Subcategories of comma categories defined by morphism properties #
Given functors L : A β₯€ T and R : B β₯€ T and morphism properties P, Q and W
on T, A and B respectively, we define the subcategory P.Comma L R Q W of
Comma L R where
- objects are objects of
Comma L Rwith the structural morphism satisfyingP, and - morphisms are morphisms of
Comma L Rwhere the left morphism satisfiesQand the right morphism satisfiesW.
For an object X : T, this specializes to P.Over Q X which is the subcategory of Over X
where the structural morphism satisfies P and where the horizontal morphisms satisfy Q.
Common examples of the latter are e.g. the category of schemes Γ©tale (finite, affine, etc.)
over a base X. Here Q = β€.
Implementation details #
The object property on Comma L R induced by a morphism property.
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The object property on CostructuredArrow L X induced by a morphism property.
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The object property on StructuredArrow X R induced by a morphism property.
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The morphism property on Over X induced by a morphism property on C.
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The morphism property on Under X induced by a morphism property on C.
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The object property on Over X induced by a morphism property.
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The object property on Under X induced by a morphism property.
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P.Comma L R Q W is the subcategory of Comma L R consisting of
objects X : Comma L R where X.hom satisfies P. The morphisms are given by
morphisms in Comma L R where the left one satisfies Q and the right one satisfies W.
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A morphism in P.Comma L R Q W is a morphism in Comma L R where the left
hom satisfies Q and the right one satisfies W.
- w : CategoryStruct.comp (L.map self.left) Y.hom = CategoryStruct.comp X.hom (R.map self.right)
- prop_hom_left : Q self.left
- prop_hom_right : W self.right
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The underlying morphism of objects in Comma L R.
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See Note [custom simps projection]
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The identity morphism of an object in P.Comma L R Q W.
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Composition of morphisms in P.Comma L R Q W.
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If i is an isomorphism in Comma L R, it is also a morphism in P.Comma L R Q W.
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Any isomorphism between objects of P.Comma L R Q W in Comma L R is also an isomorphism
in P.Comma L R Q W.
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Constructor for isomorphisms in P.Comma L R Q W from isomorphisms of the left and right
components and naturality in the forward direction.
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The forgetful functor.
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The forgetful functor from the full subcategory of Comma L R defined by P is
fully faithful.
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Weaken the conditions on all components.
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Weakening the condition on the structure morphisms is fully faithful.
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Lift a functor F : C β₯€ Comma L R to the subcategory P.Comma L R Q W under
suitable assumptions on F.
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A natural transformation Lβ βΆ Lβ induces a functor P.Comma Lβ R Q W β₯€ P.Comma Lβ R Q W.
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The functor P.Comma L R Q W β₯€ P.Comma L R Q W induced by the identity natural transformation
on L is naturally isomorphic to the identity functor.
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The functor P.Comma Lβ R Q W β₯€ P.Comma Lβ R Q W induced by the composition of two natural
transformations l : Lβ βΆ Lβ and l' : Lβ βΆ Lβ is naturally isomorphic to the composition of the
two functors induced by these natural transformations.
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Two equal natural transformations Lβ βΆ Lβ yield naturally isomorphic functors
P.Comma Lβ R Q W β₯€ P.Comma Lβ R Q W.
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A natural isomorphism Lβ β
Lβ induces an equivalence of categories
P.Comma Lβ R Q W β P.Comma Lβ R Q W.
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A natural transformation Rβ βΆ Rβ induces a functor P.Comma L Rβ Q W β₯€ P.Comma L Rβ Q W.
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The functor P.Comma L R Q W β₯€ P.Comma L R Q W induced by the identity natural transformation
on R is naturally isomorphic to the identity functor.
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The functor P.Comma L Rβ Q W β₯€ P.Comma L Rβ Q W induced by the composition of the natural
transformations r : Rβ βΆ Rβ and r' : Rβ βΆ Rβ is naturally isomorphic to the composition of the
functors induced by these natural transformations.
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Two equal natural transformations Rβ βΆ Rβ yield naturally isomorphic functors
P.Comma L Rβ Q W β₯€ P.Comma L Rβ Q W.
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A natural isomorphism Rβ β
Rβ induces an equivalence of categories
P.Comma L Rβ Q W β P.Comma L Rβ Q W.
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Given a morphism property P on a category C and an object X : C, this is the
subcategory of Over X defined by P where morphisms satisfy Q.
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The forgetful functor from the full subcategory of Over X defined by P to Over X.
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Occasionally useful for rewriting in the backwards direction.
Construct a morphism in P.Over Q X from a morphism in Over.X.
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Make an object of P.Over Q X from a morphism f : A βΆ X and a proof of P f.
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Make a morphism in P.Over Q X from a morphism in T with compatibilities.
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Make an isomorphism in P.Over Q X from an isomorphism in T with compatibilities.
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The natural inclusion induced by implications of morphism properties.
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Given a morphism property P on a category C and an object X : C, this is the
subcategory of Under X defined by P where morphisms satisfy Q.
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The forgetful functor from the full subcategory of Under X defined by P to Under X.
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Occasionally useful for rewriting in the backwards direction.
Construct a morphism in P.Under Q X from a morphism in Under.X.
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Make an object of P.Under Q X from a morphism f : A βΆ X and a proof of P f.
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Make a morphism in P.Under Q X from a morphism in T with compatibilities.
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Make an isomorphism in P.Under Q X from an isomorphism in T with compatibilities.
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Given a morphism property P on a category C and an object X : C, this is the
subcategory of CostructuredArrow F X defined by P where morphisms satisfy Q.
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Construct an object of P.CostructuredArrow Q F X from a morphism F.obj A βΆ X.
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Construct a morphism in P.CostructuredArrow Q F X by giving a morphism on the underlying
objects of C.
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The forgetful functor from the subcategory P.CostructuredArrow Q F X.
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Reinterpreting an F-costructured arrow F.obj A βΆ X as an arrow over X.