1) (hp2 : IsPiSystem p2) (hyp : CondIndepSets m' hm' p1 p2 μ) :
CondIndep m' (generateFrom p1) (generateFrom p2) hm' μ :=
Kernel.IndepSets.indep' hp1m hp2m hp1 hp2 hyp
theorem condIndepSets_piiUnionInter_of_disjoint {s : ι → Set (Set Ω)}
{S T : Set ι} (h_indep : iCondIndepSets m' hm' s μ) (hST : Disjoint S T) :
CondIndepSets m' hm' (piiUnionInter s S) (piiUnionInter s T) μ :=
Kernel.indepSets_piiUnionInter_of_disjoint h_indep hST
theorem iCondIndepSet.condIndep_generateFrom_of_disjoint {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iCondIndepSet m' hm' s μ) (S T : Set ι)
(hST : Disjoint S T) :
CondIndep m' (generateFrom { t | ∃ n ∈ S, s n = t })
(generateFrom { t | ∃ k ∈ T, s k = t }) hm' μ :=
Kernel.iIndepSet.indep_generateFrom_of_disjoint hsm hs S T hST
theorem condIndep_iSup_of_disjoint {m : ι → MeasurableSpace Ω}
(h_le : ∀ i, m i ≤ mΩ) (h_indep : iCondIndep m' hm' m μ) {S T : Set ι} (hST : Disjoint S T) :
CondIndep m' (⨆ i ∈ S, m i) (⨆ i ∈ T, m i) hm' μ :=
Kernel.indep_iSup_of_disjoint h_le h_indep hST
theorem condIndep_iSup_of_directed_le {m : ι → MeasurableSpace Ω}
(h_indep : ∀ i, CondIndep m' (m i) m₁ hm' μ)
(h_le : ∀ i, m i ≤ mΩ) (h_le' : m₁ ≤ mΩ) (hm : Directed (· ≤ ·) m) :
CondIndep m' (⨆ i, m i) m₁ hm' μ :=
Kernel.indep_iSup_of_directed_le h_indep h_le h_le' hm
theorem iCondIndepSet.condIndep_generateFrom_lt [Preorder ι] {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iCondIndepSet m' hm' s μ) (i : ι) :
CondIndep m' (generateFrom {s i}) (generateFrom { t | ∃ j < i, s j = t }) hm' μ :=
Kernel.iIndepSet.indep_generateFrom_lt hsm hs i
theorem iCondIndepSet.condIndep_generateFrom_le [Preorder ι] {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iCondIndepSet m' hm' s μ) (i : ι) {k : ι} (hk : i < k) :
CondIndep m' (generateFrom {s k}) (generateFrom { t | ∃ j ≤ i, s j = t }) hm' μ :=
Kernel.iIndepSet.indep_generateFrom_le hsm hs i hk
theorem iCondIndepSet.condIndep_generateFrom_le_nat {s : ℕ → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iCondIndepSet m' hm' s μ) (n : ℕ) :
CondIndep m' (generateFrom {s (n + 1)}) (generateFrom { t | ∃ k ≤ n, s k = t }) hm' μ :=
Kernel.iIndepSet.indep_generateFrom_le_nat hsm hs n
theorem condIndep_iSup_of_monotone [SemilatticeSup ι] {m : ι → MeasurableSpace Ω}
(h_indep : ∀ i, CondIndep m' (m i) m₁ hm' μ) (h_le : ∀ i, m i ≤ mΩ) (h_le' : m₁ ≤ mΩ)
(hm : Monotone m) :
CondIndep m' (⨆ i, m i) m₁ hm' μ :=
Kernel.indep_iSup_of_monotone h_indep h_le h_le' hm
theorem condIndep_iSup_of_antitone [SemilatticeInf ι] {m : ι → MeasurableSpace Ω}
(h_indep : ∀ i, CondIndep m' (m i) m₁ hm' μ) (h_le : ∀ i, m i ≤ mΩ) (h_le' : m₁ ≤ mΩ)
(hm : Antitone m) :
CondIndep m' (⨆ i, m i) m₁ hm' μ :=
Kernel.indep_iSup_of_antitone h_indep h_le h_le' hm
theorem iCondIndepSets.piiUnionInter_of_not_mem {π : ι → Set (Set Ω)} {a : ι} {S : Finset ι}
(hp_ind : iCondIndepSets m' hm' π μ) (haS : a ∉ S) :
CondIndepSets m' hm' (piiUnionInter π S) (π a) μ :=
Kernel.iIndepSets.piiUnionInter_of_not_mem hp_ind haS
/-- The σ-algebras generated by conditionally independent pi-systems are conditionally independent.
-/
theorem iCondIndepSets.iCondIndep (m : ι → MeasurableSpace Ω)
(h_le : ∀ i, m i ≤ mΩ) (π : ι → Set (Set Ω)) (h_pi : ∀ n, IsPiSystem (π n))
(h_generate : ∀ i, m i = generateFrom (π i)) (h_ind : iCondIndepSets m' hm' π μ) :
iCondIndep m' hm' m μ :=
Kernel.iIndepSets.iIndep m h_le π h_pi h_generate h_ind
end FromPiSystemsToMeasurableSpaces
section CondIndepSet
/-! ### Conditional independence of measurable sets
-/
variable {m' m₁ m₂ : MeasurableSpace Ω} {mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ}
{s t : Set Ω} (S T : Set (Set Ω))
theorem CondIndepSets.condIndepSet_of_mem (hs : s ∈ S) (ht : t ∈ T)
(hs_meas : MeasurableSet s) (ht_meas : MeasurableSet t) (μ : Measure Ω) [IsFiniteMeasure μ]
(h_indep : CondIndepSets m' hm' S T μ) :
CondIndepSet m' hm' s t μ :=
Kernel.IndepSets.indepSet_of_mem _ _ hs ht hs_meas ht_meas _ _ h_indep
theorem CondIndep.condIndepSet_of_measurableSet {μ : Measure Ω} [IsFiniteMeasure μ]
(h_indep : CondIndep m' m₁ m₂ hm' μ) {s t : Set Ω} (hs : MeasurableSet[m₁] s)
(ht : MeasurableSet[m₂] t) :
CondIndepSet m' hm' s t μ :=
Kernel.Indep.indepSet_of_measurableSet h_indep hs ht
theorem condIndep_iff_forall_condIndepSet (μ : Measure Ω) [IsFiniteMeasure μ] :
CondIndep m' m₁ m₂ hm' μ ↔ ∀ s t, MeasurableSet[m₁] s → MeasurableSet[m₂] t
→ CondIndepSet m' hm' s t μ :=
Kernel.indep_iff_forall_indepSet m₁ m₂ _ _
end CondIndepSet
section CondIndepFun
/-! ### Conditional independence of random variables
-/
variable {β β' : Type*} {m' : MeasurableSpace Ω}
{mΩ : MeasurableSpace Ω} [StandardBorelSpace Ω]
{hm' : m' ≤ mΩ} {μ : Measure Ω} [IsFiniteMeasure μ]
{f : Ω → β} {g : Ω → β'}
theorem condIndepFun_iff_condExp_inter_preimage_eq_mul {mβ : MeasurableSpace β}
{mβ' : MeasurableSpace β'} (hf : Measurable f) (hg : Measurable g) :
CondIndepFun m' hm' f g μ ↔
∀ s t, MeasurableSet s → MeasurableSet t
→ (μ⟦f ⁻¹' s ∩ g ⁻¹' t | m'⟧) =ᵐ[μ] fun ω ↦ (μ⟦f ⁻¹' s | m'⟧) ω * (μ⟦g ⁻¹' t | m'⟧) ω := by
rw [condIndepFun_iff _ _ _ _ hf hg]
refine ⟨fun h s t hs ht ↦ ?_, fun h s t ↦ ?_⟩
· exact h (f ⁻¹' s) (g ⁻¹' t) ⟨s, hs, rfl⟩ ⟨t, ht, rfl⟩
· rintro ⟨s, hs, rfl⟩ ⟨t, ht, rfl⟩
exact h s t hs ht
@[deprecated (since := "2025-01-21")]
alias condIndepFun_iff_condexp_inter_preimage_eq_mul :=
condIndepFun_iff_condExp_inter_preimage_eq_mul
theorem iCondIndepFun_iff_condExp_inter_preimage_eq_mul {β : ι → Type*}
(m : ∀ x, MeasurableSpace (β x)) (f : ∀ i, Ω → β i) (hf : ∀ i, Measurable (f i)) :
iCondIndepFun m' hm' f μ ↔
∀ (S : Finset ι) {sets : ∀ i : ι, Set (β i)} (_H : ∀ i, i ∈ S → MeasurableSet[m i] (sets i)),
(μ⟦⋂ i ∈ S, f i ⁻¹' sets i| m'⟧) =ᵐ[μ] ∏ i ∈ S, (μ⟦f i ⁻¹' sets i | m'⟧) := by
rw [iCondIndepFun_iff]
swap
· exact hf
refine ⟨fun h s sets h_sets ↦ ?_, fun h s sets h_sets ↦ ?_⟩
· refine h s (g := fun i ↦ f i ⁻¹' (sets i)) (fun i hi ↦ ?_)
exact ⟨sets i, h_sets i hi, rfl⟩
· classical
let g := fun i ↦ if hi : i ∈ s then (h_sets i hi).choose else Set.univ
specialize h s (sets := g) (fun i hi ↦ ?_)
· simp only [g, dif_pos hi]
exact (h_sets i hi).choose_spec.1
· have hg : ∀ i ∈ s, sets i = f i ⁻¹' g i := by
intro i hi
rw [(h_sets i hi).choose_spec.2.symm]
simp only [g, dif_pos hi]
convert h with i hi i hi <;> exact hg i hi
@[deprecated (since := "2025-01-21")]
alias iCondIndepFun_iff_condexp_inter_preimage_eq_mul :=
iCondIndepFun_iff_condExp_inter_preimage_eq_mul
theorem condIndepFun_iff_condIndepSet_preimage {mβ : MeasurableSpace β} {mβ' : MeasurableSpace β'}
(hf : Measurable f) (hg : Measurable g) :
CondIndepFun m' hm' f g μ ↔
∀ s t, MeasurableSet s → MeasurableSet t → CondIndepSet m' hm' (f ⁻¹' s) (g ⁻¹' t) μ := by
simp only [CondIndepFun, CondIndepSet, Kernel.indepFun_iff_indepSet_preimage hf hg]
@[symm]
nonrec theorem CondIndepFun.symm {_ : MeasurableSpace β} {f g : Ω → β}
(hfg : CondIndepFun m' hm' f g μ) :
CondIndepFun m' hm' g f μ :=
hfg.symm
theorem CondIndepFun.comp {γ γ' : Type*} {_mβ : MeasurableSpace β} {_mβ' : MeasurableSpace β'}
{_mγ : MeasurableSpace γ} {_mγ' : MeasurableSpace γ'} {φ : β → γ} {ψ : β' → γ'}
(hfg : CondIndepFun m' hm' f g μ) (hφ : Measurable φ) (hψ : Measurable ψ) :
CondIndepFun m' hm' (φ ∘ f) (ψ ∘ g) μ :=
Kernel.IndepFun.comp hfg hφ hψ
theorem CondIndepFun.neg_right {_mβ : MeasurableSpace β} {_mβ' : MeasurableSpace β'} [Neg β']
[MeasurableNeg β'] (hfg : CondIndepFun m' hm' f g μ) :
CondIndepFun m' hm' f (-g) μ := hfg.comp measurable_id measurable_neg
theorem CondIndepFun.neg_left {_mβ : MeasurableSpace β} {_mβ' : MeasurableSpace β'} [Neg β]
[MeasurableNeg β] (hfg : CondIndepFun m' hm' f g μ) :
CondIndepFun m' hm' (-f) g μ := hfg.comp measurable_neg measurable_id
section iCondIndepFun
variable {β : ι → Type*} {m : ∀ i, MeasurableSpace (β i)} {f : ∀ i, Ω → β i}
@[nontriviality]
lemma iCondIndepFun.of_subsingleton [Subsingleton ι] : iCondIndepFun m' hm' f μ :=
Kernel.iIndepFun.of_subsingleton
/-- If `f` is a family of mutually conditionally independent random variables
(`iCondIndepFun m' hm' m f μ`) and `S, T` are two disjoint finite index sets, then the tuple formed
by `f i` for `i ∈ S` is conditionally independent of the tuple `(f i)_i` for `i ∈ T`. -/
theorem iCondIndepFun.condIndepFun_finset {β : ι → Type*}
{m : ∀ i, MeasurableSpace (β i)} {f : ∀ i, Ω → β i} (S T : Finset ι) (hST : Disjoint S T)
(hf_Indep : iCondIndepFun m' hm' f μ) (hf_meas : ∀ i, Measurable (f i)) :
CondIndepFun m' hm' (fun a (i : S) => f i a) (fun a (i : T) => f i a) μ :=
Kernel.iIndepFun.indepFun_finset S T hST hf_Indep hf_meas
theorem iCondIndepFun.condIndepFun_prodMk {β : ι → Type*}
{m : ∀ i, MeasurableSpace (β i)} {f : ∀ i, Ω → β i} (hf_Indep : iCondIndepFun m' hm' f μ)
(hf_meas : ∀ i, Measurable (f i)) (i j k : ι) (hik : i ≠ k) (hjk : j ≠ k) :
CondIndepFun m' hm' (fun a => (f i a, f j a)) (f k) μ :=
Kernel.iIndepFun.indepFun_prodMk hf_Indep hf_meas i j k hik hjk
|
@[deprecated (since := "2025-03-05")]
alias iCondIndepFun.condIndepFun_prod_mk := iCondIndepFun.condIndepFun_prodMk
open Finset in
lemma iCondIndepFun.condIndepFun_prodMk_prodMk (h_indep : iCondIndepFun m' hm' f μ)
(hf : ∀ i, Measurable (f i))
(i j k l : ι) (hik : i ≠ k) (hil : i ≠ l) (hjk : j ≠ k) (hjl : j ≠ l) :
CondIndepFun m' hm' (fun a ↦ (f i a, f j a)) (fun a ↦ (f k a, f l a)) μ := by
classical
let g (i j : ι) (v : Π x : ({i, j} : Finset ι), β x) : β i × β j :=
⟨v ⟨i, mem_insert_self _ _⟩, v ⟨j, mem_insert_of_mem <| mem_singleton_self _⟩⟩
have hg (i j : ι) : Measurable (g i j) := by fun_prop
exact (h_indep.indepFun_finset {i, j} {k, l} (by aesop) hf).comp (hg i j) (hg k l)
| Mathlib/Probability/Independence/Conditional.lean | 727 | 741 |
/-
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.SpecialFunctions.Trigonometric.Angle
import Mathlib.Analysis.SpecialFunctions.Trigonometric.Inverse
/-!
# The argument of a complex number.
We define `arg : ℂ → ℝ`, returning a real number in the range (-π, π],
such that for `x ≠ 0`, `sin (arg x) = x.im / x.abs` and `cos (arg x) = x.re / x.abs`,
while `arg 0` defaults to `0`
-/
open Filter Metric Set
open scoped ComplexConjugate Real Topology
namespace Complex
variable {a x z : ℂ}
/-- `arg` returns values in the range (-π, π], such that for `x ≠ 0`,
`sin (arg x) = x.im / x.abs` and `cos (arg x) = x.re / x.abs`,
`arg 0` defaults to `0` -/
noncomputable def arg (x : ℂ) : ℝ :=
if 0 ≤ x.re then Real.arcsin (x.im / ‖x‖)
else if 0 ≤ x.im then Real.arcsin ((-x).im / ‖x‖) + π else Real.arcsin ((-x).im / ‖x‖) - π
theorem sin_arg (x : ℂ) : Real.sin (arg x) = x.im / ‖x‖ := by
unfold arg; split_ifs <;>
simp [sub_eq_add_neg, arg, Real.sin_arcsin (abs_le.1 (abs_im_div_norm_le_one x)).1
(abs_le.1 (abs_im_div_norm_le_one x)).2, Real.sin_add, neg_div, Real.arcsin_neg, Real.sin_neg]
theorem cos_arg {x : ℂ} (hx : x ≠ 0) : Real.cos (arg x) = x.re / ‖x‖ := by
rw [arg]
split_ifs with h₁ h₂
· rw [Real.cos_arcsin]
field_simp [Real.sqrt_sq, (norm_pos_iff.mpr hx).le, *]
· rw [Real.cos_add_pi, Real.cos_arcsin]
field_simp [Real.sqrt_div (sq_nonneg _), Real.sqrt_sq_eq_abs,
_root_.abs_of_neg (not_le.1 h₁), *]
· rw [Real.cos_sub_pi, Real.cos_arcsin]
field_simp [Real.sqrt_div (sq_nonneg _), Real.sqrt_sq_eq_abs,
_root_.abs_of_neg (not_le.1 h₁), *]
@[simp]
theorem norm_mul_exp_arg_mul_I (x : ℂ) : ‖x‖ * exp (arg x * I) = x := by
rcases eq_or_ne x 0 with (rfl | hx)
· simp
· have : ‖x‖ ≠ 0 := norm_ne_zero_iff.mpr hx
apply Complex.ext <;> field_simp [sin_arg, cos_arg hx, this, mul_comm ‖x‖]
@[simp]
theorem norm_mul_cos_add_sin_mul_I (x : ℂ) : (‖x‖ * (cos (arg x) + sin (arg x) * I) : ℂ) = x := by
rw [← exp_mul_I, norm_mul_exp_arg_mul_I]
@[simp]
lemma norm_mul_cos_arg (x : ℂ) : ‖x‖ * Real.cos (arg x) = x.re := by
simpa [-norm_mul_cos_add_sin_mul_I] using congr_arg re (norm_mul_cos_add_sin_mul_I x)
@[simp]
lemma norm_mul_sin_arg (x : ℂ) : ‖x‖ * Real.sin (arg x) = x.im := by
simpa [-norm_mul_cos_add_sin_mul_I] using congr_arg im (norm_mul_cos_add_sin_mul_I x)
theorem norm_eq_one_iff (z : ℂ) : ‖z‖ = 1 ↔ ∃ θ : ℝ, exp (θ * I) = z := by
refine ⟨fun hz => ⟨arg z, ?_⟩, ?_⟩
· calc
exp (arg z * I) = ‖z‖ * exp (arg z * I) := by rw [hz, ofReal_one, one_mul]
_ = z :=norm_mul_exp_arg_mul_I z
· rintro ⟨θ, rfl⟩
exact Complex.norm_exp_ofReal_mul_I θ
@[deprecated (since := "2025-02-16")] alias abs_mul_exp_arg_mul_I := norm_mul_exp_arg_mul_I
@[deprecated (since := "2025-02-16")] alias abs_mul_cos_add_sin_mul_I := norm_mul_cos_add_sin_mul_I
@[deprecated (since := "2025-02-16")] alias abs_mul_cos_arg := norm_mul_cos_arg
@[deprecated (since := "2025-02-16")] alias abs_mul_sin_arg := norm_mul_sin_arg
@[deprecated (since := "2025-02-16")] alias abs_eq_one_iff := norm_eq_one_iff
@[simp]
theorem range_exp_mul_I : (Set.range fun x : ℝ => exp (x * I)) = Metric.sphere 0 1 := by
ext x
simp only [mem_sphere_zero_iff_norm, norm_eq_one_iff, Set.mem_range]
theorem arg_mul_cos_add_sin_mul_I {r : ℝ} (hr : 0 < r) {θ : ℝ} (hθ : θ ∈ Set.Ioc (-π) π) :
arg (r * (cos θ + sin θ * I)) = θ := by
simp only [arg, norm_mul, norm_cos_add_sin_mul_I, Complex.norm_of_nonneg hr.le, mul_one]
simp only [re_ofReal_mul, im_ofReal_mul, neg_im, ← ofReal_cos, ← ofReal_sin, ←
mk_eq_add_mul_I, neg_div, mul_div_cancel_left₀ _ hr.ne', mul_nonneg_iff_right_nonneg_of_pos hr]
by_cases h₁ : θ ∈ Set.Icc (-(π / 2)) (π / 2)
· rw [if_pos]
exacts [Real.arcsin_sin' h₁, Real.cos_nonneg_of_mem_Icc h₁]
· rw [Set.mem_Icc, not_and_or, not_le, not_le] at h₁
rcases h₁ with h₁ | h₁
· replace hθ := hθ.1
have hcos : Real.cos θ < 0 := by
rw [← neg_pos, ← Real.cos_add_pi]
refine Real.cos_pos_of_mem_Ioo ⟨?_, ?_⟩ <;> linarith
have hsin : Real.sin θ < 0 := Real.sin_neg_of_neg_of_neg_pi_lt (by linarith) hθ
rw [if_neg, if_neg, ← Real.sin_add_pi, Real.arcsin_sin, add_sub_cancel_right] <;> [linarith;
linarith; exact hsin.not_le; exact hcos.not_le]
· replace hθ := hθ.2
have hcos : Real.cos θ < 0 := Real.cos_neg_of_pi_div_two_lt_of_lt h₁ (by linarith)
have hsin : 0 ≤ Real.sin θ := Real.sin_nonneg_of_mem_Icc ⟨by linarith, hθ⟩
rw [if_neg, if_pos, ← Real.sin_sub_pi, Real.arcsin_sin, sub_add_cancel] <;> [linarith;
linarith; exact hsin; exact hcos.not_le]
theorem arg_cos_add_sin_mul_I {θ : ℝ} (hθ : θ ∈ Set.Ioc (-π) π) : arg (cos θ + sin θ * I) = θ := by
rw [← one_mul (_ + _), ← ofReal_one, arg_mul_cos_add_sin_mul_I zero_lt_one hθ]
lemma arg_exp_mul_I (θ : ℝ) :
arg (exp (θ * I)) = toIocMod (mul_pos two_pos Real.pi_pos) (-π) θ := by
convert arg_cos_add_sin_mul_I (θ := toIocMod (mul_pos two_pos Real.pi_pos) (-π) θ) _ using 2
· rw [← exp_mul_I, eq_sub_of_add_eq <| toIocMod_add_toIocDiv_zsmul _ _ θ, ofReal_sub,
ofReal_zsmul, ofReal_mul, ofReal_ofNat, exp_mul_I_periodic.sub_zsmul_eq]
· convert toIocMod_mem_Ioc _ _ _
ring
@[simp]
theorem arg_zero : arg 0 = 0 := by simp [arg, le_refl]
theorem ext_norm_arg {x y : ℂ} (h₁ : ‖x‖ = ‖y‖) (h₂ : x.arg = y.arg) : x = y := by
rw [← norm_mul_exp_arg_mul_I x, ← norm_mul_exp_arg_mul_I y, h₁, h₂]
theorem ext_norm_arg_iff {x y : ℂ} : x = y ↔ ‖x‖ = ‖y‖ ∧ arg x = arg y :=
⟨fun h => h ▸ ⟨rfl, rfl⟩, and_imp.2 ext_norm_arg⟩
@[deprecated (since := "2025-02-16")] alias ext_abs_arg := ext_norm_arg
@[deprecated (since := "2025-02-16")] alias ext_abs_arg_iff := ext_norm_arg_iff
theorem arg_mem_Ioc (z : ℂ) : arg z ∈ Set.Ioc (-π) π := by
have hπ : 0 < π := Real.pi_pos
rcases eq_or_ne z 0 with (rfl | hz)
· simp [hπ, hπ.le]
rcases existsUnique_add_zsmul_mem_Ioc Real.two_pi_pos (arg z) (-π) with ⟨N, hN, -⟩
rw [two_mul, neg_add_cancel_left, ← two_mul, zsmul_eq_mul] at hN
rw [← norm_mul_cos_add_sin_mul_I z, ← cos_add_int_mul_two_pi _ N, ← sin_add_int_mul_two_pi _ N]
have := arg_mul_cos_add_sin_mul_I (norm_pos_iff.mpr hz) hN
push_cast at this
rwa [this]
@[simp]
theorem range_arg : Set.range arg = Set.Ioc (-π) π :=
(Set.range_subset_iff.2 arg_mem_Ioc).antisymm fun _ hx => ⟨_, arg_cos_add_sin_mul_I hx⟩
theorem arg_le_pi (x : ℂ) : arg x ≤ π :=
(arg_mem_Ioc x).2
theorem neg_pi_lt_arg (x : ℂ) : -π < arg x :=
(arg_mem_Ioc x).1
theorem abs_arg_le_pi (z : ℂ) : |arg z| ≤ π :=
abs_le.2 ⟨(neg_pi_lt_arg z).le, arg_le_pi z⟩
@[simp]
theorem arg_nonneg_iff {z : ℂ} : 0 ≤ arg z ↔ 0 ≤ z.im := by
rcases eq_or_ne z 0 with (rfl | h₀); · simp
calc
0 ≤ arg z ↔ 0 ≤ Real.sin (arg z) :=
⟨fun h => Real.sin_nonneg_of_mem_Icc ⟨h, arg_le_pi z⟩, by
contrapose!
intro h
exact Real.sin_neg_of_neg_of_neg_pi_lt h (neg_pi_lt_arg _)⟩
_ ↔ _ := by rw [sin_arg, le_div_iff₀ (norm_pos_iff.mpr h₀), zero_mul]
@[simp]
theorem arg_neg_iff {z : ℂ} : arg z < 0 ↔ z.im < 0 :=
lt_iff_lt_of_le_iff_le arg_nonneg_iff
theorem arg_real_mul (x : ℂ) {r : ℝ} (hr : 0 < r) : arg (r * x) = arg x := by
rcases eq_or_ne x 0 with (rfl | hx); · rw [mul_zero]
conv_lhs =>
rw [← norm_mul_cos_add_sin_mul_I x, ← mul_assoc, ← ofReal_mul,
arg_mul_cos_add_sin_mul_I (mul_pos hr (norm_pos_iff.mpr hx)) x.arg_mem_Ioc]
theorem arg_mul_real {r : ℝ} (hr : 0 < r) (x : ℂ) : arg (x * r) = arg x :=
mul_comm x r ▸ arg_real_mul x hr
theorem arg_eq_arg_iff {x y : ℂ} (hx : x ≠ 0) (hy : y ≠ 0) :
arg x = arg y ↔ (‖y‖ / ‖x‖ : ℂ) * x = y := by
simp only [ext_norm_arg_iff, norm_mul, norm_div, norm_real, norm_norm,
div_mul_cancel₀ _ (norm_ne_zero_iff.mpr hx), eq_self_iff_true, true_and]
rw [← ofReal_div, arg_real_mul]
exact div_pos (norm_pos_iff.mpr hy) (norm_pos_iff.mpr hx)
@[simp] lemma arg_one : arg 1 = 0 := by simp [arg, zero_le_one]
/-- This holds true for all `x : ℂ` because of the junk values `0 / 0 = 0` and `arg 0 = 0`. -/
@[simp] lemma arg_div_self (x : ℂ) : arg (x / x) = 0 := by
obtain rfl | hx := eq_or_ne x 0 <;> simp [*]
@[simp]
theorem arg_neg_one : arg (-1) = π := by simp [arg, le_refl, not_le.2 (zero_lt_one' ℝ)]
@[simp]
theorem arg_I : arg I = π / 2 := by simp [arg, le_refl]
@[simp]
theorem arg_neg_I : arg (-I) = -(π / 2) := by simp [arg, le_refl]
@[simp]
theorem tan_arg (x : ℂ) : Real.tan (arg x) = x.im / x.re := by
by_cases h : x = 0
· simp only [h, zero_div, Complex.zero_im, Complex.arg_zero, Real.tan_zero, Complex.zero_re]
rw [Real.tan_eq_sin_div_cos, sin_arg, cos_arg h,
div_div_div_cancel_right₀ (norm_ne_zero_iff.mpr h)]
theorem arg_ofReal_of_nonneg {x : ℝ} (hx : 0 ≤ x) : arg x = 0 := by simp [arg, hx]
@[simp, norm_cast]
lemma natCast_arg {n : ℕ} : arg n = 0 :=
ofReal_natCast n ▸ arg_ofReal_of_nonneg n.cast_nonneg
| Mathlib/Analysis/SpecialFunctions/Complex/Arg.lean | 213 | 213 | |
/-
Copyright (c) 2023 Rémy Degenne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Rémy Degenne
-/
import Mathlib.MeasureTheory.Measure.Decomposition.RadonNikodym
/-!
# Exponentially tilted measures
The exponential tilting of a measure `μ` on `α` by a function `f : α → ℝ` is the measure with
density `x ↦ exp (f x) / ∫ y, exp (f y) ∂μ` with respect to `μ`. This is sometimes also called
the Esscher transform.
The definition is mostly used for `f` linear, in which case the exponentially tilted measure belongs
to the natural exponential family of the base measure. Exponentially tilted measures for general `f`
can be used for example to establish variational expressions for the Kullback-Leibler divergence.
## Main definitions
* `Measure.tilted μ f`: exponential tilting of `μ` by `f`, equal to
`μ.withDensity (fun x ↦ ENNReal.ofReal (exp (f x) / ∫ x, exp (f x) ∂μ))`.
-/
open Real
open scoped ENNReal NNReal
namespace MeasureTheory
variable {α : Type*} {mα : MeasurableSpace α} {μ : Measure α} {f : α → ℝ}
/-- Exponentially tilted measure. When `x ↦ exp (f x)` is integrable, `μ.tilted f` is the
probability measure with density with respect to `μ` proportional to `exp (f x)`. Otherwise it is 0.
-/
noncomputable
def Measure.tilted (μ : Measure α) (f : α → ℝ) : Measure α :=
μ.withDensity (fun x ↦ ENNReal.ofReal (exp (f x) / ∫ x, exp (f x) ∂μ))
@[simp]
lemma tilted_of_not_integrable (hf : ¬ Integrable (fun x ↦ exp (f x)) μ) : μ.tilted f = 0 := by
rw [Measure.tilted, integral_undef hf]
simp
@[simp]
lemma tilted_of_not_aemeasurable (hf : ¬ AEMeasurable f μ) : μ.tilted f = 0 := by
refine tilted_of_not_integrable ?_
suffices ¬ AEMeasurable (fun x ↦ exp (f x)) μ by exact fun h ↦ this h.1.aemeasurable
exact fun h ↦ hf (aemeasurable_of_aemeasurable_exp h)
@[simp]
lemma tilted_zero_measure (f : α → ℝ) : (0 : Measure α).tilted f = 0 := by simp [Measure.tilted]
@[simp]
lemma tilted_const' (μ : Measure α) (c : ℝ) :
μ.tilted (fun _ ↦ c) = (μ Set.univ)⁻¹ • μ := by
cases eq_zero_or_neZero μ with
| inl h => rw [h]; simp
| inr h0 =>
simp only [Measure.tilted, withDensity_const, integral_const, smul_eq_mul]
by_cases h_univ : μ Set.univ = ∞
· simp only [measureReal_def, h_univ, ENNReal.toReal_top, zero_mul, div_zero,
ENNReal.ofReal_zero, zero_smul, ENNReal.inv_top]
congr
rw [div_eq_mul_inv, mul_inv, mul_comm, mul_assoc, inv_mul_cancel₀ (exp_pos _).ne', mul_one,
measureReal_def, ← ENNReal.toReal_inv, ENNReal.ofReal_toReal]
simp [h0.out]
lemma tilted_const (μ : Measure α) [IsProbabilityMeasure μ] (c : ℝ) :
μ.tilted (fun _ ↦ c) = μ := by simp
@[simp]
lemma tilted_zero' (μ : Measure α) : μ.tilted 0 = (μ Set.univ)⁻¹ • μ := by
change μ.tilted (fun _ ↦ 0) = (μ Set.univ)⁻¹ • μ
simp
lemma tilted_zero (μ : Measure α) [IsProbabilityMeasure μ] : μ.tilted 0 = μ := by simp
lemma tilted_congr {g : α → ℝ} (hfg : f =ᵐ[μ] g) :
μ.tilted f = μ.tilted g := by
have h_int_eq : ∫ x, exp (f x) ∂μ = ∫ x, exp (g x) ∂μ := by
refine integral_congr_ae ?_
filter_upwards [hfg] with x hx
rw [hx]
refine withDensity_congr_ae ?_
filter_upwards [hfg] with x hx
rw [h_int_eq, hx]
lemma tilted_eq_withDensity_nnreal (μ : Measure α) (f : α → ℝ) :
μ.tilted f = μ.withDensity (fun x ↦ ((↑) : ℝ≥0 → ℝ≥0∞)
(⟨exp (f x) / ∫ x, exp (f x) ∂μ, by positivity⟩ : ℝ≥0)) := by
rw [Measure.tilted]
congr with x
rw [ENNReal.ofReal_eq_coe_nnreal]
lemma tilted_apply' (μ : Measure α) (f : α → ℝ) {s : Set α} (hs : MeasurableSet s) :
μ.tilted f s = ∫⁻ a in s, ENNReal.ofReal (exp (f a) / ∫ x, exp (f x) ∂μ) ∂μ := by
rw [Measure.tilted, withDensity_apply _ hs]
lemma tilted_apply (μ : Measure α) [SFinite μ] (f : α → ℝ) (s : Set α) :
μ.tilted f s = ∫⁻ a in s, ENNReal.ofReal (exp (f a) / ∫ x, exp (f x) ∂μ) ∂μ := by
rw [Measure.tilted, withDensity_apply' _ s]
lemma tilted_apply_eq_ofReal_integral' {s : Set α} (f : α → ℝ) (hs : MeasurableSet s) :
μ.tilted f s = ENNReal.ofReal (∫ a in s, exp (f a) / ∫ x, exp (f x) ∂μ ∂μ) := by
by_cases hf : Integrable (fun x ↦ exp (f x)) μ
· rw [tilted_apply' _ _ hs, ← ofReal_integral_eq_lintegral_ofReal]
· exact hf.integrableOn.div_const _
· exact ae_of_all _ (fun _ ↦ by positivity)
· simp only [hf, not_false_eq_true, tilted_of_not_integrable, Measure.coe_zero,
Pi.zero_apply, integral_undef hf, div_zero, integral_zero, ENNReal.ofReal_zero]
lemma tilted_apply_eq_ofReal_integral [SFinite μ] (f : α → ℝ) (s : Set α) :
μ.tilted f s = ENNReal.ofReal (∫ a in s, exp (f a) / ∫ x, exp (f x) ∂μ ∂μ) := by
by_cases hf : Integrable (fun x ↦ exp (f x)) μ
· rw [tilted_apply _ _, ← ofReal_integral_eq_lintegral_ofReal]
· exact hf.integrableOn.div_const _
· exact ae_of_all _ (fun _ ↦ by positivity)
· simp [tilted_of_not_integrable hf, integral_undef hf]
lemma isProbabilityMeasure_tilted [NeZero μ] (hf : Integrable (fun x ↦ exp (f x)) μ) :
IsProbabilityMeasure (μ.tilted f) := by
constructor
simp_rw [tilted_apply' _ _ MeasurableSet.univ, setLIntegral_univ,
ENNReal.ofReal_div_of_pos (integral_exp_pos hf), div_eq_mul_inv]
rw [lintegral_mul_const'' _ hf.1.aemeasurable.ennreal_ofReal,
← ofReal_integral_eq_lintegral_ofReal hf (ae_of_all _ fun _ ↦ (exp_pos _).le),
ENNReal.mul_inv_cancel]
· simp only [ne_eq, ENNReal.ofReal_eq_zero, not_le]
exact integral_exp_pos hf
· simp
instance isZeroOrProbabilityMeasure_tilted : IsZeroOrProbabilityMeasure (μ.tilted f) := by
rcases eq_zero_or_neZero μ with hμ | hμ
· simp only [hμ, tilted_zero_measure]
infer_instance
by_cases hf : Integrable (fun x ↦ exp (f x)) μ
· have := isProbabilityMeasure_tilted hf
infer_instance
· simp only [hf, not_false_eq_true, tilted_of_not_integrable]
infer_instance
| section lintegral
lemma setLIntegral_tilted' (f : α → ℝ) (g : α → ℝ≥0∞) {s : Set α} (hs : MeasurableSet s) :
∫⁻ x in s, g x ∂(μ.tilted f)
= ∫⁻ x in s, ENNReal.ofReal (exp (f x) / ∫ x, exp (f x) ∂μ) * g x ∂μ := by
by_cases hf : AEMeasurable f μ
· rw [Measure.tilted, setLIntegral_withDensity_eq_setLIntegral_mul_non_measurable₀]
· simp only [Pi.mul_apply]
· refine AEMeasurable.restrict ?_
exact ((measurable_exp.comp_aemeasurable hf).div_const _).ennreal_ofReal
· exact hs
· filter_upwards
simp only [ENNReal.ofReal_lt_top, implies_true]
· have hf' : ¬ Integrable (fun x ↦ exp (f x)) μ := by
exact fun h ↦ hf (aemeasurable_of_aemeasurable_exp h.1.aemeasurable)
simp only [hf, not_false_eq_true, tilted_of_not_aemeasurable, Measure.restrict_zero,
lintegral_zero_measure]
| Mathlib/MeasureTheory/Measure/Tilted.lean | 144 | 160 |
/-
Copyright (c) 2018 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Kenny Lau, Johan Commelin, Mario Carneiro, Kevin Buzzard,
Amelia Livingston, Yury Kudryashov
-/
import Mathlib.Algebra.Group.Action.Faithful
import Mathlib.Algebra.Group.Nat.Defs
import Mathlib.Algebra.Group.Prod
import Mathlib.Algebra.Group.Submonoid.Basic
import Mathlib.Algebra.Group.Submonoid.MulAction
import Mathlib.Algebra.Group.TypeTags.Basic
/-!
# Operations on `Submonoid`s
In this file we define various operations on `Submonoid`s and `MonoidHom`s.
## Main definitions
### Conversion between multiplicative and additive definitions
* `Submonoid.toAddSubmonoid`, `Submonoid.toAddSubmonoid'`, `AddSubmonoid.toSubmonoid`,
`AddSubmonoid.toSubmonoid'`: convert between multiplicative and additive submonoids of `M`,
`Multiplicative M`, and `Additive M`. These are stated as `OrderIso`s.
### (Commutative) monoid structure on a submonoid
* `Submonoid.toMonoid`, `Submonoid.toCommMonoid`: a submonoid inherits a (commutative) monoid
structure.
### Group actions by submonoids
* `Submonoid.MulAction`, `Submonoid.DistribMulAction`: a submonoid inherits (distributive)
multiplicative actions.
### Operations on submonoids
* `Submonoid.comap`: preimage of a submonoid under a monoid homomorphism as a submonoid of the
domain;
* `Submonoid.map`: image of a submonoid under a monoid homomorphism as a submonoid of the codomain;
* `Submonoid.prod`: product of two submonoids `s : Submonoid M` and `t : Submonoid N` as a submonoid
of `M × N`;
### Monoid homomorphisms between submonoid
* `Submonoid.subtype`: embedding of a submonoid into the ambient monoid.
* `Submonoid.inclusion`: given two submonoids `S`, `T` such that `S ≤ T`, `S.inclusion T` is the
inclusion of `S` into `T` as a monoid homomorphism;
* `MulEquiv.submonoidCongr`: converts a proof of `S = T` into a monoid isomorphism between `S`
and `T`.
* `Submonoid.prodEquiv`: monoid isomorphism between `s.prod t` and `s × t`;
### Operations on `MonoidHom`s
* `MonoidHom.mrange`: range of a monoid homomorphism as a submonoid of the codomain;
* `MonoidHom.mker`: kernel of a monoid homomorphism as a submonoid of the domain;
* `MonoidHom.restrict`: restrict a monoid homomorphism to a submonoid;
* `MonoidHom.codRestrict`: restrict the codomain of a monoid homomorphism to a submonoid;
* `MonoidHom.mrangeRestrict`: restrict a monoid homomorphism to its range;
## Tags
submonoid, range, product, map, comap
-/
assert_not_exists MonoidWithZero
open Function
variable {M N P : Type*} [MulOneClass M] [MulOneClass N] [MulOneClass P] (S : Submonoid M)
/-!
### Conversion to/from `Additive`/`Multiplicative`
-/
section
/-- Submonoids of monoid `M` are isomorphic to additive submonoids of `Additive M`. -/
@[simps]
def Submonoid.toAddSubmonoid : Submonoid M ≃o AddSubmonoid (Additive M) where
toFun S :=
{ carrier := Additive.toMul ⁻¹' S
zero_mem' := S.one_mem'
add_mem' := fun ha hb => S.mul_mem' ha hb }
invFun S :=
{ carrier := Additive.ofMul ⁻¹' S
one_mem' := S.zero_mem'
mul_mem' := fun ha hb => S.add_mem' ha hb}
left_inv x := by cases x; rfl
right_inv x := by cases x; rfl
map_rel_iff' := Iff.rfl
/-- Additive submonoids of an additive monoid `Additive M` are isomorphic to submonoids of `M`. -/
abbrev AddSubmonoid.toSubmonoid' : AddSubmonoid (Additive M) ≃o Submonoid M :=
Submonoid.toAddSubmonoid.symm
theorem Submonoid.toAddSubmonoid_closure (S : Set M) :
Submonoid.toAddSubmonoid (Submonoid.closure S)
= AddSubmonoid.closure (Additive.toMul ⁻¹' S) :=
le_antisymm
(Submonoid.toAddSubmonoid.le_symm_apply.1 <|
Submonoid.closure_le.2 (AddSubmonoid.subset_closure (M := Additive M)))
(AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := M))
theorem AddSubmonoid.toSubmonoid'_closure (S : Set (Additive M)) :
AddSubmonoid.toSubmonoid' (AddSubmonoid.closure S)
= Submonoid.closure (Additive.ofMul ⁻¹' S) :=
le_antisymm
(AddSubmonoid.toSubmonoid'.le_symm_apply.1 <|
AddSubmonoid.closure_le.2 (Submonoid.subset_closure (M := M)))
(Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := Additive M))
end
section
variable {A : Type*} [AddZeroClass A]
/-- Additive submonoids of an additive monoid `A` are isomorphic to
multiplicative submonoids of `Multiplicative A`. -/
@[simps]
def AddSubmonoid.toSubmonoid : AddSubmonoid A ≃o Submonoid (Multiplicative A) where
toFun S :=
{ carrier := Multiplicative.toAdd ⁻¹' S
one_mem' := S.zero_mem'
mul_mem' := fun ha hb => S.add_mem' ha hb }
invFun S :=
{ carrier := Multiplicative.ofAdd ⁻¹' S
zero_mem' := S.one_mem'
add_mem' := fun ha hb => S.mul_mem' ha hb}
left_inv x := by cases x; rfl
right_inv x := by cases x; rfl
map_rel_iff' := Iff.rfl
/-- Submonoids of a monoid `Multiplicative A` are isomorphic to additive submonoids of `A`. -/
abbrev Submonoid.toAddSubmonoid' : Submonoid (Multiplicative A) ≃o AddSubmonoid A :=
AddSubmonoid.toSubmonoid.symm
theorem AddSubmonoid.toSubmonoid_closure (S : Set A) :
(AddSubmonoid.toSubmonoid) (AddSubmonoid.closure S)
= Submonoid.closure (Multiplicative.toAdd ⁻¹' S) :=
le_antisymm
(AddSubmonoid.toSubmonoid.to_galoisConnection.l_le <|
AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := Multiplicative A))
(Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := A))
theorem Submonoid.toAddSubmonoid'_closure (S : Set (Multiplicative A)) :
Submonoid.toAddSubmonoid' (Submonoid.closure S)
= AddSubmonoid.closure (Multiplicative.ofAdd ⁻¹' S) :=
le_antisymm
(Submonoid.toAddSubmonoid'.to_galoisConnection.l_le <|
Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := A))
(AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := Multiplicative A))
end
namespace Submonoid
variable {F : Type*} [FunLike F M N] [mc : MonoidHomClass F M N]
open Set
/-!
### `comap` and `map`
-/
/-- The preimage of a submonoid along a monoid homomorphism is a submonoid. -/
@[to_additive
"The preimage of an `AddSubmonoid` along an `AddMonoid` homomorphism is an `AddSubmonoid`."]
def comap (f : F) (S : Submonoid N) :
Submonoid M where
carrier := f ⁻¹' S
one_mem' := show f 1 ∈ S by rw [map_one]; exact S.one_mem
mul_mem' ha hb := show f (_ * _) ∈ S by rw [map_mul]; exact S.mul_mem ha hb
@[to_additive (attr := simp)]
theorem coe_comap (S : Submonoid N) (f : F) : (S.comap f : Set M) = f ⁻¹' S :=
rfl
@[to_additive (attr := simp)]
theorem mem_comap {S : Submonoid N} {f : F} {x : M} : x ∈ S.comap f ↔ f x ∈ S :=
Iff.rfl
@[to_additive]
theorem comap_comap (S : Submonoid P) (g : N →* P) (f : M →* N) :
(S.comap g).comap f = S.comap (g.comp f) :=
rfl
@[to_additive (attr := simp)]
theorem comap_id (S : Submonoid P) : S.comap (MonoidHom.id P) = S :=
ext (by simp)
/-- The image of a submonoid along a monoid homomorphism is a submonoid. -/
@[to_additive
"The image of an `AddSubmonoid` along an `AddMonoid` homomorphism is an `AddSubmonoid`."]
def map (f : F) (S : Submonoid M) :
Submonoid N where
carrier := f '' S
one_mem' := ⟨1, S.one_mem, map_one f⟩
mul_mem' := by
rintro _ _ ⟨x, hx, rfl⟩ ⟨y, hy, rfl⟩
exact ⟨x * y, S.mul_mem hx hy, by rw [map_mul]⟩
@[to_additive (attr := simp)]
theorem coe_map (f : F) (S : Submonoid M) : (S.map f : Set N) = f '' S :=
rfl
@[to_additive (attr := simp)]
theorem map_coe_toMonoidHom (f : F) (S : Submonoid M) : S.map (f : M →* N) = S.map f :=
rfl
@[to_additive (attr := simp)]
theorem map_coe_toMulEquiv {F} [EquivLike F M N] [MulEquivClass F M N] (f : F) (S : Submonoid M) :
S.map (f : M ≃* N) = S.map f :=
rfl
@[to_additive (attr := simp)]
theorem mem_map {f : F} {S : Submonoid M} {y : N} : y ∈ S.map f ↔ ∃ x ∈ S, f x = y := Iff.rfl
@[to_additive]
theorem mem_map_of_mem (f : F) {S : Submonoid M} {x : M} (hx : x ∈ S) : f x ∈ S.map f :=
mem_image_of_mem f hx
@[to_additive]
theorem apply_coe_mem_map (f : F) (S : Submonoid M) (x : S) : f x ∈ S.map f :=
mem_map_of_mem f x.2
@[to_additive]
theorem map_map (g : N →* P) (f : M →* N) : (S.map f).map g = S.map (g.comp f) :=
SetLike.coe_injective <| image_image _ _ _
-- The simpNF linter says that the LHS can be simplified via `Submonoid.mem_map`.
-- However this is a higher priority lemma.
-- It seems the side condition `hf` is not applied by `simpNF`.
-- https://github.com/leanprover/std4/issues/207
@[to_additive (attr := simp 1100, nolint simpNF)]
theorem mem_map_iff_mem {f : F} (hf : Function.Injective f) {S : Submonoid M} {x : M} :
f x ∈ S.map f ↔ x ∈ S :=
hf.mem_set_image
@[to_additive]
theorem map_le_iff_le_comap {f : F} {S : Submonoid M} {T : Submonoid N} :
S.map f ≤ T ↔ S ≤ T.comap f :=
image_subset_iff
@[to_additive]
theorem gc_map_comap (f : F) : GaloisConnection (map f) (comap f) := fun _ _ => map_le_iff_le_comap
@[to_additive]
theorem map_le_of_le_comap {T : Submonoid N} {f : F} : S ≤ T.comap f → S.map f ≤ T :=
(gc_map_comap f).l_le
@[to_additive]
theorem le_comap_of_map_le {T : Submonoid N} {f : F} : S.map f ≤ T → S ≤ T.comap f :=
(gc_map_comap f).le_u
@[to_additive]
theorem le_comap_map {f : F} : S ≤ (S.map f).comap f :=
(gc_map_comap f).le_u_l _
@[to_additive]
theorem map_comap_le {S : Submonoid N} {f : F} : (S.comap f).map f ≤ S :=
(gc_map_comap f).l_u_le _
@[to_additive]
theorem monotone_map {f : F} : Monotone (map f) :=
(gc_map_comap f).monotone_l
@[to_additive]
theorem monotone_comap {f : F} : Monotone (comap f) :=
(gc_map_comap f).monotone_u
@[to_additive (attr := simp)]
theorem map_comap_map {f : F} : ((S.map f).comap f).map f = S.map f :=
(gc_map_comap f).l_u_l_eq_l _
@[to_additive (attr := simp)]
theorem comap_map_comap {S : Submonoid N} {f : F} : ((S.comap f).map f).comap f = S.comap f :=
(gc_map_comap f).u_l_u_eq_u _
@[to_additive]
theorem map_sup (S T : Submonoid M) (f : F) : (S ⊔ T).map f = S.map f ⊔ T.map f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).l_sup
@[to_additive]
theorem map_iSup {ι : Sort*} (f : F) (s : ι → Submonoid M) : (iSup s).map f = ⨆ i, (s i).map f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).l_iSup
@[to_additive]
theorem map_inf (S T : Submonoid M) (f : F) (hf : Function.Injective f) :
(S ⊓ T).map f = S.map f ⊓ T.map f := SetLike.coe_injective (Set.image_inter hf)
@[to_additive]
theorem map_iInf {ι : Sort*} [Nonempty ι] (f : F) (hf : Function.Injective f)
(s : ι → Submonoid M) : (iInf s).map f = ⨅ i, (s i).map f := by
apply SetLike.coe_injective
simpa using (Set.injOn_of_injective hf).image_iInter_eq (s := SetLike.coe ∘ s)
@[to_additive]
theorem comap_inf (S T : Submonoid N) (f : F) : (S ⊓ T).comap f = S.comap f ⊓ T.comap f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).u_inf
@[to_additive]
theorem comap_iInf {ι : Sort*} (f : F) (s : ι → Submonoid N) :
(iInf s).comap f = ⨅ i, (s i).comap f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).u_iInf
@[to_additive (attr := simp)]
theorem map_bot (f : F) : (⊥ : Submonoid M).map f = ⊥ :=
(gc_map_comap f).l_bot
@[to_additive (attr := simp)]
theorem comap_top (f : F) : (⊤ : Submonoid N).comap f = ⊤ :=
(gc_map_comap f).u_top
@[to_additive (attr := simp)]
theorem map_id (S : Submonoid M) : S.map (MonoidHom.id M) = S :=
ext fun _ => ⟨fun ⟨_, h, rfl⟩ => h, fun h => ⟨_, h, rfl⟩⟩
section GaloisCoinsertion
variable {ι : Type*} {f : F}
/-- `map f` and `comap f` form a `GaloisCoinsertion` when `f` is injective. -/
@[to_additive "`map f` and `comap f` form a `GaloisCoinsertion` when `f` is injective."]
def gciMapComap (hf : Function.Injective f) : GaloisCoinsertion (map f) (comap f) :=
(gc_map_comap f).toGaloisCoinsertion fun S x => by simp [mem_comap, mem_map, hf.eq_iff]
variable (hf : Function.Injective f)
include hf
@[to_additive]
theorem comap_map_eq_of_injective (S : Submonoid M) : (S.map f).comap f = S :=
(gciMapComap hf).u_l_eq _
@[to_additive]
theorem comap_surjective_of_injective : Function.Surjective (comap f) :=
(gciMapComap hf).u_surjective
@[to_additive]
theorem map_injective_of_injective : Function.Injective (map f) :=
(gciMapComap hf).l_injective
@[to_additive]
theorem comap_inf_map_of_injective (S T : Submonoid M) : (S.map f ⊓ T.map f).comap f = S ⊓ T :=
(gciMapComap hf).u_inf_l _ _
@[to_additive]
theorem comap_iInf_map_of_injective (S : ι → Submonoid M) : (⨅ i, (S i).map f).comap f = iInf S :=
(gciMapComap hf).u_iInf_l _
@[to_additive]
theorem comap_sup_map_of_injective (S T : Submonoid M) : (S.map f ⊔ T.map f).comap f = S ⊔ T :=
(gciMapComap hf).u_sup_l _ _
@[to_additive]
theorem comap_iSup_map_of_injective (S : ι → Submonoid M) : (⨆ i, (S i).map f).comap f = iSup S :=
(gciMapComap hf).u_iSup_l _
@[to_additive]
theorem map_le_map_iff_of_injective {S T : Submonoid M} : S.map f ≤ T.map f ↔ S ≤ T :=
(gciMapComap hf).l_le_l_iff
@[to_additive]
theorem map_strictMono_of_injective : StrictMono (map f) :=
(gciMapComap hf).strictMono_l
end GaloisCoinsertion
section GaloisInsertion
variable {ι : Type*} {f : F}
/-- `map f` and `comap f` form a `GaloisInsertion` when `f` is surjective. -/
@[to_additive "`map f` and `comap f` form a `GaloisInsertion` when `f` is surjective."]
def giMapComap (hf : Function.Surjective f) : GaloisInsertion (map f) (comap f) :=
(gc_map_comap f).toGaloisInsertion fun S x h =>
let ⟨y, hy⟩ := hf x
mem_map.2 ⟨y, by simp [hy, h]⟩
variable (hf : Function.Surjective f)
include hf
@[to_additive]
theorem map_comap_eq_of_surjective (S : Submonoid N) : (S.comap f).map f = S :=
(giMapComap hf).l_u_eq _
@[to_additive]
theorem map_surjective_of_surjective : Function.Surjective (map f) :=
(giMapComap hf).l_surjective
@[to_additive]
theorem comap_injective_of_surjective : Function.Injective (comap f) :=
(giMapComap hf).u_injective
@[to_additive]
theorem map_inf_comap_of_surjective (S T : Submonoid N) : (S.comap f ⊓ T.comap f).map f = S ⊓ T :=
(giMapComap hf).l_inf_u _ _
@[to_additive]
theorem map_iInf_comap_of_surjective (S : ι → Submonoid N) : (⨅ i, (S i).comap f).map f = iInf S :=
(giMapComap hf).l_iInf_u _
@[to_additive]
theorem map_sup_comap_of_surjective (S T : Submonoid N) : (S.comap f ⊔ T.comap f).map f = S ⊔ T :=
(giMapComap hf).l_sup_u _ _
@[to_additive]
theorem map_iSup_comap_of_surjective (S : ι → Submonoid N) : (⨆ i, (S i).comap f).map f = iSup S :=
(giMapComap hf).l_iSup_u _
@[to_additive]
theorem comap_le_comap_iff_of_surjective {S T : Submonoid N} : S.comap f ≤ T.comap f ↔ S ≤ T :=
(giMapComap hf).u_le_u_iff
@[to_additive]
theorem comap_strictMono_of_surjective : StrictMono (comap f) :=
(giMapComap hf).strictMono_u
end GaloisInsertion
variable {M : Type*} [MulOneClass M] (S : Submonoid M)
/-- The top submonoid is isomorphic to the monoid. -/
@[to_additive (attr := simps) "The top additive submonoid is isomorphic to the additive monoid."]
def topEquiv : (⊤ : Submonoid M) ≃* M where
toFun x := x
invFun x := ⟨x, mem_top x⟩
left_inv x := x.eta _
right_inv _ := rfl
map_mul' _ _ := rfl
@[to_additive (attr := simp)]
theorem topEquiv_toMonoidHom : ((topEquiv : _ ≃* M) : _ →* M) = (⊤ : Submonoid M).subtype :=
rfl
/-- A subgroup is isomorphic to its image under an injective function. If you have an isomorphism,
use `MulEquiv.submonoidMap` for better definitional equalities. -/
@[to_additive "An additive subgroup is isomorphic to its image under an injective function. If you
have an isomorphism, use `AddEquiv.addSubmonoidMap` for better definitional equalities."]
noncomputable def equivMapOfInjective (f : M →* N) (hf : Function.Injective f) : S ≃* S.map f :=
{ Equiv.Set.image f S hf with map_mul' := fun _ _ => Subtype.ext (f.map_mul _ _) }
@[to_additive (attr := simp)]
theorem coe_equivMapOfInjective_apply (f : M →* N) (hf : Function.Injective f) (x : S) :
(equivMapOfInjective S f hf x : N) = f x :=
rfl
@[to_additive (attr := simp)]
theorem closure_closure_coe_preimage {s : Set M} : closure (((↑) : closure s → M) ⁻¹' s) = ⊤ :=
eq_top_iff.2 fun x _ ↦ Subtype.recOn x fun _ hx' ↦
closure_induction (fun _ h ↦ subset_closure h) (one_mem _) (fun _ _ _ _ ↦ mul_mem) hx'
/-- Given submonoids `s`, `t` of monoids `M`, `N` respectively, `s × t` as a submonoid
of `M × N`. -/
@[to_additive prod
"Given `AddSubmonoid`s `s`, `t` of `AddMonoid`s `A`, `B` respectively, `s × t`
as an `AddSubmonoid` of `A × B`."]
def prod (s : Submonoid M) (t : Submonoid N) :
Submonoid (M × N) where
carrier := s ×ˢ t
one_mem' := ⟨s.one_mem, t.one_mem⟩
mul_mem' hp hq := ⟨s.mul_mem hp.1 hq.1, t.mul_mem hp.2 hq.2⟩
@[to_additive coe_prod]
theorem coe_prod (s : Submonoid M) (t : Submonoid N) :
(s.prod t : Set (M × N)) = (s : Set M) ×ˢ (t : Set N) :=
rfl
@[to_additive mem_prod]
theorem mem_prod {s : Submonoid M} {t : Submonoid N} {p : M × N} :
p ∈ s.prod t ↔ p.1 ∈ s ∧ p.2 ∈ t :=
Iff.rfl
@[to_additive prod_mono]
theorem prod_mono {s₁ s₂ : Submonoid M} {t₁ t₂ : Submonoid N} (hs : s₁ ≤ s₂) (ht : t₁ ≤ t₂) :
s₁.prod t₁ ≤ s₂.prod t₂ :=
Set.prod_mono hs ht
@[to_additive prod_top]
theorem prod_top (s : Submonoid M) : s.prod (⊤ : Submonoid N) = s.comap (MonoidHom.fst M N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_fst]
@[to_additive top_prod]
theorem top_prod (s : Submonoid N) : (⊤ : Submonoid M).prod s = s.comap (MonoidHom.snd M N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_snd]
@[to_additive (attr := simp) top_prod_top]
theorem top_prod_top : (⊤ : Submonoid M).prod (⊤ : Submonoid N) = ⊤ :=
(top_prod _).trans <| comap_top _
@[to_additive bot_prod_bot]
theorem bot_prod_bot : (⊥ : Submonoid M).prod (⊥ : Submonoid N) = ⊥ :=
SetLike.coe_injective <| by simp [coe_prod]
/-- The product of submonoids is isomorphic to their product as monoids. -/
@[to_additive prodEquiv
"The product of additive submonoids is isomorphic to their product as additive monoids"]
def prodEquiv (s : Submonoid M) (t : Submonoid N) : s.prod t ≃* s × t :=
{ (Equiv.Set.prod (s : Set M) (t : Set N)) with
map_mul' := fun _ _ => rfl }
open MonoidHom
@[to_additive]
theorem map_inl (s : Submonoid M) : s.map (inl M N) = s.prod ⊥ :=
ext fun p =>
⟨fun ⟨_, hx, hp⟩ => hp ▸ ⟨hx, Set.mem_singleton 1⟩, fun ⟨hps, hp1⟩ =>
⟨p.1, hps, Prod.ext rfl <| (Set.eq_of_mem_singleton hp1).symm⟩⟩
@[to_additive]
theorem map_inr (s : Submonoid N) : s.map (inr M N) = prod ⊥ s :=
ext fun p =>
⟨fun ⟨_, hx, hp⟩ => hp ▸ ⟨Set.mem_singleton 1, hx⟩, fun ⟨hp1, hps⟩ =>
⟨p.2, hps, Prod.ext (Set.eq_of_mem_singleton hp1).symm rfl⟩⟩
@[to_additive (attr := simp) prod_bot_sup_bot_prod]
theorem prod_bot_sup_bot_prod (s : Submonoid M) (t : Submonoid N) :
(prod s ⊥) ⊔ (prod ⊥ t) = prod s t :=
(le_antisymm (sup_le (prod_mono (le_refl s) bot_le) (prod_mono bot_le (le_refl t))))
fun p hp => Prod.fst_mul_snd p ▸ mul_mem
((le_sup_left : prod s ⊥ ≤ prod s ⊥ ⊔ prod ⊥ t) ⟨hp.1, Set.mem_singleton 1⟩)
((le_sup_right : prod ⊥ t ≤ prod s ⊥ ⊔ prod ⊥ t) ⟨Set.mem_singleton 1, hp.2⟩)
@[to_additive]
theorem mem_map_equiv {f : M ≃* N} {K : Submonoid M} {x : N} :
x ∈ K.map f.toMonoidHom ↔ f.symm x ∈ K :=
Set.mem_image_equiv
@[to_additive]
theorem map_equiv_eq_comap_symm (f : M ≃* N) (K : Submonoid M) :
K.map f = K.comap f.symm :=
SetLike.coe_injective (f.toEquiv.image_eq_preimage K)
@[to_additive]
theorem comap_equiv_eq_map_symm (f : N ≃* M) (K : Submonoid M) :
K.comap f = K.map f.symm :=
(map_equiv_eq_comap_symm f.symm K).symm
@[to_additive (attr := simp)]
theorem map_equiv_top (f : M ≃* N) : (⊤ : Submonoid M).map f = ⊤ :=
SetLike.coe_injective <| Set.image_univ.trans f.surjective.range_eq
@[to_additive le_prod_iff]
theorem le_prod_iff {s : Submonoid M} {t : Submonoid N} {u : Submonoid (M × N)} :
u ≤ s.prod t ↔ u.map (fst M N) ≤ s ∧ u.map (snd M N) ≤ t := by
constructor
· intro h
constructor
· rintro x ⟨⟨y1, y2⟩, ⟨hy1, rfl⟩⟩
exact (h hy1).1
· rintro x ⟨⟨y1, y2⟩, ⟨hy1, rfl⟩⟩
exact (h hy1).2
· rintro ⟨hH, hK⟩ ⟨x1, x2⟩ h
exact ⟨hH ⟨_, h, rfl⟩, hK ⟨_, h, rfl⟩⟩
@[to_additive prod_le_iff]
theorem prod_le_iff {s : Submonoid M} {t : Submonoid N} {u : Submonoid (M × N)} :
s.prod t ≤ u ↔ s.map (inl M N) ≤ u ∧ t.map (inr M N) ≤ u := by
constructor
· intro h
constructor
· rintro _ ⟨x, hx, rfl⟩
apply h
exact ⟨hx, Submonoid.one_mem _⟩
· rintro _ ⟨x, hx, rfl⟩
apply h
exact ⟨Submonoid.one_mem _, hx⟩
· rintro ⟨hH, hK⟩ ⟨x1, x2⟩ ⟨h1, h2⟩
have h1' : inl M N x1 ∈ u := by
apply hH
simpa using h1
have h2' : inr M N x2 ∈ u := by
apply hK
simpa using h2
simpa using Submonoid.mul_mem _ h1' h2'
@[to_additive closure_prod]
theorem closure_prod {s : Set M} {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_of_le_comap _ <| closure_le.2 fun _x hx => subset_closure ⟨hx, ht⟩,
map_le_of_le_comap _ <| closure_le.2 fun _y hy => subset_closure ⟨hs, hy⟩⟩)
@[to_additive (attr := simp) closure_prod_zero]
lemma closure_prod_one (s : Set M) : closure (s ×ˢ ({1} : Set N)) = (closure s).prod ⊥ :=
le_antisymm
(closure_le.2 <| Set.prod_subset_prod_iff.2 <| .inl ⟨subset_closure, .rfl⟩)
(prod_le_iff.2 ⟨
map_le_of_le_comap _ <| closure_le.2 fun _x hx => subset_closure ⟨hx, rfl⟩,
by simp⟩)
@[to_additive (attr := simp) closure_zero_prod]
lemma closure_one_prod (t : Set N) : closure (({1} : Set M) ×ˢ t) = .prod ⊥ (closure t) :=
le_antisymm
(closure_le.2 <| Set.prod_subset_prod_iff.2 <| .inl ⟨.rfl, subset_closure⟩)
(prod_le_iff.2 ⟨by simp,
map_le_of_le_comap _ <| closure_le.2 fun _y hy => subset_closure ⟨rfl, hy⟩⟩)
end Submonoid
namespace MonoidHom
variable {F : Type*} [FunLike F M N] [mc : MonoidHomClass F M N]
open Submonoid
library_note "range copy pattern"/--
For many categories (monoids, modules, rings, ...) the set-theoretic image of a morphism `f` is
a subobject of the codomain. When this is the case, it is useful to define the range of a morphism
in such a way that the underlying carrier set of the range subobject is definitionally
`Set.range f`. In particular this means that the types `↥(Set.range f)` and `↥f.range` are
interchangeable without proof obligations.
A convenient candidate definition for range which is mathematically correct is `map ⊤ f`, just as
`Set.range` could have been defined as `f '' Set.univ`. However, this lacks the desired definitional
convenience, in that it both does not match `Set.range`, and that it introduces a redundant `x ∈ ⊤`
term which clutters proofs. In such a case one may resort to the `copy`
pattern. A `copy` function converts the definitional problem for the carrier set of a subobject
into a one-off propositional proof obligation which one discharges while writing the definition of
the definitionally convenient range (the parameter `hs` in the example below).
A good example is the case of a morphism of monoids. A convenient definition for
`MonoidHom.mrange` would be `(⊤ : Submonoid M).map f`. However since this lacks the required
definitional convenience, we first define `Submonoid.copy` as follows:
```lean
protected def copy (S : Submonoid M) (s : Set M) (hs : s = S) : Submonoid M :=
{ carrier := s,
one_mem' := hs.symm ▸ S.one_mem',
mul_mem' := hs.symm ▸ S.mul_mem' }
```
and then finally define:
```lean
def mrange (f : M →* N) : Submonoid N :=
((⊤ : Submonoid M).map f).copy (Set.range f) Set.image_univ.symm
```
-/
/-- The range of a monoid homomorphism is a submonoid. See Note [range copy pattern]. -/
@[to_additive "The range of an `AddMonoidHom` is an `AddSubmonoid`."]
def mrange (f : F) : Submonoid N :=
((⊤ : Submonoid M).map f).copy (Set.range f) Set.image_univ.symm
@[to_additive (attr := simp)]
theorem coe_mrange (f : F) : (mrange f : Set N) = Set.range f :=
rfl
@[to_additive (attr := simp)]
theorem mem_mrange {f : F} {y : N} : y ∈ mrange f ↔ ∃ x, f x = y :=
Iff.rfl
@[to_additive]
lemma mrange_comp {O : Type*} [MulOneClass O] (f : N →* O) (g : M →* N) :
mrange (f.comp g) = (mrange g).map f := SetLike.coe_injective <| Set.range_comp f _
@[to_additive]
theorem mrange_eq_map (f : F) : mrange f = (⊤ : Submonoid M).map f :=
Submonoid.copy_eq _
@[to_additive (attr := simp)]
theorem mrange_id : mrange (MonoidHom.id M) = ⊤ := by
simp [mrange_eq_map]
@[to_additive]
theorem map_mrange (g : N →* P) (f : M →* N) : (mrange f).map g = mrange (comp g f) := by
simpa only [mrange_eq_map] using (⊤ : Submonoid M).map_map g f
@[to_additive]
theorem mrange_eq_top {f : F} : mrange f = (⊤ : Submonoid N) ↔ Surjective f :=
SetLike.ext'_iff.trans <| Iff.trans (by rw [coe_mrange, coe_top]) Set.range_eq_univ
@[deprecated (since := "2024-11-11")]
alias mrange_top_iff_surjective := mrange_eq_top
/-- The range of a surjective monoid hom is the whole of the codomain. -/
@[to_additive (attr := simp)
"The range of a surjective `AddMonoid` hom is the whole of the codomain."]
theorem mrange_eq_top_of_surjective (f : F) (hf : Function.Surjective f) :
mrange f = (⊤ : Submonoid N) :=
mrange_eq_top.2 hf
@[deprecated (since := "2024-11-11")] alias mrange_top_of_surjective := mrange_eq_top_of_surjective
@[to_additive]
theorem mclosure_preimage_le (f : F) (s : Set N) : closure (f ⁻¹' s) ≤ (closure s).comap f :=
closure_le.2 fun _ hx => SetLike.mem_coe.2 <| mem_comap.2 <| subset_closure hx
/-- The image under a monoid hom of the submonoid generated by a set equals the submonoid generated
by the image of the set. -/
@[to_additive
"The image under an `AddMonoid` hom of the `AddSubmonoid` generated by a set equals
the `AddSubmonoid` generated by the image of the set."]
theorem map_mclosure (f : F) (s : Set M) : (closure s).map f = closure (f '' s) :=
Set.image_preimage.l_comm_of_u_comm (gc_map_comap f) (Submonoid.gi N).gc (Submonoid.gi M).gc
fun _ ↦ rfl
@[to_additive (attr := simp)]
theorem mclosure_range (f : F) : closure (Set.range f) = mrange f := by
rw [← Set.image_univ, ← map_mclosure, mrange_eq_map, closure_univ]
/-- Restriction of a monoid hom to a submonoid of the domain. -/
@[to_additive "Restriction of an `AddMonoid` hom to an `AddSubmonoid` of the domain."]
def restrict {N S : Type*} [MulOneClass N] [SetLike S M] [SubmonoidClass S M] (f : M →* N)
(s : S) : s →* N :=
f.comp (SubmonoidClass.subtype _)
@[to_additive (attr := simp)]
theorem restrict_apply {N S : Type*} [MulOneClass N] [SetLike S M] [SubmonoidClass S M]
(f : M →* N) (s : S) (x : s) : f.restrict s x = f x :=
rfl
@[to_additive (attr := simp)]
theorem restrict_mrange (f : M →* N) : mrange (f.restrict S) = S.map f := by
simp [SetLike.ext_iff]
/-- Restriction of a monoid hom to a submonoid of the codomain. -/
@[to_additive (attr := simps apply)
"Restriction of an `AddMonoid` hom to an `AddSubmonoid` of the codomain."]
def codRestrict {S} [SetLike S N] [SubmonoidClass S N] (f : M →* N) (s : S) (h : ∀ x, f x ∈ s) :
M →* s where
toFun n := ⟨f n, h n⟩
map_one' := Subtype.eq f.map_one
map_mul' x y := Subtype.eq (f.map_mul x y)
@[to_additive (attr := simp)]
lemma injective_codRestrict {S} [SetLike S N] [SubmonoidClass S N] (f : M →* N) (s : S)
(h : ∀ x, f x ∈ s) : Function.Injective (f.codRestrict s h) ↔ Function.Injective f :=
⟨fun H _ _ hxy ↦ H <| Subtype.eq hxy, fun H _ _ hxy ↦ H (congr_arg Subtype.val hxy)⟩
/-- Restriction of a monoid hom to its range interpreted as a submonoid. -/
@[to_additive "Restriction of an `AddMonoid` hom to its range interpreted as a submonoid."]
def mrangeRestrict {N} [MulOneClass N] (f : M →* N) : M →* (mrange f) :=
(f.codRestrict (mrange f)) fun x => ⟨x, rfl⟩
@[to_additive (attr := simp)]
theorem coe_mrangeRestrict {N} [MulOneClass N] (f : M →* N) (x : M) :
(f.mrangeRestrict x : N) = f x :=
rfl
@[to_additive]
theorem mrangeRestrict_surjective (f : M →* N) : Function.Surjective f.mrangeRestrict :=
fun ⟨_, ⟨x, rfl⟩⟩ => ⟨x, rfl⟩
/-- The multiplicative kernel of a monoid hom is the submonoid of elements `x : G` such
that `f x = 1` -/
@[to_additive
"The additive kernel of an `AddMonoid` hom is the `AddSubmonoid` of
elements such that `f x = 0`"]
def mker (f : F) : Submonoid M :=
(⊥ : Submonoid N).comap f
@[to_additive (attr := simp)]
theorem mem_mker {f : F} {x : M} : x ∈ mker f ↔ f x = 1 :=
Iff.rfl
@[to_additive]
theorem coe_mker (f : F) : (mker f : Set M) = (f : M → N) ⁻¹' {1} :=
rfl
@[to_additive]
instance decidableMemMker [DecidableEq N] (f : F) : DecidablePred (· ∈ mker f) := fun x =>
decidable_of_iff (f x = 1) mem_mker
@[to_additive]
theorem comap_mker (g : N →* P) (f : M →* N) : (mker g).comap f = mker (comp g f) :=
rfl
@[to_additive (attr := simp)]
theorem comap_bot' (f : F) : (⊥ : Submonoid N).comap f = mker f :=
rfl
@[to_additive (attr := simp)]
theorem restrict_mker (f : M →* N) : mker (f.restrict S) = (MonoidHom.mker f).comap S.subtype :=
rfl
@[to_additive]
theorem mrangeRestrict_mker (f : M →* N) : mker (mrangeRestrict f) = mker f := by
ext x
change (⟨f x, _⟩ : mrange f) = ⟨1, _⟩ ↔ f x = 1
simp
@[to_additive (attr := simp)]
theorem mker_one : mker (1 : M →* N) = ⊤ := by
ext
simp [mem_mker]
@[to_additive prod_map_comap_prod']
theorem prod_map_comap_prod' {M' : Type*} {N' : Type*} [MulOneClass M'] [MulOneClass N']
(f : M →* N) (g : M' →* N') (S : Submonoid N) (S' : Submonoid 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 _ _
@[to_additive mker_prod_map]
theorem mker_prod_map {M' : Type*} {N' : Type*} [MulOneClass M'] [MulOneClass N'] (f : M →* N)
(g : M' →* N') : mker (prodMap f g) = (mker f).prod (mker g) := by
rw [← comap_bot', ← comap_bot', ← comap_bot', ← prod_map_comap_prod', bot_prod_bot]
@[to_additive (attr := simp)]
theorem mker_inl : mker (inl M N) = ⊥ := by
ext x
simp [mem_mker]
@[to_additive (attr := simp)]
theorem mker_inr : mker (inr M N) = ⊥ := by
ext x
simp [mem_mker]
@[to_additive (attr := simp)]
lemma mker_fst : mker (fst M N) = .prod ⊥ ⊤ := SetLike.ext fun _ => (iff_of_eq (and_true _)).symm
@[to_additive (attr := simp)]
lemma mker_snd : mker (snd M N) = .prod ⊤ ⊥ := SetLike.ext fun _ => (iff_of_eq (true_and _)).symm
/-- The `MonoidHom` from the preimage of a submonoid to itself. -/
@[to_additive (attr := simps)
"the `AddMonoidHom` from the preimage of an additive submonoid to itself."]
def submonoidComap (f : M →* N) (N' : Submonoid N) :
N'.comap f →* N' where
toFun x := ⟨f x, x.2⟩
map_one' := Subtype.eq f.map_one
map_mul' x y := Subtype.eq (f.map_mul x y)
@[to_additive]
lemma submonoidComap_surjective_of_surjective (f : M →* N) (N' : Submonoid N) (hf : Surjective f) :
Surjective (f.submonoidComap N') := fun y ↦ by
obtain ⟨x, hx⟩ := hf y
use ⟨x, mem_comap.mpr (hx ▸ y.2)⟩
apply Subtype.val_injective
simp [hx]
/-- The `MonoidHom` from a submonoid to its image.
See `MulEquiv.SubmonoidMap` for a variant for `MulEquiv`s. -/
@[to_additive (attr := simps)
"the `AddMonoidHom` from an additive submonoid to its image. See
`AddEquiv.AddSubmonoidMap` for a variant for `AddEquiv`s."]
def submonoidMap (f : M →* N) (M' : Submonoid M) : M' →* M'.map f where
toFun x := ⟨f x, ⟨x, x.2, rfl⟩⟩
map_one' := Subtype.eq <| f.map_one
map_mul' x y := Subtype.eq <| f.map_mul x y
@[to_additive]
theorem submonoidMap_surjective (f : M →* N) (M' : Submonoid M) :
Function.Surjective (f.submonoidMap M') := by
rintro ⟨_, x, hx, rfl⟩
exact ⟨⟨x, hx⟩, rfl⟩
end MonoidHom
namespace Submonoid
open MonoidHom
@[to_additive]
theorem mrange_inl : mrange (inl M N) = prod ⊤ ⊥ := by simpa only [mrange_eq_map] using map_inl ⊤
@[to_additive]
theorem mrange_inr : mrange (inr M N) = prod ⊥ ⊤ := by simpa only [mrange_eq_map] using map_inr ⊤
@[to_additive]
theorem mrange_inl' : mrange (inl M N) = comap (snd M N) ⊥ :=
mrange_inl.trans (top_prod _)
@[to_additive]
theorem mrange_inr' : mrange (inr M N) = comap (fst M N) ⊥ :=
mrange_inr.trans (prod_top _)
@[to_additive (attr := simp)]
theorem mrange_fst : mrange (fst M N) = ⊤ :=
mrange_eq_top_of_surjective (fst M N) <| @Prod.fst_surjective _ _ ⟨1⟩
@[to_additive (attr := simp)]
theorem mrange_snd : mrange (snd M N) = ⊤ :=
mrange_eq_top_of_surjective (snd M N) <| @Prod.snd_surjective _ _ ⟨1⟩
@[to_additive prod_eq_bot_iff]
theorem prod_eq_bot_iff {s : Submonoid M} {t : Submonoid N} : s.prod t = ⊥ ↔ s = ⊥ ∧ t = ⊥ := by
simp only [eq_bot_iff, prod_le_iff, (gc_map_comap _).le_iff_le, comap_bot', mker_inl, mker_inr]
@[to_additive prod_eq_top_iff]
theorem prod_eq_top_iff {s : Submonoid M} {t : Submonoid N} : s.prod t = ⊤ ↔ s = ⊤ ∧ t = ⊤ := by
simp only [eq_top_iff, le_prod_iff, ← (gc_map_comap _).le_iff_le, ← mrange_eq_map, mrange_fst,
mrange_snd]
@[to_additive (attr := simp)]
theorem mrange_inl_sup_mrange_inr : mrange (inl M N) ⊔ mrange (inr M N) = ⊤ := by
simp only [mrange_inl, mrange_inr, prod_bot_sup_bot_prod, top_prod_top]
/-- The monoid hom associated to an inclusion of submonoids. -/
@[to_additive
"The `AddMonoid` hom associated to an inclusion of submonoids."]
def inclusion {S T : Submonoid M} (h : S ≤ T) : S →* T :=
S.subtype.codRestrict _ fun x => h x.2
@[to_additive (attr := simp)]
theorem mrange_subtype (s : Submonoid M) : mrange s.subtype = s :=
SetLike.coe_injective <| (coe_mrange _).trans <| Subtype.range_coe
-- `alias` doesn't add the deprecation suggestion to the `to_additive` version
-- see https://github.com/leanprover-community/mathlib4/issues/19424
@[to_additive] alias range_subtype := mrange_subtype
attribute [deprecated mrange_subtype (since := "2024-11-25")] range_subtype
attribute [deprecated AddSubmonoid.mrange_subtype (since := "2024-11-25")]
AddSubmonoid.range_subtype
@[to_additive]
theorem eq_top_iff' : S = ⊤ ↔ ∀ x : M, x ∈ S :=
eq_top_iff.trans ⟨fun h m => h <| mem_top m, fun h m _ => h m⟩
@[to_additive]
theorem eq_bot_iff_forall : S = ⊥ ↔ ∀ x ∈ S, x = (1 : M) :=
SetLike.ext_iff.trans <| by simp +contextual [iff_def, S.one_mem]
@[to_additive]
theorem eq_bot_of_subsingleton [Subsingleton S] : S = ⊥ := by
rw [eq_bot_iff_forall]
intro y hy
simpa using congr_arg ((↑) : S → M) <| Subsingleton.elim (⟨y, hy⟩ : S) 1
@[to_additive]
theorem nontrivial_iff_exists_ne_one (S : Submonoid M) : Nontrivial S ↔ ∃ x ∈ S, x ≠ (1 : M) :=
calc
Nontrivial S ↔ ∃ x : S, x ≠ 1 := nontrivial_iff_exists_ne 1
_ ↔ ∃ (x : _) (hx : x ∈ S), (⟨x, hx⟩ : S) ≠ ⟨1, S.one_mem⟩ := Subtype.exists
_ ↔ ∃ x ∈ S, x ≠ (1 : M) := by simp [Ne]
/-- A submonoid is either the trivial submonoid or nontrivial. -/
@[to_additive "An additive submonoid is either the trivial additive submonoid or nontrivial."]
theorem bot_or_nontrivial (S : Submonoid M) : S = ⊥ ∨ Nontrivial S := by
simp only [eq_bot_iff_forall, nontrivial_iff_exists_ne_one, ← not_forall, ← Classical.not_imp,
Classical.em]
/-- A submonoid is either the trivial submonoid or contains a nonzero element. -/
@[to_additive
"An additive submonoid is either the trivial additive submonoid or contains a nonzero
element."]
theorem bot_or_exists_ne_one (S : Submonoid M) : S = ⊥ ∨ ∃ x ∈ S, x ≠ (1 : M) :=
S.bot_or_nontrivial.imp_right S.nontrivial_iff_exists_ne_one.mp
end Submonoid
namespace MulEquiv
variable {S} {T : Submonoid M}
/-- Makes the identity isomorphism from a proof that two submonoids of a multiplicative
monoid are equal. -/
@[to_additive
"Makes the identity additive isomorphism from a proof two
submonoids of an additive monoid are equal."]
def submonoidCongr (h : S = T) : S ≃* T :=
{ Equiv.setCongr <| congr_arg _ h with map_mul' := fun _ _ => rfl }
-- this name is primed so that the version to `f.range` instead of `f.mrange` can be unprimed.
/-- A monoid homomorphism `f : M →* N` with a left-inverse `g : N → M` defines a multiplicative
equivalence between `M` and `f.mrange`.
This is a bidirectional version of `MonoidHom.mrange_restrict`. -/
@[to_additive (attr := simps +simpRhs)
"An additive monoid homomorphism `f : M →+ N` with a left-inverse `g : N → M`
defines an additive equivalence between `M` and `f.mrange`.
This is a bidirectional version of `AddMonoidHom.mrange_restrict`. "]
def ofLeftInverse' (f : M →* N) {g : N → M} (h : Function.LeftInverse g f) :
M ≃* MonoidHom.mrange f :=
{ f.mrangeRestrict with
toFun := f.mrangeRestrict
invFun := g ∘ (MonoidHom.mrange f).subtype
left_inv := h
right_inv := fun x =>
Subtype.ext <|
let ⟨x', hx'⟩ := MonoidHom.mem_mrange.mp x.2
show f (g x) = x by rw [← hx', h x'] }
/-- A `MulEquiv` `φ` between two monoids `M` and `N` induces a `MulEquiv` between
a submonoid `S ≤ M` and the submonoid `φ(S) ≤ N`.
See `MonoidHom.submonoidMap` for a variant for `MonoidHom`s. -/
@[to_additive
"An `AddEquiv` `φ` between two additive monoids `M` and `N` induces an `AddEquiv`
between a submonoid `S ≤ M` and the submonoid `φ(S) ≤ N`. See
`AddMonoidHom.addSubmonoidMap` for a variant for `AddMonoidHom`s."]
def submonoidMap (e : M ≃* N) (S : Submonoid M) : S ≃* S.map e :=
{ (e : M ≃ N).image S with map_mul' := fun _ _ => Subtype.ext (map_mul e _ _) }
@[to_additive (attr := simp)]
theorem coe_submonoidMap_apply (e : M ≃* N) (S : Submonoid M) (g : S) :
((submonoidMap e S g : S.map (e : M →* N)) : N) = e g :=
rfl
@[to_additive (attr := simp) AddEquiv.add_submonoid_map_symm_apply]
theorem submonoidMap_symm_apply (e : M ≃* N) (S : Submonoid M) (g : S.map (e : M →* N)) :
(e.submonoidMap S).symm g = ⟨e.symm g, SetLike.mem_coe.1 <| Set.mem_image_equiv.1 g.2⟩ :=
| rfl
| Mathlib/Algebra/Group/Submonoid/Operations.lean | 995 | 996 |
/-
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, Simon Hudon, Mario Carneiro
-/
import Aesop
import Mathlib.Algebra.Group.Defs
import Mathlib.Data.Nat.Init
import Mathlib.Data.Int.Init
import Mathlib.Logic.Function.Iterate
import Mathlib.Tactic.SimpRw
import Mathlib.Tactic.SplitIfs
/-!
# Basic lemmas about semigroups, monoids, and groups
This file lists various basic lemmas about semigroups, monoids, and groups. Most proofs are
one-liners from the corresponding axioms. For the definitions of semigroups, monoids and groups, see
`Algebra/Group/Defs.lean`.
-/
assert_not_exists MonoidWithZero DenselyOrdered
open Function
variable {α β G M : Type*}
section ite
variable [Pow α β]
@[to_additive (attr := simp) dite_smul]
lemma pow_dite (p : Prop) [Decidable p] (a : α) (b : p → β) (c : ¬ p → β) :
a ^ (if h : p then b h else c h) = if h : p then a ^ b h else a ^ c h := by split_ifs <;> rfl
@[to_additive (attr := simp) smul_dite]
lemma dite_pow (p : Prop) [Decidable p] (a : p → α) (b : ¬ p → α) (c : β) :
(if h : p then a h else b h) ^ c = if h : p then a h ^ c else b h ^ c := by split_ifs <;> rfl
@[to_additive (attr := simp) ite_smul]
lemma pow_ite (p : Prop) [Decidable p] (a : α) (b c : β) :
a ^ (if p then b else c) = if p then a ^ b else a ^ c := pow_dite _ _ _ _
@[to_additive (attr := simp) smul_ite]
lemma ite_pow (p : Prop) [Decidable p] (a b : α) (c : β) :
(if p then a else b) ^ c = if p then a ^ c else b ^ c := dite_pow _ _ _ _
set_option linter.existingAttributeWarning false in
attribute [to_additive (attr := simp)] dite_smul smul_dite ite_smul smul_ite
end ite
section Semigroup
variable [Semigroup α]
@[to_additive]
instance Semigroup.to_isAssociative : Std.Associative (α := α) (· * ·) := ⟨mul_assoc⟩
/-- Composing two multiplications on the left by `y` then `x`
is equal to a multiplication on the left by `x * y`.
-/
@[to_additive (attr := simp) "Composing two additions on the left by `y` then `x`
is equal to an addition on the left by `x + y`."]
theorem comp_mul_left (x y : α) : (x * ·) ∘ (y * ·) = (x * y * ·) := by
ext z
simp [mul_assoc]
/-- Composing two multiplications on the right by `y` and `x`
is equal to a multiplication on the right by `y * x`.
-/
@[to_additive (attr := simp) "Composing two additions on the right by `y` and `x`
is equal to an addition on the right by `y + x`."]
theorem comp_mul_right (x y : α) : (· * x) ∘ (· * y) = (· * (y * x)) := by
ext z
simp [mul_assoc]
end Semigroup
@[to_additive]
instance CommMagma.to_isCommutative [CommMagma G] : Std.Commutative (α := G) (· * ·) := ⟨mul_comm⟩
section MulOneClass
variable [MulOneClass M]
@[to_additive]
theorem ite_mul_one {P : Prop} [Decidable P] {a b : M} :
ite P (a * b) 1 = ite P a 1 * ite P b 1 := by
by_cases h : P <;> simp [h]
@[to_additive]
theorem ite_one_mul {P : Prop} [Decidable P] {a b : M} :
ite P 1 (a * b) = ite P 1 a * ite P 1 b := by
by_cases h : P <;> simp [h]
@[to_additive]
theorem eq_one_iff_eq_one_of_mul_eq_one {a b : M} (h : a * b = 1) : a = 1 ↔ b = 1 := by
constructor <;> (rintro rfl; simpa using h)
@[to_additive]
theorem one_mul_eq_id : ((1 : M) * ·) = id :=
funext one_mul
@[to_additive]
theorem mul_one_eq_id : (· * (1 : M)) = id :=
funext mul_one
end MulOneClass
section CommSemigroup
variable [CommSemigroup G]
@[to_additive]
theorem mul_left_comm (a b c : G) : a * (b * c) = b * (a * c) := by
rw [← mul_assoc, mul_comm a, mul_assoc]
@[to_additive]
theorem mul_right_comm (a b c : G) : a * b * c = a * c * b := by
rw [mul_assoc, mul_comm b, mul_assoc]
@[to_additive]
theorem mul_mul_mul_comm (a b c d : G) : a * b * (c * d) = a * c * (b * d) := by
simp only [mul_left_comm, mul_assoc]
@[to_additive]
theorem mul_rotate (a b c : G) : a * b * c = b * c * a := by
simp only [mul_left_comm, mul_comm]
@[to_additive]
theorem mul_rotate' (a b c : G) : a * (b * c) = b * (c * a) := by
simp only [mul_left_comm, mul_comm]
end CommSemigroup
attribute [local simp] mul_assoc sub_eq_add_neg
section Monoid
variable [Monoid M] {a b : M} {m n : ℕ}
@[to_additive boole_nsmul]
lemma pow_boole (P : Prop) [Decidable P] (a : M) :
(a ^ if P then 1 else 0) = if P then a else 1 := by simp only [pow_ite, pow_one, pow_zero]
@[to_additive nsmul_add_sub_nsmul]
lemma pow_mul_pow_sub (a : M) (h : m ≤ n) : a ^ m * a ^ (n - m) = a ^ n := by
rw [← pow_add, Nat.add_comm, Nat.sub_add_cancel h]
@[to_additive sub_nsmul_nsmul_add]
lemma pow_sub_mul_pow (a : M) (h : m ≤ n) : a ^ (n - m) * a ^ m = a ^ n := by
rw [← pow_add, Nat.sub_add_cancel h]
@[to_additive sub_one_nsmul_add]
lemma mul_pow_sub_one (hn : n ≠ 0) (a : M) : a * a ^ (n - 1) = a ^ n := by
rw [← pow_succ', Nat.sub_add_cancel <| Nat.one_le_iff_ne_zero.2 hn]
@[to_additive add_sub_one_nsmul]
lemma pow_sub_one_mul (hn : n ≠ 0) (a : M) : a ^ (n - 1) * a = a ^ n := by
rw [← pow_succ, Nat.sub_add_cancel <| Nat.one_le_iff_ne_zero.2 hn]
/-- If `x ^ n = 1`, then `x ^ m` is the same as `x ^ (m % n)` -/
@[to_additive nsmul_eq_mod_nsmul "If `n • x = 0`, then `m • x` is the same as `(m % n) • x`"]
lemma pow_eq_pow_mod (m : ℕ) (ha : a ^ n = 1) : a ^ m = a ^ (m % n) := by
calc
a ^ m = a ^ (m % n + n * (m / n)) := by rw [Nat.mod_add_div]
_ = a ^ (m % n) := by simp [pow_add, pow_mul, ha]
@[to_additive] lemma pow_mul_pow_eq_one : ∀ n, a * b = 1 → a ^ n * b ^ n = 1
| 0, _ => by simp
| n + 1, h =>
calc
a ^ n.succ * b ^ n.succ = a ^ n * a * (b * b ^ n) := by rw [pow_succ, pow_succ']
_ = a ^ n * (a * b) * b ^ n := by simp only [mul_assoc]
_ = 1 := by simp [h, pow_mul_pow_eq_one]
@[to_additive (attr := simp)]
lemma mul_left_iterate (a : M) : ∀ n : ℕ, (a * ·)^[n] = (a ^ n * ·)
| 0 => by ext; simp
| n + 1 => by ext; simp [pow_succ, mul_left_iterate]
@[to_additive (attr := simp)]
lemma mul_right_iterate (a : M) : ∀ n : ℕ, (· * a)^[n] = (· * a ^ n)
| 0 => by ext; simp
| n + 1 => by ext; simp [pow_succ', mul_right_iterate]
@[to_additive]
lemma mul_left_iterate_apply_one (a : M) : (a * ·)^[n] 1 = a ^ n := by simp [mul_right_iterate]
@[to_additive]
lemma mul_right_iterate_apply_one (a : M) : (· * a)^[n] 1 = a ^ n := by simp [mul_right_iterate]
@[to_additive (attr := simp)]
lemma pow_iterate (k : ℕ) : ∀ n : ℕ, (fun x : M ↦ x ^ k)^[n] = (· ^ k ^ n)
| 0 => by ext; simp
| n + 1 => by ext; simp [pow_iterate, Nat.pow_succ', pow_mul]
end Monoid
section CommMonoid
variable [CommMonoid M] {x y z : M}
@[to_additive]
theorem inv_unique (hy : x * y = 1) (hz : x * z = 1) : y = z :=
left_inv_eq_right_inv (Trans.trans (mul_comm _ _) hy) hz
@[to_additive nsmul_add] lemma mul_pow (a b : M) : ∀ n, (a * b) ^ n = a ^ n * b ^ n
| 0 => by rw [pow_zero, pow_zero, pow_zero, one_mul]
| n + 1 => by rw [pow_succ', pow_succ', pow_succ', mul_pow, mul_mul_mul_comm]
end CommMonoid
section LeftCancelMonoid
variable [Monoid M] [IsLeftCancelMul M] {a b : M}
@[to_additive (attr := simp)]
theorem mul_eq_left : a * b = a ↔ b = 1 := calc
a * b = a ↔ a * b = a * 1 := by rw [mul_one]
_ ↔ b = 1 := mul_left_cancel_iff
@[deprecated (since := "2025-03-05")] alias mul_right_eq_self := mul_eq_left
@[deprecated (since := "2025-03-05")] alias add_right_eq_self := add_eq_left
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] mul_right_eq_self
@[to_additive (attr := simp)]
theorem left_eq_mul : a = a * b ↔ b = 1 :=
eq_comm.trans mul_eq_left
@[deprecated (since := "2025-03-05")] alias self_eq_mul_right := left_eq_mul
@[deprecated (since := "2025-03-05")] alias self_eq_add_right := left_eq_add
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] self_eq_mul_right
@[to_additive]
theorem mul_ne_left : a * b ≠ a ↔ b ≠ 1 := mul_eq_left.not
@[deprecated (since := "2025-03-05")] alias mul_right_ne_self := mul_ne_left
@[deprecated (since := "2025-03-05")] alias add_right_ne_self := add_ne_left
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] mul_right_ne_self
@[to_additive]
theorem left_ne_mul : a ≠ a * b ↔ b ≠ 1 := left_eq_mul.not
@[deprecated (since := "2025-03-05")] alias self_ne_mul_right := left_ne_mul
@[deprecated (since := "2025-03-05")] alias self_ne_add_right := left_ne_add
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] self_ne_mul_right
end LeftCancelMonoid
section RightCancelMonoid
variable [RightCancelMonoid M] {a b : M}
@[to_additive (attr := simp)]
theorem mul_eq_right : a * b = b ↔ a = 1 := calc
a * b = b ↔ a * b = 1 * b := by rw [one_mul]
_ ↔ a = 1 := mul_right_cancel_iff
@[deprecated (since := "2025-03-05")] alias mul_left_eq_self := mul_eq_right
@[deprecated (since := "2025-03-05")] alias add_left_eq_self := add_eq_right
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] mul_left_eq_self
@[to_additive (attr := simp)]
theorem right_eq_mul : b = a * b ↔ a = 1 :=
eq_comm.trans mul_eq_right
@[deprecated (since := "2025-03-05")] alias self_eq_mul_left := right_eq_mul
@[deprecated (since := "2025-03-05")] alias self_eq_add_left := right_eq_add
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] self_eq_mul_left
@[to_additive]
theorem mul_ne_right : a * b ≠ b ↔ a ≠ 1 := mul_eq_right.not
@[deprecated (since := "2025-03-05")] alias mul_left_ne_self := mul_ne_right
@[deprecated (since := "2025-03-05")] alias add_left_ne_self := add_ne_right
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] mul_left_ne_self
@[to_additive]
theorem right_ne_mul : b ≠ a * b ↔ a ≠ 1 := right_eq_mul.not
@[deprecated (since := "2025-03-05")] alias self_ne_mul_left := right_ne_mul
@[deprecated (since := "2025-03-05")] alias self_ne_add_left := right_ne_add
set_option linter.existingAttributeWarning false in
attribute [to_additive existing] self_ne_mul_left
end RightCancelMonoid
section CancelCommMonoid
variable [CancelCommMonoid α] {a b c d : α}
@[to_additive] lemma eq_iff_eq_of_mul_eq_mul (h : a * b = c * d) : a = c ↔ b = d := by aesop
@[to_additive] lemma ne_iff_ne_of_mul_eq_mul (h : a * b = c * d) : a ≠ c ↔ b ≠ d := by aesop
end CancelCommMonoid
section InvolutiveInv
variable [InvolutiveInv G] {a b : G}
@[to_additive (attr := simp)]
theorem inv_involutive : Function.Involutive (Inv.inv : G → G) :=
inv_inv
@[to_additive (attr := simp)]
theorem inv_surjective : Function.Surjective (Inv.inv : G → G) :=
inv_involutive.surjective
@[to_additive]
theorem inv_injective : Function.Injective (Inv.inv : G → G) :=
inv_involutive.injective
@[to_additive (attr := simp)]
theorem inv_inj : a⁻¹ = b⁻¹ ↔ a = b :=
inv_injective.eq_iff
@[to_additive]
theorem inv_eq_iff_eq_inv : a⁻¹ = b ↔ a = b⁻¹ :=
⟨fun h => h ▸ (inv_inv a).symm, fun h => h.symm ▸ inv_inv b⟩
variable (G)
@[to_additive]
theorem inv_comp_inv : Inv.inv ∘ Inv.inv = @id G :=
inv_involutive.comp_self
@[to_additive]
theorem leftInverse_inv : LeftInverse (fun a : G ↦ a⁻¹) fun a ↦ a⁻¹ :=
inv_inv
@[to_additive]
theorem rightInverse_inv : RightInverse (fun a : G ↦ a⁻¹) fun a ↦ a⁻¹ :=
inv_inv
end InvolutiveInv
section DivInvMonoid
variable [DivInvMonoid G]
@[to_additive]
theorem mul_one_div (x y : G) : x * (1 / y) = x / y := by
rw [div_eq_mul_inv, one_mul, div_eq_mul_inv]
@[to_additive, field_simps] -- The attributes are out of order on purpose
theorem mul_div_assoc' (a b c : G) : a * (b / c) = a * b / c :=
(mul_div_assoc _ _ _).symm
@[to_additive]
theorem mul_div (a b c : G) : a * (b / c) = a * b / c := by simp only [mul_assoc, div_eq_mul_inv]
@[to_additive]
theorem div_eq_mul_one_div (a b : G) : a / b = a * (1 / b) := by rw [div_eq_mul_inv, one_div]
end DivInvMonoid
section DivInvOneMonoid
variable [DivInvOneMonoid G]
@[to_additive (attr := simp)]
theorem div_one (a : G) : a / 1 = a := by simp [div_eq_mul_inv]
@[to_additive]
theorem one_div_one : (1 : G) / 1 = 1 :=
div_one _
end DivInvOneMonoid
section DivisionMonoid
variable [DivisionMonoid α] {a b c d : α}
attribute [local simp] mul_assoc div_eq_mul_inv
@[to_additive]
theorem eq_inv_of_mul_eq_one_right (h : a * b = 1) : b = a⁻¹ :=
(inv_eq_of_mul_eq_one_right h).symm
@[to_additive]
theorem eq_one_div_of_mul_eq_one_left (h : b * a = 1) : b = 1 / a := by
rw [eq_inv_of_mul_eq_one_left h, one_div]
@[to_additive]
theorem eq_one_div_of_mul_eq_one_right (h : a * b = 1) : b = 1 / a := by
rw [eq_inv_of_mul_eq_one_right h, one_div]
@[to_additive]
theorem eq_of_div_eq_one (h : a / b = 1) : a = b :=
inv_injective <| inv_eq_of_mul_eq_one_right <| by rwa [← div_eq_mul_inv]
@[to_additive]
lemma eq_of_inv_mul_eq_one (h : a⁻¹ * b = 1) : a = b := by simpa using eq_inv_of_mul_eq_one_left h
@[to_additive]
lemma eq_of_mul_inv_eq_one (h : a * b⁻¹ = 1) : a = b := by simpa using eq_inv_of_mul_eq_one_left h
@[to_additive]
theorem div_ne_one_of_ne : a ≠ b → a / b ≠ 1 :=
mt eq_of_div_eq_one
variable (a b c)
@[to_additive]
theorem one_div_mul_one_div_rev : 1 / a * (1 / b) = 1 / (b * a) := by simp
@[to_additive]
theorem inv_div_left : a⁻¹ / b = (b * a)⁻¹ := by simp
@[to_additive (attr := simp)]
theorem inv_div : (a / b)⁻¹ = b / a := by simp
@[to_additive]
theorem one_div_div : 1 / (a / b) = b / a := by simp
@[to_additive]
theorem one_div_one_div : 1 / (1 / a) = a := by simp
@[to_additive]
theorem div_eq_div_iff_comm : a / b = c / d ↔ b / a = d / c :=
inv_inj.symm.trans <| by simp only [inv_div]
@[to_additive]
instance (priority := 100) DivisionMonoid.toDivInvOneMonoid : DivInvOneMonoid α :=
{ DivisionMonoid.toDivInvMonoid with
inv_one := by simpa only [one_div, inv_inv] using (inv_div (1 : α) 1).symm }
@[to_additive (attr := simp)]
lemma inv_pow (a : α) : ∀ n : ℕ, a⁻¹ ^ n = (a ^ n)⁻¹
| 0 => by rw [pow_zero, pow_zero, inv_one]
| n + 1 => by rw [pow_succ', pow_succ, inv_pow _ n, mul_inv_rev]
-- the attributes are intentionally out of order. `smul_zero` proves `zsmul_zero`.
@[to_additive zsmul_zero, simp]
lemma one_zpow : ∀ n : ℤ, (1 : α) ^ n = 1
| (n : ℕ) => by rw [zpow_natCast, one_pow]
| .negSucc n => by rw [zpow_negSucc, one_pow, inv_one]
@[to_additive (attr := simp) neg_zsmul]
lemma zpow_neg (a : α) : ∀ n : ℤ, a ^ (-n) = (a ^ n)⁻¹
| (_ + 1 : ℕ) => DivInvMonoid.zpow_neg' _ _
| 0 => by simp
| Int.negSucc n => by
rw [zpow_negSucc, inv_inv, ← zpow_natCast]
rfl
@[to_additive neg_one_zsmul_add]
lemma mul_zpow_neg_one (a b : α) : (a * b) ^ (-1 : ℤ) = b ^ (-1 : ℤ) * a ^ (-1 : ℤ) := by
simp only [zpow_neg, zpow_one, mul_inv_rev]
@[to_additive zsmul_neg]
lemma inv_zpow (a : α) : ∀ n : ℤ, a⁻¹ ^ n = (a ^ n)⁻¹
| (n : ℕ) => by rw [zpow_natCast, zpow_natCast, inv_pow]
| .negSucc n => by rw [zpow_negSucc, zpow_negSucc, inv_pow]
@[to_additive (attr := simp) zsmul_neg']
lemma inv_zpow' (a : α) (n : ℤ) : a⁻¹ ^ n = a ^ (-n) := by rw [inv_zpow, zpow_neg]
@[to_additive nsmul_zero_sub]
lemma one_div_pow (a : α) (n : ℕ) : (1 / a) ^ n = 1 / a ^ n := by simp only [one_div, inv_pow]
@[to_additive zsmul_zero_sub]
lemma one_div_zpow (a : α) (n : ℤ) : (1 / a) ^ n = 1 / a ^ n := by simp only [one_div, inv_zpow]
variable {a b c}
@[to_additive (attr := simp)]
theorem inv_eq_one : a⁻¹ = 1 ↔ a = 1 :=
inv_injective.eq_iff' inv_one
@[to_additive (attr := simp)]
theorem one_eq_inv : 1 = a⁻¹ ↔ a = 1 :=
eq_comm.trans inv_eq_one
@[to_additive]
theorem inv_ne_one : a⁻¹ ≠ 1 ↔ a ≠ 1 :=
inv_eq_one.not
@[to_additive]
theorem eq_of_one_div_eq_one_div (h : 1 / a = 1 / b) : a = b := by
rw [← one_div_one_div a, h, one_div_one_div]
-- Note that `mul_zsmul` and `zpow_mul` have the primes swapped
-- when additivised since their argument order,
-- and therefore the more "natural" choice of lemma, is reversed.
@[to_additive mul_zsmul'] lemma zpow_mul (a : α) : ∀ m n : ℤ, a ^ (m * n) = (a ^ m) ^ n
| (m : ℕ), (n : ℕ) => by
rw [zpow_natCast, zpow_natCast, ← pow_mul, ← zpow_natCast]
rfl
| (m : ℕ), .negSucc n => by
rw [zpow_natCast, zpow_negSucc, ← pow_mul, Int.ofNat_mul_negSucc, zpow_neg, inv_inj,
← zpow_natCast]
| .negSucc m, (n : ℕ) => by
rw [zpow_natCast, zpow_negSucc, ← inv_pow, ← pow_mul, Int.negSucc_mul_ofNat, zpow_neg, inv_pow,
inv_inj, ← zpow_natCast]
| .negSucc m, .negSucc n => by
rw [zpow_negSucc, zpow_negSucc, Int.negSucc_mul_negSucc, inv_pow, inv_inv, ← pow_mul, ←
zpow_natCast]
rfl
@[to_additive mul_zsmul]
lemma zpow_mul' (a : α) (m n : ℤ) : a ^ (m * n) = (a ^ n) ^ m := by rw [Int.mul_comm, zpow_mul]
@[to_additive]
theorem zpow_comm (a : α) (m n : ℤ) : (a ^ m) ^ n = (a ^ n) ^ m := by rw [← zpow_mul, zpow_mul']
variable (a b c)
@[to_additive, field_simps] -- The attributes are out of order on purpose
theorem div_div_eq_mul_div : a / (b / c) = a * c / b := by simp
@[to_additive (attr := simp)]
theorem div_inv_eq_mul : a / b⁻¹ = a * b := by simp
@[to_additive]
theorem div_mul_eq_div_div_swap : a / (b * c) = a / c / b := by
simp only [mul_assoc, mul_inv_rev, div_eq_mul_inv]
end DivisionMonoid
section DivisionCommMonoid
variable [DivisionCommMonoid α] (a b c d : α)
attribute [local simp] mul_assoc mul_comm mul_left_comm div_eq_mul_inv
@[to_additive neg_add]
theorem mul_inv : (a * b)⁻¹ = a⁻¹ * b⁻¹ := by simp
@[to_additive]
theorem inv_div' : (a / b)⁻¹ = a⁻¹ / b⁻¹ := by simp
@[to_additive]
theorem div_eq_inv_mul : a / b = b⁻¹ * a := by simp
@[to_additive]
theorem inv_mul_eq_div : a⁻¹ * b = b / a := by simp
@[to_additive] lemma inv_div_comm (a b : α) : a⁻¹ / b = b⁻¹ / a := by simp
@[to_additive]
theorem inv_mul' : (a * b)⁻¹ = a⁻¹ / b := by simp
@[to_additive]
theorem inv_div_inv : a⁻¹ / b⁻¹ = b / a := by simp
@[to_additive]
theorem inv_inv_div_inv : (a⁻¹ / b⁻¹)⁻¹ = a / b := by simp
@[to_additive]
theorem one_div_mul_one_div : 1 / a * (1 / b) = 1 / (a * b) := by simp
@[to_additive]
theorem div_right_comm : a / b / c = a / c / b := by simp
@[to_additive, field_simps]
theorem div_div : a / b / c = a / (b * c) := by simp
@[to_additive]
theorem div_mul : a / b * c = a / (b / c) := by simp
@[to_additive]
theorem mul_div_left_comm : a * (b / c) = b * (a / c) := by simp
@[to_additive]
theorem mul_div_right_comm : a * b / c = a / c * b := by simp
@[to_additive]
theorem div_mul_eq_div_div : a / (b * c) = a / b / c := by simp
@[to_additive, field_simps]
theorem div_mul_eq_mul_div : a / b * c = a * c / b := by simp
@[to_additive]
theorem one_div_mul_eq_div : 1 / a * b = b / a := by simp
@[to_additive]
theorem mul_comm_div : a / b * c = a * (c / b) := by simp
@[to_additive]
theorem div_mul_comm : a / b * c = c / b * a := by simp
@[to_additive]
theorem div_mul_eq_div_mul_one_div : a / (b * c) = a / b * (1 / c) := by simp
@[to_additive]
theorem div_div_div_eq : a / b / (c / d) = a * d / (b * c) := by simp
@[to_additive]
theorem div_div_div_comm : a / b / (c / d) = a / c / (b / d) := by simp
@[to_additive]
theorem div_mul_div_comm : a / b * (c / d) = a * c / (b * d) := by simp
@[to_additive]
theorem mul_div_mul_comm : a * b / (c * d) = a / c * (b / d) := by simp
@[to_additive zsmul_add] lemma mul_zpow : ∀ n : ℤ, (a * b) ^ n = a ^ n * b ^ n
| (n : ℕ) => by simp_rw [zpow_natCast, mul_pow]
| .negSucc n => by simp_rw [zpow_negSucc, ← inv_pow, mul_inv, mul_pow]
@[to_additive nsmul_sub]
lemma div_pow (a b : α) (n : ℕ) : (a / b) ^ n = a ^ n / b ^ n := by
simp only [div_eq_mul_inv, mul_pow, inv_pow]
@[to_additive zsmul_sub]
lemma div_zpow (a b : α) (n : ℤ) : (a / b) ^ n = a ^ n / b ^ n := by
simp only [div_eq_mul_inv, mul_zpow, inv_zpow]
attribute [field_simps] div_pow div_zpow
end DivisionCommMonoid
section Group
variable [Group G] {a b c d : G} {n : ℤ}
@[to_additive (attr := simp)]
theorem div_eq_inv_self : a / b = b⁻¹ ↔ a = 1 := by rw [div_eq_mul_inv, mul_eq_right]
@[to_additive]
theorem mul_left_surjective (a : G) : Surjective (a * ·) :=
fun x ↦ ⟨a⁻¹ * x, mul_inv_cancel_left a x⟩
@[to_additive]
theorem mul_right_surjective (a : G) : Function.Surjective fun x ↦ x * a := fun x ↦
⟨x * a⁻¹, inv_mul_cancel_right x a⟩
@[to_additive]
theorem eq_mul_inv_of_mul_eq (h : a * c = b) : a = b * c⁻¹ := by simp [h.symm]
@[to_additive]
theorem eq_inv_mul_of_mul_eq (h : b * a = c) : a = b⁻¹ * c := by simp [h.symm]
@[to_additive]
theorem inv_mul_eq_of_eq_mul (h : b = a * c) : a⁻¹ * b = c := by simp [h]
@[to_additive]
theorem mul_inv_eq_of_eq_mul (h : a = c * b) : a * b⁻¹ = c := by simp [h]
@[to_additive]
theorem eq_mul_of_mul_inv_eq (h : a * c⁻¹ = b) : a = b * c := by simp [h.symm]
@[to_additive]
theorem eq_mul_of_inv_mul_eq (h : b⁻¹ * a = c) : a = b * c := by simp [h.symm, mul_inv_cancel_left]
@[to_additive]
theorem mul_eq_of_eq_inv_mul (h : b = a⁻¹ * c) : a * b = c := by rw [h, mul_inv_cancel_left]
@[to_additive]
theorem mul_eq_of_eq_mul_inv (h : a = c * b⁻¹) : a * b = c := by simp [h]
@[to_additive]
theorem mul_eq_one_iff_eq_inv : a * b = 1 ↔ a = b⁻¹ :=
⟨eq_inv_of_mul_eq_one_left, fun h ↦ by rw [h, inv_mul_cancel]⟩
@[to_additive]
theorem mul_eq_one_iff_inv_eq : a * b = 1 ↔ a⁻¹ = b := by
rw [mul_eq_one_iff_eq_inv, inv_eq_iff_eq_inv]
/-- Variant of `mul_eq_one_iff_eq_inv` with swapped equality. -/
@[to_additive]
theorem mul_eq_one_iff_eq_inv' : a * b = 1 ↔ b = a⁻¹ := by
rw [mul_eq_one_iff_inv_eq, eq_comm]
/-- Variant of `mul_eq_one_iff_inv_eq` with swapped equality. -/
@[to_additive]
theorem mul_eq_one_iff_inv_eq' : a * b = 1 ↔ b⁻¹ = a := by
rw [mul_eq_one_iff_eq_inv, eq_comm]
@[to_additive]
theorem eq_inv_iff_mul_eq_one : a = b⁻¹ ↔ a * b = 1 :=
mul_eq_one_iff_eq_inv.symm
@[to_additive]
theorem inv_eq_iff_mul_eq_one : a⁻¹ = b ↔ a * b = 1 :=
mul_eq_one_iff_inv_eq.symm
@[to_additive]
theorem eq_mul_inv_iff_mul_eq : a = b * c⁻¹ ↔ a * c = b :=
⟨fun h ↦ by rw [h, inv_mul_cancel_right], fun h ↦ by rw [← h, mul_inv_cancel_right]⟩
@[to_additive]
theorem eq_inv_mul_iff_mul_eq : a = b⁻¹ * c ↔ b * a = c :=
⟨fun h ↦ by rw [h, mul_inv_cancel_left], fun h ↦ by rw [← h, inv_mul_cancel_left]⟩
@[to_additive]
theorem inv_mul_eq_iff_eq_mul : a⁻¹ * b = c ↔ b = a * c :=
⟨fun h ↦ by rw [← h, mul_inv_cancel_left], fun h ↦ by rw [h, inv_mul_cancel_left]⟩
@[to_additive]
theorem mul_inv_eq_iff_eq_mul : a * b⁻¹ = c ↔ a = c * b :=
⟨fun h ↦ by rw [← h, inv_mul_cancel_right], fun h ↦ by rw [h, mul_inv_cancel_right]⟩
@[to_additive]
theorem mul_inv_eq_one : a * b⁻¹ = 1 ↔ a = b := by rw [mul_eq_one_iff_eq_inv, inv_inv]
@[to_additive]
theorem inv_mul_eq_one : a⁻¹ * b = 1 ↔ a = b := by rw [mul_eq_one_iff_eq_inv, inv_inj]
@[to_additive (attr := simp)]
theorem conj_eq_one_iff : a * b * a⁻¹ = 1 ↔ b = 1 := by
rw [mul_inv_eq_one, mul_eq_left]
@[to_additive]
theorem div_left_injective : Function.Injective fun a ↦ a / b := by
-- FIXME this could be by `simpa`, but it fails. This is probably a bug in `simpa`.
simp only [div_eq_mul_inv]
exact fun a a' h ↦ mul_left_injective b⁻¹ h
@[to_additive]
theorem div_right_injective : Function.Injective fun a ↦ b / a := by
-- FIXME see above
simp only [div_eq_mul_inv]
exact fun a a' h ↦ inv_injective (mul_right_injective b h)
@[to_additive (attr := simp)]
lemma div_mul_cancel_right (a b : G) : a / (b * a) = b⁻¹ := by rw [← inv_div, mul_div_cancel_right]
@[to_additive (attr := simp)]
theorem mul_div_mul_right_eq_div (a b c : G) : a * c / (b * c) = a / b := by
rw [div_mul_eq_div_div_swap]; simp only [mul_left_inj, eq_self_iff_true, mul_div_cancel_right]
@[to_additive eq_sub_of_add_eq]
theorem eq_div_of_mul_eq' (h : a * c = b) : a = b / c := by simp [← h]
@[to_additive sub_eq_of_eq_add]
theorem div_eq_of_eq_mul'' (h : a = c * b) : a / b = c := by simp [h]
@[to_additive]
theorem eq_mul_of_div_eq (h : a / c = b) : a = b * c := by simp [← h]
@[to_additive]
theorem mul_eq_of_eq_div (h : a = c / b) : a * b = c := by simp [h]
@[to_additive (attr := simp)]
theorem div_right_inj : a / b = a / c ↔ b = c :=
div_right_injective.eq_iff
@[to_additive (attr := simp)]
theorem div_left_inj : b / a = c / a ↔ b = c := by
rw [div_eq_mul_inv, div_eq_mul_inv]
exact mul_left_inj _
@[to_additive (attr := simp)]
theorem div_mul_div_cancel (a b c : G) : a / b * (b / c) = a / c := by
rw [← mul_div_assoc, div_mul_cancel]
@[to_additive (attr := simp)]
theorem div_div_div_cancel_right (a b c : G) : a / c / (b / c) = a / b := by
rw [← inv_div c b, div_inv_eq_mul, div_mul_div_cancel]
@[to_additive]
theorem div_eq_one : a / b = 1 ↔ a = b :=
⟨eq_of_div_eq_one, fun h ↦ by rw [h, div_self']⟩
alias ⟨_, div_eq_one_of_eq⟩ := div_eq_one
alias ⟨_, sub_eq_zero_of_eq⟩ := sub_eq_zero
@[to_additive]
theorem div_ne_one : a / b ≠ 1 ↔ a ≠ b :=
not_congr div_eq_one
@[to_additive (attr := simp)]
theorem div_eq_self : a / b = a ↔ b = 1 := by rw [div_eq_mul_inv, mul_eq_left, inv_eq_one]
@[to_additive eq_sub_iff_add_eq]
theorem eq_div_iff_mul_eq' : a = b / c ↔ a * c = b := by rw [div_eq_mul_inv, eq_mul_inv_iff_mul_eq]
@[to_additive]
theorem div_eq_iff_eq_mul : a / b = c ↔ a = c * b := by rw [div_eq_mul_inv, mul_inv_eq_iff_eq_mul]
| @[to_additive]
| Mathlib/Algebra/Group/Basic.lean | 786 | 786 |
/-
Copyright (c) 2022 Cuma Kökmen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Cuma Kökmen, Yury Kudryashov
-/
import Mathlib.MeasureTheory.Integral.CircleIntegral
import Mathlib.MeasureTheory.Integral.Prod
import Mathlib.Order.Fin.Tuple
import Mathlib.Util.Superscript
/-!
# Integral over a torus in `ℂⁿ`
In this file we define the integral of a function `f : ℂⁿ → E` over a torus
`{z : ℂⁿ | ∀ i, z i ∈ Metric.sphere (c i) (R i)}`. In order to do this, we define
`torusMap (c : ℂⁿ) (R θ : ℝⁿ)` to be the point in `ℂⁿ` given by $z_k=c_k+R_ke^{θ_ki}$,
where $i$ is the imaginary unit, then define `torusIntegral f c R` as the integral over
the cube $[0, (fun _ ↦ 2π)] = \{θ\|∀ k, 0 ≤ θ_k ≤ 2π\}$ of the Jacobian of the
`torusMap` multiplied by `f (torusMap c R θ)`.
We also define a predicate saying that `f ∘ torusMap c R` is integrable on the cube
`[0, (fun _ ↦ 2π)]`.
## Main definitions
* `torusMap c R`: the generalized multidimensional exponential map from `ℝⁿ` to `ℂⁿ` that sends
$θ=(θ_0,…,θ_{n-1})$ to $z=(z_0,…,z_{n-1})$, where $z_k= c_k + R_ke^{θ_k i}$;
* `TorusIntegrable f c R`: a function `f : ℂⁿ → E` is integrable over the generalized torus
with center `c : ℂⁿ` and radius `R : ℝⁿ` if `f ∘ torusMap c R` is integrable on the
closed cube `Icc (0 : ℝⁿ) (fun _ ↦ 2 * π)`;
* `torusIntegral f c R`: the integral of a function `f : ℂⁿ → E` over a torus with
center `c ∈ ℂⁿ` and radius `R ∈ ℝⁿ` defined as
$\iiint_{[0, 2 * π]} (∏_{k = 1}^{n} i R_k e^{θ_k * i}) • f (c + Re^{θ_k i})\,dθ_0…dθ_{k-1}$.
## Main statements
* `torusIntegral_dim0`, `torusIntegral_dim1`, `torusIntegral_succ`: formulas for `torusIntegral`
in cases of dimension `0`, `1`, and `n + 1`.
## Notations
- `ℝ⁰`, `ℝ¹`, `ℝⁿ`, `ℝⁿ⁺¹`: local notation for `Fin 0 → ℝ`, `Fin 1 → ℝ`, `Fin n → ℝ`, and
`Fin (n + 1) → ℝ`, respectively;
- `ℂ⁰`, `ℂ¹`, `ℂⁿ`, `ℂⁿ⁺¹`: local notation for `Fin 0 → ℂ`, `Fin 1 → ℂ`, `Fin n → ℂ`, and
`Fin (n + 1) → ℂ`, respectively;
- `∯ z in T(c, R), f z`: notation for `torusIntegral f c R`;
- `∮ z in C(c, R), f z`: notation for `circleIntegral f c R`, defined elsewhere;
- `∏ k, f k`: notation for `Finset.prod`, defined elsewhere;
- `π`: notation for `Real.pi`, defined elsewhere.
## Tags
integral, torus
-/
variable {n : ℕ}
variable {E : Type*} [NormedAddCommGroup E]
noncomputable section
open Complex Set MeasureTheory Function Filter TopologicalSpace
open Mathlib.Tactic (superscriptTerm)
open scoped Real
local syntax:arg term:max noWs superscriptTerm : term
local macro_rules | `($t:term$n:superscript) => `(Fin $n → $t)
/-!
### `torusMap`, a parametrization of a torus
-/
/-- The n dimensional exponential map $θ_i ↦ c + R e^{θ_i*I}, θ ∈ ℝⁿ$ representing
a torus in `ℂⁿ` with center `c ∈ ℂⁿ` and generalized radius `R ∈ ℝⁿ`, so we can adjust
it to every n axis. -/
def torusMap (c : ℂⁿ) (R : ℝⁿ) : ℝⁿ → ℂⁿ := fun θ i => c i + R i * exp (θ i * I)
theorem torusMap_sub_center (c : ℂⁿ) (R : ℝⁿ) (θ : ℝⁿ) : torusMap c R θ - c = torusMap 0 R θ := by
ext1 i; simp [torusMap]
| theorem torusMap_eq_center_iff {c : ℂⁿ} {R : ℝⁿ} {θ : ℝⁿ} : torusMap c R θ = c ↔ R = 0 := by
simp [funext_iff, torusMap, exp_ne_zero]
| Mathlib/MeasureTheory/Integral/TorusIntegral.lean | 84 | 85 |
/-
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
| Mathlib/Data/Complex/Basic.lean | 328 | 328 |
/-
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.Additive
import Mathlib.Algebra.Homology.ShortComplex.Exact
import Mathlib.Algebra.Homology.ShortComplex.Preadditive
import Mathlib.Tactic.Linarith
/-!
# The short complexes attached to homological complexes
In this file, we define a functor
`shortComplexFunctor C c i : HomologicalComplex C c ⥤ ShortComplex C`.
By definition, the image of a homological complex `K` by this functor
is the short complex `K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i)`.
The homology `K.homology i` of a homological complex `K` in degree `i` is defined as
the homology of the short complex `(shortComplexFunctor C c i).obj K`, which can be
abbreviated as `K.sc i`.
-/
open CategoryTheory Category Limits
namespace HomologicalComplex
variable (C : Type*) [Category C] [HasZeroMorphisms C] {ι : Type*} (c : ComplexShape ι)
/-- The functor `HomologicalComplex C c ⥤ ShortComplex C` which sends a homological
complex `K` to the short complex `K.X i ⟶ K.X j ⟶ K.X k` for arbitrary indices `i`, `j` and `k`. -/
@[simps]
def shortComplexFunctor' (i j k : ι) : HomologicalComplex C c ⥤ ShortComplex C where
obj K := ShortComplex.mk (K.d i j) (K.d j k) (K.d_comp_d i j k)
map f :=
{ τ₁ := f.f i
τ₂ := f.f j
τ₃ := f.f k }
/-- The functor `HomologicalComplex C c ⥤ ShortComplex C` which sends a homological
complex `K` to the short complex `K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i)`. -/
@[simps!]
noncomputable def shortComplexFunctor (i : ι) :=
shortComplexFunctor' C c (c.prev i) i (c.next i)
/-- The natural isomorphism `shortComplexFunctor C c j ≅ shortComplexFunctor' C c i j k`
when `c.prev j = i` and `c.next j = k`. -/
@[simps!]
noncomputable def natIsoSc' (i j k : ι) (hi : c.prev j = i) (hk : c.next j = k) :
shortComplexFunctor C c j ≅ shortComplexFunctor' C c i j k :=
NatIso.ofComponents (fun K => ShortComplex.isoMk (K.XIsoOfEq hi) (Iso.refl _) (K.XIsoOfEq hk)
(by simp) (by simp)) (by aesop_cat)
variable {C c}
variable (K L M : HomologicalComplex C c) (φ : K ⟶ L) (ψ : L ⟶ M) (i j k : ι)
/-- The short complex `K.X i ⟶ K.X j ⟶ K.X k` for arbitrary indices `i`, `j` and `k`. -/
abbrev sc' := (shortComplexFunctor' C c i j k).obj K
/-- The short complex `K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i)`. -/
noncomputable abbrev sc := (shortComplexFunctor C c i).obj K
/-- The canonical isomorphism `K.sc j ≅ K.sc' i j k` when `c.prev j = i` and `c.next j = k`. -/
noncomputable abbrev isoSc' (hi : c.prev j = i) (hk : c.next j = k) :
K.sc j ≅ K.sc' i j k := (natIsoSc' C c i j k hi hk).app K
/-- A homological complex `K` has homology in degree `i` if the associated
short complex `K.sc i` has. -/
abbrev HasHomology := (K.sc i).HasHomology
section
variable [K.HasHomology i]
/-- The homology in degree `i` of a homological complex. -/
noncomputable def homology := (K.sc i).homology
/-- The cycles in degree `i` of a homological complex. -/
noncomputable def cycles := (K.sc i).cycles
/-- The inclusion of the cycles of a homological complex. -/
noncomputable def iCycles : K.cycles i ⟶ K.X i := (K.sc i).iCycles
/-- The homology class map from cycles to the homology of a homological complex. -/
noncomputable def homologyπ : K.cycles i ⟶ K.homology i := (K.sc i).homologyπ
variable {i}
/-- The morphism to `K.cycles i` that is induced by a "cycle", i.e. a morphism
to `K.X i` whose postcomposition with the differential is zero. -/
noncomputable def liftCycles {A : C} (k : A ⟶ K.X i) (j : ι) (hj : c.next i = j)
(hk : k ≫ K.d i j = 0) : A ⟶ K.cycles i :=
(K.sc i).liftCycles k (by subst hj; exact hk)
/-- The morphism to `K.cycles i` that is induced by a "cycle", i.e. a morphism
to `K.X i` whose postcomposition with the differential is zero. -/
noncomputable abbrev liftCycles' {A : C} (k : A ⟶ K.X i) (j : ι) (hj : c.Rel i j)
(hk : k ≫ K.d i j = 0) : A ⟶ K.cycles i :=
K.liftCycles k j (c.next_eq' hj) hk
@[reassoc (attr := simp)]
lemma liftCycles_i {A : C} (k : A ⟶ K.X i) (j : ι) (hj : c.next i = j)
(hk : k ≫ K.d i j = 0) : K.liftCycles k j hj hk ≫ K.iCycles i = k := by
dsimp [liftCycles, iCycles]
simp
variable (i)
/-- The map `K.X i ⟶ K.cycles j` induced by the differential `K.d i j`. -/
noncomputable def toCycles [K.HasHomology j] :
K.X i ⟶ K.cycles j :=
K.liftCycles (K.d i j) (c.next j) rfl (K.d_comp_d _ _ _)
@[reassoc (attr := simp)]
lemma iCycles_d : K.iCycles i ≫ K.d i j = 0 := by
by_cases hij : c.Rel i j
· obtain rfl := c.next_eq' hij
exact (K.sc i).iCycles_g
· rw [K.shape _ _ hij, comp_zero]
/-- `K.cycles i` is the kernel of `K.d i j` when `c.next i = j`. -/
noncomputable def cyclesIsKernel (hj : c.next i = j) :
IsLimit (KernelFork.ofι (K.iCycles i) (K.iCycles_d i j)) := by
obtain rfl := hj
exact (K.sc i).cyclesIsKernel
end
@[reassoc (attr := simp)]
lemma toCycles_i [K.HasHomology j] :
K.toCycles i j ≫ K.iCycles j = K.d i j :=
liftCycles_i _ _ _ _ _
section
variable [K.HasHomology i]
instance : Mono (K.iCycles i) := by
dsimp only [iCycles]
infer_instance
instance : Epi (K.homologyπ i) := by
dsimp only [homologyπ]
infer_instance
end
@[reassoc (attr := simp)]
lemma d_toCycles [K.HasHomology k] :
K.d i j ≫ K.toCycles j k = 0 := by
simp only [← cancel_mono (K.iCycles k), assoc, toCycles_i, d_comp_d, zero_comp]
variable {i j} in
lemma toCycles_eq_zero [K.HasHomology j] (hij : ¬ c.Rel i j) :
K.toCycles i j = 0 := by
rw [← cancel_mono (K.iCycles j), toCycles_i, zero_comp, K.shape _ _ hij]
variable {i}
section
variable [K.HasHomology i]
@[reassoc]
lemma comp_liftCycles {A' A : C} (k : A ⟶ K.X i) (j : ι) (hj : c.next i = j)
(hk : k ≫ K.d i j = 0) (α : A' ⟶ A) :
α ≫ K.liftCycles k j hj hk = K.liftCycles (α ≫ k) j hj (by rw [assoc, hk, comp_zero]) := by
simp only [← cancel_mono (K.iCycles i), assoc, liftCycles_i]
@[reassoc]
lemma liftCycles_homologyπ_eq_zero_of_boundary {A : C} (k : A ⟶ K.X i) (j : ι)
(hj : c.next i = j) {i' : ι} (x : A ⟶ K.X i') (hx : k = x ≫ K.d i' i) :
K.liftCycles k j hj (by rw [hx, assoc, K.d_comp_d, comp_zero]) ≫ K.homologyπ i = 0 := by
by_cases h : c.Rel i' i
· obtain rfl := c.prev_eq' h
exact (K.sc i).liftCycles_homologyπ_eq_zero_of_boundary _ x hx
· have : liftCycles K k j hj (by rw [hx, assoc, K.d_comp_d, comp_zero]) = 0 := by
rw [K.shape _ _ h, comp_zero] at hx
rw [← cancel_mono (K.iCycles i), zero_comp, liftCycles_i, hx]
rw [this, zero_comp]
end
variable (i)
@[reassoc (attr := simp)]
lemma toCycles_comp_homologyπ [K.HasHomology j] :
K.toCycles i j ≫ K.homologyπ j = 0 :=
K.liftCycles_homologyπ_eq_zero_of_boundary (K.d i j) (c.next j) rfl (𝟙 _) (by simp)
/-- `K.homology j` is the cokernel of `K.toCycles i j : K.X i ⟶ K.cycles j`
when `c.prev j = i`. -/
noncomputable def homologyIsCokernel (hi : c.prev j = i) [K.HasHomology j] :
IsColimit (CokernelCofork.ofπ (K.homologyπ j) (K.toCycles_comp_homologyπ i j)) := by
subst hi
exact (K.sc j).homologyIsCokernel
section
variable [K.HasHomology i]
/-- The opcycles in degree `i` of a homological complex. -/
noncomputable def opcycles := (K.sc i).opcycles
/-- The projection to the opcycles of a homological complex. -/
noncomputable def pOpcycles : K.X i ⟶ K.opcycles i := (K.sc i).pOpcycles
/-- The inclusion map of the homology of a homological complex into its opcycles. -/
noncomputable def homologyι : K.homology i ⟶ K.opcycles i := (K.sc i).homologyι
variable {i}
/-- The morphism from `K.opcycles i` that is induced by an "opcycle", i.e. a morphism
from `K.X i` whose precomposition with the differential is zero. -/
noncomputable def descOpcycles {A : C} (k : K.X i ⟶ A) (j : ι) (hj : c.prev i = j)
(hk : K.d j i ≫ k = 0) : K.opcycles i ⟶ A :=
(K.sc i).descOpcycles k (by subst hj; exact hk)
/-- The morphism from `K.opcycles i` that is induced by an "opcycle", i.e. a morphism
from `K.X i` whose precomposition with the differential is zero. -/
noncomputable abbrev descOpcycles' {A : C} (k : K.X i ⟶ A) (j : ι) (hj : c.Rel j i)
(hk : K.d j i ≫ k = 0) : K.opcycles i ⟶ A :=
K.descOpcycles k j (c.prev_eq' hj) hk
@[reassoc (attr := simp)]
lemma p_descOpcycles {A : C} (k : K.X i ⟶ A) (j : ι) (hj : c.prev i = j)
(hk : K.d j i ≫ k = 0) : K.pOpcycles i ≫ K.descOpcycles k j hj hk = k := by
dsimp [descOpcycles, pOpcycles]
simp
variable (i)
/-- The map `K.opcycles i ⟶ K.X j` induced by the differential `K.d i j`. -/
noncomputable def fromOpcycles :
K.opcycles i ⟶ K.X j :=
K.descOpcycles (K.d i j) (c.prev i) rfl (K.d_comp_d _ _ _)
@[reassoc (attr := simp)]
lemma d_pOpcycles [K.HasHomology j] : K.d i j ≫ K.pOpcycles j = 0 := by
by_cases hij : c.Rel i j
· obtain rfl := c.prev_eq' hij
exact (K.sc j).f_pOpcycles
· rw [K.shape _ _ hij, zero_comp]
/-- `K.opcycles j` is the cokernel of `K.d i j` when `c.prev j = i`. -/
noncomputable def opcyclesIsCokernel (hi : c.prev j = i) [K.HasHomology j] :
IsColimit (CokernelCofork.ofπ (K.pOpcycles j) (K.d_pOpcycles i j)) := by
obtain rfl := hi
exact (K.sc j).opcyclesIsCokernel
@[reassoc (attr := simp)]
lemma p_fromOpcycles :
K.pOpcycles i ≫ K.fromOpcycles i j = K.d i j :=
p_descOpcycles _ _ _ _ _
instance : Epi (K.pOpcycles i) := by
dsimp only [pOpcycles]
infer_instance
instance : Mono (K.homologyι i) := by
dsimp only [homologyι]
infer_instance
@[reassoc (attr := simp)]
lemma fromOpcycles_d :
K.fromOpcycles i j ≫ K.d j k = 0 := by
simp only [← cancel_epi (K.pOpcycles i), p_fromOpcycles_assoc, d_comp_d, comp_zero]
variable {i j} in
lemma fromOpcycles_eq_zero (hij : ¬ c.Rel i j) :
K.fromOpcycles i j = 0 := by
rw [← cancel_epi (K.pOpcycles i), p_fromOpcycles, comp_zero, K.shape _ _ hij]
variable {i}
@[reassoc]
lemma descOpcycles_comp {A A' : C} (k : K.X i ⟶ A) (j : ι) (hj : c.prev i = j)
(hk : K.d j i ≫ k = 0) (α : A ⟶ A') :
K.descOpcycles k j hj hk ≫ α = K.descOpcycles (k ≫ α) j hj
(by rw [reassoc_of% hk, zero_comp]) := by
simp only [← cancel_epi (K.pOpcycles i), p_descOpcycles_assoc, p_descOpcycles]
@[reassoc]
lemma homologyι_descOpcycles_eq_zero_of_boundary {A : C} (k : K.X i ⟶ A) (j : ι)
(hj : c.prev i = j) {i' : ι} (x : K.X i' ⟶ A) (hx : k = K.d i i' ≫ x) :
K.homologyι i ≫ K.descOpcycles k j hj (by rw [hx, K.d_comp_d_assoc, zero_comp]) = 0 := by
by_cases h : c.Rel i i'
· obtain rfl := c.next_eq' h
exact (K.sc i).homologyι_descOpcycles_eq_zero_of_boundary _ x hx
· have : K.descOpcycles k j hj (by rw [hx, K.d_comp_d_assoc, zero_comp]) = 0 := by
rw [K.shape _ _ h, zero_comp] at hx
rw [← cancel_epi (K.pOpcycles i), comp_zero, p_descOpcycles, hx]
rw [this, comp_zero]
variable (i)
@[reassoc (attr := simp)]
lemma homologyι_comp_fromOpcycles :
K.homologyι i ≫ K.fromOpcycles i j = 0 :=
K.homologyι_descOpcycles_eq_zero_of_boundary (K.d i j) _ rfl (𝟙 _) (by simp)
/-- `K.homology i` is the kernel of `K.fromOpcycles i j : K.opcycles i ⟶ K.X j`
when `c.next i = j`. -/
noncomputable def homologyIsKernel (hi : c.next i = j) :
IsLimit (KernelFork.ofι (K.homologyι i) (K.homologyι_comp_fromOpcycles i j)) := by
subst hi
exact (K.sc i).homologyIsKernel
variable {K L M}
variable [L.HasHomology i] [M.HasHomology i]
/-- The map `K.homology i ⟶ L.homology i` induced by a morphism in `HomologicalComplex`. -/
noncomputable def homologyMap : K.homology i ⟶ L.homology i :=
ShortComplex.homologyMap ((shortComplexFunctor C c i).map φ)
/-- The map `K.cycles i ⟶ L.cycles i` induced by a morphism in `HomologicalComplex`. -/
noncomputable def cyclesMap : K.cycles i ⟶ L.cycles i :=
ShortComplex.cyclesMap ((shortComplexFunctor C c i).map φ)
/-- The map `K.opcycles i ⟶ L.opcycles i` induced by a morphism in `HomologicalComplex`. -/
noncomputable def opcyclesMap : K.opcycles i ⟶ L.opcycles i :=
ShortComplex.opcyclesMap ((shortComplexFunctor C c i).map φ)
@[reassoc (attr := simp)]
lemma cyclesMap_i : cyclesMap φ i ≫ L.iCycles i = K.iCycles i ≫ φ.f i :=
ShortComplex.cyclesMap_i _
@[reassoc (attr := simp)]
lemma p_opcyclesMap : K.pOpcycles i ≫ opcyclesMap φ i = φ.f i ≫ L.pOpcycles i :=
ShortComplex.p_opcyclesMap _
instance [Mono (φ.f i)] : Mono (cyclesMap φ i) := mono_of_mono_fac (cyclesMap_i φ i)
instance [Epi (φ.f i)] : Epi (opcyclesMap φ i) := epi_of_epi_fac (p_opcyclesMap φ i)
variable (K)
@[simp]
lemma homologyMap_id : homologyMap (𝟙 K) i = 𝟙 _ :=
ShortComplex.homologyMap_id _
@[simp]
lemma cyclesMap_id : cyclesMap (𝟙 K) i = 𝟙 _ :=
ShortComplex.cyclesMap_id _
@[simp]
lemma opcyclesMap_id : opcyclesMap (𝟙 K) i = 𝟙 _ :=
ShortComplex.opcyclesMap_id _
variable {K}
@[reassoc]
lemma homologyMap_comp : homologyMap (φ ≫ ψ) i = homologyMap φ i ≫ homologyMap ψ i := by
dsimp [homologyMap]
rw [Functor.map_comp, ShortComplex.homologyMap_comp]
@[reassoc]
lemma cyclesMap_comp : cyclesMap (φ ≫ ψ) i = cyclesMap φ i ≫ cyclesMap ψ i := by
dsimp [cyclesMap]
rw [Functor.map_comp, ShortComplex.cyclesMap_comp]
@[reassoc]
lemma opcyclesMap_comp : opcyclesMap (φ ≫ ψ) i = opcyclesMap φ i ≫ opcyclesMap ψ i := by
dsimp [opcyclesMap]
rw [Functor.map_comp, ShortComplex.opcyclesMap_comp]
variable (K L)
@[simp]
lemma homologyMap_zero : homologyMap (0 : K ⟶ L) i = 0 :=
ShortComplex.homologyMap_zero _ _
@[simp]
lemma cyclesMap_zero : cyclesMap (0 : K ⟶ L) i = 0 :=
ShortComplex.cyclesMap_zero _ _
@[simp]
lemma opcyclesMap_zero : opcyclesMap (0 : K ⟶ L) i = 0 :=
ShortComplex.opcyclesMap_zero _ _
variable {K L}
@[reassoc (attr := simp)]
lemma homologyπ_naturality :
K.homologyπ i ≫ homologyMap φ i = cyclesMap φ i ≫ L.homologyπ i :=
ShortComplex.homologyπ_naturality _
@[reassoc (attr := simp)]
lemma homologyι_naturality :
homologyMap φ i ≫ L.homologyι i = K.homologyι i ≫ opcyclesMap φ i :=
ShortComplex.homologyι_naturality _
@[reassoc (attr := simp)]
lemma homology_π_ι :
K.homologyπ i ≫ K.homologyι i = K.iCycles i ≫ K.pOpcycles i :=
(K.sc i).homology_π_ι
variable {i}
@[reassoc (attr := simp)]
lemma opcyclesMap_comp_descOpcycles {A : C} (k : L.X i ⟶ A) (j : ι) (hj : c.prev i = j)
(hk : L.d j i ≫ k = 0) (φ : K ⟶ L) :
opcyclesMap φ i ≫ L.descOpcycles k j hj hk = K.descOpcycles (φ.f i ≫ k) j hj
(by rw [← φ.comm_assoc, hk, comp_zero]) := by
simp only [← cancel_epi (K.pOpcycles i), p_opcyclesMap_assoc, p_descOpcycles]
@[reassoc (attr := simp)]
lemma liftCycles_comp_cyclesMap {A : C} (k : A ⟶ K.X i) (j : ι) (hj : c.next i = j)
(hk : k ≫ K.d i j = 0) (φ : K ⟶ L) :
K.liftCycles k j hj hk ≫ cyclesMap φ i = L.liftCycles (k ≫ φ.f i) j hj
(by rw [assoc, φ.comm, reassoc_of% hk, zero_comp]) := by
simp only [← cancel_mono (L.iCycles i), assoc, cyclesMap_i, liftCycles_i_assoc, liftCycles_i]
section
variable (C c i)
attribute [local simp] homologyMap_comp cyclesMap_comp opcyclesMap_comp
/-- The `i`th homology functor `HomologicalComplex C c ⥤ C`. -/
@[simps]
noncomputable def homologyFunctor [CategoryWithHomology C] : HomologicalComplex C c ⥤ C where
obj K := K.homology i
map f := homologyMap f i
/-- The homology functor to graded objects. -/
@[simps]
noncomputable def gradedHomologyFunctor [CategoryWithHomology C] :
HomologicalComplex C c ⥤ GradedObject ι C where
obj K i := K.homology i
map f i := homologyMap f i
/-- The `i`th cycles functor `HomologicalComplex C c ⥤ C`. -/
@[simps]
noncomputable def cyclesFunctor [CategoryWithHomology C] : HomologicalComplex C c ⥤ C where
obj K := K.cycles i
map f := cyclesMap f i
/-- The `i`th opcycles functor `HomologicalComplex C c ⥤ C`. -/
@[simps]
noncomputable def opcyclesFunctor [CategoryWithHomology C] : HomologicalComplex C c ⥤ C where
obj K := K.opcycles i
map f := opcyclesMap f i
/-- The natural transformation `K.homologyπ i : K.cycles i ⟶ K.homology i`
for all `K : HomologicalComplex C c`. -/
@[simps]
noncomputable def natTransHomologyπ [CategoryWithHomology C] :
cyclesFunctor C c i ⟶ homologyFunctor C c i where
app K := K.homologyπ i
/-- The natural transformation `K.homologyι i : K.homology i ⟶ K.opcycles i`
for all `K : HomologicalComplex C c`. -/
@[simps]
noncomputable def natTransHomologyι [CategoryWithHomology C] :
homologyFunctor C c i ⟶ opcyclesFunctor C c i where
app K := K.homologyι i
/-- The natural isomorphism `K.homology i ≅ (K.sc i).homology`
for all homological complexes `K`. -/
@[simps!]
noncomputable def homologyFunctorIso [CategoryWithHomology C] :
homologyFunctor C c i ≅
shortComplexFunctor C c i ⋙ ShortComplex.homologyFunctor C :=
Iso.refl _
/-- The natural isomorphism `K.homology j ≅ (K.sc' i j k).homology`
for all homological complexes `K` when `c.prev j = i` and `c.next j = k`. -/
noncomputable def homologyFunctorIso' [CategoryWithHomology C]
(hi : c.prev j = i) (hk : c.next j = k) :
homologyFunctor C c j ≅
shortComplexFunctor' C c i j k ⋙ ShortComplex.homologyFunctor C :=
homologyFunctorIso C c j ≪≫ isoWhiskerRight (natIsoSc' C c i j k hi hk) _
instance [CategoryWithHomology C] : (homologyFunctor C c i).PreservesZeroMorphisms where
instance [CategoryWithHomology C] : (opcyclesFunctor C c i).PreservesZeroMorphisms where
instance [CategoryWithHomology C] : (cyclesFunctor C c i).PreservesZeroMorphisms where
end
end
section
variable (hj : c.next i = j) (h : K.d i j = 0) [K.HasHomology i]
include hj h
lemma isIso_iCycles : IsIso (K.iCycles i) := by
subst hj
exact ShortComplex.isIso_iCycles _ h
/-- The canonical isomorphism `K.cycles i ≅ K.X i` when the differential from `i` is zero. -/
@[simps! hom]
noncomputable def iCyclesIso : K.cycles i ≅ K.X i :=
have := K.isIso_iCycles i j hj h
asIso (K.iCycles i)
@[reassoc (attr := simp)]
lemma iCyclesIso_hom_inv_id :
K.iCycles i ≫ (K.iCyclesIso i j hj h).inv = 𝟙 _ :=
(K.iCyclesIso i j hj h).hom_inv_id
@[reassoc (attr := simp)]
lemma iCyclesIso_inv_hom_id :
(K.iCyclesIso i j hj h).inv ≫ K.iCycles i = 𝟙 _ :=
(K.iCyclesIso i j hj h).inv_hom_id
lemma isIso_homologyι : IsIso (K.homologyι i) :=
ShortComplex.isIso_homologyι _ (by aesop_cat)
/-- The canonical isomorphism `K.homology i ≅ K.opcycles i`
when the differential from `i` is zero. -/
@[simps! hom]
noncomputable def isoHomologyι : K.homology i ≅ K.opcycles i :=
have := K.isIso_homologyι i j hj h
asIso (K.homologyι i)
@[reassoc (attr := simp)]
lemma isoHomologyι_hom_inv_id :
K.homologyι i ≫ (K.isoHomologyι i j hj h).inv = 𝟙 _ :=
(K.isoHomologyι i j hj h).hom_inv_id
@[reassoc (attr := simp)]
lemma isoHomologyι_inv_hom_id :
(K.isoHomologyι i j hj h).inv ≫ K.homologyι i = 𝟙 _ :=
(K.isoHomologyι i j hj h).inv_hom_id
end
section
variable (hi : c.prev j = i) (h : K.d i j = 0) [K.HasHomology j]
include hi h
lemma isIso_pOpcycles : IsIso (K.pOpcycles j) := by
obtain rfl := hi
exact ShortComplex.isIso_pOpcycles _ h
/-- The canonical isomorphism `K.X j ≅ K.opCycles j` when the differential to `j` is zero. -/
@[simps! hom]
noncomputable def pOpcyclesIso : K.X j ≅ K.opcycles j :=
have := K.isIso_pOpcycles i j hi h
asIso (K.pOpcycles j)
@[reassoc (attr := simp)]
lemma pOpcyclesIso_hom_inv_id :
K.pOpcycles j ≫ (K.pOpcyclesIso i j hi h).inv = 𝟙 _ :=
(K.pOpcyclesIso i j hi h).hom_inv_id
@[reassoc (attr := simp)]
lemma pOpcyclesIso_inv_hom_id :
(K.pOpcyclesIso i j hi h).inv ≫ K.pOpcycles j = 𝟙 _ :=
(K.pOpcyclesIso i j hi h).inv_hom_id
lemma isIso_homologyπ : IsIso (K.homologyπ j) :=
ShortComplex.isIso_homologyπ _ (by aesop_cat)
/-- The canonical isomorphism `K.cycles j ≅ K.homology j`
when the differential to `j` is zero. -/
@[simps! hom]
noncomputable def isoHomologyπ : K.cycles j ≅ K.homology j :=
have := K.isIso_homologyπ i j hi h
asIso (K.homologyπ j)
@[reassoc (attr := simp)]
lemma isoHomologyπ_hom_inv_id :
K.homologyπ j ≫ (K.isoHomologyπ i j hi h).inv = 𝟙 _ :=
(K.isoHomologyπ i j hi h).hom_inv_id
@[reassoc (attr := simp)]
lemma isoHomologyπ_inv_hom_id :
(K.isoHomologyπ i j hi h).inv ≫ K.homologyπ j = 𝟙 _ :=
(K.isoHomologyπ i j hi h).inv_hom_id
end
section
variable {K L}
lemma epi_homologyMap_of_epi_of_not_rel (φ : K ⟶ L) (i : ι)
[K.HasHomology i] [L.HasHomology i] [Epi (φ.f i)] (hi : ∀ j, ¬ c.Rel i j) :
Epi (homologyMap φ i) :=
((MorphismProperty.epimorphisms C).arrow_mk_iso_iff
(Arrow.isoMk (K.isoHomologyι i _ rfl (shape _ _ _ (by tauto)))
(L.isoHomologyι i _ rfl (shape _ _ _ (by tauto))))).2
(MorphismProperty.epimorphisms.infer_property (opcyclesMap φ i))
lemma mono_homologyMap_of_mono_of_not_rel (φ : K ⟶ L) (j : ι)
[K.HasHomology j] [L.HasHomology j] [Mono (φ.f j)] (hj : ∀ i, ¬ c.Rel i j) :
Mono (homologyMap φ j) :=
((MorphismProperty.monomorphisms C).arrow_mk_iso_iff
(Arrow.isoMk (K.isoHomologyπ _ j rfl (shape _ _ _ (by tauto)))
(L.isoHomologyπ _ j rfl (shape _ _ _ (by tauto))))).1
(MorphismProperty.monomorphisms.infer_property (cyclesMap φ j))
end
/-- A homological complex `K` is exact at `i` if the short complex `K.sc i` is exact. -/
def ExactAt := (K.sc i).Exact
lemma exactAt_iff :
K.ExactAt i ↔ (K.sc i).Exact := by rfl
variable {K i} in
lemma ExactAt.of_iso (hK : K.ExactAt i) {L : HomologicalComplex C c} (e : K ≅ L) :
L.ExactAt i := by
rw [exactAt_iff] at hK ⊢
exact ShortComplex.exact_of_iso ((shortComplexFunctor C c i).mapIso e) hK
lemma exactAt_iff' (hi : c.prev j = i) (hk : c.next j = k) :
K.ExactAt j ↔ (K.sc' i j k).Exact :=
ShortComplex.exact_iff_of_iso (K.isoSc' i j k hi hk)
lemma exactAt_iff_isZero_homology [K.HasHomology i] :
K.ExactAt i ↔ IsZero (K.homology i) := by
dsimp [homology]
rw [exactAt_iff, ShortComplex.exact_iff_isZero_homology]
variable {K i} in
lemma ExactAt.isZero_homology [K.HasHomology i] (h : K.ExactAt i) :
IsZero (K.homology i) := by
rwa [← exactAt_iff_isZero_homology]
/-- A homological complex `K` is acyclic if it is exact at `i` for any `i`. -/
def Acyclic := ∀ i, K.ExactAt i
lemma acyclic_iff :
K.Acyclic ↔ ∀ i, K.ExactAt i := by rfl
lemma acyclic_of_isZero (hK : IsZero K) :
K.Acyclic := by
rw [acyclic_iff]
intro i
apply ShortComplex.exact_of_isZero_X₂
exact (eval _ _ i).map_isZero hK
end HomologicalComplex
namespace ChainComplex
variable {C : Type*} [Category C] [HasZeroMorphisms C]
(K L : ChainComplex C ℕ) (φ : K ⟶ L) [K.HasHomology 0]
instance isIso_homologyι₀ :
IsIso (K.homologyι 0) :=
K.isIso_homologyι 0 _ rfl (by simp)
/-- The canonical isomorphism `K.homology 0 ≅ K.opcycles 0` for a chain complex `K`
indexed by `ℕ`. -/
noncomputable abbrev isoHomologyι₀ :
K.homology 0 ≅ K.opcycles 0 := K.isoHomologyι 0 _ rfl (by simp)
variable {K L}
@[reassoc (attr := simp)]
lemma isoHomologyι₀_inv_naturality [L.HasHomology 0] :
K.isoHomologyι₀.inv ≫ HomologicalComplex.homologyMap φ 0 =
HomologicalComplex.opcyclesMap φ 0 ≫ L.isoHomologyι₀.inv := by
simp only [assoc, ← cancel_mono (L.homologyι 0),
HomologicalComplex.homologyι_naturality, HomologicalComplex.isoHomologyι_inv_hom_id_assoc,
HomologicalComplex.isoHomologyι_inv_hom_id, comp_id]
end ChainComplex
namespace CochainComplex
variable {C : Type*} [Category C] [HasZeroMorphisms C]
(K L : CochainComplex C ℕ) (φ : K ⟶ L) [K.HasHomology 0]
instance isIso_homologyπ₀ :
IsIso (K.homologyπ 0) :=
K.isIso_homologyπ _ 0 rfl (by simp)
/-- The canonical isomorphism `K.cycles 0 ≅ K.homology 0` for a cochain complex `K`
indexed by `ℕ`. -/
noncomputable abbrev isoHomologyπ₀ :
K.cycles 0 ≅ K.homology 0 := K.isoHomologyπ _ 0 rfl (by simp)
variable {K L}
@[reassoc (attr := simp)]
lemma isoHomologyπ₀_inv_naturality [L.HasHomology 0] :
HomologicalComplex.homologyMap φ 0 ≫ L.isoHomologyπ₀.inv =
K.isoHomologyπ₀.inv ≫ HomologicalComplex.cyclesMap φ 0 := by
simp only [← cancel_epi (K.homologyπ 0), HomologicalComplex.homologyπ_naturality_assoc,
HomologicalComplex.isoHomologyπ_hom_inv_id, comp_id,
HomologicalComplex.isoHomologyπ_hom_inv_id_assoc]
end CochainComplex
namespace HomologicalComplex
variable {C ι : Type*} [Category C] [Preadditive C] {c : ComplexShape ι}
{K L : HomologicalComplex C c} {f g : K ⟶ L}
variable (φ ψ : K ⟶ L) (i : ι) [K.HasHomology i] [L.HasHomology i]
@[simp]
lemma homologyMap_neg : homologyMap (-φ) i = -homologyMap φ i := by
dsimp [homologyMap]
rw [← ShortComplex.homologyMap_neg]
rfl
@[simp]
lemma homologyMap_add : homologyMap (φ + ψ) i = homologyMap φ i + homologyMap ψ i := by
dsimp [homologyMap]
rw [← ShortComplex.homologyMap_add]
rfl
@[simp]
lemma homologyMap_sub : homologyMap (φ - ψ) i = homologyMap φ i - homologyMap ψ i := by
dsimp [homologyMap]
rw [← ShortComplex.homologyMap_sub]
rfl
instance [CategoryWithHomology C] : (homologyFunctor C c i).Additive where
end HomologicalComplex
namespace CochainComplex
variable {C : Type*} [Category C] [Abelian C]
lemma isIso_liftCycles_iff (K : CochainComplex C ℕ) {X : C} (φ : X ⟶ K.X 0)
[K.HasHomology 0] (hφ : φ ≫ K.d 0 1 = 0) :
IsIso (K.liftCycles φ 1 (by simp) hφ) ↔
(ShortComplex.mk _ _ hφ).Exact ∧ Mono φ := by
suffices ∀ (i : ℕ) (hx : (ComplexShape.up ℕ).next 0 = i)
(hφ : φ ≫ K.d 0 i = 0), IsIso (K.liftCycles φ i hx hφ) ↔
(ShortComplex.mk _ _ hφ).Exact ∧ Mono φ from this 1 (by simp) hφ
rintro _ rfl hφ
let α : ShortComplex.mk (0 : X ⟶ X) (0 : X ⟶ X) (by simp) ⟶ K.sc 0 :=
{ τ₁ := 0
τ₂ := φ
τ₃ := 0 }
exact (ShortComplex.quasiIso_iff_isIso_liftCycles α rfl rfl (by simp)).symm.trans
(ShortComplex.quasiIso_iff_of_zeros α rfl rfl (by simp))
end CochainComplex
namespace ChainComplex
variable {C : Type*} [Category C] [Abelian C]
lemma isIso_descOpcycles_iff (K : ChainComplex C ℕ) {X : C} (φ : K.X 0 ⟶ X)
[K.HasHomology 0] (hφ : K.d 1 0 ≫ φ = 0) :
IsIso (K.descOpcycles φ 1 (by simp) hφ) ↔
(ShortComplex.mk _ _ hφ).Exact ∧ Epi φ := by
suffices ∀ (i : ℕ) (hx : (ComplexShape.down ℕ).prev 0 = i)
(hφ : K.d i 0 ≫ φ = 0), IsIso (K.descOpcycles φ i hx hφ) ↔
(ShortComplex.mk _ _ hφ).Exact ∧ Epi φ from this 1 (by simp) hφ
rintro _ rfl hφ
let α : K.sc 0 ⟶ ShortComplex.mk (0 : X ⟶ X) (0 : X ⟶ X) (by simp) :=
{ τ₁ := 0
τ₂ := φ
τ₃ := 0 }
exact (ShortComplex.quasiIso_iff_isIso_descOpcycles α (by simp) rfl rfl).symm.trans
(ShortComplex.quasiIso_iff_of_zeros' α (by simp) rfl rfl)
end ChainComplex
namespace HomologicalComplex
variable {C : Type*} [Category C] [HasZeroMorphisms C] {ι : Type*} {c : ComplexShape ι}
(K : HomologicalComplex C c)
(i j k : ι) (hi : c.prev j = i) (hk : c.next j = k)
[K.HasHomology j] [(K.sc' i j k).HasHomology]
/-- The cycles of a homological complex in degree `j` can be computed
by specifying a choice of `c.prev j` and `c.next j`. -/
noncomputable def cyclesIsoSc' : K.cycles j ≅ (K.sc' i j k).cycles :=
ShortComplex.cyclesMapIso (K.isoSc' i j k hi hk)
@[reassoc (attr := simp)]
lemma cyclesIsoSc'_hom_iCycles :
(K.cyclesIsoSc' i j k hi hk).hom ≫ (K.sc' i j k).iCycles = K.iCycles j := by
dsimp [cyclesIsoSc']
simp only [ShortComplex.cyclesMap_i, shortComplexFunctor_obj_X₂, shortComplexFunctor'_obj_X₂,
natIsoSc'_hom_app_τ₂, comp_id]
rfl
@[reassoc (attr := simp)]
lemma cyclesIsoSc'_inv_iCycles :
(K.cyclesIsoSc' i j k hi hk).inv ≫ K.iCycles j = (K.sc' i j k).iCycles := by
dsimp [cyclesIsoSc']
| erw [ShortComplex.cyclesMap_i]
apply comp_id
@[reassoc (attr := simp)]
lemma toCycles_cyclesIsoSc'_hom :
| Mathlib/Algebra/Homology/ShortComplex/HomologicalComplex.lean | 786 | 790 |
/-
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
-/
import Mathlib.Data.Matrix.Basic
import Mathlib.Data.Matrix.Composition
import Mathlib.Data.Matrix.ConjTranspose
/-!
# Block Matrices
## Main definitions
* `Matrix.fromBlocks`: build a block matrix out of 4 blocks
* `Matrix.toBlocks₁₁`, `Matrix.toBlocks₁₂`, `Matrix.toBlocks₂₁`, `Matrix.toBlocks₂₂`:
extract each of the four blocks from `Matrix.fromBlocks`.
* `Matrix.blockDiagonal`: block diagonal of equally sized blocks. On square blocks, this is a
ring homomorphisms, `Matrix.blockDiagonalRingHom`.
* `Matrix.blockDiag`: extract the blocks from the diagonal of a block diagonal matrix.
* `Matrix.blockDiagonal'`: block diagonal of unequally sized blocks. On square blocks, this is a
ring homomorphisms, `Matrix.blockDiagonal'RingHom`.
* `Matrix.blockDiag'`: extract the blocks from the diagonal of a block diagonal matrix.
-/
variable {l m n o p q : Type*} {m' n' p' : o → Type*}
variable {R : Type*} {S : Type*} {α : Type*} {β : Type*}
open Matrix
namespace Matrix
theorem dotProduct_block [Fintype m] [Fintype n] [Mul α] [AddCommMonoid α] (v w : m ⊕ n → α) :
v ⬝ᵥ w = v ∘ Sum.inl ⬝ᵥ w ∘ Sum.inl + v ∘ Sum.inr ⬝ᵥ w ∘ Sum.inr :=
Fintype.sum_sum_type _
section BlockMatrices
/-- We can form a single large matrix by flattening smaller 'block' matrices of compatible
dimensions. -/
@[pp_nodot]
def fromBlocks (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α) :
Matrix (n ⊕ o) (l ⊕ m) α :=
of <| Sum.elim (fun i => Sum.elim (A i) (B i)) (fun j => Sum.elim (C j) (D j))
@[simp]
theorem fromBlocks_apply₁₁ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (i : n) (j : l) : fromBlocks A B C D (Sum.inl i) (Sum.inl j) = A i j :=
rfl
@[simp]
theorem fromBlocks_apply₁₂ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (i : n) (j : m) : fromBlocks A B C D (Sum.inl i) (Sum.inr j) = B i j :=
rfl
@[simp]
theorem fromBlocks_apply₂₁ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (i : o) (j : l) : fromBlocks A B C D (Sum.inr i) (Sum.inl j) = C i j :=
rfl
@[simp]
theorem fromBlocks_apply₂₂ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (i : o) (j : m) : fromBlocks A B C D (Sum.inr i) (Sum.inr j) = D i j :=
rfl
/-- Given a matrix whose row and column indexes are sum types, we can extract the corresponding
"top left" submatrix. -/
def toBlocks₁₁ (M : Matrix (n ⊕ o) (l ⊕ m) α) : Matrix n l α :=
of fun i j => M (Sum.inl i) (Sum.inl j)
/-- Given a matrix whose row and column indexes are sum types, we can extract the corresponding
"top right" submatrix. -/
def toBlocks₁₂ (M : Matrix (n ⊕ o) (l ⊕ m) α) : Matrix n m α :=
of fun i j => M (Sum.inl i) (Sum.inr j)
/-- Given a matrix whose row and column indexes are sum types, we can extract the corresponding
"bottom left" submatrix. -/
def toBlocks₂₁ (M : Matrix (n ⊕ o) (l ⊕ m) α) : Matrix o l α :=
of fun i j => M (Sum.inr i) (Sum.inl j)
/-- Given a matrix whose row and column indexes are sum types, we can extract the corresponding
"bottom right" submatrix. -/
def toBlocks₂₂ (M : Matrix (n ⊕ o) (l ⊕ m) α) : Matrix o m α :=
of fun i j => M (Sum.inr i) (Sum.inr j)
theorem fromBlocks_toBlocks (M : Matrix (n ⊕ o) (l ⊕ m) α) :
fromBlocks M.toBlocks₁₁ M.toBlocks₁₂ M.toBlocks₂₁ M.toBlocks₂₂ = M := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> rfl
@[simp]
theorem toBlocks_fromBlocks₁₁ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D).toBlocks₁₁ = A :=
rfl
@[simp]
theorem toBlocks_fromBlocks₁₂ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D).toBlocks₁₂ = B :=
rfl
@[simp]
theorem toBlocks_fromBlocks₂₁ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D).toBlocks₂₁ = C :=
rfl
@[simp]
theorem toBlocks_fromBlocks₂₂ (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D).toBlocks₂₂ = D :=
rfl
/-- Two block matrices are equal if their blocks are equal. -/
theorem ext_iff_blocks {A B : Matrix (n ⊕ o) (l ⊕ m) α} :
A = B ↔
A.toBlocks₁₁ = B.toBlocks₁₁ ∧
A.toBlocks₁₂ = B.toBlocks₁₂ ∧ A.toBlocks₂₁ = B.toBlocks₂₁ ∧ A.toBlocks₂₂ = B.toBlocks₂₂ :=
⟨fun h => h ▸ ⟨rfl, rfl, rfl, rfl⟩, fun ⟨h₁₁, h₁₂, h₂₁, h₂₂⟩ => by
rw [← fromBlocks_toBlocks A, ← fromBlocks_toBlocks B, h₁₁, h₁₂, h₂₁, h₂₂]⟩
@[simp]
theorem fromBlocks_inj {A : Matrix n l α} {B : Matrix n m α} {C : Matrix o l α} {D : Matrix o m α}
{A' : Matrix n l α} {B' : Matrix n m α} {C' : Matrix o l α} {D' : Matrix o m α} :
fromBlocks A B C D = fromBlocks A' B' C' D' ↔ A = A' ∧ B = B' ∧ C = C' ∧ D = D' :=
ext_iff_blocks
theorem fromBlocks_map (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α)
(f : α → β) : (fromBlocks A B C D).map f =
fromBlocks (A.map f) (B.map f) (C.map f) (D.map f) := by
ext i j; rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp [fromBlocks]
theorem fromBlocks_transpose (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D)ᵀ = fromBlocks Aᵀ Cᵀ Bᵀ Dᵀ := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp [fromBlocks]
theorem fromBlocks_conjTranspose [Star α] (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : (fromBlocks A B C D)ᴴ = fromBlocks Aᴴ Cᴴ Bᴴ Dᴴ := by
simp only [conjTranspose, fromBlocks_transpose, fromBlocks_map]
@[simp]
theorem fromBlocks_submatrix_sum_swap_left (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (f : p → l ⊕ m) :
(fromBlocks A B C D).submatrix Sum.swap f = (fromBlocks C D A B).submatrix id f := by
ext i j
cases i <;> dsimp <;> cases f j <;> rfl
@[simp]
theorem fromBlocks_submatrix_sum_swap_right (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (f : p → n ⊕ o) :
(fromBlocks A B C D).submatrix f Sum.swap = (fromBlocks B A D C).submatrix f id := by
ext i j
cases j <;> dsimp <;> cases f i <;> rfl
theorem fromBlocks_submatrix_sum_swap_sum_swap {l m n o α : Type*} (A : Matrix n l α)
(B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α) :
(fromBlocks A B C D).submatrix Sum.swap Sum.swap = fromBlocks D C B A := by simp
/-- A 2x2 block matrix is block diagonal if the blocks outside of the diagonal vanish -/
def IsTwoBlockDiagonal [Zero α] (A : Matrix (n ⊕ o) (l ⊕ m) α) : Prop :=
toBlocks₁₂ A = 0 ∧ toBlocks₂₁ A = 0
/-- Let `p` pick out certain rows and `q` pick out certain columns of a matrix `M`. Then
`toBlock M p q` is the corresponding block matrix. -/
def toBlock (M : Matrix m n α) (p : m → Prop) (q : n → Prop) : Matrix { a // p a } { a // q a } α :=
M.submatrix (↑) (↑)
@[simp]
theorem toBlock_apply (M : Matrix m n α) (p : m → Prop) (q : n → Prop) (i : { a // p a })
(j : { a // q a }) : toBlock M p q i j = M ↑i ↑j :=
rfl
/-- Let `p` pick out certain rows and columns of a square matrix `M`. Then
`toSquareBlockProp M p` is the corresponding block matrix. -/
def toSquareBlockProp (M : Matrix m m α) (p : m → Prop) : Matrix { a // p a } { a // p a } α :=
toBlock M _ _
theorem toSquareBlockProp_def (M : Matrix m m α) (p : m → Prop) :
toSquareBlockProp M p = of (fun i j : { a // p a } => M ↑i ↑j) :=
rfl
/-- Let `b` map rows and columns of a square matrix `M` to blocks. Then
`toSquareBlock M b k` is the block `k` matrix. -/
def toSquareBlock (M : Matrix m m α) (b : m → β) (k : β) :
Matrix { a // b a = k } { a // b a = k } α :=
toSquareBlockProp M _
theorem toSquareBlock_def (M : Matrix m m α) (b : m → β) (k : β) :
toSquareBlock M b k = of (fun i j : { a // b a = k } => M ↑i ↑j) :=
rfl
theorem fromBlocks_smul [SMul R α] (x : R) (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) : x • fromBlocks A B C D = fromBlocks (x • A) (x • B) (x • C) (x • D) := by
ext i j; rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp [fromBlocks]
theorem fromBlocks_neg [Neg R] (A : Matrix n l R) (B : Matrix n m R) (C : Matrix o l R)
(D : Matrix o m R) : -fromBlocks A B C D = fromBlocks (-A) (-B) (-C) (-D) := by
ext i j
cases i <;> cases j <;> simp [fromBlocks]
@[simp]
theorem fromBlocks_zero [Zero α] : fromBlocks (0 : Matrix n l α) 0 0 (0 : Matrix o m α) = 0 := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> rfl
theorem fromBlocks_add [Add α] (A : Matrix n l α) (B : Matrix n m α) (C : Matrix o l α)
(D : Matrix o m α) (A' : Matrix n l α) (B' : Matrix n m α) (C' : Matrix o l α)
(D' : Matrix o m α) : fromBlocks A B C D + fromBlocks A' B' C' D' =
fromBlocks (A + A') (B + B') (C + C') (D + D') := by
ext i j; rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> rfl
theorem fromBlocks_multiply [Fintype l] [Fintype m] [NonUnitalNonAssocSemiring α] (A : Matrix n l α)
(B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α) (A' : Matrix l p α) (B' : Matrix l q α)
(C' : Matrix m p α) (D' : Matrix m q α) :
fromBlocks A B C D * fromBlocks A' B' C' D' =
fromBlocks (A * A' + B * C') (A * B' + B * D') (C * A' + D * C') (C * B' + D * D') := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp only [fromBlocks, mul_apply, of_apply,
Sum.elim_inr, Fintype.sum_sum_type, Sum.elim_inl, add_apply]
theorem fromBlocks_mulVec [Fintype l] [Fintype m] [NonUnitalNonAssocSemiring α] (A : Matrix n l α)
(B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α) (x : l ⊕ m → α) :
(fromBlocks A B C D) *ᵥ x =
Sum.elim (A *ᵥ (x ∘ Sum.inl) + B *ᵥ (x ∘ Sum.inr))
(C *ᵥ (x ∘ Sum.inl) + D *ᵥ (x ∘ Sum.inr)) := by
ext i
cases i <;> simp [mulVec, dotProduct]
theorem vecMul_fromBlocks [Fintype n] [Fintype o] [NonUnitalNonAssocSemiring α] (A : Matrix n l α)
(B : Matrix n m α) (C : Matrix o l α) (D : Matrix o m α) (x : n ⊕ o → α) :
x ᵥ* fromBlocks A B C D =
Sum.elim ((x ∘ Sum.inl) ᵥ* A + (x ∘ Sum.inr) ᵥ* C)
((x ∘ Sum.inl) ᵥ* B + (x ∘ Sum.inr) ᵥ* D) := by
ext i
cases i <;> simp [vecMul, dotProduct]
variable [DecidableEq l] [DecidableEq m]
section Zero
variable [Zero α]
theorem toBlock_diagonal_self (d : m → α) (p : m → Prop) :
Matrix.toBlock (diagonal d) p p = diagonal fun i : Subtype p => d ↑i := by
ext i j
by_cases h : i = j
· simp [h]
· simp [One.one, h, Subtype.val_injective.ne h]
theorem toBlock_diagonal_disjoint (d : m → α) {p q : m → Prop} (hpq : Disjoint p q) :
Matrix.toBlock (diagonal d) p q = 0 := by
ext ⟨i, hi⟩ ⟨j, hj⟩
have : i ≠ j := fun heq => hpq.le_bot i ⟨hi, heq.symm ▸ hj⟩
simp [diagonal_apply_ne d this]
@[simp]
theorem fromBlocks_diagonal (d₁ : l → α) (d₂ : m → α) :
fromBlocks (diagonal d₁) 0 0 (diagonal d₂) = diagonal (Sum.elim d₁ d₂) := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp [diagonal]
@[simp]
lemma toBlocks₁₁_diagonal (v : l ⊕ m → α) :
toBlocks₁₁ (diagonal v) = diagonal (fun i => v (Sum.inl i)) := by
unfold toBlocks₁₁
funext i j
simp only [ne_eq, Sum.inl.injEq, of_apply, diagonal_apply]
@[simp]
lemma toBlocks₂₂_diagonal (v : l ⊕ m → α) :
toBlocks₂₂ (diagonal v) = diagonal (fun i => v (Sum.inr i)) := by
unfold toBlocks₂₂
funext i j
simp only [ne_eq, Sum.inr.injEq, of_apply, diagonal_apply]
@[simp]
lemma toBlocks₁₂_diagonal (v : l ⊕ m → α) : toBlocks₁₂ (diagonal v) = 0 := rfl
@[simp]
lemma toBlocks₂₁_diagonal (v : l ⊕ m → α) : toBlocks₂₁ (diagonal v) = 0 := rfl
end Zero
section HasZeroHasOne
variable [Zero α] [One α]
@[simp]
theorem fromBlocks_one : fromBlocks (1 : Matrix l l α) 0 0 (1 : Matrix m m α) = 1 := by
ext i j
rcases i with ⟨⟩ <;> rcases j with ⟨⟩ <;> simp [one_apply]
@[simp]
theorem toBlock_one_self (p : m → Prop) : Matrix.toBlock (1 : Matrix m m α) p p = 1 :=
toBlock_diagonal_self _ p
theorem toBlock_one_disjoint {p q : m → Prop} (hpq : Disjoint p q) :
Matrix.toBlock (1 : Matrix m m α) p q = 0 :=
toBlock_diagonal_disjoint _ hpq
end HasZeroHasOne
end BlockMatrices
section BlockDiagonal
variable [DecidableEq o]
section Zero
variable [Zero α] [Zero β]
/-- `Matrix.blockDiagonal M` turns a homogeneously-indexed collection of matrices
`M : o → Matrix m n α'` into an `m × o`-by-`n × o` block matrix which has the entries of `M` along
the diagonal and zero elsewhere.
See also `Matrix.blockDiagonal'` if the matrices may not have the same size everywhere.
-/
def blockDiagonal (M : o → Matrix m n α) : Matrix (m × o) (n × o) α :=
of <| (fun ⟨i, k⟩ ⟨j, k'⟩ => if k = k' then M k i j else 0 : m × o → n × o → α)
-- TODO: set as an equation lemma for `blockDiagonal`, see https://github.com/leanprover-community/mathlib4/pull/3024
theorem blockDiagonal_apply' (M : o → Matrix m n α) (i k j k') :
blockDiagonal M ⟨i, k⟩ ⟨j, k'⟩ = if k = k' then M k i j else 0 :=
rfl
theorem blockDiagonal_apply (M : o → Matrix m n α) (ik jk) :
blockDiagonal M ik jk = if ik.2 = jk.2 then M ik.2 ik.1 jk.1 else 0 := by
cases ik
cases jk
rfl
@[simp]
theorem blockDiagonal_apply_eq (M : o → Matrix m n α) (i j k) :
blockDiagonal M (i, k) (j, k) = M k i j :=
if_pos rfl
theorem blockDiagonal_apply_ne (M : o → Matrix m n α) (i j) {k k'} (h : k ≠ k') :
blockDiagonal M (i, k) (j, k') = 0 :=
if_neg h
theorem blockDiagonal_map (M : o → Matrix m n α) (f : α → β) (hf : f 0 = 0) :
(blockDiagonal M).map f = blockDiagonal fun k => (M k).map f := by
ext
simp only [map_apply, blockDiagonal_apply, eq_comm]
rw [apply_ite f, hf]
@[simp]
theorem blockDiagonal_transpose (M : o → Matrix m n α) :
(blockDiagonal M)ᵀ = blockDiagonal fun k => (M k)ᵀ := by
ext
simp only [transpose_apply, blockDiagonal_apply, eq_comm]
split_ifs with h
· rw [h]
· rfl
@[simp]
theorem blockDiagonal_conjTranspose {α : Type*} [AddMonoid α] [StarAddMonoid α]
(M : o → Matrix m n α) : (blockDiagonal M)ᴴ = blockDiagonal fun k => (M k)ᴴ := by
simp only [conjTranspose, blockDiagonal_transpose]
rw [blockDiagonal_map _ star (star_zero α)]
@[simp]
theorem blockDiagonal_zero : blockDiagonal (0 : o → Matrix m n α) = 0 := by
ext
simp [blockDiagonal_apply]
@[simp]
theorem blockDiagonal_diagonal [DecidableEq m] (d : o → m → α) :
(blockDiagonal fun k => diagonal (d k)) = diagonal fun ik => d ik.2 ik.1 := by
ext ⟨i, k⟩ ⟨j, k'⟩
simp only [blockDiagonal_apply, diagonal_apply, Prod.mk_inj, ← ite_and]
congr 1
rw [and_comm]
@[simp]
theorem blockDiagonal_one [DecidableEq m] [One α] : blockDiagonal (1 : o → Matrix m m α) = 1 :=
show (blockDiagonal fun _ : o => diagonal fun _ : m => (1 : α)) = diagonal fun _ => 1 by
rw [blockDiagonal_diagonal]
end Zero
@[simp]
theorem blockDiagonal_add [AddZeroClass α] (M N : o → Matrix m n α) :
blockDiagonal (M + N) = blockDiagonal M + blockDiagonal N := by
ext
simp only [blockDiagonal_apply, Pi.add_apply, add_apply]
split_ifs <;> simp
section
variable (o m n α)
/-- `Matrix.blockDiagonal` as an `AddMonoidHom`. -/
@[simps]
def blockDiagonalAddMonoidHom [AddZeroClass α] :
(o → Matrix m n α) →+ Matrix (m × o) (n × o) α where
toFun := blockDiagonal
map_zero' := blockDiagonal_zero
map_add' := blockDiagonal_add
end
@[simp]
theorem blockDiagonal_neg [AddGroup α] (M : o → Matrix m n α) :
blockDiagonal (-M) = -blockDiagonal M :=
map_neg (blockDiagonalAddMonoidHom m n o α) M
@[simp]
theorem blockDiagonal_sub [AddGroup α] (M N : o → Matrix m n α) :
blockDiagonal (M - N) = blockDiagonal M - blockDiagonal N :=
map_sub (blockDiagonalAddMonoidHom m n o α) M N
@[simp]
theorem blockDiagonal_mul [Fintype n] [Fintype o] [NonUnitalNonAssocSemiring α]
(M : o → Matrix m n α) (N : o → Matrix n p α) :
(blockDiagonal fun k => M k * N k) = blockDiagonal M * blockDiagonal N := by
ext ⟨i, k⟩ ⟨j, k'⟩
simp only [blockDiagonal_apply, mul_apply, ← Finset.univ_product_univ, Finset.sum_product]
split_ifs with h <;> simp [h]
section
variable (α m o)
/-- `Matrix.blockDiagonal` as a `RingHom`. -/
@[simps]
def blockDiagonalRingHom [DecidableEq m] [Fintype o] [Fintype m] [NonAssocSemiring α] :
(o → Matrix m m α) →+* Matrix (m × o) (m × o) α :=
{ blockDiagonalAddMonoidHom m m o α with
toFun := blockDiagonal
map_one' := blockDiagonal_one
map_mul' := blockDiagonal_mul }
end
@[simp]
theorem blockDiagonal_pow [DecidableEq m] [Fintype o] [Fintype m] [Semiring α]
(M : o → Matrix m m α) (n : ℕ) : blockDiagonal (M ^ n) = blockDiagonal M ^ n :=
map_pow (blockDiagonalRingHom m o α) M n
@[simp]
theorem blockDiagonal_smul {R : Type*} [Zero α] [SMulZeroClass R α] (x : R)
(M : o → Matrix m n α) : blockDiagonal (x • M) = x • blockDiagonal M := by
ext
simp only [blockDiagonal_apply, Pi.smul_apply, smul_apply]
split_ifs <;> simp
end BlockDiagonal
section BlockDiag
/-- Extract a block from the diagonal of a block diagonal matrix.
This is the block form of `Matrix.diag`, and the left-inverse of `Matrix.blockDiagonal`. -/
def blockDiag (M : Matrix (m × o) (n × o) α) (k : o) : Matrix m n α :=
of fun i j => M (i, k) (j, k)
-- TODO: set as an equation lemma for `blockDiag`, see https://github.com/leanprover-community/mathlib4/pull/3024
theorem blockDiag_apply (M : Matrix (m × o) (n × o) α) (k : o) (i j) :
blockDiag M k i j = M (i, k) (j, k) :=
rfl
theorem blockDiag_map (M : Matrix (m × o) (n × o) α) (f : α → β) :
blockDiag (M.map f) = fun k => (blockDiag M k).map f :=
rfl
@[simp]
theorem blockDiag_transpose (M : Matrix (m × o) (n × o) α) (k : o) :
blockDiag Mᵀ k = (blockDiag M k)ᵀ :=
ext fun _ _ => rfl
@[simp]
theorem blockDiag_conjTranspose {α : Type*} [Star α]
(M : Matrix (m × o) (n × o) α) (k : o) : blockDiag Mᴴ k = (blockDiag M k)ᴴ :=
ext fun _ _ => rfl
section Zero
variable [Zero α] [Zero β]
@[simp]
theorem blockDiag_zero : blockDiag (0 : Matrix (m × o) (n × o) α) = 0 :=
rfl
@[simp]
theorem blockDiag_diagonal [DecidableEq o] [DecidableEq m] (d : m × o → α) (k : o) :
blockDiag (diagonal d) k = diagonal fun i => d (i, k) :=
ext fun i j => by
obtain rfl | hij := Decidable.eq_or_ne i j
· rw [blockDiag_apply, diagonal_apply_eq, diagonal_apply_eq]
· rw [blockDiag_apply, diagonal_apply_ne _ hij, diagonal_apply_ne _ (mt _ hij)]
exact Prod.fst_eq_iff.mpr
@[simp]
theorem blockDiag_blockDiagonal [DecidableEq o] (M : o → Matrix m n α) :
blockDiag (blockDiagonal M) = M :=
funext fun _ => ext fun i j => blockDiagonal_apply_eq M i j _
theorem blockDiagonal_injective [DecidableEq o] :
Function.Injective (blockDiagonal : (o → Matrix m n α) → Matrix _ _ α) :=
Function.LeftInverse.injective blockDiag_blockDiagonal
@[simp]
theorem blockDiagonal_inj [DecidableEq o] {M N : o → Matrix m n α} :
blockDiagonal M = blockDiagonal N ↔ M = N :=
blockDiagonal_injective.eq_iff
@[simp]
theorem blockDiag_one [DecidableEq o] [DecidableEq m] [One α] :
blockDiag (1 : Matrix (m × o) (m × o) α) = 1 :=
funext <| blockDiag_diagonal _
end Zero
@[simp]
theorem blockDiag_add [Add α] (M N : Matrix (m × o) (n × o) α) :
blockDiag (M + N) = blockDiag M + blockDiag N :=
rfl
section
variable (o m n α)
/-- `Matrix.blockDiag` as an `AddMonoidHom`. -/
@[simps]
def blockDiagAddMonoidHom [AddZeroClass α] : Matrix (m × o) (n × o) α →+ o → Matrix m n α where
toFun := blockDiag
map_zero' := blockDiag_zero
map_add' := blockDiag_add
end
@[simp]
theorem blockDiag_neg [AddGroup α] (M : Matrix (m × o) (n × o) α) : blockDiag (-M) = -blockDiag M :=
map_neg (blockDiagAddMonoidHom m n o α) M
@[simp]
theorem blockDiag_sub [AddGroup α] (M N : Matrix (m × o) (n × o) α) :
blockDiag (M - N) = blockDiag M - blockDiag N :=
map_sub (blockDiagAddMonoidHom m n o α) M N
@[simp]
theorem blockDiag_smul {R : Type*} [SMul R α] (x : R)
(M : Matrix (m × o) (n × o) α) : blockDiag (x • M) = x • blockDiag M :=
rfl
end BlockDiag
section BlockDiagonal'
variable [DecidableEq o]
section Zero
variable [Zero α] [Zero β]
/-- `Matrix.blockDiagonal' M` turns `M : Π i, Matrix (m i) (n i) α` into a
`Σ i, m i`-by-`Σ i, n i` block matrix which has the entries of `M` along the diagonal
and zero elsewhere.
This is the dependently-typed version of `Matrix.blockDiagonal`. -/
def blockDiagonal' (M : ∀ i, Matrix (m' i) (n' i) α) : Matrix (Σ i, m' i) (Σ i, n' i) α :=
of <|
(fun ⟨k, i⟩ ⟨k', j⟩ => if h : k = k' then M k i (cast (congr_arg n' h.symm) j) else 0 :
(Σ i, m' i) → (Σ i, n' i) → α)
-- TODO: set as an equation lemma for `blockDiagonal'`, see https://github.com/leanprover-community/mathlib4/pull/3024
theorem blockDiagonal'_apply' (M : ∀ i, Matrix (m' i) (n' i) α) (k i k' j) :
blockDiagonal' M ⟨k, i⟩ ⟨k', j⟩ =
if h : k = k' then M k i (cast (congr_arg n' h.symm) j) else 0 :=
rfl
theorem blockDiagonal'_eq_blockDiagonal (M : o → Matrix m n α) {k k'} (i j) :
blockDiagonal M (i, k) (j, k') = blockDiagonal' M ⟨k, i⟩ ⟨k', j⟩ :=
rfl
theorem blockDiagonal'_submatrix_eq_blockDiagonal (M : o → Matrix m n α) :
(blockDiagonal' M).submatrix (Prod.toSigma ∘ Prod.swap) (Prod.toSigma ∘ Prod.swap) =
blockDiagonal M :=
Matrix.ext fun ⟨_, _⟩ ⟨_, _⟩ => rfl
theorem blockDiagonal'_apply (M : ∀ i, Matrix (m' i) (n' i) α) (ik jk) :
blockDiagonal' M ik jk =
if h : ik.1 = jk.1 then M ik.1 ik.2 (cast (congr_arg n' h.symm) jk.2) else 0 := by
cases ik
cases jk
rfl
@[simp]
theorem blockDiagonal'_apply_eq (M : ∀ i, Matrix (m' i) (n' i) α) (k i j) :
blockDiagonal' M ⟨k, i⟩ ⟨k, j⟩ = M k i j :=
dif_pos rfl
theorem blockDiagonal'_apply_ne (M : ∀ i, Matrix (m' i) (n' i) α) {k k'} (i j) (h : k ≠ k') :
blockDiagonal' M ⟨k, i⟩ ⟨k', j⟩ = 0 :=
dif_neg h
theorem blockDiagonal'_map (M : ∀ i, Matrix (m' i) (n' i) α) (f : α → β) (hf : f 0 = 0) :
(blockDiagonal' M).map f = blockDiagonal' fun k => (M k).map f := by
ext
simp only [map_apply, blockDiagonal'_apply, eq_comm]
rw [apply_dite f, hf]
@[simp]
theorem blockDiagonal'_transpose (M : ∀ i, Matrix (m' i) (n' i) α) :
(blockDiagonal' M)ᵀ = blockDiagonal' fun k => (M k)ᵀ := by
ext ⟨ii, ix⟩ ⟨ji, jx⟩
simp only [transpose_apply, blockDiagonal'_apply]
split_ifs <;> cc
@[simp]
theorem blockDiagonal'_conjTranspose {α} [AddMonoid α] [StarAddMonoid α]
(M : ∀ i, Matrix (m' i) (n' i) α) : (blockDiagonal' M)ᴴ = blockDiagonal' fun k => (M k)ᴴ := by
simp only [conjTranspose, blockDiagonal'_transpose]
exact blockDiagonal'_map _ star (star_zero α)
@[simp]
theorem blockDiagonal'_zero : blockDiagonal' (0 : ∀ i, Matrix (m' i) (n' i) α) = 0 := by
ext
simp [blockDiagonal'_apply]
@[simp]
theorem blockDiagonal'_diagonal [∀ i, DecidableEq (m' i)] (d : ∀ i, m' i → α) :
(blockDiagonal' fun k => diagonal (d k)) = diagonal fun ik => d ik.1 ik.2 := by
ext ⟨i, k⟩ ⟨j, k'⟩
simp only [blockDiagonal'_apply, diagonal]
obtain rfl | hij := Decidable.eq_or_ne i j
· simp
· simp [hij]
@[simp]
theorem blockDiagonal'_one [∀ i, DecidableEq (m' i)] [One α] :
blockDiagonal' (1 : ∀ i, Matrix (m' i) (m' i) α) = 1 :=
show (blockDiagonal' fun i : o => diagonal fun _ : m' i => (1 : α)) = diagonal fun _ => 1 by
rw [blockDiagonal'_diagonal]
end Zero
@[simp]
theorem blockDiagonal'_add [AddZeroClass α] (M N : ∀ i, Matrix (m' i) (n' i) α) :
blockDiagonal' (M + N) = blockDiagonal' M + blockDiagonal' N := by
ext
simp only [blockDiagonal'_apply, Pi.add_apply, add_apply]
split_ifs <;> simp
section
variable (m' n' α)
/-- `Matrix.blockDiagonal'` as an `AddMonoidHom`. -/
@[simps]
def blockDiagonal'AddMonoidHom [AddZeroClass α] :
(∀ i, Matrix (m' i) (n' i) α) →+ Matrix (Σ i, m' i) (Σ i, n' i) α where
toFun := blockDiagonal'
map_zero' := blockDiagonal'_zero
map_add' := blockDiagonal'_add
end
@[simp]
theorem blockDiagonal'_neg [AddGroup α] (M : ∀ i, Matrix (m' i) (n' i) α) :
blockDiagonal' (-M) = -blockDiagonal' M :=
map_neg (blockDiagonal'AddMonoidHom m' n' α) M
@[simp]
theorem blockDiagonal'_sub [AddGroup α] (M N : ∀ i, Matrix (m' i) (n' i) α) :
blockDiagonal' (M - N) = blockDiagonal' M - blockDiagonal' N :=
map_sub (blockDiagonal'AddMonoidHom m' n' α) M N
@[simp]
theorem blockDiagonal'_mul [NonUnitalNonAssocSemiring α] [∀ i, Fintype (n' i)] [Fintype o]
(M : ∀ i, Matrix (m' i) (n' i) α) (N : ∀ i, Matrix (n' i) (p' i) α) :
(blockDiagonal' fun k => M k * N k) = blockDiagonal' M * blockDiagonal' N := by
ext ⟨k, i⟩ ⟨k', j⟩
simp only [blockDiagonal'_apply, mul_apply, ← Finset.univ_sigma_univ, Finset.sum_sigma]
rw [Fintype.sum_eq_single k]
· simp only [if_pos, dif_pos]
split_ifs <;> simp
· intro j' hj'
exact Finset.sum_eq_zero fun _ _ => by rw [dif_neg hj'.symm, zero_mul]
section
variable (α m')
/-- `Matrix.blockDiagonal'` as a `RingHom`. -/
@[simps]
def blockDiagonal'RingHom [∀ i, DecidableEq (m' i)] [Fintype o] [∀ i, Fintype (m' i)]
[NonAssocSemiring α] : (∀ i, Matrix (m' i) (m' i) α) →+* Matrix (Σ i, m' i) (Σ i, m' i) α :=
{ blockDiagonal'AddMonoidHom m' m' α with
toFun := blockDiagonal'
map_one' := blockDiagonal'_one
map_mul' := blockDiagonal'_mul }
end
@[simp]
theorem blockDiagonal'_pow [∀ i, DecidableEq (m' i)] [Fintype o] [∀ i, Fintype (m' i)] [Semiring α]
(M : ∀ i, Matrix (m' i) (m' i) α) (n : ℕ) : blockDiagonal' (M ^ n) = blockDiagonal' M ^ n :=
map_pow (blockDiagonal'RingHom m' α) M n
@[simp]
theorem blockDiagonal'_smul {R : Type*} [Zero α] [SMulZeroClass R α] (x : R)
(M : ∀ i, Matrix (m' i) (n' i) α) : blockDiagonal' (x • M) = x • blockDiagonal' M := by
ext
simp only [blockDiagonal'_apply, Pi.smul_apply, smul_apply]
split_ifs <;> simp
end BlockDiagonal'
section BlockDiag'
/-- Extract a block from the diagonal of a block diagonal matrix.
This is the block form of `Matrix.diag`, and the left-inverse of `Matrix.blockDiagonal'`. -/
def blockDiag' (M : Matrix (Σ i, m' i) (Σ i, n' i) α) (k : o) : Matrix (m' k) (n' k) α :=
of fun i j => M ⟨k, i⟩ ⟨k, j⟩
-- TODO: set as an equation lemma for `blockDiag'`, see https://github.com/leanprover-community/mathlib4/pull/3024
theorem blockDiag'_apply (M : Matrix (Σ i, m' i) (Σ i, n' i) α) (k : o) (i j) :
blockDiag' M k i j = M ⟨k, i⟩ ⟨k, j⟩ :=
rfl
theorem blockDiag'_map (M : Matrix (Σ i, m' i) (Σ i, n' i) α) (f : α → β) :
blockDiag' (M.map f) = fun k => (blockDiag' M k).map f :=
rfl
@[simp]
theorem blockDiag'_transpose (M : Matrix (Σ i, m' i) (Σ i, n' i) α) (k : o) :
blockDiag' Mᵀ k = (blockDiag' M k)ᵀ :=
ext fun _ _ => rfl
@[simp]
theorem blockDiag'_conjTranspose {α : Type*} [Star α]
(M : Matrix (Σ i, m' i) (Σ i, n' i) α) (k : o) : blockDiag' Mᴴ k = (blockDiag' M k)ᴴ :=
ext fun _ _ => rfl
section Zero
variable [Zero α] [Zero β]
@[simp]
theorem blockDiag'_zero : blockDiag' (0 : Matrix (Σ i, m' i) (Σ i, n' i) α) = 0 :=
rfl
@[simp]
theorem blockDiag'_diagonal
[DecidableEq o] [∀ i, DecidableEq (m' i)] (d : (Σ i, m' i) → α) (k : o) :
blockDiag' (diagonal d) k = diagonal fun i => d ⟨k, i⟩ :=
ext fun i j => by
obtain rfl | hij := Decidable.eq_or_ne i j
· rw [blockDiag'_apply, diagonal_apply_eq, diagonal_apply_eq]
· rw [blockDiag'_apply, diagonal_apply_ne _ hij, diagonal_apply_ne _ (mt (fun h => ?_) hij)]
cases h
rfl
@[simp]
theorem blockDiag'_blockDiagonal' [DecidableEq o] (M : ∀ i, Matrix (m' i) (n' i) α) :
blockDiag' (blockDiagonal' M) = M :=
funext fun _ => ext fun _ _ => blockDiagonal'_apply_eq M _ _ _
theorem blockDiagonal'_injective [DecidableEq o] :
Function.Injective (blockDiagonal' : (∀ i, Matrix (m' i) (n' i) α) → Matrix _ _ α) :=
Function.LeftInverse.injective blockDiag'_blockDiagonal'
@[simp]
theorem blockDiagonal'_inj [DecidableEq o] {M N : ∀ i, Matrix (m' i) (n' i) α} :
blockDiagonal' M = blockDiagonal' N ↔ M = N :=
| blockDiagonal'_injective.eq_iff
@[simp]
theorem blockDiag'_one [DecidableEq o] [∀ i, DecidableEq (m' i)] [One α] :
blockDiag' (1 : Matrix (Σ i, m' i) (Σ i, m' i) α) = 1 :=
funext <| blockDiag'_diagonal _
end Zero
@[simp]
| Mathlib/Data/Matrix/Block.lean | 768 | 777 |
/-
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, Sébastien Gouëzel,
Rémy Degenne, David Loeffler
-/
import Mathlib.Analysis.SpecialFunctions.Pow.Complex
import Qq
/-! # Power function on `ℝ`
We construct the power functions `x ^ y`, where `x` and `y` are real numbers.
-/
noncomputable section
open Real ComplexConjugate Finset Set
/-
## Definitions
-/
namespace Real
variable {x y z : ℝ}
/-- The real power function `x ^ y`, defined as the real part of the complex power function.
For `x > 0`, it is equal to `exp (y log x)`. For `x = 0`, one sets `0 ^ 0=1` and `0 ^ y=0` for
`y ≠ 0`. For `x < 0`, the definition is somewhat arbitrary as it depends on the choice of a complex
determination of the logarithm. With our conventions, it is equal to `exp (y log x) cos (π y)`. -/
noncomputable def rpow (x y : ℝ) :=
((x : ℂ) ^ (y : ℂ)).re
noncomputable instance : Pow ℝ ℝ := ⟨rpow⟩
@[simp]
theorem rpow_eq_pow (x y : ℝ) : rpow x y = x ^ y := rfl
theorem rpow_def (x y : ℝ) : x ^ y = ((x : ℂ) ^ (y : ℂ)).re := rfl
theorem rpow_def_of_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) := by
simp only [rpow_def, Complex.cpow_def]; split_ifs <;>
simp_all [(Complex.ofReal_log hx).symm, -Complex.ofReal_mul,
(Complex.ofReal_mul _ _).symm, Complex.exp_ofReal_re, Complex.ofReal_eq_zero]
theorem rpow_def_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : x ^ y = exp (log x * y) := by
rw [rpow_def_of_nonneg (le_of_lt hx), if_neg (ne_of_gt hx)]
theorem exp_mul (x y : ℝ) : exp (x * y) = exp x ^ y := by rw [rpow_def_of_pos (exp_pos _), log_exp]
@[simp, norm_cast]
theorem rpow_intCast (x : ℝ) (n : ℤ) : x ^ (n : ℝ) = x ^ n := by
simp only [rpow_def, ← Complex.ofReal_zpow, Complex.cpow_intCast, Complex.ofReal_intCast,
Complex.ofReal_re]
@[simp, norm_cast]
theorem rpow_natCast (x : ℝ) (n : ℕ) : x ^ (n : ℝ) = x ^ n := by simpa using rpow_intCast x n
@[simp]
theorem exp_one_rpow (x : ℝ) : exp 1 ^ x = exp x := by rw [← exp_mul, one_mul]
@[simp] lemma exp_one_pow (n : ℕ) : exp 1 ^ n = exp n := by rw [← rpow_natCast, exp_one_rpow]
theorem rpow_eq_zero_iff_of_nonneg (hx : 0 ≤ x) : x ^ y = 0 ↔ x = 0 ∧ y ≠ 0 := by
simp only [rpow_def_of_nonneg hx]
split_ifs <;> simp [*, exp_ne_zero]
@[simp]
lemma rpow_eq_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y = 0 ↔ x = 0 := by
simp [rpow_eq_zero_iff_of_nonneg, *]
@[simp]
lemma rpow_ne_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y ≠ 0 ↔ x ≠ 0 :=
Real.rpow_eq_zero hx hy |>.not
open Real
theorem rpow_def_of_neg {x : ℝ} (hx : x < 0) (y : ℝ) : x ^ y = exp (log x * y) * cos (y * π) := by
rw [rpow_def, Complex.cpow_def, if_neg]
· have : Complex.log x * y = ↑(log (-x) * y) + ↑(y * π) * Complex.I := by
simp only [Complex.log, Complex.norm_real, norm_eq_abs, abs_of_neg hx, log_neg_eq_log,
Complex.arg_ofReal_of_neg hx, Complex.ofReal_mul]
ring
rw [this, Complex.exp_add_mul_I, ← Complex.ofReal_exp, ← Complex.ofReal_cos, ←
Complex.ofReal_sin, mul_add, ← Complex.ofReal_mul, ← mul_assoc, ← Complex.ofReal_mul,
Complex.add_re, Complex.ofReal_re, Complex.mul_re, Complex.I_re, Complex.ofReal_im,
Real.log_neg_eq_log]
ring
· rw [Complex.ofReal_eq_zero]
exact ne_of_lt hx
theorem rpow_def_of_nonpos {x : ℝ} (hx : x ≤ 0) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) * cos (y * π) := by
split_ifs with h <;> simp [rpow_def, *]; exact rpow_def_of_neg (lt_of_le_of_ne hx h) _
@[bound]
theorem rpow_pos_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : 0 < x ^ y := by
rw [rpow_def_of_pos hx]; apply exp_pos
@[simp]
theorem rpow_zero (x : ℝ) : x ^ (0 : ℝ) = 1 := by simp [rpow_def]
theorem rpow_zero_pos (x : ℝ) : 0 < x ^ (0 : ℝ) := by simp
@[simp]
theorem zero_rpow {x : ℝ} (h : x ≠ 0) : (0 : ℝ) ^ x = 0 := by simp [rpow_def, *]
theorem zero_rpow_eq_iff {x : ℝ} {a : ℝ} : 0 ^ x = a ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
constructor
· intro hyp
simp only [rpow_def, Complex.ofReal_zero] at hyp
by_cases h : x = 0
· subst h
simp only [Complex.one_re, Complex.ofReal_zero, Complex.cpow_zero] at hyp
exact Or.inr ⟨rfl, hyp.symm⟩
· rw [Complex.zero_cpow (Complex.ofReal_ne_zero.mpr h)] at hyp
exact Or.inl ⟨h, hyp.symm⟩
· rintro (⟨h, rfl⟩ | ⟨rfl, rfl⟩)
· exact zero_rpow h
· exact rpow_zero _
theorem eq_zero_rpow_iff {x : ℝ} {a : ℝ} : a = 0 ^ x ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
rw [← zero_rpow_eq_iff, eq_comm]
@[simp]
theorem rpow_one (x : ℝ) : x ^ (1 : ℝ) = x := by simp [rpow_def]
@[simp]
theorem one_rpow (x : ℝ) : (1 : ℝ) ^ x = 1 := by simp [rpow_def]
theorem zero_rpow_le_one (x : ℝ) : (0 : ℝ) ^ x ≤ 1 := by
by_cases h : x = 0 <;> simp [h, zero_le_one]
theorem zero_rpow_nonneg (x : ℝ) : 0 ≤ (0 : ℝ) ^ x := by
by_cases h : x = 0 <;> simp [h, zero_le_one]
@[bound]
theorem rpow_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : 0 ≤ x ^ y := by
rw [rpow_def_of_nonneg hx]; split_ifs <;>
simp only [zero_le_one, le_refl, le_of_lt (exp_pos _)]
theorem abs_rpow_of_nonneg {x y : ℝ} (hx_nonneg : 0 ≤ x) : |x ^ y| = |x| ^ y := by
have h_rpow_nonneg : 0 ≤ x ^ y := Real.rpow_nonneg hx_nonneg _
rw [abs_eq_self.mpr hx_nonneg, abs_eq_self.mpr h_rpow_nonneg]
@[bound]
theorem abs_rpow_le_abs_rpow (x y : ℝ) : |x ^ y| ≤ |x| ^ y := by
rcases le_or_lt 0 x with hx | hx
· rw [abs_rpow_of_nonneg hx]
· rw [abs_of_neg hx, rpow_def_of_neg hx, rpow_def_of_pos (neg_pos.2 hx), log_neg_eq_log, abs_mul,
abs_of_pos (exp_pos _)]
exact mul_le_of_le_one_right (exp_pos _).le (abs_cos_le_one _)
theorem abs_rpow_le_exp_log_mul (x y : ℝ) : |x ^ y| ≤ exp (log x * y) := by
refine (abs_rpow_le_abs_rpow x y).trans ?_
by_cases hx : x = 0
· by_cases hy : y = 0 <;> simp [hx, hy, zero_le_one]
· rw [rpow_def_of_pos (abs_pos.2 hx), log_abs]
lemma rpow_inv_log (hx₀ : 0 < x) (hx₁ : x ≠ 1) : x ^ (log x)⁻¹ = exp 1 := by
rw [rpow_def_of_pos hx₀, mul_inv_cancel₀]
exact log_ne_zero.2 ⟨hx₀.ne', hx₁, (hx₀.trans' <| by norm_num).ne'⟩
/-- See `Real.rpow_inv_log` for the equality when `x ≠ 1` is strictly positive. -/
lemma rpow_inv_log_le_exp_one : x ^ (log x)⁻¹ ≤ exp 1 := by
calc
_ ≤ |x ^ (log x)⁻¹| := le_abs_self _
_ ≤ |x| ^ (log x)⁻¹ := abs_rpow_le_abs_rpow ..
rw [← log_abs]
obtain hx | hx := (abs_nonneg x).eq_or_gt
· simp [hx]
· rw [rpow_def_of_pos hx]
gcongr
exact mul_inv_le_one
theorem norm_rpow_of_nonneg {x y : ℝ} (hx_nonneg : 0 ≤ x) : ‖x ^ y‖ = ‖x‖ ^ y := by
simp_rw [Real.norm_eq_abs]
exact abs_rpow_of_nonneg hx_nonneg
variable {w x y z : ℝ}
theorem rpow_add (hx : 0 < x) (y z : ℝ) : x ^ (y + z) = x ^ y * x ^ z := by
simp only [rpow_def_of_pos hx, mul_add, exp_add]
theorem rpow_add' (hx : 0 ≤ x) (h : y + z ≠ 0) : x ^ (y + z) = x ^ y * x ^ z := by
rcases hx.eq_or_lt with (rfl | pos)
· rw [zero_rpow h, zero_eq_mul]
have : y ≠ 0 ∨ z ≠ 0 := not_and_or.1 fun ⟨hy, hz⟩ => h <| hy.symm ▸ hz.symm ▸ zero_add 0
exact this.imp zero_rpow zero_rpow
· exact rpow_add pos _ _
/-- Variant of `Real.rpow_add'` that avoids having to prove `y + z = w` twice. -/
lemma rpow_of_add_eq (hx : 0 ≤ x) (hw : w ≠ 0) (h : y + z = w) : x ^ w = x ^ y * x ^ z := by
rw [← h, rpow_add' hx]; rwa [h]
theorem rpow_add_of_nonneg (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 ≤ z) :
x ^ (y + z) = x ^ y * x ^ z := by
rcases hy.eq_or_lt with (rfl | hy)
· rw [zero_add, rpow_zero, one_mul]
exact rpow_add' hx (ne_of_gt <| add_pos_of_pos_of_nonneg hy hz)
/-- For `0 ≤ x`, the only problematic case in the equality `x ^ y * x ^ z = x ^ (y + z)` is for
`x = 0` and `y + z = 0`, where the right hand side is `1` while the left hand side can vanish.
The inequality is always true, though, and given in this lemma. -/
theorem le_rpow_add {x : ℝ} (hx : 0 ≤ x) (y z : ℝ) : x ^ y * x ^ z ≤ x ^ (y + z) := by
rcases le_iff_eq_or_lt.1 hx with (H | pos)
· by_cases h : y + z = 0
· simp only [H.symm, h, rpow_zero]
calc
(0 : ℝ) ^ y * 0 ^ z ≤ 1 * 1 :=
mul_le_mul (zero_rpow_le_one y) (zero_rpow_le_one z) (zero_rpow_nonneg z) zero_le_one
_ = 1 := by simp
· simp [rpow_add', ← H, h]
· simp [rpow_add pos]
theorem rpow_sum_of_pos {ι : Type*} {a : ℝ} (ha : 0 < a) (f : ι → ℝ) (s : Finset ι) :
(a ^ ∑ x ∈ s, f x) = ∏ x ∈ s, a ^ f x :=
map_sum (⟨⟨fun (x : ℝ) => (a ^ x : ℝ), rpow_zero a⟩, rpow_add ha⟩ : ℝ →+ (Additive ℝ)) f s
theorem rpow_sum_of_nonneg {ι : Type*} {a : ℝ} (ha : 0 ≤ a) {s : Finset ι} {f : ι → ℝ}
(h : ∀ x ∈ s, 0 ≤ f x) : (a ^ ∑ x ∈ s, f x) = ∏ x ∈ s, a ^ f x := by
induction' s using Finset.cons_induction with i s hi ihs
· rw [sum_empty, Finset.prod_empty, rpow_zero]
· rw [forall_mem_cons] at h
rw [sum_cons, prod_cons, ← ihs h.2, rpow_add_of_nonneg ha h.1 (sum_nonneg h.2)]
theorem rpow_neg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : x ^ (-y) = (x ^ y)⁻¹ := by
simp only [rpow_def_of_nonneg hx]; split_ifs <;> simp_all [exp_neg]
theorem rpow_sub {x : ℝ} (hx : 0 < x) (y z : ℝ) : x ^ (y - z) = x ^ y / x ^ z := by
simp only [sub_eq_add_neg, rpow_add hx, rpow_neg (le_of_lt hx), div_eq_mul_inv]
theorem rpow_sub' {x : ℝ} (hx : 0 ≤ x) {y z : ℝ} (h : y - z ≠ 0) : x ^ (y - z) = x ^ y / x ^ z := by
simp only [sub_eq_add_neg] at h ⊢
simp only [rpow_add' hx h, rpow_neg hx, div_eq_mul_inv]
protected theorem _root_.HasCompactSupport.rpow_const {α : Type*} [TopologicalSpace α] {f : α → ℝ}
(hf : HasCompactSupport f) {r : ℝ} (hr : r ≠ 0) : HasCompactSupport (fun x ↦ f x ^ r) :=
hf.comp_left (g := (· ^ r)) (Real.zero_rpow hr)
end Real
/-!
## Comparing real and complex powers
-/
namespace Complex
theorem ofReal_cpow {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : ((x ^ y : ℝ) : ℂ) = (x : ℂ) ^ (y : ℂ) := by
simp only [Real.rpow_def_of_nonneg hx, Complex.cpow_def, ofReal_eq_zero]; split_ifs <;>
simp [Complex.ofReal_log hx]
theorem ofReal_cpow_of_nonpos {x : ℝ} (hx : x ≤ 0) (y : ℂ) :
(x : ℂ) ^ y = (-x : ℂ) ^ y * exp (π * I * y) := by
rcases hx.eq_or_lt with (rfl | hlt)
· rcases eq_or_ne y 0 with (rfl | hy) <;> simp [*]
have hne : (x : ℂ) ≠ 0 := ofReal_ne_zero.mpr hlt.ne
rw [cpow_def_of_ne_zero hne, cpow_def_of_ne_zero (neg_ne_zero.2 hne), ← exp_add, ← add_mul, log,
log, norm_neg, arg_ofReal_of_neg hlt, ← ofReal_neg, arg_ofReal_of_nonneg (neg_nonneg.2 hx),
ofReal_zero, zero_mul, add_zero]
lemma cpow_ofReal (x : ℂ) (y : ℝ) :
x ^ (y : ℂ) = ↑(‖x‖ ^ y) * (Real.cos (arg x * y) + Real.sin (arg x * y) * I) := by
rcases eq_or_ne x 0 with rfl | hx
· simp [ofReal_cpow le_rfl]
· rw [cpow_def_of_ne_zero hx, exp_eq_exp_re_mul_sin_add_cos, mul_comm (log x)]
norm_cast
rw [re_ofReal_mul, im_ofReal_mul, log_re, log_im, mul_comm y, mul_comm y, Real.exp_mul,
Real.exp_log]
rwa [norm_pos_iff]
lemma cpow_ofReal_re (x : ℂ) (y : ℝ) : (x ^ (y : ℂ)).re = ‖x‖ ^ y * Real.cos (arg x * y) := by
rw [cpow_ofReal]; generalize arg x * y = z; simp [Real.cos]
lemma cpow_ofReal_im (x : ℂ) (y : ℝ) : (x ^ (y : ℂ)).im = ‖x‖ ^ y * Real.sin (arg x * y) := by
rw [cpow_ofReal]; generalize arg x * y = z; simp [Real.sin]
theorem norm_cpow_of_ne_zero {z : ℂ} (hz : z ≠ 0) (w : ℂ) :
‖z ^ w‖ = ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
rw [cpow_def_of_ne_zero hz, norm_exp, mul_re, log_re, log_im, Real.exp_sub,
Real.rpow_def_of_pos (norm_pos_iff.mpr hz)]
theorem norm_cpow_of_imp {z w : ℂ} (h : z = 0 → w.re = 0 → w = 0) :
‖z ^ w‖ = ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
rcases ne_or_eq z 0 with (hz | rfl) <;> [exact norm_cpow_of_ne_zero hz w; rw [norm_zero]]
rcases eq_or_ne w.re 0 with hw | hw
· simp [hw, h rfl hw]
· rw [Real.zero_rpow hw, zero_div, zero_cpow, norm_zero]
exact ne_of_apply_ne re hw
theorem norm_cpow_le (z w : ℂ) : ‖z ^ w‖ ≤ ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
by_cases h : z = 0 → w.re = 0 → w = 0
· exact (norm_cpow_of_imp h).le
· push_neg at h
simp [h]
@[simp]
theorem norm_cpow_real (x : ℂ) (y : ℝ) : ‖x ^ (y : ℂ)‖ = ‖x‖ ^ y := by
rw [norm_cpow_of_imp] <;> simp
@[simp]
theorem norm_cpow_inv_nat (x : ℂ) (n : ℕ) : ‖x ^ (n⁻¹ : ℂ)‖ = ‖x‖ ^ (n⁻¹ : ℝ) := by
rw [← norm_cpow_real]; simp
theorem norm_cpow_eq_rpow_re_of_pos {x : ℝ} (hx : 0 < x) (y : ℂ) : ‖(x : ℂ) ^ y‖ = x ^ y.re := by
rw [norm_cpow_of_ne_zero (ofReal_ne_zero.mpr hx.ne'), arg_ofReal_of_nonneg hx.le,
zero_mul, Real.exp_zero, div_one, Complex.norm_of_nonneg hx.le]
theorem norm_cpow_eq_rpow_re_of_nonneg {x : ℝ} (hx : 0 ≤ x) {y : ℂ} (hy : re y ≠ 0) :
‖(x : ℂ) ^ y‖ = x ^ re y := by
rw [norm_cpow_of_imp] <;> simp [*, arg_ofReal_of_nonneg, abs_of_nonneg]
@[deprecated (since := "2025-02-17")] alias abs_cpow_of_ne_zero := norm_cpow_of_ne_zero
@[deprecated (since := "2025-02-17")] alias abs_cpow_of_imp := norm_cpow_of_imp
@[deprecated (since := "2025-02-17")] alias abs_cpow_le := norm_cpow_le
@[deprecated (since := "2025-02-17")] alias abs_cpow_real := norm_cpow_real
@[deprecated (since := "2025-02-17")] alias abs_cpow_inv_nat := norm_cpow_inv_nat
@[deprecated (since := "2025-02-17")] alias abs_cpow_eq_rpow_re_of_pos :=
norm_cpow_eq_rpow_re_of_pos
@[deprecated (since := "2025-02-17")] alias abs_cpow_eq_rpow_re_of_nonneg :=
norm_cpow_eq_rpow_re_of_nonneg
open Filter in
lemma norm_ofReal_cpow_eventually_eq_atTop (c : ℂ) :
(fun t : ℝ ↦ ‖(t : ℂ) ^ c‖) =ᶠ[atTop] fun t ↦ t ^ c.re := by
filter_upwards [eventually_gt_atTop 0] with t ht
rw [norm_cpow_eq_rpow_re_of_pos ht]
lemma norm_natCast_cpow_of_re_ne_zero (n : ℕ) {s : ℂ} (hs : s.re ≠ 0) :
‖(n : ℂ) ^ s‖ = (n : ℝ) ^ (s.re) := by
rw [← ofReal_natCast, norm_cpow_eq_rpow_re_of_nonneg n.cast_nonneg hs]
lemma norm_natCast_cpow_of_pos {n : ℕ} (hn : 0 < n) (s : ℂ) :
‖(n : ℂ) ^ s‖ = (n : ℝ) ^ (s.re) := by
rw [← ofReal_natCast, norm_cpow_eq_rpow_re_of_pos (Nat.cast_pos.mpr hn) _]
lemma norm_natCast_cpow_pos_of_pos {n : ℕ} (hn : 0 < n) (s : ℂ) : 0 < ‖(n : ℂ) ^ s‖ :=
(norm_natCast_cpow_of_pos hn _).symm ▸ Real.rpow_pos_of_pos (Nat.cast_pos.mpr hn) _
theorem cpow_mul_ofReal_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (z : ℂ) :
(x : ℂ) ^ (↑y * z) = (↑(x ^ y) : ℂ) ^ z := by
rw [cpow_mul, ofReal_cpow hx]
· rw [← ofReal_log hx, ← ofReal_mul, ofReal_im, neg_lt_zero]; exact Real.pi_pos
· rw [← ofReal_log hx, ← ofReal_mul, ofReal_im]; exact Real.pi_pos.le
end Complex
/-! ### Positivity extension -/
namespace Mathlib.Meta.Positivity
open Lean Meta Qq
/-- Extension for the `positivity` tactic: exponentiation by a real number is positive (namely 1)
when the exponent is zero. The other cases are done in `evalRpow`. -/
@[positivity (_ : ℝ) ^ (0 : ℝ)]
def evalRpowZero : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q($a ^ (0 : ℝ)) =>
assertInstancesCommute
pure (.positive q(Real.rpow_zero_pos $a))
| _, _, _ => throwError "not Real.rpow"
/-- Extension for the `positivity` tactic: exponentiation by a real number is nonnegative when
the base is nonnegative and positive when the base is positive. -/
@[positivity (_ : ℝ) ^ (_ : ℝ)]
def evalRpow : PositivityExt where eval {u α} _zα _pα e := do
match u, α, e with
| 0, ~q(ℝ), ~q($a ^ ($b : ℝ)) =>
let ra ← core q(inferInstance) q(inferInstance) a
assertInstancesCommute
match ra with
| .positive pa =>
pure (.positive q(Real.rpow_pos_of_pos $pa $b))
| .nonnegative pa =>
pure (.nonnegative q(Real.rpow_nonneg $pa $b))
| _ => pure .none
| _, _, _ => throwError "not Real.rpow"
end Mathlib.Meta.Positivity
/-!
## Further algebraic properties of `rpow`
-/
namespace Real
variable {x y z : ℝ} {n : ℕ}
theorem rpow_mul {x : ℝ} (hx : 0 ≤ x) (y z : ℝ) : x ^ (y * z) = (x ^ y) ^ z := by
rw [← Complex.ofReal_inj, Complex.ofReal_cpow (rpow_nonneg hx _),
Complex.ofReal_cpow hx, Complex.ofReal_mul, Complex.cpow_mul, Complex.ofReal_cpow hx] <;>
simp only [(Complex.ofReal_mul _ _).symm, (Complex.ofReal_log hx).symm, Complex.ofReal_im,
neg_lt_zero, pi_pos, le_of_lt pi_pos]
lemma rpow_pow_comm {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (n : ℕ) : (x ^ y) ^ n = (x ^ n) ^ y := by
simp_rw [← rpow_natCast, ← rpow_mul hx, mul_comm y]
lemma rpow_zpow_comm {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (n : ℤ) : (x ^ y) ^ n = (x ^ n) ^ y := by
simp_rw [← rpow_intCast, ← rpow_mul hx, mul_comm y]
lemma rpow_add_intCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℤ) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_def, rpow_def, Complex.ofReal_add,
Complex.cpow_add _ _ (Complex.ofReal_ne_zero.mpr hx), Complex.ofReal_intCast,
Complex.cpow_intCast, ← Complex.ofReal_zpow, mul_comm, Complex.re_ofReal_mul, mul_comm]
lemma rpow_add_natCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y + n) = x ^ y * x ^ n := by
simpa using rpow_add_intCast hx y n
lemma rpow_sub_intCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y - n) = x ^ y / x ^ n := by
simpa using rpow_add_intCast hx y (-n)
lemma rpow_sub_natCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y - n) = x ^ y / x ^ n := by
simpa using rpow_sub_intCast hx y n
lemma rpow_add_intCast' (hx : 0 ≤ x) {n : ℤ} (h : y + n ≠ 0) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_add' hx h, rpow_intCast]
lemma rpow_add_natCast' (hx : 0 ≤ x) (h : y + n ≠ 0) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_add' hx h, rpow_natCast]
lemma rpow_sub_intCast' (hx : 0 ≤ x) {n : ℤ} (h : y - n ≠ 0) : x ^ (y - n) = x ^ y / x ^ n := by
rw [rpow_sub' hx h, rpow_intCast]
lemma rpow_sub_natCast' (hx : 0 ≤ x) (h : y - n ≠ 0) : x ^ (y - n) = x ^ y / x ^ n := by
rw [rpow_sub' hx h, rpow_natCast]
theorem rpow_add_one {x : ℝ} (hx : x ≠ 0) (y : ℝ) : x ^ (y + 1) = x ^ y * x := by
simpa using rpow_add_natCast hx y 1
theorem rpow_sub_one {x : ℝ} (hx : x ≠ 0) (y : ℝ) : x ^ (y - 1) = x ^ y / x := by
simpa using rpow_sub_natCast hx y 1
lemma rpow_add_one' (hx : 0 ≤ x) (h : y + 1 ≠ 0) : x ^ (y + 1) = x ^ y * x := by
rw [rpow_add' hx h, rpow_one]
lemma rpow_one_add' (hx : 0 ≤ x) (h : 1 + y ≠ 0) : x ^ (1 + y) = x * x ^ y := by
rw [rpow_add' hx h, rpow_one]
lemma rpow_sub_one' (hx : 0 ≤ x) (h : y - 1 ≠ 0) : x ^ (y - 1) = x ^ y / x := by
rw [rpow_sub' hx h, rpow_one]
lemma rpow_one_sub' (hx : 0 ≤ x) (h : 1 - y ≠ 0) : x ^ (1 - y) = x / x ^ y := by
rw [rpow_sub' hx h, rpow_one]
@[simp]
theorem rpow_two (x : ℝ) : x ^ (2 : ℝ) = x ^ 2 := by
rw [← rpow_natCast]
simp only [Nat.cast_ofNat]
theorem rpow_neg_one (x : ℝ) : x ^ (-1 : ℝ) = x⁻¹ := by
suffices H : x ^ ((-1 : ℤ) : ℝ) = x⁻¹ by rwa [Int.cast_neg, Int.cast_one] at H
simp only [rpow_intCast, zpow_one, zpow_neg]
theorem mul_rpow (hx : 0 ≤ x) (hy : 0 ≤ y) : (x * y) ^ z = x ^ z * y ^ z := by
iterate 2 rw [Real.rpow_def_of_nonneg]; split_ifs with h_ifs <;> simp_all
· rw [log_mul ‹_› ‹_›, add_mul, exp_add, rpow_def_of_pos (hy.lt_of_ne' ‹_›)]
all_goals positivity
theorem inv_rpow (hx : 0 ≤ x) (y : ℝ) : x⁻¹ ^ y = (x ^ y)⁻¹ := by
simp only [← rpow_neg_one, ← rpow_mul hx, mul_comm]
theorem div_rpow (hx : 0 ≤ x) (hy : 0 ≤ y) (z : ℝ) : (x / y) ^ z = x ^ z / y ^ z := by
simp only [div_eq_mul_inv, mul_rpow hx (inv_nonneg.2 hy), inv_rpow hy]
theorem log_rpow {x : ℝ} (hx : 0 < x) (y : ℝ) : log (x ^ y) = y * log x := by
apply exp_injective
rw [exp_log (rpow_pos_of_pos hx y), ← exp_log hx, mul_comm, rpow_def_of_pos (exp_pos (log x)) y]
theorem mul_log_eq_log_iff {x y z : ℝ} (hx : 0 < x) (hz : 0 < z) :
y * log x = log z ↔ x ^ y = z :=
⟨fun h ↦ log_injOn_pos (rpow_pos_of_pos hx _) hz <| log_rpow hx _ |>.trans h,
by rintro rfl; rw [log_rpow hx]⟩
@[simp] lemma rpow_rpow_inv (hx : 0 ≤ x) (hy : y ≠ 0) : (x ^ y) ^ y⁻¹ = x := by
rw [← rpow_mul hx, mul_inv_cancel₀ hy, rpow_one]
@[simp] lemma rpow_inv_rpow (hx : 0 ≤ x) (hy : y ≠ 0) : (x ^ y⁻¹) ^ y = x := by
rw [← rpow_mul hx, inv_mul_cancel₀ hy, rpow_one]
theorem pow_rpow_inv_natCast (hx : 0 ≤ x) (hn : n ≠ 0) : (x ^ n) ^ (n⁻¹ : ℝ) = x := by
have hn0 : (n : ℝ) ≠ 0 := Nat.cast_ne_zero.2 hn
rw [← rpow_natCast, ← rpow_mul hx, mul_inv_cancel₀ hn0, rpow_one]
theorem rpow_inv_natCast_pow (hx : 0 ≤ x) (hn : n ≠ 0) : (x ^ (n⁻¹ : ℝ)) ^ n = x := by
have hn0 : (n : ℝ) ≠ 0 := Nat.cast_ne_zero.2 hn
rw [← rpow_natCast, ← rpow_mul hx, inv_mul_cancel₀ hn0, rpow_one]
lemma rpow_natCast_mul (hx : 0 ≤ x) (n : ℕ) (z : ℝ) : x ^ (n * z) = (x ^ n) ^ z := by
rw [rpow_mul hx, rpow_natCast]
lemma rpow_mul_natCast (hx : 0 ≤ x) (y : ℝ) (n : ℕ) : x ^ (y * n) = (x ^ y) ^ n := by
rw [rpow_mul hx, rpow_natCast]
lemma rpow_intCast_mul (hx : 0 ≤ x) (n : ℤ) (z : ℝ) : x ^ (n * z) = (x ^ n) ^ z := by
rw [rpow_mul hx, rpow_intCast]
lemma rpow_mul_intCast (hx : 0 ≤ x) (y : ℝ) (n : ℤ) : x ^ (y * n) = (x ^ y) ^ n := by
rw [rpow_mul hx, rpow_intCast]
/-! Note: lemmas about `(∏ i ∈ s, f i ^ r)` such as `Real.finset_prod_rpow` are proved
in `Mathlib/Analysis/SpecialFunctions/Pow/NNReal.lean` instead. -/
/-!
## Order and monotonicity
-/
@[gcongr, bound]
theorem rpow_lt_rpow (hx : 0 ≤ x) (hxy : x < y) (hz : 0 < z) : x ^ z < y ^ z := by
rw [le_iff_eq_or_lt] at hx; rcases hx with hx | hx
· rw [← hx, zero_rpow (ne_of_gt hz)]
exact rpow_pos_of_pos (by rwa [← hx] at hxy) _
· rw [rpow_def_of_pos hx, rpow_def_of_pos (lt_trans hx hxy), exp_lt_exp]
exact mul_lt_mul_of_pos_right (log_lt_log hx hxy) hz
theorem strictMonoOn_rpow_Ici_of_exponent_pos {r : ℝ} (hr : 0 < r) :
StrictMonoOn (fun (x : ℝ) => x ^ r) (Set.Ici 0) :=
fun _ ha _ _ hab => rpow_lt_rpow ha hab hr
@[gcongr, bound]
theorem rpow_le_rpow {x y z : ℝ} (h : 0 ≤ x) (h₁ : x ≤ y) (h₂ : 0 ≤ z) : x ^ z ≤ y ^ z := by
rcases eq_or_lt_of_le h₁ with (rfl | h₁'); · rfl
rcases eq_or_lt_of_le h₂ with (rfl | h₂'); · simp
exact le_of_lt (rpow_lt_rpow h h₁' h₂')
theorem monotoneOn_rpow_Ici_of_exponent_nonneg {r : ℝ} (hr : 0 ≤ r) :
MonotoneOn (fun (x : ℝ) => x ^ r) (Set.Ici 0) :=
fun _ ha _ _ hab => rpow_le_rpow ha hab hr
lemma rpow_lt_rpow_of_neg (hx : 0 < x) (hxy : x < y) (hz : z < 0) : y ^ z < x ^ z := by
have := hx.trans hxy
rw [← inv_lt_inv₀, ← rpow_neg, ← rpow_neg]
on_goal 1 => refine rpow_lt_rpow ?_ hxy (neg_pos.2 hz)
all_goals positivity
lemma rpow_le_rpow_of_nonpos (hx : 0 < x) (hxy : x ≤ y) (hz : z ≤ 0) : y ^ z ≤ x ^ z := by
have := hx.trans_le hxy
rw [← inv_le_inv₀, ← rpow_neg, ← rpow_neg]
on_goal 1 => refine rpow_le_rpow ?_ hxy (neg_nonneg.2 hz)
all_goals positivity
theorem rpow_lt_rpow_iff (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z < y ^ z ↔ x < y :=
⟨lt_imp_lt_of_le_imp_le fun h => rpow_le_rpow hy h (le_of_lt hz), fun h => rpow_lt_rpow hx h hz⟩
theorem rpow_le_rpow_iff (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z ≤ y ^ z ↔ x ≤ y :=
le_iff_le_iff_lt_iff_lt.2 <| rpow_lt_rpow_iff hy hx hz
lemma rpow_lt_rpow_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) : x ^ z < y ^ z ↔ y < x :=
⟨lt_imp_lt_of_le_imp_le fun h ↦ rpow_le_rpow_of_nonpos hx h hz.le,
fun h ↦ rpow_lt_rpow_of_neg hy h hz⟩
lemma rpow_le_rpow_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) : x ^ z ≤ y ^ z ↔ y ≤ x :=
le_iff_le_iff_lt_iff_lt.2 <| rpow_lt_rpow_iff_of_neg hy hx hz
lemma le_rpow_inv_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ≤ y ^ z⁻¹ ↔ x ^ z ≤ y := by
rw [← rpow_le_rpow_iff hx _ hz, rpow_inv_rpow] <;> positivity
lemma rpow_inv_le_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z⁻¹ ≤ y ↔ x ≤ y ^ z := by
rw [← rpow_le_rpow_iff _ hy hz, rpow_inv_rpow] <;> positivity
lemma lt_rpow_inv_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x < y ^ z⁻¹ ↔ x ^ z < y :=
lt_iff_lt_of_le_iff_le <| rpow_inv_le_iff_of_pos hy hx hz
lemma rpow_inv_lt_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z⁻¹ < y ↔ x < y ^ z :=
lt_iff_lt_of_le_iff_le <| le_rpow_inv_iff_of_pos hy hx hz
theorem le_rpow_inv_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ≤ y ^ z⁻¹ ↔ y ≤ x ^ z := by
rw [← rpow_le_rpow_iff_of_neg _ hx hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem lt_rpow_inv_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x < y ^ z⁻¹ ↔ y < x ^ z := by
rw [← rpow_lt_rpow_iff_of_neg _ hx hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_inv_lt_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ^ z⁻¹ < y ↔ y ^ z < x := by
rw [← rpow_lt_rpow_iff_of_neg hy _ hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_inv_le_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ^ z⁻¹ ≤ y ↔ y ^ z ≤ x := by
rw [← rpow_le_rpow_iff_of_neg hy _ hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_lt_rpow_of_exponent_lt (hx : 1 < x) (hyz : y < z) : x ^ y < x ^ z := by
repeat' rw [rpow_def_of_pos (lt_trans zero_lt_one hx)]
rw [exp_lt_exp]; exact mul_lt_mul_of_pos_left hyz (log_pos hx)
@[gcongr]
theorem rpow_le_rpow_of_exponent_le (hx : 1 ≤ x) (hyz : y ≤ z) : x ^ y ≤ x ^ z := by
repeat' rw [rpow_def_of_pos (lt_of_lt_of_le zero_lt_one hx)]
rw [exp_le_exp]; exact mul_le_mul_of_nonneg_left hyz (log_nonneg hx)
theorem rpow_lt_rpow_of_exponent_neg {x y z : ℝ} (hy : 0 < y) (hxy : y < x) (hz : z < 0) :
x ^ z < y ^ z := by
have hx : 0 < x := hy.trans hxy
rw [← neg_neg z, Real.rpow_neg (le_of_lt hx) (-z), Real.rpow_neg (le_of_lt hy) (-z),
inv_lt_inv₀ (rpow_pos_of_pos hx _) (rpow_pos_of_pos hy _)]
exact Real.rpow_lt_rpow (by positivity) hxy <| neg_pos_of_neg hz
theorem strictAntiOn_rpow_Ioi_of_exponent_neg {r : ℝ} (hr : r < 0) :
StrictAntiOn (fun (x : ℝ) => x ^ r) (Set.Ioi 0) :=
fun _ ha _ _ hab => rpow_lt_rpow_of_exponent_neg ha hab hr
theorem rpow_le_rpow_of_exponent_nonpos {x y : ℝ} (hy : 0 < y) (hxy : y ≤ x) (hz : z ≤ 0) :
x ^ z ≤ y ^ z := by
rcases ne_or_eq z 0 with hz_zero | rfl
case inl =>
rcases ne_or_eq x y with hxy' | rfl
case inl =>
exact le_of_lt <| rpow_lt_rpow_of_exponent_neg hy (Ne.lt_of_le (id (Ne.symm hxy')) hxy)
(Ne.lt_of_le hz_zero hz)
case inr => simp
case inr => simp
theorem antitoneOn_rpow_Ioi_of_exponent_nonpos {r : ℝ} (hr : r ≤ 0) :
AntitoneOn (fun (x : ℝ) => x ^ r) (Set.Ioi 0) :=
fun _ ha _ _ hab => rpow_le_rpow_of_exponent_nonpos ha hab hr
@[simp]
theorem rpow_le_rpow_left_iff (hx : 1 < x) : x ^ y ≤ x ^ z ↔ y ≤ z := by
have x_pos : 0 < x := lt_trans zero_lt_one hx
rw [← log_le_log_iff (rpow_pos_of_pos x_pos y) (rpow_pos_of_pos x_pos z), log_rpow x_pos,
log_rpow x_pos, mul_le_mul_right (log_pos hx)]
@[simp]
theorem rpow_lt_rpow_left_iff (hx : 1 < x) : x ^ y < x ^ z ↔ y < z := by
rw [lt_iff_not_le, rpow_le_rpow_left_iff hx, lt_iff_not_le]
theorem rpow_lt_rpow_of_exponent_gt (hx0 : 0 < x) (hx1 : x < 1) (hyz : z < y) : x ^ y < x ^ z := by
repeat' rw [rpow_def_of_pos hx0]
rw [exp_lt_exp]; exact mul_lt_mul_of_neg_left hyz (log_neg hx0 hx1)
theorem rpow_le_rpow_of_exponent_ge (hx0 : 0 < x) (hx1 : x ≤ 1) (hyz : z ≤ y) : x ^ y ≤ x ^ z := by
repeat' rw [rpow_def_of_pos hx0]
rw [exp_le_exp]; exact mul_le_mul_of_nonpos_left hyz (log_nonpos (le_of_lt hx0) hx1)
@[simp]
theorem rpow_le_rpow_left_iff_of_base_lt_one (hx0 : 0 < x) (hx1 : x < 1) :
x ^ y ≤ x ^ z ↔ z ≤ y := by
rw [← log_le_log_iff (rpow_pos_of_pos hx0 y) (rpow_pos_of_pos hx0 z), log_rpow hx0, log_rpow hx0,
mul_le_mul_right_of_neg (log_neg hx0 hx1)]
@[simp]
theorem rpow_lt_rpow_left_iff_of_base_lt_one (hx0 : 0 < x) (hx1 : x < 1) :
x ^ y < x ^ z ↔ z < y := by
rw [lt_iff_not_le, rpow_le_rpow_left_iff_of_base_lt_one hx0 hx1, lt_iff_not_le]
theorem rpow_lt_one {x z : ℝ} (hx1 : 0 ≤ x) (hx2 : x < 1) (hz : 0 < z) : x ^ z < 1 := by
rw [← one_rpow z]
exact rpow_lt_rpow hx1 hx2 hz
theorem rpow_le_one {x z : ℝ} (hx1 : 0 ≤ x) (hx2 : x ≤ 1) (hz : 0 ≤ z) : x ^ z ≤ 1 := by
rw [← one_rpow z]
exact rpow_le_rpow hx1 hx2 hz
theorem rpow_lt_one_of_one_lt_of_neg {x z : ℝ} (hx : 1 < x) (hz : z < 0) : x ^ z < 1 := by
convert rpow_lt_rpow_of_exponent_lt hx hz
exact (rpow_zero x).symm
theorem rpow_le_one_of_one_le_of_nonpos {x z : ℝ} (hx : 1 ≤ x) (hz : z ≤ 0) : x ^ z ≤ 1 := by
convert rpow_le_rpow_of_exponent_le hx hz
exact (rpow_zero x).symm
theorem one_lt_rpow {x z : ℝ} (hx : 1 < x) (hz : 0 < z) : 1 < x ^ z := by
rw [← one_rpow z]
exact rpow_lt_rpow zero_le_one hx hz
theorem one_le_rpow {x z : ℝ} (hx : 1 ≤ x) (hz : 0 ≤ z) : 1 ≤ x ^ z := by
rw [← one_rpow z]
exact rpow_le_rpow zero_le_one hx hz
theorem one_lt_rpow_of_pos_of_lt_one_of_neg (hx1 : 0 < x) (hx2 : x < 1) (hz : z < 0) :
1 < x ^ z := by
convert rpow_lt_rpow_of_exponent_gt hx1 hx2 hz
exact (rpow_zero x).symm
theorem one_le_rpow_of_pos_of_le_one_of_nonpos (hx1 : 0 < x) (hx2 : x ≤ 1) (hz : z ≤ 0) :
1 ≤ x ^ z := by
convert rpow_le_rpow_of_exponent_ge hx1 hx2 hz
exact (rpow_zero x).symm
theorem rpow_lt_one_iff_of_pos (hx : 0 < x) : x ^ y < 1 ↔ 1 < x ∧ y < 0 ∨ x < 1 ∧ 0 < y := by
rw [rpow_def_of_pos hx, exp_lt_one_iff, mul_neg_iff, log_pos_iff hx.le, log_neg_iff hx]
theorem rpow_lt_one_iff (hx : 0 ≤ x) :
x ^ y < 1 ↔ x = 0 ∧ y ≠ 0 ∨ 1 < x ∧ y < 0 ∨ x < 1 ∧ 0 < y := by
rcases hx.eq_or_lt with (rfl | hx)
· rcases _root_.em (y = 0) with (rfl | hy) <;> simp [*, lt_irrefl, zero_lt_one]
· simp [rpow_lt_one_iff_of_pos hx, hx.ne.symm]
theorem rpow_lt_one_iff' {x y : ℝ} (hx : 0 ≤ x) (hy : 0 < y) :
x ^ y < 1 ↔ x < 1 := by
rw [← Real.rpow_lt_rpow_iff hx zero_le_one hy, Real.one_rpow]
theorem one_lt_rpow_iff_of_pos (hx : 0 < x) : 1 < x ^ y ↔ 1 < x ∧ 0 < y ∨ x < 1 ∧ y < 0 := by
rw [rpow_def_of_pos hx, one_lt_exp_iff, mul_pos_iff, log_pos_iff hx.le, log_neg_iff hx]
theorem one_lt_rpow_iff (hx : 0 ≤ x) : 1 < x ^ y ↔ 1 < x ∧ 0 < y ∨ 0 < x ∧ x < 1 ∧ y < 0 := by
rcases hx.eq_or_lt with (rfl | hx)
· rcases _root_.em (y = 0) with (rfl | hy) <;> simp [*, lt_irrefl, (zero_lt_one' ℝ).not_lt]
· simp [one_lt_rpow_iff_of_pos hx, hx]
/-- This is a more general but less convenient version of `rpow_le_rpow_of_exponent_ge`.
This version allows `x = 0`, so it explicitly forbids `x = y = 0`, `z ≠ 0`. -/
theorem rpow_le_rpow_of_exponent_ge_of_imp (hx0 : 0 ≤ x) (hx1 : x ≤ 1) (hyz : z ≤ y)
(h : x = 0 → y = 0 → z = 0) :
x ^ y ≤ x ^ z := by
rcases eq_or_lt_of_le hx0 with (rfl | hx0')
· rcases eq_or_ne y 0 with rfl | hy0
· rw [h rfl rfl]
· rw [zero_rpow hy0]
apply zero_rpow_nonneg
· exact rpow_le_rpow_of_exponent_ge hx0' hx1 hyz
/-- This version of `rpow_le_rpow_of_exponent_ge` allows `x = 0` but requires `0 ≤ z`.
See also `rpow_le_rpow_of_exponent_ge_of_imp` for the most general version. -/
theorem rpow_le_rpow_of_exponent_ge' (hx0 : 0 ≤ x) (hx1 : x ≤ 1) (hz : 0 ≤ z) (hyz : z ≤ y) :
x ^ y ≤ x ^ z :=
rpow_le_rpow_of_exponent_ge_of_imp hx0 hx1 hyz fun _ hy ↦ le_antisymm (hyz.trans_eq hy) hz
lemma rpow_max {x y p : ℝ} (hx : 0 ≤ x) (hy : 0 ≤ y) (hp : 0 ≤ p) :
(max x y) ^ p = max (x ^ p) (y ^ p) := by
rcases le_total x y with hxy | hxy
· rw [max_eq_right hxy, max_eq_right (rpow_le_rpow hx hxy hp)]
· rw [max_eq_left hxy, max_eq_left (rpow_le_rpow hy hxy hp)]
theorem self_le_rpow_of_le_one (h₁ : 0 ≤ x) (h₂ : x ≤ 1) (h₃ : y ≤ 1) : x ≤ x ^ y := by
simpa only [rpow_one]
using rpow_le_rpow_of_exponent_ge_of_imp h₁ h₂ h₃ fun _ ↦ (absurd · one_ne_zero)
theorem self_le_rpow_of_one_le (h₁ : 1 ≤ x) (h₂ : 1 ≤ y) : x ≤ x ^ y := by
simpa only [rpow_one] using rpow_le_rpow_of_exponent_le h₁ h₂
theorem rpow_le_self_of_le_one (h₁ : 0 ≤ x) (h₂ : x ≤ 1) (h₃ : 1 ≤ y) : x ^ y ≤ x := by
simpa only [rpow_one]
using rpow_le_rpow_of_exponent_ge_of_imp h₁ h₂ h₃ fun _ ↦ (absurd · (one_pos.trans_le h₃).ne')
theorem rpow_le_self_of_one_le (h₁ : 1 ≤ x) (h₂ : y ≤ 1) : x ^ y ≤ x := by
simpa only [rpow_one] using rpow_le_rpow_of_exponent_le h₁ h₂
theorem self_lt_rpow_of_lt_one (h₁ : 0 < x) (h₂ : x < 1) (h₃ : y < 1) : x < x ^ y := by
simpa only [rpow_one] using rpow_lt_rpow_of_exponent_gt h₁ h₂ h₃
theorem self_lt_rpow_of_one_lt (h₁ : 1 < x) (h₂ : 1 < y) : x < x ^ y := by
simpa only [rpow_one] using rpow_lt_rpow_of_exponent_lt h₁ h₂
theorem rpow_lt_self_of_lt_one (h₁ : 0 < x) (h₂ : x < 1) (h₃ : 1 < y) : x ^ y < x := by
simpa only [rpow_one] using rpow_lt_rpow_of_exponent_gt h₁ h₂ h₃
theorem rpow_lt_self_of_one_lt (h₁ : 1 < x) (h₂ : y < 1) : x ^ y < x := by
simpa only [rpow_one] using rpow_lt_rpow_of_exponent_lt h₁ h₂
theorem rpow_left_injOn {x : ℝ} (hx : x ≠ 0) : InjOn (fun y : ℝ => y ^ x) { y : ℝ | 0 ≤ y } := by
rintro y hy z hz (hyz : y ^ x = z ^ x)
rw [← rpow_one y, ← rpow_one z, ← mul_inv_cancel₀ hx, rpow_mul hy, rpow_mul hz, hyz]
lemma rpow_left_inj (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : z ≠ 0) : x ^ z = y ^ z ↔ x = y :=
(rpow_left_injOn hz).eq_iff hx hy
lemma rpow_inv_eq (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : z ≠ 0) : x ^ z⁻¹ = y ↔ x = y ^ z := by
rw [← rpow_left_inj _ hy hz, rpow_inv_rpow hx hz]; positivity
lemma eq_rpow_inv (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : z ≠ 0) : x = y ^ z⁻¹ ↔ x ^ z = y := by
rw [← rpow_left_inj hx _ hz, rpow_inv_rpow hy hz]; positivity
theorem le_rpow_iff_log_le (hx : 0 < x) (hy : 0 < y) : x ≤ y ^ z ↔ log x ≤ z * log y := by
rw [← log_le_log_iff hx (rpow_pos_of_pos hy z), log_rpow hy]
lemma le_pow_iff_log_le (hx : 0 < x) (hy : 0 < y) : x ≤ y ^ n ↔ log x ≤ n * log y :=
rpow_natCast _ _ ▸ le_rpow_iff_log_le hx hy
lemma le_zpow_iff_log_le {n : ℤ} (hx : 0 < x) (hy : 0 < y) : x ≤ y ^ n ↔ log x ≤ n * log y :=
rpow_intCast _ _ ▸ le_rpow_iff_log_le hx hy
lemma le_rpow_of_log_le (hy : 0 < y) (h : log x ≤ z * log y) : x ≤ y ^ z := by
obtain hx | hx := le_or_lt x 0
· exact hx.trans (rpow_pos_of_pos hy _).le
· exact (le_rpow_iff_log_le hx hy).2 h
lemma le_pow_of_log_le (hy : 0 < y) (h : log x ≤ n * log y) : x ≤ y ^ n :=
rpow_natCast _ _ ▸ le_rpow_of_log_le hy h
lemma le_zpow_of_log_le {n : ℤ} (hy : 0 < y) (h : log x ≤ n * log y) : x ≤ y ^ n :=
rpow_intCast _ _ ▸ le_rpow_of_log_le hy h
theorem lt_rpow_iff_log_lt (hx : 0 < x) (hy : 0 < y) : x < y ^ z ↔ log x < z * log y := by
rw [← log_lt_log_iff hx (rpow_pos_of_pos hy z), log_rpow hy]
lemma lt_pow_iff_log_lt (hx : 0 < x) (hy : 0 < y) : x < y ^ n ↔ log x < n * log y :=
rpow_natCast _ _ ▸ lt_rpow_iff_log_lt hx hy
lemma lt_zpow_iff_log_lt {n : ℤ} (hx : 0 < x) (hy : 0 < y) : x < y ^ n ↔ log x < n * log y :=
rpow_intCast _ _ ▸ lt_rpow_iff_log_lt hx hy
lemma lt_rpow_of_log_lt (hy : 0 < y) (h : log x < z * log y) : x < y ^ z := by
obtain hx | hx := le_or_lt x 0
· exact hx.trans_lt (rpow_pos_of_pos hy _)
· exact (lt_rpow_iff_log_lt hx hy).2 h
lemma lt_pow_of_log_lt (hy : 0 < y) (h : log x < n * log y) : x < y ^ n :=
rpow_natCast _ _ ▸ lt_rpow_of_log_lt hy h
lemma lt_zpow_of_log_lt {n : ℤ} (hy : 0 < y) (h : log x < n * log y) : x < y ^ n :=
rpow_intCast _ _ ▸ lt_rpow_of_log_lt hy h
lemma rpow_le_iff_le_log (hx : 0 < x) (hy : 0 < y) : x ^ z ≤ y ↔ z * log x ≤ log y := by
rw [← log_le_log_iff (rpow_pos_of_pos hx _) hy, log_rpow hx]
lemma pow_le_iff_le_log (hx : 0 < x) (hy : 0 < y) : x ^ n ≤ y ↔ n * log x ≤ log y := by
rw [← rpow_le_iff_le_log hx hy, rpow_natCast]
lemma zpow_le_iff_le_log {n : ℤ} (hx : 0 < x) (hy : 0 < y) : x ^ n ≤ y ↔ n * log x ≤ log y := by
rw [← rpow_le_iff_le_log hx hy, rpow_intCast]
lemma le_log_of_rpow_le (hx : 0 < x) (h : x ^ z ≤ y) : z * log x ≤ log y :=
log_rpow hx _ ▸ log_le_log (by positivity) h
lemma le_log_of_pow_le (hx : 0 < x) (h : x ^ n ≤ y) : n * log x ≤ log y :=
le_log_of_rpow_le hx (rpow_natCast _ _ ▸ h)
lemma le_log_of_zpow_le {n : ℤ} (hx : 0 < x) (h : x ^ n ≤ y) : n * log x ≤ log y :=
le_log_of_rpow_le hx (rpow_intCast _ _ ▸ h)
lemma rpow_le_of_le_log (hy : 0 < y) (h : log x ≤ z * log y) : x ≤ y ^ z := by
obtain hx | hx := le_or_lt x 0
· exact hx.trans (rpow_pos_of_pos hy _).le
· exact (le_rpow_iff_log_le hx hy).2 h
lemma pow_le_of_le_log (hy : 0 < y) (h : log x ≤ n * log y) : x ≤ y ^ n :=
rpow_natCast _ _ ▸ rpow_le_of_le_log hy h
lemma zpow_le_of_le_log {n : ℤ} (hy : 0 < y) (h : log x ≤ n * log y) : x ≤ y ^ n :=
rpow_intCast _ _ ▸ rpow_le_of_le_log hy h
lemma rpow_lt_iff_lt_log (hx : 0 < x) (hy : 0 < y) : x ^ z < y ↔ z * log x < log y := by
rw [← log_lt_log_iff (rpow_pos_of_pos hx _) hy, log_rpow hx]
lemma pow_lt_iff_lt_log (hx : 0 < x) (hy : 0 < y) : x ^ n < y ↔ n * log x < log y := by
rw [← rpow_lt_iff_lt_log hx hy, rpow_natCast]
lemma zpow_lt_iff_lt_log {n : ℤ} (hx : 0 < x) (hy : 0 < y) : x ^ n < y ↔ n * log x < log y := by
rw [← rpow_lt_iff_lt_log hx hy, rpow_intCast]
lemma lt_log_of_rpow_lt (hx : 0 < x) (h : x ^ z < y) : z * log x < log y :=
log_rpow hx _ ▸ log_lt_log (by positivity) h
lemma lt_log_of_pow_lt (hx : 0 < x) (h : x ^ n < y) : n * log x < log y :=
lt_log_of_rpow_lt hx (rpow_natCast _ _ ▸ h)
lemma lt_log_of_zpow_lt {n : ℤ} (hx : 0 < x) (h : x ^ n < y) : n * log x < log y :=
lt_log_of_rpow_lt hx (rpow_intCast _ _ ▸ h)
lemma rpow_lt_of_lt_log (hy : 0 < y) (h : log x < z * log y) : x < y ^ z := by
obtain hx | hx := le_or_lt x 0
· exact hx.trans_lt (rpow_pos_of_pos hy _)
· exact (lt_rpow_iff_log_lt hx hy).2 h
lemma pow_lt_of_lt_log (hy : 0 < y) (h : log x < n * log y) : x < y ^ n :=
rpow_natCast _ _ ▸ rpow_lt_of_lt_log hy h
lemma zpow_lt_of_lt_log {n : ℤ} (hy : 0 < y) (h : log x < n * log y) : x < y ^ n :=
rpow_intCast _ _ ▸ rpow_lt_of_lt_log hy h
theorem rpow_le_one_iff_of_pos (hx : 0 < x) : x ^ y ≤ 1 ↔ 1 ≤ x ∧ y ≤ 0 ∨ x ≤ 1 ∧ 0 ≤ y := by
rw [rpow_def_of_pos hx, exp_le_one_iff, mul_nonpos_iff, log_nonneg_iff hx, log_nonpos_iff hx.le]
/-- Bound for `|log x * x ^ t|` in the interval `(0, 1]`, for positive real `t`. -/
theorem abs_log_mul_self_rpow_lt (x t : ℝ) (h1 : 0 < x) (h2 : x ≤ 1) (ht : 0 < t) :
|log x * x ^ t| < 1 / t := by
rw [lt_div_iff₀ ht]
have := abs_log_mul_self_lt (x ^ t) (rpow_pos_of_pos h1 t) (rpow_le_one h1.le h2 ht.le)
rwa [log_rpow h1, mul_assoc, abs_mul, abs_of_pos ht, mul_comm] at this
/-- `log x` is bounded above by a multiple of every power of `x` with positive exponent. -/
lemma log_le_rpow_div {x ε : ℝ} (hx : 0 ≤ x) (hε : 0 < ε) : log x ≤ x ^ ε / ε := by
rcases hx.eq_or_lt with rfl | h
· rw [log_zero, zero_rpow hε.ne', zero_div]
rw [le_div_iff₀' hε]
exact (log_rpow h ε).symm.trans_le <| (log_le_sub_one_of_pos <| rpow_pos_of_pos h ε).trans
(sub_one_lt _).le
/-- The (real) logarithm of a natural number `n` is bounded by a multiple of every power of `n`
with positive exponent. -/
lemma log_natCast_le_rpow_div (n : ℕ) {ε : ℝ} (hε : 0 < ε) : log n ≤ n ^ ε / ε :=
log_le_rpow_div n.cast_nonneg hε
lemma strictMono_rpow_of_base_gt_one {b : ℝ} (hb : 1 < b) :
StrictMono (b ^ · : ℝ → ℝ) := by
simp_rw [Real.rpow_def_of_pos (zero_lt_one.trans hb)]
exact exp_strictMono.comp <| StrictMono.const_mul strictMono_id <| Real.log_pos hb
lemma monotone_rpow_of_base_ge_one {b : ℝ} (hb : 1 ≤ b) :
Monotone (b ^ · : ℝ → ℝ) := by
rcases lt_or_eq_of_le hb with hb | rfl
case inl => exact (strictMono_rpow_of_base_gt_one hb).monotone
case inr => intro _ _ _; simp
lemma strictAnti_rpow_of_base_lt_one {b : ℝ} (hb₀ : 0 < b) (hb₁ : b < 1) :
StrictAnti (b ^ · : ℝ → ℝ) := by
simp_rw [Real.rpow_def_of_pos hb₀]
exact exp_strictMono.comp_strictAnti <| StrictMono.const_mul_of_neg strictMono_id
<| Real.log_neg hb₀ hb₁
lemma antitone_rpow_of_base_le_one {b : ℝ} (hb₀ : 0 < b) (hb₁ : b ≤ 1) :
Antitone (b ^ · : ℝ → ℝ) := by
rcases lt_or_eq_of_le hb₁ with hb₁ | rfl
case inl => exact (strictAnti_rpow_of_base_lt_one hb₀ hb₁).antitone
case inr => intro _ _ _; simp
lemma rpow_right_inj (hx₀ : 0 < x) (hx₁ : x ≠ 1) : x ^ y = x ^ z ↔ y = z := by
refine ⟨fun H ↦ ?_, fun H ↦ by rw [H]⟩
rcases hx₁.lt_or_lt with h | h
· exact (strictAnti_rpow_of_base_lt_one hx₀ h).injective H
· exact (strictMono_rpow_of_base_gt_one h).injective H
/-- Guessing rule for the `bound` tactic: when trying to prove `x ^ y ≤ x ^ z`, we can either assume
`1 ≤ x` or `0 < x ≤ 1`. -/
@[bound] lemma rpow_le_rpow_of_exponent_le_or_ge {x y z : ℝ}
(h : 1 ≤ x ∧ y ≤ z ∨ 0 < x ∧ x ≤ 1 ∧ z ≤ y) : x ^ y ≤ x ^ z := by
rcases h with ⟨x1, yz⟩ | ⟨x0, x1, zy⟩
· exact Real.rpow_le_rpow_of_exponent_le x1 yz
· exact Real.rpow_le_rpow_of_exponent_ge x0 x1 zy
end Real
namespace Complex
lemma norm_prime_cpow_le_one_half (p : Nat.Primes) {s : ℂ} (hs : 1 < s.re) :
‖(p : ℂ) ^ (-s)‖ ≤ 1 / 2 := by
rw [norm_natCast_cpow_of_re_ne_zero p <| by rw [neg_re]; linarith only [hs]]
refine (Real.rpow_le_rpow_of_nonpos zero_lt_two (Nat.cast_le.mpr p.prop.two_le) <|
by rw [neg_re]; linarith only [hs]).trans ?_
rw [one_div, ← Real.rpow_neg_one]
exact Real.rpow_le_rpow_of_exponent_le one_le_two <| (neg_lt_neg hs).le
lemma one_sub_prime_cpow_ne_zero {p : ℕ} (hp : p.Prime) {s : ℂ} (hs : 1 < s.re) :
1 - (p : ℂ) ^ (-s) ≠ 0 := by
refine sub_ne_zero_of_ne fun H ↦ ?_
have := norm_prime_cpow_le_one_half ⟨p, hp⟩ hs
simp only at this
rw [← H, norm_one] at this
norm_num at this
lemma norm_natCast_cpow_le_norm_natCast_cpow_of_pos {n : ℕ} (hn : 0 < n) {w z : ℂ}
(h : w.re ≤ z.re) :
‖(n : ℂ) ^ w‖ ≤ ‖(n : ℂ) ^ z‖ := by
simp_rw [norm_natCast_cpow_of_pos hn]
exact Real.rpow_le_rpow_of_exponent_le (by exact_mod_cast hn) h
lemma norm_natCast_cpow_le_norm_natCast_cpow_iff {n : ℕ} (hn : 1 < n) {w z : ℂ} :
‖(n : ℂ) ^ w‖ ≤ ‖(n : ℂ) ^ z‖ ↔ w.re ≤ z.re := by
simp_rw [norm_natCast_cpow_of_pos (Nat.zero_lt_of_lt hn),
Real.rpow_le_rpow_left_iff (Nat.one_lt_cast.mpr hn)]
lemma norm_log_natCast_le_rpow_div (n : ℕ) {ε : ℝ} (hε : 0 < ε) : ‖log n‖ ≤ n ^ ε / ε := by
rcases n.eq_zero_or_pos with rfl | h
· rw [Nat.cast_zero, Nat.cast_zero, log_zero, norm_zero, Real.zero_rpow hε.ne', zero_div]
rw [← natCast_log, norm_real, norm_of_nonneg <| Real.log_nonneg <| by
exact_mod_cast Nat.one_le_of_lt h.lt]
exact Real.log_natCast_le_rpow_div n hε
end Complex
/-!
## Square roots of reals
-/
namespace Real
variable {z x y : ℝ}
section Sqrt
theorem sqrt_eq_rpow (x : ℝ) : √x = x ^ (1 / (2 : ℝ)) := by
obtain h | h := le_or_lt 0 x
· rw [← mul_self_inj_of_nonneg (sqrt_nonneg _) (rpow_nonneg h _), mul_self_sqrt h, ← sq,
← rpow_natCast, ← rpow_mul h]
norm_num
· have : 1 / (2 : ℝ) * π = π / (2 : ℝ) := by ring
rw [sqrt_eq_zero_of_nonpos h.le, rpow_def_of_neg h, this, cos_pi_div_two, mul_zero]
theorem rpow_div_two_eq_sqrt {x : ℝ} (r : ℝ) (hx : 0 ≤ x) : x ^ (r / 2) = √x ^ r := by
rw [sqrt_eq_rpow, ← rpow_mul hx]
congr
ring
end Sqrt
end Real
namespace Complex
lemma cpow_inv_two_re (x : ℂ) : (x ^ (2⁻¹ : ℂ)).re = sqrt ((‖x‖ + x.re) / 2) := by
| rw [← ofReal_ofNat, ← ofReal_inv, cpow_ofReal_re, ← div_eq_mul_inv, ← one_div,
← Real.sqrt_eq_rpow, cos_half, ← sqrt_mul, ← mul_div_assoc, mul_add, mul_one, norm_mul_cos_arg]
exacts [norm_nonneg _, (neg_pi_lt_arg _).le, arg_le_pi _]
| Mathlib/Analysis/SpecialFunctions/Pow/Real.lean | 999 | 1,002 |
/-
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‖ :=
| Mathlib/Geometry/Euclidean/Angle/Oriented/Basic.lean | 424 | 434 |
/-
Copyright (c) 2023 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.SetTheory.Cardinal.Arithmetic
import Mathlib.Order.Filter.Finite
import Mathlib.Order.Filter.Map
/-!
# Cardinality of a set with a countable cover
Assume that a set `t` is eventually covered by a countable family of sets, all with
cardinality `≤ a`. Then `t` itself has cardinality at most `a`. This is proved in
`Cardinal.mk_subtype_le_of_countable_eventually_mem`.
Versions are also given when `t = univ`, and with `= a` instead of `≤ a`.
-/
open Set Order Filter
open scoped Cardinal
namespace Cardinal
universe u v
|
/-- If a set `t` is eventually covered by a countable family of sets, all with cardinality at
most `a`, then the cardinality of `t` is also bounded by `a`.
Superseded by `mk_le_of_countable_eventually_mem` which does not assume
that the indexing set lives in the same universe. -/
lemma mk_subtype_le_of_countable_eventually_mem_aux {α ι : Type u} {a : Cardinal}
[Countable ι] {f : ι → Set α} {l : Filter ι} [NeBot l]
{t : Set α} (ht : ∀ x ∈ t, ∀ᶠ i in l, x ∈ f i)
(h'f : ∀ i, #(f i) ≤ a) : #t ≤ a := by
rcases lt_or_le a ℵ₀ with ha|ha
/- case `a` finite. In this case, it suffices to show that any finite subset `s` of `t` has
cardinality at most `a`. For this, we pick `i` such that `f i` contains all the points in `s`,
and apply the assumption that the cardinality of `f i` is at most `a`. -/
· obtain ⟨n, rfl⟩ : ∃ (n : ℕ), a = n := lt_aleph0.1 ha
apply mk_le_iff_forall_finset_subset_card_le.2 (fun s hs ↦ ?_)
have A : ∀ x ∈ s, ∀ᶠ i in l, x ∈ f i := fun x hx ↦ ht x (hs hx)
have B : ∀ᶠ i in l, ∀ x ∈ s, x ∈ f i := (s.eventually_all).2 A
rcases B.exists with ⟨i, hi⟩
have : ∀ i, Fintype (f i) := fun i ↦ (lt_aleph0_iff_fintype.1 ((h'f i).trans_lt ha)).some
let u : Finset α := (f i).toFinset
have I1 : s.card ≤ u.card := by
have : s ⊆ u := fun x hx ↦ by simpa only [u, Set.mem_toFinset] using hi x hx
exact Finset.card_le_card this
have I2 : (u.card : Cardinal) ≤ n := by
convert h'f i; simp only [u, Set.toFinset_card, mk_fintype]
exact I1.trans (Nat.cast_le.1 I2)
-- case `a` infinite:
· have : t ⊆ ⋃ i, f i := by
intro x hx
obtain ⟨i, hi⟩ : ∃ i, x ∈ f i := (ht x hx).exists
exact mem_iUnion_of_mem i hi
calc #t ≤ #(⋃ i, f i) := mk_le_mk_of_subset this
_ ≤ sum (fun i ↦ #(f i)) := mk_iUnion_le_sum_mk
_ ≤ sum (fun _ ↦ a) := sum_le_sum _ _ h'f
_ = #ι * a := by simp
_ ≤ ℵ₀ * a := mul_le_mul_right' mk_le_aleph0 a
| Mathlib/SetTheory/Cardinal/CountableCover.lean | 26 | 61 |
/-
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.Order.Hom.Basic
/-!
# Unbounded lattice homomorphisms
This file defines unbounded lattice homomorphisms. _Bounded_ lattice homomorphisms are defined in
`Mathlib.Order.Hom.BoundedLattice`.
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
* `SupHom`: Maps which preserve `⊔`.
* `InfHom`: Maps which preserve `⊓`.
* `LatticeHom`: Lattice homomorphisms. Maps which preserve `⊔` and `⊓`.
## Typeclasses
* `SupHomClass`
* `InfHomClass`
* `LatticeHomClass`
-/
open Function
variable {F α β γ δ : Type*}
/-- The type of `⊔`-preserving functions from `α` to `β`. -/
structure SupHom (α β : Type*) [Max α] [Max β] where
/-- The underlying function of a `SupHom`.
Do not use this function directly. Instead use the coercion coming from the `FunLike`
instance. -/
toFun : α → β
/-- A `SupHom` preserves suprema.
Do not use this directly. Use `map_sup` instead. -/
map_sup' (a b : α) : toFun (a ⊔ b) = toFun a ⊔ toFun b
/-- The type of `⊓`-preserving functions from `α` to `β`. -/
structure InfHom (α β : Type*) [Min α] [Min β] where
/-- The underlying function of an `InfHom`.
Do not use this function directly. Instead use the coercion coming from the `FunLike`
instance. -/
toFun : α → β
/-- An `InfHom` preserves infima.
Do not use this directly. Use `map_inf` instead. -/
map_inf' (a b : α) : toFun (a ⊓ b) = toFun a ⊓ toFun b
/-- The type of lattice homomorphisms from `α` to `β`. -/
structure LatticeHom (α β : Type*) [Lattice α] [Lattice β] extends SupHom α β where
/-- A `LatticeHom` preserves infima.
Do not use this directly. Use `map_inf` instead. -/
map_inf' (a b : α) : toFun (a ⊓ b) = toFun a ⊓ toFun b
-- TODO: remove this configuration and use the default configuration.
initialize_simps_projections LatticeHom (+toSupHom, -toFun)
section
/-- `SupHomClass F α β` states that `F` is a type of `⊔`-preserving morphisms.
You should extend this class when you extend `SupHom`. -/
class SupHomClass (F α β : Type*) [Max α] [Max β] [FunLike F α β] : Prop where
/-- A `SupHomClass` morphism preserves suprema. -/
map_sup (f : F) (a b : α) : f (a ⊔ b) = f a ⊔ f b
/-- `InfHomClass F α β` states that `F` is a type of `⊓`-preserving morphisms.
You should extend this class when you extend `InfHom`. -/
class InfHomClass (F α β : Type*) [Min α] [Min β] [FunLike F α β] : Prop where
/-- An `InfHomClass` morphism preserves infima. -/
map_inf (f : F) (a b : α) : f (a ⊓ b) = f a ⊓ f b
/-- `LatticeHomClass F α β` states that `F` is a type of lattice morphisms.
You should extend this class when you extend `LatticeHom`. -/
class LatticeHomClass (F α β : Type*) [Lattice α] [Lattice β] [FunLike F α β] : Prop
extends SupHomClass F α β where
/-- A `LatticeHomClass` morphism preserves infima. -/
map_inf (f : F) (a b : α) : f (a ⊓ b) = f a ⊓ f b
end
export SupHomClass (map_sup)
export InfHomClass (map_inf)
attribute [simp] map_sup map_inf
section Hom
variable [FunLike F α β]
-- See note [lower instance priority]
instance (priority := 100) SupHomClass.toOrderHomClass [SemilatticeSup α] [SemilatticeSup β]
[SupHomClass F α β] : OrderHomClass F α β :=
{ ‹SupHomClass F α β› with
map_rel := fun f a b h => by rw [← sup_eq_right, ← map_sup, sup_eq_right.2 h] }
-- See note [lower instance priority]
instance (priority := 100) InfHomClass.toOrderHomClass [SemilatticeInf α] [SemilatticeInf β]
[InfHomClass F α β] : OrderHomClass F α β :=
{ ‹InfHomClass F α β› with
map_rel := fun f a b h => by rw [← inf_eq_left, ← map_inf, inf_eq_left.2 h] }
-- See note [lower instance priority]
instance (priority := 100) LatticeHomClass.toInfHomClass [Lattice α] [Lattice β]
[LatticeHomClass F α β] : InfHomClass F α β :=
{ ‹LatticeHomClass F α β› with }
end Hom
section Equiv
variable [EquivLike F α β]
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.toSupHomClass [SemilatticeSup α] [SemilatticeSup β]
[OrderIsoClass F α β] : SupHomClass F α β :=
{ show OrderHomClass F α β from inferInstance with
map_sup := fun f a b =>
eq_of_forall_ge_iff fun c => by simp only [← le_map_inv_iff, sup_le_iff] }
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.toInfHomClass [SemilatticeInf α] [SemilatticeInf β]
[OrderIsoClass F α β] : InfHomClass F α β :=
{ show OrderHomClass F α β from inferInstance with
map_inf := fun f a b =>
eq_of_forall_le_iff fun c => by simp only [← map_inv_le_iff, le_inf_iff] }
-- See note [lower instance priority]
instance (priority := 100) OrderIsoClass.toLatticeHomClass [Lattice α] [Lattice β]
[OrderIsoClass F α β] : LatticeHomClass F α β :=
{ OrderIsoClass.toSupHomClass, OrderIsoClass.toInfHomClass with }
end Equiv
section OrderEmbedding
variable [FunLike F α β]
/-- We can regard an injective map preserving binary infima as an order embedding. -/
@[simps! apply]
def orderEmbeddingOfInjective [SemilatticeInf α] [SemilatticeInf β] (f : F) [InfHomClass F α β]
(hf : Injective f) : α ↪o β :=
OrderEmbedding.ofMapLEIff f (fun x y ↦ by
refine ⟨fun h ↦ ?_, fun h ↦ OrderHomClass.mono f h⟩
rwa [← inf_eq_left, ← hf.eq_iff, map_inf, inf_eq_left])
end OrderEmbedding
variable [FunLike F α β]
instance [Max α] [Max β] [SupHomClass F α β] : CoeTC F (SupHom α β) :=
⟨fun f => ⟨f, map_sup f⟩⟩
instance [Min α] [Min β] [InfHomClass F α β] : CoeTC F (InfHom α β) :=
⟨fun f => ⟨f, map_inf f⟩⟩
instance [Lattice α] [Lattice β] [LatticeHomClass F α β] : CoeTC F (LatticeHom α β) :=
⟨fun f =>
{ toFun := f
map_sup' := map_sup f
map_inf' := map_inf f }⟩
/-! ### Supremum homomorphisms -/
namespace SupHom
variable [Max α]
section Sup
variable [Max β] [Max γ] [Max δ]
instance : FunLike (SupHom α β) α β where
coe := SupHom.toFun
coe_injective' f g h := by cases f; cases g; congr
instance : SupHomClass (SupHom α β) α β where
map_sup := SupHom.map_sup'
@[simp] lemma toFun_eq_coe (f : SupHom 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 : SupHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
/-- Copy of a `SupHom` with a new `toFun` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (f : SupHom α β) (f' : α → β) (h : f' = f) : SupHom α β where
toFun := f'
map_sup' := h.symm ▸ f.map_sup'
@[simp]
theorem coe_copy (f : SupHom α β) (f' : α → β) (h : f' = f) : ⇑(f.copy f' h) = f' :=
rfl
theorem copy_eq (f : SupHom α β) (f' : α → β) (h : f' = f) : f.copy f' h = f :=
DFunLike.ext' h
variable (α)
/-- `id` as a `SupHom`. -/
protected def id : SupHom α α :=
⟨id, fun _ _ => rfl⟩
instance : Inhabited (SupHom α α) :=
⟨SupHom.id α⟩
@[simp, norm_cast]
theorem coe_id : ⇑(SupHom.id α) = id :=
rfl
variable {α}
@[simp]
theorem id_apply (a : α) : SupHom.id α a = a :=
rfl
/-- Composition of `SupHom`s as a `SupHom`. -/
def comp (f : SupHom β γ) (g : SupHom α β) : SupHom α γ where
toFun := f ∘ g
map_sup' a b := by rw [comp_apply, map_sup, map_sup]; rfl
@[simp]
theorem coe_comp (f : SupHom β γ) (g : SupHom α β) : (f.comp g : α → γ) = f ∘ g :=
rfl
@[simp]
theorem comp_apply (f : SupHom β γ) (g : SupHom α β) (a : α) : (f.comp g) a = f (g a) :=
rfl
@[simp]
theorem comp_assoc (f : SupHom γ δ) (g : SupHom β γ) (h : SupHom α β) :
(f.comp g).comp h = f.comp (g.comp h) :=
rfl
@[simp] theorem comp_id (f : SupHom α β) : f.comp (SupHom.id α) = f := rfl
@[simp] theorem id_comp (f : SupHom α β) : (SupHom.id β).comp f = f := rfl
@[simp]
theorem cancel_right {g₁ g₂ : SupHom β γ} {f : SupHom α β} (hf : Surjective f) :
g₁.comp f = g₂.comp f ↔ g₁ = g₂ :=
⟨fun h => SupHom.ext <| hf.forall.2 <| DFunLike.ext_iff.1 h, fun h => congr_arg₂ _ h rfl⟩
@[simp]
theorem cancel_left {g : SupHom β γ} {f₁ f₂ : SupHom α β} (hg : Injective g) :
g.comp f₁ = g.comp f₂ ↔ f₁ = f₂ :=
⟨fun h => SupHom.ext fun a => hg <| by rw [← SupHom.comp_apply, h, SupHom.comp_apply],
congr_arg _⟩
end Sup
variable (α) [SemilatticeSup β]
/-- The constant function as a `SupHom`. -/
def const (b : β) : SupHom α β := ⟨fun _ ↦ b, fun _ _ ↦ (sup_idem _).symm⟩
@[simp]
theorem coe_const (b : β) : ⇑(const α b) = Function.const α b :=
rfl
@[simp]
theorem const_apply (b : β) (a : α) : const α b a = b :=
rfl
variable {α}
instance : Max (SupHom α β) :=
⟨fun f g =>
⟨f ⊔ g, fun a b => by
rw [Pi.sup_apply, map_sup, map_sup]
exact sup_sup_sup_comm _ _ _ _⟩⟩
instance : SemilatticeSup (SupHom α β) :=
(DFunLike.coe_injective.semilatticeSup _) fun _ _ => rfl
instance [Bot β] : Bot (SupHom α β) :=
⟨SupHom.const α ⊥⟩
instance [Top β] : Top (SupHom α β) :=
⟨SupHom.const α ⊤⟩
instance [OrderBot β] : OrderBot (SupHom α β) :=
OrderBot.lift ((↑) : _ → α → β) (fun _ _ => id) rfl
instance [OrderTop β] : OrderTop (SupHom α β) :=
OrderTop.lift ((↑) : _ → α → β) (fun _ _ => id) rfl
instance [BoundedOrder β] : BoundedOrder (SupHom α β) :=
BoundedOrder.lift ((↑) : _ → α → β) (fun _ _ => id) rfl rfl
@[simp]
theorem coe_sup (f g : SupHom α β) : DFunLike.coe (f ⊔ g) = f ⊔ g :=
rfl
@[simp]
theorem coe_bot [Bot β] : ⇑(⊥ : SupHom α β) = ⊥ :=
rfl
@[simp]
theorem coe_top [Top β] : ⇑(⊤ : SupHom α β) = ⊤ :=
rfl
@[simp]
theorem sup_apply (f g : SupHom α β) (a : α) : (f ⊔ g) a = f a ⊔ g a :=
rfl
@[simp]
theorem bot_apply [Bot β] (a : α) : (⊥ : SupHom α β) a = ⊥ :=
rfl
@[simp]
theorem top_apply [Top β] (a : α) : (⊤ : SupHom α β) a = ⊤ :=
rfl
/-- `Subtype.val` as a `SupHom`. -/
def subtypeVal {P : β → Prop}
(Psup : ∀ ⦃x y : β⦄, P x → P y → P (x ⊔ y)) :
letI := Subtype.semilatticeSup Psup
SupHom {x : β // P x} β :=
letI := Subtype.semilatticeSup Psup
.mk Subtype.val (by simp)
@[simp]
lemma subtypeVal_apply {P : β → Prop}
(Psup : ∀ ⦃x y : β⦄, P x → P y → P (x ⊔ y)) (x : {x : β // P x}) :
subtypeVal Psup x = x := rfl
@[simp]
lemma subtypeVal_coe {P : β → Prop}
(Psup : ∀ ⦃x y : β⦄, P x → P y → P (x ⊔ y)) :
⇑(subtypeVal Psup) = Subtype.val := rfl
end SupHom
/-! ### Infimum homomorphisms -/
namespace InfHom
variable [Min α]
section Inf
variable [Min β] [Min γ] [Min δ]
instance : FunLike (InfHom α β) α β where
coe := InfHom.toFun
coe_injective' f g h := by cases f; cases g; congr
instance : InfHomClass (InfHom α β) α β where
map_inf := InfHom.map_inf'
@[simp] lemma toFun_eq_coe (f : InfHom α β) : f.toFun = (f : α → β) := rfl
@[simp, norm_cast] lemma coe_mk (f : α → β) (hf) : ⇑(mk f hf) = f := rfl
@[ext]
theorem ext {f g : InfHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
/-- Copy of an `InfHom` with a new `toFun` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (f : InfHom α β) (f' : α → β) (h : f' = f) : InfHom α β where
toFun := f'
map_inf' := h.symm ▸ f.map_inf'
@[simp]
theorem coe_copy (f : InfHom α β) (f' : α → β) (h : f' = f) : ⇑(f.copy f' h) = f' :=
rfl
theorem copy_eq (f : InfHom α β) (f' : α → β) (h : f' = f) : f.copy f' h = f :=
DFunLike.ext' h
variable (α)
/-- `id` as an `InfHom`. -/
protected def id : InfHom α α :=
⟨id, fun _ _ => rfl⟩
instance : Inhabited (InfHom α α) :=
⟨InfHom.id α⟩
@[simp, norm_cast]
theorem coe_id : ⇑(InfHom.id α) = id :=
rfl
variable {α}
@[simp]
theorem id_apply (a : α) : InfHom.id α a = a :=
rfl
/-- Composition of `InfHom`s as an `InfHom`. -/
def comp (f : InfHom β γ) (g : InfHom α β) : InfHom α γ where
toFun := f ∘ g
map_inf' a b := by rw [comp_apply, map_inf, map_inf]; rfl
@[simp]
theorem coe_comp (f : InfHom β γ) (g : InfHom α β) : (f.comp g : α → γ) = f ∘ g :=
rfl
@[simp]
theorem comp_apply (f : InfHom β γ) (g : InfHom α β) (a : α) : (f.comp g) a = f (g a) :=
rfl
@[simp]
theorem comp_assoc (f : InfHom γ δ) (g : InfHom β γ) (h : InfHom α β) :
(f.comp g).comp h = f.comp (g.comp h) :=
rfl
@[simp] theorem comp_id (f : InfHom α β) : f.comp (InfHom.id α) = f := rfl
@[simp] theorem id_comp (f : InfHom α β) : (InfHom.id β).comp f = f := rfl
@[simp]
theorem cancel_right {g₁ g₂ : InfHom β γ} {f : InfHom α β} (hf : Surjective f) :
g₁.comp f = g₂.comp f ↔ g₁ = g₂ :=
⟨fun h => InfHom.ext <| hf.forall.2 <| DFunLike.ext_iff.1 h, fun h => congr_arg₂ _ h rfl⟩
@[simp]
theorem cancel_left {g : InfHom β γ} {f₁ f₂ : InfHom α β} (hg : Injective g) :
g.comp f₁ = g.comp f₂ ↔ f₁ = f₂ :=
⟨fun h => InfHom.ext fun a => hg <| by rw [← InfHom.comp_apply, h, InfHom.comp_apply],
congr_arg _⟩
end Inf
variable (α) [SemilatticeInf β]
/-- The constant function as an `InfHom`. -/
def const (b : β) : InfHom α β := ⟨fun _ ↦ b, fun _ _ ↦ (inf_idem _).symm⟩
@[simp]
theorem coe_const (b : β) : ⇑(const α b) = Function.const α b :=
rfl
@[simp]
theorem const_apply (b : β) (a : α) : const α b a = b :=
rfl
variable {α}
instance : Min (InfHom α β) :=
⟨fun f g =>
⟨f ⊓ g, fun a b => by
rw [Pi.inf_apply, map_inf, map_inf]
exact inf_inf_inf_comm _ _ _ _⟩⟩
instance : SemilatticeInf (InfHom α β) :=
(DFunLike.coe_injective.semilatticeInf _) fun _ _ => rfl
instance [Bot β] : Bot (InfHom α β) :=
⟨InfHom.const α ⊥⟩
instance [Top β] : Top (InfHom α β) :=
⟨InfHom.const α ⊤⟩
instance [OrderBot β] : OrderBot (InfHom α β) :=
OrderBot.lift ((↑) : _ → α → β) (fun _ _ => id) rfl
instance [OrderTop β] : OrderTop (InfHom α β) :=
OrderTop.lift ((↑) : _ → α → β) (fun _ _ => id) rfl
instance [BoundedOrder β] : BoundedOrder (InfHom α β) :=
BoundedOrder.lift ((↑) : _ → α → β) (fun _ _ => id) rfl rfl
@[simp]
theorem coe_inf (f g : InfHom α β) : DFunLike.coe (f ⊓ g) = f ⊓ g :=
rfl
@[simp]
theorem coe_bot [Bot β] : ⇑(⊥ : InfHom α β) = ⊥ :=
rfl
@[simp]
theorem coe_top [Top β] : ⇑(⊤ : InfHom α β) = ⊤ :=
rfl
@[simp]
theorem inf_apply (f g : InfHom α β) (a : α) : (f ⊓ g) a = f a ⊓ g a :=
rfl
@[simp]
theorem bot_apply [Bot β] (a : α) : (⊥ : InfHom α β) a = ⊥ :=
rfl
@[simp]
theorem top_apply [Top β] (a : α) : (⊤ : InfHom α β) a = ⊤ :=
rfl
/-- `Subtype.val` as an `InfHom`. -/
def subtypeVal {P : β → Prop}
(Pinf : ∀ ⦃x y : β⦄, P x → P y → P (x ⊓ y)) :
letI := Subtype.semilatticeInf Pinf
InfHom {x : β // P x} β :=
letI := Subtype.semilatticeInf Pinf
.mk Subtype.val (by simp)
@[simp]
lemma subtypeVal_apply {P : β → Prop}
(Pinf : ∀ ⦃x y : β⦄, P x → P y → P (x ⊓ y)) (x : {x : β // P x}) :
subtypeVal Pinf x = x := rfl
@[simp]
lemma subtypeVal_coe {P : β → Prop}
(Pinf : ∀ ⦃x y : β⦄, P x → P y → P (x ⊓ y)) :
⇑(subtypeVal Pinf) = Subtype.val := rfl
end InfHom
/-! ### Lattice homomorphisms -/
namespace LatticeHom
variable [Lattice α] [Lattice β] [Lattice γ] [Lattice δ]
/-- Reinterpret a `LatticeHom` as an `InfHom`. -/
def toInfHom (f : LatticeHom α β) : InfHom α β :=
{ f with }
instance : FunLike (LatticeHom α β) α β where
coe f := f.toFun
coe_injective' f g h := by obtain ⟨⟨_, _⟩, _⟩ := f; obtain ⟨⟨_, _⟩, _⟩ := g; congr
instance : LatticeHomClass (LatticeHom α β) α β where
map_sup f := f.map_sup'
map_inf f := f.map_inf'
lemma toFun_eq_coe (f : LatticeHom α β) : f.toFun = f := rfl
@[simp] lemma coe_toSupHom (f : LatticeHom α β) : ⇑f.toSupHom = f := rfl
@[simp] lemma coe_toInfHom (f : LatticeHom α β) : ⇑f.toInfHom = f := rfl
@[simp] lemma coe_mk (f : SupHom α β) (hf) : ⇑(mk f hf) = f := rfl
@[ext]
theorem ext {f g : LatticeHom α β} (h : ∀ a, f a = g a) : f = g :=
DFunLike.ext f g h
/-- Copy of a `LatticeHom` with a new `toFun` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (f : LatticeHom α β) (f' : α → β) (h : f' = f) : LatticeHom α β :=
{ f.toSupHom.copy f' h, f.toInfHom.copy f' h with }
@[simp]
theorem coe_copy (f : LatticeHom α β) (f' : α → β) (h : f' = f) : ⇑(f.copy f' h) = f' :=
rfl
theorem copy_eq (f : LatticeHom α β) (f' : α → β) (h : f' = f) : f.copy f' h = f :=
DFunLike.ext' h
variable (α)
/-- `id` as a `LatticeHom`. -/
protected def id : LatticeHom α α where
toFun := id
map_sup' _ _ := rfl
map_inf' _ _ := rfl
instance : Inhabited (LatticeHom α α) :=
⟨LatticeHom.id α⟩
@[simp, norm_cast]
theorem coe_id : ⇑(LatticeHom.id α) = id :=
rfl
variable {α}
@[simp]
theorem id_apply (a : α) : LatticeHom.id α a = a :=
rfl
/-- Composition of `LatticeHom`s as a `LatticeHom`. -/
def comp (f : LatticeHom β γ) (g : LatticeHom α β) : LatticeHom α γ :=
{ f.toSupHom.comp g.toSupHom, f.toInfHom.comp g.toInfHom with }
@[simp]
theorem coe_comp (f : LatticeHom β γ) (g : LatticeHom α β) : (f.comp g : α → γ) = f ∘ g :=
rfl
@[simp]
theorem comp_apply (f : LatticeHom β γ) (g : LatticeHom α β) (a : α) : (f.comp g) a = f (g a) :=
rfl
@[simp]
-- `simp`-normal form of `coe_comp_sup_hom`
theorem coe_comp_sup_hom' (f : LatticeHom β γ) (g : LatticeHom α β) :
⟨f ∘ g, map_sup (f.comp g)⟩ = (f : SupHom β γ).comp g :=
rfl
theorem coe_comp_sup_hom (f : LatticeHom β γ) (g : LatticeHom α β) :
(f.comp g : SupHom α γ) = (f : SupHom β γ).comp g :=
rfl
@[simp]
-- `simp`-normal form of `coe_comp_inf_hom`
theorem coe_comp_inf_hom' (f : LatticeHom β γ) (g : LatticeHom α β) :
⟨f ∘ g, map_inf (f.comp g)⟩ = (f : InfHom β γ).comp g :=
rfl
theorem coe_comp_inf_hom (f : LatticeHom β γ) (g : LatticeHom α β) :
(f.comp g : InfHom α γ) = (f : InfHom β γ).comp g :=
rfl
@[simp]
theorem comp_assoc (f : LatticeHom γ δ) (g : LatticeHom β γ) (h : LatticeHom α β) :
(f.comp g).comp h = f.comp (g.comp h) :=
rfl
@[simp]
theorem comp_id (f : LatticeHom α β) : f.comp (LatticeHom.id α) = f :=
LatticeHom.ext fun _ => rfl
@[simp]
theorem id_comp (f : LatticeHom α β) : (LatticeHom.id β).comp f = f :=
LatticeHom.ext fun _ => rfl
@[simp]
theorem cancel_right {g₁ g₂ : LatticeHom β γ} {f : LatticeHom α β} (hf : Surjective f) :
g₁.comp f = g₂.comp f ↔ g₁ = g₂ :=
| ⟨fun h => LatticeHom.ext <| hf.forall.2 <| DFunLike.ext_iff.1 h, fun h => congr_arg₂ _ h rfl⟩
@[simp]
theorem cancel_left {g : LatticeHom β γ} {f₁ f₂ : LatticeHom α β} (hg : Injective g) :
| Mathlib/Order/Hom/Lattice.lean | 639 | 642 |
/-
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.Basic
import Mathlib.CategoryTheory.Limits.Shapes.Kernels
/-!
# Left Homology of short complexes
Given a short complex `S : ShortComplex C`, which consists of two composable
maps `f : X₁ ⟶ X₂` and `g : X₂ ⟶ X₃` such that `f ≫ g = 0`, we shall define
here the "left homology" `S.leftHomology` of `S`. For this, we introduce the
notion of "left homology data". Such an `h : S.LeftHomologyData` consists of the
data of morphisms `i : K ⟶ X₂` and `π : K ⟶ H` such that `i` identifies
`K` with the kernel of `g : X₂ ⟶ X₃`, and that `π` identifies `H` with the cokernel
of the induced map `f' : X₁ ⟶ K`.
When such a `S.LeftHomologyData` exists, we shall say that `[S.HasLeftHomology]`
and we define `S.leftHomology` to be the `H` field of a chosen left homology data.
Similarly, we define `S.cycles` to be the `K` field.
The dual notion is defined in `RightHomologyData.lean`. 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 left homology data for a short complex `S` consists of morphisms `i : K ⟶ S.X₂` and
`π : K ⟶ H` such that `i` identifies `K` to the kernel of `g : S.X₂ ⟶ S.X₃`,
and that `π` identifies `H` to the cokernel of the induced map `f' : S.X₁ ⟶ K` -/
structure LeftHomologyData where
/-- a choice of kernel of `S.g : S.X₂ ⟶ S.X₃` -/
K : C
/-- a choice of cokernel of the induced morphism `S.f' : S.X₁ ⟶ K` -/
H : C
/-- the inclusion of cycles in `S.X₂` -/
i : K ⟶ S.X₂
/-- the projection from cycles to the (left) homology -/
π : K ⟶ H
/-- the kernel condition for `i` -/
wi : i ≫ S.g = 0
/-- `i : K ⟶ S.X₂` is a kernel of `g : S.X₂ ⟶ S.X₃` -/
hi : IsLimit (KernelFork.ofι i wi)
/-- the cokernel condition for `π` -/
wπ : hi.lift (KernelFork.ofι _ S.zero) ≫ π = 0
/-- `π : K ⟶ H` is a cokernel of the induced morphism `S.f' : S.X₁ ⟶ K` -/
hπ : IsColimit (CokernelCofork.ofπ π wπ)
initialize_simps_projections LeftHomologyData (-hi, -hπ)
namespace LeftHomologyData
/-- The chosen kernels and cokernels of the limits API give a `LeftHomologyData` -/
@[simps]
noncomputable def ofHasKernelOfHasCokernel
[HasKernel S.g] [HasCokernel (kernel.lift S.g S.f S.zero)] :
S.LeftHomologyData where
K := kernel S.g
H := cokernel (kernel.lift S.g S.f S.zero)
i := kernel.ι _
π := cokernel.π _
wi := kernel.condition _
hi := kernelIsKernel _
wπ := cokernel.condition _
hπ := cokernelIsCokernel _
attribute [reassoc (attr := simp)] wi wπ
variable {S}
variable (h : S.LeftHomologyData) {A : C}
instance : Mono h.i := ⟨fun _ _ => Fork.IsLimit.hom_ext h.hi⟩
instance : Epi h.π := ⟨fun _ _ => Cofork.IsColimit.hom_ext h.hπ⟩
/-- Any morphism `k : A ⟶ S.X₂` that is a cycle (i.e. `k ≫ S.g = 0`) lifts
to a morphism `A ⟶ K` -/
def liftK (k : A ⟶ S.X₂) (hk : k ≫ S.g = 0) : A ⟶ h.K := h.hi.lift (KernelFork.ofι k hk)
@[reassoc (attr := simp)]
lemma liftK_i (k : A ⟶ S.X₂) (hk : k ≫ S.g = 0) : h.liftK k hk ≫ h.i = k :=
h.hi.fac _ WalkingParallelPair.zero
/-- The (left) homology class `A ⟶ H` attached to a cycle `k : A ⟶ S.X₂` -/
@[simp]
def liftH (k : A ⟶ S.X₂) (hk : k ≫ S.g = 0) : A ⟶ h.H := h.liftK k hk ≫ h.π
/-- Given `h : LeftHomologyData S`, this is morphism `S.X₁ ⟶ h.K` induced
by `S.f : S.X₁ ⟶ S.X₂` and the fact that `h.K` is a kernel of `S.g : S.X₂ ⟶ S.X₃`. -/
def f' : S.X₁ ⟶ h.K := h.liftK S.f S.zero
@[reassoc (attr := simp)] lemma f'_i : h.f' ≫ h.i = S.f := liftK_i _ _ _
@[reassoc (attr := simp)] lemma f'_π : h.f' ≫ h.π = 0 := h.wπ
@[reassoc]
lemma liftK_π_eq_zero_of_boundary (k : A ⟶ S.X₂) (x : A ⟶ S.X₁) (hx : k = x ≫ S.f) :
h.liftK k (by rw [hx, assoc, S.zero, comp_zero]) ≫ h.π = 0 := by
rw [show 0 = (x ≫ h.f') ≫ h.π by simp]
congr 1
simp only [← cancel_mono h.i, hx, liftK_i, assoc, f'_i]
/-- For `h : S.LeftHomologyData`, this is a restatement of `h.hπ`, saying that
`π : h.K ⟶ h.H` is a cokernel of `h.f' : S.X₁ ⟶ h.K`. -/
def hπ' : IsColimit (CokernelCofork.ofπ h.π h.f'_π) := h.hπ
/-- The morphism `H ⟶ A` induced by a morphism `k : K ⟶ A` such that `f' ≫ k = 0` -/
def descH (k : h.K ⟶ A) (hk : h.f' ≫ k = 0) : h.H ⟶ A :=
h.hπ.desc (CokernelCofork.ofπ k hk)
@[reassoc (attr := simp)]
lemma π_descH (k : h.K ⟶ A) (hk : h.f' ≫ k = 0) : h.π ≫ h.descH k hk = k :=
h.hπ.fac (CokernelCofork.ofπ k hk) WalkingParallelPair.one
lemma isIso_i (hg : S.g = 0) : IsIso h.i :=
⟨h.liftK (𝟙 S.X₂) (by rw [hg, id_comp]),
by simp only [← cancel_mono h.i, id_comp, assoc, liftK_i, comp_id], liftK_i _ _ _⟩
lemma isIso_π (hf : S.f = 0) : IsIso h.π := by
have ⟨φ, hφ⟩ := CokernelCofork.IsColimit.desc' h.hπ' (𝟙 _)
(by rw [← cancel_mono h.i, comp_id, f'_i, zero_comp, hf])
dsimp at hφ
exact ⟨φ, hφ, by rw [← cancel_epi h.π, reassoc_of% hφ, comp_id]⟩
variable (S)
/-- When the second map `S.g` is zero, this is the left homology data on `S` given
by any colimit cokernel cofork of `S.f` -/
@[simps]
def ofIsColimitCokernelCofork (hg : S.g = 0) (c : CokernelCofork S.f) (hc : IsColimit c) :
S.LeftHomologyData where
K := S.X₂
H := c.pt
i := 𝟙 _
π := c.π
wi := by rw [id_comp, hg]
hi := KernelFork.IsLimit.ofId _ hg
wπ := CokernelCofork.condition _
hπ := IsColimit.ofIsoColimit hc (Cofork.ext (Iso.refl _))
@[simp] lemma ofIsColimitCokernelCofork_f' (hg : S.g = 0) (c : CokernelCofork S.f)
(hc : IsColimit c) : (ofIsColimitCokernelCofork S hg c hc).f' = S.f := by
rw [← cancel_mono (ofIsColimitCokernelCofork S hg c hc).i, f'_i,
ofIsColimitCokernelCofork_i]
dsimp
rw [comp_id]
/-- When the second map `S.g` is zero, this is the left homology data on `S` given by
the chosen `cokernel S.f` -/
@[simps!]
noncomputable def ofHasCokernel [HasCokernel S.f] (hg : S.g = 0) : S.LeftHomologyData :=
ofIsColimitCokernelCofork S hg _ (cokernelIsCokernel _)
/-- When the first map `S.f` is zero, this is the left 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.LeftHomologyData where
K := c.pt
H := c.pt
i := c.ι
π := 𝟙 _
wi := KernelFork.condition _
hi := IsLimit.ofIsoLimit hc (Fork.ext (Iso.refl _))
wπ := Fork.IsLimit.hom_ext hc (by
dsimp
simp only [comp_id, zero_comp, Fork.IsLimit.lift_ι, Fork.ι_ofι, hf])
hπ := CokernelCofork.IsColimit.ofId _ (Fork.IsLimit.hom_ext hc (by
dsimp
simp only [comp_id, zero_comp, Fork.IsLimit.lift_ι, Fork.ι_ofι, hf]))
@[simp] lemma ofIsLimitKernelFork_f' (hf : S.f = 0) (c : KernelFork S.g) (hc : IsLimit c) :
(ofIsLimitKernelFork S hf c hc).f' = 0 := by
rw [← cancel_mono (ofIsLimitKernelFork S hf c hc).i, f'_i, hf, zero_comp]
/-- When the first map `S.f` is zero, this is the left homology data on `S` given
by the chosen `kernel S.g` -/
@[simp]
noncomputable def ofHasKernel [HasKernel S.g] (hf : S.f = 0) : S.LeftHomologyData :=
ofIsLimitKernelFork S hf _ (kernelIsKernel _)
/-- When both `S.f` and `S.g` are zero, the middle object `S.X₂` gives a left homology data on S -/
@[simps]
def ofZeros (hf : S.f = 0) (hg : S.g = 0) : S.LeftHomologyData where
K := S.X₂
H := S.X₂
i := 𝟙 _
π := 𝟙 _
wi := by rw [id_comp, hg]
hi := KernelFork.IsLimit.ofId _ hg
wπ := by
change S.f ≫ 𝟙 _ = 0
simp only [hf, zero_comp]
hπ := CokernelCofork.IsColimit.ofId _ hf
@[simp] lemma ofZeros_f' (hf : S.f = 0) (hg : S.g = 0) :
(ofZeros S hf hg).f' = 0 := by
rw [← cancel_mono ((ofZeros S hf hg).i), zero_comp, f'_i, hf]
end LeftHomologyData
/-- A short complex `S` has left homology when there exists a `S.LeftHomologyData` -/
class HasLeftHomology : Prop where
condition : Nonempty S.LeftHomologyData
/-- A chosen `S.LeftHomologyData` for a short complex `S` that has left homology -/
noncomputable def leftHomologyData [S.HasLeftHomology] :
S.LeftHomologyData := HasLeftHomology.condition.some
variable {S}
namespace HasLeftHomology
lemma mk' (h : S.LeftHomologyData) : HasLeftHomology S := ⟨Nonempty.intro h⟩
instance of_hasKernel_of_hasCokernel [HasKernel S.g] [HasCokernel (kernel.lift S.g S.f S.zero)] :
S.HasLeftHomology := HasLeftHomology.mk' (LeftHomologyData.ofHasKernelOfHasCokernel S)
instance of_hasCokernel {X Y : C} (f : X ⟶ Y) (Z : C) [HasCokernel f] :
(ShortComplex.mk f (0 : Y ⟶ Z) comp_zero).HasLeftHomology :=
HasLeftHomology.mk' (LeftHomologyData.ofHasCokernel _ rfl)
instance of_hasKernel {Y Z : C} (g : Y ⟶ Z) (X : C) [HasKernel g] :
(ShortComplex.mk (0 : X ⟶ Y) g zero_comp).HasLeftHomology :=
HasLeftHomology.mk' (LeftHomologyData.ofHasKernel _ rfl)
instance of_zeros (X Y Z : C) :
(ShortComplex.mk (0 : X ⟶ Y) (0 : Y ⟶ Z) zero_comp).HasLeftHomology :=
HasLeftHomology.mk' (LeftHomologyData.ofZeros _ rfl rfl)
end HasLeftHomology
section
variable (φ : S₁ ⟶ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData)
/-- Given left homology data `h₁` and `h₂` for two short complexes `S₁` and `S₂`,
a `LeftHomologyMapData` for a morphism `φ : S₁ ⟶ S₂`
consists of a description of the induced morphisms on the `K` (cycles)
and `H` (left homology) fields of `h₁` and `h₂`. -/
structure LeftHomologyMapData where
/-- the induced map on cycles -/
φK : h₁.K ⟶ h₂.K
/-- the induced map on left homology -/
φH : h₁.H ⟶ h₂.H
/-- commutation with `i` -/
commi : φK ≫ h₂.i = h₁.i ≫ φ.τ₂ := by aesop_cat
/-- commutation with `f'` -/
commf' : h₁.f' ≫ φK = φ.τ₁ ≫ h₂.f' := by aesop_cat
/-- commutation with `π` -/
commπ : h₁.π ≫ φH = φK ≫ h₂.π := by aesop_cat
namespace LeftHomologyMapData
attribute [reassoc (attr := simp)] commi commf' commπ
/-- The left homology map data associated to the zero morphism between two short complexes. -/
@[simps]
def zero (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
LeftHomologyMapData 0 h₁ h₂ where
φK := 0
φH := 0
/-- The left homology map data associated to the identity morphism of a short complex. -/
@[simps]
def id (h : S.LeftHomologyData) : LeftHomologyMapData (𝟙 S) h h where
φK := 𝟙 _
φH := 𝟙 _
/-- The composition of left homology map data. -/
@[simps]
def comp {φ : S₁ ⟶ S₂} {φ' : S₂ ⟶ S₃}
{h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {h₃ : S₃.LeftHomologyData}
(ψ : LeftHomologyMapData φ h₁ h₂) (ψ' : LeftHomologyMapData φ' h₂ h₃) :
LeftHomologyMapData (φ ≫ φ') h₁ h₃ where
φK := ψ.φK ≫ ψ'.φK
φH := ψ.φH ≫ ψ'.φH
instance : Subsingleton (LeftHomologyMapData φ h₁ h₂) :=
⟨fun ψ₁ ψ₂ => by
have hK : ψ₁.φK = ψ₂.φK := by rw [← cancel_mono h₂.i, commi, commi]
have hH : ψ₁.φH = ψ₂.φH := by rw [← cancel_epi h₁.π, commπ, commπ, hK]
cases ψ₁
cases ψ₂
congr⟩
instance : Inhabited (LeftHomologyMapData φ h₁ h₂) := ⟨by
let φK : h₁.K ⟶ h₂.K := h₂.liftK (h₁.i ≫ φ.τ₂)
(by rw [assoc, φ.comm₂₃, h₁.wi_assoc, zero_comp])
have commf' : h₁.f' ≫ φK = φ.τ₁ ≫ h₂.f' := by
rw [← cancel_mono h₂.i, assoc, assoc, LeftHomologyData.liftK_i,
LeftHomologyData.f'_i_assoc, LeftHomologyData.f'_i, φ.comm₁₂]
let φH : h₁.H ⟶ h₂.H := h₁.descH (φK ≫ h₂.π)
(by rw [reassoc_of% commf', h₂.f'_π, comp_zero])
exact ⟨φK, φH, by simp [φK], commf', by simp [φH]⟩⟩
instance : Unique (LeftHomologyMapData φ h₁ h₂) := Unique.mk' _
variable {φ h₁ h₂}
lemma congr_φH {γ₁ γ₂ : LeftHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) : γ₁.φH = γ₂.φH := by rw [eq]
lemma congr_φK {γ₁ γ₂ : LeftHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) : γ₁.φK = γ₂.φK := by rw [eq]
/-- When `S₁.f`, `S₁.g`, `S₂.f` and `S₂.g` are all zero, the action on left 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) :
LeftHomologyMapData φ (LeftHomologyData.ofZeros S₁ hf₁ hg₁)
(LeftHomologyData.ofZeros S₂ hf₂ hg₂) where
φK := φ.τ₂
φH := φ.τ₂
/-- 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 left 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) :
LeftHomologyMapData φ (LeftHomologyData.ofIsColimitCokernelCofork S₁ hg₁ c₁ hc₁)
(LeftHomologyData.ofIsColimitCokernelCofork S₂ hg₂ c₂ hc₂) where
φK := φ.τ₂
φH := f
commπ := comm.symm
commf' := by simp only [LeftHomologyData.ofIsColimitCokernelCofork_f', φ.comm₁₂]
/-- 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 left 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) :
LeftHomologyMapData φ (LeftHomologyData.ofIsLimitKernelFork S₁ hf₁ c₁ hc₁)
(LeftHomologyData.ofIsLimitKernelFork S₂ hf₂ c₂ hc₂) where
φK := f
φH := f
commi := comm.symm
variable (S)
/-- When both maps `S.f` and `S.g` of a short complex `S` are zero, this is the left homology map
data (for the identity of `S`) which relates the left homology data `ofZeros` and
`ofIsColimitCokernelCofork`. -/
@[simps]
def compatibilityOfZerosOfIsColimitCokernelCofork (hf : S.f = 0) (hg : S.g = 0)
(c : CokernelCofork S.f) (hc : IsColimit c) :
LeftHomologyMapData (𝟙 S) (LeftHomologyData.ofZeros S hf hg)
(LeftHomologyData.ofIsColimitCokernelCofork S hg c hc) where
φK := 𝟙 _
φH := c.π
/-- When both maps `S.f` and `S.g` of a short complex `S` are zero, this is the left homology map
data (for the identity of `S`) which relates the left homology data
`LeftHomologyData.ofIsLimitKernelFork` and `ofZeros` . -/
@[simps]
def compatibilityOfZerosOfIsLimitKernelFork (hf : S.f = 0) (hg : S.g = 0)
(c : KernelFork S.g) (hc : IsLimit c) :
LeftHomologyMapData (𝟙 S) (LeftHomologyData.ofIsLimitKernelFork S hf c hc)
(LeftHomologyData.ofZeros S hf hg) where
φK := c.ι
φH := c.ι
end LeftHomologyMapData
end
section
variable (S)
variable [S.HasLeftHomology]
/-- The left homology of a short complex, given by the `H` field of a chosen left homology data. -/
noncomputable def leftHomology : C := S.leftHomologyData.H
-- `S.leftHomology` is the simp normal form.
@[simp] lemma leftHomologyData_H : S.leftHomologyData.H = S.leftHomology := rfl
/-- The cycles of a short complex, given by the `K` field of a chosen left homology data. -/
noncomputable def cycles : C := S.leftHomologyData.K
/-- The "homology class" map `S.cycles ⟶ S.leftHomology`. -/
noncomputable def leftHomologyπ : S.cycles ⟶ S.leftHomology := S.leftHomologyData.π
/-- The inclusion `S.cycles ⟶ S.X₂`. -/
noncomputable def iCycles : S.cycles ⟶ S.X₂ := S.leftHomologyData.i
/-- The "boundaries" map `S.X₁ ⟶ S.cycles`. (Note that in this homology API, we make no use
of the "image" of this morphism, which under some categorical assumptions would be a subobject
of `S.X₂` contained in `S.cycles`.) -/
noncomputable def toCycles : S.X₁ ⟶ S.cycles := S.leftHomologyData.f'
@[reassoc (attr := simp)]
lemma iCycles_g : S.iCycles ≫ S.g = 0 := S.leftHomologyData.wi
@[reassoc (attr := simp)]
lemma toCycles_i : S.toCycles ≫ S.iCycles = S.f := S.leftHomologyData.f'_i
instance : Mono S.iCycles := by
dsimp only [iCycles]
infer_instance
instance : Epi S.leftHomologyπ := by
dsimp only [leftHomologyπ]
infer_instance
lemma leftHomology_ext_iff {A : C} (f₁ f₂ : S.leftHomology ⟶ A) :
f₁ = f₂ ↔ S.leftHomologyπ ≫ f₁ = S.leftHomologyπ ≫ f₂ := by
rw [cancel_epi]
@[ext]
lemma leftHomology_ext {A : C} (f₁ f₂ : S.leftHomology ⟶ A)
(h : S.leftHomologyπ ≫ f₁ = S.leftHomologyπ ≫ f₂) : f₁ = f₂ := by
| simpa only [leftHomology_ext_iff] using h
lemma cycles_ext_iff {A : C} (f₁ f₂ : A ⟶ S.cycles) :
| Mathlib/Algebra/Homology/ShortComplex/LeftHomology.lean | 431 | 433 |
/-
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.MeasureTheory.Integral.Lebesgue.Basic
import Mathlib.MeasureTheory.Integral.Lebesgue.Countable
import Mathlib.MeasureTheory.Integral.Lebesgue.MeasurePreserving
import Mathlib.MeasureTheory.Integral.Lebesgue.Norm
deprecated_module (since := "2025-04-13")
| Mathlib/MeasureTheory/Integral/Lebesgue.lean | 274 | 288 | |
/-
Copyright (c) 2018 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Abhimanyu Pallavi Sudhir, Jean Lo, Calle Sönne, Yury Kudryashov
-/
import Mathlib.Algebra.Algebra.Rat
import Mathlib.Data.Nat.Prime.Int
import Mathlib.Data.Rat.Sqrt
import Mathlib.Data.Real.Sqrt
import Mathlib.RingTheory.Algebraic.Basic
import Mathlib.Tactic.IntervalCases
/-!
# Irrational real numbers
In this file we define a predicate `Irrational` on `ℝ`, prove that the `n`-th root of an integer
number is irrational if it is not integer, and that `√(q : ℚ)` is irrational if and only if
`¬IsSquare q ∧ 0 ≤ q`.
We also provide dot-style constructors like `Irrational.add_rat`, `Irrational.rat_sub` etc.
With the `Decidable` instances in this file, is possible to prove `Irrational √n` using `decide`,
when `n` is a numeric literal or cast;
but this only works if you `unseal Nat.sqrt.iter in` before the theorem where you use this proof.
-/
open Rat Real
/-- A real number is irrational if it is not equal to any rational number. -/
def Irrational (x : ℝ) :=
x ∉ Set.range ((↑) : ℚ → ℝ)
theorem irrational_iff_ne_rational (x : ℝ) : Irrational x ↔ ∀ a b : ℤ, x ≠ a / b := by
simp only [Irrational, Rat.forall, cast_mk, not_exists, Set.mem_range, cast_intCast, cast_div,
eq_comm]
/-- A transcendental real number is irrational. -/
theorem Transcendental.irrational {r : ℝ} (tr : Transcendental ℚ r) : Irrational r := by
rintro ⟨a, rfl⟩
exact tr (isAlgebraic_algebraMap a)
/-!
### Irrationality of roots of integer and rational numbers
-/
/-- If `x^n`, `n > 0`, is integer and is not the `n`-th power of an integer, then
`x` is irrational. -/
theorem irrational_nrt_of_notint_nrt {x : ℝ} (n : ℕ) (m : ℤ) (hxr : x ^ n = m)
(hv : ¬∃ y : ℤ, x = y) (hnpos : 0 < n) : Irrational x := by
rintro ⟨⟨N, D, P, C⟩, rfl⟩
rw [← cast_pow] at hxr
| have c1 : ((D : ℤ) : ℝ) ≠ 0 := by
rw [Int.cast_ne_zero, Int.natCast_ne_zero]
exact P
have c2 : ((D : ℤ) : ℝ) ^ n ≠ 0 := pow_ne_zero _ c1
rw [mk'_eq_divInt, cast_pow, cast_mk, div_pow, div_eq_iff_mul_eq c2, ← Int.cast_pow,
← Int.cast_pow, ← Int.cast_mul, Int.cast_inj] at hxr
have hdivn : (D : ℤ) ^ n ∣ N ^ n := Dvd.intro_left m hxr
rw [← Int.dvd_natAbs, ← Int.natCast_pow, Int.natCast_dvd_natCast, Int.natAbs_pow,
Nat.pow_dvd_pow_iff hnpos.ne'] at hdivn
obtain rfl : D = 1 := by rw [← Nat.gcd_eq_right hdivn, C.gcd_eq_one]
refine hv ⟨N, ?_⟩
rw [mk'_eq_divInt, Int.ofNat_one, divInt_one, cast_intCast]
/-- If `x^n = m` is an integer and `n` does not divide the `multiplicity p m`, then `x`
is irrational. -/
theorem irrational_nrt_of_n_not_dvd_multiplicity {x : ℝ} (n : ℕ) {m : ℤ} (hm : m ≠ 0) (p : ℕ)
| Mathlib/Data/Real/Irrational.lean | 54 | 69 |
/-
Copyright (c) 2018 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Data.Vector.Defs
import Mathlib.Data.List.Nodup
import Mathlib.Data.List.OfFn
import Mathlib.Data.List.Scan
import Mathlib.Control.Applicative
import Mathlib.Control.Traversable.Basic
import Mathlib.Algebra.BigOperators.Group.List.Basic
/-!
# Additional theorems and definitions about the `Vector` type
This file introduces the infix notation `::ᵥ` for `Vector.cons`.
-/
universe u
variable {α β γ σ φ : Type*} {m n : ℕ}
namespace List.Vector
@[inherit_doc]
infixr:67 " ::ᵥ " => Vector.cons
attribute [simp] head_cons tail_cons
instance [Inhabited α] : Inhabited (Vector α n) :=
⟨ofFn default⟩
theorem toList_injective : Function.Injective (@toList α n) :=
Subtype.val_injective
/-- Two `v w : Vector α n` are equal iff they are equal at every single index. -/
@[ext]
theorem ext : ∀ {v w : Vector α n} (_ : ∀ m : Fin n, Vector.get v m = Vector.get w m), v = w
| ⟨v, hv⟩, ⟨w, hw⟩, h =>
Subtype.eq (List.ext_get (by rw [hv, hw]) fun m hm _ => h ⟨m, hv ▸ hm⟩)
/-- The empty `Vector` is a `Subsingleton`. -/
instance zero_subsingleton : Subsingleton (Vector α 0) :=
⟨fun _ _ => Vector.ext fun m => Fin.elim0 m⟩
@[simp]
theorem cons_val (a : α) : ∀ v : Vector α n, (a ::ᵥ v).val = a :: v.val
| ⟨_, _⟩ => rfl
theorem eq_cons_iff (a : α) (v : Vector α n.succ) (v' : Vector α n) :
v = a ::ᵥ v' ↔ v.head = a ∧ v.tail = v' :=
⟨fun h => h.symm ▸ ⟨head_cons a v', tail_cons a v'⟩, fun h =>
_root_.trans (cons_head_tail v).symm (by rw [h.1, h.2])⟩
theorem ne_cons_iff (a : α) (v : Vector α n.succ) (v' : Vector α n) :
v ≠ a ::ᵥ v' ↔ v.head ≠ a ∨ v.tail ≠ v' := by rw [Ne, eq_cons_iff a v v', not_and_or]
theorem exists_eq_cons (v : Vector α n.succ) : ∃ (a : α) (as : Vector α n), v = a ::ᵥ as :=
⟨v.head, v.tail, (eq_cons_iff v.head v v.tail).2 ⟨rfl, rfl⟩⟩
@[simp]
theorem toList_ofFn : ∀ {n} (f : Fin n → α), toList (ofFn f) = List.ofFn f
| 0, f => by rw [ofFn, List.ofFn_zero, toList, nil]
| n + 1, f => by rw [ofFn, List.ofFn_succ, toList_cons, toList_ofFn]
@[simp]
theorem mk_toList : ∀ (v : Vector α n) (h), (⟨toList v, h⟩ : Vector α n) = v
| ⟨_, _⟩, _ => rfl
@[simp] theorem length_val (v : Vector α n) : v.val.length = n := v.2
@[simp]
theorem pmap_cons {p : α → Prop} (f : (a : α) → p a → β) (a : α) (v : Vector α n)
(hp : ∀ x ∈ (cons a v).toList, p x) :
(cons a v).pmap f hp = cons (f a (by
simp only [Nat.succ_eq_add_one, toList_cons, List.mem_cons, forall_eq_or_imp] at hp
exact hp.1))
(v.pmap f (by
simp only [Nat.succ_eq_add_one, toList_cons, List.mem_cons, forall_eq_or_imp] at hp
exact hp.2)) := rfl
/-- Opposite direction of `Vector.pmap_cons` -/
theorem pmap_cons' {p : α → Prop} (f : (a : α) → p a → β) (a : α) (v : Vector α n)
(ha : p a) (hp : ∀ x ∈ v.toList, p x) :
cons (f a ha) (v.pmap f hp) = (cons a v).pmap f (by simpa [ha]) := rfl
@[simp]
theorem toList_map {β : Type*} (v : Vector α n) (f : α → β) :
(v.map f).toList = v.toList.map f := by cases v; rfl
@[simp]
theorem head_map {β : Type*} (v : Vector α (n + 1)) (f : α → β) : (v.map f).head = f v.head := by
obtain ⟨a, v', h⟩ := Vector.exists_eq_cons v
rw [h, map_cons, head_cons, head_cons]
@[simp]
theorem tail_map {β : Type*} (v : Vector α (n + 1)) (f : α → β) :
(v.map f).tail = v.tail.map f := by
obtain ⟨a, v', h⟩ := Vector.exists_eq_cons v
rw [h, map_cons, tail_cons, tail_cons]
@[simp]
theorem getElem_map {β : Type*} (v : Vector α n) (f : α → β) {i : ℕ} (hi : i < n) :
(v.map f)[i] = f v[i] := by
simp only [getElem_def, toList_map, List.getElem_map]
@[simp]
theorem toList_pmap {p : α → Prop} (f : (a : α) → p a → β) (v : Vector α n)
(hp : ∀ x ∈ v.toList, p x) :
(v.pmap f hp).toList = v.toList.pmap f hp := by cases v; rfl
@[simp]
theorem head_pmap {p : α → Prop} (f : (a : α) → p a → β) (v : Vector α (n + 1))
(hp : ∀ x ∈ v.toList, p x) :
(v.pmap f hp).head = f v.head (hp _ <| by
rw [← cons_head_tail v, toList_cons, head_cons, List.mem_cons]; exact .inl rfl) := by
obtain ⟨a, v', h⟩ := Vector.exists_eq_cons v
simp_rw [h, pmap_cons, head_cons]
@[simp]
theorem tail_pmap {p : α → Prop} (f : (a : α) → p a → β) (v : Vector α (n + 1))
(hp : ∀ x ∈ v.toList, p x) :
(v.pmap f hp).tail = v.tail.pmap f (fun x hx ↦ hp _ <| by
rw [← cons_head_tail v, toList_cons, List.mem_cons]; exact .inr hx) := by
obtain ⟨a, v', h⟩ := Vector.exists_eq_cons v
simp_rw [h, pmap_cons, tail_cons]
@[simp]
theorem getElem_pmap {p : α → Prop} (f : (a : α) → p a → β) (v : Vector α n)
(hp : ∀ x ∈ v.toList, p x) {i : ℕ} (hi : i < n) :
(v.pmap f hp)[i] = f v[i] (hp _ (by simp [getElem_def, List.getElem_mem])) := by
simp only [getElem_def, toList_pmap, List.getElem_pmap]
theorem get_eq_get_toList (v : Vector α n) (i : Fin n) :
v.get i = v.toList.get (Fin.cast v.toList_length.symm i) :=
rfl
@[deprecated (since := "2024-12-20")]
alias get_eq_get := get_eq_get_toList
@[simp]
theorem get_replicate (a : α) (i : Fin n) : (Vector.replicate n a).get i = a := by
apply List.getElem_replicate
@[simp]
theorem get_map {β : Type*} (v : Vector α n) (f : α → β) (i : Fin n) :
(v.map f).get i = f (v.get i) := by
cases v; simp [Vector.map, get_eq_get_toList]
@[simp]
theorem map₂_nil (f : α → β → γ) : Vector.map₂ f nil nil = nil :=
rfl
@[simp]
theorem map₂_cons (hd₁ : α) (tl₁ : Vector α n) (hd₂ : β) (tl₂ : Vector β n) (f : α → β → γ) :
Vector.map₂ f (hd₁ ::ᵥ tl₁) (hd₂ ::ᵥ tl₂) = f hd₁ hd₂ ::ᵥ (Vector.map₂ f tl₁ tl₂) :=
rfl
@[simp]
theorem get_ofFn {n} (f : Fin n → α) (i) : get (ofFn f) i = f i := by
conv_rhs => erw [← List.get_ofFn f ⟨i, by simp⟩]
simp only [get_eq_get_toList]
congr <;> simp [Fin.heq_ext_iff]
@[simp]
theorem ofFn_get (v : Vector α n) : ofFn (get v) = v := by
rcases v with ⟨l, rfl⟩
apply toList_injective
dsimp
simpa only [toList_ofFn] using List.ofFn_get _
/-- The natural equivalence between length-`n` vectors and functions from `Fin n`. -/
def _root_.Equiv.vectorEquivFin (α : Type*) (n : ℕ) : Vector α n ≃ (Fin n → α) :=
⟨Vector.get, Vector.ofFn, Vector.ofFn_get, fun f => funext <| Vector.get_ofFn f⟩
theorem get_tail (x : Vector α n) (i) : x.tail.get i = x.get ⟨i.1 + 1, by omega⟩ := by
obtain ⟨i, ih⟩ := i; dsimp
rcases x with ⟨_ | _, h⟩ <;> try rfl
rw [List.length] at h
rw [← h] at ih
contradiction
@[simp]
theorem get_tail_succ : ∀ (v : Vector α n.succ) (i : Fin n), get (tail v) i = get v i.succ
| ⟨a :: l, e⟩, ⟨i, h⟩ => by simp [get_eq_get_toList]; rfl
@[simp]
theorem tail_val : ∀ v : Vector α n.succ, v.tail.val = v.val.tail
| ⟨_ :: _, _⟩ => rfl
/-- The `tail` of a `nil` vector is `nil`. -/
@[simp]
theorem tail_nil : (@nil α).tail = nil :=
rfl
/-- The `tail` of a vector made up of one element is `nil`. -/
@[simp]
theorem singleton_tail : ∀ (v : Vector α 1), v.tail = Vector.nil
| ⟨[_], _⟩ => rfl
@[simp]
theorem tail_ofFn {n : ℕ} (f : Fin n.succ → α) : tail (ofFn f) = ofFn fun i => f i.succ :=
(ofFn_get _).symm.trans <| by
congr
funext i
rw [get_tail, get_ofFn]
rfl
@[simp]
theorem toList_empty (v : Vector α 0) : v.toList = [] :=
List.length_eq_zero_iff.mp v.2
/-- The list that makes up a `Vector` made up of a single element,
retrieved via `toList`, is equal to the list of that single element. -/
@[simp]
theorem toList_singleton (v : Vector α 1) : v.toList = [v.head] := by
rw [← v.cons_head_tail]
simp only [toList_cons, toList_nil, head_cons, eq_self_iff_true, and_self_iff, singleton_tail]
@[simp]
theorem empty_toList_eq_ff (v : Vector α (n + 1)) : v.toList.isEmpty = false :=
match v with
| ⟨_ :: _, _⟩ => rfl
theorem not_empty_toList (v : Vector α (n + 1)) : ¬v.toList.isEmpty := by
simp only [empty_toList_eq_ff, Bool.coe_sort_false, not_false_iff]
/-- Mapping under `id` does not change a vector. -/
@[simp]
theorem map_id {n : ℕ} (v : Vector α n) : Vector.map id v = v :=
Vector.eq _ _ (by simp only [List.map_id, Vector.toList_map])
theorem nodup_iff_injective_get {v : Vector α n} : v.toList.Nodup ↔ Function.Injective v.get := by
obtain ⟨l, hl⟩ := v
subst hl
exact List.nodup_iff_injective_get
theorem head?_toList : ∀ v : Vector α n.succ, (toList v).head? = some (head v)
| ⟨_ :: _, _⟩ => rfl
/-- Reverse a vector. -/
def reverse (v : Vector α n) : Vector α n :=
⟨v.toList.reverse, by simp⟩
/-- The `List` of a vector after a `reverse`, retrieved by `toList` is equal
to the `List.reverse` after retrieving a vector's `toList`. -/
theorem toList_reverse {v : Vector α n} : v.reverse.toList = v.toList.reverse :=
rfl
@[simp]
theorem reverse_reverse {v : Vector α n} : v.reverse.reverse = v := by
cases v
simp [Vector.reverse]
@[simp]
theorem get_zero : ∀ v : Vector α n.succ, get v 0 = head v
| ⟨_ :: _, _⟩ => rfl
@[simp]
theorem head_ofFn {n : ℕ} (f : Fin n.succ → α) : head (ofFn f) = f 0 := by
rw [← get_zero, get_ofFn]
theorem get_cons_zero (a : α) (v : Vector α n) : get (a ::ᵥ v) 0 = a := by simp [get_zero]
/-- Accessing the nth element of a vector made up
of one element `x : α` is `x` itself. -/
@[simp]
theorem get_cons_nil : ∀ {ix : Fin 1} (x : α), get (x ::ᵥ nil) ix = x
| ⟨0, _⟩, _ => rfl
@[simp]
theorem get_cons_succ (a : α) (v : Vector α n) (i : Fin n) : get (a ::ᵥ v) i.succ = get v i := by
rw [← get_tail_succ, tail_cons]
/-- The last element of a `Vector`, given that the vector is at least one element. -/
def last (v : Vector α (n + 1)) : α :=
v.get (Fin.last n)
/-- The last element of a `Vector`, given that the vector is at least one element. -/
theorem last_def {v : Vector α (n + 1)} : v.last = v.get (Fin.last n) :=
rfl
/-- The `last` element of a vector is the `head` of the `reverse` vector. -/
theorem reverse_get_zero {v : Vector α (n + 1)} : v.reverse.head = v.last := by
rw [← get_zero, last_def, get_eq_get_toList, get_eq_get_toList]
simp_rw [toList_reverse]
rw [List.get_eq_getElem, List.get_eq_getElem, ← Option.some_inj, Fin.cast, Fin.cast,
← List.getElem?_eq_getElem, ← List.getElem?_eq_getElem, List.getElem?_reverse]
· congr
simp
· simp
section Scan
variable {β : Type*}
variable (f : β → α → β) (b : β)
variable (v : Vector α n)
/-- Construct a `Vector β (n + 1)` from a `Vector α n` by scanning `f : β → α → β`
from the "left", that is, from 0 to `Fin.last n`, using `b : β` as the starting value.
-/
def scanl : Vector β (n + 1) :=
⟨List.scanl f b v.toList, by rw [List.length_scanl, toList_length]⟩
/-- Providing an empty vector to `scanl` gives the starting value `b : β`. -/
@[simp]
theorem scanl_nil : scanl f b nil = b ::ᵥ nil :=
rfl
/-- The recursive step of `scanl` splits a vector `x ::ᵥ v : Vector α (n + 1)`
into the provided starting value `b : β` and the recursed `scanl`
`f b x : β` as the starting value.
This lemma is the `cons` version of `scanl_get`.
-/
@[simp]
theorem scanl_cons (x : α) : scanl f b (x ::ᵥ v) = b ::ᵥ scanl f (f b x) v := by
simp only [scanl, toList_cons, List.scanl]; dsimp
simp only [cons]
/-- The underlying `List` of a `Vector` after a `scanl` is the `List.scanl`
of the underlying `List` of the original `Vector`.
-/
@[simp]
theorem scanl_val : ∀ {v : Vector α n}, (scanl f b v).val = List.scanl f b v.val
| _ => rfl
/-- The `toList` of a `Vector` after a `scanl` is the `List.scanl`
of the `toList` of the original `Vector`.
-/
@[simp]
theorem toList_scanl : (scanl f b v).toList = List.scanl f b v.toList :=
rfl
/-- The recursive step of `scanl` splits a vector made up of a single element
`x ::ᵥ nil : Vector α 1` into a `Vector` of the provided starting value `b : β`
and the mapped `f b x : β` as the last value.
-/
@[simp]
theorem scanl_singleton (v : Vector α 1) : scanl f b v = b ::ᵥ f b v.head ::ᵥ nil := by
rw [← cons_head_tail v]
simp only [scanl_cons, scanl_nil, head_cons, singleton_tail]
/-- The first element of `scanl` of a vector `v : Vector α n`,
retrieved via `head`, is the starting value `b : β`.
-/
@[simp]
theorem scanl_head : (scanl f b v).head = b := by
cases n
· have : v = nil := by simp only [eq_iff_true_of_subsingleton]
simp only [this, scanl_nil, head_cons]
· rw [← cons_head_tail v]
simp [← get_zero, get_eq_get_toList]
| /-- For an index `i : Fin n`, the nth element of `scanl` of a
vector `v : Vector α n` at `i.succ`, is equal to the application
function `f : β → α → β` of the `castSucc i` element of
| Mathlib/Data/Vector/Basic.lean | 357 | 359 |
/-
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)⟩
| Mathlib/Algebra/Group/Subgroup/Basic.lean | 307 | 309 |
/-
Copyright (c) 2022 Violeta Hernández Palacios. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Violeta Hernández Palacios
-/
import Mathlib.Algebra.Polynomial.Cardinal
import Mathlib.RingTheory.Algebraic.Basic
/-!
### Cardinality of algebraic numbers
In this file, we prove variants of the following result: the cardinality of algebraic numbers under
an R-algebra is at most `#R[X] * ℵ₀`.
Although this can be used to prove that real or complex transcendental numbers exist, a more direct
proof is given by `Liouville.transcendental`.
-/
universe u v
open Cardinal Polynomial Set
open Cardinal Polynomial
namespace Algebraic
theorem infinite_of_charZero (R A : Type*) [CommRing R] [Ring A] [Algebra R A]
[CharZero A] : { x : A | IsAlgebraic R x }.Infinite := by
letI := MulActionWithZero.nontrivial R A
exact infinite_of_injective_forall_mem Nat.cast_injective isAlgebraic_nat
theorem aleph0_le_cardinalMk_of_charZero (R A : Type*) [CommRing R] [Ring A]
[Algebra R A] [CharZero A] : ℵ₀ ≤ #{ x : A // IsAlgebraic R x } :=
infinite_iff.1 (Set.infinite_coe_iff.2 <| infinite_of_charZero R A)
@[deprecated (since := "2024-11-10")]
alias aleph0_le_cardinal_mk_of_charZero := aleph0_le_cardinalMk_of_charZero
section lift
variable (R : Type u) (A : Type v) [CommRing R] [CommRing A] [IsDomain A] [Algebra R A]
[NoZeroSMulDivisors R A]
theorem cardinalMk_lift_le_mul :
Cardinal.lift.{u} #{ x : A // IsAlgebraic R x } ≤ Cardinal.lift.{v} #R[X] * ℵ₀ := by
rw [← mk_uLift, ← mk_uLift]
choose g hg₁ hg₂ using fun x : { x : A | IsAlgebraic R x } => x.coe_prop
refine lift_mk_le_lift_mk_mul_of_lift_mk_preimage_le g fun f => ?_
rw [lift_le_aleph0, le_aleph0_iff_set_countable]
suffices MapsTo (↑) (g ⁻¹' {f}) (f.rootSet A) from
this.countable_of_injOn Subtype.coe_injective.injOn (f.rootSet_finite A).countable
rintro x (rfl : g x = f)
exact mem_rootSet.2 ⟨hg₁ x, hg₂ x⟩
@[deprecated (since := "2024-11-10")] alias cardinal_mk_lift_le_mul := cardinalMk_lift_le_mul
|
theorem cardinalMk_lift_le_max :
Cardinal.lift.{u} #{ x : A // IsAlgebraic R x } ≤ max (Cardinal.lift.{v} #R) ℵ₀ :=
(cardinalMk_lift_le_mul R A).trans <|
| Mathlib/Algebra/AlgebraicCard.lean | 57 | 60 |
/-
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.List.TakeDrop
import Mathlib.Data.List.Induction
/-!
# Prefixes, suffixes, infixes
This file proves properties about
* `List.isPrefix`: `l₁` is a prefix of `l₂` if `l₂` starts with `l₁`.
* `List.isSuffix`: `l₁` is a suffix of `l₂` if `l₂` ends with `l₁`.
* `List.isInfix`: `l₁` is an infix of `l₂` if `l₁` is a prefix of some suffix of `l₂`.
* `List.inits`: The list of prefixes of a list.
* `List.tails`: The list of prefixes of a list.
* `insert` on lists
All those (except `insert`) are defined in `Mathlib.Data.List.Defs`.
## Notation
* `l₁ <+: l₂`: `l₁` is a prefix of `l₂`.
* `l₁ <:+ l₂`: `l₁` is a suffix of `l₂`.
* `l₁ <:+: l₂`: `l₁` is an infix of `l₂`.
-/
variable {α β : Type*}
namespace List
variable {l l₁ l₂ l₃ : List α} {a b : α}
/-! ### prefix, suffix, infix -/
section Fix
@[gcongr] lemma IsPrefix.take (h : l₁ <+: l₂) (n : ℕ) : l₁.take n <+: l₂.take n := by
simpa [prefix_take_iff, Nat.min_le_left] using (take_prefix n l₁).trans h
@[gcongr] lemma IsPrefix.drop (h : l₁ <+: l₂) (n : ℕ) : l₁.drop n <+: l₂.drop n := by
rw [prefix_iff_eq_take.mp h, drop_take]; apply take_prefix
attribute [gcongr] take_prefix_take_left
lemma isPrefix_append_of_length (h : l₁.length ≤ l₂.length) : l₁ <+: l₂ ++ l₃ ↔ l₁ <+: l₂ :=
⟨fun h ↦ by rw [prefix_iff_eq_take] at *; nth_rw 1 [h, take_eq_left_iff]; tauto,
fun h ↦ h.trans <| l₂.prefix_append l₃⟩
@[simp] lemma take_isPrefix_take {m n : ℕ} : l.take m <+: l.take n ↔ m ≤ n ∨ l.length ≤ n := by
simp [prefix_take_iff, take_prefix]; omega
@[gcongr]
protected theorem IsPrefix.flatten {l₁ l₂ : List (List α)} (h : l₁ <+: l₂) :
l₁.flatten <+: l₂.flatten := by
rcases h with ⟨l, rfl⟩
simp
@[gcongr]
protected theorem IsPrefix.flatMap (h : l₁ <+: l₂) (f : α → List β) :
l₁.flatMap f <+: l₂.flatMap f :=
(h.map _).flatten
@[gcongr]
protected theorem IsSuffix.flatten {l₁ l₂ : List (List α)} (h : l₁ <:+ l₂) :
l₁.flatten <:+ l₂.flatten := by
rcases h with ⟨l, rfl⟩
simp
@[gcongr]
protected theorem IsSuffix.flatMap (h : l₁ <:+ l₂) (f : α → List β) :
l₁.flatMap f <:+ l₂.flatMap f :=
(h.map _).flatten
@[gcongr]
protected theorem IsInfix.flatten {l₁ l₂ : List (List α)} (h : l₁ <:+: l₂) :
l₁.flatten <:+: l₂.flatten := by
rcases h with ⟨l, l', rfl⟩
simp
@[gcongr]
protected theorem IsInfix.flatMap (h : l₁ <:+: l₂) (f : α → List β) :
l₁.flatMap f <:+: l₂.flatMap f :=
(h.map _).flatten
lemma dropSlice_sublist (n m : ℕ) (l : List α) : l.dropSlice n m <+ l :=
calc
l.dropSlice n m = take n l ++ drop m (drop n l) := by rw [dropSlice_eq, drop_drop, Nat.add_comm]
_ <+ take n l ++ drop n l := (Sublist.refl _).append (drop_sublist _ _)
_ = _ := take_append_drop _ _
lemma dropSlice_subset (n m : ℕ) (l : List α) : l.dropSlice n m ⊆ l :=
(dropSlice_sublist n m l).subset
lemma mem_of_mem_dropSlice {n m : ℕ} {l : List α} {a : α} (h : a ∈ l.dropSlice n m) : a ∈ l :=
dropSlice_subset n m l h
theorem tail_subset (l : List α) : tail l ⊆ l :=
(tail_sublist l).subset
theorem mem_of_mem_dropLast (h : a ∈ l.dropLast) : a ∈ l :=
dropLast_subset l h
attribute [gcongr] Sublist.drop
attribute [refl] prefix_refl suffix_refl infix_refl
theorem concat_get_prefix {x y : List α} (h : x <+: y) (hl : x.length < y.length) :
x ++ [y.get ⟨x.length, hl⟩] <+: y := by
use y.drop (x.length + 1)
nth_rw 1 [List.prefix_iff_eq_take.mp h]
convert List.take_append_drop (x.length + 1) y using 2
rw [← List.take_concat_get, List.concat_eq_append]; rfl
instance decidableInfix [DecidableEq α] : ∀ l₁ l₂ : List α, Decidable (l₁ <:+: l₂)
| [], l₂ => isTrue ⟨[], l₂, rfl⟩
| a :: l₁, [] => isFalse fun ⟨s, t, te⟩ => by simp at te
| l₁, b :: l₂ =>
letI := l₁.decidableInfix l₂
@decidable_of_decidable_of_iff (l₁ <+: b :: l₂ ∨ l₁ <:+: l₂) _ _
infix_cons_iff.symm
protected theorem IsPrefix.reduceOption {l₁ l₂ : List (Option α)} (h : l₁ <+: l₂) :
l₁.reduceOption <+: l₂.reduceOption :=
h.filterMap id
instance : IsPartialOrder (List α) (· <+: ·) where
refl _ := prefix_rfl
trans _ _ _ := IsPrefix.trans
antisymm _ _ h₁ h₂ := h₁.eq_of_length <| h₁.length_le.antisymm h₂.length_le
instance : IsPartialOrder (List α) (· <:+ ·) where
refl _ := suffix_rfl
trans _ _ _ := IsSuffix.trans
antisymm _ _ h₁ h₂ := h₁.eq_of_length <| h₁.length_le.antisymm h₂.length_le
instance : IsPartialOrder (List α) (· <:+: ·) where
refl _ := infix_rfl
trans _ _ _ := IsInfix.trans
antisymm _ _ h₁ h₂ := h₁.eq_of_length <| h₁.length_le.antisymm h₂.length_le
end Fix
section InitsTails
@[simp]
theorem mem_inits : ∀ s t : List α, s ∈ inits t ↔ s <+: t
| s, [] =>
suffices s = nil ↔ s <+: nil by simpa only [inits, mem_singleton]
⟨fun h => h.symm ▸ prefix_rfl, eq_nil_of_prefix_nil⟩
| s, a :: t =>
suffices (s = nil ∨ ∃ l ∈ inits t, a :: l = s) ↔ s <+: a :: t by simpa
⟨fun o =>
match s, o with
| _, Or.inl rfl => ⟨_, rfl⟩
| s, Or.inr ⟨r, hr, hs⟩ => by
let ⟨s, ht⟩ := (mem_inits _ _).1 hr
rw [← hs, ← ht]; exact ⟨s, rfl⟩,
fun mi =>
match s, mi with
| [], ⟨_, rfl⟩ => Or.inl rfl
| b :: s, ⟨r, hr⟩ =>
(List.noConfusion hr) fun ba (st : s ++ r = t) =>
Or.inr <| by rw [ba]; exact ⟨_, (mem_inits _ _).2 ⟨_, st⟩, rfl⟩⟩
@[simp]
theorem mem_tails : ∀ s t : List α, s ∈ tails t ↔ s <:+ t
| s, [] => by
simp only [tails, mem_singleton, suffix_nil]
| s, a :: t => by
simp only [tails, mem_cons, mem_tails s t]
exact
show s = a :: t ∨ s <:+ t ↔ s <:+ a :: t from
⟨fun o =>
match s, t, o with
| _, t, Or.inl rfl => suffix_rfl
| s, _, Or.inr ⟨l, rfl⟩ => ⟨a :: l, rfl⟩,
fun e =>
match s, t, e with
| _, t, ⟨[], rfl⟩ => Or.inl rfl
| s, t, ⟨b :: l, he⟩ => List.noConfusion he fun _ lt => Or.inr ⟨l, lt⟩⟩
theorem inits_cons (a : α) (l : List α) : inits (a :: l) = [] :: l.inits.map fun t => a :: t := by
simp
theorem tails_cons (a : α) (l : List α) : tails (a :: l) = (a :: l) :: l.tails := by simp
@[simp]
theorem inits_append : ∀ s t : List α, inits (s ++ t) = s.inits ++ t.inits.tail.map fun l => s ++ l
| [], [] => by simp
| [], a :: t => by simp
| a :: s, t => by simp [inits_append s t, Function.comp_def]
@[simp]
theorem tails_append :
∀ s t : List α, tails (s ++ t) = (s.tails.map fun l => l ++ t) ++ t.tails.tail
| [], [] => by simp
| [], a :: t => by simp
| a :: s, t => by simp [tails_append s t]
-- the lemma names `inits_eq_tails` and `tails_eq_inits` are like `sublists_eq_sublists'`
theorem inits_eq_tails : ∀ l : List α, l.inits = (reverse <| map reverse <| tails <| reverse l)
| [] => by simp
| a :: l => by simp [inits_eq_tails l, map_inj_left, ← map_reverse]
theorem tails_eq_inits : ∀ l : List α, l.tails = (reverse <| map reverse <| inits <| reverse l)
| [] => by simp
| a :: l => by simp [tails_eq_inits l, append_left_inj]
theorem inits_reverse (l : List α) : inits (reverse l) = reverse (map reverse l.tails) := by
rw [tails_eq_inits l]
simp [reverse_involutive.comp_self, ← map_reverse]
theorem tails_reverse (l : List α) : tails (reverse l) = reverse (map reverse l.inits) := by
rw [inits_eq_tails l]
simp [reverse_involutive.comp_self, ← map_reverse]
theorem map_reverse_inits (l : List α) : map reverse l.inits = (reverse <| tails <| reverse l) := by
rw [inits_eq_tails l]
simp [reverse_involutive.comp_self, ← map_reverse]
theorem map_reverse_tails (l : List α) : map reverse l.tails = (reverse <| inits <| reverse l) := by
rw [tails_eq_inits l]
simp [reverse_involutive.comp_self, ← map_reverse]
@[simp]
theorem length_tails (l : List α) : length (tails l) = length l + 1 := by
induction' l with x l IH
· simp
· simpa using IH
@[simp]
theorem length_inits (l : List α) : length (inits l) = length l + 1 := by simp [inits_eq_tails]
@[simp]
theorem getElem_tails (l : List α) (n : Nat) (h : n < (tails l).length) :
(tails l)[n] = l.drop n := by
induction l generalizing n with
| nil => simp
| cons a l ihl =>
cases n with
| zero => simp
| succ n => simp [ihl]
theorem get_tails (l : List α) (n : Fin (length (tails l))) : (tails l).get n = l.drop n := by
simp
@[simp]
theorem getElem_inits (l : List α) (n : Nat) (h : n < length (inits l)) :
(inits l)[n] = l.take n := by
induction l generalizing n with
| nil => simp
| cons a l ihl =>
cases n with
| zero => simp
| succ n => simp [ihl]
theorem get_inits (l : List α) (n : Fin (length (inits l))) : (inits l).get n = l.take n := by
simp
lemma map_inits {β : Type*} (g : α → β) : (l.map g).inits = l.inits.map (map g) := by
induction' l using reverseRecOn <;> simp [*]
lemma map_tails {β : Type*} (g : α → β) : (l.map g).tails = l.tails.map (map g) := by
induction' l using reverseRecOn <;> simp [*]
lemma take_inits {n} : (l.take n).inits = l.inits.take (n + 1) := by
apply ext_getElem <;> (simp [take_take] <;> omega)
end InitsTails
/-! ### insert -/
section Insert
variable [DecidableEq α]
theorem insert_eq_ite (a : α) (l : List α) : insert a l = if a ∈ l then l else a :: l := by
simp only [← elem_iff]
rfl
@[simp]
theorem suffix_insert (a : α) (l : List α) : l <:+ l.insert a := by
by_cases h : a ∈ l
· simp only [insert_of_mem h, insert, suffix_refl]
· simp only [insert_of_not_mem h, suffix_cons, insert]
theorem infix_insert (a : α) (l : List α) : l <:+: l.insert a :=
(suffix_insert a l).isInfix
theorem sublist_insert (a : α) (l : List α) : l <+ l.insert a :=
(suffix_insert a l).sublist
theorem subset_insert (a : α) (l : List α) : l ⊆ l.insert a :=
(sublist_insert a l).subset
end Insert
end List
| Mathlib/Data/List/Infix.lean | 430 | 432 | |
/-
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.Analytic.Within
import Mathlib.Analysis.Calculus.FDeriv.Analytic
import Mathlib.Analysis.Calculus.ContDiff.FTaylorSeries
/-!
# Higher differentiability
A function is `C^1` on a domain if it is differentiable there, and its derivative is continuous.
By induction, it is `C^n` if it is `C^{n-1}` and its (n-1)-th derivative is `C^1` there or,
equivalently, if it is `C^1` and its derivative is `C^{n-1}`.
It is `C^∞` if it is `C^n` for all n.
Finally, it is `C^ω` if it is analytic (as well as all its derivative, which is automatic if the
space is complete).
We formalize these notions with predicates `ContDiffWithinAt`, `ContDiffAt`, `ContDiffOn` and
`ContDiff` saying that the function is `C^n` within a set at a point, at a point, on a set
and on the whole space respectively.
To avoid the issue of choice when choosing a derivative in sets where the derivative is not
necessarily unique, `ContDiffOn` is not defined directly in terms of the
regularity of the specific choice `iteratedFDerivWithin 𝕜 n f s` inside `s`, but in terms of the
existence of a nice sequence of derivatives, expressed with a predicate
`HasFTaylorSeriesUpToOn` defined in the file `FTaylorSeries`.
We prove basic properties of these notions.
## Main definitions and results
Let `f : E → F` be a map between normed vector spaces over a nontrivially normed field `𝕜`.
* `ContDiff 𝕜 n f`: expresses that `f` is `C^n`, i.e., it admits a Taylor series up to
rank `n`.
* `ContDiffOn 𝕜 n f s`: expresses that `f` is `C^n` in `s`.
* `ContDiffAt 𝕜 n f x`: expresses that `f` is `C^n` around `x`.
* `ContDiffWithinAt 𝕜 n f s x`: expresses that `f` is `C^n` around `x` within the set `s`.
In sets of unique differentiability, `ContDiffOn 𝕜 n f s` can be expressed in terms of the
properties of `iteratedFDerivWithin 𝕜 m f s` for `m ≤ n`. In the whole space,
`ContDiff 𝕜 n f` can be expressed in terms of the properties of `iteratedFDeriv 𝕜 m f`
for `m ≤ n`.
## Implementation notes
The definitions in this file are designed to work on any field `𝕜`. They are sometimes slightly more
complicated than the naive definitions one would guess from the intuition over the real or complex
numbers, but they are designed to circumvent the lack of gluing properties and partitions of unity
in general. In the usual situations, they coincide with the usual definitions.
### Definition of `C^n` functions in domains
One could define `C^n` functions in a domain `s` by fixing an arbitrary choice of derivatives (this
is what we do with `iteratedFDerivWithin`) and requiring that all these derivatives up to `n` are
continuous. If the derivative is not unique, this could lead to strange behavior like two `C^n`
functions `f` and `g` on `s` whose sum is not `C^n`. A better definition is thus to say that a
function is `C^n` inside `s` if it admits a sequence of derivatives up to `n` inside `s`.
This definition still has the problem that a function which is locally `C^n` would not need to
be `C^n`, as different choices of sequences of derivatives around different points might possibly
not be glued together to give a globally defined sequence of derivatives. (Note that this issue
can not happen over reals, thanks to partition of unity, but the behavior over a general field is
not so clear, and we want a definition for general fields). Also, there are locality
problems for the order parameter: one could image a function which, for each `n`, has a nice
sequence of derivatives up to order `n`, but they do not coincide for varying `n` and can therefore
not be glued to give rise to an infinite sequence of derivatives. This would give a function
which is `C^n` for all `n`, but not `C^∞`. We solve this issue by putting locality conditions
in space and order in our definition of `ContDiffWithinAt` and `ContDiffOn`.
The resulting definition is slightly more complicated to work with (in fact not so much), but it
gives rise to completely satisfactory theorems.
For instance, with this definition, a real function which is `C^m` (but not better) on `(-1/m, 1/m)`
for each natural `m` is by definition `C^∞` at `0`.
There is another issue with the definition of `ContDiffWithinAt 𝕜 n f s x`. We can
require the existence and good behavior of derivatives up to order `n` on a neighborhood of `x`
within `s`. However, this does not imply continuity or differentiability within `s` of the function
at `x` when `x` does not belong to `s`. Therefore, we require such existence and good behavior on
a neighborhood of `x` within `s ∪ {x}` (which appears as `insert x s` in this file).
## Notations
We use the notation `E [×n]→L[𝕜] F` for the space of continuous multilinear maps on `E^n` with
values in `F`. This is the space in which the `n`-th derivative of a function from `E` to `F` lives.
In this file, we denote `(⊤ : ℕ∞) : WithTop ℕ∞` with `∞`, and `⊤ : WithTop ℕ∞` with `ω`. To
avoid ambiguities with the two tops, the theorems name use either `infty` or `omega`.
These notations are scoped in `ContDiff`.
## Tags
derivative, differentiability, higher derivative, `C^n`, multilinear, Taylor series, formal series
-/
noncomputable section
open Set Fin Filter Function
open scoped NNReal Topology ContDiff
universe u uE uF uG uX
variable {𝕜 : Type u} [NontriviallyNormedField 𝕜] {E : Type uE} [NormedAddCommGroup E]
[NormedSpace 𝕜 E] {F : Type uF} [NormedAddCommGroup F] [NormedSpace 𝕜 F] {G : Type uG}
[NormedAddCommGroup G] [NormedSpace 𝕜 G] {X : Type uX} [NormedAddCommGroup X] [NormedSpace 𝕜 X]
{s s₁ t u : Set E} {f f₁ : E → F} {g : F → G} {x x₀ : E} {c : F} {m n : WithTop ℕ∞}
{p : E → FormalMultilinearSeries 𝕜 E F}
/-! ### Smooth functions within a set around a point -/
variable (𝕜) in
/-- A function is continuously differentiable up to order `n` within a set `s` at a point `x` if
it admits continuous derivatives up to order `n` in a neighborhood of `x` in `s ∪ {x}`.
For `n = ∞`, we only require that this holds up to any finite order (where the neighborhood may
depend on the finite order we consider).
For `n = ω`, we require the function to be analytic within `s` at `x`. The precise definition we
give (all the derivatives should be analytic) is more involved to work around issues when the space
is not complete, but it is equivalent when the space is complete.
For instance, a real function which is `C^m` on `(-1/m, 1/m)` for each natural `m`, but not
better, is `C^∞` at `0` within `univ`.
-/
def ContDiffWithinAt (n : WithTop ℕ∞) (f : E → F) (s : Set E) (x : E) : Prop :=
match n with
| ω => ∃ u ∈ 𝓝[insert x s] x, ∃ p : E → FormalMultilinearSeries 𝕜 E F,
HasFTaylorSeriesUpToOn ω f p u ∧ ∀ i, AnalyticOn 𝕜 (fun x ↦ p x i) u
| (n : ℕ∞) => ∀ m : ℕ, m ≤ n → ∃ u ∈ 𝓝[insert x s] x,
∃ p : E → FormalMultilinearSeries 𝕜 E F, HasFTaylorSeriesUpToOn m f p u
lemma HasFTaylorSeriesUpToOn.analyticOn
(hf : HasFTaylorSeriesUpToOn ω f p s) (h : AnalyticOn 𝕜 (fun x ↦ p x 0) s) :
AnalyticOn 𝕜 f s := by
have : AnalyticOn 𝕜 (fun x ↦ (continuousMultilinearCurryFin0 𝕜 E F) (p x 0)) s :=
(LinearIsometryEquiv.analyticOnNhd _ _ ).comp_analyticOn
h (Set.mapsTo_univ _ _)
exact this.congr (fun y hy ↦ (hf.zero_eq _ hy).symm)
lemma ContDiffWithinAt.analyticOn (h : ContDiffWithinAt 𝕜 ω f s x) :
∃ u ∈ 𝓝[insert x s] x, AnalyticOn 𝕜 f u := by
obtain ⟨u, hu, p, hp, h'p⟩ := h
exact ⟨u, hu, hp.analyticOn (h'p 0)⟩
lemma ContDiffWithinAt.analyticWithinAt (h : ContDiffWithinAt 𝕜 ω f s x) :
AnalyticWithinAt 𝕜 f s x := by
obtain ⟨u, hu, hf⟩ := h.analyticOn
have xu : x ∈ u := mem_of_mem_nhdsWithin (by simp) hu
exact (hf x xu).mono_of_mem_nhdsWithin (nhdsWithin_mono _ (subset_insert _ _) hu)
theorem contDiffWithinAt_omega_iff_analyticWithinAt [CompleteSpace F] :
ContDiffWithinAt 𝕜 ω f s x ↔ AnalyticWithinAt 𝕜 f s x := by
refine ⟨fun h ↦ h.analyticWithinAt, fun h ↦ ?_⟩
obtain ⟨u, hu, p, hp, h'p⟩ := h.exists_hasFTaylorSeriesUpToOn ω
exact ⟨u, hu, p, hp.of_le le_top, fun i ↦ h'p i⟩
theorem contDiffWithinAt_nat {n : ℕ} :
ContDiffWithinAt 𝕜 n f s x ↔ ∃ u ∈ 𝓝[insert x s] x,
∃ p : E → FormalMultilinearSeries 𝕜 E F, HasFTaylorSeriesUpToOn n f p u :=
⟨fun H => H n le_rfl, fun ⟨u, hu, p, hp⟩ _m hm => ⟨u, hu, p, hp.of_le (mod_cast hm)⟩⟩
/-- When `n` is either a natural number or `ω`, one can characterize the property of being `C^n`
as the existence of a neighborhood on which there is a Taylor series up to order `n`,
requiring in addition that its terms are analytic in the `ω` case. -/
lemma contDiffWithinAt_iff_of_ne_infty (hn : n ≠ ∞) :
ContDiffWithinAt 𝕜 n f s x ↔ ∃ u ∈ 𝓝[insert x s] x,
∃ p : E → FormalMultilinearSeries 𝕜 E F, HasFTaylorSeriesUpToOn n f p u ∧
(n = ω → ∀ i, AnalyticOn 𝕜 (fun x ↦ p x i) u) := by
match n with
| ω => simp [ContDiffWithinAt]
| ∞ => simp at hn
| (n : ℕ) => simp [contDiffWithinAt_nat]
theorem ContDiffWithinAt.of_le (h : ContDiffWithinAt 𝕜 n f s x) (hmn : m ≤ n) :
ContDiffWithinAt 𝕜 m f s x := by
match n with
| ω => match m with
| ω => exact h
| (m : ℕ∞) =>
intro k _
obtain ⟨u, hu, p, hp, -⟩ := h
exact ⟨u, hu, p, hp.of_le le_top⟩
| (n : ℕ∞) => match m with
| ω => simp at hmn
| (m : ℕ∞) => exact fun k hk ↦ h k (le_trans hk (mod_cast hmn))
/-- In a complete space, a function which is analytic within a set at a point is also `C^ω` there.
Note that the same statement for `AnalyticOn` does not require completeness, see
`AnalyticOn.contDiffOn`. -/
theorem AnalyticWithinAt.contDiffWithinAt [CompleteSpace F] (h : AnalyticWithinAt 𝕜 f s x) :
ContDiffWithinAt 𝕜 n f s x :=
(contDiffWithinAt_omega_iff_analyticWithinAt.2 h).of_le le_top
theorem contDiffWithinAt_iff_forall_nat_le {n : ℕ∞} :
ContDiffWithinAt 𝕜 n f s x ↔ ∀ m : ℕ, ↑m ≤ n → ContDiffWithinAt 𝕜 m f s x :=
⟨fun H _ hm => H.of_le (mod_cast hm), fun H m hm => H m hm _ le_rfl⟩
theorem contDiffWithinAt_infty :
ContDiffWithinAt 𝕜 ∞ f s x ↔ ∀ n : ℕ, ContDiffWithinAt 𝕜 n f s x :=
contDiffWithinAt_iff_forall_nat_le.trans <| by simp only [forall_prop_of_true, le_top]
@[deprecated (since := "2024-11-25")] alias contDiffWithinAt_top := contDiffWithinAt_infty
theorem ContDiffWithinAt.continuousWithinAt (h : ContDiffWithinAt 𝕜 n f s x) :
ContinuousWithinAt f s x := by
have := h.of_le (zero_le _)
simp only [ContDiffWithinAt, nonpos_iff_eq_zero, Nat.cast_eq_zero,
mem_pure, forall_eq, CharP.cast_eq_zero] at this
rcases this with ⟨u, hu, p, H⟩
rw [mem_nhdsWithin_insert] at hu
exact (H.continuousOn.continuousWithinAt hu.1).mono_of_mem_nhdsWithin hu.2
theorem ContDiffWithinAt.congr_of_eventuallyEq (h : ContDiffWithinAt 𝕜 n f s x)
(h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : f₁ x = f x) : ContDiffWithinAt 𝕜 n f₁ s x := by
match n with
| ω =>
obtain ⟨u, hu, p, H, H'⟩ := h
exact ⟨{x ∈ u | f₁ x = f x}, Filter.inter_mem hu (mem_nhdsWithin_insert.2 ⟨hx, h₁⟩), p,
(H.mono (sep_subset _ _)).congr fun _ ↦ And.right,
fun i ↦ (H' i).mono (sep_subset _ _)⟩
| (n : ℕ∞) =>
intro m hm
let ⟨u, hu, p, H⟩ := h m hm
exact ⟨{ x ∈ u | f₁ x = f x }, Filter.inter_mem hu (mem_nhdsWithin_insert.2 ⟨hx, h₁⟩), p,
(H.mono (sep_subset _ _)).congr fun _ ↦ And.right⟩
theorem Filter.EventuallyEq.congr_contDiffWithinAt (h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : f₁ x = f x) :
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
⟨fun H ↦ H.congr_of_eventuallyEq h₁.symm hx.symm, fun H ↦ H.congr_of_eventuallyEq h₁ hx⟩
theorem ContDiffWithinAt.congr_of_eventuallyEq_insert (h : ContDiffWithinAt 𝕜 n f s x)
(h₁ : f₁ =ᶠ[𝓝[insert x s] x] f) : ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr_of_eventuallyEq (nhdsWithin_mono x (subset_insert x s) h₁)
(mem_of_mem_nhdsWithin (mem_insert x s) h₁ :)
theorem Filter.EventuallyEq.congr_contDiffWithinAt_of_insert (h₁ : f₁ =ᶠ[𝓝[insert x s] x] f) :
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
⟨fun H ↦ H.congr_of_eventuallyEq_insert h₁.symm, fun H ↦ H.congr_of_eventuallyEq_insert h₁⟩
theorem ContDiffWithinAt.congr_of_eventuallyEq_of_mem (h : ContDiffWithinAt 𝕜 n f s x)
(h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : x ∈ s) : ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr_of_eventuallyEq h₁ <| h₁.self_of_nhdsWithin hx
theorem Filter.EventuallyEq.congr_contDiffWithinAt_of_mem (h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : x ∈ s):
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
⟨fun H ↦ H.congr_of_eventuallyEq_of_mem h₁.symm hx, fun H ↦ H.congr_of_eventuallyEq_of_mem h₁ hx⟩
theorem ContDiffWithinAt.congr (h : ContDiffWithinAt 𝕜 n f s x) (h₁ : ∀ y ∈ s, f₁ y = f y)
(hx : f₁ x = f x) : ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr_of_eventuallyEq (Filter.eventuallyEq_of_mem self_mem_nhdsWithin h₁) hx
theorem contDiffWithinAt_congr (h₁ : ∀ y ∈ s, f₁ y = f y) (hx : f₁ x = f x) :
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
⟨fun h' ↦ h'.congr (fun x hx ↦ (h₁ x hx).symm) hx.symm, fun h' ↦ h'.congr h₁ hx⟩
theorem ContDiffWithinAt.congr_of_mem (h : ContDiffWithinAt 𝕜 n f s x) (h₁ : ∀ y ∈ s, f₁ y = f y)
(hx : x ∈ s) : ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr h₁ (h₁ _ hx)
theorem contDiffWithinAt_congr_of_mem (h₁ : ∀ y ∈ s, f₁ y = f y) (hx : x ∈ s) :
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
contDiffWithinAt_congr h₁ (h₁ x hx)
theorem ContDiffWithinAt.congr_of_insert (h : ContDiffWithinAt 𝕜 n f s x)
(h₁ : ∀ y ∈ insert x s, f₁ y = f y) : ContDiffWithinAt 𝕜 n f₁ s x :=
h.congr (fun y hy ↦ h₁ y (mem_insert_of_mem _ hy)) (h₁ x (mem_insert _ _))
theorem contDiffWithinAt_congr_of_insert (h₁ : ∀ y ∈ insert x s, f₁ y = f y) :
ContDiffWithinAt 𝕜 n f₁ s x ↔ ContDiffWithinAt 𝕜 n f s x :=
contDiffWithinAt_congr (fun y hy ↦ h₁ y (mem_insert_of_mem _ hy)) (h₁ x (mem_insert _ _))
theorem ContDiffWithinAt.mono_of_mem_nhdsWithin (h : ContDiffWithinAt 𝕜 n f s x) {t : Set E}
(hst : s ∈ 𝓝[t] x) : ContDiffWithinAt 𝕜 n f t x := by
match n with
| ω =>
obtain ⟨u, hu, p, H, H'⟩ := h
exact ⟨u, nhdsWithin_le_of_mem (insert_mem_nhdsWithin_insert hst) hu, p, H, H'⟩
| (n : ℕ∞) =>
intro m hm
rcases h m hm with ⟨u, hu, p, H⟩
exact ⟨u, nhdsWithin_le_of_mem (insert_mem_nhdsWithin_insert hst) hu, p, H⟩
@[deprecated (since := "2024-10-30")]
alias ContDiffWithinAt.mono_of_mem := ContDiffWithinAt.mono_of_mem_nhdsWithin
theorem ContDiffWithinAt.mono (h : ContDiffWithinAt 𝕜 n f s x) {t : Set E} (hst : t ⊆ s) :
ContDiffWithinAt 𝕜 n f t x :=
h.mono_of_mem_nhdsWithin <| Filter.mem_of_superset self_mem_nhdsWithin hst
theorem ContDiffWithinAt.congr_mono
(h : ContDiffWithinAt 𝕜 n f s x) (h' : EqOn f₁ f s₁) (h₁ : s₁ ⊆ s) (hx : f₁ x = f x) :
ContDiffWithinAt 𝕜 n f₁ s₁ x :=
(h.mono h₁).congr h' hx
theorem ContDiffWithinAt.congr_set (h : ContDiffWithinAt 𝕜 n f s x) {t : Set E}
(hst : s =ᶠ[𝓝 x] t) : ContDiffWithinAt 𝕜 n f t x := by
rw [← nhdsWithin_eq_iff_eventuallyEq] at hst
apply h.mono_of_mem_nhdsWithin <| hst ▸ self_mem_nhdsWithin
@[deprecated (since := "2024-10-23")]
alias ContDiffWithinAt.congr_nhds := ContDiffWithinAt.congr_set
theorem contDiffWithinAt_congr_set {t : Set E} (hst : s =ᶠ[𝓝 x] t) :
ContDiffWithinAt 𝕜 n f s x ↔ ContDiffWithinAt 𝕜 n f t x :=
⟨fun h => h.congr_set hst, fun h => h.congr_set hst.symm⟩
@[deprecated (since := "2024-10-23")]
alias contDiffWithinAt_congr_nhds := contDiffWithinAt_congr_set
theorem contDiffWithinAt_inter' (h : t ∈ 𝓝[s] x) :
ContDiffWithinAt 𝕜 n f (s ∩ t) x ↔ ContDiffWithinAt 𝕜 n f s x :=
contDiffWithinAt_congr_set (mem_nhdsWithin_iff_eventuallyEq.1 h).symm
theorem contDiffWithinAt_inter (h : t ∈ 𝓝 x) :
ContDiffWithinAt 𝕜 n f (s ∩ t) x ↔ ContDiffWithinAt 𝕜 n f s x :=
contDiffWithinAt_inter' (mem_nhdsWithin_of_mem_nhds h)
theorem contDiffWithinAt_insert_self :
ContDiffWithinAt 𝕜 n f (insert x s) x ↔ ContDiffWithinAt 𝕜 n f s x := by
match n with
| ω => simp [ContDiffWithinAt]
| (n : ℕ∞) => simp_rw [ContDiffWithinAt, insert_idem]
theorem contDiffWithinAt_insert {y : E} :
ContDiffWithinAt 𝕜 n f (insert y s) x ↔ ContDiffWithinAt 𝕜 n f s x := by
rcases eq_or_ne x y with (rfl | hx)
· exact contDiffWithinAt_insert_self
refine ⟨fun h ↦ h.mono (subset_insert _ _), fun h ↦ ?_⟩
apply h.mono_of_mem_nhdsWithin
simp [nhdsWithin_insert_of_ne hx, self_mem_nhdsWithin]
alias ⟨ContDiffWithinAt.of_insert, ContDiffWithinAt.insert'⟩ := contDiffWithinAt_insert
protected theorem ContDiffWithinAt.insert (h : ContDiffWithinAt 𝕜 n f s x) :
ContDiffWithinAt 𝕜 n f (insert x s) x :=
h.insert'
theorem contDiffWithinAt_diff_singleton {y : E} :
ContDiffWithinAt 𝕜 n f (s \ {y}) x ↔ ContDiffWithinAt 𝕜 n f s x := by
rw [← contDiffWithinAt_insert, insert_diff_singleton, contDiffWithinAt_insert]
/-- If a function is `C^n` within a set at a point, with `n ≥ 1`, then it is differentiable
within this set at this point. -/
theorem ContDiffWithinAt.differentiableWithinAt' (h : ContDiffWithinAt 𝕜 n f s x) (hn : 1 ≤ n) :
DifferentiableWithinAt 𝕜 f (insert x s) x := by
rcases contDiffWithinAt_nat.1 (h.of_le hn) with ⟨u, hu, p, H⟩
rcases mem_nhdsWithin.1 hu with ⟨t, t_open, xt, tu⟩
rw [inter_comm] at tu
exact (differentiableWithinAt_inter (IsOpen.mem_nhds t_open xt)).1 <|
((H.mono tu).differentiableOn le_rfl) x ⟨mem_insert x s, xt⟩
theorem ContDiffWithinAt.differentiableWithinAt (h : ContDiffWithinAt 𝕜 n f s x) (hn : 1 ≤ n) :
DifferentiableWithinAt 𝕜 f s x :=
(h.differentiableWithinAt' hn).mono (subset_insert x s)
/-- A function is `C^(n + 1)` on a domain iff locally, it has a derivative which is `C^n`
(and moreover the function is analytic when `n = ω`). -/
theorem contDiffWithinAt_succ_iff_hasFDerivWithinAt (hn : n ≠ ∞) :
ContDiffWithinAt 𝕜 (n + 1) f s x ↔ ∃ u ∈ 𝓝[insert x s] x, (n = ω → AnalyticOn 𝕜 f u) ∧
∃ f' : E → E →L[𝕜] F,
(∀ x ∈ u, HasFDerivWithinAt f (f' x) u x) ∧ ContDiffWithinAt 𝕜 n f' u x := by
have h'n : n + 1 ≠ ∞ := by simpa using hn
constructor
· intro h
rcases (contDiffWithinAt_iff_of_ne_infty h'n).1 h with ⟨u, hu, p, Hp, H'p⟩
refine ⟨u, hu, ?_, fun y => (continuousMultilinearCurryFin1 𝕜 E F) (p y 1),
fun y hy => Hp.hasFDerivWithinAt le_add_self hy, ?_⟩
· rintro rfl
exact Hp.analyticOn (H'p rfl 0)
apply (contDiffWithinAt_iff_of_ne_infty hn).2
refine ⟨u, ?_, fun y : E => (p y).shift, ?_⟩
· convert @self_mem_nhdsWithin _ _ x u
have : x ∈ insert x s := by simp
exact insert_eq_of_mem (mem_of_mem_nhdsWithin this hu)
· rw [hasFTaylorSeriesUpToOn_succ_iff_right] at Hp
refine ⟨Hp.2.2, ?_⟩
rintro rfl i
change AnalyticOn 𝕜
(fun x ↦ (continuousMultilinearCurryRightEquiv' 𝕜 i E F) (p x (i + 1))) u
apply (LinearIsometryEquiv.analyticOnNhd _ _).comp_analyticOn
?_ (Set.mapsTo_univ _ _)
exact H'p rfl _
· rintro ⟨u, hu, hf, f', f'_eq_deriv, Hf'⟩
rw [contDiffWithinAt_iff_of_ne_infty h'n]
rcases (contDiffWithinAt_iff_of_ne_infty hn).1 Hf' with ⟨v, hv, p', Hp', p'_an⟩
refine ⟨v ∩ u, ?_, fun x => (p' x).unshift (f x), ?_, ?_⟩
· apply Filter.inter_mem _ hu
apply nhdsWithin_le_of_mem hu
exact nhdsWithin_mono _ (subset_insert x u) hv
· rw [hasFTaylorSeriesUpToOn_succ_iff_right]
refine ⟨fun y _ => rfl, fun y hy => ?_, ?_⟩
· change
HasFDerivWithinAt (fun z => (continuousMultilinearCurryFin0 𝕜 E F).symm (f z))
(FormalMultilinearSeries.unshift (p' y) (f y) 1).curryLeft (v ∩ u) y
rw [← Function.comp_def _ f, LinearIsometryEquiv.comp_hasFDerivWithinAt_iff']
convert (f'_eq_deriv y hy.2).mono inter_subset_right
rw [← Hp'.zero_eq y hy.1]
ext z
change ((p' y 0) (init (@cons 0 (fun _ => E) z 0))) (@cons 0 (fun _ => E) z 0 (last 0)) =
((p' y 0) 0) z
congr
norm_num [eq_iff_true_of_subsingleton]
· convert (Hp'.mono inter_subset_left).congr fun x hx => Hp'.zero_eq x hx.1 using 1
· ext x y
change p' x 0 (init (@snoc 0 (fun _ : Fin 1 => E) 0 y)) y = p' x 0 0 y
rw [init_snoc]
· ext x k v y
change p' x k (init (@snoc k (fun _ : Fin k.succ => E) v y))
(@snoc k (fun _ : Fin k.succ => E) v y (last k)) = p' x k v y
rw [snoc_last, init_snoc]
· intro h i
simp only [WithTop.add_eq_top, WithTop.one_ne_top, or_false] at h
match i with
| 0 =>
simp only [FormalMultilinearSeries.unshift]
apply AnalyticOnNhd.comp_analyticOn _ ((hf h).mono inter_subset_right)
(Set.mapsTo_univ _ _)
exact LinearIsometryEquiv.analyticOnNhd _ _
| i + 1 =>
simp only [FormalMultilinearSeries.unshift, Nat.succ_eq_add_one]
apply AnalyticOnNhd.comp_analyticOn _ ((p'_an h i).mono inter_subset_left)
(Set.mapsTo_univ _ _)
exact LinearIsometryEquiv.analyticOnNhd _ _
/-- A version of `contDiffWithinAt_succ_iff_hasFDerivWithinAt` where all derivatives
are taken within the same set. -/
theorem contDiffWithinAt_succ_iff_hasFDerivWithinAt' (hn : n ≠ ∞) :
ContDiffWithinAt 𝕜 (n + 1) f s x ↔
∃ u ∈ 𝓝[insert x s] x, u ⊆ insert x s ∧ (n = ω → AnalyticOn 𝕜 f u) ∧
∃ f' : E → E →L[𝕜] F,
(∀ x ∈ u, HasFDerivWithinAt f (f' x) s x) ∧ ContDiffWithinAt 𝕜 n f' s x := by
refine ⟨fun hf => ?_, ?_⟩
· obtain ⟨u, hu, f_an, f', huf', hf'⟩ := (contDiffWithinAt_succ_iff_hasFDerivWithinAt hn).mp hf
obtain ⟨w, hw, hxw, hwu⟩ := mem_nhdsWithin.mp hu
rw [inter_comm] at hwu
refine ⟨insert x s ∩ w, inter_mem_nhdsWithin _ (hw.mem_nhds hxw), inter_subset_left, ?_, f',
fun y hy => ?_, ?_⟩
· intro h
apply (f_an h).mono hwu
· refine ((huf' y <| hwu hy).mono hwu).mono_of_mem_nhdsWithin ?_
refine mem_of_superset ?_ (inter_subset_inter_left _ (subset_insert _ _))
exact inter_mem_nhdsWithin _ (hw.mem_nhds hy.2)
· exact hf'.mono_of_mem_nhdsWithin (nhdsWithin_mono _ (subset_insert _ _) hu)
· rw [← contDiffWithinAt_insert, contDiffWithinAt_succ_iff_hasFDerivWithinAt hn,
insert_eq_of_mem (mem_insert _ _)]
rintro ⟨u, hu, hus, f_an, f', huf', hf'⟩
exact ⟨u, hu, f_an, f', fun y hy => (huf' y hy).insert'.mono hus, hf'.insert.mono hus⟩
/-! ### Smooth functions within a set -/
variable (𝕜) in
/-- A function is continuously differentiable up to `n` on `s` if, for any point `x` in `s`, it
admits continuous derivatives up to order `n` on a neighborhood of `x` in `s`.
For `n = ∞`, we only require that this holds up to any finite order (where the neighborhood may
depend on the finite order we consider).
-/
def ContDiffOn (n : WithTop ℕ∞) (f : E → F) (s : Set E) : Prop :=
∀ x ∈ s, ContDiffWithinAt 𝕜 n f s x
theorem HasFTaylorSeriesUpToOn.contDiffOn {n : ℕ∞} {f' : E → FormalMultilinearSeries 𝕜 E F}
(hf : HasFTaylorSeriesUpToOn n f f' s) : ContDiffOn 𝕜 n f s := by
intro x hx m hm
use s
simp only [Set.insert_eq_of_mem hx, self_mem_nhdsWithin, true_and]
exact ⟨f', hf.of_le (mod_cast hm)⟩
theorem ContDiffOn.contDiffWithinAt (h : ContDiffOn 𝕜 n f s) (hx : x ∈ s) :
ContDiffWithinAt 𝕜 n f s x :=
h x hx
theorem ContDiffOn.of_le (h : ContDiffOn 𝕜 n f s) (hmn : m ≤ n) : ContDiffOn 𝕜 m f s := fun x hx =>
(h x hx).of_le hmn
theorem ContDiffWithinAt.contDiffOn' (hm : m ≤ n) (h' : m = ∞ → n = ω)
(h : ContDiffWithinAt 𝕜 n f s x) :
∃ u, IsOpen u ∧ x ∈ u ∧ ContDiffOn 𝕜 m f (insert x s ∩ u) := by
rcases eq_or_ne n ω with rfl | hn
· obtain ⟨t, ht, p, hp, h'p⟩ := h
rcases mem_nhdsWithin.1 ht with ⟨u, huo, hxu, hut⟩
rw [inter_comm] at hut
refine ⟨u, huo, hxu, ?_⟩
suffices ContDiffOn 𝕜 ω f (insert x s ∩ u) from this.of_le le_top
intro y hy
refine ⟨insert x s ∩ u, ?_, p, hp.mono hut, fun i ↦ (h'p i).mono hut⟩
simp only [insert_eq_of_mem, hy, self_mem_nhdsWithin]
· match m with
| ω => simp [hn] at hm
| ∞ => exact (hn (h' rfl)).elim
| (m : ℕ) =>
rcases contDiffWithinAt_nat.1 (h.of_le hm) with ⟨t, ht, p, hp⟩
rcases mem_nhdsWithin.1 ht with ⟨u, huo, hxu, hut⟩
rw [inter_comm] at hut
exact ⟨u, huo, hxu, (hp.mono hut).contDiffOn⟩
theorem ContDiffWithinAt.contDiffOn (hm : m ≤ n) (h' : m = ∞ → n = ω)
(h : ContDiffWithinAt 𝕜 n f s x) :
∃ u ∈ 𝓝[insert x s] x, u ⊆ insert x s ∧ ContDiffOn 𝕜 m f u := by
obtain ⟨_u, uo, xu, h⟩ := h.contDiffOn' hm h'
exact ⟨_, inter_mem_nhdsWithin _ (uo.mem_nhds xu), inter_subset_left, h⟩
theorem ContDiffOn.analyticOn (h : ContDiffOn 𝕜 ω f s) : AnalyticOn 𝕜 f s :=
fun x hx ↦ (h x hx).analyticWithinAt
/-- A function is `C^n` within a set at a point, for `n : ℕ`, if and only if it is `C^n` on
a neighborhood of this point. -/
theorem contDiffWithinAt_iff_contDiffOn_nhds (hn : n ≠ ∞) :
ContDiffWithinAt 𝕜 n f s x ↔ ∃ u ∈ 𝓝[insert x s] x, ContDiffOn 𝕜 n f u := by
refine ⟨fun h ↦ ?_, fun h ↦ ?_⟩
· rcases h.contDiffOn le_rfl (by simp [hn]) with ⟨u, hu, h'u⟩
exact ⟨u, hu, h'u.2⟩
· rcases h with ⟨u, u_mem, hu⟩
have : x ∈ u := mem_of_mem_nhdsWithin (mem_insert x s) u_mem
exact (hu x this).mono_of_mem_nhdsWithin (nhdsWithin_mono _ (subset_insert x s) u_mem)
protected theorem ContDiffWithinAt.eventually (h : ContDiffWithinAt 𝕜 n f s x) (hn : n ≠ ∞) :
∀ᶠ y in 𝓝[insert x s] x, ContDiffWithinAt 𝕜 n f s y := by
rcases h.contDiffOn le_rfl (by simp [hn]) with ⟨u, hu, _, hd⟩
have : ∀ᶠ y : E in 𝓝[insert x s] x, u ∈ 𝓝[insert x s] y ∧ y ∈ u :=
(eventually_eventually_nhdsWithin.2 hu).and hu
refine this.mono fun y hy => (hd y hy.2).mono_of_mem_nhdsWithin ?_
exact nhdsWithin_mono y (subset_insert _ _) hy.1
theorem ContDiffOn.of_succ (h : ContDiffOn 𝕜 (n + 1) f s) : ContDiffOn 𝕜 n f s :=
h.of_le le_self_add
theorem ContDiffOn.one_of_succ (h : ContDiffOn 𝕜 (n + 1) f s) : ContDiffOn 𝕜 1 f s :=
h.of_le le_add_self
theorem contDiffOn_iff_forall_nat_le {n : ℕ∞} :
ContDiffOn 𝕜 n f s ↔ ∀ m : ℕ, ↑m ≤ n → ContDiffOn 𝕜 m f s :=
⟨fun H _ hm => H.of_le (mod_cast hm), fun H x hx m hm => H m hm x hx m le_rfl⟩
theorem contDiffOn_infty : ContDiffOn 𝕜 ∞ f s ↔ ∀ n : ℕ, ContDiffOn 𝕜 n f s :=
contDiffOn_iff_forall_nat_le.trans <| by simp only [le_top, forall_prop_of_true]
@[deprecated (since := "2024-11-27")] alias contDiffOn_top := contDiffOn_infty
@[deprecated (since := "2024-11-27")]
alias contDiffOn_infty_iff_contDiffOn_omega := contDiffOn_infty
theorem contDiffOn_all_iff_nat :
(∀ (n : ℕ∞), ContDiffOn 𝕜 n f s) ↔ ∀ n : ℕ, ContDiffOn 𝕜 n f s := by
refine ⟨fun H n => H n, ?_⟩
rintro H (_ | n)
exacts [contDiffOn_infty.2 H, H n]
theorem ContDiffOn.continuousOn (h : ContDiffOn 𝕜 n f s) : ContinuousOn f s := fun x hx =>
(h x hx).continuousWithinAt
theorem ContDiffOn.congr (h : ContDiffOn 𝕜 n f s) (h₁ : ∀ x ∈ s, f₁ x = f x) :
ContDiffOn 𝕜 n f₁ s := fun x hx => (h x hx).congr h₁ (h₁ x hx)
theorem contDiffOn_congr (h₁ : ∀ x ∈ s, f₁ x = f x) : ContDiffOn 𝕜 n f₁ s ↔ ContDiffOn 𝕜 n f s :=
⟨fun H => H.congr fun x hx => (h₁ x hx).symm, fun H => H.congr h₁⟩
theorem ContDiffOn.mono (h : ContDiffOn 𝕜 n f s) {t : Set E} (hst : t ⊆ s) : ContDiffOn 𝕜 n f t :=
fun x hx => (h x (hst hx)).mono hst
theorem ContDiffOn.congr_mono (hf : ContDiffOn 𝕜 n f s) (h₁ : ∀ x ∈ s₁, f₁ x = f x) (hs : s₁ ⊆ s) :
ContDiffOn 𝕜 n f₁ s₁ :=
(hf.mono hs).congr h₁
/-- If a function is `C^n` on a set with `n ≥ 1`, then it is differentiable there. -/
theorem ContDiffOn.differentiableOn (h : ContDiffOn 𝕜 n f s) (hn : 1 ≤ n) :
DifferentiableOn 𝕜 f s := fun x hx => (h x hx).differentiableWithinAt hn
/-- If a function is `C^n` around each point in a set, then it is `C^n` on the set. -/
theorem contDiffOn_of_locally_contDiffOn
(h : ∀ x ∈ s, ∃ u, IsOpen u ∧ x ∈ u ∧ ContDiffOn 𝕜 n f (s ∩ u)) : ContDiffOn 𝕜 n f s := by
intro x xs
rcases h x xs with ⟨u, u_open, xu, hu⟩
apply (contDiffWithinAt_inter _).1 (hu x ⟨xs, xu⟩)
exact IsOpen.mem_nhds u_open xu
/-- A function is `C^(n + 1)` on a domain iff locally, it has a derivative which is `C^n`. -/
theorem contDiffOn_succ_iff_hasFDerivWithinAt (hn : n ≠ ∞) :
ContDiffOn 𝕜 (n + 1) f s ↔
∀ x ∈ s, ∃ u ∈ 𝓝[insert x s] x, (n = ω → AnalyticOn 𝕜 f u) ∧ ∃ f' : E → E →L[𝕜] F,
(∀ x ∈ u, HasFDerivWithinAt f (f' x) u x) ∧ ContDiffOn 𝕜 n f' u := by
constructor
· intro h x hx
rcases (contDiffWithinAt_succ_iff_hasFDerivWithinAt hn).1 (h x hx) with
⟨u, hu, f_an, f', hf', Hf'⟩
rcases Hf'.contDiffOn le_rfl (by simp [hn]) with ⟨v, vu, v'u, hv⟩
rw [insert_eq_of_mem hx] at hu ⊢
have xu : x ∈ u := mem_of_mem_nhdsWithin hx hu
rw [insert_eq_of_mem xu] at vu v'u
exact ⟨v, nhdsWithin_le_of_mem hu vu, fun h ↦ (f_an h).mono v'u, f',
fun y hy ↦ (hf' y (v'u hy)).mono v'u, hv⟩
· intro h x hx
rw [contDiffWithinAt_succ_iff_hasFDerivWithinAt hn]
rcases h x hx with ⟨u, u_nhbd, f_an, f', hu, hf'⟩
have : x ∈ u := mem_of_mem_nhdsWithin (mem_insert _ _) u_nhbd
exact ⟨u, u_nhbd, f_an, f', hu, hf' x this⟩
/-! ### Iterated derivative within a set -/
@[simp]
theorem contDiffOn_zero : ContDiffOn 𝕜 0 f s ↔ ContinuousOn f s := by
refine ⟨fun H => H.continuousOn, fun H => fun x hx m hm ↦ ?_⟩
have : (m : WithTop ℕ∞) = 0 := le_antisymm (mod_cast hm) bot_le
rw [this]
refine ⟨insert x s, self_mem_nhdsWithin, ftaylorSeriesWithin 𝕜 f s, ?_⟩
rw [hasFTaylorSeriesUpToOn_zero_iff]
exact ⟨by rwa [insert_eq_of_mem hx], fun x _ => by simp [ftaylorSeriesWithin]⟩
theorem contDiffWithinAt_zero (hx : x ∈ s) :
ContDiffWithinAt 𝕜 0 f s x ↔ ∃ u ∈ 𝓝[s] x, ContinuousOn f (s ∩ u) := by
constructor
· intro h
obtain ⟨u, H, p, hp⟩ := h 0 le_rfl
refine ⟨u, ?_, ?_⟩
· simpa [hx] using H
· simp only [Nat.cast_zero, hasFTaylorSeriesUpToOn_zero_iff] at hp
exact hp.1.mono inter_subset_right
· rintro ⟨u, H, hu⟩
rw [← contDiffWithinAt_inter' H]
have h' : x ∈ s ∩ u := ⟨hx, mem_of_mem_nhdsWithin hx H⟩
exact (contDiffOn_zero.mpr hu).contDiffWithinAt h'
/-- When a function is `C^n` in a set `s` of unique differentiability, it admits
`ftaylorSeriesWithin 𝕜 f s` as a Taylor series up to order `n` in `s`. -/
protected theorem ContDiffOn.ftaylorSeriesWithin
(h : ContDiffOn 𝕜 n f s) (hs : UniqueDiffOn 𝕜 s) :
HasFTaylorSeriesUpToOn n f (ftaylorSeriesWithin 𝕜 f s) s := by
constructor
· intro x _
simp only [ftaylorSeriesWithin, ContinuousMultilinearMap.curry0_apply,
iteratedFDerivWithin_zero_apply]
· intro m hm x hx
have : (m + 1 : ℕ) ≤ n := ENat.add_one_natCast_le_withTop_of_lt hm
rcases (h x hx).of_le this _ le_rfl with ⟨u, hu, p, Hp⟩
rw [insert_eq_of_mem hx] at hu
rcases mem_nhdsWithin.1 hu with ⟨o, o_open, xo, ho⟩
rw [inter_comm] at ho
have : p x m.succ = ftaylorSeriesWithin 𝕜 f s x m.succ := by
change p x m.succ = iteratedFDerivWithin 𝕜 m.succ f s x
rw [← iteratedFDerivWithin_inter_open o_open xo]
exact (Hp.mono ho).eq_iteratedFDerivWithin_of_uniqueDiffOn le_rfl (hs.inter o_open) ⟨hx, xo⟩
rw [← this, ← hasFDerivWithinAt_inter (IsOpen.mem_nhds o_open xo)]
have A : ∀ y ∈ s ∩ o, p y m = ftaylorSeriesWithin 𝕜 f s y m := by
rintro y ⟨hy, yo⟩
change p y m = iteratedFDerivWithin 𝕜 m f s y
rw [← iteratedFDerivWithin_inter_open o_open yo]
exact
(Hp.mono ho).eq_iteratedFDerivWithin_of_uniqueDiffOn (mod_cast Nat.le_succ m)
(hs.inter o_open) ⟨hy, yo⟩
exact
((Hp.mono ho).fderivWithin m (mod_cast lt_add_one m) x ⟨hx, xo⟩).congr
(fun y hy => (A y hy).symm) (A x ⟨hx, xo⟩).symm
· intro m hm
apply continuousOn_of_locally_continuousOn
intro x hx
rcases (h x hx).of_le hm _ le_rfl with ⟨u, hu, p, Hp⟩
rcases mem_nhdsWithin.1 hu with ⟨o, o_open, xo, ho⟩
rw [insert_eq_of_mem hx] at ho
rw [inter_comm] at ho
refine ⟨o, o_open, xo, ?_⟩
have A : ∀ y ∈ s ∩ o, p y m = ftaylorSeriesWithin 𝕜 f s y m := by
rintro y ⟨hy, yo⟩
change p y m = iteratedFDerivWithin 𝕜 m f s y
rw [← iteratedFDerivWithin_inter_open o_open yo]
exact (Hp.mono ho).eq_iteratedFDerivWithin_of_uniqueDiffOn le_rfl (hs.inter o_open) ⟨hy, yo⟩
exact ((Hp.mono ho).cont m le_rfl).congr fun y hy => (A y hy).symm
theorem iteratedFDerivWithin_subset {n : ℕ} (st : s ⊆ t) (hs : UniqueDiffOn 𝕜 s)
(ht : UniqueDiffOn 𝕜 t) (h : ContDiffOn 𝕜 n f t) (hx : x ∈ s) :
iteratedFDerivWithin 𝕜 n f s x = iteratedFDerivWithin 𝕜 n f t x :=
(((h.ftaylorSeriesWithin ht).mono st).eq_iteratedFDerivWithin_of_uniqueDiffOn le_rfl hs hx).symm
theorem ContDiffWithinAt.eventually_hasFTaylorSeriesUpToOn {f : E → F} {s : Set E} {a : E}
(h : ContDiffWithinAt 𝕜 n f s a) (hs : UniqueDiffOn 𝕜 s) (ha : a ∈ s) {m : ℕ} (hm : m ≤ n) :
∀ᶠ t in (𝓝[s] a).smallSets, HasFTaylorSeriesUpToOn m f (ftaylorSeriesWithin 𝕜 f s) t := by
rcases h.contDiffOn' hm (by simp) with ⟨U, hUo, haU, hfU⟩
have : ∀ᶠ t in (𝓝[s] a).smallSets, t ⊆ s ∩ U := by
rw [eventually_smallSets_subset]
exact inter_mem_nhdsWithin _ <| hUo.mem_nhds haU
refine this.mono fun t ht ↦ .mono ?_ ht
rw [insert_eq_of_mem ha] at hfU
refine (hfU.ftaylorSeriesWithin (hs.inter hUo)).congr_series fun k hk x hx ↦ ?_
exact iteratedFDerivWithin_inter_open hUo hx.2
/-- On a set with unique differentiability, an analytic function is automatically `C^ω`, as its
successive derivatives are also analytic. This does not require completeness of the space. See
also `AnalyticOn.contDiffOn_of_completeSpace`. -/
theorem AnalyticOn.contDiffOn (h : AnalyticOn 𝕜 f s) (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 n f s := by
suffices ContDiffOn 𝕜 ω f s from this.of_le le_top
rcases h.exists_hasFTaylorSeriesUpToOn hs with ⟨p, hp⟩
intro x hx
refine ⟨s, ?_, p, hp⟩
rw [insert_eq_of_mem hx]
exact self_mem_nhdsWithin
/-- On a set with unique differentiability, an analytic function is automatically `C^ω`, as its
successive derivatives are also analytic. This does not require completeness of the space. See
also `AnalyticOnNhd.contDiffOn_of_completeSpace`. -/
theorem AnalyticOnNhd.contDiffOn (h : AnalyticOnNhd 𝕜 f s) (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 n f s := h.analyticOn.contDiffOn hs
/-- An analytic function is automatically `C^ω` in a complete space -/
theorem AnalyticOn.contDiffOn_of_completeSpace [CompleteSpace F] (h : AnalyticOn 𝕜 f s) :
ContDiffOn 𝕜 n f s :=
fun x hx ↦ (h x hx).contDiffWithinAt
/-- An analytic function is automatically `C^ω` in a complete space -/
theorem AnalyticOnNhd.contDiffOn_of_completeSpace [CompleteSpace F] (h : AnalyticOnNhd 𝕜 f s) :
ContDiffOn 𝕜 n f s :=
h.analyticOn.contDiffOn_of_completeSpace
theorem contDiffOn_of_continuousOn_differentiableOn {n : ℕ∞}
(Hcont : ∀ m : ℕ, m ≤ n → ContinuousOn (fun x => iteratedFDerivWithin 𝕜 m f s x) s)
(Hdiff : ∀ m : ℕ, m < n →
DifferentiableOn 𝕜 (fun x => iteratedFDerivWithin 𝕜 m f s x) s) :
ContDiffOn 𝕜 n f s := by
intro x hx m hm
rw [insert_eq_of_mem hx]
refine ⟨s, self_mem_nhdsWithin, ftaylorSeriesWithin 𝕜 f s, ?_⟩
constructor
· intro y _
simp only [ftaylorSeriesWithin, ContinuousMultilinearMap.curry0_apply,
iteratedFDerivWithin_zero_apply]
· intro k hk y hy
convert (Hdiff k (lt_of_lt_of_le (mod_cast hk) (mod_cast hm)) y hy).hasFDerivWithinAt
· intro k hk
exact Hcont k (le_trans (mod_cast hk) (mod_cast hm))
theorem contDiffOn_of_differentiableOn {n : ℕ∞}
(h : ∀ m : ℕ, m ≤ n → DifferentiableOn 𝕜 (iteratedFDerivWithin 𝕜 m f s) s) :
ContDiffOn 𝕜 n f s :=
contDiffOn_of_continuousOn_differentiableOn (fun m hm => (h m hm).continuousOn) fun m hm =>
h m (le_of_lt hm)
theorem contDiffOn_of_analyticOn_iteratedFDerivWithin
(h : ∀ m, AnalyticOn 𝕜 (iteratedFDerivWithin 𝕜 m f s) s) :
ContDiffOn 𝕜 n f s := by
suffices ContDiffOn 𝕜 ω f s from this.of_le le_top
intro x hx
refine ⟨insert x s, self_mem_nhdsWithin, ftaylorSeriesWithin 𝕜 f s, ?_, ?_⟩
· rw [insert_eq_of_mem hx]
constructor
· intro y _
simp only [ftaylorSeriesWithin, ContinuousMultilinearMap.curry0_apply,
iteratedFDerivWithin_zero_apply]
· intro k _ y hy
exact ((h k).differentiableOn y hy).hasFDerivWithinAt
· intro k _
exact (h k).continuousOn
· intro i
rw [insert_eq_of_mem hx]
exact h i
theorem contDiffOn_omega_iff_analyticOn (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 ω f s ↔ AnalyticOn 𝕜 f s :=
⟨fun h m ↦ h.analyticOn m, fun h ↦ h.contDiffOn hs⟩
theorem ContDiffOn.continuousOn_iteratedFDerivWithin {m : ℕ} (h : ContDiffOn 𝕜 n f s)
(hmn : m ≤ n) (hs : UniqueDiffOn 𝕜 s) : ContinuousOn (iteratedFDerivWithin 𝕜 m f s) s :=
((h.of_le hmn).ftaylorSeriesWithin hs).cont m le_rfl
theorem ContDiffOn.differentiableOn_iteratedFDerivWithin {m : ℕ} (h : ContDiffOn 𝕜 n f s)
(hmn : m < n) (hs : UniqueDiffOn 𝕜 s) :
DifferentiableOn 𝕜 (iteratedFDerivWithin 𝕜 m f s) s := by
intro x hx
have : (m + 1 : ℕ) ≤ n := ENat.add_one_natCast_le_withTop_of_lt hmn
apply (((h.of_le this).ftaylorSeriesWithin hs).fderivWithin m ?_ x hx).differentiableWithinAt
exact_mod_cast lt_add_one m
theorem ContDiffWithinAt.differentiableWithinAt_iteratedFDerivWithin {m : ℕ}
(h : ContDiffWithinAt 𝕜 n f s x) (hmn : m < n) (hs : UniqueDiffOn 𝕜 (insert x s)) :
DifferentiableWithinAt 𝕜 (iteratedFDerivWithin 𝕜 m f s) s x := by
have : (m + 1 : WithTop ℕ∞) ≠ ∞ := Ne.symm (ne_of_beq_false rfl)
rcases h.contDiffOn' (ENat.add_one_natCast_le_withTop_of_lt hmn) (by simp [this])
with ⟨u, uo, xu, hu⟩
set t := insert x s ∩ u
have A : t =ᶠ[𝓝[≠] x] s := by
simp only [set_eventuallyEq_iff_inf_principal, ← nhdsWithin_inter']
rw [← inter_assoc, nhdsWithin_inter_of_mem', ← diff_eq_compl_inter, insert_diff_of_mem,
diff_eq_compl_inter]
exacts [rfl, mem_nhdsWithin_of_mem_nhds (uo.mem_nhds xu)]
have B : iteratedFDerivWithin 𝕜 m f s =ᶠ[𝓝 x] iteratedFDerivWithin 𝕜 m f t :=
iteratedFDerivWithin_eventually_congr_set' _ A.symm _
have C : DifferentiableWithinAt 𝕜 (iteratedFDerivWithin 𝕜 m f t) t x :=
hu.differentiableOn_iteratedFDerivWithin (Nat.cast_lt.2 m.lt_succ_self) (hs.inter uo) x
⟨mem_insert _ _, xu⟩
rw [differentiableWithinAt_congr_set' _ A] at C
exact C.congr_of_eventuallyEq (B.filter_mono inf_le_left) B.self_of_nhds
theorem contDiffOn_iff_continuousOn_differentiableOn {n : ℕ∞} (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 n f s ↔
(∀ m : ℕ, m ≤ n → ContinuousOn (fun x => iteratedFDerivWithin 𝕜 m f s x) s) ∧
∀ m : ℕ, m < n → DifferentiableOn 𝕜 (fun x => iteratedFDerivWithin 𝕜 m f s x) s :=
⟨fun h => ⟨fun _m hm => h.continuousOn_iteratedFDerivWithin (mod_cast hm) hs,
fun _m hm => h.differentiableOn_iteratedFDerivWithin (mod_cast hm) hs⟩,
fun h => contDiffOn_of_continuousOn_differentiableOn h.1 h.2⟩
theorem contDiffOn_nat_iff_continuousOn_differentiableOn {n : ℕ} (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 n f s ↔
(∀ m : ℕ, m ≤ n → ContinuousOn (fun x => iteratedFDerivWithin 𝕜 m f s x) s) ∧
∀ m : ℕ, m < n → DifferentiableOn 𝕜 (fun x => iteratedFDerivWithin 𝕜 m f s x) s := by
rw [← WithTop.coe_natCast, contDiffOn_iff_continuousOn_differentiableOn hs]
simp
theorem contDiffOn_succ_of_fderivWithin (hf : DifferentiableOn 𝕜 f s)
(h' : n = ω → AnalyticOn 𝕜 f s)
(h : ContDiffOn 𝕜 n (fun y => fderivWithin 𝕜 f s y) s) : ContDiffOn 𝕜 (n + 1) f s := by
rcases eq_or_ne n ∞ with rfl | hn
· rw [ENat.coe_top_add_one, contDiffOn_infty]
intro m x hx
apply ContDiffWithinAt.of_le _ (show (m : WithTop ℕ∞) ≤ m + 1 from le_self_add)
rw [contDiffWithinAt_succ_iff_hasFDerivWithinAt (by simp),
insert_eq_of_mem hx]
exact ⟨s, self_mem_nhdsWithin, (by simp), fderivWithin 𝕜 f s,
fun y hy => (hf y hy).hasFDerivWithinAt, (h x hx).of_le (mod_cast le_top)⟩
· intro x hx
rw [contDiffWithinAt_succ_iff_hasFDerivWithinAt hn,
insert_eq_of_mem hx]
exact ⟨s, self_mem_nhdsWithin, h', fderivWithin 𝕜 f s,
fun y hy => (hf y hy).hasFDerivWithinAt, h x hx⟩
theorem contDiffOn_of_analyticOn_of_fderivWithin (hf : AnalyticOn 𝕜 f s)
(h : ContDiffOn 𝕜 ω (fun y ↦ fderivWithin 𝕜 f s y) s) : ContDiffOn 𝕜 n f s := by
suffices ContDiffOn 𝕜 (ω + 1) f s from this.of_le le_top
exact contDiffOn_succ_of_fderivWithin hf.differentiableOn (fun _ ↦ hf) h
/-- A function is `C^(n + 1)` on a domain with unique derivatives if and only if it is
differentiable there, and its derivative (expressed with `fderivWithin`) is `C^n`. -/
theorem contDiffOn_succ_iff_fderivWithin (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 (n + 1) f s ↔
DifferentiableOn 𝕜 f s ∧ (n = ω → AnalyticOn 𝕜 f s) ∧
ContDiffOn 𝕜 n (fderivWithin 𝕜 f s) s := by
refine ⟨fun H => ?_, fun h => contDiffOn_succ_of_fderivWithin h.1 h.2.1 h.2.2⟩
refine ⟨H.differentiableOn le_add_self, ?_, fun x hx => ?_⟩
· rintro rfl
exact H.analyticOn
have A (m : ℕ) (hm : m ≤ n) : ContDiffWithinAt 𝕜 m (fun y => fderivWithin 𝕜 f s y) s x := by
rcases (contDiffWithinAt_succ_iff_hasFDerivWithinAt (n := m) (ne_of_beq_false rfl)).1
(H.of_le (add_le_add_right hm 1) x hx) with ⟨u, hu, -, f', hff', hf'⟩
rcases mem_nhdsWithin.1 hu with ⟨o, o_open, xo, ho⟩
rw [inter_comm, insert_eq_of_mem hx] at ho
have := hf'.mono ho
rw [contDiffWithinAt_inter' (mem_nhdsWithin_of_mem_nhds (IsOpen.mem_nhds o_open xo))] at this
apply this.congr_of_eventuallyEq_of_mem _ hx
have : o ∩ s ∈ 𝓝[s] x := mem_nhdsWithin.2 ⟨o, o_open, xo, Subset.refl _⟩
rw [inter_comm] at this
refine Filter.eventuallyEq_of_mem this fun y hy => ?_
have A : fderivWithin 𝕜 f (s ∩ o) y = f' y :=
((hff' y (ho hy)).mono ho).fderivWithin (hs.inter o_open y hy)
rwa [fderivWithin_inter (o_open.mem_nhds hy.2)] at A
match n with
| ω => exact (H.analyticOn.fderivWithin hs).contDiffOn hs (n := ω) x hx
| ∞ => exact contDiffWithinAt_infty.2 (fun m ↦ A m (mod_cast le_top))
| (n : ℕ) => exact A n le_rfl
theorem contDiffOn_succ_iff_hasFDerivWithinAt_of_uniqueDiffOn (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 (n + 1) f s ↔ (n = ω → AnalyticOn 𝕜 f s) ∧
∃ f' : E → E →L[𝕜] F, ContDiffOn 𝕜 n f' s ∧ ∀ x, x ∈ s → HasFDerivWithinAt f (f' x) s x := by
rw [contDiffOn_succ_iff_fderivWithin hs]
refine ⟨fun h => ⟨h.2.1, fderivWithin 𝕜 f s, h.2.2,
fun x hx => (h.1 x hx).hasFDerivWithinAt⟩, fun ⟨f_an, h⟩ => ?_⟩
rcases h with ⟨f', h1, h2⟩
refine ⟨fun x hx => (h2 x hx).differentiableWithinAt, f_an, fun x hx => ?_⟩
exact (h1 x hx).congr_of_mem (fun y hy => (h2 y hy).fderivWithin (hs y hy)) hx
@[deprecated (since := "2024-11-27")]
alias contDiffOn_succ_iff_hasFDerivWithin := contDiffOn_succ_iff_hasFDerivWithinAt_of_uniqueDiffOn
theorem contDiffOn_infty_iff_fderivWithin (hs : UniqueDiffOn 𝕜 s) :
ContDiffOn 𝕜 ∞ f s ↔ DifferentiableOn 𝕜 f s ∧ ContDiffOn 𝕜 ∞ (fderivWithin 𝕜 f s) s := by
rw [← ENat.coe_top_add_one, contDiffOn_succ_iff_fderivWithin hs]
simp
@[deprecated (since := "2024-11-27")]
alias contDiffOn_top_iff_fderivWithin := contDiffOn_infty_iff_fderivWithin
/-- A function is `C^(n + 1)` on an open domain if and only if it is
differentiable there, and its derivative (expressed with `fderiv`) is `C^n`. -/
theorem contDiffOn_succ_iff_fderiv_of_isOpen (hs : IsOpen s) :
ContDiffOn 𝕜 (n + 1) f s ↔
DifferentiableOn 𝕜 f s ∧ (n = ω → AnalyticOn 𝕜 f s) ∧
ContDiffOn 𝕜 n (fderiv 𝕜 f) s := by
rw [contDiffOn_succ_iff_fderivWithin hs.uniqueDiffOn,
contDiffOn_congr fun x hx ↦ fderivWithin_of_isOpen hs hx]
theorem contDiffOn_infty_iff_fderiv_of_isOpen (hs : IsOpen s) :
ContDiffOn 𝕜 ∞ f s ↔ DifferentiableOn 𝕜 f s ∧ ContDiffOn 𝕜 ∞ (fderiv 𝕜 f) s := by
rw [← ENat.coe_top_add_one, contDiffOn_succ_iff_fderiv_of_isOpen hs]
simp
@[deprecated (since := "2024-11-27")]
alias contDiffOn_top_iff_fderiv_of_isOpen := contDiffOn_infty_iff_fderiv_of_isOpen
protected theorem ContDiffOn.fderivWithin (hf : ContDiffOn 𝕜 n f s) (hs : UniqueDiffOn 𝕜 s)
(hmn : m + 1 ≤ n) : ContDiffOn 𝕜 m (fderivWithin 𝕜 f s) s :=
((contDiffOn_succ_iff_fderivWithin hs).1 (hf.of_le hmn)).2.2
theorem ContDiffOn.fderiv_of_isOpen (hf : ContDiffOn 𝕜 n f s) (hs : IsOpen s) (hmn : m + 1 ≤ n) :
ContDiffOn 𝕜 m (fderiv 𝕜 f) s :=
(hf.fderivWithin hs.uniqueDiffOn hmn).congr fun _ hx => (fderivWithin_of_isOpen hs hx).symm
theorem ContDiffOn.continuousOn_fderivWithin (h : ContDiffOn 𝕜 n f s) (hs : UniqueDiffOn 𝕜 s)
(hn : 1 ≤ n) : ContinuousOn (fderivWithin 𝕜 f s) s :=
((contDiffOn_succ_iff_fderivWithin hs).1
(h.of_le (show 0 + (1 : WithTop ℕ∞) ≤ n from hn))).2.2.continuousOn
theorem ContDiffOn.continuousOn_fderiv_of_isOpen (h : ContDiffOn 𝕜 n f s) (hs : IsOpen s)
(hn : 1 ≤ n) : ContinuousOn (fderiv 𝕜 f) s :=
((contDiffOn_succ_iff_fderiv_of_isOpen hs).1
(h.of_le (show 0 + (1 : WithTop ℕ∞) ≤ n from hn))).2.2.continuousOn
/-! ### Smooth functions at a point -/
variable (𝕜) in
/-- A function is continuously differentiable up to `n` at a point `x` if, for any integer `k ≤ n`,
there is a neighborhood of `x` where `f` admits derivatives up to order `n`, which are continuous.
-/
def ContDiffAt (n : WithTop ℕ∞) (f : E → F) (x : E) : Prop :=
ContDiffWithinAt 𝕜 n f univ x
theorem contDiffWithinAt_univ : ContDiffWithinAt 𝕜 n f univ x ↔ ContDiffAt 𝕜 n f x :=
Iff.rfl
theorem contDiffAt_infty : ContDiffAt 𝕜 ∞ f x ↔ ∀ n : ℕ, ContDiffAt 𝕜 n f x := by
simp [← contDiffWithinAt_univ, contDiffWithinAt_infty]
@[deprecated (since := "2024-11-27")] alias contDiffAt_top := contDiffAt_infty
theorem ContDiffAt.contDiffWithinAt (h : ContDiffAt 𝕜 n f x) : ContDiffWithinAt 𝕜 n f s x :=
h.mono (subset_univ _)
theorem ContDiffWithinAt.contDiffAt (h : ContDiffWithinAt 𝕜 n f s x) (hx : s ∈ 𝓝 x) :
ContDiffAt 𝕜 n f x := by rwa [ContDiffAt, ← contDiffWithinAt_inter hx, univ_inter]
theorem contDiffWithinAt_iff_contDiffAt (h : s ∈ 𝓝 x) :
ContDiffWithinAt 𝕜 n f s x ↔ ContDiffAt 𝕜 n f x := by
rw [← univ_inter s, contDiffWithinAt_inter h, contDiffWithinAt_univ]
theorem IsOpen.contDiffOn_iff (hs : IsOpen s) :
ContDiffOn 𝕜 n f s ↔ ∀ ⦃a⦄, a ∈ s → ContDiffAt 𝕜 n f a :=
forall₂_congr fun _ => contDiffWithinAt_iff_contDiffAt ∘ hs.mem_nhds
theorem ContDiffOn.contDiffAt (h : ContDiffOn 𝕜 n f s) (hx : s ∈ 𝓝 x) :
ContDiffAt 𝕜 n f x :=
(h _ (mem_of_mem_nhds hx)).contDiffAt hx
theorem ContDiffAt.congr_of_eventuallyEq (h : ContDiffAt 𝕜 n f x) (hg : f₁ =ᶠ[𝓝 x] f) :
ContDiffAt 𝕜 n f₁ x :=
h.congr_of_eventuallyEq_of_mem (by rwa [nhdsWithin_univ]) (mem_univ x)
theorem ContDiffAt.of_le (h : ContDiffAt 𝕜 n f x) (hmn : m ≤ n) : ContDiffAt 𝕜 m f x :=
ContDiffWithinAt.of_le h hmn
theorem ContDiffAt.continuousAt (h : ContDiffAt 𝕜 n f x) : ContinuousAt f x := by
simpa [continuousWithinAt_univ] using h.continuousWithinAt
theorem ContDiffAt.analyticAt (h : ContDiffAt 𝕜 ω f x) : AnalyticAt 𝕜 f x := by
rw [← contDiffWithinAt_univ] at h
rw [← analyticWithinAt_univ]
exact h.analyticWithinAt
/-- In a complete space, a function which is analytic at a point is also `C^ω` there.
Note that the same statement for `AnalyticOn` does not require completeness, see
`AnalyticOn.contDiffOn`. -/
theorem AnalyticAt.contDiffAt [CompleteSpace F] (h : AnalyticAt 𝕜 f x) :
ContDiffAt 𝕜 n f x := by
rw [← contDiffWithinAt_univ]
rw [← analyticWithinAt_univ] at h
exact h.contDiffWithinAt
@[simp]
theorem contDiffWithinAt_compl_self :
ContDiffWithinAt 𝕜 n f {x}ᶜ x ↔ ContDiffAt 𝕜 n f x := by
rw [compl_eq_univ_diff, contDiffWithinAt_diff_singleton, contDiffWithinAt_univ]
/-- If a function is `C^n` with `n ≥ 1` at a point, then it is differentiable there. -/
theorem ContDiffAt.differentiableAt (h : ContDiffAt 𝕜 n f x) (hn : 1 ≤ n) :
DifferentiableAt 𝕜 f x := by
simpa [hn, differentiableWithinAt_univ] using h.differentiableWithinAt
nonrec lemma ContDiffAt.contDiffOn (h : ContDiffAt 𝕜 n f x) (hm : m ≤ n) (h' : m = ∞ → n = ω):
∃ u ∈ 𝓝 x, ContDiffOn 𝕜 m f u := by
simpa [nhdsWithin_univ] using h.contDiffOn hm h'
/-- A function is `C^(n + 1)` at a point iff locally, it has a derivative which is `C^n`. -/
theorem contDiffAt_succ_iff_hasFDerivAt {n : ℕ} :
ContDiffAt 𝕜 (n + 1) f x ↔ ∃ f' : E → E →L[𝕜] F,
(∃ u ∈ 𝓝 x, ∀ x ∈ u, HasFDerivAt f (f' x) x) ∧ ContDiffAt 𝕜 n f' x := by
rw [← contDiffWithinAt_univ, contDiffWithinAt_succ_iff_hasFDerivWithinAt (by simp)]
simp only [nhdsWithin_univ, exists_prop, mem_univ, insert_eq_of_mem]
constructor
· rintro ⟨u, H, -, f', h_fderiv, h_cont_diff⟩
rcases mem_nhds_iff.mp H with ⟨t, htu, ht, hxt⟩
refine ⟨f', ⟨t, ?_⟩, h_cont_diff.contDiffAt H⟩
refine ⟨mem_nhds_iff.mpr ⟨t, Subset.rfl, ht, hxt⟩, ?_⟩
intro y hyt
refine (h_fderiv y (htu hyt)).hasFDerivAt ?_
exact mem_nhds_iff.mpr ⟨t, htu, ht, hyt⟩
· rintro ⟨f', ⟨u, H, h_fderiv⟩, h_cont_diff⟩
refine ⟨u, H, by simp, f', fun x hxu ↦ ?_, h_cont_diff.contDiffWithinAt⟩
exact (h_fderiv x hxu).hasFDerivWithinAt
protected theorem ContDiffAt.eventually (h : ContDiffAt 𝕜 n f x) (h' : n ≠ ∞) :
∀ᶠ y in 𝓝 x, ContDiffAt 𝕜 n f y := by
simpa [nhdsWithin_univ] using ContDiffWithinAt.eventually h h'
theorem iteratedFDerivWithin_eq_iteratedFDeriv {n : ℕ}
(hs : UniqueDiffOn 𝕜 s) (h : ContDiffAt 𝕜 n f x) (hx : x ∈ s) :
iteratedFDerivWithin 𝕜 n f s x = iteratedFDeriv 𝕜 n f x := by
rw [← iteratedFDerivWithin_univ]
rcases h.contDiffOn' le_rfl (by simp) with ⟨u, u_open, xu, hu⟩
rw [← iteratedFDerivWithin_inter_open u_open xu,
← iteratedFDerivWithin_inter_open u_open xu (s := univ)]
apply iteratedFDerivWithin_subset
· exact inter_subset_inter_left _ (subset_univ _)
· exact hs.inter u_open
· apply uniqueDiffOn_univ.inter u_open
· simpa using hu
· exact ⟨hx, xu⟩
/-! ### Smooth functions -/
variable (𝕜) in
/-- A function is continuously differentiable up to `n` if it admits derivatives up to
order `n`, which are continuous. Contrary to the case of definitions in domains (where derivatives
might not be unique) we do not need to localize the definition in space or time.
-/
def ContDiff (n : WithTop ℕ∞) (f : E → F) : Prop :=
match n with
| ω => ∃ p : E → FormalMultilinearSeries 𝕜 E F, HasFTaylorSeriesUpTo ⊤ f p
∧ ∀ i, AnalyticOnNhd 𝕜 (fun x ↦ p x i) univ
| (n : ℕ∞) => ∃ p : E → FormalMultilinearSeries 𝕜 E F, HasFTaylorSeriesUpTo n f p
/-- If `f` has a Taylor series up to `n`, then it is `C^n`. -/
theorem HasFTaylorSeriesUpTo.contDiff {n : ℕ∞} {f' : E → FormalMultilinearSeries 𝕜 E F}
(hf : HasFTaylorSeriesUpTo n f f') : ContDiff 𝕜 n f :=
⟨f', hf⟩
theorem contDiffOn_univ : ContDiffOn 𝕜 n f univ ↔ ContDiff 𝕜 n f := by
match n with
| ω =>
constructor
· intro H
use ftaylorSeriesWithin 𝕜 f univ
rw [← hasFTaylorSeriesUpToOn_univ_iff]
refine ⟨H.ftaylorSeriesWithin uniqueDiffOn_univ, fun i ↦ ?_⟩
rw [← analyticOn_univ]
exact H.analyticOn.iteratedFDerivWithin uniqueDiffOn_univ _
· rintro ⟨p, hp, h'p⟩ x _
exact ⟨univ, Filter.univ_sets _, p, (hp.hasFTaylorSeriesUpToOn univ).of_le le_top,
fun i ↦ (h'p i).analyticOn⟩
| (n : ℕ∞) =>
constructor
· intro H
use ftaylorSeriesWithin 𝕜 f univ
rw [← hasFTaylorSeriesUpToOn_univ_iff]
exact H.ftaylorSeriesWithin uniqueDiffOn_univ
· rintro ⟨p, hp⟩ x _ m hm
exact ⟨univ, Filter.univ_sets _, p,
(hp.hasFTaylorSeriesUpToOn univ).of_le (mod_cast hm)⟩
theorem contDiff_iff_contDiffAt : ContDiff 𝕜 n f ↔ ∀ x, ContDiffAt 𝕜 n f x := by
simp [← contDiffOn_univ, ContDiffOn, ContDiffAt]
theorem ContDiff.contDiffAt (h : ContDiff 𝕜 n f) : ContDiffAt 𝕜 n f x :=
contDiff_iff_contDiffAt.1 h x
theorem ContDiff.contDiffWithinAt (h : ContDiff 𝕜 n f) : ContDiffWithinAt 𝕜 n f s x :=
h.contDiffAt.contDiffWithinAt
theorem contDiff_infty : ContDiff 𝕜 ∞ f ↔ ∀ n : ℕ, ContDiff 𝕜 n f := by
simp [contDiffOn_univ.symm, contDiffOn_infty]
@[deprecated (since := "2024-11-25")] alias contDiff_top := contDiff_infty
@[deprecated (since := "2024-11-25")] alias contDiff_infty_iff_contDiff_omega := contDiff_infty
theorem contDiff_all_iff_nat : (∀ n : ℕ∞, ContDiff 𝕜 n f) ↔ ∀ n : ℕ, ContDiff 𝕜 n f := by
simp only [← contDiffOn_univ, contDiffOn_all_iff_nat]
theorem ContDiff.contDiffOn (h : ContDiff 𝕜 n f) : ContDiffOn 𝕜 n f s :=
(contDiffOn_univ.2 h).mono (subset_univ _)
@[simp]
theorem contDiff_zero : ContDiff 𝕜 0 f ↔ Continuous f := by
rw [← contDiffOn_univ, continuous_iff_continuousOn_univ]
exact contDiffOn_zero
theorem contDiffAt_zero : ContDiffAt 𝕜 0 f x ↔ ∃ u ∈ 𝓝 x, ContinuousOn f u := by
rw [← contDiffWithinAt_univ]; simp [contDiffWithinAt_zero, nhdsWithin_univ]
theorem contDiffAt_one_iff :
ContDiffAt 𝕜 1 f x ↔
∃ f' : E → E →L[𝕜] F, ∃ u ∈ 𝓝 x, ContinuousOn f' u ∧ ∀ x ∈ u, HasFDerivAt f (f' x) x := by
rw [show (1 : WithTop ℕ∞) = (0 : ℕ) + 1 from rfl]
simp_rw [contDiffAt_succ_iff_hasFDerivAt, show ((0 : ℕ) : WithTop ℕ∞) = 0 from rfl,
contDiffAt_zero, exists_mem_and_iff antitone_bforall antitone_continuousOn, and_comm]
theorem ContDiff.of_le (h : ContDiff 𝕜 n f) (hmn : m ≤ n) : ContDiff 𝕜 m f :=
contDiffOn_univ.1 <| (contDiffOn_univ.2 h).of_le hmn
theorem ContDiff.of_succ (h : ContDiff 𝕜 (n + 1) f) : ContDiff 𝕜 n f :=
h.of_le le_self_add
theorem ContDiff.one_of_succ (h : ContDiff 𝕜 (n + 1) f) : ContDiff 𝕜 1 f := by
apply h.of_le le_add_self
theorem ContDiff.continuous (h : ContDiff 𝕜 n f) : Continuous f :=
contDiff_zero.1 (h.of_le bot_le)
/-- If a function is `C^n` with `n ≥ 1`, then it is differentiable. -/
theorem ContDiff.differentiable (h : ContDiff 𝕜 n f) (hn : 1 ≤ n) : Differentiable 𝕜 f :=
differentiableOn_univ.1 <| (contDiffOn_univ.2 h).differentiableOn hn
theorem contDiff_iff_forall_nat_le {n : ℕ∞} :
ContDiff 𝕜 n f ↔ ∀ m : ℕ, ↑m ≤ n → ContDiff 𝕜 m f := by
simp_rw [← contDiffOn_univ]; exact contDiffOn_iff_forall_nat_le
/-- A function is `C^(n+1)` iff it has a `C^n` derivative. -/
theorem contDiff_succ_iff_hasFDerivAt {n : ℕ} :
ContDiff 𝕜 (n + 1) f ↔
∃ f' : E → E →L[𝕜] F, ContDiff 𝕜 n f' ∧ ∀ x, HasFDerivAt f (f' x) x := by
simp only [← contDiffOn_univ, ← hasFDerivWithinAt_univ, Set.mem_univ, forall_true_left,
contDiffOn_succ_iff_hasFDerivWithinAt_of_uniqueDiffOn uniqueDiffOn_univ,
WithTop.natCast_ne_top, analyticOn_univ, false_implies, true_and]
theorem contDiff_one_iff_hasFDerivAt : ContDiff 𝕜 1 f ↔
∃ f' : E → E →L[𝕜] F, Continuous f' ∧ ∀ x, HasFDerivAt f (f' x) x := by
convert contDiff_succ_iff_hasFDerivAt using 4; simp
theorem AnalyticOn.contDiff (hf : AnalyticOn 𝕜 f univ) : ContDiff 𝕜 n f := by
rw [← contDiffOn_univ]
exact hf.contDiffOn (n := n) uniqueDiffOn_univ
theorem AnalyticOnNhd.contDiff (hf : AnalyticOnNhd 𝕜 f univ) : ContDiff 𝕜 n f :=
hf.analyticOn.contDiff
theorem ContDiff.analyticOnNhd (h : ContDiff 𝕜 ω f) : AnalyticOnNhd 𝕜 f s := by
rw [← contDiffOn_univ] at h
have := h.analyticOn
rw [analyticOn_univ] at this
exact this.mono (subset_univ _)
theorem contDiff_omega_iff_analyticOnNhd :
ContDiff 𝕜 ω f ↔ AnalyticOnNhd 𝕜 f univ :=
⟨fun h ↦ h.analyticOnNhd, fun h ↦ h.contDiff⟩
/-! ### Iterated derivative -/
/-- When a function is `C^n`, it admits `ftaylorSeries 𝕜 f` as a Taylor series up
to order `n` in `s`. -/
theorem ContDiff.ftaylorSeries (hf : ContDiff 𝕜 n f) :
HasFTaylorSeriesUpTo n f (ftaylorSeries 𝕜 f) := by
simp only [← contDiffOn_univ, ← hasFTaylorSeriesUpToOn_univ_iff, ← ftaylorSeriesWithin_univ]
at hf ⊢
exact ContDiffOn.ftaylorSeriesWithin hf uniqueDiffOn_univ
/-- For `n : ℕ∞`, a function is `C^n` iff it admits `ftaylorSeries 𝕜 f`
as a Taylor series up to order `n`. -/
theorem contDiff_iff_ftaylorSeries {n : ℕ∞} :
ContDiff 𝕜 n f ↔ HasFTaylorSeriesUpTo n f (ftaylorSeries 𝕜 f) := by
constructor
· rw [← contDiffOn_univ, ← hasFTaylorSeriesUpToOn_univ_iff, ← ftaylorSeriesWithin_univ]
exact fun h ↦ ContDiffOn.ftaylorSeriesWithin h uniqueDiffOn_univ
· exact fun h ↦ ⟨ftaylorSeries 𝕜 f, h⟩
theorem contDiff_iff_continuous_differentiable {n : ℕ∞} :
ContDiff 𝕜 n f ↔
(∀ m : ℕ, m ≤ n → Continuous fun x => iteratedFDeriv 𝕜 m f x) ∧
∀ m : ℕ, m < n → Differentiable 𝕜 fun x => iteratedFDeriv 𝕜 m f x := by
simp [contDiffOn_univ.symm, continuous_iff_continuousOn_univ, differentiableOn_univ.symm,
iteratedFDerivWithin_univ, contDiffOn_iff_continuousOn_differentiableOn uniqueDiffOn_univ]
theorem contDiff_nat_iff_continuous_differentiable {n : ℕ} :
ContDiff 𝕜 n f ↔
(∀ m : ℕ, m ≤ n → Continuous fun x => iteratedFDeriv 𝕜 m f x) ∧
∀ m : ℕ, m < n → Differentiable 𝕜 fun x => iteratedFDeriv 𝕜 m f x := by
rw [← WithTop.coe_natCast, contDiff_iff_continuous_differentiable]
simp
/-- If `f` is `C^n` then its `m`-times iterated derivative is continuous for `m ≤ n`. -/
theorem ContDiff.continuous_iteratedFDeriv {m : ℕ} (hm : m ≤ n) (hf : ContDiff 𝕜 n f) :
Continuous fun x => iteratedFDeriv 𝕜 m f x :=
(contDiff_iff_continuous_differentiable.mp (hf.of_le hm)).1 m le_rfl
/-- If `f` is `C^n` then its `m`-times iterated derivative is differentiable for `m < n`. -/
theorem ContDiff.differentiable_iteratedFDeriv {m : ℕ} (hm : m < n) (hf : ContDiff 𝕜 n f) :
Differentiable 𝕜 fun x => iteratedFDeriv 𝕜 m f x :=
(contDiff_iff_continuous_differentiable.mp
(hf.of_le (ENat.add_one_natCast_le_withTop_of_lt hm))).2 m (mod_cast lt_add_one m)
theorem contDiff_of_differentiable_iteratedFDeriv {n : ℕ∞}
(h : ∀ m : ℕ, m ≤ n → Differentiable 𝕜 (iteratedFDeriv 𝕜 m f)) : ContDiff 𝕜 n f :=
contDiff_iff_continuous_differentiable.2
⟨fun m hm => (h m hm).continuous, fun m hm => h m (le_of_lt hm)⟩
/-- A function is `C^(n + 1)` if and only if it is differentiable,
and its derivative (formulated in terms of `fderiv`) is `C^n`. -/
theorem contDiff_succ_iff_fderiv :
ContDiff 𝕜 (n + 1) f ↔ Differentiable 𝕜 f ∧ (n = ω → AnalyticOnNhd 𝕜 f univ) ∧
ContDiff 𝕜 n (fderiv 𝕜 f) := by
simp only [← contDiffOn_univ, ← differentiableOn_univ, ← fderivWithin_univ,
contDiffOn_succ_iff_fderivWithin uniqueDiffOn_univ, analyticOn_univ]
theorem contDiff_one_iff_fderiv :
ContDiff 𝕜 1 f ↔ Differentiable 𝕜 f ∧ Continuous (fderiv 𝕜 f) := by
rw [← zero_add 1, contDiff_succ_iff_fderiv]
simp
theorem contDiff_infty_iff_fderiv :
ContDiff 𝕜 ∞ f ↔ Differentiable 𝕜 f ∧ ContDiff 𝕜 ∞ (fderiv 𝕜 f) := by
rw [← ENat.coe_top_add_one, contDiff_succ_iff_fderiv]
simp
@[deprecated (since := "2024-11-27")] alias contDiff_top_iff_fderiv := contDiff_infty_iff_fderiv
theorem ContDiff.continuous_fderiv (h : ContDiff 𝕜 n f) (hn : 1 ≤ n) :
Continuous (fderiv 𝕜 f) :=
(contDiff_one_iff_fderiv.1 (h.of_le hn)).2
/-- If a function is at least `C^1`, its bundled derivative (mapping `(x, v)` to `Df(x) v`) is
continuous. -/
theorem ContDiff.continuous_fderiv_apply (h : ContDiff 𝕜 n f) (hn : 1 ≤ n) :
Continuous fun p : E × E => (fderiv 𝕜 f p.1 : E → F) p.2 :=
have A : Continuous fun q : (E →L[𝕜] F) × E => q.1 q.2 := isBoundedBilinearMap_apply.continuous
have B : Continuous fun p : E × E => (fderiv 𝕜 f p.1, p.2) :=
((h.continuous_fderiv hn).comp continuous_fst).prodMk continuous_snd
A.comp B
| Mathlib/Analysis/Calculus/ContDiff/Defs.lean | 1,713 | 1,718 | |
/-
Copyright (c) 2021 Yaël Dillies. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies
-/
import Mathlib.Data.Sigma.Lex
import Mathlib.Util.Notation3
import Mathlib.Data.Sigma.Basic
import Mathlib.Order.Lattice
import Mathlib.Order.BoundedOrder.Basic
/-!
# Orders on a sigma type
This file defines two orders on a sigma type:
* The disjoint sum of orders. `a` is less `b` iff `a` and `b` are in the same summand and `a` is
less than `b` there.
* The lexicographical order. `a` is less than `b` if its summand is strictly less than the summand
of `b` or they are in the same summand and `a` is less than `b` there.
We make the disjoint sum of orders the default set of instances. The lexicographic order goes on a
type synonym.
## Notation
* `_root_.Lex (Sigma α)`: Sigma type equipped with the lexicographic order.
Type synonym of `Σ i, α i`.
## See also
Related files are:
* `Data.Finset.CoLex`: Colexicographic order on finite sets.
* `Data.List.Lex`: Lexicographic order on lists.
* `Data.Pi.Lex`: Lexicographic order on `Πₗ i, α i`.
* `Data.PSigma.Order`: Lexicographic order on `Σₗ' i, α i`. Basically a twin of this file.
* `Data.Prod.Lex`: Lexicographic order on `α × β`.
## TODO
Upgrade `Equiv.sigma_congr_left`, `Equiv.sigma_congr`, `Equiv.sigma_assoc`,
`Equiv.sigma_prod_of_equiv`, `Equiv.sigma_equiv_prod`, ... to order isomorphisms.
-/
namespace Sigma
variable {ι : Type*} {α : ι → Type*}
/-! ### Disjoint sum of orders on `Sigma` -/
/-- Disjoint sum of orders. `⟨i, a⟩ ≤ ⟨j, b⟩` iff `i = j` and `a ≤ b`. -/
protected inductive LE [∀ i, LE (α i)] : ∀ _a _b : Σ i, α i, Prop
| fiber (i : ι) (a b : α i) : a ≤ b → Sigma.LE ⟨i, a⟩ ⟨i, b⟩
/-- Disjoint sum of orders. `⟨i, a⟩ < ⟨j, b⟩` iff `i = j` and `a < b`. -/
protected inductive LT [∀ i, LT (α i)] : ∀ _a _b : Σi, α i, Prop
| fiber (i : ι) (a b : α i) : a < b → Sigma.LT ⟨i, a⟩ ⟨i, b⟩
protected instance [∀ i, LE (α i)] : LE (Σi, α i) where
le := Sigma.LE
protected instance [∀ i, LT (α i)] : LT (Σi, α i) where
lt := Sigma.LT
@[simp]
theorem mk_le_mk_iff [∀ i, LE (α i)] {i : ι} {a b : α i} : (⟨i, a⟩ : Sigma α) ≤ ⟨i, b⟩ ↔ a ≤ b :=
⟨fun ⟨_, _, _, h⟩ => h, Sigma.LE.fiber _ _ _⟩
@[simp]
theorem mk_lt_mk_iff [∀ i, LT (α i)] {i : ι} {a b : α i} : (⟨i, a⟩ : Sigma α) < ⟨i, b⟩ ↔ a < b :=
⟨fun ⟨_, _, _, h⟩ => h, Sigma.LT.fiber _ _ _⟩
theorem le_def [∀ i, LE (α i)] {a b : Σi, α i} : a ≤ b ↔ ∃ h : a.1 = b.1, h.rec a.2 ≤ b.2 := by
constructor
· rintro ⟨i, a, b, h⟩
exact ⟨rfl, h⟩
· obtain ⟨i, a⟩ := a
obtain ⟨j, b⟩ := b
| rintro ⟨rfl : i = j, h⟩
exact LE.fiber _ _ _ h
theorem lt_def [∀ i, LT (α i)] {a b : Σi, α i} : a < b ↔ ∃ h : a.1 = b.1, h.rec a.2 < b.2 := by
constructor
· rintro ⟨i, a, b, h⟩
exact ⟨rfl, h⟩
· obtain ⟨i, a⟩ := a
| Mathlib/Data/Sigma/Order.lean | 79 | 86 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Yury Kudryashov
-/
import Mathlib.Analysis.Normed.Group.Continuity
import Mathlib.MeasureTheory.Constructions.BorelSpace.Basic
import Mathlib.Topology.MetricSpace.Thickening
/-!
# Borel sigma algebras on (pseudo-)metric spaces
## Main statements
* `measurable_dist`, `measurable_infEdist`, `measurable_norm`, `measurable_enorm`,
`Measurable.dist`, `Measurable.infEdist`, `Measurable.norm`, `Measurable.enorm`:
measurability of various metric-related notions;
* `tendsto_measure_thickening_of_isClosed`:
the measure of a closed set is the limit of the measure of its ε-thickenings as ε → 0.
* `exists_borelSpace_of_countablyGenerated_of_separatesPoints`:
if a measurable space is countably generated and separates points, it arises as the Borel sets
of some second countable separable metrizable topology.
-/
open Set Filter MeasureTheory MeasurableSpace TopologicalSpace
open scoped Topology NNReal ENNReal MeasureTheory
universe u v w x y
variable {α β γ δ : Type*} {ι : Sort y} {s t u : Set α}
section PseudoMetricSpace
variable [PseudoMetricSpace α] [MeasurableSpace α] [OpensMeasurableSpace α]
variable [MeasurableSpace β] {x : α} {ε : ℝ}
open Metric
@[measurability]
theorem measurableSet_ball : MeasurableSet (Metric.ball x ε) :=
Metric.isOpen_ball.measurableSet
@[measurability]
theorem measurableSet_closedBall : MeasurableSet (Metric.closedBall x ε) :=
Metric.isClosed_closedBall.measurableSet
@[measurability]
theorem measurable_infDist {s : Set α} : Measurable fun x => infDist x s :=
(continuous_infDist_pt s).measurable
@[measurability, fun_prop]
theorem Measurable.infDist {f : β → α} (hf : Measurable f) {s : Set α} :
Measurable fun x => infDist (f x) s :=
measurable_infDist.comp hf
@[measurability]
theorem measurable_infNndist {s : Set α} : Measurable fun x => infNndist x s :=
(continuous_infNndist_pt s).measurable
@[measurability, fun_prop]
theorem Measurable.infNndist {f : β → α} (hf : Measurable f) {s : Set α} :
Measurable fun x => infNndist (f x) s :=
measurable_infNndist.comp hf
section
variable [SecondCountableTopology α]
@[measurability]
theorem measurable_dist : Measurable fun p : α × α => dist p.1 p.2 :=
continuous_dist.measurable
@[measurability, fun_prop]
theorem Measurable.dist {f g : β → α} (hf : Measurable f) (hg : Measurable g) :
Measurable fun b => dist (f b) (g b) :=
(@continuous_dist α _).measurable2 hf hg
@[measurability]
theorem measurable_nndist : Measurable fun p : α × α => nndist p.1 p.2 :=
continuous_nndist.measurable
@[measurability, fun_prop]
theorem Measurable.nndist {f g : β → α} (hf : Measurable f) (hg : Measurable g) :
Measurable fun b => nndist (f b) (g b) :=
(@continuous_nndist α _).measurable2 hf hg
end
end PseudoMetricSpace
section PseudoEMetricSpace
variable [PseudoEMetricSpace α] [MeasurableSpace α] [OpensMeasurableSpace α]
variable [MeasurableSpace β] {x : α} {ε : ℝ≥0∞}
open EMetric
@[measurability]
theorem measurableSet_eball : MeasurableSet (EMetric.ball x ε) :=
EMetric.isOpen_ball.measurableSet
@[measurability, fun_prop]
theorem measurable_edist_right : Measurable (edist x) :=
(continuous_const.edist continuous_id).measurable
@[measurability, fun_prop]
theorem measurable_edist_left : Measurable fun y => edist y x :=
(continuous_id.edist continuous_const).measurable
@[measurability]
theorem measurable_infEdist {s : Set α} : Measurable fun x => infEdist x s :=
continuous_infEdist.measurable
@[measurability, fun_prop]
theorem Measurable.infEdist {f : β → α} (hf : Measurable f) {s : Set α} :
Measurable fun x => infEdist (f x) s :=
measurable_infEdist.comp hf
open Metric EMetric
/-- If a set has a closed thickening with finite measure, then the measure of its `r`-closed
thickenings converges to the measure of its closure as `r` tends to `0`. -/
theorem tendsto_measure_cthickening {μ : Measure α} {s : Set α}
(hs : ∃ R > 0, μ (cthickening R s) ≠ ∞) :
Tendsto (fun r => μ (cthickening r s)) (𝓝 0) (𝓝 (μ (closure s))) := by
have A : Tendsto (fun r => μ (cthickening r s)) (𝓝[Ioi 0] 0) (𝓝 (μ (closure s))) := by
rw [closure_eq_iInter_cthickening]
exact
tendsto_measure_biInter_gt (fun r _ => isClosed_cthickening.nullMeasurableSet)
(fun i j _ ij => cthickening_mono ij _) hs
have B : Tendsto (fun r => μ (cthickening r s)) (𝓝[Iic 0] 0) (𝓝 (μ (closure s))) := by
apply Tendsto.congr' _ tendsto_const_nhds
filter_upwards [self_mem_nhdsWithin (α := ℝ)] with _ hr
rw [cthickening_of_nonpos hr]
convert B.sup A
exact (nhdsLE_sup_nhdsGT 0).symm
/-- If a closed set has a closed thickening with finite measure, then the measure of its closed
`r`-thickenings converge to its measure as `r` tends to `0`. -/
theorem tendsto_measure_cthickening_of_isClosed {μ : Measure α} {s : Set α}
(hs : ∃ R > 0, μ (cthickening R s) ≠ ∞) (h's : IsClosed s) :
Tendsto (fun r => μ (cthickening r s)) (𝓝 0) (𝓝 (μ s)) := by
convert tendsto_measure_cthickening hs
exact h's.closure_eq.symm
/-- If a set has a thickening with finite measure, then the measures of its `r`-thickenings
converge to the measure of its closure as `r > 0` tends to `0`. -/
theorem tendsto_measure_thickening {μ : Measure α} {s : Set α}
(hs : ∃ R > 0, μ (thickening R s) ≠ ∞) :
Tendsto (fun r => μ (thickening r s)) (𝓝[>] 0) (𝓝 (μ (closure s))) := by
rw [closure_eq_iInter_thickening]
exact tendsto_measure_biInter_gt (fun r _ => isOpen_thickening.nullMeasurableSet)
(fun i j _ ij => thickening_mono ij _) hs
/-- If a closed set has a thickening with finite measure, then the measure of its
`r`-thickenings converge to its measure as `r > 0` tends to `0`. -/
theorem tendsto_measure_thickening_of_isClosed {μ : Measure α} {s : Set α}
(hs : ∃ R > 0, μ (thickening R s) ≠ ∞) (h's : IsClosed s) :
Tendsto (fun r => μ (thickening r s)) (𝓝[>] 0) (𝓝 (μ s)) := by
convert tendsto_measure_thickening hs
exact h's.closure_eq.symm
variable [SecondCountableTopology α]
@[measurability]
theorem measurable_edist : Measurable fun p : α × α => edist p.1 p.2 :=
continuous_edist.measurable
@[measurability, fun_prop]
theorem Measurable.edist {f g : β → α} (hf : Measurable f) (hg : Measurable g) :
Measurable fun b => edist (f b) (g b) :=
(@continuous_edist α _).measurable2 hf hg
@[measurability, fun_prop]
theorem AEMeasurable.edist {f g : β → α} {μ : Measure β} (hf : AEMeasurable f μ)
(hg : AEMeasurable g μ) : AEMeasurable (fun a => edist (f a) (g a)) μ :=
(@continuous_edist α _).aemeasurable2 hf hg
end PseudoEMetricSpace
/-- Given a compact set in a proper space, the measure of its `r`-closed thickenings converges to
its measure as `r` tends to `0`. -/
theorem tendsto_measure_cthickening_of_isCompact [MetricSpace α] [MeasurableSpace α]
[OpensMeasurableSpace α] [ProperSpace α] {μ : Measure α} [IsFiniteMeasureOnCompacts μ]
{s : Set α} (hs : IsCompact s) :
Tendsto (fun r => μ (Metric.cthickening r s)) (𝓝 0) (𝓝 (μ s)) :=
tendsto_measure_cthickening_of_isClosed
⟨1, zero_lt_one, hs.isBounded.cthickening.measure_lt_top.ne⟩ hs.isClosed
/-- If a measurable space is countably generated and separates points, it arises as
the borel sets of some second countable t4 topology (i.e. a separable metrizable one). -/
theorem exists_borelSpace_of_countablyGenerated_of_separatesPoints (α : Type*)
[m : MeasurableSpace α] [CountablyGenerated α] [SeparatesPoints α] :
∃ _ : TopologicalSpace α, SecondCountableTopology α ∧ T4Space α ∧ BorelSpace α := by
rcases measurableEquiv_nat_bool_of_countablyGenerated α with ⟨s, ⟨f⟩⟩
letI := induced f inferInstance
let F := f.toEquiv.toHomeomorphOfIsInducing <| .induced _
exact ⟨inferInstance, F.secondCountableTopology, F.symm.t4Space,
f.measurableEmbedding.borelSpace F.isInducing⟩
/-- If a measurable space on `α` is countably generated and separates points, there is some
second countable t4 topology on `α` (i.e. a separable metrizable one) for which every
open set is measurable. -/
theorem exists_opensMeasurableSpace_of_countablySeparated (α : Type*)
[m : MeasurableSpace α] [CountablySeparated α] :
∃ _ : TopologicalSpace α, SecondCountableTopology α ∧ T4Space α ∧ OpensMeasurableSpace α := by
rcases exists_countablyGenerated_le_of_countablySeparated α with ⟨m', _, _, m'le⟩
rcases exists_borelSpace_of_countablyGenerated_of_separatesPoints (m := m') with ⟨τ, _, _, τm'⟩
exact ⟨τ, ‹_›, ‹_›, @OpensMeasurableSpace.mk _ _ m (τm'.measurable_eq.symm.le.trans m'le)⟩
section ContinuousENorm
variable {ε : Type*} [MeasurableSpace ε] [TopologicalSpace ε] [ContinuousENorm ε]
| [OpensMeasurableSpace ε] [MeasurableSpace β]
@[measurability, fun_prop]
lemma measurable_enorm : Measurable (enorm : ε → ℝ≥0∞) := continuous_enorm.measurable
@[measurability, fun_prop]
protected lemma Measurable.enorm {f : β → ε} (hf : Measurable f) : Measurable (‖f ·‖ₑ) :=
measurable_enorm.comp hf
| Mathlib/MeasureTheory/Constructions/BorelSpace/Metric.lean | 217 | 224 |
/-
Copyright (c) 2020 Damiano Testa. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Damiano Testa
-/
import Mathlib.Algebra.Polynomial.Degree.TrailingDegree
import Mathlib.Algebra.Polynomial.EraseLead
/-!
# Reverse of a univariate polynomial
The main definition is `reverse`. Applying `reverse` to a polynomial `f : R[X]` produces
the polynomial with a reversed list of coefficients, equivalent to `X^f.natDegree * f(1/X)`.
The main result is that `reverse (f * g) = reverse f * reverse g`, provided the leading
coefficients of `f` and `g` do not multiply to zero.
-/
namespace Polynomial
open Finsupp Finset
open scoped Polynomial
section Semiring
variable {R : Type*} [Semiring R] {f : R[X]}
/-- If `i ≤ N`, then `revAtFun N i` returns `N - i`, otherwise it returns `i`.
This is the map used by the embedding `revAt`.
-/
def revAtFun (N i : ℕ) : ℕ :=
ite (i ≤ N) (N - i) i
theorem revAtFun_invol {N i : ℕ} : revAtFun N (revAtFun N i) = i := by
unfold revAtFun
split_ifs with h j
· exact tsub_tsub_cancel_of_le h
· exfalso
apply j
exact Nat.sub_le N i
· rfl
theorem revAtFun_inj {N : ℕ} : Function.Injective (revAtFun N) := by
intro a b hab
rw [← @revAtFun_invol N a, hab, revAtFun_invol]
/-- If `i ≤ N`, then `revAt N i` returns `N - i`, otherwise it returns `i`.
| Essentially, this embedding is only used for `i ≤ N`.
The advantage of `revAt N i` over `N - i` is that `revAt` is an involution.
-/
| Mathlib/Algebra/Polynomial/Reverse.lean | 50 | 52 |
/-
Copyright (c) 2021 Hunter Monroe. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Hunter Monroe, Kyle Miller
-/
import Mathlib.Combinatorics.SimpleGraph.Dart
import Mathlib.Data.FunLike.Fintype
import Mathlib.Logic.Embedding.Set
/-!
# Maps between graphs
This file defines two functions and three structures relating graphs.
The structures directly correspond to the classification of functions as
injective, surjective and bijective, and have corresponding notation.
## Main definitions
* `SimpleGraph.map`: the graph obtained by pushing the adjacency relation through
an injective function between vertex types.
* `SimpleGraph.comap`: the graph obtained by pulling the adjacency relation behind
an arbitrary function between vertex types.
* `SimpleGraph.induce`: the subgraph induced by the given vertex set, a wrapper around `comap`.
* `SimpleGraph.spanningCoe`: the supergraph without any additional edges, a wrapper around `map`.
* `SimpleGraph.Hom`, `G →g H`: a graph homomorphism from `G` to `H`.
* `SimpleGraph.Embedding`, `G ↪g H`: a graph embedding of `G` in `H`.
* `SimpleGraph.Iso`, `G ≃g H`: a graph isomorphism between `G` and `H`.
Note that a graph embedding is a stronger notion than an injective graph homomorphism,
since its image is an induced subgraph.
## Implementation notes
Morphisms of graphs are abbreviations for `RelHom`, `RelEmbedding` and `RelIso`.
To make use of pre-existing simp lemmas, definitions involving morphisms are
abbreviations as well.
-/
open Function
namespace SimpleGraph
variable {V W X : Type*} (G : SimpleGraph V) (G' : SimpleGraph W) {u v : V}
/-! ## Map and comap -/
/-- Given an injective function, there is a covariant induced map on graphs by pushing forward
the adjacency relation.
This is injective (see `SimpleGraph.map_injective`). -/
protected def map (f : V ↪ W) (G : SimpleGraph V) : SimpleGraph W where
Adj := Relation.Map G.Adj f f
symm a b := by -- Porting note: `obviously` used to handle this
rintro ⟨v, w, h, rfl, rfl⟩
use w, v, h.symm, rfl
loopless a := by -- Porting note: `obviously` used to handle this
rintro ⟨v, w, h, rfl, h'⟩
exact h.ne (f.injective h'.symm)
instance instDecidableMapAdj {f : V ↪ W} {a b} [Decidable (Relation.Map G.Adj f f a b)] :
Decidable ((G.map f).Adj a b) := ‹Decidable (Relation.Map G.Adj f f a b)›
@[simp]
theorem map_adj (f : V ↪ W) (G : SimpleGraph V) (u v : W) :
(G.map f).Adj u v ↔ ∃ u' v' : V, G.Adj u' v' ∧ f u' = u ∧ f v' = v :=
Iff.rfl
lemma map_adj_apply {G : SimpleGraph V} {f : V ↪ W} {a b : V} :
(G.map f).Adj (f a) (f b) ↔ G.Adj a b := by simp
theorem map_monotone (f : V ↪ W) : Monotone (SimpleGraph.map f) := by
rintro G G' h _ _ ⟨u, v, ha, rfl, rfl⟩
exact ⟨_, _, h ha, rfl, rfl⟩
@[simp] lemma map_id : G.map (Function.Embedding.refl _) = G :=
SimpleGraph.ext <| Relation.map_id_id _
@[simp] lemma map_map (f : V ↪ W) (g : W ↪ X) : (G.map f).map g = G.map (f.trans g) :=
SimpleGraph.ext <| Relation.map_map _ _ _ _ _
/-- Given a function, there is a contravariant induced map on graphs by pulling back the
adjacency relation.
This is one of the ways of creating induced graphs. See `SimpleGraph.induce` for a wrapper.
This is surjective when `f` is injective (see `SimpleGraph.comap_surjective`). -/
protected def comap (f : V → W) (G : SimpleGraph W) : SimpleGraph V where
Adj u v := G.Adj (f u) (f v)
symm _ _ h := h.symm
loopless _ := G.loopless _
@[simp] lemma comap_adj {G : SimpleGraph W} {f : V → W} :
(G.comap f).Adj u v ↔ G.Adj (f u) (f v) := Iff.rfl
@[simp] lemma comap_id {G : SimpleGraph V} : G.comap id = G := SimpleGraph.ext rfl
@[simp] lemma comap_comap {G : SimpleGraph X} (f : V → W) (g : W → X) :
(G.comap g).comap f = G.comap (g ∘ f) := rfl
instance instDecidableComapAdj (f : V → W) (G : SimpleGraph W) [DecidableRel G.Adj] :
DecidableRel (G.comap f).Adj := fun _ _ ↦ ‹DecidableRel G.Adj› _ _
lemma comap_symm (G : SimpleGraph V) (e : V ≃ W) :
G.comap e.symm.toEmbedding = G.map e.toEmbedding := by
ext; simp only [Equiv.apply_eq_iff_eq_symm_apply, comap_adj, map_adj, Equiv.toEmbedding_apply,
exists_eq_right_right, exists_eq_right]
lemma map_symm (G : SimpleGraph W) (e : V ≃ W) :
G.map e.symm.toEmbedding = G.comap e.toEmbedding := by rw [← comap_symm, e.symm_symm]
theorem comap_monotone (f : V ↪ W) : Monotone (SimpleGraph.comap f) := by
intro G G' h _ _ ha
exact h ha
@[simp]
theorem comap_map_eq (f : V ↪ W) (G : SimpleGraph V) : (G.map f).comap f = G := by
ext
| simp
| Mathlib/Combinatorics/SimpleGraph/Maps.lean | 119 | 120 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Jens Wagemaker
-/
import Mathlib.Algebra.MonoidAlgebra.Degree
import Mathlib.Algebra.Order.Ring.WithTop
import Mathlib.Algebra.Polynomial.Basic
import Mathlib.Data.Nat.Cast.WithTop
import Mathlib.Data.Nat.SuccPred
import Mathlib.Order.SuccPred.WithBot
/-!
# Degree of univariate polynomials
## Main definitions
* `Polynomial.degree`: the degree of a polynomial, where `0` has degree `⊥`
* `Polynomial.natDegree`: the degree of a polynomial, where `0` has degree `0`
* `Polynomial.leadingCoeff`: the leading coefficient of a polynomial
* `Polynomial.Monic`: a polynomial is monic if its leading coefficient is 0
* `Polynomial.nextCoeff`: the next coefficient after the leading coefficient
## Main results
* `Polynomial.degree_eq_natDegree`: the degree and natDegree coincide for nonzero polynomials
-/
noncomputable section
open Finsupp Finset
open Polynomial
namespace Polynomial
universe u v
variable {R : Type u} {S : Type v} {a b c d : R} {n m : ℕ}
section Semiring
variable [Semiring R] {p q r : R[X]}
/-- `degree p` is the degree of the polynomial `p`, i.e. the largest `X`-exponent in `p`.
`degree p = some n` when `p ≠ 0` and `n` is the highest power of `X` that appears in `p`, otherwise
`degree 0 = ⊥`. -/
def degree (p : R[X]) : WithBot ℕ :=
p.support.max
/-- `natDegree p` forces `degree p` to ℕ, by defining `natDegree 0 = 0`. -/
def natDegree (p : R[X]) : ℕ :=
(degree p).unbotD 0
/-- `leadingCoeff p` gives the coefficient of the highest power of `X` in `p`. -/
def leadingCoeff (p : R[X]) : R :=
coeff p (natDegree p)
/-- a polynomial is `Monic` if its leading coefficient is 1 -/
def Monic (p : R[X]) :=
leadingCoeff p = (1 : R)
theorem Monic.def : Monic p ↔ leadingCoeff p = 1 :=
Iff.rfl
instance Monic.decidable [DecidableEq R] : Decidable (Monic p) := by unfold Monic; infer_instance
@[simp]
theorem Monic.leadingCoeff {p : R[X]} (hp : p.Monic) : leadingCoeff p = 1 :=
hp
theorem Monic.coeff_natDegree {p : R[X]} (hp : p.Monic) : p.coeff p.natDegree = 1 :=
hp
@[simp]
theorem degree_zero : degree (0 : R[X]) = ⊥ :=
rfl
@[simp]
theorem natDegree_zero : natDegree (0 : R[X]) = 0 :=
rfl
@[simp]
theorem coeff_natDegree : coeff p (natDegree p) = leadingCoeff p :=
rfl
@[simp]
theorem degree_eq_bot : degree p = ⊥ ↔ p = 0 :=
⟨fun h => support_eq_empty.1 (Finset.max_eq_bot.1 h), fun h => h.symm ▸ rfl⟩
theorem degree_ne_bot : degree p ≠ ⊥ ↔ p ≠ 0 := degree_eq_bot.not
theorem degree_eq_natDegree (hp : p ≠ 0) : degree p = (natDegree p : WithBot ℕ) := by
let ⟨n, hn⟩ := not_forall.1 (mt Option.eq_none_iff_forall_not_mem.2 (mt degree_eq_bot.1 hp))
have hn : degree p = some n := Classical.not_not.1 hn
rw [natDegree, hn]; rfl
theorem degree_eq_iff_natDegree_eq {p : R[X]} {n : ℕ} (hp : p ≠ 0) :
p.degree = n ↔ p.natDegree = n := by rw [degree_eq_natDegree hp]; exact WithBot.coe_eq_coe
theorem degree_eq_iff_natDegree_eq_of_pos {p : R[X]} {n : ℕ} (hn : 0 < n) :
p.degree = n ↔ p.natDegree = n := by
obtain rfl|h := eq_or_ne p 0
· simp [hn.ne]
· exact degree_eq_iff_natDegree_eq h
theorem natDegree_eq_of_degree_eq_some {p : R[X]} {n : ℕ} (h : degree p = n) : natDegree p = n := by
rw [natDegree, h, Nat.cast_withBot, WithBot.unbotD_coe]
theorem degree_ne_of_natDegree_ne {n : ℕ} : p.natDegree ≠ n → degree p ≠ n :=
mt natDegree_eq_of_degree_eq_some
@[simp]
theorem degree_le_natDegree : degree p ≤ natDegree p :=
WithBot.giUnbotDBot.gc.le_u_l _
theorem natDegree_eq_of_degree_eq [Semiring S] {q : S[X]} (h : degree p = degree q) :
natDegree p = natDegree q := by unfold natDegree; rw [h]
theorem le_degree_of_ne_zero (h : coeff p n ≠ 0) : (n : WithBot ℕ) ≤ degree p := by
rw [Nat.cast_withBot]
exact Finset.le_sup (mem_support_iff.2 h)
theorem degree_mono [Semiring S] {f : R[X]} {g : S[X]} (h : f.support ⊆ g.support) :
f.degree ≤ g.degree :=
Finset.sup_mono h
theorem degree_le_degree (h : coeff q (natDegree p) ≠ 0) : degree p ≤ degree q := by
by_cases hp : p = 0
· rw [hp, degree_zero]
exact bot_le
· rw [degree_eq_natDegree hp]
exact le_degree_of_ne_zero h
theorem natDegree_le_iff_degree_le {n : ℕ} : natDegree p ≤ n ↔ degree p ≤ n :=
WithBot.unbotD_le_iff (fun _ ↦ bot_le)
theorem natDegree_lt_iff_degree_lt (hp : p ≠ 0) : p.natDegree < n ↔ p.degree < ↑n :=
WithBot.unbotD_lt_iff (absurd · (degree_eq_bot.not.mpr hp))
alias ⟨degree_le_of_natDegree_le, natDegree_le_of_degree_le⟩ := natDegree_le_iff_degree_le
theorem natDegree_le_natDegree [Semiring S] {q : S[X]} (hpq : p.degree ≤ q.degree) :
p.natDegree ≤ q.natDegree :=
WithBot.giUnbotDBot.gc.monotone_l hpq
@[simp]
theorem degree_C (ha : a ≠ 0) : degree (C a) = (0 : WithBot ℕ) := by
rw [degree, ← monomial_zero_left, support_monomial 0 ha, max_eq_sup_coe, sup_singleton,
WithBot.coe_zero]
theorem degree_C_le : degree (C a) ≤ 0 := by
by_cases h : a = 0
· rw [h, C_0]
exact bot_le
· rw [degree_C h]
theorem degree_C_lt : degree (C a) < 1 :=
degree_C_le.trans_lt <| WithBot.coe_lt_coe.mpr zero_lt_one
theorem degree_one_le : degree (1 : R[X]) ≤ (0 : WithBot ℕ) := by rw [← C_1]; exact degree_C_le
@[simp]
theorem natDegree_C (a : R) : natDegree (C a) = 0 := by
by_cases ha : a = 0
· have : C a = 0 := by rw [ha, C_0]
rw [natDegree, degree_eq_bot.2 this, WithBot.unbotD_bot]
· rw [natDegree, degree_C ha, WithBot.unbotD_zero]
@[simp]
theorem natDegree_one : natDegree (1 : R[X]) = 0 :=
natDegree_C 1
@[simp]
theorem natDegree_natCast (n : ℕ) : natDegree (n : R[X]) = 0 := by
simp only [← C_eq_natCast, natDegree_C]
@[simp]
theorem natDegree_ofNat (n : ℕ) [Nat.AtLeastTwo n] :
natDegree (ofNat(n) : R[X]) = 0 :=
natDegree_natCast _
theorem degree_natCast_le (n : ℕ) : degree (n : R[X]) ≤ 0 := degree_le_of_natDegree_le (by simp)
@[simp]
theorem degree_monomial (n : ℕ) (ha : a ≠ 0) : degree (monomial n a) = n := by
rw [degree, support_monomial n ha, max_singleton, Nat.cast_withBot]
@[simp]
theorem degree_C_mul_X_pow (n : ℕ) (ha : a ≠ 0) : degree (C a * X ^ n) = n := by
rw [C_mul_X_pow_eq_monomial, degree_monomial n ha]
theorem degree_C_mul_X (ha : a ≠ 0) : degree (C a * X) = 1 := by
simpa only [pow_one] using degree_C_mul_X_pow 1 ha
theorem degree_monomial_le (n : ℕ) (a : R) : degree (monomial n a) ≤ n :=
letI := Classical.decEq R
if h : a = 0 then by rw [h, (monomial n).map_zero, degree_zero]; exact bot_le
else le_of_eq (degree_monomial n h)
theorem degree_C_mul_X_pow_le (n : ℕ) (a : R) : degree (C a * X ^ n) ≤ n := by
rw [C_mul_X_pow_eq_monomial]
apply degree_monomial_le
theorem degree_C_mul_X_le (a : R) : degree (C a * X) ≤ 1 := by
simpa only [pow_one] using degree_C_mul_X_pow_le 1 a
@[simp]
theorem natDegree_C_mul_X_pow (n : ℕ) (a : R) (ha : a ≠ 0) : natDegree (C a * X ^ n) = n :=
natDegree_eq_of_degree_eq_some (degree_C_mul_X_pow n ha)
@[simp]
theorem natDegree_C_mul_X (a : R) (ha : a ≠ 0) : natDegree (C a * X) = 1 := by
simpa only [pow_one] using natDegree_C_mul_X_pow 1 a ha
@[simp]
theorem natDegree_monomial [DecidableEq R] (i : ℕ) (r : R) :
natDegree (monomial i r) = if r = 0 then 0 else i := by
split_ifs with hr
· simp [hr]
· rw [← C_mul_X_pow_eq_monomial, natDegree_C_mul_X_pow i r hr]
theorem natDegree_monomial_le (a : R) {m : ℕ} : (monomial m a).natDegree ≤ m := by
classical
rw [Polynomial.natDegree_monomial]
split_ifs
exacts [Nat.zero_le _, le_rfl]
theorem natDegree_monomial_eq (i : ℕ) {r : R} (r0 : r ≠ 0) : (monomial i r).natDegree = i :=
letI := Classical.decEq R
Eq.trans (natDegree_monomial _ _) (if_neg r0)
theorem coeff_ne_zero_of_eq_degree (hn : degree p = n) : coeff p n ≠ 0 := fun h =>
mem_support_iff.mp (mem_of_max hn) h
theorem degree_X_pow_le (n : ℕ) : degree (X ^ n : R[X]) ≤ n := by
simpa only [C_1, one_mul] using degree_C_mul_X_pow_le n (1 : R)
theorem degree_X_le : degree (X : R[X]) ≤ 1 :=
degree_monomial_le _ _
theorem natDegree_X_le : (X : R[X]).natDegree ≤ 1 :=
natDegree_le_of_degree_le degree_X_le
theorem withBotSucc_degree_eq_natDegree_add_one (h : p ≠ 0) : p.degree.succ = p.natDegree + 1 := by
rw [degree_eq_natDegree h]
exact WithBot.succ_coe p.natDegree
end Semiring
section NonzeroSemiring
variable [Semiring R] [Nontrivial R] {p q : R[X]}
@[simp]
theorem degree_one : degree (1 : R[X]) = (0 : WithBot ℕ) :=
degree_C one_ne_zero
@[simp]
theorem degree_X : degree (X : R[X]) = 1 :=
degree_monomial _ one_ne_zero
@[simp]
theorem natDegree_X : (X : R[X]).natDegree = 1 :=
natDegree_eq_of_degree_eq_some degree_X
end NonzeroSemiring
section Ring
variable [Ring R]
@[simp]
theorem degree_neg (p : R[X]) : degree (-p) = degree p := by unfold degree; rw [support_neg]
theorem degree_neg_le_of_le {a : WithBot ℕ} {p : R[X]} (hp : degree p ≤ a) : degree (-p) ≤ a :=
p.degree_neg.le.trans hp
@[simp]
theorem natDegree_neg (p : R[X]) : natDegree (-p) = natDegree p := by simp [natDegree]
theorem natDegree_neg_le_of_le {p : R[X]} (hp : natDegree p ≤ m) : natDegree (-p) ≤ m :=
(natDegree_neg p).le.trans hp
@[simp]
theorem natDegree_intCast (n : ℤ) : natDegree (n : R[X]) = 0 := by
rw [← C_eq_intCast, natDegree_C]
theorem degree_intCast_le (n : ℤ) : degree (n : R[X]) ≤ 0 := degree_le_of_natDegree_le (by simp)
@[simp]
theorem leadingCoeff_neg (p : R[X]) : (-p).leadingCoeff = -p.leadingCoeff := by
rw [leadingCoeff, leadingCoeff, natDegree_neg, coeff_neg]
end Ring
section Semiring
variable [Semiring R] {p : R[X]}
/-- The second-highest coefficient, or 0 for constants -/
def nextCoeff (p : R[X]) : R :=
if p.natDegree = 0 then 0 else p.coeff (p.natDegree - 1)
lemma nextCoeff_eq_zero :
p.nextCoeff = 0 ↔ p.natDegree = 0 ∨ 0 < p.natDegree ∧ p.coeff (p.natDegree - 1) = 0 := by
simp [nextCoeff, or_iff_not_imp_left, pos_iff_ne_zero]; aesop
lemma nextCoeff_ne_zero : p.nextCoeff ≠ 0 ↔ p.natDegree ≠ 0 ∧ p.coeff (p.natDegree - 1) ≠ 0 := by
simp [nextCoeff]
@[simp]
theorem nextCoeff_C_eq_zero (c : R) : nextCoeff (C c) = 0 := by
rw [nextCoeff]
simp
theorem nextCoeff_of_natDegree_pos (hp : 0 < p.natDegree) :
nextCoeff p = p.coeff (p.natDegree - 1) := by
rw [nextCoeff, if_neg]
contrapose! hp
simpa
variable {p q : R[X]} {ι : Type*}
theorem degree_add_le (p q : R[X]) : degree (p + q) ≤ max (degree p) (degree q) := by
simpa only [degree, ← support_toFinsupp, toFinsupp_add]
using AddMonoidAlgebra.sup_support_add_le _ _ _
theorem degree_add_le_of_degree_le {p q : R[X]} {n : ℕ} (hp : degree p ≤ n) (hq : degree q ≤ n) :
degree (p + q) ≤ n :=
(degree_add_le p q).trans <| max_le hp hq
theorem degree_add_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p + q) ≤ max a b :=
(p.degree_add_le q).trans <| max_le_max ‹_› ‹_›
theorem natDegree_add_le (p q : R[X]) : natDegree (p + q) ≤ max (natDegree p) (natDegree q) := by
rcases le_max_iff.1 (degree_add_le p q) with h | h <;> simp [natDegree_le_natDegree h]
theorem natDegree_add_le_of_degree_le {p q : R[X]} {n : ℕ} (hp : natDegree p ≤ n)
(hq : natDegree q ≤ n) : natDegree (p + q) ≤ n :=
(natDegree_add_le p q).trans <| max_le hp hq
theorem natDegree_add_le_of_le (hp : natDegree p ≤ m) (hq : natDegree q ≤ n) :
natDegree (p + q) ≤ max m n :=
(p.natDegree_add_le q).trans <| max_le_max ‹_› ‹_›
@[simp]
theorem leadingCoeff_zero : leadingCoeff (0 : R[X]) = 0 :=
rfl
@[simp]
theorem leadingCoeff_eq_zero : leadingCoeff p = 0 ↔ p = 0 :=
⟨fun h =>
Classical.by_contradiction fun hp =>
mt mem_support_iff.1 (Classical.not_not.2 h) (mem_of_max (degree_eq_natDegree hp)),
fun h => h.symm ▸ leadingCoeff_zero⟩
theorem leadingCoeff_ne_zero : leadingCoeff p ≠ 0 ↔ p ≠ 0 := by rw [Ne, leadingCoeff_eq_zero]
theorem leadingCoeff_eq_zero_iff_deg_eq_bot : leadingCoeff p = 0 ↔ degree p = ⊥ := by
rw [leadingCoeff_eq_zero, degree_eq_bot]
theorem natDegree_C_mul_X_pow_le (a : R) (n : ℕ) : natDegree (C a * X ^ n) ≤ n :=
natDegree_le_iff_degree_le.2 <| degree_C_mul_X_pow_le _ _
theorem degree_erase_le (p : R[X]) (n : ℕ) : degree (p.erase n) ≤ degree p := by
rcases p with ⟨p⟩
simp only [erase_def, degree, coeff, support]
apply sup_mono
rw [Finsupp.support_erase]
apply Finset.erase_subset
theorem degree_erase_lt (hp : p ≠ 0) : degree (p.erase (natDegree p)) < degree p := by
apply lt_of_le_of_ne (degree_erase_le _ _)
rw [degree_eq_natDegree hp, degree, support_erase]
exact fun h => not_mem_erase _ _ (mem_of_max h)
theorem degree_update_le (p : R[X]) (n : ℕ) (a : R) : degree (p.update n a) ≤ max (degree p) n := by
classical
rw [degree, support_update]
split_ifs
· exact (Finset.max_mono (erase_subset _ _)).trans (le_max_left _ _)
· rw [max_insert, max_comm]
exact le_rfl
theorem degree_sum_le (s : Finset ι) (f : ι → R[X]) :
degree (∑ i ∈ s, f i) ≤ s.sup fun b => degree (f b) :=
Finset.cons_induction_on s (by simp only [sum_empty, sup_empty, degree_zero, le_refl])
fun a s has ih =>
calc
degree (∑ i ∈ cons a s has, f i) ≤ max (degree (f a)) (degree (∑ i ∈ s, f i)) := by
rw [Finset.sum_cons]; exact degree_add_le _ _
_ ≤ _ := by rw [sup_cons]; exact max_le_max le_rfl ih
theorem degree_mul_le (p q : R[X]) : degree (p * q) ≤ degree p + degree q := by
simpa only [degree, ← support_toFinsupp, toFinsupp_mul]
using AddMonoidAlgebra.sup_support_mul_le (WithBot.coe_add _ _).le _ _
theorem degree_mul_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p * q) ≤ a + b :=
(p.degree_mul_le _).trans <| add_le_add ‹_› ‹_›
theorem degree_pow_le (p : R[X]) : ∀ n : ℕ, degree (p ^ n) ≤ n • degree p
| 0 => by rw [pow_zero, zero_nsmul]; exact degree_one_le
| n + 1 =>
calc
degree (p ^ (n + 1)) ≤ degree (p ^ n) + degree p := by
rw [pow_succ]; exact degree_mul_le _ _
_ ≤ _ := by rw [succ_nsmul]; exact add_le_add_right (degree_pow_le _ _) _
theorem degree_pow_le_of_le {a : WithBot ℕ} (b : ℕ) (hp : degree p ≤ a) :
degree (p ^ b) ≤ b * a := by
induction b with
| zero => simp [degree_one_le]
| succ n hn =>
rw [Nat.cast_succ, add_mul, one_mul, pow_succ]
exact degree_mul_le_of_le hn hp
@[simp]
theorem leadingCoeff_monomial (a : R) (n : ℕ) : leadingCoeff (monomial n a) = a := by
classical
by_cases ha : a = 0
· simp only [ha, (monomial n).map_zero, leadingCoeff_zero]
· rw [leadingCoeff, natDegree_monomial, if_neg ha, coeff_monomial]
simp
theorem leadingCoeff_C_mul_X_pow (a : R) (n : ℕ) : leadingCoeff (C a * X ^ n) = a := by
rw [C_mul_X_pow_eq_monomial, leadingCoeff_monomial]
theorem leadingCoeff_C_mul_X (a : R) : leadingCoeff (C a * X) = a := by
simpa only [pow_one] using leadingCoeff_C_mul_X_pow a 1
@[simp]
theorem leadingCoeff_C (a : R) : leadingCoeff (C a) = a :=
leadingCoeff_monomial a 0
theorem leadingCoeff_X_pow (n : ℕ) : leadingCoeff ((X : R[X]) ^ n) = 1 := by
simpa only [C_1, one_mul] using leadingCoeff_C_mul_X_pow (1 : R) n
theorem leadingCoeff_X : leadingCoeff (X : R[X]) = 1 := by
simpa only [pow_one] using @leadingCoeff_X_pow R _ 1
@[simp]
theorem monic_X_pow (n : ℕ) : Monic (X ^ n : R[X]) :=
leadingCoeff_X_pow n
@[simp]
theorem monic_X : Monic (X : R[X]) :=
leadingCoeff_X
theorem leadingCoeff_one : leadingCoeff (1 : R[X]) = 1 :=
leadingCoeff_C 1
@[simp]
theorem monic_one : Monic (1 : R[X]) :=
leadingCoeff_C _
theorem Monic.ne_zero {R : Type*} [Semiring R] [Nontrivial R] {p : R[X]} (hp : p.Monic) :
p ≠ 0 := by
rintro rfl
simp [Monic] at hp
theorem Monic.ne_zero_of_ne (h : (0 : R) ≠ 1) {p : R[X]} (hp : p.Monic) : p ≠ 0 := by
nontriviality R
exact hp.ne_zero
theorem Monic.ne_zero_of_polynomial_ne {r} (hp : Monic p) (hne : q ≠ r) : p ≠ 0 :=
haveI := Nontrivial.of_polynomial_ne hne
hp.ne_zero
theorem natDegree_mul_le {p q : R[X]} : natDegree (p * q) ≤ natDegree p + natDegree q := by
apply natDegree_le_of_degree_le
apply le_trans (degree_mul_le p q)
rw [Nat.cast_add]
apply add_le_add <;> apply degree_le_natDegree
theorem natDegree_mul_le_of_le (hp : natDegree p ≤ m) (hg : natDegree q ≤ n) :
natDegree (p * q) ≤ m + n :=
natDegree_mul_le.trans <| add_le_add ‹_› ‹_›
theorem natDegree_pow_le {p : R[X]} {n : ℕ} : (p ^ n).natDegree ≤ n * p.natDegree := by
induction n with
| zero => simp
| succ i hi =>
rw [pow_succ, Nat.succ_mul]
apply le_trans natDegree_mul_le (add_le_add_right hi _)
theorem natDegree_pow_le_of_le (n : ℕ) (hp : natDegree p ≤ m) :
natDegree (p ^ n) ≤ n * m :=
natDegree_pow_le.trans (Nat.mul_le_mul le_rfl ‹_›)
theorem natDegree_eq_zero_iff_degree_le_zero : p.natDegree = 0 ↔ p.degree ≤ 0 := by
rw [← nonpos_iff_eq_zero, natDegree_le_iff_degree_le, Nat.cast_zero]
theorem degree_zero_le : degree (0 : R[X]) ≤ 0 := natDegree_eq_zero_iff_degree_le_zero.mp rfl
theorem degree_le_iff_coeff_zero (f : R[X]) (n : WithBot ℕ) :
degree f ≤ n ↔ ∀ m : ℕ, n < m → coeff f m = 0 := by
simp only [degree, Finset.max, Finset.sup_le_iff, mem_support_iff, Ne, ← not_le,
not_imp_comm, Nat.cast_withBot]
theorem degree_lt_iff_coeff_zero (f : R[X]) (n : ℕ) :
degree f < n ↔ ∀ m : ℕ, n ≤ m → coeff f m = 0 := by
simp only [degree, Finset.sup_lt_iff (WithBot.bot_lt_coe n), mem_support_iff,
WithBot.coe_lt_coe, ← @not_le ℕ, max_eq_sup_coe, Nat.cast_withBot, Ne, not_imp_not]
theorem natDegree_pos_iff_degree_pos : 0 < natDegree p ↔ 0 < degree p :=
lt_iff_lt_of_le_iff_le natDegree_le_iff_degree_le
end Semiring
section NontrivialSemiring
variable [Semiring R] [Nontrivial R] {p q : R[X]} (n : ℕ)
@[simp]
theorem degree_X_pow : degree ((X : R[X]) ^ n) = n := by
rw [X_pow_eq_monomial, degree_monomial _ (one_ne_zero' R)]
@[simp]
theorem natDegree_X_pow : natDegree ((X : R[X]) ^ n) = n :=
natDegree_eq_of_degree_eq_some (degree_X_pow n)
end NontrivialSemiring
section Ring
variable [Ring R] {p q : R[X]}
theorem degree_sub_le (p q : R[X]) : degree (p - q) ≤ max (degree p) (degree q) := by
simpa only [degree_neg q] using degree_add_le p (-q)
theorem degree_sub_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p - q) ≤ max a b :=
(p.degree_sub_le q).trans <| max_le_max ‹_› ‹_›
theorem natDegree_sub_le (p q : R[X]) : natDegree (p - q) ≤ max (natDegree p) (natDegree q) := by
simpa only [← natDegree_neg q] using natDegree_add_le p (-q)
theorem natDegree_sub_le_of_le (hp : natDegree p ≤ m) (hq : natDegree q ≤ n) :
natDegree (p - q) ≤ max m n :=
(p.natDegree_sub_le q).trans <| max_le_max ‹_› ‹_›
theorem degree_sub_lt (hd : degree p = degree q) (hp0 : p ≠ 0)
(hlc : leadingCoeff p = leadingCoeff q) : degree (p - q) < degree p :=
have hp : monomial (natDegree p) (leadingCoeff p) + p.erase (natDegree p) = p :=
monomial_add_erase _ _
have hq : monomial (natDegree q) (leadingCoeff q) + q.erase (natDegree q) = q :=
monomial_add_erase _ _
have hd' : natDegree p = natDegree q := by unfold natDegree; rw [hd]
have hq0 : q ≠ 0 := mt degree_eq_bot.2 (hd ▸ mt degree_eq_bot.1 hp0)
calc
degree (p - q) = degree (erase (natDegree q) p + -erase (natDegree q) q) := by
conv =>
lhs
rw [← hp, ← hq, hlc, hd', add_sub_add_left_eq_sub, sub_eq_add_neg]
_ ≤ max (degree (erase (natDegree q) p)) (degree (erase (natDegree q) q)) :=
(degree_neg (erase (natDegree q) q) ▸ degree_add_le _ _)
_ < degree p := max_lt_iff.2 ⟨hd' ▸ degree_erase_lt hp0, hd.symm ▸ degree_erase_lt hq0⟩
theorem degree_X_sub_C_le (r : R) : (X - C r).degree ≤ 1 :=
(degree_sub_le _ _).trans (max_le degree_X_le (degree_C_le.trans zero_le_one))
theorem natDegree_X_sub_C_le (r : R) : (X - C r).natDegree ≤ 1 :=
natDegree_le_iff_degree_le.2 <| degree_X_sub_C_le r
end Ring
end Polynomial
| Mathlib/Algebra/Polynomial/Degree/Definitions.lean | 1,156 | 1,157 | |
/-
Copyright (c) 2022 Tian Chen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Tian Chen, Mantas Bakšys
-/
import Mathlib.Algebra.GeomSum
import Mathlib.Algebra.Order.Ring.Basic
import Mathlib.Algebra.Ring.Int.Parity
import Mathlib.Data.Nat.Choose.Sum
import Mathlib.Data.Nat.Prime.Int
import Mathlib.NumberTheory.Padics.PadicVal.Defs
import Mathlib.RingTheory.Ideal.Quotient.Defs
import Mathlib.RingTheory.Ideal.Span
/-!
# Multiplicity in Number Theory
This file contains results in number theory relating to multiplicity.
## Main statements
* `multiplicity.Int.pow_sub_pow` is the lifting the exponent lemma for odd primes.
We also prove several variations of the lemma.
## References
* [Wikipedia, *Lifting-the-exponent lemma*]
(https://en.wikipedia.org/wiki/Lifting-the-exponent_lemma)
-/
open Ideal Ideal.Quotient Finset
variable {R : Type*} {n : ℕ}
section CommRing
variable [CommRing R] {a b x y : R}
theorem dvd_geom_sum₂_iff_of_dvd_sub {x y p : R} (h : p ∣ x - y) :
(p ∣ ∑ i ∈ range n, x ^ i * y ^ (n - 1 - i)) ↔ p ∣ n * y ^ (n - 1) := by
rw [← mem_span_singleton, ← Ideal.Quotient.eq] at h
simp only [← mem_span_singleton, ← eq_zero_iff_mem, RingHom.map_geom_sum₂, h, geom_sum₂_self,
map_mul, map_pow, map_natCast]
theorem dvd_geom_sum₂_iff_of_dvd_sub' {x y p : R} (h : p ∣ x - y) :
(p ∣ ∑ i ∈ range n, x ^ i * y ^ (n - 1 - i)) ↔ p ∣ n * x ^ (n - 1) := by
rw [geom_sum₂_comm, dvd_geom_sum₂_iff_of_dvd_sub]; simpa using h.neg_right
theorem dvd_geom_sum₂_self {x y : R} (h : ↑n ∣ x - y) :
↑n ∣ ∑ i ∈ range n, x ^ i * y ^ (n - 1 - i) :=
(dvd_geom_sum₂_iff_of_dvd_sub h).mpr (dvd_mul_right _ _)
theorem sq_dvd_add_pow_sub_sub (p x : R) (n : ℕ) :
p ^ 2 ∣ (x + p) ^ n - x ^ (n - 1) * p * n - x ^ n := by
rcases n with - | n
· simp only [pow_zero, Nat.cast_zero, sub_zero, sub_self, dvd_zero, mul_zero]
· simp only [Nat.succ_sub_succ_eq_sub, tsub_zero, Nat.cast_succ, add_pow, Finset.sum_range_succ,
Nat.choose_self, Nat.succ_sub _, tsub_self, pow_one, Nat.choose_succ_self_right, pow_zero,
mul_one, Nat.cast_zero, zero_add, Nat.succ_eq_add_one, add_tsub_cancel_left]
suffices p ^ 2 ∣ ∑ i ∈ range n, x ^ i * p ^ (n + 1 - i) * ↑((n + 1).choose i) by
convert this; abel
apply Finset.dvd_sum
intro y hy
calc
p ^ 2 ∣ p ^ (n + 1 - y) :=
pow_dvd_pow p (le_tsub_of_add_le_left (by linarith [Finset.mem_range.mp hy]))
_ ∣ x ^ y * p ^ (n + 1 - y) * ↑((n + 1).choose y) :=
dvd_mul_of_dvd_left (dvd_mul_left _ _) _
theorem not_dvd_geom_sum₂ {p : R} (hp : Prime p) (hxy : p ∣ x - y) (hx : ¬p ∣ x) (hn : ¬p ∣ n) :
¬p ∣ ∑ i ∈ range n, x ^ i * y ^ (n - 1 - i) := fun h =>
hx <|
hp.dvd_of_dvd_pow <| (hp.dvd_or_dvd <| (dvd_geom_sum₂_iff_of_dvd_sub' hxy).mp h).resolve_left hn
variable {p : ℕ} (a b)
theorem odd_sq_dvd_geom_sum₂_sub (hp : Odd p) :
(p : R) ^ 2 ∣ (∑ i ∈ range p, (a + p * b) ^ i * a ^ (p - 1 - i)) - p * a ^ (p - 1) := by
have h1 : ∀ (i : ℕ),
(p : R) ^ 2 ∣ (a + ↑p * b) ^ i - (a ^ (i - 1) * (↑p * b) * i + a ^ i) := by
intro i
calc
↑p ^ 2 ∣ (↑p * b) ^ 2 := by simp only [mul_pow, dvd_mul_right]
_ ∣ (a + ↑p * b) ^ i - (a ^ (i - 1) * (↑p * b) * ↑i + a ^ i) := by
simp only [sq_dvd_add_pow_sub_sub (↑p * b) a i, ← sub_sub]
simp_rw [← mem_span_singleton, ← Ideal.Quotient.eq] at *
let s : R := (p : R)^2
calc
(Ideal.Quotient.mk (span {s})) (∑ i ∈ range p, (a + (p : R) * b) ^ i * a ^ (p - 1 - i)) =
∑ i ∈ Finset.range p,
mk (span {s}) ((a ^ (i - 1) * (↑p * b) * ↑i + a ^ i) * a ^ (p - 1 - i)) := by
simp_rw [s, RingHom.map_geom_sum₂, ← map_pow, h1, ← map_mul]
_ =
mk (span {s})
(∑ x ∈ Finset.range p, a ^ (x - 1) * (a ^ (p - 1 - x) * (↑p * (b * ↑x)))) +
mk (span {s}) (∑ x ∈ Finset.range p, a ^ (x + (p - 1 - x))) := by
ring_nf
simp_rw [← map_sum, sum_add_distrib, map_add]
_ =
mk (span {s})
(∑ x ∈ Finset.range p, a ^ (x - 1) * (a ^ (p - 1 - x) * (↑p * (b * ↑x)))) +
mk (span {s}) (∑ _x ∈ Finset.range p, a ^ (p - 1)) := by
rw [add_right_inj]
have : ∀ (x : ℕ), (hx : x ∈ range p) → a ^ (x + (p - 1 - x)) = a ^ (p - 1) := by
intro x hx
rw [← Nat.add_sub_assoc _ x, Nat.add_sub_cancel_left]
exact Nat.le_sub_one_of_lt (Finset.mem_range.mp hx)
rw [Finset.sum_congr rfl this]
_ =
mk (span {s})
(∑ x ∈ Finset.range p, a ^ (x - 1) * (a ^ (p - 1 - x) * (↑p * (b * ↑x)))) +
mk (span {s}) (↑p * a ^ (p - 1)) := by
simp only [add_right_inj, Finset.sum_const, Finset.card_range, nsmul_eq_mul]
_ =
mk (span {s}) (↑p * b * ∑ x ∈ Finset.range p, a ^ (p - 2) * x) +
mk (span {s}) (↑p * a ^ (p - 1)) := by
simp only [Finset.mul_sum, ← mul_assoc, ← pow_add]
rw [Finset.sum_congr rfl]
rintro (⟨⟩ | ⟨x⟩) hx
· rw [Nat.cast_zero, mul_zero, mul_zero]
· have : x.succ - 1 + (p - 1 - x.succ) = p - 2 := by
rw [← Nat.add_sub_assoc (Nat.le_sub_one_of_lt (Finset.mem_range.mp hx))]
exact congr_arg Nat.pred (Nat.add_sub_cancel_left _ _)
rw [this]
ring1
_ = mk (span {s}) (↑p * a ^ (p - 1)) := by
have : Finset.sum (range p) (fun (x : ℕ) ↦ (x : R)) =
((Finset.sum (range p) (fun (x : ℕ) ↦ (x : ℕ)))) := by simp only [Nat.cast_sum]
simp only [add_eq_right, ← Finset.mul_sum, this]
norm_cast
simp only [Finset.sum_range_id]
norm_cast
simp only [Nat.cast_mul, map_mul,
Nat.mul_div_assoc p (even_iff_two_dvd.mp (Nat.Odd.sub_odd hp odd_one))]
ring_nf
rw [mul_assoc, mul_assoc]
refine mul_eq_zero_of_left ?_ _
refine Ideal.Quotient.eq_zero_iff_mem.mpr ?_
simp [s, mem_span_singleton]
section IntegralDomain
variable [IsDomain R]
theorem emultiplicity_pow_sub_pow_of_prime {p : R} (hp : Prime p) {x y : R}
(hxy : p ∣ x - y) (hx : ¬p ∣ x) {n : ℕ} (hn : ¬p ∣ n) :
emultiplicity p (x ^ n - y ^ n) = emultiplicity p (x - y) := by
rw [← geom_sum₂_mul, emultiplicity_mul hp,
emultiplicity_eq_zero.2 (not_dvd_geom_sum₂ hp hxy hx hn), zero_add]
@[deprecated (since := "2024-11-30")]
alias multiplicity.pow_sub_pow_of_prime := emultiplicity_pow_sub_pow_of_prime
variable (hp : Prime (p : R)) (hp1 : Odd p) (hxy : ↑p ∣ x - y) (hx : ¬↑p ∣ x)
include hp hp1 hxy hx
theorem emultiplicity_geom_sum₂_eq_one :
emultiplicity (↑p) (∑ i ∈ range p, x ^ i * y ^ (p - 1 - i)) = 1 := by
rw [← Nat.cast_one]
refine emultiplicity_eq_coe.2 ⟨?_, ?_⟩
· rw [pow_one]
exact dvd_geom_sum₂_self hxy
rw [dvd_iff_dvd_of_dvd_sub hxy] at hx
obtain ⟨k, hk⟩ := hxy
rw [one_add_one_eq_two, eq_add_of_sub_eq' hk]
refine mt (dvd_iff_dvd_of_dvd_sub (@odd_sq_dvd_geom_sum₂_sub _ _ y k _ hp1)).mp ?_
rw [pow_two, mul_dvd_mul_iff_left hp.ne_zero]
exact mt hp.dvd_of_dvd_pow hx
@[deprecated (since := "2024-11-30")]
alias multiplicity.geom_sum₂_eq_one := emultiplicity_geom_sum₂_eq_one
theorem emultiplicity_pow_prime_sub_pow_prime :
emultiplicity (↑p) (x ^ p - y ^ p) = emultiplicity (↑p) (x - y) + 1 := by
rw [← geom_sum₂_mul, emultiplicity_mul hp, emultiplicity_geom_sum₂_eq_one hp hp1 hxy hx, add_comm]
@[deprecated (since := "2024-11-30")]
alias multiplicity.pow_prime_sub_pow_prime := emultiplicity_pow_prime_sub_pow_prime
theorem emultiplicity_pow_prime_pow_sub_pow_prime_pow (a : ℕ) :
emultiplicity (↑p) (x ^ p ^ a - y ^ p ^ a) = emultiplicity (↑p) (x - y) + a := by
induction a with
| zero => rw [Nat.cast_zero, add_zero, pow_zero, pow_one, pow_one]
| succ a h_ind =>
rw [Nat.cast_add, Nat.cast_one, ← add_assoc, ← h_ind, pow_succ, pow_mul, pow_mul]
apply emultiplicity_pow_prime_sub_pow_prime hp hp1
· rw [← geom_sum₂_mul]
exact dvd_mul_of_dvd_right hxy _
· exact fun h => hx (hp.dvd_of_dvd_pow h)
@[deprecated (since := "2024-11-30")]
alias multiplicity.pow_prime_pow_sub_pow_prime_pow := emultiplicity_pow_prime_pow_sub_pow_prime_pow
end IntegralDomain
section LiftingTheExponent
| variable (hp : Nat.Prime p) (hp1 : Odd p)
include hp hp1
/-- **Lifting the exponent lemma** for odd primes. -/
theorem Int.emultiplicity_pow_sub_pow {x y : ℤ} (hxy : ↑p ∣ x - y) (hx : ¬↑p ∣ x) (n : ℕ) :
emultiplicity (↑p) (x ^ n - y ^ n) = emultiplicity (↑p) (x - y) + emultiplicity p n := by
rcases n with - | n
· simp only [emultiplicity_zero, add_top, pow_zero, sub_self]
have h : FiniteMultiplicity _ _ := Nat.finiteMultiplicity_iff.mpr ⟨hp.ne_one, n.succ_pos⟩
simp only [Nat.succ_eq_add_one] at h
rcases emultiplicity_eq_coe.mp h.emultiplicity_eq_multiplicity with ⟨⟨k, hk⟩, hpn⟩
conv_lhs => rw [hk, pow_mul, pow_mul]
rw [Nat.prime_iff_prime_int] at hp
rw [emultiplicity_pow_sub_pow_of_prime hp,
emultiplicity_pow_prime_pow_sub_pow_prime_pow hp hp1 hxy hx, h.emultiplicity_eq_multiplicity]
· rw [← geom_sum₂_mul]
exact dvd_mul_of_dvd_right hxy _
| Mathlib/NumberTheory/Multiplicity.lean | 199 | 215 |
/-
Copyright (c) 2022 María Inés de Frutos-Fernández. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Antoine Chambert-Loir, María Inés de Frutos-Fernández
-/
import Mathlib.Algebra.BigOperators.Finprod
import Mathlib.Algebra.DirectSum.Decomposition
import Mathlib.Algebra.GradedMonoid
import Mathlib.Algebra.MvPolynomial.Basic
import Mathlib.Algebra.Order.Monoid.Canonical.Defs
import Mathlib.Data.Finsupp.Weight
import Mathlib.RingTheory.GradedAlgebra.Basic
/-!
# Weighted homogeneous polynomials
It is possible to assign weights (in a commutative additive monoid `M`) to the variables of a
multivariate polynomial ring, so that monomials of the ring then have a weighted degree with
respect to the weights of the variables. The weights are represented by a function `w : σ → M`,
where `σ` are the indeterminates.
A multivariate polynomial `φ` is weighted homogeneous of weighted degree `m : M` if all monomials
occurring in `φ` have the same weighted degree `m`.
## Main definitions/lemmas
* `weightedTotalDegree' w φ` : the weighted total degree of a multivariate polynomial with respect
to the weights `w`, taking values in `WithBot M`.
* `weightedTotalDegree w φ` : When `M` has a `⊥` element, we can define the weighted total degree
of a multivariate polynomial as a function taking values in `M`.
* `IsWeightedHomogeneous w φ m`: a predicate that asserts that `φ` is weighted homogeneous
of weighted degree `m` with respect to the weights `w`.
* `weightedHomogeneousSubmodule R w m`: the submodule of homogeneous polynomials
of weighted degree `m`.
* `weightedHomogeneousComponent w m`: the additive morphism that projects polynomials
onto their summand that is weighted homogeneous of degree `n` with respect to `w`.
* `sum_weightedHomogeneousComponent`: every polynomial is the sum of its weighted homogeneous
components.
-/
noncomputable section
open Set Function Finset Finsupp AddMonoidAlgebra
variable {R M : Type*} [CommSemiring R]
namespace MvPolynomial
variable {σ : Type*}
section AddCommMonoid
variable [AddCommMonoid M]
/-! ### `weight` -/
section SemilatticeSup
variable [SemilatticeSup M]
/-- The weighted total degree of a multivariate polynomial, taking values in `WithBot M`. -/
def weightedTotalDegree' (w : σ → M) (p : MvPolynomial σ R) : WithBot M :=
p.support.sup fun s => weight w s
/-- The `weightedTotalDegree'` of a polynomial `p` is `⊥` if and only if `p = 0`. -/
theorem weightedTotalDegree'_eq_bot_iff (w : σ → M) (p : MvPolynomial σ R) :
weightedTotalDegree' w p = ⊥ ↔ p = 0 := by
simp only [weightedTotalDegree', Finset.sup_eq_bot_iff, mem_support_iff, WithBot.coe_ne_bot,
MvPolynomial.eq_zero_iff]
exact forall_congr' fun _ => Classical.not_not
/-- The `weightedTotalDegree'` of the zero polynomial is `⊥`. -/
theorem weightedTotalDegree'_zero (w : σ → M) :
weightedTotalDegree' w (0 : MvPolynomial σ R) = ⊥ := by
simp only [weightedTotalDegree', support_zero, Finset.sup_empty]
section OrderBot
variable [OrderBot M]
/-- When `M` has a `⊥` element, we can define the weighted total degree of a multivariate
polynomial as a function taking values in `M`. -/
def weightedTotalDegree (w : σ → M) (p : MvPolynomial σ R) : M :=
p.support.sup fun s => weight w s
/-- This lemma relates `weightedTotalDegree` and `weightedTotalDegree'`. -/
theorem weightedTotalDegree_coe (w : σ → M) (p : MvPolynomial σ R) (hp : p ≠ 0) :
weightedTotalDegree' w p = ↑(weightedTotalDegree w p) := by
rw [Ne, ← weightedTotalDegree'_eq_bot_iff w p, ← Ne, WithBot.ne_bot_iff_exists] at hp
obtain ⟨m, hm⟩ := hp
apply le_antisymm
· simp only [weightedTotalDegree, weightedTotalDegree', Finset.sup_le_iff, WithBot.coe_le_coe]
intro b
exact Finset.le_sup
· simp only [weightedTotalDegree]
have hm' : weightedTotalDegree' w p ≤ m := le_of_eq hm.symm
rw [← hm]
simpa [weightedTotalDegree'] using hm'
/-- The `weightedTotalDegree` of the zero polynomial is `⊥`. -/
theorem weightedTotalDegree_zero (w : σ → M) :
weightedTotalDegree w (0 : MvPolynomial σ R) = ⊥ := by
simp only [weightedTotalDegree, support_zero, Finset.sup_empty]
theorem le_weightedTotalDegree (w : σ → M) {φ : MvPolynomial σ R} {d : σ →₀ ℕ}
(hd : d ∈ φ.support) : weight w d ≤ φ.weightedTotalDegree w :=
le_sup hd
end OrderBot
end SemilatticeSup
/-- A multivariate polynomial `φ` is weighted homogeneous of weighted degree `m` if all monomials
occurring in `φ` have weighted degree `m`. -/
def IsWeightedHomogeneous (w : σ → M) (φ : MvPolynomial σ R) (m : M) : Prop :=
∀ ⦃d⦄, coeff d φ ≠ 0 → weight w d = m
variable (R)
/-- The submodule of homogeneous `MvPolynomial`s of degree `n`. -/
def weightedHomogeneousSubmodule (w : σ → M) (m : M) : Submodule R (MvPolynomial σ R) where
carrier := { x | x.IsWeightedHomogeneous w m }
smul_mem' r a ha c hc := by
rw [coeff_smul] at hc
exact ha (right_ne_zero_of_mul hc)
zero_mem' _ hd := False.elim (hd <| coeff_zero _)
add_mem' {a} {b} ha hb c hc := by
rw [coeff_add] at hc
obtain h | h : coeff c a ≠ 0 ∨ coeff c b ≠ 0 := by
contrapose! hc
simp only [hc, add_zero]
· exact ha h
· exact hb h
@[simp]
theorem mem_weightedHomogeneousSubmodule (w : σ → M) (m : M) (p : MvPolynomial σ R) :
p ∈ weightedHomogeneousSubmodule R w m ↔ p.IsWeightedHomogeneous w m :=
Iff.rfl
/-- The submodule `weightedHomogeneousSubmodule R w m` of homogeneous `MvPolynomial`s of
degree `n` is equal to the `R`-submodule of all `p : (σ →₀ ℕ) →₀ R` such that
`p.support ⊆ {d | weight w d = m}`. While equal, the former has a
convenient definitional reduction. -/
theorem weightedHomogeneousSubmodule_eq_finsupp_supported (w : σ → M) (m : M) :
weightedHomogeneousSubmodule R w m = Finsupp.supported R R { d | weight w d = m } := by
ext x
rw [mem_supported, Set.subset_def]
simp only [Finsupp.mem_support_iff, mem_coe]
rfl
variable {R}
/-- The submodule generated by products `Pm * Pn` of weighted homogeneous polynomials of degrees `m`
and `n` is contained in the submodule of weighted homogeneous polynomials of degree `m + n`. -/
theorem weightedHomogeneousSubmodule_mul (w : σ → M) (m n : M) :
weightedHomogeneousSubmodule R w m * weightedHomogeneousSubmodule R w n ≤
weightedHomogeneousSubmodule R w (m + n) := by
classical
rw [Submodule.mul_le]
intro φ hφ ψ hψ c hc
rw [coeff_mul] at hc
obtain ⟨⟨d, e⟩, hde, H⟩ := Finset.exists_ne_zero_of_sum_ne_zero hc
have aux : coeff d φ ≠ 0 ∧ coeff e ψ ≠ 0 := by
contrapose! H
by_cases h : coeff d φ = 0 <;>
simp_all only [Ne, not_false_iff, zero_mul, mul_zero]
rw [← mem_antidiagonal.mp hde, ← hφ aux.1, ← hψ aux.2, map_add]
/-- Monomials are weighted homogeneous. -/
theorem isWeightedHomogeneous_monomial (w : σ → M) (d : σ →₀ ℕ) (r : R) {m : M}
(hm : weight w d = m) : IsWeightedHomogeneous w (monomial d r) m := by
classical
intro c hc
rw [coeff_monomial] at hc
split_ifs at hc with h
· subst c
exact hm
· contradiction
/-- A polynomial of weightedTotalDegree `⊥` is weighted_homogeneous of degree `⊥`. -/
theorem isWeightedHomogeneous_of_total_degree_zero [SemilatticeSup M] [OrderBot M] (w : σ → M)
{p : MvPolynomial σ R} (hp : weightedTotalDegree w p = (⊥ : M)) :
IsWeightedHomogeneous w p (⊥ : M) := by
intro d hd
have h := weightedTotalDegree_coe w p (MvPolynomial.ne_zero_iff.mpr ⟨d, hd⟩)
simp only [weightedTotalDegree', hp] at h
rw [eq_bot_iff, ← WithBot.coe_le_coe, ← h]
apply Finset.le_sup (mem_support_iff.mpr hd)
/-- Constant polynomials are weighted homogeneous of degree 0. -/
theorem isWeightedHomogeneous_C (w : σ → M) (r : R) :
IsWeightedHomogeneous w (C r : MvPolynomial σ R) 0 :=
isWeightedHomogeneous_monomial _ _ _ (map_zero _)
variable (R)
/-- 0 is weighted homogeneous of any degree. -/
theorem isWeightedHomogeneous_zero (w : σ → M) (m : M) :
IsWeightedHomogeneous w (0 : MvPolynomial σ R) m :=
(weightedHomogeneousSubmodule R w m).zero_mem
/-- 1 is weighted homogeneous of degree 0. -/
theorem isWeightedHomogeneous_one (w : σ → M) : IsWeightedHomogeneous w (1 : MvPolynomial σ R) 0 :=
isWeightedHomogeneous_C _ _
/-- An indeterminate `i : σ` is weighted homogeneous of degree `w i`. -/
theorem isWeightedHomogeneous_X (w : σ → M) (i : σ) :
IsWeightedHomogeneous w (X i : MvPolynomial σ R) (w i) := by
apply isWeightedHomogeneous_monomial
simp only [weight, LinearMap.toAddMonoidHom_coe, linearCombination_single, one_nsmul]
namespace IsWeightedHomogeneous
variable {R}
variable {φ ψ : MvPolynomial σ R} {m n : M}
/-- The weighted degree of a weighted homogeneous polynomial controls its support. -/
theorem coeff_eq_zero {w : σ → M} (hφ : IsWeightedHomogeneous w φ n) (d : σ →₀ ℕ)
(hd : weight w d ≠ n) : coeff d φ = 0 := by
have aux := mt (@hφ d) hd
rwa [Classical.not_not] at aux
/-- The weighted degree of a nonzero weighted homogeneous polynomial is well-defined. -/
theorem inj_right {w : σ → M} (hφ : φ ≠ 0) (hm : IsWeightedHomogeneous w φ m)
(hn : IsWeightedHomogeneous w φ n) : m = n := by
obtain ⟨d, hd⟩ : ∃ d, coeff d φ ≠ 0 := exists_coeff_ne_zero hφ
rw [← hm hd, ← hn hd]
/-- The sum of two weighted homogeneous polynomials of degree `n` is weighted homogeneous of
weighted degree `n`. -/
theorem add {w : σ → M} (hφ : IsWeightedHomogeneous w φ n) (hψ : IsWeightedHomogeneous w ψ n) :
IsWeightedHomogeneous w (φ + ψ) n :=
(weightedHomogeneousSubmodule R w n).add_mem hφ hψ
/-- The sum of weighted homogeneous polynomials of degree `n` is weighted homogeneous of
weighted degree `n`. -/
theorem sum {ι : Type*} (s : Finset ι) (φ : ι → MvPolynomial σ R) (n : M) {w : σ → M}
(h : ∀ i ∈ s, IsWeightedHomogeneous w (φ i) n) : IsWeightedHomogeneous w (∑ i ∈ s, φ i) n :=
(weightedHomogeneousSubmodule R w n).sum_mem h
/-- The product of weighted homogeneous polynomials of weighted degrees `m` and `n` is weighted
homogeneous of weighted degree `m + n`. -/
theorem mul {w : σ → M} (hφ : IsWeightedHomogeneous w φ m) (hψ : IsWeightedHomogeneous w ψ n) :
IsWeightedHomogeneous w (φ * ψ) (m + n) :=
weightedHomogeneousSubmodule_mul w m n <| Submodule.mul_mem_mul hφ hψ
theorem pow {w : σ → M} (hφ : IsWeightedHomogeneous w φ m) (n : ℕ) :
IsWeightedHomogeneous w (φ ^ n) (n • m) := by
induction n with
| zero => rw [pow_zero, zero_smul]; exact isWeightedHomogeneous_one R w
| succ n ih => rw [pow_succ, succ_nsmul]; exact ih.mul hφ
/-- A product of weighted homogeneous polynomials is weighted homogeneous, with weighted degree
equal to the sum of the weighted degrees. -/
theorem prod {ι : Type*} (s : Finset ι) (φ : ι → MvPolynomial σ R) (n : ι → M) {w : σ → M} :
(∀ i ∈ s, IsWeightedHomogeneous w (φ i) (n i)) →
IsWeightedHomogeneous w (∏ i ∈ s, φ i) (∑ i ∈ s, n i) := by
classical
refine Finset.induction_on s ?_ ?_
· intro
simp only [isWeightedHomogeneous_one, Finset.sum_empty, Finset.prod_empty]
· intro i s his IH h
simp only [his, Finset.prod_insert, Finset.sum_insert, not_false_iff]
apply (h i (Finset.mem_insert_self _ _)).mul (IH _)
intro j hjs
exact h j (Finset.mem_insert_of_mem hjs)
/-- A non zero weighted homogeneous polynomial of weighted degree `n` has weighted total degree
`n`. -/
theorem weighted_total_degree [SemilatticeSup M] {w : σ → M} (hφ : IsWeightedHomogeneous w φ n)
(h : φ ≠ 0) : weightedTotalDegree' w φ = n := by
simp only [weightedTotalDegree']
apply le_antisymm
· simp only [Finset.sup_le_iff, mem_support_iff, WithBot.coe_le_coe]
exact fun d hd => le_of_eq (hφ hd)
· obtain ⟨d, hd⟩ : ∃ d, coeff d φ ≠ 0 := exists_coeff_ne_zero h
simp only [← hφ hd, Finsupp.sum]
replace hd := Finsupp.mem_support_iff.mpr hd
apply Finset.le_sup hd
end IsWeightedHomogeneous
variable {R}
/-- The weighted homogeneous submodules form a graded monoid. -/
lemma WeightedHomogeneousSubmodule.gradedMonoid {w : σ → M} :
SetLike.GradedMonoid (weightedHomogeneousSubmodule R w) where
one_mem := isWeightedHomogeneous_one R w
mul_mem _ _ _ _ := IsWeightedHomogeneous.mul
/-- `weightedHomogeneousComponent w n φ` is the part of `φ` that is weighted homogeneous of
weighted degree `n`, with respect to the weights `w`.
See `sum_weightedHomogeneousComponent` for the statement that `φ` is equal to the sum
of all its weighted homogeneous components. -/
def weightedHomogeneousComponent (w : σ → M) (n : M) : MvPolynomial σ R →ₗ[R] MvPolynomial σ R :=
letI := Classical.decEq M
(Submodule.subtype _).comp <| Finsupp.restrictDom _ _ { d | weight w d = n }
section WeightedHomogeneousComponent
variable {w : σ → M} (n : M) (φ ψ : MvPolynomial σ R)
theorem coeff_weightedHomogeneousComponent [DecidableEq M] (d : σ →₀ ℕ) :
coeff d (weightedHomogeneousComponent w n φ) =
if weight w d = n then coeff d φ else 0 :=
letI := Classical.decEq M
Finsupp.filter_apply (fun d : σ →₀ ℕ => weight w d = n) φ d |>.trans <| by convert rfl
theorem weightedHomogeneousComponent_apply [DecidableEq M] :
weightedHomogeneousComponent w n φ =
∑ d ∈ φ.support with weight w d = n, monomial d (coeff d φ) :=
letI := Classical.decEq M
Finsupp.filter_eq_sum (fun d : σ →₀ ℕ => weight w d = n) φ |>.trans <| by convert rfl
/-- The `n` weighted homogeneous component of a polynomial is weighted homogeneous of
weighted degree `n`. -/
theorem weightedHomogeneousComponent_isWeightedHomogeneous :
(weightedHomogeneousComponent w n φ).IsWeightedHomogeneous w n := by
classical
intro d hd
contrapose! hd
rw [coeff_weightedHomogeneousComponent, if_neg hd]
theorem weightedHomogeneousComponent_mem (w : σ → M) (φ : MvPolynomial σ R) (m : M) :
weightedHomogeneousComponent w m φ ∈ weightedHomogeneousSubmodule R w m := by
rw [mem_weightedHomogeneousSubmodule]
exact weightedHomogeneousComponent_isWeightedHomogeneous m φ
@[simp]
theorem weightedHomogeneousComponent_C_mul (n : M) (r : R) :
weightedHomogeneousComponent w n (C r * φ) = C r * weightedHomogeneousComponent w n φ := by
simp only [C_mul', LinearMap.map_smul]
theorem weightedHomogeneousComponent_eq_zero'
(h : ∀ d : σ →₀ ℕ, d ∈ φ.support → weight w d ≠ n) :
weightedHomogeneousComponent w n φ = 0 := by
classical
rw [weightedHomogeneousComponent_apply, sum_eq_zero]
intro d hd; rw [mem_filter] at hd
exfalso; exact h _ hd.1 hd.2
theorem weightedHomogeneousComponent_eq_zero [SemilatticeSup M] [OrderBot M]
(h : weightedTotalDegree w φ < n) : weightedHomogeneousComponent w n φ = 0 := by
classical
rw [weightedHomogeneousComponent_apply, sum_eq_zero]
intro d hd
rw [Finset.mem_filter] at hd
exfalso
apply lt_irrefl n
nth_rw 1 [← hd.2]
exact lt_of_le_of_lt (le_weightedTotalDegree w hd.1) h
theorem weightedHomogeneousComponent_finsupp :
(Function.support fun m => weightedHomogeneousComponent w m φ).Finite := by
apply ((fun d : σ →₀ ℕ => (weight w) d) '' (φ.support : Set (σ →₀ ℕ))).toFinite.subset
intro m hm
by_contra hm'
apply hm (weightedHomogeneousComponent_eq_zero' m φ _)
simpa only [Set.mem_image, not_exists, not_and] using hm'
variable (w)
/-- Every polynomial is the sum of its weighted homogeneous components. -/
theorem sum_weightedHomogeneousComponent :
(finsum fun m => weightedHomogeneousComponent w m φ) = φ := by
classical
rw [finsum_eq_sum _ (weightedHomogeneousComponent_finsupp φ)]
ext1 d
simp only [coeff_sum, coeff_weightedHomogeneousComponent]
rw [Finset.sum_eq_single (weight w d)]
· rw [if_pos rfl]
· intro m _ hm'
rw [if_neg hm'.symm]
· intro hm
rw [if_pos rfl]
simp only [Finite.mem_toFinset, mem_support, Ne, Classical.not_not] at hm
have := coeff_weightedHomogeneousComponent (w := w) (weight w d) φ d
rw [hm, if_pos rfl, coeff_zero] at this
exact this.symm
theorem finsum_weightedHomogeneousComponent :
(finsum fun m => weightedHomogeneousComponent w m φ) = φ := by
rw [sum_weightedHomogeneousComponent]
variable {w}
theorem IsWeightedHomogeneous.weightedHomogeneousComponent_same {m : M} {p : MvPolynomial σ R}
(hp : IsWeightedHomogeneous w p m) :
weightedHomogeneousComponent w m p = p := by
| classical
ext x
rw [coeff_weightedHomogeneousComponent]
by_cases zero_coeff : coeff x p = 0
· split_ifs
· rfl
rw [zero_coeff]
· rw [hp zero_coeff, if_pos rfl]
theorem IsWeightedHomogeneous.weightedHomogeneousComponent_ne {m : M} (n : M)
{p : MvPolynomial σ R} (hp : IsWeightedHomogeneous w p m) :
n ≠ m → weightedHomogeneousComponent w n p = 0 := by
| Mathlib/RingTheory/MvPolynomial/WeightedHomogeneous.lean | 397 | 408 |
/-
Copyright (c) 2018 Kenny Lau. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kenny Lau, Chris Hughes, Mario Carneiro
-/
import Mathlib.Algebra.Field.IsField
import Mathlib.Data.Fin.VecNotation
import Mathlib.Data.Nat.Choose.Sum
import Mathlib.LinearAlgebra.Finsupp.LinearCombination
import Mathlib.RingTheory.Ideal.Maximal
import Mathlib.Tactic.FinCases
/-!
# Ideals over a ring
This file contains an assortment of definitions and results for `Ideal R`,
the type of (left) ideals over a ring `R`.
Note that over commutative rings, left ideals and two-sided ideals are equivalent.
## Implementation notes
`Ideal R` is implemented using `Submodule R R`, where `•` is interpreted as `*`.
## TODO
Support right ideals, and two-sided ideals over non-commutative rings.
-/
variable {ι α β F : Type*}
open Set Function
open Pointwise
section Semiring
namespace Ideal
variable {α : ι → Type*} [Π i, Semiring (α i)] (I : Π i, Ideal (α i))
section Pi
/-- `Πᵢ Iᵢ` as an ideal of `Πᵢ Rᵢ`. -/
def pi : Ideal (Π i, α i) where
carrier := { x | ∀ i, x i ∈ I i }
zero_mem' i := (I i).zero_mem
add_mem' ha hb i := (I i).add_mem (ha i) (hb i)
smul_mem' a _b hb i := (I i).mul_mem_left (a i) (hb i)
theorem mem_pi (x : Π i, α i) : x ∈ pi I ↔ ∀ i, x i ∈ I i :=
Iff.rfl
instance (priority := low) [∀ i, (I i).IsTwoSided] : (pi I).IsTwoSided :=
⟨fun _b hb i ↦ mul_mem_right _ _ (hb i)⟩
end Pi
section Commute
variable {α : Type*} [Semiring α] (I : Ideal α) {a b : α}
theorem add_pow_mem_of_pow_mem_of_le_of_commute {m n k : ℕ}
(ha : a ^ m ∈ I) (hb : b ^ n ∈ I) (hk : m + n ≤ k + 1)
(hab : Commute a b) :
(a + b) ^ k ∈ I := by
simp_rw [hab.add_pow, ← Nat.cast_comm]
apply I.sum_mem
intro c _
apply mul_mem_left
by_cases h : m ≤ c
· rw [hab.pow_pow]
exact I.mul_mem_left _ (I.pow_mem_of_pow_mem ha h)
· refine I.mul_mem_left _ (I.pow_mem_of_pow_mem hb ?_)
omega
theorem add_pow_add_pred_mem_of_pow_mem_of_commute {m n : ℕ}
(ha : a ^ m ∈ I) (hb : b ^ n ∈ I) (hab : Commute a b) :
(a + b) ^ (m + n - 1) ∈ I :=
I.add_pow_mem_of_pow_mem_of_le_of_commute ha hb (by rw [← Nat.sub_le_iff_le_add]) hab
end Commute
end Ideal
end Semiring
section CommSemiring
variable {a b : α}
-- A separate namespace definition is needed because the variables were historically in a different
-- order.
namespace Ideal
variable [CommSemiring α] (I : Ideal α)
theorem add_pow_mem_of_pow_mem_of_le {m n k : ℕ}
(ha : a ^ m ∈ I) (hb : b ^ n ∈ I) (hk : m + n ≤ k + 1) :
(a + b) ^ k ∈ I :=
I.add_pow_mem_of_pow_mem_of_le_of_commute ha hb hk (Commute.all ..)
theorem add_pow_add_pred_mem_of_pow_mem {m n : ℕ}
(ha : a ^ m ∈ I) (hb : b ^ n ∈ I) :
(a + b) ^ (m + n - 1) ∈ I :=
I.add_pow_add_pred_mem_of_pow_mem_of_commute ha hb (Commute.all ..)
theorem pow_multiset_sum_mem_span_pow [DecidableEq α] (s : Multiset α) (n : ℕ) :
s.sum ^ (Multiset.card s * n + 1) ∈
span ((s.map fun (x : α) ↦ x ^ (n + 1)).toFinset : Set α) := by
induction' s using Multiset.induction_on with a s hs
· simp
simp only [Finset.coe_insert, Multiset.map_cons, Multiset.toFinset_cons, Multiset.sum_cons,
Multiset.card_cons, add_pow]
refine Submodule.sum_mem _ ?_
intro c _hc
rw [mem_span_insert]
by_cases h : n + 1 ≤ c
· refine ⟨a ^ (c - (n + 1)) * s.sum ^ ((Multiset.card s + 1) * n + 1 - c) *
((Multiset.card s + 1) * n + 1).choose c, 0, Submodule.zero_mem _, ?_⟩
rw [mul_comm _ (a ^ (n + 1))]
simp_rw [← mul_assoc]
rw [← pow_add, add_zero, add_tsub_cancel_of_le h]
· use 0
simp_rw [zero_mul, zero_add]
refine ⟨_, ?_, rfl⟩
replace h : c ≤ n := Nat.lt_succ_iff.mp (not_le.mp h)
have : (Multiset.card s + 1) * n + 1 - c = Multiset.card s * n + 1 + (n - c) := by
rw [add_mul, one_mul, add_assoc, add_comm n 1, ← add_assoc, add_tsub_assoc_of_le h]
rw [this, pow_add]
simp_rw [mul_assoc, mul_comm (s.sum ^ (Multiset.card s * n + 1)), ← mul_assoc]
exact mul_mem_left _ _ hs
theorem sum_pow_mem_span_pow {ι} (s : Finset ι) (f : ι → α) (n : ℕ) :
(∑ i ∈ s, f i) ^ (s.card * n + 1) ∈ span ((fun i => f i ^ (n + 1)) '' s) := by
classical
simpa only [Multiset.card_map, Multiset.map_map, comp_apply, Multiset.toFinset_map,
Finset.coe_image, Finset.val_toFinset] using pow_multiset_sum_mem_span_pow (s.1.map f) n
theorem span_pow_eq_top (s : Set α) (hs : span s = ⊤) (n : ℕ) :
span ((fun (x : α) => x ^ n) '' s) = ⊤ := by
rw [eq_top_iff_one]
rcases n with - | n
· obtain rfl | ⟨x, hx⟩ := eq_empty_or_nonempty s
· rw [Set.image_empty, hs]
trivial
· exact subset_span ⟨_, hx, pow_zero _⟩
rw [eq_top_iff_one, span, Finsupp.mem_span_iff_linearCombination] at hs
rcases hs with ⟨f, hf⟩
have hf : (f.support.sum fun a => f a * a) = 1 := hf -- Porting note: was `change ... at hf`
have := sum_pow_mem_span_pow f.support (fun a => f a * a) n
rw [hf, one_pow] at this
refine span_le.mpr ?_ this
rintro _ hx
simp_rw [Set.mem_image] at hx
rcases hx with ⟨x, _, rfl⟩
have : span ({(x : α) ^ (n + 1)} : Set α) ≤ span ((fun x : α => x ^ (n + 1)) '' s) := by
rw [span_le, Set.singleton_subset_iff]
exact subset_span ⟨x, x.prop, rfl⟩
refine this ?_
rw [mul_pow, mem_span_singleton]
exact ⟨f x ^ (n + 1), mul_comm _ _⟩
theorem span_range_pow_eq_top (s : Set α) (hs : span s = ⊤) (n : s → ℕ) :
span (Set.range fun x ↦ x.1 ^ n x) = ⊤ := by
have ⟨t, hts, mem⟩ := Submodule.mem_span_finite_of_mem_span ((eq_top_iff_one _).mp hs)
| refine top_unique ((span_pow_eq_top _ ((eq_top_iff_one _).mpr mem) <|
t.attach.sup fun x ↦ n ⟨x, hts x.2⟩).ge.trans <| span_le.mpr ?_)
| Mathlib/RingTheory/Ideal/Basic.lean | 168 | 169 |
/-
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.QuasiIso
import Mathlib.CategoryTheory.Limits.Preserves.Finite
import Mathlib.CategoryTheory.Limits.Preserves.Shapes.Kernels
/-!
# Functors which preserves homology
If `F : C ⥤ D` is a functor between categories with zero morphisms, we shall
say that `F` preserves homology when `F` preserves both kernels and cokernels.
This typeclass is named `[F.PreservesHomology]`, and is automatically
satisfied when `F` preserves both finite limits and finite colimits.
If `S : ShortComplex C` and `[F.PreservesHomology]`, then there is an
isomorphism `S.mapHomologyIso F : (S.map F).homology ≅ F.obj S.homology`, which
is part of the natural isomorphism `homologyFunctorIso F` between the functors
`F.mapShortComplex ⋙ homologyFunctor D` and `homologyFunctor C ⋙ F`.
-/
namespace CategoryTheory
open Category Limits
variable {C D : Type*} [Category C] [Category D] [HasZeroMorphisms C] [HasZeroMorphisms D]
namespace Functor
variable (F : C ⥤ D)
/-- A functor preserves homology when it preserves both kernels and cokernels. -/
class PreservesHomology (F : C ⥤ D) [PreservesZeroMorphisms F] : Prop where
/-- the functor preserves kernels -/
preservesKernels ⦃X Y : C⦄ (f : X ⟶ Y) : PreservesLimit (parallelPair f 0) F := by
infer_instance
/-- the functor preserves cokernels -/
preservesCokernels ⦃X Y : C⦄ (f : X ⟶ Y) : PreservesColimit (parallelPair f 0) F := by
infer_instance
variable [PreservesZeroMorphisms F]
/-- A functor which preserves homology preserves kernels. -/
lemma PreservesHomology.preservesKernel [F.PreservesHomology] {X Y : C} (f : X ⟶ Y) :
PreservesLimit (parallelPair f 0) F :=
PreservesHomology.preservesKernels _
/-- A functor which preserves homology preserves cokernels. -/
lemma PreservesHomology.preservesCokernel [F.PreservesHomology] {X Y : C} (f : X ⟶ Y) :
PreservesColimit (parallelPair f 0) F :=
PreservesHomology.preservesCokernels _
noncomputable instance preservesHomologyOfExact
[PreservesFiniteLimits F] [PreservesFiniteColimits F] :
F.PreservesHomology where
end Functor
namespace ShortComplex
variable {S S₁ S₂ : ShortComplex C}
namespace LeftHomologyData
variable (h : S.LeftHomologyData) (F : C ⥤ D)
/-- A left homology data `h` of a short complex `S` is preserved by a functor `F` is
`F` preserves the kernel of `S.g : S.X₂ ⟶ S.X₃` and the cokernel of `h.f' : S.X₁ ⟶ h.K`. -/
class IsPreservedBy [F.PreservesZeroMorphisms] : Prop where
/-- the functor preserves the kernel of `S.g : S.X₂ ⟶ S.X₃`. -/
g : PreservesLimit (parallelPair S.g 0) F
/-- the functor preserves the cokernel of `h.f' : S.X₁ ⟶ h.K`. -/
f' : PreservesColimit (parallelPair h.f' 0) F
variable [F.PreservesZeroMorphisms]
noncomputable instance isPreservedBy_of_preservesHomology [F.PreservesHomology] :
h.IsPreservedBy F where
g := Functor.PreservesHomology.preservesKernel _ _
f' := Functor.PreservesHomology.preservesCokernel _ _
variable [h.IsPreservedBy F]
include h in
/-- When a left homology data is preserved by a functor `F`, this functor
preserves the kernel of `S.g : S.X₂ ⟶ S.X₃`. -/
lemma IsPreservedBy.hg : PreservesLimit (parallelPair S.g 0) F :=
@IsPreservedBy.g _ _ _ _ _ _ _ h F _ _
/-- When a left homology data `h` is preserved by a functor `F`, this functor
preserves the cokernel of `h.f' : S.X₁ ⟶ h.K`. -/
lemma IsPreservedBy.hf' : PreservesColimit (parallelPair h.f' 0) F := IsPreservedBy.f'
/-- When a left homology data `h` of a short complex `S` is preserved by a functor `F`,
this is the induced left homology data `h.map F` for the short complex `S.map F`. -/
@[simps]
noncomputable def map : (S.map F).LeftHomologyData := by
have := IsPreservedBy.hg h F
have := IsPreservedBy.hf' h F
have wi : F.map h.i ≫ F.map S.g = 0 := by rw [← F.map_comp, h.wi, F.map_zero]
have hi := KernelFork.mapIsLimit _ h.hi F
let f' : F.obj S.X₁ ⟶ F.obj h.K := hi.lift (KernelFork.ofι (S.map F).f (S.map F).zero)
have hf' : f' = F.map h.f' := Fork.IsLimit.hom_ext hi (by
rw [Fork.IsLimit.lift_ι hi]
simp only [KernelFork.map_ι, Fork.ι_ofι, map_f, ← F.map_comp, f'_i])
have wπ : f' ≫ F.map h.π = 0 := by rw [hf', ← F.map_comp, f'_π, F.map_zero]
have hπ : IsColimit (CokernelCofork.ofπ (F.map h.π) wπ) := by
let e : parallelPair f' 0 ≅ parallelPair (F.map h.f') 0 :=
parallelPair.ext (Iso.refl _) (Iso.refl _) (by simpa using hf') (by simp)
refine IsColimit.precomposeInvEquiv e _
(IsColimit.ofIsoColimit (CokernelCofork.mapIsColimit _ h.hπ' F) ?_)
exact Cofork.ext (Iso.refl _) (by simp [e])
exact
{ K := F.obj h.K
H := F.obj h.H
i := F.map h.i
π := F.map h.π
wi := wi
hi := hi
wπ := wπ
hπ := hπ }
@[simp]
lemma map_f' : (h.map F).f' = F.map h.f' := by
rw [← cancel_mono (h.map F).i, f'_i, map_f, map_i, ← F.map_comp, f'_i]
end LeftHomologyData
/-- Given a left homology map data `ψ : LeftHomologyMapData φ h₁ h₂` such that
both left homology data `h₁` and `h₂` are preserved by a functor `F`, this is
the induced left homology map data for the morphism `F.mapShortComplex.map φ`. -/
@[simps]
def LeftHomologyMapData.map {φ : S₁ ⟶ S₂} {h₁ : S₁.LeftHomologyData}
{h₂ : S₂.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (F : C ⥤ D)
[F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
LeftHomologyMapData (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F) where
φK := F.map ψ.φK
φH := F.map ψ.φH
commi := by simpa only [F.map_comp] using F.congr_map ψ.commi
commf' := by simpa only [LeftHomologyData.map_f', F.map_comp] using F.congr_map ψ.commf'
commπ := by simpa only [F.map_comp] using F.congr_map ψ.commπ
namespace RightHomologyData
variable (h : S.RightHomologyData) (F : C ⥤ D)
/-- A right homology data `h` of a short complex `S` is preserved by a functor `F` is
`F` preserves the cokernel of `S.f : S.X₁ ⟶ S.X₂` and the kernel of `h.g' : h.Q ⟶ S.X₃`. -/
class IsPreservedBy [F.PreservesZeroMorphisms] : Prop where
/-- the functor preserves the cokernel of `S.f : S.X₁ ⟶ S.X₂`. -/
f : PreservesColimit (parallelPair S.f 0) F
/-- the functor preserves the kernel of `h.g' : h.Q ⟶ S.X₃`. -/
g' : PreservesLimit (parallelPair h.g' 0) F
variable [F.PreservesZeroMorphisms]
noncomputable instance isPreservedBy_of_preservesHomology [F.PreservesHomology] :
h.IsPreservedBy F where
f := Functor.PreservesHomology.preservesCokernel F _
g' := Functor.PreservesHomology.preservesKernel F _
variable [h.IsPreservedBy F]
include h in
/-- When a right homology data is preserved by a functor `F`, this functor
preserves the cokernel of `S.f : S.X₁ ⟶ S.X₂`. -/
lemma IsPreservedBy.hf : PreservesColimit (parallelPair S.f 0) F :=
@IsPreservedBy.f _ _ _ _ _ _ _ h F _ _
/-- When a right homology data `h` is preserved by a functor `F`, this functor
preserves the kernel of `h.g' : h.Q ⟶ S.X₃`. -/
lemma IsPreservedBy.hg' : PreservesLimit (parallelPair h.g' 0) F :=
@IsPreservedBy.g' _ _ _ _ _ _ _ h F _ _
/-- When a right homology data `h` of a short complex `S` is preserved by a functor `F`,
this is the induced right homology data `h.map F` for the short complex `S.map F`. -/
@[simps]
noncomputable def map : (S.map F).RightHomologyData := by
have := IsPreservedBy.hf h F
have := IsPreservedBy.hg' h F
have wp : F.map S.f ≫ F.map h.p = 0 := by rw [← F.map_comp, h.wp, F.map_zero]
have hp := CokernelCofork.mapIsColimit _ h.hp F
let g' : F.obj h.Q ⟶ F.obj S.X₃ := hp.desc (CokernelCofork.ofπ (S.map F).g (S.map F).zero)
have hg' : g' = F.map h.g' := by
apply Cofork.IsColimit.hom_ext hp
rw [Cofork.IsColimit.π_desc hp]
simp only [Cofork.π_ofπ, CokernelCofork.map_π, map_g, ← F.map_comp, p_g']
have wι : F.map h.ι ≫ g' = 0 := by rw [hg', ← F.map_comp, ι_g', F.map_zero]
have hι : IsLimit (KernelFork.ofι (F.map h.ι) wι) := by
let e : parallelPair g' 0 ≅ parallelPair (F.map h.g') 0 :=
parallelPair.ext (Iso.refl _) (Iso.refl _) (by simpa using hg') (by simp)
refine IsLimit.postcomposeHomEquiv e _
(IsLimit.ofIsoLimit (KernelFork.mapIsLimit _ h.hι' F) ?_)
exact Fork.ext (Iso.refl _) (by simp [e])
exact
{ Q := F.obj h.Q
H := F.obj h.H
p := F.map h.p
ι := F.map h.ι
wp := wp
hp := hp
wι := wι
hι := hι }
@[simp]
lemma map_g' : (h.map F).g' = F.map h.g' := by
rw [← cancel_epi (h.map F).p, p_g', map_g, map_p, ← F.map_comp, p_g']
end RightHomologyData
/-- Given a right homology map data `ψ : RightHomologyMapData φ h₁ h₂` such that
both right homology data `h₁` and `h₂` are preserved by a functor `F`, this is
the induced right homology map data for the morphism `F.mapShortComplex.map φ`. -/
@[simps]
def RightHomologyMapData.map {φ : S₁ ⟶ S₂} {h₁ : S₁.RightHomologyData}
{h₂ : S₂.RightHomologyData} (ψ : RightHomologyMapData φ h₁ h₂) (F : C ⥤ D)
[F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
RightHomologyMapData (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F) where
φQ := F.map ψ.φQ
φH := F.map ψ.φH
commp := by simpa only [F.map_comp] using F.congr_map ψ.commp
commg' := by simpa only [RightHomologyData.map_g', F.map_comp] using F.congr_map ψ.commg'
commι := by simpa only [F.map_comp] using F.congr_map ψ.commι
/-- When a homology data `h` of a short complex `S` is such that both `h.left` and
`h.right` are preserved by a functor `F`, this is the induced homology data
`h.map F` for the short complex `S.map F`. -/
@[simps]
noncomputable def HomologyData.map (h : S.HomologyData) (F : C ⥤ D) [F.PreservesZeroMorphisms]
[h.left.IsPreservedBy F] [h.right.IsPreservedBy F] :
(S.map F).HomologyData where
left := h.left.map F
right := h.right.map F
iso := F.mapIso h.iso
comm := by simpa only [F.map_comp] using F.congr_map h.comm
/-- Given a homology map data `ψ : HomologyMapData φ h₁ h₂` such that
`h₁.left`, `h₁.right`, `h₂.left` and `h₂.right` are all preserved by a functor `F`, this is
the induced homology map data for the morphism `F.mapShortComplex.map φ`. -/
@[simps]
def HomologyMapData.map {φ : S₁ ⟶ S₂} {h₁ : S₁.HomologyData} {h₂ : S₂.HomologyData}
(ψ : HomologyMapData φ h₁ h₂) (F : C ⥤ D) [F.PreservesZeroMorphisms]
[h₁.left.IsPreservedBy F] [h₁.right.IsPreservedBy F]
[h₂.left.IsPreservedBy F] [h₂.right.IsPreservedBy F] :
HomologyMapData (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F) where
left := ψ.left.map F
right := ψ.right.map F
end ShortComplex
namespace Functor
variable (F : C ⥤ D) [PreservesZeroMorphisms F] (S : ShortComplex C) {S₁ S₂ : ShortComplex C}
/-- A functor preserves the left homology of a short complex `S` if it preserves all the
left homology data of `S`. -/
class PreservesLeftHomologyOf : Prop where
/-- the functor preserves all the left homology data of the short complex -/
isPreservedBy : ∀ (h : S.LeftHomologyData), h.IsPreservedBy F
/-- A functor preserves the right homology of a short complex `S` if it preserves all the
right homology data of `S`. -/
class PreservesRightHomologyOf : Prop where
/-- the functor preserves all the right homology data of the short complex -/
isPreservedBy : ∀ (h : S.RightHomologyData), h.IsPreservedBy F
instance PreservesHomology.preservesLeftHomologyOf [F.PreservesHomology] :
F.PreservesLeftHomologyOf S := ⟨inferInstance⟩
instance PreservesHomology.preservesRightHomologyOf [F.PreservesHomology] :
F.PreservesRightHomologyOf S := ⟨inferInstance⟩
variable {S}
/-- If a functor preserves a certain left homology data of a short complex `S`, then it
preserves the left homology of `S`. -/
lemma PreservesLeftHomologyOf.mk' (h : S.LeftHomologyData) [h.IsPreservedBy F] :
F.PreservesLeftHomologyOf S where
isPreservedBy h' :=
{ g := ShortComplex.LeftHomologyData.IsPreservedBy.hg h F
f' := by
have := ShortComplex.LeftHomologyData.IsPreservedBy.hf' h F
let e : parallelPair h.f' 0 ≅ parallelPair h'.f' 0 :=
parallelPair.ext (Iso.refl _) (ShortComplex.cyclesMapIso' (Iso.refl S) h h')
(by simp) (by simp)
exact preservesColimit_of_iso_diagram F e }
/-- If a functor preserves a certain right homology data of a short complex `S`, then it
preserves the right homology of `S`. -/
lemma PreservesRightHomologyOf.mk' (h : S.RightHomologyData) [h.IsPreservedBy F] :
F.PreservesRightHomologyOf S where
isPreservedBy h' :=
{ f := ShortComplex.RightHomologyData.IsPreservedBy.hf h F
g' := by
have := ShortComplex.RightHomologyData.IsPreservedBy.hg' h F
let e : parallelPair h.g' 0 ≅ parallelPair h'.g' 0 :=
parallelPair.ext (ShortComplex.opcyclesMapIso' (Iso.refl S) h h') (Iso.refl _)
(by simp) (by simp)
exact preservesLimit_of_iso_diagram F e }
end Functor
namespace ShortComplex
variable {S : ShortComplex C} (h₁ : S.LeftHomologyData) (h₂ : S.RightHomologyData)
(F : C ⥤ D) [F.PreservesZeroMorphisms]
instance LeftHomologyData.isPreservedBy_of_preserves [F.PreservesLeftHomologyOf S] :
h₁.IsPreservedBy F :=
Functor.PreservesLeftHomologyOf.isPreservedBy _
instance RightHomologyData.isPreservedBy_of_preserves [F.PreservesRightHomologyOf S] :
h₂.IsPreservedBy F :=
Functor.PreservesRightHomologyOf.isPreservedBy _
variable (S)
instance hasLeftHomology_of_preserves [S.HasLeftHomology] [F.PreservesLeftHomologyOf S] :
(S.map F).HasLeftHomology :=
HasLeftHomology.mk' (S.leftHomologyData.map F)
instance hasLeftHomology_of_preserves' [S.HasLeftHomology] [F.PreservesLeftHomologyOf S] :
(F.mapShortComplex.obj S).HasLeftHomology := by
dsimp; infer_instance
instance hasRightHomology_of_preserves [S.HasRightHomology] [F.PreservesRightHomologyOf S] :
(S.map F).HasRightHomology :=
HasRightHomology.mk' (S.rightHomologyData.map F)
instance hasRightHomology_of_preserves' [S.HasRightHomology] [F.PreservesRightHomologyOf S] :
(F.mapShortComplex.obj S).HasRightHomology := by
dsimp; infer_instance
instance hasHomology_of_preserves [S.HasHomology] [F.PreservesLeftHomologyOf S]
[F.PreservesRightHomologyOf S] :
(S.map F).HasHomology :=
HasHomology.mk' (S.homologyData.map F)
instance hasHomology_of_preserves' [S.HasHomology] [F.PreservesLeftHomologyOf S]
[F.PreservesRightHomologyOf S] :
(F.mapShortComplex.obj S).HasHomology := by
dsimp; infer_instance
section
variable
(hl : S.LeftHomologyData) (hr : S.RightHomologyData)
{S₁ S₂ : ShortComplex C} (φ : S₁ ⟶ S₂)
(hl₁ : S₁.LeftHomologyData) (hr₁ : S₁.RightHomologyData)
(hl₂ : S₂.LeftHomologyData) (hr₂ : S₂.RightHomologyData)
(h₁ : S₁.HomologyData) (h₂ : S₂.HomologyData)
(F : C ⥤ D) [F.PreservesZeroMorphisms]
namespace LeftHomologyData
variable [hl₁.IsPreservedBy F] [hl₂.IsPreservedBy F]
lemma map_cyclesMap' : F.map (ShortComplex.cyclesMap' φ hl₁ hl₂) =
ShortComplex.cyclesMap' (F.mapShortComplex.map φ) (hl₁.map F) (hl₂.map F) := by
have γ : ShortComplex.LeftHomologyMapData φ hl₁ hl₂ := default
rw [γ.cyclesMap'_eq, (γ.map F).cyclesMap'_eq, ShortComplex.LeftHomologyMapData.map_φK]
lemma map_leftHomologyMap' : F.map (ShortComplex.leftHomologyMap' φ hl₁ hl₂) =
ShortComplex.leftHomologyMap' (F.mapShortComplex.map φ) (hl₁.map F) (hl₂.map F) := by
have γ : ShortComplex.LeftHomologyMapData φ hl₁ hl₂ := default
rw [γ.leftHomologyMap'_eq, (γ.map F).leftHomologyMap'_eq,
ShortComplex.LeftHomologyMapData.map_φH]
end LeftHomologyData
namespace RightHomologyData
variable [hr₁.IsPreservedBy F] [hr₂.IsPreservedBy F]
lemma map_opcyclesMap' : F.map (ShortComplex.opcyclesMap' φ hr₁ hr₂) =
ShortComplex.opcyclesMap' (F.mapShortComplex.map φ) (hr₁.map F) (hr₂.map F) := by
have γ : ShortComplex.RightHomologyMapData φ hr₁ hr₂ := default
rw [γ.opcyclesMap'_eq, (γ.map F).opcyclesMap'_eq, ShortComplex.RightHomologyMapData.map_φQ]
lemma map_rightHomologyMap' : F.map (ShortComplex.rightHomologyMap' φ hr₁ hr₂) =
ShortComplex.rightHomologyMap' (F.mapShortComplex.map φ) (hr₁.map F) (hr₂.map F) := by
have γ : ShortComplex.RightHomologyMapData φ hr₁ hr₂ := default
rw [γ.rightHomologyMap'_eq, (γ.map F).rightHomologyMap'_eq,
ShortComplex.RightHomologyMapData.map_φH]
end RightHomologyData
lemma HomologyData.map_homologyMap'
[h₁.left.IsPreservedBy F] [h₁.right.IsPreservedBy F]
[h₂.left.IsPreservedBy F] [h₂.right.IsPreservedBy F] :
F.map (ShortComplex.homologyMap' φ h₁ h₂) =
ShortComplex.homologyMap' (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F) :=
LeftHomologyData.map_leftHomologyMap' _ _ _ _
/-- When a functor `F` preserves the left homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).cycles ≅ F.obj S.cycles`. -/
noncomputable def mapCyclesIso [S.HasLeftHomology] [F.PreservesLeftHomologyOf S] :
(S.map F).cycles ≅ F.obj S.cycles :=
(S.leftHomologyData.map F).cyclesIso
@[reassoc (attr := simp)]
lemma mapCyclesIso_hom_iCycles [S.HasLeftHomology] [F.PreservesLeftHomologyOf S] :
(S.mapCyclesIso F).hom ≫ F.map S.iCycles = (S.map F).iCycles := by
apply LeftHomologyData.cyclesIso_hom_comp_i
/-- When a functor `F` preserves the left homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).leftHomology ≅ F.obj S.leftHomology`. -/
noncomputable def mapLeftHomologyIso [S.HasLeftHomology] [F.PreservesLeftHomologyOf S] :
(S.map F).leftHomology ≅ F.obj S.leftHomology :=
(S.leftHomologyData.map F).leftHomologyIso
/-- When a functor `F` preserves the right homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).opcycles ≅ F.obj S.opcycles`. -/
noncomputable def mapOpcyclesIso [S.HasRightHomology] [F.PreservesRightHomologyOf S] :
(S.map F).opcycles ≅ F.obj S.opcycles :=
(S.rightHomologyData.map F).opcyclesIso
/-- When a functor `F` preserves the right homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).rightHomology ≅ F.obj S.rightHomology`. -/
noncomputable def mapRightHomologyIso [S.HasRightHomology] [F.PreservesRightHomologyOf S] :
(S.map F).rightHomology ≅ F.obj S.rightHomology :=
(S.rightHomologyData.map F).rightHomologyIso
/-- When a functor `F` preserves the left homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).homology ≅ F.obj S.homology`. -/
noncomputable def mapHomologyIso [S.HasHomology] [(S.map F).HasHomology]
[F.PreservesLeftHomologyOf S] :
(S.map F).homology ≅ F.obj S.homology :=
(S.homologyData.left.map F).homologyIso
/-- When a functor `F` preserves the right homology of a short complex `S`, this is the
canonical isomorphism `(S.map F).homology ≅ F.obj S.homology`. -/
noncomputable def mapHomologyIso' [S.HasHomology] [(S.map F).HasHomology]
[F.PreservesRightHomologyOf S] :
(S.map F).homology ≅ F.obj S.homology :=
(S.homologyData.right.map F).homologyIso ≪≫ F.mapIso S.homologyData.right.homologyIso.symm
variable {S}
lemma LeftHomologyData.mapCyclesIso_eq [S.HasLeftHomology]
[F.PreservesLeftHomologyOf S] :
S.mapCyclesIso F = (hl.map F).cyclesIso ≪≫ F.mapIso hl.cyclesIso.symm := by
ext
dsimp [mapCyclesIso, cyclesIso]
simp only [map_cyclesMap', ← cyclesMap'_comp, Functor.map_id, comp_id,
Functor.mapShortComplex_obj]
lemma LeftHomologyData.mapLeftHomologyIso_eq [S.HasLeftHomology]
[F.PreservesLeftHomologyOf S] :
S.mapLeftHomologyIso F = (hl.map F).leftHomologyIso ≪≫ F.mapIso hl.leftHomologyIso.symm := by
ext
dsimp [mapLeftHomologyIso, leftHomologyIso]
simp only [map_leftHomologyMap', ← leftHomologyMap'_comp, Functor.map_id, comp_id,
Functor.mapShortComplex_obj]
lemma RightHomologyData.mapOpcyclesIso_eq [S.HasRightHomology]
[F.PreservesRightHomologyOf S] :
S.mapOpcyclesIso F = (hr.map F).opcyclesIso ≪≫ F.mapIso hr.opcyclesIso.symm := by
ext
dsimp [mapOpcyclesIso, opcyclesIso]
simp only [map_opcyclesMap', ← opcyclesMap'_comp, Functor.map_id, comp_id,
Functor.mapShortComplex_obj]
lemma RightHomologyData.mapRightHomologyIso_eq [S.HasRightHomology]
[F.PreservesRightHomologyOf S] :
S.mapRightHomologyIso F = (hr.map F).rightHomologyIso ≪≫
F.mapIso hr.rightHomologyIso.symm := by
ext
dsimp [mapRightHomologyIso, rightHomologyIso]
simp only [map_rightHomologyMap', ← rightHomologyMap'_comp, Functor.map_id, comp_id,
Functor.mapShortComplex_obj]
lemma LeftHomologyData.mapHomologyIso_eq [S.HasHomology]
[(S.map F).HasHomology] [F.PreservesLeftHomologyOf S] :
S.mapHomologyIso F = (hl.map F).homologyIso ≪≫ F.mapIso hl.homologyIso.symm := by
ext
dsimp only [mapHomologyIso, homologyIso, ShortComplex.leftHomologyIso,
leftHomologyMapIso', leftHomologyIso, Functor.mapIso,
Iso.symm, Iso.trans, Iso.refl]
simp only [F.map_comp, map_leftHomologyMap', ← leftHomologyMap'_comp, comp_id,
Functor.map_id, Functor.mapShortComplex_obj]
lemma RightHomologyData.mapHomologyIso'_eq [S.HasHomology]
[(S.map F).HasHomology] [F.PreservesRightHomologyOf S] :
S.mapHomologyIso' F = (hr.map F).homologyIso ≪≫ F.mapIso hr.homologyIso.symm := by
ext
dsimp only [Iso.trans, Iso.symm, Iso.refl, Functor.mapIso, mapHomologyIso', homologyIso,
rightHomologyIso, rightHomologyMapIso', ShortComplex.rightHomologyIso]
simp only [assoc, F.map_comp, map_rightHomologyMap', ← rightHomologyMap'_comp_assoc]
@[reassoc]
lemma mapCyclesIso_hom_naturality [S₁.HasLeftHomology] [S₂.HasLeftHomology]
[F.PreservesLeftHomologyOf S₁] [F.PreservesLeftHomologyOf S₂] :
cyclesMap (F.mapShortComplex.map φ) ≫ (S₂.mapCyclesIso F).hom =
(S₁.mapCyclesIso F).hom ≫ F.map (cyclesMap φ) := by
dsimp only [cyclesMap, mapCyclesIso, LeftHomologyData.cyclesIso, cyclesMapIso', Iso.refl]
simp only [LeftHomologyData.map_cyclesMap', Functor.mapShortComplex_obj, ← cyclesMap'_comp,
comp_id, id_comp]
@[reassoc]
lemma mapCyclesIso_inv_naturality [S₁.HasLeftHomology] [S₂.HasLeftHomology]
[F.PreservesLeftHomologyOf S₁] [F.PreservesLeftHomologyOf S₂] :
F.map (cyclesMap φ) ≫ (S₂.mapCyclesIso F).inv =
(S₁.mapCyclesIso F).inv ≫ cyclesMap (F.mapShortComplex.map φ) := by
rw [← cancel_epi (S₁.mapCyclesIso F).hom, ← mapCyclesIso_hom_naturality_assoc,
Iso.hom_inv_id, comp_id, Iso.hom_inv_id_assoc]
@[reassoc]
lemma mapLeftHomologyIso_hom_naturality [S₁.HasLeftHomology] [S₂.HasLeftHomology]
[F.PreservesLeftHomologyOf S₁] [F.PreservesLeftHomologyOf S₂] :
leftHomologyMap (F.mapShortComplex.map φ) ≫ (S₂.mapLeftHomologyIso F).hom =
(S₁.mapLeftHomologyIso F).hom ≫ F.map (leftHomologyMap φ) := by
dsimp only [leftHomologyMap, mapLeftHomologyIso, LeftHomologyData.leftHomologyIso,
leftHomologyMapIso', Iso.refl]
simp only [LeftHomologyData.map_leftHomologyMap', Functor.mapShortComplex_obj,
← leftHomologyMap'_comp, comp_id, id_comp]
@[reassoc]
lemma mapLeftHomologyIso_inv_naturality [S₁.HasLeftHomology] [S₂.HasLeftHomology]
[F.PreservesLeftHomologyOf S₁] [F.PreservesLeftHomologyOf S₂] :
F.map (leftHomologyMap φ) ≫ (S₂.mapLeftHomologyIso F).inv =
(S₁.mapLeftHomologyIso F).inv ≫ leftHomologyMap (F.mapShortComplex.map φ) := by
rw [← cancel_epi (S₁.mapLeftHomologyIso F).hom, ← mapLeftHomologyIso_hom_naturality_assoc,
Iso.hom_inv_id, comp_id, Iso.hom_inv_id_assoc]
@[reassoc]
lemma mapOpcyclesIso_hom_naturality [S₁.HasRightHomology] [S₂.HasRightHomology]
[F.PreservesRightHomologyOf S₁] [F.PreservesRightHomologyOf S₂] :
opcyclesMap (F.mapShortComplex.map φ) ≫ (S₂.mapOpcyclesIso F).hom =
(S₁.mapOpcyclesIso F).hom ≫ F.map (opcyclesMap φ) := by
dsimp only [opcyclesMap, mapOpcyclesIso, RightHomologyData.opcyclesIso,
opcyclesMapIso', Iso.refl]
simp only [RightHomologyData.map_opcyclesMap', Functor.mapShortComplex_obj, ← opcyclesMap'_comp,
comp_id, id_comp]
@[reassoc]
lemma mapOpcyclesIso_inv_naturality [S₁.HasRightHomology] [S₂.HasRightHomology]
[F.PreservesRightHomologyOf S₁] [F.PreservesRightHomologyOf S₂] :
F.map (opcyclesMap φ) ≫ (S₂.mapOpcyclesIso F).inv =
(S₁.mapOpcyclesIso F).inv ≫ opcyclesMap (F.mapShortComplex.map φ) := by
rw [← cancel_epi (S₁.mapOpcyclesIso F).hom, ← mapOpcyclesIso_hom_naturality_assoc,
Iso.hom_inv_id, comp_id, Iso.hom_inv_id_assoc]
@[reassoc]
lemma mapRightHomologyIso_hom_naturality [S₁.HasRightHomology] [S₂.HasRightHomology]
[F.PreservesRightHomologyOf S₁] [F.PreservesRightHomologyOf S₂] :
rightHomologyMap (F.mapShortComplex.map φ) ≫ (S₂.mapRightHomologyIso F).hom =
(S₁.mapRightHomologyIso F).hom ≫ F.map (rightHomologyMap φ) := by
dsimp only [rightHomologyMap, mapRightHomologyIso, RightHomologyData.rightHomologyIso,
rightHomologyMapIso', Iso.refl]
simp only [RightHomologyData.map_rightHomologyMap', Functor.mapShortComplex_obj,
← rightHomologyMap'_comp, comp_id, id_comp]
@[reassoc]
lemma mapRightHomologyIso_inv_naturality [S₁.HasRightHomology] [S₂.HasRightHomology]
[F.PreservesRightHomologyOf S₁] [F.PreservesRightHomologyOf S₂] :
F.map (rightHomologyMap φ) ≫ (S₂.mapRightHomologyIso F).inv =
(S₁.mapRightHomologyIso F).inv ≫ rightHomologyMap (F.mapShortComplex.map φ) := by
rw [← cancel_epi (S₁.mapRightHomologyIso F).hom, ← mapRightHomologyIso_hom_naturality_assoc,
| Iso.hom_inv_id, comp_id, Iso.hom_inv_id_assoc]
@[reassoc]
lemma mapHomologyIso_hom_naturality [S₁.HasHomology] [S₂.HasHomology]
[(S₁.map F).HasHomology] [(S₂.map F).HasHomology]
[F.PreservesLeftHomologyOf S₁] [F.PreservesLeftHomologyOf S₂] :
@homologyMap _ _ _ (S₁.map F) (S₂.map F) (F.mapShortComplex.map φ) _ _ ≫
(S₂.mapHomologyIso F).hom = (S₁.mapHomologyIso F).hom ≫ F.map (homologyMap φ) := by
dsimp only [homologyMap, homologyMap', mapHomologyIso, LeftHomologyData.homologyIso,
LeftHomologyData.leftHomologyIso, leftHomologyMapIso', leftHomologyIso,
| Mathlib/Algebra/Homology/ShortComplex/PreservesHomology.lean | 564 | 573 |
/-
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.Analysis.InnerProductSpace.Convex
import Mathlib.Analysis.InnerProductSpace.PiL2
import Mathlib.Combinatorics.Additive.AP.Three.Defs
import Mathlib.Combinatorics.Pigeonhole
import Mathlib.Data.Complex.ExponentialBounds
/-!
# Behrend's bound on Roth numbers
This file proves Behrend's lower bound on Roth numbers. This says that we can find a subset of
`{1, ..., n}` of size `n / exp (O (sqrt (log n)))` which does not contain arithmetic progressions of
length `3`.
The idea is that the sphere (in the `n` dimensional Euclidean space) doesn't contain arithmetic
progressions (literally) because the corresponding ball is strictly convex. Thus we can take
integer points on that sphere and map them onto `ℕ` in a way that preserves arithmetic progressions
(`Behrend.map`).
## Main declarations
* `Behrend.sphere`: The intersection of the Euclidean sphere with the positive integer quadrant.
This is the set that we will map on `ℕ`.
* `Behrend.map`: Given a natural number `d`, `Behrend.map d : ℕⁿ → ℕ` reads off the coordinates as
digits in base `d`.
* `Behrend.card_sphere_le_rothNumberNat`: Implicit lower bound on Roth numbers in terms of
`Behrend.sphere`.
* `Behrend.roth_lower_bound`: Behrend's explicit lower bound on Roth numbers.
## References
* [Bryan Gillespie, *Behrend’s Construction*]
(http://www.epsilonsmall.com/resources/behrends-construction/behrend.pdf)
* Behrend, F. A., "On sets of integers which contain no three terms in arithmetical progression"
* [Wikipedia, *Salem-Spencer set*](https://en.wikipedia.org/wiki/Salem–Spencer_set)
## Tags
3AP-free, Salem-Spencer, Behrend construction, arithmetic progression, sphere, strictly convex
-/
assert_not_exists IsConformalMap Conformal
open Nat hiding log
open Finset Metric Real
open scoped Pointwise
/-- The frontier of a closed strictly convex set only contains trivial arithmetic progressions.
The idea is that an arithmetic progression is contained on a line and the frontier of a strictly
convex set does not contain lines. -/
lemma threeAPFree_frontier {𝕜 E : Type*} [Field 𝕜] [LinearOrder 𝕜] [IsStrictOrderedRing 𝕜]
[TopologicalSpace E]
[AddCommMonoid E] [Module 𝕜 E] {s : Set E} (hs₀ : IsClosed s) (hs₁ : StrictConvex 𝕜 s) :
ThreeAPFree (frontier s) := by
intro a ha b hb c hc habc
obtain rfl : (1 / 2 : 𝕜) • a + (1 / 2 : 𝕜) • c = b := by
rwa [← smul_add, one_div, inv_smul_eq_iff₀ (show (2 : 𝕜) ≠ 0 by norm_num), two_smul]
have :=
hs₁.eq (hs₀.frontier_subset ha) (hs₀.frontier_subset hc) one_half_pos one_half_pos
(add_halves _) hb.2
simp [this, ← add_smul]
ring_nf
simp
lemma threeAPFree_sphere {E : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
[StrictConvexSpace ℝ E] (x : E) (r : ℝ) : ThreeAPFree (sphere x r) := by
obtain rfl | hr := eq_or_ne r 0
· rw [sphere_zero]
exact threeAPFree_singleton _
· convert threeAPFree_frontier isClosed_closedBall (strictConvex_closedBall ℝ x r)
exact (frontier_closedBall _ hr).symm
namespace Behrend
variable {n d k N : ℕ} {x : Fin n → ℕ}
/-!
### Turning the sphere into 3AP-free set
We define `Behrend.sphere`, the intersection of the $L^2$ sphere with the positive quadrant of
integer points. Because the $L^2$ closed ball is strictly convex, the $L^2$ sphere and
`Behrend.sphere` are 3AP-free (`threeAPFree_sphere`). Then we can turn this set in
`Fin n → ℕ` into a set in `ℕ` using `Behrend.map`, which preserves `ThreeAPFree` because it is
an additive monoid homomorphism.
-/
/-- The box `{0, ..., d - 1}^n` as a `Finset`. -/
def box (n d : ℕ) : Finset (Fin n → ℕ) :=
Fintype.piFinset fun _ => range d
theorem mem_box : x ∈ box n d ↔ ∀ i, x i < d := by simp only [box, Fintype.mem_piFinset, mem_range]
@[simp]
theorem card_box : #(box n d) = d ^ n := by simp [box]
@[simp]
theorem box_zero : box (n + 1) 0 = ∅ := by simp [box]
/-- The intersection of the sphere of radius `√k` with the integer points in the positive
quadrant. -/
def sphere (n d k : ℕ) : Finset (Fin n → ℕ) := {x ∈ box n d | ∑ i, x i ^ 2 = k}
theorem sphere_zero_subset : sphere n d 0 ⊆ 0 := fun x => by simp [sphere, funext_iff]
@[simp]
theorem sphere_zero_right (n k : ℕ) : sphere (n + 1) 0 k = ∅ := by simp [sphere]
theorem sphere_subset_box : sphere n d k ⊆ box n d :=
filter_subset _ _
theorem norm_of_mem_sphere {x : Fin n → ℕ} (hx : x ∈ sphere n d k) :
‖(WithLp.equiv 2 _).symm ((↑) ∘ x : Fin n → ℝ)‖ = √↑k := by
rw [EuclideanSpace.norm_eq]
dsimp
simp_rw [abs_cast, ← cast_pow, ← cast_sum, (mem_filter.1 hx).2]
theorem sphere_subset_preimage_metric_sphere : (sphere n d k : Set (Fin n → ℕ)) ⊆
(fun x : Fin n → ℕ => (WithLp.equiv 2 _).symm ((↑) ∘ x : Fin n → ℝ)) ⁻¹'
Metric.sphere (0 : PiLp 2 fun _ : Fin n => ℝ) (√↑k) :=
fun x hx => by rw [Set.mem_preimage, mem_sphere_zero_iff_norm, norm_of_mem_sphere hx]
/-- The map that appears in Behrend's bound on Roth numbers. -/
@[simps]
def map (d : ℕ) : (Fin n → ℕ) →+ ℕ where
toFun a := ∑ i, a i * d ^ (i : ℕ)
map_zero' := by simp_rw [Pi.zero_apply, zero_mul, sum_const_zero]
map_add' a b := by simp_rw [Pi.add_apply, add_mul, sum_add_distrib]
theorem map_zero (d : ℕ) (a : Fin 0 → ℕ) : map d a = 0 := by simp [map]
theorem map_succ (a : Fin (n + 1) → ℕ) :
map d a = a 0 + (∑ x : Fin n, a x.succ * d ^ (x : ℕ)) * d := by
simp [map, Fin.sum_univ_succ, _root_.pow_succ, ← mul_assoc, ← sum_mul]
theorem map_succ' (a : Fin (n + 1) → ℕ) : map d a = a 0 + map d (a ∘ Fin.succ) * d :=
map_succ _
theorem map_monotone (d : ℕ) : Monotone (map d : (Fin n → ℕ) → ℕ) := fun x y h => by
dsimp; exact sum_le_sum fun i _ => Nat.mul_le_mul_right _ <| h i
theorem map_mod (a : Fin n.succ → ℕ) : map d a % d = a 0 % d := by
rw [map_succ, Nat.add_mul_mod_self_right]
theorem map_eq_iff {x₁ x₂ : Fin n.succ → ℕ} (hx₁ : ∀ i, x₁ i < d) (hx₂ : ∀ i, x₂ i < d) :
map d x₁ = map d x₂ ↔ x₁ 0 = x₂ 0 ∧ map d (x₁ ∘ Fin.succ) = map d (x₂ ∘ Fin.succ) := by
refine ⟨fun h => ?_, fun h => by rw [map_succ', map_succ', h.1, h.2]⟩
have : x₁ 0 = x₂ 0 := by
rw [← mod_eq_of_lt (hx₁ _), ← map_mod, ← mod_eq_of_lt (hx₂ _), ← map_mod, h]
rw [map_succ, map_succ, this, add_right_inj, mul_eq_mul_right_iff] at h
exact ⟨this, h.resolve_right (pos_of_gt (hx₁ 0)).ne'⟩
theorem map_injOn : {x : Fin n → ℕ | ∀ i, x i < d}.InjOn (map d) := by
intro x₁ hx₁ x₂ hx₂ h
induction n with
| zero => simp [eq_iff_true_of_subsingleton]
| succ n ih =>
ext i
have x := (map_eq_iff hx₁ hx₂).1 h
exact Fin.cases x.1 (congr_fun <| ih (fun _ => hx₁ _) (fun _ => hx₂ _) x.2) i
theorem map_le_of_mem_box (hx : x ∈ box n d) :
map (2 * d - 1) x ≤ ∑ i : Fin n, (d - 1) * (2 * d - 1) ^ (i : ℕ) :=
map_monotone (2 * d - 1) fun _ => Nat.le_sub_one_of_lt <| mem_box.1 hx _
nonrec theorem threeAPFree_sphere : ThreeAPFree (sphere n d k : Set (Fin n → ℕ)) := by
set f : (Fin n → ℕ) →+ EuclideanSpace ℝ (Fin n) :=
{ toFun := fun f => ((↑) : ℕ → ℝ) ∘ f
map_zero' := funext fun _ => cast_zero
map_add' := fun _ _ => funext fun _ => cast_add _ _ }
refine ThreeAPFree.of_image (AddMonoidHomClass.isAddFreimanHom f (Set.mapsTo_image _ _))
cast_injective.comp_left.injOn (Set.subset_univ _) ?_
refine (threeAPFree_sphere 0 (√↑k)).mono (Set.image_subset_iff.2 fun x => ?_)
rw [Set.mem_preimage, mem_sphere_zero_iff_norm]
exact norm_of_mem_sphere
theorem threeAPFree_image_sphere :
ThreeAPFree ((sphere n d k).image (map (2 * d - 1)) : Set ℕ) := by
rw [coe_image]
apply ThreeAPFree.image' (α := Fin n → ℕ) (β := ℕ) (s := sphere n d k) (map (2 * d - 1))
(map_injOn.mono _) threeAPFree_sphere
rw [Set.add_subset_iff]
rintro a ha b hb i
have hai := mem_box.1 (sphere_subset_box ha) i
have hbi := mem_box.1 (sphere_subset_box hb) i
rw [lt_tsub_iff_right, ← succ_le_iff, two_mul]
exact (add_add_add_comm _ _ 1 1).trans_le (_root_.add_le_add hai hbi)
theorem sum_sq_le_of_mem_box (hx : x ∈ box n d) : ∑ i : Fin n, x i ^ 2 ≤ n * (d - 1) ^ 2 := by
rw [mem_box] at hx
have : ∀ i, x i ^ 2 ≤ (d - 1) ^ 2 := fun i =>
Nat.pow_le_pow_left (Nat.le_sub_one_of_lt (hx i)) _
exact (sum_le_card_nsmul univ _ _ fun i _ => this i).trans (by rw [card_fin, smul_eq_mul])
theorem sum_eq : (∑ i : Fin n, d * (2 * d + 1) ^ (i : ℕ)) = ((2 * d + 1) ^ n - 1) / 2 := by
refine (Nat.div_eq_of_eq_mul_left zero_lt_two ?_).symm
rw [← sum_range fun i => d * (2 * d + 1) ^ (i : ℕ), ← mul_sum, mul_right_comm, mul_comm d, ←
geom_sum_mul_add, add_tsub_cancel_right, mul_comm]
theorem sum_lt : (∑ i : Fin n, d * (2 * d + 1) ^ (i : ℕ)) < (2 * d + 1) ^ n :=
sum_eq.trans_lt <| (Nat.div_le_self _ 2).trans_lt <| pred_lt (pow_pos (succ_pos _) _).ne'
theorem card_sphere_le_rothNumberNat (n d k : ℕ) :
#(sphere n d k) ≤ rothNumberNat ((2 * d - 1) ^ n) := by
cases n
· dsimp; refine (card_le_univ _).trans_eq ?_; rfl
cases d
· simp
apply threeAPFree_image_sphere.le_rothNumberNat _ _ (card_image_of_injOn _)
· simp only [subset_iff, mem_image, and_imp, forall_exists_index, mem_range,
forall_apply_eq_imp_iff₂, sphere, mem_filter]
rintro _ x hx _ rfl
exact (map_le_of_mem_box hx).trans_lt sum_lt
apply map_injOn.mono fun x => ?_
simp only [mem_coe, sphere, mem_filter, mem_box, and_imp, two_mul]
exact fun h _ i => (h i).trans_le le_self_add
/-!
### Optimization
Now that we know how to turn the integer points of any sphere into a 3AP-free set, we find a
sphere containing many integer points by the pigeonhole principle. This gives us an implicit bound
that we then optimize by tweaking the parameters. The (almost) optimal parameters are
`Behrend.nValue` and `Behrend.dValue`.
-/
theorem exists_large_sphere_aux (n d : ℕ) : ∃ k ∈ range (n * (d - 1) ^ 2 + 1),
(↑(d ^ n) / ((n * (d - 1) ^ 2 :) + 1) : ℝ) ≤ #(sphere n d k) := by
refine exists_le_card_fiber_of_nsmul_le_card_of_maps_to (fun x hx => ?_) nonempty_range_succ ?_
· rw [mem_range, Nat.lt_succ_iff]
exact sum_sq_le_of_mem_box hx
· rw [card_range, _root_.nsmul_eq_mul, mul_div_assoc', cast_add_one, mul_div_cancel_left₀,
card_box]
exact (cast_add_one_pos _).ne'
theorem exists_large_sphere (n d : ℕ) :
∃ k, ((d ^ n :) / (n * d ^ 2 :) : ℝ) ≤ #(sphere n d k) := by
obtain ⟨k, -, hk⟩ := exists_large_sphere_aux n d
refine ⟨k, ?_⟩
obtain rfl | hn := n.eq_zero_or_pos
· simp
obtain rfl | hd := d.eq_zero_or_pos
· simp
refine (div_le_div_of_nonneg_left ?_ ?_ ?_).trans hk
· exact cast_nonneg _
· exact cast_add_one_pos _
simp only [← le_sub_iff_add_le', cast_mul, ← mul_sub, cast_pow, cast_sub hd, sub_sq, one_pow,
cast_one, mul_one, sub_add, sub_sub_self]
apply one_le_mul_of_one_le_of_one_le
· rwa [one_le_cast]
rw [_root_.le_sub_iff_add_le]
norm_num
exact one_le_cast.2 hd
theorem bound_aux' (n d : ℕ) : ((d ^ n :) / (n * d ^ 2 :) : ℝ) ≤ rothNumberNat ((2 * d - 1) ^ n) :=
let ⟨_, h⟩ := exists_large_sphere n d
h.trans <| cast_le.2 <| card_sphere_le_rothNumberNat _ _ _
| theorem bound_aux (hd : d ≠ 0) (hn : 2 ≤ n) :
(d ^ (n - 2 :) / n : ℝ) ≤ rothNumberNat ((2 * d - 1) ^ n) := by
convert bound_aux' n d using 1
rw [cast_mul, cast_pow, mul_comm, ← div_div, pow_sub₀ _ _ hn, ← div_eq_mul_inv, cast_pow]
rwa [cast_ne_zero]
open scoped Filter Topology
| Mathlib/Combinatorics/Additive/AP/Three/Behrend.lean | 264 | 271 |
/-
Copyright (c) 2021 Bryan Gin-ge Chen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Adam Topaz, Bryan Gin-ge Chen, Yaël Dillies
-/
import Mathlib.Order.BooleanAlgebra
import Mathlib.Logic.Equiv.Basic
/-!
# Symmetric difference and bi-implication
This file defines the symmetric difference and bi-implication operators in (co-)Heyting algebras.
## Examples
Some examples are
* The symmetric difference of two sets is the set of elements that are in either but not both.
* The symmetric difference on propositions is `Xor'`.
* The symmetric difference on `Bool` is `Bool.xor`.
* The equivalence of propositions. Two propositions are equivalent if they imply each other.
* The symmetric difference translates to addition when considering a Boolean algebra as a Boolean
ring.
## Main declarations
* `symmDiff`: The symmetric difference operator, defined as `(a \ b) ⊔ (b \ a)`
* `bihimp`: The bi-implication operator, defined as `(b ⇨ a) ⊓ (a ⇨ b)`
In generalized Boolean algebras, the symmetric difference operator is:
* `symmDiff_comm`: commutative, and
* `symmDiff_assoc`: associative.
## Notations
* `a ∆ b`: `symmDiff a b`
* `a ⇔ b`: `bihimp a b`
## References
The proof of associativity follows the note "Associativity of the Symmetric Difference of Sets: A
Proof from the Book" by John McCuan:
* <https://people.math.gatech.edu/~mccuan/courses/4317/symmetricdifference.pdf>
## Tags
boolean ring, generalized boolean algebra, boolean algebra, symmetric difference, bi-implication,
Heyting
-/
assert_not_exists RelIso
open Function OrderDual
variable {ι α β : Type*} {π : ι → Type*}
/-- The symmetric difference operator on a type with `⊔` and `\` is `(A \ B) ⊔ (B \ A)`. -/
def symmDiff [Max α] [SDiff α] (a b : α) : α :=
a \ b ⊔ b \ a
/-- The Heyting bi-implication is `(b ⇨ a) ⊓ (a ⇨ b)`. This generalizes equivalence of
propositions. -/
def bihimp [Min α] [HImp α] (a b : α) : α :=
(b ⇨ a) ⊓ (a ⇨ b)
/-- Notation for symmDiff -/
scoped[symmDiff] infixl:100 " ∆ " => symmDiff
/-- Notation for bihimp -/
scoped[symmDiff] infixl:100 " ⇔ " => bihimp
open scoped symmDiff
theorem symmDiff_def [Max α] [SDiff α] (a b : α) : a ∆ b = a \ b ⊔ b \ a :=
rfl
theorem bihimp_def [Min α] [HImp α] (a b : α) : a ⇔ b = (b ⇨ a) ⊓ (a ⇨ b) :=
rfl
theorem symmDiff_eq_Xor' (p q : Prop) : p ∆ q = Xor' p q :=
rfl
@[simp]
theorem bihimp_iff_iff {p q : Prop} : p ⇔ q ↔ (p ↔ q) :=
iff_iff_implies_and_implies.symm.trans Iff.comm
@[simp]
theorem Bool.symmDiff_eq_xor : ∀ p q : Bool, p ∆ q = xor p q := by decide
section GeneralizedCoheytingAlgebra
variable [GeneralizedCoheytingAlgebra α] (a b c : α)
@[simp]
theorem toDual_symmDiff : toDual (a ∆ b) = toDual a ⇔ toDual b :=
rfl
@[simp]
theorem ofDual_bihimp (a b : αᵒᵈ) : ofDual (a ⇔ b) = ofDual a ∆ ofDual b :=
rfl
theorem symmDiff_comm : a ∆ b = b ∆ a := by simp only [symmDiff, sup_comm]
instance symmDiff_isCommutative : Std.Commutative (α := α) (· ∆ ·) :=
⟨symmDiff_comm⟩
@[simp]
theorem symmDiff_self : a ∆ a = ⊥ := by rw [symmDiff, sup_idem, sdiff_self]
@[simp]
theorem symmDiff_bot : a ∆ ⊥ = a := by rw [symmDiff, sdiff_bot, bot_sdiff, sup_bot_eq]
@[simp]
theorem bot_symmDiff : ⊥ ∆ a = a := by rw [symmDiff_comm, symmDiff_bot]
@[simp]
theorem symmDiff_eq_bot {a b : α} : a ∆ b = ⊥ ↔ a = b := by
simp_rw [symmDiff, sup_eq_bot_iff, sdiff_eq_bot_iff, le_antisymm_iff]
theorem symmDiff_of_le {a b : α} (h : a ≤ b) : a ∆ b = b \ a := by
rw [symmDiff, sdiff_eq_bot_iff.2 h, bot_sup_eq]
theorem symmDiff_of_ge {a b : α} (h : b ≤ a) : a ∆ b = a \ b := by
rw [symmDiff, sdiff_eq_bot_iff.2 h, sup_bot_eq]
theorem symmDiff_le {a b c : α} (ha : a ≤ b ⊔ c) (hb : b ≤ a ⊔ c) : a ∆ b ≤ c :=
sup_le (sdiff_le_iff.2 ha) <| sdiff_le_iff.2 hb
theorem symmDiff_le_iff {a b c : α} : a ∆ b ≤ c ↔ a ≤ b ⊔ c ∧ b ≤ a ⊔ c := by
simp_rw [symmDiff, sup_le_iff, sdiff_le_iff]
@[simp]
theorem symmDiff_le_sup {a b : α} : a ∆ b ≤ a ⊔ b :=
sup_le_sup sdiff_le sdiff_le
theorem symmDiff_eq_sup_sdiff_inf : a ∆ b = (a ⊔ b) \ (a ⊓ b) := by simp [sup_sdiff, symmDiff]
theorem Disjoint.symmDiff_eq_sup {a b : α} (h : Disjoint a b) : a ∆ b = a ⊔ b := by
rw [symmDiff, h.sdiff_eq_left, h.sdiff_eq_right]
theorem symmDiff_sdiff : a ∆ b \ c = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) := by
rw [symmDiff, sup_sdiff_distrib, sdiff_sdiff_left, sdiff_sdiff_left]
@[simp]
theorem symmDiff_sdiff_inf : a ∆ b \ (a ⊓ b) = a ∆ b := by
rw [symmDiff_sdiff]
simp [symmDiff]
@[simp]
theorem symmDiff_sdiff_eq_sup : a ∆ (b \ a) = a ⊔ b := by
rw [symmDiff, sdiff_idem]
exact
le_antisymm (sup_le_sup sdiff_le sdiff_le)
(sup_le le_sdiff_sup <| le_sdiff_sup.trans <| sup_le le_sup_right le_sdiff_sup)
@[simp]
theorem sdiff_symmDiff_eq_sup : (a \ b) ∆ b = a ⊔ b := by
rw [symmDiff_comm, symmDiff_sdiff_eq_sup, sup_comm]
@[simp]
theorem symmDiff_sup_inf : a ∆ b ⊔ a ⊓ b = a ⊔ b := by
refine le_antisymm (sup_le symmDiff_le_sup inf_le_sup) ?_
rw [sup_inf_left, symmDiff]
refine sup_le (le_inf le_sup_right ?_) (le_inf ?_ le_sup_right)
· rw [sup_right_comm]
exact le_sup_of_le_left le_sdiff_sup
· rw [sup_assoc]
exact le_sup_of_le_right le_sdiff_sup
@[simp]
theorem inf_sup_symmDiff : a ⊓ b ⊔ a ∆ b = a ⊔ b := by rw [sup_comm, symmDiff_sup_inf]
@[simp]
theorem symmDiff_symmDiff_inf : a ∆ b ∆ (a ⊓ b) = a ⊔ b := by
rw [← symmDiff_sdiff_inf a, sdiff_symmDiff_eq_sup, symmDiff_sup_inf]
@[simp]
theorem inf_symmDiff_symmDiff : (a ⊓ b) ∆ (a ∆ b) = a ⊔ b := by
rw [symmDiff_comm, symmDiff_symmDiff_inf]
theorem symmDiff_triangle : a ∆ c ≤ a ∆ b ⊔ b ∆ c := by
refine (sup_le_sup (sdiff_triangle a b c) <| sdiff_triangle _ b _).trans_eq ?_
rw [sup_comm (c \ b), sup_sup_sup_comm, symmDiff, symmDiff]
theorem le_symmDiff_sup_right (a b : α) : a ≤ (a ∆ b) ⊔ b := by
convert symmDiff_triangle a b ⊥ <;> rw [symmDiff_bot]
theorem le_symmDiff_sup_left (a b : α) : b ≤ (a ∆ b) ⊔ a :=
symmDiff_comm a b ▸ le_symmDiff_sup_right ..
end GeneralizedCoheytingAlgebra
section GeneralizedHeytingAlgebra
variable [GeneralizedHeytingAlgebra α] (a b c : α)
@[simp]
theorem toDual_bihimp : toDual (a ⇔ b) = toDual a ∆ toDual b :=
rfl
@[simp]
theorem ofDual_symmDiff (a b : αᵒᵈ) : ofDual (a ∆ b) = ofDual a ⇔ ofDual b :=
rfl
theorem bihimp_comm : a ⇔ b = b ⇔ a := by simp only [(· ⇔ ·), inf_comm]
instance bihimp_isCommutative : Std.Commutative (α := α) (· ⇔ ·) :=
⟨bihimp_comm⟩
@[simp]
theorem bihimp_self : a ⇔ a = ⊤ := by rw [bihimp, inf_idem, himp_self]
@[simp]
theorem bihimp_top : a ⇔ ⊤ = a := by rw [bihimp, himp_top, top_himp, inf_top_eq]
@[simp]
theorem top_bihimp : ⊤ ⇔ a = a := by rw [bihimp_comm, bihimp_top]
@[simp]
theorem bihimp_eq_top {a b : α} : a ⇔ b = ⊤ ↔ a = b :=
@symmDiff_eq_bot αᵒᵈ _ _ _
theorem bihimp_of_le {a b : α} (h : a ≤ b) : a ⇔ b = b ⇨ a := by
rw [bihimp, himp_eq_top_iff.2 h, inf_top_eq]
theorem bihimp_of_ge {a b : α} (h : b ≤ a) : a ⇔ b = a ⇨ b := by
rw [bihimp, himp_eq_top_iff.2 h, top_inf_eq]
theorem le_bihimp {a b c : α} (hb : a ⊓ b ≤ c) (hc : a ⊓ c ≤ b) : a ≤ b ⇔ c :=
le_inf (le_himp_iff.2 hc) <| le_himp_iff.2 hb
theorem le_bihimp_iff {a b c : α} : a ≤ b ⇔ c ↔ a ⊓ b ≤ c ∧ a ⊓ c ≤ b := by
simp_rw [bihimp, le_inf_iff, le_himp_iff, and_comm]
@[simp]
theorem inf_le_bihimp {a b : α} : a ⊓ b ≤ a ⇔ b :=
inf_le_inf le_himp le_himp
theorem bihimp_eq_inf_himp_inf : a ⇔ b = a ⊔ b ⇨ a ⊓ b := by simp [himp_inf_distrib, bihimp]
theorem Codisjoint.bihimp_eq_inf {a b : α} (h : Codisjoint a b) : a ⇔ b = a ⊓ b := by
rw [bihimp, h.himp_eq_left, h.himp_eq_right]
theorem himp_bihimp : a ⇨ b ⇔ c = (a ⊓ c ⇨ b) ⊓ (a ⊓ b ⇨ c) := by
rw [bihimp, himp_inf_distrib, himp_himp, himp_himp]
@[simp]
theorem sup_himp_bihimp : a ⊔ b ⇨ a ⇔ b = a ⇔ b := by
rw [himp_bihimp]
simp [bihimp]
@[simp]
theorem bihimp_himp_eq_inf : a ⇔ (a ⇨ b) = a ⊓ b :=
@symmDiff_sdiff_eq_sup αᵒᵈ _ _ _
@[simp]
theorem himp_bihimp_eq_inf : (b ⇨ a) ⇔ b = a ⊓ b :=
@sdiff_symmDiff_eq_sup αᵒᵈ _ _ _
@[simp]
theorem bihimp_inf_sup : a ⇔ b ⊓ (a ⊔ b) = a ⊓ b :=
@symmDiff_sup_inf αᵒᵈ _ _ _
@[simp]
theorem sup_inf_bihimp : (a ⊔ b) ⊓ a ⇔ b = a ⊓ b :=
@inf_sup_symmDiff αᵒᵈ _ _ _
@[simp]
theorem bihimp_bihimp_sup : a ⇔ b ⇔ (a ⊔ b) = a ⊓ b :=
@symmDiff_symmDiff_inf αᵒᵈ _ _ _
@[simp]
theorem sup_bihimp_bihimp : (a ⊔ b) ⇔ (a ⇔ b) = a ⊓ b :=
@inf_symmDiff_symmDiff αᵒᵈ _ _ _
theorem bihimp_triangle : a ⇔ b ⊓ b ⇔ c ≤ a ⇔ c :=
@symmDiff_triangle αᵒᵈ _ _ _ _
end GeneralizedHeytingAlgebra
section CoheytingAlgebra
variable [CoheytingAlgebra α] (a : α)
@[simp]
theorem symmDiff_top' : a ∆ ⊤ = ￢a := by simp [symmDiff]
@[simp]
theorem top_symmDiff' : ⊤ ∆ a = ￢a := by simp [symmDiff]
@[simp]
theorem hnot_symmDiff_self : (￢a) ∆ a = ⊤ := by
rw [eq_top_iff, symmDiff, hnot_sdiff, sup_sdiff_self]
exact Codisjoint.top_le codisjoint_hnot_left
@[simp]
theorem symmDiff_hnot_self : a ∆ (￢a) = ⊤ := by rw [symmDiff_comm, hnot_symmDiff_self]
theorem IsCompl.symmDiff_eq_top {a b : α} (h : IsCompl a b) : a ∆ b = ⊤ := by
rw [h.eq_hnot, hnot_symmDiff_self]
end CoheytingAlgebra
section HeytingAlgebra
variable [HeytingAlgebra α] (a : α)
@[simp]
theorem bihimp_bot : a ⇔ ⊥ = aᶜ := by simp [bihimp]
@[simp]
theorem bot_bihimp : ⊥ ⇔ a = aᶜ := by simp [bihimp]
@[simp]
theorem compl_bihimp_self : aᶜ ⇔ a = ⊥ :=
@hnot_symmDiff_self αᵒᵈ _ _
@[simp]
theorem bihimp_hnot_self : a ⇔ aᶜ = ⊥ :=
@symmDiff_hnot_self αᵒᵈ _ _
theorem IsCompl.bihimp_eq_bot {a b : α} (h : IsCompl a b) : a ⇔ b = ⊥ := by
rw [h.eq_compl, compl_bihimp_self]
end HeytingAlgebra
section GeneralizedBooleanAlgebra
variable [GeneralizedBooleanAlgebra α] (a b c d : α)
@[simp]
theorem sup_sdiff_symmDiff : (a ⊔ b) \ a ∆ b = a ⊓ b :=
sdiff_eq_symm inf_le_sup (by rw [symmDiff_eq_sup_sdiff_inf])
theorem disjoint_symmDiff_inf : Disjoint (a ∆ b) (a ⊓ b) := by
rw [symmDiff_eq_sup_sdiff_inf]
exact disjoint_sdiff_self_left
theorem inf_symmDiff_distrib_left : a ⊓ b ∆ c = (a ⊓ b) ∆ (a ⊓ c) := by
rw [symmDiff_eq_sup_sdiff_inf, inf_sdiff_distrib_left, inf_sup_left, inf_inf_distrib_left,
symmDiff_eq_sup_sdiff_inf]
theorem inf_symmDiff_distrib_right : a ∆ b ⊓ c = (a ⊓ c) ∆ (b ⊓ c) := by
simp_rw [inf_comm _ c, inf_symmDiff_distrib_left]
theorem sdiff_symmDiff : c \ a ∆ b = c ⊓ a ⊓ b ⊔ c \ a ⊓ c \ b := by
simp only [(· ∆ ·), sdiff_sdiff_sup_sdiff']
theorem sdiff_symmDiff' : c \ a ∆ b = c ⊓ a ⊓ b ⊔ c \ (a ⊔ b) := by
rw [sdiff_symmDiff, sdiff_sup]
@[simp]
theorem symmDiff_sdiff_left : a ∆ b \ a = b \ a := by
rw [symmDiff_def, sup_sdiff, sdiff_idem, sdiff_sdiff_self, bot_sup_eq]
@[simp]
theorem symmDiff_sdiff_right : a ∆ b \ b = a \ b := by rw [symmDiff_comm, symmDiff_sdiff_left]
@[simp]
theorem sdiff_symmDiff_left : a \ a ∆ b = a ⊓ b := by simp [sdiff_symmDiff]
@[simp]
theorem sdiff_symmDiff_right : b \ a ∆ b = a ⊓ b := by
rw [symmDiff_comm, inf_comm, sdiff_symmDiff_left]
theorem symmDiff_eq_sup : a ∆ b = a ⊔ b ↔ Disjoint a b := by
refine ⟨fun h => ?_, Disjoint.symmDiff_eq_sup⟩
rw [symmDiff_eq_sup_sdiff_inf, sdiff_eq_self_iff_disjoint] at h
exact h.of_disjoint_inf_of_le le_sup_left
@[simp]
theorem le_symmDiff_iff_left : a ≤ a ∆ b ↔ Disjoint a b := by
refine ⟨fun h => ?_, fun h => h.symmDiff_eq_sup.symm ▸ le_sup_left⟩
rw [symmDiff_eq_sup_sdiff_inf] at h
exact disjoint_iff_inf_le.mpr (le_sdiff_right.1 <| inf_le_of_left_le h).le
@[simp]
theorem le_symmDiff_iff_right : b ≤ a ∆ b ↔ Disjoint a b := by
rw [symmDiff_comm, le_symmDiff_iff_left, disjoint_comm]
theorem symmDiff_symmDiff_left :
a ∆ b ∆ c = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) ⊔ c \ (a ⊔ b) ⊔ a ⊓ b ⊓ c :=
calc
a ∆ b ∆ c = a ∆ b \ c ⊔ c \ a ∆ b := symmDiff_def _ _
_ = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) ⊔ (c \ (a ⊔ b) ⊔ c ⊓ a ⊓ b) := by
{ rw [sdiff_symmDiff', sup_comm (c ⊓ a ⊓ b), symmDiff_sdiff] }
_ = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) ⊔ c \ (a ⊔ b) ⊔ a ⊓ b ⊓ c := by ac_rfl
theorem symmDiff_symmDiff_right :
a ∆ (b ∆ c) = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) ⊔ c \ (a ⊔ b) ⊔ a ⊓ b ⊓ c :=
calc
a ∆ (b ∆ c) = a \ b ∆ c ⊔ b ∆ c \ a := symmDiff_def _ _
_ = a \ (b ⊔ c) ⊔ a ⊓ b ⊓ c ⊔ (b \ (c ⊔ a) ⊔ c \ (b ⊔ a)) := by
{ rw [sdiff_symmDiff', sup_comm (a ⊓ b ⊓ c), symmDiff_sdiff] }
_ = a \ (b ⊔ c) ⊔ b \ (a ⊔ c) ⊔ c \ (a ⊔ b) ⊔ a ⊓ b ⊓ c := by ac_rfl
theorem symmDiff_assoc : a ∆ b ∆ c = a ∆ (b ∆ c) := by
rw [symmDiff_symmDiff_left, symmDiff_symmDiff_right]
instance symmDiff_isAssociative : Std.Associative (α := α) (· ∆ ·) :=
⟨symmDiff_assoc⟩
theorem symmDiff_left_comm : a ∆ (b ∆ c) = b ∆ (a ∆ c) := by
simp_rw [← symmDiff_assoc, symmDiff_comm]
theorem symmDiff_right_comm : a ∆ b ∆ c = a ∆ c ∆ b := by simp_rw [symmDiff_assoc, symmDiff_comm]
theorem symmDiff_symmDiff_symmDiff_comm : a ∆ b ∆ (c ∆ d) = a ∆ c ∆ (b ∆ d) := by
simp_rw [symmDiff_assoc, symmDiff_left_comm]
@[simp]
theorem symmDiff_symmDiff_cancel_left : a ∆ (a ∆ b) = b := by simp [← symmDiff_assoc]
@[simp]
theorem symmDiff_symmDiff_cancel_right : b ∆ a ∆ a = b := by simp [symmDiff_assoc]
@[simp]
theorem symmDiff_symmDiff_self' : a ∆ b ∆ a = b := by
rw [symmDiff_comm, symmDiff_symmDiff_cancel_left]
theorem symmDiff_left_involutive (a : α) : Involutive (· ∆ a) :=
symmDiff_symmDiff_cancel_right _
theorem symmDiff_right_involutive (a : α) : Involutive (a ∆ ·) :=
symmDiff_symmDiff_cancel_left _
theorem symmDiff_left_injective (a : α) : Injective (· ∆ a) :=
Function.Involutive.injective (symmDiff_left_involutive a)
theorem symmDiff_right_injective (a : α) : Injective (a ∆ ·) :=
Function.Involutive.injective (symmDiff_right_involutive _)
theorem symmDiff_left_surjective (a : α) : Surjective (· ∆ a) :=
Function.Involutive.surjective (symmDiff_left_involutive _)
theorem symmDiff_right_surjective (a : α) : Surjective (a ∆ ·) :=
Function.Involutive.surjective (symmDiff_right_involutive _)
variable {a b c}
@[simp]
theorem symmDiff_left_inj : a ∆ b = c ∆ b ↔ a = c :=
(symmDiff_left_injective _).eq_iff
@[simp]
theorem symmDiff_right_inj : a ∆ b = a ∆ c ↔ b = c :=
(symmDiff_right_injective _).eq_iff
| @[simp]
theorem symmDiff_eq_left : a ∆ b = a ↔ b = ⊥ :=
calc
a ∆ b = a ↔ a ∆ b = a ∆ ⊥ := by rw [symmDiff_bot]
| Mathlib/Order/SymmDiff.lean | 450 | 453 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Jens Wagemaker
-/
import Mathlib.Algebra.Polynomial.Degree.Domain
import Mathlib.Algebra.Polynomial.Degree.Support
import Mathlib.Algebra.Polynomial.Eval.Coeff
import Mathlib.GroupTheory.GroupAction.Ring
/-!
# The derivative map on polynomials
## Main definitions
* `Polynomial.derivative`: The formal derivative of polynomials, expressed as a linear map.
* `Polynomial.derivativeFinsupp`: Iterated derivatives as a finite support function.
-/
noncomputable section
open Finset
open Polynomial
open scoped Nat
namespace Polynomial
universe u v w y z
variable {R : Type u} {S : Type v} {T : Type w} {ι : Type y} {A : Type z} {a b : R} {n : ℕ}
section Derivative
section Semiring
variable [Semiring R]
/-- `derivative p` is the formal derivative of the polynomial `p` -/
def derivative : R[X] →ₗ[R] R[X] where
toFun p := p.sum fun n a => C (a * n) * X ^ (n - 1)
map_add' p q := by
rw [sum_add_index] <;>
simp only [add_mul, forall_const, RingHom.map_add, eq_self_iff_true, zero_mul,
RingHom.map_zero]
map_smul' a p := by
dsimp; rw [sum_smul_index] <;>
simp only [mul_sum, ← C_mul', mul_assoc, coeff_C_mul, RingHom.map_mul, forall_const, zero_mul,
RingHom.map_zero, sum]
theorem derivative_apply (p : R[X]) : derivative p = p.sum fun n a => C (a * n) * X ^ (n - 1) :=
rfl
theorem coeff_derivative (p : R[X]) (n : ℕ) :
coeff (derivative p) n = coeff p (n + 1) * (n + 1) := by
rw [derivative_apply]
simp only [coeff_X_pow, coeff_sum, coeff_C_mul]
rw [sum, Finset.sum_eq_single (n + 1)]
· simp only [Nat.add_succ_sub_one, add_zero, mul_one, if_true, eq_self_iff_true]; norm_cast
· intro b
cases b
· intros
rw [Nat.cast_zero, mul_zero, zero_mul]
· intro _ H
rw [Nat.add_one_sub_one, if_neg (mt (congr_arg Nat.succ) H.symm), mul_zero]
· rw [if_pos (add_tsub_cancel_right n 1).symm, mul_one, Nat.cast_add, Nat.cast_one,
mem_support_iff]
intro h
push_neg at h
simp [h]
@[simp]
theorem derivative_zero : derivative (0 : R[X]) = 0 :=
derivative.map_zero
theorem iterate_derivative_zero {k : ℕ} : derivative^[k] (0 : R[X]) = 0 :=
iterate_map_zero derivative k
theorem derivative_monomial (a : R) (n : ℕ) :
derivative (monomial n a) = monomial (n - 1) (a * n) := by
rw [derivative_apply, sum_monomial_index, C_mul_X_pow_eq_monomial]
simp
@[simp]
theorem derivative_monomial_succ (a : R) (n : ℕ) :
derivative (monomial (n + 1) a) = monomial n (a * (n + 1)) := by
rw [derivative_monomial, add_tsub_cancel_right, Nat.cast_add, Nat.cast_one]
theorem derivative_C_mul_X (a : R) : derivative (C a * X) = C a := by
simp [C_mul_X_eq_monomial, derivative_monomial, Nat.cast_one, mul_one]
theorem derivative_C_mul_X_pow (a : R) (n : ℕ) :
derivative (C a * X ^ n) = C (a * n) * X ^ (n - 1) := by
rw [C_mul_X_pow_eq_monomial, C_mul_X_pow_eq_monomial, derivative_monomial]
theorem derivative_C_mul_X_sq (a : R) : derivative (C a * X ^ 2) = C (a * 2) * X := by
rw [derivative_C_mul_X_pow, Nat.cast_two, pow_one]
theorem derivative_X_pow (n : ℕ) : derivative (X ^ n : R[X]) = C (n : R) * X ^ (n - 1) := by
convert derivative_C_mul_X_pow (1 : R) n <;> simp
@[simp]
theorem derivative_X_pow_succ (n : ℕ) :
derivative (X ^ (n + 1) : R[X]) = C (n + 1 : R) * X ^ n := by
simp [derivative_X_pow]
theorem derivative_X_sq : derivative (X ^ 2 : R[X]) = C 2 * X := by
rw [derivative_X_pow, Nat.cast_two, pow_one]
@[simp]
theorem derivative_C {a : R} : derivative (C a) = 0 := by simp [derivative_apply]
theorem derivative_of_natDegree_zero {p : R[X]} (hp : p.natDegree = 0) : derivative p = 0 := by
rw [eq_C_of_natDegree_eq_zero hp, derivative_C]
@[simp]
theorem derivative_X : derivative (X : R[X]) = 1 :=
(derivative_monomial _ _).trans <| by simp
@[simp]
theorem derivative_one : derivative (1 : R[X]) = 0 :=
derivative_C
@[simp]
theorem derivative_add {f g : R[X]} : derivative (f + g) = derivative f + derivative g :=
derivative.map_add f g
theorem derivative_X_add_C (c : R) : derivative (X + C c) = 1 := by
rw [derivative_add, derivative_X, derivative_C, add_zero]
theorem derivative_sum {s : Finset ι} {f : ι → R[X]} :
derivative (∑ b ∈ s, f b) = ∑ b ∈ s, derivative (f b) :=
map_sum ..
theorem iterate_derivative_sum (k : ℕ) (s : Finset ι) (f : ι → R[X]) :
derivative^[k] (∑ b ∈ s, f b) = ∑ b ∈ s, derivative^[k] (f b) := by
simp_rw [← Module.End.pow_apply, map_sum]
theorem derivative_smul {S : Type*} [SMulZeroClass S R] [IsScalarTower S R R] (s : S)
(p : R[X]) : derivative (s • p) = s • derivative p :=
derivative.map_smul_of_tower s p
@[simp]
theorem iterate_derivative_smul {S : Type*} [SMulZeroClass S R] [IsScalarTower S R R]
(s : S) (p : R[X]) (k : ℕ) : derivative^[k] (s • p) = s • derivative^[k] p := by
induction k generalizing p with
| zero => simp
| succ k ih => simp [ih]
@[simp]
theorem iterate_derivative_C_mul (a : R) (p : R[X]) (k : ℕ) :
derivative^[k] (C a * p) = C a * derivative^[k] p := by
simp_rw [← smul_eq_C_mul, iterate_derivative_smul]
theorem derivative_C_mul (a : R) (p : R[X]) :
derivative (C a * p) = C a * derivative p := iterate_derivative_C_mul _ _ 1
theorem of_mem_support_derivative {p : R[X]} {n : ℕ} (h : n ∈ p.derivative.support) :
n + 1 ∈ p.support :=
mem_support_iff.2 fun h1 : p.coeff (n + 1) = 0 =>
mem_support_iff.1 h <| show p.derivative.coeff n = 0 by rw [coeff_derivative, h1, zero_mul]
theorem degree_derivative_lt {p : R[X]} (hp : p ≠ 0) : p.derivative.degree < p.degree :=
(Finset.sup_lt_iff <| bot_lt_iff_ne_bot.2 <| mt degree_eq_bot.1 hp).2 fun n hp =>
lt_of_lt_of_le (WithBot.coe_lt_coe.2 n.lt_succ_self) <|
Finset.le_sup <| of_mem_support_derivative hp
theorem degree_derivative_le {p : R[X]} : p.derivative.degree ≤ p.degree :=
letI := Classical.decEq R
if H : p = 0 then le_of_eq <| by rw [H, derivative_zero] else (degree_derivative_lt H).le
theorem natDegree_derivative_lt {p : R[X]} (hp : p.natDegree ≠ 0) :
p.derivative.natDegree < p.natDegree := by
rcases eq_or_ne (derivative p) 0 with hp' | hp'
· rw [hp', Polynomial.natDegree_zero]
exact hp.bot_lt
· rw [natDegree_lt_natDegree_iff hp']
exact degree_derivative_lt fun h => hp (h.symm ▸ natDegree_zero)
theorem natDegree_derivative_le (p : R[X]) : p.derivative.natDegree ≤ p.natDegree - 1 := by
by_cases p0 : p.natDegree = 0
· simp [p0, derivative_of_natDegree_zero]
· exact Nat.le_sub_one_of_lt (natDegree_derivative_lt p0)
theorem natDegree_iterate_derivative (p : R[X]) (k : ℕ) :
(derivative^[k] p).natDegree ≤ p.natDegree - k := by
induction k with
| zero => rw [Function.iterate_zero_apply, Nat.sub_zero]
| succ d hd =>
rw [Function.iterate_succ_apply', Nat.sub_succ']
exact (natDegree_derivative_le _).trans <| Nat.sub_le_sub_right hd 1
@[simp]
theorem derivative_natCast {n : ℕ} : derivative (n : R[X]) = 0 := by
rw [← map_natCast C n]
exact derivative_C
@[simp]
theorem derivative_ofNat (n : ℕ) [n.AtLeastTwo] :
derivative (ofNat(n) : R[X]) = 0 :=
derivative_natCast
theorem iterate_derivative_eq_zero {p : R[X]} {x : ℕ} (hx : p.natDegree < x) :
Polynomial.derivative^[x] p = 0 := by
induction' h : p.natDegree using Nat.strong_induction_on with _ ih generalizing p x
subst h
obtain ⟨t, rfl⟩ := Nat.exists_eq_succ_of_ne_zero (pos_of_gt hx).ne'
rw [Function.iterate_succ_apply]
by_cases hp : p.natDegree = 0
· rw [derivative_of_natDegree_zero hp, iterate_derivative_zero]
have := natDegree_derivative_lt hp
exact ih _ this (this.trans_le <| Nat.le_of_lt_succ hx) rfl
@[simp]
theorem iterate_derivative_C {k} (h : 0 < k) : derivative^[k] (C a : R[X]) = 0 :=
iterate_derivative_eq_zero <| (natDegree_C _).trans_lt h
@[simp]
theorem iterate_derivative_one {k} (h : 0 < k) : derivative^[k] (1 : R[X]) = 0 :=
iterate_derivative_C h
@[simp]
theorem iterate_derivative_X {k} (h : 1 < k) : derivative^[k] (X : R[X]) = 0 :=
iterate_derivative_eq_zero <| natDegree_X_le.trans_lt h
theorem natDegree_eq_zero_of_derivative_eq_zero [NoZeroSMulDivisors ℕ R] {f : R[X]}
(h : derivative f = 0) : f.natDegree = 0 := by
rcases eq_or_ne f 0 with (rfl | hf)
· exact natDegree_zero
rw [natDegree_eq_zero_iff_degree_le_zero]
by_contra! f_nat_degree_pos
rw [← natDegree_pos_iff_degree_pos] at f_nat_degree_pos
let m := f.natDegree - 1
have hm : m + 1 = f.natDegree := tsub_add_cancel_of_le f_nat_degree_pos
have h2 := coeff_derivative f m
rw [Polynomial.ext_iff] at h
rw [h m, coeff_zero, ← Nat.cast_add_one, ← nsmul_eq_mul', eq_comm, smul_eq_zero] at h2
replace h2 := h2.resolve_left m.succ_ne_zero
rw [hm, ← leadingCoeff, leadingCoeff_eq_zero] at h2
exact hf h2
theorem eq_C_of_derivative_eq_zero [NoZeroSMulDivisors ℕ R] {f : R[X]} (h : derivative f = 0) :
f = C (f.coeff 0) :=
eq_C_of_natDegree_eq_zero <| natDegree_eq_zero_of_derivative_eq_zero h
@[simp]
theorem derivative_mul {f g : R[X]} : derivative (f * g) = derivative f * g + f * derivative g := by
induction f using Polynomial.induction_on' with
| add => simp only [add_mul, map_add, add_assoc, add_left_comm, *]
| monomial m a => ?_
induction g using Polynomial.induction_on' with
| add => simp only [mul_add, map_add, add_assoc, add_left_comm, *]
| monomial n b => ?_
simp only [monomial_mul_monomial, derivative_monomial]
simp only [mul_assoc, (Nat.cast_commute _ _).eq, Nat.cast_add, mul_add, map_add]
cases m with
| zero => simp only [zero_add, Nat.cast_zero, mul_zero, map_zero]
| succ m =>
cases n with
| zero => simp only [add_zero, Nat.cast_zero, mul_zero, map_zero]
| succ n =>
simp only [Nat.add_succ_sub_one, add_tsub_cancel_right]
rw [add_assoc, add_comm n 1]
theorem derivative_eval (p : R[X]) (x : R) :
p.derivative.eval x = p.sum fun n a => a * n * x ^ (n - 1) := by
simp_rw [derivative_apply, eval_sum, eval_mul_X_pow, eval_C]
@[simp]
theorem derivative_map [Semiring S] (p : R[X]) (f : R →+* S) :
derivative (p.map f) = p.derivative.map f := by
let n := max p.natDegree (map f p).natDegree
rw [derivative_apply, derivative_apply]
rw [sum_over_range' _ _ (n + 1) ((le_max_left _ _).trans_lt (lt_add_one _))]
on_goal 1 => rw [sum_over_range' _ _ (n + 1) ((le_max_right _ _).trans_lt (lt_add_one _))]
· simp only [Polynomial.map_sum, Polynomial.map_mul, Polynomial.map_C, map_mul, coeff_map,
map_natCast, Polynomial.map_natCast, Polynomial.map_pow, map_X]
all_goals intro n; rw [zero_mul, C_0, zero_mul]
@[simp]
theorem iterate_derivative_map [Semiring S] (p : R[X]) (f : R →+* S) (k : ℕ) :
Polynomial.derivative^[k] (p.map f) = (Polynomial.derivative^[k] p).map f := by
induction' k with k ih generalizing p
· simp
· simp only [ih, Function.iterate_succ, Polynomial.derivative_map, Function.comp_apply]
theorem derivative_natCast_mul {n : ℕ} {f : R[X]} :
derivative ((n : R[X]) * f) = n * derivative f := by
simp
@[simp]
theorem iterate_derivative_natCast_mul {n k : ℕ} {f : R[X]} :
derivative^[k] ((n : R[X]) * f) = n * derivative^[k] f := by
induction' k with k ih generalizing f <;> simp [*]
theorem mem_support_derivative [NoZeroSMulDivisors ℕ R] (p : R[X]) (n : ℕ) :
n ∈ (derivative p).support ↔ n + 1 ∈ p.support := by
suffices ¬p.coeff (n + 1) * (n + 1 : ℕ) = 0 ↔ coeff p (n + 1) ≠ 0 by
simpa only [mem_support_iff, coeff_derivative, Ne, Nat.cast_succ]
rw [← nsmul_eq_mul', smul_eq_zero]
simp only [Nat.succ_ne_zero, false_or]
@[simp]
theorem degree_derivative_eq [NoZeroSMulDivisors ℕ R] (p : R[X]) (hp : 0 < natDegree p) :
degree (derivative p) = (natDegree p - 1 : ℕ) := by
apply le_antisymm
· rw [derivative_apply]
apply le_trans (degree_sum_le _ _) (Finset.sup_le _)
intro n hn
apply le_trans (degree_C_mul_X_pow_le _ _) (WithBot.coe_le_coe.2 (tsub_le_tsub_right _ _))
apply le_natDegree_of_mem_supp _ hn
· refine le_sup ?_
rw [mem_support_derivative, tsub_add_cancel_of_le, mem_support_iff]
· rw [coeff_natDegree, Ne, leadingCoeff_eq_zero]
intro h
rw [h, natDegree_zero] at hp
exact hp.false
exact hp
theorem coeff_iterate_derivative {k} (p : R[X]) (m : ℕ) :
(derivative^[k] p).coeff m = (m + k).descFactorial k • p.coeff (m + k) := by
induction k generalizing m with
| zero => simp
| succ k ih =>
calc
(derivative^[k + 1] p).coeff m
_ = Nat.descFactorial (Nat.succ (m + k)) k • p.coeff (m + k.succ) * (m + 1) := by
rw [Function.iterate_succ_apply', coeff_derivative, ih m.succ, Nat.succ_add, Nat.add_succ]
_ = ((m + 1) * Nat.descFactorial (Nat.succ (m + k)) k) • p.coeff (m + k.succ) := by
rw [← Nat.cast_add_one, ← nsmul_eq_mul', smul_smul]
_ = Nat.descFactorial (m.succ + k) k.succ • p.coeff (m + k.succ) := by
rw [← Nat.succ_add, Nat.descFactorial_succ, add_tsub_cancel_right]
_ = Nat.descFactorial (m + k.succ) k.succ • p.coeff (m + k.succ) := by
rw [Nat.succ_add_eq_add_succ]
theorem iterate_derivative_eq_sum (p : R[X]) (k : ℕ) :
derivative^[k] p =
∑ x ∈ (derivative^[k] p).support, C ((x + k).descFactorial k • p.coeff (x + k)) * X ^ x := by
conv_lhs => rw [(derivative^[k] p).as_sum_support_C_mul_X_pow]
refine sum_congr rfl fun i _ ↦ ?_
rw [coeff_iterate_derivative, Nat.descFactorial_eq_factorial_mul_choose]
theorem iterate_derivative_eq_factorial_smul_sum (p : R[X]) (k : ℕ) :
derivative^[k] p = k ! •
∑ x ∈ (derivative^[k] p).support, C ((x + k).choose k • p.coeff (x + k)) * X ^ x := by
conv_lhs => rw [iterate_derivative_eq_sum]
rw [smul_sum]
refine sum_congr rfl fun i _ ↦ ?_
rw [← smul_mul_assoc, smul_C, smul_smul, Nat.descFactorial_eq_factorial_mul_choose]
theorem iterate_derivative_mul {n} (p q : R[X]) :
derivative^[n] (p * q) =
∑ k ∈ range n.succ, (n.choose k • (derivative^[n - k] p * derivative^[k] q)) := by
induction n with
| zero =>
simp [Finset.range]
| succ n IH =>
calc
derivative^[n + 1] (p * q) =
derivative (∑ k ∈ range n.succ,
n.choose k • (derivative^[n - k] p * derivative^[k] q)) := by
rw [Function.iterate_succ_apply', IH]
_ = (∑ k ∈ range n.succ,
n.choose k • (derivative^[n - k + 1] p * derivative^[k] q)) +
∑ k ∈ range n.succ,
n.choose k • (derivative^[n - k] p * derivative^[k + 1] q) := by
simp_rw [derivative_sum, derivative_smul, derivative_mul, Function.iterate_succ_apply',
smul_add, sum_add_distrib]
_ = (∑ k ∈ range n.succ,
n.choose k.succ • (derivative^[n - k] p * derivative^[k + 1] q)) +
1 • (derivative^[n + 1] p * derivative^[0] q) +
∑ k ∈ range n.succ, n.choose k • (derivative^[n - k] p * derivative^[k + 1] q) :=
?_
_ = ((∑ k ∈ range n.succ, n.choose k • (derivative^[n - k] p * derivative^[k + 1] q)) +
∑ k ∈ range n.succ,
n.choose k.succ • (derivative^[n - k] p * derivative^[k + 1] q)) +
1 • (derivative^[n + 1] p * derivative^[0] q) := by
rw [add_comm, add_assoc]
_ = (∑ i ∈ range n.succ,
(n + 1).choose (i + 1) • (derivative^[n + 1 - (i + 1)] p * derivative^[i + 1] q)) +
1 • (derivative^[n + 1] p * derivative^[0] q) := by
simp_rw [Nat.choose_succ_succ, Nat.succ_sub_succ, add_smul, sum_add_distrib]
_ = ∑ k ∈ range n.succ.succ,
n.succ.choose k • (derivative^[n.succ - k] p * derivative^[k] q) := by
rw [sum_range_succ' _ n.succ, Nat.choose_zero_right, tsub_zero]
congr
refine (sum_range_succ' _ _).trans (congr_arg₂ (· + ·) ?_ ?_)
· rw [sum_range_succ, Nat.choose_succ_self, zero_smul, add_zero]
refine sum_congr rfl fun k hk => ?_
rw [mem_range] at hk
congr
omega
· rw [Nat.choose_zero_right, tsub_zero]
/--
Iterated derivatives as a finite support function.
-/
@[simps! apply_toFun]
noncomputable def derivativeFinsupp : R[X] →ₗ[R] ℕ →₀ R[X] where
toFun p := .onFinset (range (p.natDegree + 1)) (derivative^[·] p) fun i ↦ by
contrapose; simp_all [iterate_derivative_eq_zero, Nat.succ_le]
map_add' _ _ := by ext; simp
map_smul' _ _ := by ext; simp
@[simp]
theorem support_derivativeFinsupp_subset_range {p : R[X]} {n : ℕ} (h : p.natDegree < n) :
(derivativeFinsupp p).support ⊆ range n := by
dsimp [derivativeFinsupp]
exact Finsupp.support_onFinset_subset.trans (Finset.range_subset.mpr h)
@[simp]
theorem derivativeFinsupp_C (r : R) : derivativeFinsupp (C r : R[X]) = .single 0 (C r) := by
ext i : 1
match i with
| 0 => simp
| i + 1 => simp
@[simp]
theorem derivativeFinsupp_one : derivativeFinsupp (1 : R[X]) = .single 0 1 := by
simpa using derivativeFinsupp_C (1 : R)
@[simp]
theorem derivativeFinsupp_X : derivativeFinsupp (X : R[X]) = .single 0 X + .single 1 1 := by
ext i : 1
match i with
| 0 => simp
| 1 => simp
| (n + 2) => simp
theorem derivativeFinsupp_map [Semiring S] (p : R[X]) (f : R →+* S) :
derivativeFinsupp (p.map f) = (derivativeFinsupp p).mapRange (·.map f) (by simp) := by
ext i : 1
simp
theorem derivativeFinsupp_derivative (p : R[X]) :
derivativeFinsupp (derivative p) =
(derivativeFinsupp p).comapDomain Nat.succ Nat.succ_injective.injOn := by
ext i : 1
simp
end Semiring
section CommSemiring
variable [CommSemiring R]
theorem derivative_pow_succ (p : R[X]) (n : ℕ) :
derivative (p ^ (n + 1)) = C (n + 1 : R) * p ^ n * derivative p :=
Nat.recOn n (by simp) fun n ih => by
rw [pow_succ, derivative_mul, ih, Nat.add_one, mul_right_comm, C_add,
add_mul, add_mul, pow_succ, ← mul_assoc, C_1, one_mul]; simp [add_mul]
theorem derivative_pow (p : R[X]) (n : ℕ) :
derivative (p ^ n) = C (n : R) * p ^ (n - 1) * derivative p :=
Nat.casesOn n (by rw [pow_zero, derivative_one, Nat.cast_zero, C_0, zero_mul, zero_mul]) fun n =>
by rw [p.derivative_pow_succ n, Nat.add_one_sub_one, n.cast_succ]
theorem derivative_sq (p : R[X]) : derivative (p ^ 2) = C 2 * p * derivative p := by
rw [derivative_pow_succ, Nat.cast_one, one_add_one_eq_two, pow_one]
theorem pow_sub_one_dvd_derivative_of_pow_dvd {p q : R[X]} {n : ℕ}
(dvd : q ^ n ∣ p) : q ^ (n - 1) ∣ derivative p := by
obtain ⟨r, rfl⟩ := dvd
rw [derivative_mul, derivative_pow]
exact (((dvd_mul_left _ _).mul_right _).mul_right _).add ((pow_dvd_pow q n.pred_le).mul_right _)
theorem pow_sub_dvd_iterate_derivative_of_pow_dvd {p q : R[X]} {n : ℕ} (m : ℕ)
(dvd : q ^ n ∣ p) : q ^ (n - m) ∣ derivative^[m] p := by
induction m generalizing p with
| zero => simpa
| succ m ih =>
rw [Nat.sub_succ, Function.iterate_succ']
exact pow_sub_one_dvd_derivative_of_pow_dvd (ih dvd)
theorem pow_sub_dvd_iterate_derivative_pow (p : R[X]) (n m : ℕ) :
p ^ (n - m) ∣ derivative^[m] (p ^ n) := pow_sub_dvd_iterate_derivative_of_pow_dvd m dvd_rfl
theorem dvd_iterate_derivative_pow (f : R[X]) (n : ℕ) {m : ℕ} (c : R) (hm : m ≠ 0) :
(n : R) ∣ eval c (derivative^[m] (f ^ n)) := by
obtain ⟨m, rfl⟩ := Nat.exists_eq_succ_of_ne_zero hm
rw [Function.iterate_succ_apply, derivative_pow, mul_assoc, C_eq_natCast,
iterate_derivative_natCast_mul, eval_mul, eval_natCast]
exact dvd_mul_right _ _
theorem iterate_derivative_X_pow_eq_natCast_mul (n k : ℕ) :
derivative^[k] (X ^ n : R[X]) = ↑(Nat.descFactorial n k : R[X]) * X ^ (n - k) := by
induction k with
| zero =>
rw [Function.iterate_zero_apply, tsub_zero, Nat.descFactorial_zero, Nat.cast_one, one_mul]
| succ k ih =>
rw [Function.iterate_succ_apply', ih, derivative_natCast_mul, derivative_X_pow, C_eq_natCast,
Nat.descFactorial_succ, Nat.sub_sub, Nat.cast_mul]
simp [mul_comm, mul_assoc, mul_left_comm]
theorem iterate_derivative_X_pow_eq_C_mul (n k : ℕ) :
derivative^[k] (X ^ n : R[X]) = C (Nat.descFactorial n k : R) * X ^ (n - k) := by
rw [iterate_derivative_X_pow_eq_natCast_mul n k, C_eq_natCast]
theorem iterate_derivative_X_pow_eq_smul (n : ℕ) (k : ℕ) :
derivative^[k] (X ^ n : R[X]) = (Nat.descFactorial n k : R) • X ^ (n - k) := by
rw [iterate_derivative_X_pow_eq_C_mul n k, smul_eq_C_mul]
|
theorem derivative_X_add_C_pow (c : R) (m : ℕ) :
derivative ((X + C c) ^ m) = C (m : R) * (X + C c) ^ (m - 1) := by
| Mathlib/Algebra/Polynomial/Derivative.lean | 504 | 506 |
/-
Copyright (c) 2023 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen, Mario Carneiro
-/
import Mathlib.Tactic.NormNum.Basic
import Mathlib.Tactic.NormNum.Ineq
/-!
# `norm_num` extension for integer div/mod and divides
This file adds support for the `%`, `/`, and `∣` (divisibility) operators on `ℤ`
to the `norm_num` tactic.
-/
namespace Mathlib
open Lean
open Meta
namespace Meta.NormNum
open Qq
lemma isInt_ediv_zero : ∀ {a b r : ℤ}, IsInt a r → IsNat b (nat_lit 0) → IsNat (a / b) (nat_lit 0)
| _, _, _, ⟨rfl⟩, ⟨rfl⟩ => ⟨by simp [Int.ediv_zero]⟩
lemma isInt_ediv {a b q m a' : ℤ} {b' r : ℕ}
(ha : IsInt a a') (hb : IsNat b b')
(hm : q * b' = m) (h : r + m = a') (h₂ : Nat.blt r b' = true) :
IsInt (a / b) q := ⟨by
obtain ⟨⟨rfl⟩, ⟨rfl⟩⟩ := ha, hb
simp only [Nat.blt_eq] at h₂; simp only [← h, ← hm, Int.cast_id]
rw [Int.add_mul_ediv_right _ _ (Int.ofNat_ne_zero.2 ((Nat.zero_le ..).trans_lt h₂).ne')]
rw [Int.ediv_eq_zero_of_lt, zero_add] <;> [simp; simpa using h₂]⟩
lemma isInt_ediv_neg {a b q q' : ℤ} (h : IsInt (a / -b) q) (hq : -q = q') : IsInt (a / b) q' :=
⟨by rw [Int.cast_id, ← hq, ← @Int.cast_id q, ← h.out, ← Int.ediv_neg, Int.neg_neg]⟩
lemma isNat_neg_of_isNegNat {a : ℤ} {b : ℕ} (h : IsInt a (.negOfNat b)) : IsNat (-a) b :=
⟨by simp [h.out]⟩
attribute [local instance] monadLiftOptionMetaM in
/-- The `norm_num` extension which identifies expressions of the form `Int.ediv a b`,
such that `norm_num` successfully recognises both `a` and `b`. -/
@[norm_num (_ : ℤ) / _, Int.ediv _ _]
partial def evalIntDiv : NormNumExt where eval {u α} e := do
let .app (.app f (a : Q(ℤ))) (b : Q(ℤ)) ← whnfR e | failure
-- We assert that the default instance for `HDiv` is `Int.div` when the first parameter is `ℤ`.
guard <|← withNewMCtxDepth <| isDefEq f q(HDiv.hDiv (α := ℤ))
haveI' : u =QL 0 := ⟨⟩; haveI' : $α =Q ℤ := ⟨⟩
haveI' : $e =Q ($a / $b) := ⟨⟩
let rℤ : Q(Ring ℤ) := q(Int.instRing)
let ⟨za, na, pa⟩ ← (← derive a).toInt rℤ
match ← derive (u := .zero) b with
| .isNat inst nb pb =>
assumeInstancesCommute
if nb.natLit! == 0 then
have _ : $nb =Q nat_lit 0 := ⟨⟩
return .isNat q(instAddMonoidWithOne) q(nat_lit 0) q(isInt_ediv_zero $pa $pb)
else
let ⟨zq, q, p⟩ := core a na za pa b nb pb
return .isInt rℤ q zq p
| .isNegNat _ nb pb =>
assumeInstancesCommute
let ⟨zq, q, p⟩ := core a na za pa q(-$b) nb q(isNat_neg_of_isNegNat $pb)
have q' := mkRawIntLit (-zq)
have : Q(-$q = $q') := (q(Eq.refl $q') :)
return .isInt rℤ q' (-zq) q(isInt_ediv_neg $p $this)
| _ => failure
where
/-- Given a result for evaluating `a b` in `ℤ` where `b > 0`, evaluate `a / b`. -/
core (a na : Q(ℤ)) (za : ℤ) (pa : Q(IsInt $a $na))
(b : Q(ℤ)) (nb : Q(ℕ)) (pb : Q(IsNat $b $nb)) :
ℤ × (q : Q(ℤ)) × Q(IsInt ($a / $b) $q) :=
let b := nb.natLit!
let q := za / b
have nq := mkRawIntLit q
let r := za.natMod b
have nr : Q(ℕ) := mkRawNatLit r
let m := q * b
have nm := mkRawIntLit m
have pf₁ : Q($nq * $nb = $nm) := (q(Eq.refl $nm) :)
have pf₂ : Q($nr + $nm = $na) := (q(Eq.refl $na) :)
have pf₃ : Q(Nat.blt $nr $nb = true) := (q(Eq.refl true) :)
⟨q, nq, q(isInt_ediv $pa $pb $pf₁ $pf₂ $pf₃)⟩
lemma isInt_emod_zero : ∀ {a b r : ℤ}, IsInt a r → IsNat b (nat_lit 0) → IsInt (a % b) r
| | _, _, _, e, ⟨rfl⟩ => by simp [e]
| Mathlib/Tactic/NormNum/DivMod.lean | 87 | 88 |
/-
Copyright (c) 2020 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel, Yury Kudryashov
-/
import Mathlib.Analysis.Calculus.ContDiff.Operations
import Mathlib.Analysis.Normed.Module.FiniteDimension
/-!
# Infinitely smooth "bump" functions
A smooth bump function is an infinitely smooth function `f : E → ℝ` supported on a ball
that is equal to `1` on a ball of smaller radius.
These functions have many uses in real analysis. E.g.,
- they can be used to construct a smooth partition of unity which is a very useful tool;
- they can be used to approximate a continuous function by infinitely smooth functions.
There are two classes of spaces where bump functions are guaranteed to exist:
inner product spaces and finite dimensional spaces.
In this file we define a typeclass `HasContDiffBump`
saying that a normed space has a family of smooth bump functions with certain properties.
We also define a structure `ContDiffBump` that holds the center and radii of the balls from above.
An element `f : ContDiffBump c` can be coerced to a function which is an infinitely smooth function
such that
- `f` is equal to `1` in `Metric.closedBall c f.rIn`;
- `support f = Metric.ball c f.rOut`;
- `0 ≤ f x ≤ 1` for all `x`.
## Main Definitions
- `ContDiffBump (c : E)`: a structure holding data needed to construct
an infinitely smooth bump function.
- `ContDiffBumpBase (E : Type*)`: a family of infinitely smooth bump functions
that can be used to construct coercion of a `ContDiffBump (c : E)`
to a function.
- `HasContDiffBump (E : Type*)`: a typeclass saying that `E` has a `ContDiffBumpBase`.
Two instances of this typeclass (for inner product spaces and for finite dimensional spaces)
are provided elsewhere.
## Keywords
smooth function, smooth bump function
-/
noncomputable section
open Function Set Filter
open scoped Topology Filter ContDiff
variable {E X : Type*}
/-- `f : ContDiffBump c`, where `c` is a point in a normed vector space, is a
bundled smooth function such that
- `f` is equal to `1` in `Metric.closedBall c f.rIn`;
- `support f = Metric.ball c f.rOut`;
- `0 ≤ f x ≤ 1` for all `x`.
The structure `ContDiffBump` contains the data required to construct the function:
real numbers `rIn`, `rOut`, and proofs of `0 < rIn < rOut`. The function itself is available through
`CoeFun` when the space is nice enough, i.e., satisfies the `HasContDiffBump` typeclass. -/
structure ContDiffBump (c : E) where
/-- real numbers `0 < rIn < rOut` -/
(rIn rOut : ℝ)
rIn_pos : 0 < rIn
rIn_lt_rOut : rIn < rOut
/-- The base function from which one will construct a family of bump functions. One could
add more properties if they are useful and satisfied in the examples of inner product spaces
and finite dimensional vector spaces, notably derivative norm control in terms of `R - 1`.
TODO: do we ever need `f x = 1 ↔ ‖x‖ ≤ 1`? -/
structure ContDiffBumpBase (E : Type*) [NormedAddCommGroup E] [NormedSpace ℝ E] where
/-- The function underlying this family of bump functions -/
toFun : ℝ → E → ℝ
mem_Icc : ∀ (R : ℝ) (x : E), toFun R x ∈ Icc (0 : ℝ) 1
symmetric : ∀ (R : ℝ) (x : E), toFun R (-x) = toFun R x
smooth : ContDiffOn ℝ ∞ (uncurry toFun) (Ioi (1 : ℝ) ×ˢ (univ : Set E))
eq_one : ∀ R : ℝ, 1 < R → ∀ x : E, ‖x‖ ≤ 1 → toFun R x = 1
support : ∀ R : ℝ, 1 < R → Function.support (toFun R) = Metric.ball (0 : E) R
/-- A class registering that a real vector space admits bump functions. This will be instantiated
first for inner product spaces, and then for finite-dimensional normed spaces.
We use a specific class instead of `Nonempty (ContDiffBumpBase E)` for performance reasons. -/
class HasContDiffBump (E : Type*) [NormedAddCommGroup E] [NormedSpace ℝ E] : Prop where
out : Nonempty (ContDiffBumpBase E)
/-- In a space with `C^∞` bump functions, register some function that will be used as a basis
to construct bump functions of arbitrary size around any point. -/
def someContDiffBumpBase (E : Type*) [NormedAddCommGroup E] [NormedSpace ℝ E]
[hb : HasContDiffBump E] : ContDiffBumpBase E :=
Nonempty.some hb.out
namespace ContDiffBump
theorem rOut_pos {c : E} (f : ContDiffBump c) : 0 < f.rOut :=
f.rIn_pos.trans f.rIn_lt_rOut
theorem one_lt_rOut_div_rIn {c : E} (f : ContDiffBump c) : 1 < f.rOut / f.rIn := by
rw [one_lt_div f.rIn_pos]
exact f.rIn_lt_rOut
instance (c : E) : Inhabited (ContDiffBump c) :=
⟨⟨1, 2, zero_lt_one, one_lt_two⟩⟩
variable [NormedAddCommGroup E] [NormedSpace ℝ E] [NormedAddCommGroup X] [NormedSpace ℝ X]
[HasContDiffBump E] {c : E} (f : ContDiffBump c) {x : E} {n : ℕ∞}
/-- The function defined by `f : ContDiffBump c`. Use automatic coercion to
function instead. -/
@[coe] def toFun {c : E} (f : ContDiffBump c) : E → ℝ :=
(someContDiffBumpBase E).toFun (f.rOut / f.rIn) ∘ fun x ↦ (f.rIn⁻¹ • (x - c))
| instance : CoeFun (ContDiffBump c) fun _ => E → ℝ :=
⟨toFun⟩
| Mathlib/Analysis/Calculus/BumpFunction/Basic.lean | 118 | 120 |
/-
Copyright (c) 2015 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Data.Multiset.ZeroCons
/-!
# Basic results on multisets
-/
-- No algebra should be required
assert_not_exists Monoid
universe v
open List Subtype Nat Function
variable {α : Type*} {β : Type v} {γ : Type*}
namespace Multiset
/-! ### `Multiset.toList` -/
section ToList
/-- Produces a list of the elements in the multiset using choice. -/
noncomputable def toList (s : Multiset α) :=
s.out
@[simp, norm_cast]
theorem coe_toList (s : Multiset α) : (s.toList : Multiset α) = s :=
s.out_eq'
@[simp]
theorem toList_eq_nil {s : Multiset α} : s.toList = [] ↔ s = 0 := by
rw [← coe_eq_zero, coe_toList]
theorem empty_toList {s : Multiset α} : s.toList.isEmpty ↔ s = 0 := by simp
@[simp]
theorem toList_zero : (Multiset.toList 0 : List α) = [] :=
toList_eq_nil.mpr rfl
@[simp]
theorem mem_toList {a : α} {s : Multiset α} : a ∈ s.toList ↔ a ∈ s := by
rw [← mem_coe, coe_toList]
@[simp]
theorem toList_eq_singleton_iff {a : α} {m : Multiset α} : m.toList = [a] ↔ m = {a} := by
rw [← perm_singleton, ← coe_eq_coe, coe_toList, coe_singleton]
@[simp]
theorem toList_singleton (a : α) : ({a} : Multiset α).toList = [a] :=
Multiset.toList_eq_singleton_iff.2 rfl
@[simp]
theorem length_toList (s : Multiset α) : s.toList.length = card s := by
rw [← coe_card, coe_toList]
end ToList
/-! ### Induction principles -/
/-- The strong induction principle for multisets. -/
@[elab_as_elim]
def strongInductionOn {p : Multiset α → Sort*} (s : Multiset α) (ih : ∀ s, (∀ t < s, p t) → p s) :
p s :=
(ih s) fun t _h =>
strongInductionOn t ih
termination_by card s
decreasing_by exact card_lt_card _h
theorem strongInductionOn_eq {p : Multiset α → Sort*} (s : Multiset α) (H) :
@strongInductionOn _ p s H = H s fun t _h => @strongInductionOn _ p t H := by
rw [strongInductionOn]
@[elab_as_elim]
theorem case_strongInductionOn {p : Multiset α → Prop} (s : Multiset α) (h₀ : p 0)
(h₁ : ∀ a s, (∀ t ≤ s, p t) → p (a ::ₘ s)) : p s :=
Multiset.strongInductionOn s fun s =>
Multiset.induction_on s (fun _ => h₀) fun _a _s _ ih =>
(h₁ _ _) fun _t h => ih _ <| lt_of_le_of_lt h <| lt_cons_self _ _
/-- Suppose that, given that `p t` can be defined on all supersets of `s` of cardinality less than
`n`, one knows how to define `p s`. Then one can inductively define `p s` for all multisets `s` of
cardinality less than `n`, starting from multisets of card `n` and iterating. This
can be used either to define data, or to prove properties. -/
def strongDownwardInduction {p : Multiset α → Sort*} {n : ℕ}
(H : ∀ t₁, (∀ {t₂ : Multiset α}, card t₂ ≤ n → t₁ < t₂ → p t₂) → card t₁ ≤ n → p t₁)
(s : Multiset α) :
card s ≤ n → p s :=
H s fun {t} ht _h =>
strongDownwardInduction H t ht
termination_by n - card s
decreasing_by simp_wf; have := (card_lt_card _h); omega
theorem strongDownwardInduction_eq {p : Multiset α → Sort*} {n : ℕ}
(H : ∀ t₁, (∀ {t₂ : Multiset α}, card t₂ ≤ n → t₁ < t₂ → p t₂) → card t₁ ≤ n → p t₁)
(s : Multiset α) :
strongDownwardInduction H s = H s fun ht _hst => strongDownwardInduction H _ ht := by
rw [strongDownwardInduction]
/-- Analogue of `strongDownwardInduction` with order of arguments swapped. -/
@[elab_as_elim]
def strongDownwardInductionOn {p : Multiset α → Sort*} {n : ℕ} :
∀ s : Multiset α,
(∀ t₁, (∀ {t₂ : Multiset α}, card t₂ ≤ n → t₁ < t₂ → p t₂) → card t₁ ≤ n → p t₁) →
card s ≤ n → p s :=
fun s H => strongDownwardInduction H s
theorem strongDownwardInductionOn_eq {p : Multiset α → Sort*} (s : Multiset α) {n : ℕ}
(H : ∀ t₁, (∀ {t₂ : Multiset α}, card t₂ ≤ n → t₁ < t₂ → p t₂) → card t₁ ≤ n → p t₁) :
s.strongDownwardInductionOn H = H s fun {t} ht _h => t.strongDownwardInductionOn H ht := by
dsimp only [strongDownwardInductionOn]
rw [strongDownwardInduction]
section Choose
variable (p : α → Prop) [DecidablePred p] (l : Multiset α)
/-- Given a proof `hp` that there exists a unique `a ∈ l` such that `p a`, `chooseX p l hp` returns
that `a` together with proofs of `a ∈ l` and `p a`. -/
def chooseX : ∀ _hp : ∃! a, a ∈ l ∧ p a, { a // a ∈ l ∧ p a } :=
Quotient.recOn l (fun l' ex_unique => List.chooseX p l' (ExistsUnique.exists ex_unique))
(by
intros a b _
funext hp
suffices all_equal : ∀ x y : { t // t ∈ b ∧ p t }, x = y by
apply all_equal
rintro ⟨x, px⟩ ⟨y, py⟩
rcases hp with ⟨z, ⟨_z_mem_l, _pz⟩, z_unique⟩
congr
calc
x = z := z_unique x px
_ = y := (z_unique y py).symm
)
/-- Given a proof `hp` that there exists a unique `a ∈ l` such that `p a`, `choose p l hp` returns
that `a`. -/
def choose (hp : ∃! a, a ∈ l ∧ p a) : α :=
chooseX p l hp
theorem choose_spec (hp : ∃! a, a ∈ l ∧ p a) : choose p l hp ∈ l ∧ p (choose p l hp) :=
(chooseX p l hp).property
theorem choose_mem (hp : ∃! a, a ∈ l ∧ p a) : choose p l hp ∈ l :=
(choose_spec _ _ _).1
theorem choose_property (hp : ∃! a, a ∈ l ∧ p a) : p (choose p l hp) :=
(choose_spec _ _ _).2
end Choose
variable (α) in
/-- The equivalence between lists and multisets of a subsingleton type. -/
def subsingletonEquiv [Subsingleton α] : List α ≃ Multiset α where
toFun := ofList
invFun :=
(Quot.lift id) fun (a b : List α) (h : a ~ b) =>
(List.ext_get h.length_eq) fun _ _ _ => Subsingleton.elim _ _
left_inv _ := rfl
right_inv m := Quot.inductionOn m fun _ => rfl
@[simp]
theorem coe_subsingletonEquiv [Subsingleton α] :
(subsingletonEquiv α : List α → Multiset α) = ofList :=
rfl
section SizeOf
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-02-07")]
theorem sizeOf_lt_sizeOf_of_mem [SizeOf α] {x : α} {s : Multiset α} (hx : x ∈ s) :
SizeOf.sizeOf x < SizeOf.sizeOf s := by
induction s using Quot.inductionOn
exact List.sizeOf_lt_sizeOf_of_mem hx
end SizeOf
end Multiset
| Mathlib/Data/Multiset/Basic.lean | 1,089 | 1,091 | |
/-
Copyright (c) 2019 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Yaël Dillies
-/
import Mathlib.Algebra.Module.BigOperators
import Mathlib.GroupTheory.Perm.Basic
import Mathlib.GroupTheory.Perm.Finite
import Mathlib.GroupTheory.Perm.List
import Mathlib.GroupTheory.Perm.Sign
/-!
# Cycles of a permutation
This file starts the theory of cycles in permutations.
## Main definitions
In the following, `f : Equiv.Perm β`.
* `Equiv.Perm.SameCycle`: `f.SameCycle x y` when `x` and `y` are in the same cycle of `f`.
* `Equiv.Perm.IsCycle`: `f` is a cycle if any two nonfixed points of `f` are related by repeated
applications of `f`, and `f` is not the identity.
* `Equiv.Perm.IsCycleOn`: `f` is a cycle on a set `s` when any two points of `s` are related by
repeated applications of `f`.
## Notes
`Equiv.Perm.IsCycle` and `Equiv.Perm.IsCycleOn` are different in three ways:
* `IsCycle` is about the entire type while `IsCycleOn` is restricted to a set.
* `IsCycle` forbids the identity while `IsCycleOn` allows it (if `s` is a subsingleton).
* `IsCycleOn` forbids fixed points on `s` (if `s` is nontrivial), while `IsCycle` allows them.
-/
open Equiv Function Finset
variable {ι α β : Type*}
namespace Equiv.Perm
/-! ### `SameCycle` -/
section SameCycle
variable {f g : Perm α} {p : α → Prop} {x y z : α}
/-- The equivalence relation indicating that two points are in the same cycle of a permutation. -/
def SameCycle (f : Perm α) (x y : α) : Prop :=
∃ i : ℤ, (f ^ i) x = y
@[refl]
theorem SameCycle.refl (f : Perm α) (x : α) : SameCycle f x x :=
⟨0, rfl⟩
theorem SameCycle.rfl : SameCycle f x x :=
SameCycle.refl _ _
protected theorem _root_.Eq.sameCycle (h : x = y) (f : Perm α) : f.SameCycle x y := by rw [h]
@[symm]
theorem SameCycle.symm : SameCycle f x y → SameCycle f y x := fun ⟨i, hi⟩ =>
⟨-i, by rw [zpow_neg, ← hi, inv_apply_self]⟩
theorem sameCycle_comm : SameCycle f x y ↔ SameCycle f y x :=
⟨SameCycle.symm, SameCycle.symm⟩
@[trans]
theorem SameCycle.trans : SameCycle f x y → SameCycle f y z → SameCycle f x z :=
fun ⟨i, hi⟩ ⟨j, hj⟩ => ⟨j + i, by rw [zpow_add, mul_apply, hi, hj]⟩
variable (f) in
theorem SameCycle.equivalence : Equivalence (SameCycle f) :=
⟨SameCycle.refl f, SameCycle.symm, SameCycle.trans⟩
/-- The setoid defined by the `SameCycle` relation. -/
def SameCycle.setoid (f : Perm α) : Setoid α where
r := f.SameCycle
iseqv := SameCycle.equivalence f
@[simp]
theorem sameCycle_one : SameCycle 1 x y ↔ x = y := by simp [SameCycle]
@[simp]
theorem sameCycle_inv : SameCycle f⁻¹ x y ↔ SameCycle f x y :=
(Equiv.neg _).exists_congr_left.trans <| by simp [SameCycle]
alias ⟨SameCycle.of_inv, SameCycle.inv⟩ := sameCycle_inv
@[simp]
theorem sameCycle_conj : SameCycle (g * f * g⁻¹) x y ↔ SameCycle f (g⁻¹ x) (g⁻¹ y) :=
exists_congr fun i => by simp [conj_zpow, eq_inv_iff_eq]
theorem SameCycle.conj : SameCycle f x y → SameCycle (g * f * g⁻¹) (g x) (g y) := by
simp [sameCycle_conj]
theorem SameCycle.apply_eq_self_iff : SameCycle f x y → (f x = x ↔ f y = y) := fun ⟨i, hi⟩ => by
rw [← hi, ← mul_apply, ← zpow_one_add, add_comm, zpow_add_one, mul_apply,
(f ^ i).injective.eq_iff]
theorem SameCycle.eq_of_left (h : SameCycle f x y) (hx : IsFixedPt f x) : x = y :=
let ⟨_, hn⟩ := h
(hx.perm_zpow _).eq.symm.trans hn
theorem SameCycle.eq_of_right (h : SameCycle f x y) (hy : IsFixedPt f y) : x = y :=
h.eq_of_left <| h.apply_eq_self_iff.2 hy
@[simp]
theorem sameCycle_apply_left : SameCycle f (f x) y ↔ SameCycle f x y :=
(Equiv.addRight 1).exists_congr_left.trans <| by
simp [zpow_sub, SameCycle, Int.add_neg_one, Function.comp]
@[simp]
theorem sameCycle_apply_right : SameCycle f x (f y) ↔ SameCycle f x y := by
rw [sameCycle_comm, sameCycle_apply_left, sameCycle_comm]
@[simp]
theorem sameCycle_inv_apply_left : SameCycle f (f⁻¹ x) y ↔ SameCycle f x y := by
rw [← sameCycle_apply_left, apply_inv_self]
@[simp]
theorem sameCycle_inv_apply_right : SameCycle f x (f⁻¹ y) ↔ SameCycle f x y := by
rw [← sameCycle_apply_right, apply_inv_self]
@[simp]
theorem sameCycle_zpow_left {n : ℤ} : SameCycle f ((f ^ n) x) y ↔ SameCycle f x y :=
(Equiv.addRight (n : ℤ)).exists_congr_left.trans <| by simp [SameCycle, zpow_add]
@[simp]
theorem sameCycle_zpow_right {n : ℤ} : SameCycle f x ((f ^ n) y) ↔ SameCycle f x y := by
rw [sameCycle_comm, sameCycle_zpow_left, sameCycle_comm]
@[simp]
theorem sameCycle_pow_left {n : ℕ} : SameCycle f ((f ^ n) x) y ↔ SameCycle f x y := by
rw [← zpow_natCast, sameCycle_zpow_left]
@[simp]
theorem sameCycle_pow_right {n : ℕ} : SameCycle f x ((f ^ n) y) ↔ SameCycle f x y := by
rw [← zpow_natCast, sameCycle_zpow_right]
alias ⟨SameCycle.of_apply_left, SameCycle.apply_left⟩ := sameCycle_apply_left
alias ⟨SameCycle.of_apply_right, SameCycle.apply_right⟩ := sameCycle_apply_right
alias ⟨SameCycle.of_inv_apply_left, SameCycle.inv_apply_left⟩ := sameCycle_inv_apply_left
alias ⟨SameCycle.of_inv_apply_right, SameCycle.inv_apply_right⟩ := sameCycle_inv_apply_right
alias ⟨SameCycle.of_pow_left, SameCycle.pow_left⟩ := sameCycle_pow_left
alias ⟨SameCycle.of_pow_right, SameCycle.pow_right⟩ := sameCycle_pow_right
alias ⟨SameCycle.of_zpow_left, SameCycle.zpow_left⟩ := sameCycle_zpow_left
alias ⟨SameCycle.of_zpow_right, SameCycle.zpow_right⟩ := sameCycle_zpow_right
theorem SameCycle.of_pow {n : ℕ} : SameCycle (f ^ n) x y → SameCycle f x y := fun ⟨m, h⟩ =>
⟨n * m, by simp [zpow_mul, h]⟩
theorem SameCycle.of_zpow {n : ℤ} : SameCycle (f ^ n) x y → SameCycle f x y := fun ⟨m, h⟩ =>
⟨n * m, by simp [zpow_mul, h]⟩
@[simp]
theorem sameCycle_subtypePerm {h} {x y : { x // p x }} :
(f.subtypePerm h).SameCycle x y ↔ f.SameCycle x y :=
exists_congr fun n => by simp [Subtype.ext_iff]
alias ⟨_, SameCycle.subtypePerm⟩ := sameCycle_subtypePerm
@[simp]
theorem sameCycle_extendDomain {p : β → Prop} [DecidablePred p] {f : α ≃ Subtype p} :
SameCycle (g.extendDomain f) (f x) (f y) ↔ g.SameCycle x y :=
exists_congr fun n => by
rw [← extendDomain_zpow, extendDomain_apply_image, Subtype.coe_inj, f.injective.eq_iff]
alias ⟨_, SameCycle.extendDomain⟩ := sameCycle_extendDomain
theorem SameCycle.exists_pow_eq' [Finite α] : SameCycle f x y → ∃ i < orderOf f, (f ^ i) x = y := by
rintro ⟨k, rfl⟩
use (k % orderOf f).natAbs
have h₀ := Int.natCast_pos.mpr (orderOf_pos f)
have h₁ := Int.emod_nonneg k h₀.ne'
rw [← zpow_natCast, Int.natAbs_of_nonneg h₁, zpow_mod_orderOf]
refine ⟨?_, by rfl⟩
rw [← Int.ofNat_lt, Int.natAbs_of_nonneg h₁]
exact Int.emod_lt_of_pos _ h₀
theorem SameCycle.exists_pow_eq'' [Finite α] (h : SameCycle f x y) :
∃ i : ℕ, 0 < i ∧ i ≤ orderOf f ∧ (f ^ i) x = y := by
obtain ⟨_ | i, hi, rfl⟩ := h.exists_pow_eq'
· refine ⟨orderOf f, orderOf_pos f, le_rfl, ?_⟩
rw [pow_orderOf_eq_one, pow_zero]
· exact ⟨i.succ, i.zero_lt_succ, hi.le, by rfl⟩
theorem SameCycle.exists_fin_pow_eq [Finite α] (h : SameCycle f x y) :
∃ i : Fin (orderOf f), (f ^ (i : ℕ)) x = y := by
obtain ⟨i, hi, hx⟩ := SameCycle.exists_pow_eq' h
exact ⟨⟨i, hi⟩, hx⟩
theorem SameCycle.exists_nat_pow_eq [Finite α] (h : SameCycle f x y) :
∃ i : ℕ, (f ^ i) x = y := by
obtain ⟨i, _, hi⟩ := h.exists_pow_eq'
exact ⟨i, hi⟩
instance (f : Perm α) [DecidableRel (SameCycle f)] :
DecidableRel (SameCycle f⁻¹) := fun x y =>
decidable_of_iff (f.SameCycle x y) (sameCycle_inv).symm
instance (priority := 100) [DecidableEq α] : DecidableRel (SameCycle (1 : Perm α)) := fun x y =>
decidable_of_iff (x = y) sameCycle_one.symm
end SameCycle
/-!
### `IsCycle`
-/
section IsCycle
variable {f g : Perm α} {x y : α}
/-- A cycle is a non identity permutation where any two nonfixed points of the permutation are
related by repeated application of the permutation. -/
def IsCycle (f : Perm α) : Prop :=
∃ x, f x ≠ x ∧ ∀ ⦃y⦄, f y ≠ y → SameCycle f x y
theorem IsCycle.ne_one (h : IsCycle f) : f ≠ 1 := fun hf => by simp [hf, IsCycle] at h
@[simp]
theorem not_isCycle_one : ¬(1 : Perm α).IsCycle := fun H => H.ne_one rfl
protected theorem IsCycle.sameCycle (hf : IsCycle f) (hx : f x ≠ x) (hy : f y ≠ y) :
SameCycle f x y :=
let ⟨g, hg⟩ := hf
let ⟨a, ha⟩ := hg.2 hx
let ⟨b, hb⟩ := hg.2 hy
⟨b - a, by rw [← ha, ← mul_apply, ← zpow_add, sub_add_cancel, hb]⟩
theorem IsCycle.exists_zpow_eq : IsCycle f → f x ≠ x → f y ≠ y → ∃ i : ℤ, (f ^ i) x = y :=
IsCycle.sameCycle
theorem IsCycle.inv (hf : IsCycle f) : IsCycle f⁻¹ :=
hf.imp fun _ ⟨hx, h⟩ =>
⟨inv_eq_iff_eq.not.2 hx.symm, fun _ hy => (h <| inv_eq_iff_eq.not.2 hy.symm).inv⟩
@[simp]
theorem isCycle_inv : IsCycle f⁻¹ ↔ IsCycle f :=
⟨fun h => h.inv, IsCycle.inv⟩
theorem IsCycle.conj : IsCycle f → IsCycle (g * f * g⁻¹) := by
rintro ⟨x, hx, h⟩
refine ⟨g x, by simp [coe_mul, inv_apply_self, hx], fun y hy => ?_⟩
rw [← apply_inv_self g y]
exact (h <| eq_inv_iff_eq.not.2 hy).conj
protected theorem IsCycle.extendDomain {p : β → Prop} [DecidablePred p] (f : α ≃ Subtype p) :
IsCycle g → IsCycle (g.extendDomain f) := by
rintro ⟨a, ha, ha'⟩
refine ⟨f a, ?_, fun b hb => ?_⟩
· rw [extendDomain_apply_image]
exact Subtype.coe_injective.ne (f.injective.ne ha)
have h : b = f (f.symm ⟨b, of_not_not <| hb ∘ extendDomain_apply_not_subtype _ _⟩) := by
rw [apply_symm_apply, Subtype.coe_mk]
rw [h] at hb ⊢
simp only [extendDomain_apply_image, Subtype.coe_injective.ne_iff, f.injective.ne_iff] at hb
exact (ha' hb).extendDomain
theorem isCycle_iff_sameCycle (hx : f x ≠ x) : IsCycle f ↔ ∀ {y}, SameCycle f x y ↔ f y ≠ y :=
⟨fun hf y =>
⟨fun ⟨i, hi⟩ hy =>
hx <| by
rw [← zpow_apply_eq_self_of_apply_eq_self hy i, (f ^ i).injective.eq_iff] at hi
rw [hi, hy],
hf.exists_zpow_eq hx⟩,
fun h => ⟨x, hx, fun _ hy => h.2 hy⟩⟩
section Finite
variable [Finite α]
theorem IsCycle.exists_pow_eq (hf : IsCycle f) (hx : f x ≠ x) (hy : f y ≠ y) :
∃ i : ℕ, (f ^ i) x = y := by
let ⟨n, hn⟩ := hf.exists_zpow_eq hx hy
classical exact
⟨(n % orderOf f).toNat, by
{have := n.emod_nonneg (Int.natCast_ne_zero.mpr (ne_of_gt (orderOf_pos f)))
rwa [← zpow_natCast, Int.toNat_of_nonneg this, zpow_mod_orderOf]}⟩
end Finite
variable [DecidableEq α]
theorem isCycle_swap (hxy : x ≠ y) : IsCycle (swap x y) :=
⟨y, by rwa [swap_apply_right], fun a (ha : ite (a = x) y (ite (a = y) x a) ≠ a) =>
if hya : y = a then ⟨0, hya⟩
else
⟨1, by
rw [zpow_one, swap_apply_def]
split_ifs at * <;> tauto⟩⟩
protected theorem IsSwap.isCycle : IsSwap f → IsCycle f := by
rintro ⟨x, y, hxy, rfl⟩
exact isCycle_swap hxy
variable [Fintype α]
theorem IsCycle.two_le_card_support (h : IsCycle f) : 2 ≤ #f.support :=
two_le_card_support_of_ne_one h.ne_one
/-- The subgroup generated by a cycle is in bijection with its support -/
noncomputable def IsCycle.zpowersEquivSupport {σ : Perm α} (hσ : IsCycle σ) :
(Subgroup.zpowers σ) ≃ σ.support :=
Equiv.ofBijective
(fun (τ : ↥ ((Subgroup.zpowers σ) : Set (Perm α))) =>
⟨(τ : Perm α) (Classical.choose hσ), by
obtain ⟨τ, n, rfl⟩ := τ
rw [Subtype.coe_mk, zpow_apply_mem_support, mem_support]
exact (Classical.choose_spec hσ).1⟩)
(by
constructor
· rintro ⟨a, m, rfl⟩ ⟨b, n, rfl⟩ h
ext y
by_cases hy : σ y = y
· simp_rw [zpow_apply_eq_self_of_apply_eq_self hy]
· obtain ⟨i, rfl⟩ := (Classical.choose_spec hσ).2 hy
rw [Subtype.coe_mk, Subtype.coe_mk, zpow_apply_comm σ m i, zpow_apply_comm σ n i]
exact congr_arg _ (Subtype.ext_iff.mp h)
· rintro ⟨y, hy⟩
rw [mem_support] at hy
obtain ⟨n, rfl⟩ := (Classical.choose_spec hσ).2 hy
exact ⟨⟨σ ^ n, n, rfl⟩, rfl⟩)
@[simp]
theorem IsCycle.zpowersEquivSupport_apply {σ : Perm α} (hσ : IsCycle σ) {n : ℕ} :
hσ.zpowersEquivSupport ⟨σ ^ n, n, rfl⟩ =
⟨(σ ^ n) (Classical.choose hσ),
pow_apply_mem_support.2 (mem_support.2 (Classical.choose_spec hσ).1)⟩ :=
rfl
@[simp]
theorem IsCycle.zpowersEquivSupport_symm_apply {σ : Perm α} (hσ : IsCycle σ) (n : ℕ) :
hσ.zpowersEquivSupport.symm
⟨(σ ^ n) (Classical.choose hσ),
pow_apply_mem_support.2 (mem_support.2 (Classical.choose_spec hσ).1)⟩ =
⟨σ ^ n, n, rfl⟩ :=
(Equiv.symm_apply_eq _).2 hσ.zpowersEquivSupport_apply
protected theorem IsCycle.orderOf (hf : IsCycle f) : orderOf f = #f.support := by
rw [← Fintype.card_zpowers, ← Fintype.card_coe]
convert Fintype.card_congr (IsCycle.zpowersEquivSupport hf)
theorem isCycle_swap_mul_aux₁ {α : Type*} [DecidableEq α] :
∀ (n : ℕ) {b x : α} {f : Perm α} (_ : (swap x (f x) * f) b ≠ b) (_ : (f ^ n) (f x) = b),
∃ i : ℤ, ((swap x (f x) * f) ^ i) (f x) = b := by
intro n
induction n with
| zero => exact fun _ h => ⟨0, h⟩
| succ n hn =>
intro b x f hb h
exact if hfbx : f x = b then ⟨0, hfbx⟩
else
have : f b ≠ b ∧ b ≠ x := ne_and_ne_of_swap_mul_apply_ne_self hb
have hb' : (swap x (f x) * f) (f⁻¹ b) ≠ f⁻¹ b := by
rw [mul_apply, apply_inv_self, swap_apply_of_ne_of_ne this.2 (Ne.symm hfbx), Ne, ←
f.injective.eq_iff, apply_inv_self]
exact this.1
let ⟨i, hi⟩ := hn hb' (f.injective <| by
rw [apply_inv_self]; rwa [pow_succ', mul_apply] at h)
⟨i + 1, by
rw [add_comm, zpow_add, mul_apply, hi, zpow_one, mul_apply, apply_inv_self,
swap_apply_of_ne_of_ne (ne_and_ne_of_swap_mul_apply_ne_self hb).2 (Ne.symm hfbx)]⟩
theorem isCycle_swap_mul_aux₂ {α : Type*} [DecidableEq α] :
∀ (n : ℤ) {b x : α} {f : Perm α} (_ : (swap x (f x) * f) b ≠ b) (_ : (f ^ n) (f x) = b),
∃ i : ℤ, ((swap x (f x) * f) ^ i) (f x) = b := by
intro n
cases n with
| ofNat n => exact isCycle_swap_mul_aux₁ n
| negSucc n =>
intro b x f hb h
exact if hfbx' : f x = b then ⟨0, hfbx'⟩
else
have : f b ≠ b ∧ b ≠ x := ne_and_ne_of_swap_mul_apply_ne_self hb
have hb : (swap x (f⁻¹ x) * f⁻¹) (f⁻¹ b) ≠ f⁻¹ b := by
rw [mul_apply, swap_apply_def]
split_ifs <;>
simp only [inv_eq_iff_eq, Perm.mul_apply, zpow_negSucc, Ne, Perm.apply_inv_self] at *
<;> tauto
let ⟨i, hi⟩ :=
isCycle_swap_mul_aux₁ n hb
(show (f⁻¹ ^ n) (f⁻¹ x) = f⁻¹ b by
rw [← zpow_natCast, ← h, ← mul_apply, ← mul_apply, ← mul_apply, zpow_negSucc,
← inv_pow, pow_succ, mul_assoc, mul_assoc, inv_mul_cancel, mul_one, zpow_natCast,
← pow_succ', ← pow_succ])
have h : (swap x (f⁻¹ x) * f⁻¹) (f x) = f⁻¹ x := by
rw [mul_apply, inv_apply_self, swap_apply_left]
⟨-i, by
rw [← add_sub_cancel_right i 1, neg_sub, sub_eq_add_neg, zpow_add, zpow_one, zpow_neg,
← inv_zpow, mul_inv_rev, swap_inv, mul_swap_eq_swap_mul, inv_apply_self, swap_comm _ x,
zpow_add, zpow_one, mul_apply, mul_apply (_ ^ i), h, hi, mul_apply, apply_inv_self,
swap_apply_of_ne_of_ne this.2 (Ne.symm hfbx')]⟩
theorem IsCycle.eq_swap_of_apply_apply_eq_self {α : Type*} [DecidableEq α] {f : Perm α}
(hf : IsCycle f) {x : α} (hfx : f x ≠ x) (hffx : f (f x) = x) : f = swap x (f x) :=
Equiv.ext fun y =>
let ⟨z, hz⟩ := hf
let ⟨i, hi⟩ := hz.2 hfx
if hyx : y = x then by simp [hyx]
else
if hfyx : y = f x then by simp [hfyx, hffx]
else by
rw [swap_apply_of_ne_of_ne hyx hfyx]
refine by_contradiction fun hy => ?_
obtain ⟨j, hj⟩ := hz.2 hy
rw [← sub_add_cancel j i, zpow_add, mul_apply, hi] at hj
rcases zpow_apply_eq_of_apply_apply_eq_self hffx (j - i) with hji | hji
· rw [← hj, hji] at hyx
tauto
· rw [← hj, hji] at hfyx
tauto
theorem IsCycle.swap_mul {α : Type*} [DecidableEq α] {f : Perm α} (hf : IsCycle f) {x : α}
(hx : f x ≠ x) (hffx : f (f x) ≠ x) : IsCycle (swap x (f x) * f) :=
⟨f x, by simp [swap_apply_def, mul_apply, if_neg hffx, f.injective.eq_iff, if_neg hx, hx],
fun y hy =>
let ⟨i, hi⟩ := hf.exists_zpow_eq hx (ne_and_ne_of_swap_mul_apply_ne_self hy).1
have hi : (f ^ (i - 1)) (f x) = y :=
calc
(f ^ (i - 1) : Perm α) (f x) = (f ^ (i - 1) * f ^ (1 : ℤ) : Perm α) x := by simp
_ = y := by rwa [← zpow_add, sub_add_cancel]
isCycle_swap_mul_aux₂ (i - 1) hy hi⟩
theorem IsCycle.sign {f : Perm α} (hf : IsCycle f) : sign f = -(-1) ^ #f.support :=
let ⟨x, hx⟩ := hf
calc
Perm.sign f = Perm.sign (swap x (f x) * (swap x (f x) * f)) := by
{rw [← mul_assoc, mul_def, mul_def, swap_swap, trans_refl]}
_ = -(-1) ^ #f.support :=
if h1 : f (f x) = x then by
have h : swap x (f x) * f = 1 := by
simp only [mul_def, one_def]
rw [hf.eq_swap_of_apply_apply_eq_self hx.1 h1, swap_apply_left, swap_swap]
rw [sign_mul, sign_swap hx.1.symm, h, sign_one,
hf.eq_swap_of_apply_apply_eq_self hx.1 h1, card_support_swap hx.1.symm]
rfl
else by
have h : #(swap x (f x) * f).support + 1 = #f.support := by
rw [← insert_erase (mem_support.2 hx.1), support_swap_mul_eq _ _ h1,
card_insert_of_not_mem (not_mem_erase _ _), sdiff_singleton_eq_erase]
have : #(swap x (f x) * f).support < #f.support := card_support_swap_mul hx.1
rw [sign_mul, sign_swap hx.1.symm, (hf.swap_mul hx.1 h1).sign, ← h]
simp only [mul_neg, neg_mul, one_mul, neg_neg, pow_add, pow_one, mul_one]
termination_by #f.support
theorem IsCycle.of_pow {n : ℕ} (h1 : IsCycle (f ^ n)) (h2 : f.support ⊆ (f ^ n).support) :
IsCycle f := by
have key : ∀ x : α, (f ^ n) x ≠ x ↔ f x ≠ x := by
simp_rw [← mem_support, ← Finset.ext_iff]
exact (support_pow_le _ n).antisymm h2
obtain ⟨x, hx1, hx2⟩ := h1
refine ⟨x, (key x).mp hx1, fun y hy => ?_⟩
obtain ⟨i, _⟩ := hx2 ((key y).mpr hy)
exact ⟨n * i, by rwa [zpow_mul]⟩
-- The lemma `support_zpow_le` is relevant. It means that `h2` is equivalent to
-- `σ.support = (σ ^ n).support`, as well as to `#σ.support ≤ #(σ ^ n).support`.
theorem IsCycle.of_zpow {n : ℤ} (h1 : IsCycle (f ^ n)) (h2 : f.support ⊆ (f ^ n).support) :
IsCycle f := by
cases n
· exact h1.of_pow h2
· simp only [le_eq_subset, zpow_negSucc, Perm.support_inv] at h1 h2
exact (inv_inv (f ^ _) ▸ h1.inv).of_pow h2
theorem nodup_of_pairwise_disjoint_cycles {l : List (Perm β)} (h1 : ∀ f ∈ l, IsCycle f)
(h2 : l.Pairwise Disjoint) : l.Nodup :=
nodup_of_pairwise_disjoint (fun h => (h1 1 h).ne_one rfl) h2
/-- Unlike `support_congr`, which assumes that `∀ (x ∈ g.support), f x = g x)`, here
we have the weaker assumption that `∀ (x ∈ f.support), f x = g x`. -/
theorem IsCycle.support_congr (hf : IsCycle f) (hg : IsCycle g) (h : f.support ⊆ g.support)
(h' : ∀ x ∈ f.support, f x = g x) : f = g := by
have : f.support = g.support := by
refine le_antisymm h ?_
intro z hz
obtain ⟨x, hx, _⟩ := id hf
have hx' : g x ≠ x := by rwa [← h' x (mem_support.mpr hx)]
obtain ⟨m, hm⟩ := hg.exists_pow_eq hx' (mem_support.mp hz)
have h'' : ∀ x ∈ f.support ∩ g.support, f x = g x := by
intro x hx
exact h' x (mem_of_mem_inter_left hx)
rwa [← hm, ←
pow_eq_on_of_mem_support h'' _ x
(mem_inter_of_mem (mem_support.mpr hx) (mem_support.mpr hx')),
pow_apply_mem_support, mem_support]
refine Equiv.Perm.support_congr h ?_
simpa [← this] using h'
/-- If two cyclic permutations agree on all terms in their intersection,
and that intersection is not empty, then the two cyclic permutations must be equal. -/
theorem IsCycle.eq_on_support_inter_nonempty_congr (hf : IsCycle f) (hg : IsCycle g)
(h : ∀ x ∈ f.support ∩ g.support, f x = g x)
(hx : f x = g x) (hx' : x ∈ f.support) : f = g := by
have hx'' : x ∈ g.support := by rwa [mem_support, ← hx, ← mem_support]
have : f.support ⊆ g.support := by
intro y hy
obtain ⟨k, rfl⟩ := hf.exists_pow_eq (mem_support.mp hx') (mem_support.mp hy)
rwa [pow_eq_on_of_mem_support h _ _ (mem_inter_of_mem hx' hx''), pow_apply_mem_support]
rw [inter_eq_left.mpr this] at h
exact hf.support_congr hg this h
theorem IsCycle.support_pow_eq_iff (hf : IsCycle f) {n : ℕ} :
support (f ^ n) = support f ↔ ¬orderOf f ∣ n := by
rw [orderOf_dvd_iff_pow_eq_one]
constructor
· intro h H
refine hf.ne_one ?_
rw [← support_eq_empty_iff, ← h, H, support_one]
· intro H
apply le_antisymm (support_pow_le _ n) _
intro x hx
contrapose! H
ext z
by_cases hz : f z = z
· rw [pow_apply_eq_self_of_apply_eq_self hz, one_apply]
· obtain ⟨k, rfl⟩ := hf.exists_pow_eq hz (mem_support.mp hx)
apply (f ^ k).injective
rw [← mul_apply, (Commute.pow_pow_self _ _ _).eq, mul_apply]
simpa using H
theorem IsCycle.support_pow_of_pos_of_lt_orderOf (hf : IsCycle f) {n : ℕ} (npos : 0 < n)
(hn : n < orderOf f) : (f ^ n).support = f.support :=
hf.support_pow_eq_iff.2 <| Nat.not_dvd_of_pos_of_lt npos hn
theorem IsCycle.pow_iff [Finite β] {f : Perm β} (hf : IsCycle f) {n : ℕ} :
IsCycle (f ^ n) ↔ n.Coprime (orderOf f) := by
classical
cases nonempty_fintype β
constructor
· intro h
have hr : support (f ^ n) = support f := by
rw [hf.support_pow_eq_iff]
rintro ⟨k, rfl⟩
refine h.ne_one ?_
simp [pow_mul, pow_orderOf_eq_one]
have : orderOf (f ^ n) = orderOf f := by rw [h.orderOf, hr, hf.orderOf]
rw [orderOf_pow, Nat.div_eq_self] at this
rcases this with h | _
· exact absurd h (orderOf_pos _).ne'
· rwa [Nat.coprime_iff_gcd_eq_one, Nat.gcd_comm]
· intro h
obtain ⟨m, hm⟩ := exists_pow_eq_self_of_coprime h
have hf' : IsCycle ((f ^ n) ^ m) := by rwa [hm]
refine hf'.of_pow fun x hx => ?_
rw [hm]
exact support_pow_le _ n hx
-- TODO: Define a `Set`-valued support to get rid of the `Finite β` assumption
theorem IsCycle.pow_eq_one_iff [Finite β] {f : Perm β} (hf : IsCycle f) {n : ℕ} :
f ^ n = 1 ↔ ∃ x, f x ≠ x ∧ (f ^ n) x = x := by
classical
cases nonempty_fintype β
constructor
| · intro h
obtain ⟨x, hx, -⟩ := id hf
exact ⟨x, hx, by simp [h]⟩
· rintro ⟨x, hx, hx'⟩
by_cases h : support (f ^ n) = support f
· rw [← mem_support, ← h, mem_support] at hx
contradiction
· rw [hf.support_pow_eq_iff, Classical.not_not] at h
obtain ⟨k, rfl⟩ := h
rw [pow_mul, pow_orderOf_eq_one, one_pow]
-- TODO: Define a `Set`-valued support to get rid of the `Finite β` assumption
theorem IsCycle.pow_eq_one_iff' [Finite β] {f : Perm β} (hf : IsCycle f) {n : ℕ} {x : β}
(hx : f x ≠ x) : f ^ n = 1 ↔ (f ^ n) x = x :=
⟨fun h => DFunLike.congr_fun h x, fun h => hf.pow_eq_one_iff.2 ⟨x, hx, h⟩⟩
-- TODO: Define a `Set`-valued support to get rid of the `Finite β` assumption
| Mathlib/GroupTheory/Perm/Cycle/Basic.lean | 565 | 581 |
/-
Copyright (c) 2021 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker, Bhavik Mehta
-/
import Mathlib.Analysis.Calculus.Deriv.Support
import Mathlib.Analysis.SpecialFunctions.Pow.Deriv
import Mathlib.MeasureTheory.Function.Jacobian
import Mathlib.MeasureTheory.Integral.IntervalIntegral.IntegrationByParts
import Mathlib.MeasureTheory.Measure.Haar.NormedSpace
import Mathlib.MeasureTheory.Measure.Haar.Unique
/-!
# Links between an integral and its "improper" version
In its current state, mathlib only knows how to talk about definite ("proper") integrals,
in the sense that it treats integrals over `[x, +∞)` the same as it treats integrals over
`[y, z]`. For example, the integral over `[1, +∞)` is **not** defined to be the limit of
the integral over `[1, x]` as `x` tends to `+∞`, which is known as an **improper integral**.
Indeed, the "proper" definition is stronger than the "improper" one. The usual counterexample
is `x ↦ sin(x)/x`, which has an improper integral over `[1, +∞)` but no definite integral.
Although definite integrals have better properties, they are hardly usable when it comes to
computing integrals on unbounded sets, which is much easier using limits. Thus, in this file,
we prove various ways of studying the proper integral by studying the improper one.
## Definitions
The main definition of this file is `MeasureTheory.AECover`. It is a rather technical definition
whose sole purpose is generalizing and factoring proofs. Given an index type `ι`, a countably
generated filter `l` over `ι`, and an `ι`-indexed family `φ` of subsets of a measurable space `α`
equipped with a measure `μ`, one should think of a hypothesis `hφ : MeasureTheory.AECover μ l φ` as
a sufficient condition for being able to interpret `∫ x, f x ∂μ` (if it exists) as the limit of `∫ x
in φ i, f x ∂μ` as `i` tends to `l`.
When using this definition with a measure restricted to a set `s`, which happens fairly often, one
should not try too hard to use a `MeasureTheory.AECover` of subsets of `s`, as it often makes proofs
more complicated than necessary. See for example the proof of
`MeasureTheory.integrableOn_Iic_of_intervalIntegral_norm_tendsto` where we use `(fun x ↦ oi x)` as a
`MeasureTheory.AECover` w.r.t. `μ.restrict (Iic b)`, instead of using `(fun x ↦ Ioc x b)`.
## Main statements
- `MeasureTheory.AECover.lintegral_tendsto_of_countably_generated` : if `φ` is a
`MeasureTheory.AECover μ l`, where `l` is a countably generated filter, and if `f` is a measurable
`ENNReal`-valued function, then `∫⁻ x in φ n, f x ∂μ` tends to `∫⁻ x, f x ∂μ` as `n` tends to `l`
- `MeasureTheory.AECover.integrable_of_integral_norm_tendsto` : if `φ` is a
`MeasureTheory.AECover μ l`, where `l` is a countably generated filter, if `f` is measurable and
integrable on each `φ n`, and if `∫ x in φ n, ‖f x‖ ∂μ` tends to some `I : ℝ` as n tends to `l`,
then `f` is integrable
- `MeasureTheory.AECover.integral_tendsto_of_countably_generated` : if `φ` is a
`MeasureTheory.AECover μ l`, where `l` is a countably generated filter, and if `f` is measurable
and integrable (globally), then `∫ x in φ n, f x ∂μ` tends to `∫ x, f x ∂μ` as `n` tends to `+∞`.
We then specialize these lemmas to various use cases involving intervals, which are frequent
in analysis. In particular,
- `MeasureTheory.integral_Ioi_of_hasDerivAt_of_tendsto` is a version of FTC-2 on the interval
`(a, +∞)`, giving the formula `∫ x in (a, +∞), g' x = l - g a` if `g'` is integrable and
`g` tends to `l` at `+∞`.
- `MeasureTheory.integral_Ioi_of_hasDerivAt_of_nonneg` gives the same result assuming that
`g'` is nonnegative instead of integrable. Its automatic integrability in this context is proved
in `MeasureTheory.integrableOn_Ioi_deriv_of_nonneg`.
- `MeasureTheory.integral_comp_smul_deriv_Ioi` is a version of the change of variables formula
on semi-infinite intervals.
- `MeasureTheory.tendsto_limUnder_of_hasDerivAt_of_integrableOn_Ioi` shows that a function whose
derivative is integrable on `(a, +∞)` has a limit at `+∞`.
- `MeasureTheory.tendsto_zero_of_hasDerivAt_of_integrableOn_Ioi` shows that an integrable function
whose derivative is integrable on `(a, +∞)` tends to `0` at `+∞`.
Versions of these results are also given on the intervals `(-∞, a]` and `(-∞, +∞)`, as well as
the corresponding versions of integration by parts.
-/
open MeasureTheory Filter Set TopologicalSpace Topology
open scoped ENNReal NNReal
namespace MeasureTheory
section AECover
variable {α ι : Type*} [MeasurableSpace α] (μ : Measure α) (l : Filter ι)
/-- A sequence `φ` of subsets of `α` is a `MeasureTheory.AECover` w.r.t. a measure `μ` and a filter
`l` if almost every point (w.r.t. `μ`) of `α` eventually belongs to `φ n` (w.r.t. `l`), and if
each `φ n` is measurable. This definition is a technical way to avoid duplicating a lot of
proofs. It should be thought of as a sufficient condition for being able to interpret
`∫ x, f x ∂μ` (if it exists) as the limit of `∫ x in φ n, f x ∂μ` as `n` tends to `l`.
See for example `MeasureTheory.AECover.lintegral_tendsto_of_countably_generated`,
`MeasureTheory.AECover.integrable_of_integral_norm_tendsto` and
`MeasureTheory.AECover.integral_tendsto_of_countably_generated`. -/
structure AECover (φ : ι → Set α) : Prop where
ae_eventually_mem : ∀ᵐ x ∂μ, ∀ᶠ i in l, x ∈ φ i
protected measurableSet : ∀ i, MeasurableSet <| φ i
variable {μ} {l}
namespace AECover
/-!
## Operations on `AECover`s
-/
/-- Elementwise intersection of two `AECover`s is an `AECover`. -/
theorem inter {φ ψ : ι → Set α} (hφ : AECover μ l φ) (hψ : AECover μ l ψ) :
AECover μ l (fun i ↦ φ i ∩ ψ i) where
ae_eventually_mem := hψ.1.mp <| hφ.1.mono fun _ ↦ Eventually.and
measurableSet _ := (hφ.2 _).inter (hψ.2 _)
theorem superset {φ ψ : ι → Set α} (hφ : AECover μ l φ) (hsub : ∀ i, φ i ⊆ ψ i)
(hmeas : ∀ i, MeasurableSet (ψ i)) : AECover μ l ψ :=
⟨hφ.1.mono fun _x hx ↦ hx.mono fun i hi ↦ hsub i hi, hmeas⟩
theorem mono_ac {ν : Measure α} {φ : ι → Set α} (hφ : AECover μ l φ) (hle : ν ≪ μ) :
AECover ν l φ := ⟨hle hφ.1, hφ.2⟩
theorem mono {ν : Measure α} {φ : ι → Set α} (hφ : AECover μ l φ) (hle : ν ≤ μ) :
AECover ν l φ := hφ.mono_ac hle.absolutelyContinuous
end AECover
section MetricSpace
variable [PseudoMetricSpace α] [OpensMeasurableSpace α]
theorem aecover_ball {x : α} {r : ι → ℝ} (hr : Tendsto r l atTop) :
AECover μ l (fun i ↦ Metric.ball x (r i)) where
measurableSet _ := Metric.isOpen_ball.measurableSet
ae_eventually_mem := by
filter_upwards with y
filter_upwards [hr (Ioi_mem_atTop (dist x y))] with a ha using by simpa [dist_comm] using ha
theorem aecover_closedBall {x : α} {r : ι → ℝ} (hr : Tendsto r l atTop) :
AECover μ l (fun i ↦ Metric.closedBall x (r i)) where
measurableSet _ := Metric.isClosed_closedBall.measurableSet
ae_eventually_mem := by
filter_upwards with y
filter_upwards [hr (Ici_mem_atTop (dist x y))] with a ha using by simpa [dist_comm] using ha
end MetricSpace
section Preorderα
variable [Preorder α] [TopologicalSpace α] [OrderClosedTopology α] [OpensMeasurableSpace α]
{a b : ι → α}
theorem aecover_Ici (ha : Tendsto a l atBot) : AECover μ l fun i => Ici (a i) where
ae_eventually_mem := ae_of_all μ ha.eventually_le_atBot
measurableSet _ := measurableSet_Ici
theorem aecover_Iic (hb : Tendsto b l atTop) : AECover μ l fun i => Iic <| b i :=
aecover_Ici (α := αᵒᵈ) hb
theorem aecover_Icc (ha : Tendsto a l atBot) (hb : Tendsto b l atTop) :
AECover μ l fun i => Icc (a i) (b i) :=
(aecover_Ici ha).inter (aecover_Iic hb)
end Preorderα
section LinearOrderα
variable [LinearOrder α] [TopologicalSpace α] [OrderClosedTopology α] [OpensMeasurableSpace α]
{a b : ι → α} (ha : Tendsto a l atBot) (hb : Tendsto b l atTop)
include ha in
theorem aecover_Ioi [NoMinOrder α] : AECover μ l fun i => Ioi (a i) where
ae_eventually_mem := ae_of_all μ ha.eventually_lt_atBot
measurableSet _ := measurableSet_Ioi
include hb in
theorem aecover_Iio [NoMaxOrder α] : AECover μ l fun i => Iio (b i) := aecover_Ioi (α := αᵒᵈ) hb
include ha hb
theorem aecover_Ioo [NoMinOrder α] [NoMaxOrder α] : AECover μ l fun i => Ioo (a i) (b i) :=
(aecover_Ioi ha).inter (aecover_Iio hb)
theorem aecover_Ioc [NoMinOrder α] : AECover μ l fun i => Ioc (a i) (b i) :=
(aecover_Ioi ha).inter (aecover_Iic hb)
theorem aecover_Ico [NoMaxOrder α] : AECover μ l fun i => Ico (a i) (b i) :=
(aecover_Ici ha).inter (aecover_Iio hb)
end LinearOrderα
section FiniteIntervals
variable [LinearOrder α] [TopologicalSpace α] [OrderClosedTopology α] [OpensMeasurableSpace α]
{a b : ι → α} {A B : α} (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B))
include ha in
theorem aecover_Ioi_of_Ioi : AECover (μ.restrict (Ioi A)) l fun i ↦ Ioi (a i) where
ae_eventually_mem := (ae_restrict_mem measurableSet_Ioi).mono fun _x hx ↦ ha.eventually <|
eventually_lt_nhds hx
measurableSet _ := measurableSet_Ioi
include hb in
theorem aecover_Iio_of_Iio : AECover (μ.restrict (Iio B)) l fun i ↦ Iio (b i) :=
aecover_Ioi_of_Ioi (α := αᵒᵈ) hb
include ha in
theorem aecover_Ioi_of_Ici : AECover (μ.restrict (Ioi A)) l fun i ↦ Ici (a i) :=
(aecover_Ioi_of_Ioi ha).superset (fun _ ↦ Ioi_subset_Ici_self) fun _ ↦ measurableSet_Ici
include hb in
theorem aecover_Iio_of_Iic : AECover (μ.restrict (Iio B)) l fun i ↦ Iic (b i) :=
aecover_Ioi_of_Ici (α := αᵒᵈ) hb
include ha hb in
theorem aecover_Ioo_of_Ioo : AECover (μ.restrict <| Ioo A B) l fun i => Ioo (a i) (b i) :=
((aecover_Ioi_of_Ioi ha).mono <| Measure.restrict_mono Ioo_subset_Ioi_self le_rfl).inter
((aecover_Iio_of_Iio hb).mono <| Measure.restrict_mono Ioo_subset_Iio_self le_rfl)
include ha hb in
theorem aecover_Ioo_of_Icc : AECover (μ.restrict <| Ioo A B) l fun i => Icc (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).superset (fun _ ↦ Ioo_subset_Icc_self) fun _ ↦ measurableSet_Icc
include ha hb in
theorem aecover_Ioo_of_Ico : AECover (μ.restrict <| Ioo A B) l fun i => Ico (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).superset (fun _ ↦ Ioo_subset_Ico_self) fun _ ↦ measurableSet_Ico
include ha hb in
theorem aecover_Ioo_of_Ioc : AECover (μ.restrict <| Ioo A B) l fun i => Ioc (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).superset (fun _ ↦ Ioo_subset_Ioc_self) fun _ ↦ measurableSet_Ioc
variable [NoAtoms μ]
theorem aecover_Ioc_of_Icc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ioc A B) l fun i => Icc (a i) (b i) :=
(aecover_Ioo_of_Icc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ioc).ge
theorem aecover_Ioc_of_Ico (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ioc A B) l fun i => Ico (a i) (b i) :=
(aecover_Ioo_of_Ico ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ioc).ge
theorem aecover_Ioc_of_Ioc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ioc A B) l fun i => Ioc (a i) (b i) :=
(aecover_Ioo_of_Ioc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ioc).ge
theorem aecover_Ioc_of_Ioo (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ioc A B) l fun i => Ioo (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ioc).ge
theorem aecover_Ico_of_Icc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ico A B) l fun i => Icc (a i) (b i) :=
(aecover_Ioo_of_Icc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ico).ge
theorem aecover_Ico_of_Ico (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ico A B) l fun i => Ico (a i) (b i) :=
(aecover_Ioo_of_Ico ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ico).ge
theorem aecover_Ico_of_Ioc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ico A B) l fun i => Ioc (a i) (b i) :=
(aecover_Ioo_of_Ioc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ico).ge
theorem aecover_Ico_of_Ioo (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Ico A B) l fun i => Ioo (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Ico).ge
theorem aecover_Icc_of_Icc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Icc A B) l fun i => Icc (a i) (b i) :=
(aecover_Ioo_of_Icc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Icc).ge
theorem aecover_Icc_of_Ico (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Icc A B) l fun i => Ico (a i) (b i) :=
(aecover_Ioo_of_Ico ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Icc).ge
theorem aecover_Icc_of_Ioc (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Icc A B) l fun i => Ioc (a i) (b i) :=
(aecover_Ioo_of_Ioc ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Icc).ge
theorem aecover_Icc_of_Ioo (ha : Tendsto a l (𝓝 A)) (hb : Tendsto b l (𝓝 B)) :
AECover (μ.restrict <| Icc A B) l fun i => Ioo (a i) (b i) :=
(aecover_Ioo_of_Ioo ha hb).mono (Measure.restrict_congr_set Ioo_ae_eq_Icc).ge
end FiniteIntervals
protected theorem AECover.restrict {φ : ι → Set α} (hφ : AECover μ l φ) {s : Set α} :
AECover (μ.restrict s) l φ :=
hφ.mono Measure.restrict_le_self
theorem aecover_restrict_of_ae_imp {s : Set α} {φ : ι → Set α} (hs : MeasurableSet s)
(ae_eventually_mem : ∀ᵐ x ∂μ, x ∈ s → ∀ᶠ n in l, x ∈ φ n)
(measurable : ∀ n, MeasurableSet <| φ n) : AECover (μ.restrict s) l φ where
ae_eventually_mem := by rwa [ae_restrict_iff' hs]
measurableSet := measurable
theorem AECover.inter_restrict {φ : ι → Set α} (hφ : AECover μ l φ) {s : Set α}
(hs : MeasurableSet s) : AECover (μ.restrict s) l fun i => φ i ∩ s :=
aecover_restrict_of_ae_imp hs
(hφ.ae_eventually_mem.mono fun _x hx hxs => hx.mono fun _i hi => ⟨hi, hxs⟩) fun i =>
(hφ.measurableSet i).inter hs
theorem AECover.ae_tendsto_indicator {β : Type*} [Zero β] [TopologicalSpace β] (f : α → β)
{φ : ι → Set α} (hφ : AECover μ l φ) :
∀ᵐ x ∂μ, Tendsto (fun i => (φ i).indicator f x) l (𝓝 <| f x) :=
hφ.ae_eventually_mem.mono fun _x hx =>
tendsto_const_nhds.congr' <| hx.mono fun _n hn => (indicator_of_mem hn _).symm
theorem AECover.aemeasurable {β : Type*} [MeasurableSpace β] [l.IsCountablyGenerated] [l.NeBot]
{f : α → β} {φ : ι → Set α} (hφ : AECover μ l φ)
(hfm : ∀ i, AEMeasurable f (μ.restrict <| φ i)) : AEMeasurable f μ := by
obtain ⟨u, hu⟩ := l.exists_seq_tendsto
have := aemeasurable_iUnion_iff.mpr fun n : ℕ => hfm (u n)
rwa [Measure.restrict_eq_self_of_ae_mem] at this
filter_upwards [hφ.ae_eventually_mem] with x hx using
mem_iUnion.mpr (hu.eventually hx).exists
theorem AECover.aestronglyMeasurable {β : Type*} [TopologicalSpace β] [PseudoMetrizableSpace β]
[l.IsCountablyGenerated] [l.NeBot] {f : α → β} {φ : ι → Set α} (hφ : AECover μ l φ)
(hfm : ∀ i, AEStronglyMeasurable f (μ.restrict <| φ i)) : AEStronglyMeasurable f μ := by
obtain ⟨u, hu⟩ := l.exists_seq_tendsto
have := aestronglyMeasurable_iUnion_iff.mpr fun n : ℕ => hfm (u n)
rwa [Measure.restrict_eq_self_of_ae_mem] at this
filter_upwards [hφ.ae_eventually_mem] with x hx using mem_iUnion.mpr (hu.eventually hx).exists
end AECover
theorem AECover.comp_tendsto {α ι ι' : Type*} [MeasurableSpace α] {μ : Measure α} {l : Filter ι}
{l' : Filter ι'} {φ : ι → Set α} (hφ : AECover μ l φ) {u : ι' → ι} (hu : Tendsto u l' l) :
AECover μ l' (φ ∘ u) where
ae_eventually_mem := hφ.ae_eventually_mem.mono fun _x hx => hu.eventually hx
measurableSet i := hφ.measurableSet (u i)
section AECoverUnionInterCountable
variable {α ι : Type*} [Countable ι] [MeasurableSpace α] {μ : Measure α}
theorem AECover.biUnion_Iic_aecover [Preorder ι] {φ : ι → Set α} (hφ : AECover μ atTop φ) :
AECover μ atTop fun n : ι => ⋃ (k) (_h : k ∈ Iic n), φ k :=
hφ.superset (fun _ ↦ subset_biUnion_of_mem right_mem_Iic) fun _ ↦ .biUnion (to_countable _)
fun _ _ ↦ (hφ.2 _)
theorem AECover.biInter_Ici_aecover [Preorder ι] {φ : ι → Set α}
(hφ : AECover μ atTop φ) : AECover μ atTop fun n : ι => ⋂ (k) (_h : k ∈ Ici n), φ k where
ae_eventually_mem := hφ.ae_eventually_mem.mono fun x h ↦ by
simpa only [mem_iInter, mem_Ici, eventually_forall_ge_atTop]
measurableSet _ := .biInter (to_countable _) fun n _ => hφ.measurableSet n
end AECoverUnionInterCountable
section Lintegral
variable {α ι : Type*} [MeasurableSpace α] {μ : Measure α} {l : Filter ι}
private theorem lintegral_tendsto_of_monotone_of_nat {φ : ℕ → Set α} (hφ : AECover μ atTop φ)
(hmono : Monotone φ) {f : α → ℝ≥0∞} (hfm : AEMeasurable f μ) :
Tendsto (fun i => ∫⁻ x in φ i, f x ∂μ) atTop (𝓝 <| ∫⁻ x, f x ∂μ) :=
let F n := (φ n).indicator f
have key₁ : ∀ n, AEMeasurable (F n) μ := fun n => hfm.indicator (hφ.measurableSet n)
have key₂ : ∀ᵐ x : α ∂μ, Monotone fun n => F n x := ae_of_all _ fun x _i _j hij =>
indicator_le_indicator_of_subset (hmono hij) (fun x => zero_le <| f x) x
have key₃ : ∀ᵐ x : α ∂μ, Tendsto (fun n => F n x) atTop (𝓝 (f x)) := hφ.ae_tendsto_indicator f
(lintegral_tendsto_of_tendsto_of_monotone key₁ key₂ key₃).congr fun n =>
lintegral_indicator (hφ.measurableSet n) _
theorem AECover.lintegral_tendsto_of_nat {φ : ℕ → Set α} (hφ : AECover μ atTop φ) {f : α → ℝ≥0∞}
(hfm : AEMeasurable f μ) : Tendsto (∫⁻ x in φ ·, f x ∂μ) atTop (𝓝 <| ∫⁻ x, f x ∂μ) := by
have lim₁ := lintegral_tendsto_of_monotone_of_nat hφ.biInter_Ici_aecover
(fun i j hij => biInter_subset_biInter_left (Ici_subset_Ici.mpr hij)) hfm
have lim₂ := lintegral_tendsto_of_monotone_of_nat hφ.biUnion_Iic_aecover
(fun i j hij => biUnion_subset_biUnion_left (Iic_subset_Iic.mpr hij)) hfm
refine tendsto_of_tendsto_of_tendsto_of_le_of_le lim₁ lim₂ (fun n ↦ ?_) fun n ↦ ?_
exacts [lintegral_mono_set (biInter_subset_of_mem left_mem_Ici),
lintegral_mono_set (subset_biUnion_of_mem right_mem_Iic)]
theorem AECover.lintegral_tendsto_of_countably_generated [l.IsCountablyGenerated] {φ : ι → Set α}
(hφ : AECover μ l φ) {f : α → ℝ≥0∞} (hfm : AEMeasurable f μ) :
Tendsto (fun i => ∫⁻ x in φ i, f x ∂μ) l (𝓝 <| ∫⁻ x, f x ∂μ) :=
tendsto_of_seq_tendsto fun _u hu => (hφ.comp_tendsto hu).lintegral_tendsto_of_nat hfm
theorem AECover.lintegral_eq_of_tendsto [l.NeBot] [l.IsCountablyGenerated] {φ : ι → Set α}
(hφ : AECover μ l φ) {f : α → ℝ≥0∞} (I : ℝ≥0∞) (hfm : AEMeasurable f μ)
(htendsto : Tendsto (fun i => ∫⁻ x in φ i, f x ∂μ) l (𝓝 I)) : ∫⁻ x, f x ∂μ = I :=
tendsto_nhds_unique (hφ.lintegral_tendsto_of_countably_generated hfm) htendsto
theorem AECover.iSup_lintegral_eq_of_countably_generated [Nonempty ι] [l.NeBot]
[l.IsCountablyGenerated] {φ : ι → Set α} (hφ : AECover μ l φ) {f : α → ℝ≥0∞}
(hfm : AEMeasurable f μ) : ⨆ i : ι, ∫⁻ x in φ i, f x ∂μ = ∫⁻ x, f x ∂μ := by
have := hφ.lintegral_tendsto_of_countably_generated hfm
refine ciSup_eq_of_forall_le_of_forall_lt_exists_gt
(fun i => lintegral_mono' Measure.restrict_le_self le_rfl) fun w hw => ?_
exact (this.eventually_const_lt hw).exists
end Lintegral
section Integrable
variable {α ι E : Type*} [MeasurableSpace α] {μ : Measure α} {l : Filter ι} [NormedAddCommGroup E]
theorem AECover.integrable_of_lintegral_enorm_bounded [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ) (hfm : AEStronglyMeasurable f μ)
(hbounded : ∀ᶠ i in l, ∫⁻ x in φ i, ‖f x‖ₑ ∂μ ≤ ENNReal.ofReal I) : Integrable f μ := by
refine ⟨hfm, (le_of_tendsto ?_ hbounded).trans_lt ENNReal.ofReal_lt_top⟩
exact hφ.lintegral_tendsto_of_countably_generated hfm.enorm
@[deprecated (since := "2025-01-22")]
alias AECover.integrable_of_lintegral_nnnorm_bounded :=
AECover.integrable_of_lintegral_enorm_bounded
theorem AECover.integrable_of_lintegral_enorm_tendsto [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ) (hfm : AEStronglyMeasurable f μ)
(htendsto : Tendsto (fun i => ∫⁻ x in φ i, ‖f x‖ₑ ∂μ) l (𝓝 <| .ofReal I)) :
Integrable f μ := by
refine hφ.integrable_of_lintegral_enorm_bounded (max 1 (I + 1)) hfm ?_
refine htendsto.eventually (ge_mem_nhds ?_)
refine (ENNReal.ofReal_lt_ofReal_iff (lt_max_of_lt_left zero_lt_one)).2 ?_
exact lt_max_of_lt_right (lt_add_one I)
@[deprecated (since := "2025-01-22")]
alias AECover.integrable_of_lintegral_nnnorm_tendsto :=
AECover.integrable_of_lintegral_enorm_tendsto
theorem AECover.integrable_of_lintegral_enorm_bounded' [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ≥0) (hfm : AEStronglyMeasurable f μ)
(hbounded : ∀ᶠ i in l, ∫⁻ x in φ i, ‖f x‖ₑ ∂μ ≤ I) : Integrable f μ :=
hφ.integrable_of_lintegral_enorm_bounded I hfm
(by simpa only [ENNReal.ofReal_coe_nnreal] using hbounded)
@[deprecated (since := "2025-01-22")]
alias AECover.integrable_of_lintegral_nnnorm_bounded' :=
AECover.integrable_of_lintegral_enorm_bounded'
theorem AECover.integrable_of_lintegral_enorm_tendsto' [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ≥0) (hfm : AEStronglyMeasurable f μ)
(htendsto : Tendsto (fun i => ∫⁻ x in φ i, ‖f x‖ₑ ∂μ) l (𝓝 I)) : Integrable f μ :=
hφ.integrable_of_lintegral_enorm_tendsto I hfm
(by simpa only [ENNReal.ofReal_coe_nnreal] using htendsto)
@[deprecated (since := "2025-01-22")]
alias AECover.integrable_of_lintegral_nnnorm_tendsto' :=
AECover.integrable_of_lintegral_enorm_tendsto'
theorem AECover.integrable_of_integral_norm_bounded [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ) (hfi : ∀ i, IntegrableOn f (φ i) μ)
(hbounded : ∀ᶠ i in l, (∫ x in φ i, ‖f x‖ ∂μ) ≤ I) : Integrable f μ := by
have hfm : AEStronglyMeasurable f μ :=
hφ.aestronglyMeasurable fun i => (hfi i).aestronglyMeasurable
refine hφ.integrable_of_lintegral_enorm_bounded I hfm ?_
conv at hbounded in integral _ _ =>
rw [integral_eq_lintegral_of_nonneg_ae (ae_of_all _ fun x => @norm_nonneg E _ (f x))
hfm.norm.restrict]
conv at hbounded in ENNReal.ofReal _ =>
rw [← coe_nnnorm, ENNReal.ofReal_coe_nnreal]
refine hbounded.mono fun i hi => ?_
rw [← ENNReal.ofReal_toReal <| ne_top_of_lt <| hasFiniteIntegral_iff_enorm.mp (hfi i).2]
apply ENNReal.ofReal_le_ofReal hi
theorem AECover.integrable_of_integral_norm_tendsto [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → E} (I : ℝ) (hfi : ∀ i, IntegrableOn f (φ i) μ)
(htendsto : Tendsto (fun i => ∫ x in φ i, ‖f x‖ ∂μ) l (𝓝 I)) : Integrable f μ :=
let ⟨I', hI'⟩ := htendsto.isBoundedUnder_le
hφ.integrable_of_integral_norm_bounded I' hfi hI'
theorem AECover.integrable_of_integral_bounded_of_nonneg_ae [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → ℝ} (I : ℝ) (hfi : ∀ i, IntegrableOn f (φ i) μ)
(hnng : ∀ᵐ x ∂μ, 0 ≤ f x) (hbounded : ∀ᶠ i in l, (∫ x in φ i, f x ∂μ) ≤ I) : Integrable f μ :=
hφ.integrable_of_integral_norm_bounded I hfi <| hbounded.mono fun _i hi =>
(integral_congr_ae <| ae_restrict_of_ae <| hnng.mono fun _ => Real.norm_of_nonneg).le.trans hi
theorem AECover.integrable_of_integral_tendsto_of_nonneg_ae [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → ℝ} (I : ℝ) (hfi : ∀ i, IntegrableOn f (φ i) μ)
(hnng : ∀ᵐ x ∂μ, 0 ≤ f x) (htendsto : Tendsto (fun i => ∫ x in φ i, f x ∂μ) l (𝓝 I)) :
Integrable f μ :=
let ⟨I', hI'⟩ := htendsto.isBoundedUnder_le
hφ.integrable_of_integral_bounded_of_nonneg_ae I' hfi hnng hI'
end Integrable
section Integral
variable {α ι E : Type*} [MeasurableSpace α] {μ : Measure α} {l : Filter ι} [NormedAddCommGroup E]
[NormedSpace ℝ E]
theorem AECover.integral_tendsto_of_countably_generated [l.IsCountablyGenerated] {φ : ι → Set α}
(hφ : AECover μ l φ) {f : α → E} (hfi : Integrable f μ) :
Tendsto (fun i => ∫ x in φ i, f x ∂μ) l (𝓝 <| ∫ x, f x ∂μ) :=
suffices h : Tendsto (fun i => ∫ x : α, (φ i).indicator f x ∂μ) l (𝓝 (∫ x : α, f x ∂μ)) from by
convert h using 2; rw [integral_indicator (hφ.measurableSet _)]
tendsto_integral_filter_of_dominated_convergence (fun x => ‖f x‖)
(Eventually.of_forall fun i => hfi.aestronglyMeasurable.indicator <| hφ.measurableSet i)
(Eventually.of_forall fun _ => ae_of_all _ fun _ => norm_indicator_le_norm_self _ _) hfi.norm
(hφ.ae_tendsto_indicator f)
/-- Slight reformulation of
`MeasureTheory.AECover.integral_tendsto_of_countably_generated`. -/
theorem AECover.integral_eq_of_tendsto [l.NeBot] [l.IsCountablyGenerated] {φ : ι → Set α}
(hφ : AECover μ l φ) {f : α → E} (I : E) (hfi : Integrable f μ)
(h : Tendsto (fun n => ∫ x in φ n, f x ∂μ) l (𝓝 I)) : ∫ x, f x ∂μ = I :=
tendsto_nhds_unique (hφ.integral_tendsto_of_countably_generated hfi) h
theorem AECover.integral_eq_of_tendsto_of_nonneg_ae [l.NeBot] [l.IsCountablyGenerated]
{φ : ι → Set α} (hφ : AECover μ l φ) {f : α → ℝ} (I : ℝ) (hnng : 0 ≤ᵐ[μ] f)
(hfi : ∀ n, IntegrableOn f (φ n) μ) (htendsto : Tendsto (fun n => ∫ x in φ n, f x ∂μ) l (𝓝 I)) :
∫ x, f x ∂μ = I :=
have hfi' : Integrable f μ := hφ.integrable_of_integral_tendsto_of_nonneg_ae I hfi hnng htendsto
hφ.integral_eq_of_tendsto I hfi' htendsto
end Integral
section IntegrableOfIntervalIntegral
variable {ι E : Type*} {μ : Measure ℝ} {l : Filter ι} [Filter.NeBot l] [IsCountablyGenerated l]
[NormedAddCommGroup E] {a b : ι → ℝ} {f : ℝ → E}
theorem integrable_of_intervalIntegral_norm_bounded (I : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc (a i) (b i)) μ) (ha : Tendsto a l atBot)
(hb : Tendsto b l atTop) (h : ∀ᶠ i in l, (∫ x in a i..b i, ‖f x‖ ∂μ) ≤ I) : Integrable f μ := by
have hφ : AECover μ l _ := aecover_Ioc ha hb
refine hφ.integrable_of_integral_norm_bounded I hfi (h.mp ?_)
filter_upwards [ha.eventually (eventually_le_atBot 0),
hb.eventually (eventually_ge_atTop 0)] with i hai hbi ht
rwa [← intervalIntegral.integral_of_le (hai.trans hbi)]
/-- If `f` is integrable on intervals `Ioc (a i) (b i)`,
where `a i` tends to -∞ and `b i` tends to ∞, and
`∫ x in a i .. b i, ‖f x‖ ∂μ` converges to `I : ℝ` along a filter `l`,
then `f` is integrable on the interval (-∞, ∞) -/
theorem integrable_of_intervalIntegral_norm_tendsto (I : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc (a i) (b i)) μ) (ha : Tendsto a l atBot)
(hb : Tendsto b l atTop) (h : Tendsto (fun i => ∫ x in a i..b i, ‖f x‖ ∂μ) l (𝓝 I)) :
Integrable f μ :=
let ⟨I', hI'⟩ := h.isBoundedUnder_le
integrable_of_intervalIntegral_norm_bounded I' hfi ha hb hI'
theorem integrableOn_Iic_of_intervalIntegral_norm_bounded (I b : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc (a i) b) μ) (ha : Tendsto a l atBot)
(h : ∀ᶠ i in l, (∫ x in a i..b, ‖f x‖ ∂μ) ≤ I) : IntegrableOn f (Iic b) μ := by
have hφ : AECover (μ.restrict <| Iic b) l _ := aecover_Ioi ha
have hfi : ∀ i, IntegrableOn f (Ioi (a i)) (μ.restrict <| Iic b) := by
intro i
rw [IntegrableOn, Measure.restrict_restrict (hφ.measurableSet i)]
exact hfi i
refine hφ.integrable_of_integral_norm_bounded I hfi (h.mp ?_)
filter_upwards [ha.eventually (eventually_le_atBot b)] with i hai
rw [intervalIntegral.integral_of_le hai, Measure.restrict_restrict (hφ.measurableSet i)]
exact id
/-- If `f` is integrable on intervals `Ioc (a i) b`,
where `a i` tends to -∞, and
`∫ x in a i .. b, ‖f x‖ ∂μ` converges to `I : ℝ` along a filter `l`,
then `f` is integrable on the interval (-∞, b) -/
theorem integrableOn_Iic_of_intervalIntegral_norm_tendsto (I b : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc (a i) b) μ) (ha : Tendsto a l atBot)
(h : Tendsto (fun i => ∫ x in a i..b, ‖f x‖ ∂μ) l (𝓝 I)) : IntegrableOn f (Iic b) μ :=
let ⟨I', hI'⟩ := h.isBoundedUnder_le
integrableOn_Iic_of_intervalIntegral_norm_bounded I' b hfi ha hI'
theorem integrableOn_Ioi_of_intervalIntegral_norm_bounded (I a : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc a (b i)) μ) (hb : Tendsto b l atTop)
(h : ∀ᶠ i in l, (∫ x in a..b i, ‖f x‖ ∂μ) ≤ I) : IntegrableOn f (Ioi a) μ := by
have hφ : AECover (μ.restrict <| Ioi a) l _ := aecover_Iic hb
have hfi : ∀ i, IntegrableOn f (Iic (b i)) (μ.restrict <| Ioi a) := by
intro i
rw [IntegrableOn, Measure.restrict_restrict (hφ.measurableSet i), inter_comm]
exact hfi i
refine hφ.integrable_of_integral_norm_bounded I hfi (h.mp ?_)
filter_upwards [hb.eventually (eventually_ge_atTop a)] with i hbi
rw [intervalIntegral.integral_of_le hbi, Measure.restrict_restrict (hφ.measurableSet i),
inter_comm]
exact id
/-- If `f` is integrable on intervals `Ioc a (b i)`,
where `b i` tends to ∞, and
`∫ x in a .. b i, ‖f x‖ ∂μ` converges to `I : ℝ` along a filter `l`,
then `f` is integrable on the interval (a, ∞) -/
theorem integrableOn_Ioi_of_intervalIntegral_norm_tendsto (I a : ℝ)
(hfi : ∀ i, IntegrableOn f (Ioc a (b i)) μ) (hb : Tendsto b l atTop)
(h : Tendsto (fun i => ∫ x in a..b i, ‖f x‖ ∂μ) l (𝓝 <| I)) : IntegrableOn f (Ioi a) μ :=
let ⟨I', hI'⟩ := h.isBoundedUnder_le
integrableOn_Ioi_of_intervalIntegral_norm_bounded I' a hfi hb hI'
theorem integrableOn_Ioc_of_intervalIntegral_norm_bounded {I a₀ b₀ : ℝ}
(hfi : ∀ i, IntegrableOn f <| Ioc (a i) (b i)) (ha : Tendsto a l <| 𝓝 a₀)
(hb : Tendsto b l <| 𝓝 b₀) (h : ∀ᶠ i in l, (∫ x in Ioc (a i) (b i), ‖f x‖) ≤ I) :
IntegrableOn f (Ioc a₀ b₀) := by
refine (aecover_Ioc_of_Ioc ha hb).integrable_of_integral_norm_bounded I
(fun i => (hfi i).restrict) (h.mono fun i hi ↦ ?_)
rw [Measure.restrict_restrict measurableSet_Ioc]
refine le_trans (setIntegral_mono_set (hfi i).norm ?_ ?_) hi <;> apply ae_of_all
· simp only [Pi.zero_apply, norm_nonneg, forall_const]
· intro c hc; exact hc.1
theorem integrableOn_Ioc_of_intervalIntegral_norm_bounded_left {I a₀ b : ℝ}
(hfi : ∀ i, IntegrableOn f <| Ioc (a i) b) (ha : Tendsto a l <| 𝓝 a₀)
(h : ∀ᶠ i in l, (∫ x in Ioc (a i) b, ‖f x‖) ≤ I) : IntegrableOn f (Ioc a₀ b) :=
integrableOn_Ioc_of_intervalIntegral_norm_bounded hfi ha tendsto_const_nhds h
theorem integrableOn_Ioc_of_intervalIntegral_norm_bounded_right {I a b₀ : ℝ}
(hfi : ∀ i, IntegrableOn f <| Ioc a (b i)) (hb : Tendsto b l <| 𝓝 b₀)
(h : ∀ᶠ i in l, (∫ x in Ioc a (b i), ‖f x‖) ≤ I) : IntegrableOn f (Ioc a b₀) :=
integrableOn_Ioc_of_intervalIntegral_norm_bounded hfi tendsto_const_nhds hb h
end IntegrableOfIntervalIntegral
section IntegralOfIntervalIntegral
variable {ι E : Type*} {μ : Measure ℝ} {l : Filter ι} [IsCountablyGenerated l]
[NormedAddCommGroup E] [NormedSpace ℝ E] {a b : ι → ℝ} {f : ℝ → E}
theorem intervalIntegral_tendsto_integral (hfi : Integrable f μ) (ha : Tendsto a l atBot)
(hb : Tendsto b l atTop) : Tendsto (fun i => ∫ x in a i..b i, f x ∂μ) l (𝓝 <| ∫ x, f x ∂μ) := by
let φ i := Ioc (a i) (b i)
have hφ : AECover μ l φ := aecover_Ioc ha hb
refine (hφ.integral_tendsto_of_countably_generated hfi).congr' ?_
filter_upwards [ha.eventually (eventually_le_atBot 0),
hb.eventually (eventually_ge_atTop 0)] with i hai hbi
exact (intervalIntegral.integral_of_le (hai.trans hbi)).symm
theorem intervalIntegral_tendsto_integral_Iic (b : ℝ) (hfi : IntegrableOn f (Iic b) μ)
(ha : Tendsto a l atBot) :
Tendsto (fun i => ∫ x in a i..b, f x ∂μ) l (𝓝 <| ∫ x in Iic b, f x ∂μ) := by
let φ i := Ioi (a i)
have hφ : AECover (μ.restrict <| Iic b) l φ := aecover_Ioi ha
refine (hφ.integral_tendsto_of_countably_generated hfi).congr' ?_
filter_upwards [ha.eventually (eventually_le_atBot <| b)] with i hai
rw [intervalIntegral.integral_of_le hai, Measure.restrict_restrict (hφ.measurableSet i)]
rfl
theorem intervalIntegral_tendsto_integral_Ioi (a : ℝ) (hfi : IntegrableOn f (Ioi a) μ)
(hb : Tendsto b l atTop) :
Tendsto (fun i => ∫ x in a..b i, f x ∂μ) l (𝓝 <| ∫ x in Ioi a, f x ∂μ) := by
let φ i := Iic (b i)
have hφ : AECover (μ.restrict <| Ioi a) l φ := aecover_Iic hb
refine (hφ.integral_tendsto_of_countably_generated hfi).congr' ?_
filter_upwards [hb.eventually (eventually_ge_atTop <| a)] with i hbi
rw [intervalIntegral.integral_of_le hbi, Measure.restrict_restrict (hφ.measurableSet i),
inter_comm]
rfl
end IntegralOfIntervalIntegral
open Real
open scoped Interval
section IoiFTC
variable {E : Type*} {f f' : ℝ → E} {g g' : ℝ → ℝ} {a l : ℝ} {m : E} [NormedAddCommGroup E]
[NormedSpace ℝ E]
/-- If the derivative of a function defined on the real line is integrable close to `+∞`, then
the function has a limit at `+∞`. -/
theorem tendsto_limUnder_of_hasDerivAt_of_integrableOn_Ioi [CompleteSpace E]
(hderiv : ∀ x ∈ Ioi a, HasDerivAt f (f' x) x) (f'int : IntegrableOn f' (Ioi a)) :
Tendsto f atTop (𝓝 (limUnder atTop f)) := by
suffices ∃ a, Tendsto f atTop (𝓝 a) from tendsto_nhds_limUnder this
suffices CauchySeq f from cauchySeq_tendsto_of_complete this
apply Metric.cauchySeq_iff'.2 (fun ε εpos ↦ ?_)
have A : ∀ᶠ (n : ℕ) in atTop, ∫ (x : ℝ) in Ici ↑n, ‖f' x‖ < ε := by
have L : Tendsto (fun (n : ℕ) ↦ ∫ x in Ici (n : ℝ), ‖f' x‖) atTop
(𝓝 (∫ x in ⋂ (n : ℕ), Ici (n : ℝ), ‖f' x‖)) := by
apply tendsto_setIntegral_of_antitone (fun n ↦ measurableSet_Ici)
· intro m n hmn
exact Ici_subset_Ici.2 (Nat.cast_le.mpr hmn)
· rcases exists_nat_gt a with ⟨n, hn⟩
exact ⟨n, IntegrableOn.mono_set f'int.norm (Ici_subset_Ioi.2 hn)⟩
have B : ⋂ (n : ℕ), Ici (n : ℝ) = ∅ := by
apply eq_empty_of_forall_not_mem (fun x ↦ ?_)
simpa only [mem_iInter, mem_Ici, not_forall, not_le] using exists_nat_gt x
simp only [B, Measure.restrict_empty, integral_zero_measure] at L
exact (tendsto_order.1 L).2 _ εpos
have B : ∀ᶠ (n : ℕ) in atTop, a < n := by
rcases exists_nat_gt a with ⟨n, hn⟩
filter_upwards [Ioi_mem_atTop n] with m (hm : n < m) using hn.trans (Nat.cast_lt.mpr hm)
rcases (A.and B).exists with ⟨N, hN, h'N⟩
refine ⟨N, fun x hx ↦ ?_⟩
calc
dist (f x) (f ↑N)
= ‖f x - f N‖ := dist_eq_norm _ _
_ = ‖∫ t in Ioc ↑N x, f' t‖ := by
rw [← intervalIntegral.integral_of_le hx, intervalIntegral.integral_eq_sub_of_hasDerivAt]
· intro y hy
simp only [hx, uIcc_of_le, mem_Icc] at hy
exact hderiv _ (h'N.trans_le hy.1)
· rw [intervalIntegrable_iff_integrableOn_Ioc_of_le hx]
exact f'int.mono_set (Ioc_subset_Ioi_self.trans (Ioi_subset_Ioi h'N.le))
_ ≤ ∫ t in Ioc ↑N x, ‖f' t‖ := norm_integral_le_integral_norm fun a ↦ f' a
_ ≤ ∫ t in Ici ↑N, ‖f' t‖ := by
apply setIntegral_mono_set
· apply IntegrableOn.mono_set f'int.norm (Ici_subset_Ioi.2 h'N)
· filter_upwards with x using norm_nonneg _
· have : Ioc (↑N) x ⊆ Ici ↑N := Ioc_subset_Ioi_self.trans Ioi_subset_Ici_self
exact this.eventuallyLE
_ < ε := hN
open UniformSpace in
/-- If a function and its derivative are integrable on `(a, +∞)`, then the function tends to zero
at `+∞`. -/
theorem tendsto_zero_of_hasDerivAt_of_integrableOn_Ioi
(hderiv : ∀ x ∈ Ioi a, HasDerivAt f (f' x) x)
(f'int : IntegrableOn f' (Ioi a)) (fint : IntegrableOn f (Ioi a)) :
Tendsto f atTop (𝓝 0) := by
let F : E →L[ℝ] Completion E := Completion.toComplL
have Fderiv : ∀ x ∈ Ioi a, HasDerivAt (F ∘ f) (F (f' x)) x :=
fun x hx ↦ F.hasFDerivAt.comp_hasDerivAt _ (hderiv x hx)
have Fint : IntegrableOn (F ∘ f) (Ioi a) := by apply F.integrable_comp fint
have F'int : IntegrableOn (F ∘ f') (Ioi a) := by apply F.integrable_comp f'int
have A : Tendsto (F ∘ f) atTop (𝓝 (limUnder atTop (F ∘ f))) := by
apply tendsto_limUnder_of_hasDerivAt_of_integrableOn_Ioi Fderiv F'int
have B : limUnder atTop (F ∘ f) = F 0 := by
have : IntegrableAtFilter (F ∘ f) atTop := by exact ⟨Ioi a, Ioi_mem_atTop _, Fint⟩
apply IntegrableAtFilter.eq_zero_of_tendsto this ?_ A
intro s hs
rcases mem_atTop_sets.1 hs with ⟨b, hb⟩
rw [← top_le_iff, ← volume_Ici (a := b)]
exact measure_mono hb
rwa [B, ← IsEmbedding.tendsto_nhds_iff] at A
exact (Completion.isUniformEmbedding_coe E).isEmbedding
variable [CompleteSpace E]
/-- **Fundamental theorem of calculus-2**, on semi-infinite intervals `(a, +∞)`.
When a function has a limit at infinity `m`, and its derivative is integrable, then the
integral of the derivative on `(a, +∞)` is `m - f a`. Version assuming differentiability
on `(a, +∞)` and continuity at `a⁺`.
Note that such a function always has a limit at infinity,
see `tendsto_limUnder_of_hasDerivAt_of_integrableOn_Ioi`. -/
theorem integral_Ioi_of_hasDerivAt_of_tendsto (hcont : ContinuousWithinAt f (Ici a) a)
(hderiv : ∀ x ∈ Ioi a, HasDerivAt f (f' x) x) (f'int : IntegrableOn f' (Ioi a))
(hf : Tendsto f atTop (𝓝 m)) : ∫ x in Ioi a, f' x = m - f a := by
have hcont : ContinuousOn f (Ici a) := by
intro x hx
rcases hx.out.eq_or_lt with rfl|hx
· exact hcont
· exact (hderiv x hx).continuousAt.continuousWithinAt
refine tendsto_nhds_unique (intervalIntegral_tendsto_integral_Ioi a f'int tendsto_id) ?_
apply Tendsto.congr' _ (hf.sub_const _)
filter_upwards [Ioi_mem_atTop a] with x hx
have h'x : a ≤ id x := le_of_lt hx
symm
apply
intervalIntegral.integral_eq_sub_of_hasDerivAt_of_le h'x (hcont.mono Icc_subset_Ici_self)
fun y hy => hderiv y hy.1
rw [intervalIntegrable_iff_integrableOn_Ioc_of_le h'x]
exact f'int.mono (fun y hy => hy.1) le_rfl
/-- **Fundamental theorem of calculus-2**, on semi-infinite intervals `(a, +∞)`.
When a function has a limit at infinity `m`, and its derivative is integrable, then the
integral of the derivative on `(a, +∞)` is `m - f a`. Version assuming differentiability
on `[a, +∞)`.
Note that such a function always has a limit at infinity,
see `tendsto_limUnder_of_hasDerivAt_of_integrableOn_Ioi`. -/
theorem integral_Ioi_of_hasDerivAt_of_tendsto' (hderiv : ∀ x ∈ Ici a, HasDerivAt f (f' x) x)
(f'int : IntegrableOn f' (Ioi a)) (hf : Tendsto f atTop (𝓝 m)) :
∫ x in Ioi a, f' x = m - f a := by
refine integral_Ioi_of_hasDerivAt_of_tendsto ?_ (fun x hx => hderiv x hx.out.le)
f'int hf
exact (hderiv a left_mem_Ici).continuousAt.continuousWithinAt
/-- A special case of `integral_Ioi_of_hasDerivAt_of_tendsto` where we assume that `f` is C^1 with
compact support. -/
theorem _root_.HasCompactSupport.integral_Ioi_deriv_eq (hf : ContDiff ℝ 1 f)
(h2f : HasCompactSupport f) (b : ℝ) : ∫ x in Ioi b, deriv f x = - f b := by
have := fun x (_ : x ∈ Ioi b) ↦ hf.differentiable le_rfl x |>.hasDerivAt
rw [integral_Ioi_of_hasDerivAt_of_tendsto hf.continuous.continuousWithinAt this, zero_sub]
· refine hf.continuous_deriv le_rfl |>.integrable_of_hasCompactSupport h2f.deriv |>.integrableOn
rw [hasCompactSupport_iff_eventuallyEq, Filter.coclosedCompact_eq_cocompact] at h2f
exact h2f.filter_mono _root_.atTop_le_cocompact |>.tendsto
/-- When a function has a limit at infinity, and its derivative is nonnegative, then the derivative
is automatically integrable on `(a, +∞)`. Version assuming differentiability
on `(a, +∞)` and continuity at `a⁺`. -/
theorem integrableOn_Ioi_deriv_of_nonneg (hcont : ContinuousWithinAt g (Ici a) a)
(hderiv : ∀ x ∈ Ioi a, HasDerivAt g (g' x) x) (g'pos : ∀ x ∈ Ioi a, 0 ≤ g' x)
(hg : Tendsto g atTop (𝓝 l)) : IntegrableOn g' (Ioi a) := by
have hcont : ContinuousOn g (Ici a) := by
intro x hx
rcases hx.out.eq_or_lt with rfl|hx
· exact hcont
| · exact (hderiv x hx).continuousAt.continuousWithinAt
refine integrableOn_Ioi_of_intervalIntegral_norm_tendsto (l - g a) a (fun x => ?_) tendsto_id ?_
· exact intervalIntegral.integrableOn_deriv_of_nonneg (hcont.mono Icc_subset_Ici_self)
(fun y hy => hderiv y hy.1) fun y hy => g'pos y hy.1
apply Tendsto.congr' _ (hg.sub_const _)
filter_upwards [Ioi_mem_atTop a] with x hx
have h'x : a ≤ id x := le_of_lt hx
calc
g x - g a = ∫ y in a..id x, g' y := by
symm
apply intervalIntegral.integral_eq_sub_of_hasDerivAt_of_le h'x
(hcont.mono Icc_subset_Ici_self) fun y hy => hderiv y hy.1
rw [intervalIntegrable_iff_integrableOn_Ioc_of_le h'x]
exact intervalIntegral.integrableOn_deriv_of_nonneg (hcont.mono Icc_subset_Ici_self)
(fun y hy => hderiv y hy.1) fun y hy => g'pos y hy.1
_ = ∫ y in a..id x, ‖g' y‖ := by
simp_rw [intervalIntegral.integral_of_le h'x]
refine setIntegral_congr_fun measurableSet_Ioc fun y hy => ?_
| Mathlib/MeasureTheory/Integral/IntegralEqImproper.lean | 777 | 794 |
/-
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.CategoryTheory.Shift.CommShift
/-!
# Shift induced from a category to another
In this file, we introduce a sufficient condition on a functor
`F : C ⥤ D` so that a shift on `C` by a monoid `A` induces a shift on `D`.
More precisely, when the functor `(D ⥤ D) ⥤ C ⥤ D` given
by the precomposition with `F` is fully faithful, and that
all the shift functors on `C` can be lifted to functors `D ⥤ D`
(i.e. we have functors `s a : D ⥤ D` for all `a : A`, and isomorphisms
`F ⋙ s a ≅ shiftFunctor C a ⋙ F`), then these functors `s a` are
the shift functors of a term of type `HasShift D A`.
As this condition on the functor `F` is satisfied for quotient and localization
functors, the main construction `HasShift.induced` in this file shall be
used for both quotient and localized shifts.
-/
namespace CategoryTheory
variable {C D : Type _} [Category C] [Category D]
(F : C ⥤ D) {A : Type _} [AddMonoid A] [HasShift C A]
(s : A → D ⥤ D) (i : ∀ a, F ⋙ s a ≅ shiftFunctor C a ⋙ F)
[((whiskeringLeft C D D).obj F).Full] [((whiskeringLeft C D D).obj F).Faithful]
namespace HasShift
namespace Induced
/-- The `zero` field of the `ShiftMkCore` structure for the induced shift. -/
noncomputable def zero : s 0 ≅ 𝟭 D :=
((whiskeringLeft C D D).obj F).preimageIso ((i 0) ≪≫
isoWhiskerRight (shiftFunctorZero C A) F ≪≫ F.leftUnitor ≪≫ F.rightUnitor.symm)
/-- The `add` field of the `ShiftMkCore` structure for the induced shift. -/
noncomputable def add (a b : A) : s (a + b) ≅ s a ⋙ s b :=
((whiskeringLeft C D D).obj F).preimageIso
(i (a + b) ≪≫ isoWhiskerRight (shiftFunctorAdd C a b) F ≪≫
Functor.associator _ _ _ ≪≫
isoWhiskerLeft _ (i b).symm ≪≫ (Functor.associator _ _ _).symm ≪≫
isoWhiskerRight (i a).symm _ ≪≫ Functor.associator _ _ _)
@[simp]
lemma zero_hom_app_obj (X : C) :
(zero F s i).hom.app (F.obj X) =
(i 0).hom.app X ≫ F.map ((shiftFunctorZero C A).hom.app X) := by
have h : whiskerLeft F (zero F s i).hom = _ :=
((whiskeringLeft C D D).obj F).map_preimage _
exact (NatTrans.congr_app h X).trans (by simp)
| @[simp]
lemma zero_inv_app_obj (X : C) :
(zero F s i).inv.app (F.obj X) =
F.map ((shiftFunctorZero C A).inv.app X) ≫ (i 0).inv.app X := by
have h : whiskerLeft F (zero F s i).inv = _ :=
((whiskeringLeft C D D).obj F).map_preimage _
exact (NatTrans.congr_app h X).trans (by simp)
| Mathlib/CategoryTheory/Shift/Induced.lean | 58 | 64 |
/-
Copyright (c) 2023 Kyle Miller, Rémi Bottinelli. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kyle Miller, Rémi Bottinelli
-/
import Mathlib.Combinatorics.SimpleGraph.Path
import Mathlib.Data.Set.Card
/-!
# Connectivity of subgraphs and induced graphs
## Main definitions
* `SimpleGraph.Subgraph.Preconnected` and `SimpleGraph.Subgraph.Connected` give subgraphs
connectivity predicates via `SimpleGraph.subgraph.coe`.
-/
namespace SimpleGraph
universe u v
variable {V : Type u} {V' : Type v} {G : SimpleGraph V} {G' : SimpleGraph V'}
namespace Subgraph
/-- A subgraph is preconnected if it is preconnected when coerced to be a simple graph.
Note: This is a structure to make it so one can be precise about how dot notation resolves. -/
protected structure Preconnected (H : G.Subgraph) : Prop where
protected coe : H.coe.Preconnected
instance {H : G.Subgraph} : Coe H.Preconnected H.coe.Preconnected := ⟨Preconnected.coe⟩
instance {H : G.Subgraph} : CoeFun H.Preconnected (fun _ => ∀ u v : H.verts, H.coe.Reachable u v) :=
⟨fun h => h.coe⟩
protected lemma preconnected_iff {H : G.Subgraph} :
H.Preconnected ↔ H.coe.Preconnected := ⟨fun ⟨h⟩ => h, .mk⟩
/-- A subgraph is connected if it is connected when coerced to be a simple graph.
Note: This is a structure to make it so one can be precise about how dot notation resolves. -/
protected structure Connected (H : G.Subgraph) : Prop where
protected coe : H.coe.Connected
instance {H : G.Subgraph} : Coe H.Connected H.coe.Connected := ⟨Connected.coe⟩
instance {H : G.Subgraph} : CoeFun H.Connected (fun _ => ∀ u v : H.verts, H.coe.Reachable u v) :=
⟨fun h => h.coe⟩
protected lemma connected_iff' {H : G.Subgraph} :
H.Connected ↔ H.coe.Connected := ⟨fun ⟨h⟩ => h, .mk⟩
protected lemma connected_iff {H : G.Subgraph} :
H.Connected ↔ H.Preconnected ∧ H.verts.Nonempty := by
rw [H.connected_iff', connected_iff, H.preconnected_iff, Set.nonempty_coe_sort]
protected lemma Connected.preconnected {H : G.Subgraph} (h : H.Connected) : H.Preconnected := by
rw [H.connected_iff] at h; exact h.1
protected lemma Connected.nonempty {H : G.Subgraph} (h : H.Connected) : H.verts.Nonempty := by
rw [H.connected_iff] at h; exact h.2
theorem singletonSubgraph_connected {v : V} : (G.singletonSubgraph v).Connected := by
refine ⟨⟨?_⟩⟩
rintro ⟨a, ha⟩ ⟨b, hb⟩
simp only [singletonSubgraph_verts, Set.mem_singleton_iff] at ha hb
subst_vars
rfl
@[simp]
theorem subgraphOfAdj_connected {v w : V} (hvw : G.Adj v w) : (G.subgraphOfAdj hvw).Connected := by
refine ⟨⟨?_⟩⟩
rintro ⟨a, ha⟩ ⟨b, hb⟩
simp only [subgraphOfAdj_verts, Set.mem_insert_iff, Set.mem_singleton_iff] at ha hb
obtain rfl | rfl := ha <;> obtain rfl | rfl := hb <;>
first | rfl | (apply Adj.reachable; simp)
lemma top_induce_pair_connected_of_adj {u v : V} (huv : G.Adj u v) :
((⊤ : G.Subgraph).induce {u, v}).Connected := by
rw [← subgraphOfAdj_eq_induce huv]
exact subgraphOfAdj_connected huv
@[mono]
protected lemma Connected.mono {H H' : G.Subgraph} (hle : H ≤ H') (hv : H.verts = H'.verts)
(h : H.Connected) : H'.Connected := by
rw [← Subgraph.copy_eq H' H.verts hv H'.Adj rfl]
refine ⟨h.coe.mono ?_⟩
rintro ⟨v, hv⟩ ⟨w, hw⟩ hvw
exact hle.2 hvw
protected lemma Connected.mono' {H H' : G.Subgraph}
(hle : ∀ v w, H.Adj v w → H'.Adj v w) (hv : H.verts = H'.verts)
(h : H.Connected) : H'.Connected := by
exact h.mono ⟨hv.le, hle⟩ hv
protected lemma Connected.sup {H K : G.Subgraph}
(hH : H.Connected) (hK : K.Connected) (hn : (H ⊓ K).verts.Nonempty) :
(H ⊔ K).Connected := by
rw [Subgraph.connected_iff', connected_iff_exists_forall_reachable]
obtain ⟨u, hu, hu'⟩ := hn
exists ⟨u, Or.inl hu⟩
rintro ⟨v, (hv|hv)⟩
· exact Reachable.map (Subgraph.inclusion (le_sup_left : H ≤ H ⊔ K)) (hH ⟨u, hu⟩ ⟨v, hv⟩)
· exact Reachable.map (Subgraph.inclusion (le_sup_right : K ≤ H ⊔ K)) (hK ⟨u, hu'⟩ ⟨v, hv⟩)
/--
This lemma establishes a condition under which a subgraph is the same as a connected component.
Note the asymmetry in the hypothesis `h`: `v` is in `H.verts`, but `w` is not required to be.
-/
lemma Connected.exists_verts_eq_connectedComponentSupp {H : Subgraph G}
(hc : H.Connected) (h : ∀ v ∈ H.verts, ∀ w, G.Adj v w → H.Adj v w) :
∃ c : G.ConnectedComponent, H.verts = c.supp := by
rw [SimpleGraph.ConnectedComponent.exists]
obtain ⟨v, hv⟩ := hc.nonempty
use v
ext w
simp only [ConnectedComponent.mem_supp_iff, ConnectedComponent.eq]
exact ⟨fun hw ↦ by simpa using (hc ⟨w, hw⟩ ⟨v, hv⟩).map H.hom,
fun a ↦ a.symm.mem_subgraphVerts h hv⟩
end Subgraph
/-! ### Walks as subgraphs -/
namespace Walk
variable {u v w : V}
/-- The subgraph consisting of the vertices and edges of the walk. -/
@[simp]
protected def toSubgraph {u v : V} : G.Walk u v → G.Subgraph
| nil => G.singletonSubgraph u
| cons h p => G.subgraphOfAdj h ⊔ p.toSubgraph
theorem toSubgraph_cons_nil_eq_subgraphOfAdj (h : G.Adj u v) :
(cons h nil).toSubgraph = G.subgraphOfAdj h := by simp
theorem mem_verts_toSubgraph (p : G.Walk u v) : w ∈ p.toSubgraph.verts ↔ w ∈ p.support := by
induction p with
| nil => simp
| cons h p' ih =>
rename_i x y z
have : w = y ∨ w ∈ p'.support ↔ w ∈ p'.support :=
⟨by rintro (rfl | h) <;> simp [*], by simp +contextual⟩
simp [ih, or_assoc, this]
lemma not_nil_of_adj_toSubgraph {u v} {x : V} {p : G.Walk u v} (hadj : p.toSubgraph.Adj w x) :
¬p.Nil := by
cases p <;> simp_all
lemma start_mem_verts_toSubgraph (p : G.Walk u v) : u ∈ p.toSubgraph.verts := by
simp [mem_verts_toSubgraph]
lemma end_mem_verts_toSubgraph (p : G.Walk u v) : v ∈ p.toSubgraph.verts := by
simp [mem_verts_toSubgraph]
@[simp]
theorem verts_toSubgraph (p : G.Walk u v) : p.toSubgraph.verts = { w | w ∈ p.support } :=
Set.ext fun _ => p.mem_verts_toSubgraph
theorem mem_edges_toSubgraph (p : G.Walk u v) {e : Sym2 V} :
e ∈ p.toSubgraph.edgeSet ↔ e ∈ p.edges := by induction p <;> simp [*]
@[simp]
theorem edgeSet_toSubgraph (p : G.Walk u v) : p.toSubgraph.edgeSet = { e | e ∈ p.edges } :=
Set.ext fun _ => p.mem_edges_toSubgraph
@[simp]
theorem toSubgraph_append (p : G.Walk u v) (q : G.Walk v w) :
(p.append q).toSubgraph = p.toSubgraph ⊔ q.toSubgraph := by induction p <;> simp [*, sup_assoc]
@[simp]
theorem toSubgraph_reverse (p : G.Walk u v) : p.reverse.toSubgraph = p.toSubgraph := by
induction p with
| nil => simp
| cons _ _ _ =>
simp only [*, Walk.toSubgraph, reverse_cons, toSubgraph_append, subgraphOfAdj_symm]
rw [sup_comm]
congr
ext <;> simp [-Set.bot_eq_empty]
@[simp]
theorem toSubgraph_rotate [DecidableEq V] (c : G.Walk v v) (h : u ∈ c.support) :
(c.rotate h).toSubgraph = c.toSubgraph := by
rw [rotate, toSubgraph_append, sup_comm, ← toSubgraph_append, take_spec]
@[simp]
theorem toSubgraph_map (f : G →g G') (p : G.Walk u v) :
(p.map f).toSubgraph = p.toSubgraph.map f := by induction p <;> simp [*, Subgraph.map_sup]
lemma adj_toSubgraph_mapLe {G' : SimpleGraph V} {w x : V} {p : G.Walk u v} (h : G ≤ G') :
(p.mapLe h).toSubgraph.Adj w x ↔ p.toSubgraph.Adj w x := by
simp only [toSubgraph_map, Subgraph.map_adj]
nth_rewrite 1 [← Hom.ofLE_apply h w, ← Hom.ofLE_apply h x]
simp
@[simp]
theorem finite_neighborSet_toSubgraph (p : G.Walk u v) : (p.toSubgraph.neighborSet w).Finite := by
induction p with
| nil =>
rw [Walk.toSubgraph, neighborSet_singletonSubgraph]
apply Set.toFinite
| cons ha _ ih =>
rw [Walk.toSubgraph, Subgraph.neighborSet_sup]
refine Set.Finite.union ?_ ih
| refine Set.Finite.subset ?_ (neighborSet_subgraphOfAdj_subset ha)
apply Set.toFinite
lemma toSubgraph_le_induce_support (p : G.Walk u v) :
p.toSubgraph ≤ (⊤ : G.Subgraph).induce {v | v ∈ p.support} := by
convert Subgraph.le_induce_top_verts
exact p.verts_toSubgraph.symm
theorem toSubgraph_adj_getVert {u v} (w : G.Walk u v) {i : ℕ} (hi : i < w.length) :
w.toSubgraph.Adj (w.getVert i) (w.getVert (i + 1)) := by
induction w generalizing i with
| nil => cases hi
| Mathlib/Combinatorics/SimpleGraph/Connectivity/Subgraph.lean | 207 | 218 |
/-
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, Sébastien Gouëzel,
Rémy Degenne, David Loeffler
-/
import Mathlib.Analysis.SpecialFunctions.Pow.Complex
import Qq
/-! # Power function on `ℝ`
We construct the power functions `x ^ y`, where `x` and `y` are real numbers.
-/
noncomputable section
open Real ComplexConjugate Finset Set
/-
## Definitions
-/
namespace Real
variable {x y z : ℝ}
/-- The real power function `x ^ y`, defined as the real part of the complex power function.
For `x > 0`, it is equal to `exp (y log x)`. For `x = 0`, one sets `0 ^ 0=1` and `0 ^ y=0` for
`y ≠ 0`. For `x < 0`, the definition is somewhat arbitrary as it depends on the choice of a complex
determination of the logarithm. With our conventions, it is equal to `exp (y log x) cos (π y)`. -/
noncomputable def rpow (x y : ℝ) :=
((x : ℂ) ^ (y : ℂ)).re
noncomputable instance : Pow ℝ ℝ := ⟨rpow⟩
@[simp]
theorem rpow_eq_pow (x y : ℝ) : rpow x y = x ^ y := rfl
theorem rpow_def (x y : ℝ) : x ^ y = ((x : ℂ) ^ (y : ℂ)).re := rfl
theorem rpow_def_of_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) := by
simp only [rpow_def, Complex.cpow_def]; split_ifs <;>
simp_all [(Complex.ofReal_log hx).symm, -Complex.ofReal_mul,
(Complex.ofReal_mul _ _).symm, Complex.exp_ofReal_re, Complex.ofReal_eq_zero]
theorem rpow_def_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : x ^ y = exp (log x * y) := by
rw [rpow_def_of_nonneg (le_of_lt hx), if_neg (ne_of_gt hx)]
theorem exp_mul (x y : ℝ) : exp (x * y) = exp x ^ y := by rw [rpow_def_of_pos (exp_pos _), log_exp]
@[simp, norm_cast]
theorem rpow_intCast (x : ℝ) (n : ℤ) : x ^ (n : ℝ) = x ^ n := by
simp only [rpow_def, ← Complex.ofReal_zpow, Complex.cpow_intCast, Complex.ofReal_intCast,
Complex.ofReal_re]
@[simp, norm_cast]
theorem rpow_natCast (x : ℝ) (n : ℕ) : x ^ (n : ℝ) = x ^ n := by simpa using rpow_intCast x n
@[simp]
theorem exp_one_rpow (x : ℝ) : exp 1 ^ x = exp x := by rw [← exp_mul, one_mul]
@[simp] lemma exp_one_pow (n : ℕ) : exp 1 ^ n = exp n := by rw [← rpow_natCast, exp_one_rpow]
theorem rpow_eq_zero_iff_of_nonneg (hx : 0 ≤ x) : x ^ y = 0 ↔ x = 0 ∧ y ≠ 0 := by
simp only [rpow_def_of_nonneg hx]
split_ifs <;> simp [*, exp_ne_zero]
@[simp]
lemma rpow_eq_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y = 0 ↔ x = 0 := by
simp [rpow_eq_zero_iff_of_nonneg, *]
@[simp]
lemma rpow_ne_zero (hx : 0 ≤ x) (hy : y ≠ 0) : x ^ y ≠ 0 ↔ x ≠ 0 :=
Real.rpow_eq_zero hx hy |>.not
open Real
theorem rpow_def_of_neg {x : ℝ} (hx : x < 0) (y : ℝ) : x ^ y = exp (log x * y) * cos (y * π) := by
rw [rpow_def, Complex.cpow_def, if_neg]
· have : Complex.log x * y = ↑(log (-x) * y) + ↑(y * π) * Complex.I := by
simp only [Complex.log, Complex.norm_real, norm_eq_abs, abs_of_neg hx, log_neg_eq_log,
Complex.arg_ofReal_of_neg hx, Complex.ofReal_mul]
ring
rw [this, Complex.exp_add_mul_I, ← Complex.ofReal_exp, ← Complex.ofReal_cos, ←
Complex.ofReal_sin, mul_add, ← Complex.ofReal_mul, ← mul_assoc, ← Complex.ofReal_mul,
Complex.add_re, Complex.ofReal_re, Complex.mul_re, Complex.I_re, Complex.ofReal_im,
Real.log_neg_eq_log]
ring
· rw [Complex.ofReal_eq_zero]
exact ne_of_lt hx
theorem rpow_def_of_nonpos {x : ℝ} (hx : x ≤ 0) (y : ℝ) :
x ^ y = if x = 0 then if y = 0 then 1 else 0 else exp (log x * y) * cos (y * π) := by
split_ifs with h <;> simp [rpow_def, *]; exact rpow_def_of_neg (lt_of_le_of_ne hx h) _
@[bound]
theorem rpow_pos_of_pos {x : ℝ} (hx : 0 < x) (y : ℝ) : 0 < x ^ y := by
rw [rpow_def_of_pos hx]; apply exp_pos
@[simp]
theorem rpow_zero (x : ℝ) : x ^ (0 : ℝ) = 1 := by simp [rpow_def]
theorem rpow_zero_pos (x : ℝ) : 0 < x ^ (0 : ℝ) := by simp
@[simp]
theorem zero_rpow {x : ℝ} (h : x ≠ 0) : (0 : ℝ) ^ x = 0 := by simp [rpow_def, *]
theorem zero_rpow_eq_iff {x : ℝ} {a : ℝ} : 0 ^ x = a ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
constructor
· intro hyp
simp only [rpow_def, Complex.ofReal_zero] at hyp
by_cases h : x = 0
· subst h
simp only [Complex.one_re, Complex.ofReal_zero, Complex.cpow_zero] at hyp
exact Or.inr ⟨rfl, hyp.symm⟩
· rw [Complex.zero_cpow (Complex.ofReal_ne_zero.mpr h)] at hyp
exact Or.inl ⟨h, hyp.symm⟩
· rintro (⟨h, rfl⟩ | ⟨rfl, rfl⟩)
· exact zero_rpow h
· exact rpow_zero _
theorem eq_zero_rpow_iff {x : ℝ} {a : ℝ} : a = 0 ^ x ↔ x ≠ 0 ∧ a = 0 ∨ x = 0 ∧ a = 1 := by
rw [← zero_rpow_eq_iff, eq_comm]
@[simp]
theorem rpow_one (x : ℝ) : x ^ (1 : ℝ) = x := by simp [rpow_def]
@[simp]
theorem one_rpow (x : ℝ) : (1 : ℝ) ^ x = 1 := by simp [rpow_def]
theorem zero_rpow_le_one (x : ℝ) : (0 : ℝ) ^ x ≤ 1 := by
by_cases h : x = 0 <;> simp [h, zero_le_one]
theorem zero_rpow_nonneg (x : ℝ) : 0 ≤ (0 : ℝ) ^ x := by
by_cases h : x = 0 <;> simp [h, zero_le_one]
@[bound]
theorem rpow_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : 0 ≤ x ^ y := by
rw [rpow_def_of_nonneg hx]; split_ifs <;>
simp only [zero_le_one, le_refl, le_of_lt (exp_pos _)]
theorem abs_rpow_of_nonneg {x y : ℝ} (hx_nonneg : 0 ≤ x) : |x ^ y| = |x| ^ y := by
have h_rpow_nonneg : 0 ≤ x ^ y := Real.rpow_nonneg hx_nonneg _
rw [abs_eq_self.mpr hx_nonneg, abs_eq_self.mpr h_rpow_nonneg]
@[bound]
theorem abs_rpow_le_abs_rpow (x y : ℝ) : |x ^ y| ≤ |x| ^ y := by
rcases le_or_lt 0 x with hx | hx
· rw [abs_rpow_of_nonneg hx]
· rw [abs_of_neg hx, rpow_def_of_neg hx, rpow_def_of_pos (neg_pos.2 hx), log_neg_eq_log, abs_mul,
abs_of_pos (exp_pos _)]
exact mul_le_of_le_one_right (exp_pos _).le (abs_cos_le_one _)
theorem abs_rpow_le_exp_log_mul (x y : ℝ) : |x ^ y| ≤ exp (log x * y) := by
refine (abs_rpow_le_abs_rpow x y).trans ?_
by_cases hx : x = 0
· by_cases hy : y = 0 <;> simp [hx, hy, zero_le_one]
· rw [rpow_def_of_pos (abs_pos.2 hx), log_abs]
lemma rpow_inv_log (hx₀ : 0 < x) (hx₁ : x ≠ 1) : x ^ (log x)⁻¹ = exp 1 := by
rw [rpow_def_of_pos hx₀, mul_inv_cancel₀]
exact log_ne_zero.2 ⟨hx₀.ne', hx₁, (hx₀.trans' <| by norm_num).ne'⟩
/-- See `Real.rpow_inv_log` for the equality when `x ≠ 1` is strictly positive. -/
lemma rpow_inv_log_le_exp_one : x ^ (log x)⁻¹ ≤ exp 1 := by
calc
_ ≤ |x ^ (log x)⁻¹| := le_abs_self _
_ ≤ |x| ^ (log x)⁻¹ := abs_rpow_le_abs_rpow ..
rw [← log_abs]
obtain hx | hx := (abs_nonneg x).eq_or_gt
· simp [hx]
· rw [rpow_def_of_pos hx]
gcongr
exact mul_inv_le_one
theorem norm_rpow_of_nonneg {x y : ℝ} (hx_nonneg : 0 ≤ x) : ‖x ^ y‖ = ‖x‖ ^ y := by
simp_rw [Real.norm_eq_abs]
exact abs_rpow_of_nonneg hx_nonneg
variable {w x y z : ℝ}
theorem rpow_add (hx : 0 < x) (y z : ℝ) : x ^ (y + z) = x ^ y * x ^ z := by
simp only [rpow_def_of_pos hx, mul_add, exp_add]
theorem rpow_add' (hx : 0 ≤ x) (h : y + z ≠ 0) : x ^ (y + z) = x ^ y * x ^ z := by
rcases hx.eq_or_lt with (rfl | pos)
· rw [zero_rpow h, zero_eq_mul]
have : y ≠ 0 ∨ z ≠ 0 := not_and_or.1 fun ⟨hy, hz⟩ => h <| hy.symm ▸ hz.symm ▸ zero_add 0
exact this.imp zero_rpow zero_rpow
· exact rpow_add pos _ _
/-- Variant of `Real.rpow_add'` that avoids having to prove `y + z = w` twice. -/
lemma rpow_of_add_eq (hx : 0 ≤ x) (hw : w ≠ 0) (h : y + z = w) : x ^ w = x ^ y * x ^ z := by
rw [← h, rpow_add' hx]; rwa [h]
theorem rpow_add_of_nonneg (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 ≤ z) :
x ^ (y + z) = x ^ y * x ^ z := by
rcases hy.eq_or_lt with (rfl | hy)
· rw [zero_add, rpow_zero, one_mul]
exact rpow_add' hx (ne_of_gt <| add_pos_of_pos_of_nonneg hy hz)
/-- For `0 ≤ x`, the only problematic case in the equality `x ^ y * x ^ z = x ^ (y + z)` is for
`x = 0` and `y + z = 0`, where the right hand side is `1` while the left hand side can vanish.
The inequality is always true, though, and given in this lemma. -/
theorem le_rpow_add {x : ℝ} (hx : 0 ≤ x) (y z : ℝ) : x ^ y * x ^ z ≤ x ^ (y + z) := by
rcases le_iff_eq_or_lt.1 hx with (H | pos)
· by_cases h : y + z = 0
· simp only [H.symm, h, rpow_zero]
calc
(0 : ℝ) ^ y * 0 ^ z ≤ 1 * 1 :=
mul_le_mul (zero_rpow_le_one y) (zero_rpow_le_one z) (zero_rpow_nonneg z) zero_le_one
_ = 1 := by simp
· simp [rpow_add', ← H, h]
· simp [rpow_add pos]
theorem rpow_sum_of_pos {ι : Type*} {a : ℝ} (ha : 0 < a) (f : ι → ℝ) (s : Finset ι) :
(a ^ ∑ x ∈ s, f x) = ∏ x ∈ s, a ^ f x :=
map_sum (⟨⟨fun (x : ℝ) => (a ^ x : ℝ), rpow_zero a⟩, rpow_add ha⟩ : ℝ →+ (Additive ℝ)) f s
theorem rpow_sum_of_nonneg {ι : Type*} {a : ℝ} (ha : 0 ≤ a) {s : Finset ι} {f : ι → ℝ}
(h : ∀ x ∈ s, 0 ≤ f x) : (a ^ ∑ x ∈ s, f x) = ∏ x ∈ s, a ^ f x := by
induction' s using Finset.cons_induction with i s hi ihs
· rw [sum_empty, Finset.prod_empty, rpow_zero]
· rw [forall_mem_cons] at h
rw [sum_cons, prod_cons, ← ihs h.2, rpow_add_of_nonneg ha h.1 (sum_nonneg h.2)]
theorem rpow_neg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : x ^ (-y) = (x ^ y)⁻¹ := by
simp only [rpow_def_of_nonneg hx]; split_ifs <;> simp_all [exp_neg]
theorem rpow_sub {x : ℝ} (hx : 0 < x) (y z : ℝ) : x ^ (y - z) = x ^ y / x ^ z := by
simp only [sub_eq_add_neg, rpow_add hx, rpow_neg (le_of_lt hx), div_eq_mul_inv]
theorem rpow_sub' {x : ℝ} (hx : 0 ≤ x) {y z : ℝ} (h : y - z ≠ 0) : x ^ (y - z) = x ^ y / x ^ z := by
simp only [sub_eq_add_neg] at h ⊢
simp only [rpow_add' hx h, rpow_neg hx, div_eq_mul_inv]
protected theorem _root_.HasCompactSupport.rpow_const {α : Type*} [TopologicalSpace α] {f : α → ℝ}
(hf : HasCompactSupport f) {r : ℝ} (hr : r ≠ 0) : HasCompactSupport (fun x ↦ f x ^ r) :=
hf.comp_left (g := (· ^ r)) (Real.zero_rpow hr)
end Real
/-!
## Comparing real and complex powers
-/
namespace Complex
theorem ofReal_cpow {x : ℝ} (hx : 0 ≤ x) (y : ℝ) : ((x ^ y : ℝ) : ℂ) = (x : ℂ) ^ (y : ℂ) := by
simp only [Real.rpow_def_of_nonneg hx, Complex.cpow_def, ofReal_eq_zero]; split_ifs <;>
simp [Complex.ofReal_log hx]
theorem ofReal_cpow_of_nonpos {x : ℝ} (hx : x ≤ 0) (y : ℂ) :
(x : ℂ) ^ y = (-x : ℂ) ^ y * exp (π * I * y) := by
rcases hx.eq_or_lt with (rfl | hlt)
· rcases eq_or_ne y 0 with (rfl | hy) <;> simp [*]
have hne : (x : ℂ) ≠ 0 := ofReal_ne_zero.mpr hlt.ne
rw [cpow_def_of_ne_zero hne, cpow_def_of_ne_zero (neg_ne_zero.2 hne), ← exp_add, ← add_mul, log,
log, norm_neg, arg_ofReal_of_neg hlt, ← ofReal_neg, arg_ofReal_of_nonneg (neg_nonneg.2 hx),
ofReal_zero, zero_mul, add_zero]
lemma cpow_ofReal (x : ℂ) (y : ℝ) :
x ^ (y : ℂ) = ↑(‖x‖ ^ y) * (Real.cos (arg x * y) + Real.sin (arg x * y) * I) := by
rcases eq_or_ne x 0 with rfl | hx
· simp [ofReal_cpow le_rfl]
· rw [cpow_def_of_ne_zero hx, exp_eq_exp_re_mul_sin_add_cos, mul_comm (log x)]
norm_cast
rw [re_ofReal_mul, im_ofReal_mul, log_re, log_im, mul_comm y, mul_comm y, Real.exp_mul,
Real.exp_log]
rwa [norm_pos_iff]
lemma cpow_ofReal_re (x : ℂ) (y : ℝ) : (x ^ (y : ℂ)).re = ‖x‖ ^ y * Real.cos (arg x * y) := by
rw [cpow_ofReal]; generalize arg x * y = z; simp [Real.cos]
lemma cpow_ofReal_im (x : ℂ) (y : ℝ) : (x ^ (y : ℂ)).im = ‖x‖ ^ y * Real.sin (arg x * y) := by
rw [cpow_ofReal]; generalize arg x * y = z; simp [Real.sin]
theorem norm_cpow_of_ne_zero {z : ℂ} (hz : z ≠ 0) (w : ℂ) :
‖z ^ w‖ = ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
rw [cpow_def_of_ne_zero hz, norm_exp, mul_re, log_re, log_im, Real.exp_sub,
Real.rpow_def_of_pos (norm_pos_iff.mpr hz)]
theorem norm_cpow_of_imp {z w : ℂ} (h : z = 0 → w.re = 0 → w = 0) :
‖z ^ w‖ = ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
rcases ne_or_eq z 0 with (hz | rfl) <;> [exact norm_cpow_of_ne_zero hz w; rw [norm_zero]]
rcases eq_or_ne w.re 0 with hw | hw
· simp [hw, h rfl hw]
· rw [Real.zero_rpow hw, zero_div, zero_cpow, norm_zero]
exact ne_of_apply_ne re hw
theorem norm_cpow_le (z w : ℂ) : ‖z ^ w‖ ≤ ‖z‖ ^ w.re / Real.exp (arg z * im w) := by
by_cases h : z = 0 → w.re = 0 → w = 0
· exact (norm_cpow_of_imp h).le
· push_neg at h
simp [h]
@[simp]
theorem norm_cpow_real (x : ℂ) (y : ℝ) : ‖x ^ (y : ℂ)‖ = ‖x‖ ^ y := by
rw [norm_cpow_of_imp] <;> simp
@[simp]
theorem norm_cpow_inv_nat (x : ℂ) (n : ℕ) : ‖x ^ (n⁻¹ : ℂ)‖ = ‖x‖ ^ (n⁻¹ : ℝ) := by
rw [← norm_cpow_real]; simp
theorem norm_cpow_eq_rpow_re_of_pos {x : ℝ} (hx : 0 < x) (y : ℂ) : ‖(x : ℂ) ^ y‖ = x ^ y.re := by
rw [norm_cpow_of_ne_zero (ofReal_ne_zero.mpr hx.ne'), arg_ofReal_of_nonneg hx.le,
zero_mul, Real.exp_zero, div_one, Complex.norm_of_nonneg hx.le]
theorem norm_cpow_eq_rpow_re_of_nonneg {x : ℝ} (hx : 0 ≤ x) {y : ℂ} (hy : re y ≠ 0) :
‖(x : ℂ) ^ y‖ = x ^ re y := by
rw [norm_cpow_of_imp] <;> simp [*, arg_ofReal_of_nonneg, abs_of_nonneg]
@[deprecated (since := "2025-02-17")] alias abs_cpow_of_ne_zero := norm_cpow_of_ne_zero
@[deprecated (since := "2025-02-17")] alias abs_cpow_of_imp := norm_cpow_of_imp
@[deprecated (since := "2025-02-17")] alias abs_cpow_le := norm_cpow_le
@[deprecated (since := "2025-02-17")] alias abs_cpow_real := norm_cpow_real
@[deprecated (since := "2025-02-17")] alias abs_cpow_inv_nat := norm_cpow_inv_nat
@[deprecated (since := "2025-02-17")] alias abs_cpow_eq_rpow_re_of_pos :=
norm_cpow_eq_rpow_re_of_pos
@[deprecated (since := "2025-02-17")] alias abs_cpow_eq_rpow_re_of_nonneg :=
norm_cpow_eq_rpow_re_of_nonneg
open Filter in
lemma norm_ofReal_cpow_eventually_eq_atTop (c : ℂ) :
(fun t : ℝ ↦ ‖(t : ℂ) ^ c‖) =ᶠ[atTop] fun t ↦ t ^ c.re := by
filter_upwards [eventually_gt_atTop 0] with t ht
rw [norm_cpow_eq_rpow_re_of_pos ht]
lemma norm_natCast_cpow_of_re_ne_zero (n : ℕ) {s : ℂ} (hs : s.re ≠ 0) :
‖(n : ℂ) ^ s‖ = (n : ℝ) ^ (s.re) := by
rw [← ofReal_natCast, norm_cpow_eq_rpow_re_of_nonneg n.cast_nonneg hs]
lemma norm_natCast_cpow_of_pos {n : ℕ} (hn : 0 < n) (s : ℂ) :
‖(n : ℂ) ^ s‖ = (n : ℝ) ^ (s.re) := by
rw [← ofReal_natCast, norm_cpow_eq_rpow_re_of_pos (Nat.cast_pos.mpr hn) _]
lemma norm_natCast_cpow_pos_of_pos {n : ℕ} (hn : 0 < n) (s : ℂ) : 0 < ‖(n : ℂ) ^ s‖ :=
(norm_natCast_cpow_of_pos hn _).symm ▸ Real.rpow_pos_of_pos (Nat.cast_pos.mpr hn) _
theorem cpow_mul_ofReal_nonneg {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (z : ℂ) :
(x : ℂ) ^ (↑y * z) = (↑(x ^ y) : ℂ) ^ z := by
rw [cpow_mul, ofReal_cpow hx]
· rw [← ofReal_log hx, ← ofReal_mul, ofReal_im, neg_lt_zero]; exact Real.pi_pos
· rw [← ofReal_log hx, ← ofReal_mul, ofReal_im]; exact Real.pi_pos.le
end Complex
/-! ### Positivity extension -/
namespace Mathlib.Meta.Positivity
open Lean Meta Qq
/-- Extension for the `positivity` tactic: exponentiation by a real number is positive (namely 1)
when the exponent is zero. The other cases are done in `evalRpow`. -/
@[positivity (_ : ℝ) ^ (0 : ℝ)]
def evalRpowZero : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q($a ^ (0 : ℝ)) =>
assertInstancesCommute
pure (.positive q(Real.rpow_zero_pos $a))
| _, _, _ => throwError "not Real.rpow"
/-- Extension for the `positivity` tactic: exponentiation by a real number is nonnegative when
the base is nonnegative and positive when the base is positive. -/
@[positivity (_ : ℝ) ^ (_ : ℝ)]
def evalRpow : PositivityExt where eval {u α} _zα _pα e := do
match u, α, e with
| 0, ~q(ℝ), ~q($a ^ ($b : ℝ)) =>
let ra ← core q(inferInstance) q(inferInstance) a
assertInstancesCommute
match ra with
| .positive pa =>
pure (.positive q(Real.rpow_pos_of_pos $pa $b))
| .nonnegative pa =>
pure (.nonnegative q(Real.rpow_nonneg $pa $b))
| _ => pure .none
| _, _, _ => throwError "not Real.rpow"
end Mathlib.Meta.Positivity
/-!
## Further algebraic properties of `rpow`
-/
namespace Real
variable {x y z : ℝ} {n : ℕ}
theorem rpow_mul {x : ℝ} (hx : 0 ≤ x) (y z : ℝ) : x ^ (y * z) = (x ^ y) ^ z := by
rw [← Complex.ofReal_inj, Complex.ofReal_cpow (rpow_nonneg hx _),
Complex.ofReal_cpow hx, Complex.ofReal_mul, Complex.cpow_mul, Complex.ofReal_cpow hx] <;>
simp only [(Complex.ofReal_mul _ _).symm, (Complex.ofReal_log hx).symm, Complex.ofReal_im,
neg_lt_zero, pi_pos, le_of_lt pi_pos]
lemma rpow_pow_comm {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (n : ℕ) : (x ^ y) ^ n = (x ^ n) ^ y := by
simp_rw [← rpow_natCast, ← rpow_mul hx, mul_comm y]
lemma rpow_zpow_comm {x : ℝ} (hx : 0 ≤ x) (y : ℝ) (n : ℤ) : (x ^ y) ^ n = (x ^ n) ^ y := by
simp_rw [← rpow_intCast, ← rpow_mul hx, mul_comm y]
lemma rpow_add_intCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℤ) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_def, rpow_def, Complex.ofReal_add,
Complex.cpow_add _ _ (Complex.ofReal_ne_zero.mpr hx), Complex.ofReal_intCast,
Complex.cpow_intCast, ← Complex.ofReal_zpow, mul_comm, Complex.re_ofReal_mul, mul_comm]
lemma rpow_add_natCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y + n) = x ^ y * x ^ n := by
simpa using rpow_add_intCast hx y n
lemma rpow_sub_intCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y - n) = x ^ y / x ^ n := by
simpa using rpow_add_intCast hx y (-n)
lemma rpow_sub_natCast {x : ℝ} (hx : x ≠ 0) (y : ℝ) (n : ℕ) : x ^ (y - n) = x ^ y / x ^ n := by
simpa using rpow_sub_intCast hx y n
lemma rpow_add_intCast' (hx : 0 ≤ x) {n : ℤ} (h : y + n ≠ 0) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_add' hx h, rpow_intCast]
lemma rpow_add_natCast' (hx : 0 ≤ x) (h : y + n ≠ 0) : x ^ (y + n) = x ^ y * x ^ n := by
rw [rpow_add' hx h, rpow_natCast]
lemma rpow_sub_intCast' (hx : 0 ≤ x) {n : ℤ} (h : y - n ≠ 0) : x ^ (y - n) = x ^ y / x ^ n := by
rw [rpow_sub' hx h, rpow_intCast]
lemma rpow_sub_natCast' (hx : 0 ≤ x) (h : y - n ≠ 0) : x ^ (y - n) = x ^ y / x ^ n := by
rw [rpow_sub' hx h, rpow_natCast]
theorem rpow_add_one {x : ℝ} (hx : x ≠ 0) (y : ℝ) : x ^ (y + 1) = x ^ y * x := by
simpa using rpow_add_natCast hx y 1
theorem rpow_sub_one {x : ℝ} (hx : x ≠ 0) (y : ℝ) : x ^ (y - 1) = x ^ y / x := by
simpa using rpow_sub_natCast hx y 1
lemma rpow_add_one' (hx : 0 ≤ x) (h : y + 1 ≠ 0) : x ^ (y + 1) = x ^ y * x := by
rw [rpow_add' hx h, rpow_one]
lemma rpow_one_add' (hx : 0 ≤ x) (h : 1 + y ≠ 0) : x ^ (1 + y) = x * x ^ y := by
rw [rpow_add' hx h, rpow_one]
lemma rpow_sub_one' (hx : 0 ≤ x) (h : y - 1 ≠ 0) : x ^ (y - 1) = x ^ y / x := by
rw [rpow_sub' hx h, rpow_one]
lemma rpow_one_sub' (hx : 0 ≤ x) (h : 1 - y ≠ 0) : x ^ (1 - y) = x / x ^ y := by
rw [rpow_sub' hx h, rpow_one]
@[simp]
theorem rpow_two (x : ℝ) : x ^ (2 : ℝ) = x ^ 2 := by
rw [← rpow_natCast]
simp only [Nat.cast_ofNat]
theorem rpow_neg_one (x : ℝ) : x ^ (-1 : ℝ) = x⁻¹ := by
suffices H : x ^ ((-1 : ℤ) : ℝ) = x⁻¹ by rwa [Int.cast_neg, Int.cast_one] at H
simp only [rpow_intCast, zpow_one, zpow_neg]
theorem mul_rpow (hx : 0 ≤ x) (hy : 0 ≤ y) : (x * y) ^ z = x ^ z * y ^ z := by
iterate 2 rw [Real.rpow_def_of_nonneg]; split_ifs with h_ifs <;> simp_all
· rw [log_mul ‹_› ‹_›, add_mul, exp_add, rpow_def_of_pos (hy.lt_of_ne' ‹_›)]
all_goals positivity
theorem inv_rpow (hx : 0 ≤ x) (y : ℝ) : x⁻¹ ^ y = (x ^ y)⁻¹ := by
simp only [← rpow_neg_one, ← rpow_mul hx, mul_comm]
theorem div_rpow (hx : 0 ≤ x) (hy : 0 ≤ y) (z : ℝ) : (x / y) ^ z = x ^ z / y ^ z := by
simp only [div_eq_mul_inv, mul_rpow hx (inv_nonneg.2 hy), inv_rpow hy]
theorem log_rpow {x : ℝ} (hx : 0 < x) (y : ℝ) : log (x ^ y) = y * log x := by
apply exp_injective
rw [exp_log (rpow_pos_of_pos hx y), ← exp_log hx, mul_comm, rpow_def_of_pos (exp_pos (log x)) y]
theorem mul_log_eq_log_iff {x y z : ℝ} (hx : 0 < x) (hz : 0 < z) :
y * log x = log z ↔ x ^ y = z :=
⟨fun h ↦ log_injOn_pos (rpow_pos_of_pos hx _) hz <| log_rpow hx _ |>.trans h,
by rintro rfl; rw [log_rpow hx]⟩
@[simp] lemma rpow_rpow_inv (hx : 0 ≤ x) (hy : y ≠ 0) : (x ^ y) ^ y⁻¹ = x := by
rw [← rpow_mul hx, mul_inv_cancel₀ hy, rpow_one]
@[simp] lemma rpow_inv_rpow (hx : 0 ≤ x) (hy : y ≠ 0) : (x ^ y⁻¹) ^ y = x := by
rw [← rpow_mul hx, inv_mul_cancel₀ hy, rpow_one]
theorem pow_rpow_inv_natCast (hx : 0 ≤ x) (hn : n ≠ 0) : (x ^ n) ^ (n⁻¹ : ℝ) = x := by
have hn0 : (n : ℝ) ≠ 0 := Nat.cast_ne_zero.2 hn
rw [← rpow_natCast, ← rpow_mul hx, mul_inv_cancel₀ hn0, rpow_one]
theorem rpow_inv_natCast_pow (hx : 0 ≤ x) (hn : n ≠ 0) : (x ^ (n⁻¹ : ℝ)) ^ n = x := by
have hn0 : (n : ℝ) ≠ 0 := Nat.cast_ne_zero.2 hn
rw [← rpow_natCast, ← rpow_mul hx, inv_mul_cancel₀ hn0, rpow_one]
lemma rpow_natCast_mul (hx : 0 ≤ x) (n : ℕ) (z : ℝ) : x ^ (n * z) = (x ^ n) ^ z := by
rw [rpow_mul hx, rpow_natCast]
lemma rpow_mul_natCast (hx : 0 ≤ x) (y : ℝ) (n : ℕ) : x ^ (y * n) = (x ^ y) ^ n := by
rw [rpow_mul hx, rpow_natCast]
lemma rpow_intCast_mul (hx : 0 ≤ x) (n : ℤ) (z : ℝ) : x ^ (n * z) = (x ^ n) ^ z := by
rw [rpow_mul hx, rpow_intCast]
lemma rpow_mul_intCast (hx : 0 ≤ x) (y : ℝ) (n : ℤ) : x ^ (y * n) = (x ^ y) ^ n := by
rw [rpow_mul hx, rpow_intCast]
/-! Note: lemmas about `(∏ i ∈ s, f i ^ r)` such as `Real.finset_prod_rpow` are proved
in `Mathlib/Analysis/SpecialFunctions/Pow/NNReal.lean` instead. -/
/-!
## Order and monotonicity
-/
@[gcongr, bound]
theorem rpow_lt_rpow (hx : 0 ≤ x) (hxy : x < y) (hz : 0 < z) : x ^ z < y ^ z := by
rw [le_iff_eq_or_lt] at hx; rcases hx with hx | hx
· rw [← hx, zero_rpow (ne_of_gt hz)]
exact rpow_pos_of_pos (by rwa [← hx] at hxy) _
· rw [rpow_def_of_pos hx, rpow_def_of_pos (lt_trans hx hxy), exp_lt_exp]
exact mul_lt_mul_of_pos_right (log_lt_log hx hxy) hz
theorem strictMonoOn_rpow_Ici_of_exponent_pos {r : ℝ} (hr : 0 < r) :
StrictMonoOn (fun (x : ℝ) => x ^ r) (Set.Ici 0) :=
fun _ ha _ _ hab => rpow_lt_rpow ha hab hr
@[gcongr, bound]
theorem rpow_le_rpow {x y z : ℝ} (h : 0 ≤ x) (h₁ : x ≤ y) (h₂ : 0 ≤ z) : x ^ z ≤ y ^ z := by
rcases eq_or_lt_of_le h₁ with (rfl | h₁'); · rfl
rcases eq_or_lt_of_le h₂ with (rfl | h₂'); · simp
exact le_of_lt (rpow_lt_rpow h h₁' h₂')
theorem monotoneOn_rpow_Ici_of_exponent_nonneg {r : ℝ} (hr : 0 ≤ r) :
MonotoneOn (fun (x : ℝ) => x ^ r) (Set.Ici 0) :=
fun _ ha _ _ hab => rpow_le_rpow ha hab hr
lemma rpow_lt_rpow_of_neg (hx : 0 < x) (hxy : x < y) (hz : z < 0) : y ^ z < x ^ z := by
have := hx.trans hxy
rw [← inv_lt_inv₀, ← rpow_neg, ← rpow_neg]
on_goal 1 => refine rpow_lt_rpow ?_ hxy (neg_pos.2 hz)
all_goals positivity
lemma rpow_le_rpow_of_nonpos (hx : 0 < x) (hxy : x ≤ y) (hz : z ≤ 0) : y ^ z ≤ x ^ z := by
have := hx.trans_le hxy
rw [← inv_le_inv₀, ← rpow_neg, ← rpow_neg]
on_goal 1 => refine rpow_le_rpow ?_ hxy (neg_nonneg.2 hz)
all_goals positivity
theorem rpow_lt_rpow_iff (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z < y ^ z ↔ x < y :=
⟨lt_imp_lt_of_le_imp_le fun h => rpow_le_rpow hy h (le_of_lt hz), fun h => rpow_lt_rpow hx h hz⟩
theorem rpow_le_rpow_iff (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z ≤ y ^ z ↔ x ≤ y :=
le_iff_le_iff_lt_iff_lt.2 <| rpow_lt_rpow_iff hy hx hz
lemma rpow_lt_rpow_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) : x ^ z < y ^ z ↔ y < x :=
⟨lt_imp_lt_of_le_imp_le fun h ↦ rpow_le_rpow_of_nonpos hx h hz.le,
fun h ↦ rpow_lt_rpow_of_neg hy h hz⟩
lemma rpow_le_rpow_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) : x ^ z ≤ y ^ z ↔ y ≤ x :=
le_iff_le_iff_lt_iff_lt.2 <| rpow_lt_rpow_iff_of_neg hy hx hz
lemma le_rpow_inv_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ≤ y ^ z⁻¹ ↔ x ^ z ≤ y := by
rw [← rpow_le_rpow_iff hx _ hz, rpow_inv_rpow] <;> positivity
lemma rpow_inv_le_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z⁻¹ ≤ y ↔ x ≤ y ^ z := by
rw [← rpow_le_rpow_iff _ hy hz, rpow_inv_rpow] <;> positivity
lemma lt_rpow_inv_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x < y ^ z⁻¹ ↔ x ^ z < y :=
lt_iff_lt_of_le_iff_le <| rpow_inv_le_iff_of_pos hy hx hz
lemma rpow_inv_lt_iff_of_pos (hx : 0 ≤ x) (hy : 0 ≤ y) (hz : 0 < z) : x ^ z⁻¹ < y ↔ x < y ^ z :=
lt_iff_lt_of_le_iff_le <| le_rpow_inv_iff_of_pos hy hx hz
theorem le_rpow_inv_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ≤ y ^ z⁻¹ ↔ y ≤ x ^ z := by
rw [← rpow_le_rpow_iff_of_neg _ hx hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem lt_rpow_inv_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x < y ^ z⁻¹ ↔ y < x ^ z := by
rw [← rpow_lt_rpow_iff_of_neg _ hx hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_inv_lt_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ^ z⁻¹ < y ↔ y ^ z < x := by
rw [← rpow_lt_rpow_iff_of_neg hy _ hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_inv_le_iff_of_neg (hx : 0 < x) (hy : 0 < y) (hz : z < 0) :
x ^ z⁻¹ ≤ y ↔ y ^ z ≤ x := by
rw [← rpow_le_rpow_iff_of_neg hy _ hz, rpow_inv_rpow _ hz.ne] <;> positivity
theorem rpow_lt_rpow_of_exponent_lt (hx : 1 < x) (hyz : y < z) : x ^ y < x ^ z := by
repeat' rw [rpow_def_of_pos (lt_trans zero_lt_one hx)]
rw [exp_lt_exp]; exact mul_lt_mul_of_pos_left hyz (log_pos hx)
@[gcongr]
theorem rpow_le_rpow_of_exponent_le (hx : 1 ≤ x) (hyz : y ≤ z) : x ^ y ≤ x ^ z := by
repeat' rw [rpow_def_of_pos (lt_of_lt_of_le zero_lt_one hx)]
rw [exp_le_exp]; exact mul_le_mul_of_nonneg_left hyz (log_nonneg hx)
theorem rpow_lt_rpow_of_exponent_neg {x y z : ℝ} (hy : 0 < y) (hxy : y < x) (hz : z < 0) :
x ^ z < y ^ z := by
have hx : 0 < x := hy.trans hxy
rw [← neg_neg z, Real.rpow_neg (le_of_lt hx) (-z), Real.rpow_neg (le_of_lt hy) (-z),
inv_lt_inv₀ (rpow_pos_of_pos hx _) (rpow_pos_of_pos hy _)]
exact Real.rpow_lt_rpow (by positivity) hxy <| neg_pos_of_neg hz
theorem strictAntiOn_rpow_Ioi_of_exponent_neg {r : ℝ} (hr : r < 0) :
StrictAntiOn (fun (x : ℝ) => x ^ r) (Set.Ioi 0) :=
fun _ ha _ _ hab => rpow_lt_rpow_of_exponent_neg ha hab hr
theorem rpow_le_rpow_of_exponent_nonpos {x y : ℝ} (hy : 0 < y) (hxy : y ≤ x) (hz : z ≤ 0) :
x ^ z ≤ y ^ z := by
rcases ne_or_eq z 0 with hz_zero | rfl
case inl =>
rcases ne_or_eq x y with hxy' | rfl
case inl =>
exact le_of_lt <| rpow_lt_rpow_of_exponent_neg hy (Ne.lt_of_le (id (Ne.symm hxy')) hxy)
(Ne.lt_of_le hz_zero hz)
case inr => simp
case inr => simp
theorem antitoneOn_rpow_Ioi_of_exponent_nonpos {r : ℝ} (hr : r ≤ 0) :
AntitoneOn (fun (x : ℝ) => x ^ r) (Set.Ioi 0) :=
fun _ ha _ _ hab => rpow_le_rpow_of_exponent_nonpos ha hab hr
@[simp]
theorem rpow_le_rpow_left_iff (hx : 1 < x) : x ^ y ≤ x ^ z ↔ y ≤ z := by
have x_pos : 0 < x := lt_trans zero_lt_one hx
rw [← log_le_log_iff (rpow_pos_of_pos x_pos y) (rpow_pos_of_pos x_pos z), log_rpow x_pos,
log_rpow x_pos, mul_le_mul_right (log_pos hx)]
@[simp]
theorem rpow_lt_rpow_left_iff (hx : 1 < x) : x ^ y < x ^ z ↔ y < z := by
rw [lt_iff_not_le, rpow_le_rpow_left_iff hx, lt_iff_not_le]
theorem rpow_lt_rpow_of_exponent_gt (hx0 : 0 < x) (hx1 : x < 1) (hyz : z < y) : x ^ y < x ^ z := by
repeat' rw [rpow_def_of_pos hx0]
rw [exp_lt_exp]; exact mul_lt_mul_of_neg_left hyz (log_neg hx0 hx1)
theorem rpow_le_rpow_of_exponent_ge (hx0 : 0 < x) (hx1 : x ≤ 1) (hyz : z ≤ y) : x ^ y ≤ x ^ z := by
repeat' rw [rpow_def_of_pos hx0]
rw [exp_le_exp]; exact mul_le_mul_of_nonpos_left hyz (log_nonpos (le_of_lt hx0) hx1)
@[simp]
theorem rpow_le_rpow_left_iff_of_base_lt_one (hx0 : 0 < x) (hx1 : x < 1) :
x ^ y ≤ x ^ z ↔ z ≤ y := by
rw [← log_le_log_iff (rpow_pos_of_pos hx0 y) (rpow_pos_of_pos hx0 z), log_rpow hx0, log_rpow hx0,
mul_le_mul_right_of_neg (log_neg hx0 hx1)]
@[simp]
theorem rpow_lt_rpow_left_iff_of_base_lt_one (hx0 : 0 < x) (hx1 : x < 1) :
x ^ y < x ^ z ↔ z < y := by
rw [lt_iff_not_le, rpow_le_rpow_left_iff_of_base_lt_one hx0 hx1, lt_iff_not_le]
theorem rpow_lt_one {x z : ℝ} (hx1 : 0 ≤ x) (hx2 : x < 1) (hz : 0 < z) : x ^ z < 1 := by
rw [← one_rpow z]
exact rpow_lt_rpow hx1 hx2 hz
theorem rpow_le_one {x z : ℝ} (hx1 : 0 ≤ x) (hx2 : x ≤ 1) (hz : 0 ≤ z) : x ^ z ≤ 1 := by
rw [← one_rpow z]
exact rpow_le_rpow hx1 hx2 hz
theorem rpow_lt_one_of_one_lt_of_neg {x z : ℝ} (hx : 1 < x) (hz : z < 0) : x ^ z < 1 := by
convert rpow_lt_rpow_of_exponent_lt hx hz
exact (rpow_zero x).symm
theorem rpow_le_one_of_one_le_of_nonpos {x z : ℝ} (hx : 1 ≤ x) (hz : z ≤ 0) : x ^ z ≤ 1 := by
convert rpow_le_rpow_of_exponent_le hx hz
exact (rpow_zero x).symm
theorem one_lt_rpow {x z : ℝ} (hx : 1 < x) (hz : 0 < z) : 1 < x ^ z := by
rw [← one_rpow z]
exact rpow_lt_rpow zero_le_one hx hz
theorem one_le_rpow {x z : ℝ} (hx : 1 ≤ x) (hz : 0 ≤ z) : 1 ≤ x ^ z := by
rw [← one_rpow z]
exact rpow_le_rpow zero_le_one hx hz
theorem one_lt_rpow_of_pos_of_lt_one_of_neg (hx1 : 0 < x) (hx2 : x < 1) (hz : z < 0) :
1 < x ^ z := by
convert rpow_lt_rpow_of_exponent_gt hx1 hx2 hz
exact (rpow_zero x).symm
theorem one_le_rpow_of_pos_of_le_one_of_nonpos (hx1 : 0 < x) (hx2 : x ≤ 1) (hz : z ≤ 0) :
1 ≤ x ^ z := by
convert rpow_le_rpow_of_exponent_ge hx1 hx2 hz
exact (rpow_zero x).symm
theorem rpow_lt_one_iff_of_pos (hx : 0 < x) : x ^ y < 1 ↔ 1 < x ∧ y < 0 ∨ x < 1 ∧ 0 < y := by
rw [rpow_def_of_pos hx, exp_lt_one_iff, mul_neg_iff, log_pos_iff hx.le, log_neg_iff hx]
theorem rpow_lt_one_iff (hx : 0 ≤ x) :
x ^ y < 1 ↔ x = 0 ∧ y ≠ 0 ∨ 1 < x ∧ y < 0 ∨ x < 1 ∧ 0 < y := by
rcases hx.eq_or_lt with (rfl | hx)
· rcases _root_.em (y = 0) with (rfl | hy) <;> simp [*, lt_irrefl, zero_lt_one]
· simp [rpow_lt_one_iff_of_pos hx, hx.ne.symm]
theorem rpow_lt_one_iff' {x y : ℝ} (hx : 0 ≤ x) (hy : 0 < y) :
x ^ y < 1 ↔ x < 1 := by
rw [← Real.rpow_lt_rpow_iff hx zero_le_one hy, Real.one_rpow]
theorem one_lt_rpow_iff_of_pos (hx : 0 < x) : 1 < x ^ y ↔ 1 < x ∧ 0 < y ∨ x < 1 ∧ y < 0 := by
rw [rpow_def_of_pos hx, one_lt_exp_iff, mul_pos_iff, log_pos_iff hx.le, log_neg_iff hx]
theorem one_lt_rpow_iff (hx : 0 ≤ x) : 1 < x ^ y ↔ 1 < x ∧ 0 < y ∨ 0 < x ∧ x < 1 ∧ y < 0 := by
| rcases hx.eq_or_lt with (rfl | hx)
· rcases _root_.em (y = 0) with (rfl | hy) <;> simp [*, lt_irrefl, (zero_lt_one' ℝ).not_lt]
· simp [one_lt_rpow_iff_of_pos hx, hx]
| Mathlib/Analysis/SpecialFunctions/Pow/Real.lean | 702 | 704 |
/-
Copyright (c) 2023 Eric Wieser. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Eric Wieser
-/
import Mathlib.LinearAlgebra.BilinearForm.TensorProduct
import Mathlib.LinearAlgebra.QuadraticForm.Basic
/-!
# The quadratic form on a tensor product
## Main definitions
* `QuadraticForm.tensorDistrib (Q₁ ⊗ₜ Q₂)`: the quadratic form on `M₁ ⊗ M₂` constructed by applying
`Q₁` on `M₁` and `Q₂` on `M₂`. This construction is not available in characteristic two.
-/
universe uR uA uM₁ uM₂ uN₁ uN₂
variable {R : Type uR} {A : Type uA} {M₁ : Type uM₁} {M₂ : Type uM₂} {N₁ : Type uN₁} {N₂ : Type uN₂}
open LinearMap (BilinMap BilinForm)
open TensorProduct QuadraticMap
section CommRing
variable [CommRing R] [CommRing A]
variable [AddCommGroup M₁] [AddCommGroup M₂] [AddCommGroup N₁] [AddCommGroup N₂]
variable [Algebra R A] [Module R M₁] [Module A M₁] [Module R N₁] [Module A N₁]
variable [SMulCommClass R A M₁] [IsScalarTower R A M₁] [IsScalarTower R A N₁]
variable [Module R M₂] [Module R N₂]
section InvertibleTwo
variable [Invertible (2 : R)]
namespace QuadraticMap
variable (R A) in
/-- The tensor product of two quadratic maps injects into quadratic maps on tensor products.
Note this is heterobasic; the quadratic map on the left can take values in a module over a larger
ring than the one on the right. -/
-- `noncomputable` is a performance workaround for https://github.com/leanprover-community/mathlib4/issues/7103
noncomputable def tensorDistrib :
QuadraticMap A M₁ N₁ ⊗[R] QuadraticMap R M₂ N₂ →ₗ[A] QuadraticMap A (M₁ ⊗[R] M₂) (N₁ ⊗[R] N₂) :=
letI : Invertible (2 : A) := (Invertible.map (algebraMap R A) 2).copy 2 (map_ofNat _ _).symm
-- while `letI`s would produce a better term than `let`, they would make this already-slow
-- definition even slower.
let toQ := BilinMap.toQuadraticMapLinearMap A A (M₁ ⊗[R] M₂)
let tmulB := BilinMap.tensorDistrib R A (M₁ := M₁) (M₂ := M₂)
let toB := AlgebraTensorModule.map
(QuadraticMap.associated : QuadraticMap A M₁ N₁ →ₗ[A] BilinMap A M₁ N₁)
(QuadraticMap.associated : QuadraticMap R M₂ N₂ →ₗ[R] BilinMap R M₂ N₂)
toQ ∘ₗ tmulB ∘ₗ toB
@[simp]
theorem tensorDistrib_tmul (Q₁ : QuadraticMap A M₁ N₁) (Q₂ : QuadraticMap R M₂ N₂) (m₁ : M₁)
(m₂ : M₂) : tensorDistrib R A (Q₁ ⊗ₜ Q₂) (m₁ ⊗ₜ m₂) = Q₁ m₁ ⊗ₜ Q₂ m₂ :=
letI : Invertible (2 : A) := (Invertible.map (algebraMap R A) 2).copy 2 (map_ofNat _ _).symm
(BilinMap.tensorDistrib_tmul _ _ _ _ _ _).trans <| congr_arg₂ _
(associated_eq_self_apply _ _ _) (associated_eq_self_apply _ _ _)
/-- The tensor product of two quadratic maps, a shorthand for dot notation. -/
-- `noncomputable` is a performance workaround for https://github.com/leanprover-community/mathlib4/issues/7103
protected noncomputable abbrev tmul (Q₁ : QuadraticMap A M₁ N₁)
(Q₂ : QuadraticMap R M₂ N₂) : QuadraticMap A (M₁ ⊗[R] M₂) (N₁ ⊗[R] N₂) :=
tensorDistrib R A (Q₁ ⊗ₜ[R] Q₂)
| theorem associated_tmul [Invertible (2 : A)]
(Q₁ : QuadraticMap A M₁ N₁) (Q₂ : QuadraticMap R M₂ N₂) :
(Q₁.tmul Q₂).associated = Q₁.associated.tmul Q₂.associated := by
letI : Invertible (2 : A) := (Invertible.map (algebraMap R A) 2).copy 2 (map_ofNat _ _).symm
rw [QuadraticMap.tmul, BilinMap.tmul]
have : Subsingleton (Invertible (2 : A)) := inferInstance
convert associated_left_inverse A (LinearMap.BilinMap.tmul_isSymm
| Mathlib/LinearAlgebra/QuadraticForm/TensorProduct.lean | 69 | 75 |
/-
Copyright (c) 2020 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel, Floris van Doorn
-/
import Mathlib.Geometry.Manifold.MFDeriv.Defs
import Mathlib.Geometry.Manifold.ContMDiff.Defs
/-!
# Basic properties of the manifold Fréchet derivative
In this file, we show various properties of the manifold Fréchet derivative,
mimicking the API for Fréchet derivatives.
- basic properties of unique differentiability sets
- various general lemmas about the manifold Fréchet derivative
- deducing differentiability from smoothness,
- deriving continuity from differentiability on manifolds,
- congruence lemmas for derivatives on manifolds
- composition lemmas and the chain rule
-/
noncomputable section
assert_not_exists tangentBundleCore
open scoped Topology Manifold
open Set Bundle ChartedSpace
section DerivativesProperties
/-! ### Unique differentiability sets in manifolds -/
variable
{𝕜 : Type*} [NontriviallyNormedField 𝕜]
{E : Type*} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
{H : Type*} [TopologicalSpace H] (I : ModelWithCorners 𝕜 E H)
{M : Type*} [TopologicalSpace M] [ChartedSpace H M]
{E' : Type*} [NormedAddCommGroup E'] [NormedSpace 𝕜 E']
{H' : Type*} [TopologicalSpace H'] {I' : ModelWithCorners 𝕜 E' H'}
{M' : Type*} [TopologicalSpace M'] [ChartedSpace H' M']
{E'' : Type*} [NormedAddCommGroup E''] [NormedSpace 𝕜 E'']
{H'' : Type*} [TopologicalSpace H''] {I'' : ModelWithCorners 𝕜 E'' H''}
{M'' : Type*} [TopologicalSpace M''] [ChartedSpace H'' M'']
{f f₁ : M → M'} {x : M} {s t : Set M} {g : M' → M''} {u : Set M'}
theorem uniqueMDiffWithinAt_univ : UniqueMDiffWithinAt I univ x := by
unfold UniqueMDiffWithinAt
simp only [preimage_univ, univ_inter]
exact I.uniqueDiffOn _ (mem_range_self _)
variable {I}
theorem uniqueMDiffWithinAt_iff_inter_range {s : Set M} {x : M} :
UniqueMDiffWithinAt I s x ↔
UniqueDiffWithinAt 𝕜 ((extChartAt I x).symm ⁻¹' s ∩ range I)
((extChartAt I x) x) := Iff.rfl
theorem uniqueMDiffWithinAt_iff {s : Set M} {x : M} :
UniqueMDiffWithinAt I s x ↔
UniqueDiffWithinAt 𝕜 ((extChartAt I x).symm ⁻¹' s ∩ (extChartAt I x).target)
((extChartAt I x) x) := by
apply uniqueDiffWithinAt_congr
rw [nhdsWithin_inter, nhdsWithin_inter, nhdsWithin_extChartAt_target_eq]
nonrec theorem UniqueMDiffWithinAt.mono_nhds {s t : Set M} {x : M} (hs : UniqueMDiffWithinAt I s x)
(ht : 𝓝[s] x ≤ 𝓝[t] x) : UniqueMDiffWithinAt I t x :=
hs.mono_nhds <| by simpa only [← map_extChartAt_nhdsWithin] using Filter.map_mono ht
theorem UniqueMDiffWithinAt.mono_of_mem_nhdsWithin {s t : Set M} {x : M}
(hs : UniqueMDiffWithinAt I s x) (ht : t ∈ 𝓝[s] x) : UniqueMDiffWithinAt I t x :=
hs.mono_nhds (nhdsWithin_le_iff.2 ht)
@[deprecated (since := "2024-10-31")]
alias UniqueMDiffWithinAt.mono_of_mem := UniqueMDiffWithinAt.mono_of_mem_nhdsWithin
theorem UniqueMDiffWithinAt.mono (h : UniqueMDiffWithinAt I s x) (st : s ⊆ t) :
UniqueMDiffWithinAt I t x :=
UniqueDiffWithinAt.mono h <| inter_subset_inter (preimage_mono st) (Subset.refl _)
theorem UniqueMDiffWithinAt.inter' (hs : UniqueMDiffWithinAt I s x) (ht : t ∈ 𝓝[s] x) :
UniqueMDiffWithinAt I (s ∩ t) x :=
hs.mono_of_mem_nhdsWithin (Filter.inter_mem self_mem_nhdsWithin ht)
theorem UniqueMDiffWithinAt.inter (hs : UniqueMDiffWithinAt I s x) (ht : t ∈ 𝓝 x) :
UniqueMDiffWithinAt I (s ∩ t) x :=
hs.inter' (nhdsWithin_le_nhds ht)
theorem IsOpen.uniqueMDiffWithinAt (hs : IsOpen s) (xs : x ∈ s) : UniqueMDiffWithinAt I s x :=
(uniqueMDiffWithinAt_univ I).mono_of_mem_nhdsWithin <| nhdsWithin_le_nhds <| hs.mem_nhds xs
theorem UniqueMDiffOn.inter (hs : UniqueMDiffOn I s) (ht : IsOpen t) : UniqueMDiffOn I (s ∩ t) :=
fun _x hx => UniqueMDiffWithinAt.inter (hs _ hx.1) (ht.mem_nhds hx.2)
theorem IsOpen.uniqueMDiffOn (hs : IsOpen s) : UniqueMDiffOn I s :=
fun _x hx => hs.uniqueMDiffWithinAt hx
theorem uniqueMDiffOn_univ : UniqueMDiffOn I (univ : Set M) :=
isOpen_univ.uniqueMDiffOn
nonrec theorem UniqueMDiffWithinAt.prod {x : M} {y : M'} {s t} (hs : UniqueMDiffWithinAt I s x)
(ht : UniqueMDiffWithinAt I' t y) : UniqueMDiffWithinAt (I.prod I') (s ×ˢ t) (x, y) := by
refine (hs.prod ht).mono ?_
rw [ModelWithCorners.range_prod, ← prod_inter_prod]
rfl
theorem UniqueMDiffOn.prod {s : Set M} {t : Set M'} (hs : UniqueMDiffOn I s)
(ht : UniqueMDiffOn I' t) : UniqueMDiffOn (I.prod I') (s ×ˢ t) := fun x h ↦
(hs x.1 h.1).prod (ht x.2 h.2)
theorem MDifferentiableWithinAt.mono (hst : s ⊆ t) (h : MDifferentiableWithinAt I I' f t x) :
MDifferentiableWithinAt I I' f s x :=
⟨ContinuousWithinAt.mono h.1 hst, DifferentiableWithinAt.mono
h.differentiableWithinAt_writtenInExtChartAt
(inter_subset_inter_left _ (preimage_mono hst))⟩
theorem mdifferentiableWithinAt_univ :
MDifferentiableWithinAt I I' f univ x ↔ MDifferentiableAt I I' f x := by
simp_rw [MDifferentiableWithinAt, MDifferentiableAt, ChartedSpace.LiftPropAt]
theorem mdifferentiableWithinAt_inter (ht : t ∈ 𝓝 x) :
MDifferentiableWithinAt I I' f (s ∩ t) x ↔ MDifferentiableWithinAt I I' f s x := by
rw [MDifferentiableWithinAt, MDifferentiableWithinAt,
differentiableWithinAt_localInvariantProp.liftPropWithinAt_inter ht]
theorem mdifferentiableWithinAt_inter' (ht : t ∈ 𝓝[s] x) :
MDifferentiableWithinAt I I' f (s ∩ t) x ↔ MDifferentiableWithinAt I I' f s x := by
rw [MDifferentiableWithinAt, MDifferentiableWithinAt,
differentiableWithinAt_localInvariantProp.liftPropWithinAt_inter' ht]
theorem MDifferentiableAt.mdifferentiableWithinAt (h : MDifferentiableAt I I' f x) :
MDifferentiableWithinAt I I' f s x :=
MDifferentiableWithinAt.mono (subset_univ _) (mdifferentiableWithinAt_univ.2 h)
theorem MDifferentiableWithinAt.mdifferentiableAt (h : MDifferentiableWithinAt I I' f s x)
(hs : s ∈ 𝓝 x) : MDifferentiableAt I I' f x := by
| have : s = univ ∩ s := by rw [univ_inter]
rwa [this, mdifferentiableWithinAt_inter hs, mdifferentiableWithinAt_univ] at h
theorem MDifferentiableOn.mono (h : MDifferentiableOn I I' f t) (st : s ⊆ t) :
MDifferentiableOn I I' f s := fun x hx => (h x (st hx)).mono st
theorem mdifferentiableOn_univ : MDifferentiableOn I I' f univ ↔ MDifferentiable I I' f := by
simp only [MDifferentiableOn, mdifferentiableWithinAt_univ, mfld_simps]; rfl
| Mathlib/Geometry/Manifold/MFDeriv/Basic.lean | 137 | 145 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Yury Kudryashov, Yaël Dillies
-/
import Mathlib.Algebra.BigOperators.GroupWithZero.Action
import Mathlib.Algebra.Module.Defs
import Mathlib.Data.Fintype.BigOperators
/-!
# Finite sums over modules over a ring
-/
variable {ι κ α β R M : Type*}
section AddCommMonoid
variable [Semiring R] [AddCommMonoid M] [Module R M]
theorem List.sum_smul {l : List R} {x : M} : l.sum • x = (l.map fun r ↦ r • x).sum :=
map_list_sum ((smulAddHom R M).flip x) l
theorem Multiset.sum_smul {l : Multiset R} {x : M} : l.sum • x = (l.map fun r ↦ r • x).sum :=
((smulAddHom R M).flip x).map_multiset_sum l
theorem Multiset.sum_smul_sum {s : Multiset R} {t : Multiset M} :
s.sum • t.sum = ((s ×ˢ t).map fun p : R × M ↦ p.fst • p.snd).sum := by
induction' s using Multiset.induction with a s ih
· simp
· simp [add_smul, ih, ← Multiset.smul_sum]
theorem Finset.sum_smul {f : ι → R} {s : Finset ι} {x : M} :
(∑ i ∈ s, f i) • x = ∑ i ∈ s, f i • x := map_sum ((smulAddHom R M).flip x) f s
lemma Finset.sum_smul_sum (s : Finset α) (t : Finset β) {f : α → R} {g : β → M} :
(∑ i ∈ s, f i) • ∑ j ∈ t, g j = ∑ i ∈ s, ∑ j ∈ t, f i • g j := by
simp_rw [sum_smul, ← smul_sum]
lemma Fintype.sum_smul_sum [Fintype α] [Fintype β] (f : α → R) (g : β → M) :
(∑ i, f i) • ∑ j, g j = ∑ i, ∑ j, f i • g j := Finset.sum_smul_sum _ _
|
end AddCommMonoid
open Finset
| Mathlib/Algebra/Module/BigOperators.lean | 41 | 45 |
/-
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, Kevin Buzzard, Yury Kudryashov, Frédéric Dupuis,
Heather Macbeth
-/
import Mathlib.Algebra.Group.Subgroup.Map
import Mathlib.Algebra.Module.Submodule.Basic
import Mathlib.Algebra.Module.Submodule.Lattice
import Mathlib.Algebra.Module.Submodule.LinearMap
/-!
# `map` and `comap` for `Submodule`s
## Main declarations
* `Submodule.map`: The pushforward of a submodule `p ⊆ M` by `f : M → M₂`
* `Submodule.comap`: The pullback of a submodule `p ⊆ M₂` along `f : M → M₂`
* `Submodule.giMapComap`: `map f` and `comap f` form a `GaloisInsertion` when `f` is surjective.
* `Submodule.gciMapComap`: `map f` and `comap f` form a `GaloisCoinsertion` when `f` is injective.
## Tags
submodule, subspace, linear map, pushforward, pullback
-/
open Function Pointwise Set
variable {R : Type*} {R₁ : Type*} {R₂ : Type*} {R₃ : Type*}
variable {M : Type*} {M₁ : Type*} {M₂ : Type*} {M₃ : Type*}
namespace Submodule
section AddCommMonoid
variable [Semiring R] [Semiring R₂] [Semiring R₃]
variable [AddCommMonoid M] [AddCommMonoid M₂] [AddCommMonoid M₃]
variable [Module R M] [Module R₂ M₂] [Module R₃ M₃]
variable {σ₁₂ : R →+* R₂} {σ₂₃ : R₂ →+* R₃} {σ₁₃ : R →+* R₃}
variable [RingHomCompTriple σ₁₂ σ₂₃ σ₁₃]
variable (p p' : Submodule R M) (q q' : Submodule R₂ M₂)
variable {x : M}
section
variable [RingHomSurjective σ₁₂] {F : Type*} [FunLike F M M₂] [SemilinearMapClass F σ₁₂ M M₂]
/-- The pushforward of a submodule `p ⊆ M` by `f : M → M₂` -/
def map (f : F) (p : Submodule R M) : Submodule R₂ M₂ :=
{ p.toAddSubmonoid.map f with
carrier := f '' p
smul_mem' := by
rintro c x ⟨y, hy, rfl⟩
obtain ⟨a, rfl⟩ := σ₁₂.surjective c
exact ⟨_, p.smul_mem a hy, map_smulₛₗ f _ _⟩ }
@[simp]
theorem map_coe (f : F) (p : Submodule R M) : (map f p : Set M₂) = f '' p :=
rfl
@[simp]
theorem map_coe_toLinearMap (f : F) (p : Submodule R M) : map (f : M →ₛₗ[σ₁₂] M₂) p = map f p := rfl
theorem map_toAddSubmonoid (f : M →ₛₗ[σ₁₂] M₂) (p : Submodule R M) :
(p.map f).toAddSubmonoid = p.toAddSubmonoid.map (f : M →+ M₂) :=
SetLike.coe_injective rfl
theorem map_toAddSubmonoid' (f : M →ₛₗ[σ₁₂] M₂) (p : Submodule R M) :
(p.map f).toAddSubmonoid = p.toAddSubmonoid.map f :=
SetLike.coe_injective rfl
@[simp]
theorem _root_.AddMonoidHom.coe_toIntLinearMap_map {A A₂ : Type*} [AddCommGroup A] [AddCommGroup A₂]
(f : A →+ A₂) (s : AddSubgroup A) :
(AddSubgroup.toIntSubmodule s).map f.toIntLinearMap =
AddSubgroup.toIntSubmodule (s.map f) := rfl
@[simp]
theorem _root_.MonoidHom.coe_toAdditive_map {G G₂ : Type*} [Group G] [Group G₂] (f : G →* G₂)
(s : Subgroup G) :
s.toAddSubgroup.map (MonoidHom.toAdditive f) = Subgroup.toAddSubgroup (s.map f) := rfl
@[simp]
theorem _root_.AddMonoidHom.coe_toMultiplicative_map {G G₂ : Type*} [AddGroup G] [AddGroup G₂]
(f : G →+ G₂) (s : AddSubgroup G) :
s.toSubgroup.map (AddMonoidHom.toMultiplicative f) = AddSubgroup.toSubgroup (s.map f) := rfl
@[simp]
theorem mem_map {f : F} {p : Submodule R M} {x : M₂} : x ∈ map f p ↔ ∃ y, y ∈ p ∧ f y = x :=
Iff.rfl
theorem mem_map_of_mem {f : F} {p : Submodule R M} {r} (h : r ∈ p) : f r ∈ map f p :=
Set.mem_image_of_mem _ h
theorem apply_coe_mem_map (f : F) {p : Submodule R M} (r : p) : f r ∈ map f p :=
mem_map_of_mem r.prop
@[simp]
theorem map_id : map (LinearMap.id : M →ₗ[R] M) p = p :=
Submodule.ext fun a => by simp
| theorem map_comp [RingHomSurjective σ₂₃] [RingHomSurjective σ₁₃] (f : M →ₛₗ[σ₁₂] M₂)
(g : M₂ →ₛₗ[σ₂₃] M₃) (p : Submodule R M) : map (g.comp f : M →ₛₗ[σ₁₃] M₃) p = map g (map f p) :=
| Mathlib/Algebra/Module/Submodule/Map.lean | 102 | 103 |
/-
Copyright (c) 2016 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Mario Carneiro
-/
import Mathlib.Data.Set.Defs
import Mathlib.Logic.Basic
import Mathlib.Logic.ExistsUnique
import Mathlib.Logic.Nonempty
import Mathlib.Logic.Nontrivial.Defs
import Batteries.Tactic.Init
import Mathlib.Order.Defs.Unbundled
/-!
# Miscellaneous function constructions and lemmas
-/
open Function
universe u v w
namespace Function
section
variable {α β γ : Sort*} {f : α → β}
/-- Evaluate a function at an argument. Useful if you want to talk about the partially applied
`Function.eval x : (∀ x, β x) → β x`. -/
@[reducible, simp] def eval {β : α → Sort*} (x : α) (f : ∀ x, β x) : β x := f x
theorem eval_apply {β : α → Sort*} (x : α) (f : ∀ x, β x) : eval x f = f x :=
rfl
theorem const_def {y : β} : (fun _ : α ↦ y) = const α y :=
rfl
theorem const_injective [Nonempty α] : Injective (const α : β → α → β) := fun _ _ h ↦
let ⟨x⟩ := ‹Nonempty α›
congr_fun h x
@[simp]
theorem const_inj [Nonempty α] {y₁ y₂ : β} : const α y₁ = const α y₂ ↔ y₁ = y₂ :=
⟨fun h ↦ const_injective h, fun h ↦ h ▸ rfl⟩
theorem onFun_apply (f : β → β → γ) (g : α → β) (a b : α) : onFun f g a b = f (g a) (g b) :=
rfl
lemma hfunext {α α' : Sort u} {β : α → Sort v} {β' : α' → Sort v} {f : ∀a, β a} {f' : ∀a, β' a}
(hα : α = α') (h : ∀a a', HEq a a' → HEq (f a) (f' a')) : HEq f f' := by
subst hα
have : ∀a, HEq (f a) (f' a) := fun a ↦ h a a (HEq.refl a)
have : β = β' := by funext a; exact type_eq_of_heq (this a)
subst this
apply heq_of_eq
funext a
exact eq_of_heq (this a)
theorem ne_iff {β : α → Sort*} {f₁ f₂ : ∀ a, β a} : f₁ ≠ f₂ ↔ ∃ a, f₁ a ≠ f₂ a :=
funext_iff.not.trans not_forall
lemma funext_iff_of_subsingleton [Subsingleton α] {g : α → β} (x y : α) :
f x = g y ↔ f = g := by
refine ⟨fun h ↦ funext fun z ↦ ?_, fun h ↦ ?_⟩
· rwa [Subsingleton.elim x z, Subsingleton.elim y z] at h
· rw [h, Subsingleton.elim x y]
theorem swap_lt {α} [LT α] : swap (· < · : α → α → _) = (· > ·) := rfl
theorem swap_le {α} [LE α] : swap (· ≤ · : α → α → _) = (· ≥ ·) := rfl
theorem swap_gt {α} [LT α] : swap (· > · : α → α → _) = (· < ·) := rfl
theorem swap_ge {α} [LE α] : swap (· ≥ · : α → α → _) = (· ≤ ·) := rfl
protected theorem Bijective.injective {f : α → β} (hf : Bijective f) : Injective f := hf.1
protected theorem Bijective.surjective {f : α → β} (hf : Bijective f) : Surjective f := hf.2
theorem not_injective_iff : ¬ Injective f ↔ ∃ a b, f a = f b ∧ a ≠ b := by
simp only [Injective, not_forall, exists_prop]
/-- If the co-domain `β` of an injective function `f : α → β` has decidable equality, then
the domain `α` also has decidable equality. -/
protected def Injective.decidableEq [DecidableEq β] (I : Injective f) : DecidableEq α :=
fun _ _ ↦ decidable_of_iff _ I.eq_iff
theorem Injective.of_comp {g : γ → α} (I : Injective (f ∘ g)) : Injective g :=
fun _ _ h ↦ I <| congr_arg f h
@[simp]
theorem Injective.of_comp_iff (hf : Injective f) (g : γ → α) :
Injective (f ∘ g) ↔ Injective g :=
⟨Injective.of_comp, hf.comp⟩
theorem Injective.of_comp_right {g : γ → α} (I : Injective (f ∘ g)) (hg : Surjective g) :
Injective f := fun x y h ↦ by
obtain ⟨x, rfl⟩ := hg x
obtain ⟨y, rfl⟩ := hg y
exact congr_arg g (I h)
theorem Surjective.bijective₂_of_injective {g : γ → α} (hf : Surjective f) (hg : Surjective g)
(I : Injective (f ∘ g)) : Bijective f ∧ Bijective g :=
⟨⟨I.of_comp_right hg, hf⟩, I.of_comp, hg⟩
@[simp]
theorem Injective.of_comp_iff' (f : α → β) {g : γ → α} (hg : Bijective g) :
Injective (f ∘ g) ↔ Injective f :=
⟨fun I ↦ I.of_comp_right hg.2, fun h ↦ h.comp hg.injective⟩
theorem Injective.piMap {ι : Sort*} {α β : ι → Sort*} {f : ∀ i, α i → β i}
(hf : ∀ i, Injective (f i)) : Injective (Pi.map f) := fun _ _ h ↦
funext fun i ↦ hf i <| congrFun h _
/-- Composition by an injective function on the left is itself injective. -/
theorem Injective.comp_left {g : β → γ} (hg : Injective g) : Injective (g ∘ · : (α → β) → α → γ) :=
.piMap fun _ ↦ hg
theorem injective_comp_left_iff [Nonempty α] {g : β → γ} :
Injective (g ∘ · : (α → β) → α → γ) ↔ Injective g :=
⟨fun h b₁ b₂ eq ↦ Nonempty.elim ‹_›
(congr_fun <| h (a₁ := fun _ ↦ b₁) (a₂ := fun _ ↦ b₂) <| funext fun _ ↦ eq), (·.comp_left)⟩
@[nontriviality] theorem injective_of_subsingleton [Subsingleton α] (f : α → β) : Injective f :=
fun _ _ _ ↦ Subsingleton.elim _ _
@[nontriviality] theorem bijective_of_subsingleton [Subsingleton α] (f : α → α) : Bijective f :=
⟨injective_of_subsingleton f, fun a ↦ ⟨a, Subsingleton.elim ..⟩⟩
lemma Injective.dite (p : α → Prop) [DecidablePred p]
{f : {a : α // p a} → β} {f' : {a : α // ¬ p a} → β}
(hf : Injective f) (hf' : Injective f')
(im_disj : ∀ {x x' : α} {hx : p x} {hx' : ¬ p x'}, f ⟨x, hx⟩ ≠ f' ⟨x', hx'⟩) :
Function.Injective (fun x ↦ if h : p x then f ⟨x, h⟩ else f' ⟨x, h⟩) := fun x₁ x₂ h => by
dsimp only at h
by_cases h₁ : p x₁ <;> by_cases h₂ : p x₂
· rw [dif_pos h₁, dif_pos h₂] at h; injection (hf h)
· rw [dif_pos h₁, dif_neg h₂] at h; exact (im_disj h).elim
· rw [dif_neg h₁, dif_pos h₂] at h; exact (im_disj h.symm).elim
· rw [dif_neg h₁, dif_neg h₂] at h; injection (hf' h)
theorem Surjective.of_comp {g : γ → α} (S : Surjective (f ∘ g)) : Surjective f := fun y ↦
let ⟨x, h⟩ := S y
⟨g x, h⟩
@[simp]
theorem Surjective.of_comp_iff (f : α → β) {g : γ → α} (hg : Surjective g) :
Surjective (f ∘ g) ↔ Surjective f :=
⟨Surjective.of_comp, fun h ↦ h.comp hg⟩
theorem Surjective.of_comp_left {g : γ → α} (S : Surjective (f ∘ g)) (hf : Injective f) :
Surjective g := fun a ↦ let ⟨c, hc⟩ := S (f a); ⟨c, hf hc⟩
theorem Injective.bijective₂_of_surjective {g : γ → α} (hf : Injective f) (hg : Injective g)
(S : Surjective (f ∘ g)) : Bijective f ∧ Bijective g :=
⟨⟨hf, S.of_comp⟩, hg, S.of_comp_left hf⟩
@[simp]
theorem Surjective.of_comp_iff' (hf : Bijective f) (g : γ → α) :
Surjective (f ∘ g) ↔ Surjective g :=
⟨fun S ↦ S.of_comp_left hf.1, hf.surjective.comp⟩
instance decidableEqPFun (p : Prop) [Decidable p] (α : p → Type*) [∀ hp, DecidableEq (α hp)] :
DecidableEq (∀ hp, α hp)
| f, g => decidable_of_iff (∀ hp, f hp = g hp) funext_iff.symm
protected theorem Surjective.forall (hf : Surjective f) {p : β → Prop} :
(∀ y, p y) ↔ ∀ x, p (f x) :=
⟨fun h x ↦ h (f x), fun h y ↦
let ⟨x, hx⟩ := hf y
hx ▸ h x⟩
protected theorem Surjective.forall₂ (hf : Surjective f) {p : β → β → Prop} :
(∀ y₁ y₂, p y₁ y₂) ↔ ∀ x₁ x₂, p (f x₁) (f x₂) :=
hf.forall.trans <| forall_congr' fun _ ↦ hf.forall
protected theorem Surjective.forall₃ (hf : Surjective f) {p : β → β → β → Prop} :
(∀ y₁ y₂ y₃, p y₁ y₂ y₃) ↔ ∀ x₁ x₂ x₃, p (f x₁) (f x₂) (f x₃) :=
hf.forall.trans <| forall_congr' fun _ ↦ hf.forall₂
protected theorem Surjective.exists (hf : Surjective f) {p : β → Prop} :
(∃ y, p y) ↔ ∃ x, p (f x) :=
⟨fun ⟨y, hy⟩ ↦
let ⟨x, hx⟩ := hf y
⟨x, hx.symm ▸ hy⟩,
fun ⟨x, hx⟩ ↦ ⟨f x, hx⟩⟩
protected theorem Surjective.exists₂ (hf : Surjective f) {p : β → β → Prop} :
(∃ y₁ y₂, p y₁ y₂) ↔ ∃ x₁ x₂, p (f x₁) (f x₂) :=
hf.exists.trans <| exists_congr fun _ ↦ hf.exists
protected theorem Surjective.exists₃ (hf : Surjective f) {p : β → β → β → Prop} :
(∃ y₁ y₂ y₃, p y₁ y₂ y₃) ↔ ∃ x₁ x₂ x₃, p (f x₁) (f x₂) (f x₃) :=
hf.exists.trans <| exists_congr fun _ ↦ hf.exists₂
theorem Surjective.injective_comp_right (hf : Surjective f) : Injective fun g : β → γ ↦ g ∘ f :=
fun _ _ h ↦ funext <| hf.forall.2 <| congr_fun h
theorem injective_comp_right_iff_surjective {γ : Type*} [Nontrivial γ] :
Injective (fun g : β → γ ↦ g ∘ f) ↔ Surjective f := by
refine ⟨not_imp_not.mp fun not_surj inj ↦ not_subsingleton γ ⟨fun c c' ↦ ?_⟩,
(·.injective_comp_right)⟩
have ⟨b₀, hb⟩ := not_forall.mp not_surj
classical have := inj (a₁ := fun _ ↦ c) (a₂ := (if · = b₀ then c' else c)) ?_
· simpa using congr_fun this b₀
ext a; simp only [comp_apply, if_neg fun h ↦ hb ⟨a, h⟩]
protected theorem Surjective.right_cancellable (hf : Surjective f) {g₁ g₂ : β → γ} :
g₁ ∘ f = g₂ ∘ f ↔ g₁ = g₂ :=
hf.injective_comp_right.eq_iff
theorem surjective_of_right_cancellable_Prop (h : ∀ g₁ g₂ : β → Prop, g₁ ∘ f = g₂ ∘ f → g₁ = g₂) :
Surjective f :=
injective_comp_right_iff_surjective.mp h
theorem bijective_iff_existsUnique (f : α → β) : Bijective f ↔ ∀ b : β, ∃! a : α, f a = b :=
⟨fun hf b ↦
let ⟨a, ha⟩ := hf.surjective b
⟨a, ha, fun _ ha' ↦ hf.injective (ha'.trans ha.symm)⟩,
fun he ↦ ⟨fun {_a a'} h ↦ (he (f a')).unique h rfl, fun b ↦ (he b).exists⟩⟩
/-- Shorthand for using projection notation with `Function.bijective_iff_existsUnique`. -/
protected theorem Bijective.existsUnique {f : α → β} (hf : Bijective f) (b : β) :
∃! a : α, f a = b :=
(bijective_iff_existsUnique f).mp hf b
theorem Bijective.existsUnique_iff {f : α → β} (hf : Bijective f) {p : β → Prop} :
(∃! y, p y) ↔ ∃! x, p (f x) :=
⟨fun ⟨y, hpy, hy⟩ ↦
let ⟨x, hx⟩ := hf.surjective y
⟨x, by simpa [hx], fun z (hz : p (f z)) ↦ hf.injective <| hx.symm ▸ hy _ hz⟩,
fun ⟨x, hpx, hx⟩ ↦
⟨f x, hpx, fun y hy ↦
let ⟨z, hz⟩ := hf.surjective y
hz ▸ congr_arg f (hx _ (by simpa [hz]))⟩⟩
theorem Bijective.of_comp_iff (f : α → β) {g : γ → α} (hg : Bijective g) :
Bijective (f ∘ g) ↔ Bijective f :=
and_congr (Injective.of_comp_iff' _ hg) (Surjective.of_comp_iff _ hg.surjective)
theorem Bijective.of_comp_iff' {f : α → β} (hf : Bijective f) (g : γ → α) :
Function.Bijective (f ∘ g) ↔ Function.Bijective g :=
and_congr (Injective.of_comp_iff hf.injective _) (Surjective.of_comp_iff' hf _)
/-- **Cantor's diagonal argument** implies that there are no surjective functions from `α`
to `Set α`. -/
theorem cantor_surjective {α} (f : α → Set α) : ¬Surjective f
| h => let ⟨D, e⟩ := h {a | ¬ f a a}
@iff_not_self (D ∈ f D) <| iff_of_eq <| congr_arg (D ∈ ·) e
/-- **Cantor's diagonal argument** implies that there are no injective functions from `Set α`
to `α`. -/
theorem cantor_injective {α : Type*} (f : Set α → α) : ¬Injective f
| i => cantor_surjective (fun a ↦ {b | ∀ U, a = f U → U b}) <|
RightInverse.surjective (fun U ↦ Set.ext fun _ ↦ ⟨fun h ↦ h U rfl, fun h _ e ↦ i e ▸ h⟩)
/-- There is no surjection from `α : Type u` into `Type (max u v)`. This theorem
demonstrates why `Type : Type` would be inconsistent in Lean. -/
theorem not_surjective_Type {α : Type u} (f : α → Type max u v) : ¬Surjective f := by
intro hf
let T : Type max u v := Sigma f
cases hf (Set T) with | intro U hU =>
let g : Set T → T := fun s ↦ ⟨U, cast hU.symm s⟩
have hg : Injective g := by
intro s t h
suffices cast hU (g s).2 = cast hU (g t).2 by
simp only [g, cast_cast, cast_eq] at this
assumption
· congr
exact cantor_injective g hg
/-- `g` is a partial inverse to `f` (an injective but not necessarily
surjective function) if `g y = some x` implies `f x = y`, and `g y = none`
implies that `y` is not in the range of `f`. -/
def IsPartialInv {α β} (f : α → β) (g : β → Option α) : Prop :=
∀ x y, g y = some x ↔ f x = y
theorem isPartialInv_left {α β} {f : α → β} {g} (H : IsPartialInv f g) (x) : g (f x) = some x :=
(H _ _).2 rfl
theorem injective_of_isPartialInv {α β} {f : α → β} {g} (H : IsPartialInv f g) :
Injective f := fun _ _ h ↦
Option.some.inj <| ((H _ _).2 h).symm.trans ((H _ _).2 rfl)
theorem injective_of_isPartialInv_right {α β} {f : α → β} {g} (H : IsPartialInv f g) (x y b)
(h₁ : b ∈ g x) (h₂ : b ∈ g y) : x = y :=
((H _ _).1 h₁).symm.trans ((H _ _).1 h₂)
theorem LeftInverse.comp_eq_id {f : α → β} {g : β → α} (h : LeftInverse f g) : f ∘ g = id :=
funext h
theorem leftInverse_iff_comp {f : α → β} {g : β → α} : LeftInverse f g ↔ f ∘ g = id :=
⟨LeftInverse.comp_eq_id, congr_fun⟩
theorem RightInverse.comp_eq_id {f : α → β} {g : β → α} (h : RightInverse f g) : g ∘ f = id :=
funext h
theorem rightInverse_iff_comp {f : α → β} {g : β → α} : RightInverse f g ↔ g ∘ f = id :=
⟨RightInverse.comp_eq_id, congr_fun⟩
theorem LeftInverse.comp {f : α → β} {g : β → α} {h : β → γ} {i : γ → β} (hf : LeftInverse f g)
(hh : LeftInverse h i) : LeftInverse (h ∘ f) (g ∘ i) :=
fun a ↦ show h (f (g (i a))) = a by rw [hf (i a), hh a]
theorem RightInverse.comp {f : α → β} {g : β → α} {h : β → γ} {i : γ → β} (hf : RightInverse f g)
(hh : RightInverse h i) : RightInverse (h ∘ f) (g ∘ i) :=
LeftInverse.comp hh hf
theorem LeftInverse.rightInverse {f : α → β} {g : β → α} (h : LeftInverse g f) : RightInverse f g :=
h
theorem RightInverse.leftInverse {f : α → β} {g : β → α} (h : RightInverse g f) : LeftInverse f g :=
h
theorem LeftInverse.surjective {f : α → β} {g : β → α} (h : LeftInverse f g) : Surjective f :=
h.rightInverse.surjective
theorem RightInverse.injective {f : α → β} {g : β → α} (h : RightInverse f g) : Injective f :=
h.leftInverse.injective
theorem LeftInverse.rightInverse_of_injective {f : α → β} {g : β → α} (h : LeftInverse f g)
(hf : Injective f) : RightInverse f g :=
fun x ↦ hf <| h (f x)
theorem LeftInverse.rightInverse_of_surjective {f : α → β} {g : β → α} (h : LeftInverse f g)
(hg : Surjective g) : RightInverse f g :=
fun x ↦ let ⟨y, hy⟩ := hg x; hy ▸ congr_arg g (h y)
theorem RightInverse.leftInverse_of_surjective {f : α → β} {g : β → α} :
RightInverse f g → Surjective f → LeftInverse f g :=
LeftInverse.rightInverse_of_surjective
theorem RightInverse.leftInverse_of_injective {f : α → β} {g : β → α} :
RightInverse f g → Injective g → LeftInverse f g :=
LeftInverse.rightInverse_of_injective
theorem LeftInverse.eq_rightInverse {f : α → β} {g₁ g₂ : β → α} (h₁ : LeftInverse g₁ f)
(h₂ : RightInverse g₂ f) : g₁ = g₂ :=
calc
g₁ = g₁ ∘ f ∘ g₂ := by rw [h₂.comp_eq_id, comp_id]
_ = g₂ := by rw [← comp_assoc, h₁.comp_eq_id, id_comp]
/-- We can use choice to construct explicitly a partial inverse for
a given injective function `f`. -/
noncomputable def partialInv {α β} (f : α → β) (b : β) : Option α :=
open scoped Classical in
if h : ∃ a, f a = b then some (Classical.choose h) else none
theorem partialInv_of_injective {α β} {f : α → β} (I : Injective f) : IsPartialInv f (partialInv f)
| a, b =>
⟨fun h =>
open scoped Classical in
have hpi : partialInv f b = if h : ∃ a, f a = b then some (Classical.choose h) else none :=
rfl
if h' : ∃ a, f a = b
then by rw [hpi, dif_pos h'] at h
injection h with h
subst h
apply Classical.choose_spec h'
else by rw [hpi, dif_neg h'] at h; contradiction,
fun e => e ▸ have h : ∃ a', f a' = f a := ⟨_, rfl⟩
(dif_pos h).trans (congr_arg _ (I <| Classical.choose_spec h))⟩
theorem partialInv_left {α β} {f : α → β} (I : Injective f) : ∀ x, partialInv f (f x) = some x :=
isPartialInv_left (partialInv_of_injective I)
end
section InvFun
variable {α β : Sort*} [Nonempty α] {f : α → β} {b : β}
/-- The inverse of a function (which is a left inverse if `f` is injective
and a right inverse if `f` is surjective). -/
-- Explicit Sort so that `α` isn't inferred to be Prop via `exists_prop_decidable`
noncomputable def invFun {α : Sort u} {β} [Nonempty α] (f : α → β) : β → α :=
open scoped Classical in
fun y ↦ if h : (∃ x, f x = y) then h.choose else Classical.arbitrary α
theorem invFun_eq (h : ∃ a, f a = b) : f (invFun f b) = b := by
simp only [invFun, dif_pos h, h.choose_spec]
theorem apply_invFun_apply {α β : Type*} {f : α → β} {a : α} :
f (@invFun _ _ ⟨a⟩ f (f a)) = f a :=
@invFun_eq _ _ ⟨a⟩ _ _ ⟨_, rfl⟩
theorem invFun_neg (h : ¬∃ a, f a = b) : invFun f b = Classical.choice ‹_› :=
dif_neg h
theorem invFun_eq_of_injective_of_rightInverse {g : β → α} (hf : Injective f)
(hg : RightInverse g f) : invFun f = g :=
funext fun b ↦
hf
(by
rw [hg b]
exact invFun_eq ⟨g b, hg b⟩)
theorem rightInverse_invFun (hf : Surjective f) : RightInverse (invFun f) f :=
fun b ↦ invFun_eq <| hf b
theorem leftInverse_invFun (hf : Injective f) : LeftInverse (invFun f) f :=
fun b ↦ hf <| invFun_eq ⟨b, rfl⟩
theorem invFun_surjective (hf : Injective f) : Surjective (invFun f) :=
(leftInverse_invFun hf).surjective
theorem invFun_comp (hf : Injective f) : invFun f ∘ f = id :=
funext <| leftInverse_invFun hf
theorem Injective.hasLeftInverse (hf : Injective f) : HasLeftInverse f :=
⟨invFun f, leftInverse_invFun hf⟩
theorem injective_iff_hasLeftInverse : Injective f ↔ HasLeftInverse f :=
⟨Injective.hasLeftInverse, HasLeftInverse.injective⟩
end InvFun
section SurjInv
variable {α : Sort u} {β : Sort v} {γ : Sort w} {f : α → β}
/-- The inverse of a surjective function. (Unlike `invFun`, this does not require
`α` to be inhabited.) -/
noncomputable def surjInv {f : α → β} (h : Surjective f) (b : β) : α :=
Classical.choose (h b)
theorem surjInv_eq (h : Surjective f) (b) : f (surjInv h b) = b :=
Classical.choose_spec (h b)
theorem rightInverse_surjInv (hf : Surjective f) : RightInverse (surjInv hf) f :=
surjInv_eq hf
theorem leftInverse_surjInv (hf : Bijective f) : LeftInverse (surjInv hf.2) f :=
rightInverse_of_injective_of_leftInverse hf.1 (rightInverse_surjInv hf.2)
theorem Surjective.hasRightInverse (hf : Surjective f) : HasRightInverse f :=
⟨_, rightInverse_surjInv hf⟩
theorem surjective_iff_hasRightInverse : Surjective f ↔ HasRightInverse f :=
⟨Surjective.hasRightInverse, HasRightInverse.surjective⟩
theorem bijective_iff_has_inverse : Bijective f ↔ ∃ g, LeftInverse g f ∧ RightInverse g f :=
⟨fun hf ↦ ⟨_, leftInverse_surjInv hf, rightInverse_surjInv hf.2⟩, fun ⟨_, gl, gr⟩ ↦
⟨gl.injective, gr.surjective⟩⟩
theorem injective_surjInv (h : Surjective f) : Injective (surjInv h) :=
(rightInverse_surjInv h).injective
theorem surjective_to_subsingleton [na : Nonempty α] [Subsingleton β] (f : α → β) :
Surjective f :=
fun _ ↦ let ⟨a⟩ := na; ⟨a, Subsingleton.elim _ _⟩
theorem Surjective.piMap {ι : Sort*} {α β : ι → Sort*} {f : ∀ i, α i → β i}
(hf : ∀ i, Surjective (f i)) : Surjective (Pi.map f) := fun g ↦
⟨fun i ↦ surjInv (hf i) (g i), funext fun _ ↦ rightInverse_surjInv _ _⟩
/-- Composition by a surjective function on the left is itself surjective. -/
theorem Surjective.comp_left {g : β → γ} (hg : Surjective g) :
Surjective (g ∘ · : (α → β) → α → γ) :=
.piMap fun _ ↦ hg
theorem surjective_comp_left_iff [Nonempty α] {g : β → γ} :
Surjective (g ∘ · : (α → β) → α → γ) ↔ Surjective g := by
refine ⟨fun h c ↦ Nonempty.elim ‹_› fun a ↦ ?_, (·.comp_left)⟩
have ⟨f, hf⟩ := h fun _ ↦ c
exact ⟨f a, congr_fun hf _⟩
theorem Bijective.piMap {ι : Sort*} {α β : ι → Sort*} {f : ∀ i, α i → β i}
(hf : ∀ i, Bijective (f i)) : Bijective (Pi.map f) :=
⟨.piMap fun i ↦ (hf i).1, .piMap fun i ↦ (hf i).2⟩
/-- Composition by a bijective function on the left is itself bijective. -/
theorem Bijective.comp_left {g : β → γ} (hg : Bijective g) :
Bijective (g ∘ · : (α → β) → α → γ) :=
⟨hg.injective.comp_left, hg.surjective.comp_left⟩
end SurjInv
section Update
variable {α : Sort u} {β : α → Sort v} {α' : Sort w} [DecidableEq α]
{f : (a : α) → β a} {a : α} {b : β a}
/-- Replacing the value of a function at a given point by a given value. -/
def update (f : ∀ a, β a) (a' : α) (v : β a') (a : α) : β a :=
if h : a = a' then Eq.ndrec v h.symm else f a
@[simp]
theorem update_self (a : α) (v : β a) (f : ∀ a, β a) : update f a v a = v :=
dif_pos rfl
@[deprecated (since := "2024-12-28")] alias update_same := update_self
@[simp]
theorem update_of_ne {a a' : α} (h : a ≠ a') (v : β a') (f : ∀ a, β a) : update f a' v a = f a :=
dif_neg h
@[deprecated (since := "2024-12-28")] alias update_noteq := update_of_ne
/-- On non-dependent functions, `Function.update` can be expressed as an `ite` -/
theorem update_apply {β : Sort*} (f : α → β) (a' : α) (b : β) (a : α) :
update f a' b a = if a = a' then b else f a := by
rcases Decidable.eq_or_ne a a' with rfl | hne <;> simp [*]
@[nontriviality]
theorem update_eq_const_of_subsingleton [Subsingleton α] (a : α) (v : α') (f : α → α') :
update f a v = const α v :=
funext fun a' ↦ Subsingleton.elim a a' ▸ update_self ..
theorem surjective_eval {α : Sort u} {β : α → Sort v} [h : ∀ a, Nonempty (β a)] (a : α) :
Surjective (eval a : (∀ a, β a) → β a) := fun b ↦
⟨@update _ _ (Classical.decEq α) (fun a ↦ (h a).some) a b,
@update_self _ _ (Classical.decEq α) _ _ _⟩
theorem update_injective (f : ∀ a, β a) (a' : α) : Injective (update f a') := fun v v' h ↦ by
have := congr_fun h a'
rwa [update_self, update_self] at this
lemma forall_update_iff (f : ∀a, β a) {a : α} {b : β a} (p : ∀a, β a → Prop) :
(∀ x, p x (update f a b x)) ↔ p a b ∧ ∀ x, x ≠ a → p x (f x) := by
rw [← and_forall_ne a, update_self]
simp +contextual
theorem exists_update_iff (f : ∀ a, β a) {a : α} {b : β a} (p : ∀ a, β a → Prop) :
(∃ x, p x (update f a b x)) ↔ p a b ∨ ∃ x ≠ a, p x (f x) := by
rw [← not_forall_not, forall_update_iff f fun a b ↦ ¬p a b]
simp [-not_and, not_and_or]
theorem update_eq_iff {a : α} {b : β a} {f g : ∀ a, β a} :
update f a b = g ↔ b = g a ∧ ∀ x ≠ a, f x = g x :=
funext_iff.trans <| forall_update_iff _ fun x y ↦ y = g x
theorem eq_update_iff {a : α} {b : β a} {f g : ∀ a, β a} :
g = update f a b ↔ g a = b ∧ ∀ x ≠ a, g x = f x :=
funext_iff.trans <| forall_update_iff _ fun x y ↦ g x = y
@[simp] lemma update_eq_self_iff : update f a b = f ↔ b = f a := by simp [update_eq_iff]
@[simp] lemma eq_update_self_iff : f = update f a b ↔ f a = b := by simp [eq_update_iff]
lemma ne_update_self_iff : f ≠ update f a b ↔ f a ≠ b := eq_update_self_iff.not
lemma update_ne_self_iff : update f a b ≠ f ↔ b ≠ f a := update_eq_self_iff.not
@[simp]
theorem update_eq_self (a : α) (f : ∀ a, β a) : update f a (f a) = f :=
update_eq_iff.2 ⟨rfl, fun _ _ ↦ rfl⟩
theorem update_comp_eq_of_forall_ne' {α'} (g : ∀ a, β a) {f : α' → α} {i : α} (a : β i)
(h : ∀ x, f x ≠ i) : (fun j ↦ (update g i a) (f j)) = fun j ↦ g (f j) :=
funext fun _ ↦ update_of_ne (h _) _ _
variable [DecidableEq α']
/-- Non-dependent version of `Function.update_comp_eq_of_forall_ne'` -/
theorem update_comp_eq_of_forall_ne {α β : Sort*} (g : α' → β) {f : α → α'} {i : α'} (a : β)
(h : ∀ x, f x ≠ i) : update g i a ∘ f = g ∘ f :=
update_comp_eq_of_forall_ne' g a h
theorem update_comp_eq_of_injective' (g : ∀ a, β a) {f : α' → α} (hf : Function.Injective f)
(i : α') (a : β (f i)) : (fun j ↦ update g (f i) a (f j)) = update (fun i ↦ g (f i)) i a :=
eq_update_iff.2 ⟨update_self .., fun _ hj ↦ update_of_ne (hf.ne hj) _ _⟩
theorem update_apply_of_injective
(g : ∀ a, β a) {f : α' → α} (hf : Function.Injective f)
(i : α') (a : β (f i)) (j : α') :
update g (f i) a (f j) = update (fun i ↦ g (f i)) i a j :=
congr_fun (update_comp_eq_of_injective' g hf i a) j
/-- Non-dependent version of `Function.update_comp_eq_of_injective'` -/
theorem update_comp_eq_of_injective {β : Sort*} (g : α' → β) {f : α → α'}
(hf : Function.Injective f) (i : α) (a : β) :
Function.update g (f i) a ∘ f = Function.update (g ∘ f) i a :=
update_comp_eq_of_injective' g hf i a
/-- Recursors can be pushed inside `Function.update`.
The `ctor` argument should be a one-argument constructor like `Sum.inl`,
and `recursor` should be an inductive recursor partially applied in all but that constructor,
such as `(Sum.rec · g)`.
In future, we should build some automation to generate applications like `Option.rec_update` for all
inductive types. -/
lemma rec_update {ι κ : Sort*} {α : κ → Sort*} [DecidableEq ι] [DecidableEq κ]
{ctor : ι → κ} (hctor : Function.Injective ctor)
(recursor : ((i : ι) → α (ctor i)) → ((i : κ) → α i))
(h : ∀ f i, recursor f (ctor i) = f i)
(h2 : ∀ f₁ f₂ k, (∀ i, ctor i ≠ k) → recursor f₁ k = recursor f₂ k)
(f : (i : ι) → α (ctor i)) (i : ι) (x : α (ctor i)) :
recursor (update f i x) = update (recursor f) (ctor i) x := by
ext k
by_cases h : ∃ i, ctor i = k
· obtain ⟨i', rfl⟩ := h
obtain rfl | hi := eq_or_ne i' i
· simp [h]
· have hk := hctor.ne hi
simp [h, hi, hk, Function.update_of_ne]
· rw [not_exists] at h
rw [h2 _ f _ h]
rw [Function.update_of_ne (Ne.symm <| h i)]
@[simp]
lemma _root_.Option.rec_update {α : Type*} {β : Option α → Sort*} [DecidableEq α]
(f : β none) (g : ∀ a, β (.some a)) (a : α) (x : β (.some a)) :
Option.rec f (update g a x) = update (Option.rec f g) (.some a) x :=
Function.rec_update (@Option.some.inj _) (Option.rec f) (fun _ _ => rfl) (fun
| _, _, .some _, h => (h _ rfl).elim
| _, _, .none, _ => rfl) _ _ _
theorem apply_update {ι : Sort*} [DecidableEq ι] {α β : ι → Sort*} (f : ∀ i, α i → β i)
(g : ∀ i, α i) (i : ι) (v : α i) (j : ι) :
f j (update g i v j) = update (fun k ↦ f k (g k)) i (f i v) j := by
by_cases h : j = i
· subst j
simp
· simp [h]
theorem apply_update₂ {ι : Sort*} [DecidableEq ι] {α β γ : ι → Sort*} (f : ∀ i, α i → β i → γ i)
(g : ∀ i, α i) (h : ∀ i, β i) (i : ι) (v : α i) (w : β i) (j : ι) :
f j (update g i v j) (update h i w j) = update (fun k ↦ f k (g k) (h k)) i (f i v w) j := by
by_cases h : j = i
· subst j
simp
· simp [h]
theorem pred_update (P : ∀ ⦃a⦄, β a → Prop) (f : ∀ a, β a) (a' : α) (v : β a') (a : α) :
P (update f a' v a) ↔ a = a' ∧ P v ∨ a ≠ a' ∧ P (f a) := by
rw [apply_update P, update_apply, ite_prop_iff_or]
theorem comp_update {α' : Sort*} {β : Sort*} (f : α' → β) (g : α → α') (i : α) (v : α') :
f ∘ update g i v = update (f ∘ g) i (f v) :=
funext <| apply_update _ _ _ _
theorem update_comm {α} [DecidableEq α] {β : α → Sort*} {a b : α} (h : a ≠ b) (v : β a) (w : β b)
(f : ∀ a, β a) : update (update f a v) b w = update (update f b w) a v := by
funext c
simp only [update]
by_cases h₁ : c = b <;> by_cases h₂ : c = a
· rw [dif_pos h₁, dif_pos h₂]
cases h (h₂.symm.trans h₁)
· rw [dif_pos h₁, dif_pos h₁, dif_neg h₂]
· rw [dif_neg h₁, dif_neg h₁]
· rw [dif_neg h₁, dif_neg h₁]
@[simp]
theorem update_idem {α} [DecidableEq α] {β : α → Sort*} {a : α} (v w : β a) (f : ∀ a, β a) :
update (update f a v) a w = update f a w := by
funext b
by_cases h : b = a <;> simp [update, h]
end Update
noncomputable section Extend
variable {α β γ : Sort*} {f : α → β}
/-- Extension of a function `g : α → γ` along a function `f : α → β`.
For every `a : α`, `f a` is sent to `g a`. `f` might not be surjective, so we use an auxiliary
function `j : β → γ` by sending `b : β` not in the range of `f` to `j b`. If you do not care about
the behavior outside the range, `j` can be used as a junk value by setting it to be `0` or
`Classical.arbitrary` (assuming `γ` is nonempty).
This definition is mathematically meaningful only when `f a₁ = f a₂ → g a₁ = g a₂` (spelled
`g.FactorsThrough f`). In particular this holds if `f` is injective.
A typical use case is extending a function from a subtype to the entire type. If you wish to extend
`g : {b : β // p b} → γ` to a function `β → γ`, you should use `Function.extend Subtype.val g j`. -/
def extend (f : α → β) (g : α → γ) (j : β → γ) : β → γ := fun b ↦
open scoped Classical in
if h : ∃ a, f a = b then g (Classical.choose h) else j b
/-- g factors through f : `f a = f b → g a = g b` -/
def FactorsThrough (g : α → γ) (f : α → β) : Prop :=
∀ ⦃a b⦄, f a = f b → g a = g b
theorem extend_def (f : α → β) (g : α → γ) (e' : β → γ) (b : β) [Decidable (∃ a, f a = b)] :
extend f g e' b = if h : ∃ a, f a = b then g (Classical.choose h) else e' b := by
unfold extend
congr
lemma Injective.factorsThrough (hf : Injective f) (g : α → γ) : g.FactorsThrough f :=
fun _ _ h => congr_arg g (hf h)
lemma FactorsThrough.extend_apply {g : α → γ} (hf : g.FactorsThrough f) (e' : β → γ) (a : α) :
extend f g e' (f a) = g a := by
classical
simp only [extend_def, dif_pos, exists_apply_eq_apply]
exact hf (Classical.choose_spec (exists_apply_eq_apply f a))
@[simp]
theorem Injective.extend_apply (hf : Injective f) (g : α → γ) (e' : β → γ) (a : α) :
extend f g e' (f a) = g a :=
(hf.factorsThrough g).extend_apply e' a
@[simp]
theorem extend_apply' (g : α → γ) (e' : β → γ) (b : β) (hb : ¬∃ a, f a = b) :
extend f g e' b = e' b := by
classical
simp [Function.extend_def, hb]
lemma factorsThrough_iff (g : α → γ) [Nonempty γ] : g.FactorsThrough f ↔ ∃ (e : β → γ), g = e ∘ f :=
⟨fun hf => ⟨extend f g (const β (Classical.arbitrary γ)),
funext (fun x => by simp only [comp_apply, hf.extend_apply])⟩,
fun h _ _ hf => by rw [Classical.choose_spec h, comp_apply, comp_apply, hf]⟩
lemma apply_extend {δ} {g : α → γ} (F : γ → δ) (f : α → β) (e' : β → γ) (b : β) :
F (extend f g e' b) = extend f (F ∘ g) (F ∘ e') b :=
open scoped Classical in apply_dite F _ _ _
theorem extend_injective (hf : Injective f) (e' : β → γ) : Injective fun g ↦ extend f g e' := by
intro g₁ g₂ hg
refine funext fun x ↦ ?_
have H := congr_fun hg (f x)
simp only [hf.extend_apply] at H
exact H
lemma FactorsThrough.extend_comp {g : α → γ} (e' : β → γ) (hf : FactorsThrough g f) :
extend f g e' ∘ f = g :=
funext fun a => hf.extend_apply e' a
@[simp]
lemma extend_const (f : α → β) (c : γ) : extend f (fun _ ↦ c) (fun _ ↦ c) = fun _ ↦ c :=
funext fun _ ↦ open scoped Classical in ite_id _
@[simp]
theorem extend_comp (hf : Injective f) (g : α → γ) (e' : β → γ) : extend f g e' ∘ f = g :=
funext fun a ↦ hf.extend_apply g e' a
theorem Injective.surjective_comp_right' (hf : Injective f) (g₀ : β → γ) :
Surjective fun g : β → γ ↦ g ∘ f :=
fun g ↦ ⟨extend f g g₀, extend_comp hf _ _⟩
theorem Injective.surjective_comp_right [Nonempty γ] (hf : Injective f) :
Surjective fun g : β → γ ↦ g ∘ f :=
hf.surjective_comp_right' fun _ ↦ Classical.choice ‹_›
theorem surjective_comp_right_iff_injective {γ : Type*} [Nontrivial γ] :
Surjective (fun g : β → γ ↦ g ∘ f) ↔ Injective f := by
classical
refine ⟨not_imp_not.mp fun not_inj surj ↦ not_subsingleton γ ⟨fun c c' ↦ ?_⟩,
(·.surjective_comp_right)⟩
simp only [Injective, not_forall] at not_inj
have ⟨a₁, a₂, eq, ne⟩ := not_inj
have ⟨f, hf⟩ := surj (if · = a₂ then c else c')
have h₁ := congr_fun hf a₁
have h₂ := congr_fun hf a₂
simp only [comp_apply, if_neg ne, reduceIte] at h₁ h₂
rw [← h₁, eq, h₂]
theorem Bijective.comp_right (hf : Bijective f) : Bijective fun g : β → γ ↦ g ∘ f :=
⟨hf.surjective.injective_comp_right, fun g ↦
⟨g ∘ surjInv hf.surjective,
by simp only [comp_assoc g _ f, (leftInverse_surjInv hf).comp_eq_id, comp_id]⟩⟩
end Extend
namespace FactorsThrough
protected theorem rfl {α β : Sort*} {f : α → β} : FactorsThrough f f := fun _ _ ↦ id
theorem comp_left {α β γ δ : Sort*} {f : α → β} {g : α → γ} (h : FactorsThrough g f) (g' : γ → δ) :
FactorsThrough (g' ∘ g) f := fun _x _y hxy ↦
congr_arg g' (h hxy)
theorem comp_right {α β γ δ : Sort*} {f : α → β} {g : α → γ} (h : FactorsThrough g f) (g' : δ → α) :
FactorsThrough (g ∘ g') (f ∘ g') := fun _x _y hxy ↦
h hxy
end FactorsThrough
theorem uncurry_def {α β γ} (f : α → β → γ) : uncurry f = fun p ↦ f p.1 p.2 :=
rfl
section Bicomp
variable {α β γ δ ε : Type*}
/-- Compose a binary function `f` with a pair of unary functions `g` and `h`.
If both arguments of `f` have the same type and `g = h`, then `bicompl f g g = f on g`. -/
def bicompl (f : γ → δ → ε) (g : α → γ) (h : β → δ) (a b) :=
f (g a) (h b)
/-- Compose a unary function `f` with a binary function `g`. -/
def bicompr (f : γ → δ) (g : α → β → γ) (a b) :=
f (g a b)
-- Suggested local notation:
local notation f " ∘₂ " g => bicompr f g
theorem uncurry_bicompr (f : α → β → γ) (g : γ → δ) : uncurry (g ∘₂ f) = g ∘ uncurry f :=
rfl
theorem uncurry_bicompl (f : γ → δ → ε) (g : α → γ) (h : β → δ) :
uncurry (bicompl f g h) = uncurry f ∘ Prod.map g h :=
rfl
end Bicomp
section Uncurry
variable {α β γ δ : Type*}
/-- Records a way to turn an element of `α` into a function from `β` to `γ`. The most generic use
is to recursively uncurry. For instance `f : α → β → γ → δ` will be turned into
`↿f : α × β × γ → δ`. One can also add instances for bundled maps. -/
class HasUncurry (α : Type*) (β : outParam Type*) (γ : outParam Type*) where
/-- Uncurrying operator. The most generic use is to recursively uncurry. For instance
`f : α → β → γ → δ` will be turned into `↿f : α × β × γ → δ`. One can also add instances
for bundled maps. -/
uncurry : α → β → γ
@[inherit_doc] notation:arg "↿" x:arg => HasUncurry.uncurry x
instance hasUncurryBase : HasUncurry (α → β) α β :=
⟨id⟩
instance hasUncurryInduction [HasUncurry β γ δ] : HasUncurry (α → β) (α × γ) δ :=
⟨fun f p ↦ (↿(f p.1)) p.2⟩
end Uncurry
/-- A function is involutive, if `f ∘ f = id`. -/
def Involutive {α} (f : α → α) : Prop :=
∀ x, f (f x) = x
theorem _root_.Bool.involutive_not : Involutive not :=
Bool.not_not
namespace Involutive
variable {α : Sort u} {f : α → α} (h : Involutive f)
include h
@[simp]
theorem comp_self : f ∘ f = id :=
funext h
protected theorem leftInverse : LeftInverse f f := h
theorem leftInverse_iff {g : α → α} :
g.LeftInverse f ↔ g = f :=
⟨fun hg ↦ funext fun x ↦ by rw [← h x, hg, h], fun he ↦ he ▸ h.leftInverse⟩
protected theorem rightInverse : RightInverse f f := h
protected theorem injective : Injective f := h.leftInverse.injective
protected theorem surjective : Surjective f := fun x ↦ ⟨f x, h x⟩
protected theorem bijective : Bijective f := ⟨h.injective, h.surjective⟩
/-- Involuting an `ite` of an involuted value `x : α` negates the `Prop` condition in the `ite`. -/
protected theorem ite_not (P : Prop) [Decidable P] (x : α) :
f (ite P x (f x)) = ite (¬P) x (f x) := by rw [apply_ite f, h, ite_not]
/-- An involution commutes across an equality. Compare to `Function.Injective.eq_iff`. -/
protected theorem eq_iff {x y : α} : f x = y ↔ x = f y :=
h.injective.eq_iff' (h y)
end Involutive
lemma not_involutive : Involutive Not := fun _ ↦ propext not_not
lemma not_injective : Injective Not := not_involutive.injective
lemma not_surjective : Surjective Not := not_involutive.surjective
lemma not_bijective : Bijective Not := not_involutive.bijective
@[simp]
lemma symmetric_apply_eq_iff {α : Sort*} {f : α → α} : Symmetric (f · = ·) ↔ Involutive f := by
simp [Symmetric, Involutive]
/-- The property of a binary function `f : α → β → γ` being injective.
Mathematically this should be thought of as the corresponding function `α × β → γ` being injective.
-/
def Injective2 {α β γ : Sort*} (f : α → β → γ) : Prop :=
∀ ⦃a₁ a₂ b₁ b₂⦄, f a₁ b₁ = f a₂ b₂ → a₁ = a₂ ∧ b₁ = b₂
namespace Injective2
variable {α β γ : Sort*} {f : α → β → γ}
/-- A binary injective function is injective when only the left argument varies. -/
protected theorem left (hf : Injective2 f) (b : β) : Function.Injective fun a ↦ f a b :=
fun _ _ h ↦ (hf h).left
/-- A binary injective function is injective when only the right argument varies. -/
protected theorem right (hf : Injective2 f) (a : α) : Function.Injective (f a) :=
fun _ _ h ↦ (hf h).right
protected theorem uncurry {α β γ : Type*} {f : α → β → γ} (hf : Injective2 f) :
Function.Injective (uncurry f) :=
fun ⟨_, _⟩ ⟨_, _⟩ h ↦ (hf h).elim (congr_arg₂ _)
/-- As a map from the left argument to a unary function, `f` is injective. -/
theorem left' (hf : Injective2 f) [Nonempty β] : Function.Injective f := fun _ _ h ↦
let ⟨b⟩ := ‹Nonempty β›
hf.left b <| (congr_fun h b :)
/-- As a map from the right argument to a unary function, `f` is injective. -/
theorem right' (hf : Injective2 f) [Nonempty α] : Function.Injective fun b a ↦ f a b :=
fun _ _ h ↦
let ⟨a⟩ := ‹Nonempty α›
hf.right a <| (congr_fun h a :)
theorem eq_iff (hf : Injective2 f) {a₁ a₂ b₁ b₂} : f a₁ b₁ = f a₂ b₂ ↔ a₁ = a₂ ∧ b₁ = b₂ :=
⟨fun h ↦ hf h, fun ⟨h1, h2⟩ ↦ congr_arg₂ f h1 h2⟩
end Injective2
section Sometimes
/-- `sometimes f` evaluates to some value of `f`, if it exists. This function is especially
interesting in the case where `α` is a proposition, in which case `f` is necessarily a
constant function, so that `sometimes f = f a` for all `a`. -/
noncomputable def sometimes {α β} [Nonempty β] (f : α → β) : β :=
open scoped Classical in
if h : Nonempty α then f (Classical.choice h) else Classical.choice ‹_›
theorem sometimes_eq {p : Prop} {α} [Nonempty α] (f : p → α) (a : p) : sometimes f = f a :=
dif_pos ⟨a⟩
theorem sometimes_spec {p : Prop} {α} [Nonempty α] (P : α → Prop) (f : p → α) (a : p)
(h : P (f a)) : P (sometimes f) := by
rwa [sometimes_eq]
end Sometimes
end Function
variable {α β : Sort*}
/-- A relation `r : α → β → Prop` is "function-like"
(for each `a` there exists a unique `b` such that `r a b`)
if and only if it is `(f · = ·)` for some function `f`. -/
lemma forall_existsUnique_iff {r : α → β → Prop} :
(∀ a, ∃! b, r a b) ↔ ∃ f : α → β, ∀ {a b}, r a b ↔ f a = b := by
refine ⟨fun h ↦ ?_, ?_⟩
· refine ⟨fun a ↦ (h a).choose, fun hr ↦ ?_, fun h' ↦ h' ▸ ?_⟩
exacts [((h _).choose_spec.2 _ hr).symm, (h _).choose_spec.1]
· rintro ⟨f, hf⟩
simp [hf]
/-- A relation `r : α → β → Prop` is "function-like"
(for each `a` there exists a unique `b` such that `r a b`)
if and only if it is `(f · = ·)` for some function `f`. -/
lemma forall_existsUnique_iff' {r : α → β → Prop} :
(∀ a, ∃! b, r a b) ↔ ∃ f : α → β, r = (f · = ·) := by
simp [forall_existsUnique_iff, funext_iff]
/-- A symmetric relation `r : α → α → Prop` is "function-like"
(for each `a` there exists a unique `b` such that `r a b`)
if and only if it is `(f · = ·)` for some involutive function `f`. -/
protected lemma Symmetric.forall_existsUnique_iff' {r : α → α → Prop} (hr : Symmetric r) :
(∀ a, ∃! b, r a b) ↔ ∃ f : α → α, Involutive f ∧ r = (f · = ·) := by
refine ⟨fun h ↦ ?_, fun ⟨f, _, hf⟩ ↦ forall_existsUnique_iff'.2 ⟨f, hf⟩⟩
rcases forall_existsUnique_iff'.1 h with ⟨f, rfl : r = _⟩
exact ⟨f, symmetric_apply_eq_iff.1 hr, rfl⟩
/-- A symmetric relation `r : α → α → Prop` is "function-like"
(for each `a` there exists a unique `b` such that `r a b`)
if and only if it is `(f · = ·)` for some involutive function `f`. -/
protected lemma Symmetric.forall_existsUnique_iff {r : α → α → Prop} (hr : Symmetric r) :
(∀ a, ∃! b, r a b) ↔ ∃ f : α → α, Involutive f ∧ ∀ {a b}, r a b ↔ f a = b := by
simp [hr.forall_existsUnique_iff', funext_iff]
/-- `s.piecewise f g` is the function equal to `f` on the set `s`, and to `g` on its complement. -/
def Set.piecewise {α : Type u} {β : α → Sort v} (s : Set α) (f g : ∀ i, β i)
[∀ j, Decidable (j ∈ s)] : ∀ i, β i :=
fun i ↦ if i ∈ s then f i else g i
/-! ### Bijectivity of `Eq.rec`, `Eq.mp`, `Eq.mpr`, and `cast` -/
theorem eq_rec_on_bijective {C : α → Sort*} :
∀ {a a' : α} (h : a = a'), Function.Bijective (@Eq.ndrec _ _ C · _ h)
| _, _, rfl => ⟨fun _ _ ↦ id, fun x ↦ ⟨x, rfl⟩⟩
theorem eq_mp_bijective {α β : Sort _} (h : α = β) : Function.Bijective (Eq.mp h) := by
-- TODO: mathlib3 uses `eq_rec_on_bijective`, difference in elaboration here
-- due to `@[macro_inline]` possibly?
cases h
exact ⟨fun _ _ ↦ id, fun x ↦ ⟨x, rfl⟩⟩
theorem eq_mpr_bijective {α β : Sort _} (h : α = β) : Function.Bijective (Eq.mpr h) := by
cases h
exact ⟨fun _ _ ↦ id, fun x ↦ ⟨x, rfl⟩⟩
theorem cast_bijective {α β : Sort _} (h : α = β) : Function.Bijective (cast h) := by
cases h
exact ⟨fun _ _ ↦ id, fun x ↦ ⟨x, rfl⟩⟩
/-! Note these lemmas apply to `Type*` not `Sort*`, as the latter interferes with `simp`, and
is trivial anyway. -/
@[simp]
theorem eq_rec_inj {a a' : α} (h : a = a') {C : α → Type*} (x y : C a) :
(Eq.ndrec x h : C a') = Eq.ndrec y h ↔ x = y :=
| (eq_rec_on_bijective h).injective.eq_iff
@[simp]
| Mathlib/Logic/Function/Basic.lean | 996 | 998 |
/-
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.Homology
import Mathlib.CategoryTheory.Preadditive.AdditiveFunctor
import Mathlib.CategoryTheory.Preadditive.Opposite
/-!
# Homology of preadditive categories
In this file, it is shown that if `C` is a preadditive category, then
`ShortComplex C` is a preadditive category.
-/
namespace CategoryTheory
open Category Limits Preadditive
variable {C : Type*} [Category C] [Preadditive C]
namespace ShortComplex
variable {S₁ S₂ S₃ : ShortComplex C}
attribute [local simp] Hom.comm₁₂ Hom.comm₂₃
instance : Add (S₁ ⟶ S₂) where
add φ φ' :=
{ τ₁ := φ.τ₁ + φ'.τ₁
τ₂ := φ.τ₂ + φ'.τ₂
τ₃ := φ.τ₃ + φ'.τ₃ }
instance : Sub (S₁ ⟶ S₂) where
sub φ φ' :=
{ τ₁ := φ.τ₁ - φ'.τ₁
τ₂ := φ.τ₂ - φ'.τ₂
τ₃ := φ.τ₃ - φ'.τ₃ }
instance : Neg (S₁ ⟶ S₂) where
neg φ :=
{ τ₁ := -φ.τ₁
τ₂ := -φ.τ₂
τ₃ := -φ.τ₃ }
instance : AddCommGroup (S₁ ⟶ S₂) where
add_assoc := fun a b c => by ext <;> apply add_assoc
add_zero := fun a => by ext <;> apply add_zero
zero_add := fun a => by ext <;> apply zero_add
neg_add_cancel := fun a => by ext <;> apply neg_add_cancel
add_comm := fun a b => by ext <;> apply add_comm
sub_eq_add_neg := fun a b => by ext <;> apply sub_eq_add_neg
nsmul := nsmulRec
zsmul := zsmulRec
@[simp] lemma add_τ₁ (φ φ' : S₁ ⟶ S₂) : (φ + φ').τ₁ = φ.τ₁ + φ'.τ₁ := rfl
@[simp] lemma add_τ₂ (φ φ' : S₁ ⟶ S₂) : (φ + φ').τ₂ = φ.τ₂ + φ'.τ₂ := rfl
@[simp] lemma add_τ₃ (φ φ' : S₁ ⟶ S₂) : (φ + φ').τ₃ = φ.τ₃ + φ'.τ₃ := rfl
@[simp] lemma sub_τ₁ (φ φ' : S₁ ⟶ S₂) : (φ - φ').τ₁ = φ.τ₁ - φ'.τ₁ := rfl
@[simp] lemma sub_τ₂ (φ φ' : S₁ ⟶ S₂) : (φ - φ').τ₂ = φ.τ₂ - φ'.τ₂ := rfl
@[simp] lemma sub_τ₃ (φ φ' : S₁ ⟶ S₂) : (φ - φ').τ₃ = φ.τ₃ - φ'.τ₃ := rfl
@[simp] lemma neg_τ₁ (φ : S₁ ⟶ S₂) : (-φ).τ₁ = -φ.τ₁ := rfl
@[simp] lemma neg_τ₂ (φ : S₁ ⟶ S₂) : (-φ).τ₂ = -φ.τ₂ := rfl
@[simp] lemma neg_τ₃ (φ : S₁ ⟶ S₂) : (-φ).τ₃ = -φ.τ₃ := rfl
instance : Preadditive (ShortComplex C) where
section LeftHomology
variable {φ φ' : S₁ ⟶ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData}
namespace LeftHomologyMapData
variable (γ : LeftHomologyMapData φ h₁ h₂) (γ' : LeftHomologyMapData φ' h₁ h₂)
/-- Given a left homology map data for morphism `φ`, this is the induced left homology
map data for `-φ`. -/
@[simps]
def neg : LeftHomologyMapData (-φ) h₁ h₂ where
φK := -γ.φK
φH := -γ.φH
/-- Given left homology map data for morphisms `φ` and `φ'`, this is
the induced left homology map data for `φ + φ'`. -/
@[simps]
def add : LeftHomologyMapData (φ + φ') h₁ h₂ where
φK := γ.φK + γ'.φK
φH := γ.φH + γ'.φH
end LeftHomologyMapData
variable (h₁ h₂)
@[simp]
lemma leftHomologyMap'_neg :
leftHomologyMap' (-φ) h₁ h₂ = -leftHomologyMap' φ h₁ h₂ := by
have γ : LeftHomologyMapData φ h₁ h₂ := default
simp only [γ.leftHomologyMap'_eq, γ.neg.leftHomologyMap'_eq, LeftHomologyMapData.neg_φH]
@[simp]
lemma cyclesMap'_neg :
cyclesMap' (-φ) h₁ h₂ = -cyclesMap' φ h₁ h₂ := by
have γ : LeftHomologyMapData φ h₁ h₂ := default
simp only [γ.cyclesMap'_eq, γ.neg.cyclesMap'_eq, LeftHomologyMapData.neg_φK]
@[simp]
lemma leftHomologyMap'_add :
leftHomologyMap' (φ + φ') h₁ h₂ = leftHomologyMap' φ h₁ h₂ +
leftHomologyMap' φ' h₁ h₂ := by
have γ : LeftHomologyMapData φ h₁ h₂ := default
have γ' : LeftHomologyMapData φ' h₁ h₂ := default
simp only [γ.leftHomologyMap'_eq, γ'.leftHomologyMap'_eq,
(γ.add γ').leftHomologyMap'_eq, LeftHomologyMapData.add_φH]
@[simp]
lemma cyclesMap'_add :
cyclesMap' (φ + φ') h₁ h₂ = cyclesMap' φ h₁ h₂ +
cyclesMap' φ' h₁ h₂ := by
have γ : LeftHomologyMapData φ h₁ h₂ := default
have γ' : LeftHomologyMapData φ' h₁ h₂ := default
simp only [γ.cyclesMap'_eq, γ'.cyclesMap'_eq,
(γ.add γ').cyclesMap'_eq, LeftHomologyMapData.add_φK]
@[simp]
lemma leftHomologyMap'_sub :
leftHomologyMap' (φ - φ') h₁ h₂ = leftHomologyMap' φ h₁ h₂ -
leftHomologyMap' φ' h₁ h₂ := by
simp only [sub_eq_add_neg, leftHomologyMap'_add, leftHomologyMap'_neg]
@[simp]
lemma cyclesMap'_sub :
cyclesMap' (φ - φ') h₁ h₂ = cyclesMap' φ h₁ h₂ -
cyclesMap' φ' h₁ h₂ := by
simp only [sub_eq_add_neg, cyclesMap'_add, cyclesMap'_neg]
variable (φ φ')
section
variable [S₁.HasLeftHomology] [S₂.HasLeftHomology]
@[simp]
lemma leftHomologyMap_neg : leftHomologyMap (-φ) = -leftHomologyMap φ :=
leftHomologyMap'_neg _ _
@[simp]
lemma cyclesMap_neg : cyclesMap (-φ) = -cyclesMap φ :=
cyclesMap'_neg _ _
@[simp]
lemma leftHomologyMap_add : leftHomologyMap (φ + φ') = leftHomologyMap φ + leftHomologyMap φ' :=
leftHomologyMap'_add _ _
@[simp]
lemma cyclesMap_add : cyclesMap (φ + φ') = cyclesMap φ + cyclesMap φ' :=
cyclesMap'_add _ _
@[simp]
lemma leftHomologyMap_sub : leftHomologyMap (φ - φ') = leftHomologyMap φ - leftHomologyMap φ' :=
leftHomologyMap'_sub _ _
@[simp]
lemma cyclesMap_sub : cyclesMap (φ - φ') = cyclesMap φ - cyclesMap φ' :=
cyclesMap'_sub _ _
end
instance leftHomologyFunctor_additive [HasKernels C] [HasCokernels C] :
(leftHomologyFunctor C).Additive where
instance cyclesFunctor_additive [HasKernels C] [HasCokernels C] :
(cyclesFunctor C).Additive where
end LeftHomology
section RightHomology
variable {φ φ' : S₁ ⟶ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData}
namespace RightHomologyMapData
variable (γ : RightHomologyMapData φ h₁ h₂) (γ' : RightHomologyMapData φ' h₁ h₂)
/-- Given a right homology map data for morphism `φ`, this is the induced right homology
map data for `-φ`. -/
@[simps]
def neg : RightHomologyMapData (-φ) h₁ h₂ where
φQ := -γ.φQ
φH := -γ.φH
/-- Given right homology map data for morphisms `φ` and `φ'`, this is the induced
right homology map data for `φ + φ'`. -/
@[simps]
def add : RightHomologyMapData (φ + φ') h₁ h₂ where
φQ := γ.φQ + γ'.φQ
φH := γ.φH + γ'.φH
end RightHomologyMapData
variable (h₁ h₂)
@[simp]
lemma rightHomologyMap'_neg :
rightHomologyMap' (-φ) h₁ h₂ = -rightHomologyMap' φ h₁ h₂ := by
have γ : RightHomologyMapData φ h₁ h₂ := default
simp only [γ.rightHomologyMap'_eq, γ.neg.rightHomologyMap'_eq, RightHomologyMapData.neg_φH]
@[simp]
lemma opcyclesMap'_neg :
opcyclesMap' (-φ) h₁ h₂ = -opcyclesMap' φ h₁ h₂ := by
have γ : RightHomologyMapData φ h₁ h₂ := default
simp only [γ.opcyclesMap'_eq, γ.neg.opcyclesMap'_eq, RightHomologyMapData.neg_φQ]
@[simp]
lemma rightHomologyMap'_add :
rightHomologyMap' (φ + φ') h₁ h₂ = rightHomologyMap' φ h₁ h₂ +
rightHomologyMap' φ' h₁ h₂ := by
have γ : RightHomologyMapData φ h₁ h₂ := default
have γ' : RightHomologyMapData φ' h₁ h₂ := default
simp only [γ.rightHomologyMap'_eq, γ'.rightHomologyMap'_eq,
(γ.add γ').rightHomologyMap'_eq, RightHomologyMapData.add_φH]
@[simp]
lemma opcyclesMap'_add :
opcyclesMap' (φ + φ') h₁ h₂ = opcyclesMap' φ h₁ h₂ +
opcyclesMap' φ' h₁ h₂ := by
have γ : RightHomologyMapData φ h₁ h₂ := default
have γ' : RightHomologyMapData φ' h₁ h₂ := default
simp only [γ.opcyclesMap'_eq, γ'.opcyclesMap'_eq,
(γ.add γ').opcyclesMap'_eq, RightHomologyMapData.add_φQ]
| @[simp]
lemma rightHomologyMap'_sub :
rightHomologyMap' (φ - φ') h₁ h₂ = rightHomologyMap' φ h₁ h₂ -
rightHomologyMap' φ' h₁ h₂ := by
simp only [sub_eq_add_neg, rightHomologyMap'_add, rightHomologyMap'_neg]
| Mathlib/Algebra/Homology/ShortComplex/Preadditive.lean | 235 | 239 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Johan Commelin, Mario Carneiro
-/
import Mathlib.Algebra.Algebra.Subalgebra.Lattice
import Mathlib.Algebra.Algebra.Tower
import Mathlib.Algebra.GroupWithZero.Divisibility
import Mathlib.Algebra.MonoidAlgebra.Basic
import Mathlib.Algebra.MonoidAlgebra.Support
import Mathlib.Algebra.Regular.Pow
import Mathlib.Data.Finsupp.Antidiagonal
import Mathlib.Order.SymmDiff
/-!
# Multivariate polynomials
This file defines polynomial rings over a base ring (or even semiring),
with variables from a general type `σ` (which could be infinite).
## Important definitions
Let `R` be a commutative ring (or a semiring) and let `σ` be an arbitrary
type. This file creates the type `MvPolynomial σ R`, which mathematicians
might denote $R[X_i : i \in σ]$. It is the type of multivariate
(a.k.a. multivariable) polynomials, with variables
corresponding to the terms in `σ`, and coefficients in `R`.
### Notation
In the definitions below, we use the following notation:
+ `σ : Type*` (indexing the variables)
+ `R : Type*` `[CommSemiring R]` (the coefficients)
+ `s : σ →₀ ℕ`, a function from `σ` to `ℕ` which is zero away from a finite set.
This will give rise to a monomial in `MvPolynomial σ R` which mathematicians might call `X^s`
+ `a : R`
+ `i : σ`, with corresponding monomial `X i`, often denoted `X_i` by mathematicians
+ `p : MvPolynomial σ R`
### Definitions
* `MvPolynomial σ R` : the type of polynomials with variables of type `σ` and coefficients
in the commutative semiring `R`
* `monomial s a` : the monomial which mathematically would be denoted `a * X^s`
* `C a` : the constant polynomial with value `a`
* `X i` : the degree one monomial corresponding to i; mathematically this might be denoted `Xᵢ`.
* `coeff s p` : the coefficient of `s` in `p`.
## Implementation notes
Recall that if `Y` has a zero, then `X →₀ Y` is the type of functions from `X` to `Y` with finite
support, i.e. such that only finitely many elements of `X` get sent to non-zero terms in `Y`.
The definition of `MvPolynomial σ R` is `(σ →₀ ℕ) →₀ R`; here `σ →₀ ℕ` denotes the space of all
monomials in the variables, and the function to `R` sends a monomial to its coefficient in
the polynomial being represented.
## Tags
polynomial, multivariate polynomial, multivariable polynomial
-/
noncomputable section
open Set Function Finsupp AddMonoidAlgebra
open scoped Pointwise
universe u v w x
variable {R : Type u} {S₁ : Type v} {S₂ : Type w} {S₃ : Type x}
/-- Multivariate polynomial, where `σ` is the index set of the variables and
`R` is the coefficient ring -/
def MvPolynomial (σ : Type*) (R : Type*) [CommSemiring R] :=
AddMonoidAlgebra R (σ →₀ ℕ)
namespace MvPolynomial
-- Porting note: because of `MvPolynomial.C` and `MvPolynomial.X` this linter throws
-- tons of warnings in this file, and it's easier to just disable them globally in the file
variable {σ : Type*} {a a' a₁ a₂ : R} {e : ℕ} {n m : σ} {s : σ →₀ ℕ}
section CommSemiring
section Instances
instance decidableEqMvPolynomial [CommSemiring R] [DecidableEq σ] [DecidableEq R] :
DecidableEq (MvPolynomial σ R) :=
Finsupp.instDecidableEq
instance commSemiring [CommSemiring R] : CommSemiring (MvPolynomial σ R) :=
AddMonoidAlgebra.commSemiring
instance inhabited [CommSemiring R] : Inhabited (MvPolynomial σ R) :=
⟨0⟩
instance distribuMulAction [Monoid R] [CommSemiring S₁] [DistribMulAction R S₁] :
DistribMulAction R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.distribMulAction
instance smulZeroClass [CommSemiring S₁] [SMulZeroClass R S₁] :
SMulZeroClass R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.smulZeroClass
instance faithfulSMul [CommSemiring S₁] [SMulZeroClass R S₁] [FaithfulSMul R S₁] :
FaithfulSMul R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.faithfulSMul
instance module [Semiring R] [CommSemiring S₁] [Module R S₁] : Module R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.module
instance isScalarTower [CommSemiring S₂] [SMul R S₁] [SMulZeroClass R S₂] [SMulZeroClass S₁ S₂]
[IsScalarTower R S₁ S₂] : IsScalarTower R S₁ (MvPolynomial σ S₂) :=
AddMonoidAlgebra.isScalarTower
instance smulCommClass [CommSemiring S₂] [SMulZeroClass R S₂] [SMulZeroClass S₁ S₂]
[SMulCommClass R S₁ S₂] : SMulCommClass R S₁ (MvPolynomial σ S₂) :=
AddMonoidAlgebra.smulCommClass
instance isCentralScalar [CommSemiring S₁] [SMulZeroClass R S₁] [SMulZeroClass Rᵐᵒᵖ S₁]
[IsCentralScalar R S₁] : IsCentralScalar R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.isCentralScalar
instance algebra [CommSemiring R] [CommSemiring S₁] [Algebra R S₁] :
Algebra R (MvPolynomial σ S₁) :=
AddMonoidAlgebra.algebra
instance isScalarTower_right [CommSemiring S₁] [DistribSMul R S₁] [IsScalarTower R S₁ S₁] :
IsScalarTower R (MvPolynomial σ S₁) (MvPolynomial σ S₁) :=
AddMonoidAlgebra.isScalarTower_self _
instance smulCommClass_right [CommSemiring S₁] [DistribSMul R S₁] [SMulCommClass R S₁ S₁] :
SMulCommClass R (MvPolynomial σ S₁) (MvPolynomial σ S₁) :=
AddMonoidAlgebra.smulCommClass_self _
/-- If `R` is a subsingleton, then `MvPolynomial σ R` has a unique element -/
instance unique [CommSemiring R] [Subsingleton R] : Unique (MvPolynomial σ R) :=
AddMonoidAlgebra.unique
end Instances
variable [CommSemiring R] [CommSemiring S₁] {p q : MvPolynomial σ R}
/-- `monomial s a` is the monomial with coefficient `a` and exponents given by `s` -/
def monomial (s : σ →₀ ℕ) : R →ₗ[R] MvPolynomial σ R :=
AddMonoidAlgebra.lsingle s
theorem one_def : (1 : MvPolynomial σ R) = monomial 0 1 := rfl
theorem single_eq_monomial (s : σ →₀ ℕ) (a : R) : Finsupp.single s a = monomial s a :=
rfl
theorem mul_def : p * q = p.sum fun m a => q.sum fun n b => monomial (m + n) (a * b) :=
AddMonoidAlgebra.mul_def
/-- `C a` is the constant polynomial with value `a` -/
def C : R →+* MvPolynomial σ R :=
{ singleZeroRingHom with toFun := monomial 0 }
variable (R σ)
@[simp]
theorem algebraMap_eq : algebraMap R (MvPolynomial σ R) = C :=
rfl
variable {R σ}
/-- `X n` is the degree `1` monomial $X_n$. -/
def X (n : σ) : MvPolynomial σ R :=
monomial (Finsupp.single n 1) 1
theorem monomial_left_injective {r : R} (hr : r ≠ 0) :
Function.Injective fun s : σ →₀ ℕ => monomial s r :=
Finsupp.single_left_injective hr
@[simp]
theorem monomial_left_inj {s t : σ →₀ ℕ} {r : R} (hr : r ≠ 0) :
monomial s r = monomial t r ↔ s = t :=
Finsupp.single_left_inj hr
theorem C_apply : (C a : MvPolynomial σ R) = monomial 0 a :=
rfl
@[simp]
theorem C_0 : C 0 = (0 : MvPolynomial σ R) := map_zero _
@[simp]
theorem C_1 : C 1 = (1 : MvPolynomial σ R) :=
rfl
theorem C_mul_monomial : C a * monomial s a' = monomial s (a * a') := by
-- Porting note: this `show` feels like defeq abuse, but I can't find the appropriate lemmas
show AddMonoidAlgebra.single _ _ * AddMonoidAlgebra.single _ _ = AddMonoidAlgebra.single _ _
simp [C_apply, single_mul_single]
@[simp]
theorem C_add : (C (a + a') : MvPolynomial σ R) = C a + C a' :=
Finsupp.single_add _ _ _
@[simp]
theorem C_mul : (C (a * a') : MvPolynomial σ R) = C a * C a' :=
C_mul_monomial.symm
@[simp]
theorem C_pow (a : R) (n : ℕ) : (C (a ^ n) : MvPolynomial σ R) = C a ^ n :=
map_pow _ _ _
theorem C_injective (σ : Type*) (R : Type*) [CommSemiring R] :
Function.Injective (C : R → MvPolynomial σ R) :=
Finsupp.single_injective _
theorem C_surjective {R : Type*} [CommSemiring R] (σ : Type*) [IsEmpty σ] :
Function.Surjective (C : R → MvPolynomial σ R) := by
refine fun p => ⟨p.toFun 0, Finsupp.ext fun a => ?_⟩
simp only [C_apply, ← single_eq_monomial, (Finsupp.ext isEmptyElim (α := σ) : a = 0),
single_eq_same]
rfl
@[simp]
theorem C_inj {σ : Type*} (R : Type*) [CommSemiring R] (r s : R) :
(C r : MvPolynomial σ R) = C s ↔ r = s :=
(C_injective σ R).eq_iff
@[simp] lemma C_eq_zero : (C a : MvPolynomial σ R) = 0 ↔ a = 0 := by rw [← map_zero C, C_inj]
lemma C_ne_zero : (C a : MvPolynomial σ R) ≠ 0 ↔ a ≠ 0 :=
C_eq_zero.ne
instance nontrivial_of_nontrivial (σ : Type*) (R : Type*) [CommSemiring R] [Nontrivial R] :
Nontrivial (MvPolynomial σ R) :=
inferInstanceAs (Nontrivial <| AddMonoidAlgebra R (σ →₀ ℕ))
instance infinite_of_infinite (σ : Type*) (R : Type*) [CommSemiring R] [Infinite R] :
Infinite (MvPolynomial σ R) :=
Infinite.of_injective C (C_injective _ _)
instance infinite_of_nonempty (σ : Type*) (R : Type*) [Nonempty σ] [CommSemiring R]
[Nontrivial R] : Infinite (MvPolynomial σ R) :=
Infinite.of_injective ((fun s : σ →₀ ℕ => monomial s 1) ∘ Finsupp.single (Classical.arbitrary σ))
<| (monomial_left_injective one_ne_zero).comp (Finsupp.single_injective _)
theorem C_eq_coe_nat (n : ℕ) : (C ↑n : MvPolynomial σ R) = n := by
induction n <;> simp [*]
theorem C_mul' : MvPolynomial.C a * p = a • p :=
(Algebra.smul_def a p).symm
theorem smul_eq_C_mul (p : MvPolynomial σ R) (a : R) : a • p = C a * p :=
C_mul'.symm
theorem C_eq_smul_one : (C a : MvPolynomial σ R) = a • (1 : MvPolynomial σ R) := by
rw [← C_mul', mul_one]
theorem smul_monomial {S₁ : Type*} [SMulZeroClass S₁ R] (r : S₁) :
r • monomial s a = monomial s (r • a) :=
Finsupp.smul_single _ _ _
theorem X_injective [Nontrivial R] : Function.Injective (X : σ → MvPolynomial σ R) :=
(monomial_left_injective one_ne_zero).comp (Finsupp.single_left_injective one_ne_zero)
@[simp]
theorem X_inj [Nontrivial R] (m n : σ) : X m = (X n : MvPolynomial σ R) ↔ m = n :=
X_injective.eq_iff
theorem monomial_pow : monomial s a ^ e = monomial (e • s) (a ^ e) :=
AddMonoidAlgebra.single_pow e
@[simp]
theorem monomial_mul {s s' : σ →₀ ℕ} {a b : R} :
monomial s a * monomial s' b = monomial (s + s') (a * b) :=
AddMonoidAlgebra.single_mul_single
variable (σ R)
/-- `fun s ↦ monomial s 1` as a homomorphism. -/
def monomialOneHom : Multiplicative (σ →₀ ℕ) →* MvPolynomial σ R :=
AddMonoidAlgebra.of _ _
variable {σ R}
@[simp]
theorem monomialOneHom_apply : monomialOneHom R σ s = (monomial s 1 : MvPolynomial σ R) :=
rfl
theorem X_pow_eq_monomial : X n ^ e = monomial (Finsupp.single n e) (1 : R) := by
simp [X, monomial_pow]
theorem monomial_add_single : monomial (s + Finsupp.single n e) a = monomial s a * X n ^ e := by
rw [X_pow_eq_monomial, monomial_mul, mul_one]
theorem monomial_single_add : monomial (Finsupp.single n e + s) a = X n ^ e * monomial s a := by
rw [X_pow_eq_monomial, monomial_mul, one_mul]
theorem C_mul_X_pow_eq_monomial {s : σ} {a : R} {n : ℕ} :
C a * X s ^ n = monomial (Finsupp.single s n) a := by
rw [← zero_add (Finsupp.single s n), monomial_add_single, C_apply]
theorem C_mul_X_eq_monomial {s : σ} {a : R} : C a * X s = monomial (Finsupp.single s 1) a := by
rw [← C_mul_X_pow_eq_monomial, pow_one]
@[simp]
theorem monomial_zero {s : σ →₀ ℕ} : monomial s (0 : R) = 0 :=
Finsupp.single_zero _
@[simp]
theorem monomial_zero' : (monomial (0 : σ →₀ ℕ) : R → MvPolynomial σ R) = C :=
rfl
@[simp]
theorem monomial_eq_zero {s : σ →₀ ℕ} {b : R} : monomial s b = 0 ↔ b = 0 :=
Finsupp.single_eq_zero
@[simp]
theorem sum_monomial_eq {A : Type*} [AddCommMonoid A] {u : σ →₀ ℕ} {r : R} {b : (σ →₀ ℕ) → R → A}
(w : b u 0 = 0) : sum (monomial u r) b = b u r :=
Finsupp.sum_single_index w
@[simp]
theorem sum_C {A : Type*} [AddCommMonoid A] {b : (σ →₀ ℕ) → R → A} (w : b 0 0 = 0) :
sum (C a) b = b 0 a :=
sum_monomial_eq w
theorem monomial_sum_one {α : Type*} (s : Finset α) (f : α → σ →₀ ℕ) :
(monomial (∑ i ∈ s, f i) 1 : MvPolynomial σ R) = ∏ i ∈ s, monomial (f i) 1 :=
map_prod (monomialOneHom R σ) (fun i => Multiplicative.ofAdd (f i)) s
theorem monomial_sum_index {α : Type*} (s : Finset α) (f : α → σ →₀ ℕ) (a : R) :
monomial (∑ i ∈ s, f i) a = C a * ∏ i ∈ s, monomial (f i) 1 := by
rw [← monomial_sum_one, C_mul', ← (monomial _).map_smul, smul_eq_mul, mul_one]
theorem monomial_finsupp_sum_index {α β : Type*} [Zero β] (f : α →₀ β) (g : α → β → σ →₀ ℕ)
(a : R) : monomial (f.sum g) a = C a * f.prod fun a b => monomial (g a b) 1 :=
monomial_sum_index _ _ _
theorem monomial_eq_monomial_iff {α : Type*} (a₁ a₂ : α →₀ ℕ) (b₁ b₂ : R) :
monomial a₁ b₁ = monomial a₂ b₂ ↔ a₁ = a₂ ∧ b₁ = b₂ ∨ b₁ = 0 ∧ b₂ = 0 :=
Finsupp.single_eq_single_iff _ _ _ _
theorem monomial_eq : monomial s a = C a * (s.prod fun n e => X n ^ e : MvPolynomial σ R) := by
simp only [X_pow_eq_monomial, ← monomial_finsupp_sum_index, Finsupp.sum_single]
@[simp]
lemma prod_X_pow_eq_monomial : ∏ x ∈ s.support, X x ^ s x = monomial s (1 : R) := by
simp only [monomial_eq, map_one, one_mul, Finsupp.prod]
@[elab_as_elim]
theorem induction_on_monomial {motive : MvPolynomial σ R → Prop}
(C : ∀ a, motive (C a))
(mul_X : ∀ p n, motive p → motive (p * X n)) : ∀ s a, motive (monomial s a) := by
intro s a
apply @Finsupp.induction σ ℕ _ _ s
· show motive (monomial 0 a)
exact C a
· intro n e p _hpn _he ih
have : ∀ e : ℕ, motive (monomial p a * X n ^ e) := by
intro e
induction e with
| zero => simp [ih]
| succ e e_ih => simp [ih, pow_succ, (mul_assoc _ _ _).symm, mul_X, e_ih]
simp [add_comm, monomial_add_single, this]
/-- Analog of `Polynomial.induction_on'`.
To prove something about mv_polynomials,
it suffices to show the condition is closed under taking sums,
and it holds for monomials. -/
@[elab_as_elim]
theorem induction_on' {P : MvPolynomial σ R → Prop} (p : MvPolynomial σ R)
(monomial : ∀ (u : σ →₀ ℕ) (a : R), P (monomial u a))
(add : ∀ p q : MvPolynomial σ R, P p → P q → P (p + q)) : P p :=
Finsupp.induction p
(suffices P (MvPolynomial.monomial 0 0) by rwa [monomial_zero] at this
show P (MvPolynomial.monomial 0 0) from monomial 0 0)
fun _ _ _ _ha _hb hPf => add _ _ (monomial _ _) hPf
/--
Similar to `MvPolynomial.induction_on` but only a weak form of `h_add` is required.
In particular, this version only requires us to show
that `motive` is closed under addition of nontrivial monomials not present in the support.
-/
@[elab_as_elim]
theorem monomial_add_induction_on {motive : MvPolynomial σ R → Prop} (p : MvPolynomial σ R)
(C : ∀ a, motive (C a))
(monomial_add :
∀ (a : σ →₀ ℕ) (b : R) (f : MvPolynomial σ R),
a ∉ f.support → b ≠ 0 → motive f → motive ((monomial a b) + f)) :
motive p :=
Finsupp.induction p (C_0.rec <| C 0) monomial_add
@[deprecated (since := "2025-03-11")]
alias induction_on''' := monomial_add_induction_on
/--
Similar to `MvPolynomial.induction_on` but only a yet weaker form of `h_add` is required.
In particular, this version only requires us to show
that `motive` is closed under addition of monomials not present in the support
for which `motive` is already known to hold.
-/
theorem induction_on'' {motive : MvPolynomial σ R → Prop} (p : MvPolynomial σ R)
(C : ∀ a, motive (C a))
(monomial_add :
∀ (a : σ →₀ ℕ) (b : R) (f : MvPolynomial σ R),
a ∉ f.support → b ≠ 0 → motive f → motive (monomial a b) →
motive ((monomial a b) + f))
(mul_X : ∀ (p : MvPolynomial σ R) (n : σ), motive p → motive (p * MvPolynomial.X n)) :
motive p :=
monomial_add_induction_on p C fun a b f ha hb hf =>
monomial_add a b f ha hb hf <| induction_on_monomial C mul_X a b
/--
Analog of `Polynomial.induction_on`.
If a property holds for any constant polynomial
and is preserved under addition and multiplication by variables
then it holds for all multivariate polynomials.
-/
@[recursor 5]
theorem induction_on {motive : MvPolynomial σ R → Prop} (p : MvPolynomial σ R)
(C : ∀ a, motive (C a))
(add : ∀ p q, motive p → motive q → motive (p + q))
(mul_X : ∀ p n, motive p → motive (p * X n)) : motive p :=
induction_on'' p C (fun a b f _ha _hb hf hm => add (monomial a b) f hm hf) mul_X
theorem ringHom_ext {A : Type*} [Semiring A] {f g : MvPolynomial σ R →+* A}
(hC : ∀ r, f (C r) = g (C r)) (hX : ∀ i, f (X i) = g (X i)) : f = g := by
refine AddMonoidAlgebra.ringHom_ext' ?_ ?_
-- Porting note (https://github.com/leanprover-community/mathlib4/issues/11041): this has high priority, but Lean still chooses `RingHom.ext`, why?
-- probably because of the type synonym
· ext x
exact hC _
· apply Finsupp.mulHom_ext'; intros x
-- Porting note (https://github.com/leanprover-community/mathlib4/issues/11041): `Finsupp.mulHom_ext'` needs to have increased priority
apply MonoidHom.ext_mnat
exact hX _
/-- See note [partially-applied ext lemmas]. -/
@[ext 1100]
theorem ringHom_ext' {A : Type*} [Semiring A] {f g : MvPolynomial σ R →+* A}
(hC : f.comp C = g.comp C) (hX : ∀ i, f (X i) = g (X i)) : f = g :=
ringHom_ext (RingHom.ext_iff.1 hC) hX
theorem hom_eq_hom [Semiring S₂] (f g : MvPolynomial σ R →+* S₂) (hC : f.comp C = g.comp C)
(hX : ∀ n : σ, f (X n) = g (X n)) (p : MvPolynomial σ R) : f p = g p :=
RingHom.congr_fun (ringHom_ext' hC hX) p
theorem is_id (f : MvPolynomial σ R →+* MvPolynomial σ R) (hC : f.comp C = C)
(hX : ∀ n : σ, f (X n) = X n) (p : MvPolynomial σ R) : f p = p :=
hom_eq_hom f (RingHom.id _) hC hX p
@[ext 1100]
theorem algHom_ext' {A B : Type*} [CommSemiring A] [CommSemiring B] [Algebra R A] [Algebra R B]
{f g : MvPolynomial σ A →ₐ[R] B}
(h₁ :
f.comp (IsScalarTower.toAlgHom R A (MvPolynomial σ A)) =
g.comp (IsScalarTower.toAlgHom R A (MvPolynomial σ A)))
(h₂ : ∀ i, f (X i) = g (X i)) : f = g :=
AlgHom.coe_ringHom_injective (MvPolynomial.ringHom_ext' (congr_arg AlgHom.toRingHom h₁) h₂)
@[ext 1200]
theorem algHom_ext {A : Type*} [Semiring A] [Algebra R A] {f g : MvPolynomial σ R →ₐ[R] A}
(hf : ∀ i : σ, f (X i) = g (X i)) : f = g :=
AddMonoidAlgebra.algHom_ext' (mulHom_ext' fun X : σ => MonoidHom.ext_mnat (hf X))
@[simp]
theorem algHom_C {A : Type*} [Semiring A] [Algebra R A] (f : MvPolynomial σ R →ₐ[R] A) (r : R) :
f (C r) = algebraMap R A r :=
f.commutes r
@[simp]
theorem adjoin_range_X : Algebra.adjoin R (range (X : σ → MvPolynomial σ R)) = ⊤ := by
set S := Algebra.adjoin R (range (X : σ → MvPolynomial σ R))
refine top_unique fun p hp => ?_; clear hp
induction p using MvPolynomial.induction_on with
| C => exact S.algebraMap_mem _
| add p q hp hq => exact S.add_mem hp hq
| mul_X p i hp => exact S.mul_mem hp (Algebra.subset_adjoin <| mem_range_self _)
@[ext]
theorem linearMap_ext {M : Type*} [AddCommMonoid M] [Module R M] {f g : MvPolynomial σ R →ₗ[R] M}
(h : ∀ s, f ∘ₗ monomial s = g ∘ₗ monomial s) : f = g :=
Finsupp.lhom_ext' h
section Support
/-- The finite set of all `m : σ →₀ ℕ` such that `X^m` has a non-zero coefficient. -/
def support (p : MvPolynomial σ R) : Finset (σ →₀ ℕ) :=
Finsupp.support p
theorem finsupp_support_eq_support (p : MvPolynomial σ R) : Finsupp.support p = p.support :=
rfl
theorem support_monomial [h : Decidable (a = 0)] :
(monomial s a).support = if a = 0 then ∅ else {s} := by
rw [← Subsingleton.elim (Classical.decEq R a 0) h]
rfl
theorem support_monomial_subset : (monomial s a).support ⊆ {s} :=
support_single_subset
theorem support_add [DecidableEq σ] : (p + q).support ⊆ p.support ∪ q.support :=
Finsupp.support_add
theorem support_X [Nontrivial R] : (X n : MvPolynomial σ R).support = {Finsupp.single n 1} := by
classical rw [X, support_monomial, if_neg]; exact one_ne_zero
theorem support_X_pow [Nontrivial R] (s : σ) (n : ℕ) :
(X s ^ n : MvPolynomial σ R).support = {Finsupp.single s n} := by
classical
rw [X_pow_eq_monomial, support_monomial, if_neg (one_ne_zero' R)]
@[simp]
theorem support_zero : (0 : MvPolynomial σ R).support = ∅ :=
rfl
theorem support_smul {S₁ : Type*} [SMulZeroClass S₁ R] {a : S₁} {f : MvPolynomial σ R} :
(a • f).support ⊆ f.support :=
Finsupp.support_smul
theorem support_sum {α : Type*} [DecidableEq σ] {s : Finset α} {f : α → MvPolynomial σ R} :
(∑ x ∈ s, f x).support ⊆ s.biUnion fun x => (f x).support :=
Finsupp.support_finset_sum
end Support
section Coeff
/-- The coefficient of the monomial `m` in the multi-variable polynomial `p`. -/
def coeff (m : σ →₀ ℕ) (p : MvPolynomial σ R) : R :=
@DFunLike.coe ((σ →₀ ℕ) →₀ R) _ _ _ p m
@[simp]
theorem mem_support_iff {p : MvPolynomial σ R} {m : σ →₀ ℕ} : m ∈ p.support ↔ p.coeff m ≠ 0 := by
simp [support, coeff]
theorem not_mem_support_iff {p : MvPolynomial σ R} {m : σ →₀ ℕ} : m ∉ p.support ↔ p.coeff m = 0 :=
by simp
theorem sum_def {A} [AddCommMonoid A] {p : MvPolynomial σ R} {b : (σ →₀ ℕ) → R → A} :
p.sum b = ∑ m ∈ p.support, b m (p.coeff m) := by simp [support, Finsupp.sum, coeff]
theorem support_mul [DecidableEq σ] (p q : MvPolynomial σ R) :
(p * q).support ⊆ p.support + q.support :=
AddMonoidAlgebra.support_mul p q
@[ext]
theorem ext (p q : MvPolynomial σ R) : (∀ m, coeff m p = coeff m q) → p = q :=
Finsupp.ext
@[simp]
theorem coeff_add (m : σ →₀ ℕ) (p q : MvPolynomial σ R) : coeff m (p + q) = coeff m p + coeff m q :=
add_apply p q m
@[simp]
theorem coeff_smul {S₁ : Type*} [SMulZeroClass S₁ R] (m : σ →₀ ℕ) (C : S₁) (p : MvPolynomial σ R) :
coeff m (C • p) = C • coeff m p :=
smul_apply C p m
@[simp]
theorem coeff_zero (m : σ →₀ ℕ) : coeff m (0 : MvPolynomial σ R) = 0 :=
rfl
@[simp]
theorem coeff_zero_X (i : σ) : coeff 0 (X i : MvPolynomial σ R) = 0 :=
single_eq_of_ne fun h => by cases Finsupp.single_eq_zero.1 h
/-- `MvPolynomial.coeff m` but promoted to an `AddMonoidHom`. -/
@[simps]
def coeffAddMonoidHom (m : σ →₀ ℕ) : MvPolynomial σ R →+ R where
toFun := coeff m
map_zero' := coeff_zero m
map_add' := coeff_add m
variable (R) in
/-- `MvPolynomial.coeff m` but promoted to a `LinearMap`. -/
@[simps]
def lcoeff (m : σ →₀ ℕ) : MvPolynomial σ R →ₗ[R] R where
toFun := coeff m
map_add' := coeff_add m
map_smul' := coeff_smul m
theorem coeff_sum {X : Type*} (s : Finset X) (f : X → MvPolynomial σ R) (m : σ →₀ ℕ) :
coeff m (∑ x ∈ s, f x) = ∑ x ∈ s, coeff m (f x) :=
map_sum (@coeffAddMonoidHom R σ _ _) _ s
theorem monic_monomial_eq (m) :
monomial m (1 : R) = (m.prod fun n e => X n ^ e : MvPolynomial σ R) := by simp [monomial_eq]
@[simp]
theorem coeff_monomial [DecidableEq σ] (m n) (a) :
coeff m (monomial n a : MvPolynomial σ R) = if n = m then a else 0 :=
Finsupp.single_apply
@[simp]
theorem coeff_C [DecidableEq σ] (m) (a) :
coeff m (C a : MvPolynomial σ R) = if 0 = m then a else 0 :=
Finsupp.single_apply
lemma eq_C_of_isEmpty [IsEmpty σ] (p : MvPolynomial σ R) :
p = C (p.coeff 0) := by
obtain ⟨x, rfl⟩ := C_surjective σ p
simp
theorem coeff_one [DecidableEq σ] (m) : coeff m (1 : MvPolynomial σ R) = if 0 = m then 1 else 0 :=
coeff_C m 1
@[simp]
theorem coeff_zero_C (a) : coeff 0 (C a : MvPolynomial σ R) = a :=
single_eq_same
@[simp]
theorem coeff_zero_one : coeff 0 (1 : MvPolynomial σ R) = 1 :=
coeff_zero_C 1
theorem coeff_X_pow [DecidableEq σ] (i : σ) (m) (k : ℕ) :
coeff m (X i ^ k : MvPolynomial σ R) = if Finsupp.single i k = m then 1 else 0 := by
have := coeff_monomial m (Finsupp.single i k) (1 : R)
rwa [@monomial_eq _ _ (1 : R) (Finsupp.single i k) _, C_1, one_mul, Finsupp.prod_single_index]
at this
exact pow_zero _
theorem coeff_X' [DecidableEq σ] (i : σ) (m) :
coeff m (X i : MvPolynomial σ R) = if Finsupp.single i 1 = m then 1 else 0 := by
rw [← coeff_X_pow, pow_one]
@[simp]
theorem coeff_X (i : σ) : coeff (Finsupp.single i 1) (X i : MvPolynomial σ R) = 1 := by
classical rw [coeff_X', if_pos rfl]
@[simp]
theorem coeff_C_mul (m) (a : R) (p : MvPolynomial σ R) : coeff m (C a * p) = a * coeff m p := by
classical
rw [mul_def, sum_C]
· simp +contextual [sum_def, coeff_sum]
simp
theorem coeff_mul [DecidableEq σ] (p q : MvPolynomial σ R) (n : σ →₀ ℕ) :
coeff n (p * q) = ∑ x ∈ Finset.antidiagonal n, coeff x.1 p * coeff x.2 q :=
AddMonoidAlgebra.mul_apply_antidiagonal p q _ _ Finset.mem_antidiagonal
@[simp]
theorem coeff_mul_monomial (m) (s : σ →₀ ℕ) (r : R) (p : MvPolynomial σ R) :
coeff (m + s) (p * monomial s r) = coeff m p * r :=
AddMonoidAlgebra.mul_single_apply_aux p _ _ _ _ fun _a _ => add_left_inj _
@[simp]
theorem coeff_monomial_mul (m) (s : σ →₀ ℕ) (r : R) (p : MvPolynomial σ R) :
coeff (s + m) (monomial s r * p) = r * coeff m p :=
AddMonoidAlgebra.single_mul_apply_aux p _ _ _ _ fun _a _ => add_right_inj _
@[simp]
theorem coeff_mul_X (m) (s : σ) (p : MvPolynomial σ R) :
coeff (m + Finsupp.single s 1) (p * X s) = coeff m p :=
(coeff_mul_monomial _ _ _ _).trans (mul_one _)
@[simp]
theorem coeff_X_mul (m) (s : σ) (p : MvPolynomial σ R) :
coeff (Finsupp.single s 1 + m) (X s * p) = coeff m p :=
(coeff_monomial_mul _ _ _ _).trans (one_mul _)
| lemma coeff_single_X_pow [DecidableEq σ] (s s' : σ) (n n' : ℕ) :
(X (R := R) s ^ n).coeff (Finsupp.single s' n')
| Mathlib/Algebra/MvPolynomial/Basic.lean | 660 | 661 |
/-
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.Topology.PartialHomeomorph
import Mathlib.Topology.Connected.LocPathConnected
/-!
# Charted spaces
A smooth manifold is a topological space `M` locally modelled on a euclidean space (or a euclidean
half-space for manifolds with boundaries, or an infinite dimensional vector space for more general
notions of manifolds), i.e., the manifold is covered by open subsets on which there are local
homeomorphisms (the charts) going to a model space `H`, and the changes of charts should be smooth
maps.
In this file, we introduce a general framework describing these notions, where the model space is an
arbitrary topological space. We avoid the word *manifold*, which should be reserved for the
situation where the model space is a (subset of a) vector space, and use the terminology
*charted space* instead.
If the changes of charts satisfy some additional property (for instance if they are smooth), then
`M` inherits additional structure (it makes sense to talk about smooth manifolds). There are
therefore two different ingredients in a charted space:
* the set of charts, which is data
* the fact that changes of charts belong to some group (in fact groupoid), which is additional Prop.
We separate these two parts in the definition: the charted space structure is just the set of
charts, and then the different smoothness requirements (smooth manifold, orientable manifold,
contact manifold, and so on) are additional properties of these charts. These properties are
formalized through the notion of structure groupoid, i.e., a set of partial homeomorphisms stable
under composition and inverse, to which the change of coordinates should belong.
## Main definitions
* `StructureGroupoid H` : a subset of partial homeomorphisms of `H` stable under composition,
inverse and restriction (ex: partial diffeomorphisms).
* `continuousGroupoid H` : the groupoid of all partial homeomorphisms of `H`.
* `ChartedSpace H M` : charted space structure on `M` modelled on `H`, given by an atlas of
partial homeomorphisms from `M` to `H` whose sources cover `M`. This is a type class.
* `HasGroupoid M G` : when `G` is a structure groupoid on `H` and `M` is a charted space
modelled on `H`, require that all coordinate changes belong to `G`. This is a type class.
* `atlas H M` : when `M` is a charted space modelled on `H`, the atlas of this charted
space structure, i.e., the set of charts.
* `G.maximalAtlas M` : when `M` is a charted space modelled on `H` and admitting `G` as a
structure groupoid, one can consider all the partial homeomorphisms from `M` to `H` such that
changing coordinate from any chart to them belongs to `G`. This is a larger atlas, called the
maximal atlas (for the groupoid `G`).
* `Structomorph G M M'` : the type of diffeomorphisms between the charted spaces `M` and `M'` for
the groupoid `G`. We avoid the word diffeomorphism, keeping it for the smooth category.
As a basic example, we give the instance
`instance chartedSpaceSelf (H : Type*) [TopologicalSpace H] : ChartedSpace H H`
saying that a topological space is a charted space over itself, with the identity as unique chart.
This charted space structure is compatible with any groupoid.
Additional useful definitions:
* `Pregroupoid H` : a subset of partial maps of `H` stable under composition and
restriction, but not inverse (ex: smooth maps)
* `Pregroupoid.groupoid` : construct a groupoid from a pregroupoid, by requiring that a map and
its inverse both belong to the pregroupoid (ex: construct diffeos from smooth maps)
* `chartAt H x` is a preferred chart at `x : M` when `M` has a charted space structure modelled on
`H`.
* `G.compatible he he'` states that, for any two charts `e` and `e'` in the atlas, the composition
of `e.symm` and `e'` belongs to the groupoid `G` when `M` admits `G` as a structure groupoid.
* `G.compatible_of_mem_maximalAtlas he he'` states that, for any two charts `e` and `e'` in the
maximal atlas associated to the groupoid `G`, the composition of `e.symm` and `e'` belongs to the
`G` if `M` admits `G` as a structure groupoid.
* `ChartedSpaceCore.toChartedSpace`: consider a space without a topology, but endowed with a set
of charts (which are partial equivs) for which the change of coordinates are partial homeos.
Then one can construct a topology on the space for which the charts become partial homeos,
defining a genuine charted space structure.
## Implementation notes
The atlas in a charted space is *not* a maximal atlas in general: the notion of maximality depends
on the groupoid one considers, and changing groupoids changes the maximal atlas. With the current
formalization, it makes sense first to choose the atlas, and then to ask whether this precise atlas
defines a smooth manifold, an orientable manifold, and so on. A consequence is that structomorphisms
between `M` and `M'` do *not* induce a bijection between the atlases of `M` and `M'`: the
definition is only that, read in charts, the structomorphism locally belongs to the groupoid under
consideration. (This is equivalent to inducing a bijection between elements of the maximal atlas).
A consequence is that the invariance under structomorphisms of properties defined in terms of the
atlas is not obvious in general, and could require some work in theory (amounting to the fact
that these properties only depend on the maximal atlas, for instance). In practice, this does not
create any real difficulty.
We use the letter `H` for the model space thinking of the case of manifolds with boundary, where the
model space is a half space.
Manifolds are sometimes defined as topological spaces with an atlas of local diffeomorphisms, and
sometimes as spaces with an atlas from which a topology is deduced. We use the former approach:
otherwise, there would be an instance from manifolds to topological spaces, which means that any
instance search for topological spaces would try to find manifold structures involving a yet
unknown model space, leading to problems. However, we also introduce the latter approach,
through a structure `ChartedSpaceCore` making it possible to construct a topology out of a set of
partial equivs with compatibility conditions (but we do not register it as an instance).
In the definition of a charted space, the model space is written as an explicit parameter as there
can be several model spaces for a given topological space. For instance, a complex manifold
(modelled over `ℂ^n`) will also be seen sometimes as a real manifold modelled over `ℝ^(2n)`.
## Notations
In the locale `Manifold`, we denote the composition of partial homeomorphisms with `≫ₕ`, and the
composition of partial equivs with `≫`.
-/
noncomputable section
open TopologicalSpace Topology
universe u
variable {H : Type u} {H' : Type*} {M : Type*} {M' : Type*} {M'' : Type*}
/- Notational shortcut for the composition of partial homeomorphisms and partial equivs, i.e.,
`PartialHomeomorph.trans` and `PartialEquiv.trans`.
Note that, as is usual for equivs, the composition is from left to right, hence the direction of
the arrow. -/
@[inherit_doc] scoped[Manifold] infixr:100 " ≫ₕ " => PartialHomeomorph.trans
@[inherit_doc] scoped[Manifold] infixr:100 " ≫ " => PartialEquiv.trans
open Set PartialHomeomorph Manifold -- Porting note: Added `Manifold`
/-! ### Structure groupoids -/
section Groupoid
/-! One could add to the definition of a structure groupoid the fact that the restriction of an
element of the groupoid to any open set still belongs to the groupoid.
(This is in Kobayashi-Nomizu.)
I am not sure I want this, for instance on `H × E` where `E` is a vector space, and the groupoid is
made of functions respecting the fibers and linear in the fibers (so that a charted space over this
groupoid is naturally a vector bundle) I prefer that the members of the groupoid are always
defined on sets of the form `s × E`. There is a typeclass `ClosedUnderRestriction` for groupoids
which have the restriction property.
The only nontrivial requirement is locality: if a partial homeomorphism belongs to the groupoid
around each point in its domain of definition, then it belongs to the groupoid. Without this
requirement, the composition of structomorphisms does not have to be a structomorphism. Note that
this implies that a partial homeomorphism with empty source belongs to any structure groupoid, as
it trivially satisfies this condition.
There is also a technical point, related to the fact that a partial homeomorphism is by definition a
global map which is a homeomorphism when restricted to its source subset (and its values outside
of the source are not relevant). Therefore, we also require that being a member of the groupoid only
depends on the values on the source.
We use primes in the structure names as we will reformulate them below (without primes) using a
`Membership` instance, writing `e ∈ G` instead of `e ∈ G.members`.
-/
/-- A structure groupoid is a set of partial homeomorphisms of a topological space stable under
composition and inverse. They appear in the definition of the smoothness class of a manifold. -/
structure StructureGroupoid (H : Type u) [TopologicalSpace H] where
/-- Members of the structure groupoid are partial homeomorphisms. -/
members : Set (PartialHomeomorph H H)
/-- Structure groupoids are stable under composition. -/
trans' : ∀ e e' : PartialHomeomorph H H, e ∈ members → e' ∈ members → e ≫ₕ e' ∈ members
/-- Structure groupoids are stable under inverse. -/
symm' : ∀ e : PartialHomeomorph H H, e ∈ members → e.symm ∈ members
/-- The identity morphism lies in the structure groupoid. -/
id_mem' : PartialHomeomorph.refl H ∈ members
/-- Let `e` be a partial homeomorphism. If for every `x ∈ e.source`, the restriction of e to some
open set around `x` lies in the groupoid, then `e` lies in the groupoid. -/
locality' : ∀ e : PartialHomeomorph H H,
(∀ x ∈ e.source, ∃ s, IsOpen s ∧ x ∈ s ∧ e.restr s ∈ members) → e ∈ members
/-- Membership in a structure groupoid respects the equivalence of partial homeomorphisms. -/
mem_of_eqOnSource' : ∀ e e' : PartialHomeomorph H H, e ∈ members → e' ≈ e → e' ∈ members
variable [TopologicalSpace H]
instance : Membership (PartialHomeomorph H H) (StructureGroupoid H) :=
⟨fun (G : StructureGroupoid H) (e : PartialHomeomorph H H) ↦ e ∈ G.members⟩
instance (H : Type u) [TopologicalSpace H] :
SetLike (StructureGroupoid H) (PartialHomeomorph H H) where
coe s := s.members
coe_injective' N O h := by cases N; cases O; congr
instance : Min (StructureGroupoid H) :=
⟨fun G G' => StructureGroupoid.mk
(members := G.members ∩ G'.members)
(trans' := fun e e' he he' =>
⟨G.trans' e e' he.left he'.left, G'.trans' e e' he.right he'.right⟩)
(symm' := fun e he => ⟨G.symm' e he.left, G'.symm' e he.right⟩)
(id_mem' := ⟨G.id_mem', G'.id_mem'⟩)
(locality' := by
intro e hx
apply (mem_inter_iff e G.members G'.members).mpr
refine And.intro (G.locality' e ?_) (G'.locality' e ?_)
all_goals
intro x hex
rcases hx x hex with ⟨s, hs⟩
use s
refine And.intro hs.left (And.intro hs.right.left ?_)
· exact hs.right.right.left
· exact hs.right.right.right)
(mem_of_eqOnSource' := fun e e' he hee' =>
⟨G.mem_of_eqOnSource' e e' he.left hee', G'.mem_of_eqOnSource' e e' he.right hee'⟩)⟩
instance : InfSet (StructureGroupoid H) :=
⟨fun S => StructureGroupoid.mk
(members := ⋂ s ∈ S, s.members)
(trans' := by
simp only [mem_iInter]
intro e e' he he' i hi
exact i.trans' e e' (he i hi) (he' i hi))
(symm' := by
simp only [mem_iInter]
intro e he i hi
exact i.symm' e (he i hi))
(id_mem' := by
simp only [mem_iInter]
intro i _
exact i.id_mem')
(locality' := by
simp only [mem_iInter]
intro e he i hi
refine i.locality' e ?_
intro x hex
rcases he x hex with ⟨s, hs⟩
exact ⟨s, ⟨hs.left, ⟨hs.right.left, hs.right.right i hi⟩⟩⟩)
(mem_of_eqOnSource' := by
simp only [mem_iInter]
intro e e' he he'e
exact fun i hi => i.mem_of_eqOnSource' e e' (he i hi) he'e)⟩
theorem StructureGroupoid.trans (G : StructureGroupoid H) {e e' : PartialHomeomorph H H}
(he : e ∈ G) (he' : e' ∈ G) : e ≫ₕ e' ∈ G :=
G.trans' e e' he he'
theorem StructureGroupoid.symm (G : StructureGroupoid H) {e : PartialHomeomorph H H} (he : e ∈ G) :
e.symm ∈ G :=
G.symm' e he
theorem StructureGroupoid.id_mem (G : StructureGroupoid H) : PartialHomeomorph.refl H ∈ G :=
G.id_mem'
theorem StructureGroupoid.locality (G : StructureGroupoid H) {e : PartialHomeomorph H H}
(h : ∀ x ∈ e.source, ∃ s, IsOpen s ∧ x ∈ s ∧ e.restr s ∈ G) : e ∈ G :=
G.locality' e h
theorem StructureGroupoid.mem_of_eqOnSource (G : StructureGroupoid H) {e e' : PartialHomeomorph H H}
(he : e ∈ G) (h : e' ≈ e) : e' ∈ G :=
G.mem_of_eqOnSource' e e' he h
theorem StructureGroupoid.mem_iff_of_eqOnSource {G : StructureGroupoid H}
{e e' : PartialHomeomorph H H} (h : e ≈ e') : e ∈ G ↔ e' ∈ G :=
⟨fun he ↦ G.mem_of_eqOnSource he (Setoid.symm h), fun he' ↦ G.mem_of_eqOnSource he' h⟩
/-- Partial order on the set of groupoids, given by inclusion of the members of the groupoid. -/
instance StructureGroupoid.partialOrder : PartialOrder (StructureGroupoid H) :=
PartialOrder.lift StructureGroupoid.members fun a b h ↦ by
cases a
cases b
dsimp at h
induction h
rfl
theorem StructureGroupoid.le_iff {G₁ G₂ : StructureGroupoid H} : G₁ ≤ G₂ ↔ ∀ e, e ∈ G₁ → e ∈ G₂ :=
Iff.rfl
/-- The trivial groupoid, containing only the identity (and maps with empty source, as this is
necessary from the definition). -/
def idGroupoid (H : Type u) [TopologicalSpace H] : StructureGroupoid H where
members := {PartialHomeomorph.refl H} ∪ { e : PartialHomeomorph H H | e.source = ∅ }
trans' e e' he he' := by
rcases he with he | he
· simpa only [mem_singleton_iff.1 he, refl_trans]
· have : (e ≫ₕ e').source ⊆ e.source := sep_subset _ _
rw [he] at this
have : e ≫ₕ e' ∈ { e : PartialHomeomorph H H | e.source = ∅ } := eq_bot_iff.2 this
exact (mem_union _ _ _).2 (Or.inr this)
symm' e he := by
rcases (mem_union _ _ _).1 he with E | E
· simp [mem_singleton_iff.mp E]
· right
simpa only [e.toPartialEquiv.image_source_eq_target.symm, mfld_simps] using E
id_mem' := mem_union_left _ rfl
locality' e he := by
rcases e.source.eq_empty_or_nonempty with h | h
· right
exact h
· left
rcases h with ⟨x, hx⟩
rcases he x hx with ⟨s, open_s, xs, hs⟩
have x's : x ∈ (e.restr s).source := by
rw [restr_source, open_s.interior_eq]
exact ⟨hx, xs⟩
rcases hs with hs | hs
· replace hs : PartialHomeomorph.restr e s = PartialHomeomorph.refl H := by
simpa only using hs
have : (e.restr s).source = univ := by
rw [hs]
simp
have : e.toPartialEquiv.source ∩ interior s = univ := this
have : univ ⊆ interior s := by
rw [← this]
exact inter_subset_right
have : s = univ := by rwa [open_s.interior_eq, univ_subset_iff] at this
simpa only [this, restr_univ] using hs
· exfalso
rw [mem_setOf_eq] at hs
rwa [hs] at x's
mem_of_eqOnSource' e e' he he'e := by
rcases he with he | he
· left
have : e = e' := by
refine eq_of_eqOnSource_univ (Setoid.symm he'e) ?_ ?_ <;>
rw [Set.mem_singleton_iff.1 he] <;> rfl
rwa [← this]
· right
have he : e.toPartialEquiv.source = ∅ := he
rwa [Set.mem_setOf_eq, EqOnSource.source_eq he'e]
/-- Every structure groupoid contains the identity groupoid. -/
instance instStructureGroupoidOrderBot : OrderBot (StructureGroupoid H) where
bot := idGroupoid H
bot_le := by
intro u f hf
have hf : f ∈ {PartialHomeomorph.refl H} ∪ { e : PartialHomeomorph H H | e.source = ∅ } := hf
simp only [singleton_union, mem_setOf_eq, mem_insert_iff] at hf
rcases hf with hf | hf
· rw [hf]
apply u.id_mem
· apply u.locality
intro x hx
rw [hf, mem_empty_iff_false] at hx
exact hx.elim
instance : Inhabited (StructureGroupoid H) := ⟨idGroupoid H⟩
/-- To construct a groupoid, one may consider classes of partial homeomorphisms such that
both the function and its inverse have some property. If this property is stable under composition,
one gets a groupoid. `Pregroupoid` bundles the properties needed for this construction, with the
groupoid of smooth functions with smooth inverses as an application. -/
structure Pregroupoid (H : Type*) [TopologicalSpace H] where
/-- Property describing membership in this groupoid: the pregroupoid "contains"
all functions `H → H` having the pregroupoid property on some `s : Set H` -/
property : (H → H) → Set H → Prop
/-- The pregroupoid property is stable under composition -/
comp : ∀ {f g u v}, property f u → property g v →
IsOpen u → IsOpen v → IsOpen (u ∩ f ⁻¹' v) → property (g ∘ f) (u ∩ f ⁻¹' v)
/-- Pregroupoids contain the identity map (on `univ`) -/
id_mem : property id univ
/-- The pregroupoid property is "local", in the sense that `f` has the pregroupoid property on `u`
iff its restriction to each open subset of `u` has it -/
locality :
∀ {f u}, IsOpen u → (∀ x ∈ u, ∃ v, IsOpen v ∧ x ∈ v ∧ property f (u ∩ v)) → property f u
/-- If `f = g` on `u` and `property f u`, then `property g u` -/
congr : ∀ {f g : H → H} {u}, IsOpen u → (∀ x ∈ u, g x = f x) → property f u → property g u
/-- Construct a groupoid of partial homeos for which the map and its inverse have some property,
from a pregroupoid asserting that this property is stable under composition. -/
def Pregroupoid.groupoid (PG : Pregroupoid H) : StructureGroupoid H where
members := { e : PartialHomeomorph H H | PG.property e e.source ∧ PG.property e.symm e.target }
trans' e e' he he' := by
constructor
· apply PG.comp he.1 he'.1 e.open_source e'.open_source
apply e.continuousOn_toFun.isOpen_inter_preimage e.open_source e'.open_source
· apply PG.comp he'.2 he.2 e'.open_target e.open_target
apply e'.continuousOn_invFun.isOpen_inter_preimage e'.open_target e.open_target
symm' _ he := ⟨he.2, he.1⟩
id_mem' := ⟨PG.id_mem, PG.id_mem⟩
locality' e he := by
constructor
· refine PG.locality e.open_source fun x xu ↦ ?_
rcases he x xu with ⟨s, s_open, xs, hs⟩
refine ⟨s, s_open, xs, ?_⟩
convert hs.1 using 1
dsimp [PartialHomeomorph.restr]
rw [s_open.interior_eq]
· refine PG.locality e.open_target fun x xu ↦ ?_
rcases he (e.symm x) (e.map_target xu) with ⟨s, s_open, xs, hs⟩
refine ⟨e.target ∩ e.symm ⁻¹' s, ?_, ⟨xu, xs⟩, ?_⟩
· exact ContinuousOn.isOpen_inter_preimage e.continuousOn_invFun e.open_target s_open
· rw [← inter_assoc, inter_self]
convert hs.2 using 1
dsimp [PartialHomeomorph.restr]
rw [s_open.interior_eq]
mem_of_eqOnSource' e e' he ee' := by
constructor
· apply PG.congr e'.open_source ee'.2
simp only [ee'.1, he.1]
· have A := EqOnSource.symm' ee'
apply PG.congr e'.symm.open_source A.2
-- Porting note: was
-- convert he.2
-- rw [A.1]
-- rfl
rw [A.1, symm_toPartialEquiv, PartialEquiv.symm_source]
exact he.2
theorem mem_groupoid_of_pregroupoid {PG : Pregroupoid H} {e : PartialHomeomorph H H} :
e ∈ PG.groupoid ↔ PG.property e e.source ∧ PG.property e.symm e.target :=
Iff.rfl
theorem groupoid_of_pregroupoid_le (PG₁ PG₂ : Pregroupoid H)
(h : ∀ f s, PG₁.property f s → PG₂.property f s) : PG₁.groupoid ≤ PG₂.groupoid := by
refine StructureGroupoid.le_iff.2 fun e he ↦ ?_
rw [mem_groupoid_of_pregroupoid] at he ⊢
exact ⟨h _ _ he.1, h _ _ he.2⟩
theorem mem_pregroupoid_of_eqOnSource (PG : Pregroupoid H) {e e' : PartialHomeomorph H H}
(he' : e ≈ e') (he : PG.property e e.source) : PG.property e' e'.source := by
rw [← he'.1]
exact PG.congr e.open_source he'.eqOn.symm he
/-- The pregroupoid of all partial maps on a topological space `H`. -/
abbrev continuousPregroupoid (H : Type*) [TopologicalSpace H] : Pregroupoid H where
property _ _ := True
comp _ _ _ _ _ := trivial
id_mem := trivial
locality _ _ := trivial
congr _ _ _ := trivial
instance (H : Type*) [TopologicalSpace H] : Inhabited (Pregroupoid H) :=
⟨continuousPregroupoid H⟩
/-- The groupoid of all partial homeomorphisms on a topological space `H`. -/
def continuousGroupoid (H : Type*) [TopologicalSpace H] : StructureGroupoid H :=
Pregroupoid.groupoid (continuousPregroupoid H)
/-- Every structure groupoid is contained in the groupoid of all partial homeomorphisms. -/
instance instStructureGroupoidOrderTop : OrderTop (StructureGroupoid H) where
top := continuousGroupoid H
le_top _ _ _ := ⟨trivial, trivial⟩
instance : CompleteLattice (StructureGroupoid H) :=
{ SetLike.instPartialOrder,
completeLatticeOfInf _ (by
exact fun s =>
⟨fun S Ss F hF => mem_iInter₂.mp hF S Ss,
fun T Tl F fT => mem_iInter₂.mpr (fun i his => Tl his fT)⟩) with
le := (· ≤ ·)
lt := (· < ·)
bot := instStructureGroupoidOrderBot.bot
bot_le := instStructureGroupoidOrderBot.bot_le
top := instStructureGroupoidOrderTop.top
le_top := instStructureGroupoidOrderTop.le_top
inf := (· ⊓ ·)
le_inf := fun _ _ _ h₁₂ h₁₃ _ hm ↦ ⟨h₁₂ hm, h₁₃ hm⟩
inf_le_left := fun _ _ _ ↦ And.left
inf_le_right := fun _ _ _ ↦ And.right }
/-- A groupoid is closed under restriction if it contains all restrictions of its element local
homeomorphisms to open subsets of the source. -/
class ClosedUnderRestriction (G : StructureGroupoid H) : Prop where
closedUnderRestriction :
∀ {e : PartialHomeomorph H H}, e ∈ G → ∀ s : Set H, IsOpen s → e.restr s ∈ G
theorem closedUnderRestriction' {G : StructureGroupoid H} [ClosedUnderRestriction G]
{e : PartialHomeomorph H H} (he : e ∈ G) {s : Set H} (hs : IsOpen s) : e.restr s ∈ G :=
ClosedUnderRestriction.closedUnderRestriction he s hs
/-- The trivial restriction-closed groupoid, containing only partial homeomorphisms equivalent
to the restriction of the identity to the various open subsets. -/
def idRestrGroupoid : StructureGroupoid H where
members := { e | ∃ (s : Set H) (h : IsOpen s), e ≈ PartialHomeomorph.ofSet s h }
trans' := by
rintro e e' ⟨s, hs, hse⟩ ⟨s', hs', hse'⟩
refine ⟨s ∩ s', hs.inter hs', ?_⟩
have := PartialHomeomorph.EqOnSource.trans' hse hse'
rwa [PartialHomeomorph.ofSet_trans_ofSet] at this
symm' := by
rintro e ⟨s, hs, hse⟩
refine ⟨s, hs, ?_⟩
rw [← ofSet_symm]
exact PartialHomeomorph.EqOnSource.symm' hse
id_mem' := ⟨univ, isOpen_univ, by simp only [mfld_simps, refl]⟩
locality' := by
intro e h
refine ⟨e.source, e.open_source, by simp only [mfld_simps], ?_⟩
intro x hx
rcases h x hx with ⟨s, hs, hxs, s', hs', hes'⟩
have hes : x ∈ (e.restr s).source := by
rw [e.restr_source]
refine ⟨hx, ?_⟩
rw [hs.interior_eq]
exact hxs
simpa only [mfld_simps] using PartialHomeomorph.EqOnSource.eqOn hes' hes
mem_of_eqOnSource' := by
rintro e e' ⟨s, hs, hse⟩ hee'
exact ⟨s, hs, Setoid.trans hee' hse⟩
theorem idRestrGroupoid_mem {s : Set H} (hs : IsOpen s) : ofSet s hs ∈ @idRestrGroupoid H _ :=
⟨s, hs, refl _⟩
/-- The trivial restriction-closed groupoid is indeed `ClosedUnderRestriction`. -/
instance closedUnderRestriction_idRestrGroupoid : ClosedUnderRestriction (@idRestrGroupoid H _) :=
⟨by
rintro e ⟨s', hs', he⟩ s hs
use s' ∩ s, hs'.inter hs
refine Setoid.trans (PartialHomeomorph.EqOnSource.restr he s) ?_
exact ⟨by simp only [hs.interior_eq, mfld_simps], by simp only [mfld_simps, eqOn_refl]⟩⟩
/-- A groupoid is closed under restriction if and only if it contains the trivial restriction-closed
groupoid. -/
theorem closedUnderRestriction_iff_id_le (G : StructureGroupoid H) :
ClosedUnderRestriction G ↔ idRestrGroupoid ≤ G := by
constructor
· intro _i
rw [StructureGroupoid.le_iff]
rintro e ⟨s, hs, hes⟩
refine G.mem_of_eqOnSource ?_ hes
convert closedUnderRestriction' G.id_mem hs
-- Porting note: was
-- change s = _ ∩ _
-- rw [hs.interior_eq]
-- simp only [mfld_simps]
ext
· rw [PartialHomeomorph.restr_apply, PartialHomeomorph.refl_apply, id, ofSet_apply, id_eq]
· simp [hs]
· simp [hs.interior_eq]
· intro h
constructor
intro e he s hs
rw [← ofSet_trans (e : PartialHomeomorph H H) hs]
refine G.trans ?_ he
apply StructureGroupoid.le_iff.mp h
exact idRestrGroupoid_mem hs
/-- The groupoid of all partial homeomorphisms on a topological space `H`
is closed under restriction. -/
instance : ClosedUnderRestriction (continuousGroupoid H) :=
(closedUnderRestriction_iff_id_le _).mpr le_top
end Groupoid
/-! ### Charted spaces -/
/-- A charted space is a topological space endowed with an atlas, i.e., a set of local
homeomorphisms taking value in a model space `H`, called charts, such that the domains of the charts
cover the whole space. We express the covering property by choosing for each `x` a member
`chartAt x` of the atlas containing `x` in its source: in the smooth case, this is convenient to
construct the tangent bundle in an efficient way.
The model space is written as an explicit parameter as there can be several model spaces for a
given topological space. For instance, a complex manifold (modelled over `ℂ^n`) will also be seen
sometimes as a real manifold over `ℝ^(2n)`.
-/
@[ext]
class ChartedSpace (H : Type*) [TopologicalSpace H] (M : Type*) [TopologicalSpace M] where
/-- The atlas of charts in the `ChartedSpace`. -/
protected atlas : Set (PartialHomeomorph M H)
/-- The preferred chart at each point in the charted space. -/
protected chartAt : M → PartialHomeomorph M H
protected mem_chart_source : ∀ x, x ∈ (chartAt x).source
protected chart_mem_atlas : ∀ x, chartAt x ∈ atlas
/-- The atlas of charts in a `ChartedSpace`. -/
abbrev atlas (H : Type*) [TopologicalSpace H] (M : Type*) [TopologicalSpace M]
[ChartedSpace H M] : Set (PartialHomeomorph M H) :=
ChartedSpace.atlas
/-- The preferred chart at a point `x` in a charted space `M`. -/
abbrev chartAt (H : Type*) [TopologicalSpace H] {M : Type*} [TopologicalSpace M]
[ChartedSpace H M] (x : M) : PartialHomeomorph M H :=
ChartedSpace.chartAt x
@[simp, mfld_simps]
lemma mem_chart_source (H : Type*) {M : Type*} [TopologicalSpace H] [TopologicalSpace M]
[ChartedSpace H M] (x : M) : x ∈ (chartAt H x).source :=
ChartedSpace.mem_chart_source x
@[simp, mfld_simps]
lemma chart_mem_atlas (H : Type*) {M : Type*} [TopologicalSpace H] [TopologicalSpace M]
[ChartedSpace H M] (x : M) : chartAt H x ∈ atlas H M :=
ChartedSpace.chart_mem_atlas x
lemma nonempty_of_chartedSpace {H : Type*} {M : Type*} [TopologicalSpace H] [TopologicalSpace M]
[ChartedSpace H M] (x : M) : Nonempty H :=
⟨chartAt H x x⟩
lemma isEmpty_of_chartedSpace (H : Type*) {M : Type*} [TopologicalSpace H] [TopologicalSpace M]
[ChartedSpace H M] [IsEmpty H] : IsEmpty M := by
rcases isEmpty_or_nonempty M with hM | ⟨⟨x⟩⟩
· exact hM
· exact (IsEmpty.false (chartAt H x x)).elim
section ChartedSpace
section
variable (H) [TopologicalSpace H] [TopologicalSpace M] [ChartedSpace H M]
-- Porting note: Added `(H := H)` to avoid typeclass instance problem.
theorem mem_chart_target (x : M) : chartAt H x x ∈ (chartAt H x).target :=
(chartAt H x).map_source (mem_chart_source _ _)
theorem chart_source_mem_nhds (x : M) : (chartAt H x).source ∈ 𝓝 x :=
(chartAt H x).open_source.mem_nhds <| mem_chart_source H x
theorem chart_target_mem_nhds (x : M) : (chartAt H x).target ∈ 𝓝 (chartAt H x x) :=
(chartAt H x).open_target.mem_nhds <| mem_chart_target H x
variable (M) in
@[simp]
theorem iUnion_source_chartAt : (⋃ x : M, (chartAt H x).source) = (univ : Set M) :=
eq_univ_iff_forall.mpr fun x ↦ mem_iUnion.mpr ⟨x, mem_chart_source H x⟩
theorem ChartedSpace.isOpen_iff (s : Set M) :
IsOpen s ↔ ∀ x : M, IsOpen <| chartAt H x '' ((chartAt H x).source ∩ s) := by
rw [isOpen_iff_of_cover (fun i ↦ (chartAt H i).open_source) (iUnion_source_chartAt H M)]
simp only [(chartAt H _).isOpen_image_iff_of_subset_source inter_subset_left]
/-- `achart H x` is the chart at `x`, considered as an element of the atlas.
Especially useful for working with `BasicContMDiffVectorBundleCore`. -/
def achart (x : M) : atlas H M :=
⟨chartAt H x, chart_mem_atlas H x⟩
theorem achart_def (x : M) : achart H x = ⟨chartAt H x, chart_mem_atlas H x⟩ :=
rfl
@[simp, mfld_simps]
theorem coe_achart (x : M) : (achart H x : PartialHomeomorph M H) = chartAt H x :=
rfl
@[simp, mfld_simps]
theorem achart_val (x : M) : (achart H x).1 = chartAt H x :=
rfl
theorem mem_achart_source (x : M) : x ∈ (achart H x).1.source :=
mem_chart_source H x
open TopologicalSpace
theorem ChartedSpace.secondCountable_of_countable_cover [SecondCountableTopology H] {s : Set M}
(hs : ⋃ (x) (_ : x ∈ s), (chartAt H x).source = univ) (hsc : s.Countable) :
SecondCountableTopology M := by
haveI : ∀ x : M, SecondCountableTopology (chartAt H x).source :=
fun x ↦ (chartAt (H := H) x).secondCountableTopology_source
haveI := hsc.toEncodable
rw [biUnion_eq_iUnion] at hs
exact secondCountableTopology_of_countable_cover (fun x : s ↦ (chartAt H (x : M)).open_source) hs
variable (M)
theorem ChartedSpace.secondCountable_of_sigmaCompact [SecondCountableTopology H]
[SigmaCompactSpace M] : SecondCountableTopology M := by
obtain ⟨s, hsc, hsU⟩ : ∃ s, Set.Countable s ∧ ⋃ (x) (_ : x ∈ s), (chartAt H x).source = univ :=
countable_cover_nhds_of_sigmaCompact fun x : M ↦ chart_source_mem_nhds H x
exact ChartedSpace.secondCountable_of_countable_cover H hsU hsc
@[deprecated (since := "2024-11-13")] alias
ChartedSpace.secondCountable_of_sigma_compact := ChartedSpace.secondCountable_of_sigmaCompact
/-- If a topological space admits an atlas with locally compact charts, then the space itself
is locally compact. -/
theorem ChartedSpace.locallyCompactSpace [LocallyCompactSpace H] : LocallyCompactSpace M := by
have : ∀ x : M, (𝓝 x).HasBasis
(fun s ↦ s ∈ 𝓝 (chartAt H x x) ∧ IsCompact s ∧ s ⊆ (chartAt H x).target)
fun s ↦ (chartAt H x).symm '' s := fun x ↦ by
rw [← (chartAt H x).symm_map_nhds_eq (mem_chart_source H x)]
exact ((compact_basis_nhds (chartAt H x x)).hasBasis_self_subset
(chart_target_mem_nhds H x)).map _
refine .of_hasBasis this ?_
rintro x s ⟨_, h₂, h₃⟩
exact h₂.image_of_continuousOn ((chartAt H x).continuousOn_symm.mono h₃)
/-- If a topological space admits an atlas with locally connected charts, then the space itself is
locally connected. -/
theorem ChartedSpace.locallyConnectedSpace [LocallyConnectedSpace H] : LocallyConnectedSpace M := by
let e : M → PartialHomeomorph M H := chartAt H
refine locallyConnectedSpace_of_connected_bases (fun x s ↦ (e x).symm '' s)
(fun x s ↦ (IsOpen s ∧ e x x ∈ s ∧ IsConnected s) ∧ s ⊆ (e x).target) ?_ ?_
· intro x
simpa only [e, PartialHomeomorph.symm_map_nhds_eq, mem_chart_source] using
((LocallyConnectedSpace.open_connected_basis (e x x)).restrict_subset
((e x).open_target.mem_nhds (mem_chart_target H x))).map (e x).symm
· rintro x s ⟨⟨-, -, hsconn⟩, hssubset⟩
exact hsconn.isPreconnected.image _ ((e x).continuousOn_symm.mono hssubset)
/-- If a topological space `M` admits an atlas with locally path-connected charts,
then `M` itself is locally path-connected. -/
theorem ChartedSpace.locPathConnectedSpace [LocPathConnectedSpace H] : LocPathConnectedSpace M := by
refine ⟨fun x ↦ ⟨fun s ↦ ⟨fun hs ↦ ?_, fun ⟨u, hu⟩ ↦ Filter.mem_of_superset hu.1.1 hu.2⟩⟩⟩
let e := chartAt H x
let t := s ∩ e.source
have ht : t ∈ 𝓝 x := Filter.inter_mem hs (chart_source_mem_nhds _ _)
refine ⟨e.symm '' pathComponentIn (e x) (e '' t), ⟨?_, ?_⟩, (?_ : _ ⊆ t).trans inter_subset_left⟩
· nth_rewrite 1 [← e.left_inv (mem_chart_source _ _)]
apply e.symm.image_mem_nhds (by simp [e])
exact pathComponentIn_mem_nhds <| e.image_mem_nhds (mem_chart_source _ _) ht
· refine (isPathConnected_pathComponentIn <| mem_image_of_mem e (mem_of_mem_nhds ht)).image' ?_
refine e.continuousOn_symm.mono <| subset_trans ?_ e.map_source''
exact (pathComponentIn_mono <| image_mono inter_subset_right).trans pathComponentIn_subset
· exact (image_mono pathComponentIn_subset).trans
(PartialEquiv.symm_image_image_of_subset_source _ inter_subset_right).subset
/-- If `M` is modelled on `H'` and `H'` is itself modelled on `H`, then we can consider `M` as being
modelled on `H`. -/
def ChartedSpace.comp (H : Type*) [TopologicalSpace H] (H' : Type*) [TopologicalSpace H']
(M : Type*) [TopologicalSpace M] [ChartedSpace H H'] [ChartedSpace H' M] :
ChartedSpace H M where
atlas := image2 PartialHomeomorph.trans (atlas H' M) (atlas H H')
chartAt p := (chartAt H' p).trans (chartAt H (chartAt H' p p))
mem_chart_source p := by simp only [mfld_simps]
chart_mem_atlas p := ⟨chartAt _ p, chart_mem_atlas _ p, chartAt _ _, chart_mem_atlas _ _, rfl⟩
theorem chartAt_comp (H : Type*) [TopologicalSpace H] (H' : Type*) [TopologicalSpace H']
{M : Type*} [TopologicalSpace M] [ChartedSpace H H'] [ChartedSpace H' M] (x : M) :
(letI := ChartedSpace.comp H H' M; chartAt H x) = chartAt H' x ≫ₕ chartAt H (chartAt H' x x) :=
rfl
/-- A charted space over a T1 space is T1. Note that this is *not* true for T2 (for instance for
the real line with a double origin). -/
theorem ChartedSpace.t1Space [T1Space H] : T1Space M := by
apply t1Space_iff_exists_open.2 (fun x y hxy ↦ ?_)
by_cases hy : y ∈ (chartAt H x).source
· refine ⟨(chartAt H x).source ∩ (chartAt H x)⁻¹' ({chartAt H x y}ᶜ), ?_, ?_, by simp⟩
· exact PartialHomeomorph.isOpen_inter_preimage _ isOpen_compl_singleton
· simp only [preimage_compl, mem_inter_iff, mem_chart_source, mem_compl_iff, mem_preimage,
mem_singleton_iff, true_and]
exact (chartAt H x).injOn.ne (ChartedSpace.mem_chart_source x) hy hxy
· exact ⟨(chartAt H x).source, (chartAt H x).open_source, ChartedSpace.mem_chart_source x, hy⟩
/-- A charted space over a discrete space is discrete. -/
theorem ChartedSpace.discreteTopology [DiscreteTopology H] : DiscreteTopology M := by
apply singletons_open_iff_discrete.1 (fun x ↦ ?_)
have : IsOpen ((chartAt H x).source ∩ (chartAt H x) ⁻¹' {chartAt H x x}) :=
isOpen_inter_preimage _ (isOpen_discrete _)
convert this
refine Subset.antisymm (by simp) ?_
simp only [subset_singleton_iff, mem_inter_iff, mem_preimage, mem_singleton_iff, and_imp]
intro y hy h'y
exact (chartAt H x).injOn hy (mem_chart_source _ x) h'y
end
section Constructions
/-- An empty type is a charted space over any topological space. -/
def ChartedSpace.empty (H : Type*) [TopologicalSpace H]
(M : Type*) [TopologicalSpace M] [IsEmpty M] : ChartedSpace H M where
atlas := ∅
chartAt x := (IsEmpty.false x).elim
mem_chart_source x := (IsEmpty.false x).elim
chart_mem_atlas x := (IsEmpty.false x).elim
/-- Any space is a `ChartedSpace` modelled over itself, by just using the identity chart. -/
instance chartedSpaceSelf (H : Type*) [TopologicalSpace H] : ChartedSpace H H where
atlas := {PartialHomeomorph.refl H}
chartAt _ := PartialHomeomorph.refl H
mem_chart_source x := mem_univ x
chart_mem_atlas _ := mem_singleton _
/-- In the trivial `ChartedSpace` structure of a space modelled over itself through the identity,
the atlas members are just the identity. -/
@[simp, mfld_simps]
theorem chartedSpaceSelf_atlas {H : Type*} [TopologicalSpace H] {e : PartialHomeomorph H H} :
e ∈ atlas H H ↔ e = PartialHomeomorph.refl H :=
Iff.rfl
/-- In the model space, `chartAt` is always the identity. -/
theorem chartAt_self_eq {H : Type*} [TopologicalSpace H] {x : H} :
chartAt H x = PartialHomeomorph.refl H := rfl
/-- Any discrete space is a charted space over a singleton set.
We keep this as a definition (not an instance) to avoid instance search trying to search for
`DiscreteTopology` or `Unique` instances.
-/
def ChartedSpace.of_discreteTopology [TopologicalSpace M] [TopologicalSpace H]
[DiscreteTopology M] [h : Unique H] : ChartedSpace H M where
atlas :=
letI f := fun x : M ↦ PartialHomeomorph.const
(isOpen_discrete {x}) (isOpen_discrete {h.default})
Set.image f univ
chartAt x := PartialHomeomorph.const (isOpen_discrete {x}) (isOpen_discrete {h.default})
mem_chart_source x := by simp
chart_mem_atlas x := by simp
/-- A chart on the discrete space is the constant chart. -/
@[simp, mfld_simps]
lemma chartedSpace_of_discreteTopology_chartAt [TopologicalSpace M] [TopologicalSpace H]
[DiscreteTopology M] [h : Unique H] {x : M} :
haveI := ChartedSpace.of_discreteTopology (M := M) (H := H)
chartAt H x = PartialHomeomorph.const (isOpen_discrete {x}) (isOpen_discrete {h.default}) :=
rfl
section Products
library_note "Manifold type tags" /-- For technical reasons we introduce two type tags:
* `ModelProd H H'` is the same as `H × H'`;
* `ModelPi H` is the same as `∀ i, H i`, where `H : ι → Type*` and `ι` is a finite type.
In both cases the reason is the same, so we explain it only in the case of the product. A charted
space `M` with model `H` is a set of charts from `M` to `H` covering the space. Every space is
registered as a charted space over itself, using the only chart `id`, in `chartedSpaceSelf`. You
can also define a product of charted space `M` and `M'` (with model space `H × H'`) by taking the
products of the charts. Now, on `H × H'`, there are two charted space structures with model space
`H × H'` itself, the one coming from `chartedSpaceSelf`, and the one coming from the product of
the two `chartedSpaceSelf` on each component. They are equal, but not defeq (because the product
of `id` and `id` is not defeq to `id`), which is bad as we know. This expedient of renaming `H × H'`
solves this problem. -/
/-- Same thing as `H × H'`. We introduce it for technical reasons,
see note [Manifold type tags]. -/
def ModelProd (H : Type*) (H' : Type*) :=
H × H'
/-- Same thing as `∀ i, H i`. We introduce it for technical reasons,
see note [Manifold type tags]. -/
def ModelPi {ι : Type*} (H : ι → Type*) :=
∀ i, H i
section
-- attribute [local reducible] ModelProd -- Porting note: not available in Lean4
instance modelProdInhabited [Inhabited H] [Inhabited H'] : Inhabited (ModelProd H H') :=
instInhabitedProd
instance (H : Type*) [TopologicalSpace H] (H' : Type*) [TopologicalSpace H'] :
TopologicalSpace (ModelProd H H') :=
instTopologicalSpaceProd
-- Next lemma shows up often when dealing with derivatives, so we register it as simp lemma.
@[simp, mfld_simps]
theorem modelProd_range_prod_id {H : Type*} {H' : Type*} {α : Type*} (f : H → α) :
(range fun p : ModelProd H H' ↦ (f p.1, p.2)) = range f ×ˢ (univ : Set H') := by
rw [prod_range_univ_eq]
rfl
end
section
variable {ι : Type*} {Hi : ι → Type*}
instance modelPiInhabited [∀ i, Inhabited (Hi i)] : Inhabited (ModelPi Hi) :=
Pi.instInhabited
instance [∀ i, TopologicalSpace (Hi i)] : TopologicalSpace (ModelPi Hi) :=
Pi.topologicalSpace
end
/-- The product of two charted spaces is naturally a charted space, with the canonical
construction of the atlas of product maps. -/
instance prodChartedSpace (H : Type*) [TopologicalSpace H] (M : Type*) [TopologicalSpace M]
[ChartedSpace H M] (H' : Type*) [TopologicalSpace H'] (M' : Type*) [TopologicalSpace M']
[ChartedSpace H' M'] : ChartedSpace (ModelProd H H') (M × M') where
atlas := image2 PartialHomeomorph.prod (atlas H M) (atlas H' M')
chartAt x := (chartAt H x.1).prod (chartAt H' x.2)
mem_chart_source x := ⟨mem_chart_source H x.1, mem_chart_source H' x.2⟩
chart_mem_atlas x := mem_image2_of_mem (chart_mem_atlas H x.1) (chart_mem_atlas H' x.2)
section prodChartedSpace
@[ext]
theorem ModelProd.ext {x y : ModelProd H H'} (h₁ : x.1 = y.1) (h₂ : x.2 = y.2) : x = y :=
Prod.ext h₁ h₂
variable [TopologicalSpace H] [TopologicalSpace M] [ChartedSpace H M] [TopologicalSpace H']
[TopologicalSpace M'] [ChartedSpace H' M'] {x : M × M'}
@[simp, mfld_simps]
theorem prodChartedSpace_chartAt :
chartAt (ModelProd H H') x = (chartAt H x.fst).prod (chartAt H' x.snd) :=
rfl
theorem chartedSpaceSelf_prod : prodChartedSpace H H H' H' = chartedSpaceSelf (H × H') := by
ext1
· simp [prodChartedSpace, atlas, ChartedSpace.atlas]
· ext1
simp only [prodChartedSpace_chartAt, chartAt_self_eq, refl_prod_refl]
rfl
end prodChartedSpace
/-- The product of a finite family of charted spaces is naturally a charted space, with the
canonical construction of the atlas of finite product maps. -/
instance piChartedSpace {ι : Type*} [Finite ι] (H : ι → Type*) [∀ i, TopologicalSpace (H i)]
(M : ι → Type*) [∀ i, TopologicalSpace (M i)] [∀ i, ChartedSpace (H i) (M i)] :
ChartedSpace (ModelPi H) (∀ i, M i) where
atlas := PartialHomeomorph.pi '' Set.pi univ fun _ ↦ atlas (H _) (M _)
chartAt f := PartialHomeomorph.pi fun i ↦ chartAt (H i) (f i)
mem_chart_source f i _ := mem_chart_source (H i) (f i)
chart_mem_atlas f := mem_image_of_mem _ fun i _ ↦ chart_mem_atlas (H i) (f i)
@[simp, mfld_simps]
theorem piChartedSpace_chartAt {ι : Type*} [Finite ι] (H : ι → Type*)
[∀ i, TopologicalSpace (H i)] (M : ι → Type*) [∀ i, TopologicalSpace (M i)]
[∀ i, ChartedSpace (H i) (M i)] (f : ∀ i, M i) :
chartAt (H := ModelPi H) f = PartialHomeomorph.pi fun i ↦ chartAt (H i) (f i) :=
rfl
end Products
section sum
variable [TopologicalSpace H] [TopologicalSpace M] [TopologicalSpace M']
[cm : ChartedSpace H M] [cm' : ChartedSpace H M']
/-- The disjoint union of two charted spaces modelled on a non-empty space `H`
is a charted space over `H`. -/
def ChartedSpace.sum_of_nonempty [Nonempty H] : ChartedSpace H (M ⊕ M') where
atlas := ((fun e ↦ e.lift_openEmbedding IsOpenEmbedding.inl) '' cm.atlas) ∪
((fun e ↦ e.lift_openEmbedding IsOpenEmbedding.inr) '' cm'.atlas)
-- At `x : M`, the chart is the chart in `M`; at `x' ∈ M'`, it is the chart in `M'`.
chartAt := Sum.elim (fun x ↦ (cm.chartAt x).lift_openEmbedding IsOpenEmbedding.inl)
(fun x ↦ (cm'.chartAt x).lift_openEmbedding IsOpenEmbedding.inr)
mem_chart_source p := by
cases p with
| inl x =>
rw [Sum.elim_inl, lift_openEmbedding_source,
← PartialHomeomorph.lift_openEmbedding_source _ IsOpenEmbedding.inl]
use x, cm.mem_chart_source x
| inr x =>
rw [Sum.elim_inr, lift_openEmbedding_source,
← PartialHomeomorph.lift_openEmbedding_source _ IsOpenEmbedding.inr]
use x, cm'.mem_chart_source x
chart_mem_atlas p := by
cases p with
| inl x =>
rw [Sum.elim_inl]
left
use ChartedSpace.chartAt x, cm.chart_mem_atlas x
| inr x =>
rw [Sum.elim_inr]
right
use ChartedSpace.chartAt x, cm'.chart_mem_atlas x
open scoped Classical in
instance ChartedSpace.sum : ChartedSpace H (M ⊕ M') :=
if h : Nonempty H then ChartedSpace.sum_of_nonempty else by
simp only [not_nonempty_iff] at h
have : IsEmpty M := isEmpty_of_chartedSpace H
have : IsEmpty M' := isEmpty_of_chartedSpace H
exact empty H (M ⊕ M')
lemma ChartedSpace.sum_chartAt_inl (x : M) :
haveI : Nonempty H := nonempty_of_chartedSpace x
chartAt H (Sum.inl x)
= (chartAt H x).lift_openEmbedding (X' := M ⊕ M') IsOpenEmbedding.inl := by
simp only [chartAt, sum, nonempty_of_chartedSpace x, ↓reduceDIte]
rfl
lemma ChartedSpace.sum_chartAt_inr (x' : M') :
haveI : Nonempty H := nonempty_of_chartedSpace x'
chartAt H (Sum.inr x')
= (chartAt H x').lift_openEmbedding (X' := M ⊕ M') IsOpenEmbedding.inr := by
simp only [chartAt, sum, nonempty_of_chartedSpace x', ↓reduceDIte]
rfl
@[simp, mfld_simps] lemma sum_chartAt_inl_apply {x y : M} :
(chartAt H (.inl x : M ⊕ M')) (Sum.inl y) = (chartAt H x) y := by
haveI : Nonempty H := nonempty_of_chartedSpace x
rw [ChartedSpace.sum_chartAt_inl]
exact PartialHomeomorph.lift_openEmbedding_apply _ _
@[simp, mfld_simps] lemma sum_chartAt_inr_apply {x y : M'} :
(chartAt H (.inr x : M ⊕ M')) (Sum.inr y) = (chartAt H x) y := by
haveI : Nonempty H := nonempty_of_chartedSpace x
rw [ChartedSpace.sum_chartAt_inr]
exact PartialHomeomorph.lift_openEmbedding_apply _ _
lemma ChartedSpace.mem_atlas_sum [h : Nonempty H]
{e : PartialHomeomorph (M ⊕ M') H} (he : e ∈ atlas H (M ⊕ M')) :
(∃ f : PartialHomeomorph M H, f ∈ (atlas H M) ∧ e = (f.lift_openEmbedding IsOpenEmbedding.inl))
∨ (∃ f' : PartialHomeomorph M' H, f' ∈ (atlas H M') ∧
e = (f'.lift_openEmbedding IsOpenEmbedding.inr)) := by
simp only [atlas, sum, h, ↓reduceDIte] at he
obtain (⟨x, hx, hxe⟩ | ⟨x, hx, hxe⟩) := he
· rw [← hxe]; left; use x
· rw [← hxe]; right; use x
end sum
end Constructions
end ChartedSpace
/-! ### Constructing a topology from an atlas -/
/-- Sometimes, one may want to construct a charted space structure on a space which does not yet
have a topological structure, where the topology would come from the charts. For this, one needs
charts that are only partial equivalences, and continuity properties for their composition.
This is formalised in `ChartedSpaceCore`. -/
structure ChartedSpaceCore (H : Type*) [TopologicalSpace H] (M : Type*) where
/-- An atlas of charts, which are only `PartialEquiv`s -/
atlas : Set (PartialEquiv M H)
/-- The preferred chart at each point -/
chartAt : M → PartialEquiv M H
mem_chart_source : ∀ x, x ∈ (chartAt x).source
chart_mem_atlas : ∀ x, chartAt x ∈ atlas
open_source : ∀ e e' : PartialEquiv M H, e ∈ atlas → e' ∈ atlas → IsOpen (e.symm.trans e').source
continuousOn_toFun : ∀ e e' : PartialEquiv M H, e ∈ atlas → e' ∈ atlas →
ContinuousOn (e.symm.trans e') (e.symm.trans e').source
namespace ChartedSpaceCore
variable [TopologicalSpace H] (c : ChartedSpaceCore H M) {e : PartialEquiv M H}
/-- Topology generated by a set of charts on a Type. -/
protected def toTopologicalSpace : TopologicalSpace M :=
TopologicalSpace.generateFrom <|
⋃ (e : PartialEquiv M H) (_ : e ∈ c.atlas) (s : Set H) (_ : IsOpen s),
{e ⁻¹' s ∩ e.source}
theorem open_source' (he : e ∈ c.atlas) : IsOpen[c.toTopologicalSpace] e.source := by
apply TopologicalSpace.GenerateOpen.basic
simp only [exists_prop, mem_iUnion, mem_singleton_iff]
refine ⟨e, he, univ, isOpen_univ, ?_⟩
simp only [Set.univ_inter, Set.preimage_univ]
theorem open_target (he : e ∈ c.atlas) : IsOpen e.target := by
have E : e.target ∩ e.symm ⁻¹' e.source = e.target :=
Subset.antisymm inter_subset_left fun x hx ↦
⟨hx, PartialEquiv.target_subset_preimage_source _ hx⟩
simpa [PartialEquiv.trans_source, E] using c.open_source e e he he
/-- An element of the atlas in a charted space without topology becomes a partial homeomorphism
for the topology constructed from this atlas. The `PartialHomeomorph` version is given in this
definition. -/
protected def partialHomeomorph (e : PartialEquiv M H) (he : e ∈ c.atlas) :
@PartialHomeomorph M H c.toTopologicalSpace _ :=
{ __ := c.toTopologicalSpace
__ := e
open_source := by convert c.open_source' he
open_target := by convert c.open_target he
continuousOn_toFun := by
letI : TopologicalSpace M := c.toTopologicalSpace
rw [continuousOn_open_iff (c.open_source' he)]
intro s s_open
rw [inter_comm]
apply TopologicalSpace.GenerateOpen.basic
simp only [exists_prop, mem_iUnion, mem_singleton_iff]
exact ⟨e, he, ⟨s, s_open, rfl⟩⟩
continuousOn_invFun := by
letI : TopologicalSpace M := c.toTopologicalSpace
apply continuousOn_isOpen_of_generateFrom
intro t ht
simp only [exists_prop, mem_iUnion, mem_singleton_iff] at ht
rcases ht with ⟨e', e'_atlas, s, s_open, ts⟩
rw [ts]
let f := e.symm.trans e'
have : IsOpen (f ⁻¹' s ∩ f.source) := by
simpa [f, inter_comm] using (continuousOn_open_iff (c.open_source e e' he e'_atlas)).1
(c.continuousOn_toFun e e' he e'_atlas) s s_open
have A : e' ∘ e.symm ⁻¹' s ∩ (e.target ∩ e.symm ⁻¹' e'.source) =
e.target ∩ (e' ∘ e.symm ⁻¹' s ∩ e.symm ⁻¹' e'.source) := by
rw [← inter_assoc, ← inter_assoc]
congr 1
exact inter_comm _ _
simpa [f, PartialEquiv.trans_source, preimage_inter, preimage_comp.symm, A] using this }
/-- Given a charted space without topology, endow it with a genuine charted space structure with
respect to the topology constructed from the atlas. -/
def toChartedSpace : @ChartedSpace H _ M c.toTopologicalSpace :=
{ __ := c.toTopologicalSpace
atlas := ⋃ (e : PartialEquiv M H) (he : e ∈ c.atlas), {c.partialHomeomorph e he}
chartAt := fun x ↦ c.partialHomeomorph (c.chartAt x) (c.chart_mem_atlas x)
mem_chart_source := fun x ↦ c.mem_chart_source x
chart_mem_atlas := fun x ↦ by
simp only [mem_iUnion, mem_singleton_iff]
exact ⟨c.chartAt x, c.chart_mem_atlas x, rfl⟩}
end ChartedSpaceCore
/-! ### Charted space with a given structure groupoid -/
section HasGroupoid
variable [TopologicalSpace H] [TopologicalSpace M] [ChartedSpace H M]
/-- A charted space has an atlas in a groupoid `G` if the change of coordinates belong to the
groupoid. -/
class HasGroupoid {H : Type*} [TopologicalSpace H] (M : Type*) [TopologicalSpace M]
[ChartedSpace H M] (G : StructureGroupoid H) : Prop where
compatible : ∀ {e e' : PartialHomeomorph M H}, e ∈ atlas H M → e' ∈ atlas H M → e.symm ≫ₕ e' ∈ G
/-- Reformulate in the `StructureGroupoid` namespace the compatibility condition of charts in a
charted space admitting a structure groupoid, to make it more easily accessible with dot
notation. -/
theorem StructureGroupoid.compatible {H : Type*} [TopologicalSpace H] (G : StructureGroupoid H)
{M : Type*} [TopologicalSpace M] [ChartedSpace H M] [HasGroupoid M G]
{e e' : PartialHomeomorph M H} (he : e ∈ atlas H M) (he' : e' ∈ atlas H M) : e.symm ≫ₕ e' ∈ G :=
HasGroupoid.compatible he he'
theorem hasGroupoid_of_le {G₁ G₂ : StructureGroupoid H} (h : HasGroupoid M G₁) (hle : G₁ ≤ G₂) :
HasGroupoid M G₂ :=
⟨fun he he' ↦ hle (h.compatible he he')⟩
theorem hasGroupoid_inf_iff {G₁ G₂ : StructureGroupoid H} : HasGroupoid M (G₁ ⊓ G₂) ↔
HasGroupoid M G₁ ∧ HasGroupoid M G₂ :=
⟨(fun h ↦ ⟨hasGroupoid_of_le h inf_le_left, hasGroupoid_of_le h inf_le_right⟩),
fun ⟨h1, h2⟩ ↦ { compatible := fun he he' ↦ ⟨h1.compatible he he', h2.compatible he he'⟩ }⟩
theorem hasGroupoid_of_pregroupoid (PG : Pregroupoid H) (h : ∀ {e e' : PartialHomeomorph M H},
e ∈ atlas H M → e' ∈ atlas H M → PG.property (e.symm ≫ₕ e') (e.symm ≫ₕ e').source) :
HasGroupoid M PG.groupoid :=
⟨fun he he' ↦ mem_groupoid_of_pregroupoid.mpr ⟨h he he', h he' he⟩⟩
/-- The trivial charted space structure on the model space is compatible with any groupoid. -/
instance hasGroupoid_model_space (H : Type*) [TopologicalSpace H] (G : StructureGroupoid H) :
HasGroupoid H G where
compatible {e e'} he he' := by
rw [chartedSpaceSelf_atlas] at he he'
simp [he, he', StructureGroupoid.id_mem]
/-- Any charted space structure is compatible with the groupoid of all partial homeomorphisms. -/
instance hasGroupoid_continuousGroupoid : HasGroupoid M (continuousGroupoid H) := by
refine ⟨fun _ _ ↦ ?_⟩
rw [continuousGroupoid, mem_groupoid_of_pregroupoid]
simp only [and_self_iff]
/-- If `G` is closed under restriction, the transition function between the restriction of two
charts `e` and `e'` lies in `G`. -/
theorem StructureGroupoid.trans_restricted {e e' : PartialHomeomorph M H} {G : StructureGroupoid H}
(he : e ∈ atlas H M) (he' : e' ∈ atlas H M)
[HasGroupoid M G] [ClosedUnderRestriction G] {s : Opens M} (hs : Nonempty s) :
(e.subtypeRestr hs).symm ≫ₕ e'.subtypeRestr hs ∈ G :=
G.mem_of_eqOnSource (closedUnderRestriction' (G.compatible he he')
(e.isOpen_inter_preimage_symm s.2)) (e.subtypeRestr_symm_trans_subtypeRestr hs e')
section MaximalAtlas
variable (G : StructureGroupoid H)
variable (M) in
/-- Given a charted space admitting a structure groupoid, the maximal atlas associated to this
structure groupoid is the set of all charts that are compatible with the atlas, i.e., such
that changing coordinates with an atlas member gives an element of the groupoid. -/
def StructureGroupoid.maximalAtlas : Set (PartialHomeomorph M H) :=
{ e | ∀ e' ∈ atlas H M, e.symm ≫ₕ e' ∈ G ∧ e'.symm ≫ₕ e ∈ G }
/-- The elements of the atlas belong to the maximal atlas for any structure groupoid. -/
theorem StructureGroupoid.subset_maximalAtlas [HasGroupoid M G] : atlas H M ⊆ G.maximalAtlas M :=
fun _ he _ he' ↦ ⟨G.compatible he he', G.compatible he' he⟩
theorem StructureGroupoid.chart_mem_maximalAtlas [HasGroupoid M G] (x : M) :
chartAt H x ∈ G.maximalAtlas M :=
G.subset_maximalAtlas (chart_mem_atlas H x)
variable {G}
|
theorem mem_maximalAtlas_iff {e : PartialHomeomorph M H} :
e ∈ G.maximalAtlas M ↔ ∀ e' ∈ atlas H M, e.symm ≫ₕ e' ∈ G ∧ e'.symm ≫ₕ e ∈ G :=
Iff.rfl
/-- Changing coordinates between two elements of the maximal atlas gives rise to an element
of the structure groupoid. -/
theorem StructureGroupoid.compatible_of_mem_maximalAtlas {e e' : PartialHomeomorph M H}
(he : e ∈ G.maximalAtlas M) (he' : e' ∈ G.maximalAtlas M) : e.symm ≫ₕ e' ∈ G := by
refine G.locality fun x hx ↦ ?_
| Mathlib/Geometry/Manifold/ChartedSpace.lean | 1,144 | 1,153 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Jens Wagemaker
-/
import Mathlib.Algebra.Order.Group.Finset
import Mathlib.Algebra.Polynomial.Derivative
import Mathlib.Algebra.Polynomial.Eval.SMul
import Mathlib.Algebra.Polynomial.Roots
import Mathlib.RingTheory.EuclideanDomain
import Mathlib.RingTheory.UniqueFactorizationDomain.NormalizedFactors
/-!
# Theory of univariate polynomials
This file starts looking like the ring theory of $R[X]$
-/
noncomputable section
open Polynomial
namespace Polynomial
universe u v w y z
variable {R : Type u} {S : Type v} {k : Type y} {A : Type z} {a b : R} {n : ℕ}
section CommRing
variable [CommRing R]
theorem rootMultiplicity_sub_one_le_derivative_rootMultiplicity_of_ne_zero
(p : R[X]) (t : R) (hnezero : derivative p ≠ 0) :
p.rootMultiplicity t - 1 ≤ p.derivative.rootMultiplicity t :=
(le_rootMultiplicity_iff hnezero).2 <|
pow_sub_one_dvd_derivative_of_pow_dvd (p.pow_rootMultiplicity_dvd t)
|
theorem derivative_rootMultiplicity_of_root_of_mem_nonZeroDivisors
{p : R[X]} {t : R} (hpt : Polynomial.IsRoot p t)
(hnzd : (p.rootMultiplicity t : R) ∈ nonZeroDivisors R) :
(derivative p).rootMultiplicity t = p.rootMultiplicity t - 1 := by
by_cases h : p = 0
· simp only [h, map_zero, rootMultiplicity_zero]
obtain ⟨g, hp, hndvd⟩ := p.exists_eq_pow_rootMultiplicity_mul_and_not_dvd h t
set m := p.rootMultiplicity t
have hm : m - 1 + 1 = m := Nat.sub_add_cancel <| (rootMultiplicity_pos h).2 hpt
have hndvd : ¬(X - C t) ^ m ∣ derivative p := by
rw [hp, derivative_mul, dvd_add_left (dvd_mul_right _ _),
derivative_X_sub_C_pow, ← hm, pow_succ, hm, mul_comm (C _), mul_assoc,
dvd_cancel_left_mem_nonZeroDivisors (monic_X_sub_C t |>.pow _ |>.mem_nonZeroDivisors)]
rw [dvd_iff_isRoot, IsRoot] at hndvd ⊢
rwa [eval_mul, eval_C, mul_left_mem_nonZeroDivisors_eq_zero_iff hnzd]
have hnezero : derivative p ≠ 0 := fun h ↦ hndvd (by rw [h]; exact dvd_zero _)
exact le_antisymm (by rwa [rootMultiplicity_le_iff hnezero, hm])
| Mathlib/Algebra/Polynomial/FieldDivision.lean | 40 | 57 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Jens Wagemaker, Johan Commelin
-/
import Mathlib.Algebra.Polynomial.BigOperators
import Mathlib.Algebra.Polynomial.RingDivision
import Mathlib.Data.Set.Finite.Lemmas
import Mathlib.RingTheory.Coprime.Lemmas
import Mathlib.RingTheory.Localization.FractionRing
import Mathlib.SetTheory.Cardinal.Order
/-!
# Theory of univariate polynomials
We define the multiset of roots of a polynomial, and prove basic results about it.
## Main definitions
* `Polynomial.roots p`: The multiset containing all the roots of `p`, including their
multiplicities.
* `Polynomial.rootSet p E`: The set of distinct roots of `p` in an algebra `E`.
## Main statements
* `Polynomial.C_leadingCoeff_mul_prod_multiset_X_sub_C`: If a polynomial has as many roots as its
degree, it can be written as the product of its leading coefficient with `∏ (X - a)` where `a`
ranges through its roots.
-/
assert_not_exists Ideal
open Multiset Finset
noncomputable section
namespace Polynomial
universe u v w z
variable {R : Type u} {S : Type v} {T : Type w} {a b : R} {n : ℕ}
section CommRing
variable [CommRing R] [IsDomain R] {p q : R[X]}
section Roots
/-- `roots p` noncomputably gives a multiset containing all the roots of `p`,
including their multiplicities. -/
noncomputable def roots (p : R[X]) : Multiset R :=
haveI := Classical.decEq R
haveI := Classical.dec (p = 0)
if h : p = 0 then ∅ else Classical.choose (exists_multiset_roots h)
theorem roots_def [DecidableEq R] (p : R[X]) [Decidable (p = 0)] :
p.roots = if h : p = 0 then ∅ else Classical.choose (exists_multiset_roots h) := by
rename_i iR ip0
obtain rfl := Subsingleton.elim iR (Classical.decEq R)
obtain rfl := Subsingleton.elim ip0 (Classical.dec (p = 0))
rfl
@[simp]
theorem roots_zero : (0 : R[X]).roots = 0 :=
dif_pos rfl
theorem card_roots (hp0 : p ≠ 0) : (Multiset.card (roots p) : WithBot ℕ) ≤ degree p := by
classical
unfold roots
rw [dif_neg hp0]
exact (Classical.choose_spec (exists_multiset_roots hp0)).1
theorem card_roots' (p : R[X]) : Multiset.card p.roots ≤ natDegree p := by
by_cases hp0 : p = 0
· simp [hp0]
exact WithBot.coe_le_coe.1 (le_trans (card_roots hp0) (le_of_eq <| degree_eq_natDegree hp0))
theorem card_roots_sub_C {p : R[X]} {a : R} (hp0 : 0 < degree p) :
(Multiset.card (p - C a).roots : WithBot ℕ) ≤ degree p :=
calc
(Multiset.card (p - C a).roots : WithBot ℕ) ≤ degree (p - C a) :=
card_roots <| mt sub_eq_zero.1 fun h => not_le_of_gt hp0 <| h.symm ▸ degree_C_le
_ = degree p := by rw [sub_eq_add_neg, ← C_neg]; exact degree_add_C hp0
theorem card_roots_sub_C' {p : R[X]} {a : R} (hp0 : 0 < degree p) :
Multiset.card (p - C a).roots ≤ natDegree p :=
WithBot.coe_le_coe.1
(le_trans (card_roots_sub_C hp0)
(le_of_eq <| degree_eq_natDegree fun h => by simp_all [lt_irrefl]))
|
@[simp]
theorem count_roots [DecidableEq R] (p : R[X]) : p.roots.count a = rootMultiplicity a p := by
classical
by_cases hp : p = 0
| Mathlib/Algebra/Polynomial/Roots.lean | 91 | 95 |
/-
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.Basic
import Mathlib.Algebra.Lie.Subalgebra
import Mathlib.Algebra.Lie.Submodule
import Mathlib.Algebra.Algebra.Subalgebra.Basic
/-!
# Lie algebras of associative algebras
This file defines the Lie algebra structure that arises on an associative algebra via the ring
commutator.
Since the linear endomorphisms of a Lie algebra form an associative algebra, one can define the
adjoint action as a morphism of Lie algebras from a Lie algebra to its linear endomorphisms. We
make such a definition in this file.
## Main definitions
* `LieAlgebra.ofAssociativeAlgebra`
* `LieAlgebra.ofAssociativeAlgebraHom`
* `LieModule.toEnd`
* `LieAlgebra.ad`
* `LinearEquiv.lieConj`
* `AlgEquiv.toLieEquiv`
## Tags
lie algebra, ring commutator, adjoint action
-/
universe u v w w₁ w₂
section OfAssociative
variable {A : Type v} [Ring A]
namespace LieRing
/-- An associative ring gives rise to a Lie ring by taking the bracket to be the ring commutator. -/
instance (priority := 100) ofAssociativeRing : LieRing A where
add_lie _ _ _ := by simp only [Ring.lie_def, right_distrib, left_distrib]; abel
lie_add _ _ _ := by simp only [Ring.lie_def, right_distrib, left_distrib]; abel
lie_self := by simp only [Ring.lie_def, forall_const, sub_self]
leibniz_lie _ _ _ := by
simp only [Ring.lie_def, mul_sub_left_distrib, mul_sub_right_distrib, mul_assoc]; abel
theorem of_associative_ring_bracket (x y : A) : ⁅x, y⁆ = x * y - y * x :=
rfl
@[simp]
theorem lie_apply {α : Type*} (f g : α → A) (a : α) : ⁅f, g⁆ a = ⁅f a, g a⁆ :=
rfl
end LieRing
section AssociativeModule
variable {M : Type w} [AddCommGroup M] [Module A M]
/-- We can regard a module over an associative ring `A` as a Lie ring module over `A` with Lie
bracket equal to its ring commutator.
Note that this cannot be a global instance because it would create a diamond when `M = A`,
specifically we can build two mathematically-different `bracket A A`s:
1. `@Ring.bracket A _` which says `⁅a, b⁆ = a * b - b * a`
2. `(@LieRingModule.ofAssociativeModule A _ A _ _).toBracket` which says `⁅a, b⁆ = a • b`
(and thus `⁅a, b⁆ = a * b`)
See note [reducible non-instances] -/
abbrev LieRingModule.ofAssociativeModule : LieRingModule A M where
bracket := (· • ·)
add_lie := add_smul
lie_add := smul_add
leibniz_lie := by simp [LieRing.of_associative_ring_bracket, sub_smul, mul_smul, sub_add_cancel]
attribute [local instance] LieRingModule.ofAssociativeModule
theorem lie_eq_smul (a : A) (m : M) : ⁅a, m⁆ = a • m :=
rfl
end AssociativeModule
section LieAlgebra
variable {R : Type u} [CommRing R] [Algebra R A]
/-- An associative algebra gives rise to a Lie algebra by taking the bracket to be the ring
commutator. -/
instance (priority := 100) LieAlgebra.ofAssociativeAlgebra : LieAlgebra R A where
lie_smul t x y := by
rw [LieRing.of_associative_ring_bracket, LieRing.of_associative_ring_bracket,
Algebra.mul_smul_comm, Algebra.smul_mul_assoc, smul_sub]
attribute [local instance] LieRingModule.ofAssociativeModule
section AssociativeRepresentation
variable {M : Type w} [AddCommGroup M] [Module R M] [Module A M] [IsScalarTower R A M]
/-- A representation of an associative algebra `A` is also a representation of `A`, regarded as a
Lie algebra via the ring commutator.
See the comment at `LieRingModule.ofAssociativeModule` for why the possibility `M = A` means
this cannot be a global instance. -/
theorem LieModule.ofAssociativeModule : LieModule R A M where
smul_lie := smul_assoc
lie_smul := smul_algebra_smul_comm
instance Module.End.instLieRingModule : LieRingModule (Module.End R M) M :=
LieRingModule.ofAssociativeModule
instance Module.End.instLieModule : LieModule R (Module.End R M) M :=
LieModule.ofAssociativeModule
@[simp] lemma Module.End.lie_apply (f : Module.End R M) (m : M) : ⁅f, m⁆ = f m := rfl
end AssociativeRepresentation
namespace AlgHom
variable {B : Type w} {C : Type w₁} [Ring B] [Ring C] [Algebra R B] [Algebra R C]
variable (f : A →ₐ[R] B) (g : B →ₐ[R] C)
/-- The map `ofAssociativeAlgebra` associating a Lie algebra to an associative algebra is
functorial. -/
def toLieHom : A →ₗ⁅R⁆ B :=
{ f.toLinearMap with
map_lie' := fun {_ _} => by simp [LieRing.of_associative_ring_bracket] }
instance : Coe (A →ₐ[R] B) (A →ₗ⁅R⁆ B) :=
⟨toLieHom⟩
@[simp]
theorem coe_toLieHom : ((f : A →ₗ⁅R⁆ B) : A → B) = f :=
rfl
theorem toLieHom_apply (x : A) : f.toLieHom x = f x :=
rfl
@[simp]
theorem toLieHom_id : (AlgHom.id R A : A →ₗ⁅R⁆ A) = LieHom.id :=
rfl
@[simp]
theorem toLieHom_comp : (g.comp f : A →ₗ⁅R⁆ C) = (g : B →ₗ⁅R⁆ C).comp (f : A →ₗ⁅R⁆ B) :=
rfl
theorem toLieHom_injective {f g : A →ₐ[R] B} (h : (f : A →ₗ⁅R⁆ B) = (g : A →ₗ⁅R⁆ B)) : f = g := by
ext a; exact LieHom.congr_fun h a
end AlgHom
end LieAlgebra
end OfAssociative
section AdjointAction
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] [LieModule R L M]
/-- A Lie module yields a Lie algebra morphism into the linear endomorphisms of the module.
See also `LieModule.toModuleHom`. -/
@[simps]
def LieModule.toEnd : L →ₗ⁅R⁆ Module.End R M where
toFun x :=
{ toFun := fun m => ⁅x, m⁆
map_add' := lie_add x
map_smul' := fun t => lie_smul t x }
map_add' x y := by ext m; apply add_lie
map_smul' t x := by ext m; apply smul_lie
map_lie' {x y} := by ext m; apply lie_lie
/-- The adjoint action of a Lie algebra on itself. -/
def LieAlgebra.ad : L →ₗ⁅R⁆ Module.End R L :=
LieModule.toEnd R L L
@[simp]
theorem LieAlgebra.ad_apply (x y : L) : LieAlgebra.ad R L x y = ⁅x, y⁆ :=
rfl
@[simp]
theorem LieModule.toEnd_module_end :
LieModule.toEnd R (Module.End R M) M = LieHom.id := by ext g m; simp [lie_eq_smul]
theorem LieSubalgebra.toEnd_eq (K : LieSubalgebra R L) {x : K} :
LieModule.toEnd R K M x = LieModule.toEnd R L M x :=
rfl
@[simp]
theorem LieSubalgebra.toEnd_mk (K : LieSubalgebra R L) {x : L} (hx : x ∈ K) :
LieModule.toEnd R K M ⟨x, hx⟩ = LieModule.toEnd R L M x :=
rfl
section IsFaithful
open Function
namespace LieModule
/-- A Lie module is *faithful* if the associated map `L → End M` is injective. -/
@[mk_iff]
class IsFaithful : Prop where
injective_toEnd : Injective <| toEnd R L M
@[simp]
lemma toEnd_eq_iff [IsFaithful R L M] {x y : L} :
toEnd R L M x = toEnd R L M y ↔ x = y :=
IsFaithful.injective_toEnd.eq_iff
variable {R L} in
lemma ext_of_isFaithful [IsFaithful R L M] {x y : L} (h : ∀ m : M, ⁅x, m⁆ = ⁅y, m⁆) :
x = y :=
(toEnd_eq_iff R L M).mp <| LinearMap.ext h
@[simp]
lemma toEnd_eq_zero_iff [IsFaithful R L M] {x : L} :
toEnd R L M x = 0 ↔ x = 0 := by
simp [- LieHom.map_zero, ← (toEnd R L M).map_zero]
lemma isFaithful_iff' : IsFaithful R L M ↔ ∀ x : L, (∀ m : M, ⁅x, m⁆ = 0) → x = 0 := by
refine ⟨fun h x hx ↦ ?_, fun h ↦ ⟨fun x y hxy ↦ ?_⟩⟩
· replace hx : toEnd R L M x = 0 := by ext m; simpa using hx m
simpa using hx
· rw [← sub_eq_zero]
refine h _ fun m ↦ ?_
rw [sub_lie, sub_eq_zero, ← toEnd_apply_apply R, ← toEnd_apply_apply R, hxy]
end LieModule
end IsFaithful
section
open LieAlgebra LieModule
lemma LieSubmodule.coe_toEnd (N : LieSubmodule R L M) (x : L) (y : N) :
(toEnd R L N x y : M) = toEnd R L M x y := rfl
lemma LieSubmodule.coe_toEnd_pow (N : LieSubmodule R L M) (x : L) (y : N) (n : ℕ) :
((toEnd R L N x ^ n) y : M) = (toEnd R L M x ^ n) y := by
induction n generalizing y with
| zero => rfl
| succ n ih => simp only [pow_succ', Module.End.mul_apply, ih, LieSubmodule.coe_toEnd]
lemma LieSubalgebra.coe_ad (H : LieSubalgebra R L) (x y : H) :
(ad R H x y : L) = ad R L x y := rfl
lemma LieSubalgebra.coe_ad_pow (H : LieSubalgebra R L) (x y : H) (n : ℕ) :
((ad R H x ^ n) y : L) = (ad R L x ^ n) y :=
LieSubmodule.coe_toEnd_pow R H L H.toLieSubmodule x y n
variable {L M}
local notation "φ" => LieModule.toEnd R L M
lemma LieModule.toEnd_lie (x y : L) (z : M) :
(φ x) ⁅y, z⁆ = ⁅ad R L x y, z⁆ + ⁅y, φ x z⁆ := by
simp
lemma LieAlgebra.ad_lie (x y z : L) :
(ad R L x) ⁅y, z⁆ = ⁅ad R L x y, z⁆ + ⁅y, ad R L x z⁆ :=
toEnd_lie _ x y z
open Finset in
lemma LieModule.toEnd_pow_lie (x y : L) (z : M) (n : ℕ) :
((φ x) ^ n) ⁅y, z⁆ =
∑ ij ∈ antidiagonal n, n.choose ij.1 • ⁅((ad R L x) ^ ij.1) y, ((φ x) ^ ij.2) z⁆ := by
induction n with
| zero => simp
| succ n ih =>
rw [Finset.sum_antidiagonal_choose_succ_nsmul
(fun i j ↦ ⁅((ad R L x) ^ i) y, ((φ x) ^ j) z⁆) n]
simp only [pow_succ', Module.End.mul_apply, ih, map_sum, map_nsmul,
toEnd_lie, nsmul_add, sum_add_distrib]
rw [add_comm, add_left_cancel_iff, sum_congr rfl]
rintro ⟨i, j⟩ hij
rw [mem_antidiagonal] at hij
rw [Nat.choose_symm_of_eq_add hij.symm]
open Finset in
lemma LieAlgebra.ad_pow_lie (x y z : L) (n : ℕ) :
((ad R L x) ^ n) ⁅y, z⁆ =
∑ ij ∈ antidiagonal n, n.choose ij.1 • ⁅((ad R L x) ^ ij.1) y, ((ad R L x) ^ ij.2) z⁆ :=
toEnd_pow_lie _ x y z n
end
variable {R L M}
namespace LieModule
variable {M₂ : Type w₁} [AddCommGroup M₂] [Module R M₂] [LieRingModule L M₂] [LieModule R L M₂]
(f : M →ₗ⁅R,L⁆ M₂) (k : ℕ) (x : L)
lemma toEnd_pow_comp_lieHom :
(toEnd R L M₂ x ^ k) ∘ₗ f = f ∘ₗ toEnd R L M x ^ k := by
apply Module.End.commute_pow_left_of_commute
ext
simp
lemma toEnd_pow_apply_map (m : M) :
(toEnd R L M₂ x ^ k) (f m) = f ((toEnd R L M x ^ k) m) :=
LinearMap.congr_fun (toEnd_pow_comp_lieHom f k x) m
end LieModule
namespace LieSubmodule
open LieModule Set
variable {N : LieSubmodule R L M} {x : L}
theorem coe_map_toEnd_le :
(N : Submodule R M).map (LieModule.toEnd R L M x) ≤ N := by
rintro n ⟨m, hm, rfl⟩
exact N.lie_mem hm
| variable (N x)
theorem toEnd_comp_subtype_mem (m : M) (hm : m ∈ (N : Submodule R M)) :
| Mathlib/Algebra/Lie/OfAssociative.lean | 327 | 329 |
/-
Copyright (c) 2021 Rémy Degenne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Zhouhang Zhou, Yury Kudryashov, Sébastien Gouëzel, Rémy Degenne
-/
import Mathlib.MeasureTheory.Integral.FinMeasAdditive
/-!
# Extension of a linear function from indicators to L1
Given `T : Set α → E →L[ℝ] F` with `DominatedFinMeasAdditive μ T C`, we construct an extension
of `T` to integrable simple functions, which are finite sums of indicators of measurable sets
with finite measure, then to integrable functions, which are limits of integrable simple functions.
The main result is a continuous linear map `(α →₁[μ] E) →L[ℝ] F`.
This extension process is used to define the Bochner integral
in the `Mathlib.MeasureTheory.Integral.Bochner.Basic` file
and the conditional expectation of an integrable function
in `Mathlib.MeasureTheory.Function.ConditionalExpectation.CondexpL1`.
## Main definitions
- `setToL1 (hT : DominatedFinMeasAdditive μ T C) : (α →₁[μ] E) →L[ℝ] F`: the extension of `T`
from indicators to L1.
- `setToFun μ T (hT : DominatedFinMeasAdditive μ T C) (f : α → E) : F`: a version of the
extension which applies to functions (with value 0 if the function is not integrable).
## Properties
For most properties of `setToFun`, we provide two lemmas. One version uses hypotheses valid on
all sets, like `T = T'`, and a second version which uses a primed name uses hypotheses on
measurable sets with finite measure, like `∀ s, MeasurableSet s → μ s < ∞ → T s = T' s`.
The lemmas listed here don't show all hypotheses. Refer to the actual lemmas for details.
Linearity:
- `setToFun_zero_left : setToFun μ 0 hT f = 0`
- `setToFun_add_left : setToFun μ (T + T') _ f = setToFun μ T hT f + setToFun μ T' hT' f`
- `setToFun_smul_left : setToFun μ (fun s ↦ c • (T s)) (hT.smul c) f = c • setToFun μ T hT f`
- `setToFun_zero : setToFun μ T hT (0 : α → E) = 0`
- `setToFun_neg : setToFun μ T hT (-f) = - setToFun μ T hT f`
If `f` and `g` are integrable:
- `setToFun_add : setToFun μ T hT (f + g) = setToFun μ T hT f + setToFun μ T hT g`
- `setToFun_sub : setToFun μ T hT (f - g) = setToFun μ T hT f - setToFun μ T hT g`
If `T` is verifies `∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x`:
- `setToFun_smul : setToFun μ T hT (c • f) = c • setToFun μ T hT f`
Other:
- `setToFun_congr_ae (h : f =ᵐ[μ] g) : setToFun μ T hT f = setToFun μ T hT g`
- `setToFun_measure_zero (h : μ = 0) : setToFun μ T hT f = 0`
If the space is also an ordered additive group with an order closed topology and `T` is such that
`0 ≤ T s x` for `0 ≤ x`, we also prove order-related properties:
- `setToFun_mono_left (h : ∀ s x, T s x ≤ T' s x) : setToFun μ T hT f ≤ setToFun μ T' hT' f`
- `setToFun_nonneg (hf : 0 ≤ᵐ[μ] f) : 0 ≤ setToFun μ T hT f`
- `setToFun_mono (hfg : f ≤ᵐ[μ] g) : setToFun μ T hT f ≤ setToFun μ T hT g`
-/
noncomputable section
open scoped Topology NNReal
open Set Filter TopologicalSpace ENNReal
namespace MeasureTheory
variable {α E F F' G 𝕜 : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
[NormedAddCommGroup F] [NormedSpace ℝ F] [NormedAddCommGroup F'] [NormedSpace ℝ F']
[NormedAddCommGroup G] {m : MeasurableSpace α} {μ : Measure α}
namespace L1
open AEEqFun Lp.simpleFunc Lp
namespace SimpleFunc
theorem norm_eq_sum_mul (f : α →₁ₛ[μ] G) :
‖f‖ = ∑ x ∈ (toSimpleFunc f).range, μ.real (toSimpleFunc f ⁻¹' {x}) * ‖x‖ := by
rw [norm_toSimpleFunc, eLpNorm_one_eq_lintegral_enorm]
have h_eq := SimpleFunc.map_apply (‖·‖ₑ) (toSimpleFunc f)
simp_rw [← h_eq, measureReal_def]
rw [SimpleFunc.lintegral_eq_lintegral, SimpleFunc.map_lintegral, ENNReal.toReal_sum]
· congr
ext1 x
rw [ENNReal.toReal_mul, mul_comm, ← ofReal_norm_eq_enorm,
ENNReal.toReal_ofReal (norm_nonneg _)]
· intro x _
by_cases hx0 : x = 0
· rw [hx0]; simp
· exact
ENNReal.mul_ne_top ENNReal.coe_ne_top
(SimpleFunc.measure_preimage_lt_top_of_integrable _ (SimpleFunc.integrable f) hx0).ne
section SetToL1S
variable [NormedField 𝕜] [NormedSpace 𝕜 E]
attribute [local instance] Lp.simpleFunc.module
attribute [local instance] Lp.simpleFunc.normedSpace
/-- Extend `Set α → (E →L[ℝ] F')` to `(α →₁ₛ[μ] E) → F'`. -/
def setToL1S (T : Set α → E →L[ℝ] F) (f : α →₁ₛ[μ] E) : F :=
(toSimpleFunc f).setToSimpleFunc T
theorem setToL1S_eq_setToSimpleFunc (T : Set α → E →L[ℝ] F) (f : α →₁ₛ[μ] E) :
setToL1S T f = (toSimpleFunc f).setToSimpleFunc T :=
rfl
@[simp]
theorem setToL1S_zero_left (f : α →₁ₛ[μ] E) : setToL1S (0 : Set α → E →L[ℝ] F) f = 0 :=
SimpleFunc.setToSimpleFunc_zero _
theorem setToL1S_zero_left' {T : Set α → E →L[ℝ] F}
(h_zero : ∀ s, MeasurableSet s → μ s < ∞ → T s = 0) (f : α →₁ₛ[μ] E) : setToL1S T f = 0 :=
SimpleFunc.setToSimpleFunc_zero' h_zero _ (SimpleFunc.integrable f)
theorem setToL1S_congr (T : Set α → E →L[ℝ] F) (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T) {f g : α →₁ₛ[μ] E} (h : toSimpleFunc f =ᵐ[μ] toSimpleFunc g) :
setToL1S T f = setToL1S T g :=
SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable f) h
theorem setToL1S_congr_left (T T' : Set α → E →L[ℝ] F)
(h : ∀ s, MeasurableSet s → μ s < ∞ → T s = T' s) (f : α →₁ₛ[μ] E) :
setToL1S T f = setToL1S T' f :=
SimpleFunc.setToSimpleFunc_congr_left T T' h (simpleFunc.toSimpleFunc f) (SimpleFunc.integrable f)
/-- `setToL1S` does not change if we replace the measure `μ` by `μ'` with `μ ≪ μ'`. The statement
uses two functions `f` and `f'` because they have to belong to different types, but morally these
are the same function (we have `f =ᵐ[μ] f'`). -/
theorem setToL1S_congr_measure {μ' : Measure α} (T : Set α → E →L[ℝ] F)
(h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0) (h_add : FinMeasAdditive μ T) (hμ : μ ≪ μ')
(f : α →₁ₛ[μ] E) (f' : α →₁ₛ[μ'] E) (h : (f : α → E) =ᵐ[μ] f') :
setToL1S T f = setToL1S T f' := by
refine SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable f) ?_
refine (toSimpleFunc_eq_toFun f).trans ?_
suffices (f' : α → E) =ᵐ[μ] simpleFunc.toSimpleFunc f' from h.trans this
have goal' : (f' : α → E) =ᵐ[μ'] simpleFunc.toSimpleFunc f' := (toSimpleFunc_eq_toFun f').symm
exact hμ.ae_eq goal'
theorem setToL1S_add_left (T T' : Set α → E →L[ℝ] F) (f : α →₁ₛ[μ] E) :
setToL1S (T + T') f = setToL1S T f + setToL1S T' f :=
SimpleFunc.setToSimpleFunc_add_left T T'
theorem setToL1S_add_left' (T T' T'' : Set α → E →L[ℝ] F)
(h_add : ∀ s, MeasurableSet s → μ s < ∞ → T'' s = T s + T' s) (f : α →₁ₛ[μ] E) :
setToL1S T'' f = setToL1S T f + setToL1S T' f :=
SimpleFunc.setToSimpleFunc_add_left' T T' T'' h_add (SimpleFunc.integrable f)
theorem setToL1S_smul_left (T : Set α → E →L[ℝ] F) (c : ℝ) (f : α →₁ₛ[μ] E) :
setToL1S (fun s => c • T s) f = c • setToL1S T f :=
SimpleFunc.setToSimpleFunc_smul_left T c _
theorem setToL1S_smul_left' (T T' : Set α → E →L[ℝ] F) (c : ℝ)
(h_smul : ∀ s, MeasurableSet s → μ s < ∞ → T' s = c • T s) (f : α →₁ₛ[μ] E) :
setToL1S T' f = c • setToL1S T f :=
SimpleFunc.setToSimpleFunc_smul_left' T T' c h_smul (SimpleFunc.integrable f)
theorem setToL1S_add (T : Set α → E →L[ℝ] F) (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T) (f g : α →₁ₛ[μ] E) :
setToL1S T (f + g) = setToL1S T f + setToL1S T g := by
simp_rw [setToL1S]
rw [← SimpleFunc.setToSimpleFunc_add T h_add (SimpleFunc.integrable f)
(SimpleFunc.integrable g)]
exact
SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable _)
(add_toSimpleFunc f g)
theorem setToL1S_neg {T : Set α → E →L[ℝ] F} (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T) (f : α →₁ₛ[μ] E) : setToL1S T (-f) = -setToL1S T f := by
simp_rw [setToL1S]
have : simpleFunc.toSimpleFunc (-f) =ᵐ[μ] ⇑(-simpleFunc.toSimpleFunc f) :=
neg_toSimpleFunc f
rw [SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable _) this]
exact SimpleFunc.setToSimpleFunc_neg T h_add (SimpleFunc.integrable f)
theorem setToL1S_sub {T : Set α → E →L[ℝ] F} (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T) (f g : α →₁ₛ[μ] E) :
setToL1S T (f - g) = setToL1S T f - setToL1S T g := by
rw [sub_eq_add_neg, setToL1S_add T h_zero h_add, setToL1S_neg h_zero h_add, sub_eq_add_neg]
theorem setToL1S_smul_real (T : Set α → E →L[ℝ] F)
(h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0) (h_add : FinMeasAdditive μ T) (c : ℝ)
(f : α →₁ₛ[μ] E) : setToL1S T (c • f) = c • setToL1S T f := by
simp_rw [setToL1S]
rw [← SimpleFunc.setToSimpleFunc_smul_real T h_add c (SimpleFunc.integrable f)]
refine SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable _) ?_
exact smul_toSimpleFunc c f
theorem setToL1S_smul {E} [NormedAddCommGroup E] [NormedSpace ℝ E] [NormedSpace 𝕜 E]
[DistribSMul 𝕜 F] (T : Set α → E →L[ℝ] F) (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T) (h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) (c : 𝕜)
(f : α →₁ₛ[μ] E) : setToL1S T (c • f) = c • setToL1S T f := by
simp_rw [setToL1S]
rw [← SimpleFunc.setToSimpleFunc_smul T h_add h_smul c (SimpleFunc.integrable f)]
refine SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable _) ?_
exact smul_toSimpleFunc c f
theorem norm_setToL1S_le (T : Set α → E →L[ℝ] F) {C : ℝ}
(hT_norm : ∀ s, MeasurableSet s → μ s < ∞ → ‖T s‖ ≤ C * μ.real s) (f : α →₁ₛ[μ] E) :
‖setToL1S T f‖ ≤ C * ‖f‖ := by
rw [setToL1S, norm_eq_sum_mul f]
exact
SimpleFunc.norm_setToSimpleFunc_le_sum_mul_norm_of_integrable T hT_norm _
(SimpleFunc.integrable f)
theorem setToL1S_indicatorConst {T : Set α → E →L[ℝ] F} {s : Set α}
(h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0) (h_add : FinMeasAdditive μ T)
(hs : MeasurableSet s) (hμs : μ s < ∞) (x : E) :
setToL1S T (simpleFunc.indicatorConst 1 hs hμs.ne x) = T s x := by
have h_empty : T ∅ = 0 := h_zero _ MeasurableSet.empty measure_empty
rw [setToL1S_eq_setToSimpleFunc]
refine Eq.trans ?_ (SimpleFunc.setToSimpleFunc_indicator T h_empty hs x)
refine SimpleFunc.setToSimpleFunc_congr T h_zero h_add (SimpleFunc.integrable _) ?_
exact toSimpleFunc_indicatorConst hs hμs.ne x
theorem setToL1S_const [IsFiniteMeasure μ] {T : Set α → E →L[ℝ] F}
(h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0) (h_add : FinMeasAdditive μ T) (x : E) :
setToL1S T (simpleFunc.indicatorConst 1 MeasurableSet.univ (measure_ne_top μ _) x) = T univ x :=
setToL1S_indicatorConst h_zero h_add MeasurableSet.univ (measure_lt_top _ _) x
section Order
variable {G'' G' : Type*}
[NormedAddCommGroup G'] [PartialOrder G'] [IsOrderedAddMonoid G'] [NormedSpace ℝ G']
[NormedAddCommGroup G''] [PartialOrder G''] [IsOrderedAddMonoid G''] [NormedSpace ℝ G'']
{T : Set α → G'' →L[ℝ] G'}
theorem setToL1S_mono_left {T T' : Set α → E →L[ℝ] G''} (hTT' : ∀ s x, T s x ≤ T' s x)
(f : α →₁ₛ[μ] E) : setToL1S T f ≤ setToL1S T' f :=
SimpleFunc.setToSimpleFunc_mono_left T T' hTT' _
theorem setToL1S_mono_left' {T T' : Set α → E →L[ℝ] G''}
(hTT' : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, T s x ≤ T' s x) (f : α →₁ₛ[μ] E) :
setToL1S T f ≤ setToL1S T' f :=
SimpleFunc.setToSimpleFunc_mono_left' T T' hTT' _ (SimpleFunc.integrable f)
omit [IsOrderedAddMonoid G''] in
theorem setToL1S_nonneg (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f : α →₁ₛ[μ] G''}
(hf : 0 ≤ f) : 0 ≤ setToL1S T f := by
simp_rw [setToL1S]
obtain ⟨f', hf', hff'⟩ := exists_simpleFunc_nonneg_ae_eq hf
replace hff' : simpleFunc.toSimpleFunc f =ᵐ[μ] f' :=
(Lp.simpleFunc.toSimpleFunc_eq_toFun f).trans hff'
rw [SimpleFunc.setToSimpleFunc_congr _ h_zero h_add (SimpleFunc.integrable _) hff']
exact
SimpleFunc.setToSimpleFunc_nonneg' T hT_nonneg _ hf' ((SimpleFunc.integrable f).congr hff')
theorem setToL1S_mono (h_zero : ∀ s, MeasurableSet s → μ s = 0 → T s = 0)
(h_add : FinMeasAdditive μ T)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f g : α →₁ₛ[μ] G''}
(hfg : f ≤ g) : setToL1S T f ≤ setToL1S T g := by
rw [← sub_nonneg] at hfg ⊢
rw [← setToL1S_sub h_zero h_add]
exact setToL1S_nonneg h_zero h_add hT_nonneg hfg
end Order
variable [NormedSpace 𝕜 F]
variable (α E μ 𝕜)
/-- Extend `Set α → E →L[ℝ] F` to `(α →₁ₛ[μ] E) →L[𝕜] F`. -/
def setToL1SCLM' {T : Set α → E →L[ℝ] F} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) : (α →₁ₛ[μ] E) →L[𝕜] F :=
LinearMap.mkContinuous
⟨⟨setToL1S T, setToL1S_add T (fun _ => hT.eq_zero_of_measure_zero) hT.1⟩,
setToL1S_smul T (fun _ => hT.eq_zero_of_measure_zero) hT.1 h_smul⟩
C fun f => norm_setToL1S_le T hT.2 f
/-- Extend `Set α → E →L[ℝ] F` to `(α →₁ₛ[μ] E) →L[ℝ] F`. -/
def setToL1SCLM {T : Set α → E →L[ℝ] F} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C) :
(α →₁ₛ[μ] E) →L[ℝ] F :=
LinearMap.mkContinuous
⟨⟨setToL1S T, setToL1S_add T (fun _ => hT.eq_zero_of_measure_zero) hT.1⟩,
setToL1S_smul_real T (fun _ => hT.eq_zero_of_measure_zero) hT.1⟩
C fun f => norm_setToL1S_le T hT.2 f
variable {α E μ 𝕜}
variable {T T' T'' : Set α → E →L[ℝ] F} {C C' C'' : ℝ}
@[simp]
theorem setToL1SCLM_zero_left (hT : DominatedFinMeasAdditive μ (0 : Set α → E →L[ℝ] F) C)
(f : α →₁ₛ[μ] E) : setToL1SCLM α E μ hT f = 0 :=
setToL1S_zero_left _
theorem setToL1SCLM_zero_left' (hT : DominatedFinMeasAdditive μ T C)
(h_zero : ∀ s, MeasurableSet s → μ s < ∞ → T s = 0) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT f = 0 :=
setToL1S_zero_left' h_zero f
theorem setToL1SCLM_congr_left (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (h : T = T') (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT f = setToL1SCLM α E μ hT' f :=
setToL1S_congr_left T T' (fun _ _ _ => by rw [h]) f
theorem setToL1SCLM_congr_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (h : ∀ s, MeasurableSet s → μ s < ∞ → T s = T' s)
(f : α →₁ₛ[μ] E) : setToL1SCLM α E μ hT f = setToL1SCLM α E μ hT' f :=
setToL1S_congr_left T T' h f
theorem setToL1SCLM_congr_measure {μ' : Measure α} (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ' T C') (hμ : μ ≪ μ') (f : α →₁ₛ[μ] E) (f' : α →₁ₛ[μ'] E)
(h : (f : α → E) =ᵐ[μ] f') : setToL1SCLM α E μ hT f = setToL1SCLM α E μ' hT' f' :=
setToL1S_congr_measure T (fun _ => hT.eq_zero_of_measure_zero) hT.1 hμ _ _ h
theorem setToL1SCLM_add_left (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ (hT.add hT') f = setToL1SCLM α E μ hT f + setToL1SCLM α E μ hT' f :=
setToL1S_add_left T T' f
theorem setToL1SCLM_add_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (hT'' : DominatedFinMeasAdditive μ T'' C'')
(h_add : ∀ s, MeasurableSet s → μ s < ∞ → T'' s = T s + T' s) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT'' f = setToL1SCLM α E μ hT f + setToL1SCLM α E μ hT' f :=
setToL1S_add_left' T T' T'' h_add f
theorem setToL1SCLM_smul_left (c : ℝ) (hT : DominatedFinMeasAdditive μ T C) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ (hT.smul c) f = c • setToL1SCLM α E μ hT f :=
setToL1S_smul_left T c f
theorem setToL1SCLM_smul_left' (c : ℝ) (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C')
(h_smul : ∀ s, MeasurableSet s → μ s < ∞ → T' s = c • T s) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT' f = c • setToL1SCLM α E μ hT f :=
setToL1S_smul_left' T T' c h_smul f
theorem norm_setToL1SCLM_le {T : Set α → E →L[ℝ] F} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hC : 0 ≤ C) : ‖setToL1SCLM α E μ hT‖ ≤ C :=
LinearMap.mkContinuous_norm_le _ hC _
theorem norm_setToL1SCLM_le' {T : Set α → E →L[ℝ] F} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C) :
‖setToL1SCLM α E μ hT‖ ≤ max C 0 :=
LinearMap.mkContinuous_norm_le' _ _
theorem setToL1SCLM_const [IsFiniteMeasure μ] {T : Set α → E →L[ℝ] F} {C : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (x : E) :
setToL1SCLM α E μ hT (simpleFunc.indicatorConst 1 MeasurableSet.univ (measure_ne_top μ _) x) =
T univ x :=
setToL1S_const (fun _ => hT.eq_zero_of_measure_zero) hT.1 x
section Order
variable {G' G'' : Type*}
[NormedAddCommGroup G''] [PartialOrder G''] [IsOrderedAddMonoid G''] [NormedSpace ℝ G'']
[NormedAddCommGroup G'] [PartialOrder G'] [IsOrderedAddMonoid G'] [NormedSpace ℝ G']
theorem setToL1SCLM_mono_left {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s x, T s x ≤ T' s x) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT f ≤ setToL1SCLM α E μ hT' f :=
SimpleFunc.setToSimpleFunc_mono_left T T' hTT' _
theorem setToL1SCLM_mono_left' {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, T s x ≤ T' s x) (f : α →₁ₛ[μ] E) :
setToL1SCLM α E μ hT f ≤ setToL1SCLM α E μ hT' f :=
SimpleFunc.setToSimpleFunc_mono_left' T T' hTT' _ (SimpleFunc.integrable f)
omit [IsOrderedAddMonoid G'] in
theorem setToL1SCLM_nonneg {T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f : α →₁ₛ[μ] G'}
(hf : 0 ≤ f) : 0 ≤ setToL1SCLM α G' μ hT f :=
setToL1S_nonneg (fun _ => hT.eq_zero_of_measure_zero) hT.1 hT_nonneg hf
theorem setToL1SCLM_mono {T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f g : α →₁ₛ[μ] G'}
(hfg : f ≤ g) : setToL1SCLM α G' μ hT f ≤ setToL1SCLM α G' μ hT g :=
setToL1S_mono (fun _ => hT.eq_zero_of_measure_zero) hT.1 hT_nonneg hfg
end Order
end SetToL1S
end SimpleFunc
open SimpleFunc
section SetToL1
attribute [local instance] Lp.simpleFunc.module
attribute [local instance] Lp.simpleFunc.normedSpace
variable (𝕜) [NontriviallyNormedField 𝕜] [NormedSpace 𝕜 E] [NormedSpace 𝕜 F] [CompleteSpace F]
{T T' T'' : Set α → E →L[ℝ] F} {C C' C'' : ℝ}
/-- Extend `Set α → (E →L[ℝ] F)` to `(α →₁[μ] E) →L[𝕜] F`. -/
def setToL1' (hT : DominatedFinMeasAdditive μ T C)
(h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) : (α →₁[μ] E) →L[𝕜] F :=
(setToL1SCLM' α E 𝕜 μ hT h_smul).extend (coeToLp α E 𝕜) (simpleFunc.denseRange one_ne_top)
simpleFunc.isUniformInducing
variable {𝕜}
/-- Extend `Set α → E →L[ℝ] F` to `(α →₁[μ] E) →L[ℝ] F`. -/
def setToL1 (hT : DominatedFinMeasAdditive μ T C) : (α →₁[μ] E) →L[ℝ] F :=
(setToL1SCLM α E μ hT).extend (coeToLp α E ℝ) (simpleFunc.denseRange one_ne_top)
simpleFunc.isUniformInducing
theorem setToL1_eq_setToL1SCLM (hT : DominatedFinMeasAdditive μ T C) (f : α →₁ₛ[μ] E) :
setToL1 hT f = setToL1SCLM α E μ hT f :=
uniformly_extend_of_ind simpleFunc.isUniformInducing (simpleFunc.denseRange one_ne_top)
(setToL1SCLM α E μ hT).uniformContinuous _
theorem setToL1_eq_setToL1' (hT : DominatedFinMeasAdditive μ T C)
(h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) (f : α →₁[μ] E) :
setToL1 hT f = setToL1' 𝕜 hT h_smul f :=
rfl
@[simp]
theorem setToL1_zero_left (hT : DominatedFinMeasAdditive μ (0 : Set α → E →L[ℝ] F) C)
(f : α →₁[μ] E) : setToL1 hT f = 0 := by
suffices setToL1 hT = 0 by rw [this]; simp
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT) _ _ _ _ ?_
ext1 f
rw [setToL1SCLM_zero_left hT f, ContinuousLinearMap.zero_comp, ContinuousLinearMap.zero_apply]
theorem setToL1_zero_left' (hT : DominatedFinMeasAdditive μ T C)
(h_zero : ∀ s, MeasurableSet s → μ s < ∞ → T s = 0) (f : α →₁[μ] E) : setToL1 hT f = 0 := by
suffices setToL1 hT = 0 by rw [this]; simp
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT) _ _ _ _ ?_
ext1 f
rw [setToL1SCLM_zero_left' hT h_zero f, ContinuousLinearMap.zero_comp,
ContinuousLinearMap.zero_apply]
theorem setToL1_congr_left (T T' : Set α → E →L[ℝ] F) {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C') (h : T = T')
(f : α →₁[μ] E) : setToL1 hT f = setToL1 hT' f := by
suffices setToL1 hT = setToL1 hT' by rw [this]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT) _ _ _ _ ?_
ext1 f
suffices setToL1 hT' f = setToL1SCLM α E μ hT f by rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM]
exact setToL1SCLM_congr_left hT' hT h.symm f
theorem setToL1_congr_left' (T T' : Set α → E →L[ℝ] F) {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(h : ∀ s, MeasurableSet s → μ s < ∞ → T s = T' s) (f : α →₁[μ] E) :
setToL1 hT f = setToL1 hT' f := by
suffices setToL1 hT = setToL1 hT' by rw [this]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT) _ _ _ _ ?_
ext1 f
suffices setToL1 hT' f = setToL1SCLM α E μ hT f by rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM]
exact (setToL1SCLM_congr_left' hT hT' h f).symm
theorem setToL1_add_left (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (f : α →₁[μ] E) :
setToL1 (hT.add hT') f = setToL1 hT f + setToL1 hT' f := by
suffices setToL1 (hT.add hT') = setToL1 hT + setToL1 hT' by
rw [this, ContinuousLinearMap.add_apply]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ (hT.add hT')) _ _ _ _ ?_
ext1 f
suffices setToL1 hT f + setToL1 hT' f = setToL1SCLM α E μ (hT.add hT') f by
rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM, setToL1_eq_setToL1SCLM, setToL1SCLM_add_left hT hT']
theorem setToL1_add_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (hT'' : DominatedFinMeasAdditive μ T'' C'')
(h_add : ∀ s, MeasurableSet s → μ s < ∞ → T'' s = T s + T' s) (f : α →₁[μ] E) :
setToL1 hT'' f = setToL1 hT f + setToL1 hT' f := by
suffices setToL1 hT'' = setToL1 hT + setToL1 hT' by rw [this, ContinuousLinearMap.add_apply]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT'') _ _ _ _ ?_
ext1 f
suffices setToL1 hT f + setToL1 hT' f = setToL1SCLM α E μ hT'' f by rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM, setToL1_eq_setToL1SCLM,
setToL1SCLM_add_left' hT hT' hT'' h_add]
theorem setToL1_smul_left (hT : DominatedFinMeasAdditive μ T C) (c : ℝ) (f : α →₁[μ] E) :
setToL1 (hT.smul c) f = c • setToL1 hT f := by
suffices setToL1 (hT.smul c) = c • setToL1 hT by rw [this, ContinuousLinearMap.smul_apply]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ (hT.smul c)) _ _ _ _ ?_
ext1 f
suffices c • setToL1 hT f = setToL1SCLM α E μ (hT.smul c) f by rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM, setToL1SCLM_smul_left c hT]
theorem setToL1_smul_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (c : ℝ)
(h_smul : ∀ s, MeasurableSet s → μ s < ∞ → T' s = c • T s) (f : α →₁[μ] E) :
setToL1 hT' f = c • setToL1 hT f := by
suffices setToL1 hT' = c • setToL1 hT by rw [this, ContinuousLinearMap.smul_apply]
refine ContinuousLinearMap.extend_unique (setToL1SCLM α E μ hT') _ _ _ _ ?_
ext1 f
suffices c • setToL1 hT f = setToL1SCLM α E μ hT' f by rw [← this]; simp [coeToLp]
rw [setToL1_eq_setToL1SCLM, setToL1SCLM_smul_left' c hT hT' h_smul]
theorem setToL1_smul (hT : DominatedFinMeasAdditive μ T C)
(h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) (c : 𝕜) (f : α →₁[μ] E) :
setToL1 hT (c • f) = c • setToL1 hT f := by
rw [setToL1_eq_setToL1' hT h_smul, setToL1_eq_setToL1' hT h_smul]
exact ContinuousLinearMap.map_smul _ _ _
theorem setToL1_simpleFunc_indicatorConst (hT : DominatedFinMeasAdditive μ T C) {s : Set α}
(hs : MeasurableSet s) (hμs : μ s < ∞) (x : E) :
setToL1 hT (simpleFunc.indicatorConst 1 hs hμs.ne x) = T s x := by
rw [setToL1_eq_setToL1SCLM]
exact setToL1S_indicatorConst (fun s => hT.eq_zero_of_measure_zero) hT.1 hs hμs x
theorem setToL1_indicatorConstLp (hT : DominatedFinMeasAdditive μ T C) {s : Set α}
(hs : MeasurableSet s) (hμs : μ s ≠ ∞) (x : E) :
setToL1 hT (indicatorConstLp 1 hs hμs x) = T s x := by
rw [← Lp.simpleFunc.coe_indicatorConst hs hμs x]
exact setToL1_simpleFunc_indicatorConst hT hs hμs.lt_top x
theorem setToL1_const [IsFiniteMeasure μ] (hT : DominatedFinMeasAdditive μ T C) (x : E) :
setToL1 hT (indicatorConstLp 1 MeasurableSet.univ (measure_ne_top _ _) x) = T univ x :=
setToL1_indicatorConstLp hT MeasurableSet.univ (measure_ne_top _ _) x
section Order
variable {G' G'' : Type*}
[NormedAddCommGroup G''] [PartialOrder G''] [OrderClosedTopology G''] [IsOrderedAddMonoid G'']
[NormedSpace ℝ G''] [CompleteSpace G'']
[NormedAddCommGroup G'] [PartialOrder G'] [NormedSpace ℝ G']
theorem setToL1_mono_left' {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, T s x ≤ T' s x) (f : α →₁[μ] E) :
setToL1 hT f ≤ setToL1 hT' f := by
induction f using Lp.induction (hp_ne_top := one_ne_top) with
| @indicatorConst c s hs hμs =>
rw [setToL1_simpleFunc_indicatorConst hT hs hμs, setToL1_simpleFunc_indicatorConst hT' hs hμs]
exact hTT' s hs hμs c
| @add f g hf hg _ hf_le hg_le =>
rw [(setToL1 hT).map_add, (setToL1 hT').map_add]
exact add_le_add hf_le hg_le
| isClosed => exact isClosed_le (setToL1 hT).continuous (setToL1 hT').continuous
theorem setToL1_mono_left {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s x, T s x ≤ T' s x) (f : α →₁[μ] E) : setToL1 hT f ≤ setToL1 hT' f :=
setToL1_mono_left' hT hT' (fun s _ _ x => hTT' s x) f
theorem setToL1_nonneg {T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f : α →₁[μ] G'}
(hf : 0 ≤ f) : 0 ≤ setToL1 hT f := by
suffices ∀ f : { g : α →₁[μ] G' // 0 ≤ g }, 0 ≤ setToL1 hT f from
this (⟨f, hf⟩ : { g : α →₁[μ] G' // 0 ≤ g })
refine fun g =>
@isClosed_property { g : α →₁ₛ[μ] G' // 0 ≤ g } { g : α →₁[μ] G' // 0 ≤ g } _ _
(fun g => 0 ≤ setToL1 hT g)
(denseRange_coeSimpleFuncNonnegToLpNonneg 1 μ G' one_ne_top) ?_ ?_ g
· exact isClosed_le continuous_zero ((setToL1 hT).continuous.comp continuous_induced_dom)
· intro g
have : (coeSimpleFuncNonnegToLpNonneg 1 μ G' g : α →₁[μ] G') = (g : α →₁ₛ[μ] G') := rfl
rw [this, setToL1_eq_setToL1SCLM]
exact setToL1S_nonneg (fun s => hT.eq_zero_of_measure_zero) hT.1 hT_nonneg g.2
theorem setToL1_mono [IsOrderedAddMonoid G']
{T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f g : α →₁[μ] G'}
(hfg : f ≤ g) : setToL1 hT f ≤ setToL1 hT g := by
rw [← sub_nonneg] at hfg ⊢
rw [← (setToL1 hT).map_sub]
exact setToL1_nonneg hT hT_nonneg hfg
end Order
theorem norm_setToL1_le_norm_setToL1SCLM (hT : DominatedFinMeasAdditive μ T C) :
‖setToL1 hT‖ ≤ ‖setToL1SCLM α E μ hT‖ :=
calc
‖setToL1 hT‖ ≤ (1 : ℝ≥0) * ‖setToL1SCLM α E μ hT‖ := by
refine
ContinuousLinearMap.opNorm_extend_le (setToL1SCLM α E μ hT) (coeToLp α E ℝ)
(simpleFunc.denseRange one_ne_top) fun x => le_of_eq ?_
rw [NNReal.coe_one, one_mul]
simp [coeToLp]
_ = ‖setToL1SCLM α E μ hT‖ := by rw [NNReal.coe_one, one_mul]
theorem norm_setToL1_le_mul_norm (hT : DominatedFinMeasAdditive μ T C) (hC : 0 ≤ C)
(f : α →₁[μ] E) : ‖setToL1 hT f‖ ≤ C * ‖f‖ :=
calc
‖setToL1 hT f‖ ≤ ‖setToL1SCLM α E μ hT‖ * ‖f‖ :=
ContinuousLinearMap.le_of_opNorm_le _ (norm_setToL1_le_norm_setToL1SCLM hT) _
_ ≤ C * ‖f‖ := mul_le_mul (norm_setToL1SCLM_le hT hC) le_rfl (norm_nonneg _) hC
theorem norm_setToL1_le_mul_norm' (hT : DominatedFinMeasAdditive μ T C) (f : α →₁[μ] E) :
‖setToL1 hT f‖ ≤ max C 0 * ‖f‖ :=
calc
‖setToL1 hT f‖ ≤ ‖setToL1SCLM α E μ hT‖ * ‖f‖ :=
ContinuousLinearMap.le_of_opNorm_le _ (norm_setToL1_le_norm_setToL1SCLM hT) _
_ ≤ max C 0 * ‖f‖ :=
mul_le_mul (norm_setToL1SCLM_le' hT) le_rfl (norm_nonneg _) (le_max_right _ _)
theorem norm_setToL1_le (hT : DominatedFinMeasAdditive μ T C) (hC : 0 ≤ C) : ‖setToL1 hT‖ ≤ C :=
ContinuousLinearMap.opNorm_le_bound _ hC (norm_setToL1_le_mul_norm hT hC)
theorem norm_setToL1_le' (hT : DominatedFinMeasAdditive μ T C) : ‖setToL1 hT‖ ≤ max C 0 :=
ContinuousLinearMap.opNorm_le_bound _ (le_max_right _ _) (norm_setToL1_le_mul_norm' hT)
theorem setToL1_lipschitz (hT : DominatedFinMeasAdditive μ T C) :
LipschitzWith (Real.toNNReal C) (setToL1 hT) :=
(setToL1 hT).lipschitz.weaken (norm_setToL1_le' hT)
/-- If `fs i → f` in `L1`, then `setToL1 hT (fs i) → setToL1 hT f`. -/
theorem tendsto_setToL1 (hT : DominatedFinMeasAdditive μ T C) (f : α →₁[μ] E) {ι}
(fs : ι → α →₁[μ] E) {l : Filter ι} (hfs : Tendsto fs l (𝓝 f)) :
Tendsto (fun i => setToL1 hT (fs i)) l (𝓝 <| setToL1 hT f) :=
((setToL1 hT).continuous.tendsto _).comp hfs
end SetToL1
end L1
section Function
variable [CompleteSpace F] {T T' T'' : Set α → E →L[ℝ] F} {C C' C'' : ℝ} {f g : α → E}
variable (μ T)
open Classical in
/-- Extend `T : Set α → E →L[ℝ] F` to `(α → E) → F` (for integrable functions `α → E`). We set it to
0 if the function is not integrable. -/
def setToFun (hT : DominatedFinMeasAdditive μ T C) (f : α → E) : F :=
if hf : Integrable f μ then L1.setToL1 hT (hf.toL1 f) else 0
variable {μ T}
theorem setToFun_eq (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ) :
setToFun μ T hT f = L1.setToL1 hT (hf.toL1 f) :=
dif_pos hf
theorem L1.setToFun_eq_setToL1 (hT : DominatedFinMeasAdditive μ T C) (f : α →₁[μ] E) :
setToFun μ T hT f = L1.setToL1 hT f := by
rw [setToFun_eq hT (L1.integrable_coeFn f), Integrable.toL1_coeFn]
theorem setToFun_undef (hT : DominatedFinMeasAdditive μ T C) (hf : ¬Integrable f μ) :
setToFun μ T hT f = 0 :=
dif_neg hf
theorem setToFun_non_aestronglyMeasurable (hT : DominatedFinMeasAdditive μ T C)
(hf : ¬AEStronglyMeasurable f μ) : setToFun μ T hT f = 0 :=
setToFun_undef hT (not_and_of_not_left _ hf)
@[deprecated (since := "2025-04-09")]
alias setToFun_non_aEStronglyMeasurable := setToFun_non_aestronglyMeasurable
theorem setToFun_congr_left (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (h : T = T') (f : α → E) :
setToFun μ T hT f = setToFun μ T' hT' f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_congr_left T T' hT hT' h]
· simp_rw [setToFun_undef _ hf]
theorem setToFun_congr_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (h : ∀ s, MeasurableSet s → μ s < ∞ → T s = T' s)
(f : α → E) : setToFun μ T hT f = setToFun μ T' hT' f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_congr_left' T T' hT hT' h]
· simp_rw [setToFun_undef _ hf]
theorem setToFun_add_left (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (f : α → E) :
setToFun μ (T + T') (hT.add hT') f = setToFun μ T hT f + setToFun μ T' hT' f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_add_left hT hT']
· simp_rw [setToFun_undef _ hf, add_zero]
theorem setToFun_add_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (hT'' : DominatedFinMeasAdditive μ T'' C'')
(h_add : ∀ s, MeasurableSet s → μ s < ∞ → T'' s = T s + T' s) (f : α → E) :
setToFun μ T'' hT'' f = setToFun μ T hT f + setToFun μ T' hT' f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_add_left' hT hT' hT'' h_add]
· simp_rw [setToFun_undef _ hf, add_zero]
theorem setToFun_smul_left (hT : DominatedFinMeasAdditive μ T C) (c : ℝ) (f : α → E) :
setToFun μ (fun s => c • T s) (hT.smul c) f = c • setToFun μ T hT f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_smul_left hT c]
· simp_rw [setToFun_undef _ hf, smul_zero]
theorem setToFun_smul_left' (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ T' C') (c : ℝ)
(h_smul : ∀ s, MeasurableSet s → μ s < ∞ → T' s = c • T s) (f : α → E) :
setToFun μ T' hT' f = c • setToFun μ T hT f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf, L1.setToL1_smul_left' hT hT' c h_smul]
· simp_rw [setToFun_undef _ hf, smul_zero]
@[simp]
theorem setToFun_zero (hT : DominatedFinMeasAdditive μ T C) : setToFun μ T hT (0 : α → E) = 0 := by
rw [Pi.zero_def, setToFun_eq hT (integrable_zero _ _ _)]
simp only [← Pi.zero_def]
rw [Integrable.toL1_zero, ContinuousLinearMap.map_zero]
@[simp]
theorem setToFun_zero_left {hT : DominatedFinMeasAdditive μ (0 : Set α → E →L[ℝ] F) C} :
setToFun μ 0 hT f = 0 := by
by_cases hf : Integrable f μ
· rw [setToFun_eq hT hf]; exact L1.setToL1_zero_left hT _
· exact setToFun_undef hT hf
theorem setToFun_zero_left' (hT : DominatedFinMeasAdditive μ T C)
(h_zero : ∀ s, MeasurableSet s → μ s < ∞ → T s = 0) : setToFun μ T hT f = 0 := by
by_cases hf : Integrable f μ
· rw [setToFun_eq hT hf]; exact L1.setToL1_zero_left' hT h_zero _
· exact setToFun_undef hT hf
theorem setToFun_add (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ)
(hg : Integrable g μ) : setToFun μ T hT (f + g) = setToFun μ T hT f + setToFun μ T hT g := by
rw [setToFun_eq hT (hf.add hg), setToFun_eq hT hf, setToFun_eq hT hg, Integrable.toL1_add,
(L1.setToL1 hT).map_add]
theorem setToFun_finset_sum' (hT : DominatedFinMeasAdditive μ T C) {ι} (s : Finset ι)
{f : ι → α → E} (hf : ∀ i ∈ s, Integrable (f i) μ) :
setToFun μ T hT (∑ i ∈ s, f i) = ∑ i ∈ s, setToFun μ T hT (f i) := by
classical
revert hf
refine Finset.induction_on s ?_ ?_
· intro _
simp only [setToFun_zero, Finset.sum_empty]
· intro i s his ih hf
simp only [his, Finset.sum_insert, not_false_iff]
rw [setToFun_add hT (hf i (Finset.mem_insert_self i s)) _]
· rw [ih fun i hi => hf i (Finset.mem_insert_of_mem hi)]
· convert integrable_finset_sum s fun i hi => hf i (Finset.mem_insert_of_mem hi) with x
simp
theorem setToFun_finset_sum (hT : DominatedFinMeasAdditive μ T C) {ι} (s : Finset ι) {f : ι → α → E}
(hf : ∀ i ∈ s, Integrable (f i) μ) :
(setToFun μ T hT fun a => ∑ i ∈ s, f i a) = ∑ i ∈ s, setToFun μ T hT (f i) := by
convert setToFun_finset_sum' hT s hf with a; simp
theorem setToFun_neg (hT : DominatedFinMeasAdditive μ T C) (f : α → E) :
setToFun μ T hT (-f) = -setToFun μ T hT f := by
by_cases hf : Integrable f μ
· rw [setToFun_eq hT hf, setToFun_eq hT hf.neg, Integrable.toL1_neg,
(L1.setToL1 hT).map_neg]
· rw [setToFun_undef hT hf, setToFun_undef hT, neg_zero]
rwa [← integrable_neg_iff] at hf
theorem setToFun_sub (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ)
(hg : Integrable g μ) : setToFun μ T hT (f - g) = setToFun μ T hT f - setToFun μ T hT g := by
rw [sub_eq_add_neg, sub_eq_add_neg, setToFun_add hT hf hg.neg, setToFun_neg hT g]
theorem setToFun_smul [NontriviallyNormedField 𝕜] [NormedSpace 𝕜 E] [NormedSpace 𝕜 F]
(hT : DominatedFinMeasAdditive μ T C) (h_smul : ∀ c : 𝕜, ∀ s x, T s (c • x) = c • T s x) (c : 𝕜)
(f : α → E) : setToFun μ T hT (c • f) = c • setToFun μ T hT f := by
by_cases hf : Integrable f μ
· rw [setToFun_eq hT hf, setToFun_eq hT, Integrable.toL1_smul',
L1.setToL1_smul hT h_smul c _]
· by_cases hr : c = 0
· rw [hr]; simp
· have hf' : ¬Integrable (c • f) μ := by rwa [integrable_smul_iff hr f]
rw [setToFun_undef hT hf, setToFun_undef hT hf', smul_zero]
theorem setToFun_congr_ae (hT : DominatedFinMeasAdditive μ T C) (h : f =ᵐ[μ] g) :
setToFun μ T hT f = setToFun μ T hT g := by
by_cases hfi : Integrable f μ
· have hgi : Integrable g μ := hfi.congr h
rw [setToFun_eq hT hfi, setToFun_eq hT hgi, (Integrable.toL1_eq_toL1_iff f g hfi hgi).2 h]
· have hgi : ¬Integrable g μ := by rw [integrable_congr h] at hfi; exact hfi
rw [setToFun_undef hT hfi, setToFun_undef hT hgi]
theorem setToFun_measure_zero (hT : DominatedFinMeasAdditive μ T C) (h : μ = 0) :
setToFun μ T hT f = 0 := by
have : f =ᵐ[μ] 0 := by simp [h, EventuallyEq]
rw [setToFun_congr_ae hT this, setToFun_zero]
theorem setToFun_measure_zero' (hT : DominatedFinMeasAdditive μ T C)
(h : ∀ s, MeasurableSet s → μ s < ∞ → μ s = 0) : setToFun μ T hT f = 0 :=
setToFun_zero_left' hT fun s hs hμs => hT.eq_zero_of_measure_zero hs (h s hs hμs)
theorem setToFun_toL1 (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ) :
setToFun μ T hT (hf.toL1 f) = setToFun μ T hT f :=
setToFun_congr_ae hT hf.coeFn_toL1
theorem setToFun_indicator_const (hT : DominatedFinMeasAdditive μ T C) {s : Set α}
(hs : MeasurableSet s) (hμs : μ s ≠ ∞) (x : E) :
setToFun μ T hT (s.indicator fun _ => x) = T s x := by
rw [setToFun_congr_ae hT (@indicatorConstLp_coeFn _ _ _ 1 _ _ _ hs hμs x).symm]
rw [L1.setToFun_eq_setToL1 hT]
exact L1.setToL1_indicatorConstLp hT hs hμs x
theorem setToFun_const [IsFiniteMeasure μ] (hT : DominatedFinMeasAdditive μ T C) (x : E) :
(setToFun μ T hT fun _ => x) = T univ x := by
have : (fun _ : α => x) = Set.indicator univ fun _ => x := (indicator_univ _).symm
rw [this]
exact setToFun_indicator_const hT MeasurableSet.univ (measure_ne_top _ _) x
section Order
variable {G' G'' : Type*}
[NormedAddCommGroup G''] [PartialOrder G''] [OrderClosedTopology G''] [IsOrderedAddMonoid G'']
[NormedSpace ℝ G''] [CompleteSpace G'']
[NormedAddCommGroup G'] [PartialOrder G'] [NormedSpace ℝ G']
theorem setToFun_mono_left' {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, T s x ≤ T' s x) (f : α → E) :
setToFun μ T hT f ≤ setToFun μ T' hT' f := by
by_cases hf : Integrable f μ
· simp_rw [setToFun_eq _ hf]; exact L1.setToL1_mono_left' hT hT' hTT' _
· simp_rw [setToFun_undef _ hf, le_rfl]
theorem setToFun_mono_left {T T' : Set α → E →L[ℝ] G''} {C C' : ℝ}
(hT : DominatedFinMeasAdditive μ T C) (hT' : DominatedFinMeasAdditive μ T' C')
(hTT' : ∀ s x, T s x ≤ T' s x) (f : α →₁[μ] E) : setToFun μ T hT f ≤ setToFun μ T' hT' f :=
setToFun_mono_left' hT hT' (fun s _ _ x => hTT' s x) f
theorem setToFun_nonneg {T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f : α → G'}
(hf : 0 ≤ᵐ[μ] f) : 0 ≤ setToFun μ T hT f := by
by_cases hfi : Integrable f μ
· simp_rw [setToFun_eq _ hfi]
refine L1.setToL1_nonneg hT hT_nonneg ?_
rw [← Lp.coeFn_le]
have h0 := Lp.coeFn_zero G' 1 μ
have h := Integrable.coeFn_toL1 hfi
filter_upwards [h0, h, hf] with _ h0a ha hfa
rw [h0a, ha]
exact hfa
· simp_rw [setToFun_undef _ hfi, le_rfl]
theorem setToFun_mono [IsOrderedAddMonoid G']
{T : Set α → G' →L[ℝ] G''} {C : ℝ} (hT : DominatedFinMeasAdditive μ T C)
(hT_nonneg : ∀ s, MeasurableSet s → μ s < ∞ → ∀ x, 0 ≤ x → 0 ≤ T s x) {f g : α → G'}
(hf : Integrable f μ) (hg : Integrable g μ) (hfg : f ≤ᵐ[μ] g) :
setToFun μ T hT f ≤ setToFun μ T hT g := by
rw [← sub_nonneg, ← setToFun_sub hT hg hf]
refine setToFun_nonneg hT hT_nonneg (hfg.mono fun a ha => ?_)
rw [Pi.sub_apply, Pi.zero_apply, sub_nonneg]
exact ha
end Order
@[continuity]
theorem continuous_setToFun (hT : DominatedFinMeasAdditive μ T C) :
Continuous fun f : α →₁[μ] E => setToFun μ T hT f := by
simp_rw [L1.setToFun_eq_setToL1 hT]; exact ContinuousLinearMap.continuous _
/-- If `F i → f` in `L1`, then `setToFun μ T hT (F i) → setToFun μ T hT f`. -/
theorem tendsto_setToFun_of_L1 (hT : DominatedFinMeasAdditive μ T C) {ι} (f : α → E)
(hfi : Integrable f μ) {fs : ι → α → E} {l : Filter ι} (hfsi : ∀ᶠ i in l, Integrable (fs i) μ)
(hfs : Tendsto (fun i => ∫⁻ x, ‖fs i x - f x‖ₑ ∂μ) l (𝓝 0)) :
Tendsto (fun i => setToFun μ T hT (fs i)) l (𝓝 <| setToFun μ T hT f) := by
classical
let f_lp := hfi.toL1 f
let F_lp i := if hFi : Integrable (fs i) μ then hFi.toL1 (fs i) else 0
have tendsto_L1 : Tendsto F_lp l (𝓝 f_lp) := by
rw [Lp.tendsto_Lp_iff_tendsto_eLpNorm']
simp_rw [eLpNorm_one_eq_lintegral_enorm, Pi.sub_apply]
refine (tendsto_congr' ?_).mp hfs
filter_upwards [hfsi] with i hi
refine lintegral_congr_ae ?_
filter_upwards [hi.coeFn_toL1, hfi.coeFn_toL1] with x hxi hxf
simp_rw [F_lp, dif_pos hi, hxi, f_lp, hxf]
suffices Tendsto (fun i => setToFun μ T hT (F_lp i)) l (𝓝 (setToFun μ T hT f)) by
refine (tendsto_congr' ?_).mp this
filter_upwards [hfsi] with i hi
suffices h_ae_eq : F_lp i =ᵐ[μ] fs i from setToFun_congr_ae hT h_ae_eq
simp_rw [F_lp, dif_pos hi]
exact hi.coeFn_toL1
rw [setToFun_congr_ae hT hfi.coeFn_toL1.symm]
exact ((continuous_setToFun hT).tendsto f_lp).comp tendsto_L1
theorem tendsto_setToFun_approxOn_of_measurable (hT : DominatedFinMeasAdditive μ T C)
[MeasurableSpace E] [BorelSpace E] {f : α → E} {s : Set E} [SeparableSpace s]
(hfi : Integrable f μ) (hfm : Measurable f) (hs : ∀ᵐ x ∂μ, f x ∈ closure s) {y₀ : E}
(h₀ : y₀ ∈ s) (h₀i : Integrable (fun _ => y₀) μ) :
Tendsto (fun n => setToFun μ T hT (SimpleFunc.approxOn f hfm s y₀ h₀ n)) atTop
(𝓝 <| setToFun μ T hT f) :=
tendsto_setToFun_of_L1 hT _ hfi
(Eventually.of_forall (SimpleFunc.integrable_approxOn hfm hfi h₀ h₀i))
(SimpleFunc.tendsto_approxOn_L1_enorm hfm _ hs (hfi.sub h₀i).2)
theorem tendsto_setToFun_approxOn_of_measurable_of_range_subset
(hT : DominatedFinMeasAdditive μ T C) [MeasurableSpace E] [BorelSpace E] {f : α → E}
(fmeas : Measurable f) (hf : Integrable f μ) (s : Set E) [SeparableSpace s]
(hs : range f ∪ {0} ⊆ s) :
Tendsto (fun n => setToFun μ T hT (SimpleFunc.approxOn f fmeas s 0 (hs <| by simp) n)) atTop
(𝓝 <| setToFun μ T hT f) := by
refine tendsto_setToFun_approxOn_of_measurable hT hf fmeas ?_ _ (integrable_zero _ _ _)
exact Eventually.of_forall fun x => subset_closure (hs (Set.mem_union_left _ (mem_range_self _)))
/-- Auxiliary lemma for `setToFun_congr_measure`: the function sending `f : α →₁[μ] G` to
`f : α →₁[μ'] G` is continuous when `μ' ≤ c' • μ` for `c' ≠ ∞`. -/
theorem continuous_L1_toL1 {μ' : Measure α} (c' : ℝ≥0∞) (hc' : c' ≠ ∞) (hμ'_le : μ' ≤ c' • μ) :
Continuous fun f : α →₁[μ] G =>
(Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f)).toL1 f := by
by_cases hc'0 : c' = 0
· have hμ'0 : μ' = 0 := by rw [← Measure.nonpos_iff_eq_zero']; refine hμ'_le.trans ?_; simp [hc'0]
have h_im_zero :
(fun f : α →₁[μ] G =>
(Integrable.of_measure_le_smul hc' hμ'_le (L1.integrable_coeFn f)).toL1 f) =
0 := by
ext1 f; ext1; simp_rw [hμ'0]; simp only [ae_zero, EventuallyEq, eventually_bot]
rw [h_im_zero]
exact continuous_zero
rw [Metric.continuous_iff]
intro f ε hε_pos
use ε / 2 / c'.toReal
refine ⟨div_pos (half_pos hε_pos) (toReal_pos hc'0 hc'), ?_⟩
intro g hfg
rw [Lp.dist_def] at hfg ⊢
let h_int := fun f' : α →₁[μ] G => (L1.integrable_coeFn f').of_measure_le_smul hc' hμ'_le
have :
eLpNorm (⇑(Integrable.toL1 g (h_int g)) - ⇑(Integrable.toL1 f (h_int f))) 1 μ' =
eLpNorm (⇑g - ⇑f) 1 μ' :=
eLpNorm_congr_ae ((Integrable.coeFn_toL1 _).sub (Integrable.coeFn_toL1 _))
rw [this]
have h_eLpNorm_ne_top : eLpNorm (⇑g - ⇑f) 1 μ ≠ ∞ := by
rw [← eLpNorm_congr_ae (Lp.coeFn_sub _ _)]; exact Lp.eLpNorm_ne_top _
calc
(eLpNorm (⇑g - ⇑f) 1 μ').toReal ≤ (c' * eLpNorm (⇑g - ⇑f) 1 μ).toReal := by
refine toReal_mono (ENNReal.mul_ne_top hc' h_eLpNorm_ne_top) ?_
refine (eLpNorm_mono_measure (⇑g - ⇑f) hμ'_le).trans_eq ?_
rw [eLpNorm_smul_measure_of_ne_zero hc'0, smul_eq_mul]
simp
_ = c'.toReal * (eLpNorm (⇑g - ⇑f) 1 μ).toReal := toReal_mul
_ ≤ c'.toReal * (ε / 2 / c'.toReal) := by gcongr
_ = ε / 2 := by
refine mul_div_cancel₀ (ε / 2) ?_; rw [Ne, toReal_eq_zero_iff]; simp [hc', hc'0]
_ < ε := half_lt_self hε_pos
theorem setToFun_congr_measure_of_integrable {μ' : Measure α} (c' : ℝ≥0∞) (hc' : c' ≠ ∞)
(hμ'_le : μ' ≤ c' • μ) (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ' T C') (f : α → E) (hfμ : Integrable f μ) :
setToFun μ T hT f = setToFun μ' T hT' f := by
-- integrability for `μ` implies integrability for `μ'`.
have h_int : ∀ g : α → E, Integrable g μ → Integrable g μ' := fun g hg =>
Integrable.of_measure_le_smul hc' hμ'_le hg
-- We use `Integrable.induction`
apply hfμ.induction (P := fun f => setToFun μ T hT f = setToFun μ' T hT' f)
· intro c s hs hμs
have hμ's : μ' s ≠ ∞ := by
refine ((hμ'_le s).trans_lt ?_).ne
rw [Measure.smul_apply, smul_eq_mul]
exact ENNReal.mul_lt_top hc'.lt_top hμs
rw [setToFun_indicator_const hT hs hμs.ne, setToFun_indicator_const hT' hs hμ's]
· intro f₂ g₂ _ hf₂ hg₂ h_eq_f h_eq_g
rw [setToFun_add hT hf₂ hg₂, setToFun_add hT' (h_int f₂ hf₂) (h_int g₂ hg₂), h_eq_f, h_eq_g]
· refine isClosed_eq (continuous_setToFun hT) ?_
have :
(fun f : α →₁[μ] E => setToFun μ' T hT' f) = fun f : α →₁[μ] E =>
setToFun μ' T hT' ((h_int f (L1.integrable_coeFn f)).toL1 f) := by
ext1 f; exact setToFun_congr_ae hT' (Integrable.coeFn_toL1 _).symm
rw [this]
exact (continuous_setToFun hT').comp (continuous_L1_toL1 c' hc' hμ'_le)
· intro f₂ g₂ hfg _ hf_eq
have hfg' : f₂ =ᵐ[μ'] g₂ := (Measure.absolutelyContinuous_of_le_smul hμ'_le).ae_eq hfg
rw [← setToFun_congr_ae hT hfg, hf_eq, setToFun_congr_ae hT' hfg']
theorem setToFun_congr_measure {μ' : Measure α} (c c' : ℝ≥0∞) (hc : c ≠ ∞) (hc' : c' ≠ ∞)
(hμ_le : μ ≤ c • μ') (hμ'_le : μ' ≤ c' • μ) (hT : DominatedFinMeasAdditive μ T C)
(hT' : DominatedFinMeasAdditive μ' T C') (f : α → E) :
setToFun μ T hT f = setToFun μ' T hT' f := by
by_cases hf : Integrable f μ
· exact setToFun_congr_measure_of_integrable c' hc' hμ'_le hT hT' f hf
· -- if `f` is not integrable, both `setToFun` are 0.
have h_int : ∀ g : α → E, ¬Integrable g μ → ¬Integrable g μ' := fun g =>
mt fun h => h.of_measure_le_smul hc hμ_le
simp_rw [setToFun_undef _ hf, setToFun_undef _ (h_int f hf)]
theorem setToFun_congr_measure_of_add_right {μ' : Measure α}
(hT_add : DominatedFinMeasAdditive (μ + μ') T C') (hT : DominatedFinMeasAdditive μ T C)
(f : α → E) (hf : Integrable f (μ + μ')) :
setToFun (μ + μ') T hT_add f = setToFun μ T hT f := by
refine setToFun_congr_measure_of_integrable 1 one_ne_top ?_ hT_add hT f hf
rw [one_smul]
nth_rw 1 [← add_zero μ]
exact add_le_add le_rfl bot_le
theorem setToFun_congr_measure_of_add_left {μ' : Measure α}
(hT_add : DominatedFinMeasAdditive (μ + μ') T C') (hT : DominatedFinMeasAdditive μ' T C)
(f : α → E) (hf : Integrable f (μ + μ')) :
setToFun (μ + μ') T hT_add f = setToFun μ' T hT f := by
refine setToFun_congr_measure_of_integrable 1 one_ne_top ?_ hT_add hT f hf
rw [one_smul]
nth_rw 1 [← zero_add μ']
exact add_le_add_right bot_le μ'
theorem setToFun_top_smul_measure (hT : DominatedFinMeasAdditive (∞ • μ) T C) (f : α → E) :
setToFun (∞ • μ) T hT f = 0 := by
refine setToFun_measure_zero' hT fun s _ hμs => ?_
rw [lt_top_iff_ne_top] at hμs
simp only [true_and, Measure.smul_apply, ENNReal.mul_eq_top, eq_self_iff_true,
top_ne_zero, Ne, not_false_iff, not_or, Classical.not_not, smul_eq_mul] at hμs
simp only [hμs.right, Measure.smul_apply, mul_zero, smul_eq_mul]
theorem setToFun_congr_smul_measure (c : ℝ≥0∞) (hc_ne_top : c ≠ ∞)
(hT : DominatedFinMeasAdditive μ T C) (hT_smul : DominatedFinMeasAdditive (c • μ) T C')
(f : α → E) : setToFun μ T hT f = setToFun (c • μ) T hT_smul f := by
by_cases hc0 : c = 0
· simp [hc0] at hT_smul
have h : ∀ s, MeasurableSet s → μ s < ∞ → T s = 0 := fun s hs _ => hT_smul.eq_zero hs
rw [setToFun_zero_left' _ h, setToFun_measure_zero]
simp [hc0]
refine setToFun_congr_measure c⁻¹ c ?_ hc_ne_top (le_of_eq ?_) le_rfl hT hT_smul f
· simp [hc0]
· rw [smul_smul, ENNReal.inv_mul_cancel hc0 hc_ne_top, one_smul]
theorem norm_setToFun_le_mul_norm (hT : DominatedFinMeasAdditive μ T C) (f : α →₁[μ] E)
(hC : 0 ≤ C) : ‖setToFun μ T hT f‖ ≤ C * ‖f‖ := by
rw [L1.setToFun_eq_setToL1]; exact L1.norm_setToL1_le_mul_norm hT hC f
theorem norm_setToFun_le_mul_norm' (hT : DominatedFinMeasAdditive μ T C) (f : α →₁[μ] E) :
‖setToFun μ T hT f‖ ≤ max C 0 * ‖f‖ := by
rw [L1.setToFun_eq_setToL1]; exact L1.norm_setToL1_le_mul_norm' hT f
theorem norm_setToFun_le (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ) (hC : 0 ≤ C) :
‖setToFun μ T hT f‖ ≤ C * ‖hf.toL1 f‖ := by
rw [setToFun_eq hT hf]; exact L1.norm_setToL1_le_mul_norm hT hC _
theorem norm_setToFun_le' (hT : DominatedFinMeasAdditive μ T C) (hf : Integrable f μ) :
‖setToFun μ T hT f‖ ≤ max C 0 * ‖hf.toL1 f‖ := by
rw [setToFun_eq hT hf]; exact L1.norm_setToL1_le_mul_norm' hT _
/-- Lebesgue dominated convergence theorem provides sufficient conditions under which almost
everywhere convergence of a sequence of functions implies the convergence of their image by
`setToFun`.
We could weaken the condition `bound_integrable` to require `HasFiniteIntegral bound μ` instead
(i.e. not requiring that `bound` is measurable), but in all applications proving integrability
is easier. -/
theorem tendsto_setToFun_of_dominated_convergence (hT : DominatedFinMeasAdditive μ T C)
{fs : ℕ → α → E} {f : α → E} (bound : α → ℝ)
(fs_measurable : ∀ n, AEStronglyMeasurable (fs n) μ) (bound_integrable : Integrable bound μ)
(h_bound : ∀ n, ∀ᵐ a ∂μ, ‖fs n a‖ ≤ bound a)
(h_lim : ∀ᵐ a ∂μ, Tendsto (fun n => fs n a) atTop (𝓝 (f a))) :
Tendsto (fun n => setToFun μ T hT (fs n)) atTop (𝓝 <| setToFun μ T hT f) := by
-- `f` is a.e.-measurable, since it is the a.e.-pointwise limit of a.e.-measurable functions.
have f_measurable : AEStronglyMeasurable f μ :=
aestronglyMeasurable_of_tendsto_ae _ fs_measurable h_lim
-- all functions we consider are integrable
have fs_int : ∀ n, Integrable (fs n) μ := fun n =>
bound_integrable.mono' (fs_measurable n) (h_bound _)
have f_int : Integrable f μ :=
⟨f_measurable,
hasFiniteIntegral_of_dominated_convergence bound_integrable.hasFiniteIntegral h_bound
h_lim⟩
-- it suffices to prove the result for the corresponding L1 functions
suffices
Tendsto (fun n => L1.setToL1 hT ((fs_int n).toL1 (fs n))) atTop
(𝓝 (L1.setToL1 hT (f_int.toL1 f))) by
convert this with n
· exact setToFun_eq hT (fs_int n)
· exact setToFun_eq hT f_int
-- the convergence of setToL1 follows from the convergence of the L1 functions
refine L1.tendsto_setToL1 hT _ _ ?_
-- up to some rewriting, what we need to prove is `h_lim`
rw [tendsto_iff_norm_sub_tendsto_zero]
have lintegral_norm_tendsto_zero :
Tendsto (fun n => ENNReal.toReal <| ∫⁻ a, ENNReal.ofReal ‖fs n a - f a‖ ∂μ) atTop (𝓝 0) :=
(tendsto_toReal zero_ne_top).comp
(tendsto_lintegral_norm_of_dominated_convergence fs_measurable
bound_integrable.hasFiniteIntegral h_bound h_lim)
convert lintegral_norm_tendsto_zero with n
rw [L1.norm_def]
congr 1
refine lintegral_congr_ae ?_
rw [← Integrable.toL1_sub]
refine ((fs_int n).sub f_int).coeFn_toL1.mono fun x hx => ?_
dsimp only
rw [hx, ofReal_norm_eq_enorm, Pi.sub_apply]
/-- Lebesgue dominated convergence theorem for filters with a countable basis -/
theorem tendsto_setToFun_filter_of_dominated_convergence (hT : DominatedFinMeasAdditive μ T C) {ι}
{l : Filter ι} [l.IsCountablyGenerated] {fs : ι → α → E} {f : α → E} (bound : α → ℝ)
(hfs_meas : ∀ᶠ n in l, AEStronglyMeasurable (fs n) μ)
(h_bound : ∀ᶠ n in l, ∀ᵐ a ∂μ, ‖fs n a‖ ≤ bound a) (bound_integrable : Integrable bound μ)
(h_lim : ∀ᵐ a ∂μ, Tendsto (fun n => fs n a) l (𝓝 (f a))) :
Tendsto (fun n => setToFun μ T hT (fs n)) l (𝓝 <| setToFun μ T hT f) := by
rw [tendsto_iff_seq_tendsto]
intro x xl
have hxl : ∀ s ∈ l, ∃ a, ∀ b ≥ a, x b ∈ s := by rwa [tendsto_atTop'] at xl
have h :
{ x : ι | (fun n => AEStronglyMeasurable (fs n) μ) x } ∩
{ x : ι | (fun n => ∀ᵐ a ∂μ, ‖fs n a‖ ≤ bound a) x } ∈ l :=
inter_mem hfs_meas h_bound
obtain ⟨k, h⟩ := hxl _ h
rw [← tendsto_add_atTop_iff_nat k]
refine tendsto_setToFun_of_dominated_convergence hT bound ?_ bound_integrable ?_ ?_
· exact fun n => (h _ (self_le_add_left _ _)).1
· exact fun n => (h _ (self_le_add_left _ _)).2
· filter_upwards [h_lim]
refine fun a h_lin => @Tendsto.comp _ _ _ (fun n => x (n + k)) (fun n => fs n a) _ _ _ h_lin ?_
rwa [tendsto_add_atTop_iff_nat]
variable {X : Type*} [TopologicalSpace X] [FirstCountableTopology X]
theorem continuousWithinAt_setToFun_of_dominated (hT : DominatedFinMeasAdditive μ T C)
{fs : X → α → E} {x₀ : X} {bound : α → ℝ} {s : Set X}
(hfs_meas : ∀ᶠ x in 𝓝[s] x₀, AEStronglyMeasurable (fs x) μ)
(h_bound : ∀ᶠ x in 𝓝[s] x₀, ∀ᵐ a ∂μ, ‖fs x a‖ ≤ bound a) (bound_integrable : Integrable bound μ)
(h_cont : ∀ᵐ a ∂μ, ContinuousWithinAt (fun x => fs x a) s x₀) :
ContinuousWithinAt (fun x => setToFun μ T hT (fs x)) s x₀ :=
tendsto_setToFun_filter_of_dominated_convergence hT bound ‹_› ‹_› ‹_› ‹_›
theorem continuousAt_setToFun_of_dominated (hT : DominatedFinMeasAdditive μ T C) {fs : X → α → E}
{x₀ : X} {bound : α → ℝ} (hfs_meas : ∀ᶠ x in 𝓝 x₀, AEStronglyMeasurable (fs x) μ)
(h_bound : ∀ᶠ x in 𝓝 x₀, ∀ᵐ a ∂μ, ‖fs x a‖ ≤ bound a) (bound_integrable : Integrable bound μ)
(h_cont : ∀ᵐ a ∂μ, ContinuousAt (fun x => fs x a) x₀) :
ContinuousAt (fun x => setToFun μ T hT (fs x)) x₀ :=
tendsto_setToFun_filter_of_dominated_convergence hT bound ‹_› ‹_› ‹_› ‹_›
theorem continuousOn_setToFun_of_dominated (hT : DominatedFinMeasAdditive μ T C) {fs : X → α → E}
{bound : α → ℝ} {s : Set X} (hfs_meas : ∀ x ∈ s, AEStronglyMeasurable (fs x) μ)
(h_bound : ∀ x ∈ s, ∀ᵐ a ∂μ, ‖fs x a‖ ≤ bound a) (bound_integrable : Integrable bound μ)
(h_cont : ∀ᵐ a ∂μ, ContinuousOn (fun x => fs x a) s) :
ContinuousOn (fun x => setToFun μ T hT (fs x)) s := by
intro x hx
refine continuousWithinAt_setToFun_of_dominated hT ?_ ?_ bound_integrable ?_
· filter_upwards [self_mem_nhdsWithin] with x hx using hfs_meas x hx
· filter_upwards [self_mem_nhdsWithin] with x hx using h_bound x hx
· filter_upwards [h_cont] with a ha using ha x hx
theorem continuous_setToFun_of_dominated (hT : DominatedFinMeasAdditive μ T C) {fs : X → α → E}
{bound : α → ℝ} (hfs_meas : ∀ x, AEStronglyMeasurable (fs x) μ)
(h_bound : ∀ x, ∀ᵐ a ∂μ, ‖fs x a‖ ≤ bound a) (bound_integrable : Integrable bound μ)
(h_cont : ∀ᵐ a ∂μ, Continuous fun x => fs x a) : Continuous fun x => setToFun μ T hT (fs x) :=
continuous_iff_continuousAt.mpr fun _ =>
continuousAt_setToFun_of_dominated hT (Eventually.of_forall hfs_meas)
(Eventually.of_forall h_bound) ‹_› <|
h_cont.mono fun _ => Continuous.continuousAt
end Function
end MeasureTheory
| Mathlib/MeasureTheory/Integral/SetToL1.lean | 1,453 | 1,459 | |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Bryan Gin-ge Chen
-/
import Mathlib.Order.Heyting.Basic
/-!
# (Generalized) Boolean algebras
A Boolean algebra is a bounded distributive lattice with a complement operator. Boolean algebras
generalize the (classical) logic of propositions and the lattice of subsets of a set.
Generalized Boolean algebras may be less familiar, but they are essentially Boolean algebras which
do not necessarily have a top element (`⊤`) (and hence not all elements may have complements). One
example in mathlib is `Finset α`, the type of all finite subsets of an arbitrary
(not-necessarily-finite) type `α`.
`GeneralizedBooleanAlgebra α` is defined to be a distributive lattice with bottom (`⊥`) admitting
a *relative* complement operator, written using "set difference" notation as `x \ y` (`sdiff x y`).
For convenience, the `BooleanAlgebra` type class is defined to extend `GeneralizedBooleanAlgebra`
so that it is also bundled with a `\` operator.
(A terminological point: `x \ y` is the complement of `y` relative to the interval `[⊥, x]`. We do
not yet have relative complements for arbitrary intervals, as we do not even have lattice
intervals.)
## Main declarations
* `GeneralizedBooleanAlgebra`: a type class for generalized Boolean algebras
* `BooleanAlgebra`: a type class for Boolean algebras.
* `Prop.booleanAlgebra`: the Boolean algebra instance on `Prop`
## Implementation notes
The `sup_inf_sdiff` and `inf_inf_sdiff` axioms for the relative complement operator in
`GeneralizedBooleanAlgebra` are taken from
[Wikipedia](https://en.wikipedia.org/wiki/Boolean_algebra_(structure)#Generalizations).
[Stone's paper introducing generalized Boolean algebras][Stone1935] does not define a relative
complement operator `a \ b` for all `a`, `b`. Instead, the postulates there amount to an assumption
that for all `a, b : α` where `a ≤ b`, the equations `x ⊔ a = b` and `x ⊓ a = ⊥` have a solution
`x`. `Disjoint.sdiff_unique` proves that this `x` is in fact `b \ a`.
## References
* <https://en.wikipedia.org/wiki/Boolean_algebra_(structure)#Generalizations>
* [*Postulates for Boolean Algebras and Generalized Boolean Algebras*, M.H. Stone][Stone1935]
* [*Lattice Theory: Foundation*, George Grätzer][Gratzer2011]
## Tags
generalized Boolean algebras, Boolean algebras, lattices, sdiff, compl
-/
assert_not_exists RelIso
open Function OrderDual
universe u v
variable {α : Type u} {β : Type*} {x y z : α}
/-!
### Generalized Boolean algebras
Some of the lemmas in this section are from:
* [*Lattice Theory: Foundation*, George Grätzer][Gratzer2011]
* <https://ncatlab.org/nlab/show/relative+complement>
* <https://people.math.gatech.edu/~mccuan/courses/4317/symmetricdifference.pdf>
-/
/-- A generalized Boolean algebra is a distributive lattice with `⊥` and a relative complement
operation `\` (called `sdiff`, after "set difference") satisfying `(a ⊓ b) ⊔ (a \ b) = a` and
`(a ⊓ b) ⊓ (a \ b) = ⊥`, i.e. `a \ b` is the complement of `b` in `a`.
This is a generalization of Boolean algebras which applies to `Finset α` for arbitrary
(not-necessarily-`Fintype`) `α`. -/
class GeneralizedBooleanAlgebra (α : Type u) extends DistribLattice α, SDiff α, Bot α where
/-- For any `a`, `b`, `(a ⊓ b) ⊔ (a / b) = a` -/
sup_inf_sdiff : ∀ a b : α, a ⊓ b ⊔ a \ b = a
/-- For any `a`, `b`, `(a ⊓ b) ⊓ (a / b) = ⊥` -/
inf_inf_sdiff : ∀ a b : α, a ⊓ b ⊓ a \ b = ⊥
-- We might want an `IsCompl_of` predicate (for relative complements) generalizing `IsCompl`,
-- however we'd need another type class for lattices with bot, and all the API for that.
section GeneralizedBooleanAlgebra
variable [GeneralizedBooleanAlgebra α]
@[simp]
theorem sup_inf_sdiff (x y : α) : x ⊓ y ⊔ x \ y = x :=
GeneralizedBooleanAlgebra.sup_inf_sdiff _ _
@[simp]
theorem inf_inf_sdiff (x y : α) : x ⊓ y ⊓ x \ y = ⊥ :=
GeneralizedBooleanAlgebra.inf_inf_sdiff _ _
@[simp]
theorem sup_sdiff_inf (x y : α) : x \ y ⊔ x ⊓ y = x := by rw [sup_comm, sup_inf_sdiff]
@[simp]
theorem inf_sdiff_inf (x y : α) : x \ y ⊓ (x ⊓ y) = ⊥ := by rw [inf_comm, inf_inf_sdiff]
-- see Note [lower instance priority]
instance (priority := 100) GeneralizedBooleanAlgebra.toOrderBot : OrderBot α where
__ := GeneralizedBooleanAlgebra.toBot
bot_le a := by
rw [← inf_inf_sdiff a a, inf_assoc]
exact inf_le_left
theorem disjoint_inf_sdiff : Disjoint (x ⊓ y) (x \ y) :=
disjoint_iff_inf_le.mpr (inf_inf_sdiff x y).le
-- TODO: in distributive lattices, relative complements are unique when they exist
theorem sdiff_unique (s : x ⊓ y ⊔ z = x) (i : x ⊓ y ⊓ z = ⊥) : x \ y = z := by
conv_rhs at s => rw [← sup_inf_sdiff x y, sup_comm]
rw [sup_comm] at s
conv_rhs at i => rw [← inf_inf_sdiff x y, inf_comm]
rw [inf_comm] at i
exact (eq_of_inf_eq_sup_eq i s).symm
-- Use `sdiff_le`
private theorem sdiff_le' : x \ y ≤ x :=
calc
x \ y ≤ x ⊓ y ⊔ x \ y := le_sup_right
_ = x := sup_inf_sdiff x y
-- Use `sdiff_sup_self`
private theorem sdiff_sup_self' : y \ x ⊔ x = y ⊔ x :=
calc
y \ x ⊔ x = y \ x ⊔ (x ⊔ x ⊓ y) := by rw [sup_inf_self]
_ = y ⊓ x ⊔ y \ x ⊔ x := by ac_rfl
_ = y ⊔ x := by rw [sup_inf_sdiff]
@[simp]
theorem sdiff_inf_sdiff : x \ y ⊓ y \ x = ⊥ :=
Eq.symm <|
calc
⊥ = x ⊓ y ⊓ x \ y := by rw [inf_inf_sdiff]
_ = x ⊓ (y ⊓ x ⊔ y \ x) ⊓ x \ y := by rw [sup_inf_sdiff]
_ = (x ⊓ (y ⊓ x) ⊔ x ⊓ y \ x) ⊓ x \ y := by rw [inf_sup_left]
_ = (y ⊓ (x ⊓ x) ⊔ x ⊓ y \ x) ⊓ x \ y := by ac_rfl
_ = (y ⊓ x ⊔ x ⊓ y \ x) ⊓ x \ y := by rw [inf_idem]
_ = x ⊓ y ⊓ x \ y ⊔ x ⊓ y \ x ⊓ x \ y := by rw [inf_sup_right, inf_comm x y]
_ = x ⊓ y \ x ⊓ x \ y := by rw [inf_inf_sdiff, bot_sup_eq]
_ = x ⊓ x \ y ⊓ y \ x := by ac_rfl
_ = x \ y ⊓ y \ x := by rw [inf_of_le_right sdiff_le']
theorem disjoint_sdiff_sdiff : Disjoint (x \ y) (y \ x) :=
disjoint_iff_inf_le.mpr sdiff_inf_sdiff.le
@[simp]
theorem inf_sdiff_self_right : x ⊓ y \ x = ⊥ :=
calc
x ⊓ y \ x = (x ⊓ y ⊔ x \ y) ⊓ y \ x := by rw [sup_inf_sdiff]
_ = x ⊓ y ⊓ y \ x ⊔ x \ y ⊓ y \ x := by rw [inf_sup_right]
_ = ⊥ := by rw [inf_comm x y, inf_inf_sdiff, sdiff_inf_sdiff, bot_sup_eq]
@[simp]
theorem inf_sdiff_self_left : y \ x ⊓ x = ⊥ := by rw [inf_comm, inf_sdiff_self_right]
-- see Note [lower instance priority]
instance (priority := 100) GeneralizedBooleanAlgebra.toGeneralizedCoheytingAlgebra :
GeneralizedCoheytingAlgebra α where
__ := ‹GeneralizedBooleanAlgebra α›
__ := GeneralizedBooleanAlgebra.toOrderBot
sdiff := (· \ ·)
sdiff_le_iff y x z :=
⟨fun h =>
le_of_inf_le_sup_le
(le_of_eq
(calc
y ⊓ y \ x = y \ x := inf_of_le_right sdiff_le'
_ = x ⊓ y \ x ⊔ z ⊓ y \ x := by
rw [inf_eq_right.2 h, inf_sdiff_self_right, bot_sup_eq]
_ = (x ⊔ z) ⊓ y \ x := by rw [← inf_sup_right]))
(calc
y ⊔ y \ x = y := sup_of_le_left sdiff_le'
_ ≤ y ⊔ (x ⊔ z) := le_sup_left
_ = y \ x ⊔ x ⊔ z := by rw [← sup_assoc, ← @sdiff_sup_self' _ x y]
_ = x ⊔ z ⊔ y \ x := by ac_rfl),
fun h =>
le_of_inf_le_sup_le
(calc
y \ x ⊓ x = ⊥ := inf_sdiff_self_left
_ ≤ z ⊓ x := bot_le)
(calc
y \ x ⊔ x = y ⊔ x := sdiff_sup_self'
_ ≤ x ⊔ z ⊔ x := sup_le_sup_right h x
_ ≤ z ⊔ x := by rw [sup_assoc, sup_comm, sup_assoc, sup_idem])⟩
theorem disjoint_sdiff_self_left : Disjoint (y \ x) x :=
disjoint_iff_inf_le.mpr inf_sdiff_self_left.le
theorem disjoint_sdiff_self_right : Disjoint x (y \ x) :=
disjoint_iff_inf_le.mpr inf_sdiff_self_right.le
lemma le_sdiff : x ≤ y \ z ↔ x ≤ y ∧ Disjoint x z :=
⟨fun h ↦ ⟨h.trans sdiff_le, disjoint_sdiff_self_left.mono_left h⟩, fun h ↦
by rw [← h.2.sdiff_eq_left]; exact sdiff_le_sdiff_right h.1⟩
@[simp] lemma sdiff_eq_left : x \ y = x ↔ Disjoint x y :=
⟨fun h ↦ disjoint_sdiff_self_left.mono_left h.ge, Disjoint.sdiff_eq_left⟩
/- TODO: we could make an alternative constructor for `GeneralizedBooleanAlgebra` using
`Disjoint x (y \ x)` and `x ⊔ (y \ x) = y` as axioms. -/
theorem Disjoint.sdiff_eq_of_sup_eq (hi : Disjoint x z) (hs : x ⊔ z = y) : y \ x = z :=
have h : y ⊓ x = x := inf_eq_right.2 <| le_sup_left.trans hs.le
sdiff_unique (by rw [h, hs]) (by rw [h, hi.eq_bot])
protected theorem Disjoint.sdiff_unique (hd : Disjoint x z) (hz : z ≤ y) (hs : y ≤ x ⊔ z) :
y \ x = z :=
sdiff_unique
(by
rw [← inf_eq_right] at hs
rwa [sup_inf_right, inf_sup_right, sup_comm x, inf_sup_self, inf_comm, sup_comm z,
hs, sup_eq_left])
(by rw [inf_assoc, hd.eq_bot, inf_bot_eq])
-- cf. `IsCompl.disjoint_left_iff` and `IsCompl.disjoint_right_iff`
theorem disjoint_sdiff_iff_le (hz : z ≤ y) (hx : x ≤ y) : Disjoint z (y \ x) ↔ z ≤ x :=
⟨fun H =>
le_of_inf_le_sup_le (le_trans H.le_bot bot_le)
(by
rw [sup_sdiff_cancel_right hx]
refine le_trans (sup_le_sup_left sdiff_le z) ?_
rw [sup_eq_right.2 hz]),
fun H => disjoint_sdiff_self_right.mono_left H⟩
-- cf. `IsCompl.le_left_iff` and `IsCompl.le_right_iff`
theorem le_iff_disjoint_sdiff (hz : z ≤ y) (hx : x ≤ y) : z ≤ x ↔ Disjoint z (y \ x) :=
(disjoint_sdiff_iff_le hz hx).symm
-- cf. `IsCompl.inf_left_eq_bot_iff` and `IsCompl.inf_right_eq_bot_iff`
theorem inf_sdiff_eq_bot_iff (hz : z ≤ y) (hx : x ≤ y) : z ⊓ y \ x = ⊥ ↔ z ≤ x := by
rw [← disjoint_iff]
exact disjoint_sdiff_iff_le hz hx
-- cf. `IsCompl.left_le_iff` and `IsCompl.right_le_iff`
theorem le_iff_eq_sup_sdiff (hz : z ≤ y) (hx : x ≤ y) : x ≤ z ↔ y = z ⊔ y \ x :=
⟨fun H => by
apply le_antisymm
· conv_lhs => rw [← sup_inf_sdiff y x]
apply sup_le_sup_right
rwa [inf_eq_right.2 hx]
· apply le_trans
· apply sup_le_sup_right hz
· rw [sup_sdiff_left],
fun H => by
conv_lhs at H => rw [← sup_sdiff_cancel_right hx]
refine le_of_inf_le_sup_le ?_ H.le
rw [inf_sdiff_self_right]
exact bot_le⟩
-- cf. `IsCompl.sup_inf`
theorem sdiff_sup : y \ (x ⊔ z) = y \ x ⊓ y \ z :=
sdiff_unique
(calc
y ⊓ (x ⊔ z) ⊔ y \ x ⊓ y \ z = (y ⊓ (x ⊔ z) ⊔ y \ x) ⊓ (y ⊓ (x ⊔ z) ⊔ y \ z) := by
rw [sup_inf_left]
_ = (y ⊓ x ⊔ y ⊓ z ⊔ y \ x) ⊓ (y ⊓ x ⊔ y ⊓ z ⊔ y \ z) := by rw [@inf_sup_left _ _ y]
_ = (y ⊓ z ⊔ (y ⊓ x ⊔ y \ x)) ⊓ (y ⊓ x ⊔ (y ⊓ z ⊔ y \ z)) := by ac_rfl
_ = (y ⊓ z ⊔ y) ⊓ (y ⊓ x ⊔ y) := by rw [sup_inf_sdiff, sup_inf_sdiff]
_ = (y ⊔ y ⊓ z) ⊓ (y ⊔ y ⊓ x) := by ac_rfl
_ = y := by rw [sup_inf_self, sup_inf_self, inf_idem])
(calc
y ⊓ (x ⊔ z) ⊓ (y \ x ⊓ y \ z) = (y ⊓ x ⊔ y ⊓ z) ⊓ (y \ x ⊓ y \ z) := by rw [inf_sup_left]
_ = y ⊓ x ⊓ (y \ x ⊓ y \ z) ⊔ y ⊓ z ⊓ (y \ x ⊓ y \ z) := by rw [inf_sup_right]
_ = y ⊓ x ⊓ y \ x ⊓ y \ z ⊔ y \ x ⊓ (y \ z ⊓ (y ⊓ z)) := by ac_rfl
_ = ⊥ := by rw [inf_inf_sdiff, bot_inf_eq, bot_sup_eq, inf_comm (y \ z),
inf_inf_sdiff, inf_bot_eq])
theorem sdiff_eq_sdiff_iff_inf_eq_inf : y \ x = y \ z ↔ y ⊓ x = y ⊓ z :=
⟨fun h => eq_of_inf_eq_sup_eq (a := y \ x) (by rw [inf_inf_sdiff, h, inf_inf_sdiff])
(by rw [sup_inf_sdiff, h, sup_inf_sdiff]),
fun h => by rw [← sdiff_inf_self_right, ← sdiff_inf_self_right z y, inf_comm, h, inf_comm]⟩
theorem sdiff_eq_self_iff_disjoint : x \ y = x ↔ Disjoint y x :=
calc
x \ y = x ↔ x \ y = x \ ⊥ := by rw [sdiff_bot]
_ ↔ x ⊓ y = x ⊓ ⊥ := sdiff_eq_sdiff_iff_inf_eq_inf
_ ↔ Disjoint y x := by rw [inf_bot_eq, inf_comm, disjoint_iff]
theorem sdiff_eq_self_iff_disjoint' : x \ y = x ↔ Disjoint x y := by
rw [sdiff_eq_self_iff_disjoint, disjoint_comm]
theorem sdiff_lt (hx : y ≤ x) (hy : y ≠ ⊥) : x \ y < x := by
refine sdiff_le.lt_of_ne fun h => hy ?_
rw [sdiff_eq_self_iff_disjoint', disjoint_iff] at h
rw [← h, inf_eq_right.mpr hx]
theorem sdiff_lt_left : x \ y < x ↔ ¬ Disjoint y x := by
rw [lt_iff_le_and_ne, Ne, sdiff_eq_self_iff_disjoint, and_iff_right sdiff_le]
@[simp]
theorem le_sdiff_right : x ≤ y \ x ↔ x = ⊥ :=
⟨fun h => disjoint_self.1 (disjoint_sdiff_self_right.mono_right h), fun h => h.le.trans bot_le⟩
@[simp] lemma sdiff_eq_right : x \ y = y ↔ x = ⊥ ∧ y = ⊥ := by
rw [disjoint_sdiff_self_left.eq_iff]; aesop
lemma sdiff_ne_right : x \ y ≠ y ↔ x ≠ ⊥ ∨ y ≠ ⊥ := sdiff_eq_right.not.trans not_and_or
theorem sdiff_lt_sdiff_right (h : x < y) (hz : z ≤ x) : x \ z < y \ z :=
(sdiff_le_sdiff_right h.le).lt_of_not_le
fun h' => h.not_le <| le_sdiff_sup.trans <| sup_le_of_le_sdiff_right h' hz
theorem sup_inf_inf_sdiff : x ⊓ y ⊓ z ⊔ y \ z = x ⊓ y ⊔ y \ z :=
calc
x ⊓ y ⊓ z ⊔ y \ z = x ⊓ (y ⊓ z) ⊔ y \ z := by rw [inf_assoc]
_ = (x ⊔ y \ z) ⊓ y := by rw [sup_inf_right, sup_inf_sdiff]
_ = x ⊓ y ⊔ y \ z := by rw [inf_sup_right, inf_sdiff_left]
theorem sdiff_sdiff_right : x \ (y \ z) = x \ y ⊔ x ⊓ y ⊓ z := by
rw [sup_comm, inf_comm, ← inf_assoc, sup_inf_inf_sdiff]
apply sdiff_unique
· calc
x ⊓ y \ z ⊔ (z ⊓ x ⊔ x \ y) = (x ⊔ (z ⊓ x ⊔ x \ y)) ⊓ (y \ z ⊔ (z ⊓ x ⊔ x \ y)) := by
rw [sup_inf_right]
_ = (x ⊔ x ⊓ z ⊔ x \ y) ⊓ (y \ z ⊔ (x ⊓ z ⊔ x \ y)) := by ac_rfl
_ = x ⊓ (y \ z ⊔ x ⊓ z ⊔ x \ y) := by rw [sup_inf_self, sup_sdiff_left, ← sup_assoc]
_ = x ⊓ (y \ z ⊓ (z ⊔ y) ⊔ x ⊓ (z ⊔ y) ⊔ x \ y) := by
rw [sup_inf_left, sdiff_sup_self', inf_sup_right, sup_comm y]
_ = x ⊓ (y \ z ⊔ (x ⊓ z ⊔ x ⊓ y) ⊔ x \ y) := by
rw [inf_sdiff_sup_right, @inf_sup_left _ _ x z y]
_ = x ⊓ (y \ z ⊔ (x ⊓ z ⊔ (x ⊓ y ⊔ x \ y))) := by ac_rfl
_ = x ⊓ (y \ z ⊔ (x ⊔ x ⊓ z)) := by rw [sup_inf_sdiff, sup_comm (x ⊓ z)]
_ = x := by rw [sup_inf_self, sup_comm, inf_sup_self]
· calc
x ⊓ y \ z ⊓ (z ⊓ x ⊔ x \ y) = x ⊓ y \ z ⊓ (z ⊓ x) ⊔ x ⊓ y \ z ⊓ x \ y := by rw [inf_sup_left]
_ = x ⊓ (y \ z ⊓ z ⊓ x) ⊔ x ⊓ y \ z ⊓ x \ y := by ac_rfl
_ = x ⊓ y \ z ⊓ x \ y := by rw [inf_sdiff_self_left, bot_inf_eq, inf_bot_eq, bot_sup_eq]
_ = x ⊓ (y \ z ⊓ y) ⊓ x \ y := by conv_lhs => rw [← inf_sdiff_left]
_ = x ⊓ (y \ z ⊓ (y ⊓ x \ y)) := by ac_rfl
_ = ⊥ := by rw [inf_sdiff_self_right, inf_bot_eq, inf_bot_eq]
theorem sdiff_sdiff_right' : x \ (y \ z) = x \ y ⊔ x ⊓ z :=
calc
x \ (y \ z) = x \ y ⊔ x ⊓ y ⊓ z := sdiff_sdiff_right
_ = z ⊓ x ⊓ y ⊔ x \ y := by ac_rfl
_ = x \ y ⊔ x ⊓ z := by rw [sup_inf_inf_sdiff, sup_comm, inf_comm]
theorem sdiff_sdiff_eq_sdiff_sup (h : z ≤ x) : x \ (y \ z) = x \ y ⊔ z := by
rw [sdiff_sdiff_right', inf_eq_right.2 h]
@[simp]
theorem sdiff_sdiff_right_self : x \ (x \ y) = x ⊓ y := by
rw [sdiff_sdiff_right, inf_idem, sdiff_self, bot_sup_eq]
theorem sdiff_sdiff_eq_self (h : y ≤ x) : x \ (x \ y) = y := by
rw [sdiff_sdiff_right_self, inf_of_le_right h]
theorem sdiff_eq_symm (hy : y ≤ x) (h : x \ y = z) : x \ z = y := by
rw [← h, sdiff_sdiff_eq_self hy]
theorem sdiff_eq_comm (hy : y ≤ x) (hz : z ≤ x) : x \ y = z ↔ x \ z = y :=
⟨sdiff_eq_symm hy, sdiff_eq_symm hz⟩
theorem eq_of_sdiff_eq_sdiff (hxz : x ≤ z) (hyz : y ≤ z) (h : z \ x = z \ y) : x = y := by
rw [← sdiff_sdiff_eq_self hxz, h, sdiff_sdiff_eq_self hyz]
theorem sdiff_le_sdiff_iff_le (hx : x ≤ z) (hy : y ≤ z) : z \ x ≤ z \ y ↔ y ≤ x := by
refine ⟨fun h ↦ ?_, sdiff_le_sdiff_left⟩
rw [← sdiff_sdiff_eq_self hx, ← sdiff_sdiff_eq_self hy]
exact sdiff_le_sdiff_left h
theorem sdiff_sdiff_left' : (x \ y) \ z = x \ y ⊓ x \ z := by rw [sdiff_sdiff_left, sdiff_sup]
theorem sdiff_sdiff_sup_sdiff : z \ (x \ y ⊔ y \ x) = z ⊓ (z \ x ⊔ y) ⊓ (z \ y ⊔ x) :=
calc
z \ (x \ y ⊔ y \ x) = (z \ x ⊔ z ⊓ x ⊓ y) ⊓ (z \ y ⊔ z ⊓ y ⊓ x) := by
rw [sdiff_sup, sdiff_sdiff_right, sdiff_sdiff_right]
_ = z ⊓ (z \ x ⊔ y) ⊓ (z \ y ⊔ z ⊓ y ⊓ x) := by rw [sup_inf_left, sup_comm, sup_inf_sdiff]
_ = z ⊓ (z \ x ⊔ y) ⊓ (z ⊓ (z \ y ⊔ x)) := by
rw [sup_inf_left, sup_comm (z \ y), sup_inf_sdiff]
_ = z ⊓ z ⊓ (z \ x ⊔ y) ⊓ (z \ y ⊔ x) := by ac_rfl
_ = z ⊓ (z \ x ⊔ y) ⊓ (z \ y ⊔ x) := by rw [inf_idem]
theorem sdiff_sdiff_sup_sdiff' : z \ (x \ y ⊔ y \ x) = z ⊓ x ⊓ y ⊔ z \ x ⊓ z \ y :=
calc
z \ (x \ y ⊔ y \ x) = z \ (x \ y) ⊓ z \ (y \ x) := sdiff_sup
_ = (z \ x ⊔ z ⊓ x ⊓ y) ⊓ (z \ y ⊔ z ⊓ y ⊓ x) := by rw [sdiff_sdiff_right, sdiff_sdiff_right]
_ = (z \ x ⊔ z ⊓ y ⊓ x) ⊓ (z \ y ⊔ z ⊓ y ⊓ x) := by ac_rfl
_ = z \ x ⊓ z \ y ⊔ z ⊓ y ⊓ x := by rw [← sup_inf_right]
_ = z ⊓ x ⊓ y ⊔ z \ x ⊓ z \ y := by ac_rfl
lemma sdiff_sdiff_sdiff_cancel_left (hca : z ≤ x) : (x \ y) \ (x \ z) = z \ y :=
sdiff_sdiff_sdiff_le_sdiff.antisymm <|
(disjoint_sdiff_self_right.mono_left sdiff_le).le_sdiff_of_le_left <| sdiff_le_sdiff_right hca
lemma sdiff_sdiff_sdiff_cancel_right (hcb : z ≤ y) : (x \ z) \ (y \ z) = x \ y := by
rw [le_antisymm_iff, sdiff_le_comm]
exact ⟨sdiff_sdiff_sdiff_le_sdiff,
(disjoint_sdiff_self_left.mono_right sdiff_le).le_sdiff_of_le_left <| sdiff_le_sdiff_left hcb⟩
theorem inf_sdiff : (x ⊓ y) \ z = x \ z ⊓ y \ z :=
sdiff_unique
(calc
x ⊓ y ⊓ z ⊔ x \ z ⊓ y \ z = (x ⊓ y ⊓ z ⊔ x \ z) ⊓ (x ⊓ y ⊓ z ⊔ y \ z) := by rw [sup_inf_left]
_ = (x ⊓ y ⊓ (z ⊔ x) ⊔ x \ z) ⊓ (x ⊓ y ⊓ z ⊔ y \ z) := by
rw [sup_inf_right, sup_sdiff_self_right, inf_sup_right, inf_sdiff_sup_right]
_ = (y ⊓ (x ⊓ (x ⊔ z)) ⊔ x \ z) ⊓ (x ⊓ y ⊓ z ⊔ y \ z) := by ac_rfl
_ = (y ⊓ x ⊔ x \ z) ⊓ (x ⊓ y ⊔ y \ z) := by rw [inf_sup_self, sup_inf_inf_sdiff]
_ = x ⊓ y ⊔ x \ z ⊓ y \ z := by rw [inf_comm y, sup_inf_left]
_ = x ⊓ y := sup_eq_left.2 (inf_le_inf sdiff_le sdiff_le))
(calc
x ⊓ y ⊓ z ⊓ (x \ z ⊓ y \ z) = x ⊓ y ⊓ (z ⊓ x \ z) ⊓ y \ z := by ac_rfl
_ = ⊥ := by rw [inf_sdiff_self_right, inf_bot_eq, bot_inf_eq])
/-- See also `sdiff_inf_right_comm`. -/
theorem inf_sdiff_assoc (x y z : α) : (x ⊓ y) \ z = x ⊓ y \ z :=
sdiff_unique
(calc
x ⊓ y ⊓ z ⊔ x ⊓ y \ z = x ⊓ (y ⊓ z) ⊔ x ⊓ y \ z := by rw [inf_assoc]
_ = x ⊓ (y ⊓ z ⊔ y \ z) := by rw [← inf_sup_left]
_ = x ⊓ y := by rw [sup_inf_sdiff])
(calc
x ⊓ y ⊓ z ⊓ (x ⊓ y \ z) = x ⊓ x ⊓ (y ⊓ z ⊓ y \ z) := by ac_rfl
_ = ⊥ := by rw [inf_inf_sdiff, inf_bot_eq])
/-- See also `inf_sdiff_assoc`. -/
theorem sdiff_inf_right_comm (x y z : α) : x \ z ⊓ y = (x ⊓ y) \ z := by
rw [inf_comm x, inf_comm, inf_sdiff_assoc]
lemma inf_sdiff_left_comm (a b c : α) : a ⊓ (b \ c) = b ⊓ (a \ c) := by
simp_rw [← inf_sdiff_assoc, inf_comm]
@[deprecated (since := "2025-01-08")] alias inf_sdiff_right_comm := sdiff_inf_right_comm
theorem inf_sdiff_distrib_left (a b c : α) : a ⊓ b \ c = (a ⊓ b) \ (a ⊓ c) := by
| rw [sdiff_inf, sdiff_eq_bot_iff.2 inf_le_left, bot_sup_eq, inf_sdiff_assoc]
theorem inf_sdiff_distrib_right (a b c : α) : a \ b ⊓ c = (a ⊓ c) \ (b ⊓ c) := by
simp_rw [inf_comm _ c, inf_sdiff_distrib_left]
theorem disjoint_sdiff_comm : Disjoint (x \ z) y ↔ Disjoint x (y \ z) := by
simp_rw [disjoint_iff, sdiff_inf_right_comm, inf_sdiff_assoc]
theorem sup_eq_sdiff_sup_sdiff_sup_inf : x ⊔ y = x \ y ⊔ y \ x ⊔ x ⊓ y :=
Eq.symm <|
calc
x \ y ⊔ y \ x ⊔ x ⊓ y = (x \ y ⊔ y \ x ⊔ x) ⊓ (x \ y ⊔ y \ x ⊔ y) := by rw [sup_inf_left]
_ = (x \ y ⊔ x ⊔ y \ x) ⊓ (x \ y ⊔ (y \ x ⊔ y)) := by ac_rfl
| Mathlib/Order/BooleanAlgebra.lean | 435 | 447 |
/-
Copyright (c) 2022 Junyan Xu. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Damiano Testa, Junyan Xu
-/
import Mathlib.Data.DFinsupp.Defs
/-!
# Locus of unequal values of finitely supported dependent functions
Let `N : α → Type*` be a type family, assume that `N a` has a `0` for all `a : α` and let
`f g : Π₀ a, N a` be finitely supported dependent functions.
## Main definition
* `DFinsupp.neLocus f g : Finset α`, the finite subset of `α` where `f` and `g` differ.
In the case in which `N a` is an additive group for all `a`, `DFinsupp.neLocus f g` coincides with
`DFinsupp.support (f - g)`.
-/
variable {α : Type*} {N : α → Type*}
namespace DFinsupp
variable [DecidableEq α]
section NHasZero
variable [∀ a, DecidableEq (N a)] [∀ a, Zero (N a)] (f g : Π₀ a, N a)
/-- 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 : Π₀ a, N a) : Finset α :=
(f.support ∪ g.support).filter fun x ↦ f x ≠ g x
@[simp]
theorem mem_neLocus {f g : Π₀ a, N a} {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 : Π₀ a, N a} {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 } :=
Set.ext fun _x ↦ mem_neLocus
@[simp]
theorem neLocus_eq_empty {f g : Π₀ a, N a} : 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 : Π₀ a, N a} : (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 : Π₀ a, N a).neLocus f = f.support :=
(neLocus_comm _ _).trans (neLocus_zero_right _)
end NHasZero
section NeLocusAndMaps
variable {M P : α → Type*} [∀ a, Zero (N a)] [∀ a, Zero (M a)] [∀ a, Zero (P a)]
theorem subset_mapRange_neLocus [∀ a, DecidableEq (N a)] [∀ a, DecidableEq (M a)] (f g : Π₀ a, N a)
{F : ∀ a, N a → M a} (F0 : ∀ a, F a 0 = 0) :
(f.mapRange F F0).neLocus (g.mapRange F F0) ⊆ f.neLocus g := fun a ↦ by
simpa only [mem_neLocus, mapRange_apply, not_imp_not] using congr_arg (F a)
theorem zipWith_neLocus_eq_left [∀ a, DecidableEq (N a)] [∀ a, DecidableEq (P a)]
{F : ∀ a, M a → N a → P a} (F0 : ∀ a, F a 0 0 = 0) (f : Π₀ a, M a) (g₁ g₂ : Π₀ a, N a)
(hF : ∀ a f, Function.Injective fun g ↦ F a f g) :
(zipWith F F0 f g₁).neLocus (zipWith F F0 f g₂) = g₁.neLocus g₂ := by
ext a
simpa only [mem_neLocus] using (hF a _).ne_iff
theorem zipWith_neLocus_eq_right [∀ a, DecidableEq (M a)] [∀ a, DecidableEq (P a)]
{F : ∀ a, M a → N a → P a} (F0 : ∀ a, F a 0 0 = 0) (f₁ f₂ : Π₀ a, M a) (g : Π₀ a, N a)
(hF : ∀ a g, Function.Injective fun f ↦ F a f g) :
(zipWith F F0 f₁ g).neLocus (zipWith F F0 f₂ g) = f₁.neLocus f₂ := by
ext a
simpa only [mem_neLocus] using (hF a _).ne_iff
theorem mapRange_neLocus_eq [∀ a, DecidableEq (N a)] [∀ a, DecidableEq (M a)] (f g : Π₀ a, N a)
{F : ∀ a, N a → M a} (F0 : ∀ a, F a 0 = 0) (hF : ∀ a, Function.Injective (F a)) :
(f.mapRange F F0).neLocus (g.mapRange F F0) = f.neLocus g := by
ext a
simpa only [mem_neLocus] using (hF a).ne_iff
end NeLocusAndMaps
variable [∀ a, DecidableEq (N a)]
@[simp]
theorem neLocus_add_left [∀ a, AddLeftCancelMonoid (N a)] (f g h : Π₀ a, N a) :
(f + g).neLocus (f + h) = g.neLocus h :=
zipWith_neLocus_eq_left _ _ _ _ fun _a ↦ add_right_injective
@[simp]
theorem neLocus_add_right [∀ a, AddRightCancelMonoid (N a)] (f g h : Π₀ a, N a) :
(f + h).neLocus (g + h) = f.neLocus g :=
zipWith_neLocus_eq_right _ _ _ _ fun _a ↦ add_left_injective
section AddGroup
variable [∀ a, AddGroup (N a)] (f f₁ f₂ g g₁ g₂ : Π₀ a, N a)
@[simp]
theorem neLocus_neg_neg : neLocus (-f) (-g) = f.neLocus g :=
mapRange_neLocus_eq _ _ (fun _a ↦ neg_zero) fun _a ↦ 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 α N _ _ _ _ _ (-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 α N _ _ _, 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 α N _ _ _ _ _ _
@[simp]
theorem neLocus_self_add_right : neLocus f (f + g) = g.support := by
rw [← neLocus_zero_left, ← @neLocus_add_left α N _ _ _ 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]
end AddGroup
end DFinsupp
| Mathlib/Data/DFinsupp/NeLocus.lean | 170 | 171 | |
/-
Copyright (c) 2023 Ashvni Narayanan. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Ashvni Narayanan, Moritz Firsching, Michael Stoll
-/
import Mathlib.Algebra.Group.EvenFunction
import Mathlib.Data.ZMod.Units
import Mathlib.NumberTheory.MulChar.Basic
/-!
# Dirichlet Characters
Let `R` be a commutative monoid with zero. A Dirichlet character `χ` of level `n` over `R` is a
multiplicative character from `ZMod n` to `R` sending non-units to 0. We then obtain some properties
of `toUnitHom χ`, the restriction of `χ` to a group homomorphism `(ZMod n)ˣ →* Rˣ`.
Main definitions:
- `DirichletCharacter`: The type representing a Dirichlet character.
- `changeLevel`: Extend the Dirichlet character χ of level `n` to level `m`, where `n` divides `m`.
- `conductor`: The conductor of a Dirichlet character.
- `IsPrimitive`: If the level is equal to the conductor.
## Tags
dirichlet character, multiplicative character
-/
/-!
### Definitions
-/
/-- The type of Dirichlet characters of level `n`. -/
abbrev DirichletCharacter (R : Type*) [CommMonoidWithZero R] (n : ℕ) := MulChar (ZMod n) R
open MulChar
variable {R : Type*} [CommMonoidWithZero R] {n : ℕ} (χ : DirichletCharacter R n)
namespace DirichletCharacter
lemma toUnitHom_eq_char' {a : ZMod n} (ha : IsUnit a) : χ a = χ.toUnitHom ha.unit := by simp
lemma toUnitHom_inj (ψ : DirichletCharacter R n) : toUnitHom χ = toUnitHom ψ ↔ χ = ψ := by simp
@[deprecated (since := "2024-12-29")] alias toUnitHom_eq_iff := toUnitHom_inj
lemma eval_modulus_sub (x : ZMod n) : χ (n - x) = χ (-x) := by simp
/-!
### Changing levels
-/
/-- A function that modifies the level of a Dirichlet character to some multiple
of its original level. -/
noncomputable def changeLevel {n m : ℕ} (hm : n ∣ m) :
DirichletCharacter R n →* DirichletCharacter R m where
toFun ψ := MulChar.ofUnitHom (ψ.toUnitHom.comp (ZMod.unitsMap hm))
map_one' := by ext; simp
map_mul' ψ₁ ψ₂ := by ext; simp
lemma changeLevel_def {m : ℕ} (hm : n ∣ m) :
changeLevel hm χ = MulChar.ofUnitHom (χ.toUnitHom.comp (ZMod.unitsMap hm)) := rfl
lemma changeLevel_toUnitHom {m : ℕ} (hm : n ∣ m) :
(changeLevel hm χ).toUnitHom = χ.toUnitHom.comp (ZMod.unitsMap hm) := by
simp [changeLevel]
/-- The `changeLevel` map is injective (except in the degenerate case `m = 0`). -/
lemma changeLevel_injective {m : ℕ} [NeZero m] (hm : n ∣ m) :
Function.Injective (changeLevel (R := R) hm) := by
intro _ _ h
ext1 y
obtain ⟨z, rfl⟩ := ZMod.unitsMap_surjective hm y
rw [MulChar.ext_iff] at h
simpa [changeLevel_def] using h z
@[simp]
lemma changeLevel_eq_one_iff {m : ℕ} {χ : DirichletCharacter R n} (hm : n ∣ m) [NeZero m] :
changeLevel hm χ = 1 ↔ χ = 1 :=
map_eq_one_iff _ (changeLevel_injective hm)
@[simp]
lemma changeLevel_self : changeLevel (dvd_refl n) χ = χ := by
simp [changeLevel, ZMod.unitsMap]
lemma changeLevel_self_toUnitHom : (changeLevel (dvd_refl n) χ).toUnitHom = χ.toUnitHom := by
rw [changeLevel_self]
lemma changeLevel_trans {m d : ℕ} (hm : n ∣ m) (hd : m ∣ d) :
changeLevel (dvd_trans hm hd) χ = changeLevel hd (changeLevel hm χ) := by
simp [changeLevel_def, MonoidHom.comp_assoc, ZMod.unitsMap_comp]
lemma changeLevel_eq_cast_of_dvd {m : ℕ} (hm : n ∣ m) (a : Units (ZMod m)) :
(changeLevel hm χ) a = χ (ZMod.cast (a : ZMod m)) := by
simp [changeLevel_def, ZMod.unitsMap_val]
/-- `χ` of level `n` factors through a Dirichlet character `χ₀` of level `d` if `d ∣ n` and
`χ₀ = χ ∘ (ZMod n → ZMod d)`. -/
def FactorsThrough (d : ℕ) : Prop :=
∃ (h : d ∣ n) (χ₀ : DirichletCharacter R d), χ = changeLevel h χ₀
lemma changeLevel_factorsThrough {m : ℕ} (hm : n ∣ m) : FactorsThrough (changeLevel hm χ) n :=
⟨hm, χ, rfl⟩
namespace FactorsThrough
variable {χ}
/-- The fact that `d` divides `n` when `χ` factors through a Dirichlet character at level `d` -/
lemma dvd {d : ℕ} (h : FactorsThrough χ d) : d ∣ n := h.1
/-- The Dirichlet character at level `d` through which `χ` factors -/
noncomputable
def χ₀ {d : ℕ} (h : FactorsThrough χ d) : DirichletCharacter R d := Classical.choose h.2
/-- The fact that `χ` factors through `χ₀` of level `d` -/
lemma eq_changeLevel {d : ℕ} (h : FactorsThrough χ d) : χ = changeLevel h.dvd h.χ₀ :=
Classical.choose_spec h.2
/-- The character of level `d` through which `χ` factors is uniquely determined. -/
lemma existsUnique {d : ℕ} [NeZero n] (h : FactorsThrough χ d) :
∃! χ' : DirichletCharacter R d, χ = changeLevel h.dvd χ' := by
rcases h with ⟨hd, χ₂, rfl⟩
exact ⟨χ₂, rfl, fun χ₃ hχ₃ ↦ (changeLevel_injective hd hχ₃).symm⟩
variable (χ) in
lemma same_level : FactorsThrough χ n := ⟨dvd_refl n, χ, (changeLevel_self χ).symm⟩
end FactorsThrough
variable {χ} in
/-- A Dirichlet character `χ` factors through `d | n` iff its associated unit-group hom is trivial
on the kernel of `ZMod.unitsMap`. -/
lemma factorsThrough_iff_ker_unitsMap {d : ℕ} [NeZero n] (hd : d ∣ n) :
FactorsThrough χ d ↔ (ZMod.unitsMap hd).ker ≤ χ.toUnitHom.ker := by
refine ⟨fun ⟨_, ⟨χ₀, hχ₀⟩⟩ x hx ↦ ?_, fun h ↦ ?_⟩
· rw [MonoidHom.mem_ker, hχ₀, changeLevel_toUnitHom, MonoidHom.comp_apply, hx, map_one]
· let E := MonoidHom.liftOfSurjective _ (ZMod.unitsMap_surjective hd) ⟨_, h⟩
have hE : E.comp (ZMod.unitsMap hd) = χ.toUnitHom := MonoidHom.liftOfRightInverse_comp ..
refine ⟨hd, MulChar.ofUnitHom E, equivToUnitHom.injective (?_ : toUnitHom _ = toUnitHom _)⟩
simp_rw [changeLevel_toUnitHom, toUnitHom_eq, ofUnitHom_eq, Equiv.apply_symm_apply, hE,
toUnitHom_eq]
/-!
### Edge cases
-/
lemma level_one (χ : DirichletCharacter R 1) : χ = 1 := by
ext
simp [units_eq_one]
lemma level_one' (hn : n = 1) : χ = 1 := by
subst hn
exact level_one _
instance : Subsingleton (DirichletCharacter R 1) := by
refine subsingleton_iff.mpr (fun χ χ' ↦ ?_)
simp [level_one]
noncomputable instance : Unique (DirichletCharacter R 1) := Unique.mk' (DirichletCharacter R 1)
|
/-- A Dirichlet character of modulus `≠ 1` maps `0` to `0`. -/
lemma map_zero' (hn : n ≠ 1) : χ 0 = 0 :=
| Mathlib/NumberTheory/DirichletCharacter/Basic.lean | 162 | 164 |
/-
Copyright (c) 2020 Paul van Wamelen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Paul van Wamelen
-/
import Mathlib.Data.Int.NatPrime
import Mathlib.Data.ZMod.Basic
import Mathlib.RingTheory.Int.Basic
import Mathlib.Tactic.FieldSimp
/-!
# Pythagorean Triples
The main result is the classification of Pythagorean triples. The final result is for general
Pythagorean triples. It follows from the more interesting relatively prime case. We use the
"rational parametrization of the circle" method for the proof. The parametrization maps the point
`(x / z, y / z)` to the slope of the line through `(-1 , 0)` and `(x / z, y / z)`. This quickly
shows that `(x / z, y / z) = (2 * m * n / (m ^ 2 + n ^ 2), (m ^ 2 - n ^ 2) / (m ^ 2 + n ^ 2))` where
`m / n` is the slope. In order to identify numerators and denominators we now need results showing
that these are coprime. This is easy except for the prime 2. In order to deal with that we have to
analyze the parity of `x`, `y`, `m` and `n` and eliminate all the impossible cases. This takes up
the bulk of the proof below.
-/
assert_not_exists TwoSidedIdeal
theorem sq_ne_two_fin_zmod_four (z : ZMod 4) : z * z ≠ 2 := by
change Fin 4 at z
fin_cases z <;> decide
theorem Int.sq_ne_two_mod_four (z : ℤ) : z * z % 4 ≠ 2 := by
suffices ¬z * z % (4 : ℕ) = 2 % (4 : ℕ) by exact this
rw [← ZMod.intCast_eq_intCast_iff']
simpa using sq_ne_two_fin_zmod_four _
noncomputable section
/-- Three integers `x`, `y`, and `z` form a Pythagorean triple if `x * x + y * y = z * z`. -/
def PythagoreanTriple (x y z : ℤ) : Prop :=
x * x + y * y = z * z
/-- Pythagorean triples are interchangeable, i.e `x * x + y * y = y * y + x * x = z * z`.
This comes from additive commutativity. -/
theorem pythagoreanTriple_comm {x y z : ℤ} : PythagoreanTriple x y z ↔ PythagoreanTriple y x z := by
delta PythagoreanTriple
rw [add_comm]
/-- The zeroth Pythagorean triple is all zeros. -/
theorem PythagoreanTriple.zero : PythagoreanTriple 0 0 0 := by
simp only [PythagoreanTriple, zero_mul, zero_add]
namespace PythagoreanTriple
| variable {x y z : ℤ}
theorem eq (h : PythagoreanTriple x y z) : x * x + y * y = z * z :=
| Mathlib/NumberTheory/PythagoreanTriples.lean | 54 | 56 |
/-
Copyright (c) 2019 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Bhavik Mehta
-/
import Mathlib.CategoryTheory.Limits.Shapes.IsTerminal
import Mathlib.CategoryTheory.Limits.HasLimits
/-!
# Initial and terminal objects in a category.
## References
* [Stacks: Initial and final objects](https://stacks.math.columbia.edu/tag/002B)
-/
noncomputable section
universe w w' v v₁ v₂ u u₁ u₂
open CategoryTheory
namespace CategoryTheory.Limits
variable {C : Type u₁} [Category.{v₁} C]
variable (C)
/-- A category has a terminal object if it has a limit over the empty diagram.
Use `hasTerminal_of_unique` to construct instances.
-/
abbrev HasTerminal :=
HasLimitsOfShape (Discrete.{0} PEmpty) C
/-- A category has an initial object if it has a colimit over the empty diagram.
Use `hasInitial_of_unique` to construct instances.
-/
abbrev HasInitial :=
HasColimitsOfShape (Discrete.{0} PEmpty) C
section Univ
variable (X : C) {F₁ : Discrete.{w} PEmpty ⥤ C} {F₂ : Discrete.{w'} PEmpty ⥤ C}
theorem hasTerminalChangeDiagram (h : HasLimit F₁) : HasLimit F₂ :=
⟨⟨⟨⟨limit F₁, by aesop_cat, by simp⟩,
isLimitChangeEmptyCone C (limit.isLimit F₁) _ (eqToIso rfl)⟩⟩⟩
theorem hasTerminalChangeUniverse [h : HasLimitsOfShape (Discrete.{w} PEmpty) C] :
HasLimitsOfShape (Discrete.{w'} PEmpty) C where
has_limit _ := hasTerminalChangeDiagram C (h.1 (Functor.empty C))
theorem hasInitialChangeDiagram (h : HasColimit F₁) : HasColimit F₂ :=
⟨⟨⟨⟨colimit F₁, by aesop_cat, by simp⟩,
isColimitChangeEmptyCocone C (colimit.isColimit F₁) _ (eqToIso rfl)⟩⟩⟩
theorem hasInitialChangeUniverse [h : HasColimitsOfShape (Discrete.{w} PEmpty) C] :
HasColimitsOfShape (Discrete.{w'} PEmpty) C where
has_colimit _ := hasInitialChangeDiagram C (h.1 (Functor.empty C))
end Univ
/-- An arbitrary choice of terminal object, if one exists.
You can use the notation `⊤_ C`.
This object is characterized by having a unique morphism from any object.
-/
abbrev terminal [HasTerminal C] : C :=
limit (Functor.empty.{0} C)
/-- An arbitrary choice of initial object, if one exists.
You can use the notation `⊥_ C`.
This object is characterized by having a unique morphism to any object.
-/
abbrev initial [HasInitial C] : C :=
colimit (Functor.empty.{0} C)
/-- Notation for the terminal object in `C` -/
notation "⊤_ " C:20 => terminal C
/-- Notation for the initial object in `C` -/
notation "⊥_ " C:20 => initial C
section
variable {C}
/-- We can more explicitly show that a category has a terminal object by specifying the object,
and showing there is a unique morphism to it from any other object. -/
theorem hasTerminal_of_unique (X : C) [∀ Y, Nonempty (Y ⟶ X)] [∀ Y, Subsingleton (Y ⟶ X)] :
HasTerminal C where
has_limit F := .mk ⟨_, (isTerminalEquivUnique F X).invFun fun _ ↦
⟨Classical.inhabited_of_nonempty', (Subsingleton.elim · _)⟩⟩
theorem IsTerminal.hasTerminal {X : C} (h : IsTerminal X) : HasTerminal C :=
{ has_limit := fun F => HasLimit.mk ⟨⟨X, by aesop_cat, by simp⟩,
isLimitChangeEmptyCone _ h _ (Iso.refl _)⟩ }
/-- We can more explicitly show that a category has an initial object by specifying the object,
and showing there is a unique morphism from it to any other object. -/
theorem hasInitial_of_unique (X : C) [∀ Y, Nonempty (X ⟶ Y)] [∀ Y, Subsingleton (X ⟶ Y)] :
HasInitial C where
has_colimit F := .mk ⟨_, (isInitialEquivUnique F X).invFun fun _ ↦
⟨Classical.inhabited_of_nonempty', (Subsingleton.elim · _)⟩⟩
theorem IsInitial.hasInitial {X : C} (h : IsInitial X) : HasInitial C where
has_colimit F :=
HasColimit.mk ⟨⟨X, by aesop_cat, by simp⟩, isColimitChangeEmptyCocone _ h _ (Iso.refl _)⟩
/-- The map from an object to the terminal object. -/
abbrev terminal.from [HasTerminal C] (P : C) : P ⟶ ⊤_ C :=
limit.lift (Functor.empty C) (asEmptyCone P)
/-- The map to an object from the initial object. -/
abbrev initial.to [HasInitial C] (P : C) : ⊥_ C ⟶ P :=
colimit.desc (Functor.empty C) (asEmptyCocone P)
/-- A terminal object is terminal. -/
def terminalIsTerminal [HasTerminal C] : IsTerminal (⊤_ C) where
lift _ := terminal.from _
/-- An initial object is initial. -/
def initialIsInitial [HasInitial C] : IsInitial (⊥_ C) where
desc _ := initial.to _
instance uniqueToTerminal [HasTerminal C] (P : C) : Unique (P ⟶ ⊤_ C) :=
isTerminalEquivUnique _ (⊤_ C) terminalIsTerminal P
instance uniqueFromInitial [HasInitial C] (P : C) : Unique (⊥_ C ⟶ P) :=
isInitialEquivUnique _ (⊥_ C) initialIsInitial P
@[ext] theorem terminal.hom_ext [HasTerminal C] {P : C} (f g : P ⟶ ⊤_ C) : f = g := by ext ⟨⟨⟩⟩
@[ext] theorem initial.hom_ext [HasInitial C] {P : C} (f g : ⊥_ C ⟶ P) : f = g := by ext ⟨⟨⟩⟩
@[reassoc (attr := simp)]
theorem terminal.comp_from [HasTerminal C] {P Q : C} (f : P ⟶ Q) :
f ≫ terminal.from Q = terminal.from P := by
simp [eq_iff_true_of_subsingleton]
-- `initial.to_comp_assoc` does not need the `simp` attribute.
@[simp, reassoc]
theorem initial.to_comp [HasInitial C] {P Q : C} (f : P ⟶ Q) : initial.to P ≫ f = initial.to Q := by
simp [eq_iff_true_of_subsingleton]
/-- The (unique) isomorphism between the chosen initial object and any other initial object. -/
@[simps!]
def initialIsoIsInitial [HasInitial C] {P : C} (t : IsInitial P) : ⊥_ C ≅ P :=
initialIsInitial.uniqueUpToIso t
/-- The (unique) isomorphism between the chosen terminal object and any other terminal object. -/
@[simps!]
def terminalIsoIsTerminal [HasTerminal C] {P : C} (t : IsTerminal P) : ⊤_ C ≅ P :=
terminalIsTerminal.uniqueUpToIso t
/-- Any morphism from a terminal object is split mono. -/
instance terminal.isSplitMono_from {Y : C} [HasTerminal C] (f : ⊤_ C ⟶ Y) : IsSplitMono f :=
IsTerminal.isSplitMono_from terminalIsTerminal _
/-- Any morphism to an initial object is split epi. -/
instance initial.isSplitEpi_to {Y : C} [HasInitial C] (f : Y ⟶ ⊥_ C) : IsSplitEpi f :=
IsInitial.isSplitEpi_to initialIsInitial _
instance hasInitial_op_of_hasTerminal [HasTerminal C] : HasInitial Cᵒᵖ :=
(initialOpOfTerminal terminalIsTerminal).hasInitial
instance hasTerminal_op_of_hasInitial [HasInitial C] : HasTerminal Cᵒᵖ :=
(terminalOpOfInitial initialIsInitial).hasTerminal
theorem hasTerminal_of_hasInitial_op [HasInitial Cᵒᵖ] : HasTerminal C :=
(terminalUnopOfInitial initialIsInitial).hasTerminal
theorem hasInitial_of_hasTerminal_op [HasTerminal Cᵒᵖ] : HasInitial C :=
(initialUnopOfTerminal terminalIsTerminal).hasInitial
instance {J : Type*} [Category J] {C : Type*} [Category C] [HasTerminal C] :
HasLimit ((CategoryTheory.Functor.const J).obj (⊤_ C)) :=
HasLimit.mk
{ cone :=
{ pt := ⊤_ C
π := { app := fun _ => terminal.from _ } }
isLimit := { lift := fun _ => terminal.from _ } }
/-- The limit of the constant `⊤_ C` functor is `⊤_ C`. -/
@[simps hom]
def limitConstTerminal {J : Type*} [Category J] {C : Type*} [Category C] [HasTerminal C] :
limit ((CategoryTheory.Functor.const J).obj (⊤_ C)) ≅ ⊤_ C where
hom := terminal.from _
inv :=
limit.lift ((CategoryTheory.Functor.const J).obj (⊤_ C))
{ pt := ⊤_ C
π := { app := fun _ => terminal.from _ } }
@[reassoc (attr := simp)]
theorem limitConstTerminal_inv_π {J : Type*} [Category J] {C : Type*} [Category C] [HasTerminal C]
{j : J} :
limitConstTerminal.inv ≫ limit.π ((CategoryTheory.Functor.const J).obj (⊤_ C)) j =
terminal.from _ := by aesop_cat
instance {J : Type*} [Category J] {C : Type*} [Category C] [HasInitial C] :
HasColimit ((CategoryTheory.Functor.const J).obj (⊥_ C)) :=
HasColimit.mk
{ cocone :=
{ pt := ⊥_ C
ι := { app := fun _ => initial.to _ } }
isColimit := { desc := fun _ => initial.to _ } }
/-- The colimit of the constant `⊥_ C` functor is `⊥_ C`. -/
@[simps inv]
def colimitConstInitial {J : Type*} [Category J] {C : Type*} [Category C] [HasInitial C] :
colimit ((CategoryTheory.Functor.const J).obj (⊥_ C)) ≅ ⊥_ C where
hom :=
colimit.desc ((CategoryTheory.Functor.const J).obj (⊥_ C))
{ pt := ⊥_ C
ι := { app := fun _ => initial.to _ } }
inv := initial.to _
@[reassoc (attr := simp)]
theorem ι_colimitConstInitial_hom {J : Type*} [Category J] {C : Type*} [Category C] [HasInitial C]
{j : J} :
colimit.ι ((CategoryTheory.Functor.const J).obj (⊥_ C)) j ≫ colimitConstInitial.hom =
initial.to _ := by aesop_cat
instance (priority := 100) initial.mono_from [HasInitial C] [InitialMonoClass C] (X : C)
(f : ⊥_ C ⟶ X) : Mono f :=
initialIsInitial.mono_from f
/-- To show a category is an `InitialMonoClass` it suffices to show every morphism out of the
initial object is a monomorphism. -/
theorem InitialMonoClass.of_initial [HasInitial C] (h : ∀ X : C, Mono (initial.to X)) :
InitialMonoClass C :=
InitialMonoClass.of_isInitial initialIsInitial h
/-- To show a category is an `InitialMonoClass` it suffices to show the unique morphism from the
initial object to a terminal object is a monomorphism. -/
theorem InitialMonoClass.of_terminal [HasInitial C] [HasTerminal C] (h : Mono (initial.to (⊤_ C))) :
InitialMonoClass C :=
InitialMonoClass.of_isTerminal initialIsInitial terminalIsTerminal h
section Comparison
variable {D : Type u₂} [Category.{v₂} D] (G : C ⥤ D)
/-- The comparison morphism from the image of a terminal object to the terminal object in the target
category.
This is an isomorphism iff `G` preserves terminal objects, see
`CategoryTheory.Limits.PreservesTerminal.ofIsoComparison`.
-/
def terminalComparison [HasTerminal C] [HasTerminal D] : G.obj (⊤_ C) ⟶ ⊤_ D :=
terminal.from _
-- TODO: Show this is an isomorphism if and only if `G` preserves initial objects.
/--
The comparison morphism from the initial object in the target category to the image of the initial
object.
-/
def initialComparison [HasInitial C] [HasInitial D] : ⊥_ D ⟶ G.obj (⊥_ C) :=
initial.to _
end Comparison
variable {J : Type u} [Category.{v} J]
instance hasLimit_of_domain_hasInitial [HasInitial J] {F : J ⥤ C} : HasLimit F :=
HasLimit.mk { cone := _, isLimit := limitOfDiagramInitial (initialIsInitial) F }
-- See note [dsimp, simp]
-- This is reducible to allow usage of lemmas about `cone_point_unique_up_to_iso`.
/-- For a functor `F : J ⥤ C`, if `J` has an initial object then the image of it is isomorphic
to the limit of `F`. -/
abbrev limitOfInitial (F : J ⥤ C) [HasInitial J] : limit F ≅ F.obj (⊥_ J) :=
IsLimit.conePointUniqueUpToIso (limit.isLimit _) (limitOfDiagramInitial initialIsInitial F)
instance hasLimit_of_domain_hasTerminal [HasTerminal J] {F : J ⥤ C}
[∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] : HasLimit F :=
HasLimit.mk { cone := _, isLimit := limitOfDiagramTerminal (terminalIsTerminal) F }
-- This is reducible to allow usage of lemmas about `cone_point_unique_up_to_iso`.
/-- For a functor `F : J ⥤ C`, if `J` has a terminal object and all the morphisms in the diagram
are isomorphisms, then the image of the terminal object is isomorphic to the limit of `F`. -/
abbrev limitOfTerminal (F : J ⥤ C) [HasTerminal J] [∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] :
limit F ≅ F.obj (⊤_ J) :=
IsLimit.conePointUniqueUpToIso (limit.isLimit _) (limitOfDiagramTerminal terminalIsTerminal F)
instance hasColimit_of_domain_hasTerminal [HasTerminal J] {F : J ⥤ C} : HasColimit F :=
HasColimit.mk { cocone := _, isColimit := colimitOfDiagramTerminal (terminalIsTerminal) F }
-- This is reducible to allow usage of lemmas about `cocone_point_unique_up_to_iso`.
/-- For a functor `F : J ⥤ C`, if `J` has a terminal object then the image of it is isomorphic
to the colimit of `F`. -/
abbrev colimitOfTerminal (F : J ⥤ C) [HasTerminal J] : colimit F ≅ F.obj (⊤_ J) :=
IsColimit.coconePointUniqueUpToIso (colimit.isColimit _)
(colimitOfDiagramTerminal terminalIsTerminal F)
instance hasColimit_of_domain_hasInitial [HasInitial J] {F : J ⥤ C}
[∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] : HasColimit F :=
HasColimit.mk { cocone := _, isColimit := colimitOfDiagramInitial (initialIsInitial) F }
-- This is reducible to allow usage of lemmas about `cocone_point_unique_up_to_iso`.
/-- For a functor `F : J ⥤ C`, if `J` has an initial object and all the morphisms in the diagram
are isomorphisms, then the image of the initial object is isomorphic to the colimit of `F`. -/
abbrev colimitOfInitial (F : J ⥤ C) [HasInitial J] [∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] :
colimit F ≅ F.obj (⊥_ J) :=
IsColimit.coconePointUniqueUpToIso (colimit.isColimit _)
(colimitOfDiagramInitial initialIsInitial _)
/-- If `j` is initial in the index category, then the map `limit.π F j` is an isomorphism.
-/
theorem isIso_π_of_isInitial {j : J} (I : IsInitial j) (F : J ⥤ C) [HasLimit F] :
IsIso (limit.π F j) :=
⟨⟨limit.lift _ (coneOfDiagramInitial I F), ⟨by ext; simp, by simp⟩⟩⟩
instance isIso_π_initial [HasInitial J] (F : J ⥤ C) : IsIso (limit.π F (⊥_ J)) :=
isIso_π_of_isInitial initialIsInitial F
theorem isIso_π_of_isTerminal {j : J} (I : IsTerminal j) (F : J ⥤ C) [HasLimit F]
[∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] : IsIso (limit.π F j) :=
⟨⟨limit.lift _ (coneOfDiagramTerminal I F), by ext; simp, by simp⟩⟩
instance isIso_π_terminal [HasTerminal J] (F : J ⥤ C) [∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] :
IsIso (limit.π F (⊤_ J)) :=
isIso_π_of_isTerminal terminalIsTerminal F
/-- If `j` is terminal in the index category, then the map `colimit.ι F j` is an isomorphism.
-/
theorem isIso_ι_of_isTerminal {j : J} (I : IsTerminal j) (F : J ⥤ C) [HasColimit F] :
IsIso (colimit.ι F j) :=
⟨⟨colimit.desc _ (coconeOfDiagramTerminal I F), ⟨by simp, by ext; simp⟩⟩⟩
instance isIso_ι_terminal [HasTerminal J] (F : J ⥤ C) : IsIso (colimit.ι F (⊤_ J)) :=
isIso_ι_of_isTerminal terminalIsTerminal F
theorem isIso_ι_of_isInitial {j : J} (I : IsInitial j) (F : J ⥤ C) [HasColimit F]
[∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] : IsIso (colimit.ι F j) :=
⟨⟨colimit.desc _ (coconeOfDiagramInitial I F), by
refine ⟨?_, by ext; simp⟩
dsimp; simp only [colimit.ι_desc, coconeOfDiagramInitial_pt, coconeOfDiagramInitial_ι_app,
Functor.const_obj_obj, IsInitial.to_self, Functor.map_id]
dsimp [inv]; simp only [Category.id_comp, Category.comp_id, and_self]
apply @Classical.choose_spec _ (fun x => x = 𝟙 F.obj j) _
⟩⟩
instance isIso_ι_initial [HasInitial J] (F : J ⥤ C) [∀ (i j : J) (f : i ⟶ j), IsIso (F.map f)] :
IsIso (colimit.ι F (⊥_ J)) :=
isIso_ι_of_isInitial initialIsInitial F
end
end CategoryTheory.Limits
| Mathlib/CategoryTheory/Limits/Shapes/Terminal.lean | 790 | 798 | |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Jens Wagemaker
-/
import Mathlib.Algebra.MonoidAlgebra.Degree
import Mathlib.Algebra.Order.Ring.WithTop
import Mathlib.Algebra.Polynomial.Basic
import Mathlib.Data.Nat.Cast.WithTop
import Mathlib.Data.Nat.SuccPred
import Mathlib.Order.SuccPred.WithBot
/-!
# Degree of univariate polynomials
## Main definitions
* `Polynomial.degree`: the degree of a polynomial, where `0` has degree `⊥`
* `Polynomial.natDegree`: the degree of a polynomial, where `0` has degree `0`
* `Polynomial.leadingCoeff`: the leading coefficient of a polynomial
* `Polynomial.Monic`: a polynomial is monic if its leading coefficient is 0
* `Polynomial.nextCoeff`: the next coefficient after the leading coefficient
## Main results
* `Polynomial.degree_eq_natDegree`: the degree and natDegree coincide for nonzero polynomials
-/
noncomputable section
open Finsupp Finset
open Polynomial
namespace Polynomial
universe u v
variable {R : Type u} {S : Type v} {a b c d : R} {n m : ℕ}
section Semiring
variable [Semiring R] {p q r : R[X]}
/-- `degree p` is the degree of the polynomial `p`, i.e. the largest `X`-exponent in `p`.
`degree p = some n` when `p ≠ 0` and `n` is the highest power of `X` that appears in `p`, otherwise
`degree 0 = ⊥`. -/
def degree (p : R[X]) : WithBot ℕ :=
p.support.max
/-- `natDegree p` forces `degree p` to ℕ, by defining `natDegree 0 = 0`. -/
def natDegree (p : R[X]) : ℕ :=
(degree p).unbotD 0
/-- `leadingCoeff p` gives the coefficient of the highest power of `X` in `p`. -/
def leadingCoeff (p : R[X]) : R :=
coeff p (natDegree p)
/-- a polynomial is `Monic` if its leading coefficient is 1 -/
def Monic (p : R[X]) :=
leadingCoeff p = (1 : R)
theorem Monic.def : Monic p ↔ leadingCoeff p = 1 :=
Iff.rfl
instance Monic.decidable [DecidableEq R] : Decidable (Monic p) := by unfold Monic; infer_instance
@[simp]
theorem Monic.leadingCoeff {p : R[X]} (hp : p.Monic) : leadingCoeff p = 1 :=
hp
theorem Monic.coeff_natDegree {p : R[X]} (hp : p.Monic) : p.coeff p.natDegree = 1 :=
hp
@[simp]
theorem degree_zero : degree (0 : R[X]) = ⊥ :=
rfl
@[simp]
theorem natDegree_zero : natDegree (0 : R[X]) = 0 :=
rfl
@[simp]
theorem coeff_natDegree : coeff p (natDegree p) = leadingCoeff p :=
rfl
@[simp]
theorem degree_eq_bot : degree p = ⊥ ↔ p = 0 :=
⟨fun h => support_eq_empty.1 (Finset.max_eq_bot.1 h), fun h => h.symm ▸ rfl⟩
theorem degree_ne_bot : degree p ≠ ⊥ ↔ p ≠ 0 := degree_eq_bot.not
theorem degree_eq_natDegree (hp : p ≠ 0) : degree p = (natDegree p : WithBot ℕ) := by
let ⟨n, hn⟩ := not_forall.1 (mt Option.eq_none_iff_forall_not_mem.2 (mt degree_eq_bot.1 hp))
have hn : degree p = some n := Classical.not_not.1 hn
rw [natDegree, hn]; rfl
theorem degree_eq_iff_natDegree_eq {p : R[X]} {n : ℕ} (hp : p ≠ 0) :
p.degree = n ↔ p.natDegree = n := by rw [degree_eq_natDegree hp]; exact WithBot.coe_eq_coe
theorem degree_eq_iff_natDegree_eq_of_pos {p : R[X]} {n : ℕ} (hn : 0 < n) :
p.degree = n ↔ p.natDegree = n := by
obtain rfl|h := eq_or_ne p 0
· simp [hn.ne]
· exact degree_eq_iff_natDegree_eq h
theorem natDegree_eq_of_degree_eq_some {p : R[X]} {n : ℕ} (h : degree p = n) : natDegree p = n := by
rw [natDegree, h, Nat.cast_withBot, WithBot.unbotD_coe]
theorem degree_ne_of_natDegree_ne {n : ℕ} : p.natDegree ≠ n → degree p ≠ n :=
mt natDegree_eq_of_degree_eq_some
@[simp]
theorem degree_le_natDegree : degree p ≤ natDegree p :=
WithBot.giUnbotDBot.gc.le_u_l _
theorem natDegree_eq_of_degree_eq [Semiring S] {q : S[X]} (h : degree p = degree q) :
natDegree p = natDegree q := by unfold natDegree; rw [h]
theorem le_degree_of_ne_zero (h : coeff p n ≠ 0) : (n : WithBot ℕ) ≤ degree p := by
rw [Nat.cast_withBot]
exact Finset.le_sup (mem_support_iff.2 h)
theorem degree_mono [Semiring S] {f : R[X]} {g : S[X]} (h : f.support ⊆ g.support) :
f.degree ≤ g.degree :=
Finset.sup_mono h
theorem degree_le_degree (h : coeff q (natDegree p) ≠ 0) : degree p ≤ degree q := by
by_cases hp : p = 0
· rw [hp, degree_zero]
exact bot_le
· rw [degree_eq_natDegree hp]
exact le_degree_of_ne_zero h
theorem natDegree_le_iff_degree_le {n : ℕ} : natDegree p ≤ n ↔ degree p ≤ n :=
WithBot.unbotD_le_iff (fun _ ↦ bot_le)
theorem natDegree_lt_iff_degree_lt (hp : p ≠ 0) : p.natDegree < n ↔ p.degree < ↑n :=
WithBot.unbotD_lt_iff (absurd · (degree_eq_bot.not.mpr hp))
alias ⟨degree_le_of_natDegree_le, natDegree_le_of_degree_le⟩ := natDegree_le_iff_degree_le
theorem natDegree_le_natDegree [Semiring S] {q : S[X]} (hpq : p.degree ≤ q.degree) :
p.natDegree ≤ q.natDegree :=
WithBot.giUnbotDBot.gc.monotone_l hpq
@[simp]
theorem degree_C (ha : a ≠ 0) : degree (C a) = (0 : WithBot ℕ) := by
rw [degree, ← monomial_zero_left, support_monomial 0 ha, max_eq_sup_coe, sup_singleton,
WithBot.coe_zero]
theorem degree_C_le : degree (C a) ≤ 0 := by
by_cases h : a = 0
· rw [h, C_0]
exact bot_le
· rw [degree_C h]
theorem degree_C_lt : degree (C a) < 1 :=
degree_C_le.trans_lt <| WithBot.coe_lt_coe.mpr zero_lt_one
theorem degree_one_le : degree (1 : R[X]) ≤ (0 : WithBot ℕ) := by rw [← C_1]; exact degree_C_le
@[simp]
theorem natDegree_C (a : R) : natDegree (C a) = 0 := by
by_cases ha : a = 0
· have : C a = 0 := by rw [ha, C_0]
rw [natDegree, degree_eq_bot.2 this, WithBot.unbotD_bot]
· rw [natDegree, degree_C ha, WithBot.unbotD_zero]
@[simp]
theorem natDegree_one : natDegree (1 : R[X]) = 0 :=
natDegree_C 1
@[simp]
theorem natDegree_natCast (n : ℕ) : natDegree (n : R[X]) = 0 := by
simp only [← C_eq_natCast, natDegree_C]
@[simp]
theorem natDegree_ofNat (n : ℕ) [Nat.AtLeastTwo n] :
natDegree (ofNat(n) : R[X]) = 0 :=
natDegree_natCast _
theorem degree_natCast_le (n : ℕ) : degree (n : R[X]) ≤ 0 := degree_le_of_natDegree_le (by simp)
@[simp]
theorem degree_monomial (n : ℕ) (ha : a ≠ 0) : degree (monomial n a) = n := by
rw [degree, support_monomial n ha, max_singleton, Nat.cast_withBot]
@[simp]
theorem degree_C_mul_X_pow (n : ℕ) (ha : a ≠ 0) : degree (C a * X ^ n) = n := by
rw [C_mul_X_pow_eq_monomial, degree_monomial n ha]
theorem degree_C_mul_X (ha : a ≠ 0) : degree (C a * X) = 1 := by
simpa only [pow_one] using degree_C_mul_X_pow 1 ha
theorem degree_monomial_le (n : ℕ) (a : R) : degree (monomial n a) ≤ n :=
letI := Classical.decEq R
if h : a = 0 then by rw [h, (monomial n).map_zero, degree_zero]; exact bot_le
else le_of_eq (degree_monomial n h)
theorem degree_C_mul_X_pow_le (n : ℕ) (a : R) : degree (C a * X ^ n) ≤ n := by
rw [C_mul_X_pow_eq_monomial]
apply degree_monomial_le
theorem degree_C_mul_X_le (a : R) : degree (C a * X) ≤ 1 := by
simpa only [pow_one] using degree_C_mul_X_pow_le 1 a
@[simp]
theorem natDegree_C_mul_X_pow (n : ℕ) (a : R) (ha : a ≠ 0) : natDegree (C a * X ^ n) = n :=
natDegree_eq_of_degree_eq_some (degree_C_mul_X_pow n ha)
@[simp]
theorem natDegree_C_mul_X (a : R) (ha : a ≠ 0) : natDegree (C a * X) = 1 := by
simpa only [pow_one] using natDegree_C_mul_X_pow 1 a ha
@[simp]
theorem natDegree_monomial [DecidableEq R] (i : ℕ) (r : R) :
natDegree (monomial i r) = if r = 0 then 0 else i := by
split_ifs with hr
· simp [hr]
· rw [← C_mul_X_pow_eq_monomial, natDegree_C_mul_X_pow i r hr]
theorem natDegree_monomial_le (a : R) {m : ℕ} : (monomial m a).natDegree ≤ m := by
classical
rw [Polynomial.natDegree_monomial]
split_ifs
exacts [Nat.zero_le _, le_rfl]
theorem natDegree_monomial_eq (i : ℕ) {r : R} (r0 : r ≠ 0) : (monomial i r).natDegree = i :=
letI := Classical.decEq R
Eq.trans (natDegree_monomial _ _) (if_neg r0)
theorem coeff_ne_zero_of_eq_degree (hn : degree p = n) : coeff p n ≠ 0 := fun h =>
mem_support_iff.mp (mem_of_max hn) h
theorem degree_X_pow_le (n : ℕ) : degree (X ^ n : R[X]) ≤ n := by
simpa only [C_1, one_mul] using degree_C_mul_X_pow_le n (1 : R)
theorem degree_X_le : degree (X : R[X]) ≤ 1 :=
degree_monomial_le _ _
theorem natDegree_X_le : (X : R[X]).natDegree ≤ 1 :=
natDegree_le_of_degree_le degree_X_le
theorem withBotSucc_degree_eq_natDegree_add_one (h : p ≠ 0) : p.degree.succ = p.natDegree + 1 := by
rw [degree_eq_natDegree h]
exact WithBot.succ_coe p.natDegree
end Semiring
section NonzeroSemiring
variable [Semiring R] [Nontrivial R] {p q : R[X]}
@[simp]
theorem degree_one : degree (1 : R[X]) = (0 : WithBot ℕ) :=
degree_C one_ne_zero
@[simp]
theorem degree_X : degree (X : R[X]) = 1 :=
degree_monomial _ one_ne_zero
@[simp]
theorem natDegree_X : (X : R[X]).natDegree = 1 :=
natDegree_eq_of_degree_eq_some degree_X
end NonzeroSemiring
section Ring
variable [Ring R]
@[simp]
theorem degree_neg (p : R[X]) : degree (-p) = degree p := by unfold degree; rw [support_neg]
theorem degree_neg_le_of_le {a : WithBot ℕ} {p : R[X]} (hp : degree p ≤ a) : degree (-p) ≤ a :=
p.degree_neg.le.trans hp
@[simp]
theorem natDegree_neg (p : R[X]) : natDegree (-p) = natDegree p := by simp [natDegree]
theorem natDegree_neg_le_of_le {p : R[X]} (hp : natDegree p ≤ m) : natDegree (-p) ≤ m :=
(natDegree_neg p).le.trans hp
@[simp]
theorem natDegree_intCast (n : ℤ) : natDegree (n : R[X]) = 0 := by
rw [← C_eq_intCast, natDegree_C]
theorem degree_intCast_le (n : ℤ) : degree (n : R[X]) ≤ 0 := degree_le_of_natDegree_le (by simp)
@[simp]
theorem leadingCoeff_neg (p : R[X]) : (-p).leadingCoeff = -p.leadingCoeff := by
rw [leadingCoeff, leadingCoeff, natDegree_neg, coeff_neg]
end Ring
section Semiring
variable [Semiring R] {p : R[X]}
/-- The second-highest coefficient, or 0 for constants -/
def nextCoeff (p : R[X]) : R :=
if p.natDegree = 0 then 0 else p.coeff (p.natDegree - 1)
lemma nextCoeff_eq_zero :
p.nextCoeff = 0 ↔ p.natDegree = 0 ∨ 0 < p.natDegree ∧ p.coeff (p.natDegree - 1) = 0 := by
simp [nextCoeff, or_iff_not_imp_left, pos_iff_ne_zero]; aesop
lemma nextCoeff_ne_zero : p.nextCoeff ≠ 0 ↔ p.natDegree ≠ 0 ∧ p.coeff (p.natDegree - 1) ≠ 0 := by
simp [nextCoeff]
@[simp]
theorem nextCoeff_C_eq_zero (c : R) : nextCoeff (C c) = 0 := by
rw [nextCoeff]
simp
theorem nextCoeff_of_natDegree_pos (hp : 0 < p.natDegree) :
nextCoeff p = p.coeff (p.natDegree - 1) := by
rw [nextCoeff, if_neg]
contrapose! hp
simpa
variable {p q : R[X]} {ι : Type*}
theorem degree_add_le (p q : R[X]) : degree (p + q) ≤ max (degree p) (degree q) := by
simpa only [degree, ← support_toFinsupp, toFinsupp_add]
using AddMonoidAlgebra.sup_support_add_le _ _ _
theorem degree_add_le_of_degree_le {p q : R[X]} {n : ℕ} (hp : degree p ≤ n) (hq : degree q ≤ n) :
degree (p + q) ≤ n :=
(degree_add_le p q).trans <| max_le hp hq
theorem degree_add_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p + q) ≤ max a b :=
(p.degree_add_le q).trans <| max_le_max ‹_› ‹_›
theorem natDegree_add_le (p q : R[X]) : natDegree (p + q) ≤ max (natDegree p) (natDegree q) := by
rcases le_max_iff.1 (degree_add_le p q) with h | h <;> simp [natDegree_le_natDegree h]
theorem natDegree_add_le_of_degree_le {p q : R[X]} {n : ℕ} (hp : natDegree p ≤ n)
(hq : natDegree q ≤ n) : natDegree (p + q) ≤ n :=
(natDegree_add_le p q).trans <| max_le hp hq
theorem natDegree_add_le_of_le (hp : natDegree p ≤ m) (hq : natDegree q ≤ n) :
natDegree (p + q) ≤ max m n :=
(p.natDegree_add_le q).trans <| max_le_max ‹_› ‹_›
@[simp]
theorem leadingCoeff_zero : leadingCoeff (0 : R[X]) = 0 :=
rfl
@[simp]
theorem leadingCoeff_eq_zero : leadingCoeff p = 0 ↔ p = 0 :=
⟨fun h =>
Classical.by_contradiction fun hp =>
mt mem_support_iff.1 (Classical.not_not.2 h) (mem_of_max (degree_eq_natDegree hp)),
fun h => h.symm ▸ leadingCoeff_zero⟩
theorem leadingCoeff_ne_zero : leadingCoeff p ≠ 0 ↔ p ≠ 0 := by rw [Ne, leadingCoeff_eq_zero]
theorem leadingCoeff_eq_zero_iff_deg_eq_bot : leadingCoeff p = 0 ↔ degree p = ⊥ := by
rw [leadingCoeff_eq_zero, degree_eq_bot]
theorem natDegree_C_mul_X_pow_le (a : R) (n : ℕ) : natDegree (C a * X ^ n) ≤ n :=
natDegree_le_iff_degree_le.2 <| degree_C_mul_X_pow_le _ _
theorem degree_erase_le (p : R[X]) (n : ℕ) : degree (p.erase n) ≤ degree p := by
rcases p with ⟨p⟩
simp only [erase_def, degree, coeff, support]
apply sup_mono
rw [Finsupp.support_erase]
apply Finset.erase_subset
theorem degree_erase_lt (hp : p ≠ 0) : degree (p.erase (natDegree p)) < degree p := by
apply lt_of_le_of_ne (degree_erase_le _ _)
rw [degree_eq_natDegree hp, degree, support_erase]
exact fun h => not_mem_erase _ _ (mem_of_max h)
theorem degree_update_le (p : R[X]) (n : ℕ) (a : R) : degree (p.update n a) ≤ max (degree p) n := by
classical
rw [degree, support_update]
split_ifs
· exact (Finset.max_mono (erase_subset _ _)).trans (le_max_left _ _)
· rw [max_insert, max_comm]
exact le_rfl
theorem degree_sum_le (s : Finset ι) (f : ι → R[X]) :
degree (∑ i ∈ s, f i) ≤ s.sup fun b => degree (f b) :=
Finset.cons_induction_on s (by simp only [sum_empty, sup_empty, degree_zero, le_refl])
fun a s has ih =>
calc
degree (∑ i ∈ cons a s has, f i) ≤ max (degree (f a)) (degree (∑ i ∈ s, f i)) := by
rw [Finset.sum_cons]; exact degree_add_le _ _
_ ≤ _ := by rw [sup_cons]; exact max_le_max le_rfl ih
theorem degree_mul_le (p q : R[X]) : degree (p * q) ≤ degree p + degree q := by
simpa only [degree, ← support_toFinsupp, toFinsupp_mul]
using AddMonoidAlgebra.sup_support_mul_le (WithBot.coe_add _ _).le _ _
theorem degree_mul_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p * q) ≤ a + b :=
(p.degree_mul_le _).trans <| add_le_add ‹_› ‹_›
theorem degree_pow_le (p : R[X]) : ∀ n : ℕ, degree (p ^ n) ≤ n • degree p
| 0 => by rw [pow_zero, zero_nsmul]; exact degree_one_le
| n + 1 =>
calc
degree (p ^ (n + 1)) ≤ degree (p ^ n) + degree p := by
rw [pow_succ]; exact degree_mul_le _ _
_ ≤ _ := by rw [succ_nsmul]; exact add_le_add_right (degree_pow_le _ _) _
theorem degree_pow_le_of_le {a : WithBot ℕ} (b : ℕ) (hp : degree p ≤ a) :
degree (p ^ b) ≤ b * a := by
induction b with
| zero => simp [degree_one_le]
| succ n hn =>
rw [Nat.cast_succ, add_mul, one_mul, pow_succ]
exact degree_mul_le_of_le hn hp
@[simp]
theorem leadingCoeff_monomial (a : R) (n : ℕ) : leadingCoeff (monomial n a) = a := by
classical
by_cases ha : a = 0
· simp only [ha, (monomial n).map_zero, leadingCoeff_zero]
· rw [leadingCoeff, natDegree_monomial, if_neg ha, coeff_monomial]
simp
theorem leadingCoeff_C_mul_X_pow (a : R) (n : ℕ) : leadingCoeff (C a * X ^ n) = a := by
rw [C_mul_X_pow_eq_monomial, leadingCoeff_monomial]
theorem leadingCoeff_C_mul_X (a : R) : leadingCoeff (C a * X) = a := by
simpa only [pow_one] using leadingCoeff_C_mul_X_pow a 1
@[simp]
theorem leadingCoeff_C (a : R) : leadingCoeff (C a) = a :=
leadingCoeff_monomial a 0
theorem leadingCoeff_X_pow (n : ℕ) : leadingCoeff ((X : R[X]) ^ n) = 1 := by
simpa only [C_1, one_mul] using leadingCoeff_C_mul_X_pow (1 : R) n
theorem leadingCoeff_X : leadingCoeff (X : R[X]) = 1 := by
simpa only [pow_one] using @leadingCoeff_X_pow R _ 1
@[simp]
theorem monic_X_pow (n : ℕ) : Monic (X ^ n : R[X]) :=
leadingCoeff_X_pow n
@[simp]
theorem monic_X : Monic (X : R[X]) :=
leadingCoeff_X
theorem leadingCoeff_one : leadingCoeff (1 : R[X]) = 1 :=
leadingCoeff_C 1
@[simp]
theorem monic_one : Monic (1 : R[X]) :=
leadingCoeff_C _
theorem Monic.ne_zero {R : Type*} [Semiring R] [Nontrivial R] {p : R[X]} (hp : p.Monic) :
p ≠ 0 := by
rintro rfl
simp [Monic] at hp
theorem Monic.ne_zero_of_ne (h : (0 : R) ≠ 1) {p : R[X]} (hp : p.Monic) : p ≠ 0 := by
nontriviality R
exact hp.ne_zero
theorem Monic.ne_zero_of_polynomial_ne {r} (hp : Monic p) (hne : q ≠ r) : p ≠ 0 :=
haveI := Nontrivial.of_polynomial_ne hne
hp.ne_zero
theorem natDegree_mul_le {p q : R[X]} : natDegree (p * q) ≤ natDegree p + natDegree q := by
apply natDegree_le_of_degree_le
apply le_trans (degree_mul_le p q)
rw [Nat.cast_add]
apply add_le_add <;> apply degree_le_natDegree
theorem natDegree_mul_le_of_le (hp : natDegree p ≤ m) (hg : natDegree q ≤ n) :
natDegree (p * q) ≤ m + n :=
natDegree_mul_le.trans <| add_le_add ‹_› ‹_›
theorem natDegree_pow_le {p : R[X]} {n : ℕ} : (p ^ n).natDegree ≤ n * p.natDegree := by
induction n with
| zero => simp
| succ i hi =>
rw [pow_succ, Nat.succ_mul]
apply le_trans natDegree_mul_le (add_le_add_right hi _)
theorem natDegree_pow_le_of_le (n : ℕ) (hp : natDegree p ≤ m) :
natDegree (p ^ n) ≤ n * m :=
natDegree_pow_le.trans (Nat.mul_le_mul le_rfl ‹_›)
theorem natDegree_eq_zero_iff_degree_le_zero : p.natDegree = 0 ↔ p.degree ≤ 0 := by
rw [← nonpos_iff_eq_zero, natDegree_le_iff_degree_le, Nat.cast_zero]
theorem degree_zero_le : degree (0 : R[X]) ≤ 0 := natDegree_eq_zero_iff_degree_le_zero.mp rfl
theorem degree_le_iff_coeff_zero (f : R[X]) (n : WithBot ℕ) :
degree f ≤ n ↔ ∀ m : ℕ, n < m → coeff f m = 0 := by
simp only [degree, Finset.max, Finset.sup_le_iff, mem_support_iff, Ne, ← not_le,
not_imp_comm, Nat.cast_withBot]
theorem degree_lt_iff_coeff_zero (f : R[X]) (n : ℕ) :
degree f < n ↔ ∀ m : ℕ, n ≤ m → coeff f m = 0 := by
simp only [degree, Finset.sup_lt_iff (WithBot.bot_lt_coe n), mem_support_iff,
WithBot.coe_lt_coe, ← @not_le ℕ, max_eq_sup_coe, Nat.cast_withBot, Ne, not_imp_not]
theorem natDegree_pos_iff_degree_pos : 0 < natDegree p ↔ 0 < degree p :=
lt_iff_lt_of_le_iff_le natDegree_le_iff_degree_le
end Semiring
section NontrivialSemiring
variable [Semiring R] [Nontrivial R] {p q : R[X]} (n : ℕ)
@[simp]
theorem degree_X_pow : degree ((X : R[X]) ^ n) = n := by
rw [X_pow_eq_monomial, degree_monomial _ (one_ne_zero' R)]
@[simp]
theorem natDegree_X_pow : natDegree ((X : R[X]) ^ n) = n :=
natDegree_eq_of_degree_eq_some (degree_X_pow n)
end NontrivialSemiring
section Ring
variable [Ring R] {p q : R[X]}
theorem degree_sub_le (p q : R[X]) : degree (p - q) ≤ max (degree p) (degree q) := by
simpa only [degree_neg q] using degree_add_le p (-q)
theorem degree_sub_le_of_le {a b : WithBot ℕ} (hp : degree p ≤ a) (hq : degree q ≤ b) :
degree (p - q) ≤ max a b :=
(p.degree_sub_le q).trans <| max_le_max ‹_› ‹_›
theorem natDegree_sub_le (p q : R[X]) : natDegree (p - q) ≤ max (natDegree p) (natDegree q) := by
simpa only [← natDegree_neg q] using natDegree_add_le p (-q)
theorem natDegree_sub_le_of_le (hp : natDegree p ≤ m) (hq : natDegree q ≤ n) :
natDegree (p - q) ≤ max m n :=
(p.natDegree_sub_le q).trans <| max_le_max ‹_› ‹_›
theorem degree_sub_lt (hd : degree p = degree q) (hp0 : p ≠ 0)
(hlc : leadingCoeff p = leadingCoeff q) : degree (p - q) < degree p :=
have hp : monomial (natDegree p) (leadingCoeff p) + p.erase (natDegree p) = p :=
monomial_add_erase _ _
have hq : monomial (natDegree q) (leadingCoeff q) + q.erase (natDegree q) = q :=
monomial_add_erase _ _
have hd' : natDegree p = natDegree q := by unfold natDegree; rw [hd]
have hq0 : q ≠ 0 := mt degree_eq_bot.2 (hd ▸ mt degree_eq_bot.1 hp0)
calc
degree (p - q) = degree (erase (natDegree q) p + -erase (natDegree q) q) := by
conv =>
lhs
rw [← hp, ← hq, hlc, hd', add_sub_add_left_eq_sub, sub_eq_add_neg]
_ ≤ max (degree (erase (natDegree q) p)) (degree (erase (natDegree q) q)) :=
(degree_neg (erase (natDegree q) q) ▸ degree_add_le _ _)
_ < degree p := max_lt_iff.2 ⟨hd' ▸ degree_erase_lt hp0, hd.symm ▸ degree_erase_lt hq0⟩
theorem degree_X_sub_C_le (r : R) : (X - C r).degree ≤ 1 :=
(degree_sub_le _ _).trans (max_le degree_X_le (degree_C_le.trans zero_le_one))
theorem natDegree_X_sub_C_le (r : R) : (X - C r).natDegree ≤ 1 :=
natDegree_le_iff_degree_le.2 <| degree_X_sub_C_le r
end Ring
end Polynomial
| Mathlib/Algebra/Polynomial/Degree/Definitions.lean | 1,120 | 1,139 | |
/-
Copyright (c) 2021 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Yury Kudryashov, Sébastien Gouëzel
-/
import Mathlib.MeasureTheory.Constructions.BorelSpace.Order
import Mathlib.MeasureTheory.Measure.Typeclasses.Probability
import Mathlib.Topology.Algebra.UniformMulAction
import Mathlib.Topology.Order.LeftRightLim
/-!
# Stieltjes measures on the real line
Consider a function `f : ℝ → ℝ` which is monotone and right-continuous. Then one can define a
corresponding measure, giving mass `f b - f a` to the interval `(a, b]`.
## Main definitions
* `StieltjesFunction` is a structure containing a function from `ℝ → ℝ`, together with the
assertions that it is monotone and right-continuous. To `f : StieltjesFunction`, one associates
a Borel measure `f.measure`.
* `f.measure_Ioc` asserts that `f.measure (Ioc a b) = ofReal (f b - f a)`
* `f.measure_Ioo` asserts that `f.measure (Ioo a b) = ofReal (leftLim f b - f a)`.
* `f.measure_Icc` and `f.measure_Ico` are analogous.
-/
noncomputable section
open Set Filter Function ENNReal NNReal Topology MeasureTheory
open ENNReal (ofReal)
/-! ### Basic properties of Stieltjes functions -/
/-- Bundled monotone right-continuous real functions, used to construct Stieltjes measures. -/
structure StieltjesFunction where
toFun : ℝ → ℝ
mono' : Monotone toFun
right_continuous' : ∀ x, ContinuousWithinAt toFun (Ici x) x
namespace StieltjesFunction
attribute [coe] toFun
instance instCoeFun : CoeFun StieltjesFunction fun _ => ℝ → ℝ :=
⟨toFun⟩
initialize_simps_projections StieltjesFunction (toFun → apply)
@[ext] lemma ext {f g : StieltjesFunction} (h : ∀ x, f x = g x) : f = g := by
exact (StieltjesFunction.mk.injEq ..).mpr (funext h)
variable (f : StieltjesFunction)
theorem mono : Monotone f :=
f.mono'
theorem right_continuous (x : ℝ) : ContinuousWithinAt f (Ici x) x :=
f.right_continuous' x
theorem rightLim_eq (f : StieltjesFunction) (x : ℝ) : Function.rightLim f x = f x := by
rw [← f.mono.continuousWithinAt_Ioi_iff_rightLim_eq, continuousWithinAt_Ioi_iff_Ici]
exact f.right_continuous' x
theorem iInf_Ioi_eq (f : StieltjesFunction) (x : ℝ) : ⨅ r : Ioi x, f r = f x := by
suffices Function.rightLim f x = ⨅ r : Ioi x, f r by rw [← this, f.rightLim_eq]
rw [f.mono.rightLim_eq_sInf, sInf_image']
rw [← neBot_iff]
infer_instance
theorem iInf_rat_gt_eq (f : StieltjesFunction) (x : ℝ) :
⨅ r : { r' : ℚ // x < r' }, f r = f x := by
rw [← iInf_Ioi_eq f x]
refine (Real.iInf_Ioi_eq_iInf_rat_gt _ ?_ f.mono).symm
refine ⟨f x, fun y => ?_⟩
rintro ⟨y, hy_mem, rfl⟩
exact f.mono (le_of_lt hy_mem)
/-- The identity of `ℝ` as a Stieltjes function, used to construct Lebesgue measure. -/
@[simps]
protected def id : StieltjesFunction where
toFun := id
mono' _ _ := id
right_continuous' _ := continuousWithinAt_id
@[simp]
theorem id_leftLim (x : ℝ) : leftLim StieltjesFunction.id x = x :=
tendsto_nhds_unique (StieltjesFunction.id.mono.tendsto_leftLim x) <|
continuousAt_id.tendsto.mono_left nhdsWithin_le_nhds
instance instInhabited : Inhabited StieltjesFunction :=
⟨StieltjesFunction.id⟩
/-- Constant functions are Stieltjes function. -/
protected def const (c : ℝ) : StieltjesFunction where
toFun := fun _ ↦ c
mono' _ _ := by simp
right_continuous' _ := continuousWithinAt_const
@[simp] lemma const_apply (c x : ℝ) : (StieltjesFunction.const c) x = c := rfl
/-- The sum of two Stieltjes functions is a Stieltjes function. -/
protected def add (f g : StieltjesFunction) : StieltjesFunction where
toFun := fun x => f x + g x
mono' := f.mono.add g.mono
right_continuous' := fun x => (f.right_continuous x).add (g.right_continuous x)
instance : AddZeroClass StieltjesFunction where
add := StieltjesFunction.add
zero := StieltjesFunction.const 0
zero_add _ := ext fun _ ↦ zero_add _
add_zero _ := ext fun _ ↦ add_zero _
instance : AddCommMonoid StieltjesFunction where
nsmul n f := nsmulRec n f
add_assoc _ _ _ := ext fun _ ↦ add_assoc _ _ _
add_comm _ _ := ext fun _ ↦ add_comm _ _
__ := StieltjesFunction.instAddZeroClass
instance : Module ℝ≥0 StieltjesFunction where
smul c f := {
toFun := fun x ↦ c * f x
mono' := f.mono.const_mul c.2
right_continuous' := fun x ↦ (f.right_continuous x).const_smul c.1}
one_smul _ := ext fun _ ↦ one_mul _
mul_smul _ _ _ := ext fun _ ↦ mul_assoc _ _ _
smul_zero _ := ext fun _ ↦ mul_zero _
smul_add _ _ _ := ext fun _ ↦ mul_add _ _ _
add_smul _ _ _ := ext fun _ ↦ add_mul _ _ _
zero_smul _ := ext fun _ ↦ zero_mul _
@[simp] lemma zero_apply (x : ℝ) : (0 : StieltjesFunction) x = 0 := rfl
@[simp] lemma add_apply (f g : StieltjesFunction) (x : ℝ) : (f + g) x = f x + g x := rfl
/-- If a function `f : ℝ → ℝ` is monotone, then the function mapping `x` to the right limit of `f`
at `x` is a Stieltjes function, i.e., it is monotone and right-continuous. -/
noncomputable def _root_.Monotone.stieltjesFunction {f : ℝ → ℝ} (hf : Monotone f) :
StieltjesFunction where
toFun := rightLim f
mono' _ _ hxy := hf.rightLim hxy
right_continuous' := by
intro x s hs
obtain ⟨l, u, hlu, lus⟩ : ∃ l u : ℝ, rightLim f x ∈ Ioo l u ∧ Ioo l u ⊆ s :=
mem_nhds_iff_exists_Ioo_subset.1 hs
obtain ⟨y, xy, h'y⟩ : ∃ (y : ℝ), x < y ∧ Ioc x y ⊆ f ⁻¹' Ioo l u :=
mem_nhdsGT_iff_exists_Ioc_subset.1 (hf.tendsto_rightLim x (Ioo_mem_nhds hlu.1 hlu.2))
change ∀ᶠ y in 𝓝[≥] x, rightLim f y ∈ s
filter_upwards [Ico_mem_nhdsGE xy] with z hz
apply lus
refine ⟨hlu.1.trans_le (hf.rightLim hz.1), ?_⟩
obtain ⟨a, za, ay⟩ : ∃ a : ℝ, z < a ∧ a < y := exists_between hz.2
calc
rightLim f z ≤ f a := hf.rightLim_le za
_ < u := (h'y ⟨hz.1.trans_lt za, ay.le⟩).2
theorem _root_.Monotone.stieltjesFunction_eq {f : ℝ → ℝ} (hf : Monotone f) (x : ℝ) :
hf.stieltjesFunction x = rightLim f x :=
rfl
theorem countable_leftLim_ne (f : StieltjesFunction) : Set.Countable { x | leftLim f x ≠ f x } := by
refine Countable.mono ?_ f.mono.countable_not_continuousAt
intro x hx h'x
apply hx
exact tendsto_nhds_unique (f.mono.tendsto_leftLim x) (h'x.tendsto.mono_left nhdsWithin_le_nhds)
/-! ### The outer measure associated to a Stieltjes function -/
/-- Length of an interval. This is the largest monotone function which correctly measures all
intervals. -/
def length (s : Set ℝ) : ℝ≥0∞ :=
⨅ (a) (b) (_ : s ⊆ Ioc a b), ofReal (f b - f a)
@[simp]
theorem length_empty : f.length ∅ = 0 :=
nonpos_iff_eq_zero.1 <| iInf_le_of_le 0 <| iInf_le_of_le 0 <| by simp
@[simp]
theorem length_Ioc (a b : ℝ) : f.length (Ioc a b) = ofReal (f b - f a) := by
refine
le_antisymm (iInf_le_of_le a <| iInf₂_le b Subset.rfl)
(le_iInf fun a' => le_iInf fun b' => le_iInf fun h => ENNReal.coe_le_coe.2 ?_)
rcases le_or_lt b a with ab | ab
· rw [Real.toNNReal_of_nonpos (sub_nonpos.2 (f.mono ab))]
apply zero_le
obtain ⟨h₁, h₂⟩ := (Ioc_subset_Ioc_iff ab).1 h
exact Real.toNNReal_le_toNNReal (sub_le_sub (f.mono h₁) (f.mono h₂))
theorem length_mono {s₁ s₂ : Set ℝ} (h : s₁ ⊆ s₂) : f.length s₁ ≤ f.length s₂ :=
iInf_mono fun _ => biInf_mono fun _ => h.trans
open MeasureTheory
/-- The Stieltjes outer measure associated to a Stieltjes function. -/
protected def outer : OuterMeasure ℝ :=
OuterMeasure.ofFunction f.length f.length_empty
theorem outer_le_length (s : Set ℝ) : f.outer s ≤ f.length s :=
OuterMeasure.ofFunction_le _
/-- If a compact interval `[a, b]` is covered by a union of open interval `(c i, d i)`, then
`f b - f a ≤ ∑ f (d i) - f (c i)`. This is an auxiliary technical statement to prove the same
statement for half-open intervals, the point of the current statement being that one can use
compactness to reduce it to a finite sum, and argue by induction on the size of the covering set. -/
theorem length_subadditive_Icc_Ioo {a b : ℝ} {c d : ℕ → ℝ} (ss : Icc a b ⊆ ⋃ i, Ioo (c i) (d i)) :
ofReal (f b - f a) ≤ ∑' i, ofReal (f (d i) - f (c i)) := by
suffices
∀ (s : Finset ℕ) (b), Icc a b ⊆ (⋃ i ∈ (s : Set ℕ), Ioo (c i) (d i)) →
(ofReal (f b - f a) : ℝ≥0∞) ≤ ∑ i ∈ s, ofReal (f (d i) - f (c i)) by
rcases isCompact_Icc.elim_finite_subcover_image
(fun (i : ℕ) (_ : i ∈ univ) => @isOpen_Ioo _ _ _ _ (c i) (d i)) (by simpa using ss) with
⟨s, _, hf, hs⟩
have e : ⋃ i ∈ (hf.toFinset : Set ℕ), Ioo (c i) (d i) = ⋃ i ∈ s, Ioo (c i) (d i) := by
simp only [Set.ext_iff, exists_prop, Finset.set_biUnion_coe, mem_iUnion, forall_const,
Finite.mem_toFinset]
rw [ENNReal.tsum_eq_iSup_sum]
refine le_trans ?_ (le_iSup _ hf.toFinset)
exact this hf.toFinset _ (by simpa only [e] )
clear ss b
refine fun s => Finset.strongInductionOn s fun s IH b cv => ?_
rcases le_total b a with ab | ab
· rw [ENNReal.ofReal_eq_zero.2 (sub_nonpos.2 (f.mono ab))]
exact zero_le _
have := cv ⟨ab, le_rfl⟩
simp only [Finset.mem_coe, gt_iff_lt, not_lt, mem_iUnion, mem_Ioo, exists_and_left,
exists_prop] at this
rcases this with ⟨i, cb, is, bd⟩
rw [← Finset.insert_erase is] at cv ⊢
rw [Finset.coe_insert, biUnion_insert] at cv
rw [Finset.sum_insert (Finset.not_mem_erase _ _)]
refine le_trans ?_ (add_le_add_left (IH _ (Finset.erase_ssubset is) (c i) ?_) _)
· refine le_trans (ENNReal.ofReal_le_ofReal ?_) ENNReal.ofReal_add_le
rw [sub_add_sub_cancel]
exact sub_le_sub_right (f.mono bd.le) _
· rintro x ⟨h₁, h₂⟩
exact (cv ⟨h₁, le_trans h₂ (le_of_lt cb)⟩).resolve_left (mt And.left (not_lt_of_le h₂))
@[simp]
theorem outer_Ioc (a b : ℝ) : f.outer (Ioc a b) = ofReal (f b - f a) := by
/- It suffices to show that, if `(a, b]` is covered by sets `s i`, then `f b - f a` is bounded
by `∑ f.length (s i) + ε`. The difficulty is that `f.length` is expressed in terms of half-open
intervals, while we would like to have a compact interval covered by open intervals to use
compactness and finite sums, as provided by `length_subadditive_Icc_Ioo`. The trick is to use
the right-continuity of `f`. If `a'` is close enough to `a` on its right, then `[a', b]` is
still covered by the sets `s i` and moreover `f b - f a'` is very close to `f b - f a`
(up to `ε/2`).
Also, by definition one can cover `s i` by a half-closed interval `(p i, q i]` with `f`-length
very close to that of `s i` (within a suitably small `ε' i`, say). If one moves `q i` very
slightly to the right, then the `f`-length will change very little by right continuity, and we
will get an open interval `(p i, q' i)` covering `s i` with `f (q' i) - f (p i)` within `ε' i`
of the `f`-length of `s i`. -/
refine
le_antisymm
(by
rw [← f.length_Ioc]
apply outer_le_length)
(le_iInf₂ fun s hs => ENNReal.le_of_forall_pos_le_add fun ε εpos h => ?_)
let δ := ε / 2
have δpos : 0 < (δ : ℝ≥0∞) := by simpa [δ] using εpos.ne'
rcases ENNReal.exists_pos_sum_of_countable δpos.ne' ℕ with ⟨ε', ε'0, hε⟩
obtain ⟨a', ha', aa'⟩ : ∃ a', f a' - f a < δ ∧ a < a' := by
have A : ContinuousWithinAt (fun r => f r - f a) (Ioi a) a := by
refine ContinuousWithinAt.sub ?_ continuousWithinAt_const
exact (f.right_continuous a).mono Ioi_subset_Ici_self
have B : f a - f a < δ := by rwa [sub_self, NNReal.coe_pos, ← ENNReal.coe_pos]
exact (((tendsto_order.1 A).2 _ B).and self_mem_nhdsWithin).exists
have : ∀ i, ∃ p : ℝ × ℝ, s i ⊆ Ioo p.1 p.2 ∧
(ofReal (f p.2 - f p.1) : ℝ≥0∞) < f.length (s i) + ε' i := by
intro i
have hl :=
ENNReal.lt_add_right ((ENNReal.le_tsum i).trans_lt h).ne (ENNReal.coe_ne_zero.2 (ε'0 i).ne')
conv at hl =>
lhs
rw [length]
simp only [iInf_lt_iff, exists_prop] at hl
rcases hl with ⟨p, q', spq, hq'⟩
have : ContinuousWithinAt (fun r => ofReal (f r - f p)) (Ioi q') q' := by
apply ENNReal.continuous_ofReal.continuousAt.comp_continuousWithinAt
refine ContinuousWithinAt.sub ?_ continuousWithinAt_const
exact (f.right_continuous q').mono Ioi_subset_Ici_self
rcases (((tendsto_order.1 this).2 _ hq').and self_mem_nhdsWithin).exists with ⟨q, hq, q'q⟩
exact ⟨⟨p, q⟩, spq.trans (Ioc_subset_Ioo_right q'q), hq⟩
choose g hg using this
have I_subset : Icc a' b ⊆ ⋃ i, Ioo (g i).1 (g i).2 :=
calc
Icc a' b ⊆ Ioc a b := fun x hx => ⟨aa'.trans_le hx.1, hx.2⟩
_ ⊆ ⋃ i, s i := hs
_ ⊆ ⋃ i, Ioo (g i).1 (g i).2 := iUnion_mono fun i => (hg i).1
calc
ofReal (f b - f a) = ofReal (f b - f a' + (f a' - f a)) := by rw [sub_add_sub_cancel]
_ ≤ ofReal (f b - f a') + ofReal (f a' - f a) := ENNReal.ofReal_add_le
_ ≤ ∑' i, ofReal (f (g i).2 - f (g i).1) + ofReal δ :=
(add_le_add (f.length_subadditive_Icc_Ioo I_subset) (ENNReal.ofReal_le_ofReal ha'.le))
_ ≤ ∑' i, (f.length (s i) + ε' i) + δ :=
(add_le_add (ENNReal.tsum_le_tsum fun i => (hg i).2.le)
(by simp only [ENNReal.ofReal_coe_nnreal, le_rfl]))
_ = ∑' i, f.length (s i) + ∑' i, (ε' i : ℝ≥0∞) + δ := by rw [ENNReal.tsum_add]
_ ≤ ∑' i, f.length (s i) + δ + δ := add_le_add (add_le_add le_rfl hε.le) le_rfl
_ = ∑' i : ℕ, f.length (s i) + ε := by simp [δ, add_assoc, ENNReal.add_halves]
theorem measurableSet_Ioi {c : ℝ} : MeasurableSet[f.outer.caratheodory] (Ioi c) := by
refine OuterMeasure.ofFunction_caratheodory fun t => ?_
refine le_iInf fun a => le_iInf fun b => le_iInf fun h => ?_
refine
le_trans
(add_le_add (f.length_mono <| inter_subset_inter_left _ h)
(f.length_mono <| diff_subset_diff_left h)) ?_
rcases le_total a c with hac | hac <;> rcases le_total b c with hbc | hbc
· simp only [Ioc_inter_Ioi, f.length_Ioc, hac, hbc, le_refl, Ioc_eq_empty,
max_eq_right, min_eq_left, Ioc_diff_Ioi, f.length_empty, zero_add, not_lt]
· simp only [hac, hbc, Ioc_inter_Ioi, Ioc_diff_Ioi, f.length_Ioc, min_eq_right,
← ENNReal.ofReal_add, f.mono hac, f.mono hbc, sub_nonneg,
sub_add_sub_cancel, le_refl,
max_eq_right]
· simp only [hbc, le_refl, Ioc_eq_empty, Ioc_inter_Ioi, min_eq_left, Ioc_diff_Ioi, f.length_empty,
zero_add, or_true, le_sup_iff, f.length_Ioc, not_lt]
· simp only [hac, hbc, Ioc_inter_Ioi, Ioc_diff_Ioi, f.length_Ioc, min_eq_right,
le_refl, Ioc_eq_empty, add_zero, max_eq_left, f.length_empty, not_lt]
theorem outer_trim : f.outer.trim = f.outer := by
refine le_antisymm (fun s => ?_) (OuterMeasure.le_trim _)
rw [OuterMeasure.trim_eq_iInf]
refine le_iInf fun t => le_iInf fun ht => ENNReal.le_of_forall_pos_le_add fun ε ε0 h => ?_
rcases ENNReal.exists_pos_sum_of_countable (ENNReal.coe_pos.2 ε0).ne' ℕ with ⟨ε', ε'0, hε⟩
refine le_trans ?_ (add_le_add_left (le_of_lt hε) _)
rw [← ENNReal.tsum_add]
choose g hg using
show ∀ i, ∃ s, t i ⊆ s ∧ MeasurableSet s ∧ f.outer s ≤ f.length (t i) + ofReal (ε' i) by
intro i
have hl :=
ENNReal.lt_add_right ((ENNReal.le_tsum i).trans_lt h).ne (ENNReal.coe_pos.2 (ε'0 i)).ne'
conv at hl =>
lhs
rw [length]
simp only [iInf_lt_iff] at hl
rcases hl with ⟨a, b, h₁, h₂⟩
rw [← f.outer_Ioc] at h₂
exact ⟨_, h₁, measurableSet_Ioc, le_of_lt <| by simpa using h₂⟩
simp only [ofReal_coe_nnreal] at hg
apply iInf_le_of_le (iUnion g) _
apply iInf_le_of_le (ht.trans <| iUnion_mono fun i => (hg i).1) _
apply iInf_le_of_le (MeasurableSet.iUnion fun i => (hg i).2.1) _
exact le_trans (measure_iUnion_le _) (ENNReal.tsum_le_tsum fun i => (hg i).2.2)
| theorem borel_le_measurable : borel ℝ ≤ f.outer.caratheodory := by
rw [borel_eq_generateFrom_Ioi]
refine MeasurableSpace.generateFrom_le ?_
simp +contextual [f.measurableSet_Ioi]
/-! ### The measure associated to a Stieltjes function -/
/-- The measure associated to a Stieltjes function, giving mass `f b - f a` to the
interval `(a, b]`. -/
protected irreducible_def measure : Measure ℝ where
toOuterMeasure := f.outer
m_iUnion _s hs := f.outer.iUnion_eq_of_caratheodory fun i => f.borel_le_measurable _ (hs i)
trim_le := f.outer_trim.le
@[simp]
theorem measure_Ioc (a b : ℝ) : f.measure (Ioc a b) = ofReal (f b - f a) := by
rw [StieltjesFunction.measure]
exact f.outer_Ioc a b
@[simp]
theorem measure_singleton (a : ℝ) : f.measure {a} = ofReal (f a - leftLim f a) := by
obtain ⟨u, u_mono, u_lt_a, u_lim⟩ :
∃ u : ℕ → ℝ, StrictMono u ∧ (∀ n : ℕ, u n < a) ∧ Tendsto u atTop (𝓝 a) :=
| Mathlib/MeasureTheory/Measure/Stieltjes.lean | 348 | 371 |
/-
Copyright (c) 2020 Simon Hudon. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Simon Hudon
-/
import Mathlib.Data.Stream.Init
import Mathlib.Tactic.ApplyFun
import Mathlib.Control.Fix
import Mathlib.Order.OmegaCompletePartialOrder
/-!
# Lawful fixed point operators
This module defines the laws required of a `Fix` instance, using the theory of
omega complete partial orders (ωCPO). Proofs of the lawfulness of all `Fix` instances in
`Control.Fix` are provided.
## Main definition
* class `LawfulFix`
-/
universe u v
variable {α : Type*} {β : α → Type*}
open OmegaCompletePartialOrder
/-- Intuitively, a fixed point operator `fix` is lawful if it satisfies `fix f = f (fix f)` for all
`f`, but this is inconsistent / uninteresting in most cases due to the existence of "exotic"
functions `f`, such as the function that is defined iff its argument is not, familiar from the
halting problem. Instead, this requirement is limited to only functions that are `Continuous` in the
sense of `ω`-complete partial orders, which excludes the example because it is not monotone
(making the input argument less defined can make `f` more defined). -/
class LawfulFix (α : Type*) [OmegaCompletePartialOrder α] extends Fix α where
fix_eq : ∀ {f : α → α}, ωScottContinuous f → Fix.fix f = f (Fix.fix f)
namespace Part
open Part Nat Nat.Upto
namespace Fix
variable (f : ((a : _) → Part <| β a) →o (a : _) → Part <| β a)
theorem approx_mono' {i : ℕ} : Fix.approx f i ≤ Fix.approx f (succ i) := by
induction i with
| zero => dsimp [approx]; apply @bot_le _ _ _ (f ⊥)
| succ _ i_ih => intro; apply f.monotone; apply i_ih
theorem approx_mono ⦃i j : ℕ⦄ (hij : i ≤ j) : approx f i ≤ approx f j := by
induction' j with j ih
· cases hij
exact le_rfl
cases hij; · exact le_rfl
exact le_trans (ih ‹_›) (approx_mono' f)
theorem mem_iff (a : α) (b : β a) : b ∈ Part.fix f a ↔ ∃ i, b ∈ approx f i a := by
classical
by_cases h₀ : ∃ i : ℕ, (approx f i a).Dom
· simp only [Part.fix_def f h₀]
constructor <;> intro hh
· exact ⟨_, hh⟩
have h₁ := Nat.find_spec h₀
rw [dom_iff_mem] at h₁
obtain ⟨y, h₁⟩ := h₁
replace h₁ := approx_mono' f _ _ h₁
suffices y = b by
subst this
exact h₁
obtain ⟨i, hh⟩ := hh
revert h₁; generalize succ (Nat.find h₀) = j; intro h₁
wlog case : i ≤ j
· rcases le_total i j with H | H <;> [skip; symm] <;> apply_assumption <;> assumption
replace hh := approx_mono f case _ _ hh
apply Part.mem_unique h₁ hh
· simp only [fix_def' (⇑f) h₀, not_exists, false_iff, not_mem_none]
simp only [dom_iff_mem, not_exists] at h₀
intro; apply h₀
theorem approx_le_fix (i : ℕ) : approx f i ≤ Part.fix f := fun a b hh ↦ by
rw [mem_iff f]
exact ⟨_, hh⟩
theorem exists_fix_le_approx (x : α) : ∃ i, Part.fix f x ≤ approx f i x := by
by_cases hh : ∃ i b, b ∈ approx f i x
· rcases hh with ⟨i, b, hb⟩
exists i
intro b' h'
have hb' := approx_le_fix f i _ _ hb
obtain rfl := Part.mem_unique h' hb'
exact hb
· simp only [not_exists] at hh
exists 0
intro b' h'
simp only [mem_iff f] at h'
obtain ⟨i, h'⟩ := h'
cases hh _ _ h'
/-- The series of approximations of `fix f` (see `approx`) as a `Chain` -/
def approxChain : Chain ((a : _) → Part <| β a) :=
⟨approx f, approx_mono f⟩
theorem le_f_of_mem_approx {x} : x ∈ approxChain f → x ≤ f x := by
simp only [Membership.mem, forall_exists_index]
rintro i rfl
apply approx_mono'
theorem approx_mem_approxChain {i} : approx f i ∈ approxChain f :=
Stream'.mem_of_get_eq rfl
end Fix
open Fix
variable {α : Type*}
variable (f : ((a : _) → Part <| β a) →o (a : _) → Part <| β a)
open OmegaCompletePartialOrder
open Part hiding ωSup
open Nat
open Nat.Upto OmegaCompletePartialOrder
theorem fix_eq_ωSup : Part.fix f = ωSup (approxChain f) := by
apply le_antisymm
· intro x
obtain ⟨i, hx⟩ := exists_fix_le_approx f x
trans approx f i.succ x
· trans
· apply hx
· apply approx_mono' f
apply le_ωSup_of_le i.succ
dsimp [approx]
rfl
· apply ωSup_le _ _ _
simp only [Fix.approxChain, OrderHom.coe_mk]
intro y x
apply approx_le_fix f
theorem fix_le {X : (a : _) → Part <| β a} (hX : f X ≤ X) : Part.fix f ≤ X := by
rw [fix_eq_ωSup f]
apply ωSup_le _ _ _
simp only [Fix.approxChain, OrderHom.coe_mk]
intro i
induction i with
| zero => dsimp [Fix.approx]; apply bot_le
| succ _ i_ih =>
trans f X
· apply f.monotone i_ih
· apply hX
variable {g : ((a : _) → Part <| β a) → (a : _) → Part <| β a}
theorem fix_eq_ωSup_of_ωScottContinuous (hc : ωScottContinuous g) : Part.fix g =
ωSup (approxChain (⟨g,hc.monotone⟩ : ((a : _) → Part <| β a) →o (a : _) → Part <| β a)) := by
rw [← fix_eq_ωSup]
rfl
| theorem fix_eq_of_ωScottContinuous (hc : ωScottContinuous g) :
Part.fix g = g (Part.fix g) := by
rw [fix_eq_ωSup_of_ωScottContinuous hc, hc.map_ωSup]
apply le_antisymm
· apply ωSup_le_ωSup_of_le _
intro i
exists i
intro x
apply le_f_of_mem_approx _ ⟨i, rfl⟩
· apply ωSup_le_ωSup_of_le _
intro i
| Mathlib/Control/LawfulFix.lean | 162 | 172 |
/-
Copyright (c) 2023 Christopher Hoskin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Christopher Hoskin
-/
import Mathlib.Topology.AlexandrovDiscrete
import Mathlib.Topology.ContinuousMap.Basic
import Mathlib.Topology.Order.LowerUpperTopology
/-!
# Upper and lower sets topologies
This file introduces the upper set topology on a preorder as the topology where the open sets are
the upper sets and the lower set topology on a preorder as the topology where the open sets are
the lower sets.
In general the upper set topology does not coincide with the upper topology and the lower set
topology does not coincide with the lower topology.
## Main statements
- `Topology.IsUpperSet.toAlexandrovDiscrete`: The upper set topology is Alexandrov-discrete.
- `Topology.IsUpperSet.isClosed_iff_isLower` - a set is closed if and only if it is a Lower set
- `Topology.IsUpperSet.closure_eq_lowerClosure` - topological closure coincides with lower closure
- `Topology.IsUpperSet.monotone_iff_continuous` - the continuous functions are the monotone
functions
- `IsUpperSet.monotone_to_upperTopology_continuous`: A monotone map from a preorder with the upper
set topology to a preorder with the upper topology is continuous.
We provide the upper set topology in three ways (and similarly for the lower set topology):
* `Topology.upperSet`: The upper set topology as a `TopologicalSpace α`
* `Topology.IsUpperSet`: Prop-valued mixin typeclass stating that an existing topology is the upper
set topology.
* `Topology.WithUpperSet`: Type synonym equipping a preorder with its upper set topology.
## Motivation
An Alexandrov topology is a topology where the intersection of any collection of open sets is open.
The upper set topology is an Alexandrov topology and, given any Alexandrov topological space, we can
equip it with a preorder (namely the specialization preorder) whose upper set topology coincides
with the original topology. See `Topology.Specialization`.
## Tags
upper set topology, lower set topology, preorder, Alexandrov
-/
open Set TopologicalSpace
variable {α β γ : Type*}
namespace Topology
/-- Topology whose open sets are upper sets.
Note: In general the upper set topology does not coincide with the upper topology. -/
def upperSet (α : Type*) [Preorder α] : TopologicalSpace α where
IsOpen := IsUpperSet
isOpen_univ := isUpperSet_univ
isOpen_inter _ _ := IsUpperSet.inter
isOpen_sUnion _ := isUpperSet_sUnion
/-- Topology whose open sets are lower sets.
Note: In general the lower set topology does not coincide with the lower topology. -/
def lowerSet (α : Type*) [Preorder α] : TopologicalSpace α where
IsOpen := IsLowerSet
isOpen_univ := isLowerSet_univ
isOpen_inter _ _ := IsLowerSet.inter
isOpen_sUnion _ := isLowerSet_sUnion
/-- Type synonym for a preorder equipped with the upper set topology. -/
def WithUpperSet (α : Type*) := α
namespace WithUpperSet
/-- `toUpperSet` is the identity function to the `WithUpperSet` of a type. -/
@[match_pattern] def toUpperSet : α ≃ WithUpperSet α := Equiv.refl _
/-- `ofUpperSet` is the identity function from the `WithUpperSet` of a type. -/
@[match_pattern] def ofUpperSet : WithUpperSet α ≃ α := Equiv.refl _
@[simp] lemma toUpperSet_symm : (@toUpperSet α).symm = ofUpperSet := rfl
@[simp] lemma ofUpperSet_symm : (@ofUpperSet α).symm = toUpperSet := rfl
@[simp] lemma toUpperSet_ofUpperSet (a : WithUpperSet α) : toUpperSet (ofUpperSet a) = a := rfl
@[simp] lemma ofUpperSet_toUpperSet (a : α) : ofUpperSet (toUpperSet a) = a := rfl
lemma toUpperSet_inj {a b : α} : toUpperSet a = toUpperSet b ↔ a = b := Iff.rfl
lemma ofUpperSet_inj {a b : WithUpperSet α} : ofUpperSet a = ofUpperSet b ↔ a = b := Iff.rfl
/-- A recursor for `WithUpperSet`. Use as `induction x`. -/
@[elab_as_elim, cases_eliminator, induction_eliminator]
protected def rec {β : WithUpperSet α → Sort*} (h : ∀ a, β (toUpperSet a)) : ∀ a, β a :=
fun a => h (ofUpperSet a)
instance [Nonempty α] : Nonempty (WithUpperSet α) := ‹Nonempty α›
instance [Inhabited α] : Inhabited (WithUpperSet α) := ‹Inhabited α›
variable [Preorder α] [Preorder β]
instance : Preorder (WithUpperSet α) := ‹Preorder α›
instance : TopologicalSpace (WithUpperSet α) := upperSet α
lemma ofUpperSet_le_iff {a b : WithUpperSet α} : ofUpperSet a ≤ ofUpperSet b ↔ a ≤ b := Iff.rfl
lemma toUpperSet_le_iff {a b : α} : toUpperSet a ≤ toUpperSet b ↔ a ≤ b := Iff.rfl
/-- `ofUpperSet` as an `OrderIso` -/
def ofUpperSetOrderIso : WithUpperSet α ≃o α where
toEquiv := ofUpperSet
map_rel_iff' := ofUpperSet_le_iff
/-- `toUpperSet` as an `OrderIso` -/
def toUpperSetOrderIso : α ≃o WithUpperSet α where
toEquiv := toUpperSet
map_rel_iff' := toUpperSet_le_iff
end WithUpperSet
/-- Type synonym for a preorder equipped with the lower set topology. -/
def WithLowerSet (α : Type*) := α
namespace WithLowerSet
/-- `toLowerSet` is the identity function to the `WithLowerSet` of a type. -/
@[match_pattern] def toLowerSet : α ≃ WithLowerSet α := Equiv.refl _
/-- `ofLowerSet` is the identity function from the `WithLowerSet` of a type. -/
@[match_pattern] def ofLowerSet : WithLowerSet α ≃ α := Equiv.refl _
@[simp] lemma toLowerSet_symm : (@toLowerSet α).symm = ofLowerSet := rfl
@[simp] lemma ofLowerSet_symm : (@ofLowerSet α).symm = toLowerSet := rfl
@[simp] lemma toLowerSet_ofLowerSet (a : WithLowerSet α) : toLowerSet (ofLowerSet a) = a := rfl
@[simp] lemma ofLowerSet_toLowerSet (a : α) : ofLowerSet (toLowerSet a) = a := rfl
lemma toLowerSet_inj {a b : α} : toLowerSet a = toLowerSet b ↔ a = b := Iff.rfl
lemma ofLowerSet_inj {a b : WithLowerSet α} : ofLowerSet a = ofLowerSet b ↔ a = b := Iff.rfl
/-- A recursor for `WithLowerSet`. Use as `induction x`. -/
@[elab_as_elim, cases_eliminator, induction_eliminator]
protected def rec {β : WithLowerSet α → Sort*} (h : ∀ a, β (toLowerSet a)) : ∀ a, β a :=
fun a => h (ofLowerSet a)
instance [Nonempty α] : Nonempty (WithLowerSet α) := ‹Nonempty α›
instance [Inhabited α] : Inhabited (WithLowerSet α) := ‹Inhabited α›
variable [Preorder α]
instance : Preorder (WithLowerSet α) := ‹Preorder α›
instance : TopologicalSpace (WithLowerSet α) := lowerSet α
lemma ofLowerSet_le_iff {a b : WithLowerSet α} : ofLowerSet a ≤ ofLowerSet b ↔ a ≤ b := Iff.rfl
lemma toLowerSet_le_iff {a b : α} : toLowerSet a ≤ toLowerSet b ↔ a ≤ b := Iff.rfl
/-- `ofLowerSet` as an `OrderIso` -/
def ofLowerSetOrderIso : WithLowerSet α ≃o α where
toEquiv := ofLowerSet
map_rel_iff' := ofLowerSet_le_iff
/-- `toLowerSet` as an `OrderIso` -/
def toLowerSetOrderIso : α ≃o WithLowerSet α where
toEquiv := toLowerSet
map_rel_iff' := toLowerSet_le_iff
end WithLowerSet
/--
The Upper Set topology is homeomorphic to the Lower Set topology on the dual order
-/
def WithUpperSet.toDualHomeomorph [Preorder α] : WithUpperSet α ≃ₜ WithLowerSet αᵒᵈ where
toFun := OrderDual.toDual
invFun := OrderDual.ofDual
left_inv := OrderDual.toDual_ofDual
right_inv := OrderDual.ofDual_toDual
continuous_toFun := continuous_coinduced_rng
continuous_invFun := continuous_coinduced_rng
/-- Prop-valued mixin for an ordered topological space to be
The upper set topology is the topology where the open sets are the upper sets. In general the upper
set topology does not coincide with the upper topology.
-/
protected class IsUpperSet (α : Type*) [t : TopologicalSpace α] [Preorder α] : Prop where
topology_eq_upperSetTopology : t = upperSet α
attribute [nolint docBlame] IsUpperSet.topology_eq_upperSetTopology
instance [Preorder α] : Topology.IsUpperSet (WithUpperSet α) := ⟨rfl⟩
instance [Preorder α] : @Topology.IsUpperSet α (upperSet α) _ := by
letI := upperSet α
exact ⟨rfl⟩
/--
The lower set topology is the topology where the open sets are the lower sets. In general the lower
set topology does not coincide with the lower topology.
-/
protected class IsLowerSet (α : Type*) [t : TopologicalSpace α] [Preorder α] : Prop where
topology_eq_lowerSetTopology : t = lowerSet α
attribute [nolint docBlame] IsLowerSet.topology_eq_lowerSetTopology
instance [Preorder α] : Topology.IsLowerSet (WithLowerSet α) := ⟨rfl⟩
instance [Preorder α] : @Topology.IsLowerSet α (lowerSet α) _ := by
letI := lowerSet α
exact ⟨rfl⟩
namespace IsUpperSet
section Preorder
variable (α)
variable [Preorder α] [TopologicalSpace α] [Topology.IsUpperSet α] {s : Set α}
lemma topology_eq : ‹_› = upperSet α := topology_eq_upperSetTopology
variable {α}
instance _root_.OrderDual.instIsLowerSet [Preorder α] [TopologicalSpace α] [Topology.IsUpperSet α] :
Topology.IsLowerSet αᵒᵈ where
topology_eq_lowerSetTopology := by ext; rw [IsUpperSet.topology_eq α]
/-- If `α` is equipped with the upper set topology, then it is homeomorphic to
`WithUpperSet α`. -/
def WithUpperSetHomeomorph : WithUpperSet α ≃ₜ α :=
WithUpperSet.ofUpperSet.toHomeomorphOfIsInducing ⟨topology_eq α ▸ induced_id.symm⟩
lemma isOpen_iff_isUpperSet : IsOpen s ↔ IsUpperSet s := by
rw [topology_eq α]
rfl
instance toAlexandrovDiscrete : AlexandrovDiscrete α where
isOpen_sInter S := by simpa only [isOpen_iff_isUpperSet] using isUpperSet_sInter (α := α)
-- c.f. isClosed_iff_lower_and_subset_implies_LUB_mem
lemma isClosed_iff_isLower : IsClosed s ↔ IsLowerSet s := by
rw [← isOpen_compl_iff, isOpen_iff_isUpperSet,
isLowerSet_compl.symm, compl_compl]
lemma closure_eq_lowerClosure {s : Set α} : closure s = lowerClosure s := by
rw [subset_antisymm_iff]
refine ⟨?_, lowerClosure_min subset_closure (isClosed_iff_isLower.1 isClosed_closure)⟩
· apply closure_minimal subset_lowerClosure _
rw [isClosed_iff_isLower]
exact LowerSet.lower (lowerClosure s)
/--
The closure of a singleton `{a}` in the upper set topology is the right-closed left-infinite
interval (-∞,a].
-/
@[simp] lemma closure_singleton {a : α} : closure {a} = Iic a := by
rw [closure_eq_lowerClosure, lowerClosure_singleton]
rfl
lemma specializes_iff_le {a b : α} : a ⤳ b ↔ b ≤ a := by
simp only [specializes_iff_closure_subset, closure_singleton, Iic_subset_Iic]
end Preorder
section maps
variable [Preorder α] [Preorder β]
open Topology
protected lemma monotone_iff_continuous [TopologicalSpace α] [TopologicalSpace β]
[Topology.IsUpperSet α] [Topology.IsUpperSet β] {f : α → β} : Monotone f ↔ Continuous f := by
constructor
· intro hf
simp_rw [continuous_def, isOpen_iff_isUpperSet]
exact fun _ hs ↦ IsUpperSet.preimage hs hf
· intro hf a b hab
rw [← mem_Iic, ← closure_singleton] at hab ⊢
apply Continuous.closure_preimage_subset hf {f b}
apply mem_of_mem_of_subset hab
apply closure_mono
rw [singleton_subset_iff, mem_preimage, mem_singleton_iff]
lemma monotone_to_upperTopology_continuous [TopologicalSpace α] [TopologicalSpace β]
[Topology.IsUpperSet α] [IsUpper β] {f : α → β} (hf : Monotone f) : Continuous f := by
simp_rw [continuous_def, isOpen_iff_isUpperSet]
intro s hs
exact (IsUpper.isUpperSet_of_isOpen hs).preimage hf
lemma upperSet_le_upper {t₁ t₂ : TopologicalSpace α} [@Topology.IsUpperSet α t₁ _]
[@Topology.IsUpper α t₂ _] : t₁ ≤ t₂ := fun s hs => by
rw [@isOpen_iff_isUpperSet α _ t₁]
exact IsUpper.isUpperSet_of_isOpen hs
end maps
end IsUpperSet
namespace IsLowerSet
section Preorder
variable (α)
variable [Preorder α] [TopologicalSpace α] [Topology.IsLowerSet α] {s : Set α}
lemma topology_eq : ‹_› = lowerSet α := topology_eq_lowerSetTopology
variable {α}
instance _root_.OrderDual.instIsUpperSet [Preorder α] [TopologicalSpace α] [Topology.IsLowerSet α] :
Topology.IsUpperSet αᵒᵈ where
topology_eq_upperSetTopology := by ext; rw [IsLowerSet.topology_eq α]
/-- If `α` is equipped with the lower set topology, then it is homeomorphic to `WithLowerSet α`. -/
def WithLowerSetHomeomorph : WithLowerSet α ≃ₜ α :=
WithLowerSet.ofLowerSet.toHomeomorphOfIsInducing ⟨topology_eq α ▸ induced_id.symm⟩
lemma isOpen_iff_isLowerSet : IsOpen s ↔ IsLowerSet s := by rw [topology_eq α]; rfl
|
instance toAlexandrovDiscrete : AlexandrovDiscrete α := IsUpperSet.toAlexandrovDiscrete (α := αᵒᵈ)
| Mathlib/Topology/Order/UpperLowerSetTopology.lean | 311 | 312 |
/-
Copyright (c) 2023 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Topology.Algebra.Module.Multilinear.Bounded
import Mathlib.Topology.Algebra.Module.UniformConvergence
import Mathlib.Topology.Algebra.SeparationQuotient.Section
import Mathlib.Topology.Hom.ContinuousEvalConst
import Mathlib.Topology.Algebra.InfiniteSum.Basic
/-!
# Topology on continuous multilinear maps
In this file we define `TopologicalSpace` and `UniformSpace` structures
on `ContinuousMultilinearMap 𝕜 E F`,
where `E i` is a family of vector spaces over `𝕜` with topologies
and `F` is a topological vector space.
-/
open Bornology Function Set Topology
open scoped UniformConvergence Filter
namespace ContinuousMultilinearMap
variable {𝕜 ι : Type*} {E : ι → Type*} {F : Type*}
[NormedField 𝕜]
[∀ i, TopologicalSpace (E i)] [∀ i, AddCommGroup (E i)] [∀ i, Module 𝕜 (E i)]
[AddCommGroup F] [Module 𝕜 F]
/-- An auxiliary definition used to define topology on `ContinuousMultilinearMap 𝕜 E F`. -/
def toUniformOnFun [TopologicalSpace F] (f : ContinuousMultilinearMap 𝕜 E F) :
(Π i, E i) →ᵤ[{s | IsVonNBounded 𝕜 s}] F :=
UniformOnFun.ofFun _ f
open UniformOnFun in
lemma range_toUniformOnFun [DecidableEq ι] [TopologicalSpace F] :
range toUniformOnFun =
{f : (Π i, E i) →ᵤ[{s | IsVonNBounded 𝕜 s}] F |
Continuous (toFun _ f) ∧
(∀ (m : Π i, E i) i x y,
toFun _ f (update m i (x + y)) = toFun _ f (update m i x) + toFun _ f (update m i y)) ∧
(∀ (m : Π i, E i) i (c : 𝕜) x,
toFun _ f (update m i (c • x)) = c • toFun _ f (update m i x))} := by
ext f
constructor
· rintro ⟨f, rfl⟩
exact ⟨f.cont, f.map_update_add, f.map_update_smul⟩
· rintro ⟨hcont, hadd, hsmul⟩
exact ⟨⟨⟨f, by intro; convert hadd, by intro; convert hsmul⟩, hcont⟩, rfl⟩
@[simp]
lemma toUniformOnFun_toFun [TopologicalSpace F] (f : ContinuousMultilinearMap 𝕜 E F) :
UniformOnFun.toFun _ f.toUniformOnFun = f :=
rfl
instance instTopologicalSpace [TopologicalSpace F] [IsTopologicalAddGroup F] :
TopologicalSpace (ContinuousMultilinearMap 𝕜 E F) :=
.induced toUniformOnFun <|
@UniformOnFun.topologicalSpace _ _ (IsTopologicalAddGroup.toUniformSpace F) _
instance instUniformSpace [UniformSpace F] [IsUniformAddGroup F] :
UniformSpace (ContinuousMultilinearMap 𝕜 E F) :=
.replaceTopology (.comap toUniformOnFun <| UniformOnFun.uniformSpace _ _ _) <| by
rw [instTopologicalSpace, IsUniformAddGroup.toUniformSpace_eq]; rfl
section IsUniformAddGroup
variable [UniformSpace F] [IsUniformAddGroup F]
lemma isUniformInducing_toUniformOnFun :
IsUniformInducing (toUniformOnFun :
ContinuousMultilinearMap 𝕜 E F → ((Π i, E i) →ᵤ[{s | IsVonNBounded 𝕜 s}] F)) := ⟨rfl⟩
lemma isUniformEmbedding_toUniformOnFun :
IsUniformEmbedding (toUniformOnFun : ContinuousMultilinearMap 𝕜 E F → _) :=
⟨isUniformInducing_toUniformOnFun, DFunLike.coe_injective⟩
lemma isEmbedding_toUniformOnFun :
IsEmbedding (toUniformOnFun : ContinuousMultilinearMap 𝕜 E F →
((Π i, E i) →ᵤ[{s | IsVonNBounded 𝕜 s}] F)) :=
isUniformEmbedding_toUniformOnFun.isEmbedding
@[deprecated (since := "2024-10-26")]
alias embedding_toUniformOnFun := isEmbedding_toUniformOnFun
theorem uniformContinuous_coe_fun [∀ i, ContinuousSMul 𝕜 (E i)] :
UniformContinuous (DFunLike.coe : ContinuousMultilinearMap 𝕜 E F → (Π i, E i) → F) :=
(UniformOnFun.uniformContinuous_toFun isVonNBounded_covers).comp
isUniformEmbedding_toUniformOnFun.uniformContinuous
theorem uniformContinuous_eval_const [∀ i, ContinuousSMul 𝕜 (E i)] (x : Π i, E i) :
UniformContinuous fun f : ContinuousMultilinearMap 𝕜 E F ↦ f x :=
uniformContinuous_pi.1 uniformContinuous_coe_fun x
instance instIsUniformAddGroup : IsUniformAddGroup (ContinuousMultilinearMap 𝕜 E F) :=
let φ : ContinuousMultilinearMap 𝕜 E F →+ (Π i, E i) →ᵤ[{s | IsVonNBounded 𝕜 s}] F :=
{ toFun := toUniformOnFun, map_add' := fun _ _ ↦ rfl, map_zero' := rfl }
| isUniformEmbedding_toUniformOnFun.isUniformAddGroup φ
instance instUniformContinuousConstSMul {M : Type*}
[Monoid M] [DistribMulAction M F] [SMulCommClass 𝕜 M F] [ContinuousConstSMul M F] :
UniformContinuousConstSMul M (ContinuousMultilinearMap 𝕜 E F) :=
haveI := uniformContinuousConstSMul_of_continuousConstSMul M F
isUniformEmbedding_toUniformOnFun.uniformContinuousConstSMul fun _ _ ↦ rfl
theorem isUniformInducing_postcomp
{G : Type*} [AddCommGroup G] [UniformSpace G] [IsUniformAddGroup G] [Module 𝕜 G]
(g : F →L[𝕜] G) (hg : IsUniformInducing g) :
IsUniformInducing (g.compContinuousMultilinearMap :
ContinuousMultilinearMap 𝕜 E F → ContinuousMultilinearMap 𝕜 E G) := by
rw [← isUniformInducing_toUniformOnFun.of_comp_iff]
exact (UniformOnFun.postcomp_isUniformInducing hg).comp isUniformInducing_toUniformOnFun
| Mathlib/Topology/Algebra/Module/Multilinear/Topology.lean | 99 | 113 |
/-
Copyright (c) 2021 Yakov Pechersky. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yakov Pechersky
-/
import Mathlib.Data.List.MinMax
import Mathlib.Algebra.Tropical.Basic
import Mathlib.Order.ConditionallyCompleteLattice.Finset
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
/-!
# Tropicalization of finitary operations
This file provides the "big-op" or notation-based finitary operations on tropicalized types.
This allows easy conversion between sums to Infs and prods to sums. Results here are important
for expressing that evaluation of tropical polynomials are the minimum over a finite piecewise
collection of linear functions.
## Main declarations
* `untrop_sum`
## Implementation notes
No concrete (semi)ring is used here, only ones with inferable order/lattice structure, to support
`Real`, `Rat`, `EReal`, and others (`ERat` is not yet defined).
Minima over `List α` are defined as producing a value in `WithTop α` so proofs about lists do not
directly transfer to minima over multisets or finsets.
-/
variable {R S : Type*}
open Tropical Finset
theorem List.trop_sum [AddMonoid R] (l : List R) : trop l.sum = List.prod (l.map trop) := by
induction' l with hd tl IH
· simp
· simp [← IH]
theorem Multiset.trop_sum [AddCommMonoid R] (s : Multiset R) :
trop s.sum = Multiset.prod (s.map trop) :=
Quotient.inductionOn s (by simpa using List.trop_sum)
theorem trop_sum [AddCommMonoid R] (s : Finset S) (f : S → R) :
trop (∑ i ∈ s, f i) = ∏ i ∈ s, trop (f i) := by
convert Multiset.trop_sum (s.val.map f)
simp only [Multiset.map_map, Function.comp_apply]
| rfl
theorem List.untrop_prod [AddMonoid R] (l : List (Tropical R)) :
untrop l.prod = List.sum (l.map untrop) := by
induction' l with hd tl IH
| Mathlib/Algebra/Tropical/BigOperators.lean | 51 | 55 |
/-
Copyright (c) 2018 Patrick Massot. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Patrick Massot, Johannes Hölzl, Yaël Dillies
-/
import Mathlib.Analysis.Normed.Group.Continuity
import Mathlib.Topology.Algebra.IsUniformGroup.Basic
import Mathlib.Topology.MetricSpace.Algebra
import Mathlib.Topology.MetricSpace.IsometricSMul
/-!
# Normed groups are uniform groups
This file proves lipschitzness of normed group operations and shows that normed groups are uniform
groups.
-/
variable {𝓕 E F : Type*}
open Filter Function Metric Bornology
open scoped ENNReal NNReal Uniformity Pointwise Topology
section SeminormedGroup
variable [SeminormedGroup E] [SeminormedGroup F] {s : Set E} {a b : E} {r : ℝ}
@[to_additive]
instance NormedGroup.to_isIsometricSMul_right : IsIsometricSMul Eᵐᵒᵖ E :=
⟨fun a => Isometry.of_dist_eq fun b c => by simp [dist_eq_norm_div]⟩
@[to_additive]
theorem Isometry.norm_map_of_map_one {f : E → F} (hi : Isometry f) (h₁ : f 1 = 1) (x : E) :
‖f x‖ = ‖x‖ := by rw [← dist_one_right, ← h₁, hi.dist_eq, dist_one_right]
@[to_additive (attr := simp)]
theorem dist_mul_self_right (a b : E) : dist b (a * b) = ‖a‖ := by
rw [← dist_one_left, ← dist_mul_right 1 a b, one_mul]
@[to_additive (attr := simp)]
theorem dist_mul_self_left (a b : E) : dist (a * b) b = ‖a‖ := by
rw [dist_comm, dist_mul_self_right]
@[to_additive (attr := simp)]
theorem dist_div_eq_dist_mul_left (a b c : E) : dist (a / b) c = dist a (c * b) := by
rw [← dist_mul_right _ _ b, div_mul_cancel]
@[to_additive (attr := simp)]
theorem dist_div_eq_dist_mul_right (a b c : E) : dist a (b / c) = dist (a * c) b := by
rw [← dist_mul_right _ _ c, div_mul_cancel]
open Finset
variable [FunLike 𝓕 E F]
/-- A homomorphism `f` of seminormed groups is Lipschitz, if there exists a constant `C` such that
for all `x`, one has `‖f x‖ ≤ C * ‖x‖`. The analogous condition for a linear map of
(semi)normed spaces is in `Mathlib/Analysis/NormedSpace/OperatorNorm.lean`. -/
@[to_additive "A homomorphism `f` of seminormed groups is Lipschitz, if there exists a constant
`C` such that for all `x`, one has `‖f x‖ ≤ C * ‖x‖`. The analogous condition for a linear map of
(semi)normed spaces is in `Mathlib/Analysis/NormedSpace/OperatorNorm.lean`."]
theorem MonoidHomClass.lipschitz_of_bound [MonoidHomClass 𝓕 E F] (f : 𝓕) (C : ℝ)
(h : ∀ x, ‖f x‖ ≤ C * ‖x‖) : LipschitzWith (Real.toNNReal C) f :=
LipschitzWith.of_dist_le' fun x y => by simpa only [dist_eq_norm_div, map_div] using h (x / y)
@[to_additive]
theorem lipschitzOnWith_iff_norm_div_le {f : E → F} {C : ℝ≥0} :
LipschitzOnWith C f s ↔ ∀ ⦃x⦄, x ∈ s → ∀ ⦃y⦄, y ∈ s → ‖f x / f y‖ ≤ C * ‖x / y‖ := by
simp only [lipschitzOnWith_iff_dist_le_mul, dist_eq_norm_div]
alias ⟨LipschitzOnWith.norm_div_le, _⟩ := lipschitzOnWith_iff_norm_div_le
attribute [to_additive] LipschitzOnWith.norm_div_le
@[to_additive]
theorem LipschitzOnWith.norm_div_le_of_le {f : E → F} {C : ℝ≥0} (h : LipschitzOnWith C f s)
(ha : a ∈ s) (hb : b ∈ s) (hr : ‖a / b‖ ≤ r) : ‖f a / f b‖ ≤ C * r :=
(h.norm_div_le ha hb).trans <| by gcongr
@[to_additive]
theorem lipschitzWith_iff_norm_div_le {f : E → F} {C : ℝ≥0} :
LipschitzWith C f ↔ ∀ x y, ‖f x / f y‖ ≤ C * ‖x / y‖ := by
simp only [lipschitzWith_iff_dist_le_mul, dist_eq_norm_div]
alias ⟨LipschitzWith.norm_div_le, _⟩ := lipschitzWith_iff_norm_div_le
attribute [to_additive] LipschitzWith.norm_div_le
@[to_additive]
theorem LipschitzWith.norm_div_le_of_le {f : E → F} {C : ℝ≥0} (h : LipschitzWith C f)
(hr : ‖a / b‖ ≤ r) : ‖f a / f b‖ ≤ C * r :=
(h.norm_div_le _ _).trans <| by gcongr
/-- A homomorphism `f` of seminormed groups is continuous, if there exists a constant `C` such that
for all `x`, one has `‖f x‖ ≤ C * ‖x‖`. -/
@[to_additive "A homomorphism `f` of seminormed groups is continuous, if there exists a constant `C`
such that for all `x`, one has `‖f x‖ ≤ C * ‖x‖`"]
theorem MonoidHomClass.continuous_of_bound [MonoidHomClass 𝓕 E F] (f : 𝓕) (C : ℝ)
(h : ∀ x, ‖f x‖ ≤ C * ‖x‖) : Continuous f :=
(MonoidHomClass.lipschitz_of_bound f C h).continuous
@[to_additive]
theorem MonoidHomClass.uniformContinuous_of_bound [MonoidHomClass 𝓕 E F] (f : 𝓕) (C : ℝ)
(h : ∀ x, ‖f x‖ ≤ C * ‖x‖) : UniformContinuous f :=
(MonoidHomClass.lipschitz_of_bound f C h).uniformContinuous
@[to_additive]
theorem MonoidHomClass.isometry_iff_norm [MonoidHomClass 𝓕 E F] (f : 𝓕) :
Isometry f ↔ ∀ x, ‖f x‖ = ‖x‖ := by
simp only [isometry_iff_dist_eq, dist_eq_norm_div, ← map_div]
refine ⟨fun h x => ?_, fun h x y => h _⟩
simpa using h x 1
alias ⟨_, MonoidHomClass.isometry_of_norm⟩ := MonoidHomClass.isometry_iff_norm
attribute [to_additive] MonoidHomClass.isometry_of_norm
section NNNorm
@[to_additive]
theorem MonoidHomClass.lipschitz_of_bound_nnnorm [MonoidHomClass 𝓕 E F] (f : 𝓕) (C : ℝ≥0)
(h : ∀ x, ‖f x‖₊ ≤ C * ‖x‖₊) : LipschitzWith C f :=
@Real.toNNReal_coe C ▸ MonoidHomClass.lipschitz_of_bound f C h
@[to_additive]
theorem MonoidHomClass.antilipschitz_of_bound [MonoidHomClass 𝓕 E F] (f : 𝓕) {K : ℝ≥0}
(h : ∀ x, ‖x‖ ≤ K * ‖f x‖) : AntilipschitzWith K f :=
AntilipschitzWith.of_le_mul_dist fun x y => by
simpa only [dist_eq_norm_div, map_div] using h (x / y)
@[to_additive LipschitzWith.norm_le_mul]
theorem LipschitzWith.norm_le_mul' {f : E → F} {K : ℝ≥0} (h : LipschitzWith K f) (hf : f 1 = 1)
(x) : ‖f x‖ ≤ K * ‖x‖ := by simpa only [dist_one_right, hf] using h.dist_le_mul x 1
@[to_additive LipschitzWith.nnorm_le_mul]
theorem LipschitzWith.nnorm_le_mul' {f : E → F} {K : ℝ≥0} (h : LipschitzWith K f) (hf : f 1 = 1)
(x) : ‖f x‖₊ ≤ K * ‖x‖₊ :=
h.norm_le_mul' hf x
@[to_additive AntilipschitzWith.le_mul_norm]
theorem AntilipschitzWith.le_mul_norm' {f : E → F} {K : ℝ≥0} (h : AntilipschitzWith K f)
(hf : f 1 = 1) (x) : ‖x‖ ≤ K * ‖f x‖ := by
simpa only [dist_one_right, hf] using h.le_mul_dist x 1
@[to_additive AntilipschitzWith.le_mul_nnnorm]
theorem AntilipschitzWith.le_mul_nnnorm' {f : E → F} {K : ℝ≥0} (h : AntilipschitzWith K f)
(hf : f 1 = 1) (x) : ‖x‖₊ ≤ K * ‖f x‖₊ :=
h.le_mul_norm' hf x
@[to_additive]
theorem OneHomClass.bound_of_antilipschitz [OneHomClass 𝓕 E F] (f : 𝓕) {K : ℝ≥0}
(h : AntilipschitzWith K f) (x) : ‖x‖ ≤ K * ‖f x‖ :=
h.le_mul_nnnorm' (map_one f) x
@[to_additive]
theorem Isometry.nnnorm_map_of_map_one {f : E → F} (hi : Isometry f) (h₁ : f 1 = 1) (x : E) :
‖f x‖₊ = ‖x‖₊ :=
Subtype.ext <| hi.norm_map_of_map_one h₁ x
end NNNorm
|
@[to_additive lipschitzWith_one_norm]
theorem lipschitzWith_one_norm' : LipschitzWith 1 (norm : E → ℝ) := by
simpa using LipschitzWith.dist_right (1 : E)
| Mathlib/Analysis/Normed/Group/Uniform.lean | 159 | 162 |
/-
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]
| Mathlib/Algebra/Lie/Nilpotent.lean | 562 | 583 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Yury Kudryashov
-/
import Mathlib.Data.ENNReal.Operations
/-!
# Results about division in extended non-negative reals
This file establishes basic properties related to the inversion and division operations on `ℝ≥0∞`.
For instance, as a consequence of being a `DivInvOneMonoid`, `ℝ≥0∞` inherits a power operation
with integer exponent.
## Main results
A few order isomorphisms are worthy of mention:
- `OrderIso.invENNReal : ℝ≥0∞ ≃o ℝ≥0∞ᵒᵈ`: The map `x ↦ x⁻¹` as an order isomorphism to the dual.
- `orderIsoIicOneBirational : ℝ≥0∞ ≃o Iic (1 : ℝ≥0∞)`: The birational order isomorphism between
`ℝ≥0∞` and the unit interval `Set.Iic (1 : ℝ≥0∞)` given by `x ↦ (x⁻¹ + 1)⁻¹` with inverse
`x ↦ (x⁻¹ - 1)⁻¹`
- `orderIsoIicCoe (a : ℝ≥0) : Iic (a : ℝ≥0∞) ≃o Iic a`: Order isomorphism between an initial
interval in `ℝ≥0∞` and an initial interval in `ℝ≥0` given by the identity map.
- `orderIsoUnitIntervalBirational : ℝ≥0∞ ≃o Icc (0 : ℝ) 1`: An order isomorphism between
the extended nonnegative real numbers and the unit interval. This is `orderIsoIicOneBirational`
composed with the identity order isomorphism between `Iic (1 : ℝ≥0∞)` and `Icc (0 : ℝ) 1`.
-/
assert_not_exists Finset
open Set NNReal
namespace ENNReal
noncomputable section Inv
variable {a b c d : ℝ≥0∞} {r p q : ℝ≥0}
protected theorem div_eq_inv_mul : a / b = b⁻¹ * a := by rw [div_eq_mul_inv, mul_comm]
@[simp] theorem inv_zero : (0 : ℝ≥0∞)⁻¹ = ∞ :=
show sInf { b : ℝ≥0∞ | 1 ≤ 0 * b } = ∞ by simp
@[simp] theorem inv_top : ∞⁻¹ = 0 :=
bot_unique <| le_of_forall_gt_imp_ge_of_dense fun a (h : 0 < a) => sInf_le <| by
simp [*, h.ne', top_mul]
theorem coe_inv_le : (↑r⁻¹ : ℝ≥0∞) ≤ (↑r)⁻¹ :=
le_sInf fun b (hb : 1 ≤ ↑r * b) =>
coe_le_iff.2 <| by
rintro b rfl
apply NNReal.inv_le_of_le_mul
rwa [← coe_mul, ← coe_one, coe_le_coe] at hb
@[simp, norm_cast]
theorem coe_inv (hr : r ≠ 0) : (↑r⁻¹ : ℝ≥0∞) = (↑r)⁻¹ :=
coe_inv_le.antisymm <| sInf_le <| mem_setOf.2 <| by rw [← coe_mul, mul_inv_cancel₀ hr, coe_one]
@[norm_cast]
theorem coe_inv_two : ((2⁻¹ : ℝ≥0) : ℝ≥0∞) = 2⁻¹ := by rw [coe_inv _root_.two_ne_zero, coe_two]
@[simp, norm_cast]
theorem coe_div (hr : r ≠ 0) : (↑(p / r) : ℝ≥0∞) = p / r := by
rw [div_eq_mul_inv, div_eq_mul_inv, coe_mul, coe_inv hr]
lemma coe_div_le : ↑(p / r) ≤ (p / r : ℝ≥0∞) := by
simpa only [div_eq_mul_inv, coe_mul] using mul_le_mul_left' coe_inv_le _
theorem div_zero (h : a ≠ 0) : a / 0 = ∞ := by simp [div_eq_mul_inv, h]
instance : DivInvOneMonoid ℝ≥0∞ :=
{ inferInstanceAs (DivInvMonoid ℝ≥0∞) with
inv_one := by simpa only [coe_inv one_ne_zero, coe_one] using coe_inj.2 inv_one }
protected theorem inv_pow : ∀ {a : ℝ≥0∞} {n : ℕ}, (a ^ n)⁻¹ = a⁻¹ ^ n
| _, 0 => by simp only [pow_zero, inv_one]
| ⊤, n + 1 => by simp [top_pow]
| (a : ℝ≥0), n + 1 => by
rcases eq_or_ne a 0 with (rfl | ha)
· simp [top_pow]
· have := pow_ne_zero (n + 1) ha
norm_cast
rw [inv_pow]
protected theorem mul_inv_cancel (h0 : a ≠ 0) (ht : a ≠ ∞) : a * a⁻¹ = 1 := by
lift a to ℝ≥0 using ht
norm_cast at h0; norm_cast
exact mul_inv_cancel₀ h0
protected theorem inv_mul_cancel (h0 : a ≠ 0) (ht : a ≠ ∞) : a⁻¹ * a = 1 :=
mul_comm a a⁻¹ ▸ ENNReal.mul_inv_cancel h0 ht
/-- See `ENNReal.inv_mul_cancel_left` for a simpler version assuming `a ≠ 0`, `a ≠ ∞`. -/
protected lemma inv_mul_cancel_left' (ha₀ : a = 0 → b = 0) (ha : a = ∞ → b = 0) :
a⁻¹ * (a * b) = b := by
obtain rfl | ha₀ := eq_or_ne a 0
· simp_all
obtain rfl | ha := eq_or_ne a ⊤
· simp_all
· simp [← mul_assoc, ENNReal.inv_mul_cancel, *]
/-- See `ENNReal.inv_mul_cancel_left'` for a stronger version. -/
protected lemma inv_mul_cancel_left (ha₀ : a ≠ 0) (ha : a ≠ ∞) : a⁻¹ * (a * b) = b :=
ENNReal.inv_mul_cancel_left' (by simp [ha₀]) (by simp [ha])
/-- See `ENNReal.mul_inv_cancel_left` for a simpler version assuming `a ≠ 0`, `a ≠ ∞`. -/
protected lemma mul_inv_cancel_left' (ha₀ : a = 0 → b = 0) (ha : a = ∞ → b = 0) :
a * (a⁻¹ * b) = b := by
obtain rfl | ha₀ := eq_or_ne a 0
· simp_all
obtain rfl | ha := eq_or_ne a ⊤
· simp_all
· simp [← mul_assoc, ENNReal.mul_inv_cancel, *]
/-- See `ENNReal.mul_inv_cancel_left'` for a stronger version. -/
protected lemma mul_inv_cancel_left (ha₀ : a ≠ 0) (ha : a ≠ ∞) : a * (a⁻¹ * b) = b :=
ENNReal.mul_inv_cancel_left' (by simp [ha₀]) (by simp [ha])
/-- See `ENNReal.mul_inv_cancel_right` for a simpler version assuming `b ≠ 0`, `b ≠ ∞`. -/
protected lemma mul_inv_cancel_right' (hb₀ : b = 0 → a = 0) (hb : b = ∞ → a = 0) :
a * b * b⁻¹ = a := by
obtain rfl | hb₀ := eq_or_ne b 0
· simp_all
obtain rfl | hb := eq_or_ne b ⊤
· simp_all
· simp [mul_assoc, ENNReal.mul_inv_cancel, *]
/-- See `ENNReal.mul_inv_cancel_right'` for a stronger version. -/
protected lemma mul_inv_cancel_right (hb₀ : b ≠ 0) (hb : b ≠ ∞) : a * b * b⁻¹ = a :=
ENNReal.mul_inv_cancel_right' (by simp [hb₀]) (by simp [hb])
/-- See `ENNReal.inv_mul_cancel_right` for a simpler version assuming `b ≠ 0`, `b ≠ ∞`. -/
protected lemma inv_mul_cancel_right' (hb₀ : b = 0 → a = 0) (hb : b = ∞ → a = 0) :
a * b⁻¹ * b = a := by
obtain rfl | hb₀ := eq_or_ne b 0
· simp_all
obtain rfl | hb := eq_or_ne b ⊤
· simp_all
· simp [mul_assoc, ENNReal.inv_mul_cancel, *]
/-- See `ENNReal.inv_mul_cancel_right'` for a stronger version. -/
protected lemma inv_mul_cancel_right (hb₀ : b ≠ 0) (hb : b ≠ ∞) : a * b⁻¹ * b = a :=
ENNReal.inv_mul_cancel_right' (by simp [hb₀]) (by simp [hb])
/-- See `ENNReal.mul_div_cancel_right` for a simpler version assuming `b ≠ 0`, `b ≠ ∞`. -/
protected lemma mul_div_cancel_right' (hb₀ : b = 0 → a = 0) (hb : b = ∞ → a = 0) :
a * b / b = a := ENNReal.mul_inv_cancel_right' hb₀ hb
/-- See `ENNReal.mul_div_cancel_right'` for a stronger version. -/
protected lemma mul_div_cancel_right (hb₀ : b ≠ 0) (hb : b ≠ ∞) : a * b / b = a :=
ENNReal.mul_div_cancel_right' (by simp [hb₀]) (by simp [hb])
/-- See `ENNReal.div_mul_cancel` for a simpler version assuming `a ≠ 0`, `a ≠ ∞`. -/
protected lemma div_mul_cancel' (ha₀ : a = 0 → b = 0) (ha : a = ∞ → b = 0) : b / a * a = b :=
ENNReal.inv_mul_cancel_right' ha₀ ha
/-- See `ENNReal.div_mul_cancel'` for a stronger version. -/
protected lemma div_mul_cancel (ha₀ : a ≠ 0) (ha : a ≠ ∞) : b / a * a = b :=
ENNReal.div_mul_cancel' (by simp [ha₀]) (by simp [ha])
/-- See `ENNReal.mul_div_cancel` for a simpler version assuming `a ≠ 0`, `a ≠ ∞`. -/
protected lemma mul_div_cancel' (ha₀ : a = 0 → b = 0) (ha : a = ∞ → b = 0) : a * (b / a) = b := by
rw [mul_comm, ENNReal.div_mul_cancel' ha₀ ha]
/-- See `ENNReal.mul_div_cancel'` for a stronger version. -/
protected lemma mul_div_cancel (ha₀ : a ≠ 0) (ha : a ≠ ∞) : a * (b / a) = b :=
ENNReal.mul_div_cancel' (by simp [ha₀]) (by simp [ha])
protected theorem mul_comm_div : a / b * c = a * (c / b) := by
simp only [div_eq_mul_inv, mul_left_comm, mul_comm, mul_assoc]
protected theorem mul_div_right_comm : a * b / c = a / c * b := by
simp only [div_eq_mul_inv, mul_right_comm]
instance : InvolutiveInv ℝ≥0∞ where
inv_inv a := by
by_cases a = 0 <;> cases a <;> simp_all [none_eq_top, some_eq_coe, -coe_inv, (coe_inv _).symm]
@[simp] protected lemma inv_eq_one : a⁻¹ = 1 ↔ a = 1 := by rw [← inv_inj, inv_inv, inv_one]
@[simp] theorem inv_eq_top : a⁻¹ = ∞ ↔ a = 0 := inv_zero ▸ inv_inj
theorem inv_ne_top : a⁻¹ ≠ ∞ ↔ a ≠ 0 := by simp
@[aesop (rule_sets := [finiteness]) safe apply]
protected alias ⟨_, Finiteness.inv_ne_top⟩ := ENNReal.inv_ne_top
@[simp]
theorem inv_lt_top {x : ℝ≥0∞} : x⁻¹ < ∞ ↔ 0 < x := by
simp only [lt_top_iff_ne_top, inv_ne_top, pos_iff_ne_zero]
theorem div_lt_top {x y : ℝ≥0∞} (h1 : x ≠ ∞) (h2 : y ≠ 0) : x / y < ∞ :=
mul_lt_top h1.lt_top (inv_ne_top.mpr h2).lt_top
@[simp]
protected theorem inv_eq_zero : a⁻¹ = 0 ↔ a = ∞ :=
inv_top ▸ inv_inj
protected theorem inv_ne_zero : a⁻¹ ≠ 0 ↔ a ≠ ∞ := by simp
protected theorem div_pos (ha : a ≠ 0) (hb : b ≠ ∞) : 0 < a / b :=
ENNReal.mul_pos ha <| ENNReal.inv_ne_zero.2 hb
protected theorem inv_mul_le_iff {x y z : ℝ≥0∞} (h1 : x ≠ 0) (h2 : x ≠ ∞) :
x⁻¹ * y ≤ z ↔ y ≤ x * z := by
rw [← mul_le_mul_left h1 h2, ← mul_assoc, ENNReal.mul_inv_cancel h1 h2, one_mul]
protected theorem mul_inv_le_iff {x y z : ℝ≥0∞} (h1 : y ≠ 0) (h2 : y ≠ ∞) :
x * y⁻¹ ≤ z ↔ x ≤ z * y := by
rw [mul_comm, ENNReal.inv_mul_le_iff h1 h2, mul_comm]
protected theorem div_le_iff {x y z : ℝ≥0∞} (h1 : y ≠ 0) (h2 : y ≠ ∞) :
x / y ≤ z ↔ x ≤ z * y := by
rw [div_eq_mul_inv, ENNReal.mul_inv_le_iff h1 h2]
protected theorem div_le_iff' {x y z : ℝ≥0∞} (h1 : y ≠ 0) (h2 : y ≠ ∞) :
x / y ≤ z ↔ x ≤ y * z := by
rw [mul_comm, ENNReal.div_le_iff h1 h2]
protected theorem mul_inv {a b : ℝ≥0∞} (ha : a ≠ 0 ∨ b ≠ ∞) (hb : a ≠ ∞ ∨ b ≠ 0) :
(a * b)⁻¹ = a⁻¹ * b⁻¹ := by
induction' b with b
· replace ha : a ≠ 0 := ha.neg_resolve_right rfl
simp [ha]
induction' a with a
· replace hb : b ≠ 0 := coe_ne_zero.1 (hb.neg_resolve_left rfl)
simp [hb]
by_cases h'a : a = 0
· simp only [h'a, top_mul, ENNReal.inv_zero, ENNReal.coe_ne_top, zero_mul, Ne,
not_false_iff, ENNReal.coe_zero, ENNReal.inv_eq_zero]
by_cases h'b : b = 0
· simp only [h'b, ENNReal.inv_zero, ENNReal.coe_ne_top, mul_top, Ne, not_false_iff,
mul_zero, ENNReal.coe_zero, ENNReal.inv_eq_zero]
rw [← ENNReal.coe_mul, ← ENNReal.coe_inv, ← ENNReal.coe_inv h'a, ← ENNReal.coe_inv h'b, ←
ENNReal.coe_mul, mul_inv_rev, mul_comm]
simp [h'a, h'b]
protected theorem inv_div {a b : ℝ≥0∞} (htop : b ≠ ∞ ∨ a ≠ ∞) (hzero : b ≠ 0 ∨ a ≠ 0) :
(a / b)⁻¹ = b / a := by
rw [← ENNReal.inv_ne_zero] at htop
rw [← ENNReal.inv_ne_top] at hzero
rw [ENNReal.div_eq_inv_mul, ENNReal.div_eq_inv_mul, ENNReal.mul_inv htop hzero, mul_comm, inv_inv]
protected theorem mul_div_mul_left (a b : ℝ≥0∞) (hc : c ≠ 0) (hc' : c ≠ ⊤) :
c * a / (c * b) = a / b := by
rw [div_eq_mul_inv, div_eq_mul_inv, ENNReal.mul_inv (Or.inl hc) (Or.inl hc'), mul_mul_mul_comm,
ENNReal.mul_inv_cancel hc hc', one_mul]
protected theorem mul_div_mul_right (a b : ℝ≥0∞) (hc : c ≠ 0) (hc' : c ≠ ⊤) :
a * c / (b * c) = a / b := by
rw [div_eq_mul_inv, div_eq_mul_inv, ENNReal.mul_inv (Or.inr hc') (Or.inr hc), mul_mul_mul_comm,
ENNReal.mul_inv_cancel hc hc', mul_one]
protected theorem sub_div (h : 0 < b → b < a → c ≠ 0) : (a - b) / c = a / c - b / c := by
simp_rw [div_eq_mul_inv]
exact ENNReal.sub_mul (by simpa using h)
@[simp]
protected theorem inv_pos : 0 < a⁻¹ ↔ a ≠ ∞ :=
pos_iff_ne_zero.trans ENNReal.inv_ne_zero
theorem inv_strictAnti : StrictAnti (Inv.inv : ℝ≥0∞ → ℝ≥0∞) := by
intro a b h
lift a to ℝ≥0 using h.ne_top
induction b; · simp
rw [coe_lt_coe] at h
rcases eq_or_ne a 0 with (rfl | ha); · simp [h]
rw [← coe_inv h.ne_bot, ← coe_inv ha, coe_lt_coe]
exact NNReal.inv_lt_inv ha h
@[simp]
protected theorem inv_lt_inv : a⁻¹ < b⁻¹ ↔ b < a :=
inv_strictAnti.lt_iff_lt
theorem inv_lt_iff_inv_lt : a⁻¹ < b ↔ b⁻¹ < a := by
simpa only [inv_inv] using @ENNReal.inv_lt_inv a b⁻¹
theorem lt_inv_iff_lt_inv : a < b⁻¹ ↔ b < a⁻¹ := by
simpa only [inv_inv] using @ENNReal.inv_lt_inv a⁻¹ b
@[simp]
protected theorem inv_le_inv : a⁻¹ ≤ b⁻¹ ↔ b ≤ a :=
inv_strictAnti.le_iff_le
theorem inv_le_iff_inv_le : a⁻¹ ≤ b ↔ b⁻¹ ≤ a := by
simpa only [inv_inv] using @ENNReal.inv_le_inv a b⁻¹
theorem le_inv_iff_le_inv : a ≤ b⁻¹ ↔ b ≤ a⁻¹ := by
simpa only [inv_inv] using @ENNReal.inv_le_inv a⁻¹ b
@[gcongr] protected theorem inv_le_inv' (h : a ≤ b) : b⁻¹ ≤ a⁻¹ :=
ENNReal.inv_strictAnti.antitone h
@[gcongr] protected theorem inv_lt_inv' (h : a < b) : b⁻¹ < a⁻¹ := ENNReal.inv_strictAnti h
@[simp]
protected theorem inv_le_one : a⁻¹ ≤ 1 ↔ 1 ≤ a := by rw [inv_le_iff_inv_le, inv_one]
protected theorem one_le_inv : 1 ≤ a⁻¹ ↔ a ≤ 1 := by rw [le_inv_iff_le_inv, inv_one]
@[simp]
protected theorem inv_lt_one : a⁻¹ < 1 ↔ 1 < a := by rw [inv_lt_iff_inv_lt, inv_one]
@[simp]
protected theorem one_lt_inv : 1 < a⁻¹ ↔ a < 1 := by rw [lt_inv_iff_lt_inv, inv_one]
/-- The inverse map `fun x ↦ x⁻¹` is an order isomorphism between `ℝ≥0∞` and its `OrderDual` -/
@[simps! apply]
def _root_.OrderIso.invENNReal : ℝ≥0∞ ≃o ℝ≥0∞ᵒᵈ where
map_rel_iff' := ENNReal.inv_le_inv
toEquiv := (Equiv.inv ℝ≥0∞).trans OrderDual.toDual
@[simp]
theorem _root_.OrderIso.invENNReal_symm_apply (a : ℝ≥0∞ᵒᵈ) :
OrderIso.invENNReal.symm a = (OrderDual.ofDual a)⁻¹ :=
rfl
@[simp] theorem div_top : a / ∞ = 0 := by rw [div_eq_mul_inv, inv_top, mul_zero]
theorem top_div : ∞ / a = if a = ∞ then 0 else ∞ := by simp [div_eq_mul_inv, top_mul']
theorem top_div_of_ne_top (h : a ≠ ∞) : ∞ / a = ∞ := by simp [top_div, h]
@[simp] theorem top_div_coe : ∞ / p = ∞ := top_div_of_ne_top coe_ne_top
theorem top_div_of_lt_top (h : a < ∞) : ∞ / a = ∞ := top_div_of_ne_top h.ne
@[simp] protected theorem zero_div : 0 / a = 0 := zero_mul a⁻¹
theorem div_eq_top : a / b = ∞ ↔ a ≠ 0 ∧ b = 0 ∨ a = ∞ ∧ b ≠ ∞ := by
simp [div_eq_mul_inv, ENNReal.mul_eq_top]
protected theorem le_div_iff_mul_le (h0 : b ≠ 0 ∨ c ≠ 0) (ht : b ≠ ∞ ∨ c ≠ ∞) :
a ≤ c / b ↔ a * b ≤ c := by
induction' b with b
· lift c to ℝ≥0 using ht.neg_resolve_left rfl
rw [div_top, nonpos_iff_eq_zero]
rcases eq_or_ne a 0 with (rfl | ha) <;> simp [*]
rcases eq_or_ne b 0 with (rfl | hb)
· have hc : c ≠ 0 := h0.neg_resolve_left rfl
simp [div_zero hc]
| · rw [← coe_ne_zero] at hb
rw [← ENNReal.mul_le_mul_right hb coe_ne_top, ENNReal.div_mul_cancel hb coe_ne_top]
| Mathlib/Data/ENNReal/Inv.lean | 346 | 348 |
/-
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.Algebra.BigOperators.Group.Finset.Powerset
import Mathlib.Algebra.NoZeroSMulDivisors.Pi
import Mathlib.Data.Finset.Sort
import Mathlib.Data.Fintype.BigOperators
import Mathlib.Data.Fintype.Powerset
import Mathlib.LinearAlgebra.Pi
import Mathlib.Logic.Equiv.Fintype
import Mathlib.Tactic.Abel
/-!
# Multilinear maps
We define multilinear maps as maps from `∀ (i : ι), M₁ i` to `M₂` which are linear in each
coordinate. Here, `M₁ i` and `M₂` are modules over a ring `R`, and `ι` is an arbitrary type
(although some statements will require it to be a fintype). This space, denoted by
`MultilinearMap R M₁ M₂`, inherits a module structure by pointwise addition and multiplication.
## Main definitions
* `MultilinearMap R M₁ M₂` is the space of multilinear maps from `∀ (i : ι), M₁ i` to `M₂`.
* `f.map_update_smul` is the multiplicativity of the multilinear map `f` along each coordinate.
* `f.map_update_add` is the additivity of the multilinear map `f` along each coordinate.
* `f.map_smul_univ` expresses the multiplicativity of `f` over all coordinates at the same time,
writing `f (fun i => c i • m i)` as `(∏ i, c i) • f m`.
* `f.map_add_univ` expresses the additivity of `f` over all coordinates at the same time, writing
`f (m + m')` as the sum over all subsets `s` of `ι` of `f (s.piecewise m m')`.
* `f.map_sum` expresses `f (Σ_{j₁} g₁ j₁, ..., Σ_{jₙ} gₙ jₙ)` as the sum of
`f (g₁ (r 1), ..., gₙ (r n))` where `r` ranges over all possible functions.
See `Mathlib.LinearAlgebra.Multilinear.Curry` for the currying of multilinear maps.
## Implementation notes
Expressing that a map is linear along the `i`-th coordinate when all other coordinates are fixed
can be done in two (equivalent) different ways:
* fixing a vector `m : ∀ (j : ι - i), M₁ j.val`, and then choosing separately the `i`-th coordinate
* fixing a vector `m : ∀j, M₁ j`, and then modifying its `i`-th coordinate
The second way is more artificial as the value of `m` at `i` is not relevant, but it has the
advantage of avoiding subtype inclusion issues. This is the definition we use, based on
`Function.update` that allows to change the value of `m` at `i`.
Note that the use of `Function.update` requires a `DecidableEq ι` term to appear somewhere in the
statement of `MultilinearMap.map_update_add'` and `MultilinearMap.map_update_smul'`.
Three possible choices are:
1. Requiring `DecidableEq ι` as an argument to `MultilinearMap` (as we did originally).
2. Using `Classical.decEq ι` in the statement of `map_add'` and `map_smul'`.
3. Quantifying over all possible `DecidableEq ι` instances in the statement of `map_add'` and
`map_smul'`.
Option 1 works fine, but puts unnecessary constraints on the user
(the zero map certainly does not need decidability).
Option 2 looks great at first, but in the common case when `ι = Fin n`
it introduces non-defeq decidability instance diamonds
within the context of proving `map_update_add'` and `map_update_smul'`,
of the form `Fin.decidableEq n = Classical.decEq (Fin n)`.
Option 3 of course does something similar, but of the form `Fin.decidableEq n = _inst`,
which is much easier to clean up since `_inst` is a free variable
and so the equality can just be substituted.
-/
open Fin Function Finset Set
universe uR uS uι v v' v₁ v₂ v₃
variable {R : Type uR} {S : Type uS} {ι : Type uι} {n : ℕ}
{M : Fin n.succ → Type v} {M₁ : ι → Type v₁} {M₂ : Type v₂} {M₃ : Type v₃} {M' : Type v'}
-- Don't generate injectivity lemmas, which the `simpNF` linter will time out on.
set_option genInjectivity false in
/-- Multilinear maps over the ring `R`, from `∀ i, M₁ i` to `M₂` where `M₁ i` and `M₂` are modules
over `R`. -/
structure MultilinearMap (R : Type uR) {ι : Type uι} (M₁ : ι → Type v₁) (M₂ : Type v₂) [Semiring R]
[∀ i, AddCommMonoid (M₁ i)] [AddCommMonoid M₂] [∀ i, Module R (M₁ i)] [Module R M₂] where
/-- The underlying multivariate function of a multilinear map. -/
toFun : (∀ i, M₁ i) → M₂
/-- A multilinear map is additive in every argument. -/
map_update_add' :
∀ [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) (x y : M₁ i),
toFun (update m i (x + y)) = toFun (update m i x) + toFun (update m i y)
/-- A multilinear map is compatible with scalar multiplication in every argument. -/
map_update_smul' :
∀ [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) (c : R) (x : M₁ i),
toFun (update m i (c • x)) = c • toFun (update m i x)
namespace MultilinearMap
section Semiring
variable [Semiring R] [∀ i, AddCommMonoid (M i)] [∀ i, AddCommMonoid (M₁ i)] [AddCommMonoid M₂]
[AddCommMonoid M₃] [AddCommMonoid M'] [∀ i, Module R (M i)] [∀ i, Module R (M₁ i)] [Module R M₂]
[Module R M₃] [Module R M'] (f f' : MultilinearMap R M₁ M₂)
instance : FunLike (MultilinearMap R M₁ M₂) (∀ i, M₁ i) M₂ where
coe f := f.toFun
coe_injective' f g h := by cases f; cases g; cases h; rfl
initialize_simps_projections MultilinearMap (toFun → apply)
/-- Constructor for `MultilinearMap R M₁ M₂` when the
index type `ι` is already endowed with a `DecidableEq` instance. -/
@[simps]
def mk' [DecidableEq ι] (f : (∀ i, M₁ i) → M₂)
(h₁ : ∀ (m : ∀ i, M₁ i) (i : ι) (x y : M₁ i),
f (update m i (x + y)) = f (update m i x) + f (update m i y) := by aesop)
(h₂ : ∀ (m : ∀ i, M₁ i) (i : ι) (c : R) (x : M₁ i),
f (update m i (c • x)) = c • f (update m i x) := by aesop) :
MultilinearMap R M₁ M₂ where
toFun := f
map_update_add' m i x y := by convert h₁ m i x y
map_update_smul' m i c x := by convert h₂ m i c x
@[simp]
theorem toFun_eq_coe : f.toFun = ⇑f :=
rfl
@[simp]
theorem coe_mk (f : (∀ i, M₁ i) → M₂) (h₁ h₂) : ⇑(⟨f, h₁, h₂⟩ : MultilinearMap R M₁ M₂) = f :=
rfl
theorem congr_fun {f g : MultilinearMap R M₁ M₂} (h : f = g) (x : ∀ i, M₁ i) : f x = g x :=
DFunLike.congr_fun h x
nonrec theorem congr_arg (f : MultilinearMap R M₁ M₂) {x y : ∀ i, M₁ i} (h : x = y) : f x = f y :=
DFunLike.congr_arg f h
theorem coe_injective : Injective ((↑) : MultilinearMap R M₁ M₂ → (∀ i, M₁ i) → M₂) :=
DFunLike.coe_injective
@[norm_cast]
theorem coe_inj {f g : MultilinearMap R M₁ M₂} : (f : (∀ i, M₁ i) → M₂) = g ↔ f = g :=
DFunLike.coe_fn_eq
@[ext]
theorem ext {f f' : MultilinearMap R M₁ M₂} (H : ∀ x, f x = f' x) : f = f' :=
DFunLike.ext _ _ H
@[simp]
theorem mk_coe (f : MultilinearMap R M₁ M₂) (h₁ h₂) :
(⟨f, h₁, h₂⟩ : MultilinearMap R M₁ M₂) = f := rfl
@[simp]
protected theorem map_update_add [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) (x y : M₁ i) :
f (update m i (x + y)) = f (update m i x) + f (update m i y) :=
f.map_update_add' m i x y
@[deprecated (since := "2024-11-03")] protected alias map_add := MultilinearMap.map_update_add
@[deprecated (since := "2024-11-03")] protected alias map_add' := MultilinearMap.map_update_add
/-- Earlier, this name was used by what is now called `MultilinearMap.map_update_smul_left`. -/
@[simp]
protected theorem map_update_smul [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) (c : R) (x : M₁ i) :
f (update m i (c • x)) = c • f (update m i x) :=
f.map_update_smul' m i c x
@[deprecated (since := "2024-11-03")] protected alias map_smul := MultilinearMap.map_update_smul
@[deprecated (since := "2024-11-03")] protected alias map_smul' := MultilinearMap.map_update_smul
theorem map_coord_zero {m : ∀ i, M₁ i} (i : ι) (h : m i = 0) : f m = 0 := by
classical
have : (0 : R) • (0 : M₁ i) = 0 := by simp
rw [← update_eq_self i m, h, ← this, f.map_update_smul, zero_smul]
@[simp]
theorem map_update_zero [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) : f (update m i 0) = 0 :=
f.map_coord_zero i (update_self i 0 m)
@[simp]
theorem map_zero [Nonempty ι] : f 0 = 0 := by
obtain ⟨i, _⟩ : ∃ i : ι, i ∈ Set.univ := Set.exists_mem_of_nonempty ι
exact map_coord_zero f i rfl
instance : Add (MultilinearMap R M₁ M₂) :=
⟨fun f f' =>
⟨fun x => f x + f' x, fun m i x y => by simp [add_left_comm, add_assoc], fun m i c x => by
simp [smul_add]⟩⟩
@[simp]
theorem add_apply (m : ∀ i, M₁ i) : (f + f') m = f m + f' m :=
rfl
instance : Zero (MultilinearMap R M₁ M₂) :=
⟨⟨fun _ => 0, fun _ _ _ _ => by simp, fun _ _ c _ => by simp⟩⟩
instance : Inhabited (MultilinearMap R M₁ M₂) :=
⟨0⟩
@[simp]
theorem zero_apply (m : ∀ i, M₁ i) : (0 : MultilinearMap R M₁ M₂) m = 0 :=
rfl
section SMul
variable [DistribSMul S M₂] [SMulCommClass R S M₂]
instance : SMul S (MultilinearMap R M₁ M₂) :=
⟨fun c f =>
⟨fun m => c • f m, fun m i x y => by simp [smul_add], fun l i x d => by
simp [← smul_comm x c (_ : M₂)]⟩⟩
@[simp]
theorem smul_apply (f : MultilinearMap R M₁ M₂) (c : S) (m : ∀ i, M₁ i) : (c • f) m = c • f m :=
rfl
theorem coe_smul (c : S) (f : MultilinearMap R M₁ M₂) : ⇑(c • f) = c • (⇑ f) := rfl
end SMul
instance addCommMonoid : AddCommMonoid (MultilinearMap R M₁ M₂) :=
coe_injective.addCommMonoid _ rfl (fun _ _ => rfl) fun _ _ => rfl
/-- Coercion of a multilinear map to a function as an additive monoid homomorphism. -/
@[simps] def coeAddMonoidHom : MultilinearMap R M₁ M₂ →+ (((i : ι) → M₁ i) → M₂) where
toFun := DFunLike.coe; map_zero' := rfl; map_add' _ _ := rfl
@[simp]
theorem coe_sum {α : Type*} (f : α → MultilinearMap R M₁ M₂) (s : Finset α) :
⇑(∑ a ∈ s, f a) = ∑ a ∈ s, ⇑(f a) :=
map_sum coeAddMonoidHom f s
theorem sum_apply {α : Type*} (f : α → MultilinearMap R M₁ M₂) (m : ∀ i, M₁ i) {s : Finset α} :
(∑ a ∈ s, f a) m = ∑ a ∈ s, f a m := by simp
/-- If `f` is a multilinear map, then `f.toLinearMap m i` is the linear map obtained by fixing all
coordinates but `i` equal to those of `m`, and varying the `i`-th coordinate. -/
@[simps]
def toLinearMap [DecidableEq ι] (m : ∀ i, M₁ i) (i : ι) : M₁ i →ₗ[R] M₂ where
toFun x := f (update m i x)
map_add' x y := by simp
map_smul' c x := by simp
/-- The cartesian product of two multilinear maps, as a multilinear map. -/
@[simps]
def prod (f : MultilinearMap R M₁ M₂) (g : MultilinearMap R M₁ M₃) :
MultilinearMap R M₁ (M₂ × M₃) where
toFun m := (f m, g m)
map_update_add' m i x y := by simp
map_update_smul' m i c x := by simp
/-- Combine a family of multilinear maps with the same domain and codomains `M' i` into a
multilinear map taking values in the space of functions `∀ i, M' i`. -/
@[simps]
def pi {ι' : Type*} {M' : ι' → Type*} [∀ i, AddCommMonoid (M' i)] [∀ i, Module R (M' i)]
(f : ∀ i, MultilinearMap R M₁ (M' i)) : MultilinearMap R M₁ (∀ i, M' i) where
toFun m i := f i m
map_update_add' _ _ _ _ := funext fun j => (f j).map_update_add _ _ _ _
map_update_smul' _ _ _ _ := funext fun j => (f j).map_update_smul _ _ _ _
section
variable (R M₂ M₃)
/-- Equivalence between linear maps `M₂ →ₗ[R] M₃` and one-multilinear maps. -/
@[simps]
def ofSubsingleton [Subsingleton ι] (i : ι) :
(M₂ →ₗ[R] M₃) ≃ MultilinearMap R (fun _ : ι ↦ M₂) M₃ where
toFun f :=
{ toFun := fun x ↦ f (x i)
map_update_add' := by intros; simp [update_eq_const_of_subsingleton]
map_update_smul' := by intros; simp [update_eq_const_of_subsingleton] }
invFun f :=
{ toFun := fun x ↦ f fun _ ↦ x
map_add' := fun x y ↦ by
simpa [update_eq_const_of_subsingleton] using f.map_update_add 0 i x y
map_smul' := fun c x ↦ by
simpa [update_eq_const_of_subsingleton] using f.map_update_smul 0 i c x }
left_inv _ := rfl
right_inv f := by ext x; refine congr_arg f ?_; exact (eq_const_of_subsingleton _ _).symm
variable (M₁) {M₂}
/-- The constant map is multilinear when `ι` is empty. -/
@[simps -fullyApplied]
def constOfIsEmpty [IsEmpty ι] (m : M₂) : MultilinearMap R M₁ M₂ where
toFun := Function.const _ m
map_update_add' _ := isEmptyElim
map_update_smul' _ := isEmptyElim
end
/-- Given a multilinear map `f` on `n` variables (parameterized by `Fin n`) and a subset `s` of `k`
of these variables, one gets a new multilinear map on `Fin k` by varying these variables, and fixing
the other ones equal to a given value `z`. It is denoted by `f.restr s hk z`, where `hk` is a
proof that the cardinality of `s` is `k`. The implicit identification between `Fin k` and `s` that
we use is the canonical (increasing) bijection. -/
def restr {k n : ℕ} (f : MultilinearMap R (fun _ : Fin n => M') M₂) (s : Finset (Fin n))
(hk : #s = k) (z : M') : MultilinearMap R (fun _ : Fin k => M') M₂ where
toFun v := f fun j => if h : j ∈ s then v ((s.orderIsoOfFin hk).symm ⟨j, h⟩) else z
/- Porting note: The proofs of the following two lemmas used to only use `erw` followed by `simp`,
but it seems `erw` no longer unfolds or unifies well enough to work without more help. -/
map_update_add' v i x y := by
erw [dite_comp_equiv_update (s.orderIsoOfFin hk).toEquiv,
dite_comp_equiv_update (s.orderIsoOfFin hk).toEquiv,
dite_comp_equiv_update (s.orderIsoOfFin hk).toEquiv]
simp
map_update_smul' v i c x := by
erw [dite_comp_equiv_update (s.orderIsoOfFin hk).toEquiv,
dite_comp_equiv_update (s.orderIsoOfFin hk).toEquiv]
simp
/-- In the specific case of multilinear maps on spaces indexed by `Fin (n+1)`, where one can build
an element of `∀ (i : Fin (n+1)), M i` using `cons`, one can express directly the additivity of a
multilinear map along the first variable. -/
theorem cons_add (f : MultilinearMap R M M₂) (m : ∀ i : Fin n, M i.succ) (x y : M 0) :
f (cons (x + y) m) = f (cons x m) + f (cons y m) := by
simp_rw [← update_cons_zero x m (x + y), f.map_update_add, update_cons_zero]
/-- In the specific case of multilinear maps on spaces indexed by `Fin (n+1)`, where one can build
an element of `∀ (i : Fin (n+1)), M i` using `cons`, one can express directly the multiplicativity
of a multilinear map along the first variable. -/
theorem cons_smul (f : MultilinearMap R M M₂) (m : ∀ i : Fin n, M i.succ) (c : R) (x : M 0) :
f (cons (c • x) m) = c • f (cons x m) := by
simp_rw [← update_cons_zero x m (c • x), f.map_update_smul, update_cons_zero]
/-- In the specific case of multilinear maps on spaces indexed by `Fin (n+1)`, where one can build
an element of `∀ (i : Fin (n+1)), M i` using `snoc`, one can express directly the additivity of a
multilinear map along the first variable. -/
theorem snoc_add (f : MultilinearMap R M M₂)
(m : ∀ i : Fin n, M (castSucc i)) (x y : M (last n)) :
f (snoc m (x + y)) = f (snoc m x) + f (snoc m y) := by
simp_rw [← update_snoc_last x m (x + y), f.map_update_add, update_snoc_last]
/-- In the specific case of multilinear maps on spaces indexed by `Fin (n+1)`, where one can build
an element of `∀ (i : Fin (n+1)), M i` using `cons`, one can express directly the multiplicativity
of a multilinear map along the first variable. -/
theorem snoc_smul (f : MultilinearMap R M M₂) (m : ∀ i : Fin n, M (castSucc i)) (c : R)
(x : M (last n)) : f (snoc m (c • x)) = c • f (snoc m x) := by
simp_rw [← update_snoc_last x m (c • x), f.map_update_smul, update_snoc_last]
section
variable {M₁' : ι → Type*} [∀ i, AddCommMonoid (M₁' i)] [∀ i, Module R (M₁' i)]
variable {M₁'' : ι → Type*} [∀ i, AddCommMonoid (M₁'' i)] [∀ i, Module R (M₁'' i)]
| /-- If `g` is a multilinear map and `f` is a collection of linear maps,
then `g (f₁ m₁, ..., fₙ mₙ)` is again a multilinear map, that we call
`g.compLinearMap f`. -/
| Mathlib/LinearAlgebra/Multilinear/Basic.lean | 343 | 345 |
/-
Copyright (c) 2020 Johan Commelin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johan Commelin, Julian Kuelshammer, Heather Macbeth, Mitchell Lee
-/
import Mathlib.Algebra.Polynomial.AlgebraMap
import Mathlib.Algebra.Polynomial.Derivative
import Mathlib.Algebra.Ring.NegOnePow
import Mathlib.Tactic.LinearCombination
/-!
# Chebyshev polynomials
The Chebyshev polynomials are families of polynomials indexed by `ℤ`,
with integral coefficients.
## Main definitions
* `Polynomial.Chebyshev.T`: the Chebyshev polynomials of the first kind.
* `Polynomial.Chebyshev.U`: the Chebyshev polynomials of the second kind.
* `Polynomial.Chebyshev.C`: the rescaled Chebyshev polynomials of the first kind (also known as the
Vieta–Lucas polynomials), given by $C_n(2x) = 2T_n(x)$.
* `Polynomial.Chebyshev.S`: the rescaled Chebyshev polynomials of the second kind (also known as the
Vieta–Fibonacci polynomials), given by $S_n(2x) = U_n(x)$.
## Main statements
* The formal derivative of the Chebyshev polynomials of the first kind is a scalar multiple of the
Chebyshev polynomials of the second kind.
* `Polynomial.Chebyshev.T_mul_T`, twice the product of the `m`-th and `k`-th Chebyshev polynomials
of the first kind is the sum of the `m + k`-th and `m - k`-th Chebyshev polynomials of the first
kind. There is a similar statement `Polynomial.Chebyshev.C_mul_C` for the `C` polynomials.
* `Polynomial.Chebyshev.T_mul`, the `(m * n)`-th Chebyshev polynomial of the first kind is the
composition of the `m`-th and `n`-th Chebyshev polynomials of the first kind. There is a similar
statement `Polynomial.Chebyshev.C_mul` for the `C` polynomials.
## Implementation details
Since Chebyshev polynomials have interesting behaviour over the complex numbers and modulo `p`,
we define them to have coefficients in an arbitrary commutative ring, even though
technically `ℤ` would suffice.
The benefit of allowing arbitrary coefficient rings, is that the statements afterwards are clean,
and do not have `map (Int.castRingHom R)` interfering all the time.
## References
[Lionel Ponton, _Roots of the Chebyshev polynomials: A purely algebraic approach_]
[ponton2020chebyshev]
## TODO
* Redefine and/or relate the definition of Chebyshev polynomials to `LinearRecurrence`.
* Add explicit formula involving square roots for Chebyshev polynomials
* Compute zeroes and extrema of Chebyshev polynomials.
* Prove that the roots of the Chebyshev polynomials (except 0) are irrational.
* Prove minimax properties of Chebyshev polynomials.
-/
namespace Polynomial.Chebyshev
open Polynomial
variable (R R' : Type*) [CommRing R] [CommRing R']
/-- `T n` is the `n`-th Chebyshev polynomial of the first kind. -/
-- Well-founded definitions are now irreducible by default;
-- as this was implemented before this change,
-- we just set it back to semireducible to avoid needing to change any proofs.
@[semireducible] noncomputable def T : ℤ → R[X]
| 0 => 1
| 1 => X
| (n : ℕ) + 2 => 2 * X * T (n + 1) - T n
| -((n : ℕ) + 1) => 2 * X * T (-n) - T (-n + 1)
termination_by n => Int.natAbs n + Int.natAbs (n - 1)
/-- Induction principle used for proving facts about Chebyshev polynomials. -/
@[elab_as_elim]
protected theorem induct (motive : ℤ → Prop)
(zero : motive 0)
(one : motive 1)
(add_two : ∀ (n : ℕ), motive (↑n + 1) → motive ↑n → motive (↑n + 2))
(neg_add_one : ∀ (n : ℕ), motive (-↑n) → motive (-↑n + 1) → motive (-↑n - 1)) :
∀ (a : ℤ), motive a :=
T.induct motive zero one add_two fun n hn hnm => by
simpa only [Int.negSucc_eq, neg_add] using neg_add_one n hn hnm
@[simp]
theorem T_add_two : ∀ n, T R (n + 2) = 2 * X * T R (n + 1) - T R n
| (k : ℕ) => T.eq_3 R k
| -(k + 1 : ℕ) => by linear_combination (norm := (simp [Int.negSucc_eq]; ring_nf)) T.eq_4 R k
theorem T_add_one (n : ℤ) : T R (n + 1) = 2 * X * T R n - T R (n - 1) := by
linear_combination (norm := ring_nf) T_add_two R (n - 1)
theorem T_sub_two (n : ℤ) : T R (n - 2) = 2 * X * T R (n - 1) - T R n := by
linear_combination (norm := ring_nf) T_add_two R (n - 2)
theorem T_sub_one (n : ℤ) : T R (n - 1) = 2 * X * T R n - T R (n + 1) := by
linear_combination (norm := ring_nf) T_add_two R (n - 1)
theorem T_eq (n : ℤ) : T R n = 2 * X * T R (n - 1) - T R (n - 2) := by
linear_combination (norm := ring_nf) T_add_two R (n - 2)
@[simp]
theorem T_zero : T R 0 = 1 := rfl
@[simp]
theorem T_one : T R 1 = X := rfl
theorem T_neg_one : T R (-1) = X := show 2 * X * 1 - X = X by ring
theorem T_two : T R 2 = 2 * X ^ 2 - 1 := by
simpa [pow_two, mul_assoc] using T_add_two R 0
@[simp]
theorem T_neg (n : ℤ) : T R (-n) = T R n := by
induction n using Polynomial.Chebyshev.induct with
| | zero => rfl
| one => show 2 * X * 1 - X = X; ring
| add_two n ih1 ih2 =>
have h₁ := T_add_two R n
have h₂ := T_sub_two R (-n)
linear_combination (norm := ring_nf) (2 * (X : R[X])) * ih1 - ih2 - h₁ + h₂
| neg_add_one n ih1 ih2 =>
have h₁ := T_add_one R n
have h₂ := T_sub_one R (-n)
linear_combination (norm := ring_nf) (2 * (X : R[X])) * ih1 - ih2 + h₁ - h₂
theorem T_natAbs (n : ℤ) : T R n.natAbs = T R n := by
| Mathlib/RingTheory/Polynomial/Chebyshev.lean | 118 | 129 |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro, Jeremy Avigad, Simon Hudon
-/
import Mathlib.Algebra.Notation.Defs
import Mathlib.Data.Set.Subsingleton
import Mathlib.Logic.Equiv.Defs
/-!
# Partial values of a type
This file defines `Part α`, the partial values of a type.
`o : Part α` carries a proposition `o.Dom`, its domain, along with a function `get : o.Dom → α`, its
value. The rule is then that every partial value has a value but, to access it, you need to provide
a proof of the domain.
`Part α` behaves the same as `Option α` except that `o : Option α` is decidably `none` or `some a`
for some `a : α`, while the domain of `o : Part α` doesn't have to be decidable. That means you can
translate back and forth between a partial value with a decidable domain and an option, and
`Option α` and `Part α` are classically equivalent. In general, `Part α` is bigger than `Option α`.
In current mathlib, `Part ℕ`, aka `PartENat`, is used to move decidability of the order to
decidability of `PartENat.find` (which is the smallest natural satisfying a predicate, or `∞` if
there's none).
## Main declarations
`Option`-like declarations:
* `Part.none`: The partial value whose domain is `False`.
* `Part.some a`: The partial value whose domain is `True` and whose value is `a`.
* `Part.ofOption`: Converts an `Option α` to a `Part α` by sending `none` to `none` and `some a` to
`some a`.
* `Part.toOption`: Converts a `Part α` with a decidable domain to an `Option α`.
* `Part.equivOption`: Classical equivalence between `Part α` and `Option α`.
Monadic structure:
* `Part.bind`: `o.bind f` has value `(f (o.get _)).get _` (`f o` morally) and is defined when `o`
and `f (o.get _)` are defined.
* `Part.map`: Maps the value and keeps the same domain.
Other:
* `Part.restrict`: `Part.restrict p o` replaces the domain of `o : Part α` by `p : Prop` so long as
`p → o.Dom`.
* `Part.assert`: `assert p f` appends `p` to the domains of the values of a partial function.
* `Part.unwrap`: Gets the value of a partial value regardless of its domain. Unsound.
## Notation
For `a : α`, `o : Part α`, `a ∈ o` means that `o` is defined and equal to `a`. Formally, it means
`o.Dom` and `o.get _ = a`.
-/
assert_not_exists RelIso
open Function
/-- `Part α` is the type of "partial values" of type `α`. It
is similar to `Option α` except the domain condition can be an
arbitrary proposition, not necessarily decidable. -/
structure Part.{u} (α : Type u) : Type u where
/-- The domain of a partial value -/
Dom : Prop
/-- Extract a value from a partial value given a proof of `Dom` -/
get : Dom → α
namespace Part
variable {α : Type*} {β : Type*} {γ : Type*}
/-- Convert a `Part α` with a decidable domain to an option -/
def toOption (o : Part α) [Decidable o.Dom] : Option α :=
if h : Dom o then some (o.get h) else none
@[simp] lemma toOption_isSome (o : Part α) [Decidable o.Dom] : o.toOption.isSome ↔ o.Dom := by
by_cases h : o.Dom <;> simp [h, toOption]
@[simp] lemma toOption_eq_none (o : Part α) [Decidable o.Dom] : o.toOption = none ↔ ¬o.Dom := by
by_cases h : o.Dom <;> simp [h, toOption]
/-- `Part` extensionality -/
theorem ext' : ∀ {o p : Part α}, (o.Dom ↔ p.Dom) → (∀ h₁ h₂, o.get h₁ = p.get h₂) → o = p
| ⟨od, o⟩, ⟨pd, p⟩, H1, H2 => by
have t : od = pd := propext H1
cases t; rw [show o = p from funext fun p => H2 p p]
/-- `Part` eta expansion -/
@[simp]
theorem eta : ∀ o : Part α, (⟨o.Dom, fun h => o.get h⟩ : Part α) = o
| ⟨_, _⟩ => rfl
/-- `a ∈ o` means that `o` is defined and equal to `a` -/
protected def Mem (o : Part α) (a : α) : Prop :=
∃ h, o.get h = a
instance : Membership α (Part α) :=
⟨Part.Mem⟩
theorem mem_eq (a : α) (o : Part α) : (a ∈ o) = ∃ h, o.get h = a :=
rfl
theorem dom_iff_mem : ∀ {o : Part α}, o.Dom ↔ ∃ y, y ∈ o
| ⟨_, f⟩ => ⟨fun h => ⟨f h, h, rfl⟩, fun ⟨_, h, rfl⟩ => h⟩
theorem get_mem {o : Part α} (h) : get o h ∈ o :=
⟨_, rfl⟩
@[simp]
theorem mem_mk_iff {p : Prop} {o : p → α} {a : α} : a ∈ Part.mk p o ↔ ∃ h, o h = a :=
Iff.rfl
/-- `Part` extensionality -/
@[ext]
theorem ext {o p : Part α} (H : ∀ a, a ∈ o ↔ a ∈ p) : o = p :=
(ext' ⟨fun h => ((H _).1 ⟨h, rfl⟩).fst, fun h => ((H _).2 ⟨h, rfl⟩).fst⟩) fun _ _ =>
((H _).2 ⟨_, rfl⟩).snd
/-- The `none` value in `Part` has a `False` domain and an empty function. -/
def none : Part α :=
⟨False, False.rec⟩
instance : Inhabited (Part α) :=
⟨none⟩
@[simp]
theorem not_mem_none (a : α) : a ∉ @none α := fun h => h.fst
/-- The `some a` value in `Part` has a `True` domain and the
function returns `a`. -/
def some (a : α) : Part α :=
⟨True, fun _ => a⟩
@[simp]
theorem some_dom (a : α) : (some a).Dom :=
trivial
theorem mem_unique : ∀ {a b : α} {o : Part α}, a ∈ o → b ∈ o → a = b
| _, _, ⟨_, _⟩, ⟨_, rfl⟩, ⟨_, rfl⟩ => rfl
theorem mem_right_unique : ∀ {a : α} {o p : Part α}, a ∈ o → a ∈ p → o = p
| _, _, _, ⟨ho, _⟩, ⟨hp, _⟩ => ext' (iff_of_true ho hp) (by simp [*])
theorem Mem.left_unique : Relator.LeftUnique ((· ∈ ·) : α → Part α → Prop) := fun _ _ _ =>
mem_unique
theorem Mem.right_unique : Relator.RightUnique ((· ∈ ·) : α → Part α → Prop) := fun _ _ _ =>
mem_right_unique
theorem get_eq_of_mem {o : Part α} {a} (h : a ∈ o) (h') : get o h' = a :=
mem_unique ⟨_, rfl⟩ h
protected theorem subsingleton (o : Part α) : Set.Subsingleton { a | a ∈ o } := fun _ ha _ hb =>
mem_unique ha hb
@[simp]
theorem get_some {a : α} (ha : (some a).Dom) : get (some a) ha = a :=
rfl
theorem mem_some (a : α) : a ∈ some a :=
⟨trivial, rfl⟩
@[simp]
theorem mem_some_iff {a b} : b ∈ (some a : Part α) ↔ b = a :=
⟨fun ⟨_, e⟩ => e.symm, fun e => ⟨trivial, e.symm⟩⟩
theorem eq_some_iff {a : α} {o : Part α} : o = some a ↔ a ∈ o :=
⟨fun e => e.symm ▸ mem_some _, fun ⟨h, e⟩ => e ▸ ext' (iff_true_intro h) fun _ _ => rfl⟩
theorem eq_none_iff {o : Part α} : o = none ↔ ∀ a, a ∉ o :=
⟨fun e => e.symm ▸ not_mem_none, fun h => ext (by simpa)⟩
theorem eq_none_iff' {o : Part α} : o = none ↔ ¬o.Dom :=
⟨fun e => e.symm ▸ id, fun h => eq_none_iff.2 fun _ h' => h h'.fst⟩
@[simp]
theorem not_none_dom : ¬(none : Part α).Dom :=
id
@[simp]
theorem some_ne_none (x : α) : some x ≠ none := by
intro h
exact true_ne_false (congr_arg Dom h)
@[simp]
theorem none_ne_some (x : α) : none ≠ some x :=
(some_ne_none x).symm
theorem ne_none_iff {o : Part α} : o ≠ none ↔ ∃ x, o = some x := by
constructor
· rw [Ne, eq_none_iff', not_not]
exact fun h => ⟨o.get h, eq_some_iff.2 (get_mem h)⟩
· rintro ⟨x, rfl⟩
apply some_ne_none
theorem eq_none_or_eq_some (o : Part α) : o = none ∨ ∃ x, o = some x :=
or_iff_not_imp_left.2 ne_none_iff.1
theorem some_injective : Injective (@Part.some α) := fun _ _ h =>
congr_fun (eq_of_heq (Part.mk.inj h).2) trivial
@[simp]
theorem some_inj {a b : α} : Part.some a = some b ↔ a = b :=
some_injective.eq_iff
@[simp]
theorem some_get {a : Part α} (ha : a.Dom) : Part.some (Part.get a ha) = a :=
Eq.symm (eq_some_iff.2 ⟨ha, rfl⟩)
theorem get_eq_iff_eq_some {a : Part α} {ha : a.Dom} {b : α} : a.get ha = b ↔ a = some b :=
⟨fun h => by simp [h.symm], fun h => by simp [h]⟩
theorem get_eq_get_of_eq (a : Part α) (ha : a.Dom) {b : Part α} (h : a = b) :
a.get ha = b.get (h ▸ ha) := by
congr
theorem get_eq_iff_mem {o : Part α} {a : α} (h : o.Dom) : o.get h = a ↔ a ∈ o :=
⟨fun H => ⟨h, H⟩, fun ⟨_, H⟩ => H⟩
theorem eq_get_iff_mem {o : Part α} {a : α} (h : o.Dom) : a = o.get h ↔ a ∈ o :=
eq_comm.trans (get_eq_iff_mem h)
@[simp]
theorem none_toOption [Decidable (@none α).Dom] : (none : Part α).toOption = Option.none :=
dif_neg id
@[simp]
theorem some_toOption (a : α) [Decidable (some a).Dom] : (some a).toOption = Option.some a :=
dif_pos trivial
instance noneDecidable : Decidable (@none α).Dom :=
instDecidableFalse
instance someDecidable (a : α) : Decidable (some a).Dom :=
instDecidableTrue
/-- Retrieves the value of `a : Part α` if it exists, and return the provided default value
otherwise. -/
def getOrElse (a : Part α) [Decidable a.Dom] (d : α) :=
if ha : a.Dom then a.get ha else d
theorem getOrElse_of_dom (a : Part α) (h : a.Dom) [Decidable a.Dom] (d : α) :
getOrElse a d = a.get h :=
dif_pos h
theorem getOrElse_of_not_dom (a : Part α) (h : ¬a.Dom) [Decidable a.Dom] (d : α) :
getOrElse a d = d :=
dif_neg h
@[simp]
theorem getOrElse_none (d : α) [Decidable (none : Part α).Dom] : getOrElse none d = d :=
none.getOrElse_of_not_dom not_none_dom d
@[simp]
theorem getOrElse_some (a : α) (d : α) [Decidable (some a).Dom] : getOrElse (some a) d = a :=
(some a).getOrElse_of_dom (some_dom a) d
-- `simp`-normal form is `toOption_eq_some_iff`.
theorem mem_toOption {o : Part α} [Decidable o.Dom] {a : α} : a ∈ toOption o ↔ a ∈ o := by
unfold toOption
by_cases h : o.Dom <;> simp [h]
· exact ⟨fun h => ⟨_, h⟩, fun ⟨_, h⟩ => h⟩
· exact mt Exists.fst h
@[simp]
theorem toOption_eq_some_iff {o : Part α} [Decidable o.Dom] {a : α} :
toOption o = Option.some a ↔ a ∈ o := by
rw [← Option.mem_def, mem_toOption]
protected theorem Dom.toOption {o : Part α} [Decidable o.Dom] (h : o.Dom) : o.toOption = o.get h :=
dif_pos h
theorem toOption_eq_none_iff {a : Part α} [Decidable a.Dom] : a.toOption = Option.none ↔ ¬a.Dom :=
Ne.dite_eq_right_iff fun _ => Option.some_ne_none _
@[simp]
theorem elim_toOption {α β : Type*} (a : Part α) [Decidable a.Dom] (b : β) (f : α → β) :
a.toOption.elim b f = if h : a.Dom then f (a.get h) else b := by
split_ifs with h
· rw [h.toOption]
rfl
· rw [Part.toOption_eq_none_iff.2 h]
rfl
/-- Converts an `Option α` into a `Part α`. -/
@[coe]
def ofOption : Option α → Part α
| Option.none => none
| Option.some a => some a
@[simp]
theorem mem_ofOption {a : α} : ∀ {o : Option α}, a ∈ ofOption o ↔ a ∈ o
| Option.none => ⟨fun h => h.fst.elim, fun h => Option.noConfusion h⟩
| Option.some _ => ⟨fun h => congr_arg Option.some h.snd, fun h => ⟨trivial, Option.some.inj h⟩⟩
@[simp]
theorem ofOption_dom {α} : ∀ o : Option α, (ofOption o).Dom ↔ o.isSome
| Option.none => by simp [ofOption, none]
| Option.some a => by simp [ofOption]
theorem ofOption_eq_get {α} (o : Option α) : ofOption o = ⟨_, @Option.get _ o⟩ :=
Part.ext' (ofOption_dom o) fun h₁ h₂ => by
cases o
· simp at h₂
· rfl
instance : Coe (Option α) (Part α) :=
⟨ofOption⟩
theorem mem_coe {a : α} {o : Option α} : a ∈ (o : Part α) ↔ a ∈ o :=
mem_ofOption
@[simp]
theorem coe_none : (@Option.none α : Part α) = none :=
rfl
@[simp]
theorem coe_some (a : α) : (Option.some a : Part α) = some a :=
rfl
@[elab_as_elim]
protected theorem induction_on {P : Part α → Prop} (a : Part α) (hnone : P none)
(hsome : ∀ a : α, P (some a)) : P a :=
(Classical.em a.Dom).elim (fun h => Part.some_get h ▸ hsome _) fun h =>
(eq_none_iff'.2 h).symm ▸ hnone
instance ofOptionDecidable : ∀ o : Option α, Decidable (ofOption o).Dom
| Option.none => Part.noneDecidable
| Option.some a => Part.someDecidable a
@[simp]
theorem to_ofOption (o : Option α) : toOption (ofOption o) = o := by cases o <;> rfl
@[simp]
theorem of_toOption (o : Part α) [Decidable o.Dom] : ofOption (toOption o) = o :=
ext fun _ => mem_ofOption.trans mem_toOption
/-- `Part α` is (classically) equivalent to `Option α`. -/
noncomputable def equivOption : Part α ≃ Option α :=
haveI := Classical.dec
⟨fun o => toOption o, ofOption, fun o => of_toOption o, fun o =>
Eq.trans (by dsimp; congr) (to_ofOption o)⟩
/-- We give `Part α` the order where everything is greater than `none`. -/
instance : PartialOrder (Part
α) where
le x y := ∀ i, i ∈ x → i ∈ y
le_refl _ _ := id
le_trans _ _ _ f g _ := g _ ∘ f _
le_antisymm _ _ f g := Part.ext fun _ => ⟨f _, g _⟩
instance : OrderBot (Part α) where
bot := none
bot_le := by rintro x _ ⟨⟨_⟩, _⟩
theorem le_total_of_le_of_le {x y : Part α} (z : Part α) (hx : x ≤ z) (hy : y ≤ z) :
x ≤ y ∨ y ≤ x := by
rcases Part.eq_none_or_eq_some x with (h | ⟨b, h₀⟩)
· rw [h]
left
apply OrderBot.bot_le _
right; intro b' h₁
rw [Part.eq_some_iff] at h₀
have hx := hx _ h₀; have hy := hy _ h₁
have hx := Part.mem_unique hx hy; subst hx
exact h₀
/-- `assert p f` is a bind-like operation which appends an additional condition
`p` to the domain and uses `f` to produce the value. -/
def assert (p : Prop) (f : p → Part α) : Part α :=
⟨∃ h : p, (f h).Dom, fun ha => (f ha.fst).get ha.snd⟩
/-- The bind operation has value `g (f.get)`, and is defined when all the
parts are defined. -/
protected def bind (f : Part α) (g : α → Part β) : Part β :=
assert (Dom f) fun b => g (f.get b)
/-- The map operation for `Part` just maps the value and maintains the same domain. -/
@[simps]
def map (f : α → β) (o : Part α) : Part β :=
⟨o.Dom, f ∘ o.get⟩
theorem mem_map (f : α → β) {o : Part α} : ∀ {a}, a ∈ o → f a ∈ map f o
| _, ⟨_, rfl⟩ => ⟨_, rfl⟩
@[simp]
theorem mem_map_iff (f : α → β) {o : Part α} {b} : b ∈ map f o ↔ ∃ a ∈ o, f a = b :=
⟨fun hb => match b, hb with
| _, ⟨_, rfl⟩ => ⟨_, ⟨_, rfl⟩, rfl⟩,
fun ⟨_, h₁, h₂⟩ => h₂ ▸ mem_map f h₁⟩
@[simp]
theorem map_none (f : α → β) : map f none = none :=
eq_none_iff.2 fun a => by simp
@[simp]
theorem map_some (f : α → β) (a : α) : map f (some a) = some (f a) :=
eq_some_iff.2 <| mem_map f <| mem_some _
theorem mem_assert {p : Prop} {f : p → Part α} : ∀ {a} (h : p), a ∈ f h → a ∈ assert p f
| _, x, ⟨h, rfl⟩ => ⟨⟨x, h⟩, rfl⟩
@[simp]
theorem mem_assert_iff {p : Prop} {f : p → Part α} {a} : a ∈ assert p f ↔ ∃ h : p, a ∈ f h :=
⟨fun ha => match a, ha with
| _, ⟨_, rfl⟩ => ⟨_, ⟨_, rfl⟩⟩,
fun ⟨_, h⟩ => mem_assert _ h⟩
theorem assert_pos {p : Prop} {f : p → Part α} (h : p) : assert p f = f h := by
dsimp [assert]
cases h' : f h
simp only [h', mk.injEq, h, exists_prop_of_true, true_and]
apply Function.hfunext
· simp only [h, h', exists_prop_of_true]
· simp
theorem assert_neg {p : Prop} {f : p → Part α} (h : ¬p) : assert p f = none := by
dsimp [assert, none]; congr
· simp only [h, not_false_iff, exists_prop_of_false]
· apply Function.hfunext
· simp only [h, not_false_iff, exists_prop_of_false]
simp at *
theorem mem_bind {f : Part α} {g : α → Part β} : ∀ {a b}, a ∈ f → b ∈ g a → b ∈ f.bind g
| _, _, ⟨h, rfl⟩, ⟨h₂, rfl⟩ => ⟨⟨h, h₂⟩, rfl⟩
@[simp]
theorem mem_bind_iff {f : Part α} {g : α → Part β} {b} : b ∈ f.bind g ↔ ∃ a ∈ f, b ∈ g a :=
⟨fun hb => match b, hb with
| _, ⟨⟨_, _⟩, rfl⟩ => ⟨_, ⟨_, rfl⟩, ⟨_, rfl⟩⟩,
fun ⟨_, h₁, h₂⟩ => mem_bind h₁ h₂⟩
protected theorem Dom.bind {o : Part α} (h : o.Dom) (f : α → Part β) : o.bind f = f (o.get h) := by
ext b
simp only [Part.mem_bind_iff, exists_prop]
refine ⟨?_, fun hb => ⟨o.get h, Part.get_mem _, hb⟩⟩
rintro ⟨a, ha, hb⟩
rwa [Part.get_eq_of_mem ha]
theorem Dom.of_bind {f : α → Part β} {a : Part α} (h : (a.bind f).Dom) : a.Dom :=
h.1
@[simp]
theorem bind_none (f : α → Part β) : none.bind f = none :=
eq_none_iff.2 fun a => by simp
@[simp]
theorem bind_some (a : α) (f : α → Part β) : (some a).bind f = f a :=
ext <| by simp
theorem bind_of_mem {o : Part α} {a : α} (h : a ∈ o) (f : α → Part β) : o.bind f = f a := by
rw [eq_some_iff.2 h, bind_some]
theorem bind_some_eq_map (f : α → β) (x : Part α) : x.bind (fun y => some (f y)) = map f x :=
ext <| by simp [eq_comm]
theorem bind_toOption (f : α → Part β) (o : Part α) [Decidable o.Dom] [∀ a, Decidable (f a).Dom]
[Decidable (o.bind f).Dom] :
(o.bind f).toOption = o.toOption.elim Option.none fun a => (f a).toOption := by
by_cases h : o.Dom
· simp_rw [h.toOption, h.bind]
rfl
· rw [Part.toOption_eq_none_iff.2 h]
exact Part.toOption_eq_none_iff.2 fun ho => h ho.of_bind
theorem bind_assoc {γ} (f : Part α) (g : α → Part β) (k : β → Part γ) :
(f.bind g).bind k = f.bind fun x => (g x).bind k :=
ext fun a => by
simp only [mem_bind_iff]
exact ⟨fun ⟨_, ⟨_, h₁, h₂⟩, h₃⟩ => ⟨_, h₁, _, h₂, h₃⟩,
fun ⟨_, h₁, _, h₂, h₃⟩ => ⟨_, ⟨_, h₁, h₂⟩, h₃⟩⟩
@[simp]
theorem bind_map {γ} (f : α → β) (x) (g : β → Part γ) :
(map f x).bind g = x.bind fun y => g (f y) := by rw [← bind_some_eq_map, bind_assoc]; simp
@[simp]
theorem map_bind {γ} (f : α → Part β) (x : Part α) (g : β → γ) :
map g (x.bind f) = x.bind fun y => map g (f y) := by
rw [← bind_some_eq_map, bind_assoc]; simp [bind_some_eq_map]
theorem map_map (g : β → γ) (f : α → β) (o : Part α) : map g (map f o) = map (g ∘ f) o := by
simp [map, Function.comp_assoc]
instance : Monad Part where
pure := @some
map := @map
bind := @Part.bind
instance : LawfulMonad
Part where
bind_pure_comp := @bind_some_eq_map
id_map f := by cases f; rfl
pure_bind := @bind_some
bind_assoc := @bind_assoc
map_const := by simp [Functor.mapConst, Functor.map]
--Porting TODO : In Lean3 these were automatic by a tactic
seqLeft_eq x y := ext'
(by simp [SeqLeft.seqLeft, Part.bind, assert, Seq.seq, const, (· <$> ·), and_comm])
(fun _ _ => rfl)
seqRight_eq x y := ext'
(by simp [SeqRight.seqRight, Part.bind, assert, Seq.seq, const, (· <$> ·), and_comm])
(fun _ _ => rfl)
pure_seq x y := ext'
(by simp [Seq.seq, Part.bind, assert, (· <$> ·), pure])
(fun _ _ => rfl)
bind_map x y := ext'
(by simp [(· >>= ·), Part.bind, assert, Seq.seq, get, (· <$> ·)] )
(fun _ _ => rfl)
theorem map_id' {f : α → α} (H : ∀ x : α, f x = x) (o) : map f o = o := by
rw [show f = id from funext H]; exact id_map o
@[simp]
theorem bind_some_right (x : Part α) : x.bind some = x := by
rw [bind_some_eq_map]
simp [map_id']
@[simp]
theorem pure_eq_some (a : α) : pure a = some a :=
rfl
@[simp]
theorem ret_eq_some (a : α) : (return a : Part α) = some a :=
rfl
@[simp]
theorem map_eq_map {α β} (f : α → β) (o : Part α) : f <$> o = map f o :=
rfl
@[simp]
theorem bind_eq_bind {α β} (f : Part α) (g : α → Part β) : f >>= g = f.bind g :=
rfl
theorem bind_le {α} (x : Part α) (f : α → Part β) (y : Part β) :
x >>= f ≤ y ↔ ∀ a, a ∈ x → f a ≤ y := by
constructor <;> intro h
· intro a h' b
have h := h b
simp only [and_imp, exists_prop, bind_eq_bind, mem_bind_iff, exists_imp] at h
apply h _ h'
· intro b h'
simp only [exists_prop, bind_eq_bind, mem_bind_iff] at h'
rcases h' with ⟨a, h₀, h₁⟩
apply h _ h₀ _ h₁
-- TODO: if `MonadFail` is defined, define the below instance.
-- instance : MonadFail Part :=
-- { Part.monad with fail := fun _ _ => none }
/-- `restrict p o h` replaces the domain of `o` with `p`, and is well defined when
`p` implies `o` is defined. -/
def restrict (p : Prop) (o : Part α) (H : p → o.Dom) : Part α :=
⟨p, fun h => o.get (H h)⟩
@[simp]
theorem mem_restrict (p : Prop) (o : Part α) (h : p → o.Dom) (a : α) :
a ∈ restrict p o h ↔ p ∧ a ∈ o := by
dsimp [restrict, mem_eq]; constructor
· rintro ⟨h₀, h₁⟩
exact ⟨h₀, ⟨_, h₁⟩⟩
rintro ⟨h₀, _, h₂⟩; exact ⟨h₀, h₂⟩
/-- `unwrap o` gets the value at `o`, ignoring the condition. This function is unsound. -/
unsafe def unwrap (o : Part α) : α :=
o.get lcProof
theorem assert_defined {p : Prop} {f : p → Part α} : ∀ h : p, (f h).Dom → (assert p f).Dom :=
Exists.intro
theorem bind_defined {f : Part α} {g : α → Part β} :
∀ h : f.Dom, (g (f.get h)).Dom → (f.bind g).Dom :=
assert_defined
@[simp]
theorem bind_dom {f : Part α} {g : α → Part β} : (f.bind g).Dom ↔ ∃ h : f.Dom, (g (f.get h)).Dom :=
Iff.rfl
section Instances
/-!
We define several instances for constants and operations on `Part α` inherited from `α`.
This section could be moved to a separate file to avoid the import of `Mathlib.Algebra.Group.Defs`.
-/
@[to_additive]
instance [One α] : One (Part α) where one := pure 1
@[to_additive]
instance [Mul α] : Mul (Part α) where mul a b := (· * ·) <$> a <*> b
@[to_additive]
instance [Inv α] : Inv (Part α) where inv := map Inv.inv
@[to_additive]
instance [Div α] : Div (Part α) where div a b := (· / ·) <$> a <*> b
instance [Mod α] : Mod (Part α) where mod a b := (· % ·) <$> a <*> b
instance [Append α] : Append (Part α) where append a b := (· ++ ·) <$> a <*> b
instance [Inter α] : Inter (Part α) where inter a b := (· ∩ ·) <$> a <*> b
instance [Union α] : Union (Part α) where union a b := (· ∪ ·) <$> a <*> b
instance [SDiff α] : SDiff (Part α) where sdiff a b := (· \ ·) <$> a <*> b
section
@[to_additive]
theorem mul_def [Mul α] (a b : Part α) : a * b = bind a fun y ↦ map (y * ·) b := rfl
@[to_additive]
theorem one_def [One α] : (1 : Part α) = some 1 := rfl
@[to_additive]
theorem inv_def [Inv α] (a : Part α) : a⁻¹ = Part.map (· ⁻¹) a := rfl
@[to_additive]
theorem div_def [Div α] (a b : Part α) : a / b = bind a fun y => map (y / ·) b := rfl
theorem mod_def [Mod α] (a b : Part α) : a % b = bind a fun y => map (y % ·) b := rfl
theorem append_def [Append α] (a b : Part α) : a ++ b = bind a fun y => map (y ++ ·) b := rfl
theorem inter_def [Inter α] (a b : Part α) : a ∩ b = bind a fun y => map (y ∩ ·) b := rfl
theorem union_def [Union α] (a b : Part α) : a ∪ b = bind a fun y => map (y ∪ ·) b := rfl
theorem sdiff_def [SDiff α] (a b : Part α) : a \ b = bind a fun y => map (y \ ·) b := rfl
end
@[to_additive]
theorem one_mem_one [One α] : (1 : α) ∈ (1 : Part α) :=
⟨trivial, rfl⟩
@[to_additive]
theorem mul_mem_mul [Mul α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma * mb ∈ a * b := ⟨⟨ha.1, hb.1⟩, by simp only [← ha.2, ← hb.2]; rfl⟩
@[to_additive]
theorem left_dom_of_mul_dom [Mul α] {a b : Part α} (hab : Dom (a * b)) : a.Dom := hab.1
@[to_additive]
theorem right_dom_of_mul_dom [Mul α] {a b : Part α} (hab : Dom (a * b)) : b.Dom := hab.2
@[to_additive (attr := simp)]
theorem mul_get_eq [Mul α] (a b : Part α) (hab : Dom (a * b)) :
(a * b).get hab = a.get (left_dom_of_mul_dom hab) * b.get (right_dom_of_mul_dom hab) := rfl
@[to_additive]
theorem some_mul_some [Mul α] (a b : α) : some a * some b = some (a * b) := by simp [mul_def]
@[to_additive]
theorem inv_mem_inv [Inv α] (a : Part α) (ma : α) (ha : ma ∈ a) : ma⁻¹ ∈ a⁻¹ := by
simp [inv_def]; aesop
@[to_additive]
theorem inv_some [Inv α] (a : α) : (some a)⁻¹ = some a⁻¹ :=
rfl
@[to_additive]
theorem div_mem_div [Div α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma / mb ∈ a / b := by simp [div_def]; aesop
@[to_additive]
theorem left_dom_of_div_dom [Div α] {a b : Part α} (hab : Dom (a / b)) : a.Dom := hab.1
@[to_additive]
theorem right_dom_of_div_dom [Div α] {a b : Part α} (hab : Dom (a / b)) : b.Dom := hab.2
@[to_additive (attr := simp)]
theorem div_get_eq [Div α] (a b : Part α) (hab : Dom (a / b)) :
(a / b).get hab = a.get (left_dom_of_div_dom hab) / b.get (right_dom_of_div_dom hab) := by
simp [div_def]; aesop
@[to_additive]
theorem some_div_some [Div α] (a b : α) : some a / some b = some (a / b) := by simp [div_def]
theorem mod_mem_mod [Mod α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma % mb ∈ a % b := by simp [mod_def]; aesop
theorem left_dom_of_mod_dom [Mod α] {a b : Part α} (hab : Dom (a % b)) : a.Dom := hab.1
theorem right_dom_of_mod_dom [Mod α] {a b : Part α} (hab : Dom (a % b)) : b.Dom := hab.2
@[simp]
theorem mod_get_eq [Mod α] (a b : Part α) (hab : Dom (a % b)) :
(a % b).get hab = a.get (left_dom_of_mod_dom hab) % b.get (right_dom_of_mod_dom hab) := by
simp [mod_def]; aesop
theorem some_mod_some [Mod α] (a b : α) : some a % some b = some (a % b) := by simp [mod_def]
theorem append_mem_append [Append α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma ++ mb ∈ a ++ b := by simp [append_def]; aesop
theorem left_dom_of_append_dom [Append α] {a b : Part α} (hab : Dom (a ++ b)) : a.Dom := hab.1
theorem right_dom_of_append_dom [Append α] {a b : Part α} (hab : Dom (a ++ b)) : b.Dom := hab.2
@[simp]
theorem append_get_eq [Append α] (a b : Part α) (hab : Dom (a ++ b)) : (a ++ b).get hab =
a.get (left_dom_of_append_dom hab) ++ b.get (right_dom_of_append_dom hab) := by
simp [append_def]; aesop
theorem some_append_some [Append α] (a b : α) : some a ++ some b = some (a ++ b) := by
simp [append_def]
theorem inter_mem_inter [Inter α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma ∩ mb ∈ a ∩ b := by simp [inter_def]; aesop
theorem left_dom_of_inter_dom [Inter α] {a b : Part α} (hab : Dom (a ∩ b)) : a.Dom := hab.1
theorem right_dom_of_inter_dom [Inter α] {a b : Part α} (hab : Dom (a ∩ b)) : b.Dom := hab.2
@[simp]
theorem inter_get_eq [Inter α] (a b : Part α) (hab : Dom (a ∩ b)) :
(a ∩ b).get hab = a.get (left_dom_of_inter_dom hab) ∩ b.get (right_dom_of_inter_dom hab) := by
simp [inter_def]; aesop
theorem some_inter_some [Inter α] (a b : α) : some a ∩ some b = some (a ∩ b) := by
simp [inter_def]
theorem union_mem_union [Union α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma ∪ mb ∈ a ∪ b := by simp [union_def]; aesop
theorem left_dom_of_union_dom [Union α] {a b : Part α} (hab : Dom (a ∪ b)) : a.Dom := hab.1
theorem right_dom_of_union_dom [Union α] {a b : Part α} (hab : Dom (a ∪ b)) : b.Dom := hab.2
@[simp]
theorem union_get_eq [Union α] (a b : Part α) (hab : Dom (a ∪ b)) :
(a ∪ b).get hab = a.get (left_dom_of_union_dom hab) ∪ b.get (right_dom_of_union_dom hab) := by
simp [union_def]; aesop
theorem some_union_some [Union α] (a b : α) : some a ∪ some b = some (a ∪ b) := by simp [union_def]
theorem sdiff_mem_sdiff [SDiff α] (a b : Part α) (ma mb : α) (ha : ma ∈ a) (hb : mb ∈ b) :
ma \ mb ∈ a \ b := by simp [sdiff_def]; aesop
theorem left_dom_of_sdiff_dom [SDiff α] {a b : Part α} (hab : Dom (a \ b)) : a.Dom := hab.1
theorem right_dom_of_sdiff_dom [SDiff α] {a b : Part α} (hab : Dom (a \ b)) : b.Dom := hab.2
@[simp]
theorem sdiff_get_eq [SDiff α] (a b : Part α) (hab : Dom (a \ b)) :
(a \ b).get hab = a.get (left_dom_of_sdiff_dom hab) \ b.get (right_dom_of_sdiff_dom hab) := by
simp [sdiff_def]; aesop
theorem some_sdiff_some [SDiff α] (a b : α) : some a \ some b = some (a \ b) := by simp [sdiff_def]
end Instances
end Part
| Mathlib/Data/Part.lean | 801 | 801 | |
/-
Copyright (c) 2021 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Data.Finset.Option
import Mathlib.Data.PFun
import Mathlib.Data.Part
/-!
# Image of a `Finset α` under a partially defined function
In this file we define `Part.toFinset` and `Finset.pimage`. We also prove some trivial lemmas about
these definitions.
## Tags
finite set, image, partial function
-/
variable {α β : Type*}
namespace Part
/-- Convert an `o : Part α` with decidable `Part.Dom o` to `Finset α`. -/
def toFinset (o : Part α) [Decidable o.Dom] : Finset α :=
o.toOption.toFinset
@[simp]
theorem mem_toFinset {o : Part α} [Decidable o.Dom] {x : α} : x ∈ o.toFinset ↔ x ∈ o := by
simp [toFinset]
@[simp]
theorem toFinset_none [Decidable (none : Part α).Dom] : none.toFinset = (∅ : Finset α) := by
simp [toFinset]
@[simp]
theorem toFinset_some {a : α} [Decidable (some a).Dom] : (some a).toFinset = {a} := by
simp [toFinset]
@[simp]
theorem coe_toFinset (o : Part α) [Decidable o.Dom] : (o.toFinset : Set α) = { x | x ∈ o } :=
Set.ext fun _ => mem_toFinset
end Part
namespace Finset
variable [DecidableEq β] {f g : α →. β} [∀ x, Decidable (f x).Dom] [∀ x, Decidable (g x).Dom]
{s t : Finset α} {b : β}
/-- Image of `s : Finset α` under a partially defined function `f : α →. β`. -/
def pimage (f : α →. β) [∀ x, Decidable (f x).Dom] (s : Finset α) : Finset β :=
s.biUnion fun x => (f x).toFinset
@[simp]
theorem mem_pimage : b ∈ s.pimage f ↔ ∃ a ∈ s, b ∈ f a := by
simp [pimage]
@[simp, norm_cast]
theorem coe_pimage : (s.pimage f : Set β) = f.image s :=
Set.ext fun _ => mem_pimage
@[simp]
theorem pimage_some (s : Finset α) (f : α → β) [∀ x, Decidable (Part.some <| f x).Dom] :
(s.pimage fun x => Part.some (f x)) = s.image f := by
ext
simp [eq_comm]
theorem pimage_congr (h₁ : s = t) (h₂ : ∀ x ∈ t, f x = g x) : s.pimage f = t.pimage g := by
aesop
/-- Rewrite `s.pimage f` in terms of `Finset.filter`, `Finset.attach`, and `Finset.image`. -/
theorem pimage_eq_image_filter : s.pimage f =
{x ∈ s | (f x).Dom}.attach.image
fun x : { x // x ∈ filter (fun x => (f x).Dom) s } =>
(f x).get (mem_filter.mp x.coe_prop).2 := by
aesop (add simp Part.mem_eq)
theorem pimage_union [DecidableEq α] : (s ∪ t).pimage f = s.pimage f ∪ t.pimage f :=
coe_inj.1 <| by
simp only [coe_pimage, coe_union, ← PFun.image_union]
@[simp]
theorem pimage_empty : pimage f ∅ = ∅ := by
ext
simp
theorem pimage_subset {t : Finset β} : s.pimage f ⊆ t ↔ ∀ x ∈ s, ∀ y ∈ f x, y ∈ t := by
simp [subset_iff, @forall_swap _ β]
@[mono]
theorem pimage_mono (h : s ⊆ t) : s.pimage f ⊆ t.pimage f :=
pimage_subset.2 fun x hx _ hy => mem_pimage.2 ⟨x, h hx, hy⟩
theorem pimage_inter [DecidableEq α] : (s ∩ t).pimage f ⊆ s.pimage f ∩ t.pimage f := by
simp only [← coe_subset, coe_pimage, coe_inter, PFun.image_inter]
end Finset
| Mathlib/Data/Finset/PImage.lean | 111 | 112 | |
/-
Copyright (c) 2018 Simon Hudon. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Simon Hudon
-/
import Mathlib.Control.Applicative
import Mathlib.Control.Traversable.Basic
import Mathlib.Data.List.Forall2
import Mathlib.Data.Set.Functor
/-!
# LawfulTraversable instances
This file provides instances of `LawfulTraversable` for types from the core library: `Option`,
`List` and `Sum`.
-/
universe u v
section Option
open Functor
variable {F G : Type u → Type u}
variable [Applicative F] [Applicative G]
variable [LawfulApplicative G]
theorem Option.id_traverse {α} (x : Option α) : Option.traverse (pure : α → Id α) x = x := by
cases x <;> rfl
theorem Option.comp_traverse {α β γ} (f : β → F γ) (g : α → G β) (x : Option α) :
Option.traverse (Comp.mk ∘ (f <$> ·) ∘ g) x =
Comp.mk (Option.traverse f <$> Option.traverse g x) := by
cases x <;> (simp! [functor_norm] <;> rfl)
theorem Option.traverse_eq_map_id {α β} (f : α → β) (x : Option α) :
Option.traverse ((pure : _ → Id _) ∘ f) x = (pure : _ → Id _) (f <$> x) := by cases x <;> rfl
variable (η : ApplicativeTransformation F G)
theorem Option.naturality [LawfulApplicative F] {α β} (f : α → F β) (x : Option α) :
η (Option.traverse f x) = Option.traverse (@η _ ∘ f) x := by
-- Porting note: added `ApplicativeTransformation` theorems
rcases x with - | x <;> simp! [*, functor_norm, ApplicativeTransformation.preserves_map,
ApplicativeTransformation.preserves_seq, ApplicativeTransformation.preserves_pure]
end Option
instance : LawfulTraversable Option :=
{ show LawfulMonad Option from inferInstance with
id_traverse := Option.id_traverse
comp_traverse := Option.comp_traverse
traverse_eq_map_id := Option.traverse_eq_map_id
naturality := fun η _ _ f x => Option.naturality η f x }
namespace List
variable {F G : Type u → Type u}
variable [Applicative F] [Applicative G]
section
variable [LawfulApplicative G]
open Applicative Functor List
protected theorem id_traverse {α} (xs : List α) : List.traverse (pure : α → Id α) xs = xs := by
induction xs <;> simp! [*, List.traverse, functor_norm]; rfl
protected theorem comp_traverse {α β γ} (f : β → F γ) (g : α → G β) (x : List α) :
List.traverse (Comp.mk ∘ (f <$> ·) ∘ g) x =
Comp.mk (List.traverse f <$> List.traverse g x) := by
induction x <;> simp! [*, functor_norm] <;> rfl
protected theorem traverse_eq_map_id {α β} (f : α → β) (x : List α) :
List.traverse ((pure : _ → Id _) ∘ f) x = (pure : _ → Id _) (f <$> x) := by
| induction x <;> simp! [*, functor_norm]; rfl
variable [LawfulApplicative F] (η : ApplicativeTransformation F G)
| Mathlib/Control/Traversable/Instances.lean | 78 | 81 |
/-
Copyright (c) 2021 Damiano Testa. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Johannes Hölzl, Kim Morrison, Damiano Testa, Jens Wagemaker
-/
import Mathlib.Algebra.MonoidAlgebra.Division
import Mathlib.Algebra.Polynomial.Degree.Operations
import Mathlib.Algebra.Polynomial.EraseLead
import Mathlib.Order.Interval.Finset.Nat
/-!
# Induction on polynomials
This file contains lemmas dealing with different flavours of induction on polynomials.
-/
noncomputable section
open Polynomial
open Finset
namespace Polynomial
universe u v w z
variable {R : Type u} {S : Type v} {T : Type w} {A : Type z} {a b : R} {n : ℕ}
section Semiring
variable [Semiring R] {p q : R[X]}
/-- `divX p` returns a polynomial `q` such that `q * X + C (p.coeff 0) = p`.
It can be used in a semiring where the usual division algorithm is not possible -/
def divX (p : R[X]) : R[X] :=
⟨AddMonoidAlgebra.divOf p.toFinsupp 1⟩
@[simp]
theorem coeff_divX : (divX p).coeff n = p.coeff (n + 1) := by
rw [add_comm]; cases p; rfl
theorem divX_mul_X_add (p : R[X]) : divX p * X + C (p.coeff 0) = p :=
ext <| by rintro ⟨_ | _⟩ <;> simp [coeff_C, Nat.succ_ne_zero, coeff_mul_X]
@[simp]
theorem X_mul_divX_add (p : R[X]) : X * divX p + C (p.coeff 0) = p :=
ext <| by rintro ⟨_ | _⟩ <;> simp [coeff_C, Nat.succ_ne_zero, coeff_mul_X]
@[simp]
theorem divX_C (a : R) : divX (C a) = 0 :=
ext fun n => by simp [coeff_divX, coeff_C, Finsupp.single_eq_of_ne _]
theorem divX_eq_zero_iff : divX p = 0 ↔ p = C (p.coeff 0) :=
⟨fun h => by simpa [eq_comm, h] using divX_mul_X_add p, fun h => by rw [h, divX_C]⟩
theorem divX_add : divX (p + q) = divX p + divX q :=
ext <| by simp
@[simp]
theorem divX_zero : divX (0 : R[X]) = 0 := leadingCoeff_eq_zero.mp rfl
@[simp]
theorem divX_one : divX (1 : R[X]) = 0 := by
ext
simpa only [coeff_divX, coeff_zero] using coeff_one
@[simp]
theorem divX_C_mul : divX (C a * p) = C a * divX p := by
ext
simp
theorem divX_X_pow : divX (X ^ n : R[X]) = if (n = 0) then 0 else X ^ (n - 1) := by
cases n
· simp
· ext n
simp [coeff_X_pow]
/-- `divX` as an additive homomorphism. -/
noncomputable
def divX_hom : R[X] →+ R[X] :=
{ toFun := divX
map_zero' := divX_zero
map_add' := fun _ _ => divX_add }
@[simp] theorem divX_hom_toFun : divX_hom p = divX p := rfl
theorem natDegree_divX_eq_natDegree_tsub_one : p.divX.natDegree = p.natDegree - 1 := by
apply map_natDegree_eq_sub (φ := divX_hom)
· intro f
simpa [divX_hom, divX_eq_zero_iff] using eq_C_of_natDegree_eq_zero
· intros n c c0
rw [← C_mul_X_pow_eq_monomial, divX_hom_toFun, divX_C_mul, divX_X_pow]
split_ifs with n0
· simp [n0]
· exact natDegree_C_mul_X_pow (n - 1) c c0
theorem natDegree_divX_le : p.divX.natDegree ≤ p.natDegree :=
natDegree_divX_eq_natDegree_tsub_one.trans_le (Nat.pred_le _)
theorem divX_C_mul_X_pow : divX (C a * X ^ n) = if n = 0 then 0 else C a * X ^ (n - 1) := by
simp only [divX_C_mul, divX_X_pow, mul_ite, mul_zero]
theorem degree_divX_lt (hp0 : p ≠ 0) : (divX p).degree < p.degree := by
haveI := Nontrivial.of_polynomial_ne hp0
calc
degree (divX p) < (divX p * X + C (p.coeff 0)).degree :=
if h : degree p ≤ 0 then by
have h' : C (p.coeff 0) ≠ 0 := by rwa [← eq_C_of_degree_le_zero h]
rw [eq_C_of_degree_le_zero h, divX_C, degree_zero, zero_mul, zero_add]
exact lt_of_le_of_ne bot_le (Ne.symm (mt degree_eq_bot.1 <| by simpa using h'))
else by
have hXp0 : divX p ≠ 0 := by
simpa [divX_eq_zero_iff, -not_le, degree_le_zero_iff] using h
have : leadingCoeff (divX p) * leadingCoeff X ≠ 0 := by simpa
have : degree (C (p.coeff 0)) < degree (divX p * X) :=
calc
degree (C (p.coeff 0)) ≤ 0 := degree_C_le
_ < 1 := by decide
_ = degree (X : R[X]) := degree_X.symm
_ ≤ degree (divX p * X) := by
rw [← zero_add (degree X), degree_mul' this]
exact add_le_add
(by rw [zero_le_degree_iff, Ne, divX_eq_zero_iff]
exact fun h0 => h (h0.symm ▸ degree_C_le))
le_rfl
rw [degree_add_eq_left_of_degree_lt this]; exact degree_lt_degree_mul_X hXp0
_ = degree p := congr_arg _ (divX_mul_X_add _)
/-- An induction principle for polynomials, valued in Sort* instead of Prop. -/
@[elab_as_elim]
noncomputable def recOnHorner {M : R[X] → Sort*} (p : R[X]) (M0 : M 0)
(MC : ∀ p a, coeff p 0 = 0 → a ≠ 0 → M p → M (p + C a))
(MX : ∀ p, p ≠ 0 → M p → M (p * X)) : M p :=
letI := Classical.decEq R
if hp : p = 0 then hp ▸ M0
else by
have wf : degree (divX p) < degree p := degree_divX_lt hp
rw [← divX_mul_X_add p] at *
exact
if hcp0 : coeff p 0 = 0 then by
rw [hcp0, C_0, add_zero]
exact
MX _ (fun h : divX p = 0 => by simp [h, hcp0] at hp) (recOnHorner (divX p) M0 MC MX)
else
MC _ _ (coeff_mul_X_zero _) hcp0
(if hpX0 : divX p = 0 then show M (divX p * X) by rw [hpX0, zero_mul]; exact M0
else MX (divX p) hpX0 (recOnHorner _ M0 MC MX))
termination_by p.degree
/-- A property holds for all polynomials of positive `degree` with coefficients in a semiring `R`
if it holds for
* `a * X`, with `a ∈ R`,
* `p * X`, with `p ∈ R[X]`,
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
with appropriate restrictions on each term.
See `natDegree_ne_zero_induction_on` for a similar statement involving no explicit multiplication.
-/
@[elab_as_elim]
theorem degree_pos_induction_on {P : R[X] → Prop} (p : R[X]) (h0 : 0 < degree p)
(hC : ∀ {a}, a ≠ 0 → P (C a * X)) (hX : ∀ {p}, 0 < degree p → P p → P (p * X))
(hadd : ∀ {p} {a}, 0 < degree p → P p → P (p + C a)) : P p :=
recOnHorner p (fun h => by rw [degree_zero] at h; exact absurd h (by decide))
(fun p a heq0 _ ih h0 =>
(have : 0 < degree p :=
(lt_of_not_ge fun h =>
not_lt_of_ge (degree_C_le (a := a)) <|
by rwa [eq_C_of_degree_le_zero h, ← C_add,heq0,zero_add] at h0)
hadd this (ih this)))
(fun p _ ih h0' =>
if h0 : 0 < degree p then hX h0 (ih h0)
else by
rw [eq_C_of_degree_le_zero (le_of_not_gt h0)] at h0' ⊢
exact hC fun h : coeff p 0 = 0 => by simp [h, Nat.not_lt_zero] at h0')
h0
/-- A property holds for all polynomials of non-zero `natDegree` with coefficients in a
| semiring `R` if it holds for
* `p + a`, with `a ∈ R`, `p ∈ R[X]`,
* `p + q`, with `p, q ∈ R[X]`,
* monomials with nonzero coefficient and non-zero exponent,
with appropriate restrictions on each term.
Note that multiplication is "hidden" in the assumption on monomials, so there is no explicit
multiplication in the statement.
See `degree_pos_induction_on` for a similar statement involving more explicit multiplications.
-/
@[elab_as_elim]
theorem natDegree_ne_zero_induction_on {M : R[X] → Prop} {f : R[X]} (f0 : f.natDegree ≠ 0)
(h_C_add : ∀ {a p}, M p → M (C a + p)) (h_add : ∀ {p q}, M p → M q → M (p + q))
(h_monomial : ∀ {n : ℕ} {a : R}, a ≠ 0 → n ≠ 0 → M (monomial n a)) : M f := by
suffices f.natDegree = 0 ∨ M f from Or.recOn this (fun h => (f0 h).elim) id
refine Polynomial.induction_on f ?_ ?_ ?_
| Mathlib/Algebra/Polynomial/Inductions.lean | 179 | 193 |
/-
Copyright (c) 2021 Vladimir Goryachev. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Vladimir Goryachev, Kyle Miller, Kim Morrison, Eric Rodriguez
-/
import Mathlib.Data.List.GetD
import Mathlib.Data.Nat.Count
import Mathlib.Data.Nat.SuccPred
import Mathlib.Order.Interval.Set.Monotone
import Mathlib.Order.OrderIsoNat
import Mathlib.Order.WellFounded
import Mathlib.Order.OmegaCompletePartialOrder
import Mathlib.Data.Finset.Sort
/-!
# The `n`th Number Satisfying a Predicate
This file defines a function for "what is the `n`th number that satisfies a given predicate `p`",
and provides lemmas that deal with this function and its connection to `Nat.count`.
## Main definitions
* `Nat.nth p n`: The `n`-th natural `k` (zero-indexed) such that `p k`. If there is no
such natural (that is, `p` is true for at most `n` naturals), then `Nat.nth p n = 0`.
## Main results
* `Nat.nth_eq_orderEmbOfFin`: For a finitely-often true `p`, gives the cardinality of the set of
numbers satisfying `p` above particular values of `nth p`
* `Nat.gc_count_nth`: Establishes a Galois connection between `Nat.nth p` and `Nat.count p`.
* `Nat.nth_eq_orderIsoOfNat`: For an infinitely-often true predicate, `nth` agrees with the
order-isomorphism of the subtype to the natural numbers.
There has been some discussion on the subject of whether both of `nth` and
`Nat.Subtype.orderIsoOfNat` should exist. See discussion
[here](https://github.com/leanprover-community/mathlib/pull/9457#pullrequestreview-767221180).
Future work should address how lemmas that use these should be written.
-/
open Finset
namespace Nat
variable (p : ℕ → Prop)
/-- Find the `n`-th natural number satisfying `p` (indexed from `0`, so `nth p 0` is the first
natural number satisfying `p`), or `0` if there is no such number. See also
`Subtype.orderIsoOfNat` for the order isomorphism with ℕ when `p` is infinitely often true. -/
noncomputable def nth (p : ℕ → Prop) (n : ℕ) : ℕ := by
classical exact
if h : Set.Finite (setOf p) then (h.toFinset.sort (· ≤ ·)).getD n 0
else @Nat.Subtype.orderIsoOfNat (setOf p) (Set.Infinite.to_subtype h) n
variable {p}
/-!
### Lemmas about `Nat.nth` on a finite set
-/
theorem nth_of_card_le (hf : (setOf p).Finite) {n : ℕ} (hn : #hf.toFinset ≤ n) :
nth p n = 0 := by rw [nth, dif_pos hf, List.getD_eq_default]; rwa [Finset.length_sort]
theorem nth_eq_getD_sort (h : (setOf p).Finite) (n : ℕ) :
nth p n = (h.toFinset.sort (· ≤ ·)).getD n 0 :=
dif_pos h
theorem nth_eq_orderEmbOfFin (hf : (setOf p).Finite) {n : ℕ} (hn : n < #hf.toFinset) :
nth p n = hf.toFinset.orderEmbOfFin rfl ⟨n, hn⟩ := by
rw [nth_eq_getD_sort hf, Finset.orderEmbOfFin_apply, List.getD_eq_getElem, Fin.getElem_fin]
theorem nth_strictMonoOn (hf : (setOf p).Finite) :
StrictMonoOn (nth p) (Set.Iio #hf.toFinset) := by
rintro m (hm : m < _) n (hn : n < _) h
simp only [nth_eq_orderEmbOfFin, *]
exact OrderEmbedding.strictMono _ h
theorem nth_lt_nth_of_lt_card (hf : (setOf p).Finite) {m n : ℕ} (h : m < n)
(hn : n < #hf.toFinset) : nth p m < nth p n :=
nth_strictMonoOn hf (h.trans hn) hn h
theorem nth_le_nth_of_lt_card (hf : (setOf p).Finite) {m n : ℕ} (h : m ≤ n)
(hn : n < #hf.toFinset) : nth p m ≤ nth p n :=
(nth_strictMonoOn hf).monotoneOn (h.trans_lt hn) hn h
theorem lt_of_nth_lt_nth_of_lt_card (hf : (setOf p).Finite) {m n : ℕ} (h : nth p m < nth p n)
(hm : m < #hf.toFinset) : m < n :=
not_le.1 fun hle => h.not_le <| nth_le_nth_of_lt_card hf hle hm
theorem le_of_nth_le_nth_of_lt_card (hf : (setOf p).Finite) {m n : ℕ} (h : nth p m ≤ nth p n)
(hm : m < #hf.toFinset) : m ≤ n :=
not_lt.1 fun hlt => h.not_lt <| nth_lt_nth_of_lt_card hf hlt hm
theorem nth_injOn (hf : (setOf p).Finite) : (Set.Iio #hf.toFinset).InjOn (nth p) :=
(nth_strictMonoOn hf).injOn
theorem range_nth_of_finite (hf : (setOf p).Finite) : Set.range (nth p) = insert 0 (setOf p) := by
simpa only [← List.getD_eq_getElem?_getD, ← nth_eq_getD_sort hf, mem_sort,
Set.Finite.mem_toFinset] using Set.range_list_getD (hf.toFinset.sort (· ≤ ·)) 0
@[simp]
theorem image_nth_Iio_card (hf : (setOf p).Finite) : nth p '' Set.Iio #hf.toFinset = setOf p :=
calc
nth p '' Set.Iio #hf.toFinset = Set.range (hf.toFinset.orderEmbOfFin rfl) := by
ext x
simp only [Set.mem_image, Set.mem_range, Fin.exists_iff, ← nth_eq_orderEmbOfFin hf,
Set.mem_Iio, exists_prop]
_ = setOf p := by rw [range_orderEmbOfFin, Set.Finite.coe_toFinset]
theorem nth_mem_of_lt_card {n : ℕ} (hf : (setOf p).Finite) (hlt : n < #hf.toFinset) :
p (nth p n) :=
(image_nth_Iio_card hf).subset <| Set.mem_image_of_mem _ hlt
theorem exists_lt_card_finite_nth_eq (hf : (setOf p).Finite) {x} (h : p x) :
∃ n, n < #hf.toFinset ∧ nth p n = x := by
rwa [← @Set.mem_setOf_eq _ _ p, ← image_nth_Iio_card hf] at h
/-!
### Lemmas about `Nat.nth` on an infinite set
-/
/-- When `s` is an infinite set, `nth` agrees with `Nat.Subtype.orderIsoOfNat`. -/
theorem nth_apply_eq_orderIsoOfNat (hf : (setOf p).Infinite) (n : ℕ) :
nth p n = @Nat.Subtype.orderIsoOfNat (setOf p) hf.to_subtype n := by rw [nth, dif_neg hf]
/-- When `s` is an infinite set, `nth` agrees with `Nat.Subtype.orderIsoOfNat`. -/
theorem nth_eq_orderIsoOfNat (hf : (setOf p).Infinite) :
nth p = (↑) ∘ @Nat.Subtype.orderIsoOfNat (setOf p) hf.to_subtype :=
funext <| nth_apply_eq_orderIsoOfNat hf
theorem nth_strictMono (hf : (setOf p).Infinite) : StrictMono (nth p) := by
rw [nth_eq_orderIsoOfNat hf]
exact (Subtype.strictMono_coe _).comp (OrderIso.strictMono _)
theorem nth_injective (hf : (setOf p).Infinite) : Function.Injective (nth p) :=
(nth_strictMono hf).injective
theorem nth_monotone (hf : (setOf p).Infinite) : Monotone (nth p) :=
(nth_strictMono hf).monotone
theorem nth_lt_nth (hf : (setOf p).Infinite) {k n} : nth p k < nth p n ↔ k < n :=
(nth_strictMono hf).lt_iff_lt
theorem nth_le_nth (hf : (setOf p).Infinite) {k n} : nth p k ≤ nth p n ↔ k ≤ n :=
(nth_strictMono hf).le_iff_le
theorem range_nth_of_infinite (hf : (setOf p).Infinite) : Set.range (nth p) = setOf p := by
rw [nth_eq_orderIsoOfNat hf]
haveI := hf.to_subtype
classical exact Nat.Subtype.coe_comp_ofNat_range
theorem nth_mem_of_infinite (hf : (setOf p).Infinite) (n : ℕ) : p (nth p n) :=
Set.range_subset_iff.1 (range_nth_of_infinite hf).le n
/-!
### Lemmas that work for finite and infinite sets
-/
theorem exists_lt_card_nth_eq {x} (h : p x) :
∃ n, (∀ hf : (setOf p).Finite, n < #hf.toFinset) ∧ nth p n = x := by
refine (setOf p).finite_or_infinite.elim (fun hf => ?_) fun hf => ?_
· rcases exists_lt_card_finite_nth_eq hf h with ⟨n, hn, hx⟩
exact ⟨n, fun _ => hn, hx⟩
· rw [← @Set.mem_setOf_eq _ _ p, ← range_nth_of_infinite hf] at h
rcases h with ⟨n, hx⟩
exact ⟨n, fun hf' => absurd hf' hf, hx⟩
theorem subset_range_nth : setOf p ⊆ Set.range (nth p) := fun x (hx : p x) =>
let ⟨n, _, hn⟩ := exists_lt_card_nth_eq hx
⟨n, hn⟩
theorem range_nth_subset : Set.range (nth p) ⊆ insert 0 (setOf p) :=
(setOf p).finite_or_infinite.elim (fun h => (range_nth_of_finite h).subset) fun h =>
(range_nth_of_infinite h).trans_subset (Set.subset_insert _ _)
theorem nth_mem (n : ℕ) (h : ∀ hf : (setOf p).Finite, n < #hf.toFinset) : p (nth p n) :=
(setOf p).finite_or_infinite.elim (fun hf => nth_mem_of_lt_card hf (h hf)) fun h =>
nth_mem_of_infinite h n
theorem nth_lt_nth' {m n : ℕ} (hlt : m < n) (h : ∀ hf : (setOf p).Finite, n < #hf.toFinset) :
nth p m < nth p n :=
(setOf p).finite_or_infinite.elim (fun hf => nth_lt_nth_of_lt_card hf hlt (h _)) fun hf =>
(nth_lt_nth hf).2 hlt
theorem nth_le_nth' {m n : ℕ} (hle : m ≤ n) (h : ∀ hf : (setOf p).Finite, n < #hf.toFinset) :
nth p m ≤ nth p n :=
(setOf p).finite_or_infinite.elim (fun hf => nth_le_nth_of_lt_card hf hle (h _)) fun hf =>
(nth_le_nth hf).2 hle
theorem le_nth {n : ℕ} (h : ∀ hf : (setOf p).Finite, n < #hf.toFinset) : n ≤ nth p n :=
(setOf p).finite_or_infinite.elim
(fun hf => ((nth_strictMonoOn hf).mono <| Set.Iic_subset_Iio.2 (h _)).Iic_id_le _ le_rfl)
fun hf => (nth_strictMono hf).id_le _
theorem isLeast_nth {n} (h : ∀ hf : (setOf p).Finite, n < #hf.toFinset) :
IsLeast {i | p i ∧ ∀ k < n, nth p k < i} (nth p n) :=
⟨⟨nth_mem n h, fun _k hk => nth_lt_nth' hk h⟩, fun _x hx =>
let ⟨k, hk, hkx⟩ := exists_lt_card_nth_eq hx.1
(lt_or_le k n).elim (fun hlt => absurd hkx (hx.2 _ hlt).ne) fun hle => hkx ▸ nth_le_nth' hle hk⟩
theorem isLeast_nth_of_lt_card {n : ℕ} (hf : (setOf p).Finite) (hn : n < #hf.toFinset) :
IsLeast {i | p i ∧ ∀ k < n, nth p k < i} (nth p n) :=
isLeast_nth fun _ => hn
theorem isLeast_nth_of_infinite (hf : (setOf p).Infinite) (n : ℕ) :
IsLeast {i | p i ∧ ∀ k < n, nth p k < i} (nth p n) :=
isLeast_nth fun h => absurd h hf
/-- An alternative recursive definition of `Nat.nth`: `Nat.nth s n` is the infimum of `x ∈ s` such
that `Nat.nth s k < x` for all `k < n`, if this set is nonempty. We do not assume that the set is
nonempty because we use the same "garbage value" `0` both for `sInf` on `ℕ` and for `Nat.nth s n`
for `n ≥ #s`. -/
theorem nth_eq_sInf (p : ℕ → Prop) (n : ℕ) : nth p n = sInf {x | p x ∧ ∀ k < n, nth p k < x} := by
by_cases hn : ∀ hf : (setOf p).Finite, n < #hf.toFinset
· exact (isLeast_nth hn).csInf_eq.symm
· push_neg at hn
rcases hn with ⟨hf, hn⟩
rw [nth_of_card_le _ hn]
refine ((congr_arg sInf <| Set.eq_empty_of_forall_not_mem fun k hk => ?_).trans sInf_empty).symm
rcases exists_lt_card_nth_eq hk.1 with ⟨k, hlt, rfl⟩
exact (hk.2 _ ((hlt hf).trans_le hn)).false
theorem nth_zero : nth p 0 = sInf (setOf p) := by rw [nth_eq_sInf]; simp
@[simp]
theorem nth_zero_of_zero (h : p 0) : nth p 0 = 0 := by simp [nth_zero, h]
theorem nth_zero_of_exists [DecidablePred p] (h : ∃ n, p n) : nth p 0 = Nat.find h := by
rw [nth_zero]; convert Nat.sInf_def h
theorem nth_eq_zero {n} :
nth p n = 0 ↔ p 0 ∧ n = 0 ∨ ∃ hf : (setOf p).Finite, #hf.toFinset ≤ n := by
refine ⟨fun h => ?_, ?_⟩
· simp only [or_iff_not_imp_right, not_exists, not_le]
exact fun hn => ⟨h ▸ nth_mem _ hn, nonpos_iff_eq_zero.1 <| h ▸ le_nth hn⟩
· rintro (⟨h₀, rfl⟩ | ⟨hf, hle⟩)
exacts [nth_zero_of_zero h₀, nth_of_card_le hf hle]
lemma lt_card_toFinset_of_nth_ne_zero {n : ℕ} (h : nth p n ≠ 0) (hf : (setOf p).Finite) :
n < #hf.toFinset := by
simp only [ne_eq, nth_eq_zero, not_or, not_exists, not_le] at h
exact h.2 hf
lemma nth_mem_of_ne_zero {n : ℕ} (h : nth p n ≠ 0) : p (Nat.nth p n) :=
nth_mem n (lt_card_toFinset_of_nth_ne_zero h)
theorem nth_eq_zero_mono (h₀ : ¬p 0) {a b : ℕ} (hab : a ≤ b) (ha : nth p a = 0) : nth p b = 0 := by
simp only [nth_eq_zero, h₀, false_and, false_or] at ha ⊢
exact ha.imp fun hf hle => hle.trans hab
lemma nth_ne_zero_anti (h₀ : ¬p 0) {a b : ℕ} (hab : a ≤ b) (hb : nth p b ≠ 0) : nth p a ≠ 0 :=
mt (nth_eq_zero_mono h₀ hab) hb
theorem le_nth_of_lt_nth_succ {k a : ℕ} (h : a < nth p (k + 1)) (ha : p a) : a ≤ nth p k := by
rcases (setOf p).finite_or_infinite with hf | hf
· rcases exists_lt_card_finite_nth_eq hf ha with ⟨n, hn, rfl⟩
rcases lt_or_le (k + 1) #hf.toFinset with hk | hk
· rwa [(nth_strictMonoOn hf).lt_iff_lt hn hk, Nat.lt_succ_iff,
← (nth_strictMonoOn hf).le_iff_le hn (k.lt_succ_self.trans hk)] at h
| · rw [nth_of_card_le _ hk] at h
| Mathlib/Data/Nat/Nth.lean | 262 | 262 |
/-
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.Finset.Image
import Mathlib.Data.Fintype.Defs
import Mathlib.Data.Nat.Notation
import Mathlib.Logic.Function.Basic
/-!
# Inductive type variant of `Fin`
`Fin` is defined as a subtype of `ℕ`. This file defines an equivalent type, `Fin2`, which is
defined inductively. This is useful for its induction principle and different definitional
equalities.
## Main declarations
* `Fin2 n`: Inductive type variant of `Fin n`. `fz` corresponds to `0` and `fs n` corresponds to
`n`.
* `Fin2.toNat`, `Fin2.optOfNat`, `Fin2.ofNat'`: Conversions to and from `ℕ`. `ofNat' m` takes a
proof that `m < n` through the class `Fin2.IsLT`.
* `Fin2.add k`: Takes `i : Fin2 n` to `i + k : Fin2 (n + k)`.
* `Fin2.left`: Embeds `Fin2 n` into `Fin2 (n + k)`.
* `Fin2.insertPerm a`: Permutation of `Fin2 n` which cycles `0, ..., a - 1` and leaves
`a, ..., n - 1` unchanged.
* `Fin2.remapLeft f`: Function `Fin2 (m + k) → Fin2 (n + k)` by applying `f : Fin m → Fin n` to
`0, ..., m - 1` and sending `m + i` to `n + i`.
-/
open Nat
universe u
/-- An alternate definition of `Fin n` defined as an inductive type instead of a subtype of `ℕ`. -/
inductive Fin2 : ℕ → Type
/-- `0` as a member of `Fin (n + 1)` (`Fin 0` is empty) -/
| fz {n} : Fin2 (n + 1)
/-- `n` as a member of `Fin (n + 1)` -/
| fs {n} : Fin2 n → Fin2 (n + 1)
namespace Fin2
/-- Define a dependent function on `Fin2 (succ n)` by giving its value at
zero (`H1`) and by giving a dependent function on the rest (`H2`). -/
@[elab_as_elim]
protected def cases' {n} {C : Fin2 (succ n) → Sort u} (H1 : C fz) (H2 : ∀ n, C (fs n)) :
∀ i : Fin2 (succ n), C i
| fz => H1
| fs n => H2 n
/-- Ex falso. The dependent eliminator for the empty `Fin2 0` type. -/
def elim0 {C : Fin2 0 → Sort u} : ∀ i : Fin2 0, C i := nofun
/-- Converts a `Fin2` into a natural. -/
def toNat : ∀ {n}, Fin2 n → ℕ
| _, @fz _ => 0
| _, @fs _ i => succ (toNat i)
/-- Converts a natural into a `Fin2` if it is in range -/
def optOfNat : ∀ {n}, ℕ → Option (Fin2 n)
| 0, _ => none
| succ _, 0 => some fz
| succ m, succ k => fs <$> @optOfNat m k
/-- `i + k : Fin2 (n + k)` when `i : Fin2 n` and `k : ℕ` -/
def add {n} (i : Fin2 n) : ∀ k, Fin2 (n + k)
| 0 => i
| succ k => fs (add i k)
/-- `left k` is the embedding `Fin2 n → Fin2 (k + n)` -/
def left (k) : ∀ {n}, Fin2 n → Fin2 (k + n)
| _, @fz _ => fz
| _, @fs _ i => fs (left k i)
/-- `insertPerm a` is a permutation of `Fin2 n` with the following properties:
* `insertPerm a i = i+1` if `i < a`
* `insertPerm a a = 0`
* `insertPerm a i = i` if `i > a` -/
def insertPerm : ∀ {n}, Fin2 n → Fin2 n → Fin2 n
| _, @fz _, @fz _ => fz
| _, @fz _, @fs _ j => fs j
| _, @fs (succ _) _, @fz _ => fs fz
| _, @fs (succ _) i, @fs _ j =>
match insertPerm i j with
| fz => fz
| fs k => fs (fs k)
/-- `remapLeft f k : Fin2 (m + k) → Fin2 (n + k)` applies the function
`f : Fin2 m → Fin2 n` to inputs less than `m`, and leaves the right part
on the right (that is, `remapLeft f k (m + i) = n + i`). -/
def remapLeft {m n} (f : Fin2 m → Fin2 n) : ∀ k, Fin2 (m + k) → Fin2 (n + k)
| 0, i => f i
| _k + 1, @fz _ => fz
| _k + 1, @fs _ i => fs (remapLeft f _ i)
/-- This is a simple type class inference prover for proof obligations
of the form `m < n` where `m n : ℕ`. -/
class IsLT (m n : ℕ) : Prop where
/-- The unique field of `Fin2.IsLT`, a proof that `m < n`. -/
h : m < n
instance IsLT.zero (n) : IsLT 0 (succ n) :=
⟨succ_pos _⟩
instance IsLT.succ (m n) [l : IsLT m n] : IsLT (succ m) (succ n) :=
⟨succ_lt_succ l.h⟩
/-- Use type class inference to infer the boundedness proof, so that we can directly convert a
`Nat` into a `Fin2 n`. This supports notation like `&1 : Fin 3`. -/
def ofNat' : ∀ {n} (m) [IsLT m n], Fin2 n
| 0, _, h => absurd h.h (Nat.not_lt_zero _)
| succ _, 0, _ => fz
| succ n, succ m, h => fs (@ofNat' n m ⟨lt_of_succ_lt_succ h.h⟩)
/-- `castSucc i` embeds `i : Fin2 n` in `Fin2 (n+1)`. -/
def castSucc {n} : Fin2 n → Fin2 (n + 1)
| fz => fz
| fs k => fs <| castSucc k
/-- The greatest value of `Fin2 (n+1)`. -/
def last : {n : Nat} → Fin2 (n+1)
| 0 => fz
| n+1 => fs (@last n)
/-- Maps `0` to `n-1`, `1` to `n-2`, ..., `n-1` to `0`. -/
def rev {n : Nat} : Fin2 n → Fin2 n
| .fz => last
| .fs i => i.rev.castSucc
@[simp] lemma rev_last {n} : rev (@last n) = fz := by
induction n <;> simp_all [rev, castSucc, last]
@[simp] lemma rev_castSucc {n} (i : Fin2 n) : rev (castSucc i) = fs (rev i) := by
induction i <;> simp_all [rev, castSucc, last]
@[simp] lemma rev_rev {n} (i : Fin2 n) : i.rev.rev = i := by
induction i <;> simp_all [rev]
theorem rev_involutive {n} : Function.Involutive (@rev n) := rev_rev
@[inherit_doc] local prefix:arg "&" => ofNat'
| instance : Inhabited (Fin2 1) :=
⟨fz⟩
| Mathlib/Data/Fin/Fin2.lean | 145 | 146 |
/-
Copyright (c) 2015, 2017 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Robert Y. Lewis, Johannes Hölzl, Mario Carneiro, Sébastien Gouëzel
-/
import Mathlib.Topology.Bornology.Constructions
import Mathlib.Topology.MetricSpace.Pseudo.Defs
import Mathlib.Topology.UniformSpace.UniformEmbedding
/-!
# Products of pseudometric spaces and other constructions
This file constructs the supremum distance on binary products of pseudometric spaces and provides
instances for type synonyms.
-/
open Bornology Filter Metric Set Topology
open scoped NNReal
variable {α β : Type*} [PseudoMetricSpace α]
/-- Pseudometric space structure pulled back by a function. -/
abbrev PseudoMetricSpace.induced {α β} (f : α → β) (m : PseudoMetricSpace β) :
PseudoMetricSpace α where
dist x y := dist (f x) (f y)
dist_self _ := dist_self _
dist_comm _ _ := dist_comm _ _
dist_triangle _ _ _ := dist_triangle _ _ _
edist x y := edist (f x) (f y)
edist_dist _ _ := edist_dist _ _
toUniformSpace := UniformSpace.comap f m.toUniformSpace
uniformity_dist := (uniformity_basis_dist.comap _).eq_biInf
toBornology := Bornology.induced f
cobounded_sets := Set.ext fun s => mem_comap_iff_compl.trans <| by
simp only [← isBounded_def, isBounded_iff, forall_mem_image, mem_setOf]
/-- Pull back a pseudometric space structure by an inducing map. This is a version of
`PseudoMetricSpace.induced` useful in case if the domain already has a `TopologicalSpace`
structure. -/
def Topology.IsInducing.comapPseudoMetricSpace {α β : Type*} [TopologicalSpace α]
[m : PseudoMetricSpace β] {f : α → β} (hf : IsInducing f) : PseudoMetricSpace α :=
.replaceTopology (.induced f m) hf.eq_induced
@[deprecated (since := "2024-10-28")]
alias Inducing.comapPseudoMetricSpace := IsInducing.comapPseudoMetricSpace
/-- Pull back a pseudometric space structure by a uniform inducing map. This is a version of
`PseudoMetricSpace.induced` useful in case if the domain already has a `UniformSpace`
structure. -/
def IsUniformInducing.comapPseudoMetricSpace {α β} [UniformSpace α] [m : PseudoMetricSpace β]
(f : α → β) (h : IsUniformInducing f) : PseudoMetricSpace α :=
.replaceUniformity (.induced f m) h.comap_uniformity.symm
instance Subtype.pseudoMetricSpace {p : α → Prop} : PseudoMetricSpace (Subtype p) :=
PseudoMetricSpace.induced Subtype.val ‹_›
lemma Subtype.dist_eq {p : α → Prop} (x y : Subtype p) : dist x y = dist (x : α) y := rfl
lemma Subtype.nndist_eq {p : α → Prop} (x y : Subtype p) : nndist x y = nndist (x : α) y := rfl
namespace MulOpposite
@[to_additive]
instance instPseudoMetricSpace : PseudoMetricSpace αᵐᵒᵖ :=
PseudoMetricSpace.induced MulOpposite.unop ‹_›
@[to_additive (attr := simp)]
lemma dist_unop (x y : αᵐᵒᵖ) : dist (unop x) (unop y) = dist x y := rfl
@[to_additive (attr := simp)]
lemma dist_op (x y : α) : dist (op x) (op y) = dist x y := rfl
@[to_additive (attr := simp)]
lemma nndist_unop (x y : αᵐᵒᵖ) : nndist (unop x) (unop y) = nndist x y := rfl
@[to_additive (attr := simp)]
lemma nndist_op (x y : α) : nndist (op x) (op y) = nndist x y := rfl
end MulOpposite
section NNReal
instance : PseudoMetricSpace ℝ≥0 := Subtype.pseudoMetricSpace
lemma NNReal.dist_eq (a b : ℝ≥0) : dist a b = |(a : ℝ) - b| := rfl
lemma NNReal.nndist_eq (a b : ℝ≥0) : nndist a b = max (a - b) (b - a) :=
eq_of_forall_ge_iff fun _ => by
simp only [max_le_iff, tsub_le_iff_right (α := ℝ≥0)]
simp only [← NNReal.coe_le_coe, coe_nndist, dist_eq, abs_sub_le_iff,
tsub_le_iff_right, NNReal.coe_add]
@[simp]
lemma NNReal.nndist_zero_eq_val (z : ℝ≥0) : nndist 0 z = z := by
simp only [NNReal.nndist_eq, max_eq_right, tsub_zero, zero_tsub, zero_le']
@[simp]
lemma NNReal.nndist_zero_eq_val' (z : ℝ≥0) : nndist z 0 = z := by
rw [nndist_comm]
exact NNReal.nndist_zero_eq_val z
lemma NNReal.le_add_nndist (a b : ℝ≥0) : a ≤ b + nndist a b := by
suffices (a : ℝ) ≤ (b : ℝ) + dist a b by
rwa [← NNReal.coe_le_coe, NNReal.coe_add, coe_nndist]
rw [← sub_le_iff_le_add']
exact le_of_abs_le (dist_eq a b).ge
lemma NNReal.ball_zero_eq_Ico' (c : ℝ≥0) :
Metric.ball (0 : ℝ≥0) c.toReal = Set.Ico 0 c := by ext x; simp
lemma NNReal.ball_zero_eq_Ico (c : ℝ) :
Metric.ball (0 : ℝ≥0) c = Set.Ico 0 c.toNNReal := by
by_cases c_pos : 0 < c
· convert NNReal.ball_zero_eq_Ico' ⟨c, c_pos.le⟩
simp [Real.toNNReal, c_pos.le]
simp [not_lt.mp c_pos]
lemma NNReal.closedBall_zero_eq_Icc' (c : ℝ≥0) :
Metric.closedBall (0 : ℝ≥0) c.toReal = Set.Icc 0 c := by ext x; simp
lemma NNReal.closedBall_zero_eq_Icc {c : ℝ} (c_nn : 0 ≤ c) :
Metric.closedBall (0 : ℝ≥0) c = Set.Icc 0 c.toNNReal := by
convert NNReal.closedBall_zero_eq_Icc' ⟨c, c_nn⟩
simp [Real.toNNReal, c_nn]
end NNReal
namespace ULift
variable [PseudoMetricSpace β]
instance : PseudoMetricSpace (ULift β) := PseudoMetricSpace.induced ULift.down ‹_›
lemma dist_eq (x y : ULift β) : dist x y = dist x.down y.down := rfl
lemma nndist_eq (x y : ULift β) : nndist x y = nndist x.down y.down := rfl
@[simp] lemma dist_up_up (x y : β) : dist (ULift.up x) (ULift.up y) = dist x y := rfl
@[simp] lemma nndist_up_up (x y : β) : nndist (ULift.up x) (ULift.up y) = nndist x y := rfl
end ULift
section Prod
variable [PseudoMetricSpace β]
instance Prod.pseudoMetricSpaceMax : PseudoMetricSpace (α × β) :=
let i := PseudoEMetricSpace.toPseudoMetricSpaceOfDist
(fun x y : α × β => dist x.1 y.1 ⊔ dist x.2 y.2)
(fun _ _ => (max_lt (edist_lt_top _ _) (edist_lt_top _ _)).ne) fun x y => by
simp only [dist_edist, ← ENNReal.toReal_max (edist_ne_top _ _) (edist_ne_top _ _),
Prod.edist_eq]
i.replaceBornology fun s => by
simp only [← isBounded_image_fst_and_snd, isBounded_iff_eventually, forall_mem_image, ←
eventually_and, ← forall_and, ← max_le_iff]
rfl
lemma Prod.dist_eq {x y : α × β} : dist x y = max (dist x.1 y.1) (dist x.2 y.2) := rfl
@[simp]
lemma dist_prod_same_left {x : α} {y₁ y₂ : β} : dist (x, y₁) (x, y₂) = dist y₁ y₂ := by
simp [Prod.dist_eq, dist_nonneg]
@[simp]
lemma dist_prod_same_right {x₁ x₂ : α} {y : β} : dist (x₁, y) (x₂, y) = dist x₁ x₂ := by
simp [Prod.dist_eq, dist_nonneg]
lemma ball_prod_same (x : α) (y : β) (r : ℝ) : ball x r ×ˢ ball y r = ball (x, y) r :=
ext fun z => by simp [Prod.dist_eq]
lemma closedBall_prod_same (x : α) (y : β) (r : ℝ) :
closedBall x r ×ˢ closedBall y r = closedBall (x, y) r := ext fun z => by simp [Prod.dist_eq]
lemma sphere_prod (x : α × β) (r : ℝ) :
sphere x r = sphere x.1 r ×ˢ closedBall x.2 r ∪ closedBall x.1 r ×ˢ sphere x.2 r := by
obtain hr | rfl | hr := lt_trichotomy r 0
· simp [hr]
· cases x
simp_rw [← closedBall_eq_sphere_of_nonpos le_rfl, union_self, closedBall_prod_same]
· ext ⟨x', y'⟩
simp_rw [Set.mem_union, Set.mem_prod, Metric.mem_closedBall, Metric.mem_sphere, Prod.dist_eq,
max_eq_iff]
refine or_congr (and_congr_right ?_) (and_comm.trans (and_congr_left ?_))
all_goals rintro rfl; rfl
end Prod
lemma uniformContinuous_dist : UniformContinuous fun p : α × α => dist p.1 p.2 :=
Metric.uniformContinuous_iff.2 fun ε ε0 =>
⟨ε / 2, half_pos ε0, fun {a b} h =>
calc dist (dist a.1 a.2) (dist b.1 b.2) ≤ dist a.1 b.1 + dist a.2 b.2 :=
dist_dist_dist_le _ _ _ _
_ ≤ dist a b + dist a b := add_le_add (le_max_left _ _) (le_max_right _ _)
_ < ε / 2 + ε / 2 := add_lt_add h h
_ = ε := add_halves ε⟩
protected lemma UniformContinuous.dist [UniformSpace β] {f g : β → α} (hf : UniformContinuous f)
(hg : UniformContinuous g) : UniformContinuous fun b => dist (f b) (g b) :=
uniformContinuous_dist.comp (hf.prodMk hg)
@[continuity]
lemma continuous_dist : Continuous fun p : α × α ↦ dist p.1 p.2 := uniformContinuous_dist.continuous
@[continuity, fun_prop]
protected lemma Continuous.dist [TopologicalSpace β] {f g : β → α} (hf : Continuous f)
(hg : Continuous g) : Continuous fun b => dist (f b) (g b) :=
continuous_dist.comp₂ hf hg
protected lemma Filter.Tendsto.dist {f g : β → α} {x : Filter β} {a b : α}
(hf : Tendsto f x (𝓝 a)) (hg : Tendsto g x (𝓝 b)) :
Tendsto (fun x => dist (f x) (g x)) x (𝓝 (dist a b)) :=
(continuous_dist.tendsto (a, b)).comp (hf.prodMk_nhds hg)
lemma continuous_iff_continuous_dist [TopologicalSpace β] {f : β → α} :
Continuous f ↔ Continuous fun x : β × β => dist (f x.1) (f x.2) :=
⟨fun h => h.fst'.dist h.snd', fun h =>
continuous_iff_continuousAt.2 fun _ => tendsto_iff_dist_tendsto_zero.2 <|
(h.comp (.prodMk_left _)).tendsto' _ _ <| dist_self _⟩
lemma uniformContinuous_nndist : UniformContinuous fun p : α × α => nndist p.1 p.2 :=
uniformContinuous_dist.subtype_mk _
protected lemma UniformContinuous.nndist [UniformSpace β] {f g : β → α} (hf : UniformContinuous f)
(hg : UniformContinuous g) : UniformContinuous fun b => nndist (f b) (g b) :=
uniformContinuous_nndist.comp (hf.prodMk hg)
lemma continuous_nndist : Continuous fun p : α × α => nndist p.1 p.2 :=
uniformContinuous_nndist.continuous
@[fun_prop]
protected lemma Continuous.nndist [TopologicalSpace β] {f g : β → α} (hf : Continuous f)
(hg : Continuous g) : Continuous fun b => nndist (f b) (g b) :=
continuous_nndist.comp₂ hf hg
protected lemma Filter.Tendsto.nndist {f g : β → α} {x : Filter β} {a b : α}
(hf : Tendsto f x (𝓝 a)) (hg : Tendsto g x (𝓝 b)) :
Tendsto (fun x => nndist (f x) (g x)) x (𝓝 (nndist a b)) :=
(continuous_nndist.tendsto (a, b)).comp (hf.prodMk_nhds hg)
| Mathlib/Topology/MetricSpace/Pseudo/Constructions.lean | 411 | 426 | |
/-
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.Topology.UniformSpace.CompleteSeparated
import Mathlib.Topology.EMetricSpace.Lipschitz
import Mathlib.Topology.MetricSpace.Basic
import Mathlib.Topology.MetricSpace.Bounded
/-!
# Antilipschitz functions
We say that a map `f : α → β` between two (extended) metric spaces is
`AntilipschitzWith K`, `K ≥ 0`, if for all `x, y` we have `edist x y ≤ K * edist (f x) (f y)`.
For a metric space, the latter inequality is equivalent to `dist x y ≤ K * dist (f x) (f y)`.
## Implementation notes
The parameter `K` has type `ℝ≥0`. This way we avoid conjunction in the definition and have
coercions both to `ℝ` and `ℝ≥0∞`. We do not require `0 < K` in the definition, mostly because
we do not have a `posreal` type.
-/
open Bornology Filter Set Topology
open scoped NNReal ENNReal Uniformity
variable {α β γ : Type*}
/-- We say that `f : α → β` is `AntilipschitzWith K` if for any two points `x`, `y` we have
`edist x y ≤ K * edist (f x) (f y)`. -/
def AntilipschitzWith [PseudoEMetricSpace α] [PseudoEMetricSpace β] (K : ℝ≥0) (f : α → β) :=
∀ x y, edist x y ≤ K * edist (f x) (f y)
protected lemma AntilipschitzWith.edist_lt_top [PseudoEMetricSpace α] [PseudoMetricSpace β]
{K : ℝ≥0} {f : α → β} (h : AntilipschitzWith K f) (x y : α) : edist x y < ⊤ :=
(h x y).trans_lt <| ENNReal.mul_lt_top ENNReal.coe_lt_top (edist_lt_top _ _)
theorem AntilipschitzWith.edist_ne_top [PseudoEMetricSpace α] [PseudoMetricSpace β] {K : ℝ≥0}
{f : α → β} (h : AntilipschitzWith K f) (x y : α) : edist x y ≠ ⊤ :=
(h.edist_lt_top x y).ne
section Metric
variable [PseudoMetricSpace α] [PseudoMetricSpace β] {K : ℝ≥0} {f : α → β}
theorem antilipschitzWith_iff_le_mul_nndist :
AntilipschitzWith K f ↔ ∀ x y, nndist x y ≤ K * nndist (f x) (f y) := by
simp only [AntilipschitzWith, edist_nndist]
norm_cast
alias ⟨AntilipschitzWith.le_mul_nndist, AntilipschitzWith.of_le_mul_nndist⟩ :=
antilipschitzWith_iff_le_mul_nndist
theorem antilipschitzWith_iff_le_mul_dist :
AntilipschitzWith K f ↔ ∀ x y, dist x y ≤ K * dist (f x) (f y) := by
simp only [antilipschitzWith_iff_le_mul_nndist, dist_nndist]
norm_cast
alias ⟨AntilipschitzWith.le_mul_dist, AntilipschitzWith.of_le_mul_dist⟩ :=
antilipschitzWith_iff_le_mul_dist
namespace AntilipschitzWith
theorem mul_le_nndist (hf : AntilipschitzWith K f) (x y : α) :
K⁻¹ * nndist x y ≤ nndist (f x) (f y) := by
simpa only [div_eq_inv_mul] using NNReal.div_le_of_le_mul' (hf.le_mul_nndist x y)
theorem mul_le_dist (hf : AntilipschitzWith K f) (x y : α) :
(K⁻¹ * dist x y : ℝ) ≤ dist (f x) (f y) := mod_cast hf.mul_le_nndist x y
end AntilipschitzWith
end Metric
namespace AntilipschitzWith
variable [PseudoEMetricSpace α] [PseudoEMetricSpace β] [PseudoEMetricSpace γ]
variable {K : ℝ≥0} {f : α → β}
open EMetric
-- uses neither `f` nor `hf`
/-- Extract the constant from `hf : AntilipschitzWith K f`. This is useful, e.g.,
if `K` is given by a long formula, and we want to reuse this value. -/
@[nolint unusedArguments]
protected def k (_hf : AntilipschitzWith K f) : ℝ≥0 := K
protected theorem injective {α : Type*} {β : Type*} [EMetricSpace α] [PseudoEMetricSpace β]
{K : ℝ≥0} {f : α → β} (hf : AntilipschitzWith K f) : Function.Injective f := fun x y h => by
simpa only [h, edist_self, mul_zero, edist_le_zero] using hf x y
theorem mul_le_edist (hf : AntilipschitzWith K f) (x y : α) :
(K : ℝ≥0∞)⁻¹ * edist x y ≤ edist (f x) (f y) := by
rw [mul_comm, ← div_eq_mul_inv]
exact ENNReal.div_le_of_le_mul' (hf x y)
theorem ediam_preimage_le (hf : AntilipschitzWith K f) (s : Set β) : diam (f ⁻¹' s) ≤ K * diam s :=
diam_le fun x hx y hy => (hf x y).trans <|
mul_le_mul_left' (edist_le_diam_of_mem (mem_preimage.1 hx) hy) K
theorem le_mul_ediam_image (hf : AntilipschitzWith K f) (s : Set α) : diam s ≤ K * diam (f '' s) :=
(diam_mono (subset_preimage_image _ _)).trans (hf.ediam_preimage_le (f '' s))
protected theorem id : AntilipschitzWith 1 (id : α → α) := fun x y => by
simp only [ENNReal.coe_one, one_mul, id, le_refl]
theorem comp {Kg : ℝ≥0} {g : β → γ} (hg : AntilipschitzWith Kg g) {Kf : ℝ≥0} {f : α → β}
(hf : AntilipschitzWith Kf f) : AntilipschitzWith (Kf * Kg) (g ∘ f) := fun x y =>
calc
edist x y ≤ Kf * edist (f x) (f y) := hf x y
_ ≤ Kf * (Kg * edist (g (f x)) (g (f y))) := mul_left_mono (hg _ _)
_ = _ := by rw [ENNReal.coe_mul, mul_assoc]; rfl
theorem restrict (hf : AntilipschitzWith K f) (s : Set α) : AntilipschitzWith K (s.restrict f) :=
fun x y => hf x y
theorem codRestrict (hf : AntilipschitzWith K f) {s : Set β} (hs : ∀ x, f x ∈ s) :
AntilipschitzWith K (s.codRestrict f hs) := fun x y => hf x y
theorem to_rightInvOn' {s : Set α} (hf : AntilipschitzWith K (s.restrict f)) {g : β → α}
{t : Set β} (g_maps : MapsTo g t s) (g_inv : RightInvOn g f t) :
LipschitzWith K (t.restrict g) := fun x y => by
simpa only [restrict_apply, g_inv x.mem, g_inv y.mem, Subtype.edist_mk_mk]
using hf ⟨g x, g_maps x.mem⟩ ⟨g y, g_maps y.mem⟩
theorem to_rightInvOn (hf : AntilipschitzWith K f) {g : β → α} {t : Set β} (h : RightInvOn g f t) :
LipschitzWith K (t.restrict g) :=
(hf.restrict univ).to_rightInvOn' (mapsTo_univ g t) h
theorem to_rightInverse (hf : AntilipschitzWith K f) {g : β → α} (hg : Function.RightInverse g f) :
LipschitzWith K g := by
intro x y
have := hf (g x) (g y)
rwa [hg x, hg y] at this
theorem comap_uniformity_le (hf : AntilipschitzWith K f) : (𝓤 β).comap (Prod.map f f) ≤ 𝓤 α := by
refine ((uniformity_basis_edist.comap _).le_basis_iff uniformity_basis_edist).2 fun ε h₀ => ?_
refine ⟨(↑K)⁻¹ * ε, ENNReal.mul_pos (ENNReal.inv_ne_zero.2 ENNReal.coe_ne_top) h₀.ne', ?_⟩
refine fun x hx => (hf x.1 x.2).trans_lt ?_
rw [mul_comm, ← div_eq_mul_inv] at hx
rw [mul_comm]
exact ENNReal.mul_lt_of_lt_div hx
theorem isUniformInducing (hf : AntilipschitzWith K f) (hfc : UniformContinuous f) :
IsUniformInducing f :=
⟨le_antisymm hf.comap_uniformity_le hfc.le_comap⟩
lemma isUniformEmbedding {α β : Type*} [EMetricSpace α] [PseudoEMetricSpace β] {K : ℝ≥0} {f : α → β}
(hf : AntilipschitzWith K f) (hfc : UniformContinuous f) : IsUniformEmbedding f :=
⟨hf.isUniformInducing hfc, hf.injective⟩
theorem isComplete_range [CompleteSpace α] (hf : AntilipschitzWith K f)
(hfc : UniformContinuous f) : IsComplete (range f) :=
(hf.isUniformInducing hfc).isComplete_range
theorem isClosed_range {α β : Type*} [PseudoEMetricSpace α] [EMetricSpace β] [CompleteSpace α]
{f : α → β} {K : ℝ≥0} (hf : AntilipschitzWith K f) (hfc : UniformContinuous f) :
IsClosed (range f) :=
(hf.isComplete_range hfc).isClosed
theorem isClosedEmbedding {α : Type*} {β : Type*} [EMetricSpace α] [EMetricSpace β] {K : ℝ≥0}
{f : α → β} [CompleteSpace α] (hf : AntilipschitzWith K f) (hfc : UniformContinuous f) :
IsClosedEmbedding f :=
{ (hf.isUniformEmbedding hfc).isEmbedding with isClosed_range := hf.isClosed_range hfc }
theorem subtype_coe (s : Set α) : AntilipschitzWith 1 ((↑) : s → α) :=
AntilipschitzWith.id.restrict s
@[nontriviality]
theorem of_subsingleton [Subsingleton α] {K : ℝ≥0} : AntilipschitzWith K f := fun x y => by
simp only [Subsingleton.elim x y, edist_self, zero_le]
/-- If `f : α → β` is `0`-antilipschitz, then `α` is a `subsingleton`. -/
protected theorem subsingleton {α β} [EMetricSpace α] [PseudoEMetricSpace β] {f : α → β}
(h : AntilipschitzWith 0 f) : Subsingleton α :=
⟨fun x y => edist_le_zero.1 <| (h x y).trans_eq <| zero_mul _⟩
end AntilipschitzWith
namespace AntilipschitzWith
open Metric
variable [PseudoMetricSpace α] [PseudoMetricSpace β] [PseudoMetricSpace γ]
variable {K : ℝ≥0} {f : α → β}
theorem isBounded_preimage (hf : AntilipschitzWith K f) {s : Set β} (hs : IsBounded s) :
IsBounded (f ⁻¹' s) :=
isBounded_iff_ediam_ne_top.2 <| ne_top_of_le_ne_top
(ENNReal.mul_ne_top ENNReal.coe_ne_top hs.ediam_ne_top) (hf.ediam_preimage_le _)
theorem tendsto_cobounded (hf : AntilipschitzWith K f) : Tendsto f (cobounded α) (cobounded β) :=
compl_surjective.forall.2 fun _ ↦ hf.isBounded_preimage
/-- The image of a proper space under an expanding onto map is proper. -/
protected theorem properSpace {α : Type*} [MetricSpace α] {K : ℝ≥0} {f : α → β} [ProperSpace α]
(hK : AntilipschitzWith K f) (f_cont : Continuous f) (hf : Function.Surjective f) :
ProperSpace β := by
refine ⟨fun x₀ r => ?_⟩
let K := f ⁻¹' closedBall x₀ r
have A : IsClosed K := isClosed_closedBall.preimage f_cont
have B : IsBounded K := hK.isBounded_preimage isBounded_closedBall
have : IsCompact K := isCompact_iff_isClosed_bounded.2 ⟨A, B⟩
convert this.image f_cont
exact (hf.image_preimage _).symm
theorem isBounded_of_image2_left (f : α → β → γ) {K₁ : ℝ≥0}
(hf : ∀ b, AntilipschitzWith K₁ fun a => f a b) {s : Set α} {t : Set β}
(hst : IsBounded (Set.image2 f s t)) : IsBounded s ∨ IsBounded t := by
contrapose! hst
obtain ⟨b, hb⟩ : t.Nonempty := nonempty_of_not_isBounded hst.2
have : ¬IsBounded (Set.image2 f s {b}) := by
intro h
apply hst.1
rw [Set.image2_singleton_right] at h
replace h := (hf b).isBounded_preimage h
exact h.subset (subset_preimage_image _ _)
exact mt (IsBounded.subset · (image2_subset subset_rfl (singleton_subset_iff.mpr hb))) this
theorem isBounded_of_image2_right {f : α → β → γ} {K₂ : ℝ≥0} (hf : ∀ a, AntilipschitzWith K₂ (f a))
{s : Set α} {t : Set β} (hst : IsBounded (Set.image2 f s t)) : IsBounded s ∨ IsBounded t :=
Or.symm <| isBounded_of_image2_left (flip f) hf <| image2_swap f s t ▸ hst
end AntilipschitzWith
theorem LipschitzWith.to_rightInverse [PseudoEMetricSpace α] [PseudoEMetricSpace β] {K : ℝ≥0}
{f : α → β} (hf : LipschitzWith K f) {g : β → α} (hg : Function.RightInverse g f) :
AntilipschitzWith K g := fun x y => by simpa only [hg _] using hf (g x) (g y)
| Mathlib/Topology/MetricSpace/Antilipschitz.lean | 269 | 271 | |
/-
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.Algebra.Module.Equiv.Defs
import Mathlib.Data.DFinsupp.Module
import Mathlib.Data.Finsupp.SMul
/-!
# Conversion between `Finsupp` and homogeneous `DFinsupp`
This module provides conversions between `Finsupp` and `DFinsupp`.
It is in its own file since neither `Finsupp` or `DFinsupp` depend on each other.
## Main definitions
* "identity" maps between `Finsupp` and `DFinsupp`:
* `Finsupp.toDFinsupp : (ι →₀ M) → (Π₀ i : ι, M)`
* `DFinsupp.toFinsupp : (Π₀ i : ι, M) → (ι →₀ M)`
* Bundled equiv versions of the above:
* `finsuppEquivDFinsupp : (ι →₀ M) ≃ (Π₀ i : ι, M)`
* `finsuppAddEquivDFinsupp : (ι →₀ M) ≃+ (Π₀ i : ι, M)`
* `finsuppLequivDFinsupp R : (ι →₀ M) ≃ₗ[R] (Π₀ i : ι, M)`
* stronger versions of `Finsupp.split`:
* `sigmaFinsuppEquivDFinsupp : ((Σ i, η i) →₀ N) ≃ (Π₀ i, (η i →₀ N))`
* `sigmaFinsuppAddEquivDFinsupp : ((Σ i, η i) →₀ N) ≃+ (Π₀ i, (η i →₀ N))`
* `sigmaFinsuppLequivDFinsupp : ((Σ i, η i) →₀ N) ≃ₗ[R] (Π₀ i, (η i →₀ N))`
## Theorems
The defining features of these operations is that they preserve the function and support:
* `Finsupp.toDFinsupp_coe`
* `Finsupp.toDFinsupp_support`
* `DFinsupp.toFinsupp_coe`
* `DFinsupp.toFinsupp_support`
and therefore map `Finsupp.single` to `DFinsupp.single` and vice versa:
* `Finsupp.toDFinsupp_single`
* `DFinsupp.toFinsupp_single`
as well as preserving arithmetic operations.
For the bundled equivalences, we provide lemmas that they reduce to `Finsupp.toDFinsupp`:
* `finsupp_add_equiv_dfinsupp_apply`
* `finsupp_lequiv_dfinsupp_apply`
* `finsupp_add_equiv_dfinsupp_symm_apply`
* `finsupp_lequiv_dfinsupp_symm_apply`
## Implementation notes
We provide `DFinsupp.toFinsupp` and `finsuppEquivDFinsupp` computably by adding
`[DecidableEq ι]` and `[Π m : M, Decidable (m ≠ 0)]` arguments. To aid with definitional unfolding,
these arguments are also present on the `noncomputable` equivs.
-/
variable {ι : Type*} {R : Type*} {M : Type*}
/-! ### Basic definitions and lemmas -/
section Defs
/-- Interpret a `Finsupp` as a homogeneous `DFinsupp`. -/
def Finsupp.toDFinsupp [Zero M] (f : ι →₀ M) : Π₀ _ : ι, M where
toFun := f
support' :=
Trunc.mk
⟨f.support.1, fun i => (Classical.em (f i = 0)).symm.imp_left Finsupp.mem_support_iff.mpr⟩
@[simp]
theorem Finsupp.toDFinsupp_coe [Zero M] (f : ι →₀ M) : ⇑f.toDFinsupp = f :=
rfl
section
variable [DecidableEq ι] [Zero M]
@[simp]
theorem Finsupp.toDFinsupp_single (i : ι) (m : M) :
(Finsupp.single i m).toDFinsupp = DFinsupp.single i m := by
ext
simp [Finsupp.single_apply, DFinsupp.single_apply]
|
variable [∀ m : M, Decidable (m ≠ 0)]
@[simp]
| Mathlib/Data/Finsupp/ToDFinsupp.lean | 88 | 91 |
/-
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
-/
import Mathlib.MeasureTheory.Measure.Comap
import Mathlib.MeasureTheory.Measure.QuasiMeasurePreserving
/-!
# Restricting a measure to a subset or a subtype
Given a measure `μ` on a type `α` and a subset `s` of `α`, we define a measure `μ.restrict s` as
the restriction of `μ` to `s` (still as a measure on `α`).
We investigate how this notion interacts with usual operations on measures (sum, pushforward,
pullback), and on sets (inclusion, union, Union).
We also study the relationship between the restriction of a measure to a subtype (given by the
pullback under `Subtype.val`) and the restriction to a set as above.
-/
open scoped ENNReal NNReal Topology
open Set MeasureTheory Measure Filter MeasurableSpace ENNReal Function
variable {R α β δ γ ι : Type*}
namespace MeasureTheory
variable {m0 : MeasurableSpace α} [MeasurableSpace β] [MeasurableSpace γ]
variable {μ μ₁ μ₂ μ₃ ν ν' ν₁ ν₂ : Measure α} {s s' t : Set α}
namespace Measure
/-! ### Restricting a measure -/
/-- Restrict a measure `μ` to a set `s` as an `ℝ≥0∞`-linear map. -/
noncomputable def restrictₗ {m0 : MeasurableSpace α} (s : Set α) : Measure α →ₗ[ℝ≥0∞] Measure α :=
liftLinear (OuterMeasure.restrict s) fun μ s' hs' t => by
suffices μ (s ∩ t) = μ (s ∩ t ∩ s') + μ ((s ∩ t) \ s') by
simpa [← Set.inter_assoc, Set.inter_comm _ s, ← inter_diff_assoc]
exact le_toOuterMeasure_caratheodory _ _ hs' _
/-- Restrict a measure `μ` to a set `s`. -/
noncomputable def restrict {_m0 : MeasurableSpace α} (μ : Measure α) (s : Set α) : Measure α :=
restrictₗ s μ
@[simp]
theorem restrictₗ_apply {_m0 : MeasurableSpace α} (s : Set α) (μ : Measure α) :
restrictₗ s μ = μ.restrict s :=
rfl
/-- This lemma shows that `restrict` and `toOuterMeasure` commute. Note that the LHS has a
restrict on measures and the RHS has a restrict on outer measures. -/
theorem restrict_toOuterMeasure_eq_toOuterMeasure_restrict (h : MeasurableSet s) :
(μ.restrict s).toOuterMeasure = OuterMeasure.restrict s μ.toOuterMeasure := by
simp_rw [restrict, restrictₗ, liftLinear, LinearMap.coe_mk, AddHom.coe_mk,
toMeasure_toOuterMeasure, OuterMeasure.restrict_trim h, μ.trimmed]
theorem restrict_apply₀ (ht : NullMeasurableSet t (μ.restrict s)) : μ.restrict s t = μ (t ∩ s) := by
rw [← restrictₗ_apply, restrictₗ, liftLinear_apply₀ _ ht, OuterMeasure.restrict_apply,
coe_toOuterMeasure]
/-- If `t` is a measurable set, then the measure of `t` with respect to the restriction of
the measure to `s` equals the outer measure of `t ∩ s`. An alternate version requiring that `s`
be measurable instead of `t` exists as `Measure.restrict_apply'`. -/
@[simp]
theorem restrict_apply (ht : MeasurableSet t) : μ.restrict s t = μ (t ∩ s) :=
restrict_apply₀ ht.nullMeasurableSet
/-- Restriction of a measure to a subset is monotone both in set and in measure. -/
theorem restrict_mono' {_m0 : MeasurableSpace α} ⦃s s' : Set α⦄ ⦃μ ν : Measure α⦄ (hs : s ≤ᵐ[μ] s')
(hμν : μ ≤ ν) : μ.restrict s ≤ ν.restrict s' :=
Measure.le_iff.2 fun t ht => calc
μ.restrict s t = μ (t ∩ s) := restrict_apply ht
_ ≤ μ (t ∩ s') := (measure_mono_ae <| hs.mono fun _x hx ⟨hxt, hxs⟩ => ⟨hxt, hx hxs⟩)
_ ≤ ν (t ∩ s') := le_iff'.1 hμν (t ∩ s')
_ = ν.restrict s' t := (restrict_apply ht).symm
/-- Restriction of a measure to a subset is monotone both in set and in measure. -/
@[mono, gcongr]
theorem restrict_mono {_m0 : MeasurableSpace α} ⦃s s' : Set α⦄ (hs : s ⊆ s') ⦃μ ν : Measure α⦄
(hμν : μ ≤ ν) : μ.restrict s ≤ ν.restrict s' :=
restrict_mono' (ae_of_all _ hs) hμν
@[gcongr]
theorem restrict_mono_measure {_ : MeasurableSpace α} {μ ν : Measure α} (h : μ ≤ ν) (s : Set α) :
μ.restrict s ≤ ν.restrict s :=
restrict_mono subset_rfl h
@[gcongr]
theorem restrict_mono_set {_ : MeasurableSpace α} (μ : Measure α) {s t : Set α} (h : s ⊆ t) :
μ.restrict s ≤ μ.restrict t :=
restrict_mono h le_rfl
theorem restrict_mono_ae (h : s ≤ᵐ[μ] t) : μ.restrict s ≤ μ.restrict t :=
restrict_mono' h (le_refl μ)
theorem restrict_congr_set (h : s =ᵐ[μ] t) : μ.restrict s = μ.restrict t :=
le_antisymm (restrict_mono_ae h.le) (restrict_mono_ae h.symm.le)
/-- If `s` is a measurable set, then the outer measure of `t` with respect to the restriction of
the measure to `s` equals the outer measure of `t ∩ s`. This is an alternate version of
`Measure.restrict_apply`, requiring that `s` is measurable instead of `t`. -/
@[simp]
theorem restrict_apply' (hs : MeasurableSet s) : μ.restrict s t = μ (t ∩ s) := by
rw [← toOuterMeasure_apply,
Measure.restrict_toOuterMeasure_eq_toOuterMeasure_restrict hs,
OuterMeasure.restrict_apply s t _, toOuterMeasure_apply]
theorem restrict_apply₀' (hs : NullMeasurableSet s μ) : μ.restrict s t = μ (t ∩ s) := by
rw [← restrict_congr_set hs.toMeasurable_ae_eq,
restrict_apply' (measurableSet_toMeasurable _ _),
measure_congr ((ae_eq_refl t).inter hs.toMeasurable_ae_eq)]
theorem restrict_le_self : μ.restrict s ≤ μ :=
Measure.le_iff.2 fun t ht => calc
μ.restrict s t = μ (t ∩ s) := restrict_apply ht
_ ≤ μ t := measure_mono inter_subset_left
variable (μ)
theorem restrict_eq_self (h : s ⊆ t) : μ.restrict t s = μ s :=
(le_iff'.1 restrict_le_self s).antisymm <|
calc
μ s ≤ μ (toMeasurable (μ.restrict t) s ∩ t) :=
measure_mono (subset_inter (subset_toMeasurable _ _) h)
_ = μ.restrict t s := by
rw [← restrict_apply (measurableSet_toMeasurable _ _), measure_toMeasurable]
@[simp]
theorem restrict_apply_self (s : Set α) : (μ.restrict s) s = μ s :=
restrict_eq_self μ Subset.rfl
variable {μ}
theorem restrict_apply_univ (s : Set α) : μ.restrict s univ = μ s := by
rw [restrict_apply MeasurableSet.univ, Set.univ_inter]
theorem le_restrict_apply (s t : Set α) : μ (t ∩ s) ≤ μ.restrict s t :=
calc
μ (t ∩ s) = μ.restrict s (t ∩ s) := (restrict_eq_self μ inter_subset_right).symm
_ ≤ μ.restrict s t := measure_mono inter_subset_left
theorem restrict_apply_le (s t : Set α) : μ.restrict s t ≤ μ t :=
Measure.le_iff'.1 restrict_le_self _
theorem restrict_apply_superset (h : s ⊆ t) : μ.restrict s t = μ s :=
((measure_mono (subset_univ _)).trans_eq <| restrict_apply_univ _).antisymm
((restrict_apply_self μ s).symm.trans_le <| measure_mono h)
@[simp]
theorem restrict_add {_m0 : MeasurableSpace α} (μ ν : Measure α) (s : Set α) :
(μ + ν).restrict s = μ.restrict s + ν.restrict s :=
(restrictₗ s).map_add μ ν
@[simp]
theorem restrict_zero {_m0 : MeasurableSpace α} (s : Set α) : (0 : Measure α).restrict s = 0 :=
(restrictₗ s).map_zero
@[simp]
theorem restrict_smul {_m0 : MeasurableSpace α} {R : Type*} [SMul R ℝ≥0∞]
[IsScalarTower R ℝ≥0∞ ℝ≥0∞] (c : R) (μ : Measure α) (s : Set α) :
(c • μ).restrict s = c • μ.restrict s := by
simpa only [smul_one_smul] using (restrictₗ s).map_smul (c • 1) μ
theorem restrict_restrict₀ (hs : NullMeasurableSet s (μ.restrict t)) :
(μ.restrict t).restrict s = μ.restrict (s ∩ t) :=
ext fun u hu => by
simp only [Set.inter_assoc, restrict_apply hu,
restrict_apply₀ (hu.nullMeasurableSet.inter hs)]
@[simp]
theorem restrict_restrict (hs : MeasurableSet s) : (μ.restrict t).restrict s = μ.restrict (s ∩ t) :=
restrict_restrict₀ hs.nullMeasurableSet
theorem restrict_restrict_of_subset (h : s ⊆ t) : (μ.restrict t).restrict s = μ.restrict s := by
ext1 u hu
rw [restrict_apply hu, restrict_apply hu, restrict_eq_self]
exact inter_subset_right.trans h
theorem restrict_restrict₀' (ht : NullMeasurableSet t μ) :
(μ.restrict t).restrict s = μ.restrict (s ∩ t) :=
ext fun u hu => by simp only [restrict_apply hu, restrict_apply₀' ht, inter_assoc]
theorem restrict_restrict' (ht : MeasurableSet t) :
(μ.restrict t).restrict s = μ.restrict (s ∩ t) :=
restrict_restrict₀' ht.nullMeasurableSet
theorem restrict_comm (hs : MeasurableSet s) :
(μ.restrict t).restrict s = (μ.restrict s).restrict t := by
rw [restrict_restrict hs, restrict_restrict' hs, inter_comm]
theorem restrict_apply_eq_zero (ht : MeasurableSet t) : μ.restrict s t = 0 ↔ μ (t ∩ s) = 0 := by
rw [restrict_apply ht]
theorem measure_inter_eq_zero_of_restrict (h : μ.restrict s t = 0) : μ (t ∩ s) = 0 :=
nonpos_iff_eq_zero.1 (h ▸ le_restrict_apply _ _)
theorem restrict_apply_eq_zero' (hs : MeasurableSet s) : μ.restrict s t = 0 ↔ μ (t ∩ s) = 0 := by
rw [restrict_apply' hs]
@[simp]
theorem restrict_eq_zero : μ.restrict s = 0 ↔ μ s = 0 := by
rw [← measure_univ_eq_zero, restrict_apply_univ]
/-- If `μ s ≠ 0`, then `μ.restrict s ≠ 0`, in terms of `NeZero` instances. -/
instance restrict.neZero [NeZero (μ s)] : NeZero (μ.restrict s) :=
⟨mt restrict_eq_zero.mp <| NeZero.ne _⟩
theorem restrict_zero_set {s : Set α} (h : μ s = 0) : μ.restrict s = 0 :=
restrict_eq_zero.2 h
@[simp]
theorem restrict_empty : μ.restrict ∅ = 0 :=
restrict_zero_set measure_empty
@[simp]
theorem restrict_univ : μ.restrict univ = μ :=
ext fun s hs => by simp [hs]
theorem restrict_inter_add_diff₀ (s : Set α) (ht : NullMeasurableSet t μ) :
μ.restrict (s ∩ t) + μ.restrict (s \ t) = μ.restrict s := by
ext1 u hu
simp only [add_apply, restrict_apply hu, ← inter_assoc, diff_eq]
exact measure_inter_add_diff₀ (u ∩ s) ht
theorem restrict_inter_add_diff (s : Set α) (ht : MeasurableSet t) :
μ.restrict (s ∩ t) + μ.restrict (s \ t) = μ.restrict s :=
restrict_inter_add_diff₀ s ht.nullMeasurableSet
theorem restrict_union_add_inter₀ (s : Set α) (ht : NullMeasurableSet t μ) :
μ.restrict (s ∪ t) + μ.restrict (s ∩ t) = μ.restrict s + μ.restrict t := by
rw [← restrict_inter_add_diff₀ (s ∪ t) ht, union_inter_cancel_right, union_diff_right, ←
restrict_inter_add_diff₀ s ht, add_comm, ← add_assoc, add_right_comm]
theorem restrict_union_add_inter (s : Set α) (ht : MeasurableSet t) :
μ.restrict (s ∪ t) + μ.restrict (s ∩ t) = μ.restrict s + μ.restrict t :=
restrict_union_add_inter₀ s ht.nullMeasurableSet
theorem restrict_union_add_inter' (hs : MeasurableSet s) (t : Set α) :
μ.restrict (s ∪ t) + μ.restrict (s ∩ t) = μ.restrict s + μ.restrict t := by
simpa only [union_comm, inter_comm, add_comm] using restrict_union_add_inter t hs
theorem restrict_union₀ (h : AEDisjoint μ s t) (ht : NullMeasurableSet t μ) :
μ.restrict (s ∪ t) = μ.restrict s + μ.restrict t := by
simp [← restrict_union_add_inter₀ s ht, restrict_zero_set h]
theorem restrict_union (h : Disjoint s t) (ht : MeasurableSet t) :
μ.restrict (s ∪ t) = μ.restrict s + μ.restrict t :=
restrict_union₀ h.aedisjoint ht.nullMeasurableSet
theorem restrict_union' (h : Disjoint s t) (hs : MeasurableSet s) :
μ.restrict (s ∪ t) = μ.restrict s + μ.restrict t := by
rw [union_comm, restrict_union h.symm hs, add_comm]
@[simp]
theorem restrict_add_restrict_compl (hs : MeasurableSet s) :
μ.restrict s + μ.restrict sᶜ = μ := by
rw [← restrict_union (@disjoint_compl_right (Set α) _ _) hs.compl, union_compl_self,
restrict_univ]
@[simp]
theorem restrict_compl_add_restrict (hs : MeasurableSet s) : μ.restrict sᶜ + μ.restrict s = μ := by
rw [add_comm, restrict_add_restrict_compl hs]
theorem restrict_union_le (s s' : Set α) : μ.restrict (s ∪ s') ≤ μ.restrict s + μ.restrict s' :=
le_iff.2 fun t ht ↦ by
simpa [ht, inter_union_distrib_left] using measure_union_le (t ∩ s) (t ∩ s')
theorem restrict_iUnion_apply_ae [Countable ι] {s : ι → Set α} (hd : Pairwise (AEDisjoint μ on s))
(hm : ∀ i, NullMeasurableSet (s i) μ) {t : Set α} (ht : MeasurableSet t) :
μ.restrict (⋃ i, s i) t = ∑' i, μ.restrict (s i) t := by
simp only [restrict_apply, ht, inter_iUnion]
exact
measure_iUnion₀ (hd.mono fun i j h => h.mono inter_subset_right inter_subset_right)
fun i => ht.nullMeasurableSet.inter (hm i)
theorem restrict_iUnion_apply [Countable ι] {s : ι → Set α} (hd : Pairwise (Disjoint on s))
(hm : ∀ i, MeasurableSet (s i)) {t : Set α} (ht : MeasurableSet t) :
μ.restrict (⋃ i, s i) t = ∑' i, μ.restrict (s i) t :=
restrict_iUnion_apply_ae hd.aedisjoint (fun i => (hm i).nullMeasurableSet) ht
theorem restrict_iUnion_apply_eq_iSup [Countable ι] {s : ι → Set α} (hd : Directed (· ⊆ ·) s)
{t : Set α} (ht : MeasurableSet t) : μ.restrict (⋃ i, s i) t = ⨆ i, μ.restrict (s i) t := by
simp only [restrict_apply ht, inter_iUnion]
rw [Directed.measure_iUnion]
exacts [hd.mono_comp _ fun s₁ s₂ => inter_subset_inter_right _]
/-- The restriction of the pushforward measure is the pushforward of the restriction. For a version
assuming only `AEMeasurable`, see `restrict_map_of_aemeasurable`. -/
theorem restrict_map {f : α → β} (hf : Measurable f) {s : Set β} (hs : MeasurableSet s) :
(μ.map f).restrict s = (μ.restrict <| f ⁻¹' s).map f :=
ext fun t ht => by simp [*, hf ht]
theorem restrict_toMeasurable (h : μ s ≠ ∞) : μ.restrict (toMeasurable μ s) = μ.restrict s :=
ext fun t ht => by
rw [restrict_apply ht, restrict_apply ht, inter_comm, measure_toMeasurable_inter ht h,
inter_comm]
theorem restrict_eq_self_of_ae_mem {_m0 : MeasurableSpace α} ⦃s : Set α⦄ ⦃μ : Measure α⦄
(hs : ∀ᵐ x ∂μ, x ∈ s) : μ.restrict s = μ :=
calc
μ.restrict s = μ.restrict univ := restrict_congr_set (eventuallyEq_univ.mpr hs)
_ = μ := restrict_univ
theorem restrict_congr_meas (hs : MeasurableSet s) :
μ.restrict s = ν.restrict s ↔ ∀ t ⊆ s, MeasurableSet t → μ t = ν t :=
⟨fun H t hts ht => by
rw [← inter_eq_self_of_subset_left hts, ← restrict_apply ht, H, restrict_apply ht], fun H =>
ext fun t ht => by
rw [restrict_apply ht, restrict_apply ht, H _ inter_subset_right (ht.inter hs)]⟩
theorem restrict_congr_mono (hs : s ⊆ t) (h : μ.restrict t = ν.restrict t) :
μ.restrict s = ν.restrict s := by
rw [← restrict_restrict_of_subset hs, h, restrict_restrict_of_subset hs]
/-- If two measures agree on all measurable subsets of `s` and `t`, then they agree on all
measurable subsets of `s ∪ t`. -/
theorem restrict_union_congr :
μ.restrict (s ∪ t) = ν.restrict (s ∪ t) ↔
μ.restrict s = ν.restrict s ∧ μ.restrict t = ν.restrict t := by
refine ⟨fun h ↦ ⟨restrict_congr_mono subset_union_left h,
restrict_congr_mono subset_union_right h⟩, ?_⟩
rintro ⟨hs, ht⟩
ext1 u hu
simp only [restrict_apply hu, inter_union_distrib_left]
rcases exists_measurable_superset₂ μ ν (u ∩ s) with ⟨US, hsub, hm, hμ, hν⟩
calc
μ (u ∩ s ∪ u ∩ t) = μ (US ∪ u ∩ t) :=
measure_union_congr_of_subset hsub hμ.le Subset.rfl le_rfl
_ = μ US + μ ((u ∩ t) \ US) := (measure_add_diff hm.nullMeasurableSet _).symm
_ = restrict μ s u + restrict μ t (u \ US) := by
simp only [restrict_apply, hu, hu.diff hm, hμ, ← inter_comm t, inter_diff_assoc]
_ = restrict ν s u + restrict ν t (u \ US) := by rw [hs, ht]
_ = ν US + ν ((u ∩ t) \ US) := by
simp only [restrict_apply, hu, hu.diff hm, hν, ← inter_comm t, inter_diff_assoc]
_ = ν (US ∪ u ∩ t) := measure_add_diff hm.nullMeasurableSet _
_ = ν (u ∩ s ∪ u ∩ t) := .symm <| measure_union_congr_of_subset hsub hν.le Subset.rfl le_rfl
theorem restrict_finset_biUnion_congr {s : Finset ι} {t : ι → Set α} :
μ.restrict (⋃ i ∈ s, t i) = ν.restrict (⋃ i ∈ s, t i) ↔
∀ i ∈ s, μ.restrict (t i) = ν.restrict (t i) := by
classical
induction' s using Finset.induction_on with i s _ hs; · simp
simp only [forall_eq_or_imp, iUnion_iUnion_eq_or_left, Finset.mem_insert]
rw [restrict_union_congr, ← hs]
theorem restrict_iUnion_congr [Countable ι] {s : ι → Set α} :
μ.restrict (⋃ i, s i) = ν.restrict (⋃ i, s i) ↔ ∀ i, μ.restrict (s i) = ν.restrict (s i) := by
refine ⟨fun h i => restrict_congr_mono (subset_iUnion _ _) h, fun h => ?_⟩
ext1 t ht
have D : Directed (· ⊆ ·) fun t : Finset ι => ⋃ i ∈ t, s i :=
Monotone.directed_le fun t₁ t₂ ht => biUnion_subset_biUnion_left ht
rw [iUnion_eq_iUnion_finset]
simp only [restrict_iUnion_apply_eq_iSup D ht, restrict_finset_biUnion_congr.2 fun i _ => h i]
theorem restrict_biUnion_congr {s : Set ι} {t : ι → Set α} (hc : s.Countable) :
μ.restrict (⋃ i ∈ s, t i) = ν.restrict (⋃ i ∈ s, t i) ↔
∀ i ∈ s, μ.restrict (t i) = ν.restrict (t i) := by
haveI := hc.toEncodable
simp only [biUnion_eq_iUnion, SetCoe.forall', restrict_iUnion_congr]
theorem restrict_sUnion_congr {S : Set (Set α)} (hc : S.Countable) :
μ.restrict (⋃₀ S) = ν.restrict (⋃₀ S) ↔ ∀ s ∈ S, μ.restrict s = ν.restrict s := by
rw [sUnion_eq_biUnion, restrict_biUnion_congr hc]
/-- This lemma shows that `Inf` and `restrict` commute for measures. -/
theorem restrict_sInf_eq_sInf_restrict {m0 : MeasurableSpace α} {m : Set (Measure α)}
(hm : m.Nonempty) (ht : MeasurableSet t) :
(sInf m).restrict t = sInf ((fun μ : Measure α => μ.restrict t) '' m) := by
ext1 s hs
simp_rw [sInf_apply hs, restrict_apply hs, sInf_apply (MeasurableSet.inter hs ht),
Set.image_image, restrict_toOuterMeasure_eq_toOuterMeasure_restrict ht, ←
Set.image_image _ toOuterMeasure, ← OuterMeasure.restrict_sInf_eq_sInf_restrict _ (hm.image _),
OuterMeasure.restrict_apply]
theorem exists_mem_of_measure_ne_zero_of_ae (hs : μ s ≠ 0) {p : α → Prop}
(hp : ∀ᵐ x ∂μ.restrict s, p x) : ∃ x, x ∈ s ∧ p x := by
rw [← μ.restrict_apply_self, ← frequently_ae_mem_iff] at hs
exact (hs.and_eventually hp).exists
/-- If a quasi measure preserving map `f` maps a set `s` to a set `t`,
then it is quasi measure preserving with respect to the restrictions of the measures. -/
theorem QuasiMeasurePreserving.restrict {ν : Measure β} {f : α → β}
(hf : QuasiMeasurePreserving f μ ν) {t : Set β} (hmaps : MapsTo f s t) :
QuasiMeasurePreserving f (μ.restrict s) (ν.restrict t) where
measurable := hf.measurable
absolutelyContinuous := by
refine AbsolutelyContinuous.mk fun u hum ↦ ?_
suffices ν (u ∩ t) = 0 → μ (f ⁻¹' u ∩ s) = 0 by simpa [hum, hf.measurable, hf.measurable hum]
refine fun hu ↦ measure_mono_null ?_ (hf.preimage_null hu)
rw [preimage_inter]
gcongr
assumption
/-! ### Extensionality results -/
/-- Two measures are equal if they have equal restrictions on a spanning collection of sets
(formulated using `Union`). -/
theorem ext_iff_of_iUnion_eq_univ [Countable ι] {s : ι → Set α} (hs : ⋃ i, s i = univ) :
μ = ν ↔ ∀ i, μ.restrict (s i) = ν.restrict (s i) := by
rw [← restrict_iUnion_congr, hs, restrict_univ, restrict_univ]
alias ⟨_, ext_of_iUnion_eq_univ⟩ := ext_iff_of_iUnion_eq_univ
/-- Two measures are equal if they have equal restrictions on a spanning collection of sets
(formulated using `biUnion`). -/
theorem ext_iff_of_biUnion_eq_univ {S : Set ι} {s : ι → Set α} (hc : S.Countable)
(hs : ⋃ i ∈ S, s i = univ) : μ = ν ↔ ∀ i ∈ S, μ.restrict (s i) = ν.restrict (s i) := by
rw [← restrict_biUnion_congr hc, hs, restrict_univ, restrict_univ]
alias ⟨_, ext_of_biUnion_eq_univ⟩ := ext_iff_of_biUnion_eq_univ
/-- Two measures are equal if they have equal restrictions on a spanning collection of sets
(formulated using `sUnion`). -/
theorem ext_iff_of_sUnion_eq_univ {S : Set (Set α)} (hc : S.Countable) (hs : ⋃₀ S = univ) :
μ = ν ↔ ∀ s ∈ S, μ.restrict s = ν.restrict s :=
ext_iff_of_biUnion_eq_univ hc <| by rwa [← sUnion_eq_biUnion]
alias ⟨_, ext_of_sUnion_eq_univ⟩ := ext_iff_of_sUnion_eq_univ
theorem ext_of_generateFrom_of_cover {S T : Set (Set α)} (h_gen : ‹_› = generateFrom S)
(hc : T.Countable) (h_inter : IsPiSystem S) (hU : ⋃₀ T = univ) (htop : ∀ t ∈ T, μ t ≠ ∞)
(ST_eq : ∀ t ∈ T, ∀ s ∈ S, μ (s ∩ t) = ν (s ∩ t)) (T_eq : ∀ t ∈ T, μ t = ν t) : μ = ν := by
refine ext_of_sUnion_eq_univ hc hU fun t ht => ?_
ext1 u hu
simp only [restrict_apply hu]
induction u, hu using induction_on_inter h_gen h_inter with
| empty => simp only [Set.empty_inter, measure_empty]
| basic u hu => exact ST_eq _ ht _ hu
| compl u hu ihu =>
have := T_eq t ht
rw [Set.inter_comm] at ihu ⊢
rwa [← measure_inter_add_diff t hu, ← measure_inter_add_diff t hu, ← ihu,
ENNReal.add_right_inj] at this
exact ne_top_of_le_ne_top (htop t ht) (measure_mono Set.inter_subset_left)
| iUnion f hfd hfm ihf =>
simp only [← restrict_apply (hfm _), ← restrict_apply (MeasurableSet.iUnion hfm)] at ihf ⊢
simp only [measure_iUnion hfd hfm, ihf]
/-- Two measures are equal if they are equal on the π-system generating the σ-algebra,
and they are both finite on an increasing spanning sequence of sets in the π-system.
This lemma is formulated using `sUnion`. -/
theorem ext_of_generateFrom_of_cover_subset {S T : Set (Set α)} (h_gen : ‹_› = generateFrom S)
(h_inter : IsPiSystem S) (h_sub : T ⊆ S) (hc : T.Countable) (hU : ⋃₀ T = univ)
(htop : ∀ s ∈ T, μ s ≠ ∞) (h_eq : ∀ s ∈ S, μ s = ν s) : μ = ν := by
refine ext_of_generateFrom_of_cover h_gen hc h_inter hU htop ?_ fun t ht => h_eq t (h_sub ht)
intro t ht s hs; rcases (s ∩ t).eq_empty_or_nonempty with H | H
· simp only [H, measure_empty]
· exact h_eq _ (h_inter _ hs _ (h_sub ht) H)
/-- Two measures are equal if they are equal on the π-system generating the σ-algebra,
and they are both finite on an increasing spanning sequence of sets in the π-system.
This lemma is formulated using `iUnion`.
`FiniteSpanningSetsIn.ext` is a reformulation of this lemma. -/
theorem ext_of_generateFrom_of_iUnion (C : Set (Set α)) (B : ℕ → Set α) (hA : ‹_› = generateFrom C)
(hC : IsPiSystem C) (h1B : ⋃ i, B i = univ) (h2B : ∀ i, B i ∈ C) (hμB : ∀ i, μ (B i) ≠ ∞)
(h_eq : ∀ s ∈ C, μ s = ν s) : μ = ν := by
refine ext_of_generateFrom_of_cover_subset hA hC ?_ (countable_range B) h1B ?_ h_eq
· rintro _ ⟨i, rfl⟩
apply h2B
· rintro _ ⟨i, rfl⟩
apply hμB
@[simp]
theorem restrict_sum (μ : ι → Measure α) {s : Set α} (hs : MeasurableSet s) :
(sum μ).restrict s = sum fun i => (μ i).restrict s :=
ext fun t ht => by simp only [sum_apply, restrict_apply, ht, ht.inter hs]
@[simp]
theorem restrict_sum_of_countable [Countable ι] (μ : ι → Measure α) (s : Set α) :
(sum μ).restrict s = sum fun i => (μ i).restrict s := by
ext t ht
simp_rw [sum_apply _ ht, restrict_apply ht, sum_apply_of_countable]
lemma AbsolutelyContinuous.restrict (h : μ ≪ ν) (s : Set α) : μ.restrict s ≪ ν.restrict s := by
refine Measure.AbsolutelyContinuous.mk (fun t ht htν ↦ ?_)
rw [restrict_apply ht] at htν ⊢
exact h htν
theorem restrict_iUnion_ae [Countable ι] {s : ι → Set α} (hd : Pairwise (AEDisjoint μ on s))
(hm : ∀ i, NullMeasurableSet (s i) μ) : μ.restrict (⋃ i, s i) = sum fun i => μ.restrict (s i) :=
ext fun t ht => by simp only [sum_apply _ ht, restrict_iUnion_apply_ae hd hm ht]
theorem restrict_iUnion [Countable ι] {s : ι → Set α} (hd : Pairwise (Disjoint on s))
(hm : ∀ i, MeasurableSet (s i)) : μ.restrict (⋃ i, s i) = sum fun i => μ.restrict (s i) :=
restrict_iUnion_ae hd.aedisjoint fun i => (hm i).nullMeasurableSet
theorem restrict_iUnion_le [Countable ι] {s : ι → Set α} :
μ.restrict (⋃ i, s i) ≤ sum fun i => μ.restrict (s i) :=
le_iff.2 fun t ht ↦ by simpa [ht, inter_iUnion] using measure_iUnion_le (t ∩ s ·)
end Measure
@[simp]
theorem ae_restrict_iUnion_eq [Countable ι] (s : ι → Set α) :
ae (μ.restrict (⋃ i, s i)) = ⨆ i, ae (μ.restrict (s i)) :=
le_antisymm ((ae_sum_eq fun i => μ.restrict (s i)) ▸ ae_mono restrict_iUnion_le) <|
iSup_le fun i => ae_mono <| restrict_mono (subset_iUnion s i) le_rfl
@[simp]
theorem ae_restrict_union_eq (s t : Set α) :
ae (μ.restrict (s ∪ t)) = ae (μ.restrict s) ⊔ ae (μ.restrict t) := by
simp [union_eq_iUnion, iSup_bool_eq]
theorem ae_restrict_biUnion_eq (s : ι → Set α) {t : Set ι} (ht : t.Countable) :
ae (μ.restrict (⋃ i ∈ t, s i)) = ⨆ i ∈ t, ae (μ.restrict (s i)) := by
haveI := ht.to_subtype
rw [biUnion_eq_iUnion, ae_restrict_iUnion_eq, ← iSup_subtype'']
theorem ae_restrict_biUnion_finset_eq (s : ι → Set α) (t : Finset ι) :
ae (μ.restrict (⋃ i ∈ t, s i)) = ⨆ i ∈ t, ae (μ.restrict (s i)) :=
ae_restrict_biUnion_eq s t.countable_toSet
theorem ae_restrict_iUnion_iff [Countable ι] (s : ι → Set α) (p : α → Prop) :
(∀ᵐ x ∂μ.restrict (⋃ i, s i), p x) ↔ ∀ i, ∀ᵐ x ∂μ.restrict (s i), p x := by simp
theorem ae_restrict_union_iff (s t : Set α) (p : α → Prop) :
(∀ᵐ x ∂μ.restrict (s ∪ t), p x) ↔ (∀ᵐ x ∂μ.restrict s, p x) ∧ ∀ᵐ x ∂μ.restrict t, p x := by simp
theorem ae_restrict_biUnion_iff (s : ι → Set α) {t : Set ι} (ht : t.Countable) (p : α → Prop) :
(∀ᵐ x ∂μ.restrict (⋃ i ∈ t, s i), p x) ↔ ∀ i ∈ t, ∀ᵐ x ∂μ.restrict (s i), p x := by
simp_rw [Filter.Eventually, ae_restrict_biUnion_eq s ht, mem_iSup]
@[simp]
theorem ae_restrict_biUnion_finset_iff (s : ι → Set α) (t : Finset ι) (p : α → Prop) :
(∀ᵐ x ∂μ.restrict (⋃ i ∈ t, s i), p x) ↔ ∀ i ∈ t, ∀ᵐ x ∂μ.restrict (s i), p x := by
simp_rw [Filter.Eventually, ae_restrict_biUnion_finset_eq s, mem_iSup]
theorem ae_eq_restrict_iUnion_iff [Countable ι] (s : ι → Set α) (f g : α → δ) :
f =ᵐ[μ.restrict (⋃ i, s i)] g ↔ ∀ i, f =ᵐ[μ.restrict (s i)] g := by
simp_rw [EventuallyEq, ae_restrict_iUnion_eq, eventually_iSup]
theorem ae_eq_restrict_biUnion_iff (s : ι → Set α) {t : Set ι} (ht : t.Countable) (f g : α → δ) :
f =ᵐ[μ.restrict (⋃ i ∈ t, s i)] g ↔ ∀ i ∈ t, f =ᵐ[μ.restrict (s i)] g := by
simp_rw [ae_restrict_biUnion_eq s ht, EventuallyEq, eventually_iSup]
theorem ae_eq_restrict_biUnion_finset_iff (s : ι → Set α) (t : Finset ι) (f g : α → δ) :
f =ᵐ[μ.restrict (⋃ i ∈ t, s i)] g ↔ ∀ i ∈ t, f =ᵐ[μ.restrict (s i)] g :=
ae_eq_restrict_biUnion_iff s t.countable_toSet f g
open scoped Interval in
theorem ae_restrict_uIoc_eq [LinearOrder α] (a b : α) :
ae (μ.restrict (Ι a b)) = ae (μ.restrict (Ioc a b)) ⊔ ae (μ.restrict (Ioc b a)) := by
simp only [uIoc_eq_union, ae_restrict_union_eq]
open scoped Interval in
/-- See also `MeasureTheory.ae_uIoc_iff`. -/
theorem ae_restrict_uIoc_iff [LinearOrder α] {a b : α} {P : α → Prop} :
(∀ᵐ x ∂μ.restrict (Ι a b), P x) ↔
(∀ᵐ x ∂μ.restrict (Ioc a b), P x) ∧ ∀ᵐ x ∂μ.restrict (Ioc b a), P x := by
rw [ae_restrict_uIoc_eq, eventually_sup]
theorem ae_restrict_iff₀ {p : α → Prop} (hp : NullMeasurableSet { x | p x } (μ.restrict s)) :
(∀ᵐ x ∂μ.restrict s, p x) ↔ ∀ᵐ x ∂μ, x ∈ s → p x := by
simp only [ae_iff, ← compl_setOf, Measure.restrict_apply₀ hp.compl]
rw [iff_iff_eq]; congr with x; simp [and_comm]
theorem ae_restrict_iff {p : α → Prop} (hp : MeasurableSet { x | p x }) :
(∀ᵐ x ∂μ.restrict s, p x) ↔ ∀ᵐ x ∂μ, x ∈ s → p x :=
ae_restrict_iff₀ hp.nullMeasurableSet
theorem ae_imp_of_ae_restrict {s : Set α} {p : α → Prop} (h : ∀ᵐ x ∂μ.restrict s, p x) :
∀ᵐ x ∂μ, x ∈ s → p x := by
simp only [ae_iff] at h ⊢
simpa [setOf_and, inter_comm] using measure_inter_eq_zero_of_restrict h
theorem ae_restrict_iff'₀ {p : α → Prop} (hs : NullMeasurableSet s μ) :
(∀ᵐ x ∂μ.restrict s, p x) ↔ ∀ᵐ x ∂μ, x ∈ s → p x := by
simp only [ae_iff, ← compl_setOf, restrict_apply₀' hs]
rw [iff_iff_eq]; congr with x; simp [and_comm]
theorem ae_restrict_iff' {p : α → Prop} (hs : MeasurableSet s) :
(∀ᵐ x ∂μ.restrict s, p x) ↔ ∀ᵐ x ∂μ, x ∈ s → p x :=
ae_restrict_iff'₀ hs.nullMeasurableSet
theorem _root_.Filter.EventuallyEq.restrict {f g : α → δ} {s : Set α} (hfg : f =ᵐ[μ] g) :
f =ᵐ[μ.restrict s] g := by
-- note that we cannot use `ae_restrict_iff` since we do not require measurability
refine hfg.filter_mono ?_
rw [Measure.ae_le_iff_absolutelyContinuous]
exact Measure.absolutelyContinuous_of_le Measure.restrict_le_self
theorem ae_restrict_mem₀ (hs : NullMeasurableSet s μ) : ∀ᵐ x ∂μ.restrict s, x ∈ s :=
(ae_restrict_iff'₀ hs).2 (Filter.Eventually.of_forall fun _ => id)
theorem ae_restrict_mem (hs : MeasurableSet s) : ∀ᵐ x ∂μ.restrict s, x ∈ s :=
ae_restrict_mem₀ hs.nullMeasurableSet
theorem ae_restrict_of_forall_mem {μ : Measure α} {s : Set α}
(hs : MeasurableSet s) {p : α → Prop} (h : ∀ x ∈ s, p x) : ∀ᵐ (x : α) ∂μ.restrict s, p x :=
(ae_restrict_mem hs).mono h
theorem ae_restrict_of_ae {s : Set α} {p : α → Prop} (h : ∀ᵐ x ∂μ, p x) : ∀ᵐ x ∂μ.restrict s, p x :=
h.filter_mono (ae_mono Measure.restrict_le_self)
theorem ae_restrict_of_ae_restrict_of_subset {s t : Set α} {p : α → Prop} (hst : s ⊆ t)
(h : ∀ᵐ x ∂μ.restrict t, p x) : ∀ᵐ x ∂μ.restrict s, p x :=
h.filter_mono (ae_mono <| Measure.restrict_mono hst (le_refl μ))
theorem ae_of_ae_restrict_of_ae_restrict_compl (t : Set α) {p : α → Prop}
(ht : ∀ᵐ x ∂μ.restrict t, p x) (htc : ∀ᵐ x ∂μ.restrict tᶜ, p x) : ∀ᵐ x ∂μ, p x :=
nonpos_iff_eq_zero.1 <|
calc
μ { x | ¬p x } ≤ μ ({ x | ¬p x } ∩ t) + μ ({ x | ¬p x } ∩ tᶜ) :=
measure_le_inter_add_diff _ _ _
_ ≤ μ.restrict t { x | ¬p x } + μ.restrict tᶜ { x | ¬p x } :=
add_le_add (le_restrict_apply _ _) (le_restrict_apply _ _)
_ = 0 := by rw [ae_iff.1 ht, ae_iff.1 htc, zero_add]
theorem mem_map_restrict_ae_iff {β} {s : Set α} {t : Set β} {f : α → β} (hs : MeasurableSet s) :
t ∈ Filter.map f (ae (μ.restrict s)) ↔ μ ((f ⁻¹' t)ᶜ ∩ s) = 0 := by
rw [mem_map, mem_ae_iff, Measure.restrict_apply' hs]
|
theorem ae_add_measure_iff {p : α → Prop} {ν} :
(∀ᵐ x ∂μ + ν, p x) ↔ (∀ᵐ x ∂μ, p x) ∧ ∀ᵐ x ∂ν, p x :=
add_eq_zero
| Mathlib/MeasureTheory/Measure/Restrict.lean | 614 | 617 |
/-
Copyright (c) 2018 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Kenny Lau, Johan Commelin, Mario Carneiro, Kevin Buzzard,
Amelia Livingston, Yury Kudryashov
-/
import Mathlib.Algebra.Group.Action.Faithful
import Mathlib.Algebra.Group.Nat.Defs
import Mathlib.Algebra.Group.Prod
import Mathlib.Algebra.Group.Submonoid.Basic
import Mathlib.Algebra.Group.Submonoid.MulAction
import Mathlib.Algebra.Group.TypeTags.Basic
/-!
# Operations on `Submonoid`s
In this file we define various operations on `Submonoid`s and `MonoidHom`s.
## Main definitions
### Conversion between multiplicative and additive definitions
* `Submonoid.toAddSubmonoid`, `Submonoid.toAddSubmonoid'`, `AddSubmonoid.toSubmonoid`,
`AddSubmonoid.toSubmonoid'`: convert between multiplicative and additive submonoids of `M`,
`Multiplicative M`, and `Additive M`. These are stated as `OrderIso`s.
### (Commutative) monoid structure on a submonoid
* `Submonoid.toMonoid`, `Submonoid.toCommMonoid`: a submonoid inherits a (commutative) monoid
structure.
### Group actions by submonoids
* `Submonoid.MulAction`, `Submonoid.DistribMulAction`: a submonoid inherits (distributive)
multiplicative actions.
### Operations on submonoids
* `Submonoid.comap`: preimage of a submonoid under a monoid homomorphism as a submonoid of the
domain;
* `Submonoid.map`: image of a submonoid under a monoid homomorphism as a submonoid of the codomain;
* `Submonoid.prod`: product of two submonoids `s : Submonoid M` and `t : Submonoid N` as a submonoid
of `M × N`;
### Monoid homomorphisms between submonoid
* `Submonoid.subtype`: embedding of a submonoid into the ambient monoid.
* `Submonoid.inclusion`: given two submonoids `S`, `T` such that `S ≤ T`, `S.inclusion T` is the
inclusion of `S` into `T` as a monoid homomorphism;
* `MulEquiv.submonoidCongr`: converts a proof of `S = T` into a monoid isomorphism between `S`
and `T`.
* `Submonoid.prodEquiv`: monoid isomorphism between `s.prod t` and `s × t`;
### Operations on `MonoidHom`s
* `MonoidHom.mrange`: range of a monoid homomorphism as a submonoid of the codomain;
* `MonoidHom.mker`: kernel of a monoid homomorphism as a submonoid of the domain;
* `MonoidHom.restrict`: restrict a monoid homomorphism to a submonoid;
* `MonoidHom.codRestrict`: restrict the codomain of a monoid homomorphism to a submonoid;
* `MonoidHom.mrangeRestrict`: restrict a monoid homomorphism to its range;
## Tags
submonoid, range, product, map, comap
-/
assert_not_exists MonoidWithZero
open Function
variable {M N P : Type*} [MulOneClass M] [MulOneClass N] [MulOneClass P] (S : Submonoid M)
/-!
### Conversion to/from `Additive`/`Multiplicative`
-/
section
/-- Submonoids of monoid `M` are isomorphic to additive submonoids of `Additive M`. -/
@[simps]
def Submonoid.toAddSubmonoid : Submonoid M ≃o AddSubmonoid (Additive M) where
toFun S :=
{ carrier := Additive.toMul ⁻¹' S
zero_mem' := S.one_mem'
add_mem' := fun ha hb => S.mul_mem' ha hb }
invFun S :=
{ carrier := Additive.ofMul ⁻¹' S
one_mem' := S.zero_mem'
mul_mem' := fun ha hb => S.add_mem' ha hb}
left_inv x := by cases x; rfl
right_inv x := by cases x; rfl
map_rel_iff' := Iff.rfl
/-- Additive submonoids of an additive monoid `Additive M` are isomorphic to submonoids of `M`. -/
abbrev AddSubmonoid.toSubmonoid' : AddSubmonoid (Additive M) ≃o Submonoid M :=
Submonoid.toAddSubmonoid.symm
theorem Submonoid.toAddSubmonoid_closure (S : Set M) :
Submonoid.toAddSubmonoid (Submonoid.closure S)
= AddSubmonoid.closure (Additive.toMul ⁻¹' S) :=
le_antisymm
(Submonoid.toAddSubmonoid.le_symm_apply.1 <|
Submonoid.closure_le.2 (AddSubmonoid.subset_closure (M := Additive M)))
(AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := M))
theorem AddSubmonoid.toSubmonoid'_closure (S : Set (Additive M)) :
AddSubmonoid.toSubmonoid' (AddSubmonoid.closure S)
= Submonoid.closure (Additive.ofMul ⁻¹' S) :=
le_antisymm
(AddSubmonoid.toSubmonoid'.le_symm_apply.1 <|
AddSubmonoid.closure_le.2 (Submonoid.subset_closure (M := M)))
(Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := Additive M))
end
section
variable {A : Type*} [AddZeroClass A]
/-- Additive submonoids of an additive monoid `A` are isomorphic to
multiplicative submonoids of `Multiplicative A`. -/
@[simps]
def AddSubmonoid.toSubmonoid : AddSubmonoid A ≃o Submonoid (Multiplicative A) where
toFun S :=
{ carrier := Multiplicative.toAdd ⁻¹' S
one_mem' := S.zero_mem'
mul_mem' := fun ha hb => S.add_mem' ha hb }
invFun S :=
{ carrier := Multiplicative.ofAdd ⁻¹' S
zero_mem' := S.one_mem'
add_mem' := fun ha hb => S.mul_mem' ha hb}
left_inv x := by cases x; rfl
right_inv x := by cases x; rfl
map_rel_iff' := Iff.rfl
/-- Submonoids of a monoid `Multiplicative A` are isomorphic to additive submonoids of `A`. -/
abbrev Submonoid.toAddSubmonoid' : Submonoid (Multiplicative A) ≃o AddSubmonoid A :=
AddSubmonoid.toSubmonoid.symm
theorem AddSubmonoid.toSubmonoid_closure (S : Set A) :
(AddSubmonoid.toSubmonoid) (AddSubmonoid.closure S)
= Submonoid.closure (Multiplicative.toAdd ⁻¹' S) :=
le_antisymm
(AddSubmonoid.toSubmonoid.to_galoisConnection.l_le <|
AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := Multiplicative A))
(Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := A))
theorem Submonoid.toAddSubmonoid'_closure (S : Set (Multiplicative A)) :
Submonoid.toAddSubmonoid' (Submonoid.closure S)
= AddSubmonoid.closure (Multiplicative.ofAdd ⁻¹' S) :=
le_antisymm
(Submonoid.toAddSubmonoid'.to_galoisConnection.l_le <|
Submonoid.closure_le.2 <| AddSubmonoid.subset_closure (M := A))
(AddSubmonoid.closure_le.2 <| Submonoid.subset_closure (M := Multiplicative A))
end
namespace Submonoid
variable {F : Type*} [FunLike F M N] [mc : MonoidHomClass F M N]
open Set
/-!
### `comap` and `map`
-/
/-- The preimage of a submonoid along a monoid homomorphism is a submonoid. -/
@[to_additive
"The preimage of an `AddSubmonoid` along an `AddMonoid` homomorphism is an `AddSubmonoid`."]
def comap (f : F) (S : Submonoid N) :
Submonoid M where
carrier := f ⁻¹' S
one_mem' := show f 1 ∈ S by rw [map_one]; exact S.one_mem
mul_mem' ha hb := show f (_ * _) ∈ S by rw [map_mul]; exact S.mul_mem ha hb
@[to_additive (attr := simp)]
theorem coe_comap (S : Submonoid N) (f : F) : (S.comap f : Set M) = f ⁻¹' S :=
rfl
@[to_additive (attr := simp)]
theorem mem_comap {S : Submonoid N} {f : F} {x : M} : x ∈ S.comap f ↔ f x ∈ S :=
Iff.rfl
@[to_additive]
theorem comap_comap (S : Submonoid P) (g : N →* P) (f : M →* N) :
(S.comap g).comap f = S.comap (g.comp f) :=
rfl
@[to_additive (attr := simp)]
theorem comap_id (S : Submonoid P) : S.comap (MonoidHom.id P) = S :=
ext (by simp)
/-- The image of a submonoid along a monoid homomorphism is a submonoid. -/
@[to_additive
"The image of an `AddSubmonoid` along an `AddMonoid` homomorphism is an `AddSubmonoid`."]
def map (f : F) (S : Submonoid M) :
Submonoid N where
carrier := f '' S
one_mem' := ⟨1, S.one_mem, map_one f⟩
mul_mem' := by
rintro _ _ ⟨x, hx, rfl⟩ ⟨y, hy, rfl⟩
exact ⟨x * y, S.mul_mem hx hy, by rw [map_mul]⟩
@[to_additive (attr := simp)]
theorem coe_map (f : F) (S : Submonoid M) : (S.map f : Set N) = f '' S :=
rfl
@[to_additive (attr := simp)]
theorem map_coe_toMonoidHom (f : F) (S : Submonoid M) : S.map (f : M →* N) = S.map f :=
rfl
@[to_additive (attr := simp)]
theorem map_coe_toMulEquiv {F} [EquivLike F M N] [MulEquivClass F M N] (f : F) (S : Submonoid M) :
S.map (f : M ≃* N) = S.map f :=
rfl
@[to_additive (attr := simp)]
theorem mem_map {f : F} {S : Submonoid M} {y : N} : y ∈ S.map f ↔ ∃ x ∈ S, f x = y := Iff.rfl
@[to_additive]
theorem mem_map_of_mem (f : F) {S : Submonoid M} {x : M} (hx : x ∈ S) : f x ∈ S.map f :=
mem_image_of_mem f hx
@[to_additive]
theorem apply_coe_mem_map (f : F) (S : Submonoid M) (x : S) : f x ∈ S.map f :=
mem_map_of_mem f x.2
@[to_additive]
theorem map_map (g : N →* P) (f : M →* N) : (S.map f).map g = S.map (g.comp f) :=
SetLike.coe_injective <| image_image _ _ _
-- The simpNF linter says that the LHS can be simplified via `Submonoid.mem_map`.
-- However this is a higher priority lemma.
-- It seems the side condition `hf` is not applied by `simpNF`.
-- https://github.com/leanprover/std4/issues/207
@[to_additive (attr := simp 1100, nolint simpNF)]
theorem mem_map_iff_mem {f : F} (hf : Function.Injective f) {S : Submonoid M} {x : M} :
f x ∈ S.map f ↔ x ∈ S :=
hf.mem_set_image
@[to_additive]
theorem map_le_iff_le_comap {f : F} {S : Submonoid M} {T : Submonoid N} :
S.map f ≤ T ↔ S ≤ T.comap f :=
image_subset_iff
@[to_additive]
theorem gc_map_comap (f : F) : GaloisConnection (map f) (comap f) := fun _ _ => map_le_iff_le_comap
@[to_additive]
theorem map_le_of_le_comap {T : Submonoid N} {f : F} : S ≤ T.comap f → S.map f ≤ T :=
(gc_map_comap f).l_le
@[to_additive]
theorem le_comap_of_map_le {T : Submonoid N} {f : F} : S.map f ≤ T → S ≤ T.comap f :=
(gc_map_comap f).le_u
@[to_additive]
theorem le_comap_map {f : F} : S ≤ (S.map f).comap f :=
(gc_map_comap f).le_u_l _
@[to_additive]
theorem map_comap_le {S : Submonoid N} {f : F} : (S.comap f).map f ≤ S :=
(gc_map_comap f).l_u_le _
@[to_additive]
theorem monotone_map {f : F} : Monotone (map f) :=
(gc_map_comap f).monotone_l
@[to_additive]
theorem monotone_comap {f : F} : Monotone (comap f) :=
(gc_map_comap f).monotone_u
@[to_additive (attr := simp)]
theorem map_comap_map {f : F} : ((S.map f).comap f).map f = S.map f :=
(gc_map_comap f).l_u_l_eq_l _
@[to_additive (attr := simp)]
theorem comap_map_comap {S : Submonoid N} {f : F} : ((S.comap f).map f).comap f = S.comap f :=
(gc_map_comap f).u_l_u_eq_u _
@[to_additive]
theorem map_sup (S T : Submonoid M) (f : F) : (S ⊔ T).map f = S.map f ⊔ T.map f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).l_sup
@[to_additive]
theorem map_iSup {ι : Sort*} (f : F) (s : ι → Submonoid M) : (iSup s).map f = ⨆ i, (s i).map f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).l_iSup
@[to_additive]
theorem map_inf (S T : Submonoid M) (f : F) (hf : Function.Injective f) :
(S ⊓ T).map f = S.map f ⊓ T.map f := SetLike.coe_injective (Set.image_inter hf)
@[to_additive]
theorem map_iInf {ι : Sort*} [Nonempty ι] (f : F) (hf : Function.Injective f)
(s : ι → Submonoid M) : (iInf s).map f = ⨅ i, (s i).map f := by
apply SetLike.coe_injective
simpa using (Set.injOn_of_injective hf).image_iInter_eq (s := SetLike.coe ∘ s)
@[to_additive]
theorem comap_inf (S T : Submonoid N) (f : F) : (S ⊓ T).comap f = S.comap f ⊓ T.comap f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).u_inf
@[to_additive]
theorem comap_iInf {ι : Sort*} (f : F) (s : ι → Submonoid N) :
(iInf s).comap f = ⨅ i, (s i).comap f :=
(gc_map_comap f : GaloisConnection (map f) (comap f)).u_iInf
@[to_additive (attr := simp)]
theorem map_bot (f : F) : (⊥ : Submonoid M).map f = ⊥ :=
(gc_map_comap f).l_bot
@[to_additive (attr := simp)]
theorem comap_top (f : F) : (⊤ : Submonoid N).comap f = ⊤ :=
(gc_map_comap f).u_top
@[to_additive (attr := simp)]
theorem map_id (S : Submonoid M) : S.map (MonoidHom.id M) = S :=
ext fun _ => ⟨fun ⟨_, h, rfl⟩ => h, fun h => ⟨_, h, rfl⟩⟩
section GaloisCoinsertion
variable {ι : Type*} {f : F}
/-- `map f` and `comap f` form a `GaloisCoinsertion` when `f` is injective. -/
@[to_additive "`map f` and `comap f` form a `GaloisCoinsertion` when `f` is injective."]
def gciMapComap (hf : Function.Injective f) : GaloisCoinsertion (map f) (comap f) :=
(gc_map_comap f).toGaloisCoinsertion fun S x => by simp [mem_comap, mem_map, hf.eq_iff]
variable (hf : Function.Injective f)
include hf
@[to_additive]
theorem comap_map_eq_of_injective (S : Submonoid M) : (S.map f).comap f = S :=
(gciMapComap hf).u_l_eq _
@[to_additive]
theorem comap_surjective_of_injective : Function.Surjective (comap f) :=
(gciMapComap hf).u_surjective
@[to_additive]
theorem map_injective_of_injective : Function.Injective (map f) :=
(gciMapComap hf).l_injective
@[to_additive]
theorem comap_inf_map_of_injective (S T : Submonoid M) : (S.map f ⊓ T.map f).comap f = S ⊓ T :=
(gciMapComap hf).u_inf_l _ _
@[to_additive]
theorem comap_iInf_map_of_injective (S : ι → Submonoid M) : (⨅ i, (S i).map f).comap f = iInf S :=
(gciMapComap hf).u_iInf_l _
@[to_additive]
theorem comap_sup_map_of_injective (S T : Submonoid M) : (S.map f ⊔ T.map f).comap f = S ⊔ T :=
(gciMapComap hf).u_sup_l _ _
@[to_additive]
theorem comap_iSup_map_of_injective (S : ι → Submonoid M) : (⨆ i, (S i).map f).comap f = iSup S :=
(gciMapComap hf).u_iSup_l _
@[to_additive]
theorem map_le_map_iff_of_injective {S T : Submonoid M} : S.map f ≤ T.map f ↔ S ≤ T :=
(gciMapComap hf).l_le_l_iff
@[to_additive]
theorem map_strictMono_of_injective : StrictMono (map f) :=
(gciMapComap hf).strictMono_l
end GaloisCoinsertion
section GaloisInsertion
variable {ι : Type*} {f : F}
/-- `map f` and `comap f` form a `GaloisInsertion` when `f` is surjective. -/
@[to_additive "`map f` and `comap f` form a `GaloisInsertion` when `f` is surjective."]
def giMapComap (hf : Function.Surjective f) : GaloisInsertion (map f) (comap f) :=
(gc_map_comap f).toGaloisInsertion fun S x h =>
let ⟨y, hy⟩ := hf x
mem_map.2 ⟨y, by simp [hy, h]⟩
variable (hf : Function.Surjective f)
include hf
@[to_additive]
theorem map_comap_eq_of_surjective (S : Submonoid N) : (S.comap f).map f = S :=
(giMapComap hf).l_u_eq _
@[to_additive]
theorem map_surjective_of_surjective : Function.Surjective (map f) :=
(giMapComap hf).l_surjective
@[to_additive]
theorem comap_injective_of_surjective : Function.Injective (comap f) :=
(giMapComap hf).u_injective
@[to_additive]
theorem map_inf_comap_of_surjective (S T : Submonoid N) : (S.comap f ⊓ T.comap f).map f = S ⊓ T :=
(giMapComap hf).l_inf_u _ _
@[to_additive]
theorem map_iInf_comap_of_surjective (S : ι → Submonoid N) : (⨅ i, (S i).comap f).map f = iInf S :=
(giMapComap hf).l_iInf_u _
@[to_additive]
theorem map_sup_comap_of_surjective (S T : Submonoid N) : (S.comap f ⊔ T.comap f).map f = S ⊔ T :=
(giMapComap hf).l_sup_u _ _
@[to_additive]
theorem map_iSup_comap_of_surjective (S : ι → Submonoid N) : (⨆ i, (S i).comap f).map f = iSup S :=
(giMapComap hf).l_iSup_u _
@[to_additive]
theorem comap_le_comap_iff_of_surjective {S T : Submonoid N} : S.comap f ≤ T.comap f ↔ S ≤ T :=
(giMapComap hf).u_le_u_iff
@[to_additive]
theorem comap_strictMono_of_surjective : StrictMono (comap f) :=
(giMapComap hf).strictMono_u
end GaloisInsertion
variable {M : Type*} [MulOneClass M] (S : Submonoid M)
/-- The top submonoid is isomorphic to the monoid. -/
@[to_additive (attr := simps) "The top additive submonoid is isomorphic to the additive monoid."]
def topEquiv : (⊤ : Submonoid M) ≃* M where
toFun x := x
invFun x := ⟨x, mem_top x⟩
left_inv x := x.eta _
right_inv _ := rfl
map_mul' _ _ := rfl
@[to_additive (attr := simp)]
theorem topEquiv_toMonoidHom : ((topEquiv : _ ≃* M) : _ →* M) = (⊤ : Submonoid M).subtype :=
rfl
/-- A subgroup is isomorphic to its image under an injective function. If you have an isomorphism,
use `MulEquiv.submonoidMap` for better definitional equalities. -/
@[to_additive "An additive subgroup is isomorphic to its image under an injective function. If you
have an isomorphism, use `AddEquiv.addSubmonoidMap` for better definitional equalities."]
noncomputable def equivMapOfInjective (f : M →* N) (hf : Function.Injective f) : S ≃* S.map f :=
{ Equiv.Set.image f S hf with map_mul' := fun _ _ => Subtype.ext (f.map_mul _ _) }
@[to_additive (attr := simp)]
theorem coe_equivMapOfInjective_apply (f : M →* N) (hf : Function.Injective f) (x : S) :
(equivMapOfInjective S f hf x : N) = f x :=
rfl
@[to_additive (attr := simp)]
theorem closure_closure_coe_preimage {s : Set M} : closure (((↑) : closure s → M) ⁻¹' s) = ⊤ :=
eq_top_iff.2 fun x _ ↦ Subtype.recOn x fun _ hx' ↦
closure_induction (fun _ h ↦ subset_closure h) (one_mem _) (fun _ _ _ _ ↦ mul_mem) hx'
/-- Given submonoids `s`, `t` of monoids `M`, `N` respectively, `s × t` as a submonoid
of `M × N`. -/
@[to_additive prod
"Given `AddSubmonoid`s `s`, `t` of `AddMonoid`s `A`, `B` respectively, `s × t`
as an `AddSubmonoid` of `A × B`."]
def prod (s : Submonoid M) (t : Submonoid N) :
Submonoid (M × N) where
carrier := s ×ˢ t
one_mem' := ⟨s.one_mem, t.one_mem⟩
mul_mem' hp hq := ⟨s.mul_mem hp.1 hq.1, t.mul_mem hp.2 hq.2⟩
@[to_additive coe_prod]
theorem coe_prod (s : Submonoid M) (t : Submonoid N) :
(s.prod t : Set (M × N)) = (s : Set M) ×ˢ (t : Set N) :=
rfl
@[to_additive mem_prod]
theorem mem_prod {s : Submonoid M} {t : Submonoid N} {p : M × N} :
p ∈ s.prod t ↔ p.1 ∈ s ∧ p.2 ∈ t :=
Iff.rfl
@[to_additive prod_mono]
theorem prod_mono {s₁ s₂ : Submonoid M} {t₁ t₂ : Submonoid N} (hs : s₁ ≤ s₂) (ht : t₁ ≤ t₂) :
s₁.prod t₁ ≤ s₂.prod t₂ :=
Set.prod_mono hs ht
@[to_additive prod_top]
theorem prod_top (s : Submonoid M) : s.prod (⊤ : Submonoid N) = s.comap (MonoidHom.fst M N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_fst]
@[to_additive top_prod]
theorem top_prod (s : Submonoid N) : (⊤ : Submonoid M).prod s = s.comap (MonoidHom.snd M N) :=
ext fun x => by simp [mem_prod, MonoidHom.coe_snd]
@[to_additive (attr := simp) top_prod_top]
theorem top_prod_top : (⊤ : Submonoid M).prod (⊤ : Submonoid N) = ⊤ :=
(top_prod _).trans <| comap_top _
@[to_additive bot_prod_bot]
theorem bot_prod_bot : (⊥ : Submonoid M).prod (⊥ : Submonoid N) = ⊥ :=
SetLike.coe_injective <| by simp [coe_prod]
/-- The product of submonoids is isomorphic to their product as monoids. -/
@[to_additive prodEquiv
"The product of additive submonoids is isomorphic to their product as additive monoids"]
def prodEquiv (s : Submonoid M) (t : Submonoid N) : s.prod t ≃* s × t :=
{ (Equiv.Set.prod (s : Set M) (t : Set N)) with
map_mul' := fun _ _ => rfl }
open MonoidHom
@[to_additive]
theorem map_inl (s : Submonoid M) : s.map (inl M N) = s.prod ⊥ :=
ext fun p =>
⟨fun ⟨_, hx, hp⟩ => hp ▸ ⟨hx, Set.mem_singleton 1⟩, fun ⟨hps, hp1⟩ =>
⟨p.1, hps, Prod.ext rfl <| (Set.eq_of_mem_singleton hp1).symm⟩⟩
@[to_additive]
theorem map_inr (s : Submonoid N) : s.map (inr M N) = prod ⊥ s :=
ext fun p =>
⟨fun ⟨_, hx, hp⟩ => hp ▸ ⟨Set.mem_singleton 1, hx⟩, fun ⟨hp1, hps⟩ =>
⟨p.2, hps, Prod.ext (Set.eq_of_mem_singleton hp1).symm rfl⟩⟩
@[to_additive (attr := simp) prod_bot_sup_bot_prod]
theorem prod_bot_sup_bot_prod (s : Submonoid M) (t : Submonoid N) :
(prod s ⊥) ⊔ (prod ⊥ t) = prod s t :=
(le_antisymm (sup_le (prod_mono (le_refl s) bot_le) (prod_mono bot_le (le_refl t))))
fun p hp => Prod.fst_mul_snd p ▸ mul_mem
((le_sup_left : prod s ⊥ ≤ prod s ⊥ ⊔ prod ⊥ t) ⟨hp.1, Set.mem_singleton 1⟩)
((le_sup_right : prod ⊥ t ≤ prod s ⊥ ⊔ prod ⊥ t) ⟨Set.mem_singleton 1, hp.2⟩)
@[to_additive]
theorem mem_map_equiv {f : M ≃* N} {K : Submonoid M} {x : N} :
x ∈ K.map f.toMonoidHom ↔ f.symm x ∈ K :=
Set.mem_image_equiv
@[to_additive]
theorem map_equiv_eq_comap_symm (f : M ≃* N) (K : Submonoid M) :
K.map f = K.comap f.symm :=
SetLike.coe_injective (f.toEquiv.image_eq_preimage K)
@[to_additive]
theorem comap_equiv_eq_map_symm (f : N ≃* M) (K : Submonoid M) :
K.comap f = K.map f.symm :=
(map_equiv_eq_comap_symm f.symm K).symm
@[to_additive (attr := simp)]
theorem map_equiv_top (f : M ≃* N) : (⊤ : Submonoid M).map f = ⊤ :=
SetLike.coe_injective <| Set.image_univ.trans f.surjective.range_eq
@[to_additive le_prod_iff]
theorem le_prod_iff {s : Submonoid M} {t : Submonoid N} {u : Submonoid (M × N)} :
u ≤ s.prod t ↔ u.map (fst M N) ≤ s ∧ u.map (snd M N) ≤ t := by
constructor
· intro h
constructor
· rintro x ⟨⟨y1, y2⟩, ⟨hy1, rfl⟩⟩
exact (h hy1).1
· rintro x ⟨⟨y1, y2⟩, ⟨hy1, rfl⟩⟩
exact (h hy1).2
· rintro ⟨hH, hK⟩ ⟨x1, x2⟩ h
exact ⟨hH ⟨_, h, rfl⟩, hK ⟨_, h, rfl⟩⟩
@[to_additive prod_le_iff]
theorem prod_le_iff {s : Submonoid M} {t : Submonoid N} {u : Submonoid (M × N)} :
s.prod t ≤ u ↔ s.map (inl M N) ≤ u ∧ t.map (inr M N) ≤ u := by
constructor
· intro h
constructor
· rintro _ ⟨x, hx, rfl⟩
apply h
exact ⟨hx, Submonoid.one_mem _⟩
· rintro _ ⟨x, hx, rfl⟩
apply h
exact ⟨Submonoid.one_mem _, hx⟩
· rintro ⟨hH, hK⟩ ⟨x1, x2⟩ ⟨h1, h2⟩
have h1' : inl M N x1 ∈ u := by
apply hH
simpa using h1
have h2' : inr M N x2 ∈ u := by
apply hK
simpa using h2
simpa using Submonoid.mul_mem _ h1' h2'
@[to_additive closure_prod]
theorem closure_prod {s : Set M} {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_of_le_comap _ <| closure_le.2 fun _x hx => subset_closure ⟨hx, ht⟩,
map_le_of_le_comap _ <| closure_le.2 fun _y hy => subset_closure ⟨hs, hy⟩⟩)
@[to_additive (attr := simp) closure_prod_zero]
lemma closure_prod_one (s : Set M) : closure (s ×ˢ ({1} : Set N)) = (closure s).prod ⊥ :=
le_antisymm
(closure_le.2 <| Set.prod_subset_prod_iff.2 <| .inl ⟨subset_closure, .rfl⟩)
(prod_le_iff.2 ⟨
map_le_of_le_comap _ <| closure_le.2 fun _x hx => subset_closure ⟨hx, rfl⟩,
by simp⟩)
@[to_additive (attr := simp) closure_zero_prod]
lemma closure_one_prod (t : Set N) : closure (({1} : Set M) ×ˢ t) = .prod ⊥ (closure t) :=
le_antisymm
(closure_le.2 <| Set.prod_subset_prod_iff.2 <| .inl ⟨.rfl, subset_closure⟩)
(prod_le_iff.2 ⟨by simp,
map_le_of_le_comap _ <| closure_le.2 fun _y hy => subset_closure ⟨rfl, hy⟩⟩)
end Submonoid
namespace MonoidHom
variable {F : Type*} [FunLike F M N] [mc : MonoidHomClass F M N]
open Submonoid
library_note "range copy pattern"/--
For many categories (monoids, modules, rings, ...) the set-theoretic image of a morphism `f` is
a subobject of the codomain. When this is the case, it is useful to define the range of a morphism
in such a way that the underlying carrier set of the range subobject is definitionally
`Set.range f`. In particular this means that the types `↥(Set.range f)` and `↥f.range` are
interchangeable without proof obligations.
A convenient candidate definition for range which is mathematically correct is `map ⊤ f`, just as
`Set.range` could have been defined as `f '' Set.univ`. However, this lacks the desired definitional
convenience, in that it both does not match `Set.range`, and that it introduces a redundant `x ∈ ⊤`
term which clutters proofs. In such a case one may resort to the `copy`
pattern. A `copy` function converts the definitional problem for the carrier set of a subobject
into a one-off propositional proof obligation which one discharges while writing the definition of
the definitionally convenient range (the parameter `hs` in the example below).
A good example is the case of a morphism of monoids. A convenient definition for
`MonoidHom.mrange` would be `(⊤ : Submonoid M).map f`. However since this lacks the required
definitional convenience, we first define `Submonoid.copy` as follows:
```lean
protected def copy (S : Submonoid M) (s : Set M) (hs : s = S) : Submonoid M :=
{ carrier := s,
one_mem' := hs.symm ▸ S.one_mem',
mul_mem' := hs.symm ▸ S.mul_mem' }
```
and then finally define:
```lean
def mrange (f : M →* N) : Submonoid N :=
((⊤ : Submonoid M).map f).copy (Set.range f) Set.image_univ.symm
```
-/
/-- The range of a monoid homomorphism is a submonoid. See Note [range copy pattern]. -/
@[to_additive "The range of an `AddMonoidHom` is an `AddSubmonoid`."]
def mrange (f : F) : Submonoid N :=
((⊤ : Submonoid M).map f).copy (Set.range f) Set.image_univ.symm
@[to_additive (attr := simp)]
theorem coe_mrange (f : F) : (mrange f : Set N) = Set.range f :=
rfl
@[to_additive (attr := simp)]
theorem mem_mrange {f : F} {y : N} : y ∈ mrange f ↔ ∃ x, f x = y :=
Iff.rfl
@[to_additive]
lemma mrange_comp {O : Type*} [MulOneClass O] (f : N →* O) (g : M →* N) :
mrange (f.comp g) = (mrange g).map f := SetLike.coe_injective <| Set.range_comp f _
@[to_additive]
theorem mrange_eq_map (f : F) : mrange f = (⊤ : Submonoid M).map f :=
Submonoid.copy_eq _
@[to_additive (attr := simp)]
theorem mrange_id : mrange (MonoidHom.id M) = ⊤ := by
simp [mrange_eq_map]
@[to_additive]
theorem map_mrange (g : N →* P) (f : M →* N) : (mrange f).map g = mrange (comp g f) := by
simpa only [mrange_eq_map] using (⊤ : Submonoid M).map_map g f
@[to_additive]
theorem mrange_eq_top {f : F} : mrange f = (⊤ : Submonoid N) ↔ Surjective f :=
SetLike.ext'_iff.trans <| Iff.trans (by rw [coe_mrange, coe_top]) Set.range_eq_univ
@[deprecated (since := "2024-11-11")]
alias mrange_top_iff_surjective := mrange_eq_top
/-- The range of a surjective monoid hom is the whole of the codomain. -/
@[to_additive (attr := simp)
"The range of a surjective `AddMonoid` hom is the whole of the codomain."]
theorem mrange_eq_top_of_surjective (f : F) (hf : Function.Surjective f) :
mrange f = (⊤ : Submonoid N) :=
mrange_eq_top.2 hf
@[deprecated (since := "2024-11-11")] alias mrange_top_of_surjective := mrange_eq_top_of_surjective
@[to_additive]
theorem mclosure_preimage_le (f : F) (s : Set N) : closure (f ⁻¹' s) ≤ (closure s).comap f :=
closure_le.2 fun _ hx => SetLike.mem_coe.2 <| mem_comap.2 <| subset_closure hx
/-- The image under a monoid hom of the submonoid generated by a set equals the submonoid generated
by the image of the set. -/
@[to_additive
"The image under an `AddMonoid` hom of the `AddSubmonoid` generated by a set equals
the `AddSubmonoid` generated by the image of the set."]
theorem map_mclosure (f : F) (s : Set M) : (closure s).map f = closure (f '' s) :=
Set.image_preimage.l_comm_of_u_comm (gc_map_comap f) (Submonoid.gi N).gc (Submonoid.gi M).gc
fun _ ↦ rfl
@[to_additive (attr := simp)]
theorem mclosure_range (f : F) : closure (Set.range f) = mrange f := by
rw [← Set.image_univ, ← map_mclosure, mrange_eq_map, closure_univ]
/-- Restriction of a monoid hom to a submonoid of the domain. -/
@[to_additive "Restriction of an `AddMonoid` hom to an `AddSubmonoid` of the domain."]
def restrict {N S : Type*} [MulOneClass N] [SetLike S M] [SubmonoidClass S M] (f : M →* N)
(s : S) : s →* N :=
f.comp (SubmonoidClass.subtype _)
@[to_additive (attr := simp)]
theorem restrict_apply {N S : Type*} [MulOneClass N] [SetLike S M] [SubmonoidClass S M]
(f : M →* N) (s : S) (x : s) : f.restrict s x = f x :=
rfl
@[to_additive (attr := simp)]
theorem restrict_mrange (f : M →* N) : mrange (f.restrict S) = S.map f := by
simp [SetLike.ext_iff]
/-- Restriction of a monoid hom to a submonoid of the codomain. -/
@[to_additive (attr := simps apply)
"Restriction of an `AddMonoid` hom to an `AddSubmonoid` of the codomain."]
def codRestrict {S} [SetLike S N] [SubmonoidClass S N] (f : M →* N) (s : S) (h : ∀ x, f x ∈ s) :
M →* s where
toFun n := ⟨f n, h n⟩
map_one' := Subtype.eq f.map_one
map_mul' x y := Subtype.eq (f.map_mul x y)
@[to_additive (attr := simp)]
lemma injective_codRestrict {S} [SetLike S N] [SubmonoidClass S N] (f : M →* N) (s : S)
(h : ∀ x, f x ∈ s) : Function.Injective (f.codRestrict s h) ↔ Function.Injective f :=
⟨fun H _ _ hxy ↦ H <| Subtype.eq hxy, fun H _ _ hxy ↦ H (congr_arg Subtype.val hxy)⟩
/-- Restriction of a monoid hom to its range interpreted as a submonoid. -/
@[to_additive "Restriction of an `AddMonoid` hom to its range interpreted as a submonoid."]
def mrangeRestrict {N} [MulOneClass N] (f : M →* N) : M →* (mrange f) :=
(f.codRestrict (mrange f)) fun x => ⟨x, rfl⟩
@[to_additive (attr := simp)]
theorem coe_mrangeRestrict {N} [MulOneClass N] (f : M →* N) (x : M) :
(f.mrangeRestrict x : N) = f x :=
rfl
@[to_additive]
theorem mrangeRestrict_surjective (f : M →* N) : Function.Surjective f.mrangeRestrict :=
fun ⟨_, ⟨x, rfl⟩⟩ => ⟨x, rfl⟩
/-- The multiplicative kernel of a monoid hom is the submonoid of elements `x : G` such
that `f x = 1` -/
@[to_additive
"The additive kernel of an `AddMonoid` hom is the `AddSubmonoid` of
elements such that `f x = 0`"]
def mker (f : F) : Submonoid M :=
(⊥ : Submonoid N).comap f
@[to_additive (attr := simp)]
theorem mem_mker {f : F} {x : M} : x ∈ mker f ↔ f x = 1 :=
Iff.rfl
@[to_additive]
theorem coe_mker (f : F) : (mker f : Set M) = (f : M → N) ⁻¹' {1} :=
rfl
@[to_additive]
instance decidableMemMker [DecidableEq N] (f : F) : DecidablePred (· ∈ mker f) := fun x =>
decidable_of_iff (f x = 1) mem_mker
@[to_additive]
theorem comap_mker (g : N →* P) (f : M →* N) : (mker g).comap f = mker (comp g f) :=
rfl
@[to_additive (attr := simp)]
theorem comap_bot' (f : F) : (⊥ : Submonoid N).comap f = mker f :=
rfl
@[to_additive (attr := simp)]
theorem restrict_mker (f : M →* N) : mker (f.restrict S) = (MonoidHom.mker f).comap S.subtype :=
rfl
@[to_additive]
theorem mrangeRestrict_mker (f : M →* N) : mker (mrangeRestrict f) = mker f := by
ext x
change (⟨f x, _⟩ : mrange f) = ⟨1, _⟩ ↔ f x = 1
simp
@[to_additive (attr := simp)]
theorem mker_one : mker (1 : M →* N) = ⊤ := by
ext
simp [mem_mker]
@[to_additive prod_map_comap_prod']
theorem prod_map_comap_prod' {M' : Type*} {N' : Type*} [MulOneClass M'] [MulOneClass N']
(f : M →* N) (g : M' →* N') (S : Submonoid N) (S' : Submonoid 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 _ _
@[to_additive mker_prod_map]
theorem mker_prod_map {M' : Type*} {N' : Type*} [MulOneClass M'] [MulOneClass N'] (f : M →* N)
(g : M' →* N') : mker (prodMap f g) = (mker f).prod (mker g) := by
rw [← comap_bot', ← comap_bot', ← comap_bot', ← prod_map_comap_prod', bot_prod_bot]
@[to_additive (attr := simp)]
theorem mker_inl : mker (inl M N) = ⊥ := by
ext x
simp [mem_mker]
@[to_additive (attr := simp)]
theorem mker_inr : mker (inr M N) = ⊥ := by
ext x
simp [mem_mker]
@[to_additive (attr := simp)]
lemma mker_fst : mker (fst M N) = .prod ⊥ ⊤ := SetLike.ext fun _ => (iff_of_eq (and_true _)).symm
@[to_additive (attr := simp)]
lemma mker_snd : mker (snd M N) = .prod ⊤ ⊥ := SetLike.ext fun _ => (iff_of_eq (true_and _)).symm
/-- The `MonoidHom` from the preimage of a submonoid to itself. -/
@[to_additive (attr := simps)
"the `AddMonoidHom` from the preimage of an additive submonoid to itself."]
def submonoidComap (f : M →* N) (N' : Submonoid N) :
N'.comap f →* N' where
toFun x := ⟨f x, x.2⟩
map_one' := Subtype.eq f.map_one
map_mul' x y := Subtype.eq (f.map_mul x y)
@[to_additive]
lemma submonoidComap_surjective_of_surjective (f : M →* N) (N' : Submonoid N) (hf : Surjective f) :
Surjective (f.submonoidComap N') := fun y ↦ by
obtain ⟨x, hx⟩ := hf y
use ⟨x, mem_comap.mpr (hx ▸ y.2)⟩
apply Subtype.val_injective
simp [hx]
/-- The `MonoidHom` from a submonoid to its image.
See `MulEquiv.SubmonoidMap` for a variant for `MulEquiv`s. -/
@[to_additive (attr := simps)
"the `AddMonoidHom` from an additive submonoid to its image. See
`AddEquiv.AddSubmonoidMap` for a variant for `AddEquiv`s."]
def submonoidMap (f : M →* N) (M' : Submonoid M) : M' →* M'.map f where
toFun x := ⟨f x, ⟨x, x.2, rfl⟩⟩
map_one' := Subtype.eq <| f.map_one
map_mul' x y := Subtype.eq <| f.map_mul x y
@[to_additive]
theorem submonoidMap_surjective (f : M →* N) (M' : Submonoid M) :
Function.Surjective (f.submonoidMap M') := by
rintro ⟨_, x, hx, rfl⟩
exact ⟨⟨x, hx⟩, rfl⟩
end MonoidHom
namespace Submonoid
open MonoidHom
@[to_additive]
theorem mrange_inl : mrange (inl M N) = prod ⊤ ⊥ := by simpa only [mrange_eq_map] using map_inl ⊤
@[to_additive]
theorem mrange_inr : mrange (inr M N) = prod ⊥ ⊤ := by simpa only [mrange_eq_map] using map_inr ⊤
@[to_additive]
theorem mrange_inl' : mrange (inl M N) = comap (snd M N) ⊥ :=
mrange_inl.trans (top_prod _)
@[to_additive]
theorem mrange_inr' : mrange (inr M N) = comap (fst M N) ⊥ :=
mrange_inr.trans (prod_top _)
@[to_additive (attr := simp)]
theorem mrange_fst : mrange (fst M N) = ⊤ :=
mrange_eq_top_of_surjective (fst M N) <| @Prod.fst_surjective _ _ ⟨1⟩
@[to_additive (attr := simp)]
theorem mrange_snd : mrange (snd M N) = ⊤ :=
mrange_eq_top_of_surjective (snd M N) <| @Prod.snd_surjective _ _ ⟨1⟩
@[to_additive prod_eq_bot_iff]
theorem prod_eq_bot_iff {s : Submonoid M} {t : Submonoid N} : s.prod t = ⊥ ↔ s = ⊥ ∧ t = ⊥ := by
simp only [eq_bot_iff, prod_le_iff, (gc_map_comap _).le_iff_le, comap_bot', mker_inl, mker_inr]
@[to_additive prod_eq_top_iff]
theorem prod_eq_top_iff {s : Submonoid M} {t : Submonoid N} : s.prod t = ⊤ ↔ s = ⊤ ∧ t = ⊤ := by
simp only [eq_top_iff, le_prod_iff, ← (gc_map_comap _).le_iff_le, ← mrange_eq_map, mrange_fst,
mrange_snd]
@[to_additive (attr := simp)]
theorem mrange_inl_sup_mrange_inr : mrange (inl M N) ⊔ mrange (inr M N) = ⊤ := by
simp only [mrange_inl, mrange_inr, prod_bot_sup_bot_prod, top_prod_top]
/-- The monoid hom associated to an inclusion of submonoids. -/
@[to_additive
"The `AddMonoid` hom associated to an inclusion of submonoids."]
def inclusion {S T : Submonoid M} (h : S ≤ T) : S →* T :=
S.subtype.codRestrict _ fun x => h x.2
@[to_additive (attr := simp)]
theorem mrange_subtype (s : Submonoid M) : mrange s.subtype = s :=
SetLike.coe_injective <| (coe_mrange _).trans <| Subtype.range_coe
-- `alias` doesn't add the deprecation suggestion to the `to_additive` version
-- see https://github.com/leanprover-community/mathlib4/issues/19424
@[to_additive] alias range_subtype := mrange_subtype
attribute [deprecated mrange_subtype (since := "2024-11-25")] range_subtype
attribute [deprecated AddSubmonoid.mrange_subtype (since := "2024-11-25")]
AddSubmonoid.range_subtype
@[to_additive]
theorem eq_top_iff' : S = ⊤ ↔ ∀ x : M, x ∈ S :=
eq_top_iff.trans ⟨fun h m => h <| mem_top m, fun h m _ => h m⟩
@[to_additive]
theorem eq_bot_iff_forall : S = ⊥ ↔ ∀ x ∈ S, x = (1 : M) :=
SetLike.ext_iff.trans <| by simp +contextual [iff_def, S.one_mem]
@[to_additive]
theorem eq_bot_of_subsingleton [Subsingleton S] : S = ⊥ := by
rw [eq_bot_iff_forall]
intro y hy
simpa using congr_arg ((↑) : S → M) <| Subsingleton.elim (⟨y, hy⟩ : S) 1
@[to_additive]
theorem nontrivial_iff_exists_ne_one (S : Submonoid M) : Nontrivial S ↔ ∃ x ∈ S, x ≠ (1 : M) :=
calc
Nontrivial S ↔ ∃ x : S, x ≠ 1 := nontrivial_iff_exists_ne 1
_ ↔ ∃ (x : _) (hx : x ∈ S), (⟨x, hx⟩ : S) ≠ ⟨1, S.one_mem⟩ := Subtype.exists
_ ↔ ∃ x ∈ S, x ≠ (1 : M) := by simp [Ne]
/-- A submonoid is either the trivial submonoid or nontrivial. -/
@[to_additive "An additive submonoid is either the trivial additive submonoid or nontrivial."]
theorem bot_or_nontrivial (S : Submonoid M) : S = ⊥ ∨ Nontrivial S := by
simp only [eq_bot_iff_forall, nontrivial_iff_exists_ne_one, ← not_forall, ← Classical.not_imp,
Classical.em]
/-- A submonoid is either the trivial submonoid or contains a nonzero element. -/
@[to_additive
"An additive submonoid is either the trivial additive submonoid or contains a nonzero
element."]
theorem bot_or_exists_ne_one (S : Submonoid M) : S = ⊥ ∨ ∃ x ∈ S, x ≠ (1 : M) :=
S.bot_or_nontrivial.imp_right S.nontrivial_iff_exists_ne_one.mp
end Submonoid
namespace MulEquiv
variable {S} {T : Submonoid M}
/-- Makes the identity isomorphism from a proof that two submonoids of a multiplicative
monoid are equal. -/
@[to_additive
"Makes the identity additive isomorphism from a proof two
submonoids of an additive monoid are equal."]
def submonoidCongr (h : S = T) : S ≃* T :=
{ Equiv.setCongr <| congr_arg _ h with map_mul' := fun _ _ => rfl }
-- this name is primed so that the version to `f.range` instead of `f.mrange` can be unprimed.
/-- A monoid homomorphism `f : M →* N` with a left-inverse `g : N → M` defines a multiplicative
equivalence between `M` and `f.mrange`.
This is a bidirectional version of `MonoidHom.mrange_restrict`. -/
@[to_additive (attr := simps +simpRhs)
"An additive monoid homomorphism `f : M →+ N` with a left-inverse `g : N → M`
defines an additive equivalence between `M` and `f.mrange`.
This is a bidirectional version of `AddMonoidHom.mrange_restrict`. "]
def ofLeftInverse' (f : M →* N) {g : N → M} (h : Function.LeftInverse g f) :
M ≃* MonoidHom.mrange f :=
{ f.mrangeRestrict with
toFun := f.mrangeRestrict
invFun := g ∘ (MonoidHom.mrange f).subtype
left_inv := h
right_inv := fun x =>
Subtype.ext <|
let ⟨x', hx'⟩ := MonoidHom.mem_mrange.mp x.2
show f (g x) = x by rw [← hx', h x'] }
/-- A `MulEquiv` `φ` between two monoids `M` and `N` induces a `MulEquiv` between
a submonoid `S ≤ M` and the submonoid `φ(S) ≤ N`.
See `MonoidHom.submonoidMap` for a variant for `MonoidHom`s. -/
@[to_additive
"An `AddEquiv` `φ` between two additive monoids `M` and `N` induces an `AddEquiv`
between a submonoid `S ≤ M` and the submonoid `φ(S) ≤ N`. See
`AddMonoidHom.addSubmonoidMap` for a variant for `AddMonoidHom`s."]
def submonoidMap (e : M ≃* N) (S : Submonoid M) : S ≃* S.map e :=
| { (e : M ≃ N).image S with map_mul' := fun _ _ => Subtype.ext (map_mul e _ _) }
| Mathlib/Algebra/Group/Submonoid/Operations.lean | 985 | 986 |
/-
Copyright (c) 2020 Zhouhang Zhou. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Zhouhang Zhou
-/
import Mathlib.Data.Set.Order
import Mathlib.Order.Bounds.Basic
import Mathlib.Order.Interval.Set.Image
import Mathlib.Order.Interval.Set.LinearOrder
import Mathlib.Tactic.Common
/-!
# Intervals without endpoints ordering
In any lattice `α`, we define `uIcc a b` to be `Icc (a ⊓ b) (a ⊔ b)`, which in a linear order is
the set of elements lying between `a` and `b`.
`Icc a b` requires the assumption `a ≤ b` to be meaningful, which is sometimes inconvenient. The
interval as defined in this file is always the set of things lying between `a` and `b`, regardless
of the relative order of `a` and `b`.
For real numbers, `uIcc a b` is the same as `segment ℝ a b`.
In a product or pi type, `uIcc a b` is the smallest box containing `a` and `b`. For example,
`uIcc (1, -1) (-1, 1) = Icc (-1, -1) (1, 1)` is the square of vertices `(1, -1)`, `(-1, -1)`,
`(-1, 1)`, `(1, 1)`.
In `Finset α` (seen as a hypercube of dimension `Fintype.card α`), `uIcc a b` is the smallest
subcube containing both `a` and `b`.
## Notation
We use the localized notation `[[a, b]]` for `uIcc a b`. One can open the locale `Interval` to
make the notation available.
-/
open Function
open OrderDual (toDual ofDual)
variable {α β : Type*}
namespace Set
section Lattice
variable [Lattice α] [Lattice β] {a a₁ a₂ b b₁ b₂ x : α}
/-- `uIcc a b` is the set of elements lying between `a` and `b`, with `a` and `b` included.
Note that we define it more generally in a lattice as `Set.Icc (a ⊓ b) (a ⊔ b)`. In a product type,
`uIcc` corresponds to the bounding box of the two elements. -/
def uIcc (a b : α) : Set α := Icc (a ⊓ b) (a ⊔ b)
/-- `[[a, b]]` denotes the set of elements lying between `a` and `b`, inclusive. -/
scoped[Interval] notation "[[" a ", " b "]]" => Set.uIcc a b
open Interval
@[simp]
lemma uIcc_toDual (a b : α) : [[toDual a, toDual b]] = ofDual ⁻¹' [[a, b]] :=
-- Note: needed to hint `(α := α)` after https://github.com/leanprover-community/mathlib4/pull/8386 (elaboration order?)
Icc_toDual (α := α)
@[deprecated (since := "2025-03-20")]
alias dual_uIcc := uIcc_toDual
@[simp]
theorem uIcc_ofDual (a b : αᵒᵈ) : [[ofDual a, ofDual b]] = toDual ⁻¹' [[a, b]] :=
Icc_ofDual
@[simp]
lemma uIcc_of_le (h : a ≤ b) : [[a, b]] = Icc a b := by rw [uIcc, inf_eq_left.2 h, sup_eq_right.2 h]
@[simp]
lemma uIcc_of_ge (h : b ≤ a) : [[a, b]] = Icc b a := by rw [uIcc, inf_eq_right.2 h, sup_eq_left.2 h]
lemma uIcc_comm (a b : α) : [[a, b]] = [[b, a]] := by simp_rw [uIcc, inf_comm, sup_comm]
lemma uIcc_of_lt (h : a < b) : [[a, b]] = Icc a b := uIcc_of_le h.le
lemma uIcc_of_gt (h : b < a) : [[a, b]] = Icc b a := uIcc_of_ge h.le
lemma uIcc_self : [[a, a]] = {a} := by simp [uIcc]
@[simp] lemma nonempty_uIcc : [[a, b]].Nonempty := nonempty_Icc.2 inf_le_sup
lemma Icc_subset_uIcc : Icc a b ⊆ [[a, b]] := Icc_subset_Icc inf_le_left le_sup_right
lemma Icc_subset_uIcc' : Icc b a ⊆ [[a, b]] := Icc_subset_Icc inf_le_right le_sup_left
@[simp] lemma left_mem_uIcc : a ∈ [[a, b]] := ⟨inf_le_left, le_sup_left⟩
@[simp] lemma right_mem_uIcc : b ∈ [[a, b]] := ⟨inf_le_right, le_sup_right⟩
lemma mem_uIcc_of_le (ha : a ≤ x) (hb : x ≤ b) : x ∈ [[a, b]] := Icc_subset_uIcc ⟨ha, hb⟩
lemma mem_uIcc_of_ge (hb : b ≤ x) (ha : x ≤ a) : x ∈ [[a, b]] := Icc_subset_uIcc' ⟨hb, ha⟩
lemma uIcc_subset_uIcc (h₁ : a₁ ∈ [[a₂, b₂]]) (h₂ : b₁ ∈ [[a₂, b₂]]) :
[[a₁, b₁]] ⊆ [[a₂, b₂]] :=
Icc_subset_Icc (le_inf h₁.1 h₂.1) (sup_le h₁.2 h₂.2)
lemma uIcc_subset_Icc (ha : a₁ ∈ Icc a₂ b₂) (hb : b₁ ∈ Icc a₂ b₂) :
[[a₁, b₁]] ⊆ Icc a₂ b₂ :=
Icc_subset_Icc (le_inf ha.1 hb.1) (sup_le ha.2 hb.2)
lemma uIcc_subset_uIcc_iff_mem :
[[a₁, b₁]] ⊆ [[a₂, b₂]] ↔ a₁ ∈ [[a₂, b₂]] ∧ b₁ ∈ [[a₂, b₂]] :=
Iff.intro (fun h => ⟨h left_mem_uIcc, h right_mem_uIcc⟩) fun h =>
uIcc_subset_uIcc h.1 h.2
lemma uIcc_subset_uIcc_iff_le' :
[[a₁, b₁]] ⊆ [[a₂, b₂]] ↔ a₂ ⊓ b₂ ≤ a₁ ⊓ b₁ ∧ a₁ ⊔ b₁ ≤ a₂ ⊔ b₂ :=
Icc_subset_Icc_iff inf_le_sup
lemma uIcc_subset_uIcc_right (h : x ∈ [[a, b]]) : [[x, b]] ⊆ [[a, b]] :=
uIcc_subset_uIcc h right_mem_uIcc
lemma uIcc_subset_uIcc_left (h : x ∈ [[a, b]]) : [[a, x]] ⊆ [[a, b]] :=
uIcc_subset_uIcc left_mem_uIcc h
lemma bdd_below_bdd_above_iff_subset_uIcc (s : Set α) :
BddBelow s ∧ BddAbove s ↔ ∃ a b, s ⊆ [[a, b]] :=
bddBelow_bddAbove_iff_subset_Icc.trans
⟨fun ⟨a, b, h⟩ => ⟨a, b, fun _ hx => Icc_subset_uIcc (h hx)⟩, fun ⟨_, _, h⟩ => ⟨_, _, h⟩⟩
section Prod
@[simp]
theorem uIcc_prod_uIcc (a₁ a₂ : α) (b₁ b₂ : β) :
[[a₁, a₂]] ×ˢ [[b₁, b₂]] = [[(a₁, b₁), (a₂, b₂)]] :=
Icc_prod_Icc _ _ _ _
theorem uIcc_prod_eq (a b : α × β) : [[a, b]] = [[a.1, b.1]] ×ˢ [[a.2, b.2]] := by simp
end Prod
end Lattice
open Interval
section DistribLattice
variable [DistribLattice α] {a b c : α}
lemma eq_of_mem_uIcc_of_mem_uIcc (ha : a ∈ [[b, c]]) (hb : b ∈ [[a, c]]) : a = b :=
eq_of_inf_eq_sup_eq (inf_congr_right ha.1 hb.1) <| sup_congr_right ha.2 hb.2
lemma eq_of_mem_uIcc_of_mem_uIcc' : b ∈ [[a, c]] → c ∈ [[a, b]] → b = c := by
simpa only [uIcc_comm a] using eq_of_mem_uIcc_of_mem_uIcc
lemma uIcc_injective_right (a : α) : Injective fun b => uIcc b a := fun b c h => by
rw [Set.ext_iff] at h
exact eq_of_mem_uIcc_of_mem_uIcc ((h _).1 left_mem_uIcc) ((h _).2 left_mem_uIcc)
lemma uIcc_injective_left (a : α) : Injective (uIcc a) := by
simpa only [uIcc_comm] using uIcc_injective_right a
end DistribLattice
section LinearOrder
variable [LinearOrder α]
section Lattice
variable [Lattice β] {f : α → β} {a b : α}
lemma _root_.MonotoneOn.mapsTo_uIcc (hf : MonotoneOn f (uIcc a b)) :
MapsTo f (uIcc a b) (uIcc (f a) (f b)) := by
rw [uIcc, uIcc, ← hf.map_sup, ← hf.map_inf] <;>
apply_rules [left_mem_uIcc, right_mem_uIcc, hf.mapsTo_Icc]
lemma _root_.AntitoneOn.mapsTo_uIcc (hf : AntitoneOn f (uIcc a b)) :
MapsTo f (uIcc a b) (uIcc (f a) (f b)) := by
rw [uIcc, uIcc, ← hf.map_sup, ← hf.map_inf] <;>
apply_rules [left_mem_uIcc, right_mem_uIcc, hf.mapsTo_Icc]
lemma _root_.Monotone.mapsTo_uIcc (hf : Monotone f) : MapsTo f (uIcc a b) (uIcc (f a) (f b)) :=
(hf.monotoneOn _).mapsTo_uIcc
lemma _root_.Antitone.mapsTo_uIcc (hf : Antitone f) : MapsTo f (uIcc a b) (uIcc (f a) (f b)) :=
(hf.antitoneOn _).mapsTo_uIcc
lemma _root_.MonotoneOn.image_uIcc_subset (hf : MonotoneOn f (uIcc a b)) :
f '' uIcc a b ⊆ uIcc (f a) (f b) := hf.mapsTo_uIcc.image_subset
lemma _root_.AntitoneOn.image_uIcc_subset (hf : AntitoneOn f (uIcc a b)) :
f '' uIcc a b ⊆ uIcc (f a) (f b) := hf.mapsTo_uIcc.image_subset
lemma _root_.Monotone.image_uIcc_subset (hf : Monotone f) : f '' uIcc a b ⊆ uIcc (f a) (f b) :=
(hf.monotoneOn _).image_uIcc_subset
lemma _root_.Antitone.image_uIcc_subset (hf : Antitone f) : f '' uIcc a b ⊆ uIcc (f a) (f b) :=
(hf.antitoneOn _).image_uIcc_subset
end Lattice
variable [LinearOrder β] {f : α → β} {s : Set α} {a a₁ a₂ b b₁ b₂ c : α}
theorem Icc_min_max : Icc (min a b) (max a b) = [[a, b]] :=
rfl
lemma uIcc_of_not_le (h : ¬a ≤ b) : [[a, b]] = Icc b a := uIcc_of_gt <| lt_of_not_ge h
lemma uIcc_of_not_ge (h : ¬b ≤ a) : [[a, b]] = Icc a b := uIcc_of_lt <| lt_of_not_ge h
lemma uIcc_eq_union : [[a, b]] = Icc a b ∪ Icc b a := by rw [Icc_union_Icc', max_comm] <;> rfl
lemma mem_uIcc : a ∈ [[b, c]] ↔ b ≤ a ∧ a ≤ c ∨ c ≤ a ∧ a ≤ b := by simp [uIcc_eq_union]
lemma not_mem_uIcc_of_lt (ha : c < a) (hb : c < b) : c ∉ [[a, b]] :=
not_mem_Icc_of_lt <| lt_min_iff.mpr ⟨ha, hb⟩
lemma not_mem_uIcc_of_gt (ha : a < c) (hb : b < c) : c ∉ [[a, b]] :=
not_mem_Icc_of_gt <| max_lt_iff.mpr ⟨ha, hb⟩
lemma uIcc_subset_uIcc_iff_le :
[[a₁, b₁]] ⊆ [[a₂, b₂]] ↔ min a₂ b₂ ≤ min a₁ b₁ ∧ max a₁ b₁ ≤ max a₂ b₂ :=
uIcc_subset_uIcc_iff_le'
/-- A sort of triangle inequality. -/
lemma uIcc_subset_uIcc_union_uIcc : [[a, c]] ⊆ [[a, b]] ∪ [[b, c]] := fun x => by
simp only [mem_uIcc, mem_union]
rcases le_total x b with h2 | h2 <;> tauto
lemma monotone_or_antitone_iff_uIcc :
Monotone f ∨ Antitone f ↔ ∀ a b c, c ∈ [[a, b]] → f c ∈ [[f a, f b]] := by
constructor
· rintro (hf | hf) a b c <;> simp_rw [← Icc_min_max, ← hf.map_min, ← hf.map_max]
exacts [fun hc => ⟨hf hc.1, hf hc.2⟩, fun hc => ⟨hf hc.2, hf hc.1⟩]
contrapose!
rw [not_monotone_not_antitone_iff_exists_le_le]
rintro ⟨a, b, c, hab, hbc, ⟨hfab, hfcb⟩ | ⟨hfba, hfbc⟩⟩
· exact ⟨a, c, b, Icc_subset_uIcc ⟨hab, hbc⟩, fun h => h.2.not_lt <| max_lt hfab hfcb⟩
| · exact ⟨a, c, b, Icc_subset_uIcc ⟨hab, hbc⟩, fun h => h.1.not_lt <| lt_min hfba hfbc⟩
| Mathlib/Order/Interval/Set/UnorderedInterval.lean | 231 | 231 |
/-
Copyright (c) 2022 Michael Stoll. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Michael Stoll
-/
import Mathlib.Data.Int.Range
import Mathlib.Data.ZMod.Basic
import Mathlib.NumberTheory.MulChar.Basic
/-!
# Quadratic characters on ℤ/nℤ
This file defines some quadratic characters on the rings ℤ/4ℤ and ℤ/8ℤ.
We set them up to be of type `MulChar (ZMod n) ℤ`, where `n` is `4` or `8`.
## Tags
quadratic character, zmod
-/
/-!
### Quadratic characters mod 4 and 8
We define the primitive quadratic characters `χ₄`on `ZMod 4`
and `χ₈`, `χ₈'` on `ZMod 8`.
-/
namespace ZMod
section QuadCharModP
/-- Define the nontrivial quadratic character on `ZMod 4`, `χ₄`.
It corresponds to the extension `ℚ(√-1)/ℚ`. -/
@[simps]
def χ₄ : MulChar (ZMod 4) ℤ where
toFun a :=
match a with
| 0 | 2 => 0
| 1 => 1
| 3 => -1
map_one' := rfl
map_mul' := by decide
map_nonunit' := by decide
/-- `χ₄` takes values in `{0, 1, -1}` -/
theorem isQuadratic_χ₄ : χ₄.IsQuadratic := by
unfold MulChar.IsQuadratic
decide
/-- The value of `χ₄ n`, for `n : ℕ`, depends only on `n % 4`. -/
theorem χ₄_nat_mod_four (n : ℕ) : χ₄ n = χ₄ (n % 4 : ℕ) := by
rw [← ZMod.natCast_mod n 4]
/-- The value of `χ₄ n`, for `n : ℤ`, depends only on `n % 4`. -/
theorem χ₄_int_mod_four (n : ℤ) : χ₄ n = χ₄ (n % 4 : ℤ) := by
rw [← ZMod.intCast_mod n 4, Nat.cast_ofNat]
/-- An explicit description of `χ₄` on integers / naturals -/
theorem χ₄_int_eq_if_mod_four (n : ℤ) :
χ₄ n = if n % 2 = 0 then 0 else if n % 4 = 1 then 1 else -1 := by
have help : ∀ m : ℤ, 0 ≤ m → m < 4 → χ₄ m = if m % 2 = 0 then 0 else if m = 1 then 1 else -1 := by
decide
rw [← Int.emod_emod_of_dvd n (by omega : (2 : ℤ) ∣ 4), ← ZMod.intCast_mod n 4]
exact help (n % 4) (Int.emod_nonneg n (by omega)) (Int.emod_lt_abs n (by omega))
theorem χ₄_nat_eq_if_mod_four (n : ℕ) :
χ₄ n = if n % 2 = 0 then 0 else if n % 4 = 1 then 1 else -1 :=
mod_cast χ₄_int_eq_if_mod_four n
/-- Alternative description of `χ₄ n` for odd `n : ℕ` in terms of powers of `-1` -/
theorem χ₄_eq_neg_one_pow {n : ℕ} (hn : n % 2 = 1) : χ₄ n = (-1) ^ (n / 2) := by
rw [χ₄_nat_eq_if_mod_four]
simp only [hn, Nat.one_ne_zero, if_false]
nth_rewrite 3 [← Nat.div_add_mod n 4]
nth_rewrite 3 [show 4 = 2 * 2 by omega]
rw [mul_assoc, add_comm, Nat.add_mul_div_left _ _ zero_lt_two, pow_add, pow_mul,
neg_one_sq, one_pow, mul_one]
have help : ∀ m : ℕ, m < 4 → m % 2 = 1 → ite (m = 1) (1 : ℤ) (-1) = (-1) ^ (m / 2) := by decide
exact help _ (Nat.mod_lt n (by omega)) <| (Nat.mod_mod_of_dvd n (by omega : 2 ∣ 4)).trans hn
/-- If `n % 4 = 1`, then `χ₄ n = 1`. -/
theorem χ₄_nat_one_mod_four {n : ℕ} (hn : n % 4 = 1) : χ₄ n = 1 := by
rw [χ₄_nat_mod_four, hn]
rfl
/-- If `n % 4 = 3`, then `χ₄ n = -1`. -/
theorem χ₄_nat_three_mod_four {n : ℕ} (hn : n % 4 = 3) : χ₄ n = -1 := by
rw [χ₄_nat_mod_four, hn]
rfl
/-- If `n % 4 = 1`, then `χ₄ n = 1`. -/
theorem χ₄_int_one_mod_four {n : ℤ} (hn : n % 4 = 1) : χ₄ n = 1 := by
rw [χ₄_int_mod_four, hn]
rfl
/-- If `n % 4 = 3`, then `χ₄ n = -1`. -/
theorem χ₄_int_three_mod_four {n : ℤ} (hn : n % 4 = 3) : χ₄ n = -1 := by
rw [χ₄_int_mod_four, hn]
rfl
/-- If `n % 4 = 1`, then `(-1)^(n/2) = 1`. -/
theorem neg_one_pow_div_two_of_one_mod_four {n : ℕ} (hn : n % 4 = 1) : (-1 : ℤ) ^ (n / 2) = 1 :=
χ₄_eq_neg_one_pow (Nat.odd_of_mod_four_eq_one hn) ▸ χ₄_nat_one_mod_four hn
/-- If `n % 4 = 3`, then `(-1)^(n/2) = -1`. -/
theorem neg_one_pow_div_two_of_three_mod_four {n : ℕ} (hn : n % 4 = 3) : (-1 : ℤ) ^ (n / 2) = -1 :=
χ₄_eq_neg_one_pow (Nat.odd_of_mod_four_eq_three hn) ▸ χ₄_nat_three_mod_four hn
/-- Define the first primitive quadratic character on `ZMod 8`, `χ₈`.
It corresponds to the extension `ℚ(√2)/ℚ`. -/
@[simps]
def χ₈ : MulChar (ZMod 8) ℤ where
toFun a :=
match a with
| 0 | 2 | 4 | 6 => 0
| 1 | 7 => 1
| 3 | 5 => -1
map_one' := rfl
map_mul' := by decide
map_nonunit' := by decide
/-- `χ₈` takes values in `{0, 1, -1}` -/
theorem isQuadratic_χ₈ : χ₈.IsQuadratic := by
unfold MulChar.IsQuadratic
decide
/-- The value of `χ₈ n`, for `n : ℕ`, depends only on `n % 8`. -/
theorem χ₈_nat_mod_eight (n : ℕ) : χ₈ n = χ₈ (n % 8 : ℕ) := by
rw [← ZMod.natCast_mod n 8]
/-- The value of `χ₈ n`, for `n : ℤ`, depends only on `n % 8`. -/
theorem χ₈_int_mod_eight (n : ℤ) : χ₈ n = χ₈ (n % 8 : ℤ) := by
rw [← ZMod.intCast_mod n 8, Nat.cast_ofNat]
/-- An explicit description of `χ₈` on integers / naturals -/
theorem χ₈_int_eq_if_mod_eight (n : ℤ) :
χ₈ n = if n % 2 = 0 then 0 else if n % 8 = 1 ∨ n % 8 = 7 then 1 else -1 := by
have help :
∀ m : ℤ, 0 ≤ m → m < 8 → χ₈ m = if m % 2 = 0 then 0 else if m = 1 ∨ m = 7 then 1 else -1 := by
decide
rw [← Int.emod_emod_of_dvd n (by omega : (2 : ℤ) ∣ 8), ← ZMod.intCast_mod n 8]
exact help (n % 8) (Int.emod_nonneg n (by omega)) (Int.emod_lt_abs n (by omega))
theorem χ₈_nat_eq_if_mod_eight (n : ℕ) :
| χ₈ n = if n % 2 = 0 then 0 else if n % 8 = 1 ∨ n % 8 = 7 then 1 else -1 :=
mod_cast χ₈_int_eq_if_mod_eight n
| Mathlib/NumberTheory/LegendreSymbol/ZModChar.lean | 148 | 149 |
/-
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.MeasureTheory.Measure.Dirac
import Mathlib.Topology.Algebra.InfiniteSum.ENNReal
/-!
# Counting measure
In this file we define the counting measure `MeasurTheory.Measure.count`
as `MeasureTheory.Measure.sum MeasureTheory.Measure.dirac`
and prove basic properties of this measure.
-/
open Set
open scoped ENNReal Finset
variable {α β : Type*} [MeasurableSpace α] [MeasurableSpace β] {s : Set α}
noncomputable section
namespace MeasureTheory.Measure
/-- Counting measure on any measurable space. -/
def count : Measure α :=
sum dirac
@[simp] lemma count_ne_zero'' [Nonempty α] : (count : Measure α) ≠ 0 := by simp [count]
theorem le_count_apply : ∑' _ : s, (1 : ℝ≥0∞) ≤ count s :=
calc
(∑' _ : s, 1 : ℝ≥0∞) = ∑' i, indicator s 1 i := tsum_subtype s 1
_ ≤ ∑' i, dirac i s := ENNReal.tsum_le_tsum fun _ => le_dirac_apply
_ ≤ count s := le_sum_apply _ _
theorem count_apply (hs : MeasurableSet s) : count s = s.encard := by
simp [count, hs, ← tsum_subtype, Set.encard]
@[deprecated measure_empty (since := "2025-02-06")]
theorem count_empty : count (∅ : Set α) = 0 := measure_empty
@[simp]
theorem count_apply_finset' {s : Finset α} (hs : MeasurableSet (s : Set α)) :
count (↑s : Set α) = #s := by simp [count_apply hs]
@[simp]
theorem count_apply_finset [MeasurableSingletonClass α] (s : Finset α) :
count (↑s : Set α) = #s :=
count_apply_finset' s.measurableSet
theorem count_apply_finite' {s : Set α} (s_fin : s.Finite) (s_mble : MeasurableSet s) :
count s = #s_fin.toFinset := by
simp [←
@count_apply_finset' _ _ s_fin.toFinset (by simpa only [Finite.coe_toFinset] using s_mble)]
theorem count_apply_finite [MeasurableSingletonClass α] (s : Set α) (hs : s.Finite) :
count s = #hs.toFinset := by rw [← count_apply_finset, Finite.coe_toFinset]
/-- `count` measure evaluates to infinity at infinite sets. -/
theorem count_apply_infinite (hs : s.Infinite) : count s = ∞ := by
refine top_unique (le_of_tendsto' ENNReal.tendsto_nat_nhds_top fun n => ?_)
rcases hs.exists_subset_card_eq n with ⟨t, ht, rfl⟩
calc
(#t : ℝ≥0∞) = ∑ i ∈ t, 1 := by simp
_ = ∑' i : (t : Set α), 1 := (t.tsum_subtype 1).symm
_ ≤ count (t : Set α) := le_count_apply
_ ≤ count s := measure_mono ht
@[simp]
theorem count_apply_eq_top' (s_mble : MeasurableSet s) : count s = ∞ ↔ s.Infinite := by
by_cases hs : s.Finite
· simp [Set.Infinite, hs, count_apply_finite' hs s_mble]
· change s.Infinite at hs
simp [hs, count_apply_infinite]
@[simp]
theorem count_apply_eq_top [MeasurableSingletonClass α] : count s = ∞ ↔ s.Infinite := by
by_cases hs : s.Finite
· exact count_apply_eq_top' hs.measurableSet
· change s.Infinite at hs
simp [hs, count_apply_infinite]
@[simp]
theorem count_apply_lt_top' (s_mble : MeasurableSet s) : count s < ∞ ↔ s.Finite :=
calc
count s < ∞ ↔ count s ≠ ∞ := lt_top_iff_ne_top
_ ↔ ¬s.Infinite := not_congr (count_apply_eq_top' s_mble)
_ ↔ s.Finite := Classical.not_not
@[simp]
theorem count_apply_lt_top [MeasurableSingletonClass α] : count s < ∞ ↔ s.Finite :=
calc
count s < ∞ ↔ count s ≠ ∞ := lt_top_iff_ne_top
_ ↔ ¬s.Infinite := not_congr count_apply_eq_top
_ ↔ s.Finite := Classical.not_not
@[simp]
theorem count_eq_zero_iff : count s = 0 ↔ s = ∅ where
mp h := eq_empty_of_forall_not_mem fun x hx ↦ by
simpa [hx] using ((ENNReal.le_tsum x).trans <| le_sum_apply _ _).trans_eq h
mpr := by rintro rfl; exact measure_empty
lemma count_ne_zero_iff : count s ≠ 0 ↔ s.Nonempty :=
count_eq_zero_iff.not.trans nonempty_iff_ne_empty.symm
alias ⟨_, count_ne_zero⟩ := count_ne_zero_iff
@[deprecated (since := "2024-11-20")] alias ⟨empty_of_count_eq_zero, _⟩ := count_eq_zero_iff
@[deprecated (since := "2024-11-20")] alias empty_of_count_eq_zero' := empty_of_count_eq_zero
@[deprecated (since := "2024-11-20")] alias count_eq_zero_iff' := count_eq_zero_iff
@[deprecated (since := "2024-11-20")] alias count_ne_zero' := count_ne_zero
@[simp]
lemma ae_count_iff {p : α → Prop} : (∀ᵐ x ∂count, p x) ↔ ∀ x, p x := by
refine ⟨fun h x ↦ ?_, ae_of_all _⟩
rw [ae_iff, count_eq_zero_iff] at h
by_contra hx
rwa [← mem_empty_iff_false x, ← h]
@[simp]
theorem count_singleton' {a : α} (ha : MeasurableSet ({a} : Set α)) : count ({a} : Set α) = 1 := by
rw [count_apply_finite' (Set.finite_singleton a) ha, Set.Finite.toFinset]
simp [@toFinset_card _ _ (Set.finite_singleton a).fintype,
@Fintype.card_unique _ _ (Set.finite_singleton a).fintype]
theorem count_singleton [MeasurableSingletonClass α] (a : α) : count ({a} : Set α) = 1 :=
count_singleton' (measurableSet_singleton a)
@[simp]
theorem _root_.MeasureTheory.count_real_singleton'
{a : α} (ha : MeasurableSet ({a} : Set α)) :
count.real ({a} : Set α) = 1 := by
rw [measureReal_def, count_singleton' ha, ENNReal.toReal_one]
| theorem _root_.MeasureTheory.count_real_singleton [MeasurableSingletonClass α] (a : α) :
count.real ({a} : Set α) = 1 :=
count_real_singleton' (measurableSet_singleton a)
| Mathlib/MeasureTheory/Measure/Count.lean | 137 | 139 |
/-
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
| Mathlib/Algebra/Lie/Nilpotent.lean | 227 | 231 |
/-
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, Mitchell Lee
-/
import Mathlib.Algebra.BigOperators.Finprod
import Mathlib.Algebra.BigOperators.Pi
import Mathlib.Algebra.Group.Submonoid.Basic
import Mathlib.Algebra.Group.ULift
import Mathlib.Order.Filter.Pointwise
import Mathlib.Topology.Algebra.MulAction
import Mathlib.Topology.ContinuousMap.Defs
import Mathlib.Topology.Algebra.Monoid.Defs
/-!
# Theory of topological monoids
In this file we define mixin classes `ContinuousMul` and `ContinuousAdd`. While in many
applications the underlying type is a monoid (multiplicative or additive), we do not require this in
the definitions.
-/
universe u v
open Set Filter TopologicalSpace Topology
open scoped Topology Pointwise
variable {ι α M N X : Type*} [TopologicalSpace X]
@[to_additive (attr := continuity, fun_prop)]
theorem continuous_one [TopologicalSpace M] [One M] : Continuous (1 : X → M) :=
@continuous_const _ _ _ _ 1
section ContinuousMul
variable [TopologicalSpace M] [Mul M] [ContinuousMul M]
@[to_additive]
instance : ContinuousMul Mᵒᵈ :=
‹ContinuousMul M›
@[to_additive]
instance : ContinuousMul (ULift.{u} M) := by
constructor
apply continuous_uliftUp.comp
exact continuous_mul.comp₂ (continuous_uliftDown.comp continuous_fst)
(continuous_uliftDown.comp continuous_snd)
@[to_additive]
instance ContinuousMul.to_continuousSMul : ContinuousSMul M M :=
⟨continuous_mul⟩
@[to_additive]
instance ContinuousMul.to_continuousSMul_op : ContinuousSMul Mᵐᵒᵖ M :=
⟨show Continuous ((fun p : M × M => p.1 * p.2) ∘ Prod.swap ∘ Prod.map MulOpposite.unop id) from
continuous_mul.comp <|
continuous_swap.comp <| Continuous.prodMap MulOpposite.continuous_unop continuous_id⟩
@[to_additive]
theorem ContinuousMul.induced {α : Type*} {β : Type*} {F : Type*} [FunLike F α β] [Mul α]
[Mul β] [MulHomClass F α β] [tβ : TopologicalSpace β] [ContinuousMul β] (f : F) :
@ContinuousMul α (tβ.induced f) _ := by
let tα := tβ.induced f
refine ⟨continuous_induced_rng.2 ?_⟩
simp only [Function.comp_def, map_mul]
fun_prop
@[to_additive (attr := continuity)]
theorem continuous_mul_left (a : M) : Continuous fun b : M => a * b :=
continuous_const.mul continuous_id
@[to_additive (attr := continuity)]
theorem continuous_mul_right (a : M) : Continuous fun b : M => b * a :=
continuous_id.mul continuous_const
@[to_additive]
theorem tendsto_mul {a b : M} : Tendsto (fun p : M × M => p.fst * p.snd) (𝓝 (a, b)) (𝓝 (a * b)) :=
continuous_iff_continuousAt.mp ContinuousMul.continuous_mul (a, b)
@[to_additive]
theorem Filter.Tendsto.const_mul (b : M) {c : M} {f : α → M} {l : Filter α}
(h : Tendsto (fun k : α => f k) l (𝓝 c)) : Tendsto (fun k : α => b * f k) l (𝓝 (b * c)) :=
tendsto_const_nhds.mul h
@[to_additive]
theorem Filter.Tendsto.mul_const (b : M) {c : M} {f : α → M} {l : Filter α}
(h : Tendsto (fun k : α => f k) l (𝓝 c)) : Tendsto (fun k : α => f k * b) l (𝓝 (c * b)) :=
h.mul tendsto_const_nhds
@[to_additive]
theorem le_nhds_mul (a b : M) : 𝓝 a * 𝓝 b ≤ 𝓝 (a * b) := by
rw [← map₂_mul, ← map_uncurry_prod, ← nhds_prod_eq]
exact continuous_mul.tendsto _
@[to_additive (attr := simp)]
theorem nhds_one_mul_nhds {M} [MulOneClass M] [TopologicalSpace M] [ContinuousMul M] (a : M) :
𝓝 (1 : M) * 𝓝 a = 𝓝 a :=
((le_nhds_mul _ _).trans_eq <| congr_arg _ (one_mul a)).antisymm <|
le_mul_of_one_le_left' <| pure_le_nhds 1
@[to_additive (attr := simp)]
theorem nhds_mul_nhds_one {M} [MulOneClass M] [TopologicalSpace M] [ContinuousMul M] (a : M) :
𝓝 a * 𝓝 1 = 𝓝 a :=
((le_nhds_mul _ _).trans_eq <| congr_arg _ (mul_one a)).antisymm <|
le_mul_of_one_le_right' <| pure_le_nhds 1
section tendsto_nhds
variable {𝕜 : Type*} [Preorder 𝕜] [Zero 𝕜] [Mul 𝕜] [TopologicalSpace 𝕜] [ContinuousMul 𝕜]
{l : Filter α} {f : α → 𝕜} {b c : 𝕜} (hb : 0 < b)
include hb
theorem Filter.TendstoNhdsWithinIoi.const_mul [PosMulStrictMono 𝕜] [PosMulReflectLT 𝕜]
(h : Tendsto f l (𝓝[>] c)) : Tendsto (fun a => b * f a) l (𝓝[>] (b * c)) :=
tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _
((tendsto_nhds_of_tendsto_nhdsWithin h).const_mul b) <|
(tendsto_nhdsWithin_iff.mp h).2.mono fun _ => (mul_lt_mul_left hb).mpr
theorem Filter.TendstoNhdsWithinIio.const_mul [PosMulStrictMono 𝕜] [PosMulReflectLT 𝕜]
(h : Tendsto f l (𝓝[<] c)) : Tendsto (fun a => b * f a) l (𝓝[<] (b * c)) :=
tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _
((tendsto_nhds_of_tendsto_nhdsWithin h).const_mul b) <|
(tendsto_nhdsWithin_iff.mp h).2.mono fun _ => (mul_lt_mul_left hb).mpr
theorem Filter.TendstoNhdsWithinIoi.mul_const [MulPosStrictMono 𝕜] [MulPosReflectLT 𝕜]
(h : Tendsto f l (𝓝[>] c)) : Tendsto (fun a => f a * b) l (𝓝[>] (c * b)) :=
tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _
((tendsto_nhds_of_tendsto_nhdsWithin h).mul_const b) <|
(tendsto_nhdsWithin_iff.mp h).2.mono fun _ => (mul_lt_mul_right hb).mpr
theorem Filter.TendstoNhdsWithinIio.mul_const [MulPosStrictMono 𝕜] [MulPosReflectLT 𝕜]
(h : Tendsto f l (𝓝[<] c)) : Tendsto (fun a => f a * b) l (𝓝[<] (c * b)) :=
tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _
((tendsto_nhds_of_tendsto_nhdsWithin h).mul_const b) <|
(tendsto_nhdsWithin_iff.mp h).2.mono fun _ => (mul_lt_mul_right hb).mpr
end tendsto_nhds
@[to_additive]
protected theorem Specializes.mul {a b c d : M} (hab : a ⤳ b) (hcd : c ⤳ d) : (a * c) ⤳ (b * d) :=
hab.smul hcd
@[to_additive]
protected theorem Inseparable.mul {a b c d : M} (hab : Inseparable a b) (hcd : Inseparable c d) :
Inseparable (a * c) (b * d) :=
hab.smul hcd
@[to_additive]
protected theorem Specializes.pow {M : Type*} [Monoid M] [TopologicalSpace M] [ContinuousMul M]
{a b : M} (h : a ⤳ b) (n : ℕ) : (a ^ n) ⤳ (b ^ n) :=
Nat.recOn n (by simp only [pow_zero, specializes_rfl]) fun _ ihn ↦ by
simpa only [pow_succ] using ihn.mul h
@[to_additive]
protected theorem Inseparable.pow {M : Type*} [Monoid M] [TopologicalSpace M] [ContinuousMul M]
{a b : M} (h : Inseparable a b) (n : ℕ) : Inseparable (a ^ n) (b ^ n) :=
(h.specializes.pow n).antisymm (h.specializes'.pow n)
/-- Construct a unit from limits of units and their inverses. -/
@[to_additive (attr := simps)
"Construct an additive unit from limits of additive units and their negatives."]
def Filter.Tendsto.units [TopologicalSpace N] [Monoid N] [ContinuousMul N] [T2Space N]
{f : ι → Nˣ} {r₁ r₂ : N} {l : Filter ι} [l.NeBot] (h₁ : Tendsto (fun x => ↑(f x)) l (𝓝 r₁))
(h₂ : Tendsto (fun x => ↑(f x)⁻¹) l (𝓝 r₂)) : Nˣ where
val := r₁
inv := r₂
val_inv := by
symm
simpa using h₁.mul h₂
inv_val := by
symm
simpa using h₂.mul h₁
@[to_additive]
instance Prod.continuousMul [TopologicalSpace N] [Mul N] [ContinuousMul N] :
ContinuousMul (M × N) :=
⟨by apply Continuous.prodMk <;> fun_prop⟩
@[to_additive]
instance Pi.continuousMul {C : ι → Type*} [∀ i, TopologicalSpace (C i)] [∀ i, Mul (C i)]
[∀ i, ContinuousMul (C i)] : ContinuousMul (∀ i, C i) where
continuous_mul :=
continuous_pi fun i => (continuous_apply i).fst'.mul (continuous_apply i).snd'
/-- A version of `Pi.continuousMul` for non-dependent functions. It is needed because sometimes
Lean 3 fails to use `Pi.continuousMul` for non-dependent functions. -/
@[to_additive "A version of `Pi.continuousAdd` for non-dependent functions. It is needed
because sometimes Lean fails to use `Pi.continuousAdd` for non-dependent functions."]
instance Pi.continuousMul' : ContinuousMul (ι → M) :=
Pi.continuousMul
@[to_additive]
instance (priority := 100) continuousMul_of_discreteTopology [TopologicalSpace N] [Mul N]
[DiscreteTopology N] : ContinuousMul N :=
⟨continuous_of_discreteTopology⟩
open Filter
open Function
@[to_additive]
theorem ContinuousMul.of_nhds_one {M : Type u} [Monoid M] [TopologicalSpace M]
(hmul : Tendsto (uncurry ((· * ·) : M → M → M)) (𝓝 1 ×ˢ 𝓝 1) <| 𝓝 1)
(hleft : ∀ x₀ : M, 𝓝 x₀ = map (fun x => x₀ * x) (𝓝 1))
(hright : ∀ x₀ : M, 𝓝 x₀ = map (fun x => x * x₀) (𝓝 1)) : ContinuousMul M :=
⟨by
rw [continuous_iff_continuousAt]
rintro ⟨x₀, y₀⟩
have key : (fun p : M × M => x₀ * p.1 * (p.2 * y₀)) =
((fun x => x₀ * x) ∘ fun x => x * y₀) ∘ uncurry (· * ·) := by
ext p
simp [uncurry, mul_assoc]
have key₂ : ((fun x => x₀ * x) ∘ fun x => y₀ * x) = fun x => x₀ * y₀ * x := by
ext x
simp [mul_assoc]
calc
map (uncurry (· * ·)) (𝓝 (x₀, y₀)) = map (uncurry (· * ·)) (𝓝 x₀ ×ˢ 𝓝 y₀) := by
rw [nhds_prod_eq]
_ = map (fun p : M × M => x₀ * p.1 * (p.2 * y₀)) (𝓝 1 ×ˢ 𝓝 1) := by
-- Porting note: `rw` was able to prove this
-- Now it fails with `failed to rewrite using equation theorems for 'Function.uncurry'`
-- and `failed to rewrite using equation theorems for 'Function.comp'`.
-- Removing those two lemmas, the `rw` would succeed, but then needs a `rfl`.
simp +unfoldPartialApp only [uncurry]
simp_rw [hleft x₀, hright y₀, prod_map_map_eq, Filter.map_map, Function.comp_def]
_ = map ((fun x => x₀ * x) ∘ fun x => x * y₀) (map (uncurry (· * ·)) (𝓝 1 ×ˢ 𝓝 1)) := by
rw [key, ← Filter.map_map]
_ ≤ map ((fun x : M => x₀ * x) ∘ fun x => x * y₀) (𝓝 1) := map_mono hmul
_ = 𝓝 (x₀ * y₀) := by
rw [← Filter.map_map, ← hright, hleft y₀, Filter.map_map, key₂, ← hleft]⟩
@[to_additive]
theorem continuousMul_of_comm_of_nhds_one (M : Type u) [CommMonoid M] [TopologicalSpace M]
(hmul : Tendsto (uncurry ((· * ·) : M → M → M)) (𝓝 1 ×ˢ 𝓝 1) (𝓝 1))
(hleft : ∀ x₀ : M, 𝓝 x₀ = map (fun x => x₀ * x) (𝓝 1)) : ContinuousMul M := by
apply ContinuousMul.of_nhds_one hmul hleft
intro x₀
simp_rw [mul_comm, hleft x₀]
end ContinuousMul
section PointwiseLimits
variable (M₁ M₂ : Type*) [TopologicalSpace M₂] [T2Space M₂]
@[to_additive]
theorem isClosed_setOf_map_one [One M₁] [One M₂] : IsClosed { f : M₁ → M₂ | f 1 = 1 } :=
isClosed_eq (continuous_apply 1) continuous_const
@[to_additive]
theorem isClosed_setOf_map_mul [Mul M₁] [Mul M₂] [ContinuousMul M₂] :
IsClosed { f : M₁ → M₂ | ∀ x y, f (x * y) = f x * f y } := by
simp only [setOf_forall]
exact isClosed_iInter fun x ↦ isClosed_iInter fun y ↦
isClosed_eq (continuous_apply _) (by fun_prop)
section Semigroup
variable {M₁ M₂} [Mul M₁] [Mul M₂] [ContinuousMul M₂]
{F : Type*} [FunLike F M₁ M₂] [MulHomClass F M₁ M₂] {l : Filter α}
/-- Construct a bundled semigroup homomorphism `M₁ →ₙ* M₂` from a function `f` and a proof that it
belongs to the closure of the range of the coercion from `M₁ →ₙ* M₂` (or another type of bundled
homomorphisms that has a `MulHomClass` instance) to `M₁ → M₂`. -/
@[to_additive (attr := simps -fullyApplied)
"Construct a bundled additive semigroup homomorphism `M₁ →ₙ+ M₂` from a function `f`
and a proof that it belongs to the closure of the range of the coercion from `M₁ →ₙ+ M₂` (or another
type of bundled homomorphisms that has an `AddHomClass` instance) to `M₁ → M₂`."]
def mulHomOfMemClosureRangeCoe (f : M₁ → M₂)
(hf : f ∈ closure (range fun (f : F) (x : M₁) => f x)) : M₁ →ₙ* M₂ where
toFun := f
map_mul' := (isClosed_setOf_map_mul M₁ M₂).closure_subset_iff.2 (range_subset_iff.2 map_mul) hf
/-- Construct a bundled semigroup homomorphism from a pointwise limit of semigroup homomorphisms. -/
@[to_additive (attr := simps! -fullyApplied)
"Construct a bundled additive semigroup homomorphism from a pointwise limit of additive
semigroup homomorphisms"]
def mulHomOfTendsto (f : M₁ → M₂) (g : α → F) [l.NeBot]
(h : Tendsto (fun a x => g a x) l (𝓝 f)) : M₁ →ₙ* M₂ :=
mulHomOfMemClosureRangeCoe f <|
mem_closure_of_tendsto h <| Eventually.of_forall fun _ => mem_range_self _
variable (M₁ M₂)
@[to_additive]
theorem MulHom.isClosed_range_coe : IsClosed (Set.range ((↑) : (M₁ →ₙ* M₂) → M₁ → M₂)) :=
isClosed_of_closure_subset fun f hf => ⟨mulHomOfMemClosureRangeCoe f hf, rfl⟩
end Semigroup
section Monoid
variable {M₁ M₂} [MulOneClass M₁] [MulOneClass M₂] [ContinuousMul M₂]
{F : Type*} [FunLike F M₁ M₂] [MonoidHomClass F M₁ M₂] {l : Filter α}
/-- Construct a bundled monoid homomorphism `M₁ →* M₂` from a function `f` and a proof that it
belongs to the closure of the range of the coercion from `M₁ →* M₂` (or another type of bundled
homomorphisms that has a `MonoidHomClass` instance) to `M₁ → M₂`. -/
@[to_additive (attr := simps -fullyApplied)
"Construct a bundled additive monoid homomorphism `M₁ →+ M₂` from a function `f`
and a proof that it belongs to the closure of the range of the coercion from `M₁ →+ M₂` (or another
type of bundled homomorphisms that has an `AddMonoidHomClass` instance) to `M₁ → M₂`."]
def monoidHomOfMemClosureRangeCoe (f : M₁ → M₂)
(hf : f ∈ closure (range fun (f : F) (x : M₁) => f x)) : M₁ →* M₂ where
toFun := f
map_one' := (isClosed_setOf_map_one M₁ M₂).closure_subset_iff.2 (range_subset_iff.2 map_one) hf
map_mul' := (isClosed_setOf_map_mul M₁ M₂).closure_subset_iff.2 (range_subset_iff.2 map_mul) hf
/-- Construct a bundled monoid homomorphism from a pointwise limit of monoid homomorphisms. -/
@[to_additive (attr := simps! -fullyApplied)
"Construct a bundled additive monoid homomorphism from a pointwise limit of additive
monoid homomorphisms"]
def monoidHomOfTendsto (f : M₁ → M₂) (g : α → F) [l.NeBot]
(h : Tendsto (fun a x => g a x) l (𝓝 f)) : M₁ →* M₂ :=
monoidHomOfMemClosureRangeCoe f <|
mem_closure_of_tendsto h <| Eventually.of_forall fun _ => mem_range_self _
variable (M₁ M₂)
@[to_additive]
theorem MonoidHom.isClosed_range_coe : IsClosed (Set.range ((↑) : (M₁ →* M₂) → M₁ → M₂)) :=
isClosed_of_closure_subset fun f hf => ⟨monoidHomOfMemClosureRangeCoe f hf, rfl⟩
end Monoid
end PointwiseLimits
@[to_additive]
theorem Topology.IsInducing.continuousMul {M N F : Type*} [Mul M] [Mul N] [FunLike F M N]
[MulHomClass F M N] [TopologicalSpace M] [TopologicalSpace N] [ContinuousMul N] (f : F)
(hf : IsInducing f) : ContinuousMul M :=
⟨(hf.continuousSMul hf.continuous (map_mul f _ _)).1⟩
@[deprecated (since := "2024-10-28")] alias Inducing.continuousMul := IsInducing.continuousMul
@[to_additive]
theorem continuousMul_induced {M N F : Type*} [Mul M] [Mul N] [FunLike F M N] [MulHomClass F M N]
[TopologicalSpace N] [ContinuousMul N] (f : F) : @ContinuousMul M (induced f ‹_›) _ :=
letI := induced f ‹_›
IsInducing.continuousMul f ⟨rfl⟩
@[to_additive]
instance Subsemigroup.continuousMul [TopologicalSpace M] [Semigroup M] [ContinuousMul M]
(S : Subsemigroup M) : ContinuousMul S :=
IsInducing.continuousMul ({ toFun := (↑), map_mul' := fun _ _ => rfl} : MulHom S M) ⟨rfl⟩
@[to_additive]
| instance Submonoid.continuousMul [TopologicalSpace M] [Monoid M] [ContinuousMul M]
(S : Submonoid M) : ContinuousMul S :=
S.toSubsemigroup.continuousMul
section MulZeroClass
open Filter
variable {α β : Type*}
variable [TopologicalSpace M] [MulZeroClass M] [ContinuousMul M]
| Mathlib/Topology/Algebra/Monoid.lean | 348 | 357 |
/-
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.Algebra.Group.Nat.Even
import Mathlib.Data.Nat.Cast.Basic
import Mathlib.Data.Nat.Cast.Commute
import Mathlib.Data.Set.Operations
import Mathlib.Logic.Function.Iterate
/-!
# Even and odd elements in rings
This file defines odd elements and proves some general facts about even and odd elements of rings.
As opposed to `Even`, `Odd` does not have a multiplicative counterpart.
## TODO
Try to generalize `Even` lemmas further. For example, there are still a few lemmas whose `Semiring`
assumptions I (DT) am not convinced are necessary. If that turns out to be true, they could be moved
to `Mathlib.Algebra.Group.Even`.
## See also
`Mathlib.Algebra.Group.Even` for the definition of even elements.
-/
assert_not_exists DenselyOrdered OrderedRing
open MulOpposite
variable {F α β : Type*}
section Monoid
variable [Monoid α] [HasDistribNeg α] {n : ℕ} {a : α}
@[simp] lemma Even.neg_pow : Even n → ∀ a : α, (-a) ^ n = a ^ n := by
rintro ⟨c, rfl⟩ a
simp_rw [← two_mul, pow_mul, neg_sq]
lemma Even.neg_one_pow (h : Even n) : (-1 : α) ^ n = 1 := by rw [h.neg_pow, one_pow]
end Monoid
section DivisionMonoid
variable [DivisionMonoid α] [HasDistribNeg α] {a : α} {n : ℤ}
lemma Even.neg_zpow : Even n → ∀ a : α, (-a) ^ n = a ^ n := by
rintro ⟨c, rfl⟩ a; simp_rw [← Int.two_mul, zpow_mul, zpow_two, neg_mul_neg]
lemma Even.neg_one_zpow (h : Even n) : (-1 : α) ^ n = 1 := by rw [h.neg_zpow, one_zpow]
end DivisionMonoid
@[simp] lemma IsSquare.zero [MulZeroClass α] : IsSquare (0 : α) := ⟨0, (mul_zero _).symm⟩
section Semiring
variable [Semiring α] [Semiring β] {a b : α} {m n : ℕ}
lemma even_iff_exists_two_mul : Even a ↔ ∃ b, a = 2 * b := by simp [even_iff_exists_two_nsmul]
lemma even_iff_two_dvd : Even a ↔ 2 ∣ a := by simp [Even, Dvd.dvd, two_mul]
alias ⟨Even.two_dvd, _⟩ := even_iff_two_dvd
lemma Even.trans_dvd (ha : Even a) (hab : a ∣ b) : Even b :=
even_iff_two_dvd.2 <| ha.two_dvd.trans hab
lemma Dvd.dvd.even (hab : a ∣ b) (ha : Even a) : Even b := ha.trans_dvd hab
@[simp] lemma range_two_mul (α) [NonAssocSemiring α] :
Set.range (fun x : α ↦ 2 * x) = {a | Even a} := by
ext x
simp [eq_comm, two_mul, Even]
@[simp] lemma even_two : Even (2 : α) := ⟨1, by rw [one_add_one_eq_two]⟩
@[simp] lemma Even.mul_left (ha : Even a) (b) : Even (b * a) := ha.map (AddMonoidHom.mulLeft _)
@[simp] lemma Even.mul_right (ha : Even a) (b) : Even (a * b) := ha.map (AddMonoidHom.mulRight _)
lemma even_two_mul (a : α) : Even (2 * a) := ⟨a, two_mul _⟩
lemma Even.pow_of_ne_zero (ha : Even a) : ∀ {n : ℕ}, n ≠ 0 → Even (a ^ n)
| n + 1, _ => by rw [pow_succ]; exact ha.mul_left _
/-- An element `a` of a semiring is odd if there exists `k` such `a = 2*k + 1`. -/
def Odd (a : α) : Prop := ∃ k, a = 2 * k + 1
lemma odd_iff_exists_bit1 : Odd a ↔ ∃ b, a = 2 * b + 1 := exists_congr fun b ↦ by rw [two_mul]
alias ⟨Odd.exists_bit1, _⟩ := odd_iff_exists_bit1
@[simp] lemma range_two_mul_add_one (α : Type*) [Semiring α] :
Set.range (fun x : α ↦ 2 * x + 1) = {a | Odd a} := by ext x; simp [Odd, eq_comm]
lemma Even.add_odd : Even a → Odd b → Odd (a + b) := by
rintro ⟨a, rfl⟩ ⟨b, rfl⟩; exact ⟨a + b, by rw [mul_add, ← two_mul, add_assoc]⟩
lemma Even.odd_add (ha : Even a) (hb : Odd b) : Odd (b + a) := add_comm a b ▸ ha.add_odd hb
lemma Odd.add_even (ha : Odd a) (hb : Even b) : Odd (a + b) := add_comm a b ▸ hb.add_odd ha
lemma Odd.add_odd : Odd a → Odd b → Even (a + b) := by
rintro ⟨a, rfl⟩ ⟨b, rfl⟩
refine ⟨a + b + 1, ?_⟩
rw [two_mul, two_mul]
ac_rfl
@[simp] lemma odd_one : Odd (1 : α) :=
⟨0, (zero_add _).symm.trans (congr_arg (· + (1 : α)) (mul_zero _).symm)⟩
@[simp] lemma Even.add_one (h : Even a) : Odd (a + 1) := h.add_odd odd_one
@[simp] lemma Even.one_add (h : Even a) : Odd (1 + a) := h.odd_add odd_one
@[simp] lemma Odd.add_one (h : Odd a) : Even (a + 1) := h.add_odd odd_one
@[simp] lemma Odd.one_add (h : Odd a) : Even (1 + a) := odd_one.add_odd h
lemma odd_two_mul_add_one (a : α) : Odd (2 * a + 1) := ⟨_, rfl⟩
@[simp] lemma odd_add_self_one' : Odd (a + (a + 1)) := by simp [← add_assoc]
@[simp] lemma odd_add_one_self : Odd (a + 1 + a) := by simp [add_comm _ a]
@[simp] lemma odd_add_one_self' : Odd (a + (1 + a)) := by simp [add_comm 1 a]
lemma Odd.map [FunLike F α β] [RingHomClass F α β] (f : F) : Odd a → Odd (f a) := by
rintro ⟨a, rfl⟩; exact ⟨f a, by simp [two_mul]⟩
lemma Odd.natCast {R : Type*} [Semiring R] {n : ℕ} (hn : Odd n) : Odd (n : R) :=
hn.map <| Nat.castRingHom R
@[simp] lemma Odd.mul : Odd a → Odd b → Odd (a * b) := by
rintro ⟨a, rfl⟩ ⟨b, rfl⟩
refine ⟨2 * a * b + b + a, ?_⟩
rw [mul_add, add_mul, mul_one, ← add_assoc, one_mul, mul_assoc, ← mul_add, ← mul_add, ← mul_assoc,
← Nat.cast_two, ← Nat.cast_comm]
lemma Odd.pow (ha : Odd a) : ∀ {n : ℕ}, Odd (a ^ n)
| 0 => by
rw [pow_zero]
exact odd_one
| n + 1 => by rw [pow_succ]; exact ha.pow.mul ha
lemma Odd.pow_add_pow_eq_zero [IsCancelAdd α] (hn : Odd n) (hab : a + b = 0) :
a ^ n + b ^ n = 0 := by
obtain ⟨k, rfl⟩ := hn
induction k with | zero => simpa | succ k ih => ?_
have : a ^ 2 = b ^ 2 := add_right_cancel <|
calc
a ^ 2 + a * b = 0 := by rw [sq, ← mul_add, hab, mul_zero]
_ = b ^ 2 + a * b := by rw [sq, ← add_mul, add_comm, hab, zero_mul]
refine add_right_cancel (b := b ^ (2 * k + 1) * a ^ 2) ?_
calc
_ = (a ^ (2 * k + 1) + b ^ (2 * k + 1)) * a ^ 2 + b ^ (2 * k + 3) := by
rw [add_mul, ← pow_add, add_right_comm]; rfl
_ = _ := by rw [ih, zero_mul, zero_add, zero_add, this, ← pow_add]
end Semiring
section Monoid
variable [Monoid α] [HasDistribNeg α] {n : ℕ}
lemma Odd.neg_pow : Odd n → ∀ a : α, (-a) ^ n = -a ^ n := by
rintro ⟨c, rfl⟩ a; simp_rw [pow_add, pow_mul, neg_sq, pow_one, mul_neg]
@[simp] lemma Odd.neg_one_pow (h : Odd n) : (-1 : α) ^ n = -1 := by rw [h.neg_pow, one_pow]
end Monoid
section Ring
variable [Ring α] {a b : α} {n : ℕ}
lemma even_neg_two : Even (-2 : α) := by simp only [even_neg, even_two]
lemma Odd.neg (hp : Odd a) : Odd (-a) := by
obtain ⟨k, hk⟩ := hp
use -(k + 1)
rw [mul_neg, mul_add, neg_add, add_assoc, two_mul (1 : α), neg_add, neg_add_cancel_right,
← neg_add, hk]
@[simp] lemma odd_neg : Odd (-a) ↔ Odd a := ⟨fun h ↦ neg_neg a ▸ h.neg, Odd.neg⟩
lemma odd_neg_one : Odd (-1 : α) := by simp
lemma Odd.sub_even (ha : Odd a) (hb : Even b) : Odd (a - b) := by
rw [sub_eq_add_neg]; exact ha.add_even hb.neg
lemma Even.sub_odd (ha : Even a) (hb : Odd b) : Odd (a - b) := by
rw [sub_eq_add_neg]; exact ha.add_odd hb.neg
lemma Odd.sub_odd (ha : Odd a) (hb : Odd b) : Even (a - b) := by
rw [sub_eq_add_neg]; exact ha.add_odd hb.neg
end Ring
namespace Nat
variable {m n : ℕ}
lemma odd_iff : Odd n ↔ n % 2 = 1 :=
⟨fun ⟨m, hm⟩ ↦ by omega, fun h ↦ ⟨n / 2, (mod_add_div n 2).symm.trans (by rw [h, add_comm])⟩⟩
instance : DecidablePred (Odd : ℕ → Prop) := fun _ ↦ decidable_of_iff _ odd_iff.symm
lemma not_odd_iff : ¬Odd n ↔ n % 2 = 0 := by rw [odd_iff, mod_two_not_eq_one]
@[simp] lemma not_odd_iff_even : ¬Odd n ↔ Even n := by rw [not_odd_iff, even_iff]
@[simp] lemma not_even_iff_odd : ¬Even n ↔ Odd n := by rw [not_even_iff, odd_iff]
@[simp] lemma not_odd_zero : ¬Odd 0 := not_odd_iff.mpr rfl
lemma _root_.Odd.not_two_dvd_nat (h : Odd n) : ¬(2 ∣ n) := by
rwa [← even_iff_two_dvd, not_even_iff_odd]
lemma even_xor_odd (n : ℕ) : Xor' (Even n) (Odd n) := by
simp [Xor', ← not_even_iff_odd, Decidable.em (Even n)]
lemma even_or_odd (n : ℕ) : Even n ∨ Odd n := (even_xor_odd n).or
lemma even_or_odd' (n : ℕ) : ∃ k, n = 2 * k ∨ n = 2 * k + 1 := by
simpa only [← two_mul, exists_or, Odd, Even] using even_or_odd n
lemma even_xor_odd' (n : ℕ) : ∃ k, Xor' (n = 2 * k) (n = 2 * k + 1) := by
obtain ⟨k, rfl⟩ | ⟨k, rfl⟩ := even_or_odd n <;> use k
· simpa only [← two_mul, eq_self_iff_true, xor_true] using (succ_ne_self (2 * k)).symm
· simpa only [xor_true, xor_comm] using (succ_ne_self _)
lemma odd_add_one {n : ℕ} : Odd (n + 1) ↔ ¬ Odd n := by
rw [← not_even_iff_odd, Nat.even_add_one, not_even_iff_odd]
lemma mod_two_add_add_odd_mod_two (m : ℕ) {n : ℕ} (hn : Odd n) : m % 2 + (m + n) % 2 = 1 :=
((even_or_odd m).elim fun hm ↦ by rw [even_iff.1 hm, odd_iff.1 (hm.add_odd hn)]) fun hm ↦ by
rw [odd_iff.1 hm, even_iff.1 (hm.add_odd hn)]
@[simp] lemma mod_two_add_succ_mod_two (m : ℕ) : m % 2 + (m + 1) % 2 = 1 :=
mod_two_add_add_odd_mod_two m odd_one
@[simp] lemma succ_mod_two_add_mod_two (m : ℕ) : (m + 1) % 2 + m % 2 = 1 := by
rw [add_comm, mod_two_add_succ_mod_two]
lemma even_add' : Even (m + n) ↔ (Odd m ↔ Odd n) := by
rw [even_add, ← not_odd_iff_even, ← not_odd_iff_even, not_iff_not]
@[simp] lemma not_even_bit1 (n : ℕ) : ¬Even (2 * n + 1) := by simp [parity_simps]
lemma not_even_two_mul_add_one (n : ℕ) : ¬ Even (2 * n + 1) :=
not_even_iff_odd.2 <| odd_two_mul_add_one n
lemma even_sub' (h : n ≤ m) : Even (m - n) ↔ (Odd m ↔ Odd n) := by
rw [even_sub h, ← not_odd_iff_even, ← not_odd_iff_even, not_iff_not]
lemma Odd.sub_odd (hm : Odd m) (hn : Odd n) : Even (m - n) :=
(le_total n m).elim (fun h ↦ by simp only [even_sub' h, *]) fun h ↦ by
simp only [Nat.sub_eq_zero_iff_le.2 h, Even.zero]
alias _root_.Odd.tsub_odd := Nat.Odd.sub_odd
| lemma odd_mul : Odd (m * n) ↔ Odd m ∧ Odd n := by simp [not_or, even_mul, ← not_even_iff_odd]
| Mathlib/Algebra/Ring/Parity.lean | 256 | 257 |
/-
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.Polynomial.AlgebraMap
import Mathlib.RingTheory.IsTensorProduct
/-!
# Base change of polynomial algebras
Given `[CommSemiring R] [Semiring A] [Algebra R A]` we show `A[X] ≃ₐ[R] (A ⊗[R] R[X])`.
-/
-- This file should not become entangled with `RingTheory/MatrixAlgebra`.
assert_not_exists Matrix
universe u v w
open Polynomial TensorProduct
open Algebra.TensorProduct (algHomOfLinearMapTensorProduct includeLeft)
noncomputable section
variable (R A : Type*)
variable [CommSemiring R]
variable [Semiring A] [Algebra R A]
namespace PolyEquivTensor
/-- (Implementation detail).
The function underlying `A ⊗[R] R[X] →ₐ[R] A[X]`,
as a bilinear function of two arguments.
-/
def toFunBilinear : A →ₗ[A] R[X] →ₗ[R] A[X] :=
LinearMap.toSpanSingleton A _ (aeval (Polynomial.X : A[X])).toLinearMap
theorem toFunBilinear_apply_apply (a : A) (p : R[X]) :
toFunBilinear R A a p = a • (aeval X) p := rfl
@[simp] theorem toFunBilinear_apply_eq_smul (a : A) (p : R[X]) :
toFunBilinear R A a p = a • p.map (algebraMap R A) := rfl
theorem toFunBilinear_apply_eq_sum (a : A) (p : R[X]) :
toFunBilinear R A a p = p.sum fun n r ↦ monomial n (a * algebraMap R A r) := by
conv_lhs => rw [toFunBilinear_apply_eq_smul, ← p.sum_monomial_eq, sum, Polynomial.map_sum]
simp [Finset.smul_sum, sum, ← smul_eq_mul]
/-- (Implementation detail).
The function underlying `A ⊗[R] R[X] →ₐ[R] A[X]`,
as a linear map.
-/
def toFunLinear : A ⊗[R] R[X] →ₗ[R] A[X] :=
TensorProduct.lift (toFunBilinear R A)
@[simp]
theorem toFunLinear_tmul_apply (a : A) (p : R[X]) :
toFunLinear R A (a ⊗ₜ[R] p) = toFunBilinear R A a p :=
rfl
-- We apparently need to provide the decidable instance here
-- in order to successfully rewrite by this lemma.
theorem toFunLinear_mul_tmul_mul_aux_1 (p : R[X]) (k : ℕ) (h : Decidable ¬p.coeff k = 0) (a : A) :
ite (¬coeff p k = 0) (a * (algebraMap R A) (coeff p k)) 0 =
a * (algebraMap R A) (coeff p k) := by classical split_ifs <;> simp [*]
theorem toFunLinear_mul_tmul_mul_aux_2 (k : ℕ) (a₁ a₂ : A) (p₁ p₂ : R[X]) :
a₁ * a₂ * (algebraMap R A) ((p₁ * p₂).coeff k) =
(Finset.antidiagonal k).sum fun x =>
a₁ * (algebraMap R A) (coeff p₁ x.1) * (a₂ * (algebraMap R A) (coeff p₂ x.2)) := by
simp_rw [mul_assoc, Algebra.commutes, ← Finset.mul_sum, mul_assoc, ← Finset.mul_sum]
congr
simp_rw [Algebra.commutes (coeff p₂ _), coeff_mul, map_sum, RingHom.map_mul]
theorem toFunLinear_mul_tmul_mul (a₁ a₂ : A) (p₁ p₂ : R[X]) :
(toFunLinear R A) ((a₁ * a₂) ⊗ₜ[R] (p₁ * p₂)) =
(toFunLinear R A) (a₁ ⊗ₜ[R] p₁) * (toFunLinear R A) (a₂ ⊗ₜ[R] p₂) := by
classical
simp only [toFunLinear_tmul_apply, toFunBilinear_apply_eq_sum]
ext k
simp_rw [coeff_sum, coeff_monomial, sum_def, Finset.sum_ite_eq', mem_support_iff, Ne]
conv_rhs => rw [coeff_mul]
simp_rw [finset_sum_coeff, coeff_monomial, Finset.sum_ite_eq', mem_support_iff, Ne, mul_ite,
mul_zero, ite_mul, zero_mul]
simp_rw [← ite_zero_mul (¬coeff p₁ _ = 0) (a₁ * (algebraMap R A) (coeff p₁ _))]
simp_rw [← mul_ite_zero (¬coeff p₂ _ = 0) _ (_ * _)]
simp_rw [toFunLinear_mul_tmul_mul_aux_1, toFunLinear_mul_tmul_mul_aux_2]
theorem toFunLinear_one_tmul_one :
toFunLinear R A (1 ⊗ₜ[R] 1) = 1 := by
rw [toFunLinear_tmul_apply, toFunBilinear_apply_apply, Polynomial.aeval_one, one_smul]
/-- (Implementation detail).
The algebra homomorphism `A ⊗[R] R[X] →ₐ[R] A[X]`.
-/
def toFunAlgHom : A ⊗[R] R[X] →ₐ[R] A[X] :=
algHomOfLinearMapTensorProduct (toFunLinear R A) (toFunLinear_mul_tmul_mul R A)
(toFunLinear_one_tmul_one R A)
@[simp] theorem toFunAlgHom_apply_tmul_eq_smul (a : A) (p : R[X]) :
toFunAlgHom R A (a ⊗ₜ[R] p) = a • p.map (algebraMap R A) := rfl
theorem toFunAlgHom_apply_tmul (a : A) (p : R[X]) :
toFunAlgHom R A (a ⊗ₜ[R] p) = p.sum fun n r => monomial n (a * (algebraMap R A) r) :=
toFunBilinear_apply_eq_sum R A _ _
/-- (Implementation detail.)
The bare function `A[X] → A ⊗[R] R[X]`.
(We don't need to show that it's an algebra map, thankfully --- just that it's an inverse.)
-/
def invFun (p : A[X]) : A ⊗[R] R[X] :=
p.eval₂ (includeLeft : A →ₐ[R] A ⊗[R] R[X]) ((1 : A) ⊗ₜ[R] (X : R[X]))
@[simp]
theorem invFun_add {p q} : invFun R A (p + q) = invFun R A p + invFun R A q := by
simp only [invFun, eval₂_add]
theorem invFun_monomial (n : ℕ) (a : A) :
invFun R A (monomial n a) = (a ⊗ₜ[R] 1) * 1 ⊗ₜ[R] X ^ n :=
eval₂_monomial _ _
theorem left_inv (x : A ⊗ R[X]) : invFun R A ((toFunAlgHom R A) x) = x := by
refine TensorProduct.induction_on x ?_ ?_ ?_
· simp [invFun]
· intro a p
dsimp only [invFun]
rw [toFunAlgHom_apply_tmul, eval₂_sum]
simp_rw [eval₂_monomial, AlgHom.coe_toRingHom, Algebra.TensorProduct.tmul_pow, one_pow,
Algebra.TensorProduct.includeLeft_apply, Algebra.TensorProduct.tmul_mul_tmul, mul_one,
one_mul, ← Algebra.commutes, ← Algebra.smul_def, smul_tmul, sum_def, ← tmul_sum]
conv_rhs => rw [← sum_C_mul_X_pow_eq p]
simp only [Algebra.smul_def]
rfl
· intro p q hp hq
simp only [map_add, invFun_add, hp, hq]
theorem right_inv (x : A[X]) : (toFunAlgHom R A) (invFun R A x) = x := by
refine Polynomial.induction_on' x ?_ ?_
· intro p q hp hq
simp only [invFun_add, map_add, hp, hq]
· intro n a
rw [invFun_monomial, Algebra.TensorProduct.tmul_pow,
one_pow, Algebra.TensorProduct.tmul_mul_tmul, mul_one, one_mul, toFunAlgHom_apply_tmul,
X_pow_eq_monomial, sum_monomial_index] <;>
simp
/-- (Implementation detail)
The equivalence, ignoring the algebra structure, `(A ⊗[R] R[X]) ≃ A[X]`.
-/
def equiv : A ⊗[R] R[X] ≃ A[X] where
toFun := toFunAlgHom R A
invFun := invFun R A
left_inv := left_inv R A
right_inv := right_inv R A
end PolyEquivTensor
open PolyEquivTensor
/-- The `R`-algebra isomorphism `A[X] ≃ₐ[R] (A ⊗[R] R[X])`.
-/
def polyEquivTensor : A[X] ≃ₐ[R] A ⊗[R] R[X] :=
AlgEquiv.symm { PolyEquivTensor.toFunAlgHom R A, PolyEquivTensor.equiv R A with }
@[simp]
theorem polyEquivTensor_apply (p : A[X]) :
polyEquivTensor R A p =
p.eval₂ (includeLeft : A →ₐ[R] A ⊗[R] R[X]) ((1 : A) ⊗ₜ[R] (X : R[X])) :=
rfl
@[simp]
theorem polyEquivTensor_symm_apply_tmul_eq_smul (a : A) (p : R[X]) :
(polyEquivTensor R A).symm (a ⊗ₜ p) = a • p.map (algebraMap R A) := rfl
theorem polyEquivTensor_symm_apply_tmul (a : A) (p : R[X]) :
(polyEquivTensor R A).symm (a ⊗ₜ p) = p.sum fun n r => monomial n (a * algebraMap R A r) :=
toFunAlgHom_apply_tmul _ _ _ _
section
variable (A : Type*) [CommSemiring A] [Algebra R A]
/-- The `A`-algebra isomorphism `A[X] ≃ₐ[A] A ⊗[R] R[X]` (when `A` is commutative). -/
def polyEquivTensor' : A[X] ≃ₐ[A] A ⊗[R] R[X] where
__ := polyEquivTensor R A
commutes' a := by simp
/-- `polyEquivTensor' R A` is the same as `polyEquivTensor R A` as a function. -/
@[simp] theorem coe_polyEquivTensor' : ⇑(polyEquivTensor' R A) = polyEquivTensor R A := rfl
@[simp] theorem coe_polyEquivTensor'_symm :
⇑(polyEquivTensor' R A).symm = (polyEquivTensor R A).symm := rfl
end
/-- If `A` is an `R`-algebra, then `A[X]` is an `R[X]` algebra.
This gives a diamond for `Algebra R[X] R[X][X]`, so this is not a global instance. -/
@[reducible] def Polynomial.algebra : Algebra R[X] A[X] :=
(mapRingHom (algebraMap R A)).toAlgebra' fun _ _ ↦ by
ext; rw [coeff_mul, ← Finset.Nat.sum_antidiagonal_swap, coeff_mul]; simp [Algebra.commutes]
attribute [local instance] Polynomial.algebra
@[simp]
theorem Polynomial.algebraMap_def : algebraMap R[X] A[X] = mapRingHom (algebraMap R A) := rfl
instance : IsScalarTower R R[X] A[X] := .of_algebraMap_eq' (mapRingHom_comp_C _).symm
instance [FaithfulSMul R A] : FaithfulSMul R[X] A[X] :=
(faithfulSMul_iff_algebraMap_injective ..).mpr
(map_injective _ <| FaithfulSMul.algebraMap_injective ..)
variable {S : Type*} [CommSemiring S] [Algebra R S]
instance : Algebra.IsPushout R S R[X] S[X] where
out := .of_equiv (polyEquivTensor' R S).symm fun _ ↦
(polyEquivTensor_symm_apply_tmul_eq_smul ..).trans <| one_smul ..
instance : Algebra.IsPushout R R[X] S S[X] := .symm inferInstance
| Mathlib/RingTheory/PolynomialAlgebra.lean | 225 | 226 | |
/-
Copyright (c) 2018 Patrick Massot. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Patrick Massot, Johannes Hölzl, Yaël Dillies
-/
import Mathlib.Analysis.Normed.Group.Seminorm
import Mathlib.Data.NNReal.Basic
import Mathlib.Topology.Algebra.Support
import Mathlib.Topology.MetricSpace.Basic
import Mathlib.Topology.Order.Real
/-!
# Normed (semi)groups
In this file we define 10 classes:
* `Norm`, `NNNorm`: auxiliary classes endowing a type `α` with a function `norm : α → ℝ`
(notation: `‖x‖`) and `nnnorm : α → ℝ≥0` (notation: `‖x‖₊`), respectively;
* `Seminormed...Group`: A seminormed (additive) (commutative) group is an (additive) (commutative)
group with a norm and a compatible pseudometric space structure:
`∀ x y, dist x y = ‖x / y‖` or `∀ x y, dist x y = ‖x - y‖`, depending on the group operation.
* `Normed...Group`: A normed (additive) (commutative) group is an (additive) (commutative) group
with a norm and a compatible metric space structure.
We also prove basic properties of (semi)normed groups and provide some instances.
## Notes
The current convention `dist x y = ‖x - y‖` means that the distance is invariant under right
addition, but actions in mathlib are usually from the left. This means we might want to change it to
`dist x y = ‖-x + y‖`.
The normed group hierarchy would lend itself well to a mixin design (that is, having
`SeminormedGroup` and `SeminormedAddGroup` not extend `Group` and `AddGroup`), but we choose not
to for performance concerns.
## Tags
normed group
-/
variable {𝓕 α ι κ E F G : Type*}
open Filter Function Metric Bornology
open ENNReal Filter NNReal Uniformity Pointwise Topology
/-- Auxiliary class, endowing a type `E` with a function `norm : E → ℝ` with notation `‖x‖`. This
class is designed to be extended in more interesting classes specifying the properties of the norm.
-/
@[notation_class]
class Norm (E : Type*) where
/-- the `ℝ`-valued norm function. -/
norm : E → ℝ
/-- Auxiliary class, endowing a type `α` with a function `nnnorm : α → ℝ≥0` with notation `‖x‖₊`. -/
@[notation_class]
class NNNorm (E : Type*) where
/-- the `ℝ≥0`-valued norm function. -/
nnnorm : E → ℝ≥0
/-- Auxiliary class, endowing a type `α` with a function `enorm : α → ℝ≥0∞` with notation `‖x‖ₑ`. -/
@[notation_class]
class ENorm (E : Type*) where
/-- the `ℝ≥0∞`-valued norm function. -/
enorm : E → ℝ≥0∞
export Norm (norm)
export NNNorm (nnnorm)
export ENorm (enorm)
@[inherit_doc] notation "‖" e "‖" => norm e
@[inherit_doc] notation "‖" e "‖₊" => nnnorm e
@[inherit_doc] notation "‖" e "‖ₑ" => enorm e
section ENorm
variable {E : Type*} [NNNorm E] {x : E} {r : ℝ≥0}
instance NNNorm.toENorm : ENorm E where enorm := (‖·‖₊ : E → ℝ≥0∞)
lemma enorm_eq_nnnorm (x : E) : ‖x‖ₑ = ‖x‖₊ := rfl
@[simp] lemma toNNReal_enorm (x : E) : ‖x‖ₑ.toNNReal = ‖x‖₊ := rfl
@[simp, norm_cast] lemma coe_le_enorm : r ≤ ‖x‖ₑ ↔ r ≤ ‖x‖₊ := by simp [enorm]
@[simp, norm_cast] lemma enorm_le_coe : ‖x‖ₑ ≤ r ↔ ‖x‖₊ ≤ r := by simp [enorm]
@[simp, norm_cast] lemma coe_lt_enorm : r < ‖x‖ₑ ↔ r < ‖x‖₊ := by simp [enorm]
@[simp, norm_cast] lemma enorm_lt_coe : ‖x‖ₑ < r ↔ ‖x‖₊ < r := by simp [enorm]
@[simp] lemma enorm_ne_top : ‖x‖ₑ ≠ ∞ := by simp [enorm]
@[simp] lemma enorm_lt_top : ‖x‖ₑ < ∞ := by simp [enorm]
end ENorm
/-- A type `E` equipped with a continuous map `‖·‖ₑ : E → ℝ≥0∞`
NB. We do not demand that the topology is somehow defined by the enorm:
for ℝ≥0∞ (the motivating example behind this definition), this is not true. -/
class ContinuousENorm (E : Type*) [TopologicalSpace E] extends ENorm E where
continuous_enorm : Continuous enorm
/-- An enormed monoid is an additive monoid endowed with a continuous enorm. -/
class ENormedAddMonoid (E : Type*) [TopologicalSpace E] extends ContinuousENorm E, AddMonoid E where
enorm_eq_zero : ∀ x : E, ‖x‖ₑ = 0 ↔ x = 0
protected enorm_add_le : ∀ x y : E, ‖x + y‖ₑ ≤ ‖x‖ₑ + ‖y‖ₑ
/-- An enormed monoid is a monoid endowed with a continuous enorm. -/
@[to_additive]
class ENormedMonoid (E : Type*) [TopologicalSpace E] extends ContinuousENorm E, Monoid E where
enorm_eq_zero : ∀ x : E, ‖x‖ₑ = 0 ↔ x = 1
enorm_mul_le : ∀ x y : E, ‖x * y‖ₑ ≤ ‖x‖ₑ + ‖y‖ₑ
/-- An enormed commutative monoid is an additive commutative monoid
endowed with a continuous enorm.
We don't have `ENormedAddCommMonoid` extend `EMetricSpace`, since the canonical instance `ℝ≥0∞`
is not an `EMetricSpace`. This is because `ℝ≥0∞` carries the order topology, which is distinct from
the topology coming from `edist`. -/
class ENormedAddCommMonoid (E : Type*) [TopologicalSpace E]
extends ENormedAddMonoid E, AddCommMonoid E where
/-- An enormed commutative monoid is a commutative monoid endowed with a continuous enorm. -/
@[to_additive]
class ENormedCommMonoid (E : Type*) [TopologicalSpace E] extends ENormedMonoid E, CommMonoid E where
/-- A seminormed group is an additive group endowed with a norm for which `dist x y = ‖x - y‖`
defines a pseudometric space structure. -/
class SeminormedAddGroup (E : Type*) extends Norm E, AddGroup E, PseudoMetricSpace E where
dist := fun x y => ‖x - y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x - y‖ := by aesop
/-- A seminormed group is a group endowed with a norm for which `dist x y = ‖x / y‖` defines a
pseudometric space structure. -/
@[to_additive]
class SeminormedGroup (E : Type*) extends Norm E, Group E, PseudoMetricSpace E where
dist := fun x y => ‖x / y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x / y‖ := by aesop
/-- A normed group is an additive group endowed with a norm for which `dist x y = ‖x - y‖` defines a
metric space structure. -/
class NormedAddGroup (E : Type*) extends Norm E, AddGroup E, MetricSpace E where
dist := fun x y => ‖x - y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x - y‖ := by aesop
/-- A normed group is a group endowed with a norm for which `dist x y = ‖x / y‖` defines a metric
space structure. -/
@[to_additive]
class NormedGroup (E : Type*) extends Norm E, Group E, MetricSpace E where
dist := fun x y => ‖x / y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x / y‖ := by aesop
/-- A seminormed group is an additive group endowed with a norm for which `dist x y = ‖x - y‖`
defines a pseudometric space structure. -/
class SeminormedAddCommGroup (E : Type*) extends Norm E, AddCommGroup E,
PseudoMetricSpace E where
dist := fun x y => ‖x - y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x - y‖ := by aesop
/-- A seminormed group is a group endowed with a norm for which `dist x y = ‖x / y‖`
defines a pseudometric space structure. -/
@[to_additive]
class SeminormedCommGroup (E : Type*) extends Norm E, CommGroup E, PseudoMetricSpace E where
dist := fun x y => ‖x / y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x / y‖ := by aesop
/-- A normed group is an additive group endowed with a norm for which `dist x y = ‖x - y‖` defines a
metric space structure. -/
class NormedAddCommGroup (E : Type*) extends Norm E, AddCommGroup E, MetricSpace E where
dist := fun x y => ‖x - y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x - y‖ := by aesop
/-- A normed group is a group endowed with a norm for which `dist x y = ‖x / y‖` defines a metric
space structure. -/
@[to_additive]
class NormedCommGroup (E : Type*) extends Norm E, CommGroup E, MetricSpace E where
dist := fun x y => ‖x / y‖
/-- The distance function is induced by the norm. -/
dist_eq : ∀ x y, dist x y = ‖x / y‖ := by aesop
-- See note [lower instance priority]
@[to_additive]
instance (priority := 100) NormedGroup.toSeminormedGroup [NormedGroup E] : SeminormedGroup E :=
{ ‹NormedGroup E› with }
-- See note [lower instance priority]
@[to_additive]
instance (priority := 100) NormedCommGroup.toSeminormedCommGroup [NormedCommGroup E] :
SeminormedCommGroup E :=
{ ‹NormedCommGroup E› with }
-- See note [lower instance priority]
@[to_additive]
instance (priority := 100) SeminormedCommGroup.toSeminormedGroup [SeminormedCommGroup E] :
SeminormedGroup E :=
{ ‹SeminormedCommGroup E› with }
-- See note [lower instance priority]
@[to_additive]
instance (priority := 100) NormedCommGroup.toNormedGroup [NormedCommGroup E] : NormedGroup E :=
{ ‹NormedCommGroup E› with }
-- See note [reducible non-instances]
/-- Construct a `NormedGroup` from a `SeminormedGroup` satisfying `∀ x, ‖x‖ = 0 → x = 1`. This
avoids having to go back to the `(Pseudo)MetricSpace` level when declaring a `NormedGroup`
instance as a special case of a more general `SeminormedGroup` instance. -/
@[to_additive "Construct a `NormedAddGroup` from a `SeminormedAddGroup`
satisfying `∀ x, ‖x‖ = 0 → x = 0`. This avoids having to go back to the `(Pseudo)MetricSpace`
level when declaring a `NormedAddGroup` instance as a special case of a more general
`SeminormedAddGroup` instance."]
abbrev NormedGroup.ofSeparation [SeminormedGroup E] (h : ∀ x : E, ‖x‖ = 0 → x = 1) :
NormedGroup E where
dist_eq := ‹SeminormedGroup E›.dist_eq
toMetricSpace :=
{ eq_of_dist_eq_zero := fun hxy =>
div_eq_one.1 <| h _ <| (‹SeminormedGroup E›.dist_eq _ _).symm.trans hxy }
-- See note [reducible non-instances]
/-- Construct a `NormedCommGroup` from a `SeminormedCommGroup` satisfying
`∀ x, ‖x‖ = 0 → x = 1`. This avoids having to go back to the `(Pseudo)MetricSpace` level when
declaring a `NormedCommGroup` instance as a special case of a more general `SeminormedCommGroup`
instance. -/
@[to_additive "Construct a `NormedAddCommGroup` from a
`SeminormedAddCommGroup` satisfying `∀ x, ‖x‖ = 0 → x = 0`. This avoids having to go back to the
`(Pseudo)MetricSpace` level when declaring a `NormedAddCommGroup` instance as a special case
of a more general `SeminormedAddCommGroup` instance."]
abbrev NormedCommGroup.ofSeparation [SeminormedCommGroup E] (h : ∀ x : E, ‖x‖ = 0 → x = 1) :
NormedCommGroup E :=
{ ‹SeminormedCommGroup E›, NormedGroup.ofSeparation h with }
-- See note [reducible non-instances]
/-- Construct a seminormed group from a multiplication-invariant distance. -/
@[to_additive
"Construct a seminormed group from a translation-invariant distance."]
abbrev SeminormedGroup.ofMulDist [Norm E] [Group E] [PseudoMetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist x y ≤ dist (x * z) (y * z)) :
SeminormedGroup E where
dist_eq x y := by
rw [h₁]; apply le_antisymm
· simpa only [div_eq_mul_inv, ← mul_inv_cancel y] using h₂ _ _ _
· simpa only [div_mul_cancel, one_mul] using h₂ (x / y) 1 y
-- See note [reducible non-instances]
/-- Construct a seminormed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a seminormed group from a translation-invariant pseudodistance."]
abbrev SeminormedGroup.ofMulDist' [Norm E] [Group E] [PseudoMetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist (x * z) (y * z) ≤ dist x y) :
SeminormedGroup E where
dist_eq x y := by
rw [h₁]; apply le_antisymm
· simpa only [div_mul_cancel, one_mul] using h₂ (x / y) 1 y
· simpa only [div_eq_mul_inv, ← mul_inv_cancel y] using h₂ _ _ _
-- See note [reducible non-instances]
/-- Construct a seminormed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a seminormed group from a translation-invariant pseudodistance."]
abbrev SeminormedCommGroup.ofMulDist [Norm E] [CommGroup E] [PseudoMetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist x y ≤ dist (x * z) (y * z)) :
SeminormedCommGroup E :=
{ SeminormedGroup.ofMulDist h₁ h₂ with
mul_comm := mul_comm }
-- See note [reducible non-instances]
/-- Construct a seminormed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a seminormed group from a translation-invariant pseudodistance."]
abbrev SeminormedCommGroup.ofMulDist' [Norm E] [CommGroup E] [PseudoMetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist (x * z) (y * z) ≤ dist x y) :
SeminormedCommGroup E :=
{ SeminormedGroup.ofMulDist' h₁ h₂ with
mul_comm := mul_comm }
-- See note [reducible non-instances]
/-- Construct a normed group from a multiplication-invariant distance. -/
@[to_additive
"Construct a normed group from a translation-invariant distance."]
abbrev NormedGroup.ofMulDist [Norm E] [Group E] [MetricSpace E] (h₁ : ∀ x : E, ‖x‖ = dist x 1)
(h₂ : ∀ x y z : E, dist x y ≤ dist (x * z) (y * z)) : NormedGroup E :=
{ SeminormedGroup.ofMulDist h₁ h₂ with
eq_of_dist_eq_zero := eq_of_dist_eq_zero }
-- See note [reducible non-instances]
/-- Construct a normed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a normed group from a translation-invariant pseudodistance."]
abbrev NormedGroup.ofMulDist' [Norm E] [Group E] [MetricSpace E] (h₁ : ∀ x : E, ‖x‖ = dist x 1)
(h₂ : ∀ x y z : E, dist (x * z) (y * z) ≤ dist x y) : NormedGroup E :=
{ SeminormedGroup.ofMulDist' h₁ h₂ with
eq_of_dist_eq_zero := eq_of_dist_eq_zero }
-- See note [reducible non-instances]
/-- Construct a normed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a normed group from a translation-invariant pseudodistance."]
abbrev NormedCommGroup.ofMulDist [Norm E] [CommGroup E] [MetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist x y ≤ dist (x * z) (y * z)) :
NormedCommGroup E :=
{ NormedGroup.ofMulDist h₁ h₂ with
mul_comm := mul_comm }
-- See note [reducible non-instances]
/-- Construct a normed group from a multiplication-invariant pseudodistance. -/
@[to_additive
"Construct a normed group from a translation-invariant pseudodistance."]
abbrev NormedCommGroup.ofMulDist' [Norm E] [CommGroup E] [MetricSpace E]
(h₁ : ∀ x : E, ‖x‖ = dist x 1) (h₂ : ∀ x y z : E, dist (x * z) (y * z) ≤ dist x y) :
NormedCommGroup E :=
{ NormedGroup.ofMulDist' h₁ h₂ with
mul_comm := mul_comm }
-- See note [reducible non-instances]
/-- Construct a seminormed group from a seminorm, i.e., registering the pseudodistance and the
pseudometric space structure from the seminorm properties. Note that in most cases this instance
creates bad definitional equalities (e.g., it does not take into account a possibly existing
`UniformSpace` instance on `E`). -/
@[to_additive
"Construct a seminormed group from a seminorm, i.e., registering the pseudodistance
and the pseudometric space structure from the seminorm properties. Note that in most cases this
instance creates bad definitional equalities (e.g., it does not take into account a possibly
existing `UniformSpace` instance on `E`)."]
abbrev GroupSeminorm.toSeminormedGroup [Group E] (f : GroupSeminorm E) : SeminormedGroup E where
dist x y := f (x / y)
norm := f
dist_eq _ _ := rfl
dist_self x := by simp only [div_self', map_one_eq_zero]
dist_triangle := le_map_div_add_map_div f
dist_comm := map_div_rev f
-- See note [reducible non-instances]
/-- Construct a seminormed group from a seminorm, i.e., registering the pseudodistance and the
pseudometric space structure from the seminorm properties. Note that in most cases this instance
creates bad definitional equalities (e.g., it does not take into account a possibly existing
`UniformSpace` instance on `E`). -/
@[to_additive
"Construct a seminormed group from a seminorm, i.e., registering the pseudodistance
and the pseudometric space structure from the seminorm properties. Note that in most cases this
instance creates bad definitional equalities (e.g., it does not take into account a possibly
existing `UniformSpace` instance on `E`)."]
abbrev GroupSeminorm.toSeminormedCommGroup [CommGroup E] (f : GroupSeminorm E) :
SeminormedCommGroup E :=
{ f.toSeminormedGroup with
mul_comm := mul_comm }
-- See note [reducible non-instances]
/-- Construct a normed group from a norm, i.e., registering the distance and the metric space
structure from the norm properties. Note that in most cases this instance creates bad definitional
equalities (e.g., it does not take into account a possibly existing `UniformSpace` instance on
`E`). -/
@[to_additive
"Construct a normed group from a norm, i.e., registering the distance and the metric
space structure from the norm properties. Note that in most cases this instance creates bad
definitional equalities (e.g., it does not take into account a possibly existing `UniformSpace`
instance on `E`)."]
abbrev GroupNorm.toNormedGroup [Group E] (f : GroupNorm E) : NormedGroup E :=
{ f.toGroupSeminorm.toSeminormedGroup with
eq_of_dist_eq_zero := fun h => div_eq_one.1 <| eq_one_of_map_eq_zero f h }
-- See note [reducible non-instances]
/-- Construct a normed group from a norm, i.e., registering the distance and the metric space
structure from the norm properties. Note that in most cases this instance creates bad definitional
equalities (e.g., it does not take into account a possibly existing `UniformSpace` instance on
`E`). -/
@[to_additive
"Construct a normed group from a norm, i.e., registering the distance and the metric
space structure from the norm properties. Note that in most cases this instance creates bad
definitional equalities (e.g., it does not take into account a possibly existing `UniformSpace`
instance on `E`)."]
abbrev GroupNorm.toNormedCommGroup [CommGroup E] (f : GroupNorm E) : NormedCommGroup E :=
{ f.toNormedGroup with
mul_comm := mul_comm }
section SeminormedGroup
variable [SeminormedGroup E] [SeminormedGroup F] [SeminormedGroup G] {s : Set E}
{a a₁ a₂ b c : E} {r r₁ r₂ : ℝ}
@[to_additive]
theorem dist_eq_norm_div (a b : E) : dist a b = ‖a / b‖ :=
SeminormedGroup.dist_eq _ _
@[to_additive]
theorem dist_eq_norm_div' (a b : E) : dist a b = ‖b / a‖ := by rw [dist_comm, dist_eq_norm_div]
alias dist_eq_norm := dist_eq_norm_sub
alias dist_eq_norm' := dist_eq_norm_sub'
@[to_additive of_forall_le_norm]
lemma DiscreteTopology.of_forall_le_norm' (hpos : 0 < r) (hr : ∀ x : E, x ≠ 1 → r ≤ ‖x‖) :
DiscreteTopology E :=
.of_forall_le_dist hpos fun x y hne ↦ by
simp only [dist_eq_norm_div]
exact hr _ (div_ne_one.2 hne)
@[to_additive (attr := simp)]
theorem dist_one_right (a : E) : dist a 1 = ‖a‖ := by rw [dist_eq_norm_div, div_one]
@[to_additive]
theorem inseparable_one_iff_norm {a : E} : Inseparable a 1 ↔ ‖a‖ = 0 := by
rw [Metric.inseparable_iff, dist_one_right]
@[to_additive]
lemma dist_one_left (a : E) : dist 1 a = ‖a‖ := by rw [dist_comm, dist_one_right]
@[to_additive (attr := simp)]
lemma dist_one : dist (1 : E) = norm := funext dist_one_left
@[to_additive]
theorem norm_div_rev (a b : E) : ‖a / b‖ = ‖b / a‖ := by
simpa only [dist_eq_norm_div] using dist_comm a b
@[to_additive (attr := simp) norm_neg]
theorem norm_inv' (a : E) : ‖a⁻¹‖ = ‖a‖ := by simpa using norm_div_rev 1 a
@[to_additive (attr := simp) norm_abs_zsmul]
theorem norm_zpow_abs (a : E) (n : ℤ) : ‖a ^ |n|‖ = ‖a ^ n‖ := by
rcases le_total 0 n with hn | hn <;> simp [hn, abs_of_nonneg, abs_of_nonpos]
@[to_additive (attr := simp) norm_natAbs_smul]
theorem norm_pow_natAbs (a : E) (n : ℤ) : ‖a ^ n.natAbs‖ = ‖a ^ n‖ := by
rw [← zpow_natCast, ← Int.abs_eq_natAbs, norm_zpow_abs]
@[to_additive norm_isUnit_zsmul]
theorem norm_zpow_isUnit (a : E) {n : ℤ} (hn : IsUnit n) : ‖a ^ n‖ = ‖a‖ := by
rw [← norm_pow_natAbs, Int.isUnit_iff_natAbs_eq.mp hn, pow_one]
@[simp]
theorem norm_units_zsmul {E : Type*} [SeminormedAddGroup E] (n : ℤˣ) (a : E) : ‖n • a‖ = ‖a‖ :=
norm_isUnit_zsmul a n.isUnit
open scoped symmDiff in
@[to_additive]
theorem dist_mulIndicator (s t : Set α) (f : α → E) (x : α) :
dist (s.mulIndicator f x) (t.mulIndicator f x) = ‖(s ∆ t).mulIndicator f x‖ := by
rw [dist_eq_norm_div, Set.apply_mulIndicator_symmDiff norm_inv']
/-- **Triangle inequality** for the norm. -/
@[to_additive norm_add_le "**Triangle inequality** for the norm."]
theorem norm_mul_le' (a b : E) : ‖a * b‖ ≤ ‖a‖ + ‖b‖ := by
simpa [dist_eq_norm_div] using dist_triangle a 1 b⁻¹
/-- **Triangle inequality** for the norm. -/
@[to_additive norm_add_le_of_le "**Triangle inequality** for the norm."]
theorem norm_mul_le_of_le' (h₁ : ‖a₁‖ ≤ r₁) (h₂ : ‖a₂‖ ≤ r₂) : ‖a₁ * a₂‖ ≤ r₁ + r₂ :=
(norm_mul_le' a₁ a₂).trans <| add_le_add h₁ h₂
/-- **Triangle inequality** for the norm. -/
@[to_additive norm_add₃_le "**Triangle inequality** for the norm."]
lemma norm_mul₃_le' : ‖a * b * c‖ ≤ ‖a‖ + ‖b‖ + ‖c‖ := norm_mul_le_of_le' (norm_mul_le' _ _) le_rfl
@[to_additive]
lemma norm_div_le_norm_div_add_norm_div (a b c : E) : ‖a / c‖ ≤ ‖a / b‖ + ‖b / c‖ := by
simpa only [dist_eq_norm_div] using dist_triangle a b c
@[to_additive (attr := simp) norm_nonneg]
theorem norm_nonneg' (a : E) : 0 ≤ ‖a‖ := by
rw [← dist_one_right]
exact dist_nonneg
attribute [bound] norm_nonneg
@[to_additive (attr := simp) abs_norm]
theorem abs_norm' (z : E) : |‖z‖| = ‖z‖ := abs_of_nonneg <| norm_nonneg' _
@[to_additive (attr := simp) norm_zero]
theorem norm_one' : ‖(1 : E)‖ = 0 := by rw [← dist_one_right, dist_self]
@[to_additive]
theorem ne_one_of_norm_ne_zero : ‖a‖ ≠ 0 → a ≠ 1 :=
mt <| by
rintro rfl
exact norm_one'
@[to_additive (attr := nontriviality) norm_of_subsingleton]
theorem norm_of_subsingleton' [Subsingleton E] (a : E) : ‖a‖ = 0 := by
rw [Subsingleton.elim a 1, norm_one']
@[to_additive zero_lt_one_add_norm_sq]
theorem zero_lt_one_add_norm_sq' (x : E) : 0 < 1 + ‖x‖ ^ 2 := by
positivity
@[to_additive]
theorem norm_div_le (a b : E) : ‖a / b‖ ≤ ‖a‖ + ‖b‖ := by
simpa [dist_eq_norm_div] using dist_triangle a 1 b
attribute [bound] norm_sub_le
@[to_additive]
theorem norm_div_le_of_le {r₁ r₂ : ℝ} (H₁ : ‖a₁‖ ≤ r₁) (H₂ : ‖a₂‖ ≤ r₂) : ‖a₁ / a₂‖ ≤ r₁ + r₂ :=
(norm_div_le a₁ a₂).trans <| add_le_add H₁ H₂
@[to_additive dist_le_norm_add_norm]
theorem dist_le_norm_add_norm' (a b : E) : dist a b ≤ ‖a‖ + ‖b‖ := by
rw [dist_eq_norm_div]
apply norm_div_le
@[to_additive abs_norm_sub_norm_le]
theorem abs_norm_sub_norm_le' (a b : E) : |‖a‖ - ‖b‖| ≤ ‖a / b‖ := by
simpa [dist_eq_norm_div] using abs_dist_sub_le a b 1
@[to_additive norm_sub_norm_le]
theorem norm_sub_norm_le' (a b : E) : ‖a‖ - ‖b‖ ≤ ‖a / b‖ :=
(le_abs_self _).trans (abs_norm_sub_norm_le' a b)
@[to_additive (attr := bound)]
theorem norm_sub_le_norm_mul (a b : E) : ‖a‖ - ‖b‖ ≤ ‖a * b‖ := by
simpa using norm_mul_le' (a * b) (b⁻¹)
@[to_additive dist_norm_norm_le]
theorem dist_norm_norm_le' (a b : E) : dist ‖a‖ ‖b‖ ≤ ‖a / b‖ :=
abs_norm_sub_norm_le' a b
@[to_additive]
theorem norm_le_norm_add_norm_div' (u v : E) : ‖u‖ ≤ ‖v‖ + ‖u / v‖ := by
rw [add_comm]
refine (norm_mul_le' _ _).trans_eq' ?_
rw [div_mul_cancel]
@[to_additive]
theorem norm_le_norm_add_norm_div (u v : E) : ‖v‖ ≤ ‖u‖ + ‖u / v‖ := by
rw [norm_div_rev]
exact norm_le_norm_add_norm_div' v u
alias norm_le_insert' := norm_le_norm_add_norm_sub'
alias norm_le_insert := norm_le_norm_add_norm_sub
@[to_additive]
theorem norm_le_mul_norm_add (u v : E) : ‖u‖ ≤ ‖u * v‖ + ‖v‖ :=
calc
‖u‖ = ‖u * v / v‖ := by rw [mul_div_cancel_right]
_ ≤ ‖u * v‖ + ‖v‖ := norm_div_le _ _
/-- An analogue of `norm_le_mul_norm_add` for the multiplication from the left. -/
@[to_additive "An analogue of `norm_le_add_norm_add` for the addition from the left."]
theorem norm_le_mul_norm_add' (u v : E) : ‖v‖ ≤ ‖u * v‖ + ‖u‖ :=
calc
‖v‖ = ‖u⁻¹ * (u * v)‖ := by rw [← mul_assoc, inv_mul_cancel, one_mul]
_ ≤ ‖u⁻¹‖ + ‖u * v‖ := norm_mul_le' u⁻¹ (u * v)
_ = ‖u * v‖ + ‖u‖ := by rw [norm_inv', add_comm]
@[to_additive]
lemma norm_mul_eq_norm_right {x : E} (y : E) (h : ‖x‖ = 0) : ‖x * y‖ = ‖y‖ := by
apply le_antisymm ?_ ?_
· simpa [h] using norm_mul_le' x y
· simpa [h] using norm_le_mul_norm_add' x y
@[to_additive]
lemma norm_mul_eq_norm_left (x : E) {y : E} (h : ‖y‖ = 0) : ‖x * y‖ = ‖x‖ := by
apply le_antisymm ?_ ?_
· simpa [h] using norm_mul_le' x y
· simpa [h] using norm_le_mul_norm_add x y
@[to_additive]
lemma norm_div_eq_norm_right {x : E} (y : E) (h : ‖x‖ = 0) : ‖x / y‖ = ‖y‖ := by
apply le_antisymm ?_ ?_
· simpa [h] using norm_div_le x y
· simpa [h, norm_div_rev x y] using norm_sub_norm_le' y x
@[to_additive]
lemma norm_div_eq_norm_left (x : E) {y : E} (h : ‖y‖ = 0) : ‖x / y‖ = ‖x‖ := by
apply le_antisymm ?_ ?_
· simpa [h] using norm_div_le x y
· simpa [h] using norm_sub_norm_le' x y
@[to_additive ball_eq]
theorem ball_eq' (y : E) (ε : ℝ) : ball y ε = { x | ‖x / y‖ < ε } :=
Set.ext fun a => by simp [dist_eq_norm_div]
@[to_additive]
theorem ball_one_eq (r : ℝ) : ball (1 : E) r = { x | ‖x‖ < r } :=
Set.ext fun a => by simp
@[to_additive mem_ball_iff_norm]
theorem mem_ball_iff_norm'' : b ∈ ball a r ↔ ‖b / a‖ < r := by rw [mem_ball, dist_eq_norm_div]
@[to_additive mem_ball_iff_norm']
theorem mem_ball_iff_norm''' : b ∈ ball a r ↔ ‖a / b‖ < r := by rw [mem_ball', dist_eq_norm_div]
@[to_additive]
theorem mem_ball_one_iff : a ∈ ball (1 : E) r ↔ ‖a‖ < r := by rw [mem_ball, dist_one_right]
@[to_additive mem_closedBall_iff_norm]
theorem mem_closedBall_iff_norm'' : b ∈ closedBall a r ↔ ‖b / a‖ ≤ r := by
rw [mem_closedBall, dist_eq_norm_div]
@[to_additive]
theorem mem_closedBall_one_iff : a ∈ closedBall (1 : E) r ↔ ‖a‖ ≤ r := by
rw [mem_closedBall, dist_one_right]
@[to_additive mem_closedBall_iff_norm']
theorem mem_closedBall_iff_norm''' : b ∈ closedBall a r ↔ ‖a / b‖ ≤ r := by
rw [mem_closedBall', dist_eq_norm_div]
@[to_additive norm_le_of_mem_closedBall]
theorem norm_le_of_mem_closedBall' (h : b ∈ closedBall a r) : ‖b‖ ≤ ‖a‖ + r :=
(norm_le_norm_add_norm_div' _ _).trans <| add_le_add_left (by rwa [← dist_eq_norm_div]) _
@[to_additive norm_le_norm_add_const_of_dist_le]
theorem norm_le_norm_add_const_of_dist_le' : dist a b ≤ r → ‖a‖ ≤ ‖b‖ + r :=
norm_le_of_mem_closedBall'
@[to_additive norm_lt_of_mem_ball]
theorem norm_lt_of_mem_ball' (h : b ∈ ball a r) : ‖b‖ < ‖a‖ + r :=
(norm_le_norm_add_norm_div' _ _).trans_lt <| add_lt_add_left (by rwa [← dist_eq_norm_div]) _
@[to_additive]
theorem norm_div_sub_norm_div_le_norm_div (u v w : E) : ‖u / w‖ - ‖v / w‖ ≤ ‖u / v‖ := by
simpa only [div_div_div_cancel_right] using norm_sub_norm_le' (u / w) (v / w)
@[to_additive (attr := simp 1001) mem_sphere_iff_norm]
-- Porting note: increase priority so the left-hand side doesn't reduce
theorem mem_sphere_iff_norm' : b ∈ sphere a r ↔ ‖b / a‖ = r := by simp [dist_eq_norm_div]
@[to_additive] -- `simp` can prove this
theorem mem_sphere_one_iff_norm : a ∈ sphere (1 : E) r ↔ ‖a‖ = r := by simp [dist_eq_norm_div]
@[to_additive (attr := simp) norm_eq_of_mem_sphere]
theorem norm_eq_of_mem_sphere' (x : sphere (1 : E) r) : ‖(x : E)‖ = r :=
mem_sphere_one_iff_norm.mp x.2
@[to_additive]
theorem ne_one_of_mem_sphere (hr : r ≠ 0) (x : sphere (1 : E) r) : (x : E) ≠ 1 :=
ne_one_of_norm_ne_zero <| by rwa [norm_eq_of_mem_sphere' x]
@[to_additive ne_zero_of_mem_unit_sphere]
theorem ne_one_of_mem_unit_sphere (x : sphere (1 : E) 1) : (x : E) ≠ 1 :=
ne_one_of_mem_sphere one_ne_zero _
variable (E)
/-- The norm of a seminormed group as a group seminorm. -/
@[to_additive "The norm of a seminormed group as an additive group seminorm."]
def normGroupSeminorm : GroupSeminorm E :=
⟨norm, norm_one', norm_mul_le', norm_inv'⟩
@[to_additive (attr := simp)]
theorem coe_normGroupSeminorm : ⇑(normGroupSeminorm E) = norm :=
rfl
variable {E}
@[to_additive]
theorem NormedCommGroup.tendsto_nhds_one {f : α → E} {l : Filter α} :
Tendsto f l (𝓝 1) ↔ ∀ ε > 0, ∀ᶠ x in l, ‖f x‖ < ε :=
Metric.tendsto_nhds.trans <| by simp only [dist_one_right]
@[to_additive]
theorem NormedCommGroup.tendsto_nhds_nhds {f : E → F} {x : E} {y : F} :
Tendsto f (𝓝 x) (𝓝 y) ↔ ∀ ε > 0, ∃ δ > 0, ∀ x', ‖x' / x‖ < δ → ‖f x' / y‖ < ε := by
simp_rw [Metric.tendsto_nhds_nhds, dist_eq_norm_div]
@[to_additive]
theorem NormedCommGroup.nhds_basis_norm_lt (x : E) :
(𝓝 x).HasBasis (fun ε : ℝ => 0 < ε) fun ε => { y | ‖y / x‖ < ε } := by
simp_rw [← ball_eq']
exact Metric.nhds_basis_ball
@[to_additive]
theorem NormedCommGroup.nhds_one_basis_norm_lt :
(𝓝 (1 : E)).HasBasis (fun ε : ℝ => 0 < ε) fun ε => { y | ‖y‖ < ε } := by
convert NormedCommGroup.nhds_basis_norm_lt (1 : E)
simp
@[to_additive]
theorem NormedCommGroup.uniformity_basis_dist :
(𝓤 E).HasBasis (fun ε : ℝ => 0 < ε) fun ε => { p : E × E | ‖p.fst / p.snd‖ < ε } := by
convert Metric.uniformity_basis_dist (α := E) using 1
simp [dist_eq_norm_div]
open Finset
variable [FunLike 𝓕 E F]
section NNNorm
-- See note [lower instance priority]
@[to_additive]
instance (priority := 100) SeminormedGroup.toNNNorm : NNNorm E :=
⟨fun a => ⟨‖a‖, norm_nonneg' a⟩⟩
@[to_additive (attr := simp, norm_cast) coe_nnnorm]
theorem coe_nnnorm' (a : E) : (‖a‖₊ : ℝ) = ‖a‖ := rfl
@[to_additive (attr := simp) coe_comp_nnnorm]
theorem coe_comp_nnnorm' : (toReal : ℝ≥0 → ℝ) ∘ (nnnorm : E → ℝ≥0) = norm :=
rfl
@[to_additive (attr := simp) norm_toNNReal]
theorem norm_toNNReal' : ‖a‖.toNNReal = ‖a‖₊ :=
@Real.toNNReal_coe ‖a‖₊
@[to_additive (attr := simp) toReal_enorm]
lemma toReal_enorm' (x : E) : ‖x‖ₑ.toReal = ‖x‖ := by simp [enorm]
@[to_additive (attr := simp) ofReal_norm]
lemma ofReal_norm' (x : E) : .ofReal ‖x‖ = ‖x‖ₑ := by
simp [enorm, ENNReal.ofReal, Real.toNNReal, nnnorm]
@[to_additive enorm_eq_iff_norm_eq]
theorem enorm'_eq_iff_norm_eq {x : E} {y : F} : ‖x‖ₑ = ‖y‖ₑ ↔ ‖x‖ = ‖y‖ := by
simp only [← ofReal_norm']
refine ⟨fun h ↦ ?_, fun h ↦ by congr⟩
exact (Real.toNNReal_eq_toNNReal_iff (norm_nonneg' _) (norm_nonneg' _)).mp (ENNReal.coe_inj.mp h)
@[to_additive enorm_le_iff_norm_le]
theorem enorm'_le_iff_norm_le {x : E} {y : F} : ‖x‖ₑ ≤ ‖y‖ₑ ↔ ‖x‖ ≤ ‖y‖ := by
simp only [← ofReal_norm']
refine ⟨fun h ↦ ?_, fun h ↦ by gcongr⟩
rw [ENNReal.ofReal_le_ofReal_iff (norm_nonneg' _)] at h
exact h
@[to_additive]
theorem nndist_eq_nnnorm_div (a b : E) : nndist a b = ‖a / b‖₊ :=
NNReal.eq <| dist_eq_norm_div _ _
alias nndist_eq_nnnorm := nndist_eq_nnnorm_sub
@[to_additive (attr := simp)]
theorem nndist_one_right (a : E) : nndist a 1 = ‖a‖₊ := by simp [nndist_eq_nnnorm_div]
@[to_additive (attr := simp)]
lemma edist_one_right (a : E) : edist a 1 = ‖a‖ₑ := by simp [edist_nndist, nndist_one_right, enorm]
@[to_additive (attr := simp) nnnorm_zero]
theorem nnnorm_one' : ‖(1 : E)‖₊ = 0 := NNReal.eq norm_one'
@[to_additive]
theorem ne_one_of_nnnorm_ne_zero {a : E} : ‖a‖₊ ≠ 0 → a ≠ 1 :=
mt <| by
rintro rfl
exact nnnorm_one'
@[to_additive nnnorm_add_le]
theorem nnnorm_mul_le' (a b : E) : ‖a * b‖₊ ≤ ‖a‖₊ + ‖b‖₊ :=
NNReal.coe_le_coe.1 <| norm_mul_le' a b
@[to_additive norm_nsmul_le]
lemma norm_pow_le_mul_norm : ∀ {n : ℕ}, ‖a ^ n‖ ≤ n * ‖a‖
| 0 => by simp
| n + 1 => by simpa [pow_succ, add_mul] using norm_mul_le_of_le' norm_pow_le_mul_norm le_rfl
@[to_additive nnnorm_nsmul_le]
lemma nnnorm_pow_le_mul_norm {n : ℕ} : ‖a ^ n‖₊ ≤ n * ‖a‖₊ := by
simpa only [← NNReal.coe_le_coe, NNReal.coe_mul, NNReal.coe_natCast] using norm_pow_le_mul_norm
@[to_additive (attr := simp) nnnorm_neg]
theorem nnnorm_inv' (a : E) : ‖a⁻¹‖₊ = ‖a‖₊ :=
NNReal.eq <| norm_inv' a
@[to_additive (attr := simp) nnnorm_abs_zsmul]
theorem nnnorm_zpow_abs (a : E) (n : ℤ) : ‖a ^ |n|‖₊ = ‖a ^ n‖₊ :=
NNReal.eq <| norm_zpow_abs a n
@[to_additive (attr := simp) nnnorm_natAbs_smul]
theorem nnnorm_pow_natAbs (a : E) (n : ℤ) : ‖a ^ n.natAbs‖₊ = ‖a ^ n‖₊ :=
NNReal.eq <| norm_pow_natAbs a n
@[to_additive nnnorm_isUnit_zsmul]
theorem nnnorm_zpow_isUnit (a : E) {n : ℤ} (hn : IsUnit n) : ‖a ^ n‖₊ = ‖a‖₊ :=
NNReal.eq <| norm_zpow_isUnit a hn
@[simp]
theorem nnnorm_units_zsmul {E : Type*} [SeminormedAddGroup E] (n : ℤˣ) (a : E) : ‖n • a‖₊ = ‖a‖₊ :=
NNReal.eq <| norm_isUnit_zsmul a n.isUnit
@[to_additive (attr := simp)]
theorem nndist_one_left (a : E) : nndist 1 a = ‖a‖₊ := by simp [nndist_eq_nnnorm_div]
@[to_additive (attr := simp)]
theorem edist_one_left (a : E) : edist 1 a = ‖a‖₊ := by
rw [edist_nndist, nndist_one_left]
open scoped symmDiff in
@[to_additive]
theorem nndist_mulIndicator (s t : Set α) (f : α → E) (x : α) :
nndist (s.mulIndicator f x) (t.mulIndicator f x) = ‖(s ∆ t).mulIndicator f x‖₊ :=
NNReal.eq <| dist_mulIndicator s t f x
@[to_additive]
theorem nnnorm_div_le (a b : E) : ‖a / b‖₊ ≤ ‖a‖₊ + ‖b‖₊ :=
NNReal.coe_le_coe.1 <| norm_div_le _ _
@[to_additive]
lemma enorm_div_le : ‖a / b‖ₑ ≤ ‖a‖ₑ + ‖b‖ₑ := by
simpa [enorm, ← ENNReal.coe_add] using nnnorm_div_le a b
@[to_additive nndist_nnnorm_nnnorm_le]
theorem nndist_nnnorm_nnnorm_le' (a b : E) : nndist ‖a‖₊ ‖b‖₊ ≤ ‖a / b‖₊ :=
NNReal.coe_le_coe.1 <| dist_norm_norm_le' a b
@[to_additive]
theorem nnnorm_le_nnnorm_add_nnnorm_div (a b : E) : ‖b‖₊ ≤ ‖a‖₊ + ‖a / b‖₊ :=
norm_le_norm_add_norm_div _ _
@[to_additive]
theorem nnnorm_le_nnnorm_add_nnnorm_div' (a b : E) : ‖a‖₊ ≤ ‖b‖₊ + ‖a / b‖₊ :=
norm_le_norm_add_norm_div' _ _
alias nnnorm_le_insert' := nnnorm_le_nnnorm_add_nnnorm_sub'
alias nnnorm_le_insert := nnnorm_le_nnnorm_add_nnnorm_sub
@[to_additive]
theorem nnnorm_le_mul_nnnorm_add (a b : E) : ‖a‖₊ ≤ ‖a * b‖₊ + ‖b‖₊ :=
norm_le_mul_norm_add _ _
/-- An analogue of `nnnorm_le_mul_nnnorm_add` for the multiplication from the left. -/
@[to_additive "An analogue of `nnnorm_le_add_nnnorm_add` for the addition from the left."]
theorem nnnorm_le_mul_nnnorm_add' (a b : E) : ‖b‖₊ ≤ ‖a * b‖₊ + ‖a‖₊ :=
norm_le_mul_norm_add' _ _
@[to_additive]
lemma nnnorm_mul_eq_nnnorm_right {x : E} (y : E) (h : ‖x‖₊ = 0) : ‖x * y‖₊ = ‖y‖₊ :=
NNReal.eq <| norm_mul_eq_norm_right _ <| congr_arg NNReal.toReal h
@[to_additive]
lemma nnnorm_mul_eq_nnnorm_left (x : E) {y : E} (h : ‖y‖₊ = 0) : ‖x * y‖₊ = ‖x‖₊ :=
NNReal.eq <| norm_mul_eq_norm_left _ <| congr_arg NNReal.toReal h
@[to_additive]
lemma nnnorm_div_eq_nnnorm_right {x : E} (y : E) (h : ‖x‖₊ = 0) : ‖x / y‖₊ = ‖y‖₊ :=
NNReal.eq <| norm_div_eq_norm_right _ <| congr_arg NNReal.toReal h
@[to_additive]
lemma nnnorm_div_eq_nnnorm_left (x : E) {y : E} (h : ‖y‖₊ = 0) : ‖x / y‖₊ = ‖x‖₊ :=
NNReal.eq <| norm_div_eq_norm_left _ <| congr_arg NNReal.toReal h
/-- The non negative norm seen as an `ENNReal` and then as a `Real` is equal to the norm. -/
@[to_additive toReal_coe_nnnorm "The non negative norm seen as an `ENNReal` and
then as a `Real` is equal to the norm."]
theorem toReal_coe_nnnorm' (a : E) : (‖a‖₊ : ℝ≥0∞).toReal = ‖a‖ := rfl
open scoped symmDiff in
@[to_additive]
theorem edist_mulIndicator (s t : Set α) (f : α → E) (x : α) :
edist (s.mulIndicator f x) (t.mulIndicator f x) = ‖(s ∆ t).mulIndicator f x‖₊ := by
rw [edist_nndist, nndist_mulIndicator]
end NNNorm
section ENorm
@[to_additive (attr := simp) enorm_zero]
lemma enorm_one' {E : Type*} [TopologicalSpace E] [ENormedMonoid E] : ‖(1 : E)‖ₑ = 0 := by
rw [ENormedMonoid.enorm_eq_zero]
@[to_additive exists_enorm_lt]
lemma exists_enorm_lt' (E : Type*) [TopologicalSpace E] [ENormedMonoid E]
[hbot : NeBot (𝓝[≠] (1 : E))] {c : ℝ≥0∞} (hc : c ≠ 0) : ∃ x ≠ (1 : E), ‖x‖ₑ < c :=
frequently_iff_neBot.mpr hbot |>.and_eventually
(ContinuousENorm.continuous_enorm.tendsto' 1 0 (by simp) |>.eventually_lt_const hc.bot_lt)
|>.exists
@[to_additive (attr := simp) enorm_neg]
lemma enorm_inv' (a : E) : ‖a⁻¹‖ₑ = ‖a‖ₑ := by simp [enorm]
@[to_additive ofReal_norm_eq_enorm]
lemma ofReal_norm_eq_enorm' (a : E) : .ofReal ‖a‖ = ‖a‖ₑ := ENNReal.ofReal_eq_coe_nnreal _
@[deprecated (since := "2025-01-17")] alias ofReal_norm_eq_coe_nnnorm := ofReal_norm_eq_enorm
@[deprecated (since := "2025-01-17")] alias ofReal_norm_eq_coe_nnnorm' := ofReal_norm_eq_enorm'
instance : ENorm ℝ≥0∞ where
enorm x := x
@[simp] lemma enorm_eq_self (x : ℝ≥0∞) : ‖x‖ₑ = x := rfl
@[to_additive]
theorem edist_eq_enorm_div (a b : E) : edist a b = ‖a / b‖ₑ := by
rw [edist_dist, dist_eq_norm_div, ofReal_norm_eq_enorm']
@[deprecated (since := "2025-01-17")] alias edist_eq_coe_nnnorm_sub := edist_eq_enorm_sub
@[deprecated (since := "2025-01-17")] alias edist_eq_coe_nnnorm_div := edist_eq_enorm_div
@[to_additive]
theorem edist_one_eq_enorm (x : E) : edist x 1 = ‖x‖ₑ := by rw [edist_eq_enorm_div, div_one]
@[deprecated (since := "2025-01-17")] alias edist_eq_coe_nnnorm := edist_zero_eq_enorm
@[deprecated (since := "2025-01-17")] alias edist_eq_coe_nnnorm' := edist_one_eq_enorm
@[to_additive]
theorem mem_emetric_ball_one_iff {r : ℝ≥0∞} : a ∈ EMetric.ball 1 r ↔ ‖a‖ₑ < r := by
rw [EMetric.mem_ball, edist_one_eq_enorm]
end ENorm
section ContinuousENorm
variable {E : Type*} [TopologicalSpace E] [ContinuousENorm E]
@[continuity, fun_prop]
lemma continuous_enorm : Continuous fun a : E ↦ ‖a‖ₑ := ContinuousENorm.continuous_enorm
variable {X : Type*} [TopologicalSpace X] {f : X → E} {s : Set X} {a : X}
@[fun_prop]
lemma Continuous.enorm : Continuous f → Continuous (‖f ·‖ₑ) :=
continuous_enorm.comp
lemma ContinuousAt.enorm {a : X} (h : ContinuousAt f a) : ContinuousAt (‖f ·‖ₑ) a := by fun_prop
@[fun_prop]
lemma ContinuousWithinAt.enorm {s : Set X} {a : X} (h : ContinuousWithinAt f s a) :
ContinuousWithinAt (‖f ·‖ₑ) s a :=
(ContinuousENorm.continuous_enorm.continuousWithinAt).comp (t := Set.univ) h
(fun _ _ ↦ by trivial)
@[fun_prop]
lemma ContinuousOn.enorm (h : ContinuousOn f s) : ContinuousOn (‖f ·‖ₑ) s :=
(ContinuousENorm.continuous_enorm.continuousOn).comp (t := Set.univ) h <| Set.mapsTo_univ _ _
end ContinuousENorm
section ENormedMonoid
variable {E : Type*} [TopologicalSpace E] [ENormedMonoid E]
@[to_additive enorm_add_le]
lemma enorm_mul_le' (a b : E) : ‖a * b‖ₑ ≤ ‖a‖ₑ + ‖b‖ₑ := ENormedMonoid.enorm_mul_le a b
@[to_additive (attr := simp) enorm_eq_zero]
lemma enorm_eq_zero' {a : E} : ‖a‖ₑ = 0 ↔ a = 1 := by
simp [enorm, ENormedMonoid.enorm_eq_zero]
@[to_additive enorm_ne_zero]
lemma enorm_ne_zero' {a : E} : ‖a‖ₑ ≠ 0 ↔ a ≠ 1 :=
enorm_eq_zero'.ne
@[to_additive (attr := simp) enorm_pos]
lemma enorm_pos' {a : E} : 0 < ‖a‖ₑ ↔ a ≠ 1 :=
pos_iff_ne_zero.trans enorm_ne_zero'
end ENormedMonoid
instance : ENormedAddCommMonoid ℝ≥0∞ where
continuous_enorm := continuous_id
enorm_eq_zero := by simp
enorm_add_le := by simp
open Set in
@[to_additive]
lemma SeminormedGroup.disjoint_nhds (x : E) (f : Filter E) :
Disjoint (𝓝 x) f ↔ ∃ δ > 0, ∀ᶠ y in f, δ ≤ ‖y / x‖ := by
simp [NormedCommGroup.nhds_basis_norm_lt x |>.disjoint_iff_left, compl_setOf, eventually_iff]
@[to_additive]
lemma SeminormedGroup.disjoint_nhds_one (f : Filter E) :
Disjoint (𝓝 1) f ↔ ∃ δ > 0, ∀ᶠ y in f, δ ≤ ‖y‖ := by
simpa using disjoint_nhds 1 f
end SeminormedGroup
section Induced
variable (E F)
variable [FunLike 𝓕 E F]
-- See note [reducible non-instances]
/-- A group homomorphism from a `Group` to a `SeminormedGroup` induces a `SeminormedGroup`
structure on the domain. -/
@[to_additive "A group homomorphism from an `AddGroup` to a
`SeminormedAddGroup` induces a `SeminormedAddGroup` structure on the domain."]
abbrev SeminormedGroup.induced [Group E] [SeminormedGroup F] [MonoidHomClass 𝓕 E F] (f : 𝓕) :
SeminormedGroup E :=
{ PseudoMetricSpace.induced f toPseudoMetricSpace with
norm := fun x => ‖f x‖
dist_eq := fun x y => by simp only [map_div, ← dist_eq_norm_div]; rfl }
-- See note [reducible non-instances]
/-- A group homomorphism from a `CommGroup` to a `SeminormedGroup` induces a
`SeminormedCommGroup` structure on the domain. -/
@[to_additive "A group homomorphism from an `AddCommGroup` to a
`SeminormedAddGroup` induces a `SeminormedAddCommGroup` structure on the domain."]
abbrev SeminormedCommGroup.induced
[CommGroup E] [SeminormedGroup F] [MonoidHomClass 𝓕 E F] (f : 𝓕) :
SeminormedCommGroup E :=
{ SeminormedGroup.induced E F f with
mul_comm := mul_comm }
-- See note [reducible non-instances].
/-- An injective group homomorphism from a `Group` to a `NormedGroup` induces a `NormedGroup`
structure on the domain. -/
@[to_additive "An injective group homomorphism from an `AddGroup` to a
`NormedAddGroup` induces a `NormedAddGroup` structure on the domain."]
abbrev NormedGroup.induced
[Group E] [NormedGroup F] [MonoidHomClass 𝓕 E F] (f : 𝓕) (h : Injective f) :
NormedGroup E :=
{ SeminormedGroup.induced E F f, MetricSpace.induced f h _ with }
-- See note [reducible non-instances].
/-- An injective group homomorphism from a `CommGroup` to a `NormedGroup` induces a
`NormedCommGroup` structure on the domain. -/
@[to_additive "An injective group homomorphism from a `CommGroup` to a
`NormedCommGroup` induces a `NormedCommGroup` structure on the domain."]
abbrev NormedCommGroup.induced [CommGroup E] [NormedGroup F] [MonoidHomClass 𝓕 E F] (f : 𝓕)
(h : Injective f) : NormedCommGroup E :=
{ SeminormedGroup.induced E F f, MetricSpace.induced f h _ with
mul_comm := mul_comm }
end Induced
namespace Real
variable {r : ℝ}
instance norm : Norm ℝ where
norm r := |r|
@[simp]
theorem norm_eq_abs (r : ℝ) : ‖r‖ = |r| :=
rfl
instance normedAddCommGroup : NormedAddCommGroup ℝ :=
⟨fun _r _y => rfl⟩
theorem norm_of_nonneg (hr : 0 ≤ r) : ‖r‖ = r :=
abs_of_nonneg hr
theorem norm_of_nonpos (hr : r ≤ 0) : ‖r‖ = -r :=
abs_of_nonpos hr
theorem le_norm_self (r : ℝ) : r ≤ ‖r‖ :=
le_abs_self r
@[simp 1100] lemma norm_natCast (n : ℕ) : ‖(n : ℝ)‖ = n := abs_of_nonneg n.cast_nonneg
@[simp 1100] lemma nnnorm_natCast (n : ℕ) : ‖(n : ℝ)‖₊ = n := NNReal.eq <| norm_natCast _
@[simp 1100] lemma enorm_natCast (n : ℕ) : ‖(n : ℝ)‖ₑ = n := by simp [enorm]
@[simp 1100] lemma norm_ofNat (n : ℕ) [n.AtLeastTwo] :
‖(ofNat(n) : ℝ)‖ = ofNat(n) := norm_natCast n
@[simp 1100] lemma nnnorm_ofNat (n : ℕ) [n.AtLeastTwo] :
‖(ofNat(n) : ℝ)‖₊ = ofNat(n) := nnnorm_natCast n
lemma norm_two : ‖(2 : ℝ)‖ = 2 := abs_of_pos zero_lt_two
lemma nnnorm_two : ‖(2 : ℝ)‖₊ = 2 := NNReal.eq <| by simp
@[simp 1100, norm_cast]
lemma norm_nnratCast (q : ℚ≥0) : ‖(q : ℝ)‖ = q := norm_of_nonneg q.cast_nonneg
@[simp 1100, norm_cast]
lemma nnnorm_nnratCast (q : ℚ≥0) : ‖(q : ℝ)‖₊ = q := by simp [nnnorm, -norm_eq_abs]
theorem nnnorm_of_nonneg (hr : 0 ≤ r) : ‖r‖₊ = ⟨r, hr⟩ :=
NNReal.eq <| norm_of_nonneg hr
lemma enorm_of_nonneg (hr : 0 ≤ r) : ‖r‖ₑ = .ofReal r := by
simp [enorm, nnnorm_of_nonneg hr, ENNReal.ofReal, toNNReal, hr]
@[simp] lemma nnnorm_abs (r : ℝ) : ‖|r|‖₊ = ‖r‖₊ := by simp [nnnorm]
@[simp] lemma enorm_abs (r : ℝ) : ‖|r|‖ₑ = ‖r‖ₑ := by simp [enorm]
theorem enorm_eq_ofReal (hr : 0 ≤ r) : ‖r‖ₑ = .ofReal r := by
rw [← ofReal_norm_eq_enorm, norm_of_nonneg hr]
@[deprecated (since := "2025-01-17")] alias ennnorm_eq_ofReal := enorm_eq_ofReal
theorem enorm_eq_ofReal_abs (r : ℝ) : ‖r‖ₑ = ENNReal.ofReal |r| := by
rw [← enorm_eq_ofReal (abs_nonneg _), enorm_abs]
@[deprecated (since := "2025-01-17")] alias ennnorm_eq_ofReal_abs := enorm_eq_ofReal_abs
theorem toNNReal_eq_nnnorm_of_nonneg (hr : 0 ≤ r) : r.toNNReal = ‖r‖₊ := by
rw [Real.toNNReal_of_nonneg hr]
ext
rw [coe_mk, coe_nnnorm r, Real.norm_eq_abs r, abs_of_nonneg hr]
-- Porting note: this is due to the change from `Subtype.val` to `NNReal.toReal` for the coercion
theorem ofReal_le_enorm (r : ℝ) : ENNReal.ofReal r ≤ ‖r‖ₑ := by
rw [enorm_eq_ofReal_abs]; gcongr; exact le_abs_self _
@[deprecated (since := "2025-01-17")] alias ofReal_le_ennnorm := ofReal_le_enorm
end Real
namespace NNReal
instance : NNNorm ℝ≥0 where
nnnorm x := x
@[simp] lemma nnnorm_eq_self (x : ℝ≥0) : ‖x‖₊ = x := rfl
end NNReal
section SeminormedCommGroup
variable [SeminormedCommGroup E] [SeminormedCommGroup F] {a b : E} {r : ℝ}
@[to_additive]
theorem dist_inv (x y : E) : dist x⁻¹ y = dist x y⁻¹ := by
simp_rw [dist_eq_norm_div, ← norm_inv' (x⁻¹ / y), inv_div, div_inv_eq_mul, mul_comm]
theorem norm_multiset_sum_le {E} [SeminormedAddCommGroup E] (m : Multiset E) :
‖m.sum‖ ≤ (m.map fun x => ‖x‖).sum :=
m.le_sum_of_subadditive norm norm_zero norm_add_le
@[to_additive existing]
theorem norm_multiset_prod_le (m : Multiset E) : ‖m.prod‖ ≤ (m.map fun x => ‖x‖).sum := by
rw [← Multiplicative.ofAdd_le, ofAdd_multiset_prod, Multiset.map_map]
refine Multiset.le_prod_of_submultiplicative (Multiplicative.ofAdd ∘ norm) ?_ (fun x y => ?_) _
· simp only [comp_apply, norm_one', ofAdd_zero]
· exact norm_mul_le' x y
@[bound]
theorem norm_sum_le {ι E} [SeminormedAddCommGroup E] (s : Finset ι) (f : ι → E) :
‖∑ i ∈ s, f i‖ ≤ ∑ i ∈ s, ‖f i‖ :=
s.le_sum_of_subadditive norm norm_zero norm_add_le f
@[to_additive existing]
theorem norm_prod_le (s : Finset ι) (f : ι → E) : ‖∏ i ∈ s, f i‖ ≤ ∑ i ∈ s, ‖f i‖ := by
rw [← Multiplicative.ofAdd_le, ofAdd_sum]
refine Finset.le_prod_of_submultiplicative (Multiplicative.ofAdd ∘ norm) ?_ (fun x y => ?_) _ _
· simp only [comp_apply, norm_one', ofAdd_zero]
· exact norm_mul_le' x y
@[to_additive]
theorem norm_prod_le_of_le (s : Finset ι) {f : ι → E} {n : ι → ℝ} (h : ∀ b ∈ s, ‖f b‖ ≤ n b) :
‖∏ b ∈ s, f b‖ ≤ ∑ b ∈ s, n b :=
(norm_prod_le s f).trans <| Finset.sum_le_sum h
@[to_additive]
theorem dist_prod_prod_le_of_le (s : Finset ι) {f a : ι → E} {d : ι → ℝ}
(h : ∀ b ∈ s, dist (f b) (a b) ≤ d b) :
dist (∏ b ∈ s, f b) (∏ b ∈ s, a b) ≤ ∑ b ∈ s, d b := by
simp only [dist_eq_norm_div, ← Finset.prod_div_distrib] at *
exact norm_prod_le_of_le s h
@[to_additive]
theorem dist_prod_prod_le (s : Finset ι) (f a : ι → E) :
dist (∏ b ∈ s, f b) (∏ b ∈ s, a b) ≤ ∑ b ∈ s, dist (f b) (a b) :=
dist_prod_prod_le_of_le s fun _ _ => le_rfl
@[to_additive]
theorem mul_mem_ball_iff_norm : a * b ∈ ball a r ↔ ‖b‖ < r := by
rw [mem_ball_iff_norm'', mul_div_cancel_left]
@[to_additive]
theorem mul_mem_closedBall_iff_norm : a * b ∈ closedBall a r ↔ ‖b‖ ≤ r := by
rw [mem_closedBall_iff_norm'', mul_div_cancel_left]
@[to_additive (attr := simp 1001)]
-- Porting note: increase priority so that the left-hand side doesn't simplify
theorem preimage_mul_ball (a b : E) (r : ℝ) : (b * ·) ⁻¹' ball a r = ball (a / b) r := by
ext c
simp only [dist_eq_norm_div, Set.mem_preimage, mem_ball, div_div_eq_mul_div, mul_comm]
@[to_additive (attr := simp 1001)]
-- Porting note: increase priority so that the left-hand side doesn't simplify
theorem preimage_mul_closedBall (a b : E) (r : ℝ) :
(b * ·) ⁻¹' closedBall a r = closedBall (a / b) r := by
ext c
simp only [dist_eq_norm_div, Set.mem_preimage, mem_closedBall, div_div_eq_mul_div, mul_comm]
@[to_additive (attr := simp)]
theorem preimage_mul_sphere (a b : E) (r : ℝ) : (b * ·) ⁻¹' sphere a r = sphere (a / b) r := by
ext c
simp only [Set.mem_preimage, mem_sphere_iff_norm', div_div_eq_mul_div, mul_comm]
@[to_additive]
theorem pow_mem_closedBall {n : ℕ} (h : a ∈ closedBall b r) :
a ^ n ∈ closedBall (b ^ n) (n • r) := by
simp only [mem_closedBall, dist_eq_norm_div, ← div_pow] at h ⊢
refine norm_pow_le_mul_norm.trans ?_
simpa only [nsmul_eq_mul] using mul_le_mul_of_nonneg_left h n.cast_nonneg
@[to_additive]
theorem pow_mem_ball {n : ℕ} (hn : 0 < n) (h : a ∈ ball b r) : a ^ n ∈ ball (b ^ n) (n • r) := by
simp only [mem_ball, dist_eq_norm_div, ← div_pow] at h ⊢
refine lt_of_le_of_lt norm_pow_le_mul_norm ?_
replace hn : 0 < (n : ℝ) := by norm_cast
rw [nsmul_eq_mul]
nlinarith
@[to_additive]
theorem mul_mem_closedBall_mul_iff {c : E} : a * c ∈ closedBall (b * c) r ↔ a ∈ closedBall b r := by
simp only [mem_closedBall, dist_eq_norm_div, mul_div_mul_right_eq_div]
@[to_additive]
theorem mul_mem_ball_mul_iff {c : E} : a * c ∈ ball (b * c) r ↔ a ∈ ball b r := by
simp only [mem_ball, dist_eq_norm_div, mul_div_mul_right_eq_div]
@[to_additive]
theorem smul_closedBall'' : a • closedBall b r = closedBall (a • b) r := by
ext
simp [mem_closedBall, Set.mem_smul_set, dist_eq_norm_div, div_eq_inv_mul, ←
eq_inv_mul_iff_mul_eq, mul_assoc]
@[to_additive]
theorem smul_ball'' : a • ball b r = ball (a • b) r := by
ext
simp [mem_ball, Set.mem_smul_set, dist_eq_norm_div, _root_.div_eq_inv_mul,
← eq_inv_mul_iff_mul_eq, mul_assoc]
@[to_additive]
theorem nnnorm_multiset_prod_le (m : Multiset E) : ‖m.prod‖₊ ≤ (m.map fun x => ‖x‖₊).sum :=
NNReal.coe_le_coe.1 <| by
push_cast
rw [Multiset.map_map]
exact norm_multiset_prod_le _
@[to_additive]
theorem nnnorm_prod_le (s : Finset ι) (f : ι → E) : ‖∏ a ∈ s, f a‖₊ ≤ ∑ a ∈ s, ‖f a‖₊ :=
NNReal.coe_le_coe.1 <| by
push_cast
exact norm_prod_le _ _
@[to_additive]
theorem nnnorm_prod_le_of_le (s : Finset ι) {f : ι → E} {n : ι → ℝ≥0} (h : ∀ b ∈ s, ‖f b‖₊ ≤ n b) :
‖∏ b ∈ s, f b‖₊ ≤ ∑ b ∈ s, n b :=
(norm_prod_le_of_le s h).trans_eq (NNReal.coe_sum ..).symm
-- Porting note: increase priority so that the LHS doesn't simplify
@[to_additive (attr := simp 1001) norm_norm]
lemma norm_norm' (x : E) : ‖‖x‖‖ = ‖x‖ := Real.norm_of_nonneg (norm_nonneg' _)
@[to_additive (attr := simp) nnnorm_norm]
lemma nnnorm_norm' (x : E) : ‖‖x‖‖₊ = ‖x‖₊ := by simp [nnnorm]
@[to_additive (attr := simp) enorm_norm]
lemma enorm_norm' (x : E) : ‖‖x‖‖ₑ = ‖x‖ₑ := by simp [enorm]
lemma enorm_enorm {ε : Type*} [ENorm ε] (x : ε) : ‖‖x‖ₑ‖ₑ = ‖x‖ₑ := by simp [enorm]
end SeminormedCommGroup
section NormedGroup
variable [NormedGroup E] {a b : E}
@[to_additive (attr := simp) norm_le_zero_iff]
lemma norm_le_zero_iff' : ‖a‖ ≤ 0 ↔ a = 1 := by rw [← dist_one_right, dist_le_zero]
@[to_additive (attr := simp) norm_pos_iff]
lemma norm_pos_iff' : 0 < ‖a‖ ↔ a ≠ 1 := by rw [← not_le, norm_le_zero_iff']
@[to_additive (attr := simp) norm_eq_zero]
lemma norm_eq_zero' : ‖a‖ = 0 ↔ a = 1 := (norm_nonneg' a).le_iff_eq.symm.trans norm_le_zero_iff'
@[to_additive norm_ne_zero_iff]
lemma norm_ne_zero_iff' : ‖a‖ ≠ 0 ↔ a ≠ 1 := norm_eq_zero'.not
@[deprecated (since := "2024-11-24")] alias norm_le_zero_iff'' := norm_le_zero_iff'
@[deprecated (since := "2024-11-24")] alias norm_le_zero_iff''' := norm_le_zero_iff'
@[deprecated (since := "2024-11-24")] alias norm_pos_iff'' := norm_pos_iff'
@[deprecated (since := "2024-11-24")] alias norm_eq_zero'' := norm_eq_zero'
@[deprecated (since := "2024-11-24")] alias norm_eq_zero''' := norm_eq_zero'
@[to_additive]
theorem norm_div_eq_zero_iff : ‖a / b‖ = 0 ↔ a = b := by rw [norm_eq_zero', div_eq_one]
@[to_additive]
theorem norm_div_pos_iff : 0 < ‖a / b‖ ↔ a ≠ b := by
rw [(norm_nonneg' _).lt_iff_ne, ne_comm]
exact norm_div_eq_zero_iff.not
@[to_additive eq_of_norm_sub_le_zero]
theorem eq_of_norm_div_le_zero (h : ‖a / b‖ ≤ 0) : a = b := by
rwa [← div_eq_one, ← norm_le_zero_iff']
alias ⟨eq_of_norm_div_eq_zero, _⟩ := norm_div_eq_zero_iff
attribute [to_additive] eq_of_norm_div_eq_zero
@[to_additive]
theorem eq_one_or_norm_pos (a : E) : a = 1 ∨ 0 < ‖a‖ := by
simpa [eq_comm] using (norm_nonneg' a).eq_or_lt
@[to_additive]
theorem eq_one_or_nnnorm_pos (a : E) : a = 1 ∨ 0 < ‖a‖₊ :=
eq_one_or_norm_pos a
@[to_additive (attr := simp) nnnorm_eq_zero]
theorem nnnorm_eq_zero' : ‖a‖₊ = 0 ↔ a = 1 := by
rw [← NNReal.coe_eq_zero, coe_nnnorm', norm_eq_zero']
@[to_additive nnnorm_ne_zero_iff]
theorem nnnorm_ne_zero_iff' : ‖a‖₊ ≠ 0 ↔ a ≠ 1 :=
nnnorm_eq_zero'.not
@[to_additive (attr := simp) nnnorm_pos]
lemma nnnorm_pos' : 0 < ‖a‖₊ ↔ a ≠ 1 := pos_iff_ne_zero.trans nnnorm_ne_zero_iff'
variable (E)
/-- The norm of a normed group as a group norm. -/
@[to_additive "The norm of a normed group as an additive group norm."]
def normGroupNorm : GroupNorm E :=
{ normGroupSeminorm _ with eq_one_of_map_eq_zero' := fun _ => norm_eq_zero'.1 }
@[simp]
theorem coe_normGroupNorm : ⇑(normGroupNorm E) = norm :=
rfl
end NormedGroup
section NormedAddGroup
variable [NormedAddGroup E] [TopologicalSpace α] {f : α → E}
/-! Some relations with `HasCompactSupport` -/
theorem hasCompactSupport_norm_iff : (HasCompactSupport fun x => ‖f x‖) ↔ HasCompactSupport f :=
hasCompactSupport_comp_left norm_eq_zero
alias ⟨_, HasCompactSupport.norm⟩ := hasCompactSupport_norm_iff
end NormedAddGroup
lemma tendsto_norm_atTop_atTop : Tendsto (norm : ℝ → ℝ) atTop atTop := tendsto_abs_atTop_atTop
/-! ### `positivity` extensions -/
namespace Mathlib.Meta.Positivity
open Lean Meta Qq Function
/-- Extension for the `positivity` tactic: multiplicative norms are always nonnegative, and positive
on non-one inputs. -/
@[positivity ‖_‖]
def evalMulNorm : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q(@Norm.norm $E $_n $a) =>
let _seminormedGroup_E ← synthInstanceQ q(SeminormedGroup $E)
assertInstancesCommute
-- Check whether we are in a normed group and whether the context contains a `a ≠ 1` assumption
let o : Option (Q(NormedGroup $E) × Q($a ≠ 1)) := ← do
let .some normedGroup_E ← trySynthInstanceQ q(NormedGroup $E) | return none
let some pa ← findLocalDeclWithTypeQ? q($a ≠ 1) | return none
return some (normedGroup_E, pa)
match o with
-- If so, return a proof of `0 < ‖a‖`
| some (_normedGroup_E, pa) =>
assertInstancesCommute
return .positive q(norm_pos_iff'.2 $pa)
-- Else, return a proof of `0 ≤ ‖a‖`
| none => return .nonnegative q(norm_nonneg' $a)
| _, _, _ => throwError "not `‖·‖`"
/-- Extension for the `positivity` tactic: additive norms are always nonnegative, and positive
on non-zero inputs. -/
@[positivity ‖_‖]
def evalAddNorm : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q(@Norm.norm $E $_n $a) =>
let _seminormedAddGroup_E ← synthInstanceQ q(SeminormedAddGroup $E)
assertInstancesCommute
-- Check whether we are in a normed group and whether the context contains a `a ≠ 0` assumption
let o : Option (Q(NormedAddGroup $E) × Q($a ≠ 0)) := ← do
let .some normedAddGroup_E ← trySynthInstanceQ q(NormedAddGroup $E) | return none
let some pa ← findLocalDeclWithTypeQ? q($a ≠ 0) | return none
return some (normedAddGroup_E, pa)
match o with
-- If so, return a proof of `0 < ‖a‖`
| some (_normedAddGroup_E, pa) =>
assertInstancesCommute
return .positive q(norm_pos_iff.2 $pa)
-- Else, return a proof of `0 ≤ ‖a‖`
| none => return .nonnegative q(norm_nonneg $a)
| _, _, _ => throwError "not `‖·‖`"
end Mathlib.Meta.Positivity
| Mathlib/Analysis/Normed/Group/Basic.lean | 1,391 | 1,400 | |
/-
Copyright (c) 2024 Andrew Yang. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Andrew Yang
-/
import Mathlib.LinearAlgebra.Dimension.Constructions
import Mathlib.LinearAlgebra.Dimension.Finite
import Mathlib.LinearAlgebra.Isomorphisms
import Mathlib.Logic.Equiv.Fin.Rotate
/-!
# The rank nullity theorem
In this file we provide the rank nullity theorem as a typeclass, and prove various corollaries
of the theorem. The main definition is `HasRankNullity.{u} R`, which states that
1. Every `R`-module `M : Type u` has a linear independent subset of cardinality `Module.rank R M`.
2. `rank (M ⧸ N) + rank N = rank M` for every `R`-module `M : Type u` and every `N : Submodule R M`.
The following instances are provided in mathlib:
1. `DivisionRing.hasRankNullity` for division rings in `LinearAlgebra/Dimension/DivisionRing.lean`.
2. `IsDomain.hasRankNullity` for commutative domains in `LinearAlgebra/Dimension/Localization.lean`.
TODO: prove the rank-nullity theorem for `[Ring R] [IsDomain R] [StrongRankCondition R]`.
See `nonempty_oreSet_of_strongRankCondition` for a start.
-/
universe u v
open Function Set Cardinal Submodule LinearMap
variable {R} {M M₁ M₂ M₃ : Type u} {M' : Type v} [Ring R]
variable [AddCommGroup M] [AddCommGroup M₁] [AddCommGroup M₂] [AddCommGroup M₃] [AddCommGroup M']
variable [Module R M] [Module R M₁] [Module R M₂] [Module R M₃] [Module R M']
/--
`HasRankNullity.{u}` is a class of rings satisfying
1. Every `R`-module `M : Type u` has a linear independent subset of cardinality `Module.rank R M`.
2. `rank (M ⧸ N) + rank N = rank M` for every `R`-module `M : Type u` and every `N : Submodule R M`.
Usually such a ring satisfies `HasRankNullity.{w}` for all universes `w`, and the universe
argument is there because of technical limitations to universe polymorphism.
See `DivisionRing.hasRankNullity` and `IsDomain.hasRankNullity`.
-/
@[pp_with_univ]
class HasRankNullity (R : Type v) [inst : Ring R] : Prop where
exists_set_linearIndependent : ∀ (M : Type u) [AddCommGroup M] [Module R M],
∃ s : Set M, #s = Module.rank R M ∧ LinearIndepOn R id s
rank_quotient_add_rank : ∀ {M : Type u} [AddCommGroup M] [Module R M] (N : Submodule R M),
Module.rank R (M ⧸ N) + Module.rank R N = Module.rank R M
variable [HasRankNullity.{u} R]
lemma Submodule.rank_quotient_add_rank (N : Submodule R M) :
Module.rank R (M ⧸ N) + Module.rank R N = Module.rank R M :=
HasRankNullity.rank_quotient_add_rank N
variable (R M) in
lemma exists_set_linearIndependent :
∃ s : Set M, #s = Module.rank R M ∧ LinearIndependent (ι := s) R Subtype.val :=
HasRankNullity.exists_set_linearIndependent M
variable (R) in
theorem nontrivial_of_hasRankNullity : Nontrivial R := by
refine (subsingleton_or_nontrivial R).resolve_left fun H ↦ ?_
have := rank_quotient_add_rank (R := R) (M := PUnit) ⊥
simp [one_add_one_eq_two] at this
|
attribute [local instance] nontrivial_of_hasRankNullity
theorem LinearMap.lift_rank_range_add_rank_ker (f : M →ₗ[R] M') :
lift.{u} (Module.rank R (LinearMap.range f)) + lift.{v} (Module.rank R (LinearMap.ker f)) =
| Mathlib/LinearAlgebra/Dimension/RankNullity.lean | 68 | 72 |
/-
Copyright (c) 2018 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Kenny Lau, Johan Commelin, Mario Carneiro, Kevin Buzzard,
Amelia Livingston, Yury Kudryashov
-/
import Mathlib.Algebra.BigOperators.Group.Multiset.Defs
import Mathlib.Algebra.FreeMonoid.Basic
import Mathlib.Algebra.Group.Idempotent
import Mathlib.Algebra.Group.Nat.Hom
import Mathlib.Algebra.Group.Submonoid.MulOpposite
import Mathlib.Algebra.Group.Submonoid.Operations
import Mathlib.Data.Fintype.EquivFin
import Mathlib.Data.Int.Basic
/-!
# Submonoids: membership criteria
In this file we prove various facts about membership in a submonoid:
* `pow_mem`, `nsmul_mem`: if `x ∈ S` where `S` is a multiplicative (resp., additive) submonoid and
`n` is a natural number, then `x^n` (resp., `n • x`) belongs to `S`;
* `mem_iSup_of_directed`, `coe_iSup_of_directed`, `mem_sSup_of_directedOn`,
`coe_sSup_of_directedOn`: the supremum of a directed collection of submonoid is their union.
* `sup_eq_range`, `mem_sup`: supremum of two submonoids `S`, `T` of a commutative monoid is the set
of products;
* `closure_singleton_eq`, `mem_closure_singleton`, `mem_closure_pair`: the multiplicative (resp.,
additive) closure of `{x}` consists of powers (resp., natural multiples) of `x`, and a similar
result holds for the closure of `{x, y}`.
## Tags
submonoid, submonoids
-/
assert_not_exists MonoidWithZero
variable {M A B : Type*}
section Assoc
variable [Monoid M] [SetLike B M] [SubmonoidClass B M] {S : B}
end Assoc
section NonAssoc
variable [MulOneClass M]
open Set
namespace Submonoid
-- TODO: this section can be generalized to `[SubmonoidClass B M] [CompleteLattice B]`
-- such that `CompleteLattice.LE` coincides with `SetLike.LE`
@[to_additive]
theorem mem_iSup_of_directed {ι} [hι : Nonempty ι] {S : ι → Submonoid M} (hS : Directed (· ≤ ·) S)
{x : M} : (x ∈ ⨆ i, S i) ↔ ∃ i, x ∈ S i := by
refine ⟨?_, fun ⟨i, hi⟩ ↦ le_iSup S i hi⟩
suffices x ∈ closure (⋃ i, (S i : Set M)) → ∃ i, x ∈ S i by
simpa only [closure_iUnion, closure_eq (S _)] using this
refine closure_induction (fun _ ↦ mem_iUnion.1) ?_ ?_
· exact hι.elim fun i ↦ ⟨i, (S i).one_mem⟩
· rintro x y - - ⟨i, hi⟩ ⟨j, hj⟩
rcases hS i j with ⟨k, hki, hkj⟩
exact ⟨k, (S k).mul_mem (hki hi) (hkj hj)⟩
@[to_additive]
theorem coe_iSup_of_directed {ι} [Nonempty ι] {S : ι → Submonoid M} (hS : Directed (· ≤ ·) S) :
((⨆ i, S i : Submonoid M) : Set M) = ⋃ i, S i :=
Set.ext fun x ↦ by simp [mem_iSup_of_directed hS]
@[to_additive]
theorem mem_sSup_of_directedOn {S : Set (Submonoid M)} (Sne : S.Nonempty)
(hS : DirectedOn (· ≤ ·) S) {x : M} : x ∈ sSup S ↔ ∃ s ∈ S, x ∈ s := by
haveI : Nonempty S := Sne.to_subtype
simp [sSup_eq_iSup', mem_iSup_of_directed hS.directed_val, SetCoe.exists, Subtype.coe_mk]
@[to_additive]
theorem coe_sSup_of_directedOn {S : Set (Submonoid M)} (Sne : S.Nonempty)
(hS : DirectedOn (· ≤ ·) S) : (↑(sSup S) : Set M) = ⋃ s ∈ S, ↑s :=
Set.ext fun x => by simp [mem_sSup_of_directedOn Sne hS]
@[to_additive]
theorem mem_sup_left {S T : Submonoid M} : ∀ {x : M}, x ∈ S → x ∈ S ⊔ T := by
rw [← SetLike.le_def]
exact le_sup_left
@[to_additive]
theorem mem_sup_right {S T : Submonoid M} : ∀ {x : M}, x ∈ T → x ∈ S ⊔ T := by
rw [← SetLike.le_def]
exact le_sup_right
@[to_additive]
theorem mul_mem_sup {S T : Submonoid M} {x y : M} (hx : x ∈ S) (hy : y ∈ T) : x * y ∈ S ⊔ T :=
(S ⊔ T).mul_mem (mem_sup_left hx) (mem_sup_right hy)
@[to_additive]
theorem mem_iSup_of_mem {ι : Sort*} {S : ι → Submonoid M} (i : ι) :
∀ {x : M}, x ∈ S i → x ∈ iSup S := by
rw [← SetLike.le_def]
exact le_iSup _ _
@[to_additive]
theorem mem_sSup_of_mem {S : Set (Submonoid M)} {s : Submonoid M} (hs : s ∈ S) :
∀ {x : M}, x ∈ s → x ∈ sSup S := by
rw [← SetLike.le_def]
exact le_sSup hs
/-- An induction principle for elements of `⨆ i, S i`.
If `C` holds for `1` and all elements of `S i` for all `i`, and is preserved under multiplication,
then it holds for all elements of the supremum of `S`. -/
@[to_additive (attr := elab_as_elim)
" An induction principle for elements of `⨆ i, S i`.
If `C` holds for `0` and all elements of `S i` for all `i`, and is preserved under addition,
then it holds for all elements of the supremum of `S`. "]
theorem iSup_induction {ι : Sort*} (S : ι → Submonoid M) {motive : M → Prop} {x : M}
(hx : x ∈ ⨆ i, S i) (mem : ∀ (i), ∀ x ∈ S i, motive x) (one : motive 1)
(mul : ∀ x y, motive x → motive y → motive (x * y)) : motive x := by
rw [iSup_eq_closure] at hx
refine closure_induction (fun x hx => ?_) one (fun _ _ _ _ ↦ mul _ _) hx
obtain ⟨i, hi⟩ := Set.mem_iUnion.mp hx
exact mem _ _ hi
/-- A dependent version of `Submonoid.iSup_induction`. -/
@[to_additive (attr := elab_as_elim) "A dependent version of `AddSubmonoid.iSup_induction`. "]
theorem iSup_induction' {ι : Sort*} (S : ι → Submonoid M) {motive : ∀ x, (x ∈ ⨆ i, S i) → Prop}
(mem : ∀ (i), ∀ (x) (hxS : x ∈ S i), motive x (mem_iSup_of_mem i hxS))
(one : motive 1 (one_mem _))
(mul : ∀ x y hx hy, motive x hx → motive y hy → motive (x * y) (mul_mem ‹_› ‹_›)) {x : M}
(hx : x ∈ ⨆ i, S i) : motive x hx := by
refine Exists.elim (?_ : ∃ Hx, motive x Hx) fun (hx : x ∈ ⨆ i, S i) (hc : motive x hx) => hc
refine @iSup_induction _ _ ι S (fun m => ∃ hm, motive m hm) _ hx (fun i x hx => ?_) ?_
fun x y => ?_
· exact ⟨_, mem _ _ hx⟩
· exact ⟨_, one⟩
· rintro ⟨_, Cx⟩ ⟨_, Cy⟩
exact ⟨_, mul _ _ _ _ Cx Cy⟩
end Submonoid
end NonAssoc
namespace FreeMonoid
variable {α : Type*}
open Submonoid
@[to_additive]
theorem closure_range_of : closure (Set.range <| @of α) = ⊤ :=
eq_top_iff.2 fun x _ =>
FreeMonoid.recOn x (one_mem _) fun _x _xs hxs =>
mul_mem (subset_closure <| Set.mem_range_self _) hxs
end FreeMonoid
namespace Submonoid
variable [Monoid M] {a : M}
open MonoidHom
theorem closure_singleton_eq (x : M) : closure ({x} : Set M) = mrange (powersHom M x) :=
closure_eq_of_le (Set.singleton_subset_iff.2 ⟨Multiplicative.ofAdd 1, pow_one x⟩) fun _ ⟨_, hn⟩ =>
hn ▸ pow_mem (subset_closure <| Set.mem_singleton _) _
/-- The submonoid generated by an element of a monoid equals the set of natural number powers of
the element. -/
theorem mem_closure_singleton {x y : M} : y ∈ closure ({x} : Set M) ↔ ∃ n : ℕ, x ^ n = y := by
rw [closure_singleton_eq, mem_mrange]; rfl
theorem mem_closure_singleton_self {y : M} : y ∈ closure ({y} : Set M) :=
mem_closure_singleton.2 ⟨1, pow_one y⟩
theorem closure_singleton_one : closure ({1} : Set M) = ⊥ := by
simp [eq_bot_iff_forall, mem_closure_singleton]
section Submonoid
variable {S : Submonoid M} [Fintype S]
open Fintype
/- curly brackets `{}` are used here instead of instance brackets `[]` because
the instance in a goal is often not the same as the one inferred by type class inference. -/
@[to_additive]
theorem card_bot {_ : Fintype (⊥ : Submonoid M)} : card (⊥ : Submonoid M) = 1 :=
card_eq_one_iff.2
⟨⟨(1 : M), Set.mem_singleton 1⟩, fun ⟨_y, hy⟩ => Subtype.eq <| mem_bot.1 hy⟩
@[to_additive]
theorem eq_bot_of_card_le (h : card S ≤ 1) : S = ⊥ :=
let _ := card_le_one_iff_subsingleton.mp h
eq_bot_of_subsingleton S
@[to_additive]
theorem eq_bot_of_card_eq (h : card S = 1) : S = ⊥ :=
S.eq_bot_of_card_le (le_of_eq h)
@[to_additive card_le_one_iff_eq_bot]
theorem card_le_one_iff_eq_bot : card S ≤ 1 ↔ S = ⊥ :=
⟨fun h =>
(eq_bot_iff_forall _).2 fun x hx => by
simpa [Subtype.ext_iff] using card_le_one_iff.1 h ⟨x, hx⟩ 1,
fun h => by simp [h]⟩
@[to_additive]
lemma eq_bot_iff_card : S = ⊥ ↔ card S = 1 :=
⟨by rintro rfl; exact card_bot, eq_bot_of_card_eq⟩
end Submonoid
@[to_additive]
theorem _root_.FreeMonoid.mrange_lift {α} (f : α → M) :
mrange (FreeMonoid.lift f) = closure (Set.range f) := by
rw [mrange_eq_map, ← FreeMonoid.closure_range_of, map_mclosure, ← Set.range_comp,
FreeMonoid.lift_comp_of]
@[to_additive]
theorem closure_eq_mrange (s : Set M) : closure s = mrange (FreeMonoid.lift ((↑) : s → M)) := by
rw [FreeMonoid.mrange_lift, Subtype.range_coe]
@[to_additive]
theorem closure_eq_image_prod (s : Set M) :
(closure s : Set M) = List.prod '' { l : List M | ∀ x ∈ l, x ∈ s } := by
rw [closure_eq_mrange, coe_mrange, ← Set.range_list_map_coe, ← Set.range_comp]
exact congrArg _ (funext <| FreeMonoid.lift_apply _)
@[to_additive]
theorem exists_list_of_mem_closure {s : Set M} {x : M} (hx : x ∈ closure s) :
∃ l : List M, (∀ y ∈ l, y ∈ s) ∧ l.prod = x := by
rwa [← SetLike.mem_coe, closure_eq_image_prod, Set.mem_image] at hx
@[to_additive]
theorem exists_multiset_of_mem_closure {M : Type*} [CommMonoid M] {s : Set M} {x : M}
(hx : x ∈ closure s) : ∃ l : Multiset M, (∀ y ∈ l, y ∈ s) ∧ l.prod = x := by
obtain ⟨l, h1, h2⟩ := exists_list_of_mem_closure hx
exact ⟨l, h1, (Multiset.prod_coe l).trans h2⟩
@[to_additive (attr := elab_as_elim)]
theorem closure_induction_left {s : Set M} {p : (m : M) → m ∈ closure s → Prop}
(one : p 1 (one_mem _))
(mul_left : ∀ x (hx : x ∈ s), ∀ (y) hy, p y hy → p (x * y) (mul_mem (subset_closure hx) hy))
{x : M} (h : x ∈ closure s) :
p x h := by
simp_rw [closure_eq_mrange] at h
obtain ⟨l, rfl⟩ := h
induction l using FreeMonoid.inductionOn' with
| one => exact one
| mul_of x y ih =>
simp only [map_mul, FreeMonoid.lift_eval_of]
refine mul_left _ x.prop (FreeMonoid.lift Subtype.val y) _ (ih ?_)
simp only [closure_eq_mrange, mem_mrange, exists_apply_eq_apply]
@[to_additive (attr := elab_as_elim)]
theorem induction_of_closure_eq_top_left {s : Set M} {p : M → Prop} (hs : closure s = ⊤) (x : M)
(one : p 1) (mul : ∀ x ∈ s, ∀ (y), p y → p (x * y)) : p x := by
have : x ∈ closure s := by simp [hs]
induction this using closure_induction_left with
| one => exact one
| mul_left x hx y _ ih => exact mul x hx y ih
@[to_additive (attr := elab_as_elim)]
theorem closure_induction_right {s : Set M} {p : (m : M) → m ∈ closure s → Prop}
(one : p 1 (one_mem _))
(mul_right : ∀ x hx, ∀ (y) (hy : y ∈ s), p x hx → p (x * y) (mul_mem hx (subset_closure hy)))
{x : M} (h : x ∈ closure s) : p x h :=
closure_induction_left (s := MulOpposite.unop ⁻¹' s)
(p := fun m hm => p m.unop <| by rwa [← op_closure] at hm)
one
(fun _x hx _y _ => mul_right _ _ _ hx)
(by rwa [← op_closure])
@[to_additive (attr := elab_as_elim)]
theorem induction_of_closure_eq_top_right {s : Set M} {p : M → Prop} (hs : closure s = ⊤) (x : M)
(H1 : p 1) (Hmul : ∀ (x), ∀ y ∈ s, p x → p (x * y)) : p x := by
have : x ∈ closure s := by simp [hs]
induction this using closure_induction_right with
| one => exact H1
| mul_right x _ y hy ih => exact Hmul x y hy ih
/-- The submonoid generated by an element. -/
def powers (n : M) : Submonoid M :=
Submonoid.copy (mrange (powersHom M n)) (Set.range (n ^ · : ℕ → M)) <|
Set.ext fun n => exists_congr fun i => by simp; rfl
theorem mem_powers (n : M) : n ∈ powers n :=
⟨1, pow_one _⟩
theorem coe_powers (x : M) : ↑(powers x) = Set.range fun n : ℕ => x ^ n :=
rfl
theorem mem_powers_iff (x z : M) : x ∈ powers z ↔ ∃ n : ℕ, z ^ n = x :=
Iff.rfl
noncomputable instance decidableMemPowers : DecidablePred (· ∈ Submonoid.powers a) :=
Classical.decPred _
-- Porting note (https://github.com/leanprover-community/mathlib4/issues/11215): TODO the following instance should follow from a more general principle
-- See also https://github.com/leanprover-community/mathlib4/issues/2417
noncomputable instance fintypePowers [Fintype M] : Fintype (powers a) :=
inferInstanceAs <| Fintype {y // y ∈ powers a}
theorem powers_eq_closure (n : M) : powers n = closure {n} := by
ext
exact mem_closure_singleton.symm
lemma powers_le {n : M} {P : Submonoid M} : powers n ≤ P ↔ n ∈ P := by simp [powers_eq_closure]
lemma powers_one : powers (1 : M) = ⊥ := bot_unique <| powers_le.2 <| one_mem _
theorem _root_.IsIdempotentElem.coe_powers {a : M} (ha : IsIdempotentElem a) :
(Submonoid.powers a : Set M) = {1, a} :=
let S : Submonoid M :=
{ carrier := {1, a},
mul_mem' := by
rintro _ _ (rfl|rfl) (rfl|rfl)
· rw [one_mul]; exact .inl rfl
· rw [one_mul]; exact .inr rfl
· rw [mul_one]; exact .inr rfl
· rw [ha]; exact .inr rfl
one_mem' := .inl rfl }
suffices Submonoid.powers a = S from congr_arg _ this
le_antisymm (Submonoid.powers_le.mpr <| .inr rfl)
(by rintro _ (rfl|rfl); exacts [one_mem _, Submonoid.mem_powers _])
/-- The submonoid generated by an element is a group if that element has finite order. -/
abbrev groupPowers {x : M} {n : ℕ} (hpos : 0 < n) (hx : x ^ n = 1) : Group (powers x) where
inv x := x ^ (n - 1)
inv_mul_cancel y := Subtype.ext <| by
obtain ⟨_, k, rfl⟩ := y
simp only [coe_one, coe_mul, SubmonoidClass.coe_pow]
rw [← pow_succ, Nat.sub_add_cancel hpos, ← pow_mul, mul_comm, pow_mul, hx, one_pow]
zpow z x := x ^ z.natMod n
zpow_zero' z := by simp only [Int.natMod, Int.zero_emod, Int.toNat_zero, pow_zero]
zpow_neg' m x := Subtype.ext <| by
obtain ⟨_, k, rfl⟩ := x
simp only [← pow_mul, Int.natMod, SubmonoidClass.coe_pow]
rw [Int.negSucc_eq, ← Int.natCast_succ, ← Int.add_mul_emod_self_right (b := (m + 1 : ℕ))]
nth_rw 1 [← mul_one ((m + 1 : ℕ) : ℤ)]
rw [← sub_eq_neg_add, ← Int.mul_sub, ← Int.natCast_pred_of_pos hpos]; norm_cast
simp only [Int.toNat_natCast]
rw [mul_comm, pow_mul, ← pow_eq_pow_mod _ hx, mul_comm k, mul_assoc, pow_mul _ (_ % _),
← pow_eq_pow_mod _ hx, pow_mul, pow_mul]
zpow_succ' m x := Subtype.ext <| by
obtain ⟨_, k, rfl⟩ := x
simp only [← pow_mul, Int.natMod, SubmonoidClass.coe_pow, coe_mul]
norm_cast
iterate 2 rw [Int.toNat_natCast, mul_comm, pow_mul, ← pow_eq_pow_mod _ hx]
rw [← pow_mul _ m, mul_comm, pow_mul, ← pow_succ, ← pow_mul, mul_comm, pow_mul]
/-- Exponentiation map from natural numbers to powers. -/
@[simps!]
def pow (n : M) (m : ℕ) : powers n :=
(powersHom M n).mrangeRestrict (Multiplicative.ofAdd m)
theorem pow_apply (n : M) (m : ℕ) : Submonoid.pow n m = ⟨n ^ m, m, rfl⟩ :=
rfl
/-- Logarithms from powers to natural numbers. -/
def log [DecidableEq M] {n : M} (p : powers n) : ℕ :=
Nat.find <| (mem_powers_iff p.val n).mp p.prop
@[simp]
theorem pow_log_eq_self [DecidableEq M] {n : M} (p : powers n) : pow n (log p) = p :=
Subtype.ext <| Nat.find_spec p.prop
theorem pow_right_injective_iff_pow_injective {n : M} :
(Function.Injective fun m : ℕ => n ^ m) ↔ Function.Injective (pow n) :=
Subtype.coe_injective.of_comp_iff (pow n)
@[simp]
theorem log_pow_eq_self [DecidableEq M] {n : M} (h : Function.Injective fun m : ℕ => n ^ m)
(m : ℕ) : log (pow n m) = m :=
pow_right_injective_iff_pow_injective.mp h <| pow_log_eq_self _
/-- The exponentiation map is an isomorphism from the additive monoid on natural numbers to powers
when it is injective. The inverse is given by the logarithms. -/
@[simps]
def powLogEquiv [DecidableEq M] {n : M} (h : Function.Injective fun m : ℕ => n ^ m) :
Multiplicative ℕ ≃* powers n where
toFun m := pow n m.toAdd
invFun m := Multiplicative.ofAdd (log m)
left_inv := log_pow_eq_self h
right_inv := pow_log_eq_self
map_mul' _ _ := by simp only [pow, map_mul, ofAdd_add, toAdd_mul]
theorem log_mul [DecidableEq M] {n : M} (h : Function.Injective fun m : ℕ => n ^ m)
(x y : powers (n : M)) : log (x * y) = log x + log y :=
map_mul (powLogEquiv h).symm x y
theorem log_pow_int_eq_self {x : ℤ} (h : 1 < x.natAbs) (m : ℕ) : log (pow x m) = m :=
(powLogEquiv (Int.pow_right_injective h)).symm_apply_apply _
@[simp]
theorem map_powers {N : Type*} {F : Type*} [Monoid N] [FunLike F M N] [MonoidHomClass F M N]
(f : F) (m : M) :
(powers m).map f = powers (f m) := by
simp only [powers_eq_closure, map_mclosure f, Set.image_singleton]
end Submonoid
@[to_additive]
theorem IsScalarTower.of_mclosure_eq_top {N α} [Monoid M] [MulAction M N] [SMul N α] [MulAction M α]
{s : Set M} (htop : Submonoid.closure s = ⊤)
(hs : ∀ x ∈ s, ∀ (y : N) (z : α), (x • y) • z = x • y • z) : IsScalarTower M N α := by
refine ⟨fun x => Submonoid.induction_of_closure_eq_top_left htop x ?_ ?_⟩
· intro y z
rw [one_smul, one_smul]
· clear x
intro x hx x' hx' y z
rw [mul_smul, mul_smul, hs x hx, hx']
@[to_additive]
theorem SMulCommClass.of_mclosure_eq_top {N α} [Monoid M] [SMul N α] [MulAction M α] {s : Set M}
(htop : Submonoid.closure s = ⊤) (hs : ∀ x ∈ s, ∀ (y : N) (z : α), x • y • z = y • x • z) :
SMulCommClass M N α := by
refine ⟨fun x => Submonoid.induction_of_closure_eq_top_left htop x ?_ ?_⟩
· intro y z
rw [one_smul, one_smul]
· clear x
intro x hx x' hx' y z
rw [mul_smul, mul_smul, hx', hs x hx]
namespace Submonoid
variable {N : Type*} [CommMonoid N]
open MonoidHom
@[to_additive]
theorem sup_eq_range (s t : Submonoid N) : s ⊔ t = mrange (s.subtype.coprod t.subtype) := by
rw [mrange_eq_map, ← mrange_inl_sup_mrange_inr, map_sup, map_mrange, coprod_comp_inl, map_mrange,
coprod_comp_inr, mrange_subtype, mrange_subtype]
@[to_additive]
theorem mem_sup {s t : Submonoid N} {x : N} : x ∈ s ⊔ t ↔ ∃ y ∈ s, ∃ z ∈ t, y * z = x := by
simp only [sup_eq_range, mem_mrange, coprod_apply, coe_subtype, Prod.exists,
Subtype.exists, exists_prop]
end Submonoid
namespace AddSubmonoid
variable [AddMonoid A]
open Set
theorem closure_singleton_eq (x : A) :
closure ({x} : Set A) = AddMonoidHom.mrange (multiplesHom A x) :=
closure_eq_of_le (Set.singleton_subset_iff.2 ⟨1, one_nsmul x⟩) fun _ ⟨_n, hn⟩ =>
hn ▸ nsmul_mem (subset_closure <| Set.mem_singleton _) _
/-- The `AddSubmonoid` generated by an element of an `AddMonoid` equals the set of
natural number multiples of the element. -/
theorem mem_closure_singleton {x y : A} : y ∈ closure ({x} : Set A) ↔ ∃ n : ℕ, n • x = y := by
rw [closure_singleton_eq, AddMonoidHom.mem_mrange]; rfl
theorem closure_singleton_zero : closure ({0} : Set A) = ⊥ := by
simp [eq_bot_iff_forall, mem_closure_singleton, nsmul_zero]
/-- The additive submonoid generated by an element. -/
def multiples (x : A) : AddSubmonoid A :=
AddSubmonoid.copy (AddMonoidHom.mrange (multiplesHom A x)) (Set.range (fun i => i • x : ℕ → A)) <|
Set.ext fun n => exists_congr fun i => by simp
attribute [to_additive existing] Submonoid.powers
attribute [to_additive (attr := simp)] Submonoid.mem_powers
attribute [to_additive (attr := norm_cast)] Submonoid.coe_powers
attribute [to_additive] Submonoid.mem_powers_iff
attribute [to_additive] Submonoid.decidableMemPowers
attribute [to_additive] Submonoid.fintypePowers
attribute [to_additive] Submonoid.powers_eq_closure
attribute [to_additive] Submonoid.powers_le
attribute [to_additive (attr := simp)] Submonoid.powers_one
attribute [to_additive "The additive submonoid generated by an element is
an additive group if that element has finite order."] Submonoid.groupPowers
end AddSubmonoid
namespace Submonoid
/-- An element is in the closure of a two-element set if it is a linear combination of those two
elements. -/
@[to_additive
"An element is in the closure of a two-element set if it is a linear combination of
those two elements."]
theorem mem_closure_pair {A : Type*} [CommMonoid A] (a b c : A) :
c ∈ Submonoid.closure ({a, b} : Set A) ↔ ∃ m n : ℕ, a ^ m * b ^ n = c := by
rw [← Set.singleton_union, Submonoid.closure_union, mem_sup]
simp_rw [mem_closure_singleton, exists_exists_eq_and]
end Submonoid
section mul_add
theorem ofMul_image_powers_eq_multiples_ofMul [Monoid M] {x : M} :
Additive.ofMul '' (Submonoid.powers x : Set M) = AddSubmonoid.multiples (Additive.ofMul x) := by
ext
constructor
· rintro ⟨y, ⟨n, hy1⟩, hy2⟩
use n
simpa [← ofMul_pow, hy1]
· rintro ⟨n, hn⟩
refine ⟨x ^ n, ⟨n, rfl⟩, ?_⟩
rwa [ofMul_pow]
theorem ofAdd_image_multiples_eq_powers_ofAdd [AddMonoid A] {x : A} :
Multiplicative.ofAdd '' (AddSubmonoid.multiples x : Set A) =
Submonoid.powers (Multiplicative.ofAdd x) := by
symm
rw [Equiv.eq_image_iff_symm_image_eq]
exact ofMul_image_powers_eq_multiples_ofMul
end mul_add
| Mathlib/Algebra/Group/Submonoid/Membership.lean | 786 | 791 | |
/-
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.Algebra.Group.Action.Pointwise.Set.Basic
import Mathlib.Algebra.Group.Submonoid.Membership
import Mathlib.Algebra.Order.BigOperators.Group.List
import Mathlib.Order.WellFoundedSet
/-!
# Pointwise instances on `Submonoid`s and `AddSubmonoid`s
This file provides:
* `Submonoid.inv`
* `AddSubmonoid.neg`
and the actions
* `Submonoid.pointwiseMulAction`
* `AddSubmonoid.pointwiseAddAction`
which matches the action of `Set.mulActionSet`.
## Implementation notes
Most of the lemmas in this file are direct copies of lemmas from
`Mathlib.Algebra.Group.Pointwise.Set.Basic` and `Mathlib.Algebra.Group.Action.Pointwise.Set.Basic`.
While the statements of these lemmas are defeq, we repeat them here due to them not being
syntactically equal. Before adding new lemmas here, consider if they would also apply to the action
on `Set`s.
-/
assert_not_exists GroupWithZero
open Set Pointwise
variable {α G M R A S : Type*}
variable [Monoid M] [AddMonoid A]
@[to_additive (attr := simp, norm_cast)]
lemma coe_mul_coe [SetLike S M] [SubmonoidClass S M] (H : S) : H * H = (H : Set M) := by
aesop (add simp mem_mul)
set_option linter.unusedVariables false in
@[to_additive (attr := simp)]
lemma coe_set_pow [SetLike S M] [SubmonoidClass S M] :
∀ {n} (hn : n ≠ 0) (H : S), (H ^ n : Set M) = H
| 1, _, H => by simp
| n + 2, _, H => by rw [pow_succ, coe_set_pow n.succ_ne_zero, coe_mul_coe]
/-! Some lemmas about pointwise multiplication and submonoids. Ideally we put these in
`GroupTheory.Submonoid.Basic`, but currently we cannot because that file is imported by this. -/
namespace Submonoid
variable {s t u : Set M}
@[to_additive]
theorem mul_subset {S : Submonoid M} (hs : s ⊆ S) (ht : t ⊆ S) : s * t ⊆ S :=
mul_subset_iff.2 fun _x hx _y hy ↦ mul_mem (hs hx) (ht hy)
@[to_additive]
theorem mul_subset_closure (hs : s ⊆ u) (ht : t ⊆ u) : s * t ⊆ Submonoid.closure u :=
mul_subset (Subset.trans hs Submonoid.subset_closure) (Subset.trans ht Submonoid.subset_closure)
@[to_additive]
theorem coe_mul_self_eq (s : Submonoid M) : (s : Set M) * s = s := by
ext x
refine ⟨?_, fun h => ⟨x, h, 1, s.one_mem, mul_one x⟩⟩
rintro ⟨a, ha, b, hb, rfl⟩
exact s.mul_mem ha hb
@[to_additive]
theorem closure_mul_le (S T : Set M) : closure (S * T) ≤ closure S ⊔ closure T :=
sInf_le fun _x ⟨_s, hs, _t, ht, hx⟩ => hx ▸
(closure S ⊔ closure T).mul_mem (SetLike.le_def.mp le_sup_left <| subset_closure hs)
(SetLike.le_def.mp le_sup_right <| subset_closure ht)
@[to_additive]
lemma closure_pow_le : ∀ {n}, n ≠ 0 → closure (s ^ n) ≤ closure s
| 1, _ => by simp
| n + 2, _ =>
calc
closure (s ^ (n + 2))
_ = closure (s ^ (n + 1) * s) := by rw [pow_succ]
_ ≤ closure (s ^ (n + 1)) ⊔ closure s := closure_mul_le ..
_ ≤ closure s ⊔ closure s := by gcongr ?_ ⊔ _; exact closure_pow_le n.succ_ne_zero
_ = closure s := sup_idem _
@[to_additive]
lemma closure_pow {n : ℕ} (hs : 1 ∈ s) (hn : n ≠ 0) : closure (s ^ n) = closure s :=
(closure_pow_le hn).antisymm <| by gcongr; exact subset_pow hs hn
@[to_additive]
theorem sup_eq_closure_mul (H K : Submonoid M) : H ⊔ K = closure ((H : Set M) * (K : Set M)) :=
le_antisymm
(sup_le (fun h hh => subset_closure ⟨h, hh, 1, K.one_mem, mul_one h⟩) fun k hk =>
subset_closure ⟨1, H.one_mem, k, hk, one_mul k⟩)
((closure_mul_le _ _).trans <| by rw [closure_eq, closure_eq])
@[to_additive]
theorem pow_smul_mem_closure_smul {N : Type*} [CommMonoid N] [MulAction M N] [IsScalarTower M N N]
(r : M) (s : Set N) {x : N} (hx : x ∈ closure s) : ∃ n : ℕ, r ^ n • x ∈ closure (r • s) := by
induction hx using closure_induction with
| mem x hx => exact ⟨1, subset_closure ⟨_, hx, by rw [pow_one]⟩⟩
| one => exact ⟨0, by simpa using one_mem _⟩
| mul x y _ _ hx hy =>
obtain ⟨⟨nx, hx⟩, ⟨ny, hy⟩⟩ := And.intro hx hy
use ny + nx
rw [pow_add, mul_smul, ← smul_mul_assoc, mul_comm, ← smul_mul_assoc]
exact mul_mem hy hx
variable [Group G]
/-- The submonoid with every element inverted. -/
@[to_additive "The additive submonoid with every element negated."]
protected def inv : Inv (Submonoid G) where
inv S :=
{ carrier := (S : Set G)⁻¹
mul_mem' := fun ha hb => by rw [mem_inv, mul_inv_rev]; exact mul_mem hb ha
one_mem' := mem_inv.2 <| by rw [inv_one]; exact S.one_mem' }
scoped[Pointwise] attribute [instance] Submonoid.inv AddSubmonoid.neg
@[to_additive (attr := simp)]
theorem coe_inv (S : Submonoid G) : ↑S⁻¹ = (S : Set G)⁻¹ :=
rfl
@[to_additive (attr := simp)]
theorem mem_inv {g : G} {S : Submonoid G} : g ∈ S⁻¹ ↔ g⁻¹ ∈ S :=
Iff.rfl
/-- Inversion is involutive on submonoids. -/
@[to_additive "Inversion is involutive on additive submonoids."]
def involutiveInv : InvolutiveInv (Submonoid G) :=
SetLike.coe_injective.involutiveInv _ fun _ => rfl
scoped[Pointwise] attribute [instance] Submonoid.involutiveInv AddSubmonoid.involutiveNeg
@[to_additive (attr := simp)]
theorem inv_le_inv (S T : Submonoid G) : S⁻¹ ≤ T⁻¹ ↔ S ≤ T :=
SetLike.coe_subset_coe.symm.trans Set.inv_subset_inv
@[to_additive]
theorem inv_le (S T : Submonoid G) : S⁻¹ ≤ T ↔ S ≤ T⁻¹ :=
SetLike.coe_subset_coe.symm.trans Set.inv_subset
/-- Pointwise inversion of submonoids as an order isomorphism. -/
@[to_additive (attr := simps!) "Pointwise negation of additive submonoids as an order isomorphism"]
def invOrderIso : Submonoid G ≃o Submonoid G where
toEquiv := Equiv.inv _
map_rel_iff' := inv_le_inv _ _
@[to_additive]
theorem closure_inv (s : Set G) : closure s⁻¹ = (closure s)⁻¹ := by
apply le_antisymm
· rw [closure_le, coe_inv, ← Set.inv_subset, inv_inv]
exact subset_closure
· rw [inv_le, closure_le, coe_inv, ← Set.inv_subset]
exact subset_closure
@[to_additive]
lemma mem_closure_inv (s : Set G) (x : G) : x ∈ closure s⁻¹ ↔ x⁻¹ ∈ closure s := by
rw [closure_inv, mem_inv]
@[to_additive (attr := simp)]
theorem inv_inf (S T : Submonoid G) : (S ⊓ T)⁻¹ = S⁻¹ ⊓ T⁻¹ :=
SetLike.coe_injective Set.inter_inv
@[to_additive (attr := simp)]
theorem inv_sup (S T : Submonoid G) : (S ⊔ T)⁻¹ = S⁻¹ ⊔ T⁻¹ :=
(invOrderIso : Submonoid G ≃o Submonoid G).map_sup S T
@[to_additive (attr := simp)]
theorem inv_bot : (⊥ : Submonoid G)⁻¹ = ⊥ :=
SetLike.coe_injective <| (Set.inv_singleton 1).trans <| congr_arg _ inv_one
@[to_additive (attr := simp)]
theorem inv_top : (⊤ : Submonoid G)⁻¹ = ⊤ :=
SetLike.coe_injective <| Set.inv_univ
@[to_additive (attr := simp)]
theorem inv_iInf {ι : Sort*} (S : ι → Submonoid G) : (⨅ i, S i)⁻¹ = ⨅ i, (S i)⁻¹ :=
(invOrderIso : Submonoid G ≃o Submonoid G).map_iInf _
@[to_additive (attr := simp)]
theorem inv_iSup {ι : Sort*} (S : ι → Submonoid G) : (⨆ i, S i)⁻¹ = ⨆ i, (S i)⁻¹ :=
(invOrderIso : Submonoid G ≃o Submonoid G).map_iSup _
end Submonoid
namespace Submonoid
section Monoid
variable [Monoid α] [MulDistribMulAction α M]
-- todo: add `to_additive`?
/-- The action on a submonoid corresponding to applying the action to every element.
This is available as an instance in the `Pointwise` locale. -/
protected def pointwiseMulAction : MulAction α (Submonoid M) where
smul a S := S.map (MulDistribMulAction.toMonoidEnd _ M a)
one_smul S := by
change S.map _ = S
simpa only [map_one] using S.map_id
mul_smul _ _ S :=
(congr_arg (fun f : Monoid.End M => S.map f) (MonoidHom.map_mul _ _ _)).trans
(S.map_map _ _).symm
scoped[Pointwise] attribute [instance] Submonoid.pointwiseMulAction
@[simp]
theorem coe_pointwise_smul (a : α) (S : Submonoid M) : ↑(a • S) = a • (S : Set M) :=
rfl
theorem smul_mem_pointwise_smul (m : M) (a : α) (S : Submonoid M) : m ∈ S → a • m ∈ a • S :=
(Set.smul_mem_smul_set : _ → _ ∈ a • (S : Set M))
instance : CovariantClass α (Submonoid M) HSMul.hSMul LE.le :=
⟨fun _ _ => image_subset _⟩
theorem mem_smul_pointwise_iff_exists (m : M) (a : α) (S : Submonoid M) :
m ∈ a • S ↔ ∃ s : M, s ∈ S ∧ a • s = m :=
(Set.mem_smul_set : m ∈ a • (S : Set M) ↔ _)
@[simp]
theorem smul_bot (a : α) : a • (⊥ : Submonoid M) = ⊥ :=
map_bot _
theorem smul_sup (a : α) (S T : Submonoid M) : a • (S ⊔ T) = a • S ⊔ a • T :=
map_sup _ _ _
theorem smul_closure (a : α) (s : Set M) : a • closure s = closure (a • s) :=
MonoidHom.map_mclosure _ _
lemma pointwise_isCentralScalar [MulDistribMulAction αᵐᵒᵖ M] [IsCentralScalar α M] :
IsCentralScalar α (Submonoid M) :=
⟨fun _ S => (congr_arg fun f : Monoid.End M => S.map f) <| MonoidHom.ext <| op_smul_eq_smul _⟩
scoped[Pointwise] attribute [instance] Submonoid.pointwise_isCentralScalar
end Monoid
section Group
variable [Group α] [MulDistribMulAction α M]
@[simp]
theorem smul_mem_pointwise_smul_iff {a : α} {S : Submonoid M} {x : M} : a • x ∈ a • S ↔ x ∈ S :=
smul_mem_smul_set_iff
theorem mem_pointwise_smul_iff_inv_smul_mem {a : α} {S : Submonoid M} {x : M} :
x ∈ a • S ↔ a⁻¹ • x ∈ S :=
mem_smul_set_iff_inv_smul_mem
theorem mem_inv_pointwise_smul_iff {a : α} {S : Submonoid M} {x : M} : x ∈ a⁻¹ • S ↔ a • x ∈ S :=
mem_inv_smul_set_iff
@[simp]
theorem pointwise_smul_le_pointwise_smul_iff {a : α} {S T : Submonoid M} : a • S ≤ a • T ↔ S ≤ T :=
smul_set_subset_smul_set_iff
theorem pointwise_smul_subset_iff {a : α} {S T : Submonoid M} : a • S ≤ T ↔ S ≤ a⁻¹ • T :=
smul_set_subset_iff_subset_inv_smul_set
theorem subset_pointwise_smul_iff {a : α} {S T : Submonoid M} : S ≤ a • T ↔ a⁻¹ • S ≤ T :=
subset_smul_set_iff
end Group
end Submonoid
namespace Set.IsPWO
variable [CommMonoid α] [PartialOrder α] [IsOrderedCancelMonoid α] {s : Set α}
@[to_additive]
theorem submonoid_closure (hpos : ∀ x : α, x ∈ s → 1 ≤ x) (h : s.IsPWO) :
IsPWO (Submonoid.closure s : Set α) := by
rw [Submonoid.closure_eq_image_prod]
refine (h.partiallyWellOrderedOn_sublistForall₂ (· ≤ ·)).image_of_monotone_on ?_
exact fun l1 _ l2 hl2 h12 => h12.prod_le_prod' fun x hx => hpos x <| hl2 x hx
end Set.IsPWO
| Mathlib/Algebra/Group/Submonoid/Pointwise.lean | 553 | 564 |
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