Light profinite spaces #
We construct the category LightProfinite of light profinite topological spaces. These are
implemented as totally disconnected second countable compact Hausdorff spaces.
This file also defines the category LightDiagram, which consists of those spaces that can be
written as a sequential limit (in Profinite) of finite sets.
We define an equivalence of categories LightProfinite ≌ LightDiagram and prove that these are
essentially small categories.
LightProfinite is the category of second countable profinite spaces.
- toCompHaus : CompHaus
The underlying compact Hausdorff space of a light profinite space.
- isTotallyDisconnected : TotallyDisconnectedSpace ↑self.toCompHaus.toTop
A light profinite space is totally disconnected
- secondCountable : SecondCountableTopology ↑self.toCompHaus.toTop
A light profinite space is second countable
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A light profinite space is totally disconnected
A light profinite space is second countable
Construct a term of LightProfinite from a type endowed with the structure of a compact,
Hausdorff, totally disconnected and second countable topological space.
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- LightProfinite.of X = LightProfinite.mk (CompHaus.mk { α := X, str := inferInstance })
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- LightProfinite.instInhabited = { default := LightProfinite.of PEmpty.{u_1 + 1} }
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- LightProfinite.hasForget₂ = CategoryTheory.InducedCategory.hasForget₂ fun (X : CategoryTheory.InducedCategory CompHaus LightProfinite.toCompHaus) => X.toCompHaus.toTop
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- LightProfinite.instCoeSortType = { coe := fun (X : LightProfinite) => ↑X.toCompHaus.toTop }
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- ⋯ = ⋯
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- ⋯ = ⋯
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- LightProfinite.instTopologicalSpaceObjForget = let_fun this := inferInstance; this
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
The fully faithful embedding of LightProfinite in Profinite.
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lightToProfinite is fully faithful.
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- lightToProfiniteFullyFaithful = CategoryTheory.fullyFaithfulInducedFunctor fun (X : LightProfinite) => Profinite.of ↑X.toCompHaus.toTop
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The fully faithful embedding of LightProfinite in CompHaus.
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- ⋯ = ⋯
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- ⋯ = ⋯
The fully faithful embedding of LightProfinite in TopCat.
This is definitionally the same as the obvious composite.
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LightProfinite.toTopCat is fully faithful.
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- LightProfinite.toTopCatFullyFaithful = CategoryTheory.fullyFaithfulInducedFunctor fun (X : CategoryTheory.InducedCategory CompHaus LightProfinite.toCompHaus) => X.toCompHaus.toTop
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The natural functor from Fintype to LightProfinite, endowing a finite type with the
discrete topology.
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FintypeCat.toLightProfinite is fully faithful.
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- ⋯ = ⋯
An explicit limit cone for a functor F : J ⥤ LightProfinite, for a countable category J
defined in terms of CompHaus.limitCone, which is defined in terms of TopCat.limitCone.
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The limit cone LightProfinite.limitCone F is indeed a limit cone.
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Any morphism of light profinite spaces is a closed map.
Any continuous bijection of light profinite spaces induces an isomorphism.
Any continuous bijection of light profinite spaces induces an isomorphism.
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Construct an isomorphism from a homeomorphism.
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- LightProfinite.isoOfHomeo f = lightProfiniteToCompHausFullyFaithful.preimageIso (CompHaus.isoOfHomeo f)
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Construct a homeomorphism from an isomorphism.
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The equivalence between isomorphisms in LightProfinite and homeomorphisms
of topological spaces.
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- LightProfinite.isoEquivHomeo = { toFun := LightProfinite.homeoOfIso, invFun := LightProfinite.isoOfHomeo, left_inv := ⋯, right_inv := ⋯ }
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- ⋯ = ⋯
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- ⋯ = ⋯
A structure containing the data of sequential limit in Profinite of finite sets.
- diagram : CategoryTheory.Functor ℕᵒᵖ FintypeCat
The indexing diagram.
- cone : CategoryTheory.Limits.Cone (self.diagram.comp FintypeCat.toProfinite)
The limit cone.
- isLimit : CategoryTheory.Limits.IsLimit self.cone
The limit cone is limiting.
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The fully faithful embedding LightDiagram ⥤ Profinite
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- instTopologicalSpaceObjLightDiagramForget = inferInstance
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
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- ⋯ = ⋯
A profinite space which is light gives rise to a light profinite space.
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The functor part of the equivalence LightProfinite ≌ LightDiagram
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- ⋯ = ⋯
The inverse part of the equivalence LightProfinite ≌ LightDiagram
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The equivalence of categories LightProfinite ≌ LightDiagram
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This is an auxiliary definition used to show that LightDiagram is essentially small.
Note that below we put a category instance on this structure which is completely different from the
category instance on ℕᵒᵖ ⥤ FintypeCat.Skeleton.{u}. Neither the morphisms nor the objects are the
same.
- diagram : CategoryTheory.Functor ℕᵒᵖ FintypeCat.Skeleton
The diagram takes values in a small category equivalent to
FintypeCat.
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A LightDiagram' yields a Profinite.
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- S.toProfinite = CategoryTheory.Limits.limit (S.diagram.comp (FintypeCat.Skeleton.equivalence.functor.comp FintypeCat.toProfinite))
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The functor part of the equivalence of categories LightDiagram' ≌ LightDiagram.
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The equivalence beween LightDiagram and a small category.
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- LightDiagram.equivSmall = LightDiagram'.toLightFunctor.asEquivalence.symm