Documentation

Mathlib.Topology.Sets.Compacts

Compact sets #

We define a few types of compact sets in a topological space.

Main Definitions #

For a topological space α,

Compact sets #

structure TopologicalSpace.Compacts (α : Type u_4) [TopologicalSpace α] :
Type u_4

The type of compact sets of a topological space.

  • carrier : Set α

    the carrier set, i.e. the points in this set

  • isCompact' : IsCompact self.carrier

See Note [custom simps projection].

Equations
theorem TopologicalSpace.Compacts.ext {α : Type u_1} [TopologicalSpace α] {s t : Compacts α} (h : s = t) :
s = t
theorem TopologicalSpace.Compacts.ext_iff {α : Type u_1} [TopologicalSpace α] {s t : Compacts α} :
s = t s = t
@[simp]
theorem TopologicalSpace.Compacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Set α) (h : IsCompact s) :
{ carrier := s, isCompact' := h } = s
Equations
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The type of compact sets is inhabited, with default element the empty set.

Equations
@[simp]
theorem TopologicalSpace.Compacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : Compacts α) :
(st) = s t
@[simp]
theorem TopologicalSpace.Compacts.coe_inf {α : Type u_1} [TopologicalSpace α] [T2Space α] (s t : Compacts α) :
(st) = s t
@[simp]
theorem TopologicalSpace.Compacts.coe_finset_sup {α : Type u_1} [TopologicalSpace α] {ι : Type u_4} {s : Finset ι} {f : ιCompacts α} :
(s.sup f) = s.sup fun (i : ι) => (f i)
def TopologicalSpace.Compacts.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (K : Compacts α) :

The image of a compact set under a continuous function.

Equations
@[simp]
theorem TopologicalSpace.Compacts.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (s : Compacts α) :
(Compacts.map f hf s) = f '' s
@[simp]
theorem TopologicalSpace.Compacts.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (K : Compacts α) :
Compacts.map (f g) K = Compacts.map f hf (Compacts.map g hg K)

A homeomorphism induces an equivalence on compact sets, by taking the image.

Equations
@[simp]
theorem TopologicalSpace.Compacts.equiv_symm_apply {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts β) :
@[simp]
theorem TopologicalSpace.Compacts.equiv_apply {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts α) :
(Compacts.equiv f) K = Compacts.map f K
@[simp]
theorem TopologicalSpace.Compacts.equiv_trans {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : α ≃ₜ β) (g : β ≃ₜ γ) :
theorem TopologicalSpace.Compacts.coe_equiv_apply_eq_preimage {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : α ≃ₜ β) (K : Compacts α) :
((Compacts.equiv f) K) = f.symm ⁻¹' K

The image of a compact set under a homeomorphism can also be expressed as a preimage.

def TopologicalSpace.Compacts.prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : Compacts α) (L : Compacts β) :
Compacts (α × β)

The product of two TopologicalSpace.Compacts, as a TopologicalSpace.Compacts in the product space.

Equations
  • K.prod L = { carrier := K ×ˢ L, isCompact' := }
@[simp]
theorem TopologicalSpace.Compacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : Compacts α) (L : Compacts β) :
(K.prod L) = K ×ˢ L

Nonempty compact sets #

The type of nonempty compact sets of a topological space.

See Note [custom simps projection].

Equations

Reinterpret a nonempty compact as a closed set.

Equations
  • s.toCloseds = { carrier := s, isClosed' := }
theorem TopologicalSpace.NonemptyCompacts.ext {α : Type u_1} [TopologicalSpace α] {s t : NonemptyCompacts α} (h : s = t) :
s = t
@[simp]
theorem TopologicalSpace.NonemptyCompacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : s.carrier.Nonempty) :
{ toCompacts := s, nonempty' := h } = s
Equations
@[simp]
theorem TopologicalSpace.NonemptyCompacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : NonemptyCompacts α) :
(st) = s t

In an inhabited space, the type of nonempty compact subsets is also inhabited, with default element the singleton set containing the default element.

Equations

The product of two TopologicalSpace.NonemptyCompacts, as a TopologicalSpace.NonemptyCompacts in the product space.

Equations
@[simp]
theorem TopologicalSpace.NonemptyCompacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : NonemptyCompacts α) (L : NonemptyCompacts β) :
(K.prod L) = K ×ˢ L

Positive compact sets #

The type of compact sets with nonempty interior of a topological space. See also TopologicalSpace.Compacts and TopologicalSpace.NonemptyCompacts.

See Note [custom simps projection].

Equations

Reinterpret a positive compact as a nonempty compact.

Equations
theorem TopologicalSpace.PositiveCompacts.ext {α : Type u_1} [TopologicalSpace α] {s t : PositiveCompacts α} (h : s = t) :
s = t
@[simp]
theorem TopologicalSpace.PositiveCompacts.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : (interior s.carrier).Nonempty) :
{ toCompacts := s, interior_nonempty' := h } = s
Equations
@[simp]
theorem TopologicalSpace.PositiveCompacts.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : PositiveCompacts α) :
(st) = s t
def TopologicalSpace.PositiveCompacts.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (K : PositiveCompacts α) :

The image of a positive compact set under a continuous open map.

Equations
@[simp]
theorem TopologicalSpace.PositiveCompacts.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (hf' : IsOpenMap f) (s : PositiveCompacts α) :
(PositiveCompacts.map f hf hf' s) = f '' s
theorem TopologicalSpace.PositiveCompacts.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (hf' : IsOpenMap f) (hg' : IsOpenMap g) (K : PositiveCompacts α) :
theorem exists_positiveCompacts_subset {α : Type u_1} [TopologicalSpace α] [LocallyCompactSpace α] {U : Set α} (ho : IsOpen U) (hn : U.Nonempty) :

In a nonempty locally compact space, there exists a compact set with nonempty interior.

The product of two TopologicalSpace.PositiveCompacts, as a TopologicalSpace.PositiveCompacts in the product space.

Equations
@[simp]
theorem TopologicalSpace.PositiveCompacts.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : PositiveCompacts α) (L : PositiveCompacts β) :
(K.prod L) = K ×ˢ L

Compact open sets #

The type of compact open sets of a topological space. This is useful in non Hausdorff contexts, in particular spectral spaces.

See Note [custom simps projection].

Equations

Reinterpret a compact open as an open.

Equations
  • s.toOpens = { carrier := s, is_open' := }

Reinterpret a compact open as a clopen.

Equations
  • s.toClopens = { carrier := s, isClopen' := }
theorem TopologicalSpace.CompactOpens.ext {α : Type u_1} [TopologicalSpace α] {s t : CompactOpens α} (h : s = t) :
s = t
theorem TopologicalSpace.CompactOpens.ext_iff {α : Type u_1} [TopologicalSpace α] {s t : CompactOpens α} :
s = t s = t
@[simp]
theorem TopologicalSpace.CompactOpens.coe_mk {α : Type u_1} [TopologicalSpace α] (s : Compacts α) (h : IsOpen s.carrier) :
{ toCompacts := s, isOpen' := h } = s
Equations
Equations
@[simp]
theorem TopologicalSpace.CompactOpens.coe_sup {α : Type u_1} [TopologicalSpace α] (s t : CompactOpens α) :
(st) = s t
@[simp]
theorem TopologicalSpace.CompactOpens.coe_finsetSup {α : Type u_1} [TopologicalSpace α] {ι : Type u_4} {f : ιCompactOpens α} {s : Finset ι} :
(s.sup f) = is, (f i)
Equations
@[simp]
theorem TopologicalSpace.CompactOpens.coe_inf {α : Type u_1} [TopologicalSpace α] [QuasiSeparatedSpace α] (s t : CompactOpens α) :
(st) = s t
Equations
@[simp]
theorem TopologicalSpace.CompactOpens.coe_sdiff {α : Type u_1} [TopologicalSpace α] [T2Space α] (s t : CompactOpens α) :
↑(s \ t) = s \ t
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@[simp]
@[simp]
theorem TopologicalSpace.CompactOpens.coe_himp {α : Type u_1} [TopologicalSpace α] [CompactSpace α] [T2Space α] (s t : CompactOpens α) :
↑(s t) = s t
def TopologicalSpace.CompactOpens.map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :

The image of a compact open under a continuous open map.

Equations
@[simp]
theorem TopologicalSpace.CompactOpens.map_toCompacts {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (f : αβ) (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :
(map f hf hf' s).toCompacts = Compacts.map f hf s.toCompacts
@[simp]
theorem TopologicalSpace.CompactOpens.coe_map {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] {f : αβ} (hf : Continuous f) (hf' : IsOpenMap f) (s : CompactOpens α) :
(map f hf hf' s) = f '' s
@[simp]
theorem TopologicalSpace.CompactOpens.map_id {α : Type u_1} [TopologicalSpace α] (K : CompactOpens α) :
map id K = K
theorem TopologicalSpace.CompactOpens.map_comp {α : Type u_1} {β : Type u_2} {γ : Type u_3} [TopologicalSpace α] [TopologicalSpace β] [TopologicalSpace γ] (f : βγ) (g : αβ) (hf : Continuous f) (hg : Continuous g) (hf' : IsOpenMap f) (hg' : IsOpenMap g) (K : CompactOpens α) :
map (f g) K = map f hf hf' (map g hg hg' K)

The product of two TopologicalSpace.CompactOpens, as a TopologicalSpace.CompactOpens in the product space.

Equations
@[simp]
theorem TopologicalSpace.CompactOpens.coe_prod {α : Type u_1} {β : Type u_2} [TopologicalSpace α] [TopologicalSpace β] (K : CompactOpens α) (L : CompactOpens β) :
(K.prod L) = K ×ˢ L