mathlib documentation

data.equiv.set

Equivalences and sets #

In this file we provide lemmas linking equivalences to sets.

Some notable definitions are:

This file is separate from equiv/basic such that we do not require the full lattice structure on sets before defining what an equivalence is.

@[simp]
theorem equiv.range_eq_univ {α : Type u_1} {β : Type u_2} (e : α β) :
@[protected]
theorem equiv.image_eq_preimage {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :
e '' s = (e.symm) ⁻¹' s
theorem set.mem_image_equiv {α : Type u_1} {β : Type u_2} {S : set α} {f : α β} {x : β} :
x f '' S (f.symm) x S
theorem set.image_equiv_eq_preimage_symm {α : Type u_1} {β : Type u_2} (S : set α) (f : α β) :
f '' S = (f.symm) ⁻¹' S

Alias for equiv.image_eq_preimage

theorem set.preimage_equiv_eq_image_symm {α : Type u_1} {β : Type u_2} (S : set α) (f : β α) :
f ⁻¹' S = (f.symm) '' S

Alias for equiv.image_eq_preimage

@[protected, simp]
theorem equiv.subset_image {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (t : set β) :
(e.symm) '' t s t e '' s
@[protected, simp]
theorem equiv.subset_image' {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (t : set β) :
s (e.symm) '' t e '' s t
@[simp]
theorem equiv.symm_image_image {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :
(e.symm) '' (e '' s) = s
theorem equiv.eq_image_iff_symm_image_eq {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (t : set β) :
t = e '' s (e.symm) '' t = s
@[simp]
theorem equiv.image_symm_image {α : Type u_1} {β : Type u_2} (e : α β) (s : set β) :
e '' ((e.symm) '' s) = s
@[simp]
theorem equiv.image_preimage {α : Type u_1} {β : Type u_2} (e : α β) (s : set β) :
e '' (e ⁻¹' s) = s
@[simp]
theorem equiv.preimage_image {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :
e ⁻¹' (e '' s) = s
@[protected]
theorem equiv.image_compl {α : Type u_1} {β : Type u_2} (f : α β) (s : set α) :
f '' s = (f '' s)
@[simp]
theorem equiv.symm_preimage_preimage {α : Type u_1} {β : Type u_2} (e : α β) (s : set β) :
@[simp]
theorem equiv.preimage_symm_preimage {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :
@[simp]
theorem equiv.preimage_subset {α : Type u_1} {β : Type u_2} (e : α β) (s t : set β) :
@[simp]
theorem equiv.image_subset {α : Type u_1} {β : Type u_2} (e : α β) (s t : set α) :
e '' s e '' t s t
@[simp]
theorem equiv.image_eq_iff_eq {α : Type u_1} {β : Type u_2} (e : α β) (s t : set α) :
e '' s = e '' t s = t
theorem equiv.preimage_eq_iff_eq_image {α : Type u_1} {β : Type u_2} (e : α β) (s : set β) (t : set α) :
e ⁻¹' s = t s = e '' t
theorem equiv.eq_preimage_iff_image_eq {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (t : set β) :
s = e ⁻¹' t e '' s = t
theorem equiv.prod_assoc_preimage {α : Type u_1} {β : Type u_2} {γ : Type u_3} {s : set α} {t : set β} {u : set γ} :
(equiv.prod_assoc α β γ) ⁻¹' s.prod (t.prod u) = (s.prod t).prod u
def equiv.set_prod_equiv_sigma {α : Type u_1} {β : Type u_2} (s : set × β)) :
s Σ (x : α), {y : β | (x, y) s}

A set s in α × β is equivalent to the sigma-type Σ x, {y | (x, y) ∈ s}.

Equations
def equiv.set_congr {α : Type u_1} {s t : set α} (h : s = t) :

The subtypes corresponding to equal sets are equivalent.

Equations
@[simp]
theorem equiv.set_congr_apply {α : Type u_1} {s t : set α} (h : s = t) (x : {a // (λ (a : α), (λ (x : α), x s) a) a}) :
@[simp]
theorem equiv.image_apply_coe {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (x : s) :
((e.image s) x) = e x.val
def equiv.image {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :

A set is equivalent to its image under an equivalence.

Equations
@[simp]
theorem equiv.image_symm_apply_coe {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) (y : (e '' s)) :
(((e.image s).symm) y) = (e.symm) y.val
@[simp]
theorem equiv.set.univ_symm_apply (α : Type u_1) (a : α) :
@[protected]
def equiv.set.univ (α : Type u_1) :

univ α is equivalent to α.

Equations
@[simp]
theorem equiv.set.univ_apply (α : Type u_1) (ᾰ : set.univ) :
(equiv.set.univ α) =
@[protected]
def equiv.set.empty (α : Type u_1) :

An empty set is equivalent to the empty type.

Equations
@[protected]
def equiv.set.pempty (α : Type u_1) :

An empty set is equivalent to a pempty type.

Equations
@[protected]
def equiv.set.union' {α : Type u_1} {s t : set α} (p : α → Prop) [decidable_pred p] (hs : ∀ (x : α), x sp x) (ht : ∀ (x : α), x t¬p x) :
(s t) s t

If sets s and t are separated by a decidable predicate, then s ∪ t is equivalent to s ⊕ t.

Equations
@[protected]
def equiv.set.union {α : Type u_1} {s t : set α} [decidable_pred (λ (x : α), x s)] (H : s t ) :
(s t) s t

If sets s and t are disjoint, then s ∪ t is equivalent to s ⊕ t.

Equations
theorem equiv.set.union_apply_left {α : Type u_1} {s t : set α} [decidable_pred (λ (x : α), x s)] (H : s t ) {a : (s t)} (ha : a s) :
theorem equiv.set.union_apply_right {α : Type u_1} {s t : set α} [decidable_pred (λ (x : α), x s)] (H : s t ) {a : (s t)} (ha : a t) :
@[simp]
theorem equiv.set.union_symm_apply_left {α : Type u_1} {s t : set α} [decidable_pred (λ (x : α), x s)] (H : s t ) (a : s) :
@[simp]
theorem equiv.set.union_symm_apply_right {α : Type u_1} {s t : set α} [decidable_pred (λ (x : α), x s)] (H : s t ) (a : t) :
@[protected]
def equiv.set.singleton {α : Type u_1} (a : α) :

A singleton set is equivalent to a punit type.

Equations
@[simp]
theorem equiv.set.of_eq_apply {α : Type u} {s t : set α} (h : s = t) (x : s) :
@[protected]
def equiv.set.of_eq {α : Type u} {s t : set α} (h : s = t) :

Equal sets are equivalent.

Equations
@[simp]
theorem equiv.set.of_eq_symm_apply {α : Type u} {s t : set α} (h : s = t) (x : t) :
@[protected]
def equiv.set.insert {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {a : α} (H : a s) :

If a ∉ s, then insert a s is equivalent to s ⊕ punit.

Equations
@[simp]
theorem equiv.set.insert_symm_apply_inl {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {a : α} (H : a s) (b : s) :
@[simp]
theorem equiv.set.insert_symm_apply_inr {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {a : α} (H : a s) (b : punit) :
@[simp]
theorem equiv.set.insert_apply_left {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {a : α} (H : a s) :
@[simp]
theorem equiv.set.insert_apply_right {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {a : α} (H : a s) (b : s) :
@[protected]
def equiv.set.sum_compl {α : Type u_1} (s : set α) [decidable_pred (λ (_x : α), _x s)] :

If s : set α is a set with decidable membership, then s ⊕ sᶜ is equivalent to α.

Equations
@[simp]
theorem equiv.set.sum_compl_apply_inl {α : Type u} (s : set α) [decidable_pred (λ (_x : α), _x s)] (x : s) :
@[simp]
theorem equiv.set.sum_compl_apply_inr {α : Type u} (s : set α) [decidable_pred (λ (_x : α), _x s)] (x : s) :
theorem equiv.set.sum_compl_symm_apply_of_mem {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {x : α} (hx : x s) :
theorem equiv.set.sum_compl_symm_apply_of_not_mem {α : Type u} {s : set α} [decidable_pred (λ (_x : α), _x s)] {x : α} (hx : x s) :
@[simp]
theorem equiv.set.sum_compl_symm_apply {α : Type u_1} {s : set α} [decidable_pred (λ (_x : α), _x s)] {x : s} :
@[simp]
theorem equiv.set.sum_compl_symm_apply_compl {α : Type u_1} {s : set α} [decidable_pred (λ (_x : α), _x s)] {x : s} :
@[protected]
def equiv.set.sum_diff_subset {α : Type u_1} {s t : set α} (h : s t) [decidable_pred (λ (_x : α), _x s)] :
s (t \ s) t

sum_diff_subset s t is the natural equivalence between s ⊕ (t \ s) and t, where s and t are two sets.

Equations
@[simp]
theorem equiv.set.sum_diff_subset_apply_inl {α : Type u_1} {s t : set α} (h : s t) [decidable_pred (λ (_x : α), _x s)] (x : s) :
@[simp]
theorem equiv.set.sum_diff_subset_apply_inr {α : Type u_1} {s t : set α} (h : s t) [decidable_pred (λ (_x : α), _x s)] (x : (t \ s)) :
theorem equiv.set.sum_diff_subset_symm_apply_of_mem {α : Type u_1} {s t : set α} (h : s t) [decidable_pred (λ (_x : α), _x s)] {x : t} (hx : x.val s) :
theorem equiv.set.sum_diff_subset_symm_apply_of_not_mem {α : Type u_1} {s t : set α} (h : s t) [decidable_pred (λ (_x : α), _x s)] {x : t} (hx : x.val s) :
@[protected]
def equiv.set.union_sum_inter {α : Type u} (s t : set α) [decidable_pred (λ (_x : α), _x s)] :
(s t) (s t) s t

If s is a set with decidable membership, then the sum of s ∪ t and s ∩ t is equivalent to s ⊕ t.

Equations
@[protected]
def equiv.set.compl {α : Type u} {β : Type v} {s : set α} {t : set β} [decidable_pred (λ (_x : α), _x s)] [decidable_pred (λ (_x : β), _x t)] (e₀ : s t) :
{e // ∀ (x : s), e x = (e₀ x)} (s t)

Given an equivalence e₀ between sets s : set α and t : set β, the set of equivalences e : α ≃ β such that e ↑x = ↑(e₀ x) for each x : s is equivalent to the set of equivalences between sᶜ and tᶜ.

Equations
@[protected]
def equiv.set.prod {α : Type u_1} {β : Type u_2} (s : set α) (t : set β) :
(s.prod t) s × t

The set product of two sets is equivalent to the type product of their coercions to types.

Equations
@[protected]
noncomputable def equiv.set.image_of_inj_on {α : Type u_1} {β : Type u_2} (f : α → β) (s : set α) (H : set.inj_on f s) :
s (f '' s)

If a function f is injective on a set s, then s is equivalent to f '' s.

Equations
@[protected]
noncomputable def equiv.set.image {α : Type u_1} {β : Type u_2} (f : α → β) (s : set α) (H : function.injective f) :
s (f '' s)

If f is an injective function, then s is equivalent to f '' s.

Equations
@[simp]
theorem equiv.set.image_apply {α : Type u_1} {β : Type u_2} (f : α → β) (s : set α) (H : function.injective f) (p : s) :
(equiv.set.image f s H) p = f p, _⟩
@[protected, simp]
theorem equiv.set.image_symm_apply {α : Type u_1} {β : Type u_2} (f : α → β) (s : set α) (H : function.injective f) (x : α) (h : x s) :
((equiv.set.image f s H).symm) f x, _⟩ = x, h⟩
theorem equiv.set.image_symm_preimage {α : Type u_1} {β : Type u_2} {f : α → β} (hf : function.injective f) (u s : set α) :
(λ (x : (f '' s)), (((equiv.set.image f s hf).symm) x)) ⁻¹' u = coe ⁻¹' (f '' u)
@[simp]
theorem equiv.set.congr_apply {α : Type u_1} {β : Type u_2} (e : α β) (s : set α) :
@[protected]
def equiv.set.congr {α : Type u_1} {β : Type u_2} (e : α β) :
set α set β

If α is equivalent to β, then set α is equivalent to set β.

Equations
@[simp]
theorem equiv.set.congr_symm_apply {α : Type u_1} {β : Type u_2} (e : α β) (t : set β) :
@[protected]
def equiv.set.sep {α : Type u} (s : set α) (t : α → Prop) :
{x ∈ s | t x} {x : s | t x}

The set {x ∈ s | t x} is equivalent to the set of x : s such that t x.

Equations
@[protected]
def equiv.set.powerset {α : Type u_1} (S : set α) :

The set 𝒫 S := {x | x ⊆ S} is equivalent to the type set S.

Equations
@[simp]
theorem equiv.set.range_splitting_image_equiv_symm_apply_coe {α : Type u_1} {β : Type u_2} (f : α → β) (s : set (set.range f)) (x : s) :
noncomputable def equiv.set.range_splitting_image_equiv {α : Type u_1} {β : Type u_2} (f : α → β) (s : set (set.range f)) :

If s is a set in range f, then its image under range_splitting f is in bijection (via f) with s.

Equations
@[simp]
theorem equiv.set.range_splitting_image_equiv_apply_coe_coe {α : Type u_1} {β : Type u_2} (f : α → β) (s : set (set.range f)) (x : (set.range_splitting f '' s)) :
@[simp]
theorem equiv.of_left_inverse_symm_apply {α : Sort u_1} {β : Type u_2} (f : α → β) (f_inv : nonempty αβ → α) (hf : ∀ (h : nonempty α), function.left_inverse (f_inv h) f) (b : (set.range f)) :
((equiv.of_left_inverse f f_inv hf).symm) b = f_inv _ b
def equiv.of_left_inverse {α : Sort u_1} {β : Type u_2} (f : α → β) (f_inv : nonempty αβ → α) (hf : ∀ (h : nonempty α), function.left_inverse (f_inv h) f) :

If f : α → β has a left-inverse when α is nonempty, then α is computably equivalent to the range of f.

While awkward, the nonempty α hypothesis on f_inv and hf allows this to be used when α is empty too. This hypothesis is absent on analogous definitions on stronger equivs like linear_equiv.of_left_inverse and ring_equiv.of_left_inverse as their typeclass assumptions are already sufficient to ensure non-emptiness.

Equations
@[simp]
theorem equiv.of_left_inverse_apply_coe {α : Sort u_1} {β : Type u_2} (f : α → β) (f_inv : nonempty αβ → α) (hf : ∀ (h : nonempty α), function.left_inverse (f_inv h) f) (a : α) :
((equiv.of_left_inverse f f_inv hf) a) = f a
def equiv.of_left_inverse' {α : Sort u_1} {β : Type u_2} (f : α → β) (f_inv : β → α) (hf : function.left_inverse f_inv f) :

If f : α → β has a left-inverse, then α is computably equivalent to the range of f.

Note that if α is empty, no such f_inv exists and so this definition can't be used, unlike the stronger but less convenient of_left_inverse.

@[simp]
theorem equiv.of_injective_apply {α : Sort u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) (a : α) :
(equiv.of_injective f hf) a = f a, _⟩
noncomputable def equiv.of_injective {α : Sort u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) :

If f : α → β is an injective function, then domain α is equivalent to the range of f.

Equations
theorem equiv.apply_of_injective_symm {α : Sort u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) (b : (set.range f)) :
@[simp]
theorem equiv.of_injective_symm_apply {α : Sort u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) (a : α) :
((equiv.of_injective f hf).symm) f a, _⟩ = a
theorem equiv.coe_of_injective_symm {α : Type u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) :
@[simp]
theorem equiv.self_comp_of_injective_symm {α : Sort u_1} {β : Type u_2} (f : α → β) (hf : function.injective f) :
theorem equiv.of_left_inverse_eq_of_injective {α : Type u_1} {β : Type u_2} (f : α → β) (f_inv : nonempty αβ → α) (hf : ∀ (h : nonempty α), function.left_inverse (f_inv h) f) :
theorem equiv.of_left_inverse'_eq_of_injective {α : Type u_1} {β : Type u_2} (f : α → β) (f_inv : β → α) (hf : function.left_inverse f_inv f) :
@[protected]
theorem equiv.set_forall_iff {α : Type u_1} {β : Type u_2} (e : α β) {p : set α → Prop} :
(∀ (a : set α), p a) ∀ (a : set β), p (e ⁻¹' a)
@[protected]
theorem equiv.preimage_sUnion {α : Type u_1} {β : Type u_2} (f : α β) {s : set (set β)} :
noncomputable def set.bij_on.equiv {α : Type u_1} {β : Type u_2} {s : set α} {t : set β} (f : α → β) (h : set.bij_on f s t) :

If a function is a bijection between two sets s and t, then it induces an equivalence between the types ↥s and ``↥t`.

Equations
theorem dite_comp_equiv_update {α : Type u_1} {β : Sort u_2} {γ : Sort u_3} {s : set α} (e : β s) (v : β → γ) (w : α → γ) (j : β) (x : γ) [decidable_eq β] [decidable_eq α] [Π (j : α), decidable (j s)] :
(λ (i : α), dite (i s) (λ (h : i s), function.update v j x ((e.symm) i, h⟩)) (λ (h : i s), w i)) = function.update (λ (i : α), dite (i s) (λ (h : i s), v ((e.symm) i, h⟩)) (λ (h : i s), w i)) (e j) x

The composition of an updated function with an equiv on a subset can be expressed as an updated function.