Gluing data #
We define GlueData as a family of data needed to glue topological spaces, schemes, etc. We
provide the API to realize it as a multispan diagram, and also state lemmas about its
interaction with a functor that preserves certain pullbacks.
A gluing datum consists of
- An index type
J - An object
U ifor eachi : J. - An object
V i jfor eachi j : J. - A monomorphism
f i j : V i j ⟶ U ifor eachi j : J. - A transition map
t i j : V i j ⟶ V j ifor eachi j : J. such that f i iis an isomorphism.t i iis the identity.- The pullback for
f i jandf i kexists. V i j ×[U i] V i k ⟶ V i j ⟶ V j ifactors throughV j k ×[U j] V j i ⟶ V j ivia somet' : V i j ×[U i] V i k ⟶ V j k ×[U j] V j i.t' i j k ≫ t' j k i ≫ t' k i j = 𝟙 _.
- J : Type v
- U : self.J → C
- V : self.J × self.J → C
- f : (i j : self.J) → self.V (i, j) ⟶ self.U i
- f_mono : ∀ (i j : self.J), CategoryTheory.Mono (self.f i j)
- f_hasPullback : ∀ (i j k : self.J), CategoryTheory.Limits.HasPullback (self.f i j) (self.f i k)
- f_id : ∀ (i : self.J), CategoryTheory.IsIso (self.f i i)
- t : (i j : self.J) → self.V (i, j) ⟶ self.V (j, i)
- t_id : ∀ (i : self.J), self.t i i = CategoryTheory.CategoryStruct.id (self.V (i, i))
- t' : (i j k : self.J) → CategoryTheory.Limits.pullback (self.f i j) (self.f i k) ⟶ CategoryTheory.Limits.pullback (self.f j k) (self.f j i)
- t_fac : ∀ (i j k : self.J), CategoryTheory.CategoryStruct.comp (self.t' i j k) CategoryTheory.Limits.pullback.snd = CategoryTheory.CategoryStruct.comp CategoryTheory.Limits.pullback.fst (self.t i j)
- cocycle : ∀ (i j k : self.J), CategoryTheory.CategoryStruct.comp (self.t' i j k) (CategoryTheory.CategoryStruct.comp (self.t' j k i) (self.t' k i j)) = CategoryTheory.CategoryStruct.id (CategoryTheory.Limits.pullback (self.f i j) (self.f i k))
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- ⋯ = ⋯
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- ⋯ = ⋯
(Implementation) The disjoint union of U i.
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(Implementation) The diagram to take colimit of.
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The glued object given a family of gluing data.
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The map D.U i ⟶ D.glued for each i.
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The pullback cone spanned by V i j ⟶ U i and V i j ⟶ U j.
This will often be a pullback diagram.
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- CategoryTheory.GlueData.vPullbackCone D i j = CategoryTheory.Limits.PullbackCone.mk (D.f i j) (CategoryTheory.CategoryStruct.comp (D.t i j) (D.f j i)) ⋯
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The projection ∐ D.U ⟶ D.glued given by the colimit.
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- ⋯ = ⋯
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- ⋯ = ⋯
A functor that preserves the pullbacks of f i j and f i k can map a family of glue data.
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The diagram of the image of a GlueData under a functor F is naturally isomorphic to the
original diagram of the GlueData via F.
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If F preserves the gluing, we obtain an iso between the glued objects.
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If F preserves the gluing, and reflects the pullback of U i ⟶ glued and U j ⟶ glued,
then F reflects the fact that V_pullback_cone is a pullback.
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If there is a forgetful functor into Type that preserves enough (co)limits, then D.ι will
be jointly surjective.