Cartesian monoidal structure on slices induced by chosen pullbacks #
Main declarations #
cartesianMonoidalCategoryOverprovides a cartesian monoidal structure on the slice categoriesOver Xfor all objectsX : C, induced by chosen pullbacks in the base categoryC. This is the computable analogue of the noncomputable instanceCategoryTheory.Over.cartesianMonoidalCategory.For a cartesian monoidal category
C, and for any objectXofC,toOver Xis a functor fromCtoOver Xwhich maps an objectA : Cto the projectionA ⊗ X ⟶ XinOver X. This is the computable analogue of the functorOver.star.
Main results #
cartesianMonoidalCategoryOverproves that the slices of a category with chosen pullbacks are cartesian monoidal.toOverPullbackIsoToOvershows that in a category with chosen pullbacks, for any morphismf : Y ⟶ X, the functorstoOver X ⋙ pullback fandtoOver Yare naturally isomorphic.toOverIteratedSliceForwardIsoPullbackshows that in a category with chosen pullbacks the functorpullback f : Over X ⥤ Over Yis naturally isomorphic totoOver (Over.mk f) : Over X ⥤ Over (Over.mk f)post-composed with the iterated slice equivalenceOver (Over.mk f) ⥤ Over Y. Note that the functortoOver (Over.mk f)exists by the resultcartesianMonoidalCategoryOver.
TODO #
- Show that the functors
pullback fare monoidal with respect to the cartesian monoidal structures on slices.
The binary fan provided by fst' and snd'.
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The binary fan provided by fst' and snd' is a binary product in Over X.
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A computable instance of CartesianMonoidalCategory for Over X when C has
chosen pullbacks. Contrast this with the noncomputable instance provided by
CategoryTheory.Over.cartesianMonoidalCategory.
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The functor which maps an object A in C to the projection A ⊗ X ⟶ X in Over X.
This is the computable analogue of the functor Over.star.
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The functor from C to Over (𝟙_ C) which sends X : C to Over.mk <| toUnit X.
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The slice category over the terminal unit object is equivalent to the original category.
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The isomorphism of functors toOverUnit C ⋙ ChosenPullbacksAlong.pullback (toUnit X) and
toOver X.
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The functor toOver X is the right adjoint to the functor Over.forget X.
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The isomorphism of functors toOver (𝟙_ C) and toOverUnit C.
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A natural isomorphism between the functors toOver Y and toOver X ⋙ pullback f
for any morphism f : X ⟶ Y.
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The functor pullback f : Over X ⥤ Over Y is naturally isomorphic to
toOver : Over X ⥤ Over (Over.mk f) post-composed with the
iterated slice equivalence Over (Over.mk f) ⥤ Over Y.
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