The core of a category #
The core of a category C is the (non-full) subcategory of C consisting of all objects,
and all isomorphisms. We construct it as a CategoryTheory.Groupoid.
CategoryTheory.Core.inclusion : Core C β₯€ C gives the faithful inclusion into the original
category.
Any functor F from a groupoid G into C factors through CategoryTheory.Core C,
but this is not functorial with respect to F.
The core of a category C is the groupoid whose morphisms are all the isomorphisms of C.
- of : C
The object of the base category underlying an object in
Core C.
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The hom-type between two objects of Core C.
It is defined as a one-field structure to prevent defeq abuses.
The isomorphism of objects of
Cunderlying a morphism inCore C.
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The core of a category is naturally included in the category.
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Construct an isomorphism in Core C from an isomorphism in C.
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A functor from a groupoid to a category C factors through the core of C.
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We can functorially associate to any functor from a groupoid to the core of a category C,
a functor from the groupoid to C, simply by composing with the embedding Core C β₯€ C.
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A functor C β₯€ D induces a functor Core C β₯€ Core D.
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The core of the identity functor is the identity functor on the cores.
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The core of the composition of F and G is the composition of the cores.
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The natural isomorphism
F.core
Core C β₯€ Core D
inclusion C β β inclusion D
V V
C β₯€ D
F
thought of as pseudonaturality of inclusion,
when viewing Core as a pseudofunctor.
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A natural isomorphism of functors induces a natural isomorphism between their cores.
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The functor functorToCore (F β H) factors through functorToCore H.
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The functor functorToCore (H β F) factors through functorToCore H.
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The functor functorToCore (π G) is a section of inclusion G.
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The functor functorToCore (inclusion C) is isomorphic to the identity on Core C.
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Equivalent categories have equivalent cores.
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Taking the core of a functor is functorial if we discard non-invertible natural transformations.
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ofEquivFunctor m lifts a type-level EquivFunctor
to a categorical functor Core (Type uβ) β₯€ Core (Type uβ).