Equivalences of sheaf categories #
Given a site (C, J)
and a category D
which is equivalent to C
, with C
and D
possibly large
and possibly in different universes, we transport the Grothendieck topology J
on C
to D
and
prove that the sheaf categories are equivalent.
We also prove that sheafification and the property HasSheafCompose
transport nicely over this
equivalence, and apply it to essentially small sites. We also provide instances for existence of
sufficiently small limits in the sheaf category on the essentially small site.
Main definitions #
CategoryTheory.Equivalence.sheafCongr
is the equivalence of sheaf categories.CategoryTheory.Equivalence.transportAndSheafify
is the functor which takes a presheaf onC
, transports it over the equivalence toD
, sheafifies there and then transports back toC
.CategoryTheory.Equivalence.transportSheafificationAdjunction
:transportAndSheafify
is left adjoint to the functor taking a sheaf to its underlying presheaf.CategoryTheory.smallSheafify
is the functor which takes a presheaf on an essentially small site(C, J)
, transports to a small model, sheafifies there and then transports back toC
.CategoryTheory.smallSheafificationAdjunction
:smallSheafify
is left adjoint to the functor taking a sheaf to its underlying presheaf.
The functor in the equivalence of sheaf categories.
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The inverse in the equivalence of sheaf categories.
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The unit iso in the equivalence of sheaf categories.
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The counit iso in the equivalence of sheaf categories.
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The equivalence of sheaf categories.
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Transport a presheaf to the equivalent category and sheafify there.
Equations
- CategoryTheory.Equivalence.transportAndSheafify J K e A = e.op.congrLeft.functor.comp ((CategoryTheory.presheafToSheaf K A).comp (CategoryTheory.Equivalence.sheafCongr J K e A).inverse)
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An auxiliary definition for the sheafification adjunction.
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Transporting and sheafifying is left adjoint to taking the underlying presheaf.
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Transport HasSheafify
along an equivalence of sites.
Transport to a small model and sheafify there.
Equations
- CategoryTheory.smallSheafify J A = CategoryTheory.Equivalence.transportAndSheafify J ((CategoryTheory.equivSmallModel C).inverse.inducedTopology J) (CategoryTheory.equivSmallModel C) A
Instances For
Transporting to a small model and sheafifying there is left adjoint to the underlying presheaf functor
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