Documentation

Mathlib.Topology.Sets.Opens

Open sets #

Summary #

We define the subtype of open sets in a topological space.

Main Definitions #

Bundled open sets #

Bundled open neighborhoods #

Main results #

We define order structures on both Opens α (CompleteLattice, Frame) and OpenNhdsOf x (OrderTop, DistribLattice).

TODO #

theorem TopologicalSpace.Opens.forall {α : Type u_2} [TopologicalSpace α] {p : Opens αProp} :
(∀ (U : Opens α), p U) ∀ (U : Set α) (hU : IsOpen U), p { carrier := U, is_open' := hU }
@[simp]
@[simp]
theorem TopologicalSpace.Opens.coe_mk {α : Type u_2} [TopologicalSpace α] {U : Set α} {hU : IsOpen U} :
{ carrier := U, is_open' := hU } = U

the coercion Opens α → Set α applied to a pair is the same as taking the first component

@[simp]
theorem TopologicalSpace.Opens.mem_mk {α : Type u_2} [TopologicalSpace α] {x : α} {U : Set α} {h : IsOpen U} :
x { carrier := U, is_open' := h } x U
theorem TopologicalSpace.Opens.nonempty_coe {α : Type u_2} [TopologicalSpace α] {U : Opens α} :
(↑U).Nonempty ∃ (x : α), x U
theorem TopologicalSpace.Opens.ext {α : Type u_2} [TopologicalSpace α] {U V : Opens α} (h : U = V) :
U = V
theorem TopologicalSpace.Opens.coe_inj {α : Type u_2} [TopologicalSpace α] {U V : Opens α} :
U = V U = V
@[reducible, inline]
abbrev TopologicalSpace.Opens.inclusion {α : Type u_2} [TopologicalSpace α] {U V : Opens α} (h : U V) :
UV

A version of Set.inclusion not requiring definitional abuse

Equations
@[simp]
theorem TopologicalSpace.Opens.mk_coe {α : Type u_2} [TopologicalSpace α] (U : Opens α) :
{ carrier := U, is_open' := } = U

See Note [custom simps projection].

Equations

The interior of a set, as an element of Opens.

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@[simp]

The galois coinsertion between sets and opens.

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  • One or more equations did not get rendered due to their size.
@[simp]
theorem TopologicalSpace.Opens.mk_inf_mk {α : Type u_2} [TopologicalSpace α] {U V : Set α} {hU : IsOpen U} {hV : IsOpen V} :
{ carrier := U, is_open' := hU } { carrier := V, is_open' := hV } = { carrier := U V, is_open' := }
@[simp]
theorem TopologicalSpace.Opens.coe_inf {α : Type u_2} [TopologicalSpace α] (s t : Opens α) :
↑(s t) = s t
@[simp]
theorem TopologicalSpace.Opens.mem_inf {α : Type u_2} [TopologicalSpace α] {s t : Opens α} {x : α} :
x s t x s x t
@[simp]
theorem TopologicalSpace.Opens.coe_sup {α : Type u_2} [TopologicalSpace α] (s t : Opens α) :
↑(s t) = s t
@[simp]
@[simp]
theorem TopologicalSpace.Opens.mk_empty {α : Type u_2} [TopologicalSpace α] :
{ carrier := , is_open' := } =
@[simp]
theorem TopologicalSpace.Opens.coe_eq_empty {α : Type u_2} [TopologicalSpace α] {U : Opens α} :
U = U =
@[simp]
theorem TopologicalSpace.Opens.mem_top {α : Type u_2} [TopologicalSpace α] (x : α) :
@[simp]
theorem TopologicalSpace.Opens.mk_univ {α : Type u_2} [TopologicalSpace α] :
{ carrier := Set.univ, is_open' := } =
@[simp]
@[simp]
theorem TopologicalSpace.Opens.coe_sSup {α : Type u_2} [TopologicalSpace α] {S : Set (Opens α)} :
(sSup S) = iS, i
@[simp]
theorem TopologicalSpace.Opens.coe_finset_sup {ι : Type u_1} {α : Type u_2} [TopologicalSpace α] (f : ιOpens α) (s : Finset ι) :
(s.sup f) = s.sup (SetLike.coe f)
@[simp]
theorem TopologicalSpace.Opens.coe_finset_inf {ι : Type u_1} {α : Type u_2} [TopologicalSpace α] (f : ιOpens α) (s : Finset ι) :
(s.inf f) = s.inf (SetLike.coe f)
@[simp]
theorem TopologicalSpace.Opens.coe_iSup {α : Type u_2} [TopologicalSpace α] {ι : Sort u_5} (s : ιOpens α) :
(⨆ (i : ι), s i) = ⋃ (i : ι), (s i)
theorem TopologicalSpace.Opens.iSup_def {α : Type u_2} [TopologicalSpace α] {ι : Sort u_5} (s : ιOpens α) :
⨆ (i : ι), s i = { carrier := ⋃ (i : ι), (s i), is_open' := }
@[simp]
theorem TopologicalSpace.Opens.iSup_mk {α : Type u_2} [TopologicalSpace α] {ι : Sort u_5} (s : ιSet α) (h : ∀ (i : ι), IsOpen (s i)) :
⨆ (i : ι), { carrier := s i, is_open' := } = { carrier := ⋃ (i : ι), s i, is_open' := }
@[simp]
theorem TopologicalSpace.Opens.mem_iSup {α : Type u_2} [TopologicalSpace α] {ι : Sort u_5} {x : α} {s : ιOpens α} :
x iSup s ∃ (i : ι), x s i
@[simp]
theorem TopologicalSpace.Opens.mem_sSup {α : Type u_2} [TopologicalSpace α] {Us : Set (Opens α)} {x : α} :
x sSup Us uUs, x u
@[deprecated TopologicalSpace.Opens.isOpenEmbedding' (since := "2024-10-18")]

Alias of TopologicalSpace.Opens.isOpenEmbedding'.

@[deprecated TopologicalSpace.Opens.isOpenEmbedding_of_le (since := "2024-10-18")]

Alias of TopologicalSpace.Opens.isOpenEmbedding_of_le.

theorem TopologicalSpace.Opens.eq_bot_or_top {α : Type u_5} [t : TopologicalSpace α] (h : t = ) (U : Opens α) :
U = U =

An open set in the indiscrete topology is either empty or the whole space.

A set of opens α is a basis if the set of corresponding sets is a topological basis.

Equations
theorem TopologicalSpace.Opens.isBasis_iff_nbhd {α : Type u_2} [TopologicalSpace α] {B : Set (Opens α)} :
IsBasis B ∀ {U : Opens α} {x : α}, x UU'B, x U' U' U
theorem TopologicalSpace.Opens.isBasis_iff_cover {α : Type u_2} [TopologicalSpace α] {B : Set (Opens α)} :
IsBasis B ∀ (U : Opens α), UsB, U = sSup Us
theorem TopologicalSpace.Opens.IsBasis.isCompact_open_iff_eq_finite_iUnion {α : Type u_2} [TopologicalSpace α] {ι : Type u_5} (b : ιOpens α) (hb : IsBasis (Set.range b)) (hb' : ∀ (i : ι), IsCompact (b i)) (U : Set α) :
IsCompact U IsOpen U ∃ (s : Set ι), s.Finite U = is, (b i)

If α has a basis consisting of compact opens, then an open set in α is compact open iff it is a finite union of some elements in the basis

theorem TopologicalSpace.Opens.IsBasis.le_iff {α : Type u_5} {t₁ t₂ : TopologicalSpace α} {Us : Set (Opens α)} (hUs : IsBasis Us) :
t₁ t₂ UUs, IsOpen U
def TopologicalSpace.Opens.comap {α : Type u_2} {β : Type u_3} [TopologicalSpace α] [TopologicalSpace β] (f : C(α, β)) :
FrameHom (Opens β) (Opens α)

The preimage of an open set, as an open set.

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theorem TopologicalSpace.Opens.comap_mono {α : Type u_2} {β : Type u_3} [TopologicalSpace α] [TopologicalSpace β] (f : C(α, β)) {s t : Opens β} (h : s t) :
(comap f) s (comap f) t
@[simp]
theorem TopologicalSpace.Opens.coe_comap {α : Type u_2} {β : Type u_3} [TopologicalSpace α] [TopologicalSpace β] (f : C(α, β)) (U : Opens β) :
((comap f) U) = f ⁻¹' U
@[simp]
theorem TopologicalSpace.Opens.mem_comap {α : Type u_2} {β : Type u_3} [TopologicalSpace α] [TopologicalSpace β] {f : C(α, β)} {U : Opens β} {x : α} :
x (comap f) U f x U
theorem TopologicalSpace.Opens.comap_comp {α : Type u_2} {β : Type u_3} {γ : Type u_4} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (g : C(β, γ)) (f : C(α, β)) :
comap (g.comp f) = (comap f).comp (comap g)
theorem TopologicalSpace.Opens.comap_comap {α : Type u_2} {β : Type u_3} {γ : Type u_4} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (g : C(β, γ)) (f : C(α, β)) (U : Opens γ) :
(comap f) ((comap g) U) = (comap (g.comp f)) U

A homeomorphism induces an order-preserving equivalence on open sets, by taking comaps.

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@[simp]
@[simp]
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instance TopologicalSpace.OpenNhdsOf.canLiftSet {α : Type u_2} [TopologicalSpace α] {x : α} :
CanLift (Set α) (OpenNhdsOf x) SetLike.coe fun (s : Set α) => IsOpen s x s
theorem TopologicalSpace.OpenNhdsOf.mem {α : Type u_2} [TopologicalSpace α] {x : α} (U : OpenNhdsOf x) :
x U
theorem TopologicalSpace.OpenNhdsOf.isOpen {α : Type u_2} [TopologicalSpace α] {x : α} (U : OpenNhdsOf x) :
IsOpen U
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def TopologicalSpace.OpenNhdsOf.comap {α : Type u_2} {β : Type u_3} [TopologicalSpace α] [TopologicalSpace β] (f : C(α, β)) (x : α) :

Preimage of an open neighborhood of f x under a continuous map f as a LatticeHom.

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  • One or more equations did not get rendered due to their size.