Context stringlengths 227 76.5k | target stringlengths 0 11.6k | file_name stringlengths 21 79 | start int64 14 3.67k | end int64 16 3.69k |
|---|---|---|---|---|
/-
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.Set.Basic
import Mathlib.Tactic.Order
/-!
# Circular order hierarchy
This file defines circular preorders, circular partial orders and circular orders.
## Hierarchy
* A ternary "betweenness" relation `btw : α → α → α → Prop` forms a `CircularOrder` if it is
- reflexive: `btw a a a`
- cyclic: `btw a b c → btw b c a`
- antisymmetric: `btw a b c → btw c b a → a = b ∨ b = c ∨ c = a`
- total: `btw a b c ∨ btw c b a`
along with a strict betweenness relation `sbtw : α → α → α → Prop` which respects
`sbtw a b c ↔ btw a b c ∧ ¬ btw c b a`, analogously to how `<` and `≤` are related, and is
- transitive: `sbtw a b c → sbtw b d c → sbtw a d c`.
* A `CircularPartialOrder` drops totality.
* A `CircularPreorder` further drops antisymmetry.
The intuition is that a circular order is a circle and `btw a b c` means that going around
clockwise from `a` you reach `b` before `c` (`b` is between `a` and `c` is meaningless on an
unoriented circle). A circular partial order is several, potentially intersecting, circles. A
circular preorder is like a circular partial order, but several points can coexist.
Note that the relations between `CircularPreorder`, `CircularPartialOrder` and `CircularOrder`
are subtler than between `Preorder`, `PartialOrder`, `LinearOrder`. In particular, one cannot
simply extend the `Btw` of a `CircularPartialOrder` to make it a `CircularOrder`.
One can translate from usual orders to circular ones by "closing the necklace at infinity". See
`LE.toBtw` and `LT.toSBtw`. Going the other way involves "cutting the necklace" or
"rolling the necklace open".
## Examples
Some concrete circular orders one encounters in the wild are `ZMod n` for `0 < n`, `Circle`,
`Real.Angle`...
## Main definitions
* `Set.cIcc`: Closed-closed circular interval.
* `Set.cIoo`: Open-open circular interval.
## Notes
There's an unsolved diamond on `OrderDual α` here. The instances `LE α → Btw αᵒᵈ` and
`LT α → SBtw αᵒᵈ` can each be inferred in two ways:
* `LE α` → `Btw α` → `Btw αᵒᵈ` vs
`LE α` → `LE αᵒᵈ` → `Btw αᵒᵈ`
* `LT α` → `SBtw α` → `SBtw αᵒᵈ` vs
`LT α` → `LT αᵒᵈ` → `SBtw αᵒᵈ`
The fields are propeq, but not defeq. It is temporarily fixed by turning the circularizing instances
into definitions.
## TODO
Antisymmetry is quite weak in the sense that there's no way to discriminate which two points are
equal. This prevents defining closed-open intervals `cIco` and `cIoc` in the neat `=`-less way. We
currently haven't defined them at all.
What is the correct generality of "rolling the necklace" open? At least, this works for `α × β` and
`β × α` where `α` is a circular order and `β` is a linear order.
What's next is to define circular groups and provide instances for `ZMod n`, the usual circle group
`Circle`, and `RootsOfUnity M`. What conditions do we need on `M` for this last one
to work?
We should have circular order homomorphisms. The typical example is
`daysToMonth : DaysOfTheYear →c MonthsOfTheYear` which relates the circular order of days
and the circular order of months. Is `α →c β` a good notation?
## References
* https://en.wikipedia.org/wiki/Cyclic_order
* https://en.wikipedia.org/wiki/Partial_cyclic_order
## Tags
circular order, cyclic order, circularly ordered set, cyclically ordered set
-/
assert_not_exists RelIso
/-- Syntax typeclass for a betweenness relation. -/
class Btw (α : Type*) where
/-- Betweenness for circular orders. `btw a b c` states that `b` is between `a` and `c` (in that
order). -/
btw : α → α → α → Prop
export Btw (btw)
/-- Syntax typeclass for a strict betweenness relation. -/
class SBtw (α : Type*) where
/-- Strict betweenness for circular orders. `sbtw a b c` states that `b` is strictly between `a`
and `c` (in that order). -/
sbtw : α → α → α → Prop
export SBtw (sbtw)
/-- A circular preorder is the analogue of a preorder where you can loop around. `≤` and `<` are
replaced by ternary relations `btw` and `sbtw`. `btw` is reflexive and cyclic. `sbtw` is transitive.
-/
class CircularPreorder (α : Type*) extends Btw α, SBtw α where
/-- `a` is between `a` and `a`. -/
btw_refl (a : α) : btw a a a
/-- If `b` is between `a` and `c`, then `c` is between `b` and `a`.
This is motivated by imagining three points on a circle. -/
btw_cyclic_left {a b c : α} : btw a b c → btw b c a
sbtw := fun a b c => btw a b c ∧ ¬btw c b a
/-- Strict betweenness is given by betweenness in one direction and non-betweenness in the other.
I.e., if `b` is between `a` and `c` but not between `c` and `a`, then we say `b` is strictly
between `a` and `c`. -/
sbtw_iff_btw_not_btw {a b c : α} : sbtw a b c ↔ btw a b c ∧ ¬btw c b a := by intros; rfl
/-- For any fixed `c`, `fun a b ↦ sbtw a b c` is a transitive relation.
I.e., given `a` `b` `d` `c` in that "order", if we have `b` strictly between `a` and `c`, and `d`
strictly between `b` and `c`, then `d` is strictly between `a` and `c`. -/
sbtw_trans_left {a b c d : α} : sbtw a b c → sbtw b d c → sbtw a d c
export CircularPreorder (btw_refl btw_cyclic_left sbtw_trans_left)
/-- A circular partial order is the analogue of a partial order where you can loop around. `≤` and
`<` are replaced by ternary relations `btw` and `sbtw`. `btw` is reflexive, cyclic and
antisymmetric. `sbtw` is transitive. -/
class CircularPartialOrder (α : Type*) extends CircularPreorder α where
/-- If `b` is between `a` and `c` and also between `c` and `a`, then at least one pair of points
among `a`, `b`, `c` are identical. -/
btw_antisymm {a b c : α} : btw a b c → btw c b a → a = b ∨ b = c ∨ c = a
export CircularPartialOrder (btw_antisymm)
/-- A circular order is the analogue of a linear order where you can loop around. `≤` and `<` are
replaced by ternary relations `btw` and `sbtw`. `btw` is reflexive, cyclic, antisymmetric and total.
`sbtw` is transitive. -/
class CircularOrder (α : Type*) extends CircularPartialOrder α where
/-- For any triple of points, the second is between the other two one way or another. -/
btw_total : ∀ a b c : α, btw a b c ∨ btw c b a
export CircularOrder (btw_total)
/-! ### Circular preorders -/
section CircularPreorder
variable {α : Type*} [CircularPreorder α]
theorem btw_rfl {a : α} : btw a a a :=
btw_refl _
-- TODO: `alias` creates a def instead of a lemma (because `btw_cyclic_left` is a def).
-- alias btw_cyclic_left ← Btw.btw.cyclic_left
theorem Btw.btw.cyclic_left {a b c : α} (h : btw a b c) : btw b c a :=
btw_cyclic_left h
theorem btw_cyclic_right {a b c : α} (h : btw a b c) : btw c a b :=
h.cyclic_left.cyclic_left
alias Btw.btw.cyclic_right := btw_cyclic_right
/-- The order of the `↔` has been chosen so that `rw [btw_cyclic]` cycles to the right while
`rw [← btw_cyclic]` cycles to the left (thus following the prepended arrow). -/
theorem btw_cyclic {a b c : α} : btw a b c ↔ btw c a b :=
⟨btw_cyclic_right, btw_cyclic_left⟩
theorem sbtw_iff_btw_not_btw {a b c : α} : sbtw a b c ↔ btw a b c ∧ ¬btw c b a :=
CircularPreorder.sbtw_iff_btw_not_btw
theorem btw_of_sbtw {a b c : α} (h : sbtw a b c) : btw a b c :=
(sbtw_iff_btw_not_btw.1 h).1
alias SBtw.sbtw.btw := btw_of_sbtw
theorem not_btw_of_sbtw {a b c : α} (h : sbtw a b c) : ¬btw c b a :=
(sbtw_iff_btw_not_btw.1 h).2
alias SBtw.sbtw.not_btw := not_btw_of_sbtw
theorem not_sbtw_of_btw {a b c : α} (h : btw a b c) : ¬sbtw c b a := fun h' => h'.not_btw h
alias Btw.btw.not_sbtw := not_sbtw_of_btw
theorem sbtw_of_btw_not_btw {a b c : α} (habc : btw a b c) (hcba : ¬btw c b a) : sbtw a b c :=
sbtw_iff_btw_not_btw.2 ⟨habc, hcba⟩
alias Btw.btw.sbtw_of_not_btw := sbtw_of_btw_not_btw
theorem sbtw_cyclic_left {a b c : α} (h : sbtw a b c) : sbtw b c a :=
h.btw.cyclic_left.sbtw_of_not_btw fun h' => h.not_btw h'.cyclic_left
alias SBtw.sbtw.cyclic_left := sbtw_cyclic_left
theorem sbtw_cyclic_right {a b c : α} (h : sbtw a b c) : sbtw c a b :=
h.cyclic_left.cyclic_left
alias SBtw.sbtw.cyclic_right := sbtw_cyclic_right
/-- The order of the `↔` has been chosen so that `rw [sbtw_cyclic]` cycles to the right while
`rw [← sbtw_cyclic]` cycles to the left (thus following the prepended arrow). -/
theorem sbtw_cyclic {a b c : α} : sbtw a b c ↔ sbtw c a b :=
⟨sbtw_cyclic_right, sbtw_cyclic_left⟩
-- TODO: `alias` creates a def instead of a lemma (because `sbtw_trans_left` is a def).
-- alias btw_trans_left ← SBtw.sbtw.trans_left
theorem SBtw.sbtw.trans_left {a b c d : α} (h : sbtw a b c) : sbtw b d c → sbtw a d c :=
sbtw_trans_left h
theorem sbtw_trans_right {a b c d : α} (hbc : sbtw a b c) (hcd : sbtw a c d) : sbtw a b d :=
(hbc.cyclic_left.trans_left hcd.cyclic_left).cyclic_right
alias SBtw.sbtw.trans_right := sbtw_trans_right
theorem sbtw_asymm {a b c : α} (h : sbtw a b c) : ¬sbtw c b a :=
h.btw.not_sbtw
alias SBtw.sbtw.not_sbtw := sbtw_asymm
theorem sbtw_irrefl_left_right {a b : α} : ¬sbtw a b a := fun h => h.not_btw h.btw
theorem sbtw_irrefl_left {a b : α} : ¬sbtw a a b := fun h => sbtw_irrefl_left_right h.cyclic_left
theorem sbtw_irrefl_right {a b : α} : ¬sbtw a b b := fun h => sbtw_irrefl_left_right h.cyclic_right
theorem sbtw_irrefl (a : α) : ¬sbtw a a a :=
sbtw_irrefl_left_right
end CircularPreorder
/-! ### Circular partial orders -/
section CircularPartialOrder
variable {α : Type*} [CircularPartialOrder α]
-- TODO: `alias` creates a def instead of a lemma (because `btw_antisymm` is a def).
-- alias btw_antisymm ← Btw.btw.antisymm
theorem Btw.btw.antisymm {a b c : α} (h : btw a b c) : btw c b a → a = b ∨ b = c ∨ c = a :=
btw_antisymm h
end CircularPartialOrder
/-! ### Circular orders -/
section CircularOrder
variable {α : Type*} [CircularOrder α]
theorem btw_refl_left_right (a b : α) : btw a b a :=
or_self_iff.1 (btw_total a b a)
theorem btw_rfl_left_right {a b : α} : btw a b a :=
btw_refl_left_right _ _
theorem btw_refl_left (a b : α) : btw a a b :=
btw_rfl_left_right.cyclic_right
theorem btw_rfl_left {a b : α} : btw a a b :=
btw_refl_left _ _
theorem btw_refl_right (a b : α) : btw a b b :=
btw_rfl_left_right.cyclic_left
theorem btw_rfl_right {a b : α} : btw a b b :=
btw_refl_right _ _
theorem sbtw_iff_not_btw {a b c : α} : sbtw a b c ↔ ¬btw c b a := by
rw [sbtw_iff_btw_not_btw]
exact and_iff_right_of_imp (btw_total _ _ _).resolve_left
theorem btw_iff_not_sbtw {a b c : α} : btw a b c ↔ ¬sbtw c b a :=
iff_not_comm.1 sbtw_iff_not_btw
end CircularOrder
/-! ### Circular intervals -/
namespace Set
section CircularPreorder
variable {α : Type*} [CircularPreorder α]
/-- Closed-closed circular interval -/
def cIcc (a b : α) : Set α :=
{ x | btw a x b }
/-- Open-open circular interval -/
def cIoo (a b : α) : Set α :=
{ x | sbtw a x b }
@[simp]
theorem mem_cIcc {a b x : α} : x ∈ cIcc a b ↔ btw a x b :=
Iff.rfl
@[simp]
theorem mem_cIoo {a b x : α} : x ∈ cIoo a b ↔ sbtw a x b :=
Iff.rfl
end CircularPreorder
section CircularOrder
variable {α : Type*} [CircularOrder α]
| theorem left_mem_cIcc (a b : α) : a ∈ cIcc a b :=
btw_rfl_left
| Mathlib/Order/Circular.lean | 315 | 317 |
/-
Copyright (c) 2016 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad
-/
import Batteries.Data.List.Perm
import Mathlib.Data.List.OfFn
import Mathlib.Data.List.Nodup
import Mathlib.Data.List.TakeWhile
import Mathlib.Order.Fin.Basic
/-!
# Sorting algorithms on lists
In this file we define `List.Sorted r l` to be an alias for `List.Pairwise r l`.
This alias is preferred in the case that `r` is a `<` or `≤`-like relation.
Then we define the sorting algorithm
`List.insertionSort` and prove its correctness.
-/
open List.Perm
universe u v
namespace List
/-!
### The predicate `List.Sorted`
-/
section Sorted
variable {α : Type u} {r : α → α → Prop} {a : α} {l : List α}
/-- `Sorted r l` is the same as `List.Pairwise r l`, preferred in the case that `r`
is a `<` or `≤`-like relation (transitive and antisymmetric or asymmetric) -/
def Sorted :=
@Pairwise
instance decidableSorted [DecidableRel r] (l : List α) : Decidable (Sorted r l) :=
List.instDecidablePairwise _
protected theorem Sorted.le_of_lt [Preorder α] {l : List α} (h : l.Sorted (· < ·)) :
l.Sorted (· ≤ ·) :=
h.imp le_of_lt
protected theorem Sorted.lt_of_le [PartialOrder α] {l : List α} (h₁ : l.Sorted (· ≤ ·))
(h₂ : l.Nodup) : l.Sorted (· < ·) :=
h₁.imp₂ (fun _ _ => lt_of_le_of_ne) h₂
protected theorem Sorted.ge_of_gt [Preorder α] {l : List α} (h : l.Sorted (· > ·)) :
l.Sorted (· ≥ ·) :=
h.imp le_of_lt
protected theorem Sorted.gt_of_ge [PartialOrder α] {l : List α} (h₁ : l.Sorted (· ≥ ·))
(h₂ : l.Nodup) : l.Sorted (· > ·) :=
h₁.imp₂ (fun _ _ => lt_of_le_of_ne) <| by simp_rw [ne_comm]; exact h₂
@[simp]
theorem sorted_nil : Sorted r [] :=
Pairwise.nil
theorem Sorted.of_cons : Sorted r (a :: l) → Sorted r l :=
Pairwise.of_cons
theorem Sorted.tail {r : α → α → Prop} {l : List α} (h : Sorted r l) : Sorted r l.tail :=
Pairwise.tail h
theorem rel_of_sorted_cons {a : α} {l : List α} : Sorted r (a :: l) → ∀ b ∈ l, r a b :=
rel_of_pairwise_cons
nonrec theorem Sorted.cons {r : α → α → Prop} [IsTrans α r] {l : List α} {a b : α}
(hab : r a b) (h : Sorted r (b :: l)) : Sorted r (a :: b :: l) :=
h.cons <| forall_mem_cons.2 ⟨hab, fun _ hx => _root_.trans hab <| rel_of_sorted_cons h _ hx⟩
theorem sorted_cons_cons {r : α → α → Prop} [IsTrans α r] {l : List α} {a b : α} :
Sorted r (b :: a :: l) ↔ r b a ∧ Sorted r (a :: l) := by
constructor
· intro h
exact ⟨rel_of_sorted_cons h _ mem_cons_self, h.of_cons⟩
· rintro ⟨h, ha⟩
exact ha.cons h
theorem Sorted.head!_le [Inhabited α] [Preorder α] {a : α} {l : List α} (h : Sorted (· < ·) l)
(ha : a ∈ l) : l.head! ≤ a := by
rw [← List.cons_head!_tail (List.ne_nil_of_mem ha)] at h ha
cases ha
· exact le_rfl
· exact le_of_lt (rel_of_sorted_cons h a (by assumption))
theorem Sorted.le_head! [Inhabited α] [Preorder α] {a : α} {l : List α} (h : Sorted (· > ·) l)
(ha : a ∈ l) : a ≤ l.head! := by
rw [← List.cons_head!_tail (List.ne_nil_of_mem ha)] at h ha
cases ha
· exact le_rfl
· exact le_of_lt (rel_of_sorted_cons h a (by assumption))
@[simp]
theorem sorted_cons {a : α} {l : List α} : Sorted r (a :: l) ↔ (∀ b ∈ l, r a b) ∧ Sorted r l :=
pairwise_cons
protected theorem Sorted.nodup {r : α → α → Prop} [IsIrrefl α r] {l : List α} (h : Sorted r l) :
Nodup l :=
Pairwise.nodup h
protected theorem Sorted.filter {l : List α} (f : α → Bool) (h : Sorted r l) :
Sorted r (filter f l) :=
h.sublist filter_sublist
theorem eq_of_perm_of_sorted [IsAntisymm α r] {l₁ l₂ : List α} (hp : l₁ ~ l₂) (hs₁ : Sorted r l₁)
(hs₂ : Sorted r l₂) : l₁ = l₂ := by
induction hs₁ generalizing l₂ with
| nil => exact hp.nil_eq
| @cons a l₁ h₁ hs₁ IH =>
have : a ∈ l₂ := hp.subset mem_cons_self
rcases append_of_mem this with ⟨u₂, v₂, rfl⟩
have hp' := (perm_cons a).1 (hp.trans perm_middle)
obtain rfl := IH hp' (hs₂.sublist <| by simp)
change a :: u₂ ++ v₂ = u₂ ++ ([a] ++ v₂)
rw [← append_assoc]
congr
have : ∀ x ∈ u₂, x = a := fun x m =>
antisymm ((pairwise_append.1 hs₂).2.2 _ m a mem_cons_self) (h₁ _ (by simp [m]))
rw [(@eq_replicate_iff _ a (length u₂ + 1) (a :: u₂)).2,
(@eq_replicate_iff _ a (length u₂ + 1) (u₂ ++ [a])).2] <;>
constructor <;>
simp [iff_true_intro this, or_comm]
theorem Sorted.eq_of_mem_iff [IsAntisymm α r] [IsIrrefl α r] {l₁ l₂ : List α}
(h₁ : Sorted r l₁) (h₂ : Sorted r l₂) (h : ∀ a : α, a ∈ l₁ ↔ a ∈ l₂) : l₁ = l₂ :=
eq_of_perm_of_sorted ((perm_ext_iff_of_nodup h₁.nodup h₂.nodup).2 h) h₁ h₂
theorem sublist_of_subperm_of_sorted [IsAntisymm α r] {l₁ l₂ : List α} (hp : l₁ <+~ l₂)
(hs₁ : l₁.Sorted r) (hs₂ : l₂.Sorted r) : l₁ <+ l₂ := by
let ⟨_, h, h'⟩ := hp
rwa [← eq_of_perm_of_sorted h (hs₂.sublist h') hs₁]
@[simp 1100] -- Higher priority shortcut lemma.
theorem sorted_singleton (a : α) : Sorted r [a] := by
simp
theorem sorted_lt_range (n : ℕ) : Sorted (· < ·) (range n) := by
rw [Sorted, pairwise_iff_get]
simp
theorem sorted_replicate (n : ℕ) (a : α) : Sorted r (replicate n a) ↔ n ≤ 1 ∨ r a a :=
pairwise_replicate
theorem sorted_le_replicate (n : ℕ) (a : α) [Preorder α] : Sorted (· ≤ ·) (replicate n a) := by
simp [sorted_replicate]
theorem sorted_le_range (n : ℕ) : Sorted (· ≤ ·) (range n) :=
(sorted_lt_range n).le_of_lt
lemma sorted_lt_range' (a b) {s} (hs : s ≠ 0) :
Sorted (· < ·) (range' a b s) := by
induction b generalizing a with
| zero => simp
| succ n ih =>
rw [List.range'_succ]
refine List.sorted_cons.mpr ⟨fun b hb ↦ ?_, @ih (a + s)⟩
exact lt_of_lt_of_le (Nat.lt_add_of_pos_right (Nat.zero_lt_of_ne_zero hs))
(List.left_le_of_mem_range' hb)
lemma sorted_le_range' (a b s) :
Sorted (· ≤ ·) (range' a b s) := by
by_cases hs : s ≠ 0
· exact (sorted_lt_range' a b hs).le_of_lt
· rw [ne_eq, Decidable.not_not] at hs
simpa [hs] using sorted_le_replicate b a
theorem Sorted.rel_get_of_lt {l : List α} (h : l.Sorted r) {a b : Fin l.length} (hab : a < b) :
r (l.get a) (l.get b) :=
List.pairwise_iff_get.1 h _ _ hab
theorem Sorted.rel_get_of_le [IsRefl α r] {l : List α} (h : l.Sorted r) {a b : Fin l.length}
(hab : a ≤ b) : r (l.get a) (l.get b) := by
obtain rfl | hlt := Fin.eq_or_lt_of_le hab; exacts [refl _, h.rel_get_of_lt hlt]
theorem Sorted.rel_of_mem_take_of_mem_drop {l : List α} (h : List.Sorted r l) {k : ℕ} {x y : α}
(hx : x ∈ List.take k l) (hy : y ∈ List.drop k l) : r x y := by
obtain ⟨iy, hiy, rfl⟩ := getElem_of_mem hy
obtain ⟨ix, hix, rfl⟩ := getElem_of_mem hx
rw [getElem_take, getElem_drop]
rw [length_take] at hix
exact h.rel_get_of_lt (Nat.lt_add_right _ (Nat.lt_min.mp hix).left)
/--
If a list is sorted with respect to a decidable relation,
then it is sorted with respect to the corresponding Bool-valued relation.
-/
theorem Sorted.decide [DecidableRel r] (l : List α) (h : Sorted r l) :
Sorted (fun a b => decide (r a b) = true) l := by
refine h.imp fun {a b} h => by simpa using h
end Sorted
section Monotone
variable {n : ℕ} {α : Type u} {f : Fin n → α}
open scoped Relator in
theorem sorted_ofFn_iff {r : α → α → Prop} : (ofFn f).Sorted r ↔ ((· < ·) ⇒ r) f f := by
simp_rw [Sorted, pairwise_iff_get, get_ofFn, Relator.LiftFun]
exact Iff.symm (Fin.rightInverse_cast _).surjective.forall₂
variable [Preorder α]
/-- The list `List.ofFn f` is strictly sorted with respect to `(· ≤ ·)` if and only if `f` is
strictly monotone. -/
@[simp] theorem sorted_lt_ofFn_iff : (ofFn f).Sorted (· < ·) ↔ StrictMono f := sorted_ofFn_iff
/-- The list `List.ofFn f` is strictly sorted with respect to `(· ≥ ·)` if and only if `f` is
strictly antitone. -/
@[simp] theorem sorted_gt_ofFn_iff : (ofFn f).Sorted (· > ·) ↔ StrictAnti f := sorted_ofFn_iff
/-- The list `List.ofFn f` is sorted with respect to `(· ≤ ·)` if and only if `f` is monotone. -/
@[simp] theorem sorted_le_ofFn_iff : (ofFn f).Sorted (· ≤ ·) ↔ Monotone f :=
sorted_ofFn_iff.trans monotone_iff_forall_lt.symm
/-- The list obtained from a monotone tuple is sorted. -/
alias ⟨_, _root_.Monotone.ofFn_sorted⟩ := sorted_le_ofFn_iff
/-- The list `List.ofFn f` is sorted with respect to `(· ≥ ·)` if and only if `f` is antitone. -/
@[simp] theorem sorted_ge_ofFn_iff : (ofFn f).Sorted (· ≥ ·) ↔ Antitone f :=
sorted_ofFn_iff.trans antitone_iff_forall_lt.symm
/-- The list obtained from an antitone tuple is sorted. -/
alias ⟨_, _root_.Antitone.ofFn_sorted⟩ := sorted_ge_ofFn_iff
end Monotone
lemma Sorted.filterMap {α β : Type*} {p : α → Option β} {l : List α}
{r : α → α → Prop} {r' : β → β → Prop} (hl : l.Sorted r)
(hp : ∀ (a b : α) (c d : β), p a = some c → p b = some d → r a b → r' c d) :
(l.filterMap p).Sorted r' := by
induction l with
| nil => simp
| cons a l ih =>
rw [List.filterMap_cons]
cases ha : p a with
| none =>
exact ih (List.sorted_cons.mp hl).right
| some b =>
rw [List.sorted_cons]
refine ⟨fun x hx ↦ ?_, ih (List.sorted_cons.mp hl).right⟩
obtain ⟨u, hu, hu'⟩ := List.mem_filterMap.mp hx
exact hp a u b x ha hu' <| (List.sorted_cons.mp hl).left u hu
end List
open List
namespace RelEmbedding
variable {α β : Type*} {ra : α → α → Prop} {rb : β → β → Prop}
@[simp]
theorem sorted_listMap (e : ra ↪r rb) {l : List α} : (l.map e).Sorted rb ↔ l.Sorted ra := by
simp [Sorted, pairwise_map, e.map_rel_iff]
@[simp]
theorem sorted_swap_listMap (e : ra ↪r rb) {l : List α} :
(l.map e).Sorted (Function.swap rb) ↔ l.Sorted (Function.swap ra) := by
simp [Sorted, pairwise_map, e.map_rel_iff]
end RelEmbedding
namespace OrderEmbedding
variable {α β : Type*} [Preorder α] [Preorder β]
@[simp]
theorem sorted_lt_listMap (e : α ↪o β) {l : List α} :
(l.map e).Sorted (· < ·) ↔ l.Sorted (· < ·) :=
e.ltEmbedding.sorted_listMap
@[simp]
theorem sorted_gt_listMap (e : α ↪o β) {l : List α} :
(l.map e).Sorted (· > ·) ↔ l.Sorted (· > ·) :=
e.ltEmbedding.sorted_swap_listMap
end OrderEmbedding
namespace RelIso
variable {α β : Type*} {ra : α → α → Prop} {rb : β → β → Prop}
@[simp]
theorem sorted_listMap (e : ra ≃r rb) {l : List α} : (l.map e).Sorted rb ↔ l.Sorted ra :=
e.toRelEmbedding.sorted_listMap
@[simp]
theorem sorted_swap_listMap (e : ra ≃r rb) {l : List α} :
(l.map e).Sorted (Function.swap rb) ↔ l.Sorted (Function.swap ra) :=
e.toRelEmbedding.sorted_swap_listMap
|
end RelIso
namespace OrderIso
variable {α β : Type*} [Preorder α] [Preorder β]
| Mathlib/Data/List/Sort.lean | 297 | 303 |
/-
Copyright (c) 2024 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Algebra.Order.Hom.Ring
import Mathlib.Data.ENat.Basic
import Mathlib.SetTheory.Cardinal.Basic
/-!
# Conversion between `Cardinal` and `ℕ∞`
In this file we define a coercion `Cardinal.ofENat : ℕ∞ → Cardinal`
and a projection `Cardinal.toENat : Cardinal →+*o ℕ∞`.
We also prove basic theorems about these definitions.
## Implementation notes
We define `Cardinal.ofENat` as a function instead of a bundled homomorphism
so that we can use it as a coercion and delaborate its application to `↑n`.
We define `Cardinal.toENat` as a bundled homomorphism
so that we can use all the theorems about homomorphisms without specializing them to this function.
Since it is not registered as a coercion, the argument about delaboration does not apply.
## Keywords
set theory, cardinals, extended natural numbers
-/
assert_not_exists Field
open Function Set
universe u v
namespace Cardinal
/-- Coercion `ℕ∞ → Cardinal`. It sends natural numbers to natural numbers and `⊤` to `ℵ₀`.
See also `Cardinal.ofENatHom` for a bundled homomorphism version. -/
@[coe] def ofENat : ℕ∞ → Cardinal
| (n : ℕ) => n
| ⊤ => ℵ₀
instance : Coe ENat Cardinal := ⟨Cardinal.ofENat⟩
@[simp, norm_cast] lemma ofENat_top : ofENat ⊤ = ℵ₀ := rfl
@[simp, norm_cast] lemma ofENat_nat (n : ℕ) : ofENat n = n := rfl
@[simp, norm_cast] lemma ofENat_zero : ofENat 0 = 0 := rfl
@[simp, norm_cast] lemma ofENat_one : ofENat 1 = 1 := rfl
@[simp, norm_cast] lemma ofENat_ofNat (n : ℕ) [n.AtLeastTwo] :
((ofNat(n) : ℕ∞) : Cardinal) = OfNat.ofNat n :=
rfl
lemma ofENat_strictMono : StrictMono ofENat :=
WithTop.strictMono_iff.2 ⟨Nat.strictMono_cast, nat_lt_aleph0⟩
@[simp, norm_cast]
lemma ofENat_lt_ofENat {m n : ℕ∞} : (m : Cardinal) < n ↔ m < n :=
ofENat_strictMono.lt_iff_lt
@[gcongr, mono] alias ⟨_, ofENat_lt_ofENat_of_lt⟩ := ofENat_lt_ofENat
@[simp, norm_cast]
lemma ofENat_lt_aleph0 {m : ℕ∞} : (m : Cardinal) < ℵ₀ ↔ m < ⊤ :=
ofENat_lt_ofENat (n := ⊤)
@[simp] lemma ofENat_lt_nat {m : ℕ∞} {n : ℕ} : ofENat m < n ↔ m < n := by norm_cast
@[simp] lemma ofENat_lt_ofNat {m : ℕ∞} {n : ℕ} [n.AtLeastTwo] :
ofENat m < ofNat(n) ↔ m < OfNat.ofNat n := ofENat_lt_nat
@[simp] lemma nat_lt_ofENat {m : ℕ} {n : ℕ∞} : (m : Cardinal) < n ↔ m < n := by norm_cast
@[simp] lemma ofENat_pos {m : ℕ∞} : 0 < (m : Cardinal) ↔ 0 < m := by norm_cast
@[simp] lemma one_lt_ofENat {m : ℕ∞} : 1 < (m : Cardinal) ↔ 1 < m := by norm_cast
@[simp, norm_cast] lemma ofNat_lt_ofENat {m : ℕ} [m.AtLeastTwo] {n : ℕ∞} :
(ofNat(m) : Cardinal) < n ↔ OfNat.ofNat m < n := nat_lt_ofENat
lemma ofENat_mono : Monotone ofENat := ofENat_strictMono.monotone
@[simp, norm_cast]
lemma ofENat_le_ofENat {m n : ℕ∞} : (m : Cardinal) ≤ n ↔ m ≤ n := ofENat_strictMono.le_iff_le
@[gcongr, mono] alias ⟨_, ofENat_le_ofENat_of_le⟩ := ofENat_le_ofENat
@[simp] lemma ofENat_le_aleph0 (n : ℕ∞) : ↑n ≤ ℵ₀ := ofENat_le_ofENat.2 le_top
@[simp] lemma ofENat_le_nat {m : ℕ∞} {n : ℕ} : ofENat m ≤ n ↔ m ≤ n := by norm_cast
@[simp] lemma ofENat_le_one {m : ℕ∞} : ofENat m ≤ 1 ↔ m ≤ 1 := by norm_cast
@[simp] lemma ofENat_le_ofNat {m : ℕ∞} {n : ℕ} [n.AtLeastTwo] :
ofENat m ≤ ofNat(n) ↔ m ≤ OfNat.ofNat n := ofENat_le_nat
@[simp] lemma nat_le_ofENat {m : ℕ} {n : ℕ∞} : (m : Cardinal) ≤ n ↔ m ≤ n := by norm_cast
@[simp] lemma one_le_ofENat {n : ℕ∞} : 1 ≤ (n : Cardinal) ↔ 1 ≤ n := by norm_cast
@[simp]
lemma ofNat_le_ofENat {m : ℕ} [m.AtLeastTwo] {n : ℕ∞} :
(ofNat(m) : Cardinal) ≤ n ↔ OfNat.ofNat m ≤ n := nat_le_ofENat
lemma ofENat_injective : Injective ofENat := ofENat_strictMono.injective
@[simp, norm_cast]
lemma ofENat_inj {m n : ℕ∞} : (m : Cardinal) = n ↔ m = n := ofENat_injective.eq_iff
@[simp] lemma ofENat_eq_nat {m : ℕ∞} {n : ℕ} : (m : Cardinal) = n ↔ m = n := by norm_cast
@[simp] lemma nat_eq_ofENat {m : ℕ} {n : ℕ∞} : (m : Cardinal) = n ↔ m = n := by norm_cast
@[simp] lemma ofENat_eq_zero {m : ℕ∞} : (m : Cardinal) = 0 ↔ m = 0 := by norm_cast
@[simp] lemma zero_eq_ofENat {m : ℕ∞} : 0 = (m : Cardinal) ↔ m = 0 := by norm_cast; apply eq_comm
@[simp] lemma ofENat_eq_one {m : ℕ∞} : (m : Cardinal) = 1 ↔ m = 1 := by norm_cast
@[simp] lemma one_eq_ofENat {m : ℕ∞} : 1 = (m : Cardinal) ↔ m = 1 := by norm_cast; apply eq_comm
@[simp] lemma ofENat_eq_ofNat {m : ℕ∞} {n : ℕ} [n.AtLeastTwo] :
(m : Cardinal) = ofNat(n) ↔ m = OfNat.ofNat n := ofENat_eq_nat
@[simp] lemma ofNat_eq_ofENat {m : ℕ} {n : ℕ∞} [m.AtLeastTwo] :
ofNat(m) = (n : Cardinal) ↔ OfNat.ofNat m = n := nat_eq_ofENat
@[simp, norm_cast] lemma lift_ofENat : ∀ m : ℕ∞, lift.{u, v} m = m
| (m : ℕ) => lift_natCast m
| ⊤ => lift_aleph0
@[simp] lemma lift_lt_ofENat {x : Cardinal.{v}} {m : ℕ∞} : lift.{u} x < m ↔ x < m := by
rw [← lift_ofENat.{u, v}, lift_lt]
@[simp] lemma lift_le_ofENat {x : Cardinal.{v}} {m : ℕ∞} : lift.{u} x ≤ m ↔ x ≤ m := by
rw [← lift_ofENat.{u, v}, lift_le]
@[simp] lemma lift_eq_ofENat {x : Cardinal.{v}} {m : ℕ∞} : lift.{u} x = m ↔ x = m := by
rw [← lift_ofENat.{u, v}, lift_inj]
@[simp] lemma ofENat_lt_lift {x : Cardinal.{v}} {m : ℕ∞} : m < lift.{u} x ↔ m < x := by
rw [← lift_ofENat.{u, v}, lift_lt]
@[simp] lemma ofENat_le_lift {x : Cardinal.{v}} {m : ℕ∞} : m ≤ lift.{u} x ↔ m ≤ x := by
rw [← lift_ofENat.{u, v}, lift_le]
@[simp] lemma ofENat_eq_lift {x : Cardinal.{v}} {m : ℕ∞} : m = lift.{u} x ↔ m = x := by
rw [← lift_ofENat.{u, v}, lift_inj]
@[simp]
lemma range_ofENat : range ofENat = Iic ℵ₀ := by
refine (range_subset_iff.2 ofENat_le_aleph0).antisymm fun x (hx : x ≤ ℵ₀) ↦ ?_
rcases hx.lt_or_eq with hlt | rfl
· lift x to ℕ using hlt
exact mem_range_self (x : ℕ∞)
· exact mem_range_self (⊤ : ℕ∞)
instance : CanLift Cardinal ℕ∞ (↑) (· ≤ ℵ₀) where
prf x := (Set.ext_iff.1 range_ofENat x).2
/-- Unbundled version of `Cardinal.toENat`. -/
noncomputable def toENatAux : Cardinal.{u} → ℕ∞ := extend Nat.cast Nat.cast fun _ ↦ ⊤
lemma toENatAux_nat (n : ℕ) : toENatAux n = n := Nat.cast_injective.extend_apply ..
lemma toENatAux_zero : toENatAux 0 = 0 := toENatAux_nat 0
lemma toENatAux_eq_top {a : Cardinal} (ha : ℵ₀ ≤ a) : toENatAux a = ⊤ :=
extend_apply' _ _ _ fun ⟨n, hn⟩ ↦ ha.not_lt <| hn ▸ nat_lt_aleph0 n
lemma toENatAux_ofENat : ∀ n : ℕ∞, toENatAux n = n
| (n : ℕ) => toENatAux_nat n
| ⊤ => toENatAux_eq_top le_rfl
attribute [local simp] toENatAux_nat toENatAux_zero toENatAux_ofENat
lemma toENatAux_gc : GaloisConnection (↑) toENatAux := fun n x ↦ by
cases lt_or_le x ℵ₀ with
| inl hx => lift x to ℕ using hx; simp
| inr hx => simp [toENatAux_eq_top hx, (ofENat_le_aleph0 n).trans hx]
theorem toENatAux_le_nat {x : Cardinal} {n : ℕ} : toENatAux x ≤ n ↔ x ≤ n := by
cases lt_or_le x ℵ₀ with
| inl hx => lift x to ℕ using hx; simp
| inr hx => simp [toENatAux_eq_top hx, (nat_lt_aleph0 n).trans_le hx]
lemma toENatAux_eq_nat {x : Cardinal} {n : ℕ} : toENatAux x = n ↔ x = n := by
simp only [le_antisymm_iff, toENatAux_le_nat, ← toENatAux_gc _, ofENat_nat]
lemma toENatAux_eq_zero {x : Cardinal} : toENatAux x = 0 ↔ x = 0 := toENatAux_eq_nat
/-- Projection from cardinals to `ℕ∞`. Sends all infinite cardinals to `⊤`.
We define this function as a bundled monotone ring homomorphism. -/
noncomputable def toENat : Cardinal.{u} →+*o ℕ∞ where
toFun := toENatAux
map_one' := toENatAux_nat 1
map_mul' x y := by
wlog hle : x ≤ y; · rw [mul_comm, this y x (le_of_not_le hle), mul_comm]
cases lt_or_le y ℵ₀ with
| inl hy =>
lift x to ℕ using hle.trans_lt hy; lift y to ℕ using hy
simp only [← Nat.cast_mul, toENatAux_nat]
| inr hy =>
rcases eq_or_ne x 0 with rfl | hx
· simp
· simp only [toENatAux_eq_top hy]
rw [toENatAux_eq_top, ENat.mul_top]
· rwa [Ne, toENatAux_eq_zero]
· exact le_mul_of_one_le_of_le (one_le_iff_ne_zero.2 hx) hy
map_add' x y := by
wlog hle : x ≤ y; · rw [add_comm, this y x (le_of_not_le hle), add_comm]
cases lt_or_le y ℵ₀ with
| inl hy =>
lift x to ℕ using hle.trans_lt hy; lift y to ℕ using hy
simp only [← Nat.cast_add, toENatAux_nat]
| inr hy =>
simp only [toENatAux_eq_top hy, add_top]
exact toENatAux_eq_top <| le_add_left hy
map_zero' := toENatAux_zero
monotone' := toENatAux_gc.monotone_u
/-- The coercion `Cardinal.ofENat` and the projection `Cardinal.toENat` form a Galois connection.
See also `Cardinal.gciENat`. -/
lemma enat_gc : GaloisConnection (↑) toENat := toENatAux_gc
@[simp] lemma toENat_ofENat (n : ℕ∞) : toENat n = n := toENatAux_ofENat n
@[simp] lemma toENat_comp_ofENat : toENat ∘ (↑) = id := funext toENat_ofENat
/-- The coercion `Cardinal.ofENat` and the projection `Cardinal.toENat`
form a Galois coinsertion. -/
noncomputable def gciENat : GaloisCoinsertion (↑) toENat :=
| enat_gc.toGaloisCoinsertion fun n ↦ (toENat_ofENat n).le
lemma toENat_strictMonoOn : StrictMonoOn toENat (Iic ℵ₀) := by
| Mathlib/SetTheory/Cardinal/ENat.lean | 226 | 228 |
/-
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.Algebra.CharP.Reduced
import Mathlib.RingTheory.IntegralDomain
-- TODO: remove Mathlib.Algebra.CharP.Reduced and move the last two lemmas to Lemmas
/-!
# Roots of unity
We define roots of unity in the context of an arbitrary commutative monoid,
as a subgroup of the group of units.
## Main definitions
* `rootsOfUnity n M`, for `n : ℕ` is the subgroup of the units of a commutative monoid `M`
consisting of elements `x` that satisfy `x ^ n = 1`.
## Main results
* `rootsOfUnity.isCyclic`: the roots of unity in an integral domain form a cyclic group.
## Implementation details
It is desirable that `rootsOfUnity` is a subgroup,
and it will mainly be applied to rings (e.g. the ring of integers in a number field) and fields.
We therefore implement it as a subgroup of the units of a commutative monoid.
We have chosen to define `rootsOfUnity n` for `n : ℕ` and add a `[NeZero n]` typeclass
assumption when we need `n` to be non-zero (which is the case for most interesting statements).
Note that `rootsOfUnity 0 M` is the top subgroup of `Mˣ` (as the condition `ζ^0 = 1` is
satisfied for all units).
-/
noncomputable section
open Polynomial
open Finset
variable {M N G R S F : Type*}
variable [CommMonoid M] [CommMonoid N] [DivisionCommMonoid G]
section rootsOfUnity
variable {k l : ℕ}
/-- `rootsOfUnity k M` is the subgroup of elements `m : Mˣ` that satisfy `m ^ k = 1`. -/
def rootsOfUnity (k : ℕ) (M : Type*) [CommMonoid M] : Subgroup Mˣ where
carrier := {ζ | ζ ^ k = 1}
one_mem' := one_pow _
mul_mem' _ _ := by simp_all only [Set.mem_setOf_eq, mul_pow, one_mul]
inv_mem' _ := by simp_all only [Set.mem_setOf_eq, inv_pow, inv_one]
@[simp]
theorem mem_rootsOfUnity (k : ℕ) (ζ : Mˣ) : ζ ∈ rootsOfUnity k M ↔ ζ ^ k = 1 :=
Iff.rfl
/-- A variant of `mem_rootsOfUnity` using `ζ : Mˣ`. -/
theorem mem_rootsOfUnity' (k : ℕ) (ζ : Mˣ) : ζ ∈ rootsOfUnity k M ↔ (ζ : M) ^ k = 1 := by
rw [mem_rootsOfUnity]; norm_cast
@[simp]
theorem rootsOfUnity_one (M : Type*) [CommMonoid M] : rootsOfUnity 1 M = ⊥ := by
ext1
simp only [mem_rootsOfUnity, pow_one, Subgroup.mem_bot]
@[simp]
lemma rootsOfUnity_zero (M : Type*) [CommMonoid M] : rootsOfUnity 0 M = ⊤ := by
ext1
simp only [mem_rootsOfUnity, pow_zero, Subgroup.mem_top]
theorem rootsOfUnity.coe_injective {n : ℕ} :
Function.Injective (fun x : rootsOfUnity n M ↦ x.val.val) :=
Units.ext.comp fun _ _ ↦ Subtype.eq
/-- Make an element of `rootsOfUnity` from a member of the base ring, and a proof that it has
a positive power equal to one. -/
@[simps! coe_val]
def rootsOfUnity.mkOfPowEq (ζ : M) {n : ℕ} [NeZero n] (h : ζ ^ n = 1) : rootsOfUnity n M :=
⟨Units.ofPowEqOne ζ n h <| NeZero.ne n, Units.pow_ofPowEqOne _ _⟩
@[simp]
theorem rootsOfUnity.coe_mkOfPowEq {ζ : M} {n : ℕ} [NeZero n] (h : ζ ^ n = 1) :
((rootsOfUnity.mkOfPowEq _ h : Mˣ) : M) = ζ :=
rfl
theorem rootsOfUnity_le_of_dvd (h : k ∣ l) : rootsOfUnity k M ≤ rootsOfUnity l M := by
obtain ⟨d, rfl⟩ := h
intro ζ h
simp_all only [mem_rootsOfUnity, pow_mul, one_pow]
theorem map_rootsOfUnity (f : Mˣ →* Nˣ) (k : ℕ) : (rootsOfUnity k M).map f ≤ rootsOfUnity k N := by
rintro _ ⟨ζ, h, rfl⟩
simp_all only [← map_pow, mem_rootsOfUnity, SetLike.mem_coe, MonoidHom.map_one]
@[norm_cast]
theorem rootsOfUnity.coe_pow [CommMonoid R] (ζ : rootsOfUnity k R) (m : ℕ) :
(((ζ ^ m :) : Rˣ) : R) = ((ζ : Rˣ) : R) ^ m := by
rw [Subgroup.coe_pow, Units.val_pow_eq_pow_val]
/-- The canonical isomorphism from the `n`th roots of unity in `Mˣ`
to the `n`th roots of unity in `M`. -/
def rootsOfUnityUnitsMulEquiv (M : Type*) [CommMonoid M] (n : ℕ) :
rootsOfUnity n Mˣ ≃* rootsOfUnity n M where
toFun ζ := ⟨ζ.val, (mem_rootsOfUnity ..).mpr <| (mem_rootsOfUnity' ..).mp ζ.prop⟩
invFun ζ := ⟨toUnits ζ.val, by
simp only [mem_rootsOfUnity, ← map_pow, EmbeddingLike.map_eq_one_iff]
exact (mem_rootsOfUnity ..).mp ζ.prop⟩
left_inv ζ := by simp only [toUnits_val_apply, Subtype.coe_eta]
right_inv ζ := by simp only [val_toUnits_apply, Subtype.coe_eta]
map_mul' ζ ζ' := by simp only [Subgroup.coe_mul, Units.val_mul, MulMemClass.mk_mul_mk]
section CommMonoid
variable [CommMonoid R] [CommMonoid S] [FunLike F R S]
/-- Restrict a ring homomorphism to the nth roots of unity. -/
def restrictRootsOfUnity [MonoidHomClass F R S] (σ : F) (n : ℕ) :
rootsOfUnity n R →* rootsOfUnity n S :=
{ toFun := fun ξ ↦ ⟨Units.map σ (ξ : Rˣ), by
rw [mem_rootsOfUnity, ← map_pow, Units.ext_iff, Units.coe_map, ξ.prop]
exact map_one σ⟩
map_one' := by ext1; simp only [OneMemClass.coe_one, map_one]
map_mul' := fun ξ₁ ξ₂ ↦ by
ext1; simp only [Subgroup.coe_mul, map_mul, MulMemClass.mk_mul_mk] }
@[simp]
theorem restrictRootsOfUnity_coe_apply [MonoidHomClass F R S] (σ : F) (ζ : rootsOfUnity k R) :
(restrictRootsOfUnity σ k ζ : Sˣ) = σ (ζ : Rˣ) :=
rfl
/-- Restrict a monoid isomorphism to the nth roots of unity. -/
nonrec def MulEquiv.restrictRootsOfUnity (σ : R ≃* S) (n : ℕ) :
rootsOfUnity n R ≃* rootsOfUnity n S where
toFun := restrictRootsOfUnity σ n
invFun := restrictRootsOfUnity σ.symm n
left_inv ξ := by ext; exact σ.symm_apply_apply _
right_inv ξ := by ext; exact σ.apply_symm_apply _
map_mul' := (restrictRootsOfUnity _ n).map_mul
@[simp]
theorem MulEquiv.restrictRootsOfUnity_coe_apply (σ : R ≃* S) (ζ : rootsOfUnity k R) :
(σ.restrictRootsOfUnity k ζ : Sˣ) = σ (ζ : Rˣ) :=
rfl
@[simp]
theorem MulEquiv.restrictRootsOfUnity_symm (σ : R ≃* S) :
(σ.restrictRootsOfUnity k).symm = σ.symm.restrictRootsOfUnity k :=
rfl
end CommMonoid
section IsDomain
-- The following results need `k` to be nonzero.
variable [NeZero k] [CommRing R] [IsDomain R]
theorem mem_rootsOfUnity_iff_mem_nthRoots {ζ : Rˣ} :
ζ ∈ rootsOfUnity k R ↔ (ζ : R) ∈ nthRoots k (1 : R) := by
simp only [mem_rootsOfUnity, mem_nthRoots (NeZero.pos k), Units.ext_iff, Units.val_one,
Units.val_pow_eq_pow_val]
variable (k R)
/-- Equivalence between the `k`-th roots of unity in `R` and the `k`-th roots of `1`.
This is implemented as equivalence of subtypes,
because `rootsOfUnity` is a subgroup of the group of units,
whereas `nthRoots` is a multiset. -/
def rootsOfUnityEquivNthRoots : rootsOfUnity k R ≃ { x // x ∈ nthRoots k (1 : R) } where
toFun x := ⟨(x : Rˣ), mem_rootsOfUnity_iff_mem_nthRoots.mp x.2⟩
invFun x := by
refine ⟨⟨x, ↑x ^ (k - 1 : ℕ), ?_, ?_⟩, ?_⟩
all_goals
rcases x with ⟨x, hx⟩; rw [mem_nthRoots <| NeZero.pos k] at hx
simp only [← pow_succ, ← pow_succ', hx, tsub_add_cancel_of_le NeZero.one_le]
simp only [mem_rootsOfUnity, Units.ext_iff, Units.val_pow_eq_pow_val, hx, Units.val_one]
left_inv := by rintro ⟨x, hx⟩; ext; rfl
right_inv := by rintro ⟨x, hx⟩; ext; rfl
variable {k R}
@[simp]
theorem rootsOfUnityEquivNthRoots_apply (x : rootsOfUnity k R) :
(rootsOfUnityEquivNthRoots R k x : R) = ((x : Rˣ) : R) :=
rfl
@[simp]
theorem rootsOfUnityEquivNthRoots_symm_apply (x : { x // x ∈ nthRoots k (1 : R) }) :
(((rootsOfUnityEquivNthRoots R k).symm x : Rˣ) : R) = (x : R) :=
rfl
variable (k R)
instance rootsOfUnity.fintype : Fintype (rootsOfUnity k R) := by
classical
exact Fintype.ofEquiv { x // x ∈ nthRoots k (1 : R) } (rootsOfUnityEquivNthRoots R k).symm
instance rootsOfUnity.isCyclic : IsCyclic (rootsOfUnity k R) :=
isCyclic_of_subgroup_isDomain ((Units.coeHom R).comp (rootsOfUnity k R).subtype) coe_injective
theorem card_rootsOfUnity : Fintype.card (rootsOfUnity k R) ≤ k := by
classical
calc
Fintype.card (rootsOfUnity k R) = Fintype.card { x // x ∈ nthRoots k (1 : R) } :=
Fintype.card_congr (rootsOfUnityEquivNthRoots R k)
_ ≤ Multiset.card (nthRoots k (1 : R)).attach := Multiset.card_le_card (Multiset.dedup_le _)
_ = Multiset.card (nthRoots k (1 : R)) := Multiset.card_attach
_ ≤ k := card_nthRoots k 1
variable {k R}
theorem map_rootsOfUnity_eq_pow_self [FunLike F R R] [MonoidHomClass F R R] (σ : F)
(ζ : rootsOfUnity k R) :
∃ m : ℕ, σ (ζ : Rˣ) = ((ζ : Rˣ) : R) ^ m := by
obtain ⟨m, hm⟩ := MonoidHom.map_cyclic (restrictRootsOfUnity σ k)
rw [← restrictRootsOfUnity_coe_apply, hm, ← zpow_mod_orderOf, ← Int.toNat_of_nonneg
(m.emod_nonneg (Int.natCast_ne_zero.mpr (pos_iff_ne_zero.mp (orderOf_pos ζ)))),
zpow_natCast, rootsOfUnity.coe_pow]
exact ⟨(m % orderOf ζ).toNat, rfl⟩
end IsDomain
section Reduced
variable (R) [CommRing R] [IsReduced R]
-- @[simp] -- Porting note: simp normal form is `mem_rootsOfUnity_prime_pow_mul_iff'`
theorem mem_rootsOfUnity_prime_pow_mul_iff (p k : ℕ) (m : ℕ) [ExpChar R p] {ζ : Rˣ} :
ζ ∈ rootsOfUnity (p ^ k * m) R ↔ ζ ∈ rootsOfUnity m R := by
simp only [mem_rootsOfUnity', ExpChar.pow_prime_pow_mul_eq_one_iff]
/-- A variant of `mem_rootsOfUnity_prime_pow_mul_iff` in terms of `ζ ^ _` -/
@[simp]
theorem mem_rootsOfUnity_prime_pow_mul_iff' (p k : ℕ) (m : ℕ) [ExpChar R p] {ζ : Rˣ} :
ζ ^ (p ^ k * m) = 1 ↔ ζ ∈ rootsOfUnity m R := by
rw [← mem_rootsOfUnity, mem_rootsOfUnity_prime_pow_mul_iff]
end Reduced
end rootsOfUnity
section cyclic
namespace IsCyclic
/-- The isomorphism from the group of group homomorphisms from a finite cyclic group `G` of order
`n` into another group `G'` to the group of `n`th roots of unity in `G'` determined by a generator
`g` of `G`. It sends `φ : G →* G'` to `φ g`. -/
noncomputable
def monoidHomMulEquivRootsOfUnityOfGenerator {G : Type*} [CommGroup G] {g : G}
(hg : ∀ (x : G), x ∈ Subgroup.zpowers g) (G' : Type*) [CommGroup G'] :
(G →* G') ≃* rootsOfUnity (Nat.card G) G' where
toFun φ := ⟨(IsUnit.map φ <| Group.isUnit g).unit, by
simp only [mem_rootsOfUnity, Units.ext_iff, Units.val_pow_eq_pow_val, IsUnit.unit_spec,
← map_pow, pow_card_eq_one', map_one, Units.val_one]⟩
invFun ζ := monoidHomOfForallMemZpowers hg (g' := (ζ.val : G')) <| by
simpa only [orderOf_eq_card_of_forall_mem_zpowers hg, orderOf_dvd_iff_pow_eq_one,
← Units.val_pow_eq_pow_val, Units.val_eq_one] using ζ.prop
left_inv φ := (MonoidHom.eq_iff_eq_on_generator hg _ φ).mpr <| by
simp only [IsUnit.unit_spec, monoidHomOfForallMemZpowers_apply_gen]
right_inv φ := Subtype.ext <| by
simp only [monoidHomOfForallMemZpowers_apply_gen, IsUnit.unit_of_val_units]
map_mul' x y := by
simp only [MonoidHom.mul_apply, MulMemClass.mk_mul_mk, Subtype.mk.injEq, Units.ext_iff,
IsUnit.unit_spec, Units.val_mul]
/-- The group of group homomorphisms from a finite cyclic group `G` of order `n` into another
group `G'` is (noncanonically) isomorphic to the group of `n`th roots of unity in `G'`. -/
lemma monoidHom_mulEquiv_rootsOfUnity (G : Type*) [CommGroup G] [IsCyclic G]
(G' : Type*) [CommGroup G'] :
Nonempty <| (G →* G') ≃* rootsOfUnity (Nat.card G) G' := by
obtain ⟨g, hg⟩ := IsCyclic.exists_generator (α := G)
exact ⟨monoidHomMulEquivRootsOfUnityOfGenerator hg G'⟩
end IsCyclic
end cyclic
| Mathlib/RingTheory/RootsOfUnity/Basic.lean | 478 | 486 | |
/-
Copyright (c) 2020 Markus Himmel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Markus Himmel, Jakob von Raumer
-/
import Mathlib.Algebra.Group.Hom.Defs
import Mathlib.Algebra.Group.Action.Units
import Mathlib.Algebra.Module.End
import Mathlib.CategoryTheory.Endomorphism
import Mathlib.CategoryTheory.Limits.Shapes.Kernels
import Mathlib.Algebra.BigOperators.Group.Finset.Defs
/-!
# Preadditive categories
A preadditive category is a category in which `X ⟶ Y` is an abelian group in such a way that
composition of morphisms is linear in both variables.
This file contains a definition of preadditive category that directly encodes the definition given
above. The definition could also be phrased as follows: A preadditive category is a category
enriched over the category of Abelian groups. Once the general framework to state this in Lean is
available, the contents of this file should become obsolete.
## Main results
* Definition of preadditive categories and basic properties
* In a preadditive category, `f : Q ⟶ R` is mono if and only if `g ≫ f = 0 → g = 0` for all
composable `g`.
* A preadditive category with kernels has equalizers.
## Implementation notes
The simp normal form for negation and composition is to push negations as far as possible to
the outside. For example, `f ≫ (-g)` and `(-f) ≫ g` both become `-(f ≫ g)`, and `(-f) ≫ (-g)`
is simplified to `f ≫ g`.
## References
* [F. Borceux, *Handbook of Categorical Algebra 2*][borceux-vol2]
## Tags
additive, preadditive, Hom group, Ab-category, Ab-enriched
-/
universe v u
open CategoryTheory.Limits
namespace CategoryTheory
variable (C : Type u) [Category.{v} C]
/-- A category is called preadditive if `P ⟶ Q` is an abelian group such that composition is
linear in both variables. -/
@[stacks 00ZY]
class Preadditive where
homGroup : ∀ P Q : C, AddCommGroup (P ⟶ Q) := by infer_instance
add_comp : ∀ (P Q R : C) (f f' : P ⟶ Q) (g : Q ⟶ R), (f + f') ≫ g = f ≫ g + f' ≫ g := by
aesop_cat
comp_add : ∀ (P Q R : C) (f : P ⟶ Q) (g g' : Q ⟶ R), f ≫ (g + g') = f ≫ g + f ≫ g' := by
aesop_cat
attribute [inherit_doc Preadditive] Preadditive.homGroup Preadditive.add_comp Preadditive.comp_add
attribute [instance] Preadditive.homGroup
-- simp can already prove reassoc version
attribute [reassoc, simp] Preadditive.add_comp
attribute [reassoc] Preadditive.comp_add
attribute [simp] Preadditive.comp_add
end CategoryTheory
open CategoryTheory
namespace CategoryTheory
namespace Preadditive
section Preadditive
open AddMonoidHom
variable {C : Type u} [Category.{v} C] [Preadditive C]
section InducedCategory
universe u'
variable {D : Type u'} (F : D → C)
instance inducedCategory : Preadditive.{v} (InducedCategory C F) where
homGroup P Q := @Preadditive.homGroup C _ _ (F P) (F Q)
add_comp _ _ _ _ _ _ := add_comp _ _ _ _ _ _
comp_add _ _ _ _ _ _ := comp_add _ _ _ _ _ _
end InducedCategory
instance fullSubcategory (Z : ObjectProperty C) : Preadditive Z.FullSubcategory where
homGroup P Q := @Preadditive.homGroup C _ _ P.obj Q.obj
add_comp _ _ _ _ _ _ := add_comp _ _ _ _ _ _
comp_add _ _ _ _ _ _ := comp_add _ _ _ _ _ _
instance (X : C) : AddCommGroup (End X) := by
dsimp [End]
infer_instance
/-- Composition by a fixed left argument as a group homomorphism -/
def leftComp {P Q : C} (R : C) (f : P ⟶ Q) : (Q ⟶ R) →+ (P ⟶ R) :=
mk' (fun g => f ≫ g) fun g g' => by simp
/-- Composition by a fixed right argument as a group homomorphism -/
def rightComp (P : C) {Q R : C} (g : Q ⟶ R) : (P ⟶ Q) →+ (P ⟶ R) :=
mk' (fun f => f ≫ g) fun f f' => by simp
variable {P Q R : C} (f f' : P ⟶ Q) (g g' : Q ⟶ R)
/-- Composition as a bilinear group homomorphism -/
def compHom : (P ⟶ Q) →+ (Q ⟶ R) →+ (P ⟶ R) :=
AddMonoidHom.mk' (fun f => leftComp _ f) fun f₁ f₂ =>
AddMonoidHom.ext fun g => (rightComp _ g).map_add f₁ f₂
-- simp can prove the reassoc version
@[reassoc, simp]
theorem sub_comp : (f - f') ≫ g = f ≫ g - f' ≫ g :=
map_sub (rightComp P g) f f'
-- simp can prove the reassoc version
@[reassoc, simp]
theorem comp_sub : f ≫ (g - g') = f ≫ g - f ≫ g' :=
map_sub (leftComp R f) g g'
-- simp can prove the reassoc version
@[reassoc, simp]
theorem neg_comp : (-f) ≫ g = -f ≫ g :=
map_neg (rightComp P g) f
-- simp can prove the reassoc version
@[reassoc, simp]
theorem comp_neg : f ≫ (-g) = -f ≫ g :=
map_neg (leftComp R f) g
@[reassoc]
theorem neg_comp_neg : (-f) ≫ (-g) = f ≫ g := by simp
theorem nsmul_comp (n : ℕ) : (n • f) ≫ g = n • f ≫ g :=
map_nsmul (rightComp P g) n f
theorem comp_nsmul (n : ℕ) : f ≫ (n • g) = n • f ≫ g :=
map_nsmul (leftComp R f) n g
theorem zsmul_comp (n : ℤ) : (n • f) ≫ g = n • f ≫ g :=
map_zsmul (rightComp P g) n f
theorem comp_zsmul (n : ℤ) : f ≫ (n • g) = n • f ≫ g :=
map_zsmul (leftComp R f) n g
@[reassoc]
theorem comp_sum {P Q R : C} {J : Type*} (s : Finset J) (f : P ⟶ Q) (g : J → (Q ⟶ R)) :
(f ≫ ∑ j ∈ s, g j) = ∑ j ∈ s, f ≫ g j :=
map_sum (leftComp R f) _ _
@[reassoc]
theorem sum_comp {P Q R : C} {J : Type*} (s : Finset J) (f : J → (P ⟶ Q)) (g : Q ⟶ R) :
(∑ j ∈ s, f j) ≫ g = ∑ j ∈ s, f j ≫ g :=
map_sum (rightComp P g) _ _
@[reassoc]
theorem sum_comp' {P Q R S : C} {J : Type*} (s : Finset J) (f : J → (P ⟶ Q)) (g : J → (Q ⟶ R))
(h : R ⟶ S) : (∑ j ∈ s, f j ≫ g j) ≫ h = ∑ j ∈ s, f j ≫ g j ≫ h := by
simp only [← Category.assoc]
apply sum_comp
instance {P Q : C} {f : P ⟶ Q} [Epi f] : Epi (-f) :=
⟨fun g g' H => by rwa [neg_comp, neg_comp, ← comp_neg, ← comp_neg, cancel_epi, neg_inj] at H⟩
instance {P Q : C} {f : P ⟶ Q} [Mono f] : Mono (-f) :=
⟨fun g g' H => by rwa [comp_neg, comp_neg, ← neg_comp, ← neg_comp, cancel_mono, neg_inj] at H⟩
instance (priority := 100) preadditiveHasZeroMorphisms : HasZeroMorphisms C where
zero := inferInstance
comp_zero f R := show leftComp R f 0 = 0 from map_zero _
zero_comp P _ _ f := show rightComp P f 0 = 0 from map_zero _
/-- Porting note: adding this before the ring instance allowed moduleEndRight to find
the correct Monoid structure on End. Moved both down after preadditiveHasZeroMorphisms
to make use of them -/
instance {X : C} : Semiring (End X) :=
{ End.monoid with
zero_mul := fun f => by dsimp [mul]; exact HasZeroMorphisms.comp_zero f _
mul_zero := fun f => by dsimp [mul]; exact HasZeroMorphisms.zero_comp _ f
left_distrib := fun f g h => Preadditive.add_comp X X X g h f
right_distrib := fun f g h => Preadditive.comp_add X X X h f g }
/-- Porting note: It looks like Ring's parent classes changed in
Lean 4 so the previous instance needed modification. Was following my nose here. -/
instance {X : C} : Ring (End X) :=
{ (inferInstance : Semiring (End X)),
(inferInstance : AddCommGroup (End X)) with
neg_add_cancel := neg_add_cancel }
instance moduleEndRight {X Y : C} : Module (End Y) (X ⟶ Y) where
smul_add _ _ _ := add_comp _ _ _ _ _ _
smul_zero _ := zero_comp
add_smul _ _ _ := comp_add _ _ _ _ _ _
zero_smul _ := comp_zero
theorem mono_of_cancel_zero {Q R : C} (f : Q ⟶ R) (h : ∀ {P : C} (g : P ⟶ Q), g ≫ f = 0 → g = 0) :
Mono f where
right_cancellation := fun {Z} g₁ g₂ hg =>
sub_eq_zero.1 <| h _ <| (map_sub (rightComp Z f) g₁ g₂).trans <| sub_eq_zero.2 hg
theorem mono_iff_cancel_zero {Q R : C} (f : Q ⟶ R) :
Mono f ↔ ∀ (P : C) (g : P ⟶ Q), g ≫ f = 0 → g = 0 :=
⟨fun _ _ _ => zero_of_comp_mono _, mono_of_cancel_zero f⟩
theorem mono_of_kernel_zero {X Y : C} {f : X ⟶ Y} [HasLimit (parallelPair f 0)]
(w : kernel.ι f = 0) : Mono f :=
mono_of_cancel_zero f fun g h => by rw [← kernel.lift_ι f g h, w, Limits.comp_zero]
lemma mono_of_isZero_kernel' {X Y : C} {f : X ⟶ Y} (c : KernelFork f) (hc : IsLimit c)
(h : IsZero c.pt) : Mono f := mono_of_cancel_zero _ (fun g hg => by
obtain ⟨a, ha⟩ := KernelFork.IsLimit.lift' hc _ hg
rw [← ha, h.eq_of_tgt a 0, Limits.zero_comp])
lemma mono_of_isZero_kernel {X Y : C} (f : X ⟶ Y) [HasKernel f] (h : IsZero (kernel f)) :
Mono f :=
mono_of_isZero_kernel' _ (kernelIsKernel _) h
theorem epi_of_cancel_zero {P Q : C} (f : P ⟶ Q) (h : ∀ {R : C} (g : Q ⟶ R), f ≫ g = 0 → g = 0) :
Epi f :=
⟨fun {Z} g g' hg =>
sub_eq_zero.1 <| h _ <| (map_sub (leftComp Z f) g g').trans <| sub_eq_zero.2 hg⟩
theorem epi_iff_cancel_zero {P Q : C} (f : P ⟶ Q) :
Epi f ↔ ∀ (R : C) (g : Q ⟶ R), f ≫ g = 0 → g = 0 :=
⟨fun _ _ _ => zero_of_epi_comp _, epi_of_cancel_zero f⟩
theorem epi_of_cokernel_zero {X Y : C} {f : X ⟶ Y} [HasColimit (parallelPair f 0)]
(w : cokernel.π f = 0) : Epi f :=
epi_of_cancel_zero f fun g h => by rw [← cokernel.π_desc f g h, w, Limits.zero_comp]
lemma epi_of_isZero_cokernel' {X Y : C} {f : X ⟶ Y} (c : CokernelCofork f) (hc : IsColimit c)
(h : IsZero c.pt) : Epi f := epi_of_cancel_zero _ (fun g hg => by
obtain ⟨a, ha⟩ := CokernelCofork.IsColimit.desc' hc _ hg
rw [← ha, h.eq_of_src a 0, Limits.comp_zero])
lemma epi_of_isZero_cokernel {X Y : C} (f : X ⟶ Y) [HasCokernel f] (h : IsZero (cokernel f)) :
Epi f :=
epi_of_isZero_cokernel' _ (cokernelIsCokernel _) h
namespace IsIso
@[simp]
theorem comp_left_eq_zero [IsIso f] : f ≫ g = 0 ↔ g = 0 := by
rw [← IsIso.eq_inv_comp, Limits.comp_zero]
@[simp]
theorem comp_right_eq_zero [IsIso g] : f ≫ g = 0 ↔ f = 0 := by
rw [← IsIso.eq_comp_inv, Limits.zero_comp]
end IsIso
open ZeroObject
variable [HasZeroObject C]
theorem mono_of_kernel_iso_zero {X Y : C} {f : X ⟶ Y} [HasLimit (parallelPair f 0)]
(w : kernel f ≅ 0) : Mono f :=
mono_of_kernel_zero (zero_of_source_iso_zero _ w)
theorem epi_of_cokernel_iso_zero {X Y : C} {f : X ⟶ Y} [HasColimit (parallelPair f 0)]
(w : cokernel f ≅ 0) : Epi f :=
epi_of_cokernel_zero (zero_of_target_iso_zero _ w)
end Preadditive
section Equalizers
variable {C : Type u} [Category.{v} C] [Preadditive C]
section
variable {X Y : C} {f : X ⟶ Y} {g : X ⟶ Y}
/-- Map a kernel cone on the difference of two morphisms to the equalizer fork. -/
@[simps! pt]
def forkOfKernelFork (c : KernelFork (f - g)) : Fork f g :=
Fork.ofι c.ι <| by rw [← sub_eq_zero, ← comp_sub, c.condition]
@[simp]
theorem forkOfKernelFork_ι (c : KernelFork (f - g)) : (forkOfKernelFork c).ι = c.ι :=
rfl
/-- Map any equalizer fork to a cone on the difference of the two morphisms. -/
def kernelForkOfFork (c : Fork f g) : KernelFork (f - g) :=
Fork.ofι c.ι <| by rw [comp_sub, comp_zero, sub_eq_zero, c.condition]
@[simp]
theorem kernelForkOfFork_ι (c : Fork f g) : (kernelForkOfFork c).ι = c.ι :=
rfl
@[simp]
theorem kernelForkOfFork_ofι {P : C} (ι : P ⟶ X) (w : ι ≫ f = ι ≫ g) :
kernelForkOfFork (Fork.ofι ι w) = KernelFork.ofι ι (by simp [w]) :=
rfl
/-- A kernel of `f - g` is an equalizer of `f` and `g`. -/
def isLimitForkOfKernelFork {c : KernelFork (f - g)} (i : IsLimit c) :
IsLimit (forkOfKernelFork c) :=
Fork.IsLimit.mk' _ fun s =>
⟨i.lift (kernelForkOfFork s), i.fac _ _, fun h => by apply Fork.IsLimit.hom_ext i; aesop_cat⟩
@[simp]
theorem isLimitForkOfKernelFork_lift {c : KernelFork (f - g)} (i : IsLimit c) (s : Fork f g) :
(isLimitForkOfKernelFork i).lift s = i.lift (kernelForkOfFork s) :=
rfl
/-- An equalizer of `f` and `g` is a kernel of `f - g`. -/
def isLimitKernelForkOfFork {c : Fork f g} (i : IsLimit c) : IsLimit (kernelForkOfFork c) :=
Fork.IsLimit.mk' _ fun s =>
⟨i.lift (forkOfKernelFork s), i.fac _ _, fun h => by apply Fork.IsLimit.hom_ext i; aesop_cat⟩
variable (f g)
/-- A preadditive category has an equalizer for `f` and `g` if it has a kernel for `f - g`. -/
theorem hasEqualizer_of_hasKernel [HasKernel (f - g)] : HasEqualizer f g :=
HasLimit.mk
{ cone := forkOfKernelFork _
isLimit := isLimitForkOfKernelFork (equalizerIsEqualizer (f - g) 0) }
/-- A preadditive category has a kernel for `f - g` if it has an equalizer for `f` and `g`. -/
theorem hasKernel_of_hasEqualizer [HasEqualizer f g] : HasKernel (f - g) :=
HasLimit.mk
{ cone := kernelForkOfFork (equalizer.fork f g)
isLimit := isLimitKernelForkOfFork (limit.isLimit (parallelPair f g)) }
variable {f g}
/-- Map a cokernel cocone on the difference of two morphisms to the coequalizer cofork. -/
@[simps! pt]
def coforkOfCokernelCofork (c : CokernelCofork (f - g)) : Cofork f g :=
Cofork.ofπ c.π <| by rw [← sub_eq_zero, ← sub_comp, c.condition]
@[simp]
theorem coforkOfCokernelCofork_π (c : CokernelCofork (f - g)) :
(coforkOfCokernelCofork c).π = c.π :=
rfl
/-- Map any coequalizer cofork to a cocone on the difference of the two morphisms. -/
def cokernelCoforkOfCofork (c : Cofork f g) : CokernelCofork (f - g) :=
Cofork.ofπ c.π <| by rw [sub_comp, zero_comp, sub_eq_zero, c.condition]
@[simp]
theorem cokernelCoforkOfCofork_π (c : Cofork f g) : (cokernelCoforkOfCofork c).π = c.π :=
rfl
@[simp]
theorem cokernelCoforkOfCofork_ofπ {P : C} (π : Y ⟶ P) (w : f ≫ π = g ≫ π) :
cokernelCoforkOfCofork (Cofork.ofπ π w) = CokernelCofork.ofπ π (by simp [w]) :=
rfl
/-- A cokernel of `f - g` is a coequalizer of `f` and `g`. -/
def isColimitCoforkOfCokernelCofork {c : CokernelCofork (f - g)} (i : IsColimit c) :
IsColimit (coforkOfCokernelCofork c) :=
Cofork.IsColimit.mk' _ fun s =>
⟨i.desc (cokernelCoforkOfCofork s), i.fac _ _, fun h => by
apply Cofork.IsColimit.hom_ext i; aesop_cat⟩
@[simp]
theorem isColimitCoforkOfCokernelCofork_desc {c : CokernelCofork (f - g)} (i : IsColimit c)
(s : Cofork f g) :
(isColimitCoforkOfCokernelCofork i).desc s = i.desc (cokernelCoforkOfCofork s) :=
rfl
/-- A coequalizer of `f` and `g` is a cokernel of `f - g`. -/
def isColimitCokernelCoforkOfCofork {c : Cofork f g} (i : IsColimit c) :
IsColimit (cokernelCoforkOfCofork c) :=
Cofork.IsColimit.mk' _ fun s =>
⟨i.desc (coforkOfCokernelCofork s), i.fac _ _, fun h => by
apply Cofork.IsColimit.hom_ext i; aesop_cat⟩
variable (f g)
/-- A preadditive category has a coequalizer for `f` and `g` if it has a cokernel for `f - g`. -/
theorem hasCoequalizer_of_hasCokernel [HasCokernel (f - g)] : HasCoequalizer f g :=
HasColimit.mk
{ cocone := coforkOfCokernelCofork _
isColimit := isColimitCoforkOfCokernelCofork (coequalizerIsCoequalizer (f - g) 0) }
/-- A preadditive category has a cokernel for `f - g` if it has a coequalizer for `f` and `g`. -/
theorem hasCokernel_of_hasCoequalizer [HasCoequalizer f g] : HasCokernel (f - g) :=
HasColimit.mk
{ cocone := cokernelCoforkOfCofork (coequalizer.cofork f g)
isColimit := isColimitCokernelCoforkOfCofork (colimit.isColimit (parallelPair f g)) }
end
| /-- If a preadditive category has all kernels, then it also has all equalizers. -/
theorem hasEqualizers_of_hasKernels [HasKernels C] : HasEqualizers C :=
@hasEqualizers_of_hasLimit_parallelPair _ _ fun {_} {_} f g => hasEqualizer_of_hasKernel f g
| Mathlib/CategoryTheory/Preadditive/Basic.lean | 403 | 405 |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Algebra.Ring.Associated
import Mathlib.Algebra.Star.Unitary
import Mathlib.RingTheory.PrincipalIdealDomain
import Mathlib.Tactic.Ring
import Mathlib.Algebra.EuclideanDomain.Int
/-! # ℤ[√d]
The ring of integers adjoined with a square root of `d : ℤ`.
After defining the norm, we show that it is a linearly ordered commutative ring,
as well as an integral domain.
We provide the universal property, that ring homomorphisms `ℤ√d →+* R` correspond
to choices of square roots of `d` in `R`.
-/
/-- The ring of integers adjoined with a square root of `d`.
These have the form `a + b √d` where `a b : ℤ`. The components
are called `re` and `im` by analogy to the negative `d` case. -/
@[ext]
structure Zsqrtd (d : ℤ) where
/-- Component of the integer not multiplied by `√d` -/
re : ℤ
/-- Component of the integer multiplied by `√d` -/
im : ℤ
deriving DecidableEq
@[inherit_doc] prefix:100 "ℤ√" => Zsqrtd
namespace Zsqrtd
section
variable {d : ℤ}
/-- Convert an integer to a `ℤ√d` -/
def ofInt (n : ℤ) : ℤ√d :=
⟨n, 0⟩
theorem ofInt_re (n : ℤ) : (ofInt n : ℤ√d).re = n :=
rfl
theorem ofInt_im (n : ℤ) : (ofInt n : ℤ√d).im = 0 :=
rfl
/-- The zero of the ring -/
instance : Zero (ℤ√d) :=
⟨ofInt 0⟩
@[simp]
theorem zero_re : (0 : ℤ√d).re = 0 :=
rfl
@[simp]
theorem zero_im : (0 : ℤ√d).im = 0 :=
rfl
instance : Inhabited (ℤ√d) :=
⟨0⟩
/-- The one of the ring -/
instance : One (ℤ√d) :=
⟨ofInt 1⟩
@[simp]
theorem one_re : (1 : ℤ√d).re = 1 :=
rfl
@[simp]
theorem one_im : (1 : ℤ√d).im = 0 :=
rfl
/-- The representative of `√d` in the ring -/
def sqrtd : ℤ√d :=
⟨0, 1⟩
@[simp]
theorem sqrtd_re : (sqrtd : ℤ√d).re = 0 :=
rfl
@[simp]
theorem sqrtd_im : (sqrtd : ℤ√d).im = 1 :=
rfl
/-- Addition of elements of `ℤ√d` -/
instance : Add (ℤ√d) :=
⟨fun z w => ⟨z.1 + w.1, z.2 + w.2⟩⟩
@[simp]
theorem add_def (x y x' y' : ℤ) : (⟨x, y⟩ + ⟨x', y'⟩ : ℤ√d) = ⟨x + x', y + y'⟩ :=
rfl
@[simp]
theorem add_re (z w : ℤ√d) : (z + w).re = z.re + w.re :=
rfl
@[simp]
theorem add_im (z w : ℤ√d) : (z + w).im = z.im + w.im :=
rfl
/-- Negation in `ℤ√d` -/
instance : Neg (ℤ√d) :=
⟨fun z => ⟨-z.1, -z.2⟩⟩
@[simp]
theorem neg_re (z : ℤ√d) : (-z).re = -z.re :=
rfl
@[simp]
theorem neg_im (z : ℤ√d) : (-z).im = -z.im :=
rfl
/-- Multiplication in `ℤ√d` -/
instance : Mul (ℤ√d) :=
⟨fun z w => ⟨z.1 * w.1 + d * z.2 * w.2, z.1 * w.2 + z.2 * w.1⟩⟩
@[simp]
theorem mul_re (z w : ℤ√d) : (z * w).re = z.re * w.re + d * z.im * w.im :=
rfl
@[simp]
theorem mul_im (z w : ℤ√d) : (z * w).im = z.re * w.im + z.im * w.re :=
rfl
instance addCommGroup : AddCommGroup (ℤ√d) := by
refine
{ add := (· + ·)
zero := (0 : ℤ√d)
sub := fun a b => a + -b
neg := Neg.neg
nsmul := @nsmulRec (ℤ√d) ⟨0⟩ ⟨(· + ·)⟩
zsmul := @zsmulRec (ℤ√d) ⟨0⟩ ⟨(· + ·)⟩ ⟨Neg.neg⟩ (@nsmulRec (ℤ√d) ⟨0⟩ ⟨(· + ·)⟩)
add_assoc := ?_
zero_add := ?_
add_zero := ?_
neg_add_cancel := ?_
add_comm := ?_ } <;>
intros <;>
ext <;>
simp [add_comm, add_left_comm]
@[simp]
theorem sub_re (z w : ℤ√d) : (z - w).re = z.re - w.re :=
rfl
@[simp]
theorem sub_im (z w : ℤ√d) : (z - w).im = z.im - w.im :=
rfl
instance addGroupWithOne : AddGroupWithOne (ℤ√d) :=
{ Zsqrtd.addCommGroup with
natCast := fun n => ofInt n
intCast := ofInt
one := 1 }
instance commRing : CommRing (ℤ√d) := by
refine
{ Zsqrtd.addGroupWithOne with
mul := (· * ·)
npow := @npowRec (ℤ√d) ⟨1⟩ ⟨(· * ·)⟩,
add_comm := ?_
left_distrib := ?_
right_distrib := ?_
zero_mul := ?_
mul_zero := ?_
mul_assoc := ?_
one_mul := ?_
mul_one := ?_
mul_comm := ?_ } <;>
intros <;>
ext <;>
simp <;>
ring
instance : AddMonoid (ℤ√d) := by infer_instance
instance : Monoid (ℤ√d) := by infer_instance
instance : CommMonoid (ℤ√d) := by infer_instance
instance : CommSemigroup (ℤ√d) := by infer_instance
instance : Semigroup (ℤ√d) := by infer_instance
instance : AddCommSemigroup (ℤ√d) := by infer_instance
instance : AddSemigroup (ℤ√d) := by infer_instance
instance : CommSemiring (ℤ√d) := by infer_instance
instance : Semiring (ℤ√d) := by infer_instance
instance : Ring (ℤ√d) := by infer_instance
instance : Distrib (ℤ√d) := by infer_instance
/-- Conjugation in `ℤ√d`. The conjugate of `a + b √d` is `a - b √d`. -/
instance : Star (ℤ√d) where
star z := ⟨z.1, -z.2⟩
@[simp]
theorem star_mk (x y : ℤ) : star (⟨x, y⟩ : ℤ√d) = ⟨x, -y⟩ :=
rfl
@[simp]
theorem star_re (z : ℤ√d) : (star z).re = z.re :=
rfl
@[simp]
theorem star_im (z : ℤ√d) : (star z).im = -z.im :=
rfl
instance : StarRing (ℤ√d) where
star_involutive _ := Zsqrtd.ext rfl (neg_neg _)
star_mul a b := by ext <;> simp <;> ring
star_add _ _ := Zsqrtd.ext rfl (neg_add _ _)
-- Porting note: proof was `by decide`
instance nontrivial : Nontrivial (ℤ√d) :=
⟨⟨0, 1, Zsqrtd.ext_iff.not.mpr (by simp)⟩⟩
@[simp]
theorem natCast_re (n : ℕ) : (n : ℤ√d).re = n :=
rfl
@[simp]
theorem ofNat_re (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℤ√d).re = n :=
rfl
@[simp]
theorem natCast_im (n : ℕ) : (n : ℤ√d).im = 0 :=
rfl
@[simp]
theorem ofNat_im (n : ℕ) [n.AtLeastTwo] : (ofNat(n) : ℤ√d).im = 0 :=
rfl
theorem natCast_val (n : ℕ) : (n : ℤ√d) = ⟨n, 0⟩ :=
rfl
@[simp]
theorem intCast_re (n : ℤ) : (n : ℤ√d).re = n := by cases n <;> rfl
@[simp]
theorem intCast_im (n : ℤ) : (n : ℤ√d).im = 0 := by cases n <;> rfl
theorem intCast_val (n : ℤ) : (n : ℤ√d) = ⟨n, 0⟩ := by ext <;> simp
instance : CharZero (ℤ√d) where cast_injective m n := by simp [Zsqrtd.ext_iff]
@[simp]
theorem ofInt_eq_intCast (n : ℤ) : (ofInt n : ℤ√d) = n := by ext <;> simp [ofInt_re, ofInt_im]
@[simp]
theorem nsmul_val (n : ℕ) (x y : ℤ) : (n : ℤ√d) * ⟨x, y⟩ = ⟨n * x, n * y⟩ := by ext <;> simp
@[simp]
theorem smul_val (n x y : ℤ) : (n : ℤ√d) * ⟨x, y⟩ = ⟨n * x, n * y⟩ := by ext <;> simp
theorem smul_re (a : ℤ) (b : ℤ√d) : (↑a * b).re = a * b.re := by simp
theorem smul_im (a : ℤ) (b : ℤ√d) : (↑a * b).im = a * b.im := by simp
@[simp]
theorem muld_val (x y : ℤ) : sqrtd (d := d) * ⟨x, y⟩ = ⟨d * y, x⟩ := by ext <;> simp
@[simp]
theorem dmuld : sqrtd (d := d) * sqrtd (d := d) = d := by ext <;> simp
@[simp]
theorem smuld_val (n x y : ℤ) : sqrtd * (n : ℤ√d) * ⟨x, y⟩ = ⟨d * n * y, n * x⟩ := by ext <;> simp
theorem decompose {x y : ℤ} : (⟨x, y⟩ : ℤ√d) = x + sqrtd (d := d) * y := by ext <;> simp
theorem mul_star {x y : ℤ} : (⟨x, y⟩ * star ⟨x, y⟩ : ℤ√d) = x * x - d * y * y := by
ext <;> simp [sub_eq_add_neg, mul_comm]
theorem intCast_dvd (z : ℤ) (a : ℤ√d) : ↑z ∣ a ↔ z ∣ a.re ∧ z ∣ a.im := by
constructor
· rintro ⟨x, rfl⟩
simp only [add_zero, intCast_re, zero_mul, mul_im, dvd_mul_right, and_self_iff,
mul_re, mul_zero, intCast_im]
· rintro ⟨⟨r, hr⟩, ⟨i, hi⟩⟩
use ⟨r, i⟩
rw [smul_val, Zsqrtd.ext_iff]
exact ⟨hr, hi⟩
@[simp, norm_cast]
theorem intCast_dvd_intCast (a b : ℤ) : (a : ℤ√d) ∣ b ↔ a ∣ b := by
rw [intCast_dvd]
constructor
· rintro ⟨hre, -⟩
rwa [intCast_re] at hre
· rw [intCast_re, intCast_im]
exact fun hc => ⟨hc, dvd_zero a⟩
protected theorem eq_of_smul_eq_smul_left {a : ℤ} {b c : ℤ√d} (ha : a ≠ 0) (h : ↑a * b = a * c) :
b = c := by
rw [Zsqrtd.ext_iff] at h ⊢
apply And.imp _ _ h <;> simpa only [smul_re, smul_im] using mul_left_cancel₀ ha
section Gcd
theorem gcd_eq_zero_iff (a : ℤ√d) : Int.gcd a.re a.im = 0 ↔ a = 0 := by
simp only [Int.gcd_eq_zero_iff, Zsqrtd.ext_iff, eq_self_iff_true, zero_im, zero_re]
theorem gcd_pos_iff (a : ℤ√d) : 0 < Int.gcd a.re a.im ↔ a ≠ 0 :=
pos_iff_ne_zero.trans <| not_congr a.gcd_eq_zero_iff
theorem isCoprime_of_dvd_isCoprime {a b : ℤ√d} (hcoprime : IsCoprime a.re a.im) (hdvd : b ∣ a) :
IsCoprime b.re b.im := by
apply isCoprime_of_dvd
· rintro ⟨hre, him⟩
obtain rfl : b = 0 := Zsqrtd.ext hre him
rw [zero_dvd_iff] at hdvd
simp [hdvd, zero_im, zero_re, not_isCoprime_zero_zero] at hcoprime
· rintro z hz - hzdvdu hzdvdv
apply hz
obtain ⟨ha, hb⟩ : z ∣ a.re ∧ z ∣ a.im := by
rw [← intCast_dvd]
apply dvd_trans _ hdvd
rw [intCast_dvd]
exact ⟨hzdvdu, hzdvdv⟩
exact hcoprime.isUnit_of_dvd' ha hb
@[deprecated (since := "2025-01-23")] alias coprime_of_dvd_coprime := isCoprime_of_dvd_isCoprime
theorem exists_coprime_of_gcd_pos {a : ℤ√d} (hgcd : 0 < Int.gcd a.re a.im) :
∃ b : ℤ√d, a = ((Int.gcd a.re a.im : ℤ) : ℤ√d) * b ∧ IsCoprime b.re b.im := by
obtain ⟨re, im, H1, Hre, Him⟩ := Int.exists_gcd_one hgcd
rw [mul_comm] at Hre Him
refine ⟨⟨re, im⟩, ?_, ?_⟩
· rw [smul_val, ← Hre, ← Him]
· rw [Int.isCoprime_iff_gcd_eq_one, H1]
end Gcd
/-- Read `SqLe a c b d` as `a √c ≤ b √d` -/
def SqLe (a c b d : ℕ) : Prop :=
c * a * a ≤ d * b * b
theorem sqLe_of_le {c d x y z w : ℕ} (xz : z ≤ x) (yw : y ≤ w) (xy : SqLe x c y d) : SqLe z c w d :=
le_trans (mul_le_mul (Nat.mul_le_mul_left _ xz) xz (Nat.zero_le _) (Nat.zero_le _)) <|
le_trans xy (mul_le_mul (Nat.mul_le_mul_left _ yw) yw (Nat.zero_le _) (Nat.zero_le _))
theorem sqLe_add_mixed {c d x y z w : ℕ} (xy : SqLe x c y d) (zw : SqLe z c w d) :
c * (x * z) ≤ d * (y * w) :=
Nat.mul_self_le_mul_self_iff.1 <| by
simpa [mul_comm, mul_left_comm] using mul_le_mul xy zw (Nat.zero_le _) (Nat.zero_le _)
theorem sqLe_add {c d x y z w : ℕ} (xy : SqLe x c y d) (zw : SqLe z c w d) :
SqLe (x + z) c (y + w) d := by
have xz := sqLe_add_mixed xy zw
simp? [SqLe, mul_assoc] at xy zw says simp only [SqLe, mul_assoc] at xy zw
simp [SqLe, mul_add, mul_comm, mul_left_comm, add_le_add, *]
theorem sqLe_cancel {c d x y z w : ℕ} (zw : SqLe y d x c) (h : SqLe (x + z) c (y + w) d) :
SqLe z c w d := by
apply le_of_not_gt
intro l
refine not_le_of_gt ?_ h
simp only [SqLe, mul_add, mul_comm, mul_left_comm, add_assoc, gt_iff_lt]
have hm := sqLe_add_mixed zw (le_of_lt l)
simp only [SqLe, mul_assoc, gt_iff_lt] at l zw
exact
lt_of_le_of_lt (add_le_add_right zw _)
(add_lt_add_left (add_lt_add_of_le_of_lt hm (add_lt_add_of_le_of_lt hm l)) _)
theorem sqLe_smul {c d x y : ℕ} (n : ℕ) (xy : SqLe x c y d) : SqLe (n * x) c (n * y) d := by
simpa [SqLe, mul_left_comm, mul_assoc] using Nat.mul_le_mul_left (n * n) xy
theorem sqLe_mul {d x y z w : ℕ} :
(SqLe x 1 y d → SqLe z 1 w d → SqLe (x * w + y * z) d (x * z + d * y * w) 1) ∧
(SqLe x 1 y d → SqLe w d z 1 → SqLe (x * z + d * y * w) 1 (x * w + y * z) d) ∧
(SqLe y d x 1 → SqLe z 1 w d → SqLe (x * z + d * y * w) 1 (x * w + y * z) d) ∧
(SqLe y d x 1 → SqLe w d z 1 → SqLe (x * w + y * z) d (x * z + d * y * w) 1) := by
refine ⟨?_, ?_, ?_, ?_⟩ <;>
· intro xy zw
have :=
Int.mul_nonneg (sub_nonneg_of_le (Int.ofNat_le_ofNat_of_le xy))
(sub_nonneg_of_le (Int.ofNat_le_ofNat_of_le zw))
refine Int.le_of_ofNat_le_ofNat (le_of_sub_nonneg ?_)
convert this using 1
simp only [one_mul, Int.natCast_add, Int.natCast_mul]
ring
open Int in
/-- "Generalized" `nonneg`. `nonnegg c d x y` means `a √c + b √d ≥ 0`;
we are interested in the case `c = 1` but this is more symmetric -/
def Nonnegg (c d : ℕ) : ℤ → ℤ → Prop
| (a : ℕ), (b : ℕ) => True
| (a : ℕ), -[b+1] => SqLe (b + 1) c a d
| -[a+1], (b : ℕ) => SqLe (a + 1) d b c
| -[_+1], -[_+1] => False
theorem nonnegg_comm {c d : ℕ} {x y : ℤ} : Nonnegg c d x y = Nonnegg d c y x := by
cases x <;> cases y <;> rfl
theorem nonnegg_neg_pos {c d} : ∀ {a b : ℕ}, Nonnegg c d (-a) b ↔ SqLe a d b c
| 0, b => ⟨by simp [SqLe, Nat.zero_le], fun _ => trivial⟩
| a + 1, b => by rfl
theorem nonnegg_pos_neg {c d} {a b : ℕ} : Nonnegg c d a (-b) ↔ SqLe b c a d := by
rw [nonnegg_comm]; exact nonnegg_neg_pos
open Int in
theorem nonnegg_cases_right {c d} {a : ℕ} :
∀ {b : ℤ}, (∀ x : ℕ, b = -x → SqLe x c a d) → Nonnegg c d a b
| (b : Nat), _ => trivial
| -[b+1], h => h (b + 1) rfl
theorem nonnegg_cases_left {c d} {b : ℕ} {a : ℤ} (h : ∀ x : ℕ, a = -x → SqLe x d b c) :
Nonnegg c d a b :=
cast nonnegg_comm (nonnegg_cases_right h)
section Norm
/-- The norm of an element of `ℤ[√d]`. -/
def norm (n : ℤ√d) : ℤ :=
n.re * n.re - d * n.im * n.im
theorem norm_def (n : ℤ√d) : n.norm = n.re * n.re - d * n.im * n.im :=
rfl
@[simp]
theorem norm_zero : norm (0 : ℤ√d) = 0 := by simp [norm]
@[simp]
theorem norm_one : norm (1 : ℤ√d) = 1 := by simp [norm]
@[simp]
theorem norm_intCast (n : ℤ) : norm (n : ℤ√d) = n * n := by simp [norm]
@[simp]
theorem norm_natCast (n : ℕ) : norm (n : ℤ√d) = n * n :=
norm_intCast n
@[simp]
theorem norm_mul (n m : ℤ√d) : norm (n * m) = norm n * norm m := by
simp only [norm, mul_im, mul_re]
ring
/-- `norm` as a `MonoidHom`. -/
def normMonoidHom : ℤ√d →* ℤ where
toFun := norm
map_mul' := norm_mul
map_one' := norm_one
theorem norm_eq_mul_conj (n : ℤ√d) : (norm n : ℤ√d) = n * star n := by
ext <;> simp [norm, star, mul_comm, sub_eq_add_neg]
@[simp]
theorem norm_neg (x : ℤ√d) : (-x).norm = x.norm :=
(Int.cast_inj (α := ℤ√d)).1 <| by simp [norm_eq_mul_conj]
@[simp]
theorem norm_conj (x : ℤ√d) : (star x).norm = x.norm :=
(Int.cast_inj (α := ℤ√d)).1 <| by simp [norm_eq_mul_conj, mul_comm]
theorem norm_nonneg (hd : d ≤ 0) (n : ℤ√d) : 0 ≤ n.norm :=
add_nonneg (mul_self_nonneg _)
(by
rw [mul_assoc, neg_mul_eq_neg_mul]
exact mul_nonneg (neg_nonneg.2 hd) (mul_self_nonneg _))
theorem norm_eq_one_iff {x : ℤ√d} : x.norm.natAbs = 1 ↔ IsUnit x :=
⟨fun h =>
isUnit_iff_dvd_one.2 <|
(le_total 0 (norm x)).casesOn
(fun hx =>
⟨star x, by
rwa [← Int.natCast_inj, Int.natAbs_of_nonneg hx, ← @Int.cast_inj (ℤ√d) _ _,
norm_eq_mul_conj, eq_comm] at h⟩)
fun hx =>
⟨-star x, by
rwa [← Int.natCast_inj, Int.ofNat_natAbs_of_nonpos hx, ← @Int.cast_inj (ℤ√d) _ _,
Int.cast_neg, norm_eq_mul_conj, neg_mul_eq_mul_neg, eq_comm] at h⟩,
fun h => by
let ⟨y, hy⟩ := isUnit_iff_dvd_one.1 h
have := congr_arg (Int.natAbs ∘ norm) hy
rw [Function.comp_apply, Function.comp_apply, norm_mul, Int.natAbs_mul, norm_one,
Int.natAbs_one, eq_comm, mul_eq_one] at this
exact this.1⟩
theorem isUnit_iff_norm_isUnit {d : ℤ} (z : ℤ√d) : IsUnit z ↔ IsUnit z.norm := by
rw [Int.isUnit_iff_natAbs_eq, norm_eq_one_iff]
theorem norm_eq_one_iff' {d : ℤ} (hd : d ≤ 0) (z : ℤ√d) : z.norm = 1 ↔ IsUnit z := by
rw [← norm_eq_one_iff, ← Int.natCast_inj, Int.natAbs_of_nonneg (norm_nonneg hd z), Int.ofNat_one]
theorem norm_eq_zero_iff {d : ℤ} (hd : d < 0) (z : ℤ√d) : z.norm = 0 ↔ z = 0 := by
constructor
· intro h
rw [norm_def, sub_eq_add_neg, mul_assoc] at h
have left := mul_self_nonneg z.re
have right := neg_nonneg.mpr (mul_nonpos_of_nonpos_of_nonneg hd.le (mul_self_nonneg z.im))
obtain ⟨ha, hb⟩ := (add_eq_zero_iff_of_nonneg left right).mp h
ext <;> apply eq_zero_of_mul_self_eq_zero
· exact ha
· rw [neg_eq_zero, mul_eq_zero] at hb
exact hb.resolve_left hd.ne
· rintro rfl
exact norm_zero
theorem norm_eq_of_associated {d : ℤ} (hd : d ≤ 0) {x y : ℤ√d} (h : Associated x y) :
x.norm = y.norm := by
obtain ⟨u, rfl⟩ := h
rw [norm_mul, (norm_eq_one_iff' hd _).mpr u.isUnit, mul_one]
end Norm
end
section
variable {d : ℕ}
/-- Nonnegativity of an element of `ℤ√d`. -/
def Nonneg : ℤ√d → Prop
| ⟨a, b⟩ => Nonnegg d 1 a b
instance : LE (ℤ√d) :=
⟨fun a b => Nonneg (b - a)⟩
instance : LT (ℤ√d) :=
⟨fun a b => ¬b ≤ a⟩
instance decidableNonnegg (c d a b) : Decidable (Nonnegg c d a b) := by
cases a <;> cases b <;> unfold Nonnegg SqLe <;> infer_instance
instance decidableNonneg : ∀ a : ℤ√d, Decidable (Nonneg a)
| ⟨_, _⟩ => Zsqrtd.decidableNonnegg _ _ _ _
instance decidableLE : DecidableLE (ℤ√d) := fun _ _ => decidableNonneg _
open Int in
theorem nonneg_cases : ∀ {a : ℤ√d}, Nonneg a → ∃ x y : ℕ, a = ⟨x, y⟩ ∨ a = ⟨x, -y⟩ ∨ a = ⟨-x, y⟩
| ⟨(x : ℕ), (y : ℕ)⟩, _ => ⟨x, y, Or.inl rfl⟩
| ⟨(x : ℕ), -[y+1]⟩, _ => ⟨x, y + 1, Or.inr <| Or.inl rfl⟩
| ⟨-[x+1], (y : ℕ)⟩, _ => ⟨x + 1, y, Or.inr <| Or.inr rfl⟩
| ⟨-[_+1], -[_+1]⟩, h => False.elim h
open Int in
theorem nonneg_add_lem {x y z w : ℕ} (xy : Nonneg (⟨x, -y⟩ : ℤ√d)) (zw : Nonneg (⟨-z, w⟩ : ℤ√d)) :
Nonneg (⟨x, -y⟩ + ⟨-z, w⟩ : ℤ√d) := by
have : Nonneg ⟨Int.subNatNat x z, Int.subNatNat w y⟩ :=
Int.subNatNat_elim x z
(fun m n i => SqLe y d m 1 → SqLe n 1 w d → Nonneg ⟨i, Int.subNatNat w y⟩)
(fun j k =>
Int.subNatNat_elim w y
(fun m n i => SqLe n d (k + j) 1 → SqLe k 1 m d → Nonneg ⟨Int.ofNat j, i⟩)
(fun _ _ _ _ => trivial) fun m n xy zw => sqLe_cancel zw xy)
(fun j k =>
Int.subNatNat_elim w y
(fun m n i => SqLe n d k 1 → SqLe (k + j + 1) 1 m d → Nonneg ⟨-[j+1], i⟩)
(fun m n xy zw => sqLe_cancel xy zw) fun m n xy zw =>
let t := Nat.le_trans zw (sqLe_of_le (Nat.le_add_right n (m + 1)) le_rfl xy)
have : k + j + 1 ≤ k :=
Nat.mul_self_le_mul_self_iff.1 (by simpa [one_mul] using t)
absurd this (not_le_of_gt <| Nat.succ_le_succ <| Nat.le_add_right _ _))
(nonnegg_pos_neg.1 xy) (nonnegg_neg_pos.1 zw)
rw [add_def, neg_add_eq_sub]
rwa [Int.subNatNat_eq_coe, Int.subNatNat_eq_coe] at this
theorem Nonneg.add {a b : ℤ√d} (ha : Nonneg a) (hb : Nonneg b) : Nonneg (a + b) := by
rcases nonneg_cases ha with ⟨x, y, rfl | rfl | rfl⟩ <;>
rcases nonneg_cases hb with ⟨z, w, rfl | rfl | rfl⟩
· trivial
· refine nonnegg_cases_right fun i h => sqLe_of_le ?_ ?_ (nonnegg_pos_neg.1 hb)
· dsimp only at h
exact Int.ofNat_le.1 (le_of_neg_le_neg (Int.le.intro y (by simp [add_comm, *])))
· apply Nat.le_add_left
· refine nonnegg_cases_left fun i h => sqLe_of_le ?_ ?_ (nonnegg_neg_pos.1 hb)
· dsimp only at h
exact Int.ofNat_le.1 (le_of_neg_le_neg (Int.le.intro x (by simp [add_comm, *])))
· apply Nat.le_add_left
· refine nonnegg_cases_right fun i h => sqLe_of_le ?_ ?_ (nonnegg_pos_neg.1 ha)
· dsimp only at h
exact Int.ofNat_le.1 (le_of_neg_le_neg (Int.le.intro w (by simp [*])))
· apply Nat.le_add_right
· have : Nonneg ⟨_, _⟩ :=
nonnegg_pos_neg.2 (sqLe_add (nonnegg_pos_neg.1 ha) (nonnegg_pos_neg.1 hb))
rw [Nat.cast_add, Nat.cast_add, neg_add] at this
rwa [add_def]
· exact nonneg_add_lem ha hb
· refine nonnegg_cases_left fun i h => sqLe_of_le ?_ ?_ (nonnegg_neg_pos.1 ha)
· dsimp only at h
exact Int.ofNat_le.1 (le_of_neg_le_neg (Int.le.intro _ h))
· apply Nat.le_add_right
· dsimp
rw [add_comm, add_comm (y : ℤ)]
exact nonneg_add_lem hb ha
· have : Nonneg ⟨_, _⟩ :=
nonnegg_neg_pos.2 (sqLe_add (nonnegg_neg_pos.1 ha) (nonnegg_neg_pos.1 hb))
rw [Nat.cast_add, Nat.cast_add, neg_add] at this
rwa [add_def]
theorem nonneg_iff_zero_le {a : ℤ√d} : Nonneg a ↔ 0 ≤ a :=
show _ ↔ Nonneg _ by simp
theorem le_of_le_le {x y z w : ℤ} (xz : x ≤ z) (yw : y ≤ w) : (⟨x, y⟩ : ℤ√d) ≤ ⟨z, w⟩ :=
show Nonneg ⟨z - x, w - y⟩ from
match z - x, w - y, Int.le.dest_sub xz, Int.le.dest_sub yw with
| _, _, ⟨_, rfl⟩, ⟨_, rfl⟩ => trivial
open Int in
protected theorem nonneg_total : ∀ a : ℤ√d, Nonneg a ∨ Nonneg (-a)
| ⟨(x : ℕ), (y : ℕ)⟩ => Or.inl trivial
| ⟨-[_+1], -[_+1]⟩ => Or.inr trivial
| ⟨0, -[_+1]⟩ => Or.inr trivial
| ⟨-[_+1], 0⟩ => Or.inr trivial
| ⟨(_ + 1 : ℕ), -[_+1]⟩ => Nat.le_total _ _
| ⟨-[_+1], (_ + 1 : ℕ)⟩ => Nat.le_total _ _
protected theorem le_total (a b : ℤ√d) : a ≤ b ∨ b ≤ a := by
have t := (b - a).nonneg_total
rwa [neg_sub] at t
instance preorder : Preorder (ℤ√d) where
le := (· ≤ ·)
le_refl a := show Nonneg (a - a) by simp only [sub_self]; trivial
le_trans a b c hab hbc := by simpa [sub_add_sub_cancel'] using hab.add hbc
lt := (· < ·)
lt_iff_le_not_le _ _ := (and_iff_right_of_imp (Zsqrtd.le_total _ _).resolve_left).symm
open Int in
theorem le_arch (a : ℤ√d) : ∃ n : ℕ, a ≤ n := by
obtain ⟨x, y, (h : a ≤ ⟨x, y⟩)⟩ : ∃ x y : ℕ, Nonneg (⟨x, y⟩ + -a) :=
match -a with
| ⟨Int.ofNat x, Int.ofNat y⟩ => ⟨0, 0, by trivial⟩
| ⟨Int.ofNat x, -[y+1]⟩ => ⟨0, y + 1, by simp [add_def, Int.negSucc_eq, add_assoc]; trivial⟩
| ⟨-[x+1], Int.ofNat y⟩ => ⟨x + 1, 0, by simp [Int.negSucc_eq, add_assoc]; trivial⟩
| ⟨-[x+1], -[y+1]⟩ => ⟨x + 1, y + 1, by simp [Int.negSucc_eq, add_assoc]; trivial⟩
refine ⟨x + d * y, h.trans ?_⟩
change Nonneg ⟨↑x + d * y - ↑x, 0 - ↑y⟩
rcases y with - | y
· simp
trivial
have h : ∀ y, SqLe y d (d * y) 1 := fun y => by
simpa [SqLe, mul_comm, mul_left_comm] using Nat.mul_le_mul_right (y * y) (Nat.le_mul_self d)
rw [show (x : ℤ) + d * Nat.succ y - x = d * Nat.succ y by simp]
exact h (y + 1)
protected theorem add_le_add_left (a b : ℤ√d) (ab : a ≤ b) (c : ℤ√d) : c + a ≤ c + b :=
show Nonneg _ by rw [add_sub_add_left_eq_sub]; exact ab
protected theorem le_of_add_le_add_left (a b c : ℤ√d) (h : c + a ≤ c + b) : a ≤ b := by
simpa using Zsqrtd.add_le_add_left _ _ h (-c)
protected theorem add_lt_add_left (a b : ℤ√d) (h : a < b) (c) : c + a < c + b := fun h' =>
h (Zsqrtd.le_of_add_le_add_left _ _ _ h')
theorem nonneg_smul {a : ℤ√d} {n : ℕ} (ha : Nonneg a) : Nonneg ((n : ℤ√d) * a) := by
rw [← Int.cast_natCast n]
exact
match a, nonneg_cases ha, ha with
| _, ⟨x, y, Or.inl rfl⟩, _ => by rw [smul_val]; trivial
| _, ⟨x, y, Or.inr <| Or.inl rfl⟩, ha => by
rw [smul_val]; simpa using nonnegg_pos_neg.2 (sqLe_smul n <| nonnegg_pos_neg.1 ha)
| _, ⟨x, y, Or.inr <| Or.inr rfl⟩, ha => by
rw [smul_val]; simpa using nonnegg_neg_pos.2 (sqLe_smul n <| nonnegg_neg_pos.1 ha)
theorem nonneg_muld {a : ℤ√d} (ha : Nonneg a) : Nonneg (sqrtd * a) :=
match a, nonneg_cases ha, ha with
| _, ⟨_, _, Or.inl rfl⟩, _ => trivial
| _, ⟨x, y, Or.inr <| Or.inl rfl⟩, ha => by
simp only [muld_val, mul_neg]
apply nonnegg_neg_pos.2
simpa [SqLe, mul_comm, mul_left_comm] using Nat.mul_le_mul_left d (nonnegg_pos_neg.1 ha)
| _, ⟨x, y, Or.inr <| Or.inr rfl⟩, ha => by
simp only [muld_val]
apply nonnegg_pos_neg.2
simpa [SqLe, mul_comm, mul_left_comm] using Nat.mul_le_mul_left d (nonnegg_neg_pos.1 ha)
theorem nonneg_mul_lem {x y : ℕ} {a : ℤ√d} (ha : Nonneg a) : Nonneg (⟨x, y⟩ * a) := by
have : (⟨x, y⟩ * a : ℤ√d) = (x : ℤ√d) * a + sqrtd * ((y : ℤ√d) * a) := by
rw [decompose, right_distrib, mul_assoc, Int.cast_natCast, Int.cast_natCast]
rw [this]
exact (nonneg_smul ha).add (nonneg_muld <| nonneg_smul ha)
theorem nonneg_mul {a b : ℤ√d} (ha : Nonneg a) (hb : Nonneg b) : Nonneg (a * b) :=
match a, b, nonneg_cases ha, nonneg_cases hb, ha, hb with
| _, _, ⟨_, _, Or.inl rfl⟩, ⟨_, _, Or.inl rfl⟩, _, _ => trivial
| _, _, ⟨x, y, Or.inl rfl⟩, ⟨z, w, Or.inr <| Or.inr rfl⟩, _, hb => nonneg_mul_lem hb
| _, _, ⟨x, y, Or.inl rfl⟩, ⟨z, w, Or.inr <| Or.inl rfl⟩, _, hb => nonneg_mul_lem hb
| _, _, ⟨x, y, Or.inr <| Or.inr rfl⟩, ⟨z, w, Or.inl rfl⟩, ha, _ => by
rw [mul_comm]; exact nonneg_mul_lem ha
| _, _, ⟨x, y, Or.inr <| Or.inl rfl⟩, ⟨z, w, Or.inl rfl⟩, ha, _ => by
rw [mul_comm]; exact nonneg_mul_lem ha
| _, _, ⟨x, y, Or.inr <| Or.inr rfl⟩, ⟨z, w, Or.inr <| Or.inr rfl⟩, ha, hb => by
rw [calc
(⟨-x, y⟩ * ⟨-z, w⟩ : ℤ√d) = ⟨_, _⟩ := rfl
_ = ⟨x * z + d * y * w, -(x * w + y * z)⟩ := by simp [add_comm]
]
exact nonnegg_pos_neg.2 (sqLe_mul.left (nonnegg_neg_pos.1 ha) (nonnegg_neg_pos.1 hb))
| _, _, ⟨x, y, Or.inr <| Or.inr rfl⟩, ⟨z, w, Or.inr <| Or.inl rfl⟩, ha, hb => by
rw [calc
(⟨-x, y⟩ * ⟨z, -w⟩ : ℤ√d) = ⟨_, _⟩ := rfl
_ = ⟨-(x * z + d * y * w), x * w + y * z⟩ := by simp [add_comm]
]
exact nonnegg_neg_pos.2 (sqLe_mul.right.left (nonnegg_neg_pos.1 ha) (nonnegg_pos_neg.1 hb))
| _, _, ⟨x, y, Or.inr <| Or.inl rfl⟩, ⟨z, w, Or.inr <| Or.inr rfl⟩, ha, hb => by
rw [calc
(⟨x, -y⟩ * ⟨-z, w⟩ : ℤ√d) = ⟨_, _⟩ := rfl
_ = ⟨-(x * z + d * y * w), x * w + y * z⟩ := by simp [add_comm]
]
exact
nonnegg_neg_pos.2 (sqLe_mul.right.right.left (nonnegg_pos_neg.1 ha) (nonnegg_neg_pos.1 hb))
| _, _, ⟨x, y, Or.inr <| Or.inl rfl⟩, ⟨z, w, Or.inr <| Or.inl rfl⟩, ha, hb => by
rw [calc
(⟨x, -y⟩ * ⟨z, -w⟩ : ℤ√d) = ⟨_, _⟩ := rfl
_ = ⟨x * z + d * y * w, -(x * w + y * z)⟩ := by simp [add_comm]
]
exact
nonnegg_pos_neg.2
(sqLe_mul.right.right.right (nonnegg_pos_neg.1 ha) (nonnegg_pos_neg.1 hb))
protected theorem mul_nonneg (a b : ℤ√d) : 0 ≤ a → 0 ≤ b → 0 ≤ a * b := by
simp_rw [← nonneg_iff_zero_le]
exact nonneg_mul
theorem not_sqLe_succ (c d y) (h : 0 < c) : ¬SqLe (y + 1) c 0 d :=
not_le_of_gt <| mul_pos (mul_pos h <| Nat.succ_pos _) <| Nat.succ_pos _
-- Porting note: renamed field and added theorem to make `x` explicit
/-- A nonsquare is a natural number that is not equal to the square of an
integer. This is implemented as a typeclass because it's a necessary condition
for much of the Pell equation theory. -/
class Nonsquare (x : ℕ) : Prop where
ns' : ∀ n : ℕ, x ≠ n * n
theorem Nonsquare.ns (x : ℕ) [Nonsquare x] : ∀ n : ℕ, x ≠ n * n := ns'
variable [dnsq : Nonsquare d]
theorem d_pos : 0 < d :=
lt_of_le_of_ne (Nat.zero_le _) <| Ne.symm <| Nonsquare.ns d 0
theorem divides_sq_eq_zero {x y} (h : x * x = d * y * y) : x = 0 ∧ y = 0 :=
let g := x.gcd y
Or.elim g.eq_zero_or_pos
(fun H => ⟨Nat.eq_zero_of_gcd_eq_zero_left H, Nat.eq_zero_of_gcd_eq_zero_right H⟩) fun gpos =>
False.elim <| by
let ⟨m, n, co, (hx : x = m * g), (hy : y = n * g)⟩ := Nat.exists_coprime _ _
rw [hx, hy] at h
have : m * m = d * (n * n) := by
refine mul_left_cancel₀ (mul_pos gpos gpos).ne' ?_
-- Porting note: was `simpa [mul_comm, mul_left_comm] using h`
calc
g * g * (m * m)
_ = m * g * (m * g) := by ring
_ = d * (n * g) * (n * g) := h
_ = g * g * (d * (n * n)) := by ring
have co2 :=
let co1 := co.mul_right co
co1.mul co1
exact
Nonsquare.ns d m
(Nat.dvd_antisymm (by rw [this]; apply dvd_mul_right) <|
co2.dvd_of_dvd_mul_right <| by simp [this])
theorem divides_sq_eq_zero_z {x y : ℤ} (h : x * x = d * y * y) : x = 0 ∧ y = 0 := by
rw [mul_assoc, ← Int.natAbs_mul_self, ← Int.natAbs_mul_self, ← Int.natCast_mul, ← mul_assoc] at h
exact
let ⟨h1, h2⟩ := divides_sq_eq_zero (Int.ofNat.inj h)
⟨Int.natAbs_eq_zero.mp h1, Int.natAbs_eq_zero.mp h2⟩
theorem not_divides_sq (x y) : (x + 1) * (x + 1) ≠ d * (y + 1) * (y + 1) := fun e => by
have t := (divides_sq_eq_zero e).left
contradiction
open Int in
theorem nonneg_antisymm : ∀ {a : ℤ√d}, Nonneg a → Nonneg (-a) → a = 0
| ⟨0, 0⟩, _, _ => rfl
| ⟨-[_+1], -[_+1]⟩, xy, _ => False.elim xy
| ⟨(_ + 1 : Nat), (_ + 1 : Nat)⟩, _, yx => False.elim yx
| ⟨-[_+1], 0⟩, xy, _ => absurd xy (not_sqLe_succ _ _ _ (by decide))
| ⟨(_ + 1 : Nat), 0⟩, _, yx => absurd yx (not_sqLe_succ _ _ _ (by decide))
| ⟨0, -[_+1]⟩, xy, _ => absurd xy (not_sqLe_succ _ _ _ d_pos)
| ⟨0, (_ + 1 : Nat)⟩, _, yx => absurd yx (not_sqLe_succ _ _ _ d_pos)
| ⟨(x + 1 : Nat), -[y+1]⟩, (xy : SqLe _ _ _ _), (yx : SqLe _ _ _ _) => by
let t := le_antisymm yx xy
rw [one_mul] at t
exact absurd t (not_divides_sq _ _)
| ⟨-[x+1], (y + 1 : Nat)⟩, (xy : SqLe _ _ _ _), (yx : SqLe _ _ _ _) => by
let t := le_antisymm xy yx
rw [one_mul] at t
exact absurd t (not_divides_sq _ _)
theorem le_antisymm {a b : ℤ√d} (ab : a ≤ b) (ba : b ≤ a) : a = b :=
eq_of_sub_eq_zero <| nonneg_antisymm ba (by rwa [neg_sub])
instance linearOrder : LinearOrder (ℤ√d) :=
{ Zsqrtd.preorder with
le_antisymm := fun _ _ => Zsqrtd.le_antisymm
le_total := Zsqrtd.le_total
toDecidableLE := Zsqrtd.decidableLE
toDecidableEq := inferInstance }
protected theorem eq_zero_or_eq_zero_of_mul_eq_zero : ∀ {a b : ℤ√d}, a * b = 0 → a = 0 ∨ b = 0
| ⟨x, y⟩, ⟨z, w⟩, h => by
injection h with h1 h2
have h1 : x * z = -(d * y * w) := eq_neg_of_add_eq_zero_left h1
have h2 : x * w = -(y * z) := eq_neg_of_add_eq_zero_left h2
have fin : x * x = d * y * y → (⟨x, y⟩ : ℤ√d) = 0 := fun e =>
match x, y, divides_sq_eq_zero_z e with
| _, _, ⟨rfl, rfl⟩ => rfl
exact
if z0 : z = 0 then
if w0 : w = 0 then
Or.inr
(match z, w, z0, w0 with
| _, _, rfl, rfl => rfl)
else
Or.inl <|
fin <|
mul_right_cancel₀ w0 <|
calc
x * x * w = -y * (x * z) := by simp [h2, mul_assoc, mul_left_comm]
_ = d * y * y * w := by simp [h1, mul_assoc, mul_left_comm]
else
Or.inl <|
fin <|
mul_right_cancel₀ z0 <|
calc
x * x * z = d * -y * (x * w) := by simp [h1, mul_assoc, mul_left_comm]
_ = d * y * y * z := by simp [h2, mul_assoc, mul_left_comm]
instance : NoZeroDivisors (ℤ√d) where
eq_zero_or_eq_zero_of_mul_eq_zero := Zsqrtd.eq_zero_or_eq_zero_of_mul_eq_zero
instance : IsDomain (ℤ√d) :=
NoZeroDivisors.to_isDomain _
protected theorem mul_pos (a b : ℤ√d) (a0 : 0 < a) (b0 : 0 < b) : 0 < a * b := fun ab =>
Or.elim
(eq_zero_or_eq_zero_of_mul_eq_zero
(le_antisymm ab (Zsqrtd.mul_nonneg _ _ (le_of_lt a0) (le_of_lt b0))))
(fun e => ne_of_gt a0 e) fun e => ne_of_gt b0 e
instance : ZeroLEOneClass (ℤ√d) :=
{ zero_le_one := by trivial }
instance : IsOrderedAddMonoid (ℤ√d) :=
{ add_le_add_left := Zsqrtd.add_le_add_left }
instance : IsStrictOrderedRing (ℤ√d) :=
.of_mul_pos Zsqrtd.mul_pos
end
theorem norm_eq_zero {d : ℤ} (h_nonsquare : ∀ n : ℤ, d ≠ n * n) (a : ℤ√d) : norm a = 0 ↔ a = 0 := by
refine ⟨fun ha => Zsqrtd.ext_iff.mpr ?_, fun h => by rw [h, norm_zero]⟩
dsimp only [norm] at ha
rw [sub_eq_zero] at ha
by_cases h : 0 ≤ d
· obtain ⟨d', rfl⟩ := Int.eq_ofNat_of_zero_le h
haveI : Nonsquare d' := ⟨fun n h => h_nonsquare n <| mod_cast h⟩
exact divides_sq_eq_zero_z ha
· push_neg at h
suffices a.re * a.re = 0 by
rw [eq_zero_of_mul_self_eq_zero this] at ha ⊢
simpa only [true_and, or_self_right, zero_re, zero_im, eq_self_iff_true, zero_eq_mul,
mul_zero, mul_eq_zero, h.ne, false_or, or_self_iff] using ha
apply _root_.le_antisymm _ (mul_self_nonneg _)
rw [ha, mul_assoc]
exact mul_nonpos_of_nonpos_of_nonneg h.le (mul_self_nonneg _)
|
variable {R : Type}
@[ext]
theorem hom_ext [NonAssocRing R] {d : ℤ} (f g : ℤ√d →+* R) (h : f sqrtd = g sqrtd) : f = g := by
ext ⟨x_re, x_im⟩
simp [decompose, h]
variable [CommRing R]
/-- The unique `RingHom` from `ℤ√d` to a ring `R`, constructed by replacing `√d` with the provided
root. Conversely, this associates to every mapping `ℤ√d →+* R` a value of `√d` in `R`. -/
@[simps]
def lift {d : ℤ} : { r : R // r * r = ↑d } ≃ (ℤ√d →+* R) where
toFun r :=
{ toFun := fun a => a.1 + a.2 * (r : R)
map_zero' := by simp
map_add' := fun a b => by
simp only [add_re, Int.cast_add, add_im]
ring
map_one' := by simp
map_mul' := fun a b => by
| Mathlib/NumberTheory/Zsqrtd/Basic.lean | 876 | 897 |
/-
Copyright (c) 2015 Leonardo de Moura. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Leonardo de Moura, Mario Carneiro
-/
import Mathlib.Data.List.Basic
import Mathlib.Data.Prod.Basic
/-!
# Lists in product and sigma types
This file proves basic properties of `List.product` and `List.sigma`, which are list constructions
living in `Prod` and `Sigma` types respectively. Their definitions can be found in
[`Data.List.Defs`](./defs). Beware, this is not about `List.prod`, the multiplicative product.
-/
variable {α β : Type*}
namespace List
/-! ### product -/
@[simp]
theorem nil_product (l : List β) : (@nil α) ×ˢ l = [] :=
rfl
@[simp]
theorem product_cons (a : α) (l₁ : List α) (l₂ : List β) :
(a :: l₁) ×ˢ l₂ = map (fun b => (a, b)) l₂ ++ (l₁ ×ˢ l₂) :=
rfl
@[simp]
theorem product_nil : ∀ l : List α, l ×ˢ (@nil β) = []
| [] => rfl
| _ :: l => by simp [product_cons, product_nil l]
@[simp]
theorem mem_product {l₁ : List α} {l₂ : List β} {a : α} {b : β} :
(a, b) ∈ l₁ ×ˢ l₂ ↔ a ∈ l₁ ∧ b ∈ l₂ := by
simp_all [SProd.sprod, product, mem_flatMap, mem_map, Prod.ext_iff, exists_prop, and_left_comm,
exists_and_left, exists_eq_left, exists_eq_right]
theorem length_product (l₁ : List α) (l₂ : List β) :
length (l₁ ×ˢ l₂) = length l₁ * length l₂ := by
induction' l₁ with x l₁ IH
· exact (Nat.zero_mul _).symm
· simp only [length, product_cons, length_append, IH, Nat.add_mul, Nat.one_mul, length_map,
Nat.add_comm]
|
/-! ### sigma -/
variable {σ : α → Type*}
| Mathlib/Data/List/ProdSigma.lean | 51 | 56 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Sébastien Gouëzel, Yury Kudryashov
-/
import Mathlib.MeasureTheory.Integral.Bochner.Set
import Mathlib.MeasureTheory.Measure.Lebesgue.Basic
import Mathlib.MeasureTheory.Measure.Haar.Unique
/-! # Properties of integration with respect to the Lebesgue measure -/
open Set Filter MeasureTheory MeasureTheory.Measure TopologicalSpace
section regionBetween
variable {α : Type*}
variable [MeasurableSpace α] {μ : Measure α} {f g : α → ℝ} {s : Set α}
theorem volume_regionBetween_eq_integral' [SigmaFinite μ] (f_int : IntegrableOn f s μ)
(g_int : IntegrableOn g s μ) (hs : MeasurableSet s) (hfg : f ≤ᵐ[μ.restrict s] g) :
μ.prod volume (regionBetween f g s) = ENNReal.ofReal (∫ y in s, (g - f) y ∂μ) := by
have h : g - f =ᵐ[μ.restrict s] fun x => Real.toNNReal (g x - f x) :=
hfg.mono fun x hx => (Real.coe_toNNReal _ <| sub_nonneg.2 hx).symm
rw [volume_regionBetween_eq_lintegral f_int.aemeasurable g_int.aemeasurable hs,
integral_congr_ae h, lintegral_congr_ae,
lintegral_coe_eq_integral _ ((integrable_congr h).mp (g_int.sub f_int))]
dsimp only
rfl
/-- If two functions are integrable on a measurable set, and one function is less than
or equal to the other on that set, then the volume of the region
between the two functions can be represented as an integral. -/
theorem volume_regionBetween_eq_integral [SigmaFinite μ] (f_int : IntegrableOn f s μ)
(g_int : IntegrableOn g s μ) (hs : MeasurableSet s) (hfg : ∀ x ∈ s, f x ≤ g x) :
μ.prod volume (regionBetween f g s) = ENNReal.ofReal (∫ y in s, (g - f) y ∂μ) :=
volume_regionBetween_eq_integral' f_int g_int hs
((ae_restrict_iff' hs).mpr (Eventually.of_forall hfg))
end regionBetween
section SummableNormIcc
open ContinuousMap
/- The following lemma is a minor variation on `integrable_of_summable_norm_restrict` in
`Mathlib/MeasureTheory/Integral/SetIntegral.lean`, but it is placed here because it needs to know
that `Icc a b` has volume `b - a`. -/
/-- If the sequence with `n`-th term the sup norm of `fun x ↦ f (x + n)` on the interval `Icc 0 1`,
for `n ∈ ℤ`, is summable, then `f` is integrable on `ℝ`. -/
theorem Real.integrable_of_summable_norm_Icc {E : Type*} [NormedAddCommGroup E] {f : C(ℝ, E)}
(hf : Summable fun n : ℤ => ‖(f.comp <| ContinuousMap.addRight n).restrict (Icc 0 1)‖) :
Integrable f := by
refine integrable_of_summable_norm_restrict (.of_nonneg_of_le
(fun n : ℤ => mul_nonneg (norm_nonneg
(f.restrict (⟨Icc (n : ℝ) ((n : ℝ) + 1), isCompact_Icc⟩ : Compacts ℝ)))
ENNReal.toReal_nonneg) (fun n => ?_) hf) ?_
· simp only [Compacts.coe_mk, le_add_iff_nonneg_right, zero_le_one, volume_real_Icc_of_le,
add_sub_cancel_left, mul_one, norm_le _ (norm_nonneg _), ContinuousMap.restrict_apply,
mem_Icc, and_imp]
intro x
have := ((f.comp <| ContinuousMap.addRight n).restrict (Icc 0 1)).norm_coe_le_norm
⟨x - n, ⟨sub_nonneg.mpr x.2.1, sub_le_iff_le_add'.mpr x.2.2⟩⟩
simpa only [ContinuousMap.restrict_apply, comp_apply, coe_addRight, Subtype.coe_mk,
sub_add_cancel] using this
· exact iUnion_Icc_intCast ℝ
end SummableNormIcc
/-!
### Substituting `-x` for `x`
These lemmas are stated in terms of either `Iic` or `Ioi` (neglecting `Iio` and `Ici`) to match
mathlib's conventions for integrals over finite intervals (see `intervalIntegral`). For the case
of finite integrals, see `intervalIntegral.integral_comp_neg`.
-/
/- @[simp] Porting note: Linter complains it does not apply to itself. Although it does apply to
itself, it does not apply when `f` is more complicated -/
theorem integral_comp_neg_Iic {E : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
(c : ℝ) (f : ℝ → E) : (∫ x in Iic c, f (-x)) = ∫ x in Ioi (-c), f x := by
have A : MeasurableEmbedding fun x : ℝ => -x :=
(Homeomorph.neg ℝ).isClosedEmbedding.measurableEmbedding
have := MeasurableEmbedding.setIntegral_map (μ := volume) A f (Ici (-c))
rw [Measure.map_neg_eq_self (volume : Measure ℝ)] at this
simp_rw [← integral_Ici_eq_integral_Ioi, this, neg_preimage, neg_Ici, neg_neg]
/- @[simp] Porting note: Linter complains it does not apply to itself. Although it does apply to
itself, it does not apply when `f` is more complicated -/
theorem integral_comp_neg_Ioi {E : Type*} [NormedAddCommGroup E] [NormedSpace ℝ E]
(c : ℝ) (f : ℝ → E) : (∫ x in Ioi c, f (-x)) = ∫ x in Iic (-c), f x := by
rw [← neg_neg c, ← integral_comp_neg_Iic]
simp only [neg_neg]
theorem integral_comp_abs {f : ℝ → ℝ} :
∫ x, f |x| = 2 * ∫ x in Ioi (0 : ℝ), f x := by
have eq : ∫ (x : ℝ) in Ioi 0, f |x| = ∫ (x : ℝ) in Ioi 0, f x := by
refine setIntegral_congr_fun measurableSet_Ioi (fun _ hx => ?_)
rw [abs_eq_self.mpr (le_of_lt (by exact hx))]
by_cases hf : IntegrableOn (fun x => f |x|) (Ioi 0)
| · have int_Iic : IntegrableOn (fun x ↦ f |x|) (Iic 0) := by
rw [← Measure.map_neg_eq_self (volume : Measure ℝ)]
let m : MeasurableEmbedding fun x : ℝ => -x := (Homeomorph.neg ℝ).measurableEmbedding
rw [m.integrableOn_map_iff]
simp_rw [Function.comp_def, abs_neg, neg_preimage, neg_Iic, neg_zero]
exact integrableOn_Ici_iff_integrableOn_Ioi.mpr hf
calc
_ = (∫ x in Iic 0, f |x|) + ∫ x in Ioi 0, f |x| := by
rw [← setIntegral_union (Iic_disjoint_Ioi le_rfl) measurableSet_Ioi int_Iic hf,
Iic_union_Ioi, restrict_univ]
_ = 2 * ∫ x in Ioi 0, f x := by
rw [two_mul, eq]
congr! 1
rw [← neg_zero, ← integral_comp_neg_Iic, neg_zero]
refine setIntegral_congr_fun measurableSet_Iic (fun _ hx => ?_)
rw [abs_eq_neg_self.mpr (by exact hx)]
· have : ¬ Integrable (fun x => f |x|) := by
contrapose! hf
exact hf.integrableOn
rw [← eq, integral_undef hf, integral_undef this, mul_zero]
| Mathlib/MeasureTheory/Measure/Lebesgue/Integral.lean | 102 | 127 |
/-
Copyright (c) 2022 Xavier Roblot. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Alex J. Best, Xavier Roblot
-/
import Mathlib.Algebra.Algebra.Hom.Rat
import Mathlib.Analysis.Complex.Polynomial.Basic
import Mathlib.NumberTheory.NumberField.Norm
import Mathlib.RingTheory.RootsOfUnity.PrimitiveRoots
import Mathlib.Topology.Instances.Complex
/-!
# Embeddings of number fields
This file defines the embeddings of a number field into an algebraic closed field.
## Main Definitions and Results
* `NumberField.Embeddings.range_eval_eq_rootSet_minpoly`: let `x ∈ K` with `K` number field and
let `A` be an algebraic closed field of char. 0, then the images of `x` by the embeddings of `K`
in `A` are exactly the roots in `A` of the minimal polynomial of `x` over `ℚ`.
* `NumberField.Embeddings.pow_eq_one_of_norm_eq_one`: an algebraic integer whose conjugates are
all of norm one is a root of unity.
* `NumberField.InfinitePlace`: the type of infinite places of a number field `K`.
* `NumberField.InfinitePlace.mk_eq_iff`: two complex embeddings define the same infinite place iff
they are equal or complex conjugates.
* `NumberField.InfinitePlace.prod_eq_abs_norm`: the infinite part of the product formula, that is
for `x ∈ K`, we have `Π_w ‖x‖_w = |norm(x)|` where the product is over the infinite place `w` and
`‖·‖_w` is the normalized absolute value for `w`.
## Tags
number field, embeddings, places, infinite places
-/
open scoped Finset
namespace NumberField.Embeddings
section Fintype
open Module
variable (K : Type*) [Field K] [NumberField K]
variable (A : Type*) [Field A] [CharZero A]
/-- There are finitely many embeddings of a number field. -/
noncomputable instance : Fintype (K →+* A) :=
Fintype.ofEquiv (K →ₐ[ℚ] A) RingHom.equivRatAlgHom.symm
variable [IsAlgClosed A]
/-- The number of embeddings of a number field is equal to its finrank. -/
theorem card : Fintype.card (K →+* A) = finrank ℚ K := by
rw [Fintype.ofEquiv_card RingHom.equivRatAlgHom.symm, AlgHom.card]
instance : Nonempty (K →+* A) := by
rw [← Fintype.card_pos_iff, NumberField.Embeddings.card K A]
exact Module.finrank_pos
end Fintype
section Roots
open Set Polynomial
variable (K A : Type*) [Field K] [NumberField K] [Field A] [Algebra ℚ A] [IsAlgClosed A] (x : K)
/-- Let `A` be an algebraically closed field and let `x ∈ K`, with `K` a number field.
The images of `x` by the embeddings of `K` in `A` are exactly the roots in `A` of
the minimal polynomial of `x` over `ℚ`. -/
theorem range_eval_eq_rootSet_minpoly :
(range fun φ : K →+* A => φ x) = (minpoly ℚ x).rootSet A := by
convert (NumberField.isAlgebraic K).range_eval_eq_rootSet_minpoly A x using 1
ext a
exact ⟨fun ⟨φ, hφ⟩ => ⟨φ.toRatAlgHom, hφ⟩, fun ⟨φ, hφ⟩ => ⟨φ.toRingHom, hφ⟩⟩
end Roots
section Bounded
open Module Polynomial Set
variable {K : Type*} [Field K] [NumberField K]
variable {A : Type*} [NormedField A] [IsAlgClosed A] [NormedAlgebra ℚ A]
theorem coeff_bdd_of_norm_le {B : ℝ} {x : K} (h : ∀ φ : K →+* A, ‖φ x‖ ≤ B) (i : ℕ) :
‖(minpoly ℚ x).coeff i‖ ≤ max B 1 ^ finrank ℚ K * (finrank ℚ K).choose (finrank ℚ K / 2) := by
have hx := Algebra.IsSeparable.isIntegral ℚ x
rw [← norm_algebraMap' A, ← coeff_map (algebraMap ℚ A)]
refine coeff_bdd_of_roots_le _ (minpoly.monic hx)
(IsAlgClosed.splits_codomain _) (minpoly.natDegree_le x) (fun z hz => ?_) i
classical
rw [← Multiset.mem_toFinset] at hz
obtain ⟨φ, rfl⟩ := (range_eval_eq_rootSet_minpoly K A x).symm.subset hz
exact h φ
variable (K A)
/-- Let `B` be a real number. The set of algebraic integers in `K` whose conjugates are all
smaller in norm than `B` is finite. -/
theorem finite_of_norm_le (B : ℝ) : {x : K | IsIntegral ℤ x ∧ ∀ φ : K →+* A, ‖φ x‖ ≤ B}.Finite := by
classical
let C := Nat.ceil (max B 1 ^ finrank ℚ K * (finrank ℚ K).choose (finrank ℚ K / 2))
have := bUnion_roots_finite (algebraMap ℤ K) (finrank ℚ K) (finite_Icc (-C : ℤ) C)
refine this.subset fun x hx => ?_; simp_rw [mem_iUnion]
have h_map_ℚ_minpoly := minpoly.isIntegrallyClosed_eq_field_fractions' ℚ hx.1
refine ⟨_, ⟨?_, fun i => ?_⟩, mem_rootSet.2 ⟨minpoly.ne_zero hx.1, minpoly.aeval ℤ x⟩⟩
· rw [← (minpoly.monic hx.1).natDegree_map (algebraMap ℤ ℚ), ← h_map_ℚ_minpoly]
exact minpoly.natDegree_le x
rw [mem_Icc, ← abs_le, ← @Int.cast_le ℝ]
refine (Eq.trans_le ?_ <| coeff_bdd_of_norm_le hx.2 i).trans (Nat.le_ceil _)
rw [h_map_ℚ_minpoly, coeff_map, eq_intCast, Int.norm_cast_rat, Int.norm_eq_abs, Int.cast_abs]
/-- An algebraic integer whose conjugates are all of norm one is a root of unity. -/
theorem pow_eq_one_of_norm_eq_one {x : K} (hxi : IsIntegral ℤ x) (hx : ∀ φ : K →+* A, ‖φ x‖ = 1) :
∃ (n : ℕ) (_ : 0 < n), x ^ n = 1 := by
obtain ⟨a, -, b, -, habne, h⟩ :=
@Set.Infinite.exists_ne_map_eq_of_mapsTo _ _ _ _ (x ^ · : ℕ → K) Set.infinite_univ
(by exact fun a _ => ⟨hxi.pow a, fun φ => by simp [hx φ]⟩) (finite_of_norm_le K A (1 : ℝ))
wlog hlt : b < a
· exact this K A hxi hx b a habne.symm h.symm (habne.lt_or_lt.resolve_right hlt)
refine ⟨a - b, tsub_pos_of_lt hlt, ?_⟩
rw [← Nat.sub_add_cancel hlt.le, pow_add, mul_left_eq_self₀] at h
refine h.resolve_right fun hp => ?_
specialize hx (IsAlgClosed.lift (R := ℚ)).toRingHom
rw [pow_eq_zero hp, map_zero, norm_zero] at hx; norm_num at hx
end Bounded
end NumberField.Embeddings
section Place
variable {K : Type*} [Field K] {A : Type*} [NormedDivisionRing A] [Nontrivial A] (φ : K →+* A)
/-- An embedding into a normed division ring defines a place of `K` -/
def NumberField.place : AbsoluteValue K ℝ :=
(IsAbsoluteValue.toAbsoluteValue (norm : A → ℝ)).comp φ.injective
@[simp]
theorem NumberField.place_apply (x : K) : (NumberField.place φ) x = norm (φ x) := rfl
end Place
namespace NumberField.ComplexEmbedding
open Complex NumberField
open scoped ComplexConjugate
variable {K : Type*} [Field K] {k : Type*} [Field k]
variable (K) in
/--
A (random) lift of the complex embedding `φ : k →+* ℂ` to an extension `K` of `k`.
-/
noncomputable def lift [Algebra k K] [Algebra.IsAlgebraic k K] (φ : k →+* ℂ) : K →+* ℂ := by
letI := φ.toAlgebra
exact (IsAlgClosed.lift (R := k)).toRingHom
@[simp]
theorem lift_comp_algebraMap [Algebra k K] [Algebra.IsAlgebraic k K] (φ : k →+* ℂ) :
(lift K φ).comp (algebraMap k K) = φ := by
unfold lift
letI := φ.toAlgebra
rw [AlgHom.toRingHom_eq_coe, AlgHom.comp_algebraMap_of_tower, RingHom.algebraMap_toAlgebra']
@[simp]
theorem lift_algebraMap_apply [Algebra k K] [Algebra.IsAlgebraic k K] (φ : k →+* ℂ) (x : k) :
lift K φ (algebraMap k K x) = φ x :=
RingHom.congr_fun (lift_comp_algebraMap φ) x
/-- The conjugate of a complex embedding as a complex embedding. -/
abbrev conjugate (φ : K →+* ℂ) : K →+* ℂ := star φ
@[simp]
theorem conjugate_coe_eq (φ : K →+* ℂ) (x : K) : (conjugate φ) x = conj (φ x) := rfl
theorem place_conjugate (φ : K →+* ℂ) : place (conjugate φ) = place φ := by
ext; simp only [place_apply, norm_conj, conjugate_coe_eq]
/-- An embedding into `ℂ` is real if it is fixed by complex conjugation. -/
abbrev IsReal (φ : K →+* ℂ) : Prop := IsSelfAdjoint φ
theorem isReal_iff {φ : K →+* ℂ} : IsReal φ ↔ conjugate φ = φ := isSelfAdjoint_iff
theorem isReal_conjugate_iff {φ : K →+* ℂ} : IsReal (conjugate φ) ↔ IsReal φ :=
IsSelfAdjoint.star_iff
/-- A real embedding as a ring homomorphism from `K` to `ℝ` . -/
def IsReal.embedding {φ : K →+* ℂ} (hφ : IsReal φ) : K →+* ℝ where
toFun x := (φ x).re
map_one' := by simp only [map_one, one_re]
map_mul' := by
simp only [Complex.conj_eq_iff_im.mp (RingHom.congr_fun hφ _), map_mul, mul_re,
mul_zero, tsub_zero, eq_self_iff_true, forall_const]
map_zero' := by simp only [map_zero, zero_re]
map_add' := by simp only [map_add, add_re, eq_self_iff_true, forall_const]
@[simp]
theorem IsReal.coe_embedding_apply {φ : K →+* ℂ} (hφ : IsReal φ) (x : K) :
(hφ.embedding x : ℂ) = φ x := by
apply Complex.ext
· rfl
· rw [ofReal_im, eq_comm, ← Complex.conj_eq_iff_im]
exact RingHom.congr_fun hφ x
lemma IsReal.comp (f : k →+* K) {φ : K →+* ℂ} (hφ : IsReal φ) :
IsReal (φ.comp f) := by ext1 x; simpa using RingHom.congr_fun hφ (f x)
lemma isReal_comp_iff {f : k ≃+* K} {φ : K →+* ℂ} :
IsReal (φ.comp (f : k →+* K)) ↔ IsReal φ :=
⟨fun H ↦ by convert H.comp f.symm.toRingHom; ext1; simp, IsReal.comp _⟩
lemma exists_comp_symm_eq_of_comp_eq [Algebra k K] [IsGalois k K] (φ ψ : K →+* ℂ)
(h : φ.comp (algebraMap k K) = ψ.comp (algebraMap k K)) :
∃ σ : K ≃ₐ[k] K, φ.comp σ.symm = ψ := by
letI := (φ.comp (algebraMap k K)).toAlgebra
letI := φ.toAlgebra
have : IsScalarTower k K ℂ := IsScalarTower.of_algebraMap_eq' rfl
let ψ' : K →ₐ[k] ℂ := { ψ with commutes' := fun r ↦ (RingHom.congr_fun h r).symm }
use (AlgHom.restrictNormal' ψ' K).symm
ext1 x
exact AlgHom.restrictNormal_commutes ψ' K x
variable [Algebra k K] (φ : K →+* ℂ) (σ : K ≃ₐ[k] K)
/--
`IsConj φ σ` states that `σ : K ≃ₐ[k] K` is the conjugation under the embedding `φ : K →+* ℂ`.
-/
def IsConj : Prop := conjugate φ = φ.comp σ
variable {φ σ}
lemma IsConj.eq (h : IsConj φ σ) (x) : φ (σ x) = star (φ x) := RingHom.congr_fun h.symm x
lemma IsConj.ext {σ₁ σ₂ : K ≃ₐ[k] K} (h₁ : IsConj φ σ₁) (h₂ : IsConj φ σ₂) : σ₁ = σ₂ :=
AlgEquiv.ext fun x ↦ φ.injective ((h₁.eq x).trans (h₂.eq x).symm)
lemma IsConj.ext_iff {σ₁ σ₂ : K ≃ₐ[k] K} (h₁ : IsConj φ σ₁) : σ₁ = σ₂ ↔ IsConj φ σ₂ :=
⟨fun e ↦ e ▸ h₁, h₁.ext⟩
lemma IsConj.isReal_comp (h : IsConj φ σ) : IsReal (φ.comp (algebraMap k K)) := by
ext1 x
simp only [conjugate_coe_eq, RingHom.coe_comp, Function.comp_apply, ← h.eq,
starRingEnd_apply, AlgEquiv.commutes]
lemma isConj_one_iff : IsConj φ (1 : K ≃ₐ[k] K) ↔ IsReal φ := Iff.rfl
alias ⟨_, IsReal.isConjGal_one⟩ := ComplexEmbedding.isConj_one_iff
lemma IsConj.symm (hσ : IsConj φ σ) :
IsConj φ σ.symm := RingHom.ext fun x ↦ by simpa using congr_arg star (hσ.eq (σ.symm x))
lemma isConj_symm : IsConj φ σ.symm ↔ IsConj φ σ :=
⟨IsConj.symm, IsConj.symm⟩
end NumberField.ComplexEmbedding
section InfinitePlace
open NumberField
variable {k : Type*} [Field k] (K : Type*) [Field K] {F : Type*} [Field F]
/-- An infinite place of a number field `K` is a place associated to a complex embedding. -/
def NumberField.InfinitePlace := { w : AbsoluteValue K ℝ // ∃ φ : K →+* ℂ, place φ = w }
instance [NumberField K] : Nonempty (NumberField.InfinitePlace K) := Set.instNonemptyRange _
variable {K}
/-- Return the infinite place defined by a complex embedding `φ`. -/
noncomputable def NumberField.InfinitePlace.mk (φ : K →+* ℂ) : NumberField.InfinitePlace K :=
⟨place φ, ⟨φ, rfl⟩⟩
namespace NumberField.InfinitePlace
open NumberField
instance {K : Type*} [Field K] : FunLike (InfinitePlace K) K ℝ where
coe w x := w.1 x
coe_injective' _ _ h := Subtype.eq (AbsoluteValue.ext fun x => congr_fun h x)
lemma coe_apply {K : Type*} [Field K] (v : InfinitePlace K) (x : K) :
v x = v.1 x := rfl
@[ext]
lemma ext {K : Type*} [Field K] (v₁ v₂ : InfinitePlace K) (h : ∀ k, v₁ k = v₂ k) : v₁ = v₂ :=
Subtype.ext <| AbsoluteValue.ext h
instance : MonoidWithZeroHomClass (InfinitePlace K) K ℝ where
map_mul w _ _ := w.1.map_mul _ _
map_one w := w.1.map_one
map_zero w := w.1.map_zero
instance : NonnegHomClass (InfinitePlace K) K ℝ where
apply_nonneg w _ := w.1.nonneg _
@[simp]
theorem apply (φ : K →+* ℂ) (x : K) : (mk φ) x = ‖φ x‖ := rfl
/-- For an infinite place `w`, return an embedding `φ` such that `w = infinite_place φ` . -/
noncomputable def embedding (w : InfinitePlace K) : K →+* ℂ := w.2.choose
@[simp]
theorem mk_embedding (w : InfinitePlace K) : mk (embedding w) = w := Subtype.ext w.2.choose_spec
@[simp]
theorem mk_conjugate_eq (φ : K →+* ℂ) : mk (ComplexEmbedding.conjugate φ) = mk φ := by
refine DFunLike.ext _ _ (fun x => ?_)
rw [apply, apply, ComplexEmbedding.conjugate_coe_eq, Complex.norm_conj]
theorem norm_embedding_eq (w : InfinitePlace K) (x : K) :
‖(embedding w) x‖ = w x := by
nth_rewrite 2 [← mk_embedding w]
rfl
theorem eq_iff_eq (x : K) (r : ℝ) : (∀ w : InfinitePlace K, w x = r) ↔ ∀ φ : K →+* ℂ, ‖φ x‖ = r :=
⟨fun hw φ => hw (mk φ), by rintro hφ ⟨w, ⟨φ, rfl⟩⟩; exact hφ φ⟩
theorem le_iff_le (x : K) (r : ℝ) : (∀ w : InfinitePlace K, w x ≤ r) ↔ ∀ φ : K →+* ℂ, ‖φ x‖ ≤ r :=
⟨fun hw φ => hw (mk φ), by rintro hφ ⟨w, ⟨φ, rfl⟩⟩; exact hφ φ⟩
theorem pos_iff {w : InfinitePlace K} {x : K} : 0 < w x ↔ x ≠ 0 := AbsoluteValue.pos_iff w.1
@[simp]
theorem mk_eq_iff {φ ψ : K →+* ℂ} : mk φ = mk ψ ↔ φ = ψ ∨ ComplexEmbedding.conjugate φ = ψ := by
constructor
· -- We prove that the map ψ ∘ φ⁻¹ between φ(K) and ℂ is uniform continuous, thus it is either the
-- inclusion or the complex conjugation using `Complex.uniformContinuous_ringHom_eq_id_or_conj`
intro h₀
obtain ⟨j, hiφ⟩ := (φ.injective).hasLeftInverse
let ι := RingEquiv.ofLeftInverse hiφ
have hlip : LipschitzWith 1 (RingHom.comp ψ ι.symm.toRingHom) := by
change LipschitzWith 1 (ψ ∘ ι.symm)
apply LipschitzWith.of_dist_le_mul
intro x y
rw [NNReal.coe_one, one_mul, NormedField.dist_eq, Function.comp_apply, Function.comp_apply,
← map_sub, ← map_sub]
apply le_of_eq
suffices ‖φ (ι.symm (x - y))‖ = ‖ψ (ι.symm (x - y))‖ by
rw [← this, ← RingEquiv.ofLeftInverse_apply hiφ _, RingEquiv.apply_symm_apply ι _]
rfl
exact congrFun (congrArg (↑) h₀) _
cases
Complex.uniformContinuous_ringHom_eq_id_or_conj φ.fieldRange hlip.uniformContinuous with
| inl h =>
left; ext1 x
conv_rhs => rw [← hiφ x]
exact (congrFun h (ι x)).symm
| inr h =>
right; ext1 x
conv_rhs => rw [← hiφ x]
exact (congrFun h (ι x)).symm
· rintro (⟨h⟩ | ⟨h⟩)
· exact congr_arg mk h
· rw [← mk_conjugate_eq]
exact congr_arg mk h
/-- An infinite place is real if it is defined by a real embedding. -/
def IsReal (w : InfinitePlace K) : Prop := ∃ φ : K →+* ℂ, ComplexEmbedding.IsReal φ ∧ mk φ = w
/-- An infinite place is complex if it is defined by a complex (ie. not real) embedding. -/
def IsComplex (w : InfinitePlace K) : Prop := ∃ φ : K →+* ℂ, ¬ComplexEmbedding.IsReal φ ∧ mk φ = w
theorem embedding_mk_eq (φ : K →+* ℂ) :
embedding (mk φ) = φ ∨ embedding (mk φ) = ComplexEmbedding.conjugate φ := by
rw [@eq_comm _ _ φ, @eq_comm _ _ (ComplexEmbedding.conjugate φ), ← mk_eq_iff, mk_embedding]
@[simp]
theorem embedding_mk_eq_of_isReal {φ : K →+* ℂ} (h : ComplexEmbedding.IsReal φ) :
embedding (mk φ) = φ := by
have := embedding_mk_eq φ
rwa [ComplexEmbedding.isReal_iff.mp h, or_self] at this
theorem isReal_iff {w : InfinitePlace K} :
IsReal w ↔ ComplexEmbedding.IsReal (embedding w) := by
refine ⟨?_, fun h => ⟨embedding w, h, mk_embedding w⟩⟩
rintro ⟨φ, ⟨hφ, rfl⟩⟩
rwa [embedding_mk_eq_of_isReal hφ]
theorem isComplex_iff {w : InfinitePlace K} :
IsComplex w ↔ ¬ComplexEmbedding.IsReal (embedding w) := by
refine ⟨?_, fun h => ⟨embedding w, h, mk_embedding w⟩⟩
rintro ⟨φ, ⟨hφ, rfl⟩⟩
contrapose! hφ
cases mk_eq_iff.mp (mk_embedding (mk φ)) with
| inl h => rwa [h] at hφ
| inr h => rwa [← ComplexEmbedding.isReal_conjugate_iff, h] at hφ
@[simp]
theorem conjugate_embedding_eq_of_isReal {w : InfinitePlace K} (h : IsReal w) :
ComplexEmbedding.conjugate (embedding w) = embedding w :=
ComplexEmbedding.isReal_iff.mpr (isReal_iff.mp h)
@[simp]
theorem not_isReal_iff_isComplex {w : InfinitePlace K} : ¬IsReal w ↔ IsComplex w := by
rw [isComplex_iff, isReal_iff]
@[simp]
theorem not_isComplex_iff_isReal {w : InfinitePlace K} : ¬IsComplex w ↔ IsReal w := by
rw [isComplex_iff, isReal_iff, not_not]
theorem isReal_or_isComplex (w : InfinitePlace K) : IsReal w ∨ IsComplex w := by
rw [← not_isReal_iff_isComplex]; exact em _
theorem ne_of_isReal_isComplex {w w' : InfinitePlace K} (h : IsReal w) (h' : IsComplex w') :
w ≠ w' := fun h_eq ↦ not_isReal_iff_isComplex.mpr h' (h_eq ▸ h)
variable (K) in
theorem disjoint_isReal_isComplex :
Disjoint {(w : InfinitePlace K) | IsReal w} {(w : InfinitePlace K) | IsComplex w} :=
Set.disjoint_iff.2 <| fun _ hw ↦ not_isReal_iff_isComplex.2 hw.2 hw.1
/-- The real embedding associated to a real infinite place. -/
noncomputable def embedding_of_isReal {w : InfinitePlace K} (hw : IsReal w) : K →+* ℝ :=
ComplexEmbedding.IsReal.embedding (isReal_iff.mp hw)
@[simp]
theorem embedding_of_isReal_apply {w : InfinitePlace K} (hw : IsReal w) (x : K) :
((embedding_of_isReal hw) x : ℂ) = (embedding w) x :=
ComplexEmbedding.IsReal.coe_embedding_apply (isReal_iff.mp hw) x
theorem norm_embedding_of_isReal {w : InfinitePlace K} (hw : IsReal w) (x : K) :
‖embedding_of_isReal hw x‖ = w x := by
rw [← norm_embedding_eq, ← embedding_of_isReal_apply hw, Complex.norm_real]
@[simp]
theorem isReal_of_mk_isReal {φ : K →+* ℂ} (h : IsReal (mk φ)) :
ComplexEmbedding.IsReal φ := by
contrapose! h
rw [not_isReal_iff_isComplex]
exact ⟨φ, h, rfl⟩
lemma isReal_mk_iff {φ : K →+* ℂ} :
IsReal (mk φ) ↔ ComplexEmbedding.IsReal φ :=
⟨isReal_of_mk_isReal, fun H ↦ ⟨_, H, rfl⟩⟩
lemma isComplex_mk_iff {φ : K →+* ℂ} :
IsComplex (mk φ) ↔ ¬ ComplexEmbedding.IsReal φ :=
not_isReal_iff_isComplex.symm.trans isReal_mk_iff.not
@[simp]
theorem not_isReal_of_mk_isComplex {φ : K →+* ℂ} (h : IsComplex (mk φ)) :
¬ ComplexEmbedding.IsReal φ := by rwa [← isComplex_mk_iff]
open scoped Classical in
/-- The multiplicity of an infinite place, that is the number of distinct complex embeddings that
define it, see `card_filter_mk_eq`. -/
noncomputable def mult (w : InfinitePlace K) : ℕ := if (IsReal w) then 1 else 2
@[simp]
theorem mult_isReal (w : {w : InfinitePlace K // IsReal w}) :
mult w.1 = 1 := by
rw [mult, if_pos w.prop]
@[simp]
theorem mult_isComplex (w : {w : InfinitePlace K // IsComplex w}) :
mult w.1 = 2 := by
rw [mult, if_neg (not_isReal_iff_isComplex.mpr w.prop)]
theorem mult_pos {w : InfinitePlace K} : 0 < mult w := by
rw [mult]
split_ifs <;> norm_num
@[simp]
theorem mult_ne_zero {w : InfinitePlace K} : mult w ≠ 0 := ne_of_gt mult_pos
theorem mult_coe_ne_zero {w : InfinitePlace K} : (mult w : ℝ) ≠ 0 :=
Nat.cast_ne_zero.mpr mult_ne_zero
theorem one_le_mult {w : InfinitePlace K} : (1 : ℝ) ≤ mult w := by
rw [← Nat.cast_one, Nat.cast_le]
exact mult_pos
open scoped Classical in
theorem card_filter_mk_eq [NumberField K] (w : InfinitePlace K) : #{φ | mk φ = w} = mult w := by
conv_lhs =>
congr; congr; ext
rw [← mk_embedding w, mk_eq_iff, ComplexEmbedding.conjugate, star_involutive.eq_iff]
simp_rw [Finset.filter_or, Finset.filter_eq' _ (embedding w),
Finset.filter_eq' _ (ComplexEmbedding.conjugate (embedding w)),
Finset.mem_univ, ite_true, mult]
split_ifs with hw
· rw [ComplexEmbedding.isReal_iff.mp (isReal_iff.mp hw), Finset.union_idempotent,
Finset.card_singleton]
· refine Finset.card_pair ?_
rwa [Ne, eq_comm, ← ComplexEmbedding.isReal_iff, ← isReal_iff]
open scoped Classical in
noncomputable instance NumberField.InfinitePlace.fintype [NumberField K] :
Fintype (InfinitePlace K) := Set.fintypeRange _
open scoped Classical in
@[to_additive]
theorem prod_eq_prod_mul_prod {α : Type*} [CommMonoid α] [NumberField K] (f : InfinitePlace K → α) :
∏ w, f w = (∏ w : {w // IsReal w}, f w.1) * (∏ w : {w // IsComplex w}, f w.1) := by
rw [← Equiv.prod_comp (Equiv.subtypeEquivRight (fun _ ↦ not_isReal_iff_isComplex))]
simp [Fintype.prod_subtype_mul_prod_subtype]
theorem sum_mult_eq [NumberField K] :
∑ w : InfinitePlace K, mult w = Module.finrank ℚ K := by
classical
rw [← Embeddings.card K ℂ, Fintype.card, Finset.card_eq_sum_ones, ← Finset.univ.sum_fiberwise
(fun φ => InfinitePlace.mk φ)]
exact Finset.sum_congr rfl
(fun _ _ => by rw [Finset.sum_const, smul_eq_mul, mul_one, card_filter_mk_eq])
/-- The map from real embeddings to real infinite places as an equiv -/
noncomputable def mkReal :
{ φ : K →+* ℂ // ComplexEmbedding.IsReal φ } ≃ { w : InfinitePlace K // IsReal w } := by
refine (Equiv.ofBijective (fun φ => ⟨mk φ, ?_⟩) ⟨fun φ ψ h => ?_, fun w => ?_⟩)
· exact ⟨φ, φ.prop, rfl⟩
· rwa [Subtype.mk.injEq, mk_eq_iff, ComplexEmbedding.isReal_iff.mp φ.prop, or_self,
← Subtype.ext_iff] at h
· exact ⟨⟨embedding w, isReal_iff.mp w.prop⟩, by simp⟩
/-- The map from nonreal embeddings to complex infinite places -/
noncomputable def mkComplex :
{ φ : K →+* ℂ // ¬ComplexEmbedding.IsReal φ } → { w : InfinitePlace K // IsComplex w } :=
Subtype.map mk fun φ hφ => ⟨φ, hφ, rfl⟩
@[simp]
theorem mkReal_coe (φ : { φ : K →+* ℂ // ComplexEmbedding.IsReal φ }) :
(mkReal φ : InfinitePlace K) = mk (φ : K →+* ℂ) := rfl
@[simp]
theorem mkComplex_coe (φ : { φ : K →+* ℂ // ¬ComplexEmbedding.IsReal φ }) :
(mkComplex φ : InfinitePlace K) = mk (φ : K →+* ℂ) := rfl
section NumberField
variable [NumberField K]
/-- The infinite part of the product formula : for `x ∈ K`, we have `Π_w ‖x‖_w = |norm(x)|` where
`‖·‖_w` is the normalized absolute value for `w`. -/
theorem prod_eq_abs_norm (x : K) :
∏ w : InfinitePlace K, w x ^ mult w = abs (Algebra.norm ℚ x) := by
classical
convert (congr_arg (‖·‖) (@Algebra.norm_eq_prod_embeddings ℚ _ _ _ _ ℂ _ _ _ _ _ x)).symm
· rw [norm_prod, ← Fintype.prod_equiv RingHom.equivRatAlgHom (fun f => ‖f x‖)
(fun φ => ‖φ x‖) fun _ => by simp [RingHom.equivRatAlgHom_apply]]
rw [← Finset.prod_fiberwise Finset.univ mk (fun φ => ‖φ x‖)]
have (w : InfinitePlace K) (φ) (hφ : φ ∈ ({φ | mk φ = w} : Finset _)) :
‖φ x‖ = w x := by rw [← (Finset.mem_filter.mp hφ).2, apply]
simp_rw [Finset.prod_congr rfl (this _), Finset.prod_const, card_filter_mk_eq]
· rw [eq_ratCast, Rat.cast_abs, ← Real.norm_eq_abs, ← Complex.norm_real, Complex.ofReal_ratCast]
theorem one_le_of_lt_one {w : InfinitePlace K} {a : (𝓞 K)} (ha : a ≠ 0)
(h : ∀ ⦃z⦄, z ≠ w → z a < 1) : 1 ≤ w a := by
suffices (1 : ℝ) ≤ |Algebra.norm ℚ (a : K)| by
contrapose! this
rw [← InfinitePlace.prod_eq_abs_norm, ← Finset.prod_const_one]
refine Finset.prod_lt_prod_of_nonempty (fun _ _ ↦ ?_) (fun z _ ↦ ?_) Finset.univ_nonempty
· exact pow_pos (pos_iff.mpr ((Subalgebra.coe_eq_zero _).not.mpr ha)) _
· refine pow_lt_one₀ (apply_nonneg _ _) ?_ (by rw [mult]; split_ifs <;> norm_num)
by_cases hz : z = w
· rwa [hz]
· exact h hz
rw [← Algebra.coe_norm_int, ← Int.cast_one, ← Int.cast_abs, Rat.cast_intCast, Int.cast_le]
exact Int.one_le_abs (Algebra.norm_ne_zero_iff.mpr ha)
open scoped IntermediateField in
theorem _root_.NumberField.is_primitive_element_of_infinitePlace_lt {x : 𝓞 K}
{w : InfinitePlace K} (h₁ : x ≠ 0) (h₂ : ∀ ⦃w'⦄, w' ≠ w → w' x < 1)
(h₃ : IsReal w ∨ |(w.embedding x).re| < 1) : ℚ⟮(x : K)⟯ = ⊤ := by
rw [Field.primitive_element_iff_algHom_eq_of_eval ℚ ℂ ?_ _ w.embedding.toRatAlgHom]
· intro ψ hψ
have h : 1 ≤ w x := one_le_of_lt_one h₁ h₂
have main : w = InfinitePlace.mk ψ.toRingHom := by
simp at hψ
rw [← norm_embedding_eq, hψ] at h
contrapose! h
exact h₂ h.symm
rw [(mk_embedding w).symm, mk_eq_iff] at main
cases h₃ with
| inl hw =>
rw [conjugate_embedding_eq_of_isReal hw, or_self] at main
exact congr_arg RingHom.toRatAlgHom main
| inr hw =>
refine congr_arg RingHom.toRatAlgHom (main.resolve_right fun h' ↦ hw.not_le ?_)
have : (embedding w x).im = 0 := by
rw [← Complex.conj_eq_iff_im]
have := RingHom.congr_fun h' x
simp at this
rw [this]
exact hψ.symm
rwa [← norm_embedding_eq, ← Complex.re_add_im (embedding w x), this, Complex.ofReal_zero,
zero_mul, add_zero, Complex.norm_real] at h
· exact fun x ↦ IsAlgClosed.splits_codomain (minpoly ℚ x)
theorem _root_.NumberField.adjoin_eq_top_of_infinitePlace_lt {x : 𝓞 K} {w : InfinitePlace K}
(h₁ : x ≠ 0) (h₂ : ∀ ⦃w'⦄, w' ≠ w → w' x < 1) (h₃ : IsReal w ∨ |(w.embedding x).re| < 1) :
Algebra.adjoin ℚ {(x : K)} = ⊤ := by
rw [← IntermediateField.adjoin_simple_toSubalgebra_of_integral (IsIntegral.of_finite ℚ _)]
exact congr_arg IntermediateField.toSubalgebra <|
NumberField.is_primitive_element_of_infinitePlace_lt h₁ h₂ h₃
end NumberField
open Fintype Module
variable (K)
section NumberField
variable [NumberField K]
open scoped Classical in
/-- The number of infinite real places of the number field `K`. -/
noncomputable abbrev nrRealPlaces := card { w : InfinitePlace K // IsReal w }
@[deprecated (since := "2024-10-24")] alias NrRealPlaces := nrRealPlaces
open scoped Classical in
/-- The number of infinite complex places of the number field `K`. -/
noncomputable abbrev nrComplexPlaces := card { w : InfinitePlace K // IsComplex w }
@[deprecated (since := "2024-10-24")] alias NrComplexPlaces := nrComplexPlaces
open scoped Classical in
theorem card_real_embeddings :
card { φ : K →+* ℂ // ComplexEmbedding.IsReal φ } = nrRealPlaces K := Fintype.card_congr mkReal
theorem card_eq_nrRealPlaces_add_nrComplexPlaces :
Fintype.card (InfinitePlace K) = nrRealPlaces K + nrComplexPlaces K := by
classical
convert Fintype.card_subtype_or_disjoint (IsReal (K := K)) (IsComplex (K := K))
(disjoint_isReal_isComplex K) using 1
exact (Fintype.card_of_subtype _ (fun w ↦ ⟨fun _ ↦ isReal_or_isComplex w, fun _ ↦ by simp⟩)).symm
open scoped Classical in
theorem card_complex_embeddings :
card { φ : K →+* ℂ // ¬ComplexEmbedding.IsReal φ } = 2 * nrComplexPlaces K := by
suffices ∀ w : { w : InfinitePlace K // IsComplex w },
#{φ : {φ //¬ ComplexEmbedding.IsReal φ} | mkComplex φ = w} = 2 by
rw [Fintype.card, Finset.card_eq_sum_ones, ← Finset.sum_fiberwise _ (fun φ => mkComplex φ)]
simp_rw [Finset.sum_const, this, smul_eq_mul, mul_one, Fintype.card, Finset.card_eq_sum_ones,
Finset.mul_sum, Finset.sum_const, smul_eq_mul, mul_one]
rintro ⟨w, hw⟩
convert card_filter_mk_eq w
· rw [← Fintype.card_subtype, ← Fintype.card_subtype]
refine Fintype.card_congr (Equiv.ofBijective ?_ ⟨fun _ _ h => ?_, fun ⟨φ, hφ⟩ => ?_⟩)
· exact fun ⟨φ, hφ⟩ => ⟨φ.val, by rwa [Subtype.ext_iff] at hφ⟩
· rwa [Subtype.mk_eq_mk, ← Subtype.ext_iff, ← Subtype.ext_iff] at h
· refine ⟨⟨⟨φ, not_isReal_of_mk_isComplex (hφ.symm ▸ hw)⟩, ?_⟩, rfl⟩
rwa [Subtype.ext_iff, mkComplex_coe]
· simp_rw [mult, not_isReal_iff_isComplex.mpr hw, ite_false]
theorem card_add_two_mul_card_eq_rank :
nrRealPlaces K + 2 * nrComplexPlaces K = finrank ℚ K := by
classical
rw [← card_real_embeddings, ← card_complex_embeddings, Fintype.card_subtype_compl,
← Embeddings.card K ℂ, Nat.add_sub_of_le]
exact Fintype.card_subtype_le _
variable {K}
theorem nrComplexPlaces_eq_zero_of_finrank_eq_one (h : finrank ℚ K = 1) :
nrComplexPlaces K = 0 := by linarith [card_add_two_mul_card_eq_rank K]
| theorem nrRealPlaces_eq_one_of_finrank_eq_one (h : finrank ℚ K = 1) :
nrRealPlaces K = 1 := by
have := card_add_two_mul_card_eq_rank K
rwa [nrComplexPlaces_eq_zero_of_finrank_eq_one h, h, mul_zero, add_zero] at this
| Mathlib/NumberTheory/NumberField/Embeddings.lean | 661 | 665 |
/-
Copyright (c) 2020 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers
-/
import Mathlib.Data.Finset.Sort
import Mathlib.Data.Fin.VecNotation
import Mathlib.Data.Sign
import Mathlib.LinearAlgebra.AffineSpace.Combination
import Mathlib.LinearAlgebra.AffineSpace.AffineEquiv
import Mathlib.LinearAlgebra.Basis.VectorSpace
/-!
# Affine independence
This file defines affinely independent families of points.
## Main definitions
* `AffineIndependent` defines affinely independent families of points
as those where no nontrivial weighted subtraction is `0`. This is
proved equivalent to two other formulations: linear independence of
the results of subtracting a base point in the family from the other
points in the family, or any equal affine combinations having the
same weights. A bundled type `Simplex` is provided for finite
affinely independent families of points, with an abbreviation
`Triangle` for the case of three points.
## References
* https://en.wikipedia.org/wiki/Affine_space
-/
noncomputable section
open Finset Function
open scoped Affine
section AffineIndependent
variable (k : Type*) {V : Type*} {P : Type*} [Ring k] [AddCommGroup V] [Module k V]
variable [AffineSpace V P] {ι : Type*}
/-- An indexed family is said to be affinely independent if no
nontrivial weighted subtractions (where the sum of weights is 0) are
0. -/
def AffineIndependent (p : ι → P) : Prop :=
∀ (s : Finset ι) (w : ι → k),
∑ i ∈ s, w i = 0 → s.weightedVSub p w = (0 : V) → ∀ i ∈ s, w i = 0
/-- The definition of `AffineIndependent`. -/
theorem affineIndependent_def (p : ι → P) :
AffineIndependent k p ↔
∀ (s : Finset ι) (w : ι → k),
∑ i ∈ s, w i = 0 → s.weightedVSub p w = (0 : V) → ∀ i ∈ s, w i = 0 :=
Iff.rfl
/-- A family with at most one point is affinely independent. -/
theorem affineIndependent_of_subsingleton [Subsingleton ι] (p : ι → P) : AffineIndependent k p :=
fun _ _ h _ i hi => Fintype.eq_of_subsingleton_of_sum_eq h i hi
/-- A family indexed by a `Fintype` is affinely independent if and
only if no nontrivial weighted subtractions over `Finset.univ` (where
the sum of the weights is 0) are 0. -/
theorem affineIndependent_iff_of_fintype [Fintype ι] (p : ι → P) :
AffineIndependent k p ↔
∀ w : ι → k, ∑ i, w i = 0 → Finset.univ.weightedVSub p w = (0 : V) → ∀ i, w i = 0 := by
constructor
· exact fun h w hw hs i => h Finset.univ w hw hs i (Finset.mem_univ _)
· intro h s w hw hs i hi
rw [Finset.weightedVSub_indicator_subset _ _ (Finset.subset_univ s)] at hs
rw [← Finset.sum_indicator_subset _ (Finset.subset_univ s)] at hw
replace h := h ((↑s : Set ι).indicator w) hw hs i
simpa [hi] using h
@[simp] lemma affineIndependent_vadd {p : ι → P} {v : V} :
AffineIndependent k (v +ᵥ p) ↔ AffineIndependent k p := by
simp +contextual [AffineIndependent, weightedVSub_vadd]
protected alias ⟨AffineIndependent.of_vadd, AffineIndependent.vadd⟩ := affineIndependent_vadd
@[simp] lemma affineIndependent_smul {G : Type*} [Group G] [DistribMulAction G V]
[SMulCommClass G k V] {p : ι → V} {a : G} :
AffineIndependent k (a • p) ↔ AffineIndependent k p := by
simp +contextual [AffineIndependent, weightedVSub_smul,
← smul_comm (α := V) a, ← smul_sum, smul_eq_zero_iff_eq]
protected alias ⟨AffineIndependent.of_smul, AffineIndependent.smul⟩ := affineIndependent_smul
/-- A family is affinely independent if and only if the differences
from a base point in that family are linearly independent. -/
theorem affineIndependent_iff_linearIndependent_vsub (p : ι → P) (i1 : ι) :
AffineIndependent k p ↔ LinearIndependent k fun i : { x // x ≠ i1 } => (p i -ᵥ p i1 : V) := by
classical
constructor
· intro h
rw [linearIndependent_iff']
intro s g hg i hi
set f : ι → k := fun x => if hx : x = i1 then -∑ y ∈ s, g y else g ⟨x, hx⟩ with hfdef
let s2 : Finset ι := insert i1 (s.map (Embedding.subtype _))
have hfg : ∀ x : { x // x ≠ i1 }, g x = f x := by
intro x
rw [hfdef]
dsimp only
rw [dif_neg x.property, Subtype.coe_eta]
rw [hfg]
have hf : ∑ ι ∈ s2, f ι = 0 := by
rw [Finset.sum_insert
(Finset.not_mem_map_subtype_of_not_property s (Classical.not_not.2 rfl)),
Finset.sum_subtype_map_embedding fun x _ => (hfg x).symm]
rw [hfdef]
dsimp only
rw [dif_pos rfl]
exact neg_add_cancel _
have hs2 : s2.weightedVSub p f = (0 : V) := by
set f2 : ι → V := fun x => f x • (p x -ᵥ p i1) with hf2def
set g2 : { x // x ≠ i1 } → V := fun x => g x • (p x -ᵥ p i1)
have hf2g2 : ∀ x : { x // x ≠ i1 }, f2 x = g2 x := by
simp only [g2, hf2def]
refine fun x => ?_
rw [hfg]
rw [Finset.weightedVSub_eq_weightedVSubOfPoint_of_sum_eq_zero s2 f p hf (p i1),
Finset.weightedVSubOfPoint_insert, Finset.weightedVSubOfPoint_apply,
Finset.sum_subtype_map_embedding fun x _ => hf2g2 x]
exact hg
exact h s2 f hf hs2 i (Finset.mem_insert_of_mem (Finset.mem_map.2 ⟨i, hi, rfl⟩))
· intro h
rw [linearIndependent_iff'] at h
intro s w hw hs i hi
rw [Finset.weightedVSub_eq_weightedVSubOfPoint_of_sum_eq_zero s w p hw (p i1), ←
s.weightedVSubOfPoint_erase w p i1, Finset.weightedVSubOfPoint_apply] at hs
let f : ι → V := fun i => w i • (p i -ᵥ p i1)
have hs2 : (∑ i ∈ (s.erase i1).subtype fun i => i ≠ i1, f i) = 0 := by
rw [← hs]
convert Finset.sum_subtype_of_mem f fun x => Finset.ne_of_mem_erase
have h2 := h ((s.erase i1).subtype fun i => i ≠ i1) (fun x => w x) hs2
simp_rw [Finset.mem_subtype] at h2
have h2b : ∀ i ∈ s, i ≠ i1 → w i = 0 := fun i his hi =>
h2 ⟨i, hi⟩ (Finset.mem_erase_of_ne_of_mem hi his)
exact Finset.eq_zero_of_sum_eq_zero hw h2b i hi
/-- A set is affinely independent if and only if the differences from
a base point in that set are linearly independent. -/
theorem affineIndependent_set_iff_linearIndependent_vsub {s : Set P} {p₁ : P} (hp₁ : p₁ ∈ s) :
AffineIndependent k (fun p => p : s → P) ↔
LinearIndependent k (fun v => v : (fun p => (p -ᵥ p₁ : V)) '' (s \ {p₁}) → V) := by
rw [affineIndependent_iff_linearIndependent_vsub k (fun p => p : s → P) ⟨p₁, hp₁⟩]
constructor
· intro h
have hv : ∀ v : (fun p => (p -ᵥ p₁ : V)) '' (s \ {p₁}), (v : V) +ᵥ p₁ ∈ s \ {p₁} := fun v =>
(vsub_left_injective p₁).mem_set_image.1 ((vadd_vsub (v : V) p₁).symm ▸ v.property)
let f : (fun p : P => (p -ᵥ p₁ : V)) '' (s \ {p₁}) → { x : s // x ≠ ⟨p₁, hp₁⟩ } := fun x =>
⟨⟨(x : V) +ᵥ p₁, Set.mem_of_mem_diff (hv x)⟩, fun hx =>
Set.not_mem_of_mem_diff (hv x) (Subtype.ext_iff.1 hx)⟩
convert h.comp f fun x1 x2 hx =>
Subtype.ext (vadd_right_cancel p₁ (Subtype.ext_iff.1 (Subtype.ext_iff.1 hx)))
ext v
exact (vadd_vsub (v : V) p₁).symm
· intro h
let f : { x : s // x ≠ ⟨p₁, hp₁⟩ } → (fun p : P => (p -ᵥ p₁ : V)) '' (s \ {p₁}) := fun x =>
⟨((x : s) : P) -ᵥ p₁, ⟨x, ⟨⟨(x : s).property, fun hx => x.property (Subtype.ext hx)⟩, rfl⟩⟩⟩
convert h.comp f fun x1 x2 hx =>
Subtype.ext (Subtype.ext (vsub_left_cancel (Subtype.ext_iff.1 hx)))
/-- A set of nonzero vectors is linearly independent if and only if,
given a point `p₁`, the vectors added to `p₁` and `p₁` itself are
affinely independent. -/
theorem linearIndependent_set_iff_affineIndependent_vadd_union_singleton {s : Set V}
(hs : ∀ v ∈ s, v ≠ (0 : V)) (p₁ : P) : LinearIndependent k (fun v => v : s → V) ↔
AffineIndependent k (fun p => p : ({p₁} ∪ (fun v => v +ᵥ p₁) '' s : Set P) → P) := by
rw [affineIndependent_set_iff_linearIndependent_vsub k
(Set.mem_union_left _ (Set.mem_singleton p₁))]
have h : (fun p => (p -ᵥ p₁ : V)) '' (({p₁} ∪ (fun v => v +ᵥ p₁) '' s) \ {p₁}) = s := by
simp_rw [Set.union_diff_left, Set.image_diff (vsub_left_injective p₁), Set.image_image,
Set.image_singleton, vsub_self, vadd_vsub, Set.image_id']
exact Set.diff_singleton_eq_self fun h => hs 0 h rfl
rw [h]
/-- A family is affinely independent if and only if any affine
combinations (with sum of weights 1) that evaluate to the same point
have equal `Set.indicator`. -/
theorem affineIndependent_iff_indicator_eq_of_affineCombination_eq (p : ι → P) :
AffineIndependent k p ↔
∀ (s1 s2 : Finset ι) (w1 w2 : ι → k),
∑ i ∈ s1, w1 i = 1 →
∑ i ∈ s2, w2 i = 1 →
s1.affineCombination k p w1 = s2.affineCombination k p w2 →
Set.indicator (↑s1) w1 = Set.indicator (↑s2) w2 := by
classical
constructor
· intro ha s1 s2 w1 w2 hw1 hw2 heq
ext i
by_cases hi : i ∈ s1 ∪ s2
· rw [← sub_eq_zero]
rw [← Finset.sum_indicator_subset w1 (s1.subset_union_left (s₂ := s2))] at hw1
rw [← Finset.sum_indicator_subset w2 (s1.subset_union_right)] at hw2
have hws : (∑ i ∈ s1 ∪ s2, (Set.indicator (↑s1) w1 - Set.indicator (↑s2) w2) i) = 0 := by
simp [hw1, hw2]
rw [Finset.affineCombination_indicator_subset w1 p (s1.subset_union_left (s₂ := s2)),
Finset.affineCombination_indicator_subset w2 p s1.subset_union_right,
← @vsub_eq_zero_iff_eq V, Finset.affineCombination_vsub] at heq
exact ha (s1 ∪ s2) (Set.indicator (↑s1) w1 - Set.indicator (↑s2) w2) hws heq i hi
· rw [← Finset.mem_coe, Finset.coe_union] at hi
have h₁ : Set.indicator (↑s1) w1 i = 0 := by
simp only [Set.indicator, Finset.mem_coe, ite_eq_right_iff]
intro h
by_contra
exact (mt (@Set.mem_union_left _ i ↑s1 ↑s2) hi) h
have h₂ : Set.indicator (↑s2) w2 i = 0 := by
simp only [Set.indicator, Finset.mem_coe, ite_eq_right_iff]
intro h
by_contra
exact (mt (@Set.mem_union_right _ i ↑s2 ↑s1) hi) h
simp [h₁, h₂]
· intro ha s w hw hs i0 hi0
let w1 : ι → k := Function.update (Function.const ι 0) i0 1
have hw1 : ∑ i ∈ s, w1 i = 1 := by
rw [Finset.sum_update_of_mem hi0]
simp only [Finset.sum_const_zero, add_zero, const_apply]
have hw1s : s.affineCombination k p w1 = p i0 :=
s.affineCombination_of_eq_one_of_eq_zero w1 p hi0 (Function.update_self ..)
fun _ _ hne => Function.update_of_ne hne ..
let w2 := w + w1
have hw2 : ∑ i ∈ s, w2 i = 1 := by
simp_all only [w2, Pi.add_apply, Finset.sum_add_distrib, zero_add]
have hw2s : s.affineCombination k p w2 = p i0 := by
simp_all only [w2, ← Finset.weightedVSub_vadd_affineCombination, zero_vadd]
replace ha := ha s s w2 w1 hw2 hw1 (hw1s.symm ▸ hw2s)
have hws : w2 i0 - w1 i0 = 0 := by
rw [← Finset.mem_coe] at hi0
rw [← Set.indicator_of_mem hi0 w2, ← Set.indicator_of_mem hi0 w1, ha, sub_self]
simpa [w2] using hws
/-- A finite family is affinely independent if and only if any affine
combinations (with sum of weights 1) that evaluate to the same point are equal. -/
theorem affineIndependent_iff_eq_of_fintype_affineCombination_eq [Fintype ι] (p : ι → P) :
AffineIndependent k p ↔ ∀ w1 w2 : ι → k, ∑ i, w1 i = 1 → ∑ i, w2 i = 1 →
Finset.univ.affineCombination k p w1 = Finset.univ.affineCombination k p w2 → w1 = w2 := by
rw [affineIndependent_iff_indicator_eq_of_affineCombination_eq]
constructor
· intro h w1 w2 hw1 hw2 hweq
simpa only [Set.indicator_univ, Finset.coe_univ] using h _ _ w1 w2 hw1 hw2 hweq
· intro h s1 s2 w1 w2 hw1 hw2 hweq
have hw1' : (∑ i, (s1 : Set ι).indicator w1 i) = 1 := by
rwa [Finset.sum_indicator_subset _ (Finset.subset_univ s1)]
have hw2' : (∑ i, (s2 : Set ι).indicator w2 i) = 1 := by
rwa [Finset.sum_indicator_subset _ (Finset.subset_univ s2)]
rw [Finset.affineCombination_indicator_subset w1 p (Finset.subset_univ s1),
Finset.affineCombination_indicator_subset w2 p (Finset.subset_univ s2)] at hweq
exact h _ _ hw1' hw2' hweq
variable {k}
/-- If we single out one member of an affine-independent family of points and affinely transport
all others along the line joining them to this member, the resulting new family of points is affine-
independent.
This is the affine version of `LinearIndependent.units_smul`. -/
theorem AffineIndependent.units_lineMap {p : ι → P} (hp : AffineIndependent k p) (j : ι)
(w : ι → Units k) : AffineIndependent k fun i => AffineMap.lineMap (p j) (p i) (w i : k) := by
rw [affineIndependent_iff_linearIndependent_vsub k _ j] at hp ⊢
simp only [AffineMap.lineMap_vsub_left, AffineMap.coe_const, AffineMap.lineMap_same, const_apply]
exact hp.units_smul fun i => w i
theorem AffineIndependent.indicator_eq_of_affineCombination_eq {p : ι → P}
(ha : AffineIndependent k p) (s₁ s₂ : Finset ι) (w₁ w₂ : ι → k) (hw₁ : ∑ i ∈ s₁, w₁ i = 1)
(hw₂ : ∑ i ∈ s₂, w₂ i = 1) (h : s₁.affineCombination k p w₁ = s₂.affineCombination k p w₂) :
Set.indicator (↑s₁) w₁ = Set.indicator (↑s₂) w₂ :=
(affineIndependent_iff_indicator_eq_of_affineCombination_eq k p).1 ha s₁ s₂ w₁ w₂ hw₁ hw₂ h
/-- An affinely independent family is injective, if the underlying
ring is nontrivial. -/
protected theorem AffineIndependent.injective [Nontrivial k] {p : ι → P}
(ha : AffineIndependent k p) : Function.Injective p := by
intro i j hij
rw [affineIndependent_iff_linearIndependent_vsub _ _ j] at ha
by_contra hij'
refine ha.ne_zero ⟨i, hij'⟩ (vsub_eq_zero_iff_eq.mpr ?_)
simp_all only [ne_eq]
/-- If a family is affinely independent, so is any subfamily given by
composition of an embedding into index type with the original
family. -/
theorem AffineIndependent.comp_embedding {ι2 : Type*} (f : ι2 ↪ ι) {p : ι → P}
(ha : AffineIndependent k p) : AffineIndependent k (p ∘ f) := by
classical
intro fs w hw hs i0 hi0
let fs' := fs.map f
let w' i := if h : ∃ i2, f i2 = i then w h.choose else 0
have hw' : ∀ i2 : ι2, w' (f i2) = w i2 := by
intro i2
have h : ∃ i : ι2, f i = f i2 := ⟨i2, rfl⟩
have hs : h.choose = i2 := f.injective h.choose_spec
simp_rw [w', dif_pos h, hs]
have hw's : ∑ i ∈ fs', w' i = 0 := by
rw [← hw, Finset.sum_map]
simp [hw']
have hs' : fs'.weightedVSub p w' = (0 : V) := by
rw [← hs, Finset.weightedVSub_map]
congr with i
simp_all only [comp_apply, EmbeddingLike.apply_eq_iff_eq, exists_eq, dite_true]
rw [← ha fs' w' hw's hs' (f i0) ((Finset.mem_map' _).2 hi0), hw']
/-- If a family is affinely independent, so is any subfamily indexed
by a subtype of the index type. -/
protected theorem AffineIndependent.subtype {p : ι → P} (ha : AffineIndependent k p) (s : Set ι) :
AffineIndependent k fun i : s => p i :=
ha.comp_embedding (Embedding.subtype _)
/-- If an indexed family of points is affinely independent, so is the
corresponding set of points. -/
protected theorem AffineIndependent.range {p : ι → P} (ha : AffineIndependent k p) :
AffineIndependent k (fun x => x : Set.range p → P) := by
let f : Set.range p → ι := fun x => x.property.choose
have hf : ∀ x, p (f x) = x := fun x => x.property.choose_spec
let fe : Set.range p ↪ ι := ⟨f, fun x₁ x₂ he => Subtype.ext (hf x₁ ▸ hf x₂ ▸ he ▸ rfl)⟩
convert ha.comp_embedding fe
ext
simp [fe, hf]
theorem affineIndependent_equiv {ι' : Type*} (e : ι ≃ ι') {p : ι' → P} :
AffineIndependent k (p ∘ e) ↔ AffineIndependent k p := by
refine ⟨?_, AffineIndependent.comp_embedding e.toEmbedding⟩
intro h
have : p = p ∘ e ∘ e.symm.toEmbedding := by
ext
simp
rw [this]
exact h.comp_embedding e.symm.toEmbedding
/-- If a set of points is affinely independent, so is any subset. -/
protected theorem AffineIndependent.mono {s t : Set P}
(ha : AffineIndependent k (fun x => x : t → P)) (hs : s ⊆ t) :
AffineIndependent k (fun x => x : s → P) :=
ha.comp_embedding (s.embeddingOfSubset t hs)
/-- If the range of an injective indexed family of points is affinely
independent, so is that family. -/
theorem AffineIndependent.of_set_of_injective {p : ι → P}
(ha : AffineIndependent k (fun x => x : Set.range p → P)) (hi : Function.Injective p) :
AffineIndependent k p :=
ha.comp_embedding
(⟨fun i => ⟨p i, Set.mem_range_self _⟩, fun _ _ h => hi (Subtype.mk_eq_mk.1 h)⟩ :
ι ↪ Set.range p)
section Composition
variable {V₂ P₂ : Type*} [AddCommGroup V₂] [Module k V₂] [AffineSpace V₂ P₂]
/-- If the image of a family of points in affine space under an affine transformation is affine-
independent, then the original family of points is also affine-independent. -/
theorem AffineIndependent.of_comp {p : ι → P} (f : P →ᵃ[k] P₂) (hai : AffineIndependent k (f ∘ p)) :
AffineIndependent k p := by
rcases isEmpty_or_nonempty ι with h | h
· haveI := h
apply affineIndependent_of_subsingleton
obtain ⟨i⟩ := h
rw [affineIndependent_iff_linearIndependent_vsub k p i]
simp_rw [affineIndependent_iff_linearIndependent_vsub k (f ∘ p) i, Function.comp_apply, ←
f.linearMap_vsub] at hai
exact LinearIndependent.of_comp f.linear hai
/-- The image of a family of points in affine space, under an injective affine transformation, is
affine-independent. -/
theorem AffineIndependent.map' {p : ι → P} (hai : AffineIndependent k p) (f : P →ᵃ[k] P₂)
(hf : Function.Injective f) : AffineIndependent k (f ∘ p) := by
rcases isEmpty_or_nonempty ι with h | h
· haveI := h
apply affineIndependent_of_subsingleton
obtain ⟨i⟩ := h
rw [affineIndependent_iff_linearIndependent_vsub k p i] at hai
simp_rw [affineIndependent_iff_linearIndependent_vsub k (f ∘ p) i, Function.comp_apply, ←
f.linearMap_vsub]
have hf' : LinearMap.ker f.linear = ⊥ := by rwa [LinearMap.ker_eq_bot, f.linear_injective_iff]
exact LinearIndependent.map' hai f.linear hf'
/-- Injective affine maps preserve affine independence. -/
theorem AffineMap.affineIndependent_iff {p : ι → P} (f : P →ᵃ[k] P₂) (hf : Function.Injective f) :
AffineIndependent k (f ∘ p) ↔ AffineIndependent k p :=
⟨AffineIndependent.of_comp f, fun hai => AffineIndependent.map' hai f hf⟩
/-- Affine equivalences preserve affine independence of families of points. -/
theorem AffineEquiv.affineIndependent_iff {p : ι → P} (e : P ≃ᵃ[k] P₂) :
AffineIndependent k (e ∘ p) ↔ AffineIndependent k p :=
e.toAffineMap.affineIndependent_iff e.toEquiv.injective
/-- Affine equivalences preserve affine independence of subsets. -/
theorem AffineEquiv.affineIndependent_set_of_eq_iff {s : Set P} (e : P ≃ᵃ[k] P₂) :
AffineIndependent k ((↑) : e '' s → P₂) ↔ AffineIndependent k ((↑) : s → P) := by
have : e ∘ ((↑) : s → P) = ((↑) : e '' s → P₂) ∘ (e : P ≃ P₂).image s := rfl
-- This used to be `rw`, but we need `erw` after https://github.com/leanprover/lean4/pull/2644
erw [← e.affineIndependent_iff, this, affineIndependent_equiv]
end Composition
/-- If a family is affinely independent, and the spans of points
indexed by two subsets of the index type have a point in common, those
subsets of the index type have an element in common, if the underlying
ring is nontrivial. -/
theorem AffineIndependent.exists_mem_inter_of_exists_mem_inter_affineSpan [Nontrivial k] {p : ι → P}
(ha : AffineIndependent k p) {s1 s2 : Set ι} {p0 : P} (hp0s1 : p0 ∈ affineSpan k (p '' s1))
(hp0s2 : p0 ∈ affineSpan k (p '' s2)) : ∃ i : ι, i ∈ s1 ∩ s2 := by
rw [Set.image_eq_range] at hp0s1 hp0s2
rw [mem_affineSpan_iff_eq_affineCombination, ←
Finset.eq_affineCombination_subset_iff_eq_affineCombination_subtype] at hp0s1 hp0s2
rcases hp0s1 with ⟨fs1, hfs1, w1, hw1, hp0s1⟩
rcases hp0s2 with ⟨fs2, hfs2, w2, hw2, hp0s2⟩
rw [affineIndependent_iff_indicator_eq_of_affineCombination_eq] at ha
replace ha := ha fs1 fs2 w1 w2 hw1 hw2 (hp0s1 ▸ hp0s2)
have hnz : ∑ i ∈ fs1, w1 i ≠ 0 := hw1.symm ▸ one_ne_zero
rcases Finset.exists_ne_zero_of_sum_ne_zero hnz with ⟨i, hifs1, hinz⟩
simp_rw [← Set.indicator_of_mem (Finset.mem_coe.2 hifs1) w1, ha] at hinz
use i, hfs1 hifs1
exact hfs2 (Set.mem_of_indicator_ne_zero hinz)
/-- If a family is affinely independent, the spans of points indexed
by disjoint subsets of the index type are disjoint, if the underlying
ring is nontrivial. -/
theorem AffineIndependent.affineSpan_disjoint_of_disjoint [Nontrivial k] {p : ι → P}
(ha : AffineIndependent k p) {s1 s2 : Set ι} (hd : Disjoint s1 s2) :
Disjoint (affineSpan k (p '' s1) : Set P) (affineSpan k (p '' s2)) := by
refine Set.disjoint_left.2 fun p0 hp0s1 hp0s2 => ?_
obtain ⟨i, hi⟩ := ha.exists_mem_inter_of_exists_mem_inter_affineSpan hp0s1 hp0s2
exact Set.disjoint_iff.1 hd hi
/-- If a family is affinely independent, a point in the family is in
the span of some of the points given by a subset of the index type if
and only if that point's index is in the subset, if the underlying
ring is nontrivial. -/
@[simp]
protected theorem AffineIndependent.mem_affineSpan_iff [Nontrivial k] {p : ι → P}
(ha : AffineIndependent k p) (i : ι) (s : Set ι) : p i ∈ affineSpan k (p '' s) ↔ i ∈ s := by
constructor
· intro hs
have h :=
AffineIndependent.exists_mem_inter_of_exists_mem_inter_affineSpan ha hs
(mem_affineSpan k (Set.mem_image_of_mem _ (Set.mem_singleton _)))
rwa [← Set.nonempty_def, Set.inter_singleton_nonempty] at h
· exact fun h => mem_affineSpan k (Set.mem_image_of_mem p h)
/-- If a family is affinely independent, a point in the family is not
in the affine span of the other points, if the underlying ring is
nontrivial. -/
theorem AffineIndependent.not_mem_affineSpan_diff [Nontrivial k] {p : ι → P}
(ha : AffineIndependent k p) (i : ι) (s : Set ι) : p i ∉ affineSpan k (p '' (s \ {i})) := by
simp [ha]
theorem exists_nontrivial_relation_sum_zero_of_not_affine_ind {t : Finset V}
(h : ¬AffineIndependent k ((↑) : t → V)) :
∃ f : V → k, ∑ e ∈ t, f e • e = 0 ∧ ∑ e ∈ t, f e = 0 ∧ ∃ x ∈ t, f x ≠ 0 := by
classical
rw [affineIndependent_iff_of_fintype] at h
simp only [exists_prop, not_forall] at h
obtain ⟨w, hw, hwt, i, hi⟩ := h
simp only [Finset.weightedVSub_eq_weightedVSubOfPoint_of_sum_eq_zero _ w ((↑) : t → V) hw 0,
vsub_eq_sub, Finset.weightedVSubOfPoint_apply, sub_zero] at hwt
let f : ∀ x : V, x ∈ t → k := fun x hx => w ⟨x, hx⟩
refine ⟨fun x => if hx : x ∈ t then f x hx else (0 : k), ?_, ?_, by use i; simp [f, hi]⟩
on_goal 1 =>
suffices (∑ e ∈ t, dite (e ∈ t) (fun hx => f e hx • e) fun _ => 0) = 0 by
convert this
rename V => x
by_cases hx : x ∈ t <;> simp [hx]
all_goals
simp only [f, Finset.sum_dite_of_true fun _ h => h, Finset.mk_coe, hwt, hw]
variable {s : Finset ι} {w w₁ w₂ : ι → k} {p : ι → V}
/-- Viewing a module as an affine space modelled on itself, we can characterise affine independence
in terms of linear combinations. -/
theorem affineIndependent_iff {ι} {p : ι → V} :
AffineIndependent k p ↔
∀ (s : Finset ι) (w : ι → k), s.sum w = 0 → ∑ e ∈ s, w e • p e = 0 → ∀ e ∈ s, w e = 0 :=
forall₃_congr fun s w hw => by simp [s.weightedVSub_eq_linear_combination hw]
lemma AffineIndependent.eq_zero_of_sum_eq_zero (hp : AffineIndependent k p)
(hw₀ : ∑ i ∈ s, w i = 0) (hw₁ : ∑ i ∈ s, w i • p i = 0) : ∀ i ∈ s, w i = 0 :=
affineIndependent_iff.1 hp _ _ hw₀ hw₁
lemma AffineIndependent.eq_of_sum_eq_sum (hp : AffineIndependent k p)
(hw : ∑ i ∈ s, w₁ i = ∑ i ∈ s, w₂ i) (hwp : ∑ i ∈ s, w₁ i • p i = ∑ i ∈ s, w₂ i • p i) :
∀ i ∈ s, w₁ i = w₂ i := by
refine fun i hi ↦ sub_eq_zero.1 (hp.eq_zero_of_sum_eq_zero (w := w₁ - w₂) ?_ ?_ _ hi) <;>
simpa [sub_mul, sub_smul, sub_eq_zero]
lemma AffineIndependent.eq_zero_of_sum_eq_zero_subtype {s : Finset V}
(hp : AffineIndependent k ((↑) : s → V)) {w : V → k} (hw₀ : ∑ x ∈ s, w x = 0)
(hw₁ : ∑ x ∈ s, w x • x = 0) : ∀ x ∈ s, w x = 0 := by
rw [← sum_attach] at hw₀ hw₁
exact fun x hx ↦ hp.eq_zero_of_sum_eq_zero hw₀ hw₁ ⟨x, hx⟩ (mem_univ _)
lemma AffineIndependent.eq_of_sum_eq_sum_subtype {s : Finset V}
(hp : AffineIndependent k ((↑) : s → V)) {w₁ w₂ : V → k} (hw : ∑ i ∈ s, w₁ i = ∑ i ∈ s, w₂ i)
(hwp : ∑ i ∈ s, w₁ i • i = ∑ i ∈ s, w₂ i • i) : ∀ i ∈ s, w₁ i = w₂ i := by
refine fun i hi => sub_eq_zero.1 (hp.eq_zero_of_sum_eq_zero_subtype (w := w₁ - w₂) ?_ ?_ _ hi) <;>
simpa [sub_mul, sub_smul, sub_eq_zero]
/-- Given an affinely independent family of points, a weighted subtraction lies in the
`vectorSpan` of two points given as affine combinations if and only if it is a weighted
subtraction with weights a multiple of the difference between the weights of the two points. -/
theorem weightedVSub_mem_vectorSpan_pair {p : ι → P} (h : AffineIndependent k p) {w w₁ w₂ : ι → k}
{s : Finset ι} (hw : ∑ i ∈ s, w i = 0) (hw₁ : ∑ i ∈ s, w₁ i = 1)
(hw₂ : ∑ i ∈ s, w₂ i = 1) :
s.weightedVSub p w ∈
vectorSpan k ({s.affineCombination k p w₁, s.affineCombination k p w₂} : Set P) ↔
∃ r : k, ∀ i ∈ s, w i = r * (w₁ i - w₂ i) := by
rw [mem_vectorSpan_pair]
refine ⟨fun h => ?_, fun h => ?_⟩
· rcases h with ⟨r, hr⟩
refine ⟨r, fun i hi => ?_⟩
rw [s.affineCombination_vsub, ← s.weightedVSub_const_smul, ← sub_eq_zero, ← map_sub] at hr
have hw' : (∑ j ∈ s, (r • (w₁ - w₂) - w) j) = 0 := by
simp_rw [Pi.sub_apply, Pi.smul_apply, Pi.sub_apply, smul_sub, Finset.sum_sub_distrib, ←
Finset.smul_sum, hw, hw₁, hw₂, sub_self]
have hr' := h s _ hw' hr i hi
rw [eq_comm, ← sub_eq_zero, ← smul_eq_mul]
exact hr'
· rcases h with ⟨r, hr⟩
refine ⟨r, ?_⟩
let w' i := r * (w₁ i - w₂ i)
change ∀ i ∈ s, w i = w' i at hr
rw [s.weightedVSub_congr hr fun _ _ => rfl, s.affineCombination_vsub, ←
s.weightedVSub_const_smul]
congr
/-- Given an affinely independent family of points, an affine combination lies in the
span of two points given as affine combinations if and only if it is an affine combination
with weights those of one point plus a multiple of the difference between the weights of the
two points. -/
theorem affineCombination_mem_affineSpan_pair {p : ι → P} (h : AffineIndependent k p)
{w w₁ w₂ : ι → k} {s : Finset ι} (_ : ∑ i ∈ s, w i = 1) (hw₁ : ∑ i ∈ s, w₁ i = 1)
(hw₂ : ∑ i ∈ s, w₂ i = 1) :
s.affineCombination k p w ∈ line[k, s.affineCombination k p w₁, s.affineCombination k p w₂] ↔
∃ r : k, ∀ i ∈ s, w i = r * (w₂ i - w₁ i) + w₁ i := by
rw [← vsub_vadd (s.affineCombination k p w) (s.affineCombination k p w₁),
AffineSubspace.vadd_mem_iff_mem_direction _ (left_mem_affineSpan_pair _ _ _),
direction_affineSpan, s.affineCombination_vsub, Set.pair_comm,
weightedVSub_mem_vectorSpan_pair h _ hw₂ hw₁]
· simp only [Pi.sub_apply, sub_eq_iff_eq_add]
· simp_all only [Pi.sub_apply, Finset.sum_sub_distrib, sub_self]
end AffineIndependent
section DivisionRing
variable {k : Type*} {V : Type*} {P : Type*} [DivisionRing k] [AddCommGroup V] [Module k V]
variable [AffineSpace V P] {ι : Type*}
/-- An affinely independent set of points can be extended to such a
set that spans the whole space. -/
theorem exists_subset_affineIndependent_affineSpan_eq_top {s : Set P}
(h : AffineIndependent k (fun p => p : s → P)) :
∃ t : Set P, s ⊆ t ∧ AffineIndependent k (fun p => p : t → P) ∧ affineSpan k t = ⊤ := by
rcases s.eq_empty_or_nonempty with (rfl | ⟨p₁, hp₁⟩)
· have p₁ : P := AddTorsor.nonempty.some
let hsv := Basis.ofVectorSpace k V
have hsvi := hsv.linearIndependent
have hsvt := hsv.span_eq
rw [Basis.coe_ofVectorSpace] at hsvi hsvt
have h0 : ∀ v : V, v ∈ Basis.ofVectorSpaceIndex k V → v ≠ 0 := by
intro v hv
simpa [hsv] using hsv.ne_zero ⟨v, hv⟩
rw [linearIndependent_set_iff_affineIndependent_vadd_union_singleton k h0 p₁] at hsvi
exact
⟨{p₁} ∪ (fun v => v +ᵥ p₁) '' _, Set.empty_subset _, hsvi,
affineSpan_singleton_union_vadd_eq_top_of_span_eq_top p₁ hsvt⟩
· rw [affineIndependent_set_iff_linearIndependent_vsub k hp₁] at h
let bsv := Basis.extend h
have hsvi := bsv.linearIndependent
have hsvt := bsv.span_eq
rw [Basis.coe_extend] at hsvi hsvt
rw [linearIndependent_subtype_iff] at hsvi h
have hsv := h.subset_extend (Set.subset_univ _)
have h0 : ∀ v : V, v ∈ h.extend (Set.subset_univ _) → v ≠ 0 := by
intro v hv
simpa [bsv] using bsv.ne_zero ⟨v, hv⟩
rw [← linearIndependent_subtype_iff,
linearIndependent_set_iff_affineIndependent_vadd_union_singleton k h0 p₁] at hsvi
refine ⟨{p₁} ∪ (fun v => v +ᵥ p₁) '' h.extend (Set.subset_univ _), ?_, ?_⟩
· refine Set.Subset.trans ?_ (Set.union_subset_union_right _ (Set.image_subset _ hsv))
simp [Set.image_image]
· use hsvi
exact affineSpan_singleton_union_vadd_eq_top_of_span_eq_top p₁ hsvt
variable (k V)
theorem exists_affineIndependent (s : Set P) :
∃ t ⊆ s, affineSpan k t = affineSpan k s ∧ AffineIndependent k ((↑) : t → P) := by
rcases s.eq_empty_or_nonempty with (rfl | ⟨p, hp⟩)
· exact ⟨∅, Set.empty_subset ∅, rfl, affineIndependent_of_subsingleton k _⟩
obtain ⟨b, hb₁, hb₂, hb₃⟩ := exists_linearIndependent k ((Equiv.vaddConst p).symm '' s)
have hb₀ : ∀ v : V, v ∈ b → v ≠ 0 := fun v hv => hb₃.ne_zero (⟨v, hv⟩ : b)
rw [linearIndependent_set_iff_affineIndependent_vadd_union_singleton k hb₀ p] at hb₃
refine ⟨{p} ∪ Equiv.vaddConst p '' b, ?_, ?_, hb₃⟩
· apply Set.union_subset (Set.singleton_subset_iff.mpr hp)
rwa [← (Equiv.vaddConst p).subset_symm_image b s]
· rw [Equiv.coe_vaddConst_symm, ← vectorSpan_eq_span_vsub_set_right k hp] at hb₂
apply AffineSubspace.ext_of_direction_eq
· have : Submodule.span k b = Submodule.span k (insert 0 b) := by simp
simp only [direction_affineSpan, ← hb₂, Equiv.coe_vaddConst, Set.singleton_union,
vectorSpan_eq_span_vsub_set_right k (Set.mem_insert p _), this]
congr
change (Equiv.vaddConst p).symm '' insert p (Equiv.vaddConst p '' b) = _
rw [Set.image_insert_eq, ← Set.image_comp]
simp
· use p
simp only [Equiv.coe_vaddConst, Set.singleton_union, Set.mem_inter_iff]
exact ⟨mem_affineSpan k (Set.mem_insert p _), mem_affineSpan k hp⟩
variable {V}
/-- Two different points are affinely independent. -/
theorem affineIndependent_of_ne {p₁ p₂ : P} (h : p₁ ≠ p₂) : AffineIndependent k ![p₁, p₂] := by
rw [affineIndependent_iff_linearIndependent_vsub k ![p₁, p₂] 0]
let i₁ : { x // x ≠ (0 : Fin 2) } := ⟨1, by norm_num⟩
have he' : ∀ i, i = i₁ := by
rintro ⟨i, hi⟩
ext
fin_cases i
· simp at hi
· simp [i₁]
haveI : Unique { x // x ≠ (0 : Fin 2) } := ⟨⟨i₁⟩, he'⟩
apply linearIndependent_unique
rw [he' default]
simpa using h.symm
variable {k}
/-- If all but one point of a family are affinely independent, and that point does not lie in
the affine span of that family, the family is affinely independent. -/
theorem AffineIndependent.affineIndependent_of_not_mem_span {p : ι → P} {i : ι}
(ha : AffineIndependent k fun x : { y // y ≠ i } => p x)
(hi : p i ∉ affineSpan k (p '' { x | x ≠ i })) : AffineIndependent k p := by
classical
intro s w hw hs
let s' : Finset { y // y ≠ i } := s.subtype (· ≠ i)
let p' : { y // y ≠ i } → P := fun x => p x
by_cases his : i ∈ s ∧ w i ≠ 0
· refine False.elim (hi ?_)
let wm : ι → k := -(w i)⁻¹ • w
have hms : s.weightedVSub p wm = (0 : V) := by simp [wm, hs]
have hwm : ∑ i ∈ s, wm i = 0 := by simp [wm, ← Finset.mul_sum, hw]
have hwmi : wm i = -1 := by simp [wm, his.2]
let w' : { y // y ≠ i } → k := fun x => wm x
have hw' : ∑ x ∈ s', w' x = 1 := by
simp_rw [w', s', Finset.sum_subtype_eq_sum_filter]
rw [← s.sum_filter_add_sum_filter_not (· ≠ i)] at hwm
simpa only [not_not, Finset.filter_eq' _ i, if_pos his.1, sum_singleton, hwmi,
add_neg_eq_zero] using hwm
rw [← s.affineCombination_eq_of_weightedVSub_eq_zero_of_eq_neg_one hms his.1 hwmi, ←
| (Subtype.range_coe : _ = { x | x ≠ i }), ← Set.range_comp, ←
s.affineCombination_subtype_eq_filter]
exact affineCombination_mem_affineSpan hw' p'
· rw [not_and_or, Classical.not_not] at his
let w' : { y // y ≠ i } → k := fun x => w x
have hw' : ∑ x ∈ s', w' x = 0 := by
simp_rw [w', s', Finset.sum_subtype_eq_sum_filter]
rw [Finset.sum_filter_of_ne, hw]
rintro x hxs hwx rfl
exact hwx (his.neg_resolve_left hxs)
have hs' : s'.weightedVSub p' w' = (0 : V) := by
simp_rw [w', s', p', Finset.weightedVSub_subtype_eq_filter]
rw [Finset.weightedVSub_filter_of_ne, hs]
rintro x hxs hwx rfl
exact hwx (his.neg_resolve_left hxs)
intro j hj
by_cases hji : j = i
· rw [hji] at hj
exact hji.symm ▸ his.neg_resolve_left hj
· exact ha s' w' hw' hs' ⟨j, hji⟩ (Finset.mem_subtype.2 hj)
/-- If distinct points `p₁` and `p₂` lie in `s` but `p₃` does not, the three points are affinely
independent. -/
theorem affineIndependent_of_ne_of_mem_of_mem_of_not_mem {s : AffineSubspace k P} {p₁ p₂ p₃ : P}
(hp₁p₂ : p₁ ≠ p₂) (hp₁ : p₁ ∈ s) (hp₂ : p₂ ∈ s) (hp₃ : p₃ ∉ s) :
AffineIndependent k ![p₁, p₂, p₃] := by
have ha : AffineIndependent k fun x : { x : Fin 3 // x ≠ 2 } => ![p₁, p₂, p₃] x := by
rw [← affineIndependent_equiv (finSuccAboveEquiv (2 : Fin 3))]
convert affineIndependent_of_ne k hp₁p₂
ext x
fin_cases x <;> rfl
refine ha.affineIndependent_of_not_mem_span ?_
intro h
refine hp₃ ((AffineSubspace.le_def' _ s).1 ?_ p₃ h)
simp_rw [affineSpan_le, Set.image_subset_iff, Set.subset_def, Set.mem_preimage]
intro x
fin_cases x <;> simp +decide [hp₁, hp₂]
/-- If distinct points `p₁` and `p₃` lie in `s` but `p₂` does not, the three points are affinely
independent. -/
theorem affineIndependent_of_ne_of_mem_of_not_mem_of_mem {s : AffineSubspace k P} {p₁ p₂ p₃ : P}
(hp₁p₃ : p₁ ≠ p₃) (hp₁ : p₁ ∈ s) (hp₂ : p₂ ∉ s) (hp₃ : p₃ ∈ s) :
AffineIndependent k ![p₁, p₂, p₃] := by
| Mathlib/LinearAlgebra/AffineSpace/Independent.lean | 653 | 695 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl
-/
import Mathlib.Data.Fintype.Card
import Mathlib.Algebra.Order.BigOperators.Group.Multiset
import Mathlib.Algebra.Order.Group.Nat
import Mathlib.Data.Multiset.OrderedMonoid
import Mathlib.Tactic.Bound.Attribute
import Mathlib.Algebra.BigOperators.Group.Finset.Sigma
import Mathlib.Data.Multiset.Powerset
/-!
# Big operators on a finset in ordered groups
This file contains the results concerning the interaction of multiset big operators with ordered
groups/monoids.
-/
assert_not_exists Ring
open Function
variable {ι α β M N G k R : Type*}
namespace Finset
section OrderedCommMonoid
variable [CommMonoid M] [CommMonoid N] [PartialOrder N] [IsOrderedMonoid N]
/-- Let `{x | p x}` be a subsemigroup of a commutative monoid `M`. Let `f : M → N` be a map
submultiplicative on `{x | p x}`, i.e., `p x → p y → f (x * y) ≤ f x * f y`. Let `g i`, `i ∈ s`, be
a nonempty finite family of elements of `M` such that `∀ i ∈ s, p (g i)`. Then
`f (∏ x ∈ s, g x) ≤ ∏ x ∈ s, f (g x)`. -/
@[to_additive le_sum_nonempty_of_subadditive_on_pred]
theorem le_prod_nonempty_of_submultiplicative_on_pred (f : M → N) (p : M → Prop)
(h_mul : ∀ x y, p x → p y → f (x * y) ≤ f x * f y) (hp_mul : ∀ x y, p x → p y → p (x * y))
(g : ι → M) (s : Finset ι) (hs_nonempty : s.Nonempty) (hs : ∀ i ∈ s, p (g i)) :
f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i) := by
refine le_trans
(Multiset.le_prod_nonempty_of_submultiplicative_on_pred f p h_mul hp_mul _ ?_ ?_) ?_
· simp [hs_nonempty.ne_empty]
· exact Multiset.forall_mem_map_iff.mpr hs
rw [Multiset.map_map]
rfl
/-- Let `{x | p x}` be an additive subsemigroup of an additive commutative monoid `M`. Let
`f : M → N` be a map subadditive on `{x | p x}`, i.e., `p x → p y → f (x + y) ≤ f x + f y`. Let
`g i`, `i ∈ s`, be a nonempty finite family of elements of `M` such that `∀ i ∈ s, p (g i)`. Then
`f (∑ i ∈ s, g i) ≤ ∑ i ∈ s, f (g i)`. -/
add_decl_doc le_sum_nonempty_of_subadditive_on_pred
/-- If `f : M → N` is a submultiplicative function, `f (x * y) ≤ f x * f y` and `g i`, `i ∈ s`, is a
nonempty finite family of elements of `M`, then `f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i)`. -/
@[to_additive le_sum_nonempty_of_subadditive]
theorem le_prod_nonempty_of_submultiplicative (f : M → N) (h_mul : ∀ x y, f (x * y) ≤ f x * f y)
{s : Finset ι} (hs : s.Nonempty) (g : ι → M) : f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i) :=
le_prod_nonempty_of_submultiplicative_on_pred f (fun _ ↦ True) (fun x y _ _ ↦ h_mul x y)
(fun _ _ _ _ ↦ trivial) g s hs fun _ _ ↦ trivial
/-- If `f : M → N` is a subadditive function, `f (x + y) ≤ f x + f y` and `g i`, `i ∈ s`, is a
nonempty finite family of elements of `M`, then `f (∑ i ∈ s, g i) ≤ ∑ i ∈ s, f (g i)`. -/
add_decl_doc le_sum_nonempty_of_subadditive
/-- Let `{x | p x}` be a subsemigroup of a commutative monoid `M`. Let `f : M → N` be a map
such that `f 1 = 1` and `f` is submultiplicative on `{x | p x}`, i.e.,
`p x → p y → f (x * y) ≤ f x * f y`. Let `g i`, `i ∈ s`, be a finite family of elements of `M` such
that `∀ i ∈ s, p (g i)`. Then `f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i)`. -/
@[to_additive le_sum_of_subadditive_on_pred]
theorem le_prod_of_submultiplicative_on_pred (f : M → N) (p : M → Prop) (h_one : f 1 = 1)
(h_mul : ∀ x y, p x → p y → f (x * y) ≤ f x * f y) (hp_mul : ∀ x y, p x → p y → p (x * y))
(g : ι → M) {s : Finset ι} (hs : ∀ i ∈ s, p (g i)) : f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i) := by
rcases eq_empty_or_nonempty s with (rfl | hs_nonempty)
· simp [h_one]
· exact le_prod_nonempty_of_submultiplicative_on_pred f p h_mul hp_mul g s hs_nonempty hs
/-- Let `{x | p x}` be a subsemigroup of a commutative additive monoid `M`. Let `f : M → N` be a map
such that `f 0 = 0` and `f` is subadditive on `{x | p x}`, i.e. `p x → p y → f (x + y) ≤ f x + f y`.
Let `g i`, `i ∈ s`, be a finite family of elements of `M` such that `∀ i ∈ s, p (g i)`. Then
`f (∑ x ∈ s, g x) ≤ ∑ x ∈ s, f (g x)`. -/
add_decl_doc le_sum_of_subadditive_on_pred
/-- If `f : M → N` is a submultiplicative function, `f (x * y) ≤ f x * f y`, `f 1 = 1`, and `g i`,
`i ∈ s`, is a finite family of elements of `M`, then `f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i)`. -/
@[to_additive le_sum_of_subadditive]
theorem le_prod_of_submultiplicative (f : M → N) (h_one : f 1 = 1)
(h_mul : ∀ x y, f (x * y) ≤ f x * f y) (s : Finset ι) (g : ι → M) :
f (∏ i ∈ s, g i) ≤ ∏ i ∈ s, f (g i) := by
refine le_trans (Multiset.le_prod_of_submultiplicative f h_one h_mul _) ?_
rw [Multiset.map_map]
rfl
/-- If `f : M → N` is a subadditive function, `f (x + y) ≤ f x + f y`, `f 0 = 0`, and `g i`,
`i ∈ s`, is a finite family of elements of `M`, then `f (∑ i ∈ s, g i) ≤ ∑ i ∈ s, f (g i)`. -/
add_decl_doc le_sum_of_subadditive
variable {f g : ι → N} {s t : Finset ι}
/-- In an ordered commutative monoid, if each factor `f i` of one finite product is less than or
equal to the corresponding factor `g i` of another finite product, then
`∏ i ∈ s, f i ≤ ∏ i ∈ s, g i`. -/
@[to_additive (attr := gcongr) sum_le_sum]
theorem prod_le_prod' (h : ∀ i ∈ s, f i ≤ g i) : ∏ i ∈ s, f i ≤ ∏ i ∈ s, g i :=
Multiset.prod_map_le_prod_map f g h
attribute [bound] sum_le_sum
/-- In an ordered additive commutative monoid, if each summand `f i` of one finite sum is less than
or equal to the corresponding summand `g i` of another finite sum, then
`∑ i ∈ s, f i ≤ ∑ i ∈ s, g i`. -/
add_decl_doc sum_le_sum
@[to_additive sum_nonneg]
theorem one_le_prod' (h : ∀ i ∈ s, 1 ≤ f i) : 1 ≤ ∏ i ∈ s, f i :=
le_trans (by rw [prod_const_one]) (prod_le_prod' h)
@[to_additive Finset.sum_nonneg']
theorem one_le_prod'' (h : ∀ i : ι, 1 ≤ f i) : 1 ≤ ∏ i ∈ s, f i :=
Finset.one_le_prod' fun i _ ↦ h i
@[to_additive sum_nonpos]
theorem prod_le_one' (h : ∀ i ∈ s, f i ≤ 1) : ∏ i ∈ s, f i ≤ 1 :=
(prod_le_prod' h).trans_eq (by rw [prod_const_one])
@[to_additive (attr := gcongr) sum_le_sum_of_subset_of_nonneg]
theorem prod_le_prod_of_subset_of_one_le' (h : s ⊆ t) (hf : ∀ i ∈ t, i ∉ s → 1 ≤ f i) :
∏ i ∈ s, f i ≤ ∏ i ∈ t, f i := by
classical calc
∏ i ∈ s, f i ≤ (∏ i ∈ t \ s, f i) * ∏ i ∈ s, f i :=
le_mul_of_one_le_left' <| one_le_prod' <| by simpa only [mem_sdiff, and_imp]
_ = ∏ i ∈ t \ s ∪ s, f i := (prod_union sdiff_disjoint).symm
_ = ∏ i ∈ t, f i := by rw [sdiff_union_of_subset h]
@[to_additive sum_mono_set_of_nonneg]
theorem prod_mono_set_of_one_le' (hf : ∀ x, 1 ≤ f x) : Monotone fun s ↦ ∏ x ∈ s, f x :=
fun _ _ hst ↦ prod_le_prod_of_subset_of_one_le' hst fun x _ _ ↦ hf x
@[to_additive sum_le_univ_sum_of_nonneg]
theorem prod_le_univ_prod_of_one_le' [Fintype ι] {s : Finset ι} (w : ∀ x, 1 ≤ f x) :
∏ x ∈ s, f x ≤ ∏ x, f x :=
prod_le_prod_of_subset_of_one_le' (subset_univ s) fun a _ _ ↦ w a
@[to_additive sum_eq_zero_iff_of_nonneg]
theorem prod_eq_one_iff_of_one_le' :
(∀ i ∈ s, 1 ≤ f i) → ((∏ i ∈ s, f i) = 1 ↔ ∀ i ∈ s, f i = 1) := by
classical
refine Finset.induction_on s
(fun _ ↦ ⟨fun _ _ h ↦ False.elim (Finset.not_mem_empty _ h), fun _ ↦ rfl⟩) ?_
intro a s ha ih H
have : ∀ i ∈ s, 1 ≤ f i := fun _ ↦ H _ ∘ mem_insert_of_mem
rw [prod_insert ha, mul_eq_one_iff_of_one_le (H _ <| mem_insert_self _ _) (one_le_prod' this),
forall_mem_insert, ih this]
@[to_additive sum_eq_zero_iff_of_nonpos]
theorem prod_eq_one_iff_of_le_one' :
(∀ i ∈ s, f i ≤ 1) → ((∏ i ∈ s, f i) = 1 ↔ ∀ i ∈ s, f i = 1) :=
prod_eq_one_iff_of_one_le' (N := Nᵒᵈ)
@[to_additive single_le_sum]
theorem single_le_prod' (hf : ∀ i ∈ s, 1 ≤ f i) {a} (h : a ∈ s) : f a ≤ ∏ x ∈ s, f x :=
calc
f a = ∏ i ∈ {a}, f i := (prod_singleton _ _).symm
_ ≤ ∏ i ∈ s, f i :=
prod_le_prod_of_subset_of_one_le' (singleton_subset_iff.2 h) fun i hi _ ↦ hf i hi
@[to_additive]
lemma mul_le_prod {i j : ι} (hf : ∀ i ∈ s, 1 ≤ f i) (hi : i ∈ s) (hj : j ∈ s) (hne : i ≠ j) :
f i * f j ≤ ∏ k ∈ s, f k :=
calc
f i * f j = ∏ k ∈ .cons i {j} (by simpa), f k := by rw [prod_cons, prod_singleton]
_ ≤ ∏ k ∈ s, f k := by
refine prod_le_prod_of_subset_of_one_le' ?_ fun k hk _ ↦ hf k hk
simp [cons_subset, *]
@[to_additive sum_le_card_nsmul]
theorem prod_le_pow_card (s : Finset ι) (f : ι → N) (n : N) (h : ∀ x ∈ s, f x ≤ n) :
s.prod f ≤ n ^ #s := by
refine (Multiset.prod_le_pow_card (s.val.map f) n ?_).trans ?_
· simpa using h
· simp
@[to_additive card_nsmul_le_sum]
theorem pow_card_le_prod (s : Finset ι) (f : ι → N) (n : N) (h : ∀ x ∈ s, n ≤ f x) :
n ^ #s ≤ s.prod f := Finset.prod_le_pow_card (N := Nᵒᵈ) _ _ _ h
theorem card_biUnion_le_card_mul [DecidableEq β] (s : Finset ι) (f : ι → Finset β) (n : ℕ)
(h : ∀ a ∈ s, #(f a) ≤ n) : #(s.biUnion f) ≤ #s * n :=
card_biUnion_le.trans <| sum_le_card_nsmul _ _ _ h
variable {ι' : Type*} [DecidableEq ι']
@[to_additive sum_fiberwise_le_sum_of_sum_fiber_nonneg]
theorem prod_fiberwise_le_prod_of_one_le_prod_fiber' {t : Finset ι'} {g : ι → ι'} {f : ι → N}
(h : ∀ y ∉ t, (1 : N) ≤ ∏ x ∈ s with g x = y, f x) :
(∏ y ∈ t, ∏ x ∈ s with g x = y, f x) ≤ ∏ x ∈ s, f x :=
calc
(∏ y ∈ t, ∏ x ∈ s with g x = y, f x) ≤
∏ y ∈ t ∪ s.image g, ∏ x ∈ s with g x = y, f x :=
prod_le_prod_of_subset_of_one_le' subset_union_left fun y _ ↦ h y
_ = ∏ x ∈ s, f x :=
prod_fiberwise_of_maps_to (fun _ hx ↦ mem_union.2 <| Or.inr <| mem_image_of_mem _ hx) _
@[to_additive sum_le_sum_fiberwise_of_sum_fiber_nonpos]
theorem prod_le_prod_fiberwise_of_prod_fiber_le_one' {t : Finset ι'} {g : ι → ι'} {f : ι → N}
(h : ∀ y ∉ t, ∏ x ∈ s with g x = y, f x ≤ 1) :
∏ x ∈ s, f x ≤ ∏ y ∈ t, ∏ x ∈ s with g x = y, f x :=
prod_fiberwise_le_prod_of_one_le_prod_fiber' (N := Nᵒᵈ) h
@[to_additive]
lemma prod_image_le_of_one_le
{g : ι → ι'} {f : ι' → N} (hf : ∀ u ∈ s.image g, 1 ≤ f u) :
∏ u ∈ s.image g, f u ≤ ∏ u ∈ s, f (g u) := by
rw [prod_comp f g]
refine prod_le_prod' fun a hag ↦ ?_
obtain ⟨i, hi, hig⟩ := Finset.mem_image.mp hag
apply le_self_pow (hf a hag)
rw [← Nat.pos_iff_ne_zero, card_pos]
exact ⟨i, mem_filter.mpr ⟨hi, hig⟩⟩
end OrderedCommMonoid
@[to_additive]
lemma max_prod_le [CommMonoid M] [LinearOrder M] [IsOrderedMonoid M] {f g : ι → M} {s : Finset ι} :
max (s.prod f) (s.prod g) ≤ s.prod (fun i ↦ max (f i) (g i)) :=
Multiset.max_prod_le
@[to_additive]
lemma prod_min_le [CommMonoid M] [LinearOrder M] [IsOrderedMonoid M] {f g : ι → M} {s : Finset ι} :
s.prod (fun i ↦ min (f i) (g i)) ≤ min (s.prod f) (s.prod g) :=
Multiset.prod_min_le
theorem abs_sum_le_sum_abs {G : Type*} [AddCommGroup G] [LinearOrder G] [IsOrderedAddMonoid G]
(f : ι → G) (s : Finset ι) :
|∑ i ∈ s, f i| ≤ ∑ i ∈ s, |f i| := le_sum_of_subadditive _ abs_zero abs_add s f
theorem abs_sum_of_nonneg {G : Type*} [AddCommGroup G] [LinearOrder G] [IsOrderedAddMonoid G]
{f : ι → G} {s : Finset ι}
(hf : ∀ i ∈ s, 0 ≤ f i) : |∑ i ∈ s, f i| = ∑ i ∈ s, f i := by
rw [abs_of_nonneg (Finset.sum_nonneg hf)]
theorem abs_sum_of_nonneg' {G : Type*} [AddCommGroup G] [LinearOrder G] [IsOrderedAddMonoid G]
{f : ι → G} {s : Finset ι}
(hf : ∀ i, 0 ≤ f i) : |∑ i ∈ s, f i| = ∑ i ∈ s, f i := by
rw [abs_of_nonneg (Finset.sum_nonneg' hf)]
section CommMonoid
variable [CommMonoid α] [LE α] [MulLeftMono α] {s : Finset ι} {f : ι → α}
@[to_additive (attr := simp)]
lemma mulLECancellable_prod :
MulLECancellable (∏ i ∈ s, f i) ↔ ∀ ⦃i⦄, i ∈ s → MulLECancellable (f i) := by
induction' s using Finset.cons_induction with i s hi ih <;> simp [*]
end CommMonoid
section Pigeonhole
variable [DecidableEq β]
theorem card_le_mul_card_image_of_maps_to {f : α → β} {s : Finset α} {t : Finset β}
(Hf : ∀ a ∈ s, f a ∈ t) (n : ℕ) (hn : ∀ b ∈ t, #{a ∈ s | f a = b} ≤ n) : #s ≤ n * #t :=
calc
#s = ∑ b ∈ t, #{a ∈ s | f a = b} := card_eq_sum_card_fiberwise Hf
_ ≤ ∑ _b ∈ t, n := sum_le_sum hn
_ = _ := by simp [mul_comm]
theorem card_le_mul_card_image {f : α → β} (s : Finset α) (n : ℕ)
(hn : ∀ b ∈ s.image f, #{a ∈ s | f a = b} ≤ n) : #s ≤ n * #(s.image f) :=
card_le_mul_card_image_of_maps_to (fun _ ↦ mem_image_of_mem _) n hn
theorem mul_card_image_le_card_of_maps_to {f : α → β} {s : Finset α} {t : Finset β}
(Hf : ∀ a ∈ s, f a ∈ t) (n : ℕ) (hn : ∀ b ∈ t, n ≤ #{a ∈ s | f a = b}) :
n * #t ≤ #s :=
calc
n * #t = ∑ _a ∈ t, n := by simp [mul_comm]
_ ≤ ∑ b ∈ t, #{a ∈ s | f a = b} := sum_le_sum hn
_ = #s := by rw [← card_eq_sum_card_fiberwise Hf]
theorem mul_card_image_le_card {f : α → β} (s : Finset α) (n : ℕ)
(hn : ∀ b ∈ s.image f, n ≤ #{a ∈ s | f a = b}) : n * #(s.image f) ≤ #s :=
mul_card_image_le_card_of_maps_to (fun _ ↦ mem_image_of_mem _) n hn
end Pigeonhole
section DoubleCounting
variable [DecidableEq α] {s : Finset α} {B : Finset (Finset α)} {n : ℕ}
/-- If every element belongs to at most `n` Finsets, then the sum of their sizes is at most `n`
times how many they are. -/
theorem sum_card_inter_le (h : ∀ a ∈ s, #{b ∈ B | a ∈ b} ≤ n) : (∑ t ∈ B, #(s ∩ t)) ≤ #s * n := by
refine le_trans ?_ (s.sum_le_card_nsmul _ _ h)
simp_rw [← filter_mem_eq_inter, card_eq_sum_ones, sum_filter]
exact sum_comm.le
/-- If every element belongs to at most `n` Finsets, then the sum of their sizes is at most `n`
times how many they are. -/
lemma sum_card_le [Fintype α] (h : ∀ a, #{b ∈ B | a ∈ b} ≤ n) : ∑ s ∈ B, #s ≤ Fintype.card α * n :=
calc
∑ s ∈ B, #s = ∑ s ∈ B, #(univ ∩ s) := by simp_rw [univ_inter]
_ ≤ Fintype.card α * n := sum_card_inter_le fun a _ ↦ h a
/-- If every element belongs to at least `n` Finsets, then the sum of their sizes is at least `n`
times how many they are. -/
theorem le_sum_card_inter (h : ∀ a ∈ s, n ≤ #{b ∈ B | a ∈ b}) : #s * n ≤ ∑ t ∈ B, #(s ∩ t) := by
apply (s.card_nsmul_le_sum _ _ h).trans
simp_rw [← filter_mem_eq_inter, card_eq_sum_ones, sum_filter]
exact sum_comm.le
/-- If every element belongs to at least `n` Finsets, then the sum of their sizes is at least `n`
times how many they are. -/
theorem le_sum_card [Fintype α] (h : ∀ a, n ≤ #{b ∈ B | a ∈ b}) :
Fintype.card α * n ≤ ∑ s ∈ B, #s :=
calc
Fintype.card α * n ≤ ∑ s ∈ B, #(univ ∩ s) := le_sum_card_inter fun a _ ↦ h a
_ = ∑ s ∈ B, #s := by simp_rw [univ_inter]
/-- If every element belongs to exactly `n` Finsets, then the sum of their sizes is `n` times how
many they are. -/
theorem sum_card_inter (h : ∀ a ∈ s, #{b ∈ B | a ∈ b} = n) :
(∑ t ∈ B, #(s ∩ t)) = #s * n :=
(sum_card_inter_le fun a ha ↦ (h a ha).le).antisymm (le_sum_card_inter fun a ha ↦ (h a ha).ge)
/-- If every element belongs to exactly `n` Finsets, then the sum of their sizes is `n` times how
many they are. -/
theorem sum_card [Fintype α] (h : ∀ a, #{b ∈ B | a ∈ b} = n) :
∑ s ∈ B, #s = Fintype.card α * n := by
simp_rw [Fintype.card, ← sum_card_inter fun a _ ↦ h a, univ_inter]
theorem card_le_card_biUnion {s : Finset ι} {f : ι → Finset α} (hs : (s : Set ι).PairwiseDisjoint f)
(hf : ∀ i ∈ s, (f i).Nonempty) : #s ≤ #(s.biUnion f) := by
rw [card_biUnion hs, card_eq_sum_ones]
exact sum_le_sum fun i hi ↦ (hf i hi).card_pos
theorem card_le_card_biUnion_add_card_fiber {s : Finset ι} {f : ι → Finset α}
(hs : (s : Set ι).PairwiseDisjoint f) : #s ≤ #(s.biUnion f) + #{i ∈ s | f i = ∅} := by
rw [← Finset.filter_card_add_filter_neg_card_eq_card fun i ↦ f i = ∅, add_comm]
exact
add_le_add_right
((card_le_card_biUnion (hs.subset <| filter_subset _ _) fun i hi ↦
nonempty_of_ne_empty <| (mem_filter.1 hi).2).trans <|
card_le_card <| biUnion_subset_biUnion_of_subset_left _ <| filter_subset _ _)
_
theorem card_le_card_biUnion_add_one {s : Finset ι} {f : ι → Finset α} (hf : Injective f)
(hs : (s : Set ι).PairwiseDisjoint f) : #s ≤ #(s.biUnion f) + 1 :=
(card_le_card_biUnion_add_card_fiber hs).trans <|
add_le_add_left
(card_le_one.2 fun _ hi _ hj ↦ hf <| (mem_filter.1 hi).2.trans (mem_filter.1 hj).2.symm) _
end DoubleCounting
section CanonicallyOrderedMul
variable [CommMonoid M] [PartialOrder M] [IsOrderedMonoid M] [CanonicallyOrderedMul M]
{f : ι → M} {s t : Finset ι}
/-- In a canonically-ordered monoid, a product bounds each of its terms.
See also `Finset.single_le_prod'`. -/
@[to_additive "In a canonically-ordered additive monoid, a sum bounds each of its terms.
See also `Finset.single_le_sum`."]
lemma _root_.CanonicallyOrderedCommMonoid.single_le_prod {i : ι} (hi : i ∈ s) :
f i ≤ ∏ j ∈ s, f j :=
single_le_prod' (fun _ _ ↦ one_le _) hi
@[to_additive sum_le_sum_of_subset]
theorem prod_le_prod_of_subset' (h : s ⊆ t) : ∏ x ∈ s, f x ≤ ∏ x ∈ t, f x :=
prod_le_prod_of_subset_of_one_le' h fun _ _ _ ↦ one_le _
@[to_additive sum_mono_set]
theorem prod_mono_set' (f : ι → M) : Monotone fun s ↦ ∏ x ∈ s, f x := fun _ _ hs ↦
prod_le_prod_of_subset' hs
@[to_additive sum_le_sum_of_ne_zero]
theorem prod_le_prod_of_ne_one' (h : ∀ x ∈ s, f x ≠ 1 → x ∈ t) :
∏ x ∈ s, f x ≤ ∏ x ∈ t, f x := by
classical calc
∏ x ∈ s, f x = (∏ x ∈ s with f x = 1, f x) * ∏ x ∈ s with f x ≠ 1, f x := by
rw [← prod_union, filter_union_filter_neg_eq]
exact disjoint_filter.2 fun _ _ h n_h ↦ n_h h
_ ≤ ∏ x ∈ t, f x :=
mul_le_of_le_one_of_le
(prod_le_one' <| by simp only [mem_filter, and_imp]; exact fun _ _ ↦ le_of_eq)
(prod_le_prod_of_subset' <| by simpa only [subset_iff, mem_filter, and_imp] )
end CanonicallyOrderedMul
section OrderedCancelCommMonoid
variable [CommMonoid M] [PartialOrder M] [IsOrderedCancelMonoid M] {f g : ι → M} {s t : Finset ι}
@[to_additive sum_lt_sum]
theorem prod_lt_prod' (hle : ∀ i ∈ s, f i ≤ g i) (hlt : ∃ i ∈ s, f i < g i) :
∏ i ∈ s, f i < ∏ i ∈ s, g i :=
Multiset.prod_lt_prod' hle hlt
/-- In an ordered commutative monoid, if each factor `f i` of one nontrivial finite product is
strictly less than the corresponding factor `g i` of another nontrivial finite product, then
`s.prod f < s.prod g`. -/
@[to_additive (attr := gcongr) sum_lt_sum_of_nonempty]
theorem prod_lt_prod_of_nonempty' (hs : s.Nonempty) (hlt : ∀ i ∈ s, f i < g i) :
∏ i ∈ s, f i < ∏ i ∈ s, g i :=
Multiset.prod_lt_prod_of_nonempty' (by aesop) hlt
/-- In an ordered additive commutative monoid, if each summand `f i` of one nontrivial finite sum is
strictly less than the corresponding summand `g i` of another nontrivial finite sum, then
`s.sum f < s.sum g`. -/
add_decl_doc sum_lt_sum_of_nonempty
@[to_additive sum_lt_sum_of_subset]
theorem prod_lt_prod_of_subset' (h : s ⊆ t) {i : ι} (ht : i ∈ t) (hs : i ∉ s) (hlt : 1 < f i)
(hle : ∀ j ∈ t, j ∉ s → 1 ≤ f j) : ∏ j ∈ s, f j < ∏ j ∈ t, f j := by
classical calc
∏ j ∈ s, f j < ∏ j ∈ insert i s, f j := by
rw [prod_insert hs]
exact lt_mul_of_one_lt_left' (∏ j ∈ s, f j) hlt
_ ≤ ∏ j ∈ t, f j := by
apply prod_le_prod_of_subset_of_one_le'
· simp [Finset.insert_subset_iff, h, ht]
· intro x hx h'x
simp only [mem_insert, not_or] at h'x
exact hle x hx h'x.2
@[to_additive single_lt_sum]
theorem single_lt_prod' {i j : ι} (hij : j ≠ i) (hi : i ∈ s) (hj : j ∈ s) (hlt : 1 < f j)
(hle : ∀ k ∈ s, k ≠ i → 1 ≤ f k) : f i < ∏ k ∈ s, f k :=
calc
f i = ∏ k ∈ {i}, f k := by rw [prod_singleton]
_ < ∏ k ∈ s, f k :=
prod_lt_prod_of_subset' (singleton_subset_iff.2 hi) hj (mt mem_singleton.1 hij) hlt
fun k hks hki ↦ hle k hks (mt mem_singleton.2 hki)
@[to_additive sum_pos]
theorem one_lt_prod (h : ∀ i ∈ s, 1 < f i) (hs : s.Nonempty) : 1 < ∏ i ∈ s, f i :=
lt_of_le_of_lt (by rw [prod_const_one]) <| prod_lt_prod_of_nonempty' hs h
@[to_additive]
theorem prod_lt_one (h : ∀ i ∈ s, f i < 1) (hs : s.Nonempty) : ∏ i ∈ s, f i < 1 :=
(prod_lt_prod_of_nonempty' hs h).trans_le (by rw [prod_const_one])
@[to_additive sum_pos']
theorem one_lt_prod' (h : ∀ i ∈ s, 1 ≤ f i) (hs : ∃ i ∈ s, 1 < f i) : 1 < ∏ i ∈ s, f i :=
prod_const_one.symm.trans_lt <| prod_lt_prod' h hs
@[to_additive]
theorem prod_lt_one' (h : ∀ i ∈ s, f i ≤ 1) (hs : ∃ i ∈ s, f i < 1) : ∏ i ∈ s, f i < 1 :=
prod_const_one.le.trans_lt' <| prod_lt_prod' h hs
@[to_additive]
theorem prod_eq_prod_iff_of_le {f g : ι → M} (h : ∀ i ∈ s, f i ≤ g i) :
((∏ i ∈ s, f i) = ∏ i ∈ s, g i) ↔ ∀ i ∈ s, f i = g i := by
classical
revert h
refine Finset.induction_on s (fun _ ↦ ⟨fun _ _ h ↦ False.elim (Finset.not_mem_empty _ h),
fun _ ↦ rfl⟩) fun a s ha ih H ↦ ?_
specialize ih fun i ↦ H i ∘ Finset.mem_insert_of_mem
rw [Finset.prod_insert ha, Finset.prod_insert ha, Finset.forall_mem_insert, ← ih]
exact
mul_eq_mul_iff_eq_and_eq (H a (s.mem_insert_self a))
(Finset.prod_le_prod' fun i ↦ H i ∘ Finset.mem_insert_of_mem)
variable [DecidableEq ι]
@[to_additive] lemma prod_sdiff_le_prod_sdiff :
∏ i ∈ s \ t, f i ≤ ∏ i ∈ t \ s, f i ↔ ∏ i ∈ s, f i ≤ ∏ i ∈ t, f i := by
rw [← mul_le_mul_iff_right, ← prod_union (disjoint_sdiff_inter _ _), sdiff_union_inter,
← prod_union, inter_comm, sdiff_union_inter]
simpa only [inter_comm] using disjoint_sdiff_inter t s
@[to_additive] lemma prod_sdiff_lt_prod_sdiff :
∏ i ∈ s \ t, f i < ∏ i ∈ t \ s, f i ↔ ∏ i ∈ s, f i < ∏ i ∈ t, f i := by
rw [← mul_lt_mul_iff_right, ← prod_union (disjoint_sdiff_inter _ _), sdiff_union_inter,
← prod_union, inter_comm, sdiff_union_inter]
simpa only [inter_comm] using disjoint_sdiff_inter t s
end OrderedCancelCommMonoid
section LinearOrderedCancelCommMonoid
variable [CommMonoid M] [LinearOrder M] [IsOrderedCancelMonoid M] {f g : ι → M} {s t : Finset ι}
@[to_additive exists_lt_of_sum_lt]
theorem exists_lt_of_prod_lt' (Hlt : ∏ i ∈ s, f i < ∏ i ∈ s, g i) : ∃ i ∈ s, f i < g i := by
contrapose! Hlt with Hle
exact prod_le_prod' Hle
@[to_additive exists_le_of_sum_le]
theorem exists_le_of_prod_le' (hs : s.Nonempty) (Hle : ∏ i ∈ s, f i ≤ ∏ i ∈ s, g i) :
∃ i ∈ s, f i ≤ g i := by
contrapose! Hle with Hlt
exact prod_lt_prod_of_nonempty' hs Hlt
@[to_additive exists_pos_of_sum_zero_of_exists_nonzero]
theorem exists_one_lt_of_prod_one_of_exists_ne_one' (f : ι → M) (h₁ : ∏ i ∈ s, f i = 1)
(h₂ : ∃ i ∈ s, f i ≠ 1) : ∃ i ∈ s, 1 < f i := by
contrapose! h₁
obtain ⟨i, m, i_ne⟩ : ∃ i ∈ s, f i ≠ 1 := h₂
apply ne_of_lt
calc
∏ j ∈ s, f j < ∏ j ∈ s, 1 := prod_lt_prod' h₁ ⟨i, m, (h₁ i m).lt_of_ne i_ne⟩
_ = 1 := prod_const_one
end LinearOrderedCancelCommMonoid
end Finset
namespace Fintype
section OrderedCommMonoid
variable [Fintype ι] [CommMonoid M] [PartialOrder M] [IsOrderedMonoid M] {f : ι → M}
@[to_additive (attr := mono) sum_mono]
theorem prod_mono' : Monotone fun f : ι → M ↦ ∏ i, f i := fun _ _ hfg ↦
Finset.prod_le_prod' fun x _ ↦ hfg x
@[to_additive sum_nonneg]
lemma one_le_prod (hf : 1 ≤ f) : 1 ≤ ∏ i, f i := Finset.one_le_prod' fun _ _ ↦ hf _
@[to_additive] lemma prod_le_one (hf : f ≤ 1) : ∏ i, f i ≤ 1 := Finset.prod_le_one' fun _ _ ↦ hf _
@[to_additive]
lemma prod_eq_one_iff_of_one_le (hf : 1 ≤ f) : ∏ i, f i = 1 ↔ f = 1 :=
(Finset.prod_eq_one_iff_of_one_le' fun i _ ↦ hf i).trans <| by simp [funext_iff]
@[to_additive]
lemma prod_eq_one_iff_of_le_one (hf : f ≤ 1) : ∏ i, f i = 1 ↔ f = 1 :=
(Finset.prod_eq_one_iff_of_le_one' fun i _ ↦ hf i).trans <| by simp [funext_iff]
|
end OrderedCommMonoid
section OrderedCancelCommMonoid
variable [Fintype ι] [CommMonoid M] [PartialOrder M] [IsOrderedCancelMonoid M] {f : ι → M}
@[to_additive sum_strictMono]
theorem prod_strictMono' : StrictMono fun f : ι → M ↦ ∏ x, f x :=
fun _ _ hfg ↦
let ⟨hle, i, hlt⟩ := Pi.lt_def.mp hfg
Finset.prod_lt_prod' (fun i _ ↦ hle i) ⟨i, Finset.mem_univ i, hlt⟩
| Mathlib/Algebra/Order/BigOperators/Group/Finset.lean | 531 | 541 |
/-
Copyright (c) 2024 David Loeffler. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: David Loeffler
-/
import Mathlib.NumberTheory.LSeries.AbstractFuncEq
import Mathlib.NumberTheory.ModularForms.JacobiTheta.Bounds
import Mathlib.Analysis.SpecialFunctions.Gamma.Deligne
import Mathlib.NumberTheory.LSeries.MellinEqDirichlet
import Mathlib.NumberTheory.LSeries.Basic
import Mathlib.Analysis.Complex.RemovableSingularity
/-!
# Even Hurwitz zeta functions
In this file we study the functions on `ℂ` which are the meromorphic continuation of the following
series (convergent for `1 < re s`), where `a ∈ ℝ` is a parameter:
`hurwitzZetaEven a s = 1 / 2 * ∑' n : ℤ, 1 / |n + a| ^ s`
and
`cosZeta a s = ∑' n : ℕ, cos (2 * π * a * n) / |n| ^ s`.
Note that the term for `n = -a` in the first sum is omitted if `a` is an integer, and the term for
`n = 0` is omitted in the second sum (always).
Of course, we cannot *define* these functions by the above formulae (since existence of the
meromorphic continuation is not at all obvious); we in fact construct them as Mellin transforms of
various versions of the Jacobi theta function.
We also define completed versions of these functions with nicer functional equations (satisfying
`completedHurwitzZetaEven a s = Gammaℝ s * hurwitzZetaEven a s`, and similarly for `cosZeta`); and
modified versions with a subscript `0`, which are entire functions differing from the above by
multiples of `1 / s` and `1 / (1 - s)`.
## Main definitions and theorems
* `hurwitzZetaEven` and `cosZeta`: the zeta functions
* `completedHurwitzZetaEven` and `completedCosZeta`: completed variants
* `differentiableAt_hurwitzZetaEven` and `differentiableAt_cosZeta`:
differentiability away from `s = 1`
* `completedHurwitzZetaEven_one_sub`: the functional equation
`completedHurwitzZetaEven a (1 - s) = completedCosZeta a s`
* `hasSum_int_hurwitzZetaEven` and `hasSum_nat_cosZeta`: relation between the zeta functions and
the corresponding Dirichlet series for `1 < re s`.
-/
noncomputable section
open Complex Filter Topology Asymptotics Real Set MeasureTheory
namespace HurwitzZeta
section kernel_defs
/-!
## Definitions and elementary properties of kernels
-/
/-- Even Hurwitz zeta kernel (function whose Mellin transform will be the even part of the
completed Hurwit zeta function). See `evenKernel_def` for the defining formula, and
`hasSum_int_evenKernel` for an expression as a sum over `ℤ`. -/
@[irreducible] def evenKernel (a : UnitAddCircle) (x : ℝ) : ℝ :=
(show Function.Periodic
(fun ξ : ℝ ↦ rexp (-π * ξ ^ 2 * x) * re (jacobiTheta₂ (ξ * I * x) (I * x))) 1 by
intro ξ
simp only [ofReal_add, ofReal_one, add_mul, one_mul, jacobiTheta₂_add_left']
have : cexp (-↑π * I * ((I * ↑x) + 2 * (↑ξ * I * ↑x))) = rexp (π * (x + 2 * ξ * x)) := by
ring_nf
simp [I_sq]
rw [this, re_ofReal_mul, ← mul_assoc, ← Real.exp_add]
congr
ring).lift a
lemma evenKernel_def (a x : ℝ) :
↑(evenKernel ↑a x) = cexp (-π * a ^ 2 * x) * jacobiTheta₂ (a * I * x) (I * x) := by
simp [evenKernel, re_eq_add_conj, jacobiTheta₂_conj, ← mul_two,
mul_div_cancel_right₀ _ (two_ne_zero' ℂ)]
/-- For `x ≤ 0` the defining sum diverges, so the kernel is 0. -/
lemma evenKernel_undef (a : UnitAddCircle) {x : ℝ} (hx : x ≤ 0) : evenKernel a x = 0 := by
induction a using QuotientAddGroup.induction_on with
| H a' => simp [← ofReal_inj, evenKernel_def, jacobiTheta₂_undef _ (by simpa : (I * ↑x).im ≤ 0)]
/-- Cosine Hurwitz zeta kernel. See `cosKernel_def` for the defining formula, and
`hasSum_int_cosKernel` for expression as a sum. -/
@[irreducible] def cosKernel (a : UnitAddCircle) (x : ℝ) : ℝ :=
(show Function.Periodic (fun ξ : ℝ ↦ re (jacobiTheta₂ ξ (I * x))) 1 by
intro ξ; simp [jacobiTheta₂_add_left]).lift a
lemma cosKernel_def (a x : ℝ) : ↑(cosKernel ↑a x) = jacobiTheta₂ a (I * x) := by
simp [cosKernel, re_eq_add_conj, jacobiTheta₂_conj, ← mul_two,
mul_div_cancel_right₀ _ (two_ne_zero' ℂ)]
lemma cosKernel_undef (a : UnitAddCircle) {x : ℝ} (hx : x ≤ 0) : cosKernel a x = 0 := by
induction a using QuotientAddGroup.induction_on with
| H => simp [← ofReal_inj, cosKernel_def, jacobiTheta₂_undef _ (by simpa : (I * ↑x).im ≤ 0)]
/-- For `a = 0`, both kernels agree. -/
lemma evenKernel_eq_cosKernel_of_zero : evenKernel 0 = cosKernel 0 := by
ext1 x
simp [← QuotientAddGroup.mk_zero, ← ofReal_inj, evenKernel_def, cosKernel_def]
@[simp]
lemma evenKernel_neg (a : UnitAddCircle) (x : ℝ) : evenKernel (-a) x = evenKernel a x := by
induction a using QuotientAddGroup.induction_on with
| H => simp [← QuotientAddGroup.mk_neg, ← ofReal_inj, evenKernel_def, jacobiTheta₂_neg_left]
@[simp]
lemma cosKernel_neg (a : UnitAddCircle) (x : ℝ) : cosKernel (-a) x = cosKernel a x := by
induction a using QuotientAddGroup.induction_on with
| H => simp [← QuotientAddGroup.mk_neg, ← ofReal_inj, cosKernel_def]
lemma continuousOn_evenKernel (a : UnitAddCircle) : ContinuousOn (evenKernel a) (Ioi 0) := by
induction a using QuotientAddGroup.induction_on with | H a' =>
apply continuous_re.comp_continuousOn (f := fun x ↦ (evenKernel a' x : ℂ))
simp only [evenKernel_def]
refine continuousOn_of_forall_continuousAt (fun x hx ↦ .mul (by fun_prop) ?_)
exact (continuousAt_jacobiTheta₂ (a' * I * x) <| by simpa).comp
(f := fun u : ℝ ↦ (a' * I * u, I * u)) (by fun_prop)
lemma continuousOn_cosKernel (a : UnitAddCircle) : ContinuousOn (cosKernel a) (Ioi 0) := by
induction a using QuotientAddGroup.induction_on with | H a' =>
apply continuous_re.comp_continuousOn (f := fun x ↦ (cosKernel a' x : ℂ))
simp only [cosKernel_def]
refine continuousOn_of_forall_continuousAt (fun x hx ↦ ?_)
exact (continuousAt_jacobiTheta₂ a' <| by simpa).comp
(f := fun u : ℝ ↦ ((a' : ℂ), I * u)) (by fun_prop)
lemma evenKernel_functional_equation (a : UnitAddCircle) (x : ℝ) :
evenKernel a x = 1 / x ^ (1 / 2 : ℝ) * cosKernel a (1 / x) := by
rcases le_or_lt x 0 with hx | hx
· rw [evenKernel_undef _ hx, cosKernel_undef, mul_zero]
exact div_nonpos_of_nonneg_of_nonpos zero_le_one hx
induction a using QuotientAddGroup.induction_on with | H a =>
rw [← ofReal_inj, ofReal_mul, evenKernel_def, cosKernel_def, jacobiTheta₂_functional_equation]
have h1 : I * ↑(1 / x) = -1 / (I * x) := by
push_cast
rw [← div_div, mul_one_div, div_I, neg_one_mul, neg_neg]
have hx' : I * x ≠ 0 := mul_ne_zero I_ne_zero (ofReal_ne_zero.mpr hx.ne')
have h2 : a * I * x / (I * x) = a := by
rw [div_eq_iff hx']
ring
have h3 : 1 / (-I * (I * x)) ^ (1 / 2 : ℂ) = 1 / ↑(x ^ (1 / 2 : ℝ)) := by
rw [neg_mul, ← mul_assoc, I_mul_I, neg_one_mul, neg_neg,ofReal_cpow hx.le, ofReal_div,
ofReal_one, ofReal_ofNat]
have h4 : -π * I * (a * I * x) ^ 2 / (I * x) = - (-π * a ^ 2 * x) := by
rw [mul_pow, mul_pow, I_sq, div_eq_iff hx']
ring
rw [h1, h2, h3, h4, ← mul_assoc, mul_comm (cexp _), mul_assoc _ (cexp _) (cexp _),
← Complex.exp_add, neg_add_cancel, Complex.exp_zero, mul_one, ofReal_div, ofReal_one]
end kernel_defs
section asymp
/-!
## Formulae for the kernels as sums
-/
lemma hasSum_int_evenKernel (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℤ ↦ rexp (-π * (n + a) ^ 2 * t)) (evenKernel a t) := by
rw [← hasSum_ofReal, evenKernel_def]
have (n : ℤ) : cexp (-(π * (n + a) ^ 2 * t)) = cexp (-(π * a ^ 2 * t)) *
jacobiTheta₂_term n (a * I * t) (I * t) := by
rw [jacobiTheta₂_term, ← Complex.exp_add]
ring_nf
simp
simpa [this] using (hasSum_jacobiTheta₂_term _ (by simpa)).mul_left _
lemma hasSum_int_cosKernel (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℤ ↦ cexp (2 * π * I * a * n) * rexp (-π * n ^ 2 * t)) ↑(cosKernel a t) := by
rw [cosKernel_def a t]
have (n : ℤ) : cexp (2 * π * I * a * n) * cexp (-(π * n ^ 2 * t)) =
jacobiTheta₂_term n a (I * ↑t) := by
rw [jacobiTheta₂_term, ← Complex.exp_add]
ring_nf
simp [sub_eq_add_neg]
simpa [this] using hasSum_jacobiTheta₂_term _ (by simpa)
/-- Modified version of `hasSum_int_evenKernel` omitting the constant term at `∞`. -/
lemma hasSum_int_evenKernel₀ (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℤ ↦ if n + a = 0 then 0 else rexp (-π * (n + a) ^ 2 * t))
(evenKernel a t - if (a : UnitAddCircle) = 0 then 1 else 0) := by
haveI := Classical.propDecidable -- speed up instance search for `if / then / else`
simp_rw [AddCircle.coe_eq_zero_iff, zsmul_one]
split_ifs with h
· obtain ⟨k, rfl⟩ := h
simpa [← Int.cast_add, add_eq_zero_iff_eq_neg]
using hasSum_ite_sub_hasSum (hasSum_int_evenKernel (k : ℝ) ht) (-k)
· suffices ∀ (n : ℤ), n + a ≠ 0 by simpa [this] using hasSum_int_evenKernel a ht
contrapose! h
let ⟨n, hn⟩ := h
exact ⟨-n, by simpa [neg_eq_iff_add_eq_zero]⟩
lemma hasSum_int_cosKernel₀ (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℤ ↦ if n = 0 then 0 else cexp (2 * π * I * a * n) * rexp (-π * n ^ 2 * t))
(↑(cosKernel a t) - 1) := by
simpa using hasSum_ite_sub_hasSum (hasSum_int_cosKernel a ht) 0
lemma hasSum_nat_cosKernel₀ (a : ℝ) {t : ℝ} (ht : 0 < t) :
HasSum (fun n : ℕ ↦ 2 * Real.cos (2 * π * a * (n + 1)) * rexp (-π * (n + 1) ^ 2 * t))
(cosKernel a t - 1) := by
rw [← hasSum_ofReal, ofReal_sub, ofReal_one]
have := (hasSum_int_cosKernel a ht).nat_add_neg
rw [← hasSum_nat_add_iff' 1] at this
simp_rw [Finset.sum_range_one, Nat.cast_zero, neg_zero, Int.cast_zero, zero_pow two_ne_zero,
mul_zero, zero_mul, Complex.exp_zero, Real.exp_zero, ofReal_one, mul_one, Int.cast_neg,
Int.cast_natCast, neg_sq, ← add_mul, add_sub_assoc, ← sub_sub, sub_self, zero_sub,
← sub_eq_add_neg, mul_neg] at this
refine this.congr_fun fun n ↦ ?_
push_cast
rw [Complex.cos, mul_div_cancel₀ _ two_ne_zero]
congr 3 <;> ring
/-!
## Asymptotics of the kernels as `t → ∞`
-/
/-- The function `evenKernel a - L` has exponential decay at `+∞`, where `L = 1` if
`a = 0` and `L = 0` otherwise. -/
lemma isBigO_atTop_evenKernel_sub (a : UnitAddCircle) : ∃ p : ℝ, 0 < p ∧
(evenKernel a · - (if a = 0 then 1 else 0)) =O[atTop] (rexp <| -p * ·) := by
induction a using QuotientAddGroup.induction_on with | H b =>
obtain ⟨p, hp, hp'⟩ := HurwitzKernelBounds.isBigO_atTop_F_int_zero_sub b
refine ⟨p, hp, (EventuallyEq.isBigO ?_).trans hp'⟩
filter_upwards [eventually_gt_atTop 0] with t h
simp [← (hasSum_int_evenKernel b h).tsum_eq, HurwitzKernelBounds.F_int, HurwitzKernelBounds.f_int]
/-- The function `cosKernel a - 1` has exponential decay at `+∞`, for any `a`. -/
lemma isBigO_atTop_cosKernel_sub (a : UnitAddCircle) :
∃ p, 0 < p ∧ IsBigO atTop (cosKernel a · - 1) (fun x ↦ Real.exp (-p * x)) := by
induction a using QuotientAddGroup.induction_on with | H a =>
obtain ⟨p, hp, hp'⟩ := HurwitzKernelBounds.isBigO_atTop_F_nat_zero_sub zero_le_one
refine ⟨p, hp, (Eventually.isBigO ?_).trans (hp'.const_mul_left 2)⟩
filter_upwards [eventually_gt_atTop 0] with t ht
simp only [eq_false_intro one_ne_zero, if_false, sub_zero,
← (hasSum_nat_cosKernel₀ a ht).tsum_eq, HurwitzKernelBounds.F_nat]
apply tsum_of_norm_bounded ((HurwitzKernelBounds.summable_f_nat 0 1 ht).hasSum.mul_left 2)
intro n
rw [norm_mul, norm_mul, norm_two, mul_assoc, mul_le_mul_iff_of_pos_left two_pos,
norm_of_nonneg (exp_pos _).le, HurwitzKernelBounds.f_nat, pow_zero, one_mul, Real.norm_eq_abs]
exact mul_le_of_le_one_left (exp_pos _).le (abs_cos_le_one _)
end asymp
section FEPair
/-!
## Construction of a FE-pair
-/
/-- A `WeakFEPair` structure with `f = evenKernel a` and `g = cosKernel a`. -/
def hurwitzEvenFEPair (a : UnitAddCircle) : WeakFEPair ℂ where
f := ofReal ∘ evenKernel a
g := ofReal ∘ cosKernel a
hf_int := (continuous_ofReal.comp_continuousOn (continuousOn_evenKernel a)).locallyIntegrableOn
measurableSet_Ioi
hg_int := (continuous_ofReal.comp_continuousOn (continuousOn_cosKernel a)).locallyIntegrableOn
measurableSet_Ioi
k := 1 / 2
hk := one_half_pos
ε := 1
hε := one_ne_zero
f₀ := if a = 0 then 1 else 0
hf_top r := by
let ⟨v, hv, hv'⟩ := isBigO_atTop_evenKernel_sub a
rw [← isBigO_norm_left] at hv' ⊢
conv at hv' =>
enter [2, x]; rw [← norm_real, ofReal_sub, apply_ite ((↑) : ℝ → ℂ), ofReal_one, ofReal_zero]
exact hv'.trans (isLittleO_exp_neg_mul_rpow_atTop hv _).isBigO
g₀ := 1
hg_top r := by
obtain ⟨p, hp, hp'⟩ := isBigO_atTop_cosKernel_sub a
simpa using isBigO_ofReal_left.mpr <| hp'.trans (isLittleO_exp_neg_mul_rpow_atTop hp r).isBigO
h_feq x hx := by simp [← ofReal_mul, evenKernel_functional_equation, inv_rpow (le_of_lt hx)]
@[simp]
lemma hurwitzEvenFEPair_zero_symm :
(hurwitzEvenFEPair 0).symm = hurwitzEvenFEPair 0 := by
unfold hurwitzEvenFEPair WeakFEPair.symm
congr 1 <;> simp [evenKernel_eq_cosKernel_of_zero]
@[simp]
lemma hurwitzEvenFEPair_neg (a : UnitAddCircle) : hurwitzEvenFEPair (-a) = hurwitzEvenFEPair a := by
unfold hurwitzEvenFEPair
congr 1 <;> simp [Function.comp_def]
/-!
## Definition of the completed even Hurwitz zeta function
-/
/--
The meromorphic function of `s` which agrees with
`1 / 2 * Gamma (s / 2) * π ^ (-s / 2) * ∑' (n : ℤ), 1 / |n + a| ^ s` for `1 < re s`.
-/
def completedHurwitzZetaEven (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzEvenFEPair a).Λ (s / 2)) / 2
/-- The entire function differing from `completedHurwitzZetaEven a s` by a linear combination of
`1 / s` and `1 / (1 - s)`. -/
def completedHurwitzZetaEven₀ (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzEvenFEPair a).Λ₀ (s / 2)) / 2
lemma completedHurwitzZetaEven_eq (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaEven a s =
completedHurwitzZetaEven₀ a s - (if a = 0 then 1 else 0) / s - 1 / (1 - s) := by
rw [completedHurwitzZetaEven, WeakFEPair.Λ, sub_div, sub_div]
congr 1
· change completedHurwitzZetaEven₀ a s - (1 / (s / 2)) • (if a = 0 then 1 else 0) / 2 =
completedHurwitzZetaEven₀ a s - (if a = 0 then 1 else 0) / s
rw [smul_eq_mul, mul_comm, mul_div_assoc, div_div, div_mul_cancel₀ _ two_ne_zero, mul_one_div]
· change (1 / (↑(1 / 2 : ℝ) - s / 2)) • 1 / 2 = 1 / (1 - s)
push_cast
rw [smul_eq_mul, mul_one, ← sub_div, div_div, div_mul_cancel₀ _ two_ne_zero]
/--
The meromorphic function of `s` which agrees with
`Gamma (s / 2) * π ^ (-s / 2) * ∑' n : ℕ, cos (2 * π * a * n) / n ^ s` for `1 < re s`.
-/
def completedCosZeta (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzEvenFEPair a).symm.Λ (s / 2)) / 2
/-- The entire function differing from `completedCosZeta a s` by a linear combination of
`1 / s` and `1 / (1 - s)`. -/
def completedCosZeta₀ (a : UnitAddCircle) (s : ℂ) : ℂ :=
((hurwitzEvenFEPair a).symm.Λ₀ (s / 2)) / 2
lemma completedCosZeta_eq (a : UnitAddCircle) (s : ℂ) :
completedCosZeta a s =
completedCosZeta₀ a s - 1 / s - (if a = 0 then 1 else 0) / (1 - s) := by
rw [completedCosZeta, WeakFEPair.Λ, sub_div, sub_div]
congr 1
· rw [completedCosZeta₀, WeakFEPair.symm, hurwitzEvenFEPair, smul_eq_mul, mul_one, div_div,
div_mul_cancel₀ _ (two_ne_zero' ℂ)]
· simp_rw [WeakFEPair.symm, hurwitzEvenFEPair, push_cast, inv_one, smul_eq_mul,
mul_comm _ (if _ then _ else _), mul_div_assoc, div_div, ← sub_div,
div_mul_cancel₀ _ (two_ne_zero' ℂ), mul_one_div]
/-!
## Parity and functional equations
-/
@[simp]
lemma completedHurwitzZetaEven_neg (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaEven (-a) s = completedHurwitzZetaEven a s := by
simp [completedHurwitzZetaEven]
@[simp]
lemma completedHurwitzZetaEven₀_neg (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaEven₀ (-a) s = completedHurwitzZetaEven₀ a s := by
simp [completedHurwitzZetaEven₀]
@[simp]
lemma completedCosZeta_neg (a : UnitAddCircle) (s : ℂ) :
completedCosZeta (-a) s = completedCosZeta a s := by
simp [completedCosZeta]
@[simp]
lemma completedCosZeta₀_neg (a : UnitAddCircle) (s : ℂ) :
completedCosZeta₀ (-a) s = completedCosZeta₀ a s := by
simp [completedCosZeta₀]
/-- Functional equation for the even Hurwitz zeta function. -/
lemma completedHurwitzZetaEven_one_sub (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaEven a (1 - s) = completedCosZeta a s := by
rw [completedHurwitzZetaEven, completedCosZeta, sub_div,
(by norm_num : (1 / 2 : ℂ) = ↑(1 / 2 : ℝ)),
(by rfl : (1 / 2 : ℝ) = (hurwitzEvenFEPair a).k),
(hurwitzEvenFEPair a).functional_equation (s / 2),
(by rfl : (hurwitzEvenFEPair a).ε = 1),
one_smul]
/-- Functional equation for the even Hurwitz zeta function with poles removed. -/
lemma completedHurwitzZetaEven₀_one_sub (a : UnitAddCircle) (s : ℂ) :
completedHurwitzZetaEven₀ a (1 - s) = completedCosZeta₀ a s := by
rw [completedHurwitzZetaEven₀, completedCosZeta₀, sub_div,
(by norm_num : (1 / 2 : ℂ) = ↑(1 / 2 : ℝ)),
(by rfl : (1 / 2 : ℝ) = (hurwitzEvenFEPair a).k),
(hurwitzEvenFEPair a).functional_equation₀ (s / 2),
(by rfl : (hurwitzEvenFEPair a).ε = 1),
one_smul]
/-- Functional equation for the even Hurwitz zeta function (alternative form). -/
lemma completedCosZeta_one_sub (a : UnitAddCircle) (s : ℂ) :
completedCosZeta a (1 - s) = completedHurwitzZetaEven a s := by
rw [← completedHurwitzZetaEven_one_sub, sub_sub_cancel]
/-- Functional equation for the even Hurwitz zeta function with poles removed (alternative form). -/
lemma completedCosZeta₀_one_sub (a : UnitAddCircle) (s : ℂ) :
completedCosZeta₀ a (1 - s) = completedHurwitzZetaEven₀ a s := by
rw [← completedHurwitzZetaEven₀_one_sub, sub_sub_cancel]
end FEPair
/-!
## Differentiability and residues
-/
section FEPair
/--
The even Hurwitz completed zeta is differentiable away from `s = 0` and `s = 1` (and also at
`s = 0` if `a ≠ 0`)
-/
lemma differentiableAt_completedHurwitzZetaEven
(a : UnitAddCircle) {s : ℂ} (hs : s ≠ 0 ∨ a ≠ 0) (hs' : s ≠ 1) :
DifferentiableAt ℂ (completedHurwitzZetaEven a) s := by
refine (((hurwitzEvenFEPair a).differentiableAt_Λ ?_ (Or.inl ?_)).comp s
(differentiableAt_id.div_const _)).div_const _
· rcases hs with h | h <;>
simp [hurwitzEvenFEPair, h]
· change s / 2 ≠ ↑(1 / 2 : ℝ)
rw [ofReal_div, ofReal_one, ofReal_ofNat]
exact hs' ∘ (div_left_inj' two_ne_zero).mp
lemma differentiable_completedHurwitzZetaEven₀ (a : UnitAddCircle) :
Differentiable ℂ (completedHurwitzZetaEven₀ a) :=
((hurwitzEvenFEPair a).differentiable_Λ₀.comp (differentiable_id.div_const _)).div_const _
/-- The difference of two completed even Hurwitz zeta functions is differentiable at `s = 1`. -/
lemma differentiableAt_one_completedHurwitzZetaEven_sub_completedHurwitzZetaEven
(a b : UnitAddCircle) :
DifferentiableAt ℂ (fun s ↦ completedHurwitzZetaEven a s - completedHurwitzZetaEven b s) 1 := by
have (s) : completedHurwitzZetaEven a s - completedHurwitzZetaEven b s =
completedHurwitzZetaEven₀ a s - completedHurwitzZetaEven₀ b s -
((if a = 0 then 1 else 0) - (if b = 0 then 1 else 0)) / s := by
simp_rw [completedHurwitzZetaEven_eq, sub_div]
abel
rw [funext this]
refine .sub ?_ <| (differentiable_const _ _).div (differentiable_id _) one_ne_zero
apply DifferentiableAt.sub <;> apply differentiable_completedHurwitzZetaEven₀
lemma differentiableAt_completedCosZeta
(a : UnitAddCircle) {s : ℂ} (hs : s ≠ 0) (hs' : s ≠ 1 ∨ a ≠ 0) :
DifferentiableAt ℂ (completedCosZeta a) s := by
refine (((hurwitzEvenFEPair a).symm.differentiableAt_Λ (Or.inl ?_) ?_).comp s
(differentiableAt_id.div_const _)).div_const _
· exact div_ne_zero_iff.mpr ⟨hs, two_ne_zero⟩
· change s / 2 ≠ ↑(1 / 2 : ℝ) ∨ (if a = 0 then 1 else 0) = 0
refine Or.imp (fun h ↦ ?_) (fun ha ↦ ?_) hs'
· simpa [push_cast] using h ∘ (div_left_inj' two_ne_zero).mp
· simpa
lemma differentiable_completedCosZeta₀ (a : UnitAddCircle) :
Differentiable ℂ (completedCosZeta₀ a) :=
((hurwitzEvenFEPair a).symm.differentiable_Λ₀.comp (differentiable_id.div_const _)).div_const _
private lemma tendsto_div_two_punctured_nhds (a : ℂ) :
Tendsto (fun s : ℂ ↦ s / 2) (𝓝[≠] a) (𝓝[≠] (a / 2)) :=
le_of_eq ((Homeomorph.mulRight₀ _ (inv_ne_zero (two_ne_zero' ℂ))).map_punctured_nhds_eq a)
/-- The residue of `completedHurwitzZetaEven a s` at `s = 1` is equal to `1`. -/
lemma completedHurwitzZetaEven_residue_one (a : UnitAddCircle) :
Tendsto (fun s ↦ (s - 1) * completedHurwitzZetaEven a s) (𝓝[≠] 1) (𝓝 1) := by
have h1 : Tendsto (fun s : ℂ ↦ (s - ↑(1 / 2 : ℝ)) * _) (𝓝[≠] ↑(1 / 2 : ℝ))
(𝓝 ((1 : ℂ) * (1 : ℂ))) := (hurwitzEvenFEPair a).Λ_residue_k
simp only [push_cast, one_mul] at h1
refine (h1.comp <| tendsto_div_two_punctured_nhds 1).congr (fun s ↦ ?_)
rw [completedHurwitzZetaEven, Function.comp_apply, ← sub_div, div_mul_eq_mul_div, mul_div_assoc]
/-- The residue of `completedHurwitzZetaEven a s` at `s = 0` is equal to `-1` if `a = 0`, and `0`
otherwise. -/
lemma completedHurwitzZetaEven_residue_zero (a : UnitAddCircle) :
Tendsto (fun s ↦ s * completedHurwitzZetaEven a s) (𝓝[≠] 0) (𝓝 (if a = 0 then -1 else 0)) := by
have h1 : Tendsto (fun s : ℂ ↦ s * _) (𝓝[≠] 0)
(𝓝 (-(if a = 0 then 1 else 0))) := (hurwitzEvenFEPair a).Λ_residue_zero
have : -(if a = 0 then (1 : ℂ) else 0) = (if a = 0 then -1 else 0) := by { split_ifs <;> simp }
simp only [this, push_cast, one_mul] at h1
refine (h1.comp <| zero_div (2 : ℂ) ▸ (tendsto_div_two_punctured_nhds 0)).congr (fun s ↦ ?_)
simp [completedHurwitzZetaEven, div_mul_eq_mul_div, mul_div_assoc]
lemma completedCosZeta_residue_zero (a : UnitAddCircle) :
Tendsto (fun s ↦ s * completedCosZeta a s) (𝓝[≠] 0) (𝓝 (-1)) := by
have h1 : Tendsto (fun s : ℂ ↦ s * _) (𝓝[≠] 0)
(𝓝 (-1)) := (hurwitzEvenFEPair a).symm.Λ_residue_zero
refine (h1.comp <| zero_div (2 : ℂ) ▸ (tendsto_div_two_punctured_nhds 0)).congr (fun s ↦ ?_)
simp [completedCosZeta, div_mul_eq_mul_div, mul_div_assoc]
end FEPair
/-!
## Relation to the Dirichlet series for `1 < re s`
-/
/-- Formula for `completedCosZeta` as a Dirichlet series in the convergence range
(first version, with sum over `ℤ`). -/
lemma hasSum_int_completedCosZeta (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ Gammaℝ s * cexp (2 * π * I * a * n) / (↑|n| : ℂ) ^ s / 2)
(completedCosZeta a s) := by
let c (n : ℤ) : ℂ := cexp (2 * π * I * a * n) / 2
have hF t (ht : 0 < t) : HasSum (fun n : ℤ ↦ if n = 0 then 0 else c n * rexp (-π * n ^ 2 * t))
((cosKernel a t - 1) / 2) := by
refine ((hasSum_int_cosKernel₀ a ht).div_const 2).congr_fun fun n ↦ ?_
split_ifs <;> simp [c, div_mul_eq_mul_div]
simp only [← Int.cast_eq_zero (α := ℝ)] at hF
rw [show completedCosZeta a s = mellin (fun t ↦ (cosKernel a t - 1 : ℂ) / 2) (s / 2) by
rw [mellin_div_const, completedCosZeta]
congr 1
refine ((hurwitzEvenFEPair a).symm.hasMellin (?_ : 1 / 2 < (s / 2).re)).2.symm
rwa [div_ofNat_re, div_lt_div_iff_of_pos_right two_pos]]
refine (hasSum_mellin_pi_mul_sq (zero_lt_one.trans hs) hF ?_).congr_fun fun n ↦ ?_
· apply (((summable_one_div_int_add_rpow 0 s.re).mpr hs).div_const 2).of_norm_bounded
intro i
simp only [c, (by { push_cast; ring } : 2 * π * I * a * i = ↑(2 * π * a * i) * I), norm_div,
RCLike.norm_ofNat, norm_norm, Complex.norm_exp_ofReal_mul_I, add_zero, norm_one,
norm_of_nonneg (by positivity : 0 ≤ |(i : ℝ)| ^ s.re), div_right_comm, le_rfl]
· simp [c, ← Int.cast_abs, div_right_comm, mul_div_assoc]
/-- Formula for `completedCosZeta` as a Dirichlet series in the convergence range
(second version, with sum over `ℕ`). -/
lemma hasSum_nat_completedCosZeta (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℕ ↦ if n = 0 then 0 else Gammaℝ s * Real.cos (2 * π * a * n) / (n : ℂ) ^ s)
(completedCosZeta a s) := by
have aux : ((|0| : ℤ) : ℂ) ^ s = 0 := by
rw [abs_zero, Int.cast_zero, zero_cpow (ne_zero_of_one_lt_re hs)]
have hint := (hasSum_int_completedCosZeta a hs).nat_add_neg
rw [aux, div_zero, zero_div, add_zero] at hint
refine hint.congr_fun fun n ↦ ?_
split_ifs with h
· simp only [h, Nat.cast_zero, aux, div_zero, zero_div, neg_zero, zero_add]
· simp only [ofReal_cos, ofReal_mul, ofReal_ofNat, ofReal_natCast, Complex.cos,
show 2 * π * a * n * I = 2 * π * I * a * n by ring, neg_mul, mul_div_assoc,
div_right_comm _ (2 : ℂ), Int.cast_natCast, Nat.abs_cast, Int.cast_neg, mul_neg, abs_neg, ←
mul_add, ← add_div]
/-- Formula for `completedHurwitzZetaEven` as a Dirichlet series in the convergence range. -/
lemma hasSum_int_completedHurwitzZetaEven (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ Gammaℝ s / (↑|n + a| : ℂ) ^ s / 2) (completedHurwitzZetaEven a s) := by
have hF (t : ℝ) (ht : 0 < t) : HasSum (fun n : ℤ ↦ if n + a = 0 then 0
else (1 / 2 : ℂ) * rexp (-π * (n + a) ^ 2 * t))
((evenKernel a t - (if (a : UnitAddCircle) = 0 then 1 else 0 : ℝ)) / 2) := by
refine (ofReal_sub .. ▸ (hasSum_ofReal.mpr (hasSum_int_evenKernel₀ a ht)).div_const
2).congr_fun fun n ↦ ?_
split_ifs
· rw [ofReal_zero, zero_div]
· rw [mul_comm, mul_one_div]
rw [show completedHurwitzZetaEven a s = mellin (fun t ↦ ((evenKernel (↑a) t : ℂ) -
↑(if (a : UnitAddCircle) = 0 then 1 else 0 : ℝ)) / 2) (s / 2) by
simp_rw [mellin_div_const, apply_ite ofReal, ofReal_one, ofReal_zero]
refine congr_arg (· / 2) ((hurwitzEvenFEPair a).hasMellin (?_ : 1 / 2 < (s / 2).re)).2.symm
rwa [div_ofNat_re, div_lt_div_iff_of_pos_right two_pos]]
refine (hasSum_mellin_pi_mul_sq (zero_lt_one.trans hs) hF ?_).congr_fun fun n ↦ ?_
· simp_rw [← mul_one_div ‖_‖]
apply Summable.mul_left
rwa [summable_one_div_int_add_rpow]
· rw [mul_one_div, div_right_comm]
/-!
## The un-completed even Hurwitz zeta
-/
/-- Technical lemma which will give us differentiability of Hurwitz zeta at `s = 0`. -/
lemma differentiableAt_update_of_residue
{Λ : ℂ → ℂ} (hf : ∀ (s : ℂ) (_ : s ≠ 0) (_ : s ≠ 1), DifferentiableAt ℂ Λ s)
{L : ℂ} (h_lim : Tendsto (fun s ↦ s * Λ s) (𝓝[≠] 0) (𝓝 L)) (s : ℂ) (hs' : s ≠ 1) :
DifferentiableAt ℂ (Function.update (fun s ↦ Λ s / Gammaℝ s) 0 (L / 2)) s := by
have claim (t) (ht : t ≠ 0) (ht' : t ≠ 1) : DifferentiableAt ℂ (fun u : ℂ ↦ Λ u / Gammaℝ u) t :=
(hf t ht ht').mul differentiable_Gammaℝ_inv.differentiableAt
have claim2 : Tendsto (fun s : ℂ ↦ Λ s / Gammaℝ s) (𝓝[≠] 0) (𝓝 <| L / 2) := by
refine Tendsto.congr' ?_ (h_lim.div Gammaℝ_residue_zero two_ne_zero)
filter_upwards [self_mem_nhdsWithin] with s (hs : s ≠ 0)
rw [Pi.div_apply, ← div_div, mul_div_cancel_left₀ _ hs]
rcases ne_or_eq s 0 with hs | rfl
· -- Easy case : `s ≠ 0`
refine (claim s hs hs').congr_of_eventuallyEq ?_
filter_upwards [isOpen_compl_singleton.mem_nhds hs] with x hx
simp [Function.update_of_ne hx]
· -- Hard case : `s = 0`
simp_rw [← claim2.limUnder_eq]
have S_nhds : {(1 : ℂ)}ᶜ ∈ 𝓝 (0 : ℂ) := isOpen_compl_singleton.mem_nhds hs'
refine ((Complex.differentiableOn_update_limUnder_of_isLittleO S_nhds
(fun t ht ↦ (claim t ht.2 ht.1).differentiableWithinAt) ?_) 0 hs').differentiableAt S_nhds
simp only [Gammaℝ, zero_div, div_zero, Complex.Gamma_zero, mul_zero, cpow_zero, sub_zero]
-- Remains to show completed zeta is `o (s ^ (-1))` near 0.
refine (isBigO_const_of_tendsto claim2 <| one_ne_zero' ℂ).trans_isLittleO ?_
rw [isLittleO_iff_tendsto']
· exact Tendsto.congr (fun x ↦ by rw [← one_div, one_div_one_div]) nhdsWithin_le_nhds
· exact eventually_of_mem self_mem_nhdsWithin fun x hx hx' ↦ (hx <| inv_eq_zero.mp hx').elim
/-- The even part of the Hurwitz zeta function, i.e. the meromorphic function of `s` which agrees
with `1 / 2 * ∑' (n : ℤ), 1 / |n + a| ^ s` for `1 < re s` -/
noncomputable def hurwitzZetaEven (a : UnitAddCircle) :=
Function.update (fun s ↦ completedHurwitzZetaEven a s / Gammaℝ s)
0 (if a = 0 then -1 / 2 else 0)
lemma hurwitzZetaEven_def_of_ne_or_ne {a : UnitAddCircle} {s : ℂ} (h : a ≠ 0 ∨ s ≠ 0) :
hurwitzZetaEven a s = completedHurwitzZetaEven a s / Gammaℝ s := by
rw [hurwitzZetaEven]
rcases ne_or_eq s 0 with h' | rfl
· rw [Function.update_of_ne h']
· simpa [Gammaℝ] using h
lemma hurwitzZetaEven_apply_zero (a : UnitAddCircle) :
hurwitzZetaEven a 0 = if a = 0 then -1 / 2 else 0 :=
Function.update_self ..
lemma hurwitzZetaEven_neg (a : UnitAddCircle) (s : ℂ) :
hurwitzZetaEven (-a) s = hurwitzZetaEven a s := by
simp [hurwitzZetaEven]
/-- The trivial zeroes of the even Hurwitz zeta function. -/
theorem hurwitzZetaEven_neg_two_mul_nat_add_one (a : UnitAddCircle) (n : ℕ) :
hurwitzZetaEven a (-2 * (n + 1)) = 0 := by
have : (-2 : ℂ) * (n + 1) ≠ 0 :=
mul_ne_zero (neg_ne_zero.mpr two_ne_zero) (Nat.cast_add_one_ne_zero n)
rw [hurwitzZetaEven, Function.update_of_ne this, Gammaℝ_eq_zero_iff.mpr ⟨n + 1, by simp⟩,
div_zero]
/-- The Hurwitz zeta function is differentiable everywhere except at `s = 1`. This is true
even in the delicate case `a = 0` and `s = 0` (where the completed zeta has a pole, but this is
cancelled out by the Gamma factor). -/
lemma differentiableAt_hurwitzZetaEven (a : UnitAddCircle) {s : ℂ} (hs' : s ≠ 1) :
DifferentiableAt ℂ (hurwitzZetaEven a) s := by
have := differentiableAt_update_of_residue
(fun t ht ht' ↦ differentiableAt_completedHurwitzZetaEven a (Or.inl ht) ht')
(completedHurwitzZetaEven_residue_zero a) s hs'
simp_rw [div_eq_mul_inv, ite_mul, zero_mul, ← div_eq_mul_inv] at this
exact this
lemma hurwitzZetaEven_residue_one (a : UnitAddCircle) :
Tendsto (fun s ↦ (s - 1) * hurwitzZetaEven a s) (𝓝[≠] 1) (𝓝 1) := by
have : Tendsto (fun s ↦ (s - 1) * completedHurwitzZetaEven a s / Gammaℝ s) (𝓝[≠] 1) (𝓝 1) := by
simpa only [Gammaℝ_one, inv_one, mul_one] using (completedHurwitzZetaEven_residue_one a).mul
<| (differentiable_Gammaℝ_inv.continuous.tendsto _).mono_left nhdsWithin_le_nhds
refine this.congr' ?_
filter_upwards [eventually_ne_nhdsWithin one_ne_zero] with s hs
simp [hurwitzZetaEven_def_of_ne_or_ne (Or.inr hs), mul_div_assoc]
lemma differentiableAt_hurwitzZetaEven_sub_one_div (a : UnitAddCircle) :
DifferentiableAt ℂ (fun s ↦ hurwitzZetaEven a s - 1 / (s - 1) / Gammaℝ s) 1 := by
suffices DifferentiableAt ℂ
(fun s ↦ completedHurwitzZetaEven a s / Gammaℝ s - 1 / (s - 1) / Gammaℝ s) 1 by
apply this.congr_of_eventuallyEq
filter_upwards [eventually_ne_nhds one_ne_zero] with x hx
rw [hurwitzZetaEven, Function.update_of_ne hx]
simp_rw [← sub_div, div_eq_mul_inv _ (Gammaℝ _)]
refine DifferentiableAt.mul ?_ differentiable_Gammaℝ_inv.differentiableAt
simp_rw [completedHurwitzZetaEven_eq, sub_sub, add_assoc]
conv => enter [2, s, 2]; rw [← neg_sub, div_neg, neg_add_cancel, add_zero]
exact (differentiable_completedHurwitzZetaEven₀ a _).sub
<| (differentiableAt_const _).div differentiableAt_id one_ne_zero
/-- Expression for `hurwitzZetaEven a 1` as a limit. (Mathematically `hurwitzZetaEven a 1` is
undefined, but our construction assigns some value to it; this lemma is mostly of interest for
determining what that value is). -/
lemma tendsto_hurwitzZetaEven_sub_one_div_nhds_one (a : UnitAddCircle) :
Tendsto (fun s ↦ hurwitzZetaEven a s - 1 / (s - 1) / Gammaℝ s) (𝓝 1)
(𝓝 (hurwitzZetaEven a 1)) := by
simpa using (differentiableAt_hurwitzZetaEven_sub_one_div a).continuousAt.tendsto
lemma differentiable_hurwitzZetaEven_sub_hurwitzZetaEven (a b : UnitAddCircle) :
| Differentiable ℂ (fun s ↦ hurwitzZetaEven a s - hurwitzZetaEven b s) := by
intro z
rcases ne_or_eq z 1 with hz | rfl
· exact (differentiableAt_hurwitzZetaEven a hz).sub (differentiableAt_hurwitzZetaEven b hz)
· convert (differentiableAt_hurwitzZetaEven_sub_one_div a).sub
(differentiableAt_hurwitzZetaEven_sub_one_div b) using 2 with s
abel
/--
Formula for `hurwitzZetaEven` as a Dirichlet series in the convergence range, with sum over `ℤ`.
-/
lemma hasSum_int_hurwitzZetaEven (a : ℝ) {s : ℂ} (hs : 1 < re s) :
HasSum (fun n : ℤ ↦ 1 / (↑|n + a| : ℂ) ^ s / 2) (hurwitzZetaEven a s) := by
| Mathlib/NumberTheory/LSeries/HurwitzZetaEven.lean | 650 | 662 |
/-
Copyright (c) 2019 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Yaël Dillies
-/
import Mathlib.Order.Cover
import Mathlib.Order.Interval.Finset.Defs
/-!
# Intervals as finsets
This file provides basic results about all the `Finset.Ixx`, which are defined in
`Order.Interval.Finset.Defs`.
In addition, it shows that in a locally finite order `≤` and `<` are the transitive closures of,
respectively, `⩿` and `⋖`, which then leads to a characterization of monotone and strictly
functions whose domain is a locally finite order. In particular, this file proves:
* `le_iff_transGen_wcovBy`: `≤` is the transitive closure of `⩿`
* `lt_iff_transGen_covBy`: `<` is the transitive closure of `⋖`
* `monotone_iff_forall_wcovBy`: Characterization of monotone functions
* `strictMono_iff_forall_covBy`: Characterization of strictly monotone functions
## TODO
This file was originally only about `Finset.Ico a b` where `a b : ℕ`. No care has yet been taken to
generalize these lemmas properly and many lemmas about `Icc`, `Ioc`, `Ioo` are missing. In general,
what's to do is taking the lemmas in `Data.X.Intervals` and abstract away the concrete structure.
Complete the API. See
https://github.com/leanprover-community/mathlib/pull/14448#discussion_r906109235
for some ideas.
-/
assert_not_exists MonoidWithZero Finset.sum
open Function OrderDual
open FinsetInterval
variable {ι α : Type*} {a a₁ a₂ b b₁ b₂ c x : α}
namespace Finset
section Preorder
variable [Preorder α]
section LocallyFiniteOrder
variable [LocallyFiniteOrder α]
@[simp]
theorem nonempty_Icc : (Icc a b).Nonempty ↔ a ≤ b := by
rw [← coe_nonempty, coe_Icc, Set.nonempty_Icc]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Icc_of_le⟩ := nonempty_Icc
@[simp]
theorem nonempty_Ico : (Ico a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ico, Set.nonempty_Ico]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ico_of_lt⟩ := nonempty_Ico
@[simp]
theorem nonempty_Ioc : (Ioc a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ioc, Set.nonempty_Ioc]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ioc_of_lt⟩ := nonempty_Ioc
-- TODO: This is nonsense. A locally finite order is never densely ordered
@[simp]
theorem nonempty_Ioo [DenselyOrdered α] : (Ioo a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ioo, Set.nonempty_Ioo]
@[simp]
theorem Icc_eq_empty_iff : Icc a b = ∅ ↔ ¬a ≤ b := by
rw [← coe_eq_empty, coe_Icc, Set.Icc_eq_empty_iff]
@[simp]
theorem Ico_eq_empty_iff : Ico a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ico, Set.Ico_eq_empty_iff]
@[simp]
theorem Ioc_eq_empty_iff : Ioc a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ioc, Set.Ioc_eq_empty_iff]
-- TODO: This is nonsense. A locally finite order is never densely ordered
@[simp]
theorem Ioo_eq_empty_iff [DenselyOrdered α] : Ioo a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ioo, Set.Ioo_eq_empty_iff]
alias ⟨_, Icc_eq_empty⟩ := Icc_eq_empty_iff
alias ⟨_, Ico_eq_empty⟩ := Ico_eq_empty_iff
alias ⟨_, Ioc_eq_empty⟩ := Ioc_eq_empty_iff
@[simp]
theorem Ioo_eq_empty (h : ¬a < b) : Ioo a b = ∅ :=
eq_empty_iff_forall_not_mem.2 fun _ hx => h ((mem_Ioo.1 hx).1.trans (mem_Ioo.1 hx).2)
@[simp]
theorem Icc_eq_empty_of_lt (h : b < a) : Icc a b = ∅ :=
Icc_eq_empty h.not_le
@[simp]
theorem Ico_eq_empty_of_le (h : b ≤ a) : Ico a b = ∅ :=
Ico_eq_empty h.not_lt
@[simp]
theorem Ioc_eq_empty_of_le (h : b ≤ a) : Ioc a b = ∅ :=
Ioc_eq_empty h.not_lt
@[simp]
theorem Ioo_eq_empty_of_le (h : b ≤ a) : Ioo a b = ∅ :=
Ioo_eq_empty h.not_lt
theorem left_mem_Icc : a ∈ Icc a b ↔ a ≤ b := by simp only [mem_Icc, true_and, le_rfl]
theorem left_mem_Ico : a ∈ Ico a b ↔ a < b := by simp only [mem_Ico, true_and, le_refl]
theorem right_mem_Icc : b ∈ Icc a b ↔ a ≤ b := by simp only [mem_Icc, and_true, le_rfl]
theorem right_mem_Ioc : b ∈ Ioc a b ↔ a < b := by simp only [mem_Ioc, and_true, le_rfl]
theorem left_not_mem_Ioc : a ∉ Ioc a b := fun h => lt_irrefl _ (mem_Ioc.1 h).1
theorem left_not_mem_Ioo : a ∉ Ioo a b := fun h => lt_irrefl _ (mem_Ioo.1 h).1
theorem right_not_mem_Ico : b ∉ Ico a b := fun h => lt_irrefl _ (mem_Ico.1 h).2
theorem right_not_mem_Ioo : b ∉ Ioo a b := fun h => lt_irrefl _ (mem_Ioo.1 h).2
@[gcongr]
theorem Icc_subset_Icc (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Icc a₁ b₁ ⊆ Icc a₂ b₂ := by
simpa [← coe_subset] using Set.Icc_subset_Icc ha hb
@[gcongr]
theorem Ico_subset_Ico (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ico a₁ b₁ ⊆ Ico a₂ b₂ := by
simpa [← coe_subset] using Set.Ico_subset_Ico ha hb
@[gcongr]
theorem Ioc_subset_Ioc (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ioc a₁ b₁ ⊆ Ioc a₂ b₂ := by
simpa [← coe_subset] using Set.Ioc_subset_Ioc ha hb
@[gcongr]
theorem Ioo_subset_Ioo (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ioo a₁ b₁ ⊆ Ioo a₂ b₂ := by
simpa [← coe_subset] using Set.Ioo_subset_Ioo ha hb
@[gcongr]
theorem Icc_subset_Icc_left (h : a₁ ≤ a₂) : Icc a₂ b ⊆ Icc a₁ b :=
Icc_subset_Icc h le_rfl
@[gcongr]
theorem Ico_subset_Ico_left (h : a₁ ≤ a₂) : Ico a₂ b ⊆ Ico a₁ b :=
Ico_subset_Ico h le_rfl
@[gcongr]
theorem Ioc_subset_Ioc_left (h : a₁ ≤ a₂) : Ioc a₂ b ⊆ Ioc a₁ b :=
Ioc_subset_Ioc h le_rfl
@[gcongr]
theorem Ioo_subset_Ioo_left (h : a₁ ≤ a₂) : Ioo a₂ b ⊆ Ioo a₁ b :=
Ioo_subset_Ioo h le_rfl
@[gcongr]
theorem Icc_subset_Icc_right (h : b₁ ≤ b₂) : Icc a b₁ ⊆ Icc a b₂ :=
Icc_subset_Icc le_rfl h
@[gcongr]
theorem Ico_subset_Ico_right (h : b₁ ≤ b₂) : Ico a b₁ ⊆ Ico a b₂ :=
Ico_subset_Ico le_rfl h
@[gcongr]
theorem Ioc_subset_Ioc_right (h : b₁ ≤ b₂) : Ioc a b₁ ⊆ Ioc a b₂ :=
Ioc_subset_Ioc le_rfl h
@[gcongr]
theorem Ioo_subset_Ioo_right (h : b₁ ≤ b₂) : Ioo a b₁ ⊆ Ioo a b₂ :=
Ioo_subset_Ioo le_rfl h
theorem Ico_subset_Ioo_left (h : a₁ < a₂) : Ico a₂ b ⊆ Ioo a₁ b := by
rw [← coe_subset, coe_Ico, coe_Ioo]
exact Set.Ico_subset_Ioo_left h
theorem Ioc_subset_Ioo_right (h : b₁ < b₂) : Ioc a b₁ ⊆ Ioo a b₂ := by
rw [← coe_subset, coe_Ioc, coe_Ioo]
exact Set.Ioc_subset_Ioo_right h
theorem Icc_subset_Ico_right (h : b₁ < b₂) : Icc a b₁ ⊆ Ico a b₂ := by
rw [← coe_subset, coe_Icc, coe_Ico]
exact Set.Icc_subset_Ico_right h
theorem Ioo_subset_Ico_self : Ioo a b ⊆ Ico a b := by
rw [← coe_subset, coe_Ioo, coe_Ico]
exact Set.Ioo_subset_Ico_self
theorem Ioo_subset_Ioc_self : Ioo a b ⊆ Ioc a b := by
rw [← coe_subset, coe_Ioo, coe_Ioc]
exact Set.Ioo_subset_Ioc_self
theorem Ico_subset_Icc_self : Ico a b ⊆ Icc a b := by
rw [← coe_subset, coe_Ico, coe_Icc]
exact Set.Ico_subset_Icc_self
theorem Ioc_subset_Icc_self : Ioc a b ⊆ Icc a b := by
rw [← coe_subset, coe_Ioc, coe_Icc]
exact Set.Ioc_subset_Icc_self
theorem Ioo_subset_Icc_self : Ioo a b ⊆ Icc a b :=
Ioo_subset_Ico_self.trans Ico_subset_Icc_self
theorem Icc_subset_Icc_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Icc a₂ b₂ ↔ a₂ ≤ a₁ ∧ b₁ ≤ b₂ := by
rw [← coe_subset, coe_Icc, coe_Icc, Set.Icc_subset_Icc_iff h₁]
theorem Icc_subset_Ioo_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ioo a₂ b₂ ↔ a₂ < a₁ ∧ b₁ < b₂ := by
rw [← coe_subset, coe_Icc, coe_Ioo, Set.Icc_subset_Ioo_iff h₁]
theorem Icc_subset_Ico_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ico a₂ b₂ ↔ a₂ ≤ a₁ ∧ b₁ < b₂ := by
rw [← coe_subset, coe_Icc, coe_Ico, Set.Icc_subset_Ico_iff h₁]
theorem Icc_subset_Ioc_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ioc a₂ b₂ ↔ a₂ < a₁ ∧ b₁ ≤ b₂ :=
(Icc_subset_Ico_iff h₁.dual).trans and_comm
--TODO: `Ico_subset_Ioo_iff`, `Ioc_subset_Ioo_iff`
theorem Icc_ssubset_Icc_left (hI : a₂ ≤ b₂) (ha : a₂ < a₁) (hb : b₁ ≤ b₂) :
Icc a₁ b₁ ⊂ Icc a₂ b₂ := by
rw [← coe_ssubset, coe_Icc, coe_Icc]
exact Set.Icc_ssubset_Icc_left hI ha hb
theorem Icc_ssubset_Icc_right (hI : a₂ ≤ b₂) (ha : a₂ ≤ a₁) (hb : b₁ < b₂) :
Icc a₁ b₁ ⊂ Icc a₂ b₂ := by
rw [← coe_ssubset, coe_Icc, coe_Icc]
exact Set.Icc_ssubset_Icc_right hI ha hb
@[simp]
theorem Ioc_disjoint_Ioc_of_le {d : α} (hbc : b ≤ c) : Disjoint (Ioc a b) (Ioc c d) :=
disjoint_left.2 fun _ h1 h2 ↦ not_and_of_not_left _
((mem_Ioc.1 h1).2.trans hbc).not_lt (mem_Ioc.1 h2)
variable (a)
theorem Ico_self : Ico a a = ∅ :=
Ico_eq_empty <| lt_irrefl _
theorem Ioc_self : Ioc a a = ∅ :=
Ioc_eq_empty <| lt_irrefl _
theorem Ioo_self : Ioo a a = ∅ :=
Ioo_eq_empty <| lt_irrefl _
variable {a}
/-- A set with upper and lower bounds in a locally finite order is a fintype -/
def _root_.Set.fintypeOfMemBounds {s : Set α} [DecidablePred (· ∈ s)] (ha : a ∈ lowerBounds s)
(hb : b ∈ upperBounds s) : Fintype s :=
Set.fintypeSubset (Set.Icc a b) fun _ hx => ⟨ha hx, hb hx⟩
section Filter
theorem Ico_filter_lt_of_le_left [DecidablePred (· < c)] (hca : c ≤ a) :
{x ∈ Ico a b | x < c} = ∅ :=
filter_false_of_mem fun _ hx => (hca.trans (mem_Ico.1 hx).1).not_lt
theorem Ico_filter_lt_of_right_le [DecidablePred (· < c)] (hbc : b ≤ c) :
{x ∈ Ico a b | x < c} = Ico a b :=
filter_true_of_mem fun _ hx => (mem_Ico.1 hx).2.trans_le hbc
theorem Ico_filter_lt_of_le_right [DecidablePred (· < c)] (hcb : c ≤ b) :
{x ∈ Ico a b | x < c} = Ico a c := by
ext x
rw [mem_filter, mem_Ico, mem_Ico, and_right_comm]
exact and_iff_left_of_imp fun h => h.2.trans_le hcb
theorem Ico_filter_le_of_le_left {a b c : α} [DecidablePred (c ≤ ·)] (hca : c ≤ a) :
{x ∈ Ico a b | c ≤ x} = Ico a b :=
filter_true_of_mem fun _ hx => hca.trans (mem_Ico.1 hx).1
theorem Ico_filter_le_of_right_le {a b : α} [DecidablePred (b ≤ ·)] :
{x ∈ Ico a b | b ≤ x} = ∅ :=
filter_false_of_mem fun _ hx => (mem_Ico.1 hx).2.not_le
theorem Ico_filter_le_of_left_le {a b c : α} [DecidablePred (c ≤ ·)] (hac : a ≤ c) :
{x ∈ Ico a b | c ≤ x} = Ico c b := by
ext x
rw [mem_filter, mem_Ico, mem_Ico, and_comm, and_left_comm]
exact and_iff_right_of_imp fun h => hac.trans h.1
theorem Icc_filter_lt_of_lt_right {a b c : α} [DecidablePred (· < c)] (h : b < c) :
{x ∈ Icc a b | x < c} = Icc a b :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Icc.1 hx).2 h
theorem Ioc_filter_lt_of_lt_right {a b c : α} [DecidablePred (· < c)] (h : b < c) :
{x ∈ Ioc a b | x < c} = Ioc a b :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Ioc.1 hx).2 h
theorem Iic_filter_lt_of_lt_right {α} [Preorder α] [LocallyFiniteOrderBot α] {a c : α}
[DecidablePred (· < c)] (h : a < c) : {x ∈ Iic a | x < c} = Iic a :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Iic.1 hx) h
variable (a b) [Fintype α]
theorem filter_lt_lt_eq_Ioo [DecidablePred fun j => a < j ∧ j < b] :
({j | a < j ∧ j < b} : Finset _) = Ioo a b := by ext; simp
theorem filter_lt_le_eq_Ioc [DecidablePred fun j => a < j ∧ j ≤ b] :
({j | a < j ∧ j ≤ b} : Finset _) = Ioc a b := by ext; simp
theorem filter_le_lt_eq_Ico [DecidablePred fun j => a ≤ j ∧ j < b] :
({j | a ≤ j ∧ j < b} : Finset _) = Ico a b := by ext; simp
theorem filter_le_le_eq_Icc [DecidablePred fun j => a ≤ j ∧ j ≤ b] :
({j | a ≤ j ∧ j ≤ b} : Finset _) = Icc a b := by ext; simp
end Filter
end LocallyFiniteOrder
section LocallyFiniteOrderTop
variable [LocallyFiniteOrderTop α]
@[simp]
theorem Ioi_eq_empty : Ioi a = ∅ ↔ IsMax a := by
rw [← coe_eq_empty, coe_Ioi, Set.Ioi_eq_empty_iff]
@[simp] alias ⟨_, _root_.IsMax.finsetIoi_eq⟩ := Ioi_eq_empty
@[simp] lemma Ioi_nonempty : (Ioi a).Nonempty ↔ ¬ IsMax a := by simp [nonempty_iff_ne_empty]
theorem Ioi_top [OrderTop α] : Ioi (⊤ : α) = ∅ := Ioi_eq_empty.mpr isMax_top
@[simp]
theorem Ici_bot [OrderBot α] [Fintype α] : Ici (⊥ : α) = univ := by
ext a; simp only [mem_Ici, bot_le, mem_univ]
@[simp, aesop safe apply (rule_sets := [finsetNonempty])]
lemma nonempty_Ici : (Ici a).Nonempty := ⟨a, mem_Ici.2 le_rfl⟩
lemma nonempty_Ioi : (Ioi a).Nonempty ↔ ¬ IsMax a := by simp [Finset.Nonempty]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ioi_of_not_isMax⟩ := nonempty_Ioi
@[simp]
theorem Ici_subset_Ici : Ici a ⊆ Ici b ↔ b ≤ a := by
simp [← coe_subset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Ici_subset_Ici⟩ := Ici_subset_Ici
@[simp]
theorem Ici_ssubset_Ici : Ici a ⊂ Ici b ↔ b < a := by
simp [← coe_ssubset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Ici_ssubset_Ici⟩ := Ici_ssubset_Ici
@[gcongr]
theorem Ioi_subset_Ioi (h : a ≤ b) : Ioi b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioi_subset_Ioi h
@[gcongr]
theorem Ioi_ssubset_Ioi (h : a < b) : Ioi b ⊂ Ioi a := by
simpa [← coe_ssubset] using Set.Ioi_ssubset_Ioi h
variable [LocallyFiniteOrder α]
theorem Icc_subset_Ici_self : Icc a b ⊆ Ici a := by
simpa [← coe_subset] using Set.Icc_subset_Ici_self
theorem Ico_subset_Ici_self : Ico a b ⊆ Ici a := by
simpa [← coe_subset] using Set.Ico_subset_Ici_self
theorem Ioc_subset_Ioi_self : Ioc a b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioc_subset_Ioi_self
theorem Ioo_subset_Ioi_self : Ioo a b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioo_subset_Ioi_self
theorem Ioc_subset_Ici_self : Ioc a b ⊆ Ici a :=
Ioc_subset_Icc_self.trans Icc_subset_Ici_self
theorem Ioo_subset_Ici_self : Ioo a b ⊆ Ici a :=
Ioo_subset_Ico_self.trans Ico_subset_Ici_self
end LocallyFiniteOrderTop
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α]
@[simp]
theorem Iio_eq_empty : Iio a = ∅ ↔ IsMin a := Ioi_eq_empty (α := αᵒᵈ)
@[simp] alias ⟨_, _root_.IsMin.finsetIio_eq⟩ := Iio_eq_empty
@[simp] lemma Iio_nonempty : (Iio a).Nonempty ↔ ¬ IsMin a := by simp [nonempty_iff_ne_empty]
theorem Iio_bot [OrderBot α] : Iio (⊥ : α) = ∅ := Iio_eq_empty.mpr isMin_bot
@[simp]
theorem Iic_top [OrderTop α] [Fintype α] : Iic (⊤ : α) = univ := by
ext a; simp only [mem_Iic, le_top, mem_univ]
@[simp, aesop safe apply (rule_sets := [finsetNonempty])]
lemma nonempty_Iic : (Iic a).Nonempty := ⟨a, mem_Iic.2 le_rfl⟩
lemma nonempty_Iio : (Iio a).Nonempty ↔ ¬ IsMin a := by simp [Finset.Nonempty]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Iio_of_not_isMin⟩ := nonempty_Iio
@[simp]
theorem Iic_subset_Iic : Iic a ⊆ Iic b ↔ a ≤ b := by
simp [← coe_subset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Iic_subset_Iic⟩ := Iic_subset_Iic
@[simp]
theorem Iic_ssubset_Iic : Iic a ⊂ Iic b ↔ a < b := by
simp [← coe_ssubset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Iic_ssubset_Iic⟩ := Iic_ssubset_Iic
@[gcongr]
theorem Iio_subset_Iio (h : a ≤ b) : Iio a ⊆ Iio b := by
simpa [← coe_subset] using Set.Iio_subset_Iio h
@[gcongr]
theorem Iio_ssubset_Iio (h : a < b) : Iio a ⊂ Iio b := by
simpa [← coe_ssubset] using Set.Iio_ssubset_Iio h
variable [LocallyFiniteOrder α]
theorem Icc_subset_Iic_self : Icc a b ⊆ Iic b := by
simpa [← coe_subset] using Set.Icc_subset_Iic_self
theorem Ioc_subset_Iic_self : Ioc a b ⊆ Iic b := by
simpa [← coe_subset] using Set.Ioc_subset_Iic_self
theorem Ico_subset_Iio_self : Ico a b ⊆ Iio b := by
simpa [← coe_subset] using Set.Ico_subset_Iio_self
theorem Ioo_subset_Iio_self : Ioo a b ⊆ Iio b := by
simpa [← coe_subset] using Set.Ioo_subset_Iio_self
theorem Ico_subset_Iic_self : Ico a b ⊆ Iic b :=
Ico_subset_Icc_self.trans Icc_subset_Iic_self
theorem Ioo_subset_Iic_self : Ioo a b ⊆ Iic b :=
Ioo_subset_Ioc_self.trans Ioc_subset_Iic_self
theorem Iic_disjoint_Ioc (h : a ≤ b) : Disjoint (Iic a) (Ioc b c) :=
disjoint_left.2 fun _ hax hbcx ↦ (mem_Iic.1 hax).not_lt <| lt_of_le_of_lt h (mem_Ioc.1 hbcx).1
/-- An equivalence between `Finset.Iic a` and `Set.Iic a`. -/
def _root_.Equiv.IicFinsetSet (a : α) : Iic a ≃ Set.Iic a where
toFun b := ⟨b.1, coe_Iic a ▸ mem_coe.2 b.2⟩
invFun b := ⟨b.1, by rw [← mem_coe, coe_Iic a]; exact b.2⟩
left_inv := fun _ ↦ rfl
right_inv := fun _ ↦ rfl
end LocallyFiniteOrderBot
section LocallyFiniteOrderTop
variable [LocallyFiniteOrderTop α] {a : α}
theorem Ioi_subset_Ici_self : Ioi a ⊆ Ici a := by
simpa [← coe_subset] using Set.Ioi_subset_Ici_self
theorem _root_.BddBelow.finite {s : Set α} (hs : BddBelow s) : s.Finite :=
let ⟨a, ha⟩ := hs
(Ici a).finite_toSet.subset fun _ hx => mem_Ici.2 <| ha hx
theorem _root_.Set.Infinite.not_bddBelow {s : Set α} : s.Infinite → ¬BddBelow s :=
mt BddBelow.finite
variable [Fintype α]
theorem filter_lt_eq_Ioi [DecidablePred (a < ·)] : ({x | a < x} : Finset _) = Ioi a := by ext; simp
theorem filter_le_eq_Ici [DecidablePred (a ≤ ·)] : ({x | a ≤ x} : Finset _) = Ici a := by ext; simp
end LocallyFiniteOrderTop
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α] {a : α}
theorem Iio_subset_Iic_self : Iio a ⊆ Iic a := by
simpa [← coe_subset] using Set.Iio_subset_Iic_self
theorem _root_.BddAbove.finite {s : Set α} (hs : BddAbove s) : s.Finite :=
hs.dual.finite
theorem _root_.Set.Infinite.not_bddAbove {s : Set α} : s.Infinite → ¬BddAbove s :=
mt BddAbove.finite
variable [Fintype α]
theorem filter_gt_eq_Iio [DecidablePred (· < a)] : ({x | x < a} : Finset _) = Iio a := by ext; simp
theorem filter_ge_eq_Iic [DecidablePred (· ≤ a)] : ({x | x ≤ a} : Finset _) = Iic a := by ext; simp
end LocallyFiniteOrderBot
section LocallyFiniteOrder
variable [LocallyFiniteOrder α]
@[simp]
theorem Icc_bot [OrderBot α] : Icc (⊥ : α) a = Iic a := rfl
@[simp]
theorem Icc_top [OrderTop α] : Icc a (⊤ : α) = Ici a := rfl
@[simp]
theorem Ico_bot [OrderBot α] : Ico (⊥ : α) a = Iio a := rfl
@[simp]
theorem Ioc_top [OrderTop α] : Ioc a (⊤ : α) = Ioi a := rfl
theorem Icc_bot_top [BoundedOrder α] [Fintype α] : Icc (⊥ : α) (⊤ : α) = univ := by
rw [Icc_bot, Iic_top]
end LocallyFiniteOrder
variable [LocallyFiniteOrderTop α] [LocallyFiniteOrderBot α]
theorem disjoint_Ioi_Iio (a : α) : Disjoint (Ioi a) (Iio a) :=
disjoint_left.2 fun _ hab hba => (mem_Ioi.1 hab).not_lt <| mem_Iio.1 hba
end Preorder
section PartialOrder
variable [PartialOrder α] [LocallyFiniteOrder α] {a b c : α}
@[simp]
theorem Icc_self (a : α) : Icc a a = {a} := by rw [← coe_eq_singleton, coe_Icc, Set.Icc_self]
@[simp]
theorem Icc_eq_singleton_iff : Icc a b = {c} ↔ a = c ∧ b = c := by
rw [← coe_eq_singleton, coe_Icc, Set.Icc_eq_singleton_iff]
theorem Ico_disjoint_Ico_consecutive (a b c : α) : Disjoint (Ico a b) (Ico b c) :=
disjoint_left.2 fun _ hab hbc => (mem_Ico.mp hab).2.not_le (mem_Ico.mp hbc).1
@[simp]
theorem Ici_top [OrderTop α] : Ici (⊤ : α) = {⊤} := Icc_eq_singleton_iff.2 ⟨rfl, rfl⟩
@[simp]
theorem Iic_bot [OrderBot α] : Iic (⊥ : α) = {⊥} := Icc_eq_singleton_iff.2 ⟨rfl, rfl⟩
section DecidableEq
variable [DecidableEq α]
@[simp]
theorem Icc_erase_left (a b : α) : (Icc a b).erase a = Ioc a b := by simp [← coe_inj]
@[simp]
theorem Icc_erase_right (a b : α) : (Icc a b).erase b = Ico a b := by simp [← coe_inj]
@[simp]
theorem Ico_erase_left (a b : α) : (Ico a b).erase a = Ioo a b := by simp [← coe_inj]
@[simp]
theorem Ioc_erase_right (a b : α) : (Ioc a b).erase b = Ioo a b := by simp [← coe_inj]
@[simp]
theorem Icc_diff_both (a b : α) : Icc a b \ {a, b} = Ioo a b := by simp [← coe_inj]
@[simp]
theorem Ico_insert_right (h : a ≤ b) : insert b (Ico a b) = Icc a b := by
rw [← coe_inj, coe_insert, coe_Icc, coe_Ico, Set.insert_eq, Set.union_comm, Set.Ico_union_right h]
@[simp]
theorem Ioc_insert_left (h : a ≤ b) : insert a (Ioc a b) = Icc a b := by
rw [← coe_inj, coe_insert, coe_Ioc, coe_Icc, Set.insert_eq, Set.union_comm, Set.Ioc_union_left h]
@[simp]
theorem Ioo_insert_left (h : a < b) : insert a (Ioo a b) = Ico a b := by
rw [← coe_inj, coe_insert, coe_Ioo, coe_Ico, Set.insert_eq, Set.union_comm, Set.Ioo_union_left h]
@[simp]
theorem Ioo_insert_right (h : a < b) : insert b (Ioo a b) = Ioc a b := by
rw [← coe_inj, coe_insert, coe_Ioo, coe_Ioc, Set.insert_eq, Set.union_comm, Set.Ioo_union_right h]
@[simp]
theorem Icc_diff_Ico_self (h : a ≤ b) : Icc a b \ Ico a b = {b} := by simp [← coe_inj, h]
@[simp]
theorem Icc_diff_Ioc_self (h : a ≤ b) : Icc a b \ Ioc a b = {a} := by simp [← coe_inj, h]
@[simp]
theorem Icc_diff_Ioo_self (h : a ≤ b) : Icc a b \ Ioo a b = {a, b} := by simp [← coe_inj, h]
@[simp]
theorem Ico_diff_Ioo_self (h : a < b) : Ico a b \ Ioo a b = {a} := by simp [← coe_inj, h]
@[simp]
theorem Ioc_diff_Ioo_self (h : a < b) : Ioc a b \ Ioo a b = {b} := by simp [← coe_inj, h]
@[simp]
theorem Ico_inter_Ico_consecutive (a b c : α) : Ico a b ∩ Ico b c = ∅ :=
(Ico_disjoint_Ico_consecutive a b c).eq_bot
end DecidableEq
-- Those lemmas are purposefully the other way around
/-- `Finset.cons` version of `Finset.Ico_insert_right`. -/
theorem Icc_eq_cons_Ico (h : a ≤ b) : Icc a b = (Ico a b).cons b right_not_mem_Ico := by
classical rw [cons_eq_insert, Ico_insert_right h]
/-- `Finset.cons` version of `Finset.Ioc_insert_left`. -/
theorem Icc_eq_cons_Ioc (h : a ≤ b) : Icc a b = (Ioc a b).cons a left_not_mem_Ioc := by
classical rw [cons_eq_insert, Ioc_insert_left h]
/-- `Finset.cons` version of `Finset.Ioo_insert_right`. -/
theorem Ioc_eq_cons_Ioo (h : a < b) : Ioc a b = (Ioo a b).cons b right_not_mem_Ioo := by
classical rw [cons_eq_insert, Ioo_insert_right h]
/-- `Finset.cons` version of `Finset.Ioo_insert_left`. -/
theorem Ico_eq_cons_Ioo (h : a < b) : Ico a b = (Ioo a b).cons a left_not_mem_Ioo := by
classical rw [cons_eq_insert, Ioo_insert_left h]
theorem Ico_filter_le_left {a b : α} [DecidablePred (· ≤ a)] (hab : a < b) :
{x ∈ Ico a b | x ≤ a} = {a} := by
ext x
rw [mem_filter, mem_Ico, mem_singleton, and_right_comm, ← le_antisymm_iff, eq_comm]
exact and_iff_left_of_imp fun h => h.le.trans_lt hab
theorem card_Ico_eq_card_Icc_sub_one (a b : α) : #(Ico a b) = #(Icc a b) - 1 := by
classical
by_cases h : a ≤ b
· rw [Icc_eq_cons_Ico h, card_cons]
exact (Nat.add_sub_cancel _ _).symm
· rw [Ico_eq_empty fun h' => h h'.le, Icc_eq_empty h, card_empty, Nat.zero_sub]
theorem card_Ioc_eq_card_Icc_sub_one (a b : α) : #(Ioc a b) = #(Icc a b) - 1 :=
@card_Ico_eq_card_Icc_sub_one αᵒᵈ _ _ _ _
theorem card_Ioo_eq_card_Ico_sub_one (a b : α) : #(Ioo a b) = #(Ico a b) - 1 := by
classical
by_cases h : a < b
· rw [Ico_eq_cons_Ioo h, card_cons]
exact (Nat.add_sub_cancel _ _).symm
· rw [Ioo_eq_empty h, Ico_eq_empty h, card_empty, Nat.zero_sub]
theorem card_Ioo_eq_card_Ioc_sub_one (a b : α) : #(Ioo a b) = #(Ioc a b) - 1 :=
@card_Ioo_eq_card_Ico_sub_one αᵒᵈ _ _ _ _
theorem card_Ioo_eq_card_Icc_sub_two (a b : α) : #(Ioo a b) = #(Icc a b) - 2 := by
rw [card_Ioo_eq_card_Ico_sub_one, card_Ico_eq_card_Icc_sub_one]
rfl
end PartialOrder
section Prod
variable {β : Type*}
section sectL
lemma uIcc_map_sectL [Lattice α] [Lattice β] [LocallyFiniteOrder α] [LocallyFiniteOrder β]
[DecidableLE (α × β)] (a b : α) (c : β) :
(uIcc a b).map (.sectL _ c) = uIcc (a, c) (b, c) := by
aesop (add safe forward [le_antisymm])
variable [Preorder α] [PartialOrder β] [LocallyFiniteOrder α] [LocallyFiniteOrder β]
[DecidableLE (α × β)] (a b : α) (c : β)
lemma Icc_map_sectL : (Icc a b).map (.sectL _ c) = Icc (a, c) (b, c) := by
aesop (add safe forward [le_antisymm])
lemma Ioc_map_sectL : (Ioc a b).map (.sectL _ c) = Ioc (a, c) (b, c) := by
aesop (add safe forward [le_antisymm, le_of_lt])
lemma Ico_map_sectL : (Ico a b).map (.sectL _ c) = Ico (a, c) (b, c) := by
aesop (add safe forward [le_antisymm, le_of_lt])
lemma Ioo_map_sectL : (Ioo a b).map (.sectL _ c) = Ioo (a, c) (b, c) := by
aesop (add safe forward [le_antisymm, le_of_lt])
end sectL
section sectR
lemma uIcc_map_sectR [Lattice α] [Lattice β] [LocallyFiniteOrder α] [LocallyFiniteOrder β]
[DecidableLE (α × β)] (c : α) (a b : β) :
(uIcc a b).map (.sectR c _) = uIcc (c, a) (c, b) := by
aesop (add safe forward [le_antisymm])
variable [PartialOrder α] [Preorder β] [LocallyFiniteOrder α] [LocallyFiniteOrder β]
[DecidableLE (α × β)] (c : α) (a b : β)
lemma Icc_map_sectR : (Icc a b).map (.sectR c _) = Icc (c, a) (c, b) := by
aesop (add safe forward [le_antisymm])
lemma Ioc_map_sectR : (Ioc a b).map (.sectR c _) = Ioc (c, a) (c, b) := by
aesop (add safe forward [le_antisymm, le_of_lt])
lemma Ico_map_sectR : (Ico a b).map (.sectR c _) = Ico (c, a) (c, b) := by
aesop (add safe forward [le_antisymm, le_of_lt])
lemma Ioo_map_sectR : (Ioo a b).map (.sectR c _) = Ioo (c, a) (c, b) := by
aesop (add safe forward [le_antisymm, le_of_lt])
end sectR
end Prod
section BoundedPartialOrder
variable [PartialOrder α]
section OrderTop
variable [LocallyFiniteOrderTop α]
@[simp]
theorem Ici_erase [DecidableEq α] (a : α) : (Ici a).erase a = Ioi a := by
ext
simp_rw [Finset.mem_erase, mem_Ici, mem_Ioi, lt_iff_le_and_ne, and_comm, ne_comm]
@[simp]
theorem Ioi_insert [DecidableEq α] (a : α) : insert a (Ioi a) = Ici a := by
ext
simp_rw [Finset.mem_insert, mem_Ici, mem_Ioi, le_iff_lt_or_eq, or_comm, eq_comm]
theorem not_mem_Ioi_self {b : α} : b ∉ Ioi b := fun h => lt_irrefl _ (mem_Ioi.1 h)
-- Purposefully written the other way around
/-- `Finset.cons` version of `Finset.Ioi_insert`. -/
theorem Ici_eq_cons_Ioi (a : α) : Ici a = (Ioi a).cons a not_mem_Ioi_self := by
classical rw [cons_eq_insert, Ioi_insert]
theorem card_Ioi_eq_card_Ici_sub_one (a : α) : #(Ioi a) = #(Ici a) - 1 := by
rw [Ici_eq_cons_Ioi, card_cons, Nat.add_sub_cancel_right]
end OrderTop
section OrderBot
variable [LocallyFiniteOrderBot α]
@[simp]
theorem Iic_erase [DecidableEq α] (b : α) : (Iic b).erase b = Iio b := by
ext
simp_rw [Finset.mem_erase, mem_Iic, mem_Iio, lt_iff_le_and_ne, and_comm]
@[simp]
theorem Iio_insert [DecidableEq α] (b : α) : insert b (Iio b) = Iic b := by
ext
simp_rw [Finset.mem_insert, mem_Iic, mem_Iio, le_iff_lt_or_eq, or_comm]
theorem not_mem_Iio_self {b : α} : b ∉ Iio b := fun h => lt_irrefl _ (mem_Iio.1 h)
-- Purposefully written the other way around
/-- `Finset.cons` version of `Finset.Iio_insert`. -/
theorem Iic_eq_cons_Iio (b : α) : Iic b = (Iio b).cons b not_mem_Iio_self := by
classical rw [cons_eq_insert, Iio_insert]
theorem card_Iio_eq_card_Iic_sub_one (a : α) : #(Iio a) = #(Iic a) - 1 := by
rw [Iic_eq_cons_Iio, card_cons, Nat.add_sub_cancel_right]
end OrderBot
end BoundedPartialOrder
section SemilatticeSup
variable [SemilatticeSup α] [LocallyFiniteOrderBot α]
-- TODO: Why does `id_eq` simplify the LHS here but not the LHS of `Finset.sup_Iic`?
lemma sup'_Iic (a : α) : (Iic a).sup' nonempty_Iic id = a :=
le_antisymm (sup'_le _ _ fun _ ↦ mem_Iic.1) <| le_sup' (f := id) <| mem_Iic.2 <| le_refl a
@[simp] lemma sup_Iic [OrderBot α] (a : α) : (Iic a).sup id = a :=
le_antisymm (Finset.sup_le fun _ ↦ mem_Iic.1) <| le_sup (f := id) <| mem_Iic.2 <| le_refl a
lemma image_subset_Iic_sup [OrderBot α] [DecidableEq α] (f : ι → α) (s : Finset ι) :
s.image f ⊆ Iic (s.sup f) := by
refine fun i hi ↦ mem_Iic.2 ?_
obtain ⟨j, hj, rfl⟩ := mem_image.1 hi
exact le_sup hj
lemma subset_Iic_sup_id [OrderBot α] (s : Finset α) : s ⊆ Iic (s.sup id) :=
fun _ h ↦ mem_Iic.2 <| le_sup (f := id) h
end SemilatticeSup
section SemilatticeInf
variable [SemilatticeInf α] [LocallyFiniteOrderTop α]
lemma inf'_Ici (a : α) : (Ici a).inf' nonempty_Ici id = a :=
ge_antisymm (le_inf' _ _ fun _ ↦ mem_Ici.1) <| inf'_le (f := id) <| mem_Ici.2 <| le_refl a
@[simp] lemma inf_Ici [OrderTop α] (a : α) : (Ici a).inf id = a :=
le_antisymm (inf_le (f := id) <| mem_Ici.2 <| le_refl a) <| Finset.le_inf fun _ ↦ mem_Ici.1
end SemilatticeInf
section LinearOrder
variable [LinearOrder α]
section LocallyFiniteOrder
variable [LocallyFiniteOrder α]
theorem Ico_subset_Ico_iff {a₁ b₁ a₂ b₂ : α} (h : a₁ < b₁) :
Ico a₁ b₁ ⊆ Ico a₂ b₂ ↔ a₂ ≤ a₁ ∧ b₁ ≤ b₂ := by
rw [← coe_subset, coe_Ico, coe_Ico, Set.Ico_subset_Ico_iff h]
theorem Ico_union_Ico_eq_Ico {a b c : α} (hab : a ≤ b) (hbc : b ≤ c) :
Ico a b ∪ Ico b c = Ico a c := by
rw [← coe_inj, coe_union, coe_Ico, coe_Ico, coe_Ico, Set.Ico_union_Ico_eq_Ico hab hbc]
@[simp]
theorem Ioc_union_Ioc_eq_Ioc {a b c : α} (h₁ : a ≤ b) (h₂ : b ≤ c) :
Ioc a b ∪ Ioc b c = Ioc a c := by
rw [← coe_inj, coe_union, coe_Ioc, coe_Ioc, coe_Ioc, Set.Ioc_union_Ioc_eq_Ioc h₁ h₂]
theorem Ico_subset_Ico_union_Ico {a b c : α} : Ico a c ⊆ Ico a b ∪ Ico b c := by
rw [← coe_subset, coe_union, coe_Ico, coe_Ico, coe_Ico]
exact Set.Ico_subset_Ico_union_Ico
theorem Ico_union_Ico' {a b c d : α} (hcb : c ≤ b) (had : a ≤ d) :
Ico a b ∪ Ico c d = Ico (min a c) (max b d) := by
rw [← coe_inj, coe_union, coe_Ico, coe_Ico, coe_Ico, Set.Ico_union_Ico' hcb had]
theorem Ico_union_Ico {a b c d : α} (h₁ : min a b ≤ max c d) (h₂ : min c d ≤ max a b) :
Ico a b ∪ Ico c d = Ico (min a c) (max b d) := by
rw [← coe_inj, coe_union, coe_Ico, coe_Ico, coe_Ico, Set.Ico_union_Ico h₁ h₂]
theorem Ico_inter_Ico {a b c d : α} : Ico a b ∩ Ico c d = Ico (max a c) (min b d) := by
rw [← coe_inj, coe_inter, coe_Ico, coe_Ico, coe_Ico, Set.Ico_inter_Ico]
theorem Ioc_inter_Ioc {a b c d : α} : Ioc a b ∩ Ioc c d = Ioc (max a c) (min b d) := by
rw [← coe_inj]
push_cast
exact Set.Ioc_inter_Ioc
@[simp]
theorem Ico_filter_lt (a b c : α) : {x ∈ Ico a b | x < c} = Ico a (min b c) := by
cases le_total b c with
| inl h => rw [Ico_filter_lt_of_right_le h, min_eq_left h]
| inr h => rw [Ico_filter_lt_of_le_right h, min_eq_right h]
@[simp]
theorem Ico_filter_le (a b c : α) : {x ∈ Ico a b | c ≤ x} = Ico (max a c) b := by
cases le_total a c with
| inl h => rw [Ico_filter_le_of_left_le h, max_eq_right h]
| inr h => rw [Ico_filter_le_of_le_left h, max_eq_left h]
@[simp]
theorem Ioo_filter_lt (a b c : α) : {x ∈ Ioo a b | x < c} = Ioo a (min b c) := by
ext
simp [and_assoc]
@[simp]
theorem Iio_filter_lt {α} [LinearOrder α] [LocallyFiniteOrderBot α] (a b : α) :
{x ∈ Iio a | x < b} = Iio (min a b) := by
ext
simp [and_assoc]
@[simp]
theorem Ico_diff_Ico_left (a b c : α) : Ico a b \ Ico a c = Ico (max a c) b := by
cases le_total a c with
| inl h =>
ext x
rw [mem_sdiff, mem_Ico, mem_Ico, mem_Ico, max_eq_right h, and_right_comm, not_and, not_lt]
exact and_congr_left' ⟨fun hx => hx.2 hx.1, fun hx => ⟨h.trans hx, fun _ => hx⟩⟩
| inr h => rw [Ico_eq_empty_of_le h, sdiff_empty, max_eq_left h]
@[simp]
theorem Ico_diff_Ico_right (a b c : α) : Ico a b \ Ico c b = Ico a (min b c) := by
cases le_total b c with
| inl h => rw [Ico_eq_empty_of_le h, sdiff_empty, min_eq_left h]
| inr h =>
ext x
rw [mem_sdiff, mem_Ico, mem_Ico, mem_Ico, min_eq_right h, and_assoc, not_and', not_le]
exact and_congr_right' ⟨fun hx => hx.2 hx.1, fun hx => ⟨hx.trans_le h, fun _ => hx⟩⟩
@[simp]
theorem Ioc_disjoint_Ioc : Disjoint (Ioc a₁ a₂) (Ioc b₁ b₂) ↔ min a₂ b₂ ≤ max a₁ b₁ := by
simp_rw [disjoint_iff_inter_eq_empty, Ioc_inter_Ioc, Ioc_eq_empty_iff, not_lt]
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α]
theorem Iic_diff_Ioc : Iic b \ Ioc a b = Iic (a ⊓ b) := by
rw [← coe_inj]
push_cast
exact Set.Iic_diff_Ioc
theorem Iic_diff_Ioc_self_of_le (hab : a ≤ b) : Iic b \ Ioc a b = Iic a := by
rw [Iic_diff_Ioc, min_eq_left hab]
theorem Iic_union_Ioc_eq_Iic (h : a ≤ b) : Iic a ∪ Ioc a b = Iic b := by
rw [← coe_inj]
push_cast
exact Set.Iic_union_Ioc_eq_Iic h
end LocallyFiniteOrderBot
end LocallyFiniteOrder
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α] {s : Set α}
theorem _root_.Set.Infinite.exists_gt (hs : s.Infinite) : ∀ a, ∃ b ∈ s, a < b :=
not_bddAbove_iff.1 hs.not_bddAbove
theorem _root_.Set.infinite_iff_exists_gt [Nonempty α] : s.Infinite ↔ ∀ a, ∃ b ∈ s, a < b :=
⟨Set.Infinite.exists_gt, Set.infinite_of_forall_exists_gt⟩
|
end LocallyFiniteOrderBot
| Mathlib/Order/Interval/Finset/Basic.lean | 924 | 925 |
/-
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.Combinatorics.SetFamily.Compression.Down
import Mathlib.Data.Fintype.Powerset
import Mathlib.Order.Interval.Finset.Nat
import Mathlib.Algebra.BigOperators.Group.Finset.Basic
/-!
# Shattering families
This file defines the shattering property and VC-dimension of set families.
## Main declarations
* `Finset.Shatters`: The shattering property.
* `Finset.shatterer`: The set family of sets shattered by a set family.
* `Finset.vcDim`: The Vapnik-Chervonenkis dimension.
## TODO
* Order-shattering
* Strong shattering
-/
open scoped FinsetFamily
namespace Finset
variable {α : Type*} [DecidableEq α] {𝒜 ℬ : Finset (Finset α)} {s t : Finset α} {a : α}
/-- A set family `𝒜` shatters a set `s` if all subsets of `s` can be obtained as the intersection
of `s` and some element of the set family, and we denote this `𝒜.Shatters s`. We also say that `s`
is *traced* by `𝒜`. -/
def Shatters (𝒜 : Finset (Finset α)) (s : Finset α) : Prop := ∀ ⦃t⦄, t ⊆ s → ∃ u ∈ 𝒜, s ∩ u = t
instance : DecidablePred 𝒜.Shatters := fun _s ↦ decidableForallOfDecidableSubsets
lemma Shatters.exists_inter_eq_singleton (hs : Shatters 𝒜 s) (ha : a ∈ s) : ∃ t ∈ 𝒜, s ∩ t = {a} :=
hs <| singleton_subset_iff.2 ha
lemma Shatters.mono_left (h : 𝒜 ⊆ ℬ) (h𝒜 : 𝒜.Shatters s) : ℬ.Shatters s :=
fun _t ht ↦ let ⟨u, hu, hut⟩ := h𝒜 ht; ⟨u, h hu, hut⟩
lemma Shatters.mono_right (h : t ⊆ s) (hs : 𝒜.Shatters s) : 𝒜.Shatters t := fun u hu ↦ by
obtain ⟨v, hv, rfl⟩ := hs (hu.trans h); exact ⟨v, hv, inf_congr_right hu <| inf_le_of_left_le h⟩
lemma Shatters.exists_superset (h : 𝒜.Shatters s) : ∃ t ∈ 𝒜, s ⊆ t :=
let ⟨t, ht, hst⟩ := h Subset.rfl; ⟨t, ht, inter_eq_left.1 hst⟩
lemma shatters_of_forall_subset (h : ∀ t, t ⊆ s → t ∈ 𝒜) : 𝒜.Shatters s :=
fun t ht ↦ ⟨t, h _ ht, inter_eq_right.2 ht⟩
protected lemma Shatters.nonempty (h : 𝒜.Shatters s) : 𝒜.Nonempty :=
let ⟨t, ht, _⟩ := h Subset.rfl; ⟨t, ht⟩
@[simp] lemma shatters_empty : 𝒜.Shatters ∅ ↔ 𝒜.Nonempty :=
⟨Shatters.nonempty, fun ⟨s, hs⟩ t ht ↦ ⟨s, hs, by rwa [empty_inter, eq_comm, ← subset_empty]⟩⟩
protected lemma Shatters.subset_iff (h : 𝒜.Shatters s) : t ⊆ s ↔ ∃ u ∈ 𝒜, s ∩ u = t :=
⟨fun ht ↦ h ht, by rintro ⟨u, _, rfl⟩; exact inter_subset_left⟩
lemma shatters_iff : 𝒜.Shatters s ↔ 𝒜.image (fun t ↦ s ∩ t) = s.powerset :=
⟨fun h ↦ by ext t; rw [mem_image, mem_powerset, h.subset_iff],
fun h t ht ↦ by rwa [← mem_powerset, ← h, mem_image] at ht⟩
lemma univ_shatters [Fintype α] : univ.Shatters s :=
shatters_of_forall_subset fun _ _ ↦ mem_univ _
@[simp] lemma shatters_univ [Fintype α] : 𝒜.Shatters univ ↔ 𝒜 = univ := by
rw [shatters_iff, powerset_univ]; simp_rw [univ_inter, image_id']
/-- The set family of sets that are shattered by `𝒜`. -/
def shatterer (𝒜 : Finset (Finset α)) : Finset (Finset α) :=
{s ∈ 𝒜.biUnion powerset | 𝒜.Shatters s}
@[simp] lemma mem_shatterer : s ∈ 𝒜.shatterer ↔ 𝒜.Shatters s := by
refine mem_filter.trans <| and_iff_right_of_imp fun h ↦ ?_
simp_rw [mem_biUnion, mem_powerset]
exact h.exists_superset
@[gcongr] lemma shatterer_mono (h : 𝒜 ⊆ ℬ) : 𝒜.shatterer ⊆ ℬ.shatterer :=
fun _ ↦ by simpa using Shatters.mono_left h
lemma subset_shatterer (h : IsLowerSet (𝒜 : Set (Finset α))) : 𝒜 ⊆ 𝒜.shatterer :=
fun _s hs ↦ mem_shatterer.2 fun t ht ↦ ⟨t, h ht hs, inter_eq_right.2 ht⟩
|
@[simp] lemma isLowerSet_shatterer (𝒜 : Finset (Finset α)) :
| Mathlib/Combinatorics/SetFamily/Shatter.lean | 88 | 89 |
/-
Copyright (c) 2024 Josha Dekker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Josha Dekker
-/
import Mathlib.Analysis.SpecialFunctions.Exponential
import Mathlib.Probability.ProbabilityMassFunction.Basic
import Mathlib.MeasureTheory.Function.StronglyMeasurable.Basic
/-! # Poisson distributions over ℕ
Define the Poisson measure over the natural numbers
## Main definitions
* `poissonPMFReal`: the function `fun n ↦ exp (- λ) * λ ^ n / n!`
for `n ∈ ℕ`, which is the probability density function of a Poisson distribution with
rate `λ > 0`.
* `poissonPMF`: `ℝ≥0∞`-valued pdf,
`poissonPMF λ = ENNReal.ofReal (poissonPMFReal λ)`.
* `poissonMeasure`: a Poisson measure on `ℕ`, parametrized by its rate `λ`.
-/
open scoped ENNReal NNReal Nat
open MeasureTheory Real Set Filter Topology
namespace ProbabilityTheory
section PoissonPMF
/-- The pmf of the Poisson distribution depending on its rate, as a function to ℝ -/
noncomputable
def poissonPMFReal (r : ℝ≥0) (n : ℕ) : ℝ := exp (- r) * r ^ n / n !
lemma poissonPMFRealSum (r : ℝ≥0) : HasSum (fun n ↦ poissonPMFReal r n) 1 := by
let r := r.toReal
unfold poissonPMFReal
apply (hasSum_mul_left_iff (exp_ne_zero r)).mp
simp only [mul_one]
have : (fun i ↦ rexp r * (rexp (-r) * r ^ i / ↑(Nat.factorial i))) =
fun i ↦ r ^ i / ↑(Nat.factorial i) := by
ext n
rw [mul_div_assoc, exp_neg, ← mul_assoc, ← div_eq_mul_inv, div_self (exp_ne_zero r), one_mul]
rw [this, exp_eq_exp_ℝ]
exact NormedSpace.expSeries_div_hasSum_exp ℝ r
/-- The Poisson pmf is positive for all natural numbers -/
lemma poissonPMFReal_pos {r : ℝ≥0} {n : ℕ} (hr : 0 < r) : 0 < poissonPMFReal r n := by
rw [poissonPMFReal]
positivity
lemma poissonPMFReal_nonneg {r : ℝ≥0} {n : ℕ} : 0 ≤ poissonPMFReal r n := by
unfold poissonPMFReal
positivity
/-- The pmf of the Poisson distribution depending on its rate, as a PMF. -/
noncomputable
def poissonPMF (r : ℝ≥0) : PMF ℕ := by
refine ⟨fun n ↦ ENNReal.ofReal (poissonPMFReal r n), ?_⟩
apply ENNReal.hasSum_coe.mpr
rw [← toNNReal_one]
exact (poissonPMFRealSum r).toNNReal (fun n ↦ poissonPMFReal_nonneg)
/-- The Poisson pmf is measurable. -/
| @[measurability]
lemma measurable_poissonPMFReal (r : ℝ≥0) : Measurable (poissonPMFReal r) := by measurability
| Mathlib/Probability/Distributions/Poisson.lean | 66 | 68 |
/-
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]
| Mathlib/Algebra/Polynomial/Degree/Definitions.lean | 556 | 557 |
/-
Copyright (c) 2019 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes
-/
import Mathlib.Data.Matrix.Mul
import Mathlib.Data.PEquiv
/-!
# partial equivalences for matrices
Using partial equivalences to represent matrices.
This file introduces the function `PEquiv.toMatrix`, which returns a matrix containing ones and
zeros. For any partial equivalence `f`, `f.toMatrix i j = 1 ↔ f i = some j`.
The following important properties of this function are proved
`toMatrix_trans : (f.trans g).toMatrix = f.toMatrix * g.toMatrix`
`toMatrix_symm : f.symm.toMatrix = f.toMatrixᵀ`
`toMatrix_refl : (PEquiv.refl n).toMatrix = 1`
`toMatrix_bot : ⊥.toMatrix = 0`
This theory gives the matrix representation of projection linear maps, and their right inverses.
For example, the matrix `(single (0 : Fin 1) (i : Fin n)).toMatrix` corresponds to the ith
projection map from R^n to R.
Any injective function `Fin m → Fin n` gives rise to a `PEquiv`, whose matrix is the projection
map from R^m → R^n represented by the same function. The transpose of this matrix is the right
inverse of this map, sending anything not in the image to zero.
## notations
This file uses `ᵀ` for `Matrix.transpose`.
-/
assert_not_exists Field
namespace PEquiv
open Matrix
universe u v
variable {k l m n : Type*}
variable {α β : Type*}
open Matrix
/-- `toMatrix` returns a matrix containing ones and zeros. `f.toMatrix i j` is `1` if
`f i = some j` and `0` otherwise -/
def toMatrix [DecidableEq n] [Zero α] [One α] (f : m ≃. n) : Matrix m n α :=
of fun i j => if j ∈ f i then (1 : α) else 0
-- TODO: set as an equation lemma for `toMatrix`, see https://github.com/leanprover-community/mathlib4/pull/3024
@[simp]
theorem toMatrix_apply [DecidableEq n] [Zero α] [One α] (f : m ≃. n) (i j) :
toMatrix f i j = if j ∈ f i then (1 : α) else 0 :=
rfl
theorem toMatrix_mul_apply [Fintype m] [DecidableEq m] [NonAssocSemiring α] (f : l ≃. m) (i j)
(M : Matrix m n α) : (f.toMatrix * M :) i j = Option.casesOn (f i) 0 fun fi => M fi j := by
dsimp [toMatrix, Matrix.mul_apply]
rcases h : f i with - | fi
· simp [h]
· rw [Finset.sum_eq_single fi] <;> simp +contextual [h, eq_comm]
@[deprecated (since := "2025-01-27")] alias mul_matrix_apply := toMatrix_mul_apply
theorem mul_toMatrix_apply [Fintype m] [NonAssocSemiring α] [DecidableEq n] (M : Matrix l m α)
(f : m ≃. n) (i j) : (M * f.toMatrix :) i j = Option.casesOn (f.symm j) 0 (M i) := by
| dsimp [Matrix.mul_apply, toMatrix_apply]
rcases h : f.symm j with - | fj
· simp [h, ← f.eq_some_iff]
· rw [Finset.sum_eq_single fj]
· simp [h, ← f.eq_some_iff]
| Mathlib/Data/Matrix/PEquiv.lean | 70 | 74 |
/-
Copyright (c) 2019 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Algebra.Group.Units.Equiv
import Mathlib.CategoryTheory.Endomorphism
import Mathlib.CategoryTheory.HomCongr
/-!
# Conjugate morphisms by isomorphisms
An isomorphism `α : X ≅ Y` defines
- a monoid isomorphism
`CategoryTheory.Iso.conj : End X ≃* End Y` by `α.conj f = α.inv ≫ f ≫ α.hom`;
- a group isomorphism `CategoryTheory.Iso.conjAut : Aut X ≃* Aut Y` by
`α.conjAut f = α.symm ≪≫ f ≪≫ α`
using
`CategoryTheory.Iso.homCongr : (X ≅ X₁) → (Y ≅ Y₁) → (X ⟶ Y) ≃ (X₁ ⟶ Y₁)`
and `CategoryTheory.Iso.isoCongr : (f : X₁ ≅ X₂) → (g : Y₁ ≅ Y₂) → (X₁ ≅ Y₁) ≃ (X₂ ≅ Y₂)`
which are defined in `CategoryTheory.HomCongr`.
-/
universe v u
namespace CategoryTheory
namespace Iso
variable {C : Type u} [Category.{v} C]
variable {X Y : C} (α : X ≅ Y)
/-- An isomorphism between two objects defines a monoid isomorphism between their
monoid of endomorphisms. -/
def conj : End X ≃* End Y :=
{ homCongr α α with map_mul' := fun f g => homCongr_comp α α α g f }
theorem conj_apply (f : End X) : α.conj f = α.inv ≫ f ≫ α.hom :=
rfl
@[simp]
theorem conj_comp (f g : End X) : α.conj (f ≫ g) = α.conj f ≫ α.conj g :=
map_mul α.conj g f
@[simp]
theorem conj_id : α.conj (𝟙 X) = 𝟙 Y :=
map_one α.conj
@[simp]
theorem refl_conj (f : End X) : (Iso.refl X).conj f = f := by
rw [conj_apply, Iso.refl_inv, Iso.refl_hom, Category.id_comp, Category.comp_id]
@[simp]
theorem trans_conj {Z : C} (β : Y ≅ Z) (f : End X) : (α ≪≫ β).conj f = β.conj (α.conj f) :=
homCongr_trans α α β β f
@[simp]
theorem symm_self_conj (f : End X) : α.symm.conj (α.conj f) = f := by
rw [← trans_conj, α.self_symm_id, refl_conj]
@[simp]
theorem self_symm_conj (f : End Y) : α.conj (α.symm.conj f) = f :=
α.symm.symm_self_conj f
@[simp]
theorem conj_pow (f : End X) (n : ℕ) : α.conj (f ^ n) = α.conj f ^ n :=
α.conj.toMonoidHom.map_pow f n
-- Porting note (https://github.com/leanprover-community/mathlib4/issues/11215): TODO: change definition so that `conjAut_apply` becomes a `rfl`?
/-- `conj` defines a group isomorphisms between groups of automorphisms -/
def conjAut : Aut X ≃* Aut Y :=
(Aut.unitsEndEquivAut X).symm.trans <| (Units.mapEquiv α.conj).trans <| Aut.unitsEndEquivAut Y
theorem conjAut_apply (f : Aut X) : α.conjAut f = α.symm ≪≫ f ≪≫ α := by aesop_cat
@[simp]
theorem conjAut_hom (f : Aut X) : (α.conjAut f).hom = α.conj f.hom :=
rfl
@[simp]
theorem trans_conjAut {Z : C} (β : Y ≅ Z) (f : Aut X) :
(α ≪≫ β).conjAut f = β.conjAut (α.conjAut f) := by
simp only [conjAut_apply, Iso.trans_symm, Iso.trans_assoc]
@[simp]
theorem conjAut_mul (f g : Aut X) : α.conjAut (f * g) = α.conjAut f * α.conjAut g :=
map_mul α.conjAut f g
@[simp]
theorem conjAut_trans (f g : Aut X) : α.conjAut (f ≪≫ g) = α.conjAut f ≪≫ α.conjAut g :=
conjAut_mul α g f
@[simp]
theorem conjAut_pow (f : Aut X) (n : ℕ) : α.conjAut (f ^ n) = α.conjAut f ^ n :=
map_pow α.conjAut f n
@[simp]
theorem conjAut_zpow (f : Aut X) (n : ℤ) : α.conjAut (f ^ n) = α.conjAut f ^ n :=
map_zpow α.conjAut f n
end Iso
namespace Functor
universe v₁ u₁
variable {C : Type u} [Category.{v} C] {D : Type u₁} [Category.{v₁} D] (F : C ⥤ D)
theorem map_conj {X Y : C} (α : X ≅ Y) (f : End X) :
F.map (α.conj f) = (F.mapIso α).conj (F.map f) :=
map_homCongr F α α f
| theorem map_conjAut (F : C ⥤ D) {X Y : C} (α : X ≅ Y) (f : Aut X) :
F.mapIso (α.conjAut f) = (F.mapIso α).conjAut (F.mapIso f) := by
| Mathlib/CategoryTheory/Conj.lean | 114 | 115 |
/-
Copyright (c) 2015 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Leonardo de Moura, Jeremy Avigad, Mario Carneiro
-/
import Mathlib.Algebra.BigOperators.Ring.List
import Mathlib.Data.Nat.GCD.Basic
import Mathlib.Data.Nat.Prime.Basic
import Mathlib.Data.List.Prime
import Mathlib.Data.List.Sort
import Mathlib.Data.List.Perm.Subperm
/-!
# Prime numbers
This file deals with the factors of natural numbers.
## Important declarations
- `Nat.factors n`: the prime factorization of `n`
- `Nat.factors_unique`: uniqueness of the prime factorisation
-/
assert_not_exists Multiset
open Bool Subtype
open Nat
namespace Nat
/-- `primeFactorsList n` is the prime factorization of `n`, listed in increasing order. -/
def primeFactorsList : ℕ → List ℕ
| 0 => []
| 1 => []
| k + 2 =>
let m := minFac (k + 2)
m :: primeFactorsList ((k + 2) / m)
decreasing_by exact factors_lemma
@[simp]
theorem primeFactorsList_zero : primeFactorsList 0 = [] := by rw [primeFactorsList]
@[simp]
theorem primeFactorsList_one : primeFactorsList 1 = [] := by rw [primeFactorsList]
@[simp]
theorem primeFactorsList_two : primeFactorsList 2 = [2] := by simp [primeFactorsList]
theorem prime_of_mem_primeFactorsList {n : ℕ} : ∀ {p : ℕ}, p ∈ primeFactorsList n → Prime p := by
match n with
| 0 => simp
| 1 => simp
| k + 2 =>
intro p h
let m := minFac (k + 2)
have : (k + 2) / m < (k + 2) := factors_lemma
have h₁ : p = m ∨ p ∈ primeFactorsList ((k + 2) / m) :=
List.mem_cons.1 (by rwa [primeFactorsList] at h)
exact Or.casesOn h₁ (fun h₂ => h₂.symm ▸ minFac_prime (by simp)) prime_of_mem_primeFactorsList
theorem pos_of_mem_primeFactorsList {n p : ℕ} (h : p ∈ primeFactorsList n) : 0 < p :=
Prime.pos (prime_of_mem_primeFactorsList h)
theorem prod_primeFactorsList : ∀ {n}, n ≠ 0 → List.prod (primeFactorsList n) = n
| 0 => by simp
| 1 => by simp
| k + 2 => fun _ =>
let m := minFac (k + 2)
have : (k + 2) / m < (k + 2) := factors_lemma
show (primeFactorsList (k + 2)).prod = (k + 2) by
have h₁ : (k + 2) / m ≠ 0 := fun h => by
have : (k + 2) = 0 * m := (Nat.div_eq_iff_eq_mul_left (minFac_pos _) (minFac_dvd _)).1 h
rw [zero_mul] at this; exact (show k + 2 ≠ 0 by simp) this
rw [primeFactorsList, List.prod_cons, prod_primeFactorsList h₁,
Nat.mul_div_cancel' (minFac_dvd _)]
theorem primeFactorsList_prime {p : ℕ} (hp : Nat.Prime p) : p.primeFactorsList = [p] := by
have : p = p - 2 + 2 := Nat.eq_add_of_sub_eq hp.two_le rfl
rw [this, primeFactorsList]
simp only [Eq.symm this]
have : Nat.minFac p = p := (Nat.prime_def_minFac.mp hp).2
simp only [this, primeFactorsList, Nat.div_self (Nat.Prime.pos hp)]
theorem primeFactorsList_chain {n : ℕ} :
∀ {a}, (∀ p, Prime p → p ∣ n → a ≤ p) → List.Chain (· ≤ ·) a (primeFactorsList n) := by
match n with
| 0 => simp
| 1 => simp
| k + 2 =>
intro a h
let m := minFac (k + 2)
have : (k + 2) / m < (k + 2) := factors_lemma
rw [primeFactorsList]
refine List.Chain.cons ((le_minFac.2 h).resolve_left (by simp)) (primeFactorsList_chain ?_)
exact fun p pp d => minFac_le_of_dvd pp.two_le (d.trans <| div_dvd_of_dvd <| minFac_dvd _)
theorem primeFactorsList_chain_2 (n) : List.Chain (· ≤ ·) 2 (primeFactorsList n) :=
primeFactorsList_chain fun _ pp _ => pp.two_le
theorem primeFactorsList_chain' (n) : List.Chain' (· ≤ ·) (primeFactorsList n) :=
@List.Chain'.tail _ _ (_ :: _) (primeFactorsList_chain_2 _)
theorem primeFactorsList_sorted (n : ℕ) : List.Sorted (· ≤ ·) (primeFactorsList n) :=
List.chain'_iff_pairwise.1 (primeFactorsList_chain' _)
/-- `primeFactorsList` can be constructed inductively by extracting `minFac`, for sufficiently
large `n`. -/
theorem primeFactorsList_add_two (n : ℕ) :
primeFactorsList (n + 2) = minFac (n + 2) :: primeFactorsList ((n + 2) / minFac (n + 2)) := by
rw [primeFactorsList]
@[simp]
theorem primeFactorsList_eq_nil (n : ℕ) : n.primeFactorsList = [] ↔ n = 0 ∨ n = 1 := by
constructor <;> intro h
· rcases n with (_ | _ | n)
· exact Or.inl rfl
· exact Or.inr rfl
· rw [primeFactorsList] at h
injection h
· rcases h with (rfl | rfl)
· exact primeFactorsList_zero
· exact primeFactorsList_one
open scoped List in
theorem eq_of_perm_primeFactorsList {a b : ℕ} (ha : a ≠ 0) (hb : b ≠ 0)
(h : a.primeFactorsList ~ b.primeFactorsList) : a = b := by
simpa [prod_primeFactorsList ha, prod_primeFactorsList hb] using List.Perm.prod_eq h
section
open List
theorem mem_primeFactorsList_iff_dvd {n p : ℕ} (hn : n ≠ 0) (hp : Prime p) :
p ∈ primeFactorsList n ↔ p ∣ n where
mp h := prod_primeFactorsList hn ▸ List.dvd_prod h
mpr h := mem_list_primes_of_dvd_prod (prime_iff.mp hp)
(fun _ h ↦ prime_iff.mp (prime_of_mem_primeFactorsList h)) ((prod_primeFactorsList hn).symm ▸ h)
theorem dvd_of_mem_primeFactorsList {n p : ℕ} (h : p ∈ n.primeFactorsList) : p ∣ n := by
rcases n.eq_zero_or_pos with (rfl | hn)
· exact dvd_zero p
· rwa [← mem_primeFactorsList_iff_dvd hn.ne' (prime_of_mem_primeFactorsList h)]
theorem mem_primeFactorsList {n p} (hn : n ≠ 0) : p ∈ primeFactorsList n ↔ Prime p ∧ p ∣ n :=
⟨fun h => ⟨prime_of_mem_primeFactorsList h, dvd_of_mem_primeFactorsList h⟩, fun ⟨hprime, hdvd⟩ =>
(mem_primeFactorsList_iff_dvd hn hprime).mpr hdvd⟩
@[simp] lemma mem_primeFactorsList' {n p} : p ∈ n.primeFactorsList ↔ p.Prime ∧ p ∣ n ∧ n ≠ 0 := by
cases n <;> simp [mem_primeFactorsList, *]
theorem le_of_mem_primeFactorsList {n p : ℕ} (h : p ∈ n.primeFactorsList) : p ≤ n := by
rcases n.eq_zero_or_pos with (rfl | hn)
· rw [primeFactorsList_zero] at h
cases h
· exact le_of_dvd hn (dvd_of_mem_primeFactorsList h)
/-- **Fundamental theorem of arithmetic** -/
theorem primeFactorsList_unique {n : ℕ} {l : List ℕ} (h₁ : prod l = n) (h₂ : ∀ p ∈ l, Prime p) :
l ~ primeFactorsList n := by
refine perm_of_prod_eq_prod ?_ ?_ ?_
· rw [h₁]
refine (prod_primeFactorsList ?_).symm
rintro rfl
| rw [prod_eq_zero_iff] at h₁
exact Prime.ne_zero (h₂ 0 h₁) rfl
· simp_rw [← prime_iff]
exact h₂
· simp_rw [← prime_iff]
| Mathlib/Data/Nat/Factors.lean | 166 | 170 |
/-
Copyright (c) 2014 Robert Y. Lewis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Robert Y. Lewis, Leonardo de Moura, Mario Carneiro, Floris van Doorn
-/
import Mathlib.Algebra.Field.Basic
import Mathlib.Algebra.GroupWithZero.Units.Lemmas
import Mathlib.Algebra.Order.Ring.Abs
import Mathlib.Order.Bounds.Basic
import Mathlib.Order.Bounds.OrderIso
import Mathlib.Tactic.Positivity.Core
/-!
# Lemmas about linear ordered (semi)fields
-/
open Function OrderDual
variable {ι α β : Type*}
section LinearOrderedSemifield
variable [Semifield α] [LinearOrder α] [IsStrictOrderedRing α] {a b c d e : α} {m n : ℤ}
/-!
### Relating two divisions.
-/
@[deprecated div_le_div_iff_of_pos_right (since := "2024-11-12")]
theorem div_le_div_right (hc : 0 < c) : a / c ≤ b / c ↔ a ≤ b := div_le_div_iff_of_pos_right hc
@[deprecated div_lt_div_iff_of_pos_right (since := "2024-11-12")]
theorem div_lt_div_right (hc : 0 < c) : a / c < b / c ↔ a < b := div_lt_div_iff_of_pos_right hc
@[deprecated div_lt_div_iff_of_pos_left (since := "2024-11-13")]
theorem div_lt_div_left (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : a / b < a / c ↔ c < b :=
div_lt_div_iff_of_pos_left ha hb hc
@[deprecated div_le_div_iff_of_pos_left (since := "2024-11-12")]
theorem div_le_div_left (ha : 0 < a) (hb : 0 < b) (hc : 0 < c) : a / b ≤ a / c ↔ c ≤ b :=
div_le_div_iff_of_pos_left ha hb hc
@[deprecated div_lt_div_iff₀ (since := "2024-11-12")]
theorem div_lt_div_iff (b0 : 0 < b) (d0 : 0 < d) : a / b < c / d ↔ a * d < c * b :=
div_lt_div_iff₀ b0 d0
@[deprecated div_le_div_iff₀ (since := "2024-11-12")]
theorem div_le_div_iff (b0 : 0 < b) (d0 : 0 < d) : a / b ≤ c / d ↔ a * d ≤ c * b :=
div_le_div_iff₀ b0 d0
@[deprecated div_le_div₀ (since := "2024-11-12")]
theorem div_le_div (hc : 0 ≤ c) (hac : a ≤ c) (hd : 0 < d) (hbd : d ≤ b) : a / b ≤ c / d :=
div_le_div₀ hc hac hd hbd
@[deprecated div_lt_div₀ (since := "2024-11-12")]
theorem div_lt_div (hac : a < c) (hbd : d ≤ b) (c0 : 0 ≤ c) (d0 : 0 < d) : a / b < c / d :=
div_lt_div₀ hac hbd c0 d0
@[deprecated div_lt_div₀' (since := "2024-11-12")]
theorem div_lt_div' (hac : a ≤ c) (hbd : d < b) (c0 : 0 < c) (d0 : 0 < d) : a / b < c / d :=
div_lt_div₀' hac hbd c0 d0
/-!
### Relating one division and involving `1`
-/
@[bound]
theorem div_le_self (ha : 0 ≤ a) (hb : 1 ≤ b) : a / b ≤ a := by
simpa only [div_one] using div_le_div_of_nonneg_left ha zero_lt_one hb
@[bound]
theorem div_lt_self (ha : 0 < a) (hb : 1 < b) : a / b < a := by
simpa only [div_one] using div_lt_div_of_pos_left ha zero_lt_one hb
@[bound]
theorem le_div_self (ha : 0 ≤ a) (hb₀ : 0 < b) (hb₁ : b ≤ 1) : a ≤ a / b := by
simpa only [div_one] using div_le_div_of_nonneg_left ha hb₀ hb₁
theorem one_le_div (hb : 0 < b) : 1 ≤ a / b ↔ b ≤ a := by rw [le_div_iff₀ hb, one_mul]
theorem div_le_one (hb : 0 < b) : a / b ≤ 1 ↔ a ≤ b := by rw [div_le_iff₀ hb, one_mul]
theorem one_lt_div (hb : 0 < b) : 1 < a / b ↔ b < a := by rw [lt_div_iff₀ hb, one_mul]
theorem div_lt_one (hb : 0 < b) : a / b < 1 ↔ a < b := by rw [div_lt_iff₀ hb, one_mul]
theorem one_div_le (ha : 0 < a) (hb : 0 < b) : 1 / a ≤ b ↔ 1 / b ≤ a := by
simpa using inv_le_comm₀ ha hb
theorem one_div_lt (ha : 0 < a) (hb : 0 < b) : 1 / a < b ↔ 1 / b < a := by
simpa using inv_lt_comm₀ ha hb
theorem le_one_div (ha : 0 < a) (hb : 0 < b) : a ≤ 1 / b ↔ b ≤ 1 / a := by
simpa using le_inv_comm₀ ha hb
theorem lt_one_div (ha : 0 < a) (hb : 0 < b) : a < 1 / b ↔ b < 1 / a := by
simpa using lt_inv_comm₀ ha hb
@[bound] lemma Bound.one_lt_div_of_pos_of_lt (b0 : 0 < b) : b < a → 1 < a / b := (one_lt_div b0).mpr
@[bound] lemma Bound.div_lt_one_of_pos_of_lt (b0 : 0 < b) : a < b → a / b < 1 := (div_lt_one b0).mpr
/-!
### Relating two divisions, involving `1`
-/
theorem one_div_le_one_div_of_le (ha : 0 < a) (h : a ≤ b) : 1 / b ≤ 1 / a := by
simpa using inv_anti₀ ha h
theorem one_div_lt_one_div_of_lt (ha : 0 < a) (h : a < b) : 1 / b < 1 / a := by
rwa [lt_div_iff₀' ha, ← div_eq_mul_one_div, div_lt_one (ha.trans h)]
theorem le_of_one_div_le_one_div (ha : 0 < a) (h : 1 / a ≤ 1 / b) : b ≤ a :=
le_imp_le_of_lt_imp_lt (one_div_lt_one_div_of_lt ha) h
theorem lt_of_one_div_lt_one_div (ha : 0 < a) (h : 1 / a < 1 / b) : b < a :=
lt_imp_lt_of_le_imp_le (one_div_le_one_div_of_le ha) h
/-- For the single implications with fewer assumptions, see `one_div_le_one_div_of_le` and
`le_of_one_div_le_one_div` -/
theorem one_div_le_one_div (ha : 0 < a) (hb : 0 < b) : 1 / a ≤ 1 / b ↔ b ≤ a :=
div_le_div_iff_of_pos_left zero_lt_one ha hb
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_lt_one_div (ha : 0 < a) (hb : 0 < b) : 1 / a < 1 / b ↔ b < a :=
div_lt_div_iff_of_pos_left zero_lt_one ha hb
theorem one_lt_one_div (h1 : 0 < a) (h2 : a < 1) : 1 < 1 / a := by
rwa [lt_one_div (@zero_lt_one α _ _ _ _ _) h1, one_div_one]
theorem one_le_one_div (h1 : 0 < a) (h2 : a ≤ 1) : 1 ≤ 1 / a := by
rwa [le_one_div (@zero_lt_one α _ _ _ _ _) h1, one_div_one]
/-!
### Results about halving.
The equalities also hold in semifields of characteristic `0`.
-/
theorem half_pos (h : 0 < a) : 0 < a / 2 :=
div_pos h zero_lt_two
theorem one_half_pos : (0 : α) < 1 / 2 :=
half_pos zero_lt_one
@[simp]
theorem half_le_self_iff : a / 2 ≤ a ↔ 0 ≤ a := by
rw [div_le_iff₀ (zero_lt_two' α), mul_two, le_add_iff_nonneg_left]
@[simp]
theorem half_lt_self_iff : a / 2 < a ↔ 0 < a := by
rw [div_lt_iff₀ (zero_lt_two' α), mul_two, lt_add_iff_pos_left]
alias ⟨_, half_le_self⟩ := half_le_self_iff
alias ⟨_, half_lt_self⟩ := half_lt_self_iff
alias div_two_lt_of_pos := half_lt_self
theorem one_half_lt_one : (1 / 2 : α) < 1 :=
half_lt_self zero_lt_one
theorem two_inv_lt_one : (2⁻¹ : α) < 1 :=
(one_div _).symm.trans_lt one_half_lt_one
theorem left_lt_add_div_two : a < (a + b) / 2 ↔ a < b := by simp [lt_div_iff₀, mul_two]
theorem add_div_two_lt_right : (a + b) / 2 < b ↔ a < b := by simp [div_lt_iff₀, mul_two]
theorem add_thirds (a : α) : a / 3 + a / 3 + a / 3 = a := by
rw [div_add_div_same, div_add_div_same, ← two_mul, ← add_one_mul 2 a, two_add_one_eq_three,
mul_div_cancel_left₀ a three_ne_zero]
/-!
### Miscellaneous lemmas
-/
@[simp] lemma div_pos_iff_of_pos_left (ha : 0 < a) : 0 < a / b ↔ 0 < b := by
simp only [div_eq_mul_inv, mul_pos_iff_of_pos_left ha, inv_pos]
@[simp] lemma div_pos_iff_of_pos_right (hb : 0 < b) : 0 < a / b ↔ 0 < a := by
simp only [div_eq_mul_inv, mul_pos_iff_of_pos_right (inv_pos.2 hb)]
theorem mul_le_mul_of_mul_div_le (h : a * (b / c) ≤ d) (hc : 0 < c) : b * a ≤ d * c := by
rw [← mul_div_assoc] at h
rwa [mul_comm b, ← div_le_iff₀ hc]
theorem div_mul_le_div_mul_of_div_le_div (h : a / b ≤ c / d) (he : 0 ≤ e) :
a / (b * e) ≤ c / (d * e) := by
rw [div_mul_eq_div_mul_one_div, div_mul_eq_div_mul_one_div]
exact mul_le_mul_of_nonneg_right h (one_div_nonneg.2 he)
theorem exists_pos_mul_lt {a : α} (h : 0 < a) (b : α) : ∃ c : α, 0 < c ∧ b * c < a := by
have : 0 < a / max (b + 1) 1 := div_pos h (lt_max_iff.2 (Or.inr zero_lt_one))
refine ⟨a / max (b + 1) 1, this, ?_⟩
rw [← lt_div_iff₀ this, div_div_cancel₀ h.ne']
exact lt_max_iff.2 (Or.inl <| lt_add_one _)
theorem exists_pos_lt_mul {a : α} (h : 0 < a) (b : α) : ∃ c : α, 0 < c ∧ b < c * a :=
let ⟨c, hc₀, hc⟩ := exists_pos_mul_lt h b;
⟨c⁻¹, inv_pos.2 hc₀, by rwa [← div_eq_inv_mul, lt_div_iff₀ hc₀]⟩
lemma monotone_div_right_of_nonneg (ha : 0 ≤ a) : Monotone (· / a) :=
fun _b _c hbc ↦ div_le_div_of_nonneg_right hbc ha
lemma strictMono_div_right_of_pos (ha : 0 < a) : StrictMono (· / a) :=
fun _b _c hbc ↦ div_lt_div_of_pos_right hbc ha
theorem Monotone.div_const {β : Type*} [Preorder β] {f : β → α} (hf : Monotone f) {c : α}
(hc : 0 ≤ c) : Monotone fun x => f x / c := (monotone_div_right_of_nonneg hc).comp hf
theorem StrictMono.div_const {β : Type*} [Preorder β] {f : β → α} (hf : StrictMono f) {c : α}
(hc : 0 < c) : StrictMono fun x => f x / c := by
simpa only [div_eq_mul_inv] using hf.mul_const (inv_pos.2 hc)
-- see Note [lower instance priority]
instance (priority := 100) LinearOrderedSemiField.toDenselyOrdered : DenselyOrdered α where
dense a₁ a₂ h :=
⟨(a₁ + a₂) / 2,
calc
a₁ = (a₁ + a₁) / 2 := (add_self_div_two a₁).symm
_ < (a₁ + a₂) / 2 := div_lt_div_of_pos_right (add_lt_add_left h _) zero_lt_two
,
calc
(a₁ + a₂) / 2 < (a₂ + a₂) / 2 := div_lt_div_of_pos_right (add_lt_add_right h _) zero_lt_two
_ = a₂ := add_self_div_two a₂
⟩
theorem min_div_div_right {c : α} (hc : 0 ≤ c) (a b : α) : min (a / c) (b / c) = min a b / c :=
(monotone_div_right_of_nonneg hc).map_min.symm
theorem max_div_div_right {c : α} (hc : 0 ≤ c) (a b : α) : max (a / c) (b / c) = max a b / c :=
(monotone_div_right_of_nonneg hc).map_max.symm
theorem one_div_strictAntiOn : StrictAntiOn (fun x : α => 1 / x) (Set.Ioi 0) :=
fun _ x1 _ y1 xy => (one_div_lt_one_div (Set.mem_Ioi.mp y1) (Set.mem_Ioi.mp x1)).mpr xy
theorem one_div_pow_le_one_div_pow_of_le (a1 : 1 ≤ a) {m n : ℕ} (mn : m ≤ n) :
1 / a ^ n ≤ 1 / a ^ m := by
refine (one_div_le_one_div ?_ ?_).mpr (pow_right_mono₀ a1 mn) <;>
exact pow_pos (zero_lt_one.trans_le a1) _
theorem one_div_pow_lt_one_div_pow_of_lt (a1 : 1 < a) {m n : ℕ} (mn : m < n) :
1 / a ^ n < 1 / a ^ m := by
refine (one_div_lt_one_div ?_ ?_).2 (pow_lt_pow_right₀ a1 mn) <;>
exact pow_pos (zero_lt_one.trans a1) _
theorem one_div_pow_anti (a1 : 1 ≤ a) : Antitone fun n : ℕ => 1 / a ^ n := fun _ _ =>
one_div_pow_le_one_div_pow_of_le a1
theorem one_div_pow_strictAnti (a1 : 1 < a) : StrictAnti fun n : ℕ => 1 / a ^ n := fun _ _ =>
one_div_pow_lt_one_div_pow_of_lt a1
theorem inv_strictAntiOn : StrictAntiOn (fun x : α => x⁻¹) (Set.Ioi 0) := fun _ hx _ hy xy =>
(inv_lt_inv₀ hy hx).2 xy
theorem inv_pow_le_inv_pow_of_le (a1 : 1 ≤ a) {m n : ℕ} (mn : m ≤ n) : (a ^ n)⁻¹ ≤ (a ^ m)⁻¹ := by
convert one_div_pow_le_one_div_pow_of_le a1 mn using 1 <;> simp
theorem inv_pow_lt_inv_pow_of_lt (a1 : 1 < a) {m n : ℕ} (mn : m < n) : (a ^ n)⁻¹ < (a ^ m)⁻¹ := by
convert one_div_pow_lt_one_div_pow_of_lt a1 mn using 1 <;> simp
theorem inv_pow_anti (a1 : 1 ≤ a) : Antitone fun n : ℕ => (a ^ n)⁻¹ := fun _ _ =>
inv_pow_le_inv_pow_of_le a1
theorem inv_pow_strictAnti (a1 : 1 < a) : StrictAnti fun n : ℕ => (a ^ n)⁻¹ := fun _ _ =>
inv_pow_lt_inv_pow_of_lt a1
theorem le_iff_forall_one_lt_le_mul₀ {α : Type*}
[Semifield α] [LinearOrder α] [IsStrictOrderedRing α]
{a b : α} (hb : 0 ≤ b) : a ≤ b ↔ ∀ ε, 1 < ε → a ≤ b * ε := by
refine ⟨fun h _ hε ↦ h.trans <| le_mul_of_one_le_right hb hε.le, fun h ↦ ?_⟩
obtain rfl|hb := hb.eq_or_lt
· simp_rw [zero_mul] at h
exact h 2 one_lt_two
refine le_of_forall_gt_imp_ge_of_dense fun x hbx => ?_
convert h (x / b) ((one_lt_div hb).mpr hbx)
rw [mul_div_cancel₀ _ hb.ne']
/-! ### Results about `IsGLB` -/
theorem IsGLB.mul_left {s : Set α} (ha : 0 ≤ a) (hs : IsGLB s b) :
IsGLB ((fun b => a * b) '' s) (a * b) := by
rcases lt_or_eq_of_le ha with (ha | rfl)
· exact (OrderIso.mulLeft₀ _ ha).isGLB_image'.2 hs
· simp_rw [zero_mul]
rw [hs.nonempty.image_const]
exact isGLB_singleton
theorem IsGLB.mul_right {s : Set α} (ha : 0 ≤ a) (hs : IsGLB s b) :
IsGLB ((fun b => b * a) '' s) (b * a) := by simpa [mul_comm] using hs.mul_left ha
end LinearOrderedSemifield
section
variable [Field α] [LinearOrder α] [IsStrictOrderedRing α] {a b c d : α} {n : ℤ}
/-! ### Lemmas about pos, nonneg, nonpos, neg -/
theorem div_pos_iff : 0 < a / b ↔ 0 < a ∧ 0 < b ∨ a < 0 ∧ b < 0 := by
simp only [division_def, mul_pos_iff, inv_pos, inv_lt_zero]
theorem div_neg_iff : a / b < 0 ↔ 0 < a ∧ b < 0 ∨ a < 0 ∧ 0 < b := by
simp [division_def, mul_neg_iff]
theorem div_nonneg_iff : 0 ≤ a / b ↔ 0 ≤ a ∧ 0 ≤ b ∨ a ≤ 0 ∧ b ≤ 0 := by
simp [division_def, mul_nonneg_iff]
theorem div_nonpos_iff : a / b ≤ 0 ↔ 0 ≤ a ∧ b ≤ 0 ∨ a ≤ 0 ∧ 0 ≤ b := by
simp [division_def, mul_nonpos_iff]
theorem div_nonneg_of_nonpos (ha : a ≤ 0) (hb : b ≤ 0) : 0 ≤ a / b :=
div_nonneg_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_pos_of_neg_of_neg (ha : a < 0) (hb : b < 0) : 0 < a / b :=
div_pos_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_neg_of_neg_of_pos (ha : a < 0) (hb : 0 < b) : a / b < 0 :=
div_neg_iff.2 <| Or.inr ⟨ha, hb⟩
theorem div_neg_of_pos_of_neg (ha : 0 < a) (hb : b < 0) : a / b < 0 :=
div_neg_iff.2 <| Or.inl ⟨ha, hb⟩
/-! ### Relating one division with another term -/
theorem div_le_iff_of_neg (hc : c < 0) : b / c ≤ a ↔ a * c ≤ b :=
⟨fun h => div_mul_cancel₀ b (ne_of_lt hc) ▸ mul_le_mul_of_nonpos_right h hc.le, fun h =>
calc
a = a * c * (1 / c) := mul_mul_div a (ne_of_lt hc)
_ ≥ b * (1 / c) := mul_le_mul_of_nonpos_right h (one_div_neg.2 hc).le
_ = b / c := (div_eq_mul_one_div b c).symm
⟩
theorem div_le_iff_of_neg' (hc : c < 0) : b / c ≤ a ↔ c * a ≤ b := by
rw [mul_comm, div_le_iff_of_neg hc]
theorem le_div_iff_of_neg (hc : c < 0) : a ≤ b / c ↔ b ≤ a * c := by
rw [← neg_neg c, mul_neg, div_neg, le_neg, div_le_iff₀ (neg_pos.2 hc), neg_mul]
theorem le_div_iff_of_neg' (hc : c < 0) : a ≤ b / c ↔ b ≤ c * a := by
rw [mul_comm, le_div_iff_of_neg hc]
theorem div_lt_iff_of_neg (hc : c < 0) : b / c < a ↔ a * c < b :=
lt_iff_lt_of_le_iff_le <| le_div_iff_of_neg hc
theorem div_lt_iff_of_neg' (hc : c < 0) : b / c < a ↔ c * a < b := by
rw [mul_comm, div_lt_iff_of_neg hc]
theorem lt_div_iff_of_neg (hc : c < 0) : a < b / c ↔ b < a * c :=
lt_iff_lt_of_le_iff_le <| div_le_iff_of_neg hc
theorem lt_div_iff_of_neg' (hc : c < 0) : a < b / c ↔ b < c * a := by
rw [mul_comm, lt_div_iff_of_neg hc]
theorem div_le_one_of_ge (h : b ≤ a) (hb : b ≤ 0) : a / b ≤ 1 := by
simpa only [neg_div_neg_eq] using div_le_one_of_le₀ (neg_le_neg h) (neg_nonneg_of_nonpos hb)
/-! ### Bi-implications of inequalities using inversions -/
theorem inv_le_inv_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ ≤ b⁻¹ ↔ b ≤ a := by
rw [← one_div, div_le_iff_of_neg ha, ← div_eq_inv_mul, div_le_iff_of_neg hb, one_mul]
theorem inv_le_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ ≤ b ↔ b⁻¹ ≤ a := by
rw [← inv_le_inv_of_neg hb (inv_lt_zero.2 ha), inv_inv]
theorem le_inv_of_neg (ha : a < 0) (hb : b < 0) : a ≤ b⁻¹ ↔ b ≤ a⁻¹ := by
rw [← inv_le_inv_of_neg (inv_lt_zero.2 hb) ha, inv_inv]
theorem inv_lt_inv_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ < b⁻¹ ↔ b < a :=
lt_iff_lt_of_le_iff_le (inv_le_inv_of_neg hb ha)
theorem inv_lt_of_neg (ha : a < 0) (hb : b < 0) : a⁻¹ < b ↔ b⁻¹ < a :=
lt_iff_lt_of_le_iff_le (le_inv_of_neg hb ha)
theorem lt_inv_of_neg (ha : a < 0) (hb : b < 0) : a < b⁻¹ ↔ b < a⁻¹ :=
lt_iff_lt_of_le_iff_le (inv_le_of_neg hb ha)
/-!
### Monotonicity results involving inversion
-/
theorem sub_inv_antitoneOn_Ioi :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Ioi c) :=
antitoneOn_iff_forall_lt.mpr fun _ ha _ hb hab ↦
inv_le_inv₀ (sub_pos.mpr hb) (sub_pos.mpr ha) |>.mpr <| sub_le_sub (le_of_lt hab) le_rfl
theorem sub_inv_antitoneOn_Iio :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Iio c) :=
antitoneOn_iff_forall_lt.mpr fun _ ha _ hb hab ↦
inv_le_inv_of_neg (sub_neg.mpr hb) (sub_neg.mpr ha) |>.mpr <| sub_le_sub (le_of_lt hab) le_rfl
theorem sub_inv_antitoneOn_Icc_right (ha : c < a) :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Icc a b) := by
by_cases hab : a ≤ b
· exact sub_inv_antitoneOn_Ioi.mono <| (Set.Icc_subset_Ioi_iff hab).mpr ha
· simp [hab, Set.Subsingleton.antitoneOn]
theorem sub_inv_antitoneOn_Icc_left (ha : b < c) :
AntitoneOn (fun x ↦ (x-c)⁻¹) (Set.Icc a b) := by
by_cases hab : a ≤ b
· exact sub_inv_antitoneOn_Iio.mono <| (Set.Icc_subset_Iio_iff hab).mpr ha
· simp [hab, Set.Subsingleton.antitoneOn]
theorem inv_antitoneOn_Ioi :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Ioi 0) := by
convert sub_inv_antitoneOn_Ioi (α := α)
exact (sub_zero _).symm
theorem inv_antitoneOn_Iio :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Iio 0) := by
convert sub_inv_antitoneOn_Iio (α := α)
exact (sub_zero _).symm
theorem inv_antitoneOn_Icc_right (ha : 0 < a) :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Icc a b) := by
convert sub_inv_antitoneOn_Icc_right ha
exact (sub_zero _).symm
theorem inv_antitoneOn_Icc_left (hb : b < 0) :
AntitoneOn (fun x : α ↦ x⁻¹) (Set.Icc a b) := by
convert sub_inv_antitoneOn_Icc_left hb
exact (sub_zero _).symm
/-! ### Relating two divisions -/
theorem div_le_div_of_nonpos_of_le (hc : c ≤ 0) (h : b ≤ a) : a / c ≤ b / c := by
rw [div_eq_mul_one_div a c, div_eq_mul_one_div b c]
exact mul_le_mul_of_nonpos_right h (one_div_nonpos.2 hc)
theorem div_lt_div_of_neg_of_lt (hc : c < 0) (h : b < a) : a / c < b / c := by
rw [div_eq_mul_one_div a c, div_eq_mul_one_div b c]
exact mul_lt_mul_of_neg_right h (one_div_neg.2 hc)
theorem div_le_div_right_of_neg (hc : c < 0) : a / c ≤ b / c ↔ b ≤ a :=
⟨le_imp_le_of_lt_imp_lt <| div_lt_div_of_neg_of_lt hc, div_le_div_of_nonpos_of_le <| hc.le⟩
theorem div_lt_div_right_of_neg (hc : c < 0) : a / c < b / c ↔ b < a :=
lt_iff_lt_of_le_iff_le <| div_le_div_right_of_neg hc
/-! ### Relating one division and involving `1` -/
theorem one_le_div_of_neg (hb : b < 0) : 1 ≤ a / b ↔ a ≤ b := by rw [le_div_iff_of_neg hb, one_mul]
theorem div_le_one_of_neg (hb : b < 0) : a / b ≤ 1 ↔ b ≤ a := by rw [div_le_iff_of_neg hb, one_mul]
theorem one_lt_div_of_neg (hb : b < 0) : 1 < a / b ↔ a < b := by rw [lt_div_iff_of_neg hb, one_mul]
theorem div_lt_one_of_neg (hb : b < 0) : a / b < 1 ↔ b < a := by rw [div_lt_iff_of_neg hb, one_mul]
theorem one_div_le_of_neg (ha : a < 0) (hb : b < 0) : 1 / a ≤ b ↔ 1 / b ≤ a := by
simpa using inv_le_of_neg ha hb
theorem one_div_lt_of_neg (ha : a < 0) (hb : b < 0) : 1 / a < b ↔ 1 / b < a := by
simpa using inv_lt_of_neg ha hb
theorem le_one_div_of_neg (ha : a < 0) (hb : b < 0) : a ≤ 1 / b ↔ b ≤ 1 / a := by
simpa using le_inv_of_neg ha hb
theorem lt_one_div_of_neg (ha : a < 0) (hb : b < 0) : a < 1 / b ↔ b < 1 / a := by
simpa using lt_inv_of_neg ha hb
theorem one_lt_div_iff : 1 < a / b ↔ 0 < b ∧ b < a ∨ b < 0 ∧ a < b := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, one_lt_div_of_neg]
· simp [lt_irrefl, zero_le_one]
· simp [hb, hb.not_lt, one_lt_div]
theorem one_le_div_iff : 1 ≤ a / b ↔ 0 < b ∧ b ≤ a ∨ b < 0 ∧ a ≤ b := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, one_le_div_of_neg]
· simp [lt_irrefl, zero_lt_one.not_le, zero_lt_one]
· simp [hb, hb.not_lt, one_le_div]
theorem div_lt_one_iff : a / b < 1 ↔ 0 < b ∧ a < b ∨ b = 0 ∨ b < 0 ∧ b < a := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, hb.ne, div_lt_one_of_neg]
· simp [zero_lt_one]
· simp [hb, hb.not_lt, div_lt_one, hb.ne.symm]
theorem div_le_one_iff : a / b ≤ 1 ↔ 0 < b ∧ a ≤ b ∨ b = 0 ∨ b < 0 ∧ b ≤ a := by
rcases lt_trichotomy b 0 with (hb | rfl | hb)
· simp [hb, hb.not_lt, hb.ne, div_le_one_of_neg]
· simp [zero_le_one]
· simp [hb, hb.not_lt, div_le_one, hb.ne.symm]
/-! ### Relating two divisions, involving `1` -/
theorem one_div_le_one_div_of_neg_of_le (hb : b < 0) (h : a ≤ b) : 1 / b ≤ 1 / a := by
rwa [div_le_iff_of_neg' hb, ← div_eq_mul_one_div, div_le_one_of_neg (h.trans_lt hb)]
theorem one_div_lt_one_div_of_neg_of_lt (hb : b < 0) (h : a < b) : 1 / b < 1 / a := by
rwa [div_lt_iff_of_neg' hb, ← div_eq_mul_one_div, div_lt_one_of_neg (h.trans hb)]
theorem le_of_neg_of_one_div_le_one_div (hb : b < 0) (h : 1 / a ≤ 1 / b) : b ≤ a :=
le_imp_le_of_lt_imp_lt (one_div_lt_one_div_of_neg_of_lt hb) h
theorem lt_of_neg_of_one_div_lt_one_div (hb : b < 0) (h : 1 / a < 1 / b) : b < a :=
lt_imp_lt_of_le_imp_le (one_div_le_one_div_of_neg_of_le hb) h
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_neg_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_le_one_div_of_neg (ha : a < 0) (hb : b < 0) : 1 / a ≤ 1 / b ↔ b ≤ a := by
simpa [one_div] using inv_le_inv_of_neg ha hb
/-- For the single implications with fewer assumptions, see `one_div_lt_one_div_of_lt` and
`lt_of_one_div_lt_one_div` -/
theorem one_div_lt_one_div_of_neg (ha : a < 0) (hb : b < 0) : 1 / a < 1 / b ↔ b < a :=
lt_iff_lt_of_le_iff_le (one_div_le_one_div_of_neg hb ha)
theorem one_div_lt_neg_one (h1 : a < 0) (h2 : -1 < a) : 1 / a < -1 :=
suffices 1 / a < 1 / -1 by rwa [one_div_neg_one_eq_neg_one] at this
one_div_lt_one_div_of_neg_of_lt h1 h2
theorem one_div_le_neg_one (h1 : a < 0) (h2 : -1 ≤ a) : 1 / a ≤ -1 :=
suffices 1 / a ≤ 1 / -1 by rwa [one_div_neg_one_eq_neg_one] at this
one_div_le_one_div_of_neg_of_le h1 h2
/-! ### Results about halving -/
theorem sub_self_div_two (a : α) : a - a / 2 = a / 2 := by
suffices a / 2 + a / 2 - a / 2 = a / 2 by rwa [add_halves] at this
rw [add_sub_cancel_right]
theorem div_two_sub_self (a : α) : a / 2 - a = -(a / 2) := by
suffices a / 2 - (a / 2 + a / 2) = -(a / 2) by rwa [add_halves] at this
rw [sub_add_eq_sub_sub, sub_self, zero_sub]
theorem add_sub_div_two_lt (h : a < b) : a + (b - a) / 2 < b := by
rwa [← div_sub_div_same, sub_eq_add_neg, add_comm (b / 2), ← add_assoc, ← sub_eq_add_neg, ←
lt_sub_iff_add_lt, sub_self_div_two, sub_self_div_two,
div_lt_div_iff_of_pos_right (zero_lt_two' α)]
/-- An inequality involving `2`. -/
theorem sub_one_div_inv_le_two (a2 : 2 ≤ a) : (1 - 1 / a)⁻¹ ≤ 2 := by
-- Take inverses on both sides to obtain `2⁻¹ ≤ 1 - 1 / a`
refine (inv_anti₀ (inv_pos.2 <| zero_lt_two' α) ?_).trans_eq (inv_inv (2 : α))
-- move `1 / a` to the left and `2⁻¹` to the right.
rw [le_sub_iff_add_le, add_comm, ← le_sub_iff_add_le]
-- take inverses on both sides and use the assumption `2 ≤ a`.
convert (one_div a).le.trans (inv_anti₀ zero_lt_two a2) using 1
-- show `1 - 1 / 2 = 1 / 2`.
rw [sub_eq_iff_eq_add, ← two_mul, mul_inv_cancel₀ two_ne_zero]
/-! ### Results about `IsLUB` -/
-- TODO: Generalize to `LinearOrderedSemifield`
theorem IsLUB.mul_left {s : Set α} (ha : 0 ≤ a) (hs : IsLUB s b) :
IsLUB ((fun b => a * b) '' s) (a * b) := by
rcases lt_or_eq_of_le ha with (ha | rfl)
· exact (OrderIso.mulLeft₀ _ ha).isLUB_image'.2 hs
· simp_rw [zero_mul]
rw [hs.nonempty.image_const]
exact isLUB_singleton
-- TODO: Generalize to `LinearOrderedSemifield`
theorem IsLUB.mul_right {s : Set α} (ha : 0 ≤ a) (hs : IsLUB s b) :
IsLUB ((fun b => b * a) '' s) (b * a) := by simpa [mul_comm] using hs.mul_left ha
/-! ### Miscellaneous lemmas -/
theorem mul_sub_mul_div_mul_neg_iff (hc : c ≠ 0) (hd : d ≠ 0) :
(a * d - b * c) / (c * d) < 0 ↔ a / c < b / d := by
rw [mul_comm b c, ← div_sub_div _ _ hc hd, sub_lt_zero]
theorem mul_sub_mul_div_mul_nonpos_iff (hc : c ≠ 0) (hd : d ≠ 0) :
(a * d - b * c) / (c * d) ≤ 0 ↔ a / c ≤ b / d := by
rw [mul_comm b c, ← div_sub_div _ _ hc hd, sub_nonpos]
alias ⟨div_lt_div_of_mul_sub_mul_div_neg, mul_sub_mul_div_mul_neg⟩ := mul_sub_mul_div_mul_neg_iff
alias ⟨div_le_div_of_mul_sub_mul_div_nonpos, mul_sub_mul_div_mul_nonpos⟩ :=
mul_sub_mul_div_mul_nonpos_iff
theorem exists_add_lt_and_pos_of_lt (h : b < a) : ∃ c, b + c < a ∧ 0 < c :=
⟨(a - b) / 2, add_sub_div_two_lt h, div_pos (sub_pos_of_lt h) zero_lt_two⟩
theorem le_of_forall_sub_le (h : ∀ ε > 0, b - ε ≤ a) : b ≤ a := by
contrapose! h
simpa only [@and_comm ((0 : α) < _), lt_sub_iff_add_lt, gt_iff_lt] using
exists_add_lt_and_pos_of_lt h
private lemma exists_lt_mul_left_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c) (h : c < a * b) :
∃ a' ∈ Set.Ico 0 a, c < a' * b := by
have hb : 0 < b := pos_of_mul_pos_right (hc.trans_lt h) ha
obtain ⟨a', ha', a_a'⟩ := exists_between ((div_lt_iff₀ hb).2 h)
exact ⟨a', ⟨(div_nonneg hc hb.le).trans ha'.le, a_a'⟩, (div_lt_iff₀ hb).1 ha'⟩
private lemma exists_lt_mul_right_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c) (h : c < a * b) :
∃ b' ∈ Set.Ico 0 b, c < a * b' := by
have hb : 0 < b := pos_of_mul_pos_right (hc.trans_lt h) ha
simp_rw [mul_comm a] at h ⊢
exact exists_lt_mul_left_of_nonneg hb.le hc h
private lemma exists_mul_left_lt₀ {a b c : α} (hc : a * b < c) : ∃ a' > a, a' * b < c := by
rcases le_or_lt b 0 with hb | hb
· obtain ⟨a', ha'⟩ := exists_gt a
exact ⟨a', ha', hc.trans_le' (antitone_mul_right hb ha'.le)⟩
· obtain ⟨a', ha', hc'⟩ := exists_between ((lt_div_iff₀ hb).2 hc)
exact ⟨a', ha', (lt_div_iff₀ hb).1 hc'⟩
private lemma exists_mul_right_lt₀ {a b c : α} (hc : a * b < c) : ∃ b' > b, a * b' < c := by
simp_rw [mul_comm a] at hc ⊢; exact exists_mul_left_lt₀ hc
lemma le_mul_of_forall_lt₀ {a b c : α} (h : ∀ a' > a, ∀ b' > b, c ≤ a' * b') : c ≤ a * b := by
refine le_of_forall_gt_imp_ge_of_dense fun d hd ↦ ?_
obtain ⟨a', ha', hd⟩ := exists_mul_left_lt₀ hd
obtain ⟨b', hb', hd⟩ := exists_mul_right_lt₀ hd
exact (h a' ha' b' hb').trans hd.le
lemma mul_le_of_forall_lt_of_nonneg {a b c : α} (ha : 0 ≤ a) (hc : 0 ≤ c)
(h : ∀ a' ≥ 0, a' < a → ∀ b' ≥ 0, b' < b → a' * b' ≤ c) : a * b ≤ c := by
refine le_of_forall_lt_imp_le_of_dense fun d d_ab ↦ ?_
rcases lt_or_le d 0 with hd | hd
· exact hd.le.trans hc
obtain ⟨a', ha', d_ab⟩ := exists_lt_mul_left_of_nonneg ha hd d_ab
obtain ⟨b', hb', d_ab⟩ := exists_lt_mul_right_of_nonneg ha'.1 hd d_ab
exact d_ab.le.trans (h a' ha'.1 ha'.2 b' hb'.1 hb'.2)
theorem mul_self_inj_of_nonneg (a0 : 0 ≤ a) (b0 : 0 ≤ b) : a * a = b * b ↔ a = b :=
mul_self_eq_mul_self_iff.trans <|
or_iff_left_of_imp fun h => by
subst a
have : b = 0 := le_antisymm (neg_nonneg.1 a0) b0
rw [this, neg_zero]
theorem min_div_div_right_of_nonpos (hc : c ≤ 0) (a b : α) : min (a / c) (b / c) = max a b / c :=
Eq.symm <| Antitone.map_max fun _ _ => div_le_div_of_nonpos_of_le hc
theorem max_div_div_right_of_nonpos (hc : c ≤ 0) (a b : α) : max (a / c) (b / c) = min a b / c :=
Eq.symm <| Antitone.map_min fun _ _ => div_le_div_of_nonpos_of_le hc
theorem abs_inv (a : α) : |a⁻¹| = |a|⁻¹ :=
map_inv₀ (absHom : α →*₀ α) a
theorem abs_div (a b : α) : |a / b| = |a| / |b| :=
map_div₀ (absHom : α →*₀ α) a b
theorem abs_one_div (a : α) : |1 / a| = 1 / |a| := by rw [abs_div, abs_one]
theorem uniform_continuous_npow_on_bounded (B : α) {ε : α} (hε : 0 < ε) (n : ℕ) :
∃ δ > 0, ∀ q r : α, |r| ≤ B → |q - r| ≤ δ → |q ^ n - r ^ n| < ε := by
wlog B_pos : 0 < B generalizing B
· have ⟨δ, δ_pos, cont⟩ := this 1 zero_lt_one
exact ⟨δ, δ_pos, fun q r hr ↦ cont q r (hr.trans ((le_of_not_lt B_pos).trans zero_le_one))⟩
have pos : 0 < 1 + ↑n * (B + 1) ^ (n - 1) := zero_lt_one.trans_le <| le_add_of_nonneg_right <|
mul_nonneg n.cast_nonneg <| (pow_pos (B_pos.trans <| lt_add_of_pos_right _ zero_lt_one) _).le
refine ⟨min 1 (ε / (1 + n * (B + 1) ^ (n - 1))), lt_min zero_lt_one (div_pos hε pos),
fun q r hr hqr ↦ (abs_pow_sub_pow_le ..).trans_lt ?_⟩
rw [le_inf_iff, le_div_iff₀ pos, mul_one_add, ← mul_assoc] at hqr
obtain h | h := (abs_nonneg (q - r)).eq_or_lt
· simpa only [← h, zero_mul] using hε
refine (lt_of_le_of_lt ?_ <| lt_add_of_pos_left _ h).trans_le hqr.2
refine mul_le_mul_of_nonneg_left (pow_le_pow_left₀ ((abs_nonneg _).trans le_sup_left) ?_ _)
(mul_nonneg (abs_nonneg _) n.cast_nonneg)
refine max_le ?_ (hr.trans <| le_add_of_nonneg_right zero_le_one)
exact add_sub_cancel r q ▸ (abs_add_le ..).trans (add_le_add hr hqr.1)
| end
| Mathlib/Algebra/Order/Field/Basic.lean | 673 | 674 |
/-
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.Basic
import Mathlib.Topology.Order.ProjIcc
/-!
# Inverse trigonometric functions.
See also `Analysis.SpecialFunctions.Trigonometric.Arctan` for the inverse tan function.
(This is delayed as it is easier to set up after developing complex trigonometric functions.)
Basic inequalities on trigonometric functions.
-/
noncomputable section
open Topology Filter Set Filter Real
namespace Real
variable {x y : ℝ}
/-- Inverse of the `sin` function, returns values in the range `-π / 2 ≤ arcsin x ≤ π / 2`.
It defaults to `-π / 2` on `(-∞, -1)` and to `π / 2` to `(1, ∞)`. -/
@[pp_nodot]
noncomputable def arcsin : ℝ → ℝ :=
Subtype.val ∘ IccExtend (neg_le_self zero_le_one) sinOrderIso.symm
theorem arcsin_mem_Icc (x : ℝ) : arcsin x ∈ Icc (-(π / 2)) (π / 2) :=
Subtype.coe_prop _
@[simp]
theorem range_arcsin : range arcsin = Icc (-(π / 2)) (π / 2) := by
rw [arcsin, range_comp Subtype.val]
simp [Icc]
theorem arcsin_le_pi_div_two (x : ℝ) : arcsin x ≤ π / 2 :=
(arcsin_mem_Icc x).2
theorem neg_pi_div_two_le_arcsin (x : ℝ) : -(π / 2) ≤ arcsin x :=
(arcsin_mem_Icc x).1
theorem arcsin_projIcc (x : ℝ) :
arcsin (projIcc (-1) 1 (neg_le_self zero_le_one) x) = arcsin x := by
rw [arcsin, Function.comp_apply, IccExtend_val, Function.comp_apply, IccExtend,
Function.comp_apply]
theorem sin_arcsin' {x : ℝ} (hx : x ∈ Icc (-1 : ℝ) 1) : sin (arcsin x) = x := by
simpa [arcsin, IccExtend_of_mem _ _ hx, -OrderIso.apply_symm_apply] using
Subtype.ext_iff.1 (sinOrderIso.apply_symm_apply ⟨x, hx⟩)
theorem sin_arcsin {x : ℝ} (hx₁ : -1 ≤ x) (hx₂ : x ≤ 1) : sin (arcsin x) = x :=
sin_arcsin' ⟨hx₁, hx₂⟩
theorem arcsin_sin' {x : ℝ} (hx : x ∈ Icc (-(π / 2)) (π / 2)) : arcsin (sin x) = x :=
injOn_sin (arcsin_mem_Icc _) hx <| by rw [sin_arcsin (neg_one_le_sin _) (sin_le_one _)]
theorem arcsin_sin {x : ℝ} (hx₁ : -(π / 2) ≤ x) (hx₂ : x ≤ π / 2) : arcsin (sin x) = x :=
arcsin_sin' ⟨hx₁, hx₂⟩
theorem strictMonoOn_arcsin : StrictMonoOn arcsin (Icc (-1) 1) :=
(Subtype.strictMono_coe _).comp_strictMonoOn <|
sinOrderIso.symm.strictMono.strictMonoOn_IccExtend _
@[gcongr]
theorem arcsin_lt_arcsin {x y : ℝ} (hx : -1 ≤ x) (hlt : x < y) (hy : y ≤ 1) :
arcsin x < arcsin y :=
strictMonoOn_arcsin ⟨hx, hlt.le.trans hy⟩ ⟨hx.trans hlt.le, hy⟩ hlt
theorem monotone_arcsin : Monotone arcsin :=
(Subtype.mono_coe _).comp <| sinOrderIso.symm.monotone.IccExtend _
@[gcongr]
theorem arcsin_le_arcsin {x y : ℝ} (h : x ≤ y) : arcsin x ≤ arcsin y := monotone_arcsin h
theorem injOn_arcsin : InjOn arcsin (Icc (-1) 1) :=
strictMonoOn_arcsin.injOn
theorem arcsin_inj {x y : ℝ} (hx₁ : -1 ≤ x) (hx₂ : x ≤ 1) (hy₁ : -1 ≤ y) (hy₂ : y ≤ 1) :
arcsin x = arcsin y ↔ x = y :=
injOn_arcsin.eq_iff ⟨hx₁, hx₂⟩ ⟨hy₁, hy₂⟩
@[continuity, fun_prop]
theorem continuous_arcsin : Continuous arcsin :=
continuous_subtype_val.comp sinOrderIso.symm.continuous.Icc_extend'
@[fun_prop]
theorem continuousAt_arcsin {x : ℝ} : ContinuousAt arcsin x :=
continuous_arcsin.continuousAt
theorem arcsin_eq_of_sin_eq {x y : ℝ} (h₁ : sin x = y) (h₂ : x ∈ Icc (-(π / 2)) (π / 2)) :
arcsin y = x := by
subst y
exact injOn_sin (arcsin_mem_Icc _) h₂ (sin_arcsin' (sin_mem_Icc x))
@[simp]
theorem arcsin_zero : arcsin 0 = 0 :=
arcsin_eq_of_sin_eq sin_zero ⟨neg_nonpos.2 pi_div_two_pos.le, pi_div_two_pos.le⟩
@[simp]
theorem arcsin_one : arcsin 1 = π / 2 :=
arcsin_eq_of_sin_eq sin_pi_div_two <| right_mem_Icc.2 (neg_le_self pi_div_two_pos.le)
theorem arcsin_of_one_le {x : ℝ} (hx : 1 ≤ x) : arcsin x = π / 2 := by
rw [← arcsin_projIcc, projIcc_of_right_le _ hx, Subtype.coe_mk, arcsin_one]
theorem arcsin_neg_one : arcsin (-1) = -(π / 2) :=
arcsin_eq_of_sin_eq (by rw [sin_neg, sin_pi_div_two]) <|
left_mem_Icc.2 (neg_le_self pi_div_two_pos.le)
theorem arcsin_of_le_neg_one {x : ℝ} (hx : x ≤ -1) : arcsin x = -(π / 2) := by
rw [← arcsin_projIcc, projIcc_of_le_left _ hx, Subtype.coe_mk, arcsin_neg_one]
@[simp]
theorem arcsin_neg (x : ℝ) : arcsin (-x) = -arcsin x := by
rcases le_total x (-1) with hx₁ | hx₁
· rw [arcsin_of_le_neg_one hx₁, neg_neg, arcsin_of_one_le (le_neg.2 hx₁)]
rcases le_total 1 x with hx₂ | hx₂
· rw [arcsin_of_one_le hx₂, arcsin_of_le_neg_one (neg_le_neg hx₂)]
refine arcsin_eq_of_sin_eq ?_ ?_
· rw [sin_neg, sin_arcsin hx₁ hx₂]
· exact ⟨neg_le_neg (arcsin_le_pi_div_two _), neg_le.2 (neg_pi_div_two_le_arcsin _)⟩
theorem arcsin_le_iff_le_sin {x y : ℝ} (hx : x ∈ Icc (-1 : ℝ) 1) (hy : y ∈ Icc (-(π / 2)) (π / 2)) :
arcsin x ≤ y ↔ x ≤ sin y := by
rw [← arcsin_sin' hy, strictMonoOn_arcsin.le_iff_le hx (sin_mem_Icc _), arcsin_sin' hy]
theorem arcsin_le_iff_le_sin' {x y : ℝ} (hy : y ∈ Ico (-(π / 2)) (π / 2)) :
arcsin x ≤ y ↔ x ≤ sin y := by
rcases le_total x (-1) with hx₁ | hx₁
· simp [arcsin_of_le_neg_one hx₁, hy.1, hx₁.trans (neg_one_le_sin _)]
rcases lt_or_le 1 x with hx₂ | hx₂
· simp [arcsin_of_one_le hx₂.le, hy.2.not_le, (sin_le_one y).trans_lt hx₂]
exact arcsin_le_iff_le_sin ⟨hx₁, hx₂⟩ (mem_Icc_of_Ico hy)
theorem le_arcsin_iff_sin_le {x y : ℝ} (hx : x ∈ Icc (-(π / 2)) (π / 2)) (hy : y ∈ Icc (-1 : ℝ) 1) :
x ≤ arcsin y ↔ sin x ≤ y := by
rw [← neg_le_neg_iff, ← arcsin_neg,
arcsin_le_iff_le_sin ⟨neg_le_neg hy.2, neg_le.2 hy.1⟩ ⟨neg_le_neg hx.2, neg_le.2 hx.1⟩, sin_neg,
neg_le_neg_iff]
theorem le_arcsin_iff_sin_le' {x y : ℝ} (hx : x ∈ Ioc (-(π / 2)) (π / 2)) :
x ≤ arcsin y ↔ sin x ≤ y := by
rw [← neg_le_neg_iff, ← arcsin_neg, arcsin_le_iff_le_sin' ⟨neg_le_neg hx.2, neg_lt.2 hx.1⟩,
sin_neg, neg_le_neg_iff]
theorem arcsin_lt_iff_lt_sin {x y : ℝ} (hx : x ∈ Icc (-1 : ℝ) 1) (hy : y ∈ Icc (-(π / 2)) (π / 2)) :
arcsin x < y ↔ x < sin y :=
not_le.symm.trans <| (not_congr <| le_arcsin_iff_sin_le hy hx).trans not_le
theorem arcsin_lt_iff_lt_sin' {x y : ℝ} (hy : y ∈ Ioc (-(π / 2)) (π / 2)) :
arcsin x < y ↔ x < sin y :=
not_le.symm.trans <| (not_congr <| le_arcsin_iff_sin_le' hy).trans not_le
theorem lt_arcsin_iff_sin_lt {x y : ℝ} (hx : x ∈ Icc (-(π / 2)) (π / 2)) (hy : y ∈ Icc (-1 : ℝ) 1) :
x < arcsin y ↔ sin x < y :=
not_le.symm.trans <| (not_congr <| arcsin_le_iff_le_sin hy hx).trans not_le
theorem lt_arcsin_iff_sin_lt' {x y : ℝ} (hx : x ∈ Ico (-(π / 2)) (π / 2)) :
x < arcsin y ↔ sin x < y :=
not_le.symm.trans <| (not_congr <| arcsin_le_iff_le_sin' hx).trans not_le
theorem arcsin_eq_iff_eq_sin {x y : ℝ} (hy : y ∈ Ioo (-(π / 2)) (π / 2)) :
arcsin x = y ↔ x = sin y := by
simp only [le_antisymm_iff, arcsin_le_iff_le_sin' (mem_Ico_of_Ioo hy),
le_arcsin_iff_sin_le' (mem_Ioc_of_Ioo hy)]
@[simp]
theorem arcsin_nonneg {x : ℝ} : 0 ≤ arcsin x ↔ 0 ≤ x :=
(le_arcsin_iff_sin_le' ⟨neg_lt_zero.2 pi_div_two_pos, pi_div_two_pos.le⟩).trans <| by
rw [sin_zero]
@[simp]
theorem arcsin_nonpos {x : ℝ} : arcsin x ≤ 0 ↔ x ≤ 0 :=
neg_nonneg.symm.trans <| arcsin_neg x ▸ arcsin_nonneg.trans neg_nonneg
@[simp]
theorem arcsin_eq_zero_iff {x : ℝ} : arcsin x = 0 ↔ x = 0 := by simp [le_antisymm_iff]
@[simp]
theorem zero_eq_arcsin_iff {x} : 0 = arcsin x ↔ x = 0 :=
eq_comm.trans arcsin_eq_zero_iff
@[simp]
theorem arcsin_pos {x : ℝ} : 0 < arcsin x ↔ 0 < x :=
lt_iff_lt_of_le_iff_le arcsin_nonpos
@[simp]
theorem arcsin_lt_zero {x : ℝ} : arcsin x < 0 ↔ x < 0 :=
lt_iff_lt_of_le_iff_le arcsin_nonneg
@[simp]
theorem arcsin_lt_pi_div_two {x : ℝ} : arcsin x < π / 2 ↔ x < 1 :=
(arcsin_lt_iff_lt_sin' (right_mem_Ioc.2 <| neg_lt_self pi_div_two_pos)).trans <| by
rw [sin_pi_div_two]
@[simp]
theorem neg_pi_div_two_lt_arcsin {x : ℝ} : -(π / 2) < arcsin x ↔ -1 < x :=
(lt_arcsin_iff_sin_lt' <| left_mem_Ico.2 <| neg_lt_self pi_div_two_pos).trans <| by
rw [sin_neg, sin_pi_div_two]
@[simp]
theorem arcsin_eq_pi_div_two {x : ℝ} : arcsin x = π / 2 ↔ 1 ≤ x :=
⟨fun h => not_lt.1 fun h' => (arcsin_lt_pi_div_two.2 h').ne h, arcsin_of_one_le⟩
@[simp]
theorem pi_div_two_eq_arcsin {x} : π / 2 = arcsin x ↔ 1 ≤ x :=
eq_comm.trans arcsin_eq_pi_div_two
@[simp]
theorem pi_div_two_le_arcsin {x} : π / 2 ≤ arcsin x ↔ 1 ≤ x :=
(arcsin_le_pi_div_two x).le_iff_eq.trans pi_div_two_eq_arcsin
@[simp]
theorem arcsin_eq_neg_pi_div_two {x : ℝ} : arcsin x = -(π / 2) ↔ x ≤ -1 :=
⟨fun h => not_lt.1 fun h' => (neg_pi_div_two_lt_arcsin.2 h').ne' h, arcsin_of_le_neg_one⟩
@[simp]
theorem neg_pi_div_two_eq_arcsin {x} : -(π / 2) = arcsin x ↔ x ≤ -1 :=
eq_comm.trans arcsin_eq_neg_pi_div_two
@[simp]
theorem arcsin_le_neg_pi_div_two {x} : arcsin x ≤ -(π / 2) ↔ x ≤ -1 :=
(neg_pi_div_two_le_arcsin x).le_iff_eq.trans arcsin_eq_neg_pi_div_two
@[simp]
theorem pi_div_four_le_arcsin {x} : π / 4 ≤ arcsin x ↔ √2 / 2 ≤ x := by
rw [← sin_pi_div_four, le_arcsin_iff_sin_le']
have := pi_pos
constructor <;> linarith
theorem mapsTo_sin_Ioo : MapsTo sin (Ioo (-(π / 2)) (π / 2)) (Ioo (-1) 1) := fun x h => by
rwa [mem_Ioo, ← arcsin_lt_pi_div_two, ← neg_pi_div_two_lt_arcsin, arcsin_sin h.1.le h.2.le]
/-- `Real.sin` as a `PartialHomeomorph` between `(-π / 2, π / 2)` and `(-1, 1)`. -/
@[simp]
def sinPartialHomeomorph : PartialHomeomorph ℝ ℝ where
toFun := sin
invFun := arcsin
source := Ioo (-(π / 2)) (π / 2)
target := Ioo (-1) 1
map_source' := mapsTo_sin_Ioo
map_target' _ hy := ⟨neg_pi_div_two_lt_arcsin.2 hy.1, arcsin_lt_pi_div_two.2 hy.2⟩
left_inv' _ hx := arcsin_sin hx.1.le hx.2.le
right_inv' _ hy := sin_arcsin hy.1.le hy.2.le
open_source := isOpen_Ioo
open_target := isOpen_Ioo
continuousOn_toFun := continuous_sin.continuousOn
continuousOn_invFun := continuous_arcsin.continuousOn
theorem cos_arcsin_nonneg (x : ℝ) : 0 ≤ cos (arcsin x) :=
cos_nonneg_of_mem_Icc ⟨neg_pi_div_two_le_arcsin _, arcsin_le_pi_div_two _⟩
-- The junk values for `arcsin` and `sqrt` make this true even outside `[-1, 1]`.
theorem cos_arcsin (x : ℝ) : cos (arcsin x) = √(1 - x ^ 2) := by
by_cases hx₁ : -1 ≤ x; swap
· rw [not_le] at hx₁
rw [arcsin_of_le_neg_one hx₁.le, cos_neg, cos_pi_div_two, sqrt_eq_zero_of_nonpos]
nlinarith
by_cases hx₂ : x ≤ 1; swap
· rw [not_le] at hx₂
rw [arcsin_of_one_le hx₂.le, cos_pi_div_two, sqrt_eq_zero_of_nonpos]
nlinarith
have : sin (arcsin x) ^ 2 + cos (arcsin x) ^ 2 = 1 := sin_sq_add_cos_sq (arcsin x)
rw [← eq_sub_iff_add_eq', ← sqrt_inj (sq_nonneg _) (sub_nonneg.2 (sin_sq_le_one (arcsin x))), sq,
sqrt_mul_self (cos_arcsin_nonneg _)] at this
rw [this, sin_arcsin hx₁ hx₂]
-- The junk values for `arcsin` and `sqrt` make this true even outside `[-1, 1]`.
theorem tan_arcsin (x : ℝ) : tan (arcsin x) = x / √(1 - x ^ 2) := by
rw [tan_eq_sin_div_cos, cos_arcsin]
by_cases hx₁ : -1 ≤ x; swap
· have h : √(1 - x ^ 2) = 0 := sqrt_eq_zero_of_nonpos (by nlinarith)
rw [h]
simp
by_cases hx₂ : x ≤ 1; swap
· have h : √(1 - x ^ 2) = 0 := sqrt_eq_zero_of_nonpos (by nlinarith)
rw [h]
simp
rw [sin_arcsin hx₁ hx₂]
/-- Inverse of the `cos` function, returns values in the range `0 ≤ arccos x` and `arccos x ≤ π`.
It defaults to `π` on `(-∞, -1)` and to `0` to `(1, ∞)`. -/
@[pp_nodot]
noncomputable def arccos (x : ℝ) : ℝ :=
π / 2 - arcsin x
theorem arccos_eq_pi_div_two_sub_arcsin (x : ℝ) : arccos x = π / 2 - arcsin x :=
rfl
theorem arcsin_eq_pi_div_two_sub_arccos (x : ℝ) : arcsin x = π / 2 - arccos x := by simp [arccos]
theorem arccos_le_pi (x : ℝ) : arccos x ≤ π := by
unfold arccos; linarith [neg_pi_div_two_le_arcsin x]
theorem arccos_nonneg (x : ℝ) : 0 ≤ arccos x := by
unfold arccos; linarith [arcsin_le_pi_div_two x]
@[simp]
theorem arccos_pos {x : ℝ} : 0 < arccos x ↔ x < 1 := by simp [arccos]
theorem cos_arccos {x : ℝ} (hx₁ : -1 ≤ x) (hx₂ : x ≤ 1) : cos (arccos x) = x := by
rw [arccos, cos_pi_div_two_sub, sin_arcsin hx₁ hx₂]
theorem arccos_cos {x : ℝ} (hx₁ : 0 ≤ x) (hx₂ : x ≤ π) : arccos (cos x) = x := by
rw [arccos, ← sin_pi_div_two_sub, arcsin_sin] <;> simp [sub_eq_add_neg] <;> linarith
lemma arccos_eq_of_eq_cos (hy₀ : 0 ≤ y) (hy₁ : y ≤ π) (hxy : x = cos y) : arccos x = y := by
rw [hxy, arccos_cos hy₀ hy₁]
theorem strictAntiOn_arccos : StrictAntiOn arccos (Icc (-1) 1) := fun _ hx _ hy h =>
sub_lt_sub_left (strictMonoOn_arcsin hx hy h) _
@[gcongr]
lemma arccos_lt_arccos {x y : ℝ} (hx : -1 ≤ x) (hlt : x < y) (hy : y ≤ 1) :
arccos y < arccos x := by
unfold arccos; gcongr <;> assumption
@[gcongr]
lemma arccos_le_arccos {x y : ℝ} (hlt : x ≤ y) : arccos y ≤ arccos x := by unfold arccos; gcongr
theorem antitone_arccos : Antitone arccos := fun _ _ ↦ arccos_le_arccos
theorem arccos_injOn : InjOn arccos (Icc (-1) 1) :=
strictAntiOn_arccos.injOn
theorem arccos_inj {x y : ℝ} (hx₁ : -1 ≤ x) (hx₂ : x ≤ 1) (hy₁ : -1 ≤ y) (hy₂ : y ≤ 1) :
arccos x = arccos y ↔ x = y :=
arccos_injOn.eq_iff ⟨hx₁, hx₂⟩ ⟨hy₁, hy₂⟩
@[simp]
theorem arccos_zero : arccos 0 = π / 2 := by simp [arccos]
@[simp]
theorem arccos_one : arccos 1 = 0 := by simp [arccos]
@[simp]
theorem arccos_neg_one : arccos (-1) = π := by simp [arccos, add_halves]
@[simp]
theorem arccos_eq_zero {x} : arccos x = 0 ↔ 1 ≤ x := by simp [arccos, sub_eq_zero]
@[simp]
theorem arccos_eq_pi_div_two {x} : arccos x = π / 2 ↔ x = 0 := by simp [arccos]
@[simp]
theorem arccos_eq_pi {x} : arccos x = π ↔ x ≤ -1 := by
rw [arccos, sub_eq_iff_eq_add, ← sub_eq_iff_eq_add', div_two_sub_self, neg_pi_div_two_eq_arcsin]
theorem arccos_neg (x : ℝ) : arccos (-x) = π - arccos x := by
rw [← add_halves π, arccos, arcsin_neg, arccos, add_sub_assoc, sub_sub_self, sub_neg_eq_add]
theorem arccos_of_one_le {x : ℝ} (hx : 1 ≤ x) : arccos x = 0 := by
rw [arccos, arcsin_of_one_le hx, sub_self]
theorem arccos_of_le_neg_one {x : ℝ} (hx : x ≤ -1) : arccos x = π := by
rw [arccos, arcsin_of_le_neg_one hx, sub_neg_eq_add, add_halves]
-- The junk values for `arccos` and `sqrt` make this true even outside `[-1, 1]`.
theorem sin_arccos (x : ℝ) : sin (arccos x) = √(1 - x ^ 2) := by
by_cases hx₁ : -1 ≤ x; swap
· rw [not_le] at hx₁
rw [arccos_of_le_neg_one hx₁.le, sin_pi, sqrt_eq_zero_of_nonpos]
nlinarith
by_cases hx₂ : x ≤ 1; swap
· rw [not_le] at hx₂
rw [arccos_of_one_le hx₂.le, sin_zero, sqrt_eq_zero_of_nonpos]
nlinarith
rw [arccos_eq_pi_div_two_sub_arcsin, sin_pi_div_two_sub, cos_arcsin]
@[simp]
theorem arccos_le_pi_div_two {x} : arccos x ≤ π / 2 ↔ 0 ≤ x := by simp [arccos]
@[simp]
theorem arccos_lt_pi_div_two {x : ℝ} : arccos x < π / 2 ↔ 0 < x := by simp [arccos]
@[simp]
theorem arccos_le_pi_div_four {x} : arccos x ≤ π / 4 ↔ √2 / 2 ≤ x := by
rw [arccos, ← pi_div_four_le_arcsin]
constructor <;>
· intro
linarith
@[continuity, fun_prop]
theorem continuous_arccos : Continuous arccos :=
continuous_const.sub continuous_arcsin
-- The junk values for `arccos` and `sqrt` make this true even outside `[-1, 1]`.
theorem tan_arccos (x : ℝ) : tan (arccos x) = √(1 - x ^ 2) / x := by
rw [arccos, tan_pi_div_two_sub, tan_arcsin, inv_div]
-- The junk values for `arccos` and `sqrt` make this true even for `1 < x`.
theorem arccos_eq_arcsin {x : ℝ} (h : 0 ≤ x) : arccos x = arcsin (√(1 - x ^ 2)) :=
(arcsin_eq_of_sin_eq (sin_arccos _)
⟨(Left.neg_nonpos_iff.2 (div_nonneg pi_pos.le (by norm_num))).trans (arccos_nonneg _),
arccos_le_pi_div_two.2 h⟩).symm
-- The junk values for `arcsin` and `sqrt` make this true even for `1 < x`.
theorem arcsin_eq_arccos {x : ℝ} (h : 0 ≤ x) : arcsin x = arccos (√(1 - x ^ 2)) := by
rw [eq_comm, ← cos_arcsin]
exact
arccos_cos (arcsin_nonneg.2 h)
((arcsin_le_pi_div_two _).trans (div_le_self pi_pos.le one_le_two))
end Real
open Real
/-!
### Convenience dot notation lemmas
-/
namespace Filter.Tendsto
variable {α : Type*} {l : Filter α} {x : ℝ} {f : α → ℝ}
protected theorem arcsin (h : Tendsto f l (𝓝 x)) : Tendsto (arcsin <| f ·) l (𝓝 (arcsin x)) :=
(continuous_arcsin.tendsto _).comp h
theorem arcsin_nhdsLE (h : Tendsto f l (𝓝[≤] x)) :
Tendsto (arcsin <| f ·) l (𝓝[≤] (arcsin x)) := by
refine ((continuous_arcsin.tendsto _).inf <| MapsTo.tendsto fun y hy ↦ ?_).comp h
exact monotone_arcsin hy
theorem arcsin_nhdsGE (h : Tendsto f l (𝓝[≥] x)) : Tendsto (arcsin <| f ·) l (𝓝[≥] (arcsin x)) :=
((continuous_arcsin.tendsto _).inf <| MapsTo.tendsto fun _ ↦ arcsin_le_arcsin).comp h
protected theorem arccos (h : Tendsto f l (𝓝 x)) : Tendsto (arccos <| f ·) l (𝓝 (arccos x)) :=
(continuous_arccos.tendsto _).comp h
theorem arccos_nhdsLE (h : Tendsto f l (𝓝[≤] x)) : Tendsto (arccos <| f ·) l (𝓝[≥] (arccos x)) :=
((continuous_arccos.tendsto _).inf <| MapsTo.tendsto fun _ ↦ arccos_le_arccos).comp h
theorem arccos_nhdsGE (h : Tendsto f l (𝓝[≥] x)) :
Tendsto (arccos <| f ·) l (𝓝[≤] (arccos x)) := by
refine ((continuous_arccos.tendsto _).inf <| MapsTo.tendsto fun y hy ↦ ?_).comp h
| simp only [mem_Ici, mem_Iic] at hy ⊢
| Mathlib/Analysis/SpecialFunctions/Trigonometric/Inverse.lean | 440 | 440 |
/-
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.Algebra.Group.PUnit
import Mathlib.Algebra.Group.Subgroup.Ker
import Mathlib.Algebra.Group.Submonoid.Membership
import Mathlib.GroupTheory.Congruence.Basic
/-!
# Coproduct (free product) of two monoids or groups
In this file we define `Monoid.Coprod M N` (notation: `M ∗ N`)
to be the coproduct (a.k.a. free product) of two monoids.
The same type is used for the coproduct of two monoids and for the coproduct of two groups.
The coproduct `M ∗ N` has the following universal property:
for any monoid `P` and homomorphisms `f : M →* P`, `g : N →* P`,
there exists a unique homomorphism `fg : M ∗ N →* P`
such that `fg ∘ Monoid.Coprod.inl = f` and `fg ∘ Monoid.Coprod.inr = g`,
where `Monoid.Coprod.inl : M →* M ∗ N`
and `Monoid.Coprod.inr : N →* M ∗ N` are canonical embeddings.
This homomorphism `fg` is given by `Monoid.Coprod.lift f g`.
We also define some homomorphisms and isomorphisms about `M ∗ N`,
and provide additive versions of all definitions and theorems.
## Main definitions
### Types
* `Monoid.Coprod M N` (a.k.a. `M ∗ N`):
the free product (a.k.a. coproduct) of two monoids `M` and `N`.
* `AddMonoid.Coprod M N` (no notation): the additive version of `Monoid.Coprod`.
In other sections, we only list multiplicative definitions.
### Instances
* `MulOneClass`, `Monoid`, and `Group` structures on the coproduct `M ∗ N`.
### Monoid homomorphisms
* `Monoid.Coprod.mk`: the projection `FreeMonoid (M ⊕ N) →* M ∗ N`.
* `Monoid.Coprod.inl`, `Monoid.Coprod.inr`: canonical embeddings `M →* M ∗ N` and `N →* M ∗ N`.
* `Monoid.Coprod.lift`: construct a monoid homomorphism `M ∗ N →* P`
from homomorphisms `M →* P` and `N →* P`; see also `Monoid.Coprod.liftEquiv`.
* `Monoid.Coprod.clift`: a constructor for homomorphisms `M ∗ N →* P`
that allows the user to control the computational behavior.
* `Monoid.Coprod.map`: combine two homomorphisms `f : M →* N` and `g : M' →* N'`
into `M ∗ M' →* N ∗ N'`.
* `Monoid.Coprod.swap`: the natural homomorphism `M ∗ N →* N ∗ M`.
* `Monoid.Coprod.fst`, `Monoid.Coprod.snd`, and `Monoid.Coprod.toProd`:
natural projections `M ∗ N →* M`, `M ∗ N →* N`, and `M ∗ N →* M × N`.
### Monoid isomorphisms
* `MulEquiv.coprodCongr`: a `MulEquiv` version of `Monoid.Coprod.map`.
* `MulEquiv.coprodComm`: a `MulEquiv` version of `Monoid.Coprod.swap`.
* `MulEquiv.coprodAssoc`: associativity of the coproduct.
* `MulEquiv.coprodPUnit`, `MulEquiv.punitCoprod`:
free product by `PUnit` on the left or on the right is isomorphic to the original monoid.
## Main results
The universal property of the coproduct
is given by the definition `Monoid.Coprod.lift` and the lemma `Monoid.Coprod.lift_unique`.
We also prove a slightly more general extensionality lemma `Monoid.Coprod.hom_ext`
for homomorphisms `M ∗ N →* P` and prove lots of basic lemmas like `Monoid.Coprod.fst_comp_inl`.
## Implementation details
The definition of the coproduct of an indexed family of monoids is formalized in `Monoid.CoprodI`.
While mathematically `M ∗ N` is a particular case
of the coproduct of an indexed family of monoids,
it is easier to build API from scratch instead of using something like
```
def Monoid.Coprod M N := Monoid.CoprodI ![M, N]
```
or
```
def Monoid.Coprod M N := Monoid.CoprodI (fun b : Bool => cond b M N)
```
There are several reasons to build an API from scratch.
- API about `Con` makes it easy to define the required type and prove the universal property,
so there is little overhead compared to transferring API from `Monoid.CoprodI`.
- If `M` and `N` live in different universes, then the definition has to add `ULift`s;
this makes it harder to transfer API and definitions.
- As of now, we have no way
to automatically build an instance of `(k : Fin 2) → Monoid (![M, N] k)`
from `[Monoid M]` and `[Monoid N]`,
not even speaking about more advanced typeclass assumptions that involve both `M` and `N`.
- Using a list of `M ⊕ N` instead of, e.g., a list of `Σ k : Fin 2, ![M, N] k`
as the underlying type makes it possible to write computationally effective code
(though this point is not tested yet).
## TODO
- Prove `Monoid.CoprodI (f : Fin 2 → Type*) ≃* f 0 ∗ f 1` and
`Monoid.CoprodI (f : Bool → Type*) ≃* f false ∗ f true`.
## Tags
group, monoid, coproduct, free product
-/
assert_not_exists MonoidWithZero
open FreeMonoid Function List Set
namespace Monoid
/-- The minimal congruence relation `c` on `FreeMonoid (M ⊕ N)`
such that `FreeMonoid.of ∘ Sum.inl` and `FreeMonoid.of ∘ Sum.inr` are monoid homomorphisms
to the quotient by `c`. -/
@[to_additive "The minimal additive congruence relation `c` on `FreeAddMonoid (M ⊕ N)`
such that `FreeAddMonoid.of ∘ Sum.inl` and `FreeAddMonoid.of ∘ Sum.inr`
are additive monoid homomorphisms to the quotient by `c`."]
def coprodCon (M N : Type*) [MulOneClass M] [MulOneClass N] : Con (FreeMonoid (M ⊕ N)) :=
sInf {c |
(∀ x y : M, c (of (Sum.inl (x * y))) (of (Sum.inl x) * of (Sum.inl y)))
∧ (∀ x y : N, c (of (Sum.inr (x * y))) (of (Sum.inr x) * of (Sum.inr y)))
∧ c (of <| Sum.inl 1) 1 ∧ c (of <| Sum.inr 1) 1}
/-- Coproduct of two monoids or groups. -/
@[to_additive "Coproduct of two additive monoids or groups."]
def Coprod (M N : Type*) [MulOneClass M] [MulOneClass N] := (coprodCon M N).Quotient
namespace Coprod
@[inherit_doc]
scoped infix:30 " ∗ " => Coprod
section MulOneClass
variable {M N M' N' P : Type*} [MulOneClass M] [MulOneClass N] [MulOneClass M'] [MulOneClass N']
[MulOneClass P]
@[to_additive] protected instance : MulOneClass (M ∗ N) := Con.mulOneClass _
/-- The natural projection `FreeMonoid (M ⊕ N) →* M ∗ N`. -/
@[to_additive "The natural projection `FreeAddMonoid (M ⊕ N) →+ AddMonoid.Coprod M N`."]
def mk : FreeMonoid (M ⊕ N) →* M ∗ N := Con.mk' _
@[to_additive (attr := simp)]
theorem con_ker_mk : Con.ker mk = coprodCon M N := Con.mk'_ker _
@[to_additive]
theorem mk_surjective : Surjective (@mk M N _ _) := Quot.mk_surjective
@[to_additive (attr := simp)]
theorem mrange_mk : MonoidHom.mrange (@mk M N _ _) = ⊤ := Con.mrange_mk'
@[to_additive]
theorem mk_eq_mk {w₁ w₂ : FreeMonoid (M ⊕ N)} : mk w₁ = mk w₂ ↔ coprodCon M N w₁ w₂ := Con.eq _
/-- The natural embedding `M →* M ∗ N`. -/
@[to_additive "The natural embedding `M →+ AddMonoid.Coprod M N`."]
def inl : M →* M ∗ N where
toFun := fun x => mk (of (.inl x))
map_one' := mk_eq_mk.2 fun _c hc => hc.2.2.1
map_mul' := fun x y => mk_eq_mk.2 fun _c hc => hc.1 x y
/-- The natural embedding `N →* M ∗ N`. -/
@[to_additive "The natural embedding `N →+ AddMonoid.Coprod M N`."]
def inr : N →* M ∗ N where
toFun := fun x => mk (of (.inr x))
map_one' := mk_eq_mk.2 fun _c hc => hc.2.2.2
map_mul' := fun x y => mk_eq_mk.2 fun _c hc => hc.2.1 x y
@[to_additive (attr := simp)]
theorem mk_of_inl (x : M) : (mk (of (.inl x)) : M ∗ N) = inl x := rfl
@[to_additive (attr := simp)]
theorem mk_of_inr (x : N) : (mk (of (.inr x)) : M ∗ N) = inr x := rfl
@[to_additive (attr := elab_as_elim)]
theorem induction_on' {C : M ∗ N → Prop} (m : M ∗ N)
(one : C 1)
(inl_mul : ∀ m x, C x → C (inl m * x))
(inr_mul : ∀ n x, C x → C (inr n * x)) : C m := by
rcases mk_surjective m with ⟨x, rfl⟩
induction x using FreeMonoid.inductionOn' with
| one => exact one
| mul_of x xs ih =>
cases x with
| inl m => simpa using inl_mul m _ ih
| inr n => simpa using inr_mul n _ ih
@[to_additive (attr := elab_as_elim)]
theorem induction_on {C : M ∗ N → Prop} (m : M ∗ N)
(inl : ∀ m, C (inl m)) (inr : ∀ n, C (inr n)) (mul : ∀ x y, C x → C y → C (x * y)) : C m :=
induction_on' m (by simpa using inl 1) (fun _ _ ↦ mul _ _ (inl _)) fun _ _ ↦ mul _ _ (inr _)
/-- Lift a monoid homomorphism `FreeMonoid (M ⊕ N) →* P` satisfying additional properties to
`M ∗ N →* P`. In many cases, `Coprod.lift` is more convenient.
Compared to `Coprod.lift`,
this definition allows a user to provide a custom computational behavior.
Also, it only needs `MulOneclass` assumptions while `Coprod.lift` needs a `Monoid` structure.
-/
@[to_additive "Lift an additive monoid homomorphism `FreeAddMonoid (M ⊕ N) →+ P` satisfying
additional properties to `AddMonoid.Coprod M N →+ P`.
Compared to `AddMonoid.Coprod.lift`,
this definition allows a user to provide a custom computational behavior.
Also, it only needs `AddZeroclass` assumptions
while `AddMonoid.Coprod.lift` needs an `AddMonoid` structure. "]
def clift (f : FreeMonoid (M ⊕ N) →* P)
(hM₁ : f (of (.inl 1)) = 1) (hN₁ : f (of (.inr 1)) = 1)
(hM : ∀ x y, f (of (.inl (x * y))) = f (of (.inl x) * of (.inl y)))
(hN : ∀ x y, f (of (.inr (x * y))) = f (of (.inr x) * of (.inr y))) :
M ∗ N →* P :=
Con.lift _ f <| sInf_le ⟨hM, hN, hM₁.trans (map_one f).symm, hN₁.trans (map_one f).symm⟩
@[to_additive (attr := simp)]
theorem clift_apply_inl (f : FreeMonoid (M ⊕ N) →* P) (hM₁ hN₁ hM hN) (x : M) :
clift f hM₁ hN₁ hM hN (inl x) = f (of (.inl x)) :=
rfl
@[to_additive (attr := simp)]
theorem clift_apply_inr (f : FreeMonoid (M ⊕ N) →* P) (hM₁ hN₁ hM hN) (x : N) :
clift f hM₁ hN₁ hM hN (inr x) = f (of (.inr x)) :=
rfl
@[to_additive (attr := simp)]
theorem clift_apply_mk (f : FreeMonoid (M ⊕ N) →* P) (hM₁ hN₁ hM hN w) :
clift f hM₁ hN₁ hM hN (mk w) = f w :=
rfl
@[to_additive (attr := simp)]
theorem clift_comp_mk (f : FreeMonoid (M ⊕ N) →* P) (hM₁ hN₁ hM hN) :
(clift f hM₁ hN₁ hM hN).comp mk = f :=
DFunLike.ext' rfl
@[to_additive (attr := simp)]
theorem mclosure_range_inl_union_inr :
Submonoid.closure (range (inl : M →* M ∗ N) ∪ range (inr : N →* M ∗ N)) = ⊤ := by
rw [← mrange_mk, MonoidHom.mrange_eq_map, ← closure_range_of, MonoidHom.map_mclosure,
← range_comp, Sum.range_eq]; rfl
@[to_additive (attr := simp)] theorem mrange_inl_sup_mrange_inr :
MonoidHom.mrange (inl : M →* M ∗ N) ⊔ MonoidHom.mrange (inr : N →* M ∗ N) = ⊤ := by
rw [← mclosure_range_inl_union_inr, Submonoid.closure_union, ← MonoidHom.coe_mrange,
← MonoidHom.coe_mrange, Submonoid.closure_eq, Submonoid.closure_eq]
@[to_additive]
theorem codisjoint_mrange_inl_mrange_inr :
Codisjoint (MonoidHom.mrange (inl : M →* M ∗ N)) (MonoidHom.mrange inr) :=
codisjoint_iff.2 mrange_inl_sup_mrange_inr
@[to_additive] theorem mrange_eq (f : M ∗ N →* P) :
MonoidHom.mrange f = MonoidHom.mrange (f.comp inl) ⊔ MonoidHom.mrange (f.comp inr) := by
rw [MonoidHom.mrange_eq_map, ← mrange_inl_sup_mrange_inr, Submonoid.map_sup, MonoidHom.map_mrange,
MonoidHom.map_mrange]
/-- Extensionality lemma for monoid homomorphisms `M ∗ N →* P`.
If two homomorphisms agree on the ranges of `Monoid.Coprod.inl` and `Monoid.Coprod.inr`,
then they are equal. -/
@[to_additive (attr := ext 1100)
"Extensionality lemma for additive monoid homomorphisms `AddMonoid.Coprod M N →+ P`.
If two homomorphisms agree on the ranges of `AddMonoid.Coprod.inl` and `AddMonoid.Coprod.inr`,
then they are equal."]
theorem hom_ext {f g : M ∗ N →* P} (h₁ : f.comp inl = g.comp inl) (h₂ : f.comp inr = g.comp inr) :
f = g :=
MonoidHom.eq_of_eqOn_denseM mclosure_range_inl_union_inr <| eqOn_union.2
⟨eqOn_range.2 <| DFunLike.ext'_iff.1 h₁, eqOn_range.2 <| DFunLike.ext'_iff.1 h₂⟩
@[to_additive (attr := simp)]
theorem clift_mk :
clift (mk : FreeMonoid (M ⊕ N) →* M ∗ N) (map_one inl) (map_one inr) (map_mul inl)
(map_mul inr) = .id _ :=
hom_ext rfl rfl
/-- Map `M ∗ N` to `M' ∗ N'` by applying `Sum.map f g` to each element of the underlying list. -/
@[to_additive "Map `AddMonoid.Coprod M N` to `AddMonoid.Coprod M' N'`
by applying `Sum.map f g` to each element of the underlying list."]
def map (f : M →* M') (g : N →* N') : M ∗ N →* M' ∗ N' :=
clift (mk.comp <| FreeMonoid.map <| Sum.map f g)
(by simp only [MonoidHom.comp_apply, map_of, Sum.map_inl, map_one, mk_of_inl])
(by simp only [MonoidHom.comp_apply, map_of, Sum.map_inr, map_one, mk_of_inr])
(fun x y => by simp only [MonoidHom.comp_apply, map_of, Sum.map_inl, map_mul, mk_of_inl])
fun x y => by simp only [MonoidHom.comp_apply, map_of, Sum.map_inr, map_mul, mk_of_inr]
@[to_additive (attr := simp)]
theorem map_mk_ofList (f : M →* M') (g : N →* N') (l : List (M ⊕ N)) :
map f g (mk (ofList l)) = mk (ofList (l.map (Sum.map f g))) :=
rfl
@[to_additive (attr := simp)]
theorem map_apply_inl (f : M →* M') (g : N →* N') (x : M) : map f g (inl x) = inl (f x) := rfl
@[to_additive (attr := simp)]
theorem map_apply_inr (f : M →* M') (g : N →* N') (x : N) : map f g (inr x) = inr (g x) := rfl
@[to_additive (attr := simp)]
theorem map_comp_inl (f : M →* M') (g : N →* N') : (map f g).comp inl = inl.comp f := rfl
@[to_additive (attr := simp)]
theorem map_comp_inr (f : M →* M') (g : N →* N') : (map f g).comp inr = inr.comp g := rfl
@[to_additive (attr := simp)]
theorem map_id_id : map (.id M) (.id N) = .id (M ∗ N) := hom_ext rfl rfl
@[to_additive]
theorem map_comp_map {M'' N''} [MulOneClass M''] [MulOneClass N''] (f' : M' →* M'') (g' : N' →* N'')
(f : M →* M') (g : N →* N') : (map f' g').comp (map f g) = map (f'.comp f) (g'.comp g) :=
hom_ext rfl rfl
@[to_additive]
theorem map_map {M'' N''} [MulOneClass M''] [MulOneClass N''] (f' : M' →* M'') (g' : N' →* N'')
(f : M →* M') (g : N →* N') (x : M ∗ N) :
map f' g' (map f g x) = map (f'.comp f) (g'.comp g) x :=
DFunLike.congr_fun (map_comp_map f' g' f g) x
variable (M N)
/-- Map `M ∗ N` to `N ∗ M` by applying `Sum.swap` to each element of the underlying list.
See also `MulEquiv.coprodComm` for a `MulEquiv` version. -/
@[to_additive "Map `AddMonoid.Coprod M N` to `AddMonoid.Coprod N M`
by applying `Sum.swap` to each element of the underlying list.
See also `AddEquiv.coprodComm` for an `AddEquiv` version."]
def swap : M ∗ N →* N ∗ M :=
clift (mk.comp <| FreeMonoid.map Sum.swap)
(by simp only [MonoidHom.comp_apply, map_of, Sum.swap_inl, mk_of_inr, map_one])
(by simp only [MonoidHom.comp_apply, map_of, Sum.swap_inr, mk_of_inl, map_one])
(fun x y => by simp only [MonoidHom.comp_apply, map_of, Sum.swap_inl, mk_of_inr, map_mul])
(fun x y => by simp only [MonoidHom.comp_apply, map_of, Sum.swap_inr, mk_of_inl, map_mul])
@[to_additive (attr := simp)]
theorem swap_comp_swap : (swap M N).comp (swap N M) = .id _ := hom_ext rfl rfl
variable {M N}
@[to_additive (attr := simp)]
theorem swap_swap (x : M ∗ N) : swap N M (swap M N x) = x :=
DFunLike.congr_fun (swap_comp_swap _ _) x
@[to_additive]
theorem swap_comp_map (f : M →* M') (g : N →* N') :
(swap M' N').comp (map f g) = (map g f).comp (swap M N) :=
hom_ext rfl rfl
@[to_additive]
theorem swap_map (f : M →* M') (g : N →* N') (x : M ∗ N) :
swap M' N' (map f g x) = map g f (swap M N x) :=
DFunLike.congr_fun (swap_comp_map f g) x
@[to_additive (attr := simp)] theorem swap_comp_inl : (swap M N).comp inl = inr := rfl
@[to_additive (attr := simp)] theorem swap_inl (x : M) : swap M N (inl x) = inr x := rfl
@[to_additive (attr := simp)] theorem swap_comp_inr : (swap M N).comp inr = inl := rfl
@[to_additive (attr := simp)] theorem swap_inr (x : N) : swap M N (inr x) = inl x := rfl
@[to_additive]
theorem swap_injective : Injective (swap M N) := LeftInverse.injective swap_swap
@[to_additive (attr := simp)]
theorem swap_inj {x y : M ∗ N} : swap M N x = swap M N y ↔ x = y := swap_injective.eq_iff
@[to_additive (attr := simp)]
theorem swap_eq_one {x : M ∗ N} : swap M N x = 1 ↔ x = 1 := swap_injective.eq_iff' (map_one _)
@[to_additive]
theorem swap_surjective : Surjective (swap M N) := LeftInverse.surjective swap_swap
@[to_additive]
theorem swap_bijective : Bijective (swap M N) := ⟨swap_injective, swap_surjective⟩
@[to_additive (attr := simp)]
theorem mker_swap : MonoidHom.mker (swap M N) = ⊥ := Submonoid.ext fun _ ↦ swap_eq_one
@[to_additive (attr := simp)]
theorem mrange_swap : MonoidHom.mrange (swap M N) = ⊤ :=
MonoidHom.mrange_eq_top_of_surjective _ swap_surjective
end MulOneClass
section Lift
variable {M N P : Type*} [MulOneClass M] [MulOneClass N] [Monoid P]
/-- Lift a pair of monoid homomorphisms `f : M →* P`, `g : N →* P`
to a monoid homomorphism `M ∗ N →* P`.
See also `Coprod.clift` for a version that allows custom computational behavior
and works for a `MulOneClass` codomain.
-/
@[to_additive "Lift a pair of additive monoid homomorphisms `f : M →+ P`, `g : N →+ P`
to an additive monoid homomorphism `AddMonoid.Coprod M N →+ P`.
See also `AddMonoid.Coprod.clift` for a version that allows custom computational behavior
and works for an `AddZeroClass` codomain."]
def lift (f : M →* P) (g : N →* P) : (M ∗ N) →* P :=
clift (FreeMonoid.lift <| Sum.elim f g) (map_one f) (map_one g) (map_mul f) (map_mul g)
@[to_additive (attr := simp)]
theorem lift_apply_mk (f : M →* P) (g : N →* P) (x : FreeMonoid (M ⊕ N)) :
lift f g (mk x) = FreeMonoid.lift (Sum.elim f g) x :=
rfl
@[to_additive (attr := simp)]
theorem lift_apply_inl (f : M →* P) (g : N →* P) (x : M) : lift f g (inl x) = f x :=
rfl
@[to_additive]
theorem lift_unique {f : M →* P} {g : N →* P} {fg : M ∗ N →* P} (h₁ : fg.comp inl = f)
(h₂ : fg.comp inr = g) : fg = lift f g :=
hom_ext h₁ h₂
@[to_additive (attr := simp)]
theorem lift_comp_inl (f : M →* P) (g : N →* P) : (lift f g).comp inl = f := rfl
@[to_additive (attr := simp)]
theorem lift_apply_inr (f : M →* P) (g : N →* P) (x : N) : lift f g (inr x) = g x :=
rfl
@[to_additive (attr := simp)]
theorem lift_comp_inr (f : M →* P) (g : N →* P) : (lift f g).comp inr = g := rfl
@[to_additive (attr := simp)]
theorem lift_comp_swap (f : M →* P) (g : N →* P) : (lift f g).comp (swap N M) = lift g f :=
hom_ext rfl rfl
@[to_additive (attr := simp)]
theorem lift_swap (f : M →* P) (g : N →* P) (x : N ∗ M) : lift f g (swap N M x) = lift g f x :=
DFunLike.congr_fun (lift_comp_swap f g) x
@[to_additive]
theorem comp_lift {P' : Type*} [Monoid P'] (f : P →* P') (g₁ : M →* P) (g₂ : N →* P) :
f.comp (lift g₁ g₂) = lift (f.comp g₁) (f.comp g₂) :=
hom_ext (by rw [MonoidHom.comp_assoc, lift_comp_inl, lift_comp_inl]) <| by
rw [MonoidHom.comp_assoc, lift_comp_inr, lift_comp_inr]
/-- `Coprod.lift` as an equivalence. -/
@[to_additive "`AddMonoid.Coprod.lift` as an equivalence."]
def liftEquiv : (M →* P) × (N →* P) ≃ (M ∗ N →* P) where
toFun fg := lift fg.1 fg.2
invFun f := (f.comp inl, f.comp inr)
left_inv _ := rfl
right_inv _ := Eq.symm <| lift_unique rfl rfl
@[to_additive (attr := simp)]
theorem mrange_lift (f : M →* P) (g : N →* P) :
MonoidHom.mrange (lift f g) = MonoidHom.mrange f ⊔ MonoidHom.mrange g := by
simp [mrange_eq]
end Lift
section ToProd
variable {M N : Type*} [Monoid M] [Monoid N]
@[to_additive] instance : Monoid (M ∗ N) :=
{ mul_assoc := (Con.monoid _).mul_assoc
one_mul := (Con.monoid _).one_mul
mul_one := (Con.monoid _).mul_one }
/-- The natural projection `M ∗ N →* M`. -/
@[to_additive "The natural projection `AddMonoid.Coprod M N →+ M`."]
def fst : M ∗ N →* M := lift (.id M) 1
/-- The natural projection `M ∗ N →* N`. -/
@[to_additive "The natural projection `AddMonoid.Coprod M N →+ N`."]
def snd : M ∗ N →* N := lift 1 (.id N)
/-- The natural projection `M ∗ N →* M × N`. -/
@[to_additive toProd "The natural projection `AddMonoid.Coprod M N →+ M × N`."]
def toProd : M ∗ N →* M × N := lift (.inl _ _) (.inr _ _)
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.toSum := AddMonoid.Coprod.toProd
@[to_additive (attr := simp)] theorem fst_comp_inl : (fst : M ∗ N →* M).comp inl = .id _ := rfl
@[to_additive (attr := simp)] theorem fst_apply_inl (x : M) : fst (inl x : M ∗ N) = x := rfl
@[to_additive (attr := simp)] theorem fst_comp_inr : (fst : M ∗ N →* M).comp inr = 1 := rfl
@[to_additive (attr := simp)] theorem fst_apply_inr (x : N) : fst (inr x : M ∗ N) = 1 := rfl
@[to_additive (attr := simp)] theorem snd_comp_inl : (snd : M ∗ N →* N).comp inl = 1 := rfl
@[to_additive (attr := simp)] theorem snd_apply_inl (x : M) : snd (inl x : M ∗ N) = 1 := rfl
@[to_additive (attr := simp)] theorem snd_comp_inr : (snd : M ∗ N →* N).comp inr = .id _ := rfl
@[to_additive (attr := simp)] theorem snd_apply_inr (x : N) : snd (inr x : M ∗ N) = x := rfl
@[to_additive (attr := simp) toProd_comp_inl]
theorem toProd_comp_inl : (toProd : M ∗ N →* M × N).comp inl = .inl _ _ := rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.toSum_comp_inl := AddMonoid.Coprod.toProd_comp_inl
@[to_additive (attr := simp) toProd_comp_inr]
theorem toProd_comp_inr : (toProd : M ∗ N →* M × N).comp inr = .inr _ _ := rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.toSum_comp_inr := AddMonoid.Coprod.toProd_comp_inr
@[to_additive (attr := simp) toProd_apply_inl]
theorem toProd_apply_inl (x : M) : toProd (inl x : M ∗ N) = (x, 1) := rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.toSum_apply_inl := AddMonoid.Coprod.toProd_apply_inl
@[to_additive (attr := simp) toProd_apply_inr]
theorem toProd_apply_inr (x : N) : toProd (inr x : M ∗ N) = (1, x) := rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.toSum_apply_inr := AddMonoid.Coprod.toProd_apply_inr
@[to_additive (attr := simp) fst_prod_snd]
theorem fst_prod_snd : (fst : M ∗ N →* M).prod snd = toProd := by ext1 <;> rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.fst_sum_snd := AddMonoid.Coprod.fst_prod_snd
@[to_additive (attr := simp) prod_mk_fst_snd]
theorem prod_mk_fst_snd (x : M ∗ N) : (fst x, snd x) = toProd x := by
rw [← fst_prod_snd, MonoidHom.prod_apply]
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.sum_mk_fst_snd := AddMonoid.Coprod.prod_mk_fst_snd
@[to_additive (attr := simp) fst_comp_toProd]
theorem fst_comp_toProd : (MonoidHom.fst M N).comp toProd = fst := by
rw [← fst_prod_snd, MonoidHom.fst_comp_prod]
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.fst_comp_toSum := AddMonoid.Coprod.fst_comp_toProd
@[to_additive (attr := simp) fst_toProd]
theorem fst_toProd (x : M ∗ N) : (toProd x).1 = fst x := by
rw [← fst_comp_toProd]; rfl
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.fst_toSum := AddMonoid.Coprod.fst_toProd
@[to_additive (attr := simp) snd_comp_toProd]
theorem snd_comp_toProd : (MonoidHom.snd M N).comp toProd = snd := by
rw [← fst_prod_snd, MonoidHom.snd_comp_prod]
@[deprecated (since := "2025-03-11")]
alias _root_.AddMonoid.Coprod.snd_comp_toSum := AddMonoid.Coprod.snd_comp_toProd
@[to_additive (attr := simp) snd_toProd]
theorem snd_toProd (x : M ∗ N) : (toProd x).2 = snd x := by
rw [← snd_comp_toProd]; rfl
|
@[deprecated (since := "2025-03-11")]
| Mathlib/GroupTheory/Coprod/Basic.lean | 558 | 559 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Abhimanyu Pallavi Sudhir
-/
import Mathlib.Algebra.CharP.Defs
import Mathlib.Algebra.Order.CauSeq.BigOperators
import Mathlib.Algebra.Order.Star.Basic
import Mathlib.Data.Complex.BigOperators
import Mathlib.Data.Complex.Norm
import Mathlib.Data.Nat.Choose.Sum
/-!
# Exponential Function
This file contains the definitions of the real and complex exponential function.
## Main definitions
* `Complex.exp`: The complex exponential function, defined via its Taylor series
* `Real.exp`: The real exponential function, defined as the real part of the complex exponential
-/
open CauSeq Finset IsAbsoluteValue
open scoped ComplexConjugate
namespace Complex
theorem isCauSeq_norm_exp (z : ℂ) :
IsCauSeq abs fun n => ∑ m ∈ range n, ‖z ^ m / m.factorial‖ :=
let ⟨n, hn⟩ := exists_nat_gt ‖z‖
have hn0 : (0 : ℝ) < n := lt_of_le_of_lt (norm_nonneg _) hn
IsCauSeq.series_ratio_test n (‖z‖ / n) (div_nonneg (norm_nonneg _) (le_of_lt hn0))
(by rwa [div_lt_iff₀ hn0, one_mul]) fun m hm => by
rw [abs_norm, abs_norm, Nat.factorial_succ, pow_succ', mul_comm m.succ, Nat.cast_mul,
← div_div, mul_div_assoc, mul_div_right_comm, Complex.norm_mul, Complex.norm_div,
norm_natCast]
gcongr
exact le_trans hm (Nat.le_succ _)
@[deprecated (since := "2025-02-16")] alias isCauSeq_abs_exp := isCauSeq_norm_exp
noncomputable section
theorem isCauSeq_exp (z : ℂ) : IsCauSeq (‖·‖) fun n => ∑ m ∈ range n, z ^ m / m.factorial :=
(isCauSeq_norm_exp z).of_abv
/-- The Cauchy sequence consisting of partial sums of the Taylor series of
the complex exponential function -/
@[pp_nodot]
def exp' (z : ℂ) : CauSeq ℂ (‖·‖) :=
⟨fun n => ∑ m ∈ range n, z ^ m / m.factorial, isCauSeq_exp z⟩
/-- The complex exponential function, defined via its Taylor series -/
@[pp_nodot]
def exp (z : ℂ) : ℂ :=
CauSeq.lim (exp' z)
/-- scoped notation for the complex exponential function -/
scoped notation "cexp" => Complex.exp
end
end Complex
namespace Real
open Complex
noncomputable section
/-- The real exponential function, defined as the real part of the complex exponential -/
@[pp_nodot]
nonrec def exp (x : ℝ) : ℝ :=
(exp x).re
/-- scoped notation for the real exponential function -/
scoped notation "rexp" => Real.exp
end
end Real
namespace Complex
variable (x y : ℂ)
@[simp]
theorem exp_zero : exp 0 = 1 := by
rw [exp]
refine lim_eq_of_equiv_const fun ε ε0 => ⟨1, fun j hj => ?_⟩
convert (config := .unfoldSameFun) ε0 -- ε0 : ε > 0 but goal is _ < ε
rcases j with - | j
· exact absurd hj (not_le_of_gt zero_lt_one)
· dsimp [exp']
induction' j with j ih
· dsimp [exp']; simp [show Nat.succ 0 = 1 from rfl]
· rw [← ih (by simp [Nat.succ_le_succ])]
simp only [sum_range_succ, pow_succ]
simp
theorem exp_add : exp (x + y) = exp x * exp y := by
have hj : ∀ j : ℕ, (∑ m ∈ range j, (x + y) ^ m / m.factorial) =
∑ i ∈ range j, ∑ k ∈ range (i + 1), x ^ k / k.factorial *
(y ^ (i - k) / (i - k).factorial) := by
intro j
refine Finset.sum_congr rfl fun m _ => ?_
rw [add_pow, div_eq_mul_inv, sum_mul]
refine Finset.sum_congr rfl fun I hi => ?_
have h₁ : (m.choose I : ℂ) ≠ 0 :=
Nat.cast_ne_zero.2 (pos_iff_ne_zero.1 (Nat.choose_pos (Nat.le_of_lt_succ (mem_range.1 hi))))
have h₂ := Nat.choose_mul_factorial_mul_factorial (Nat.le_of_lt_succ <| Finset.mem_range.1 hi)
rw [← h₂, Nat.cast_mul, Nat.cast_mul, mul_inv, mul_inv]
simp only [mul_left_comm (m.choose I : ℂ), mul_assoc, mul_left_comm (m.choose I : ℂ)⁻¹,
mul_comm (m.choose I : ℂ)]
rw [inv_mul_cancel₀ h₁]
simp [div_eq_mul_inv, mul_comm, mul_assoc, mul_left_comm]
simp_rw [exp, exp', lim_mul_lim]
apply (lim_eq_lim_of_equiv _).symm
simp only [hj]
exact cauchy_product (isCauSeq_norm_exp x) (isCauSeq_exp y)
/-- the exponential function as a monoid hom from `Multiplicative ℂ` to `ℂ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℂ) ℂ :=
{ toFun := fun z => exp z.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℂ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℂ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℂ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℂ) ℂ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℂ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℂ) expMonoidHom f s
lemma exp_nsmul (x : ℂ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℂ) ℂ _ _ expMonoidHom _ _
theorem exp_nat_mul (x : ℂ) : ∀ n : ℕ, exp (n * x) = exp x ^ n
| 0 => by rw [Nat.cast_zero, zero_mul, exp_zero, pow_zero]
| Nat.succ n => by rw [pow_succ, Nat.cast_add_one, add_mul, exp_add, ← exp_nat_mul _ n, one_mul]
@[simp]
theorem exp_ne_zero : exp x ≠ 0 := fun h =>
zero_ne_one (α := ℂ) <| by rw [← exp_zero, ← add_neg_cancel x, exp_add, h]; simp
theorem exp_neg : exp (-x) = (exp x)⁻¹ := by
rw [← mul_right_inj' (exp_ne_zero x), ← exp_add]; simp [mul_inv_cancel₀ (exp_ne_zero x)]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
theorem exp_int_mul (z : ℂ) (n : ℤ) : Complex.exp (n * z) = Complex.exp z ^ n := by
cases n
· simp [exp_nat_mul]
· simp [exp_add, add_mul, pow_add, exp_neg, exp_nat_mul]
@[simp]
theorem exp_conj : exp (conj x) = conj (exp x) := by
dsimp [exp]
rw [← lim_conj]
refine congr_arg CauSeq.lim (CauSeq.ext fun _ => ?_)
dsimp [exp', Function.comp_def, cauSeqConj]
rw [map_sum (starRingEnd _)]
refine sum_congr rfl fun n _ => ?_
rw [map_div₀, map_pow, ← ofReal_natCast, conj_ofReal]
@[simp]
theorem ofReal_exp_ofReal_re (x : ℝ) : ((exp x).re : ℂ) = exp x :=
conj_eq_iff_re.1 <| by rw [← exp_conj, conj_ofReal]
@[simp, norm_cast]
theorem ofReal_exp (x : ℝ) : (Real.exp x : ℂ) = exp x :=
ofReal_exp_ofReal_re _
@[simp]
theorem exp_ofReal_im (x : ℝ) : (exp x).im = 0 := by rw [← ofReal_exp_ofReal_re, ofReal_im]
theorem exp_ofReal_re (x : ℝ) : (exp x).re = Real.exp x :=
rfl
end Complex
namespace Real
open Complex
variable (x y : ℝ)
@[simp]
theorem exp_zero : exp 0 = 1 := by simp [Real.exp]
nonrec theorem exp_add : exp (x + y) = exp x * exp y := by simp [exp_add, exp]
/-- the exponential function as a monoid hom from `Multiplicative ℝ` to `ℝ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℝ) ℝ :=
{ toFun := fun x => exp x.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℝ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℝ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℝ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℝ) ℝ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℝ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℝ) expMonoidHom f s
lemma exp_nsmul (x : ℝ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℝ) ℝ _ _ expMonoidHom _ _
nonrec theorem exp_nat_mul (x : ℝ) (n : ℕ) : exp (n * x) = exp x ^ n :=
ofReal_injective (by simp [exp_nat_mul])
@[simp]
nonrec theorem exp_ne_zero : exp x ≠ 0 := fun h =>
exp_ne_zero x <| by rw [exp, ← ofReal_inj] at h; simp_all
nonrec theorem exp_neg : exp (-x) = (exp x)⁻¹ :=
ofReal_injective <| by simp [exp_neg]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
open IsAbsoluteValue Nat
theorem sum_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) (n : ℕ) : ∑ i ∈ range n, x ^ i / i ! ≤ exp x :=
calc
∑ i ∈ range n, x ^ i / i ! ≤ lim (⟨_, isCauSeq_re (exp' x)⟩ : CauSeq ℝ abs) := by
refine le_lim (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp only [exp', const_apply, re_sum]
norm_cast
refine sum_le_sum_of_subset_of_nonneg (range_mono hj) fun _ _ _ ↦ ?_
positivity
_ = exp x := by rw [exp, Complex.exp, ← cauSeqRe, lim_re]
lemma pow_div_factorial_le_exp (hx : 0 ≤ x) (n : ℕ) : x ^ n / n ! ≤ exp x :=
calc
x ^ n / n ! ≤ ∑ k ∈ range (n + 1), x ^ k / k ! :=
single_le_sum (f := fun k ↦ x ^ k / k !) (fun k _ ↦ by positivity) (self_mem_range_succ n)
_ ≤ exp x := sum_le_exp_of_nonneg hx _
theorem quadratic_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : 1 + x + x ^ 2 / 2 ≤ exp x :=
calc
1 + x + x ^ 2 / 2 = ∑ i ∈ range 3, x ^ i / i ! := by
simp only [sum_range_succ, range_one, sum_singleton, _root_.pow_zero, factorial, cast_one,
ne_eq, one_ne_zero, not_false_eq_true, div_self, pow_one, mul_one, div_one, Nat.mul_one,
cast_succ, add_right_inj]
ring_nf
_ ≤ exp x := sum_le_exp_of_nonneg hx 3
private theorem add_one_lt_exp_of_pos {x : ℝ} (hx : 0 < x) : x + 1 < exp x :=
(by nlinarith : x + 1 < 1 + x + x ^ 2 / 2).trans_le (quadratic_le_exp_of_nonneg hx.le)
private theorem add_one_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : x + 1 ≤ exp x := by
rcases eq_or_lt_of_le hx with (rfl | h)
· simp
exact (add_one_lt_exp_of_pos h).le
theorem one_le_exp {x : ℝ} (hx : 0 ≤ x) : 1 ≤ exp x := by linarith [add_one_le_exp_of_nonneg hx]
@[bound]
theorem exp_pos (x : ℝ) : 0 < exp x :=
(le_total 0 x).elim (lt_of_lt_of_le zero_lt_one ∘ one_le_exp) fun h => by
rw [← neg_neg x, Real.exp_neg]
exact inv_pos.2 (lt_of_lt_of_le zero_lt_one (one_le_exp (neg_nonneg.2 h)))
@[bound]
lemma exp_nonneg (x : ℝ) : 0 ≤ exp x := x.exp_pos.le
@[simp]
theorem abs_exp (x : ℝ) : |exp x| = exp x :=
abs_of_pos (exp_pos _)
lemma exp_abs_le (x : ℝ) : exp |x| ≤ exp x + exp (-x) := by
cases le_total x 0 <;> simp [abs_of_nonpos, abs_of_nonneg, exp_nonneg, *]
@[mono]
theorem exp_strictMono : StrictMono exp := fun x y h => by
rw [← sub_add_cancel y x, Real.exp_add]
exact (lt_mul_iff_one_lt_left (exp_pos _)).2
(lt_of_lt_of_le (by linarith) (add_one_le_exp_of_nonneg (by linarith)))
@[gcongr]
theorem exp_lt_exp_of_lt {x y : ℝ} (h : x < y) : exp x < exp y := exp_strictMono h
@[mono]
theorem exp_monotone : Monotone exp :=
exp_strictMono.monotone
@[gcongr, bound]
theorem exp_le_exp_of_le {x y : ℝ} (h : x ≤ y) : exp x ≤ exp y := exp_monotone h
@[simp]
theorem exp_lt_exp {x y : ℝ} : exp x < exp y ↔ x < y :=
exp_strictMono.lt_iff_lt
@[simp]
theorem exp_le_exp {x y : ℝ} : exp x ≤ exp y ↔ x ≤ y :=
exp_strictMono.le_iff_le
theorem exp_injective : Function.Injective exp :=
exp_strictMono.injective
@[simp]
theorem exp_eq_exp {x y : ℝ} : exp x = exp y ↔ x = y :=
exp_injective.eq_iff
@[simp]
theorem exp_eq_one_iff : exp x = 1 ↔ x = 0 :=
exp_injective.eq_iff' exp_zero
@[simp]
theorem one_lt_exp_iff {x : ℝ} : 1 < exp x ↔ 0 < x := by rw [← exp_zero, exp_lt_exp]
@[bound] private alias ⟨_, Bound.one_lt_exp_of_pos⟩ := one_lt_exp_iff
@[simp]
theorem exp_lt_one_iff {x : ℝ} : exp x < 1 ↔ x < 0 := by rw [← exp_zero, exp_lt_exp]
@[simp]
theorem exp_le_one_iff {x : ℝ} : exp x ≤ 1 ↔ x ≤ 0 :=
exp_zero ▸ exp_le_exp
@[simp]
theorem one_le_exp_iff {x : ℝ} : 1 ≤ exp x ↔ 0 ≤ x :=
exp_zero ▸ exp_le_exp
end Real
namespace Complex
theorem sum_div_factorial_le {α : Type*} [Field α] [LinearOrder α] [IsStrictOrderedRing α]
(n j : ℕ) (hn : 0 < n) :
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) ≤ n.succ / (n.factorial * n) :=
calc
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) =
∑ m ∈ range (j - n), (1 / ((m + n).factorial : α)) := by
refine sum_nbij' (· - n) (· + n) ?_ ?_ ?_ ?_ ?_ <;>
simp +contextual [lt_tsub_iff_right, tsub_add_cancel_of_le]
_ ≤ ∑ m ∈ range (j - n), ((n.factorial : α) * (n.succ : α) ^ m)⁻¹ := by
simp_rw [one_div]
gcongr
rw [← Nat.cast_pow, ← Nat.cast_mul, Nat.cast_le, add_comm]
exact Nat.factorial_mul_pow_le_factorial
_ = (n.factorial : α)⁻¹ * ∑ m ∈ range (j - n), (n.succ : α)⁻¹ ^ m := by
simp [mul_inv, ← mul_sum, ← sum_mul, mul_comm, inv_pow]
_ = ((n.succ : α) - n.succ * (n.succ : α)⁻¹ ^ (j - n)) / (n.factorial * n) := by
have h₁ : (n.succ : α) ≠ 1 :=
@Nat.cast_one α _ ▸ mt Nat.cast_inj.1 (mt Nat.succ.inj (pos_iff_ne_zero.1 hn))
have h₂ : (n.succ : α) ≠ 0 := by positivity
have h₃ : (n.factorial * n : α) ≠ 0 := by positivity
have h₄ : (n.succ - 1 : α) = n := by simp
rw [geom_sum_inv h₁ h₂, eq_div_iff_mul_eq h₃, mul_comm _ (n.factorial * n : α),
← mul_assoc (n.factorial⁻¹ : α), ← mul_inv_rev, h₄, ← mul_assoc (n.factorial * n : α),
mul_comm (n : α) n.factorial, mul_inv_cancel₀ h₃, one_mul, mul_comm]
_ ≤ n.succ / (n.factorial * n : α) := by gcongr; apply sub_le_self; positivity
theorem exp_bound {x : ℂ} (hx : ‖x‖ ≤ 1) {n : ℕ} (hn : 0 < n) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹) := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _), exp, sub_eq_add_neg,
← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show
‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹)
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (1 / m.factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr
rw [Complex.norm_pow]
exact pow_le_one₀ (norm_nonneg _) hx
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (1 / m.factorial : ℝ) := by
simp [abs_mul, abv_pow abs, abs_div, ← mul_sum]
_ ≤ ‖x‖ ^ n * (n.succ * (n.factorial * n : ℝ)⁻¹) := by
gcongr
exact sum_div_factorial_le _ _ hn
theorem exp_bound' {x : ℂ} {n : ℕ} (hx : ‖x‖ / n.succ ≤ 1 / 2) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n / n.factorial * 2 := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _),
exp, sub_eq_add_neg, ← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n / n.factorial * 2
let k := j - n
have hj : j = n + k := (add_tsub_cancel_of_le hj).symm
rw [hj, sum_range_add_sub_sum_range]
calc
‖∑ i ∈ range k, x ^ (n + i) / ((n + i).factorial : ℂ)‖ ≤
∑ i ∈ range k, ‖x ^ (n + i) / ((n + i).factorial : ℂ)‖ :=
IsAbsoluteValue.abv_sum _ _ _
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / (n + i).factorial := by
simp [norm_natCast, Complex.norm_pow]
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / ((n.factorial : ℝ) * (n.succ : ℝ) ^ i) := ?_
_ = ∑ i ∈ range k, ‖x‖ ^ n / n.factorial * (‖x‖ ^ i / (n.succ : ℝ) ^ i) := ?_
_ ≤ ‖x‖ ^ n / ↑n.factorial * 2 := ?_
· gcongr
exact mod_cast Nat.factorial_mul_pow_le_factorial
· refine Finset.sum_congr rfl fun _ _ => ?_
simp only [pow_add, div_eq_inv_mul, mul_inv, mul_left_comm, mul_assoc]
· rw [← mul_sum]
gcongr
simp_rw [← div_pow]
rw [geom_sum_eq, div_le_iff_of_neg]
· trans (-1 : ℝ)
· linarith
· simp only [neg_le_sub_iff_le_add, div_pow, Nat.cast_succ, le_add_iff_nonneg_left]
positivity
· linarith
· linarith
theorem norm_exp_sub_one_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1‖ ≤ 2 * ‖x‖ :=
calc
‖exp x - 1‖ = ‖exp x - ∑ m ∈ range 1, x ^ m / m.factorial‖ := by simp [sum_range_succ]
_ ≤ ‖x‖ ^ 1 * ((Nat.succ 1 : ℝ) * ((Nat.factorial 1) * (1 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ = 2 * ‖x‖ := by simp [two_mul, mul_two, mul_add, mul_comm, add_mul, Nat.factorial]
theorem norm_exp_sub_one_sub_id_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1 - x‖ ≤ ‖x‖ ^ 2 :=
calc
‖exp x - 1 - x‖ = ‖exp x - ∑ m ∈ range 2, x ^ m / m.factorial‖ := by
simp [sub_eq_add_neg, sum_range_succ_comm, add_assoc, Nat.factorial]
_ ≤ ‖x‖ ^ 2 * ((Nat.succ 2 : ℝ) * (Nat.factorial 2 * (2 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ ≤ ‖x‖ ^ 2 * 1 := by gcongr; norm_num [Nat.factorial]
_ = ‖x‖ ^ 2 := by rw [mul_one]
lemma norm_exp_sub_sum_le_exp_norm_sub_sum (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖
≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
calc ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖
_ ≤ (∑ m ∈ range j, ‖x‖ ^ m / m.factorial) - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [sum_range_sub_sum_range hj, sum_range_sub_sum_range hj]
refine (IsAbsoluteValue.abv_sum norm ..).trans_eq ?_
congr with i
simp [Complex.norm_pow]
_ ≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
gcongr
exact Real.sum_le_exp_of_nonneg (norm_nonneg _) _
lemma norm_exp_le_exp_norm (x : ℂ) : ‖exp x‖ ≤ Real.exp ‖x‖ := by
convert norm_exp_sub_sum_le_exp_norm_sub_sum x 0 using 1 <;> simp
lemma norm_exp_sub_sum_le_norm_mul_exp (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ _
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (‖x‖ ^ (m - n) / (m - n).factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr with i hi
· rw [Complex.norm_pow]
· simp
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (‖x‖ ^ (m - n) / (m - n).factorial) := by
rw [← mul_sum]
_ = ‖x‖ ^ n * ∑ m ∈ range (j - n), (‖x‖ ^ m / m.factorial) := by
congr 1
refine (sum_bij (fun m hm ↦ m + n) ?_ ?_ ?_ ?_).symm
· intro a ha
simp only [mem_filter, mem_range, le_add_iff_nonneg_left, zero_le, and_true]
simp only [mem_range] at ha
rwa [← lt_tsub_iff_right]
· intro a ha b hb hab
simpa using hab
· intro b hb
simp only [mem_range, exists_prop]
simp only [mem_filter, mem_range] at hb
refine ⟨b - n, ?_, ?_⟩
· rw [tsub_lt_tsub_iff_right hb.2]
exact hb.1
· rw [tsub_add_cancel_of_le hb.2]
· simp
_ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
gcongr
refine Real.sum_le_exp_of_nonneg ?_ _
exact norm_nonneg _
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_le := norm_exp_sub_one_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_sub_id_le := norm_exp_sub_one_sub_id_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_exp_abs_sub_sum :=
norm_exp_sub_sum_le_exp_norm_sub_sum
@[deprecated (since := "2025-02-16")] alias abs_exp_le_exp_abs := norm_exp_le_exp_norm
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_abs_mul_exp :=
norm_exp_sub_sum_le_norm_mul_exp
end Complex
namespace Real
open Complex Finset
nonrec theorem exp_bound {x : ℝ} (hx : |x| ≤ 1) {n : ℕ} (hn : 0 < n) :
|exp x - ∑ m ∈ range n, x ^ m / m.factorial| ≤ |x| ^ n * (n.succ / (n.factorial * n)) := by
have hxc : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
convert exp_bound hxc hn using 2 <;>
norm_cast
theorem exp_bound' {x : ℝ} (h1 : 0 ≤ x) (h2 : x ≤ 1) {n : ℕ} (hn : 0 < n) :
Real.exp x ≤ (∑ m ∈ Finset.range n, x ^ m / m.factorial) +
x ^ n * (n + 1) / (n.factorial * n) := by
have h3 : |x| = x := by simpa
have h4 : |x| ≤ 1 := by rwa [h3]
have h' := Real.exp_bound h4 hn
rw [h3] at h'
have h'' := (abs_sub_le_iff.1 h').1
have t := sub_le_iff_le_add'.1 h''
simpa [mul_div_assoc] using t
theorem abs_exp_sub_one_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1| ≤ 2 * |x| := by
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_le (x := x) this
theorem abs_exp_sub_one_sub_id_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1 - x| ≤ x ^ 2 := by
rw [← sq_abs]
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_sub_id_le this
/-- A finite initial segment of the exponential series, followed by an arbitrary tail.
For fixed `n` this is just a linear map wrt `r`, and each map is a simple linear function
of the previous (see `expNear_succ`), with `expNear n x r ⟶ exp x` as `n ⟶ ∞`,
for any `r`. -/
noncomputable def expNear (n : ℕ) (x r : ℝ) : ℝ :=
(∑ m ∈ range n, x ^ m / m.factorial) + x ^ n / n.factorial * r
@[simp]
theorem expNear_zero (x r) : expNear 0 x r = r := by simp [expNear]
@[simp]
theorem expNear_succ (n x r) : expNear (n + 1) x r = expNear n x (1 + x / (n + 1) * r) := by
simp [expNear, range_succ, mul_add, add_left_comm, add_assoc, pow_succ, div_eq_mul_inv,
mul_inv, Nat.factorial]
ac_rfl
theorem expNear_sub (n x r₁ r₂) : expNear n x r₁ -
expNear n x r₂ = x ^ n / n.factorial * (r₁ - r₂) := by
simp [expNear, mul_sub]
theorem exp_approx_end (n m : ℕ) (x : ℝ) (e₁ : n + 1 = m) (h : |x| ≤ 1) :
|exp x - expNear m x 0| ≤ |x| ^ m / m.factorial * ((m + 1) / m) := by
simp only [expNear, mul_zero, add_zero]
convert exp_bound (n := m) h ?_ using 1
· field_simp [mul_comm]
· omega
theorem exp_approx_succ {n} {x a₁ b₁ : ℝ} (m : ℕ) (e₁ : n + 1 = m) (a₂ b₂ : ℝ)
(e : |1 + x / m * a₂ - a₁| ≤ b₁ - |x| / m * b₂)
(h : |exp x - expNear m x a₂| ≤ |x| ^ m / m.factorial * b₂) :
|exp x - expNear n x a₁| ≤ |x| ^ n / n.factorial * b₁ := by
refine (abs_sub_le _ _ _).trans ((add_le_add_right h _).trans ?_)
subst e₁; rw [expNear_succ, expNear_sub, abs_mul]
convert mul_le_mul_of_nonneg_left (a := |x| ^ n / ↑(Nat.factorial n))
(le_sub_iff_add_le'.1 e) ?_ using 1
· simp [mul_add, pow_succ', div_eq_mul_inv, abs_mul, abs_inv, ← pow_abs, mul_inv, Nat.factorial]
ac_rfl
· simp [div_nonneg, abs_nonneg]
theorem exp_approx_end' {n} {x a b : ℝ} (m : ℕ) (e₁ : n + 1 = m) (rm : ℝ) (er : ↑m = rm)
(h : |x| ≤ 1) (e : |1 - a| ≤ b - |x| / rm * ((rm + 1) / rm)) :
|exp x - expNear n x a| ≤ |x| ^ n / n.factorial * b := by
subst er
exact exp_approx_succ _ e₁ _ _ (by simpa using e) (exp_approx_end _ _ _ e₁ h)
theorem exp_1_approx_succ_eq {n} {a₁ b₁ : ℝ} {m : ℕ} (en : n + 1 = m) {rm : ℝ} (er : ↑m = rm)
(h : |exp 1 - expNear m 1 ((a₁ - 1) * rm)| ≤ |1| ^ m / m.factorial * (b₁ * rm)) :
|exp 1 - expNear n 1 a₁| ≤ |1| ^ n / n.factorial * b₁ := by
subst er
refine exp_approx_succ _ en _ _ ?_ h
field_simp [show (m : ℝ) ≠ 0 by norm_cast; omega]
theorem exp_approx_start (x a b : ℝ) (h : |exp x - expNear 0 x a| ≤ |x| ^ 0 / Nat.factorial 0 * b) :
|exp x - a| ≤ b := by simpa using h
theorem exp_bound_div_one_sub_of_interval' {x : ℝ} (h1 : 0 < x) (h2 : x < 1) :
Real.exp x < 1 / (1 - x) := by
have H : 0 < 1 - (1 + x + x ^ 2) * (1 - x) := calc
0 < x ^ 3 := by positivity
_ = 1 - (1 + x + x ^ 2) * (1 - x) := by ring
calc
exp x ≤ _ := exp_bound' h1.le h2.le zero_lt_three
_ ≤ 1 + x + x ^ 2 := by
-- Porting note: was `norm_num [Finset.sum] <;> nlinarith`
-- This proof should be restored after the norm_num plugin for big operators is ported.
-- (It may also need the positivity extensions in https://github.com/leanprover-community/mathlib4/pull/3907.)
rw [show 3 = 1 + 1 + 1 from rfl]
repeat rw [Finset.sum_range_succ]
norm_num [Nat.factorial]
nlinarith
_ < 1 / (1 - x) := by rw [lt_div_iff₀] <;> nlinarith
theorem exp_bound_div_one_sub_of_interval {x : ℝ} (h1 : 0 ≤ x) (h2 : x < 1) :
Real.exp x ≤ 1 / (1 - x) := by
rcases eq_or_lt_of_le h1 with (rfl | h1)
· simp
· exact (exp_bound_div_one_sub_of_interval' h1 h2).le
theorem add_one_lt_exp {x : ℝ} (hx : x ≠ 0) : x + 1 < Real.exp x := by
obtain hx | hx := hx.symm.lt_or_lt
· exact add_one_lt_exp_of_pos hx
obtain h' | h' := le_or_lt 1 (-x)
· linarith [x.exp_pos]
have hx' : 0 < x + 1 := by linarith
simpa [add_comm, exp_neg, inv_lt_inv₀ (exp_pos _) hx']
using exp_bound_div_one_sub_of_interval' (neg_pos.2 hx) h'
theorem add_one_le_exp (x : ℝ) : x + 1 ≤ Real.exp x := by
obtain rfl | hx := eq_or_ne x 0
· simp
· exact (add_one_lt_exp hx).le
lemma one_sub_lt_exp_neg {x : ℝ} (hx : x ≠ 0) : 1 - x < exp (-x) :=
(sub_eq_neg_add _ _).trans_lt <| add_one_lt_exp <| neg_ne_zero.2 hx
lemma one_sub_le_exp_neg (x : ℝ) : 1 - x ≤ exp (-x) :=
(sub_eq_neg_add _ _).trans_le <| add_one_le_exp _
theorem one_sub_div_pow_le_exp_neg {n : ℕ} {t : ℝ} (ht' : t ≤ n) : (1 - t / n) ^ n ≤ exp (-t) := by
rcases eq_or_ne n 0 with (rfl | hn)
· simp
rwa [Nat.cast_zero] at ht'
calc
(1 - t / n) ^ n ≤ rexp (-(t / n)) ^ n := by
gcongr
· exact sub_nonneg.2 <| div_le_one_of_le₀ ht' n.cast_nonneg
· exact one_sub_le_exp_neg _
_ = rexp (-t) := by rw [← Real.exp_nat_mul, mul_neg, mul_comm, div_mul_cancel₀]; positivity
lemma le_inv_mul_exp (x : ℝ) {c : ℝ} (hc : 0 < c) : x ≤ c⁻¹ * exp (c * x) := by
rw [le_inv_mul_iff₀ hc]
calc c * x
_ ≤ c * x + 1 := le_add_of_nonneg_right zero_le_one
_ ≤ _ := Real.add_one_le_exp (c * x)
end Real
namespace Mathlib.Meta.Positivity
open Lean.Meta Qq
/-- Extension for the `positivity` tactic: `Real.exp` is always positive. -/
@[positivity Real.exp _]
def evalExp : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q(Real.exp $a) =>
assertInstancesCommute
pure (.positive q(Real.exp_pos $a))
| _, _, _ => throwError "not Real.exp"
end Mathlib.Meta.Positivity
namespace Complex
@[simp]
theorem norm_exp_ofReal (x : ℝ) : ‖exp x‖ = Real.exp x := by
rw [← ofReal_exp]
exact Complex.norm_of_nonneg (le_of_lt (Real.exp_pos _))
@[deprecated (since := "2025-02-16")] alias abs_exp_ofReal := norm_exp_ofReal
end Complex
| Mathlib/Data/Complex/Exponential.lean | 1,075 | 1,076 | |
/-
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.Semisimple.Defs
import Mathlib.Order.BooleanGenerators
/-!
# Semisimple Lie algebras
The famous Cartan-Dynkin-Killing classification of semisimple Lie algebras renders them one of the
most important classes of Lie algebras. In this file we prove basic results
about simple and semisimple Lie algebras.
## Main declarations
* `LieAlgebra.IsSemisimple.instHasTrivialRadical`: A semisimple Lie algebra has trivial radical.
* `LieAlgebra.IsSemisimple.instBooleanAlgebra`:
The lattice of ideals in a semisimple Lie algebra is a boolean algebra.
In particular, this implies that the lattice of ideals is atomistic:
every ideal is a direct sum of atoms (simple ideals) in a unique way.
* `LieAlgebra.hasTrivialRadical_iff_no_solvable_ideals`
* `LieAlgebra.hasTrivialRadical_iff_no_abelian_ideals`
* `LieAlgebra.abelian_radical_iff_solvable_is_abelian`
## Tags
lie algebra, radical, simple, semisimple
-/
section Irreducible
variable (R L M : Type*) [CommRing R] [LieRing L] [AddCommGroup M] [Module R M] [LieRingModule L M]
lemma LieModule.nontrivial_of_isIrreducible [LieModule.IsIrreducible R L M] : Nontrivial M where
exists_pair_ne := by
have aux : (⊥ : LieSubmodule R L M) ≠ ⊤ := bot_ne_top
contrapose! aux
ext m
simpa using aux m 0
end Irreducible
namespace LieAlgebra
variable (R L : Type*) [CommRing R] [LieRing L] [LieAlgebra R L]
variable {R L} in
theorem HasTrivialRadical.eq_bot_of_isSolvable [HasTrivialRadical R L]
(I : LieIdeal R L) [hI : IsSolvable I] : I = ⊥ :=
sSup_eq_bot.mp radical_eq_bot _ hI
instance [HasTrivialRadical R L] : LieModule.IsFaithful R L L := by
rw [isFaithful_self_iff]
exact HasTrivialRadical.eq_bot_of_isSolvable _
variable {R L} in
theorem hasTrivialRadical_of_no_solvable_ideals (h : ∀ I : LieIdeal R L, IsSolvable I → I = ⊥) :
HasTrivialRadical R L :=
⟨sSup_eq_bot.mpr h⟩
theorem hasTrivialRadical_iff_no_solvable_ideals :
HasTrivialRadical R L ↔ ∀ I : LieIdeal R L, IsSolvable I → I = ⊥ :=
⟨@HasTrivialRadical.eq_bot_of_isSolvable _ _ _ _ _, hasTrivialRadical_of_no_solvable_ideals⟩
theorem hasTrivialRadical_iff_no_abelian_ideals :
HasTrivialRadical R L ↔ ∀ I : LieIdeal R L, IsLieAbelian I → I = ⊥ := by
rw [hasTrivialRadical_iff_no_solvable_ideals]
constructor <;> intro h₁ I h₂
· exact h₁ _ <| LieAlgebra.ofAbelianIsSolvable I
· rw [← abelian_of_solvable_ideal_eq_bot_iff]
exact h₁ _ <| abelian_derivedAbelianOfIdeal I
namespace IsSimple
variable [IsSimple R L]
instance : LieModule.IsIrreducible R L L := by
suffices Nontrivial (LieIdeal R L) from ⟨IsSimple.eq_bot_or_eq_top⟩
rw [LieSubmodule.nontrivial_iff, ← not_subsingleton_iff_nontrivial]
have _i : ¬ IsLieAbelian L := IsSimple.non_abelian R
contrapose! _i
infer_instance
protected lemma isAtom_top : IsAtom (⊤ : LieIdeal R L) := isAtom_top
variable {R L} in
protected lemma isAtom_iff_eq_top (I : LieIdeal R L) : IsAtom I ↔ I = ⊤ := isAtom_iff_eq_top
variable {R L} in
lemma eq_top_of_isAtom (I : LieIdeal R L) (hI : IsAtom I) : I = ⊤ := isAtom_iff_eq_top.mp hI
instance : HasTrivialRadical R L := by
rw [hasTrivialRadical_iff_no_abelian_ideals]
intro I hI
apply (IsSimple.eq_bot_or_eq_top I).resolve_right
rintro rfl
rw [lie_abelian_iff_equiv_lie_abelian LieIdeal.topEquiv] at hI
exact IsSimple.non_abelian R (L := L) hI
end IsSimple
namespace IsSemisimple
open CompleteLattice IsCompactlyGenerated
variable {R L}
variable [IsSemisimple R L]
lemma isSimple_of_isAtom (I : LieIdeal R L) (hI : IsAtom I) : IsSimple R I where
non_abelian := IsSemisimple.non_abelian_of_isAtom I hI
eq_bot_or_eq_top := by
-- Suppose that `J` is an ideal of `I`.
intro J
-- We first show that `J` is also an ideal of the ambient Lie algebra `L`.
let J' : LieIdeal R L :=
{ __ := J.toSubmodule.map I.incl.toLinearMap
lie_mem := by
rintro x _ ⟨y, hy, rfl⟩
-- We need to show that `⁅x, y⁆ ∈ J` for any `x ∈ L` and `y ∈ J`.
-- Since `L` is semisimple, `x` is contained
-- in the supremum of `I` and the atoms not equal to `I`.
have hx : x ∈ I ⊔ sSup ({I' : LieIdeal R L | IsAtom I'} \ {I}) := by
nth_rewrite 1 [← sSup_singleton (a := I)]
rw [← sSup_union, Set.union_diff_self, Set.union_eq_self_of_subset_left,
IsSemisimple.sSup_atoms_eq_top]
· apply LieSubmodule.mem_top
· simp only [Set.singleton_subset_iff, Set.mem_setOf_eq, hI]
-- Hence we can write `x` as `a + b` with `a ∈ I`
-- and `b` in the supremum of the atoms not equal to `I`.
rw [LieSubmodule.mem_sup] at hx
obtain ⟨a, ha, b, hb, rfl⟩ := hx
-- Therefore it suffices to show that `⁅a, y⁆ ∈ J` and `⁅b, y⁆ ∈ J`.
simp only [Submodule.carrier_eq_coe, add_lie, SetLike.mem_coe]
apply add_mem
-- Now `⁅a, y⁆ ∈ J` since `a ∈ I`, `y ∈ J`, and `J` is an ideal of `I`.
· simp only [Submodule.mem_map, LieSubmodule.mem_toSubmodule, Subtype.exists]
erw [Submodule.coe_subtype]
simp only [exists_and_right, exists_eq_right, ha, lie_mem_left, exists_true_left]
exact lie_mem_right R I J ⟨a, ha⟩ y hy
-- Finally `⁅b, y⁆ = 0`, by the independence of the atoms.
· suffices ⁅b, y.val⁆ = 0 by erw [this]; simp only [zero_mem]
rw [← LieSubmodule.mem_bot (R := R) (L := L),
← (IsSemisimple.sSupIndep_isAtom hI).eq_bot]
exact ⟨lie_mem_right R L I b y y.2, lie_mem_left _ _ _ _ _ hb⟩ }
-- Now that we know that `J` is an ideal of `L`,
-- we start with the proof that `I` is a simple Lie algebra.
-- Assume that `J ≠ ⊤`.
rw [or_iff_not_imp_right]
intro hJ
suffices J' = ⊥ by
rw [eq_bot_iff] at this ⊢
intro x hx
suffices x ∈ J → x = 0 from this hx
have := @this x.1
simp only [LieIdeal.incl_coe, LieIdeal.toLieSubalgebra_toSubmodule,
LieSubmodule.mem_mk_iff', Submodule.mem_map, LieSubmodule.mem_toSubmodule, Subtype.exists,
LieSubmodule.mem_bot, ZeroMemClass.coe_eq_zero, forall_exists_index, and_imp, J'] at this
exact fun _ ↦ this (↑x) x.property hx rfl
-- We need to show that `J = ⊥`.
-- Since `J` is an ideal of `L`, and `I` is an atom,
-- it suffices to show that `J < I`.
apply hI.2
rw [lt_iff_le_and_ne]
constructor
-- We know that `J ≤ I` since `J` is an ideal of `I`.
· rintro _ ⟨x, -, rfl⟩
exact x.2
-- So we need to show `J ≠ I` as ideals of `L`.
-- This follows from our assumption that `J ≠ ⊤` as ideals of `I`.
contrapose! hJ
rw [eq_top_iff]
rintro ⟨x, hx⟩ -
rw [← hJ] at hx
rcases hx with ⟨y, hy, rfl⟩
exact hy
/--
In a semisimple Lie algebra,
Lie ideals that are contained in the supremum of a finite collection of atoms
are themselves the supremum of a finite subcollection of those atoms.
By a compactness argument, this statement can be extended to arbitrary sets of atoms.
See `atomistic`.
The proof is by induction on the finite set of atoms.
-/
private
lemma finitelyAtomistic : ∀ s : Finset (LieIdeal R L), ↑s ⊆ {I : LieIdeal R L | IsAtom I} →
∀ I : LieIdeal R L, I ≤ s.sup id → ∃ t ⊆ s, I = t.sup id := by
intro s hs I hI
let S := {I : LieIdeal R L | IsAtom I}
obtain rfl | hI := hI.eq_or_lt
· exact ⟨s, Finset.Subset.rfl, rfl⟩
-- We assume that `I` is strictly smaller than the supremum of `s`.
-- Hence there must exist an atom `J` that is not contained in `I`.
obtain ⟨J, hJs, hJI⟩ : ∃ J ∈ s, ¬ J ≤ I := by
by_contra! H
exact hI.ne (le_antisymm hI.le (s.sup_le H))
classical
let s' := s.erase J
have hs' : s' ⊂ s := Finset.erase_ssubset hJs
have hs'S : ↑s' ⊆ S := Set.Subset.trans (Finset.coe_subset.mpr hs'.subset) hs
-- If we show that `I` is contained in the supremum `K` of the complement of `J` in `s`,
-- then we are done by recursion.
set K := s'.sup id
suffices I ≤ K by
obtain ⟨t, hts', htI⟩ := finitelyAtomistic s' hs'S I this
#adaptation_note /-- https://github.com/leanprover/lean4/pull/6024
we could write `hts'.trans hs'.subset` instead of
`Finset.Subset.trans hts' hs'.subset` in the next line. -/
exact ⟨t, Finset.Subset.trans hts' hs'.subset, htI⟩
-- Since `I` is contained in the supremum of `J` with the supremum of `s'`,
-- any element `x` of `I` can be written as `y + z` for some `y ∈ J` and `z ∈ K`.
intro x hx
obtain ⟨y, hy, z, hz, rfl⟩ : ∃ y ∈ id J, ∃ z ∈ K, y + z = x := by
rw [← LieSubmodule.mem_sup, ← Finset.sup_insert, Finset.insert_erase hJs]
exact hI.le hx
-- If we show that `y` is contained in the center of `J`,
-- then we find `x = z`, and hence `x` is contained in the supremum of `s'`.
-- Since `x` was arbitrary, we have shown that `I` is contained in the supremum of `s'`.
suffices ⟨y, hy⟩ ∈ LieAlgebra.center R J by
have _inst := isSimple_of_isAtom J (hs hJs)
rw [center_eq_bot R J, LieSubmodule.mem_bot] at this
apply_fun Subtype.val at this
dsimp at this
rwa [this, zero_add]
-- To show that `y` is in the center of `J`,
-- we show that any `j ∈ J` brackets to `0` with `z` and with `x = y + z`.
-- By a simple computation, that implies `⁅j, y⁆ = 0`, for all `j`, as desired.
intro j
suffices ⁅(j : L), z⁆ = 0 ∧ ⁅(j : L), y + z⁆ = 0 by
rw [lie_add, this.1, add_zero] at this
ext
exact this.2
rw [← LieSubmodule.mem_bot (R := R) (L := L), ← LieSubmodule.mem_bot (R := R) (L := L)]
constructor
-- `j` brackets to `0` with `z`, since `⁅j, z⁆` is contained in `⁅J, K⁆ ≤ J ⊓ K`,
-- and `J ⊓ K = ⊥` by the independence of the atoms.
· apply (sSupIndep_isAtom.disjoint_sSup (hs hJs) hs'S (Finset.not_mem_erase _ _)).le_bot
apply LieSubmodule.lie_le_inf
apply LieSubmodule.lie_mem_lie j.2
simpa only [K, Finset.sup_id_eq_sSup] using hz
-- By similar reasoning, `j` brackets to `0` with `x = y + z ∈ I`, if we show `J ⊓ I = ⊥`.
suffices J ⊓ I = ⊥ by
apply this.le
apply LieSubmodule.lie_le_inf
exact LieSubmodule.lie_mem_lie j.2 hx
-- Indeed `J ⊓ I = ⊥`, since `J` is an atom that is not contained in `I`.
apply ((hs hJs).le_iff.mp _).resolve_right
· contrapose! hJI
rw [← hJI]
exact inf_le_right
exact inf_le_left
termination_by s => s.card
decreasing_by exact Finset.card_lt_card hs'
variable (R L) in
lemma booleanGenerators : BooleanGenerators {I : LieIdeal R L | IsAtom I} where
isAtom _ hI := hI
finitelyAtomistic _ _ hs _ hIs := finitelyAtomistic _ hs _ hIs
instance (priority := 100) instDistribLattice : DistribLattice (LieIdeal R L) :=
(booleanGenerators R L).distribLattice_of_sSup_eq_top sSup_atoms_eq_top
noncomputable
instance (priority := 100) instBooleanAlgebra : BooleanAlgebra (LieIdeal R L) :=
(booleanGenerators R L).booleanAlgebra_of_sSup_eq_top sSup_atoms_eq_top
/-- A semisimple Lie algebra has trivial radical. -/
instance (priority := 100) instHasTrivialRadical : HasTrivialRadical R L := by
rw [hasTrivialRadical_iff_no_abelian_ideals]
intro I hI
apply (eq_bot_or_exists_atom_le I).resolve_right
rintro ⟨J, hJ, hJ'⟩
apply IsSemisimple.non_abelian_of_isAtom J hJ
constructor
intro x y
ext
simp only [LieIdeal.coe_bracket_of_module, LieSubmodule.coe_bracket, ZeroMemClass.coe_zero]
have : (⁅(⟨x, hJ' x.2⟩ : I), ⟨y, hJ' y.2⟩⁆ : I) = 0 := trivial_lie_zero _ _ _ _
apply_fun Subtype.val at this
exact this
end IsSemisimple
/-- A simple Lie algebra is semisimple. -/
instance (priority := 100) IsSimple.instIsSemisimple [IsSimple R L] :
IsSemisimple R L := by
constructor
· simp
· simpa using sSupIndep_singleton _
· intro I hI₁ hI₂
apply IsSimple.non_abelian (R := R) (L := L)
rw [IsSimple.isAtom_iff_eq_top] at hI₁
rwa [hI₁, lie_abelian_iff_equiv_lie_abelian LieIdeal.topEquiv] at hI₂
/-- An abelian Lie algebra with trivial radical is trivial. -/
theorem subsingleton_of_hasTrivialRadical_lie_abelian [HasTrivialRadical R L] [h : IsLieAbelian L] :
Subsingleton L := by
rw [isLieAbelian_iff_center_eq_top R L, center_eq_bot] at h
exact (LieSubmodule.subsingleton_iff R L L).mp (subsingleton_of_bot_eq_top h)
theorem abelian_radical_of_hasTrivialRadical [HasTrivialRadical R L] :
IsLieAbelian (radical R L) := by
rw [HasTrivialRadical.radical_eq_bot]; exact LieIdeal.isLieAbelian_of_trivial ..
theorem abelian_radical_iff_solvable_is_abelian [IsNoetherian R L] :
IsLieAbelian (radical R L) ↔ ∀ I : LieIdeal R L, IsSolvable I → IsLieAbelian I := by
constructor
· rintro h₁ I h₂
rw [LieIdeal.solvable_iff_le_radical] at h₂
exact (LieIdeal.inclusion_injective h₂).isLieAbelian h₁
· intro h; apply h; infer_instance
theorem ad_ker_eq_bot_of_hasTrivialRadical [HasTrivialRadical R L] : (ad R L).ker = ⊥ := by simp
end LieAlgebra
| Mathlib/Algebra/Lie/Semisimple/Basic.lean | 327 | 327 | |
/-
Copyright (c) 2019 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Justus Springer
-/
import Mathlib.Topology.Category.TopCat.OpenNhds
import Mathlib.Topology.Sheaves.SheafCondition.UniqueGluing
/-!
# Stalks
For a presheaf `F` on a topological space `X`, valued in some category `C`, the *stalk* of `F`
at the point `x : X` is defined as the colimit of the composition of the inclusion of categories
`(OpenNhds x)ᵒᵖ ⥤ (Opens X)ᵒᵖ` and the functor `F : (Opens X)ᵒᵖ ⥤ C`.
For an open neighborhood `U` of `x`, we define the map `F.germ x : F.obj (op U) ⟶ F.stalk x` as the
canonical morphism into this colimit.
Taking stalks is functorial: For every point `x : X` we define a functor `stalkFunctor C x`,
sending presheaves on `X` to objects of `C`. Furthermore, for a map `f : X ⟶ Y` between
topological spaces, we define `stalkPushforward` as the induced map on the stalks
`(f _* ℱ).stalk (f x) ⟶ ℱ.stalk x`.
Some lemmas about stalks and germs only hold for certain classes of concrete categories. A basic
property of forgetful functors of categories of algebraic structures (like `MonCat`,
`CommRingCat`,...) is that they preserve filtered colimits. Since stalks are filtered colimits,
this ensures that the stalks of presheaves valued in these categories behave exactly as for
`Type`-valued presheaves. For example, in `germ_exist` we prove that in such a category, every
element of the stalk is the germ of a section.
Furthermore, if we require the forgetful functor to reflect isomorphisms and preserve limits (as
is the case for most algebraic structures), we have access to the unique gluing API and can prove
further properties. Most notably, in `is_iso_iff_stalk_functor_map_iso`, we prove that in such
a category, a morphism of sheaves is an isomorphism if and only if all of its stalk maps are
isomorphisms.
See also the definition of "algebraic structures" in the stacks project:
https://stacks.math.columbia.edu/tag/007L
-/
assert_not_exists OrderedCommMonoid
noncomputable section
universe v u v' u'
open CategoryTheory
open TopCat
open CategoryTheory.Limits
open TopologicalSpace Topology
open Opposite
open scoped AlgebraicGeometry
variable {C : Type u} [Category.{v} C]
variable [HasColimits.{v} C]
variable {X Y Z : TopCat.{v}}
namespace TopCat.Presheaf
variable (C) in
/-- Stalks are functorial with respect to morphisms of presheaves over a fixed `X`. -/
def stalkFunctor (x : X) : X.Presheaf C ⥤ C :=
(whiskeringLeft _ _ C).obj (OpenNhds.inclusion x).op ⋙ colim
/-- The stalk of a presheaf `F` at a point `x` is calculated as the colimit of the functor
nbhds x ⥤ opens F.X ⥤ C
-/
def stalk (ℱ : X.Presheaf C) (x : X) : C :=
(stalkFunctor C x).obj ℱ
-- -- colimit ((open_nhds.inclusion x).op ⋙ ℱ)
@[simp]
theorem stalkFunctor_obj (ℱ : X.Presheaf C) (x : X) : (stalkFunctor C x).obj ℱ = ℱ.stalk x :=
rfl
/-- The germ of a section of a presheaf over an open at a point of that open.
-/
def germ (F : X.Presheaf C) (U : Opens X) (x : X) (hx : x ∈ U) : F.obj (op U) ⟶ stalk F x :=
colimit.ι ((OpenNhds.inclusion x).op ⋙ F) (op ⟨U, hx⟩)
/-- The germ of a global section of a presheaf at a point. -/
def Γgerm (F : X.Presheaf C) (x : X) : F.obj (op ⊤) ⟶ stalk F x :=
F.germ ⊤ x True.intro
@[reassoc]
theorem germ_res (F : X.Presheaf C) {U V : Opens X} (i : U ⟶ V) (x : X) (hx : x ∈ U) :
F.map i.op ≫ F.germ U x hx = F.germ V x (i.le hx) :=
let i' : (⟨U, hx⟩ : OpenNhds x) ⟶ ⟨V, i.le hx⟩ := i
colimit.w ((OpenNhds.inclusion x).op ⋙ F) i'.op
/-- A variant of `germ_res` with `op V ⟶ op U`
so that the LHS is more general and simp fires more easier. -/
@[reassoc (attr := simp)]
theorem germ_res' (F : X.Presheaf C) {U V : Opens X} (i : op V ⟶ op U) (x : X) (hx : x ∈ U) :
F.map i ≫ F.germ U x hx = F.germ V x (i.unop.le hx) :=
let i' : (⟨U, hx⟩ : OpenNhds x) ⟶ ⟨V, i.unop.le hx⟩ := i.unop
colimit.w ((OpenNhds.inclusion x).op ⋙ F) i'.op
@[reassoc]
lemma map_germ_eq_Γgerm (F : X.Presheaf C) {U : Opens X} {i : U ⟶ ⊤} (x : X) (hx : x ∈ U) :
F.map i.op ≫ F.germ U x hx = F.Γgerm x :=
germ_res F i x hx
variable {FC : C → C → Type*} {CC : C → Type*} [∀ X Y, FunLike (FC X Y) (CC X) (CC Y)]
theorem germ_res_apply (F : X.Presheaf C)
{U V : Opens X} (i : U ⟶ V) (x : X) (hx : x ∈ U) [ConcreteCategory C FC] (s) :
F.germ U x hx (F.map i.op s) = F.germ V x (i.le hx) s := by
rw [← ConcreteCategory.comp_apply, germ_res]
theorem germ_res_apply' (F : X.Presheaf C)
{U V : Opens X} (i : op V ⟶ op U) (x : X) (hx : x ∈ U) [ConcreteCategory C FC] (s) :
F.germ U x hx (F.map i s) = F.germ V x (i.unop.le hx) s := by
rw [← ConcreteCategory.comp_apply, germ_res']
lemma Γgerm_res_apply (F : X.Presheaf C)
{U : Opens X} {i : U ⟶ ⊤} (x : X) (hx : x ∈ U) [ConcreteCategory C FC] (s) :
F.germ U x hx (F.map i.op s) = F.Γgerm x s := F.germ_res_apply i x hx s
/-- A morphism from the stalk of `F` at `x` to some object `Y` is completely determined by its
composition with the `germ` morphisms.
-/
@[ext]
theorem stalk_hom_ext (F : X.Presheaf C) {x} {Y : C} {f₁ f₂ : F.stalk x ⟶ Y}
(ih : ∀ (U : Opens X) (hxU : x ∈ U), F.germ U x hxU ≫ f₁ = F.germ U x hxU ≫ f₂) : f₁ = f₂ :=
colimit.hom_ext fun U => by
induction U with | op U => obtain ⟨U, hxU⟩ := U; exact ih U hxU
@[reassoc (attr := simp)]
theorem stalkFunctor_map_germ {F G : X.Presheaf C} (U : Opens X) (x : X) (hx : x ∈ U) (f : F ⟶ G) :
F.germ U x hx ≫ (stalkFunctor C x).map f = f.app (op U) ≫ G.germ U x hx :=
colimit.ι_map (whiskerLeft (OpenNhds.inclusion x).op f) (op ⟨U, hx⟩)
theorem stalkFunctor_map_germ_apply [ConcreteCategory C FC]
{F G : X.Presheaf C} (U : Opens X) (x : X) (hx : x ∈ U) (f : F ⟶ G) (s) :
(stalkFunctor C x).map f (F.germ U x hx s) = G.germ U x hx (f.app (op U) s) := by
rw [← ConcreteCategory.comp_apply, ← stalkFunctor_map_germ, ConcreteCategory.comp_apply]
rfl
-- a variant of `stalkFunctor_map_germ_apply` that makes simpNF happy.
@[simp]
theorem stalkFunctor_map_germ_apply' [ConcreteCategory C FC]
{F G : X.Presheaf C} (U : Opens X) (x : X) (hx : x ∈ U) (f : F ⟶ G) (s) :
DFunLike.coe (F := ToHom (F.stalk x) (G.stalk x))
(ConcreteCategory.hom ((stalkFunctor C x).map f)) (F.germ U x hx s) =
G.germ U x hx (f.app (op U) s) :=
stalkFunctor_map_germ_apply U x hx f s
variable (C)
/-- For a presheaf `F` on a space `X`, a continuous map `f : X ⟶ Y` induces a morphisms between the
stalk of `f _ * F` at `f x` and the stalk of `F` at `x`.
-/
def stalkPushforward (f : X ⟶ Y) (F : X.Presheaf C) (x : X) : (f _* F).stalk (f x) ⟶ F.stalk x := by
-- This is a hack; Lean doesn't like to elaborate the term written directly.
refine ?_ ≫ colimit.pre _ (OpenNhds.map f x).op
exact colim.map (whiskerRight (NatTrans.op (OpenNhds.inclusionMapIso f x).inv) F)
@[reassoc (attr := simp), elementwise (attr := simp)]
theorem stalkPushforward_germ (f : X ⟶ Y) (F : X.Presheaf C) (U : Opens Y)
(x : X) (hx : f x ∈ U) :
(f _* F).germ U (f x) hx ≫ F.stalkPushforward C f x = F.germ ((Opens.map f).obj U) x hx := by
simp [germ, stalkPushforward]
-- Here are two other potential solutions, suggested by @fpvandoorn at
-- <https://github.com/leanprover-community/mathlib/pull/1018#discussion_r283978240>
-- However, I can't get the subsequent two proofs to work with either one.
-- def stalkPushforward'' (f : X ⟶ Y) (ℱ : X.Presheaf C) (x : X) :
-- (f _* ℱ).stalk (f x) ⟶ ℱ.stalk x :=
-- colim.map ((Functor.associator _ _ _).inv ≫
-- whiskerRight (NatTrans.op (OpenNhds.inclusionMapIso f x).inv) ℱ) ≫
-- colimit.pre ((OpenNhds.inclusion x).op ⋙ ℱ) (OpenNhds.map f x).op
-- def stalkPushforward''' (f : X ⟶ Y) (ℱ : X.Presheaf C) (x : X) :
-- (f _* ℱ).stalk (f x) ⟶ ℱ.stalk x :=
-- (colim.map (whiskerRight (NatTrans.op (OpenNhds.inclusionMapIso f x).inv) ℱ) :
-- colim.obj ((OpenNhds.inclusion (f x) ⋙ Opens.map f).op ⋙ ℱ) ⟶ _) ≫
-- colimit.pre ((OpenNhds.inclusion x).op ⋙ ℱ) (OpenNhds.map f x).op
namespace stalkPushforward
@[simp]
theorem id (ℱ : X.Presheaf C) (x : X) :
ℱ.stalkPushforward C (𝟙 X) x = (stalkFunctor C x).map (Pushforward.id ℱ).hom := by
ext
simp only [stalkPushforward, germ, colim_map, ι_colimMap_assoc, whiskerRight_app]
erw [CategoryTheory.Functor.map_id]
simp [stalkFunctor]
@[simp]
theorem comp (ℱ : X.Presheaf C) (f : X ⟶ Y) (g : Y ⟶ Z) (x : X) :
ℱ.stalkPushforward C (f ≫ g) x =
(f _* ℱ).stalkPushforward C g (f x) ≫ ℱ.stalkPushforward C f x := by
ext
simp [germ, stalkPushforward]
theorem stalkPushforward_iso_of_isInducing {f : X ⟶ Y} (hf : IsInducing f)
(F : X.Presheaf C) (x : X) : IsIso (F.stalkPushforward _ f x) := by
haveI := Functor.initial_of_adjunction (hf.adjunctionNhds x)
convert (Functor.Final.colimitIso (OpenNhds.map f x).op ((OpenNhds.inclusion x).op ⋙ F)).isIso_hom
refine stalk_hom_ext _ fun U hU ↦ (stalkPushforward_germ _ f F _ x hU).trans ?_
symm
exact colimit.ι_pre ((OpenNhds.inclusion x).op ⋙ F) (OpenNhds.map f x).op _
@[deprecated (since := "2024-10-27")]
alias stalkPushforward_iso_of_isOpenEmbedding := stalkPushforward_iso_of_isInducing
end stalkPushforward
section stalkPullback
/-- The morphism `ℱ_{f x} ⟶ (f⁻¹ℱ)ₓ` that factors through `(f_*f⁻¹ℱ)_{f x}`. -/
def stalkPullbackHom (f : X ⟶ Y) (F : Y.Presheaf C) (x : X) :
F.stalk (f x) ⟶ ((pullback C f).obj F).stalk x :=
(stalkFunctor _ (f x)).map ((pushforwardPullbackAdjunction C f).unit.app F) ≫
stalkPushforward _ _ _ x
@[reassoc (attr := simp)]
lemma germ_stalkPullbackHom
(f : X ⟶ Y) (F : Y.Presheaf C) (x : X) (U : Opens Y) (hU : f x ∈ U) :
F.germ U (f x) hU ≫ stalkPullbackHom C f F x =
((pushforwardPullbackAdjunction C f).unit.app F).app _ ≫
((pullback C f).obj F).germ ((Opens.map f).obj U) x hU := by
simp [stalkPullbackHom, germ, stalkFunctor, stalkPushforward]
/-- The morphism `(f⁻¹ℱ)(U) ⟶ ℱ_{f(x)}` for some `U ∋ x`. -/
def germToPullbackStalk (f : X ⟶ Y) (F : Y.Presheaf C) (U : Opens X) (x : X) (hx : x ∈ U) :
((pullback C f).obj F).obj (op U) ⟶ F.stalk (f x) :=
((Opens.map f).op.isPointwiseLeftKanExtensionLeftKanExtensionUnit F (op U)).desc
{ pt := F.stalk ((f : X → Y) (x : X))
ι :=
{ app := fun V => F.germ _ (f x) (V.hom.unop.le hx)
naturality := fun _ _ i => by simp } }
variable {C} in
@[ext]
lemma pullback_obj_obj_ext {Z : C} {f : X ⟶ Y} {F : Y.Presheaf C} (U : (Opens X)ᵒᵖ)
{φ ψ : ((pullback C f).obj F).obj U ⟶ Z}
(h : ∀ (V : Opens Y) (hV : U.unop ≤ (Opens.map f).obj V),
((pushforwardPullbackAdjunction C f).unit.app F).app (op V) ≫
((pullback C f).obj F).map (homOfLE hV).op ≫ φ =
((pushforwardPullbackAdjunction C f).unit.app F).app (op V) ≫
((pullback C f).obj F).map (homOfLE hV).op ≫ ψ) : φ = ψ := by
obtain ⟨U⟩ := U
apply ((Opens.map f).op.isPointwiseLeftKanExtensionLeftKanExtensionUnit F _).hom_ext
rintro ⟨⟨V⟩, ⟨⟩, ⟨b⟩⟩
simpa [pushforwardPullbackAdjunction, Functor.lanAdjunction_unit]
using h V (leOfHom b)
@[reassoc (attr := simp)]
lemma pushforwardPullbackAdjunction_unit_pullback_map_germToPullbackStalk
(f : X ⟶ Y) (F : Y.Presheaf C) (U : Opens X) (x : X) (hx : x ∈ U) (V : Opens Y)
(hV : U ≤ (Opens.map f).obj V) :
((pushforwardPullbackAdjunction C f).unit.app F).app (op V) ≫
((pullback C f).obj F).map (homOfLE hV).op ≫ germToPullbackStalk C f F U x hx =
F.germ _ (f x) (hV hx) := by
simpa [pushforwardPullbackAdjunction] using
((Opens.map f).op.isPointwiseLeftKanExtensionLeftKanExtensionUnit F (op U)).fac _
(CostructuredArrow.mk (homOfLE hV).op)
@[reassoc (attr := simp)]
lemma germToPullbackStalk_stalkPullbackHom
(f : X ⟶ Y) (F : Y.Presheaf C) (U : Opens X) (x : X) (hx : x ∈ U) :
germToPullbackStalk C f F U x hx ≫ stalkPullbackHom C f F x =
((pullback C f).obj F).germ _ x hx := by
ext V hV
dsimp
simp only [pushforwardPullbackAdjunction_unit_pullback_map_germToPullbackStalk_assoc,
germ_stalkPullbackHom, germ_res]
@[reassoc (attr := simp)]
lemma pushforwardPullbackAdjunction_unit_app_app_germToPullbackStalk
(f : X ⟶ Y) (F : Y.Presheaf C) (V : (Opens Y)ᵒᵖ) (x : X) (hx : f x ∈ V.unop) :
((pushforwardPullbackAdjunction C f).unit.app F).app V ≫ germToPullbackStalk C f F _ x hx =
F.germ _ (f x) hx := by
simpa using pushforwardPullbackAdjunction_unit_pullback_map_germToPullbackStalk
C f F ((Opens.map f).obj V.unop) x hx V.unop (by rfl)
/-- The morphism `(f⁻¹ℱ)ₓ ⟶ ℱ_{f(x)}`. -/
def stalkPullbackInv (f : X ⟶ Y) (F : Y.Presheaf C) (x : X) :
((pullback C f).obj F).stalk x ⟶ F.stalk (f x) :=
colimit.desc ((OpenNhds.inclusion x).op ⋙ (Presheaf.pullback C f).obj F)
{ pt := F.stalk (f x)
ι :=
{ app := fun U => F.germToPullbackStalk _ f (unop U).1 x (unop U).2
naturality := fun U V i => by
dsimp
ext W hW
dsimp [OpenNhds.inclusion]
rw [Category.comp_id, ← Functor.map_comp_assoc,
pushforwardPullbackAdjunction_unit_pullback_map_germToPullbackStalk]
erw [pushforwardPullbackAdjunction_unit_pullback_map_germToPullbackStalk] } }
@[reassoc (attr := simp)]
lemma germ_stalkPullbackInv (f : X ⟶ Y) (F : Y.Presheaf C) (x : X) (V : Opens X) (hV : x ∈ V) :
((pullback C f).obj F).germ _ x hV ≫ stalkPullbackInv C f F x =
F.germToPullbackStalk _ f V x hV := by
apply colimit.ι_desc
/-- The isomorphism `ℱ_{f(x)} ≅ (f⁻¹ℱ)ₓ`. -/
def stalkPullbackIso (f : X ⟶ Y) (F : Y.Presheaf C) (x : X) :
F.stalk (f x) ≅ ((pullback C f).obj F).stalk x where
hom := stalkPullbackHom _ _ _ _
inv := stalkPullbackInv _ _ _ _
hom_inv_id := by
ext U hU
dsimp
rw [germ_stalkPullbackHom_assoc, germ_stalkPullbackInv, Category.comp_id,
pushforwardPullbackAdjunction_unit_app_app_germToPullbackStalk]
inv_hom_id := by
ext V hV
dsimp
rw [germ_stalkPullbackInv_assoc, Category.comp_id, germToPullbackStalk_stalkPullbackHom]
end stalkPullback
section stalkSpecializes
variable {C}
/-- If `x` specializes to `y`, then there is a natural map `F.stalk y ⟶ F.stalk x`. -/
noncomputable def stalkSpecializes (F : X.Presheaf C) {x y : X} (h : x ⤳ y) :
F.stalk y ⟶ F.stalk x := by
refine colimit.desc _ ⟨_, fun U => ?_, ?_⟩
· exact
colimit.ι ((OpenNhds.inclusion x).op ⋙ F)
(op ⟨(unop U).1, (specializes_iff_forall_open.mp h _ (unop U).1.2 (unop U).2 :)⟩)
· intro U V i
dsimp
rw [Category.comp_id]
let U' : OpenNhds x := ⟨_, (specializes_iff_forall_open.mp h _ (unop U).1.2 (unop U).2 :)⟩
let V' : OpenNhds x := ⟨_, (specializes_iff_forall_open.mp h _ (unop V).1.2 (unop V).2 :)⟩
exact colimit.w ((OpenNhds.inclusion x).op ⋙ F) (show V' ⟶ U' from i.unop).op
@[reassoc (attr := simp), elementwise nosimp]
theorem germ_stalkSpecializes (F : X.Presheaf C)
{U : Opens X} {y : X} (hy : y ∈ U) {x : X} (h : x ⤳ y) :
F.germ U y hy ≫ F.stalkSpecializes h = F.germ U x (h.mem_open U.isOpen hy) :=
colimit.ι_desc _ _
@[simp]
theorem stalkSpecializes_refl {C : Type*} [Category C] [Limits.HasColimits C] {X : TopCat}
(F : X.Presheaf C) (x : X) : F.stalkSpecializes (specializes_refl x) = 𝟙 _ := by
ext
simp
@[reassoc (attr := simp), elementwise (attr := simp)]
theorem stalkSpecializes_comp {C : Type*} [Category C] [Limits.HasColimits C] {X : TopCat}
(F : X.Presheaf C) {x y z : X} (h : x ⤳ y) (h' : y ⤳ z) :
F.stalkSpecializes h' ≫ F.stalkSpecializes h = F.stalkSpecializes (h.trans h') := by
ext
simp
@[reassoc (attr := simp), elementwise (attr := simp)]
theorem stalkSpecializes_stalkFunctor_map {F G : X.Presheaf C} (f : F ⟶ G) {x y : X} (h : x ⤳ y) :
F.stalkSpecializes h ≫ (stalkFunctor C x).map f =
(stalkFunctor C y).map f ≫ G.stalkSpecializes h := by
change (_ : colimit _ ⟶ _) = (_ : colimit _ ⟶ _)
ext; delta stalkFunctor; simpa [stalkSpecializes] using by rfl
-- See https://github.com/leanprover-community/batteries/issues/365 for the simpNF issue.
-- It seems the side condition `h` is not applied by `simpNF`.
@[reassoc, elementwise, simp, nolint simpNF]
theorem stalkSpecializes_stalkPushforward (f : X ⟶ Y) (F : X.Presheaf C) {x y : X} (h : x ⤳ y) :
(f _* F).stalkSpecializes (f.hom.map_specializes h) ≫ F.stalkPushforward _ f x =
F.stalkPushforward _ f y ≫ F.stalkSpecializes h := by
change (_ : colimit _ ⟶ _) = (_ : colimit _ ⟶ _)
ext; delta stalkPushforward
simp only [stalkSpecializes, colimit.ι_desc_assoc, colimit.ι_map_assoc, colimit.ι_pre,
Category.assoc, colimit.pre_desc, colimit.ι_desc]
rfl
/-- The stalks are isomorphic on inseparable points -/
@[simps]
def stalkCongr {X : TopCat} {C : Type*} [Category C] [HasColimits C] (F : X.Presheaf C) {x y : X}
(e : Inseparable x y) : F.stalk x ≅ F.stalk y :=
⟨F.stalkSpecializes e.ge, F.stalkSpecializes e.le, by simp, by simp⟩
end stalkSpecializes
section Concrete
variable {C} {CC : C → Type v} [∀ X Y, FunLike (FC X Y) (CC X) (CC Y)]
variable [instCC : ConcreteCategory.{v} C FC]
-- Porting note (https://github.com/leanprover-community/mathlib4/issues/11215): TODO: @[ext] attribute only applies to structures or lemmas proving x = y
-- @[ext]
theorem germ_ext (F : X.Presheaf C) {U V : Opens X} {x : X} {hxU : x ∈ U} {hxV : x ∈ V}
(W : Opens X) (hxW : x ∈ W) (iWU : W ⟶ U) (iWV : W ⟶ V)
{sU : ToType (F.obj (op U))} {sV : ToType (F.obj (op V))}
(ih : F.map iWU.op sU = F.map iWV.op sV) :
F.germ _ x hxU sU = F.germ _ x hxV sV := by
rw [← F.germ_res iWU x hxW, ← F.germ_res iWV x hxW, ConcreteCategory.comp_apply,
ConcreteCategory.comp_apply, ih]
variable [PreservesFilteredColimits (forget C)]
/--
For presheaves valued in a concrete category whose forgetful functor preserves filtered colimits,
every element of the stalk is the germ of a section.
-/
theorem germ_exist (F : X.Presheaf C) (x : X) (t : ToType (stalk.{v, u} F x)) :
∃ (U : Opens X) (m : x ∈ U) (s : ToType (F.obj (op U))), F.germ _ x m s = t := by
obtain ⟨U, s, e⟩ :=
Types.jointly_surjective.{v, v} _ (isColimitOfPreserves (forget C) (colimit.isColimit _)) t
revert s e
induction U with | op U => ?_
obtain ⟨V, m⟩ := U
intro s e
exact ⟨V, m, s, e⟩
theorem germ_eq (F : X.Presheaf C) {U V : Opens X} (x : X) (mU : x ∈ U) (mV : x ∈ V)
(s : ToType (F.obj (op U))) (t : ToType (F.obj (op V)))
(h : F.germ U x mU s = F.germ V x mV t) :
∃ (W : Opens X) (_m : x ∈ W) (iU : W ⟶ U) (iV : W ⟶ V), F.map iU.op s = F.map iV.op t := by
obtain ⟨W, iU, iV, e⟩ :=
(Types.FilteredColimit.isColimit_eq_iff.{v, v} _
(isColimitOfPreserves (forget C) (colimit.isColimit ((OpenNhds.inclusion x).op ⋙ F)))).mp
h
exact ⟨(unop W).1, (unop W).2, iU.unop, iV.unop, e⟩
theorem stalkFunctor_map_injective_of_app_injective {F G : Presheaf C X} (f : F ⟶ G)
(h : ∀ U : Opens X, Function.Injective (f.app (op U))) (x : X) :
Function.Injective ((stalkFunctor C x).map f) := fun s t hst => by
rcases germ_exist F x s with ⟨U₁, hxU₁, s, rfl⟩
rcases germ_exist F x t with ⟨U₂, hxU₂, t, rfl⟩
rw [stalkFunctor_map_germ_apply, stalkFunctor_map_germ_apply] at hst
obtain ⟨W, hxW, iWU₁, iWU₂, heq⟩ := G.germ_eq x hxU₁ hxU₂ _ _ hst
rw [← ConcreteCategory.comp_apply, ← ConcreteCategory.comp_apply, ← f.naturality, ← f.naturality,
ConcreteCategory.comp_apply, ConcreteCategory.comp_apply] at heq
replace heq := h W heq
convert congr_arg (F.germ _ x hxW) heq using 1
exacts [(F.germ_res_apply iWU₁ x hxW s).symm, (F.germ_res_apply iWU₂ x hxW t).symm]
variable [HasLimits C] [PreservesLimits (forget C)] [(forget C).ReflectsIsomorphisms]
/-- Let `F` be a sheaf valued in a concrete category, whose forgetful functor reflects isomorphisms,
preserves limits and filtered colimits. Then two sections who agree on every stalk must be equal.
-/
theorem section_ext (F : Sheaf C X) (U : Opens X) (s t : ToType (F.1.obj (op U)))
(h : ∀ (x : X) (hx : x ∈ U), F.presheaf.germ U x hx s = F.presheaf.germ U x hx t) : s = t := by
-- We use `germ_eq` and the axiom of choice, to pick for every point `x` a neighbourhood
-- `V x`, such that the restrictions of `s` and `t` to `V x` coincide.
choose V m i₁ i₂ heq using fun x : U => F.presheaf.germ_eq x.1 x.2 x.2 s t (h x.1 x.2)
-- Since `F` is a sheaf, we can prove the equality locally, if we can show that these
-- neighborhoods form a cover of `U`.
apply F.eq_of_locally_eq' V U i₁
· intro x hxU
simp only [Opens.coe_iSup, Set.mem_iUnion, SetLike.mem_coe]
exact ⟨⟨x, hxU⟩, m ⟨x, hxU⟩⟩
· intro x
rw [heq, Subsingleton.elim (i₁ x) (i₂ x)]
/-
Note that the analogous statement for surjectivity is false: Surjectivity on stalks does not
imply surjectivity of the components of a sheaf morphism. However it does imply that the morphism
is an epi, but this fact is not yet formalized.
-/
theorem app_injective_of_stalkFunctor_map_injective {F : Sheaf C X} {G : Presheaf C X} (f : F.1 ⟶ G)
(U : Opens X) (h : ∀ x ∈ U, Function.Injective ((stalkFunctor C x).map f)) :
Function.Injective (f.app (op U)) := fun s t hst =>
section_ext F _ _ _ fun x hx =>
h x hx <| by rw [stalkFunctor_map_germ_apply, stalkFunctor_map_germ_apply, hst]
theorem app_injective_iff_stalkFunctor_map_injective {F : Sheaf C X} {G : Presheaf C X}
(f : F.1 ⟶ G) :
(∀ x : X, Function.Injective ((stalkFunctor C x).map f)) ↔
∀ U : Opens X, Function.Injective (f.app (op U)) :=
⟨fun h U => app_injective_of_stalkFunctor_map_injective f U fun x _ => h x,
stalkFunctor_map_injective_of_app_injective f⟩
instance stalkFunctor_preserves_mono (x : X) :
Functor.PreservesMonomorphisms (Sheaf.forget.{v} C X ⋙ stalkFunctor C x) :=
⟨@fun _𝓐 _𝓑 f _ =>
ConcreteCategory.mono_of_injective _ <|
(app_injective_iff_stalkFunctor_map_injective f.1).mpr
(fun c =>
(ConcreteCategory.mono_iff_injective_of_preservesPullback (f.1.app (op c))).mp
((NatTrans.mono_iff_mono_app f.1).mp
(CategoryTheory.presheaf_mono_of_mono ..) <|
op c))
x⟩
include instCC in
theorem stalk_mono_of_mono {F G : Sheaf C X} (f : F ⟶ G) [Mono f] :
∀ x, Mono <| (stalkFunctor C x).map f.1 :=
fun x => Functor.map_mono (Sheaf.forget.{v} C X ⋙ stalkFunctor C x) f
include instCC in
theorem mono_of_stalk_mono {F G : Sheaf C X} (f : F ⟶ G) [∀ x, Mono <| (stalkFunctor C x).map f.1] :
Mono f :=
(Sheaf.Hom.mono_iff_presheaf_mono _ _ _).mpr <|
(NatTrans.mono_iff_mono_app _).mpr fun U =>
(ConcreteCategory.mono_iff_injective_of_preservesPullback _).mpr <|
app_injective_of_stalkFunctor_map_injective f.1 U.unop fun _x _hx =>
(ConcreteCategory.mono_iff_injective_of_preservesPullback
((stalkFunctor C _).map f.val)).mp <| inferInstance
include instCC in
theorem mono_iff_stalk_mono {F G : Sheaf C X} (f : F ⟶ G) :
Mono f ↔ ∀ x, Mono ((stalkFunctor C x).map f.1) :=
⟨fun _ => stalk_mono_of_mono _, fun _ => mono_of_stalk_mono _⟩
/-- For surjectivity, we are given an arbitrary section `t` and need to find a preimage for it.
We claim that it suffices to find preimages *locally*. That is, for each `x : U` we construct
a neighborhood `V ≤ U` and a section `s : F.obj (op V))` such that `f.app (op V) s` and `t`
agree on `V`. -/
theorem app_surjective_of_injective_of_locally_surjective {F G : Sheaf C X} (f : F ⟶ G)
(U : Opens X) (hinj : ∀ x ∈ U, Function.Injective ((stalkFunctor C x).map f.1))
(hsurj : ∀ (t x) (_ : x ∈ U), ∃ (V : Opens X) (_ : x ∈ V) (iVU : V ⟶ U)
(s : ToType (F.1.obj (op V))), f.1.app (op V) s = G.1.map iVU.op t) :
Function.Surjective (f.1.app (op U)) := by
conv at hsurj =>
enter [t]
rw [Subtype.forall' (p := (· ∈ U))]
intro t
-- We use the axiom of choice to pick around each point `x` an open neighborhood `V` and a
-- preimage under `f` on `V`.
choose V mV iVU sf heq using hsurj t
-- These neighborhoods clearly cover all of `U`.
have V_cover : U ≤ iSup V := by
intro x hxU
simp only [Opens.coe_iSup, Set.mem_iUnion, SetLike.mem_coe]
exact ⟨⟨x, hxU⟩, mV ⟨x, hxU⟩⟩
suffices IsCompatible F.val V sf by
-- Since `F` is a sheaf, we can glue all the local preimages together to get a global preimage.
obtain ⟨s, s_spec, -⟩ := F.existsUnique_gluing' V U iVU V_cover sf this
· use s
apply G.eq_of_locally_eq' V U iVU V_cover
intro x
rw [← ConcreteCategory.comp_apply, ← f.1.naturality, ConcreteCategory.comp_apply, s_spec, heq]
intro x y
-- What's left to show here is that the sections `sf` are compatible, i.e. they agree on
-- the intersections `V x ⊓ V y`. We prove this by showing that all germs are equal.
apply section_ext
intro z hz
-- Here, we need to use injectivity of the stalk maps.
apply hinj z ((iVU x).le ((inf_le_left : V x ⊓ V y ≤ V x) hz))
dsimp only
rw [stalkFunctor_map_germ_apply, stalkFunctor_map_germ_apply]
simp_rw [← ConcreteCategory.comp_apply, f.1.naturality, ConcreteCategory.comp_apply, heq,
← ConcreteCategory.comp_apply, ← G.1.map_comp]
rfl
theorem app_surjective_of_stalkFunctor_map_bijective {F G : Sheaf C X} (f : F ⟶ G) (U : Opens X)
(h : ∀ x ∈ U, Function.Bijective ((stalkFunctor C x).map f.1)) :
Function.Surjective (f.1.app (op U)) := by
refine app_surjective_of_injective_of_locally_surjective f U (And.left <| h · ·) fun t x hx => ?_
-- Now we need to prove our initial claim: That we can find preimages of `t` locally.
-- Since `f` is surjective on stalks, we can find a preimage `s₀` of the germ of `t` at `x`
obtain ⟨s₀, hs₀⟩ := (h x hx).2 (G.presheaf.germ U x hx t)
-- ... and this preimage must come from some section `s₁` defined on some open neighborhood `V₁`
obtain ⟨V₁, hxV₁, s₁, hs₁⟩ := F.presheaf.germ_exist x s₀
subst hs₁; rename' hs₀ => hs₁
rw [stalkFunctor_map_germ_apply V₁ x hxV₁ f.1 s₁] at hs₁
-- Now, the germ of `f.app (op V₁) s₁` equals the germ of `t`, hence they must coincide on
-- some open neighborhood `V₂`.
obtain ⟨V₂, hxV₂, iV₂V₁, iV₂U, heq⟩ := G.presheaf.germ_eq x hxV₁ hx _ _ hs₁
-- The restriction of `s₁` to that neighborhood is our desired local preimage.
use V₂, hxV₂, iV₂U, F.1.map iV₂V₁.op s₁
rw [← ConcreteCategory.comp_apply, f.1.naturality, ConcreteCategory.comp_apply, heq]
theorem app_bijective_of_stalkFunctor_map_bijective {F G : Sheaf C X} (f : F ⟶ G) (U : Opens X)
(h : ∀ x ∈ U, Function.Bijective ((stalkFunctor C x).map f.1)) :
Function.Bijective (f.1.app (op U)) :=
⟨app_injective_of_stalkFunctor_map_injective f.1 U fun x hx => (h x hx).1,
app_surjective_of_stalkFunctor_map_bijective f U h⟩
include instCC in
theorem app_isIso_of_stalkFunctor_map_iso {F G : Sheaf C X} (f : F ⟶ G) (U : Opens X)
[∀ x : U, IsIso ((stalkFunctor C x.val).map f.1)] : IsIso (f.1.app (op U)) := by
-- Since the forgetful functor of `C` reflects isomorphisms, it suffices to see that the
-- underlying map between types is an isomorphism, i.e. bijective.
suffices IsIso ((forget C).map (f.1.app (op U))) by
exact isIso_of_reflects_iso (f.1.app (op U)) (forget C)
rw [isIso_iff_bijective]
apply app_bijective_of_stalkFunctor_map_bijective
intro x hx
apply (isIso_iff_bijective _).mp
exact Functor.map_isIso (forget C) ((stalkFunctor C (⟨x, hx⟩ : U).1).map f.1)
include instCC in
-- Making this an instance would cause a loop in typeclass resolution with `Functor.map_isIso`
/-- Let `F` and `G` be sheaves valued in a concrete category, whose forgetful functor reflects
isomorphisms, preserves limits and filtered colimits. Then if the stalk maps of a morphism
| `f : F ⟶ G` are all isomorphisms, `f` must be an isomorphism.
-/
theorem isIso_of_stalkFunctor_map_iso {F G : Sheaf C X} (f : F ⟶ G)
[∀ x : X, IsIso ((stalkFunctor C x).map f.1)] : IsIso f := by
-- Since the inclusion functor from sheaves to presheaves is fully faithful, it suffices to
-- show that `f`, as a morphism between _presheaves_, is an isomorphism.
suffices IsIso ((Sheaf.forget C X).map f) by exact isIso_of_fully_faithful (Sheaf.forget C X) f
-- We show that all components of `f` are isomorphisms.
suffices ∀ U : (Opens X)ᵒᵖ, IsIso (f.1.app U) by
exact @NatIso.isIso_of_isIso_app _ _ _ _ F.1 G.1 f.1 this
intro U; induction U
| Mathlib/Topology/Sheaves/Stalks.lean | 590 | 600 |
/-
Copyright (c) 2022 Jujian Zhang. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jujian Zhang
-/
import Mathlib.LinearAlgebra.LinearPMap
import Mathlib.Algebra.Equiv.TransferInstance
import Mathlib.Logic.Small.Basic
import Mathlib.RingTheory.Ideal.Defs
/-!
# Injective modules
## Main definitions
* `Module.Injective`: an `R`-module `Q` is injective if and only if every injective `R`-linear
map descends to a linear map to `Q`, i.e. in the following diagram, if `f` is injective then there
is an `R`-linear map `h : Y ⟶ Q` such that `g = h ∘ f`
```
X --- f ---> Y
|
| g
v
Q
```
* `Module.Baer`: an `R`-module `Q` satisfies Baer's criterion if any `R`-linear map from an
`Ideal R` extends to an `R`-linear map `R ⟶ Q`
## Main statements
* `Module.Baer.injective`: an `R`-module is injective if it is Baer.
-/
assert_not_exists ModuleCat
noncomputable section
universe u v v'
variable (R : Type u) [Ring R] (Q : Type v) [AddCommGroup Q] [Module R Q]
/--
An `R`-module `Q` is injective if and only if every injective `R`-linear map descends to a linear
map to `Q`, i.e. in the following diagram, if `f` is injective then there is an `R`-linear map
`h : Y ⟶ Q` such that `g = h ∘ f`
```
X --- f ---> Y
|
| g
v
Q
```
-/
@[mk_iff] class Module.Injective : Prop where
out : ∀ ⦃X Y : Type v⦄ [AddCommGroup X] [AddCommGroup Y] [Module R X] [Module R Y]
(f : X →ₗ[R] Y) (_ : Function.Injective f) (g : X →ₗ[R] Q),
∃ h : Y →ₗ[R] Q, ∀ x, h (f x) = g x
/-- An `R`-module `Q` satisfies Baer's criterion if any `R`-linear map from an `Ideal R` extends to
an `R`-linear map `R ⟶ Q` -/
def Module.Baer : Prop :=
∀ (I : Ideal R) (g : I →ₗ[R] Q), ∃ g' : R →ₗ[R] Q, ∀ (x : R) (mem : x ∈ I), g' x = g ⟨x, mem⟩
namespace Module.Baer
variable {R Q} {M N : Type*} [AddCommGroup M] [AddCommGroup N]
variable [Module R M] [Module R N] (i : M →ₗ[R] N) (f : M →ₗ[R] Q)
lemma of_equiv (e : Q ≃ₗ[R] M) (h : Module.Baer R Q) : Module.Baer R M := fun I g ↦
have ⟨g', h'⟩ := h I (e.symm ∘ₗ g)
⟨e ∘ₗ g', by simpa [LinearEquiv.eq_symm_apply] using h'⟩
lemma congr (e : Q ≃ₗ[R] M) : Module.Baer R Q ↔ Module.Baer R M := ⟨of_equiv e, of_equiv e.symm⟩
/-- If we view `M` as a submodule of `N` via the injective linear map `i : M ↪ N`, then a submodule
between `M` and `N` is a submodule `N'` of `N`. To prove Baer's criterion, we need to consider
pairs of `(N', f')` such that `M ≤ N' ≤ N` and `f'` extends `f`. -/
structure ExtensionOf extends LinearPMap R N Q where
le : LinearMap.range i ≤ domain
is_extension : ∀ m : M, f m = toLinearPMap ⟨i m, le ⟨m, rfl⟩⟩
section Ext
variable {i f}
@[ext (iff := false)]
theorem ExtensionOf.ext {a b : ExtensionOf i f} (domain_eq : a.domain = b.domain)
(to_fun_eq : ∀ ⦃x : N⦄ ⦃ha : x ∈ a.domain⦄ ⦃hb : x ∈ b.domain⦄,
a.toLinearPMap ⟨x, ha⟩ = b.toLinearPMap ⟨x, hb⟩) :
a = b := by
rcases a with ⟨a, a_le, e1⟩
rcases b with ⟨b, b_le, e2⟩
congr
exact LinearPMap.ext domain_eq to_fun_eq
/-- A dependent version of `ExtensionOf.ext` -/
theorem ExtensionOf.dExt {a b : ExtensionOf i f} (domain_eq : a.domain = b.domain)
(to_fun_eq :
∀ ⦃x : a.domain⦄ ⦃y : b.domain⦄, (x : N) = y → a.toLinearPMap x = b.toLinearPMap y) :
a = b :=
ext domain_eq fun _ _ _ ↦ to_fun_eq rfl
theorem ExtensionOf.dExt_iff {a b : ExtensionOf i f} :
a = b ↔ ∃ _ : a.domain = b.domain, ∀ ⦃x : a.domain⦄ ⦃y : b.domain⦄,
(x : N) = y → a.toLinearPMap x = b.toLinearPMap y :=
⟨fun r => r ▸ ⟨rfl, fun _ _ h => congr_arg a.toFun <| mod_cast h⟩, fun ⟨h1, h2⟩ =>
ExtensionOf.dExt h1 h2⟩
end Ext
instance : Min (ExtensionOf i f) where
min X1 X2 :=
{ X1.toLinearPMap ⊓ X2.toLinearPMap with
le := fun x hx =>
(by
rcases hx with ⟨x, rfl⟩
refine ⟨X1.le (Set.mem_range_self _), X2.le (Set.mem_range_self _), ?_⟩
rw [← X1.is_extension x, ← X2.is_extension x] :
x ∈ X1.toLinearPMap.eqLocus X2.toLinearPMap)
is_extension := fun _ => X1.is_extension _ }
instance : SemilatticeInf (ExtensionOf i f) :=
Function.Injective.semilatticeInf ExtensionOf.toLinearPMap
(fun X Y h ↦
ExtensionOf.ext (by rw [h]) <| by
rw [h]
intros
rfl)
fun X Y ↦ LinearPMap.ext rfl fun x y h => by congr
variable {i f}
theorem chain_linearPMap_of_chain_extensionOf {c : Set (ExtensionOf i f)}
(hchain : IsChain (· ≤ ·) c) :
IsChain (· ≤ ·) <| (fun x : ExtensionOf i f => x.toLinearPMap) '' c := by
rintro _ ⟨a, a_mem, rfl⟩ _ ⟨b, b_mem, rfl⟩ neq
exact hchain a_mem b_mem (ne_of_apply_ne _ neq)
/-- The maximal element of every nonempty chain of `extension_of i f`. -/
def ExtensionOf.max {c : Set (ExtensionOf i f)} (hchain : IsChain (· ≤ ·) c)
(hnonempty : c.Nonempty) : ExtensionOf i f :=
{ LinearPMap.sSup _
(IsChain.directedOn <| chain_linearPMap_of_chain_extensionOf hchain) with
le := by
refine le_trans hnonempty.some.le <|
(LinearPMap.le_sSup _ <|
(Set.mem_image _ _ _).mpr ⟨hnonempty.some, hnonempty.choose_spec, rfl⟩).1
is_extension := fun m => by
refine Eq.trans (hnonempty.some.is_extension m) ?_
symm
generalize_proofs _ _ h1
exact
LinearPMap.sSup_apply (IsChain.directedOn <| chain_linearPMap_of_chain_extensionOf hchain)
((Set.mem_image _ _ _).mpr ⟨hnonempty.some, hnonempty.choose_spec, rfl⟩) ⟨i m, h1⟩ }
theorem ExtensionOf.le_max {c : Set (ExtensionOf i f)} (hchain : IsChain (· ≤ ·) c)
(hnonempty : c.Nonempty) (a : ExtensionOf i f) (ha : a ∈ c) :
a ≤ ExtensionOf.max hchain hnonempty :=
LinearPMap.le_sSup (IsChain.directedOn <| chain_linearPMap_of_chain_extensionOf hchain) <|
(Set.mem_image _ _ _).mpr ⟨a, ha, rfl⟩
variable (i f) [Fact <| Function.Injective i]
instance ExtensionOf.inhabited : Inhabited (ExtensionOf i f) where
default :=
{ domain := LinearMap.range i
toFun :=
{ toFun := fun x => f x.2.choose
map_add' := fun x y => by
have eq1 : _ + _ = (x + y).1 := congr_arg₂ (· + ·) x.2.choose_spec y.2.choose_spec
rw [← map_add, ← (x + y).2.choose_spec] at eq1
dsimp
rw [← Fact.out (p := Function.Injective i) eq1, map_add]
map_smul' := fun r x => by
have eq1 : r • _ = (r • x).1 := congr_arg (r • ·) x.2.choose_spec
rw [← LinearMap.map_smul, ← (r • x).2.choose_spec] at eq1
dsimp
rw [← Fact.out (p := Function.Injective i) eq1, LinearMap.map_smul] }
le := le_refl _
is_extension := fun m => by
simp only [LinearPMap.mk_apply, LinearMap.coe_mk]
dsimp
apply congrArg
exact Fact.out (p := Function.Injective i)
(⟨i m, ⟨_, rfl⟩⟩ : LinearMap.range i).2.choose_spec.symm }
/-- Since every nonempty chain has a maximal element, by Zorn's lemma, there is a maximal
`extension_of i f`. -/
def extensionOfMax : ExtensionOf i f :=
(@zorn_le_nonempty (ExtensionOf i f) _ ⟨Inhabited.default⟩ fun _ hchain hnonempty =>
⟨ExtensionOf.max hchain hnonempty, ExtensionOf.le_max hchain hnonempty⟩).choose
theorem extensionOfMax_is_max :
∀ (a : ExtensionOf i f), extensionOfMax i f ≤ a → a = extensionOfMax i f :=
fun _ ↦ (@zorn_le_nonempty (ExtensionOf i f) _ ⟨Inhabited.default⟩ fun _ hchain hnonempty =>
⟨ExtensionOf.max hchain hnonempty, ExtensionOf.le_max hchain hnonempty⟩).choose_spec.eq_of_ge
-- Porting note: helper function. Lean looks for an instance of `Sup (Type u)` when the
-- right hand side is substituted in directly
abbrev supExtensionOfMaxSingleton (y : N) : Submodule R N :=
(extensionOfMax i f).domain ⊔ (Submodule.span R {y})
variable {f}
private theorem extensionOfMax_adjoin.aux1 {y : N} (x : supExtensionOfMaxSingleton i f y) :
∃ (a : (extensionOfMax i f).domain) (b : R), x.1 = a.1 + b • y := by
have mem1 : x.1 ∈ (_ : Set _) := x.2
rw [Submodule.coe_sup] at mem1
rcases mem1 with ⟨a, a_mem, b, b_mem : b ∈ (Submodule.span R _ : Submodule R N), eq1⟩
rw [Submodule.mem_span_singleton] at b_mem
rcases b_mem with ⟨z, eq2⟩
exact ⟨⟨a, a_mem⟩, z, by rw [← eq1, ← eq2]⟩
/-- If `x ∈ M ⊔ ⟨y⟩`, then `x = m + r • y`, `fst` pick an arbitrary such `m`. -/
def ExtensionOfMaxAdjoin.fst {y : N} (x : supExtensionOfMaxSingleton i f y) :
(extensionOfMax i f).domain :=
(extensionOfMax_adjoin.aux1 i x).choose
/-- If `x ∈ M ⊔ ⟨y⟩`, then `x = m + r • y`, `snd` pick an arbitrary such `r`. -/
def ExtensionOfMaxAdjoin.snd {y : N} (x : supExtensionOfMaxSingleton i f y) : R :=
(extensionOfMax_adjoin.aux1 i x).choose_spec.choose
theorem ExtensionOfMaxAdjoin.eqn {y : N} (x : supExtensionOfMaxSingleton i f y) :
↑x = ↑(ExtensionOfMaxAdjoin.fst i x) + ExtensionOfMaxAdjoin.snd i x • y :=
(extensionOfMax_adjoin.aux1 i x).choose_spec.choose_spec
variable (f)
-- TODO: refactor to use colon ideals?
/-- The ideal `I = {r | r • y ∈ N}` -/
def ExtensionOfMaxAdjoin.ideal (y : N) : Ideal R :=
(extensionOfMax i f).domain.comap ((LinearMap.id : R →ₗ[R] R).smulRight y)
/-- A linear map `I ⟶ Q` by `x ↦ f' (x • y)` where `f'` is the maximal extension -/
def ExtensionOfMaxAdjoin.idealTo (y : N) : ExtensionOfMaxAdjoin.ideal i f y →ₗ[R] Q where
toFun (z : { x // x ∈ ideal i f y }) := (extensionOfMax i f).toLinearPMap ⟨(↑z : R) • y, z.prop⟩
map_add' (z1 z2 : { x // x ∈ ideal i f y }) := by
simp_rw [← (extensionOfMax i f).toLinearPMap.map_add]
congr
apply add_smul
map_smul' z1 (z2 : {x // x ∈ ideal i f y}) := by
simp_rw [← (extensionOfMax i f).toLinearPMap.map_smul]
congr 2
apply mul_smul
/-- Since we assumed `Q` being Baer, the linear map `x ↦ f' (x • y) : I ⟶ Q` extends to `R ⟶ Q`,
call this extended map `φ` -/
def ExtensionOfMaxAdjoin.extendIdealTo (h : Module.Baer R Q) (y : N) : R →ₗ[R] Q :=
(h (ExtensionOfMaxAdjoin.ideal i f y) (ExtensionOfMaxAdjoin.idealTo i f y)).choose
theorem ExtensionOfMaxAdjoin.extendIdealTo_is_extension (h : Module.Baer R Q) (y : N) :
∀ (x : R) (mem : x ∈ ExtensionOfMaxAdjoin.ideal i f y),
ExtensionOfMaxAdjoin.extendIdealTo i f h y x = ExtensionOfMaxAdjoin.idealTo i f y ⟨x, mem⟩ :=
(h (ExtensionOfMaxAdjoin.ideal i f y) (ExtensionOfMaxAdjoin.idealTo i f y)).choose_spec
theorem ExtensionOfMaxAdjoin.extendIdealTo_wd' (h : Module.Baer R Q) {y : N} (r : R)
(eq1 : r • y = 0) : ExtensionOfMaxAdjoin.extendIdealTo i f h y r = 0 := by
have : r ∈ ideal i f y := by
change (r • y) ∈ (extensionOfMax i f).toLinearPMap.domain
rw [eq1]
apply Submodule.zero_mem _
rw [ExtensionOfMaxAdjoin.extendIdealTo_is_extension i f h y r this]
dsimp [ExtensionOfMaxAdjoin.idealTo]
simp only [LinearMap.coe_mk, eq1, Subtype.coe_mk, ← ZeroMemClass.zero_def,
(extensionOfMax i f).toLinearPMap.map_zero]
theorem ExtensionOfMaxAdjoin.extendIdealTo_wd (h : Module.Baer R Q) {y : N} (r r' : R)
(eq1 : r • y = r' • y) : ExtensionOfMaxAdjoin.extendIdealTo i f h y r =
ExtensionOfMaxAdjoin.extendIdealTo i f h y r' := by
rw [← sub_eq_zero, ← map_sub]
convert ExtensionOfMaxAdjoin.extendIdealTo_wd' i f h (r - r') _
rw [sub_smul, sub_eq_zero, eq1]
theorem ExtensionOfMaxAdjoin.extendIdealTo_eq (h : Module.Baer R Q) {y : N} (r : R)
(hr : r • y ∈ (extensionOfMax i f).domain) : ExtensionOfMaxAdjoin.extendIdealTo i f h y r =
(extensionOfMax i f).toLinearPMap ⟨r • y, hr⟩ := by
simp only [ExtensionOfMaxAdjoin.extendIdealTo_is_extension i f h _ _ hr,
ExtensionOfMaxAdjoin.idealTo, LinearMap.coe_mk, Subtype.coe_mk, AddHom.coe_mk]
/-- We can finally define a linear map `M ⊔ ⟨y⟩ ⟶ Q` by `x + r • y ↦ f x + φ r`
-/
def ExtensionOfMaxAdjoin.extensionToFun (h : Module.Baer R Q) {y : N} :
supExtensionOfMaxSingleton i f y → Q := fun x =>
(extensionOfMax i f).toLinearPMap (ExtensionOfMaxAdjoin.fst i x) +
ExtensionOfMaxAdjoin.extendIdealTo i f h y (ExtensionOfMaxAdjoin.snd i x)
theorem ExtensionOfMaxAdjoin.extensionToFun_wd (h : Module.Baer R Q) {y : N}
(x : supExtensionOfMaxSingleton i f y) (a : (extensionOfMax i f).domain)
(r : R) (eq1 : ↑x = ↑a + r • y) :
ExtensionOfMaxAdjoin.extensionToFun i f h x =
(extensionOfMax i f).toLinearPMap a + ExtensionOfMaxAdjoin.extendIdealTo i f h y r := by
obtain ⟨a, ha⟩ := a
have eq2 :
(ExtensionOfMaxAdjoin.fst i x - a : N) = (r - ExtensionOfMaxAdjoin.snd i x) • y := by
change x = a + r • y at eq1
rwa [ExtensionOfMaxAdjoin.eqn, ← sub_eq_zero, ← sub_sub_sub_eq, sub_eq_zero, ← sub_smul]
at eq1
have eq3 :=
ExtensionOfMaxAdjoin.extendIdealTo_eq i f h (r - ExtensionOfMaxAdjoin.snd i x)
(by rw [← eq2]; exact Submodule.sub_mem _ (ExtensionOfMaxAdjoin.fst i x).2 ha)
simp only [map_sub, sub_smul, sub_eq_iff_eq_add] at eq3
unfold ExtensionOfMaxAdjoin.extensionToFun
rw [eq3, ← add_assoc, ← (extensionOfMax i f).toLinearPMap.map_add, AddMemClass.mk_add_mk]
congr
ext
dsimp
rw [Subtype.coe_mk, add_sub, ← eq1]
exact eq_sub_of_add_eq (ExtensionOfMaxAdjoin.eqn i x).symm
/-- The linear map `M ⊔ ⟨y⟩ ⟶ Q` by `x + r • y ↦ f x + φ r` is an extension of `f` -/
def extensionOfMaxAdjoin (h : Module.Baer R Q) (y : N) : ExtensionOf i f where
domain := supExtensionOfMaxSingleton i f y -- (extensionOfMax i f).domain ⊔ Submodule.span R {y}
le := le_trans (extensionOfMax i f).le le_sup_left
toFun :=
{ toFun := ExtensionOfMaxAdjoin.extensionToFun i f h
map_add' := fun a b => by
have eq1 :
↑a + ↑b =
↑(ExtensionOfMaxAdjoin.fst i a + ExtensionOfMaxAdjoin.fst i b) +
(ExtensionOfMaxAdjoin.snd i a + ExtensionOfMaxAdjoin.snd i b) • y := by
rw [ExtensionOfMaxAdjoin.eqn, ExtensionOfMaxAdjoin.eqn, add_smul, Submodule.coe_add]
ac_rfl
rw [ExtensionOfMaxAdjoin.extensionToFun_wd (y := y) i f h (a + b) _ _ eq1,
LinearPMap.map_add, map_add]
unfold ExtensionOfMaxAdjoin.extensionToFun
abel
map_smul' := fun r a => by
dsimp
have eq1 :
r • (a : N) =
↑(r • ExtensionOfMaxAdjoin.fst i a) + (r • ExtensionOfMaxAdjoin.snd i a) • y := by
rw [ExtensionOfMaxAdjoin.eqn, smul_add, smul_eq_mul, mul_smul]
rfl
rw [ExtensionOfMaxAdjoin.extensionToFun_wd i f h (r • a :) _ _ eq1, LinearMap.map_smul,
LinearPMap.map_smul, ← smul_add]
congr }
is_extension m := by
dsimp
rw [(extensionOfMax i f).is_extension,
ExtensionOfMaxAdjoin.extensionToFun_wd i f h _ ⟨i m, _⟩ 0 _, map_zero, add_zero]
simp
theorem extensionOfMax_le (h : Module.Baer R Q) {y : N} :
extensionOfMax i f ≤ extensionOfMaxAdjoin i f h y :=
⟨le_sup_left, fun x x' EQ => by
symm
change ExtensionOfMaxAdjoin.extensionToFun i f h _ = _
rw [ExtensionOfMaxAdjoin.extensionToFun_wd i f h x' x 0 (by simp [EQ]), map_zero,
add_zero]⟩
theorem extensionOfMax_to_submodule_eq_top (h : Module.Baer R Q) :
(extensionOfMax i f).domain = ⊤ := by
refine Submodule.eq_top_iff'.mpr fun y => ?_
dsimp
rw [← extensionOfMax_is_max i f _ (extensionOfMax_le i f h), extensionOfMaxAdjoin,
Submodule.mem_sup]
exact ⟨0, Submodule.zero_mem _, y, Submodule.mem_span_singleton_self _, zero_add _⟩
protected theorem extension_property (h : Module.Baer R Q)
(f : M →ₗ[R] N) (hf : Function.Injective f) (g : M →ₗ[R] Q) : ∃ h, h ∘ₗ f = g :=
haveI : Fact (Function.Injective f) := ⟨hf⟩
Exists.intro
{ toFun := ((extensionOfMax f g).toLinearPMap
⟨·, (extensionOfMax_to_submodule_eq_top f g h).symm ▸ ⟨⟩⟩)
map_add' := fun x y ↦ by rw [← LinearPMap.map_add]; congr
map_smul' := fun r x ↦ by rw [← LinearPMap.map_smul]; dsimp } <|
LinearMap.ext fun x ↦ ((extensionOfMax f g).is_extension x).symm
theorem extension_property_addMonoidHom (h : Module.Baer ℤ Q)
(f : M →+ N) (hf : Function.Injective f) (g : M →+ Q) : ∃ h : N →+ Q, h.comp f = g :=
have ⟨g', hg'⟩ := h.extension_property f.toIntLinearMap hf g.toIntLinearMap
⟨g', congr(LinearMap.toAddMonoidHom $hg')⟩
/-- **Baer's criterion** for injective module : a Baer module is an injective module, i.e. if every
linear map from an ideal can be extended, then the module is injective. -/
protected theorem injective (h : Module.Baer R Q) : Module.Injective R Q where
out X Y _ _ _ _ i hi f := by
obtain ⟨h, H⟩ := Module.Baer.extension_property h i hi f
exact ⟨h, DFunLike.congr_fun H⟩
protected theorem of_injective [Small.{v} R] (inj : Module.Injective R Q) : Module.Baer R Q := by
intro I g
let eI := Shrink.linearEquiv I R
let eR := Shrink.linearEquiv R R
obtain ⟨g', hg'⟩ := Module.Injective.out (eR.symm.toLinearMap ∘ₗ I.subtype ∘ₗ eI.toLinearMap)
(eR.symm.injective.comp <| Subtype.val_injective.comp eI.injective) (g ∘ₗ eI.toLinearMap)
exact ⟨g' ∘ₗ eR.symm.toLinearMap, fun x mx ↦ by simpa [eI, eR] using hg' (equivShrink I ⟨x, mx⟩)⟩
protected theorem iff_injective [Small.{v} R] : Module.Baer R Q ↔ Module.Injective R Q :=
⟨Module.Baer.injective, Module.Baer.of_injective⟩
end Module.Baer
section ULift
variable {M : Type v} [AddCommGroup M] [Module R M]
lemma Module.ulift_injective_of_injective [Small.{v} R]
(inj : Module.Injective R M) :
Module.Injective R (ULift.{v'} M) := Module.Baer.injective fun I g ↦
have ⟨g', hg'⟩ := Module.Baer.iff_injective.mpr inj I (ULift.moduleEquiv.toLinearMap ∘ₗ g)
⟨ULift.moduleEquiv.symm.toLinearMap ∘ₗ g', fun r hr ↦ ULift.ext _ _ <| hg' r hr⟩
lemma Module.injective_of_ulift_injective
(inj : Module.Injective R (ULift.{v'} M)) :
Module.Injective R M where
out X Y _ _ _ _ f hf g :=
let eX := ULift.moduleEquiv.{_,_,v'} (R := R) (M := X)
have ⟨g', hg'⟩ := inj.out (ULift.moduleEquiv.{_,_,v'}.symm.toLinearMap ∘ₗ f ∘ₗ eX.toLinearMap)
(by exact ULift.moduleEquiv.symm.injective.comp <| hf.comp eX.injective)
(ULift.moduleEquiv.symm.toLinearMap ∘ₗ g ∘ₗ eX.toLinearMap)
⟨ULift.moduleEquiv.toLinearMap ∘ₗ g' ∘ₗ ULift.moduleEquiv.symm.toLinearMap,
fun x ↦ by exact congr(ULift.down $(hg' ⟨x⟩))⟩
variable (M) [Small.{v} R]
lemma Module.injective_iff_ulift_injective :
Module.Injective R M ↔ Module.Injective R (ULift.{v'} M) :=
⟨Module.ulift_injective_of_injective R,
Module.injective_of_ulift_injective R⟩
end ULift
section lifting_property
universe uR uM uP uP'
| variable (R : Type uR) [Ring R] [Small.{uM} R]
variable (M : Type uM) [AddCommGroup M] [Module R M] [inj : Module.Injective R M]
variable (P : Type uP) [AddCommGroup P] [Module R P]
variable (P' : Type uP') [AddCommGroup P'] [Module R P']
lemma Module.Injective.extension_property
(f : P →ₗ[R] P') (hf : Function.Injective f)
| Mathlib/Algebra/Module/Injective.lean | 429 | 435 |
/-
Copyright (c) 2020 Kenny Lau. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kenny Lau
-/
import Mathlib.Algebra.CharP.Frobenius
import Mathlib.Algebra.CharP.Pi
import Mathlib.Algebra.CharP.Quotient
import Mathlib.Algebra.CharP.Subring
import Mathlib.Analysis.SpecialFunctions.Pow.NNReal
import Mathlib.FieldTheory.Perfect
import Mathlib.RingTheory.Valuation.Integers
/-!
# Ring Perfection and Tilt
In this file we define the perfection of a ring of characteristic p, and the tilt of a field
given a valuation to `ℝ≥0`.
## TODO
Define the valuation on the tilt, and define a characteristic predicate for the tilt.
-/
universe u₁ u₂ u₃ u₄
open scoped NNReal
/-- The perfection of a monoid `M`, defined to be the projective limit of `M`
using the `p`-th power maps `M → M` indexed by the natural numbers, implemented as
`{ f : ℕ → M | ∀ n, f (n + 1) ^ p = f n }`. -/
def Monoid.perfection (M : Type u₁) [CommMonoid M] (p : ℕ) : Submonoid (ℕ → M) where
carrier := { f | ∀ n, f (n + 1) ^ p = f n }
one_mem' _ := one_pow _
mul_mem' hf hg n := (mul_pow _ _ _).trans <| congr_arg₂ _ (hf n) (hg n)
/-- The perfection of a ring `R` with characteristic `p`, as a subsemiring,
defined to be the projective limit of `R` using the Frobenius maps `R → R`
indexed by the natural numbers, implemented as `{ f : ℕ → R | ∀ n, f (n + 1) ^ p = f n }`. -/
def Ring.perfectionSubsemiring (R : Type u₁) [CommSemiring R] (p : ℕ) [hp : Fact p.Prime]
[CharP R p] : Subsemiring (ℕ → R) :=
{ Monoid.perfection R p with
zero_mem' := fun _ ↦ zero_pow hp.1.ne_zero
add_mem' := fun hf hg n => (frobenius_add R p _ _).trans <| congr_arg₂ _ (hf n) (hg n) }
/-- The perfection of a ring `R` with characteristic `p`, as a subring,
defined to be the projective limit of `R` using the Frobenius maps `R → R`
indexed by the natural numbers, implemented as `{ f : ℕ → R | ∀ n, f (n + 1) ^ p = f n }`. -/
def Ring.perfectionSubring (R : Type u₁) [CommRing R] (p : ℕ) [hp : Fact p.Prime] [CharP R p] :
Subring (ℕ → R) :=
(Ring.perfectionSubsemiring R p).toSubring fun n => by
simp_rw [← frobenius_def, Pi.neg_apply, Pi.one_apply, RingHom.map_neg, RingHom.map_one]
/-- The perfection of a ring `R` with characteristic `p`,
defined to be the projective limit of `R` using the Frobenius maps `R → R`
indexed by the natural numbers, implemented as `{f : ℕ → R // ∀ n, f (n + 1) ^ p = f n}`. -/
def Ring.Perfection (R : Type u₁) [CommSemiring R] (p : ℕ) : Type u₁ :=
{ f // ∀ n : ℕ, (f : ℕ → R) (n + 1) ^ p = f n }
namespace Perfection
variable (R : Type u₁) [CommSemiring R] (p : ℕ) [hp : Fact p.Prime] [CharP R p]
instance commSemiring : CommSemiring (Ring.Perfection R p) :=
(Ring.perfectionSubsemiring R p).toCommSemiring
instance charP : CharP (Ring.Perfection R p) p :=
CharP.subsemiring (ℕ → R) p (Ring.perfectionSubsemiring R p)
instance ring (R : Type u₁) [CommRing R] [CharP R p] : Ring (Ring.Perfection R p) :=
(Ring.perfectionSubring R p).toRing
instance commRing (R : Type u₁) [CommRing R] [CharP R p] : CommRing (Ring.Perfection R p) :=
(Ring.perfectionSubring R p).toCommRing
instance : Inhabited (Ring.Perfection R p) := ⟨0⟩
/-- The `n`-th coefficient of an element of the perfection. -/
def coeff (n : ℕ) : Ring.Perfection R p →+* R where
toFun f := f.1 n
map_one' := rfl
map_mul' _ _ := rfl
map_zero' := rfl
map_add' _ _ := rfl
variable {R p}
@[ext]
theorem ext {f g : Ring.Perfection R p} (h : ∀ n, coeff R p n f = coeff R p n g) : f = g :=
Subtype.eq <| funext h
variable (R p)
/-- The `p`-th root of an element of the perfection. -/
def pthRoot : Ring.Perfection R p →+* Ring.Perfection R p where
toFun f := ⟨fun n => coeff R p (n + 1) f, fun _ => f.2 _⟩
map_one' := rfl
map_mul' _ _ := rfl
map_zero' := rfl
map_add' _ _ := rfl
variable {R p}
@[simp]
theorem coeff_mk (f : ℕ → R) (hf) (n : ℕ) : coeff R p n ⟨f, hf⟩ = f n := rfl
theorem coeff_pthRoot (f : Ring.Perfection R p) (n : ℕ) :
coeff R p n (pthRoot R p f) = coeff R p (n + 1) f := rfl
theorem coeff_pow_p (f : Ring.Perfection R p) (n : ℕ) :
coeff R p (n + 1) (f ^ p) = coeff R p n f := by rw [RingHom.map_pow]; exact f.2 n
theorem coeff_pow_p' (f : Ring.Perfection R p) (n : ℕ) : coeff R p (n + 1) f ^ p = coeff R p n f :=
f.2 n
theorem coeff_frobenius (f : Ring.Perfection R p) (n : ℕ) :
coeff R p (n + 1) (frobenius _ p f) = coeff R p n f := by apply coeff_pow_p f n
-- `coeff_pow_p f n` also works but is slow!
theorem coeff_iterate_frobenius (f : Ring.Perfection R p) (n m : ℕ) :
coeff R p (n + m) ((frobenius _ p)^[m] f) = coeff R p n f :=
Nat.recOn m rfl fun m ih => by
rw [Function.iterate_succ_apply', Nat.add_succ, coeff_frobenius, ih]
theorem coeff_iterate_frobenius' (f : Ring.Perfection R p) (n m : ℕ) (hmn : m ≤ n) :
coeff R p n ((frobenius _ p)^[m] f) = coeff R p (n - m) f :=
Eq.symm <| (coeff_iterate_frobenius _ _ m).symm.trans <| (tsub_add_cancel_of_le hmn).symm ▸ rfl
theorem pthRoot_frobenius : (pthRoot R p).comp (frobenius _ p) = RingHom.id _ :=
RingHom.ext fun x =>
ext fun n => by rw [RingHom.comp_apply, RingHom.id_apply, coeff_pthRoot, coeff_frobenius]
theorem frobenius_pthRoot : (frobenius _ p).comp (pthRoot R p) = RingHom.id _ :=
RingHom.ext fun x =>
ext fun n => by
rw [RingHom.comp_apply, RingHom.id_apply, RingHom.map_frobenius, coeff_pthRoot,
← @RingHom.map_frobenius (Ring.Perfection R p) _ R, coeff_frobenius]
theorem coeff_add_ne_zero {f : Ring.Perfection R p} {n : ℕ} (hfn : coeff R p n f ≠ 0) (k : ℕ) :
coeff R p (n + k) f ≠ 0 :=
Nat.recOn k hfn fun k ih h => ih <| by
rw [Nat.add_succ] at h
rw [← coeff_pow_p, RingHom.map_pow, h, zero_pow hp.1.ne_zero]
theorem coeff_ne_zero_of_le {f : Ring.Perfection R p} {m n : ℕ} (hfm : coeff R p m f ≠ 0)
(hmn : m ≤ n) : coeff R p n f ≠ 0 :=
let ⟨k, hk⟩ := Nat.exists_eq_add_of_le hmn
hk.symm ▸ coeff_add_ne_zero hfm k
| variable (R p)
instance perfectRing : PerfectRing (Ring.Perfection R p) p where
| Mathlib/RingTheory/Perfection.lean | 152 | 154 |
/-
Copyright (c) 2020 Anatole Dedecker. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anatole Dedecker
-/
import Mathlib.Analysis.Calculus.Deriv.Inv
import Mathlib.Analysis.Calculus.Deriv.MeanValue
/-!
# L'Hôpital's rule for 0/0 indeterminate forms
In this file, we prove several forms of "L'Hôpital's rule" for computing 0/0
indeterminate forms. The proof of `HasDerivAt.lhopital_zero_right_on_Ioo`
is based on the one given in the corresponding
[Wikibooks](https://en.wikibooks.org/wiki/Calculus/L%27H%C3%B4pital%27s_Rule)
chapter, and all other statements are derived from this one by composing by
carefully chosen functions.
Note that the filter `f'/g'` tends to isn't required to be one of `𝓝 a`,
`atTop` or `atBot`. In fact, we give a slightly stronger statement by
allowing it to be any filter on `ℝ`.
Each statement is available in a `HasDerivAt` form and a `deriv` form, which
is denoted by each statement being in either the `HasDerivAt` or the `deriv`
namespace.
## Tags
L'Hôpital's rule, L'Hopital's rule
-/
open Filter Set
open scoped Filter Topology Pointwise
variable {a b : ℝ} {l : Filter ℝ} {f f' g g' : ℝ → ℝ}
/-!
## Interval-based versions
We start by proving statements where all conditions (derivability, `g' ≠ 0`) have
to be satisfied on an explicitly-provided interval.
-/
namespace HasDerivAt
theorem lhopital_zero_right_on_Ioo (hab : a < b) (hff' : ∀ x ∈ Ioo a b, HasDerivAt f (f' x) x)
(hgg' : ∀ x ∈ Ioo a b, HasDerivAt g (g' x) x) (hg' : ∀ x ∈ Ioo a b, g' x ≠ 0)
(hfa : Tendsto f (𝓝[>] a) (𝓝 0)) (hga : Tendsto g (𝓝[>] a) (𝓝 0))
(hdiv : Tendsto (fun x => f' x / g' x) (𝓝[>] a) l) :
Tendsto (fun x => f x / g x) (𝓝[>] a) l := by
have sub : ∀ x ∈ Ioo a b, Ioo a x ⊆ Ioo a b := fun x hx =>
Ioo_subset_Ioo (le_refl a) (le_of_lt hx.2)
have hg : ∀ x ∈ Ioo a b, g x ≠ 0 := by
intro x hx h
have : Tendsto g (𝓝[<] x) (𝓝 0) := by
rw [← h, ← nhdsWithin_Ioo_eq_nhdsLT hx.1]
exact ((hgg' x hx).continuousAt.continuousWithinAt.mono <| sub x hx).tendsto
obtain ⟨y, hyx, hy⟩ : ∃ c ∈ Ioo a x, g' c = 0 :=
exists_hasDerivAt_eq_zero' hx.1 hga this fun y hy => hgg' y <| sub x hx hy
exact hg' y (sub x hx hyx) hy
have : ∀ x ∈ Ioo a b, ∃ c ∈ Ioo a x, f x * g' c = g x * f' c := by
intro x hx
rw [← sub_zero (f x), ← sub_zero (g x)]
exact exists_ratio_hasDerivAt_eq_ratio_slope' g g' hx.1 f f' (fun y hy => hgg' y <| sub x hx hy)
(fun y hy => hff' y <| sub x hx hy) hga hfa
(tendsto_nhdsWithin_of_tendsto_nhds (hgg' x hx).continuousAt.tendsto)
(tendsto_nhdsWithin_of_tendsto_nhds (hff' x hx).continuousAt.tendsto)
choose! c hc using this
have : ∀ x ∈ Ioo a b, ((fun x' => f' x' / g' x') ∘ c) x = f x / g x := by
intro x hx
rcases hc x hx with ⟨h₁, h₂⟩
field_simp [hg x hx, hg' (c x) ((sub x hx) h₁)]
simp only [h₂]
rw [mul_comm]
have cmp : ∀ x ∈ Ioo a b, a < c x ∧ c x < x := fun x hx => (hc x hx).1
rw [← nhdsWithin_Ioo_eq_nhdsGT hab]
apply tendsto_nhdsWithin_congr this
apply hdiv.comp
refine tendsto_nhdsWithin_of_tendsto_nhds_of_eventually_within _
(tendsto_of_tendsto_of_tendsto_of_le_of_le' tendsto_const_nhds
(tendsto_nhdsWithin_of_tendsto_nhds tendsto_id) ?_ ?_) ?_
all_goals
apply eventually_nhdsWithin_of_forall
intro x hx
have := cmp x hx
try simp
linarith [this]
theorem lhopital_zero_right_on_Ico (hab : a < b) (hff' : ∀ x ∈ Ioo a b, HasDerivAt f (f' x) x)
(hgg' : ∀ x ∈ Ioo a b, HasDerivAt g (g' x) x) (hcf : ContinuousOn f (Ico a b))
(hcg : ContinuousOn g (Ico a b)) (hg' : ∀ x ∈ Ioo a b, g' x ≠ 0) (hfa : f a = 0) (hga : g a = 0)
(hdiv : Tendsto (fun x => f' x / g' x) (𝓝[>] a) l) :
Tendsto (fun x => f x / g x) (𝓝[>] a) l := by
refine lhopital_zero_right_on_Ioo hab hff' hgg' hg' ?_ ?_ hdiv
· rw [← hfa, ← nhdsWithin_Ioo_eq_nhdsGT hab]
exact ((hcf a <| left_mem_Ico.mpr hab).mono Ioo_subset_Ico_self).tendsto
· rw [← hga, ← nhdsWithin_Ioo_eq_nhdsGT hab]
exact ((hcg a <| left_mem_Ico.mpr hab).mono Ioo_subset_Ico_self).tendsto
theorem lhopital_zero_left_on_Ioo (hab : a < b) (hff' : ∀ x ∈ Ioo a b, HasDerivAt f (f' x) x)
(hgg' : ∀ x ∈ Ioo a b, HasDerivAt g (g' x) x) (hg' : ∀ x ∈ Ioo a b, g' x ≠ 0)
(hfb : Tendsto f (𝓝[<] b) (𝓝 0)) (hgb : Tendsto g (𝓝[<] b) (𝓝 0))
(hdiv : Tendsto (fun x => f' x / g' x) (𝓝[<] b) l) :
Tendsto (fun x => f x / g x) (𝓝[<] b) l := by
-- Here, we essentially compose by `Neg.neg`. The following is mostly technical details.
have hdnf : ∀ x ∈ -Ioo a b, HasDerivAt (f ∘ Neg.neg) (f' (-x) * -1) x := fun x hx =>
comp x (hff' (-x) hx) (hasDerivAt_neg x)
have hdng : ∀ x ∈ -Ioo a b, HasDerivAt (g ∘ Neg.neg) (g' (-x) * -1) x := fun x hx =>
comp x (hgg' (-x) hx) (hasDerivAt_neg x)
rw [neg_Ioo] at hdnf
rw [neg_Ioo] at hdng
have := lhopital_zero_right_on_Ioo (neg_lt_neg hab) hdnf hdng (by
intro x hx h
apply hg' _ (by rw [← neg_Ioo] at hx; exact hx)
rwa [mul_comm, ← neg_eq_neg_one_mul, neg_eq_zero] at h)
(hfb.comp tendsto_neg_nhdsGT_neg) (hgb.comp tendsto_neg_nhdsGT_neg)
(by
simp only [neg_div_neg_eq, mul_one, mul_neg]
exact hdiv.comp tendsto_neg_nhdsGT_neg)
have := this.comp tendsto_neg_nhdsLT
unfold Function.comp at this
simpa only [neg_neg]
theorem lhopital_zero_left_on_Ioc (hab : a < b) (hff' : ∀ x ∈ Ioo a b, HasDerivAt f (f' x) x)
(hgg' : ∀ x ∈ Ioo a b, HasDerivAt g (g' x) x) (hcf : ContinuousOn f (Ioc a b))
(hcg : ContinuousOn g (Ioc a b)) (hg' : ∀ x ∈ Ioo a b, g' x ≠ 0) (hfb : f b = 0) (hgb : g b = 0)
(hdiv : Tendsto (fun x => f' x / g' x) (𝓝[<] b) l) :
Tendsto (fun x => f x / g x) (𝓝[<] b) l := by
| refine lhopital_zero_left_on_Ioo hab hff' hgg' hg' ?_ ?_ hdiv
· rw [← hfb, ← nhdsWithin_Ioo_eq_nhdsLT hab]
exact ((hcf b <| right_mem_Ioc.mpr hab).mono Ioo_subset_Ioc_self).tendsto
· rw [← hgb, ← nhdsWithin_Ioo_eq_nhdsLT hab]
exact ((hcg b <| right_mem_Ioc.mpr hab).mono Ioo_subset_Ioc_self).tendsto
theorem lhopital_zero_atTop_on_Ioi (hff' : ∀ x ∈ Ioi a, HasDerivAt f (f' x) x)
(hgg' : ∀ x ∈ Ioi a, HasDerivAt g (g' x) x) (hg' : ∀ x ∈ Ioi a, g' x ≠ 0)
(hftop : Tendsto f atTop (𝓝 0)) (hgtop : Tendsto g atTop (𝓝 0))
(hdiv : Tendsto (fun x => f' x / g' x) atTop l) : Tendsto (fun x => f x / g x) atTop l := by
| Mathlib/Analysis/Calculus/LHopital.lean | 132 | 141 |
/-
Copyright (c) 2019 Gabriel Ebner. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Gabriel Ebner, Sébastien Gouëzel
-/
import Mathlib.Analysis.Calculus.FDeriv.Basic
import Mathlib.Analysis.NormedSpace.OperatorNorm.NormedSpace
/-!
# One-dimensional derivatives
This file defines the derivative of a function `f : 𝕜 → F` where `𝕜` is a
normed field and `F` is a normed space over this field. The derivative of
such a function `f` at a point `x` is given by an element `f' : F`.
The theory is developed analogously to the [Fréchet
derivatives](./fderiv.html). We first introduce predicates defined in terms
of the corresponding predicates for Fréchet derivatives:
- `HasDerivAtFilter f f' x L` states that the function `f` has the
derivative `f'` at the point `x` as `x` goes along the filter `L`.
- `HasDerivWithinAt f f' s x` states that the function `f` has the
derivative `f'` at the point `x` within the subset `s`.
- `HasDerivAt f f' x` states that the function `f` has the derivative `f'`
at the point `x`.
- `HasStrictDerivAt f f' x` states that the function `f` has the derivative `f'`
at the point `x` in the sense of strict differentiability, i.e.,
`f y - f z = (y - z) • f' + o (y - z)` as `y, z → x`.
For the last two notions we also define a functional version:
- `derivWithin f s x` is a derivative of `f` at `x` within `s`. If the
derivative does not exist, then `derivWithin f s x` equals zero.
- `deriv f x` is a derivative of `f` at `x`. If the derivative does not
exist, then `deriv f x` equals zero.
The theorems `fderivWithin_derivWithin` and `fderiv_deriv` show that the
one-dimensional derivatives coincide with the general Fréchet derivatives.
We also show the existence and compute the derivatives of:
- constants
- the identity function
- linear maps (in `Linear.lean`)
- addition (in `Add.lean`)
- sum of finitely many functions (in `Add.lean`)
- negation (in `Add.lean`)
- subtraction (in `Add.lean`)
- star (in `Star.lean`)
- multiplication of two functions in `𝕜 → 𝕜` (in `Mul.lean`)
- multiplication of a function in `𝕜 → 𝕜` and of a function in `𝕜 → E` (in `Mul.lean`)
- powers of a function (in `Pow.lean` and `ZPow.lean`)
- inverse `x → x⁻¹` (in `Inv.lean`)
- division (in `Inv.lean`)
- composition of a function in `𝕜 → F` with a function in `𝕜 → 𝕜` (in `Comp.lean`)
- composition of a function in `F → E` with a function in `𝕜 → F` (in `Comp.lean`)
- inverse function (assuming that it exists; the inverse function theorem is in `Inverse.lean`)
- polynomials (in `Polynomial.lean`)
For most binary operations we also define `const_op` and `op_const` theorems for the cases when
the first or second argument is a constant. This makes writing chains of `HasDerivAt`'s easier,
and they more frequently lead to the desired result.
We set up the simplifier so that it can compute the derivative of simple functions. For instance,
```lean
example (x : ℝ) :
deriv (fun x ↦ cos (sin x) * exp x) x = (cos (sin x) - sin (sin x) * cos x) * exp x := by
simp; ring
```
The relationship between the derivative of a function and its definition from a standard
undergraduate course as the limit of the slope `(f y - f x) / (y - x)` as `y` tends to `𝓝[≠] x`
is developed in the file `Slope.lean`.
## Implementation notes
Most of the theorems are direct restatements of the corresponding theorems
for Fréchet derivatives.
The strategy to construct simp lemmas that give the simplifier the possibility to compute
derivatives is the same as the one for differentiability statements, as explained in
`FDeriv/Basic.lean`. See the explanations there.
-/
universe u v w
noncomputable section
open scoped Topology ENNReal NNReal
open Filter Asymptotics Set
open ContinuousLinearMap (smulRight smulRight_one_eq_iff)
section TVS
variable {𝕜 : Type u} [NontriviallyNormedField 𝕜]
variable {F : Type v} [AddCommGroup F] [Module 𝕜 F] [TopologicalSpace F]
section
variable [ContinuousSMul 𝕜 F]
/-- `f` has the derivative `f'` at the point `x` as `x` goes along the filter `L`.
That is, `f x' = f x + (x' - x) • f' + o(x' - x)` where `x'` converges along the filter `L`.
-/
def HasDerivAtFilter (f : 𝕜 → F) (f' : F) (x : 𝕜) (L : Filter 𝕜) :=
HasFDerivAtFilter f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') x L
/-- `f` has the derivative `f'` at the point `x` within the subset `s`.
That is, `f x' = f x + (x' - x) • f' + o(x' - x)` where `x'` converges to `x` inside `s`.
-/
def HasDerivWithinAt (f : 𝕜 → F) (f' : F) (s : Set 𝕜) (x : 𝕜) :=
HasDerivAtFilter f f' x (𝓝[s] x)
/-- `f` has the derivative `f'` at the point `x`.
That is, `f x' = f x + (x' - x) • f' + o(x' - x)` where `x'` converges to `x`.
-/
def HasDerivAt (f : 𝕜 → F) (f' : F) (x : 𝕜) :=
HasDerivAtFilter f f' x (𝓝 x)
/-- `f` has the derivative `f'` at the point `x` in the sense of strict differentiability.
That is, `f y - f z = (y - z) • f' + o(y - z)` as `y, z → x`. -/
def HasStrictDerivAt (f : 𝕜 → F) (f' : F) (x : 𝕜) :=
HasStrictFDerivAt f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') x
end
/-- Derivative of `f` at the point `x` within the set `s`, if it exists. Zero otherwise.
If the derivative exists (i.e., `∃ f', HasDerivWithinAt f f' s x`), then
`f x' = f x + (x' - x) • derivWithin f s x + o(x' - x)` where `x'` converges to `x` inside `s`.
-/
def derivWithin (f : 𝕜 → F) (s : Set 𝕜) (x : 𝕜) :=
fderivWithin 𝕜 f s x 1
/-- Derivative of `f` at the point `x`, if it exists. Zero otherwise.
If the derivative exists (i.e., `∃ f', HasDerivAt f f' x`), then
`f x' = f x + (x' - x) • deriv f x + o(x' - x)` where `x'` converges to `x`.
-/
def deriv (f : 𝕜 → F) (x : 𝕜) :=
fderiv 𝕜 f x 1
variable {f f₀ f₁ : 𝕜 → F}
variable {f' f₀' f₁' g' : F}
variable {x : 𝕜}
variable {s t : Set 𝕜}
variable {L L₁ L₂ : Filter 𝕜}
section
variable [ContinuousSMul 𝕜 F]
/-- Expressing `HasFDerivAtFilter f f' x L` in terms of `HasDerivAtFilter` -/
theorem hasFDerivAtFilter_iff_hasDerivAtFilter {f' : 𝕜 →L[𝕜] F} :
HasFDerivAtFilter f f' x L ↔ HasDerivAtFilter f (f' 1) x L := by simp [HasDerivAtFilter]
theorem HasFDerivAtFilter.hasDerivAtFilter {f' : 𝕜 →L[𝕜] F} :
HasFDerivAtFilter f f' x L → HasDerivAtFilter f (f' 1) x L :=
hasFDerivAtFilter_iff_hasDerivAtFilter.mp
/-- Expressing `HasFDerivWithinAt f f' s x` in terms of `HasDerivWithinAt` -/
theorem hasFDerivWithinAt_iff_hasDerivWithinAt {f' : 𝕜 →L[𝕜] F} :
HasFDerivWithinAt f f' s x ↔ HasDerivWithinAt f (f' 1) s x :=
hasFDerivAtFilter_iff_hasDerivAtFilter
/-- Expressing `HasDerivWithinAt f f' s x` in terms of `HasFDerivWithinAt` -/
theorem hasDerivWithinAt_iff_hasFDerivWithinAt {f' : F} :
HasDerivWithinAt f f' s x ↔ HasFDerivWithinAt f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') s x :=
Iff.rfl
theorem HasFDerivWithinAt.hasDerivWithinAt {f' : 𝕜 →L[𝕜] F} :
HasFDerivWithinAt f f' s x → HasDerivWithinAt f (f' 1) s x :=
hasFDerivWithinAt_iff_hasDerivWithinAt.mp
theorem HasDerivWithinAt.hasFDerivWithinAt {f' : F} :
HasDerivWithinAt f f' s x → HasFDerivWithinAt f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') s x :=
hasDerivWithinAt_iff_hasFDerivWithinAt.mp
/-- Expressing `HasFDerivAt f f' x` in terms of `HasDerivAt` -/
theorem hasFDerivAt_iff_hasDerivAt {f' : 𝕜 →L[𝕜] F} : HasFDerivAt f f' x ↔ HasDerivAt f (f' 1) x :=
hasFDerivAtFilter_iff_hasDerivAtFilter
theorem HasFDerivAt.hasDerivAt {f' : 𝕜 →L[𝕜] F} : HasFDerivAt f f' x → HasDerivAt f (f' 1) x :=
hasFDerivAt_iff_hasDerivAt.mp
theorem hasStrictFDerivAt_iff_hasStrictDerivAt {f' : 𝕜 →L[𝕜] F} :
HasStrictFDerivAt f f' x ↔ HasStrictDerivAt f (f' 1) x := by
simp [HasStrictDerivAt, HasStrictFDerivAt]
protected theorem HasStrictFDerivAt.hasStrictDerivAt {f' : 𝕜 →L[𝕜] F} :
HasStrictFDerivAt f f' x → HasStrictDerivAt f (f' 1) x :=
hasStrictFDerivAt_iff_hasStrictDerivAt.mp
theorem hasStrictDerivAt_iff_hasStrictFDerivAt :
HasStrictDerivAt f f' x ↔ HasStrictFDerivAt f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') x :=
Iff.rfl
alias ⟨HasStrictDerivAt.hasStrictFDerivAt, _⟩ := hasStrictDerivAt_iff_hasStrictFDerivAt
/-- Expressing `HasDerivAt f f' x` in terms of `HasFDerivAt` -/
theorem hasDerivAt_iff_hasFDerivAt {f' : F} :
HasDerivAt f f' x ↔ HasFDerivAt f (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') x :=
Iff.rfl
alias ⟨HasDerivAt.hasFDerivAt, _⟩ := hasDerivAt_iff_hasFDerivAt
end
theorem derivWithin_zero_of_not_differentiableWithinAt (h : ¬DifferentiableWithinAt 𝕜 f s x) :
derivWithin f s x = 0 := by
unfold derivWithin
rw [fderivWithin_zero_of_not_differentiableWithinAt h]
simp
theorem differentiableWithinAt_of_derivWithin_ne_zero (h : derivWithin f s x ≠ 0) :
DifferentiableWithinAt 𝕜 f s x :=
not_imp_comm.1 derivWithin_zero_of_not_differentiableWithinAt h
end TVS
variable {𝕜 : Type u} [NontriviallyNormedField 𝕜]
variable {F : Type v} [NormedAddCommGroup F] [NormedSpace 𝕜 F]
variable {f f₀ f₁ : 𝕜 → F}
variable {f' f₀' f₁' g' : F}
variable {x : 𝕜}
variable {s t : Set 𝕜}
variable {L L₁ L₂ : Filter 𝕜}
theorem derivWithin_zero_of_not_accPt (h : ¬AccPt x (𝓟 s)) : derivWithin f s x = 0 := by
rw [derivWithin, fderivWithin_zero_of_not_accPt h, ContinuousLinearMap.zero_apply]
theorem derivWithin_zero_of_not_uniqueDiffWithinAt (h : ¬UniqueDiffWithinAt 𝕜 s x) :
derivWithin f s x = 0 :=
derivWithin_zero_of_not_accPt <| mt AccPt.uniqueDiffWithinAt h
set_option linter.deprecated false in
@[deprecated derivWithin_zero_of_not_accPt (since := "2025-04-20")]
theorem derivWithin_zero_of_isolated (h : 𝓝[s \ {x}] x = ⊥) : derivWithin f s x = 0 := by
rw [derivWithin, fderivWithin_zero_of_isolated h, ContinuousLinearMap.zero_apply]
theorem derivWithin_zero_of_nmem_closure (h : x ∉ closure s) : derivWithin f s x = 0 := by
rw [derivWithin, fderivWithin_zero_of_nmem_closure h, ContinuousLinearMap.zero_apply]
theorem deriv_zero_of_not_differentiableAt (h : ¬DifferentiableAt 𝕜 f x) : deriv f x = 0 := by
unfold deriv
rw [fderiv_zero_of_not_differentiableAt h]
simp
theorem differentiableAt_of_deriv_ne_zero (h : deriv f x ≠ 0) : DifferentiableAt 𝕜 f x :=
not_imp_comm.1 deriv_zero_of_not_differentiableAt h
theorem UniqueDiffWithinAt.eq_deriv (s : Set 𝕜) (H : UniqueDiffWithinAt 𝕜 s x)
(h : HasDerivWithinAt f f' s x) (h₁ : HasDerivWithinAt f f₁' s x) : f' = f₁' :=
smulRight_one_eq_iff.mp <| UniqueDiffWithinAt.eq H h h₁
theorem hasDerivAtFilter_iff_isLittleO :
HasDerivAtFilter f f' x L ↔ (fun x' : 𝕜 => f x' - f x - (x' - x) • f') =o[L] fun x' => x' - x :=
hasFDerivAtFilter_iff_isLittleO ..
theorem hasDerivAtFilter_iff_tendsto :
HasDerivAtFilter f f' x L ↔
Tendsto (fun x' : 𝕜 => ‖x' - x‖⁻¹ * ‖f x' - f x - (x' - x) • f'‖) L (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasDerivWithinAt_iff_isLittleO :
HasDerivWithinAt f f' s x ↔
(fun x' : 𝕜 => f x' - f x - (x' - x) • f') =o[𝓝[s] x] fun x' => x' - x :=
hasFDerivAtFilter_iff_isLittleO ..
theorem hasDerivWithinAt_iff_tendsto :
HasDerivWithinAt f f' s x ↔
Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - (x' - x) • f'‖) (𝓝[s] x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasDerivAt_iff_isLittleO :
HasDerivAt f f' x ↔ (fun x' : 𝕜 => f x' - f x - (x' - x) • f') =o[𝓝 x] fun x' => x' - x :=
hasFDerivAtFilter_iff_isLittleO ..
theorem hasDerivAt_iff_tendsto :
HasDerivAt f f' x ↔ Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - (x' - x) • f'‖) (𝓝 x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem HasDerivAtFilter.isBigO_sub (h : HasDerivAtFilter f f' x L) :
(fun x' => f x' - f x) =O[L] fun x' => x' - x :=
HasFDerivAtFilter.isBigO_sub h
nonrec theorem HasDerivAtFilter.isBigO_sub_rev (hf : HasDerivAtFilter f f' x L) (hf' : f' ≠ 0) :
(fun x' => x' - x) =O[L] fun x' => f x' - f x :=
suffices AntilipschitzWith ‖f'‖₊⁻¹ (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') from hf.isBigO_sub_rev this
AddMonoidHomClass.antilipschitz_of_bound (smulRight (1 : 𝕜 →L[𝕜] 𝕜) f') fun x => by
simp [norm_smul, ← div_eq_inv_mul, mul_div_cancel_right₀ _ (mt norm_eq_zero.1 hf')]
theorem HasStrictDerivAt.hasDerivAt (h : HasStrictDerivAt f f' x) : HasDerivAt f f' x :=
h.hasFDerivAt
theorem hasDerivWithinAt_congr_set' {s t : Set 𝕜} (y : 𝕜) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
HasDerivWithinAt f f' s x ↔ HasDerivWithinAt f f' t x :=
hasFDerivWithinAt_congr_set' y h
theorem hasDerivWithinAt_congr_set {s t : Set 𝕜} (h : s =ᶠ[𝓝 x] t) :
HasDerivWithinAt f f' s x ↔ HasDerivWithinAt f f' t x :=
hasFDerivWithinAt_congr_set h
alias ⟨HasDerivWithinAt.congr_set, _⟩ := hasDerivWithinAt_congr_set
@[simp]
theorem hasDerivWithinAt_diff_singleton :
HasDerivWithinAt f f' (s \ {x}) x ↔ HasDerivWithinAt f f' s x :=
hasFDerivWithinAt_diff_singleton _
@[simp]
theorem hasDerivWithinAt_Ioi_iff_Ici [PartialOrder 𝕜] :
HasDerivWithinAt f f' (Ioi x) x ↔ HasDerivWithinAt f f' (Ici x) x := by
rw [← Ici_diff_left, hasDerivWithinAt_diff_singleton]
alias ⟨HasDerivWithinAt.Ici_of_Ioi, HasDerivWithinAt.Ioi_of_Ici⟩ := hasDerivWithinAt_Ioi_iff_Ici
@[simp]
theorem hasDerivWithinAt_Iio_iff_Iic [PartialOrder 𝕜] :
HasDerivWithinAt f f' (Iio x) x ↔ HasDerivWithinAt f f' (Iic x) x := by
rw [← Iic_diff_right, hasDerivWithinAt_diff_singleton]
alias ⟨HasDerivWithinAt.Iic_of_Iio, HasDerivWithinAt.Iio_of_Iic⟩ := hasDerivWithinAt_Iio_iff_Iic
theorem HasDerivWithinAt.Ioi_iff_Ioo [LinearOrder 𝕜] [OrderClosedTopology 𝕜] {x y : 𝕜} (h : x < y) :
HasDerivWithinAt f f' (Ioo x y) x ↔ HasDerivWithinAt f f' (Ioi x) x :=
hasFDerivWithinAt_inter <| Iio_mem_nhds h
alias ⟨HasDerivWithinAt.Ioi_of_Ioo, HasDerivWithinAt.Ioo_of_Ioi⟩ := HasDerivWithinAt.Ioi_iff_Ioo
theorem hasDerivAt_iff_isLittleO_nhds_zero :
HasDerivAt f f' x ↔ (fun h => f (x + h) - f x - h • f') =o[𝓝 0] fun h => h :=
hasFDerivAt_iff_isLittleO_nhds_zero
theorem HasDerivAtFilter.mono (h : HasDerivAtFilter f f' x L₂) (hst : L₁ ≤ L₂) :
HasDerivAtFilter f f' x L₁ :=
HasFDerivAtFilter.mono h hst
theorem HasDerivWithinAt.mono (h : HasDerivWithinAt f f' t x) (hst : s ⊆ t) :
HasDerivWithinAt f f' s x :=
HasFDerivWithinAt.mono h hst
theorem HasDerivWithinAt.mono_of_mem_nhdsWithin (h : HasDerivWithinAt f f' t x) (hst : t ∈ 𝓝[s] x) :
HasDerivWithinAt f f' s x :=
HasFDerivWithinAt.mono_of_mem_nhdsWithin h hst
@[deprecated (since := "2024-10-31")]
alias HasDerivWithinAt.mono_of_mem := HasDerivWithinAt.mono_of_mem_nhdsWithin
theorem HasDerivAt.hasDerivAtFilter (h : HasDerivAt f f' x) (hL : L ≤ 𝓝 x) :
HasDerivAtFilter f f' x L :=
HasFDerivAt.hasFDerivAtFilter h hL
theorem HasDerivAt.hasDerivWithinAt (h : HasDerivAt f f' x) : HasDerivWithinAt f f' s x :=
HasFDerivAt.hasFDerivWithinAt h
theorem HasDerivWithinAt.differentiableWithinAt (h : HasDerivWithinAt f f' s x) :
DifferentiableWithinAt 𝕜 f s x :=
HasFDerivWithinAt.differentiableWithinAt h
theorem HasDerivAt.differentiableAt (h : HasDerivAt f f' x) : DifferentiableAt 𝕜 f x :=
HasFDerivAt.differentiableAt h
@[simp]
theorem hasDerivWithinAt_univ : HasDerivWithinAt f f' univ x ↔ HasDerivAt f f' x :=
hasFDerivWithinAt_univ
theorem HasDerivAt.unique (h₀ : HasDerivAt f f₀' x) (h₁ : HasDerivAt f f₁' x) : f₀' = f₁' :=
smulRight_one_eq_iff.mp <| h₀.hasFDerivAt.unique h₁
theorem hasDerivWithinAt_inter' (h : t ∈ 𝓝[s] x) :
HasDerivWithinAt f f' (s ∩ t) x ↔ HasDerivWithinAt f f' s x :=
hasFDerivWithinAt_inter' h
theorem hasDerivWithinAt_inter (h : t ∈ 𝓝 x) :
HasDerivWithinAt f f' (s ∩ t) x ↔ HasDerivWithinAt f f' s x :=
hasFDerivWithinAt_inter h
theorem HasDerivWithinAt.union (hs : HasDerivWithinAt f f' s x) (ht : HasDerivWithinAt f f' t x) :
HasDerivWithinAt f f' (s ∪ t) x :=
hs.hasFDerivWithinAt.union ht.hasFDerivWithinAt
theorem HasDerivWithinAt.hasDerivAt (h : HasDerivWithinAt f f' s x) (hs : s ∈ 𝓝 x) :
HasDerivAt f f' x :=
HasFDerivWithinAt.hasFDerivAt h hs
theorem DifferentiableWithinAt.hasDerivWithinAt (h : DifferentiableWithinAt 𝕜 f s x) :
HasDerivWithinAt f (derivWithin f s x) s x :=
h.hasFDerivWithinAt.hasDerivWithinAt
theorem DifferentiableAt.hasDerivAt (h : DifferentiableAt 𝕜 f x) : HasDerivAt f (deriv f x) x :=
h.hasFDerivAt.hasDerivAt
@[simp]
theorem hasDerivAt_deriv_iff : HasDerivAt f (deriv f x) x ↔ DifferentiableAt 𝕜 f x :=
⟨fun h => h.differentiableAt, fun h => h.hasDerivAt⟩
@[simp]
theorem hasDerivWithinAt_derivWithin_iff :
HasDerivWithinAt f (derivWithin f s x) s x ↔ DifferentiableWithinAt 𝕜 f s x :=
⟨fun h => h.differentiableWithinAt, fun h => h.hasDerivWithinAt⟩
theorem DifferentiableOn.hasDerivAt (h : DifferentiableOn 𝕜 f s) (hs : s ∈ 𝓝 x) :
HasDerivAt f (deriv f x) x :=
(h.hasFDerivAt hs).hasDerivAt
theorem HasDerivAt.deriv (h : HasDerivAt f f' x) : deriv f x = f' :=
h.differentiableAt.hasDerivAt.unique h
theorem deriv_eq {f' : 𝕜 → F} (h : ∀ x, HasDerivAt f (f' x) x) : deriv f = f' :=
funext fun x => (h x).deriv
theorem HasDerivWithinAt.derivWithin (h : HasDerivWithinAt f f' s x)
(hxs : UniqueDiffWithinAt 𝕜 s x) : derivWithin f s x = f' :=
hxs.eq_deriv _ h.differentiableWithinAt.hasDerivWithinAt h
theorem fderivWithin_derivWithin : (fderivWithin 𝕜 f s x : 𝕜 → F) 1 = derivWithin f s x :=
rfl
theorem derivWithin_fderivWithin :
smulRight (1 : 𝕜 →L[𝕜] 𝕜) (derivWithin f s x) = fderivWithin 𝕜 f s x := by simp [derivWithin]
theorem norm_derivWithin_eq_norm_fderivWithin : ‖derivWithin f s x‖ = ‖fderivWithin 𝕜 f s x‖ := by
simp [← derivWithin_fderivWithin]
theorem fderiv_deriv : (fderiv 𝕜 f x : 𝕜 → F) 1 = deriv f x :=
rfl
@[simp]
theorem fderiv_eq_smul_deriv (y : 𝕜) : (fderiv 𝕜 f x : 𝕜 → F) y = y • deriv f x := by
rw [← fderiv_deriv, ← ContinuousLinearMap.map_smul]
simp only [smul_eq_mul, mul_one]
theorem deriv_fderiv : smulRight (1 : 𝕜 →L[𝕜] 𝕜) (deriv f x) = fderiv 𝕜 f x := by
simp only [deriv, ContinuousLinearMap.smulRight_one_one]
lemma fderiv_eq_deriv_mul {f : 𝕜 → 𝕜} {x y : 𝕜} : (fderiv 𝕜 f x : 𝕜 → 𝕜) y = (deriv f x) * y := by
simp [mul_comm]
theorem norm_deriv_eq_norm_fderiv : ‖deriv f x‖ = ‖fderiv 𝕜 f x‖ := by
simp [← deriv_fderiv]
theorem DifferentiableAt.derivWithin (h : DifferentiableAt 𝕜 f x) (hxs : UniqueDiffWithinAt 𝕜 s x) :
derivWithin f s x = deriv f x := by
unfold _root_.derivWithin deriv
rw [h.fderivWithin hxs]
theorem HasDerivWithinAt.deriv_eq_zero (hd : HasDerivWithinAt f 0 s x)
(H : UniqueDiffWithinAt 𝕜 s x) : deriv f x = 0 :=
(em' (DifferentiableAt 𝕜 f x)).elim deriv_zero_of_not_differentiableAt fun h =>
H.eq_deriv _ h.hasDerivAt.hasDerivWithinAt hd
theorem derivWithin_of_mem_nhdsWithin (st : t ∈ 𝓝[s] x) (ht : UniqueDiffWithinAt 𝕜 s x)
(h : DifferentiableWithinAt 𝕜 f t x) : derivWithin f s x = derivWithin f t x :=
((DifferentiableWithinAt.hasDerivWithinAt h).mono_of_mem_nhdsWithin st).derivWithin ht
@[deprecated (since := "2024-10-31")] alias derivWithin_of_mem := derivWithin_of_mem_nhdsWithin
theorem derivWithin_subset (st : s ⊆ t) (ht : UniqueDiffWithinAt 𝕜 s x)
(h : DifferentiableWithinAt 𝕜 f t x) : derivWithin f s x = derivWithin f t x :=
((DifferentiableWithinAt.hasDerivWithinAt h).mono st).derivWithin ht
theorem derivWithin_congr_set' (y : 𝕜) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
derivWithin f s x = derivWithin f t x := by simp only [derivWithin, fderivWithin_congr_set' y h]
theorem derivWithin_congr_set (h : s =ᶠ[𝓝 x] t) : derivWithin f s x = derivWithin f t x := by
simp only [derivWithin, fderivWithin_congr_set h]
@[simp]
| theorem derivWithin_univ : derivWithin f univ = deriv f := by
ext
| Mathlib/Analysis/Calculus/Deriv/Basic.lean | 474 | 475 |
/-
Copyright (c) 2022 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Oliver Nash
-/
import Mathlib.MeasureTheory.Measure.Doubling
import Mathlib.MeasureTheory.Covering.Vitali
import Mathlib.MeasureTheory.Covering.Differentiation
/-!
# Uniformly locally doubling measures and Lebesgue's density theorem
Lebesgue's density theorem states that given a set `S` in a sigma compact metric space with
locally-finite uniformly locally doubling measure `μ` then for almost all points `x` in `S`, for any
sequence of closed balls `B₀, B₁, B₂, ...` containing `x`, the limit `μ (S ∩ Bⱼ) / μ (Bⱼ) → 1` as
`j → ∞`.
In this file we combine general results about existence of Vitali families for uniformly locally
doubling measures with results about differentiation along a Vitali family to obtain an explicit
form of Lebesgue's density theorem.
## Main results
* `IsUnifLocDoublingMeasure.ae_tendsto_measure_inter_div`: a version of Lebesgue's density
theorem for sequences of balls converging on a point but whose centres are not required to be
fixed.
-/
noncomputable section
open Set Filter Metric MeasureTheory TopologicalSpace
open scoped NNReal Topology
namespace IsUnifLocDoublingMeasure
variable {α : Type*} [PseudoMetricSpace α] [MeasurableSpace α] (μ : Measure α)
[IsUnifLocDoublingMeasure μ]
section
variable [SecondCountableTopology α] [BorelSpace α] [IsLocallyFiniteMeasure μ]
open scoped Topology
/-- A Vitali family in a space with a uniformly locally doubling measure, designed so that the sets
at `x` contain all `closedBall y r` when `dist x y ≤ K * r`. -/
irreducible_def vitaliFamily (K : ℝ) : VitaliFamily μ := by
/- the Vitali covering theorem gives a family that works well at small scales, thanks to the
doubling property. We enlarge this family to add large sets, to make sure that all balls and not
only small ones belong to the family, for convenience. -/
let R := scalingScaleOf μ (max (4 * K + 3) 3)
have Rpos : 0 < R := scalingScaleOf_pos _ _
have A : ∀ x : α, ∃ᶠ r in 𝓝[>] (0 : ℝ),
μ (closedBall x (3 * r)) ≤ scalingConstantOf μ (max (4 * K + 3) 3) * μ (closedBall x r) := by
intro x
apply frequently_iff.2 fun {U} hU => ?_
obtain ⟨ε, εpos, hε⟩ := mem_nhdsGT_iff_exists_Ioc_subset.1 hU
refine ⟨min ε R, hε ⟨lt_min εpos Rpos, min_le_left _ _⟩, ?_⟩
exact measure_mul_le_scalingConstantOf_mul μ
⟨zero_lt_three, le_max_right _ _⟩ (min_le_right _ _)
exact (Vitali.vitaliFamily μ (scalingConstantOf μ (max (4 * K + 3) 3)) A).enlarge (R / 4)
(by linarith)
/-- In the Vitali family `IsUnifLocDoublingMeasure.vitaliFamily K`, the sets based at `x`
contain all balls `closedBall y r` when `dist x y ≤ K * r`. -/
theorem closedBall_mem_vitaliFamily_of_dist_le_mul {K : ℝ} {x y : α} {r : ℝ} (h : dist x y ≤ K * r)
(rpos : 0 < r) : closedBall y r ∈ (vitaliFamily μ K).setsAt x := by
let R := scalingScaleOf μ (max (4 * K + 3) 3)
simp only [vitaliFamily, VitaliFamily.enlarge, Vitali.vitaliFamily, mem_union, mem_setOf_eq,
isClosed_closedBall, true_and, (nonempty_ball.2 rpos).mono ball_subset_interior_closedBall,
measurableSet_closedBall]
/- The measure is doubling on scales smaller than `R`. Therefore, we treat differently small
and large balls. For large balls, this follows directly from the enlargement we used in the
definition. -/
by_cases H : closedBall y r ⊆ closedBall x (R / 4)
swap; · exact Or.inr H
left
/- For small balls, there is the difficulty that `r` could be large but still the ball could be
small, if the annulus `{y | ε ≤ dist y x ≤ R/4}` is empty. We split between the cases `r ≤ R`
and `r > R`, and use the doubling for the former and rough estimates for the latter. -/
rcases le_or_lt r R with (hr | hr)
· refine ⟨(K + 1) * r, ?_⟩
constructor
· apply closedBall_subset_closedBall'
rw [dist_comm]
linarith
· have I1 : closedBall x (3 * ((K + 1) * r)) ⊆ closedBall y ((4 * K + 3) * r) := by
apply closedBall_subset_closedBall'
linarith
have I2 : closedBall y ((4 * K + 3) * r) ⊆ closedBall y (max (4 * K + 3) 3 * r) := by
apply closedBall_subset_closedBall
exact mul_le_mul_of_nonneg_right (le_max_left _ _) rpos.le
apply (measure_mono (I1.trans I2)).trans
exact measure_mul_le_scalingConstantOf_mul _
⟨zero_lt_three.trans_le (le_max_right _ _), le_rfl⟩ hr
· refine ⟨R / 4, H, ?_⟩
have : closedBall x (3 * (R / 4)) ⊆ closedBall y r := by
apply closedBall_subset_closedBall'
have A : y ∈ closedBall y r := mem_closedBall_self rpos.le
have B := mem_closedBall'.1 (H A)
linarith
apply (measure_mono this).trans _
refine le_mul_of_one_le_left (zero_le _) ?_
exact ENNReal.one_le_coe_iff.2 (le_max_right _ _)
theorem tendsto_closedBall_filterAt {K : ℝ} {x : α} {ι : Type*} {l : Filter ι} (w : ι → α)
(δ : ι → ℝ) (δlim : Tendsto δ l (𝓝[>] 0)) (xmem : ∀ᶠ j in l, x ∈ closedBall (w j) (K * δ j)) :
Tendsto (fun j => closedBall (w j) (δ j)) l ((vitaliFamily μ K).filterAt x) := by
refine (vitaliFamily μ K).tendsto_filterAt_iff.mpr ⟨?_, fun ε hε => ?_⟩
· filter_upwards [xmem, δlim self_mem_nhdsWithin] with j hj h'j
exact closedBall_mem_vitaliFamily_of_dist_le_mul μ hj h'j
· rcases l.eq_or_neBot with rfl | h
· simp
have hK : 0 ≤ K := by
rcases (xmem.and (δlim self_mem_nhdsWithin)).exists with ⟨j, hj, h'j⟩
have : 0 ≤ K * δ j := nonempty_closedBall.1 ⟨x, hj⟩
exact (mul_nonneg_iff_left_nonneg_of_pos (mem_Ioi.1 h'j)).1 this
have δpos := eventually_mem_of_tendsto_nhdsWithin δlim
replace δlim := tendsto_nhds_of_tendsto_nhdsWithin δlim
replace hK : 0 < K + 1 := by linarith
apply (((Metric.tendsto_nhds.mp δlim _ (div_pos hε hK)).and δpos).and xmem).mono
rintro j ⟨⟨hjε, hj₀ : 0 < δ j⟩, hx⟩ y hy
replace hjε : (K + 1) * δ j < ε := by
simpa [abs_eq_self.mpr hj₀.le] using (lt_div_iff₀' hK).mp hjε
simp only [mem_closedBall] at hx hy ⊢
linarith [dist_triangle_right y x (w j)]
end
section Applications
variable [SecondCountableTopology α] [BorelSpace α] [IsLocallyFiniteMeasure μ] {E : Type*}
[NormedAddCommGroup E]
/-- A version of **Lebesgue's density theorem** for a sequence of closed balls whose centers are
not required to be fixed.
See also `Besicovitch.ae_tendsto_measure_inter_div`. -/
theorem ae_tendsto_measure_inter_div (S : Set α) (K : ℝ) : ∀ᵐ x ∂μ.restrict S,
∀ {ι : Type*} {l : Filter ι} (w : ι → α) (δ : ι → ℝ) (_ : Tendsto δ l (𝓝[>] 0))
(_ : ∀ᶠ j in l, x ∈ closedBall (w j) (K * δ j)),
Tendsto (fun j => μ (S ∩ closedBall (w j) (δ j)) / μ (closedBall (w j) (δ j))) l (𝓝 1) := by
filter_upwards [(vitaliFamily μ K).ae_tendsto_measure_inter_div S] with x hx ι l w δ δlim
| xmem using hx.comp (tendsto_closedBall_filterAt μ _ _ δlim xmem)
/-- A version of **Lebesgue differentiation theorem** for a sequence of closed balls whose
centers are not required to be fixed. -/
theorem ae_tendsto_average_norm_sub {f : α → E} (hf : LocallyIntegrable f μ) (K : ℝ) : ∀ᵐ x ∂μ,
∀ {ι : Type*} {l : Filter ι} (w : ι → α) (δ : ι → ℝ) (_ : Tendsto δ l (𝓝[>] 0))
| Mathlib/MeasureTheory/Covering/DensityTheorem.lean | 146 | 151 |
/-
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.ConditionalProbability
import Mathlib.Probability.Kernel.Basic
import Mathlib.Probability.Kernel.Composition.MeasureComp
import Mathlib.Tactic.Peel
import Mathlib.MeasureTheory.MeasurableSpace.Pi
/-!
# Independence with respect to a kernel and a measure
A family of sets of sets `π : ι → Set (Set Ω)` is independent with respect to a kernel
`κ : Kernel α Ω` and a measure `μ` on `α` 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 for `μ`-almost every `a : α`,
`κ a (⋂ i in s, f i) = ∏ i ∈ s, κ a (f i)`.
This notion of independence is a generalization of both independence and conditional independence.
For conditional independence, `κ` is the conditional kernel `ProbabilityTheory.condExpKernel` and
`μ` is the ambient measure. For (non-conditional) independence, `κ = Kernel.const Unit μ` and the
measure is the Dirac measure on `Unit`.
The main purpose of this file is to prove only once the properties that hold for both conditional
and non-conditional independence.
## Main definitions
* `ProbabilityTheory.Kernel.iIndepSets`: independence of a family of sets of sets.
Variant for two sets of sets: `ProbabilityTheory.Kernel.IndepSets`.
* `ProbabilityTheory.Kernel.iIndep`: independence of a family of σ-algebras. Variant for two
σ-algebras: `Indep`.
* `ProbabilityTheory.Kernel.iIndepSet`: independence of a family of sets. Variant for two sets:
`ProbabilityTheory.Kernel.IndepSet`.
* `ProbabilityTheory.Kernel.iIndepFun`: independence of a family of functions (random variables).
Variant for two functions: `ProbabilityTheory.Kernel.IndepFun`.
See the file `Mathlib/Probability/Kernel/Basic.lean` for a more detailed discussion of these
definitions in the particular case of the usual independence notion.
## Main statements
* `ProbabilityTheory.Kernel.iIndepSets.iIndep`: if π-systems are independent as sets of sets,
then the measurable space structures they generate are independent.
* `ProbabilityTheory.Kernel.IndepSets.Indep`: variant with two π-systems.
-/
open Set MeasureTheory MeasurableSpace
open scoped MeasureTheory ENNReal
namespace ProbabilityTheory.Kernel
variable {α Ω ι : Type*}
section Definitions
variable {_mα : MeasurableSpace α}
/-- A family of sets of sets `π : ι → Set (Set Ω)` is independent with respect to a kernel `κ` and
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 `∀ᵐ a ∂μ, κ a (⋂ i in s, f i) = ∏ i ∈ s, κ a (f i)`.
It will be used for families of pi_systems. -/
def iIndepSets {_mΩ : MeasurableSpace Ω}
(π : ι → Set (Set Ω)) (κ : Kernel α Ω) (μ : Measure α := by volume_tac) : Prop :=
∀ (s : Finset ι) {f : ι → Set Ω} (_H : ∀ i, i ∈ s → f i ∈ π i),
∀ᵐ a ∂μ, κ a (⋂ i ∈ s, f i) = ∏ i ∈ s, κ a (f i)
/-- Two sets of sets `s₁, s₂` are independent with respect to a kernel `κ` and a measure `μ` if for
any sets `t₁ ∈ s₁, t₂ ∈ s₂`, then `∀ᵐ a ∂μ, κ a (t₁ ∩ t₂) = κ a (t₁) * κ a (t₂)` -/
def IndepSets {_mΩ : MeasurableSpace Ω}
(s1 s2 : Set (Set Ω)) (κ : Kernel α Ω) (μ : Measure α := by volume_tac) : Prop :=
∀ t1 t2 : Set Ω, t1 ∈ s1 → t2 ∈ s2 → (∀ᵐ a ∂μ, κ a (t1 ∩ t2) = κ a t1 * κ a t2)
/-- A family of measurable space structures (i.e. of σ-algebras) is independent with respect to a
kernel `κ` and a measure `μ` if the family of sets of measurable sets they define is independent. -/
def iIndep (m : ι → MeasurableSpace Ω) {_mΩ : MeasurableSpace Ω} (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
iIndepSets (fun x ↦ {s | MeasurableSet[m x] s}) κ μ
/-- Two measurable space structures (or σ-algebras) `m₁, m₂` are independent with respect to a
kernel `κ` and a measure `μ` if for any sets `t₁ ∈ m₁, t₂ ∈ m₂`,
`∀ᵐ a ∂μ, κ a (t₁ ∩ t₂) = κ a (t₁) * κ a (t₂)` -/
def Indep (m₁ m₂ : MeasurableSpace Ω) {_mΩ : MeasurableSpace Ω} (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
IndepSets {s | MeasurableSet[m₁] s} {s | MeasurableSet[m₂] s} κ μ
/-- A family of sets is independent if the family of measurable space structures they generate is
independent. For a set `s`, the generated measurable space has measurable sets `∅, s, sᶜ, univ`. -/
def iIndepSet {_mΩ : MeasurableSpace Ω} (s : ι → Set Ω) (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
iIndep (m := fun i ↦ generateFrom {s i}) κ μ
/-- Two sets are independent if the two measurable space structures they generate are independent.
For a set `s`, the generated measurable space structure has measurable sets `∅, s, sᶜ, univ`. -/
def IndepSet {_mΩ : MeasurableSpace Ω} (s t : Set Ω) (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
Indep (generateFrom {s}) (generateFrom {t}) κ μ
/-- A family of functions defined on the same space `Ω` and taking values in possibly different
spaces, each with a measurable space structure, is independent if the family of measurable space
structures they generate on `Ω` is independent. For a function `g` with codomain having measurable
space structure `m`, the generated measurable space structure is `MeasurableSpace.comap g m`. -/
def iIndepFun {_mΩ : MeasurableSpace Ω} {β : ι → Type*} [m : ∀ x : ι, MeasurableSpace (β x)]
(f : ∀ x : ι, Ω → β x) (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
iIndep (m := fun x ↦ MeasurableSpace.comap (f x) (m x)) κ μ
/-- Two functions are independent if the two measurable space structures they generate are
independent. For a function `f` with codomain having measurable space structure `m`, the generated
measurable space structure is `MeasurableSpace.comap f m`. -/
def IndepFun {β γ} {_mΩ : MeasurableSpace Ω} [mβ : MeasurableSpace β] [mγ : MeasurableSpace γ]
(f : Ω → β) (g : Ω → γ) (κ : Kernel α Ω)
(μ : Measure α := by volume_tac) : Prop :=
Indep (MeasurableSpace.comap f mβ) (MeasurableSpace.comap g mγ) κ μ
end Definitions
section ByDefinition
variable {β : ι → Type*} {mβ : ∀ i, MeasurableSpace (β i)}
{_mα : MeasurableSpace α} {m : ι → MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ η : Kernel α Ω} {μ : Measure α}
{π : ι → Set (Set Ω)} {s : ι → Set Ω} {S : Finset ι} {f : ∀ x : ι, Ω → β x}
{s1 s2 : Set (Set Ω)}
@[simp] lemma iIndepSets_zero_right : iIndepSets π κ 0 := by simp [iIndepSets]
@[simp] lemma indepSets_zero_right : IndepSets s1 s2 κ 0 := by simp [IndepSets]
@[simp] lemma indepSets_zero_left : IndepSets s1 s2 (0 : Kernel α Ω) μ := by simp [IndepSets]
@[simp] lemma iIndep_zero_right : iIndep m κ 0 := by simp [iIndep]
@[simp] lemma indep_zero_right {m₁ m₂ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} : Indep m₁ m₂ κ 0 := by simp [Indep]
@[simp] lemma indep_zero_left {m₁ m₂ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω} :
Indep m₁ m₂ (0 : Kernel α Ω) μ := by simp [Indep]
@[simp] lemma iIndepSet_zero_right : iIndepSet s κ 0 := by simp [iIndepSet]
@[simp] lemma indepSet_zero_right {s t : Set Ω} : IndepSet s t κ 0 := by simp [IndepSet]
@[simp] lemma indepSet_zero_left {s t : Set Ω} : IndepSet s t (0 : Kernel α Ω) μ := by
simp [IndepSet]
@[simp] lemma iIndepFun_zero_right {β : ι → Type*} {m : ∀ x : ι, MeasurableSpace (β x)}
{f : ∀ x : ι, Ω → β x} : iIndepFun f κ 0 := by simp [iIndepFun]
@[simp] lemma indepFun_zero_right {β γ} [MeasurableSpace β] [MeasurableSpace γ]
{f : Ω → β} {g : Ω → γ} : IndepFun f g κ 0 := by simp [IndepFun]
@[simp] lemma indepFun_zero_left {β γ} [MeasurableSpace β] [MeasurableSpace γ]
{f : Ω → β} {g : Ω → γ} : IndepFun f g (0 : Kernel α Ω) μ := by simp [IndepFun]
lemma iIndepSets_congr (h : κ =ᵐ[μ] η) : iIndepSets π κ μ ↔ iIndepSets π η μ := by
peel 3
refine ⟨fun h' ↦ ?_, fun h' ↦ ?_⟩ <;>
· filter_upwards [h, h'] with a ha h'a
simpa [ha] using h'a
alias ⟨iIndepSets.congr, _⟩ := iIndepSets_congr
lemma indepSets_congr (h : κ =ᵐ[μ] η) : IndepSets s1 s2 κ μ ↔ IndepSets s1 s2 η μ := by
peel 4
refine ⟨fun h' ↦ ?_, fun h' ↦ ?_⟩ <;>
· filter_upwards [h, h'] with a ha h'a
simpa [ha] using h'a
alias ⟨IndepSets.congr, _⟩ := indepSets_congr
lemma iIndep_congr (h : κ =ᵐ[μ] η) : iIndep m κ μ ↔ iIndep m η μ :=
iIndepSets_congr h
alias ⟨iIndep.congr, _⟩ := iIndep_congr
lemma indep_congr {m₁ m₂ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ η : Kernel α Ω} (h : κ =ᵐ[μ] η) : Indep m₁ m₂ κ μ ↔ Indep m₁ m₂ η μ :=
indepSets_congr h
alias ⟨Indep.congr, _⟩ := indep_congr
lemma iIndepSet_congr (h : κ =ᵐ[μ] η) : iIndepSet s κ μ ↔ iIndepSet s η μ :=
iIndep_congr h
alias ⟨iIndepSet.congr, _⟩ := iIndepSet_congr
lemma indepSet_congr {s t : Set Ω} (h : κ =ᵐ[μ] η) : IndepSet s t κ μ ↔ IndepSet s t η μ :=
indep_congr h
alias ⟨indepSet.congr, _⟩ := indepSet_congr
lemma iIndepFun_congr {β : ι → Type*} {m : ∀ x : ι, MeasurableSpace (β x)}
{f : ∀ x : ι, Ω → β x} (h : κ =ᵐ[μ] η) : iIndepFun f κ μ ↔ iIndepFun f η μ :=
iIndep_congr h
alias ⟨iIndepFun.congr, _⟩ := iIndepFun_congr
lemma indepFun_congr {β γ} [MeasurableSpace β] [MeasurableSpace γ]
{f : Ω → β} {g : Ω → γ} (h : κ =ᵐ[μ] η) : IndepFun f g κ μ ↔ IndepFun f g η μ :=
indep_congr h
alias ⟨IndepFun.congr, _⟩ := indepFun_congr
lemma iIndepSets.meas_biInter (h : iIndepSets π κ μ) (s : Finset ι)
{f : ι → Set Ω} (hf : ∀ i, i ∈ s → f i ∈ π i) :
∀ᵐ a ∂μ, κ a (⋂ i ∈ s, f i) = ∏ i ∈ s, κ a (f i) := h s hf
lemma iIndepSets.ae_isProbabilityMeasure (h : iIndepSets π κ μ) :
∀ᵐ a ∂μ, IsProbabilityMeasure (κ a) := by
filter_upwards [h.meas_biInter ∅ (f := fun _ ↦ Set.univ) (by simp)] with a ha
exact ⟨by simpa using ha⟩
lemma iIndepSets.meas_iInter [Fintype ι] (h : iIndepSets π κ μ) (hs : ∀ i, s i ∈ π i) :
∀ᵐ a ∂μ, κ a (⋂ i, s i) = ∏ i, κ a (s i) := by
filter_upwards [h.meas_biInter Finset.univ (fun _i _ ↦ hs _)] with a ha using by simp [← ha]
lemma iIndep.iIndepSets' (hμ : iIndep m κ μ) :
iIndepSets (fun x ↦ {s | MeasurableSet[m x] s}) κ μ := hμ
lemma iIndep.ae_isProbabilityMeasure (h : iIndep m κ μ) :
∀ᵐ a ∂μ, IsProbabilityMeasure (κ a) :=
h.iIndepSets'.ae_isProbabilityMeasure
lemma iIndep.meas_biInter (hμ : iIndep m κ μ) (hs : ∀ i, i ∈ S → MeasurableSet[m i] (s i)) :
∀ᵐ a ∂μ, κ a (⋂ i ∈ S, s i) = ∏ i ∈ S, κ a (s i) := hμ _ hs
lemma iIndep.meas_iInter [Fintype ι] (h : iIndep m κ μ) (hs : ∀ i, MeasurableSet[m i] (s i)) :
∀ᵐ a ∂μ, κ a (⋂ i, s i) = ∏ i, κ a (s i) := by
filter_upwards [h.meas_biInter (fun i (_ : i ∈ Finset.univ) ↦ hs _)] with a ha
simp [← ha]
@[nontriviality, simp]
lemma iIndepSets.of_subsingleton [Subsingleton ι] {m : ι → Set (Set Ω)} {κ : Kernel α Ω}
[IsMarkovKernel κ] : iIndepSets m κ μ := by
rintro s f hf
obtain rfl | ⟨i, rfl⟩ : s = ∅ ∨ ∃ i, s = {i} := by
simpa using (subsingleton_of_subsingleton (s := s.toSet)).eq_empty_or_singleton
all_goals simp
@[nontriviality, simp]
lemma iIndep.of_subsingleton [Subsingleton ι] {m : ι → MeasurableSpace Ω} {κ : Kernel α Ω}
[IsMarkovKernel κ] : iIndep m κ μ := by simp [iIndep]
@[nontriviality, simp]
lemma iIndepFun.of_subsingleton [Subsingleton ι] {β : ι → Type*} {m : ∀ i, MeasurableSpace (β i)}
{f : ∀ i, Ω → β i} [IsMarkovKernel κ] : iIndepFun f κ μ := by
simp [iIndepFun]
protected lemma iIndepFun.iIndep (hf : iIndepFun f κ μ) :
iIndep (fun x ↦ (mβ x).comap (f x)) κ μ := hf
lemma iIndepFun.ae_isProbabilityMeasure (h : iIndepFun f κ μ) :
∀ᵐ a ∂μ, IsProbabilityMeasure (κ a) :=
h.iIndep.ae_isProbabilityMeasure
lemma iIndepFun.meas_biInter (hf : iIndepFun f κ μ)
(hs : ∀ i, i ∈ S → MeasurableSet[(mβ i).comap (f i)] (s i)) :
∀ᵐ a ∂μ, κ a (⋂ i ∈ S, s i) = ∏ i ∈ S, κ a (s i) := hf.iIndep.meas_biInter hs
lemma iIndepFun.meas_iInter [Fintype ι] (hf : iIndepFun f κ μ)
(hs : ∀ i, MeasurableSet[(mβ i).comap (f i)] (s i)) :
∀ᵐ a ∂μ, κ a (⋂ i, s i) = ∏ i, κ a (s i) := hf.iIndep.meas_iInter hs
lemma IndepFun.meas_inter {β γ : Type*} [mβ : MeasurableSpace β] [mγ : MeasurableSpace γ]
{f : Ω → β} {g : Ω → γ} (hfg : IndepFun f g κ μ)
{s t : Set Ω} (hs : MeasurableSet[mβ.comap f] s) (ht : MeasurableSet[mγ.comap g] t) :
∀ᵐ a ∂μ, κ a (s ∩ t) = κ a s * κ a t := hfg _ _ hs ht
end ByDefinition
section Indep
variable {_mα : MeasurableSpace α}
@[symm]
theorem IndepSets.symm {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω} {μ : Measure α}
{s₁ s₂ : Set (Set Ω)} (h : IndepSets s₁ s₂ κ μ) :
IndepSets s₂ s₁ κ μ := by
intros t1 t2 ht1 ht2
filter_upwards [h t2 t1 ht2 ht1] with a ha
rwa [Set.inter_comm, mul_comm]
@[symm]
theorem Indep.symm {m₁ m₂ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
{μ : Measure α} (h : Indep m₁ m₂ κ μ) :
Indep m₂ m₁ κ μ :=
IndepSets.symm h
theorem indep_bot_right (m' : MeasurableSpace Ω) {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ] :
Indep m' ⊥ κ μ := by
intros s t _ ht
rw [Set.mem_setOf_eq, MeasurableSpace.measurableSet_bot_iff] at ht
rcases eq_zero_or_isMarkovKernel κ with rfl| h
· simp
refine Filter.Eventually.of_forall (fun a ↦ ?_)
rcases ht with ht | ht
· rw [ht, Set.inter_empty, measure_empty, mul_zero]
· rw [ht, Set.inter_univ, measure_univ, mul_one]
theorem indep_bot_left (m' : MeasurableSpace Ω) {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ] :
Indep ⊥ m' κ μ := (indep_bot_right m').symm
theorem indepSet_empty_right {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ] (s : Set Ω) :
IndepSet s ∅ κ μ := by
simp only [IndepSet, generateFrom_singleton_empty]
exact indep_bot_right _
theorem indepSet_empty_left {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
{μ : Measure α} [IsZeroOrMarkovKernel κ] (s : Set Ω) :
IndepSet ∅ s κ μ :=
(indepSet_empty_right s).symm
theorem indepSets_of_indepSets_of_le_left {s₁ s₂ s₃ : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h_indep : IndepSets s₁ s₂ κ μ) (h31 : s₃ ⊆ s₁) :
IndepSets s₃ s₂ κ μ :=
fun t1 t2 ht1 ht2 => h_indep t1 t2 (Set.mem_of_subset_of_mem h31 ht1) ht2
theorem indepSets_of_indepSets_of_le_right {s₁ s₂ s₃ : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h_indep : IndepSets s₁ s₂ κ μ) (h32 : s₃ ⊆ s₂) :
IndepSets s₁ s₃ κ μ :=
fun t1 t2 ht1 ht2 => h_indep t1 t2 ht1 (Set.mem_of_subset_of_mem h32 ht2)
theorem indep_of_indep_of_le_left {m₁ m₂ m₃ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h_indep : Indep m₁ m₂ κ μ) (h31 : m₃ ≤ m₁) :
Indep m₃ m₂ κ μ :=
fun t1 t2 ht1 ht2 => h_indep t1 t2 (h31 _ ht1) ht2
theorem indep_of_indep_of_le_right {m₁ m₂ m₃ : MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h_indep : Indep m₁ m₂ κ μ) (h32 : m₃ ≤ m₂) :
Indep m₁ m₃ κ μ :=
fun t1 t2 ht1 ht2 => h_indep t1 t2 ht1 (h32 _ ht2)
theorem IndepSets.union {s₁ s₂ s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α}
(h₁ : IndepSets s₁ s' κ μ) (h₂ : IndepSets s₂ s' κ μ) :
IndepSets (s₁ ∪ s₂) s' κ μ := by
intro t1 t2 ht1 ht2
rcases (Set.mem_union _ _ _).mp ht1 with ht1₁ | ht1₂
· exact h₁ t1 t2 ht1₁ ht2
· exact h₂ t1 t2 ht1₂ ht2
@[simp]
theorem IndepSets.union_iff {s₁ s₂ s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} :
IndepSets (s₁ ∪ s₂) s' κ μ ↔ IndepSets s₁ s' κ μ ∧ IndepSets s₂ s' κ μ :=
⟨fun h =>
⟨indepSets_of_indepSets_of_le_left h Set.subset_union_left,
indepSets_of_indepSets_of_le_left h Set.subset_union_right⟩,
fun h => IndepSets.union h.left h.right⟩
theorem IndepSets.iUnion {s : ι → Set (Set Ω)} {s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (hyp : ∀ n, IndepSets (s n) s' κ μ) :
IndepSets (⋃ n, s n) s' κ μ := by
intro t1 t2 ht1 ht2
rw [Set.mem_iUnion] at ht1
obtain ⟨n, ht1⟩ := ht1
exact hyp n t1 t2 ht1 ht2
theorem IndepSets.bUnion {s : ι → Set (Set Ω)} {s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} {u : Set ι} (hyp : ∀ n ∈ u, IndepSets (s n) s' κ μ) :
IndepSets (⋃ n ∈ u, s n) s' κ μ := by
intro t1 t2 ht1 ht2
simp_rw [Set.mem_iUnion] at ht1
rcases ht1 with ⟨n, hpn, ht1⟩
exact hyp n hpn t1 t2 ht1 ht2
theorem IndepSets.inter {s₁ s' : Set (Set Ω)} (s₂ : Set (Set Ω)) {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h₁ : IndepSets s₁ s' κ μ) :
IndepSets (s₁ ∩ s₂) s' κ μ :=
fun t1 t2 ht1 ht2 => h₁ t1 t2 ((Set.mem_inter_iff _ _ _).mp ht1).left ht2
theorem IndepSets.iInter {s : ι → Set (Set Ω)} {s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h : ∃ n, IndepSets (s n) s' κ μ) :
IndepSets (⋂ n, s n) s' κ μ := by
intro t1 t2 ht1 ht2; obtain ⟨n, h⟩ := h; exact h t1 t2 (Set.mem_iInter.mp ht1 n) ht2
theorem IndepSets.bInter {s : ι → Set (Set Ω)} {s' : Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} {u : Set ι} (h : ∃ n ∈ u, IndepSets (s n) s' κ μ) :
IndepSets (⋂ n ∈ u, s n) s' κ μ := by
intro t1 t2 ht1 ht2
rcases h with ⟨n, hn, h⟩
exact h t1 t2 (Set.biInter_subset_of_mem hn ht1) ht2
theorem iIndep_comap_mem_iff {f : ι → Set Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} :
iIndep (fun i => MeasurableSpace.comap (· ∈ f i) ⊤) κ μ ↔ iIndepSet f κ μ := by
simp_rw [← generateFrom_singleton, iIndepSet]
theorem iIndepSets_singleton_iff {s : ι → Set Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} :
iIndepSets (fun i ↦ {s i}) κ μ ↔
∀ S : Finset ι, ∀ᵐ a ∂μ, κ a (⋂ i ∈ S, s i) = ∏ i ∈ S, κ a (s i) := by
refine ⟨fun h S ↦ h S (fun i _ ↦ rfl), fun h S f hf ↦ ?_⟩
filter_upwards [h S] with a ha
have : ∀ i ∈ S, κ a (f i) = κ a (s i) := fun i hi ↦ by rw [hf i hi]
rwa [Finset.prod_congr rfl this, Set.iInter₂_congr hf]
theorem indepSets_singleton_iff {s t : Set Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} :
IndepSets {s} {t} κ μ ↔ ∀ᵐ a ∂μ, κ a (s ∩ t) = κ a s * κ a t :=
⟨fun h ↦ h s t rfl rfl,
fun h s1 t1 hs1 ht1 ↦ by rwa [Set.mem_singleton_iff.mp hs1, Set.mem_singleton_iff.mp ht1]⟩
end Indep
/-! ### Deducing `Indep` from `iIndep` -/
section FromiIndepToIndep
variable {_mα : MeasurableSpace α}
theorem iIndepSets.indepSets {s : ι → Set (Set Ω)} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} (h_indep : iIndepSets s κ μ) {i j : ι} (hij : i ≠ j) :
IndepSets (s i) (s j) κ μ := by
classical
intro t₁ t₂ ht₁ ht₂
have hf_m : ∀ x : ι, x ∈ ({i, j} : Finset ι) → ite (x = i) t₁ t₂ ∈ s x := by
intro x hx
rcases Finset.mem_insert.mp hx with hx | hx
· simp [hx, ht₁]
· simp [Finset.mem_singleton.mp hx, hij.symm, ht₂]
have h1 : t₁ = ite (i = i) t₁ t₂ := by simp only [if_true, eq_self_iff_true]
have h2 : t₂ = ite (j = i) t₁ t₂ := by simp only [hij.symm, if_false]
have h_inter : ⋂ (t : ι) (_ : t ∈ ({i, j} : Finset ι)), ite (t = i) t₁ t₂ =
ite (i = i) t₁ t₂ ∩ ite (j = i) t₁ t₂ := by
simp only [Finset.set_biInter_singleton, Finset.set_biInter_insert]
filter_upwards [h_indep {i, j} hf_m] with a h_indep'
have h_prod : (∏ t ∈ ({i, j} : Finset ι), κ a (ite (t = i) t₁ t₂))
= κ a (ite (i = i) t₁ t₂) * κ a (ite (j = i) t₁ t₂) := by
simp only [hij, Finset.prod_singleton, Finset.prod_insert, not_false_iff,
Finset.mem_singleton]
rw [h1]
nth_rw 2 [h2]
nth_rw 4 [h2]
rw [← h_inter, ← h_prod, h_indep']
theorem iIndep.indep {m : ι → MeasurableSpace Ω} {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α}
(h_indep : iIndep m κ μ) {i j : ι} (hij : i ≠ j) : Indep (m i) (m j) κ μ :=
iIndepSets.indepSets h_indep hij
theorem iIndepFun.indepFun {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} {β : ι → Type*}
{m : ∀ x, MeasurableSpace (β x)} {f : ∀ i, Ω → β i} (hf_Indep : iIndepFun f κ μ) {i j : ι}
(hij : i ≠ j) : IndepFun (f i) (f j) κ μ :=
hf_Indep.indep hij
end FromiIndepToIndep
/-!
## π-system lemma
Independence of measurable spaces is equivalent to independence of generating π-systems.
-/
section FromMeasurableSpacesToSetsOfSets
/-! ### Independence of measurable space structures implies independence of generating π-systems -/
variable {_mα : MeasurableSpace α}
theorem iIndep.iIndepSets {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} {m : ι → MeasurableSpace Ω}
{s : ι → Set (Set Ω)} (hms : ∀ n, m n = generateFrom (s n)) (h_indep : iIndep m κ μ) :
iIndepSets s κ μ :=
fun S f hfs =>
h_indep S fun x hxS =>
((hms x).symm ▸ measurableSet_generateFrom (hfs x hxS) : MeasurableSet[m x] (f x))
theorem Indep.indepSets {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} {s1 s2 : Set (Set Ω)}
(h_indep : Indep (generateFrom s1) (generateFrom s2) κ μ) :
IndepSets s1 s2 κ μ :=
fun t1 t2 ht1 ht2 =>
h_indep t1 t2 (measurableSet_generateFrom ht1) (measurableSet_generateFrom ht2)
end FromMeasurableSpacesToSetsOfSets
section FromPiSystemsToMeasurableSpaces
/-! ### Independence of generating π-systems implies independence of measurable space structures -/
variable {_mα : MeasurableSpace α}
theorem IndepSets.indep_aux {m₂ m : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ] {p1 p2 : Set (Set Ω)} (h2 : m₂ ≤ m)
(hp2 : IsPiSystem p2) (hpm2 : m₂ = generateFrom p2) (hyp : IndepSets p1 p2 κ μ) {t1 t2 : Set Ω}
(ht1 : t1 ∈ p1) (ht1m : MeasurableSet[m] t1) (ht2m : MeasurableSet[m₂] t2) :
∀ᵐ a ∂μ, κ a (t1 ∩ t2) = κ a t1 * κ a t2 := by
rcases eq_zero_or_isMarkovKernel κ with rfl | h
· simp
induction t2, ht2m using induction_on_inter hpm2 hp2 with
| empty => simp
| basic u hu => exact hyp t1 u ht1 hu
| compl u hu ihu =>
filter_upwards [ihu] with a ha
rw [← Set.diff_eq, ← Set.diff_self_inter,
measure_diff inter_subset_left (ht1m.inter (h2 _ hu)).nullMeasurableSet (measure_ne_top _ _),
ha, measure_compl (h2 _ hu) (measure_ne_top _ _), measure_univ, ENNReal.mul_sub, mul_one]
exact fun _ _ ↦ measure_ne_top _ _
| iUnion f hfd hfm ihf =>
rw [← ae_all_iff] at ihf
filter_upwards [ihf] with a ha
rw [inter_iUnion, measure_iUnion, measure_iUnion hfd fun i ↦ h2 _ (hfm i)]
· simp only [ENNReal.tsum_mul_left, ha]
· exact hfd.mono fun i j h ↦ (h.inter_left' _).inter_right' _
· exact fun i ↦ .inter ht1m (h2 _ <| hfm i)
/-- The measurable space structures generated by independent pi-systems are independent. -/
theorem IndepSets.indep {m1 m2 m : MeasurableSpace Ω} {κ : Kernel α Ω} {μ : Measure α}
[IsZeroOrMarkovKernel κ] {p1 p2 : Set (Set Ω)} (h1 : m1 ≤ m) (h2 : m2 ≤ m) (hp1 : IsPiSystem p1)
(hp2 : IsPiSystem p2) (hpm1 : m1 = generateFrom p1) (hpm2 : m2 = generateFrom p2)
(hyp : IndepSets p1 p2 κ μ) :
Indep m1 m2 κ μ := by
rcases eq_zero_or_isMarkovKernel κ with rfl | h
· simp
intros t1 t2 ht1 ht2
induction t1, ht1 using induction_on_inter hpm1 hp1 with
| empty =>
simp only [Set.empty_inter, measure_empty, zero_mul, eq_self_iff_true, Filter.eventually_true]
| basic t ht =>
refine IndepSets.indep_aux h2 hp2 hpm2 hyp ht (h1 _ ?_) ht2
rw [hpm1]
exact measurableSet_generateFrom ht
| compl t ht iht =>
filter_upwards [iht] with a ha
have : tᶜ ∩ t2 = t2 \ (t ∩ t2) := by
rw [Set.inter_comm t, Set.diff_self_inter, Set.diff_eq_compl_inter]
rw [this, Set.inter_comm t t2,
measure_diff Set.inter_subset_left ((h2 _ ht2).inter (h1 _ ht)).nullMeasurableSet
(measure_ne_top (κ a) _),
Set.inter_comm, ha, measure_compl (h1 _ ht) (measure_ne_top (κ a) t), measure_univ,
mul_comm (1 - κ a t), ENNReal.mul_sub (fun _ _ ↦ measure_ne_top (κ a) _), mul_one, mul_comm]
| iUnion f hf_disj hf_meas h =>
rw [← ae_all_iff] at h
filter_upwards [h] with a ha
rw [Set.inter_comm, Set.inter_iUnion, measure_iUnion]
· rw [measure_iUnion hf_disj (fun i ↦ h1 _ (hf_meas i))]
rw [← ENNReal.tsum_mul_right]
congr 1 with i
rw [Set.inter_comm t2, ha i]
· intros i j hij
rw [Function.onFun, Set.inter_comm t2, Set.inter_comm t2]
exact Disjoint.inter_left _ (Disjoint.inter_right _ (hf_disj hij))
· exact fun i ↦ (h2 _ ht2).inter (h1 _ (hf_meas i))
theorem IndepSets.indep' {_mΩ : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ]
{p1 p2 : Set (Set Ω)} (hp1m : ∀ s ∈ p1, MeasurableSet s) (hp2m : ∀ s ∈ p2, MeasurableSet s)
(hp1 : IsPiSystem p1) (hp2 : IsPiSystem p2) (hyp : IndepSets p1 p2 κ μ) :
Indep (generateFrom p1) (generateFrom p2) κ μ :=
hyp.indep (generateFrom_le hp1m) (generateFrom_le hp2m) hp1 hp2 rfl rfl
variable {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω} {μ : Measure α}
theorem indepSets_piiUnionInter_of_disjoint {s : ι → Set (Set Ω)}
{S T : Set ι} (h_indep : iIndepSets s κ μ) (hST : Disjoint S T) :
IndepSets (piiUnionInter s S) (piiUnionInter s T) κ μ := by
rintro t1 t2 ⟨p1, hp1, f1, ht1_m, ht1_eq⟩ ⟨p2, hp2, f2, ht2_m, ht2_eq⟩
classical
let g i := ite (i ∈ p1) (f1 i) Set.univ ∩ ite (i ∈ p2) (f2 i) Set.univ
have h_P_inter : ∀ᵐ a ∂μ, κ a (t1 ∩ t2) = ∏ n ∈ p1 ∪ p2, κ a (g n) := by
have hgm : ∀ i ∈ p1 ∪ p2, g i ∈ s i := by
intro i hi_mem_union
rw [Finset.mem_union] at hi_mem_union
rcases hi_mem_union with hi1 | hi2
· have hi2 : i ∉ p2 := fun hip2 => Set.disjoint_left.mp hST (hp1 hi1) (hp2 hip2)
simp_rw [g, if_pos hi1, if_neg hi2, Set.inter_univ]
exact ht1_m i hi1
· have hi1 : i ∉ p1 := fun hip1 => Set.disjoint_right.mp hST (hp2 hi2) (hp1 hip1)
simp_rw [g, if_neg hi1, if_pos hi2, Set.univ_inter]
exact ht2_m i hi2
have h_p1_inter_p2 :
((⋂ x ∈ p1, f1 x) ∩ ⋂ x ∈ p2, f2 x) =
⋂ i ∈ p1 ∪ p2, ite (i ∈ p1) (f1 i) Set.univ ∩ ite (i ∈ p2) (f2 i) Set.univ := by
ext1 x
simp only [Set.mem_ite_univ_right, Set.mem_inter_iff, Set.mem_iInter, Finset.mem_union]
exact
⟨fun h i _ => ⟨h.1 i, h.2 i⟩, fun h =>
⟨fun i hi => (h i (Or.inl hi)).1 hi, fun i hi => (h i (Or.inr hi)).2 hi⟩⟩
filter_upwards [h_indep _ hgm] with a ha
rw [ht1_eq, ht2_eq, h_p1_inter_p2, ← ha]
filter_upwards [h_P_inter, h_indep p1 ht1_m, h_indep p2 ht2_m, h_indep.ae_isProbabilityMeasure]
with a h_P_inter ha1 ha2 h'
have h_μg : ∀ n, κ a (g n) = (ite (n ∈ p1) (κ a (f1 n)) 1) * (ite (n ∈ p2) (κ a (f2 n)) 1) := by
intro n
dsimp only [g]
split_ifs with h1 h2
· exact absurd rfl (Set.disjoint_iff_forall_ne.mp hST (hp1 h1) (hp2 h2))
all_goals simp only [measure_univ, one_mul, mul_one, Set.inter_univ, Set.univ_inter]
simp_rw [h_P_inter, h_μg, Finset.prod_mul_distrib,
Finset.prod_ite_mem (p1 ∪ p2) p1 (fun x ↦ κ a (f1 x)), Finset.union_inter_cancel_left,
Finset.prod_ite_mem (p1 ∪ p2) p2 (fun x => κ a (f2 x)), Finset.union_inter_cancel_right, ht1_eq,
← ha1, ht2_eq, ← ha2]
theorem iIndepSet.indep_generateFrom_of_disjoint {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iIndepSet s κ μ) (S T : Set ι) (hST : Disjoint S T) :
Indep (generateFrom { t | ∃ n ∈ S, s n = t }) (generateFrom { t | ∃ k ∈ T, s k = t }) κ μ := by
classical
rcases eq_or_ne μ 0 with rfl | hμ
· simp
obtain ⟨η, η_eq, hη⟩ : ∃ (η : Kernel α Ω), κ =ᵐ[μ] η ∧ IsMarkovKernel η :=
exists_ae_eq_isMarkovKernel hs.ae_isProbabilityMeasure hμ
apply Indep.congr (Filter.EventuallyEq.symm η_eq)
rw [← generateFrom_piiUnionInter_singleton_left, ← generateFrom_piiUnionInter_singleton_left]
refine
IndepSets.indep'
(fun t ht => generateFrom_piiUnionInter_le _ ?_ _ _ (measurableSet_generateFrom ht))
(fun t ht => generateFrom_piiUnionInter_le _ ?_ _ _ (measurableSet_generateFrom ht)) ?_ ?_ ?_
· exact fun k => generateFrom_le fun t ht => (Set.mem_singleton_iff.1 ht).symm ▸ hsm k
· exact fun k => generateFrom_le fun t ht => (Set.mem_singleton_iff.1 ht).symm ▸ hsm k
· exact isPiSystem_piiUnionInter _ (fun k => IsPiSystem.singleton _) _
· exact isPiSystem_piiUnionInter _ (fun k => IsPiSystem.singleton _) _
· exact indepSets_piiUnionInter_of_disjoint (iIndep.iIndepSets (fun n => rfl) (hs.congr η_eq)) hST
theorem indep_iSup_of_disjoint {m : ι → MeasurableSpace Ω}
(h_le : ∀ i, m i ≤ _mΩ) (h_indep : iIndep m κ μ) {S T : Set ι} (hST : Disjoint S T) :
Indep (⨆ i ∈ S, m i) (⨆ i ∈ T, m i) κ μ := by
classical
rcases eq_or_ne μ 0 with rfl | hμ
· simp
obtain ⟨η, η_eq, hη⟩ : ∃ (η : Kernel α Ω), κ =ᵐ[μ] η ∧ IsMarkovKernel η :=
exists_ae_eq_isMarkovKernel h_indep.ae_isProbabilityMeasure hμ
apply Indep.congr (Filter.EventuallyEq.symm η_eq)
refine
IndepSets.indep (iSup₂_le fun i _ => h_le i) (iSup₂_le fun i _ => h_le i) ?_ ?_
(generateFrom_piiUnionInter_measurableSet m S).symm
(generateFrom_piiUnionInter_measurableSet m T).symm ?_
· exact isPiSystem_piiUnionInter _ (fun n => @isPiSystem_measurableSet Ω (m n)) _
· exact isPiSystem_piiUnionInter _ (fun n => @isPiSystem_measurableSet Ω (m n)) _
· exact indepSets_piiUnionInter_of_disjoint (h_indep.congr η_eq) hST
theorem indep_iSup_of_directed_le {Ω} {m : ι → MeasurableSpace Ω} {m' m0 : MeasurableSpace Ω}
{κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ] (h_indep : ∀ i, Indep (m i) m' κ μ)
(h_le : ∀ i, m i ≤ m0) (h_le' : m' ≤ m0) (hm : Directed (· ≤ ·) m) :
Indep (⨆ i, m i) m' κ μ := by
let p : ι → Set (Set Ω) := fun n => { t | MeasurableSet[m n] t }
have hp : ∀ n, IsPiSystem (p n) := fun n => @isPiSystem_measurableSet Ω (m n)
have h_gen_n : ∀ n, m n = generateFrom (p n) := fun n =>
(@generateFrom_measurableSet Ω (m n)).symm
have hp_supr_pi : IsPiSystem (⋃ n, p n) := isPiSystem_iUnion_of_directed_le p hp hm
let p' := { t : Set Ω | MeasurableSet[m'] t }
have hp'_pi : IsPiSystem p' := @isPiSystem_measurableSet Ω m'
have h_gen' : m' = generateFrom p' := (@generateFrom_measurableSet Ω m').symm
-- the π-systems defined are independent
have h_pi_system_indep : IndepSets (⋃ n, p n) p' κ μ := by
refine IndepSets.iUnion ?_
conv at h_indep =>
intro i
rw [h_gen_n i, h_gen']
exact fun n => (h_indep n).indepSets
-- now go from π-systems to σ-algebras
refine IndepSets.indep (iSup_le h_le) h_le' hp_supr_pi hp'_pi ?_ h_gen' h_pi_system_indep
exact (generateFrom_iUnion_measurableSet _).symm
theorem iIndepSet.indep_generateFrom_lt [Preorder ι] {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iIndepSet s κ μ) (i : ι) :
Indep (generateFrom {s i}) (generateFrom { t | ∃ j < i, s j = t }) κ μ := by
convert iIndepSet.indep_generateFrom_of_disjoint hsm hs {i} { j | j < i }
(Set.disjoint_singleton_left.mpr (lt_irrefl _)) using 1
simp only [Set.mem_singleton_iff, exists_prop, exists_eq_left, Set.setOf_eq_eq_singleton']
theorem iIndepSet.indep_generateFrom_le [Preorder ι] {s : ι → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iIndepSet s κ μ) (i : ι) {k : ι} (hk : i < k) :
Indep (generateFrom {s k}) (generateFrom { t | ∃ j ≤ i, s j = t }) κ μ := by
convert iIndepSet.indep_generateFrom_of_disjoint hsm hs {k} { j | j ≤ i }
(Set.disjoint_singleton_left.mpr hk.not_le) using 1
simp only [Set.mem_singleton_iff, exists_prop, exists_eq_left, Set.setOf_eq_eq_singleton']
theorem iIndepSet.indep_generateFrom_le_nat {s : ℕ → Set Ω}
(hsm : ∀ n, MeasurableSet (s n)) (hs : iIndepSet s κ μ) (n : ℕ) :
Indep (generateFrom {s (n + 1)}) (generateFrom { t | ∃ k ≤ n, s k = t }) κ μ :=
iIndepSet.indep_generateFrom_le hsm hs _ n.lt_succ_self
theorem indep_iSup_of_monotone [SemilatticeSup ι] {Ω} {m : ι → MeasurableSpace Ω}
{m' m0 : MeasurableSpace Ω} {κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ]
(h_indep : ∀ i, Indep (m i) m' κ μ) (h_le : ∀ i, m i ≤ m0) (h_le' : m' ≤ m0)
(hm : Monotone m) :
Indep (⨆ i, m i) m' κ μ :=
indep_iSup_of_directed_le h_indep h_le h_le' (Monotone.directed_le hm)
theorem indep_iSup_of_antitone [SemilatticeInf ι] {Ω} {m : ι → MeasurableSpace Ω}
{m' m0 : MeasurableSpace Ω} {κ : Kernel α Ω} {μ : Measure α} [IsZeroOrMarkovKernel κ]
(h_indep : ∀ i, Indep (m i) m' κ μ) (h_le : ∀ i, m i ≤ m0) (h_le' : m' ≤ m0)
(hm : Antitone m) :
Indep (⨆ i, m i) m' κ μ :=
indep_iSup_of_directed_le h_indep h_le h_le' hm.directed_le
theorem iIndepSets.piiUnionInter_of_not_mem {π : ι → Set (Set Ω)} {a : ι} {S : Finset ι}
(hp_ind : iIndepSets π κ μ) (haS : a ∉ S) :
IndepSets (piiUnionInter π S) (π a) κ μ := by
rintro t1 t2 ⟨s, hs_mem, ft1, hft1_mem, ht1_eq⟩ ht2_mem_pia
rw [Finset.coe_subset] at hs_mem
classical
let f := fun n => ite (n = a) t2 (ite (n ∈ s) (ft1 n) Set.univ)
have h_f_mem : ∀ n ∈ insert a s, f n ∈ π n := by
intro n hn_mem_insert
dsimp only [f]
rcases Finset.mem_insert.mp hn_mem_insert with hn_mem | hn_mem
· simp [hn_mem, ht2_mem_pia]
· have hn_ne_a : n ≠ a := by rintro rfl; exact haS (hs_mem hn_mem)
simp [hn_ne_a, hn_mem, hft1_mem n hn_mem]
have h_f_mem_pi : ∀ n ∈ s, f n ∈ π n := fun x hxS => h_f_mem x (by simp [hxS])
have h_t1 : t1 = ⋂ n ∈ s, f n := by
suffices h_forall : ∀ n ∈ s, f n = ft1 n by
rw [ht1_eq]
ext x
simp_rw [Set.mem_iInter]
conv => lhs; intro i hns; rw [← h_forall i hns]
intro n hnS
have hn_ne_a : n ≠ a := by rintro rfl; exact haS (hs_mem hnS)
simp_rw [f, if_pos hnS, if_neg hn_ne_a]
have h_μ_t1 : ∀ᵐ a' ∂μ, κ a' t1 = ∏ n ∈ s, κ a' (f n) := by
filter_upwards [hp_ind s h_f_mem_pi] with a' ha'
rw [h_t1, ← ha']
have h_t2 : t2 = f a := by simp [f]
have h_μ_inter : ∀ᵐ a' ∂μ, κ a' (t1 ∩ t2) = ∏ n ∈ insert a s, κ a' (f n) := by
have h_t1_inter_t2 : t1 ∩ t2 = ⋂ n ∈ insert a s, f n := by
rw [h_t1, h_t2, Finset.set_biInter_insert, Set.inter_comm]
filter_upwards [hp_ind (insert a s) h_f_mem] with a' ha'
rw [h_t1_inter_t2, ← ha']
have has : a ∉ s := fun has_mem => haS (hs_mem has_mem)
filter_upwards [h_μ_t1, h_μ_inter] with a' ha1 ha2
rw [ha2, Finset.prod_insert has, h_t2, mul_comm, ha1]
/-- The measurable space structures generated by independent pi-systems are independent. -/
theorem iIndepSets.iIndep (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 : iIndepSets π κ μ) :
iIndep m κ μ := by
classical
rcases eq_or_ne μ 0 with rfl | hμ
· simp
obtain ⟨η, η_eq, hη⟩ : ∃ (η : Kernel α Ω), κ =ᵐ[μ] η ∧ IsMarkovKernel η :=
exists_ae_eq_isMarkovKernel h_ind.ae_isProbabilityMeasure hμ
apply iIndep.congr (Filter.EventuallyEq.symm η_eq)
intro s f
refine Finset.induction ?_ ?_ s
· simp only [Finset.not_mem_empty, Set.mem_setOf_eq, IsEmpty.forall_iff, implies_true,
Set.iInter_of_empty, Set.iInter_univ, measure_univ, Finset.prod_empty,
Filter.eventually_true, forall_true_left]
· intro a S ha_notin_S h_rec hf_m
have hf_m_S : ∀ x ∈ S, MeasurableSet[m x] (f x) := fun x hx => hf_m x (by simp [hx])
let p := piiUnionInter π S
set m_p := generateFrom p with hS_eq_generate
have h_indep : Indep m_p (m a) η μ := by
have hp : IsPiSystem p := isPiSystem_piiUnionInter π h_pi S
have h_le' : ∀ i, generateFrom (π i) ≤ _mΩ := fun i ↦ (h_generate i).symm.trans_le (h_le i)
have hm_p : m_p ≤ _mΩ := generateFrom_piiUnionInter_le π h_le' S
exact IndepSets.indep hm_p (h_le a) hp (h_pi a) hS_eq_generate (h_generate a)
(iIndepSets.piiUnionInter_of_not_mem (h_ind.congr η_eq) ha_notin_S)
have h := h_indep.symm (f a) (⋂ n ∈ S, f n) (hf_m a (Finset.mem_insert_self a S)) ?_
· filter_upwards [h_rec hf_m_S, h] with a' ha' h'
rwa [Finset.set_biInter_insert, Finset.prod_insert ha_notin_S, ← ha']
· have h_le_p : ∀ i ∈ S, m i ≤ m_p := by
intros n hn
rw [hS_eq_generate, h_generate n]
exact le_generateFrom_piiUnionInter (S : Set ι) hn
have h_S_f : ∀ i ∈ S, MeasurableSet[m_p] (f i) :=
fun i hi ↦ (h_le_p i hi) (f i) (hf_m_S i hi)
exact S.measurableSet_biInter h_S_f
end FromPiSystemsToMeasurableSpaces
section IndepSet
/-! ### Independence of measurable sets
We prove the following equivalences on `IndepSet`, for measurable sets `s, t`.
* `IndepSet s t κ μ ↔ ∀ᵐ a ∂μ, κ a (s ∩ t) = κ a s * κ a t`,
* `IndepSet s t κ μ ↔ IndepSets {s} {t} κ μ`.
-/
variable {_mα : MeasurableSpace α}
theorem iIndepSet_iff_iIndepSets_singleton {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
{μ : Measure α} {f : ι → Set Ω} (hf : ∀ i, MeasurableSet (f i)) :
iIndepSet f κ μ ↔ iIndepSets (fun i ↦ {f i}) κ μ :=
⟨iIndep.iIndepSets fun _ ↦ rfl,
iIndepSets.iIndep _ (fun i ↦ generateFrom_le <| by rintro t (rfl : t = _); exact hf _) _
(fun _ ↦ IsPiSystem.singleton _) fun _ ↦ rfl⟩
theorem iIndepSet.meas_biInter {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
{μ : Measure α} {f : ι → Set Ω} (h : iIndepSet f κ μ) (s : Finset ι) :
| ∀ᵐ a ∂μ, κ a (⋂ i ∈ s, f i) = ∏ i ∈ s, κ a (f i) :=
iIndep.iIndepSets (fun _ ↦ rfl) h _ (by simp)
theorem iIndepSet_iff_meas_biInter {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
{μ : Measure α} {f : ι → Set Ω} (hf : ∀ i, MeasurableSet (f i)) :
iIndepSet f κ μ ↔ ∀ s, ∀ᵐ a ∂μ, κ a (⋂ i ∈ s, f i) = ∏ i ∈ s, κ a (f i) :=
(iIndepSet_iff_iIndepSets_singleton hf).trans iIndepSets_singleton_iff
theorem iIndepSets.iIndepSet_of_mem {_mΩ : MeasurableSpace Ω} {κ : Kernel α Ω}
| Mathlib/Probability/Independence/Kernel.lean | 793 | 801 |
/-
Copyright (c) 2020 Kenny Lau. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kenny Lau
-/
import Mathlib.Algebra.CharP.Algebra
import Mathlib.Data.Multiset.Fintype
import Mathlib.FieldTheory.IsAlgClosed.Basic
import Mathlib.FieldTheory.SplittingField.Construction
/-!
# Algebraic Closure
In this file we construct the algebraic closure of a field
## Main Definitions
- `AlgebraicClosure k` is an algebraic closure of `k` (in the same universe).
It is constructed by taking the polynomial ring generated by indeterminates
$X_{f,1}, \dots, X_{f,\deg f}$ corresponding to roots of monic irreducible
polynomials `f` with coefficients in `k`, and quotienting out by a maximal
ideal containing every $f - \prod_i (X - X_{f,i})$. The proof follows
https://kconrad.math.uconn.edu/blurbs/galoistheory/algclosureshorter.pdf.
## Tags
algebraic closure, algebraically closed
-/
universe u v w
noncomputable section
open Polynomial
variable (k : Type u) [Field k]
namespace AlgebraicClosure
/-- The subtype of monic polynomials. -/
def Monics : Type u := {f : k[X] // f.Monic}
/-- `Vars k` provides `n` variables $X_{f,1}, \dots, X_{f,n}$ for each monic polynomial
`f : k[X]` of degree `n`. -/
def Vars : Type u := Σ f : Monics k, Fin f.1.natDegree
variable {k} in
/-- Given a monic polynomial `f : k[X]`,
`subProdXSubC f` is the polynomial $f - \prod_i (X - X_{f,i})$. -/
def subProdXSubC (f : Monics k) : (MvPolynomial (Vars k) k)[X] :=
f.1.map (algebraMap _ _) - ∏ i : Fin f.1.natDegree, (X - C (MvPolynomial.X ⟨f, i⟩))
/-- The span of all coefficients of `subProdXSubC f` as `f` ranges all polynomials in `k[X]`. -/
def spanCoeffs : Ideal (MvPolynomial (Vars k) k) :=
Ideal.span <| Set.range fun fn : Monics k × ℕ ↦ (subProdXSubC fn.1).coeff fn.2
variable {k}
/-- If a monic polynomial `f : k[X]` splits in `K`,
then it has as many roots (counting multiplicity) as its degree. -/
def finEquivRoots {K} [Field K] [DecidableEq K] {i : k →+* K} {f : Monics k} (hf : f.1.Splits i) :
Fin f.1.natDegree ≃ (f.1.map i).roots.toEnumFinset :=
.symm <| Finset.equivFinOfCardEq <| by
rwa [← splits_id_iff_splits, splits_iff_card_roots,
← Multiset.card_toEnumFinset, f.2.natDegree_map] at hf
lemma Monics.splits_finsetProd {s : Finset (Monics k)} {f : Monics k} (hf : f ∈ s) :
f.1.Splits (algebraMap k (SplittingField (∏ f ∈ s, f.1))) :=
(splits_prod_iff _ fun j _ ↦ j.2.ne_zero).1 (SplittingField.splits _) _ hf
open Classical in
/-- Given a finite set of monic polynomials, construct an algebra homomorphism
to the splitting field of the product of the polynomials
sending indeterminates $X_{f_i}$ to the distinct roots of `f`. -/
def toSplittingField (s : Finset (Monics k)) :
MvPolynomial (Vars k) k →ₐ[k] SplittingField (∏ f ∈ s, f.1) :=
MvPolynomial.aeval fun fi ↦
if hf : fi.1 ∈ s then (finEquivRoots (Monics.splits_finsetProd hf) fi.2).1.1 else 37
theorem toSplittingField_coeff {s : Finset (Monics k)} {f} (h : f ∈ s) (n) :
toSplittingField s ((subProdXSubC f).coeff n) = 0 := by
classical
simp_rw [← AlgHom.coe_toRingHom, ← coeff_map, subProdXSubC, Polynomial.map_sub,
Polynomial.map_prod, Polynomial.map_sub, map_X, map_C, toSplittingField,
AlgHom.coe_toRingHom, MvPolynomial.aeval_X, dif_pos h,
← (finEquivRoots (Monics.splits_finsetProd h)).symm.prod_comp, Equiv.apply_symm_apply]
rw [Finset.prod_coe_sort (f := fun x : _ × ℕ ↦ X - C x.1), (Multiset.toEnumFinset _)
|>.prod_eq_multiset_prod, ← Function.comp_def (X - C ·) Prod.fst, ← Multiset.map_map,
Multiset.map_toEnumFinset_fst, map_map, AlgHom.comp_algebraMap]
conv in map _ _ => rw [eq_prod_roots_of_splits (Monics.splits_finsetProd h)]
rw [f.2, map_one, C_1, one_mul, sub_self, coeff_zero]
variable (k)
theorem spanCoeffs_ne_top : spanCoeffs k ≠ ⊤ := by
rw [Ideal.ne_top_iff_one, spanCoeffs, Ideal.span, ← Set.image_univ,
Finsupp.mem_span_image_iff_linearCombination]
rintro ⟨v, _, hv⟩
classical
replace hv := congr_arg (toSplittingField <| v.support.image Prod.fst) hv
rw [map_one, Finsupp.linearCombination_apply, Finsupp.sum, map_sum, Finset.sum_eq_zero] at hv
· exact zero_ne_one hv
intro j hj
rw [smul_eq_mul, map_mul, toSplittingField_coeff (Finset.mem_image_of_mem _ hj), mul_zero]
/-- A random maximal ideal that contains `spanEval k` -/
def maxIdeal : Ideal (MvPolynomial (Vars k) k) :=
Classical.choose <| Ideal.exists_le_maximal _ <| spanCoeffs_ne_top k
instance maxIdeal.isMaximal : (maxIdeal k).IsMaximal :=
(Classical.choose_spec <| Ideal.exists_le_maximal _ <| spanCoeffs_ne_top k).1
theorem le_maxIdeal : spanCoeffs k ≤ maxIdeal k :=
(Classical.choose_spec <| Ideal.exists_le_maximal _ <| spanCoeffs_ne_top k).2
end AlgebraicClosure
open AlgebraicClosure in
/-- The canonical algebraic closure of a field, the direct limit of adding roots to the field for
each polynomial over the field. -/
@[stacks 09GT]
def AlgebraicClosure : Type u :=
MvPolynomial (Vars k) k ⧸ maxIdeal k
namespace AlgebraicClosure
instance instCommRing : CommRing (AlgebraicClosure k) := Ideal.Quotient.commRing _
instance instInhabited : Inhabited (AlgebraicClosure k) := ⟨37⟩
instance {S : Type*} [DistribSMul S k] [IsScalarTower S k k] : SMul S (AlgebraicClosure k) :=
Submodule.Quotient.instSMul' _
instance instAlgebra {R : Type*} [CommSemiring R] [Algebra R k] : Algebra R (AlgebraicClosure k) :=
Ideal.Quotient.algebra _
instance {R S : Type*} [CommSemiring R] [CommSemiring S] [Algebra R S] [Algebra S k] [Algebra R k]
[IsScalarTower R S k] : IsScalarTower R S (AlgebraicClosure k) :=
Ideal.Quotient.isScalarTower _ _ _
instance instGroupWithZero : GroupWithZero (AlgebraicClosure k) where
__ := Ideal.Quotient.field _
instance instField : Field (AlgebraicClosure k) where
__ := instCommRing _
__ := instGroupWithZero _
nnqsmul := (· • ·)
qsmul := (· • ·)
nnratCast q := algebraMap k _ q
ratCast q := algebraMap k _ q
nnratCast_def q := by change algebraMap k _ _ = _; simp_rw [NNRat.cast_def, map_div₀, map_natCast]
ratCast_def q := by
change algebraMap k _ _ = _; rw [Rat.cast_def, map_div₀, map_intCast, map_natCast]
nnqsmul_def q x := Quotient.inductionOn x fun p ↦ congr_arg Quotient.mk'' <| by
ext; simp [MvPolynomial.algebraMap_eq, NNRat.smul_def]
qsmul_def q x := Quotient.inductionOn x fun p ↦ congr_arg Quotient.mk'' <| by
ext; simp [MvPolynomial.algebraMap_eq, Rat.smul_def]
theorem Monics.map_eq_prod {f : Monics k} :
f.1.map (algebraMap k (AlgebraicClosure k)) =
∏ i, map (Ideal.Quotient.mk <| maxIdeal k) (X - C (MvPolynomial.X ⟨f, i⟩)) := by
ext
dsimp [AlgebraicClosure]
rw [← Ideal.Quotient.mk_comp_algebraMap, ← map_map, ← Polynomial.map_prod, ← sub_eq_zero,
← coeff_sub, ← Polynomial.map_sub, ← subProdXSubC, coeff_map, Ideal.Quotient.eq_zero_iff_mem]
refine le_maxIdeal _ (Ideal.subset_span ⟨⟨f, _⟩, rfl⟩)
instance isAlgebraic : Algebra.IsAlgebraic k (AlgebraicClosure k) :=
⟨fun z =>
IsIntegral.isAlgebraic <| by
let ⟨p, hp⟩ := Ideal.Quotient.mk_surjective z
rw [← hp]
induction p using MvPolynomial.induction_on generalizing z with
| C => exact isIntegral_algebraMap
| add _ _ ha hb => exact (ha _ rfl).add (hb _ rfl)
| mul_X p fi ih =>
rw [map_mul]
refine (ih _ rfl).mul ⟨_, fi.1.2, ?_⟩
simp_rw [← eval_map, Monics.map_eq_prod, eval_prod, Polynomial.map_sub, eval_sub]
apply Finset.prod_eq_zero (Finset.mem_univ fi.2)
rw [map_C]
-- The `erw` is needed here because the `R` in `eval` is `AlgebraicClosure k`,
-- but this has been unfolded in the arguments of `eval`.
erw [eval_C]
simp⟩
instance : IsAlgClosure k (AlgebraicClosure k) := .of_splits fun f hf _ ↦ by
rw [show f = (⟨f, hf⟩ : Monics k) from rfl, ← splits_id_iff_splits, Monics.map_eq_prod]
exact splits_prod _ fun _ _ ↦ (splits_id_iff_splits _).mpr (splits_X_sub_C _)
instance isAlgClosed : IsAlgClosed (AlgebraicClosure k) := IsAlgClosure.isAlgClosed k
instance [CharZero k] : CharZero (AlgebraicClosure k) :=
charZero_of_injective_algebraMap (RingHom.injective (algebraMap k (AlgebraicClosure k)))
instance {p : ℕ} [CharP k p] : CharP (AlgebraicClosure k) p :=
charP_of_injective_algebraMap (RingHom.injective (algebraMap k (AlgebraicClosure k))) p
instance {L : Type*} [Field k] [Field L] [Algebra k L] [Algebra.IsAlgebraic k L] :
IsAlgClosure k (AlgebraicClosure L) where
isAlgebraic := .trans k L _
isAlgClosed := inferInstance
end AlgebraicClosure
| Mathlib/FieldTheory/IsAlgClosed/AlgebraicClosure.lean | 348 | 357 | |
/-
Copyright (c) 2022 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Probability.IdentDistrib
import Mathlib.Probability.Independence.Integrable
import Mathlib.MeasureTheory.Integral.DominatedConvergence
import Mathlib.Analysis.SpecificLimits.FloorPow
import Mathlib.Analysis.PSeries
import Mathlib.Analysis.Asymptotics.SpecificAsymptotics
/-!
# The strong law of large numbers
We prove the strong law of large numbers, in `ProbabilityTheory.strong_law_ae`:
If `X n` is a sequence of independent identically distributed integrable random
variables, then `∑ i ∈ range n, X i / n` converges almost surely to `𝔼[X 0]`.
We give here the strong version, due to Etemadi, that only requires pairwise independence.
This file also contains the Lᵖ version of the strong law of large numbers provided by
`ProbabilityTheory.strong_law_Lp` which shows `∑ i ∈ range n, X i / n` converges in Lᵖ to
`𝔼[X 0]` provided `X n` is independent identically distributed and is Lᵖ.
## Implementation
The main point is to prove the result for real-valued random variables, as the general case
of Banach-space valued random variables follows from this case and approximation by simple
functions. The real version is given in `ProbabilityTheory.strong_law_ae_real`.
We follow the proof by Etemadi
[Etemadi, *An elementary proof of the strong law of large numbers*][etemadi_strong_law],
which goes as follows.
It suffices to prove the result for nonnegative `X`, as one can prove the general result by
splitting a general `X` into its positive part and negative part.
Consider `Xₙ` a sequence of nonnegative integrable identically distributed pairwise independent
random variables. Let `Yₙ` be the truncation of `Xₙ` up to `n`. We claim that
* Almost surely, `Xₙ = Yₙ` for all but finitely many indices. Indeed, `∑ ℙ (Xₙ ≠ Yₙ)` is bounded by
`1 + 𝔼[X]` (see `sum_prob_mem_Ioc_le` and `tsum_prob_mem_Ioi_lt_top`).
* Let `c > 1`. Along the sequence `n = c ^ k`, then `(∑_{i=0}^{n-1} Yᵢ - 𝔼[Yᵢ])/n` converges almost
surely to `0`. This follows from a variance control, as
```
∑_k ℙ (|∑_{i=0}^{c^k - 1} Yᵢ - 𝔼[Yᵢ]| > c^k ε)
≤ ∑_k (c^k ε)^{-2} ∑_{i=0}^{c^k - 1} Var[Yᵢ] (by Markov inequality)
≤ ∑_i (C/i^2) Var[Yᵢ] (as ∑_{c^k > i} 1/(c^k)^2 ≤ C/i^2)
≤ ∑_i (C/i^2) 𝔼[Yᵢ^2]
≤ 2C 𝔼[X^2] (see `sum_variance_truncation_le`)
```
* As `𝔼[Yᵢ]` converges to `𝔼[X]`, it follows from the two previous items and Cesàro that, along
the sequence `n = c^k`, one has `(∑_{i=0}^{n-1} Xᵢ) / n → 𝔼[X]` almost surely.
* To generalize it to all indices, we use the fact that `∑_{i=0}^{n-1} Xᵢ` is nondecreasing and
that, if `c` is close enough to `1`, the gap between `c^k` and `c^(k+1)` is small.
-/
noncomputable section
open MeasureTheory Filter Finset Asymptotics
open Set (indicator)
open scoped Topology MeasureTheory ProbabilityTheory ENNReal NNReal
open scoped Function -- required for scoped `on` notation
namespace ProbabilityTheory
/-! ### Prerequisites on truncations -/
section Truncation
variable {α : Type*}
/-- Truncating a real-valued function to the interval `(-A, A]`. -/
def truncation (f : α → ℝ) (A : ℝ) :=
indicator (Set.Ioc (-A) A) id ∘ f
variable {m : MeasurableSpace α} {μ : Measure α} {f : α → ℝ}
theorem _root_.MeasureTheory.AEStronglyMeasurable.truncation (hf : AEStronglyMeasurable f μ)
{A : ℝ} : AEStronglyMeasurable (truncation f A) μ := by
apply AEStronglyMeasurable.comp_aemeasurable _ hf.aemeasurable
exact (stronglyMeasurable_id.indicator measurableSet_Ioc).aestronglyMeasurable
theorem abs_truncation_le_bound (f : α → ℝ) (A : ℝ) (x : α) : |truncation f A x| ≤ |A| := by
simp only [truncation, Set.indicator, Set.mem_Icc, id, Function.comp_apply]
split_ifs with h
· exact abs_le_abs h.2 (neg_le.2 h.1.le)
· simp [abs_nonneg]
@[simp]
theorem truncation_zero (f : α → ℝ) : truncation f 0 = 0 := by simp [truncation]; rfl
theorem abs_truncation_le_abs_self (f : α → ℝ) (A : ℝ) (x : α) : |truncation f A x| ≤ |f x| := by
simp only [truncation, indicator, Set.mem_Icc, id, Function.comp_apply]
split_ifs
· exact le_rfl
· simp [abs_nonneg]
theorem truncation_eq_self {f : α → ℝ} {A : ℝ} {x : α} (h : |f x| < A) :
truncation f A x = f x := by
simp only [truncation, indicator, Set.mem_Icc, id, Function.comp_apply, ite_eq_left_iff]
intro H
apply H.elim
simp [(abs_lt.1 h).1, (abs_lt.1 h).2.le]
theorem truncation_eq_of_nonneg {f : α → ℝ} {A : ℝ} (h : ∀ x, 0 ≤ f x) :
truncation f A = indicator (Set.Ioc 0 A) id ∘ f := by
ext x
rcases (h x).lt_or_eq with (hx | hx)
· simp only [truncation, indicator, hx, Set.mem_Ioc, id, Function.comp_apply]
by_cases h'x : f x ≤ A
· have : -A < f x := by linarith [h x]
simp only [this, true_and]
· simp only [h'x, and_false]
· simp only [truncation, indicator, hx, id, Function.comp_apply, ite_self]
theorem truncation_nonneg {f : α → ℝ} (A : ℝ) {x : α} (h : 0 ≤ f x) : 0 ≤ truncation f A x :=
Set.indicator_apply_nonneg fun _ => h
theorem _root_.MeasureTheory.AEStronglyMeasurable.memLp_truncation [IsFiniteMeasure μ]
(hf : AEStronglyMeasurable f μ) {A : ℝ} {p : ℝ≥0∞} : MemLp (truncation f A) p μ :=
MemLp.of_bound hf.truncation |A| (Eventually.of_forall fun _ => abs_truncation_le_bound _ _ _)
theorem _root_.MeasureTheory.AEStronglyMeasurable.integrable_truncation [IsFiniteMeasure μ]
(hf : AEStronglyMeasurable f μ) {A : ℝ} : Integrable (truncation f A) μ := by
rw [← memLp_one_iff_integrable]; exact hf.memLp_truncation
theorem moment_truncation_eq_intervalIntegral (hf : AEStronglyMeasurable f μ) {A : ℝ} (hA : 0 ≤ A)
{n : ℕ} (hn : n ≠ 0) : ∫ x, truncation f A x ^ n ∂μ = ∫ y in -A..A, y ^ n ∂Measure.map f μ := by
have M : MeasurableSet (Set.Ioc (-A) A) := measurableSet_Ioc
change ∫ x, (fun z => indicator (Set.Ioc (-A) A) id z ^ n) (f x) ∂μ = _
rw [← integral_map (f := fun z => _ ^ n) hf.aemeasurable, intervalIntegral.integral_of_le,
← integral_indicator M]
· simp only [indicator, zero_pow hn, id, ite_pow]
· linarith
· exact ((measurable_id.indicator M).pow_const n).aestronglyMeasurable
theorem moment_truncation_eq_intervalIntegral_of_nonneg (hf : AEStronglyMeasurable f μ) {A : ℝ}
{n : ℕ} (hn : n ≠ 0) (h'f : 0 ≤ f) :
∫ x, truncation f A x ^ n ∂μ = ∫ y in (0)..A, y ^ n ∂Measure.map f μ := by
have M : MeasurableSet (Set.Ioc 0 A) := measurableSet_Ioc
have M' : MeasurableSet (Set.Ioc A 0) := measurableSet_Ioc
rw [truncation_eq_of_nonneg h'f]
change ∫ x, (fun z => indicator (Set.Ioc 0 A) id z ^ n) (f x) ∂μ = _
rcases le_or_lt 0 A with (hA | hA)
· rw [← integral_map (f := fun z => _ ^ n) hf.aemeasurable, intervalIntegral.integral_of_le hA,
← integral_indicator M]
· simp only [indicator, zero_pow hn, id, ite_pow]
· exact ((measurable_id.indicator M).pow_const n).aestronglyMeasurable
· rw [← integral_map (f := fun z => _ ^ n) hf.aemeasurable, intervalIntegral.integral_of_ge hA.le,
← integral_indicator M']
· simp only [Set.Ioc_eq_empty_of_le hA.le, zero_pow hn, Set.indicator_empty, integral_zero,
zero_eq_neg]
apply integral_eq_zero_of_ae
have : ∀ᵐ x ∂Measure.map f μ, (0 : ℝ) ≤ x :=
(ae_map_iff hf.aemeasurable measurableSet_Ici).2 (Eventually.of_forall h'f)
filter_upwards [this] with x hx
simp only [indicator, Set.mem_Ioc, Pi.zero_apply, ite_eq_right_iff, and_imp]
intro _ h''x
have : x = 0 := by linarith
simp [this, zero_pow hn]
· exact ((measurable_id.indicator M).pow_const n).aestronglyMeasurable
theorem integral_truncation_eq_intervalIntegral (hf : AEStronglyMeasurable f μ) {A : ℝ}
(hA : 0 ≤ A) : ∫ x, truncation f A x ∂μ = ∫ y in -A..A, y ∂Measure.map f μ := by
simpa using moment_truncation_eq_intervalIntegral hf hA one_ne_zero
theorem integral_truncation_eq_intervalIntegral_of_nonneg (hf : AEStronglyMeasurable f μ) {A : ℝ}
(h'f : 0 ≤ f) : ∫ x, truncation f A x ∂μ = ∫ y in (0)..A, y ∂Measure.map f μ := by
simpa using moment_truncation_eq_intervalIntegral_of_nonneg hf one_ne_zero h'f
theorem integral_truncation_le_integral_of_nonneg (hf : Integrable f μ) (h'f : 0 ≤ f) {A : ℝ} :
∫ x, truncation f A x ∂μ ≤ ∫ x, f x ∂μ := by
apply integral_mono_of_nonneg
(Eventually.of_forall fun x => ?_) hf (Eventually.of_forall fun x => ?_)
· exact truncation_nonneg _ (h'f x)
· calc
truncation f A x ≤ |truncation f A x| := le_abs_self _
_ ≤ |f x| := abs_truncation_le_abs_self _ _ _
_ = f x := abs_of_nonneg (h'f x)
/-- If a function is integrable, then the integral of its truncated versions converges to the
integral of the whole function. -/
theorem tendsto_integral_truncation {f : α → ℝ} (hf : Integrable f μ) :
Tendsto (fun A => ∫ x, truncation f A x ∂μ) atTop (𝓝 (∫ x, f x ∂μ)) := by
refine tendsto_integral_filter_of_dominated_convergence (fun x => abs (f x)) ?_ ?_ ?_ ?_
· exact Eventually.of_forall fun A ↦ hf.aestronglyMeasurable.truncation
· filter_upwards with A
filter_upwards with x
rw [Real.norm_eq_abs]
exact abs_truncation_le_abs_self _ _ _
· exact hf.abs
· filter_upwards with x
apply tendsto_const_nhds.congr' _
filter_upwards [Ioi_mem_atTop (abs (f x))] with A hA
exact (truncation_eq_self hA).symm
| theorem IdentDistrib.truncation {β : Type*} [MeasurableSpace β] {ν : Measure β} {f : α → ℝ}
{g : β → ℝ} (h : IdentDistrib f g μ ν) {A : ℝ} :
IdentDistrib (truncation f A) (truncation g A) μ ν :=
h.comp (measurable_id.indicator measurableSet_Ioc)
end Truncation
section StrongLawAeReal
variable {Ω : Type*} [MeasureSpace Ω] [IsProbabilityMeasure (ℙ : Measure Ω)]
section MomentEstimates
| Mathlib/Probability/StrongLaw.lean | 201 | 213 |
/-
Copyright (c) 2021 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers
-/
import Mathlib.Algebra.BigOperators.Fin
import Mathlib.Algebra.Order.Module.Algebra
import Mathlib.Algebra.Ring.Subring.Units
import Mathlib.LinearAlgebra.LinearIndependent.Defs
import Mathlib.Tactic.LinearCombination
import Mathlib.Tactic.Module
import Mathlib.Tactic.Positivity.Basic
/-!
# Rays in modules
This file defines rays in modules.
## Main definitions
* `SameRay`: two vectors belong to the same ray if they are proportional with a nonnegative
coefficient.
* `Module.Ray` is a type for the equivalence class of nonzero vectors in a module with some
common positive multiple.
-/
noncomputable section
section StrictOrderedCommSemiring
-- TODO: remove `[IsStrictOrderedRing R]` and `@[nolint unusedArguments]`.
/-- Two vectors are in the same ray if either one of them is zero or some positive multiples of them
are equal (in the typical case over a field, this means one of them is a nonnegative multiple of
the other). -/
@[nolint unusedArguments]
def SameRay (R : Type*) [CommSemiring R] [PartialOrder R] [IsStrictOrderedRing R]
{M : Type*} [AddCommMonoid M] [Module R M] (v₁ v₂ : M) : Prop :=
v₁ = 0 ∨ v₂ = 0 ∨ ∃ r₁ r₂ : R, 0 < r₁ ∧ 0 < r₂ ∧ r₁ • v₁ = r₂ • v₂
variable {R : Type*} [CommSemiring R] [PartialOrder R] [IsStrictOrderedRing R]
variable {M : Type*} [AddCommMonoid M] [Module R M]
variable {N : Type*} [AddCommMonoid N] [Module R N]
variable (ι : Type*) [DecidableEq ι]
namespace SameRay
variable {x y z : M}
@[simp]
theorem zero_left (y : M) : SameRay R 0 y :=
Or.inl rfl
@[simp]
theorem zero_right (x : M) : SameRay R x 0 :=
Or.inr <| Or.inl rfl
@[nontriviality]
theorem of_subsingleton [Subsingleton M] (x y : M) : SameRay R x y := by
rw [Subsingleton.elim x 0]
exact zero_left _
@[nontriviality]
theorem of_subsingleton' [Subsingleton R] (x y : M) : SameRay R x y :=
haveI := Module.subsingleton R M
of_subsingleton x y
/-- `SameRay` is reflexive. -/
@[refl]
theorem refl (x : M) : SameRay R x x := by
nontriviality R
exact Or.inr (Or.inr <| ⟨1, 1, zero_lt_one, zero_lt_one, rfl⟩)
protected theorem rfl : SameRay R x x :=
refl _
/-- `SameRay` is symmetric. -/
@[symm]
theorem symm (h : SameRay R x y) : SameRay R y x :=
(or_left_comm.1 h).imp_right <| Or.imp_right fun ⟨r₁, r₂, h₁, h₂, h⟩ => ⟨r₂, r₁, h₂, h₁, h.symm⟩
/-- If `x` and `y` are nonzero vectors on the same ray, then there exist positive numbers `r₁ r₂`
such that `r₁ • x = r₂ • y`. -/
theorem exists_pos (h : SameRay R x y) (hx : x ≠ 0) (hy : y ≠ 0) :
∃ r₁ r₂ : R, 0 < r₁ ∧ 0 < r₂ ∧ r₁ • x = r₂ • y :=
(h.resolve_left hx).resolve_left hy
theorem sameRay_comm : SameRay R x y ↔ SameRay R y x :=
⟨SameRay.symm, SameRay.symm⟩
/-- `SameRay` is transitive unless the vector in the middle is zero and both other vectors are
nonzero. -/
theorem trans (hxy : SameRay R x y) (hyz : SameRay R y z) (hy : y = 0 → x = 0 ∨ z = 0) :
SameRay R x z := by
rcases eq_or_ne x 0 with (rfl | hx); · exact zero_left z
rcases eq_or_ne z 0 with (rfl | hz); · exact zero_right x
rcases eq_or_ne y 0 with (rfl | hy)
· exact (hy rfl).elim (fun h => (hx h).elim) fun h => (hz h).elim
rcases hxy.exists_pos hx hy with ⟨r₁, r₂, hr₁, hr₂, h₁⟩
rcases hyz.exists_pos hy hz with ⟨r₃, r₄, hr₃, hr₄, h₂⟩
refine Or.inr (Or.inr <| ⟨r₃ * r₁, r₂ * r₄, mul_pos hr₃ hr₁, mul_pos hr₂ hr₄, ?_⟩)
rw [mul_smul, mul_smul, h₁, ← h₂, smul_comm]
variable {S : Type*} [CommSemiring S] [PartialOrder S]
[Algebra S R] [Module S M] [SMulPosMono S R]
[IsScalarTower S R M] {a : S}
/-- A vector is in the same ray as a nonnegative multiple of itself. -/
lemma sameRay_nonneg_smul_right (v : M) (h : 0 ≤ a) : SameRay R v (a • v) := by
obtain h | h := (algebraMap_nonneg R h).eq_or_gt
· rw [← algebraMap_smul R a v, h, zero_smul]
exact zero_right _
· refine Or.inr <| Or.inr ⟨algebraMap S R a, 1, h, by nontriviality R; exact zero_lt_one, ?_⟩
module
/-- A nonnegative multiple of a vector is in the same ray as that vector. -/
lemma sameRay_nonneg_smul_left (v : M) (ha : 0 ≤ a) : SameRay R (a • v) v :=
(sameRay_nonneg_smul_right v ha).symm
/-- A vector is in the same ray as a positive multiple of itself. -/
lemma sameRay_pos_smul_right (v : M) (ha : 0 < a) : SameRay R v (a • v) :=
sameRay_nonneg_smul_right v ha.le
/-- A positive multiple of a vector is in the same ray as that vector. -/
lemma sameRay_pos_smul_left (v : M) (ha : 0 < a) : SameRay R (a • v) v :=
sameRay_nonneg_smul_left v ha.le
/-- A vector is in the same ray as a nonnegative multiple of one it is in the same ray as. -/
lemma nonneg_smul_right (h : SameRay R x y) (ha : 0 ≤ a) : SameRay R x (a • y) :=
h.trans (sameRay_nonneg_smul_right y ha) fun hy => Or.inr <| by rw [hy, smul_zero]
/-- A nonnegative multiple of a vector is in the same ray as one it is in the same ray as. -/
lemma nonneg_smul_left (h : SameRay R x y) (ha : 0 ≤ a) : SameRay R (a • x) y :=
(h.symm.nonneg_smul_right ha).symm
/-- A vector is in the same ray as a positive multiple of one it is in the same ray as. -/
theorem pos_smul_right (h : SameRay R x y) (ha : 0 < a) : SameRay R x (a • y) :=
h.nonneg_smul_right ha.le
/-- A positive multiple of a vector is in the same ray as one it is in the same ray as. -/
theorem pos_smul_left (h : SameRay R x y) (hr : 0 < a) : SameRay R (a • x) y :=
h.nonneg_smul_left hr.le
/-- If two vectors are on the same ray then they remain so after applying a linear map. -/
theorem map (f : M →ₗ[R] N) (h : SameRay R x y) : SameRay R (f x) (f y) :=
(h.imp fun hx => by rw [hx, map_zero]) <|
Or.imp (fun hy => by rw [hy, map_zero]) fun ⟨r₁, r₂, hr₁, hr₂, h⟩ =>
⟨r₁, r₂, hr₁, hr₂, by rw [← f.map_smul, ← f.map_smul, h]⟩
/-- The images of two vectors under an injective linear map are on the same ray if and only if the
original vectors are on the same ray. -/
theorem _root_.Function.Injective.sameRay_map_iff
{F : Type*} [FunLike F M N] [LinearMapClass F R M N]
{f : F} (hf : Function.Injective f) :
SameRay R (f x) (f y) ↔ SameRay R x y := by
simp only [SameRay, map_zero, ← hf.eq_iff, map_smul]
/-- The images of two vectors under a linear equivalence are on the same ray if and only if the
original vectors are on the same ray. -/
@[simp]
theorem sameRay_map_iff (e : M ≃ₗ[R] N) : SameRay R (e x) (e y) ↔ SameRay R x y :=
Function.Injective.sameRay_map_iff (EquivLike.injective e)
/-- If two vectors are on the same ray then both scaled by the same action are also on the same
ray. -/
theorem smul {S : Type*} [Monoid S] [DistribMulAction S M] [SMulCommClass R S M]
(h : SameRay R x y) (s : S) : SameRay R (s • x) (s • y) :=
h.map (s • (LinearMap.id : M →ₗ[R] M))
/-- If `x` and `y` are on the same ray as `z`, then so is `x + y`. -/
theorem add_left (hx : SameRay R x z) (hy : SameRay R y z) : SameRay R (x + y) z := by
rcases eq_or_ne x 0 with (rfl | hx₀); · rwa [zero_add]
rcases eq_or_ne y 0 with (rfl | hy₀); · rwa [add_zero]
rcases eq_or_ne z 0 with (rfl | hz₀); · apply zero_right
rcases hx.exists_pos hx₀ hz₀ with ⟨rx, rz₁, hrx, hrz₁, Hx⟩
rcases hy.exists_pos hy₀ hz₀ with ⟨ry, rz₂, hry, hrz₂, Hy⟩
refine Or.inr (Or.inr ⟨rx * ry, ry * rz₁ + rx * rz₂, mul_pos hrx hry, ?_, ?_⟩)
· positivity
· convert congr(ry • $Hx + rx • $Hy) using 1 <;> module
/-- If `y` and `z` are on the same ray as `x`, then so is `y + z`. -/
theorem add_right (hy : SameRay R x y) (hz : SameRay R x z) : SameRay R x (y + z) :=
(hy.symm.add_left hz.symm).symm
end SameRay
set_option linter.unusedVariables false in
/-- Nonzero vectors, as used to define rays. This type depends on an unused argument `R` so that
`RayVector.Setoid` can be an instance. -/
@[nolint unusedArguments]
def RayVector (R M : Type*) [Zero M] :=
{ v : M // v ≠ 0 }
instance RayVector.coe [Zero M] : CoeOut (RayVector R M) M where
coe := Subtype.val
instance {R M : Type*} [Zero M] [Nontrivial M] : Nonempty (RayVector R M) :=
let ⟨x, hx⟩ := exists_ne (0 : M)
⟨⟨x, hx⟩⟩
variable (R M)
/-- The setoid of the `SameRay` relation for the subtype of nonzero vectors. -/
instance RayVector.Setoid : Setoid (RayVector R M) where
r x y := SameRay R (x : M) y
iseqv :=
⟨fun _ => SameRay.refl _, fun h => h.symm, by
intros x y z hxy hyz
exact hxy.trans hyz fun hy => (y.2 hy).elim⟩
/-- A ray (equivalence class of nonzero vectors with common positive multiples) in a module. -/
def Module.Ray :=
Quotient (RayVector.Setoid R M)
variable {R M}
/-- Equivalence of nonzero vectors, in terms of `SameRay`. -/
theorem equiv_iff_sameRay {v₁ v₂ : RayVector R M} : v₁ ≈ v₂ ↔ SameRay R (v₁ : M) v₂ :=
Iff.rfl
variable (R)
/-- The ray given by a nonzero vector. -/
def rayOfNeZero (v : M) (h : v ≠ 0) : Module.Ray R M :=
⟦⟨v, h⟩⟧
/-- An induction principle for `Module.Ray`, used as `induction x using Module.Ray.ind`. -/
theorem Module.Ray.ind {C : Module.Ray R M → Prop} (h : ∀ (v) (hv : v ≠ 0), C (rayOfNeZero R v hv))
(x : Module.Ray R M) : C x :=
Quotient.ind (Subtype.rec <| h) x
variable {R}
instance [Nontrivial M] : Nonempty (Module.Ray R M) :=
Nonempty.map Quotient.mk' inferInstance
/-- The rays given by two nonzero vectors are equal if and only if those vectors
satisfy `SameRay`. -/
theorem ray_eq_iff {v₁ v₂ : M} (hv₁ : v₁ ≠ 0) (hv₂ : v₂ ≠ 0) :
rayOfNeZero R _ hv₁ = rayOfNeZero R _ hv₂ ↔ SameRay R v₁ v₂ :=
Quotient.eq'
/-- The ray given by a positive multiple of a nonzero vector. -/
@[simp]
theorem ray_pos_smul {v : M} (h : v ≠ 0) {r : R} (hr : 0 < r) (hrv : r • v ≠ 0) :
rayOfNeZero R (r • v) hrv = rayOfNeZero R v h :=
(ray_eq_iff _ _).2 <| SameRay.sameRay_pos_smul_left v hr
/-- An equivalence between modules implies an equivalence between ray vectors. -/
def RayVector.mapLinearEquiv (e : M ≃ₗ[R] N) : RayVector R M ≃ RayVector R N :=
Equiv.subtypeEquiv e.toEquiv fun _ => e.map_ne_zero_iff.symm
/-- An equivalence between modules implies an equivalence between rays. -/
def Module.Ray.map (e : M ≃ₗ[R] N) : Module.Ray R M ≃ Module.Ray R N :=
Quotient.congr (RayVector.mapLinearEquiv e) fun _ _=> (SameRay.sameRay_map_iff _).symm
@[simp]
theorem Module.Ray.map_apply (e : M ≃ₗ[R] N) (v : M) (hv : v ≠ 0) :
Module.Ray.map e (rayOfNeZero _ v hv) = rayOfNeZero _ (e v) (e.map_ne_zero_iff.2 hv) :=
rfl
@[simp]
theorem Module.Ray.map_refl : (Module.Ray.map <| LinearEquiv.refl R M) = Equiv.refl _ :=
Equiv.ext <| Module.Ray.ind R fun _ _ => rfl
@[simp]
theorem Module.Ray.map_symm (e : M ≃ₗ[R] N) : (Module.Ray.map e).symm = Module.Ray.map e.symm :=
rfl
section Action
variable {G : Type*} [Group G] [DistribMulAction G M]
/-- Any invertible action preserves the non-zeroness of ray vectors. This is primarily of interest
when `G = Rˣ` -/
instance {R : Type*} : MulAction G (RayVector R M) where
smul r := Subtype.map (r • ·) fun _ => (smul_ne_zero_iff_ne _).2
mul_smul a b _ := Subtype.ext <| mul_smul a b _
one_smul _ := Subtype.ext <| one_smul _ _
variable [SMulCommClass R G M]
/-- Any invertible action preserves the non-zeroness of rays. This is primarily of interest when
`G = Rˣ` -/
instance : MulAction G (Module.Ray R M) where
smul r := Quotient.map (r • ·) fun _ _ h => h.smul _
mul_smul a b := Quotient.ind fun _ => congr_arg Quotient.mk' <| mul_smul a b _
one_smul := Quotient.ind fun _ => congr_arg Quotient.mk' <| one_smul _ _
/-- The action via `LinearEquiv.apply_distribMulAction` corresponds to `Module.Ray.map`. -/
@[simp]
theorem Module.Ray.linearEquiv_smul_eq_map (e : M ≃ₗ[R] M) (v : Module.Ray R M) :
e • v = Module.Ray.map e v :=
rfl
@[simp]
theorem smul_rayOfNeZero (g : G) (v : M) (hv) :
g • rayOfNeZero R v hv = rayOfNeZero R (g • v) ((smul_ne_zero_iff_ne _).2 hv) :=
rfl
end Action
namespace Module.Ray
/-- Scaling by a positive unit is a no-op. -/
theorem units_smul_of_pos (u : Rˣ) (hu : 0 < (u : R)) (v : Module.Ray R M) : u • v = v := by
induction v using Module.Ray.ind
rw [smul_rayOfNeZero, ray_eq_iff]
exact SameRay.sameRay_pos_smul_left _ hu
/-- An arbitrary `RayVector` giving a ray. -/
def someRayVector (x : Module.Ray R M) : RayVector R M :=
Quotient.out x
/-- The ray of `someRayVector`. -/
@[simp]
theorem someRayVector_ray (x : Module.Ray R M) : (⟦x.someRayVector⟧ : Module.Ray R M) = x :=
Quotient.out_eq _
/-- An arbitrary nonzero vector giving a ray. -/
def someVector (x : Module.Ray R M) : M :=
x.someRayVector
/-- `someVector` is nonzero. -/
@[simp]
theorem someVector_ne_zero (x : Module.Ray R M) : x.someVector ≠ 0 :=
x.someRayVector.property
/-- The ray of `someVector`. -/
@[simp]
theorem someVector_ray (x : Module.Ray R M) : rayOfNeZero R _ x.someVector_ne_zero = x :=
(congr_arg _ (Subtype.coe_eta _ _) :).trans x.out_eq
end Module.Ray
end StrictOrderedCommSemiring
section StrictOrderedCommRing
variable {R : Type*} [CommRing R] [PartialOrder R] [IsStrictOrderedRing R]
variable {M N : Type*} [AddCommGroup M] [AddCommGroup N] [Module R M] [Module R N] {x y : M}
/-- `SameRay.neg` as an `iff`. -/
@[simp]
theorem sameRay_neg_iff : SameRay R (-x) (-y) ↔ SameRay R x y := by
simp only [SameRay, neg_eq_zero, smul_neg, neg_inj]
alias ⟨SameRay.of_neg, SameRay.neg⟩ := sameRay_neg_iff
theorem sameRay_neg_swap : SameRay R (-x) y ↔ SameRay R x (-y) := by rw [← sameRay_neg_iff, neg_neg]
theorem eq_zero_of_sameRay_neg_smul_right [NoZeroSMulDivisors R M] {r : R} (hr : r < 0)
(h : SameRay R x (r • x)) : x = 0 := by
rcases h with (rfl | h₀ | ⟨r₁, r₂, hr₁, hr₂, h⟩)
· rfl
· simpa [hr.ne] using h₀
· rw [← sub_eq_zero, smul_smul, ← sub_smul, smul_eq_zero] at h
refine h.resolve_left (ne_of_gt <| sub_pos.2 ?_)
exact (mul_neg_of_pos_of_neg hr₂ hr).trans hr₁
/-- If a vector is in the same ray as its negation, that vector is zero. -/
theorem eq_zero_of_sameRay_self_neg [NoZeroSMulDivisors R M] (h : SameRay R x (-x)) : x = 0 := by
nontriviality M; haveI : Nontrivial R := Module.nontrivial R M
refine eq_zero_of_sameRay_neg_smul_right (neg_lt_zero.2 (zero_lt_one' R)) ?_
rwa [neg_one_smul]
namespace RayVector
/-- Negating a nonzero vector. -/
instance {R : Type*} : Neg (RayVector R M) :=
⟨fun v => ⟨-v, neg_ne_zero.2 v.prop⟩⟩
/-- Negating a nonzero vector commutes with coercion to the underlying module. -/
@[simp, norm_cast]
theorem coe_neg {R : Type*} (v : RayVector R M) : ↑(-v) = -(v : M) :=
rfl
/-- Negating a nonzero vector twice produces the original vector. -/
instance {R : Type*} : InvolutiveNeg (RayVector R M) where
neg := Neg.neg
neg_neg v := by rw [Subtype.ext_iff, coe_neg, coe_neg, neg_neg]
/-- If two nonzero vectors are equivalent, so are their negations. -/
@[simp]
theorem equiv_neg_iff {v₁ v₂ : RayVector R M} : -v₁ ≈ -v₂ ↔ v₁ ≈ v₂ :=
sameRay_neg_iff
end RayVector
variable (R)
/-- Negating a ray. -/
instance : Neg (Module.Ray R M) :=
⟨Quotient.map (fun v => -v) fun _ _ => RayVector.equiv_neg_iff.2⟩
/-- The ray given by the negation of a nonzero vector. -/
@[simp]
theorem neg_rayOfNeZero (v : M) (h : v ≠ 0) :
-rayOfNeZero R _ h = rayOfNeZero R (-v) (neg_ne_zero.2 h) :=
rfl
namespace Module.Ray
variable {R}
/-- Negating a ray twice produces the original ray. -/
instance : InvolutiveNeg (Module.Ray R M) where
neg := Neg.neg
neg_neg x := by apply ind R (by simp) x
-- Quotient.ind (fun a => congr_arg Quotient.mk' <| neg_neg _) x
/-- A ray does not equal its own negation. -/
theorem ne_neg_self [NoZeroSMulDivisors R M] (x : Module.Ray R M) : x ≠ -x := by
induction x using Module.Ray.ind with | h x hx =>
rw [neg_rayOfNeZero, Ne, ray_eq_iff]
exact mt eq_zero_of_sameRay_self_neg hx
theorem neg_units_smul (u : Rˣ) (v : Module.Ray R M) : -u • v = -(u • v) := by
induction v using Module.Ray.ind
simp only [smul_rayOfNeZero, Units.smul_def, Units.val_neg, neg_smul, neg_rayOfNeZero]
/-- Scaling by a negative unit is negation. -/
theorem units_smul_of_neg (u : Rˣ) (hu : (u : R) < 0) (v : Module.Ray R M) : u • v = -v := by
rw [← neg_inj, neg_neg, ← neg_units_smul, units_smul_of_pos]
rwa [Units.val_neg, Right.neg_pos_iff]
@[simp]
protected theorem map_neg (f : M ≃ₗ[R] N) (v : Module.Ray R M) : map f (-v) = -map f v := by
induction v using Module.Ray.ind with | h g hg => simp
end Module.Ray
end StrictOrderedCommRing
section LinearOrderedCommRing
variable {R : Type*} [CommRing R] [LinearOrder R] [IsStrictOrderedRing R]
variable {M : Type*} [AddCommGroup M] [Module R M]
/-- `SameRay` follows from membership of `MulAction.orbit` for the `Units.posSubgroup`. -/
theorem sameRay_of_mem_orbit {v₁ v₂ : M} (h : v₁ ∈ MulAction.orbit (Units.posSubgroup R) v₂) :
SameRay R v₁ v₂ := by
rcases h with ⟨⟨r, hr : 0 < r.1⟩, rfl : r • v₂ = v₁⟩
exact SameRay.sameRay_pos_smul_left _ hr
/-- Scaling by an inverse unit is the same as scaling by itself. -/
@[simp]
theorem units_inv_smul (u : Rˣ) (v : Module.Ray R M) : u⁻¹ • v = u • v :=
have := mul_self_pos.2 u.ne_zero
calc
u⁻¹ • v = (u * u) • u⁻¹ • v := Eq.symm <| (u⁻¹ • v).units_smul_of_pos _ (by exact this)
_ = u • v := by rw [mul_smul, smul_inv_smul]
section
variable [NoZeroSMulDivisors R M]
@[simp]
theorem sameRay_smul_right_iff {v : M} {r : R} : SameRay R v (r • v) ↔ 0 ≤ r ∨ v = 0 :=
⟨fun hrv => or_iff_not_imp_left.2 fun hr => eq_zero_of_sameRay_neg_smul_right (not_le.1 hr) hrv,
or_imp.2 ⟨SameRay.sameRay_nonneg_smul_right v, fun h => h.symm ▸ SameRay.zero_left _⟩⟩
/-- A nonzero vector is in the same ray as a multiple of itself if and only if that multiple
is positive. -/
theorem sameRay_smul_right_iff_of_ne {v : M} (hv : v ≠ 0) {r : R} (hr : r ≠ 0) :
SameRay R v (r • v) ↔ 0 < r := by
simp only [sameRay_smul_right_iff, hv, or_false, hr.symm.le_iff_lt]
@[simp]
theorem sameRay_smul_left_iff {v : M} {r : R} : SameRay R (r • v) v ↔ 0 ≤ r ∨ v = 0 :=
SameRay.sameRay_comm.trans sameRay_smul_right_iff
/-- A multiple of a nonzero vector is in the same ray as that vector if and only if that multiple
is positive. -/
theorem sameRay_smul_left_iff_of_ne {v : M} (hv : v ≠ 0) {r : R} (hr : r ≠ 0) :
SameRay R (r • v) v ↔ 0 < r :=
SameRay.sameRay_comm.trans (sameRay_smul_right_iff_of_ne hv hr)
@[simp]
theorem sameRay_neg_smul_right_iff {v : M} {r : R} : SameRay R (-v) (r • v) ↔ r ≤ 0 ∨ v = 0 := by
rw [← sameRay_neg_iff, neg_neg, ← neg_smul, sameRay_smul_right_iff, neg_nonneg]
theorem sameRay_neg_smul_right_iff_of_ne {v : M} {r : R} (hv : v ≠ 0) (hr : r ≠ 0) :
SameRay R (-v) (r • v) ↔ r < 0 := by
simp only [sameRay_neg_smul_right_iff, hv, or_false, hr.le_iff_lt]
@[simp]
theorem sameRay_neg_smul_left_iff {v : M} {r : R} : SameRay R (r • v) (-v) ↔ r ≤ 0 ∨ v = 0 :=
SameRay.sameRay_comm.trans sameRay_neg_smul_right_iff
theorem sameRay_neg_smul_left_iff_of_ne {v : M} {r : R} (hv : v ≠ 0) (hr : r ≠ 0) :
SameRay R (r • v) (-v) ↔ r < 0 :=
SameRay.sameRay_comm.trans <| sameRay_neg_smul_right_iff_of_ne hv hr
@[simp]
theorem units_smul_eq_self_iff {u : Rˣ} {v : Module.Ray R M} : u • v = v ↔ 0 < (u : R) := by
induction v using Module.Ray.ind with | h v hv =>
simp only [smul_rayOfNeZero, ray_eq_iff, Units.smul_def, sameRay_smul_left_iff_of_ne hv u.ne_zero]
@[simp]
theorem units_smul_eq_neg_iff {u : Rˣ} {v : Module.Ray R M} : u • v = -v ↔ u.1 < 0 := by
rw [← neg_inj, neg_neg, ← Module.Ray.neg_units_smul, units_smul_eq_self_iff, Units.val_neg,
neg_pos]
/-- Two vectors are in the same ray, or the first is in the same ray as the negation of the
second, if and only if they are not linearly independent. -/
theorem sameRay_or_sameRay_neg_iff_not_linearIndependent {x y : M} :
SameRay R x y ∨ SameRay R x (-y) ↔ ¬LinearIndependent R ![x, y] := by
by_cases hx : x = 0; · simpa [hx] using fun h : LinearIndependent R ![0, y] => h.ne_zero 0 rfl
by_cases hy : y = 0; · simpa [hy] using fun h : LinearIndependent R ![x, 0] => h.ne_zero 1 rfl
simp_rw [Fintype.not_linearIndependent_iff]
refine ⟨fun h => ?_, fun h => ?_⟩
· rcases h with ((hx0 | hy0 | ⟨r₁, r₂, hr₁, _, h⟩) | (hx0 | hy0 | ⟨r₁, r₂, hr₁, _, h⟩))
· exact False.elim (hx hx0)
· exact False.elim (hy hy0)
· refine ⟨![r₁, -r₂], ?_⟩
rw [Fin.sum_univ_two, Fin.exists_fin_two]
simp [h, hr₁.ne.symm]
· exact False.elim (hx hx0)
· exact False.elim (hy (neg_eq_zero.1 hy0))
· refine ⟨![r₁, r₂], ?_⟩
rw [Fin.sum_univ_two, Fin.exists_fin_two]
simp [h, hr₁.ne.symm]
· rcases h with ⟨m, hm, hmne⟩
rw [Fin.sum_univ_two, add_eq_zero_iff_eq_neg] at hm
dsimp only [Matrix.cons_val] at hm
rcases lt_trichotomy (m 0) 0 with (hm0 | hm0 | hm0) <;>
rcases lt_trichotomy (m 1) 0 with (hm1 | hm1 | hm1)
· refine
Or.inr (Or.inr (Or.inr ⟨-m 0, -m 1, Left.neg_pos_iff.2 hm0, Left.neg_pos_iff.2 hm1, ?_⟩))
linear_combination (norm := module) -hm
· exfalso
simp [hm1, hx, hm0.ne] at hm
· refine Or.inl (Or.inr (Or.inr ⟨-m 0, m 1, Left.neg_pos_iff.2 hm0, hm1, ?_⟩))
linear_combination (norm := module) -hm
· exfalso
simp [hm0, hy, hm1.ne] at hm
· rw [Fin.exists_fin_two] at hmne
exact False.elim (not_and_or.2 hmne ⟨hm0, hm1⟩)
· exfalso
simp [hm0, hy, hm1.ne.symm] at hm
· refine Or.inl (Or.inr (Or.inr ⟨m 0, -m 1, hm0, Left.neg_pos_iff.2 hm1, ?_⟩))
rwa [neg_smul]
· exfalso
simp [hm1, hx, hm0.ne.symm] at hm
· refine Or.inr (Or.inr (Or.inr ⟨m 0, m 1, hm0, hm1, ?_⟩))
rwa [smul_neg]
/-- Two vectors are in the same ray, or they are nonzero and the first is in the same ray as the
negation of the second, if and only if they are not linearly independent. -/
theorem sameRay_or_ne_zero_and_sameRay_neg_iff_not_linearIndependent {x y : M} :
SameRay R x y ∨ x ≠ 0 ∧ y ≠ 0 ∧ SameRay R x (-y) ↔ ¬LinearIndependent R ![x, y] := by
rw [← sameRay_or_sameRay_neg_iff_not_linearIndependent]
by_cases hx : x = 0; · simp [hx]
by_cases hy : y = 0 <;> simp [hx, hy]
end
end LinearOrderedCommRing
namespace SameRay
variable {R : Type*} [Field R] [LinearOrder R] [IsStrictOrderedRing R]
variable {M : Type*} [AddCommGroup M] [Module R M] {x y v₁ v₂ : M}
theorem exists_pos_left (h : SameRay R x y) (hx : x ≠ 0) (hy : y ≠ 0) :
∃ r : R, 0 < r ∧ r • x = y :=
let ⟨r₁, r₂, hr₁, hr₂, h⟩ := h.exists_pos hx hy
⟨r₂⁻¹ * r₁, mul_pos (inv_pos.2 hr₂) hr₁, by rw [mul_smul, h, inv_smul_smul₀ hr₂.ne']⟩
theorem exists_pos_right (h : SameRay R x y) (hx : x ≠ 0) (hy : y ≠ 0) :
∃ r : R, 0 < r ∧ x = r • y :=
(h.symm.exists_pos_left hy hx).imp fun _ => And.imp_right Eq.symm
/-- If a vector `v₂` is on the same ray as a nonzero vector `v₁`, then it is equal to `c • v₁` for
some nonnegative `c`. -/
theorem exists_nonneg_left (h : SameRay R x y) (hx : x ≠ 0) : ∃ r : R, 0 ≤ r ∧ r • x = y := by
obtain rfl | hy := eq_or_ne y 0
· exact ⟨0, le_rfl, zero_smul _ _⟩
· exact (h.exists_pos_left hx hy).imp fun _ => And.imp_left le_of_lt
/-- If a vector `v₁` is on the same ray as a nonzero vector `v₂`, then it is equal to `c • v₂` for
some nonnegative `c`. -/
theorem exists_nonneg_right (h : SameRay R x y) (hy : y ≠ 0) : ∃ r : R, 0 ≤ r ∧ x = r • y :=
(h.symm.exists_nonneg_left hy).imp fun _ => And.imp_right Eq.symm
/-- If vectors `v₁` and `v₂` are on the same ray, then for some nonnegative `a b`, `a + b = 1`, we
have `v₁ = a • (v₁ + v₂)` and `v₂ = b • (v₁ + v₂)`. -/
theorem exists_eq_smul_add (h : SameRay R v₁ v₂) :
∃ a b : R, 0 ≤ a ∧ 0 ≤ b ∧ a + b = 1 ∧ v₁ = a • (v₁ + v₂) ∧ v₂ = b • (v₁ + v₂) := by
rcases h with (rfl | rfl | ⟨r₁, r₂, h₁, h₂, H⟩)
· use 0, 1
simp
· use 1, 0
simp
· have h₁₂ : 0 < r₁ + r₂ := add_pos h₁ h₂
refine
⟨r₂ / (r₁ + r₂), r₁ / (r₁ + r₂), div_nonneg h₂.le h₁₂.le, div_nonneg h₁.le h₁₂.le, ?_, ?_, ?_⟩
· rw [← add_div, add_comm, div_self h₁₂.ne']
· rw [div_eq_inv_mul, mul_smul, smul_add, ← H, ← add_smul, add_comm r₂, inv_smul_smul₀ h₁₂.ne']
· rw [div_eq_inv_mul, mul_smul, smul_add, H, ← add_smul, add_comm r₂, inv_smul_smul₀ h₁₂.ne']
/-- If vectors `v₁` and `v₂` are on the same ray, then they are nonnegative multiples of the same
vector. Actually, this vector can be assumed to be `v₁ + v₂`, see `SameRay.exists_eq_smul_add`. -/
theorem exists_eq_smul (h : SameRay R v₁ v₂) :
∃ (u : M) (a b : R), 0 ≤ a ∧ 0 ≤ b ∧ a + b = 1 ∧ v₁ = a • u ∧ v₂ = b • u :=
⟨v₁ + v₂, h.exists_eq_smul_add⟩
end SameRay
section LinearOrderedField
variable {R : Type*} [Field R] [LinearOrder R] [IsStrictOrderedRing R]
variable {M : Type*} [AddCommGroup M] [Module R M] {x y : M}
theorem exists_pos_left_iff_sameRay (hx : x ≠ 0) (hy : y ≠ 0) :
(∃ r : R, 0 < r ∧ r • x = y) ↔ SameRay R x y := by
refine ⟨fun h => ?_, fun h => h.exists_pos_left hx hy⟩
rcases h with ⟨r, hr, rfl⟩
exact SameRay.sameRay_pos_smul_right x hr
theorem exists_pos_left_iff_sameRay_and_ne_zero (hx : x ≠ 0) :
(∃ r : R, 0 < r ∧ r • x = y) ↔ SameRay R x y ∧ y ≠ 0 := by
constructor
· rintro ⟨r, hr, rfl⟩
simp [hx, hr.le, hr.ne']
· rintro ⟨hxy, hy⟩
exact (exists_pos_left_iff_sameRay hx hy).2 hxy
theorem exists_nonneg_left_iff_sameRay (hx : x ≠ 0) :
(∃ r : R, 0 ≤ r ∧ r • x = y) ↔ SameRay R x y := by
refine ⟨fun h => ?_, fun h => h.exists_nonneg_left hx⟩
rcases h with ⟨r, hr, rfl⟩
exact SameRay.sameRay_nonneg_smul_right x hr
theorem exists_pos_right_iff_sameRay (hx : x ≠ 0) (hy : y ≠ 0) :
(∃ r : R, 0 < r ∧ x = r • y) ↔ SameRay R x y := by
rw [SameRay.sameRay_comm]
simp_rw [eq_comm (a := x)]
exact exists_pos_left_iff_sameRay hy hx
theorem exists_pos_right_iff_sameRay_and_ne_zero (hy : y ≠ 0) :
(∃ r : R, 0 < r ∧ x = r • y) ↔ SameRay R x y ∧ x ≠ 0 := by
rw [SameRay.sameRay_comm]
simp_rw [eq_comm (a := x)]
exact exists_pos_left_iff_sameRay_and_ne_zero hy
theorem exists_nonneg_right_iff_sameRay (hy : y ≠ 0) :
(∃ r : R, 0 ≤ r ∧ x = r • y) ↔ SameRay R x y := by
rw [SameRay.sameRay_comm]
simp_rw [eq_comm (a := x)]
exact exists_nonneg_left_iff_sameRay (R := R) hy
end LinearOrderedField
| Mathlib/LinearAlgebra/Ray.lean | 658 | 661 | |
/-
Copyright (c) 2019 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Patrick Massot, Casper Putz, Anne Baanen, Wen Yang
-/
import Mathlib.LinearAlgebra.Matrix.Transvection
import Mathlib.LinearAlgebra.Matrix.NonsingularInverse
import Mathlib.Tactic.FinCases
/-!
# Block matrices and their determinant
This file defines a predicate `Matrix.BlockTriangular` saying a matrix
is block triangular, and proves the value of the determinant for various
matrices built out of blocks.
## Main definitions
* `Matrix.BlockTriangular` expresses that an `o` by `o` matrix is block triangular,
if the rows and columns are ordered according to some order `b : o → α`
## Main results
* `Matrix.det_of_blockTriangular`: the determinant of a block triangular matrix
is equal to the product of the determinants of all the blocks
* `Matrix.det_of_upperTriangular` and `Matrix.det_of_lowerTriangular`: the determinant of
a triangular matrix is the product of the entries along the diagonal
## Tags
matrix, diagonal, det, block triangular
-/
open Finset Function OrderDual
open Matrix
universe v
variable {α β m n o : Type*} {m' n' : α → Type*}
variable {R : Type v} {M N : Matrix m m R} {b : m → α}
namespace Matrix
section LT
variable [LT α]
section Zero
variable [Zero R]
/-- Let `b` map rows and columns of a square matrix `M` to blocks indexed by `α`s. Then
`BlockTriangular M n b` says the matrix is block triangular. -/
def BlockTriangular (M : Matrix m m R) (b : m → α) : Prop :=
∀ ⦃i j⦄, b j < b i → M i j = 0
@[simp]
protected theorem BlockTriangular.submatrix {f : n → m} (h : M.BlockTriangular b) :
(M.submatrix f f).BlockTriangular (b ∘ f) := fun _ _ hij => h hij
| theorem blockTriangular_reindex_iff {b : n → α} {e : m ≃ n} :
(reindex e e M).BlockTriangular b ↔ M.BlockTriangular (b ∘ e) := by
refine ⟨fun h => ?_, fun h => ?_⟩
· convert h.submatrix
simp only [reindex_apply, submatrix_submatrix, submatrix_id_id, Equiv.symm_comp_self]
· convert h.submatrix
simp only [comp_assoc b e e.symm, Equiv.self_comp_symm, comp_id]
| Mathlib/LinearAlgebra/Matrix/Block.lean | 63 | 69 |
/-
Copyright (c) 2020 Johan Commelin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johan Commelin, Robert Y. Lewis
-/
import Mathlib.Algebra.CharP.Invertible
import Mathlib.Algebra.MvPolynomial.Variables
import Mathlib.Algebra.MvPolynomial.CommRing
import Mathlib.Algebra.MvPolynomial.Expand
import Mathlib.Algebra.Order.Ring.Rat
import Mathlib.Data.Fintype.BigOperators
import Mathlib.Data.ZMod.Basic
/-!
# Witt polynomials
To endow `WittVector p R` with a ring structure,
we need to study the so-called Witt polynomials.
Fix a base value `p : ℕ`.
The `p`-adic Witt polynomials are an infinite family of polynomials
indexed by a natural number `n`, taking values in an arbitrary ring `R`.
The variables of these polynomials are represented by natural numbers.
The variable set of the `n`th Witt polynomial contains at most `n+1` elements `{0, ..., n}`,
with exactly these variables when `R` has characteristic `0`.
These polynomials are used to define the addition and multiplication operators
on the type of Witt vectors. (While this type itself is not complicated,
the ring operations are what make it interesting.)
When the base `p` is invertible in `R`, the `p`-adic Witt polynomials
form a basis for `MvPolynomial ℕ R`, equivalent to the standard basis.
## Main declarations
* `WittPolynomial p R n`: the `n`-th Witt polynomial, viewed as polynomial over the ring `R`
* `xInTermsOfW p R n`: if `p` is invertible, the polynomial `X n` is contained in the subalgebra
generated by the Witt polynomials. `xInTermsOfW p R n` is the explicit polynomial,
which upon being bound to the Witt polynomials yields `X n`.
* `bind₁_wittPolynomial_xInTermsOfW`: the proof of the claim that
`bind₁ (xInTermsOfW p R) (W_ R n) = X n`
* `bind₁_xInTermsOfW_wittPolynomial`: the converse of the above statement
## Notation
In this file we use the following notation
* `p` is a natural number, typically assumed to be prime.
* `R` and `S` are commutative rings
* `W n` (and `W_ R n` when the ring needs to be explicit) denotes the `n`th Witt polynomial
## References
* [Hazewinkel, *Witt Vectors*][Haze09]
* [Commelin and Lewis, *Formalizing the Ring of Witt Vectors*][CL21]
-/
open MvPolynomial
open Finset hiding map
open Finsupp (single)
--attribute [-simp] coe_eval₂_hom
variable (p : ℕ)
variable (R : Type*) [CommRing R]
/-- `wittPolynomial p R n` is the `n`-th Witt polynomial
with respect to a prime `p` with coefficients in a commutative ring `R`.
It is defined as:
`∑_{i ≤ n} p^i X_i^{p^{n-i}} ∈ R[X_0, X_1, X_2, …]`. -/
noncomputable def wittPolynomial (n : ℕ) : MvPolynomial ℕ R :=
∑ i ∈ range (n + 1), monomial (single i (p ^ (n - i))) ((p : R) ^ i)
theorem wittPolynomial_eq_sum_C_mul_X_pow (n : ℕ) :
wittPolynomial p R n = ∑ i ∈ range (n + 1), C ((p : R) ^ i) * X i ^ p ^ (n - i) := by
apply sum_congr rfl
rintro i -
rw [monomial_eq, Finsupp.prod_single_index]
rw [pow_zero]
/-! We set up notation locally to this file, to keep statements short and comprehensible.
This allows us to simply write `W n` or `W_ ℤ n`. -/
-- Notation with ring of coefficients explicit
set_option quotPrecheck false in
@[inherit_doc]
scoped[Witt] notation "W_" => wittPolynomial p
-- Notation with ring of coefficients implicit
set_option quotPrecheck false in
@[inherit_doc]
scoped[Witt] notation "W" => wittPolynomial p _
open Witt
open MvPolynomial
/-! The first observation is that the Witt polynomial doesn't really depend on the coefficient ring.
If we map the coefficients through a ring homomorphism, we obtain the corresponding Witt polynomial
over the target ring. -/
section
variable {R} {S : Type*} [CommRing S]
@[simp]
theorem map_wittPolynomial (f : R →+* S) (n : ℕ) : map f (W n) = W n := by
rw [wittPolynomial, map_sum, wittPolynomial]
refine sum_congr rfl fun i _ => ?_
rw [map_monomial, RingHom.map_pow, map_natCast]
variable (R)
@[simp]
theorem constantCoeff_wittPolynomial [hp : Fact p.Prime] (n : ℕ) :
constantCoeff (wittPolynomial p R n) = 0 := by
simp only [wittPolynomial, map_sum, constantCoeff_monomial]
rw [sum_eq_zero]
rintro i _
rw [if_neg]
rw [Finsupp.single_eq_zero]
exact ne_of_gt (pow_pos hp.1.pos _)
@[simp]
theorem wittPolynomial_zero : wittPolynomial p R 0 = X 0 := by
simp only [wittPolynomial, X, sum_singleton, range_one, pow_zero, zero_add, tsub_self]
@[simp]
theorem wittPolynomial_one : wittPolynomial p R 1 = C (p : R) * X 1 + X 0 ^ p := by
simp only [wittPolynomial_eq_sum_C_mul_X_pow, sum_range_succ_comm, range_one, sum_singleton,
one_mul, pow_one, C_1, pow_zero, tsub_self, tsub_zero]
theorem aeval_wittPolynomial {A : Type*} [CommRing A] [Algebra R A] (f : ℕ → A) (n : ℕ) :
aeval f (W_ R n) = ∑ i ∈ range (n + 1), (p : A) ^ i * f i ^ p ^ (n - i) := by
simp [wittPolynomial, map_sum, aeval_monomial, Finsupp.prod_single_index]
|
/-- Over the ring `ZMod (p^(n+1))`, we produce the `n+1`st Witt polynomial
by expanding the `n`th Witt polynomial by `p`. -/
| Mathlib/RingTheory/WittVector/WittPolynomial.lean | 141 | 143 |
/-
Copyright (c) 2019 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Yaël Dillies
-/
import Mathlib.Order.Cover
import Mathlib.Order.Interval.Finset.Defs
/-!
# Intervals as finsets
This file provides basic results about all the `Finset.Ixx`, which are defined in
`Order.Interval.Finset.Defs`.
In addition, it shows that in a locally finite order `≤` and `<` are the transitive closures of,
respectively, `⩿` and `⋖`, which then leads to a characterization of monotone and strictly
functions whose domain is a locally finite order. In particular, this file proves:
* `le_iff_transGen_wcovBy`: `≤` is the transitive closure of `⩿`
* `lt_iff_transGen_covBy`: `<` is the transitive closure of `⋖`
* `monotone_iff_forall_wcovBy`: Characterization of monotone functions
* `strictMono_iff_forall_covBy`: Characterization of strictly monotone functions
## TODO
This file was originally only about `Finset.Ico a b` where `a b : ℕ`. No care has yet been taken to
generalize these lemmas properly and many lemmas about `Icc`, `Ioc`, `Ioo` are missing. In general,
what's to do is taking the lemmas in `Data.X.Intervals` and abstract away the concrete structure.
Complete the API. See
https://github.com/leanprover-community/mathlib/pull/14448#discussion_r906109235
for some ideas.
-/
assert_not_exists MonoidWithZero Finset.sum
open Function OrderDual
open FinsetInterval
variable {ι α : Type*} {a a₁ a₂ b b₁ b₂ c x : α}
namespace Finset
section Preorder
variable [Preorder α]
section LocallyFiniteOrder
variable [LocallyFiniteOrder α]
@[simp]
theorem nonempty_Icc : (Icc a b).Nonempty ↔ a ≤ b := by
rw [← coe_nonempty, coe_Icc, Set.nonempty_Icc]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Icc_of_le⟩ := nonempty_Icc
@[simp]
theorem nonempty_Ico : (Ico a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ico, Set.nonempty_Ico]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ico_of_lt⟩ := nonempty_Ico
@[simp]
theorem nonempty_Ioc : (Ioc a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ioc, Set.nonempty_Ioc]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ioc_of_lt⟩ := nonempty_Ioc
-- TODO: This is nonsense. A locally finite order is never densely ordered
@[simp]
theorem nonempty_Ioo [DenselyOrdered α] : (Ioo a b).Nonempty ↔ a < b := by
rw [← coe_nonempty, coe_Ioo, Set.nonempty_Ioo]
@[simp]
theorem Icc_eq_empty_iff : Icc a b = ∅ ↔ ¬a ≤ b := by
rw [← coe_eq_empty, coe_Icc, Set.Icc_eq_empty_iff]
@[simp]
theorem Ico_eq_empty_iff : Ico a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ico, Set.Ico_eq_empty_iff]
@[simp]
theorem Ioc_eq_empty_iff : Ioc a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ioc, Set.Ioc_eq_empty_iff]
-- TODO: This is nonsense. A locally finite order is never densely ordered
@[simp]
theorem Ioo_eq_empty_iff [DenselyOrdered α] : Ioo a b = ∅ ↔ ¬a < b := by
rw [← coe_eq_empty, coe_Ioo, Set.Ioo_eq_empty_iff]
alias ⟨_, Icc_eq_empty⟩ := Icc_eq_empty_iff
alias ⟨_, Ico_eq_empty⟩ := Ico_eq_empty_iff
alias ⟨_, Ioc_eq_empty⟩ := Ioc_eq_empty_iff
@[simp]
theorem Ioo_eq_empty (h : ¬a < b) : Ioo a b = ∅ :=
eq_empty_iff_forall_not_mem.2 fun _ hx => h ((mem_Ioo.1 hx).1.trans (mem_Ioo.1 hx).2)
@[simp]
theorem Icc_eq_empty_of_lt (h : b < a) : Icc a b = ∅ :=
Icc_eq_empty h.not_le
@[simp]
theorem Ico_eq_empty_of_le (h : b ≤ a) : Ico a b = ∅ :=
Ico_eq_empty h.not_lt
@[simp]
theorem Ioc_eq_empty_of_le (h : b ≤ a) : Ioc a b = ∅ :=
Ioc_eq_empty h.not_lt
@[simp]
theorem Ioo_eq_empty_of_le (h : b ≤ a) : Ioo a b = ∅ :=
Ioo_eq_empty h.not_lt
theorem left_mem_Icc : a ∈ Icc a b ↔ a ≤ b := by simp only [mem_Icc, true_and, le_rfl]
theorem left_mem_Ico : a ∈ Ico a b ↔ a < b := by simp only [mem_Ico, true_and, le_refl]
theorem right_mem_Icc : b ∈ Icc a b ↔ a ≤ b := by simp only [mem_Icc, and_true, le_rfl]
theorem right_mem_Ioc : b ∈ Ioc a b ↔ a < b := by simp only [mem_Ioc, and_true, le_rfl]
theorem left_not_mem_Ioc : a ∉ Ioc a b := fun h => lt_irrefl _ (mem_Ioc.1 h).1
theorem left_not_mem_Ioo : a ∉ Ioo a b := fun h => lt_irrefl _ (mem_Ioo.1 h).1
theorem right_not_mem_Ico : b ∉ Ico a b := fun h => lt_irrefl _ (mem_Ico.1 h).2
theorem right_not_mem_Ioo : b ∉ Ioo a b := fun h => lt_irrefl _ (mem_Ioo.1 h).2
@[gcongr]
theorem Icc_subset_Icc (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Icc a₁ b₁ ⊆ Icc a₂ b₂ := by
simpa [← coe_subset] using Set.Icc_subset_Icc ha hb
@[gcongr]
theorem Ico_subset_Ico (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ico a₁ b₁ ⊆ Ico a₂ b₂ := by
simpa [← coe_subset] using Set.Ico_subset_Ico ha hb
@[gcongr]
theorem Ioc_subset_Ioc (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ioc a₁ b₁ ⊆ Ioc a₂ b₂ := by
simpa [← coe_subset] using Set.Ioc_subset_Ioc ha hb
@[gcongr]
theorem Ioo_subset_Ioo (ha : a₂ ≤ a₁) (hb : b₁ ≤ b₂) : Ioo a₁ b₁ ⊆ Ioo a₂ b₂ := by
simpa [← coe_subset] using Set.Ioo_subset_Ioo ha hb
@[gcongr]
theorem Icc_subset_Icc_left (h : a₁ ≤ a₂) : Icc a₂ b ⊆ Icc a₁ b :=
Icc_subset_Icc h le_rfl
@[gcongr]
theorem Ico_subset_Ico_left (h : a₁ ≤ a₂) : Ico a₂ b ⊆ Ico a₁ b :=
Ico_subset_Ico h le_rfl
@[gcongr]
theorem Ioc_subset_Ioc_left (h : a₁ ≤ a₂) : Ioc a₂ b ⊆ Ioc a₁ b :=
Ioc_subset_Ioc h le_rfl
@[gcongr]
theorem Ioo_subset_Ioo_left (h : a₁ ≤ a₂) : Ioo a₂ b ⊆ Ioo a₁ b :=
Ioo_subset_Ioo h le_rfl
@[gcongr]
theorem Icc_subset_Icc_right (h : b₁ ≤ b₂) : Icc a b₁ ⊆ Icc a b₂ :=
Icc_subset_Icc le_rfl h
@[gcongr]
theorem Ico_subset_Ico_right (h : b₁ ≤ b₂) : Ico a b₁ ⊆ Ico a b₂ :=
Ico_subset_Ico le_rfl h
@[gcongr]
theorem Ioc_subset_Ioc_right (h : b₁ ≤ b₂) : Ioc a b₁ ⊆ Ioc a b₂ :=
Ioc_subset_Ioc le_rfl h
@[gcongr]
theorem Ioo_subset_Ioo_right (h : b₁ ≤ b₂) : Ioo a b₁ ⊆ Ioo a b₂ :=
Ioo_subset_Ioo le_rfl h
theorem Ico_subset_Ioo_left (h : a₁ < a₂) : Ico a₂ b ⊆ Ioo a₁ b := by
rw [← coe_subset, coe_Ico, coe_Ioo]
exact Set.Ico_subset_Ioo_left h
theorem Ioc_subset_Ioo_right (h : b₁ < b₂) : Ioc a b₁ ⊆ Ioo a b₂ := by
rw [← coe_subset, coe_Ioc, coe_Ioo]
exact Set.Ioc_subset_Ioo_right h
theorem Icc_subset_Ico_right (h : b₁ < b₂) : Icc a b₁ ⊆ Ico a b₂ := by
rw [← coe_subset, coe_Icc, coe_Ico]
exact Set.Icc_subset_Ico_right h
theorem Ioo_subset_Ico_self : Ioo a b ⊆ Ico a b := by
rw [← coe_subset, coe_Ioo, coe_Ico]
exact Set.Ioo_subset_Ico_self
theorem Ioo_subset_Ioc_self : Ioo a b ⊆ Ioc a b := by
rw [← coe_subset, coe_Ioo, coe_Ioc]
exact Set.Ioo_subset_Ioc_self
theorem Ico_subset_Icc_self : Ico a b ⊆ Icc a b := by
rw [← coe_subset, coe_Ico, coe_Icc]
exact Set.Ico_subset_Icc_self
theorem Ioc_subset_Icc_self : Ioc a b ⊆ Icc a b := by
rw [← coe_subset, coe_Ioc, coe_Icc]
exact Set.Ioc_subset_Icc_self
theorem Ioo_subset_Icc_self : Ioo a b ⊆ Icc a b :=
Ioo_subset_Ico_self.trans Ico_subset_Icc_self
theorem Icc_subset_Icc_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Icc a₂ b₂ ↔ a₂ ≤ a₁ ∧ b₁ ≤ b₂ := by
rw [← coe_subset, coe_Icc, coe_Icc, Set.Icc_subset_Icc_iff h₁]
theorem Icc_subset_Ioo_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ioo a₂ b₂ ↔ a₂ < a₁ ∧ b₁ < b₂ := by
rw [← coe_subset, coe_Icc, coe_Ioo, Set.Icc_subset_Ioo_iff h₁]
theorem Icc_subset_Ico_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ico a₂ b₂ ↔ a₂ ≤ a₁ ∧ b₁ < b₂ := by
rw [← coe_subset, coe_Icc, coe_Ico, Set.Icc_subset_Ico_iff h₁]
theorem Icc_subset_Ioc_iff (h₁ : a₁ ≤ b₁) : Icc a₁ b₁ ⊆ Ioc a₂ b₂ ↔ a₂ < a₁ ∧ b₁ ≤ b₂ :=
(Icc_subset_Ico_iff h₁.dual).trans and_comm
--TODO: `Ico_subset_Ioo_iff`, `Ioc_subset_Ioo_iff`
theorem Icc_ssubset_Icc_left (hI : a₂ ≤ b₂) (ha : a₂ < a₁) (hb : b₁ ≤ b₂) :
Icc a₁ b₁ ⊂ Icc a₂ b₂ := by
rw [← coe_ssubset, coe_Icc, coe_Icc]
exact Set.Icc_ssubset_Icc_left hI ha hb
theorem Icc_ssubset_Icc_right (hI : a₂ ≤ b₂) (ha : a₂ ≤ a₁) (hb : b₁ < b₂) :
Icc a₁ b₁ ⊂ Icc a₂ b₂ := by
rw [← coe_ssubset, coe_Icc, coe_Icc]
exact Set.Icc_ssubset_Icc_right hI ha hb
@[simp]
theorem Ioc_disjoint_Ioc_of_le {d : α} (hbc : b ≤ c) : Disjoint (Ioc a b) (Ioc c d) :=
disjoint_left.2 fun _ h1 h2 ↦ not_and_of_not_left _
((mem_Ioc.1 h1).2.trans hbc).not_lt (mem_Ioc.1 h2)
variable (a)
theorem Ico_self : Ico a a = ∅ :=
Ico_eq_empty <| lt_irrefl _
theorem Ioc_self : Ioc a a = ∅ :=
Ioc_eq_empty <| lt_irrefl _
theorem Ioo_self : Ioo a a = ∅ :=
Ioo_eq_empty <| lt_irrefl _
variable {a}
/-- A set with upper and lower bounds in a locally finite order is a fintype -/
def _root_.Set.fintypeOfMemBounds {s : Set α} [DecidablePred (· ∈ s)] (ha : a ∈ lowerBounds s)
(hb : b ∈ upperBounds s) : Fintype s :=
Set.fintypeSubset (Set.Icc a b) fun _ hx => ⟨ha hx, hb hx⟩
section Filter
theorem Ico_filter_lt_of_le_left [DecidablePred (· < c)] (hca : c ≤ a) :
{x ∈ Ico a b | x < c} = ∅ :=
filter_false_of_mem fun _ hx => (hca.trans (mem_Ico.1 hx).1).not_lt
theorem Ico_filter_lt_of_right_le [DecidablePred (· < c)] (hbc : b ≤ c) :
{x ∈ Ico a b | x < c} = Ico a b :=
filter_true_of_mem fun _ hx => (mem_Ico.1 hx).2.trans_le hbc
theorem Ico_filter_lt_of_le_right [DecidablePred (· < c)] (hcb : c ≤ b) :
{x ∈ Ico a b | x < c} = Ico a c := by
ext x
rw [mem_filter, mem_Ico, mem_Ico, and_right_comm]
exact and_iff_left_of_imp fun h => h.2.trans_le hcb
theorem Ico_filter_le_of_le_left {a b c : α} [DecidablePred (c ≤ ·)] (hca : c ≤ a) :
{x ∈ Ico a b | c ≤ x} = Ico a b :=
filter_true_of_mem fun _ hx => hca.trans (mem_Ico.1 hx).1
theorem Ico_filter_le_of_right_le {a b : α} [DecidablePred (b ≤ ·)] :
{x ∈ Ico a b | b ≤ x} = ∅ :=
filter_false_of_mem fun _ hx => (mem_Ico.1 hx).2.not_le
theorem Ico_filter_le_of_left_le {a b c : α} [DecidablePred (c ≤ ·)] (hac : a ≤ c) :
{x ∈ Ico a b | c ≤ x} = Ico c b := by
ext x
rw [mem_filter, mem_Ico, mem_Ico, and_comm, and_left_comm]
exact and_iff_right_of_imp fun h => hac.trans h.1
theorem Icc_filter_lt_of_lt_right {a b c : α} [DecidablePred (· < c)] (h : b < c) :
{x ∈ Icc a b | x < c} = Icc a b :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Icc.1 hx).2 h
theorem Ioc_filter_lt_of_lt_right {a b c : α} [DecidablePred (· < c)] (h : b < c) :
{x ∈ Ioc a b | x < c} = Ioc a b :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Ioc.1 hx).2 h
theorem Iic_filter_lt_of_lt_right {α} [Preorder α] [LocallyFiniteOrderBot α] {a c : α}
[DecidablePred (· < c)] (h : a < c) : {x ∈ Iic a | x < c} = Iic a :=
filter_true_of_mem fun _ hx => lt_of_le_of_lt (mem_Iic.1 hx) h
variable (a b) [Fintype α]
theorem filter_lt_lt_eq_Ioo [DecidablePred fun j => a < j ∧ j < b] :
({j | a < j ∧ j < b} : Finset _) = Ioo a b := by ext; simp
theorem filter_lt_le_eq_Ioc [DecidablePred fun j => a < j ∧ j ≤ b] :
({j | a < j ∧ j ≤ b} : Finset _) = Ioc a b := by ext; simp
theorem filter_le_lt_eq_Ico [DecidablePred fun j => a ≤ j ∧ j < b] :
({j | a ≤ j ∧ j < b} : Finset _) = Ico a b := by ext; simp
theorem filter_le_le_eq_Icc [DecidablePred fun j => a ≤ j ∧ j ≤ b] :
({j | a ≤ j ∧ j ≤ b} : Finset _) = Icc a b := by ext; simp
end Filter
end LocallyFiniteOrder
section LocallyFiniteOrderTop
variable [LocallyFiniteOrderTop α]
@[simp]
theorem Ioi_eq_empty : Ioi a = ∅ ↔ IsMax a := by
rw [← coe_eq_empty, coe_Ioi, Set.Ioi_eq_empty_iff]
@[simp] alias ⟨_, _root_.IsMax.finsetIoi_eq⟩ := Ioi_eq_empty
@[simp] lemma Ioi_nonempty : (Ioi a).Nonempty ↔ ¬ IsMax a := by simp [nonempty_iff_ne_empty]
theorem Ioi_top [OrderTop α] : Ioi (⊤ : α) = ∅ := Ioi_eq_empty.mpr isMax_top
@[simp]
theorem Ici_bot [OrderBot α] [Fintype α] : Ici (⊥ : α) = univ := by
ext a; simp only [mem_Ici, bot_le, mem_univ]
@[simp, aesop safe apply (rule_sets := [finsetNonempty])]
lemma nonempty_Ici : (Ici a).Nonempty := ⟨a, mem_Ici.2 le_rfl⟩
lemma nonempty_Ioi : (Ioi a).Nonempty ↔ ¬ IsMax a := by simp [Finset.Nonempty]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Ioi_of_not_isMax⟩ := nonempty_Ioi
@[simp]
theorem Ici_subset_Ici : Ici a ⊆ Ici b ↔ b ≤ a := by
simp [← coe_subset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Ici_subset_Ici⟩ := Ici_subset_Ici
@[simp]
theorem Ici_ssubset_Ici : Ici a ⊂ Ici b ↔ b < a := by
simp [← coe_ssubset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Ici_ssubset_Ici⟩ := Ici_ssubset_Ici
@[gcongr]
theorem Ioi_subset_Ioi (h : a ≤ b) : Ioi b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioi_subset_Ioi h
@[gcongr]
theorem Ioi_ssubset_Ioi (h : a < b) : Ioi b ⊂ Ioi a := by
simpa [← coe_ssubset] using Set.Ioi_ssubset_Ioi h
variable [LocallyFiniteOrder α]
theorem Icc_subset_Ici_self : Icc a b ⊆ Ici a := by
simpa [← coe_subset] using Set.Icc_subset_Ici_self
theorem Ico_subset_Ici_self : Ico a b ⊆ Ici a := by
simpa [← coe_subset] using Set.Ico_subset_Ici_self
theorem Ioc_subset_Ioi_self : Ioc a b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioc_subset_Ioi_self
theorem Ioo_subset_Ioi_self : Ioo a b ⊆ Ioi a := by
simpa [← coe_subset] using Set.Ioo_subset_Ioi_self
theorem Ioc_subset_Ici_self : Ioc a b ⊆ Ici a :=
Ioc_subset_Icc_self.trans Icc_subset_Ici_self
theorem Ioo_subset_Ici_self : Ioo a b ⊆ Ici a :=
Ioo_subset_Ico_self.trans Ico_subset_Ici_self
end LocallyFiniteOrderTop
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α]
@[simp]
theorem Iio_eq_empty : Iio a = ∅ ↔ IsMin a := Ioi_eq_empty (α := αᵒᵈ)
@[simp] alias ⟨_, _root_.IsMin.finsetIio_eq⟩ := Iio_eq_empty
@[simp] lemma Iio_nonempty : (Iio a).Nonempty ↔ ¬ IsMin a := by simp [nonempty_iff_ne_empty]
theorem Iio_bot [OrderBot α] : Iio (⊥ : α) = ∅ := Iio_eq_empty.mpr isMin_bot
@[simp]
theorem Iic_top [OrderTop α] [Fintype α] : Iic (⊤ : α) = univ := by
ext a; simp only [mem_Iic, le_top, mem_univ]
@[simp, aesop safe apply (rule_sets := [finsetNonempty])]
lemma nonempty_Iic : (Iic a).Nonempty := ⟨a, mem_Iic.2 le_rfl⟩
lemma nonempty_Iio : (Iio a).Nonempty ↔ ¬ IsMin a := by simp [Finset.Nonempty]
@[aesop safe apply (rule_sets := [finsetNonempty])]
alias ⟨_, Aesop.nonempty_Iio_of_not_isMin⟩ := nonempty_Iio
@[simp]
theorem Iic_subset_Iic : Iic a ⊆ Iic b ↔ a ≤ b := by
simp [← coe_subset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Iic_subset_Iic⟩ := Iic_subset_Iic
@[simp]
theorem Iic_ssubset_Iic : Iic a ⊂ Iic b ↔ a < b := by
simp [← coe_ssubset]
@[gcongr]
alias ⟨_, _root_.GCongr.Finset.Iic_ssubset_Iic⟩ := Iic_ssubset_Iic
@[gcongr]
theorem Iio_subset_Iio (h : a ≤ b) : Iio a ⊆ Iio b := by
simpa [← coe_subset] using Set.Iio_subset_Iio h
@[gcongr]
theorem Iio_ssubset_Iio (h : a < b) : Iio a ⊂ Iio b := by
simpa [← coe_ssubset] using Set.Iio_ssubset_Iio h
variable [LocallyFiniteOrder α]
theorem Icc_subset_Iic_self : Icc a b ⊆ Iic b := by
simpa [← coe_subset] using Set.Icc_subset_Iic_self
theorem Ioc_subset_Iic_self : Ioc a b ⊆ Iic b := by
simpa [← coe_subset] using Set.Ioc_subset_Iic_self
theorem Ico_subset_Iio_self : Ico a b ⊆ Iio b := by
simpa [← coe_subset] using Set.Ico_subset_Iio_self
theorem Ioo_subset_Iio_self : Ioo a b ⊆ Iio b := by
simpa [← coe_subset] using Set.Ioo_subset_Iio_self
theorem Ico_subset_Iic_self : Ico a b ⊆ Iic b :=
Ico_subset_Icc_self.trans Icc_subset_Iic_self
theorem Ioo_subset_Iic_self : Ioo a b ⊆ Iic b :=
Ioo_subset_Ioc_self.trans Ioc_subset_Iic_self
theorem Iic_disjoint_Ioc (h : a ≤ b) : Disjoint (Iic a) (Ioc b c) :=
disjoint_left.2 fun _ hax hbcx ↦ (mem_Iic.1 hax).not_lt <| lt_of_le_of_lt h (mem_Ioc.1 hbcx).1
/-- An equivalence between `Finset.Iic a` and `Set.Iic a`. -/
def _root_.Equiv.IicFinsetSet (a : α) : Iic a ≃ Set.Iic a where
toFun b := ⟨b.1, coe_Iic a ▸ mem_coe.2 b.2⟩
invFun b := ⟨b.1, by rw [← mem_coe, coe_Iic a]; exact b.2⟩
left_inv := fun _ ↦ rfl
right_inv := fun _ ↦ rfl
end LocallyFiniteOrderBot
section LocallyFiniteOrderTop
variable [LocallyFiniteOrderTop α] {a : α}
theorem Ioi_subset_Ici_self : Ioi a ⊆ Ici a := by
simpa [← coe_subset] using Set.Ioi_subset_Ici_self
theorem _root_.BddBelow.finite {s : Set α} (hs : BddBelow s) : s.Finite :=
let ⟨a, ha⟩ := hs
(Ici a).finite_toSet.subset fun _ hx => mem_Ici.2 <| ha hx
theorem _root_.Set.Infinite.not_bddBelow {s : Set α} : s.Infinite → ¬BddBelow s :=
mt BddBelow.finite
variable [Fintype α]
theorem filter_lt_eq_Ioi [DecidablePred (a < ·)] : ({x | a < x} : Finset _) = Ioi a := by ext; simp
theorem filter_le_eq_Ici [DecidablePred (a ≤ ·)] : ({x | a ≤ x} : Finset _) = Ici a := by ext; simp
end LocallyFiniteOrderTop
section LocallyFiniteOrderBot
variable [LocallyFiniteOrderBot α] {a : α}
theorem Iio_subset_Iic_self : Iio a ⊆ Iic a := by
simpa [← coe_subset] using Set.Iio_subset_Iic_self
theorem _root_.BddAbove.finite {s : Set α} (hs : BddAbove s) : s.Finite :=
hs.dual.finite
theorem _root_.Set.Infinite.not_bddAbove {s : Set α} : s.Infinite → ¬BddAbove s :=
mt BddAbove.finite
variable [Fintype α]
theorem filter_gt_eq_Iio [DecidablePred (· < a)] : ({x | x < a} : Finset _) = Iio a := by ext; simp
theorem filter_ge_eq_Iic [DecidablePred (· ≤ a)] : ({x | x ≤ a} : Finset _) = Iic a := by ext; simp
end LocallyFiniteOrderBot
section LocallyFiniteOrder
variable [LocallyFiniteOrder α]
@[simp]
theorem Icc_bot [OrderBot α] : Icc (⊥ : α) a = Iic a := rfl
@[simp]
theorem Icc_top [OrderTop α] : Icc a (⊤ : α) = Ici a := rfl
@[simp]
theorem Ico_bot [OrderBot α] : Ico (⊥ : α) a = Iio a := rfl
@[simp]
theorem Ioc_top [OrderTop α] : Ioc a (⊤ : α) = Ioi a := rfl
theorem Icc_bot_top [BoundedOrder α] [Fintype α] : Icc (⊥ : α) (⊤ : α) = univ := by
rw [Icc_bot, Iic_top]
end LocallyFiniteOrder
variable [LocallyFiniteOrderTop α] [LocallyFiniteOrderBot α]
theorem disjoint_Ioi_Iio (a : α) : Disjoint (Ioi a) (Iio a) :=
disjoint_left.2 fun _ hab hba => (mem_Ioi.1 hab).not_lt <| mem_Iio.1 hba
end Preorder
section PartialOrder
variable [PartialOrder α] [LocallyFiniteOrder α] {a b c : α}
@[simp]
theorem Icc_self (a : α) : Icc a a = {a} := by rw [← coe_eq_singleton, coe_Icc, Set.Icc_self]
@[simp]
theorem Icc_eq_singleton_iff : Icc a b = {c} ↔ a = c ∧ b = c := by
rw [← coe_eq_singleton, coe_Icc, Set.Icc_eq_singleton_iff]
theorem Ico_disjoint_Ico_consecutive (a b c : α) : Disjoint (Ico a b) (Ico b c) :=
disjoint_left.2 fun _ hab hbc => (mem_Ico.mp hab).2.not_le (mem_Ico.mp hbc).1
@[simp]
theorem Ici_top [OrderTop α] : Ici (⊤ : α) = {⊤} := Icc_eq_singleton_iff.2 ⟨rfl, rfl⟩
@[simp]
theorem Iic_bot [OrderBot α] : Iic (⊥ : α) = {⊥} := Icc_eq_singleton_iff.2 ⟨rfl, rfl⟩
section DecidableEq
variable [DecidableEq α]
@[simp]
theorem Icc_erase_left (a b : α) : (Icc a b).erase a = Ioc a b := by simp [← coe_inj]
@[simp]
theorem Icc_erase_right (a b : α) : (Icc a b).erase b = Ico a b := by simp [← coe_inj]
@[simp]
theorem Ico_erase_left (a b : α) : (Ico a b).erase a = Ioo a b := by simp [← coe_inj]
| @[simp]
| Mathlib/Order/Interval/Finset/Basic.lean | 572 | 572 |
/-
Copyright (c) 2020 Bhavik Mehta. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Bhavik Mehta, Kim Morrison
-/
import Mathlib.CategoryTheory.Subobject.MonoOver
import Mathlib.CategoryTheory.Skeletal
import Mathlib.CategoryTheory.ConcreteCategory.Basic
import Mathlib.CategoryTheory.Limits.Shapes.Pullback.CommSq
import Mathlib.Tactic.ApplyFun
import Mathlib.Tactic.CategoryTheory.Elementwise
/-!
# Subobjects
We define `Subobject X` as the quotient (by isomorphisms) of
`MonoOver X := {f : Over X // Mono f.hom}`.
Here `MonoOver X` is a thin category (a pair of objects has at most one morphism between them),
so we can think of it as a preorder. However as it is not skeletal, it is not a partial order.
There is a coercion from `Subobject X` back to the ambient category `C`
(using choice to pick a representative), and for `P : Subobject X`,
`P.arrow : (P : C) ⟶ X` is the inclusion morphism.
We provide
* `def pullback [HasPullbacks C] (f : X ⟶ Y) : Subobject Y ⥤ Subobject X`
* `def map (f : X ⟶ Y) [Mono f] : Subobject X ⥤ Subobject Y`
* `def «exists_» [HasImages C] (f : X ⟶ Y) : Subobject X ⥤ Subobject Y`
and prove their basic properties and relationships.
These are all easy consequences of the earlier development
of the corresponding functors for `MonoOver`.
The subobjects of `X` form a preorder making them into a category. We have `X ≤ Y` if and only if
`X.arrow` factors through `Y.arrow`: see `ofLE`/`ofLEMk`/`ofMkLE`/`ofMkLEMk` and
`le_of_comm`. Similarly, to show that two subobjects are equal, we can supply an isomorphism between
the underlying objects that commutes with the arrows (`eq_of_comm`).
See also
* `CategoryTheory.Subobject.factorThru` :
an API describing factorization of morphisms through subobjects.
* `CategoryTheory.Subobject.lattice` :
the lattice structures on subobjects.
## Notes
This development originally appeared in Bhavik Mehta's "Topos theory for Lean" repository,
and was ported to mathlib by Kim Morrison.
### Implementation note
Currently we describe `pullback`, `map`, etc., as functors.
It may be better to just say that they are monotone functions,
and even avoid using categorical language entirely when describing `Subobject X`.
(It's worth keeping this in mind in future use; it should be a relatively easy change here
if it looks preferable.)
### Relation to pseudoelements
There is a separate development of pseudoelements in `CategoryTheory.Abelian.Pseudoelements`,
as a quotient (but not by isomorphism) of `Over X`.
When a morphism `f` has an image, the image represents the same pseudoelement.
In a category with images `Pseudoelements X` could be constructed as a quotient of `MonoOver X`.
In fact, in an abelian category (I'm not sure in what generality beyond that),
`Pseudoelements X` agrees with `Subobject X`, but we haven't developed this in mathlib yet.
-/
universe v₁ v₂ u₁ u₂
noncomputable section
namespace CategoryTheory
open CategoryTheory CategoryTheory.Category CategoryTheory.Limits
variable {C : Type u₁} [Category.{v₁} C] {X Y Z : C}
variable {D : Type u₂} [Category.{v₂} D]
/-!
We now construct the subobject lattice for `X : C`,
as the quotient by isomorphisms of `MonoOver X`.
Since `MonoOver X` is a thin category, we use `ThinSkeleton` to take the quotient.
Essentially all the structure defined above on `MonoOver X` descends to `Subobject X`,
with morphisms becoming inequalities, and isomorphisms becoming equations.
-/
/-- The category of subobjects of `X : C`, defined as isomorphism classes of monomorphisms into `X`.
-/
def Subobject (X : C) :=
ThinSkeleton (MonoOver X)
instance (X : C) : PartialOrder (Subobject X) :=
inferInstanceAs <| PartialOrder (ThinSkeleton (MonoOver X))
namespace Subobject
-- Porting note: made it a def rather than an abbreviation
-- because Lean would make it too transparent
/-- Convenience constructor for a subobject. -/
def mk {X A : C} (f : A ⟶ X) [Mono f] : Subobject X :=
(toThinSkeleton _).obj (MonoOver.mk' f)
section
attribute [local ext] CategoryTheory.Comma
protected theorem ind {X : C} (p : Subobject X → Prop)
(h : ∀ ⦃A : C⦄ (f : A ⟶ X) [Mono f], p (Subobject.mk f)) (P : Subobject X) : p P := by
apply Quotient.inductionOn'
intro a
exact h a.arrow
protected theorem ind₂ {X : C} (p : Subobject X → Subobject X → Prop)
(h : ∀ ⦃A B : C⦄ (f : A ⟶ X) (g : B ⟶ X) [Mono f] [Mono g],
p (Subobject.mk f) (Subobject.mk g))
(P Q : Subobject X) : p P Q := by
apply Quotient.inductionOn₂'
intro a b
exact h a.arrow b.arrow
end
/-- Declare a function on subobjects of `X` by specifying a function on monomorphisms with
codomain `X`. -/
protected def lift {α : Sort*} {X : C} (F : ∀ ⦃A : C⦄ (f : A ⟶ X) [Mono f], α)
(h :
∀ ⦃A B : C⦄ (f : A ⟶ X) (g : B ⟶ X) [Mono f] [Mono g] (i : A ≅ B),
i.hom ≫ g = f → F f = F g) :
Subobject X → α := fun P =>
Quotient.liftOn' P (fun m => F m.arrow) fun m n ⟨i⟩ =>
h m.arrow n.arrow ((MonoOver.forget X ⋙ Over.forget X).mapIso i) (Over.w i.hom)
@[simp]
protected theorem lift_mk {α : Sort*} {X : C} (F : ∀ ⦃A : C⦄ (f : A ⟶ X) [Mono f], α) {h A}
(f : A ⟶ X) [Mono f] : Subobject.lift F h (Subobject.mk f) = F f :=
rfl
/-- The category of subobjects is equivalent to the `MonoOver` category. It is more convenient to
use the former due to the partial order instance, but oftentimes it is easier to define structures
on the latter. -/
noncomputable def equivMonoOver (X : C) : Subobject X ≌ MonoOver X :=
ThinSkeleton.equivalence _
/-- Use choice to pick a representative `MonoOver X` for each `Subobject X`.
-/
noncomputable def representative {X : C} : Subobject X ⥤ MonoOver X :=
(equivMonoOver X).functor
instance : (representative (X := X)).IsEquivalence :=
(equivMonoOver X).isEquivalence_functor
/-- Starting with `A : MonoOver X`, we can take its equivalence class in `Subobject X`
then pick an arbitrary representative using `representative.obj`.
This is isomorphic (in `MonoOver X`) to the original `A`.
-/
noncomputable def representativeIso {X : C} (A : MonoOver X) :
representative.obj ((toThinSkeleton _).obj A) ≅ A :=
(equivMonoOver X).counitIso.app A
/-- Use choice to pick a representative underlying object in `C` for any `Subobject X`.
Prefer to use the coercion `P : C` rather than explicitly writing `underlying.obj P`.
-/
noncomputable def underlying {X : C} : Subobject X ⥤ C :=
representative ⋙ MonoOver.forget _ ⋙ Over.forget _
instance : CoeOut (Subobject X) C where coe Y := underlying.obj Y
-- Porting note: removed as it has become a syntactic tautology
-- @[simp]
-- theorem underlying_as_coe {X : C} (P : Subobject X) : underlying.obj P = P :=
-- rfl
/-- If we construct a `Subobject Y` from an explicit `f : X ⟶ Y` with `[Mono f]`,
then pick an arbitrary choice of underlying object `(Subobject.mk f : C)` back in `C`,
it is isomorphic (in `C`) to the original `X`.
-/
noncomputable def underlyingIso {X Y : C} (f : X ⟶ Y) [Mono f] : (Subobject.mk f : C) ≅ X :=
(MonoOver.forget _ ⋙ Over.forget _).mapIso (representativeIso (MonoOver.mk' f))
/-- The morphism in `C` from the arbitrarily chosen underlying object to the ambient object.
-/
noncomputable def arrow {X : C} (Y : Subobject X) : (Y : C) ⟶ X :=
(representative.obj Y).obj.hom
instance arrow_mono {X : C} (Y : Subobject X) : Mono Y.arrow :=
(representative.obj Y).property
@[simp]
theorem arrow_congr {A : C} (X Y : Subobject A) (h : X = Y) :
eqToHom (congr_arg (fun X : Subobject A => (X : C)) h) ≫ Y.arrow = X.arrow := by
induction h
simp
@[simp]
theorem representative_coe (Y : Subobject X) : (representative.obj Y : C) = (Y : C) :=
rfl
@[simp]
theorem representative_arrow (Y : Subobject X) : (representative.obj Y).arrow = Y.arrow :=
rfl
@[reassoc (attr := simp)]
theorem underlying_arrow {X : C} {Y Z : Subobject X} (f : Y ⟶ Z) :
underlying.map f ≫ arrow Z = arrow Y :=
Over.w (representative.map f)
@[reassoc (attr := simp), elementwise (attr := simp)]
theorem underlyingIso_arrow {X Y : C} (f : X ⟶ Y) [Mono f] :
(underlyingIso f).inv ≫ (Subobject.mk f).arrow = f :=
Over.w _
@[reassoc (attr := simp)]
theorem underlyingIso_hom_comp_eq_mk {X Y : C} (f : X ⟶ Y) [Mono f] :
(underlyingIso f).hom ≫ f = (mk f).arrow :=
(Iso.eq_inv_comp _).1 (underlyingIso_arrow f).symm
/-- Two morphisms into a subobject are equal exactly if
the morphisms into the ambient object are equal -/
@[ext]
theorem eq_of_comp_arrow_eq {X Y : C} {P : Subobject Y} {f g : X ⟶ P}
(h : f ≫ P.arrow = g ≫ P.arrow) : f = g :=
(cancel_mono P.arrow).mp h
theorem mk_le_mk_of_comm {B A₁ A₂ : C} {f₁ : A₁ ⟶ B} {f₂ : A₂ ⟶ B} [Mono f₁] [Mono f₂] (g : A₁ ⟶ A₂)
(w : g ≫ f₂ = f₁) : mk f₁ ≤ mk f₂ :=
⟨MonoOver.homMk _ w⟩
@[simp]
theorem mk_arrow (P : Subobject X) : mk P.arrow = P :=
Quotient.inductionOn' P fun Q => by
obtain ⟨e⟩ := @Quotient.mk_out' _ (isIsomorphicSetoid _) Q
exact Quotient.sound' ⟨MonoOver.isoMk (Iso.refl _) ≪≫ e⟩
theorem le_of_comm {B : C} {X Y : Subobject B} (f : (X : C) ⟶ (Y : C)) (w : f ≫ Y.arrow = X.arrow) :
X ≤ Y := by
convert mk_le_mk_of_comm _ w <;> simp
theorem le_mk_of_comm {B A : C} {X : Subobject B} {f : A ⟶ B} [Mono f] (g : (X : C) ⟶ A)
(w : g ≫ f = X.arrow) : X ≤ mk f :=
le_of_comm (g ≫ (underlyingIso f).inv) <| by simp [w]
theorem mk_le_of_comm {B A : C} {X : Subobject B} {f : A ⟶ B} [Mono f] (g : A ⟶ (X : C))
(w : g ≫ X.arrow = f) : mk f ≤ X :=
le_of_comm ((underlyingIso f).hom ≫ g) <| by simp [w]
/-- To show that two subobjects are equal, it suffices to exhibit an isomorphism commuting with
the arrows. -/
@[ext (iff := false)]
theorem eq_of_comm {B : C} {X Y : Subobject B} (f : (X : C) ≅ (Y : C))
(w : f.hom ≫ Y.arrow = X.arrow) : X = Y :=
le_antisymm (le_of_comm f.hom w) <| le_of_comm f.inv <| f.inv_comp_eq.2 w.symm
/-- To show that two subobjects are equal, it suffices to exhibit an isomorphism commuting with
the arrows. -/
theorem eq_mk_of_comm {B A : C} {X : Subobject B} (f : A ⟶ B) [Mono f] (i : (X : C) ≅ A)
(w : i.hom ≫ f = X.arrow) : X = mk f :=
eq_of_comm (i.trans (underlyingIso f).symm) <| by simp [w]
/-- To show that two subobjects are equal, it suffices to exhibit an isomorphism commuting with
the arrows. -/
theorem mk_eq_of_comm {B A : C} {X : Subobject B} (f : A ⟶ B) [Mono f] (i : A ≅ (X : C))
(w : i.hom ≫ X.arrow = f) : mk f = X :=
Eq.symm <| eq_mk_of_comm _ i.symm <| by rw [Iso.symm_hom, Iso.inv_comp_eq, w]
/-- To show that two subobjects are equal, it suffices to exhibit an isomorphism commuting with
the arrows. -/
theorem mk_eq_mk_of_comm {B A₁ A₂ : C} (f : A₁ ⟶ B) (g : A₂ ⟶ B) [Mono f] [Mono g] (i : A₁ ≅ A₂)
(w : i.hom ≫ g = f) : mk f = mk g :=
eq_mk_of_comm _ ((underlyingIso f).trans i) <| by simp [w]
lemma mk_surjective {X : C} (S : Subobject X) :
∃ (A : C) (i : A ⟶ X) (_ : Mono i), S = Subobject.mk i :=
⟨_, S.arrow, inferInstance, by simp⟩
-- We make `X` and `Y` explicit arguments here so that when `ofLE` appears in goal statements
-- it is possible to see its source and target
-- (`h` will just display as `_`, because it is in `Prop`).
/-- An inequality of subobjects is witnessed by some morphism between the corresponding objects. -/
def ofLE {B : C} (X Y : Subobject B) (h : X ≤ Y) : (X : C) ⟶ (Y : C) :=
underlying.map <| h.hom
@[reassoc (attr := simp)]
theorem ofLE_arrow {B : C} {X Y : Subobject B} (h : X ≤ Y) : ofLE X Y h ≫ Y.arrow = X.arrow :=
underlying_arrow _
instance {B : C} (X Y : Subobject B) (h : X ≤ Y) : Mono (ofLE X Y h) := by
fconstructor
intro Z f g w
replace w := w =≫ Y.arrow
ext
simpa using w
theorem ofLE_mk_le_mk_of_comm {B A₁ A₂ : C} {f₁ : A₁ ⟶ B} {f₂ : A₂ ⟶ B} [Mono f₁] [Mono f₂]
(g : A₁ ⟶ A₂) (w : g ≫ f₂ = f₁) :
ofLE _ _ (mk_le_mk_of_comm g w) = (underlyingIso _).hom ≫ g ≫ (underlyingIso _).inv := by
ext
simp [w]
/-- An inequality of subobjects is witnessed by some morphism between the corresponding objects. -/
def ofLEMk {B A : C} (X : Subobject B) (f : A ⟶ B) [Mono f] (h : X ≤ mk f) : (X : C) ⟶ A :=
ofLE X (mk f) h ≫ (underlyingIso f).hom
instance {B A : C} (X : Subobject B) (f : A ⟶ B) [Mono f] (h : X ≤ mk f) :
Mono (ofLEMk X f h) := by
dsimp only [ofLEMk]
infer_instance
@[simp]
theorem ofLEMk_comp {B A : C} {X : Subobject B} {f : A ⟶ B} [Mono f] (h : X ≤ mk f) :
ofLEMk X f h ≫ f = X.arrow := by simp [ofLEMk]
/-- An inequality of subobjects is witnessed by some morphism between the corresponding objects. -/
def ofMkLE {B A : C} (f : A ⟶ B) [Mono f] (X : Subobject B) (h : mk f ≤ X) : A ⟶ (X : C) :=
(underlyingIso f).inv ≫ ofLE (mk f) X h
instance {B A : C} (f : A ⟶ B) [Mono f] (X : Subobject B) (h : mk f ≤ X) :
Mono (ofMkLE f X h) := by
dsimp only [ofMkLE]
infer_instance
@[simp]
theorem ofMkLE_arrow {B A : C} {f : A ⟶ B} [Mono f] {X : Subobject B} (h : mk f ≤ X) :
ofMkLE f X h ≫ X.arrow = f := by simp [ofMkLE]
/-- An inequality of subobjects is witnessed by some morphism between the corresponding objects. -/
def ofMkLEMk {B A₁ A₂ : C} (f : A₁ ⟶ B) (g : A₂ ⟶ B) [Mono f] [Mono g] (h : mk f ≤ mk g) :
A₁ ⟶ A₂ :=
(underlyingIso f).inv ≫ ofLE (mk f) (mk g) h ≫ (underlyingIso g).hom
instance {B A₁ A₂ : C} (f : A₁ ⟶ B) (g : A₂ ⟶ B) [Mono f] [Mono g] (h : mk f ≤ mk g) :
Mono (ofMkLEMk f g h) := by
dsimp only [ofMkLEMk]
infer_instance
@[simp]
theorem ofMkLEMk_comp {B A₁ A₂ : C} {f : A₁ ⟶ B} {g : A₂ ⟶ B} [Mono f] [Mono g] (h : mk f ≤ mk g) :
ofMkLEMk f g h ≫ g = f := by simp [ofMkLEMk]
@[reassoc (attr := simp)]
theorem ofLE_comp_ofLE {B : C} (X Y Z : Subobject B) (h₁ : X ≤ Y) (h₂ : Y ≤ Z) :
ofLE X Y h₁ ≫ ofLE Y Z h₂ = ofLE X Z (h₁.trans h₂) := by
simp only [ofLE, ← Functor.map_comp underlying]
congr 1
@[reassoc (attr := simp)]
theorem ofLE_comp_ofLEMk {B A : C} (X Y : Subobject B) (f : A ⟶ B) [Mono f] (h₁ : X ≤ Y)
(h₂ : Y ≤ mk f) : ofLE X Y h₁ ≫ ofLEMk Y f h₂ = ofLEMk X f (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ← Functor.map_comp_assoc underlying]
congr 1
@[reassoc (attr := simp)]
theorem ofLEMk_comp_ofMkLE {B A : C} (X : Subobject B) (f : A ⟶ B) [Mono f] (Y : Subobject B)
(h₁ : X ≤ mk f) (h₂ : mk f ≤ Y) : ofLEMk X f h₁ ≫ ofMkLE f Y h₂ = ofLE X Y (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ← Functor.map_comp underlying, assoc, Iso.hom_inv_id_assoc]
congr 1
@[reassoc (attr := simp)]
theorem ofLEMk_comp_ofMkLEMk {B A₁ A₂ : C} (X : Subobject B) (f : A₁ ⟶ B) [Mono f] (g : A₂ ⟶ B)
[Mono g] (h₁ : X ≤ mk f) (h₂ : mk f ≤ mk g) :
ofLEMk X f h₁ ≫ ofMkLEMk f g h₂ = ofLEMk X g (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ofMkLEMk, ← Functor.map_comp_assoc underlying,
assoc, Iso.hom_inv_id_assoc]
congr 1
@[reassoc (attr := simp)]
theorem ofMkLE_comp_ofLE {B A₁ : C} (f : A₁ ⟶ B) [Mono f] (X Y : Subobject B) (h₁ : mk f ≤ X)
(h₂ : X ≤ Y) : ofMkLE f X h₁ ≫ ofLE X Y h₂ = ofMkLE f Y (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ofMkLEMk, ← Functor.map_comp underlying,
assoc]
congr 1
@[reassoc (attr := simp)]
theorem ofMkLE_comp_ofLEMk {B A₁ A₂ : C} (f : A₁ ⟶ B) [Mono f] (X : Subobject B) (g : A₂ ⟶ B)
[Mono g] (h₁ : mk f ≤ X) (h₂ : X ≤ mk g) :
ofMkLE f X h₁ ≫ ofLEMk X g h₂ = ofMkLEMk f g (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ofMkLEMk, ← Functor.map_comp_assoc underlying, assoc]
congr 1
@[reassoc (attr := simp)]
theorem ofMkLEMk_comp_ofMkLE {B A₁ A₂ : C} (f : A₁ ⟶ B) [Mono f] (g : A₂ ⟶ B) [Mono g]
(X : Subobject B) (h₁ : mk f ≤ mk g) (h₂ : mk g ≤ X) :
ofMkLEMk f g h₁ ≫ ofMkLE g X h₂ = ofMkLE f X (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ofMkLEMk, ← Functor.map_comp underlying,
assoc, Iso.hom_inv_id_assoc]
congr 1
@[reassoc (attr := simp)]
theorem ofMkLEMk_comp_ofMkLEMk {B A₁ A₂ A₃ : C} (f : A₁ ⟶ B) [Mono f] (g : A₂ ⟶ B) [Mono g]
(h : A₃ ⟶ B) [Mono h] (h₁ : mk f ≤ mk g) (h₂ : mk g ≤ mk h) :
ofMkLEMk f g h₁ ≫ ofMkLEMk g h h₂ = ofMkLEMk f h (h₁.trans h₂) := by
simp only [ofMkLE, ofLEMk, ofLE, ofMkLEMk, ← Functor.map_comp_assoc underlying, assoc,
Iso.hom_inv_id_assoc]
congr 1
@[simp]
theorem ofLE_refl {B : C} (X : Subobject B) : ofLE X X le_rfl = 𝟙 _ := by
apply (cancel_mono X.arrow).mp
simp
@[simp]
theorem ofMkLEMk_refl {B A₁ : C} (f : A₁ ⟶ B) [Mono f] : ofMkLEMk f f le_rfl = 𝟙 _ := by
apply (cancel_mono f).mp
simp
-- As with `ofLE`, we have `X` and `Y` as explicit arguments for readability.
/-- An equality of subobjects gives an isomorphism of the corresponding objects.
(One could use `underlying.mapIso (eqToIso h))` here, but this is more readable.) -/
@[simps]
def isoOfEq {B : C} (X Y : Subobject B) (h : X = Y) : (X : C) ≅ (Y : C) where
hom := ofLE _ _ h.le
inv := ofLE _ _ h.ge
/-- An equality of subobjects gives an isomorphism of the corresponding objects. -/
@[simps]
def isoOfEqMk {B A : C} (X : Subobject B) (f : A ⟶ B) [Mono f] (h : X = mk f) : (X : C) ≅ A where
hom := ofLEMk X f h.le
inv := ofMkLE f X h.ge
/-- An equality of subobjects gives an isomorphism of the corresponding objects. -/
@[simps]
def isoOfMkEq {B A : C} (f : A ⟶ B) [Mono f] (X : Subobject B) (h : mk f = X) : A ≅ (X : C) where
hom := ofMkLE f X h.le
inv := ofLEMk X f h.ge
/-- An equality of subobjects gives an isomorphism of the corresponding objects. -/
@[simps]
def isoOfMkEqMk {B A₁ A₂ : C} (f : A₁ ⟶ B) (g : A₂ ⟶ B) [Mono f] [Mono g] (h : mk f = mk g) :
A₁ ≅ A₂ where
hom := ofMkLEMk f g h.le
inv := ofMkLEMk g f h.ge
lemma mk_lt_mk_of_comm {X A₁ A₂ : C} {i₁ : A₁ ⟶ X} {i₂ : A₂ ⟶ X} [Mono i₁] [Mono i₂]
(f : A₁ ⟶ A₂) (fac : f ≫ i₂ = i₁) (hf : ¬ IsIso f) :
Subobject.mk i₁ < Subobject.mk i₂ := by
obtain _ | h := (mk_le_mk_of_comm _ fac).lt_or_eq
· assumption
· exfalso
apply hf
convert (isoOfMkEqMk i₁ i₂ h).isIso_hom
rw [← cancel_mono i₂, isoOfMkEqMk_hom, ofMkLEMk_comp, fac]
lemma mk_lt_mk_iff_of_comm {X A₁ A₂ : C} {i₁ : A₁ ⟶ X} {i₂ : A₂ ⟶ X} [Mono i₁] [Mono i₂]
(f : A₁ ⟶ A₂) (fac : f ≫ i₂ = i₁) :
Subobject.mk i₁ < Subobject.mk i₂ ↔ ¬ IsIso f :=
⟨fun h hf ↦ by simp only [mk_eq_mk_of_comm i₁ i₂ (asIso f) fac, lt_self_iff_false] at h,
mk_lt_mk_of_comm f fac⟩
end Subobject
namespace MonoOver
variable {P Q : MonoOver X} (f : P ⟶ Q)
include f in
lemma subobjectMk_le_mk_of_hom :
Subobject.mk P.obj.hom ≤ Subobject.mk Q.obj.hom :=
Subobject.mk_le_mk_of_comm f.left (by simp)
lemma isIso_left_iff_subobjectMk_eq :
IsIso f.left ↔ Subobject.mk P.1.hom = Subobject.mk Q.1.hom :=
⟨fun _ ↦ Subobject.mk_eq_mk_of_comm _ _ (asIso f.left) (by simp),
fun h ↦ ⟨Subobject.ofMkLEMk _ _ h.symm.le, by simp [← cancel_mono P.1.hom],
by simp [← cancel_mono Q.1.hom]⟩⟩
lemma isIso_iff_subobjectMk_eq :
IsIso f ↔ Subobject.mk P.1.hom = Subobject.mk Q.1.hom := by
rw [isIso_iff_isIso_left, isIso_left_iff_subobjectMk_eq]
end MonoOver
open CategoryTheory.Limits
namespace Subobject
/-- Any functor `MonoOver X ⥤ MonoOver Y` descends to a functor
`Subobject X ⥤ Subobject Y`, because `MonoOver Y` is thin. -/
def lower {Y : D} (F : MonoOver X ⥤ MonoOver Y) : Subobject X ⥤ Subobject Y :=
ThinSkeleton.map F
/-- Isomorphic functors become equal when lowered to `Subobject`.
(It's not as evil as usual to talk about equality between functors
because the categories are thin and skeletal.) -/
theorem lower_iso (F₁ F₂ : MonoOver X ⥤ MonoOver Y) (h : F₁ ≅ F₂) : lower F₁ = lower F₂ :=
ThinSkeleton.map_iso_eq h
/-- A ternary version of `Subobject.lower`. -/
def lower₂ (F : MonoOver X ⥤ MonoOver Y ⥤ MonoOver Z) : Subobject X ⥤ Subobject Y ⥤ Subobject Z :=
ThinSkeleton.map₂ F
@[simp]
theorem lower_comm (F : MonoOver Y ⥤ MonoOver X) :
toThinSkeleton _ ⋙ lower F = F ⋙ toThinSkeleton _ :=
rfl
/-- An adjunction between `MonoOver A` and `MonoOver B` gives an adjunction
between `Subobject A` and `Subobject B`. -/
def lowerAdjunction {A : C} {B : D} {L : MonoOver A ⥤ MonoOver B} {R : MonoOver B ⥤ MonoOver A}
(h : L ⊣ R) : lower L ⊣ lower R :=
ThinSkeleton.lowerAdjunction _ _ h
/-- An equivalence between `MonoOver A` and `MonoOver B` gives an equivalence
between `Subobject A` and `Subobject B`. -/
@[simps]
def lowerEquivalence {A : C} {B : D} (e : MonoOver A ≌ MonoOver B) : Subobject A ≌ Subobject B where
functor := lower e.functor
inverse := lower e.inverse
unitIso := by
apply eqToIso
convert ThinSkeleton.map_iso_eq e.unitIso
· exact ThinSkeleton.map_id_eq.symm
· exact (ThinSkeleton.map_comp_eq _ _).symm
counitIso := by
apply eqToIso
convert ThinSkeleton.map_iso_eq e.counitIso
· exact (ThinSkeleton.map_comp_eq _ _).symm
· exact ThinSkeleton.map_id_eq.symm
section Pullback
variable [HasPullbacks C]
/-- When `C` has pullbacks, a morphism `f : X ⟶ Y` induces a functor `Subobject Y ⥤ Subobject X`,
by pulling back a monomorphism along `f`. -/
def pullback (f : X ⟶ Y) : Subobject Y ⥤ Subobject X :=
lower (MonoOver.pullback f)
theorem pullback_id (x : Subobject X) : (pullback (𝟙 X)).obj x = x := by
induction' x using Quotient.inductionOn' with f
exact Quotient.sound ⟨MonoOver.pullbackId.app f⟩
theorem pullback_comp (f : X ⟶ Y) (g : Y ⟶ Z) (x : Subobject Z) :
(pullback (f ≫ g)).obj x = (pullback f).obj ((pullback g).obj x) := by
induction' x using Quotient.inductionOn' with t
exact Quotient.sound ⟨(MonoOver.pullbackComp _ _).app t⟩
theorem pullback_obj_mk {A B X Y : C} {f : Y ⟶ X} {i : A ⟶ X} [Mono i]
{j : B ⟶ Y} [Mono j] {f' : B ⟶ A}
(h : IsPullback f' j i f) :
(pullback f).obj (mk i) = mk j :=
((equivMonoOver Y).inverse.mapIso
(MonoOver.pullbackObjIsoOfIsPullback _ _ _ _ h)).to_eq
theorem pullback_obj {X Y : C} (f : Y ⟶ X) (x : Subobject X) :
(pullback f).obj x = mk (pullback.snd x.arrow f) := by
obtain ⟨Z, i, _, rfl⟩ := mk_surjective x
rw [pullback_obj_mk (IsPullback.of_hasPullback i f)]
exact mk_eq_mk_of_comm _ _ (asIso (pullback.map i f (mk i).arrow f
(underlyingIso i).inv (𝟙 _) (𝟙 _) (by simp) (by simp))) (by simp)
instance (f : X ⟶ Y) : (pullback f).Faithful where
end Pullback
section Map
/-- We can map subobjects of `X` to subobjects of `Y`
by post-composition with a monomorphism `f : X ⟶ Y`.
-/
def map (f : X ⟶ Y) [Mono f] : Subobject X ⥤ Subobject Y :=
lower (MonoOver.map f)
lemma map_mk {A X Y : C} (i : A ⟶ X) [Mono i] (f : X ⟶ Y) [Mono f] :
(map f).obj (mk i) = mk (i ≫ f) :=
rfl
theorem map_id (x : Subobject X) : (map (𝟙 X)).obj x = x := by
induction' x using Quotient.inductionOn' with f
exact Quotient.sound ⟨(MonoOver.mapId _).app f⟩
theorem map_comp (f : X ⟶ Y) (g : Y ⟶ Z) [Mono f] [Mono g] (x : Subobject X) :
| (map (f ≫ g)).obj x = (map g).obj ((map f).obj x) := by
induction' x using Quotient.inductionOn' with t
exact Quotient.sound ⟨(MonoOver.mapComp _ _).app t⟩
| Mathlib/CategoryTheory/Subobject/Basic.lean | 580 | 582 |
/-
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.Module.Submodule.Ker
import Mathlib.Algebra.Module.Submodule.RestrictScalars
import Mathlib.Data.Set.Finite.Range
/-!
# Range of linear maps
The range `LinearMap.range` of a (semi)linear map `f : M → M₂` is a submodule of `M₂`.
More specifically, `LinearMap.range` applies to any `SemilinearMapClass` over a `RingHomSurjective`
ring homomorphism.
Note that this also means that dot notation (i.e. `f.range` for a linear map `f`) does not work.
## Notations
* We continue to use the notations `M →ₛₗ[σ] M₂` and `M →ₗ[R] M₂` for the type of semilinear
(resp. linear) maps from `M` to `M₂` over the ring homomorphism `σ` (resp. over the ring `R`).
## Tags
linear algebra, vector space, module, range
-/
open Function
variable {R : Type*} {R₂ : Type*} {R₃ : Type*}
variable {K : Type*}
variable {M : Type*} {M₂ : Type*} {M₃ : Type*}
variable {V : Type*} {V₂ : Type*}
namespace LinearMap
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]
open Submodule
variable {τ₁₂ : R →+* R₂} {τ₂₃ : R₂ →+* R₃} {τ₁₃ : R →+* R₃}
variable [RingHomCompTriple τ₁₂ τ₂₃ τ₁₃]
section
variable {F : Type*} [FunLike F M M₂] [SemilinearMapClass F τ₁₂ M M₂]
/-- The range of a linear map `f : M → M₂` is a submodule of `M₂`.
See Note [range copy pattern]. -/
def range [RingHomSurjective τ₁₂] (f : F) : Submodule R₂ M₂ :=
(map f ⊤).copy (Set.range f) Set.image_univ.symm
theorem range_coe [RingHomSurjective τ₁₂] (f : F) : (range f : Set M₂) = Set.range f :=
rfl
theorem range_toAddSubmonoid [RingHomSurjective τ₁₂] (f : M →ₛₗ[τ₁₂] M₂) :
(range f).toAddSubmonoid = AddMonoidHom.mrange f :=
rfl
@[simp]
theorem mem_range [RingHomSurjective τ₁₂] {f : F} {x} : x ∈ range f ↔ ∃ y, f y = x :=
Iff.rfl
theorem range_eq_map [RingHomSurjective τ₁₂] (f : F) : range f = map f ⊤ := by
ext
simp
theorem mem_range_self [RingHomSurjective τ₁₂] (f : F) (x : M) : f x ∈ range f :=
⟨x, rfl⟩
@[simp]
theorem range_id : range (LinearMap.id : M →ₗ[R] M) = ⊤ :=
SetLike.coe_injective Set.range_id
theorem range_comp [RingHomSurjective τ₁₂] [RingHomSurjective τ₂₃] [RingHomSurjective τ₁₃]
(f : M →ₛₗ[τ₁₂] M₂) (g : M₂ →ₛₗ[τ₂₃] M₃) : range (g.comp f : M →ₛₗ[τ₁₃] M₃) = map g (range f) :=
SetLike.coe_injective (Set.range_comp g f)
theorem range_comp_le_range [RingHomSurjective τ₂₃] [RingHomSurjective τ₁₃] (f : M →ₛₗ[τ₁₂] M₂)
(g : M₂ →ₛₗ[τ₂₃] M₃) : range (g.comp f : M →ₛₗ[τ₁₃] M₃) ≤ range g :=
SetLike.coe_mono (Set.range_comp_subset_range f g)
theorem range_eq_top [RingHomSurjective τ₁₂] {f : F} :
range f = ⊤ ↔ Surjective f := by
rw [SetLike.ext'_iff, range_coe, top_coe, Set.range_eq_univ]
theorem range_eq_top_of_surjective [RingHomSurjective τ₁₂] (f : F) (hf : Surjective f) :
range f = ⊤ := range_eq_top.2 hf
theorem range_le_iff_comap [RingHomSurjective τ₁₂] {f : F} {p : Submodule R₂ M₂} :
range f ≤ p ↔ comap f p = ⊤ := by rw [range_eq_map, map_le_iff_le_comap, eq_top_iff]
theorem map_le_range [RingHomSurjective τ₁₂] {f : F} {p : Submodule R M} : map f p ≤ range f :=
SetLike.coe_mono (Set.image_subset_range f p)
@[simp]
theorem range_neg {R : Type*} {R₂ : Type*} {M : Type*} {M₂ : Type*} [Semiring R] [Ring R₂]
[AddCommMonoid M] [AddCommGroup M₂] [Module R M] [Module R₂ M₂] {τ₁₂ : R →+* R₂}
[RingHomSurjective τ₁₂] (f : M →ₛₗ[τ₁₂] M₂) : LinearMap.range (-f) = LinearMap.range f := by
change range ((-LinearMap.id : M₂ →ₗ[R₂] M₂).comp f) = _
rw [range_comp, Submodule.map_neg, Submodule.map_id]
@[simp] lemma range_domRestrict [Module R M₂] (K : Submodule R M) (f : M →ₗ[R] M₂) :
range (domRestrict f K) = K.map f := by ext; simp
lemma range_domRestrict_le_range [RingHomSurjective τ₁₂] (f : M →ₛₗ[τ₁₂] M₂) (S : Submodule R M) :
LinearMap.range (f.domRestrict S) ≤ LinearMap.range f := by
rintro x ⟨⟨y, hy⟩, rfl⟩
exact LinearMap.mem_range_self f y
@[simp]
theorem _root_.AddMonoidHom.coe_toIntLinearMap_range {M M₂ : Type*} [AddCommGroup M]
[AddCommGroup M₂] (f : M →+ M₂) :
LinearMap.range f.toIntLinearMap = AddSubgroup.toIntSubmodule f.range := rfl
lemma _root_.Submodule.map_comap_eq_of_le [RingHomSurjective τ₁₂] {f : F} {p : Submodule R₂ M₂}
(h : p ≤ LinearMap.range f) : (p.comap f).map f = p :=
SetLike.coe_injective <| Set.image_preimage_eq_of_subset h
lemma range_restrictScalars [SMul R R₂] [Module R₂ M] [Module R M₂] [CompatibleSMul M M₂ R R₂]
[IsScalarTower R R₂ M₂] (f : M →ₗ[R₂] M₂) :
LinearMap.range (f.restrictScalars R) = (LinearMap.range f).restrictScalars R := rfl
end
/-- The decreasing sequence of submodules consisting of the ranges of the iterates of a linear map.
-/
@[simps]
def iterateRange (f : M →ₗ[R] M) : ℕ →o (Submodule R M)ᵒᵈ where
toFun n := LinearMap.range (f ^ n)
monotone' n m w x h := by
obtain ⟨c, rfl⟩ := Nat.exists_eq_add_of_le w
rw [LinearMap.mem_range] at h
obtain ⟨m, rfl⟩ := h
rw [LinearMap.mem_range]
use (f ^ c) m
rw [pow_add, Module.End.mul_apply]
/-- Restrict the codomain of a linear map `f` to `f.range`.
This is the bundled version of `Set.rangeFactorization`. -/
abbrev rangeRestrict [RingHomSurjective τ₁₂] (f : M →ₛₗ[τ₁₂] M₂) : M →ₛₗ[τ₁₂] LinearMap.range f :=
f.codRestrict (LinearMap.range f) (LinearMap.mem_range_self f)
/-- The range of a linear map is finite if the domain is finite.
Note: this instance can form a diamond with `Subtype.fintype` in the
presence of `Fintype M₂`. -/
instance fintypeRange [Fintype M] [DecidableEq M₂] [RingHomSurjective τ₁₂] (f : M →ₛₗ[τ₁₂] M₂) :
Fintype (range f) :=
Set.fintypeRange f
variable {F : Type*} [FunLike F M M₂] [SemilinearMapClass F τ₁₂ M M₂]
theorem range_codRestrict {τ₂₁ : R₂ →+* R} [RingHomSurjective τ₂₁] (p : Submodule R M)
(f : M₂ →ₛₗ[τ₂₁] M) (hf) :
range (codRestrict p f hf) = comap p.subtype (LinearMap.range f) := by
simpa only [range_eq_map] using map_codRestrict _ _ _ _
theorem _root_.Submodule.map_comap_eq [RingHomSurjective τ₁₂] (f : F) (q : Submodule R₂ M₂) :
map f (comap f q) = range f ⊓ q :=
le_antisymm (le_inf map_le_range (map_comap_le _ _)) <| by
rintro _ ⟨⟨x, _, rfl⟩, hx⟩; exact ⟨x, hx, rfl⟩
theorem _root_.Submodule.map_comap_eq_self [RingHomSurjective τ₁₂] {f : F} {q : Submodule R₂ M₂}
(h : q ≤ range f) : map f (comap f q) = q := by rwa [Submodule.map_comap_eq, inf_eq_right]
@[simp]
theorem range_zero [RingHomSurjective τ₁₂] : range (0 : M →ₛₗ[τ₁₂] M₂) = ⊥ := by
simpa only [range_eq_map] using Submodule.map_zero _
section
variable [RingHomSurjective τ₁₂]
theorem range_le_bot_iff (f : M →ₛₗ[τ₁₂] M₂) : range f ≤ ⊥ ↔ f = 0 := by
rw [range_le_iff_comap]; exact ker_eq_top
theorem range_eq_bot {f : M →ₛₗ[τ₁₂] M₂} : range f = ⊥ ↔ f = 0 := by
rw [← range_le_bot_iff, le_bot_iff]
theorem range_le_ker_iff {f : M →ₛₗ[τ₁₂] M₂} {g : M₂ →ₛₗ[τ₂₃] M₃} :
range f ≤ ker g ↔ (g.comp f : M →ₛₗ[τ₁₃] M₃) = 0 :=
⟨fun h => ker_eq_top.1 <| eq_top_iff'.2 fun _ => h <| ⟨_, rfl⟩, fun h x hx =>
mem_ker.2 <| Exists.elim hx fun y hy => by rw [← hy, ← comp_apply, h, zero_apply]⟩
theorem comap_le_comap_iff {f : F} (hf : range f = ⊤) {p p'} : comap f p ≤ comap f p' ↔ p ≤ p' :=
⟨fun H ↦ by rwa [SetLike.le_def, (range_eq_top.1 hf).forall], comap_mono⟩
theorem comap_injective {f : F} (hf : range f = ⊤) : Injective (comap f) := fun _ _ h =>
le_antisymm ((comap_le_comap_iff hf).1 (le_of_eq h)) ((comap_le_comap_iff hf).1 (ge_of_eq h))
-- TODO (?): generalize to semilinear maps with `f ∘ₗ g` bijective.
theorem ker_eq_range_of_comp_eq_id {M P} [AddCommGroup M] [Module R M]
[AddCommGroup P] [Module R P] {f : M →ₗ[R] P} {g : P →ₗ[R] M} (h : f ∘ₗ g = .id) :
ker f = range (LinearMap.id - g ∘ₗ f) :=
le_antisymm (fun x hx ↦ ⟨x, show x - g (f x) = x by rw [hx, map_zero, sub_zero]⟩) <|
range_le_ker_iff.mpr <| by rw [comp_sub, comp_id, ← comp_assoc, h, id_comp, sub_self]
end
|
end AddCommMonoid
| Mathlib/Algebra/Module/Submodule/Range.lean | 206 | 207 |
/-
Copyright (c) 2019 Calle Sönne. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Calle Sönne
-/
import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic
import Mathlib.Analysis.Normed.Group.AddCircle
import Mathlib.Algebra.CharZero.Quotient
import Mathlib.Topology.Instances.Sign
/-!
# The type of angles
In this file we define `Real.Angle` to be the quotient group `ℝ/2πℤ` and prove a few simple lemmas
about trigonometric functions and angles.
-/
open Real
noncomputable section
namespace Real
/-- The type of angles -/
def Angle : Type :=
AddCircle (2 * π)
-- The `NormedAddCommGroup, Inhabited` instances should be constructed by a deriving handler.
-- https://github.com/leanprover-community/mathlib4/issues/380
namespace Angle
instance : NormedAddCommGroup Angle :=
inferInstanceAs (NormedAddCommGroup (AddCircle (2 * π)))
instance : Inhabited Angle :=
inferInstanceAs (Inhabited (AddCircle (2 * π)))
/-- The canonical map from `ℝ` to the quotient `Angle`. -/
@[coe]
protected def coe (r : ℝ) : Angle := QuotientAddGroup.mk r
instance : Coe ℝ Angle := ⟨Angle.coe⟩
instance : CircularOrder Real.Angle :=
QuotientAddGroup.circularOrder (hp' := ⟨by norm_num [pi_pos]⟩)
@[continuity]
theorem continuous_coe : Continuous ((↑) : ℝ → Angle) :=
continuous_quotient_mk'
/-- Coercion `ℝ → Angle` as an additive homomorphism. -/
def coeHom : ℝ →+ Angle :=
QuotientAddGroup.mk' _
@[simp]
theorem coe_coeHom : (coeHom : ℝ → Angle) = ((↑) : ℝ → Angle) :=
rfl
/-- An induction principle to deduce results for `Angle` from those for `ℝ`, used with
`induction θ using Real.Angle.induction_on`. -/
@[elab_as_elim]
protected theorem induction_on {p : Angle → Prop} (θ : Angle) (h : ∀ x : ℝ, p x) : p θ :=
Quotient.inductionOn' θ h
@[simp]
theorem coe_zero : ↑(0 : ℝ) = (0 : Angle) :=
rfl
@[simp]
theorem coe_add (x y : ℝ) : ↑(x + y : ℝ) = (↑x + ↑y : Angle) :=
rfl
@[simp]
theorem coe_neg (x : ℝ) : ↑(-x : ℝ) = -(↑x : Angle) :=
rfl
@[simp]
theorem coe_sub (x y : ℝ) : ↑(x - y : ℝ) = (↑x - ↑y : Angle) :=
rfl
theorem coe_nsmul (n : ℕ) (x : ℝ) : ↑(n • x : ℝ) = n • (↑x : Angle) :=
rfl
theorem coe_zsmul (z : ℤ) (x : ℝ) : ↑(z • x : ℝ) = z • (↑x : Angle) :=
rfl
theorem coe_eq_zero_iff {x : ℝ} : (x : Angle) = 0 ↔ ∃ n : ℤ, n • (2 * π) = x :=
AddCircle.coe_eq_zero_iff (2 * π)
@[simp, norm_cast]
theorem natCast_mul_eq_nsmul (x : ℝ) (n : ℕ) : ↑((n : ℝ) * x) = n • (↑x : Angle) := by
simpa only [nsmul_eq_mul] using coeHom.map_nsmul x n
@[simp, norm_cast]
theorem intCast_mul_eq_zsmul (x : ℝ) (n : ℤ) : ↑((n : ℝ) * x : ℝ) = n • (↑x : Angle) := by
simpa only [zsmul_eq_mul] using coeHom.map_zsmul x n
theorem angle_eq_iff_two_pi_dvd_sub {ψ θ : ℝ} : (θ : Angle) = ψ ↔ ∃ k : ℤ, θ - ψ = 2 * π * k := by
simp only [QuotientAddGroup.eq, AddSubgroup.zmultiples_eq_closure,
AddSubgroup.mem_closure_singleton, zsmul_eq_mul', (sub_eq_neg_add _ _).symm, eq_comm]
rw [Angle.coe, Angle.coe, QuotientAddGroup.eq]
simp only [AddSubgroup.zmultiples_eq_closure,
AddSubgroup.mem_closure_singleton, zsmul_eq_mul', (sub_eq_neg_add _ _).symm, eq_comm]
@[simp]
theorem coe_two_pi : ↑(2 * π : ℝ) = (0 : Angle) :=
angle_eq_iff_two_pi_dvd_sub.2 ⟨1, by rw [sub_zero, Int.cast_one, mul_one]⟩
@[simp]
theorem neg_coe_pi : -(π : Angle) = π := by
rw [← coe_neg, angle_eq_iff_two_pi_dvd_sub]
use -1
simp [two_mul, sub_eq_add_neg]
@[simp]
theorem two_nsmul_coe_div_two (θ : ℝ) : (2 : ℕ) • (↑(θ / 2) : Angle) = θ := by
rw [← coe_nsmul, two_nsmul, add_halves]
@[simp]
theorem two_zsmul_coe_div_two (θ : ℝ) : (2 : ℤ) • (↑(θ / 2) : Angle) = θ := by
rw [← coe_zsmul, two_zsmul, add_halves]
theorem two_nsmul_neg_pi_div_two : (2 : ℕ) • (↑(-π / 2) : Angle) = π := by
rw [two_nsmul_coe_div_two, coe_neg, neg_coe_pi]
theorem two_zsmul_neg_pi_div_two : (2 : ℤ) • (↑(-π / 2) : Angle) = π := by
rw [two_zsmul, ← two_nsmul, two_nsmul_neg_pi_div_two]
theorem sub_coe_pi_eq_add_coe_pi (θ : Angle) : θ - π = θ + π := by
rw [sub_eq_add_neg, neg_coe_pi]
@[simp]
theorem two_nsmul_coe_pi : (2 : ℕ) • (π : Angle) = 0 := by simp [← natCast_mul_eq_nsmul]
@[simp]
theorem two_zsmul_coe_pi : (2 : ℤ) • (π : Angle) = 0 := by simp [← intCast_mul_eq_zsmul]
@[simp]
theorem coe_pi_add_coe_pi : (π : Real.Angle) + π = 0 := by rw [← two_nsmul, two_nsmul_coe_pi]
theorem zsmul_eq_iff {ψ θ : Angle} {z : ℤ} (hz : z ≠ 0) :
z • ψ = z • θ ↔ ∃ k : Fin z.natAbs, ψ = θ + (k : ℕ) • (2 * π / z : ℝ) :=
QuotientAddGroup.zmultiples_zsmul_eq_zsmul_iff hz
theorem nsmul_eq_iff {ψ θ : Angle} {n : ℕ} (hz : n ≠ 0) :
n • ψ = n • θ ↔ ∃ k : Fin n, ψ = θ + (k : ℕ) • (2 * π / n : ℝ) :=
QuotientAddGroup.zmultiples_nsmul_eq_nsmul_iff hz
theorem two_zsmul_eq_iff {ψ θ : Angle} : (2 : ℤ) • ψ = (2 : ℤ) • θ ↔ ψ = θ ∨ ψ = θ + ↑π := by
have : Int.natAbs 2 = 2 := rfl
rw [zsmul_eq_iff two_ne_zero, this, Fin.exists_fin_two, Fin.val_zero,
Fin.val_one, zero_smul, add_zero, one_smul, Int.cast_two,
mul_div_cancel_left₀ (_ : ℝ) two_ne_zero]
theorem two_nsmul_eq_iff {ψ θ : Angle} : (2 : ℕ) • ψ = (2 : ℕ) • θ ↔ ψ = θ ∨ ψ = θ + ↑π := by
simp_rw [← natCast_zsmul, Nat.cast_ofNat, two_zsmul_eq_iff]
theorem two_nsmul_eq_zero_iff {θ : Angle} : (2 : ℕ) • θ = 0 ↔ θ = 0 ∨ θ = π := by
convert two_nsmul_eq_iff <;> simp
theorem two_nsmul_ne_zero_iff {θ : Angle} : (2 : ℕ) • θ ≠ 0 ↔ θ ≠ 0 ∧ θ ≠ π := by
rw [← not_or, ← two_nsmul_eq_zero_iff]
theorem two_zsmul_eq_zero_iff {θ : Angle} : (2 : ℤ) • θ = 0 ↔ θ = 0 ∨ θ = π := by
simp_rw [two_zsmul, ← two_nsmul, two_nsmul_eq_zero_iff]
theorem two_zsmul_ne_zero_iff {θ : Angle} : (2 : ℤ) • θ ≠ 0 ↔ θ ≠ 0 ∧ θ ≠ π := by
rw [← not_or, ← two_zsmul_eq_zero_iff]
theorem eq_neg_self_iff {θ : Angle} : θ = -θ ↔ θ = 0 ∨ θ = π := by
rw [← add_eq_zero_iff_eq_neg, ← two_nsmul, two_nsmul_eq_zero_iff]
theorem ne_neg_self_iff {θ : Angle} : θ ≠ -θ ↔ θ ≠ 0 ∧ θ ≠ π := by
rw [← not_or, ← eq_neg_self_iff.not]
theorem neg_eq_self_iff {θ : Angle} : -θ = θ ↔ θ = 0 ∨ θ = π := by rw [eq_comm, eq_neg_self_iff]
theorem neg_ne_self_iff {θ : Angle} : -θ ≠ θ ↔ θ ≠ 0 ∧ θ ≠ π := by
rw [← not_or, ← neg_eq_self_iff.not]
theorem two_nsmul_eq_pi_iff {θ : Angle} : (2 : ℕ) • θ = π ↔ θ = (π / 2 : ℝ) ∨ θ = (-π / 2 : ℝ) := by
have h : (π : Angle) = ((2 : ℕ) • (π / 2 : ℝ):) := by rw [two_nsmul, add_halves]
nth_rw 1 [h]
rw [coe_nsmul, two_nsmul_eq_iff]
-- Porting note: `congr` didn't simplify the goal of iff of `Or`s
convert Iff.rfl
rw [add_comm, ← coe_add, ← sub_eq_zero, ← coe_sub, neg_div, ← neg_sub, sub_neg_eq_add, add_assoc,
add_halves, ← two_mul, coe_neg, coe_two_pi, neg_zero]
theorem two_zsmul_eq_pi_iff {θ : Angle} : (2 : ℤ) • θ = π ↔ θ = (π / 2 : ℝ) ∨ θ = (-π / 2 : ℝ) := by
rw [two_zsmul, ← two_nsmul, two_nsmul_eq_pi_iff]
theorem cos_eq_iff_coe_eq_or_eq_neg {θ ψ : ℝ} :
cos θ = cos ψ ↔ (θ : Angle) = ψ ∨ (θ : Angle) = -ψ := by
constructor
· intro Hcos
rw [← sub_eq_zero, cos_sub_cos, mul_eq_zero, mul_eq_zero, neg_eq_zero,
eq_false (two_ne_zero' ℝ), false_or, sin_eq_zero_iff, sin_eq_zero_iff] at Hcos
rcases Hcos with (⟨n, hn⟩ | ⟨n, hn⟩)
· right
rw [eq_div_iff_mul_eq (two_ne_zero' ℝ), ← sub_eq_iff_eq_add] at hn
rw [← hn, coe_sub, eq_neg_iff_add_eq_zero, sub_add_cancel, mul_assoc, intCast_mul_eq_zsmul,
mul_comm, coe_two_pi, zsmul_zero]
· left
rw [eq_div_iff_mul_eq (two_ne_zero' ℝ), eq_sub_iff_add_eq] at hn
rw [← hn, coe_add, mul_assoc, intCast_mul_eq_zsmul, mul_comm, coe_two_pi, zsmul_zero,
zero_add]
· rw [angle_eq_iff_two_pi_dvd_sub, ← coe_neg, angle_eq_iff_two_pi_dvd_sub]
rintro (⟨k, H⟩ | ⟨k, H⟩)
· rw [← sub_eq_zero, cos_sub_cos, H, mul_assoc 2 π k, mul_div_cancel_left₀ _ (two_ne_zero' ℝ),
mul_comm π _, sin_int_mul_pi, mul_zero]
rw [← sub_eq_zero, cos_sub_cos, ← sub_neg_eq_add, H, mul_assoc 2 π k,
mul_div_cancel_left₀ _ (two_ne_zero' ℝ), mul_comm π _, sin_int_mul_pi, mul_zero,
zero_mul]
theorem sin_eq_iff_coe_eq_or_add_eq_pi {θ ψ : ℝ} :
sin θ = sin ψ ↔ (θ : Angle) = ψ ∨ (θ : Angle) + ψ = π := by
constructor
· intro Hsin
rw [← cos_pi_div_two_sub, ← cos_pi_div_two_sub] at Hsin
rcases cos_eq_iff_coe_eq_or_eq_neg.mp Hsin with h | h
· left
rw [coe_sub, coe_sub] at h
exact sub_right_inj.1 h
right
rw [coe_sub, coe_sub, eq_neg_iff_add_eq_zero, add_sub, sub_add_eq_add_sub, ← coe_add,
add_halves, sub_sub, sub_eq_zero] at h
exact h.symm
· rw [angle_eq_iff_two_pi_dvd_sub, ← eq_sub_iff_add_eq, ← coe_sub, angle_eq_iff_two_pi_dvd_sub]
rintro (⟨k, H⟩ | ⟨k, H⟩)
· rw [← sub_eq_zero, sin_sub_sin, H, mul_assoc 2 π k, mul_div_cancel_left₀ _ (two_ne_zero' ℝ),
mul_comm π _, sin_int_mul_pi, mul_zero, zero_mul]
have H' : θ + ψ = 2 * k * π + π := by
rwa [← sub_add, sub_add_eq_add_sub, sub_eq_iff_eq_add, mul_assoc, mul_comm π _, ←
mul_assoc] at H
rw [← sub_eq_zero, sin_sub_sin, H', add_div, mul_assoc 2 _ π,
| mul_div_cancel_left₀ _ (two_ne_zero' ℝ), cos_add_pi_div_two, sin_int_mul_pi, neg_zero,
mul_zero]
| Mathlib/Analysis/SpecialFunctions/Trigonometric/Angle.lean | 239 | 240 |
/-
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.Fintype.List
import Mathlib.Data.Fintype.OfMap
/-!
# Cycles of a list
Lists have an equivalence relation of whether they are rotational permutations of one another.
This relation is defined as `IsRotated`.
Based on this, we define the quotient of lists by the rotation relation, called `Cycle`.
We also define a representation of concrete cycles, available when viewing them in a goal state or
via `#eval`, when over representable types. For example, the cycle `(2 1 4 3)` will be shown
as `c[2, 1, 4, 3]`. Two equal cycles may be printed differently if their internal representation
is different.
-/
assert_not_exists MonoidWithZero
namespace List
variable {α : Type*} [DecidableEq α]
/-- Return the `z` such that `x :: z :: _` appears in `xs`, or `default` if there is no such `z`. -/
def nextOr : ∀ (_ : List α) (_ _ : α), α
| [], _, default => default
| [_], _, default => default
-- Handles the not-found and the wraparound case
| y :: z :: xs, x, default => if x = y then z else nextOr (z :: xs) x default
@[simp]
theorem nextOr_nil (x d : α) : nextOr [] x d = d :=
rfl
@[simp]
theorem nextOr_singleton (x y d : α) : nextOr [y] x d = d :=
rfl
@[simp]
theorem nextOr_self_cons_cons (xs : List α) (x y d : α) : nextOr (x :: y :: xs) x d = y :=
if_pos rfl
theorem nextOr_cons_of_ne (xs : List α) (y x d : α) (h : x ≠ y) :
nextOr (y :: xs) x d = nextOr xs x d := by
rcases xs with - | ⟨z, zs⟩
· rfl
· exact if_neg h
/-- `nextOr` does not depend on the default value, if the next value appears. -/
theorem nextOr_eq_nextOr_of_mem_of_ne (xs : List α) (x d d' : α) (x_mem : x ∈ xs)
(x_ne : x ≠ xs.getLast (ne_nil_of_mem x_mem)) : nextOr xs x d = nextOr xs x d' := by
induction' xs with y ys IH
· cases x_mem
rcases ys with - | ⟨z, zs⟩
· simp at x_mem x_ne
contradiction
by_cases h : x = y
· rw [h, nextOr_self_cons_cons, nextOr_self_cons_cons]
· rw [nextOr, nextOr, IH]
· simpa [h] using x_mem
· simpa using x_ne
theorem mem_of_nextOr_ne {xs : List α} {x d : α} (h : nextOr xs x d ≠ d) : x ∈ xs := by
induction' xs with y ys IH
· simp at h
rcases ys with - | ⟨z, zs⟩
· simp at h
· by_cases hx : x = y
· simp [hx]
· rw [nextOr_cons_of_ne _ _ _ _ hx] at h
simpa [hx] using IH h
theorem nextOr_concat {xs : List α} {x : α} (d : α) (h : x ∉ xs) : nextOr (xs ++ [x]) x d = d := by
induction' xs with z zs IH
· simp
· obtain ⟨hz, hzs⟩ := not_or.mp (mt mem_cons.2 h)
rw [cons_append, nextOr_cons_of_ne _ _ _ _ hz, IH hzs]
theorem nextOr_mem {xs : List α} {x d : α} (hd : d ∈ xs) : nextOr xs x d ∈ xs := by
revert hd
suffices ∀ xs' : List α, (∀ x ∈ xs, x ∈ xs') → d ∈ xs' → nextOr xs x d ∈ xs' by
exact this xs fun _ => id
intro xs' hxs' hd
induction' xs with y ys ih
· exact hd
rcases ys with - | ⟨z, zs⟩
· exact hd
rw [nextOr]
split_ifs with h
· exact hxs' _ (mem_cons_of_mem _ mem_cons_self)
· exact ih fun _ h => hxs' _ (mem_cons_of_mem _ h)
/-- Given an element `x : α` of `l : List α` such that `x ∈ l`, get the next
element of `l`. This works from head to tail, (including a check for last element)
so it will match on first hit, ignoring later duplicates.
For example:
* `next [1, 2, 3] 2 _ = 3`
* `next [1, 2, 3] 3 _ = 1`
* `next [1, 2, 3, 2, 4] 2 _ = 3`
* `next [1, 2, 3, 2] 2 _ = 3`
* `next [1, 1, 2, 3, 2] 1 _ = 1`
-/
def next (l : List α) (x : α) (h : x ∈ l) : α :=
nextOr l x (l.get ⟨0, length_pos_of_mem h⟩)
/-- Given an element `x : α` of `l : List α` such that `x ∈ l`, get the previous
element of `l`. This works from head to tail, (including a check for last element)
so it will match on first hit, ignoring later duplicates.
* `prev [1, 2, 3] 2 _ = 1`
* `prev [1, 2, 3] 1 _ = 3`
* `prev [1, 2, 3, 2, 4] 2 _ = 1`
* `prev [1, 2, 3, 4, 2] 2 _ = 1`
* `prev [1, 1, 2] 1 _ = 2`
-/
def prev : ∀ l : List α, ∀ x ∈ l, α
| [], _, h => by simp at h
| [y], _, _ => y
| y :: z :: xs, x, h =>
if hx : x = y then getLast (z :: xs) (cons_ne_nil _ _)
else if x = z then y else prev (z :: xs) x (by simpa [hx] using h)
variable (l : List α) (x : α)
@[simp]
theorem next_singleton (x y : α) (h : x ∈ [y]) : next [y] x h = y :=
rfl
@[simp]
theorem prev_singleton (x y : α) (h : x ∈ [y]) : prev [y] x h = y :=
rfl
theorem next_cons_cons_eq' (y z : α) (h : x ∈ y :: z :: l) (hx : x = y) :
next (y :: z :: l) x h = z := by rw [next, nextOr, if_pos hx]
@[simp]
theorem next_cons_cons_eq (z : α) (h : x ∈ x :: z :: l) : next (x :: z :: l) x h = z :=
next_cons_cons_eq' l x x z h rfl
theorem next_ne_head_ne_getLast (h : x ∈ l) (y : α) (h : x ∈ y :: l) (hy : x ≠ y)
(hx : x ≠ getLast (y :: l) (cons_ne_nil _ _)) :
next (y :: l) x h = next l x (by simpa [hy] using h) := by
rw [next, next, nextOr_cons_of_ne _ _ _ _ hy, nextOr_eq_nextOr_of_mem_of_ne]
· rwa [getLast_cons] at hx
exact ne_nil_of_mem (by assumption)
· rwa [getLast_cons] at hx
theorem next_cons_concat (y : α) (hy : x ≠ y) (hx : x ∉ l)
(h : x ∈ y :: l ++ [x] := mem_append_right _ (mem_singleton_self x)) :
next (y :: l ++ [x]) x h = y := by
rw [next, nextOr_concat]
· rfl
· simp [hy, hx]
theorem next_getLast_cons (h : x ∈ l) (y : α) (h : x ∈ y :: l) (hy : x ≠ y)
(hx : x = getLast (y :: l) (cons_ne_nil _ _)) (hl : Nodup l) : next (y :: l) x h = y := by
rw [next, get, ← dropLast_append_getLast (cons_ne_nil y l), hx, nextOr_concat]
subst hx
intro H
obtain ⟨_ | k, hk, hk'⟩ := getElem_of_mem H
· rw [← Option.some_inj] at hk'
rw [← getElem?_eq_getElem, dropLast_eq_take, getElem?_take_of_lt, getElem?_cons_zero,
Option.some_inj] at hk'
· exact hy (Eq.symm hk')
rw [length_cons]
exact length_pos_of_mem (by assumption)
suffices k + 1 = l.length by simp [this] at hk
rcases l with - | ⟨hd, tl⟩
· simp at hk
· rw [nodup_iff_injective_get] at hl
rw [length, Nat.succ_inj]
refine Fin.val_eq_of_eq <| @hl ⟨k, Nat.lt_of_succ_lt <| by simpa using hk⟩
⟨tl.length, by simp⟩ ?_
rw [← Option.some_inj] at hk'
rw [← getElem?_eq_getElem, dropLast_eq_take, getElem?_take_of_lt, getElem?_cons_succ,
getElem?_eq_getElem, Option.some_inj] at hk'
· rw [get_eq_getElem, hk']
simp only [getLast_eq_getElem, length_cons, Nat.succ_eq_add_one, Nat.succ_sub_succ_eq_sub,
Nat.sub_zero, get_eq_getElem, getElem_cons_succ]
simpa using hk
theorem prev_getLast_cons' (y : α) (hxy : x ∈ y :: l) (hx : x = y) :
prev (y :: l) x hxy = getLast (y :: l) (cons_ne_nil _ _) := by cases l <;> simp [prev, hx]
@[simp]
theorem prev_getLast_cons (h : x ∈ x :: l) :
prev (x :: l) x h = getLast (x :: l) (cons_ne_nil _ _) :=
prev_getLast_cons' l x x h rfl
theorem prev_cons_cons_eq' (y z : α) (h : x ∈ y :: z :: l) (hx : x = y) :
prev (y :: z :: l) x h = getLast (z :: l) (cons_ne_nil _ _) := by rw [prev, dif_pos hx]
theorem prev_cons_cons_eq (z : α) (h : x ∈ x :: z :: l) :
prev (x :: z :: l) x h = getLast (z :: l) (cons_ne_nil _ _) :=
prev_cons_cons_eq' l x x z h rfl
theorem prev_cons_cons_of_ne' (y z : α) (h : x ∈ y :: z :: l) (hy : x ≠ y) (hz : x = z) :
prev (y :: z :: l) x h = y := by
cases l
· simp [prev, hy, hz]
· rw [prev, dif_neg hy, if_pos hz]
theorem prev_cons_cons_of_ne (y : α) (h : x ∈ y :: x :: l) (hy : x ≠ y) :
prev (y :: x :: l) x h = y :=
prev_cons_cons_of_ne' _ _ _ _ _ hy rfl
theorem prev_ne_cons_cons (y z : α) (h : x ∈ y :: z :: l) (hy : x ≠ y) (hz : x ≠ z) :
prev (y :: z :: l) x h = prev (z :: l) x (by simpa [hy] using h) := by
cases l
· simp [hy, hz] at h
· rw [prev, dif_neg hy, if_neg hz]
theorem next_mem (h : x ∈ l) : l.next x h ∈ l :=
nextOr_mem (get_mem _ _)
theorem prev_mem (h : x ∈ l) : l.prev x h ∈ l := by
rcases l with - | ⟨hd, tl⟩
· simp at h
induction' tl with hd' tl hl generalizing hd
· simp
· by_cases hx : x = hd
· simp only [hx, prev_cons_cons_eq]
exact mem_cons_of_mem _ (getLast_mem _)
· rw [prev, dif_neg hx]
split_ifs with hm
· exact mem_cons_self
· exact mem_cons_of_mem _ (hl _ _)
theorem next_getElem (l : List α) (h : Nodup l) (i : Nat) (hi : i < l.length) :
next l l[i] (get_mem _ _) =
(l[(i + 1) % l.length]'(Nat.mod_lt _ (i.zero_le.trans_lt hi))) :=
match l, h, i, hi with
| [], _, i, hi => by simp at hi
| [_], _, _, _ => by simp
| x::y::l, _h, 0, h0 => by
have h₁ : (x :: y :: l)[0] = x := by simp
rw [next_cons_cons_eq' _ _ _ _ _ h₁]
simp
| x::y::l, hn, i+1, hi => by
have hx' : (x :: y :: l)[i+1] ≠ x := by
intro H
suffices (i + 1 : ℕ) = 0 by simpa
rw [nodup_iff_injective_get] at hn
refine Fin.val_eq_of_eq (@hn ⟨i + 1, hi⟩ ⟨0, by simp⟩ ?_)
simpa using H
have hi' : i ≤ l.length := Nat.le_of_lt_succ (Nat.succ_lt_succ_iff.1 hi)
rcases hi'.eq_or_lt with (hi' | hi')
· subst hi'
rw [next_getLast_cons]
· simp [hi', get]
· rw [getElem_cons_succ]; exact get_mem _ _
· exact hx'
· simp [getLast_eq_getElem]
· exact hn.of_cons
· rw [next_ne_head_ne_getLast _ _ _ _ _ hx']
· simp only [getElem_cons_succ]
rw [next_getElem (y::l), ← getElem_cons_succ (a := x)]
· congr
dsimp
rw [Nat.mod_eq_of_lt (Nat.succ_lt_succ_iff.2 hi'),
Nat.mod_eq_of_lt (Nat.succ_lt_succ_iff.2 (Nat.succ_lt_succ_iff.2 hi'))]
· simp [Nat.mod_eq_of_lt (Nat.succ_lt_succ_iff.2 hi'), hi']
· exact hn.of_cons
· rw [getLast_eq_getElem]
intro h
have := nodup_iff_injective_get.1 hn h
simp at this; simp [this] at hi'
· rw [getElem_cons_succ]; exact get_mem _ _
@[deprecated (since := "2025-02-015")] alias next_get := next_getElem
-- Unused variable linter incorrectly reports that `h` is unused here.
set_option linter.unusedVariables false in
theorem prev_getElem (l : List α) (h : Nodup l) (i : Nat) (hi : i < l.length) :
prev l l[i] (get_mem _ _) =
(l[(i + (l.length - 1)) % l.length]'(Nat.mod_lt _ (by omega))) :=
match l with
| [] => by simp at hi
| x::l => by
induction l generalizing i x with
| nil => simp
| cons y l hl =>
rcases i with (_ | _ | i)
· simp [getLast_eq_getElem]
· simp only [mem_cons, nodup_cons] at h
push_neg at h
simp only [zero_add, getElem_cons_succ, getElem_cons_zero,
List.prev_cons_cons_of_ne _ _ _ _ h.left.left.symm, length, add_comm,
Nat.add_sub_cancel_left, Nat.mod_self]
· rw [prev_ne_cons_cons]
· convert hl i.succ y h.of_cons (Nat.le_of_succ_le_succ hi) using 1
have : ∀ k hk, (y :: l)[k] = (x :: y :: l)[k + 1]'(Nat.succ_lt_succ hk) := by
simp
rw [this]
congr
simp only [Nat.add_succ_sub_one, add_zero, length]
simp only [length, Nat.succ_lt_succ_iff] at hi
set k := l.length
rw [Nat.succ_add, ← Nat.add_succ, Nat.add_mod_right, Nat.succ_add, ← Nat.add_succ _ k,
Nat.add_mod_right, Nat.mod_eq_of_lt, Nat.mod_eq_of_lt]
· exact Nat.lt_succ_of_lt hi
· exact Nat.succ_lt_succ (Nat.lt_succ_of_lt hi)
· intro H
suffices i.succ.succ = 0 by simpa
suffices Fin.mk _ hi = ⟨0, by omega⟩ by rwa [Fin.mk.inj_iff] at this
rw [nodup_iff_injective_get] at h
apply h; rw [← H]; simp
· intro H
suffices i.succ.succ = 1 by simpa
suffices Fin.mk _ hi = ⟨1, by omega⟩ by rwa [Fin.mk.inj_iff] at this
rw [nodup_iff_injective_get] at h
apply h; rw [← H]; simp
@[deprecated (since := "2025-02-15")] alias prev_get := prev_getElem
theorem pmap_next_eq_rotate_one (h : Nodup l) : (l.pmap l.next fun _ h => h) = l.rotate 1 := by
apply List.ext_getElem
· simp
· intros
rw [getElem_pmap, getElem_rotate, next_getElem _ h]
theorem pmap_prev_eq_rotate_length_sub_one (h : Nodup l) :
(l.pmap l.prev fun _ h => h) = l.rotate (l.length - 1) := by
apply List.ext_getElem
· simp
· intro n hn hn'
rw [getElem_rotate, getElem_pmap, prev_getElem _ h]
theorem prev_next (l : List α) (h : Nodup l) (x : α) (hx : x ∈ l) :
prev l (next l x hx) (next_mem _ _ _) = x := by
obtain ⟨n, hn, rfl⟩ := getElem_of_mem hx
simp only [next_getElem, prev_getElem, h, Nat.mod_add_mod]
rcases l with - | ⟨hd, tl⟩
· simp at hn
· have : (n + 1 + length tl) % (length tl + 1) = n := by
rw [length_cons] at hn
rw [add_assoc, add_comm 1, Nat.add_mod_right, Nat.mod_eq_of_lt hn]
simp only [length_cons, Nat.succ_sub_succ_eq_sub, Nat.sub_zero, Nat.succ_eq_add_one, this]
theorem next_prev (l : List α) (h : Nodup l) (x : α) (hx : x ∈ l) :
next l (prev l x hx) (prev_mem _ _ _) = x := by
obtain ⟨n, hn, rfl⟩ := getElem_of_mem hx
simp only [next_getElem, prev_getElem, h, Nat.mod_add_mod]
rcases l with - | ⟨hd, tl⟩
· simp at hn
· have : (n + length tl + 1) % (length tl + 1) = n := by
rw [length_cons] at hn
rw [add_assoc, Nat.add_mod_right, Nat.mod_eq_of_lt hn]
simp [this]
theorem prev_reverse_eq_next (l : List α) (h : Nodup l) (x : α) (hx : x ∈ l) :
prev l.reverse x (mem_reverse.mpr hx) = next l x hx := by
obtain ⟨k, hk, rfl⟩ := getElem_of_mem hx
have lpos : 0 < l.length := k.zero_le.trans_lt hk
have key : l.length - 1 - k < l.length := by omega
rw [← getElem_pmap l.next (fun _ h => h) (by simpa using hk)]
simp_rw [getElem_eq_getElem_reverse (l := l), pmap_next_eq_rotate_one _ h]
rw [← getElem_pmap l.reverse.prev fun _ h => h]
· simp_rw [pmap_prev_eq_rotate_length_sub_one _ (nodup_reverse.mpr h), rotate_reverse,
length_reverse, Nat.mod_eq_of_lt (Nat.sub_lt lpos Nat.succ_pos'),
Nat.sub_sub_self (Nat.succ_le_of_lt lpos)]
rw [getElem_eq_getElem_reverse]
· simp [Nat.sub_sub_self (Nat.le_sub_one_of_lt hk)]
· simpa
theorem next_reverse_eq_prev (l : List α) (h : Nodup l) (x : α) (hx : x ∈ l) :
next l.reverse x (mem_reverse.mpr hx) = prev l x hx := by
convert (prev_reverse_eq_next l.reverse (nodup_reverse.mpr h) x (mem_reverse.mpr hx)).symm
exact (reverse_reverse l).symm
theorem isRotated_next_eq {l l' : List α} (h : l ~r l') (hn : Nodup l) {x : α} (hx : x ∈ l) :
l.next x hx = l'.next x (h.mem_iff.mp hx) := by
obtain ⟨k, hk, rfl⟩ := getElem_of_mem hx
obtain ⟨n, rfl⟩ := id h
rw [next_getElem _ hn]
simp_rw [getElem_eq_getElem_rotate _ n k]
rw [next_getElem _ (h.nodup_iff.mp hn), getElem_eq_getElem_rotate _ n]
simp [add_assoc]
theorem isRotated_prev_eq {l l' : List α} (h : l ~r l') (hn : Nodup l) {x : α} (hx : x ∈ l) :
l.prev x hx = l'.prev x (h.mem_iff.mp hx) := by
rw [← next_reverse_eq_prev _ hn, ← next_reverse_eq_prev _ (h.nodup_iff.mp hn)]
exact isRotated_next_eq h.reverse (nodup_reverse.mpr hn) _
end List
open List
/-- `Cycle α` is the quotient of `List α` by cyclic permutation.
Duplicates are allowed.
-/
def Cycle (α : Type*) : Type _ :=
Quotient (IsRotated.setoid α)
namespace Cycle
variable {α : Type*}
/-- The coercion from `List α` to `Cycle α` -/
@[coe] def ofList : List α → Cycle α :=
Quot.mk _
instance : Coe (List α) (Cycle α) :=
⟨ofList⟩
@[simp]
theorem coe_eq_coe {l₁ l₂ : List α} : (l₁ : Cycle α) = (l₂ : Cycle α) ↔ l₁ ~r l₂ :=
@Quotient.eq _ (IsRotated.setoid _) _ _
@[simp]
theorem mk_eq_coe (l : List α) : Quot.mk _ l = (l : Cycle α) :=
rfl
@[simp]
theorem mk''_eq_coe (l : List α) : Quotient.mk'' l = (l : Cycle α) :=
rfl
theorem coe_cons_eq_coe_append (l : List α) (a : α) :
(↑(a :: l) : Cycle α) = (↑(l ++ [a]) : Cycle α) :=
Quot.sound ⟨1, by rw [rotate_cons_succ, rotate_zero]⟩
/-- The unique empty cycle. -/
def nil : Cycle α :=
([] : List α)
@[simp]
theorem coe_nil : ↑([] : List α) = @nil α :=
rfl
@[simp]
theorem coe_eq_nil (l : List α) : (l : Cycle α) = nil ↔ l = [] :=
coe_eq_coe.trans isRotated_nil_iff
/-- For consistency with `EmptyCollection (List α)`. -/
instance : EmptyCollection (Cycle α) :=
⟨nil⟩
@[simp]
theorem empty_eq : ∅ = @nil α :=
rfl
instance : Inhabited (Cycle α) :=
⟨nil⟩
/-- An induction principle for `Cycle`. Use as `induction s`. -/
@[elab_as_elim, induction_eliminator]
theorem induction_on {C : Cycle α → Prop} (s : Cycle α) (H0 : C nil)
(HI : ∀ (a) (l : List α), C ↑l → C ↑(a :: l)) : C s :=
Quotient.inductionOn' s fun l => by
refine List.recOn l ?_ ?_ <;> simp only [mk''_eq_coe, coe_nil]
assumption'
/-- For `x : α`, `s : Cycle α`, `x ∈ s` indicates that `x` occurs at least once in `s`. -/
def Mem (s : Cycle α) (a : α) : Prop :=
Quot.liftOn s (fun l => a ∈ l) fun _ _ e => propext <| e.mem_iff
instance : Membership α (Cycle α) :=
⟨Mem⟩
@[simp]
theorem mem_coe_iff {a : α} {l : List α} : a ∈ (↑l : Cycle α) ↔ a ∈ l :=
Iff.rfl
@[simp]
theorem not_mem_nil (a : α) : a ∉ nil :=
List.not_mem_nil
instance [DecidableEq α] : DecidableEq (Cycle α) := fun s₁ s₂ =>
Quotient.recOnSubsingleton₂' s₁ s₂ fun _ _ => decidable_of_iff' _ Quotient.eq''
instance [DecidableEq α] (x : α) (s : Cycle α) : Decidable (x ∈ s) :=
Quotient.recOnSubsingleton' s fun l => show Decidable (x ∈ l) from inferInstance
/-- Reverse a `s : Cycle α` by reversing the underlying `List`. -/
nonrec def reverse (s : Cycle α) : Cycle α :=
Quot.map reverse (fun _ _ => IsRotated.reverse) s
@[simp]
theorem reverse_coe (l : List α) : (l : Cycle α).reverse = l.reverse :=
rfl
@[simp]
theorem mem_reverse_iff {a : α} {s : Cycle α} : a ∈ s.reverse ↔ a ∈ s :=
Quot.inductionOn s fun _ => mem_reverse
@[simp]
theorem reverse_reverse (s : Cycle α) : s.reverse.reverse = s :=
Quot.inductionOn s fun _ => by simp
@[simp]
theorem reverse_nil : nil.reverse = @nil α :=
rfl
/-- The length of the `s : Cycle α`, which is the number of elements, counting duplicates. -/
def length (s : Cycle α) : ℕ :=
Quot.liftOn s List.length fun _ _ e => e.perm.length_eq
@[simp]
theorem length_coe (l : List α) : length (l : Cycle α) = l.length :=
rfl
@[simp]
theorem length_nil : length (@nil α) = 0 :=
rfl
@[simp]
theorem length_reverse (s : Cycle α) : s.reverse.length = s.length :=
Quot.inductionOn s fun _ => List.length_reverse
/-- A `s : Cycle α` that is at most one element. -/
def Subsingleton (s : Cycle α) : Prop :=
s.length ≤ 1
theorem subsingleton_nil : Subsingleton (@nil α) := Nat.zero_le _
theorem length_subsingleton_iff {s : Cycle α} : Subsingleton s ↔ length s ≤ 1 :=
Iff.rfl
@[simp]
theorem subsingleton_reverse_iff {s : Cycle α} : s.reverse.Subsingleton ↔ s.Subsingleton := by
simp [length_subsingleton_iff]
theorem Subsingleton.congr {s : Cycle α} (h : Subsingleton s) :
∀ ⦃x⦄ (_hx : x ∈ s) ⦃y⦄ (_hy : y ∈ s), x = y := by
induction' s using Quot.inductionOn with l
simp only [length_subsingleton_iff, length_coe, mk_eq_coe, le_iff_lt_or_eq, Nat.lt_add_one_iff,
length_eq_zero_iff, length_eq_one_iff, Nat.not_lt_zero, false_or] at h
rcases h with (rfl | ⟨z, rfl⟩) <;> simp
/-- A `s : Cycle α` that is made up of at least two unique elements. -/
def Nontrivial (s : Cycle α) : Prop :=
∃ x y : α, x ≠ y ∧ x ∈ s ∧ y ∈ s
@[simp]
theorem nontrivial_coe_nodup_iff {l : List α} (hl : l.Nodup) :
Nontrivial (l : Cycle α) ↔ 2 ≤ l.length := by
rw [Nontrivial]
rcases l with (_ | ⟨hd, _ | ⟨hd', tl⟩⟩)
· simp
· simp
· simp only [mem_cons, exists_prop, mem_coe_iff, List.length, Ne, Nat.succ_le_succ_iff,
Nat.zero_le, iff_true]
refine ⟨hd, hd', ?_, by simp⟩
simp only [not_or, mem_cons, nodup_cons] at hl
exact hl.left.left
@[simp]
theorem nontrivial_reverse_iff {s : Cycle α} : s.reverse.Nontrivial ↔ s.Nontrivial := by
simp [Nontrivial]
theorem length_nontrivial {s : Cycle α} (h : Nontrivial s) : 2 ≤ length s := by
obtain ⟨x, y, hxy, hx, hy⟩ := h
induction' s using Quot.inductionOn with l
rcases l with (_ | ⟨hd, _ | ⟨hd', tl⟩⟩)
· simp at hx
· simp only [mem_coe_iff, mk_eq_coe, mem_singleton] at hx hy
simp [hx, hy] at hxy
· simp [Nat.succ_le_succ_iff]
/-- The `s : Cycle α` contains no duplicates. -/
nonrec def Nodup (s : Cycle α) : Prop :=
Quot.liftOn s Nodup fun _l₁ _l₂ e => propext <| e.nodup_iff
@[simp]
nonrec theorem nodup_nil : Nodup (@nil α) :=
nodup_nil
@[simp]
theorem nodup_coe_iff {l : List α} : Nodup (l : Cycle α) ↔ l.Nodup :=
Iff.rfl
@[simp]
theorem nodup_reverse_iff {s : Cycle α} : s.reverse.Nodup ↔ s.Nodup :=
Quot.inductionOn s fun _ => nodup_reverse
theorem Subsingleton.nodup {s : Cycle α} (h : Subsingleton s) : Nodup s := by
induction' s using Quot.inductionOn with l
obtain - | ⟨hd, tl⟩ := l
· simp
· have : tl = [] := by simpa [Subsingleton, length_eq_zero_iff, Nat.succ_le_succ_iff] using h
simp [this]
theorem Nodup.nontrivial_iff {s : Cycle α} (h : Nodup s) : Nontrivial s ↔ ¬Subsingleton s := by
rw [length_subsingleton_iff]
induction s using Quotient.inductionOn'
simp only [mk''_eq_coe, nodup_coe_iff] at h
simp [h, Nat.succ_le_iff]
/-- The `s : Cycle α` as a `Multiset α`.
-/
def toMultiset (s : Cycle α) : Multiset α :=
Quotient.liftOn' s (↑) fun _ _ h => Multiset.coe_eq_coe.mpr h.perm
@[simp]
theorem coe_toMultiset (l : List α) : (l : Cycle α).toMultiset = l :=
rfl
@[simp]
theorem nil_toMultiset : nil.toMultiset = (0 : Multiset α) :=
rfl
@[simp]
theorem card_toMultiset (s : Cycle α) : Multiset.card s.toMultiset = s.length :=
Quotient.inductionOn' s (by simp)
@[simp]
theorem toMultiset_eq_nil {s : Cycle α} : s.toMultiset = 0 ↔ s = Cycle.nil :=
Quotient.inductionOn' s (by simp)
/-- The lift of `list.map`. -/
def map {β : Type*} (f : α → β) : Cycle α → Cycle β :=
Quotient.map' (List.map f) fun _ _ h => h.map _
@[simp]
theorem map_nil {β : Type*} (f : α → β) : map f nil = nil :=
rfl
@[simp]
theorem map_coe {β : Type*} (f : α → β) (l : List α) : map f ↑l = List.map f l :=
rfl
@[simp]
theorem map_eq_nil {β : Type*} (f : α → β) (s : Cycle α) : map f s = nil ↔ s = nil :=
Quotient.inductionOn' s (by simp)
@[simp]
theorem mem_map {β : Type*} {f : α → β} {b : β} {s : Cycle α} :
b ∈ s.map f ↔ ∃ a, a ∈ s ∧ f a = b :=
Quotient.inductionOn' s (by simp)
/-- The `Multiset` of lists that can make the cycle. -/
def lists (s : Cycle α) : Multiset (List α) :=
Quotient.liftOn' s (fun l => (l.cyclicPermutations : Multiset (List α))) fun l₁ l₂ h => by
simpa using h.cyclicPermutations.perm
@[simp]
theorem lists_coe (l : List α) : lists (l : Cycle α) = ↑l.cyclicPermutations :=
rfl
@[simp]
theorem mem_lists_iff_coe_eq {s : Cycle α} {l : List α} : l ∈ s.lists ↔ (l : Cycle α) = s :=
Quotient.inductionOn' s fun l => by
rw [lists, Quotient.liftOn'_mk'']
simp
@[simp]
theorem lists_nil : lists (@nil α) = {([] : List α)} := by
rw [nil, lists_coe, cyclicPermutations_nil, Multiset.coe_singleton]
section Decidable
variable [DecidableEq α]
/-- Auxiliary decidability algorithm for lists that contain at least two unique elements.
-/
def decidableNontrivialCoe : ∀ l : List α, Decidable (Nontrivial (l : Cycle α))
| [] => isFalse (by simp [Nontrivial])
| [x] => isFalse (by simp [Nontrivial])
| x :: y :: l =>
if h : x = y then
@decidable_of_iff' _ (Nontrivial (x :: l : Cycle α)) (by simp [h, Nontrivial])
(decidableNontrivialCoe (x :: l))
else isTrue ⟨x, y, h, by simp, by simp⟩
instance {s : Cycle α} : Decidable (Nontrivial s) :=
Quot.recOnSubsingleton s decidableNontrivialCoe
instance {s : Cycle α} : Decidable (Nodup s) :=
Quot.recOnSubsingleton s List.nodupDecidable
instance fintypeNodupCycle [Fintype α] : Fintype { s : Cycle α // s.Nodup } :=
Fintype.ofSurjective (fun l : { l : List α // l.Nodup } => ⟨l.val, by simpa using l.prop⟩)
fun ⟨s, hs⟩ => by
induction' s using Quotient.inductionOn' with s hs
exact ⟨⟨s, hs⟩, by simp⟩
instance fintypeNodupNontrivialCycle [Fintype α] :
Fintype { s : Cycle α // s.Nodup ∧ s.Nontrivial } :=
Fintype.subtype
(((Finset.univ : Finset { s : Cycle α // s.Nodup }).map (Function.Embedding.subtype _)).filter
Cycle.Nontrivial)
(by simp)
/-- The `s : Cycle α` as a `Finset α`. -/
def toFinset (s : Cycle α) : Finset α :=
s.toMultiset.toFinset
@[simp]
theorem toFinset_toMultiset (s : Cycle α) : s.toMultiset.toFinset = s.toFinset :=
rfl
@[simp]
theorem coe_toFinset (l : List α) : (l : Cycle α).toFinset = l.toFinset :=
rfl
@[simp]
theorem nil_toFinset : (@nil α).toFinset = ∅ :=
rfl
@[simp]
theorem toFinset_eq_nil {s : Cycle α} : s.toFinset = ∅ ↔ s = Cycle.nil :=
Quotient.inductionOn' s (by simp)
/-- Given a `s : Cycle α` such that `Nodup s`, retrieve the next element after `x ∈ s`. -/
nonrec def next : ∀ (s : Cycle α) (_hs : Nodup s) (x : α) (_hx : x ∈ s), α := fun s =>
Quot.hrecOn (motive := fun (s : Cycle α) => ∀ (_hs : Cycle.Nodup s) (x : α) (_hx : x ∈ s), α) s
(fun l _hn x hx => next l x hx) fun l₁ l₂ h =>
Function.hfunext (propext h.nodup_iff) fun h₁ h₂ _he =>
Function.hfunext rfl fun x y hxy =>
Function.hfunext (propext (by rw [eq_of_heq hxy]; simpa [eq_of_heq hxy] using h.mem_iff))
fun hm hm' he' => heq_of_eq
(by rw [heq_iff_eq] at hxy; subst x; simpa using isRotated_next_eq h h₁ _)
/-- Given a `s : Cycle α` such that `Nodup s`, retrieve the previous element before `x ∈ s`. -/
nonrec def prev : ∀ (s : Cycle α) (_hs : Nodup s) (x : α) (_hx : x ∈ s), α := fun s =>
Quot.hrecOn (motive := fun (s : Cycle α) => ∀ (_hs : Cycle.Nodup s) (x : α) (_hx : x ∈ s), α) s
(fun l _hn x hx => prev l x hx) fun l₁ l₂ h =>
Function.hfunext (propext h.nodup_iff) fun h₁ h₂ _he =>
Function.hfunext rfl fun x y hxy =>
Function.hfunext (propext (by rw [eq_of_heq hxy]; simpa [eq_of_heq hxy] using h.mem_iff))
fun hm hm' he' => heq_of_eq
(by rw [heq_iff_eq] at hxy; subst x; simpa using isRotated_prev_eq h h₁ _)
-- `simp` cannot infer the proofs: see `prev_reverse_eq_next'` for `@[simp]` lemma.
nonrec theorem prev_reverse_eq_next (s : Cycle α) : ∀ (hs : Nodup s) (x : α) (hx : x ∈ s),
s.reverse.prev (nodup_reverse_iff.mpr hs) x (mem_reverse_iff.mpr hx) = s.next hs x hx :=
Quotient.inductionOn' s prev_reverse_eq_next
@[simp]
nonrec theorem prev_reverse_eq_next' (s : Cycle α) (hs : Nodup s.reverse) (x : α)
(hx : x ∈ s.reverse) :
s.reverse.prev hs x hx = s.next (nodup_reverse_iff.mp hs) x (mem_reverse_iff.mp hx) :=
prev_reverse_eq_next s (nodup_reverse_iff.mp hs) x (mem_reverse_iff.mp hx)
-- `simp` cannot infer the proofs: see `next_reverse_eq_prev'` for `@[simp]` lemma.
theorem next_reverse_eq_prev (s : Cycle α) (hs : Nodup s) (x : α) (hx : x ∈ s) :
s.reverse.next (nodup_reverse_iff.mpr hs) x (mem_reverse_iff.mpr hx) = s.prev hs x hx := by
simp [← prev_reverse_eq_next]
@[simp]
theorem next_reverse_eq_prev' (s : Cycle α) (hs : Nodup s.reverse) (x : α) (hx : x ∈ s.reverse) :
s.reverse.next hs x hx = s.prev (nodup_reverse_iff.mp hs) x (mem_reverse_iff.mp hx) := by
simp [← prev_reverse_eq_next]
@[simp]
nonrec theorem next_mem (s : Cycle α) (hs : Nodup s) (x : α) (hx : x ∈ s) : s.next hs x hx ∈ s := by
induction s using Quot.inductionOn
apply next_mem; assumption
theorem prev_mem (s : Cycle α) (hs : Nodup s) (x : α) (hx : x ∈ s) : s.prev hs x hx ∈ s := by
rw [← next_reverse_eq_prev, ← mem_reverse_iff]
apply next_mem
@[simp]
nonrec theorem prev_next (s : Cycle α) : ∀ (hs : Nodup s) (x : α) (hx : x ∈ s),
s.prev hs (s.next hs x hx) (next_mem s hs x hx) = x :=
Quotient.inductionOn' s prev_next
@[simp]
nonrec theorem next_prev (s : Cycle α) : ∀ (hs : Nodup s) (x : α) (hx : x ∈ s),
s.next hs (s.prev hs x hx) (prev_mem s hs x hx) = x :=
Quotient.inductionOn' s next_prev
end Decidable
/-- We define a representation of concrete cycles, available when viewing them in a goal state or
via `#eval`, when over representable types. For example, the cycle `(2 1 4 3)` will be shown
as `c[2, 1, 4, 3]`. Two equal cycles may be printed differently if their internal representation
is different.
-/
unsafe instance [Repr α] : Repr (Cycle α) :=
⟨fun s _ => "c[" ++ Std.Format.joinSep (s.map repr).lists.unquot.head! ", " ++ "]"⟩
/-- `chain R s` means that `R` holds between adjacent elements of `s`.
`chain R ([a, b, c] : Cycle α) ↔ R a b ∧ R b c ∧ R c a` -/
nonrec def Chain (r : α → α → Prop) (c : Cycle α) : Prop :=
Quotient.liftOn' c
(fun l =>
match l with
| [] => True
| a :: m => Chain r a (m ++ [a]))
fun a b hab =>
propext <| by
rcases a with - | ⟨a, l⟩ <;> rcases b with - | ⟨b, m⟩
· rfl
· have := isRotated_nil_iff'.1 hab
contradiction
· have := isRotated_nil_iff.1 hab
contradiction
· dsimp only
obtain ⟨n, hn⟩ := hab
induction' n with d hd generalizing a b l m
· simp only [rotate_zero, cons.injEq] at hn
rw [hn.1, hn.2]
· rcases l with - | ⟨c, s⟩
· simp only [rotate_cons_succ, nil_append, rotate_singleton, cons.injEq] at hn
rw [hn.1, hn.2]
· rw [Nat.add_comm, ← rotate_rotate, rotate_cons_succ, rotate_zero, cons_append] at hn
rw [← hd c _ _ _ hn]
simp [and_comm]
@[simp]
theorem Chain.nil (r : α → α → Prop) : Cycle.Chain r (@nil α) := by trivial
@[simp]
theorem chain_coe_cons (r : α → α → Prop) (a : α) (l : List α) :
Chain r (a :: l) ↔ List.Chain r a (l ++ [a]) :=
Iff.rfl
theorem chain_singleton (r : α → α → Prop) (a : α) : Chain r [a] ↔ r a a := by
rw [chain_coe_cons, nil_append, List.chain_singleton]
theorem chain_ne_nil (r : α → α → Prop) {l : List α} :
∀ hl : l ≠ [], Chain r l ↔ List.Chain r (getLast l hl) l :=
l.reverseRecOn (fun hm => hm.irrefl.elim) (by
intro m a _H _
rw [← coe_cons_eq_coe_append, chain_coe_cons, getLast_append_singleton])
theorem chain_map {β : Type*} {r : α → α → Prop} (f : β → α) {s : Cycle β} :
Chain r (s.map f) ↔ Chain (fun a b => r (f a) (f b)) s :=
Quotient.inductionOn s fun l => by
rcases l with - | ⟨a, l⟩
· rfl
· simp [← concat_eq_append, ← List.map_concat, List.chain_map f]
nonrec theorem chain_range_succ (r : ℕ → ℕ → Prop) (n : ℕ) :
Chain r (List.range n.succ) ↔ r n 0 ∧ ∀ m < n, r m m.succ := by
rw [range_succ, ← coe_cons_eq_coe_append, chain_coe_cons, ← range_succ, chain_range_succ]
variable {r : α → α → Prop} {s : Cycle α}
theorem Chain.imp {r₁ r₂ : α → α → Prop} (H : ∀ a b, r₁ a b → r₂ a b) (p : Chain r₁ s) :
Chain r₂ s := by
induction s
· trivial
· rw [chain_coe_cons] at p ⊢
exact p.imp H
/-- As a function from a relation to a predicate, `chain` is monotonic. -/
theorem chain_mono : Monotone (Chain : (α → α → Prop) → Cycle α → Prop) := fun _a _b hab _s =>
Chain.imp hab
theorem chain_of_pairwise : (∀ a ∈ s, ∀ b ∈ s, r a b) → Chain r s := by
induction' s with a l _
· exact fun _ => Cycle.Chain.nil r
intro hs
have Ha : a ∈ (a :: l : Cycle α) := by simp
have Hl : ∀ {b} (_hb : b ∈ l), b ∈ (a :: l : Cycle α) := @fun b hb => by simp [hb]
rw [Cycle.chain_coe_cons]
apply Pairwise.chain
rw [pairwise_cons]
refine
⟨fun b hb => ?_,
pairwise_append.2
⟨pairwise_of_forall_mem_list fun b hb c hc => hs b (Hl hb) c (Hl hc),
pairwise_singleton r a, fun b hb c hc => ?_⟩⟩
· rw [mem_append] at hb
rcases hb with hb | hb
· exact hs a Ha b (Hl hb)
· rw [mem_singleton] at hb
rw [hb]
exact hs a Ha a Ha
· rw [mem_singleton] at hc
rw [hc]
exact hs b (Hl hb) a Ha
theorem chain_iff_pairwise [IsTrans α r] : Chain r s ↔ ∀ a ∈ s, ∀ b ∈ s, r a b :=
⟨by
induction' s with a l _
· exact fun _ b hb => (not_mem_nil _ hb).elim
intro hs b hb c hc
rw [Cycle.chain_coe_cons, List.chain_iff_pairwise] at hs
simp only [pairwise_append, pairwise_cons, mem_append, mem_singleton, List.not_mem_nil,
IsEmpty.forall_iff, imp_true_iff, Pairwise.nil, forall_eq, true_and] at hs
simp only [mem_coe_iff, mem_cons] at hb hc
rcases hb with (rfl | hb) <;> rcases hc with (rfl | hc)
· exact hs.1 c (Or.inr rfl)
· exact hs.1 c (Or.inl hc)
· exact hs.2.2 b hb
· exact _root_.trans (hs.2.2 b hb) (hs.1 c (Or.inl hc)), Cycle.chain_of_pairwise⟩
theorem Chain.eq_nil_of_irrefl [IsTrans α r] [IsIrrefl α r] (h : Chain r s) : s = Cycle.nil := by
induction' s with a l _ h
· rfl
· have ha : a ∈ a :: l := mem_cons_self
exact (irrefl_of r a <| chain_iff_pairwise.1 h a ha a ha).elim
theorem Chain.eq_nil_of_well_founded [IsWellFounded α r] (h : Chain r s) : s = Cycle.nil :=
Chain.eq_nil_of_irrefl <| h.imp fun _ _ => Relation.TransGen.single
theorem forall_eq_of_chain [IsTrans α r] [IsAntisymm α r] (hs : Chain r s) {a b : α} (ha : a ∈ s)
(hb : b ∈ s) : a = b := by
rw [chain_iff_pairwise] at hs
exact antisymm (hs a ha b hb) (hs b hb a ha)
end Cycle
| Mathlib/Data/List/Cycle.lean | 966 | 971 | |
/-
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.MeasurableSpace.MeasurablyGenerated
import Mathlib.MeasureTheory.Measure.NullMeasurable
import Mathlib.Order.Interval.Set.Monotone
/-!
# Measure spaces
The definition of a measure and a measure space are in `MeasureTheory.MeasureSpaceDef`, with
only a few basic properties. This file provides many more properties of these objects.
This separation allows the measurability tactic to import only the file `MeasureSpaceDef`, and to
be available in `MeasureSpace` (through `MeasurableSpace`).
Given a measurable space `α`, a measure on `α` is a function that sends measurable sets to the
extended nonnegative reals that satisfies the following conditions:
1. `μ ∅ = 0`;
2. `μ` is countably additive. This means that the measure of a countable union of pairwise disjoint
sets is equal to the measure of the individual sets.
Every measure can be canonically extended to an outer measure, so that it assigns values to
all subsets, not just the measurable subsets. On the other hand, a measure that is countably
additive on measurable sets can be restricted to measurable sets to obtain a measure.
In this file a measure is defined to be an outer measure that is countably additive on
measurable sets, with the additional assumption that the outer measure is the canonical
extension of the restricted measure.
Measures on `α` form a complete lattice, and are closed under scalar multiplication with `ℝ≥0∞`.
Given a measure, the null sets are the sets where `μ s = 0`, where `μ` denotes the corresponding
outer measure (so `s` might not be measurable). We can then define the completion of `μ` as the
measure on the least `σ`-algebra that also contains all null sets, by defining the measure to be `0`
on the null sets.
## Main statements
* `completion` is the completion of a measure to all null measurable sets.
* `Measure.ofMeasurable` and `OuterMeasure.toMeasure` are two important ways to define a measure.
## Implementation notes
Given `μ : Measure α`, `μ s` is the value of the *outer measure* applied to `s`.
This conveniently allows us to apply the measure to sets without proving that they are measurable.
We get countable subadditivity for all sets, but only countable additivity for measurable sets.
You often don't want to define a measure via its constructor.
Two ways that are sometimes more convenient:
* `Measure.ofMeasurable` is a way to define a measure by only giving its value on measurable sets
and proving the properties (1) and (2) mentioned above.
* `OuterMeasure.toMeasure` is a way of obtaining a measure from an outer measure by showing that
all measurable sets in the measurable space are Carathéodory measurable.
To prove that two measures are equal, there are multiple options:
* `ext`: two measures are equal if they are equal on all measurable sets.
* `ext_of_generateFrom_of_iUnion`: two measures are equal if they are equal on a π-system generating
the measurable sets, if the π-system contains a spanning increasing sequence of sets where the
measures take finite value (in particular the measures are σ-finite). This is a special case of
the more general `ext_of_generateFrom_of_cover`
* `ext_of_generate_finite`: two finite measures are equal if they are equal on a π-system
generating the measurable sets. This is a special case of `ext_of_generateFrom_of_iUnion` using
`C ∪ {univ}`, but is easier to work with.
A `MeasureSpace` is a class that is a measurable space with a canonical measure.
The measure is denoted `volume`.
## References
* <https://en.wikipedia.org/wiki/Measure_(mathematics)>
* <https://en.wikipedia.org/wiki/Complete_measure>
* <https://en.wikipedia.org/wiki/Almost_everywhere>
## Tags
measure, almost everywhere, measure space, completion, null set, null measurable set
-/
noncomputable section
open Set
open Filter hiding map
open Function MeasurableSpace Topology Filter ENNReal NNReal Interval MeasureTheory
open scoped symmDiff
variable {α β γ δ ι R R' : Type*}
namespace MeasureTheory
section
variable {m : MeasurableSpace α} {μ μ₁ μ₂ : Measure α} {s s₁ s₂ t : Set α}
instance ae_isMeasurablyGenerated : IsMeasurablyGenerated (ae μ) :=
⟨fun _s hs =>
let ⟨t, hst, htm, htμ⟩ := exists_measurable_superset_of_null hs
⟨tᶜ, compl_mem_ae_iff.2 htμ, htm.compl, compl_subset_comm.1 hst⟩⟩
/-- See also `MeasureTheory.ae_restrict_uIoc_iff`. -/
theorem ae_uIoc_iff [LinearOrder α] {a b : α} {P : α → Prop} :
(∀ᵐ x ∂μ, x ∈ Ι a b → P x) ↔ (∀ᵐ x ∂μ, x ∈ Ioc a b → P x) ∧ ∀ᵐ x ∂μ, x ∈ Ioc b a → P x := by
simp only [uIoc_eq_union, mem_union, or_imp, eventually_and]
theorem measure_union (hd : Disjoint s₁ s₂) (h : MeasurableSet s₂) : μ (s₁ ∪ s₂) = μ s₁ + μ s₂ :=
measure_union₀ h.nullMeasurableSet hd.aedisjoint
theorem measure_union' (hd : Disjoint s₁ s₂) (h : MeasurableSet s₁) : μ (s₁ ∪ s₂) = μ s₁ + μ s₂ :=
measure_union₀' h.nullMeasurableSet hd.aedisjoint
theorem measure_inter_add_diff (s : Set α) (ht : MeasurableSet t) : μ (s ∩ t) + μ (s \ t) = μ s :=
measure_inter_add_diff₀ _ ht.nullMeasurableSet
theorem measure_diff_add_inter (s : Set α) (ht : MeasurableSet t) : μ (s \ t) + μ (s ∩ t) = μ s :=
(add_comm _ _).trans (measure_inter_add_diff s ht)
theorem measure_diff_eq_top (hs : μ s = ∞) (ht : μ t ≠ ∞) : μ (s \ t) = ∞ := by
contrapose! hs
exact ((measure_mono (subset_diff_union s t)).trans_lt
((measure_union_le _ _).trans_lt (ENNReal.add_lt_top.2 ⟨hs.lt_top, ht.lt_top⟩))).ne
theorem measure_union_add_inter (s : Set α) (ht : MeasurableSet t) :
μ (s ∪ t) + μ (s ∩ t) = μ s + μ t := by
rw [← measure_inter_add_diff (s ∪ t) ht, Set.union_inter_cancel_right, union_diff_right, ←
measure_inter_add_diff s ht]
ac_rfl
theorem measure_union_add_inter' (hs : MeasurableSet s) (t : Set α) :
μ (s ∪ t) + μ (s ∩ t) = μ s + μ t := by
rw [union_comm, inter_comm, measure_union_add_inter t hs, add_comm]
lemma measure_symmDiff_eq (hs : NullMeasurableSet s μ) (ht : NullMeasurableSet t μ) :
μ (s ∆ t) = μ (s \ t) + μ (t \ s) := by
simpa only [symmDiff_def, sup_eq_union]
using measure_union₀ (ht.diff hs) disjoint_sdiff_sdiff.aedisjoint
lemma measure_symmDiff_le (s t u : Set α) :
μ (s ∆ u) ≤ μ (s ∆ t) + μ (t ∆ u) :=
le_trans (μ.mono <| symmDiff_triangle s t u) (measure_union_le (s ∆ t) (t ∆ u))
theorem measure_symmDiff_eq_top (hs : μ s ≠ ∞) (ht : μ t = ∞) : μ (s ∆ t) = ∞ :=
measure_mono_top subset_union_right (measure_diff_eq_top ht hs)
theorem measure_add_measure_compl (h : MeasurableSet s) : μ s + μ sᶜ = μ univ :=
measure_add_measure_compl₀ h.nullMeasurableSet
theorem measure_biUnion₀ {s : Set β} {f : β → Set α} (hs : s.Countable)
(hd : s.Pairwise (AEDisjoint μ on f)) (h : ∀ b ∈ s, NullMeasurableSet (f b) μ) :
μ (⋃ b ∈ s, f b) = ∑' p : s, μ (f p) := by
haveI := hs.toEncodable
rw [biUnion_eq_iUnion]
exact measure_iUnion₀ (hd.on_injective Subtype.coe_injective fun x => x.2) fun x => h x x.2
theorem measure_biUnion {s : Set β} {f : β → Set α} (hs : s.Countable) (hd : s.PairwiseDisjoint f)
(h : ∀ b ∈ s, MeasurableSet (f b)) : μ (⋃ b ∈ s, f b) = ∑' p : s, μ (f p) :=
measure_biUnion₀ hs hd.aedisjoint fun b hb => (h b hb).nullMeasurableSet
theorem measure_sUnion₀ {S : Set (Set α)} (hs : S.Countable) (hd : S.Pairwise (AEDisjoint μ))
(h : ∀ s ∈ S, NullMeasurableSet s μ) : μ (⋃₀ S) = ∑' s : S, μ s := by
rw [sUnion_eq_biUnion, measure_biUnion₀ hs hd h]
theorem measure_sUnion {S : Set (Set α)} (hs : S.Countable) (hd : S.Pairwise Disjoint)
(h : ∀ s ∈ S, MeasurableSet s) : μ (⋃₀ S) = ∑' s : S, μ s := by
rw [sUnion_eq_biUnion, measure_biUnion hs hd h]
theorem measure_biUnion_finset₀ {s : Finset ι} {f : ι → Set α}
(hd : Set.Pairwise (↑s) (AEDisjoint μ on f)) (hm : ∀ b ∈ s, NullMeasurableSet (f b) μ) :
μ (⋃ b ∈ s, f b) = ∑ p ∈ s, μ (f p) := by
rw [← Finset.sum_attach, Finset.attach_eq_univ, ← tsum_fintype]
exact measure_biUnion₀ s.countable_toSet hd hm
theorem measure_biUnion_finset {s : Finset ι} {f : ι → Set α} (hd : PairwiseDisjoint (↑s) f)
(hm : ∀ b ∈ s, MeasurableSet (f b)) : μ (⋃ b ∈ s, f b) = ∑ p ∈ s, μ (f p) :=
measure_biUnion_finset₀ hd.aedisjoint fun b hb => (hm b hb).nullMeasurableSet
/-- The measure of an a.e. disjoint union (even uncountable) of null-measurable sets is at least
the sum of the measures of the sets. -/
theorem tsum_meas_le_meas_iUnion_of_disjoint₀ {ι : Type*} {_ : MeasurableSpace α} (μ : Measure α)
{As : ι → Set α} (As_mble : ∀ i : ι, NullMeasurableSet (As i) μ)
(As_disj : Pairwise (AEDisjoint μ on As)) : (∑' i, μ (As i)) ≤ μ (⋃ i, As i) := by
rw [ENNReal.tsum_eq_iSup_sum, iSup_le_iff]
intro s
simp only [← measure_biUnion_finset₀ (fun _i _hi _j _hj hij => As_disj hij) fun i _ => As_mble i]
gcongr
exact iUnion_subset fun _ ↦ Subset.rfl
/-- The measure of a disjoint union (even uncountable) of measurable sets is at least the sum of
the measures of the sets. -/
theorem tsum_meas_le_meas_iUnion_of_disjoint {ι : Type*} {_ : MeasurableSpace α} (μ : Measure α)
{As : ι → Set α} (As_mble : ∀ i : ι, MeasurableSet (As i))
(As_disj : Pairwise (Disjoint on As)) : (∑' i, μ (As i)) ≤ μ (⋃ i, As i) :=
tsum_meas_le_meas_iUnion_of_disjoint₀ μ (fun i ↦ (As_mble i).nullMeasurableSet)
(fun _ _ h ↦ Disjoint.aedisjoint (As_disj h))
/-- If `s` is a countable set, then the measure of its preimage can be found as the sum of measures
of the fibers `f ⁻¹' {y}`. -/
theorem tsum_measure_preimage_singleton {s : Set β} (hs : s.Countable) {f : α → β}
(hf : ∀ y ∈ s, MeasurableSet (f ⁻¹' {y})) : (∑' b : s, μ (f ⁻¹' {↑b})) = μ (f ⁻¹' s) := by
rw [← Set.biUnion_preimage_singleton, measure_biUnion hs (pairwiseDisjoint_fiber f s) hf]
lemma measure_preimage_eq_zero_iff_of_countable {s : Set β} {f : α → β} (hs : s.Countable) :
μ (f ⁻¹' s) = 0 ↔ ∀ x ∈ s, μ (f ⁻¹' {x}) = 0 := by
rw [← biUnion_preimage_singleton, measure_biUnion_null_iff hs]
/-- If `s` is a `Finset`, then the measure of its preimage can be found as the sum of measures
of the fibers `f ⁻¹' {y}`. -/
theorem sum_measure_preimage_singleton (s : Finset β) {f : α → β}
(hf : ∀ y ∈ s, MeasurableSet (f ⁻¹' {y})) : (∑ b ∈ s, μ (f ⁻¹' {b})) = μ (f ⁻¹' ↑s) := by
simp only [← measure_biUnion_finset (pairwiseDisjoint_fiber f s) hf,
Finset.set_biUnion_preimage_singleton]
@[simp] lemma sum_measure_singleton {s : Finset α} [MeasurableSingletonClass α] :
∑ x ∈ s, μ {x} = μ s := by
trans ∑ x ∈ s, μ (id ⁻¹' {x})
· simp
rw [sum_measure_preimage_singleton]
· simp
· simp
theorem measure_diff_null' (h : μ (s₁ ∩ s₂) = 0) : μ (s₁ \ s₂) = μ s₁ :=
measure_congr <| diff_ae_eq_self.2 h
theorem measure_add_diff (hs : NullMeasurableSet s μ) (t : Set α) :
μ s + μ (t \ s) = μ (s ∪ t) := by
rw [← measure_union₀' hs disjoint_sdiff_right.aedisjoint, union_diff_self]
theorem measure_diff' (s : Set α) (hm : NullMeasurableSet t μ) (h_fin : μ t ≠ ∞) :
μ (s \ t) = μ (s ∪ t) - μ t :=
ENNReal.eq_sub_of_add_eq h_fin <| by rw [add_comm, measure_add_diff hm, union_comm]
theorem measure_diff (h : s₂ ⊆ s₁) (h₂ : NullMeasurableSet s₂ μ) (h_fin : μ s₂ ≠ ∞) :
μ (s₁ \ s₂) = μ s₁ - μ s₂ := by rw [measure_diff' _ h₂ h_fin, union_eq_self_of_subset_right h]
theorem le_measure_diff : μ s₁ - μ s₂ ≤ μ (s₁ \ s₂) :=
tsub_le_iff_left.2 <| (measure_le_inter_add_diff μ s₁ s₂).trans <| by
gcongr; apply inter_subset_right
/-- If the measure of the symmetric difference of two sets is finite,
then one has infinite measure if and only if the other one does. -/
theorem measure_eq_top_iff_of_symmDiff (hμst : μ (s ∆ t) ≠ ∞) : μ s = ∞ ↔ μ t = ∞ := by
suffices h : ∀ u v, μ (u ∆ v) ≠ ∞ → μ u = ∞ → μ v = ∞
from ⟨h s t hμst, h t s (symmDiff_comm s t ▸ hμst)⟩
intro u v hμuv hμu
by_contra! hμv
apply hμuv
rw [Set.symmDiff_def, eq_top_iff]
calc
∞ = μ u - μ v := by rw [ENNReal.sub_eq_top_iff.2 ⟨hμu, hμv⟩]
_ ≤ μ (u \ v) := le_measure_diff
_ ≤ μ (u \ v ∪ v \ u) := measure_mono subset_union_left
/-- If the measure of the symmetric difference of two sets is finite,
then one has finite measure if and only if the other one does. -/
theorem measure_ne_top_iff_of_symmDiff (hμst : μ (s ∆ t) ≠ ∞) : μ s ≠ ∞ ↔ μ t ≠ ∞ :=
(measure_eq_top_iff_of_symmDiff hμst).ne
theorem measure_diff_lt_of_lt_add (hs : NullMeasurableSet s μ) (hst : s ⊆ t) (hs' : μ s ≠ ∞)
{ε : ℝ≥0∞} (h : μ t < μ s + ε) : μ (t \ s) < ε := by
rw [measure_diff hst hs hs']; rw [add_comm] at h
exact ENNReal.sub_lt_of_lt_add (measure_mono hst) h
theorem measure_diff_le_iff_le_add (hs : NullMeasurableSet s μ) (hst : s ⊆ t) (hs' : μ s ≠ ∞)
{ε : ℝ≥0∞} : μ (t \ s) ≤ ε ↔ μ t ≤ μ s + ε := by
rw [measure_diff hst hs hs', tsub_le_iff_left]
theorem measure_eq_measure_of_null_diff {s t : Set α} (hst : s ⊆ t) (h_nulldiff : μ (t \ s) = 0) :
μ s = μ t := measure_congr <|
EventuallyLE.antisymm (HasSubset.Subset.eventuallyLE hst) (ae_le_set.mpr h_nulldiff)
theorem measure_eq_measure_of_between_null_diff {s₁ s₂ s₃ : Set α} (h12 : s₁ ⊆ s₂) (h23 : s₂ ⊆ s₃)
(h_nulldiff : μ (s₃ \ s₁) = 0) : μ s₁ = μ s₂ ∧ μ s₂ = μ s₃ := by
have le12 : μ s₁ ≤ μ s₂ := measure_mono h12
have le23 : μ s₂ ≤ μ s₃ := measure_mono h23
have key : μ s₃ ≤ μ s₁ :=
calc
μ s₃ = μ (s₃ \ s₁ ∪ s₁) := by rw [diff_union_of_subset (h12.trans h23)]
_ ≤ μ (s₃ \ s₁) + μ s₁ := measure_union_le _ _
_ = μ s₁ := by simp only [h_nulldiff, zero_add]
exact ⟨le12.antisymm (le23.trans key), le23.antisymm (key.trans le12)⟩
theorem measure_eq_measure_smaller_of_between_null_diff {s₁ s₂ s₃ : Set α} (h12 : s₁ ⊆ s₂)
(h23 : s₂ ⊆ s₃) (h_nulldiff : μ (s₃ \ s₁) = 0) : μ s₁ = μ s₂ :=
(measure_eq_measure_of_between_null_diff h12 h23 h_nulldiff).1
theorem measure_eq_measure_larger_of_between_null_diff {s₁ s₂ s₃ : Set α} (h12 : s₁ ⊆ s₂)
(h23 : s₂ ⊆ s₃) (h_nulldiff : μ (s₃ \ s₁) = 0) : μ s₂ = μ s₃ :=
(measure_eq_measure_of_between_null_diff h12 h23 h_nulldiff).2
lemma measure_compl₀ (h : NullMeasurableSet s μ) (hs : μ s ≠ ∞) :
μ sᶜ = μ Set.univ - μ s := by
rw [← measure_add_measure_compl₀ h, ENNReal.add_sub_cancel_left hs]
theorem measure_compl (h₁ : MeasurableSet s) (h_fin : μ s ≠ ∞) : μ sᶜ = μ univ - μ s :=
measure_compl₀ h₁.nullMeasurableSet h_fin
lemma measure_inter_conull' (ht : μ (s \ t) = 0) : μ (s ∩ t) = μ s := by
rw [← diff_compl, measure_diff_null']; rwa [← diff_eq]
lemma measure_inter_conull (ht : μ tᶜ = 0) : μ (s ∩ t) = μ s := by
rw [← diff_compl, measure_diff_null ht]
@[simp]
theorem union_ae_eq_left_iff_ae_subset : (s ∪ t : Set α) =ᵐ[μ] s ↔ t ≤ᵐ[μ] s := by
rw [ae_le_set]
refine
⟨fun h => by simpa only [union_diff_left] using (ae_eq_set.mp h).1, fun h =>
eventuallyLE_antisymm_iff.mpr
⟨by rwa [ae_le_set, union_diff_left],
HasSubset.Subset.eventuallyLE subset_union_left⟩⟩
@[simp]
theorem union_ae_eq_right_iff_ae_subset : (s ∪ t : Set α) =ᵐ[μ] t ↔ s ≤ᵐ[μ] t := by
rw [union_comm, union_ae_eq_left_iff_ae_subset]
theorem ae_eq_of_ae_subset_of_measure_ge (h₁ : s ≤ᵐ[μ] t) (h₂ : μ t ≤ μ s)
(hsm : NullMeasurableSet s μ) (ht : μ t ≠ ∞) : s =ᵐ[μ] t := by
refine eventuallyLE_antisymm_iff.mpr ⟨h₁, ae_le_set.mpr ?_⟩
replace h₂ : μ t = μ s := h₂.antisymm (measure_mono_ae h₁)
replace ht : μ s ≠ ∞ := h₂ ▸ ht
rw [measure_diff' t hsm ht, measure_congr (union_ae_eq_left_iff_ae_subset.mpr h₁), h₂, tsub_self]
/-- If `s ⊆ t`, `μ t ≤ μ s`, `μ t ≠ ∞`, and `s` is measurable, then `s =ᵐ[μ] t`. -/
theorem ae_eq_of_subset_of_measure_ge (h₁ : s ⊆ t) (h₂ : μ t ≤ μ s) (hsm : NullMeasurableSet s μ)
(ht : μ t ≠ ∞) : s =ᵐ[μ] t :=
ae_eq_of_ae_subset_of_measure_ge (HasSubset.Subset.eventuallyLE h₁) h₂ hsm ht
theorem measure_iUnion_congr_of_subset {ι : Sort*} [Countable ι] {s : ι → Set α} {t : ι → Set α}
(hsub : ∀ i, s i ⊆ t i) (h_le : ∀ i, μ (t i) ≤ μ (s i)) : μ (⋃ i, s i) = μ (⋃ i, t i) := by
refine le_antisymm (by gcongr; apply hsub) ?_
rcases Classical.em (∃ i, μ (t i) = ∞) with (⟨i, hi⟩ | htop)
· calc
μ (⋃ i, t i) ≤ ∞ := le_top
_ ≤ μ (s i) := hi ▸ h_le i
_ ≤ μ (⋃ i, s i) := measure_mono <| subset_iUnion _ _
push_neg at htop
set M := toMeasurable μ
have H : ∀ b, (M (t b) ∩ M (⋃ b, s b) : Set α) =ᵐ[μ] M (t b) := by
refine fun b => ae_eq_of_subset_of_measure_ge inter_subset_left ?_ ?_ ?_
· calc
μ (M (t b)) = μ (t b) := measure_toMeasurable _
_ ≤ μ (s b) := h_le b
_ ≤ μ (M (t b) ∩ M (⋃ b, s b)) :=
measure_mono <|
subset_inter ((hsub b).trans <| subset_toMeasurable _ _)
((subset_iUnion _ _).trans <| subset_toMeasurable _ _)
· measurability
· rw [measure_toMeasurable]
exact htop b
calc
μ (⋃ b, t b) ≤ μ (⋃ b, M (t b)) := measure_mono (iUnion_mono fun b => subset_toMeasurable _ _)
_ = μ (⋃ b, M (t b) ∩ M (⋃ b, s b)) := measure_congr (EventuallyEq.countable_iUnion H).symm
_ ≤ μ (M (⋃ b, s b)) := measure_mono (iUnion_subset fun b => inter_subset_right)
_ = μ (⋃ b, s b) := measure_toMeasurable _
theorem measure_union_congr_of_subset {t₁ t₂ : Set α} (hs : s₁ ⊆ s₂) (hsμ : μ s₂ ≤ μ s₁)
(ht : t₁ ⊆ t₂) (htμ : μ t₂ ≤ μ t₁) : μ (s₁ ∪ t₁) = μ (s₂ ∪ t₂) := by
rw [union_eq_iUnion, union_eq_iUnion]
exact measure_iUnion_congr_of_subset (Bool.forall_bool.2 ⟨ht, hs⟩) (Bool.forall_bool.2 ⟨htμ, hsμ⟩)
@[simp]
theorem measure_iUnion_toMeasurable {ι : Sort*} [Countable ι] (s : ι → Set α) :
μ (⋃ i, toMeasurable μ (s i)) = μ (⋃ i, s i) :=
Eq.symm <| measure_iUnion_congr_of_subset (fun _i => subset_toMeasurable _ _) fun _i ↦
(measure_toMeasurable _).le
theorem measure_biUnion_toMeasurable {I : Set β} (hc : I.Countable) (s : β → Set α) :
μ (⋃ b ∈ I, toMeasurable μ (s b)) = μ (⋃ b ∈ I, s b) := by
haveI := hc.toEncodable
simp only [biUnion_eq_iUnion, measure_iUnion_toMeasurable]
@[simp]
theorem measure_toMeasurable_union : μ (toMeasurable μ s ∪ t) = μ (s ∪ t) :=
Eq.symm <|
measure_union_congr_of_subset (subset_toMeasurable _ _) (measure_toMeasurable _).le Subset.rfl
le_rfl
@[simp]
theorem measure_union_toMeasurable : μ (s ∪ toMeasurable μ t) = μ (s ∪ t) :=
Eq.symm <|
measure_union_congr_of_subset Subset.rfl le_rfl (subset_toMeasurable _ _)
(measure_toMeasurable _).le
theorem sum_measure_le_measure_univ {s : Finset ι} {t : ι → Set α}
(h : ∀ i ∈ s, NullMeasurableSet (t i) μ) (H : Set.Pairwise s (AEDisjoint μ on t)) :
(∑ i ∈ s, μ (t i)) ≤ μ (univ : Set α) := by
rw [← measure_biUnion_finset₀ H h]
exact measure_mono (subset_univ _)
theorem tsum_measure_le_measure_univ {s : ι → Set α} (hs : ∀ i, NullMeasurableSet (s i) μ)
(H : Pairwise (AEDisjoint μ on s)) : ∑' i, μ (s i) ≤ μ (univ : Set α) := by
rw [ENNReal.tsum_eq_iSup_sum]
exact iSup_le fun s =>
sum_measure_le_measure_univ (fun i _hi => hs i) fun i _hi j _hj hij => H hij
/-- Pigeonhole principle for measure spaces: if `∑' i, μ (s i) > μ univ`, then
one of the intersections `s i ∩ s j` is not empty. -/
theorem exists_nonempty_inter_of_measure_univ_lt_tsum_measure {m : MeasurableSpace α}
(μ : Measure α) {s : ι → Set α} (hs : ∀ i, NullMeasurableSet (s i) μ)
(H : μ (univ : Set α) < ∑' i, μ (s i)) : ∃ i j, i ≠ j ∧ (s i ∩ s j).Nonempty := by
contrapose! H
apply tsum_measure_le_measure_univ hs
intro i j hij
exact (disjoint_iff_inter_eq_empty.mpr (H i j hij)).aedisjoint
/-- Pigeonhole principle for measure spaces: if `s` is a `Finset` and
`∑ i ∈ s, μ (t i) > μ univ`, then one of the intersections `t i ∩ t j` is not empty. -/
theorem exists_nonempty_inter_of_measure_univ_lt_sum_measure {m : MeasurableSpace α} (μ : Measure α)
{s : Finset ι} {t : ι → Set α} (h : ∀ i ∈ s, NullMeasurableSet (t i) μ)
(H : μ (univ : Set α) < ∑ i ∈ s, μ (t i)) :
∃ i ∈ s, ∃ j ∈ s, ∃ _h : i ≠ j, (t i ∩ t j).Nonempty := by
contrapose! H
apply sum_measure_le_measure_univ h
intro i hi j hj hij
exact (disjoint_iff_inter_eq_empty.mpr (H i hi j hj hij)).aedisjoint
/-- If two sets `s` and `t` are included in a set `u`, and `μ s + μ t > μ u`,
then `s` intersects `t`. Version assuming that `t` is measurable. -/
theorem nonempty_inter_of_measure_lt_add {m : MeasurableSpace α} (μ : Measure α) {s t u : Set α}
(ht : MeasurableSet t) (h's : s ⊆ u) (h't : t ⊆ u) (h : μ u < μ s + μ t) :
(s ∩ t).Nonempty := by
rw [← Set.not_disjoint_iff_nonempty_inter]
contrapose! h
| calc
μ s + μ t = μ (s ∪ t) := (measure_union h ht).symm
_ ≤ μ u := measure_mono (union_subset h's h't)
/-- If two sets `s` and `t` are included in a set `u`, and `μ s + μ t > μ u`,
then `s` intersects `t`. Version assuming that `s` is measurable. -/
theorem nonempty_inter_of_measure_lt_add' {m : MeasurableSpace α} (μ : Measure α) {s t u : Set α}
| Mathlib/MeasureTheory/Measure/MeasureSpace.lean | 425 | 431 |
/-
Copyright (c) 2021 Yaël Dillies, Bhavik Mehta. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Bhavik Mehta
-/
import Mathlib.Analysis.Convex.Topology
import Mathlib.Analysis.NormedSpace.Pointwise
import Mathlib.Analysis.Seminorm
import Mathlib.Analysis.LocallyConvex.Bounded
import Mathlib.Analysis.RCLike.Basic
/-!
# The Minkowski functional
This file defines the Minkowski functional, aka gauge.
The Minkowski functional of a set `s` is the function which associates each point to how much you
need to scale `s` for `x` to be inside it. When `s` is symmetric, convex and absorbent, its gauge is
a seminorm. Reciprocally, any seminorm arises as the gauge of some set, namely its unit ball. This
induces the equivalence of seminorms and locally convex topological vector spaces.
## Main declarations
For a real vector space,
* `gauge`: Aka Minkowski functional. `gauge s x` is the least (actually, an infimum) `r` such
that `x ∈ r • s`.
* `gaugeSeminorm`: The Minkowski functional as a seminorm, when `s` is symmetric, convex and
absorbent.
## References
* [H. H. Schaefer, *Topological Vector Spaces*][schaefer1966]
## Tags
Minkowski functional, gauge
-/
open NormedField Set
open scoped Pointwise Topology NNReal
noncomputable section
variable {𝕜 E : Type*}
section AddCommGroup
variable [AddCommGroup E] [Module ℝ E]
/-- The Minkowski functional. Given a set `s` in a real vector space, `gauge s` is the functional
which sends `x : E` to the smallest `r : ℝ` such that `x` is in `s` scaled by `r`. -/
def gauge (s : Set E) (x : E) : ℝ :=
sInf { r : ℝ | 0 < r ∧ x ∈ r • s }
variable {s t : Set E} {x : E} {a : ℝ}
theorem gauge_def : gauge s x = sInf ({ r ∈ Set.Ioi (0 : ℝ) | x ∈ r • s }) :=
rfl
/-- An alternative definition of the gauge using scalar multiplication on the element rather than on
the set. -/
theorem gauge_def' : gauge s x = sInf {r ∈ Set.Ioi (0 : ℝ) | r⁻¹ • x ∈ s} := by
congrm sInf {r | ?_}
exact and_congr_right fun hr => mem_smul_set_iff_inv_smul_mem₀ hr.ne' _ _
private theorem gauge_set_bddBelow : BddBelow { r : ℝ | 0 < r ∧ x ∈ r • s } :=
⟨0, fun _ hr => hr.1.le⟩
/-- If the given subset is `Absorbent` then the set we take an infimum over in `gauge` is nonempty,
which is useful for proving many properties about the gauge. -/
theorem Absorbent.gauge_set_nonempty (absorbs : Absorbent ℝ s) :
{ r : ℝ | 0 < r ∧ x ∈ r • s }.Nonempty :=
let ⟨r, hr₁, hr₂⟩ := (absorbs x).exists_pos
⟨r, hr₁, hr₂ r (Real.norm_of_nonneg hr₁.le).ge rfl⟩
theorem gauge_mono (hs : Absorbent ℝ s) (h : s ⊆ t) : gauge t ≤ gauge s := fun _ =>
csInf_le_csInf gauge_set_bddBelow hs.gauge_set_nonempty fun _ hr => ⟨hr.1, smul_set_mono h hr.2⟩
theorem exists_lt_of_gauge_lt (absorbs : Absorbent ℝ s) (h : gauge s x < a) :
∃ b, 0 < b ∧ b < a ∧ x ∈ b • s := by
obtain ⟨b, ⟨hb, hx⟩, hba⟩ := exists_lt_of_csInf_lt absorbs.gauge_set_nonempty h
exact ⟨b, hb, hba, hx⟩
/-- The gauge evaluated at `0` is always zero (mathematically this requires `0` to be in the set `s`
but, the real infimum of the empty set in Lean being defined as `0`, it holds unconditionally). -/
@[simp]
theorem gauge_zero : gauge s 0 = 0 := by
rw [gauge_def']
by_cases h : (0 : E) ∈ s
· simp only [smul_zero, sep_true, h, csInf_Ioi]
· simp only [smul_zero, sep_false, h, Real.sInf_empty]
@[simp]
theorem gauge_zero' : gauge (0 : Set E) = 0 := by
ext x
rw [gauge_def']
obtain rfl | hx := eq_or_ne x 0
· simp only [csInf_Ioi, mem_zero, Pi.zero_apply, eq_self_iff_true, sep_true, smul_zero]
· simp only [mem_zero, Pi.zero_apply, inv_eq_zero, smul_eq_zero]
convert Real.sInf_empty
exact eq_empty_iff_forall_not_mem.2 fun r hr => hr.2.elim (ne_of_gt hr.1) hx
@[simp]
theorem gauge_empty : gauge (∅ : Set E) = 0 := by
ext
simp only [gauge_def', Real.sInf_empty, mem_empty_iff_false, Pi.zero_apply, sep_false]
theorem gauge_of_subset_zero (h : s ⊆ 0) : gauge s = 0 := by
obtain rfl | rfl := subset_singleton_iff_eq.1 h
exacts [gauge_empty, gauge_zero']
/-- The gauge is always nonnegative. -/
theorem gauge_nonneg (x : E) : 0 ≤ gauge s x :=
Real.sInf_nonneg fun _ hx => hx.1.le
theorem gauge_neg (symmetric : ∀ x ∈ s, -x ∈ s) (x : E) : gauge s (-x) = gauge s x := by
have : ∀ x, -x ∈ s ↔ x ∈ s := fun x => ⟨fun h => by simpa using symmetric _ h, symmetric x⟩
simp_rw [gauge_def', smul_neg, this]
theorem gauge_neg_set_neg (x : E) : gauge (-s) (-x) = gauge s x := by
simp_rw [gauge_def', smul_neg, neg_mem_neg]
theorem gauge_neg_set_eq_gauge_neg (x : E) : gauge (-s) x = gauge s (-x) := by
rw [← gauge_neg_set_neg, neg_neg]
theorem gauge_le_of_mem (ha : 0 ≤ a) (hx : x ∈ a • s) : gauge s x ≤ a := by
obtain rfl | ha' := ha.eq_or_lt
· rw [mem_singleton_iff.1 (zero_smul_set_subset _ hx), gauge_zero]
· exact csInf_le gauge_set_bddBelow ⟨ha', hx⟩
theorem gauge_le_eq (hs₁ : Convex ℝ s) (hs₀ : (0 : E) ∈ s) (hs₂ : Absorbent ℝ s) (ha : 0 ≤ a) :
{ x | gauge s x ≤ a } = ⋂ (r : ℝ) (_ : a < r), r • s := by
ext x
simp_rw [Set.mem_iInter, Set.mem_setOf_eq]
refine ⟨fun h r hr => ?_, fun h => le_of_forall_pos_lt_add fun ε hε => ?_⟩
· have hr' := ha.trans_lt hr
rw [mem_smul_set_iff_inv_smul_mem₀ hr'.ne']
obtain ⟨δ, δ_pos, hδr, hδ⟩ := exists_lt_of_gauge_lt hs₂ (h.trans_lt hr)
suffices (r⁻¹ * δ) • δ⁻¹ • x ∈ s by rwa [smul_smul, mul_inv_cancel_right₀ δ_pos.ne'] at this
rw [mem_smul_set_iff_inv_smul_mem₀ δ_pos.ne'] at hδ
refine hs₁.smul_mem_of_zero_mem hs₀ hδ ⟨by positivity, ?_⟩
rw [inv_mul_le_iff₀ hr', mul_one]
exact hδr.le
· have hε' := (lt_add_iff_pos_right a).2 (half_pos hε)
exact
(gauge_le_of_mem (ha.trans hε'.le) <| h _ hε').trans_lt (add_lt_add_left (half_lt_self hε) _)
theorem gauge_lt_eq' (absorbs : Absorbent ℝ s) (a : ℝ) :
{ x | gauge s x < a } = ⋃ (r : ℝ) (_ : 0 < r) (_ : r < a), r • s := by
ext
simp_rw [mem_setOf, mem_iUnion, exists_prop]
exact
⟨exists_lt_of_gauge_lt absorbs, fun ⟨r, hr₀, hr₁, hx⟩ =>
(gauge_le_of_mem hr₀.le hx).trans_lt hr₁⟩
theorem gauge_lt_eq (absorbs : Absorbent ℝ s) (a : ℝ) :
{ x | gauge s x < a } = ⋃ r ∈ Set.Ioo 0 (a : ℝ), r • s := by
ext
simp_rw [mem_setOf, mem_iUnion, exists_prop, mem_Ioo, and_assoc]
exact
⟨exists_lt_of_gauge_lt absorbs, fun ⟨r, hr₀, hr₁, hx⟩ =>
(gauge_le_of_mem hr₀.le hx).trans_lt hr₁⟩
theorem mem_openSegment_of_gauge_lt_one (absorbs : Absorbent ℝ s) (hgauge : gauge s x < 1) :
∃ y ∈ s, x ∈ openSegment ℝ 0 y := by
rcases exists_lt_of_gauge_lt absorbs hgauge with ⟨r, hr₀, hr₁, y, hy, rfl⟩
refine ⟨y, hy, 1 - r, r, ?_⟩
simp [*]
theorem gauge_lt_one_subset_self (hs : Convex ℝ s) (h₀ : (0 : E) ∈ s) (absorbs : Absorbent ℝ s) :
{ x | gauge s x < 1 } ⊆ s := fun _x hx ↦
let ⟨_y, hys, hx⟩ := mem_openSegment_of_gauge_lt_one absorbs hx
hs.openSegment_subset h₀ hys hx
theorem gauge_le_one_of_mem {x : E} (hx : x ∈ s) : gauge s x ≤ 1 :=
gauge_le_of_mem zero_le_one <| by rwa [one_smul]
/-- Gauge is subadditive. -/
theorem gauge_add_le (hs : Convex ℝ s) (absorbs : Absorbent ℝ s) (x y : E) :
gauge s (x + y) ≤ gauge s x + gauge s y := by
refine le_of_forall_pos_lt_add fun ε hε => ?_
obtain ⟨a, ha, ha', x, hx, rfl⟩ :=
exists_lt_of_gauge_lt absorbs (lt_add_of_pos_right (gauge s x) (half_pos hε))
obtain ⟨b, hb, hb', y, hy, rfl⟩ :=
exists_lt_of_gauge_lt absorbs (lt_add_of_pos_right (gauge s y) (half_pos hε))
calc
gauge s (a • x + b • y) ≤ a + b := gauge_le_of_mem (by positivity) <| by
rw [hs.add_smul ha.le hb.le]
exact add_mem_add (smul_mem_smul_set hx) (smul_mem_smul_set hy)
_ < gauge s (a • x) + gauge s (b • y) + ε := by linarith
theorem self_subset_gauge_le_one : s ⊆ { x | gauge s x ≤ 1 } := fun _ => gauge_le_one_of_mem
theorem Convex.gauge_le (hs : Convex ℝ s) (h₀ : (0 : E) ∈ s) (absorbs : Absorbent ℝ s) (a : ℝ) :
Convex ℝ { x | gauge s x ≤ a } := by
by_cases ha : 0 ≤ a
· rw [gauge_le_eq hs h₀ absorbs ha]
exact convex_iInter fun i => convex_iInter fun _ => hs.smul _
· convert convex_empty (𝕜 := ℝ)
exact eq_empty_iff_forall_not_mem.2 fun x hx => ha <| (gauge_nonneg _).trans hx
theorem Balanced.starConvex (hs : Balanced ℝ s) : StarConvex ℝ 0 s :=
starConvex_zero_iff.2 fun _ hx a ha₀ ha₁ =>
hs _ (by rwa [Real.norm_of_nonneg ha₀]) (smul_mem_smul_set hx)
theorem le_gauge_of_not_mem (hs₀ : StarConvex ℝ 0 s) (hs₂ : Absorbs ℝ s {x}) (hx : x ∉ a • s) :
a ≤ gauge s x := by
rw [starConvex_zero_iff] at hs₀
obtain ⟨r, hr, h⟩ := hs₂.exists_pos
refine le_csInf ⟨r, hr, singleton_subset_iff.1 <| h _ (Real.norm_of_nonneg hr.le).ge⟩ ?_
rintro b ⟨hb, x, hx', rfl⟩
refine not_lt.1 fun hba => hx ?_
have ha := hb.trans hba
refine ⟨(a⁻¹ * b) • x, hs₀ hx' (by positivity) ?_, ?_⟩
· rw [← div_eq_inv_mul]
exact div_le_one_of_le₀ hba.le ha.le
· dsimp only
rw [← mul_smul, mul_inv_cancel_left₀ ha.ne']
theorem one_le_gauge_of_not_mem (hs₁ : StarConvex ℝ 0 s) (hs₂ : Absorbs ℝ s {x}) (hx : x ∉ s) :
1 ≤ gauge s x :=
le_gauge_of_not_mem hs₁ hs₂ <| by rwa [one_smul]
section LinearOrderedField
variable {α : Type*} [Field α] [LinearOrder α] [IsStrictOrderedRing α]
[MulActionWithZero α ℝ] [OrderedSMul α ℝ]
theorem gauge_smul_of_nonneg [MulActionWithZero α E] [IsScalarTower α ℝ (Set E)] {s : Set E} {a : α}
(ha : 0 ≤ a) (x : E) : gauge s (a • x) = a • gauge s x := by
obtain rfl | ha' := ha.eq_or_lt
· rw [zero_smul, gauge_zero, zero_smul]
rw [gauge_def', gauge_def', ← Real.sInf_smul_of_nonneg ha]
congr 1
ext r
simp_rw [Set.mem_smul_set, Set.mem_sep_iff]
constructor
· rintro ⟨hr, hx⟩
simp_rw [mem_Ioi] at hr ⊢
rw [← mem_smul_set_iff_inv_smul_mem₀ hr.ne'] at hx
have := smul_pos (inv_pos.2 ha') hr
refine ⟨a⁻¹ • r, ⟨this, ?_⟩, smul_inv_smul₀ ha'.ne' _⟩
rwa [← mem_smul_set_iff_inv_smul_mem₀ this.ne', smul_assoc,
mem_smul_set_iff_inv_smul_mem₀ (inv_ne_zero ha'.ne'), inv_inv]
· rintro ⟨r, ⟨hr, hx⟩, rfl⟩
rw [mem_Ioi] at hr ⊢
rw [← mem_smul_set_iff_inv_smul_mem₀ hr.ne'] at hx
have := smul_pos ha' hr
refine ⟨this, ?_⟩
rw [← mem_smul_set_iff_inv_smul_mem₀ this.ne', smul_assoc]
exact smul_mem_smul_set hx
theorem gauge_smul_left_of_nonneg [MulActionWithZero α E] [SMulCommClass α ℝ ℝ]
[IsScalarTower α ℝ ℝ] [IsScalarTower α ℝ E] {s : Set E} {a : α} (ha : 0 ≤ a) :
gauge (a • s) = a⁻¹ • gauge s := by
obtain rfl | ha' := ha.eq_or_lt
· rw [inv_zero, zero_smul, gauge_of_subset_zero (zero_smul_set_subset _)]
ext x
rw [gauge_def', Pi.smul_apply, gauge_def', ← Real.sInf_smul_of_nonneg (inv_nonneg.2 ha)]
congr 1
ext r
simp_rw [Set.mem_smul_set, Set.mem_sep_iff]
constructor
· rintro ⟨hr, y, hy, h⟩
simp_rw [mem_Ioi] at hr ⊢
refine ⟨a • r, ⟨smul_pos ha' hr, ?_⟩, inv_smul_smul₀ ha'.ne' _⟩
rwa [smul_inv₀, smul_assoc, ← h, inv_smul_smul₀ ha'.ne']
· rintro ⟨r, ⟨hr, hx⟩, rfl⟩
rw [mem_Ioi] at hr ⊢
refine ⟨smul_pos (inv_pos.2 ha') hr, r⁻¹ • x, hx, ?_⟩
rw [smul_inv₀, smul_assoc, inv_inv]
theorem gauge_smul_left [Module α E] [SMulCommClass α ℝ ℝ] [IsScalarTower α ℝ ℝ]
[IsScalarTower α ℝ E] {s : Set E} (symmetric : ∀ x ∈ s, -x ∈ s) (a : α) :
gauge (a • s) = |a|⁻¹ • gauge s := by
rw [← gauge_smul_left_of_nonneg (abs_nonneg a)]
obtain h | h := abs_choice a
· rw [h]
· rw [h, Set.neg_smul_set, ← Set.smul_set_neg]
-- Porting note: was congr
apply congr_arg
apply congr_arg
ext y
refine ⟨symmetric _, fun hy => ?_⟩
rw [← neg_neg y]
exact symmetric _ hy
end LinearOrderedField
section RCLike
variable [RCLike 𝕜] [Module 𝕜 E] [IsScalarTower ℝ 𝕜 E]
theorem gauge_norm_smul (hs : Balanced 𝕜 s) (r : 𝕜) (x : E) :
gauge s (‖r‖ • x) = gauge s (r • x) := by
unfold gauge
congr with θ
rw [@RCLike.real_smul_eq_coe_smul 𝕜]
refine and_congr_right fun hθ => (hs.smul _).smul_mem_iff ?_
rw [RCLike.norm_ofReal, abs_norm]
/-- If `s` is balanced, then the Minkowski functional is ℂ-homogeneous. -/
theorem gauge_smul (hs : Balanced 𝕜 s) (r : 𝕜) (x : E) : gauge s (r • x) = ‖r‖ * gauge s x := by
rw [← smul_eq_mul, ← gauge_smul_of_nonneg (norm_nonneg r), gauge_norm_smul hs]
end RCLike
open Filter
section TopologicalSpace
variable [TopologicalSpace E]
theorem comap_gauge_nhds_zero_le (ha : Absorbent ℝ s) (hb : Bornology.IsVonNBounded ℝ s) :
comap (gauge s) (𝓝 0) ≤ 𝓝 0 := fun u hu ↦ by
rcases (hb hu).exists_pos with ⟨r, hr₀, hr⟩
filter_upwards [preimage_mem_comap (gt_mem_nhds (inv_pos.2 hr₀))] with x (hx : gauge s x < r⁻¹)
rcases exists_lt_of_gauge_lt ha hx with ⟨c, hc₀, hcr, y, hy, rfl⟩
have hrc := (lt_inv_comm₀ hr₀ hc₀).2 hcr
rcases hr c⁻¹ (hrc.le.trans (le_abs_self _)) hy with ⟨z, hz, rfl⟩
simpa only [smul_inv_smul₀ hc₀.ne']
variable [T1Space E]
theorem gauge_eq_zero (hs : Absorbent ℝ s) (hb : Bornology.IsVonNBounded ℝ s) :
gauge s x = 0 ↔ x = 0 := by
refine ⟨fun h₀ ↦ by_contra fun (hne : x ≠ 0) ↦ ?_, fun h ↦ h.symm ▸ gauge_zero⟩
have : {x}ᶜ ∈ comap (gauge s) (𝓝 0) :=
comap_gauge_nhds_zero_le hs hb (isOpen_compl_singleton.mem_nhds hne.symm)
rcases ((nhds_basis_zero_abs_lt _).comap _).mem_iff.1 this with ⟨r, hr₀, hr⟩
exact hr (by simpa [h₀]) rfl
theorem gauge_pos (hs : Absorbent ℝ s) (hb : Bornology.IsVonNBounded ℝ s) :
0 < gauge s x ↔ x ≠ 0 := by
simp only [(gauge_nonneg _).gt_iff_ne, Ne, gauge_eq_zero hs hb]
end TopologicalSpace
section ContinuousSMul
variable [TopologicalSpace E] [ContinuousSMul ℝ E]
open Filter in
theorem interior_subset_gauge_lt_one (s : Set E) : interior s ⊆ { x | gauge s x < 1 } := by
intro x hx
have H₁ : Tendsto (fun r : ℝ ↦ r⁻¹ • x) (𝓝[<] 1) (𝓝 ((1 : ℝ)⁻¹ • x)) :=
((tendsto_id.inv₀ one_ne_zero).smul tendsto_const_nhds).mono_left inf_le_left
rw [inv_one, one_smul] at H₁
have H₂ : ∀ᶠ r in 𝓝[<] (1 : ℝ), x ∈ r • s ∧ 0 < r ∧ r < 1 := by
filter_upwards [H₁ (mem_interior_iff_mem_nhds.1 hx), Ioo_mem_nhdsLT one_pos] with r h₁ h₂
exact ⟨(mem_smul_set_iff_inv_smul_mem₀ h₂.1.ne' _ _).2 h₁, h₂⟩
rcases H₂.exists with ⟨r, hxr, hr₀, hr₁⟩
exact (gauge_le_of_mem hr₀.le hxr).trans_lt hr₁
theorem gauge_lt_one_eq_self_of_isOpen (hs₁ : Convex ℝ s) (hs₀ : (0 : E) ∈ s) (hs₂ : IsOpen s) :
{ x | gauge s x < 1 } = s := by
refine (gauge_lt_one_subset_self hs₁ ‹_› <| absorbent_nhds_zero <| hs₂.mem_nhds hs₀).antisymm ?_
convert interior_subset_gauge_lt_one s
exact hs₂.interior_eq.symm
theorem gauge_lt_one_of_mem_of_isOpen (hs₂ : IsOpen s) {x : E} (hx : x ∈ s) :
gauge s x < 1 :=
interior_subset_gauge_lt_one s <| by rwa [hs₂.interior_eq]
theorem gauge_lt_of_mem_smul (x : E) (ε : ℝ) (hε : 0 < ε) (hs₂ : IsOpen s) (hx : x ∈ ε • s) :
gauge s x < ε := by
have : ε⁻¹ • x ∈ s := by rwa [← mem_smul_set_iff_inv_smul_mem₀ hε.ne']
have h_gauge_lt := gauge_lt_one_of_mem_of_isOpen hs₂ this
rwa [gauge_smul_of_nonneg (inv_nonneg.2 hε.le), smul_eq_mul, inv_mul_lt_iff₀ hε, mul_one]
at h_gauge_lt
theorem mem_closure_of_gauge_le_one (hc : Convex ℝ s) (hs₀ : 0 ∈ s) (ha : Absorbent ℝ s)
(h : gauge s x ≤ 1) : x ∈ closure s := by
have : ∀ᶠ r : ℝ in 𝓝[<] 1, r • x ∈ s := by
filter_upwards [Ico_mem_nhdsLT one_pos] with r ⟨hr₀, hr₁⟩
apply gauge_lt_one_subset_self hc hs₀ ha
rw [mem_setOf_eq, gauge_smul_of_nonneg hr₀]
exact mul_lt_one_of_nonneg_of_lt_one_left hr₀ hr₁ h
refine mem_closure_of_tendsto ?_ this
exact Filter.Tendsto.mono_left (Continuous.tendsto' (by fun_prop) _ _ (one_smul _ _))
inf_le_left
theorem mem_frontier_of_gauge_eq_one (hc : Convex ℝ s) (hs₀ : 0 ∈ s) (ha : Absorbent ℝ s)
(h : gauge s x = 1) : x ∈ frontier s :=
⟨mem_closure_of_gauge_le_one hc hs₀ ha h.le, fun h' ↦
(interior_subset_gauge_lt_one s h').out.ne h⟩
theorem tendsto_gauge_nhds_zero_nhdsGE (hs : s ∈ 𝓝 0) : Tendsto (gauge s) (𝓝 0) (𝓝[≥] 0) := by
refine nhdsGE_basis_Icc.tendsto_right_iff.2 fun ε hε ↦ ?_
rw [← set_smul_mem_nhds_zero_iff hε.ne'] at hs
filter_upwards [hs] with x hx
exact ⟨gauge_nonneg _, gauge_le_of_mem hε.le hx⟩
@[deprecated (since := "2025-03-02")]
alias tendsto_gauge_nhds_zero' := tendsto_gauge_nhds_zero_nhdsGE
theorem tendsto_gauge_nhds_zero (hs : s ∈ 𝓝 0) : Tendsto (gauge s) (𝓝 0) (𝓝 0) :=
(tendsto_gauge_nhds_zero_nhdsGE hs).mono_right inf_le_left
/-- If `s` is a neighborhood of the origin, then `gauge s` is continuous at the origin.
See also `continuousAt_gauge`. -/
theorem continuousAt_gauge_zero (hs : s ∈ 𝓝 0) : ContinuousAt (gauge s) 0 := by
rw [ContinuousAt, gauge_zero]
exact tendsto_gauge_nhds_zero hs
theorem comap_gauge_nhds_zero (hb : Bornology.IsVonNBounded ℝ s) (h₀ : s ∈ 𝓝 0) :
comap (gauge s) (𝓝 0) = 𝓝 0 :=
(comap_gauge_nhds_zero_le (absorbent_nhds_zero h₀) hb).antisymm
(tendsto_gauge_nhds_zero h₀).le_comap
end ContinuousSMul
section TopologicalVectorSpace
open Filter
variable [TopologicalSpace E] [IsTopologicalAddGroup E] [ContinuousSMul ℝ E]
/-- If `s` is a convex neighborhood of the origin in a topological real vector space, then `gauge s`
is continuous. If the ambient space is a normed space, then `gauge s` is Lipschitz continuous, see
`Convex.lipschitz_gauge`. -/
theorem continuousAt_gauge (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) : ContinuousAt (gauge s) x := by
have ha : Absorbent ℝ s := absorbent_nhds_zero hs₀
refine (nhds_basis_Icc_pos _).tendsto_right_iff.2 fun ε hε₀ ↦ ?_
rw [← map_add_left_nhds_zero, eventually_map]
have : ε • s ∩ -(ε • s) ∈ 𝓝 0 :=
inter_mem ((set_smul_mem_nhds_zero_iff hε₀.ne').2 hs₀)
(neg_mem_nhds_zero _ ((set_smul_mem_nhds_zero_iff hε₀.ne').2 hs₀))
filter_upwards [this] with y hy
constructor
· rw [sub_le_iff_le_add]
calc
gauge s x = gauge s (x + y + (-y)) := by simp
_ ≤ gauge s (x + y) + gauge s (-y) := gauge_add_le hc ha _ _
_ ≤ gauge s (x + y) + ε := add_le_add_left (gauge_le_of_mem hε₀.le (mem_neg.1 hy.2)) _
· calc
gauge s (x + y) ≤ gauge s x + gauge s y := gauge_add_le hc ha _ _
_ ≤ gauge s x + ε := add_le_add_left (gauge_le_of_mem hε₀.le hy.1) _
/-- If `s` is a convex neighborhood of the origin in a topological real vector space, then `gauge s`
is continuous. If the ambient space is a normed space, then `gauge s` is Lipschitz continuous, see
`Convex.lipschitz_gauge`. -/
@[continuity]
theorem continuous_gauge (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) : Continuous (gauge s) :=
continuous_iff_continuousAt.2 fun _ ↦ continuousAt_gauge hc hs₀
theorem gauge_lt_one_eq_interior (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) :
{ x | gauge s x < 1 } = interior s := by
refine Subset.antisymm (fun x hx ↦ ?_) (interior_subset_gauge_lt_one s)
rcases mem_openSegment_of_gauge_lt_one (absorbent_nhds_zero hs₀) hx with ⟨y, hys, hxy⟩
exact hc.openSegment_interior_self_subset_interior (mem_interior_iff_mem_nhds.2 hs₀) hys hxy
theorem gauge_lt_one_iff_mem_interior (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) :
gauge s x < 1 ↔ x ∈ interior s :=
Set.ext_iff.1 (gauge_lt_one_eq_interior hc hs₀) _
theorem gauge_le_one_iff_mem_closure (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) :
gauge s x ≤ 1 ↔ x ∈ closure s :=
⟨mem_closure_of_gauge_le_one hc (mem_of_mem_nhds hs₀) (absorbent_nhds_zero hs₀), fun h ↦
le_on_closure (fun _ ↦ gauge_le_one_of_mem) (continuous_gauge hc hs₀).continuousOn
continuousOn_const h⟩
theorem gauge_eq_one_iff_mem_frontier (hc : Convex ℝ s) (hs₀ : s ∈ 𝓝 0) :
gauge s x = 1 ↔ x ∈ frontier s := by
rw [eq_iff_le_not_lt, gauge_le_one_iff_mem_closure hc hs₀, gauge_lt_one_iff_mem_interior hc hs₀]
rfl
end TopologicalVectorSpace
section RCLike
variable [RCLike 𝕜] [Module 𝕜 E] [IsScalarTower ℝ 𝕜 E]
/-- `gauge s` as a seminorm when `s` is balanced, convex and absorbent. -/
@[simps!]
def gaugeSeminorm (hs₀ : Balanced 𝕜 s) (hs₁ : Convex ℝ s) (hs₂ : Absorbent ℝ s) : Seminorm 𝕜 E :=
Seminorm.of (gauge s) (gauge_add_le hs₁ hs₂) (gauge_smul hs₀)
variable {hs₀ : Balanced 𝕜 s} {hs₁ : Convex ℝ s} {hs₂ : Absorbent ℝ s} [TopologicalSpace E]
[ContinuousSMul ℝ E]
theorem gaugeSeminorm_lt_one_of_isOpen (hs : IsOpen s) {x : E} (hx : x ∈ s) :
gaugeSeminorm hs₀ hs₁ hs₂ x < 1 :=
gauge_lt_one_of_mem_of_isOpen hs hx
theorem gaugeSeminorm_ball_one (hs : IsOpen s) : (gaugeSeminorm hs₀ hs₁ hs₂).ball 0 1 = s := by
rw [Seminorm.ball_zero_eq]
exact gauge_lt_one_eq_self_of_isOpen hs₁ hs₂.zero_mem hs
end RCLike
/-- Any seminorm arises as the gauge of its unit ball. -/
@[simp]
protected theorem Seminorm.gauge_ball (p : Seminorm ℝ E) : gauge (p.ball 0 1) = p := by
ext x
obtain hp | hp := { r : ℝ | 0 < r ∧ x ∈ r • p.ball 0 1 }.eq_empty_or_nonempty
· rw [gauge, hp, Real.sInf_empty]
by_contra h
have hpx : 0 < p x := (apply_nonneg _ _).lt_of_ne h
have hpx₂ : 0 < 2 * p x := mul_pos zero_lt_two hpx
refine hp.subset ⟨hpx₂, (2 * p x)⁻¹ • x, ?_, smul_inv_smul₀ hpx₂.ne' _⟩
rw [p.mem_ball_zero, map_smul_eq_mul, Real.norm_eq_abs, abs_of_pos (inv_pos.2 hpx₂),
inv_mul_lt_iff₀ hpx₂, mul_one]
exact lt_mul_of_one_lt_left hpx one_lt_two
refine IsGLB.csInf_eq ⟨fun r => ?_, fun r hr => le_of_forall_pos_le_add fun ε hε => ?_⟩ hp
· rintro ⟨hr, y, hy, rfl⟩
rw [p.mem_ball_zero] at hy
rw [map_smul_eq_mul, Real.norm_eq_abs, abs_of_pos hr]
exact mul_le_of_le_one_right hr.le hy.le
· have hpε : 0 < p x + ε := by positivity
refine hr ⟨hpε, (p x + ε)⁻¹ • x, ?_, smul_inv_smul₀ hpε.ne' _⟩
rw [p.mem_ball_zero, map_smul_eq_mul, Real.norm_eq_abs, abs_of_pos (inv_pos.2 hpε),
inv_mul_lt_iff₀ hpε, mul_one]
exact lt_add_of_pos_right _ hε
theorem Seminorm.gaugeSeminorm_ball (p : Seminorm ℝ E) :
gaugeSeminorm (p.balanced_ball_zero 1) (p.convex_ball 0 1) (p.absorbent_ball_zero zero_lt_one) =
p :=
DFunLike.coe_injective p.gauge_ball
end AddCommGroup
section Seminormed
variable [SeminormedAddCommGroup E] [NormedSpace ℝ E] {s : Set E} {r : ℝ} {x : E}
open Metric
theorem gauge_unit_ball (x : E) : gauge (ball (0 : E) 1) x = ‖x‖ := by
rw [← ball_normSeminorm ℝ, Seminorm.gauge_ball, coe_normSeminorm]
theorem gauge_ball (hr : 0 ≤ r) (x : E) : gauge (ball (0 : E) r) x = ‖x‖ / r := by
rcases hr.eq_or_lt with rfl | hr
· simp
· rw [← smul_unitBall_of_pos hr, gauge_smul_left, Pi.smul_apply, gauge_unit_ball, smul_eq_mul,
abs_of_nonneg hr.le, div_eq_inv_mul]
simp_rw [mem_ball_zero_iff, norm_neg]
exact fun _ => id
@[simp]
theorem gauge_closure_zero : gauge (closure (0 : Set E)) = 0 := funext fun x ↦ by
simp only [← singleton_zero, gauge_def', mem_closure_zero_iff_norm, norm_smul, mul_eq_zero,
norm_eq_zero, inv_eq_zero]
rcases (norm_nonneg x).eq_or_gt with hx | hx
· convert csInf_Ioi (a := (0 : ℝ))
exact Set.ext fun r ↦ and_iff_left (.inr hx)
· convert Real.sInf_empty
exact eq_empty_of_forall_not_mem fun r ⟨hr₀, hr⟩ ↦ hx.ne' <| hr.resolve_left hr₀.out.ne'
@[simp]
theorem gauge_closedBall (hr : 0 ≤ r) (x : E) : gauge (closedBall (0 : E) r) x = ‖x‖ / r := by
rcases hr.eq_or_lt with rfl | hr'
· rw [div_zero, closedBall_zero', singleton_zero, gauge_closure_zero]; rfl
· apply le_antisymm
· rw [← gauge_ball hr]
exact gauge_mono (absorbent_ball_zero hr') ball_subset_closedBall x
· suffices ∀ᶠ R in 𝓝[>] r, ‖x‖ / R ≤ gauge (closedBall 0 r) x by
refine le_of_tendsto ?_ this
exact tendsto_const_nhds.div inf_le_left hr'.ne'
filter_upwards [self_mem_nhdsWithin] with R hR
rw [← gauge_ball (hr.trans hR.out.le)]
refine gauge_mono ?_ (closedBall_subset_ball hR) _
exact (absorbent_ball_zero hr').mono ball_subset_closedBall
theorem mul_gauge_le_norm (hs : Metric.ball (0 : E) r ⊆ s) : r * gauge s x ≤ ‖x‖ := by
obtain hr | hr := le_or_lt r 0
· exact (mul_nonpos_of_nonpos_of_nonneg hr <| gauge_nonneg _).trans (norm_nonneg _)
rw [mul_comm, ← le_div_iff₀ hr, ← gauge_ball hr.le]
exact gauge_mono (absorbent_ball_zero hr) hs x
theorem Convex.lipschitzWith_gauge {r : ℝ≥0} (hc : Convex ℝ s) (hr : 0 < r)
(hs : Metric.ball (0 : E) r ⊆ s) : LipschitzWith r⁻¹ (gauge s) :=
| have : Absorbent ℝ (Metric.ball (0 : E) r) := absorbent_ball_zero hr
LipschitzWith.of_le_add_mul _ fun x y =>
| Mathlib/Analysis/Convex/Gauge.lean | 572 | 573 |
/-
Copyright (c) 2019 Minchao Wu. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Minchao Wu, Mario Carneiro
-/
import Mathlib.Computability.Halting
/-!
# Strong reducibility and degrees.
This file defines the notions of computable many-one reduction and one-one
reduction between sets, and shows that the corresponding degrees form a
semilattice.
## Notations
This file uses the local notation `⊕'` for `Sum.elim` to denote the disjoint union of two degrees.
## References
* [Robert Soare, *Recursively enumerable sets and degrees*][soare1987]
## Tags
computability, reducibility, reduction
-/
universe u v w
open Function
/--
`p` is many-one reducible to `q` if there is a computable function translating questions about `p`
to questions about `q`.
-/
def ManyOneReducible {α β} [Primcodable α] [Primcodable β] (p : α → Prop) (q : β → Prop) :=
∃ f, Computable f ∧ ∀ a, p a ↔ q (f a)
@[inherit_doc ManyOneReducible]
infixl:1000 " ≤₀ " => ManyOneReducible
theorem ManyOneReducible.mk {α β} [Primcodable α] [Primcodable β] {f : α → β} (q : β → Prop)
(h : Computable f) : (fun a => q (f a)) ≤₀ q :=
⟨f, h, fun _ => Iff.rfl⟩
@[refl]
theorem manyOneReducible_refl {α} [Primcodable α] (p : α → Prop) : p ≤₀ p :=
⟨id, Computable.id, by simp⟩
@[trans]
theorem ManyOneReducible.trans {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} : p ≤₀ q → q ≤₀ r → p ≤₀ r
| ⟨f, c₁, h₁⟩, ⟨g, c₂, h₂⟩ =>
⟨g ∘ f, c₂.comp c₁,
fun a => ⟨fun h => by rw [comp_apply, ← h₂, ← h₁]; assumption, fun h => by rwa [h₁, h₂]⟩⟩
theorem reflexive_manyOneReducible {α} [Primcodable α] : Reflexive (@ManyOneReducible α α _ _) :=
manyOneReducible_refl
theorem transitive_manyOneReducible {α} [Primcodable α] : Transitive (@ManyOneReducible α α _ _) :=
fun _ _ _ => ManyOneReducible.trans
/--
`p` is one-one reducible to `q` if there is an injective computable function translating questions
about `p` to questions about `q`.
-/
def OneOneReducible {α β} [Primcodable α] [Primcodable β] (p : α → Prop) (q : β → Prop) :=
∃ f, Computable f ∧ Injective f ∧ ∀ a, p a ↔ q (f a)
@[inherit_doc OneOneReducible]
infixl:1000 " ≤₁ " => OneOneReducible
theorem OneOneReducible.mk {α β} [Primcodable α] [Primcodable β] {f : α → β} (q : β → Prop)
(h : Computable f) (i : Injective f) : (fun a => q (f a)) ≤₁ q :=
⟨f, h, i, fun _ => Iff.rfl⟩
@[refl]
theorem oneOneReducible_refl {α} [Primcodable α] (p : α → Prop) : p ≤₁ p :=
⟨id, Computable.id, injective_id, by simp⟩
@[trans]
theorem OneOneReducible.trans {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ] {p : α → Prop}
{q : β → Prop} {r : γ → Prop} : p ≤₁ q → q ≤₁ r → p ≤₁ r
| ⟨f, c₁, i₁, h₁⟩, ⟨g, c₂, i₂, h₂⟩ =>
⟨g ∘ f, c₂.comp c₁, i₂.comp i₁, fun a =>
⟨fun h => by rw [comp_apply, ← h₂, ← h₁]; assumption, fun h => by rwa [h₁, h₂]⟩⟩
theorem OneOneReducible.to_many_one {α β} [Primcodable α] [Primcodable β] {p : α → Prop}
{q : β → Prop} : p ≤₁ q → p ≤₀ q
| ⟨f, c, _, h⟩ => ⟨f, c, h⟩
theorem OneOneReducible.of_equiv {α β} [Primcodable α] [Primcodable β] {e : α ≃ β} (q : β → Prop)
(h : Computable e) : (q ∘ e) ≤₁ q :=
OneOneReducible.mk _ h e.injective
theorem OneOneReducible.of_equiv_symm {α β} [Primcodable α] [Primcodable β] {e : α ≃ β}
(q : β → Prop) (h : Computable e.symm) : q ≤₁ (q ∘ e) := by
convert OneOneReducible.of_equiv _ h; funext; simp
theorem reflexive_oneOneReducible {α} [Primcodable α] : Reflexive (@OneOneReducible α α _ _) :=
oneOneReducible_refl
theorem transitive_oneOneReducible {α} [Primcodable α] : Transitive (@OneOneReducible α α _ _) :=
fun _ _ _ => OneOneReducible.trans
namespace ComputablePred
variable {α : Type*} {β : Type*} [Primcodable α] [Primcodable β]
open Computable
theorem computable_of_manyOneReducible {p : α → Prop} {q : β → Prop} (h₁ : p ≤₀ q)
(h₂ : ComputablePred q) : ComputablePred p := by
rcases h₁ with ⟨f, c, hf⟩
rw [show p = fun a => q (f a) from Set.ext hf]
rcases computable_iff.1 h₂ with ⟨g, hg, rfl⟩
exact ⟨by infer_instance, by simpa using hg.comp c⟩
theorem computable_of_oneOneReducible {p : α → Prop} {q : β → Prop} (h : p ≤₁ q) :
ComputablePred q → ComputablePred p :=
computable_of_manyOneReducible h.to_many_one
end ComputablePred
/-- `p` and `q` are many-one equivalent if each one is many-one reducible to the other. -/
def ManyOneEquiv {α β} [Primcodable α] [Primcodable β] (p : α → Prop) (q : β → Prop) :=
p ≤₀ q ∧ q ≤₀ p
/-- `p` and `q` are one-one equivalent if each one is one-one reducible to the other. -/
def OneOneEquiv {α β} [Primcodable α] [Primcodable β] (p : α → Prop) (q : β → Prop) :=
p ≤₁ q ∧ q ≤₁ p
@[refl]
theorem manyOneEquiv_refl {α} [Primcodable α] (p : α → Prop) : ManyOneEquiv p p :=
⟨manyOneReducible_refl _, manyOneReducible_refl _⟩
@[symm]
theorem ManyOneEquiv.symm {α β} [Primcodable α] [Primcodable β] {p : α → Prop} {q : β → Prop} :
ManyOneEquiv p q → ManyOneEquiv q p :=
And.symm
@[trans]
theorem ManyOneEquiv.trans {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ] {p : α → Prop}
{q : β → Prop} {r : γ → Prop} : ManyOneEquiv p q → ManyOneEquiv q r → ManyOneEquiv p r
| ⟨pq, qp⟩, ⟨qr, rq⟩ => ⟨pq.trans qr, rq.trans qp⟩
theorem equivalence_of_manyOneEquiv {α} [Primcodable α] : Equivalence (@ManyOneEquiv α α _ _) :=
⟨manyOneEquiv_refl, fun {_ _} => ManyOneEquiv.symm, fun {_ _ _} => ManyOneEquiv.trans⟩
@[refl]
theorem oneOneEquiv_refl {α} [Primcodable α] (p : α → Prop) : OneOneEquiv p p :=
⟨oneOneReducible_refl _, oneOneReducible_refl _⟩
@[symm]
theorem OneOneEquiv.symm {α β} [Primcodable α] [Primcodable β] {p : α → Prop} {q : β → Prop} :
OneOneEquiv p q → OneOneEquiv q p :=
And.symm
@[trans]
theorem OneOneEquiv.trans {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ] {p : α → Prop}
{q : β → Prop} {r : γ → Prop} : OneOneEquiv p q → OneOneEquiv q r → OneOneEquiv p r
| ⟨pq, qp⟩, ⟨qr, rq⟩ => ⟨pq.trans qr, rq.trans qp⟩
theorem equivalence_of_oneOneEquiv {α} [Primcodable α] : Equivalence (@OneOneEquiv α α _ _) :=
⟨oneOneEquiv_refl, fun {_ _} => OneOneEquiv.symm, fun {_ _ _} => OneOneEquiv.trans⟩
theorem OneOneEquiv.to_many_one {α β} [Primcodable α] [Primcodable β] {p : α → Prop}
{q : β → Prop} : OneOneEquiv p q → ManyOneEquiv p q
| ⟨pq, qp⟩ => ⟨pq.to_many_one, qp.to_many_one⟩
/-- a computable bijection -/
nonrec def Equiv.Computable {α β} [Primcodable α] [Primcodable β] (e : α ≃ β) :=
Computable e ∧ Computable e.symm
theorem Equiv.Computable.symm {α β} [Primcodable α] [Primcodable β] {e : α ≃ β} :
e.Computable → e.symm.Computable :=
And.symm
theorem Equiv.Computable.trans {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ] {e₁ : α ≃ β}
{e₂ : β ≃ γ} : e₁.Computable → e₂.Computable → (e₁.trans e₂).Computable
| ⟨l₁, r₁⟩, ⟨l₂, r₂⟩ => ⟨l₂.comp l₁, r₁.comp r₂⟩
theorem Computable.eqv (α) [Denumerable α] : (Denumerable.eqv α).Computable :=
⟨Computable.encode, Computable.ofNat _⟩
theorem Computable.equiv₂ (α β) [Denumerable α] [Denumerable β] :
(Denumerable.equiv₂ α β).Computable :=
(Computable.eqv _).trans (Computable.eqv _).symm
theorem OneOneEquiv.of_equiv {α β} [Primcodable α] [Primcodable β] {e : α ≃ β} (h : e.Computable)
{p} : OneOneEquiv (p ∘ e) p :=
⟨OneOneReducible.of_equiv _ h.1, OneOneReducible.of_equiv_symm _ h.2⟩
theorem ManyOneEquiv.of_equiv {α β} [Primcodable α] [Primcodable β] {e : α ≃ β} (h : e.Computable)
{p} : ManyOneEquiv (p ∘ e) p :=
(OneOneEquiv.of_equiv h).to_many_one
theorem ManyOneEquiv.le_congr_left {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : ManyOneEquiv p q) : p ≤₀ r ↔ q ≤₀ r :=
⟨h.2.trans, h.1.trans⟩
theorem ManyOneEquiv.le_congr_right {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : ManyOneEquiv q r) : p ≤₀ q ↔ p ≤₀ r :=
⟨fun h' => h'.trans h.1, fun h' => h'.trans h.2⟩
theorem OneOneEquiv.le_congr_left {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : OneOneEquiv p q) : p ≤₁ r ↔ q ≤₁ r :=
⟨h.2.trans, h.1.trans⟩
theorem OneOneEquiv.le_congr_right {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : OneOneEquiv q r) : p ≤₁ q ↔ p ≤₁ r :=
⟨fun h' => h'.trans h.1, fun h' => h'.trans h.2⟩
theorem ManyOneEquiv.congr_left {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : ManyOneEquiv p q) :
ManyOneEquiv p r ↔ ManyOneEquiv q r :=
and_congr h.le_congr_left h.le_congr_right
theorem ManyOneEquiv.congr_right {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : ManyOneEquiv q r) :
ManyOneEquiv p q ↔ ManyOneEquiv p r :=
and_congr h.le_congr_right h.le_congr_left
theorem OneOneEquiv.congr_left {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : OneOneEquiv p q) :
OneOneEquiv p r ↔ OneOneEquiv q r :=
and_congr h.le_congr_left h.le_congr_right
theorem OneOneEquiv.congr_right {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} (h : OneOneEquiv q r) :
OneOneEquiv p q ↔ OneOneEquiv p r :=
and_congr h.le_congr_right h.le_congr_left
@[simp]
theorem ULower.down_computable {α} [Primcodable α] : (ULower.equiv α).Computable :=
⟨Primrec.ulower_down.to_comp, Primrec.ulower_up.to_comp⟩
theorem manyOneEquiv_up {α} [Primcodable α] {p : α → Prop} : ManyOneEquiv (p ∘ ULower.up) p :=
ManyOneEquiv.of_equiv ULower.down_computable.symm
local infixl:1001 " ⊕' " => Sum.elim
open Nat.Primrec
theorem OneOneReducible.disjoin_left {α β} [Primcodable α] [Primcodable β] {p : α → Prop}
{q : β → Prop} : p ≤₁ p ⊕' q :=
⟨Sum.inl, Computable.sumInl, fun _ _ => Sum.inl.inj_iff.1, fun _ => Iff.rfl⟩
theorem OneOneReducible.disjoin_right {α β} [Primcodable α] [Primcodable β] {p : α → Prop}
{q : β → Prop} : q ≤₁ p ⊕' q :=
⟨Sum.inr, Computable.sumInr, fun _ _ => Sum.inr.inj_iff.1, fun _ => Iff.rfl⟩
theorem disjoin_manyOneReducible {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ]
{p : α → Prop} {q : β → Prop} {r : γ → Prop} : p ≤₀ r → q ≤₀ r → (p ⊕' q) ≤₀ r
| ⟨f, c₁, h₁⟩, ⟨g, c₂, h₂⟩ =>
⟨Sum.elim f g,
Computable.id.sumCasesOn (c₁.comp Computable.snd).to₂ (c₂.comp Computable.snd).to₂,
fun x => by cases x <;> [apply h₁; apply h₂]⟩
theorem disjoin_le {α β γ} [Primcodable α] [Primcodable β] [Primcodable γ] {p : α → Prop}
{q : β → Prop} {r : γ → Prop} : (p ⊕' q) ≤₀ r ↔ p ≤₀ r ∧ q ≤₀ r :=
⟨fun h =>
⟨OneOneReducible.disjoin_left.to_many_one.trans h,
OneOneReducible.disjoin_right.to_many_one.trans h⟩,
fun ⟨h₁, h₂⟩ => disjoin_manyOneReducible h₁ h₂⟩
variable {α : Type u} [Primcodable α] [Inhabited α] {β : Type v} [Primcodable β] [Inhabited β]
/-- Computable and injective mapping of predicates to sets of natural numbers.
-/
def toNat (p : Set α) : Set ℕ :=
{ n | p ((Encodable.decode (α := α) n).getD default) }
@[simp]
theorem toNat_manyOneReducible {p : Set α} : toNat p ≤₀ p :=
⟨fun n => (Encodable.decode (α := α) n).getD default,
Computable.option_getD Computable.decode (Computable.const _), fun _ => Iff.rfl⟩
@[simp]
theorem manyOneReducible_toNat {p : Set α} : p ≤₀ toNat p :=
⟨Encodable.encode, Computable.encode, by simp [toNat, setOf]⟩
@[simp]
theorem manyOneReducible_toNat_toNat {p : Set α} {q : Set β} : toNat p ≤₀ toNat q ↔ p ≤₀ q :=
⟨fun h => manyOneReducible_toNat.trans (h.trans toNat_manyOneReducible), fun h =>
toNat_manyOneReducible.trans (h.trans manyOneReducible_toNat)⟩
@[simp]
theorem toNat_manyOneEquiv {p : Set α} : ManyOneEquiv (toNat p) p := by simp [ManyOneEquiv]
@[simp]
theorem manyOneEquiv_toNat (p : Set α) (q : Set β) :
ManyOneEquiv (toNat p) (toNat q) ↔ ManyOneEquiv p q := by simp [ManyOneEquiv]
/-- A many-one degree is an equivalence class of sets up to many-one equivalence. -/
def ManyOneDegree : Type :=
Quotient (⟨ManyOneEquiv, equivalence_of_manyOneEquiv⟩ : Setoid (Set ℕ))
namespace ManyOneDegree
/-- The many-one degree of a set on a primcodable type. -/
def of (p : α → Prop) : ManyOneDegree :=
Quotient.mk'' (toNat p)
@[elab_as_elim]
protected theorem ind_on {C : ManyOneDegree → Prop} (d : ManyOneDegree)
(h : ∀ p : Set ℕ, C (of p)) : C d :=
Quotient.inductionOn' d h
/-- Lifts a function on sets of natural numbers to many-one degrees. -/
protected abbrev liftOn {φ} (d : ManyOneDegree) (f : Set ℕ → φ)
(h : ∀ p q, ManyOneEquiv p q → f p = f q) : φ :=
Quotient.liftOn' d f h
@[simp]
protected theorem liftOn_eq {φ} (p : Set ℕ) (f : Set ℕ → φ)
(h : ∀ p q, ManyOneEquiv p q → f p = f q) : (of p).liftOn f h = f p :=
rfl
/-- Lifts a binary function on sets of natural numbers to many-one degrees. -/
@[reducible, simp]
protected def liftOn₂ {φ} (d₁ d₂ : ManyOneDegree) (f : Set ℕ → Set ℕ → φ)
(h : ∀ p₁ p₂ q₁ q₂, ManyOneEquiv p₁ p₂ → ManyOneEquiv q₁ q₂ → f p₁ q₁ = f p₂ q₂) : φ :=
d₁.liftOn (fun p => d₂.liftOn (f p) fun _ _ hq => h _ _ _ _ (by rfl) hq)
(by
intro p₁ p₂ hp
induction d₂ using ManyOneDegree.ind_on
apply h
· assumption
· rfl)
@[simp]
protected theorem liftOn₂_eq {φ} (p q : Set ℕ) (f : Set ℕ → Set ℕ → φ)
(h : ∀ p₁ p₂ q₁ q₂, ManyOneEquiv p₁ p₂ → ManyOneEquiv q₁ q₂ → f p₁ q₁ = f p₂ q₂) :
(of p).liftOn₂ (of q) f h = f p q :=
rfl
@[simp]
theorem of_eq_of {p : α → Prop} {q : β → Prop} : of p = of q ↔ ManyOneEquiv p q := by
rw [of, of, Quotient.eq'']
simp
instance instInhabited : Inhabited ManyOneDegree :=
⟨of (∅ : Set ℕ)⟩
/-- For many-one degrees `d₁` and `d₂`, `d₁ ≤ d₂` if the sets in `d₁` are many-one reducible to the
sets in `d₂`.
-/
instance instLE : LE ManyOneDegree :=
⟨fun d₁ d₂ =>
ManyOneDegree.liftOn₂ d₁ d₂ (· ≤₀ ·) fun _p₁ _p₂ _q₁ _q₂ hp hq =>
propext (hp.le_congr_left.trans hq.le_congr_right)⟩
@[simp]
theorem of_le_of {p : α → Prop} {q : β → Prop} : of p ≤ of q ↔ p ≤₀ q :=
manyOneReducible_toNat_toNat
private theorem le_refl (d : ManyOneDegree) : d ≤ d := by
induction d using ManyOneDegree.ind_on; simp; rfl
private theorem le_antisymm {d₁ d₂ : ManyOneDegree} : d₁ ≤ d₂ → d₂ ≤ d₁ → d₁ = d₂ := by
induction d₁ using ManyOneDegree.ind_on
induction d₂ using ManyOneDegree.ind_on
intro hp hq
simp_all only [ManyOneEquiv, of_le_of, of_eq_of, true_and]
private theorem le_trans {d₁ d₂ d₃ : ManyOneDegree} : d₁ ≤ d₂ → d₂ ≤ d₃ → d₁ ≤ d₃ := by
induction d₁ using ManyOneDegree.ind_on
induction d₂ using ManyOneDegree.ind_on
induction d₃ using ManyOneDegree.ind_on
apply ManyOneReducible.trans
instance instPartialOrder : PartialOrder ManyOneDegree where
le := (· ≤ ·)
le_refl := le_refl
le_trans _ _ _ := le_trans
le_antisymm _ _ := le_antisymm
/-- The join of two degrees, induced by the disjoint union of two underlying sets. -/
instance instAdd : Add ManyOneDegree :=
⟨fun d₁ d₂ =>
d₁.liftOn₂ d₂ (fun a b => of (a ⊕' b))
(by
rintro a b c d ⟨hl₁, hr₁⟩ ⟨hl₂, hr₂⟩
rw [of_eq_of]
exact
⟨disjoin_manyOneReducible (hl₁.trans OneOneReducible.disjoin_left.to_many_one)
(hl₂.trans OneOneReducible.disjoin_right.to_many_one),
disjoin_manyOneReducible (hr₁.trans OneOneReducible.disjoin_left.to_many_one)
(hr₂.trans OneOneReducible.disjoin_right.to_many_one)⟩)⟩
@[simp]
theorem add_of (p : Set α) (q : Set β) : of (p ⊕' q) = of p + of q :=
of_eq_of.mpr
⟨disjoin_manyOneReducible
(manyOneReducible_toNat.trans OneOneReducible.disjoin_left.to_many_one)
(manyOneReducible_toNat.trans OneOneReducible.disjoin_right.to_many_one),
disjoin_manyOneReducible
(toNat_manyOneReducible.trans OneOneReducible.disjoin_left.to_many_one)
(toNat_manyOneReducible.trans OneOneReducible.disjoin_right.to_many_one)⟩
@[simp]
protected theorem add_le {d₁ d₂ d₃ : ManyOneDegree} : d₁ + d₂ ≤ d₃ ↔ d₁ ≤ d₃ ∧ d₂ ≤ d₃ := by
induction d₁ using ManyOneDegree.ind_on
induction d₂ using ManyOneDegree.ind_on
induction d₃ using ManyOneDegree.ind_on
simpa only [← add_of, of_le_of] using disjoin_le
@[simp]
protected theorem le_add_left (d₁ d₂ : ManyOneDegree) : d₁ ≤ d₁ + d₂ :=
(ManyOneDegree.add_le.1 (le_refl _)).1
@[simp]
protected theorem le_add_right (d₁ d₂ : ManyOneDegree) : d₂ ≤ d₁ + d₂ :=
(ManyOneDegree.add_le.1 (le_refl _)).2
instance instSemilatticeSup : SemilatticeSup ManyOneDegree :=
{ ManyOneDegree.instPartialOrder with
sup := (· + ·)
le_sup_left := ManyOneDegree.le_add_left
le_sup_right := ManyOneDegree.le_add_right
sup_le := fun _ _ _ h₁ h₂ => ManyOneDegree.add_le.2 ⟨h₁, h₂⟩ }
end ManyOneDegree
| Mathlib/Computability/Reduce.lean | 443 | 447 | |
/-
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.Order.Interval.Set.IsoIoo
import Mathlib.Topology.ContinuousMap.Bounded.Normed
import Mathlib.Topology.UrysohnsBounded
/-!
# Tietze extension theorem
In this file we prove a few version of the Tietze extension theorem. The theorem says that a
continuous function `s → ℝ` defined on a closed set in a normal topological space `Y` can be
extended to a continuous function on the whole space. Moreover, if all values of the original
function belong to some (finite or infinite, open or closed) interval, then the extension can be
chosen so that it takes values in the same interval. In particular, if the original function is a
bounded function, then there exists a bounded extension of the same norm.
The proof mostly follows <https://ncatlab.org/nlab/show/Tietze+extension+theorem>. We patch a small
gap in the proof for unbounded functions, see
`exists_extension_forall_exists_le_ge_of_isClosedEmbedding`.
In addition we provide a class `TietzeExtension` encoding the idea that a topological space
satisfies the Tietze extension theorem. This allows us to get a version of the Tietze extension
theorem that simultaneously applies to `ℝ`, `ℝ × ℝ`, `ℂ`, `ι → ℝ`, `ℝ≥0` et cetera. At some point
in the future, it may be desirable to provide instead a more general approach via
*absolute retracts*, but the current implementation covers the most common use cases easily.
## Implementation notes
We first prove the theorems for a closed embedding `e : X → Y` of a topological space into a normal
topological space, then specialize them to the case `X = s : Set Y`, `e = (↑)`.
## Tags
Tietze extension theorem, Urysohn's lemma, normal topological space
-/
open Topology
/-! ### The `TietzeExtension` class -/
section TietzeExtensionClass
universe u u₁ u₂ v w
-- TODO: define *absolute retracts* and then prove they satisfy Tietze extension.
-- Then make instances of that instead and remove this class.
/-- A class encoding the concept that a space satisfies the Tietze extension property. -/
class TietzeExtension (Y : Type v) [TopologicalSpace Y] : Prop where
exists_restrict_eq' {X : Type u} [TopologicalSpace X] [NormalSpace X] (s : Set X)
(hs : IsClosed s) (f : C(s, Y)) : ∃ (g : C(X, Y)), g.restrict s = f
variable {X₁ : Type u₁} [TopologicalSpace X₁]
variable {X : Type u} [TopologicalSpace X] [NormalSpace X] {s : Set X}
variable {e : X₁ → X}
variable {Y : Type v} [TopologicalSpace Y] [TietzeExtension.{u, v} Y]
/-- **Tietze extension theorem** for `TietzeExtension` spaces, a version for a closed set. Let
`s` be a closed set in a normal topological space `X`. Let `f` be a continuous function
on `s` with values in a `TietzeExtension` space `Y`. Then there exists a continuous function
`g : C(X, Y)` such that `g.restrict s = f`. -/
theorem ContinuousMap.exists_restrict_eq (hs : IsClosed s) (f : C(s, Y)) :
∃ (g : C(X, Y)), g.restrict s = f :=
TietzeExtension.exists_restrict_eq' s hs f
/-- **Tietze extension theorem** for `TietzeExtension` spaces. Let `e` be a closed embedding of a
nonempty topological space `X₁` into a normal topological space `X`. Let `f` be a continuous
function on `X₁` with values in a `TietzeExtension` space `Y`. Then there exists a
continuous function `g : C(X, Y)` such that `g ∘ e = f`. -/
theorem ContinuousMap.exists_extension (he : IsClosedEmbedding e) (f : C(X₁, Y)) :
∃ (g : C(X, Y)), g.comp ⟨e, he.continuous⟩ = f := by
let e' : X₁ ≃ₜ Set.range e := he.isEmbedding.toHomeomorph
obtain ⟨g, hg⟩ := (f.comp e'.symm).exists_restrict_eq he.isClosed_range
exact ⟨g, by ext x; simpa using congr($(hg) ⟨e' x, x, rfl⟩)⟩
/-- **Tietze extension theorem** for `TietzeExtension` spaces. Let `e` be a closed embedding of a
nonempty topological space `X₁` into a normal topological space `X`. Let `f` be a continuous
function on `X₁` with values in a `TietzeExtension` space `Y`. Then there exists a
continuous function `g : C(X, Y)` such that `g ∘ e = f`.
This version is provided for convenience and backwards compatibility. Here the composition is
phrased in terms of bare functions. -/
theorem ContinuousMap.exists_extension' (he : IsClosedEmbedding e) (f : C(X₁, Y)) :
∃ (g : C(X, Y)), g ∘ e = f :=
f.exists_extension he |>.imp fun g hg ↦ by ext x; congrm($(hg) x)
/-- This theorem is not intended to be used directly because it is rare for a set alone to
satisfy `[TietzeExtension t]`. For example, `Metric.ball` in `ℝ` only satisfies it when
the radius is strictly positive, so finding this as an instance will fail.
Instead, it is intended to be used as a constructor for theorems about sets which *do* satisfy
`[TietzeExtension t]` under some hypotheses. -/
theorem ContinuousMap.exists_forall_mem_restrict_eq (hs : IsClosed s)
{Y : Type v} [TopologicalSpace Y] (f : C(s, Y))
{t : Set Y} (hf : ∀ x, f x ∈ t) [ht : TietzeExtension.{u, v} t] :
∃ (g : C(X, Y)), (∀ x, g x ∈ t) ∧ g.restrict s = f := by
obtain ⟨g, hg⟩ := mk _ (map_continuous f |>.codRestrict hf) |>.exists_restrict_eq hs
exact ⟨comp ⟨Subtype.val, by continuity⟩ g, by simp, by ext x; congrm(($(hg) x : Y))⟩
/-- This theorem is not intended to be used directly because it is rare for a set alone to
satisfy `[TietzeExtension t]`. For example, `Metric.ball` in `ℝ` only satisfies it when
the radius is strictly positive, so finding this as an instance will fail.
Instead, it is intended to be used as a constructor for theorems about sets which *do* satisfy
`[TietzeExtension t]` under some hypotheses. -/
theorem ContinuousMap.exists_extension_forall_mem (he : IsClosedEmbedding e)
{Y : Type v} [TopologicalSpace Y] (f : C(X₁, Y))
{t : Set Y} (hf : ∀ x, f x ∈ t) [ht : TietzeExtension.{u, v} t] :
∃ (g : C(X, Y)), (∀ x, g x ∈ t) ∧ g.comp ⟨e, he.continuous⟩ = f := by
obtain ⟨g, hg⟩ := mk _ (map_continuous f |>.codRestrict hf) |>.exists_extension he
exact ⟨comp ⟨Subtype.val, by continuity⟩ g, by simp, by ext x; congrm(($(hg) x : Y))⟩
instance Pi.instTietzeExtension {ι : Type*} {Y : ι → Type v} [∀ i, TopologicalSpace (Y i)]
[∀ i, TietzeExtension.{u} (Y i)] : TietzeExtension.{u} (∀ i, Y i) where
exists_restrict_eq' s hs f := by
obtain ⟨g', hg'⟩ := Classical.skolem.mp <| fun i ↦
ContinuousMap.exists_restrict_eq hs (ContinuousMap.piEquiv _ _ |>.symm f i)
exact ⟨ContinuousMap.piEquiv _ _ g', by ext x i; congrm($(hg' i) x)⟩
instance Prod.instTietzeExtension {Y : Type v} {Z : Type w} [TopologicalSpace Y]
[TietzeExtension.{u, v} Y] [TopologicalSpace Z] [TietzeExtension.{u, w} Z] :
TietzeExtension.{u, max w v} (Y × Z) where
exists_restrict_eq' s hs f := by
obtain ⟨g₁, hg₁⟩ := (ContinuousMap.fst.comp f).exists_restrict_eq hs
obtain ⟨g₂, hg₂⟩ := (ContinuousMap.snd.comp f).exists_restrict_eq hs
exact ⟨g₁.prodMk g₂, by ext1 x; congrm(($(hg₁) x), $(hg₂) x)⟩
instance Unique.instTietzeExtension {Y : Type v} [TopologicalSpace Y]
[Nonempty Y] [Subsingleton Y] : TietzeExtension.{u, v} Y where
exists_restrict_eq' _ _ f := ‹Nonempty Y›.elim fun y ↦ ⟨.const _ y, by ext; subsingleton⟩
/-- Any retract of a `TietzeExtension` space is one itself. -/
theorem TietzeExtension.of_retract {Y : Type v} {Z : Type w} [TopologicalSpace Y]
[TopologicalSpace Z] [TietzeExtension.{u, w} Z] (ι : C(Y, Z)) (r : C(Z, Y))
(h : r.comp ι = .id Y) : TietzeExtension.{u, v} Y where
exists_restrict_eq' s hs f := by
obtain ⟨g, hg⟩ := (ι.comp f).exists_restrict_eq hs
use r.comp g
ext1 x
have := congr(r.comp $(hg))
rw [← r.comp_assoc ι, h, f.id_comp] at this
congrm($this x)
/-- Any homeomorphism from a `TietzeExtension` space is one itself. -/
theorem TietzeExtension.of_homeo {Y : Type v} {Z : Type w} [TopologicalSpace Y]
[TopologicalSpace Z] [TietzeExtension.{u, w} Z] (e : Y ≃ₜ Z) :
TietzeExtension.{u, v} Y :=
.of_retract (e : C(Y, Z)) (e.symm : C(Z, Y)) <| by simp
end TietzeExtensionClass
/-! The Tietze extension theorem for `ℝ`. -/
variable {X Y : Type*} [TopologicalSpace X] [TopologicalSpace Y] [NormalSpace Y]
open Metric Set Filter
open BoundedContinuousFunction Topology
noncomputable section
namespace BoundedContinuousFunction
/-- One step in the proof of the Tietze extension theorem. If `e : C(X, Y)` is a closed embedding
of a topological space into a normal topological space and `f : X →ᵇ ℝ` is a bounded continuous
function, then there exists a bounded continuous function `g : Y →ᵇ ℝ` of the norm `‖g‖ ≤ ‖f‖ / 3`
such that the distance between `g ∘ e` and `f` is at most `(2 / 3) * ‖f‖`. -/
theorem tietze_extension_step (f : X →ᵇ ℝ) (e : C(X, Y)) (he : IsClosedEmbedding e) :
∃ g : Y →ᵇ ℝ, ‖g‖ ≤ ‖f‖ / 3 ∧ dist (g.compContinuous e) f ≤ 2 / 3 * ‖f‖ := by
have h3 : (0 : ℝ) < 3 := by norm_num1
have h23 : 0 < (2 / 3 : ℝ) := by norm_num1
-- In the trivial case `f = 0`, we take `g = 0`
rcases eq_or_ne f 0 with (rfl | hf)
· use 0
simp
replace hf : 0 < ‖f‖ := norm_pos_iff.2 hf
/- Otherwise, the closed sets `e '' (f ⁻¹' (Iic (-‖f‖ / 3)))` and `e '' (f ⁻¹' (Ici (‖f‖ / 3)))`
are disjoint, hence by Urysohn's lemma there exists a function `g` that is equal to `-‖f‖ / 3`
on the former set and is equal to `‖f‖ / 3` on the latter set. This function `g` satisfies the
assertions of the lemma. -/
have hf3 : -‖f‖ / 3 < ‖f‖ / 3 := (div_lt_div_iff_of_pos_right h3).2 (Left.neg_lt_self hf)
have hc₁ : IsClosed (e '' (f ⁻¹' Iic (-‖f‖ / 3))) :=
he.isClosedMap _ (isClosed_Iic.preimage f.continuous)
have hc₂ : IsClosed (e '' (f ⁻¹' Ici (‖f‖ / 3))) :=
he.isClosedMap _ (isClosed_Ici.preimage f.continuous)
have hd : Disjoint (e '' (f ⁻¹' Iic (-‖f‖ / 3))) (e '' (f ⁻¹' Ici (‖f‖ / 3))) := by
refine disjoint_image_of_injective he.injective (Disjoint.preimage _ ?_)
rwa [Iic_disjoint_Ici, not_le]
rcases exists_bounded_mem_Icc_of_closed_of_le hc₁ hc₂ hd hf3.le with ⟨g, hg₁, hg₂, hgf⟩
refine ⟨g, ?_, ?_⟩
· refine (norm_le <| div_nonneg hf.le h3.le).mpr fun y => ?_
simpa [abs_le, neg_div] using hgf y
· refine (dist_le <| mul_nonneg h23.le hf.le).mpr fun x => ?_
have hfx : -‖f‖ ≤ f x ∧ f x ≤ ‖f‖ := by
simpa only [Real.norm_eq_abs, abs_le] using f.norm_coe_le_norm x
rcases le_total (f x) (-‖f‖ / 3) with hle₁ | hle₁
· calc
|g (e x) - f x| = -‖f‖ / 3 - f x := by
rw [hg₁ (mem_image_of_mem _ hle₁), Function.const_apply,
abs_of_nonneg (sub_nonneg.2 hle₁)]
_ ≤ 2 / 3 * ‖f‖ := by linarith
· rcases le_total (f x) (‖f‖ / 3) with hle₂ | hle₂
· simp only [neg_div] at *
calc
dist (g (e x)) (f x) ≤ |g (e x)| + |f x| := dist_le_norm_add_norm _ _
_ ≤ ‖f‖ / 3 + ‖f‖ / 3 := (add_le_add (abs_le.2 <| hgf _) (abs_le.2 ⟨hle₁, hle₂⟩))
_ = 2 / 3 * ‖f‖ := by linarith
· calc
|g (e x) - f x| = f x - ‖f‖ / 3 := by
rw [hg₂ (mem_image_of_mem _ hle₂), abs_sub_comm, Function.const_apply,
abs_of_nonneg (sub_nonneg.2 hle₂)]
_ ≤ 2 / 3 * ‖f‖ := by linarith
/-- **Tietze extension theorem** for real-valued bounded continuous maps, a version with a closed
embedding and bundled composition. If `e : C(X, Y)` is a closed embedding of a topological space
into a normal topological space and `f : X →ᵇ ℝ` is a bounded continuous function, then there exists
a bounded continuous function `g : Y →ᵇ ℝ` of the same norm such that `g ∘ e = f`. -/
theorem exists_extension_norm_eq_of_isClosedEmbedding' (f : X →ᵇ ℝ) (e : C(X, Y))
(he : IsClosedEmbedding e) : ∃ g : Y →ᵇ ℝ, ‖g‖ = ‖f‖ ∧ g.compContinuous e = f := by
/- For the proof, we iterate `tietze_extension_step`. Each time we apply it to the difference
between the previous approximation and `f`. -/
choose F hF_norm hF_dist using fun f : X →ᵇ ℝ => tietze_extension_step f e he
set g : ℕ → Y →ᵇ ℝ := fun n => (fun g => g + F (f - g.compContinuous e))^[n] 0
have g0 : g 0 = 0 := rfl
have g_succ : ∀ n, g (n + 1) = g n + F (f - (g n).compContinuous e) := fun n =>
Function.iterate_succ_apply' _ _ _
have hgf : ∀ n, dist ((g n).compContinuous e) f ≤ (2 / 3) ^ n * ‖f‖ := by
intro n
induction n with
| zero => simp [g0]
| succ n ihn =>
rw [g_succ n, add_compContinuous, ← dist_sub_right, add_sub_cancel_left, pow_succ', mul_assoc]
refine (hF_dist _).trans (mul_le_mul_of_nonneg_left ?_ (by norm_num1))
rwa [← dist_eq_norm']
have hg_dist : ∀ n, dist (g n) (g (n + 1)) ≤ 1 / 3 * ‖f‖ * (2 / 3) ^ n := by
intro n
calc
dist (g n) (g (n + 1)) = ‖F (f - (g n).compContinuous e)‖ := by
rw [g_succ, dist_eq_norm', add_sub_cancel_left]
_ ≤ ‖f - (g n).compContinuous e‖ / 3 := hF_norm _
_ = 1 / 3 * dist ((g n).compContinuous e) f := by rw [dist_eq_norm', one_div, div_eq_inv_mul]
_ ≤ 1 / 3 * ((2 / 3) ^ n * ‖f‖) := mul_le_mul_of_nonneg_left (hgf n) (by norm_num1)
_ = 1 / 3 * ‖f‖ * (2 / 3) ^ n := by ac_rfl
have hg_cau : CauchySeq g := cauchySeq_of_le_geometric _ _ (by norm_num1) hg_dist
have :
Tendsto (fun n => (g n).compContinuous e) atTop
(𝓝 <| (limUnder atTop g).compContinuous e) :=
((continuous_compContinuous e).tendsto _).comp hg_cau.tendsto_limUnder
have hge : (limUnder atTop g).compContinuous e = f := by
refine tendsto_nhds_unique this (tendsto_iff_dist_tendsto_zero.2 ?_)
refine squeeze_zero (fun _ => dist_nonneg) hgf ?_
rw [← zero_mul ‖f‖]
refine (tendsto_pow_atTop_nhds_zero_of_lt_one ?_ ?_).mul tendsto_const_nhds <;> norm_num1
refine ⟨limUnder atTop g, le_antisymm ?_ ?_, hge⟩
· rw [← dist_zero_left, ← g0]
refine
(dist_le_of_le_geometric_of_tendsto₀ _ _ (by norm_num1)
hg_dist hg_cau.tendsto_limUnder).trans_eq ?_
field_simp [show (3 - 2 : ℝ) = 1 by norm_num1]
· rw [← hge]
exact norm_compContinuous_le _ _
/-- **Tietze extension theorem** for real-valued bounded continuous maps, a version with a closed
embedding and unbundled composition. If `e : C(X, Y)` is a closed embedding of a topological space
into a normal topological space and `f : X →ᵇ ℝ` is a bounded continuous function, then there exists
a bounded continuous function `g : Y →ᵇ ℝ` of the same norm such that `g ∘ e = f`. -/
| theorem exists_extension_norm_eq_of_isClosedEmbedding (f : X →ᵇ ℝ) {e : X → Y}
(he : IsClosedEmbedding e) : ∃ g : Y →ᵇ ℝ, ‖g‖ = ‖f‖ ∧ g ∘ e = f := by
rcases exists_extension_norm_eq_of_isClosedEmbedding' f ⟨e, he.continuous⟩ he with ⟨g, hg, rfl⟩
exact ⟨g, hg, rfl⟩
| Mathlib/Topology/TietzeExtension.lean | 269 | 272 |
/-
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.Geometry.Manifold.Algebra.Structures
import Mathlib.Geometry.Manifold.BumpFunction
import Mathlib.Topology.MetricSpace.PartitionOfUnity
import Mathlib.Topology.ShrinkingLemma
/-!
# Smooth partition of unity
In this file we define two structures, `SmoothBumpCovering` and `SmoothPartitionOfUnity`. Both
structures describe coverings of a set by a locally finite family of supports of smooth functions
with some additional properties. The former structure is mostly useful as an intermediate step in
the construction of a smooth partition of unity but some proofs that traditionally deal with a
partition of unity can use a `SmoothBumpCovering` as well.
Given a real manifold `M` and its subset `s`, a `SmoothBumpCovering ι I M s` is a collection of
`SmoothBumpFunction`s `f i` indexed by `i : ι` such that
* the center of each `f i` belongs to `s`;
* the family of sets `support (f i)` is locally finite;
* for each `x ∈ s`, there exists `i : ι` such that `f i =ᶠ[𝓝 x] 1`.
In the same settings, a `SmoothPartitionOfUnity ι I M s` is a collection of smooth nonnegative
functions `f i : C^∞⟮I, M; 𝓘(ℝ), ℝ⟯`, `i : ι`, such that
* the family of sets `support (f i)` is locally finite;
* for each `x ∈ s`, the sum `∑ᶠ i, f i x` equals one;
* for each `x`, the sum `∑ᶠ i, f i x` is less than or equal to one.
We say that `f : SmoothBumpCovering ι I M s` is *subordinate* to a map `U : M → Set M` if for each
index `i`, we have `tsupport (f i) ⊆ U (f i).c`. This notion is a bit more general than
being subordinate to an open covering of `M`, because we make no assumption about the way `U x`
depends on `x`.
We prove that on a smooth finitely dimensional real manifold with `σ`-compact Hausdorff topology,
for any `U : M → Set M` such that `∀ x ∈ s, U x ∈ 𝓝 x` there exists a `SmoothBumpCovering ι I M s`
subordinate to `U`. Then we use this fact to prove a similar statement about smooth partitions of
unity, see `SmoothPartitionOfUnity.exists_isSubordinate`.
Finally, we use existence of a partition of unity to prove lemma
`exists_smooth_forall_mem_convex_of_local` that allows us to construct a globally defined smooth
function from local functions.
## TODO
* Build a framework for to transfer local definitions to global using partition of unity and use it
to define, e.g., the integral of a differential form over a manifold. Lemma
`exists_smooth_forall_mem_convex_of_local` is a first step in this direction.
## Tags
smooth bump function, partition of unity
-/
universe uι uE uH uM uF
open Function Filter Module Set
open scoped Topology Manifold ContDiff
noncomputable section
variable {ι : Type uι} {E : Type uE} [NormedAddCommGroup E] [NormedSpace ℝ E]
{F : Type uF} [NormedAddCommGroup F] [NormedSpace ℝ F] {H : Type uH}
[TopologicalSpace H] (I : ModelWithCorners ℝ E H) {M : Type uM} [TopologicalSpace M]
[ChartedSpace H M]
/-!
### Covering by supports of smooth bump functions
In this section we define `SmoothBumpCovering ι I M s` to be a collection of
`SmoothBumpFunction`s such that their supports is a locally finite family of sets and for each
`x ∈ s` some function `f i` from the collection is equal to `1` in a neighborhood of `x`. A covering
of this type is useful to construct a smooth partition of unity and can be used instead of a
partition of unity in some proofs.
We prove that on a smooth finite dimensional real manifold with `σ`-compact Hausdorff topology, for
any `U : M → Set M` such that `∀ x ∈ s, U x ∈ 𝓝 x` there exists a `SmoothBumpCovering ι I M s`
subordinate to `U`. -/
variable (ι M)
/-- We say that a collection of `SmoothBumpFunction`s is a `SmoothBumpCovering` of a set `s` if
* `(f i).c ∈ s` for all `i`;
* the family `fun i ↦ support (f i)` is locally finite;
* for each point `x ∈ s` there exists `i` such that `f i =ᶠ[𝓝 x] 1`;
in other words, `x` belongs to the interior of `{y | f i y = 1}`;
If `M` is a finite dimensional real manifold which is a `σ`-compact Hausdorff topological space,
then for every covering `U : M → Set M`, `∀ x, U x ∈ 𝓝 x`, there exists a `SmoothBumpCovering`
subordinate to `U`, see `SmoothBumpCovering.exists_isSubordinate`.
This covering can be used, e.g., to construct a partition of unity and to prove the weak
Whitney embedding theorem. -/
structure SmoothBumpCovering [FiniteDimensional ℝ E] (s : Set M := univ) where
/-- The center point of each bump in the smooth covering. -/
c : ι → M
/-- A smooth bump function around `c i`. -/
toFun : ∀ i, SmoothBumpFunction I (c i)
/-- All the bump functions in the covering are centered at points in `s`. -/
c_mem' : ∀ i, c i ∈ s
/-- Around each point, there are only finitely many nonzero bump functions in the family. -/
locallyFinite' : LocallyFinite fun i => support (toFun i)
/-- Around each point in `s`, one of the bump functions is equal to `1`. -/
eventuallyEq_one' : ∀ x ∈ s, ∃ i, toFun i =ᶠ[𝓝 x] 1
/-- We say that a collection of functions form a smooth partition of unity on a set `s` if
* all functions are infinitely smooth and nonnegative;
* the family `fun i ↦ support (f i)` is locally finite;
* for all `x ∈ s` the sum `∑ᶠ i, f i x` equals one;
* for all `x`, the sum `∑ᶠ i, f i x` is less than or equal to one. -/
structure SmoothPartitionOfUnity (s : Set M := univ) where
/-- The family of functions forming the partition of unity. -/
toFun : ι → C^∞⟮I, M; 𝓘(ℝ), ℝ⟯
/-- Around each point, there are only finitely many nonzero functions in the family. -/
locallyFinite' : LocallyFinite fun i => support (toFun i)
/-- All the functions in the partition of unity are nonnegative. -/
nonneg' : ∀ i x, 0 ≤ toFun i x
/-- The functions in the partition of unity add up to `1` at any point of `s`. -/
sum_eq_one' : ∀ x ∈ s, ∑ᶠ i, toFun i x = 1
/-- The functions in the partition of unity add up to at most `1` everywhere. -/
sum_le_one' : ∀ x, ∑ᶠ i, toFun i x ≤ 1
variable {ι I M}
namespace SmoothPartitionOfUnity
variable {s : Set M} (f : SmoothPartitionOfUnity ι I M s) {n : ℕ∞}
instance {s : Set M} : FunLike (SmoothPartitionOfUnity ι I M s) ι C^∞⟮I, M; 𝓘(ℝ), ℝ⟯ where
coe := toFun
coe_injective' f g h := by cases f; cases g; congr
protected theorem locallyFinite : LocallyFinite fun i => support (f i) :=
f.locallyFinite'
theorem nonneg (i : ι) (x : M) : 0 ≤ f i x :=
f.nonneg' i x
theorem sum_eq_one {x} (hx : x ∈ s) : ∑ᶠ i, f i x = 1 :=
f.sum_eq_one' x hx
theorem exists_pos_of_mem {x} (hx : x ∈ s) : ∃ i, 0 < f i x := by
by_contra! h
have H : ∀ i, f i x = 0 := fun i ↦ le_antisymm (h i) (f.nonneg i x)
have := f.sum_eq_one hx
simp_rw [H] at this
simpa
theorem sum_le_one (x : M) : ∑ᶠ i, f i x ≤ 1 :=
f.sum_le_one' x
/-- Reinterpret a smooth partition of unity as a continuous partition of unity. -/
@[simps]
def toPartitionOfUnity : PartitionOfUnity ι M s :=
{ f with toFun := fun i => f i }
theorem contMDiff_sum : ContMDiff I 𝓘(ℝ) ∞ fun x => ∑ᶠ i, f i x :=
contMDiff_finsum (fun i => (f i).contMDiff) f.locallyFinite
@[deprecated (since := "2024-11-21")] alias smooth_sum := contMDiff_sum
theorem le_one (i : ι) (x : M) : f i x ≤ 1 :=
f.toPartitionOfUnity.le_one i x
theorem sum_nonneg (x : M) : 0 ≤ ∑ᶠ i, f i x :=
f.toPartitionOfUnity.sum_nonneg x
theorem finsum_smul_mem_convex {g : ι → M → F} {t : Set F} {x : M} (hx : x ∈ s)
(hg : ∀ i, f i x ≠ 0 → g i x ∈ t) (ht : Convex ℝ t) : ∑ᶠ i, f i x • g i x ∈ t :=
ht.finsum_mem (fun _ => f.nonneg _ _) (f.sum_eq_one hx) hg
theorem contMDiff_smul {g : M → F} {i} (hg : ∀ x ∈ tsupport (f i), ContMDiffAt I 𝓘(ℝ, F) n g x) :
ContMDiff I 𝓘(ℝ, F) n fun x => f i x • g x :=
contMDiff_of_tsupport fun x hx =>
((f i).contMDiff.contMDiffAt.of_le (mod_cast le_top)).smul <| hg x
<| tsupport_smul_subset_left _ _ hx
@[deprecated (since := "2024-11-21")] alias smooth_smul := contMDiff_smul
/-- If `f` is a smooth partition of unity on a set `s : Set M` and `g : ι → M → F` is a family of
functions such that `g i` is $C^n$ smooth at every point of the topological support of `f i`, then
the sum `fun x ↦ ∑ᶠ i, f i x • g i x` is smooth on the whole manifold. -/
theorem contMDiff_finsum_smul {g : ι → M → F}
(hg : ∀ (i), ∀ x ∈ tsupport (f i), ContMDiffAt I 𝓘(ℝ, F) n (g i) x) :
ContMDiff I 𝓘(ℝ, F) n fun x => ∑ᶠ i, f i x • g i x :=
(contMDiff_finsum fun i => f.contMDiff_smul (hg i)) <|
f.locallyFinite.subset fun _ => support_smul_subset_left _ _
@[deprecated (since := "2024-11-21")] alias smooth_finsum_smul := contMDiff_finsum_smul
theorem contMDiffAt_finsum {x₀ : M} {g : ι → M → F}
(hφ : ∀ i, x₀ ∈ tsupport (f i) → ContMDiffAt I 𝓘(ℝ, F) n (g i) x₀) :
ContMDiffAt I 𝓘(ℝ, F) n (fun x ↦ ∑ᶠ i, f i x • g i x) x₀ := by
refine _root_.contMDiffAt_finsum (f.locallyFinite.smul_left _) fun i ↦ ?_
by_cases hx : x₀ ∈ tsupport (f i)
· exact ContMDiffAt.smul ((f i).contMDiff.of_le (mod_cast le_top)).contMDiffAt (hφ i hx)
· exact contMDiffAt_of_not_mem (compl_subset_compl.mpr
(tsupport_smul_subset_left (f i) (g i)) hx) n
theorem contDiffAt_finsum {s : Set E} (f : SmoothPartitionOfUnity ι 𝓘(ℝ, E) E s) {x₀ : E}
{g : ι → E → F} (hφ : ∀ i, x₀ ∈ tsupport (f i) → ContDiffAt ℝ n (g i) x₀) :
ContDiffAt ℝ n (fun x ↦ ∑ᶠ i, f i x • g i x) x₀ := by
simp only [← contMDiffAt_iff_contDiffAt] at *
exact f.contMDiffAt_finsum hφ
section finsupport
variable {s : Set M} (ρ : SmoothPartitionOfUnity ι I M s) (x₀ : M)
/-- The support of a smooth partition of unity at a point `x₀` as a `Finset`.
This is the set of `i : ι` such that `x₀ ∈ support f i`, i.e. `f i ≠ x₀`. -/
def finsupport : Finset ι := ρ.toPartitionOfUnity.finsupport x₀
@[simp]
theorem mem_finsupport {i : ι} : i ∈ ρ.finsupport x₀ ↔ i ∈ support fun i ↦ ρ i x₀ :=
ρ.toPartitionOfUnity.mem_finsupport x₀
@[simp]
theorem coe_finsupport : (ρ.finsupport x₀ : Set ι) = support fun i ↦ ρ i x₀ :=
ρ.toPartitionOfUnity.coe_finsupport x₀
theorem sum_finsupport (hx₀ : x₀ ∈ s) : ∑ i ∈ ρ.finsupport x₀, ρ i x₀ = 1 :=
ρ.toPartitionOfUnity.sum_finsupport hx₀
theorem sum_finsupport' (hx₀ : x₀ ∈ s) {I : Finset ι} (hI : ρ.finsupport x₀ ⊆ I) :
∑ i ∈ I, ρ i x₀ = 1 :=
ρ.toPartitionOfUnity.sum_finsupport' hx₀ hI
theorem sum_finsupport_smul_eq_finsum {A : Type*} [AddCommGroup A] [Module ℝ A] (φ : ι → M → A) :
∑ i ∈ ρ.finsupport x₀, ρ i x₀ • φ i x₀ = ∑ᶠ i, ρ i x₀ • φ i x₀ :=
ρ.toPartitionOfUnity.sum_finsupport_smul_eq_finsum φ
end finsupport
section fintsupport -- smooth partitions of unity have locally finite `tsupport`
variable {s : Set M} (ρ : SmoothPartitionOfUnity ι I M s) (x₀ : M)
/-- The `tsupport`s of a smooth partition of unity are locally finite. -/
theorem finite_tsupport : {i | x₀ ∈ tsupport (ρ i)}.Finite :=
ρ.toPartitionOfUnity.finite_tsupport _
/-- The tsupport of a partition of unity at a point `x₀` as a `Finset`.
This is the set of `i : ι` such that `x₀ ∈ tsupport f i`. -/
def fintsupport (x : M) : Finset ι :=
(ρ.finite_tsupport x).toFinset
theorem mem_fintsupport_iff (i : ι) : i ∈ ρ.fintsupport x₀ ↔ x₀ ∈ tsupport (ρ i) :=
Finite.mem_toFinset _
theorem eventually_fintsupport_subset : ∀ᶠ y in 𝓝 x₀, ρ.fintsupport y ⊆ ρ.fintsupport x₀ :=
ρ.toPartitionOfUnity.eventually_fintsupport_subset _
theorem finsupport_subset_fintsupport : ρ.finsupport x₀ ⊆ ρ.fintsupport x₀ :=
ρ.toPartitionOfUnity.finsupport_subset_fintsupport x₀
theorem eventually_finsupport_subset : ∀ᶠ y in 𝓝 x₀, ρ.finsupport y ⊆ ρ.fintsupport x₀ :=
ρ.toPartitionOfUnity.eventually_finsupport_subset x₀
end fintsupport
section IsSubordinate
/-- A smooth partition of unity `f i` is subordinate to a family of sets `U i` indexed by the same
type if for each `i` the closure of the support of `f i` is a subset of `U i`. -/
def IsSubordinate (f : SmoothPartitionOfUnity ι I M s) (U : ι → Set M) :=
∀ i, tsupport (f i) ⊆ U i
variable {f}
variable {U : ι → Set M}
@[simp]
theorem isSubordinate_toPartitionOfUnity :
f.toPartitionOfUnity.IsSubordinate U ↔ f.IsSubordinate U :=
Iff.rfl
alias ⟨_, IsSubordinate.toPartitionOfUnity⟩ := isSubordinate_toPartitionOfUnity
/-- If `f` is a smooth partition of unity on a set `s : Set M` subordinate to a family of open sets
`U : ι → Set M` and `g : ι → M → F` is a family of functions such that `g i` is $C^n$ smooth on
`U i`, then the sum `fun x ↦ ∑ᶠ i, f i x • g i x` is $C^n$ smooth on the whole manifold. -/
theorem IsSubordinate.contMDiff_finsum_smul {g : ι → M → F} (hf : f.IsSubordinate U)
(ho : ∀ i, IsOpen (U i)) (hg : ∀ i, ContMDiffOn I 𝓘(ℝ, F) n (g i) (U i)) :
ContMDiff I 𝓘(ℝ, F) n fun x => ∑ᶠ i, f i x • g i x :=
f.contMDiff_finsum_smul fun i _ hx => (hg i).contMDiffAt <| (ho i).mem_nhds (hf i hx)
@[deprecated (since := "2024-11-21")]
alias IsSubordinate.smooth_finsum_smul := IsSubordinate.contMDiff_finsum_smul
end IsSubordinate
end SmoothPartitionOfUnity
namespace BumpCovering
-- Repeat variables to drop `[FiniteDimensional ℝ E]` and `[IsManifold I ∞ M]`
theorem contMDiff_toPartitionOfUnity {E : Type uE} [NormedAddCommGroup E] [NormedSpace ℝ E]
{H : Type uH} [TopologicalSpace H] {I : ModelWithCorners ℝ E H} {M : Type uM}
[TopologicalSpace M] [ChartedSpace H M] {s : Set M} (f : BumpCovering ι M s)
(hf : ∀ i, ContMDiff I 𝓘(ℝ) ∞ (f i)) (i : ι) : ContMDiff I 𝓘(ℝ) ∞ (f.toPartitionOfUnity i) :=
(hf i).mul <| (contMDiff_finprod_cond fun j _ => contMDiff_const.sub (hf j)) <| by
simp only [Pi.sub_def, mulSupport_one_sub]
exact f.locallyFinite
@[deprecated (since := "2024-11-21")]
alias smooth_toPartitionOfUnity := contMDiff_toPartitionOfUnity
variable {s : Set M}
/-- A `BumpCovering` such that all functions in this covering are smooth generates a smooth
partition of unity.
In our formalization, not every `f : BumpCovering ι M s` with smooth functions `f i` is a
`SmoothBumpCovering`; instead, a `SmoothBumpCovering` is a covering by supports of
`SmoothBumpFunction`s. So, we define `BumpCovering.toSmoothPartitionOfUnity`, then reuse it
in `SmoothBumpCovering.toSmoothPartitionOfUnity`. -/
def toSmoothPartitionOfUnity (f : BumpCovering ι M s) (hf : ∀ i, ContMDiff I 𝓘(ℝ) ∞ (f i)) :
SmoothPartitionOfUnity ι I M s :=
{ f.toPartitionOfUnity with
toFun := fun i => ⟨f.toPartitionOfUnity i, f.contMDiff_toPartitionOfUnity hf i⟩ }
@[simp]
theorem toSmoothPartitionOfUnity_toPartitionOfUnity (f : BumpCovering ι M s)
(hf : ∀ i, ContMDiff I 𝓘(ℝ) ∞ (f i)) :
(f.toSmoothPartitionOfUnity hf).toPartitionOfUnity = f.toPartitionOfUnity :=
rfl
@[simp]
theorem coe_toSmoothPartitionOfUnity (f : BumpCovering ι M s) (hf : ∀ i, ContMDiff I 𝓘(ℝ) ∞ (f i))
(i : ι) : ⇑(f.toSmoothPartitionOfUnity hf i) = f.toPartitionOfUnity i :=
rfl
theorem IsSubordinate.toSmoothPartitionOfUnity {f : BumpCovering ι M s} {U : ι → Set M}
(h : f.IsSubordinate U) (hf : ∀ i, ContMDiff I 𝓘(ℝ) ∞ (f i)) :
(f.toSmoothPartitionOfUnity hf).IsSubordinate U :=
h.toPartitionOfUnity
end BumpCovering
namespace SmoothBumpCovering
variable [FiniteDimensional ℝ E]
variable {s : Set M} {U : M → Set M} (fs : SmoothBumpCovering ι I M s)
instance : CoeFun (SmoothBumpCovering ι I M s) fun x => ∀ i : ι, SmoothBumpFunction I (x.c i) :=
⟨toFun⟩
/--
We say that `f : SmoothBumpCovering ι I M s` is *subordinate* to a map `U : M → Set M` if for each
index `i`, we have `tsupport (f i) ⊆ U (f i).c`. This notion is a bit more general than
being subordinate to an open covering of `M`, because we make no assumption about the way `U x`
depends on `x`.
-/
def IsSubordinate {s : Set M} (f : SmoothBumpCovering ι I M s) (U : M → Set M) :=
∀ i, tsupport (f i) ⊆ U (f.c i)
theorem IsSubordinate.support_subset {fs : SmoothBumpCovering ι I M s} {U : M → Set M}
(h : fs.IsSubordinate U) (i : ι) : support (fs i) ⊆ U (fs.c i) :=
Subset.trans subset_closure (h i)
variable (I) in
/-- Let `M` be a smooth manifold modelled on a finite dimensional real vector space.
Suppose also that `M` is a Hausdorff `σ`-compact topological space. Let `s` be a closed set
in `M` and `U : M → Set M` be a collection of sets such that `U x ∈ 𝓝 x` for every `x ∈ s`.
Then there exists a smooth bump covering of `s` that is subordinate to `U`. -/
theorem exists_isSubordinate [T2Space M] [SigmaCompactSpace M] (hs : IsClosed s)
(hU : ∀ x ∈ s, U x ∈ 𝓝 x) :
∃ (ι : Type uM) (f : SmoothBumpCovering ι I M s), f.IsSubordinate U := by
-- First we deduce some missing instances
haveI : LocallyCompactSpace H := I.locallyCompactSpace
haveI : LocallyCompactSpace M := ChartedSpace.locallyCompactSpace H M
-- Next we choose a covering by supports of smooth bump functions
have hB := fun x hx => SmoothBumpFunction.nhds_basis_support (I := I) (hU x hx)
rcases refinement_of_locallyCompact_sigmaCompact_of_nhds_basis_set hs hB with
⟨ι, c, f, hf, hsub', hfin⟩
choose hcs hfU using hf
-- Then we use the shrinking lemma to get a covering by smaller open
rcases exists_subset_iUnion_closed_subset hs (fun i => (f i).isOpen_support)
(fun x _ => hfin.point_finite x) hsub' with ⟨V, hsV, hVc, hVf⟩
choose r hrR hr using fun i => (f i).exists_r_pos_lt_subset_ball (hVc i) (hVf i)
refine ⟨ι, ⟨c, fun i => (f i).updateRIn (r i) (hrR i), hcs, ?_, fun x hx => ?_⟩, fun i => ?_⟩
· simpa only [SmoothBumpFunction.support_updateRIn]
· refine (mem_iUnion.1 <| hsV hx).imp fun i hi => ?_
exact ((f i).updateRIn _ _).eventuallyEq_one_of_dist_lt
((f i).support_subset_source <| hVf _ hi) (hr i hi).2
· simpa only [SmoothBumpFunction.support_updateRIn, tsupport] using hfU i
protected theorem locallyFinite : LocallyFinite fun i => support (fs i) :=
fs.locallyFinite'
protected theorem point_finite (x : M) : {i | fs i x ≠ 0}.Finite :=
fs.locallyFinite.point_finite x
/-- Index of a bump function such that `fs i =ᶠ[𝓝 x] 1`. -/
def ind (x : M) (hx : x ∈ s) : ι :=
(fs.eventuallyEq_one' x hx).choose
theorem eventuallyEq_one (x : M) (hx : x ∈ s) : fs (fs.ind x hx) =ᶠ[𝓝 x] 1 :=
(fs.eventuallyEq_one' x hx).choose_spec
theorem apply_ind (x : M) (hx : x ∈ s) : fs (fs.ind x hx) x = 1 :=
(fs.eventuallyEq_one x hx).eq_of_nhds
theorem mem_support_ind (x : M) (hx : x ∈ s) : x ∈ support (fs <| fs.ind x hx) := by
simp [fs.apply_ind x hx]
theorem mem_chartAt_source_of_eq_one {i : ι} {x : M} (h : fs i x = 1) :
x ∈ (chartAt H (fs.c i)).source :=
(fs i).support_subset_source <| by simp [h]
theorem mem_extChartAt_source_of_eq_one {i : ι} {x : M} (h : fs i x = 1) :
x ∈ (extChartAt I (fs.c i)).source := by
rw [extChartAt_source]; exact fs.mem_chartAt_source_of_eq_one h
theorem mem_chartAt_ind_source (x : M) (hx : x ∈ s) : x ∈ (chartAt H (fs.c (fs.ind x hx))).source :=
fs.mem_chartAt_source_of_eq_one (fs.apply_ind x hx)
theorem mem_extChartAt_ind_source (x : M) (hx : x ∈ s) :
x ∈ (extChartAt I (fs.c (fs.ind x hx))).source :=
fs.mem_extChartAt_source_of_eq_one (fs.apply_ind x hx)
/-- The index type of a `SmoothBumpCovering` of a compact manifold is finite. -/
protected def fintype [CompactSpace M] : Fintype ι :=
fs.locallyFinite.fintypeOfCompact fun i => (fs i).nonempty_support
variable [T2Space M]
variable [IsManifold I ∞ M]
/-- Reinterpret a `SmoothBumpCovering` as a continuous `BumpCovering`. Note that not every
`f : BumpCovering ι M s` with smooth functions `f i` is a `SmoothBumpCovering`. -/
def toBumpCovering : BumpCovering ι M s where
toFun i := ⟨fs i, (fs i).continuous⟩
locallyFinite' := fs.locallyFinite
nonneg' i _ := (fs i).nonneg
le_one' i _ := (fs i).le_one
eventuallyEq_one' := fs.eventuallyEq_one'
@[simp]
theorem isSubordinate_toBumpCovering {f : SmoothBumpCovering ι I M s} {U : M → Set M} :
(f.toBumpCovering.IsSubordinate fun i => U (f.c i)) ↔ f.IsSubordinate U :=
Iff.rfl
alias ⟨_, IsSubordinate.toBumpCovering⟩ := isSubordinate_toBumpCovering
/-- Every `SmoothBumpCovering` defines a smooth partition of unity. -/
def toSmoothPartitionOfUnity : SmoothPartitionOfUnity ι I M s :=
fs.toBumpCovering.toSmoothPartitionOfUnity fun i => (fs i).contMDiff
theorem toSmoothPartitionOfUnity_apply (i : ι) (x : M) :
fs.toSmoothPartitionOfUnity i x = fs i x * ∏ᶠ (j) (_ : WellOrderingRel j i), (1 - fs j x) :=
rfl
open Classical in
theorem toSmoothPartitionOfUnity_eq_mul_prod (i : ι) (x : M) (t : Finset ι)
(ht : ∀ j, WellOrderingRel j i → fs j x ≠ 0 → j ∈ t) :
fs.toSmoothPartitionOfUnity i x = fs i x * ∏ j ∈ t with WellOrderingRel j i, (1 - fs j x) :=
fs.toBumpCovering.toPartitionOfUnity_eq_mul_prod i x t ht
open Classical in
theorem exists_finset_toSmoothPartitionOfUnity_eventuallyEq (i : ι) (x : M) :
∃ t : Finset ι,
fs.toSmoothPartitionOfUnity i =ᶠ[𝓝 x]
fs i * ∏ j ∈ t with WellOrderingRel j i, ((1 : M → ℝ) - fs j) := by
-- Porting note: was defeq, now the continuous lemma uses bundled homs
simpa using fs.toBumpCovering.exists_finset_toPartitionOfUnity_eventuallyEq i x
theorem toSmoothPartitionOfUnity_zero_of_zero {i : ι} {x : M} (h : fs i x = 0) :
fs.toSmoothPartitionOfUnity i x = 0 :=
fs.toBumpCovering.toPartitionOfUnity_zero_of_zero h
theorem support_toSmoothPartitionOfUnity_subset (i : ι) :
support (fs.toSmoothPartitionOfUnity i) ⊆ support (fs i) :=
fs.toBumpCovering.support_toPartitionOfUnity_subset i
theorem IsSubordinate.toSmoothPartitionOfUnity {f : SmoothBumpCovering ι I M s} {U : M → Set M}
(h : f.IsSubordinate U) : f.toSmoothPartitionOfUnity.IsSubordinate fun i => U (f.c i) :=
h.toBumpCovering.toPartitionOfUnity
theorem sum_toSmoothPartitionOfUnity_eq (x : M) :
∑ᶠ i, fs.toSmoothPartitionOfUnity i x = 1 - ∏ᶠ i, (1 - fs i x) :=
fs.toBumpCovering.sum_toPartitionOfUnity_eq x
end SmoothBumpCovering
variable (I)
variable [FiniteDimensional ℝ E]
variable [IsManifold I ∞ M]
/-- Given two disjoint closed sets `s, t` in a Hausdorff σ-compact finite dimensional manifold,
there exists an infinitely smooth function that is equal to `0` on `s` and to `1` on `t`.
See also `exists_msmooth_zero_iff_one_iff_of_isClosed`, which ensures additionally that
`f` is equal to `0` exactly on `s` and to `1` exactly on `t`. -/
theorem exists_smooth_zero_one_of_isClosed [T2Space M] [SigmaCompactSpace M] {s t : Set M}
(hs : IsClosed s) (ht : IsClosed t) (hd : Disjoint s t) :
∃ f : C^∞⟮I, M; 𝓘(ℝ), ℝ⟯, EqOn f 0 s ∧ EqOn f 1 t ∧ ∀ x, f x ∈ Icc 0 1 := by
have : ∀ x ∈ t, sᶜ ∈ 𝓝 x := fun x hx => hs.isOpen_compl.mem_nhds (disjoint_right.1 hd hx)
rcases SmoothBumpCovering.exists_isSubordinate I ht this with ⟨ι, f, hf⟩
set g := f.toSmoothPartitionOfUnity
refine
⟨⟨_, g.contMDiff_sum⟩, fun x hx => ?_, fun x => g.sum_eq_one, fun x =>
⟨g.sum_nonneg x, g.sum_le_one x⟩⟩
suffices ∀ i, g i x = 0 by simp only [this, ContMDiffMap.coeFn_mk, finsum_zero, Pi.zero_apply]
refine fun i => f.toSmoothPartitionOfUnity_zero_of_zero ?_
exact nmem_support.1 (subset_compl_comm.1 (hf.support_subset i) hx)
/-- Given two disjoint closed sets `s, t` in a Hausdorff normal σ-compact finite dimensional
manifold `M`, there exists a smooth function `f : M → [0,1]` that vanishes in a neighbourhood of `s`
and is equal to `1` in a neighbourhood of `t`. -/
theorem exists_smooth_zero_one_nhds_of_isClosed [T2Space M] [NormalSpace M] [SigmaCompactSpace M]
{s t : Set M} (hs : IsClosed s) (ht : IsClosed t) (hd : Disjoint s t) :
∃ f : C^∞⟮I, M; 𝓘(ℝ), ℝ⟯, (∀ᶠ x in 𝓝ˢ s, f x = 0) ∧ (∀ᶠ x in 𝓝ˢ t, f x = 1) ∧
∀ x, f x ∈ Icc 0 1 := by
obtain ⟨u, u_op, hsu, hut⟩ := normal_exists_closure_subset hs ht.isOpen_compl
(subset_compl_iff_disjoint_left.mpr hd.symm)
obtain ⟨v, v_op, htv, hvu⟩ := normal_exists_closure_subset ht isClosed_closure.isOpen_compl
(subset_compl_comm.mp hut)
obtain ⟨f, hfu, hfv, hf⟩ := exists_smooth_zero_one_of_isClosed I isClosed_closure isClosed_closure
(subset_compl_iff_disjoint_left.mp hvu)
refine ⟨f, ?_, ?_, hf⟩
· exact eventually_of_mem (mem_of_superset (u_op.mem_nhdsSet.mpr hsu) subset_closure) hfu
· exact eventually_of_mem (mem_of_superset (v_op.mem_nhdsSet.mpr htv) subset_closure) hfv
/-- Given two sets `s, t` in a Hausdorff normal σ-compact finite-dimensional manifold `M`
with `s` open and `s ⊆ interior t`, there is a smooth function `f : M → [0,1]` which is equal to `s`
in a neighbourhood of `s` and has support contained in `t`. -/
theorem exists_smooth_one_nhds_of_subset_interior [T2Space M] [NormalSpace M] [SigmaCompactSpace M]
{s t : Set M} (hs : IsClosed s) (hd : s ⊆ interior t) :
∃ f : C^∞⟮I, M; 𝓘(ℝ), ℝ⟯, (∀ᶠ x in 𝓝ˢ s, f x = 1) ∧ (∀ x ∉ t, f x = 0) ∧
∀ x, f x ∈ Icc 0 1 := by
rcases exists_smooth_zero_one_nhds_of_isClosed I isOpen_interior.isClosed_compl hs
(by rwa [← subset_compl_iff_disjoint_left, compl_compl]) with ⟨f, h0, h1, hf⟩
refine ⟨f, h1, fun x hx ↦ ?_, hf⟩
exact h0.self_of_nhdsSet _ fun hx' ↦ hx <| interior_subset hx'
namespace SmoothPartitionOfUnity
/-- A `SmoothPartitionOfUnity` that consists of a single function, uniformly equal to one,
defined as an example for `Inhabited` instance. -/
def single (i : ι) (s : Set M) : SmoothPartitionOfUnity ι I M s :=
(BumpCovering.single i s).toSmoothPartitionOfUnity fun j => by
classical
rcases eq_or_ne j i with (rfl | h)
· simp only [contMDiff_one, ContinuousMap.coe_one, BumpCovering.coe_single, Pi.single_eq_same]
· simp only [contMDiff_zero, BumpCovering.coe_single, Pi.single_eq_of_ne h,
ContinuousMap.coe_zero]
instance [Inhabited ι] (s : Set M) : Inhabited (SmoothPartitionOfUnity ι I M s) :=
⟨single I default s⟩
variable [T2Space M] [SigmaCompactSpace M]
/-- If `X` is a paracompact normal topological space and `U` is an open covering of a closed set
`s`, then there exists a `SmoothPartitionOfUnity ι M s` that is subordinate to `U`. -/
theorem exists_isSubordinate {s : Set M} (hs : IsClosed s) (U : ι → Set M) (ho : ∀ i, IsOpen (U i))
(hU : s ⊆ ⋃ i, U i) : ∃ f : SmoothPartitionOfUnity ι I M s, f.IsSubordinate U := by
haveI : LocallyCompactSpace H := I.locallyCompactSpace
haveI : LocallyCompactSpace M := ChartedSpace.locallyCompactSpace H M
-- porting note(https://github.com/leanprover/std4/issues/116):
-- split `rcases` into `have` + `rcases`
have := BumpCovering.exists_isSubordinate_of_prop (ContMDiff I 𝓘(ℝ) ∞) ?_ hs U ho hU
· rcases this with ⟨f, hf, hfU⟩
exact ⟨f.toSmoothPartitionOfUnity hf, hfU.toSmoothPartitionOfUnity hf⟩
· intro s t hs ht hd
rcases exists_smooth_zero_one_of_isClosed I hs ht hd with ⟨f, hf⟩
exact ⟨f, f.contMDiff, hf⟩
theorem exists_isSubordinate_chartAt_source_of_isClosed {s : Set M} (hs : IsClosed s) :
∃ f : SmoothPartitionOfUnity s I M s,
f.IsSubordinate (fun x ↦ (chartAt H (x : M)).source) := by
apply exists_isSubordinate _ hs _ (fun i ↦ (chartAt H _).open_source) (fun x hx ↦ ?_)
exact mem_iUnion_of_mem ⟨x, hx⟩ (mem_chart_source H x)
|
variable (M)
theorem exists_isSubordinate_chartAt_source :
∃ f : SmoothPartitionOfUnity M I M univ, f.IsSubordinate (fun x ↦ (chartAt H x).source) := by
apply exists_isSubordinate _ isClosed_univ _ (fun i ↦ (chartAt H _).open_source) (fun x _ ↦ ?_)
exact mem_iUnion_of_mem x (mem_chart_source H x)
end SmoothPartitionOfUnity
variable [SigmaCompactSpace M] [T2Space M] {t : M → Set F} {n : ℕ∞}
/-- Let `M` be a σ-compact Hausdorff finite dimensional topological manifold. Let `t : M → Set F`
be a family of convex sets. Suppose that for each point `x : M` there exists a neighborhood
| Mathlib/Geometry/Manifold/PartitionOfUnity.lean | 576 | 588 |
/-
Copyright (c) 2024 David Loeffler. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: David Loeffler
-/
import Mathlib.Analysis.Convex.Deriv
import Mathlib.Analysis.SpecialFunctions.Gamma.Deligne
import Mathlib.Data.Nat.Factorial.Basic
import Mathlib.NumberTheory.Harmonic.EulerMascheroni
/-!
# Derivative of Γ at positive integers
We prove the formula for the derivative of `Real.Gamma` at a positive integer:
`deriv Real.Gamma (n + 1) = Nat.factorial n * (-Real.eulerMascheroniConstant + harmonic n)`
-/
open Nat Set Filter Topology
local notation "γ" => Real.eulerMascheroniConstant
namespace Real
|
/-- Explicit formula for the derivative of the Gamma function at positive integers, in terms of
harmonic numbers and the Euler-Mascheroni constant `γ`. -/
lemma deriv_Gamma_nat (n : ℕ) :
deriv Gamma (n + 1) = n ! * (-γ + harmonic n) := by
/- This follows from two properties of the function `f n = log (Gamma n)`:
firstly, the elementary computation that `deriv f (n + 1) = deriv f n + 1 / n`, so that
`deriv f n = deriv f 1 + harmonic n`; secondly, the convexity of `f` (the Bohr-Mollerup theorem),
which shows that `deriv f n` is `log n + o(1)` as `n → ∞`. -/
let f := log ∘ Gamma
-- First reduce to computing derivative of `log ∘ Gamma`.
suffices deriv (log ∘ Gamma) (n + 1) = -γ + harmonic n by
rwa [Function.comp_def, deriv.log (differentiableAt_Gamma (fun m ↦ by linarith))
(by positivity), Gamma_nat_eq_factorial, div_eq_iff_mul_eq (by positivity),
mul_comm, Eq.comm] at this
have hc : ConvexOn ℝ (Ioi 0) f := convexOn_log_Gamma
have h_rec (x : ℝ) (hx : 0 < x) : f (x + 1) = f x + log x := by simp only [f, Function.comp_apply,
Gamma_add_one hx.ne', log_mul hx.ne' (Gamma_pos_of_pos hx).ne', add_comm]
have hder {x : ℝ} (hx : 0 < x) : DifferentiableAt ℝ f x := by
refine ((differentiableAt_Gamma ?_).log (Gamma_ne_zero ?_)) <;>
exact fun m ↦ ne_of_gt (by linarith)
-- Express derivative at general `n` in terms of value at `1` using recurrence relation
have hder_rec (x : ℝ) (hx : 0 < x) : deriv f (x + 1) = deriv f x + 1 / x := by
rw [← deriv_comp_add_const, one_div, ← deriv_log,
← deriv_add (hder <| by positivity) (differentiableAt_log hx.ne')]
apply EventuallyEq.deriv_eq
filter_upwards [eventually_gt_nhds hx] using h_rec
have hder_nat (n : ℕ) : deriv f (n + 1) = deriv f 1 + harmonic n := by
induction n with
| zero => simp
| succ n hn =>
rw [cast_succ, hder_rec (n + 1) (by positivity), hn, harmonic_succ]
push_cast
ring
suffices -deriv f 1 = γ by rw [hder_nat n, ← this, neg_neg]
-- Use convexity to show derivative of `f` at `n + 1` is between `log n` and `log (n + 1)`
have derivLB (n : ℕ) (hn : 0 < n) : log n ≤ deriv f (n + 1) := by
refine (le_of_eq ?_).trans <| hc.slope_le_deriv (mem_Ioi.mpr <| Nat.cast_pos.mpr hn)
(by positivity : _ < (_ : ℝ)) (by linarith) (hder <| by positivity)
rw [slope_def_field, show n + 1 - n = (1 : ℝ) by ring, div_one, h_rec n (by positivity),
add_sub_cancel_left]
have derivUB (n : ℕ) : deriv f (n + 1) ≤ log (n + 1) := by
refine (hc.deriv_le_slope (by positivity : (0 : ℝ) < n + 1) (by positivity : (0 : ℝ) < n + 2)
(by linarith) (hder <| by positivity)).trans (le_of_eq ?_)
rw [slope_def_field, show n + 2 - (n + 1) = (1 : ℝ) by ring, div_one,
show n + 2 = (n + 1) + (1 : ℝ) by ring, h_rec (n + 1) (by positivity), add_sub_cancel_left]
-- deduce `-deriv f 1` is bounded above + below by sequences which both tend to `γ`
apply le_antisymm
· apply ge_of_tendsto tendsto_harmonic_sub_log
filter_upwards [eventually_gt_atTop 0] with n hn
rw [le_sub_iff_add_le', ← sub_eq_add_neg, sub_le_iff_le_add', ← hder_nat]
exact derivLB n hn
· apply le_of_tendsto tendsto_harmonic_sub_log_add_one
filter_upwards with n
rw [sub_le_iff_le_add', ← sub_eq_add_neg, le_sub_iff_add_le', ← hder_nat]
| Mathlib/NumberTheory/Harmonic/GammaDeriv.lean | 26 | 80 |
/-
Copyright (c) 2024 Violeta Hernández Palacios. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Violeta Hernández Palacios
-/
import Mathlib.SetTheory.Cardinal.Arithmetic
import Mathlib.SetTheory.Ordinal.Principal
/-!
# Ordinal arithmetic with cardinals
This file collects results about the cardinality of different ordinal operations.
-/
universe u v
open Cardinal Ordinal Set
/-! ### Cardinal operations with ordinal indices -/
namespace Cardinal
/-- Bounds the cardinal of an ordinal-indexed union of sets. -/
lemma mk_iUnion_Ordinal_lift_le_of_le {β : Type v} {o : Ordinal.{u}} {c : Cardinal.{v}}
(ho : lift.{v} o.card ≤ lift.{u} c) (hc : ℵ₀ ≤ c) (A : Ordinal → Set β)
(hA : ∀ j < o, #(A j) ≤ c) : #(⋃ j < o, A j) ≤ c := by
simp_rw [← mem_Iio, biUnion_eq_iUnion, iUnion, iSup, ← o.enumIsoToType.symm.surjective.range_comp]
rw [← lift_le.{u}]
apply ((mk_iUnion_le_lift _).trans _).trans_eq (mul_eq_self (aleph0_le_lift.2 hc))
rw [mk_toType]
refine mul_le_mul' ho (ciSup_le' ?_)
intro i
simpa using hA _ (o.enumIsoToType.symm i).2
lemma mk_iUnion_Ordinal_le_of_le {β : Type*} {o : Ordinal} {c : Cardinal}
(ho : o.card ≤ c) (hc : ℵ₀ ≤ c) (A : Ordinal → Set β)
(hA : ∀ j < o, #(A j) ≤ c) : #(⋃ j < o, A j) ≤ c := by
apply mk_iUnion_Ordinal_lift_le_of_le _ hc A hA
rwa [Cardinal.lift_le]
end Cardinal
@[deprecated mk_iUnion_Ordinal_le_of_le (since := "2024-11-02")]
alias Ordinal.Cardinal.mk_iUnion_Ordinal_le_of_le := mk_iUnion_Ordinal_le_of_le
/-! ### Cardinality of ordinals -/
namespace Ordinal
theorem lift_card_iSup_le_sum_card {ι : Type u} [Small.{v} ι] (f : ι → Ordinal.{v}) :
Cardinal.lift.{u} (⨆ i, f i).card ≤ Cardinal.sum fun i ↦ (f i).card := by
simp_rw [← mk_toType]
rw [← mk_sigma, ← Cardinal.lift_id'.{v} #(Σ _, _), ← Cardinal.lift_umax.{v, u}]
apply lift_mk_le_lift_mk_of_surjective (f := enumIsoToType _ ∘ (⟨(enumIsoToType _).symm ·.2,
(mem_Iio.mp ((enumIsoToType _).symm _).2).trans_le (Ordinal.le_iSup _ _)⟩))
rw [EquivLike.comp_surjective]
rintro ⟨x, hx⟩
obtain ⟨i, hi⟩ := Ordinal.lt_iSup_iff.mp hx
exact ⟨⟨i, enumIsoToType _ ⟨x, hi⟩⟩, by simp⟩
theorem card_iSup_le_sum_card {ι : Type u} (f : ι → Ordinal.{max u v}) :
(⨆ i, f i).card ≤ Cardinal.sum (fun i ↦ (f i).card) := by
have := lift_card_iSup_le_sum_card f
rwa [Cardinal.lift_id'] at this
theorem card_iSup_Iio_le_sum_card {o : Ordinal.{u}} (f : Iio o → Ordinal.{max u v}) :
(⨆ a : Iio o, f a).card ≤ Cardinal.sum fun i ↦ (f ((enumIsoToType o).symm i)).card := by
apply le_of_eq_of_le (congr_arg _ _).symm (card_iSup_le_sum_card _)
simpa using (enumIsoToType o).symm.iSup_comp (g := fun x ↦ f x)
theorem card_iSup_Iio_le_card_mul_iSup {o : Ordinal.{u}} (f : Iio o → Ordinal.{max u v}) :
(⨆ a : Iio o, f a).card ≤ Cardinal.lift.{v} o.card * ⨆ a : Iio o, (f a).card := by
apply (card_iSup_Iio_le_sum_card f).trans
convert ← sum_le_iSup_lift _
· exact mk_toType o
· exact (enumIsoToType o).symm.iSup_comp (g := fun x ↦ (f x).card)
theorem card_opow_le_of_omega0_le_left {a : Ordinal} (ha : ω ≤ a) (b : Ordinal) :
(a ^ b).card ≤ max a.card b.card := by
refine limitRecOn b ?_ ?_ ?_
· simpa using one_lt_omega0.le.trans ha
· intro b IH
rw [opow_succ, card_mul, card_succ, Cardinal.mul_eq_max_of_aleph0_le_right, max_comm]
· apply (max_le_max_left _ IH).trans
rw [← max_assoc, max_self]
exact max_le_max_left _ le_self_add
· rw [ne_eq, card_eq_zero, opow_eq_zero]
rintro ⟨rfl, -⟩
cases omega0_pos.not_le ha
· rwa [aleph0_le_card]
· intro b hb IH
rw [(isNormal_opow (one_lt_omega0.trans_le ha)).apply_of_isLimit hb]
apply (card_iSup_Iio_le_card_mul_iSup _).trans
rw [Cardinal.lift_id, Cardinal.mul_eq_max_of_aleph0_le_right, max_comm]
· apply max_le _ (le_max_right _ _)
apply ciSup_le'
intro c
exact (IH c.1 c.2).trans (max_le_max_left _ (card_le_card c.2.le))
· simpa using hb.pos.ne'
· refine le_ciSup_of_le ?_ ⟨1, one_lt_omega0.trans_le <| omega0_le_of_isLimit hb⟩ ?_
· exact Cardinal.bddAbove_of_small _
· simpa
theorem card_opow_le_of_omega0_le_right (a : Ordinal) {b : Ordinal} (hb : ω ≤ b) :
(a ^ b).card ≤ max a.card b.card := by
obtain ⟨n, rfl⟩ | ha := eq_nat_or_omega0_le a
· apply (card_le_card <| opow_le_opow_left b (nat_lt_omega0 n).le).trans
apply (card_opow_le_of_omega0_le_left le_rfl _).trans
simp [hb]
· exact card_opow_le_of_omega0_le_left ha b
theorem card_opow_le (a b : Ordinal) : (a ^ b).card ≤ max ℵ₀ (max a.card b.card) := by
obtain ⟨n, rfl⟩ | ha := eq_nat_or_omega0_le a
· obtain ⟨m, rfl⟩ | hb := eq_nat_or_omega0_le b
· rw [← natCast_opow, card_nat]
exact le_max_of_le_left (nat_lt_aleph0 _).le
· exact (card_opow_le_of_omega0_le_right _ hb).trans (le_max_right _ _)
· exact (card_opow_le_of_omega0_le_left ha _).trans (le_max_right _ _)
theorem card_opow_eq_of_omega0_le_left {a b : Ordinal} (ha : ω ≤ a) (hb : 0 < b) :
(a ^ b).card = max a.card b.card := by
apply (card_opow_le_of_omega0_le_left ha b).antisymm (max_le _ _) <;> apply card_le_card
· exact left_le_opow a hb
· exact right_le_opow b (one_lt_omega0.trans_le ha)
theorem card_opow_eq_of_omega0_le_right {a b : Ordinal} (ha : 1 < a) (hb : ω ≤ b) :
(a ^ b).card = max a.card b.card := by
apply (card_opow_le_of_omega0_le_right a hb).antisymm (max_le _ _) <;> apply card_le_card
· exact left_le_opow a (omega0_pos.trans_le hb)
· exact right_le_opow b ha
theorem card_omega0_opow {a : Ordinal} (h : a ≠ 0) : card (ω ^ a) = max ℵ₀ a.card := by
rw [card_opow_eq_of_omega0_le_left le_rfl h.bot_lt, card_omega0]
theorem card_opow_omega0 {a : Ordinal} (h : 1 < a) : card (a ^ ω) = max ℵ₀ a.card := by
rw [card_opow_eq_of_omega0_le_right h le_rfl, card_omega0, max_comm]
theorem principal_opow_omega (o : Ordinal) : Principal (· ^ ·) (ω_ o) := by
obtain rfl | ho := Ordinal.eq_zero_or_pos o
· rw [omega_zero]
exact principal_opow_omega0
· intro a b ha hb
rw [lt_omega_iff_card_lt] at ha hb ⊢
apply (card_opow_le a b).trans_lt (max_lt _ (max_lt ha hb))
rwa [← aleph_zero, aleph_lt_aleph]
theorem IsInitial.principal_opow {o : Ordinal} (h : IsInitial o) (ho : ω ≤ o) :
Principal (· ^ ·) o := by
obtain ⟨a, rfl⟩ := mem_range_omega_iff.2 ⟨ho, h⟩
exact principal_opow_omega a
theorem principal_opow_ord {c : Cardinal} (hc : ℵ₀ ≤ c) : Principal (· ^ ·) c.ord := by
apply (isInitial_ord c).principal_opow
rwa [omega0_le_ord]
/-! ### Initial ordinals are principal -/
theorem principal_add_ord {c : Cardinal} (hc : ℵ₀ ≤ c) : Principal (· + ·) c.ord := by
intro a b ha hb
rw [lt_ord, card_add] at *
exact add_lt_of_lt hc ha hb
theorem IsInitial.principal_add {o : Ordinal} (h : IsInitial o) (ho : ω ≤ o) :
Principal (· + ·) o := by
rw [← h.ord_card]
apply principal_add_ord
rwa [aleph0_le_card]
theorem principal_add_omega (o : Ordinal) : Principal (· + ·) (ω_ o) :=
(isInitial_omega o).principal_add (omega0_le_omega o)
theorem principal_mul_ord {c : Cardinal} (hc : ℵ₀ ≤ c) : Principal (· * ·) c.ord := by
intro a b ha hb
rw [lt_ord, card_mul] at *
exact mul_lt_of_lt hc ha hb
theorem IsInitial.principal_mul {o : Ordinal} (h : IsInitial o) (ho : ω ≤ o) :
Principal (· * ·) o := by
rw [← h.ord_card]
apply principal_mul_ord
rwa [aleph0_le_card]
theorem principal_mul_omega (o : Ordinal) : Principal (· * ·) (ω_ o) :=
(isInitial_omega o).principal_mul (omega0_le_omega o)
@[deprecated principal_add_omega (since := "2024-11-08")]
theorem _root_.Cardinal.principal_add_aleph (o : Ordinal) : Principal (· + ·) (ℵ_ o).ord :=
principal_add_ord <| aleph0_le_aleph o
end Ordinal
| Mathlib/SetTheory/Cardinal/Ordinal.lean | 1,249 | 1,249 | |
/-
Copyright (c) 2021 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen
-/
import Mathlib.RingTheory.DedekindDomain.Ideal
/-!
# The ideal class group
This file defines the ideal class group `ClassGroup R` of fractional ideals of `R`
inside its field of fractions.
## Main definitions
- `toPrincipalIdeal` sends an invertible `x : K` to an invertible fractional ideal
- `ClassGroup` is the quotient of invertible fractional ideals modulo `toPrincipalIdeal.range`
- `ClassGroup.mk0` sends a nonzero integral ideal in a Dedekind domain to its class
## Main results
- `ClassGroup.mk0_eq_mk0_iff` shows the equivalence with the "classical" definition,
where `I ~ J` iff `x I = y J` for `x y ≠ (0 : R)`
## Implementation details
The definition of `ClassGroup R` involves `FractionRing R`. However, the API should be completely
identical no matter the choice of field of fractions for `R`.
-/
variable {R K : Type*} [CommRing R] [Field K] [Algebra R K] [IsFractionRing R K]
open scoped nonZeroDivisors
open IsLocalization IsFractionRing FractionalIdeal Units
section
variable (R K)
/-- `toPrincipalIdeal R K x` sends `x ≠ 0 : K` to the fractional `R`-ideal generated by `x` -/
irreducible_def toPrincipalIdeal : Kˣ →* (FractionalIdeal R⁰ K)ˣ :=
{ toFun := fun x =>
⟨spanSingleton _ x, spanSingleton _ x⁻¹, by
simp only [spanSingleton_one, Units.mul_inv', spanSingleton_mul_spanSingleton], by
simp only [spanSingleton_one, Units.inv_mul', spanSingleton_mul_spanSingleton]⟩
map_mul' := fun x y =>
ext (by simp only [Units.val_mk, Units.val_mul, spanSingleton_mul_spanSingleton])
map_one' := ext (by simp only [spanSingleton_one, Units.val_mk, Units.val_one]) }
variable {R K}
@[simp]
theorem coe_toPrincipalIdeal (x : Kˣ) :
(toPrincipalIdeal R K x : FractionalIdeal R⁰ K) = spanSingleton _ (x : K) := by
simp only [toPrincipalIdeal]; rfl
@[simp]
theorem toPrincipalIdeal_eq_iff {I : (FractionalIdeal R⁰ K)ˣ} {x : Kˣ} :
toPrincipalIdeal R K x = I ↔ spanSingleton R⁰ (x : K) = I := by
simp only [toPrincipalIdeal]; exact Units.ext_iff
theorem mem_principal_ideals_iff {I : (FractionalIdeal R⁰ K)ˣ} :
I ∈ (toPrincipalIdeal R K).range ↔ ∃ x : K, spanSingleton R⁰ x = I := by
simp only [MonoidHom.mem_range, toPrincipalIdeal_eq_iff]
constructor <;> rintro ⟨x, hx⟩
· exact ⟨x, hx⟩
· refine ⟨Units.mk0 x ?_, hx⟩
rintro rfl
simp [I.ne_zero.symm] at hx
instance PrincipalIdeals.normal : (toPrincipalIdeal R K).range.Normal :=
Subgroup.normal_of_comm _
end
variable (R)
variable [IsDomain R]
/-- The ideal class group of `R` is the group of invertible fractional ideals
modulo the principal ideals. -/
def ClassGroup :=
(FractionalIdeal R⁰ (FractionRing R))ˣ ⧸ (toPrincipalIdeal R (FractionRing R)).range
noncomputable instance : CommGroup (ClassGroup R) :=
QuotientGroup.Quotient.commGroup (toPrincipalIdeal R (FractionRing R)).range
noncomputable instance : Inhabited (ClassGroup R) := ⟨1⟩
variable {R}
/-- Send a nonzero fractional ideal to the corresponding class in the class group. -/
noncomputable def ClassGroup.mk : (FractionalIdeal R⁰ K)ˣ →* ClassGroup R :=
(QuotientGroup.mk' (toPrincipalIdeal R (FractionRing R)).range).comp
(Units.map (FractionalIdeal.canonicalEquiv R⁰ K (FractionRing R)))
lemma ClassGroup.mk_def (I : (FractionalIdeal R⁰ K)ˣ) :
ClassGroup.mk I =
(QuotientGroup.mk' (toPrincipalIdeal R (FractionRing R)).range)
(Units.map (FractionalIdeal.canonicalEquiv R⁰ K (FractionRing R)) I) := rfl
-- Can't be `@[simp]` because it can't figure out the quotient relation.
theorem ClassGroup.Quot_mk_eq_mk (I : (FractionalIdeal R⁰ (FractionRing R))ˣ) :
Quot.mk _ I = ClassGroup.mk I := by
rw [ClassGroup.mk_def, canonicalEquiv_self, RingEquiv.coe_monoidHom_refl, Units.map_id,
MonoidHom.id_apply, QuotientGroup.mk'_apply]
rfl
theorem ClassGroup.mk_eq_mk {I J : (FractionalIdeal R⁰ <| FractionRing R)ˣ} :
ClassGroup.mk I = ClassGroup.mk J ↔
∃ x : (FractionRing R)ˣ, I * toPrincipalIdeal R (FractionRing R) x = J := by
rw [mk_def, mk_def, QuotientGroup.mk'_eq_mk']
simp [RingEquiv.coe_monoidHom_refl, MonoidHom.mem_range, -toPrincipalIdeal_eq_iff]
theorem ClassGroup.mk_eq_mk_of_coe_ideal {I J : (FractionalIdeal R⁰ <| FractionRing R)ˣ}
{I' J' : Ideal R} (hI : (I : FractionalIdeal R⁰ <| FractionRing R) = I')
(hJ : (J : FractionalIdeal R⁰ <| FractionRing R) = J') :
ClassGroup.mk I = ClassGroup.mk J ↔
∃ x y : R, x ≠ 0 ∧ y ≠ 0 ∧ Ideal.span {x} * I' = Ideal.span {y} * J' := by
rw [ClassGroup.mk_eq_mk]
constructor
· rintro ⟨x, rfl⟩
rw [Units.val_mul, hI, coe_toPrincipalIdeal, mul_comm,
spanSingleton_mul_coeIdeal_eq_coeIdeal] at hJ
exact ⟨_, _, sec_fst_ne_zero x.ne_zero,
sec_snd_ne_zero (R := R) le_rfl (x : FractionRing R), hJ⟩
· rintro ⟨x, y, hx, hy, h⟩
have : IsUnit (mk' (FractionRing R) x ⟨y, mem_nonZeroDivisors_of_ne_zero hy⟩) := by
simpa only [isUnit_iff_ne_zero, ne_eq, mk'_eq_zero_iff_eq_zero] using hx
refine ⟨this.unit, ?_⟩
rw [mul_comm, ← Units.eq_iff, Units.val_mul, coe_toPrincipalIdeal]
convert
(mk'_mul_coeIdeal_eq_coeIdeal (FractionRing R) <| mem_nonZeroDivisors_of_ne_zero hy).2 h
theorem ClassGroup.mk_eq_one_of_coe_ideal {I : (FractionalIdeal R⁰ <| FractionRing R)ˣ}
{I' : Ideal R} (hI : (I : FractionalIdeal R⁰ <| FractionRing R) = I') :
ClassGroup.mk I = 1 ↔ ∃ x : R, x ≠ 0 ∧ I' = Ideal.span {x} := by
rw [← map_one (ClassGroup.mk (R := R) (K := FractionRing R)),
ClassGroup.mk_eq_mk_of_coe_ideal hI]
any_goals rfl
constructor
· rintro ⟨x, y, hx, hy, h⟩
rw [Ideal.mul_top] at h
rcases Ideal.mem_span_singleton_mul.mp ((Ideal.span_singleton_le_iff_mem _).mp h.ge) with
⟨i, _hi, rfl⟩
rw [← Ideal.span_singleton_mul_span_singleton, Ideal.span_singleton_mul_right_inj hx] at h
exact ⟨i, right_ne_zero_of_mul hy, h⟩
· rintro ⟨x, hx, rfl⟩
exact ⟨1, x, one_ne_zero, hx, by rw [Ideal.span_singleton_one, Ideal.top_mul, Ideal.mul_top]⟩
variable (K)
/-- Induction principle for the class group: to show something holds for all `x : ClassGroup R`,
we can choose a fraction field `K` and show it holds for the equivalence class of each
`I : FractionalIdeal R⁰ K`. -/
@[elab_as_elim]
theorem ClassGroup.induction {P : ClassGroup R → Prop}
(h : ∀ I : (FractionalIdeal R⁰ K)ˣ, P (ClassGroup.mk I)) (x : ClassGroup R) : P x :=
QuotientGroup.induction_on x fun I => by
have : I = (Units.mapEquiv (canonicalEquiv R⁰ K (FractionRing R)).toMulEquiv)
(Units.mapEquiv (canonicalEquiv R⁰ (FractionRing R) K).toMulEquiv I) := by
simp [← Units.eq_iff]
rw [congr_arg (QuotientGroup.mk (s := (toPrincipalIdeal R (FractionRing R)).range)) this]
exact h _
/-- The definition of the class group does not depend on the choice of field of fractions. -/
noncomputable def ClassGroup.equiv :
ClassGroup R ≃* (FractionalIdeal R⁰ K)ˣ ⧸ (toPrincipalIdeal R K).range := by
haveI : Subgroup.map
(Units.mapEquiv (canonicalEquiv R⁰ (FractionRing R) K).toMulEquiv).toMonoidHom
(toPrincipalIdeal R (FractionRing R)).range = (toPrincipalIdeal R K).range := by
ext I
simp only [Subgroup.mem_map, mem_principal_ideals_iff]
constructor
· rintro ⟨I, ⟨x, hx⟩, rfl⟩
refine ⟨FractionRing.algEquiv R K x, ?_⟩
simp only [RingEquiv.toMulEquiv_eq_coe, MulEquiv.coe_toMonoidHom, coe_mapEquiv, ← hx,
RingEquiv.coe_toMulEquiv, canonicalEquiv_spanSingleton]
rfl
· rintro ⟨x, hx⟩
refine ⟨Units.mapEquiv (canonicalEquiv R⁰ K (FractionRing R)).toMulEquiv I,
⟨(FractionRing.algEquiv R K).symm x, ?_⟩, Units.ext ?_⟩
· simp only [RingEquiv.toMulEquiv_eq_coe, coe_mapEquiv, ← hx, RingEquiv.coe_toMulEquiv,
canonicalEquiv_spanSingleton]
rfl
· simp only [RingEquiv.toMulEquiv_eq_coe, MulEquiv.coe_toMonoidHom, coe_mapEquiv,
RingEquiv.coe_toMulEquiv, canonicalEquiv_canonicalEquiv, canonicalEquiv_self,
RingEquiv.refl_apply]
exact @QuotientGroup.congr (FractionalIdeal R⁰ (FractionRing R))ˣ _ (FractionalIdeal R⁰ K)ˣ _
(toPrincipalIdeal R (FractionRing R)).range (toPrincipalIdeal R K).range _ _
(Units.mapEquiv (FractionalIdeal.canonicalEquiv R⁰ (FractionRing R) K).toMulEquiv) this
@[simp]
theorem ClassGroup.equiv_mk (K' : Type*) [Field K'] [Algebra R K'] [IsFractionRing R K']
(I : (FractionalIdeal R⁰ K)ˣ) :
ClassGroup.equiv K' (ClassGroup.mk I) =
QuotientGroup.mk' _ (Units.mapEquiv (↑(FractionalIdeal.canonicalEquiv R⁰ K K')) I) := by
-- `simp` can't apply `ClassGroup.mk_def` and `rw` can't unfold `ClassGroup`.
rw [ClassGroup.equiv, ClassGroup.mk_def]
simp only [ClassGroup, QuotientGroup.congr_mk']
congr
rw [← Units.eq_iff, Units.coe_mapEquiv, Units.coe_mapEquiv, Units.coe_map]
exact FractionalIdeal.canonicalEquiv_canonicalEquiv _ _ _ _ _
@[simp]
theorem ClassGroup.mk_canonicalEquiv (K' : Type*) [Field K'] [Algebra R K'] [IsFractionRing R K']
(I : (FractionalIdeal R⁰ K)ˣ) :
ClassGroup.mk (Units.map (↑(canonicalEquiv R⁰ K K')) I : (FractionalIdeal R⁰ K')ˣ) =
ClassGroup.mk I := by
rw [ClassGroup.mk_def, ClassGroup.mk_def, ← MonoidHom.comp_apply (Units.map _),
← Units.map_comp, ← RingEquiv.coe_monoidHom_trans,
FractionalIdeal.canonicalEquiv_trans_canonicalEquiv]
/-- Send a nonzero integral ideal to an invertible fractional ideal. -/
noncomputable def FractionalIdeal.mk0 [IsDedekindDomain R] :
(Ideal R)⁰ →* (FractionalIdeal R⁰ K)ˣ where
toFun I := Units.mk0 I (coeIdeal_ne_zero.mpr <| mem_nonZeroDivisors_iff_ne_zero.mp I.2)
map_one' := by simp
map_mul' x y := by simp
@[simp]
theorem FractionalIdeal.coe_mk0 [IsDedekindDomain R] (I : (Ideal R)⁰) :
(FractionalIdeal.mk0 K I : FractionalIdeal R⁰ K) = I := rfl
theorem FractionalIdeal.canonicalEquiv_mk0 [IsDedekindDomain R] (K' : Type*) [Field K']
[Algebra R K'] [IsFractionRing R K'] (I : (Ideal R)⁰) :
FractionalIdeal.canonicalEquiv R⁰ K K' (FractionalIdeal.mk0 K I) =
FractionalIdeal.mk0 K' I := by
simp only [FractionalIdeal.coe_mk0, FractionalIdeal.canonicalEquiv_coeIdeal]
@[simp]
theorem FractionalIdeal.map_canonicalEquiv_mk0 [IsDedekindDomain R] (K' : Type*) [Field K']
[Algebra R K'] [IsFractionRing R K'] (I : (Ideal R)⁰) :
Units.map (↑(FractionalIdeal.canonicalEquiv R⁰ K K')) (FractionalIdeal.mk0 K I) =
FractionalIdeal.mk0 K' I :=
Units.ext (FractionalIdeal.canonicalEquiv_mk0 K K' I)
/-- Send a nonzero ideal to the corresponding class in the class group. -/
noncomputable def ClassGroup.mk0 [IsDedekindDomain R] : (Ideal R)⁰ →* ClassGroup R :=
ClassGroup.mk.comp (FractionalIdeal.mk0 (FractionRing R))
@[simp]
theorem ClassGroup.mk_mk0 [IsDedekindDomain R] (I : (Ideal R)⁰) :
ClassGroup.mk (FractionalIdeal.mk0 K I) = ClassGroup.mk0 I := by
rw [ClassGroup.mk0, MonoidHom.comp_apply, ← ClassGroup.mk_canonicalEquiv K (FractionRing R),
FractionalIdeal.map_canonicalEquiv_mk0]
@[simp]
theorem ClassGroup.equiv_mk0 [IsDedekindDomain R] (I : (Ideal R)⁰) :
ClassGroup.equiv K (ClassGroup.mk0 I) =
QuotientGroup.mk' (toPrincipalIdeal R K).range (FractionalIdeal.mk0 K I) := by
rw [ClassGroup.mk0, MonoidHom.comp_apply, ClassGroup.equiv_mk]
congr 1
simp [← Units.eq_iff]
theorem ClassGroup.mk0_eq_mk0_iff_exists_fraction_ring [IsDedekindDomain R] {I J : (Ideal R)⁰} :
ClassGroup.mk0 I =
ClassGroup.mk0 J ↔ ∃ (x : _) (_ : x ≠ (0 : K)), spanSingleton R⁰ x * I = J := by
refine (ClassGroup.equiv K).injective.eq_iff.symm.trans ?_
simp only [ClassGroup.equiv_mk0, QuotientGroup.mk'_eq_mk', mem_principal_ideals_iff,
Units.ext_iff, Units.val_mul, FractionalIdeal.coe_mk0, exists_prop]
constructor
· rintro ⟨X, ⟨x, hX⟩, hx⟩
refine ⟨x, ?_, ?_⟩
· rintro rfl; simp [X.ne_zero.symm] at hX
simpa only [hX, mul_comm] using hx
· rintro ⟨x, hx, eq_J⟩
refine ⟨Units.mk0 _ (spanSingleton_ne_zero_iff.mpr hx), ⟨x, rfl⟩, ?_⟩
simpa only [mul_comm] using eq_J
variable {K}
theorem ClassGroup.mk0_eq_mk0_iff [IsDedekindDomain R] {I J : (Ideal R)⁰} :
ClassGroup.mk0 I = ClassGroup.mk0 J ↔
∃ (x y : R) (_hx : x ≠ 0) (_hy : y ≠ 0), Ideal.span {x} * (I : Ideal R) =
Ideal.span {y} * J := by
refine (ClassGroup.mk0_eq_mk0_iff_exists_fraction_ring (FractionRing R)).trans ⟨?_, ?_⟩
· rintro ⟨z, hz, h⟩
obtain ⟨x, ⟨y, hy⟩, rfl⟩ := IsLocalization.mk'_surjective R⁰ z
refine ⟨x, y, ?_, mem_nonZeroDivisors_iff_ne_zero.mp hy, ?_⟩
· rintro hx; apply hz
rw [hx, IsFractionRing.mk'_eq_div, map_zero, zero_div]
· exact (FractionalIdeal.mk'_mul_coeIdeal_eq_coeIdeal _ hy).mp h
· rintro ⟨x, y, hx, hy, h⟩
have hy' : y ∈ R⁰ := mem_nonZeroDivisors_iff_ne_zero.mpr hy
refine ⟨IsLocalization.mk' _ x ⟨y, hy'⟩, ?_, ?_⟩
· contrapose! hx
rwa [mk'_eq_iff_eq_mul, zero_mul, ← (algebraMap R (FractionRing R)).map_zero,
(IsFractionRing.injective R (FractionRing R)).eq_iff] at hx
· exact (FractionalIdeal.mk'_mul_coeIdeal_eq_coeIdeal _ hy').mpr h
/-- Maps a nonzero fractional ideal to an integral representative in the class group. -/
noncomputable def ClassGroup.integralRep (I : FractionalIdeal R⁰ (FractionRing R)) :
Ideal R := I.num
theorem ClassGroup.integralRep_mem_nonZeroDivisors
{I : FractionalIdeal R⁰ (FractionRing R)} (hI : I ≠ 0) :
I.num ∈ (Ideal R)⁰ := by
rwa [mem_nonZeroDivisors_iff_ne_zero, ne_eq, FractionalIdeal.num_eq_zero_iff]
theorem ClassGroup.mk0_integralRep [IsDedekindDomain R]
(I : (FractionalIdeal R⁰ (FractionRing R))ˣ) :
ClassGroup.mk0 ⟨ClassGroup.integralRep I, ClassGroup.integralRep_mem_nonZeroDivisors I.ne_zero⟩
= ClassGroup.mk I := by
rw [← ClassGroup.mk_mk0 (FractionRing R), eq_comm, ClassGroup.mk_eq_mk]
have fd_ne_zero : (algebraMap R (FractionRing R)) I.1.den ≠ 0 := by
exact IsFractionRing.to_map_ne_zero_of_mem_nonZeroDivisors (SetLike.coe_mem _)
refine ⟨Units.mk0 (algebraMap R _ I.1.den) fd_ne_zero, ?_⟩
apply Units.ext
rw [mul_comm, val_mul, coe_toPrincipalIdeal, val_mk0]
exact FractionalIdeal.den_mul_self_eq_num' R⁰ (FractionRing R) I
theorem ClassGroup.mk0_surjective [IsDedekindDomain R] :
Function.Surjective (ClassGroup.mk0 : (Ideal R)⁰ → ClassGroup R) := by
rintro ⟨I⟩
refine ⟨⟨ClassGroup.integralRep I.1, ClassGroup.integralRep_mem_nonZeroDivisors I.ne_zero⟩, ?_⟩
rw [ClassGroup.mk0_integralRep, ClassGroup.Quot_mk_eq_mk]
theorem ClassGroup.mk_eq_one_iff {I : (FractionalIdeal R⁰ K)ˣ} :
ClassGroup.mk I = 1 ↔ (I : Submodule R K).IsPrincipal := by
rw [← (ClassGroup.equiv K).injective.eq_iff]
simp only [equiv_mk, canonicalEquiv_self, RingEquiv.coe_mulEquiv_refl, QuotientGroup.mk'_apply,
map_one, QuotientGroup.eq_one_iff, MonoidHom.mem_range, Units.ext_iff,
coe_toPrincipalIdeal, coe_mapEquiv, MulEquiv.refl_apply]
refine ⟨fun ⟨x, hx⟩ => ⟨⟨x, by rw [← hx, coe_spanSingleton]⟩⟩, ?_⟩
intro hI
obtain ⟨x, hx⟩ := @Submodule.IsPrincipal.principal _ _ _ _ _ _ hI
have hx' : (I : FractionalIdeal R⁰ K) = spanSingleton R⁰ x := by
apply Subtype.coe_injective
simp only [val_eq_coe, hx, coe_spanSingleton]
refine ⟨Units.mk0 x ?_, ?_⟩
· intro x_eq; apply Units.ne_zero I; simp [hx', x_eq]
· simp [hx']
theorem ClassGroup.mk0_eq_one_iff [IsDedekindDomain R] {I : Ideal R} (hI : I ∈ (Ideal R)⁰) :
ClassGroup.mk0 ⟨I, hI⟩ = 1 ↔ I.IsPrincipal :=
ClassGroup.mk_eq_one_iff.trans (coeSubmodule_isPrincipal R _)
theorem ClassGroup.mk0_eq_mk0_inv_iff [IsDedekindDomain R] {I J : (Ideal R)⁰} :
ClassGroup.mk0 I = (ClassGroup.mk0 J)⁻¹ ↔
∃ x ≠ (0 : R), I * J = Ideal.span {x} := by
rw [eq_inv_iff_mul_eq_one, ← map_mul, ClassGroup.mk0_eq_one_iff,
Submodule.isPrincipal_iff, Submonoid.coe_mul]
refine ⟨fun ⟨a, ha⟩ ↦ ⟨a, ?_, ha⟩, fun ⟨a, _, ha⟩ ↦ ⟨a, ha⟩⟩
by_contra!
rw [this, Submodule.span_zero_singleton] at ha
exact nonZeroDivisors.coe_ne_zero _ <| J.prop _ ha
/-- The class group of principal ideal domain is finite (in fact a singleton).
See `ClassGroup.fintypeOfAdmissibleOfFinite` for a finiteness proof that works for rings of integers
of global fields.
-/
noncomputable instance [IsPrincipalIdealRing R] : Fintype (ClassGroup R) where
elems := {1}
complete := by
refine ClassGroup.induction (R := R) (FractionRing R) (fun I => ?_)
rw [Finset.mem_singleton]
exact ClassGroup.mk_eq_one_iff.mpr (I : FractionalIdeal R⁰ (FractionRing R)).isPrincipal
/-- The class number of a principal ideal domain is `1`. -/
theorem card_classGroup_eq_one [IsPrincipalIdealRing R] : Fintype.card (ClassGroup R) = 1 := by
rw [Fintype.card_eq_one_iff]
use 1
refine ClassGroup.induction (R := R) (FractionRing R) (fun I => ?_)
exact ClassGroup.mk_eq_one_iff.mpr (I : FractionalIdeal R⁰ (FractionRing R)).isPrincipal
/-- The class number is `1` iff the ring of integers is a principal ideal domain. -/
theorem card_classGroup_eq_one_iff [IsDedekindDomain R] [Fintype (ClassGroup R)] :
| Fintype.card (ClassGroup R) = 1 ↔ IsPrincipalIdealRing R := by
constructor; swap; · intros; convert card_classGroup_eq_one (R := R)
rw [Fintype.card_eq_one_iff]
rintro ⟨I, hI⟩
have eq_one : ∀ J : ClassGroup R, J = 1 := fun J => (hI J).trans (hI 1).symm
refine ⟨fun I => ?_⟩
by_cases hI : I = ⊥
· rw [hI]; exact bot_isPrincipal
· exact (ClassGroup.mk0_eq_one_iff (mem_nonZeroDivisors_iff_ne_zero.mpr hI)).mp (eq_one _)
| Mathlib/RingTheory/ClassGroup.lean | 369 | 377 |
/-
Copyright (c) 2021 David Wärn. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: David Wärn, Joachim Breitner
-/
import Mathlib.Algebra.Group.Action.End
import Mathlib.Algebra.Group.Action.Pointwise.Set.Basic
import Mathlib.Algebra.Group.Submonoid.Membership
import Mathlib.GroupTheory.Congruence.Basic
import Mathlib.GroupTheory.FreeGroup.IsFreeGroup
import Mathlib.SetTheory.Cardinal.Basic
/-!
# The coproduct (a.k.a. the free product) of groups or monoids
Given an `ι`-indexed family `M` of monoids,
we define their coproduct (a.k.a. free product) `Monoid.CoprodI M`.
As usual, we use the suffix `I` for an indexed (co)product,
leaving `Coprod` for the coproduct of two monoids.
When `ι` and all `M i` have decidable equality,
the free product bijects with the type `Monoid.CoprodI.Word M` of reduced words.
This bijection is constructed
by defining an action of `Monoid.CoprodI M` on `Monoid.CoprodI.Word M`.
When `M i` are all groups, `Monoid.CoprodI M` is also a group
(and the coproduct in the category of groups).
## Main definitions
- `Monoid.CoprodI M`: the free product, defined as a quotient of a free monoid.
- `Monoid.CoprodI.of {i} : M i →* Monoid.CoprodI M`.
- `Monoid.CoprodI.lift : (∀ {i}, M i →* N) ≃ (Monoid.CoprodI M →* N)`: the universal property.
- `Monoid.CoprodI.Word M`: the type of reduced words.
- `Monoid.CoprodI.Word.equiv M : Monoid.CoprodI M ≃ word M`.
- `Monoid.CoprodI.NeWord M i j`: an inductive description of non-empty words
with first letter from `M i` and last letter from `M j`,
together with an API (`singleton`, `append`, `head`, `tail`, `to_word`, `Prod`, `inv`).
Used in the proof of the Ping-Pong-lemma.
- `Monoid.CoprodI.lift_injective_of_ping_pong`: The Ping-Pong-lemma,
proving injectivity of the `lift`. See the documentation of that theorem for more information.
## Remarks
There are many answers to the question "what is the coproduct of a family `M` of monoids?",
and they are all equivalent but not obviously equivalent.
We provide two answers.
The first, almost tautological answer is given by `Monoid.CoprodI M`,
which is a quotient of the type of words in the alphabet `Σ i, M i`.
It's straightforward to define and easy to prove its universal property.
But this answer is not completely satisfactory,
because it's difficult to tell when two elements `x y : Monoid.CoprodI M` are distinct
since `Monoid.CoprodI M` is defined as a quotient.
The second, maximally efficient answer is given by `Monoid.CoprodI.Word M`.
An element of `Monoid.CoprodI.Word M` is a word in the alphabet `Σ i, M i`,
where the letter `⟨i, 1⟩` doesn't occur and no adjacent letters share an index `i`.
Since we only work with reduced words, there is no need for quotienting,
and it is easy to tell when two elements are distinct.
However it's not obvious that this is even a monoid!
We prove that every element of `Monoid.CoprodI M` can be represented by a unique reduced word,
i.e. `Monoid.CoprodI M` and `Monoid.CoprodI.Word M` are equivalent types.
This means that `Monoid.CoprodI.Word M` can be given a monoid structure,
and it lets us tell when two elements of `Monoid.CoprodI M` are distinct.
There is also a completely tautological, maximally inefficient answer
given by `MonCat.Colimits.ColimitType`.
Whereas `Monoid.CoprodI M` at least ensures that
(any instance of) associativity holds by reflexivity,
in this answer associativity holds because of quotienting.
Yet another answer, which is constructively more satisfying,
could be obtained by showing that `Monoid.CoprodI.Rel` is confluent.
## References
[van der Waerden, *Free products of groups*][MR25465]
-/
open Set
variable {ι : Type*} (M : ι → Type*) [∀ i, Monoid (M i)]
/-- A relation on the free monoid on alphabet `Σ i, M i`,
relating `⟨i, 1⟩` with `1` and `⟨i, x⟩ * ⟨i, y⟩` with `⟨i, x * y⟩`. -/
inductive Monoid.CoprodI.Rel : FreeMonoid (Σ i, M i) → FreeMonoid (Σ i, M i) → Prop
| of_one (i : ι) : Monoid.CoprodI.Rel (FreeMonoid.of ⟨i, 1⟩) 1
| of_mul {i : ι} (x y : M i) :
Monoid.CoprodI.Rel (FreeMonoid.of ⟨i, x⟩ * FreeMonoid.of ⟨i, y⟩) (FreeMonoid.of ⟨i, x * y⟩)
/-- The free product (categorical coproduct) of an indexed family of monoids. -/
def Monoid.CoprodI : Type _ := (conGen (Monoid.CoprodI.Rel M)).Quotient
-- The `Monoid` instance should be constructed by a deriving handler.
-- https://github.com/leanprover-community/mathlib4/issues/380
instance : Monoid (Monoid.CoprodI M) := by
delta Monoid.CoprodI; infer_instance
instance : Inhabited (Monoid.CoprodI M) :=
⟨1⟩
namespace Monoid.CoprodI
/-- The type of reduced words. A reduced word cannot contain a letter `1`, and no two adjacent
letters can come from the same summand. -/
@[ext]
structure Word where
/-- A `Word` is a `List (Σ i, M i)`, such that `1` is not in the list, and no
two adjacent letters are from the same summand -/
toList : List (Σi, M i)
/-- A reduced word does not contain `1` -/
ne_one : ∀ l ∈ toList, Sigma.snd l ≠ 1
/-- Adjacent letters are not from the same summand. -/
chain_ne : toList.Chain' fun l l' => Sigma.fst l ≠ Sigma.fst l'
variable {M}
/-- The inclusion of a summand into the free product. -/
def of {i : ι} : M i →* CoprodI M where
toFun x := Con.mk' _ (FreeMonoid.of <| Sigma.mk i x)
map_one' := (Con.eq _).mpr (ConGen.Rel.of _ _ (CoprodI.Rel.of_one i))
map_mul' x y := Eq.symm <| (Con.eq _).mpr (ConGen.Rel.of _ _ (CoprodI.Rel.of_mul x y))
theorem of_apply {i} (m : M i) : of m = Con.mk' _ (FreeMonoid.of <| Sigma.mk i m) :=
rfl
variable {N : Type*} [Monoid N]
/-- See note [partially-applied ext lemmas]. -/
-- Porting note: higher `ext` priority
@[ext 1100]
theorem ext_hom (f g : CoprodI M →* N) (h : ∀ i, f.comp (of : M i →* _) = g.comp of) : f = g :=
(MonoidHom.cancel_right Con.mk'_surjective).mp <|
FreeMonoid.hom_eq fun ⟨i, x⟩ => by
rw [MonoidHom.comp_apply, MonoidHom.comp_apply, ← of_apply]
unfold CoprodI
rw [← MonoidHom.comp_apply, ← MonoidHom.comp_apply, h]
/-- A map out of the free product corresponds to a family of maps out of the summands. This is the
universal property of the free product, characterizing it as a categorical coproduct. -/
@[simps symm_apply]
def lift : (∀ i, M i →* N) ≃ (CoprodI M →* N) where
toFun fi :=
Con.lift _ (FreeMonoid.lift fun p : Σi, M i => fi p.fst p.snd) <|
Con.conGen_le <| by
simp_rw [Con.ker_rel]
rintro _ _ (i | ⟨x, y⟩) <;> simp
invFun f _ := f.comp of
left_inv := by
intro fi
ext i x
rfl
right_inv := by
intro f
ext i x
rfl
@[simp]
theorem lift_comp_of {N} [Monoid N] (fi : ∀ i, M i →* N) i : (lift fi).comp of = fi i :=
congr_fun (lift.symm_apply_apply fi) i
@[simp]
theorem lift_of {N} [Monoid N] (fi : ∀ i, M i →* N) {i} (m : M i) : lift fi (of m) = fi i m :=
DFunLike.congr_fun (lift_comp_of ..) m
@[simp]
theorem lift_comp_of' {N} [Monoid N] (f : CoprodI M →* N) :
lift (fun i ↦ f.comp (of (i := i))) = f :=
lift.apply_symm_apply f
@[simp]
theorem lift_of' : lift (fun i ↦ (of : M i →* CoprodI M)) = .id (CoprodI M) :=
lift_comp_of' (.id _)
theorem of_leftInverse [DecidableEq ι] (i : ι) :
Function.LeftInverse (lift <| Pi.mulSingle i (MonoidHom.id (M i))) of := fun x => by
simp only [lift_of, Pi.mulSingle_eq_same, MonoidHom.id_apply]
theorem of_injective (i : ι) : Function.Injective (of : M i →* _) := by
classical exact (of_leftInverse i).injective
theorem mrange_eq_iSup {N} [Monoid N] (f : ∀ i, M i →* N) :
MonoidHom.mrange (lift f) = ⨆ i, MonoidHom.mrange (f i) := by
rw [lift, Equiv.coe_fn_mk, Con.lift_range, FreeMonoid.mrange_lift,
range_sigma_eq_iUnion_range, Submonoid.closure_iUnion]
simp only [MonoidHom.mclosure_range]
theorem lift_mrange_le {N} [Monoid N] (f : ∀ i, M i →* N) {s : Submonoid N} :
MonoidHom.mrange (lift f) ≤ s ↔ ∀ i, MonoidHom.mrange (f i) ≤ s := by
simp [mrange_eq_iSup]
@[simp]
theorem iSup_mrange_of : ⨆ i, MonoidHom.mrange (of : M i →* CoprodI M) = ⊤ := by
simp [← mrange_eq_iSup]
@[simp]
theorem mclosure_iUnion_range_of :
Submonoid.closure (⋃ i, Set.range (of : M i →* CoprodI M)) = ⊤ := by
simp [Submonoid.closure_iUnion]
@[elab_as_elim]
theorem induction_left {motive : CoprodI M → Prop} (m : CoprodI M) (one : motive 1)
(mul : ∀ {i} (m : M i) x, motive x → motive (of m * x)) : motive m := by
induction m using Submonoid.induction_of_closure_eq_top_left mclosure_iUnion_range_of with
| one => exact one
| mul x hx y ihy =>
obtain ⟨i, m, rfl⟩ : ∃ (i : ι) (m : M i), of m = x := by simpa using hx
exact mul m y ihy
@[elab_as_elim]
theorem induction_on {motive : CoprodI M → Prop} (m : CoprodI M) (one : motive 1)
(of : ∀ (i) (m : M i), motive (of m))
(mul : ∀ x y, motive x → motive y → motive (x * y)) : motive m := by
induction m using CoprodI.induction_left with
| one => exact one
| mul m x hx => exact mul _ _ (of _ _) hx
section Group
variable (G : ι → Type*) [∀ i, Group (G i)]
instance : Inv (CoprodI G) where
inv :=
MulOpposite.unop ∘ lift fun i => (of : G i →* _).op.comp (MulEquiv.inv' (G i)).toMonoidHom
theorem inv_def (x : CoprodI G) :
x⁻¹ =
MulOpposite.unop
(lift (fun i => (of : G i →* _).op.comp (MulEquiv.inv' (G i)).toMonoidHom) x) :=
rfl
instance : Group (CoprodI G) :=
{ inv_mul_cancel := by
intro m
rw [inv_def]
induction m using CoprodI.induction_on with
| one => rw [MonoidHom.map_one, MulOpposite.unop_one, one_mul]
| of m ih =>
change of _⁻¹ * of _ = 1
rw [← of.map_mul, inv_mul_cancel, of.map_one]
| mul x y ihx ihy =>
rw [MonoidHom.map_mul, MulOpposite.unop_mul, mul_assoc, ← mul_assoc _ x y, ihx, one_mul,
ihy] }
theorem lift_range_le {N} [Group N] (f : ∀ i, G i →* N) {s : Subgroup N}
(h : ∀ i, (f i).range ≤ s) : (lift f).range ≤ s := by
rintro _ ⟨x, rfl⟩
induction x using CoprodI.induction_on with
| one => exact s.one_mem
| of i x =>
simp only [lift_of, SetLike.mem_coe]
exact h i (Set.mem_range_self x)
| mul x y hx hy =>
simp only [map_mul, SetLike.mem_coe]
exact s.mul_mem hx hy
theorem range_eq_iSup {N} [Group N] (f : ∀ i, G i →* N) : (lift f).range = ⨆ i, (f i).range := by
apply le_antisymm (lift_range_le _ f fun i => le_iSup (fun i => MonoidHom.range (f i)) i)
apply iSup_le _
rintro i _ ⟨x, rfl⟩
exact ⟨of x, by simp only [lift_of]⟩
end Group
namespace Word
/-- The empty reduced word. -/
@[simps]
def empty : Word M where
toList := []
ne_one := by simp
chain_ne := List.chain'_nil
instance : Inhabited (Word M) :=
⟨empty⟩
/-- A reduced word determines an element of the free product, given by multiplication. -/
def prod (w : Word M) : CoprodI M :=
List.prod (w.toList.map fun l => of l.snd)
@[simp]
theorem prod_empty : prod (empty : Word M) = 1 :=
rfl
/-- `fstIdx w` is `some i` if the first letter of `w` is `⟨i, m⟩` with `m : M i`. If `w` is empty
then it's `none`. -/
def fstIdx (w : Word M) : Option ι :=
w.toList.head?.map Sigma.fst
theorem fstIdx_ne_iff {w : Word M} {i} :
fstIdx w ≠ some i ↔ ∀ l ∈ w.toList.head?, i ≠ Sigma.fst l :=
not_iff_not.mp <| by simp [fstIdx]
variable (M)
/-- Given an index `i : ι`, `Pair M i` is the type of pairs `(head, tail)` where `head : M i` and
`tail : Word M`, subject to the constraint that first letter of `tail` can't be `⟨i, m⟩`.
By prepending `head` to `tail`, one obtains a new word. We'll show that any word can be uniquely
obtained in this way. -/
@[ext]
structure Pair (i : ι) where
/-- An element of `M i`, the first letter of the word. -/
head : M i
/-- The remaining letters of the word, excluding the first letter -/
tail : Word M
/-- The index first letter of tail of a `Pair M i` is not equal to `i` -/
fstIdx_ne : fstIdx tail ≠ some i
instance (i : ι) : Inhabited (Pair M i) :=
⟨⟨1, empty, by tauto⟩⟩
variable {M}
/-- Construct a new `Word` without any reduction. The underlying list of
`cons m w _ _` is `⟨_, m⟩::w` -/
@[simps]
def cons {i} (m : M i) (w : Word M) (hmw : w.fstIdx ≠ some i) (h1 : m ≠ 1) : Word M :=
{ toList := ⟨i, m⟩ :: w.toList,
ne_one := by
simp only [List.mem_cons]
rintro l (rfl | hl)
· exact h1
· exact w.ne_one l hl
chain_ne := w.chain_ne.cons' (fstIdx_ne_iff.mp hmw) }
@[simp]
theorem fstIdx_cons {i} (m : M i) (w : Word M) (hmw : w.fstIdx ≠ some i) (h1 : m ≠ 1) :
fstIdx (cons m w hmw h1) = some i := by simp [cons, fstIdx]
@[simp]
theorem prod_cons (i) (m : M i) (w : Word M) (h1 : m ≠ 1) (h2 : w.fstIdx ≠ some i) :
prod (cons m w h2 h1) = of m * prod w := by
simp [cons, prod, List.map_cons, List.prod_cons]
section
variable [∀ i, DecidableEq (M i)]
/-- Given a pair `(head, tail)`, we can form a word by prepending `head` to `tail`, except if `head`
is `1 : M i` then we have to just return `Word` since we need the result to be reduced. -/
def rcons {i} (p : Pair M i) : Word M :=
if h : p.head = 1 then p.tail
else cons p.head p.tail p.fstIdx_ne h
@[simp]
theorem prod_rcons {i} (p : Pair M i) : prod (rcons p) = of p.head * prod p.tail :=
if hm : p.head = 1 then by rw [rcons, dif_pos hm, hm, MonoidHom.map_one, one_mul]
else by rw [rcons, dif_neg hm, cons, prod, List.map_cons, List.prod_cons, prod]
theorem rcons_inj {i} : Function.Injective (rcons : Pair M i → Word M) := by
rintro ⟨m, w, h⟩ ⟨m', w', h'⟩ he
by_cases hm : m = 1 <;> by_cases hm' : m' = 1
· simp only [rcons, dif_pos hm, dif_pos hm'] at he
aesop
· exfalso
simp only [rcons, dif_pos hm, dif_neg hm'] at he
rw [he] at h
exact h rfl
· exfalso
simp only [rcons, dif_pos hm', dif_neg hm] at he
rw [← he] at h'
exact h' rfl
· have : m = m' ∧ w.toList = w'.toList := by
simpa [cons, rcons, dif_neg hm, dif_neg hm', eq_self_iff_true, Subtype.mk_eq_mk,
heq_iff_eq, ← Subtype.ext_iff_val] using he
rcases this with ⟨rfl, h⟩
congr
exact Word.ext h
theorem mem_rcons_iff {i j : ι} (p : Pair M i) (m : M j) :
⟨_, m⟩ ∈ (rcons p).toList ↔ ⟨_, m⟩ ∈ p.tail.toList ∨
m ≠ 1 ∧ (∃ h : i = j, m = h ▸ p.head) := by
simp only [rcons, cons, ne_eq]
by_cases hij : i = j
· subst i
by_cases hm : m = p.head
· subst m
split_ifs <;> simp_all
· split_ifs <;> simp_all
· split_ifs <;> simp_all [Ne.symm hij]
end
/-- Induct on a word by adding letters one at a time without reduction,
effectively inducting on the underlying `List`. -/
@[elab_as_elim]
def consRecOn {motive : Word M → Sort*} (w : Word M) (empty : motive empty)
(cons : ∀ (i) (m : M i) (w) h1 h2, motive w → motive (cons m w h1 h2)) :
motive w := by
rcases w with ⟨w, h1, h2⟩
induction w with
| nil => exact empty
| cons m w ih =>
refine cons m.1 m.2 ⟨w, fun _ hl => h1 _ (List.mem_cons_of_mem _ hl), h2.tail⟩ ?_ ?_ (ih _ _)
· rw [List.chain'_cons'] at h2
simp only [fstIdx, ne_eq, Option.map_eq_some_iff,
Sigma.exists, exists_and_right, exists_eq_right, not_exists]
intro m' hm'
exact h2.1 _ hm' rfl
· exact h1 _ List.mem_cons_self
@[simp]
theorem consRecOn_empty {motive : Word M → Sort*} (h_empty : motive empty)
(h_cons : ∀ (i) (m : M i) (w) h1 h2, motive w → motive (cons m w h1 h2)) :
consRecOn empty h_empty h_cons = h_empty := rfl
@[simp]
theorem consRecOn_cons {motive : Word M → Sort*} (i) (m : M i) (w : Word M) h1 h2
(h_empty : motive empty)
(h_cons : ∀ (i) (m : M i) (w) h1 h2, motive w → motive (cons m w h1 h2)) :
consRecOn (cons m w h1 h2) h_empty h_cons = h_cons i m w h1 h2
(consRecOn w h_empty h_cons) := rfl
variable [DecidableEq ι] [∀ i, DecidableEq (M i)]
-- This definition is computable but not very nice to look at. Thankfully we don't have to inspect
-- it, since `rcons` is known to be injective.
/-- Given `i : ι`, any reduced word can be decomposed into a pair `p` such that `w = rcons p`. -/
private def equivPairAux (i) (w : Word M) : { p : Pair M i // rcons p = w } :=
consRecOn w ⟨⟨1, .empty, by simp [fstIdx, empty]⟩, by simp [rcons]⟩ <|
fun j m w h1 h2 _ =>
if ij : i = j then
{ val :=
{ head := ij ▸ m
tail := w
fstIdx_ne := ij ▸ h1 }
property := by subst ij; simp [rcons, h2] }
else ⟨⟨1, cons m w h1 h2, by simp [cons, fstIdx, Ne.symm ij]⟩, by simp [rcons]⟩
/-- The equivalence between words and pairs. Given a word, it decomposes it as a pair by removing
the first letter if it comes from `M i`. Given a pair, it prepends the head to the tail. -/
def equivPair (i) : Word M ≃ Pair M i where
toFun w := (equivPairAux i w).val
invFun := rcons
left_inv w := (equivPairAux i w).property
right_inv _ := rcons_inj (equivPairAux i _).property
theorem equivPair_symm (i) (p : Pair M i) : (equivPair i).symm p = rcons p :=
rfl
theorem equivPair_eq_of_fstIdx_ne {i} {w : Word M} (h : fstIdx w ≠ some i) :
equivPair i w = ⟨1, w, h⟩ :=
(equivPair i).apply_eq_iff_eq_symm_apply.mpr <| Eq.symm (dif_pos rfl)
theorem mem_equivPair_tail_iff {i j : ι} {w : Word M} (m : M i) :
(⟨i, m⟩ ∈ (equivPair j w).tail.toList) ↔ ⟨i, m⟩ ∈ w.toList.tail
∨ i ≠ j ∧ ∃ h : w.toList ≠ [], w.toList.head h = ⟨i, m⟩ := by
simp only [equivPair, equivPairAux, ne_eq, Equiv.coe_fn_mk]
induction w using consRecOn with
| empty => simp
| cons k g tail h1 h2 ih =>
simp only [consRecOn_cons]
split_ifs with h
· subst k
by_cases hij : j = i <;> simp_all
· by_cases hik : i = k
· subst i; simp_all [@eq_comm _ m g, @eq_comm _ k j, or_comm]
· simp [hik, Ne.symm hik]
theorem mem_of_mem_equivPair_tail {i j : ι} {w : Word M} (m : M i) :
(⟨i, m⟩ ∈ (equivPair j w).tail.toList) → ⟨i, m⟩ ∈ w.toList := by
rw [mem_equivPair_tail_iff]
rintro (h | h)
· exact List.mem_of_mem_tail h
· revert h; cases w.toList <;> simp +contextual
theorem equivPair_head {i : ι} {w : Word M} :
(equivPair i w).head =
if h : ∃ (h : w.toList ≠ []), (w.toList.head h).1 = i
then h.snd ▸ (w.toList.head h.1).2
else 1 := by
simp only [equivPair, equivPairAux]
induction w using consRecOn with
| empty => simp
| cons head =>
by_cases hi : i = head
· subst hi; simp
· simp [hi, Ne.symm hi]
instance summandAction (i) : MulAction (M i) (Word M) where
smul m w := rcons { equivPair i w with head := m * (equivPair i w).head }
one_smul w := by
apply (equivPair i).symm_apply_eq.mpr
simp [equivPair]
mul_smul m m' w := by
dsimp [instHSMul]
simp [mul_assoc, ← equivPair_symm, Equiv.apply_symm_apply]
instance : MulAction (CoprodI M) (Word M) :=
MulAction.ofEndHom (lift fun _ => MulAction.toEndHom)
theorem smul_def {i} (m : M i) (w : Word M) :
m • w = rcons { equivPair i w with head := m * (equivPair i w).head } :=
rfl
theorem of_smul_def (i) (w : Word M) (m : M i) :
of m • w = rcons { equivPair i w with head := m * (equivPair i w).head } :=
rfl
theorem equivPair_smul_same {i} (m : M i) (w : Word M) :
equivPair i (of m • w) = ⟨m * (equivPair i w).head, (equivPair i w).tail,
(equivPair i w).fstIdx_ne⟩ := by
rw [of_smul_def, ← equivPair_symm]
simp
@[simp]
theorem equivPair_tail {i} (p : Pair M i) :
equivPair i p.tail = ⟨1, p.tail, p.fstIdx_ne⟩ :=
equivPair_eq_of_fstIdx_ne _
theorem smul_eq_of_smul {i} (m : M i) (w : Word M) :
m • w = of m • w := rfl
theorem mem_smul_iff {i j : ι} {m₁ : M i} {m₂ : M j} {w : Word M} :
⟨_, m₁⟩ ∈ (of m₂ • w).toList ↔
(¬i = j ∧ ⟨i, m₁⟩ ∈ w.toList)
∨ (m₁ ≠ 1 ∧ ∃ (hij : i = j),(⟨i, m₁⟩ ∈ w.toList.tail) ∨
(∃ m', ⟨j, m'⟩ ∈ w.toList.head? ∧ m₁ = hij ▸ (m₂ * m')) ∨
(w.fstIdx ≠ some j ∧ m₁ = hij ▸ m₂)) := by
rw [of_smul_def, mem_rcons_iff, mem_equivPair_tail_iff, equivPair_head, or_assoc]
by_cases hij : i = j
· subst i
simp only [not_true, ne_eq, false_and, exists_prop, true_and, false_or]
by_cases hw : ⟨j, m₁⟩ ∈ w.toList.tail
· simp [hw, show m₁ ≠ 1 from w.ne_one _ (List.mem_of_mem_tail hw)]
· simp only [hw, false_or, Option.mem_def, ne_eq, and_congr_right_iff]
intro hm1
split_ifs with h
· rcases h with ⟨hnil, rfl⟩
simp only [List.head?_eq_head hnil, Option.some.injEq, ne_eq]
constructor
· rintro rfl
exact Or.inl ⟨_, rfl, rfl⟩
· rintro (⟨_, h, rfl⟩ | hm')
· simp only [Sigma.ext_iff, heq_eq_eq, true_and] at h
subst h
rfl
· simp only [fstIdx, Option.map_eq_some_iff, Sigma.exists,
exists_and_right, exists_eq_right, not_exists, ne_eq] at hm'
exact (hm'.1 (w.toList.head hnil).2 (by rw [List.head?_eq_head])).elim
· revert h
rw [fstIdx]
cases w.toList
· simp
· simp +contextual [Sigma.ext_iff]
· rcases w with ⟨_ | _, _, _⟩ <;>
simp [or_comm, hij, Ne.symm hij]; rw [eq_comm]
theorem mem_smul_iff_of_ne {i j : ι} (hij : i ≠ j) {m₁ : M i} {m₂ : M j} {w : Word M} :
⟨_, m₁⟩ ∈ (of m₂ • w).toList ↔ ⟨i, m₁⟩ ∈ w.toList := by
simp [mem_smul_iff, *]
theorem cons_eq_smul {i} {m : M i} {ls h1 h2} :
cons m ls h1 h2 = of m • ls := by
rw [of_smul_def, equivPair_eq_of_fstIdx_ne _]
· simp [cons, rcons, h2]
· exact h1
theorem rcons_eq_smul {i} (p : Pair M i) :
rcons p = of p.head • p.tail := by
simp [of_smul_def]
@[simp]
theorem equivPair_head_smul_equivPair_tail {i : ι} (w : Word M) :
of (equivPair i w).head • (equivPair i w).tail = w := by
rw [← rcons_eq_smul, ← equivPair_symm, Equiv.symm_apply_apply]
theorem equivPair_tail_eq_inv_smul {G : ι → Type*} [∀ i, Group (G i)]
[∀ i, DecidableEq (G i)] {i} (w : Word G) :
(equivPair i w).tail = (of (equivPair i w).head)⁻¹ • w :=
Eq.symm <| inv_smul_eq_iff.2 (equivPair_head_smul_equivPair_tail w).symm
@[elab_as_elim]
theorem smul_induction {motive : Word M → Prop} (empty : motive empty)
(smul : ∀ (i) (m : M i) (w), motive w → motive (of m • w)) (w : Word M) : motive w := by
induction w using consRecOn with
| empty => exact empty
| cons _ _ _ _ _ ih =>
rw [cons_eq_smul]
exact smul _ _ _ ih
@[simp]
theorem prod_smul (m) : ∀ w : Word M, prod (m • w) = m * prod w := by
induction m using CoprodI.induction_on with
| one =>
intro
rw [one_smul, one_mul]
| of _ =>
intros
rw [of_smul_def, prod_rcons, of.map_mul, mul_assoc, ← prod_rcons, ← equivPair_symm,
Equiv.symm_apply_apply]
| mul x y hx hy =>
intro w
rw [mul_smul, hx, hy, mul_assoc]
/-- Each element of the free product corresponds to a unique reduced word. -/
def equiv : CoprodI M ≃ Word M where
toFun m := m • empty
| invFun w := prod w
left_inv m := by dsimp only; rw [prod_smul, prod_empty, mul_one]
right_inv := by
| Mathlib/GroupTheory/CoprodI.lean | 600 | 602 |
/-
Copyright (c) 2023 Yaël Dillies, Christopher Hoskin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yaël Dillies, Christopher Hoskin
-/
import Mathlib.Data.Finset.Lattice.Prod
import Mathlib.Data.Finset.Powerset
import Mathlib.Data.Set.Finite.Basic
import Mathlib.Order.Closure
import Mathlib.Order.ConditionallyCompleteLattice.Finset
/-!
# Sets closed under join/meet
This file defines predicates for sets closed under `⊔` and shows that each set in a join-semilattice
generates a join-closed set and that a semilattice where every directed set has a least upper bound
is automatically complete. All dually for `⊓`.
## Main declarations
* `SupClosed`: Predicate for a set to be closed under join (`a ∈ s` and `b ∈ s` imply `a ⊔ b ∈ s`).
* `InfClosed`: Predicate for a set to be closed under meet (`a ∈ s` and `b ∈ s` imply `a ⊓ b ∈ s`).
* `IsSublattice`: Predicate for a set to be closed under meet and join.
* `supClosure`: Sup-closure. Smallest sup-closed set containing a given set.
* `infClosure`: Inf-closure. Smallest inf-closed set containing a given set.
* `latticeClosure`: Smallest sublattice containing a given set.
* `SemilatticeSup.toCompleteSemilatticeSup`: A join-semilattice where every sup-closed set has a
least upper bound is automatically complete.
* `SemilatticeInf.toCompleteSemilatticeInf`: A meet-semilattice where every inf-closed set has a
greatest lower bound is automatically complete.
-/
variable {ι : Sort*} {F α β : Type*}
section SemilatticeSup
variable [SemilatticeSup α] [SemilatticeSup β]
section Set
variable {ι : Sort*} {S : Set (Set α)} {f : ι → Set α} {s t : Set α} {a : α}
open Set
/-- A set `s` is *sup-closed* if `a ⊔ b ∈ s` for all `a ∈ s`, `b ∈ s`. -/
def SupClosed (s : Set α) : Prop := ∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → a ⊔ b ∈ s
@[simp] lemma supClosed_empty : SupClosed (∅ : Set α) := by simp [SupClosed]
@[simp] lemma supClosed_singleton : SupClosed ({a} : Set α) := by simp [SupClosed]
@[simp] lemma supClosed_univ : SupClosed (univ : Set α) := by simp [SupClosed]
lemma SupClosed.inter (hs : SupClosed s) (ht : SupClosed t) : SupClosed (s ∩ t) :=
fun _a ha _b hb ↦ ⟨hs ha.1 hb.1, ht ha.2 hb.2⟩
lemma supClosed_sInter (hS : ∀ s ∈ S, SupClosed s) : SupClosed (⋂₀ S) :=
fun _a ha _b hb _s hs ↦ hS _ hs (ha _ hs) (hb _ hs)
lemma supClosed_iInter (hf : ∀ i, SupClosed (f i)) : SupClosed (⋂ i, f i) :=
supClosed_sInter <| forall_mem_range.2 hf
lemma SupClosed.directedOn (hs : SupClosed s) : DirectedOn (· ≤ ·) s :=
fun _a ha _b hb ↦ ⟨_, hs ha hb, le_sup_left, le_sup_right⟩
lemma IsUpperSet.supClosed (hs : IsUpperSet s) : SupClosed s := fun _a _ _b ↦ hs le_sup_right
lemma SupClosed.preimage [FunLike F β α] [SupHomClass F β α] (hs : SupClosed s) (f : F) :
SupClosed (f ⁻¹' s) :=
fun a ha b hb ↦ by simpa [map_sup] using hs ha hb
lemma SupClosed.image [FunLike F α β] [SupHomClass F α β] (hs : SupClosed s) (f : F) :
SupClosed (f '' s) := by
rintro _ ⟨a, ha, rfl⟩ _ ⟨b, hb, rfl⟩
rw [← map_sup]
exact Set.mem_image_of_mem _ <| hs ha hb
lemma supClosed_range [FunLike F α β] [SupHomClass F α β] (f : F) : SupClosed (Set.range f) := by
simpa using supClosed_univ.image f
lemma SupClosed.prod {t : Set β} (hs : SupClosed s) (ht : SupClosed t) : SupClosed (s ×ˢ t) :=
fun _a ha _b hb ↦ ⟨hs ha.1 hb.1, ht ha.2 hb.2⟩
lemma supClosed_pi {ι : Type*} {α : ι → Type*} [∀ i, SemilatticeSup (α i)] {s : Set ι}
{t : ∀ i, Set (α i)} (ht : ∀ i ∈ s, SupClosed (t i)) : SupClosed (s.pi t) :=
fun _a ha _b hb _i hi ↦ ht _ hi (ha _ hi) (hb _ hi)
lemma SupClosed.insert_upperBounds {s : Set α} {a : α} (hs : SupClosed s) (ha : a ∈ upperBounds s) :
SupClosed (insert a s) := by
rw [SupClosed]
aesop
lemma SupClosed.insert_lowerBounds {s : Set α} {a : α} (h : SupClosed s) (ha : a ∈ lowerBounds s) :
SupClosed (insert a s) := by
rw [SupClosed]
have ha' : ∀ b ∈ s, a ≤ b := fun _ a ↦ ha a
aesop
end Set
section Finset
variable {ι : Type*} {f : ι → α} {s : Set α} {t : Finset ι} {a : α}
open Finset
lemma SupClosed.finsetSup'_mem (hs : SupClosed s) (ht : t.Nonempty) :
(∀ i ∈ t, f i ∈ s) → t.sup' ht f ∈ s :=
sup'_induction _ _ hs
lemma SupClosed.finsetSup_mem [OrderBot α] (hs : SupClosed s) (ht : t.Nonempty) :
(∀ i ∈ t, f i ∈ s) → t.sup f ∈ s :=
sup'_eq_sup ht f ▸ hs.finsetSup'_mem ht
end Finset
end SemilatticeSup
section SemilatticeInf
variable [SemilatticeInf α] [SemilatticeInf β]
section Set
variable {ι : Sort*} {S : Set (Set α)} {f : ι → Set α} {s t : Set α} {a : α}
open Set
/-- A set `s` is *inf-closed* if `a ⊓ b ∈ s` for all `a ∈ s`, `b ∈ s`. -/
def InfClosed (s : Set α) : Prop := ∀ ⦃a⦄, a ∈ s → ∀ ⦃b⦄, b ∈ s → a ⊓ b ∈ s
@[simp] lemma infClosed_empty : InfClosed (∅ : Set α) := by simp [InfClosed]
@[simp] lemma infClosed_singleton : InfClosed ({a} : Set α) := by simp [InfClosed]
@[simp] lemma infClosed_univ : InfClosed (univ : Set α) := by simp [InfClosed]
lemma InfClosed.inter (hs : InfClosed s) (ht : InfClosed t) : InfClosed (s ∩ t) :=
fun _a ha _b hb ↦ ⟨hs ha.1 hb.1, ht ha.2 hb.2⟩
lemma infClosed_sInter (hS : ∀ s ∈ S, InfClosed s) : InfClosed (⋂₀ S) :=
fun _a ha _b hb _s hs ↦ hS _ hs (ha _ hs) (hb _ hs)
lemma infClosed_iInter (hf : ∀ i, InfClosed (f i)) : InfClosed (⋂ i, f i) :=
infClosed_sInter <| forall_mem_range.2 hf
lemma InfClosed.codirectedOn (hs : InfClosed s) : DirectedOn (· ≥ ·) s :=
fun _a ha _b hb ↦ ⟨_, hs ha hb, inf_le_left, inf_le_right⟩
lemma IsLowerSet.infClosed (hs : IsLowerSet s) : InfClosed s := fun _a _ _b ↦ hs inf_le_right
lemma InfClosed.preimage [FunLike F β α] [InfHomClass F β α] (hs : InfClosed s) (f : F) :
InfClosed (f ⁻¹' s) :=
fun a ha b hb ↦ by simpa [map_inf] using hs ha hb
lemma InfClosed.image [FunLike F α β] [InfHomClass F α β] (hs : InfClosed s) (f : F) :
InfClosed (f '' s) := by
rintro _ ⟨a, ha, rfl⟩ _ ⟨b, hb, rfl⟩
rw [← map_inf]
exact Set.mem_image_of_mem _ <| hs ha hb
lemma infClosed_range [FunLike F α β] [InfHomClass F α β] (f : F) : InfClosed (Set.range f) := by
simpa using infClosed_univ.image f
lemma InfClosed.prod {t : Set β} (hs : InfClosed s) (ht : InfClosed t) : InfClosed (s ×ˢ t) :=
fun _a ha _b hb ↦ ⟨hs ha.1 hb.1, ht ha.2 hb.2⟩
lemma infClosed_pi {ι : Type*} {α : ι → Type*} [∀ i, SemilatticeInf (α i)] {s : Set ι}
{t : ∀ i, Set (α i)} (ht : ∀ i ∈ s, InfClosed (t i)) : InfClosed (s.pi t) :=
fun _a ha _b hb _i hi ↦ ht _ hi (ha _ hi) (hb _ hi)
lemma InfClosed.insert_upperBounds {s : Set α} {a : α} (hs : InfClosed s) (ha : a ∈ upperBounds s) :
InfClosed (insert a s) := by
rw [InfClosed]
have ha' : ∀ b ∈ s, b ≤ a := fun _ a ↦ ha a
aesop
lemma InfClosed.insert_lowerBounds {s : Set α} {a : α} (h : InfClosed s) (ha : a ∈ lowerBounds s) :
InfClosed (insert a s) := by
rw [InfClosed]
aesop
end Set
section Finset
variable {ι : Type*} {f : ι → α} {s : Set α} {t : Finset ι} {a : α}
open Finset
lemma InfClosed.finsetInf'_mem (hs : InfClosed s) (ht : t.Nonempty) :
(∀ i ∈ t, f i ∈ s) → t.inf' ht f ∈ s :=
inf'_induction _ _ hs
lemma InfClosed.finsetInf_mem [OrderTop α] (hs : InfClosed s) (ht : t.Nonempty) :
(∀ i ∈ t, f i ∈ s) → t.inf f ∈ s :=
inf'_eq_inf ht f ▸ hs.finsetInf'_mem ht
end Finset
end SemilatticeInf
open Finset OrderDual
section Lattice
variable {ι : Sort*} [Lattice α] [Lattice β] {S : Set (Set α)} {f : ι → Set α} {s t : Set α} {a : α}
open Set
/-- A set `s` is a *sublattice* if `a ⊔ b ∈ s` and `a ⊓ b ∈ s` for all `a ∈ s`, `b ∈ s`.
Note: This is not the preferred way to declare a sublattice. One should instead use `Sublattice`.
TODO: Define `Sublattice`. -/
structure IsSublattice (s : Set α) : Prop where
supClosed : SupClosed s
infClosed : InfClosed s
@[simp] lemma isSublattice_empty : IsSublattice (∅ : Set α) := ⟨supClosed_empty, infClosed_empty⟩
@[simp] lemma isSublattice_singleton : IsSublattice ({a} : Set α) :=
⟨supClosed_singleton, infClosed_singleton⟩
@[simp] lemma isSublattice_univ : IsSublattice (Set.univ : Set α) :=
⟨supClosed_univ, infClosed_univ⟩
lemma IsSublattice.inter (hs : IsSublattice s) (ht : IsSublattice t) : IsSublattice (s ∩ t) :=
⟨hs.1.inter ht.1, hs.2.inter ht.2⟩
lemma isSublattice_sInter (hS : ∀ s ∈ S, IsSublattice s) : IsSublattice (⋂₀ S) :=
⟨supClosed_sInter fun _s hs ↦ (hS _ hs).1, infClosed_sInter fun _s hs ↦ (hS _ hs).2⟩
lemma isSublattice_iInter (hf : ∀ i, IsSublattice (f i)) : IsSublattice (⋂ i, f i) :=
⟨supClosed_iInter fun _i ↦ (hf _).1, infClosed_iInter fun _i ↦ (hf _).2⟩
lemma IsSublattice.preimage [FunLike F β α] [LatticeHomClass F β α]
(hs : IsSublattice s) (f : F) :
IsSublattice (f ⁻¹' s) := ⟨hs.1.preimage _, hs.2.preimage _⟩
lemma IsSublattice.image [FunLike F α β] [LatticeHomClass F α β] (hs : IsSublattice s) (f : F) :
IsSublattice (f '' s) := ⟨hs.1.image _, hs.2.image _⟩
lemma IsSublattice_range [FunLike F α β] [LatticeHomClass F α β] (f : F) :
IsSublattice (Set.range f) :=
⟨supClosed_range _, infClosed_range _⟩
lemma IsSublattice.prod {t : Set β} (hs : IsSublattice s) (ht : IsSublattice t) :
IsSublattice (s ×ˢ t) := ⟨hs.1.prod ht.1, hs.2.prod ht.2⟩
lemma isSublattice_pi {ι : Type*} {α : ι → Type*} [∀ i, Lattice (α i)] {s : Set ι}
{t : ∀ i, Set (α i)} (ht : ∀ i ∈ s, IsSublattice (t i)) : IsSublattice (s.pi t) :=
⟨supClosed_pi fun _i hi ↦ (ht _ hi).1, infClosed_pi fun _i hi ↦ (ht _ hi).2⟩
@[simp] lemma supClosed_preimage_toDual {s : Set αᵒᵈ} :
SupClosed (toDual ⁻¹' s) ↔ InfClosed s := Iff.rfl
@[simp] lemma infClosed_preimage_toDual {s : Set αᵒᵈ} :
InfClosed (toDual ⁻¹' s) ↔ SupClosed s := Iff.rfl
@[simp] lemma supClosed_preimage_ofDual {s : Set α} :
SupClosed (ofDual ⁻¹' s) ↔ InfClosed s := Iff.rfl
@[simp] lemma infClosed_preimage_ofDual {s : Set α} :
InfClosed (ofDual ⁻¹' s) ↔ SupClosed s := Iff.rfl
@[simp] lemma isSublattice_preimage_toDual {s : Set αᵒᵈ} :
IsSublattice (toDual ⁻¹' s) ↔ IsSublattice s := ⟨fun h ↦ ⟨h.2, h.1⟩, fun h ↦ ⟨h.2, h.1⟩⟩
@[simp] lemma isSublattice_preimage_ofDual :
IsSublattice (ofDual ⁻¹' s) ↔ IsSublattice s := ⟨fun h ↦ ⟨h.2, h.1⟩, fun h ↦ ⟨h.2, h.1⟩⟩
alias ⟨_, InfClosed.dual⟩ := supClosed_preimage_ofDual
alias ⟨_, SupClosed.dual⟩ := infClosed_preimage_ofDual
alias ⟨_, IsSublattice.dual⟩ := isSublattice_preimage_ofDual
alias ⟨_, IsSublattice.of_dual⟩ := isSublattice_preimage_toDual
end Lattice
section LinearOrder
variable [LinearOrder α]
@[simp] protected lemma LinearOrder.supClosed (s : Set α) : SupClosed s :=
fun a ha b hb ↦ by cases le_total a b <;> simp [*]
@[simp] protected lemma LinearOrder.infClosed (s : Set α) : InfClosed s :=
fun a ha b hb ↦ by cases le_total a b <;> simp [*]
@[simp] protected lemma LinearOrder.isSublattice (s : Set α) : IsSublattice s :=
⟨LinearOrder.supClosed _, LinearOrder.infClosed _⟩
end LinearOrder
/-! ## Closure -/
open Finset
section SemilatticeSup
variable [SemilatticeSup α] [SemilatticeSup β] {s t : Set α} {a b : α}
/-- Every set in a join-semilattice generates a set closed under join. -/
@[simps! isClosed]
def supClosure : ClosureOperator (Set α) := .ofPred
(fun s ↦ {a | ∃ (t : Finset α) (ht : t.Nonempty), ↑t ⊆ s ∧ t.sup' ht id = a})
SupClosed
(fun s a ha ↦ ⟨{a}, singleton_nonempty _, by simpa⟩)
(by
classical
rintro s _ ⟨t, ht, hts, rfl⟩ _ ⟨u, hu, hus, rfl⟩
refine ⟨_, ht.mono subset_union_left, ?_, sup'_union ht hu _⟩
rw [coe_union]
exact Set.union_subset hts hus)
(by rintro s₁ s₂ hs h₂ _ ⟨t, ht, hts, rfl⟩; exact h₂.finsetSup'_mem ht fun i hi ↦ hs <| hts hi)
@[simp] lemma subset_supClosure {s : Set α} : s ⊆ supClosure s := supClosure.le_closure _
@[simp] lemma supClosed_supClosure : SupClosed (supClosure s) := supClosure.isClosed_closure _
lemma supClosure_mono : Monotone (supClosure : Set α → Set α) := supClosure.monotone
@[simp] lemma supClosure_eq_self : supClosure s = s ↔ SupClosed s := supClosure.isClosed_iff.symm
alias ⟨_, SupClosed.supClosure_eq⟩ := supClosure_eq_self
lemma supClosure_idem (s : Set α) : supClosure (supClosure s) = supClosure s :=
supClosure.idempotent _
@[simp] lemma supClosure_empty : supClosure (∅ : Set α) = ∅ := by simp
@[simp] lemma supClosure_singleton : supClosure {a} = {a} := by simp
@[simp] lemma supClosure_univ : supClosure (Set.univ : Set α) = Set.univ := by simp
@[simp] lemma upperBounds_supClosure (s : Set α) : upperBounds (supClosure s) = upperBounds s :=
(upperBounds_mono_set subset_supClosure).antisymm <| by
rintro a ha _ ⟨t, ht, hts, rfl⟩
exact sup'_le _ _ fun b hb ↦ ha <| hts hb
@[simp] lemma isLUB_supClosure : IsLUB (supClosure s) a ↔ IsLUB s a := by simp [IsLUB]
lemma sup_mem_supClosure (ha : a ∈ s) (hb : b ∈ s) : a ⊔ b ∈ supClosure s :=
supClosed_supClosure (subset_supClosure ha) (subset_supClosure hb)
lemma finsetSup'_mem_supClosure {ι : Type*} {t : Finset ι} (ht : t.Nonempty) {f : ι → α}
(hf : ∀ i ∈ t, f i ∈ s) : t.sup' ht f ∈ supClosure s :=
supClosed_supClosure.finsetSup'_mem _ fun _i hi ↦ subset_supClosure <| hf _ hi
lemma supClosure_min : s ⊆ t → SupClosed t → supClosure s ⊆ t := supClosure.closure_min
/-- The semilatice generated by a finite set is finite. -/
protected lemma Set.Finite.supClosure (hs : s.Finite) : (supClosure s).Finite := by
lift s to Finset α using hs
classical
refine ({t ∈ s.powerset | t.Nonempty}.attach.image
fun t ↦ t.1.sup' (mem_filter.1 t.2).2 id).finite_toSet.subset ?_
rintro _ ⟨t, ht, hts, rfl⟩
simp only [id_eq, coe_image, mem_image, mem_coe, mem_attach, true_and, Subtype.exists,
Finset.mem_powerset, Finset.not_nonempty_iff_eq_empty, mem_filter]
exact ⟨t, ⟨hts, ht⟩, rfl⟩
@[simp] lemma supClosure_prod (s : Set α) (t : Set β) :
supClosure (s ×ˢ t) = supClosure s ×ˢ supClosure t :=
le_antisymm (supClosure_min (Set.prod_mono subset_supClosure subset_supClosure) <|
supClosed_supClosure.prod supClosed_supClosure) <| by
rintro ⟨_, _⟩ ⟨⟨u, hu, hus, rfl⟩, v, hv, hvt, rfl⟩
refine ⟨u ×ˢ v, hu.product hv, ?_, ?_⟩
· simpa only [coe_product] using Set.prod_mono hus hvt
· simp [prodMk_sup'_sup']
end SemilatticeSup
section SemilatticeInf
| variable [SemilatticeInf α] [SemilatticeInf β] {s t : Set α} {a b : α}
| Mathlib/Order/SupClosed.lean | 351 | 351 |
/-
Copyright (c) 2022 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers, Heather Macbeth
-/
import Mathlib.Analysis.InnerProductSpace.TwoDim
import Mathlib.Geometry.Euclidean.Angle.Unoriented.Basic
/-!
# Oriented angles.
This file defines oriented angles in real inner product spaces.
## Main definitions
* `Orientation.oangle` is the oriented angle between two vectors with respect to an orientation.
## Implementation notes
The definitions here use the `Real.angle` type, angles modulo `2 * π`. For some purposes,
angles modulo `π` are more convenient, because results are true for such angles with less
configuration dependence. Results that are only equalities modulo `π` can be represented
modulo `2 * π` as equalities of `(2 : ℤ) • θ`.
## References
* Evan Chen, Euclidean Geometry in Mathematical Olympiads.
-/
noncomputable section
open Module Complex
open scoped Real RealInnerProductSpace ComplexConjugate
namespace Orientation
attribute [local instance] Complex.finrank_real_complex_fact
variable {V V' : Type*}
variable [NormedAddCommGroup V] [NormedAddCommGroup V']
variable [InnerProductSpace ℝ V] [InnerProductSpace ℝ V']
variable [Fact (finrank ℝ V = 2)] [Fact (finrank ℝ V' = 2)] (o : Orientation ℝ V (Fin 2))
local notation "ω" => o.areaForm
/-- The oriented angle from `x` to `y`, modulo `2 * π`. If either vector is 0, this is 0.
See `InnerProductGeometry.angle` for the corresponding unoriented angle definition. -/
def oangle (x y : V) : Real.Angle :=
Complex.arg (o.kahler x y)
/-- Oriented angles are continuous when the vectors involved are nonzero. -/
@[fun_prop]
theorem continuousAt_oangle {x : V × V} (hx1 : x.1 ≠ 0) (hx2 : x.2 ≠ 0) :
ContinuousAt (fun y : V × V => o.oangle y.1 y.2) x := by
refine (Complex.continuousAt_arg_coe_angle ?_).comp ?_
· exact o.kahler_ne_zero hx1 hx2
exact ((continuous_ofReal.comp continuous_inner).add
((continuous_ofReal.comp o.areaForm'.continuous₂).mul continuous_const)).continuousAt
/-- If the first vector passed to `oangle` is 0, the result is 0. -/
@[simp]
theorem oangle_zero_left (x : V) : o.oangle 0 x = 0 := by simp [oangle]
/-- If the second vector passed to `oangle` is 0, the result is 0. -/
@[simp]
theorem oangle_zero_right (x : V) : o.oangle x 0 = 0 := by simp [oangle]
/-- If the two vectors passed to `oangle` are the same, the result is 0. -/
@[simp]
theorem oangle_self (x : V) : o.oangle x x = 0 := by
rw [oangle, kahler_apply_self, ← ofReal_pow]
convert QuotientAddGroup.mk_zero (AddSubgroup.zmultiples (2 * π))
apply arg_ofReal_of_nonneg
positivity
/-- If the angle between two vectors is nonzero, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : x ≠ 0 := by
rintro rfl; simp at h
/-- If the angle between two vectors is nonzero, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : y ≠ 0 := by
rintro rfl; simp at h
/-- If the angle between two vectors is nonzero, the vectors are not equal. -/
theorem ne_of_oangle_ne_zero {x y : V} (h : o.oangle x y ≠ 0) : x ≠ y := by
rintro rfl; simp at h
/-- If the angle between two vectors is `π`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π`, the vectors are not equal. -/
theorem ne_of_oangle_eq_pi {x y : V} (h : o.oangle x y = π) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `π / 2`, the vectors are not equal. -/
theorem ne_of_oangle_eq_pi_div_two {x y : V} (h : o.oangle x y = (π / 2 : ℝ)) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) :
y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the angle between two vectors is `-π / 2`, the vectors are not equal. -/
theorem ne_of_oangle_eq_neg_pi_div_two {x y : V} (h : o.oangle x y = (-π / 2 : ℝ)) : x ≠ y :=
o.ne_of_oangle_ne_zero (h.symm ▸ Real.Angle.neg_pi_div_two_ne_zero : o.oangle x y ≠ 0)
/-- If the sign of the angle between two vectors is nonzero, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : x ≠ 0 :=
o.left_ne_zero_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is nonzero, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : y ≠ 0 :=
o.right_ne_zero_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is nonzero, the vectors are not equal. -/
theorem ne_of_oangle_sign_ne_zero {x y : V} (h : (o.oangle x y).sign ≠ 0) : x ≠ y :=
o.ne_of_oangle_ne_zero (Real.Angle.sign_ne_zero_iff.1 h).1
/-- If the sign of the angle between two vectors is positive, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : x ≠ 0 :=
o.left_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is positive, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : y ≠ 0 :=
o.right_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is positive, the vectors are not equal. -/
theorem ne_of_oangle_sign_eq_one {x y : V} (h : (o.oangle x y).sign = 1) : x ≠ y :=
o.ne_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the first vector is nonzero. -/
theorem left_ne_zero_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : x ≠ 0 :=
o.left_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the second vector is nonzero. -/
theorem right_ne_zero_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : y ≠ 0 :=
o.right_ne_zero_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- If the sign of the angle between two vectors is negative, the vectors are not equal. -/
theorem ne_of_oangle_sign_eq_neg_one {x y : V} (h : (o.oangle x y).sign = -1) : x ≠ y :=
o.ne_of_oangle_sign_ne_zero (h.symm ▸ by decide : (o.oangle x y).sign ≠ 0)
/-- Swapping the two vectors passed to `oangle` negates the angle. -/
theorem oangle_rev (x y : V) : o.oangle y x = -o.oangle x y := by
simp only [oangle, o.kahler_swap y x, Complex.arg_conj_coe_angle]
/-- Adding the angles between two vectors in each order results in 0. -/
@[simp]
theorem oangle_add_oangle_rev (x y : V) : o.oangle x y + o.oangle y x = 0 := by
simp [o.oangle_rev y x]
/-- Negating the first vector passed to `oangle` adds `π` to the angle. -/
theorem oangle_neg_left {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle (-x) y = o.oangle x y + π := by
simp only [oangle, map_neg]
convert Complex.arg_neg_coe_angle _
exact o.kahler_ne_zero hx hy
/-- Negating the second vector passed to `oangle` adds `π` to the angle. -/
theorem oangle_neg_right {x y : V} (hx : x ≠ 0) (hy : y ≠ 0) :
o.oangle x (-y) = o.oangle x y + π := by
simp only [oangle, map_neg]
convert Complex.arg_neg_coe_angle _
exact o.kahler_ne_zero hx hy
/-- Negating the first vector passed to `oangle` does not change twice the angle. -/
@[simp]
theorem two_zsmul_oangle_neg_left (x y : V) :
(2 : ℤ) • o.oangle (-x) y = (2 : ℤ) • o.oangle x y := by
by_cases hx : x = 0
· simp [hx]
· by_cases hy : y = 0
· simp [hy]
· simp [o.oangle_neg_left hx hy]
/-- Negating the second vector passed to `oangle` does not change twice the angle. -/
@[simp]
theorem two_zsmul_oangle_neg_right (x y : V) :
(2 : ℤ) • o.oangle x (-y) = (2 : ℤ) • o.oangle x y := by
by_cases hx : x = 0
· simp [hx]
· by_cases hy : y = 0
· simp [hy]
· simp [o.oangle_neg_right hx hy]
/-- Negating both vectors passed to `oangle` does not change the angle. -/
@[simp]
theorem oangle_neg_neg (x y : V) : o.oangle (-x) (-y) = o.oangle x y := by simp [oangle]
/-- Negating the first vector produces the same angle as negating the second vector. -/
theorem oangle_neg_left_eq_neg_right (x y : V) : o.oangle (-x) y = o.oangle x (-y) := by
rw [← neg_neg y, oangle_neg_neg, neg_neg]
/-- The angle between the negation of a nonzero vector and that vector is `π`. -/
@[simp]
theorem oangle_neg_self_left {x : V} (hx : x ≠ 0) : o.oangle (-x) x = π := by
simp [oangle_neg_left, hx]
/-- The angle between a nonzero vector and its negation is `π`. -/
@[simp]
theorem oangle_neg_self_right {x : V} (hx : x ≠ 0) : o.oangle x (-x) = π := by
simp [oangle_neg_right, hx]
/-- Twice the angle between the negation of a vector and that vector is 0. -/
theorem two_zsmul_oangle_neg_self_left (x : V) : (2 : ℤ) • o.oangle (-x) x = 0 := by
by_cases hx : x = 0 <;> simp [hx]
/-- Twice the angle between a vector and its negation is 0. -/
theorem two_zsmul_oangle_neg_self_right (x : V) : (2 : ℤ) • o.oangle x (-x) = 0 := by
by_cases hx : x = 0 <;> simp [hx]
/-- Adding the angles between two vectors in each order, with the first vector in each angle
negated, results in 0. -/
@[simp]
theorem oangle_add_oangle_rev_neg_left (x y : V) : o.oangle (-x) y + o.oangle (-y) x = 0 := by
rw [oangle_neg_left_eq_neg_right, oangle_rev, neg_add_cancel]
/-- Adding the angles between two vectors in each order, with the second vector in each angle
negated, results in 0. -/
@[simp]
theorem oangle_add_oangle_rev_neg_right (x y : V) : o.oangle x (-y) + o.oangle y (-x) = 0 := by
rw [o.oangle_rev (-x), oangle_neg_left_eq_neg_right, add_neg_cancel]
/-- Multiplying the first vector passed to `oangle` by a positive real does not change the
angle. -/
@[simp]
theorem oangle_smul_left_of_pos (x y : V) {r : ℝ} (hr : 0 < r) :
o.oangle (r • x) y = o.oangle x y := by simp [oangle, Complex.arg_real_mul _ hr]
/-- Multiplying the second vector passed to `oangle` by a positive real does not change the
angle. -/
@[simp]
theorem oangle_smul_right_of_pos (x y : V) {r : ℝ} (hr : 0 < r) :
o.oangle x (r • y) = o.oangle x y := by simp [oangle, Complex.arg_real_mul _ hr]
/-- Multiplying the first vector passed to `oangle` by a negative real produces the same angle
as negating that vector. -/
@[simp]
theorem oangle_smul_left_of_neg (x y : V) {r : ℝ} (hr : r < 0) :
o.oangle (r • x) y = o.oangle (-x) y := by
rw [← neg_neg r, neg_smul, ← smul_neg, o.oangle_smul_left_of_pos _ _ (neg_pos_of_neg hr)]
/-- Multiplying the second vector passed to `oangle` by a negative real produces the same angle
as negating that vector. -/
@[simp]
theorem oangle_smul_right_of_neg (x y : V) {r : ℝ} (hr : r < 0) :
o.oangle x (r • y) = o.oangle x (-y) := by
rw [← neg_neg r, neg_smul, ← smul_neg, o.oangle_smul_right_of_pos _ _ (neg_pos_of_neg hr)]
/-- The angle between a nonnegative multiple of a vector and that vector is 0. -/
@[simp]
theorem oangle_smul_left_self_of_nonneg (x : V) {r : ℝ} (hr : 0 ≤ r) : o.oangle (r • x) x = 0 := by
rcases hr.lt_or_eq with (h | h)
· simp [h]
· simp [h.symm]
/-- The angle between a vector and a nonnegative multiple of that vector is 0. -/
@[simp]
theorem oangle_smul_right_self_of_nonneg (x : V) {r : ℝ} (hr : 0 ≤ r) : o.oangle x (r • x) = 0 := by
rcases hr.lt_or_eq with (h | h)
· simp [h]
· simp [h.symm]
/-- The angle between two nonnegative multiples of the same vector is 0. -/
@[simp]
theorem oangle_smul_smul_self_of_nonneg (x : V) {r₁ r₂ : ℝ} (hr₁ : 0 ≤ r₁) (hr₂ : 0 ≤ r₂) :
o.oangle (r₁ • x) (r₂ • x) = 0 := by
rcases hr₁.lt_or_eq with (h | h)
· simp [h, hr₂]
· simp [h.symm]
/-- Multiplying the first vector passed to `oangle` by a nonzero real does not change twice the
angle. -/
@[simp]
theorem two_zsmul_oangle_smul_left_of_ne_zero (x y : V) {r : ℝ} (hr : r ≠ 0) :
(2 : ℤ) • o.oangle (r • x) y = (2 : ℤ) • o.oangle x y := by
rcases hr.lt_or_lt with (h | h) <;> simp [h]
/-- Multiplying the second vector passed to `oangle` by a nonzero real does not change twice the
angle. -/
@[simp]
theorem two_zsmul_oangle_smul_right_of_ne_zero (x y : V) {r : ℝ} (hr : r ≠ 0) :
(2 : ℤ) • o.oangle x (r • y) = (2 : ℤ) • o.oangle x y := by
rcases hr.lt_or_lt with (h | h) <;> simp [h]
/-- Twice the angle between a multiple of a vector and that vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_left_self (x : V) {r : ℝ} : (2 : ℤ) • o.oangle (r • x) x = 0 := by
rcases lt_or_le r 0 with (h | h) <;> simp [h]
/-- Twice the angle between a vector and a multiple of that vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_right_self (x : V) {r : ℝ} : (2 : ℤ) • o.oangle x (r • x) = 0 := by
rcases lt_or_le r 0 with (h | h) <;> simp [h]
/-- Twice the angle between two multiples of a vector is 0. -/
@[simp]
theorem two_zsmul_oangle_smul_smul_self (x : V) {r₁ r₂ : ℝ} :
(2 : ℤ) • o.oangle (r₁ • x) (r₂ • x) = 0 := by by_cases h : r₁ = 0 <;> simp [h]
/-- If the spans of two vectors are equal, twice angles with those vectors on the left are
equal. -/
theorem two_zsmul_oangle_left_of_span_eq {x y : V} (z : V) (h : (ℝ ∙ x) = ℝ ∙ y) :
(2 : ℤ) • o.oangle x z = (2 : ℤ) • o.oangle y z := by
rw [Submodule.span_singleton_eq_span_singleton] at h
rcases h with ⟨r, rfl⟩
exact (o.two_zsmul_oangle_smul_left_of_ne_zero _ _ (Units.ne_zero _)).symm
/-- If the spans of two vectors are equal, twice angles with those vectors on the right are
equal. -/
theorem two_zsmul_oangle_right_of_span_eq (x : V) {y z : V} (h : (ℝ ∙ y) = ℝ ∙ z) :
(2 : ℤ) • o.oangle x y = (2 : ℤ) • o.oangle x z := by
rw [Submodule.span_singleton_eq_span_singleton] at h
rcases h with ⟨r, rfl⟩
exact (o.two_zsmul_oangle_smul_right_of_ne_zero _ _ (Units.ne_zero _)).symm
/-- If the spans of two pairs of vectors are equal, twice angles between those vectors are
equal. -/
theorem two_zsmul_oangle_of_span_eq_of_span_eq {w x y z : V} (hwx : (ℝ ∙ w) = ℝ ∙ x)
(hyz : (ℝ ∙ y) = ℝ ∙ z) : (2 : ℤ) • o.oangle w y = (2 : ℤ) • o.oangle x z := by
rw [o.two_zsmul_oangle_left_of_span_eq y hwx, o.two_zsmul_oangle_right_of_span_eq x hyz]
/-- The oriented angle between two vectors is zero if and only if the angle with the vectors
swapped is zero. -/
theorem oangle_eq_zero_iff_oangle_rev_eq_zero {x y : V} : o.oangle x y = 0 ↔ o.oangle y x = 0 := by
rw [oangle_rev, neg_eq_zero]
/-- The oriented angle between two vectors is zero if and only if they are on the same ray. -/
theorem oangle_eq_zero_iff_sameRay {x y : V} : o.oangle x y = 0 ↔ SameRay ℝ x y := by
rw [oangle, kahler_apply_apply, Complex.arg_coe_angle_eq_iff_eq_toReal, Real.Angle.toReal_zero,
Complex.arg_eq_zero_iff]
simpa using o.nonneg_inner_and_areaForm_eq_zero_iff_sameRay x y
/-- The oriented angle between two vectors is `π` if and only if the angle with the vectors
swapped is `π`. -/
theorem oangle_eq_pi_iff_oangle_rev_eq_pi {x y : V} : o.oangle x y = π ↔ o.oangle y x = π := by
rw [oangle_rev, neg_eq_iff_eq_neg, Real.Angle.neg_coe_pi]
/-- The oriented angle between two vectors is `π` if and only they are nonzero and the first is
on the same ray as the negation of the second. -/
theorem oangle_eq_pi_iff_sameRay_neg {x y : V} :
o.oangle x y = π ↔ x ≠ 0 ∧ y ≠ 0 ∧ SameRay ℝ x (-y) := by
rw [← o.oangle_eq_zero_iff_sameRay]
constructor
· intro h
by_cases hx : x = 0; · simp [hx, Real.Angle.pi_ne_zero.symm] at h
by_cases hy : y = 0; · simp [hy, Real.Angle.pi_ne_zero.symm] at h
refine ⟨hx, hy, ?_⟩
rw [o.oangle_neg_right hx hy, h, Real.Angle.coe_pi_add_coe_pi]
· rintro ⟨hx, hy, h⟩
rwa [o.oangle_neg_right hx hy, ← Real.Angle.sub_coe_pi_eq_add_coe_pi, sub_eq_zero] at h
/-- The oriented angle between two vectors is zero or `π` if and only if those two vectors are
not linearly independent. -/
theorem oangle_eq_zero_or_eq_pi_iff_not_linearIndependent {x y : V} :
o.oangle x y = 0 ∨ o.oangle x y = π ↔ ¬LinearIndependent ℝ ![x, y] := by
rw [oangle_eq_zero_iff_sameRay, oangle_eq_pi_iff_sameRay_neg,
sameRay_or_ne_zero_and_sameRay_neg_iff_not_linearIndependent]
/-- The oriented angle between two vectors is zero or `π` if and only if the first vector is zero
or the second is a multiple of the first. -/
theorem oangle_eq_zero_or_eq_pi_iff_right_eq_smul {x y : V} :
o.oangle x y = 0 ∨ o.oangle x y = π ↔ x = 0 ∨ ∃ r : ℝ, y = r • x := by
rw [oangle_eq_zero_iff_sameRay, oangle_eq_pi_iff_sameRay_neg]
refine ⟨fun h => ?_, fun h => ?_⟩
· rcases h with (h | ⟨-, -, h⟩)
· by_cases hx : x = 0; · simp [hx]
obtain ⟨r, -, rfl⟩ := h.exists_nonneg_left hx
exact Or.inr ⟨r, rfl⟩
· by_cases hx : x = 0; · simp [hx]
obtain ⟨r, -, hy⟩ := h.exists_nonneg_left hx
refine Or.inr ⟨-r, ?_⟩
simp [hy]
· rcases h with (rfl | ⟨r, rfl⟩); · simp
by_cases hx : x = 0; · simp [hx]
rcases lt_trichotomy r 0 with (hr | hr | hr)
· rw [← neg_smul]
exact Or.inr ⟨hx, smul_ne_zero hr.ne hx,
SameRay.sameRay_pos_smul_right x (Left.neg_pos_iff.2 hr)⟩
· simp [hr]
· exact Or.inl (SameRay.sameRay_pos_smul_right x hr)
/-- The oriented angle between two vectors is not zero or `π` if and only if those two vectors
are linearly independent. -/
theorem oangle_ne_zero_and_ne_pi_iff_linearIndependent {x y : V} :
o.oangle x y ≠ 0 ∧ o.oangle x y ≠ π ↔ LinearIndependent ℝ ![x, y] := by
rw [← not_or, ← not_iff_not, Classical.not_not,
oangle_eq_zero_or_eq_pi_iff_not_linearIndependent]
/-- Two vectors are equal if and only if they have equal norms and zero angle between them. -/
theorem eq_iff_norm_eq_and_oangle_eq_zero (x y : V) : x = y ↔ ‖x‖ = ‖y‖ ∧ o.oangle x y = 0 := by
rw [oangle_eq_zero_iff_sameRay]
constructor
· rintro rfl
simp; rfl
· rcases eq_or_ne y 0 with (rfl | hy)
· simp
rintro ⟨h₁, h₂⟩
obtain ⟨r, hr, rfl⟩ := h₂.exists_nonneg_right hy
have : ‖y‖ ≠ 0 := by simpa using hy
obtain rfl : r = 1 := by
apply mul_right_cancel₀ this
simpa [norm_smul, abs_of_nonneg hr] using h₁
simp
/-- Two vectors with equal norms are equal if and only if they have zero angle between them. -/
theorem eq_iff_oangle_eq_zero_of_norm_eq {x y : V} (h : ‖x‖ = ‖y‖) : x = y ↔ o.oangle x y = 0 :=
⟨fun he => ((o.eq_iff_norm_eq_and_oangle_eq_zero x y).1 he).2, fun ha =>
(o.eq_iff_norm_eq_and_oangle_eq_zero x y).2 ⟨h, ha⟩⟩
/-- Two vectors with zero angle between them are equal if and only if they have equal norms. -/
theorem eq_iff_norm_eq_of_oangle_eq_zero {x y : V} (h : o.oangle x y = 0) : x = y ↔ ‖x‖ = ‖y‖ :=
⟨fun he => ((o.eq_iff_norm_eq_and_oangle_eq_zero x y).1 he).1, fun hn =>
(o.eq_iff_norm_eq_and_oangle_eq_zero x y).2 ⟨hn, h⟩⟩
/-- Given three nonzero vectors, the angle between the first and the second plus the angle
between the second and the third equals the angle between the first and the third. -/
@[simp]
theorem oangle_add {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x y + o.oangle y z = o.oangle x z := by
simp_rw [oangle]
rw [← Complex.arg_mul_coe_angle, o.kahler_mul y x z]
· congr 1
exact mod_cast Complex.arg_real_mul _ (by positivity : 0 < ‖y‖ ^ 2)
| · exact o.kahler_ne_zero hx hy
· exact o.kahler_ne_zero hy hz
/-- Given three nonzero vectors, the angle between the second and the third plus the angle
between the first and the second equals the angle between the first and the third. -/
@[simp]
theorem oangle_add_swap {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle y z + o.oangle x y = o.oangle x z := by rw [add_comm, o.oangle_add hx hy hz]
/-- Given three nonzero vectors, the angle between the first and the third minus the angle
between the first and the second equals the angle between the second and the third. -/
@[simp]
theorem oangle_sub_left {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
o.oangle x z - o.oangle x y = o.oangle y z := by
rw [sub_eq_iff_eq_add, o.oangle_add_swap hx hy hz]
/-- Given three nonzero vectors, the angle between the first and the third minus the angle
between the second and the third equals the angle between the first and the second. -/
@[simp]
theorem oangle_sub_right {x y z : V} (hx : x ≠ 0) (hy : y ≠ 0) (hz : z ≠ 0) :
| Mathlib/Geometry/Euclidean/Angle/Oriented/Basic.lean | 447 | 466 |
/-
Copyright (c) 2018 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl
-/
import Mathlib.Logic.Relator
import Mathlib.Tactic.Use
import Mathlib.Tactic.MkIffOfInductiveProp
import Mathlib.Tactic.SimpRw
import Mathlib.Logic.Basic
import Mathlib.Order.Defs.Unbundled
/-!
# Relation closures
This file defines the reflexive, transitive, reflexive transitive and equivalence closures
of relations and proves some basic results on them.
Note that this is about unbundled relations, that is terms of types of the form `α → β → Prop`. For
the bundled version, see `Rel`.
## Definitions
* `Relation.ReflGen`: Reflexive closure. `ReflGen r` relates everything `r` related, plus for all
`a` it relates `a` with itself. So `ReflGen r a b ↔ r a b ∨ a = b`.
* `Relation.TransGen`: Transitive closure. `TransGen r` relates everything `r` related
transitively. So `TransGen r a b ↔ ∃ x₀ ... xₙ, r a x₀ ∧ r x₀ x₁ ∧ ... ∧ r xₙ b`.
* `Relation.ReflTransGen`: Reflexive transitive closure. `ReflTransGen r` relates everything
`r` related transitively, plus for all `a` it relates `a` with itself. So
`ReflTransGen r a b ↔ (∃ x₀ ... xₙ, r a x₀ ∧ r x₀ x₁ ∧ ... ∧ r xₙ b) ∨ a = b`. It is the same as
the reflexive closure of the transitive closure, or the transitive closure of the reflexive
closure. In terms of rewriting systems, this means that `a` can be rewritten to `b` in a number of
rewrites.
* `Relation.EqvGen`: Equivalence closure. `EqvGen r` relates everything `ReflTransGen r` relates,
plus for all related pairs it relates them in the opposite order.
* `Relation.Comp`: Relation composition. We provide notation `∘r`. For `r : α → β → Prop` and
`s : β → γ → Prop`, `r ∘r s`relates `a : α` and `c : γ` iff there exists `b : β` that's related to
both.
* `Relation.Map`: Image of a relation under a pair of maps. For `r : α → β → Prop`, `f : α → γ`,
`g : β → δ`, `Map r f g` is the relation `γ → δ → Prop` relating `f a` and `g b` for all `a`, `b`
related by `r`.
* `Relation.Join`: Join of a relation. For `r : α → α → Prop`, `Join r a b ↔ ∃ c, r a c ∧ r b c`. In
terms of rewriting systems, this means that `a` and `b` can be rewritten to the same term.
-/
open Function
variable {α β γ δ ε ζ : Type*}
section NeImp
variable {r : α → α → Prop}
theorem IsRefl.reflexive [IsRefl α r] : Reflexive r := fun x ↦ IsRefl.refl x
/-- To show a reflexive relation `r : α → α → Prop` holds over `x y : α`,
it suffices to show it holds when `x ≠ y`. -/
theorem Reflexive.rel_of_ne_imp (h : Reflexive r) {x y : α} (hr : x ≠ y → r x y) : r x y := by
by_cases hxy : x = y
· exact hxy ▸ h x
· exact hr hxy
/-- If a reflexive relation `r : α → α → Prop` holds over `x y : α`,
then it holds whether or not `x ≠ y`. -/
theorem Reflexive.ne_imp_iff (h : Reflexive r) {x y : α} : x ≠ y → r x y ↔ r x y :=
⟨h.rel_of_ne_imp, fun hr _ ↦ hr⟩
/-- If a reflexive relation `r : α → α → Prop` holds over `x y : α`,
then it holds whether or not `x ≠ y`. Unlike `Reflexive.ne_imp_iff`, this uses `[IsRefl α r]`. -/
theorem reflexive_ne_imp_iff [IsRefl α r] {x y : α} : x ≠ y → r x y ↔ r x y :=
IsRefl.reflexive.ne_imp_iff
protected theorem Symmetric.iff (H : Symmetric r) (x y : α) : r x y ↔ r y x :=
⟨fun h ↦ H h, fun h ↦ H h⟩
theorem Symmetric.flip_eq (h : Symmetric r) : flip r = r :=
funext₂ fun _ _ ↦ propext <| h.iff _ _
theorem Symmetric.swap_eq : Symmetric r → swap r = r :=
Symmetric.flip_eq
theorem flip_eq_iff : flip r = r ↔ Symmetric r :=
⟨fun h _ _ ↦ (congr_fun₂ h _ _).mp, Symmetric.flip_eq⟩
theorem swap_eq_iff : swap r = r ↔ Symmetric r :=
flip_eq_iff
end NeImp
section Comap
variable {r : β → β → Prop}
theorem Reflexive.comap (h : Reflexive r) (f : α → β) : Reflexive (r on f) := fun a ↦ h (f a)
theorem Symmetric.comap (h : Symmetric r) (f : α → β) : Symmetric (r on f) := fun _ _ hab ↦ h hab
theorem Transitive.comap (h : Transitive r) (f : α → β) : Transitive (r on f) :=
fun _ _ _ hab hbc ↦ h hab hbc
theorem Equivalence.comap (h : Equivalence r) (f : α → β) : Equivalence (r on f) :=
⟨fun a ↦ h.refl (f a), h.symm, h.trans⟩
end Comap
namespace Relation
section Comp
variable {r : α → β → Prop} {p : β → γ → Prop} {q : γ → δ → Prop}
/-- The composition of two relations, yielding a new relation. The result
relates a term of `α` and a term of `γ` if there is an intermediate
term of `β` related to both.
-/
def Comp (r : α → β → Prop) (p : β → γ → Prop) (a : α) (c : γ) : Prop :=
∃ b, r a b ∧ p b c
@[inherit_doc]
local infixr:80 " ∘r " => Relation.Comp
@[simp]
theorem comp_eq_fun (f : γ → β) : r ∘r (· = f ·) = (r · <| f ·) := by
ext x y
simp [Comp]
@[simp]
theorem comp_eq : r ∘r (· = ·) = r := comp_eq_fun ..
@[simp]
theorem fun_eq_comp (f : γ → α) : (f · = ·) ∘r r = (r <| f ·) := by
ext x y
simp [Comp]
@[simp]
theorem eq_comp : (· = ·) ∘r r = r := fun_eq_comp ..
@[simp]
theorem iff_comp {r : Prop → α → Prop} : (· ↔ ·) ∘r r = r := by
have : (· ↔ ·) = (· = ·) := by funext a b; exact iff_eq_eq
rw [this, eq_comp]
@[simp]
theorem comp_iff {r : α → Prop → Prop} : r ∘r (· ↔ ·) = r := by
have : (· ↔ ·) = (· = ·) := by funext a b; exact iff_eq_eq
rw [this, comp_eq]
theorem comp_assoc : (r ∘r p) ∘r q = r ∘r p ∘r q := by
funext a d
apply propext
constructor
· exact fun ⟨c, ⟨b, hab, hbc⟩, hcd⟩ ↦ ⟨b, hab, c, hbc, hcd⟩
· exact fun ⟨b, hab, c, hbc, hcd⟩ ↦ ⟨c, ⟨b, hab, hbc⟩, hcd⟩
theorem flip_comp : flip (r ∘r p) = flip p ∘r flip r := by
funext c a
apply propext
constructor
· exact fun ⟨b, hab, hbc⟩ ↦ ⟨b, hbc, hab⟩
· exact fun ⟨b, hbc, hab⟩ ↦ ⟨b, hab, hbc⟩
end Comp
section Fibration
variable (rα : α → α → Prop) (rβ : β → β → Prop) (f : α → β)
/-- A function `f : α → β` is a fibration between the relation `rα` and `rβ` if for all
`a : α` and `b : β`, whenever `b : β` and `f a` are related by `rβ`, `b` is the image
of some `a' : α` under `f`, and `a'` and `a` are related by `rα`. -/
def Fibration :=
∀ ⦃a b⦄, rβ b (f a) → ∃ a', rα a' a ∧ f a' = b
variable {rα rβ}
/-- If `f : α → β` is a fibration between relations `rα` and `rβ`, and `a : α` is
accessible under `rα`, then `f a` is accessible under `rβ`. -/
theorem _root_.Acc.of_fibration (fib : Fibration rα rβ f) {a} (ha : Acc rα a) : Acc rβ (f a) := by
induction ha with | intro a _ ih => ?_
refine Acc.intro (f a) fun b hr ↦ ?_
obtain ⟨a', hr', rfl⟩ := fib hr
exact ih a' hr'
theorem _root_.Acc.of_downward_closed (dc : ∀ {a b}, rβ b (f a) → ∃ c, f c = b) (a : α)
(ha : Acc (InvImage rβ f) a) : Acc rβ (f a) :=
ha.of_fibration f fun a _ h ↦
let ⟨a', he⟩ := dc h
⟨a', by simp_all [InvImage], he⟩
end Fibration
section Map
variable {r : α → β → Prop} {f : α → γ} {g : β → δ} {c : γ} {d : δ}
/-- The map of a relation `r` through a pair of functions pushes the
relation to the codomains of the functions. The resulting relation is
defined by having pairs of terms related if they have preimages
related by `r`.
-/
protected def Map (r : α → β → Prop) (f : α → γ) (g : β → δ) : γ → δ → Prop := fun c d ↦
∃ a b, r a b ∧ f a = c ∧ g b = d
lemma map_apply : Relation.Map r f g c d ↔ ∃ a b, r a b ∧ f a = c ∧ g b = d := Iff.rfl
@[simp] lemma map_map (r : α → β → Prop) (f₁ : α → γ) (g₁ : β → δ) (f₂ : γ → ε) (g₂ : δ → ζ) :
Relation.Map (Relation.Map r f₁ g₁) f₂ g₂ = Relation.Map r (f₂ ∘ f₁) (g₂ ∘ g₁) := by
ext a b
simp_rw [Relation.Map, Function.comp_apply, ← exists_and_right, @exists_comm γ, @exists_comm δ]
refine exists₂_congr fun a b ↦ ⟨?_, fun h ↦ ⟨_, _, ⟨⟨h.1, rfl, rfl⟩, h.2⟩⟩⟩
rintro ⟨_, _, ⟨hab, rfl, rfl⟩, h⟩
exact ⟨hab, h⟩
@[simp]
lemma map_apply_apply (hf : Injective f) (hg : Injective g) (r : α → β → Prop) (a : α) (b : β) :
Relation.Map r f g (f a) (g b) ↔ r a b := by simp [Relation.Map, hf.eq_iff, hg.eq_iff]
@[simp] lemma map_id_id (r : α → β → Prop) : Relation.Map r id id = r := by ext; simp [Relation.Map]
instance [Decidable (∃ a b, r a b ∧ f a = c ∧ g b = d)] : Decidable (Relation.Map r f g c d) :=
‹Decidable _›
lemma map_reflexive {r : α → α → Prop} (hr : Reflexive r) {f : α → β} (hf : f.Surjective) :
Reflexive (Relation.Map r f f) := by
intro x
obtain ⟨y, rfl⟩ := hf x
exact ⟨y, y, hr y, rfl, rfl⟩
lemma map_symmetric {r : α → α → Prop} (hr : Symmetric r) (f : α → β) :
Symmetric (Relation.Map r f f) := by
rintro _ _ ⟨x, y, hxy, rfl, rfl⟩; exact ⟨_, _, hr hxy, rfl, rfl⟩
lemma map_transitive {r : α → α → Prop} (hr : Transitive r) {f : α → β}
(hf : ∀ x y, f x = f y → r x y) :
Transitive (Relation.Map r f f) := by
rintro _ _ _ ⟨x, y, hxy, rfl, rfl⟩ ⟨y', z, hyz, hy, rfl⟩
exact ⟨x, z, hr hxy <| hr (hf _ _ hy.symm) hyz, rfl, rfl⟩
lemma map_equivalence {r : α → α → Prop} (hr : Equivalence r) (f : α → β)
(hf : f.Surjective) (hf_ker : ∀ x y, f x = f y → r x y) :
Equivalence (Relation.Map r f f) where
refl := map_reflexive hr.reflexive hf
symm := @(map_symmetric hr.symmetric _)
trans := @(map_transitive hr.transitive hf_ker)
-- TODO: state this using `≤`, after adjusting imports.
lemma map_mono {r s : α → β → Prop} {f : α → γ} {g : β → δ} (h : ∀ x y, r x y → s x y) :
∀ x y, Relation.Map r f g x y → Relation.Map s f g x y :=
fun _ _ ⟨x, y, hxy, hx, hy⟩ => ⟨x, y, h _ _ hxy, hx, hy⟩
end Map
variable {r : α → α → Prop} {a b c : α}
/-- `ReflTransGen r`: reflexive transitive closure of `r` -/
@[mk_iff ReflTransGen.cases_tail_iff]
inductive ReflTransGen (r : α → α → Prop) (a : α) : α → Prop
| refl : ReflTransGen r a a
| tail {b c} : ReflTransGen r a b → r b c → ReflTransGen r a c
attribute [refl] ReflTransGen.refl
/-- `ReflGen r`: reflexive closure of `r` -/
@[mk_iff]
inductive ReflGen (r : α → α → Prop) (a : α) : α → Prop
| refl : ReflGen r a a
| single {b} : r a b → ReflGen r a b
variable (r) in
/-- `EqvGen r`: equivalence closure of `r`. -/
@[mk_iff]
inductive EqvGen : α → α → Prop
| rel x y : r x y → EqvGen x y
| refl x : EqvGen x x
| symm x y : EqvGen x y → EqvGen y x
| trans x y z : EqvGen x y → EqvGen y z → EqvGen x z
attribute [mk_iff] TransGen
attribute [refl] ReflGen.refl
namespace ReflGen
theorem to_reflTransGen : ∀ {a b}, ReflGen r a b → ReflTransGen r a b
| a, _, refl => by rfl
| _, _, single h => ReflTransGen.tail ReflTransGen.refl h
theorem mono {p : α → α → Prop} (hp : ∀ a b, r a b → p a b) : ∀ {a b}, ReflGen r a b → ReflGen p a b
| a, _, ReflGen.refl => by rfl
| a, b, single h => single (hp a b h)
instance : IsRefl α (ReflGen r) :=
⟨@refl α r⟩
end ReflGen
namespace ReflTransGen
@[trans]
theorem trans (hab : ReflTransGen r a b) (hbc : ReflTransGen r b c) : ReflTransGen r a c := by
induction hbc with
| refl => assumption
| tail _ hcd hac => exact hac.tail hcd
theorem single (hab : r a b) : ReflTransGen r a b :=
refl.tail hab
theorem head (hab : r a b) (hbc : ReflTransGen r b c) : ReflTransGen r a c := by
induction hbc with
| refl => exact refl.tail hab
| tail _ hcd hac => exact hac.tail hcd
theorem symmetric (h : Symmetric r) : Symmetric (ReflTransGen r) := by
intro x y h
induction h with
| refl => rfl
| tail _ b c => apply Relation.ReflTransGen.head (h b) c
theorem cases_tail : ReflTransGen r a b → b = a ∨ ∃ c, ReflTransGen r a c ∧ r c b :=
(cases_tail_iff r a b).1
@[elab_as_elim]
theorem head_induction_on {P : ∀ a : α, ReflTransGen r a b → Prop} {a : α} (h : ReflTransGen r a b)
(refl : P b refl)
(head : ∀ {a c} (h' : r a c) (h : ReflTransGen r c b), P c h → P a (h.head h')) : P a h := by
induction h with
| refl => exact refl
| @tail b c _ hbc ih =>
apply ih
· exact head hbc _ refl
· exact fun h1 h2 ↦ head h1 (h2.tail hbc)
@[elab_as_elim]
theorem trans_induction_on {P : ∀ {a b : α}, ReflTransGen r a b → Prop} {a b : α}
(h : ReflTransGen r a b) (ih₁ : ∀ a, @P a a refl) (ih₂ : ∀ {a b} (h : r a b), P (single h))
(ih₃ : ∀ {a b c} (h₁ : ReflTransGen r a b) (h₂ : ReflTransGen r b c), P h₁ → P h₂ →
P (h₁.trans h₂)) : P h := by
induction h with
| refl => exact ih₁ a
| tail hab hbc ih => exact ih₃ hab (single hbc) ih (ih₂ hbc)
theorem cases_head (h : ReflTransGen r a b) : a = b ∨ ∃ c, r a c ∧ ReflTransGen r c b := by
induction h using Relation.ReflTransGen.head_induction_on
· left
rfl
· right
exact ⟨_, by assumption, by assumption⟩
theorem cases_head_iff : ReflTransGen r a b ↔ a = b ∨ ∃ c, r a c ∧ ReflTransGen r c b := by
use cases_head
rintro (rfl | ⟨c, hac, hcb⟩)
· rfl
· exact head hac hcb
theorem total_of_right_unique (U : Relator.RightUnique r) (ab : ReflTransGen r a b)
(ac : ReflTransGen r a c) : ReflTransGen r b c ∨ ReflTransGen r c b := by
induction ab with
| refl => exact Or.inl ac
| tail _ bd IH =>
rcases IH with (IH | IH)
· rcases cases_head IH with (rfl | ⟨e, be, ec⟩)
· exact Or.inr (single bd)
· cases U bd be
exact Or.inl ec
· exact Or.inr (IH.tail bd)
end ReflTransGen
namespace TransGen
theorem to_reflTransGen {a b} (h : TransGen r a b) : ReflTransGen r a b := by
induction h with
| single h => exact ReflTransGen.single h
| tail _ bc ab => exact ReflTransGen.tail ab bc
theorem trans_left (hab : TransGen r a b) (hbc : ReflTransGen r b c) : TransGen r a c := by
induction hbc with
| refl => assumption
| tail _ hcd hac => exact hac.tail hcd
instance : Trans (TransGen r) (ReflTransGen r) (TransGen r) :=
⟨trans_left⟩
attribute [trans] trans
instance : Trans (TransGen r) (TransGen r) (TransGen r) :=
⟨trans⟩
theorem head' (hab : r a b) (hbc : ReflTransGen r b c) : TransGen r a c :=
trans_left (single hab) hbc
theorem tail' (hab : ReflTransGen r a b) (hbc : r b c) : TransGen r a c := by
induction hab generalizing c with
| refl => exact single hbc
| tail _ hdb IH => exact tail (IH hdb) hbc
theorem head (hab : r a b) (hbc : TransGen r b c) : TransGen r a c :=
head' hab hbc.to_reflTransGen
@[elab_as_elim]
theorem head_induction_on {P : ∀ a : α, TransGen r a b → Prop} {a : α} (h : TransGen r a b)
(base : ∀ {a} (h : r a b), P a (single h))
(ih : ∀ {a c} (h' : r a c) (h : TransGen r c b), P c h → P a (h.head h')) : P a h := by
induction h with
| single h => exact base h
| @tail b c _ hbc h_ih =>
apply h_ih
· exact fun h ↦ ih h (single hbc) (base hbc)
· exact fun hab hbc ↦ ih hab _
@[elab_as_elim]
theorem trans_induction_on {P : ∀ {a b : α}, TransGen r a b → Prop} {a b : α} (h : TransGen r a b)
(base : ∀ {a b} (h : r a b), P (single h))
(ih : ∀ {a b c} (h₁ : TransGen r a b) (h₂ : TransGen r b c), P h₁ → P h₂ → P (h₁.trans h₂)) :
P h := by
induction h with
| single h => exact base h
| tail hab hbc h_ih => exact ih hab (single hbc) h_ih (base hbc)
theorem trans_right (hab : ReflTransGen r a b) (hbc : TransGen r b c) : TransGen r a c := by
induction hbc with
| single hbc => exact tail' hab hbc
| tail _ hcd hac => exact hac.tail hcd
instance : Trans (ReflTransGen r) (TransGen r) (TransGen r) :=
⟨trans_right⟩
theorem tail'_iff : TransGen r a c ↔ ∃ b, ReflTransGen r a b ∧ r b c := by
refine ⟨fun h ↦ ?_, fun ⟨b, hab, hbc⟩ ↦ tail' hab hbc⟩
cases h with
| single hac => exact ⟨_, by rfl, hac⟩
| tail hab hbc => exact ⟨_, hab.to_reflTransGen, hbc⟩
theorem head'_iff : TransGen r a c ↔ ∃ b, r a b ∧ ReflTransGen r b c := by
refine ⟨fun h ↦ ?_, fun ⟨b, hab, hbc⟩ ↦ head' hab hbc⟩
induction h with
| single hac => exact ⟨_, hac, by rfl⟩
| tail _ hbc IH =>
rcases IH with ⟨d, had, hdb⟩
exact ⟨_, had, hdb.tail hbc⟩
end TransGen
section reflGen
lemma reflGen_eq_self (hr : Reflexive r) : ReflGen r = r := by
ext x y
simpa only [reflGen_iff, or_iff_right_iff_imp] using fun h ↦ h ▸ hr y
lemma reflexive_reflGen : Reflexive (ReflGen r) := fun _ ↦ .refl
lemma reflGen_minimal {r' : α → α → Prop} (hr' : Reflexive r') (h : ∀ x y, r x y → r' x y) {x y : α}
(hxy : ReflGen r x y) : r' x y := by
simpa [reflGen_eq_self hr'] using ReflGen.mono h hxy
end reflGen
section TransGen
theorem transGen_eq_self (trans : Transitive r) : TransGen r = r :=
funext fun a ↦ funext fun b ↦ propext <|
⟨fun h ↦ by
induction h with
| single hc => exact hc
| tail _ hcd hac => exact trans hac hcd, TransGen.single⟩
theorem transitive_transGen : Transitive (TransGen r) := fun _ _ _ ↦ TransGen.trans
instance : IsTrans α (TransGen r) :=
⟨@TransGen.trans α r⟩
theorem transGen_idem : TransGen (TransGen r) = TransGen r :=
transGen_eq_self transitive_transGen
theorem TransGen.lift {p : β → β → Prop} {a b : α} (f : α → β) (h : ∀ a b, r a b → p (f a) (f b))
(hab : TransGen r a b) : TransGen p (f a) (f b) := by
induction hab with
| single hac => exact TransGen.single (h a _ hac)
| tail _ hcd hac => exact TransGen.tail hac (h _ _ hcd)
theorem TransGen.lift' {p : β → β → Prop} {a b : α} (f : α → β)
(h : ∀ a b, r a b → TransGen p (f a) (f b)) (hab : TransGen r a b) :
TransGen p (f a) (f b) := by
simpa [transGen_idem] using hab.lift f h
theorem TransGen.closed {p : α → α → Prop} :
(∀ a b, r a b → TransGen p a b) → TransGen r a b → TransGen p a b :=
TransGen.lift' id
lemma TransGen.closed' {P : α → Prop} (dc : ∀ {a b}, r a b → P b → P a)
{a b : α} (h : TransGen r a b) : P b → P a :=
h.head_induction_on dc fun hr _ hi ↦ dc hr ∘ hi
theorem TransGen.mono {p : α → α → Prop} :
(∀ a b, r a b → p a b) → TransGen r a b → TransGen p a b :=
TransGen.lift id
lemma transGen_minimal {r' : α → α → Prop} (hr' : Transitive r') (h : ∀ x y, r x y → r' x y)
{x y : α} (hxy : TransGen r x y) : r' x y := by
simpa [transGen_eq_self hr'] using TransGen.mono h hxy
theorem TransGen.swap (h : TransGen r b a) : TransGen (swap r) a b := by
induction h with
| single h => exact TransGen.single h
| tail _ hbc ih => exact ih.head hbc
theorem transGen_swap : TransGen (swap r) a b ↔ TransGen r b a :=
⟨TransGen.swap, TransGen.swap⟩
end TransGen
section ReflTransGen
open ReflTransGen
theorem reflTransGen_iff_eq (h : ∀ b, ¬r a b) : ReflTransGen r a b ↔ b = a := by
rw [cases_head_iff]; simp [h, eq_comm]
theorem reflTransGen_iff_eq_or_transGen : ReflTransGen r a b ↔ b = a ∨ TransGen r a b := by
refine ⟨fun h ↦ ?_, fun h ↦ ?_⟩
· cases h with
| refl => exact Or.inl rfl
| tail hac hcb => exact Or.inr (TransGen.tail' hac hcb)
· rcases h with (rfl | h)
· rfl
· exact h.to_reflTransGen
theorem ReflTransGen.lift {p : β → β → Prop} {a b : α} (f : α → β)
(h : ∀ a b, r a b → p (f a) (f b)) (hab : ReflTransGen r a b) : ReflTransGen p (f a) (f b) :=
ReflTransGen.trans_induction_on hab (fun _ ↦ refl) (ReflTransGen.single ∘ h _ _) fun _ _ ↦ trans
theorem ReflTransGen.mono {p : α → α → Prop} : (∀ a b, r a b → p a b) →
ReflTransGen r a b → ReflTransGen p a b :=
ReflTransGen.lift id
theorem reflTransGen_eq_self (refl : Reflexive r) (trans : Transitive r) : ReflTransGen r = r :=
funext fun a ↦ funext fun b ↦ propext <|
⟨fun h ↦ by
induction h with
| refl => apply refl
| tail _ h₂ IH => exact trans IH h₂, single⟩
lemma reflTransGen_minimal {r' : α → α → Prop} (hr₁ : Reflexive r') (hr₂ : Transitive r')
(h : ∀ x y, r x y → r' x y) {x y : α} (hxy : ReflTransGen r x y) : r' x y := by
simpa [reflTransGen_eq_self hr₁ hr₂] using ReflTransGen.mono h hxy
theorem reflexive_reflTransGen : Reflexive (ReflTransGen r) := fun _ ↦ refl
theorem transitive_reflTransGen : Transitive (ReflTransGen r) := fun _ _ _ ↦ trans
instance : IsRefl α (ReflTransGen r) :=
⟨@ReflTransGen.refl α r⟩
instance : IsTrans α (ReflTransGen r) :=
⟨@ReflTransGen.trans α r⟩
theorem reflTransGen_idem : ReflTransGen (ReflTransGen r) = ReflTransGen r :=
reflTransGen_eq_self reflexive_reflTransGen transitive_reflTransGen
theorem ReflTransGen.lift' {p : β → β → Prop} {a b : α} (f : α → β)
(h : ∀ a b, r a b → ReflTransGen p (f a) (f b))
(hab : ReflTransGen r a b) : ReflTransGen p (f a) (f b) := by
simpa [reflTransGen_idem] using hab.lift f h
theorem reflTransGen_closed {p : α → α → Prop} :
(∀ a b, r a b → ReflTransGen p a b) → ReflTransGen r a b → ReflTransGen p a b :=
ReflTransGen.lift' id
theorem ReflTransGen.swap (h : ReflTransGen r b a) : ReflTransGen (swap r) a b := by
induction h with
| refl => rfl
| tail _ hbc ih => exact ih.head hbc
theorem reflTransGen_swap : ReflTransGen (swap r) a b ↔ ReflTransGen r b a :=
⟨ReflTransGen.swap, ReflTransGen.swap⟩
@[simp] lemma reflGen_transGen : ReflGen (TransGen r) = ReflTransGen r := by
ext x y
simp_rw [reflTransGen_iff_eq_or_transGen, reflGen_iff]
@[simp] lemma transGen_reflGen : TransGen (ReflGen r) = ReflTransGen r := by
ext x y
refine ⟨fun h ↦ ?_, fun h ↦ ?_⟩
· simpa [reflTransGen_idem]
using TransGen.to_reflTransGen <| TransGen.mono (fun _ _ ↦ ReflGen.to_reflTransGen) h
· obtain (rfl | h) := reflTransGen_iff_eq_or_transGen.mp h
· exact .single .refl
· exact TransGen.mono (fun _ _ ↦ .single) h
@[simp] lemma reflTransGen_reflGen : ReflTransGen (ReflGen r) = ReflTransGen r := by
simp only [← transGen_reflGen, reflGen_eq_self reflexive_reflGen]
@[simp] lemma reflTransGen_transGen : ReflTransGen (TransGen r) = ReflTransGen r := by
simp only [← reflGen_transGen, transGen_idem]
lemma reflTransGen_eq_transGen (hr : Reflexive r) :
ReflTransGen r = TransGen r := by
rw [← transGen_reflGen, reflGen_eq_self hr]
lemma reflTransGen_eq_reflGen (hr : Transitive r) :
ReflTransGen r = ReflGen r := by
rw [← reflGen_transGen, transGen_eq_self hr]
end ReflTransGen
namespace EqvGen
variable (r)
| theorem is_equivalence : Equivalence (@EqvGen α r) :=
Equivalence.mk EqvGen.refl (EqvGen.symm _ _) (EqvGen.trans _ _ _)
/-- `EqvGen.setoid r` is the setoid generated by a relation `r`.
| Mathlib/Logic/Relation.lean | 611 | 614 |
/-
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.HomotopyCategory.HomComplex
import Mathlib.Algebra.Homology.HomotopyCofiber
/-! # The mapping cone of a morphism of cochain complexes
In this file, we study the homotopy cofiber `HomologicalComplex.homotopyCofiber`
of a morphism `φ : F ⟶ G` of cochain complexes indexed by `ℤ`. In this case,
we redefine it as `CochainComplex.mappingCone φ`. The API involves definitions
- `mappingCone.inl φ : Cochain F (mappingCone φ) (-1)`,
- `mappingCone.inr φ : G ⟶ mappingCone φ`,
- `mappingCone.fst φ : Cocycle (mappingCone φ) F 1` and
- `mappingCone.snd φ : Cochain (mappingCone φ) G 0`.
-/
assert_not_exists TwoSidedIdeal
open CategoryTheory Limits
variable {C D : Type*} [Category C] [Category D] [Preadditive C] [Preadditive D]
namespace CochainComplex
open HomologicalComplex
section
variable {ι : Type*} [AddRightCancelSemigroup ι] [One ι]
{F G : CochainComplex C ι} (φ : F ⟶ G)
instance [∀ p, HasBinaryBiproduct (F.X (p + 1)) (G.X p)] :
HasHomotopyCofiber φ where
hasBinaryBiproduct := by
rintro i _ rfl
infer_instance
end
variable {F G : CochainComplex C ℤ} (φ : F ⟶ G)
variable [HasHomotopyCofiber φ]
/-- The mapping cone of a morphism of cochain complexes indexed by `ℤ`. -/
noncomputable def mappingCone := homotopyCofiber φ
namespace mappingCone
open HomComplex
/-- The left inclusion in the mapping cone, as a cochain of degree `-1`. -/
noncomputable def inl : Cochain F (mappingCone φ) (-1) :=
Cochain.mk (fun p q hpq => homotopyCofiber.inlX φ p q (by dsimp; omega))
/-- The right inclusion in the mapping cone. -/
noncomputable def inr : G ⟶ mappingCone φ := homotopyCofiber.inr φ
/-- The first projection from the mapping cone, as a cocyle of degree `1`. -/
noncomputable def fst : Cocycle (mappingCone φ) F 1 :=
Cocycle.mk (Cochain.mk (fun p q hpq => homotopyCofiber.fstX φ p q hpq)) 2 (by omega) (by
ext p _ rfl
simp [δ_v 1 2 (by omega) _ p (p + 2) (by omega) (p + 1) (p + 1) (by omega) rfl,
homotopyCofiber.d_fstX φ p (p + 1) (p + 2) rfl, mappingCone,
show Int.negOnePow 2 = 1 by rfl])
/-- The second projection from the mapping cone, as a cochain of degree `0`. -/
noncomputable def snd : Cochain (mappingCone φ) G 0 :=
Cochain.ofHoms (homotopyCofiber.sndX φ)
@[reassoc (attr := simp)]
lemma inl_v_fst_v (p q : ℤ) (hpq : q + 1 = p) :
(inl φ).v p q (by rw [← hpq, add_neg_cancel_right]) ≫
(fst φ : Cochain (mappingCone φ) F 1).v q p hpq = 𝟙 _ := by
simp [inl, fst]
@[reassoc (attr := simp)]
lemma inl_v_snd_v (p q : ℤ) (hpq : p + (-1) = q) :
(inl φ).v p q hpq ≫ (snd φ).v q q (add_zero q) = 0 := by
simp [inl, snd]
@[reassoc (attr := simp)]
lemma inr_f_fst_v (p q : ℤ) (hpq : p + 1 = q) :
(inr φ).f p ≫ (fst φ).1.v p q hpq = 0 := by
simp [inr, fst]
@[reassoc (attr := simp)]
lemma inr_f_snd_v (p : ℤ) :
(inr φ).f p ≫ (snd φ).v p p (add_zero p) = 𝟙 _ := by
simp [inr, snd]
@[simp]
lemma inl_fst :
(inl φ).comp (fst φ).1 (neg_add_cancel 1) = Cochain.ofHom (𝟙 F) := by
ext p
simp [Cochain.comp_v _ _ (neg_add_cancel 1) p (p-1) p rfl (by omega)]
@[simp]
lemma inl_snd :
(inl φ).comp (snd φ) (add_zero (-1)) = 0 := by
ext p q hpq
simp [Cochain.comp_v _ _ (add_zero (-1)) p q q (by omega) (by omega)]
@[simp]
lemma inr_fst :
(Cochain.ofHom (inr φ)).comp (fst φ).1 (zero_add 1) = 0 := by
ext p q hpq
simp [Cochain.comp_v _ _ (zero_add 1) p p q (by omega) (by omega)]
@[simp]
lemma inr_snd :
(Cochain.ofHom (inr φ)).comp (snd φ) (zero_add 0) = Cochain.ofHom (𝟙 G) := by aesop_cat
/-! In order to obtain identities of cochains involving `inl`, `inr`, `fst` and `snd`,
it is often convenient to use an `ext` lemma, and use simp lemmas like `inl_v_f_fst_v`,
but it is sometimes possible to get identities of cochains by using rewrites of
identities of cochains like `inl_fst`. Then, similarly as in category theory,
if we associate the compositions of cochains to the right as much as possible,
it is also interesting to have `reassoc` variants of lemmas, like `inl_fst_assoc`. -/
@[simp]
lemma inl_fst_assoc {K : CochainComplex C ℤ} {d e : ℤ} (γ : Cochain F K d) (he : 1 + d = e) :
(inl φ).comp ((fst φ).1.comp γ he) (by rw [← he, neg_add_cancel_left]) = γ := by
rw [← Cochain.comp_assoc _ _ _ (neg_add_cancel 1) (by omega) (by omega), inl_fst,
Cochain.id_comp]
@[simp]
lemma inl_snd_assoc {K : CochainComplex C ℤ} {d e f : ℤ} (γ : Cochain G K d)
(he : 0 + d = e) (hf : -1 + e = f) :
(inl φ).comp ((snd φ).comp γ he) hf = 0 := by
obtain rfl : e = d := by omega
rw [← Cochain.comp_assoc_of_second_is_zero_cochain, inl_snd, Cochain.zero_comp]
@[simp]
lemma inr_fst_assoc {K : CochainComplex C ℤ} {d e f : ℤ} (γ : Cochain F K d)
(he : 1 + d = e) (hf : 0 + e = f) :
(Cochain.ofHom (inr φ)).comp ((fst φ).1.comp γ he) hf = 0 := by
obtain rfl : e = f := by omega
rw [← Cochain.comp_assoc_of_first_is_zero_cochain, inr_fst, Cochain.zero_comp]
@[simp]
lemma inr_snd_assoc {K : CochainComplex C ℤ} {d e : ℤ} (γ : Cochain G K d) (he : 0 + d = e) :
(Cochain.ofHom (inr φ)).comp ((snd φ).comp γ he) (by simp only [← he, zero_add]) = γ := by
obtain rfl : d = e := by omega
rw [← Cochain.comp_assoc_of_first_is_zero_cochain, inr_snd, Cochain.id_comp]
lemma ext_to (i j : ℤ) (hij : i + 1 = j) {A : C} {f g : A ⟶ (mappingCone φ).X i}
(h₁ : f ≫ (fst φ).1.v i j hij = g ≫ (fst φ).1.v i j hij)
(h₂ : f ≫ (snd φ).v i i (add_zero i) = g ≫ (snd φ).v i i (add_zero i)) :
f = g :=
homotopyCofiber.ext_to_X φ i j hij h₁ (by simpa [snd] using h₂)
lemma ext_to_iff (i j : ℤ) (hij : i + 1 = j) {A : C} (f g : A ⟶ (mappingCone φ).X i) :
f = g ↔ f ≫ (fst φ).1.v i j hij = g ≫ (fst φ).1.v i j hij ∧
f ≫ (snd φ).v i i (add_zero i) = g ≫ (snd φ).v i i (add_zero i) := by
constructor
· rintro rfl
tauto
· rintro ⟨h₁, h₂⟩
exact ext_to φ i j hij h₁ h₂
lemma ext_from (i j : ℤ) (hij : j + 1 = i) {A : C} {f g : (mappingCone φ).X j ⟶ A}
(h₁ : (inl φ).v i j (by omega) ≫ f = (inl φ).v i j (by omega) ≫ g)
(h₂ : (inr φ).f j ≫ f = (inr φ).f j ≫ g) :
f = g :=
homotopyCofiber.ext_from_X φ i j hij h₁ h₂
lemma ext_from_iff (i j : ℤ) (hij : j + 1 = i) {A : C} (f g : (mappingCone φ).X j ⟶ A) :
f = g ↔ (inl φ).v i j (by omega) ≫ f = (inl φ).v i j (by omega) ≫ g ∧
(inr φ).f j ≫ f = (inr φ).f j ≫ g := by
constructor
· rintro rfl
tauto
· rintro ⟨h₁, h₂⟩
exact ext_from φ i j hij h₁ h₂
lemma decomp_to {i : ℤ} {A : C} (f : A ⟶ (mappingCone φ).X i) (j : ℤ) (hij : i + 1 = j) :
∃ (a : A ⟶ F.X j) (b : A ⟶ G.X i), f = a ≫ (inl φ).v j i (by omega) + b ≫ (inr φ).f i :=
⟨f ≫ (fst φ).1.v i j hij, f ≫ (snd φ).v i i (add_zero i),
by apply ext_to φ i j hij <;> simp⟩
lemma decomp_from {j : ℤ} {A : C} (f : (mappingCone φ).X j ⟶ A) (i : ℤ) (hij : j + 1 = i) :
∃ (a : F.X i ⟶ A) (b : G.X j ⟶ A),
f = (fst φ).1.v j i hij ≫ a + (snd φ).v j j (add_zero j) ≫ b :=
⟨(inl φ).v i j (by omega) ≫ f, (inr φ).f j ≫ f,
by apply ext_from φ i j hij <;> simp⟩
lemma ext_cochain_to_iff (i j : ℤ) (hij : i + 1 = j)
{K : CochainComplex C ℤ} {γ₁ γ₂ : Cochain K (mappingCone φ) i} :
γ₁ = γ₂ ↔ γ₁.comp (fst φ).1 hij = γ₂.comp (fst φ).1 hij ∧
γ₁.comp (snd φ) (add_zero i) = γ₂.comp (snd φ) (add_zero i) := by
constructor
· rintro rfl
tauto
· rintro ⟨h₁, h₂⟩
ext p q hpq
rw [ext_to_iff φ q (q + 1) rfl]
replace h₁ := Cochain.congr_v h₁ p (q + 1) (by omega)
replace h₂ := Cochain.congr_v h₂ p q hpq
simp only [Cochain.comp_v _ _ _ p q (q + 1) hpq rfl] at h₁
simp only [Cochain.comp_zero_cochain_v] at h₂
exact ⟨h₁, h₂⟩
lemma ext_cochain_from_iff (i j : ℤ) (hij : i + 1 = j)
{K : CochainComplex C ℤ} {γ₁ γ₂ : Cochain (mappingCone φ) K j} :
γ₁ = γ₂ ↔
(inl φ).comp γ₁ (show _ = i by omega) = (inl φ).comp γ₂ (by omega) ∧
(Cochain.ofHom (inr φ)).comp γ₁ (zero_add j) =
(Cochain.ofHom (inr φ)).comp γ₂ (zero_add j) := by
constructor
· rintro rfl
tauto
· rintro ⟨h₁, h₂⟩
ext p q hpq
rw [ext_from_iff φ (p + 1) p rfl]
replace h₁ := Cochain.congr_v h₁ (p + 1) q (by omega)
replace h₂ := Cochain.congr_v h₂ p q (by omega)
simp only [Cochain.comp_v (inl φ) _ _ (p + 1) p q (by omega) hpq] at h₁
simp only [Cochain.zero_cochain_comp_v, Cochain.ofHom_v] at h₂
exact ⟨h₁, h₂⟩
lemma id :
(fst φ).1.comp (inl φ) (add_neg_cancel 1) +
(snd φ).comp (Cochain.ofHom (inr φ)) (add_zero 0) = Cochain.ofHom (𝟙 _) := by
simp [ext_cochain_from_iff φ (-1) 0 (neg_add_cancel 1)]
lemma id_X (p q : ℤ) (hpq : p + 1 = q) :
(fst φ).1.v p q hpq ≫ (inl φ).v q p (by omega) +
(snd φ).v p p (add_zero p) ≫ (inr φ).f p = 𝟙 ((mappingCone φ).X p) := by
simpa only [Cochain.add_v, Cochain.comp_zero_cochain_v, Cochain.ofHom_v, id_f,
Cochain.comp_v _ _ (add_neg_cancel 1) p q p hpq (by omega)]
using Cochain.congr_v (id φ) p p (add_zero p)
@[reassoc]
lemma inl_v_d (i j k : ℤ) (hij : i + (-1) = j) (hik : k + (-1) = i) :
(inl φ).v i j hij ≫ (mappingCone φ).d j i =
φ.f i ≫ (inr φ).f i - F.d i k ≫ (inl φ).v _ _ hik := by
dsimp [mappingCone, inl, inr]
rw [homotopyCofiber.inlX_d φ j i k (by dsimp; omega) (by dsimp; omega)]
abel
@[reassoc]
lemma inr_f_d (n₁ n₂ : ℤ) :
(inr φ).f n₁ ≫ (mappingCone φ).d n₁ n₂ = G.d n₁ n₂ ≫ (inr φ).f n₂ := by
simp
@[reassoc]
lemma d_fst_v (i j k : ℤ) (hij : i + 1 = j) (hjk : j + 1 = k) :
(mappingCone φ).d i j ≫ (fst φ).1.v j k hjk =
-(fst φ).1.v i j hij ≫ F.d j k := by
apply homotopyCofiber.d_fstX
@[reassoc (attr := simp)]
lemma d_fst_v' (i j : ℤ) (hij : i + 1 = j) :
(mappingCone φ).d (i - 1) i ≫ (fst φ).1.v i j hij =
-(fst φ).1.v (i - 1) i (by omega) ≫ F.d i j :=
d_fst_v φ (i - 1) i j (by omega) hij
@[reassoc]
lemma d_snd_v (i j : ℤ) (hij : i + 1 = j) :
(mappingCone φ).d i j ≫ (snd φ).v j j (add_zero _) =
(fst φ).1.v i j hij ≫ φ.f j + (snd φ).v i i (add_zero i) ≫ G.d i j := by
dsimp [mappingCone, snd, fst]
simp only [Cochain.ofHoms_v]
apply homotopyCofiber.d_sndX
@[reassoc (attr := simp)]
lemma d_snd_v' (n : ℤ) :
(mappingCone φ).d (n - 1) n ≫ (snd φ).v n n (add_zero n) =
(fst φ : Cochain (mappingCone φ) F 1).v (n - 1) n (by omega) ≫ φ.f n +
(snd φ).v (n - 1) (n - 1) (add_zero _) ≫ G.d (n - 1) n := by
apply d_snd_v
@[simp]
lemma δ_inl :
δ (-1) 0 (inl φ) = Cochain.ofHom (φ ≫ inr φ) := by
ext p
simp [δ_v (-1) 0 (neg_add_cancel 1) (inl φ) p p (add_zero p) _ _ rfl rfl,
inl_v_d φ p (p - 1) (p + 1) (by omega) (by omega)]
@[simp]
lemma δ_snd :
δ 0 1 (snd φ) = -(fst φ).1.comp (Cochain.ofHom φ) (add_zero 1) := by
ext p q hpq
simp [d_snd_v φ p q hpq]
section
variable {K : CochainComplex C ℤ} {n m : ℤ}
/-- Given `φ : F ⟶ G`, this is the cochain in `Cochain (mappingCone φ) K n` that is
constructed from two cochains `α : Cochain F K m` (with `m + 1 = n`) and `β : Cochain F K n`. -/
noncomputable def descCochain (α : Cochain F K m) (β : Cochain G K n) (h : m + 1 = n) :
Cochain (mappingCone φ) K n :=
(fst φ).1.comp α (by rw [← h, add_comm]) + (snd φ).comp β (zero_add n)
variable (α : Cochain F K m) (β : Cochain G K n) (h : m + 1 = n)
@[simp]
lemma inl_descCochain :
(inl φ).comp (descCochain φ α β h) (by omega) = α := by
simp [descCochain]
@[simp]
lemma inr_descCochain :
(Cochain.ofHom (inr φ)).comp (descCochain φ α β h) (zero_add n) = β := by
simp [descCochain]
@[reassoc (attr := simp)]
lemma inl_v_descCochain_v (p₁ p₂ p₃ : ℤ) (h₁₂ : p₁ + (-1) = p₂) (h₂₃ : p₂ + n = p₃) :
(inl φ).v p₁ p₂ h₁₂ ≫ (descCochain φ α β h).v p₂ p₃ h₂₃ =
α.v p₁ p₃ (by rw [← h₂₃, ← h₁₂, ← h, add_comm m, add_assoc, neg_add_cancel_left]) := by
simpa only [Cochain.comp_v _ _ (show -1 + n = m by omega) p₁ p₂ p₃
(by omega) (by omega)] using
Cochain.congr_v (inl_descCochain φ α β h) p₁ p₃ (by omega)
@[reassoc (attr := simp)]
lemma inr_f_descCochain_v (p₁ p₂ : ℤ) (h₁₂ : p₁ + n = p₂) :
(inr φ).f p₁ ≫ (descCochain φ α β h).v p₁ p₂ h₁₂ = β.v p₁ p₂ h₁₂ := by
simpa only [Cochain.comp_v _ _ (zero_add n) p₁ p₁ p₂ (add_zero p₁) h₁₂, Cochain.ofHom_v]
using Cochain.congr_v (inr_descCochain φ α β h) p₁ p₂ (by omega)
lemma δ_descCochain (n' : ℤ) (hn' : n + 1 = n') :
δ n n' (descCochain φ α β h) =
(fst φ).1.comp (δ m n α +
n'.negOnePow • (Cochain.ofHom φ).comp β (zero_add n)) (by omega) +
(snd φ).comp (δ n n' β) (zero_add n') := by
dsimp only [descCochain]
simp only [δ_add, Cochain.comp_add, δ_comp (fst φ).1 α _ 2 n n' hn' (by omega) (by omega),
Cocycle.δ_eq_zero, Cochain.zero_comp, smul_zero, add_zero,
δ_comp (snd φ) β (zero_add n) 1 n' n' hn' (zero_add 1) hn', δ_snd, Cochain.neg_comp,
smul_neg, Cochain.comp_assoc_of_second_is_zero_cochain, Cochain.comp_units_smul, ← hn',
Int.negOnePow_succ, Units.neg_smul, Cochain.comp_neg]
abel
end
/-- Given `φ : F ⟶ G`, this is the cocycle in `Cocycle (mappingCone φ) K n` that is
constructed from `α : Cochain F K m` (with `m + 1 = n`) and `β : Cocycle F K n`,
when a suitable cocycle relation is satisfied. -/
@[simps!]
noncomputable def descCocycle {K : CochainComplex C ℤ} {n m : ℤ}
(α : Cochain F K m) (β : Cocycle G K n)
(h : m + 1 = n) (eq : δ m n α = n.negOnePow • (Cochain.ofHom φ).comp β.1 (zero_add n)) :
Cocycle (mappingCone φ) K n :=
Cocycle.mk (descCochain φ α β.1 h) (n + 1) rfl
(by simp [δ_descCochain _ _ _ _ _ rfl, eq, Int.negOnePow_succ])
section
variable {K : CochainComplex C ℤ}
/-- Given `φ : F ⟶ G`, this is the morphism `mappingCone φ ⟶ K` that is constructed
from a cochain `α : Cochain F K (-1)` and a morphism `β : G ⟶ K` such that
`δ (-1) 0 α = Cochain.ofHom (φ ≫ β)`. -/
noncomputable def desc (α : Cochain F K (-1)) (β : G ⟶ K)
(eq : δ (-1) 0 α = Cochain.ofHom (φ ≫ β)) : mappingCone φ ⟶ K :=
Cocycle.homOf (descCocycle φ α (Cocycle.ofHom β) (neg_add_cancel 1) (by simp [eq]))
variable (α : Cochain F K (-1)) (β : G ⟶ K) (eq : δ (-1) 0 α = Cochain.ofHom (φ ≫ β))
@[simp]
lemma ofHom_desc :
Cochain.ofHom (desc φ α β eq) = descCochain φ α (Cochain.ofHom β) (neg_add_cancel 1) := by
simp [desc]
@[reassoc (attr := simp)]
lemma inl_v_desc_f (p q : ℤ) (h : p + (-1) = q) :
(inl φ).v p q h ≫ (desc φ α β eq).f q = α.v p q h := by
simp [desc]
lemma inl_desc :
(inl φ).comp (Cochain.ofHom (desc φ α β eq)) (add_zero _) = α := by
simp
@[reassoc (attr := simp)]
lemma inr_f_desc_f (p : ℤ) :
(inr φ).f p ≫ (desc φ α β eq).f p = β.f p := by
simp [desc]
@[reassoc (attr := simp)]
lemma inr_desc : inr φ ≫ desc φ α β eq = β := by aesop_cat
lemma desc_f (p q : ℤ) (hpq : p + 1 = q) :
(desc φ α β eq).f p = (fst φ).1.v p q hpq ≫ α.v q p (by omega) +
(snd φ).v p p (add_zero p) ≫ β.f p := by
simp [ext_from_iff _ _ _ hpq]
end
/-- Constructor for homotopies between morphisms from a mapping cone. -/
noncomputable def descHomotopy {K : CochainComplex C ℤ} (f₁ f₂ : mappingCone φ ⟶ K)
(γ₁ : Cochain F K (-2)) (γ₂ : Cochain G K (-1))
(h₁ : (inl φ).comp (Cochain.ofHom f₁) (add_zero (-1)) =
δ (-2) (-1) γ₁ + (Cochain.ofHom φ).comp γ₂ (zero_add (-1)) +
(inl φ).comp (Cochain.ofHom f₂) (add_zero (-1)))
(h₂ : Cochain.ofHom (inr φ ≫ f₁) = δ (-1) 0 γ₂ + Cochain.ofHom (inr φ ≫ f₂)) :
Homotopy f₁ f₂ :=
(Cochain.equivHomotopy f₁ f₂).symm ⟨descCochain φ γ₁ γ₂ (by norm_num), by
simp only [Cochain.ofHom_comp] at h₂
simp [ext_cochain_from_iff _ _ _ (neg_add_cancel 1),
δ_descCochain _ _ _ _ _ (neg_add_cancel 1), h₁, h₂]⟩
section
variable {K : CochainComplex C ℤ} {n m : ℤ}
/-- Given `φ : F ⟶ G`, this is the cochain in `Cochain (mappingCone φ) K n` that is
constructed from two cochains `α : Cochain F K m` (with `m + 1 = n`) and `β : Cochain F K n`. -/
noncomputable def liftCochain (α : Cochain K F m) (β : Cochain K G n) (h : n + 1 = m) :
Cochain K (mappingCone φ) n :=
α.comp (inl φ) (by omega) + β.comp (Cochain.ofHom (inr φ)) (add_zero n)
variable (α : Cochain K F m) (β : Cochain K G n) (h : n + 1 = m)
@[simp]
lemma liftCochain_fst :
(liftCochain φ α β h).comp (fst φ).1 h = α := by
simp [liftCochain]
@[simp]
lemma liftCochain_snd :
(liftCochain φ α β h).comp (snd φ) (add_zero n) = β := by
simp [liftCochain]
@[reassoc (attr := simp)]
lemma liftCochain_v_fst_v (p₁ p₂ p₃ : ℤ) (h₁₂ : p₁ + n = p₂) (h₂₃ : p₂ + 1 = p₃) :
(liftCochain φ α β h).v p₁ p₂ h₁₂ ≫ (fst φ).1.v p₂ p₃ h₂₃ = α.v p₁ p₃ (by omega) := by
simpa only [Cochain.comp_v _ _ h p₁ p₂ p₃ h₁₂ h₂₃]
using Cochain.congr_v (liftCochain_fst φ α β h) p₁ p₃ (by omega)
@[reassoc (attr := simp)]
lemma liftCochain_v_snd_v (p₁ p₂ : ℤ) (h₁₂ : p₁ + n = p₂) :
(liftCochain φ α β h).v p₁ p₂ h₁₂ ≫ (snd φ).v p₂ p₂ (add_zero p₂) = β.v p₁ p₂ h₁₂ := by
simpa only [Cochain.comp_v _ _ (add_zero n) p₁ p₂ p₂ h₁₂ (add_zero p₂)]
using Cochain.congr_v (liftCochain_snd φ α β h) p₁ p₂ (by omega)
lemma δ_liftCochain (m' : ℤ) (hm' : m + 1 = m') :
δ n m (liftCochain φ α β h) = -(δ m m' α).comp (inl φ) (by omega) +
(δ n m β + α.comp (Cochain.ofHom φ) (add_zero m)).comp
(Cochain.ofHom (inr φ)) (add_zero m) := by
dsimp only [liftCochain]
simp only [δ_add, δ_comp α (inl φ) _ m' _ _ h hm' (neg_add_cancel 1),
δ_comp_zero_cochain _ _ _ h, δ_inl, Cochain.ofHom_comp,
Int.negOnePow_neg, Int.negOnePow_one, Units.neg_smul, one_smul,
δ_ofHom, Cochain.comp_zero, zero_add, Cochain.add_comp,
Cochain.comp_assoc_of_second_is_zero_cochain]
abel
end
/-- Given `φ : F ⟶ G`, this is the cocycle in `Cocycle K (mappingCone φ) n` that is
constructed from `α : Cochain K F m` (with `n + 1 = m`) and `β : Cocycle K G n`,
when a suitable cocycle relation is satisfied. -/
@[simps!]
noncomputable def liftCocycle {K : CochainComplex C ℤ} {n m : ℤ}
(α : Cocycle K F m) (β : Cochain K G n) (h : n + 1 = m)
(eq : δ n m β + α.1.comp (Cochain.ofHom φ) (add_zero m) = 0) :
Cocycle K (mappingCone φ) n :=
Cocycle.mk (liftCochain φ α β h) m h (by
simp only [δ_liftCochain φ α β h (m+1) rfl, eq,
Cocycle.δ_eq_zero, Cochain.zero_comp, neg_zero, add_zero])
section
variable {K : CochainComplex C ℤ} (α : Cocycle K F 1) (β : Cochain K G 0)
(eq : δ 0 1 β + α.1.comp (Cochain.ofHom φ) (add_zero 1) = 0)
/-- Given `φ : F ⟶ G`, this is the morphism `K ⟶ mappingCone φ` that is constructed
from a cocycle `α : Cochain K F 1` and a cochain `β : Cochain K G 0`
when a suitable cocycle relation is satisfied. -/
noncomputable def lift :
K ⟶ mappingCone φ :=
Cocycle.homOf (liftCocycle φ α β (zero_add 1) eq)
@[simp]
lemma ofHom_lift :
Cochain.ofHom (lift φ α β eq) = liftCochain φ α β (zero_add 1) := by
simp only [lift, Cocycle.cochain_ofHom_homOf_eq_coe, liftCocycle_coe]
| @[reassoc (attr := simp)]
lemma lift_f_fst_v (p q : ℤ) (hpq : p + 1 = q) :
(lift φ α β eq).f p ≫ (fst φ).1.v p q hpq = α.1.v p q hpq := by
simp [lift]
| Mathlib/Algebra/Homology/HomotopyCategory/MappingCone.lean | 483 | 487 |
/-
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.Fin.Tuple.Basic
/-!
# Lists from functions
Theorems and lemmas for dealing with `List.ofFn`, which converts a function on `Fin n` to a list
of length `n`.
## Main Statements
The main statements pertain to lists generated using `List.ofFn`
- `List.get?_ofFn`, which tells us the nth element of such a list
- `List.equivSigmaTuple`, which is an `Equiv` between lists and the functions that generate them
via `List.ofFn`.
-/
assert_not_exists Monoid
universe u
variable {α : Type u}
open Nat
namespace List
theorem get_ofFn {n} (f : Fin n → α) (i) : get (ofFn f) i = f (Fin.cast (by simp) i) := by
simp; congr
@[deprecated (since := "2025-02-15")] alias get?_ofFn := List.getElem?_ofFn
@[simp]
theorem map_ofFn {β : Type*} {n : ℕ} (f : Fin n → α) (g : α → β) :
map g (ofFn f) = ofFn (g ∘ f) :=
ext_get (by simp) fun i h h' => by simp
@[congr]
theorem ofFn_congr {m n : ℕ} (h : m = n) (f : Fin m → α) :
ofFn f = ofFn fun i : Fin n => f (Fin.cast h.symm i) := by
subst h
simp_rw [Fin.cast_refl, id]
theorem ofFn_succ' {n} (f : Fin (succ n) → α) :
ofFn f = (ofFn fun i => f (Fin.castSucc i)).concat (f (Fin.last _)) := by
induction' n with n IH
· rw [ofFn_zero, concat_nil, ofFn_succ, ofFn_zero]
rfl
· rw [ofFn_succ, IH, ofFn_succ, concat_cons, Fin.castSucc_zero]
congr
/-- Note this matches the convention of `List.ofFn_succ'`, putting the `Fin m` elements first. -/
theorem ofFn_add {m n} (f : Fin (m + n) → α) :
List.ofFn f =
(List.ofFn fun i => f (Fin.castAdd n i)) ++ List.ofFn fun j => f (Fin.natAdd m j) := by
induction' n with n IH
· rw [ofFn_zero, append_nil, Fin.castAdd_zero, Fin.cast_refl]
rfl
· rw [ofFn_succ', ofFn_succ', IH, append_concat]
rfl
@[simp]
theorem ofFn_fin_append {m n} (a : Fin m → α) (b : Fin n → α) :
List.ofFn (Fin.append a b) = List.ofFn a ++ List.ofFn b := by
simp_rw [ofFn_add, Fin.append_left, Fin.append_right]
/-- This breaks a list of `m*n` items into `m` groups each containing `n` elements. -/
theorem ofFn_mul {m n} (f : Fin (m * n) → α) :
List.ofFn f = List.flatten (List.ofFn fun i : Fin m => List.ofFn fun j : Fin n => f ⟨i * n + j,
calc
↑i * n + j < (i + 1) * n :=
(Nat.add_lt_add_left j.prop _).trans_eq (by rw [Nat.add_mul, Nat.one_mul])
_ ≤ _ := Nat.mul_le_mul_right _ i.prop⟩) := by
induction' m with m IH
· simp [ofFn_zero, Nat.zero_mul, ofFn_zero, flatten]
· simp_rw [ofFn_succ', succ_mul]
simp [flatten_concat, ofFn_add, IH]
rfl
/-- This breaks a list of `m*n` items into `n` groups each containing `m` elements. -/
theorem ofFn_mul' {m n} (f : Fin (m * n) → α) :
List.ofFn f = List.flatten (List.ofFn fun i : Fin n => List.ofFn fun j : Fin m => f ⟨m * i + j,
calc
m * i + j < m * (i + 1) :=
(Nat.add_lt_add_left j.prop _).trans_eq (by rw [Nat.mul_add, Nat.mul_one])
_ ≤ _ := Nat.mul_le_mul_left _ i.prop⟩) := by simp_rw [m.mul_comm, ofFn_mul, Fin.cast_mk]
@[simp]
theorem ofFn_get : ∀ l : List α, (ofFn (get l)) = l
| [] => by rw [ofFn_zero]
| a :: l => by
rw [ofFn_succ]
congr
exact ofFn_get l
@[simp]
theorem ofFn_getElem : ∀ l : List α, (ofFn (fun i : Fin l.length => l[(i : Nat)])) = l
| [] => by rw [ofFn_zero]
| a :: l => by
rw [ofFn_succ]
congr
exact ofFn_get l
@[simp]
theorem ofFn_getElem_eq_map {β : Type*} (l : List α) (f : α → β) :
ofFn (fun i : Fin l.length => f <| l[(i : Nat)]) = l.map f := by
rw [← Function.comp_def, ← map_ofFn, ofFn_getElem]
-- Note there is a now another `mem_ofFn` defined in Lean, with an existential on the RHS,
-- which is marked as a simp lemma.
theorem mem_ofFn' {n} (f : Fin n → α) (a : α) : a ∈ ofFn f ↔ a ∈ Set.range f := by
simp only [mem_iff_get, Set.mem_range, get_ofFn]
exact ⟨fun ⟨i, hi⟩ => ⟨Fin.cast (by simp) i, hi⟩, fun ⟨i, hi⟩ => ⟨Fin.cast (by simp) i, hi⟩⟩
theorem forall_mem_ofFn_iff {n : ℕ} {f : Fin n → α} {P : α → Prop} :
(∀ i ∈ ofFn f, P i) ↔ ∀ j : Fin n, P (f j) := by simp
@[simp]
theorem ofFn_const : ∀ (n : ℕ) (c : α), (ofFn fun _ : Fin n => c) = replicate n c
| 0, c => by rw [ofFn_zero, replicate_zero]
| n+1, c => by rw [replicate, ← ofFn_const n]; simp
@[simp]
theorem ofFn_fin_repeat {m} (a : Fin m → α) (n : ℕ) :
List.ofFn (Fin.repeat n a) = (List.replicate n (List.ofFn a)).flatten := by
simp_rw [ofFn_mul, ← ofFn_const, Fin.repeat, Fin.modNat, Nat.add_comm,
Nat.add_mul_mod_self_right, Nat.mod_eq_of_lt (Fin.is_lt _)]
@[simp]
theorem pairwise_ofFn {R : α → α → Prop} {n} {f : Fin n → α} :
(ofFn f).Pairwise R ↔ ∀ ⦃i j⦄, i < j → R (f i) (f j) := by
simp only [pairwise_iff_getElem, length_ofFn, List.getElem_ofFn,
(Fin.rightInverse_cast length_ofFn).surjective.forall, Fin.forall_iff, Fin.cast_mk,
Fin.mk_lt_mk, forall_comm (α := (_ : Prop)) (β := ℕ)]
lemma getLast_ofFn_succ {n : ℕ} (f : Fin n.succ → α) :
(ofFn f).getLast (mt ofFn_eq_nil_iff.1 (Nat.succ_ne_zero _)) = f (Fin.last _) :=
getLast_ofFn _
@[deprecated getLast_ofFn (since := "2024-11-06")]
theorem last_ofFn {n : ℕ} (f : Fin n → α) (h : ofFn f ≠ [])
(hn : n - 1 < n := Nat.pred_lt <| ofFn_eq_nil_iff.not.mp h) :
getLast (ofFn f) h = f ⟨n - 1, hn⟩ := by simp [getLast_eq_getElem]
@[deprecated getLast_ofFn_succ (since := "2024-11-06")]
theorem last_ofFn_succ {n : ℕ} (f : Fin n.succ → α)
(h : ofFn f ≠ [] := mt ofFn_eq_nil_iff.mp (Nat.succ_ne_zero _)) :
getLast (ofFn f) h = f (Fin.last _) :=
getLast_ofFn_succ _
lemma ofFn_cons {n} (a : α) (f : Fin n → α) : ofFn (Fin.cons a f) = a :: ofFn f := by
rw [ofFn_succ]
rfl
lemma find?_ofFn_eq_some {n} {f : Fin n → α} {p : α → Bool} {b : α} :
(ofFn f).find? p = some b ↔ p b = true ∧ ∃ i, f i = b ∧ ∀ j < i, ¬(p (f j) = true) := by
rw [find?_eq_some_iff_getElem]
exact ⟨fun ⟨hpb, i, hi, hfb, h⟩ ↦
⟨hpb, ⟨⟨i, length_ofFn (f := f) ▸ hi⟩, by simpa using hfb, fun j hj ↦ by simpa using h j hj⟩⟩,
fun ⟨hpb, i, hfb, h⟩ ↦
⟨hpb, ⟨i, (length_ofFn (f := f)).symm ▸ i.isLt, by simpa using hfb,
fun j hj ↦ by simpa using h ⟨j, by omega⟩ (by simpa using hj)⟩⟩⟩
lemma find?_ofFn_eq_some_of_injective {n} {f : Fin n → α} {p : α → Bool} {i : Fin n}
(h : Function.Injective f) :
(ofFn f).find? p = some (f i) ↔ p (f i) = true ∧ ∀ j < i, ¬(p (f j) = true) := by
simp only [find?_ofFn_eq_some, h.eq_iff, Bool.not_eq_true, exists_eq_left]
/-- Lists are equivalent to the sigma type of tuples of a given length. -/
@[simps]
def equivSigmaTuple : List α ≃ Σn, Fin n → α where
toFun l := ⟨l.length, l.get⟩
invFun f := List.ofFn f.2
left_inv := List.ofFn_get
right_inv := fun ⟨_, f⟩ =>
Fin.sigma_eq_of_eq_comp_cast length_ofFn <| funext fun i => get_ofFn f i
/-- A recursor for lists that expands a list into a function mapping to its elements.
This can be used with `induction l using List.ofFnRec`. -/
@[elab_as_elim]
def ofFnRec {C : List α → Sort*} (h : ∀ (n) (f : Fin n → α), C (List.ofFn f)) (l : List α) : C l :=
cast (congr_arg C l.ofFn_get) <|
h l.length l.get
@[simp]
theorem ofFnRec_ofFn {C : List α → Sort*} (h : ∀ (n) (f : Fin n → α), C (List.ofFn f)) {n : ℕ}
(f : Fin n → α) : @ofFnRec _ C h (List.ofFn f) = h _ f :=
equivSigmaTuple.rightInverse_symm.cast_eq (fun s => h s.1 s.2) ⟨n, f⟩
theorem exists_iff_exists_tuple {P : List α → Prop} :
(∃ l : List α, P l) ↔ ∃ (n : _) (f : Fin n → α), P (List.ofFn f) :=
equivSigmaTuple.symm.surjective.exists.trans Sigma.exists
theorem forall_iff_forall_tuple {P : List α → Prop} :
(∀ l : List α, P l) ↔ ∀ (n) (f : Fin n → α), P (List.ofFn f) :=
equivSigmaTuple.symm.surjective.forall.trans Sigma.forall
/-- `Fin.sigma_eq_iff_eq_comp_cast` may be useful to work with the RHS of this expression. -/
theorem ofFn_inj' {m n : ℕ} {f : Fin m → α} {g : Fin n → α} :
ofFn f = ofFn g ↔ (⟨m, f⟩ : Σn, Fin n → α) = ⟨n, g⟩ :=
Iff.symm <| equivSigmaTuple.symm.injective.eq_iff.symm
/-- Note we can only state this when the two functions are indexed by defeq `n`. -/
theorem ofFn_injective {n : ℕ} : Function.Injective (ofFn : (Fin n → α) → List α) := fun f g h =>
eq_of_heq <| by rw [ofFn_inj'] at h; cases h; rfl
/-- A special case of `List.ofFn_inj` for when the two functions are indexed by defeq `n`. -/
@[simp]
theorem ofFn_inj {n : ℕ} {f g : Fin n → α} : ofFn f = ofFn g ↔ f = g :=
ofFn_injective.eq_iff
end List
| Mathlib/Data/List/OfFn.lean | 233 | 235 | |
/-
Copyright (c) 2022 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Jireh Loreaux
-/
import Mathlib.Algebra.Algebra.Subalgebra.Lattice
import Mathlib.Algebra.Algebra.Tower
import Mathlib.Algebra.Star.Module
import Mathlib.Algebra.Star.NonUnitalSubalgebra
/-!
# Star subalgebras
A *-subalgebra is a subalgebra of a *-algebra which is closed under *.
The centralizer of a *-closed set is a *-subalgebra.
-/
universe u v
/-- A *-subalgebra is a subalgebra of a *-algebra which is closed under *. -/
structure StarSubalgebra (R : Type u) (A : Type v) [CommSemiring R] [StarRing R] [Semiring A]
[StarRing A] [Algebra R A] [StarModule R A] : Type v extends Subalgebra R A where
/-- The `carrier` is closed under the `star` operation. -/
star_mem' {a} : a ∈ carrier → star a ∈ carrier
namespace StarSubalgebra
/-- Forgetting that a *-subalgebra is closed under *.
-/
add_decl_doc StarSubalgebra.toSubalgebra
variable {F R A B C : Type*} [CommSemiring R] [StarRing R]
variable [Semiring A] [StarRing A] [Algebra R A] [StarModule R A]
variable [Semiring B] [StarRing B] [Algebra R B] [StarModule R B]
variable [Semiring C] [StarRing C] [Algebra R C] [StarModule R C]
instance setLike : SetLike (StarSubalgebra R A) A where
coe S := S.carrier
coe_injective' p q h := by obtain ⟨⟨⟨⟨⟨_, _⟩, _⟩, _⟩, _⟩, _⟩ := p; cases q; congr
/-- The actual `StarSubalgebra` obtained from an element of a type satisfying `SubsemiringClass`,
`SMulMemClass` and `StarMemClass`. -/
@[simps]
def ofClass {S R A : Type*} [CommSemiring R] [Semiring A] [Algebra R A] [StarRing R] [StarRing A]
[StarModule R A] [SetLike S A] [SubsemiringClass S A] [SMulMemClass S R A] [StarMemClass S A]
(s : S) : StarSubalgebra R A where
carrier := s
add_mem' := add_mem
zero_mem' := zero_mem _
mul_mem' := mul_mem
one_mem' := one_mem _
algebraMap_mem' := algebraMap_mem s
star_mem' := star_mem
instance (priority := 100) : CanLift (Set A) (StarSubalgebra R A) (↑)
(fun s ↦ (∀ {x y}, x ∈ s → y ∈ s → x + y ∈ s) ∧ (∀ {x y}, x ∈ s → y ∈ s → x * y ∈ s) ∧
(∀ (r : R), algebraMap R A r ∈ s) ∧ ∀ {x}, x ∈ s → star x ∈ s) where
prf s h :=
⟨ { carrier := s
zero_mem' := by simpa using h.2.2.1 0
add_mem' := h.1
one_mem' := by simpa using h.2.2.1 1
mul_mem' := h.2.1
algebraMap_mem' := h.2.2.1
star_mem' := h.2.2.2 },
rfl ⟩
instance starMemClass : StarMemClass (StarSubalgebra R A) A where
star_mem {s} := s.star_mem'
instance subsemiringClass : SubsemiringClass (StarSubalgebra R A) A where
add_mem {s} := s.add_mem'
mul_mem {s} := s.mul_mem'
one_mem {s} := s.one_mem'
zero_mem {s} := s.zero_mem'
instance smulMemClass : SMulMemClass (StarSubalgebra R A) R A where
smul_mem {s} r a (ha : a ∈ s.toSubalgebra) :=
(SMulMemClass.smul_mem r ha : r • a ∈ s.toSubalgebra)
instance subringClass {R A} [CommRing R] [StarRing R] [Ring A] [StarRing A] [Algebra R A]
[StarModule R A] : SubringClass (StarSubalgebra R A) A where
neg_mem {s a} ha := show -a ∈ s.toSubalgebra from neg_mem ha
-- this uses the `Star` instance `s` inherits from `StarMemClass (StarSubalgebra R A) A`
instance starRing (s : StarSubalgebra R A) : StarRing s :=
{ StarMemClass.instStar s with
star_involutive := fun r => Subtype.ext (star_star (r : A))
star_mul := fun r₁ r₂ => Subtype.ext (star_mul (r₁ : A) (r₂ : A))
star_add := fun r₁ r₂ => Subtype.ext (star_add (r₁ : A) (r₂ : A)) }
instance algebra (s : StarSubalgebra R A) : Algebra R s :=
s.toSubalgebra.algebra'
instance starModule (s : StarSubalgebra R A) : StarModule R s where
star_smul r a := Subtype.ext (star_smul r (a : A))
/-- Turn a `StarSubalgebra` into a `NonUnitalStarSubalgebra` by forgetting that it contains `1`. -/
def toNonUnitalStarSubalgebra (S : StarSubalgebra R A) : NonUnitalStarSubalgebra R A where
__ := S
smul_mem' r _x hx := S.smul_mem hx r
lemma one_mem_toNonUnitalStarSubalgebra (S : StarSubalgebra R A) :
1 ∈ S.toNonUnitalStarSubalgebra := S.one_mem'
theorem mem_carrier {s : StarSubalgebra R A} {x : A} : x ∈ s.carrier ↔ x ∈ s :=
Iff.rfl
@[ext]
theorem ext {S T : StarSubalgebra R A} (h : ∀ x : A, x ∈ S ↔ x ∈ T) : S = T :=
SetLike.ext h
@[simp]
lemma coe_mk (S : Subalgebra R A) (h) : ((⟨S, h⟩ : StarSubalgebra R A) : Set A) = S := rfl
@[simp]
theorem mem_toSubalgebra {S : StarSubalgebra R A} {x} : x ∈ S.toSubalgebra ↔ x ∈ S :=
Iff.rfl
@[simp]
theorem coe_toSubalgebra (S : StarSubalgebra R A) : (S.toSubalgebra : Set A) = S :=
rfl
theorem toSubalgebra_injective :
Function.Injective (toSubalgebra : StarSubalgebra R A → Subalgebra R A) := fun S T h =>
ext fun x => by rw [← mem_toSubalgebra, ← mem_toSubalgebra, h]
theorem toSubalgebra_inj {S U : StarSubalgebra R A} : S.toSubalgebra = U.toSubalgebra ↔ S = U :=
toSubalgebra_injective.eq_iff
theorem toSubalgebra_le_iff {S₁ S₂ : StarSubalgebra R A} :
S₁.toSubalgebra ≤ S₂.toSubalgebra ↔ S₁ ≤ S₂ :=
Iff.rfl
/-- Copy of a star subalgebra with a new `carrier` equal to the old one. Useful to fix definitional
equalities. -/
protected def copy (S : StarSubalgebra R A) (s : Set A) (hs : s = ↑S) : StarSubalgebra R A where
toSubalgebra := Subalgebra.copy S.toSubalgebra s hs
star_mem' {a} ha := hs ▸ S.star_mem' (by simpa [hs] using ha)
@[simp]
theorem coe_copy (S : StarSubalgebra R A) (s : Set A) (hs : s = ↑S) : (S.copy s hs : Set A) = s :=
rfl
theorem copy_eq (S : StarSubalgebra R A) (s : Set A) (hs : s = ↑S) : S.copy s hs = S :=
SetLike.coe_injective hs
variable (S : StarSubalgebra R A)
protected theorem algebraMap_mem (r : R) : algebraMap R A r ∈ S :=
S.algebraMap_mem' r
theorem rangeS_le : (algebraMap R A).rangeS ≤ S.toSubalgebra.toSubsemiring := fun _x ⟨r, hr⟩ =>
hr ▸ S.algebraMap_mem r
theorem range_subset : Set.range (algebraMap R A) ⊆ S := fun _x ⟨r, hr⟩ => hr ▸ S.algebraMap_mem r
theorem range_le : Set.range (algebraMap R A) ≤ S :=
S.range_subset
protected theorem smul_mem {x : A} (hx : x ∈ S) (r : R) : r • x ∈ S :=
(Algebra.smul_def r x).symm ▸ mul_mem (S.algebraMap_mem r) hx
/-- Embedding of a subalgebra into the algebra. -/
def subtype : S →⋆ₐ[R] A where
toFun := ((↑) : S → A)
map_one' := rfl
map_mul' _ _ := rfl
map_zero' := rfl
map_add' _ _ := rfl
commutes' _ := rfl
map_star' _ := rfl
@[simp]
theorem coe_subtype : (S.subtype : S → A) = Subtype.val :=
rfl
theorem subtype_apply (x : S) : S.subtype x = (x : A) :=
rfl
@[simp]
theorem toSubalgebra_subtype : S.toSubalgebra.val = S.subtype.toAlgHom :=
rfl
/-- The inclusion map between `StarSubalgebra`s given by `Subtype.map id` as a `StarAlgHom`. -/
@[simps]
def inclusion {S₁ S₂ : StarSubalgebra R A} (h : S₁ ≤ S₂) : S₁ →⋆ₐ[R] S₂ where
toFun := Subtype.map id h
map_one' := rfl
map_mul' _ _ := rfl
map_zero' := rfl
map_add' _ _ := rfl
commutes' _ := rfl
map_star' _ := rfl
theorem inclusion_injective {S₁ S₂ : StarSubalgebra R A} (h : S₁ ≤ S₂) :
Function.Injective <| inclusion h :=
Set.inclusion_injective h
@[simp]
theorem subtype_comp_inclusion {S₁ S₂ : StarSubalgebra R A} (h : S₁ ≤ S₂) :
S₂.subtype.comp (inclusion h) = S₁.subtype :=
rfl
section Map
/-- Transport a star subalgebra via a star algebra homomorphism. -/
def map (f : A →⋆ₐ[R] B) (S : StarSubalgebra R A) : StarSubalgebra R B :=
{ S.toSubalgebra.map f.toAlgHom with
star_mem' := by
rintro _ ⟨a, ha, rfl⟩
exact map_star f a ▸ Set.mem_image_of_mem _ (S.star_mem' ha) }
theorem map_mono {S₁ S₂ : StarSubalgebra R A} {f : A →⋆ₐ[R] B} : S₁ ≤ S₂ → S₁.map f ≤ S₂.map f :=
Set.image_subset f
theorem map_injective {f : A →⋆ₐ[R] B} (hf : Function.Injective f) : Function.Injective (map f) :=
fun _S₁ _S₂ ih =>
ext <| Set.ext_iff.1 <| Set.image_injective.2 hf <| Set.ext <| SetLike.ext_iff.mp ih
@[simp]
theorem map_id (S : StarSubalgebra R A) : S.map (StarAlgHom.id R A) = S :=
SetLike.coe_injective <| Set.image_id _
theorem map_map (S : StarSubalgebra R A) (g : B →⋆ₐ[R] C) (f : A →⋆ₐ[R] B) :
(S.map f).map g = S.map (g.comp f) :=
SetLike.coe_injective <| Set.image_image _ _ _
@[simp]
theorem mem_map {S : StarSubalgebra R A} {f : A →⋆ₐ[R] B} {y : B} :
y ∈ map f S ↔ ∃ x ∈ S, f x = y :=
Subsemiring.mem_map
theorem map_toSubalgebra {S : StarSubalgebra R A} {f : A →⋆ₐ[R] B} :
(S.map f).toSubalgebra = S.toSubalgebra.map f.toAlgHom :=
SetLike.coe_injective rfl
@[simp]
theorem coe_map (S : StarSubalgebra R A) (f : A →⋆ₐ[R] B) : (S.map f : Set B) = f '' S :=
rfl
/-- Preimage of a star subalgebra under a star algebra homomorphism. -/
def comap (f : A →⋆ₐ[R] B) (S : StarSubalgebra R B) : StarSubalgebra R A :=
{ S.toSubalgebra.comap f.toAlgHom with
star_mem' := @fun a ha => show f (star a) ∈ S from (map_star f a).symm ▸ star_mem ha }
theorem map_le_iff_le_comap {S : StarSubalgebra R A} {f : A →⋆ₐ[R] B} {U : StarSubalgebra R B} :
map f S ≤ U ↔ S ≤ comap f U :=
Set.image_subset_iff
theorem gc_map_comap (f : A →⋆ₐ[R] B) : GaloisConnection (map f) (comap f) := fun _S _U =>
map_le_iff_le_comap
theorem comap_mono {S₁ S₂ : StarSubalgebra R B} {f : A →⋆ₐ[R] B} :
S₁ ≤ S₂ → S₁.comap f ≤ S₂.comap f :=
Set.preimage_mono
theorem comap_injective {f : A →⋆ₐ[R] B} (hf : Function.Surjective f) :
Function.Injective (comap f) := fun _S₁ _S₂ h =>
ext fun b =>
let ⟨x, hx⟩ := hf b
let this := SetLike.ext_iff.1 h x
hx ▸ this
@[simp]
theorem comap_id (S : StarSubalgebra R A) : S.comap (StarAlgHom.id R A) = S :=
SetLike.coe_injective <| Set.preimage_id
theorem comap_comap (S : StarSubalgebra R C) (g : B →⋆ₐ[R] C) (f : A →⋆ₐ[R] B) :
(S.comap g).comap f = S.comap (g.comp f) :=
SetLike.coe_injective <| by exact Set.preimage_preimage
@[simp]
theorem mem_comap (S : StarSubalgebra R B) (f : A →⋆ₐ[R] B) (x : A) : x ∈ S.comap f ↔ f x ∈ S :=
Iff.rfl
@[simp, norm_cast]
theorem coe_comap (S : StarSubalgebra R B) (f : A →⋆ₐ[R] B) :
(S.comap f : Set A) = f ⁻¹' (S : Set B) :=
rfl
end Map
section Centralizer
variable (R)
/-- The centralizer, or commutant, of the star-closure of a set as a star subalgebra. -/
def centralizer (s : Set A) : StarSubalgebra R A where
toSubalgebra := Subalgebra.centralizer R (s ∪ star s)
star_mem' := Set.star_mem_centralizer
@[simp, norm_cast]
theorem coe_centralizer (s : Set A) : (centralizer R s : Set A) = (s ∪ star s).centralizer :=
rfl
open Set in
nonrec theorem mem_centralizer_iff {s : Set A} {z : A} :
z ∈ centralizer R s ↔ ∀ g ∈ s, g * z = z * g ∧ star g * z = z * star g := by
simp [← SetLike.mem_coe, centralizer_union, ← image_star, mem_centralizer_iff, forall_and]
theorem centralizer_le (s t : Set A) (h : s ⊆ t) : centralizer R t ≤ centralizer R s :=
Set.centralizer_subset (Set.union_subset_union h <| Set.preimage_mono h)
theorem centralizer_toSubalgebra (s : Set A) :
(centralizer R s).toSubalgebra = Subalgebra.centralizer R (s ∪ star s):=
rfl
theorem coe_centralizer_centralizer (s : Set A) :
(centralizer R (centralizer R s : Set A)) = (s ∪ star s).centralizer.centralizer := by
rw [coe_centralizer, StarMemClass.star_coe_eq, Set.union_self, coe_centralizer]
end Centralizer
end StarSubalgebra
/-! ### The star closure of a subalgebra -/
namespace Subalgebra
open Pointwise
variable {F R A B : Type*} [CommSemiring R] [StarRing R]
variable [Semiring A] [Algebra R A] [StarRing A] [StarModule R A]
variable [Semiring B] [Algebra R B] [StarRing B] [StarModule R B]
/-- The pointwise `star` of a subalgebra is a subalgebra. -/
instance involutiveStar : InvolutiveStar (Subalgebra R A) where
star S :=
{ carrier := star S.carrier
mul_mem' := fun {x y} hx hy => by
simp only [Set.mem_star, Subalgebra.mem_carrier] at *
exact (star_mul x y).symm ▸ mul_mem hy hx
one_mem' := Set.mem_star.mp ((star_one A).symm ▸ one_mem S : star (1 : A) ∈ S)
add_mem' := fun {x y} hx hy => by
simp only [Set.mem_star, Subalgebra.mem_carrier] at *
exact (star_add x y).symm ▸ add_mem hx hy
zero_mem' := Set.mem_star.mp ((star_zero A).symm ▸ zero_mem S : star (0 : A) ∈ S)
algebraMap_mem' := fun r => by
simpa only [Set.mem_star, Subalgebra.mem_carrier, ← algebraMap_star_comm] using
S.algebraMap_mem (star r) }
star_involutive S :=
Subalgebra.ext fun x =>
⟨fun hx => star_star x ▸ hx, fun hx => ((star_star x).symm ▸ hx : star (star x) ∈ S)⟩
@[simp]
theorem mem_star_iff (S : Subalgebra R A) (x : A) : x ∈ star S ↔ star x ∈ S :=
Iff.rfl
theorem star_mem_star_iff (S : Subalgebra R A) (x : A) : star x ∈ star S ↔ x ∈ S := by
simp
@[simp]
theorem coe_star (S : Subalgebra R A) : ((star S : Subalgebra R A) : Set A) = star (S : Set A) :=
rfl
theorem star_mono : Monotone (star : Subalgebra R A → Subalgebra R A) := fun _ _ h _ hx => h hx
variable (R) in
/-- The star operation on `Subalgebra` commutes with `Algebra.adjoin`. -/
theorem star_adjoin_comm (s : Set A) : star (Algebra.adjoin R s) = Algebra.adjoin R (star s) :=
have this : ∀ t : Set A, Algebra.adjoin R (star t) ≤ star (Algebra.adjoin R t) := fun _ =>
Algebra.adjoin_le fun _ hx => Algebra.subset_adjoin hx
le_antisymm (by simpa only [star_star] using Subalgebra.star_mono (this (star s))) (this s)
/-- The `StarSubalgebra` obtained from `S : Subalgebra R A` by taking the smallest subalgebra
containing both `S` and `star S`. -/
@[simps!]
def starClosure (S : Subalgebra R A) : StarSubalgebra R A where
toSubalgebra := S ⊔ star S
star_mem' := fun {a} ha => by
simp only [Subalgebra.mem_carrier, ← (@Algebra.gi R A _ _ _).l_sup_u _ _] at *
rw [← mem_star_iff _ a, star_adjoin_comm, sup_comm]
simpa using ha
theorem starClosure_toSubalgebra (S : Subalgebra R A) : S.starClosure.toSubalgebra = S ⊔ star S :=
rfl
theorem starClosure_le {S₁ : Subalgebra R A} {S₂ : StarSubalgebra R A} (h : S₁ ≤ S₂.toSubalgebra) :
S₁.starClosure ≤ S₂ :=
StarSubalgebra.toSubalgebra_le_iff.1 <|
sup_le h fun x hx =>
(star_star x ▸ star_mem (show star x ∈ S₂ from h <| (S₁.mem_star_iff _).1 hx) : x ∈ S₂)
theorem starClosure_le_iff {S₁ : Subalgebra R A} {S₂ : StarSubalgebra R A} :
S₁.starClosure ≤ S₂ ↔ S₁ ≤ S₂.toSubalgebra :=
⟨fun h => le_sup_left.trans h, starClosure_le⟩
end Subalgebra
/-! ### The star subalgebra generated by a set -/
namespace StarAlgebra
open StarSubalgebra
variable {F R A B : Type*} [CommSemiring R] [StarRing R]
variable [Semiring A] [Algebra R A] [StarRing A] [StarModule R A]
variable [Semiring B] [Algebra R B] [StarRing B] [StarModule R B]
variable (R)
/-- The minimal star subalgebra that contains `s`. -/
@[simps!]
def adjoin (s : Set A) : StarSubalgebra R A :=
{ Algebra.adjoin R (s ∪ star s) with
star_mem' := fun hx => by
rwa [Subalgebra.mem_carrier, ← Subalgebra.mem_star_iff, Subalgebra.star_adjoin_comm,
Set.union_star, star_star, Set.union_comm] }
theorem adjoin_eq_starClosure_adjoin (s : Set A) : adjoin R s = (Algebra.adjoin R s).starClosure :=
toSubalgebra_injective <|
show Algebra.adjoin R (s ∪ star s) = Algebra.adjoin R s ⊔ star (Algebra.adjoin R s) from
(Subalgebra.star_adjoin_comm R s).symm ▸ Algebra.adjoin_union s (star s)
theorem adjoin_toSubalgebra (s : Set A) :
(adjoin R s).toSubalgebra = Algebra.adjoin R (s ∪ star s) :=
rfl
@[aesop safe 20 apply (rule_sets := [SetLike])]
theorem subset_adjoin (s : Set A) : s ⊆ adjoin R s :=
Set.subset_union_left.trans Algebra.subset_adjoin
theorem star_subset_adjoin (s : Set A) : star s ⊆ adjoin R s :=
Set.subset_union_right.trans Algebra.subset_adjoin
theorem self_mem_adjoin_singleton (x : A) : x ∈ adjoin R ({x} : Set A) :=
Algebra.subset_adjoin <| Set.mem_union_left _ (Set.mem_singleton x)
theorem star_self_mem_adjoin_singleton (x : A) : star x ∈ adjoin R ({x} : Set A) :=
star_mem <| self_mem_adjoin_singleton R x
variable {R}
protected theorem gc : GaloisConnection (adjoin R : Set A → StarSubalgebra R A) (↑) := by
intro s S
rw [← toSubalgebra_le_iff, adjoin_toSubalgebra, Algebra.adjoin_le_iff, coe_toSubalgebra]
exact
⟨fun h => Set.subset_union_left.trans h, fun h =>
Set.union_subset h fun x hx => star_star x ▸ star_mem (show star x ∈ S from h hx)⟩
/-- Galois insertion between `adjoin` and `coe`. -/
protected def gi : GaloisInsertion (adjoin R : Set A → StarSubalgebra R A) (↑) where
choice s hs := (adjoin R s).copy s <| le_antisymm (StarAlgebra.gc.le_u_l s) hs
gc := StarAlgebra.gc
le_l_u S := (StarAlgebra.gc (S : Set A) (adjoin R S)).1 <| le_rfl
choice_eq _ _ := StarSubalgebra.copy_eq _ _ _
theorem adjoin_le {S : StarSubalgebra R A} {s : Set A} (hs : s ⊆ S) : adjoin R s ≤ S :=
StarAlgebra.gc.l_le hs
theorem adjoin_le_iff {S : StarSubalgebra R A} {s : Set A} : adjoin R s ≤ S ↔ s ⊆ S :=
StarAlgebra.gc _ _
lemma adjoin_eq (S : StarSubalgebra R A) : adjoin R (S : Set A) = S :=
le_antisymm (adjoin_le le_rfl) (subset_adjoin R (S : Set A))
open Submodule in
lemma adjoin_eq_span (s : Set A) :
Subalgebra.toSubmodule (adjoin R s).toSubalgebra = span R (Submonoid.closure (s ∪ star s)) := by
rw [adjoin_toSubalgebra, Algebra.adjoin_eq_span]
open Submodule in
lemma adjoin_nonUnitalStarSubalgebra_eq_span (s : NonUnitalStarSubalgebra R A) :
(adjoin R (s : Set A)).toSubalgebra.toSubmodule = span R {1} ⊔ s.toSubmodule := by
rw [adjoin_eq_span, Submonoid.closure_eq_one_union, span_union,
← NonUnitalStarAlgebra.adjoin_eq_span, NonUnitalStarAlgebra.adjoin_eq]
theorem _root_.Subalgebra.starClosure_eq_adjoin (S : Subalgebra R A) :
S.starClosure = adjoin R (S : Set A) :=
le_antisymm (Subalgebra.starClosure_le_iff.2 <| subset_adjoin R (S : Set A))
(adjoin_le (le_sup_left : S ≤ S ⊔ star S))
/-- If some predicate holds for all `x ∈ (s : Set A)` and this predicate is closed under the
`algebraMap`, addition, multiplication and star operations, then it holds for `a ∈ adjoin R s`. -/
@[elab_as_elim]
theorem adjoin_induction {s : Set A} {p : (x : A) → x ∈ adjoin R s → Prop}
(mem : ∀ (x) (h : x ∈ s), p x (subset_adjoin R s h))
(algebraMap : ∀ r, p (_root_.algebraMap R _ r) (_root_.algebraMap_mem _ r))
(add : ∀ x y hx hy, p x hx → p y hy → p (x + y) (add_mem hx hy))
(mul : ∀ x y hx hy, p x hx → p y hy → p (x * y) (mul_mem hx hy))
(star : ∀ x hx, p x hx → p (star x) (star_mem hx))
{a : A} (ha : a ∈ adjoin R s) : p a ha := by
refine Algebra.adjoin_induction (fun x hx ↦ ?_) algebraMap add mul ha
simp only [Set.mem_union, Set.mem_star] at hx
obtain (hx | hx) := hx
· exact mem x hx
· simpa using star _ (Algebra.subset_adjoin (by simpa using Or.inl hx)) (mem _ hx)
@[elab_as_elim]
theorem adjoin_induction₂ {s : Set A} {p : (x y : A) → x ∈ adjoin R s → y ∈ adjoin R s → Prop}
(mem_mem : ∀ (x) (y) (hx : x ∈ s) (hy : y ∈ s), p x y (subset_adjoin R s hx)
(subset_adjoin R s hy))
(algebraMap_both : ∀ r₁ r₂, p (algebraMap R A r₁) (algebraMap R A r₂)
(_root_.algebraMap_mem _ r₁) (_root_.algebraMap_mem _ r₂))
(algebraMap_left : ∀ (r) (x) (hx : x ∈ s), p (algebraMap R A r) x (_root_.algebraMap_mem _ r)
(subset_adjoin R s hx))
(algebraMap_right : ∀ (r) (x) (hx : x ∈ s), p x (algebraMap R A r) (subset_adjoin R s hx)
(_root_.algebraMap_mem _ r))
(add_left : ∀ x y z hx hy hz, p x z hx hz → p y z hy hz → p (x + y) z (add_mem hx hy) hz)
(add_right : ∀ x y z hx hy hz, p x y hx hy → p x z hx hz → p x (y + z) hx (add_mem hy hz))
(mul_left : ∀ x y z hx hy hz, p x z hx hz → p y z hy hz → p (x * y) z (mul_mem hx hy) hz)
(mul_right : ∀ x y z hx hy hz, p x y hx hy → p x z hx hz → p x (y * z) hx (mul_mem hy hz))
(star_left : ∀ x y hx hy, p x y hx hy → p (star x) y (star_mem hx) hy)
(star_right : ∀ x y hx hy, p x y hx hy → p x (star y) hx (star_mem hy))
{a b : A} (ha : a ∈ adjoin R s) (hb : b ∈ adjoin R s) :
p a b ha hb := by
induction hb using adjoin_induction with
| mem z hz => induction ha using adjoin_induction with
| mem _ h => exact mem_mem _ _ h hz
| algebraMap _ => exact algebraMap_left _ _ hz
| mul _ _ _ _ h₁ h₂ => exact mul_left _ _ _ _ _ _ h₁ h₂
| add _ _ _ _ h₁ h₂ => exact add_left _ _ _ _ _ _ h₁ h₂
| star _ _ h => exact star_left _ _ _ _ h
| algebraMap r =>
| induction ha using adjoin_induction with
| mem _ h => exact algebraMap_right _ _ h
| algebraMap _ => exact algebraMap_both _ _
| mul _ _ _ _ h₁ h₂ => exact mul_left _ _ _ _ _ _ h₁ h₂
| add _ _ _ _ h₁ h₂ => exact add_left _ _ _ _ _ _ h₁ h₂
| star _ _ h => exact star_left _ _ _ _ h
| mul _ _ _ _ h₁ h₂ => exact mul_right _ _ _ _ _ _ h₁ h₂
| add _ _ _ _ h₁ h₂ => exact add_right _ _ _ _ _ _ h₁ h₂
| star _ _ h => exact star_right _ _ _ _ h
/-- The difference with `StarSubalgebra.adjoin_induction` is that this acts on the subtype. -/
@[elab_as_elim]
theorem adjoin_induction_subtype {s : Set A} {p : adjoin R s → Prop} (a : adjoin R s)
(mem : ∀ (x) (h : x ∈ s), p ⟨x, subset_adjoin R s h⟩) (algebraMap : ∀ r, p (algebraMap R _ r))
(add : ∀ x y, p x → p y → p (x + y)) (mul : ∀ x y, p x → p y → p (x * y))
(star : ∀ x, p x → p (star x)) : p a :=
Subtype.recOn a fun b hb => by
induction hb using adjoin_induction with
| mem _ h => exact mem _ h
| algebraMap _ => exact algebraMap _
| mul _ _ _ _ h₁ h₂ => exact mul _ _ h₁ h₂
| add _ _ _ _ h₁ h₂ => exact add _ _ h₁ h₂
| star _ _ h => exact star _ h
variable (R)
| Mathlib/Algebra/Star/Subalgebra.lean | 519 | 543 |
/-
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 | 928 | 933 | |
/-
Copyright (c) 2020 Frédéric Dupuis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Frédéric Dupuis
-/
import Mathlib.Algebra.Algebra.Field
import Mathlib.Algebra.BigOperators.Balance
import Mathlib.Algebra.Order.BigOperators.Expect
import Mathlib.Algebra.Order.Star.Basic
import Mathlib.Analysis.CStarAlgebra.Basic
import Mathlib.Analysis.Normed.Operator.ContinuousLinearMap
import Mathlib.Data.Real.Sqrt
import Mathlib.LinearAlgebra.Basis.VectorSpace
/-!
# `RCLike`: a typeclass for ℝ or ℂ
This file defines the typeclass `RCLike` intended to have only two instances:
ℝ and ℂ. It is meant for definitions and theorems which hold for both the real and the complex case,
and in particular when the real case follows directly from the complex case by setting `re` to `id`,
`im` to zero and so on. Its API follows closely that of ℂ.
Applications include defining inner products and Hilbert spaces for both the real and
complex case. One typically produces the definitions and proof for an arbitrary field of this
typeclass, which basically amounts to doing the complex case, and the two cases then fall out
immediately from the two instances of the class.
The instance for `ℝ` is registered in this file.
The instance for `ℂ` is declared in `Mathlib/Analysis/Complex/Basic.lean`.
## Implementation notes
The coercion from reals into an `RCLike` field is done by registering `RCLike.ofReal` as
a `CoeTC`. For this to work, we must proceed carefully to avoid problems involving circular
coercions in the case `K=ℝ`; in particular, we cannot use the plain `Coe` and must set
priorities carefully. This problem was already solved for `ℕ`, and we copy the solution detailed
in `Mathlib/Data/Nat/Cast/Defs.lean`. See also Note [coercion into rings] for more details.
In addition, several lemmas need to be set at priority 900 to make sure that they do not override
their counterparts in `Mathlib/Analysis/Complex/Basic.lean` (which causes linter errors).
A few lemmas requiring heavier imports are in `Mathlib/Analysis/RCLike/Lemmas.lean`.
-/
open Fintype
open scoped BigOperators ComplexConjugate
section
local notation "𝓚" => algebraMap ℝ _
/--
This typeclass captures properties shared by ℝ and ℂ, with an API that closely matches that of ℂ.
-/
class RCLike (K : semiOutParam Type*) extends DenselyNormedField K, StarRing K,
NormedAlgebra ℝ K, CompleteSpace K where
/-- The real part as an additive monoid homomorphism -/
re : K →+ ℝ
/-- The imaginary part as an additive monoid homomorphism -/
im : K →+ ℝ
/-- Imaginary unit in `K`. Meant to be set to `0` for `K = ℝ`. -/
I : K
I_re_ax : re I = 0
I_mul_I_ax : I = 0 ∨ I * I = -1
re_add_im_ax : ∀ z : K, 𝓚 (re z) + 𝓚 (im z) * I = z
ofReal_re_ax : ∀ r : ℝ, re (𝓚 r) = r
ofReal_im_ax : ∀ r : ℝ, im (𝓚 r) = 0
mul_re_ax : ∀ z w : K, re (z * w) = re z * re w - im z * im w
mul_im_ax : ∀ z w : K, im (z * w) = re z * im w + im z * re w
conj_re_ax : ∀ z : K, re (conj z) = re z
conj_im_ax : ∀ z : K, im (conj z) = -im z
conj_I_ax : conj I = -I
norm_sq_eq_def_ax : ∀ z : K, ‖z‖ ^ 2 = re z * re z + im z * im z
mul_im_I_ax : ∀ z : K, im z * im I = im z
/-- only an instance in the `ComplexOrder` locale -/
[toPartialOrder : PartialOrder K]
le_iff_re_im {z w : K} : z ≤ w ↔ re z ≤ re w ∧ im z = im w
-- note we cannot put this in the `extends` clause
[toDecidableEq : DecidableEq K]
scoped[ComplexOrder] attribute [instance 100] RCLike.toPartialOrder
attribute [instance 100] RCLike.toDecidableEq
end
variable {K E : Type*} [RCLike K]
namespace RCLike
/-- Coercion from `ℝ` to an `RCLike` field. -/
@[coe] abbrev ofReal : ℝ → K := Algebra.cast
/- The priority must be set at 900 to ensure that coercions are tried in the right order.
See Note [coercion into rings], or `Mathlib/Data/Nat/Cast/Basic.lean` for more details. -/
noncomputable instance (priority := 900) algebraMapCoe : CoeTC ℝ K :=
⟨ofReal⟩
theorem ofReal_alg (x : ℝ) : (x : K) = x • (1 : K) :=
Algebra.algebraMap_eq_smul_one x
theorem real_smul_eq_coe_mul (r : ℝ) (z : K) : r • z = (r : K) * z :=
Algebra.smul_def r z
theorem real_smul_eq_coe_smul [AddCommGroup E] [Module K E] [Module ℝ E] [IsScalarTower ℝ K E]
(r : ℝ) (x : E) : r • x = (r : K) • x := by rw [RCLike.ofReal_alg, smul_one_smul]
theorem algebraMap_eq_ofReal : ⇑(algebraMap ℝ K) = ofReal :=
rfl
@[simp, rclike_simps]
theorem re_add_im (z : K) : (re z : K) + im z * I = z :=
RCLike.re_add_im_ax z
@[simp, norm_cast, rclike_simps]
theorem ofReal_re : ∀ r : ℝ, re (r : K) = r :=
RCLike.ofReal_re_ax
@[simp, norm_cast, rclike_simps]
theorem ofReal_im : ∀ r : ℝ, im (r : K) = 0 :=
RCLike.ofReal_im_ax
@[simp, rclike_simps]
theorem mul_re : ∀ z w : K, re (z * w) = re z * re w - im z * im w :=
RCLike.mul_re_ax
@[simp, rclike_simps]
theorem mul_im : ∀ z w : K, im (z * w) = re z * im w + im z * re w :=
RCLike.mul_im_ax
theorem ext_iff {z w : K} : z = w ↔ re z = re w ∧ im z = im w :=
⟨fun h => h ▸ ⟨rfl, rfl⟩, fun ⟨h₁, h₂⟩ => re_add_im z ▸ re_add_im w ▸ h₁ ▸ h₂ ▸ rfl⟩
theorem ext {z w : K} (hre : re z = re w) (him : im z = im w) : z = w :=
ext_iff.2 ⟨hre, him⟩
@[norm_cast]
theorem ofReal_zero : ((0 : ℝ) : K) = 0 :=
algebraMap.coe_zero
@[rclike_simps]
theorem zero_re' : re (0 : K) = (0 : ℝ) :=
map_zero re
@[norm_cast]
theorem ofReal_one : ((1 : ℝ) : K) = 1 :=
map_one (algebraMap ℝ K)
@[simp, rclike_simps]
theorem one_re : re (1 : K) = 1 := by rw [← ofReal_one, ofReal_re]
@[simp, rclike_simps]
theorem one_im : im (1 : K) = 0 := by rw [← ofReal_one, ofReal_im]
theorem ofReal_injective : Function.Injective ((↑) : ℝ → K) :=
(algebraMap ℝ K).injective
@[norm_cast]
theorem ofReal_inj {z w : ℝ} : (z : K) = (w : K) ↔ z = w :=
algebraMap.coe_inj
-- replaced by `RCLike.ofNat_re`
-- replaced by `RCLike.ofNat_im`
theorem ofReal_eq_zero {x : ℝ} : (x : K) = 0 ↔ x = 0 :=
algebraMap.lift_map_eq_zero_iff x
theorem ofReal_ne_zero {x : ℝ} : (x : K) ≠ 0 ↔ x ≠ 0 :=
ofReal_eq_zero.not
@[rclike_simps, norm_cast]
theorem ofReal_add (r s : ℝ) : ((r + s : ℝ) : K) = r + s :=
algebraMap.coe_add _ _
-- replaced by `RCLike.ofReal_ofNat`
@[rclike_simps, norm_cast]
theorem ofReal_neg (r : ℝ) : ((-r : ℝ) : K) = -r :=
algebraMap.coe_neg r
@[rclike_simps, norm_cast]
theorem ofReal_sub (r s : ℝ) : ((r - s : ℝ) : K) = r - s :=
map_sub (algebraMap ℝ K) r s
@[rclike_simps, norm_cast]
theorem ofReal_sum {α : Type*} (s : Finset α) (f : α → ℝ) :
((∑ i ∈ s, f i : ℝ) : K) = ∑ i ∈ s, (f i : K) :=
map_sum (algebraMap ℝ K) _ _
@[simp, rclike_simps, norm_cast]
theorem ofReal_finsupp_sum {α M : Type*} [Zero M] (f : α →₀ M) (g : α → M → ℝ) :
((f.sum fun a b => g a b : ℝ) : K) = f.sum fun a b => (g a b : K) :=
map_finsuppSum (algebraMap ℝ K) f g
@[rclike_simps, norm_cast]
theorem ofReal_mul (r s : ℝ) : ((r * s : ℝ) : K) = r * s :=
algebraMap.coe_mul _ _
@[rclike_simps, norm_cast]
theorem ofReal_pow (r : ℝ) (n : ℕ) : ((r ^ n : ℝ) : K) = (r : K) ^ n :=
map_pow (algebraMap ℝ K) r n
@[rclike_simps, norm_cast]
theorem ofReal_prod {α : Type*} (s : Finset α) (f : α → ℝ) :
((∏ i ∈ s, f i : ℝ) : K) = ∏ i ∈ s, (f i : K) :=
map_prod (algebraMap ℝ K) _ _
@[simp, rclike_simps, norm_cast]
theorem ofReal_finsuppProd {α M : Type*} [Zero M] (f : α →₀ M) (g : α → M → ℝ) :
((f.prod fun a b => g a b : ℝ) : K) = f.prod fun a b => (g a b : K) :=
map_finsuppProd _ f g
@[deprecated (since := "2025-04-06")] alias ofReal_finsupp_prod := ofReal_finsuppProd
@[simp, norm_cast, rclike_simps]
theorem real_smul_ofReal (r x : ℝ) : r • (x : K) = (r : K) * (x : K) :=
real_smul_eq_coe_mul _ _
@[rclike_simps]
theorem re_ofReal_mul (r : ℝ) (z : K) : re (↑r * z) = r * re z := by
simp only [mul_re, ofReal_im, zero_mul, ofReal_re, sub_zero]
@[rclike_simps]
theorem im_ofReal_mul (r : ℝ) (z : K) : im (↑r * z) = r * im z := by
simp only [add_zero, ofReal_im, zero_mul, ofReal_re, mul_im]
@[rclike_simps]
theorem smul_re (r : ℝ) (z : K) : re (r • z) = r * re z := by
rw [real_smul_eq_coe_mul, re_ofReal_mul]
@[rclike_simps]
theorem smul_im (r : ℝ) (z : K) : im (r • z) = r * im z := by
rw [real_smul_eq_coe_mul, im_ofReal_mul]
@[rclike_simps, norm_cast]
theorem norm_ofReal (r : ℝ) : ‖(r : K)‖ = |r| :=
norm_algebraMap' K r
/-! ### Characteristic zero -/
-- see Note [lower instance priority]
/-- ℝ and ℂ are both of characteristic zero. -/
instance (priority := 100) charZero_rclike : CharZero K :=
(RingHom.charZero_iff (algebraMap ℝ K).injective).1 inferInstance
@[rclike_simps, norm_cast]
lemma ofReal_expect {α : Type*} (s : Finset α) (f : α → ℝ) : 𝔼 i ∈ s, f i = 𝔼 i ∈ s, (f i : K) :=
map_expect (algebraMap ..) ..
@[norm_cast]
lemma ofReal_balance {ι : Type*} [Fintype ι] (f : ι → ℝ) (i : ι) :
((balance f i : ℝ) : K) = balance ((↑) ∘ f) i := map_balance (algebraMap ..) ..
@[simp] lemma ofReal_comp_balance {ι : Type*} [Fintype ι] (f : ι → ℝ) :
ofReal ∘ balance f = balance (ofReal ∘ f : ι → K) := funext <| ofReal_balance _
/-! ### The imaginary unit, `I` -/
/-- The imaginary unit. -/
@[simp, rclike_simps]
theorem I_re : re (I : K) = 0 :=
I_re_ax
@[simp, rclike_simps]
theorem I_im (z : K) : im z * im (I : K) = im z :=
mul_im_I_ax z
@[simp, rclike_simps]
theorem I_im' (z : K) : im (I : K) * im z = im z := by rw [mul_comm, I_im]
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem I_mul_re (z : K) : re (I * z) = -im z := by
simp only [I_re, zero_sub, I_im', zero_mul, mul_re]
theorem I_mul_I : (I : K) = 0 ∨ (I : K) * I = -1 :=
I_mul_I_ax
variable (𝕜) in
lemma I_eq_zero_or_im_I_eq_one : (I : K) = 0 ∨ im (I : K) = 1 :=
I_mul_I (K := K) |>.imp_right fun h ↦ by simpa [h] using (I_mul_re (I : K)).symm
@[simp, rclike_simps]
theorem conj_re (z : K) : re (conj z) = re z :=
RCLike.conj_re_ax z
@[simp, rclike_simps]
theorem conj_im (z : K) : im (conj z) = -im z :=
RCLike.conj_im_ax z
@[simp, rclike_simps]
theorem conj_I : conj (I : K) = -I :=
RCLike.conj_I_ax
@[simp, rclike_simps]
theorem conj_ofReal (r : ℝ) : conj (r : K) = (r : K) := by
rw [ext_iff]
simp only [ofReal_im, conj_im, eq_self_iff_true, conj_re, and_self_iff, neg_zero]
-- replaced by `RCLike.conj_ofNat`
theorem conj_nat_cast (n : ℕ) : conj (n : K) = n := map_natCast _ _
theorem conj_ofNat (n : ℕ) [n.AtLeastTwo] : conj (ofNat(n) : K) = ofNat(n) :=
map_ofNat _ _
@[rclike_simps, simp]
theorem conj_neg_I : conj (-I) = (I : K) := by rw [map_neg, conj_I, neg_neg]
theorem conj_eq_re_sub_im (z : K) : conj z = re z - im z * I :=
(congr_arg conj (re_add_im z).symm).trans <| by
rw [map_add, map_mul, conj_I, conj_ofReal, conj_ofReal, mul_neg, sub_eq_add_neg]
theorem sub_conj (z : K) : z - conj z = 2 * im z * I :=
calc
z - conj z = re z + im z * I - (re z - im z * I) := by rw [re_add_im, ← conj_eq_re_sub_im]
_ = 2 * im z * I := by rw [add_sub_sub_cancel, ← two_mul, mul_assoc]
@[rclike_simps]
theorem conj_smul (r : ℝ) (z : K) : conj (r • z) = r • conj z := by
rw [conj_eq_re_sub_im, conj_eq_re_sub_im, smul_re, smul_im, ofReal_mul, ofReal_mul,
real_smul_eq_coe_mul r (_ - _), mul_sub, mul_assoc]
theorem add_conj (z : K) : z + conj z = 2 * re z :=
calc
z + conj z = re z + im z * I + (re z - im z * I) := by rw [re_add_im, conj_eq_re_sub_im]
_ = 2 * re z := by rw [add_add_sub_cancel, two_mul]
theorem re_eq_add_conj (z : K) : ↑(re z) = (z + conj z) / 2 := by
rw [add_conj, mul_div_cancel_left₀ (re z : K) two_ne_zero]
theorem im_eq_conj_sub (z : K) : ↑(im z) = I * (conj z - z) / 2 := by
rw [← neg_inj, ← ofReal_neg, ← I_mul_re, re_eq_add_conj, map_mul, conj_I, ← neg_div, ← mul_neg,
neg_sub, mul_sub, neg_mul, sub_eq_add_neg]
open List in
/-- There are several equivalent ways to say that a number `z` is in fact a real number. -/
theorem is_real_TFAE (z : K) : TFAE [conj z = z, ∃ r : ℝ, (r : K) = z, ↑(re z) = z, im z = 0] := by
tfae_have 1 → 4
| h => by
rw [← @ofReal_inj K, im_eq_conj_sub, h, sub_self, mul_zero, zero_div,
ofReal_zero]
tfae_have 4 → 3
| h => by
conv_rhs => rw [← re_add_im z, h, ofReal_zero, zero_mul, add_zero]
tfae_have 3 → 2 := fun h => ⟨_, h⟩
tfae_have 2 → 1 := fun ⟨r, hr⟩ => hr ▸ conj_ofReal _
tfae_finish
theorem conj_eq_iff_real {z : K} : conj z = z ↔ ∃ r : ℝ, z = (r : K) :=
calc
_ ↔ ∃ r : ℝ, (r : K) = z := (is_real_TFAE z).out 0 1
_ ↔ _ := by simp only [eq_comm]
theorem conj_eq_iff_re {z : K} : conj z = z ↔ (re z : K) = z :=
(is_real_TFAE z).out 0 2
theorem conj_eq_iff_im {z : K} : conj z = z ↔ im z = 0 :=
(is_real_TFAE z).out 0 3
@[simp]
theorem star_def : (Star.star : K → K) = conj :=
rfl
variable (K)
/-- Conjugation as a ring equivalence. This is used to convert the inner product into a
sesquilinear product. -/
abbrev conjToRingEquiv : K ≃+* Kᵐᵒᵖ :=
starRingEquiv
variable {K} {z : K}
/-- The norm squared function. -/
def normSq : K →*₀ ℝ where
toFun z := re z * re z + im z * im z
map_zero' := by simp only [add_zero, mul_zero, map_zero]
map_one' := by simp only [one_im, add_zero, mul_one, one_re, mul_zero]
map_mul' z w := by
simp only [mul_im, mul_re]
ring
theorem normSq_apply (z : K) : normSq z = re z * re z + im z * im z :=
rfl
theorem norm_sq_eq_def {z : K} : ‖z‖ ^ 2 = re z * re z + im z * im z :=
norm_sq_eq_def_ax z
theorem normSq_eq_def' (z : K) : normSq z = ‖z‖ ^ 2 :=
norm_sq_eq_def.symm
@[rclike_simps]
theorem normSq_zero : normSq (0 : K) = 0 :=
normSq.map_zero
@[rclike_simps]
theorem normSq_one : normSq (1 : K) = 1 :=
normSq.map_one
theorem normSq_nonneg (z : K) : 0 ≤ normSq z :=
add_nonneg (mul_self_nonneg _) (mul_self_nonneg _)
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem normSq_eq_zero {z : K} : normSq z = 0 ↔ z = 0 :=
map_eq_zero _
@[simp, rclike_simps]
theorem normSq_pos {z : K} : 0 < normSq z ↔ z ≠ 0 := by
rw [lt_iff_le_and_ne, Ne, eq_comm]; simp [normSq_nonneg]
@[simp, rclike_simps]
theorem normSq_neg (z : K) : normSq (-z) = normSq z := by simp only [normSq_eq_def', norm_neg]
@[simp, rclike_simps]
theorem normSq_conj (z : K) : normSq (conj z) = normSq z := by
simp only [normSq_apply, neg_mul, mul_neg, neg_neg, rclike_simps]
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem normSq_mul (z w : K) : normSq (z * w) = normSq z * normSq w :=
map_mul _ z w
theorem normSq_add (z w : K) : normSq (z + w) = normSq z + normSq w + 2 * re (z * conj w) := by
simp only [normSq_apply, map_add, rclike_simps]
ring
theorem re_sq_le_normSq (z : K) : re z * re z ≤ normSq z :=
le_add_of_nonneg_right (mul_self_nonneg _)
theorem im_sq_le_normSq (z : K) : im z * im z ≤ normSq z :=
le_add_of_nonneg_left (mul_self_nonneg _)
theorem mul_conj (z : K) : z * conj z = ‖z‖ ^ 2 := by
apply ext <;> simp [← ofReal_pow, norm_sq_eq_def, mul_comm]
theorem conj_mul (z : K) : conj z * z = ‖z‖ ^ 2 := by rw [mul_comm, mul_conj]
lemma inv_eq_conj (hz : ‖z‖ = 1) : z⁻¹ = conj z :=
inv_eq_of_mul_eq_one_left <| by simp_rw [conj_mul, hz, algebraMap.coe_one, one_pow]
theorem normSq_sub (z w : K) : normSq (z - w) = normSq z + normSq w - 2 * re (z * conj w) := by
simp only [normSq_add, sub_eq_add_neg, map_neg, mul_neg, normSq_neg, map_neg]
theorem sqrt_normSq_eq_norm {z : K} : √(normSq z) = ‖z‖ := by
rw [normSq_eq_def', Real.sqrt_sq (norm_nonneg _)]
/-! ### Inversion -/
@[rclike_simps, norm_cast]
theorem ofReal_inv (r : ℝ) : ((r⁻¹ : ℝ) : K) = (r : K)⁻¹ :=
map_inv₀ _ r
theorem inv_def (z : K) : z⁻¹ = conj z * ((‖z‖ ^ 2)⁻¹ : ℝ) := by
rcases eq_or_ne z 0 with (rfl | h₀)
· simp
· apply inv_eq_of_mul_eq_one_right
rw [← mul_assoc, mul_conj, ofReal_inv, ofReal_pow, mul_inv_cancel₀]
simpa
@[simp, rclike_simps]
theorem inv_re (z : K) : re z⁻¹ = re z / normSq z := by
rw [inv_def, normSq_eq_def', mul_comm, re_ofReal_mul, conj_re, div_eq_inv_mul]
@[simp, rclike_simps]
theorem inv_im (z : K) : im z⁻¹ = -im z / normSq z := by
rw [inv_def, normSq_eq_def', mul_comm, im_ofReal_mul, conj_im, div_eq_inv_mul]
theorem div_re (z w : K) : re (z / w) = re z * re w / normSq w + im z * im w / normSq w := by
simp only [div_eq_mul_inv, mul_assoc, sub_eq_add_neg, neg_mul, mul_neg, neg_neg, map_neg,
rclike_simps]
theorem div_im (z w : K) : im (z / w) = im z * re w / normSq w - re z * im w / normSq w := by
simp only [div_eq_mul_inv, mul_assoc, sub_eq_add_neg, add_comm, neg_mul, mul_neg, map_neg,
rclike_simps]
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem conj_inv (x : K) : conj x⁻¹ = (conj x)⁻¹ :=
star_inv₀ _
lemma conj_div (x y : K) : conj (x / y) = conj x / conj y := map_div' conj conj_inv _ _
--TODO: Do we rather want the map as an explicit definition?
lemma exists_norm_eq_mul_self (x : K) : ∃ c, ‖c‖ = 1 ∧ ↑‖x‖ = c * x := by
obtain rfl | hx := eq_or_ne x 0
· exact ⟨1, by simp⟩
· exact ⟨‖x‖ / x, by simp [norm_ne_zero_iff.2, hx]⟩
lemma exists_norm_mul_eq_self (x : K) : ∃ c, ‖c‖ = 1 ∧ c * ‖x‖ = x := by
obtain rfl | hx := eq_or_ne x 0
· exact ⟨1, by simp⟩
· exact ⟨x / ‖x‖, by simp [norm_ne_zero_iff.2, hx]⟩
@[rclike_simps, norm_cast]
theorem ofReal_div (r s : ℝ) : ((r / s : ℝ) : K) = r / s :=
map_div₀ (algebraMap ℝ K) r s
theorem div_re_ofReal {z : K} {r : ℝ} : re (z / r) = re z / r := by
rw [div_eq_inv_mul, div_eq_inv_mul, ← ofReal_inv, re_ofReal_mul]
@[rclike_simps, norm_cast]
theorem ofReal_zpow (r : ℝ) (n : ℤ) : ((r ^ n : ℝ) : K) = (r : K) ^ n :=
map_zpow₀ (algebraMap ℝ K) r n
theorem I_mul_I_of_nonzero : (I : K) ≠ 0 → (I : K) * I = -1 :=
I_mul_I_ax.resolve_left
@[simp, rclike_simps]
theorem inv_I : (I : K)⁻¹ = -I := by
by_cases h : (I : K) = 0
· simp [h]
· field_simp [I_mul_I_of_nonzero h]
@[simp, rclike_simps]
theorem div_I (z : K) : z / I = -(z * I) := by rw [div_eq_mul_inv, inv_I, mul_neg]
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem normSq_inv (z : K) : normSq z⁻¹ = (normSq z)⁻¹ :=
map_inv₀ normSq z
@[rclike_simps] -- Porting note (https://github.com/leanprover-community/mathlib4/issues/11119): was `simp`
theorem normSq_div (z w : K) : normSq (z / w) = normSq z / normSq w :=
map_div₀ normSq z w
@[simp 1100, rclike_simps]
theorem norm_conj (z : K) : ‖conj z‖ = ‖z‖ := by simp only [← sqrt_normSq_eq_norm, normSq_conj]
@[simp, rclike_simps] lemma nnnorm_conj (z : K) : ‖conj z‖₊ = ‖z‖₊ := by simp [nnnorm]
@[simp, rclike_simps] lemma enorm_conj (z : K) : ‖conj z‖ₑ = ‖z‖ₑ := by simp [enorm]
instance (priority := 100) : CStarRing K where
norm_mul_self_le x := le_of_eq <| ((norm_mul _ _).trans <| congr_arg (· * ‖x‖) (norm_conj _)).symm
instance : StarModule ℝ K where
star_smul r a := by
apply RCLike.ext <;> simp [RCLike.smul_re, RCLike.smul_im]
/-! ### Cast lemmas -/
@[rclike_simps, norm_cast]
theorem ofReal_natCast (n : ℕ) : ((n : ℝ) : K) = n :=
map_natCast (algebraMap ℝ K) n
@[rclike_simps, norm_cast]
lemma ofReal_nnratCast (q : ℚ≥0) : ((q : ℝ) : K) = q := map_nnratCast (algebraMap ℝ K) _
@[simp, rclike_simps] -- Porting note: removed `norm_cast`
theorem natCast_re (n : ℕ) : re (n : K) = n := by rw [← ofReal_natCast, ofReal_re]
@[simp, rclike_simps, norm_cast]
theorem natCast_im (n : ℕ) : im (n : K) = 0 := by rw [← ofReal_natCast, ofReal_im]
@[simp, rclike_simps]
theorem ofNat_re (n : ℕ) [n.AtLeastTwo] : re (ofNat(n) : K) = ofNat(n) :=
natCast_re n
@[simp, rclike_simps]
theorem ofNat_im (n : ℕ) [n.AtLeastTwo] : im (ofNat(n) : K) = 0 :=
natCast_im n
@[rclike_simps, norm_cast]
theorem ofReal_ofNat (n : ℕ) [n.AtLeastTwo] : ((ofNat(n) : ℝ) : K) = ofNat(n) :=
ofReal_natCast n
theorem ofNat_mul_re (n : ℕ) [n.AtLeastTwo] (z : K) :
re (ofNat(n) * z) = ofNat(n) * re z := by
rw [← ofReal_ofNat, re_ofReal_mul]
theorem ofNat_mul_im (n : ℕ) [n.AtLeastTwo] (z : K) :
im (ofNat(n) * z) = ofNat(n) * im z := by
rw [← ofReal_ofNat, im_ofReal_mul]
@[rclike_simps, norm_cast]
theorem ofReal_intCast (n : ℤ) : ((n : ℝ) : K) = n :=
map_intCast _ n
@[simp, rclike_simps] -- Porting note: removed `norm_cast`
theorem intCast_re (n : ℤ) : re (n : K) = n := by rw [← ofReal_intCast, ofReal_re]
@[simp, rclike_simps, norm_cast]
theorem intCast_im (n : ℤ) : im (n : K) = 0 := by rw [← ofReal_intCast, ofReal_im]
@[rclike_simps, norm_cast]
theorem ofReal_ratCast (n : ℚ) : ((n : ℝ) : K) = n :=
map_ratCast _ n
@[simp, rclike_simps] -- Porting note: removed `norm_cast`
theorem ratCast_re (q : ℚ) : re (q : K) = q := by rw [← ofReal_ratCast, ofReal_re]
@[simp, rclike_simps, norm_cast]
theorem ratCast_im (q : ℚ) : im (q : K) = 0 := by rw [← ofReal_ratCast, ofReal_im]
/-! ### Norm -/
theorem norm_of_nonneg {r : ℝ} (h : 0 ≤ r) : ‖(r : K)‖ = r :=
(norm_ofReal _).trans (abs_of_nonneg h)
@[simp, rclike_simps, norm_cast]
theorem norm_natCast (n : ℕ) : ‖(n : K)‖ = n := by
rw [← ofReal_natCast]
exact norm_of_nonneg (Nat.cast_nonneg n)
@[simp, rclike_simps, norm_cast] lemma nnnorm_natCast (n : ℕ) : ‖(n : K)‖₊ = n := by simp [nnnorm]
@[simp, rclike_simps]
theorem norm_ofNat (n : ℕ) [n.AtLeastTwo] : ‖(ofNat(n) : K)‖ = ofNat(n) :=
norm_natCast n
@[simp, rclike_simps]
lemma nnnorm_ofNat (n : ℕ) [n.AtLeastTwo] : ‖(ofNat(n) : K)‖₊ = ofNat(n) :=
nnnorm_natCast n
lemma norm_two : ‖(2 : K)‖ = 2 := norm_ofNat 2
lemma nnnorm_two : ‖(2 : K)‖₊ = 2 := nnnorm_ofNat 2
@[simp, rclike_simps, norm_cast]
lemma norm_nnratCast (q : ℚ≥0) : ‖(q : K)‖ = q := by
rw [← ofReal_nnratCast]; exact norm_of_nonneg q.cast_nonneg
@[simp, rclike_simps, norm_cast]
lemma nnnorm_nnratCast (q : ℚ≥0) : ‖(q : K)‖₊ = q := by simp [nnnorm]
variable (K) in
lemma norm_nsmul [NormedAddCommGroup E] [NormedSpace K E] (n : ℕ) (x : E) : ‖n • x‖ = n • ‖x‖ := by
simpa [Nat.cast_smul_eq_nsmul] using norm_smul (n : K) x
variable (K) in
lemma nnnorm_nsmul [NormedAddCommGroup E] [NormedSpace K E] (n : ℕ) (x : E) :
‖n • x‖₊ = n • ‖x‖₊ := by simpa [Nat.cast_smul_eq_nsmul] using nnnorm_smul (n : K) x
section NormedField
variable [NormedField E] [CharZero E] [NormedSpace K E]
include K
variable (K) in
lemma norm_nnqsmul (q : ℚ≥0) (x : E) : ‖q • x‖ = q • ‖x‖ := by
simpa [NNRat.cast_smul_eq_nnqsmul] using norm_smul (q : K) x
variable (K) in
lemma nnnorm_nnqsmul (q : ℚ≥0) (x : E) : ‖q • x‖₊ = q • ‖x‖₊ := by
simpa [NNRat.cast_smul_eq_nnqsmul] using nnnorm_smul (q : K) x
@[bound]
lemma norm_expect_le {ι : Type*} {s : Finset ι} {f : ι → E} : ‖𝔼 i ∈ s, f i‖ ≤ 𝔼 i ∈ s, ‖f i‖ :=
Finset.le_expect_of_subadditive norm_zero norm_add_le fun _ _ ↦ by rw [norm_nnqsmul K]
end NormedField
theorem mul_self_norm (z : K) : ‖z‖ * ‖z‖ = normSq z := by rw [normSq_eq_def', sq]
attribute [rclike_simps] norm_zero norm_one norm_eq_zero abs_norm norm_inv norm_div
theorem abs_re_le_norm (z : K) : |re z| ≤ ‖z‖ := by
rw [mul_self_le_mul_self_iff (abs_nonneg _) (norm_nonneg _), abs_mul_abs_self, mul_self_norm]
apply re_sq_le_normSq
theorem abs_im_le_norm (z : K) : |im z| ≤ ‖z‖ := by
rw [mul_self_le_mul_self_iff (abs_nonneg _) (norm_nonneg _), abs_mul_abs_self, mul_self_norm]
apply im_sq_le_normSq
theorem norm_re_le_norm (z : K) : ‖re z‖ ≤ ‖z‖ :=
abs_re_le_norm z
theorem norm_im_le_norm (z : K) : ‖im z‖ ≤ ‖z‖ :=
abs_im_le_norm z
theorem re_le_norm (z : K) : re z ≤ ‖z‖ :=
(abs_le.1 (abs_re_le_norm z)).2
theorem im_le_norm (z : K) : im z ≤ ‖z‖ :=
(abs_le.1 (abs_im_le_norm _)).2
theorem im_eq_zero_of_le {a : K} (h : ‖a‖ ≤ re a) : im a = 0 := by
simpa only [mul_self_norm a, normSq_apply, left_eq_add, mul_self_eq_zero]
using congr_arg (fun z => z * z) ((re_le_norm a).antisymm h)
theorem re_eq_self_of_le {a : K} (h : ‖a‖ ≤ re a) : (re a : K) = a := by
rw [← conj_eq_iff_re, conj_eq_iff_im, im_eq_zero_of_le h]
open IsAbsoluteValue
theorem abs_re_div_norm_le_one (z : K) : |re z / ‖z‖| ≤ 1 := by
rw [abs_div, abs_norm]
exact div_le_one_of_le₀ (abs_re_le_norm _) (norm_nonneg _)
theorem abs_im_div_norm_le_one (z : K) : |im z / ‖z‖| ≤ 1 := by
rw [abs_div, abs_norm]
exact div_le_one_of_le₀ (abs_im_le_norm _) (norm_nonneg _)
theorem norm_I_of_ne_zero (hI : (I : K) ≠ 0) : ‖(I : K)‖ = 1 := by
rw [← mul_self_inj_of_nonneg (norm_nonneg I) zero_le_one, one_mul, ← norm_mul,
I_mul_I_of_nonzero hI, norm_neg, norm_one]
theorem re_eq_norm_of_mul_conj (x : K) : re (x * conj x) = ‖x * conj x‖ := by
rw [mul_conj, ← ofReal_pow]; simp [-map_pow]
theorem norm_sq_re_add_conj (x : K) : ‖x + conj x‖ ^ 2 = re (x + conj x) ^ 2 := by
rw [add_conj, ← ofReal_ofNat, ← ofReal_mul, norm_ofReal, sq_abs, ofReal_re]
theorem norm_sq_re_conj_add (x : K) : ‖conj x + x‖ ^ 2 = re (conj x + x) ^ 2 := by
rw [add_comm, norm_sq_re_add_conj]
/-! ### Cauchy sequences -/
| theorem isCauSeq_re (f : CauSeq K norm) : IsCauSeq abs fun n => re (f n) := fun _ ε0 =>
(f.cauchy ε0).imp fun i H j ij =>
lt_of_le_of_lt (by simpa only [map_sub] using abs_re_le_norm (f j - f i)) (H _ ij)
| Mathlib/Analysis/RCLike/Basic.lean | 700 | 702 |
/-
Copyright (c) 2020 Aaron Anderson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Aaron Anderson
-/
import Mathlib.Algebra.Squarefree.Basic
import Mathlib.Data.Nat.Factorization.PrimePow
import Mathlib.RingTheory.UniqueFactorizationDomain.Nat
/-!
# Lemmas about squarefreeness of natural numbers
A number is squarefree when it is not divisible by any squares except the squares of units.
## Main Results
- `Nat.squarefree_iff_nodup_primeFactorsList`: A positive natural number `x` is squarefree iff
the list `factors x` has no duplicate factors.
## Tags
squarefree, multiplicity
-/
open Finset
namespace Nat
theorem squarefree_iff_nodup_primeFactorsList {n : ℕ} (h0 : n ≠ 0) :
Squarefree n ↔ n.primeFactorsList.Nodup := by
rw [UniqueFactorizationMonoid.squarefree_iff_nodup_normalizedFactors h0, Nat.factors_eq]
simp
end Nat
theorem Squarefree.nodup_primeFactorsList {n : ℕ} (hn : Squarefree n) : n.primeFactorsList.Nodup :=
(Nat.squarefree_iff_nodup_primeFactorsList hn.ne_zero).mp hn
namespace Nat
variable {s : Finset ℕ} {m n p : ℕ}
theorem squarefree_iff_prime_squarefree {n : ℕ} : Squarefree n ↔ ∀ x, Prime x → ¬x * x ∣ n :=
squarefree_iff_irreducible_sq_not_dvd_of_exists_irreducible ⟨_, prime_two⟩
theorem _root_.Squarefree.natFactorization_le_one {n : ℕ} (p : ℕ) (hn : Squarefree n) :
n.factorization p ≤ 1 := by
rcases eq_or_ne n 0 with (rfl | hn')
· simp
rw [squarefree_iff_emultiplicity_le_one] at hn
by_cases hp : p.Prime
· have := hn p
rw [← multiplicity_eq_factorization hp hn']
simp only [Nat.isUnit_iff, hp.ne_one, or_false] at this
exact multiplicity_le_of_emultiplicity_le this
· rw [factorization_eq_zero_of_non_prime _ hp]
exact zero_le_one
lemma factorization_eq_one_of_squarefree (hn : Squarefree n) (hp : p.Prime) (hpn : p ∣ n) :
factorization n p = 1 :=
(hn.natFactorization_le_one _).antisymm <| (hp.dvd_iff_one_le_factorization hn.ne_zero).1 hpn
theorem squarefree_of_factorization_le_one {n : ℕ} (hn : n ≠ 0) (hn' : ∀ p, n.factorization p ≤ 1) :
Squarefree n := by
rw [squarefree_iff_nodup_primeFactorsList hn, List.nodup_iff_count_le_one]
intro a
rw [primeFactorsList_count_eq]
apply hn'
theorem squarefree_iff_factorization_le_one {n : ℕ} (hn : n ≠ 0) :
Squarefree n ↔ ∀ p, n.factorization p ≤ 1 :=
⟨fun hn => hn.natFactorization_le_one, squarefree_of_factorization_le_one hn⟩
theorem Squarefree.ext_iff {n m : ℕ} (hn : Squarefree n) (hm : Squarefree m) :
n = m ↔ ∀ p, Prime p → (p ∣ n ↔ p ∣ m) := by
refine ⟨by rintro rfl; simp, fun h => eq_of_factorization_eq hn.ne_zero hm.ne_zero fun p => ?_⟩
by_cases hp : p.Prime
· have h₁ := h _ hp
rw [← not_iff_not, hp.dvd_iff_one_le_factorization hn.ne_zero, not_le, lt_one_iff,
hp.dvd_iff_one_le_factorization hm.ne_zero, not_le, lt_one_iff] at h₁
have h₂ := hn.natFactorization_le_one p
have h₃ := hm.natFactorization_le_one p
omega
rw [factorization_eq_zero_of_non_prime _ hp, factorization_eq_zero_of_non_prime _ hp]
theorem squarefree_pow_iff {n k : ℕ} (hn : n ≠ 1) (hk : k ≠ 0) :
Squarefree (n ^ k) ↔ Squarefree n ∧ k = 1 := by
refine ⟨fun h => ?_, by rintro ⟨hn, rfl⟩; simpa⟩
rcases eq_or_ne n 0 with (rfl | -)
· simp [zero_pow hk] at h
refine ⟨h.squarefree_of_dvd (dvd_pow_self _ hk), by_contradiction fun h₁ => ?_⟩
have : 2 ≤ k := k.two_le_iff.mpr ⟨hk, h₁⟩
apply hn (Nat.isUnit_iff.1 (h _ _))
rw [← sq]
exact pow_dvd_pow _ this
theorem squarefree_and_prime_pow_iff_prime {n : ℕ} : Squarefree n ∧ IsPrimePow n ↔ Prime n := by
refine ⟨?_, fun hn => ⟨hn.squarefree, hn.isPrimePow⟩⟩
rw [isPrimePow_nat_iff]
rintro ⟨h, p, k, hp, hk, rfl⟩
rw [squarefree_pow_iff hp.ne_one hk.ne'] at h
rwa [h.2, pow_one]
/-- Assuming that `n` has no factors less than `k`, returns the smallest prime `p` such that
`p^2 ∣ n`. -/
def minSqFacAux : ℕ → ℕ → Option ℕ
| n, k =>
if h : n < k * k then none
else
have : Nat.sqrt n - k < Nat.sqrt n + 2 - k := by
exact Nat.minFac_lemma n k h
if k ∣ n then
let n' := n / k
have : Nat.sqrt n' - k < Nat.sqrt n + 2 - k :=
lt_of_le_of_lt (Nat.sub_le_sub_right (Nat.sqrt_le_sqrt <| Nat.div_le_self _ _) k) this
if k ∣ n' then some k else minSqFacAux n' (k + 2)
else minSqFacAux n (k + 2)
termination_by n k => sqrt n + 2 - k
/-- Returns the smallest prime factor `p` of `n` such that `p^2 ∣ n`, or `none` if there is no
such `p` (that is, `n` is squarefree). See also `Nat.squarefree_iff_minSqFac`. -/
def minSqFac (n : ℕ) : Option ℕ :=
if 2 ∣ n then
let n' := n / 2
if 2 ∣ n' then some 2 else minSqFacAux n' 3
else minSqFacAux n 3
/-- The correctness property of the return value of `minSqFac`.
* If `none`, then `n` is squarefree;
* If `some d`, then `d` is a minimal square factor of `n` -/
def MinSqFacProp (n : ℕ) : Option ℕ → Prop
| none => Squarefree n
| some d => Prime d ∧ d * d ∣ n ∧ ∀ p, Prime p → p * p ∣ n → d ≤ p
theorem minSqFacProp_div (n) {k} (pk : Prime k) (dk : k ∣ n) (dkk : ¬k * k ∣ n) {o}
(H : MinSqFacProp (n / k) o) : MinSqFacProp n o := by
have : ∀ p, Prime p → p * p ∣ n → k * (p * p) ∣ n := fun p pp dp =>
have :=
(coprime_primes pk pp).2 fun e => by
subst e
contradiction
(coprime_mul_iff_right.2 ⟨this, this⟩).mul_dvd_of_dvd_of_dvd dk dp
rcases o with - | d
· rw [MinSqFacProp, squarefree_iff_prime_squarefree] at H ⊢
exact fun p pp dp => H p pp ((dvd_div_iff_mul_dvd dk).2 (this _ pp dp))
· obtain ⟨H1, H2, H3⟩ := H
simp only [dvd_div_iff_mul_dvd dk] at H2 H3
exact ⟨H1, dvd_trans (dvd_mul_left _ _) H2, fun p pp dp => H3 _ pp (this _ pp dp)⟩
theorem minSqFacAux_has_prop {n : ℕ} (k) (n0 : 0 < n) (i) (e : k = 2 * i + 3)
(ih : ∀ m, Prime m → m ∣ n → k ≤ m) : MinSqFacProp n (minSqFacAux n k) := by
rw [minSqFacAux]
by_cases h : n < k * k <;> simp only [h, ↓reduceDIte]
· refine squarefree_iff_prime_squarefree.2 fun p pp d => ?_
have := ih p pp (dvd_trans ⟨_, rfl⟩ d)
have := Nat.mul_le_mul this this
exact not_le_of_lt h (le_trans this (le_of_dvd n0 d))
have k2 : 2 ≤ k := by omega
have k0 : 0 < k := lt_of_lt_of_le (by decide) k2
have IH : ∀ n', n' ∣ n → ¬k ∣ n' → MinSqFacProp n' (n'.minSqFacAux (k + 2)) := by
intro n' nd' nk
have hn' := le_of_dvd n0 nd'
refine
have : Nat.sqrt n' - k < Nat.sqrt n + 2 - k :=
lt_of_le_of_lt (Nat.sub_le_sub_right (Nat.sqrt_le_sqrt hn') _) (Nat.minFac_lemma n k h)
@minSqFacAux_has_prop n' (k + 2) (pos_of_dvd_of_pos nd' n0) (i + 1)
(by simp [e, left_distrib]) fun m m2 d => ?_
rcases Nat.eq_or_lt_of_le (ih m m2 (dvd_trans d nd')) with me | ml
· subst me
contradiction
apply (Nat.eq_or_lt_of_le ml).resolve_left
intro me
rw [← me, e] at d
change 2 * (i + 2) ∣ n' at d
have := ih _ prime_two (dvd_trans (dvd_of_mul_right_dvd d) nd')
rw [e] at this
exact absurd this (by omega)
have pk : k ∣ n → Prime k := by
refine fun dk => prime_def_minFac.2 ⟨k2, le_antisymm (minFac_le k0) ?_⟩
exact ih _ (minFac_prime (ne_of_gt k2)) (dvd_trans (minFac_dvd _) dk)
split_ifs with dk dkk
· exact ⟨pk dk, (Nat.dvd_div_iff_mul_dvd dk).1 dkk, fun p pp d => ih p pp (dvd_trans ⟨_, rfl⟩ d)⟩
· specialize IH (n / k) (div_dvd_of_dvd dk) dkk
exact minSqFacProp_div _ (pk dk) dk (mt (Nat.dvd_div_iff_mul_dvd dk).2 dkk) IH
· exact IH n (dvd_refl _) dk
termination_by n.sqrt + 2 - k
theorem minSqFac_has_prop (n : ℕ) : MinSqFacProp n (minSqFac n) := by
dsimp only [minSqFac]; split_ifs with d2 d4
· exact ⟨prime_two, (dvd_div_iff_mul_dvd d2).1 d4, fun p pp _ => pp.two_le⟩
· rcases Nat.eq_zero_or_pos n with n0 | n0
· subst n0
cases d4 (by decide)
refine minSqFacProp_div _ prime_two d2 (mt (dvd_div_iff_mul_dvd d2).2 d4) ?_
refine minSqFacAux_has_prop 3 (Nat.div_pos (le_of_dvd n0 d2) (by decide)) 0 rfl ?_
refine fun p pp dp => succ_le_of_lt (lt_of_le_of_ne pp.two_le ?_)
rintro rfl
contradiction
· rcases Nat.eq_zero_or_pos n with n0 | n0
· subst n0
cases d2 (by decide)
refine minSqFacAux_has_prop _ n0 0 rfl ?_
refine fun p pp dp => succ_le_of_lt (lt_of_le_of_ne pp.two_le ?_)
rintro rfl
contradiction
theorem minSqFac_prime {n d : ℕ} (h : n.minSqFac = some d) : Prime d := by
have := minSqFac_has_prop n
rw [h] at this
exact this.1
theorem minSqFac_dvd {n d : ℕ} (h : n.minSqFac = some d) : d * d ∣ n := by
have := minSqFac_has_prop n
rw [h] at this
exact this.2.1
theorem minSqFac_le_of_dvd {n d : ℕ} (h : n.minSqFac = some d) {m} (m2 : 2 ≤ m) (md : m * m ∣ n) :
d ≤ m := by
have := minSqFac_has_prop n; rw [h] at this
have fd := minFac_dvd m
exact
le_trans (this.2.2 _ (minFac_prime <| ne_of_gt m2) (dvd_trans (mul_dvd_mul fd fd) md))
(minFac_le <| lt_of_lt_of_le (by decide) m2)
theorem squarefree_iff_minSqFac {n : ℕ} : Squarefree n ↔ n.minSqFac = none := by
have := minSqFac_has_prop n
constructor <;> intro H
· rcases e : n.minSqFac with - | d
· rfl
rw [e] at this
cases squarefree_iff_prime_squarefree.1 H _ this.1 this.2.1
· rwa [H] at this
instance : DecidablePred (Squarefree : ℕ → Prop) := fun _ =>
decidable_of_iff' _ squarefree_iff_minSqFac
theorem squarefree_two : Squarefree 2 := by
rw [squarefree_iff_nodup_primeFactorsList] <;> simp
theorem divisors_filter_squarefree_of_squarefree {n : ℕ} (hn : Squarefree n) :
{d ∈ n.divisors | Squarefree d} = n.divisors :=
Finset.ext fun d => ⟨@Finset.filter_subset _ _ _ _ d, fun hd =>
Finset.mem_filter.mpr ⟨hd, hn.squarefree_of_dvd (Nat.dvd_of_mem_divisors hd) ⟩⟩
open UniqueFactorizationMonoid
theorem divisors_filter_squarefree {n : ℕ} (h0 : n ≠ 0) :
{d ∈ n.divisors | Squarefree d}.val =
(UniqueFactorizationMonoid.normalizedFactors n).toFinset.powerset.val.map fun x =>
x.val.prod := by
rw [(Finset.nodup _).ext ((Finset.nodup _).map_on _)]
· intro a
simp only [Multiset.mem_filter, id, Multiset.mem_map, Finset.filter_val, ← Finset.mem_def,
mem_divisors]
constructor
· rintro ⟨⟨an, h0⟩, hsq⟩
use (UniqueFactorizationMonoid.normalizedFactors a).toFinset
simp only [id, Finset.mem_powerset]
rcases an with ⟨b, rfl⟩
rw [mul_ne_zero_iff] at h0
rw [UniqueFactorizationMonoid.squarefree_iff_nodup_normalizedFactors h0.1] at hsq
rw [Multiset.toFinset_subset, Multiset.toFinset_val, hsq.dedup, ← associated_iff_eq,
normalizedFactors_mul h0.1 h0.2]
exact ⟨Multiset.subset_of_le (Multiset.le_add_right _ _), prod_normalizedFactors h0.1⟩
· rintro ⟨s, hs, rfl⟩
rw [Finset.mem_powerset, ← Finset.val_le_iff, Multiset.toFinset_val] at hs
have hs0 : s.val.prod ≠ 0 := by
rw [Ne, Multiset.prod_eq_zero_iff]
intro con
apply
not_irreducible_zero
(irreducible_of_normalized_factor 0 (Multiset.mem_dedup.1 (Multiset.mem_of_le hs con)))
rw [(prod_normalizedFactors h0).symm.dvd_iff_dvd_right]
refine ⟨⟨Multiset.prod_dvd_prod_of_le (le_trans hs (Multiset.dedup_le _)), h0⟩, ?_⟩
have h :=
UniqueFactorizationMonoid.factors_unique irreducible_of_normalized_factor
(fun x hx =>
irreducible_of_normalized_factor x
(Multiset.mem_of_le (le_trans hs (Multiset.dedup_le _)) hx))
(prod_normalizedFactors hs0)
rw [associated_eq_eq, Multiset.rel_eq] at h
rw [UniqueFactorizationMonoid.squarefree_iff_nodup_normalizedFactors hs0, h]
apply s.nodup
· intro x hx y hy h
rw [← Finset.val_inj, ← Multiset.rel_eq, ← associated_eq_eq]
rw [← Finset.mem_def, Finset.mem_powerset] at hx hy
apply UniqueFactorizationMonoid.factors_unique _ _ (associated_iff_eq.2 h)
· intro z hz
apply irreducible_of_normalized_factor z
· rw [← Multiset.mem_toFinset]
apply hx hz
· intro z hz
apply irreducible_of_normalized_factor z
· rw [← Multiset.mem_toFinset]
apply hy hz
theorem sum_divisors_filter_squarefree {n : ℕ} (h0 : n ≠ 0) {α : Type*} [AddCommMonoid α]
{f : ℕ → α} :
∑ d ∈ n.divisors with Squarefree d, f d =
∑ i ∈ (UniqueFactorizationMonoid.normalizedFactors n).toFinset.powerset, f i.val.prod := by
rw [Finset.sum_eq_multiset_sum, divisors_filter_squarefree h0, Multiset.map_map,
Finset.sum_eq_multiset_sum]
rfl
theorem sq_mul_squarefree_of_pos {n : ℕ} (hn : 0 < n) :
∃ a b : ℕ, 0 < a ∧ 0 < b ∧ b ^ 2 * a = n ∧ Squarefree a := by
classical
set S := {s ∈ range (n + 1) | s ∣ n ∧ ∃ x, s = x ^ 2}
have hSne : S.Nonempty := by
use 1
have h1 : 0 < n ∧ ∃ x : ℕ, 1 = x ^ 2 := ⟨hn, ⟨1, (one_pow 2).symm⟩⟩
simp [S, h1]
let s := Finset.max' S hSne
have hs : s ∈ S := Finset.max'_mem S hSne
simp only [S, Finset.mem_filter, Finset.mem_range] at hs
obtain ⟨-, ⟨a, hsa⟩, ⟨b, hsb⟩⟩ := hs
rw [hsa] at hn
obtain ⟨hlts, hlta⟩ := CanonicallyOrderedAdd.mul_pos.mp hn
rw [hsb] at hsa hn hlts
refine ⟨a, b, hlta, (pow_pos_iff two_ne_zero).mp hlts, hsa.symm, ?_⟩
rintro x ⟨y, hy⟩
rw [Nat.isUnit_iff]
by_contra hx
refine Nat.lt_le_asymm ?_ (Finset.le_max' S ((b * x) ^ 2) ?_)
· convert lt_mul_of_one_lt_right hlts
(one_lt_pow two_ne_zero (one_lt_iff_ne_zero_and_ne_one.mpr ⟨fun h => by simp_all, hx⟩))
using 1
rw [mul_pow]
· simp_rw [S, hsa, Finset.mem_filter, Finset.mem_range]
refine ⟨Nat.lt_succ_iff.mpr (le_of_dvd hn ?_), ?_, ⟨b * x, rfl⟩⟩ <;> use y <;> rw [hy] <;> ring
theorem sq_mul_squarefree_of_pos' {n : ℕ} (h : 0 < n) :
∃ a b : ℕ, (b + 1) ^ 2 * (a + 1) = n ∧ Squarefree (a + 1) := by
obtain ⟨a₁, b₁, ha₁, hb₁, hab₁, hab₂⟩ := sq_mul_squarefree_of_pos h
refine ⟨a₁.pred, b₁.pred, ?_, ?_⟩ <;> simpa only [add_one, succ_pred_eq_of_pos, ha₁, hb₁]
theorem sq_mul_squarefree (n : ℕ) : ∃ a b : ℕ, b ^ 2 * a = n ∧ Squarefree a := by
rcases n with - | n
· exact ⟨1, 0, by simp, squarefree_one⟩
· obtain ⟨a, b, -, -, h₁, h₂⟩ := sq_mul_squarefree_of_pos (succ_pos n)
exact ⟨a, b, h₁, h₂⟩
/-- `Squarefree` is multiplicative. Note that the → direction does not require `hmn`
and generalizes to arbitrary commutative monoids. See `Squarefree.of_mul_left` and
`Squarefree.of_mul_right` above for auxiliary lemmas. -/
theorem squarefree_mul {m n : ℕ} (hmn : m.Coprime n) :
Squarefree (m * n) ↔ Squarefree m ∧ Squarefree n := by
simp only [squarefree_iff_prime_squarefree, ← sq, ← forall_and]
refine forall₂_congr fun p hp => ?_
simp only [hmn.isPrimePow_dvd_mul (hp.isPrimePow.pow two_ne_zero), not_or]
theorem coprime_of_squarefree_mul {m n : ℕ} (h : Squarefree (m * n)) : m.Coprime n :=
coprime_of_dvd fun p hp hm hn => squarefree_iff_prime_squarefree.mp h p hp (mul_dvd_mul hm hn)
theorem squarefree_mul_iff {m n : ℕ} :
Squarefree (m * n) ↔ m.Coprime n ∧ Squarefree m ∧ Squarefree n :=
⟨fun h => ⟨coprime_of_squarefree_mul h, (squarefree_mul <| coprime_of_squarefree_mul h).mp h⟩,
fun h => (squarefree_mul h.1).mpr h.2⟩
lemma coprime_div_gcd_of_squarefree (hm : Squarefree m) (hn : n ≠ 0) : Coprime (m / gcd m n) n := by
have : Coprime (m / gcd m n) (gcd m n) :=
coprime_of_squarefree_mul <| by simpa [Nat.div_mul_cancel, gcd_dvd_left]
simpa [Nat.div_mul_cancel, gcd_dvd_right] using
(coprime_div_gcd_div_gcd (m := m) (gcd_ne_zero_right hn).bot_lt).mul_right this
lemma prod_primeFactors_of_squarefree (hn : Squarefree n) : ∏ p ∈ n.primeFactors, p = n := by
rw [← toFinset_factors, List.prod_toFinset _ hn.nodup_primeFactorsList,
List.map_id', Nat.prod_primeFactorsList hn.ne_zero]
lemma primeFactors_prod (hs : ∀ p ∈ s, p.Prime) : primeFactors (∏ p ∈ s, p) = s := by
have hn : ∏ p ∈ s, p ≠ 0 := prod_ne_zero_iff.2 fun p hp ↦ (hs _ hp).ne_zero
ext p
rw [mem_primeFactors_of_ne_zero hn, and_congr_right (fun hp ↦ hp.prime.dvd_finset_prod_iff _)]
refine ⟨?_, fun hp ↦ ⟨hs _ hp, _, hp, dvd_rfl⟩⟩
rintro ⟨hp, q, hq, hpq⟩
rwa [← ((hs _ hq).dvd_iff_eq hp.ne_one).1 hpq]
lemma primeFactors_div_gcd (hm : Squarefree m) (hn : n ≠ 0) :
primeFactors (m / m.gcd n) = primeFactors m \ primeFactors n := by
ext p
have : m / m.gcd n ≠ 0 := by simp [gcd_ne_zero_right hn, gcd_le_left _ hm.ne_zero.bot_lt]
simp only [mem_primeFactors, ne_eq, this, not_false_eq_true, and_true, not_and, mem_sdiff,
hm.ne_zero, hn, dvd_div_iff_mul_dvd (gcd_dvd_left _ _)]
refine ⟨fun hp ↦ ⟨⟨hp.1, dvd_of_mul_left_dvd hp.2⟩, fun _ hpn ↦ hp.1.not_isUnit <| hm _ <|
(mul_dvd_mul_right (dvd_gcd (dvd_of_mul_left_dvd hp.2) hpn) _).trans hp.2⟩, fun hp ↦
⟨hp.1.1, Coprime.mul_dvd_of_dvd_of_dvd ?_ (gcd_dvd_left _ _) hp.1.2⟩⟩
rw [coprime_comm, hp.1.1.coprime_iff_not_dvd]
exact fun hpn ↦ hp.2 hp.1.1 <| hpn.trans <| gcd_dvd_right _ _
lemma prod_primeFactors_invOn_squarefree :
Set.InvOn (fun n : ℕ ↦ (factorization n).support) (fun s ↦ ∏ p ∈ s, p)
{s | ∀ p ∈ s, p.Prime} {n | Squarefree n} :=
⟨fun _s ↦ primeFactors_prod, fun _n ↦ prod_primeFactors_of_squarefree⟩
theorem prod_primeFactors_sdiff_of_squarefree {n : ℕ} (hn : Squarefree n) {t : Finset ℕ}
(ht : t ⊆ n.primeFactors) :
| ∏ a ∈ (n.primeFactors \ t), a = n / ∏ a ∈ t, a := by
refine symm <| Nat.div_eq_of_eq_mul_left (Finset.prod_pos
fun p hp => (prime_of_mem_primeFactorsList (List.mem_toFinset.mp (ht hp))).pos) ?_
| Mathlib/Data/Nat/Squarefree.lean | 394 | 396 |
/-
Copyright (c) 2021 Christopher Hoskin. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Christopher Hoskin
-/
import Mathlib.Analysis.Normed.Group.Constructions
import Mathlib.Analysis.Normed.Group.Rat
import Mathlib.Analysis.Normed.Group.Uniform
import Mathlib.Topology.Order.Lattice
/-!
# Normed lattice ordered groups
Motivated by the theory of Banach Lattices, we then define `NormedLatticeAddCommGroup` as a
lattice with a covariant normed group addition satisfying the solid axiom.
## Main statements
We show that a normed lattice ordered group is a topological lattice with respect to the norm
topology.
## References
* [Meyer-Nieberg, Banach lattices][MeyerNieberg1991]
## Tags
normed, lattice, ordered, group
-/
/-!
### Normed lattice ordered groups
Motivated by the theory of Banach Lattices, this section introduces normed lattice ordered groups.
-/
section SolidNorm
/-- Let `α` be an `AddCommGroup` with a `Lattice` structure. A norm on `α` is *solid* if, for `a`
and `b` in `α`, with absolute values `|a|` and `|b|` respectively, `|a| ≤ |b|` implies `‖a‖ ≤ ‖b‖`.
-/
class HasSolidNorm (α : Type*) [NormedAddCommGroup α] [Lattice α] : Prop where
solid : ∀ ⦃x y : α⦄, |x| ≤ |y| → ‖x‖ ≤ ‖y‖
variable {α : Type*} [NormedAddCommGroup α] [Lattice α] [HasSolidNorm α]
theorem norm_le_norm_of_abs_le_abs {a b : α} (h : |a| ≤ |b|) : ‖a‖ ≤ ‖b‖ :=
HasSolidNorm.solid h
/-- If `α` has a solid norm, then the balls centered at the origin of `α` are solid sets. -/
theorem LatticeOrderedAddCommGroup.isSolid_ball (r : ℝ) :
LatticeOrderedAddCommGroup.IsSolid (Metric.ball (0 : α) r) := fun _ hx _ hxy =>
mem_ball_zero_iff.mpr ((HasSolidNorm.solid hxy).trans_lt (mem_ball_zero_iff.mp hx))
instance : HasSolidNorm ℝ := ⟨fun _ _ => id⟩
instance : HasSolidNorm ℚ := ⟨fun _ _ _ => by simpa only [norm, ← Rat.cast_abs, Rat.cast_le]⟩
end SolidNorm
/--
Let `α` be a normed commutative group equipped with a partial order covariant with addition, with
respect which `α` forms a lattice. Suppose that `α` is *solid*, that is to say, for `a` and `b` in
`α`, with absolute values `|a|` and `|b|` respectively, `|a| ≤ |b|` implies `‖a‖ ≤ ‖b‖`. Then `α` is
said to be a normed lattice ordered group.
-/
@[deprecated
"Use `[NormedAddCommGroup α] [Lattice α] [HasSolidNorm α] [IsOrderedAddMonoid α]` instead."
(since := "2025-04-10")]
structure NormedLatticeAddCommGroup (α : Type*) extends
NormedAddCommGroup α, Lattice α, HasSolidNorm α where
add_le_add_left : ∀ a b : α, a ≤ b → ∀ c : α, c + a ≤ c + b
instance Int.hasSolidNorm : HasSolidNorm ℤ where
solid x y h := by simpa [← Int.norm_cast_real, ← Int.cast_abs] using h
instance Rat.hasSolidNorm : HasSolidNorm ℚ where
solid x y h := by simpa [← Rat.norm_cast_real, ← Rat.cast_abs] using h
variable {α : Type*} [NormedAddCommGroup α] [Lattice α] [HasSolidNorm α] [IsOrderedAddMonoid α]
open HasSolidNorm
theorem dual_solid (a b : α) (h : b ⊓ -b ≤ a ⊓ -a) : ‖a‖ ≤ ‖b‖ := by
apply solid
rw [abs]
nth_rw 1 [← neg_neg a]
rw [← neg_inf]
rw [abs]
nth_rw 1 [← neg_neg b]
rwa [← neg_inf, neg_le_neg_iff, inf_comm _ b, inf_comm _ a]
-- see Note [lower instance priority]
/-- Let `α` be a normed lattice ordered group, then the order dual is also a
normed lattice ordered group.
-/
instance (priority := 100) OrderDual.instHasSolidNorm :
HasSolidNorm αᵒᵈ :=
{ solid := dual_solid (α := α) }
theorem norm_abs_eq_norm (a : α) : ‖|a|‖ = ‖a‖ :=
(solid (abs_abs a).le).antisymm (solid (abs_abs a).symm.le)
theorem norm_inf_sub_inf_le_add_norm (a b c d : α) : ‖a ⊓ b - c ⊓ d‖ ≤ ‖a - c‖ + ‖b - d‖ := by
rw [← norm_abs_eq_norm (a - c), ← norm_abs_eq_norm (b - d)]
refine le_trans (solid ?_) (norm_add_le |a - c| |b - d|)
rw [abs_of_nonneg (add_nonneg (abs_nonneg (a - c)) (abs_nonneg (b - d)))]
calc
|a ⊓ b - c ⊓ d| = |a ⊓ b - c ⊓ b + (c ⊓ b - c ⊓ d)| := by rw [sub_add_sub_cancel]
_ ≤ |a ⊓ b - c ⊓ b| + |c ⊓ b - c ⊓ d| := abs_add_le _ _
_ ≤ |a - c| + |b - d| := by
apply add_le_add
· exact abs_inf_sub_inf_le_abs _ _ _
· rw [inf_comm c, inf_comm c]
exact abs_inf_sub_inf_le_abs _ _ _
theorem norm_sup_sub_sup_le_add_norm (a b c d : α) : ‖a ⊔ b - c ⊔ d‖ ≤ ‖a - c‖ + ‖b - d‖ := by
rw [← norm_abs_eq_norm (a - c), ← norm_abs_eq_norm (b - d)]
refine le_trans (solid ?_) (norm_add_le |a - c| |b - d|)
rw [abs_of_nonneg (add_nonneg (abs_nonneg (a - c)) (abs_nonneg (b - d)))]
calc
|a ⊔ b - c ⊔ d| = |a ⊔ b - c ⊔ b + (c ⊔ b - c ⊔ d)| := by rw [sub_add_sub_cancel]
_ ≤ |a ⊔ b - c ⊔ b| + |c ⊔ b - c ⊔ d| := abs_add_le _ _
_ ≤ |a - c| + |b - d| := by
apply add_le_add
· exact abs_sup_sub_sup_le_abs _ _ _
· rw [sup_comm c, sup_comm c]
exact abs_sup_sub_sup_le_abs _ _ _
theorem norm_inf_le_add (x y : α) : ‖x ⊓ y‖ ≤ ‖x‖ + ‖y‖ := by
have h : ‖x ⊓ y - 0 ⊓ 0‖ ≤ ‖x - 0‖ + ‖y - 0‖ := norm_inf_sub_inf_le_add_norm x y 0 0
simpa only [inf_idem, sub_zero] using h
theorem norm_sup_le_add (x y : α) : ‖x ⊔ y‖ ≤ ‖x‖ + ‖y‖ := by
have h : ‖x ⊔ y - 0 ⊔ 0‖ ≤ ‖x - 0‖ + ‖y - 0‖ := norm_sup_sub_sup_le_add_norm x y 0 0
simpa only [sup_idem, sub_zero] using h
-- see Note [lower instance priority]
/-- Let `α` be a normed lattice ordered group. Then the infimum is jointly continuous.
-/
instance (priority := 100) HasSolidNorm.continuousInf : ContinuousInf α := by
refine ⟨continuous_iff_continuousAt.2 fun q => tendsto_iff_norm_sub_tendsto_zero.2 <| ?_⟩
have : ∀ p : α × α, ‖p.1 ⊓ p.2 - q.1 ⊓ q.2‖ ≤ ‖p.1 - q.1‖ + ‖p.2 - q.2‖ := fun _ =>
norm_inf_sub_inf_le_add_norm _ _ _ _
refine squeeze_zero (fun e => norm_nonneg _) this ?_
convert ((continuous_fst.tendsto q).sub <| tendsto_const_nhds).norm.add
((continuous_snd.tendsto q).sub <| tendsto_const_nhds).norm
simp
-- see Note [lower instance priority]
instance (priority := 100) HasSolidNorm.continuousSup {α : Type*}
| [NormedAddCommGroup α] [Lattice α] [HasSolidNorm α] [IsOrderedAddMonoid α] : ContinuousSup α :=
OrderDual.continuousSup αᵒᵈ
| Mathlib/Analysis/Normed/Order/Lattice.lean | 153 | 155 |
/-
Copyright (c) 2019 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Analysis.SpecificLimits.Basic
import Mathlib.Topology.MetricSpace.IsometricSMul
/-!
# Hausdorff distance
The Hausdorff distance on subsets of a metric (or emetric) space.
Given two subsets `s` and `t` of a metric space, their Hausdorff distance is the smallest `d`
such that any point `s` is within `d` of a point in `t`, and conversely. This quantity
is often infinite (think of `s` bounded and `t` unbounded), and therefore better
expressed in the setting of emetric spaces.
## Main definitions
This files introduces:
* `EMetric.infEdist x s`, the infimum edistance of a point `x` to a set `s` in an emetric space
* `EMetric.hausdorffEdist s t`, the Hausdorff edistance of two sets in an emetric space
* Versions of these notions on metric spaces, called respectively `Metric.infDist`
and `Metric.hausdorffDist`
## Main results
* `infEdist_closure`: the edistance to a set and its closure coincide
* `EMetric.mem_closure_iff_infEdist_zero`: a point `x` belongs to the closure of `s` iff
`infEdist x s = 0`
* `IsCompact.exists_infEdist_eq_edist`: if `s` is compact and non-empty, there exists a point `y`
which attains this edistance
* `IsOpen.exists_iUnion_isClosed`: every open set `U` can be written as the increasing union
of countably many closed subsets of `U`
* `hausdorffEdist_closure`: replacing a set by its closure does not change the Hausdorff edistance
* `hausdorffEdist_zero_iff_closure_eq_closure`: two sets have Hausdorff edistance zero
iff their closures coincide
* the Hausdorff edistance is symmetric and satisfies the triangle inequality
* in particular, closed sets in an emetric space are an emetric space
(this is shown in `EMetricSpace.closeds.emetricspace`)
* versions of these notions on metric spaces
* `hausdorffEdist_ne_top_of_nonempty_of_bounded`: if two sets in a metric space
are nonempty and bounded in a metric space, they are at finite Hausdorff edistance.
## Tags
metric space, Hausdorff distance
-/
noncomputable section
open NNReal ENNReal Topology Set Filter Pointwise Bornology
universe u v w
variable {ι : Sort*} {α : Type u} {β : Type v}
namespace EMetric
section InfEdist
variable [PseudoEMetricSpace α] [PseudoEMetricSpace β] {x y : α} {s t : Set α} {Φ : α → β}
/-! ### Distance of a point to a set as a function into `ℝ≥0∞`. -/
/-- The minimal edistance of a point to a set -/
def infEdist (x : α) (s : Set α) : ℝ≥0∞ :=
⨅ y ∈ s, edist x y
@[simp]
theorem infEdist_empty : infEdist x ∅ = ∞ :=
iInf_emptyset
theorem le_infEdist {d} : d ≤ infEdist x s ↔ ∀ y ∈ s, d ≤ edist x y := by
simp only [infEdist, le_iInf_iff]
/-- The edist to a union is the minimum of the edists -/
@[simp]
theorem infEdist_union : infEdist x (s ∪ t) = infEdist x s ⊓ infEdist x t :=
iInf_union
@[simp]
theorem infEdist_iUnion (f : ι → Set α) (x : α) : infEdist x (⋃ i, f i) = ⨅ i, infEdist x (f i) :=
iInf_iUnion f _
lemma infEdist_biUnion {ι : Type*} (f : ι → Set α) (I : Set ι) (x : α) :
infEdist x (⋃ i ∈ I, f i) = ⨅ i ∈ I, infEdist x (f i) := by simp only [infEdist_iUnion]
/-- The edist to a singleton is the edistance to the single point of this singleton -/
@[simp]
theorem infEdist_singleton : infEdist x {y} = edist x y :=
iInf_singleton
/-- The edist to a set is bounded above by the edist to any of its points -/
theorem infEdist_le_edist_of_mem (h : y ∈ s) : infEdist x s ≤ edist x y :=
iInf₂_le y h
/-- If a point `x` belongs to `s`, then its edist to `s` vanishes -/
theorem infEdist_zero_of_mem (h : x ∈ s) : infEdist x s = 0 :=
nonpos_iff_eq_zero.1 <| @edist_self _ _ x ▸ infEdist_le_edist_of_mem h
/-- The edist is antitone with respect to inclusion. -/
theorem infEdist_anti (h : s ⊆ t) : infEdist x t ≤ infEdist x s :=
iInf_le_iInf_of_subset h
/-- The edist to a set is `< r` iff there exists a point in the set at edistance `< r` -/
theorem infEdist_lt_iff {r : ℝ≥0∞} : infEdist x s < r ↔ ∃ y ∈ s, edist x y < r := by
simp_rw [infEdist, iInf_lt_iff, exists_prop]
/-- The edist of `x` to `s` is bounded by the sum of the edist of `y` to `s` and
the edist from `x` to `y` -/
theorem infEdist_le_infEdist_add_edist : infEdist x s ≤ infEdist y s + edist x y :=
calc
⨅ z ∈ s, edist x z ≤ ⨅ z ∈ s, edist y z + edist x y :=
iInf₂_mono fun _ _ => (edist_triangle _ _ _).trans_eq (add_comm _ _)
_ = (⨅ z ∈ s, edist y z) + edist x y := by simp only [ENNReal.iInf_add]
theorem infEdist_le_edist_add_infEdist : infEdist x s ≤ edist x y + infEdist y s := by
rw [add_comm]
exact infEdist_le_infEdist_add_edist
theorem edist_le_infEdist_add_ediam (hy : y ∈ s) : edist x y ≤ infEdist x s + diam s := by
simp_rw [infEdist, ENNReal.iInf_add]
refine le_iInf₂ fun i hi => ?_
calc
edist x y ≤ edist x i + edist i y := edist_triangle _ _ _
_ ≤ edist x i + diam s := add_le_add le_rfl (edist_le_diam_of_mem hi hy)
/-- The edist to a set depends continuously on the point -/
@[continuity]
theorem continuous_infEdist : Continuous fun x => infEdist x s :=
continuous_of_le_add_edist 1 (by simp) <| by
simp only [one_mul, infEdist_le_infEdist_add_edist, forall₂_true_iff]
/-- The edist to a set and to its closure coincide -/
theorem infEdist_closure : infEdist x (closure s) = infEdist x s := by
refine le_antisymm (infEdist_anti subset_closure) ?_
refine ENNReal.le_of_forall_pos_le_add fun ε εpos h => ?_
have ε0 : 0 < (ε / 2 : ℝ≥0∞) := by simpa [pos_iff_ne_zero] using εpos
have : infEdist x (closure s) < infEdist x (closure s) + ε / 2 :=
ENNReal.lt_add_right h.ne ε0.ne'
obtain ⟨y : α, ycs : y ∈ closure s, hy : edist x y < infEdist x (closure s) + ↑ε / 2⟩ :=
infEdist_lt_iff.mp this
obtain ⟨z : α, zs : z ∈ s, dyz : edist y z < ↑ε / 2⟩ := EMetric.mem_closure_iff.1 ycs (ε / 2) ε0
calc
infEdist x s ≤ edist x z := infEdist_le_edist_of_mem zs
_ ≤ edist x y + edist y z := edist_triangle _ _ _
_ ≤ infEdist x (closure s) + ε / 2 + ε / 2 := add_le_add (le_of_lt hy) (le_of_lt dyz)
_ = infEdist x (closure s) + ↑ε := by rw [add_assoc, ENNReal.add_halves]
/-- A point belongs to the closure of `s` iff its infimum edistance to this set vanishes -/
theorem mem_closure_iff_infEdist_zero : x ∈ closure s ↔ infEdist x s = 0 :=
⟨fun h => by
rw [← infEdist_closure]
exact infEdist_zero_of_mem h,
fun h =>
EMetric.mem_closure_iff.2 fun ε εpos => infEdist_lt_iff.mp <| by rwa [h]⟩
/-- Given a closed set `s`, a point belongs to `s` iff its infimum edistance to this set vanishes -/
theorem mem_iff_infEdist_zero_of_closed (h : IsClosed s) : x ∈ s ↔ infEdist x s = 0 := by
rw [← mem_closure_iff_infEdist_zero, h.closure_eq]
/-- The infimum edistance of a point to a set is positive if and only if the point is not in the
closure of the set. -/
theorem infEdist_pos_iff_not_mem_closure {x : α} {E : Set α} :
0 < infEdist x E ↔ x ∉ closure E := by
rw [mem_closure_iff_infEdist_zero, pos_iff_ne_zero]
theorem infEdist_closure_pos_iff_not_mem_closure {x : α} {E : Set α} :
0 < infEdist x (closure E) ↔ x ∉ closure E := by
rw [infEdist_closure, infEdist_pos_iff_not_mem_closure]
theorem exists_real_pos_lt_infEdist_of_not_mem_closure {x : α} {E : Set α} (h : x ∉ closure E) :
∃ ε : ℝ, 0 < ε ∧ ENNReal.ofReal ε < infEdist x E := by
rw [← infEdist_pos_iff_not_mem_closure, ENNReal.lt_iff_exists_real_btwn] at h
rcases h with ⟨ε, ⟨_, ⟨ε_pos, ε_lt⟩⟩⟩
exact ⟨ε, ⟨ENNReal.ofReal_pos.mp ε_pos, ε_lt⟩⟩
theorem disjoint_closedBall_of_lt_infEdist {r : ℝ≥0∞} (h : r < infEdist x s) :
Disjoint (closedBall x r) s := by
rw [disjoint_left]
intro y hy h'y
apply lt_irrefl (infEdist x s)
calc
infEdist x s ≤ edist x y := infEdist_le_edist_of_mem h'y
_ ≤ r := by rwa [mem_closedBall, edist_comm] at hy
_ < infEdist x s := h
/-- The infimum edistance is invariant under isometries -/
theorem infEdist_image (hΦ : Isometry Φ) : infEdist (Φ x) (Φ '' t) = infEdist x t := by
simp only [infEdist, iInf_image, hΦ.edist_eq]
@[to_additive (attr := simp)]
theorem infEdist_smul {M} [SMul M α] [IsIsometricSMul M α] (c : M) (x : α) (s : Set α) :
infEdist (c • x) (c • s) = infEdist x s :=
infEdist_image (isometry_smul _ _)
theorem _root_.IsOpen.exists_iUnion_isClosed {U : Set α} (hU : IsOpen U) :
∃ F : ℕ → Set α, (∀ n, IsClosed (F n)) ∧ (∀ n, F n ⊆ U) ∧ ⋃ n, F n = U ∧ Monotone F := by
obtain ⟨a, a_pos, a_lt_one⟩ : ∃ a : ℝ≥0∞, 0 < a ∧ a < 1 := exists_between zero_lt_one
let F := fun n : ℕ => (fun x => infEdist x Uᶜ) ⁻¹' Ici (a ^ n)
have F_subset : ∀ n, F n ⊆ U := fun n x hx ↦ by
by_contra h
have : infEdist x Uᶜ ≠ 0 := ((ENNReal.pow_pos a_pos _).trans_le hx).ne'
exact this (infEdist_zero_of_mem h)
refine ⟨F, fun n => IsClosed.preimage continuous_infEdist isClosed_Ici, F_subset, ?_, ?_⟩
· show ⋃ n, F n = U
refine Subset.antisymm (by simp only [iUnion_subset_iff, F_subset, forall_const]) fun x hx => ?_
have : ¬x ∈ Uᶜ := by simpa using hx
rw [mem_iff_infEdist_zero_of_closed hU.isClosed_compl] at this
have B : 0 < infEdist x Uᶜ := by simpa [pos_iff_ne_zero] using this
have : Filter.Tendsto (fun n => a ^ n) atTop (𝓝 0) :=
ENNReal.tendsto_pow_atTop_nhds_zero_of_lt_one a_lt_one
rcases ((tendsto_order.1 this).2 _ B).exists with ⟨n, hn⟩
simp only [mem_iUnion, mem_Ici, mem_preimage]
exact ⟨n, hn.le⟩
show Monotone F
intro m n hmn x hx
simp only [F, mem_Ici, mem_preimage] at hx ⊢
apply le_trans (pow_le_pow_right_of_le_one' a_lt_one.le hmn) hx
theorem _root_.IsCompact.exists_infEdist_eq_edist (hs : IsCompact s) (hne : s.Nonempty) (x : α) :
∃ y ∈ s, infEdist x s = edist x y := by
have A : Continuous fun y => edist x y := continuous_const.edist continuous_id
obtain ⟨y, ys, hy⟩ := hs.exists_isMinOn hne A.continuousOn
exact ⟨y, ys, le_antisymm (infEdist_le_edist_of_mem ys) (by rwa [le_infEdist])⟩
theorem exists_pos_forall_lt_edist (hs : IsCompact s) (ht : IsClosed t) (hst : Disjoint s t) :
∃ r : ℝ≥0, 0 < r ∧ ∀ x ∈ s, ∀ y ∈ t, (r : ℝ≥0∞) < edist x y := by
rcases s.eq_empty_or_nonempty with (rfl | hne)
· use 1
simp
obtain ⟨x, hx, h⟩ := hs.exists_isMinOn hne continuous_infEdist.continuousOn
have : 0 < infEdist x t :=
pos_iff_ne_zero.2 fun H => hst.le_bot ⟨hx, (mem_iff_infEdist_zero_of_closed ht).mpr H⟩
rcases ENNReal.lt_iff_exists_nnreal_btwn.1 this with ⟨r, h₀, hr⟩
exact ⟨r, ENNReal.coe_pos.mp h₀, fun y hy z hz => hr.trans_le <| le_infEdist.1 (h hy) z hz⟩
end InfEdist
/-! ### The Hausdorff distance as a function into `ℝ≥0∞`. -/
/-- The Hausdorff edistance between two sets is the smallest `r` such that each set
is contained in the `r`-neighborhood of the other one -/
irreducible_def hausdorffEdist {α : Type u} [PseudoEMetricSpace α] (s t : Set α) : ℝ≥0∞ :=
(⨆ x ∈ s, infEdist x t) ⊔ ⨆ y ∈ t, infEdist y s
section HausdorffEdist
variable [PseudoEMetricSpace α] [PseudoEMetricSpace β] {x : α} {s t u : Set α} {Φ : α → β}
/-- The Hausdorff edistance of a set to itself vanishes. -/
@[simp]
theorem hausdorffEdist_self : hausdorffEdist s s = 0 := by
simp only [hausdorffEdist_def, sup_idem, ENNReal.iSup_eq_zero]
exact fun x hx => infEdist_zero_of_mem hx
/-- The Haudorff edistances of `s` to `t` and of `t` to `s` coincide. -/
theorem hausdorffEdist_comm : hausdorffEdist s t = hausdorffEdist t s := by
simp only [hausdorffEdist_def]; apply sup_comm
/-- Bounding the Hausdorff edistance by bounding the edistance of any point
in each set to the other set -/
theorem hausdorffEdist_le_of_infEdist {r : ℝ≥0∞} (H1 : ∀ x ∈ s, infEdist x t ≤ r)
(H2 : ∀ x ∈ t, infEdist x s ≤ r) : hausdorffEdist s t ≤ r := by
simp only [hausdorffEdist_def, sup_le_iff, iSup_le_iff]
exact ⟨H1, H2⟩
/-- Bounding the Hausdorff edistance by exhibiting, for any point in each set,
another point in the other set at controlled distance -/
theorem hausdorffEdist_le_of_mem_edist {r : ℝ≥0∞} (H1 : ∀ x ∈ s, ∃ y ∈ t, edist x y ≤ r)
(H2 : ∀ x ∈ t, ∃ y ∈ s, edist x y ≤ r) : hausdorffEdist s t ≤ r := by
refine hausdorffEdist_le_of_infEdist (fun x xs ↦ ?_) (fun x xt ↦ ?_)
· rcases H1 x xs with ⟨y, yt, hy⟩
exact le_trans (infEdist_le_edist_of_mem yt) hy
· rcases H2 x xt with ⟨y, ys, hy⟩
exact le_trans (infEdist_le_edist_of_mem ys) hy
/-- The distance to a set is controlled by the Hausdorff distance. -/
theorem infEdist_le_hausdorffEdist_of_mem (h : x ∈ s) : infEdist x t ≤ hausdorffEdist s t := by
rw [hausdorffEdist_def]
refine le_trans ?_ le_sup_left
exact le_iSup₂ (α := ℝ≥0∞) x h
/-- If the Hausdorff distance is `< r`, then any point in one of the sets has
a corresponding point at distance `< r` in the other set. -/
theorem exists_edist_lt_of_hausdorffEdist_lt {r : ℝ≥0∞} (h : x ∈ s) (H : hausdorffEdist s t < r) :
∃ y ∈ t, edist x y < r :=
infEdist_lt_iff.mp <|
calc
infEdist x t ≤ hausdorffEdist s t := infEdist_le_hausdorffEdist_of_mem h
_ < r := H
/-- The distance from `x` to `s` or `t` is controlled in terms of the Hausdorff distance
between `s` and `t`. -/
theorem infEdist_le_infEdist_add_hausdorffEdist :
infEdist x t ≤ infEdist x s + hausdorffEdist s t :=
ENNReal.le_of_forall_pos_le_add fun ε εpos h => by
have ε0 : (ε / 2 : ℝ≥0∞) ≠ 0 := by simpa [pos_iff_ne_zero] using εpos
have : infEdist x s < infEdist x s + ε / 2 :=
ENNReal.lt_add_right (ENNReal.add_lt_top.1 h).1.ne ε0
obtain ⟨y : α, ys : y ∈ s, dxy : edist x y < infEdist x s + ↑ε / 2⟩ := infEdist_lt_iff.mp this
have : hausdorffEdist s t < hausdorffEdist s t + ε / 2 :=
ENNReal.lt_add_right (ENNReal.add_lt_top.1 h).2.ne ε0
obtain ⟨z : α, zt : z ∈ t, dyz : edist y z < hausdorffEdist s t + ↑ε / 2⟩ :=
exists_edist_lt_of_hausdorffEdist_lt ys this
calc
infEdist x t ≤ edist x z := infEdist_le_edist_of_mem zt
_ ≤ edist x y + edist y z := edist_triangle _ _ _
_ ≤ infEdist x s + ε / 2 + (hausdorffEdist s t + ε / 2) := add_le_add dxy.le dyz.le
_ = infEdist x s + hausdorffEdist s t + ε := by
simp [ENNReal.add_halves, add_comm, add_left_comm]
/-- The Hausdorff edistance is invariant under isometries. -/
theorem hausdorffEdist_image (h : Isometry Φ) :
hausdorffEdist (Φ '' s) (Φ '' t) = hausdorffEdist s t := by
simp only [hausdorffEdist_def, iSup_image, infEdist_image h]
/-- The Hausdorff distance is controlled by the diameter of the union. -/
theorem hausdorffEdist_le_ediam (hs : s.Nonempty) (ht : t.Nonempty) :
hausdorffEdist s t ≤ diam (s ∪ t) := by
rcases hs with ⟨x, xs⟩
rcases ht with ⟨y, yt⟩
refine hausdorffEdist_le_of_mem_edist ?_ ?_
· intro z hz
exact ⟨y, yt, edist_le_diam_of_mem (subset_union_left hz) (subset_union_right yt)⟩
· intro z hz
exact ⟨x, xs, edist_le_diam_of_mem (subset_union_right hz) (subset_union_left xs)⟩
/-- The Hausdorff distance satisfies the triangle inequality. -/
theorem hausdorffEdist_triangle : hausdorffEdist s u ≤ hausdorffEdist s t + hausdorffEdist t u := by
rw [hausdorffEdist_def]
simp only [sup_le_iff, iSup_le_iff]
constructor
· show ∀ x ∈ s, infEdist x u ≤ hausdorffEdist s t + hausdorffEdist t u
exact fun x xs =>
calc
infEdist x u ≤ infEdist x t + hausdorffEdist t u :=
infEdist_le_infEdist_add_hausdorffEdist
_ ≤ hausdorffEdist s t + hausdorffEdist t u :=
add_le_add_right (infEdist_le_hausdorffEdist_of_mem xs) _
· show ∀ x ∈ u, infEdist x s ≤ hausdorffEdist s t + hausdorffEdist t u
exact fun x xu =>
calc
infEdist x s ≤ infEdist x t + hausdorffEdist t s :=
infEdist_le_infEdist_add_hausdorffEdist
_ ≤ hausdorffEdist u t + hausdorffEdist t s :=
add_le_add_right (infEdist_le_hausdorffEdist_of_mem xu) _
_ = hausdorffEdist s t + hausdorffEdist t u := by simp [hausdorffEdist_comm, add_comm]
/-- Two sets are at zero Hausdorff edistance if and only if they have the same closure. -/
theorem hausdorffEdist_zero_iff_closure_eq_closure :
hausdorffEdist s t = 0 ↔ closure s = closure t := by
simp only [hausdorffEdist_def, ENNReal.sup_eq_zero, ENNReal.iSup_eq_zero, ← subset_def,
← mem_closure_iff_infEdist_zero, subset_antisymm_iff, isClosed_closure.closure_subset_iff]
/-- The Hausdorff edistance between a set and its closure vanishes. -/
@[simp]
theorem hausdorffEdist_self_closure : hausdorffEdist s (closure s) = 0 := by
rw [hausdorffEdist_zero_iff_closure_eq_closure, closure_closure]
/-- Replacing a set by its closure does not change the Hausdorff edistance. -/
@[simp]
theorem hausdorffEdist_closure₁ : hausdorffEdist (closure s) t = hausdorffEdist s t := by
refine le_antisymm ?_ ?_
· calc
_ ≤ hausdorffEdist (closure s) s + hausdorffEdist s t := hausdorffEdist_triangle
_ = hausdorffEdist s t := by simp [hausdorffEdist_comm]
· calc
_ ≤ hausdorffEdist s (closure s) + hausdorffEdist (closure s) t := hausdorffEdist_triangle
_ = hausdorffEdist (closure s) t := by simp
/-- Replacing a set by its closure does not change the Hausdorff edistance. -/
@[simp]
theorem hausdorffEdist_closure₂ : hausdorffEdist s (closure t) = hausdorffEdist s t := by
simp [@hausdorffEdist_comm _ _ s _]
/-- The Hausdorff edistance between sets or their closures is the same. -/
theorem hausdorffEdist_closure : hausdorffEdist (closure s) (closure t) = hausdorffEdist s t := by
simp
/-- Two closed sets are at zero Hausdorff edistance if and only if they coincide. -/
theorem hausdorffEdist_zero_iff_eq_of_closed (hs : IsClosed s) (ht : IsClosed t) :
hausdorffEdist s t = 0 ↔ s = t := by
rw [hausdorffEdist_zero_iff_closure_eq_closure, hs.closure_eq, ht.closure_eq]
/-- The Haudorff edistance to the empty set is infinite. -/
theorem hausdorffEdist_empty (ne : s.Nonempty) : hausdorffEdist s ∅ = ∞ := by
rcases ne with ⟨x, xs⟩
have : infEdist x ∅ ≤ hausdorffEdist s ∅ := infEdist_le_hausdorffEdist_of_mem xs
simpa using this
/-- If a set is at finite Hausdorff edistance of a nonempty set, it is nonempty. -/
theorem nonempty_of_hausdorffEdist_ne_top (hs : s.Nonempty) (fin : hausdorffEdist s t ≠ ⊤) :
t.Nonempty :=
t.eq_empty_or_nonempty.resolve_left fun ht ↦ fin (ht.symm ▸ hausdorffEdist_empty hs)
theorem empty_or_nonempty_of_hausdorffEdist_ne_top (fin : hausdorffEdist s t ≠ ⊤) :
(s = ∅ ∧ t = ∅) ∨ (s.Nonempty ∧ t.Nonempty) := by
rcases s.eq_empty_or_nonempty with hs | hs
· rcases t.eq_empty_or_nonempty with ht | ht
· exact Or.inl ⟨hs, ht⟩
· rw [hausdorffEdist_comm] at fin
exact Or.inr ⟨nonempty_of_hausdorffEdist_ne_top ht fin, ht⟩
· exact Or.inr ⟨hs, nonempty_of_hausdorffEdist_ne_top hs fin⟩
end HausdorffEdist
-- section
end EMetric
/-! Now, we turn to the same notions in metric spaces. To avoid the difficulties related to
`sInf` and `sSup` on `ℝ` (which is only conditionally complete), we use the notions in `ℝ≥0∞`
formulated in terms of the edistance, and coerce them to `ℝ`.
Then their properties follow readily from the corresponding properties in `ℝ≥0∞`,
modulo some tedious rewriting of inequalities from one to the other. -/
--namespace
namespace Metric
section
variable [PseudoMetricSpace α] [PseudoMetricSpace β] {s t u : Set α} {x y : α} {Φ : α → β}
open EMetric
/-! ### Distance of a point to a set as a function into `ℝ`. -/
/-- The minimal distance of a point to a set -/
def infDist (x : α) (s : Set α) : ℝ :=
ENNReal.toReal (infEdist x s)
theorem infDist_eq_iInf : infDist x s = ⨅ y : s, dist x y := by
rw [infDist, infEdist, iInf_subtype', ENNReal.toReal_iInf]
· simp only [dist_edist]
· exact fun _ ↦ edist_ne_top _ _
/-- The minimal distance is always nonnegative -/
theorem infDist_nonneg : 0 ≤ infDist x s := toReal_nonneg
/-- The minimal distance to the empty set is 0 (if you want to have the more reasonable
value `∞` instead, use `EMetric.infEdist`, which takes values in `ℝ≥0∞`) -/
@[simp]
theorem infDist_empty : infDist x ∅ = 0 := by simp [infDist]
lemma isGLB_infDist (hs : s.Nonempty) : IsGLB ((dist x ·) '' s) (infDist x s) := by
simpa [infDist_eq_iInf, sInf_image']
using isGLB_csInf (hs.image _) ⟨0, by simp [lowerBounds, dist_nonneg]⟩
/-- In a metric space, the minimal edistance to a nonempty set is finite. -/
theorem infEdist_ne_top (h : s.Nonempty) : infEdist x s ≠ ⊤ := by
rcases h with ⟨y, hy⟩
exact ne_top_of_le_ne_top (edist_ne_top _ _) (infEdist_le_edist_of_mem hy)
@[simp]
theorem infEdist_eq_top_iff : infEdist x s = ∞ ↔ s = ∅ := by
rcases s.eq_empty_or_nonempty with rfl | hs <;> simp [*, Nonempty.ne_empty, infEdist_ne_top]
/-- The minimal distance of a point to a set containing it vanishes. -/
theorem infDist_zero_of_mem (h : x ∈ s) : infDist x s = 0 := by
simp [infEdist_zero_of_mem h, infDist]
/-- The minimal distance to a singleton is the distance to the unique point in this singleton. -/
@[simp]
theorem infDist_singleton : infDist x {y} = dist x y := by simp [infDist, dist_edist]
/-- The minimal distance to a set is bounded by the distance to any point in this set. -/
theorem infDist_le_dist_of_mem (h : y ∈ s) : infDist x s ≤ dist x y := by
rw [dist_edist, infDist]
exact ENNReal.toReal_mono (edist_ne_top _ _) (infEdist_le_edist_of_mem h)
/-- The minimal distance is monotone with respect to inclusion. -/
theorem infDist_le_infDist_of_subset (h : s ⊆ t) (hs : s.Nonempty) : infDist x t ≤ infDist x s :=
ENNReal.toReal_mono (infEdist_ne_top hs) (infEdist_anti h)
lemma le_infDist {r : ℝ} (hs : s.Nonempty) : r ≤ infDist x s ↔ ∀ ⦃y⦄, y ∈ s → r ≤ dist x y := by
simp_rw [infDist, ← ENNReal.ofReal_le_iff_le_toReal (infEdist_ne_top hs), le_infEdist,
ENNReal.ofReal_le_iff_le_toReal (edist_ne_top _ _), ← dist_edist]
/-- The minimal distance to a set `s` is `< r` iff there exists a point in `s` at distance `< r`. -/
theorem infDist_lt_iff {r : ℝ} (hs : s.Nonempty) : infDist x s < r ↔ ∃ y ∈ s, dist x y < r := by
simp [← not_le, le_infDist hs]
/-- The minimal distance from `x` to `s` is bounded by the distance from `y` to `s`, modulo
the distance between `x` and `y`. -/
theorem infDist_le_infDist_add_dist : infDist x s ≤ infDist y s + dist x y := by
rw [infDist, infDist, dist_edist]
refine ENNReal.toReal_le_add' infEdist_le_infEdist_add_edist ?_ (flip absurd (edist_ne_top _ _))
simp only [infEdist_eq_top_iff, imp_self]
theorem not_mem_of_dist_lt_infDist (h : dist x y < infDist x s) : y ∉ s := fun hy =>
h.not_le <| infDist_le_dist_of_mem hy
theorem disjoint_ball_infDist : Disjoint (ball x (infDist x s)) s :=
disjoint_left.2 fun _y hy => not_mem_of_dist_lt_infDist <| mem_ball'.1 hy
theorem ball_infDist_subset_compl : ball x (infDist x s) ⊆ sᶜ :=
(disjoint_ball_infDist (s := s)).subset_compl_right
theorem ball_infDist_compl_subset : ball x (infDist x sᶜ) ⊆ s :=
ball_infDist_subset_compl.trans_eq (compl_compl s)
theorem disjoint_closedBall_of_lt_infDist {r : ℝ} (h : r < infDist x s) :
Disjoint (closedBall x r) s :=
disjoint_ball_infDist.mono_left <| closedBall_subset_ball h
theorem dist_le_infDist_add_diam (hs : IsBounded s) (hy : y ∈ s) :
dist x y ≤ infDist x s + diam s := by
rw [infDist, diam, dist_edist]
exact toReal_le_add (edist_le_infEdist_add_ediam hy) (infEdist_ne_top ⟨y, hy⟩) hs.ediam_ne_top
variable (s)
/-- The minimal distance to a set is Lipschitz in point with constant 1 -/
theorem lipschitz_infDist_pt : LipschitzWith 1 (infDist · s) :=
LipschitzWith.of_le_add fun _ _ => infDist_le_infDist_add_dist
/-- The minimal distance to a set is uniformly continuous in point -/
theorem uniformContinuous_infDist_pt : UniformContinuous (infDist · s) :=
(lipschitz_infDist_pt s).uniformContinuous
/-- The minimal distance to a set is continuous in point -/
@[continuity]
theorem continuous_infDist_pt : Continuous (infDist · s) :=
(uniformContinuous_infDist_pt s).continuous
variable {s}
/-- The minimal distances to a set and its closure coincide. -/
theorem infDist_closure : infDist x (closure s) = infDist x s := by
simp [infDist, infEdist_closure]
/-- If a point belongs to the closure of `s`, then its infimum distance to `s` equals zero.
The converse is true provided that `s` is nonempty, see `Metric.mem_closure_iff_infDist_zero`. -/
theorem infDist_zero_of_mem_closure (hx : x ∈ closure s) : infDist x s = 0 := by
rw [← infDist_closure]
exact infDist_zero_of_mem hx
/-- A point belongs to the closure of `s` iff its infimum distance to this set vanishes. -/
theorem mem_closure_iff_infDist_zero (h : s.Nonempty) : x ∈ closure s ↔ infDist x s = 0 := by
simp [mem_closure_iff_infEdist_zero, infDist, ENNReal.toReal_eq_zero_iff, infEdist_ne_top h]
theorem infDist_pos_iff_not_mem_closure (hs : s.Nonempty) :
x ∉ closure s ↔ 0 < infDist x s :=
(mem_closure_iff_infDist_zero hs).not.trans infDist_nonneg.gt_iff_ne.symm
/-- Given a closed set `s`, a point belongs to `s` iff its infimum distance to this set vanishes -/
theorem _root_.IsClosed.mem_iff_infDist_zero (h : IsClosed s) (hs : s.Nonempty) :
x ∈ s ↔ infDist x s = 0 := by rw [← mem_closure_iff_infDist_zero hs, h.closure_eq]
/-- Given a closed set `s`, a point belongs to `s` iff its infimum distance to this set vanishes. -/
theorem _root_.IsClosed.not_mem_iff_infDist_pos (h : IsClosed s) (hs : s.Nonempty) :
x ∉ s ↔ 0 < infDist x s := by
simp [h.mem_iff_infDist_zero hs, infDist_nonneg.gt_iff_ne]
theorem continuousAt_inv_infDist_pt (h : x ∉ closure s) :
ContinuousAt (fun x ↦ (infDist x s)⁻¹) x := by
rcases s.eq_empty_or_nonempty with (rfl | hs)
· simp only [infDist_empty, continuousAt_const]
· refine (continuous_infDist_pt s).continuousAt.inv₀ ?_
rwa [Ne, ← mem_closure_iff_infDist_zero hs]
/-- The infimum distance is invariant under isometries. -/
theorem infDist_image (hΦ : Isometry Φ) : infDist (Φ x) (Φ '' t) = infDist x t := by
simp [infDist, infEdist_image hΦ]
theorem infDist_inter_closedBall_of_mem (h : y ∈ s) :
infDist x (s ∩ closedBall x (dist y x)) = infDist x s := by
replace h : y ∈ s ∩ closedBall x (dist y x) := ⟨h, mem_closedBall.2 le_rfl⟩
refine le_antisymm ?_ (infDist_le_infDist_of_subset inter_subset_left ⟨y, h⟩)
refine not_lt.1 fun hlt => ?_
rcases (infDist_lt_iff ⟨y, h.1⟩).mp hlt with ⟨z, hzs, hz⟩
rcases le_or_lt (dist z x) (dist y x) with hle | hlt
· exact hz.not_le (infDist_le_dist_of_mem ⟨hzs, hle⟩)
· rw [dist_comm z, dist_comm y] at hlt
exact (hlt.trans hz).not_le (infDist_le_dist_of_mem h)
theorem _root_.IsCompact.exists_infDist_eq_dist (h : IsCompact s) (hne : s.Nonempty) (x : α) :
∃ y ∈ s, infDist x s = dist x y :=
let ⟨y, hys, hy⟩ := h.exists_infEdist_eq_edist hne x
⟨y, hys, by rw [infDist, dist_edist, hy]⟩
theorem _root_.IsClosed.exists_infDist_eq_dist [ProperSpace α] (h : IsClosed s) (hne : s.Nonempty)
(x : α) : ∃ y ∈ s, infDist x s = dist x y := by
rcases hne with ⟨z, hz⟩
rw [← infDist_inter_closedBall_of_mem hz]
set t := s ∩ closedBall x (dist z x)
have htc : IsCompact t := (isCompact_closedBall x (dist z x)).inter_left h
have htne : t.Nonempty := ⟨z, hz, mem_closedBall.2 le_rfl⟩
obtain ⟨y, ⟨hys, -⟩, hyd⟩ : ∃ y ∈ t, infDist x t = dist x y := htc.exists_infDist_eq_dist htne x
exact ⟨y, hys, hyd⟩
theorem exists_mem_closure_infDist_eq_dist [ProperSpace α] (hne : s.Nonempty) (x : α) :
∃ y ∈ closure s, infDist x s = dist x y := by
simpa only [infDist_closure] using isClosed_closure.exists_infDist_eq_dist hne.closure x
/-! ### Distance of a point to a set as a function into `ℝ≥0`. -/
/-- The minimal distance of a point to a set as a `ℝ≥0` -/
def infNndist (x : α) (s : Set α) : ℝ≥0 :=
ENNReal.toNNReal (infEdist x s)
@[simp]
theorem coe_infNndist : (infNndist x s : ℝ) = infDist x s :=
rfl
| /-- The minimal distance to a set (as `ℝ≥0`) is Lipschitz in point with constant 1 -/
theorem lipschitz_infNndist_pt (s : Set α) : LipschitzWith 1 fun x => infNndist x s :=
| Mathlib/Topology/MetricSpace/HausdorffDistance.lean | 609 | 610 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl
-/
import Aesop
import Mathlib.Order.BoundedOrder.Lattice
/-!
# Disjointness and complements
This file defines `Disjoint`, `Codisjoint`, and the `IsCompl` predicate.
## Main declarations
* `Disjoint x y`: two elements of a lattice are disjoint if their `inf` is the bottom element.
* `Codisjoint x y`: two elements of a lattice are codisjoint if their `join` is the top element.
* `IsCompl x y`: In a bounded lattice, predicate for "`x` is a complement of `y`". Note that in a
non distributive lattice, an element can have several complements.
* `ComplementedLattice α`: Typeclass stating that any element of a lattice has a complement.
-/
open Function
variable {α : Type*}
section Disjoint
section PartialOrderBot
variable [PartialOrder α] [OrderBot α] {a b c d : α}
/-- Two elements of a lattice are disjoint if their inf is the bottom element.
(This generalizes disjoint sets, viewed as members of the subset lattice.)
Note that we define this without reference to `⊓`, as this allows us to talk about orders where
the infimum is not unique, or where implementing `Inf` would require additional `Decidable`
arguments. -/
def Disjoint (a b : α) : Prop :=
∀ ⦃x⦄, x ≤ a → x ≤ b → x ≤ ⊥
@[simp]
theorem disjoint_of_subsingleton [Subsingleton α] : Disjoint a b :=
fun x _ _ ↦ le_of_eq (Subsingleton.elim x ⊥)
theorem disjoint_comm : Disjoint a b ↔ Disjoint b a :=
forall_congr' fun _ ↦ forall_swap
@[symm]
theorem Disjoint.symm ⦃a b : α⦄ : Disjoint a b → Disjoint b a :=
disjoint_comm.1
theorem symmetric_disjoint : Symmetric (Disjoint : α → α → Prop) :=
Disjoint.symm
@[simp]
theorem disjoint_bot_left : Disjoint ⊥ a := fun _ hbot _ ↦ hbot
@[simp]
theorem disjoint_bot_right : Disjoint a ⊥ := fun _ _ hbot ↦ hbot
theorem Disjoint.mono (h₁ : a ≤ b) (h₂ : c ≤ d) : Disjoint b d → Disjoint a c :=
fun h _ ha hc ↦ h (ha.trans h₁) (hc.trans h₂)
theorem Disjoint.mono_left (h : a ≤ b) : Disjoint b c → Disjoint a c :=
Disjoint.mono h le_rfl
theorem Disjoint.mono_right : b ≤ c → Disjoint a c → Disjoint a b :=
Disjoint.mono le_rfl
@[simp]
theorem disjoint_self : Disjoint a a ↔ a = ⊥ :=
⟨fun hd ↦ bot_unique <| hd le_rfl le_rfl, fun h _ ha _ ↦ ha.trans_eq h⟩
/- TODO: Rename `Disjoint.eq_bot` to `Disjoint.inf_eq` and `Disjoint.eq_bot_of_self` to
`Disjoint.eq_bot` -/
alias ⟨Disjoint.eq_bot_of_self, _⟩ := disjoint_self
theorem Disjoint.ne (ha : a ≠ ⊥) (hab : Disjoint a b) : a ≠ b :=
fun h ↦ ha <| disjoint_self.1 <| by rwa [← h] at hab
theorem Disjoint.eq_bot_of_le (hab : Disjoint a b) (h : a ≤ b) : a = ⊥ :=
eq_bot_iff.2 <| hab le_rfl h
theorem Disjoint.eq_bot_of_ge (hab : Disjoint a b) : b ≤ a → b = ⊥ :=
hab.symm.eq_bot_of_le
lemma Disjoint.eq_iff (hab : Disjoint a b) : a = b ↔ a = ⊥ ∧ b = ⊥ := by aesop
lemma Disjoint.ne_iff (hab : Disjoint a b) : a ≠ b ↔ a ≠ ⊥ ∨ b ≠ ⊥ :=
hab.eq_iff.not.trans not_and_or
theorem disjoint_of_le_iff_left_eq_bot (h : a ≤ b) :
Disjoint a b ↔ a = ⊥ :=
⟨fun hd ↦ hd.eq_bot_of_le h, fun h ↦ h ▸ disjoint_bot_left⟩
end PartialOrderBot
section PartialBoundedOrder
variable [PartialOrder α] [BoundedOrder α] {a : α}
@[simp]
theorem disjoint_top : Disjoint a ⊤ ↔ a = ⊥ :=
⟨fun h ↦ bot_unique <| h le_rfl le_top, fun h _ ha _ ↦ ha.trans_eq h⟩
@[simp]
theorem top_disjoint : Disjoint ⊤ a ↔ a = ⊥ :=
⟨fun h ↦ bot_unique <| h le_top le_rfl, fun h _ _ ha ↦ ha.trans_eq h⟩
end PartialBoundedOrder
section SemilatticeInfBot
variable [SemilatticeInf α] [OrderBot α] {a b c : α}
theorem disjoint_iff_inf_le : Disjoint a b ↔ a ⊓ b ≤ ⊥ :=
⟨fun hd ↦ hd inf_le_left inf_le_right, fun h _ ha hb ↦ (le_inf ha hb).trans h⟩
theorem disjoint_iff : Disjoint a b ↔ a ⊓ b = ⊥ :=
disjoint_iff_inf_le.trans le_bot_iff
theorem Disjoint.le_bot : Disjoint a b → a ⊓ b ≤ ⊥ :=
disjoint_iff_inf_le.mp
theorem Disjoint.eq_bot : Disjoint a b → a ⊓ b = ⊥ :=
bot_unique ∘ Disjoint.le_bot
theorem disjoint_assoc : Disjoint (a ⊓ b) c ↔ Disjoint a (b ⊓ c) := by
rw [disjoint_iff_inf_le, disjoint_iff_inf_le, inf_assoc]
theorem disjoint_left_comm : Disjoint a (b ⊓ c) ↔ Disjoint b (a ⊓ c) := by
simp_rw [disjoint_iff_inf_le, inf_left_comm]
theorem disjoint_right_comm : Disjoint (a ⊓ b) c ↔ Disjoint (a ⊓ c) b := by
simp_rw [disjoint_iff_inf_le, inf_right_comm]
variable (c)
theorem Disjoint.inf_left (h : Disjoint a b) : Disjoint (a ⊓ c) b :=
h.mono_left inf_le_left
theorem Disjoint.inf_left' (h : Disjoint a b) : Disjoint (c ⊓ a) b :=
h.mono_left inf_le_right
theorem Disjoint.inf_right (h : Disjoint a b) : Disjoint a (b ⊓ c) :=
h.mono_right inf_le_left
theorem Disjoint.inf_right' (h : Disjoint a b) : Disjoint a (c ⊓ b) :=
h.mono_right inf_le_right
variable {c}
theorem Disjoint.of_disjoint_inf_of_le (h : Disjoint (a ⊓ b) c) (hle : a ≤ c) : Disjoint a b :=
disjoint_iff.2 <| h.eq_bot_of_le <| inf_le_of_left_le hle
theorem Disjoint.of_disjoint_inf_of_le' (h : Disjoint (a ⊓ b) c) (hle : b ≤ c) : Disjoint a b :=
disjoint_iff.2 <| h.eq_bot_of_le <| inf_le_of_right_le hle
end SemilatticeInfBot
theorem Disjoint.right_lt_sup_of_left_ne_bot [SemilatticeSup α] [OrderBot α] {a b : α}
(h : Disjoint a b) (ha : a ≠ ⊥) : b < a ⊔ b :=
le_sup_right.lt_of_ne fun eq ↦ ha (le_bot_iff.mp <| h le_rfl <| sup_eq_right.mp eq.symm)
section DistribLatticeBot
variable [DistribLattice α] [OrderBot α] {a b c : α}
@[simp]
theorem disjoint_sup_left : Disjoint (a ⊔ b) c ↔ Disjoint a c ∧ Disjoint b c := by
simp only [disjoint_iff, inf_sup_right, sup_eq_bot_iff]
@[simp]
theorem disjoint_sup_right : Disjoint a (b ⊔ c) ↔ Disjoint a b ∧ Disjoint a c := by
simp only [disjoint_iff, inf_sup_left, sup_eq_bot_iff]
theorem Disjoint.sup_left (ha : Disjoint a c) (hb : Disjoint b c) : Disjoint (a ⊔ b) c :=
disjoint_sup_left.2 ⟨ha, hb⟩
theorem Disjoint.sup_right (hb : Disjoint a b) (hc : Disjoint a c) : Disjoint a (b ⊔ c) :=
disjoint_sup_right.2 ⟨hb, hc⟩
theorem Disjoint.left_le_of_le_sup_right (h : a ≤ b ⊔ c) (hd : Disjoint a c) : a ≤ b :=
le_of_inf_le_sup_le (le_trans hd.le_bot bot_le) <| sup_le h le_sup_right
theorem Disjoint.left_le_of_le_sup_left (h : a ≤ c ⊔ b) (hd : Disjoint a c) : a ≤ b :=
hd.left_le_of_le_sup_right <| by rwa [sup_comm]
end DistribLatticeBot
end Disjoint
section Codisjoint
section PartialOrderTop
variable [PartialOrder α] [OrderTop α] {a b c d : α}
/-- Two elements of a lattice are codisjoint if their sup is the top element.
Note that we define this without reference to `⊔`, as this allows us to talk about orders where
the supremum is not unique, or where implement `Sup` would require additional `Decidable`
arguments. -/
def Codisjoint (a b : α) : Prop :=
∀ ⦃x⦄, a ≤ x → b ≤ x → ⊤ ≤ x
theorem codisjoint_comm : Codisjoint a b ↔ Codisjoint b a :=
forall_congr' fun _ ↦ forall_swap
@[deprecated (since := "2024-11-23")] alias Codisjoint_comm := codisjoint_comm
@[symm]
theorem Codisjoint.symm ⦃a b : α⦄ : Codisjoint a b → Codisjoint b a :=
codisjoint_comm.1
theorem symmetric_codisjoint : Symmetric (Codisjoint : α → α → Prop) :=
Codisjoint.symm
@[simp]
theorem codisjoint_top_left : Codisjoint ⊤ a := fun _ htop _ ↦ htop
@[simp]
theorem codisjoint_top_right : Codisjoint a ⊤ := fun _ _ htop ↦ htop
theorem Codisjoint.mono (h₁ : a ≤ b) (h₂ : c ≤ d) : Codisjoint a c → Codisjoint b d :=
fun h _ ha hc ↦ h (h₁.trans ha) (h₂.trans hc)
theorem Codisjoint.mono_left (h : a ≤ b) : Codisjoint a c → Codisjoint b c :=
Codisjoint.mono h le_rfl
theorem Codisjoint.mono_right : b ≤ c → Codisjoint a b → Codisjoint a c :=
Codisjoint.mono le_rfl
@[simp]
theorem codisjoint_self : Codisjoint a a ↔ a = ⊤ :=
⟨fun hd ↦ top_unique <| hd le_rfl le_rfl, fun h _ ha _ ↦ h.symm.trans_le ha⟩
/- TODO: Rename `Codisjoint.eq_top` to `Codisjoint.sup_eq` and `Codisjoint.eq_top_of_self` to
`Codisjoint.eq_top` -/
alias ⟨Codisjoint.eq_top_of_self, _⟩ := codisjoint_self
theorem Codisjoint.ne (ha : a ≠ ⊤) (hab : Codisjoint a b) : a ≠ b :=
fun h ↦ ha <| codisjoint_self.1 <| by rwa [← h] at hab
theorem Codisjoint.eq_top_of_le (hab : Codisjoint a b) (h : b ≤ a) : a = ⊤ :=
eq_top_iff.2 <| hab le_rfl h
theorem Codisjoint.eq_top_of_ge (hab : Codisjoint a b) : a ≤ b → b = ⊤ :=
hab.symm.eq_top_of_le
lemma Codisjoint.eq_iff (hab : Codisjoint a b) : a = b ↔ a = ⊤ ∧ b = ⊤ := by aesop
lemma Codisjoint.ne_iff (hab : Codisjoint a b) : a ≠ b ↔ a ≠ ⊤ ∨ b ≠ ⊤ :=
hab.eq_iff.not.trans not_and_or
end PartialOrderTop
section PartialBoundedOrder
variable [PartialOrder α] [BoundedOrder α] {a b : α}
@[simp]
theorem codisjoint_bot : Codisjoint a ⊥ ↔ a = ⊤ :=
⟨fun h ↦ top_unique <| h le_rfl bot_le, fun h _ ha _ ↦ h.symm.trans_le ha⟩
@[simp]
theorem bot_codisjoint : Codisjoint ⊥ a ↔ a = ⊤ :=
⟨fun h ↦ top_unique <| h bot_le le_rfl, fun h _ _ ha ↦ h.symm.trans_le ha⟩
lemma Codisjoint.ne_bot_of_ne_top (h : Codisjoint a b) (ha : a ≠ ⊤) : b ≠ ⊥ := by
rintro rfl; exact ha <| by simpa using h
lemma Codisjoint.ne_bot_of_ne_top' (h : Codisjoint a b) (hb : b ≠ ⊤) : a ≠ ⊥ := by
rintro rfl; exact hb <| by simpa using h
end PartialBoundedOrder
section SemilatticeSupTop
variable [SemilatticeSup α] [OrderTop α] {a b c : α}
theorem codisjoint_iff_le_sup : Codisjoint a b ↔ ⊤ ≤ a ⊔ b :=
@disjoint_iff_inf_le αᵒᵈ _ _ _ _
theorem codisjoint_iff : Codisjoint a b ↔ a ⊔ b = ⊤ :=
@disjoint_iff αᵒᵈ _ _ _ _
theorem Codisjoint.top_le : Codisjoint a b → ⊤ ≤ a ⊔ b :=
@Disjoint.le_bot αᵒᵈ _ _ _ _
theorem Codisjoint.eq_top : Codisjoint a b → a ⊔ b = ⊤ :=
@Disjoint.eq_bot αᵒᵈ _ _ _ _
theorem codisjoint_assoc : Codisjoint (a ⊔ b) c ↔ Codisjoint a (b ⊔ c) :=
@disjoint_assoc αᵒᵈ _ _ _ _ _
theorem codisjoint_left_comm : Codisjoint a (b ⊔ c) ↔ Codisjoint b (a ⊔ c) :=
@disjoint_left_comm αᵒᵈ _ _ _ _ _
theorem codisjoint_right_comm : Codisjoint (a ⊔ b) c ↔ Codisjoint (a ⊔ c) b :=
@disjoint_right_comm αᵒᵈ _ _ _ _ _
variable (c)
theorem Codisjoint.sup_left (h : Codisjoint a b) : Codisjoint (a ⊔ c) b :=
h.mono_left le_sup_left
theorem Codisjoint.sup_left' (h : Codisjoint a b) : Codisjoint (c ⊔ a) b :=
h.mono_left le_sup_right
theorem Codisjoint.sup_right (h : Codisjoint a b) : Codisjoint a (b ⊔ c) :=
h.mono_right le_sup_left
theorem Codisjoint.sup_right' (h : Codisjoint a b) : Codisjoint a (c ⊔ b) :=
h.mono_right le_sup_right
variable {c}
theorem Codisjoint.of_codisjoint_sup_of_le (h : Codisjoint (a ⊔ b) c) (hle : c ≤ a) :
Codisjoint a b :=
@Disjoint.of_disjoint_inf_of_le αᵒᵈ _ _ _ _ _ h hle
theorem Codisjoint.of_codisjoint_sup_of_le' (h : Codisjoint (a ⊔ b) c) (hle : c ≤ b) :
Codisjoint a b :=
@Disjoint.of_disjoint_inf_of_le' αᵒᵈ _ _ _ _ _ h hle
end SemilatticeSupTop
section DistribLatticeTop
variable [DistribLattice α] [OrderTop α] {a b c : α}
@[simp]
theorem codisjoint_inf_left : Codisjoint (a ⊓ b) c ↔ Codisjoint a c ∧ Codisjoint b c := by
simp only [codisjoint_iff, sup_inf_right, inf_eq_top_iff]
@[simp]
theorem codisjoint_inf_right : Codisjoint a (b ⊓ c) ↔ Codisjoint a b ∧ Codisjoint a c := by
simp only [codisjoint_iff, sup_inf_left, inf_eq_top_iff]
theorem Codisjoint.inf_left (ha : Codisjoint a c) (hb : Codisjoint b c) : Codisjoint (a ⊓ b) c :=
codisjoint_inf_left.2 ⟨ha, hb⟩
theorem Codisjoint.inf_right (hb : Codisjoint a b) (hc : Codisjoint a c) : Codisjoint a (b ⊓ c) :=
codisjoint_inf_right.2 ⟨hb, hc⟩
theorem Codisjoint.left_le_of_le_inf_right (h : a ⊓ b ≤ c) (hd : Codisjoint b c) : a ≤ c :=
@Disjoint.left_le_of_le_sup_right αᵒᵈ _ _ _ _ _ h hd.symm
theorem Codisjoint.left_le_of_le_inf_left (h : b ⊓ a ≤ c) (hd : Codisjoint b c) : a ≤ c :=
hd.left_le_of_le_inf_right <| by rwa [inf_comm]
end DistribLatticeTop
end Codisjoint
open OrderDual
theorem Disjoint.dual [PartialOrder α] [OrderBot α] {a b : α} :
Disjoint a b → Codisjoint (toDual a) (toDual b) :=
id
theorem Codisjoint.dual [PartialOrder α] [OrderTop α] {a b : α} :
Codisjoint a b → Disjoint (toDual a) (toDual b) :=
id
@[simp]
theorem disjoint_toDual_iff [PartialOrder α] [OrderTop α] {a b : α} :
Disjoint (toDual a) (toDual b) ↔ Codisjoint a b :=
Iff.rfl
@[simp]
theorem disjoint_ofDual_iff [PartialOrder α] [OrderBot α] {a b : αᵒᵈ} :
Disjoint (ofDual a) (ofDual b) ↔ Codisjoint a b :=
Iff.rfl
@[simp]
theorem codisjoint_toDual_iff [PartialOrder α] [OrderBot α] {a b : α} :
Codisjoint (toDual a) (toDual b) ↔ Disjoint a b :=
Iff.rfl
@[simp]
theorem codisjoint_ofDual_iff [PartialOrder α] [OrderTop α] {a b : αᵒᵈ} :
Codisjoint (ofDual a) (ofDual b) ↔ Disjoint a b :=
Iff.rfl
section DistribLattice
variable [DistribLattice α] [BoundedOrder α] {a b c : α}
theorem Disjoint.le_of_codisjoint (hab : Disjoint a b) (hbc : Codisjoint b c) : a ≤ c := by
rw [← @inf_top_eq _ _ _ a, ← @bot_sup_eq _ _ _ c, ← hab.eq_bot, ← hbc.eq_top, sup_inf_right]
exact inf_le_inf_right _ le_sup_left
end DistribLattice
section IsCompl
/-- Two elements `x` and `y` are complements of each other if `x ⊔ y = ⊤` and `x ⊓ y = ⊥`. -/
structure IsCompl [PartialOrder α] [BoundedOrder α] (x y : α) : Prop where
/-- If `x` and `y` are to be complementary in an order, they should be disjoint. -/
protected disjoint : Disjoint x y
/-- If `x` and `y` are to be complementary in an order, they should be codisjoint. -/
protected codisjoint : Codisjoint x y
theorem isCompl_iff [PartialOrder α] [BoundedOrder α] {a b : α} :
IsCompl a b ↔ Disjoint a b ∧ Codisjoint a b :=
⟨fun h ↦ ⟨h.1, h.2⟩, fun h ↦ ⟨h.1, h.2⟩⟩
namespace IsCompl
section BoundedPartialOrder
variable [PartialOrder α] [BoundedOrder α] {x y : α}
@[symm]
protected theorem symm (h : IsCompl x y) : IsCompl y x :=
⟨h.1.symm, h.2.symm⟩
lemma _root_.isCompl_comm : IsCompl x y ↔ IsCompl y x := ⟨IsCompl.symm, IsCompl.symm⟩
theorem dual (h : IsCompl x y) : IsCompl (toDual x) (toDual y) :=
⟨h.2, h.1⟩
theorem ofDual {a b : αᵒᵈ} (h : IsCompl a b) : IsCompl (ofDual a) (ofDual b) :=
⟨h.2, h.1⟩
end BoundedPartialOrder
section BoundedLattice
variable [Lattice α] [BoundedOrder α] {x y : α}
theorem of_le (h₁ : x ⊓ y ≤ ⊥) (h₂ : ⊤ ≤ x ⊔ y) : IsCompl x y :=
⟨disjoint_iff_inf_le.mpr h₁, codisjoint_iff_le_sup.mpr h₂⟩
theorem of_eq (h₁ : x ⊓ y = ⊥) (h₂ : x ⊔ y = ⊤) : IsCompl x y :=
⟨disjoint_iff.mpr h₁, codisjoint_iff.mpr h₂⟩
theorem inf_eq_bot (h : IsCompl x y) : x ⊓ y = ⊥ :=
h.disjoint.eq_bot
theorem sup_eq_top (h : IsCompl x y) : x ⊔ y = ⊤ :=
h.codisjoint.eq_top
end BoundedLattice
variable [DistribLattice α] [BoundedOrder α] {a b x y z : α}
theorem inf_left_le_of_le_sup_right (h : IsCompl x y) (hle : a ≤ b ⊔ y) : a ⊓ x ≤ b :=
calc
a ⊓ x ≤ (b ⊔ y) ⊓ x := inf_le_inf hle le_rfl
_ = b ⊓ x ⊔ y ⊓ x := inf_sup_right _ _ _
_ = b ⊓ x := by rw [h.symm.inf_eq_bot, sup_bot_eq]
_ ≤ b := inf_le_left
theorem le_sup_right_iff_inf_left_le {a b} (h : IsCompl x y) : a ≤ b ⊔ y ↔ a ⊓ x ≤ b :=
⟨h.inf_left_le_of_le_sup_right, h.symm.dual.inf_left_le_of_le_sup_right⟩
theorem inf_left_eq_bot_iff (h : IsCompl y z) : x ⊓ y = ⊥ ↔ x ≤ z := by
rw [← le_bot_iff, ← h.le_sup_right_iff_inf_left_le, bot_sup_eq]
theorem inf_right_eq_bot_iff (h : IsCompl y z) : x ⊓ z = ⊥ ↔ x ≤ y :=
h.symm.inf_left_eq_bot_iff
theorem disjoint_left_iff (h : IsCompl y z) : Disjoint x y ↔ x ≤ z := by
rw [disjoint_iff]
exact h.inf_left_eq_bot_iff
theorem disjoint_right_iff (h : IsCompl y z) : Disjoint x z ↔ x ≤ y :=
h.symm.disjoint_left_iff
theorem le_left_iff (h : IsCompl x y) : z ≤ x ↔ Disjoint z y :=
h.disjoint_right_iff.symm
theorem le_right_iff (h : IsCompl x y) : z ≤ y ↔ Disjoint z x :=
h.symm.le_left_iff
theorem left_le_iff (h : IsCompl x y) : x ≤ z ↔ Codisjoint z y :=
h.dual.le_left_iff
theorem right_le_iff (h : IsCompl x y) : y ≤ z ↔ Codisjoint z x :=
h.symm.left_le_iff
protected theorem Antitone {x' y'} (h : IsCompl x y) (h' : IsCompl x' y') (hx : x ≤ x') : y' ≤ y :=
h'.right_le_iff.2 <| h.symm.codisjoint.mono_right hx
theorem right_unique (hxy : IsCompl x y) (hxz : IsCompl x z) : y = z :=
le_antisymm (hxz.Antitone hxy <| le_refl x) (hxy.Antitone hxz <| le_refl x)
theorem left_unique (hxz : IsCompl x z) (hyz : IsCompl y z) : x = y :=
hxz.symm.right_unique hyz.symm
theorem sup_inf {x' y'} (h : IsCompl x y) (h' : IsCompl x' y') : IsCompl (x ⊔ x') (y ⊓ y') :=
of_eq
(by rw [inf_sup_right, ← inf_assoc, h.inf_eq_bot, bot_inf_eq, bot_sup_eq, inf_left_comm,
h'.inf_eq_bot, inf_bot_eq])
(by rw [sup_inf_left, sup_comm x, sup_assoc, h.sup_eq_top, sup_top_eq, top_inf_eq,
sup_assoc, sup_left_comm, h'.sup_eq_top, sup_top_eq])
theorem inf_sup {x' y'} (h : IsCompl x y) (h' : IsCompl x' y') : IsCompl (x ⊓ x') (y ⊔ y') :=
(h.symm.sup_inf h'.symm).symm
end IsCompl
namespace Prod
variable {β : Type*} [PartialOrder α] [PartialOrder β]
protected theorem disjoint_iff [OrderBot α] [OrderBot β] {x y : α × β} :
Disjoint x y ↔ Disjoint x.1 y.1 ∧ Disjoint x.2 y.2 := by
constructor
· intro h
refine ⟨fun a hx hy ↦ (@h (a, ⊥) ⟨hx, ?_⟩ ⟨hy, ?_⟩).1,
fun b hx hy ↦ (@h (⊥, b) ⟨?_, hx⟩ ⟨?_, hy⟩).2⟩
all_goals exact bot_le
· rintro ⟨ha, hb⟩ z hza hzb
exact ⟨ha hza.1 hzb.1, hb hza.2 hzb.2⟩
protected theorem codisjoint_iff [OrderTop α] [OrderTop β] {x y : α × β} :
Codisjoint x y ↔ Codisjoint x.1 y.1 ∧ Codisjoint x.2 y.2 :=
@Prod.disjoint_iff αᵒᵈ βᵒᵈ _ _ _ _ _ _
protected theorem isCompl_iff [BoundedOrder α] [BoundedOrder β] {x y : α × β} :
IsCompl x y ↔ IsCompl x.1 y.1 ∧ IsCompl x.2 y.2 := by
simp_rw [isCompl_iff, Prod.disjoint_iff, Prod.codisjoint_iff, and_and_and_comm]
end Prod
section
variable [Lattice α] [BoundedOrder α] {a b x : α}
@[simp]
theorem isCompl_toDual_iff : IsCompl (toDual a) (toDual b) ↔ IsCompl a b :=
⟨IsCompl.ofDual, IsCompl.dual⟩
@[simp]
theorem isCompl_ofDual_iff {a b : αᵒᵈ} : IsCompl (ofDual a) (ofDual b) ↔ IsCompl a b :=
⟨IsCompl.dual, IsCompl.ofDual⟩
theorem isCompl_bot_top : IsCompl (⊥ : α) ⊤ :=
IsCompl.of_eq (bot_inf_eq _) (sup_top_eq _)
theorem isCompl_top_bot : IsCompl (⊤ : α) ⊥ :=
IsCompl.of_eq (inf_bot_eq _) (top_sup_eq _)
theorem eq_top_of_isCompl_bot (h : IsCompl x ⊥) : x = ⊤ := by rw [← sup_bot_eq x, h.sup_eq_top]
theorem eq_top_of_bot_isCompl (h : IsCompl ⊥ x) : x = ⊤ :=
eq_top_of_isCompl_bot h.symm
theorem eq_bot_of_isCompl_top (h : IsCompl x ⊤) : x = ⊥ :=
eq_top_of_isCompl_bot h.dual
theorem eq_bot_of_top_isCompl (h : IsCompl ⊤ x) : x = ⊥ :=
eq_top_of_bot_isCompl h.dual
end
section IsComplemented
section Lattice
variable [Lattice α] [BoundedOrder α]
/-- An element is *complemented* if it has a complement. -/
def IsComplemented (a : α) : Prop :=
∃ b, IsCompl a b
theorem isComplemented_bot : IsComplemented (⊥ : α) :=
⟨⊤, isCompl_bot_top⟩
theorem isComplemented_top : IsComplemented (⊤ : α) :=
⟨⊥, isCompl_top_bot⟩
end Lattice
variable [DistribLattice α] [BoundedOrder α] {a b : α}
theorem IsComplemented.sup : IsComplemented a → IsComplemented b → IsComplemented (a ⊔ b) :=
fun ⟨a', ha⟩ ⟨b', hb⟩ => ⟨a' ⊓ b', ha.sup_inf hb⟩
theorem IsComplemented.inf : IsComplemented a → IsComplemented b → IsComplemented (a ⊓ b) :=
fun ⟨a', ha⟩ ⟨b', hb⟩ => ⟨a' ⊔ b', ha.inf_sup hb⟩
end IsComplemented
/-- A complemented bounded lattice is one where every element has a (not necessarily unique)
complement. -/
class ComplementedLattice (α) [Lattice α] [BoundedOrder α] : Prop where
/-- In a `ComplementedLattice`, every element admits a complement. -/
exists_isCompl : ∀ a : α, ∃ b : α, IsCompl a b
lemma complementedLattice_iff (α) [Lattice α] [BoundedOrder α] :
ComplementedLattice α ↔ ∀ a : α, ∃ b : α, IsCompl a b :=
⟨fun ⟨h⟩ ↦ h, fun h ↦ ⟨h⟩⟩
export ComplementedLattice (exists_isCompl)
instance Subsingleton.instComplementedLattice
[Lattice α] [BoundedOrder α] [Subsingleton α] : ComplementedLattice α := by
refine ⟨fun a ↦ ⟨⊥, disjoint_bot_right, ?_⟩⟩
rw [Subsingleton.elim ⊥ ⊤]
exact codisjoint_top_right
namespace ComplementedLattice
variable [Lattice α] [BoundedOrder α] [ComplementedLattice α]
instance : ComplementedLattice αᵒᵈ :=
⟨fun a ↦
let ⟨b, hb⟩ := exists_isCompl (show α from a)
⟨b, hb.dual⟩⟩
end ComplementedLattice
-- TODO: Define as a sublattice?
/-- The sublattice of complemented elements. -/
abbrev Complementeds (α : Type*) [Lattice α] [BoundedOrder α] : Type _ :=
{a : α // IsComplemented a}
namespace Complementeds
section Lattice
variable [Lattice α] [BoundedOrder α] {a b : Complementeds α}
instance hasCoeT : CoeTC (Complementeds α) α := ⟨Subtype.val⟩
theorem coe_injective : Injective ((↑) : Complementeds α → α) := Subtype.coe_injective
@[simp, norm_cast]
theorem coe_inj : (a : α) = b ↔ a = b := Subtype.coe_inj
@[norm_cast]
theorem coe_le_coe : (a : α) ≤ b ↔ a ≤ b := by simp
@[norm_cast]
theorem coe_lt_coe : (a : α) < b ↔ a < b := by simp
instance : BoundedOrder (Complementeds α) :=
Subtype.boundedOrder isComplemented_bot isComplemented_top
@[simp, norm_cast]
theorem coe_bot : ((⊥ : Complementeds α) : α) = ⊥ := rfl
@[simp, norm_cast]
theorem coe_top : ((⊤ : Complementeds α) : α) = ⊤ := rfl
theorem mk_bot : (⟨⊥, isComplemented_bot⟩ : Complementeds α) = ⊥ := by simp
theorem mk_top : (⟨⊤, isComplemented_top⟩ : Complementeds α) = ⊤ := by simp
instance : Inhabited (Complementeds α) := ⟨⊥⟩
end Lattice
variable [DistribLattice α] [BoundedOrder α] {a b : Complementeds α}
instance : Max (Complementeds α) :=
⟨fun a b => ⟨a ⊔ b, a.2.sup b.2⟩⟩
instance : Min (Complementeds α) :=
⟨fun a b => ⟨a ⊓ b, a.2.inf b.2⟩⟩
@[simp, norm_cast]
theorem coe_sup (a b : Complementeds α) : ↑(a ⊔ b) = (a : α) ⊔ b := rfl
@[simp, norm_cast]
theorem coe_inf (a b : Complementeds α) : ↑(a ⊓ b) = (a : α) ⊓ b := rfl
@[simp]
theorem mk_sup_mk {a b : α} (ha : IsComplemented a) (hb : IsComplemented b) :
(⟨a, ha⟩ ⊔ ⟨b, hb⟩ : Complementeds α) = ⟨a ⊔ b, ha.sup hb⟩ := rfl
@[simp]
theorem mk_inf_mk {a b : α} (ha : IsComplemented a) (hb : IsComplemented b) :
(⟨a, ha⟩ ⊓ ⟨b, hb⟩ : Complementeds α) = ⟨a ⊓ b, ha.inf hb⟩ := rfl
instance : DistribLattice (Complementeds α) :=
Complementeds.coe_injective.distribLattice _ coe_sup coe_inf
@[simp, norm_cast]
theorem disjoint_coe : Disjoint (a : α) b ↔ Disjoint a b := by
rw [disjoint_iff, disjoint_iff, ← coe_inf, ← coe_bot, coe_inj]
@[simp, norm_cast]
theorem codisjoint_coe : Codisjoint (a : α) b ↔ Codisjoint a b := by
rw [codisjoint_iff, codisjoint_iff, ← coe_sup, ← coe_top, coe_inj]
@[simp, norm_cast]
theorem isCompl_coe : IsCompl (a : α) b ↔ IsCompl a b := by
simp_rw [isCompl_iff, disjoint_coe, codisjoint_coe]
instance : ComplementedLattice (Complementeds α) :=
⟨fun ⟨a, b, h⟩ => ⟨⟨b, a, h.symm⟩, isCompl_coe.1 h⟩⟩
end Complementeds
end IsCompl
| Mathlib/Order/Disjoint.lean | 809 | 810 | |
/-
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.Nat.Bits
import Mathlib.Data.Nat.Pairing
/-!
# Equivalences involving `ℕ`
This file defines some additional constructive equivalences using `Encodable` and the pairing
function on `ℕ`.
-/
assert_not_exists Monoid
open Nat Function
namespace Equiv
variable {α : Type*}
/-- An equivalence between `Bool × ℕ` and `ℕ`, by mapping `(true, x)` to `2 * x + 1` and
`(false, x)` to `2 * x`. -/
@[simps]
def boolProdNatEquivNat : Bool × ℕ ≃ ℕ where
toFun := uncurry bit
invFun := boddDiv2
left_inv := fun ⟨b, n⟩ => by simp only [bodd_bit, div2_bit, uncurry_apply_pair, boddDiv2_eq]
right_inv n := by simp only [bit_decomp, boddDiv2_eq, uncurry_apply_pair]
/-- An equivalence between `ℕ ⊕ ℕ` and `ℕ`, by mapping `(Sum.inl x)` to `2 * x` and `(Sum.inr x)` to
`2 * x + 1`.
-/
@[simps! symm_apply]
def natSumNatEquivNat : ℕ ⊕ ℕ ≃ ℕ :=
(boolProdEquivSum ℕ).symm.trans boolProdNatEquivNat
@[simp]
theorem natSumNatEquivNat_apply : ⇑natSumNatEquivNat = Sum.elim (2 * ·) (2 * · + 1) := by
ext (x | x) <;> rfl
/-- An equivalence between `ℤ` and `ℕ`, through `ℤ ≃ ℕ ⊕ ℕ` and `ℕ ⊕ ℕ ≃ ℕ`.
-/
def intEquivNat : ℤ ≃ ℕ :=
intEquivNatSumNat.trans natSumNatEquivNat
|
/-- An equivalence between `α × α` and `α`, given that there is an equivalence between `α` and `ℕ`.
| Mathlib/Logic/Equiv/Nat.lean | 48 | 49 |
/-
Copyright (c) 2019 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad, Sébastien Gouëzel, Yury Kudryashov
-/
import Mathlib.Analysis.Calculus.TangentCone
import Mathlib.Analysis.NormedSpace.OperatorNorm.Asymptotics
import Mathlib.Analysis.Asymptotics.TVS
import Mathlib.Analysis.Asymptotics.Lemmas
/-!
# The Fréchet derivative
Let `E` and `F` be normed spaces, `f : E → F`, and `f' : E →L[𝕜] F` a
continuous 𝕜-linear map, where `𝕜` is a non-discrete normed field. Then
`HasFDerivWithinAt f f' s x`
says that `f` has derivative `f'` at `x`, where the domain of interest
is restricted to `s`. We also have
`HasFDerivAt f f' x := HasFDerivWithinAt f f' x univ`
Finally,
`HasStrictFDerivAt f f' x`
means that `f : E → F` has derivative `f' : E →L[𝕜] F` in the sense of strict differentiability,
i.e., `f y - f z - f'(y - z) = o(y - z)` as `y, z → x`. This notion is used in the inverse
function theorem, and is defined here only to avoid proving theorems like
`IsBoundedBilinearMap.hasFDerivAt` twice: first for `HasFDerivAt`, then for
`HasStrictFDerivAt`.
## Main results
In addition to the definition and basic properties of the derivative,
the folder `Analysis/Calculus/FDeriv/` contains the usual formulas
(and existence assertions) for the derivative of
* constants
* the identity
* bounded linear maps (`Linear.lean`)
* bounded bilinear maps (`Bilinear.lean`)
* sum of two functions (`Add.lean`)
* sum of finitely many functions (`Add.lean`)
* multiplication of a function by a scalar constant (`Add.lean`)
* negative of a function (`Add.lean`)
* subtraction of two functions (`Add.lean`)
* multiplication of a function by a scalar function (`Mul.lean`)
* multiplication of two scalar functions (`Mul.lean`)
* composition of functions (the chain rule) (`Comp.lean`)
* inverse function (`Mul.lean`)
(assuming that it exists; the inverse function theorem is in `../Inverse.lean`)
For most binary operations we also define `const_op` and `op_const` theorems for the cases when
the first or second argument is a constant. This makes writing chains of `HasDerivAt`'s easier,
and they more frequently lead to the desired result.
One can also interpret the derivative of a function `f : 𝕜 → E` as an element of `E` (by identifying
a linear function from `𝕜` to `E` with its value at `1`). Results on the Fréchet derivative are
translated to this more elementary point of view on the derivative in the file `Deriv.lean`. The
derivative of polynomials is handled there, as it is naturally one-dimensional.
The simplifier is set up to prove automatically that some functions are differentiable, or
differentiable at a point (but not differentiable on a set or within a set at a point, as checking
automatically that the good domains are mapped one to the other when using composition is not
something the simplifier can easily do). This means that one can write
`example (x : ℝ) : Differentiable ℝ (fun x ↦ sin (exp (3 + x^2)) - 5 * cos x) := by simp`.
If there are divisions, one needs to supply to the simplifier proofs that the denominators do
not vanish, as in
```lean
example (x : ℝ) (h : 1 + sin x ≠ 0) : DifferentiableAt ℝ (fun x ↦ exp x / (1 + sin x)) x := by
simp [h]
```
Of course, these examples only work once `exp`, `cos` and `sin` have been shown to be
differentiable, in `Mathlib.Analysis.SpecialFunctions.Trigonometric.Deriv`.
The simplifier is not set up to compute the Fréchet derivative of maps (as these are in general
complicated multidimensional linear maps), but it will compute one-dimensional derivatives,
see `Deriv.lean`.
## Implementation details
The derivative is defined in terms of the `IsLittleOTVS` relation to ensure the definition does not
ingrain a choice of norm, and is then quickly translated to the more convenient `IsLittleO` in the
subsequent theorems.
It is also characterized in terms of the `Tendsto` relation.
We also introduce predicates `DifferentiableWithinAt 𝕜 f s x` (where `𝕜` is the base field,
`f` the function to be differentiated, `x` the point at which the derivative is asserted to exist,
and `s` the set along which the derivative is defined), as well as `DifferentiableAt 𝕜 f x`,
`DifferentiableOn 𝕜 f s` and `Differentiable 𝕜 f` to express the existence of a derivative.
To be able to compute with derivatives, we write `fderivWithin 𝕜 f s x` and `fderiv 𝕜 f x`
for some choice of a derivative if it exists, and the zero function otherwise. This choice only
behaves well along sets for which the derivative is unique, i.e., those for which the tangent
directions span a dense subset of the whole space. The predicates `UniqueDiffWithinAt s x` and
`UniqueDiffOn s`, defined in `TangentCone.lean` express this property. We prove that indeed
they imply the uniqueness of the derivative. This is satisfied for open subsets, and in particular
for `univ`. This uniqueness only holds when the field is non-discrete, which we request at the very
beginning: otherwise, a derivative can be defined, but it has no interesting properties whatsoever.
To make sure that the simplifier can prove automatically that functions are differentiable, we tag
many lemmas with the `simp` attribute, for instance those saying that the sum of differentiable
functions is differentiable, as well as their product, their cartesian product, and so on. A notable
exception is the chain rule: we do not mark as a simp lemma the fact that, if `f` and `g` are
differentiable, then their composition also is: `simp` would always be able to match this lemma,
by taking `f` or `g` to be the identity. Instead, for every reasonable function (say, `exp`),
we add a lemma that if `f` is differentiable then so is `(fun x ↦ exp (f x))`. This means adding
some boilerplate lemmas, but these can also be useful in their own right.
Tests for this ability of the simplifier (with more examples) are provided in
`Tests/Differentiable.lean`.
## TODO
Generalize more results to topological vector spaces.
## Tags
derivative, differentiable, Fréchet, calculus
-/
open Filter Asymptotics ContinuousLinearMap Set Metric Topology NNReal ENNReal
noncomputable section
section TVS
variable {𝕜 : Type*} [NontriviallyNormedField 𝕜]
variable {E : Type*} [AddCommGroup E] [Module 𝕜 E] [TopologicalSpace E]
variable {F : Type*} [AddCommGroup F] [Module 𝕜 F] [TopologicalSpace F]
/-- A function `f` has the continuous linear map `f'` as derivative along the filter `L` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` converges along the filter `L`. This definition
is designed to be specialized for `L = 𝓝 x` (in `HasFDerivAt`), giving rise to the usual notion
of Fréchet derivative, and for `L = 𝓝[s] x` (in `HasFDerivWithinAt`), giving rise to
the notion of Fréchet derivative along the set `s`. -/
@[mk_iff hasFDerivAtFilter_iff_isLittleOTVS]
structure HasFDerivAtFilter (f : E → F) (f' : E →L[𝕜] F) (x : E) (L : Filter E) : Prop where
of_isLittleOTVS ::
isLittleOTVS : (fun x' => f x' - f x - f' (x' - x)) =o[𝕜; L] (fun x' => x' - x)
/-- A function `f` has the continuous linear map `f'` as derivative at `x` within a set `s` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` tends to `x` inside `s`. -/
@[fun_prop]
def HasFDerivWithinAt (f : E → F) (f' : E →L[𝕜] F) (s : Set E) (x : E) :=
HasFDerivAtFilter f f' x (𝓝[s] x)
/-- A function `f` has the continuous linear map `f'` as derivative at `x` if
`f x' = f x + f' (x' - x) + o (x' - x)` when `x'` tends to `x`. -/
@[fun_prop]
def HasFDerivAt (f : E → F) (f' : E →L[𝕜] F) (x : E) :=
HasFDerivAtFilter f f' x (𝓝 x)
/-- A function `f` has derivative `f'` at `a` in the sense of *strict differentiability*
if `f x - f y - f' (x - y) = o(x - y)` as `x, y → a`. This form of differentiability is required,
e.g., by the inverse function theorem. Any `C^1` function on a vector space over `ℝ` is strictly
differentiable but this definition works, e.g., for vector spaces over `p`-adic numbers. -/
@[fun_prop, mk_iff hasStrictFDerivAt_iff_isLittleOTVS]
structure HasStrictFDerivAt (f : E → F) (f' : E →L[𝕜] F) (x : E) where
of_isLittleOTVS ::
isLittleOTVS :
(fun p : E × E => f p.1 - f p.2 - f' (p.1 - p.2))
=o[𝕜; 𝓝 (x, x)] (fun p : E × E => p.1 - p.2)
variable (𝕜)
/-- A function `f` is differentiable at a point `x` within a set `s` if it admits a derivative
there (possibly non-unique). -/
@[fun_prop]
def DifferentiableWithinAt (f : E → F) (s : Set E) (x : E) :=
∃ f' : E →L[𝕜] F, HasFDerivWithinAt f f' s x
/-- A function `f` is differentiable at a point `x` if it admits a derivative there (possibly
non-unique). -/
@[fun_prop]
def DifferentiableAt (f : E → F) (x : E) :=
∃ f' : E →L[𝕜] F, HasFDerivAt f f' x
open scoped Classical in
/-- If `f` has a derivative at `x` within `s`, then `fderivWithin 𝕜 f s x` is such a derivative.
Otherwise, it is set to `0`. We also set it to be zero, if zero is one of possible derivatives. -/
irreducible_def fderivWithin (f : E → F) (s : Set E) (x : E) : E →L[𝕜] F :=
if HasFDerivWithinAt f (0 : E →L[𝕜] F) s x
then 0
else if h : DifferentiableWithinAt 𝕜 f s x
then Classical.choose h
else 0
/-- If `f` has a derivative at `x`, then `fderiv 𝕜 f x` is such a derivative. Otherwise, it is
set to `0`. -/
irreducible_def fderiv (f : E → F) (x : E) : E →L[𝕜] F :=
fderivWithin 𝕜 f univ x
/-- `DifferentiableOn 𝕜 f s` means that `f` is differentiable within `s` at any point of `s`. -/
@[fun_prop]
def DifferentiableOn (f : E → F) (s : Set E) :=
∀ x ∈ s, DifferentiableWithinAt 𝕜 f s x
/-- `Differentiable 𝕜 f` means that `f` is differentiable at any point. -/
@[fun_prop]
def Differentiable (f : E → F) :=
∀ x, DifferentiableAt 𝕜 f x
variable {𝕜}
variable {f f₀ f₁ g : E → F}
variable {f' f₀' f₁' g' : E →L[𝕜] F}
variable {x : E}
variable {s t : Set E}
variable {L L₁ L₂ : Filter E}
theorem fderivWithin_zero_of_not_differentiableWithinAt (h : ¬DifferentiableWithinAt 𝕜 f s x) :
fderivWithin 𝕜 f s x = 0 := by
simp [fderivWithin, h]
@[simp]
theorem fderivWithin_univ : fderivWithin 𝕜 f univ = fderiv 𝕜 f := by
ext
rw [fderiv]
end TVS
section
variable {𝕜 : Type*} [NontriviallyNormedField 𝕜]
variable {E : Type*} [NormedAddCommGroup E] [NormedSpace 𝕜 E]
variable {F : Type*} [NormedAddCommGroup F] [NormedSpace 𝕜 F]
variable {f f₀ f₁ g : E → F}
variable {f' f₀' f₁' g' : E →L[𝕜] F}
variable {x : E}
variable {s t : Set E}
variable {L L₁ L₂ : Filter E}
theorem hasFDerivAtFilter_iff_isLittleO :
HasFDerivAtFilter f f' x L ↔ (fun x' => f x' - f x - f' (x' - x)) =o[L] fun x' => x' - x :=
(hasFDerivAtFilter_iff_isLittleOTVS ..).trans isLittleOTVS_iff_isLittleO
alias ⟨HasFDerivAtFilter.isLittleO, HasFDerivAtFilter.of_isLittleO⟩ :=
hasFDerivAtFilter_iff_isLittleO
theorem hasStrictFDerivAt_iff_isLittleO :
HasStrictFDerivAt f f' x ↔
(fun p : E × E => f p.1 - f p.2 - f' (p.1 - p.2)) =o[𝓝 (x, x)] fun p : E × E => p.1 - p.2 :=
(hasStrictFDerivAt_iff_isLittleOTVS ..).trans isLittleOTVS_iff_isLittleO
alias ⟨HasStrictFDerivAt.isLittleO, HasStrictFDerivAt.of_isLittleO⟩ :=
hasStrictFDerivAt_iff_isLittleO
section DerivativeUniqueness
/- In this section, we discuss the uniqueness of the derivative.
We prove that the definitions `UniqueDiffWithinAt` and `UniqueDiffOn` indeed imply the
uniqueness of the derivative. -/
/-- If a function f has a derivative f' at x, a rescaled version of f around x converges to f',
i.e., `n (f (x + (1/n) v) - f x)` converges to `f' v`. More generally, if `c n` tends to infinity
and `c n * d n` tends to `v`, then `c n * (f (x + d n) - f x)` tends to `f' v`. This lemma expresses
this fact, for functions having a derivative within a set. Its specific formulation is useful for
tangent cone related discussions. -/
theorem HasFDerivWithinAt.lim (h : HasFDerivWithinAt f f' s x) {α : Type*} (l : Filter α)
{c : α → 𝕜} {d : α → E} {v : E} (dtop : ∀ᶠ n in l, x + d n ∈ s)
(clim : Tendsto (fun n => ‖c n‖) l atTop) (cdlim : Tendsto (fun n => c n • d n) l (𝓝 v)) :
Tendsto (fun n => c n • (f (x + d n) - f x)) l (𝓝 (f' v)) := by
have tendsto_arg : Tendsto (fun n => x + d n) l (𝓝[s] x) := by
conv in 𝓝[s] x => rw [← add_zero x]
rw [nhdsWithin, tendsto_inf]
constructor
· apply tendsto_const_nhds.add (tangentConeAt.lim_zero l clim cdlim)
· rwa [tendsto_principal]
have : (fun y => f y - f x - f' (y - x)) =o[𝓝[s] x] fun y => y - x := h.isLittleO
have : (fun n => f (x + d n) - f x - f' (x + d n - x)) =o[l] fun n => x + d n - x :=
this.comp_tendsto tendsto_arg
have : (fun n => f (x + d n) - f x - f' (d n)) =o[l] d := by simpa only [add_sub_cancel_left]
have : (fun n => c n • (f (x + d n) - f x - f' (d n))) =o[l] fun n => c n • d n :=
(isBigO_refl c l).smul_isLittleO this
have : (fun n => c n • (f (x + d n) - f x - f' (d n))) =o[l] fun _ => (1 : ℝ) :=
this.trans_isBigO (cdlim.isBigO_one ℝ)
have L1 : Tendsto (fun n => c n • (f (x + d n) - f x - f' (d n))) l (𝓝 0) :=
(isLittleO_one_iff ℝ).1 this
have L2 : Tendsto (fun n => f' (c n • d n)) l (𝓝 (f' v)) :=
Tendsto.comp f'.cont.continuousAt cdlim
have L3 :
Tendsto (fun n => c n • (f (x + d n) - f x - f' (d n)) + f' (c n • d n)) l (𝓝 (0 + f' v)) :=
L1.add L2
have :
(fun n => c n • (f (x + d n) - f x - f' (d n)) + f' (c n • d n)) = fun n =>
c n • (f (x + d n) - f x) := by
ext n
simp [smul_add, smul_sub]
rwa [this, zero_add] at L3
/-- If `f'` and `f₁'` are two derivatives of `f` within `s` at `x`, then they are equal on the
tangent cone to `s` at `x` -/
theorem HasFDerivWithinAt.unique_on (hf : HasFDerivWithinAt f f' s x)
(hg : HasFDerivWithinAt f f₁' s x) : EqOn f' f₁' (tangentConeAt 𝕜 s x) :=
fun _ ⟨_, _, dtop, clim, cdlim⟩ =>
tendsto_nhds_unique (hf.lim atTop dtop clim cdlim) (hg.lim atTop dtop clim cdlim)
/-- `UniqueDiffWithinAt` achieves its goal: it implies the uniqueness of the derivative. -/
theorem UniqueDiffWithinAt.eq (H : UniqueDiffWithinAt 𝕜 s x) (hf : HasFDerivWithinAt f f' s x)
(hg : HasFDerivWithinAt f f₁' s x) : f' = f₁' :=
ContinuousLinearMap.ext_on H.1 (hf.unique_on hg)
theorem UniqueDiffOn.eq (H : UniqueDiffOn 𝕜 s) (hx : x ∈ s) (h : HasFDerivWithinAt f f' s x)
(h₁ : HasFDerivWithinAt f f₁' s x) : f' = f₁' :=
(H x hx).eq h h₁
end DerivativeUniqueness
section FDerivProperties
/-! ### Basic properties of the derivative -/
theorem hasFDerivAtFilter_iff_tendsto :
HasFDerivAtFilter f f' x L ↔
Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) L (𝓝 0) := by
have h : ∀ x', ‖x' - x‖ = 0 → ‖f x' - f x - f' (x' - x)‖ = 0 := fun x' hx' => by
rw [sub_eq_zero.1 (norm_eq_zero.1 hx')]
simp
rw [hasFDerivAtFilter_iff_isLittleO, ← isLittleO_norm_left, ← isLittleO_norm_right,
isLittleO_iff_tendsto h]
exact tendsto_congr fun _ => div_eq_inv_mul _ _
theorem hasFDerivWithinAt_iff_tendsto :
HasFDerivWithinAt f f' s x ↔
Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) (𝓝[s] x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasFDerivAt_iff_tendsto :
HasFDerivAt f f' x ↔ Tendsto (fun x' => ‖x' - x‖⁻¹ * ‖f x' - f x - f' (x' - x)‖) (𝓝 x) (𝓝 0) :=
hasFDerivAtFilter_iff_tendsto
theorem hasFDerivAt_iff_isLittleO_nhds_zero :
HasFDerivAt f f' x ↔ (fun h : E => f (x + h) - f x - f' h) =o[𝓝 0] fun h => h := by
rw [HasFDerivAt, hasFDerivAtFilter_iff_isLittleO, ← map_add_left_nhds_zero x, isLittleO_map]
simp [Function.comp_def]
nonrec theorem HasFDerivAtFilter.mono (h : HasFDerivAtFilter f f' x L₂) (hst : L₁ ≤ L₂) :
HasFDerivAtFilter f f' x L₁ :=
.of_isLittleOTVS <| h.isLittleOTVS.mono hst
theorem HasFDerivWithinAt.mono_of_mem_nhdsWithin
(h : HasFDerivWithinAt f f' t x) (hst : t ∈ 𝓝[s] x) :
HasFDerivWithinAt f f' s x :=
h.mono <| nhdsWithin_le_iff.mpr hst
@[deprecated (since := "2024-10-31")]
alias HasFDerivWithinAt.mono_of_mem := HasFDerivWithinAt.mono_of_mem_nhdsWithin
nonrec theorem HasFDerivWithinAt.mono (h : HasFDerivWithinAt f f' t x) (hst : s ⊆ t) :
HasFDerivWithinAt f f' s x :=
h.mono <| nhdsWithin_mono _ hst
theorem HasFDerivAt.hasFDerivAtFilter (h : HasFDerivAt f f' x) (hL : L ≤ 𝓝 x) :
HasFDerivAtFilter f f' x L :=
h.mono hL
@[fun_prop]
theorem HasFDerivAt.hasFDerivWithinAt (h : HasFDerivAt f f' x) : HasFDerivWithinAt f f' s x :=
h.hasFDerivAtFilter inf_le_left
@[fun_prop]
theorem HasFDerivWithinAt.differentiableWithinAt (h : HasFDerivWithinAt f f' s x) :
DifferentiableWithinAt 𝕜 f s x :=
⟨f', h⟩
@[fun_prop]
theorem HasFDerivAt.differentiableAt (h : HasFDerivAt f f' x) : DifferentiableAt 𝕜 f x :=
⟨f', h⟩
@[simp]
theorem hasFDerivWithinAt_univ : HasFDerivWithinAt f f' univ x ↔ HasFDerivAt f f' x := by
simp only [HasFDerivWithinAt, nhdsWithin_univ, HasFDerivAt]
alias ⟨HasFDerivWithinAt.hasFDerivAt_of_univ, _⟩ := hasFDerivWithinAt_univ
theorem differentiableWithinAt_univ :
DifferentiableWithinAt 𝕜 f univ x ↔ DifferentiableAt 𝕜 f x := by
simp only [DifferentiableWithinAt, hasFDerivWithinAt_univ, DifferentiableAt]
theorem fderiv_zero_of_not_differentiableAt (h : ¬DifferentiableAt 𝕜 f x) : fderiv 𝕜 f x = 0 := by
rw [fderiv, fderivWithin_zero_of_not_differentiableWithinAt]
rwa [differentiableWithinAt_univ]
theorem hasFDerivWithinAt_of_mem_nhds (h : s ∈ 𝓝 x) :
HasFDerivWithinAt f f' s x ↔ HasFDerivAt f f' x := by
rw [HasFDerivAt, HasFDerivWithinAt, nhdsWithin_eq_nhds.mpr h]
lemma hasFDerivWithinAt_of_isOpen (h : IsOpen s) (hx : x ∈ s) :
HasFDerivWithinAt f f' s x ↔ HasFDerivAt f f' x :=
hasFDerivWithinAt_of_mem_nhds (h.mem_nhds hx)
@[simp]
theorem hasFDerivWithinAt_insert {y : E} :
HasFDerivWithinAt f f' (insert y s) x ↔ HasFDerivWithinAt f f' s x := by
rcases eq_or_ne x y with (rfl | h)
· simp_rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleOTVS]
apply isLittleOTVS_insert
simp only [sub_self, map_zero]
refine ⟨fun h => h.mono <| subset_insert y s, fun hf => hf.mono_of_mem_nhdsWithin ?_⟩
simp_rw [nhdsWithin_insert_of_ne h, self_mem_nhdsWithin]
alias ⟨HasFDerivWithinAt.of_insert, HasFDerivWithinAt.insert'⟩ := hasFDerivWithinAt_insert
protected theorem HasFDerivWithinAt.insert (h : HasFDerivWithinAt g g' s x) :
HasFDerivWithinAt g g' (insert x s) x :=
h.insert'
@[simp]
theorem hasFDerivWithinAt_diff_singleton (y : E) :
HasFDerivWithinAt f f' (s \ {y}) x ↔ HasFDerivWithinAt f f' s x := by
rw [← hasFDerivWithinAt_insert, insert_diff_singleton, hasFDerivWithinAt_insert]
@[simp]
protected theorem HasFDerivWithinAt.empty : HasFDerivWithinAt f f' ∅ x := by
simp [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleOTVS]
@[simp]
protected theorem DifferentiableWithinAt.empty : DifferentiableWithinAt 𝕜 f ∅ x :=
⟨0, .empty⟩
theorem HasFDerivWithinAt.of_finite (h : s.Finite) : HasFDerivWithinAt f f' s x := by
induction s, h using Set.Finite.induction_on with
| empty => exact .empty
| insert _ _ ih => exact ih.insert'
theorem DifferentiableWithinAt.of_finite (h : s.Finite) : DifferentiableWithinAt 𝕜 f s x :=
⟨0, .of_finite h⟩
@[simp]
protected theorem HasFDerivWithinAt.singleton {y} : HasFDerivWithinAt f f' {x} y :=
.of_finite <| finite_singleton _
@[simp]
protected theorem DifferentiableWithinAt.singleton {y} : DifferentiableWithinAt 𝕜 f {x} y :=
⟨0, .singleton⟩
theorem HasFDerivWithinAt.of_subsingleton (h : s.Subsingleton) : HasFDerivWithinAt f f' s x :=
.of_finite h.finite
theorem DifferentiableWithinAt.of_subsingleton (h : s.Subsingleton) :
DifferentiableWithinAt 𝕜 f s x :=
.of_finite h.finite
theorem HasStrictFDerivAt.isBigO_sub (hf : HasStrictFDerivAt f f' x) :
(fun p : E × E => f p.1 - f p.2) =O[𝓝 (x, x)] fun p : E × E => p.1 - p.2 :=
hf.isLittleO.isBigO.congr_of_sub.2 (f'.isBigO_comp _ _)
theorem HasFDerivAtFilter.isBigO_sub (h : HasFDerivAtFilter f f' x L) :
(fun x' => f x' - f x) =O[L] fun x' => x' - x :=
h.isLittleO.isBigO.congr_of_sub.2 (f'.isBigO_sub _ _)
@[fun_prop]
protected theorem HasStrictFDerivAt.hasFDerivAt (hf : HasStrictFDerivAt f f' x) :
HasFDerivAt f f' x :=
.of_isLittleOTVS <| by
simpa only using hf.isLittleOTVS.comp_tendsto (tendsto_id.prodMk_nhds tendsto_const_nhds)
protected theorem HasStrictFDerivAt.differentiableAt (hf : HasStrictFDerivAt f f' x) :
DifferentiableAt 𝕜 f x :=
hf.hasFDerivAt.differentiableAt
/-- If `f` is strictly differentiable at `x` with derivative `f'` and `K > ‖f'‖₊`, then `f` is
`K`-Lipschitz in a neighborhood of `x`. -/
theorem HasStrictFDerivAt.exists_lipschitzOnWith_of_nnnorm_lt (hf : HasStrictFDerivAt f f' x)
(K : ℝ≥0) (hK : ‖f'‖₊ < K) : ∃ s ∈ 𝓝 x, LipschitzOnWith K f s := by
have := hf.isLittleO.add_isBigOWith (f'.isBigOWith_comp _ _) hK
simp only [sub_add_cancel, IsBigOWith] at this
rcases exists_nhds_square this with ⟨U, Uo, xU, hU⟩
exact
⟨U, Uo.mem_nhds xU, lipschitzOnWith_iff_norm_sub_le.2 fun x hx y hy => hU (mk_mem_prod hx hy)⟩
/-- If `f` is strictly differentiable at `x` with derivative `f'`, then `f` is Lipschitz in a
neighborhood of `x`. See also `HasStrictFDerivAt.exists_lipschitzOnWith_of_nnnorm_lt` for a
more precise statement. -/
theorem HasStrictFDerivAt.exists_lipschitzOnWith (hf : HasStrictFDerivAt f f' x) :
∃ K, ∃ s ∈ 𝓝 x, LipschitzOnWith K f s :=
(exists_gt _).imp hf.exists_lipschitzOnWith_of_nnnorm_lt
/-- Directional derivative agrees with `HasFDeriv`. -/
theorem HasFDerivAt.lim (hf : HasFDerivAt f f' x) (v : E) {α : Type*} {c : α → 𝕜} {l : Filter α}
(hc : Tendsto (fun n => ‖c n‖) l atTop) :
Tendsto (fun n => c n • (f (x + (c n)⁻¹ • v) - f x)) l (𝓝 (f' v)) := by
refine (hasFDerivWithinAt_univ.2 hf).lim _ univ_mem hc ?_
intro U hU
refine (eventually_ne_of_tendsto_norm_atTop hc (0 : 𝕜)).mono fun y hy => ?_
convert mem_of_mem_nhds hU
dsimp only
rw [← mul_smul, mul_inv_cancel₀ hy, one_smul]
theorem HasFDerivAt.unique (h₀ : HasFDerivAt f f₀' x) (h₁ : HasFDerivAt f f₁' x) : f₀' = f₁' := by
rw [← hasFDerivWithinAt_univ] at h₀ h₁
exact uniqueDiffWithinAt_univ.eq h₀ h₁
theorem hasFDerivWithinAt_inter' (h : t ∈ 𝓝[s] x) :
HasFDerivWithinAt f f' (s ∩ t) x ↔ HasFDerivWithinAt f f' s x := by
simp [HasFDerivWithinAt, nhdsWithin_restrict'' s h]
theorem hasFDerivWithinAt_inter (h : t ∈ 𝓝 x) :
HasFDerivWithinAt f f' (s ∩ t) x ↔ HasFDerivWithinAt f f' s x := by
simp [HasFDerivWithinAt, nhdsWithin_restrict' s h]
theorem HasFDerivWithinAt.union (hs : HasFDerivWithinAt f f' s x)
(ht : HasFDerivWithinAt f f' t x) : HasFDerivWithinAt f f' (s ∪ t) x := by
simp only [HasFDerivWithinAt, nhdsWithin_union]
exact .of_isLittleOTVS <| hs.isLittleOTVS.sup ht.isLittleOTVS
theorem HasFDerivWithinAt.hasFDerivAt (h : HasFDerivWithinAt f f' s x) (hs : s ∈ 𝓝 x) :
HasFDerivAt f f' x := by
rwa [← univ_inter s, hasFDerivWithinAt_inter hs, hasFDerivWithinAt_univ] at h
theorem DifferentiableWithinAt.differentiableAt (h : DifferentiableWithinAt 𝕜 f s x)
(hs : s ∈ 𝓝 x) : DifferentiableAt 𝕜 f x :=
h.imp fun _ hf' => hf'.hasFDerivAt hs
/-- If `x` is isolated in `s`, then `f` has any derivative at `x` within `s`,
as this statement is empty. -/
theorem HasFDerivWithinAt.of_not_accPt (h : ¬AccPt x (𝓟 s)) : HasFDerivWithinAt f f' s x := by
rw [accPt_principal_iff_nhdsWithin, not_neBot] at h
rw [← hasFDerivWithinAt_diff_singleton x, HasFDerivWithinAt, h,
hasFDerivAtFilter_iff_isLittleOTVS]
exact .bot
/-- If `x` is isolated in `s`, then `f` has any derivative at `x` within `s`,
as this statement is empty. -/
@[deprecated HasFDerivWithinAt.of_not_accPt (since := "2025-04-20")]
theorem HasFDerivWithinAt.of_nhdsWithin_eq_bot (h : 𝓝[s \ {x}] x = ⊥) :
HasFDerivWithinAt f f' s x :=
.of_not_accPt <| by rwa [accPt_principal_iff_nhdsWithin, not_neBot]
/-- If `x` is not in the closure of `s`, then `f` has any derivative at `x` within `s`,
as this statement is empty. -/
theorem HasFDerivWithinAt.of_not_mem_closure (h : x ∉ closure s) : HasFDerivWithinAt f f' s x :=
.of_not_accPt (h ·.clusterPt.mem_closure)
@[deprecated (since := "2025-04-20")]
alias hasFDerivWithinAt_of_nmem_closure := HasFDerivWithinAt.of_not_mem_closure
theorem fderivWithin_zero_of_not_accPt (h : ¬AccPt x (𝓟 s)) : fderivWithin 𝕜 f s x = 0 := by
rw [fderivWithin, if_pos (.of_not_accPt h)]
set_option linter.deprecated false in
@[deprecated fderivWithin_zero_of_not_accPt (since := "2025-04-20")]
theorem fderivWithin_zero_of_isolated (h : 𝓝[s \ {x}] x = ⊥) : fderivWithin 𝕜 f s x = 0 := by
rw [fderivWithin, if_pos (.of_nhdsWithin_eq_bot h)]
theorem fderivWithin_zero_of_nmem_closure (h : x ∉ closure s) : fderivWithin 𝕜 f s x = 0 :=
fderivWithin_zero_of_not_accPt (h ·.clusterPt.mem_closure)
theorem DifferentiableWithinAt.hasFDerivWithinAt (h : DifferentiableWithinAt 𝕜 f s x) :
HasFDerivWithinAt f (fderivWithin 𝕜 f s x) s x := by
simp only [fderivWithin, dif_pos h]
split_ifs with h₀
exacts [h₀, Classical.choose_spec h]
theorem DifferentiableAt.hasFDerivAt (h : DifferentiableAt 𝕜 f x) :
HasFDerivAt f (fderiv 𝕜 f x) x := by
rw [fderiv, ← hasFDerivWithinAt_univ]
rw [← differentiableWithinAt_univ] at h
exact h.hasFDerivWithinAt
theorem DifferentiableOn.hasFDerivAt (h : DifferentiableOn 𝕜 f s) (hs : s ∈ 𝓝 x) :
HasFDerivAt f (fderiv 𝕜 f x) x :=
((h x (mem_of_mem_nhds hs)).differentiableAt hs).hasFDerivAt
theorem DifferentiableOn.differentiableAt (h : DifferentiableOn 𝕜 f s) (hs : s ∈ 𝓝 x) :
DifferentiableAt 𝕜 f x :=
(h.hasFDerivAt hs).differentiableAt
theorem DifferentiableOn.eventually_differentiableAt (h : DifferentiableOn 𝕜 f s) (hs : s ∈ 𝓝 x) :
∀ᶠ y in 𝓝 x, DifferentiableAt 𝕜 f y :=
(eventually_eventually_nhds.2 hs).mono fun _ => h.differentiableAt
protected theorem HasFDerivAt.fderiv (h : HasFDerivAt f f' x) : fderiv 𝕜 f x = f' := by
ext
rw [h.unique h.differentiableAt.hasFDerivAt]
theorem fderiv_eq {f' : E → E →L[𝕜] F} (h : ∀ x, HasFDerivAt f (f' x) x) : fderiv 𝕜 f = f' :=
funext fun x => (h x).fderiv
protected theorem HasFDerivWithinAt.fderivWithin (h : HasFDerivWithinAt f f' s x)
(hxs : UniqueDiffWithinAt 𝕜 s x) : fderivWithin 𝕜 f s x = f' :=
(hxs.eq h h.differentiableWithinAt.hasFDerivWithinAt).symm
theorem DifferentiableWithinAt.mono (h : DifferentiableWithinAt 𝕜 f t x) (st : s ⊆ t) :
DifferentiableWithinAt 𝕜 f s x := by
rcases h with ⟨f', hf'⟩
exact ⟨f', hf'.mono st⟩
theorem DifferentiableWithinAt.mono_of_mem_nhdsWithin
(h : DifferentiableWithinAt 𝕜 f s x) {t : Set E} (hst : s ∈ 𝓝[t] x) :
DifferentiableWithinAt 𝕜 f t x :=
(h.hasFDerivWithinAt.mono_of_mem_nhdsWithin hst).differentiableWithinAt
@[deprecated (since := "2024-10-31")]
alias DifferentiableWithinAt.mono_of_mem := DifferentiableWithinAt.mono_of_mem_nhdsWithin
theorem DifferentiableWithinAt.congr_nhds (h : DifferentiableWithinAt 𝕜 f s x) {t : Set E}
(hst : 𝓝[s] x = 𝓝[t] x) : DifferentiableWithinAt 𝕜 f t x :=
h.mono_of_mem_nhdsWithin <| hst ▸ self_mem_nhdsWithin
theorem differentiableWithinAt_congr_nhds {t : Set E} (hst : 𝓝[s] x = 𝓝[t] x) :
DifferentiableWithinAt 𝕜 f s x ↔ DifferentiableWithinAt 𝕜 f t x :=
⟨fun h => h.congr_nhds hst, fun h => h.congr_nhds hst.symm⟩
theorem differentiableWithinAt_inter (ht : t ∈ 𝓝 x) :
DifferentiableWithinAt 𝕜 f (s ∩ t) x ↔ DifferentiableWithinAt 𝕜 f s x := by
simp only [DifferentiableWithinAt, hasFDerivWithinAt_inter ht]
theorem differentiableWithinAt_inter' (ht : t ∈ 𝓝[s] x) :
DifferentiableWithinAt 𝕜 f (s ∩ t) x ↔ DifferentiableWithinAt 𝕜 f s x := by
simp only [DifferentiableWithinAt, hasFDerivWithinAt_inter' ht]
theorem differentiableWithinAt_insert_self :
DifferentiableWithinAt 𝕜 f (insert x s) x ↔ DifferentiableWithinAt 𝕜 f s x :=
⟨fun h ↦ h.mono (subset_insert x s), fun h ↦ h.hasFDerivWithinAt.insert.differentiableWithinAt⟩
theorem differentiableWithinAt_insert {y : E} :
DifferentiableWithinAt 𝕜 f (insert y s) x ↔ DifferentiableWithinAt 𝕜 f s x := by
rcases eq_or_ne x y with (rfl | h)
· exact differentiableWithinAt_insert_self
apply differentiableWithinAt_congr_nhds
exact nhdsWithin_insert_of_ne h
alias ⟨DifferentiableWithinAt.of_insert, DifferentiableWithinAt.insert'⟩ :=
differentiableWithinAt_insert
protected theorem DifferentiableWithinAt.insert (h : DifferentiableWithinAt 𝕜 f s x) :
DifferentiableWithinAt 𝕜 f (insert x s) x :=
h.insert'
theorem DifferentiableAt.differentiableWithinAt (h : DifferentiableAt 𝕜 f x) :
DifferentiableWithinAt 𝕜 f s x :=
(differentiableWithinAt_univ.2 h).mono (subset_univ _)
@[fun_prop]
theorem Differentiable.differentiableAt (h : Differentiable 𝕜 f) : DifferentiableAt 𝕜 f x :=
h x
protected theorem DifferentiableAt.fderivWithin (h : DifferentiableAt 𝕜 f x)
(hxs : UniqueDiffWithinAt 𝕜 s x) : fderivWithin 𝕜 f s x = fderiv 𝕜 f x :=
h.hasFDerivAt.hasFDerivWithinAt.fderivWithin hxs
theorem DifferentiableOn.mono (h : DifferentiableOn 𝕜 f t) (st : s ⊆ t) : DifferentiableOn 𝕜 f s :=
fun x hx => (h x (st hx)).mono st
theorem differentiableOn_univ : DifferentiableOn 𝕜 f univ ↔ Differentiable 𝕜 f := by
simp only [DifferentiableOn, Differentiable, differentiableWithinAt_univ, mem_univ,
forall_true_left]
@[fun_prop]
theorem Differentiable.differentiableOn (h : Differentiable 𝕜 f) : DifferentiableOn 𝕜 f s :=
(differentiableOn_univ.2 h).mono (subset_univ _)
theorem differentiableOn_of_locally_differentiableOn
(h : ∀ x ∈ s, ∃ u, IsOpen u ∧ x ∈ u ∧ DifferentiableOn 𝕜 f (s ∩ u)) :
DifferentiableOn 𝕜 f s := by
intro x xs
rcases h x xs with ⟨t, t_open, xt, ht⟩
exact (differentiableWithinAt_inter (IsOpen.mem_nhds t_open xt)).1 (ht x ⟨xs, xt⟩)
theorem fderivWithin_of_mem_nhdsWithin (st : t ∈ 𝓝[s] x) (ht : UniqueDiffWithinAt 𝕜 s x)
(h : DifferentiableWithinAt 𝕜 f t x) : fderivWithin 𝕜 f s x = fderivWithin 𝕜 f t x :=
((DifferentiableWithinAt.hasFDerivWithinAt h).mono_of_mem_nhdsWithin st).fderivWithin ht
@[deprecated (since := "2024-10-31")]
alias fderivWithin_of_mem := fderivWithin_of_mem_nhdsWithin
theorem fderivWithin_subset (st : s ⊆ t) (ht : UniqueDiffWithinAt 𝕜 s x)
(h : DifferentiableWithinAt 𝕜 f t x) : fderivWithin 𝕜 f s x = fderivWithin 𝕜 f t x :=
fderivWithin_of_mem_nhdsWithin (nhdsWithin_mono _ st self_mem_nhdsWithin) ht h
theorem fderivWithin_inter (ht : t ∈ 𝓝 x) : fderivWithin 𝕜 f (s ∩ t) x = fderivWithin 𝕜 f s x := by
classical
simp [fderivWithin, hasFDerivWithinAt_inter ht, DifferentiableWithinAt]
theorem fderivWithin_of_mem_nhds (h : s ∈ 𝓝 x) : fderivWithin 𝕜 f s x = fderiv 𝕜 f x := by
rw [← fderivWithin_univ, ← univ_inter s, fderivWithin_inter h]
theorem fderivWithin_of_isOpen (hs : IsOpen s) (hx : x ∈ s) : fderivWithin 𝕜 f s x = fderiv 𝕜 f x :=
fderivWithin_of_mem_nhds (hs.mem_nhds hx)
theorem fderivWithin_eq_fderiv (hs : UniqueDiffWithinAt 𝕜 s x) (h : DifferentiableAt 𝕜 f x) :
fderivWithin 𝕜 f s x = fderiv 𝕜 f x := by
rw [← fderivWithin_univ]
exact fderivWithin_subset (subset_univ _) hs h.differentiableWithinAt
theorem fderiv_mem_iff {f : E → F} {s : Set (E →L[𝕜] F)} {x : E} : fderiv 𝕜 f x ∈ s ↔
DifferentiableAt 𝕜 f x ∧ fderiv 𝕜 f x ∈ s ∨ ¬DifferentiableAt 𝕜 f x ∧ (0 : E →L[𝕜] F) ∈ s := by
by_cases hx : DifferentiableAt 𝕜 f x <;> simp [fderiv_zero_of_not_differentiableAt, *]
theorem fderivWithin_mem_iff {f : E → F} {t : Set E} {s : Set (E →L[𝕜] F)} {x : E} :
fderivWithin 𝕜 f t x ∈ s ↔
DifferentiableWithinAt 𝕜 f t x ∧ fderivWithin 𝕜 f t x ∈ s ∨
¬DifferentiableWithinAt 𝕜 f t x ∧ (0 : E →L[𝕜] F) ∈ s := by
by_cases hx : DifferentiableWithinAt 𝕜 f t x <;>
simp [fderivWithin_zero_of_not_differentiableWithinAt, *]
theorem Asymptotics.IsBigO.hasFDerivWithinAt {s : Set E} {x₀ : E} {n : ℕ}
(h : f =O[𝓝[s] x₀] fun x => ‖x - x₀‖ ^ n) (hx₀ : x₀ ∈ s) (hn : 1 < n) :
HasFDerivWithinAt f (0 : E →L[𝕜] F) s x₀ := by
simp_rw [HasFDerivWithinAt, hasFDerivAtFilter_iff_isLittleO,
h.eq_zero_of_norm_pow_within hx₀ hn.ne_bot, zero_apply, sub_zero,
h.trans_isLittleO ((isLittleO_pow_sub_sub x₀ hn).mono nhdsWithin_le_nhds)]
theorem Asymptotics.IsBigO.hasFDerivAt {x₀ : E} {n : ℕ} (h : f =O[𝓝 x₀] fun x => ‖x - x₀‖ ^ n)
(hn : 1 < n) : HasFDerivAt f (0 : E →L[𝕜] F) x₀ := by
rw [← nhdsWithin_univ] at h
exact (h.hasFDerivWithinAt (mem_univ _) hn).hasFDerivAt_of_univ
nonrec theorem HasFDerivWithinAt.isBigO_sub {f : E → F} {s : Set E} {x₀ : E} {f' : E →L[𝕜] F}
(h : HasFDerivWithinAt f f' s x₀) : (f · - f x₀) =O[𝓝[s] x₀] (· - x₀) :=
h.isBigO_sub
lemma DifferentiableWithinAt.isBigO_sub {f : E → F} {s : Set E} {x₀ : E}
(h : DifferentiableWithinAt 𝕜 f s x₀) : (f · - f x₀) =O[𝓝[s] x₀] (· - x₀) :=
h.hasFDerivWithinAt.isBigO_sub
nonrec theorem HasFDerivAt.isBigO_sub {f : E → F} {x₀ : E} {f' : E →L[𝕜] F}
(h : HasFDerivAt f f' x₀) : (f · - f x₀) =O[𝓝 x₀] (· - x₀) :=
h.isBigO_sub
nonrec theorem DifferentiableAt.isBigO_sub {f : E → F} {x₀ : E} (h : DifferentiableAt 𝕜 f x₀) :
(f · - f x₀) =O[𝓝 x₀] (· - x₀) :=
h.hasFDerivAt.isBigO_sub
end FDerivProperties
section Continuous
/-! ### Deducing continuity from differentiability -/
theorem HasFDerivAtFilter.tendsto_nhds (hL : L ≤ 𝓝 x) (h : HasFDerivAtFilter f f' x L) :
Tendsto f L (𝓝 (f x)) := by
have : Tendsto (fun x' => f x' - f x) L (𝓝 0) := by
refine h.isBigO_sub.trans_tendsto (Tendsto.mono_left ?_ hL)
rw [← sub_self x]
exact tendsto_id.sub tendsto_const_nhds
have := this.add (tendsto_const_nhds (x := f x))
rw [zero_add (f x)] at this
exact this.congr (by simp only [sub_add_cancel, eq_self_iff_true, forall_const])
theorem HasFDerivWithinAt.continuousWithinAt (h : HasFDerivWithinAt f f' s x) :
ContinuousWithinAt f s x :=
HasFDerivAtFilter.tendsto_nhds inf_le_left h
theorem HasFDerivAt.continuousAt (h : HasFDerivAt f f' x) : ContinuousAt f x :=
HasFDerivAtFilter.tendsto_nhds le_rfl h
@[fun_prop]
theorem DifferentiableWithinAt.continuousWithinAt (h : DifferentiableWithinAt 𝕜 f s x) :
ContinuousWithinAt f s x :=
let ⟨_, hf'⟩ := h
hf'.continuousWithinAt
@[fun_prop]
theorem DifferentiableAt.continuousAt (h : DifferentiableAt 𝕜 f x) : ContinuousAt f x :=
let ⟨_, hf'⟩ := h
hf'.continuousAt
@[fun_prop]
theorem DifferentiableOn.continuousOn (h : DifferentiableOn 𝕜 f s) : ContinuousOn f s := fun x hx =>
(h x hx).continuousWithinAt
@[fun_prop]
theorem Differentiable.continuous (h : Differentiable 𝕜 f) : Continuous f :=
continuous_iff_continuousAt.2 fun x => (h x).continuousAt
protected theorem HasStrictFDerivAt.continuousAt (hf : HasStrictFDerivAt f f' x) :
ContinuousAt f x :=
hf.hasFDerivAt.continuousAt
theorem HasStrictFDerivAt.isBigO_sub_rev {f' : E ≃L[𝕜] F}
(hf : HasStrictFDerivAt f (f' : E →L[𝕜] F) x) :
(fun p : E × E => p.1 - p.2) =O[𝓝 (x, x)] fun p : E × E => f p.1 - f p.2 :=
((f'.isBigO_comp_rev _ _).trans
(hf.isLittleO.trans_isBigO (f'.isBigO_comp_rev _ _)).right_isBigO_add).congr
(fun _ => rfl) fun _ => sub_add_cancel _ _
theorem HasFDerivAtFilter.isBigO_sub_rev (hf : HasFDerivAtFilter f f' x L) {C}
(hf' : AntilipschitzWith C f') : (fun x' => x' - x) =O[L] fun x' => f x' - f x :=
have : (fun x' => x' - x) =O[L] fun x' => f' (x' - x) :=
isBigO_iff.2 ⟨C, Eventually.of_forall fun _ => ZeroHomClass.bound_of_antilipschitz f' hf' _⟩
(this.trans (hf.isLittleO.trans_isBigO this).right_isBigO_add).congr (fun _ => rfl) fun _ =>
sub_add_cancel _ _
end Continuous
section congr
/-! ### congr properties of the derivative -/
theorem hasFDerivWithinAt_congr_set' (y : E) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
HasFDerivWithinAt f f' s x ↔ HasFDerivWithinAt f f' t x :=
calc
HasFDerivWithinAt f f' s x ↔ HasFDerivWithinAt f f' (s \ {y}) x :=
(hasFDerivWithinAt_diff_singleton _).symm
_ ↔ HasFDerivWithinAt f f' (t \ {y}) x := by
suffices 𝓝[s \ {y}] x = 𝓝[t \ {y}] x by simp only [HasFDerivWithinAt, this]
simpa only [set_eventuallyEq_iff_inf_principal, ← nhdsWithin_inter', diff_eq,
inter_comm] using h
_ ↔ HasFDerivWithinAt f f' t x := hasFDerivWithinAt_diff_singleton _
theorem hasFDerivWithinAt_congr_set (h : s =ᶠ[𝓝 x] t) :
HasFDerivWithinAt f f' s x ↔ HasFDerivWithinAt f f' t x :=
hasFDerivWithinAt_congr_set' x <| h.filter_mono inf_le_left
theorem differentiableWithinAt_congr_set' (y : E) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
DifferentiableWithinAt 𝕜 f s x ↔ DifferentiableWithinAt 𝕜 f t x :=
exists_congr fun _ => hasFDerivWithinAt_congr_set' _ h
theorem differentiableWithinAt_congr_set (h : s =ᶠ[𝓝 x] t) :
DifferentiableWithinAt 𝕜 f s x ↔ DifferentiableWithinAt 𝕜 f t x :=
exists_congr fun _ => hasFDerivWithinAt_congr_set h
theorem fderivWithin_congr_set' (y : E) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
fderivWithin 𝕜 f s x = fderivWithin 𝕜 f t x := by
classical
simp only [fderivWithin, differentiableWithinAt_congr_set' _ h, hasFDerivWithinAt_congr_set' _ h]
theorem fderivWithin_congr_set (h : s =ᶠ[𝓝 x] t) : fderivWithin 𝕜 f s x = fderivWithin 𝕜 f t x :=
fderivWithin_congr_set' x <| h.filter_mono inf_le_left
theorem fderivWithin_eventually_congr_set' (y : E) (h : s =ᶠ[𝓝[{y}ᶜ] x] t) :
fderivWithin 𝕜 f s =ᶠ[𝓝 x] fderivWithin 𝕜 f t :=
(eventually_nhds_nhdsWithin.2 h).mono fun _ => fderivWithin_congr_set' y
theorem fderivWithin_eventually_congr_set (h : s =ᶠ[𝓝 x] t) :
fderivWithin 𝕜 f s =ᶠ[𝓝 x] fderivWithin 𝕜 f t :=
fderivWithin_eventually_congr_set' x <| h.filter_mono inf_le_left
theorem Filter.EventuallyEq.hasStrictFDerivAt_iff (h : f₀ =ᶠ[𝓝 x] f₁) (h' : ∀ y, f₀' y = f₁' y) :
HasStrictFDerivAt f₀ f₀' x ↔ HasStrictFDerivAt f₁ f₁' x := by
rw [hasStrictFDerivAt_iff_isLittleOTVS, hasStrictFDerivAt_iff_isLittleOTVS]
refine isLittleOTVS_congr ((h.prodMk_nhds h).mono ?_) .rfl
rintro p ⟨hp₁, hp₂⟩
simp only [*]
theorem HasStrictFDerivAt.congr_fderiv (h : HasStrictFDerivAt f f' x) (h' : f' = g') :
HasStrictFDerivAt f g' x :=
h' ▸ h
theorem HasFDerivAt.congr_fderiv (h : HasFDerivAt f f' x) (h' : f' = g') : HasFDerivAt f g' x :=
h' ▸ h
theorem HasFDerivWithinAt.congr_fderiv (h : HasFDerivWithinAt f f' s x) (h' : f' = g') :
HasFDerivWithinAt f g' s x :=
h' ▸ h
theorem HasStrictFDerivAt.congr_of_eventuallyEq (h : HasStrictFDerivAt f f' x)
(h₁ : f =ᶠ[𝓝 x] f₁) : HasStrictFDerivAt f₁ f' x :=
(h₁.hasStrictFDerivAt_iff fun _ => rfl).1 h
theorem Filter.EventuallyEq.hasFDerivAtFilter_iff (h₀ : f₀ =ᶠ[L] f₁) (hx : f₀ x = f₁ x)
(h₁ : ∀ x, f₀' x = f₁' x) : HasFDerivAtFilter f₀ f₀' x L ↔ HasFDerivAtFilter f₁ f₁' x L := by
simp only [hasFDerivAtFilter_iff_isLittleOTVS]
exact isLittleOTVS_congr (h₀.mono fun y hy => by simp only [hy, h₁, hx]) .rfl
theorem HasFDerivAtFilter.congr_of_eventuallyEq (h : HasFDerivAtFilter f f' x L) (hL : f₁ =ᶠ[L] f)
(hx : f₁ x = f x) : HasFDerivAtFilter f₁ f' x L :=
(hL.hasFDerivAtFilter_iff hx fun _ => rfl).2 h
theorem Filter.EventuallyEq.hasFDerivAt_iff (h : f₀ =ᶠ[𝓝 x] f₁) :
HasFDerivAt f₀ f' x ↔ HasFDerivAt f₁ f' x :=
h.hasFDerivAtFilter_iff h.eq_of_nhds fun _ => _root_.rfl
theorem Filter.EventuallyEq.differentiableAt_iff (h : f₀ =ᶠ[𝓝 x] f₁) :
DifferentiableAt 𝕜 f₀ x ↔ DifferentiableAt 𝕜 f₁ x :=
exists_congr fun _ => h.hasFDerivAt_iff
theorem Filter.EventuallyEq.hasFDerivWithinAt_iff (h : f₀ =ᶠ[𝓝[s] x] f₁) (hx : f₀ x = f₁ x) :
HasFDerivWithinAt f₀ f' s x ↔ HasFDerivWithinAt f₁ f' s x :=
h.hasFDerivAtFilter_iff hx fun _ => _root_.rfl
theorem Filter.EventuallyEq.hasFDerivWithinAt_iff_of_mem (h : f₀ =ᶠ[𝓝[s] x] f₁) (hx : x ∈ s) :
HasFDerivWithinAt f₀ f' s x ↔ HasFDerivWithinAt f₁ f' s x :=
h.hasFDerivWithinAt_iff (h.eq_of_nhdsWithin hx)
theorem Filter.EventuallyEq.differentiableWithinAt_iff (h : f₀ =ᶠ[𝓝[s] x] f₁) (hx : f₀ x = f₁ x) :
DifferentiableWithinAt 𝕜 f₀ s x ↔ DifferentiableWithinAt 𝕜 f₁ s x :=
exists_congr fun _ => h.hasFDerivWithinAt_iff hx
theorem Filter.EventuallyEq.differentiableWithinAt_iff_of_mem (h : f₀ =ᶠ[𝓝[s] x] f₁) (hx : x ∈ s) :
DifferentiableWithinAt 𝕜 f₀ s x ↔ DifferentiableWithinAt 𝕜 f₁ s x :=
h.differentiableWithinAt_iff (h.eq_of_nhdsWithin hx)
theorem HasFDerivWithinAt.congr_mono (h : HasFDerivWithinAt f f' s x) (ht : EqOn f₁ f t)
(hx : f₁ x = f x) (h₁ : t ⊆ s) : HasFDerivWithinAt f₁ f' t x :=
HasFDerivAtFilter.congr_of_eventuallyEq (h.mono h₁) (Filter.mem_inf_of_right ht) hx
theorem HasFDerivWithinAt.congr (h : HasFDerivWithinAt f f' s x) (hs : EqOn f₁ f s)
(hx : f₁ x = f x) : HasFDerivWithinAt f₁ f' s x :=
h.congr_mono hs hx (Subset.refl _)
theorem HasFDerivWithinAt.congr' (h : HasFDerivWithinAt f f' s x) (hs : EqOn f₁ f s) (hx : x ∈ s) :
HasFDerivWithinAt f₁ f' s x :=
h.congr hs (hs hx)
theorem HasFDerivWithinAt.congr_of_eventuallyEq (h : HasFDerivWithinAt f f' s x)
(h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : f₁ x = f x) : HasFDerivWithinAt f₁ f' s x :=
HasFDerivAtFilter.congr_of_eventuallyEq h h₁ hx
theorem HasFDerivAt.congr_of_eventuallyEq (h : HasFDerivAt f f' x) (h₁ : f₁ =ᶠ[𝓝 x] f) :
HasFDerivAt f₁ f' x :=
HasFDerivAtFilter.congr_of_eventuallyEq h h₁ (mem_of_mem_nhds h₁ :)
theorem DifferentiableWithinAt.congr_mono (h : DifferentiableWithinAt 𝕜 f s x) (ht : EqOn f₁ f t)
(hx : f₁ x = f x) (h₁ : t ⊆ s) : DifferentiableWithinAt 𝕜 f₁ t x :=
(HasFDerivWithinAt.congr_mono h.hasFDerivWithinAt ht hx h₁).differentiableWithinAt
theorem DifferentiableWithinAt.congr (h : DifferentiableWithinAt 𝕜 f s x) (ht : ∀ x ∈ s, f₁ x = f x)
(hx : f₁ x = f x) : DifferentiableWithinAt 𝕜 f₁ s x :=
DifferentiableWithinAt.congr_mono h ht hx (Subset.refl _)
theorem DifferentiableWithinAt.congr_of_eventuallyEq (h : DifferentiableWithinAt 𝕜 f s x)
(h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : f₁ x = f x) : DifferentiableWithinAt 𝕜 f₁ s x :=
(h.hasFDerivWithinAt.congr_of_eventuallyEq h₁ hx).differentiableWithinAt
theorem DifferentiableWithinAt.congr_of_eventuallyEq_of_mem (h : DifferentiableWithinAt 𝕜 f s x)
(h₁ : f₁ =ᶠ[𝓝[s] x] f) (hx : x ∈ s) : DifferentiableWithinAt 𝕜 f₁ s x :=
h.congr_of_eventuallyEq h₁ (mem_of_mem_nhdsWithin hx h₁ :)
theorem DifferentiableWithinAt.congr_of_eventuallyEq_insert (h : DifferentiableWithinAt 𝕜 f s x)
(h₁ : f₁ =ᶠ[𝓝[insert x s] x] f) : DifferentiableWithinAt 𝕜 f₁ s x :=
(h.insert.congr_of_eventuallyEq_of_mem h₁ (mem_insert _ _)).of_insert
theorem DifferentiableOn.congr_mono (h : DifferentiableOn 𝕜 f s) (h' : ∀ x ∈ t, f₁ x = f x)
(h₁ : t ⊆ s) : DifferentiableOn 𝕜 f₁ t := fun x hx => (h x (h₁ hx)).congr_mono h' (h' x hx) h₁
theorem DifferentiableOn.congr (h : DifferentiableOn 𝕜 f s) (h' : ∀ x ∈ s, f₁ x = f x) :
DifferentiableOn 𝕜 f₁ s := fun x hx => (h x hx).congr h' (h' x hx)
theorem differentiableOn_congr (h' : ∀ x ∈ s, f₁ x = f x) :
DifferentiableOn 𝕜 f₁ s ↔ DifferentiableOn 𝕜 f s :=
⟨fun h => DifferentiableOn.congr h fun y hy => (h' y hy).symm, fun h =>
DifferentiableOn.congr h h'⟩
theorem DifferentiableAt.congr_of_eventuallyEq (h : DifferentiableAt 𝕜 f x) (hL : f₁ =ᶠ[𝓝 x] f) :
DifferentiableAt 𝕜 f₁ x :=
hL.differentiableAt_iff.2 h
theorem DifferentiableWithinAt.fderivWithin_congr_mono (h : DifferentiableWithinAt 𝕜 f s x)
(hs : EqOn f₁ f t) (hx : f₁ x = f x) (hxt : UniqueDiffWithinAt 𝕜 t x) (h₁ : t ⊆ s) :
fderivWithin 𝕜 f₁ t x = fderivWithin 𝕜 f s x :=
(HasFDerivWithinAt.congr_mono h.hasFDerivWithinAt hs hx h₁).fderivWithin hxt
theorem Filter.EventuallyEq.fderivWithin_eq (hs : f₁ =ᶠ[𝓝[s] x] f) (hx : f₁ x = f x) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x := by
classical
simp only [fderivWithin, DifferentiableWithinAt, hs.hasFDerivWithinAt_iff hx]
theorem Filter.EventuallyEq.fderivWithin_eq_of_mem (hs : f₁ =ᶠ[𝓝[s] x] f) (hx : x ∈ s) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x :=
hs.fderivWithin_eq (mem_of_mem_nhdsWithin hx hs :)
theorem Filter.EventuallyEq.fderivWithin_eq_of_insert (hs : f₁ =ᶠ[𝓝[insert x s] x] f) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x := by
apply Filter.EventuallyEq.fderivWithin_eq (nhdsWithin_mono _ (subset_insert x s) hs)
exact (mem_of_mem_nhdsWithin (mem_insert x s) hs :)
theorem Filter.EventuallyEq.fderivWithin' (hs : f₁ =ᶠ[𝓝[s] x] f) (ht : t ⊆ s) :
fderivWithin 𝕜 f₁ t =ᶠ[𝓝[s] x] fderivWithin 𝕜 f t :=
(eventually_eventually_nhdsWithin.2 hs).mp <|
eventually_mem_nhdsWithin.mono fun _y hys hs =>
EventuallyEq.fderivWithin_eq (hs.filter_mono <| nhdsWithin_mono _ ht)
(hs.self_of_nhdsWithin hys)
protected theorem Filter.EventuallyEq.fderivWithin (hs : f₁ =ᶠ[𝓝[s] x] f) :
fderivWithin 𝕜 f₁ s =ᶠ[𝓝[s] x] fderivWithin 𝕜 f s :=
hs.fderivWithin' Subset.rfl
theorem Filter.EventuallyEq.fderivWithin_eq_nhds (h : f₁ =ᶠ[𝓝 x] f) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x :=
(h.filter_mono nhdsWithin_le_nhds).fderivWithin_eq h.self_of_nhds
theorem fderivWithin_congr (hs : EqOn f₁ f s) (hx : f₁ x = f x) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x :=
(hs.eventuallyEq.filter_mono inf_le_right).fderivWithin_eq hx
theorem fderivWithin_congr' (hs : EqOn f₁ f s) (hx : x ∈ s) :
fderivWithin 𝕜 f₁ s x = fderivWithin 𝕜 f s x :=
fderivWithin_congr hs (hs hx)
theorem Filter.EventuallyEq.fderiv_eq (h : f₁ =ᶠ[𝓝 x] f) : fderiv 𝕜 f₁ x = fderiv 𝕜 f x := by
rw [← fderivWithin_univ, ← fderivWithin_univ, h.fderivWithin_eq_nhds]
protected theorem Filter.EventuallyEq.fderiv (h : f₁ =ᶠ[𝓝 x] f) : fderiv 𝕜 f₁ =ᶠ[𝓝 x] fderiv 𝕜 f :=
h.eventuallyEq_nhds.mono fun _ h => h.fderiv_eq
end congr
section id
/-! ### Derivative of the identity -/
@[fun_prop]
theorem hasStrictFDerivAt_id (x : E) : HasStrictFDerivAt id (id 𝕜 E) x :=
.of_isLittleOTVS <| (IsLittleOTVS.zero _ _).congr_left <| by simp
theorem hasFDerivAtFilter_id (x : E) (L : Filter E) : HasFDerivAtFilter id (id 𝕜 E) x L :=
.of_isLittleOTVS <| (IsLittleOTVS.zero _ _).congr_left <| by simp
@[fun_prop]
theorem hasFDerivWithinAt_id (x : E) (s : Set E) : HasFDerivWithinAt id (id 𝕜 E) s x :=
hasFDerivAtFilter_id _ _
@[fun_prop]
theorem hasFDerivAt_id (x : E) : HasFDerivAt id (id 𝕜 E) x :=
hasFDerivAtFilter_id _ _
@[simp, fun_prop]
theorem differentiableAt_id : DifferentiableAt 𝕜 id x :=
(hasFDerivAt_id x).differentiableAt
/-- Variant with `fun x => x` rather than `id` -/
@[simp]
theorem differentiableAt_id' : DifferentiableAt 𝕜 (fun x => x) x :=
(hasFDerivAt_id x).differentiableAt
@[fun_prop]
theorem differentiableWithinAt_id : DifferentiableWithinAt 𝕜 id s x :=
differentiableAt_id.differentiableWithinAt
/-- Variant with `fun x => x` rather than `id` -/
@[fun_prop]
theorem differentiableWithinAt_id' : DifferentiableWithinAt 𝕜 (fun x => x) s x :=
differentiableWithinAt_id
@[simp, fun_prop]
theorem differentiable_id : Differentiable 𝕜 (id : E → E) := fun _ => differentiableAt_id
/-- Variant with `fun x => x` rather than `id` -/
@[simp]
theorem differentiable_id' : Differentiable 𝕜 fun x : E => x := fun _ => differentiableAt_id
@[fun_prop]
theorem differentiableOn_id : DifferentiableOn 𝕜 id s :=
differentiable_id.differentiableOn
@[simp]
theorem fderiv_id : fderiv 𝕜 id x = id 𝕜 E :=
HasFDerivAt.fderiv (hasFDerivAt_id x)
@[simp]
theorem fderiv_id' : fderiv 𝕜 (fun x : E => x) x = ContinuousLinearMap.id 𝕜 E :=
fderiv_id
theorem fderivWithin_id (hxs : UniqueDiffWithinAt 𝕜 s x) : fderivWithin 𝕜 id s x = id 𝕜 E := by
rw [DifferentiableAt.fderivWithin differentiableAt_id hxs]
exact fderiv_id
theorem fderivWithin_id' (hxs : UniqueDiffWithinAt 𝕜 s x) :
fderivWithin 𝕜 (fun x : E => x) s x = ContinuousLinearMap.id 𝕜 E :=
fderivWithin_id hxs
end id
section Const
/-! ### Derivative of constant functions
This include the constant functions `0`, `1`, `Nat.cast n`, `Int.cast z`, and other numerals.
-/
@[fun_prop]
theorem hasStrictFDerivAt_const (c : F) (x : E) :
HasStrictFDerivAt (fun _ => c) (0 : E →L[𝕜] F) x :=
.of_isLittleOTVS <| (IsLittleOTVS.zero _ _).congr_left fun _ => by
simp only [zero_apply, sub_self, Pi.zero_apply]
@[fun_prop]
theorem hasStrictFDerivAt_zero (x : E) :
HasStrictFDerivAt (0 : E → F) (0 : E →L[𝕜] F) x := hasStrictFDerivAt_const _ _
@[fun_prop]
theorem hasStrictFDerivAt_one [One F] (x : E) :
HasStrictFDerivAt (1 : E → F) (0 : E →L[𝕜] F) x := hasStrictFDerivAt_const _ _
@[fun_prop]
| theorem hasStrictFDerivAt_natCast [NatCast F] (n : ℕ) (x : E) :
HasStrictFDerivAt (n : E → F) (0 : E →L[𝕜] F) x := hasStrictFDerivAt_const _ _
| Mathlib/Analysis/Calculus/FDeriv/Basic.lean | 1,081 | 1,082 |
/-
Copyright (c) 2023 Kalle Kytölä. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kalle Kytölä
-/
import Mathlib.MeasureTheory.Measure.ProbabilityMeasure
import Mathlib.MeasureTheory.Measure.Prod
/-!
# Products of finite measures and probability measures
This file introduces binary products of finite measures and probability measures. The constructions
are obtained from special cases of products of general measures. Taking products nevertheless has
specific properties in the cases of finite measures and probability measures, notably the fact that
the product measures depend continuously on their factors in the topology of weak convergence when
the underlying space is metrizable and separable.
## Main definitions
* `MeasureTheory.FiniteMeasure.prod`: The product of two finite measures.
* `MeasureTheory.ProbabilityMeasure.prod`: The product of two probability measures.
## TODO
* Add continuous dependence of the product measures on the factors.
-/
open MeasureTheory Topology Metric Filter Set ENNReal NNReal
open scoped Topology ENNReal NNReal BoundedContinuousFunction
namespace MeasureTheory
section FiniteMeasure_product
namespace FiniteMeasure
variable {α : Type*} [MeasurableSpace α] {β : Type*} [MeasurableSpace β]
/-- The binary product of finite measures. -/
noncomputable def prod (μ : FiniteMeasure α) (ν : FiniteMeasure β) : FiniteMeasure (α × β) :=
⟨μ.toMeasure.prod ν.toMeasure, inferInstance⟩
variable (μ : FiniteMeasure α) (ν : FiniteMeasure β)
@[simp] lemma toMeasure_prod : (μ.prod ν).toMeasure = μ.toMeasure.prod ν.toMeasure := rfl
lemma prod_apply (s : Set (α × β)) (s_mble : MeasurableSet s) :
μ.prod ν s = ENNReal.toNNReal (∫⁻ x, ν.toMeasure (Prod.mk x ⁻¹' s) ∂μ) := by
simp [coeFn_def, Measure.prod_apply s_mble]
lemma prod_apply_symm (s : Set (α × β)) (s_mble : MeasurableSet s) :
μ.prod ν s = ENNReal.toNNReal (∫⁻ y, μ.toMeasure ((fun x ↦ ⟨x, y⟩) ⁻¹' s) ∂ν) := by
simp [coeFn_def, Measure.prod_apply_symm s_mble]
lemma prod_prod (s : Set α) (t : Set β) : μ.prod ν (s ×ˢ t) = μ s * ν t := by simp [coeFn_def]
| @[simp] lemma mass_prod : (μ.prod ν).mass = μ.mass * ν.mass := by
simp only [coeFn_def, mass, univ_prod_univ.symm, toMeasure_prod]
rw [← ENNReal.toNNReal_mul]
exact congr_arg ENNReal.toNNReal (Measure.prod_prod univ univ)
| Mathlib/MeasureTheory/Measure/FiniteMeasureProd.lean | 59 | 62 |
/-
Copyright (c) 2022 Floris van Doorn. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Floris van Doorn
-/
import Mathlib.Analysis.Calculus.ContDiff.Basic
import Mathlib.Analysis.Calculus.ParametricIntegral
import Mathlib.MeasureTheory.Integral.Prod
import Mathlib.MeasureTheory.Function.LocallyIntegrable
import Mathlib.MeasureTheory.Group.Integral
import Mathlib.MeasureTheory.Group.Prod
import Mathlib.MeasureTheory.Integral.IntervalIntegral.Basic
/-!
# Convolution of functions
This file defines the convolution on two functions, i.e. `x ↦ ∫ f(t)g(x - t) ∂t`.
In the general case, these functions can be vector-valued, and have an arbitrary (additive)
group as domain. We use a continuous bilinear operation `L` on these function values as
"multiplication". The domain must be equipped with a Haar measure `μ`
(though many individual results have weaker conditions on `μ`).
For many applications we can take `L = ContinuousLinearMap.lsmul ℝ ℝ` or
`L = ContinuousLinearMap.mul ℝ ℝ`.
We also define `ConvolutionExists` and `ConvolutionExistsAt` to state that the convolution is
well-defined (everywhere or at a single point). These conditions are needed for pointwise
computations (e.g. `ConvolutionExistsAt.distrib_add`), but are generally not strong enough for any
local (or global) properties of the convolution. For this we need stronger assumptions on `f`
and/or `g`, and generally if we impose stronger conditions on one of the functions, we can impose
weaker conditions on the other.
We have proven many of the properties of the convolution assuming one of these functions
has compact support (in which case the other function only needs to be locally integrable).
We still need to prove the properties for other pairs of conditions (e.g. both functions are
rapidly decreasing)
# Design Decisions
We use a bilinear map `L` to "multiply" the two functions in the integrand.
This generality has several advantages
* This allows us to compute the total derivative of the convolution, in case the functions are
multivariate. The total derivative is again a convolution, but where the codomains of the
functions can be higher-dimensional. See `HasCompactSupport.hasFDerivAt_convolution_right`.
* This allows us to use `@[to_additive]` everywhere (which would not be possible if we would use
`mul`/`smul` in the integral, since `@[to_additive]` will incorrectly also try to additivize
those definitions).
* We need to support the case where at least one of the functions is vector-valued, but if we use
`smul` to multiply the functions, that would be an asymmetric definition.
# Main Definitions
* `MeasureTheory.convolution f g L μ x = (f ⋆[L, μ] g) x = ∫ t, L (f t) (g (x - t)) ∂μ`
is the convolution of `f` and `g` w.r.t. the continuous bilinear map `L` and measure `μ`.
* `MeasureTheory.ConvolutionExistsAt f g x L μ` states that the convolution `(f ⋆[L, μ] g) x`
is well-defined (i.e. the integral exists).
* `MeasureTheory.ConvolutionExists f g L μ` states that the convolution `f ⋆[L, μ] g`
is well-defined at each point.
# Main Results
* `HasCompactSupport.hasFDerivAt_convolution_right` and
`HasCompactSupport.hasFDerivAt_convolution_left`: we can compute the total derivative
of the convolution as a convolution with the total derivative of the right (left) function.
* `HasCompactSupport.contDiff_convolution_right` and
`HasCompactSupport.contDiff_convolution_left`: the convolution is `𝒞ⁿ` if one of the functions
is `𝒞ⁿ` with compact support and the other function in locally integrable.
Versions of these statements for functions depending on a parameter are also given.
* `MeasureTheory.convolution_tendsto_right`: Given a sequence of nonnegative normalized functions
whose support tends to a small neighborhood around `0`, the convolution tends to the right
argument. This is specialized to bump functions in `ContDiffBump.convolution_tendsto_right`.
# Notation
The following notations are localized in the locale `Convolution`:
* `f ⋆[L, μ] g` for the convolution. Note: you have to use parentheses to apply the convolution
to an argument: `(f ⋆[L, μ] g) x`.
* `f ⋆[L] g := f ⋆[L, volume] g`
* `f ⋆ g := f ⋆[lsmul ℝ ℝ] g`
# To do
* Existence and (uniform) continuity of the convolution if
one of the maps is in `ℒ^p` and the other in `ℒ^q` with `1 / p + 1 / q = 1`.
This might require a generalization of `MeasureTheory.MemLp.smul` where `smul` is generalized
to a continuous bilinear map.
(see e.g. [Fremlin, *Measure Theory* (volume 2)][fremlin_vol2], 255K)
* The convolution is an `AEStronglyMeasurable` function
(see e.g. [Fremlin, *Measure Theory* (volume 2)][fremlin_vol2], 255I).
* Prove properties about the convolution if both functions are rapidly decreasing.
* Use `@[to_additive]` everywhere (this likely requires changes in `to_additive`)
-/
open Set Function Filter MeasureTheory MeasureTheory.Measure TopologicalSpace
open Bornology ContinuousLinearMap Metric Topology
open scoped Pointwise NNReal Filter
universe u𝕜 uG uE uE' uE'' uF uF' uF'' uP
variable {𝕜 : Type u𝕜} {G : Type uG} {E : Type uE} {E' : Type uE'} {E'' : Type uE''} {F : Type uF}
{F' : Type uF'} {F'' : Type uF''} {P : Type uP}
variable [NormedAddCommGroup E] [NormedAddCommGroup E'] [NormedAddCommGroup E'']
[NormedAddCommGroup F] {f f' : G → E} {g g' : G → E'} {x x' : G} {y y' : E}
namespace MeasureTheory
section NontriviallyNormedField
variable [NontriviallyNormedField 𝕜]
variable [NormedSpace 𝕜 E] [NormedSpace 𝕜 E'] [NormedSpace 𝕜 E''] [NormedSpace 𝕜 F]
variable (L : E →L[𝕜] E' →L[𝕜] F)
section NoMeasurability
variable [AddGroup G] [TopologicalSpace G]
theorem convolution_integrand_bound_right_of_le_of_subset {C : ℝ} (hC : ∀ i, ‖g i‖ ≤ C) {x t : G}
{s u : Set G} (hx : x ∈ s) (hu : -tsupport g + s ⊆ u) :
‖L (f t) (g (x - t))‖ ≤ u.indicator (fun t => ‖L‖ * ‖f t‖ * C) t := by
-- Porting note: had to add `f := _`
refine le_indicator (f := fun t ↦ ‖L (f t) (g (x - t))‖) (fun t _ => ?_) (fun t ht => ?_) t
· apply_rules [L.le_of_opNorm₂_le_of_le, le_rfl]
· have : x - t ∉ support g := by
refine mt (fun hxt => hu ?_) ht
refine ⟨_, Set.neg_mem_neg.mpr (subset_closure hxt), _, hx, ?_⟩
simp only [neg_sub, sub_add_cancel]
simp only [nmem_support.mp this, (L _).map_zero, norm_zero, le_rfl]
theorem _root_.HasCompactSupport.convolution_integrand_bound_right_of_subset
(hcg : HasCompactSupport g) (hg : Continuous g)
{x t : G} {s u : Set G} (hx : x ∈ s) (hu : -tsupport g + s ⊆ u) :
‖L (f t) (g (x - t))‖ ≤ u.indicator (fun t => ‖L‖ * ‖f t‖ * ⨆ i, ‖g i‖) t := by
refine convolution_integrand_bound_right_of_le_of_subset _ (fun i => ?_) hx hu
exact le_ciSup (hg.norm.bddAbove_range_of_hasCompactSupport hcg.norm) _
theorem _root_.HasCompactSupport.convolution_integrand_bound_right (hcg : HasCompactSupport g)
(hg : Continuous g) {x t : G} {s : Set G} (hx : x ∈ s) :
‖L (f t) (g (x - t))‖ ≤ (-tsupport g + s).indicator (fun t => ‖L‖ * ‖f t‖ * ⨆ i, ‖g i‖) t :=
hcg.convolution_integrand_bound_right_of_subset L hg hx Subset.rfl
theorem _root_.Continuous.convolution_integrand_fst [ContinuousSub G] (hg : Continuous g) (t : G) :
Continuous fun x => L (f t) (g (x - t)) :=
L.continuous₂.comp₂ continuous_const <| hg.comp <| continuous_id.sub continuous_const
theorem _root_.HasCompactSupport.convolution_integrand_bound_left (hcf : HasCompactSupport f)
(hf : Continuous f) {x t : G} {s : Set G} (hx : x ∈ s) :
‖L (f (x - t)) (g t)‖ ≤
(-tsupport f + s).indicator (fun t => (‖L‖ * ⨆ i, ‖f i‖) * ‖g t‖) t := by
convert hcf.convolution_integrand_bound_right L.flip hf hx using 1
simp_rw [L.opNorm_flip, mul_right_comm]
end NoMeasurability
section Measurability
variable [MeasurableSpace G] {μ ν : Measure G}
/-- The convolution of `f` and `g` exists at `x` when the function `t ↦ L (f t) (g (x - t))` is
integrable. There are various conditions on `f` and `g` to prove this. -/
def ConvolutionExistsAt [Sub G] (f : G → E) (g : G → E') (x : G) (L : E →L[𝕜] E' →L[𝕜] F)
(μ : Measure G := by volume_tac) : Prop :=
Integrable (fun t => L (f t) (g (x - t))) μ
/-- The convolution of `f` and `g` exists when the function `t ↦ L (f t) (g (x - t))` is integrable
for all `x : G`. There are various conditions on `f` and `g` to prove this. -/
def ConvolutionExists [Sub G] (f : G → E) (g : G → E') (L : E →L[𝕜] E' →L[𝕜] F)
(μ : Measure G := by volume_tac) : Prop :=
∀ x : G, ConvolutionExistsAt f g x L μ
section ConvolutionExists
variable {L} in
theorem ConvolutionExistsAt.integrable [Sub G] {x : G} (h : ConvolutionExistsAt f g x L μ) :
Integrable (fun t => L (f t) (g (x - t))) μ :=
h
section Group
variable [AddGroup G]
theorem AEStronglyMeasurable.convolution_integrand' [MeasurableAdd₂ G]
[MeasurableNeg G] (hf : AEStronglyMeasurable f ν)
(hg : AEStronglyMeasurable g <| map (fun p : G × G => p.1 - p.2) (μ.prod ν)) :
AEStronglyMeasurable (fun p : G × G => L (f p.2) (g (p.1 - p.2))) (μ.prod ν) :=
L.aestronglyMeasurable_comp₂ hf.snd <| hg.comp_measurable measurable_sub
section
variable [MeasurableAdd G] [MeasurableNeg G]
theorem AEStronglyMeasurable.convolution_integrand_snd'
(hf : AEStronglyMeasurable f μ) {x : G}
(hg : AEStronglyMeasurable g <| map (fun t => x - t) μ) :
AEStronglyMeasurable (fun t => L (f t) (g (x - t))) μ :=
L.aestronglyMeasurable_comp₂ hf <| hg.comp_measurable <| measurable_id.const_sub x
theorem AEStronglyMeasurable.convolution_integrand_swap_snd' {x : G}
(hf : AEStronglyMeasurable f <| map (fun t => x - t) μ) (hg : AEStronglyMeasurable g μ) :
AEStronglyMeasurable (fun t => L (f (x - t)) (g t)) μ :=
L.aestronglyMeasurable_comp₂ (hf.comp_measurable <| measurable_id.const_sub x) hg
/-- A sufficient condition to prove that `f ⋆[L, μ] g` exists.
We assume that `f` is integrable on a set `s` and `g` is bounded and ae strongly measurable
on `x₀ - s` (note that both properties hold if `g` is continuous with compact support). -/
theorem _root_.BddAbove.convolutionExistsAt' {x₀ : G} {s : Set G}
(hbg : BddAbove ((fun i => ‖g i‖) '' ((fun t => -t + x₀) ⁻¹' s))) (hs : MeasurableSet s)
(h2s : (support fun t => L (f t) (g (x₀ - t))) ⊆ s) (hf : IntegrableOn f s μ)
(hmg : AEStronglyMeasurable g <| map (fun t => x₀ - t) (μ.restrict s)) :
ConvolutionExistsAt f g x₀ L μ := by
rw [ConvolutionExistsAt]
rw [← integrableOn_iff_integrable_of_support_subset h2s]
set s' := (fun t => -t + x₀) ⁻¹' s
have : ∀ᵐ t : G ∂μ.restrict s,
‖L (f t) (g (x₀ - t))‖ ≤ s.indicator (fun t => ‖L‖ * ‖f t‖ * ⨆ i : s', ‖g i‖) t := by
filter_upwards
refine le_indicator (fun t ht => ?_) fun t ht => ?_
· apply_rules [L.le_of_opNorm₂_le_of_le, le_rfl]
refine (le_ciSup_set hbg <| mem_preimage.mpr ?_)
rwa [neg_sub, sub_add_cancel]
· have : t ∉ support fun t => L (f t) (g (x₀ - t)) := mt (fun h => h2s h) ht
rw [nmem_support.mp this, norm_zero]
refine Integrable.mono' ?_ ?_ this
· rw [integrable_indicator_iff hs]; exact ((hf.norm.const_mul _).mul_const _).integrableOn
· exact hf.aestronglyMeasurable.convolution_integrand_snd' L hmg
/-- If `‖f‖ *[μ] ‖g‖` exists, then `f *[L, μ] g` exists. -/
theorem ConvolutionExistsAt.of_norm' {x₀ : G}
(h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ)
(hmf : AEStronglyMeasurable f μ) (hmg : AEStronglyMeasurable g <| map (fun t => x₀ - t) μ) :
ConvolutionExistsAt f g x₀ L μ := by
refine (h.const_mul ‖L‖).mono'
(hmf.convolution_integrand_snd' L hmg) (Eventually.of_forall fun x => ?_)
rw [mul_apply', ← mul_assoc]
apply L.le_opNorm₂
@[deprecated (since := "2025-02-07")]
alias ConvolutionExistsAt.ofNorm' := ConvolutionExistsAt.of_norm'
end
section Left
variable [MeasurableAdd₂ G] [MeasurableNeg G] [SFinite μ] [IsAddRightInvariant μ]
theorem AEStronglyMeasurable.convolution_integrand_snd (hf : AEStronglyMeasurable f μ)
(hg : AEStronglyMeasurable g μ) (x : G) :
AEStronglyMeasurable (fun t => L (f t) (g (x - t))) μ :=
hf.convolution_integrand_snd' L <|
hg.mono_ac <| (quasiMeasurePreserving_sub_left_of_right_invariant μ x).absolutelyContinuous
theorem AEStronglyMeasurable.convolution_integrand_swap_snd
(hf : AEStronglyMeasurable f μ) (hg : AEStronglyMeasurable g μ) (x : G) :
AEStronglyMeasurable (fun t => L (f (x - t)) (g t)) μ :=
(hf.mono_ac
(quasiMeasurePreserving_sub_left_of_right_invariant μ
x).absolutelyContinuous).convolution_integrand_swap_snd'
L hg
/-- If `‖f‖ *[μ] ‖g‖` exists, then `f *[L, μ] g` exists. -/
theorem ConvolutionExistsAt.of_norm {x₀ : G}
(h : ConvolutionExistsAt (fun x => ‖f x‖) (fun x => ‖g x‖) x₀ (mul ℝ ℝ) μ)
(hmf : AEStronglyMeasurable f μ) (hmg : AEStronglyMeasurable g μ) :
ConvolutionExistsAt f g x₀ L μ :=
h.of_norm' L hmf <|
hmg.mono_ac (quasiMeasurePreserving_sub_left_of_right_invariant μ x₀).absolutelyContinuous
@[deprecated (since := "2025-02-07")]
alias ConvolutionExistsAt.ofNorm := ConvolutionExistsAt.of_norm
end Left
section Right
variable [MeasurableAdd₂ G] [MeasurableNeg G] [SFinite μ] [IsAddRightInvariant μ] [SFinite ν]
theorem AEStronglyMeasurable.convolution_integrand (hf : AEStronglyMeasurable f ν)
(hg : AEStronglyMeasurable g μ) :
AEStronglyMeasurable (fun p : G × G => L (f p.2) (g (p.1 - p.2))) (μ.prod ν) :=
hf.convolution_integrand' L <|
hg.mono_ac (quasiMeasurePreserving_sub_of_right_invariant μ ν).absolutelyContinuous
theorem Integrable.convolution_integrand (hf : Integrable f ν) (hg : Integrable g μ) :
Integrable (fun p : G × G => L (f p.2) (g (p.1 - p.2))) (μ.prod ν) := by
have h_meas : AEStronglyMeasurable (fun p : G × G => L (f p.2) (g (p.1 - p.2))) (μ.prod ν) :=
hf.aestronglyMeasurable.convolution_integrand L hg.aestronglyMeasurable
have h2_meas : AEStronglyMeasurable (fun y : G => ∫ x : G, ‖L (f y) (g (x - y))‖ ∂μ) ν :=
h_meas.prod_swap.norm.integral_prod_right'
simp_rw [integrable_prod_iff' h_meas]
refine ⟨Eventually.of_forall fun t => (L (f t)).integrable_comp (hg.comp_sub_right t), ?_⟩
refine Integrable.mono' ?_ h2_meas
(Eventually.of_forall fun t => (?_ : _ ≤ ‖L‖ * ‖f t‖ * ∫ x, ‖g (x - t)‖ ∂μ))
· simp only [integral_sub_right_eq_self (‖g ·‖)]
exact (hf.norm.const_mul _).mul_const _
· simp_rw [← integral_const_mul]
rw [Real.norm_of_nonneg (by positivity)]
exact integral_mono_of_nonneg (Eventually.of_forall fun t => norm_nonneg _)
((hg.comp_sub_right t).norm.const_mul _) (Eventually.of_forall fun t => L.le_opNorm₂ _ _)
theorem Integrable.ae_convolution_exists (hf : Integrable f ν) (hg : Integrable g μ) :
∀ᵐ x ∂μ, ConvolutionExistsAt f g x L ν :=
((integrable_prod_iff <|
hf.aestronglyMeasurable.convolution_integrand L hg.aestronglyMeasurable).mp <|
hf.convolution_integrand L hg).1
end Right
variable [TopologicalSpace G] [IsTopologicalAddGroup G] [BorelSpace G]
theorem _root_.HasCompactSupport.convolutionExistsAt {x₀ : G}
(h : HasCompactSupport fun t => L (f t) (g (x₀ - t))) (hf : LocallyIntegrable f μ)
(hg : Continuous g) : ConvolutionExistsAt f g x₀ L μ := by
let u := (Homeomorph.neg G).trans (Homeomorph.addRight x₀)
let v := (Homeomorph.neg G).trans (Homeomorph.addLeft x₀)
apply ((u.isCompact_preimage.mpr h).bddAbove_image hg.norm.continuousOn).convolutionExistsAt' L
isClosed_closure.measurableSet subset_closure (hf.integrableOn_isCompact h)
have A : AEStronglyMeasurable (g ∘ v)
(μ.restrict (tsupport fun t : G => L (f t) (g (x₀ - t)))) := by
apply (hg.comp v.continuous).continuousOn.aestronglyMeasurable_of_isCompact h
exact (isClosed_tsupport _).measurableSet
convert ((v.continuous.measurable.measurePreserving
(μ.restrict (tsupport fun t => L (f t) (g (x₀ - t))))).aestronglyMeasurable_comp_iff
v.measurableEmbedding).1 A
ext x
simp only [v, Homeomorph.neg, sub_eq_add_neg, val_toAddUnits_apply, Homeomorph.trans_apply,
Equiv.neg_apply, Equiv.toFun_as_coe, Homeomorph.homeomorph_mk_coe, Equiv.coe_fn_mk,
Homeomorph.coe_addLeft]
theorem _root_.HasCompactSupport.convolutionExists_right (hcg : HasCompactSupport g)
(hf : LocallyIntegrable f μ) (hg : Continuous g) : ConvolutionExists f g L μ := by
intro x₀
refine HasCompactSupport.convolutionExistsAt L ?_ hf hg
refine (hcg.comp_homeomorph (Homeomorph.subLeft x₀)).mono ?_
refine fun t => mt fun ht : g (x₀ - t) = 0 => ?_
simp_rw [ht, (L _).map_zero]
theorem _root_.HasCompactSupport.convolutionExists_left_of_continuous_right
(hcf : HasCompactSupport f) (hf : LocallyIntegrable f μ) (hg : Continuous g) :
ConvolutionExists f g L μ := by
intro x₀
refine HasCompactSupport.convolutionExistsAt L ?_ hf hg
refine hcf.mono ?_
refine fun t => mt fun ht : f t = 0 => ?_
simp_rw [ht, L.map_zero₂]
end Group
section CommGroup
variable [AddCommGroup G]
section MeasurableGroup
variable [MeasurableNeg G] [IsAddLeftInvariant μ]
/-- A sufficient condition to prove that `f ⋆[L, μ] g` exists.
We assume that the integrand has compact support and `g` is bounded on this support (note that
both properties hold if `g` is continuous with compact support). We also require that `f` is
integrable on the support of the integrand, and that both functions are strongly measurable.
This is a variant of `BddAbove.convolutionExistsAt'` in an abelian group with a left-invariant
measure. This allows us to state the boundedness and measurability of `g` in a more natural way. -/
theorem _root_.BddAbove.convolutionExistsAt [MeasurableAdd₂ G] [SFinite μ] {x₀ : G} {s : Set G}
(hbg : BddAbove ((fun i => ‖g i‖) '' ((fun t => x₀ - t) ⁻¹' s))) (hs : MeasurableSet s)
(h2s : (support fun t => L (f t) (g (x₀ - t))) ⊆ s) (hf : IntegrableOn f s μ)
(hmg : AEStronglyMeasurable g μ) : ConvolutionExistsAt f g x₀ L μ := by
refine BddAbove.convolutionExistsAt' L ?_ hs h2s hf ?_
· simp_rw [← sub_eq_neg_add, hbg]
· have : AEStronglyMeasurable g (map (fun t : G => x₀ - t) μ) :=
hmg.mono_ac (quasiMeasurePreserving_sub_left_of_right_invariant μ x₀).absolutelyContinuous
apply this.mono_measure
exact map_mono restrict_le_self (measurable_const.sub measurable_id')
variable {L} [MeasurableAdd G] [IsNegInvariant μ]
theorem convolutionExistsAt_flip :
ConvolutionExistsAt g f x L.flip μ ↔ ConvolutionExistsAt f g x L μ := by
simp_rw [ConvolutionExistsAt, ← integrable_comp_sub_left (fun t => L (f t) (g (x - t))) x,
sub_sub_cancel, flip_apply]
theorem ConvolutionExistsAt.integrable_swap (h : ConvolutionExistsAt f g x L μ) :
Integrable (fun t => L (f (x - t)) (g t)) μ := by
convert h.comp_sub_left x
simp_rw [sub_sub_self]
theorem convolutionExistsAt_iff_integrable_swap :
ConvolutionExistsAt f g x L μ ↔ Integrable (fun t => L (f (x - t)) (g t)) μ :=
convolutionExistsAt_flip.symm
end MeasurableGroup
variable [TopologicalSpace G] [IsTopologicalAddGroup G] [BorelSpace G]
variable [IsAddLeftInvariant μ] [IsNegInvariant μ]
theorem _root_.HasCompactSupport.convolutionExists_left
(hcf : HasCompactSupport f) (hf : Continuous f)
(hg : LocallyIntegrable g μ) : ConvolutionExists f g L μ := fun x₀ =>
convolutionExistsAt_flip.mp <| hcf.convolutionExists_right L.flip hg hf x₀
@[deprecated (since := "2025-02-06")]
alias _root_.HasCompactSupport.convolutionExistsLeft := HasCompactSupport.convolutionExists_left
theorem _root_.HasCompactSupport.convolutionExists_right_of_continuous_left
(hcg : HasCompactSupport g) (hf : Continuous f) (hg : LocallyIntegrable g μ) :
ConvolutionExists f g L μ := fun x₀ =>
convolutionExistsAt_flip.mp <| hcg.convolutionExists_left_of_continuous_right L.flip hg hf x₀
@[deprecated (since := "2025-02-06")]
alias _root_.HasCompactSupport.convolutionExistsRightOfContinuousLeft :=
HasCompactSupport.convolutionExists_right_of_continuous_left
end CommGroup
end ConvolutionExists
variable [NormedSpace ℝ F]
/-- The convolution of two functions `f` and `g` with respect to a continuous bilinear map `L` and
measure `μ`. It is defined to be `(f ⋆[L, μ] g) x = ∫ t, L (f t) (g (x - t)) ∂μ`. -/
noncomputable def convolution [Sub G] (f : G → E) (g : G → E') (L : E →L[𝕜] E' →L[𝕜] F)
(μ : Measure G := by volume_tac) : G → F := fun x =>
∫ t, L (f t) (g (x - t)) ∂μ
/-- The convolution of two functions with respect to a bilinear operation `L` and a measure `μ`. -/
scoped[Convolution] notation:67 f " ⋆[" L:67 ", " μ:67 "] " g:66 => convolution f g L μ
/-- The convolution of two functions with respect to a bilinear operation `L` and the volume. -/
scoped[Convolution]
notation:67 f " ⋆[" L:67 "]" g:66 => convolution f g L MeasureSpace.volume
/-- The convolution of two real-valued functions with respect to volume. -/
scoped[Convolution]
notation:67 f " ⋆ " g:66 =>
convolution f g (ContinuousLinearMap.lsmul ℝ ℝ) MeasureSpace.volume
open scoped Convolution
theorem convolution_def [Sub G] : (f ⋆[L, μ] g) x = ∫ t, L (f t) (g (x - t)) ∂μ :=
rfl
/-- The definition of convolution where the bilinear operator is scalar multiplication.
Note: it often helps the elaborator to give the type of the convolution explicitly. -/
theorem convolution_lsmul [Sub G] {f : G → 𝕜} {g : G → F} :
(f ⋆[lsmul 𝕜 𝕜, μ] g : G → F) x = ∫ t, f t • g (x - t) ∂μ :=
rfl
/-- The definition of convolution where the bilinear operator is multiplication. -/
theorem convolution_mul [Sub G] [NormedSpace ℝ 𝕜] {f : G → 𝕜} {g : G → 𝕜} :
(f ⋆[mul 𝕜 𝕜, μ] g) x = ∫ t, f t * g (x - t) ∂μ :=
rfl
section Group
variable {L} [AddGroup G]
theorem smul_convolution [SMulCommClass ℝ 𝕜 F] {y : 𝕜} : y • f ⋆[L, μ] g = y • (f ⋆[L, μ] g) := by
ext; simp only [Pi.smul_apply, convolution_def, ← integral_smul, L.map_smul₂]
theorem convolution_smul [SMulCommClass ℝ 𝕜 F] {y : 𝕜} : f ⋆[L, μ] y • g = y • (f ⋆[L, μ] g) := by
ext; simp only [Pi.smul_apply, convolution_def, ← integral_smul, (L _).map_smul]
@[simp]
theorem zero_convolution : 0 ⋆[L, μ] g = 0 := by
ext
simp_rw [convolution_def, Pi.zero_apply, L.map_zero₂, integral_zero]
@[simp]
theorem convolution_zero : f ⋆[L, μ] 0 = 0 := by
ext
simp_rw [convolution_def, Pi.zero_apply, (L _).map_zero, integral_zero]
theorem ConvolutionExistsAt.distrib_add {x : G} (hfg : ConvolutionExistsAt f g x L μ)
(hfg' : ConvolutionExistsAt f g' x L μ) :
(f ⋆[L, μ] (g + g')) x = (f ⋆[L, μ] g) x + (f ⋆[L, μ] g') x := by
simp only [convolution_def, (L _).map_add, Pi.add_apply, integral_add hfg hfg']
theorem ConvolutionExists.distrib_add (hfg : ConvolutionExists f g L μ)
(hfg' : ConvolutionExists f g' L μ) : f ⋆[L, μ] (g + g') = f ⋆[L, μ] g + f ⋆[L, μ] g' := by
ext x
exact (hfg x).distrib_add (hfg' x)
theorem ConvolutionExistsAt.add_distrib {x : G} (hfg : ConvolutionExistsAt f g x L μ)
(hfg' : ConvolutionExistsAt f' g x L μ) :
((f + f') ⋆[L, μ] g) x = (f ⋆[L, μ] g) x + (f' ⋆[L, μ] g) x := by
simp only [convolution_def, L.map_add₂, Pi.add_apply, integral_add hfg hfg']
theorem ConvolutionExists.add_distrib (hfg : ConvolutionExists f g L μ)
(hfg' : ConvolutionExists f' g L μ) : (f + f') ⋆[L, μ] g = f ⋆[L, μ] g + f' ⋆[L, μ] g := by
ext x
exact (hfg x).add_distrib (hfg' x)
theorem convolution_mono_right {f g g' : G → ℝ} (hfg : ConvolutionExistsAt f g x (lsmul ℝ ℝ) μ)
(hfg' : ConvolutionExistsAt f g' x (lsmul ℝ ℝ) μ) (hf : ∀ x, 0 ≤ f x) (hg : ∀ x, g x ≤ g' x) :
(f ⋆[lsmul ℝ ℝ, μ] g) x ≤ (f ⋆[lsmul ℝ ℝ, μ] g') x := by
apply integral_mono hfg hfg'
simp only [lsmul_apply, Algebra.id.smul_eq_mul]
intro t
apply mul_le_mul_of_nonneg_left (hg _) (hf _)
theorem convolution_mono_right_of_nonneg {f g g' : G → ℝ}
(hfg' : ConvolutionExistsAt f g' x (lsmul ℝ ℝ) μ) (hf : ∀ x, 0 ≤ f x) (hg : ∀ x, g x ≤ g' x)
(hg' : ∀ x, 0 ≤ g' x) : (f ⋆[lsmul ℝ ℝ, μ] g) x ≤ (f ⋆[lsmul ℝ ℝ, μ] g') x := by
by_cases H : ConvolutionExistsAt f g x (lsmul ℝ ℝ) μ
· exact convolution_mono_right H hfg' hf hg
have : (f ⋆[lsmul ℝ ℝ, μ] g) x = 0 := integral_undef H
rw [this]
exact integral_nonneg fun y => mul_nonneg (hf y) (hg' (x - y))
variable (L)
theorem convolution_congr [MeasurableAdd₂ G] [MeasurableNeg G] [SFinite μ]
[IsAddRightInvariant μ] (h1 : f =ᵐ[μ] f') (h2 : g =ᵐ[μ] g') : f ⋆[L, μ] g = f' ⋆[L, μ] g' := by
ext x
apply integral_congr_ae
exact (h1.prodMk <| h2.comp_tendsto
(quasiMeasurePreserving_sub_left_of_right_invariant μ x).tendsto_ae).fun_comp ↿fun x y ↦ L x y
theorem support_convolution_subset_swap : support (f ⋆[L, μ] g) ⊆ support g + support f := by
intro x h2x
by_contra hx
apply h2x
simp_rw [Set.mem_add, ← exists_and_left, not_exists, not_and_or, nmem_support] at hx
rw [convolution_def]
convert integral_zero G F using 2
ext t
rcases hx (x - t) t with (h | h | h)
· rw [h, (L _).map_zero]
· rw [h, L.map_zero₂]
· exact (h <| sub_add_cancel x t).elim
section
variable [MeasurableAdd₂ G] [MeasurableNeg G] [SFinite μ] [IsAddRightInvariant μ]
theorem Integrable.integrable_convolution (hf : Integrable f μ)
(hg : Integrable g μ) : Integrable (f ⋆[L, μ] g) μ :=
(hf.convolution_integrand L hg).integral_prod_left
end
variable [TopologicalSpace G]
variable [IsTopologicalAddGroup G]
protected theorem _root_.HasCompactSupport.convolution [T2Space G] (hcf : HasCompactSupport f)
(hcg : HasCompactSupport g) : HasCompactSupport (f ⋆[L, μ] g) :=
(hcg.isCompact.add hcf).of_isClosed_subset isClosed_closure <|
closure_minimal
((support_convolution_subset_swap L).trans <| add_subset_add subset_closure subset_closure)
(hcg.isCompact.add hcf).isClosed
variable [BorelSpace G] [TopologicalSpace P]
/-- The convolution `f * g` is continuous if `f` is locally integrable and `g` is continuous and
compactly supported. Version where `g` depends on an additional parameter in a subset `s` of
a parameter space `P` (and the compact support `k` is independent of the parameter in `s`). -/
theorem continuousOn_convolution_right_with_param {g : P → G → E'} {s : Set P} {k : Set G}
(hk : IsCompact k) (hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0)
(hf : LocallyIntegrable f μ) (hg : ContinuousOn (↿g) (s ×ˢ univ)) :
ContinuousOn (fun q : P × G => (f ⋆[L, μ] g q.1) q.2) (s ×ˢ univ) := by
/- First get rid of the case where the space is not locally compact. Then `g` vanishes everywhere
and the conclusion is trivial. -/
by_cases H : ∀ p ∈ s, ∀ x, g p x = 0
· apply (continuousOn_const (c := 0)).congr
rintro ⟨p, x⟩ ⟨hp, -⟩
apply integral_eq_zero_of_ae (Eventually.of_forall (fun y ↦ ?_))
simp [H p hp _]
have : LocallyCompactSpace G := by
push_neg at H
rcases H with ⟨p, hp, x, hx⟩
have A : support (g p) ⊆ k := support_subset_iff'.2 (fun y hy ↦ hgs p y hp hy)
have B : Continuous (g p) := by
refine hg.comp_continuous (.prodMk_right _) fun x => ?_
simpa only [prodMk_mem_set_prod_eq, mem_univ, and_true] using hp
rcases eq_zero_or_locallyCompactSpace_of_support_subset_isCompact_of_addGroup hk A B with H|H
· simp [H] at hx
· exact H
/- Since `G` is locally compact, one may thicken `k` a little bit into a larger compact set
`(-k) + t`, outside of which all functions that appear in the convolution vanish. Then we can
apply a continuity statement for integrals depending on a parameter, with respect to
locally integrable functions and compactly supported continuous functions. -/
rintro ⟨q₀, x₀⟩ ⟨hq₀, -⟩
obtain ⟨t, t_comp, ht⟩ : ∃ t, IsCompact t ∧ t ∈ 𝓝 x₀ := exists_compact_mem_nhds x₀
let k' : Set G := (-k) +ᵥ t
have k'_comp : IsCompact k' := IsCompact.vadd_set hk.neg t_comp
let g' : (P × G) → G → E' := fun p x ↦ g p.1 (p.2 - x)
let s' : Set (P × G) := s ×ˢ t
have A : ContinuousOn g'.uncurry (s' ×ˢ univ) := by
have : g'.uncurry = g.uncurry ∘ (fun w ↦ (w.1.1, w.1.2 - w.2)) := by ext y; rfl
rw [this]
refine hg.comp (by fun_prop) ?_
simp +contextual [s', MapsTo]
have B : ContinuousOn (fun a ↦ ∫ x, L (f x) (g' a x) ∂μ) s' := by
apply continuousOn_integral_bilinear_of_locally_integrable_of_compact_support L k'_comp A _
(hf.integrableOn_isCompact k'_comp)
rintro ⟨p, x⟩ y ⟨hp, hx⟩ hy
apply hgs p _ hp
contrapose! hy
exact ⟨y - x, by simpa using hy, x, hx, by simp⟩
apply ContinuousWithinAt.mono_of_mem_nhdsWithin (B (q₀, x₀) ⟨hq₀, mem_of_mem_nhds ht⟩)
exact mem_nhdsWithin_prod_iff.2 ⟨s, self_mem_nhdsWithin, t, nhdsWithin_le_nhds ht, Subset.rfl⟩
/-- The convolution `f * g` is continuous if `f` is locally integrable and `g` is continuous and
compactly supported. Version where `g` depends on an additional parameter in an open subset `s` of
a parameter space `P` (and the compact support `k` is independent of the parameter in `s`),
given in terms of compositions with an additional continuous map. -/
theorem continuousOn_convolution_right_with_param_comp {s : Set P} {v : P → G}
(hv : ContinuousOn v s) {g : P → G → E'} {k : Set G} (hk : IsCompact k)
(hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0) (hf : LocallyIntegrable f μ)
(hg : ContinuousOn (↿g) (s ×ˢ univ)) : ContinuousOn (fun x => (f ⋆[L, μ] g x) (v x)) s := by
apply
(continuousOn_convolution_right_with_param L hk hgs hf hg).comp (continuousOn_id.prodMk hv)
intro x hx
simp only [hx, prodMk_mem_set_prod_eq, mem_univ, and_self_iff, _root_.id]
/-- The convolution is continuous if one function is locally integrable and the other has compact
support and is continuous. -/
theorem _root_.HasCompactSupport.continuous_convolution_right (hcg : HasCompactSupport g)
(hf : LocallyIntegrable f μ) (hg : Continuous g) : Continuous (f ⋆[L, μ] g) := by
rw [continuous_iff_continuousOn_univ]
let g' : G → G → E' := fun _ q => g q
have : ContinuousOn (↿g') (univ ×ˢ univ) := (hg.comp continuous_snd).continuousOn
exact continuousOn_convolution_right_with_param_comp L
(continuous_iff_continuousOn_univ.1 continuous_id) hcg
(fun p x _ hx => image_eq_zero_of_nmem_tsupport hx) hf this
/-- The convolution is continuous if one function is integrable and the other is bounded and
continuous. -/
theorem _root_.BddAbove.continuous_convolution_right_of_integrable
[FirstCountableTopology G] [SecondCountableTopologyEither G E']
(hbg : BddAbove (range fun x => ‖g x‖)) (hf : Integrable f μ) (hg : Continuous g) :
Continuous (f ⋆[L, μ] g) := by
refine continuous_iff_continuousAt.mpr fun x₀ => ?_
have : ∀ᶠ x in 𝓝 x₀, ∀ᵐ t : G ∂μ, ‖L (f t) (g (x - t))‖ ≤ ‖L‖ * ‖f t‖ * ⨆ i, ‖g i‖ := by
filter_upwards with x; filter_upwards with t
apply_rules [L.le_of_opNorm₂_le_of_le, le_rfl, le_ciSup hbg (x - t)]
refine continuousAt_of_dominated ?_ this ?_ ?_
· exact Eventually.of_forall fun x =>
hf.aestronglyMeasurable.convolution_integrand_snd' L hg.aestronglyMeasurable
· exact (hf.norm.const_mul _).mul_const _
· exact Eventually.of_forall fun t => (L.continuous₂.comp₂ continuous_const <|
hg.comp <| continuous_id.sub continuous_const).continuousAt
end Group
section CommGroup
variable [AddCommGroup G]
theorem support_convolution_subset : support (f ⋆[L, μ] g) ⊆ support f + support g :=
(support_convolution_subset_swap L).trans (add_comm _ _).subset
variable [IsAddLeftInvariant μ] [IsNegInvariant μ]
section Measurable
variable [MeasurableNeg G]
variable [MeasurableAdd G]
/-- Commutativity of convolution -/
theorem convolution_flip : g ⋆[L.flip, μ] f = f ⋆[L, μ] g := by
ext1 x
simp_rw [convolution_def]
rw [← integral_sub_left_eq_self _ μ x]
simp_rw [sub_sub_self, flip_apply]
/-- The symmetric definition of convolution. -/
theorem convolution_eq_swap : (f ⋆[L, μ] g) x = ∫ t, L (f (x - t)) (g t) ∂μ := by
rw [← convolution_flip]; rfl
/-- The symmetric definition of convolution where the bilinear operator is scalar multiplication. -/
theorem convolution_lsmul_swap {f : G → 𝕜} {g : G → F} :
(f ⋆[lsmul 𝕜 𝕜, μ] g : G → F) x = ∫ t, f (x - t) • g t ∂μ :=
convolution_eq_swap _
/-- The symmetric definition of convolution where the bilinear operator is multiplication. -/
theorem convolution_mul_swap [NormedSpace ℝ 𝕜] {f : G → 𝕜} {g : G → 𝕜} :
(f ⋆[mul 𝕜 𝕜, μ] g) x = ∫ t, f (x - t) * g t ∂μ :=
convolution_eq_swap _
/-- The convolution of two even functions is also even. -/
theorem convolution_neg_of_neg_eq (h1 : ∀ᵐ x ∂μ, f (-x) = f x) (h2 : ∀ᵐ x ∂μ, g (-x) = g x) :
(f ⋆[L, μ] g) (-x) = (f ⋆[L, μ] g) x :=
calc
∫ t : G, (L (f t)) (g (-x - t)) ∂μ = ∫ t : G, (L (f (-t))) (g (x + t)) ∂μ := by
apply integral_congr_ae
filter_upwards [h1, (eventually_add_left_iff μ x).2 h2] with t ht h't
simp_rw [ht, ← h't, neg_add']
_ = ∫ t : G, (L (f t)) (g (x - t)) ∂μ := by
rw [← integral_neg_eq_self]
simp only [neg_neg, ← sub_eq_add_neg]
end Measurable
variable [TopologicalSpace G]
variable [IsTopologicalAddGroup G]
variable [BorelSpace G]
theorem _root_.HasCompactSupport.continuous_convolution_left
(hcf : HasCompactSupport f) (hf : Continuous f) (hg : LocallyIntegrable g μ) :
Continuous (f ⋆[L, μ] g) := by
rw [← convolution_flip]
exact hcf.continuous_convolution_right L.flip hg hf
theorem _root_.BddAbove.continuous_convolution_left_of_integrable
[FirstCountableTopology G] [SecondCountableTopologyEither G E]
(hbf : BddAbove (range fun x => ‖f x‖)) (hf : Continuous f) (hg : Integrable g μ) :
Continuous (f ⋆[L, μ] g) := by
rw [← convolution_flip]
exact hbf.continuous_convolution_right_of_integrable L.flip hg hf
end CommGroup
section NormedAddCommGroup
variable [SeminormedAddCommGroup G]
/-- Compute `(f ⋆ g) x₀` if the support of the `f` is within `Metric.ball 0 R`, and `g` is constant
on `Metric.ball x₀ R`.
We can simplify the RHS further if we assume `f` is integrable, but also if `L = (•)` or more
generally if `L` has an `AntilipschitzWith`-condition. -/
theorem convolution_eq_right' {x₀ : G} {R : ℝ} (hf : support f ⊆ ball (0 : G) R)
(hg : ∀ x ∈ ball x₀ R, g x = g x₀) : (f ⋆[L, μ] g) x₀ = ∫ t, L (f t) (g x₀) ∂μ := by
have h2 : ∀ t, L (f t) (g (x₀ - t)) = L (f t) (g x₀) := fun t ↦ by
by_cases ht : t ∈ support f
· have h2t := hf ht
rw [mem_ball_zero_iff] at h2t
specialize hg (x₀ - t)
rw [sub_eq_add_neg, add_mem_ball_iff_norm, norm_neg, ← sub_eq_add_neg] at hg
rw [hg h2t]
· rw [nmem_support] at ht
simp_rw [ht, L.map_zero₂]
simp_rw [convolution_def, h2]
variable [BorelSpace G] [SecondCountableTopology G]
variable [IsAddLeftInvariant μ] [SFinite μ]
/-- Approximate `(f ⋆ g) x₀` if the support of the `f` is bounded within a ball, and `g` is near
`g x₀` on a ball with the same radius around `x₀`. See `dist_convolution_le` for a special case.
We can simplify the second argument of `dist` further if we add some extra type-classes on `E`
and `𝕜` or if `L` is scalar multiplication. -/
theorem dist_convolution_le' {x₀ : G} {R ε : ℝ} {z₀ : E'} (hε : 0 ≤ ε) (hif : Integrable f μ)
(hf : support f ⊆ ball (0 : G) R) (hmg : AEStronglyMeasurable g μ)
(hg : ∀ x ∈ ball x₀ R, dist (g x) z₀ ≤ ε) :
dist ((f ⋆[L, μ] g : G → F) x₀) (∫ t, L (f t) z₀ ∂μ) ≤ (‖L‖ * ∫ x, ‖f x‖ ∂μ) * ε := by
have hfg : ConvolutionExistsAt f g x₀ L μ := by
refine BddAbove.convolutionExistsAt L ?_ Metric.isOpen_ball.measurableSet (Subset.trans ?_ hf)
hif.integrableOn hmg
swap; · refine fun t => mt fun ht : f t = 0 => ?_; simp_rw [ht, L.map_zero₂]
rw [bddAbove_def]
refine ⟨‖z₀‖ + ε, ?_⟩
rintro _ ⟨x, hx, rfl⟩
refine norm_le_norm_add_const_of_dist_le (hg x ?_)
rwa [mem_ball_iff_norm, norm_sub_rev, ← mem_ball_zero_iff]
have h2 : ∀ t, dist (L (f t) (g (x₀ - t))) (L (f t) z₀) ≤ ‖L (f t)‖ * ε := by
intro t; by_cases ht : t ∈ support f
· have h2t := hf ht
rw [mem_ball_zero_iff] at h2t
specialize hg (x₀ - t)
rw [sub_eq_add_neg, add_mem_ball_iff_norm, norm_neg, ← sub_eq_add_neg] at hg
refine ((L (f t)).dist_le_opNorm _ _).trans ?_
exact mul_le_mul_of_nonneg_left (hg h2t) (norm_nonneg _)
· rw [nmem_support] at ht
simp_rw [ht, L.map_zero₂, L.map_zero, norm_zero, zero_mul, dist_self]
rfl
simp_rw [convolution_def]
simp_rw [dist_eq_norm] at h2 ⊢
rw [← integral_sub hfg.integrable]; swap; · exact (L.flip z₀).integrable_comp hif
refine (norm_integral_le_of_norm_le ((L.integrable_comp hif).norm.mul_const ε)
(Eventually.of_forall h2)).trans ?_
rw [integral_mul_const]
refine mul_le_mul_of_nonneg_right ?_ hε
have h3 : ∀ t, ‖L (f t)‖ ≤ ‖L‖ * ‖f t‖ := by
intro t
exact L.le_opNorm (f t)
refine (integral_mono (L.integrable_comp hif).norm (hif.norm.const_mul _) h3).trans_eq ?_
rw [integral_const_mul]
variable [NormedSpace ℝ E] [NormedSpace ℝ E'] [CompleteSpace E']
/-- Approximate `f ⋆ g` if the support of the `f` is bounded within a ball, and `g` is near `g x₀`
on a ball with the same radius around `x₀`.
This is a special case of `dist_convolution_le'` where `L` is `(•)`, `f` has integral 1 and `f` is
nonnegative. -/
theorem dist_convolution_le {f : G → ℝ} {x₀ : G} {R ε : ℝ} {z₀ : E'} (hε : 0 ≤ ε)
(hf : support f ⊆ ball (0 : G) R) (hnf : ∀ x, 0 ≤ f x) (hintf : ∫ x, f x ∂μ = 1)
(hmg : AEStronglyMeasurable g μ) (hg : ∀ x ∈ ball x₀ R, dist (g x) z₀ ≤ ε) :
dist ((f ⋆[lsmul ℝ ℝ, μ] g : G → E') x₀) z₀ ≤ ε := by
have hif : Integrable f μ := integrable_of_integral_eq_one hintf
convert (dist_convolution_le' (lsmul ℝ ℝ) hε hif hf hmg hg).trans _
· simp_rw [lsmul_apply, integral_smul_const, hintf, one_smul]
· simp_rw [Real.norm_of_nonneg (hnf _), hintf, mul_one]
exact (mul_le_mul_of_nonneg_right opNorm_lsmul_le hε).trans_eq (one_mul ε)
/-- `(φ i ⋆ g i) (k i)` tends to `z₀` as `i` tends to some filter `l` if
* `φ` is a sequence of nonnegative functions with integral `1` as `i` tends to `l`;
* The support of `φ` tends to small neighborhoods around `(0 : G)` as `i` tends to `l`;
* `g i` is `mu`-a.e. strongly measurable as `i` tends to `l`;
* `g i x` tends to `z₀` as `(i, x)` tends to `l ×ˢ 𝓝 x₀`;
* `k i` tends to `x₀`.
See also `ContDiffBump.convolution_tendsto_right`.
-/
theorem convolution_tendsto_right {ι} {g : ι → G → E'} {l : Filter ι} {x₀ : G} {z₀ : E'}
{φ : ι → G → ℝ} {k : ι → G} (hnφ : ∀ᶠ i in l, ∀ x, 0 ≤ φ i x)
(hiφ : ∀ᶠ i in l, ∫ x, φ i x ∂μ = 1)
-- todo: we could weaken this to "the integral tends to 1"
(hφ : Tendsto (fun n => support (φ n)) l (𝓝 0).smallSets)
(hmg : ∀ᶠ i in l, AEStronglyMeasurable (g i) μ) (hcg : Tendsto (uncurry g) (l ×ˢ 𝓝 x₀) (𝓝 z₀))
(hk : Tendsto k l (𝓝 x₀)) :
Tendsto (fun i : ι => (φ i ⋆[lsmul ℝ ℝ, μ] g i : G → E') (k i)) l (𝓝 z₀) := by
simp_rw [tendsto_smallSets_iff] at hφ
rw [Metric.tendsto_nhds] at hcg ⊢
simp_rw [Metric.eventually_prod_nhds_iff] at hcg
intro ε hε
have h2ε : 0 < ε / 3 := div_pos hε (by norm_num)
obtain ⟨p, hp, δ, hδ, hgδ⟩ := hcg _ h2ε
dsimp only [uncurry] at hgδ
have h2k := hk.eventually (ball_mem_nhds x₀ <| half_pos hδ)
have h2φ := hφ (ball (0 : G) _) <| ball_mem_nhds _ (half_pos hδ)
filter_upwards [hp, h2k, h2φ, hnφ, hiφ, hmg] with i hpi hki hφi hnφi hiφi hmgi
have hgi : dist (g i (k i)) z₀ < ε / 3 := hgδ hpi (hki.trans <| half_lt_self hδ)
have h1 : ∀ x' ∈ ball (k i) (δ / 2), dist (g i x') (g i (k i)) ≤ ε / 3 + ε / 3 := by
intro x' hx'
refine (dist_triangle_right _ _ _).trans (add_le_add (hgδ hpi ?_).le hgi.le)
exact ((dist_triangle _ _ _).trans_lt (add_lt_add hx'.out hki)).trans_eq (add_halves δ)
have := dist_convolution_le (add_pos h2ε h2ε).le hφi hnφi hiφi hmgi h1
refine ((dist_triangle _ _ _).trans_lt (add_lt_add_of_le_of_lt this hgi)).trans_eq ?_
field_simp; ring_nf
end NormedAddCommGroup
end Measurability
end NontriviallyNormedField
open scoped Convolution
section RCLike
variable [RCLike 𝕜]
variable [NormedSpace 𝕜 E]
variable [NormedSpace 𝕜 E']
variable [NormedSpace 𝕜 E'']
variable [NormedSpace ℝ F] [NormedSpace 𝕜 F]
variable {n : ℕ∞}
variable [MeasurableSpace G] {μ ν : Measure G}
variable (L : E →L[𝕜] E' →L[𝕜] F)
section Assoc
variable [CompleteSpace F]
variable [NormedAddCommGroup F'] [NormedSpace ℝ F'] [NormedSpace 𝕜 F'] [CompleteSpace F']
variable [NormedAddCommGroup F''] [NormedSpace ℝ F''] [NormedSpace 𝕜 F''] [CompleteSpace F'']
variable {k : G → E''}
variable (L₂ : F →L[𝕜] E'' →L[𝕜] F')
variable (L₃ : E →L[𝕜] F'' →L[𝕜] F')
variable (L₄ : E' →L[𝕜] E'' →L[𝕜] F'')
variable [AddGroup G]
variable [SFinite μ] [SFinite ν] [IsAddRightInvariant μ]
theorem integral_convolution [MeasurableAdd₂ G] [MeasurableNeg G] [NormedSpace ℝ E]
[NormedSpace ℝ E'] [CompleteSpace E] [CompleteSpace E'] (hf : Integrable f ν)
(hg : Integrable g μ) : ∫ x, (f ⋆[L, ν] g) x ∂μ = L (∫ x, f x ∂ν) (∫ x, g x ∂μ) := by
refine (integral_integral_swap (by apply hf.convolution_integrand L hg)).trans ?_
simp_rw [integral_comp_comm _ (hg.comp_sub_right _), integral_sub_right_eq_self]
exact (L.flip (∫ x, g x ∂μ)).integral_comp_comm hf
variable [MeasurableAdd₂ G] [IsAddRightInvariant ν] [MeasurableNeg G]
/-- Convolution is associative. This has a weak but inconvenient integrability condition.
See also `MeasureTheory.convolution_assoc`. -/
theorem convolution_assoc' (hL : ∀ (x : E) (y : E') (z : E''), L₂ (L x y) z = L₃ x (L₄ y z))
{x₀ : G} (hfg : ∀ᵐ y ∂μ, ConvolutionExistsAt f g y L ν)
(hgk : ∀ᵐ x ∂ν, ConvolutionExistsAt g k x L₄ μ)
(hi : Integrable (uncurry fun x y => (L₃ (f y)) ((L₄ (g (x - y))) (k (x₀ - x)))) (μ.prod ν)) :
((f ⋆[L, ν] g) ⋆[L₂, μ] k) x₀ = (f ⋆[L₃, ν] g ⋆[L₄, μ] k) x₀ :=
calc
((f ⋆[L, ν] g) ⋆[L₂, μ] k) x₀ = ∫ t, L₂ (∫ s, L (f s) (g (t - s)) ∂ν) (k (x₀ - t)) ∂μ := rfl
_ = ∫ t, ∫ s, L₂ (L (f s) (g (t - s))) (k (x₀ - t)) ∂ν ∂μ :=
(integral_congr_ae (hfg.mono fun t ht => ((L₂.flip (k (x₀ - t))).integral_comp_comm ht).symm))
_ = ∫ t, ∫ s, L₃ (f s) (L₄ (g (t - s)) (k (x₀ - t))) ∂ν ∂μ := by simp_rw [hL]
_ = ∫ s, ∫ t, L₃ (f s) (L₄ (g (t - s)) (k (x₀ - t))) ∂μ ∂ν := by rw [integral_integral_swap hi]
_ = ∫ s, ∫ u, L₃ (f s) (L₄ (g u) (k (x₀ - s - u))) ∂μ ∂ν := by
congr; ext t
rw [eq_comm, ← integral_sub_right_eq_self _ t]
simp_rw [sub_sub_sub_cancel_right]
_ = ∫ s, L₃ (f s) (∫ u, L₄ (g u) (k (x₀ - s - u)) ∂μ) ∂ν := by
refine integral_congr_ae ?_
refine ((quasiMeasurePreserving_sub_left_of_right_invariant ν x₀).ae hgk).mono fun t ht => ?_
exact (L₃ (f t)).integral_comp_comm ht
_ = (f ⋆[L₃, ν] g ⋆[L₄, μ] k) x₀ := rfl
/-- Convolution is associative. This requires that
* all maps are a.e. strongly measurable w.r.t one of the measures
* `f ⋆[L, ν] g` exists almost everywhere
* `‖g‖ ⋆[μ] ‖k‖` exists almost everywhere
* `‖f‖ ⋆[ν] (‖g‖ ⋆[μ] ‖k‖)` exists at `x₀` -/
theorem convolution_assoc (hL : ∀ (x : E) (y : E') (z : E''), L₂ (L x y) z = L₃ x (L₄ y z)) {x₀ : G}
(hf : AEStronglyMeasurable f ν) (hg : AEStronglyMeasurable g μ) (hk : AEStronglyMeasurable k μ)
(hfg : ∀ᵐ y ∂μ, ConvolutionExistsAt f g y L ν)
(hgk : ∀ᵐ x ∂ν, ConvolutionExistsAt (fun x => ‖g x‖) (fun x => ‖k x‖) x (mul ℝ ℝ) μ)
(hfgk :
ConvolutionExistsAt (fun x => ‖f x‖) ((fun x => ‖g x‖) ⋆[mul ℝ ℝ, μ] fun x => ‖k x‖) x₀
(mul ℝ ℝ) ν) :
((f ⋆[L, ν] g) ⋆[L₂, μ] k) x₀ = (f ⋆[L₃, ν] g ⋆[L₄, μ] k) x₀ := by
refine convolution_assoc' L L₂ L₃ L₄ hL hfg (hgk.mono fun x hx => hx.of_norm L₄ hg hk) ?_
-- the following is similar to `Integrable.convolution_integrand`
have h_meas :
AEStronglyMeasurable (uncurry fun x y => L₃ (f y) (L₄ (g x) (k (x₀ - y - x))))
(μ.prod ν) := by
refine L₃.aestronglyMeasurable_comp₂ hf.snd ?_
refine L₄.aestronglyMeasurable_comp₂ hg.fst ?_
refine (hk.mono_ac ?_).comp_measurable
((measurable_const.sub measurable_snd).sub measurable_fst)
refine QuasiMeasurePreserving.absolutelyContinuous ?_
refine QuasiMeasurePreserving.prod_of_left
((measurable_const.sub measurable_snd).sub measurable_fst) (Eventually.of_forall fun y => ?_)
dsimp only
exact quasiMeasurePreserving_sub_left_of_right_invariant μ _
have h2_meas :
AEStronglyMeasurable (fun y => ∫ x, ‖L₃ (f y) (L₄ (g x) (k (x₀ - y - x)))‖ ∂μ) ν :=
h_meas.prod_swap.norm.integral_prod_right'
have h3 : map (fun z : G × G => (z.1 - z.2, z.2)) (μ.prod ν) = μ.prod ν :=
(measurePreserving_sub_prod μ ν).map_eq
suffices Integrable (uncurry fun x y => L₃ (f y) (L₄ (g x) (k (x₀ - y - x)))) (μ.prod ν) by
rw [← h3] at this
convert this.comp_measurable (measurable_sub.prodMk measurable_snd)
ext ⟨x, y⟩
simp +unfoldPartialApp only [uncurry, Function.comp_apply,
sub_sub_sub_cancel_right]
simp_rw [integrable_prod_iff' h_meas]
refine ⟨((quasiMeasurePreserving_sub_left_of_right_invariant ν x₀).ae hgk).mono fun t ht =>
(L₃ (f t)).integrable_comp <| ht.of_norm L₄ hg hk, ?_⟩
refine (hfgk.const_mul (‖L₃‖ * ‖L₄‖)).mono' h2_meas
(((quasiMeasurePreserving_sub_left_of_right_invariant ν x₀).ae hgk).mono fun t ht => ?_)
simp_rw [convolution_def, mul_apply', mul_mul_mul_comm ‖L₃‖ ‖L₄‖, ← integral_const_mul]
rw [Real.norm_of_nonneg (by positivity)]
refine integral_mono_of_nonneg (Eventually.of_forall fun t => norm_nonneg _)
((ht.const_mul _).const_mul _) (Eventually.of_forall fun s => ?_)
simp only [← mul_assoc ‖L₄‖]
apply_rules [ContinuousLinearMap.le_of_opNorm₂_le_of_le, le_rfl]
end Assoc
variable [NormedAddCommGroup G] [BorelSpace G]
theorem convolution_precompR_apply {g : G → E'' →L[𝕜] E'} (hf : LocallyIntegrable f μ)
(hcg : HasCompactSupport g) (hg : Continuous g) (x₀ : G) (x : E'') :
(f ⋆[L.precompR E'', μ] g) x₀ x = (f ⋆[L, μ] fun a => g a x) x₀ := by
have := hcg.convolutionExists_right (L.precompR E'' :) hf hg x₀
simp_rw [convolution_def, ContinuousLinearMap.integral_apply this]
rfl
variable [NormedSpace 𝕜 G] [SFinite μ] [IsAddLeftInvariant μ]
/-- Compute the total derivative of `f ⋆ g` if `g` is `C^1` with compact support and `f` is locally
integrable. To write down the total derivative as a convolution, we use
`ContinuousLinearMap.precompR`. -/
theorem _root_.HasCompactSupport.hasFDerivAt_convolution_right (hcg : HasCompactSupport g)
(hf : LocallyIntegrable f μ) (hg : ContDiff 𝕜 1 g) (x₀ : G) :
HasFDerivAt (f ⋆[L, μ] g) ((f ⋆[L.precompR G, μ] fderiv 𝕜 g) x₀) x₀ := by
rcases hcg.eq_zero_or_finiteDimensional 𝕜 hg.continuous with (rfl | fin_dim)
· have : fderiv 𝕜 (0 : G → E') = 0 := fderiv_const (0 : E')
simp only [this, convolution_zero, Pi.zero_apply]
exact hasFDerivAt_const (0 : F) x₀
have : ProperSpace G := FiniteDimensional.proper_rclike 𝕜 G
set L' := L.precompR G
have h1 : ∀ᶠ x in 𝓝 x₀, AEStronglyMeasurable (fun t => L (f t) (g (x - t))) μ :=
Eventually.of_forall
(hf.aestronglyMeasurable.convolution_integrand_snd L hg.continuous.aestronglyMeasurable)
have h2 : ∀ x, AEStronglyMeasurable (fun t => L' (f t) (fderiv 𝕜 g (x - t))) μ :=
hf.aestronglyMeasurable.convolution_integrand_snd L'
(hg.continuous_fderiv le_rfl).aestronglyMeasurable
have h3 : ∀ x t, HasFDerivAt (fun x => g (x - t)) (fderiv 𝕜 g (x - t)) x := fun x t ↦ by
simpa using
(hg.differentiable le_rfl).differentiableAt.hasFDerivAt.comp x
((hasFDerivAt_id x).sub (hasFDerivAt_const t x))
let K' := -tsupport (fderiv 𝕜 g) + closedBall x₀ 1
have hK' : IsCompact K' := (hcg.fderiv 𝕜).neg.add (isCompact_closedBall x₀ 1)
apply hasFDerivAt_integral_of_dominated_of_fderiv_le zero_lt_one h1 _ (h2 x₀)
· filter_upwards with t x hx using
(hcg.fderiv 𝕜).convolution_integrand_bound_right L' (hg.continuous_fderiv le_rfl)
(ball_subset_closedBall hx)
· rw [integrable_indicator_iff hK'.measurableSet]
exact ((hf.integrableOn_isCompact hK').norm.const_mul _).mul_const _
· exact Eventually.of_forall fun t x _ => (L _).hasFDerivAt.comp x (h3 x t)
· exact hcg.convolutionExists_right L hf hg.continuous x₀
theorem _root_.HasCompactSupport.hasFDerivAt_convolution_left [IsNegInvariant μ]
(hcf : HasCompactSupport f) (hf : ContDiff 𝕜 1 f) (hg : LocallyIntegrable g μ) (x₀ : G) :
HasFDerivAt (f ⋆[L, μ] g) ((fderiv 𝕜 f ⋆[L.precompL G, μ] g) x₀) x₀ := by
simp +singlePass only [← convolution_flip]
exact hcf.hasFDerivAt_convolution_right L.flip hg hf x₀
end RCLike
section Real
/-! The one-variable case -/
variable [RCLike 𝕜]
variable [NormedSpace 𝕜 E]
variable [NormedSpace 𝕜 E']
variable [NormedSpace ℝ F] [NormedSpace 𝕜 F]
variable {f₀ : 𝕜 → E} {g₀ : 𝕜 → E'}
variable {n : ℕ∞}
variable (L : E →L[𝕜] E' →L[𝕜] F)
variable {μ : Measure 𝕜}
variable [IsAddLeftInvariant μ] [SFinite μ]
theorem _root_.HasCompactSupport.hasDerivAt_convolution_right (hf : LocallyIntegrable f₀ μ)
(hcg : HasCompactSupport g₀) (hg : ContDiff 𝕜 1 g₀) (x₀ : 𝕜) :
HasDerivAt (f₀ ⋆[L, μ] g₀) ((f₀ ⋆[L, μ] deriv g₀) x₀) x₀ := by
convert (hcg.hasFDerivAt_convolution_right L hf hg x₀).hasDerivAt using 1
rw [convolution_precompR_apply L hf (hcg.fderiv 𝕜) (hg.continuous_fderiv le_rfl)]
rfl
theorem _root_.HasCompactSupport.hasDerivAt_convolution_left [IsNegInvariant μ]
(hcf : HasCompactSupport f₀) (hf : ContDiff 𝕜 1 f₀) (hg : LocallyIntegrable g₀ μ) (x₀ : 𝕜) :
HasDerivAt (f₀ ⋆[L, μ] g₀) ((deriv f₀ ⋆[L, μ] g₀) x₀) x₀ := by
simp +singlePass only [← convolution_flip]
exact hcf.hasDerivAt_convolution_right L.flip hg hf x₀
end Real
section WithParam
variable [RCLike 𝕜] [NormedSpace 𝕜 E] [NormedSpace 𝕜 E'] [NormedSpace 𝕜 E''] [NormedSpace ℝ F]
[NormedSpace 𝕜 F] [MeasurableSpace G] [NormedAddCommGroup G] [BorelSpace G]
[NormedSpace 𝕜 G] [NormedAddCommGroup P] [NormedSpace 𝕜 P] {μ : Measure G}
(L : E →L[𝕜] E' →L[𝕜] F)
/-- The derivative of the convolution `f * g` is given by `f * Dg`, when `f` is locally integrable
and `g` is `C^1` and compactly supported. Version where `g` depends on an additional parameter in an
open subset `s` of a parameter space `P` (and the compact support `k` is independent of the
parameter in `s`). -/
theorem hasFDerivAt_convolution_right_with_param {g : P → G → E'} {s : Set P} {k : Set G}
(hs : IsOpen s) (hk : IsCompact k) (hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0)
(hf : LocallyIntegrable f μ) (hg : ContDiffOn 𝕜 1 (↿g) (s ×ˢ univ)) (q₀ : P × G)
(hq₀ : q₀.1 ∈ s) :
HasFDerivAt (fun q : P × G => (f ⋆[L, μ] g q.1) q.2)
((f ⋆[L.precompR (P × G), μ] fun x : G => fderiv 𝕜 (↿g) (q₀.1, x)) q₀.2) q₀ := by
let g' := fderiv 𝕜 ↿g
have A : ∀ p ∈ s, Continuous (g p) := fun p hp ↦ by
refine hg.continuousOn.comp_continuous (.prodMk_right _) fun x => ?_
simpa only [prodMk_mem_set_prod_eq, mem_univ, and_true] using hp
have A' : ∀ q : P × G, q.1 ∈ s → s ×ˢ univ ∈ 𝓝 q := fun q hq ↦ by
apply (hs.prod isOpen_univ).mem_nhds
simpa only [mem_prod, mem_univ, and_true] using hq
-- The derivative of `g` vanishes away from `k`.
have g'_zero : ∀ p x, p ∈ s → x ∉ k → g' (p, x) = 0 := by
intro p x hp hx
refine (hasFDerivAt_zero_of_eventually_const 0 ?_).fderiv
have M2 : kᶜ ∈ 𝓝 x := hk.isClosed.isOpen_compl.mem_nhds hx
have M1 : s ∈ 𝓝 p := hs.mem_nhds hp
rw [nhds_prod_eq]
filter_upwards [prod_mem_prod M1 M2]
rintro ⟨p, y⟩ ⟨hp, hy⟩
exact hgs p y hp hy
/- We find a small neighborhood of `{q₀.1} × k` on which the derivative is uniformly bounded. This
follows from the continuity at all points of the compact set `k`. -/
obtain ⟨ε, C, εpos, h₀ε, hε⟩ :
∃ ε C, 0 < ε ∧ ball q₀.1 ε ⊆ s ∧ ∀ p x, ‖p - q₀.1‖ < ε → ‖g' (p, x)‖ ≤ C := by
have A : IsCompact ({q₀.1} ×ˢ k) := isCompact_singleton.prod hk
obtain ⟨t, kt, t_open, ht⟩ : ∃ t, {q₀.1} ×ˢ k ⊆ t ∧ IsOpen t ∧ IsBounded (g' '' t) := by
have B : ContinuousOn g' (s ×ˢ univ) :=
hg.continuousOn_fderiv_of_isOpen (hs.prod isOpen_univ) le_rfl
apply exists_isOpen_isBounded_image_of_isCompact_of_continuousOn A (hs.prod isOpen_univ) _ B
simp only [prod_subset_prod_iff, hq₀, singleton_subset_iff, subset_univ, and_self_iff,
true_or]
obtain ⟨ε, εpos, hε, h'ε⟩ :
∃ ε : ℝ, 0 < ε ∧ thickening ε ({q₀.fst} ×ˢ k) ⊆ t ∧ ball q₀.1 ε ⊆ s := by
obtain ⟨ε, εpos, hε⟩ : ∃ ε : ℝ, 0 < ε ∧ thickening ε (({q₀.fst} : Set P) ×ˢ k) ⊆ t :=
A.exists_thickening_subset_open t_open kt
obtain ⟨δ, δpos, hδ⟩ : ∃ δ : ℝ, 0 < δ ∧ ball q₀.1 δ ⊆ s := Metric.isOpen_iff.1 hs _ hq₀
refine ⟨min ε δ, lt_min εpos δpos, ?_, ?_⟩
· exact Subset.trans (thickening_mono (min_le_left _ _) _) hε
· exact Subset.trans (ball_subset_ball (min_le_right _ _)) hδ
obtain ⟨C, Cpos, hC⟩ : ∃ C, 0 < C ∧ g' '' t ⊆ closedBall 0 C := ht.subset_closedBall_lt 0 0
refine ⟨ε, C, εpos, h'ε, fun p x hp => ?_⟩
have hps : p ∈ s := h'ε (mem_ball_iff_norm.2 hp)
by_cases hx : x ∈ k
· have H : (p, x) ∈ t := by
apply hε
refine mem_thickening_iff.2 ⟨(q₀.1, x), ?_, ?_⟩
· simp only [hx, singleton_prod, mem_image, Prod.mk_inj, eq_self_iff_true, true_and,
exists_eq_right]
· rw [← dist_eq_norm] at hp
simpa only [Prod.dist_eq, εpos, dist_self, max_lt_iff, and_true] using hp
have : g' (p, x) ∈ closedBall (0 : P × G →L[𝕜] E') C := hC (mem_image_of_mem _ H)
rwa [mem_closedBall_zero_iff] at this
· have : g' (p, x) = 0 := g'_zero _ _ hps hx
rw [this]
simpa only [norm_zero] using Cpos.le
/- Now, we wish to apply a theorem on differentiation of integrals. For this, we need to check
trivial measurability or integrability assumptions (in `I1`, `I2`, `I3`), as well as a uniform
integrability assumption over the derivative (in `I4` and `I5`) and pointwise differentiability
in `I6`. -/
have I1 :
∀ᶠ x : P × G in 𝓝 q₀, AEStronglyMeasurable (fun a : G => L (f a) (g x.1 (x.2 - a))) μ := by
filter_upwards [A' q₀ hq₀]
rintro ⟨p, x⟩ ⟨hp, -⟩
refine (HasCompactSupport.convolutionExists_right L ?_ hf (A _ hp) _).1
apply hk.of_isClosed_subset (isClosed_tsupport _)
exact closure_minimal (support_subset_iff'.2 fun z hz => hgs _ _ hp hz) hk.isClosed
have I2 : Integrable (fun a : G => L (f a) (g q₀.1 (q₀.2 - a))) μ := by
have M : HasCompactSupport (g q₀.1) := HasCompactSupport.intro hk fun x hx => hgs q₀.1 x hq₀ hx
apply M.convolutionExists_right L hf (A q₀.1 hq₀) q₀.2
have I3 : AEStronglyMeasurable (fun a : G => (L (f a)).comp (g' (q₀.fst, q₀.snd - a))) μ := by
have T : HasCompactSupport fun y => g' (q₀.1, y) :=
HasCompactSupport.intro hk fun x hx => g'_zero q₀.1 x hq₀ hx
apply (HasCompactSupport.convolutionExists_right (L.precompR (P × G) :) T hf _ q₀.2).1
have : ContinuousOn g' (s ×ˢ univ) :=
hg.continuousOn_fderiv_of_isOpen (hs.prod isOpen_univ) le_rfl
apply this.comp_continuous (.prodMk_right _)
intro x
simpa only [prodMk_mem_set_prod_eq, mem_univ, and_true] using hq₀
set K' := (-k + {q₀.2} : Set G) with K'_def
have hK' : IsCompact K' := hk.neg.add isCompact_singleton
obtain ⟨U, U_open, K'U, hU⟩ : ∃ U, IsOpen U ∧ K' ⊆ U ∧ IntegrableOn f U μ :=
hf.integrableOn_nhds_isCompact hK'
obtain ⟨δ, δpos, δε, hδ⟩ : ∃ δ, (0 : ℝ) < δ ∧ δ ≤ ε ∧ K' + ball 0 δ ⊆ U := by
obtain ⟨V, V_mem, hV⟩ : ∃ V ∈ 𝓝 (0 : G), K' + V ⊆ U :=
compact_open_separated_add_right hK' U_open K'U
rcases Metric.mem_nhds_iff.1 V_mem with ⟨δ, δpos, hδ⟩
refine ⟨min δ ε, lt_min δpos εpos, min_le_right δ ε, ?_⟩
exact (add_subset_add_left ((ball_subset_ball (min_le_left _ _)).trans hδ)).trans hV
letI := ContinuousLinearMap.hasOpNorm (𝕜 := 𝕜) (𝕜₂ := 𝕜) (E := E)
(F := (P × G →L[𝕜] E') →L[𝕜] P × G →L[𝕜] F) (σ₁₂ := RingHom.id 𝕜)
let bound : G → ℝ := indicator U fun t => ‖(L.precompR (P × G))‖ * ‖f t‖ * C
have I4 : ∀ᵐ a : G ∂μ, ∀ x : P × G, dist x q₀ < δ →
‖L.precompR (P × G) (f a) (g' (x.fst, x.snd - a))‖ ≤ bound a := by
filter_upwards with a x hx
rw [Prod.dist_eq, dist_eq_norm, dist_eq_norm] at hx
have : (-tsupport fun a => g' (x.1, a)) + ball q₀.2 δ ⊆ U := by
apply Subset.trans _ hδ
rw [K'_def, add_assoc]
apply add_subset_add
· rw [neg_subset_neg]
refine closure_minimal (support_subset_iff'.2 fun z hz => ?_) hk.isClosed
apply g'_zero x.1 z (h₀ε _) hz
rw [mem_ball_iff_norm]
exact ((le_max_left _ _).trans_lt hx).trans_le δε
· simp only [add_ball, thickening_singleton, zero_vadd, subset_rfl]
apply convolution_integrand_bound_right_of_le_of_subset _ _ _ this
· intro y
exact hε _ _ (((le_max_left _ _).trans_lt hx).trans_le δε)
· rw [mem_ball_iff_norm]
exact (le_max_right _ _).trans_lt hx
have I5 : Integrable bound μ := by
rw [integrable_indicator_iff U_open.measurableSet]
exact (hU.norm.const_mul _).mul_const _
have I6 : ∀ᵐ a : G ∂μ, ∀ x : P × G, dist x q₀ < δ →
HasFDerivAt (fun x : P × G => L (f a) (g x.1 (x.2 - a)))
((L (f a)).comp (g' (x.fst, x.snd - a))) x := by
filter_upwards with a x hx
apply (L _).hasFDerivAt.comp x
have N : s ×ˢ univ ∈ 𝓝 (x.1, x.2 - a) := by
apply A'
apply h₀ε
rw [Prod.dist_eq] at hx
exact lt_of_lt_of_le (lt_of_le_of_lt (le_max_left _ _) hx) δε
have Z := ((hg.differentiableOn le_rfl).differentiableAt N).hasFDerivAt
have Z' :
HasFDerivAt (fun x : P × G => (x.1, x.2 - a)) (ContinuousLinearMap.id 𝕜 (P × G)) x := by
have : (fun x : P × G => (x.1, x.2 - a)) = _root_.id - fun x => (0, a) := by
ext x <;> simp only [Pi.sub_apply, _root_.id, Prod.fst_sub, sub_zero, Prod.snd_sub]
rw [this]
exact (hasFDerivAt_id x).sub_const (0, a)
exact Z.comp x Z'
exact hasFDerivAt_integral_of_dominated_of_fderiv_le δpos I1 I2 I3 I4 I5 I6
/-- The convolution `f * g` is `C^n` when `f` is locally integrable and `g` is `C^n` and compactly
supported. Version where `g` depends on an additional parameter in an open subset `s` of a
parameter space `P` (and the compact support `k` is independent of the parameter in `s`).
In this version, all the types belong to the same universe (to get an induction working in the
proof). Use instead `contDiffOn_convolution_right_with_param`, which removes this restriction. -/
theorem contDiffOn_convolution_right_with_param_aux {G : Type uP} {E' : Type uP} {F : Type uP}
{P : Type uP} [NormedAddCommGroup E'] [NormedAddCommGroup F] [NormedSpace 𝕜 E']
[NormedSpace ℝ F] [NormedSpace 𝕜 F] [MeasurableSpace G]
{μ : Measure G}
[NormedAddCommGroup G] [BorelSpace G] [NormedSpace 𝕜 G] [NormedAddCommGroup P] [NormedSpace 𝕜 P]
{f : G → E} {n : ℕ∞} (L : E →L[𝕜] E' →L[𝕜] F) {g : P → G → E'} {s : Set P} {k : Set G}
(hs : IsOpen s) (hk : IsCompact k) (hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0)
(hf : LocallyIntegrable f μ) (hg : ContDiffOn 𝕜 n (↿g) (s ×ˢ univ)) :
ContDiffOn 𝕜 n (fun q : P × G => (f ⋆[L, μ] g q.1) q.2) (s ×ˢ univ) := by
/- We have a formula for the derivation of `f * g`, which is of the same form, thanks to
`hasFDerivAt_convolution_right_with_param`. Therefore, we can prove the result by induction on
`n` (but for this we need the spaces at the different steps of the induction to live in the same
universe, which is why we make the assumption in the lemma that all the relevant spaces
come from the same universe). -/
induction n using ENat.nat_induction generalizing g E' F with
| h0 =>
rw [WithTop.coe_zero, contDiffOn_zero] at hg ⊢
exact continuousOn_convolution_right_with_param L hk hgs hf hg
| hsuc n ih =>
simp only [Nat.succ_eq_add_one, Nat.cast_add, Nat.cast_one, WithTop.coe_add,
WithTop.coe_natCast, WithTop.coe_one] at hg ⊢
let f' : P → G → P × G →L[𝕜] F := fun p a =>
(f ⋆[L.precompR (P × G), μ] fun x : G => fderiv 𝕜 (uncurry g) (p, x)) a
have A : ∀ q₀ : P × G, q₀.1 ∈ s →
HasFDerivAt (fun q : P × G => (f ⋆[L, μ] g q.1) q.2) (f' q₀.1 q₀.2) q₀ :=
hasFDerivAt_convolution_right_with_param L hs hk hgs hf hg.one_of_succ
rw [contDiffOn_succ_iff_fderiv_of_isOpen (hs.prod (@isOpen_univ G _))] at hg ⊢
refine ⟨?_, by simp, ?_⟩
· rintro ⟨p, x⟩ ⟨hp, -⟩
exact (A (p, x) hp).differentiableAt.differentiableWithinAt
· suffices H : ContDiffOn 𝕜 n (↿f') (s ×ˢ univ) by
apply H.congr
rintro ⟨p, x⟩ ⟨hp, -⟩
exact (A (p, x) hp).fderiv
have B : ∀ (p : P) (x : G), p ∈ s → x ∉ k → fderiv 𝕜 (uncurry g) (p, x) = 0 := by
intro p x hp hx
apply (hasFDerivAt_zero_of_eventually_const (0 : E') _).fderiv
have M2 : kᶜ ∈ 𝓝 x := IsOpen.mem_nhds hk.isClosed.isOpen_compl hx
have M1 : s ∈ 𝓝 p := hs.mem_nhds hp
rw [nhds_prod_eq]
filter_upwards [prod_mem_prod M1 M2]
rintro ⟨p, y⟩ ⟨hp, hy⟩
exact hgs p y hp hy
apply ih (L.precompR (P × G) :) B
convert hg.2.2
| htop ih =>
rw [contDiffOn_infty] at hg ⊢
exact fun n ↦ ih n L hgs (hg n)
/-- The convolution `f * g` is `C^n` when `f` is locally integrable and `g` is `C^n` and compactly
supported. Version where `g` depends on an additional parameter in an open subset `s` of a
parameter space `P` (and the compact support `k` is independent of the parameter in `s`). -/
theorem contDiffOn_convolution_right_with_param {f : G → E} {n : ℕ∞} (L : E →L[𝕜] E' →L[𝕜] F)
{g : P → G → E'} {s : Set P} {k : Set G} (hs : IsOpen s) (hk : IsCompact k)
(hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0) (hf : LocallyIntegrable f μ)
(hg : ContDiffOn 𝕜 n (↿g) (s ×ˢ univ)) :
ContDiffOn 𝕜 n (fun q : P × G => (f ⋆[L, μ] g q.1) q.2) (s ×ˢ univ) := by
/- The result is known when all the universes are the same, from
`contDiffOn_convolution_right_with_param_aux`. We reduce to this situation by pushing
everything through `ULift` continuous linear equivalences. -/
let eG : Type max uG uE' uF uP := ULift.{max uE' uF uP} G
borelize eG
let eE' : Type max uE' uG uF uP := ULift.{max uG uF uP} E'
let eF : Type max uF uG uE' uP := ULift.{max uG uE' uP} F
let eP : Type max uP uG uE' uF := ULift.{max uG uE' uF} P
let isoG : eG ≃L[𝕜] G := ContinuousLinearEquiv.ulift
let isoE' : eE' ≃L[𝕜] E' := ContinuousLinearEquiv.ulift
let isoF : eF ≃L[𝕜] F := ContinuousLinearEquiv.ulift
let isoP : eP ≃L[𝕜] P := ContinuousLinearEquiv.ulift
let ef := f ∘ isoG
let eμ : Measure eG := Measure.map isoG.symm μ
let eg : eP → eG → eE' := fun ep ex => isoE'.symm (g (isoP ep) (isoG ex))
let eL :=
ContinuousLinearMap.comp
((ContinuousLinearEquiv.arrowCongr isoE' isoF).symm : (E' →L[𝕜] F) →L[𝕜] eE' →L[𝕜] eF) L
let R := fun q : eP × eG => (ef ⋆[eL, eμ] eg q.1) q.2
have R_contdiff : ContDiffOn 𝕜 n R ((isoP ⁻¹' s) ×ˢ univ) := by
have hek : IsCompact (isoG ⁻¹' k) := isoG.toHomeomorph.isClosedEmbedding.isCompact_preimage hk
have hes : IsOpen (isoP ⁻¹' s) := isoP.continuous.isOpen_preimage _ hs
refine contDiffOn_convolution_right_with_param_aux eL hes hek ?_ ?_ ?_
· intro p x hp hx
simp only [eg, (· ∘ ·), ContinuousLinearEquiv.prod_apply, LinearIsometryEquiv.coe_coe,
ContinuousLinearEquiv.map_eq_zero_iff]
exact hgs _ _ hp hx
· exact (locallyIntegrable_map_homeomorph isoG.symm.toHomeomorph).2 hf
· apply isoE'.symm.contDiff.comp_contDiffOn
apply hg.comp (isoP.prod isoG).contDiff.contDiffOn
rintro ⟨p, x⟩ ⟨hp, -⟩
simpa only [mem_preimage, ContinuousLinearEquiv.prod_apply, prodMk_mem_set_prod_eq, mem_univ,
and_true] using hp
have A : ContDiffOn 𝕜 n (isoF ∘ R ∘ (isoP.prod isoG).symm) (s ×ˢ univ) := by
apply isoF.contDiff.comp_contDiffOn
apply R_contdiff.comp (ContinuousLinearEquiv.contDiff _).contDiffOn
rintro ⟨p, x⟩ ⟨hp, -⟩
simpa only [mem_preimage, mem_prod, mem_univ, and_true, ContinuousLinearEquiv.prod_symm,
ContinuousLinearEquiv.prod_apply, ContinuousLinearEquiv.apply_symm_apply] using hp
have : isoF ∘ R ∘ (isoP.prod isoG).symm = fun q : P × G => (f ⋆[L, μ] g q.1) q.2 := by
apply funext
rintro ⟨p, x⟩
simp only [LinearIsometryEquiv.coe_coe, (· ∘ ·), ContinuousLinearEquiv.prod_symm,
ContinuousLinearEquiv.prod_apply]
simp only [R, convolution, coe_comp', ContinuousLinearEquiv.coe_coe, (· ∘ ·)]
rw [IsClosedEmbedding.integral_map, ← isoF.integral_comp_comm]
· rfl
· exact isoG.symm.toHomeomorph.isClosedEmbedding
simp_rw [this] at A
exact A
/-- The convolution `f * g` is `C^n` when `f` is locally integrable and `g` is `C^n` and compactly
supported. Version where `g` depends on an additional parameter in an open subset `s` of a
parameter space `P` (and the compact support `k` is independent of the parameter in `s`),
given in terms of composition with an additional `C^n` function. -/
theorem contDiffOn_convolution_right_with_param_comp {n : ℕ∞} (L : E →L[𝕜] E' →L[𝕜] F) {s : Set P}
{v : P → G} (hv : ContDiffOn 𝕜 n v s) {f : G → E} {g : P → G → E'} {k : Set G} (hs : IsOpen s)
(hk : IsCompact k) (hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0) (hf : LocallyIntegrable f μ)
(hg : ContDiffOn 𝕜 n (↿g) (s ×ˢ univ)) : ContDiffOn 𝕜 n (fun x => (f ⋆[L, μ] g x) (v x)) s := by
apply (contDiffOn_convolution_right_with_param L hs hk hgs hf hg).comp (contDiffOn_id.prodMk hv)
intro x hx
simp only [hx, mem_preimage, prodMk_mem_set_prod_eq, mem_univ, and_self_iff, _root_.id]
/-- The convolution `g * f` is `C^n` when `f` is locally integrable and `g` is `C^n` and compactly
supported. Version where `g` depends on an additional parameter in an open subset `s` of a
parameter space `P` (and the compact support `k` is independent of the parameter in `s`). -/
theorem contDiffOn_convolution_left_with_param [μ.IsAddLeftInvariant] [μ.IsNegInvariant]
(L : E' →L[𝕜] E →L[𝕜] F) {f : G → E} {n : ℕ∞} {g : P → G → E'} {s : Set P} {k : Set G}
(hs : IsOpen s) (hk : IsCompact k) (hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0)
(hf : LocallyIntegrable f μ) (hg : ContDiffOn 𝕜 n (↿g) (s ×ˢ univ)) :
ContDiffOn 𝕜 n (fun q : P × G => (g q.1 ⋆[L, μ] f) q.2) (s ×ˢ univ) := by
simpa only [convolution_flip] using contDiffOn_convolution_right_with_param L.flip hs hk hgs hf hg
/-- The convolution `g * f` is `C^n` when `f` is locally integrable and `g` is `C^n` and compactly
supported. Version where `g` depends on an additional parameter in an open subset `s` of a
parameter space `P` (and the compact support `k` is independent of the parameter in `s`),
given in terms of composition with additional `C^n` functions. -/
theorem contDiffOn_convolution_left_with_param_comp [μ.IsAddLeftInvariant] [μ.IsNegInvariant]
(L : E' →L[𝕜] E →L[𝕜] F) {s : Set P} {n : ℕ∞} {v : P → G} (hv : ContDiffOn 𝕜 n v s) {f : G → E}
{g : P → G → E'} {k : Set G} (hs : IsOpen s) (hk : IsCompact k)
(hgs : ∀ p, ∀ x, p ∈ s → x ∉ k → g p x = 0) (hf : LocallyIntegrable f μ)
(hg : ContDiffOn 𝕜 n (↿g) (s ×ˢ univ)) : ContDiffOn 𝕜 n (fun x => (g x ⋆[L, μ] f) (v x)) s := by
apply (contDiffOn_convolution_left_with_param L hs hk hgs hf hg).comp (contDiffOn_id.prodMk hv)
intro x hx
simp only [hx, mem_preimage, prodMk_mem_set_prod_eq, mem_univ, and_self_iff, _root_.id]
theorem _root_.HasCompactSupport.contDiff_convolution_right {n : ℕ∞} (hcg : HasCompactSupport g)
(hf : LocallyIntegrable f μ) (hg : ContDiff 𝕜 n g) : ContDiff 𝕜 n (f ⋆[L, μ] g) := by
rcases exists_compact_iff_hasCompactSupport.2 hcg with ⟨k, hk, h'k⟩
rw [← contDiffOn_univ]
exact contDiffOn_convolution_right_with_param_comp L contDiffOn_id isOpen_univ hk
(fun p x _ hx => h'k x hx) hf (hg.comp contDiff_snd).contDiffOn
theorem _root_.HasCompactSupport.contDiff_convolution_left [μ.IsAddLeftInvariant] [μ.IsNegInvariant]
{n : ℕ∞} (hcf : HasCompactSupport f) (hf : ContDiff 𝕜 n f) (hg : LocallyIntegrable g μ) :
ContDiff 𝕜 n (f ⋆[L, μ] g) := by
rw [← convolution_flip]
exact hcf.contDiff_convolution_right L.flip hg hf
end WithParam
section Nonneg
variable [NormedSpace ℝ E] [NormedSpace ℝ E'] [NormedSpace ℝ F]
/-- The forward convolution of two functions `f` and `g` on `ℝ`, with respect to a continuous
bilinear map `L` and measure `ν`. It is defined to be the function mapping `x` to
`∫ t in 0..x, L (f t) (g (x - t)) ∂ν` if `0 < x`, and 0 otherwise. -/
noncomputable def posConvolution (f : ℝ → E) (g : ℝ → E') (L : E →L[ℝ] E' →L[ℝ] F)
(ν : Measure ℝ := by volume_tac) : ℝ → F :=
indicator (Ioi (0 : ℝ)) fun x => ∫ t in (0)..x, L (f t) (g (x - t)) ∂ν
theorem posConvolution_eq_convolution_indicator (f : ℝ → E) (g : ℝ → E') (L : E →L[ℝ] E' →L[ℝ] F)
(ν : Measure ℝ := by volume_tac) [NoAtoms ν] :
posConvolution f g L ν = convolution (indicator (Ioi 0) f) (indicator (Ioi 0) g) L ν := by
ext1 x
rw [convolution, posConvolution, indicator]
split_ifs with h
· rw [intervalIntegral.integral_of_le (le_of_lt h), integral_Ioc_eq_integral_Ioo, ←
integral_indicator (measurableSet_Ioo : MeasurableSet (Ioo 0 x))]
congr 1 with t : 1
have : t ≤ 0 ∨ t ∈ Ioo 0 x ∨ x ≤ t := by
rcases le_or_lt t 0 with (h | h)
· exact Or.inl h
· rcases lt_or_le t x with (h' | h')
exacts [Or.inr (Or.inl ⟨h, h'⟩), Or.inr (Or.inr h')]
rcases this with (ht | ht | ht)
· rw [indicator_of_not_mem (not_mem_Ioo_of_le ht), indicator_of_not_mem (not_mem_Ioi.mpr ht),
ContinuousLinearMap.map_zero, ContinuousLinearMap.zero_apply]
· rw [indicator_of_mem ht, indicator_of_mem (mem_Ioi.mpr ht.1),
indicator_of_mem (mem_Ioi.mpr <| sub_pos.mpr ht.2)]
· rw [indicator_of_not_mem (not_mem_Ioo_of_ge ht),
indicator_of_not_mem (not_mem_Ioi.mpr (sub_nonpos_of_le ht)),
ContinuousLinearMap.map_zero]
· convert (integral_zero ℝ F).symm with t
by_cases ht : 0 < t
· rw [indicator_of_not_mem (_ : x - t ∉ Ioi 0), ContinuousLinearMap.map_zero]
rw [not_mem_Ioi] at h ⊢
exact sub_nonpos.mpr (h.trans ht.le)
· rw [indicator_of_not_mem (mem_Ioi.not.mpr ht), ContinuousLinearMap.map_zero,
ContinuousLinearMap.zero_apply]
theorem integrable_posConvolution {f : ℝ → E} {g : ℝ → E'} {μ ν : Measure ℝ} [SFinite μ]
[SFinite ν] [IsAddRightInvariant μ] [NoAtoms ν] (hf : IntegrableOn f (Ioi 0) ν)
(hg : IntegrableOn g (Ioi 0) μ) (L : E →L[ℝ] E' →L[ℝ] F) :
Integrable (posConvolution f g L ν) μ := by
rw [← integrable_indicator_iff (measurableSet_Ioi : MeasurableSet (Ioi (0 : ℝ)))] at hf hg
rw [posConvolution_eq_convolution_indicator f g L ν]
exact (hf.convolution_integrand L hg).integral_prod_left
/-- The integral over `Ioi 0` of a forward convolution of two functions is equal to the product
of their integrals over this set. (Compare `integral_convolution` for the two-sided convolution.) -/
theorem integral_posConvolution [CompleteSpace E] [CompleteSpace E'] [CompleteSpace F]
{μ ν : Measure ℝ}
[SFinite μ] [SFinite ν] [IsAddRightInvariant μ] [NoAtoms ν] {f : ℝ → E} {g : ℝ → E'}
(hf : IntegrableOn f (Ioi 0) ν) (hg : IntegrableOn g (Ioi 0) μ) (L : E →L[ℝ] E' →L[ℝ] F) :
∫ x : ℝ in Ioi 0, ∫ t : ℝ in (0)..x, L (f t) (g (x - t)) ∂ν ∂μ =
L (∫ x : ℝ in Ioi 0, f x ∂ν) (∫ x : ℝ in Ioi 0, g x ∂μ) := by
rw [← integrable_indicator_iff measurableSet_Ioi] at hf hg
simp_rw [← integral_indicator measurableSet_Ioi]
| convert integral_convolution L hf hg using 4 with x
apply posConvolution_eq_convolution_indicator
end Nonneg
end MeasureTheory
| Mathlib/Analysis/Convolution.lean | 1,392 | 1,399 |
/-
Copyright (c) 2021 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison
-/
import Mathlib.LinearAlgebra.Basis.Basic
import Mathlib.LinearAlgebra.Basis.Submodule
import Mathlib.LinearAlgebra.Dimension.Finrank
import Mathlib.LinearAlgebra.InvariantBasisNumber
/-!
# Lemmas about rank and finrank in rings satisfying strong rank condition.
## Main statements
For modules over rings satisfying the rank condition
* `Basis.le_span`:
the cardinality of a basis is bounded by the cardinality of any spanning set
For modules over rings satisfying the strong rank condition
* `linearIndependent_le_span`:
For any linearly independent family `v : ι → M`
and any finite spanning set `w : Set M`,
the cardinality of `ι` is bounded by the cardinality of `w`.
* `linearIndependent_le_basis`:
If `b` is a basis for a module `M`,
and `s` is a linearly independent set,
then the cardinality of `s` is bounded by the cardinality of `b`.
For modules over rings with invariant basis number
(including all commutative rings and all noetherian rings)
* `mk_eq_mk_of_basis`: the dimension theorem, any two bases of the same vector space have the same
cardinality.
## Additional definition
* `Algebra.IsQuadraticExtension`: An extension of rings `R ⊆ S` is quadratic if `S` is a
free `R`-algebra of rank `2`.
-/
noncomputable section
universe u v w w'
variable {R : Type u} {M : Type v} [Semiring R] [AddCommMonoid M] [Module R M]
variable {ι : Type w} {ι' : Type w'}
open Cardinal Basis Submodule Function Set Module
attribute [local instance] nontrivial_of_invariantBasisNumber
section InvariantBasisNumber
variable [InvariantBasisNumber R]
/-- The dimension theorem: if `v` and `v'` are two bases, their index types
have the same cardinalities. -/
theorem mk_eq_mk_of_basis (v : Basis ι R M) (v' : Basis ι' R M) :
Cardinal.lift.{w'} #ι = Cardinal.lift.{w} #ι' := by
classical
haveI := nontrivial_of_invariantBasisNumber R
cases fintypeOrInfinite ι
· -- `v` is a finite basis, so by `basis_finite_of_finite_spans` so is `v'`.
-- haveI : Finite (range v) := Set.finite_range v
haveI := basis_finite_of_finite_spans (Set.finite_range v) v.span_eq v'
cases nonempty_fintype ι'
-- We clean up a little:
rw [Cardinal.mk_fintype, Cardinal.mk_fintype]
simp only [Cardinal.lift_natCast, Nat.cast_inj]
-- Now we can use invariant basis number to show they have the same cardinality.
apply card_eq_of_linearEquiv R
exact
(Finsupp.linearEquivFunOnFinite R R ι).symm.trans v.repr.symm ≪≫ₗ v'.repr ≪≫ₗ
Finsupp.linearEquivFunOnFinite R R ι'
· -- `v` is an infinite basis,
-- so by `infinite_basis_le_maximal_linearIndependent`, `v'` is at least as big,
-- and then applying `infinite_basis_le_maximal_linearIndependent` again
-- we see they have the same cardinality.
have w₁ := infinite_basis_le_maximal_linearIndependent' v _ v'.linearIndependent v'.maximal
rcases Cardinal.lift_mk_le'.mp w₁ with ⟨f⟩
haveI : Infinite ι' := Infinite.of_injective f f.2
have w₂ := infinite_basis_le_maximal_linearIndependent' v' _ v.linearIndependent v.maximal
exact le_antisymm w₁ w₂
/-- Given two bases indexed by `ι` and `ι'` of an `R`-module, where `R` satisfies the invariant
basis number property, an equiv `ι ≃ ι'`. -/
def Basis.indexEquiv (v : Basis ι R M) (v' : Basis ι' R M) : ι ≃ ι' :=
(Cardinal.lift_mk_eq'.1 <| mk_eq_mk_of_basis v v').some
theorem mk_eq_mk_of_basis' {ι' : Type w} (v : Basis ι R M) (v' : Basis ι' R M) : #ι = #ι' :=
Cardinal.lift_inj.1 <| mk_eq_mk_of_basis v v'
end InvariantBasisNumber
section RankCondition
variable [RankCondition R]
/-- An auxiliary lemma for `Basis.le_span`.
If `R` satisfies the rank condition,
then for any finite basis `b : Basis ι R M`,
and any finite spanning set `w : Set M`,
the cardinality of `ι` is bounded by the cardinality of `w`.
-/
theorem Basis.le_span'' {ι : Type*} [Fintype ι] (b : Basis ι R M) {w : Set M} [Fintype w]
(s : span R w = ⊤) : Fintype.card ι ≤ Fintype.card w := by
-- We construct a surjective linear map `(w → R) →ₗ[R] (ι → R)`,
-- by expressing a linear combination in `w` as a linear combination in `ι`.
fapply card_le_of_surjective' R
· exact b.repr.toLinearMap.comp (Finsupp.linearCombination R (↑))
· apply Surjective.comp (g := b.repr.toLinearMap)
· apply LinearEquiv.surjective
rw [← LinearMap.range_eq_top, Finsupp.range_linearCombination]
simpa using s
/--
Another auxiliary lemma for `Basis.le_span`, which does not require assuming the basis is finite,
but still assumes we have a finite spanning set.
-/
theorem basis_le_span' {ι : Type*} (b : Basis ι R M) {w : Set M} [Fintype w] (s : span R w = ⊤) :
#ι ≤ Fintype.card w := by
haveI := nontrivial_of_invariantBasisNumber R
haveI := basis_finite_of_finite_spans w.toFinite s b
cases nonempty_fintype ι
rw [Cardinal.mk_fintype ι]
simp only [Nat.cast_le]
exact Basis.le_span'' b s
-- Note that if `R` satisfies the strong rank condition,
-- this also follows from `linearIndependent_le_span` below.
/-- If `R` satisfies the rank condition,
then the cardinality of any basis is bounded by the cardinality of any spanning set.
-/
theorem Basis.le_span {J : Set M} (v : Basis ι R M) (hJ : span R J = ⊤) : #(range v) ≤ #J := by
haveI := nontrivial_of_invariantBasisNumber R
cases fintypeOrInfinite J
· rw [← Cardinal.lift_le, Cardinal.mk_range_eq_of_injective v.injective, Cardinal.mk_fintype J]
convert Cardinal.lift_le.{v}.2 (basis_le_span' v hJ)
simp
· let S : J → Set ι := fun j => ↑(v.repr j).support
let S' : J → Set M := fun j => v '' S j
have hs : range v ⊆ ⋃ j, S' j := by
intro b hb
rcases mem_range.1 hb with ⟨i, hi⟩
have : span R J ≤ comap v.repr.toLinearMap (Finsupp.supported R R (⋃ j, S j)) :=
span_le.2 fun j hj x hx => ⟨_, ⟨⟨j, hj⟩, rfl⟩, hx⟩
rw [hJ] at this
replace : v.repr (v i) ∈ Finsupp.supported R R (⋃ j, S j) := this trivial
rw [v.repr_self, Finsupp.mem_supported, Finsupp.support_single_ne_zero _ one_ne_zero] at this
· subst b
rcases mem_iUnion.1 (this (Finset.mem_singleton_self _)) with ⟨j, hj⟩
exact mem_iUnion.2 ⟨j, (mem_image _ _ _).2 ⟨i, hj, rfl⟩⟩
refine le_of_not_lt fun IJ => ?_
suffices #(⋃ j, S' j) < #(range v) by exact not_le_of_lt this ⟨Set.embeddingOfSubset _ _ hs⟩
refine lt_of_le_of_lt (le_trans Cardinal.mk_iUnion_le_sum_mk
(Cardinal.sum_le_sum _ (fun _ => ℵ₀) ?_)) ?_
· exact fun j => (Cardinal.lt_aleph0_of_finite _).le
· simpa
end RankCondition
section StrongRankCondition
variable [StrongRankCondition R]
open Submodule Finsupp
-- An auxiliary lemma for `linearIndependent_le_span'`,
-- with the additional assumption that the linearly independent family is finite.
theorem linearIndependent_le_span_aux' {ι : Type*} [Fintype ι] (v : ι → M)
(i : LinearIndependent R v) (w : Set M) [Fintype w] (s : range v ≤ span R w) :
Fintype.card ι ≤ Fintype.card w := by
-- We construct an injective linear map `(ι → R) →ₗ[R] (w → R)`,
-- by thinking of `f : ι → R` as a linear combination of the finite family `v`,
-- and expressing that (using the axiom of choice) as a linear combination over `w`.
-- We can do this linearly by constructing the map on a basis.
fapply card_le_of_injective' R
· apply Finsupp.linearCombination
exact fun i => Span.repr R w ⟨v i, s (mem_range_self i)⟩
· intro f g h
apply_fun linearCombination R ((↑) : w → M) at h
simp only [linearCombination_linearCombination, Submodule.coe_mk,
Span.finsupp_linearCombination_repr] at h
exact i h
/-- If `R` satisfies the strong rank condition,
then any linearly independent family `v : ι → M`
contained in the span of some finite `w : Set M`,
is itself finite.
-/
lemma LinearIndependent.finite_of_le_span_finite {ι : Type*} (v : ι → M) (i : LinearIndependent R v)
(w : Set M) [Finite w] (s : range v ≤ span R w) : Finite ι :=
letI := Fintype.ofFinite w
Fintype.finite <| fintypeOfFinsetCardLe (Fintype.card w) fun t => by
let v' := fun x : (t : Set ι) => v x
have i' : LinearIndependent R v' := i.comp _ Subtype.val_injective
have s' : range v' ≤ span R w := (range_comp_subset_range _ _).trans s
simpa using linearIndependent_le_span_aux' v' i' w s'
/-- If `R` satisfies the strong rank condition,
then for any linearly independent family `v : ι → M`
contained in the span of some finite `w : Set M`,
the cardinality of `ι` is bounded by the cardinality of `w`.
-/
theorem linearIndependent_le_span' {ι : Type*} (v : ι → M) (i : LinearIndependent R v) (w : Set M)
[Fintype w] (s : range v ≤ span R w) : #ι ≤ Fintype.card w := by
haveI : Finite ι := i.finite_of_le_span_finite v w s
letI := Fintype.ofFinite ι
rw [Cardinal.mk_fintype]
simp only [Nat.cast_le]
exact linearIndependent_le_span_aux' v i w s
/-- If `R` satisfies the strong rank condition,
then for any linearly independent family `v : ι → M`
and any finite spanning set `w : Set M`,
the cardinality of `ι` is bounded by the cardinality of `w`.
-/
theorem linearIndependent_le_span {ι : Type*} (v : ι → M) (i : LinearIndependent R v) (w : Set M)
[Fintype w] (s : span R w = ⊤) : #ι ≤ Fintype.card w := by
apply linearIndependent_le_span' v i w
rw [s]
exact le_top
/-- A version of `linearIndependent_le_span` for `Finset`. -/
theorem linearIndependent_le_span_finset {ι : Type*} (v : ι → M) (i : LinearIndependent R v)
(w : Finset M) (s : span R (w : Set M) = ⊤) : #ι ≤ w.card := by
simpa only [Finset.coe_sort_coe, Fintype.card_coe] using linearIndependent_le_span v i w s
/-- An auxiliary lemma for `linearIndependent_le_basis`:
we handle the case where the basis `b` is infinite.
-/
theorem linearIndependent_le_infinite_basis {ι : Type w} (b : Basis ι R M) [Infinite ι] {κ : Type w}
(v : κ → M) (i : LinearIndependent R v) : #κ ≤ #ι := by
classical
by_contra h
rw [not_le, ← Cardinal.mk_finset_of_infinite ι] at h
let Φ := fun k : κ => (b.repr (v k)).support
obtain ⟨s, w : Infinite ↑(Φ ⁻¹' {s})⟩ := Cardinal.exists_infinite_fiber Φ h (by infer_instance)
let v' := fun k : Φ ⁻¹' {s} => v k
have i' : LinearIndependent R v' := i.comp _ Subtype.val_injective
have w' : Finite (Φ ⁻¹' {s}) := by
apply i'.finite_of_le_span_finite v' (s.image b)
rintro m ⟨⟨p, ⟨rfl⟩⟩, rfl⟩
simp only [SetLike.mem_coe, Subtype.coe_mk, Finset.coe_image]
apply Basis.mem_span_repr_support
exact w.false
/-- Over any ring `R` satisfying the strong rank condition,
if `b` is a basis for a module `M`,
and `s` is a linearly independent set,
then the cardinality of `s` is bounded by the cardinality of `b`.
-/
theorem linearIndependent_le_basis {ι : Type w} (b : Basis ι R M) {κ : Type w} (v : κ → M)
(i : LinearIndependent R v) : #κ ≤ #ι := by
classical
-- We split into cases depending on whether `ι` is infinite.
cases fintypeOrInfinite ι
· rw [Cardinal.mk_fintype ι] -- When `ι` is finite, we have `linearIndependent_le_span`,
haveI : Nontrivial R := nontrivial_of_invariantBasisNumber R
rw [Fintype.card_congr (Equiv.ofInjective b b.injective)]
exact linearIndependent_le_span v i (range b) b.span_eq
· -- and otherwise we have `linearIndependent_le_infinite_basis`.
exact linearIndependent_le_infinite_basis b v i
/-- `StrongRankCondition` implies that if there is an injective linear map `(α →₀ R) →ₗ[R] β →₀ R`,
then the cardinal of `α` is smaller than or equal to the cardinal of `β`.
-/
theorem card_le_of_injective'' {α : Type v} {β : Type v} (f : (α →₀ R) →ₗ[R] β →₀ R)
(i : Injective f) : #α ≤ #β := by
let b : Basis β R (β →₀ R) := ⟨1⟩
apply linearIndependent_le_basis b (fun (i : α) ↦ f (Finsupp.single i 1))
rw [LinearIndependent]
have : (linearCombination R fun i ↦ f (Finsupp.single i 1)) = f := by ext a b; simp
exact this.symm ▸ i
/-- If `R` satisfies the strong rank condition, then for any linearly independent family `v : ι → M`
and spanning set `w : Set M`, the cardinality of `ι` is bounded by the cardinality of `w`.
-/
theorem linearIndependent_le_span'' {ι : Type v} {v : ι → M} (i : LinearIndependent R v) (w : Set M)
(s : span R w = ⊤) : #ι ≤ #w := by
fapply card_le_of_injective'' (R := R)
· apply Finsupp.linearCombination
exact fun i ↦ Span.repr R w ⟨v i, s ▸ trivial⟩
· intro f g h
apply_fun linearCombination R ((↑) : w → M) at h
simp only [linearCombination_linearCombination, Submodule.coe_mk,
Span.finsupp_linearCombination_repr] at h
exact i h
/-- Let `R` satisfy the strong rank condition. If `m` elements of a free rank `n` `R`-module are
linearly independent, then `m ≤ n`. -/
theorem Basis.card_le_card_of_linearIndependent_aux {R : Type*} [Semiring R] [StrongRankCondition R]
(n : ℕ) {m : ℕ} (v : Fin m → Fin n → R) : LinearIndependent R v → m ≤ n := fun h => by
simpa using linearIndependent_le_basis (Pi.basisFun R (Fin n)) v h
-- When the basis is not infinite this need not be true!
/-- Over any ring `R` satisfying the strong rank condition,
if `b` is an infinite basis for a module `M`,
then every maximal linearly independent set has the same cardinality as `b`.
This proof (along with some of the lemmas above) comes from
[Les familles libres maximales d'un module ont-elles le meme cardinal?][lazarus1973]
-/
theorem maximal_linearIndependent_eq_infinite_basis {ι : Type w} (b : Basis ι R M) [Infinite ι]
{κ : Type w} (v : κ → M) (i : LinearIndependent R v) (m : i.Maximal) : #κ = #ι := by
apply le_antisymm
· exact linearIndependent_le_basis b v i
· haveI : Nontrivial R := nontrivial_of_invariantBasisNumber R
exact infinite_basis_le_maximal_linearIndependent b v i m
theorem Basis.mk_eq_rank'' {ι : Type v} (v : Basis ι R M) : #ι = Module.rank R M := by
haveI := nontrivial_of_invariantBasisNumber R
rw [Module.rank_def]
apply le_antisymm
· trans
swap
· apply le_ciSup (Cardinal.bddAbove_range _)
exact
⟨Set.range v, by
rw [LinearIndepOn]
convert v.reindexRange.linearIndependent
simp⟩
· exact (Cardinal.mk_range_eq v v.injective).ge
· apply ciSup_le'
rintro ⟨s, li⟩
apply linearIndependent_le_basis v _ li
|
theorem Basis.mk_range_eq_rank (v : Basis ι R M) : #(range v) = Module.rank R M :=
v.reindexRange.mk_eq_rank''
/-- If a vector space has a finite basis, then its dimension (seen as a cardinal) is equal to the
| Mathlib/LinearAlgebra/Dimension/StrongRankCondition.lean | 333 | 337 |
/-
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, Sander Dahmen, Kim Morrison
-/
import Mathlib.SetTheory.Cardinal.Cofinality
import Mathlib.LinearAlgebra.FreeModule.Finite.Basic
import Mathlib.LinearAlgebra.Dimension.StrongRankCondition
import Mathlib.LinearAlgebra.Dimension.Constructions
/-!
# Conditions for rank to be finite
Also contains characterization for when rank equals zero or rank equals one.
-/
noncomputable section
universe u v v' w
variable {R : Type u} {M M₁ : Type v} {M' : Type v'} {ι : Type w}
variable [Ring R] [AddCommGroup M] [AddCommGroup M'] [AddCommGroup M₁]
variable [Module R M] [Module R M'] [Module R M₁]
attribute [local instance] nontrivial_of_invariantBasisNumber
open Basis Cardinal Function Module Set Submodule
/-- If every finite set of linearly independent vectors has cardinality at most `n`,
then the same is true for arbitrary sets of linearly independent vectors.
-/
theorem linearIndependent_bounded_of_finset_linearIndependent_bounded {n : ℕ}
(H : ∀ s : Finset M, (LinearIndependent R fun i : s => (i : M)) → s.card ≤ n) :
∀ s : Set M, LinearIndependent R ((↑) : s → M) → #s ≤ n := by
intro s li
apply Cardinal.card_le_of
intro t
rw [← Finset.card_map (Embedding.subtype s)]
apply H
apply linearIndependent_finset_map_embedding_subtype _ li
theorem rank_le {n : ℕ}
(H : ∀ s : Finset M, (LinearIndependent R fun i : s => (i : M)) → s.card ≤ n) :
Module.rank R M ≤ n := by
rw [Module.rank_def]
apply ciSup_le'
rintro ⟨s, li⟩
exact linearIndependent_bounded_of_finset_linearIndependent_bounded H _ li
section RankZero
/-- See `rank_zero_iff` for a stronger version with `NoZeroSMulDivisor R M`. -/
lemma rank_eq_zero_iff :
Module.rank R M = 0 ↔ ∀ x : M, ∃ a : R, a ≠ 0 ∧ a • x = 0 := by
nontriviality R
constructor
· contrapose!
rintro ⟨x, hx⟩
rw [← Cardinal.one_le_iff_ne_zero]
have : LinearIndependent R (fun _ : Unit ↦ x) :=
linearIndependent_iff.mpr (fun l hl ↦ Finsupp.unique_ext <| not_not.mp fun H ↦
hx _ H ((Finsupp.linearCombination_unique _ _ _).symm.trans hl))
simpa using this.cardinal_lift_le_rank
· intro h
rw [← le_zero_iff, Module.rank_def]
apply ciSup_le'
intro ⟨s, hs⟩
rw [nonpos_iff_eq_zero, Cardinal.mk_eq_zero_iff, ← not_nonempty_iff]
rintro ⟨i : s⟩
obtain ⟨a, ha, ha'⟩ := h i
apply ha
simpa using DFunLike.congr_fun (linearIndependent_iff.mp hs (Finsupp.single i a) (by simpa)) i
theorem rank_pos_of_free [Module.Free R M] [Nontrivial M] :
0 < Module.rank R M :=
have := Module.nontrivial R M
(pos_of_ne_zero <| Cardinal.mk_ne_zero _).trans_le
(Free.chooseBasis R M).linearIndependent.cardinal_le_rank
variable [Nontrivial R]
section
variable [NoZeroSMulDivisors R M]
theorem rank_zero_iff_forall_zero :
Module.rank R M = 0 ↔ ∀ x : M, x = 0 := by
simp_rw [rank_eq_zero_iff, smul_eq_zero, and_or_left, not_and_self_iff, false_or,
exists_and_right, and_iff_right (exists_ne (0 : R))]
/-- See `rank_subsingleton` for the reason that `Nontrivial R` is needed.
Also see `rank_eq_zero_iff` for the version without `NoZeroSMulDivisor R M`. -/
theorem rank_zero_iff : Module.rank R M = 0 ↔ Subsingleton M :=
rank_zero_iff_forall_zero.trans (subsingleton_iff_forall_eq 0).symm
theorem rank_pos_iff_exists_ne_zero : 0 < Module.rank R M ↔ ∃ x : M, x ≠ 0 := by
rw [← not_iff_not]
simpa using rank_zero_iff_forall_zero
theorem rank_pos_iff_nontrivial : 0 < Module.rank R M ↔ Nontrivial M :=
rank_pos_iff_exists_ne_zero.trans (nontrivial_iff_exists_ne 0).symm
theorem rank_pos [Nontrivial M] : 0 < Module.rank R M :=
rank_pos_iff_nontrivial.mpr ‹_›
end
variable (R M)
/-- See `rank_subsingleton` that assumes `Subsingleton R` instead. -/
@[nontriviality]
theorem rank_subsingleton' [Subsingleton M] : Module.rank R M = 0 :=
rank_eq_zero_iff.mpr fun _ ↦ ⟨1, one_ne_zero, Subsingleton.elim _ _⟩
@[simp]
theorem rank_punit : Module.rank R PUnit = 0 := rank_subsingleton' _ _
@[simp]
theorem rank_bot : Module.rank R (⊥ : Submodule R M) = 0 := rank_subsingleton' _ _
variable {R M}
theorem exists_mem_ne_zero_of_rank_pos {s : Submodule R M} (h : 0 < Module.rank R s) :
∃ b : M, b ∈ s ∧ b ≠ 0 :=
exists_mem_ne_zero_of_ne_bot fun eq => by rw [eq, rank_bot] at h; exact lt_irrefl _ h
end RankZero
section Finite
theorem Module.finite_of_rank_eq_nat [Module.Free R M] {n : ℕ} (h : Module.rank R M = n) :
Module.Finite R M := by
nontriviality R
obtain ⟨⟨ι, b⟩⟩ := Module.Free.exists_basis (R := R) (M := M)
have := mk_lt_aleph0_iff.mp <|
b.linearIndependent.cardinal_le_rank |>.trans_eq h |>.trans_lt <| nat_lt_aleph0 n
exact Module.Finite.of_basis b
theorem Module.finite_of_rank_eq_zero [NoZeroSMulDivisors R M]
(h : Module.rank R M = 0) :
Module.Finite R M := by
nontriviality R
rw [rank_zero_iff] at h
infer_instance
theorem Module.finite_of_rank_eq_one [Module.Free R M] (h : Module.rank R M = 1) :
Module.Finite R M :=
Module.finite_of_rank_eq_nat <| h.trans Nat.cast_one.symm
section
variable [StrongRankCondition R]
/-- If a module has a finite dimension, all bases are indexed by a finite type. -/
theorem Basis.nonempty_fintype_index_of_rank_lt_aleph0 {ι : Type*} (b : Basis ι R M)
(h : Module.rank R M < ℵ₀) : Nonempty (Fintype ι) := by
rwa [← Cardinal.lift_lt, ← b.mk_eq_rank, Cardinal.lift_aleph0, Cardinal.lift_lt_aleph0,
Cardinal.lt_aleph0_iff_fintype] at h
/-- If a module has a finite dimension, all bases are indexed by a finite type. -/
noncomputable def Basis.fintypeIndexOfRankLtAleph0 {ι : Type*} (b : Basis ι R M)
(h : Module.rank R M < ℵ₀) : Fintype ι :=
Classical.choice (b.nonempty_fintype_index_of_rank_lt_aleph0 h)
/-- If a module has a finite dimension, all bases are indexed by a finite set. -/
theorem Basis.finite_index_of_rank_lt_aleph0 {ι : Type*} {s : Set ι} (b : Basis s R M)
(h : Module.rank R M < ℵ₀) : s.Finite :=
finite_def.2 (b.nonempty_fintype_index_of_rank_lt_aleph0 h)
end
namespace LinearIndependent
variable [StrongRankCondition R]
theorem cardinalMk_le_finrank [Module.Finite R M]
{ι : Type w} {b : ι → M} (h : LinearIndependent R b) : #ι ≤ finrank R M := by
rw [← lift_le.{max v w}]
simpa only [← finrank_eq_rank, lift_natCast, lift_le_nat_iff] using h.cardinal_lift_le_rank
@[deprecated (since := "2024-11-10")] alias cardinal_mk_le_finrank := cardinalMk_le_finrank
theorem fintype_card_le_finrank [Module.Finite R M]
{ι : Type*} [Fintype ι] {b : ι → M} (h : LinearIndependent R b) :
Fintype.card ι ≤ finrank R M := by
simpa using h.cardinalMk_le_finrank
theorem finset_card_le_finrank [Module.Finite R M]
{b : Finset M} (h : LinearIndependent R (fun x => x : b → M)) :
b.card ≤ finrank R M := by
rw [← Fintype.card_coe]
exact h.fintype_card_le_finrank
theorem lt_aleph0_of_finite {ι : Type w}
[Module.Finite R M] {v : ι → M} (h : LinearIndependent R v) : #ι < ℵ₀ := by
apply Cardinal.lift_lt.1
apply lt_of_le_of_lt
· apply h.cardinal_lift_le_rank
· rw [← finrank_eq_rank, Cardinal.lift_aleph0, Cardinal.lift_natCast]
apply Cardinal.nat_lt_aleph0
theorem finite [Module.Finite R M] {ι : Type*} {f : ι → M}
(h : LinearIndependent R f) : Finite ι :=
Cardinal.lt_aleph0_iff_finite.1 <| h.lt_aleph0_of_finite
theorem setFinite [Module.Finite R M] {b : Set M}
(h : LinearIndependent R fun x : b => (x : M)) : b.Finite :=
Cardinal.lt_aleph0_iff_set_finite.mp h.lt_aleph0_of_finite
end LinearIndependent
lemma exists_set_linearIndependent_of_lt_rank {n : Cardinal} (hn : n < Module.rank R M) :
∃ s : Set M, #s = n ∧ LinearIndepOn R id s := by
obtain ⟨⟨s, hs⟩, hs'⟩ := exists_lt_of_lt_ciSup' (hn.trans_eq (Module.rank_def R M))
obtain ⟨t, ht, ht'⟩ := le_mk_iff_exists_subset.mp hs'.le
exact ⟨t, ht', hs.mono ht⟩
lemma exists_finset_linearIndependent_of_le_rank {n : ℕ} (hn : n ≤ Module.rank R M) :
∃ s : Finset M, s.card = n ∧ LinearIndepOn R id (s : Set M) := by
have := nonempty_linearIndependent_set
rcases hn.eq_or_lt with h | h
· obtain ⟨⟨s, hs⟩, hs'⟩ := Cardinal.exists_eq_natCast_of_iSup_eq _
(Cardinal.bddAbove_range _) _ (h.trans (Module.rank_def R M)).symm
have : Finite s := lt_aleph0_iff_finite.mp (hs' ▸ nat_lt_aleph0 n)
cases nonempty_fintype s
refine ⟨s.toFinset, by simpa using hs', by simpa⟩
· obtain ⟨s, hs, hs'⟩ := exists_set_linearIndependent_of_lt_rank h
have : Finite s := lt_aleph0_iff_finite.mp (hs ▸ nat_lt_aleph0 n)
cases nonempty_fintype s
exact ⟨s.toFinset, by simpa using hs, by simpa⟩
lemma exists_linearIndependent_of_le_rank {n : ℕ} (hn : n ≤ Module.rank R M) :
∃ f : Fin n → M, LinearIndependent R f :=
have ⟨_, hs, hs'⟩ := exists_finset_linearIndependent_of_le_rank hn
⟨_, (linearIndependent_equiv (Finset.equivFinOfCardEq hs).symm).mpr hs'⟩
lemma natCast_le_rank_iff [Nontrivial R] {n : ℕ} :
n ≤ Module.rank R M ↔ ∃ f : Fin n → M, LinearIndependent R f :=
⟨exists_linearIndependent_of_le_rank,
fun H ↦ by simpa using H.choose_spec.cardinal_lift_le_rank⟩
lemma natCast_le_rank_iff_finset [Nontrivial R] {n : ℕ} :
n ≤ Module.rank R M ↔ ∃ s : Finset M, s.card = n ∧ LinearIndependent R ((↑) : s → M) :=
⟨exists_finset_linearIndependent_of_le_rank,
fun ⟨s, h₁, h₂⟩ ↦ by simpa [h₁] using h₂.cardinal_le_rank⟩
lemma exists_finset_linearIndependent_of_le_finrank {n : ℕ} (hn : n ≤ finrank R M) :
∃ s : Finset M, s.card = n ∧ LinearIndependent R ((↑) : s → M) := by
by_cases h : finrank R M = 0
· rw [le_zero_iff.mp (hn.trans_eq h)]
exact ⟨∅, rfl, by convert linearIndependent_empty R M using 2 <;> aesop⟩
exact exists_finset_linearIndependent_of_le_rank
((Nat.cast_le.mpr hn).trans_eq (cast_toNat_of_lt_aleph0 (toNat_ne_zero.mp h).2))
lemma exists_linearIndependent_of_le_finrank {n : ℕ} (hn : n ≤ finrank R M) :
∃ f : Fin n → M, LinearIndependent R f :=
have ⟨_, hs, hs'⟩ := exists_finset_linearIndependent_of_le_finrank hn
⟨_, (linearIndependent_equiv (Finset.equivFinOfCardEq hs).symm).mpr hs'⟩
variable [Module.Finite R M] [StrongRankCondition R] in
theorem Module.Finite.not_linearIndependent_of_infinite {ι : Type*} [Infinite ι]
(v : ι → M) : ¬LinearIndependent R v := mt LinearIndependent.finite <| @not_finite _ _
section
variable [NoZeroSMulDivisors R M]
theorem iSupIndep.subtype_ne_bot_le_rank [Nontrivial R]
{V : ι → Submodule R M} (hV : iSupIndep V) :
Cardinal.lift.{v} #{ i : ι // V i ≠ ⊥ } ≤ Cardinal.lift.{w} (Module.rank R M) := by
set I := { i : ι // V i ≠ ⊥ }
have hI : ∀ i : I, ∃ v ∈ V i, v ≠ (0 : M) := by
intro i
rw [← Submodule.ne_bot_iff]
exact i.prop
choose v hvV hv using hI
have : LinearIndependent R v := (hV.comp Subtype.coe_injective).linearIndependent _ hvV hv
exact this.cardinal_lift_le_rank
@[deprecated (since := "2024-11-24")]
alias CompleteLattice.Independent.subtype_ne_bot_le_rank := iSupIndep.subtype_ne_bot_le_rank
variable [Module.Finite R M] [StrongRankCondition R]
theorem iSupIndep.subtype_ne_bot_le_finrank_aux
{p : ι → Submodule R M} (hp : iSupIndep p) :
#{ i // p i ≠ ⊥ } ≤ (finrank R M : Cardinal.{w}) := by
suffices Cardinal.lift.{v} #{ i // p i ≠ ⊥ } ≤ Cardinal.lift.{v} (finrank R M : Cardinal.{w}) by
rwa [Cardinal.lift_le] at this
calc
Cardinal.lift.{v} #{ i // p i ≠ ⊥ } ≤ Cardinal.lift.{w} (Module.rank R M) :=
hp.subtype_ne_bot_le_rank
_ = Cardinal.lift.{w} (finrank R M : Cardinal.{v}) := by rw [finrank_eq_rank]
_ = Cardinal.lift.{v} (finrank R M : Cardinal.{w}) := by simp
/-- If `p` is an independent family of submodules of a `R`-finite module `M`, then the
number of nontrivial subspaces in the family `p` is finite. -/
noncomputable def iSupIndep.fintypeNeBotOfFiniteDimensional
{p : ι → Submodule R M} (hp : iSupIndep p) :
Fintype { i : ι // p i ≠ ⊥ } := by
suffices #{ i // p i ≠ ⊥ } < (ℵ₀ : Cardinal.{w}) by
rw [Cardinal.lt_aleph0_iff_fintype] at this
exact this.some
refine lt_of_le_of_lt hp.subtype_ne_bot_le_finrank_aux ?_
simp [Cardinal.nat_lt_aleph0]
/-- If `p` is an independent family of submodules of a `R`-finite module `M`, then the
number of nontrivial subspaces in the family `p` is bounded above by the dimension of `M`.
Note that the `Fintype` hypothesis required here can be provided by
`iSupIndep.fintypeNeBotOfFiniteDimensional`. -/
theorem iSupIndep.subtype_ne_bot_le_finrank
{p : ι → Submodule R M} (hp : iSupIndep p) [Fintype { i // p i ≠ ⊥ }] :
Fintype.card { i // p i ≠ ⊥ } ≤ finrank R M := by simpa using hp.subtype_ne_bot_le_finrank_aux
end
variable [Module.Finite R M] [StrongRankCondition R]
section
open Finset
/-- If a finset has cardinality larger than the rank of a module,
then there is a nontrivial linear relation amongst its elements. -/
theorem Module.exists_nontrivial_relation_of_finrank_lt_card {t : Finset M}
(h : finrank R M < t.card) : ∃ f : M → R, ∑ e ∈ t, f e • e = 0 ∧ ∃ x ∈ t, f x ≠ 0 := by
obtain ⟨g, sum, z, nonzero⟩ := Fintype.not_linearIndependent_iff.mp
(mt LinearIndependent.finset_card_le_finrank h.not_le)
refine ⟨Subtype.val.extend g 0, ?_, z, z.2, by rwa [Subtype.val_injective.extend_apply]⟩
rw [← Finset.sum_finset_coe]; convert sum; apply Subtype.val_injective.extend_apply
/-- If a finset has cardinality larger than `finrank + 1`,
then there is a nontrivial linear relation amongst its elements,
such that the coefficients of the relation sum to zero. -/
theorem Module.exists_nontrivial_relation_sum_zero_of_finrank_succ_lt_card
{t : Finset M} (h : finrank R M + 1 < t.card) :
∃ f : M → R, ∑ e ∈ t, f e • e = 0 ∧ ∑ e ∈ t, f e = 0 ∧ ∃ x ∈ t, f x ≠ 0 := by
-- Pick an element x₀ ∈ t,
obtain ⟨x₀, x₀_mem⟩ := card_pos.1 ((Nat.succ_pos _).trans h)
-- and apply the previous lemma to the {xᵢ - x₀}
let shift : M ↪ M := ⟨(· - x₀), sub_left_injective⟩
classical
let t' := (t.erase x₀).map shift
have h' : finrank R M < t'.card := by
rw [card_map, card_erase_of_mem x₀_mem]
exact Nat.lt_pred_iff.mpr h
-- to obtain a function `g`.
obtain ⟨g, gsum, x₁, x₁_mem, nz⟩ := exists_nontrivial_relation_of_finrank_lt_card h'
-- Then obtain `f` by translating back by `x₀`,
-- and setting the value of `f` at `x₀` to ensure `∑ e ∈ t, f e = 0`.
let f : M → R := fun z ↦ if z = x₀ then -∑ z ∈ t.erase x₀, g (z - x₀) else g (z - x₀)
refine ⟨f, ?_, ?_, ?_⟩
-- After this, it's a matter of verifying the properties,
-- based on the corresponding properties for `g`.
· rw [sum_map, Embedding.coeFn_mk] at gsum
simp_rw [f, ← t.sum_erase_add _ x₀_mem, if_pos, neg_smul, sum_smul,
← sub_eq_add_neg, ← sum_sub_distrib, ← gsum, smul_sub]
refine sum_congr rfl fun x x_mem ↦ ?_
rw [if_neg (mem_erase.mp x_mem).1]
· simp_rw [f, ← t.sum_erase_add _ x₀_mem, if_pos, add_neg_eq_zero]
exact sum_congr rfl fun x x_mem ↦ if_neg (mem_erase.mp x_mem).1
· obtain ⟨x₁, x₁_mem', rfl⟩ := Finset.mem_map.mp x₁_mem
have := mem_erase.mp x₁_mem'
exact ⟨x₁, by
simpa only [f, Embedding.coeFn_mk, sub_add_cancel, this.2, true_and, if_neg this.1]⟩
end
end Finite
section FinrankZero
section
variable [Nontrivial R]
/-- A (finite dimensional) space that is a subsingleton has zero `finrank`. -/
@[nontriviality]
theorem Module.finrank_zero_of_subsingleton [Subsingleton M] :
finrank R M = 0 := by
rw [finrank, rank_subsingleton', map_zero]
lemma LinearIndependent.finrank_eq_zero_of_infinite {ι} [Infinite ι] {v : ι → M}
(hv : LinearIndependent R v) : finrank R M = 0 := toNat_eq_zero.mpr <| .inr hv.aleph0_le_rank
section
variable [NoZeroSMulDivisors R M]
/-- A finite dimensional space is nontrivial if it has positive `finrank`. -/
theorem Module.nontrivial_of_finrank_pos (h : 0 < finrank R M) : Nontrivial M :=
rank_pos_iff_nontrivial.mp (lt_rank_of_lt_finrank h)
/-- A finite dimensional space is nontrivial if it has `finrank` equal to the successor of a
natural number. -/
theorem Module.nontrivial_of_finrank_eq_succ {n : ℕ}
(hn : finrank R M = n.succ) : Nontrivial M :=
nontrivial_of_finrank_pos (R := R) (by rw [hn]; exact n.succ_pos)
end
variable (R M)
@[simp]
theorem finrank_bot : finrank R (⊥ : Submodule R M) = 0 :=
finrank_eq_of_rank_eq (rank_bot _ _)
end
section StrongRankCondition
variable [StrongRankCondition R] [Module.Finite R M]
/-- A finite rank torsion-free module has positive `finrank` iff it has a nonzero element. -/
theorem Module.finrank_pos_iff_exists_ne_zero [NoZeroSMulDivisors R M] :
0 < finrank R M ↔ ∃ x : M, x ≠ 0 := by
rw [← @rank_pos_iff_exists_ne_zero R M, ← finrank_eq_rank]
norm_cast
/-- An `R`-finite torsion-free module has positive `finrank` iff it is nontrivial. -/
theorem Module.finrank_pos_iff [NoZeroSMulDivisors R M] :
0 < finrank R M ↔ Nontrivial M := by
rw [← rank_pos_iff_nontrivial (R := R), ← finrank_eq_rank]
norm_cast
/-- A nontrivial finite dimensional space has positive `finrank`. -/
theorem Module.finrank_pos [NoZeroSMulDivisors R M] [h : Nontrivial M] :
0 < finrank R M :=
finrank_pos_iff.mpr h
/-- See `Module.finrank_zero_iff`
for the stronger version with `NoZeroSMulDivisors R M`. -/
theorem Module.finrank_eq_zero_iff :
finrank R M = 0 ↔ ∀ x : M, ∃ a : R, a ≠ 0 ∧ a • x = 0 := by
rw [← rank_eq_zero_iff (R := R), ← finrank_eq_rank]
norm_cast
/-- A finite dimensional space has zero `finrank` iff it is a subsingleton.
This is the `finrank` version of `rank_zero_iff`. -/
theorem Module.finrank_zero_iff [NoZeroSMulDivisors R M] :
finrank R M = 0 ↔ Subsingleton M := by
rw [← rank_zero_iff (R := R), ← finrank_eq_rank]
norm_cast
/-- Similar to `rank_quotient_add_rank_le` but for `finrank` and a finite `M`. -/
lemma Module.finrank_quotient_add_finrank_le (N : Submodule R M) :
finrank R (M ⧸ N) + finrank R N ≤ finrank R M := by
haveI := nontrivial_of_invariantBasisNumber R
have := rank_quotient_add_rank_le N
rw [← finrank_eq_rank R M, ← finrank_eq_rank R, ← N.finrank_eq_rank] at this
exact mod_cast this
end StrongRankCondition
theorem Module.finrank_eq_zero_of_rank_eq_zero (h : Module.rank R M = 0) :
finrank R M = 0 := by
delta finrank
rw [h, zero_toNat]
theorem Submodule.bot_eq_top_of_rank_eq_zero [NoZeroSMulDivisors R M] (h : Module.rank R M = 0) :
(⊥ : Submodule R M) = ⊤ := by
nontriviality R
rw [rank_zero_iff] at h
subsingleton
/-- See `rank_subsingleton` for the reason that `Nontrivial R` is needed. -/
@[simp]
theorem Submodule.rank_eq_zero [Nontrivial R] [NoZeroSMulDivisors R M] {S : Submodule R M} :
Module.rank R S = 0 ↔ S = ⊥ :=
⟨fun h =>
(Submodule.eq_bot_iff _).2 fun x hx =>
congr_arg Subtype.val <|
((Submodule.eq_bot_iff _).1 <| Eq.symm <| Submodule.bot_eq_top_of_rank_eq_zero h) ⟨x, hx⟩
Submodule.mem_top,
fun h => by rw [h, rank_bot]⟩
@[simp]
theorem Submodule.finrank_eq_zero [StrongRankCondition R] [NoZeroSMulDivisors R M]
{S : Submodule R M} [Module.Finite R S] :
finrank R S = 0 ↔ S = ⊥ := by
rw [← Submodule.rank_eq_zero, ← finrank_eq_rank, ← @Nat.cast_zero Cardinal, Nat.cast_inj]
@[simp]
lemma Submodule.one_le_finrank_iff [StrongRankCondition R] [NoZeroSMulDivisors R M]
{S : Submodule R M} [Module.Finite R S] :
1 ≤ finrank R S ↔ S ≠ ⊥ := by
simp [← not_iff_not]
variable [Module.Free R M]
theorem finrank_eq_zero_of_basis_imp_not_finite
(h : ∀ s : Set M, Basis.{v} (s : Set M) R M → ¬s.Finite) : finrank R M = 0 := by
cases subsingleton_or_nontrivial R
· have := Module.subsingleton R M
exact (h ∅ ⟨LinearEquiv.ofSubsingleton _ _⟩ Set.finite_empty).elim
obtain ⟨_, ⟨b⟩⟩ := (Module.free_iff_set R M).mp ‹_›
have := Set.Infinite.to_subtype (h _ b)
exact b.linearIndependent.finrank_eq_zero_of_infinite
theorem finrank_eq_zero_of_basis_imp_false (h : ∀ s : Finset M, Basis.{v} (s : Set M) R M → False) :
finrank R M = 0 :=
finrank_eq_zero_of_basis_imp_not_finite fun s b hs =>
h hs.toFinset
(by
convert b
simp)
|
theorem finrank_eq_zero_of_not_exists_basis
(h : ¬∃ s : Finset M, Nonempty (Basis (s : Set M) R M)) : finrank R M = 0 :=
finrank_eq_zero_of_basis_imp_false fun s b => h ⟨s, ⟨b⟩⟩
theorem finrank_eq_zero_of_not_exists_basis_finite
(h : ¬∃ (s : Set M) (_ : Basis.{v} (s : Set M) R M), s.Finite) : finrank R M = 0 :=
| Mathlib/LinearAlgebra/Dimension/Finite.lean | 503 | 509 |
/-
Copyright (c) 2018 Jeremy Avigad. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jeremy Avigad
-/
import Mathlib.Data.PFunctor.Univariate.M
/-!
# Quotients of Polynomial Functors
We assume the following:
* `P`: a polynomial functor
* `W`: its W-type
* `M`: its M-type
* `F`: a functor
We define:
* `q`: `QPF` data, representing `F` as a quotient of `P`
The main goal is to construct:
* `Fix`: the initial algebra with structure map `F Fix → Fix`.
* `Cofix`: the final coalgebra with structure map `Cofix → F Cofix`
We also show that the composition of qpfs is a qpf, and that the quotient of a qpf
is a qpf.
The present theory focuses on the univariate case for qpfs
## References
* [Jeremy Avigad, Mario M. Carneiro and Simon Hudon, *Data Types as Quotients of Polynomial
Functors*][avigad-carneiro-hudon2019]
-/
universe u
/-- Quotients of polynomial functors.
Roughly speaking, saying that `F` is a quotient of a polynomial functor means that for each `α`,
elements of `F α` are represented by pairs `⟨a, f⟩`, where `a` is the shape of the object and
`f` indexes the relevant elements of `α`, in a suitably natural manner.
-/
class QPF (F : Type u → Type u) extends Functor F where
P : PFunctor.{u}
abs : ∀ {α}, P α → F α
repr : ∀ {α}, F α → P α
abs_repr : ∀ {α} (x : F α), abs (repr x) = x
abs_map : ∀ {α β} (f : α → β) (p : P α), abs (P.map f p) = f <$> abs p
namespace QPF
variable {F : Type u → Type u} [q : QPF F]
open Functor (Liftp Liftr)
/-
Show that every qpf is a lawful functor.
Note: every functor has a field, `map_const`, and `lawfulFunctor` has the defining
characterization. We can only propagate the assumption.
-/
theorem id_map {α : Type _} (x : F α) : id <$> x = x := by
rw [← abs_repr x]
obtain ⟨a, f⟩ := repr x
rw [← abs_map]
rfl
theorem comp_map {α β γ : Type _} (f : α → β) (g : β → γ) (x : F α) :
(g ∘ f) <$> x = g <$> f <$> x := by
rw [← abs_repr x]
obtain ⟨a, f⟩ := repr x
rw [← abs_map, ← abs_map, ← abs_map]
rfl
theorem lawfulFunctor
(h : ∀ α β : Type u, @Functor.mapConst F _ α _ = Functor.map ∘ Function.const β) :
LawfulFunctor F :=
{ map_const := @h
id_map := @id_map F _
comp_map := @comp_map F _ }
/-
Lifting predicates and relations
-/
section
open Functor
theorem liftp_iff {α : Type u} (p : α → Prop) (x : F α) :
Liftp p x ↔ ∃ a f, x = abs ⟨a, f⟩ ∧ ∀ i, p (f i) := by
constructor
· rintro ⟨y, hy⟩
rcases h : repr y with ⟨a, f⟩
use a, fun i => (f i).val
constructor
· rw [← hy, ← abs_repr y, h, ← abs_map]
rfl
intro i
apply (f i).property
rintro ⟨a, f, h₀, h₁⟩
use abs ⟨a, fun i => ⟨f i, h₁ i⟩⟩
rw [← abs_map, h₀]; rfl
theorem liftp_iff' {α : Type u} (p : α → Prop) (x : F α) :
Liftp p x ↔ ∃ u : q.P α, abs u = x ∧ ∀ i, p (u.snd i) := by
constructor
· rintro ⟨y, hy⟩
rcases h : repr y with ⟨a, f⟩
use ⟨a, fun i => (f i).val⟩
dsimp
constructor
· rw [← hy, ← abs_repr y, h, ← abs_map]
rfl
intro i
apply (f i).property
rintro ⟨⟨a, f⟩, h₀, h₁⟩; dsimp at *
use abs ⟨a, fun i => ⟨f i, h₁ i⟩⟩
rw [← abs_map, ← h₀]; rfl
theorem liftr_iff {α : Type u} (r : α → α → Prop) (x y : F α) :
Liftr r x y ↔ ∃ a f₀ f₁, x = abs ⟨a, f₀⟩ ∧ y = abs ⟨a, f₁⟩ ∧ ∀ i, r (f₀ i) (f₁ i) := by
constructor
· rintro ⟨u, xeq, yeq⟩
rcases h : repr u with ⟨a, f⟩
use a, fun i => (f i).val.fst, fun i => (f i).val.snd
constructor
· rw [← xeq, ← abs_repr u, h, ← abs_map]
rfl
constructor
· rw [← yeq, ← abs_repr u, h, ← abs_map]
rfl
intro i
exact (f i).property
rintro ⟨a, f₀, f₁, xeq, yeq, h⟩
use abs ⟨a, fun i => ⟨(f₀ i, f₁ i), h i⟩⟩
constructor
· rw [xeq, ← abs_map]
rfl
rw [yeq, ← abs_map]; rfl
end
/-
Think of trees in the `W` type corresponding to `P` as representatives of elements of the
least fixed point of `F`, and assign a canonical representative to each equivalence class
of trees.
-/
/-- does recursion on `q.P.W` using `g : F α → α` rather than `g : P α → α` -/
def recF {α : Type _} (g : F α → α) : q.P.W → α
| ⟨a, f⟩ => g (abs ⟨a, fun x => recF g (f x)⟩)
theorem recF_eq {α : Type _} (g : F α → α) (x : q.P.W) :
recF g x = g (abs (q.P.map (recF g) x.dest)) := by
cases x
rfl
theorem recF_eq' {α : Type _} (g : F α → α) (a : q.P.A) (f : q.P.B a → q.P.W) :
recF g ⟨a, f⟩ = g (abs (q.P.map (recF g) ⟨a, f⟩)) :=
rfl
/-- two trees are equivalent if their F-abstractions are -/
inductive Wequiv : q.P.W → q.P.W → Prop
| ind (a : q.P.A) (f f' : q.P.B a → q.P.W) : (∀ x, Wequiv (f x) (f' x)) → Wequiv ⟨a, f⟩ ⟨a, f'⟩
| abs (a : q.P.A) (f : q.P.B a → q.P.W) (a' : q.P.A) (f' : q.P.B a' → q.P.W) :
abs ⟨a, f⟩ = abs ⟨a', f'⟩ → Wequiv ⟨a, f⟩ ⟨a', f'⟩
| trans (u v w : q.P.W) : Wequiv u v → Wequiv v w → Wequiv u w
/-- `recF` is insensitive to the representation -/
theorem recF_eq_of_Wequiv {α : Type u} (u : F α → α) (x y : q.P.W) :
Wequiv x y → recF u x = recF u y := by
intro h
induction h with
| ind a f f' _ ih => simp only [recF_eq', PFunctor.map_eq, Function.comp_def, ih]
| abs a f a' f' h => simp only [recF_eq', abs_map, h]
| trans x y z _ _ ih₁ ih₂ => exact Eq.trans ih₁ ih₂
theorem Wequiv.abs' (x y : q.P.W) (h : QPF.abs x.dest = QPF.abs y.dest) : Wequiv x y := by
cases x
cases y
apply Wequiv.abs
apply h
theorem Wequiv.refl (x : q.P.W) : Wequiv x x := by
obtain ⟨a, f⟩ := x
exact Wequiv.abs a f a f rfl
theorem Wequiv.symm (x y : q.P.W) : Wequiv x y → Wequiv y x := by
intro h
induction h with
| ind a f f' _ ih => exact Wequiv.ind _ _ _ ih
| abs a f a' f' h => exact Wequiv.abs _ _ _ _ h.symm
| trans x y z _ _ ih₁ ih₂ => exact QPF.Wequiv.trans _ _ _ ih₂ ih₁
/-- maps every element of the W type to a canonical representative -/
def Wrepr : q.P.W → q.P.W :=
recF (PFunctor.W.mk ∘ repr)
theorem Wrepr_equiv (x : q.P.W) : Wequiv (Wrepr x) x := by
induction' x with a f ih
apply Wequiv.trans
· change Wequiv (Wrepr ⟨a, f⟩) (PFunctor.W.mk (q.P.map Wrepr ⟨a, f⟩))
apply Wequiv.abs'
have : Wrepr ⟨a, f⟩ = PFunctor.W.mk (repr (abs (q.P.map Wrepr ⟨a, f⟩))) := rfl
rw [this, PFunctor.W.dest_mk, abs_repr]
rfl
apply Wequiv.ind; exact ih
/-- Define the fixed point as the quotient of trees under the equivalence relation `Wequiv`. -/
def Wsetoid : Setoid q.P.W :=
⟨Wequiv, @Wequiv.refl _ _, @Wequiv.symm _ _, @Wequiv.trans _ _⟩
attribute [local instance] Wsetoid
/-- inductive type defined as initial algebra of a Quotient of Polynomial Functor -/
def Fix (F : Type u → Type u) [q : QPF F] :=
Quotient (Wsetoid : Setoid q.P.W)
/-- recursor of a type defined by a qpf -/
def Fix.rec {α : Type _} (g : F α → α) : Fix F → α :=
Quot.lift (recF g) (recF_eq_of_Wequiv g)
/-- access the underlying W-type of a fixpoint data type -/
def fixToW : Fix F → q.P.W :=
Quotient.lift Wrepr (recF_eq_of_Wequiv fun x => @PFunctor.W.mk q.P (repr x))
/-- constructor of a type defined by a qpf -/
def Fix.mk (x : F (Fix F)) : Fix F :=
Quot.mk _ (PFunctor.W.mk (q.P.map fixToW (repr x)))
/-- destructor of a type defined by a qpf -/
def Fix.dest : Fix F → F (Fix F) :=
Fix.rec (Functor.map Fix.mk)
theorem Fix.rec_eq {α : Type _} (g : F α → α) (x : F (Fix F)) :
Fix.rec g (Fix.mk x) = g (Fix.rec g <$> x) := by
have : recF g ∘ fixToW = Fix.rec g := by
ext ⟨x⟩
apply recF_eq_of_Wequiv
rw [fixToW]
apply Wrepr_equiv
conv =>
lhs
rw [Fix.rec, Fix.mk]
dsimp
rcases h : repr x with ⟨a, f⟩
rw [PFunctor.map_eq, recF_eq, ← PFunctor.map_eq, PFunctor.W.dest_mk, PFunctor.map_map, abs_map,
← h, abs_repr, this]
theorem Fix.ind_aux (a : q.P.A) (f : q.P.B a → q.P.W) :
Fix.mk (abs ⟨a, fun x => ⟦f x⟧⟩) = ⟦⟨a, f⟩⟧ := by
have : Fix.mk (abs ⟨a, fun x => ⟦f x⟧⟩) = ⟦Wrepr ⟨a, f⟩⟧ := by
apply Quot.sound; apply Wequiv.abs'
rw [PFunctor.W.dest_mk, abs_map, abs_repr, ← abs_map, PFunctor.map_eq]
simp only [Wrepr, recF_eq, PFunctor.W.dest_mk, abs_repr, Function.comp]
rfl
rw [this]
apply Quot.sound
apply Wrepr_equiv
theorem Fix.ind_rec {α : Type u} (g₁ g₂ : Fix F → α)
(h : ∀ x : F (Fix F), g₁ <$> x = g₂ <$> x → g₁ (Fix.mk x) = g₂ (Fix.mk x)) :
∀ x, g₁ x = g₂ x := by
rintro ⟨x⟩
induction' x with a f ih
change g₁ ⟦⟨a, f⟩⟧ = g₂ ⟦⟨a, f⟩⟧
rw [← Fix.ind_aux a f]; apply h
rw [← abs_map, ← abs_map, PFunctor.map_eq, PFunctor.map_eq]
congr with x
apply ih
theorem Fix.rec_unique {α : Type u} (g : F α → α) (h : Fix F → α)
(hyp : ∀ x, h (Fix.mk x) = g (h <$> x)) : Fix.rec g = h := by
ext x
apply Fix.ind_rec
intro x hyp'
rw [hyp, ← hyp', Fix.rec_eq]
theorem Fix.mk_dest (x : Fix F) : Fix.mk (Fix.dest x) = x := by
change (Fix.mk ∘ Fix.dest) x = id x
apply Fix.ind_rec (mk ∘ dest) id
intro x
rw [Function.comp_apply, id_eq, Fix.dest, Fix.rec_eq, id_map, comp_map]
intro h
rw [h]
theorem Fix.dest_mk (x : F (Fix F)) : Fix.dest (Fix.mk x) = x := by
unfold Fix.dest; rw [Fix.rec_eq, ← Fix.dest, ← comp_map]
conv =>
rhs
rw [← id_map x]
congr with x
apply Fix.mk_dest
theorem Fix.ind (p : Fix F → Prop) (h : ∀ x : F (Fix F), Liftp p x → p (Fix.mk x)) : ∀ x, p x := by
rintro ⟨x⟩
induction' x with a f ih
change p ⟦⟨a, f⟩⟧
rw [← Fix.ind_aux a f]
apply h
rw [liftp_iff]
refine ⟨_, _, rfl, ?_⟩
convert ih
end QPF
/-
Construct the final coalgebra to a qpf.
-/
namespace QPF
variable {F : Type u → Type u} [q : QPF F]
open Functor (Liftp Liftr)
/-- does recursion on `q.P.M` using `g : α → F α` rather than `g : α → P α` -/
| def corecF {α : Type _} (g : α → F α) : α → q.P.M :=
PFunctor.M.corec fun x => repr (g x)
theorem corecF_eq {α : Type _} (g : α → F α) (x : α) :
PFunctor.M.dest (corecF g x) = q.P.map (corecF g) (repr (g x)) := by
rw [corecF, PFunctor.M.dest_corec]
| Mathlib/Data/QPF/Univariate/Basic.lean | 322 | 327 |
/-
Copyright (c) 2020 Patrick Massot. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Patrick Massot
-/
import Mathlib.Topology.Path
/-!
# Path connectedness
Continuing from `Mathlib.Topology.Path`, this file defines path components and path-connected
spaces.
## Main definitions
In the file the unit interval `[0, 1]` in `ℝ` is denoted by `I`, and `X` is a topological space.
* `Joined (x y : X)` means there is a path between `x` and `y`.
* `Joined.somePath (h : Joined x y)` selects some path between two points `x` and `y`.
* `pathComponent (x : X)` is the set of points joined to `x`.
* `PathConnectedSpace X` is a predicate class asserting that `X` is non-empty and every two
points of `X` are joined.
Then there are corresponding relative notions for `F : Set X`.
* `JoinedIn F (x y : X)` means there is a path `γ` joining `x` to `y` with values in `F`.
* `JoinedIn.somePath (h : JoinedIn F x y)` selects a path from `x` to `y` inside `F`.
* `pathComponentIn F (x : X)` is the set of points joined to `x` in `F`.
* `IsPathConnected F` asserts that `F` is non-empty and every two
points of `F` are joined in `F`.
## Main theorems
* `Joined` is an equivalence relation, while `JoinedIn F` is at least symmetric and transitive.
One can link the absolute and relative version in two directions, using `(univ : Set X)` or the
subtype `↥F`.
* `pathConnectedSpace_iff_univ : PathConnectedSpace X ↔ IsPathConnected (univ : Set X)`
* `isPathConnected_iff_pathConnectedSpace : IsPathConnected F ↔ PathConnectedSpace ↥F`
Furthermore, it is shown that continuous images and quotients of path-connected sets/spaces are
path-connected, and that every path-connected set/space is also connected.
-/
noncomputable section
open Topology Filter unitInterval Set Function
variable {X Y : Type*} [TopologicalSpace X] [TopologicalSpace Y] {x y z : X} {ι : Type*}
/-! ### Being joined by a path -/
/-- The relation "being joined by a path". This is an equivalence relation. -/
def Joined (x y : X) : Prop :=
Nonempty (Path x y)
@[refl]
theorem Joined.refl (x : X) : Joined x x :=
⟨Path.refl x⟩
/-- When two points are joined, choose some path from `x` to `y`. -/
def Joined.somePath (h : Joined x y) : Path x y :=
Nonempty.some h
@[symm]
theorem Joined.symm {x y : X} (h : Joined x y) : Joined y x :=
⟨h.somePath.symm⟩
@[trans]
theorem Joined.trans {x y z : X} (hxy : Joined x y) (hyz : Joined y z) : Joined x z :=
⟨hxy.somePath.trans hyz.somePath⟩
variable (X)
/-- The setoid corresponding the equivalence relation of being joined by a continuous path. -/
def pathSetoid : Setoid X where
r := Joined
iseqv := Equivalence.mk Joined.refl Joined.symm Joined.trans
/-- The quotient type of points of a topological space modulo being joined by a continuous path. -/
def ZerothHomotopy :=
Quotient (pathSetoid X)
instance ZerothHomotopy.inhabited : Inhabited (ZerothHomotopy ℝ) :=
⟨@Quotient.mk' ℝ (pathSetoid ℝ) 0⟩
variable {X}
/-! ### Being joined by a path inside a set -/
/-- The relation "being joined by a path in `F`". Not quite an equivalence relation since it's not
reflexive for points that do not belong to `F`. -/
def JoinedIn (F : Set X) (x y : X) : Prop :=
∃ γ : Path x y, ∀ t, γ t ∈ F
variable {F : Set X}
theorem JoinedIn.mem (h : JoinedIn F x y) : x ∈ F ∧ y ∈ F := by
rcases h with ⟨γ, γ_in⟩
have : γ 0 ∈ F ∧ γ 1 ∈ F := by constructor <;> apply γ_in
simpa using this
theorem JoinedIn.source_mem (h : JoinedIn F x y) : x ∈ F :=
h.mem.1
theorem JoinedIn.target_mem (h : JoinedIn F x y) : y ∈ F :=
h.mem.2
/-- When `x` and `y` are joined in `F`, choose a path from `x` to `y` inside `F` -/
def JoinedIn.somePath (h : JoinedIn F x y) : Path x y :=
Classical.choose h
theorem JoinedIn.somePath_mem (h : JoinedIn F x y) (t : I) : h.somePath t ∈ F :=
Classical.choose_spec h t
/-- If `x` and `y` are joined in the set `F`, then they are joined in the subtype `F`. -/
theorem JoinedIn.joined_subtype (h : JoinedIn F x y) :
Joined (⟨x, h.source_mem⟩ : F) (⟨y, h.target_mem⟩ : F) :=
⟨{ toFun := fun t => ⟨h.somePath t, h.somePath_mem t⟩
continuous_toFun := by fun_prop
source' := by simp
target' := by simp }⟩
theorem JoinedIn.ofLine {f : ℝ → X} (hf : ContinuousOn f I) (h₀ : f 0 = x) (h₁ : f 1 = y)
(hF : f '' I ⊆ F) : JoinedIn F x y :=
⟨Path.ofLine hf h₀ h₁, fun t => hF <| Path.ofLine_mem hf h₀ h₁ t⟩
theorem JoinedIn.joined (h : JoinedIn F x y) : Joined x y :=
⟨h.somePath⟩
theorem joinedIn_iff_joined (x_in : x ∈ F) (y_in : y ∈ F) :
JoinedIn F x y ↔ Joined (⟨x, x_in⟩ : F) (⟨y, y_in⟩ : F) :=
⟨fun h => h.joined_subtype, fun h => ⟨h.somePath.map continuous_subtype_val, by simp⟩⟩
@[simp]
theorem joinedIn_univ : JoinedIn univ x y ↔ Joined x y := by
simp [JoinedIn, Joined, exists_true_iff_nonempty]
theorem JoinedIn.mono {U V : Set X} (h : JoinedIn U x y) (hUV : U ⊆ V) : JoinedIn V x y :=
⟨h.somePath, fun t => hUV (h.somePath_mem t)⟩
theorem JoinedIn.refl (h : x ∈ F) : JoinedIn F x x :=
⟨Path.refl x, fun _t => h⟩
@[symm]
theorem JoinedIn.symm (h : JoinedIn F x y) : JoinedIn F y x := by
obtain ⟨hx, hy⟩ := h.mem
simp_all only [joinedIn_iff_joined]
exact h.symm
theorem JoinedIn.trans (hxy : JoinedIn F x y) (hyz : JoinedIn F y z) : JoinedIn F x z := by
obtain ⟨hx, hy⟩ := hxy.mem
obtain ⟨hx, hy⟩ := hyz.mem
simp_all only [joinedIn_iff_joined]
exact hxy.trans hyz
theorem Specializes.joinedIn (h : x ⤳ y) (hx : x ∈ F) (hy : y ∈ F) : JoinedIn F x y := by
refine ⟨⟨⟨Set.piecewise {1} (const I y) (const I x), ?_⟩, by simp, by simp⟩, fun t ↦ ?_⟩
· exact isClosed_singleton.continuous_piecewise_of_specializes continuous_const continuous_const
fun _ ↦ h
· simp only [Path.coe_mk_mk, piecewise]
split_ifs <;> assumption
theorem Inseparable.joinedIn (h : Inseparable x y) (hx : x ∈ F) (hy : y ∈ F) : JoinedIn F x y :=
h.specializes.joinedIn hx hy
theorem JoinedIn.map_continuousOn (h : JoinedIn F x y) {f : X → Y} (hf : ContinuousOn f F) :
JoinedIn (f '' F) (f x) (f y) :=
let ⟨γ, hγ⟩ := h
⟨γ.map' <| hf.mono (range_subset_iff.mpr hγ), fun t ↦ mem_image_of_mem _ (hγ t)⟩
theorem JoinedIn.map (h : JoinedIn F x y) {f : X → Y} (hf : Continuous f) :
JoinedIn (f '' F) (f x) (f y) :=
h.map_continuousOn hf.continuousOn
theorem Topology.IsInducing.joinedIn_image {f : X → Y} (hf : IsInducing f) (hx : x ∈ F)
(hy : y ∈ F) : JoinedIn (f '' F) (f x) (f y) ↔ JoinedIn F x y := by
refine ⟨?_, (.map · hf.continuous)⟩
rintro ⟨γ, hγ⟩
choose γ' hγ'F hγ' using hγ
have h₀ : x ⤳ γ' 0 := by rw [← hf.specializes_iff, hγ', γ.source]
have h₁ : γ' 1 ⤳ y := by rw [← hf.specializes_iff, hγ', γ.target]
have h : JoinedIn F (γ' 0) (γ' 1) := by
refine ⟨⟨⟨γ', ?_⟩, rfl, rfl⟩, hγ'F⟩
simpa only [hf.continuous_iff, comp_def, hγ'] using map_continuous γ
exact (h₀.joinedIn hx (hγ'F _)).trans <| h.trans <| h₁.joinedIn (hγ'F _) hy
@[deprecated (since := "2024-10-28")] alias Inducing.joinedIn_image := IsInducing.joinedIn_image
/-! ### Path component -/
/-- The path component of `x` is the set of points that can be joined to `x`. -/
def pathComponent (x : X) :=
{ y | Joined x y }
theorem mem_pathComponent_iff : x ∈ pathComponent y ↔ Joined y x := .rfl
@[simp]
theorem mem_pathComponent_self (x : X) : x ∈ pathComponent x :=
Joined.refl x
@[simp]
theorem pathComponent.nonempty (x : X) : (pathComponent x).Nonempty :=
⟨x, mem_pathComponent_self x⟩
theorem mem_pathComponent_of_mem (h : x ∈ pathComponent y) : y ∈ pathComponent x :=
Joined.symm h
theorem pathComponent_symm : x ∈ pathComponent y ↔ y ∈ pathComponent x :=
⟨fun h => mem_pathComponent_of_mem h, fun h => mem_pathComponent_of_mem h⟩
theorem pathComponent_congr (h : x ∈ pathComponent y) : pathComponent x = pathComponent y := by
ext z
constructor
· intro h'
rw [pathComponent_symm]
exact (h.trans h').symm
· intro h'
rw [pathComponent_symm] at h' ⊢
exact h'.trans h
theorem pathComponent_subset_component (x : X) : pathComponent x ⊆ connectedComponent x :=
fun y h =>
(isConnected_range h.somePath.continuous).subset_connectedComponent ⟨0, by simp⟩ ⟨1, by simp⟩
/-- The path component of `x` in `F` is the set of points that can be joined to `x` in `F`. -/
def pathComponentIn (x : X) (F : Set X) :=
{ y | JoinedIn F x y }
@[simp]
theorem pathComponentIn_univ (x : X) : pathComponentIn x univ = pathComponent x := by
simp [pathComponentIn, pathComponent, JoinedIn, Joined, exists_true_iff_nonempty]
theorem Joined.mem_pathComponent (hyz : Joined y z) (hxy : y ∈ pathComponent x) :
z ∈ pathComponent x :=
hxy.trans hyz
theorem mem_pathComponentIn_self (h : x ∈ F) : x ∈ pathComponentIn x F :=
JoinedIn.refl h
theorem pathComponentIn_subset : pathComponentIn x F ⊆ F :=
fun _ hy ↦ hy.target_mem
theorem pathComponentIn_nonempty_iff : (pathComponentIn x F).Nonempty ↔ x ∈ F :=
⟨fun ⟨_, ⟨γ, hγ⟩⟩ ↦ γ.source ▸ hγ 0, fun hx ↦ ⟨x, mem_pathComponentIn_self hx⟩⟩
theorem pathComponentIn_congr (h : x ∈ pathComponentIn y F) :
pathComponentIn x F = pathComponentIn y F := by
ext; exact ⟨h.trans, h.symm.trans⟩
@[gcongr]
theorem pathComponentIn_mono {G : Set X} (h : F ⊆ G) :
pathComponentIn x F ⊆ pathComponentIn x G :=
fun _ ⟨γ, hγ⟩ ↦ ⟨γ, fun t ↦ h (hγ t)⟩
/-! ### Path connected sets -/
/-- A set `F` is path connected if it contains a point that can be joined to all other in `F`. -/
def IsPathConnected (F : Set X) : Prop :=
∃ x ∈ F, ∀ {y}, y ∈ F → JoinedIn F x y
theorem isPathConnected_iff_eq : IsPathConnected F ↔ ∃ x ∈ F, pathComponentIn x F = F := by
constructor <;> rintro ⟨x, x_in, h⟩ <;> use x, x_in
· ext y
exact ⟨fun hy => hy.mem.2, h⟩
· intro y y_in
rwa [← h] at y_in
theorem IsPathConnected.joinedIn (h : IsPathConnected F) :
∀ᵉ (x ∈ F) (y ∈ F), JoinedIn F x y := fun _x x_in _y y_in =>
let ⟨_b, _b_in, hb⟩ := h
(hb x_in).symm.trans (hb y_in)
theorem isPathConnected_iff :
IsPathConnected F ↔ F.Nonempty ∧ ∀ᵉ (x ∈ F) (y ∈ F), JoinedIn F x y :=
⟨fun h =>
⟨let ⟨b, b_in, _hb⟩ := h; ⟨b, b_in⟩, h.joinedIn⟩,
fun ⟨⟨b, b_in⟩, h⟩ => ⟨b, b_in, fun x_in => h _ b_in _ x_in⟩⟩
/-- If `f` is continuous on `F` and `F` is path-connected, so is `f(F)`. -/
theorem IsPathConnected.image' (hF : IsPathConnected F)
{f : X → Y} (hf : ContinuousOn f F) : IsPathConnected (f '' F) := by
rcases hF with ⟨x, x_in, hx⟩
use f x, mem_image_of_mem f x_in
rintro _ ⟨y, y_in, rfl⟩
refine ⟨(hx y_in).somePath.map' ?_, fun t ↦ ⟨_, (hx y_in).somePath_mem t, rfl⟩⟩
exact hf.mono (range_subset_iff.2 (hx y_in).somePath_mem)
/-- If `f` is continuous and `F` is path-connected, so is `f(F)`. -/
theorem IsPathConnected.image (hF : IsPathConnected F) {f : X → Y} (hf : Continuous f) :
IsPathConnected (f '' F) :=
hF.image' hf.continuousOn
/-- If `f : X → Y` is an inducing map, `f(F)` is path-connected iff `F` is. -/
nonrec theorem Topology.IsInducing.isPathConnected_iff {f : X → Y} (hf : IsInducing f) :
IsPathConnected F ↔ IsPathConnected (f '' F) := by
simp only [IsPathConnected, forall_mem_image, exists_mem_image]
refine exists_congr fun x ↦ and_congr_right fun hx ↦ forall₂_congr fun y hy ↦ ?_
rw [hf.joinedIn_image hx hy]
@[deprecated (since := "2024-10-28")]
alias Inducing.isPathConnected_iff := IsInducing.isPathConnected_iff
/-- If `h : X → Y` is a homeomorphism, `h(s)` is path-connected iff `s` is. -/
@[simp]
theorem Homeomorph.isPathConnected_image {s : Set X} (h : X ≃ₜ Y) :
IsPathConnected (h '' s) ↔ IsPathConnected s :=
h.isInducing.isPathConnected_iff.symm
/-- If `h : X → Y` is a homeomorphism, `h⁻¹(s)` is path-connected iff `s` is. -/
@[simp]
theorem Homeomorph.isPathConnected_preimage {s : Set Y} (h : X ≃ₜ Y) :
IsPathConnected (h ⁻¹' s) ↔ IsPathConnected s := by
rw [← Homeomorph.image_symm]; exact h.symm.isPathConnected_image
theorem IsPathConnected.mem_pathComponent (h : IsPathConnected F) (x_in : x ∈ F) (y_in : y ∈ F) :
y ∈ pathComponent x :=
(h.joinedIn x x_in y y_in).joined
theorem IsPathConnected.subset_pathComponent (h : IsPathConnected F) (x_in : x ∈ F) :
F ⊆ pathComponent x := fun _y y_in => h.mem_pathComponent x_in y_in
theorem IsPathConnected.subset_pathComponentIn {s : Set X} (hs : IsPathConnected s)
(hxs : x ∈ s) (hsF : s ⊆ F) : s ⊆ pathComponentIn x F :=
fun y hys ↦ (hs.joinedIn x hxs y hys).mono hsF
theorem isPathConnected_singleton (x : X) : IsPathConnected ({x} : Set X) := by
refine ⟨x, rfl, ?_⟩
rintro y rfl
exact JoinedIn.refl rfl
theorem isPathConnected_pathComponentIn (h : x ∈ F) : IsPathConnected (pathComponentIn x F) :=
⟨x, mem_pathComponentIn_self h, fun ⟨γ, hγ⟩ ↦ by
refine ⟨γ, fun t ↦
⟨(γ.truncateOfLE t.2.1).cast (γ.extend_zero.symm) (γ.extend_extends' t).symm, fun t' ↦ ?_⟩⟩
dsimp [Path.truncateOfLE, Path.truncate]
exact γ.extend_extends' ⟨min (max t'.1 0) t.1, by simp [t.2.1, t.2.2]⟩ ▸ hγ _⟩
theorem isPathConnected_pathComponent : IsPathConnected (pathComponent x) := by
rw [← pathComponentIn_univ]
exact isPathConnected_pathComponentIn (mem_univ x)
theorem IsPathConnected.union {U V : Set X} (hU : IsPathConnected U) (hV : IsPathConnected V)
(hUV : (U ∩ V).Nonempty) : IsPathConnected (U ∪ V) := by
rcases hUV with ⟨x, xU, xV⟩
use x, Or.inl xU
rintro y (yU | yV)
· exact (hU.joinedIn x xU y yU).mono subset_union_left
· exact (hV.joinedIn x xV y yV).mono subset_union_right
/-- If a set `W` is path-connected, then it is also path-connected when seen as a set in a smaller
ambient type `U` (when `U` contains `W`). -/
theorem IsPathConnected.preimage_coe {U W : Set X} (hW : IsPathConnected W) (hWU : W ⊆ U) :
IsPathConnected (((↑) : U → X) ⁻¹' W) := by
rwa [IsInducing.subtypeVal.isPathConnected_iff, Subtype.image_preimage_val, inter_eq_right.2 hWU]
theorem IsPathConnected.exists_path_through_family {n : ℕ}
{s : Set X} (h : IsPathConnected s) (p : Fin (n + 1) → X) (hp : ∀ i, p i ∈ s) :
∃ γ : Path (p 0) (p n), range γ ⊆ s ∧ ∀ i, p i ∈ range γ := by
let p' : ℕ → X := fun k => if h : k < n + 1 then p ⟨k, h⟩ else p ⟨0, n.zero_lt_succ⟩
obtain ⟨γ, hγ⟩ : ∃ γ : Path (p' 0) (p' n), (∀ i ≤ n, p' i ∈ range γ) ∧ range γ ⊆ s := by
have hp' : ∀ i ≤ n, p' i ∈ s := by
intro i hi
simp [p', Nat.lt_succ_of_le hi, hp]
clear_value p'
clear hp p
induction n with
| zero =>
use Path.refl (p' 0)
constructor
· rintro i hi
rw [Nat.le_zero.mp hi]
exact ⟨0, rfl⟩
· rw [range_subset_iff]
rintro _x
exact hp' 0 le_rfl
| succ n hn =>
rcases hn fun i hi => hp' i <| Nat.le_succ_of_le hi with ⟨γ₀, hγ₀⟩
rcases h.joinedIn (p' n) (hp' n n.le_succ) (p' <| n + 1) (hp' (n + 1) <| le_rfl) with
⟨γ₁, hγ₁⟩
let γ : Path (p' 0) (p' <| n + 1) := γ₀.trans γ₁
use γ
have range_eq : range γ = range γ₀ ∪ range γ₁ := γ₀.trans_range γ₁
constructor
· rintro i hi
by_cases hi' : i ≤ n
· rw [range_eq]
left
exact hγ₀.1 i hi'
· rw [not_le, ← Nat.succ_le_iff] at hi'
have : i = n.succ := le_antisymm hi hi'
rw [this]
use 1
exact γ.target
· rw [range_eq]
apply union_subset hγ₀.2
rw [range_subset_iff]
exact hγ₁
have hpp' : ∀ k < n + 1, p k = p' k := by
intro k hk
simp only [p', hk, dif_pos]
congr
ext
rw [Fin.val_cast_of_lt hk]
use γ.cast (hpp' 0 n.zero_lt_succ) (hpp' n n.lt_succ_self)
simp only [γ.cast_coe]
refine And.intro hγ.2 ?_
rintro ⟨i, hi⟩
suffices p ⟨i, hi⟩ = p' i by convert hγ.1 i (Nat.le_of_lt_succ hi)
rw [← hpp' i hi]
suffices i = i % n.succ by congr
rw [Nat.mod_eq_of_lt hi]
theorem IsPathConnected.exists_path_through_family' {n : ℕ}
{s : Set X} (h : IsPathConnected s) (p : Fin (n + 1) → X) (hp : ∀ i, p i ∈ s) :
∃ (γ : Path (p 0) (p n)) (t : Fin (n + 1) → I), (∀ t, γ t ∈ s) ∧ ∀ i, γ (t i) = p i := by
rcases h.exists_path_through_family p hp with ⟨γ, hγ⟩
rcases hγ with ⟨h₁, h₂⟩
simp only [range, mem_setOf_eq] at h₂
rw [range_subset_iff] at h₁
choose! t ht using h₂
exact ⟨γ, t, h₁, ht⟩
/-! ### Path connected spaces -/
/-- A topological space is path-connected if it is non-empty and every two points can be
joined by a continuous path. -/
@[mk_iff]
class PathConnectedSpace (X : Type*) [TopologicalSpace X] : Prop where
/-- A path-connected space must be nonempty. -/
nonempty : Nonempty X
/-- Any two points in a path-connected space must be joined by a continuous path. -/
joined : ∀ x y : X, Joined x y
theorem pathConnectedSpace_iff_zerothHomotopy :
PathConnectedSpace X ↔ Nonempty (ZerothHomotopy X) ∧ Subsingleton (ZerothHomotopy X) := by
letI := pathSetoid X
constructor
· intro h
refine ⟨(nonempty_quotient_iff _).mpr h.1, ⟨?_⟩⟩
rintro ⟨x⟩ ⟨y⟩
exact Quotient.sound (PathConnectedSpace.joined x y)
· unfold ZerothHomotopy
rintro ⟨h, h'⟩
exact ⟨(nonempty_quotient_iff _).mp h, fun x y => Quotient.exact <| Subsingleton.elim ⟦x⟧ ⟦y⟧⟩
namespace PathConnectedSpace
variable [PathConnectedSpace X]
/-- Use path-connectedness to build a path between two points. -/
def somePath (x y : X) : Path x y :=
Nonempty.some (joined x y)
end PathConnectedSpace
theorem pathConnectedSpace_iff_univ : PathConnectedSpace X ↔ IsPathConnected (univ : Set X) := by
simp [pathConnectedSpace_iff, isPathConnected_iff, nonempty_iff_univ_nonempty]
theorem isPathConnected_iff_pathConnectedSpace : IsPathConnected F ↔ PathConnectedSpace F := by
rw [pathConnectedSpace_iff_univ, IsInducing.subtypeVal.isPathConnected_iff, image_univ,
Subtype.range_val_subtype, setOf_mem_eq]
theorem isPathConnected_univ [PathConnectedSpace X] : IsPathConnected (univ : Set X) :=
pathConnectedSpace_iff_univ.mp inferInstance
theorem isPathConnected_range [PathConnectedSpace X] {f : X → Y} (hf : Continuous f) :
IsPathConnected (range f) := by
rw [← image_univ]
exact isPathConnected_univ.image hf
theorem Function.Surjective.pathConnectedSpace [PathConnectedSpace X]
{f : X → Y} (hf : Surjective f) (hf' : Continuous f) : PathConnectedSpace Y := by
rw [pathConnectedSpace_iff_univ, ← hf.range_eq]
exact isPathConnected_range hf'
instance Quotient.instPathConnectedSpace {s : Setoid X} [PathConnectedSpace X] :
PathConnectedSpace (Quotient s) :=
Quotient.mk'_surjective.pathConnectedSpace continuous_coinduced_rng
/-- This is a special case of `NormedSpace.instPathConnectedSpace` (and
`IsTopologicalAddGroup.pathConnectedSpace`). It exists only to simplify dependencies. -/
instance Real.instPathConnectedSpace : PathConnectedSpace ℝ where
joined x y := ⟨⟨⟨fun (t : I) ↦ (1 - t) * x + t * y, by fun_prop⟩, by simp, by simp⟩⟩
nonempty := inferInstance
theorem pathConnectedSpace_iff_eq : PathConnectedSpace X ↔ ∃ x : X, pathComponent x = univ := by
simp [pathConnectedSpace_iff_univ, isPathConnected_iff_eq]
-- see Note [lower instance priority]
instance (priority := 100) PathConnectedSpace.connectedSpace [PathConnectedSpace X] :
ConnectedSpace X := by
rw [connectedSpace_iff_connectedComponent]
rcases isPathConnected_iff_eq.mp (pathConnectedSpace_iff_univ.mp ‹_›) with ⟨x, _x_in, hx⟩
use x
rw [← univ_subset_iff]
exact (by simpa using hx : pathComponent x = univ) ▸ pathComponent_subset_component x
theorem IsPathConnected.isConnected (hF : IsPathConnected F) : IsConnected F := by
rw [isConnected_iff_connectedSpace]
rw [isPathConnected_iff_pathConnectedSpace] at hF
exact @PathConnectedSpace.connectedSpace _ _ hF
namespace PathConnectedSpace
variable [PathConnectedSpace X]
theorem exists_path_through_family {n : ℕ} (p : Fin (n + 1) → X) :
∃ γ : Path (p 0) (p n), ∀ i, p i ∈ range γ := by
have : IsPathConnected (univ : Set X) := pathConnectedSpace_iff_univ.mp (by infer_instance)
rcases this.exists_path_through_family p fun _i => True.intro with ⟨γ, -, h⟩
exact ⟨γ, h⟩
theorem exists_path_through_family' {n : ℕ} (p : Fin (n + 1) → X) :
∃ (γ : Path (p 0) (p n)) (t : Fin (n + 1) → I), ∀ i, γ (t i) = p i := by
have : IsPathConnected (univ : Set X) := pathConnectedSpace_iff_univ.mp (by infer_instance)
rcases this.exists_path_through_family' p fun _i => True.intro with ⟨γ, t, -, h⟩
exact ⟨γ, t, h⟩
end PathConnectedSpace
| Mathlib/Topology/Connected/PathConnected.lean | 857 | 858 | |
/-
Copyright (c) 2019 Reid Barton. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Topology.Constructions
/-!
# Neighborhoods and continuity relative to a subset
This file develops API on the relative versions
* `nhdsWithin` of `nhds`
* `ContinuousOn` of `Continuous`
* `ContinuousWithinAt` of `ContinuousAt`
related to continuity, which are defined in previous definition files.
Their basic properties studied in this file include the relationships between
these restricted notions and the corresponding notions for the subtype
equipped with the subspace topology.
## Notation
* `𝓝 x`: the filter of neighborhoods of a point `x`;
* `𝓟 s`: the principal filter of a set `s`;
* `𝓝[s] x`: the filter `nhdsWithin x s` of neighborhoods of a point `x` within a set `s`.
-/
open Set Filter Function Topology Filter
variable {α β γ δ : Type*}
variable [TopologicalSpace α]
/-!
## Properties of the neighborhood-within filter
-/
@[simp]
theorem nhds_bind_nhdsWithin {a : α} {s : Set α} : ((𝓝 a).bind fun x => 𝓝[s] x) = 𝓝[s] a :=
bind_inf_principal.trans <| congr_arg₂ _ nhds_bind_nhds rfl
@[simp]
theorem eventually_nhds_nhdsWithin {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ y in 𝓝 a, ∀ᶠ x in 𝓝[s] y, p x) ↔ ∀ᶠ x in 𝓝[s] a, p x :=
Filter.ext_iff.1 nhds_bind_nhdsWithin { x | p x }
theorem eventually_nhdsWithin_iff {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ x in 𝓝[s] a, p x) ↔ ∀ᶠ x in 𝓝 a, x ∈ s → p x :=
eventually_inf_principal
theorem frequently_nhdsWithin_iff {z : α} {s : Set α} {p : α → Prop} :
(∃ᶠ x in 𝓝[s] z, p x) ↔ ∃ᶠ x in 𝓝 z, p x ∧ x ∈ s :=
frequently_inf_principal.trans <| by simp only [and_comm]
theorem mem_closure_ne_iff_frequently_within {z : α} {s : Set α} :
z ∈ closure (s \ {z}) ↔ ∃ᶠ x in 𝓝[≠] z, x ∈ s := by
simp [mem_closure_iff_frequently, frequently_nhdsWithin_iff]
@[simp]
theorem eventually_eventually_nhdsWithin {a : α} {s : Set α} {p : α → Prop} :
(∀ᶠ y in 𝓝[s] a, ∀ᶠ x in 𝓝[s] y, p x) ↔ ∀ᶠ x in 𝓝[s] a, p x := by
refine ⟨fun h => ?_, fun h => (eventually_nhds_nhdsWithin.2 h).filter_mono inf_le_left⟩
simp only [eventually_nhdsWithin_iff] at h ⊢
exact h.mono fun x hx hxs => (hx hxs).self_of_nhds hxs
@[simp]
theorem eventually_mem_nhdsWithin_iff {x : α} {s t : Set α} :
(∀ᶠ x' in 𝓝[s] x, t ∈ 𝓝[s] x') ↔ t ∈ 𝓝[s] x :=
eventually_eventually_nhdsWithin
theorem nhdsWithin_eq (a : α) (s : Set α) :
𝓝[s] a = ⨅ t ∈ { t : Set α | a ∈ t ∧ IsOpen t }, 𝓟 (t ∩ s) :=
((nhds_basis_opens a).inf_principal s).eq_biInf
@[simp] lemma nhdsWithin_univ (a : α) : 𝓝[Set.univ] a = 𝓝 a := by
rw [nhdsWithin, principal_univ, inf_top_eq]
theorem nhdsWithin_hasBasis {ι : Sort*} {p : ι → Prop} {s : ι → Set α} {a : α}
(h : (𝓝 a).HasBasis p s) (t : Set α) : (𝓝[t] a).HasBasis p fun i => s i ∩ t :=
h.inf_principal t
theorem nhdsWithin_basis_open (a : α) (t : Set α) :
(𝓝[t] a).HasBasis (fun u => a ∈ u ∧ IsOpen u) fun u => u ∩ t :=
nhdsWithin_hasBasis (nhds_basis_opens a) t
theorem mem_nhdsWithin {t : Set α} {a : α} {s : Set α} :
t ∈ 𝓝[s] a ↔ ∃ u, IsOpen u ∧ a ∈ u ∧ u ∩ s ⊆ t := by
simpa only [and_assoc, and_left_comm] using (nhdsWithin_basis_open a s).mem_iff
theorem mem_nhdsWithin_iff_exists_mem_nhds_inter {t : Set α} {a : α} {s : Set α} :
t ∈ 𝓝[s] a ↔ ∃ u ∈ 𝓝 a, u ∩ s ⊆ t :=
(nhdsWithin_hasBasis (𝓝 a).basis_sets s).mem_iff
theorem diff_mem_nhdsWithin_compl {x : α} {s : Set α} (hs : s ∈ 𝓝 x) (t : Set α) :
s \ t ∈ 𝓝[tᶜ] x :=
diff_mem_inf_principal_compl hs t
theorem diff_mem_nhdsWithin_diff {x : α} {s t : Set α} (hs : s ∈ 𝓝[t] x) (t' : Set α) :
s \ t' ∈ 𝓝[t \ t'] x := by
rw [nhdsWithin, diff_eq, diff_eq, ← inf_principal, ← inf_assoc]
exact inter_mem_inf hs (mem_principal_self _)
theorem nhds_of_nhdsWithin_of_nhds {s t : Set α} {a : α} (h1 : s ∈ 𝓝 a) (h2 : t ∈ 𝓝[s] a) :
t ∈ 𝓝 a := by
rcases mem_nhdsWithin_iff_exists_mem_nhds_inter.mp h2 with ⟨_, Hw, hw⟩
exact (𝓝 a).sets_of_superset ((𝓝 a).inter_sets Hw h1) hw
theorem mem_nhdsWithin_iff_eventually {s t : Set α} {x : α} :
| t ∈ 𝓝[s] x ↔ ∀ᶠ y in 𝓝 x, y ∈ s → y ∈ t :=
eventually_inf_principal
theorem mem_nhdsWithin_iff_eventuallyEq {s t : Set α} {x : α} :
| Mathlib/Topology/ContinuousOn.lean | 110 | 113 |
/-
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.Analysis.Analytic.CPolynomial
import Mathlib.Analysis.Analytic.Inverse
import Mathlib.Analysis.Analytic.Within
import Mathlib.Analysis.Calculus.Deriv.Basic
import Mathlib.Analysis.Calculus.ContDiff.FTaylorSeries
import Mathlib.Analysis.Calculus.FDeriv.Add
import Mathlib.Analysis.Calculus.FDeriv.Prod
import Mathlib.Analysis.Normed.Module.Completion
/-!
# Frechet derivatives of analytic functions.
A function expressible as a power series at a point has a Frechet derivative there.
Also the special case in terms of `deriv` when the domain is 1-dimensional.
As an application, we show that continuous multilinear maps are smooth. We also compute their
iterated derivatives, in `ContinuousMultilinearMap.iteratedFDeriv_eq`.
## Main definitions and results
* `AnalyticAt.differentiableAt` : an analytic function at a point is differentiable there.
* `AnalyticOnNhd.fderiv` : in a complete space, if a function is analytic on a
neighborhood of a set `s`, so is its derivative.
* `AnalyticOnNhd.fderiv_of_isOpen` : if a function is analytic on a neighborhood of an
open set `s`, so is its derivative.
* `AnalyticOn.fderivWithin` : if a function is analytic on a set of unique differentiability,
so is its derivative within this set.
* `PartialHomeomorph.analyticAt_symm` : if a partial homeomorphism `f` is analytic at a
point `f.symm a`, with invertible derivative, then its inverse is analytic at `a`.
## Comments on completeness
Some theorems need a complete space, some don't, for the following reason.
|
(1) If a function is analytic at a point `x`, then it is differentiable there (with derivative given
by the first term in the power series). There is no issue of convergence here.
(2) If a function has a power series on a ball `B (x, r)`, there is no guarantee that the power
series for the derivative will converge at `y ≠ x`, if the space is not complete. So, to deduce
| Mathlib/Analysis/Calculus/FDeriv/Analytic.lean | 39 | 44 |
/-
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 :=
| Mathlib/Algebra/Group/Basic.lean | 766 | 766 |
/-
Copyright (c) 2019 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen, Eric Wieser
-/
import Mathlib.Data.Matrix.ConjTranspose
/-!
# Row and column matrices
This file provides results about row and column matrices.
## Main definitions
* `Matrix.replicateRow ι r : Matrix ι n α`: the matrix where every row is the vector `r : n → α`
* `Matrix.replicateCol ι c : Matrix m ι α`: the matrix where every column is the vector `c : m → α`
* `Matrix.updateRow M i r`: update the `i`th row of `M` to `r`
* `Matrix.updateCol M j c`: update the `j`th column of `M` to `c`
-/
variable {l m n o : Type*}
universe u v w
variable {R : Type*} {α : Type v} {β : Type w}
namespace Matrix
/--
`Matrix.replicateCol ι u` is the matrix with all columns equal to the vector `u`.
To get a column matrix with exactly one column,
`Matrix.replicateCol (Fin 1) u` is the canonical choice.
-/
def replicateCol (ι : Type*) (w : m → α) : Matrix m ι α :=
of fun x _ => w x
-- TODO: set as an equation lemma for `replicateCol`, see https://github.com/leanprover-community/mathlib4/pull/3024
@[simp]
theorem replicateCol_apply {ι : Type*} (w : m → α) (i) (j : ι) : replicateCol ι w i j = w i :=
rfl
/--
`Matrix.replicateRow ι u` is the matrix with all rows equal to the vector `u`.
To get a row matrix with exactly one row, `Matrix.replicateRow (Fin 1) u` is the canonical choice.
-/
def replicateRow (ι : Type*) (v : n → α) : Matrix ι n α :=
of fun _ y => v y
variable {ι : Type*}
-- TODO: set as an equation lemma for `replicateRow`, see https://github.com/leanprover-community/mathlib4/pull/3024
@[simp]
theorem replicateRow_apply (v : n → α) (i : ι) (j) : replicateRow ι v i j = v j :=
rfl
theorem replicateCol_injective [Nonempty ι] :
Function.Injective (replicateCol ι : (m → α) → Matrix m ι α) := by
inhabit ι
exact fun _x _y h => funext fun i => congr_fun₂ h i default
@[deprecated (since := "2025-03-20")] alias col_injective := replicateCol_injective
@[simp] theorem replicateCol_inj [Nonempty ι] {v w : m → α} :
replicateCol ι v = replicateCol ι w ↔ v = w :=
replicateCol_injective.eq_iff
@[deprecated (since := "2025-03-20")] alias col_inj := replicateCol_inj
@[simp] theorem replicateCol_zero [Zero α] : replicateCol ι (0 : m → α) = 0 := rfl
@[deprecated (since := "2025-03-20")] alias col_zero := replicateCol_zero
@[simp] theorem replicateCol_eq_zero [Zero α] [Nonempty ι] (v : m → α) :
replicateCol ι v = 0 ↔ v = 0 :=
replicateCol_inj
@[deprecated (since := "2025-03-20")] alias col_eq_zero := replicateCol_eq_zero
@[simp]
theorem replicateCol_add [Add α] (v w : m → α) :
replicateCol ι (v + w) = replicateCol ι v + replicateCol ι w := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias col_add := replicateCol_add
@[simp]
theorem replicateCol_smul [SMul R α] (x : R) (v : m → α) :
replicateCol ι (x • v) = x • replicateCol ι v := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias col_smul := replicateCol_smul
theorem replicateRow_injective [Nonempty ι] :
Function.Injective (replicateRow ι : (n → α) → Matrix ι n α) := by
inhabit ι
exact fun _x _y h => funext fun j => congr_fun₂ h default j
@[deprecated (since := "2025-03-20")] alias row_injective := replicateRow_injective
@[simp] theorem replicateRow_inj [Nonempty ι] {v w : n → α} :
replicateRow ι v = replicateRow ι w ↔ v = w :=
replicateRow_injective.eq_iff
@[simp] theorem replicateRow_zero [Zero α] : replicateRow ι (0 : n → α) = 0 := rfl
@[deprecated (since := "2025-03-20")] alias row_zero := replicateRow_zero
@[simp] theorem replicateRow_eq_zero [Zero α] [Nonempty ι] (v : n → α) :
replicateRow ι v = 0 ↔ v = 0 :=
replicateRow_inj
@[deprecated (since := "2025-03-20")] alias row_eq_zero := replicateRow_eq_zero
@[simp]
theorem replicateRow_add [Add α] (v w : m → α) :
replicateRow ι (v + w) = replicateRow ι v + replicateRow ι w := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias row_add := replicateRow_add
@[simp]
theorem replicateRow_smul [SMul R α] (x : R) (v : m → α) :
replicateRow ι (x • v) = x • replicateRow ι v := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias row_smul := replicateRow_smul
@[simp]
theorem transpose_replicateCol (v : m → α) : (replicateCol ι v)ᵀ = replicateRow ι v := by
ext
rfl
@[simp]
theorem transpose_replicateRow (v : m → α) : (replicateRow ι v)ᵀ = replicateCol ι v := by
ext
rfl
@[simp]
theorem conjTranspose_replicateCol [Star α] (v : m → α) :
(replicateCol ι v)ᴴ = replicateRow ι (star v) := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias conjTranspose_col := conjTranspose_replicateCol
@[simp]
theorem conjTranspose_replicateRow [Star α] (v : m → α) :
(replicateRow ι v)ᴴ = replicateCol ι (star v) := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias conjTranspose_row := conjTranspose_replicateRow
theorem replicateRow_vecMul [Fintype m] [NonUnitalNonAssocSemiring α] (M : Matrix m n α)
(v : m → α) : replicateRow ι (v ᵥ* M) = replicateRow ι v * M := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias row_vecMul := replicateRow_vecMul
theorem replicateCol_vecMul [Fintype m] [NonUnitalNonAssocSemiring α] (M : Matrix m n α)
(v : m → α) : replicateCol ι (v ᵥ* M) = (replicateRow ι v * M)ᵀ := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias col_vecMul := replicateCol_vecMul
theorem replicateCol_mulVec [Fintype n] [NonUnitalNonAssocSemiring α] (M : Matrix m n α)
(v : n → α) : replicateCol ι (M *ᵥ v) = M * replicateCol ι v := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias col_mulVec := replicateCol_mulVec
theorem replicateRow_mulVec [Fintype n] [NonUnitalNonAssocSemiring α] (M : Matrix m n α)
(v : n → α) : replicateRow ι (M *ᵥ v) = (M * replicateCol ι v)ᵀ := by
ext
rfl
@[deprecated (since := "2025-03-20")] alias row_mulVec := replicateRow_mulVec
theorem replicateRow_mulVec_eq_const [Fintype m] [NonUnitalNonAssocSemiring α] (v w : m → α) :
replicateRow ι v *ᵥ w = Function.const _ (v ⬝ᵥ w) := rfl
@[deprecated (since := "2025-03-20")] alias row_mulVec_eq_const := replicateRow_mulVec_eq_const
theorem mulVec_replicateCol_eq_const [Fintype m] [NonUnitalNonAssocSemiring α] (v w : m → α) :
v ᵥ* replicateCol ι w = Function.const _ (v ⬝ᵥ w) := rfl
@[deprecated (since := "2025-03-20")] alias mulVec_col_eq_const := mulVec_replicateCol_eq_const
theorem replicateRow_mul_replicateCol [Fintype m] [Mul α] [AddCommMonoid α] (v w : m → α) :
replicateRow ι v * replicateCol ι w = of fun _ _ => v ⬝ᵥ w :=
rfl
@[deprecated (since := "2025-03-20")] alias row_mul_col := replicateRow_mul_replicateCol
@[simp]
theorem replicateRow_mul_replicateCol_apply [Fintype m] [Mul α] [AddCommMonoid α] (v w : m → α)
(i j) : (replicateRow ι v * replicateCol ι w) i j = v ⬝ᵥ w :=
rfl
@[deprecated (since := "2025-03-20")] alias row_mul_col_apply := replicateRow_mul_replicateCol_apply
@[simp]
theorem diag_replicateCol_mul_replicateRow [Mul α] [AddCommMonoid α] [Unique ι] (a b : n → α) :
diag (replicateCol ι a * replicateRow ι b) = a * b := by
ext
simp [Matrix.mul_apply, replicateCol, replicateRow]
@[deprecated (since := "2025-03-20")] alias diag_col_mul_row := diag_replicateCol_mul_replicateRow
variable (ι)
|
theorem vecMulVec_eq [Mul α] [AddCommMonoid α] [Unique ι] (w : m → α) (v : n → α) :
vecMulVec w v = replicateCol ι w * replicateRow ι v := by
ext
simp [vecMulVec, mul_apply]
| Mathlib/Data/Matrix/RowCol.lean | 220 | 224 |
/-
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 | 1,919 | 1,936 | |
/-
Copyright (c) 2017 Mario Carneiro. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Algebra.BigOperators.Group.Finset.Piecewise
import Mathlib.Algebra.BigOperators.Group.Finset.Sigma
import Mathlib.Algebra.BigOperators.Option
import Mathlib.Data.Fintype.Option
import Mathlib.Data.Fintype.Prod
import Mathlib.Data.Fintype.Sigma
import Mathlib.Data.Fintype.Sum
import Mathlib.Data.Fintype.Vector
/-!
Results about "big operations" over a `Fintype`, and consequent
results about cardinalities of certain types.
## Implementation note
This content had previously been in `Data.Fintype.Basic`, but was moved here to avoid
requiring `Algebra.BigOperators` (and hence many other imports) as a
dependency of `Fintype`.
However many of the results here really belong in `Algebra.BigOperators.Group.Finset`
and should be moved at some point.
-/
assert_not_exists MulAction
open Mathlib
universe u v
variable {α : Type*} {β : Type*} {γ : Type*}
namespace Fintype
@[to_additive]
theorem prod_bool [CommMonoid α] (f : Bool → α) : ∏ b, f b = f true * f false := by simp
theorem card_eq_sum_ones {α} [Fintype α] : Fintype.card α = ∑ _a : α, 1 :=
Finset.card_eq_sum_ones _
section
open Finset
variable {ι : Type*} [DecidableEq ι] [Fintype ι]
@[to_additive]
theorem prod_extend_by_one [CommMonoid α] (s : Finset ι) (f : ι → α) :
∏ i, (if i ∈ s then f i else 1) = ∏ i ∈ s, f i := by
rw [← prod_filter, filter_mem_eq_inter, univ_inter]
end
section
variable {M : Type*} [Fintype α] [CommMonoid M]
@[to_additive]
theorem prod_eq_one (f : α → M) (h : ∀ a, f a = 1) : ∏ a, f a = 1 :=
Finset.prod_eq_one fun a _ha => h a
@[to_additive]
theorem prod_congr (f g : α → M) (h : ∀ a, f a = g a) : ∏ a, f a = ∏ a, g a :=
Finset.prod_congr rfl fun a _ha => h a
@[to_additive]
theorem prod_eq_single {f : α → M} (a : α) (h : ∀ x ≠ a, f x = 1) : ∏ x, f x = f a :=
Finset.prod_eq_single a (fun x _ hx => h x hx) fun ha => (ha (Finset.mem_univ a)).elim
@[to_additive]
theorem prod_eq_mul {f : α → M} (a b : α) (h₁ : a ≠ b) (h₂ : ∀ x, x ≠ a ∧ x ≠ b → f x = 1) :
∏ x, f x = f a * f b := by
apply Finset.prod_eq_mul a b h₁ fun x _ hx => h₂ x hx <;>
exact fun hc => (hc (Finset.mem_univ _)).elim
/-- If a product of a `Finset` of a subsingleton type has a given
value, so do the terms in that product. -/
@[to_additive "If a sum of a `Finset` of a subsingleton type has a given
value, so do the terms in that sum."]
theorem eq_of_subsingleton_of_prod_eq {ι : Type*} [Subsingleton ι] {s : Finset ι} {f : ι → M}
{b : M} (h : ∏ i ∈ s, f i = b) : ∀ i ∈ s, f i = b :=
Finset.eq_of_card_le_one_of_prod_eq (Finset.card_le_one_of_subsingleton s) h
end
end Fintype
open Finset
section
variable {M : Type*} [Fintype α] [CommMonoid M]
@[to_additive (attr := simp)]
theorem Fintype.prod_option (f : Option α → M) : ∏ i, f i = f none * ∏ i, f (some i) :=
Finset.prod_insertNone f univ
@[to_additive]
theorem Fintype.prod_eq_mul_prod_subtype_ne [DecidableEq α] (f : α → M) (a : α) :
∏ i, f i = f a * ∏ i : {i // i ≠ a}, f i.1 := by
simp_rw [← (Equiv.optionSubtypeNe a).prod_comp, prod_option, Equiv.optionSubtypeNe_none,
Equiv.optionSubtypeNe_some]
end
open Finset
section Pi
variable {ι κ : Type*} {α : ι → Type*} [DecidableEq ι] [DecidableEq κ]
@[simp] lemma Finset.card_pi (s : Finset ι) (t : ∀ i, Finset (α i)) :
#(s.pi t) = ∏ i ∈ s, #(t i) := Multiset.card_pi _ _
namespace Fintype
variable [Fintype ι]
@[simp] lemma card_piFinset (s : ∀ i, Finset (α i)) :
#(piFinset s) = ∏ i, #(s i) := by simp [piFinset, card_map]
/-- This lemma is specifically designed to be used backwards, whence the specialisation to `Fin n`
as the indexing type doesn't matter in practice. The more general forward direction lemma here is
`Fintype.card_piFinset`. -/
lemma card_piFinset_const {α : Type*} (s : Finset α) (n : ℕ) :
#(piFinset fun _ : Fin n ↦ s) = #s ^ n := by simp
@[simp] lemma card_pi [∀ i, Fintype (α i)] : card (∀ i, α i) = ∏ i, card (α i) :=
card_piFinset _
/-- This lemma is specifically designed to be used backwards, whence the specialisation to `Fin n`
as the indexing type doesn't matter in practice. The more general forward direction lemma here is
`Fintype.card_pi`. -/
lemma card_pi_const (α : Type*) [Fintype α] (n : ℕ) : card (Fin n → α) = card α ^ n :=
card_piFinset_const _ _
/-- Product over a sigma type equals the repeated product.
This is a version of `Finset.prod_sigma` specialized to the case
of multiplication over `Finset.univ`. -/
@[to_additive "Sum over a sigma type equals the repeated sum.
This is a version of `Finset.sum_sigma` specialized to the case of summation over `Finset.univ`."]
theorem prod_sigma {ι} {α : ι → Type*} {M : Type*} [Fintype ι] [∀ i, Fintype (α i)] [CommMonoid M]
(f : Sigma α → M) : ∏ x, f x = ∏ x, ∏ y, f ⟨x, y⟩ :=
Finset.prod_sigma ..
/-- Product over a sigma type equals the repeated product, curried version.
This version is useful to rewrite from right to left. -/
@[to_additive "Sum over a sigma type equals the repeated sum, curried version.
This version is useful to rewrite from right to left."]
theorem prod_sigma' {ι} {α : ι → Type*} {M : Type*} [Fintype ι] [∀ i, Fintype (α i)] [CommMonoid M]
(f : (i : ι) → α i → M) : ∏ x : Sigma α, f x.1 x.2 = ∏ x, ∏ y, f x y :=
prod_sigma ..
@[simp] nonrec lemma card_sigma {ι} {α : ι → Type*} [Fintype ι] [∀ i, Fintype (α i)] :
card (Sigma α) = ∑ i, card (α i) := card_sigma _ _
/-- The number of dependent maps `f : Π j, s j` for which the `i` component is `a` is the product
over all `j ≠ i` of `#(s j)`.
Note that this is just a composition of easier lemmas, but there's some glue missing to make that
smooth enough not to need this lemma. -/
lemma card_filter_piFinset_eq_of_mem [∀ i, DecidableEq (α i)]
(s : ∀ i, Finset (α i)) (i : ι) {a : α i} (ha : a ∈ s i) :
#{f ∈ piFinset s | f i = a} = ∏ j ∈ univ.erase i, #(s j) := by
calc
_ = ∏ j, #(Function.update s i {a} j) := by
rw [← piFinset_update_singleton_eq_filter_piFinset_eq _ _ ha, Fintype.card_piFinset]
_ = ∏ j, Function.update (fun j ↦ #(s j)) i 1 j :=
Fintype.prod_congr _ _ fun j ↦ by obtain rfl | hji := eq_or_ne j i <;> simp [*]
_ = _ := by simp [prod_update_of_mem, erase_eq]
lemma card_filter_piFinset_const_eq_of_mem (s : Finset κ) (i : ι) {x : κ} (hx : x ∈ s) :
#{f ∈ piFinset fun _ ↦ s | f i = x} = #s ^ (card ι - 1) :=
(card_filter_piFinset_eq_of_mem _ _ hx).trans <| by
| rw [prod_const #s, card_erase_of_mem (mem_univ _), card_univ]
lemma card_filter_piFinset_eq [∀ i, DecidableEq (α i)] (s : ∀ i, Finset (α i)) (i : ι) (a : α i) :
| Mathlib/Data/Fintype/BigOperators.lean | 179 | 181 |
/-
Copyright (c) 2018 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel, Johannes Hölzl, Rémy Degenne
-/
import Mathlib.Order.ConditionallyCompleteLattice.Indexed
import Mathlib.Order.Filter.IsBounded
import Mathlib.Order.Hom.CompleteLattice
/-!
# liminfs and limsups of functions and filters
Defines the liminf/limsup of a function taking values in a conditionally complete lattice, with
respect to an arbitrary filter.
We define `limsSup f` (`limsInf f`) where `f` is a filter taking values in a conditionally complete
lattice. `limsSup f` is the smallest element `a` such that, eventually, `u ≤ a` (and vice versa for
`limsInf f`). To work with the Limsup along a function `u` use `limsSup (map u f)`.
Usually, one defines the Limsup as `inf (sup s)` where the Inf is taken over all sets in the filter.
For instance, in ℕ along a function `u`, this is `inf_n (sup_{k ≥ n} u k)` (and the latter quantity
decreases with `n`, so this is in fact a limit.). There is however a difficulty: it is well possible
that `u` is not bounded on the whole space, only eventually (think of `limsup (fun x ↦ 1/x)` on ℝ.
Then there is no guarantee that the quantity above really decreases (the value of the `sup`
beforehand is not really well defined, as one can not use ∞), so that the Inf could be anything.
So one can not use this `inf sup ...` definition in conditionally complete lattices, and one has
to use a less tractable definition.
In conditionally complete lattices, the definition is only useful for filters which are eventually
bounded above (otherwise, the Limsup would morally be +∞, which does not belong to the space) and
which are frequently bounded below (otherwise, the Limsup would morally be -∞, which is not in the
space either). We start with definitions of these concepts for arbitrary filters, before turning to
the definitions of Limsup and Liminf.
In complete lattices, however, it coincides with the `Inf Sup` definition.
-/
open Filter Set Function
variable {α β γ ι ι' : Type*}
namespace Filter
section ConditionallyCompleteLattice
variable [ConditionallyCompleteLattice α] {s : Set α} {u : β → α}
/-- The `limsSup` of a filter `f` is the infimum of the `a` such that, eventually for `f`,
holds `x ≤ a`. -/
def limsSup (f : Filter α) : α :=
sInf { a | ∀ᶠ n in f, n ≤ a }
/-- The `limsInf` of a filter `f` is the supremum of the `a` such that, eventually for `f`,
holds `x ≥ a`. -/
def limsInf (f : Filter α) : α :=
sSup { a | ∀ᶠ n in f, a ≤ n }
/-- The `limsup` of a function `u` along a filter `f` is the infimum of the `a` such that,
eventually for `f`, holds `u x ≤ a`. -/
def limsup (u : β → α) (f : Filter β) : α :=
limsSup (map u f)
/-- The `liminf` of a function `u` along a filter `f` is the supremum of the `a` such that,
eventually for `f`, holds `u x ≥ a`. -/
def liminf (u : β → α) (f : Filter β) : α :=
limsInf (map u f)
/-- The `blimsup` of a function `u` along a filter `f`, bounded by a predicate `p`, is the infimum
of the `a` such that, eventually for `f`, `u x ≤ a` whenever `p x` holds. -/
def blimsup (u : β → α) (f : Filter β) (p : β → Prop) :=
sInf { a | ∀ᶠ x in f, p x → u x ≤ a }
/-- The `bliminf` of a function `u` along a filter `f`, bounded by a predicate `p`, is the supremum
of the `a` such that, eventually for `f`, `a ≤ u x` whenever `p x` holds. -/
def bliminf (u : β → α) (f : Filter β) (p : β → Prop) :=
sSup { a | ∀ᶠ x in f, p x → a ≤ u x }
section
variable {f : Filter β} {u : β → α} {p : β → Prop}
theorem limsup_eq : limsup u f = sInf { a | ∀ᶠ n in f, u n ≤ a } :=
rfl
theorem liminf_eq : liminf u f = sSup { a | ∀ᶠ n in f, a ≤ u n } :=
rfl
theorem blimsup_eq : blimsup u f p = sInf { a | ∀ᶠ x in f, p x → u x ≤ a } :=
rfl
theorem bliminf_eq : bliminf u f p = sSup { a | ∀ᶠ x in f, p x → a ≤ u x } :=
rfl
lemma liminf_comp (u : β → α) (v : γ → β) (f : Filter γ) :
liminf (u ∘ v) f = liminf u (map v f) := rfl
lemma limsup_comp (u : β → α) (v : γ → β) (f : Filter γ) :
limsup (u ∘ v) f = limsup u (map v f) := rfl
end
@[simp]
theorem blimsup_true (f : Filter β) (u : β → α) : (blimsup u f fun _ => True) = limsup u f := by
simp [blimsup_eq, limsup_eq]
@[simp]
theorem bliminf_true (f : Filter β) (u : β → α) : (bliminf u f fun _ => True) = liminf u f := by
simp [bliminf_eq, liminf_eq]
lemma blimsup_eq_limsup {f : Filter β} {u : β → α} {p : β → Prop} :
blimsup u f p = limsup u (f ⊓ 𝓟 {x | p x}) := by
simp only [blimsup_eq, limsup_eq, eventually_inf_principal, mem_setOf_eq]
lemma bliminf_eq_liminf {f : Filter β} {u : β → α} {p : β → Prop} :
bliminf u f p = liminf u (f ⊓ 𝓟 {x | p x}) :=
blimsup_eq_limsup (α := αᵒᵈ)
theorem blimsup_eq_limsup_subtype {f : Filter β} {u : β → α} {p : β → Prop} :
blimsup u f p = limsup (u ∘ ((↑) : { x | p x } → β)) (comap (↑) f) := by
rw [blimsup_eq_limsup, limsup, limsup, ← map_map, map_comap_setCoe_val]
theorem bliminf_eq_liminf_subtype {f : Filter β} {u : β → α} {p : β → Prop} :
bliminf u f p = liminf (u ∘ ((↑) : { x | p x } → β)) (comap (↑) f) :=
blimsup_eq_limsup_subtype (α := αᵒᵈ)
theorem limsSup_le_of_le {f : Filter α} {a}
(hf : f.IsCobounded (· ≤ ·) := by isBoundedDefault)
(h : ∀ᶠ n in f, n ≤ a) : limsSup f ≤ a :=
csInf_le hf h
theorem le_limsInf_of_le {f : Filter α} {a}
(hf : f.IsCobounded (· ≥ ·) := by isBoundedDefault)
(h : ∀ᶠ n in f, a ≤ n) : a ≤ limsInf f :=
le_csSup hf h
theorem limsup_le_of_le {f : Filter β} {u : β → α} {a}
(hf : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(h : ∀ᶠ n in f, u n ≤ a) : limsup u f ≤ a :=
csInf_le hf h
theorem le_liminf_of_le {f : Filter β} {u : β → α} {a}
(hf : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h : ∀ᶠ n in f, a ≤ u n) : a ≤ liminf u f :=
le_csSup hf h
theorem le_limsSup_of_le {f : Filter α} {a}
(hf : f.IsBounded (· ≤ ·) := by isBoundedDefault)
(h : ∀ b, (∀ᶠ n in f, n ≤ b) → a ≤ b) : a ≤ limsSup f :=
le_csInf hf h
theorem limsInf_le_of_le {f : Filter α} {a}
(hf : f.IsBounded (· ≥ ·) := by isBoundedDefault)
(h : ∀ b, (∀ᶠ n in f, b ≤ n) → b ≤ a) : limsInf f ≤ a :=
csSup_le hf h
theorem le_limsup_of_le {f : Filter β} {u : β → α} {a}
(hf : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault)
(h : ∀ b, (∀ᶠ n in f, u n ≤ b) → a ≤ b) : a ≤ limsup u f :=
le_csInf hf h
theorem liminf_le_of_le {f : Filter β} {u : β → α} {a}
(hf : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault)
(h : ∀ b, (∀ᶠ n in f, b ≤ u n) → b ≤ a) : liminf u f ≤ a :=
csSup_le hf h
theorem limsInf_le_limsSup {f : Filter α} [NeBot f]
(h₁ : f.IsBounded (· ≤ ·) := by isBoundedDefault)
(h₂ : f.IsBounded (· ≥ ·) := by isBoundedDefault) :
limsInf f ≤ limsSup f :=
liminf_le_of_le h₂ fun a₀ ha₀ =>
le_limsup_of_le h₁ fun a₁ ha₁ =>
show a₀ ≤ a₁ from
let ⟨_, hb₀, hb₁⟩ := (ha₀.and ha₁).exists
le_trans hb₀ hb₁
theorem liminf_le_limsup {f : Filter β} [NeBot f] {u : β → α}
(h : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault)
(h' : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
liminf u f ≤ limsup u f :=
limsInf_le_limsSup h h'
theorem limsSup_le_limsSup {f g : Filter α}
(hf : f.IsCobounded (· ≤ ·) := by isBoundedDefault)
(hg : g.IsBounded (· ≤ ·) := by isBoundedDefault)
(h : ∀ a, (∀ᶠ n in g, n ≤ a) → ∀ᶠ n in f, n ≤ a) : limsSup f ≤ limsSup g :=
csInf_le_csInf hf hg h
theorem limsInf_le_limsInf {f g : Filter α}
(hf : f.IsBounded (· ≥ ·) := by isBoundedDefault)
(hg : g.IsCobounded (· ≥ ·) := by isBoundedDefault)
(h : ∀ a, (∀ᶠ n in f, a ≤ n) → ∀ᶠ n in g, a ≤ n) : limsInf f ≤ limsInf g :=
csSup_le_csSup hg hf h
theorem limsup_le_limsup {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} {u v : α → β}
(h : u ≤ᶠ[f] v)
(hu : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(hv : f.IsBoundedUnder (· ≤ ·) v := by isBoundedDefault) :
limsup u f ≤ limsup v f :=
limsSup_le_limsSup hu hv fun _ => h.trans
theorem liminf_le_liminf {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} {u v : α → β}
(h : ∀ᶠ a in f, u a ≤ v a)
(hu : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault)
(hv : f.IsCoboundedUnder (· ≥ ·) v := by isBoundedDefault) :
liminf u f ≤ liminf v f :=
limsup_le_limsup (β := βᵒᵈ) h hv hu
theorem limsSup_le_limsSup_of_le {f g : Filter α} (h : f ≤ g)
(hf : f.IsCobounded (· ≤ ·) := by isBoundedDefault)
(hg : g.IsBounded (· ≤ ·) := by isBoundedDefault) :
limsSup f ≤ limsSup g :=
limsSup_le_limsSup hf hg fun _ ha => h ha
theorem limsInf_le_limsInf_of_le {f g : Filter α} (h : g ≤ f)
(hf : f.IsBounded (· ≥ ·) := by isBoundedDefault)
(hg : g.IsCobounded (· ≥ ·) := by isBoundedDefault) :
limsInf f ≤ limsInf g :=
limsInf_le_limsInf hf hg fun _ ha => h ha
theorem limsup_le_limsup_of_le {α β} [ConditionallyCompleteLattice β] {f g : Filter α} (h : f ≤ g)
{u : α → β}
(hf : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(hg : g.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
limsup u f ≤ limsup u g :=
limsSup_le_limsSup_of_le (map_mono h) hf hg
theorem liminf_le_liminf_of_le {α β} [ConditionallyCompleteLattice β] {f g : Filter α} (h : g ≤ f)
{u : α → β}
(hf : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault)
(hg : g.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault) :
liminf u f ≤ liminf u g :=
limsInf_le_limsInf_of_le (map_mono h) hf hg
lemma limsSup_principal_eq_csSup (h : BddAbove s) (hs : s.Nonempty) : limsSup (𝓟 s) = sSup s := by
simp only [limsSup, eventually_principal]; exact csInf_upperBounds_eq_csSup h hs
lemma limsInf_principal_eq_csSup (h : BddBelow s) (hs : s.Nonempty) : limsInf (𝓟 s) = sInf s :=
limsSup_principal_eq_csSup (α := αᵒᵈ) h hs
lemma limsup_top_eq_ciSup [Nonempty β] (hu : BddAbove (range u)) : limsup u ⊤ = ⨆ i, u i := by
rw [limsup, map_top, limsSup_principal_eq_csSup hu (range_nonempty _), sSup_range]
lemma liminf_top_eq_ciInf [Nonempty β] (hu : BddBelow (range u)) : liminf u ⊤ = ⨅ i, u i := by
rw [liminf, map_top, limsInf_principal_eq_csSup hu (range_nonempty _), sInf_range]
theorem limsup_congr {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} {u v : α → β}
(h : ∀ᶠ a in f, u a = v a) : limsup u f = limsup v f := by
rw [limsup_eq]
congr with b
exact eventually_congr (h.mono fun x hx => by simp [hx])
theorem blimsup_congr {f : Filter β} {u v : β → α} {p : β → Prop} (h : ∀ᶠ a in f, p a → u a = v a) :
blimsup u f p = blimsup v f p := by
simpa only [blimsup_eq_limsup] using limsup_congr <| eventually_inf_principal.2 h
theorem bliminf_congr {f : Filter β} {u v : β → α} {p : β → Prop} (h : ∀ᶠ a in f, p a → u a = v a) :
bliminf u f p = bliminf v f p :=
blimsup_congr (α := αᵒᵈ) h
theorem liminf_congr {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} {u v : α → β}
(h : ∀ᶠ a in f, u a = v a) : liminf u f = liminf v f :=
limsup_congr (β := βᵒᵈ) h
@[simp]
theorem limsup_const {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} [NeBot f]
(b : β) : limsup (fun _ => b) f = b := by
simpa only [limsup_eq, eventually_const] using csInf_Ici
@[simp]
theorem liminf_const {α : Type*} [ConditionallyCompleteLattice β] {f : Filter α} [NeBot f]
(b : β) : liminf (fun _ => b) f = b :=
limsup_const (β := βᵒᵈ) b
theorem HasBasis.liminf_eq_sSup_iUnion_iInter {ι ι' : Type*} {f : ι → α} {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} (hv : v.HasBasis p s) :
liminf f v = sSup (⋃ (j : Subtype p), ⋂ (i : s j), Iic (f i)) := by
simp_rw [liminf_eq, hv.eventually_iff]
congr
ext x
simp only [mem_setOf_eq, iInter_coe_set, mem_iUnion, mem_iInter, mem_Iic, Subtype.exists,
exists_prop]
theorem HasBasis.liminf_eq_sSup_univ_of_empty {f : ι → α} {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} (hv : v.HasBasis p s) (i : ι') (hi : p i) (h'i : s i = ∅) :
liminf f v = sSup univ := by
simp [hv.eq_bot_iff.2 ⟨i, hi, h'i⟩, liminf_eq]
theorem HasBasis.limsup_eq_sInf_iUnion_iInter {ι ι' : Type*} {f : ι → α} {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} (hv : v.HasBasis p s) :
limsup f v = sInf (⋃ (j : Subtype p), ⋂ (i : s j), Ici (f i)) :=
HasBasis.liminf_eq_sSup_iUnion_iInter (α := αᵒᵈ) hv
theorem HasBasis.limsup_eq_sInf_univ_of_empty {f : ι → α} {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} (hv : v.HasBasis p s) (i : ι') (hi : p i) (h'i : s i = ∅) :
limsup f v = sInf univ :=
HasBasis.liminf_eq_sSup_univ_of_empty (α := αᵒᵈ) hv i hi h'i
@[simp]
theorem liminf_nat_add (f : ℕ → α) (k : ℕ) :
liminf (fun i => f (i + k)) atTop = liminf f atTop := by
rw [← Function.comp_def, liminf, liminf, ← map_map, map_add_atTop_eq_nat]
@[simp]
theorem limsup_nat_add (f : ℕ → α) (k : ℕ) : limsup (fun i => f (i + k)) atTop = limsup f atTop :=
@liminf_nat_add αᵒᵈ _ f k
end ConditionallyCompleteLattice
section CompleteLattice
variable [CompleteLattice α]
@[simp]
theorem limsSup_bot : limsSup (⊥ : Filter α) = ⊥ :=
bot_unique <| sInf_le <| by simp
@[simp] theorem limsup_bot (f : β → α) : limsup f ⊥ = ⊥ := by simp [limsup]
@[simp]
theorem limsInf_bot : limsInf (⊥ : Filter α) = ⊤ :=
top_unique <| le_sSup <| by simp
@[simp] theorem liminf_bot (f : β → α) : liminf f ⊥ = ⊤ := by simp [liminf]
@[simp]
theorem limsSup_top : limsSup (⊤ : Filter α) = ⊤ :=
top_unique <| le_sInf <| by simpa [eq_univ_iff_forall] using fun b hb => top_unique <| hb _
@[simp]
theorem limsInf_top : limsInf (⊤ : Filter α) = ⊥ :=
bot_unique <| sSup_le <| by simpa [eq_univ_iff_forall] using fun b hb => bot_unique <| hb _
@[simp]
theorem blimsup_false {f : Filter β} {u : β → α} : (blimsup u f fun _ => False) = ⊥ := by
simp [blimsup_eq]
@[simp]
theorem bliminf_false {f : Filter β} {u : β → α} : (bliminf u f fun _ => False) = ⊤ := by
simp [bliminf_eq]
/-- Same as limsup_const applied to `⊥` but without the `NeBot f` assumption -/
@[simp]
theorem limsup_const_bot {f : Filter β} : limsup (fun _ : β => (⊥ : α)) f = (⊥ : α) := by
rw [limsup_eq, eq_bot_iff]
exact sInf_le (Eventually.of_forall fun _ => le_rfl)
/-- Same as limsup_const applied to `⊤` but without the `NeBot f` assumption -/
@[simp]
theorem liminf_const_top {f : Filter β} : liminf (fun _ : β => (⊤ : α)) f = (⊤ : α) :=
limsup_const_bot (α := αᵒᵈ)
theorem HasBasis.limsSup_eq_iInf_sSup {ι} {p : ι → Prop} {s} {f : Filter α} (h : f.HasBasis p s) :
limsSup f = ⨅ (i) (_ : p i), sSup (s i) :=
le_antisymm (le_iInf₂ fun i hi => sInf_le <| h.eventually_iff.2 ⟨i, hi, fun _ => le_sSup⟩)
(le_sInf fun _ ha =>
let ⟨_, hi, ha⟩ := h.eventually_iff.1 ha
iInf₂_le_of_le _ hi <| sSup_le ha)
theorem HasBasis.limsInf_eq_iSup_sInf {p : ι → Prop} {s : ι → Set α} {f : Filter α}
(h : f.HasBasis p s) : limsInf f = ⨆ (i) (_ : p i), sInf (s i) :=
HasBasis.limsSup_eq_iInf_sSup (α := αᵒᵈ) h
theorem limsSup_eq_iInf_sSup {f : Filter α} : limsSup f = ⨅ s ∈ f, sSup s :=
f.basis_sets.limsSup_eq_iInf_sSup
theorem limsInf_eq_iSup_sInf {f : Filter α} : limsInf f = ⨆ s ∈ f, sInf s :=
limsSup_eq_iInf_sSup (α := αᵒᵈ)
theorem limsup_le_iSup {f : Filter β} {u : β → α} : limsup u f ≤ ⨆ n, u n :=
limsup_le_of_le (by isBoundedDefault) (Eventually.of_forall (le_iSup u))
theorem iInf_le_liminf {f : Filter β} {u : β → α} : ⨅ n, u n ≤ liminf u f :=
le_liminf_of_le (by isBoundedDefault) (Eventually.of_forall (iInf_le u))
/-- In a complete lattice, the limsup of a function is the infimum over sets `s` in the filter
of the supremum of the function over `s` -/
theorem limsup_eq_iInf_iSup {f : Filter β} {u : β → α} : limsup u f = ⨅ s ∈ f, ⨆ a ∈ s, u a :=
(f.basis_sets.map u).limsSup_eq_iInf_sSup.trans <| by simp only [sSup_image, id]
theorem limsup_eq_iInf_iSup_of_nat {u : ℕ → α} : limsup u atTop = ⨅ n : ℕ, ⨆ i ≥ n, u i :=
(atTop_basis.map u).limsSup_eq_iInf_sSup.trans <| by simp only [sSup_image, iInf_const]; rfl
theorem limsup_eq_iInf_iSup_of_nat' {u : ℕ → α} : limsup u atTop = ⨅ n : ℕ, ⨆ i : ℕ, u (i + n) := by
simp only [limsup_eq_iInf_iSup_of_nat, iSup_ge_eq_iSup_nat_add]
theorem HasBasis.limsup_eq_iInf_iSup {p : ι → Prop} {s : ι → Set β} {f : Filter β} {u : β → α}
(h : f.HasBasis p s) : limsup u f = ⨅ (i) (_ : p i), ⨆ a ∈ s i, u a :=
(h.map u).limsSup_eq_iInf_sSup.trans <| by simp only [sSup_image, id]
lemma limsSup_principal_eq_sSup (s : Set α) : limsSup (𝓟 s) = sSup s := by
simpa only [limsSup, eventually_principal] using sInf_upperBounds_eq_csSup s
lemma limsInf_principal_eq_sInf (s : Set α) : limsInf (𝓟 s) = sInf s := by
simpa only [limsInf, eventually_principal] using sSup_lowerBounds_eq_sInf s
@[simp] lemma limsup_top_eq_iSup (u : β → α) : limsup u ⊤ = ⨆ i, u i := by
rw [limsup, map_top, limsSup_principal_eq_sSup, sSup_range]
@[simp] lemma liminf_top_eq_iInf (u : β → α) : liminf u ⊤ = ⨅ i, u i := by
rw [liminf, map_top, limsInf_principal_eq_sInf, sInf_range]
theorem blimsup_congr' {f : Filter β} {p q : β → Prop} {u : β → α}
(h : ∀ᶠ x in f, u x ≠ ⊥ → (p x ↔ q x)) : blimsup u f p = blimsup u f q := by
simp only [blimsup_eq]
congr with a
refine eventually_congr (h.mono fun b hb => ?_)
rcases eq_or_ne (u b) ⊥ with hu | hu; · simp [hu]
rw [hb hu]
theorem bliminf_congr' {f : Filter β} {p q : β → Prop} {u : β → α}
(h : ∀ᶠ x in f, u x ≠ ⊤ → (p x ↔ q x)) : bliminf u f p = bliminf u f q :=
blimsup_congr' (α := αᵒᵈ) h
lemma HasBasis.blimsup_eq_iInf_iSup {p : ι → Prop} {s : ι → Set β} {f : Filter β} {u : β → α}
(hf : f.HasBasis p s) {q : β → Prop} :
blimsup u f q = ⨅ (i) (_ : p i), ⨆ a ∈ s i, ⨆ (_ : q a), u a := by
simp only [blimsup_eq_limsup, (hf.inf_principal _).limsup_eq_iInf_iSup, mem_inter_iff, iSup_and,
mem_setOf_eq]
theorem blimsup_eq_iInf_biSup {f : Filter β} {p : β → Prop} {u : β → α} :
blimsup u f p = ⨅ s ∈ f, ⨆ (b) (_ : p b ∧ b ∈ s), u b := by
simp only [f.basis_sets.blimsup_eq_iInf_iSup, iSup_and', id, and_comm]
theorem blimsup_eq_iInf_biSup_of_nat {p : ℕ → Prop} {u : ℕ → α} :
blimsup u atTop p = ⨅ i, ⨆ (j) (_ : p j ∧ i ≤ j), u j := by
simp only [atTop_basis.blimsup_eq_iInf_iSup, @and_comm (p _), iSup_and, mem_Ici, iInf_true]
/-- In a complete lattice, the liminf of a function is the infimum over sets `s` in the filter
of the supremum of the function over `s` -/
theorem liminf_eq_iSup_iInf {f : Filter β} {u : β → α} : liminf u f = ⨆ s ∈ f, ⨅ a ∈ s, u a :=
limsup_eq_iInf_iSup (α := αᵒᵈ)
theorem liminf_eq_iSup_iInf_of_nat {u : ℕ → α} : liminf u atTop = ⨆ n : ℕ, ⨅ i ≥ n, u i :=
@limsup_eq_iInf_iSup_of_nat αᵒᵈ _ u
theorem liminf_eq_iSup_iInf_of_nat' {u : ℕ → α} : liminf u atTop = ⨆ n : ℕ, ⨅ i : ℕ, u (i + n) :=
@limsup_eq_iInf_iSup_of_nat' αᵒᵈ _ _
theorem HasBasis.liminf_eq_iSup_iInf {p : ι → Prop} {s : ι → Set β} {f : Filter β} {u : β → α}
(h : f.HasBasis p s) : liminf u f = ⨆ (i) (_ : p i), ⨅ a ∈ s i, u a :=
HasBasis.limsup_eq_iInf_iSup (α := αᵒᵈ) h
theorem bliminf_eq_iSup_biInf {f : Filter β} {p : β → Prop} {u : β → α} :
bliminf u f p = ⨆ s ∈ f, ⨅ (b) (_ : p b ∧ b ∈ s), u b :=
@blimsup_eq_iInf_biSup αᵒᵈ β _ f p u
theorem bliminf_eq_iSup_biInf_of_nat {p : ℕ → Prop} {u : ℕ → α} :
bliminf u atTop p = ⨆ i, ⨅ (j) (_ : p j ∧ i ≤ j), u j :=
@blimsup_eq_iInf_biSup_of_nat αᵒᵈ _ p u
theorem limsup_eq_sInf_sSup {ι R : Type*} (F : Filter ι) [CompleteLattice R] (a : ι → R) :
limsup a F = sInf ((fun I => sSup (a '' I)) '' F.sets) := by
apply le_antisymm
· rw [limsup_eq]
refine sInf_le_sInf fun x hx => ?_
rcases (mem_image _ F.sets x).mp hx with ⟨I, ⟨I_mem_F, hI⟩⟩
filter_upwards [I_mem_F] with i hi
exact hI ▸ le_sSup (mem_image_of_mem _ hi)
· refine le_sInf fun b hb => sInf_le_of_le (mem_image_of_mem _ hb) <| sSup_le ?_
rintro _ ⟨_, h, rfl⟩
exact h
theorem liminf_eq_sSup_sInf {ι R : Type*} (F : Filter ι) [CompleteLattice R] (a : ι → R) :
liminf a F = sSup ((fun I => sInf (a '' I)) '' F.sets) :=
@Filter.limsup_eq_sInf_sSup ι (OrderDual R) _ _ a
theorem liminf_le_of_frequently_le' {α β} [CompleteLattice β] {f : Filter α} {u : α → β} {x : β}
(h : ∃ᶠ a in f, u a ≤ x) : liminf u f ≤ x := by
rw [liminf_eq]
refine sSup_le fun b hb => ?_
have hbx : ∃ᶠ _ in f, b ≤ x := by
revert h
rw [← not_imp_not, not_frequently, not_frequently]
exact fun h => hb.mp (h.mono fun a hbx hba hax => hbx (hba.trans hax))
exact hbx.exists.choose_spec
theorem le_limsup_of_frequently_le' {α β} [CompleteLattice β] {f : Filter α} {u : α → β} {x : β}
(h : ∃ᶠ a in f, x ≤ u a) : x ≤ limsup u f :=
liminf_le_of_frequently_le' (β := βᵒᵈ) h
/-- If `f : α → α` is a morphism of complete lattices, then the limsup of its iterates of any
`a : α` is a fixed point. -/
@[simp]
theorem _root_.CompleteLatticeHom.apply_limsup_iterate (f : CompleteLatticeHom α α) (a : α) :
f (limsup (fun n => f^[n] a) atTop) = limsup (fun n => f^[n] a) atTop := by
rw [limsup_eq_iInf_iSup_of_nat', map_iInf]
simp_rw [_root_.map_iSup, ← Function.comp_apply (f := f), ← Function.iterate_succ' f,
← Nat.add_succ]
conv_rhs => rw [iInf_split _ (0 < ·)]
simp only [not_lt, Nat.le_zero, iInf_iInf_eq_left, add_zero, iInf_nat_gt_zero_eq, left_eq_inf]
refine (iInf_le (fun i => ⨆ j, f^[j + (i + 1)] a) 0).trans ?_
simp only [zero_add, Function.comp_apply, iSup_le_iff]
exact fun i => le_iSup (fun i => f^[i] a) (i + 1)
/-- If `f : α → α` is a morphism of complete lattices, then the liminf of its iterates of any
`a : α` is a fixed point. -/
theorem _root_.CompleteLatticeHom.apply_liminf_iterate (f : CompleteLatticeHom α α) (a : α) :
f (liminf (fun n => f^[n] a) atTop) = liminf (fun n => f^[n] a) atTop :=
(CompleteLatticeHom.dual f).apply_limsup_iterate _
variable {f g : Filter β} {p q : β → Prop} {u v : β → α}
theorem blimsup_mono (h : ∀ x, p x → q x) : blimsup u f p ≤ blimsup u f q :=
sInf_le_sInf fun a ha => ha.mono <| by tauto
theorem bliminf_antitone (h : ∀ x, p x → q x) : bliminf u f q ≤ bliminf u f p :=
sSup_le_sSup fun a ha => ha.mono <| by tauto
theorem mono_blimsup' (h : ∀ᶠ x in f, p x → u x ≤ v x) : blimsup u f p ≤ blimsup v f p :=
sInf_le_sInf fun _ ha => (ha.and h).mono fun _ hx hx' => (hx.2 hx').trans (hx.1 hx')
theorem mono_blimsup (h : ∀ x, p x → u x ≤ v x) : blimsup u f p ≤ blimsup v f p :=
mono_blimsup' <| Eventually.of_forall h
theorem mono_bliminf' (h : ∀ᶠ x in f, p x → u x ≤ v x) : bliminf u f p ≤ bliminf v f p :=
sSup_le_sSup fun _ ha => (ha.and h).mono fun _ hx hx' => (hx.1 hx').trans (hx.2 hx')
theorem mono_bliminf (h : ∀ x, p x → u x ≤ v x) : bliminf u f p ≤ bliminf v f p :=
mono_bliminf' <| Eventually.of_forall h
theorem bliminf_antitone_filter (h : f ≤ g) : bliminf u g p ≤ bliminf u f p :=
sSup_le_sSup fun _ ha => ha.filter_mono h
theorem blimsup_monotone_filter (h : f ≤ g) : blimsup u f p ≤ blimsup u g p :=
sInf_le_sInf fun _ ha => ha.filter_mono h
theorem blimsup_and_le_inf : (blimsup u f fun x => p x ∧ q x) ≤ blimsup u f p ⊓ blimsup u f q :=
le_inf (blimsup_mono <| by tauto) (blimsup_mono <| by tauto)
@[simp]
theorem bliminf_sup_le_inf_aux_left :
(blimsup u f fun x => p x ∧ q x) ≤ blimsup u f p :=
blimsup_and_le_inf.trans inf_le_left
@[simp]
theorem bliminf_sup_le_inf_aux_right :
(blimsup u f fun x => p x ∧ q x) ≤ blimsup u f q :=
blimsup_and_le_inf.trans inf_le_right
theorem bliminf_sup_le_and : bliminf u f p ⊔ bliminf u f q ≤ bliminf u f fun x => p x ∧ q x :=
blimsup_and_le_inf (α := αᵒᵈ)
@[simp]
theorem bliminf_sup_le_and_aux_left : bliminf u f p ≤ bliminf u f fun x => p x ∧ q x :=
le_sup_left.trans bliminf_sup_le_and
@[simp]
theorem bliminf_sup_le_and_aux_right : bliminf u f q ≤ bliminf u f fun x => p x ∧ q x :=
le_sup_right.trans bliminf_sup_le_and
/-- See also `Filter.blimsup_or_eq_sup`. -/
theorem blimsup_sup_le_or : blimsup u f p ⊔ blimsup u f q ≤ blimsup u f fun x => p x ∨ q x :=
sup_le (blimsup_mono <| by tauto) (blimsup_mono <| by tauto)
@[simp]
theorem bliminf_sup_le_or_aux_left : blimsup u f p ≤ blimsup u f fun x => p x ∨ q x :=
le_sup_left.trans blimsup_sup_le_or
@[simp]
theorem bliminf_sup_le_or_aux_right : blimsup u f q ≤ blimsup u f fun x => p x ∨ q x :=
le_sup_right.trans blimsup_sup_le_or
/-- See also `Filter.bliminf_or_eq_inf`. -/
theorem bliminf_or_le_inf : (bliminf u f fun x => p x ∨ q x) ≤ bliminf u f p ⊓ bliminf u f q :=
blimsup_sup_le_or (α := αᵒᵈ)
@[simp]
theorem bliminf_or_le_inf_aux_left : (bliminf u f fun x => p x ∨ q x) ≤ bliminf u f p :=
bliminf_or_le_inf.trans inf_le_left
@[simp]
theorem bliminf_or_le_inf_aux_right : (bliminf u f fun x => p x ∨ q x) ≤ bliminf u f q :=
bliminf_or_le_inf.trans inf_le_right
theorem _root_.OrderIso.apply_blimsup [CompleteLattice γ] (e : α ≃o γ) :
e (blimsup u f p) = blimsup (e ∘ u) f p := by
simp only [blimsup_eq, map_sInf, Function.comp_apply, e.image_eq_preimage,
Set.preimage_setOf_eq, e.le_symm_apply]
theorem _root_.OrderIso.apply_bliminf [CompleteLattice γ] (e : α ≃o γ) :
e (bliminf u f p) = bliminf (e ∘ u) f p :=
e.dual.apply_blimsup
theorem _root_.sSupHom.apply_blimsup_le [CompleteLattice γ] (g : sSupHom α γ) :
g (blimsup u f p) ≤ blimsup (g ∘ u) f p := by
simp only [blimsup_eq_iInf_biSup, Function.comp]
refine ((OrderHomClass.mono g).map_iInf₂_le _).trans ?_
simp only [_root_.map_iSup, le_refl]
theorem _root_.sInfHom.le_apply_bliminf [CompleteLattice γ] (g : sInfHom α γ) :
bliminf (g ∘ u) f p ≤ g (bliminf u f p) :=
(sInfHom.dual g).apply_blimsup_le
end CompleteLattice
section CompleteDistribLattice
variable [CompleteDistribLattice α] {f : Filter β} {p q : β → Prop} {u : β → α}
lemma limsup_sup_filter {g} : limsup u (f ⊔ g) = limsup u f ⊔ limsup u g := by
refine le_antisymm ?_
(sup_le (limsup_le_limsup_of_le le_sup_left) (limsup_le_limsup_of_le le_sup_right))
simp_rw [limsup_eq, sInf_sup_eq, sup_sInf_eq, mem_setOf_eq, le_iInf₂_iff]
intro a ha b hb
exact sInf_le ⟨ha.mono fun _ h ↦ h.trans le_sup_left, hb.mono fun _ h ↦ h.trans le_sup_right⟩
lemma liminf_sup_filter {g} : liminf u (f ⊔ g) = liminf u f ⊓ liminf u g :=
limsup_sup_filter (α := αᵒᵈ)
@[simp]
theorem blimsup_or_eq_sup : (blimsup u f fun x => p x ∨ q x) = blimsup u f p ⊔ blimsup u f q := by
simp only [blimsup_eq_limsup, ← limsup_sup_filter, ← inf_sup_left, sup_principal, setOf_or]
@[simp]
theorem bliminf_or_eq_inf : (bliminf u f fun x => p x ∨ q x) = bliminf u f p ⊓ bliminf u f q :=
blimsup_or_eq_sup (α := αᵒᵈ)
@[simp]
lemma blimsup_sup_not : blimsup u f p ⊔ blimsup u f (¬p ·) = limsup u f := by
simp_rw [← blimsup_or_eq_sup, or_not, blimsup_true]
@[simp]
lemma bliminf_inf_not : bliminf u f p ⊓ bliminf u f (¬p ·) = liminf u f :=
blimsup_sup_not (α := αᵒᵈ)
@[simp]
lemma blimsup_not_sup : blimsup u f (¬p ·) ⊔ blimsup u f p = limsup u f := by
simpa only [not_not] using blimsup_sup_not (p := (¬p ·))
@[simp]
lemma bliminf_not_inf : bliminf u f (¬p ·) ⊓ bliminf u f p = liminf u f :=
blimsup_not_sup (α := αᵒᵈ)
lemma limsup_piecewise {s : Set β} [DecidablePred (· ∈ s)] {v} :
limsup (s.piecewise u v) f = blimsup u f (· ∈ s) ⊔ blimsup v f (· ∉ s) := by
rw [← blimsup_sup_not (p := (· ∈ s))]
refine congr_arg₂ _ (blimsup_congr ?_) (blimsup_congr ?_) <;>
filter_upwards with _ h using by simp [h]
lemma liminf_piecewise {s : Set β} [DecidablePred (· ∈ s)] {v} :
liminf (s.piecewise u v) f = bliminf u f (· ∈ s) ⊓ bliminf v f (· ∉ s) :=
limsup_piecewise (α := αᵒᵈ)
theorem sup_limsup [NeBot f] (a : α) : a ⊔ limsup u f = limsup (fun x => a ⊔ u x) f := by
simp only [limsup_eq_iInf_iSup, iSup_sup_eq, sup_iInf₂_eq]
congr; ext s; congr; ext hs; congr
exact (biSup_const (nonempty_of_mem hs)).symm
theorem inf_liminf [NeBot f] (a : α) : a ⊓ liminf u f = liminf (fun x => a ⊓ u x) f :=
sup_limsup (α := αᵒᵈ) a
theorem sup_liminf (a : α) : a ⊔ liminf u f = liminf (fun x => a ⊔ u x) f := by
simp only [liminf_eq_iSup_iInf]
rw [sup_comm, biSup_sup (⟨univ, univ_mem⟩ : ∃ i : Set β, i ∈ f)]
simp_rw [iInf₂_sup_eq, sup_comm (a := a)]
theorem inf_limsup (a : α) : a ⊓ limsup u f = limsup (fun x => a ⊓ u x) f :=
sup_liminf (α := αᵒᵈ) a
end CompleteDistribLattice
section CompleteBooleanAlgebra
variable [CompleteBooleanAlgebra α] (f : Filter β) (u : β → α)
theorem limsup_compl : (limsup u f)ᶜ = liminf (compl ∘ u) f := by
simp only [limsup_eq_iInf_iSup, compl_iInf, compl_iSup, liminf_eq_iSup_iInf, Function.comp_apply]
theorem liminf_compl : (liminf u f)ᶜ = limsup (compl ∘ u) f := by
simp only [limsup_eq_iInf_iSup, compl_iInf, compl_iSup, liminf_eq_iSup_iInf, Function.comp_apply]
theorem limsup_sdiff (a : α) : limsup u f \ a = limsup (fun b => u b \ a) f := by
simp only [limsup_eq_iInf_iSup, sdiff_eq]
rw [biInf_inf (⟨univ, univ_mem⟩ : ∃ i : Set β, i ∈ f)]
simp_rw [inf_comm, inf_iSup₂_eq, inf_comm]
theorem liminf_sdiff [NeBot f] (a : α) : liminf u f \ a = liminf (fun b => u b \ a) f := by
simp only [sdiff_eq, inf_comm _ aᶜ, inf_liminf]
theorem sdiff_limsup [NeBot f] (a : α) : a \ limsup u f = liminf (fun b => a \ u b) f := by
rw [← compl_inj_iff]
simp only [sdiff_eq, liminf_compl, comp_def, compl_inf, compl_compl, sup_limsup]
theorem sdiff_liminf (a : α) : a \ liminf u f = limsup (fun b => a \ u b) f := by
rw [← compl_inj_iff]
simp only [sdiff_eq, limsup_compl, comp_def, compl_inf, compl_compl, sup_liminf]
end CompleteBooleanAlgebra
section SetLattice
variable {p : ι → Prop} {s : ι → Set α} {𝓕 : Filter ι} {a : α}
lemma mem_liminf_iff_eventually_mem : (a ∈ liminf s 𝓕) ↔ (∀ᶠ i in 𝓕, a ∈ s i) := by
simpa only [liminf_eq_iSup_iInf, iSup_eq_iUnion, iInf_eq_iInter, mem_iUnion, mem_iInter]
using ⟨fun ⟨S, hS, hS'⟩ ↦ mem_of_superset hS (by tauto), fun h ↦ ⟨{i | a ∈ s i}, h, by tauto⟩⟩
lemma mem_limsup_iff_frequently_mem : (a ∈ limsup s 𝓕) ↔ (∃ᶠ i in 𝓕, a ∈ s i) := by
simp only [Filter.Frequently, iff_not_comm, ← mem_compl_iff, limsup_compl, comp_apply,
mem_liminf_iff_eventually_mem]
theorem cofinite.blimsup_set_eq :
blimsup s cofinite p = { x | { n | p n ∧ x ∈ s n }.Infinite } := by
simp only [blimsup_eq, le_eq_subset, eventually_cofinite, not_forall, sInf_eq_sInter, exists_prop]
ext x
refine ⟨fun h => ?_, fun hx t h => ?_⟩ <;> contrapose! h
· simp only [mem_sInter, mem_setOf_eq, not_forall, exists_prop]
exact ⟨{x}ᶜ, by simpa using h, by simp⟩
· exact hx.mono fun i hi => ⟨hi.1, fun hit => h (hit hi.2)⟩
theorem cofinite.bliminf_set_eq : bliminf s cofinite p = { x | { n | p n ∧ x ∉ s n }.Finite } := by
rw [← compl_inj_iff]
simp only [bliminf_eq_iSup_biInf, compl_iInf, compl_iSup, ← blimsup_eq_iInf_biSup,
cofinite.blimsup_set_eq]
rfl
/-- In other words, `limsup cofinite s` is the set of elements lying inside the family `s`
infinitely often. -/
theorem cofinite.limsup_set_eq : limsup s cofinite = { x | { n | x ∈ s n }.Infinite } := by
simp only [← cofinite.blimsup_true s, cofinite.blimsup_set_eq, true_and]
/-- In other words, `liminf cofinite s` is the set of elements lying outside the family `s`
finitely often. -/
theorem cofinite.liminf_set_eq : liminf s cofinite = { x | { n | x ∉ s n }.Finite } := by
simp only [← cofinite.bliminf_true s, cofinite.bliminf_set_eq, true_and]
theorem exists_forall_mem_of_hasBasis_mem_blimsup {l : Filter β} {b : ι → Set β} {q : ι → Prop}
(hl : l.HasBasis q b) {u : β → Set α} {p : β → Prop} {x : α} (hx : x ∈ blimsup u l p) :
∃ f : { i | q i } → β, ∀ i, x ∈ u (f i) ∧ p (f i) ∧ f i ∈ b i := by
rw [blimsup_eq_iInf_biSup] at hx
simp only [iSup_eq_iUnion, iInf_eq_iInter, mem_iInter, mem_iUnion, exists_prop] at hx
choose g hg hg' using hx
refine ⟨fun i : { i | q i } => g (b i) (hl.mem_of_mem i.2), fun i => ⟨?_, ?_⟩⟩
· exact hg' (b i) (hl.mem_of_mem i.2)
· exact hg (b i) (hl.mem_of_mem i.2)
theorem exists_forall_mem_of_hasBasis_mem_blimsup' {l : Filter β} {b : ι → Set β}
(hl : l.HasBasis (fun _ => True) b) {u : β → Set α} {p : β → Prop} {x : α}
(hx : x ∈ blimsup u l p) : ∃ f : ι → β, ∀ i, x ∈ u (f i) ∧ p (f i) ∧ f i ∈ b i := by
obtain ⟨f, hf⟩ := exists_forall_mem_of_hasBasis_mem_blimsup hl hx
exact ⟨fun i => f ⟨i, trivial⟩, fun i => hf ⟨i, trivial⟩⟩
end SetLattice
section ConditionallyCompleteLinearOrder
theorem frequently_lt_of_lt_limsSup {f : Filter α} [ConditionallyCompleteLinearOrder α] {a : α}
(hf : f.IsCobounded (· ≤ ·) := by isBoundedDefault)
(h : a < limsSup f) : ∃ᶠ n in f, a < n := by
contrapose! h
simp only [not_frequently, not_lt] at h
exact limsSup_le_of_le hf h
theorem frequently_lt_of_limsInf_lt {f : Filter α} [ConditionallyCompleteLinearOrder α] {a : α}
(hf : f.IsCobounded (· ≥ ·) := by isBoundedDefault)
(h : limsInf f < a) : ∃ᶠ n in f, n < a :=
frequently_lt_of_lt_limsSup (α := OrderDual α) hf h
theorem eventually_lt_of_lt_liminf {f : Filter α} [ConditionallyCompleteLinearOrder β] {u : α → β}
{b : β} (h : b < liminf u f)
(hu : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
∀ᶠ a in f, b < u a := by
obtain ⟨c, hc, hbc⟩ : ∃ (c : β) (_ : c ∈ { c : β | ∀ᶠ n : α in f, c ≤ u n }), b < c := by
simp_rw [exists_prop]
exact exists_lt_of_lt_csSup hu h
exact hc.mono fun x hx => lt_of_lt_of_le hbc hx
theorem eventually_lt_of_limsup_lt {f : Filter α} [ConditionallyCompleteLinearOrder β] {u : α → β}
{b : β} (h : limsup u f < b)
(hu : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
∀ᶠ a in f, u a < b :=
eventually_lt_of_lt_liminf (β := βᵒᵈ) h hu
section ConditionallyCompleteLinearOrder
variable [ConditionallyCompleteLinearOrder α]
/-- If `Filter.limsup u atTop ≤ x`, then for all `ε > 0`, eventually we have `u b < x + ε`. -/
theorem eventually_lt_add_pos_of_limsup_le [Preorder β] [AddZeroClass α] [AddLeftStrictMono α]
{x ε : α} {u : β → α} (hu_bdd : IsBoundedUnder LE.le atTop u) (hu : Filter.limsup u atTop ≤ x)
(hε : 0 < ε) :
∀ᶠ b : β in atTop, u b < x + ε :=
eventually_lt_of_limsup_lt (lt_of_le_of_lt hu (lt_add_of_pos_right x hε)) hu_bdd
/-- If `x ≤ Filter.liminf u atTop`, then for all `ε < 0`, eventually we have `x + ε < u b`. -/
theorem eventually_add_neg_lt_of_le_liminf [Preorder β] [AddZeroClass α] [AddLeftStrictMono α]
{x ε : α} {u : β → α} (hu_bdd : IsBoundedUnder GE.ge atTop u) (hu : x ≤ Filter.liminf u atTop)
(hε : ε < 0) :
∀ᶠ b : β in atTop, x + ε < u b :=
eventually_lt_of_lt_liminf (lt_of_lt_of_le (add_lt_of_neg_right x hε) hu) hu_bdd
/-- If `Filter.limsup u atTop ≤ x`, then for all `ε > 0`, there exists a positive natural
number `n` such that `u n < x + ε`. -/
theorem exists_lt_of_limsup_le [AddZeroClass α] [AddLeftStrictMono α] {x ε : α} {u : ℕ → α}
(hu_bdd : IsBoundedUnder LE.le atTop u) (hu : Filter.limsup u atTop ≤ x) (hε : 0 < ε) :
∃ n : PNat, u n < x + ε := by
have h : ∀ᶠ n : ℕ in atTop, u n < x + ε := eventually_lt_add_pos_of_limsup_le hu_bdd hu hε
simp only [eventually_atTop] at h
obtain ⟨n, hn⟩ := h
exact ⟨⟨n + 1, Nat.succ_pos _⟩, hn (n + 1) (Nat.le_succ _)⟩
/-- If `x ≤ Filter.liminf u atTop`, then for all `ε < 0`, there exists a positive natural
number `n` such that ` x + ε < u n`. -/
theorem exists_lt_of_le_liminf [AddZeroClass α] [AddLeftStrictMono α] {x ε : α} {u : ℕ → α}
(hu_bdd : IsBoundedUnder GE.ge atTop u) (hu : x ≤ Filter.liminf u atTop) (hε : ε < 0) :
∃ n : PNat, x + ε < u n := by
have h : ∀ᶠ n : ℕ in atTop, x + ε < u n := eventually_add_neg_lt_of_le_liminf hu_bdd hu hε
simp only [eventually_atTop] at h
obtain ⟨n, hn⟩ := h
exact ⟨⟨n + 1, Nat.succ_pos _⟩, hn (n + 1) (Nat.le_succ _)⟩
end ConditionallyCompleteLinearOrder
variable [ConditionallyCompleteLinearOrder β] {f : Filter α} {u : α → β}
theorem le_limsup_of_frequently_le {b : β} (hu_le : ∃ᶠ x in f, b ≤ u x)
(hu : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
b ≤ limsup u f := by
revert hu_le
rw [← not_imp_not, not_frequently]
simp_rw [← lt_iff_not_ge]
exact fun h => eventually_lt_of_limsup_lt h hu
theorem liminf_le_of_frequently_le {b : β} (hu_le : ∃ᶠ x in f, u x ≤ b)
(hu : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
liminf u f ≤ b :=
le_limsup_of_frequently_le (β := βᵒᵈ) hu_le hu
theorem frequently_lt_of_lt_limsup {b : β}
(hu : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(h : b < limsup u f) : ∃ᶠ x in f, b < u x := by
contrapose! h
apply limsSup_le_of_le hu
simpa using h
theorem frequently_lt_of_liminf_lt {b : β}
(hu : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h : liminf u f < b) : ∃ᶠ x in f, u x < b :=
frequently_lt_of_lt_limsup (β := βᵒᵈ) hu h
theorem limsup_le_iff {x : β} (h₁ : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
limsup u f ≤ x ↔ ∀ y > x, ∀ᶠ a in f, u a < y := by
refine ⟨fun h _ h' ↦ eventually_lt_of_limsup_lt (h.trans_lt h') h₂, fun h ↦ ?_⟩
--Two cases: Either `x` is a cluster point from above, or it is not.
--In the first case, we use `forall_lt_iff_le'` and split an interval.
--In the second case, the function `u` must eventually be smaller or equal to `x`.
by_cases h' : ∀ y > x, ∃ z, x < z ∧ z < y
· rw [← forall_lt_iff_le']
intro y x_y
rcases h' y x_y with ⟨z, x_z, z_y⟩
exact (limsup_le_of_le h₁ ((h z x_z).mono (fun _ ↦ le_of_lt))).trans_lt z_y
· apply limsup_le_of_le h₁
set_option push_neg.use_distrib true in push_neg at h'
rcases h' with ⟨z, x_z, hz⟩
exact (h z x_z).mono <| fun w hw ↦ (or_iff_left (not_le_of_lt hw)).1 (hz (u w))
/- A version of `limsup_le_iff` with large inequalities in densely ordered spaces.-/
lemma limsup_le_iff' [DenselyOrdered β] {x : β}
(h₁ : IsCoboundedUnder (· ≤ ·) f u := by isBoundedDefault)
(h₂ : IsBoundedUnder (· ≤ ·) f u := by isBoundedDefault) :
limsup u f ≤ x ↔ ∀ y > x, ∀ᶠ (a : α) in f, u a ≤ y := by
refine ⟨fun h _ h' ↦ (eventually_lt_of_limsup_lt (h.trans_lt h') h₂).mono fun _ ↦ le_of_lt, ?_⟩
rw [← forall_lt_iff_le']
intro h y x_y
obtain ⟨z, x_z, z_y⟩ := exists_between x_y
exact (limsup_le_of_le h₁ (h z x_z)).trans_lt z_y
theorem le_limsup_iff {x : β} (h₁ : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
x ≤ limsup u f ↔ ∀ y < x, ∃ᶠ a in f, y < u a := by
refine ⟨fun h _ h' ↦ frequently_lt_of_lt_limsup h₁ (h'.trans_le h), fun h ↦ ?_⟩
--Two cases: Either `x` is a cluster point from below, or it is not.
--In the first case, we use `forall_lt_iff_le` and split an interval.
--In the second case, the function `u` must frequently be larger or equal to `x`.
by_cases h' : ∀ y < x, ∃ z, y < z ∧ z < x
· rw [← forall_lt_iff_le]
intro y y_x
obtain ⟨z, y_z, z_x⟩ := h' y y_x
exact y_z.trans_le (le_limsup_of_frequently_le ((h z z_x).mono (fun _ ↦ le_of_lt)) h₂)
· apply le_limsup_of_frequently_le _ h₂
set_option push_neg.use_distrib true in push_neg at h'
rcases h' with ⟨z, z_x, hz⟩
exact (h z z_x).mono <| fun w hw ↦ (or_iff_right (not_le_of_lt hw)).1 (hz (u w))
/- A version of `le_limsup_iff` with large inequalities in densely ordered spaces.-/
lemma le_limsup_iff' [DenselyOrdered β] {x : β}
(h₁ : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault) :
x ≤ limsup u f ↔ ∀ y < x, ∃ᶠ a in f, y ≤ u a := by
refine ⟨fun h _ h' ↦ (frequently_lt_of_lt_limsup h₁ (h'.trans_le h)).mono fun _ ↦ le_of_lt, ?_⟩
rw [← forall_lt_iff_le]
intro h y y_x
obtain ⟨z, y_z, z_x⟩ := exists_between y_x
exact y_z.trans_le (le_limsup_of_frequently_le (h z z_x) h₂)
theorem le_liminf_iff {x : β} (h₁ : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
x ≤ liminf u f ↔ ∀ y < x, ∀ᶠ a in f, y < u a := limsup_le_iff (β := βᵒᵈ) h₁ h₂
/- A version of `le_liminf_iff` with large inequalities in densely ordered spaces.-/
theorem le_liminf_iff' [DenselyOrdered β] {x : β}
(h₁ : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
x ≤ liminf u f ↔ ∀ y < x, ∀ᶠ a in f, y ≤ u a := limsup_le_iff' (β := βᵒᵈ) h₁ h₂
theorem liminf_le_iff {x : β} (h₁ : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
liminf u f ≤ x ↔ ∀ y > x, ∃ᶠ a in f, u a < y := le_limsup_iff (β := βᵒᵈ) h₁ h₂
/- A version of `liminf_le_iff` with large inequalities in densely ordered spaces.-/
theorem liminf_le_iff' [DenselyOrdered β] {x : β}
(h₁ : f.IsCoboundedUnder (· ≥ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault) :
liminf u f ≤ x ↔ ∀ y > x, ∃ᶠ a in f, u a ≤ y := le_limsup_iff' (β := βᵒᵈ) h₁ h₂
lemma liminf_le_limsup_of_frequently_le {v : α → β} (h : ∃ᶠ x in f, u x ≤ v x)
(h₁ : f.IsBoundedUnder (· ≥ ·) u := by isBoundedDefault)
(h₂ : f.IsBoundedUnder (· ≤ ·) v := by isBoundedDefault) :
liminf u f ≤ limsup v f := by
rcases f.eq_or_neBot with rfl | _
· exact (frequently_bot h).rec
have h₃ : f.IsCoboundedUnder (· ≥ ·) u := by
obtain ⟨a, ha⟩ := h₂.eventually_le
apply IsCoboundedUnder.of_frequently_le (a := a)
exact (h.and_eventually ha).mono fun x ⟨u_x, v_x⟩ ↦ u_x.trans v_x
have h₄ : f.IsCoboundedUnder (· ≤ ·) v := by
obtain ⟨a, ha⟩ := h₁.eventually_ge
apply IsCoboundedUnder.of_frequently_ge (a := a)
exact (ha.and_frequently h).mono fun x ⟨u_x, v_x⟩ ↦ u_x.trans v_x
refine (le_limsup_iff h₄ h₂).2 fun y y_v ↦ ?_
have := (le_liminf_iff h₃ h₁).1 (le_refl (liminf u f)) y y_v
exact (h.and_eventually this).mono fun x ⟨ux_vx, y_ux⟩ ↦ y_ux.trans_le ux_vx
variable [ConditionallyCompleteLinearOrder α] {f : Filter α} {b : α}
-- The linter erroneously claims that I'm not referring to `c`
set_option linter.unusedVariables false in
theorem lt_mem_sets_of_limsSup_lt (h : f.IsBounded (· ≤ ·)) (l : f.limsSup < b) :
∀ᶠ a in f, a < b :=
let ⟨c, (h : ∀ᶠ a in f, a ≤ c), hcb⟩ := exists_lt_of_csInf_lt h l
mem_of_superset h fun _a => hcb.trans_le'
theorem gt_mem_sets_of_limsInf_gt : f.IsBounded (· ≥ ·) → b < f.limsInf → ∀ᶠ a in f, b < a :=
@lt_mem_sets_of_limsSup_lt αᵒᵈ _ _ _
section Classical
open Classical in
/-- Given an indexed family of sets `s j` over `j : Subtype p` and a function `f`, then
`liminf_reparam j` is equal to `j` if `f` is bounded below on `s j`, and otherwise to some
index `k` such that `f` is bounded below on `s k` (if there exists one).
To ensure good measurability behavior, this index `k` is chosen as the minimal suitable index.
This function is used to write down a liminf in a measurable way,
in `Filter.HasBasis.liminf_eq_ciSup_ciInf` and `Filter.HasBasis.liminf_eq_ite`. -/
noncomputable def liminf_reparam
(f : ι → α) (s : ι' → Set ι) (p : ι' → Prop) [Countable (Subtype p)] [Nonempty (Subtype p)]
(j : Subtype p) : Subtype p :=
let m : Set (Subtype p) := {j | BddBelow (range (fun (i : s j) ↦ f i))}
let g : ℕ → Subtype p := (exists_surjective_nat _).choose
have Z : ∃ n, g n ∈ m ∨ ∀ j, j ∉ m := by
by_cases H : ∃ j, j ∈ m
· rcases H with ⟨j, hj⟩
rcases (exists_surjective_nat (Subtype p)).choose_spec j with ⟨n, rfl⟩
exact ⟨n, Or.inl hj⟩
· push_neg at H
exact ⟨0, Or.inr H⟩
if j ∈ m then j else g (Nat.find Z)
/-- Writing a liminf as a supremum of infimum, in a (possibly non-complete) conditionally complete
linear order. A reparametrization trick is needed to avoid taking the infimum of sets which are
not bounded below. -/
theorem HasBasis.liminf_eq_ciSup_ciInf {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} [Countable (Subtype p)] [Nonempty (Subtype p)]
(hv : v.HasBasis p s) {f : ι → α} (hs : ∀ (j : Subtype p), (s j).Nonempty)
(H : ∃ (j : Subtype p), BddBelow (range (fun (i : s j) ↦ f i))) :
liminf f v = ⨆ (j : Subtype p), ⨅ (i : s (liminf_reparam f s p j)), f i := by
classical
rcases H with ⟨j0, hj0⟩
let m : Set (Subtype p) := {j | BddBelow (range (fun (i : s j) ↦ f i))}
have : ∀ (j : Subtype p), Nonempty (s j) := fun j ↦ Nonempty.coe_sort (hs j)
have A : ⋃ (j : Subtype p), ⋂ (i : s j), Iic (f i) =
⋃ (j : Subtype p), ⋂ (i : s (liminf_reparam f s p j)), Iic (f i) := by
apply Subset.antisymm
· apply iUnion_subset (fun j ↦ ?_)
by_cases hj : j ∈ m
· have : j = liminf_reparam f s p j := by simp only [m, liminf_reparam, hj, ite_true]
conv_lhs => rw [this]
apply subset_iUnion _ j
· simp only [m, mem_setOf_eq, ← nonempty_iInter_Iic_iff, not_nonempty_iff_eq_empty] at hj
simp only [hj, empty_subset]
· apply iUnion_subset (fun j ↦ ?_)
exact subset_iUnion (fun (k : Subtype p) ↦ (⋂ (i : s k), Iic (f i))) (liminf_reparam f s p j)
have B : ∀ (j : Subtype p), ⋂ (i : s (liminf_reparam f s p j)), Iic (f i) =
Iic (⨅ (i : s (liminf_reparam f s p j)), f i) := by
intro j
apply (Iic_ciInf _).symm
change liminf_reparam f s p j ∈ m
by_cases Hj : j ∈ m
· simpa only [m, liminf_reparam, if_pos Hj] using Hj
· simp only [m, liminf_reparam, if_neg Hj]
have Z : ∃ n, (exists_surjective_nat (Subtype p)).choose n ∈ m ∨ ∀ j, j ∉ m := by
rcases (exists_surjective_nat (Subtype p)).choose_spec j0 with ⟨n, rfl⟩
exact ⟨n, Or.inl hj0⟩
rcases Nat.find_spec Z with hZ|hZ
· exact hZ
· exact (hZ j0 hj0).elim
simp_rw [hv.liminf_eq_sSup_iUnion_iInter, A, B, sSup_iUnion_Iic]
open Classical in
/-- Writing a liminf as a supremum of infimum, in a (possibly non-complete) conditionally complete
linear order. A reparametrization trick is needed to avoid taking the infimum of sets which are
not bounded below. -/
theorem HasBasis.liminf_eq_ite {v : Filter ι} {p : ι' → Prop} {s : ι' → Set ι}
[Countable (Subtype p)] [Nonempty (Subtype p)] (hv : v.HasBasis p s) (f : ι → α) :
liminf f v = if ∃ (j : Subtype p), s j = ∅ then sSup univ else
if ∀ (j : Subtype p), ¬BddBelow (range (fun (i : s j) ↦ f i)) then sSup ∅
else ⨆ (j : Subtype p), ⨅ (i : s (liminf_reparam f s p j)), f i := by
by_cases H : ∃ (j : Subtype p), s j = ∅
· rw [if_pos H]
rcases H with ⟨j, hj⟩
simp [hv.liminf_eq_sSup_univ_of_empty j j.2 hj]
rw [if_neg H]
by_cases H' : ∀ (j : Subtype p), ¬BddBelow (range (fun (i : s j) ↦ f i))
· have A : ∀ (j : Subtype p), ⋂ (i : s j), Iic (f i) = ∅ := by
simp_rw [← not_nonempty_iff_eq_empty, nonempty_iInter_Iic_iff]
exact H'
simp_rw [if_pos H', hv.liminf_eq_sSup_iUnion_iInter, A, iUnion_empty]
rw [if_neg H']
apply hv.liminf_eq_ciSup_ciInf
· push_neg at H
simpa only [nonempty_iff_ne_empty] using H
· push_neg at H'
exact H'
/-- Given an indexed family of sets `s j` and a function `f`, then `limsup_reparam j` is equal
to `j` if `f` is bounded above on `s j`, and otherwise to some index `k` such that `f` is bounded
above on `s k` (if there exists one). To ensure good measurability behavior, this index `k` is
chosen as the minimal suitable index. This function is used to write down a limsup in a measurable
way, in `Filter.HasBasis.limsup_eq_ciInf_ciSup` and `Filter.HasBasis.limsup_eq_ite`. -/
noncomputable def limsup_reparam
(f : ι → α) (s : ι' → Set ι) (p : ι' → Prop) [Countable (Subtype p)] [Nonempty (Subtype p)]
(j : Subtype p) : Subtype p :=
liminf_reparam (α := αᵒᵈ) f s p j
/-- Writing a limsup as an infimum of supremum, in a (possibly non-complete) conditionally complete
linear order. A reparametrization trick is needed to avoid taking the supremum of sets which are
not bounded above. -/
theorem HasBasis.limsup_eq_ciInf_ciSup {v : Filter ι}
{p : ι' → Prop} {s : ι' → Set ι} [Countable (Subtype p)] [Nonempty (Subtype p)]
(hv : v.HasBasis p s) {f : ι → α} (hs : ∀ (j : Subtype p), (s j).Nonempty)
(H : ∃ (j : Subtype p), BddAbove (range (fun (i : s j) ↦ f i))) :
limsup f v = ⨅ (j : Subtype p), ⨆ (i : s (limsup_reparam f s p j)), f i :=
HasBasis.liminf_eq_ciSup_ciInf (α := αᵒᵈ) hv hs H
open Classical in
/-- Writing a limsup as an infimum of supremum, in a (possibly non-complete) conditionally complete
linear order. A reparametrization trick is needed to avoid taking the supremum of sets which are
not bounded below. -/
theorem HasBasis.limsup_eq_ite {v : Filter ι} {p : ι' → Prop} {s : ι' → Set ι}
[Countable (Subtype p)] [Nonempty (Subtype p)] (hv : v.HasBasis p s) (f : ι → α) :
limsup f v = if ∃ (j : Subtype p), s j = ∅ then sInf univ else
if ∀ (j : Subtype p), ¬BddAbove (range (fun (i : s j) ↦ f i)) then sInf ∅
else ⨅ (j : Subtype p), ⨆ (i : s (limsup_reparam f s p j)), f i :=
HasBasis.liminf_eq_ite (α := αᵒᵈ) hv f
end Classical
end ConditionallyCompleteLinearOrder
end Filter
section Order
theorem GaloisConnection.l_limsup_le [ConditionallyCompleteLattice β]
[ConditionallyCompleteLattice γ] {f : Filter α} {v : α → β} {l : β → γ} {u : γ → β}
(gc : GaloisConnection l u)
(hlv : f.IsBoundedUnder (· ≤ ·) fun x => l (v x) := by isBoundedDefault)
(hv_co : f.IsCoboundedUnder (· ≤ ·) v := by isBoundedDefault) :
l (limsup v f) ≤ limsup (fun x => l (v x)) f := by
refine le_limsSup_of_le hlv fun c hc => ?_
rw [Filter.eventually_map] at hc
simp_rw [gc _ _] at hc ⊢
exact limsSup_le_of_le hv_co hc
theorem OrderIso.limsup_apply {γ} [ConditionallyCompleteLattice β] [ConditionallyCompleteLattice γ]
{f : Filter α} {u : α → β} (g : β ≃o γ)
(hu : f.IsBoundedUnder (· ≤ ·) u := by isBoundedDefault)
(hu_co : f.IsCoboundedUnder (· ≤ ·) u := by isBoundedDefault)
(hgu : f.IsBoundedUnder (· ≤ ·) fun x => g (u x) := by isBoundedDefault)
(hgu_co : f.IsCoboundedUnder (· ≤ ·) fun x => g (u x) := by isBoundedDefault) :
g (limsup u f) = limsup (fun x => g (u x)) f := by
refine le_antisymm ((OrderIso.to_galoisConnection g).l_limsup_le hgu hu_co) ?_
| rw [← g.symm.symm_apply_apply <| limsup (fun x => g (u x)) f, g.symm_symm]
refine g.monotone ?_
have hf : u = fun i => g.symm (g (u i)) := funext fun i => (g.symm_apply_apply (u i)).symm
nth_rw 2 [hf]
refine (OrderIso.to_galoisConnection g.symm).l_limsup_le ?_ hgu_co
simp_rw [g.symm_apply_apply]
| Mathlib/Order/LiminfLimsup.lean | 1,093 | 1,098 |
/-
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.LinearAlgebra.Matrix.ToLin
import Mathlib.LinearAlgebra.Quotient.Basic
import Mathlib.RingTheory.Ideal.Maps
import Mathlib.RingTheory.Nilpotent.Defs
/-!
# Nilpotent elements
This file contains results about nilpotent elements that involve ring theory.
-/
universe u v
open Function Set
variable {R S : Type*} {x y : R}
theorem RingHom.ker_isRadical_iff_reduced_of_surjective {S F} [CommSemiring R] [Semiring S]
[FunLike F R S] [RingHomClass F R S] {f : F} (hf : Function.Surjective f) :
(RingHom.ker f).IsRadical ↔ IsReduced S := by
simp_rw [isReduced_iff, hf.forall, IsNilpotent, ← map_pow, ← RingHom.mem_ker]
rfl
theorem isRadical_iff_span_singleton [CommSemiring R] :
IsRadical y ↔ (Ideal.span ({y} : Set R)).IsRadical := by
simp_rw [IsRadical, ← Ideal.mem_span_singleton]
exact forall_swap.trans (forall_congr' fun r => exists_imp.symm)
theorem isNilpotent_iff_zero_mem_powers [Monoid R] [Zero R] {x : R} :
IsNilpotent x ↔ 0 ∈ Submonoid.powers x := Iff.rfl
section CommSemiring
variable [CommSemiring R] {x y : R}
/-- The nilradical of a commutative semiring is the ideal of nilpotent elements. -/
def nilradical (R : Type*) [CommSemiring R] : Ideal R :=
(0 : Ideal R).radical
theorem mem_nilradical : x ∈ nilradical R ↔ IsNilpotent x :=
Iff.rfl
theorem nilradical_eq_sInf (R : Type*) [CommSemiring R] :
nilradical R = sInf { J : Ideal R | J.IsPrime } :=
(Ideal.radical_eq_sInf ⊥).trans <| by simp_rw [and_iff_right bot_le]
theorem nilpotent_iff_mem_prime : IsNilpotent x ↔ ∀ J : Ideal R, J.IsPrime → x ∈ J := by
rw [← mem_nilradical, nilradical_eq_sInf, Submodule.mem_sInf]
rfl
theorem nilradical_le_prime (J : Ideal R) [H : J.IsPrime] : nilradical R ≤ J :=
(nilradical_eq_sInf R).symm ▸ sInf_le H
@[simp]
theorem nilradical_eq_zero (R : Type*) [CommSemiring R] [IsReduced R] : nilradical R = 0 :=
| Ideal.ext fun _ => isNilpotent_iff_eq_zero
theorem nilradical_eq_bot_iff {R : Type*} [CommSemiring R] : nilradical R = ⊥ ↔ IsReduced R := by
| Mathlib/RingTheory/Nilpotent/Lemmas.lean | 61 | 63 |
/-
Copyright (c) 2017 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Mario Carneiro
-/
import Mathlib.Data.WSeq.Basic
import Mathlib.Data.WSeq.Defs
import Mathlib.Data.WSeq.Productive
import Mathlib.Data.WSeq.Relation
deprecated_module (since := "2025-04-13")
| Mathlib/Data/Seq/WSeq.lean | 1,119 | 1,119 | |
/-
Copyright (c) 2019 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov
-/
import Mathlib.Algebra.Order.BigOperators.Ring.Finset
import Mathlib.Analysis.Convex.Hull
import Mathlib.LinearAlgebra.AffineSpace.Basis
/-!
# Convex combinations
This file defines convex combinations of points in a vector space.
## Main declarations
* `Finset.centerMass`: Center of mass of a finite family of points.
## Implementation notes
We divide by the sum of the weights in the definition of `Finset.centerMass` because of the way
mathematical arguments go: one doesn't change weights, but merely adds some. This also makes a few
lemmas unconditional on the sum of the weights being `1`.
-/
open Set Function Pointwise
universe u u'
section
variable {R R' E F ι ι' α : Type*} [Field R] [Field R'] [AddCommGroup E] [AddCommGroup F]
[AddCommGroup α] [LinearOrder α] [Module R E] [Module R F] [Module R α] {s : Set E}
/-- Center of mass of a finite collection of points with prescribed weights.
Note that we require neither `0 ≤ w i` nor `∑ w = 1`. -/
def Finset.centerMass (t : Finset ι) (w : ι → R) (z : ι → E) : E :=
(∑ i ∈ t, w i)⁻¹ • ∑ i ∈ t, w i • z i
variable (i j : ι) (c : R) (t : Finset ι) (w : ι → R) (z : ι → E)
open Finset
theorem Finset.centerMass_empty : (∅ : Finset ι).centerMass w z = 0 := by
simp only [centerMass, sum_empty, smul_zero]
theorem Finset.centerMass_pair [DecidableEq ι] (hne : i ≠ j) :
({i, j} : Finset ι).centerMass w z = (w i / (w i + w j)) • z i + (w j / (w i + w j)) • z j := by
simp only [centerMass, sum_pair hne]
module
variable {w}
theorem Finset.centerMass_insert [DecidableEq ι] (ha : i ∉ t) (hw : ∑ j ∈ t, w j ≠ 0) :
(insert i t).centerMass w z =
(w i / (w i + ∑ j ∈ t, w j)) • z i +
((∑ j ∈ t, w j) / (w i + ∑ j ∈ t, w j)) • t.centerMass w z := by
simp only [centerMass, sum_insert ha, smul_add, (mul_smul _ _ _).symm, ← div_eq_inv_mul]
congr 2
rw [div_mul_eq_mul_div, mul_inv_cancel₀ hw, one_div]
theorem Finset.centerMass_singleton (hw : w i ≠ 0) : ({i} : Finset ι).centerMass w z = z i := by
rw [centerMass, sum_singleton, sum_singleton]
match_scalars
field_simp
@[simp] lemma Finset.centerMass_neg_left : t.centerMass (-w) z = t.centerMass w z := by
simp [centerMass, inv_neg]
lemma Finset.centerMass_smul_left {c : R'} [Module R' R] [Module R' E] [SMulCommClass R' R R]
[IsScalarTower R' R R] [SMulCommClass R R' E] [IsScalarTower R' R E] (hc : c ≠ 0) :
t.centerMass (c • w) z = t.centerMass w z := by
simp [centerMass, -smul_assoc, smul_assoc c, ← smul_sum, smul_inv₀, smul_smul_smul_comm, hc]
theorem Finset.centerMass_eq_of_sum_1 (hw : ∑ i ∈ t, w i = 1) :
t.centerMass w z = ∑ i ∈ t, w i • z i := by
simp only [Finset.centerMass, hw, inv_one, one_smul]
theorem Finset.centerMass_smul : (t.centerMass w fun i => c • z i) = c • t.centerMass w z := by
simp only [Finset.centerMass, Finset.smul_sum, (mul_smul _ _ _).symm, mul_comm c, mul_assoc]
/-- A convex combination of two centers of mass is a center of mass as well. This version
deals with two different index types. -/
theorem Finset.centerMass_segment' (s : Finset ι) (t : Finset ι') (ws : ι → R) (zs : ι → E)
(wt : ι' → R) (zt : ι' → E) (hws : ∑ i ∈ s, ws i = 1) (hwt : ∑ i ∈ t, wt i = 1) (a b : R)
(hab : a + b = 1) : a • s.centerMass ws zs + b • t.centerMass wt zt = (s.disjSum t).centerMass
(Sum.elim (fun i => a * ws i) fun j => b * wt j) (Sum.elim zs zt) := by
rw [s.centerMass_eq_of_sum_1 _ hws, t.centerMass_eq_of_sum_1 _ hwt, smul_sum, smul_sum, ←
Finset.sum_sumElim, Finset.centerMass_eq_of_sum_1]
· congr with ⟨⟩ <;> simp only [Sum.elim_inl, Sum.elim_inr, mul_smul]
· rw [sum_sumElim, ← mul_sum, ← mul_sum, hws, hwt, mul_one, mul_one, hab]
| /-- A convex combination of two centers of mass is a center of mass as well. This version
works if two centers of mass share the set of original points. -/
theorem Finset.centerMass_segment (s : Finset ι) (w₁ w₂ : ι → R) (z : ι → E)
(hw₁ : ∑ i ∈ s, w₁ i = 1) (hw₂ : ∑ i ∈ s, w₂ i = 1) (a b : R) (hab : a + b = 1) :
a • s.centerMass w₁ z + b • s.centerMass w₂ z =
s.centerMass (fun i => a * w₁ i + b * w₂ i) z := by
have hw : (∑ i ∈ s, (a * w₁ i + b * w₂ i)) = 1 := by
simp only [← mul_sum, sum_add_distrib, mul_one, *]
| Mathlib/Analysis/Convex/Combination.lean | 93 | 100 |
/-
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.Countable
import Mathlib.MeasureTheory.Measure.Decomposition.Exhaustion
import Mathlib.MeasureTheory.Measure.Prod
/-!
# Measure with a given density with respect to another measure
For a measure `μ` on `α` and a function `f : α → ℝ≥0∞`, we define a new measure `μ.withDensity f`.
On a measurable set `s`, that measure has value `∫⁻ a in s, f a ∂μ`.
An important result about `withDensity` is the Radon-Nikodym theorem. It states that, given measures
`μ, ν`, if `HaveLebesgueDecomposition μ ν` then `μ` is absolutely continuous with respect to
`ν` if and only if there exists a measurable function `f : α → ℝ≥0∞` such that
`μ = ν.withDensity f`.
See `MeasureTheory.Measure.absolutelyContinuous_iff_withDensity_rnDeriv_eq`.
-/
open Set hiding restrict restrict_apply
open Filter ENNReal NNReal MeasureTheory.Measure
namespace MeasureTheory
variable {α : Type*} {m0 : MeasurableSpace α} {μ : Measure α}
/-- Given a measure `μ : Measure α` and a function `f : α → ℝ≥0∞`, `μ.withDensity f` is the
measure such that for a measurable set `s` we have `μ.withDensity f s = ∫⁻ a in s, f a ∂μ`. -/
noncomputable
def Measure.withDensity {m : MeasurableSpace α} (μ : Measure α) (f : α → ℝ≥0∞) : Measure α :=
Measure.ofMeasurable (fun s _ => ∫⁻ a in s, f a ∂μ) (by simp) fun _ hs hd =>
lintegral_iUnion hs hd _
@[simp]
theorem withDensity_apply (f : α → ℝ≥0∞) {s : Set α} (hs : MeasurableSet s) :
μ.withDensity f s = ∫⁻ a in s, f a ∂μ :=
Measure.ofMeasurable_apply s hs
theorem withDensity_apply_le (f : α → ℝ≥0∞) (s : Set α) :
∫⁻ a in s, f a ∂μ ≤ μ.withDensity f s := by
let t := toMeasurable (μ.withDensity f) s
calc
∫⁻ a in s, f a ∂μ ≤ ∫⁻ a in t, f a ∂μ :=
lintegral_mono_set (subset_toMeasurable (withDensity μ f) s)
_ = μ.withDensity f t :=
(withDensity_apply f (measurableSet_toMeasurable (withDensity μ f) s)).symm
_ = μ.withDensity f s := measure_toMeasurable s
/-! In the next theorem, the s-finiteness assumption is necessary. Here is a counterexample
without this assumption. Let `α` be an uncountable space, let `x₀` be some fixed point, and consider
the σ-algebra made of those sets which are countable and do not contain `x₀`, and of their
complements. This is the σ-algebra generated by the sets `{x}` for `x ≠ x₀`. Define a measure equal
to `+∞` on nonempty sets. Let `s = {x₀}` and `f` the indicator of `sᶜ`. Then
* `∫⁻ a in s, f a ∂μ = 0`. Indeed, consider a simple function `g ≤ f`. It vanishes on `s`. Then
`∫⁻ a in s, g a ∂μ = 0`. Taking the supremum over `g` gives the claim.
* `μ.withDensity f s = +∞`. Indeed, this is the infimum of `μ.withDensity f t` over measurable sets
`t` containing `s`. As `s` is not measurable, such a set `t` contains a point `x ≠ x₀`. Then
`μ.withDensity f t ≥ μ.withDensity f {x} = ∫⁻ a in {x}, f a ∂μ = μ {x} = +∞`.
One checks that `μ.withDensity f = μ`, while `μ.restrict s` gives zero mass to sets not
containing `x₀`, and infinite mass to those that contain it. -/
| theorem withDensity_apply' [SFinite μ] (f : α → ℝ≥0∞) (s : Set α) :
μ.withDensity f s = ∫⁻ a in s, f a ∂μ := by
apply le_antisymm ?_ (withDensity_apply_le f s)
let t := toMeasurable μ s
calc
μ.withDensity f s ≤ μ.withDensity f t := measure_mono (subset_toMeasurable μ s)
_ = ∫⁻ a in t, f a ∂μ := withDensity_apply f (measurableSet_toMeasurable μ s)
_ = ∫⁻ a in s, f a ∂μ := by congr 1; exact restrict_toMeasurable_of_sFinite s
| Mathlib/MeasureTheory/Measure/WithDensity.lean | 68 | 75 |
/-
Copyright (c) 2018 Chris Hughes. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Chris Hughes, Abhimanyu Pallavi Sudhir
-/
import Mathlib.Algebra.CharP.Defs
import Mathlib.Algebra.Order.CauSeq.BigOperators
import Mathlib.Algebra.Order.Star.Basic
import Mathlib.Data.Complex.BigOperators
import Mathlib.Data.Complex.Norm
import Mathlib.Data.Nat.Choose.Sum
/-!
# Exponential Function
This file contains the definitions of the real and complex exponential function.
## Main definitions
* `Complex.exp`: The complex exponential function, defined via its Taylor series
* `Real.exp`: The real exponential function, defined as the real part of the complex exponential
-/
open CauSeq Finset IsAbsoluteValue
open scoped ComplexConjugate
namespace Complex
theorem isCauSeq_norm_exp (z : ℂ) :
IsCauSeq abs fun n => ∑ m ∈ range n, ‖z ^ m / m.factorial‖ :=
let ⟨n, hn⟩ := exists_nat_gt ‖z‖
have hn0 : (0 : ℝ) < n := lt_of_le_of_lt (norm_nonneg _) hn
IsCauSeq.series_ratio_test n (‖z‖ / n) (div_nonneg (norm_nonneg _) (le_of_lt hn0))
(by rwa [div_lt_iff₀ hn0, one_mul]) fun m hm => by
rw [abs_norm, abs_norm, Nat.factorial_succ, pow_succ', mul_comm m.succ, Nat.cast_mul,
← div_div, mul_div_assoc, mul_div_right_comm, Complex.norm_mul, Complex.norm_div,
norm_natCast]
gcongr
exact le_trans hm (Nat.le_succ _)
@[deprecated (since := "2025-02-16")] alias isCauSeq_abs_exp := isCauSeq_norm_exp
noncomputable section
theorem isCauSeq_exp (z : ℂ) : IsCauSeq (‖·‖) fun n => ∑ m ∈ range n, z ^ m / m.factorial :=
(isCauSeq_norm_exp z).of_abv
/-- The Cauchy sequence consisting of partial sums of the Taylor series of
the complex exponential function -/
@[pp_nodot]
def exp' (z : ℂ) : CauSeq ℂ (‖·‖) :=
⟨fun n => ∑ m ∈ range n, z ^ m / m.factorial, isCauSeq_exp z⟩
/-- The complex exponential function, defined via its Taylor series -/
@[pp_nodot]
def exp (z : ℂ) : ℂ :=
CauSeq.lim (exp' z)
/-- scoped notation for the complex exponential function -/
scoped notation "cexp" => Complex.exp
end
end Complex
namespace Real
open Complex
noncomputable section
/-- The real exponential function, defined as the real part of the complex exponential -/
@[pp_nodot]
nonrec def exp (x : ℝ) : ℝ :=
(exp x).re
/-- scoped notation for the real exponential function -/
scoped notation "rexp" => Real.exp
end
end Real
namespace Complex
variable (x y : ℂ)
@[simp]
theorem exp_zero : exp 0 = 1 := by
rw [exp]
refine lim_eq_of_equiv_const fun ε ε0 => ⟨1, fun j hj => ?_⟩
convert (config := .unfoldSameFun) ε0 -- ε0 : ε > 0 but goal is _ < ε
rcases j with - | j
· exact absurd hj (not_le_of_gt zero_lt_one)
· dsimp [exp']
induction' j with j ih
· dsimp [exp']; simp [show Nat.succ 0 = 1 from rfl]
· rw [← ih (by simp [Nat.succ_le_succ])]
simp only [sum_range_succ, pow_succ]
simp
theorem exp_add : exp (x + y) = exp x * exp y := by
have hj : ∀ j : ℕ, (∑ m ∈ range j, (x + y) ^ m / m.factorial) =
∑ i ∈ range j, ∑ k ∈ range (i + 1), x ^ k / k.factorial *
(y ^ (i - k) / (i - k).factorial) := by
intro j
refine Finset.sum_congr rfl fun m _ => ?_
rw [add_pow, div_eq_mul_inv, sum_mul]
refine Finset.sum_congr rfl fun I hi => ?_
have h₁ : (m.choose I : ℂ) ≠ 0 :=
Nat.cast_ne_zero.2 (pos_iff_ne_zero.1 (Nat.choose_pos (Nat.le_of_lt_succ (mem_range.1 hi))))
have h₂ := Nat.choose_mul_factorial_mul_factorial (Nat.le_of_lt_succ <| Finset.mem_range.1 hi)
rw [← h₂, Nat.cast_mul, Nat.cast_mul, mul_inv, mul_inv]
simp only [mul_left_comm (m.choose I : ℂ), mul_assoc, mul_left_comm (m.choose I : ℂ)⁻¹,
mul_comm (m.choose I : ℂ)]
rw [inv_mul_cancel₀ h₁]
simp [div_eq_mul_inv, mul_comm, mul_assoc, mul_left_comm]
simp_rw [exp, exp', lim_mul_lim]
apply (lim_eq_lim_of_equiv _).symm
simp only [hj]
exact cauchy_product (isCauSeq_norm_exp x) (isCauSeq_exp y)
/-- the exponential function as a monoid hom from `Multiplicative ℂ` to `ℂ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℂ) ℂ :=
{ toFun := fun z => exp z.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℂ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℂ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℂ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℂ) ℂ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℂ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℂ) expMonoidHom f s
lemma exp_nsmul (x : ℂ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℂ) ℂ _ _ expMonoidHom _ _
theorem exp_nat_mul (x : ℂ) : ∀ n : ℕ, exp (n * x) = exp x ^ n
| 0 => by rw [Nat.cast_zero, zero_mul, exp_zero, pow_zero]
| Nat.succ n => by rw [pow_succ, Nat.cast_add_one, add_mul, exp_add, ← exp_nat_mul _ n, one_mul]
@[simp]
theorem exp_ne_zero : exp x ≠ 0 := fun h =>
zero_ne_one (α := ℂ) <| by rw [← exp_zero, ← add_neg_cancel x, exp_add, h]; simp
theorem exp_neg : exp (-x) = (exp x)⁻¹ := by
rw [← mul_right_inj' (exp_ne_zero x), ← exp_add]; simp [mul_inv_cancel₀ (exp_ne_zero x)]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
theorem exp_int_mul (z : ℂ) (n : ℤ) : Complex.exp (n * z) = Complex.exp z ^ n := by
cases n
· simp [exp_nat_mul]
· simp [exp_add, add_mul, pow_add, exp_neg, exp_nat_mul]
@[simp]
theorem exp_conj : exp (conj x) = conj (exp x) := by
dsimp [exp]
rw [← lim_conj]
refine congr_arg CauSeq.lim (CauSeq.ext fun _ => ?_)
dsimp [exp', Function.comp_def, cauSeqConj]
rw [map_sum (starRingEnd _)]
refine sum_congr rfl fun n _ => ?_
rw [map_div₀, map_pow, ← ofReal_natCast, conj_ofReal]
@[simp]
theorem ofReal_exp_ofReal_re (x : ℝ) : ((exp x).re : ℂ) = exp x :=
conj_eq_iff_re.1 <| by rw [← exp_conj, conj_ofReal]
@[simp, norm_cast]
theorem ofReal_exp (x : ℝ) : (Real.exp x : ℂ) = exp x :=
ofReal_exp_ofReal_re _
@[simp]
theorem exp_ofReal_im (x : ℝ) : (exp x).im = 0 := by rw [← ofReal_exp_ofReal_re, ofReal_im]
theorem exp_ofReal_re (x : ℝ) : (exp x).re = Real.exp x :=
rfl
end Complex
namespace Real
open Complex
variable (x y : ℝ)
@[simp]
theorem exp_zero : exp 0 = 1 := by simp [Real.exp]
nonrec theorem exp_add : exp (x + y) = exp x * exp y := by simp [exp_add, exp]
/-- the exponential function as a monoid hom from `Multiplicative ℝ` to `ℝ` -/
@[simps]
noncomputable def expMonoidHom : MonoidHom (Multiplicative ℝ) ℝ :=
{ toFun := fun x => exp x.toAdd,
map_one' := by simp,
map_mul' := by simp [exp_add] }
theorem exp_list_sum (l : List ℝ) : exp l.sum = (l.map exp).prod :=
map_list_prod (M := Multiplicative ℝ) expMonoidHom l
theorem exp_multiset_sum (s : Multiset ℝ) : exp s.sum = (s.map exp).prod :=
@MonoidHom.map_multiset_prod (Multiplicative ℝ) ℝ _ _ expMonoidHom s
theorem exp_sum {α : Type*} (s : Finset α) (f : α → ℝ) :
exp (∑ x ∈ s, f x) = ∏ x ∈ s, exp (f x) :=
map_prod (β := Multiplicative ℝ) expMonoidHom f s
lemma exp_nsmul (x : ℝ) (n : ℕ) : exp (n • x) = exp x ^ n :=
@MonoidHom.map_pow (Multiplicative ℝ) ℝ _ _ expMonoidHom _ _
nonrec theorem exp_nat_mul (x : ℝ) (n : ℕ) : exp (n * x) = exp x ^ n :=
ofReal_injective (by simp [exp_nat_mul])
@[simp]
nonrec theorem exp_ne_zero : exp x ≠ 0 := fun h =>
exp_ne_zero x <| by rw [exp, ← ofReal_inj] at h; simp_all
nonrec theorem exp_neg : exp (-x) = (exp x)⁻¹ :=
ofReal_injective <| by simp [exp_neg]
theorem exp_sub : exp (x - y) = exp x / exp y := by
simp [sub_eq_add_neg, exp_add, exp_neg, div_eq_mul_inv]
open IsAbsoluteValue Nat
theorem sum_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) (n : ℕ) : ∑ i ∈ range n, x ^ i / i ! ≤ exp x :=
calc
∑ i ∈ range n, x ^ i / i ! ≤ lim (⟨_, isCauSeq_re (exp' x)⟩ : CauSeq ℝ abs) := by
refine le_lim (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp only [exp', const_apply, re_sum]
norm_cast
refine sum_le_sum_of_subset_of_nonneg (range_mono hj) fun _ _ _ ↦ ?_
positivity
_ = exp x := by rw [exp, Complex.exp, ← cauSeqRe, lim_re]
lemma pow_div_factorial_le_exp (hx : 0 ≤ x) (n : ℕ) : x ^ n / n ! ≤ exp x :=
calc
x ^ n / n ! ≤ ∑ k ∈ range (n + 1), x ^ k / k ! :=
single_le_sum (f := fun k ↦ x ^ k / k !) (fun k _ ↦ by positivity) (self_mem_range_succ n)
_ ≤ exp x := sum_le_exp_of_nonneg hx _
theorem quadratic_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : 1 + x + x ^ 2 / 2 ≤ exp x :=
calc
1 + x + x ^ 2 / 2 = ∑ i ∈ range 3, x ^ i / i ! := by
simp only [sum_range_succ, range_one, sum_singleton, _root_.pow_zero, factorial, cast_one,
ne_eq, one_ne_zero, not_false_eq_true, div_self, pow_one, mul_one, div_one, Nat.mul_one,
cast_succ, add_right_inj]
ring_nf
_ ≤ exp x := sum_le_exp_of_nonneg hx 3
private theorem add_one_lt_exp_of_pos {x : ℝ} (hx : 0 < x) : x + 1 < exp x :=
(by nlinarith : x + 1 < 1 + x + x ^ 2 / 2).trans_le (quadratic_le_exp_of_nonneg hx.le)
private theorem add_one_le_exp_of_nonneg {x : ℝ} (hx : 0 ≤ x) : x + 1 ≤ exp x := by
rcases eq_or_lt_of_le hx with (rfl | h)
· simp
exact (add_one_lt_exp_of_pos h).le
theorem one_le_exp {x : ℝ} (hx : 0 ≤ x) : 1 ≤ exp x := by linarith [add_one_le_exp_of_nonneg hx]
@[bound]
theorem exp_pos (x : ℝ) : 0 < exp x :=
(le_total 0 x).elim (lt_of_lt_of_le zero_lt_one ∘ one_le_exp) fun h => by
rw [← neg_neg x, Real.exp_neg]
exact inv_pos.2 (lt_of_lt_of_le zero_lt_one (one_le_exp (neg_nonneg.2 h)))
@[bound]
lemma exp_nonneg (x : ℝ) : 0 ≤ exp x := x.exp_pos.le
@[simp]
theorem abs_exp (x : ℝ) : |exp x| = exp x :=
abs_of_pos (exp_pos _)
lemma exp_abs_le (x : ℝ) : exp |x| ≤ exp x + exp (-x) := by
cases le_total x 0 <;> simp [abs_of_nonpos, abs_of_nonneg, exp_nonneg, *]
@[mono]
theorem exp_strictMono : StrictMono exp := fun x y h => by
rw [← sub_add_cancel y x, Real.exp_add]
exact (lt_mul_iff_one_lt_left (exp_pos _)).2
(lt_of_lt_of_le (by linarith) (add_one_le_exp_of_nonneg (by linarith)))
@[gcongr]
theorem exp_lt_exp_of_lt {x y : ℝ} (h : x < y) : exp x < exp y := exp_strictMono h
@[mono]
theorem exp_monotone : Monotone exp :=
exp_strictMono.monotone
@[gcongr, bound]
theorem exp_le_exp_of_le {x y : ℝ} (h : x ≤ y) : exp x ≤ exp y := exp_monotone h
@[simp]
theorem exp_lt_exp {x y : ℝ} : exp x < exp y ↔ x < y :=
exp_strictMono.lt_iff_lt
@[simp]
theorem exp_le_exp {x y : ℝ} : exp x ≤ exp y ↔ x ≤ y :=
exp_strictMono.le_iff_le
theorem exp_injective : Function.Injective exp :=
exp_strictMono.injective
@[simp]
theorem exp_eq_exp {x y : ℝ} : exp x = exp y ↔ x = y :=
exp_injective.eq_iff
@[simp]
theorem exp_eq_one_iff : exp x = 1 ↔ x = 0 :=
exp_injective.eq_iff' exp_zero
@[simp]
theorem one_lt_exp_iff {x : ℝ} : 1 < exp x ↔ 0 < x := by rw [← exp_zero, exp_lt_exp]
@[bound] private alias ⟨_, Bound.one_lt_exp_of_pos⟩ := one_lt_exp_iff
@[simp]
theorem exp_lt_one_iff {x : ℝ} : exp x < 1 ↔ x < 0 := by rw [← exp_zero, exp_lt_exp]
@[simp]
theorem exp_le_one_iff {x : ℝ} : exp x ≤ 1 ↔ x ≤ 0 :=
exp_zero ▸ exp_le_exp
@[simp]
theorem one_le_exp_iff {x : ℝ} : 1 ≤ exp x ↔ 0 ≤ x :=
exp_zero ▸ exp_le_exp
end Real
namespace Complex
theorem sum_div_factorial_le {α : Type*} [Field α] [LinearOrder α] [IsStrictOrderedRing α]
(n j : ℕ) (hn : 0 < n) :
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) ≤ n.succ / (n.factorial * n) :=
calc
(∑ m ∈ range j with n ≤ m, (1 / m.factorial : α)) =
∑ m ∈ range (j - n), (1 / ((m + n).factorial : α)) := by
refine sum_nbij' (· - n) (· + n) ?_ ?_ ?_ ?_ ?_ <;>
simp +contextual [lt_tsub_iff_right, tsub_add_cancel_of_le]
_ ≤ ∑ m ∈ range (j - n), ((n.factorial : α) * (n.succ : α) ^ m)⁻¹ := by
simp_rw [one_div]
gcongr
rw [← Nat.cast_pow, ← Nat.cast_mul, Nat.cast_le, add_comm]
exact Nat.factorial_mul_pow_le_factorial
_ = (n.factorial : α)⁻¹ * ∑ m ∈ range (j - n), (n.succ : α)⁻¹ ^ m := by
simp [mul_inv, ← mul_sum, ← sum_mul, mul_comm, inv_pow]
_ = ((n.succ : α) - n.succ * (n.succ : α)⁻¹ ^ (j - n)) / (n.factorial * n) := by
have h₁ : (n.succ : α) ≠ 1 :=
@Nat.cast_one α _ ▸ mt Nat.cast_inj.1 (mt Nat.succ.inj (pos_iff_ne_zero.1 hn))
have h₂ : (n.succ : α) ≠ 0 := by positivity
have h₃ : (n.factorial * n : α) ≠ 0 := by positivity
have h₄ : (n.succ - 1 : α) = n := by simp
rw [geom_sum_inv h₁ h₂, eq_div_iff_mul_eq h₃, mul_comm _ (n.factorial * n : α),
← mul_assoc (n.factorial⁻¹ : α), ← mul_inv_rev, h₄, ← mul_assoc (n.factorial * n : α),
mul_comm (n : α) n.factorial, mul_inv_cancel₀ h₃, one_mul, mul_comm]
_ ≤ n.succ / (n.factorial * n : α) := by gcongr; apply sub_le_self; positivity
theorem exp_bound {x : ℂ} (hx : ‖x‖ ≤ 1) {n : ℕ} (hn : 0 < n) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹) := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _), exp, sub_eq_add_neg,
← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show
‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n * ((n.succ : ℝ) * (n.factorial * n : ℝ)⁻¹)
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (1 / m.factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr
rw [Complex.norm_pow]
exact pow_le_one₀ (norm_nonneg _) hx
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (1 / m.factorial : ℝ) := by
simp [abs_mul, abv_pow abs, abs_div, ← mul_sum]
_ ≤ ‖x‖ ^ n * (n.succ * (n.factorial * n : ℝ)⁻¹) := by
gcongr
exact sum_div_factorial_le _ _ hn
theorem exp_bound' {x : ℂ} {n : ℕ} (hx : ‖x‖ / n.succ ≤ 1 / 2) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n / n.factorial * 2 := by
rw [← lim_const (abv := norm) (∑ m ∈ range n, _),
exp, sub_eq_add_neg, ← lim_neg, lim_add, ← lim_norm]
refine lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤
‖x‖ ^ n / n.factorial * 2
let k := j - n
have hj : j = n + k := (add_tsub_cancel_of_le hj).symm
rw [hj, sum_range_add_sub_sum_range]
calc
‖∑ i ∈ range k, x ^ (n + i) / ((n + i).factorial : ℂ)‖ ≤
∑ i ∈ range k, ‖x ^ (n + i) / ((n + i).factorial : ℂ)‖ :=
IsAbsoluteValue.abv_sum _ _ _
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / (n + i).factorial := by
simp [norm_natCast, Complex.norm_pow]
_ ≤ ∑ i ∈ range k, ‖x‖ ^ (n + i) / ((n.factorial : ℝ) * (n.succ : ℝ) ^ i) := ?_
_ = ∑ i ∈ range k, ‖x‖ ^ n / n.factorial * (‖x‖ ^ i / (n.succ : ℝ) ^ i) := ?_
_ ≤ ‖x‖ ^ n / ↑n.factorial * 2 := ?_
· gcongr
exact mod_cast Nat.factorial_mul_pow_le_factorial
· refine Finset.sum_congr rfl fun _ _ => ?_
simp only [pow_add, div_eq_inv_mul, mul_inv, mul_left_comm, mul_assoc]
· rw [← mul_sum]
gcongr
simp_rw [← div_pow]
rw [geom_sum_eq, div_le_iff_of_neg]
· trans (-1 : ℝ)
· linarith
· simp only [neg_le_sub_iff_le_add, div_pow, Nat.cast_succ, le_add_iff_nonneg_left]
positivity
· linarith
· linarith
theorem norm_exp_sub_one_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1‖ ≤ 2 * ‖x‖ :=
calc
‖exp x - 1‖ = ‖exp x - ∑ m ∈ range 1, x ^ m / m.factorial‖ := by simp [sum_range_succ]
_ ≤ ‖x‖ ^ 1 * ((Nat.succ 1 : ℝ) * ((Nat.factorial 1) * (1 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ = 2 * ‖x‖ := by simp [two_mul, mul_two, mul_add, mul_comm, add_mul, Nat.factorial]
theorem norm_exp_sub_one_sub_id_le {x : ℂ} (hx : ‖x‖ ≤ 1) : ‖exp x - 1 - x‖ ≤ ‖x‖ ^ 2 :=
calc
‖exp x - 1 - x‖ = ‖exp x - ∑ m ∈ range 2, x ^ m / m.factorial‖ := by
simp [sub_eq_add_neg, sum_range_succ_comm, add_assoc, Nat.factorial]
_ ≤ ‖x‖ ^ 2 * ((Nat.succ 2 : ℝ) * (Nat.factorial 2 * (2 : ℕ) : ℝ)⁻¹) :=
(exp_bound hx (by decide))
_ ≤ ‖x‖ ^ 2 * 1 := by gcongr; norm_num [Nat.factorial]
_ = ‖x‖ ^ 2 := by rw [mul_one]
lemma norm_exp_sub_sum_le_exp_norm_sub_sum (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖
≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
calc ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖
_ ≤ (∑ m ∈ range j, ‖x‖ ^ m / m.factorial) - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
rw [sum_range_sub_sum_range hj, sum_range_sub_sum_range hj]
refine (IsAbsoluteValue.abv_sum norm ..).trans_eq ?_
congr with i
simp [Complex.norm_pow]
_ ≤ Real.exp ‖x‖ - ∑ m ∈ range n, ‖x‖ ^ m / m.factorial := by
gcongr
exact Real.sum_le_exp_of_nonneg (norm_nonneg _) _
lemma norm_exp_le_exp_norm (x : ℂ) : ‖exp x‖ ≤ Real.exp ‖x‖ := by
convert norm_exp_sub_sum_le_exp_norm_sub_sum x 0 using 1 <;> simp
lemma norm_exp_sub_sum_le_norm_mul_exp (x : ℂ) (n : ℕ) :
‖exp x - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
rw [← CauSeq.lim_const (abv := norm) (∑ m ∈ range n, _), Complex.exp, sub_eq_add_neg,
← CauSeq.lim_neg, CauSeq.lim_add, ← lim_norm]
refine CauSeq.lim_le (CauSeq.le_of_exists ⟨n, fun j hj => ?_⟩)
simp_rw [← sub_eq_add_neg]
show ‖(∑ m ∈ range j, x ^ m / m.factorial) - ∑ m ∈ range n, x ^ m / m.factorial‖ ≤ _
rw [sum_range_sub_sum_range hj]
calc
‖∑ m ∈ range j with n ≤ m, (x ^ m / m.factorial : ℂ)‖
= ‖∑ m ∈ range j with n ≤ m, (x ^ n * (x ^ (m - n) / m.factorial) : ℂ)‖ := by
refine congr_arg norm (sum_congr rfl fun m hm => ?_)
rw [mem_filter, mem_range] at hm
rw [← mul_div_assoc, ← pow_add, add_tsub_cancel_of_le hm.2]
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x ^ n * (x ^ (m - n) / m.factorial)‖ :=
IsAbsoluteValue.abv_sum norm ..
_ ≤ ∑ m ∈ range j with n ≤ m, ‖x‖ ^ n * (‖x‖ ^ (m - n) / (m - n).factorial) := by
simp_rw [Complex.norm_mul, Complex.norm_pow, Complex.norm_div, norm_natCast]
gcongr with i hi
· rw [Complex.norm_pow]
· simp
_ = ‖x‖ ^ n * ∑ m ∈ range j with n ≤ m, (‖x‖ ^ (m - n) / (m - n).factorial) := by
rw [← mul_sum]
_ = ‖x‖ ^ n * ∑ m ∈ range (j - n), (‖x‖ ^ m / m.factorial) := by
congr 1
refine (sum_bij (fun m hm ↦ m + n) ?_ ?_ ?_ ?_).symm
· intro a ha
simp only [mem_filter, mem_range, le_add_iff_nonneg_left, zero_le, and_true]
simp only [mem_range] at ha
rwa [← lt_tsub_iff_right]
· intro a ha b hb hab
simpa using hab
· intro b hb
simp only [mem_range, exists_prop]
simp only [mem_filter, mem_range] at hb
refine ⟨b - n, ?_, ?_⟩
· rw [tsub_lt_tsub_iff_right hb.2]
exact hb.1
· rw [tsub_add_cancel_of_le hb.2]
· simp
_ ≤ ‖x‖ ^ n * Real.exp ‖x‖ := by
gcongr
refine Real.sum_le_exp_of_nonneg ?_ _
exact norm_nonneg _
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_le := norm_exp_sub_one_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_one_sub_id_le := norm_exp_sub_one_sub_id_le
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_exp_abs_sub_sum :=
norm_exp_sub_sum_le_exp_norm_sub_sum
@[deprecated (since := "2025-02-16")] alias abs_exp_le_exp_abs := norm_exp_le_exp_norm
@[deprecated (since := "2025-02-16")] alias abs_exp_sub_sum_le_abs_mul_exp :=
norm_exp_sub_sum_le_norm_mul_exp
end Complex
namespace Real
open Complex Finset
nonrec theorem exp_bound {x : ℝ} (hx : |x| ≤ 1) {n : ℕ} (hn : 0 < n) :
|exp x - ∑ m ∈ range n, x ^ m / m.factorial| ≤ |x| ^ n * (n.succ / (n.factorial * n)) := by
have hxc : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
convert exp_bound hxc hn using 2 <;>
norm_cast
theorem exp_bound' {x : ℝ} (h1 : 0 ≤ x) (h2 : x ≤ 1) {n : ℕ} (hn : 0 < n) :
Real.exp x ≤ (∑ m ∈ Finset.range n, x ^ m / m.factorial) +
x ^ n * (n + 1) / (n.factorial * n) := by
have h3 : |x| = x := by simpa
have h4 : |x| ≤ 1 := by rwa [h3]
have h' := Real.exp_bound h4 hn
rw [h3] at h'
have h'' := (abs_sub_le_iff.1 h').1
have t := sub_le_iff_le_add'.1 h''
simpa [mul_div_assoc] using t
theorem abs_exp_sub_one_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1| ≤ 2 * |x| := by
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_le (x := x) this
theorem abs_exp_sub_one_sub_id_le {x : ℝ} (hx : |x| ≤ 1) : |exp x - 1 - x| ≤ x ^ 2 := by
rw [← sq_abs]
have : ‖(x : ℂ)‖ ≤ 1 := mod_cast hx
exact_mod_cast Complex.norm_exp_sub_one_sub_id_le this
/-- A finite initial segment of the exponential series, followed by an arbitrary tail.
For fixed `n` this is just a linear map wrt `r`, and each map is a simple linear function
of the previous (see `expNear_succ`), with `expNear n x r ⟶ exp x` as `n ⟶ ∞`,
for any `r`. -/
noncomputable def expNear (n : ℕ) (x r : ℝ) : ℝ :=
(∑ m ∈ range n, x ^ m / m.factorial) + x ^ n / n.factorial * r
@[simp]
theorem expNear_zero (x r) : expNear 0 x r = r := by simp [expNear]
@[simp]
theorem expNear_succ (n x r) : expNear (n + 1) x r = expNear n x (1 + x / (n + 1) * r) := by
simp [expNear, range_succ, mul_add, add_left_comm, add_assoc, pow_succ, div_eq_mul_inv,
mul_inv, Nat.factorial]
ac_rfl
theorem expNear_sub (n x r₁ r₂) : expNear n x r₁ -
expNear n x r₂ = x ^ n / n.factorial * (r₁ - r₂) := by
simp [expNear, mul_sub]
theorem exp_approx_end (n m : ℕ) (x : ℝ) (e₁ : n + 1 = m) (h : |x| ≤ 1) :
|exp x - expNear m x 0| ≤ |x| ^ m / m.factorial * ((m + 1) / m) := by
simp only [expNear, mul_zero, add_zero]
convert exp_bound (n := m) h ?_ using 1
· field_simp [mul_comm]
· omega
theorem exp_approx_succ {n} {x a₁ b₁ : ℝ} (m : ℕ) (e₁ : n + 1 = m) (a₂ b₂ : ℝ)
(e : |1 + x / m * a₂ - a₁| ≤ b₁ - |x| / m * b₂)
(h : |exp x - expNear m x a₂| ≤ |x| ^ m / m.factorial * b₂) :
|exp x - expNear n x a₁| ≤ |x| ^ n / n.factorial * b₁ := by
refine (abs_sub_le _ _ _).trans ((add_le_add_right h _).trans ?_)
subst e₁; rw [expNear_succ, expNear_sub, abs_mul]
convert mul_le_mul_of_nonneg_left (a := |x| ^ n / ↑(Nat.factorial n))
(le_sub_iff_add_le'.1 e) ?_ using 1
· simp [mul_add, pow_succ', div_eq_mul_inv, abs_mul, abs_inv, ← pow_abs, mul_inv, Nat.factorial]
ac_rfl
· simp [div_nonneg, abs_nonneg]
theorem exp_approx_end' {n} {x a b : ℝ} (m : ℕ) (e₁ : n + 1 = m) (rm : ℝ) (er : ↑m = rm)
(h : |x| ≤ 1) (e : |1 - a| ≤ b - |x| / rm * ((rm + 1) / rm)) :
|exp x - expNear n x a| ≤ |x| ^ n / n.factorial * b := by
subst er
exact exp_approx_succ _ e₁ _ _ (by simpa using e) (exp_approx_end _ _ _ e₁ h)
theorem exp_1_approx_succ_eq {n} {a₁ b₁ : ℝ} {m : ℕ} (en : n + 1 = m) {rm : ℝ} (er : ↑m = rm)
(h : |exp 1 - expNear m 1 ((a₁ - 1) * rm)| ≤ |1| ^ m / m.factorial * (b₁ * rm)) :
|exp 1 - expNear n 1 a₁| ≤ |1| ^ n / n.factorial * b₁ := by
subst er
refine exp_approx_succ _ en _ _ ?_ h
field_simp [show (m : ℝ) ≠ 0 by norm_cast; omega]
theorem exp_approx_start (x a b : ℝ) (h : |exp x - expNear 0 x a| ≤ |x| ^ 0 / Nat.factorial 0 * b) :
|exp x - a| ≤ b := by simpa using h
theorem exp_bound_div_one_sub_of_interval' {x : ℝ} (h1 : 0 < x) (h2 : x < 1) :
Real.exp x < 1 / (1 - x) := by
have H : 0 < 1 - (1 + x + x ^ 2) * (1 - x) := calc
0 < x ^ 3 := by positivity
_ = 1 - (1 + x + x ^ 2) * (1 - x) := by ring
calc
exp x ≤ _ := exp_bound' h1.le h2.le zero_lt_three
_ ≤ 1 + x + x ^ 2 := by
-- Porting note: was `norm_num [Finset.sum] <;> nlinarith`
-- This proof should be restored after the norm_num plugin for big operators is ported.
-- (It may also need the positivity extensions in https://github.com/leanprover-community/mathlib4/pull/3907.)
rw [show 3 = 1 + 1 + 1 from rfl]
repeat rw [Finset.sum_range_succ]
norm_num [Nat.factorial]
nlinarith
_ < 1 / (1 - x) := by rw [lt_div_iff₀] <;> nlinarith
theorem exp_bound_div_one_sub_of_interval {x : ℝ} (h1 : 0 ≤ x) (h2 : x < 1) :
Real.exp x ≤ 1 / (1 - x) := by
rcases eq_or_lt_of_le h1 with (rfl | h1)
· simp
· exact (exp_bound_div_one_sub_of_interval' h1 h2).le
theorem add_one_lt_exp {x : ℝ} (hx : x ≠ 0) : x + 1 < Real.exp x := by
obtain hx | hx := hx.symm.lt_or_lt
· exact add_one_lt_exp_of_pos hx
obtain h' | h' := le_or_lt 1 (-x)
· linarith [x.exp_pos]
have hx' : 0 < x + 1 := by linarith
simpa [add_comm, exp_neg, inv_lt_inv₀ (exp_pos _) hx']
using exp_bound_div_one_sub_of_interval' (neg_pos.2 hx) h'
theorem add_one_le_exp (x : ℝ) : x + 1 ≤ Real.exp x := by
obtain rfl | hx := eq_or_ne x 0
· simp
· exact (add_one_lt_exp hx).le
lemma one_sub_lt_exp_neg {x : ℝ} (hx : x ≠ 0) : 1 - x < exp (-x) :=
(sub_eq_neg_add _ _).trans_lt <| add_one_lt_exp <| neg_ne_zero.2 hx
lemma one_sub_le_exp_neg (x : ℝ) : 1 - x ≤ exp (-x) :=
(sub_eq_neg_add _ _).trans_le <| add_one_le_exp _
theorem one_sub_div_pow_le_exp_neg {n : ℕ} {t : ℝ} (ht' : t ≤ n) : (1 - t / n) ^ n ≤ exp (-t) := by
rcases eq_or_ne n 0 with (rfl | hn)
· simp
rwa [Nat.cast_zero] at ht'
calc
(1 - t / n) ^ n ≤ rexp (-(t / n)) ^ n := by
gcongr
· exact sub_nonneg.2 <| div_le_one_of_le₀ ht' n.cast_nonneg
· exact one_sub_le_exp_neg _
_ = rexp (-t) := by rw [← Real.exp_nat_mul, mul_neg, mul_comm, div_mul_cancel₀]; positivity
lemma le_inv_mul_exp (x : ℝ) {c : ℝ} (hc : 0 < c) : x ≤ c⁻¹ * exp (c * x) := by
rw [le_inv_mul_iff₀ hc]
calc c * x
_ ≤ c * x + 1 := le_add_of_nonneg_right zero_le_one
_ ≤ _ := Real.add_one_le_exp (c * x)
end Real
namespace Mathlib.Meta.Positivity
open Lean.Meta Qq
/-- Extension for the `positivity` tactic: `Real.exp` is always positive. -/
@[positivity Real.exp _]
def evalExp : PositivityExt where eval {u α} _ _ e := do
match u, α, e with
| 0, ~q(ℝ), ~q(Real.exp $a) =>
assertInstancesCommute
pure (.positive q(Real.exp_pos $a))
| _, _, _ => throwError "not Real.exp"
end Mathlib.Meta.Positivity
namespace Complex
@[simp]
theorem norm_exp_ofReal (x : ℝ) : ‖exp x‖ = Real.exp x := by
rw [← ofReal_exp]
exact Complex.norm_of_nonneg (le_of_lt (Real.exp_pos _))
@[deprecated (since := "2025-02-16")] alias abs_exp_ofReal := norm_exp_ofReal
end Complex
| Mathlib/Data/Complex/Exponential.lean | 1,573 | 1,584 | |
/-
Copyright (c) 2022 Joseph Myers. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Joseph Myers
-/
import Mathlib.Analysis.Convex.Between
import Mathlib.Analysis.Normed.Group.AddTorsor
import Mathlib.Analysis.Normed.Module.Convex
/-!
# Sides of affine subspaces
This file defines notions of two points being on the same or opposite sides of an affine subspace.
## Main definitions
* `s.WSameSide x y`: The points `x` and `y` are weakly on the same side of the affine
subspace `s`.
* `s.SSameSide x y`: The points `x` and `y` are strictly on the same side of the affine
subspace `s`.
* `s.WOppSide x y`: The points `x` and `y` are weakly on opposite sides of the affine
subspace `s`.
* `s.SOppSide x y`: The points `x` and `y` are strictly on opposite sides of the affine
subspace `s`.
-/
variable {R V V' P P' : Type*}
open AffineEquiv AffineMap
namespace AffineSubspace
section StrictOrderedCommRing
variable [CommRing R] [PartialOrder R] [IsStrictOrderedRing R]
[AddCommGroup V] [Module R V] [AddTorsor V P]
variable [AddCommGroup V'] [Module R V'] [AddTorsor V' P']
/-- The points `x` and `y` are weakly on the same side of `s`. -/
def WSameSide (s : AffineSubspace R P) (x y : P) : Prop :=
∃ᵉ (p₁ ∈ s) (p₂ ∈ s), SameRay R (x -ᵥ p₁) (y -ᵥ p₂)
/-- The points `x` and `y` are strictly on the same side of `s`. -/
def SSameSide (s : AffineSubspace R P) (x y : P) : Prop :=
s.WSameSide x y ∧ x ∉ s ∧ y ∉ s
/-- The points `x` and `y` are weakly on opposite sides of `s`. -/
def WOppSide (s : AffineSubspace R P) (x y : P) : Prop :=
∃ᵉ (p₁ ∈ s) (p₂ ∈ s), SameRay R (x -ᵥ p₁) (p₂ -ᵥ y)
/-- The points `x` and `y` are strictly on opposite sides of `s`. -/
def SOppSide (s : AffineSubspace R P) (x y : P) : Prop :=
s.WOppSide x y ∧ x ∉ s ∧ y ∉ s
theorem WSameSide.map {s : AffineSubspace R P} {x y : P} (h : s.WSameSide x y) (f : P →ᵃ[R] P') :
(s.map f).WSameSide (f x) (f y) := by
rcases h with ⟨p₁, hp₁, p₂, hp₂, h⟩
refine ⟨f p₁, mem_map_of_mem f hp₁, f p₂, mem_map_of_mem f hp₂, ?_⟩
simp_rw [← linearMap_vsub]
exact h.map f.linear
theorem _root_.Function.Injective.wSameSide_map_iff {s : AffineSubspace R P} {x y : P}
{f : P →ᵃ[R] P'} (hf : Function.Injective f) :
(s.map f).WSameSide (f x) (f y) ↔ s.WSameSide x y := by
refine ⟨fun h => ?_, fun h => h.map _⟩
rcases h with ⟨fp₁, hfp₁, fp₂, hfp₂, h⟩
rw [mem_map] at hfp₁ hfp₂
rcases hfp₁ with ⟨p₁, hp₁, rfl⟩
rcases hfp₂ with ⟨p₂, hp₂, rfl⟩
refine ⟨p₁, hp₁, p₂, hp₂, ?_⟩
simp_rw [← linearMap_vsub, (f.linear_injective_iff.2 hf).sameRay_map_iff] at h
exact h
theorem _root_.Function.Injective.sSameSide_map_iff {s : AffineSubspace R P} {x y : P}
{f : P →ᵃ[R] P'} (hf : Function.Injective f) :
(s.map f).SSameSide (f x) (f y) ↔ s.SSameSide x y := by
simp_rw [SSameSide, hf.wSameSide_map_iff, mem_map_iff_mem_of_injective hf]
@[simp]
theorem _root_.AffineEquiv.wSameSide_map_iff {s : AffineSubspace R P} {x y : P} (f : P ≃ᵃ[R] P') :
(s.map ↑f).WSameSide (f x) (f y) ↔ s.WSameSide x y :=
(show Function.Injective f.toAffineMap from f.injective).wSameSide_map_iff
@[simp]
theorem _root_.AffineEquiv.sSameSide_map_iff {s : AffineSubspace R P} {x y : P} (f : P ≃ᵃ[R] P') :
(s.map ↑f).SSameSide (f x) (f y) ↔ s.SSameSide x y :=
(show Function.Injective f.toAffineMap from f.injective).sSameSide_map_iff
theorem WOppSide.map {s : AffineSubspace R P} {x y : P} (h : s.WOppSide x y) (f : P →ᵃ[R] P') :
(s.map f).WOppSide (f x) (f y) := by
rcases h with ⟨p₁, hp₁, p₂, hp₂, h⟩
refine ⟨f p₁, mem_map_of_mem f hp₁, f p₂, mem_map_of_mem f hp₂, ?_⟩
simp_rw [← linearMap_vsub]
exact h.map f.linear
theorem _root_.Function.Injective.wOppSide_map_iff {s : AffineSubspace R P} {x y : P}
{f : P →ᵃ[R] P'} (hf : Function.Injective f) :
(s.map f).WOppSide (f x) (f y) ↔ s.WOppSide x y := by
refine ⟨fun h => ?_, fun h => h.map _⟩
rcases h with ⟨fp₁, hfp₁, fp₂, hfp₂, h⟩
rw [mem_map] at hfp₁ hfp₂
rcases hfp₁ with ⟨p₁, hp₁, rfl⟩
rcases hfp₂ with ⟨p₂, hp₂, rfl⟩
refine ⟨p₁, hp₁, p₂, hp₂, ?_⟩
simp_rw [← linearMap_vsub, (f.linear_injective_iff.2 hf).sameRay_map_iff] at h
exact h
theorem _root_.Function.Injective.sOppSide_map_iff {s : AffineSubspace R P} {x y : P}
{f : P →ᵃ[R] P'} (hf : Function.Injective f) :
(s.map f).SOppSide (f x) (f y) ↔ s.SOppSide x y := by
simp_rw [SOppSide, hf.wOppSide_map_iff, mem_map_iff_mem_of_injective hf]
@[simp]
theorem _root_.AffineEquiv.wOppSide_map_iff {s : AffineSubspace R P} {x y : P} (f : P ≃ᵃ[R] P') :
(s.map ↑f).WOppSide (f x) (f y) ↔ s.WOppSide x y :=
(show Function.Injective f.toAffineMap from f.injective).wOppSide_map_iff
@[simp]
theorem _root_.AffineEquiv.sOppSide_map_iff {s : AffineSubspace R P} {x y : P} (f : P ≃ᵃ[R] P') :
(s.map ↑f).SOppSide (f x) (f y) ↔ s.SOppSide x y :=
(show Function.Injective f.toAffineMap from f.injective).sOppSide_map_iff
theorem WSameSide.nonempty {s : AffineSubspace R P} {x y : P} (h : s.WSameSide x y) :
(s : Set P).Nonempty :=
⟨h.choose, h.choose_spec.left⟩
theorem SSameSide.nonempty {s : AffineSubspace R P} {x y : P} (h : s.SSameSide x y) :
(s : Set P).Nonempty :=
⟨h.1.choose, h.1.choose_spec.left⟩
theorem WOppSide.nonempty {s : AffineSubspace R P} {x y : P} (h : s.WOppSide x y) :
(s : Set P).Nonempty :=
⟨h.choose, h.choose_spec.left⟩
theorem SOppSide.nonempty {s : AffineSubspace R P} {x y : P} (h : s.SOppSide x y) :
(s : Set P).Nonempty :=
⟨h.1.choose, h.1.choose_spec.left⟩
theorem SSameSide.wSameSide {s : AffineSubspace R P} {x y : P} (h : s.SSameSide x y) :
s.WSameSide x y :=
h.1
theorem SSameSide.left_not_mem {s : AffineSubspace R P} {x y : P} (h : s.SSameSide x y) : x ∉ s :=
h.2.1
theorem SSameSide.right_not_mem {s : AffineSubspace R P} {x y : P} (h : s.SSameSide x y) : y ∉ s :=
h.2.2
theorem SOppSide.wOppSide {s : AffineSubspace R P} {x y : P} (h : s.SOppSide x y) :
s.WOppSide x y :=
h.1
theorem SOppSide.left_not_mem {s : AffineSubspace R P} {x y : P} (h : s.SOppSide x y) : x ∉ s :=
h.2.1
theorem SOppSide.right_not_mem {s : AffineSubspace R P} {x y : P} (h : s.SOppSide x y) : y ∉ s :=
h.2.2
theorem wSameSide_comm {s : AffineSubspace R P} {x y : P} : s.WSameSide x y ↔ s.WSameSide y x :=
⟨fun ⟨p₁, hp₁, p₂, hp₂, h⟩ => ⟨p₂, hp₂, p₁, hp₁, h.symm⟩,
fun ⟨p₁, hp₁, p₂, hp₂, h⟩ => ⟨p₂, hp₂, p₁, hp₁, h.symm⟩⟩
alias ⟨WSameSide.symm, _⟩ := wSameSide_comm
theorem sSameSide_comm {s : AffineSubspace R P} {x y : P} : s.SSameSide x y ↔ s.SSameSide y x := by
rw [SSameSide, SSameSide, wSameSide_comm, and_comm (b := x ∉ s)]
alias ⟨SSameSide.symm, _⟩ := sSameSide_comm
theorem wOppSide_comm {s : AffineSubspace R P} {x y : P} : s.WOppSide x y ↔ s.WOppSide y x := by
constructor
· rintro ⟨p₁, hp₁, p₂, hp₂, h⟩
refine ⟨p₂, hp₂, p₁, hp₁, ?_⟩
rwa [SameRay.sameRay_comm, ← sameRay_neg_iff, neg_vsub_eq_vsub_rev, neg_vsub_eq_vsub_rev]
· rintro ⟨p₁, hp₁, p₂, hp₂, h⟩
refine ⟨p₂, hp₂, p₁, hp₁, ?_⟩
rwa [SameRay.sameRay_comm, ← sameRay_neg_iff, neg_vsub_eq_vsub_rev, neg_vsub_eq_vsub_rev]
alias ⟨WOppSide.symm, _⟩ := wOppSide_comm
theorem sOppSide_comm {s : AffineSubspace R P} {x y : P} : s.SOppSide x y ↔ s.SOppSide y x := by
rw [SOppSide, SOppSide, wOppSide_comm, and_comm (b := x ∉ s)]
alias ⟨SOppSide.symm, _⟩ := sOppSide_comm
theorem not_wSameSide_bot (x y : P) : ¬(⊥ : AffineSubspace R P).WSameSide x y :=
fun ⟨_, h, _⟩ => h.elim
theorem not_sSameSide_bot (x y : P) : ¬(⊥ : AffineSubspace R P).SSameSide x y :=
fun h => not_wSameSide_bot x y h.wSameSide
theorem not_wOppSide_bot (x y : P) : ¬(⊥ : AffineSubspace R P).WOppSide x y :=
fun ⟨_, h, _⟩ => h.elim
theorem not_sOppSide_bot (x y : P) : ¬(⊥ : AffineSubspace R P).SOppSide x y :=
fun h => not_wOppSide_bot x y h.wOppSide
@[simp]
theorem wSameSide_self_iff {s : AffineSubspace R P} {x : P} :
s.WSameSide x x ↔ (s : Set P).Nonempty :=
⟨fun h => h.nonempty, fun ⟨p, hp⟩ => ⟨p, hp, p, hp, SameRay.rfl⟩⟩
theorem sSameSide_self_iff {s : AffineSubspace R P} {x : P} :
s.SSameSide x x ↔ (s : Set P).Nonempty ∧ x ∉ s :=
⟨fun ⟨h, hx, _⟩ => ⟨wSameSide_self_iff.1 h, hx⟩, fun ⟨h, hx⟩ => ⟨wSameSide_self_iff.2 h, hx, hx⟩⟩
theorem wSameSide_of_left_mem {s : AffineSubspace R P} {x : P} (y : P) (hx : x ∈ s) :
s.WSameSide x y := by
refine ⟨x, hx, x, hx, ?_⟩
rw [vsub_self]
apply SameRay.zero_left
|
theorem wSameSide_of_right_mem {s : AffineSubspace R P} (x : P) {y : P} (hy : y ∈ s) :
| Mathlib/Analysis/Convex/Side.lean | 214 | 215 |
/-
Copyright (c) 2021 Martin Zinkevich. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Martin Zinkevich, Rémy Degenne
-/
import Mathlib.Logic.Encodable.Lattice
import Mathlib.MeasureTheory.MeasurableSpace.Defs
import Mathlib.Order.Disjointed
/-!
# Induction principles for measurable sets, related to π-systems and λ-systems.
## Main statements
* The main theorem of this file is Dynkin's π-λ theorem, which appears
here as an induction principle `induction_on_inter`. Suppose `s` is a
collection of subsets of `α` such that the intersection of two members
of `s` belongs to `s` whenever it is nonempty. Let `m` be the σ-algebra
generated by `s`. In order to check that a predicate `C` holds on every
member of `m`, it suffices to check that `C` holds on the members of `s` and
that `C` is preserved by complementation and *disjoint* countable
unions.
* The proof of this theorem relies on the notion of `IsPiSystem`, i.e., a collection of sets
which is closed under binary non-empty intersections. Note that this is a small variation around
the usual notion in the literature, which often requires that a π-system is non-empty, and closed
also under disjoint intersections. This variation turns out to be convenient for the
formalization.
* The proof of Dynkin's π-λ theorem also requires the notion of `DynkinSystem`, i.e., a collection
of sets which contains the empty set, is closed under complementation and under countable union
of pairwise disjoint sets. The disjointness condition is the only difference with `σ`-algebras.
* `generatePiSystem g` gives the minimal π-system containing `g`.
This can be considered a Galois insertion into both measurable spaces and sets.
* `generateFrom_generatePiSystem_eq` proves that if you start from a collection of sets `g`,
take the generated π-system, and then the generated σ-algebra, you get the same result as
the σ-algebra generated from `g`. This is useful because there are connections between
independent sets that are π-systems and the generated independent spaces.
* `mem_generatePiSystem_iUnion_elim` and `mem_generatePiSystem_iUnion_elim'` show that any
element of the π-system generated from the union of a set of π-systems can be
represented as the intersection of a finite number of elements from these sets.
* `piiUnionInter` defines a new π-system from a family of π-systems `π : ι → Set (Set α)` and a
set of indices `S : Set ι`. `piiUnionInter π S` is the set of sets that can be written
as `⋂ x ∈ t, f x` for some finset `t ∈ S` and sets `f x ∈ π x`.
## Implementation details
* `IsPiSystem` is a predicate, not a type. Thus, we don't explicitly define the galois
insertion, nor do we define a complete lattice. In theory, we could define a complete
lattice and galois insertion on the subtype corresponding to `IsPiSystem`.
-/
open MeasurableSpace Set
open MeasureTheory
variable {α β : Type*}
/-- A π-system is a collection of subsets of `α` that is closed under binary intersection of
non-disjoint sets. Usually it is also required that the collection is nonempty, but we don't do
that here. -/
def IsPiSystem (C : Set (Set α)) : Prop :=
∀ᵉ (s ∈ C) (t ∈ C), (s ∩ t : Set α).Nonempty → s ∩ t ∈ C
namespace MeasurableSpace
theorem isPiSystem_measurableSet {α : Type*} [MeasurableSpace α] :
IsPiSystem { s : Set α | MeasurableSet s } := fun _ hs _ ht _ => hs.inter ht
end MeasurableSpace
theorem IsPiSystem.singleton (S : Set α) : IsPiSystem ({S} : Set (Set α)) := by
intro s h_s t h_t _
rw [Set.mem_singleton_iff.1 h_s, Set.mem_singleton_iff.1 h_t, Set.inter_self,
Set.mem_singleton_iff]
theorem IsPiSystem.insert_empty {S : Set (Set α)} (h_pi : IsPiSystem S) :
IsPiSystem (insert ∅ S) := by
intro s hs t ht hst
rcases hs with hs | hs
· simp [hs]
· rcases ht with ht | ht
· simp [ht]
· exact Set.mem_insert_of_mem _ (h_pi s hs t ht hst)
theorem IsPiSystem.insert_univ {S : Set (Set α)} (h_pi : IsPiSystem S) :
IsPiSystem (insert Set.univ S) := by
intro s hs t ht hst
rcases hs with hs | hs
· rcases ht with ht | ht <;> simp [hs, ht]
· rcases ht with ht | ht
· simp [hs, ht]
· exact Set.mem_insert_of_mem _ (h_pi s hs t ht hst)
theorem IsPiSystem.comap {α β} {S : Set (Set β)} (h_pi : IsPiSystem S) (f : α → β) :
IsPiSystem { s : Set α | ∃ t ∈ S, f ⁻¹' t = s } := by
rintro _ ⟨s, hs_mem, rfl⟩ _ ⟨t, ht_mem, rfl⟩ hst
rw [← Set.preimage_inter] at hst ⊢
exact ⟨s ∩ t, h_pi s hs_mem t ht_mem (nonempty_of_nonempty_preimage hst), rfl⟩
|
theorem isPiSystem_iUnion_of_directed_le {α ι} (p : ι → Set (Set α))
(hp_pi : ∀ n, IsPiSystem (p n)) (hp_directed : Directed (· ≤ ·) p) :
IsPiSystem (⋃ n, p n) := by
intro t1 ht1 t2 ht2 h
| Mathlib/MeasureTheory/PiSystem.lean | 105 | 109 |
/-
Copyright (c) 2014 Parikshit Khanna. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Parikshit Khanna, Jeremy Avigad, Leonardo de Moura, Floris van Doorn, Mario Carneiro
-/
import Mathlib.Data.List.Lemmas
import Mathlib.Data.Nat.Factorial.Basic
import Mathlib.Data.List.Count
import Mathlib.Data.List.Duplicate
import Mathlib.Data.List.InsertIdx
import Mathlib.Data.List.Induction
import Batteries.Data.List.Perm
import Mathlib.Data.List.Perm.Basic
/-!
# Permutations of a list
In this file we prove properties about `List.Permutations`, a list of all permutations of a list. It
is defined in `Data.List.Defs`.
## Order of the permutations
Designed for performance, the order in which the permutations appear in `List.Permutations` is
rather intricate and not very amenable to induction. That's why we also provide `List.Permutations'`
as a less efficient but more straightforward way of listing permutations.
### `List.Permutations`
TODO. In the meantime, you can try decrypting the docstrings.
### `List.Permutations'`
The list of partitions is built by recursion. The permutations of `[]` are `[[]]`. Then, the
permutations of `a :: l` are obtained by taking all permutations of `l` in order and adding `a` in
all positions. Hence, to build `[0, 1, 2, 3].permutations'`, it does
* `[[]]`
* `[[3]]`
* `[[2, 3], [3, 2]]]`
* `[[1, 2, 3], [2, 1, 3], [2, 3, 1], [1, 3, 2], [3, 1, 2], [3, 2, 1]]`
* `[[0, 1, 2, 3], [1, 0, 2, 3], [1, 2, 0, 3], [1, 2, 3, 0],`
`[0, 2, 1, 3], [2, 0, 1, 3], [2, 1, 0, 3], [2, 1, 3, 0],`
`[0, 2, 3, 1], [2, 0, 3, 1], [2, 3, 0, 1], [2, 3, 1, 0],`
`[0, 1, 3, 2], [1, 0, 3, 2], [1, 3, 0, 2], [1, 3, 2, 0],`
`[0, 3, 1, 2], [3, 0, 1, 2], [3, 1, 0, 2], [3, 1, 2, 0],`
`[0, 3, 2, 1], [3, 0, 2, 1], [3, 2, 0, 1], [3, 2, 1, 0]]`
-/
-- Make sure we don't import algebra
assert_not_exists Monoid
open Nat Function
variable {α β : Type*}
namespace List
theorem permutationsAux2_fst (t : α) (ts : List α) (r : List β) :
∀ (ys : List α) (f : List α → β), (permutationsAux2 t ts r ys f).1 = ys ++ ts
| [], _ => rfl
| y :: ys, f => by simp [permutationsAux2, permutationsAux2_fst t _ _ ys]
@[simp]
theorem permutationsAux2_snd_nil (t : α) (ts : List α) (r : List β) (f : List α → β) :
(permutationsAux2 t ts r [] f).2 = r :=
rfl
@[simp]
theorem permutationsAux2_snd_cons (t : α) (ts : List α) (r : List β) (y : α) (ys : List α)
| (f : List α → β) :
(permutationsAux2 t ts r (y :: ys) f).2 =
f (t :: y :: ys ++ ts) :: (permutationsAux2 t ts r ys fun x : List α => f (y :: x)).2 := by
simp [permutationsAux2, permutationsAux2_fst t _ _ ys]
| Mathlib/Data/List/Permutation.lean | 69 | 73 |
/-
Copyright (c) 2022 Sébastien Gouëzel. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Sébastien Gouëzel
-/
import Mathlib.Analysis.Calculus.ContDiff.Operations
import Mathlib.Analysis.Calculus.UniformLimitsDeriv
import Mathlib.Topology.Algebra.InfiniteSum.Module
import Mathlib.Analysis.NormedSpace.FunctionSeries
/-!
# Smoothness of series
We show that series of functions are differentiable, or smooth, when each individual
function in the series is and additionally suitable uniform summable bounds are satisfied.
More specifically,
* `differentiable_tsum` ensures that a series of differentiable functions is differentiable.
* `contDiff_tsum` ensures that a series of `C^n` functions is `C^n`.
We also give versions of these statements which are localized to a set.
-/
open Set Metric TopologicalSpace Function Asymptotics Filter
open scoped Topology NNReal
variable {α β 𝕜 E F : Type*} [NontriviallyNormedField 𝕜] [IsRCLikeNormedField 𝕜]
[NormedAddCommGroup E] [NormedSpace 𝕜 E] [NormedAddCommGroup F] [CompleteSpace F] {u : α → ℝ}
/-! ### Differentiability -/
variable [NormedSpace 𝕜 F]
variable {f : α → E → F} {f' : α → E → E →L[𝕜] F} {g : α → 𝕜 → F} {g' : α → 𝕜 → F} {v : ℕ → α → ℝ}
{s : Set E} {t : Set 𝕜} {x₀ x : E} {y₀ y : 𝕜} {N : ℕ∞}
/-- Consider a series of functions `∑' n, f n x` on a preconnected open set. If the series converges
at a point, and all functions in the series are differentiable with a summable bound on the
derivatives, then the series converges everywhere on the set. -/
theorem summable_of_summable_hasFDerivAt_of_isPreconnected (hu : Summable u) (hs : IsOpen s)
(h's : IsPreconnected s) (hf : ∀ n x, x ∈ s → HasFDerivAt (f n) (f' n x) x)
(hf' : ∀ n x, x ∈ s → ‖f' n x‖ ≤ u n) (hx₀ : x₀ ∈ s) (hf0 : Summable (f · x₀))
(hx : x ∈ s) : Summable fun n => f n x := by
haveI := Classical.decEq α
rw [summable_iff_cauchySeq_finset] at hf0 ⊢
have A : UniformCauchySeqOn (fun t : Finset α => fun x => ∑ i ∈ t, f' i x) atTop s :=
(tendstoUniformlyOn_tsum hu hf').uniformCauchySeqOn
refine cauchy_map_of_uniformCauchySeqOn_fderiv (f := fun t x ↦ ∑ i ∈ t, f i x)
hs h's A (fun t y hy => ?_) hx₀ hx hf0
exact HasFDerivAt.sum fun i _ => hf i y hy
/-- Consider a series of functions `∑' n, f n x` on a preconnected open set. If the series converges
at a point, and all functions in the series are differentiable with a summable bound on the
derivatives, then the series converges everywhere on the set. -/
theorem summable_of_summable_hasDerivAt_of_isPreconnected (hu : Summable u) (ht : IsOpen t)
(h't : IsPreconnected t) (hg : ∀ n y, y ∈ t → HasDerivAt (g n) (g' n y) y)
(hg' : ∀ n y, y ∈ t → ‖g' n y‖ ≤ u n) (hy₀ : y₀ ∈ t) (hg0 : Summable (g · y₀))
(hy : y ∈ t) : Summable fun n => g n y := by
simp_rw [hasDerivAt_iff_hasFDerivAt] at hg
refine summable_of_summable_hasFDerivAt_of_isPreconnected hu ht h't hg ?_ hy₀ hg0 hy
simpa? says simpa only [ContinuousLinearMap.norm_smulRight_apply, norm_one, one_mul]
/-- Consider a series of functions `∑' n, f n x` on a preconnected open set. If the series converges
at a point, and all functions in the series are differentiable with a summable bound on the
derivatives, then the series is differentiable on the set and its derivative is the sum of the
derivatives. -/
theorem hasFDerivAt_tsum_of_isPreconnected (hu : Summable u) (hs : IsOpen s)
(h's : IsPreconnected s) (hf : ∀ n x, x ∈ s → HasFDerivAt (f n) (f' n x) x)
(hf' : ∀ n x, x ∈ s → ‖f' n x‖ ≤ u n) (hx₀ : x₀ ∈ s) (hf0 : Summable fun n => f n x₀)
(hx : x ∈ s) : HasFDerivAt (fun y => ∑' n, f n y) (∑' n, f' n x) x := by
classical
have A :
∀ x : E, x ∈ s → Tendsto (fun t : Finset α => ∑ n ∈ t, f n x) atTop (𝓝 (∑' n, f n x)) := by
intro y hy
apply Summable.hasSum
exact summable_of_summable_hasFDerivAt_of_isPreconnected hu hs h's hf hf' hx₀ hf0 hy
refine hasFDerivAt_of_tendstoUniformlyOn hs (tendstoUniformlyOn_tsum hu hf')
(fun t y hy => ?_) A hx
exact HasFDerivAt.sum fun n _ => hf n y hy
/-- Consider a series of functions `∑' n, f n x` on a preconnected open set. If the series converges
at a point, and all functions in the series are differentiable with a summable bound on the
derivatives, then the series is differentiable on the set and its derivative is the sum of the
derivatives. -/
theorem hasDerivAt_tsum_of_isPreconnected (hu : Summable u) (ht : IsOpen t)
(h't : IsPreconnected t) (hg : ∀ n y, y ∈ t → HasDerivAt (g n) (g' n y) y)
(hg' : ∀ n y, y ∈ t → ‖g' n y‖ ≤ u n) (hy₀ : y₀ ∈ t) (hg0 : Summable fun n => g n y₀)
(hy : y ∈ t) : HasDerivAt (fun z => ∑' n, g n z) (∑' n, g' n y) y := by
simp_rw [hasDerivAt_iff_hasFDerivAt] at hg ⊢
convert hasFDerivAt_tsum_of_isPreconnected hu ht h't hg ?_ hy₀ hg0 hy
· exact (ContinuousLinearMap.smulRightL 𝕜 𝕜 F 1).map_tsum <|
.of_norm_bounded u hu fun n ↦ hg' n y hy
· simpa? says simpa only [ContinuousLinearMap.norm_smulRight_apply, norm_one, one_mul]
/-- Consider a series of functions `∑' n, f n x`. If the series converges at a
point, and all functions in the series are differentiable with a summable bound on the derivatives,
then the series converges everywhere. -/
theorem summable_of_summable_hasFDerivAt (hu : Summable u)
(hf : ∀ n x, HasFDerivAt (f n) (f' n x) x) (hf' : ∀ n x, ‖f' n x‖ ≤ u n)
(hf0 : Summable fun n => f n x₀) (x : E) : Summable fun n => f n x := by
letI : RCLike 𝕜 := IsRCLikeNormedField.rclike 𝕜
let _ : NormedSpace ℝ E := NormedSpace.restrictScalars ℝ 𝕜 _
exact summable_of_summable_hasFDerivAt_of_isPreconnected hu isOpen_univ isPreconnected_univ
(fun n x _ => hf n x) (fun n x _ => hf' n x) (mem_univ _) hf0 (mem_univ _)
/-- Consider a series of functions `∑' n, f n x`. If the series converges at a
point, and all functions in the series are differentiable with a summable bound on the derivatives,
then the series converges everywhere. -/
theorem summable_of_summable_hasDerivAt (hu : Summable u)
(hg : ∀ n y, HasDerivAt (g n) (g' n y) y) (hg' : ∀ n y, ‖g' n y‖ ≤ u n)
(hg0 : Summable fun n => g n y₀) (y : 𝕜) : Summable fun n => g n y := by
exact summable_of_summable_hasDerivAt_of_isPreconnected hu isOpen_univ isPreconnected_univ
(fun n x _ => hg n x) (fun n x _ => hg' n x) (mem_univ _) hg0 (mem_univ _)
/-- Consider a series of functions `∑' n, f n x`. If the series converges at a
point, and all functions in the series are differentiable with a summable bound on the derivatives,
then the series is differentiable and its derivative is the sum of the derivatives. -/
theorem hasFDerivAt_tsum (hu : Summable u) (hf : ∀ n x, HasFDerivAt (f n) (f' n x) x)
(hf' : ∀ n x, ‖f' n x‖ ≤ u n) (hf0 : Summable fun n => f n x₀) (x : E) :
HasFDerivAt (fun y => ∑' n, f n y) (∑' n, f' n x) x := by
letI : RCLike 𝕜 := IsRCLikeNormedField.rclike 𝕜
let A : NormedSpace ℝ E := NormedSpace.restrictScalars ℝ 𝕜 _
exact hasFDerivAt_tsum_of_isPreconnected hu isOpen_univ isPreconnected_univ
(fun n x _ => hf n x) (fun n x _ => hf' n x) (mem_univ _) hf0 (mem_univ _)
/-- Consider a series of functions `∑' n, f n x`. If the series converges at a
point, and all functions in the series are differentiable with a summable bound on the derivatives,
then the series is differentiable and its derivative is the sum of the derivatives. -/
theorem hasDerivAt_tsum (hu : Summable u) (hg : ∀ n y, HasDerivAt (g n) (g' n y) y)
(hg' : ∀ n y, ‖g' n y‖ ≤ u n) (hg0 : Summable fun n => g n y₀) (y : 𝕜) :
HasDerivAt (fun z => ∑' n, g n z) (∑' n, g' n y) y := by
exact hasDerivAt_tsum_of_isPreconnected hu isOpen_univ isPreconnected_univ
(fun n y _ => hg n y) (fun n y _ => hg' n y) (mem_univ _) hg0 (mem_univ _)
/-- Consider a series of functions `∑' n, f n x`. If all functions in the series are differentiable
with a summable bound on the derivatives, then the series is differentiable.
Note that our assumptions do not ensure the pointwise convergence, but if there is no pointwise
convergence then the series is zero everywhere so the result still holds. -/
theorem differentiable_tsum (hu : Summable u) (hf : ∀ n x, HasFDerivAt (f n) (f' n x) x)
(hf' : ∀ n x, ‖f' n x‖ ≤ u n) : Differentiable 𝕜 fun y => ∑' n, f n y := by
by_cases h : ∃ x₀, Summable fun n => f n x₀
· rcases h with ⟨x₀, hf0⟩
intro x
exact (hasFDerivAt_tsum hu hf hf' hf0 x).differentiableAt
· push_neg at h
have : (fun x => ∑' n, f n x) = 0 := by ext1 x; exact tsum_eq_zero_of_not_summable (h x)
rw [this]
exact differentiable_const 0
/-- Consider a series of functions `∑' n, f n x`. If all functions in the series are differentiable
with a summable bound on the derivatives, then the series is differentiable.
Note that our assumptions do not ensure the pointwise convergence, but if there is no pointwise
convergence then the series is zero everywhere so the result still holds. -/
theorem differentiable_tsum' (hu : Summable u) (hg : ∀ n y, HasDerivAt (g n) (g' n y) y)
(hg' : ∀ n y, ‖g' n y‖ ≤ u n) : Differentiable 𝕜 fun z => ∑' n, g n z := by
simp_rw [hasDerivAt_iff_hasFDerivAt] at hg
refine differentiable_tsum hu hg ?_
simpa? says simpa only [ContinuousLinearMap.norm_smulRight_apply, norm_one, one_mul]
theorem fderiv_tsum_apply (hu : Summable u) (hf : ∀ n, Differentiable 𝕜 (f n))
(hf' : ∀ n x, ‖fderiv 𝕜 (f n) x‖ ≤ u n) (hf0 : Summable fun n => f n x₀) (x : E) :
fderiv 𝕜 (fun y => ∑' n, f n y) x = ∑' n, fderiv 𝕜 (f n) x :=
(hasFDerivAt_tsum hu (fun n x => (hf n x).hasFDerivAt) hf' hf0 _).fderiv
theorem deriv_tsum_apply (hu : Summable u) (hg : ∀ n, Differentiable 𝕜 (g n))
(hg' : ∀ n y, ‖deriv (g n) y‖ ≤ u n) (hg0 : Summable fun n => g n y₀) (y : 𝕜) :
deriv (fun z => ∑' n, g n z) y = ∑' n, deriv (g n) y :=
(hasDerivAt_tsum hu (fun n y => (hg n y).hasDerivAt) hg' hg0 _).deriv
theorem fderiv_tsum (hu : Summable u) (hf : ∀ n, Differentiable 𝕜 (f n))
(hf' : ∀ n x, ‖fderiv 𝕜 (f n) x‖ ≤ u n) (hf0 : Summable fun n => f n x₀) :
(fderiv 𝕜 fun y => ∑' n, f n y) = fun x => ∑' n, fderiv 𝕜 (f n) x := by
ext1 x
exact fderiv_tsum_apply hu hf hf' hf0 x
theorem deriv_tsum (hu : Summable u) (hg : ∀ n, Differentiable 𝕜 (g n))
(hg' : ∀ n y, ‖deriv (g n) y‖ ≤ u n) (hg0 : Summable fun n => g n y₀) :
(deriv fun y => ∑' n, g n y) = fun y => ∑' n, deriv (g n) y := by
ext1 x
exact deriv_tsum_apply hu hg hg' hg0 x
/-! ### Higher smoothness -/
| /-- Consider a series of `C^n` functions, with summable uniform bounds on the successive
derivatives. Then the iterated derivative of the sum is the sum of the iterated derivative. -/
theorem iteratedFDeriv_tsum (hf : ∀ i, ContDiff 𝕜 N (f i))
(hv : ∀ k : ℕ, (k : ℕ∞) ≤ N → Summable (v k))
(h'f : ∀ (k : ℕ) (i : α) (x : E), (k : ℕ∞) ≤ N → ‖iteratedFDeriv 𝕜 k (f i) x‖ ≤ v k i) {k : ℕ}
| Mathlib/Analysis/Calculus/SmoothSeries.lean | 185 | 189 |
/-
Copyright (c) 2022 Wrenna Robson. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Wrenna Robson
-/
import Mathlib.Topology.MetricSpace.Basic
/-!
# Infimum separation
This file defines the extended infimum separation of a set. This is approximately dual to the
diameter of a set, but where the extended diameter of a set is the supremum of the extended distance
between elements of the set, the extended infimum separation is the infimum of the (extended)
distance between *distinct* elements in the set.
We also define the infimum separation as the cast of the extended infimum separation to the reals.
This is the infimum of the distance between distinct elements of the set when in a pseudometric
space.
All lemmas and definitions are in the `Set` namespace to give access to dot notation.
## Main definitions
* `Set.einfsep`: Extended infimum separation of a set.
* `Set.infsep`: Infimum separation of a set (when in a pseudometric space).
-/
variable {α β : Type*}
namespace Set
section Einfsep
open ENNReal
open Function
/-- The "extended infimum separation" of a set with an edist function. -/
noncomputable def einfsep [EDist α] (s : Set α) : ℝ≥0∞ :=
⨅ (x ∈ s) (y ∈ s) (_ : x ≠ y), edist x y
section EDist
variable [EDist α] {x y : α} {s t : Set α}
theorem le_einfsep_iff {d} :
d ≤ s.einfsep ↔ ∀ x ∈ s, ∀ y ∈ s, x ≠ y → d ≤ edist x y := by
simp_rw [einfsep, le_iInf_iff]
theorem einfsep_zero : s.einfsep = 0 ↔ ∀ C > 0, ∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ edist x y < C := by
simp_rw [einfsep, ← _root_.bot_eq_zero, iInf_eq_bot, iInf_lt_iff, exists_prop]
theorem einfsep_pos : 0 < s.einfsep ↔ ∃ C > 0, ∀ x ∈ s, ∀ y ∈ s, x ≠ y → C ≤ edist x y := by
rw [pos_iff_ne_zero, Ne, einfsep_zero]
simp only [not_forall, not_exists, not_lt, exists_prop, not_and]
theorem einfsep_top :
s.einfsep = ∞ ↔ ∀ x ∈ s, ∀ y ∈ s, x ≠ y → edist x y = ∞ := by
simp_rw [einfsep, iInf_eq_top]
theorem einfsep_lt_top :
s.einfsep < ∞ ↔ ∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ edist x y < ∞ := by
simp_rw [einfsep, iInf_lt_iff, exists_prop]
theorem einfsep_ne_top :
s.einfsep ≠ ∞ ↔ ∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ edist x y ≠ ∞ := by
simp_rw [← lt_top_iff_ne_top, einfsep_lt_top]
theorem einfsep_lt_iff {d} :
s.einfsep < d ↔ ∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ edist x y < d := by
simp_rw [einfsep, iInf_lt_iff, exists_prop]
theorem nontrivial_of_einfsep_lt_top (hs : s.einfsep < ∞) : s.Nontrivial := by
rcases einfsep_lt_top.1 hs with ⟨_, hx, _, hy, hxy, _⟩
exact ⟨_, hx, _, hy, hxy⟩
theorem nontrivial_of_einfsep_ne_top (hs : s.einfsep ≠ ∞) : s.Nontrivial :=
nontrivial_of_einfsep_lt_top (lt_top_iff_ne_top.mpr hs)
theorem Subsingleton.einfsep (hs : s.Subsingleton) : s.einfsep = ∞ := by
rw [einfsep_top]
exact fun _ hx _ hy hxy => (hxy <| hs hx hy).elim
theorem le_einfsep_image_iff {d} {f : β → α} {s : Set β} : d ≤ einfsep (f '' s)
↔ ∀ x ∈ s, ∀ y ∈ s, f x ≠ f y → d ≤ edist (f x) (f y) := by
simp_rw [le_einfsep_iff, forall_mem_image]
theorem le_edist_of_le_einfsep {d x} (hx : x ∈ s) {y} (hy : y ∈ s) (hxy : x ≠ y)
(hd : d ≤ s.einfsep) : d ≤ edist x y :=
le_einfsep_iff.1 hd x hx y hy hxy
theorem einfsep_le_edist_of_mem {x} (hx : x ∈ s) {y} (hy : y ∈ s) (hxy : x ≠ y) :
s.einfsep ≤ edist x y :=
le_edist_of_le_einfsep hx hy hxy le_rfl
theorem einfsep_le_of_mem_of_edist_le {d x} (hx : x ∈ s) {y} (hy : y ∈ s) (hxy : x ≠ y)
(hxy' : edist x y ≤ d) : s.einfsep ≤ d :=
le_trans (einfsep_le_edist_of_mem hx hy hxy) hxy'
theorem le_einfsep {d} (h : ∀ x ∈ s, ∀ y ∈ s, x ≠ y → d ≤ edist x y) : d ≤ s.einfsep :=
le_einfsep_iff.2 h
@[simp]
theorem einfsep_empty : (∅ : Set α).einfsep = ∞ :=
subsingleton_empty.einfsep
@[simp]
theorem einfsep_singleton : ({x} : Set α).einfsep = ∞ :=
subsingleton_singleton.einfsep
theorem einfsep_iUnion_mem_option {ι : Type*} (o : Option ι) (s : ι → Set α) :
(⋃ i ∈ o, s i).einfsep = ⨅ i ∈ o, (s i).einfsep := by cases o <;> simp
theorem einfsep_anti (hst : s ⊆ t) : t.einfsep ≤ s.einfsep :=
le_einfsep fun _x hx _y hy => einfsep_le_edist_of_mem (hst hx) (hst hy)
theorem einfsep_insert_le : (insert x s).einfsep ≤ ⨅ (y ∈ s) (_ : x ≠ y), edist x y := by
simp_rw [le_iInf_iff]
exact fun _ hy hxy => einfsep_le_edist_of_mem (mem_insert _ _) (mem_insert_of_mem _ hy) hxy
theorem le_einfsep_pair : edist x y ⊓ edist y x ≤ ({x, y} : Set α).einfsep := by
simp_rw [le_einfsep_iff, inf_le_iff, mem_insert_iff, mem_singleton_iff]
rintro a (rfl | rfl) b (rfl | rfl) hab <;> (try simp only [le_refl, true_or, or_true]) <;>
contradiction
theorem einfsep_pair_le_left (hxy : x ≠ y) : ({x, y} : Set α).einfsep ≤ edist x y :=
einfsep_le_edist_of_mem (mem_insert _ _) (mem_insert_of_mem _ (mem_singleton _)) hxy
theorem einfsep_pair_le_right (hxy : x ≠ y) : ({x, y} : Set α).einfsep ≤ edist y x := by
rw [pair_comm]; exact einfsep_pair_le_left hxy.symm
theorem einfsep_pair_eq_inf (hxy : x ≠ y) : ({x, y} : Set α).einfsep = edist x y ⊓ edist y x :=
le_antisymm (le_inf (einfsep_pair_le_left hxy) (einfsep_pair_le_right hxy)) le_einfsep_pair
theorem einfsep_eq_iInf : s.einfsep = ⨅ d : s.offDiag, (uncurry edist) (d : α × α) := by
refine eq_of_forall_le_iff fun _ => ?_
simp_rw [le_einfsep_iff, le_iInf_iff, imp_forall_iff, SetCoe.forall, mem_offDiag,
Prod.forall, uncurry_apply_pair, and_imp]
theorem einfsep_of_fintype [DecidableEq α] [Fintype s] :
s.einfsep = s.offDiag.toFinset.inf (uncurry edist) := by
refine eq_of_forall_le_iff fun _ => ?_
simp_rw [le_einfsep_iff, imp_forall_iff, Finset.le_inf_iff, mem_toFinset, mem_offDiag,
Prod.forall, uncurry_apply_pair, and_imp]
theorem Finite.einfsep (hs : s.Finite) : s.einfsep = hs.offDiag.toFinset.inf (uncurry edist) := by
refine eq_of_forall_le_iff fun _ => ?_
simp_rw [le_einfsep_iff, imp_forall_iff, Finset.le_inf_iff, Finite.mem_toFinset, mem_offDiag,
Prod.forall, uncurry_apply_pair, and_imp]
theorem Finset.coe_einfsep [DecidableEq α] {s : Finset α} :
(s : Set α).einfsep = s.offDiag.inf (uncurry edist) := by
simp_rw [einfsep_of_fintype, ← Finset.coe_offDiag, Finset.toFinset_coe]
theorem Nontrivial.einfsep_exists_of_finite [Finite s] (hs : s.Nontrivial) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ s.einfsep = edist x y := by
classical
cases nonempty_fintype s
simp_rw [einfsep_of_fintype]
rcases Finset.exists_mem_eq_inf s.offDiag.toFinset (by simpa) (uncurry edist) with ⟨w, hxy, hed⟩
simp_rw [mem_toFinset] at hxy
exact ⟨w.fst, hxy.1, w.snd, hxy.2.1, hxy.2.2, hed⟩
theorem Finite.einfsep_exists_of_nontrivial (hsf : s.Finite) (hs : s.Nontrivial) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ s.einfsep = edist x y :=
letI := hsf.fintype
hs.einfsep_exists_of_finite
end EDist
section PseudoEMetricSpace
variable [PseudoEMetricSpace α] {x y z : α} {s : Set α}
theorem einfsep_pair (hxy : x ≠ y) : ({x, y} : Set α).einfsep = edist x y := by
nth_rw 1 [← min_self (edist x y)]
convert einfsep_pair_eq_inf hxy using 2
rw [edist_comm]
theorem einfsep_insert : einfsep (insert x s) =
(⨅ (y ∈ s) (_ : x ≠ y), edist x y) ⊓ s.einfsep := by
refine le_antisymm (le_min einfsep_insert_le (einfsep_anti (subset_insert _ _))) ?_
simp_rw [le_einfsep_iff, inf_le_iff, mem_insert_iff]
rintro y (rfl | hy) z (rfl | hz) hyz
· exact False.elim (hyz rfl)
· exact Or.inl (iInf_le_of_le _ (iInf₂_le hz hyz))
· rw [edist_comm]
exact Or.inl (iInf_le_of_le _ (iInf₂_le hy hyz.symm))
· exact Or.inr (einfsep_le_edist_of_mem hy hz hyz)
theorem einfsep_triple (hxy : x ≠ y) (hyz : y ≠ z) (hxz : x ≠ z) :
einfsep ({x, y, z} : Set α) = edist x y ⊓ edist x z ⊓ edist y z := by
simp_rw [einfsep_insert, iInf_insert, iInf_singleton, einfsep_singleton, inf_top_eq,
ciInf_pos hxy, ciInf_pos hyz, ciInf_pos hxz]
theorem le_einfsep_pi_of_le {π : β → Type*} [Fintype β] [∀ b, PseudoEMetricSpace (π b)]
{s : ∀ b : β, Set (π b)} {c : ℝ≥0∞} (h : ∀ b, c ≤ einfsep (s b)) :
c ≤ einfsep (Set.pi univ s) := by
refine le_einfsep fun x hx y hy hxy => ?_
rw [mem_univ_pi] at hx hy
rcases Function.ne_iff.mp hxy with ⟨i, hi⟩
exact le_trans (le_einfsep_iff.1 (h i) _ (hx _) _ (hy _) hi) (edist_le_pi_edist _ _ i)
end PseudoEMetricSpace
section PseudoMetricSpace
variable [PseudoMetricSpace α] {s : Set α}
theorem subsingleton_of_einfsep_eq_top (hs : s.einfsep = ∞) : s.Subsingleton := by
rw [einfsep_top] at hs
exact fun _ hx _ hy => of_not_not fun hxy => edist_ne_top _ _ (hs _ hx _ hy hxy)
theorem einfsep_eq_top_iff : s.einfsep = ∞ ↔ s.Subsingleton :=
⟨subsingleton_of_einfsep_eq_top, Subsingleton.einfsep⟩
theorem Nontrivial.einfsep_ne_top (hs : s.Nontrivial) : s.einfsep ≠ ∞ := by
contrapose! hs
rw [not_nontrivial_iff]
exact subsingleton_of_einfsep_eq_top hs
theorem Nontrivial.einfsep_lt_top (hs : s.Nontrivial) : s.einfsep < ∞ := by
rw [lt_top_iff_ne_top]
exact hs.einfsep_ne_top
theorem einfsep_lt_top_iff : s.einfsep < ∞ ↔ s.Nontrivial :=
⟨nontrivial_of_einfsep_lt_top, Nontrivial.einfsep_lt_top⟩
theorem einfsep_ne_top_iff : s.einfsep ≠ ∞ ↔ s.Nontrivial :=
⟨nontrivial_of_einfsep_ne_top, Nontrivial.einfsep_ne_top⟩
theorem le_einfsep_of_forall_dist_le {d} (h : ∀ x ∈ s, ∀ y ∈ s, x ≠ y → d ≤ dist x y) :
ENNReal.ofReal d ≤ s.einfsep :=
le_einfsep fun x hx y hy hxy => (edist_dist x y).symm ▸ ENNReal.ofReal_le_ofReal (h x hx y hy hxy)
end PseudoMetricSpace
section EMetricSpace
variable [EMetricSpace α] {s : Set α}
theorem einfsep_pos_of_finite [Finite s] : 0 < s.einfsep := by
cases nonempty_fintype s
by_cases hs : s.Nontrivial
· rcases hs.einfsep_exists_of_finite with ⟨x, _hx, y, _hy, hxy, hxy'⟩
exact hxy'.symm ▸ edist_pos.2 hxy
· rw [not_nontrivial_iff] at hs
exact hs.einfsep.symm ▸ WithTop.top_pos
theorem relatively_discrete_of_finite [Finite s] :
∃ C > 0, ∀ x ∈ s, ∀ y ∈ s, x ≠ y → C ≤ edist x y := by
rw [← einfsep_pos]
exact einfsep_pos_of_finite
theorem Finite.einfsep_pos (hs : s.Finite) : 0 < s.einfsep :=
letI := hs.fintype
einfsep_pos_of_finite
theorem Finite.relatively_discrete (hs : s.Finite) :
∃ C > 0, ∀ x ∈ s, ∀ y ∈ s, x ≠ y → C ≤ edist x y :=
letI := hs.fintype
relatively_discrete_of_finite
end EMetricSpace
end Einfsep
section Infsep
open ENNReal
open Set Function
/-- The "infimum separation" of a set with an edist function. -/
noncomputable def infsep [EDist α] (s : Set α) : ℝ :=
ENNReal.toReal s.einfsep
section EDist
variable [EDist α] {x y : α} {s : Set α}
theorem infsep_zero : s.infsep = 0 ↔ s.einfsep = 0 ∨ s.einfsep = ∞ := by
rw [infsep, ENNReal.toReal_eq_zero_iff]
theorem infsep_nonneg : 0 ≤ s.infsep :=
ENNReal.toReal_nonneg
theorem infsep_pos : 0 < s.infsep ↔ 0 < s.einfsep ∧ s.einfsep < ∞ := by
simp_rw [infsep, ENNReal.toReal_pos_iff]
theorem Subsingleton.infsep_zero (hs : s.Subsingleton) : s.infsep = 0 :=
Set.infsep_zero.mpr <| Or.inr hs.einfsep
theorem nontrivial_of_infsep_pos (hs : 0 < s.infsep) : s.Nontrivial := by
contrapose hs
rw [not_nontrivial_iff] at hs
exact hs.infsep_zero ▸ lt_irrefl _
theorem infsep_empty : (∅ : Set α).infsep = 0 :=
subsingleton_empty.infsep_zero
theorem infsep_singleton : ({x} : Set α).infsep = 0 :=
subsingleton_singleton.infsep_zero
theorem infsep_pair_le_toReal_inf (hxy : x ≠ y) :
({x, y} : Set α).infsep ≤ (edist x y ⊓ edist y x).toReal := by
simp_rw [infsep, einfsep_pair_eq_inf hxy]
simp
end EDist
section PseudoEMetricSpace
variable [PseudoEMetricSpace α] {x y : α}
theorem infsep_pair_eq_toReal : ({x, y} : Set α).infsep = (edist x y).toReal := by
by_cases hxy : x = y
· rw [hxy]
simp only [infsep_singleton, pair_eq_singleton, edist_self, ENNReal.toReal_zero]
· rw [infsep, einfsep_pair hxy]
end PseudoEMetricSpace
section PseudoMetricSpace
variable [PseudoMetricSpace α] {x y z : α} {s t : Set α}
theorem Nontrivial.le_infsep_iff {d} (hs : s.Nontrivial) :
d ≤ s.infsep ↔ ∀ x ∈ s, ∀ y ∈ s, x ≠ y → d ≤ dist x y := by
simp_rw [infsep, ← ENNReal.ofReal_le_iff_le_toReal hs.einfsep_ne_top, le_einfsep_iff, edist_dist,
ENNReal.ofReal_le_ofReal_iff dist_nonneg]
theorem Nontrivial.infsep_lt_iff {d} (hs : s.Nontrivial) :
s.infsep < d ↔ ∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ dist x y < d := by
rw [← not_iff_not]
push_neg
exact hs.le_infsep_iff
theorem Nontrivial.le_infsep {d} (hs : s.Nontrivial)
(h : ∀ x ∈ s, ∀ y ∈ s, x ≠ y → d ≤ dist x y) : d ≤ s.infsep :=
hs.le_infsep_iff.2 h
theorem le_edist_of_le_infsep {d x} (hx : x ∈ s) {y} (hy : y ∈ s) (hxy : x ≠ y)
(hd : d ≤ s.infsep) : d ≤ dist x y := by
by_cases hs : s.Nontrivial
· exact hs.le_infsep_iff.1 hd x hx y hy hxy
· rw [not_nontrivial_iff] at hs
rw [hs.infsep_zero] at hd
exact le_trans hd dist_nonneg
theorem infsep_le_dist_of_mem (hx : x ∈ s) (hy : y ∈ s) (hxy : x ≠ y) : s.infsep ≤ dist x y :=
le_edist_of_le_infsep hx hy hxy le_rfl
theorem infsep_le_of_mem_of_edist_le {d x} (hx : x ∈ s) {y} (hy : y ∈ s) (hxy : x ≠ y)
(hxy' : dist x y ≤ d) : s.infsep ≤ d :=
le_trans (infsep_le_dist_of_mem hx hy hxy) hxy'
theorem infsep_pair : ({x, y} : Set α).infsep = dist x y := by
rw [infsep_pair_eq_toReal, edist_dist]
exact ENNReal.toReal_ofReal dist_nonneg
theorem infsep_triple (hxy : x ≠ y) (hyz : y ≠ z) (hxz : x ≠ z) :
({x, y, z} : Set α).infsep = dist x y ⊓ dist x z ⊓ dist y z := by
simp only [infsep, einfsep_triple hxy hyz hxz, ENNReal.toReal_inf, edist_ne_top x y,
edist_ne_top x z, edist_ne_top y z, dist_edist, Ne, inf_eq_top_iff, and_self_iff,
not_false_iff]
theorem Nontrivial.infsep_anti (hs : s.Nontrivial) (hst : s ⊆ t) : t.infsep ≤ s.infsep :=
ENNReal.toReal_mono hs.einfsep_ne_top (einfsep_anti hst)
theorem infsep_eq_iInf [Decidable s.Nontrivial] :
s.infsep = if s.Nontrivial then ⨅ d : s.offDiag, (uncurry dist) (d : α × α) else 0 := by
split_ifs with hs
· have hb : BddBelow (uncurry dist '' s.offDiag) := by
refine ⟨0, fun d h => ?_⟩
simp_rw [mem_image, Prod.exists, uncurry_apply_pair] at h
rcases h with ⟨_, _, _, rfl⟩
exact dist_nonneg
refine eq_of_forall_le_iff fun _ => ?_
simp_rw [hs.le_infsep_iff, le_ciInf_set_iff (offDiag_nonempty.mpr hs) hb, imp_forall_iff,
mem_offDiag, Prod.forall, uncurry_apply_pair, and_imp]
· exact (not_nontrivial_iff.mp hs).infsep_zero
theorem Nontrivial.infsep_eq_iInf (hs : s.Nontrivial) :
s.infsep = ⨅ d : s.offDiag, (uncurry dist) (d : α × α) := by
classical rw [Set.infsep_eq_iInf, if_pos hs]
theorem infsep_of_fintype [Decidable s.Nontrivial] [DecidableEq α] [Fintype s] : s.infsep =
if hs : s.Nontrivial then s.offDiag.toFinset.inf' (by simpa) (uncurry dist) else 0 := by
split_ifs with hs
· refine eq_of_forall_le_iff fun _ => ?_
simp_rw [hs.le_infsep_iff, imp_forall_iff, Finset.le_inf'_iff, mem_toFinset, mem_offDiag,
Prod.forall, uncurry_apply_pair, and_imp]
· rw [not_nontrivial_iff] at hs
exact hs.infsep_zero
theorem Nontrivial.infsep_of_fintype [DecidableEq α] [Fintype s] (hs : s.Nontrivial) :
s.infsep = s.offDiag.toFinset.inf' (by simpa) (uncurry dist) := by
classical rw [Set.infsep_of_fintype, dif_pos hs]
theorem Finite.infsep [Decidable s.Nontrivial] (hsf : s.Finite) :
s.infsep =
if hs : s.Nontrivial then hsf.offDiag.toFinset.inf' (by simpa) (uncurry dist) else 0 := by
split_ifs with hs
· refine eq_of_forall_le_iff fun _ => ?_
simp_rw [hs.le_infsep_iff, imp_forall_iff, Finset.le_inf'_iff, Finite.mem_toFinset,
mem_offDiag, Prod.forall, uncurry_apply_pair, and_imp]
· rw [not_nontrivial_iff] at hs
exact hs.infsep_zero
theorem Finite.infsep_of_nontrivial (hsf : s.Finite) (hs : s.Nontrivial) :
s.infsep = hsf.offDiag.toFinset.inf' (by simpa) (uncurry dist) := by
classical simp_rw [hsf.infsep, dif_pos hs]
theorem _root_.Finset.coe_infsep [DecidableEq α] (s : Finset α) : (s : Set α).infsep =
if hs : s.offDiag.Nonempty then s.offDiag.inf' hs (uncurry dist) else 0 := by
have H : (s : Set α).Nontrivial ↔ s.offDiag.Nonempty := by
rw [← Set.offDiag_nonempty, ← Finset.coe_offDiag, Finset.coe_nonempty]
split_ifs with hs
· simp_rw [(H.mpr hs).infsep_of_fintype, ← Finset.coe_offDiag, Finset.toFinset_coe]
· exact (not_nontrivial_iff.mp (H.mp.mt hs)).infsep_zero
theorem _root_.Finset.coe_infsep_of_offDiag_nonempty [DecidableEq α] {s : Finset α}
(hs : s.offDiag.Nonempty) : (s : Set α).infsep = s.offDiag.inf' hs (uncurry dist) := by
rw [Finset.coe_infsep, dif_pos hs]
theorem _root_.Finset.coe_infsep_of_offDiag_empty
[DecidableEq α] {s : Finset α} (hs : s.offDiag = ∅) : (s : Set α).infsep = 0 := by
rw [← Finset.not_nonempty_iff_eq_empty] at hs
rw [Finset.coe_infsep, dif_neg hs]
theorem Nontrivial.infsep_exists_of_finite [Finite s] (hs : s.Nontrivial) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ s.infsep = dist x y := by
classical
cases nonempty_fintype s
simp_rw [hs.infsep_of_fintype]
rcases Finset.exists_mem_eq_inf' (s := s.offDiag.toFinset) (by simpa) (uncurry dist) with
⟨w, hxy, hed⟩
simp_rw [mem_toFinset] at hxy
exact ⟨w.fst, hxy.1, w.snd, hxy.2.1, hxy.2.2, hed⟩
theorem Finite.infsep_exists_of_nontrivial (hsf : s.Finite) (hs : s.Nontrivial) :
∃ x ∈ s, ∃ y ∈ s, x ≠ y ∧ s.infsep = dist x y :=
letI := hsf.fintype
hs.infsep_exists_of_finite
end PseudoMetricSpace
section MetricSpace
variable [MetricSpace α] {s : Set α}
|
theorem infsep_zero_iff_subsingleton_of_finite [Finite s] : s.infsep = 0 ↔ s.Subsingleton := by
rw [infsep_zero, einfsep_eq_top_iff, or_iff_right_iff_imp]
| Mathlib/Topology/MetricSpace/Infsep.lean | 453 | 455 |
/-
Copyright (c) 2020 Yury Kudryashov. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Yury Kudryashov, Patrick Massot, Sébastien Gouëzel
-/
import Mathlib.MeasureTheory.Integral.IntervalIntegral.Basic
import Mathlib.MeasureTheory.Integral.IntervalIntegral.FundThmCalculus
import Mathlib.MeasureTheory.Integral.IntervalIntegral.IntegrationByParts
deprecated_module (since := "2025-04-13")
| Mathlib/MeasureTheory/Integral/IntervalIntegral.lean | 1,124 | 1,132 | |
/-
Copyright (c) 2022 Julian Kuelshammer. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Julian Kuelshammer
-/
import Mathlib.Algebra.BigOperators.Fin
import Mathlib.Algebra.BigOperators.NatAntidiagonal
import Mathlib.Data.Nat.Choose.Central
import Mathlib.Tactic.FieldSimp
import Mathlib.Tactic.GCongr
import Mathlib.Tactic.Positivity
/-!
# Catalan numbers
The Catalan numbers (http://oeis.org/A000108) are probably the most ubiquitous sequence of integers
in mathematics. They enumerate several important objects like binary trees, Dyck paths, and
triangulations of convex polygons.
## Main definitions
* `catalan n`: the `n`th Catalan number, defined recursively as
`catalan (n + 1) = ∑ i : Fin n.succ, catalan i * catalan (n - i)`.
## Main results
* `catalan_eq_centralBinom_div`: The explicit formula for the Catalan number using the central
binomial coefficient, `catalan n = Nat.centralBinom n / (n + 1)`.
* `treesOfNumNodesEq_card_eq_catalan`: The number of binary trees with `n` internal nodes
is `catalan n`
## Implementation details
The proof of `catalan_eq_centralBinom_div` follows https://math.stackexchange.com/questions/3304415
## TODO
* Prove that the Catalan numbers enumerate many interesting objects.
* Provide the many variants of Catalan numbers, e.g. associated to complex reflection groups,
Fuss-Catalan, etc.
-/
open Finset
open Finset.antidiagonal (fst_le snd_le)
/-- The recursive definition of the sequence of Catalan numbers:
`catalan (n + 1) = ∑ i : Fin n.succ, catalan i * catalan (n - i)` -/
def catalan : ℕ → ℕ
| 0 => 1
| n + 1 =>
∑ i : Fin n.succ,
catalan i * catalan (n - i)
@[simp]
theorem catalan_zero : catalan 0 = 1 := by rw [catalan]
theorem catalan_succ (n : ℕ) : catalan (n + 1) = ∑ i : Fin n.succ, catalan i * catalan (n - i) := by
rw [catalan]
theorem catalan_succ' (n : ℕ) :
catalan (n + 1) = ∑ ij ∈ antidiagonal n, catalan ij.1 * catalan ij.2 := by
rw [catalan_succ, Nat.sum_antidiagonal_eq_sum_range_succ (fun x y => catalan x * catalan y) n,
sum_range]
@[simp]
theorem catalan_one : catalan 1 = 1 := by simp [catalan_succ]
/-- A helper sequence that can be used to prove the equality of the recursive and the explicit
definition using a telescoping sum argument. -/
private def gosperCatalan (n j : ℕ) : ℚ :=
Nat.centralBinom j * Nat.centralBinom (n - j) * (2 * j - n) / (2 * n * (n + 1))
private theorem gosper_trick {n i : ℕ} (h : i ≤ n) :
gosperCatalan (n + 1) (i + 1) - gosperCatalan (n + 1) i =
Nat.centralBinom i / (i + 1) * Nat.centralBinom (n - i) / (n - i + 1) := by
have l₁ : (i : ℚ) + 1 ≠ 0 := by norm_cast
have l₂ : (n : ℚ) - i + 1 ≠ 0 := by norm_cast
have h₁ := (mul_div_cancel_left₀ (↑(Nat.centralBinom (i + 1))) l₁).symm
have h₂ := (mul_div_cancel_left₀ (↑(Nat.centralBinom (n - i + 1))) l₂).symm
have h₃ : ((i : ℚ) + 1) * (i + 1).centralBinom = 2 * (2 * i + 1) * i.centralBinom :=
mod_cast Nat.succ_mul_centralBinom_succ i
have h₄ :
((n : ℚ) - i + 1) * (n - i + 1).centralBinom = 2 * (2 * (n - i) + 1) * (n - i).centralBinom :=
mod_cast Nat.succ_mul_centralBinom_succ (n - i)
simp only [gosperCatalan]
push_cast
rw [show n + 1 - i = n - i + 1 by rw [Nat.add_comm (n - i) 1, ← (Nat.add_sub_assoc h 1),
add_comm]]
rw [h₁, h₂, h₃, h₄]
field_simp
ring
private theorem gosper_catalan_sub_eq_central_binom_div (n : ℕ) : gosperCatalan (n + 1) (n + 1) -
gosperCatalan (n + 1) 0 = Nat.centralBinom (n + 1) / (n + 2) := by
have : (n : ℚ) + 1 ≠ 0 := by norm_cast
have : (n : ℚ) + 1 + 1 ≠ 0 := by norm_cast
have h : (n : ℚ) + 2 ≠ 0 := by norm_cast
simp only [gosperCatalan, Nat.sub_zero, Nat.centralBinom_zero, Nat.sub_self]
field_simp
ring
theorem catalan_eq_centralBinom_div (n : ℕ) : catalan n = n.centralBinom / (n + 1) := by
| suffices (catalan n : ℚ) = Nat.centralBinom n / (n + 1) by
have h := Nat.succ_dvd_centralBinom n
exact mod_cast this
induction n using Nat.caseStrongRecOn with
| zero => simp
| ind d hd =>
simp_rw [catalan_succ, Nat.cast_sum, Nat.cast_mul]
trans (∑ i : Fin d.succ, Nat.centralBinom i / (i + 1) *
| Mathlib/Combinatorics/Enumerative/Catalan.lean | 107 | 114 |
/-
Copyright (c) 2018 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison, Johan Commelin, Bhavik Mehta
-/
import Mathlib.CategoryTheory.Iso
import Mathlib.CategoryTheory.Functor.Category
import Mathlib.CategoryTheory.EqToHom
import Mathlib.CategoryTheory.Products.Unitor
/-!
# Comma categories
A comma category is a construction in category theory, which builds a category out of two functors
with a common codomain. Specifically, for functors `L : A ⥤ T` and `R : B ⥤ T`, an object in
`Comma L R` is a morphism `hom : L.obj left ⟶ R.obj right` for some objects `left : A` and
`right : B`, and a morphism in `Comma L R` between `hom : L.obj left ⟶ R.obj right` and
`hom' : L.obj left' ⟶ R.obj right'` is a commutative square
```
L.obj left ⟶ L.obj left'
| |
hom | | hom'
↓ ↓
R.obj right ⟶ R.obj right',
```
where the top and bottom morphism come from morphisms `left ⟶ left'` and `right ⟶ right'`,
respectively.
## Main definitions
* `Comma L R`: the comma category of the functors `L` and `R`.
* `Over X`: the over category of the object `X` (developed in `Over.lean`).
* `Under X`: the under category of the object `X` (also developed in `Over.lean`).
* `Arrow T`: the arrow category of the category `T` (developed in `Arrow.lean`).
## References
* <https://ncatlab.org/nlab/show/comma+category>
## Tags
comma, slice, coslice, over, under, arrow
-/
namespace CategoryTheory
open Category
-- declare the `v`'s first; see `CategoryTheory.Category` for an explanation
universe v₁ v₂ v₃ v₄ v₅ v₆ u₁ u₂ u₃ u₄ u₅ u₆
variable {A : Type u₁} [Category.{v₁} A]
variable {B : Type u₂} [Category.{v₂} B]
variable {T : Type u₃} [Category.{v₃} T]
variable {A' : Type u₄} [Category.{v₄} A']
variable {B' : Type u₅} [Category.{v₅} B']
variable {T' : Type u₆} [Category.{v₆} T']
/-- The objects of the comma category are triples of an object `left : A`, an object
`right : B` and a morphism `hom : L.obj left ⟶ R.obj right`. -/
structure Comma (L : A ⥤ T) (R : B ⥤ T) : Type max u₁ u₂ v₃ where
/-- The left subobject -/
left : A
/-- The right subobject -/
right : B
/-- A morphism from `L.obj left` to `R.obj right` -/
hom : L.obj left ⟶ R.obj right
-- Satisfying the inhabited linter
instance Comma.inhabited [Inhabited T] : Inhabited (Comma (𝟭 T) (𝟭 T)) where
default :=
{ left := default
right := default
hom := 𝟙 default }
variable {L : A ⥤ T} {R : B ⥤ T}
/-- A morphism between two objects in the comma category is a commutative square connecting the
morphisms coming from the two objects using morphisms in the image of the functors `L` and `R`.
-/
@[ext]
structure CommaMorphism (X Y : Comma L R) where
/-- Morphism on left objects -/
left : X.left ⟶ Y.left
/-- Morphism on right objects -/
right : X.right ⟶ Y.right
w : L.map left ≫ Y.hom = X.hom ≫ R.map right := by aesop_cat
-- Satisfying the inhabited linter
instance CommaMorphism.inhabited [Inhabited (Comma L R)] :
Inhabited (CommaMorphism (default : Comma L R) default) :=
⟨{ left := 𝟙 _, right := 𝟙 _}⟩
attribute [reassoc (attr := simp)] CommaMorphism.w
instance commaCategory : Category (Comma L R) where
Hom X Y := CommaMorphism X Y
id X :=
{ left := 𝟙 X.left
right := 𝟙 X.right }
comp f g :=
{ left := f.left ≫ g.left
right := f.right ≫ g.right }
namespace Comma
section
variable {X Y Z : Comma L R} {f : X ⟶ Y} {g : Y ⟶ Z}
@[ext]
lemma hom_ext (f g : X ⟶ Y) (h₁ : f.left = g.left) (h₂ : f.right = g.right) : f = g :=
CommaMorphism.ext h₁ h₂
@[simp]
theorem id_left : (𝟙 X : CommaMorphism X X).left = 𝟙 X.left :=
rfl
@[simp]
theorem id_right : (𝟙 X : CommaMorphism X X).right = 𝟙 X.right :=
rfl
@[simp]
theorem comp_left : (f ≫ g).left = f.left ≫ g.left :=
rfl
@[simp]
theorem comp_right : (f ≫ g).right = f.right ≫ g.right :=
rfl
end
variable (L) (R)
/-- The functor sending an object `X` in the comma category to `X.left`. -/
@[simps]
def fst : Comma L R ⥤ A where
obj X := X.left
map f := f.left
/-- The functor sending an object `X` in the comma category to `X.right`. -/
@[simps]
def snd : Comma L R ⥤ B where
obj X := X.right
map f := f.right
/-- We can interpret the commutative square constituting a morphism in the comma category as a
natural transformation between the functors `fst ⋙ L` and `snd ⋙ R` from the comma category
to `T`, where the components are given by the morphism that constitutes an object of the comma
category. -/
@[simps]
def natTrans : fst L R ⋙ L ⟶ snd L R ⋙ R where app X := X.hom
@[simp]
theorem eqToHom_left (X Y : Comma L R) (H : X = Y) :
CommaMorphism.left (eqToHom H) = eqToHom (by cases H; rfl) := by
cases H
rfl
@[simp]
theorem eqToHom_right (X Y : Comma L R) (H : X = Y) :
CommaMorphism.right (eqToHom H) = eqToHom (by cases H; rfl) := by
| cases H
rfl
section
| Mathlib/CategoryTheory/Comma/Basic.lean | 166 | 169 |
/-
Copyright (c) 2020 Kim Morrison. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Kim Morrison
-/
import Mathlib.Algebra.Group.TypeTags.Finite
import Mathlib.Algebra.MonoidAlgebra.Basic
import Mathlib.LinearAlgebra.Basis.VectorSpace
import Mathlib.RingTheory.SimpleModule.Basic
/-!
# Maschke's theorem
We prove **Maschke's theorem** for finite groups,
in the formulation that every submodule of a `k[G]` module has a complement,
when `k` is a field with `Fintype.card G` invertible in `k`.
We do the core computation in greater generality.
For any commutative ring `k` in which `Fintype.card G` is invertible,
and a `k[G]`-linear map `i : V → W` which admits a `k`-linear retraction `π`,
we produce a `k[G]`-linear retraction by
taking the average over `G` of the conjugates of `π`.
## Implementation Notes
* These results assume `IsUnit (Fintype.card G : k)` which is equivalent to the more
familiar `¬(ringChar k ∣ Fintype.card G)`.
## Future work
It's not so far to give the usual statement, that every finite dimensional representation
of a finite group is semisimple (i.e. a direct sum of irreducibles).
-/
universe u v w
noncomputable section
open Module MonoidAlgebra
/-!
We now do the key calculation in Maschke's theorem.
Given `V → W`, an inclusion of `k[G]` modules,
assume we have some retraction `π` (i.e. `∀ v, π (i v) = v`),
just as a `k`-linear map.
(When `k` is a field, this will be available cheaply, by choosing a basis.)
We now construct a retraction of the inclusion as a `k[G]`-linear map,
by the formula
$$ \frac{1}{|G|} \sum_{g \in G} g⁻¹ • π(g • -). $$
-/
namespace LinearMap
-- At first we work with any `[CommRing k]`, and add the assumption that
-- `IsUnit (Fintype.card G : k)` when it is required.
variable {k : Type u} [CommRing k] {G : Type u} [Group G]
variable {V : Type v} [AddCommGroup V] [Module k V] [Module (MonoidAlgebra k G) V]
variable [IsScalarTower k (MonoidAlgebra k G) V]
variable {W : Type w} [AddCommGroup W] [Module k W] [Module (MonoidAlgebra k G) W]
variable [IsScalarTower k (MonoidAlgebra k G) W]
variable (π : W →ₗ[k] V)
/-- We define the conjugate of `π` by `g`, as a `k`-linear map. -/
def conjugate (g : G) : W →ₗ[k] V :=
GroupSMul.linearMap k V g⁻¹ ∘ₗ π ∘ₗ GroupSMul.linearMap k W g
theorem conjugate_apply (g : G) (v : W) :
π.conjugate g v = MonoidAlgebra.single g⁻¹ (1 : k) • π (MonoidAlgebra.single g (1 : k) • v) :=
rfl
variable (i : V →ₗ[MonoidAlgebra k G] W)
section
theorem conjugate_i (h : ∀ v : V, π (i v) = v) (g : G) (v : V) :
(conjugate π g : W → V) (i v) = v := by
rw [conjugate_apply, ← i.map_smul, h, ← mul_smul, single_mul_single, mul_one, inv_mul_cancel,
| ← one_def, one_smul]
end
| Mathlib/RepresentationTheory/Maschke.lean | 81 | 83 |
/-
Copyright (c) 2021 Anne Baanen. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Anne Baanen, Ashvni Narayanan
-/
import Mathlib.FieldTheory.RatFunc.Degree
import Mathlib.RingTheory.DedekindDomain.IntegralClosure
import Mathlib.RingTheory.IntegralClosure.IntegrallyClosed
import Mathlib.Topology.Algebra.Valued.ValuedField
/-!
# Function fields
This file defines a function field and the ring of integers corresponding to it.
## Main definitions
- `FunctionField Fq F` states that `F` is a function field over the (finite) field `Fq`,
i.e. it is a finite extension of the field of rational functions in one variable over `Fq`.
- `FunctionField.ringOfIntegers` defines the ring of integers corresponding to a function field
as the integral closure of `Fq[X]` in the function field.
- `FunctionField.inftyValuation` : The place at infinity on `Fq(t)` is the nonarchimedean
valuation on `Fq(t)` with uniformizer `1/t`.
- `FunctionField.FqtInfty` : The completion `Fq((t⁻¹))` of `Fq(t)` with respect to the
valuation at infinity.
## Implementation notes
The definitions that involve a field of fractions choose a canonical field of fractions,
but are independent of that choice. We also omit assumptions like `Finite Fq` or
`IsScalarTower Fq[X] (FractionRing Fq[X]) F` in definitions,
adding them back in lemmas when they are needed.
## References
* [D. Marcus, *Number Fields*][marcus1977number]
* [J.W.S. Cassels, A. Fröhlich, *Algebraic Number Theory*][cassels1967algebraic]
* [P. Samuel, *Algebraic Theory of Numbers*][samuel1967]
## Tags
function field, ring of integers
-/
noncomputable section
open scoped nonZeroDivisors Polynomial Multiplicative
variable (Fq F : Type*) [Field Fq] [Field F]
/-- `F` is a function field over the finite field `Fq` if it is a finite
extension of the field of rational functions in one variable over `Fq`.
Note that `F` can be a function field over multiple, non-isomorphic, `Fq`.
-/
abbrev FunctionField [Algebra (RatFunc Fq) F] : Prop :=
FiniteDimensional (RatFunc Fq) F
/-- `F` is a function field over `Fq` iff it is a finite extension of `Fq(t)`. -/
theorem functionField_iff (Fqt : Type*) [Field Fqt] [Algebra Fq[X] Fqt]
[IsFractionRing Fq[X] Fqt] [Algebra (RatFunc Fq) F] [Algebra Fqt F] [Algebra Fq[X] F]
[IsScalarTower Fq[X] Fqt F] [IsScalarTower Fq[X] (RatFunc Fq) F] :
FunctionField Fq F ↔ FiniteDimensional Fqt F := by
let e := IsLocalization.algEquiv Fq[X]⁰ (RatFunc Fq) Fqt
have : ∀ (c) (x : F), e c • x = c • x := by
intro c x
rw [Algebra.smul_def, Algebra.smul_def]
congr
refine congr_fun (f := fun c => algebraMap Fqt F (e c)) ?_ c
refine IsLocalization.ext (nonZeroDivisors Fq[X]) _ _ ?_ ?_ ?_ ?_ ?_ <;> intros <;>
simp only [map_one, map_mul, AlgEquiv.commutes, ← IsScalarTower.algebraMap_apply]
constructor <;> intro h
· let b := Module.finBasis (RatFunc Fq) F
exact FiniteDimensional.of_fintype_basis (b.mapCoeffs e this)
· let b := Module.finBasis Fqt F
refine FiniteDimensional.of_fintype_basis (b.mapCoeffs e.symm ?_)
intro c x; convert (this (e.symm c) x).symm; simp only [e.apply_symm_apply]
namespace FunctionField
theorem algebraMap_injective [Algebra Fq[X] F] [Algebra (RatFunc Fq) F]
[IsScalarTower Fq[X] (RatFunc Fq) F] : Function.Injective (⇑(algebraMap Fq[X] F)) := by
rw [IsScalarTower.algebraMap_eq Fq[X] (RatFunc Fq) F]
exact (algebraMap (RatFunc Fq) F).injective.comp (IsFractionRing.injective Fq[X] (RatFunc Fq))
@[deprecated (since := "2025-03-03")]
alias _root_.algebraMap_injective := FunctionField.algebraMap_injective
/-- The function field analogue of `NumberField.ringOfIntegers`:
`FunctionField.ringOfIntegers Fq Fqt F` is the integral closure of `Fq[t]` in `F`.
We don't actually assume `F` is a function field over `Fq` in the definition,
only when proving its properties.
-/
def ringOfIntegers [Algebra Fq[X] F] :=
integralClosure Fq[X] F
namespace ringOfIntegers
variable [Algebra Fq[X] F]
instance : IsDomain (ringOfIntegers Fq F) :=
(ringOfIntegers Fq F).isDomain
instance : IsIntegralClosure (ringOfIntegers Fq F) Fq[X] F :=
integralClosure.isIntegralClosure _ _
variable [Algebra (RatFunc Fq) F] [IsScalarTower Fq[X] (RatFunc Fq) F]
theorem algebraMap_injective : Function.Injective (⇑(algebraMap Fq[X] (ringOfIntegers Fq F))) := by
have hinj : Function.Injective (⇑(algebraMap Fq[X] F)) := by
rw [IsScalarTower.algebraMap_eq Fq[X] (RatFunc Fq) F]
exact (algebraMap (RatFunc Fq) F).injective.comp (IsFractionRing.injective Fq[X] (RatFunc Fq))
rw [injective_iff_map_eq_zero (algebraMap Fq[X] (↥(ringOfIntegers Fq F)))]
intro p hp
rw [← Subtype.coe_inj, Subalgebra.coe_zero] at hp
rw [injective_iff_map_eq_zero (algebraMap Fq[X] F)] at hinj
exact hinj p hp
theorem not_isField : ¬IsField (ringOfIntegers Fq F) := by
simpa [← (IsIntegralClosure.isIntegral_algebra Fq[X] F).isField_iff_isField
(algebraMap_injective Fq F)] using
Polynomial.not_isField Fq
variable [FunctionField Fq F]
instance : IsFractionRing (ringOfIntegers Fq F) F :=
integralClosure.isFractionRing_of_finite_extension (RatFunc Fq) F
instance : IsIntegrallyClosed (ringOfIntegers Fq F) :=
integralClosure.isIntegrallyClosedOfFiniteExtension (RatFunc Fq)
instance [Algebra.IsSeparable (RatFunc Fq) F] : IsNoetherian Fq[X] (ringOfIntegers Fq F) :=
IsIntegralClosure.isNoetherian _ (RatFunc Fq) F _
instance [Algebra.IsSeparable (RatFunc Fq) F] : IsDedekindDomain (ringOfIntegers Fq F) :=
IsIntegralClosure.isDedekindDomain Fq[X] (RatFunc Fq) F _
end ringOfIntegers
/-! ### The place at infinity on Fq(t) -/
section InftyValuation
variable [DecidableEq (RatFunc Fq)]
/-- The valuation at infinity is the nonarchimedean valuation on `Fq(t)` with uniformizer `1/t`.
Explicitly, if `f/g ∈ Fq(t)` is a nonzero quotient of polynomials, its valuation at infinity is
`Multiplicative.ofAdd(degree(f) - degree(g))`. -/
def inftyValuationDef (r : RatFunc Fq) : ℤₘ₀ :=
if r = 0 then 0 else ↑(Multiplicative.ofAdd r.intDegree)
theorem InftyValuation.map_zero' : inftyValuationDef Fq 0 = 0 :=
if_pos rfl
theorem InftyValuation.map_one' : inftyValuationDef Fq 1 = 1 :=
(if_neg one_ne_zero).trans <| by rw [RatFunc.intDegree_one, ofAdd_zero, WithZero.coe_one]
theorem InftyValuation.map_mul' (x y : RatFunc Fq) :
inftyValuationDef Fq (x * y) = inftyValuationDef Fq x * inftyValuationDef Fq y := by
rw [inftyValuationDef, inftyValuationDef, inftyValuationDef]
by_cases hx : x = 0
· rw [hx, zero_mul, if_pos (Eq.refl _), zero_mul]
· by_cases hy : y = 0
· rw [hy, mul_zero, if_pos (Eq.refl _), mul_zero]
· rw [if_neg hx, if_neg hy, if_neg (mul_ne_zero hx hy), ← WithZero.coe_mul, WithZero.coe_inj,
← ofAdd_add, RatFunc.intDegree_mul hx hy]
theorem InftyValuation.map_add_le_max' (x y : RatFunc Fq) :
inftyValuationDef Fq (x + y) ≤ max (inftyValuationDef Fq x) (inftyValuationDef Fq y) := by
by_cases hx : x = 0
· rw [hx, zero_add]
conv_rhs => rw [inftyValuationDef, if_pos (Eq.refl _)]
rw [max_eq_right (WithZero.zero_le (inftyValuationDef Fq y))]
· by_cases hy : y = 0
· rw [hy, add_zero]
conv_rhs => rw [max_comm, inftyValuationDef, if_pos (Eq.refl _)]
rw [max_eq_right (WithZero.zero_le (inftyValuationDef Fq x))]
· by_cases hxy : x + y = 0
· rw [inftyValuationDef, if_pos hxy]; exact zero_le'
· rw [inftyValuationDef, inftyValuationDef, inftyValuationDef, if_neg hx, if_neg hy,
if_neg hxy]
rw [le_max_iff, WithZero.coe_le_coe, Multiplicative.ofAdd_le, WithZero.coe_le_coe,
Multiplicative.ofAdd_le, ← le_max_iff]
exact RatFunc.intDegree_add_le hy hxy
@[simp]
theorem inftyValuation_of_nonzero {x : RatFunc Fq} (hx : x ≠ 0) :
inftyValuationDef Fq x = Multiplicative.ofAdd x.intDegree := by
rw [inftyValuationDef, if_neg hx]
/-- The valuation at infinity on `Fq(t)`. -/
def inftyValuation : Valuation (RatFunc Fq) ℤₘ₀ where
toFun := inftyValuationDef Fq
map_zero' := InftyValuation.map_zero' Fq
map_one' := InftyValuation.map_one' Fq
map_mul' := InftyValuation.map_mul' Fq
map_add_le_max' := InftyValuation.map_add_le_max' Fq
@[simp]
theorem inftyValuation_apply {x : RatFunc Fq} : inftyValuation Fq x = inftyValuationDef Fq x :=
rfl
@[simp]
theorem inftyValuation.C {k : Fq} (hk : k ≠ 0) :
inftyValuationDef Fq (RatFunc.C k) = Multiplicative.ofAdd (0 : ℤ) := by
have hCk : RatFunc.C k ≠ 0 := (map_ne_zero _).mpr hk
rw [inftyValuationDef, if_neg hCk, RatFunc.intDegree_C]
@[simp]
theorem inftyValuation.X : inftyValuationDef Fq RatFunc.X = Multiplicative.ofAdd (1 : ℤ) := by
rw [inftyValuationDef, if_neg RatFunc.X_ne_zero, RatFunc.intDegree_X]
-- Dropped attribute `@[simp]` due to issue described here:
-- https://leanprover.zulipchat.com/#narrow/channel/287929-mathlib4/topic/.60synthInstance.2EmaxHeartbeats.60.20error.20but.20only.20in.20.60simpNF.60
theorem inftyValuation.polynomial {p : Fq[X]} (hp : p ≠ 0) :
inftyValuationDef Fq (algebraMap Fq[X] (RatFunc Fq) p) =
Multiplicative.ofAdd (p.natDegree : ℤ) := by
have hp' : algebraMap Fq[X] (RatFunc Fq) p ≠ 0 := by simpa
rw [inftyValuationDef, if_neg hp', RatFunc.intDegree_polynomial]
/-- The valued field `Fq(t)` with the valuation at infinity. -/
def inftyValuedFqt : Valued (RatFunc Fq) ℤₘ₀ :=
Valued.mk' <| inftyValuation Fq
theorem inftyValuedFqt.def {x : RatFunc Fq} :
@Valued.v (RatFunc Fq) _ _ _ (inftyValuedFqt Fq) x = inftyValuationDef Fq x :=
rfl
/-- The completion `Fq((t⁻¹))` of `Fq(t)` with respect to the valuation at infinity. -/
def FqtInfty :=
@UniformSpace.Completion (RatFunc Fq) <| (inftyValuedFqt Fq).toUniformSpace
| instance : Field (FqtInfty Fq) :=
letI := inftyValuedFqt Fq
UniformSpace.Completion.instField
instance : Inhabited (FqtInfty Fq) :=
⟨(0 : FqtInfty Fq)⟩
| Mathlib/NumberTheory/FunctionField.lean | 232 | 237 |
/-
Copyright (c) 2017 Johannes Hölzl. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Johannes Hölzl, Jeremy Avigad
-/
import Mathlib.Algebra.Group.Basic
import Mathlib.Algebra.Notation.Pi
import Mathlib.Data.Set.Lattice
import Mathlib.Order.Filter.Defs
/-!
# Theory of filters on sets
A *filter* on a type `α` is a collection of sets of `α` which contains the whole `α`,
is upwards-closed, and is stable under intersection. They are mostly used to
abstract two related kinds of ideas:
* *limits*, including finite or infinite limits of sequences, finite or infinite limits of functions
at a point or at infinity, etc...
* *things happening eventually*, including things happening for large enough `n : ℕ`, or near enough
a point `x`, or for close enough pairs of points, or things happening almost everywhere in the
sense of measure theory. Dually, filters can also express the idea of *things happening often*:
for arbitrarily large `n`, or at a point in any neighborhood of given a point etc...
## Main definitions
In this file, we endow `Filter α` it with a complete lattice structure.
This structure is lifted from the lattice structure on `Set (Set X)` using the Galois
insertion which maps a filter to its elements in one direction, and an arbitrary set of sets to
the smallest filter containing it in the other direction.
We also prove `Filter` is a monadic functor, with a push-forward operation
`Filter.map` and a pull-back operation `Filter.comap` that form a Galois connections for the
order on filters.
The examples of filters appearing in the description of the two motivating ideas are:
* `(Filter.atTop : Filter ℕ)` : made of sets of `ℕ` containing `{n | n ≥ N}` for some `N`
* `𝓝 x` : made of neighborhoods of `x` in a topological space (defined in topology.basic)
* `𝓤 X` : made of entourages of a uniform space (those space are generalizations of metric spaces
defined in `Mathlib/Topology/UniformSpace/Basic.lean`)
* `MeasureTheory.ae` : made of sets whose complement has zero measure with respect to `μ`
(defined in `Mathlib/MeasureTheory/OuterMeasure/AE`)
The predicate "happening eventually" is `Filter.Eventually`, and "happening often" is
`Filter.Frequently`, whose definitions are immediate after `Filter` is defined (but they come
rather late in this file in order to immediately relate them to the lattice structure).
## Notations
* `∀ᶠ x in f, p x` : `f.Eventually p`;
* `∃ᶠ x in f, p x` : `f.Frequently p`;
* `f =ᶠ[l] g` : `∀ᶠ x in l, f x = g x`;
* `f ≤ᶠ[l] g` : `∀ᶠ x in l, f x ≤ g x`;
* `𝓟 s` : `Filter.Principal s`, localized in `Filter`.
## References
* [N. Bourbaki, *General Topology*][bourbaki1966]
Important note: Bourbaki requires that a filter on `X` cannot contain all sets of `X`, which
we do *not* require. This gives `Filter X` better formal properties, in particular a bottom element
`⊥` for its lattice structure, at the cost of including the assumption
`[NeBot f]` in a number of lemmas and definitions.
-/
assert_not_exists OrderedSemiring Fintype
open Function Set Order
open scoped symmDiff
universe u v w x y
namespace Filter
variable {α : Type u} {f g : Filter α} {s t : Set α}
instance inhabitedMem : Inhabited { s : Set α // s ∈ f } :=
⟨⟨univ, f.univ_sets⟩⟩
theorem filter_eq_iff : f = g ↔ f.sets = g.sets :=
⟨congr_arg _, filter_eq⟩
@[simp] theorem sets_subset_sets : f.sets ⊆ g.sets ↔ g ≤ f := .rfl
@[simp] theorem sets_ssubset_sets : f.sets ⊂ g.sets ↔ g < f := .rfl
/-- An extensionality lemma that is useful for filters with good lemmas about `sᶜ ∈ f` (e.g.,
`Filter.comap`, `Filter.coprod`, `Filter.Coprod`, `Filter.cofinite`). -/
protected theorem coext (h : ∀ s, sᶜ ∈ f ↔ sᶜ ∈ g) : f = g :=
Filter.ext <| compl_surjective.forall.2 h
instance : Trans (· ⊇ ·) ((· ∈ ·) : Set α → Filter α → Prop) (· ∈ ·) where
trans h₁ h₂ := mem_of_superset h₂ h₁
instance : Trans Membership.mem (· ⊆ ·) (Membership.mem : Filter α → Set α → Prop) where
trans h₁ h₂ := mem_of_superset h₁ h₂
@[simp]
theorem inter_mem_iff {s t : Set α} : s ∩ t ∈ f ↔ s ∈ f ∧ t ∈ f :=
⟨fun h => ⟨mem_of_superset h inter_subset_left, mem_of_superset h inter_subset_right⟩,
and_imp.2 inter_mem⟩
theorem diff_mem {s t : Set α} (hs : s ∈ f) (ht : tᶜ ∈ f) : s \ t ∈ f :=
inter_mem hs ht
theorem congr_sets (h : { x | x ∈ s ↔ x ∈ t } ∈ f) : s ∈ f ↔ t ∈ f :=
⟨fun hs => mp_mem hs (mem_of_superset h fun _ => Iff.mp), fun hs =>
mp_mem hs (mem_of_superset h fun _ => Iff.mpr)⟩
lemma copy_eq {S} (hmem : ∀ s, s ∈ S ↔ s ∈ f) : f.copy S hmem = f := Filter.ext hmem
/-- Weaker version of `Filter.biInter_mem` that assumes `Subsingleton β` rather than `Finite β`. -/
theorem biInter_mem' {β : Type v} {s : β → Set α} {is : Set β} (hf : is.Subsingleton) :
(⋂ i ∈ is, s i) ∈ f ↔ ∀ i ∈ is, s i ∈ f := by
apply Subsingleton.induction_on hf <;> simp
/-- Weaker version of `Filter.iInter_mem` that assumes `Subsingleton β` rather than `Finite β`. -/
theorem iInter_mem' {β : Sort v} {s : β → Set α} [Subsingleton β] :
(⋂ i, s i) ∈ f ↔ ∀ i, s i ∈ f := by
rw [← sInter_range, sInter_eq_biInter, biInter_mem' (subsingleton_range s), forall_mem_range]
theorem exists_mem_subset_iff : (∃ t ∈ f, t ⊆ s) ↔ s ∈ f :=
⟨fun ⟨_, ht, ts⟩ => mem_of_superset ht ts, fun hs => ⟨s, hs, Subset.rfl⟩⟩
theorem monotone_mem {f : Filter α} : Monotone fun s => s ∈ f := fun _ _ hst h =>
mem_of_superset h hst
theorem exists_mem_and_iff {P : Set α → Prop} {Q : Set α → Prop} (hP : Antitone P)
(hQ : Antitone Q) : ((∃ u ∈ f, P u) ∧ ∃ u ∈ f, Q u) ↔ ∃ u ∈ f, P u ∧ Q u := by
constructor
· rintro ⟨⟨u, huf, hPu⟩, v, hvf, hQv⟩
exact
⟨u ∩ v, inter_mem huf hvf, hP inter_subset_left hPu, hQ inter_subset_right hQv⟩
· rintro ⟨u, huf, hPu, hQu⟩
exact ⟨⟨u, huf, hPu⟩, u, huf, hQu⟩
theorem forall_in_swap {β : Type*} {p : Set α → β → Prop} :
(∀ a ∈ f, ∀ (b), p a b) ↔ ∀ (b), ∀ a ∈ f, p a b :=
Set.forall_in_swap
end Filter
namespace Filter
variable {α : Type u} {β : Type v} {γ : Type w} {δ : Type*} {ι : Sort x}
theorem mem_principal_self (s : Set α) : s ∈ 𝓟 s := Subset.rfl
section Lattice
variable {f g : Filter α} {s t : Set α}
protected theorem not_le : ¬f ≤ g ↔ ∃ s ∈ g, s ∉ f := by simp_rw [le_def, not_forall, exists_prop]
/-- `GenerateSets g s`: `s` is in the filter closure of `g`. -/
inductive GenerateSets (g : Set (Set α)) : Set α → Prop
| basic {s : Set α} : s ∈ g → GenerateSets g s
| univ : GenerateSets g univ
| superset {s t : Set α} : GenerateSets g s → s ⊆ t → GenerateSets g t
| inter {s t : Set α} : GenerateSets g s → GenerateSets g t → GenerateSets g (s ∩ t)
/-- `generate g` is the largest filter containing the sets `g`. -/
def generate (g : Set (Set α)) : Filter α where
sets := {s | GenerateSets g s}
univ_sets := GenerateSets.univ
sets_of_superset := GenerateSets.superset
inter_sets := GenerateSets.inter
lemma mem_generate_of_mem {s : Set <| Set α} {U : Set α} (h : U ∈ s) :
U ∈ generate s := GenerateSets.basic h
theorem le_generate_iff {s : Set (Set α)} {f : Filter α} : f ≤ generate s ↔ s ⊆ f.sets :=
Iff.intro (fun h _ hu => h <| GenerateSets.basic <| hu) fun h _ hu =>
hu.recOn (fun h' => h h') univ_mem (fun _ hxy hx => mem_of_superset hx hxy) fun _ _ hx hy =>
inter_mem hx hy
@[simp] lemma generate_singleton (s : Set α) : generate {s} = 𝓟 s :=
le_antisymm (fun _t ht ↦ mem_of_superset (mem_generate_of_mem <| mem_singleton _) ht) <|
le_generate_iff.2 <| singleton_subset_iff.2 Subset.rfl
/-- `mkOfClosure s hs` constructs a filter on `α` whose elements set is exactly
`s : Set (Set α)`, provided one gives the assumption `hs : (generate s).sets = s`. -/
protected def mkOfClosure (s : Set (Set α)) (hs : (generate s).sets = s) : Filter α where
sets := s
univ_sets := hs ▸ univ_mem
sets_of_superset := hs ▸ mem_of_superset
inter_sets := hs ▸ inter_mem
theorem mkOfClosure_sets {s : Set (Set α)} {hs : (generate s).sets = s} :
Filter.mkOfClosure s hs = generate s :=
Filter.ext fun u =>
show u ∈ (Filter.mkOfClosure s hs).sets ↔ u ∈ (generate s).sets from hs.symm ▸ Iff.rfl
/-- Galois insertion from sets of sets into filters. -/
def giGenerate (α : Type*) :
@GaloisInsertion (Set (Set α)) (Filter α)ᵒᵈ _ _ Filter.generate Filter.sets where
gc _ _ := le_generate_iff
le_l_u _ _ h := GenerateSets.basic h
choice s hs := Filter.mkOfClosure s (le_antisymm hs <| le_generate_iff.1 <| le_rfl)
choice_eq _ _ := mkOfClosure_sets
theorem mem_inf_iff {f g : Filter α} {s : Set α} : s ∈ f ⊓ g ↔ ∃ t₁ ∈ f, ∃ t₂ ∈ g, s = t₁ ∩ t₂ :=
Iff.rfl
theorem mem_inf_of_left {f g : Filter α} {s : Set α} (h : s ∈ f) : s ∈ f ⊓ g :=
⟨s, h, univ, univ_mem, (inter_univ s).symm⟩
theorem mem_inf_of_right {f g : Filter α} {s : Set α} (h : s ∈ g) : s ∈ f ⊓ g :=
⟨univ, univ_mem, s, h, (univ_inter s).symm⟩
theorem inter_mem_inf {α : Type u} {f g : Filter α} {s t : Set α} (hs : s ∈ f) (ht : t ∈ g) :
s ∩ t ∈ f ⊓ g :=
⟨s, hs, t, ht, rfl⟩
theorem mem_inf_of_inter {f g : Filter α} {s t u : Set α} (hs : s ∈ f) (ht : t ∈ g)
(h : s ∩ t ⊆ u) : u ∈ f ⊓ g :=
mem_of_superset (inter_mem_inf hs ht) h
theorem mem_inf_iff_superset {f g : Filter α} {s : Set α} :
s ∈ f ⊓ g ↔ ∃ t₁ ∈ f, ∃ t₂ ∈ g, t₁ ∩ t₂ ⊆ s :=
⟨fun ⟨t₁, h₁, t₂, h₂, Eq⟩ => ⟨t₁, h₁, t₂, h₂, Eq ▸ Subset.rfl⟩, fun ⟨_, h₁, _, h₂, sub⟩ =>
mem_inf_of_inter h₁ h₂ sub⟩
section CompleteLattice
/-- Complete lattice structure on `Filter α`. -/
instance instCompleteLatticeFilter : CompleteLattice (Filter α) where
inf a b := min a b
sup a b := max a b
le_sup_left _ _ _ h := h.1
le_sup_right _ _ _ h := h.2
sup_le _ _ _ h₁ h₂ _ h := ⟨h₁ h, h₂ h⟩
inf_le_left _ _ _ := mem_inf_of_left
inf_le_right _ _ _ := mem_inf_of_right
le_inf := fun _ _ _ h₁ h₂ _s ⟨_a, ha, _b, hb, hs⟩ => hs.symm ▸ inter_mem (h₁ ha) (h₂ hb)
le_sSup _ _ h₁ _ h₂ := h₂ h₁
sSup_le _ _ h₁ _ h₂ _ h₃ := h₁ _ h₃ h₂
sInf_le _ _ h₁ _ h₂ := by rw [← Filter.sSup_lowerBounds]; exact fun _ h₃ ↦ h₃ h₁ h₂
le_sInf _ _ h₁ _ h₂ := by rw [← Filter.sSup_lowerBounds] at h₂; exact h₂ h₁
le_top _ _ := univ_mem'
bot_le _ _ _ := trivial
instance : Inhabited (Filter α) := ⟨⊥⟩
end CompleteLattice
theorem NeBot.ne {f : Filter α} (hf : NeBot f) : f ≠ ⊥ := hf.ne'
@[simp] theorem not_neBot {f : Filter α} : ¬f.NeBot ↔ f = ⊥ := neBot_iff.not_left
theorem NeBot.mono {f g : Filter α} (hf : NeBot f) (hg : f ≤ g) : NeBot g :=
⟨ne_bot_of_le_ne_bot hf.1 hg⟩
theorem neBot_of_le {f g : Filter α} [hf : NeBot f] (hg : f ≤ g) : NeBot g :=
hf.mono hg
@[simp] theorem sup_neBot {f g : Filter α} : NeBot (f ⊔ g) ↔ NeBot f ∨ NeBot g := by
simp only [neBot_iff, not_and_or, Ne, sup_eq_bot_iff]
theorem not_disjoint_self_iff : ¬Disjoint f f ↔ f.NeBot := by rw [disjoint_self, neBot_iff]
theorem bot_sets_eq : (⊥ : Filter α).sets = univ := rfl
/-- Either `f = ⊥` or `Filter.NeBot f`. This is a version of `eq_or_ne` that uses `Filter.NeBot`
as the second alternative, to be used as an instance. -/
theorem eq_or_neBot (f : Filter α) : f = ⊥ ∨ NeBot f := (eq_or_ne f ⊥).imp_right NeBot.mk
theorem sup_sets_eq {f g : Filter α} : (f ⊔ g).sets = f.sets ∩ g.sets :=
(giGenerate α).gc.u_inf
theorem sSup_sets_eq {s : Set (Filter α)} : (sSup s).sets = ⋂ f ∈ s, (f : Filter α).sets :=
(giGenerate α).gc.u_sInf
theorem iSup_sets_eq {f : ι → Filter α} : (iSup f).sets = ⋂ i, (f i).sets :=
(giGenerate α).gc.u_iInf
theorem generate_empty : Filter.generate ∅ = (⊤ : Filter α) :=
(giGenerate α).gc.l_bot
theorem generate_univ : Filter.generate univ = (⊥ : Filter α) :=
bot_unique fun _ _ => GenerateSets.basic (mem_univ _)
theorem generate_union {s t : Set (Set α)} :
Filter.generate (s ∪ t) = Filter.generate s ⊓ Filter.generate t :=
(giGenerate α).gc.l_sup
theorem generate_iUnion {s : ι → Set (Set α)} :
Filter.generate (⋃ i, s i) = ⨅ i, Filter.generate (s i) :=
(giGenerate α).gc.l_iSup
@[simp]
theorem mem_sup {f g : Filter α} {s : Set α} : s ∈ f ⊔ g ↔ s ∈ f ∧ s ∈ g :=
Iff.rfl
theorem union_mem_sup {f g : Filter α} {s t : Set α} (hs : s ∈ f) (ht : t ∈ g) : s ∪ t ∈ f ⊔ g :=
⟨mem_of_superset hs subset_union_left, mem_of_superset ht subset_union_right⟩
@[simp]
theorem mem_iSup {x : Set α} {f : ι → Filter α} : x ∈ iSup f ↔ ∀ i, x ∈ f i := by
simp only [← Filter.mem_sets, iSup_sets_eq, mem_iInter]
@[simp]
theorem iSup_neBot {f : ι → Filter α} : (⨆ i, f i).NeBot ↔ ∃ i, (f i).NeBot := by
simp [neBot_iff]
theorem iInf_eq_generate (s : ι → Filter α) : iInf s = generate (⋃ i, (s i).sets) :=
eq_of_forall_le_iff fun _ ↦ by simp [le_generate_iff]
theorem mem_iInf_of_mem {f : ι → Filter α} (i : ι) {s} (hs : s ∈ f i) : s ∈ ⨅ i, f i :=
iInf_le f i hs
@[simp]
theorem le_principal_iff {s : Set α} {f : Filter α} : f ≤ 𝓟 s ↔ s ∈ f :=
⟨fun h => h Subset.rfl, fun hs _ ht => mem_of_superset hs ht⟩
theorem Iic_principal (s : Set α) : Iic (𝓟 s) = { l | s ∈ l } :=
Set.ext fun _ => le_principal_iff
theorem principal_mono {s t : Set α} : 𝓟 s ≤ 𝓟 t ↔ s ⊆ t := by
simp only [le_principal_iff, mem_principal]
@[gcongr] alias ⟨_, _root_.GCongr.filter_principal_mono⟩ := principal_mono
@[mono]
theorem monotone_principal : Monotone (𝓟 : Set α → Filter α) := fun _ _ => principal_mono.2
@[simp] theorem principal_eq_iff_eq {s t : Set α} : 𝓟 s = 𝓟 t ↔ s = t := by
simp only [le_antisymm_iff, le_principal_iff, mem_principal]; rfl
@[simp] theorem join_principal_eq_sSup {s : Set (Filter α)} : join (𝓟 s) = sSup s := rfl
@[simp] theorem principal_univ : 𝓟 (univ : Set α) = ⊤ :=
top_unique <| by simp only [le_principal_iff, mem_top, eq_self_iff_true]
@[simp]
theorem principal_empty : 𝓟 (∅ : Set α) = ⊥ :=
bot_unique fun _ _ => empty_subset _
theorem generate_eq_biInf (S : Set (Set α)) : generate S = ⨅ s ∈ S, 𝓟 s :=
eq_of_forall_le_iff fun f => by simp [le_generate_iff, le_principal_iff, subset_def]
/-! ### Lattice equations -/
theorem empty_mem_iff_bot {f : Filter α} : ∅ ∈ f ↔ f = ⊥ :=
⟨fun h => bot_unique fun s _ => mem_of_superset h (empty_subset s), fun h => h.symm ▸ mem_bot⟩
theorem nonempty_of_mem {f : Filter α} [hf : NeBot f] {s : Set α} (hs : s ∈ f) : s.Nonempty :=
s.eq_empty_or_nonempty.elim (fun h => absurd hs (h.symm ▸ mt empty_mem_iff_bot.mp hf.1)) id
theorem NeBot.nonempty_of_mem {f : Filter α} (hf : NeBot f) {s : Set α} (hs : s ∈ f) : s.Nonempty :=
@Filter.nonempty_of_mem α f hf s hs
@[simp]
theorem empty_not_mem (f : Filter α) [NeBot f] : ¬∅ ∈ f := fun h => (nonempty_of_mem h).ne_empty rfl
theorem nonempty_of_neBot (f : Filter α) [NeBot f] : Nonempty α :=
nonempty_of_exists <| nonempty_of_mem (univ_mem : univ ∈ f)
theorem compl_not_mem {f : Filter α} {s : Set α} [NeBot f] (h : s ∈ f) : sᶜ ∉ f := fun hsc =>
(nonempty_of_mem (inter_mem h hsc)).ne_empty <| inter_compl_self s
theorem filter_eq_bot_of_isEmpty [IsEmpty α] (f : Filter α) : f = ⊥ :=
empty_mem_iff_bot.mp <| univ_mem' isEmptyElim
protected lemma disjoint_iff {f g : Filter α} : Disjoint f g ↔ ∃ s ∈ f, ∃ t ∈ g, Disjoint s t := by
simp only [disjoint_iff, ← empty_mem_iff_bot, mem_inf_iff, inf_eq_inter, bot_eq_empty,
@eq_comm _ ∅]
theorem disjoint_of_disjoint_of_mem {f g : Filter α} {s t : Set α} (h : Disjoint s t) (hs : s ∈ f)
(ht : t ∈ g) : Disjoint f g :=
Filter.disjoint_iff.mpr ⟨s, hs, t, ht, h⟩
theorem NeBot.not_disjoint (hf : f.NeBot) (hs : s ∈ f) (ht : t ∈ f) : ¬Disjoint s t := fun h =>
not_disjoint_self_iff.2 hf <| Filter.disjoint_iff.2 ⟨s, hs, t, ht, h⟩
theorem inf_eq_bot_iff {f g : Filter α} : f ⊓ g = ⊥ ↔ ∃ U ∈ f, ∃ V ∈ g, U ∩ V = ∅ := by
simp only [← disjoint_iff, Filter.disjoint_iff, Set.disjoint_iff_inter_eq_empty]
/-- There is exactly one filter on an empty type. -/
instance unique [IsEmpty α] : Unique (Filter α) where
default := ⊥
uniq := filter_eq_bot_of_isEmpty
theorem NeBot.nonempty (f : Filter α) [hf : f.NeBot] : Nonempty α :=
not_isEmpty_iff.mp fun _ ↦ hf.ne (Subsingleton.elim _ _)
/-- There are only two filters on a `Subsingleton`: `⊥` and `⊤`. If the type is empty, then they are
equal. -/
theorem eq_top_of_neBot [Subsingleton α] (l : Filter α) [NeBot l] : l = ⊤ := by
refine top_unique fun s hs => ?_
obtain rfl : s = univ := Subsingleton.eq_univ_of_nonempty (nonempty_of_mem hs)
exact univ_mem
theorem forall_mem_nonempty_iff_neBot {f : Filter α} :
(∀ s : Set α, s ∈ f → s.Nonempty) ↔ NeBot f :=
⟨fun h => ⟨fun hf => not_nonempty_empty (h ∅ <| hf.symm ▸ mem_bot)⟩, @nonempty_of_mem _ _⟩
instance instNeBotTop [Nonempty α] : NeBot (⊤ : Filter α) :=
forall_mem_nonempty_iff_neBot.1 fun s hs => by rwa [mem_top.1 hs, ← nonempty_iff_univ_nonempty]
instance instNontrivialFilter [Nonempty α] : Nontrivial (Filter α) :=
⟨⟨⊤, ⊥, instNeBotTop.ne⟩⟩
theorem nontrivial_iff_nonempty : Nontrivial (Filter α) ↔ Nonempty α :=
⟨fun _ =>
by_contra fun h' =>
haveI := not_nonempty_iff.1 h'
not_subsingleton (Filter α) inferInstance,
@Filter.instNontrivialFilter α⟩
theorem eq_sInf_of_mem_iff_exists_mem {S : Set (Filter α)} {l : Filter α}
(h : ∀ {s}, s ∈ l ↔ ∃ f ∈ S, s ∈ f) : l = sInf S :=
le_antisymm (le_sInf fun f hf _ hs => h.2 ⟨f, hf, hs⟩)
fun _ hs => let ⟨_, hf, hs⟩ := h.1 hs; (sInf_le hf) hs
theorem eq_iInf_of_mem_iff_exists_mem {f : ι → Filter α} {l : Filter α}
(h : ∀ {s}, s ∈ l ↔ ∃ i, s ∈ f i) : l = iInf f :=
eq_sInf_of_mem_iff_exists_mem <| h.trans (exists_range_iff (p := (_ ∈ ·))).symm
theorem eq_biInf_of_mem_iff_exists_mem {f : ι → Filter α} {p : ι → Prop} {l : Filter α}
(h : ∀ {s}, s ∈ l ↔ ∃ i, p i ∧ s ∈ f i) : l = ⨅ (i) (_ : p i), f i := by
rw [iInf_subtype']
exact eq_iInf_of_mem_iff_exists_mem fun {_} => by simp only [Subtype.exists, h, exists_prop]
theorem iInf_sets_eq {f : ι → Filter α} (h : Directed (· ≥ ·) f) [ne : Nonempty ι] :
(iInf f).sets = ⋃ i, (f i).sets :=
let ⟨i⟩ := ne
let u :=
{ sets := ⋃ i, (f i).sets
univ_sets := mem_iUnion.2 ⟨i, univ_mem⟩
sets_of_superset := by
simp only [mem_iUnion, exists_imp]
exact fun i hx hxy => ⟨i, mem_of_superset hx hxy⟩
inter_sets := by
simp only [mem_iUnion, exists_imp]
intro x y a hx b hy
rcases h a b with ⟨c, ha, hb⟩
exact ⟨c, inter_mem (ha hx) (hb hy)⟩ }
have : u = iInf f := eq_iInf_of_mem_iff_exists_mem mem_iUnion
congr_arg Filter.sets this.symm
theorem mem_iInf_of_directed {f : ι → Filter α} (h : Directed (· ≥ ·) f) [Nonempty ι] (s) :
s ∈ iInf f ↔ ∃ i, s ∈ f i := by
simp only [← Filter.mem_sets, iInf_sets_eq h, mem_iUnion]
theorem mem_biInf_of_directed {f : β → Filter α} {s : Set β} (h : DirectedOn (f ⁻¹'o (· ≥ ·)) s)
(ne : s.Nonempty) {t : Set α} : (t ∈ ⨅ i ∈ s, f i) ↔ ∃ i ∈ s, t ∈ f i := by
haveI := ne.to_subtype
simp_rw [iInf_subtype', mem_iInf_of_directed h.directed_val, Subtype.exists, exists_prop]
theorem biInf_sets_eq {f : β → Filter α} {s : Set β} (h : DirectedOn (f ⁻¹'o (· ≥ ·)) s)
(ne : s.Nonempty) : (⨅ i ∈ s, f i).sets = ⋃ i ∈ s, (f i).sets :=
ext fun t => by simp [mem_biInf_of_directed h ne]
@[simp]
theorem sup_join {f₁ f₂ : Filter (Filter α)} : join f₁ ⊔ join f₂ = join (f₁ ⊔ f₂) :=
Filter.ext fun x => by simp only [mem_sup, mem_join]
@[simp]
theorem iSup_join {ι : Sort w} {f : ι → Filter (Filter α)} : ⨆ x, join (f x) = join (⨆ x, f x) :=
Filter.ext fun x => by simp only [mem_iSup, mem_join]
instance : DistribLattice (Filter α) :=
{ Filter.instCompleteLatticeFilter with
le_sup_inf := by
intro x y z s
simp only [and_assoc, mem_inf_iff, mem_sup, exists_prop, exists_imp, and_imp]
rintro hs t₁ ht₁ t₂ ht₂ rfl
exact
⟨t₁, x.sets_of_superset hs inter_subset_left, ht₁, t₂,
x.sets_of_superset hs inter_subset_right, ht₂, rfl⟩ }
/-- If `f : ι → Filter α` is directed, `ι` is not empty, and `∀ i, f i ≠ ⊥`, then `iInf f ≠ ⊥`.
See also `iInf_neBot_of_directed` for a version assuming `Nonempty α` instead of `Nonempty ι`. -/
theorem iInf_neBot_of_directed' {f : ι → Filter α} [Nonempty ι] (hd : Directed (· ≥ ·) f) :
(∀ i, NeBot (f i)) → NeBot (iInf f) :=
not_imp_not.1 <| by simpa only [not_forall, not_neBot, ← empty_mem_iff_bot,
mem_iInf_of_directed hd] using id
/-- If `f : ι → Filter α` is directed, `α` is not empty, and `∀ i, f i ≠ ⊥`, then `iInf f ≠ ⊥`.
See also `iInf_neBot_of_directed'` for a version assuming `Nonempty ι` instead of `Nonempty α`. -/
theorem iInf_neBot_of_directed {f : ι → Filter α} [hn : Nonempty α] (hd : Directed (· ≥ ·) f)
(hb : ∀ i, NeBot (f i)) : NeBot (iInf f) := by
cases isEmpty_or_nonempty ι
· constructor
simp [iInf_of_empty f, top_ne_bot]
· exact iInf_neBot_of_directed' hd hb
theorem sInf_neBot_of_directed' {s : Set (Filter α)} (hne : s.Nonempty) (hd : DirectedOn (· ≥ ·) s)
(hbot : ⊥ ∉ s) : NeBot (sInf s) :=
(sInf_eq_iInf' s).symm ▸
@iInf_neBot_of_directed' _ _ _ hne.to_subtype hd.directed_val fun ⟨_, hf⟩ =>
⟨ne_of_mem_of_not_mem hf hbot⟩
theorem sInf_neBot_of_directed [Nonempty α] {s : Set (Filter α)} (hd : DirectedOn (· ≥ ·) s)
(hbot : ⊥ ∉ s) : NeBot (sInf s) :=
(sInf_eq_iInf' s).symm ▸
iInf_neBot_of_directed hd.directed_val fun ⟨_, hf⟩ => ⟨ne_of_mem_of_not_mem hf hbot⟩
theorem iInf_neBot_iff_of_directed' {f : ι → Filter α} [Nonempty ι] (hd : Directed (· ≥ ·) f) :
NeBot (iInf f) ↔ ∀ i, NeBot (f i) :=
⟨fun H i => H.mono (iInf_le _ i), iInf_neBot_of_directed' hd⟩
theorem iInf_neBot_iff_of_directed {f : ι → Filter α} [Nonempty α] (hd : Directed (· ≥ ·) f) :
NeBot (iInf f) ↔ ∀ i, NeBot (f i) :=
⟨fun H i => H.mono (iInf_le _ i), iInf_neBot_of_directed hd⟩
/-! #### `principal` equations -/
@[simp]
theorem inf_principal {s t : Set α} : 𝓟 s ⊓ 𝓟 t = 𝓟 (s ∩ t) :=
le_antisymm
(by simp only [le_principal_iff, mem_inf_iff]; exact ⟨s, Subset.rfl, t, Subset.rfl, rfl⟩)
(by simp [le_inf_iff, inter_subset_left, inter_subset_right])
@[simp]
theorem sup_principal {s t : Set α} : 𝓟 s ⊔ 𝓟 t = 𝓟 (s ∪ t) :=
Filter.ext fun u => by simp only [union_subset_iff, mem_sup, mem_principal]
@[simp]
theorem iSup_principal {ι : Sort w} {s : ι → Set α} : ⨆ x, 𝓟 (s x) = 𝓟 (⋃ i, s i) :=
Filter.ext fun x => by simp only [mem_iSup, mem_principal, iUnion_subset_iff]
@[simp]
theorem principal_eq_bot_iff {s : Set α} : 𝓟 s = ⊥ ↔ s = ∅ :=
empty_mem_iff_bot.symm.trans <| mem_principal.trans subset_empty_iff
@[simp]
theorem principal_neBot_iff {s : Set α} : NeBot (𝓟 s) ↔ s.Nonempty :=
neBot_iff.trans <| (not_congr principal_eq_bot_iff).trans nonempty_iff_ne_empty.symm
alias ⟨_, _root_.Set.Nonempty.principal_neBot⟩ := principal_neBot_iff
theorem isCompl_principal (s : Set α) : IsCompl (𝓟 s) (𝓟 sᶜ) :=
IsCompl.of_eq (by rw [inf_principal, inter_compl_self, principal_empty]) <| by
rw [sup_principal, union_compl_self, principal_univ]
theorem mem_inf_principal' {f : Filter α} {s t : Set α} : s ∈ f ⊓ 𝓟 t ↔ tᶜ ∪ s ∈ f := by
simp only [← le_principal_iff, (isCompl_principal s).le_left_iff, disjoint_assoc, inf_principal,
← (isCompl_principal (t ∩ sᶜ)).le_right_iff, compl_inter, compl_compl]
lemma mem_inf_principal {f : Filter α} {s t : Set α} : s ∈ f ⊓ 𝓟 t ↔ { x | x ∈ t → x ∈ s } ∈ f := by
simp only [mem_inf_principal', imp_iff_not_or, setOf_or, compl_def, setOf_mem_eq]
lemma iSup_inf_principal (f : ι → Filter α) (s : Set α) : ⨆ i, f i ⊓ 𝓟 s = (⨆ i, f i) ⊓ 𝓟 s := by
ext
simp only [mem_iSup, mem_inf_principal]
theorem inf_principal_eq_bot {f : Filter α} {s : Set α} : f ⊓ 𝓟 s = ⊥ ↔ sᶜ ∈ f := by
rw [← empty_mem_iff_bot, mem_inf_principal]
simp only [mem_empty_iff_false, imp_false, compl_def]
theorem mem_of_eq_bot {f : Filter α} {s : Set α} (h : f ⊓ 𝓟 sᶜ = ⊥) : s ∈ f := by
rwa [inf_principal_eq_bot, compl_compl] at h
theorem diff_mem_inf_principal_compl {f : Filter α} {s : Set α} (hs : s ∈ f) (t : Set α) :
s \ t ∈ f ⊓ 𝓟 tᶜ :=
inter_mem_inf hs <| mem_principal_self tᶜ
theorem principal_le_iff {s : Set α} {f : Filter α} : 𝓟 s ≤ f ↔ ∀ V ∈ f, s ⊆ V := by
simp_rw [le_def, mem_principal]
end Lattice
@[mono, gcongr]
theorem join_mono {f₁ f₂ : Filter (Filter α)} (h : f₁ ≤ f₂) : join f₁ ≤ join f₂ := fun _ hs => h hs
/-! ### Eventually -/
theorem eventually_iff {f : Filter α} {P : α → Prop} : (∀ᶠ x in f, P x) ↔ { x | P x } ∈ f :=
Iff.rfl
@[simp]
theorem eventually_mem_set {s : Set α} {l : Filter α} : (∀ᶠ x in l, x ∈ s) ↔ s ∈ l :=
Iff.rfl
protected theorem ext' {f₁ f₂ : Filter α}
(h : ∀ p : α → Prop, (∀ᶠ x in f₁, p x) ↔ ∀ᶠ x in f₂, p x) : f₁ = f₂ :=
Filter.ext h
theorem Eventually.filter_mono {f₁ f₂ : Filter α} (h : f₁ ≤ f₂) {p : α → Prop}
(hp : ∀ᶠ x in f₂, p x) : ∀ᶠ x in f₁, p x :=
h hp
theorem eventually_of_mem {f : Filter α} {P : α → Prop} {U : Set α} (hU : U ∈ f)
(h : ∀ x ∈ U, P x) : ∀ᶠ x in f, P x :=
mem_of_superset hU h
protected theorem Eventually.and {p q : α → Prop} {f : Filter α} :
f.Eventually p → f.Eventually q → ∀ᶠ x in f, p x ∧ q x :=
inter_mem
@[simp] theorem eventually_true (f : Filter α) : ∀ᶠ _ in f, True := univ_mem
theorem Eventually.of_forall {p : α → Prop} {f : Filter α} (hp : ∀ x, p x) : ∀ᶠ x in f, p x :=
univ_mem' hp
@[simp]
theorem eventually_false_iff_eq_bot {f : Filter α} : (∀ᶠ _ in f, False) ↔ f = ⊥ :=
empty_mem_iff_bot
@[simp]
theorem eventually_const {f : Filter α} [t : NeBot f] {p : Prop} : (∀ᶠ _ in f, p) ↔ p := by
by_cases h : p <;> simp [h, t.ne]
theorem eventually_iff_exists_mem {p : α → Prop} {f : Filter α} :
(∀ᶠ x in f, p x) ↔ ∃ v ∈ f, ∀ y ∈ v, p y :=
exists_mem_subset_iff.symm
theorem Eventually.exists_mem {p : α → Prop} {f : Filter α} (hp : ∀ᶠ x in f, p x) :
∃ v ∈ f, ∀ y ∈ v, p y :=
eventually_iff_exists_mem.1 hp
theorem Eventually.mp {p q : α → Prop} {f : Filter α} (hp : ∀ᶠ x in f, p x)
(hq : ∀ᶠ x in f, p x → q x) : ∀ᶠ x in f, q x :=
mp_mem hp hq
theorem Eventually.mono {p q : α → Prop} {f : Filter α} (hp : ∀ᶠ x in f, p x)
(hq : ∀ x, p x → q x) : ∀ᶠ x in f, q x :=
hp.mp (Eventually.of_forall hq)
theorem forall_eventually_of_eventually_forall {f : Filter α} {p : α → β → Prop}
(h : ∀ᶠ x in f, ∀ y, p x y) : ∀ y, ∀ᶠ x in f, p x y :=
fun y => h.mono fun _ h => h y
@[simp]
theorem eventually_and {p q : α → Prop} {f : Filter α} :
(∀ᶠ x in f, p x ∧ q x) ↔ (∀ᶠ x in f, p x) ∧ ∀ᶠ x in f, q x :=
inter_mem_iff
theorem Eventually.congr {f : Filter α} {p q : α → Prop} (h' : ∀ᶠ x in f, p x)
(h : ∀ᶠ x in f, p x ↔ q x) : ∀ᶠ x in f, q x :=
h'.mp (h.mono fun _ hx => hx.mp)
theorem eventually_congr {f : Filter α} {p q : α → Prop} (h : ∀ᶠ x in f, p x ↔ q x) :
(∀ᶠ x in f, p x) ↔ ∀ᶠ x in f, q x :=
⟨fun hp => hp.congr h, fun hq => hq.congr <| by simpa only [Iff.comm] using h⟩
@[simp]
theorem eventually_or_distrib_left {f : Filter α} {p : Prop} {q : α → Prop} :
(∀ᶠ x in f, p ∨ q x) ↔ p ∨ ∀ᶠ x in f, q x :=
by_cases (fun h : p => by simp [h]) fun h => by simp [h]
@[simp]
theorem eventually_or_distrib_right {f : Filter α} {p : α → Prop} {q : Prop} :
(∀ᶠ x in f, p x ∨ q) ↔ (∀ᶠ x in f, p x) ∨ q := by
simp only [@or_comm _ q, eventually_or_distrib_left]
theorem eventually_imp_distrib_left {f : Filter α} {p : Prop} {q : α → Prop} :
(∀ᶠ x in f, p → q x) ↔ p → ∀ᶠ x in f, q x := by
simp only [imp_iff_not_or, eventually_or_distrib_left]
@[simp]
theorem eventually_bot {p : α → Prop} : ∀ᶠ x in ⊥, p x :=
⟨⟩
@[simp]
theorem eventually_top {p : α → Prop} : (∀ᶠ x in ⊤, p x) ↔ ∀ x, p x :=
Iff.rfl
@[simp]
theorem eventually_sup {p : α → Prop} {f g : Filter α} :
| (∀ᶠ x in f ⊔ g, p x) ↔ (∀ᶠ x in f, p x) ∧ ∀ᶠ x in g, p x :=
Iff.rfl
@[simp]
theorem eventually_sSup {p : α → Prop} {fs : Set (Filter α)} :
| Mathlib/Order/Filter/Basic.lean | 660 | 664 |
/-
Copyright (c) 2020 Oliver Nash. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Oliver Nash
-/
import Mathlib.Algebra.Lie.Matrix
import Mathlib.LinearAlgebra.Matrix.SesquilinearForm
import Mathlib.Tactic.NoncommRing
/-!
# Lie algebras of skew-adjoint endomorphisms of a bilinear form
When a module carries a bilinear form, the Lie algebra of endomorphisms of the module contains a
distinguished Lie subalgebra: the skew-adjoint endomorphisms. Such subalgebras are important
because they provide a simple, explicit construction of the so-called classical Lie algebras.
This file defines the Lie subalgebra of skew-adjoint endomorphisms cut out by a bilinear form on
a module and proves some basic related results. It also provides the corresponding definitions and
results for the Lie algebra of square matrices.
## Main definitions
* `skewAdjointLieSubalgebra`
* `skewAdjointLieSubalgebraEquiv`
* `skewAdjointMatricesLieSubalgebra`
* `skewAdjointMatricesLieSubalgebraEquiv`
## Tags
lie algebra, skew-adjoint, bilinear form
-/
universe u v w w₁
section SkewAdjointEndomorphisms
open LinearMap (BilinForm)
variable {R : Type u} {M : Type v} [CommRing R] [AddCommGroup M] [Module R M]
variable (B : BilinForm R M)
theorem LinearMap.BilinForm.isSkewAdjoint_bracket {f g : Module.End R M}
(hf : f ∈ B.skewAdjointSubmodule) (hg : g ∈ B.skewAdjointSubmodule) :
⁅f, g⁆ ∈ B.skewAdjointSubmodule := by
rw [mem_skewAdjointSubmodule] at *
have hfg : IsAdjointPair B B (f * g) (g * f) := by rw [← neg_mul_neg g f]; exact hg.comp hf
have hgf : IsAdjointPair B B (g * f) (f * g) := by rw [← neg_mul_neg f g]; exact hf.comp hg
change IsAdjointPair B B (f * g - g * f) (-(f * g - g * f)); rw [neg_sub]
exact hfg.sub hgf
/-- Given an `R`-module `M`, equipped with a bilinear form, the skew-adjoint endomorphisms form a
Lie subalgebra of the Lie algebra of endomorphisms. -/
def skewAdjointLieSubalgebra : LieSubalgebra R (Module.End R M) :=
{ B.skewAdjointSubmodule with
lie_mem' := B.isSkewAdjoint_bracket }
variable {N : Type w} [AddCommGroup N] [Module R N] (e : N ≃ₗ[R] M)
/-- An equivalence of modules with bilinear forms gives equivalence of Lie algebras of skew-adjoint
endomorphisms. -/
def skewAdjointLieSubalgebraEquiv :
skewAdjointLieSubalgebra (B.compl₁₂ (e : N →ₗ[R] M) e) ≃ₗ⁅R⁆ skewAdjointLieSubalgebra B := by
apply LieEquiv.ofSubalgebras _ _ e.lieConj
ext f
simp only [LieSubalgebra.mem_coe, Submodule.mem_map_equiv, LieSubalgebra.mem_map_submodule,
LinearEquiv.coe_coe]
exact (LinearMap.isPairSelfAdjoint_equiv (B := -B) (F := B) e f).symm
@[simp]
theorem skewAdjointLieSubalgebraEquiv_apply
(f : skewAdjointLieSubalgebra (B.compl₁₂ (Qₗ := N) (Qₗ' := N) ↑e ↑e)) :
↑(skewAdjointLieSubalgebraEquiv B e f) = e.lieConj f := by
simp [skewAdjointLieSubalgebraEquiv]
@[simp]
| theorem skewAdjointLieSubalgebraEquiv_symm_apply (f : skewAdjointLieSubalgebra B) :
↑((skewAdjointLieSubalgebraEquiv B e).symm f) = e.symm.lieConj f := by
simp [skewAdjointLieSubalgebraEquiv]
| Mathlib/Algebra/Lie/SkewAdjoint.lean | 77 | 80 |
/-
Copyright (c) 2021 Aaron Anderson, Jesse Michael Han, Floris van Doorn. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Aaron Anderson, Jesse Michael Han, Floris van Doorn
-/
import Mathlib.Data.Finset.Basic
import Mathlib.ModelTheory.Syntax
import Mathlib.Data.List.ProdSigma
/-!
# Basics on First-Order Semantics
This file defines the interpretations of first-order terms, formulas, sentences, and theories
in a style inspired by the [Flypitch project](https://flypitch.github.io/).
## Main Definitions
- `FirstOrder.Language.Term.realize` is defined so that `t.realize v` is the term `t` evaluated at
variables `v`.
- `FirstOrder.Language.BoundedFormula.Realize` is defined so that `φ.Realize v xs` is the bounded
formula `φ` evaluated at tuples of variables `v` and `xs`.
- `FirstOrder.Language.Formula.Realize` is defined so that `φ.Realize v` is the formula `φ`
evaluated at variables `v`.
- `FirstOrder.Language.Sentence.Realize` is defined so that `φ.Realize M` is the sentence `φ`
evaluated in the structure `M`. Also denoted `M ⊨ φ`.
- `FirstOrder.Language.Theory.Model` is defined so that `T.Model M` is true if and only if every
sentence of `T` is realized in `M`. Also denoted `T ⊨ φ`.
## Main Results
- Several results in this file show that syntactic constructions such as `relabel`, `castLE`,
`liftAt`, `subst`, and the actions of language maps commute with realization of terms, formulas,
sentences, and theories.
## Implementation Notes
- Formulas use a modified version of de Bruijn variables. Specifically, a `L.BoundedFormula α n`
is a formula with some variables indexed by a type `α`, which cannot be quantified over, and some
indexed by `Fin n`, which can. For any `φ : L.BoundedFormula α (n + 1)`, we define the formula
`∀' φ : L.BoundedFormula α n` by universally quantifying over the variable indexed by
`n : Fin (n + 1)`.
## References
For the Flypitch project:
- [J. Han, F. van Doorn, *A formal proof of the independence of the continuum hypothesis*]
[flypitch_cpp]
- [J. Han, F. van Doorn, *A formalization of forcing and the unprovability of
the continuum hypothesis*][flypitch_itp]
-/
universe u v w u' v'
namespace FirstOrder
namespace Language
variable {L : Language.{u, v}} {L' : Language}
variable {M : Type w} {N P : Type*} [L.Structure M] [L.Structure N] [L.Structure P]
variable {α : Type u'} {β : Type v'} {γ : Type*}
open FirstOrder Cardinal
open Structure Cardinal Fin
namespace Term
/-- A term `t` with variables indexed by `α` can be evaluated by giving a value to each variable. -/
def realize (v : α → M) : ∀ _t : L.Term α, M
| var k => v k
| func f ts => funMap f fun i => (ts i).realize v
@[simp]
theorem realize_var (v : α → M) (k) : realize v (var k : L.Term α) = v k := rfl
@[simp]
theorem realize_func (v : α → M) {n} (f : L.Functions n) (ts) :
realize v (func f ts : L.Term α) = funMap f fun i => (ts i).realize v := rfl
@[simp]
theorem realize_relabel {t : L.Term α} {g : α → β} {v : β → M} :
(t.relabel g).realize v = t.realize (v ∘ g) := by
induction t with
| var => rfl
| func f ts ih => simp [ih]
@[simp]
theorem realize_liftAt {n n' m : ℕ} {t : L.Term (α ⊕ (Fin n))} {v : α ⊕ (Fin (n + n')) → M} :
(t.liftAt n' m).realize v =
t.realize (v ∘ Sum.map id fun i : Fin _ =>
if ↑i < m then Fin.castAdd n' i else Fin.addNat i n') :=
realize_relabel
@[simp]
theorem realize_constants {c : L.Constants} {v : α → M} : c.term.realize v = c :=
funMap_eq_coe_constants
@[simp]
theorem realize_functions_apply₁ {f : L.Functions 1} {t : L.Term α} {v : α → M} :
(f.apply₁ t).realize v = funMap f ![t.realize v] := by
rw [Functions.apply₁, Term.realize]
refine congr rfl (funext fun i => ?_)
simp only [Matrix.cons_val_fin_one]
@[simp]
theorem realize_functions_apply₂ {f : L.Functions 2} {t₁ t₂ : L.Term α} {v : α → M} :
(f.apply₂ t₁ t₂).realize v = funMap f ![t₁.realize v, t₂.realize v] := by
rw [Functions.apply₂, Term.realize]
refine congr rfl (funext (Fin.cases ?_ ?_))
· simp only [Matrix.cons_val_zero]
· simp only [Matrix.cons_val_succ, Matrix.cons_val_fin_one, forall_const]
theorem realize_con {A : Set M} {a : A} {v : α → M} : (L.con a).term.realize v = a :=
rfl
@[simp]
theorem realize_subst {t : L.Term α} {tf : α → L.Term β} {v : β → M} :
(t.subst tf).realize v = t.realize fun a => (tf a).realize v := by
induction t with
| var => rfl
| func _ _ ih => simp [ih]
theorem realize_restrictVar [DecidableEq α] {t : L.Term α} {f : t.varFinset → β}
{v : β → M} (v' : α → M) (hv' : ∀ a, v (f a) = v' a) :
(t.restrictVar f).realize v = t.realize v' := by
induction t with
| var => simp [restrictVar, hv']
| func _ _ ih =>
exact congr rfl (funext fun i => ih i ((by simp [Function.comp_apply, hv'])))
/-- A special case of `realize_restrictVar`, included because we can add the `simp` attribute
to it -/
@[simp]
theorem realize_restrictVar' [DecidableEq α] {t : L.Term α} {s : Set α} (h : ↑t.varFinset ⊆ s)
{v : α → M} : (t.restrictVar (Set.inclusion h)).realize (v ∘ (↑)) = t.realize v :=
realize_restrictVar _ (by simp)
theorem realize_restrictVarLeft [DecidableEq α] {γ : Type*} {t : L.Term (α ⊕ γ)}
{f : t.varFinsetLeft → β}
{xs : β ⊕ γ → M} (xs' : α → M) (hxs' : ∀ a, xs (Sum.inl (f a)) = xs' a) :
(t.restrictVarLeft f).realize xs = t.realize (Sum.elim xs' (xs ∘ Sum.inr)) := by
induction t with
| var a => cases a <;> simp [restrictVarLeft, hxs']
| func _ _ ih =>
exact congr rfl (funext fun i => ih i (by simp [hxs']))
/-- A special case of `realize_restrictVarLeft`, included because we can add the `simp` attribute
to it -/
@[simp]
theorem realize_restrictVarLeft' [DecidableEq α] {γ : Type*} {t : L.Term (α ⊕ γ)} {s : Set α}
(h : ↑t.varFinsetLeft ⊆ s) {v : α → M} {xs : γ → M} :
(t.restrictVarLeft (Set.inclusion h)).realize (Sum.elim (v ∘ (↑)) xs) =
t.realize (Sum.elim v xs) :=
realize_restrictVarLeft _ (by simp)
@[simp]
theorem realize_constantsToVars [L[[α]].Structure M] [(lhomWithConstants L α).IsExpansionOn M]
{t : L[[α]].Term β} {v : β → M} :
t.constantsToVars.realize (Sum.elim (fun a => ↑(L.con a)) v) = t.realize v := by
induction t with
| var => simp
| @func n f ts ih =>
cases n
· cases f
· simp only [realize, ih, constantsOn, constantsOnFunc, constantsToVars]
-- Porting note: below lemma does not work with simp for some reason
rw [withConstants_funMap_sumInl]
· simp only [realize, constantsToVars, Sum.elim_inl, funMap_eq_coe_constants]
rfl
· obtain - | f := f
· simp only [realize, ih, constantsOn, constantsOnFunc, constantsToVars]
-- Porting note: below lemma does not work with simp for some reason
rw [withConstants_funMap_sumInl]
· exact isEmptyElim f
@[simp]
theorem realize_varsToConstants [L[[α]].Structure M] [(lhomWithConstants L α).IsExpansionOn M]
{t : L.Term (α ⊕ β)} {v : β → M} :
t.varsToConstants.realize v = t.realize (Sum.elim (fun a => ↑(L.con a)) v) := by
induction t with
| var ab => rcases ab with a | b <;> simp [Language.con]
| func f ts ih =>
simp only [realize, constantsOn, constantsOnFunc, ih, varsToConstants]
-- Porting note: below lemma does not work with simp for some reason
rw [withConstants_funMap_sumInl]
theorem realize_constantsVarsEquivLeft [L[[α]].Structure M]
[(lhomWithConstants L α).IsExpansionOn M] {n} {t : L[[α]].Term (β ⊕ (Fin n))} {v : β → M}
{xs : Fin n → M} :
(constantsVarsEquivLeft t).realize (Sum.elim (Sum.elim (fun a => ↑(L.con a)) v) xs) =
t.realize (Sum.elim v xs) := by
simp only [constantsVarsEquivLeft, realize_relabel, Equiv.coe_trans, Function.comp_apply,
constantsVarsEquiv_apply, relabelEquiv_symm_apply]
refine _root_.trans ?_ realize_constantsToVars
rcongr x
rcases x with (a | (b | i)) <;> simp
end Term
namespace LHom
@[simp]
theorem realize_onTerm [L'.Structure M] (φ : L →ᴸ L') [φ.IsExpansionOn M] (t : L.Term α)
(v : α → M) : (φ.onTerm t).realize v = t.realize v := by
induction t with
| var => rfl
| func f ts ih => simp only [Term.realize, LHom.onTerm, LHom.map_onFunction, ih]
end LHom
@[simp]
theorem HomClass.realize_term {F : Type*} [FunLike F M N] [HomClass L F M N]
(g : F) {t : L.Term α} {v : α → M} :
t.realize (g ∘ v) = g (t.realize v) := by
induction t
· rfl
· rw [Term.realize, Term.realize, HomClass.map_fun]
refine congr rfl ?_
ext x
simp [*]
variable {n : ℕ}
namespace BoundedFormula
open Term
/-- A bounded formula can be evaluated as true or false by giving values to each free variable. -/
def Realize : ∀ {l} (_f : L.BoundedFormula α l) (_v : α → M) (_xs : Fin l → M), Prop
| _, falsum, _v, _xs => False
| _, equal t₁ t₂, v, xs => t₁.realize (Sum.elim v xs) = t₂.realize (Sum.elim v xs)
| _, rel R ts, v, xs => RelMap R fun i => (ts i).realize (Sum.elim v xs)
| _, imp f₁ f₂, v, xs => Realize f₁ v xs → Realize f₂ v xs
| _, all f, v, xs => ∀ x : M, Realize f v (snoc xs x)
variable {l : ℕ} {φ ψ : L.BoundedFormula α l} {θ : L.BoundedFormula α l.succ}
variable {v : α → M} {xs : Fin l → M}
@[simp]
theorem realize_bot : (⊥ : L.BoundedFormula α l).Realize v xs ↔ False :=
Iff.rfl
@[simp]
theorem realize_not : φ.not.Realize v xs ↔ ¬φ.Realize v xs :=
Iff.rfl
@[simp]
theorem realize_bdEqual (t₁ t₂ : L.Term (α ⊕ (Fin l))) :
(t₁.bdEqual t₂).Realize v xs ↔ t₁.realize (Sum.elim v xs) = t₂.realize (Sum.elim v xs) :=
Iff.rfl
@[simp]
theorem realize_top : (⊤ : L.BoundedFormula α l).Realize v xs ↔ True := by simp [Top.top]
@[simp]
theorem realize_inf : (φ ⊓ ψ).Realize v xs ↔ φ.Realize v xs ∧ ψ.Realize v xs := by
simp [Inf.inf, Realize]
@[simp]
theorem realize_foldr_inf (l : List (L.BoundedFormula α n)) (v : α → M) (xs : Fin n → M) :
(l.foldr (· ⊓ ·) ⊤).Realize v xs ↔ ∀ φ ∈ l, BoundedFormula.Realize φ v xs := by
induction' l with φ l ih
· simp
· simp [ih]
@[simp]
theorem realize_imp : (φ.imp ψ).Realize v xs ↔ φ.Realize v xs → ψ.Realize v xs := by
simp only [Realize]
@[simp]
theorem realize_rel {k : ℕ} {R : L.Relations k} {ts : Fin k → L.Term _} :
(R.boundedFormula ts).Realize v xs ↔ RelMap R fun i => (ts i).realize (Sum.elim v xs) :=
Iff.rfl
@[simp]
theorem realize_rel₁ {R : L.Relations 1} {t : L.Term _} :
(R.boundedFormula₁ t).Realize v xs ↔ RelMap R ![t.realize (Sum.elim v xs)] := by
rw [Relations.boundedFormula₁, realize_rel, iff_eq_eq]
refine congr rfl (funext fun _ => ?_)
simp only [Matrix.cons_val_fin_one]
@[simp]
theorem realize_rel₂ {R : L.Relations 2} {t₁ t₂ : L.Term _} :
(R.boundedFormula₂ t₁ t₂).Realize v xs ↔
RelMap R ![t₁.realize (Sum.elim v xs), t₂.realize (Sum.elim v xs)] := by
rw [Relations.boundedFormula₂, realize_rel, iff_eq_eq]
refine congr rfl (funext (Fin.cases ?_ ?_))
· simp only [Matrix.cons_val_zero]
· simp only [Matrix.cons_val_succ, Matrix.cons_val_fin_one, forall_const]
@[simp]
theorem realize_sup : (φ ⊔ ψ).Realize v xs ↔ φ.Realize v xs ∨ ψ.Realize v xs := by
simp only [realize, max, realize_not, eq_iff_iff]
tauto
@[simp]
theorem realize_foldr_sup (l : List (L.BoundedFormula α n)) (v : α → M) (xs : Fin n → M) :
(l.foldr (· ⊔ ·) ⊥).Realize v xs ↔ ∃ φ ∈ l, BoundedFormula.Realize φ v xs := by
induction' l with φ l ih
· simp
· simp_rw [List.foldr_cons, realize_sup, ih, List.mem_cons, or_and_right, exists_or,
exists_eq_left]
@[simp]
theorem realize_all : (all θ).Realize v xs ↔ ∀ a : M, θ.Realize v (Fin.snoc xs a) :=
Iff.rfl
@[simp]
theorem realize_ex : θ.ex.Realize v xs ↔ ∃ a : M, θ.Realize v (Fin.snoc xs a) := by
rw [BoundedFormula.ex, realize_not, realize_all, not_forall]
simp_rw [realize_not, Classical.not_not]
@[simp]
theorem realize_iff : (φ.iff ψ).Realize v xs ↔ (φ.Realize v xs ↔ ψ.Realize v xs) := by
simp only [BoundedFormula.iff, realize_inf, realize_imp, and_imp, ← iff_def]
theorem realize_castLE_of_eq {m n : ℕ} (h : m = n) {h' : m ≤ n} {φ : L.BoundedFormula α m}
{v : α → M} {xs : Fin n → M} : (φ.castLE h').Realize v xs ↔ φ.Realize v (xs ∘ Fin.cast h) := by
subst h
simp only [castLE_rfl, cast_refl, OrderIso.coe_refl, Function.comp_id]
theorem realize_mapTermRel_id [L'.Structure M]
{ft : ∀ n, L.Term (α ⊕ (Fin n)) → L'.Term (β ⊕ (Fin n))}
{fr : ∀ n, L.Relations n → L'.Relations n} {n} {φ : L.BoundedFormula α n} {v : α → M}
{v' : β → M} {xs : Fin n → M}
(h1 :
∀ (n) (t : L.Term (α ⊕ (Fin n))) (xs : Fin n → M),
(ft n t).realize (Sum.elim v' xs) = t.realize (Sum.elim v xs))
(h2 : ∀ (n) (R : L.Relations n) (x : Fin n → M), RelMap (fr n R) x = RelMap R x) :
(φ.mapTermRel ft fr fun _ => id).Realize v' xs ↔ φ.Realize v xs := by
induction φ with
| falsum => rfl
| equal => simp [mapTermRel, Realize, h1]
| rel => simp [mapTermRel, Realize, h1, h2]
| imp _ _ ih1 ih2 => simp [mapTermRel, Realize, ih1, ih2]
| all _ ih => simp only [mapTermRel, Realize, ih, id]
theorem realize_mapTermRel_add_castLe [L'.Structure M] {k : ℕ}
{ft : ∀ n, L.Term (α ⊕ (Fin n)) → L'.Term (β ⊕ (Fin (k + n)))}
{fr : ∀ n, L.Relations n → L'.Relations n} {n} {φ : L.BoundedFormula α n}
(v : ∀ {n}, (Fin (k + n) → M) → α → M) {v' : β → M} (xs : Fin (k + n) → M)
(h1 :
∀ (n) (t : L.Term (α ⊕ (Fin n))) (xs' : Fin (k + n) → M),
(ft n t).realize (Sum.elim v' xs') = t.realize (Sum.elim (v xs') (xs' ∘ Fin.natAdd _)))
(h2 : ∀ (n) (R : L.Relations n) (x : Fin n → M), RelMap (fr n R) x = RelMap R x)
(hv : ∀ (n) (xs : Fin (k + n) → M) (x : M), @v (n + 1) (snoc xs x : Fin _ → M) = v xs) :
(φ.mapTermRel ft fr fun _ => castLE (add_assoc _ _ _).symm.le).Realize v' xs ↔
φ.Realize (v xs) (xs ∘ Fin.natAdd _) := by
induction φ with
| falsum => rfl
| equal => simp [mapTermRel, Realize, h1]
| rel => simp [mapTermRel, Realize, h1, h2]
| imp _ _ ih1 ih2 => simp [mapTermRel, Realize, ih1, ih2]
| all _ ih => simp [mapTermRel, Realize, ih, hv]
@[simp]
theorem realize_relabel {m n : ℕ} {φ : L.BoundedFormula α n} {g : α → β ⊕ (Fin m)} {v : β → M}
{xs : Fin (m + n) → M} :
(φ.relabel g).Realize v xs ↔
φ.Realize (Sum.elim v (xs ∘ Fin.castAdd n) ∘ g) (xs ∘ Fin.natAdd m) := by
apply realize_mapTermRel_add_castLe <;> simp
theorem realize_liftAt {n n' m : ℕ} {φ : L.BoundedFormula α n} {v : α → M} {xs : Fin (n + n') → M}
(hmn : m + n' ≤ n + 1) :
(φ.liftAt n' m).Realize v xs ↔
φ.Realize v (xs ∘ fun i => if ↑i < m then Fin.castAdd n' i else Fin.addNat i n') := by
rw [liftAt]
induction φ with
| falsum => simp [mapTermRel, Realize]
| equal => simp [mapTermRel, Realize, realize_rel, realize_liftAt, Sum.elim_comp_map]
| rel => simp [mapTermRel, Realize, realize_rel, realize_liftAt, Sum.elim_comp_map]
| imp _ _ ih1 ih2 => simp only [mapTermRel, Realize, ih1 hmn, ih2 hmn]
| @all k _ ih3 =>
have h : k + 1 + n' = k + n' + 1 := by rw [add_assoc, add_comm 1 n', ← add_assoc]
simp only [mapTermRel, Realize, realize_castLE_of_eq h, ih3 (hmn.trans k.succ.le_succ)]
refine forall_congr' fun x => iff_eq_eq.mpr (congr rfl (funext (Fin.lastCases ?_ fun i => ?_)))
· simp only [Function.comp_apply, val_last, snoc_last]
refine (congr rfl (Fin.ext ?_)).trans (snoc_last _ _)
split_ifs <;> dsimp; omega
· simp only [Function.comp_apply, Fin.snoc_castSucc]
refine (congr rfl (Fin.ext ?_)).trans (snoc_castSucc _ _ _)
simp only [coe_castSucc, coe_cast]
split_ifs <;> simp
theorem realize_liftAt_one {n m : ℕ} {φ : L.BoundedFormula α n} {v : α → M} {xs : Fin (n + 1) → M}
(hmn : m ≤ n) :
(φ.liftAt 1 m).Realize v xs ↔
φ.Realize v (xs ∘ fun i => if ↑i < m then castSucc i else i.succ) := by
simp [realize_liftAt (add_le_add_right hmn 1), castSucc]
@[simp]
theorem realize_liftAt_one_self {n : ℕ} {φ : L.BoundedFormula α n} {v : α → M}
{xs : Fin (n + 1) → M} : (φ.liftAt 1 n).Realize v xs ↔ φ.Realize v (xs ∘ castSucc) := by
rw [realize_liftAt_one (refl n), iff_eq_eq]
refine congr rfl (congr rfl (funext fun i => ?_))
rw [if_pos i.is_lt]
@[simp]
theorem realize_subst {φ : L.BoundedFormula α n} {tf : α → L.Term β} {v : β → M} {xs : Fin n → M} :
(φ.subst tf).Realize v xs ↔ φ.Realize (fun a => (tf a).realize v) xs :=
realize_mapTermRel_id
(fun n t x => by
rw [Term.realize_subst]
rcongr a
cases a
· simp only [Sum.elim_inl, Function.comp_apply, Term.realize_relabel, Sum.elim_comp_inl]
· rfl)
(by simp)
theorem realize_restrictFreeVar [DecidableEq α] {n : ℕ} {φ : L.BoundedFormula α n}
{f : φ.freeVarFinset → β} {v : β → M} {xs : Fin n → M}
(v' : α → M) (hv' : ∀ a, v (f a) = v' a) :
(φ.restrictFreeVar f).Realize v xs ↔ φ.Realize v' xs := by
induction φ with
| falsum => rfl
| equal =>
simp only [Realize, restrictFreeVar, freeVarFinset.eq_2]
rw [realize_restrictVarLeft v' (by simp [hv']), realize_restrictVarLeft v' (by simp [hv'])]
simp [Function.comp_apply]
| rel =>
simp only [Realize, freeVarFinset.eq_3, Finset.biUnion_val, restrictFreeVar]
congr!
rw [realize_restrictVarLeft v' (by simp [hv'])]
simp [Function.comp_apply]
| imp _ _ ih1 ih2 =>
simp only [Realize, restrictFreeVar, freeVarFinset.eq_4]
rw [ih1, ih2] <;> simp [hv']
| all _ ih3 =>
simp only [restrictFreeVar, Realize]
refine forall_congr' (fun _ => ?_)
rw [ih3]; simp [hv']
/-- A special case of `realize_restrictFreeVar`, included because we can add the `simp` attribute
to it -/
@[simp]
theorem realize_restrictFreeVar' [DecidableEq α] {n : ℕ} {φ : L.BoundedFormula α n} {s : Set α}
(h : ↑φ.freeVarFinset ⊆ s) {v : α → M} {xs : Fin n → M} :
(φ.restrictFreeVar (Set.inclusion h)).Realize (v ∘ (↑)) xs ↔ φ.Realize v xs :=
realize_restrictFreeVar _ (by simp)
theorem realize_constantsVarsEquiv [L[[α]].Structure M] [(lhomWithConstants L α).IsExpansionOn M]
{n} {φ : L[[α]].BoundedFormula β n} {v : β → M} {xs : Fin n → M} :
(constantsVarsEquiv φ).Realize (Sum.elim (fun a => ↑(L.con a)) v) xs ↔ φ.Realize v xs := by
refine realize_mapTermRel_id (fun n t xs => realize_constantsVarsEquivLeft) fun n R xs => ?_
-- This used to be `rw`, but we need `erw` after https://github.com/leanprover/lean4/pull/2644
erw [← (lhomWithConstants L α).map_onRelation
(Equiv.sumEmpty (L.Relations n) ((constantsOn α).Relations n) R) xs]
rcongr
obtain - | R := R
· simp
· exact isEmptyElim R
@[simp]
theorem realize_relabelEquiv {g : α ≃ β} {k} {φ : L.BoundedFormula α k} {v : β → M}
{xs : Fin k → M} : (relabelEquiv g φ).Realize v xs ↔ φ.Realize (v ∘ g) xs := by
simp only [relabelEquiv, mapTermRelEquiv_apply, Equiv.coe_refl]
refine realize_mapTermRel_id (fun n t xs => ?_) fun _ _ _ => rfl
simp only [relabelEquiv_apply, Term.realize_relabel]
refine congr (congr rfl ?_) rfl
ext (i | i) <;> rfl
variable [Nonempty M]
theorem realize_all_liftAt_one_self {n : ℕ} {φ : L.BoundedFormula α n} {v : α → M}
{xs : Fin n → M} : (φ.liftAt 1 n).all.Realize v xs ↔ φ.Realize v xs := by
inhabit M
simp only [realize_all, realize_liftAt_one_self]
refine ⟨fun h => ?_, fun h a => ?_⟩
· refine (congr rfl (funext fun i => ?_)).mp (h default)
simp
· refine (congr rfl (funext fun i => ?_)).mp h
simp
end BoundedFormula
namespace LHom
open BoundedFormula
@[simp]
theorem realize_onBoundedFormula [L'.Structure M] (φ : L →ᴸ L') [φ.IsExpansionOn M] {n : ℕ}
(ψ : L.BoundedFormula α n) {v : α → M} {xs : Fin n → M} :
(φ.onBoundedFormula ψ).Realize v xs ↔ ψ.Realize v xs := by
induction ψ with
| falsum => rfl
| equal => simp only [onBoundedFormula, realize_bdEqual, realize_onTerm]; rfl
| rel =>
simp only [onBoundedFormula, realize_rel, LHom.map_onRelation,
Function.comp_apply, realize_onTerm]
rfl
| imp _ _ ih1 ih2 => simp only [onBoundedFormula, ih1, ih2, realize_imp]
| all _ ih3 => simp only [onBoundedFormula, ih3, realize_all]
end LHom
namespace Formula
/-- A formula can be evaluated as true or false by giving values to each free variable. -/
nonrec def Realize (φ : L.Formula α) (v : α → M) : Prop :=
φ.Realize v default
variable {φ ψ : L.Formula α} {v : α → M}
@[simp]
theorem realize_not : φ.not.Realize v ↔ ¬φ.Realize v :=
Iff.rfl
@[simp]
theorem realize_bot : (⊥ : L.Formula α).Realize v ↔ False :=
Iff.rfl
@[simp]
theorem realize_top : (⊤ : L.Formula α).Realize v ↔ True :=
BoundedFormula.realize_top
@[simp]
theorem realize_inf : (φ ⊓ ψ).Realize v ↔ φ.Realize v ∧ ψ.Realize v :=
BoundedFormula.realize_inf
@[simp]
theorem realize_imp : (φ.imp ψ).Realize v ↔ φ.Realize v → ψ.Realize v :=
BoundedFormula.realize_imp
@[simp]
theorem realize_rel {k : ℕ} {R : L.Relations k} {ts : Fin k → L.Term α} :
(R.formula ts).Realize v ↔ RelMap R fun i => (ts i).realize v :=
BoundedFormula.realize_rel.trans (by simp)
@[simp]
theorem realize_rel₁ {R : L.Relations 1} {t : L.Term _} :
(R.formula₁ t).Realize v ↔ RelMap R ![t.realize v] := by
rw [Relations.formula₁, realize_rel, iff_eq_eq]
refine congr rfl (funext fun _ => ?_)
simp only [Matrix.cons_val_fin_one]
@[simp]
theorem realize_rel₂ {R : L.Relations 2} {t₁ t₂ : L.Term _} :
(R.formula₂ t₁ t₂).Realize v ↔ RelMap R ![t₁.realize v, t₂.realize v] := by
rw [Relations.formula₂, realize_rel, iff_eq_eq]
refine congr rfl (funext (Fin.cases ?_ ?_))
· simp only [Matrix.cons_val_zero]
· simp only [Matrix.cons_val_succ, Matrix.cons_val_fin_one, forall_const]
@[simp]
theorem realize_sup : (φ ⊔ ψ).Realize v ↔ φ.Realize v ∨ ψ.Realize v :=
BoundedFormula.realize_sup
@[simp]
theorem realize_iff : (φ.iff ψ).Realize v ↔ (φ.Realize v ↔ ψ.Realize v) :=
BoundedFormula.realize_iff
@[simp]
theorem realize_relabel {φ : L.Formula α} {g : α → β} {v : β → M} :
(φ.relabel g).Realize v ↔ φ.Realize (v ∘ g) := by
rw [Realize, Realize, relabel, BoundedFormula.realize_relabel, iff_eq_eq, Fin.castAdd_zero]
exact congr rfl (funext finZeroElim)
theorem realize_relabel_sumInr (φ : L.Formula (Fin n)) {v : Empty → M} {x : Fin n → M} :
(BoundedFormula.relabel Sum.inr φ).Realize v x ↔ φ.Realize x := by
rw [BoundedFormula.realize_relabel, Formula.Realize, Sum.elim_comp_inr, Fin.castAdd_zero,
cast_refl, Function.comp_id,
Subsingleton.elim (x ∘ (natAdd n : Fin 0 → Fin n)) default]
@[deprecated (since := "2025-02-21")] alias realize_relabel_sum_inr := realize_relabel_sumInr
@[simp]
theorem realize_equal {t₁ t₂ : L.Term α} {x : α → M} :
(t₁.equal t₂).Realize x ↔ t₁.realize x = t₂.realize x := by simp [Term.equal, Realize]
@[simp]
theorem realize_graph {f : L.Functions n} {x : Fin n → M} {y : M} :
(Formula.graph f).Realize (Fin.cons y x : _ → M) ↔ funMap f x = y := by
simp only [Formula.graph, Term.realize, realize_equal, Fin.cons_zero, Fin.cons_succ]
rw [eq_comm]
theorem boundedFormula_realize_eq_realize (φ : L.Formula α) (x : α → M) (y : Fin 0 → M) :
BoundedFormula.Realize φ x y ↔ φ.Realize x := by
rw [Formula.Realize, iff_iff_eq]
congr
ext i; exact Fin.elim0 i
end Formula
@[simp]
theorem LHom.realize_onFormula [L'.Structure M] (φ : L →ᴸ L') [φ.IsExpansionOn M] (ψ : L.Formula α)
{v : α → M} : (φ.onFormula ψ).Realize v ↔ ψ.Realize v :=
φ.realize_onBoundedFormula ψ
@[simp]
theorem LHom.setOf_realize_onFormula [L'.Structure M] (φ : L →ᴸ L') [φ.IsExpansionOn M]
(ψ : L.Formula α) : (setOf (φ.onFormula ψ).Realize : Set (α → M)) = setOf ψ.Realize := by
ext
simp
variable (M)
/-- A sentence can be evaluated as true or false in a structure. -/
nonrec def Sentence.Realize (φ : L.Sentence) : Prop :=
φ.Realize (default : _ → M)
-- input using \|= or \vDash, but not using \models
@[inherit_doc Sentence.Realize]
infixl:51 " ⊨ " => Sentence.Realize
@[simp]
theorem Sentence.realize_not {φ : L.Sentence} : M ⊨ φ.not ↔ ¬M ⊨ φ :=
Iff.rfl
namespace Formula
@[simp]
theorem realize_equivSentence_symm_con [L[[α]].Structure M]
[(L.lhomWithConstants α).IsExpansionOn M] (φ : L[[α]].Sentence) :
((equivSentence.symm φ).Realize fun a => (L.con a : M)) ↔ φ.Realize M := by
simp only [equivSentence, _root_.Equiv.symm_symm, Equiv.coe_trans, Realize,
BoundedFormula.realize_relabelEquiv, Function.comp]
refine _root_.trans ?_ BoundedFormula.realize_constantsVarsEquiv
rw [iff_iff_eq]
congr with (_ | a)
· simp
· cases a
@[simp]
theorem realize_equivSentence [L[[α]].Structure M] [(L.lhomWithConstants α).IsExpansionOn M]
(φ : L.Formula α) : (equivSentence φ).Realize M ↔ φ.Realize fun a => (L.con a : M) := by
rw [← realize_equivSentence_symm_con M (equivSentence φ), _root_.Equiv.symm_apply_apply]
theorem realize_equivSentence_symm (φ : L[[α]].Sentence) (v : α → M) :
(equivSentence.symm φ).Realize v ↔
@Sentence.Realize _ M (@Language.withConstantsStructure L M _ α (constantsOn.structure v))
φ :=
letI := constantsOn.structure v
realize_equivSentence_symm_con M φ
end Formula
@[simp]
theorem LHom.realize_onSentence [L'.Structure M] (φ : L →ᴸ L') [φ.IsExpansionOn M]
(ψ : L.Sentence) : M ⊨ φ.onSentence ψ ↔ M ⊨ ψ :=
φ.realize_onFormula ψ
variable (L)
/-- The complete theory of a structure `M` is the set of all sentences `M` satisfies. -/
def completeTheory : L.Theory :=
{ φ | M ⊨ φ }
variable (N)
/-- Two structures are elementarily equivalent when they satisfy the same sentences. -/
def ElementarilyEquivalent : Prop :=
L.completeTheory M = L.completeTheory N
@[inherit_doc FirstOrder.Language.ElementarilyEquivalent]
scoped[FirstOrder]
notation:25 A " ≅[" L "] " B:50 => FirstOrder.Language.ElementarilyEquivalent L A B
variable {L} {M} {N}
@[simp]
theorem mem_completeTheory {φ : Sentence L} : φ ∈ L.completeTheory M ↔ M ⊨ φ :=
Iff.rfl
theorem elementarilyEquivalent_iff : M ≅[L] N ↔ ∀ φ : L.Sentence, M ⊨ φ ↔ N ⊨ φ := by
simp only [ElementarilyEquivalent, Set.ext_iff, completeTheory, Set.mem_setOf_eq]
variable (M)
/-- A model of a theory is a structure in which every sentence is realized as true. -/
class Theory.Model (T : L.Theory) : Prop where
realize_of_mem : ∀ φ ∈ T, M ⊨ φ
-- input using \|= or \vDash, but not using \models
@[inherit_doc Theory.Model]
infixl:51 " ⊨ " => Theory.Model
|
variable {M} (T : L.Theory)
@[simp default - 10]
theorem Theory.model_iff : M ⊨ T ↔ ∀ φ ∈ T, M ⊨ φ :=
| Mathlib/ModelTheory/Semantics.lean | 677 | 681 |
/-
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.FieldTheory.PurelyInseparable.Basic
import Mathlib.FieldTheory.PerfectClosure
/-!
# `IsPerfectClosure` predicate
This file contains `IsPerfectClosure` which asserts that `L` is a perfect closure of `K` under a
ring homomorphism `i : K →+* L`, as well as its basic properties.
## Main definitions
- `pNilradical`: given a natural number `p`, the `p`-nilradical of a ring is defined to be the
nilradical if `p > 1` (`pNilradical_eq_nilradical`), and defined to be the zero ideal if `p ≤ 1`
(`pNilradical_eq_bot'`). Equivalently, it is the ideal consisting of elements `x` such that
`x ^ p ^ n = 0` for some `n` (`mem_pNilradical`).
- `IsPRadical`: a ring homomorphism `i : K →+* L` of characteristic `p` rings is called `p`-radical,
if or any element `x` of `L` there is `n : ℕ` such that `x ^ (p ^ n)` is contained in `K`,
and the kernel of `i` is contained in the `p`-nilradical of `K`.
A generalization of purely inseparable extension for fields.
- `IsPerfectClosure`: if `i : K →+* L` is `p`-radical ring homomorphism, then it makes `L` a
perfect closure of `K`, if `L` is perfect.
Our definition makes it synonymous to `IsPRadical` if `PerfectRing L p` is present. A caveat is
that you need to write `[PerfectRing L p] [IsPerfectClosure i p]`. This is similar to
`PerfectRing` which has `ExpChar` as a prerequisite.
- `PerfectRing.lift`: if a `p`-radical ring homomorphism `K →+* L` is given, `M` is a perfect ring,
then any ring homomorphism `K →+* M` can be lifted to `L →+* M`.
This is similar to `IsAlgClosed.lift` and `IsSepClosed.lift`.
- `PerfectRing.liftEquiv`: `K →+* M` is one-to-one correspondence to `L →+* M`,
given by `PerfectRing.lift`. This is a generalization to `PerfectClosure.lift`.
- `IsPerfectClosure.equiv`: perfect closures of a ring are isomorphic.
## Main results
- `IsPRadical.trans`: composition of `p`-radical ring homomorphisms is also `p`-radical.
- `PerfectClosure.isPRadical`: the absolute perfect closure `PerfectClosure` is a `p`-radical
extension over the base ring, in particular, it is a perfect closure of the base ring.
- `IsPRadical.isPurelyInseparable`, `IsPurelyInseparable.isPRadical`: `p`-radical and
purely inseparable are equivalent for fields.
- The (relative) perfect closure `perfectClosure` is a perfect closure
(inferred from `IsPurelyInseparable.isPRadical` automatically by Lean).
## Tags
perfect ring, perfect closure, purely inseparable
-/
open Module Polynomial IntermediateField Field
noncomputable section
/-- Given a natural number `p`, the `p`-nilradical of a ring is defined to be the
nilradical if `p > 1` (`pNilradical_eq_nilradical`), and defined to be the zero ideal if `p ≤ 1`
(`pNilradical_eq_bot'`). Equivalently, it is the ideal consisting of elements `x` such that
`x ^ p ^ n = 0` for some `n` (`mem_pNilradical`). -/
def pNilradical (R : Type*) [CommSemiring R] (p : ℕ) : Ideal R := if 1 < p then nilradical R else ⊥
theorem pNilradical_le_nilradical {R : Type*} [CommSemiring R] {p : ℕ} :
pNilradical R p ≤ nilradical R := by
by_cases hp : 1 < p
· rw [pNilradical, if_pos hp]
simp_rw [pNilradical, if_neg hp, bot_le]
theorem pNilradical_eq_nilradical {R : Type*} [CommSemiring R] {p : ℕ} (hp : 1 < p) :
pNilradical R p = nilradical R := by rw [pNilradical, if_pos hp]
theorem pNilradical_eq_bot {R : Type*} [CommSemiring R] {p : ℕ} (hp : ¬ 1 < p) :
pNilradical R p = ⊥ := by rw [pNilradical, if_neg hp]
theorem pNilradical_eq_bot' {R : Type*} [CommSemiring R] {p : ℕ} (hp : p ≤ 1) :
pNilradical R p = ⊥ := pNilradical_eq_bot (not_lt.2 hp)
theorem pNilradical_prime {R : Type*} [CommSemiring R] {p : ℕ} (hp : p.Prime) :
pNilradical R p = nilradical R := pNilradical_eq_nilradical hp.one_lt
theorem pNilradical_one {R : Type*} [CommSemiring R] :
pNilradical R 1 = ⊥ := pNilradical_eq_bot' rfl.le
theorem mem_pNilradical {R : Type*} [CommSemiring R] {p : ℕ} {x : R} :
x ∈ pNilradical R p ↔ ∃ n : ℕ, x ^ p ^ n = 0 := by
by_cases hp : 1 < p
· rw [pNilradical_eq_nilradical hp]
refine ⟨fun ⟨n, h⟩ ↦ ⟨n, ?_⟩, fun ⟨n, h⟩ ↦ ⟨p ^ n, h⟩⟩
rw [← Nat.sub_add_cancel ((n.lt_pow_self hp).le), pow_add, h, mul_zero]
rw [pNilradical_eq_bot hp, Ideal.mem_bot]
refine ⟨fun h ↦ ⟨0, by rw [pow_zero, pow_one, h]⟩, fun ⟨n, h⟩ ↦ ?_⟩
rcases Nat.le_one_iff_eq_zero_or_eq_one.1 (not_lt.1 hp) with hp | hp
· by_cases hn : n = 0
· rwa [hn, pow_zero, pow_one] at h
rw [hp, zero_pow hn, pow_zero] at h
subsingleton [subsingleton_of_zero_eq_one h.symm]
rwa [hp, one_pow, pow_one] at h
theorem sub_mem_pNilradical_iff_pow_expChar_pow_eq {R : Type*} [CommRing R] {p : ℕ} [ExpChar R p]
{x y : R} : x - y ∈ pNilradical R p ↔ ∃ n : ℕ, x ^ p ^ n = y ^ p ^ n := by
simp_rw [mem_pNilradical, sub_pow_expChar_pow, sub_eq_zero]
theorem pow_expChar_pow_inj_of_pNilradical_eq_bot (R : Type*) [CommRing R] (p : ℕ) [ExpChar R p]
(h : pNilradical R p = ⊥) (n : ℕ) : Function.Injective fun x : R ↦ x ^ p ^ n := fun _ _ H ↦
sub_eq_zero.1 <| Ideal.mem_bot.1 <| h ▸ sub_mem_pNilradical_iff_pow_expChar_pow_eq.2 ⟨n, H⟩
theorem pNilradical_eq_bot_of_frobenius_inj (R : Type*) [CommSemiring R] (p : ℕ) [ExpChar R p]
(h : Function.Injective (frobenius R p)) : pNilradical R p = ⊥ := bot_unique fun x ↦ by
rw [mem_pNilradical, Ideal.mem_bot]
exact fun ⟨n, _⟩ ↦ h.iterate n (by rwa [← coe_iterateFrobenius, map_zero])
theorem PerfectRing.pNilradical_eq_bot (R : Type*) [CommSemiring R] (p : ℕ) [ExpChar R p]
[PerfectRing R p] : pNilradical R p = ⊥ :=
pNilradical_eq_bot_of_frobenius_inj R p (injective_frobenius R p)
section IsPerfectClosure
variable {K L M N : Type*}
section CommSemiring
variable [CommSemiring K] [CommSemiring L] [CommSemiring M]
(i : K →+* L) (j : K →+* M) (f : L →+* M) (p : ℕ)
/-- If `i : K →+* L` is a ring homomorphism of characteristic `p` rings, then it is called
`p`-radical if the following conditions are satisfied:
- For any element `x` of `L` there is `n : ℕ` such that `x ^ (p ^ n)` is contained in `K`.
- The kernel of `i` is contained in the `p`-nilradical of `K`.
It is a generalization of purely inseparable extension for fields. -/
@[mk_iff]
class IsPRadical : Prop where
pow_mem' : ∀ x : L, ∃ (n : ℕ) (y : K), i y = x ^ p ^ n
ker_le' : RingHom.ker i ≤ pNilradical K p
theorem IsPRadical.pow_mem [IsPRadical i p] (x : L) :
∃ (n : ℕ) (y : K), i y = x ^ p ^ n := pow_mem' x
theorem IsPRadical.ker_le [IsPRadical i p] :
RingHom.ker i ≤ pNilradical K p := ker_le'
theorem IsPRadical.comap_pNilradical [IsPRadical i p] :
(pNilradical L p).comap i = pNilradical K p := by
refine le_antisymm (fun x h ↦ mem_pNilradical.2 ?_) (fun x h ↦ ?_)
· obtain ⟨n, h⟩ := mem_pNilradical.1 <| Ideal.mem_comap.1 h
obtain ⟨m, h⟩ := mem_pNilradical.1 <| ker_le i p ((map_pow i x _).symm ▸ h)
exact ⟨n + m, by rwa [pow_add, pow_mul]⟩
simp only [Ideal.mem_comap, mem_pNilradical] at h ⊢
obtain ⟨n, h⟩ := h
exact ⟨n, by simpa only [map_pow, map_zero] using congr(i $h)⟩
variable (K) in
instance IsPRadical.of_id : IsPRadical (RingHom.id K) p where
pow_mem' x := ⟨0, x, by simp⟩
ker_le' x h := by convert Ideal.zero_mem _
/-- Composition of `p`-radical ring homomorphisms is also `p`-radical. -/
theorem IsPRadical.trans [IsPRadical i p] [IsPRadical f p] :
IsPRadical (f.comp i) p where
pow_mem' x := by
obtain ⟨n, y, hy⟩ := pow_mem f p x
| obtain ⟨m, z, hz⟩ := pow_mem i p y
exact ⟨n + m, z, by rw [RingHom.comp_apply, hz, map_pow, hy, pow_add, pow_mul]⟩
ker_le' x h := by
rw [RingHom.mem_ker, RingHom.comp_apply, ← RingHom.mem_ker] at h
simpa only [← Ideal.mem_comap, comap_pNilradical] using ker_le f p h
/-- If `i : K →+* L` is a `p`-radical ring homomorphism, then it makes `L` a perfect closure
of `K`, if `L` is perfect.
In this case the kernel of `i` is equal to the `p`-nilradical of `K`
| Mathlib/FieldTheory/IsPerfectClosure.lean | 173 | 181 |
/-
Copyright (c) 2020 Jannis Limperg. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Jannis Limperg
-/
import Mathlib.Data.List.Induction
/-!
# Lemmas about List.*Idx functions.
Some specification lemmas for `List.mapIdx`, `List.mapIdxM`, `List.foldlIdx` and `List.foldrIdx`.
As of 2025-01-29, these are not used anywhere in Mathlib. Moreover, with
`List.enum` and `List.enumFrom` being replaced by `List.zipIdx`
in Lean's `nightly-2025-01-29` release, they now use deprecated functions and theorems.
Rather than updating this unused material, we are deprecating it.
Anyone wanting to restore this material is welcome to do so, but will need to update uses of
`List.enum` and `List.enumFrom` to use `List.zipIdx` instead.
However, note that this material will later be implemented in the Lean standard library.
-/
assert_not_exists MonoidWithZero
universe u v
open Function
namespace List
variable {α : Type u} {β : Type v}
section MapIdx
@[deprecated reverseRecOn (since := "2025-01-28")]
theorem list_reverse_induction (p : List α → Prop) (base : p [])
(ind : ∀ (l : List α) (e : α), p l → p (l ++ [e])) : (∀ (l : List α), p l) :=
fun l => l.reverseRecOn base ind
theorem mapIdx_append_one : ∀ {f : ℕ → α → β} {l : List α} {e : α},
mapIdx f (l ++ [e]) = mapIdx f l ++ [f l.length e] :=
mapIdx_concat
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29"), local simp]
theorem map_enumFrom_eq_zipWith : ∀ (l : List α) (n : ℕ) (f : ℕ → α → β),
map (uncurry f) (enumFrom n l) = zipWith (fun i ↦ f (i + n)) (range (length l)) l := by
intro l
generalize e : l.length = len
revert l
induction' len with len ih <;> intros l e n f
· have : l = [] := by
cases l
· rfl
· contradiction
rw [this]; rfl
· rcases l with - | ⟨head, tail⟩
· contradiction
· simp only [enumFrom_cons, map_cons, range_succ_eq_map, zipWith_cons_cons,
Nat.zero_add, zipWith_map_left, true_and]
rw [ih]
· suffices (fun i ↦ f (i + (n + 1))) = ((fun i ↦ f (i + n)) ∘ Nat.succ) by
rw [this]
rfl
funext n' a
simp only [comp, Nat.add_assoc, Nat.add_comm, Nat.add_succ]
simp only [length_cons, Nat.succ.injEq] at e; exact e
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem get_mapIdx (l : List α) (f : ℕ → α → β) (i : ℕ) (h : i < l.length)
(h' : i < (l.mapIdx f).length := h.trans_le length_mapIdx.ge) :
(l.mapIdx f).get ⟨i, h'⟩ = f i (l.get ⟨i, h⟩) := by
simp [mapIdx_eq_zipIdx_map, enum_eq_zip_range]
theorem mapIdx_eq_ofFn (l : List α) (f : ℕ → α → β) :
l.mapIdx f = ofFn fun i : Fin l.length ↦ f (i : ℕ) (l.get i) := by
induction l generalizing f with
| nil => simp
| cons _ _ IH => simp [IH]
end MapIdx
section FoldrIdx
-- Porting note: Changed argument order of `foldrIdxSpec` to align better with `foldrIdx`.
set_option linter.deprecated false in
/-- Specification of `foldrIdx`. -/
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
def foldrIdxSpec (f : ℕ → α → β → β) (b : β) (as : List α) (start : ℕ) : β :=
foldr (uncurry f) b <| enumFrom start as
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldrIdxSpec_cons (f : ℕ → α → β → β) (b a as start) :
foldrIdxSpec f b (a :: as) start = f start a (foldrIdxSpec f b as (start + 1)) :=
rfl
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldrIdx_eq_foldrIdxSpec (f : ℕ → α → β → β) (b as start) :
foldrIdx f b as start = foldrIdxSpec f b as start := by
induction as generalizing start
· rfl
· simp only [foldrIdx, foldrIdxSpec_cons, *]
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldrIdx_eq_foldr_enum (f : ℕ → α → β → β) (b : β) (as : List α) :
foldrIdx f b as = foldr (uncurry f) b (enum as) := by
simp only [foldrIdx, foldrIdxSpec, foldrIdx_eq_foldrIdxSpec, enum]
end FoldrIdx
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem indexesValues_eq_filter_enum (p : α → Prop) [DecidablePred p] (as : List α) :
indexesValues p as = filter (p ∘ Prod.snd) (enum as) := by
simp +unfoldPartialApp [indexesValues, foldrIdx_eq_foldr_enum, uncurry,
filter_eq_foldr, cond_eq_if]
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem findIdxs_eq_map_indexesValues (p : α → Prop) [DecidablePred p] (as : List α) :
findIdxs p as = map Prod.fst (indexesValues p as) := by
simp +unfoldPartialApp only [indexesValues_eq_filter_enum,
map_filter_eq_foldr, findIdxs, uncurry, foldrIdx_eq_foldr_enum, decide_eq_true_eq, comp_apply,
Bool.cond_decide]
section FoldlIdx
-- Porting note: Changed argument order of `foldlIdxSpec` to align better with `foldlIdx`.
set_option linter.deprecated false in
/-- Specification of `foldlIdx`. -/
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
def foldlIdxSpec (f : ℕ → α → β → α) (a : α) (bs : List β) (start : ℕ) : α :=
foldl (fun a p ↦ f p.fst a p.snd) a <| enumFrom start bs
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldlIdxSpec_cons (f : ℕ → α → β → α) (a b bs start) :
foldlIdxSpec f a (b :: bs) start = foldlIdxSpec f (f start a b) bs (start + 1) :=
rfl
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldlIdx_eq_foldlIdxSpec (f : ℕ → α → β → α) (a bs start) :
foldlIdx f a bs start = foldlIdxSpec f a bs start := by
induction bs generalizing start a
· rfl
· simp [foldlIdxSpec, *]
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldlIdx_eq_foldl_enum (f : ℕ → α → β → α) (a : α) (bs : List β) :
foldlIdx f a bs = foldl (fun a p ↦ f p.fst a p.snd) a (enum bs) := by
simp only [foldlIdx, foldlIdxSpec, foldlIdx_eq_foldlIdxSpec, enum]
end FoldlIdx
section FoldIdxM
-- Porting note: `foldrM_eq_foldr` now depends on `[LawfulMonad m]`
variable {m : Type u → Type v} [Monad m]
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldrIdxM_eq_foldrM_enum {β} (f : ℕ → α → β → m β) (b : β) (as : List α) [LawfulMonad m] :
foldrIdxM f b as = foldrM (uncurry f) b (enum as) := by
simp +unfoldPartialApp only [foldrIdxM, foldrM_eq_foldr,
foldrIdx_eq_foldr_enum, uncurry]
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem foldlIdxM_eq_foldlM_enum [LawfulMonad m] {β} (f : ℕ → β → α → m β) (b : β) (as : List α) :
foldlIdxM f b as = List.foldlM (fun b p ↦ f p.fst b p.snd) b (enum as) := by
rw [foldlIdxM, foldlM_eq_foldl, foldlIdx_eq_foldl_enum]
end FoldIdxM
section MapIdxM
-- Porting note: `[Applicative m]` replaced by `[Monad m] [LawfulMonad m]`
variable {m : Type u → Type v} [Monad m]
set_option linter.deprecated false in
/-- Specification of `mapIdxMAux`. -/
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
def mapIdxMAuxSpec {β} (f : ℕ → α → m β) (start : ℕ) (as : List α) : m (List β) :=
List.traverse (uncurry f) <| enumFrom start as
-- Note: `traverse` the class method would require a less universe-polymorphic
-- `m : Type u → Type u`.
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem mapIdxMAuxSpec_cons {β} (f : ℕ → α → m β) (start : ℕ) (a : α) (as : List α) :
mapIdxMAuxSpec f start (a :: as) = cons <$> f start a <*> mapIdxMAuxSpec f (start + 1) as :=
rfl
|
set_option linter.deprecated false in
@[deprecated "Deprecated without replacement." (since := "2025-01-29")]
theorem mapIdxMGo_eq_mapIdxMAuxSpec
| Mathlib/Data/List/Indexes.lean | 198 | 201 |
/-
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.OuterMeasure.Operations
import Mathlib.Analysis.SpecificLimits.Basic
/-!
# Outer measures from functions
Given an arbitrary function `m : Set α → ℝ≥0∞` that sends `∅` to `0` we can define an outer
measure on `α` that on `s` is defined to be the infimum of `∑ᵢ, m (sᵢ)` for all collections of sets
`sᵢ` that cover `s`. This is the unique maximal outer measure that is at most the given function.
Given an outer measure `m`, the Carathéodory-measurable sets are the sets `s` such that
for all sets `t` we have `m t = m (t ∩ s) + m (t \ s)`. This forms a measurable space.
## Main definitions and statements
* `OuterMeasure.boundedBy` is the greatest outer measure that is at most the given function.
If you know that the given function sends `∅` to `0`, then `OuterMeasure.ofFunction` is a
special case.
* `sInf_eq_boundedBy_sInfGen` is a characterization of the infimum of outer measures.
## References
* <https://en.wikipedia.org/wiki/Outer_measure>
* <https://en.wikipedia.org/wiki/Carath%C3%A9odory%27s_criterion>
## Tags
outer measure, Carathéodory-measurable, Carathéodory's criterion
-/
assert_not_exists Basis
noncomputable section
open Set Function Filter
open scoped NNReal Topology ENNReal
namespace MeasureTheory
namespace OuterMeasure
section OfFunction
variable {α : Type*}
/-- Given any function `m` assigning measures to sets satisfying `m ∅ = 0`, there is
a unique maximal outer measure `μ` satisfying `μ s ≤ m s` for all `s : Set α`. -/
protected def ofFunction (m : Set α → ℝ≥0∞) (m_empty : m ∅ = 0) : OuterMeasure α :=
let μ s := ⨅ (f : ℕ → Set α) (_ : s ⊆ ⋃ i, f i), ∑' i, m (f i)
{ measureOf := μ
empty :=
le_antisymm
((iInf_le_of_le fun _ => ∅) <| iInf_le_of_le (empty_subset _) <| by simp [m_empty])
(zero_le _)
mono := fun {_ _} hs => iInf_mono fun _ => iInf_mono' fun hb => ⟨hs.trans hb, le_rfl⟩
iUnion_nat := fun s _ =>
ENNReal.le_of_forall_pos_le_add <| by
intro ε hε (hb : (∑' i, μ (s i)) < ∞)
rcases ENNReal.exists_pos_sum_of_countable (ENNReal.coe_pos.2 hε).ne' ℕ with ⟨ε', hε', hl⟩
refine le_trans ?_ (add_le_add_left (le_of_lt hl) _)
rw [← ENNReal.tsum_add]
choose f hf using
show ∀ i, ∃ f : ℕ → Set α, (s i ⊆ ⋃ i, f i) ∧ (∑' i, m (f i)) < μ (s i) + ε' i by
intro i
have : μ (s i) < μ (s i) + ε' i :=
ENNReal.lt_add_right (ne_top_of_le_ne_top hb.ne <| ENNReal.le_tsum _)
(by simpa using (hε' i).ne')
rcases iInf_lt_iff.mp this with ⟨t, ht⟩
exists t
contrapose! ht
exact le_iInf ht
refine le_trans ?_ (ENNReal.tsum_le_tsum fun i => le_of_lt (hf i).2)
rw [← ENNReal.tsum_prod, ← Nat.pairEquiv.symm.tsum_eq]
refine iInf_le_of_le _ (iInf_le _ ?_)
apply iUnion_subset
intro i
apply Subset.trans (hf i).1
apply iUnion_subset
simp only [Nat.pairEquiv_symm_apply]
rw [iUnion_unpair]
intro j
apply subset_iUnion₂ i }
variable (m : Set α → ℝ≥0∞) (m_empty : m ∅ = 0)
/-- `ofFunction` of a set `s` is the infimum of `∑ᵢ, m (tᵢ)` for all collections of sets
`tᵢ` that cover `s`. -/
theorem ofFunction_apply (s : Set α) :
OuterMeasure.ofFunction m m_empty s = ⨅ (t : ℕ → Set α) (_ : s ⊆ iUnion t), ∑' n, m (t n) :=
rfl
/-- `ofFunction` of a set `s` is the infimum of `∑ᵢ, m (tᵢ)` for all collections of sets
`tᵢ` that cover `s`, with all `tᵢ` satisfying a predicate `P` such that `m` is infinite for sets
that don't satisfy `P`.
This is similar to `ofFunction_apply`, except that the sets `tᵢ` satisfy `P`.
The hypothesis `m_top` applies in particular to a function of the form `extend m'`. -/
theorem ofFunction_eq_iInf_mem {P : Set α → Prop} (m_top : ∀ s, ¬ P s → m s = ∞) (s : Set α) :
OuterMeasure.ofFunction m m_empty s =
⨅ (t : ℕ → Set α) (_ : ∀ i, P (t i)) (_ : s ⊆ ⋃ i, t i), ∑' i, m (t i) := by
rw [OuterMeasure.ofFunction_apply]
apply le_antisymm
· exact le_iInf fun t ↦ le_iInf fun _ ↦ le_iInf fun h ↦ iInf₂_le _ (by exact h)
· simp_rw [le_iInf_iff]
refine fun t ht_subset ↦ iInf_le_of_le t ?_
by_cases ht : ∀ i, P (t i)
· exact iInf_le_of_le ht (iInf_le_of_le ht_subset le_rfl)
· simp only [ht, not_false_eq_true, iInf_neg, top_le_iff]
push_neg at ht
obtain ⟨i, hti_not_mem⟩ := ht
have hfi_top : m (t i) = ∞ := m_top _ hti_not_mem
exact ENNReal.tsum_eq_top_of_eq_top ⟨i, hfi_top⟩
variable {m m_empty}
theorem ofFunction_le (s : Set α) : OuterMeasure.ofFunction m m_empty s ≤ m s :=
let f : ℕ → Set α := fun i => Nat.casesOn i s fun _ => ∅
iInf_le_of_le f <|
iInf_le_of_le (subset_iUnion f 0) <|
le_of_eq <| tsum_eq_single 0 <| by
rintro (_ | i)
· simp
· simp [f, m_empty]
theorem ofFunction_eq (s : Set α) (m_mono : ∀ ⦃t : Set α⦄, s ⊆ t → m s ≤ m t)
(m_subadd : ∀ s : ℕ → Set α, m (⋃ i, s i) ≤ ∑' i, m (s i)) :
OuterMeasure.ofFunction m m_empty s = m s :=
le_antisymm (ofFunction_le s) <|
le_iInf fun f => le_iInf fun hf => le_trans (m_mono hf) (m_subadd f)
theorem le_ofFunction {μ : OuterMeasure α} :
μ ≤ OuterMeasure.ofFunction m m_empty ↔ ∀ s, μ s ≤ m s :=
⟨fun H s => le_trans (H s) (ofFunction_le s), fun H _ =>
le_iInf fun f =>
le_iInf fun hs =>
le_trans (μ.mono hs) <| le_trans (measure_iUnion_le f) <| ENNReal.tsum_le_tsum fun _ => H _⟩
theorem isGreatest_ofFunction :
IsGreatest { μ : OuterMeasure α | ∀ s, μ s ≤ m s } (OuterMeasure.ofFunction m m_empty) :=
⟨fun _ => ofFunction_le _, fun _ => le_ofFunction.2⟩
theorem ofFunction_eq_sSup : OuterMeasure.ofFunction m m_empty = sSup { μ | ∀ s, μ s ≤ m s } :=
(@isGreatest_ofFunction α m m_empty).isLUB.sSup_eq.symm
/-- If `m u = ∞` for any set `u` that has nonempty intersection both with `s` and `t`, then
`μ (s ∪ t) = μ s + μ t`, where `μ = MeasureTheory.OuterMeasure.ofFunction m m_empty`.
E.g., if `α` is an (e)metric space and `m u = ∞` on any set of diameter `≥ r`, then this lemma
implies that `μ (s ∪ t) = μ s + μ t` on any two sets such that `r ≤ edist x y` for all `x ∈ s`
and `y ∈ t`. -/
theorem ofFunction_union_of_top_of_nonempty_inter {s t : Set α}
(h : ∀ u, (s ∩ u).Nonempty → (t ∩ u).Nonempty → m u = ∞) :
OuterMeasure.ofFunction m m_empty (s ∪ t) =
OuterMeasure.ofFunction m m_empty s + OuterMeasure.ofFunction m m_empty t := by
refine le_antisymm (measure_union_le _ _) (le_iInf₂ fun f hf ↦ ?_)
set μ := OuterMeasure.ofFunction m m_empty
rcases Classical.em (∃ i, (s ∩ f i).Nonempty ∧ (t ∩ f i).Nonempty) with (⟨i, hs, ht⟩ | he)
· calc
μ s + μ t ≤ ∞ := le_top
_ = m (f i) := (h (f i) hs ht).symm
_ ≤ ∑' i, m (f i) := ENNReal.le_tsum i
set I := fun s => { i : ℕ | (s ∩ f i).Nonempty }
have hd : Disjoint (I s) (I t) := disjoint_iff_inf_le.mpr fun i hi => he ⟨i, hi⟩
have hI : ∀ u ⊆ s ∪ t, μ u ≤ ∑' i : I u, μ (f i) := fun u hu =>
calc
μ u ≤ μ (⋃ i : I u, f i) :=
μ.mono fun x hx =>
let ⟨i, hi⟩ := mem_iUnion.1 (hf (hu hx))
mem_iUnion.2 ⟨⟨i, ⟨x, hx, hi⟩⟩, hi⟩
_ ≤ ∑' i : I u, μ (f i) := measure_iUnion_le _
calc
μ s + μ t ≤ (∑' i : I s, μ (f i)) + ∑' i : I t, μ (f i) :=
add_le_add (hI _ subset_union_left) (hI _ subset_union_right)
_ = ∑' i : ↑(I s ∪ I t), μ (f i) :=
(ENNReal.summable.tsum_union_disjoint (f := fun i => μ (f i)) hd ENNReal.summable).symm
_ ≤ ∑' i, μ (f i) :=
(ENNReal.summable.tsum_le_tsum_of_inj (↑) Subtype.coe_injective (fun _ _ => zero_le _)
(fun _ => le_rfl) ENNReal.summable)
_ ≤ ∑' i, m (f i) := ENNReal.tsum_le_tsum fun i => ofFunction_le _
theorem comap_ofFunction {β} (f : β → α) (h : Monotone m ∨ Surjective f) :
comap f (OuterMeasure.ofFunction m m_empty) =
OuterMeasure.ofFunction (fun s => m (f '' s)) (by simp; simp [m_empty]) := by
refine le_antisymm (le_ofFunction.2 fun s => ?_) fun s => ?_
· rw [comap_apply]
apply ofFunction_le
· rw [comap_apply, ofFunction_apply, ofFunction_apply]
refine iInf_mono' fun t => ⟨fun k => f ⁻¹' t k, ?_⟩
refine iInf_mono' fun ht => ?_
rw [Set.image_subset_iff, preimage_iUnion] at ht
refine ⟨ht, ENNReal.tsum_le_tsum fun n => ?_⟩
rcases h with hl | hr
exacts [hl (image_preimage_subset _ _), (congr_arg m (hr.image_preimage (t n))).le]
theorem map_ofFunction_le {β} (f : α → β) :
map f (OuterMeasure.ofFunction m m_empty) ≤
OuterMeasure.ofFunction (fun s => m (f ⁻¹' s)) m_empty :=
le_ofFunction.2 fun s => by
rw [map_apply]
apply ofFunction_le
theorem map_ofFunction {β} {f : α → β} (hf : Injective f) :
map f (OuterMeasure.ofFunction m m_empty) =
OuterMeasure.ofFunction (fun s => m (f ⁻¹' s)) m_empty := by
refine (map_ofFunction_le _).antisymm fun s => ?_
simp only [ofFunction_apply, map_apply, le_iInf_iff]
intro t ht
refine iInf_le_of_le (fun n => (range f)ᶜ ∪ f '' t n) (iInf_le_of_le ?_ ?_)
· rw [← union_iUnion, ← inter_subset, ← image_preimage_eq_inter_range, ← image_iUnion]
exact image_subset _ ht
· refine ENNReal.tsum_le_tsum fun n => le_of_eq ?_
simp [hf.preimage_image]
-- TODO (kmill): change `m (t ∩ s)` to `m (s ∩ t)`
theorem restrict_ofFunction (s : Set α) (hm : Monotone m) :
restrict s (OuterMeasure.ofFunction m m_empty) =
OuterMeasure.ofFunction (fun t => m (t ∩ s)) (by simp; simp [m_empty]) := by
rw [restrict]
simp only [inter_comm _ s, LinearMap.comp_apply]
rw [comap_ofFunction _ (Or.inl hm)]
simp only [map_ofFunction Subtype.coe_injective, Subtype.image_preimage_coe]
theorem smul_ofFunction {c : ℝ≥0∞} (hc : c ≠ ∞) : c • OuterMeasure.ofFunction m m_empty =
OuterMeasure.ofFunction (c • m) (by simp [m_empty]) := by
ext1 s
haveI : Nonempty { t : ℕ → Set α // s ⊆ ⋃ i, t i } := ⟨⟨fun _ => s, subset_iUnion (fun _ => s) 0⟩⟩
simp only [smul_apply, ofFunction_apply, ENNReal.tsum_mul_left, Pi.smul_apply, smul_eq_mul,
iInf_subtype']
rw [ENNReal.mul_iInf fun h => (hc h).elim]
end OfFunction
section BoundedBy
variable {α : Type*} (m : Set α → ℝ≥0∞)
/-- Given any function `m` assigning measures to sets, there is a unique maximal outer measure `μ`
satisfying `μ s ≤ m s` for all `s : Set α`. This is the same as `OuterMeasure.ofFunction`,
except that it doesn't require `m ∅ = 0`. -/
def boundedBy : OuterMeasure α :=
OuterMeasure.ofFunction (fun s => ⨆ _ : s.Nonempty, m s) (by simp [Set.not_nonempty_empty])
variable {m}
theorem boundedBy_le (s : Set α) : boundedBy m s ≤ m s :=
(ofFunction_le _).trans iSup_const_le
theorem boundedBy_eq_ofFunction (m_empty : m ∅ = 0) (s : Set α) :
boundedBy m s = OuterMeasure.ofFunction m m_empty s := by
have : (fun s : Set α => ⨆ _ : s.Nonempty, m s) = m := by
ext1 t
rcases t.eq_empty_or_nonempty with h | h <;> simp [h, Set.not_nonempty_empty, m_empty]
simp [boundedBy, this]
|
theorem boundedBy_apply (s : Set α) :
boundedBy m s = ⨅ (t : ℕ → Set α) (_ : s ⊆ iUnion t),
| Mathlib/MeasureTheory/OuterMeasure/OfFunction.lean | 260 | 262 |
/-
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.Order.ConditionallyCompleteLattice.Basic
import Mathlib.Order.Cover
import Mathlib.Order.Iterate
/-!
# Successor and predecessor
This file defines successor and predecessor orders. `succ a`, the successor of an element `a : α` is
the least element greater than `a`. `pred a` is the greatest element less than `a`. Typical examples
include `ℕ`, `ℤ`, `ℕ+`, `Fin n`, but also `ENat`, the lexicographic order of a successor/predecessor
order...
## Typeclasses
* `SuccOrder`: Order equipped with a sensible successor function.
* `PredOrder`: Order equipped with a sensible predecessor function.
## Implementation notes
Maximal elements don't have a sensible successor. Thus the naïve typeclass
```lean
class NaiveSuccOrder (α : Type*) [Preorder α] where
(succ : α → α)
(succ_le_iff : ∀ {a b}, succ a ≤ b ↔ a < b)
(lt_succ_iff : ∀ {a b}, a < succ b ↔ a ≤ b)
```
can't apply to an `OrderTop` because plugging in `a = b = ⊤` into either of `succ_le_iff` and
`lt_succ_iff` yields `⊤ < ⊤` (or more generally `m < m` for a maximal element `m`).
The solution taken here is to remove the implications `≤ → <` and instead require that `a < succ a`
for all non maximal elements (enforced by the combination of `le_succ` and the contrapositive of
`max_of_succ_le`).
The stricter condition of every element having a sensible successor can be obtained through the
combination of `SuccOrder α` and `NoMaxOrder α`.
-/
open Function OrderDual Set
variable {α β : Type*}
/-- Order equipped with a sensible successor function. -/
@[ext]
class SuccOrder (α : Type*) [Preorder α] where
/-- Successor function -/
succ : α → α
/-- Proof of basic ordering with respect to `succ` -/
le_succ : ∀ a, a ≤ succ a
/-- Proof of interaction between `succ` and maximal element -/
max_of_succ_le {a} : succ a ≤ a → IsMax a
/-- Proof that `succ a` is the least element greater than `a` -/
succ_le_of_lt {a b} : a < b → succ a ≤ b
/-- Order equipped with a sensible predecessor function. -/
@[ext]
class PredOrder (α : Type*) [Preorder α] where
/-- Predecessor function -/
pred : α → α
/-- Proof of basic ordering with respect to `pred` -/
pred_le : ∀ a, pred a ≤ a
/-- Proof of interaction between `pred` and minimal element -/
min_of_le_pred {a} : a ≤ pred a → IsMin a
/-- Proof that `pred b` is the greatest element less than `b` -/
le_pred_of_lt {a b} : a < b → a ≤ pred b
instance [Preorder α] [SuccOrder α] :
PredOrder αᵒᵈ where
pred := toDual ∘ SuccOrder.succ ∘ ofDual
pred_le := by
simp only [comp, OrderDual.forall, ofDual_toDual, toDual_le_toDual,
SuccOrder.le_succ, implies_true]
min_of_le_pred h := by apply SuccOrder.max_of_succ_le h
le_pred_of_lt := by intro a b h; exact SuccOrder.succ_le_of_lt h
instance [Preorder α] [PredOrder α] :
SuccOrder αᵒᵈ where
succ := toDual ∘ PredOrder.pred ∘ ofDual
le_succ := by
simp only [comp, OrderDual.forall, ofDual_toDual, toDual_le_toDual,
PredOrder.pred_le, implies_true]
max_of_succ_le h := by apply PredOrder.min_of_le_pred h
succ_le_of_lt := by intro a b h; exact PredOrder.le_pred_of_lt h
section Preorder
variable [Preorder α]
/-- A constructor for `SuccOrder α` usable when `α` has no maximal element. -/
def SuccOrder.ofSuccLeIff (succ : α → α) (hsucc_le_iff : ∀ {a b}, succ a ≤ b ↔ a < b) :
SuccOrder α :=
{ succ
le_succ := fun _ => (hsucc_le_iff.1 le_rfl).le
max_of_succ_le := fun ha => (lt_irrefl _ <| hsucc_le_iff.1 ha).elim
succ_le_of_lt := fun h => hsucc_le_iff.2 h }
/-- A constructor for `PredOrder α` usable when `α` has no minimal element. -/
def PredOrder.ofLePredIff (pred : α → α) (hle_pred_iff : ∀ {a b}, a ≤ pred b ↔ a < b) :
PredOrder α :=
{ pred
pred_le := fun _ => (hle_pred_iff.1 le_rfl).le
min_of_le_pred := fun ha => (lt_irrefl _ <| hle_pred_iff.1 ha).elim
le_pred_of_lt := fun h => hle_pred_iff.2 h }
end Preorder
section LinearOrder
variable [LinearOrder α]
/-- A constructor for `SuccOrder α` for `α` a linear order. -/
@[simps]
def SuccOrder.ofCore (succ : α → α) (hn : ∀ {a}, ¬IsMax a → ∀ b, a < b ↔ succ a ≤ b)
(hm : ∀ a, IsMax a → succ a = a) : SuccOrder α :=
{ succ
succ_le_of_lt := fun {a b} =>
by_cases (fun h hab => (hm a h).symm ▸ hab.le) fun h => (hn h b).mp
le_succ := fun a =>
by_cases (fun h => (hm a h).symm.le) fun h => le_of_lt <| by simpa using (hn h a).not
max_of_succ_le := fun {a} => not_imp_not.mp fun h => by simpa using (hn h a).not }
/-- A constructor for `PredOrder α` for `α` a linear order. -/
@[simps]
def PredOrder.ofCore (pred : α → α)
(hn : ∀ {a}, ¬IsMin a → ∀ b, b ≤ pred a ↔ b < a) (hm : ∀ a, IsMin a → pred a = a) :
PredOrder α :=
{ pred
le_pred_of_lt := fun {a b} =>
by_cases (fun h hab => (hm b h).symm ▸ hab.le) fun h => (hn h a).mpr
pred_le := fun a =>
by_cases (fun h => (hm a h).le) fun h => le_of_lt <| by simpa using (hn h a).not
min_of_le_pred := fun {a} => not_imp_not.mp fun h => by simpa using (hn h a).not }
variable (α)
open Classical in
/-- A well-order is a `SuccOrder`. -/
noncomputable def SuccOrder.ofLinearWellFoundedLT [WellFoundedLT α] : SuccOrder α :=
ofCore (fun a ↦ if h : (Ioi a).Nonempty then wellFounded_lt.min _ h else a)
(fun ha _ ↦ by
rw [not_isMax_iff] at ha
simp_rw [Set.Nonempty, mem_Ioi, dif_pos ha]
exact ⟨(wellFounded_lt.min_le · ha), lt_of_lt_of_le (wellFounded_lt.min_mem _ ha)⟩)
fun _ ha ↦ dif_neg (not_not_intro ha <| not_isMax_iff.mpr ·)
/-- A linear order with well-founded greater-than relation is a `PredOrder`. -/
noncomputable def PredOrder.ofLinearWellFoundedGT (α) [LinearOrder α] [WellFoundedGT α] :
PredOrder α := letI := SuccOrder.ofLinearWellFoundedLT αᵒᵈ; inferInstanceAs (PredOrder αᵒᵈᵒᵈ)
end LinearOrder
/-! ### Successor order -/
namespace Order
section Preorder
variable [Preorder α] [SuccOrder α] {a b : α}
/-- The successor of an element. If `a` is not maximal, then `succ a` is the least element greater
than `a`. If `a` is maximal, then `succ a = a`. -/
def succ : α → α :=
SuccOrder.succ
theorem le_succ : ∀ a : α, a ≤ succ a :=
SuccOrder.le_succ
theorem max_of_succ_le {a : α} : succ a ≤ a → IsMax a :=
SuccOrder.max_of_succ_le
theorem succ_le_of_lt {a b : α} : a < b → succ a ≤ b :=
SuccOrder.succ_le_of_lt
alias _root_.LT.lt.succ_le := succ_le_of_lt
@[simp]
theorem succ_le_iff_isMax : succ a ≤ a ↔ IsMax a :=
⟨max_of_succ_le, fun h => h <| le_succ _⟩
alias ⟨_root_.IsMax.of_succ_le, _root_.IsMax.succ_le⟩ := succ_le_iff_isMax
@[simp]
theorem lt_succ_iff_not_isMax : a < succ a ↔ ¬IsMax a :=
⟨not_isMax_of_lt, fun ha => (le_succ a).lt_of_not_le fun h => ha <| max_of_succ_le h⟩
alias ⟨_, lt_succ_of_not_isMax⟩ := lt_succ_iff_not_isMax
theorem wcovBy_succ (a : α) : a ⩿ succ a :=
⟨le_succ a, fun _ hb => (succ_le_of_lt hb).not_lt⟩
theorem covBy_succ_of_not_isMax (h : ¬IsMax a) : a ⋖ succ a :=
(wcovBy_succ a).covBy_of_lt <| lt_succ_of_not_isMax h
theorem lt_succ_of_le_of_not_isMax (hab : b ≤ a) (ha : ¬IsMax a) : b < succ a :=
hab.trans_lt <| lt_succ_of_not_isMax ha
theorem succ_le_iff_of_not_isMax (ha : ¬IsMax a) : succ a ≤ b ↔ a < b :=
⟨(lt_succ_of_not_isMax ha).trans_le, succ_le_of_lt⟩
lemma succ_lt_succ_of_not_isMax (h : a < b) (hb : ¬ IsMax b) : succ a < succ b :=
lt_succ_of_le_of_not_isMax (succ_le_of_lt h) hb
@[simp, mono, gcongr]
theorem succ_le_succ (h : a ≤ b) : succ a ≤ succ b := by
by_cases hb : IsMax b
· by_cases hba : b ≤ a
· exact (hb <| hba.trans <| le_succ _).trans (le_succ _)
· exact succ_le_of_lt ((h.lt_of_not_le hba).trans_le <| le_succ b)
· rw [succ_le_iff_of_not_isMax fun ha => hb <| ha.mono h]
apply lt_succ_of_le_of_not_isMax h hb
theorem succ_mono : Monotone (succ : α → α) := fun _ _ => succ_le_succ
/-- See also `Order.succ_eq_of_covBy`. -/
lemma le_succ_of_wcovBy (h : a ⩿ b) : b ≤ succ a := by
obtain hab | ⟨-, hba⟩ := h.covBy_or_le_and_le
· by_contra hba
exact h.2 (lt_succ_of_not_isMax hab.lt.not_isMax) <| hab.lt.succ_le.lt_of_not_le hba
· exact hba.trans (le_succ _)
alias _root_.WCovBy.le_succ := le_succ_of_wcovBy
theorem le_succ_iterate (k : ℕ) (x : α) : x ≤ succ^[k] x :=
id_le_iterate_of_id_le le_succ _ _
theorem isMax_iterate_succ_of_eq_of_lt {n m : ℕ} (h_eq : succ^[n] a = succ^[m] a)
(h_lt : n < m) : IsMax (succ^[n] a) := by
refine max_of_succ_le (le_trans ?_ h_eq.symm.le)
rw [← iterate_succ_apply' succ]
have h_le : n + 1 ≤ m := Nat.succ_le_of_lt h_lt
exact Monotone.monotone_iterate_of_le_map succ_mono (le_succ a) h_le
theorem isMax_iterate_succ_of_eq_of_ne {n m : ℕ} (h_eq : succ^[n] a = succ^[m] a)
(h_ne : n ≠ m) : IsMax (succ^[n] a) := by
rcases le_total n m with h | h
· exact isMax_iterate_succ_of_eq_of_lt h_eq (lt_of_le_of_ne h h_ne)
· rw [h_eq]
exact isMax_iterate_succ_of_eq_of_lt h_eq.symm (lt_of_le_of_ne h h_ne.symm)
theorem Iic_subset_Iio_succ_of_not_isMax (ha : ¬IsMax a) : Iic a ⊆ Iio (succ a) :=
fun _ => (lt_succ_of_le_of_not_isMax · ha)
theorem Ici_succ_of_not_isMax (ha : ¬IsMax a) : Ici (succ a) = Ioi a :=
Set.ext fun _ => succ_le_iff_of_not_isMax ha
theorem Icc_subset_Ico_succ_right_of_not_isMax (hb : ¬IsMax b) : Icc a b ⊆ Ico a (succ b) := by
rw [← Ici_inter_Iio, ← Ici_inter_Iic]
gcongr
intro _ h
apply lt_succ_of_le_of_not_isMax h hb
theorem Ioc_subset_Ioo_succ_right_of_not_isMax (hb : ¬IsMax b) : Ioc a b ⊆ Ioo a (succ b) := by
rw [← Ioi_inter_Iio, ← Ioi_inter_Iic]
gcongr
intro _ h
apply Iic_subset_Iio_succ_of_not_isMax hb h
theorem Icc_succ_left_of_not_isMax (ha : ¬IsMax a) : Icc (succ a) b = Ioc a b := by
rw [← Ici_inter_Iic, Ici_succ_of_not_isMax ha, Ioi_inter_Iic]
theorem Ico_succ_left_of_not_isMax (ha : ¬IsMax a) : Ico (succ a) b = Ioo a b := by
rw [← Ici_inter_Iio, Ici_succ_of_not_isMax ha, Ioi_inter_Iio]
section NoMaxOrder
variable [NoMaxOrder α]
theorem lt_succ (a : α) : a < succ a :=
lt_succ_of_not_isMax <| not_isMax a
@[simp]
theorem lt_succ_of_le : a ≤ b → a < succ b :=
(lt_succ_of_le_of_not_isMax · <| not_isMax b)
@[simp]
theorem succ_le_iff : succ a ≤ b ↔ a < b :=
succ_le_iff_of_not_isMax <| not_isMax a
@[gcongr] theorem succ_lt_succ (hab : a < b) : succ a < succ b := by simp [hab]
theorem succ_strictMono : StrictMono (succ : α → α) := fun _ _ => succ_lt_succ
theorem covBy_succ (a : α) : a ⋖ succ a :=
covBy_succ_of_not_isMax <| not_isMax a
theorem Iic_subset_Iio_succ (a : α) : Iic a ⊆ Iio (succ a) := by simp
@[simp]
theorem Ici_succ (a : α) : Ici (succ a) = Ioi a :=
Ici_succ_of_not_isMax <| not_isMax _
@[simp]
theorem Icc_subset_Ico_succ_right (a b : α) : Icc a b ⊆ Ico a (succ b) :=
Icc_subset_Ico_succ_right_of_not_isMax <| not_isMax _
@[simp]
theorem Ioc_subset_Ioo_succ_right (a b : α) : Ioc a b ⊆ Ioo a (succ b) :=
Ioc_subset_Ioo_succ_right_of_not_isMax <| not_isMax _
@[simp]
theorem Icc_succ_left (a b : α) : Icc (succ a) b = Ioc a b :=
Icc_succ_left_of_not_isMax <| not_isMax _
@[simp]
theorem Ico_succ_left (a b : α) : Ico (succ a) b = Ioo a b :=
Ico_succ_left_of_not_isMax <| not_isMax _
end NoMaxOrder
end Preorder
section PartialOrder
variable [PartialOrder α] [SuccOrder α] {a b : α}
@[simp]
theorem succ_eq_iff_isMax : succ a = a ↔ IsMax a :=
⟨fun h => max_of_succ_le h.le, fun h => h.eq_of_ge <| le_succ _⟩
alias ⟨_, _root_.IsMax.succ_eq⟩ := succ_eq_iff_isMax
lemma le_iff_eq_or_succ_le : a ≤ b ↔ a = b ∨ succ a ≤ b := by
by_cases ha : IsMax a
· simpa [ha.succ_eq] using le_of_eq
· rw [succ_le_iff_of_not_isMax ha, le_iff_eq_or_lt]
theorem le_le_succ_iff : a ≤ b ∧ b ≤ succ a ↔ b = a ∨ b = succ a := by
refine
⟨fun h =>
or_iff_not_imp_left.2 fun hba : b ≠ a =>
h.2.antisymm (succ_le_of_lt <| h.1.lt_of_ne <| hba.symm),
?_⟩
rintro (rfl | rfl)
· exact ⟨le_rfl, le_succ b⟩
· exact ⟨le_succ a, le_rfl⟩
/-- See also `Order.le_succ_of_wcovBy`. -/
lemma succ_eq_of_covBy (h : a ⋖ b) : succ a = b := (succ_le_of_lt h.lt).antisymm h.wcovBy.le_succ
alias _root_.CovBy.succ_eq := succ_eq_of_covBy
theorem _root_.OrderIso.map_succ [PartialOrder β] [SuccOrder β] (f : α ≃o β) (a : α) :
f (succ a) = succ (f a) := by
by_cases h : IsMax a
· rw [h.succ_eq, (f.isMax_apply.2 h).succ_eq]
· exact (f.map_covBy.2 <| covBy_succ_of_not_isMax h).succ_eq.symm
section NoMaxOrder
variable [NoMaxOrder α]
theorem succ_eq_iff_covBy : succ a = b ↔ a ⋖ b :=
⟨by rintro rfl; exact covBy_succ _, CovBy.succ_eq⟩
end NoMaxOrder
section OrderTop
variable [OrderTop α]
@[simp]
theorem succ_top : succ (⊤ : α) = ⊤ := by
rw [succ_eq_iff_isMax, isMax_iff_eq_top]
theorem succ_le_iff_eq_top : succ a ≤ a ↔ a = ⊤ :=
succ_le_iff_isMax.trans isMax_iff_eq_top
theorem lt_succ_iff_ne_top : a < succ a ↔ a ≠ ⊤ :=
lt_succ_iff_not_isMax.trans not_isMax_iff_ne_top
end OrderTop
section OrderBot
variable [OrderBot α] [Nontrivial α]
theorem bot_lt_succ (a : α) : ⊥ < succ a :=
(lt_succ_of_not_isMax not_isMax_bot).trans_le <| succ_mono bot_le
theorem succ_ne_bot (a : α) : succ a ≠ ⊥ :=
(bot_lt_succ a).ne'
end OrderBot
end PartialOrder
section LinearOrder
variable [LinearOrder α] [SuccOrder α] {a b : α}
theorem le_of_lt_succ {a b : α} : a < succ b → a ≤ b := fun h ↦ by
by_contra! nh
exact (h.trans_le (succ_le_of_lt nh)).false
theorem lt_succ_iff_of_not_isMax (ha : ¬IsMax a) : b < succ a ↔ b ≤ a :=
⟨le_of_lt_succ, fun h => h.trans_lt <| lt_succ_of_not_isMax ha⟩
theorem succ_lt_succ_iff_of_not_isMax (ha : ¬IsMax a) (hb : ¬IsMax b) :
succ a < succ b ↔ a < b := by
rw [lt_succ_iff_of_not_isMax hb, succ_le_iff_of_not_isMax ha]
theorem succ_le_succ_iff_of_not_isMax (ha : ¬IsMax a) (hb : ¬IsMax b) :
succ a ≤ succ b ↔ a ≤ b := by
rw [succ_le_iff_of_not_isMax ha, lt_succ_iff_of_not_isMax hb]
theorem Iio_succ_of_not_isMax (ha : ¬IsMax a) : Iio (succ a) = Iic a :=
Set.ext fun _ => lt_succ_iff_of_not_isMax ha
theorem Ico_succ_right_of_not_isMax (hb : ¬IsMax b) : Ico a (succ b) = Icc a b := by
rw [← Ici_inter_Iio, Iio_succ_of_not_isMax hb, Ici_inter_Iic]
theorem Ioo_succ_right_of_not_isMax (hb : ¬IsMax b) : Ioo a (succ b) = Ioc a b := by
rw [← Ioi_inter_Iio, Iio_succ_of_not_isMax hb, Ioi_inter_Iic]
theorem succ_eq_succ_iff_of_not_isMax (ha : ¬IsMax a) (hb : ¬IsMax b) :
succ a = succ b ↔ a = b := by
rw [eq_iff_le_not_lt, eq_iff_le_not_lt, succ_le_succ_iff_of_not_isMax ha hb,
succ_lt_succ_iff_of_not_isMax ha hb]
theorem le_succ_iff_eq_or_le : a ≤ succ b ↔ a = succ b ∨ a ≤ b := by
by_cases hb : IsMax b
· rw [hb.succ_eq, or_iff_right_of_imp le_of_eq]
· rw [← lt_succ_iff_of_not_isMax hb, le_iff_eq_or_lt]
theorem lt_succ_iff_eq_or_lt_of_not_isMax (hb : ¬IsMax b) : a < succ b ↔ a = b ∨ a < b :=
(lt_succ_iff_of_not_isMax hb).trans le_iff_eq_or_lt
theorem not_isMin_succ [Nontrivial α] (a : α) : ¬ IsMin (succ a) := by
obtain ha | ha := (le_succ a).eq_or_lt
· exact (ha ▸ succ_eq_iff_isMax.1 ha.symm).not_isMin
· exact not_isMin_of_lt ha
theorem Iic_succ (a : α) : Iic (succ a) = insert (succ a) (Iic a) :=
ext fun _ => le_succ_iff_eq_or_le
theorem Icc_succ_right (h : a ≤ succ b) : Icc a (succ b) = insert (succ b) (Icc a b) := by
simp_rw [← Ici_inter_Iic, Iic_succ, inter_insert_of_mem (mem_Ici.2 h)]
theorem Ioc_succ_right (h : a < succ b) : Ioc a (succ b) = insert (succ b) (Ioc a b) := by
simp_rw [← Ioi_inter_Iic, Iic_succ, inter_insert_of_mem (mem_Ioi.2 h)]
theorem Iio_succ_eq_insert_of_not_isMax (h : ¬IsMax a) : Iio (succ a) = insert a (Iio a) :=
ext fun _ => lt_succ_iff_eq_or_lt_of_not_isMax h
theorem Ico_succ_right_eq_insert_of_not_isMax (h₁ : a ≤ b) (h₂ : ¬IsMax b) :
Ico a (succ b) = insert b (Ico a b) := by
simp_rw [← Iio_inter_Ici, Iio_succ_eq_insert_of_not_isMax h₂, insert_inter_of_mem (mem_Ici.2 h₁)]
theorem Ioo_succ_right_eq_insert_of_not_isMax (h₁ : a < b) (h₂ : ¬IsMax b) :
Ioo a (succ b) = insert b (Ioo a b) := by
simp_rw [← Iio_inter_Ioi, Iio_succ_eq_insert_of_not_isMax h₂, insert_inter_of_mem (mem_Ioi.2 h₁)]
section NoMaxOrder
variable [NoMaxOrder α]
@[simp]
theorem lt_succ_iff : a < succ b ↔ a ≤ b :=
lt_succ_iff_of_not_isMax <| not_isMax b
theorem succ_le_succ_iff : succ a ≤ succ b ↔ a ≤ b := by simp
theorem succ_lt_succ_iff : succ a < succ b ↔ a < b := by simp
alias ⟨le_of_succ_le_succ, _⟩ := succ_le_succ_iff
alias ⟨lt_of_succ_lt_succ, _⟩ := succ_lt_succ_iff
-- TODO: prove for a succ-archimedean non-linear order with bottom
@[simp]
theorem Iio_succ (a : α) : Iio (succ a) = Iic a :=
Iio_succ_of_not_isMax <| not_isMax _
@[simp]
theorem Ico_succ_right (a b : α) : Ico a (succ b) = Icc a b :=
Ico_succ_right_of_not_isMax <| not_isMax _
-- TODO: prove for a succ-archimedean non-linear order
@[simp]
theorem Ioo_succ_right (a b : α) : Ioo a (succ b) = Ioc a b :=
Ioo_succ_right_of_not_isMax <| not_isMax _
@[simp]
theorem succ_eq_succ_iff : succ a = succ b ↔ a = b :=
succ_eq_succ_iff_of_not_isMax (not_isMax a) (not_isMax b)
theorem succ_injective : Injective (succ : α → α) := fun _ _ => succ_eq_succ_iff.1
theorem succ_ne_succ_iff : succ a ≠ succ b ↔ a ≠ b :=
succ_injective.ne_iff
alias ⟨_, succ_ne_succ⟩ := succ_ne_succ_iff
theorem lt_succ_iff_eq_or_lt : a < succ b ↔ a = b ∨ a < b :=
lt_succ_iff.trans le_iff_eq_or_lt
theorem Iio_succ_eq_insert (a : α) : Iio (succ a) = insert a (Iio a) :=
Iio_succ_eq_insert_of_not_isMax <| not_isMax a
theorem Ico_succ_right_eq_insert (h : a ≤ b) : Ico a (succ b) = insert b (Ico a b) :=
Ico_succ_right_eq_insert_of_not_isMax h <| not_isMax b
theorem Ioo_succ_right_eq_insert (h : a < b) : Ioo a (succ b) = insert b (Ioo a b) :=
Ioo_succ_right_eq_insert_of_not_isMax h <| not_isMax b
@[simp]
theorem Ioo_eq_empty_iff_le_succ : Ioo a b = ∅ ↔ b ≤ succ a := by
refine ⟨fun h ↦ ?_, fun h ↦ ?_⟩
· contrapose! h
exact ⟨succ a, lt_succ_iff_not_isMax.mpr (not_isMax a), h⟩
· ext x
suffices a < x → b ≤ x by simpa
exact fun hx ↦ le_of_lt_succ <| lt_of_le_of_lt h <| succ_strictMono hx
end NoMaxOrder
section OrderBot
variable [OrderBot α]
theorem lt_succ_bot_iff [NoMaxOrder α] : a < succ ⊥ ↔ a = ⊥ := by rw [lt_succ_iff, le_bot_iff]
theorem le_succ_bot_iff : a ≤ succ ⊥ ↔ a = ⊥ ∨ a = succ ⊥ := by
rw [le_succ_iff_eq_or_le, le_bot_iff, or_comm]
end OrderBot
end LinearOrder
/-- There is at most one way to define the successors in a `PartialOrder`. -/
instance [PartialOrder α] : Subsingleton (SuccOrder α) :=
⟨by
intro h₀ h₁
ext a
by_cases ha : IsMax a
· exact (@IsMax.succ_eq _ _ h₀ _ ha).trans ha.succ_eq.symm
· exact @CovBy.succ_eq _ _ h₀ _ _ (covBy_succ_of_not_isMax ha)⟩
theorem succ_eq_sInf [CompleteLattice α] [SuccOrder α] (a : α) :
succ a = sInf (Set.Ioi a) := by
apply (le_sInf fun b => succ_le_of_lt).antisymm
obtain rfl | ha := eq_or_ne a ⊤
· rw [succ_top]
exact le_top
· exact sInf_le (lt_succ_iff_ne_top.2 ha)
theorem succ_eq_iInf [CompleteLattice α] [SuccOrder α] (a : α) : succ a = ⨅ b > a, b := by
rw [succ_eq_sInf, iInf_subtype', iInf, Subtype.range_coe_subtype, Ioi]
theorem succ_eq_csInf [ConditionallyCompleteLattice α] [SuccOrder α] [NoMaxOrder α] (a : α) :
succ a = sInf (Set.Ioi a) := by
apply (le_csInf nonempty_Ioi fun b => succ_le_of_lt).antisymm
exact csInf_le ⟨a, fun b => le_of_lt⟩ <| lt_succ a
/-! ### Predecessor order -/
section Preorder
variable [Preorder α] [PredOrder α] {a b : α}
/-- The predecessor of an element. If `a` is not minimal, then `pred a` is the greatest element less
than `a`. If `a` is minimal, then `pred a = a`. -/
def pred : α → α :=
PredOrder.pred
theorem pred_le : ∀ a : α, pred a ≤ a :=
PredOrder.pred_le
theorem min_of_le_pred {a : α} : a ≤ pred a → IsMin a :=
PredOrder.min_of_le_pred
theorem le_pred_of_lt {a b : α} : a < b → a ≤ pred b :=
PredOrder.le_pred_of_lt
alias _root_.LT.lt.le_pred := le_pred_of_lt
@[simp]
theorem le_pred_iff_isMin : a ≤ pred a ↔ IsMin a :=
⟨min_of_le_pred, fun h => h <| pred_le _⟩
alias ⟨_root_.IsMin.of_le_pred, _root_.IsMin.le_pred⟩ := le_pred_iff_isMin
@[simp]
theorem pred_lt_iff_not_isMin : pred a < a ↔ ¬IsMin a :=
⟨not_isMin_of_lt, fun ha => (pred_le a).lt_of_not_le fun h => ha <| min_of_le_pred h⟩
alias ⟨_, pred_lt_of_not_isMin⟩ := pred_lt_iff_not_isMin
theorem pred_wcovBy (a : α) : pred a ⩿ a :=
⟨pred_le a, fun _ hb nh => (le_pred_of_lt nh).not_lt hb⟩
theorem pred_covBy_of_not_isMin (h : ¬IsMin a) : pred a ⋖ a :=
(pred_wcovBy a).covBy_of_lt <| pred_lt_of_not_isMin h
theorem pred_lt_of_not_isMin_of_le (ha : ¬IsMin a) : a ≤ b → pred a < b :=
(pred_lt_of_not_isMin ha).trans_le
theorem le_pred_iff_of_not_isMin (ha : ¬IsMin a) : b ≤ pred a ↔ b < a :=
⟨fun h => h.trans_lt <| pred_lt_of_not_isMin ha, le_pred_of_lt⟩
lemma pred_lt_pred_of_not_isMin (h : a < b) (ha : ¬ IsMin a) : pred a < pred b :=
pred_lt_of_not_isMin_of_le ha <| le_pred_of_lt h
theorem pred_le_pred_of_not_isMin_of_le (ha : ¬IsMin a) (hb : ¬IsMin b) :
a ≤ b → pred a ≤ pred b := by
rw [le_pred_iff_of_not_isMin hb]
apply pred_lt_of_not_isMin_of_le ha
@[simp, mono, gcongr]
theorem pred_le_pred {a b : α} (h : a ≤ b) : pred a ≤ pred b :=
succ_le_succ h.dual
theorem pred_mono : Monotone (pred : α → α) := fun _ _ => pred_le_pred
/-- See also `Order.pred_eq_of_covBy`. -/
lemma pred_le_of_wcovBy (h : a ⩿ b) : pred b ≤ a := by
obtain hab | ⟨-, hba⟩ := h.covBy_or_le_and_le
· by_contra hba
exact h.2 (hab.lt.le_pred.lt_of_not_le hba) (pred_lt_of_not_isMin hab.lt.not_isMin)
· exact (pred_le _).trans hba
alias _root_.WCovBy.pred_le := pred_le_of_wcovBy
theorem pred_iterate_le (k : ℕ) (x : α) : pred^[k] x ≤ x := by
conv_rhs => rw [(by simp only [Function.iterate_id, id] : x = id^[k] x)]
exact Monotone.iterate_le_of_le pred_mono pred_le k x
theorem isMin_iterate_pred_of_eq_of_lt {n m : ℕ} (h_eq : pred^[n] a = pred^[m] a)
(h_lt : n < m) : IsMin (pred^[n] a) :=
@isMax_iterate_succ_of_eq_of_lt αᵒᵈ _ _ _ _ _ h_eq h_lt
theorem isMin_iterate_pred_of_eq_of_ne {n m : ℕ} (h_eq : pred^[n] a = pred^[m] a)
(h_ne : n ≠ m) : IsMin (pred^[n] a) :=
@isMax_iterate_succ_of_eq_of_ne αᵒᵈ _ _ _ _ _ h_eq h_ne
theorem Ici_subset_Ioi_pred_of_not_isMin (ha : ¬IsMin a) : Ici a ⊆ Ioi (pred a) :=
fun _ ↦ pred_lt_of_not_isMin_of_le ha
theorem Iic_pred_of_not_isMin (ha : ¬IsMin a) : Iic (pred a) = Iio a :=
Set.ext fun _ => le_pred_iff_of_not_isMin ha
theorem Icc_subset_Ioc_pred_left_of_not_isMin (ha : ¬IsMin a) : Icc a b ⊆ Ioc (pred a) b := by
rw [← Ioi_inter_Iic, ← Ici_inter_Iic]
gcongr
apply Ici_subset_Ioi_pred_of_not_isMin ha
theorem Ico_subset_Ioo_pred_left_of_not_isMin (ha : ¬IsMin a) : Ico a b ⊆ Ioo (pred a) b := by
rw [← Ioi_inter_Iio, ← Ici_inter_Iio]
gcongr
apply Ici_subset_Ioi_pred_of_not_isMin ha
theorem Icc_pred_right_of_not_isMin (ha : ¬IsMin b) : Icc a (pred b) = Ico a b := by
rw [← Ici_inter_Iic, Iic_pred_of_not_isMin ha, Ici_inter_Iio]
theorem Ioc_pred_right_of_not_isMin (ha : ¬IsMin b) : Ioc a (pred b) = Ioo a b := by
rw [← Ioi_inter_Iic, Iic_pred_of_not_isMin ha, Ioi_inter_Iio]
section NoMinOrder
variable [NoMinOrder α]
theorem pred_lt (a : α) : pred a < a :=
pred_lt_of_not_isMin <| not_isMin a
@[simp]
theorem pred_lt_of_le : a ≤ b → pred a < b :=
pred_lt_of_not_isMin_of_le <| not_isMin a
@[simp]
theorem le_pred_iff : a ≤ pred b ↔ a < b :=
le_pred_iff_of_not_isMin <| not_isMin b
theorem pred_le_pred_of_le : a ≤ b → pred a ≤ pred b := by intro; simp_all
theorem pred_lt_pred : a < b → pred a < pred b := by intro; simp_all
theorem pred_strictMono : StrictMono (pred : α → α) := fun _ _ => pred_lt_pred
theorem pred_covBy (a : α) : pred a ⋖ a :=
pred_covBy_of_not_isMin <| not_isMin a
theorem Ici_subset_Ioi_pred (a : α) : Ici a ⊆ Ioi (pred a) := by simp
@[simp]
theorem Iic_pred (a : α) : Iic (pred a) = Iio a :=
Iic_pred_of_not_isMin <| not_isMin a
@[simp]
theorem Icc_subset_Ioc_pred_left (a b : α) : Icc a b ⊆ Ioc (pred a) b :=
Icc_subset_Ioc_pred_left_of_not_isMin <| not_isMin _
@[simp]
theorem Ico_subset_Ioo_pred_left (a b : α) : Ico a b ⊆ Ioo (pred a) b :=
Ico_subset_Ioo_pred_left_of_not_isMin <| not_isMin _
@[simp]
theorem Icc_pred_right (a b : α) : Icc a (pred b) = Ico a b :=
Icc_pred_right_of_not_isMin <| not_isMin _
@[simp]
theorem Ioc_pred_right (a b : α) : Ioc a (pred b) = Ioo a b :=
Ioc_pred_right_of_not_isMin <| not_isMin _
end NoMinOrder
end Preorder
section PartialOrder
variable [PartialOrder α] [PredOrder α] {a b : α}
@[simp]
theorem pred_eq_iff_isMin : pred a = a ↔ IsMin a :=
⟨fun h => min_of_le_pred h.ge, fun h => h.eq_of_le <| pred_le _⟩
alias ⟨_, _root_.IsMin.pred_eq⟩ := pred_eq_iff_isMin
lemma le_iff_eq_or_le_pred : a ≤ b ↔ a = b ∨ a ≤ pred b := by
by_cases hb : IsMin b
· simpa [hb.pred_eq] using le_of_eq
· rw [le_pred_iff_of_not_isMin hb, le_iff_eq_or_lt]
theorem pred_le_le_iff {a b : α} : pred a ≤ b ∧ b ≤ a ↔ b = a ∨ b = pred a := by
refine
⟨fun h =>
or_iff_not_imp_left.2 fun hba : b ≠ a => (le_pred_of_lt <| h.2.lt_of_ne hba).antisymm h.1, ?_⟩
rintro (rfl | rfl)
· exact ⟨pred_le b, le_rfl⟩
· exact ⟨le_rfl, pred_le a⟩
/-- See also `Order.pred_le_of_wcovBy`. -/
lemma pred_eq_of_covBy (h : a ⋖ b) : pred b = a := h.wcovBy.pred_le.antisymm (le_pred_of_lt h.lt)
alias _root_.CovBy.pred_eq := pred_eq_of_covBy
theorem _root_.OrderIso.map_pred {β : Type*} [PartialOrder β] [PredOrder β] (f : α ≃o β) (a : α) :
f (pred a) = pred (f a) :=
f.dual.map_succ a
section NoMinOrder
| variable [NoMinOrder α]
| Mathlib/Order/SuccPred/Basic.lean | 743 | 743 |
/-
Copyright (c) 2015 Microsoft Corporation. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Authors: Leonardo de Moura, Jeremy Avigad, Minchao Wu, Mario Carneiro
-/
import Mathlib.Algebra.NeZero
import Mathlib.Data.Finset.Attach
import Mathlib.Data.Finset.Disjoint
import Mathlib.Data.Finset.Erase
import Mathlib.Data.Finset.Filter
import Mathlib.Data.Finset.Range
import Mathlib.Data.Finset.SDiff
/-! # Image and map operations on finite sets
This file provides the finite analog of `Set.image`, along with some other similar functions.
Note there are two ways to take the image over a finset; via `Finset.image` which applies the
function then removes duplicates (requiring `DecidableEq`), or via `Finset.map` which exploits
injectivity of the function to avoid needing to deduplicate. Choosing between these is similar to
choosing between `insert` and `Finset.cons`, or between `Finset.union` and `Finset.disjUnion`.
## Main definitions
* `Finset.image`: Given a function `f : α → β`, `s.image f` is the image finset in `β`.
* `Finset.map`: Given an embedding `f : α ↪ β`, `s.map f` is the image finset in `β`.
* `Finset.filterMap` Given a function `f : α → Option β`, `s.filterMap f` is the
image finset in `β`, filtering out `none`s.
* `Finset.subtype`: `s.subtype p` is the finset of `Subtype p` whose elements belong to `s`.
* `Finset.fin`:`s.fin n` is the finset of all elements of `s` less than `n`.
-/
assert_not_exists Monoid OrderedCommMonoid
variable {α β γ : Type*}
open Multiset
open Function
namespace Finset
/-! ### map -/
section Map
open Function
/-- When `f` is an embedding of `α` in `β` and `s` is a finset in `α`, then `s.map f` is the image
finset in `β`. The embedding condition guarantees that there are no duplicates in the image. -/
def map (f : α ↪ β) (s : Finset α) : Finset β :=
⟨s.1.map f, s.2.map f.2⟩
@[simp]
theorem map_val (f : α ↪ β) (s : Finset α) : (map f s).1 = s.1.map f :=
rfl
@[simp]
theorem map_empty (f : α ↪ β) : (∅ : Finset α).map f = ∅ :=
rfl
variable {f : α ↪ β} {s : Finset α}
@[simp]
theorem mem_map {b : β} : b ∈ s.map f ↔ ∃ a ∈ s, f a = b :=
Multiset.mem_map
-- Higher priority to apply before `mem_map`.
@[simp 1100]
theorem mem_map_equiv {f : α ≃ β} {b : β} : b ∈ s.map f.toEmbedding ↔ f.symm b ∈ s := by
rw [mem_map]
exact
⟨by
rintro ⟨a, H, rfl⟩
simpa, fun h => ⟨_, h, by simp⟩⟩
@[simp 1100]
theorem mem_map' (f : α ↪ β) {a} {s : Finset α} : f a ∈ s.map f ↔ a ∈ s :=
mem_map_of_injective f.2
theorem mem_map_of_mem (f : α ↪ β) {a} {s : Finset α} : a ∈ s → f a ∈ s.map f :=
(mem_map' _).2
theorem forall_mem_map {f : α ↪ β} {s : Finset α} {p : ∀ a, a ∈ s.map f → Prop} :
(∀ y (H : y ∈ s.map f), p y H) ↔ ∀ x (H : x ∈ s), p (f x) (mem_map_of_mem _ H) :=
⟨fun h y hy => h (f y) (mem_map_of_mem _ hy),
fun h x hx => by
obtain ⟨y, hy, rfl⟩ := mem_map.1 hx
exact h _ hy⟩
theorem apply_coe_mem_map (f : α ↪ β) (s : Finset α) (x : s) : f x ∈ s.map f :=
mem_map_of_mem f x.prop
@[simp, norm_cast]
theorem coe_map (f : α ↪ β) (s : Finset α) : (s.map f : Set β) = f '' s :=
Set.ext (by simp only [mem_coe, mem_map, Set.mem_image, implies_true])
theorem coe_map_subset_range (f : α ↪ β) (s : Finset α) : (s.map f : Set β) ⊆ Set.range f :=
calc
↑(s.map f) = f '' s := coe_map f s
_ ⊆ Set.range f := Set.image_subset_range f ↑s
/-- If the only elements outside `s` are those left fixed by `σ`, then mapping by `σ` has no effect.
-/
theorem map_perm {σ : Equiv.Perm α} (hs : { a | σ a ≠ a } ⊆ s) : s.map (σ : α ↪ α) = s :=
coe_injective <| (coe_map _ _).trans <| Set.image_perm hs
theorem map_toFinset [DecidableEq α] [DecidableEq β] {s : Multiset α} :
s.toFinset.map f = (s.map f).toFinset :=
ext fun _ => by simp only [mem_map, Multiset.mem_map, exists_prop, Multiset.mem_toFinset]
@[simp]
theorem map_refl : s.map (Embedding.refl _) = s :=
ext fun _ => by simpa only [mem_map, exists_prop] using exists_eq_right
@[simp]
theorem map_cast_heq {α β} (h : α = β) (s : Finset α) :
HEq (s.map (Equiv.cast h).toEmbedding) s := by
subst h
simp
theorem map_map (f : α ↪ β) (g : β ↪ γ) (s : Finset α) : (s.map f).map g = s.map (f.trans g) :=
eq_of_veq <| by simp only [map_val, Multiset.map_map]; rfl
theorem map_comm {β'} {f : β ↪ γ} {g : α ↪ β} {f' : α ↪ β'} {g' : β' ↪ γ}
(h_comm : ∀ a, f (g a) = g' (f' a)) : (s.map g).map f = (s.map f').map g' := by
simp_rw [map_map, Embedding.trans, Function.comp_def, h_comm]
theorem _root_.Function.Semiconj.finset_map {f : α ↪ β} {ga : α ↪ α} {gb : β ↪ β}
(h : Function.Semiconj f ga gb) : Function.Semiconj (map f) (map ga) (map gb) := fun _ =>
map_comm h
theorem _root_.Function.Commute.finset_map {f g : α ↪ α} (h : Function.Commute f g) :
Function.Commute (map f) (map g) :=
Function.Semiconj.finset_map h
@[simp]
theorem map_subset_map {s₁ s₂ : Finset α} : s₁.map f ⊆ s₂.map f ↔ s₁ ⊆ s₂ :=
⟨fun h _ xs => (mem_map' _).1 <| h <| (mem_map' f).2 xs,
fun h => by simp [subset_def, Multiset.map_subset_map h]⟩
@[gcongr] alias ⟨_, _root_.GCongr.finsetMap_subset⟩ := map_subset_map
/-- The `Finset` version of `Equiv.subset_symm_image`. -/
theorem subset_map_symm {t : Finset β} {f : α ≃ β} : s ⊆ t.map f.symm ↔ s.map f ⊆ t := by
constructor <;> intro h x hx
· simp only [mem_map_equiv, Equiv.symm_symm] at hx
simpa using h hx
· simp only [mem_map_equiv]
exact h (by simp [hx])
/-- The `Finset` version of `Equiv.symm_image_subset`. -/
theorem map_symm_subset {t : Finset β} {f : α ≃ β} : t.map f.symm ⊆ s ↔ t ⊆ s.map f := by
simp only [← subset_map_symm, Equiv.symm_symm]
/-- Associate to an embedding `f` from `α` to `β` the order embedding that maps a finset to its
image under `f`. -/
def mapEmbedding (f : α ↪ β) : Finset α ↪o Finset β :=
OrderEmbedding.ofMapLEIff (map f) fun _ _ => map_subset_map
@[simp]
theorem map_inj {s₁ s₂ : Finset α} : s₁.map f = s₂.map f ↔ s₁ = s₂ :=
(mapEmbedding f).injective.eq_iff
theorem map_injective (f : α ↪ β) : Injective (map f) :=
(mapEmbedding f).injective
@[simp]
theorem map_ssubset_map {s t : Finset α} : s.map f ⊂ t.map f ↔ s ⊂ t := (mapEmbedding f).lt_iff_lt
@[gcongr] alias ⟨_, _root_.GCongr.finsetMap_ssubset⟩ := map_ssubset_map
@[simp]
theorem mapEmbedding_apply : mapEmbedding f s = map f s :=
rfl
theorem filter_map {p : β → Prop} [DecidablePred p] :
(s.map f).filter p = (s.filter (p ∘ f)).map f :=
eq_of_veq (Multiset.filter_map _ _ _)
lemma map_filter' (p : α → Prop) [DecidablePred p] (f : α ↪ β) (s : Finset α)
[DecidablePred (∃ a, p a ∧ f a = ·)] :
(s.filter p).map f = (s.map f).filter fun b => ∃ a, p a ∧ f a = b := by
simp [Function.comp_def, filter_map, f.injective.eq_iff]
lemma filter_attach' [DecidableEq α] (s : Finset α) (p : s → Prop) [DecidablePred p] :
s.attach.filter p =
(s.filter fun x => ∃ h, p ⟨x, h⟩).attach.map
⟨Subtype.map id <| filter_subset _ _, Subtype.map_injective _ injective_id⟩ :=
eq_of_veq <| Multiset.filter_attach' _ _
lemma filter_attach (p : α → Prop) [DecidablePred p] (s : Finset α) :
s.attach.filter (fun a : s ↦ p a) =
(s.filter p).attach.map ((Embedding.refl _).subtypeMap mem_of_mem_filter) :=
eq_of_veq <| Multiset.filter_attach _ _
theorem map_filter {f : α ≃ β} {p : α → Prop} [DecidablePred p] :
(s.filter p).map f.toEmbedding = (s.map f.toEmbedding).filter (p ∘ f.symm) := by
simp only [filter_map, Function.comp_def, Equiv.toEmbedding_apply, Equiv.symm_apply_apply]
@[simp]
theorem disjoint_map {s t : Finset α} (f : α ↪ β) :
Disjoint (s.map f) (t.map f) ↔ Disjoint s t :=
mod_cast Set.disjoint_image_iff f.injective (s := s) (t := t)
theorem map_disjUnion {f : α ↪ β} (s₁ s₂ : Finset α) (h) (h' := (disjoint_map _).mpr h) :
(s₁.disjUnion s₂ h).map f = (s₁.map f).disjUnion (s₂.map f) h' :=
eq_of_veq <| Multiset.map_add _ _ _
/-- A version of `Finset.map_disjUnion` for writing in the other direction. -/
theorem map_disjUnion' {f : α ↪ β} (s₁ s₂ : Finset α) (h') (h := (disjoint_map _).mp h') :
(s₁.disjUnion s₂ h).map f = (s₁.map f).disjUnion (s₂.map f) h' :=
map_disjUnion _ _ _
theorem map_union [DecidableEq α] [DecidableEq β] {f : α ↪ β} (s₁ s₂ : Finset α) :
(s₁ ∪ s₂).map f = s₁.map f ∪ s₂.map f :=
mod_cast Set.image_union f s₁ s₂
theorem map_inter [DecidableEq α] [DecidableEq β] {f : α ↪ β} (s₁ s₂ : Finset α) :
(s₁ ∩ s₂).map f = s₁.map f ∩ s₂.map f :=
mod_cast Set.image_inter f.injective (s := s₁) (t := s₂)
@[simp]
theorem map_singleton (f : α ↪ β) (a : α) : map f {a} = {f a} :=
coe_injective <| by simp only [coe_map, coe_singleton, Set.image_singleton]
@[simp]
theorem map_insert [DecidableEq α] [DecidableEq β] (f : α ↪ β) (a : α) (s : Finset α) :
(insert a s).map f = insert (f a) (s.map f) := by
simp only [insert_eq, map_union, map_singleton]
@[simp]
theorem map_cons (f : α ↪ β) (a : α) (s : Finset α) (ha : a ∉ s) :
(cons a s ha).map f = cons (f a) (s.map f) (by simpa using ha) :=
eq_of_veq <| Multiset.map_cons f a s.val
@[simp]
theorem map_eq_empty : s.map f = ∅ ↔ s = ∅ := (map_injective f).eq_iff' (map_empty f)
@[simp]
theorem map_nonempty : (s.map f).Nonempty ↔ s.Nonempty :=
mod_cast Set.image_nonempty (f := f) (s := s)
@[aesop safe apply (rule_sets := [finsetNonempty])]
protected alias ⟨_, Nonempty.map⟩ := map_nonempty
@[simp]
theorem map_nontrivial : (s.map f).Nontrivial ↔ s.Nontrivial :=
mod_cast Set.image_nontrivial f.injective (s := s)
theorem attach_map_val {s : Finset α} : s.attach.map (Embedding.subtype _) = s :=
eq_of_veq <| by rw [map_val, attach_val]; exact Multiset.attach_map_val _
end Map
theorem range_add_one' (n : ℕ) :
range (n + 1) = insert 0 ((range n).map ⟨fun i => i + 1, fun i j => by simp⟩) := by
ext (⟨⟩ | ⟨n⟩) <;> simp [Nat.zero_lt_succ n]
/-! ### image -/
section Image
variable [DecidableEq β]
/-- `image f s` is the forward image of `s` under `f`. -/
def image (f : α → β) (s : Finset α) : Finset β :=
(s.1.map f).toFinset
@[simp]
theorem image_val (f : α → β) (s : Finset α) : (image f s).1 = (s.1.map f).dedup :=
rfl
@[simp]
theorem image_empty (f : α → β) : (∅ : Finset α).image f = ∅ :=
rfl
variable {f g : α → β} {s : Finset α} {t : Finset β} {a : α} {b c : β}
@[simp]
theorem mem_image : b ∈ s.image f ↔ ∃ a ∈ s, f a = b := by
simp only [mem_def, image_val, mem_dedup, Multiset.mem_map, exists_prop]
theorem mem_image_of_mem (f : α → β) {a} (h : a ∈ s) : f a ∈ s.image f :=
mem_image.2 ⟨_, h, rfl⟩
lemma forall_mem_image {p : β → Prop} : (∀ y ∈ s.image f, p y) ↔ ∀ ⦃x⦄, x ∈ s → p (f x) := by simp
lemma exists_mem_image {p : β → Prop} : (∃ y ∈ s.image f, p y) ↔ ∃ x ∈ s, p (f x) := by simp
@[deprecated (since := "2024-11-23")] alias forall_image := forall_mem_image
theorem map_eq_image (f : α ↪ β) (s : Finset α) : s.map f = s.image f :=
eq_of_veq (s.map f).2.dedup.symm
-- Not `@[simp]` since `mem_image` already gets most of the way there.
theorem mem_image_const : c ∈ s.image (const α b) ↔ s.Nonempty ∧ b = c := by
rw [mem_image]
simp only [exists_prop, const_apply, exists_and_right]
rfl
theorem mem_image_const_self : b ∈ s.image (const α b) ↔ s.Nonempty :=
mem_image_const.trans <| and_iff_left rfl
instance canLift (c) (p) [CanLift β α c p] :
CanLift (Finset β) (Finset α) (image c) fun s => ∀ x ∈ s, p x where
prf := by
rintro ⟨⟨l⟩, hd : l.Nodup⟩ hl
lift l to List α using hl
exact ⟨⟨l, hd.of_map _⟩, ext fun a => by simp⟩
theorem image_congr (h : (s : Set α).EqOn f g) : Finset.image f s = Finset.image g s := by
ext
simp_rw [mem_image, ← bex_def]
exact exists₂_congr fun x hx => by rw [h hx]
theorem _root_.Function.Injective.mem_finset_image (hf : Injective f) :
f a ∈ s.image f ↔ a ∈ s := by
refine ⟨fun h => ?_, Finset.mem_image_of_mem f⟩
obtain ⟨y, hy, heq⟩ := mem_image.1 h
exact hf heq ▸ hy
@[simp, norm_cast]
theorem coe_image : ↑(s.image f) = f '' ↑s :=
Set.ext <| by simp only [mem_coe, mem_image, Set.mem_image, implies_true]
@[simp]
lemma image_nonempty : (s.image f).Nonempty ↔ s.Nonempty :=
mod_cast Set.image_nonempty (f := f) (s := (s : Set α))
@[aesop safe apply (rule_sets := [finsetNonempty])]
protected theorem Nonempty.image (h : s.Nonempty) (f : α → β) : (s.image f).Nonempty :=
image_nonempty.2 h
alias ⟨Nonempty.of_image, _⟩ := image_nonempty
theorem image_toFinset [DecidableEq α] {s : Multiset α} :
s.toFinset.image f = (s.map f).toFinset :=
ext fun _ => by simp only [mem_image, Multiset.mem_toFinset, exists_prop, Multiset.mem_map]
theorem image_val_of_injOn (H : Set.InjOn f s) : (image f s).1 = s.1.map f :=
(s.2.map_on H).dedup
@[simp]
theorem image_id [DecidableEq α] : s.image id = s :=
ext fun _ => by simp only [mem_image, exists_prop, id, exists_eq_right]
@[simp]
theorem image_id' [DecidableEq α] : (s.image fun x => x) = s :=
image_id
theorem image_image [DecidableEq γ] {g : β → γ} : (s.image f).image g = s.image (g ∘ f) :=
eq_of_veq <| by simp only [image_val, dedup_map_dedup_eq, Multiset.map_map]
theorem image_comm {β'} [DecidableEq β'] [DecidableEq γ] {f : β → γ} {g : α → β} {f' : α → β'}
{g' : β' → γ} (h_comm : ∀ a, f (g a) = g' (f' a)) :
(s.image g).image f = (s.image f').image g' := by simp_rw [image_image, comp_def, h_comm]
theorem _root_.Function.Semiconj.finset_image [DecidableEq α] {f : α → β} {ga : α → α} {gb : β → β}
(h : Function.Semiconj f ga gb) : Function.Semiconj (image f) (image ga) (image gb) := fun _ =>
image_comm h
theorem _root_.Function.Commute.finset_image [DecidableEq α] {f g : α → α}
(h : Function.Commute f g) : Function.Commute (image f) (image g) :=
Function.Semiconj.finset_image h
theorem image_subset_image {s₁ s₂ : Finset α} (h : s₁ ⊆ s₂) : s₁.image f ⊆ s₂.image f := by
simp only [subset_def, image_val, subset_dedup', dedup_subset', Multiset.map_subset_map h]
theorem image_subset_iff : s.image f ⊆ t ↔ ∀ x ∈ s, f x ∈ t :=
calc
s.image f ⊆ t ↔ f '' ↑s ⊆ ↑t := by norm_cast
_ ↔ _ := Set.image_subset_iff
theorem image_mono (f : α → β) : Monotone (Finset.image f) := fun _ _ => image_subset_image
lemma image_injective (hf : Injective f) : Injective (image f) := by
simpa only [funext (map_eq_image _)] using map_injective ⟨f, hf⟩
lemma image_inj {t : Finset α} (hf : Injective f) : s.image f = t.image f ↔ s = t :=
(image_injective hf).eq_iff
theorem image_subset_image_iff {t : Finset α} (hf : Injective f) :
s.image f ⊆ t.image f ↔ s ⊆ t :=
mod_cast Set.image_subset_image_iff hf (s := s) (t := t)
lemma image_ssubset_image {t : Finset α} (hf : Injective f) : s.image f ⊂ t.image f ↔ s ⊂ t := by
simp_rw [← lt_iff_ssubset]
exact lt_iff_lt_of_le_iff_le' (image_subset_image_iff hf) (image_subset_image_iff hf)
theorem coe_image_subset_range : ↑(s.image f) ⊆ Set.range f :=
calc
↑(s.image f) = f '' ↑s := coe_image
_ ⊆ Set.range f := Set.image_subset_range f ↑s
theorem filter_image {p : β → Prop} [DecidablePred p] :
(s.image f).filter p = (s.filter fun a ↦ p (f a)).image f :=
ext fun b => by
simp only [mem_filter, mem_image, exists_prop]
exact
⟨by rintro ⟨⟨x, h1, rfl⟩, h2⟩; exact ⟨x, ⟨h1, h2⟩, rfl⟩,
by rintro ⟨x, ⟨h1, h2⟩, rfl⟩; exact ⟨⟨x, h1, rfl⟩, h2⟩⟩
theorem fiber_nonempty_iff_mem_image {y : β} : (s.filter (f · = y)).Nonempty ↔ y ∈ s.image f := by
simp [Finset.Nonempty]
theorem image_union [DecidableEq α] {f : α → β} (s₁ s₂ : Finset α) :
(s₁ ∪ s₂).image f = s₁.image f ∪ s₂.image f :=
mod_cast Set.image_union f s₁ s₂
theorem image_inter_subset [DecidableEq α] (f : α → β) (s t : Finset α) :
(s ∩ t).image f ⊆ s.image f ∩ t.image f :=
(image_mono f).map_inf_le s t
theorem image_inter_of_injOn [DecidableEq α] {f : α → β} (s t : Finset α)
(hf : Set.InjOn f (s ∪ t)) : (s ∩ t).image f = s.image f ∩ t.image f :=
coe_injective <| by
push_cast
exact Set.image_inter_on fun a ha b hb => hf (Or.inr ha) <| Or.inl hb
theorem image_inter [DecidableEq α] (s₁ s₂ : Finset α) (hf : Injective f) :
(s₁ ∩ s₂).image f = s₁.image f ∩ s₂.image f :=
image_inter_of_injOn _ _ hf.injOn
@[simp]
theorem image_singleton (f : α → β) (a : α) : image f {a} = {f a} :=
ext fun x => by simpa only [mem_image, exists_prop, mem_singleton, exists_eq_left] using eq_comm
@[simp]
theorem image_insert [DecidableEq α] (f : α → β) (a : α) (s : Finset α) :
(insert a s).image f = insert (f a) (s.image f) := by
simp only [insert_eq, image_singleton, image_union]
theorem erase_image_subset_image_erase [DecidableEq α] (f : α → β) (s : Finset α) (a : α) :
(s.image f).erase (f a) ⊆ (s.erase a).image f := by
simp only [subset_iff, and_imp, exists_prop, mem_image, exists_imp, mem_erase]
rintro b hb x hx rfl
exact ⟨_, ⟨ne_of_apply_ne f hb, hx⟩, rfl⟩
@[simp]
theorem image_erase [DecidableEq α] {f : α → β} (hf : Injective f) (s : Finset α) (a : α) :
(s.erase a).image f = (s.image f).erase (f a) :=
coe_injective <| by push_cast [Set.image_diff hf, Set.image_singleton]; rfl
@[simp]
theorem image_eq_empty : s.image f = ∅ ↔ s = ∅ := mod_cast Set.image_eq_empty (f := f) (s := s)
theorem image_sdiff [DecidableEq α] {f : α → β} (s t : Finset α) (hf : Injective f) :
(s \ t).image f = s.image f \ t.image f :=
mod_cast Set.image_diff hf s t
lemma image_sdiff_of_injOn [DecidableEq α] {t : Finset α} (hf : Set.InjOn f s) (hts : t ⊆ s) :
(s \ t).image f = s.image f \ t.image f :=
mod_cast Set.image_diff_of_injOn hf <| coe_subset.2 hts
theorem _root_.Disjoint.of_image_finset {s t : Finset α} {f : α → β}
(h : Disjoint (s.image f) (t.image f)) : Disjoint s t :=
disjoint_iff_ne.2 fun _ ha _ hb =>
ne_of_apply_ne f <| h.forall_ne_finset (mem_image_of_mem _ ha) (mem_image_of_mem _ hb)
theorem mem_range_iff_mem_finset_range_of_mod_eq' [DecidableEq α] {f : ℕ → α} {a : α} {n : ℕ}
(hn : 0 < n) (h : ∀ i, f (i % n) = f i) :
a ∈ Set.range f ↔ a ∈ (Finset.range n).image fun i => f i := by
constructor
· rintro ⟨i, hi⟩
simp only [mem_image, exists_prop, mem_range]
exact ⟨i % n, Nat.mod_lt i hn, (rfl.congr hi).mp (h i)⟩
· rintro h
simp only [mem_image, exists_prop, Set.mem_range, mem_range] at *
rcases h with ⟨i, _, ha⟩
exact ⟨i, ha⟩
theorem mem_range_iff_mem_finset_range_of_mod_eq [DecidableEq α] {f : ℤ → α} {a : α} {n : ℕ}
(hn : 0 < n) (h : ∀ i, f (i % n) = f i) :
a ∈ Set.range f ↔ a ∈ (Finset.range n).image (fun (i : ℕ) => f i) :=
suffices (∃ i, f (i % n) = a) ↔ ∃ i, i < n ∧ f ↑i = a by simpa [h]
have hn' : 0 < (n : ℤ) := Int.ofNat_lt.mpr hn
Iff.intro
(fun ⟨i, hi⟩ =>
have : 0 ≤ i % ↑n := Int.emod_nonneg _ (ne_of_gt hn')
⟨Int.toNat (i % n), by
rw [← Int.ofNat_lt, Int.toNat_of_nonneg this]; exact ⟨Int.emod_lt_of_pos i hn', hi⟩⟩)
fun ⟨i, hi, ha⟩ =>
⟨i, by rw [Int.emod_eq_of_lt (Int.ofNat_zero_le _) (Int.ofNat_lt_ofNat_of_lt hi), ha]⟩
@[simp]
theorem attach_image_val [DecidableEq α] {s : Finset α} : s.attach.image Subtype.val = s :=
eq_of_veq <| by rw [image_val, attach_val, Multiset.attach_map_val, dedup_eq_self]
@[simp]
theorem attach_insert [DecidableEq α] {a : α} {s : Finset α} :
attach (insert a s) =
insert (⟨a, mem_insert_self a s⟩ : { x // x ∈ insert a s })
((attach s).image fun x => ⟨x.1, mem_insert_of_mem x.2⟩) :=
ext fun ⟨x, hx⟩ =>
⟨Or.casesOn (mem_insert.1 hx)
(fun h : x = a => fun _ => mem_insert.2 <| Or.inl <| Subtype.eq h) fun h : x ∈ s => fun _ =>
mem_insert_of_mem <| mem_image.2 <| ⟨⟨x, h⟩, mem_attach _ _, Subtype.eq rfl⟩,
fun _ => Finset.mem_attach _ _⟩
@[simp]
theorem disjoint_image {s t : Finset α} {f : α → β} (hf : Injective f) :
Disjoint (s.image f) (t.image f) ↔ Disjoint s t :=
mod_cast Set.disjoint_image_iff hf (s := s) (t := t)
theorem image_const {s : Finset α} (h : s.Nonempty) (b : β) : (s.image fun _ => b) = singleton b :=
mod_cast Set.Nonempty.image_const (coe_nonempty.2 h) b
@[simp]
theorem map_erase [DecidableEq α] (f : α ↪ β) (s : Finset α) (a : α) :
(s.erase a).map f = (s.map f).erase (f a) := by
simp_rw [map_eq_image]
exact s.image_erase f.2 a
end Image
/-! ### filterMap -/
section FilterMap
/-- `filterMap f s` is a combination filter/map operation on `s`.
The function `f : α → Option β` is applied to each element of `s`;
if `f a` is `some b` then `b` is included in the result, otherwise
`a` is excluded from the resulting finset.
In notation, `filterMap f s` is the finset `{b : β | ∃ a ∈ s , f a = some b}`. -/
-- TODO: should there be `filterImage` too?
def filterMap (f : α → Option β) (s : Finset α)
(f_inj : ∀ a a' b, b ∈ f a → b ∈ f a' → a = a') : Finset β :=
⟨s.val.filterMap f, s.nodup.filterMap f f_inj⟩
variable (f : α → Option β) (s' : Finset α) {s t : Finset α}
{f_inj : ∀ a a' b, b ∈ f a → b ∈ f a' → a = a'}
@[simp]
theorem filterMap_val : (filterMap f s' f_inj).1 = s'.1.filterMap f := rfl
@[simp]
theorem filterMap_empty : (∅ : Finset α).filterMap f f_inj = ∅ := rfl
@[simp]
theorem mem_filterMap {b : β} : b ∈ s.filterMap f f_inj ↔ ∃ a ∈ s, f a = some b :=
s.val.mem_filterMap f
@[simp, norm_cast]
theorem coe_filterMap : (s.filterMap f f_inj : Set β) = {b | ∃ a ∈ s, f a = some b} :=
Set.ext (by simp only [mem_coe, mem_filterMap, Option.mem_def, Set.mem_setOf_eq, implies_true])
@[simp]
theorem filterMap_some : s.filterMap some (by simp) = s :=
ext fun _ => by simp only [mem_filterMap, Option.some.injEq, exists_eq_right]
theorem filterMap_mono (h : s ⊆ t) :
filterMap f s f_inj ⊆ filterMap f t f_inj := by
rw [← val_le_iff] at h ⊢
exact Multiset.filterMap_le_filterMap f h
@[simp]
theorem _root_.List.toFinset_filterMap [DecidableEq α] [DecidableEq β] (s : List α) :
(s.filterMap f).toFinset = s.toFinset.filterMap f f_inj := by
simp [← Finset.coe_inj]
end FilterMap
/-! ### Subtype -/
section Subtype
/-- Given a finset `s` and a predicate `p`, `s.subtype p` is the finset of `Subtype p` whose
elements belong to `s`. -/
protected def subtype {α} (p : α → Prop) [DecidablePred p] (s : Finset α) : Finset (Subtype p) :=
(s.filter p).attach.map
⟨fun x => ⟨x.1, by simpa using (Finset.mem_filter.1 x.2).2⟩,
fun _ _ H => Subtype.eq <| Subtype.mk.inj H⟩
@[simp]
theorem mem_subtype {p : α → Prop} [DecidablePred p] {s : Finset α} :
∀ {a : Subtype p}, a ∈ s.subtype p ↔ (a : α) ∈ s
| ⟨a, ha⟩ => by simp [Finset.subtype, ha]
theorem subtype_eq_empty {p : α → Prop} [DecidablePred p] {s : Finset α} :
s.subtype p = ∅ ↔ ∀ x, p x → x ∉ s := by simp [Finset.ext_iff, Subtype.forall, Subtype.coe_mk]
@[mono]
theorem subtype_mono {p : α → Prop} [DecidablePred p] : Monotone (Finset.subtype p) :=
fun _ _ h _ hx => mem_subtype.2 <| h <| mem_subtype.1 hx
/-- `s.subtype p` converts back to `s.filter p` with
`Embedding.subtype`. -/
@[simp]
theorem subtype_map (p : α → Prop) [DecidablePred p] {s : Finset α} :
(s.subtype p).map (Embedding.subtype _) = s.filter p := by
ext x
simp [@and_comm _ (_ = _), @and_left_comm _ (_ = _), @and_comm (p x) (x ∈ s)]
/-- If all elements of a `Finset` satisfy the predicate `p`,
`s.subtype p` converts back to `s` with `Embedding.subtype`. -/
theorem subtype_map_of_mem {p : α → Prop} [DecidablePred p] {s : Finset α} (h : ∀ x ∈ s, p x) :
(s.subtype p).map (Embedding.subtype _) = s := ext <| by simpa [subtype_map] using h
/-- If a `Finset` of a subtype is converted to the main type with
`Embedding.subtype`, all elements of the result have the property of
the subtype. -/
theorem property_of_mem_map_subtype {p : α → Prop} (s : Finset { x // p x }) {a : α}
(h : a ∈ s.map (Embedding.subtype _)) : p a := by
rcases mem_map.1 h with ⟨x, _, rfl⟩
exact x.2
/-- If a `Finset` of a subtype is converted to the main type with
`Embedding.subtype`, the result does not contain any value that does
not satisfy the property of the subtype. -/
theorem not_mem_map_subtype_of_not_property {p : α → Prop} (s : Finset { x // p x }) {a : α}
(h : ¬p a) : a ∉ s.map (Embedding.subtype _) :=
mt s.property_of_mem_map_subtype h
/-- If a `Finset` of a subtype is converted to the main type with
`Embedding.subtype`, the result is a subset of the set giving the
subtype. -/
theorem map_subtype_subset {t : Set α} (s : Finset t) : ↑(s.map (Embedding.subtype _)) ⊆ t := by
intro a ha
rw [mem_coe] at ha
convert property_of_mem_map_subtype s ha
end Subtype
/-- If a `Finset` is a subset of the image of a `Set` under `f`,
then it is equal to the `Finset.image` of a `Finset` subset of that `Set`. -/
theorem subset_set_image_iff [DecidableEq β] {s : Set α} {t : Finset β} {f : α → β} :
↑t ⊆ f '' s ↔ ∃ s' : Finset α, ↑s' ⊆ s ∧ s'.image f = t := by
constructor
· intro h
letI : CanLift β s (f ∘ (↑)) fun y => y ∈ f '' s := ⟨fun y ⟨x, hxt, hy⟩ => ⟨⟨x, hxt⟩, hy⟩⟩
lift t to Finset s using h
refine ⟨t.map (Embedding.subtype _), map_subtype_subset _, ?_⟩
ext y; simp
· rintro ⟨t, ht, rfl⟩
rw [coe_image]
exact Set.image_subset f ht
/--
If a finset `t` is a subset of the image of another finset `s` under `f`, then it is equal to the
image of a subset of `s`.
For the version where `s` is a set, see `subset_set_image_iff`.
-/
| theorem subset_image_iff [DecidableEq β] {s : Finset α} {t : Finset β} {f : α → β} :
t ⊆ s.image f ↔ ∃ s' : Finset α, s' ⊆ s ∧ s'.image f = t := by
simp only [← coe_subset, coe_image, subset_set_image_iff]
| Mathlib/Data/Finset/Image.lean | 648 | 651 |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.