The category of open sets in a topological space. #
We define toTopCat : Opens X ⥤ TopCat
and
map (f : X ⟶ Y) : Opens Y ⥤ Opens X
, given by taking preimages of open sets.
Unfortunately Opens
isn't (usefully) a functor TopCat ⥤ Cat
.
(One can in fact define such a functor,
but using it results in unresolvable Eq.rec
terms in goals.)
Really it's a 2-functor from (spaces, continuous functions, equalities)
to (categories, functors, natural isomorphisms).
We don't attempt to set up the full theory here, but do provide the natural isomorphisms
mapId : map (𝟙 X) ≅ 𝟭 (Opens X)
and
mapComp : map (f ≫ g) ≅ map g ⋙ map f
.
Beyond that, there's a collection of simp lemmas for working with these constructions.
Since Opens X
has a partial order, it automatically receives a Category
instance.
Unfortunately, because we do not allow morphisms in Prop
,
the morphisms U ⟶ V
are not just proofs U ≤ V
, but rather
ULift (PLift (U ≤ V))
.
We now construct as morphisms various inclusions of open sets.
The inclusion U ⊓ V ⟶ U
as a morphism in the category of open sets.
Equations
- U.infLELeft V = ⋯.hom
Instances For
The inclusion U ⊓ V ⟶ V
as a morphism in the category of open sets.
Equations
- U.infLERight V = ⋯.hom
Instances For
The inclusion U i ⟶ iSup U
as a morphism in the category of open sets.
Equations
- TopologicalSpace.Opens.leSupr U i = ⋯.hom
Instances For
The inclusion ⊥ ⟶ U
as a morphism in the category of open sets.
Equations
- U.botLE = ⋯.hom
Instances For
The inclusion U ⟶ ⊤
as a morphism in the category of open sets.
Equations
- U.leTop = ⋯.hom
Instances For
The functor from open sets in X
to TopCat
,
realising each open set as a topological space itself.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The inclusion map from an open subset to the whole space, as a morphism in TopCat
.
Equations
- U.inclusion' = { toFun := Subtype.val, continuous_toFun := ⋯ }
Instances For
Alias of TopologicalSpace.Opens.isOpenEmbedding
.
The inclusion of the top open subset (i.e. the whole space) is an isomorphism.
Equations
- TopologicalSpace.Opens.inclusionTopIso X = { hom := ⊤.inclusion', inv := { toFun := fun (x : ↑X) => ⟨x, trivial⟩, continuous_toFun := ⋯ }, hom_inv_id := ⋯, inv_hom_id := ⋯ }
Instances For
Opens.map f
gives the functor from open sets in Y to open set in X,
given by taking preimages under f.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The inclusion U ⟶ (map f).obj ⊤
as a morphism in the category of open sets.
Equations
- TopologicalSpace.Opens.leMapTop f U = U.leTop
Instances For
The functor Opens X ⥤ Opens X
given by taking preimages under the identity function
is naturally isomorphic to the identity functor.
Equations
- One or more equations did not get rendered due to their size.
Instances For
The natural isomorphism between taking preimages under f ≫ g
, and the composite
of taking preimages under g
, then preimages under f
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
If two continuous maps f g : X ⟶ Y
are equal,
then the functors Opens Y ⥤ Opens X
they induce are isomorphic.
Equations
- TopologicalSpace.Opens.mapIso f g h = CategoryTheory.NatIso.ofComponents (fun (U : TopologicalSpace.Opens ↑Y) => CategoryTheory.eqToIso ⋯) ⋯
Instances For
A homeomorphism of spaces gives an equivalence of categories of open sets.
TODO: define OrderIso.equivalence
, use it.
Equations
- One or more equations did not get rendered due to their size.
Instances For
An open map f : X ⟶ Y
induces a functor Opens X ⥤ Opens Y
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
An open map f : X ⟶ Y
induces an adjunction between Opens X
and Opens Y
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
Given an inducing map X ⟶ Y
and some U : Opens X
, this is the union of all open sets
whose preimage is U
. This is right adjoint to Opens.map
.
Equations
- x.functorObj U = sSup {s : TopologicalSpace.Opens ↑Y | (TopologicalSpace.Opens.map f).obj s = U}
Instances For
An inducing map f : X ⟶ Y
induces a Galois insertion between Opens Y
and Opens X
.
Equations
- One or more equations did not get rendered due to their size.
Instances For
An inducing map f : X ⟶ Y
induces a functor Opens X ⥤ Opens Y
.
Equations
- hf.functor = { obj := hf.functorObj, map := fun {U V : TopologicalSpace.Opens ↑X} (h : U ⟶ V) => CategoryTheory.homOfLE ⋯, map_id := ⋯, map_comp := ⋯ }
Instances For
An inducing map f : X ⟶ Y
induces an adjunction between Opens Y
and Opens X
.
Equations
- hf.adjunction = ⋯.adjunction