Day convolution is closed #
Let C be a monoidal category and V a monoidal closed category in which every functor
Cᵒᵖ ⥤ C ⥤ V has an end. Then the Day convolution monoidal structure on C ⊛⥤ V is closed: the
internal hom [F, G] is the functor
c ↦ ∫_j [F j, G (j ⊗ c)].
Mathlib's DayConvolutionInternalHom F G H records that H is such an end, and constructs from it
the evaluation F ⊛ H ⟶ G, the coevaluation G ⟶ [F, F ⊛ G] and their triangle identities. We
choose the ends functorially through endFunctor, so that [F, -] is a functor, check that it
satisfies DayConvolutionInternalHom, and assemble the evaluation and coevaluation into an
adjunction tensorLeft F ⊣ [F, -]. This turns the construction of Mathlib's
CategoryTheory.MonoidalCategory.DayConvolution.Closed into an actual MonoidalClosed instance on
C ⊛⥤ V.
Main definitions #
DayFunctor.internalHom F: the internal hom functor[F, -]for Day convolution.DayFunctor.dayConvolutionInternalHom F G:[F, G]is an internal hom ofFandGin the sense ofDayConvolutionInternalHom.DayFunctor.internalHomAdjunction F: the adjunctiontensorLeft F ⊣ [F, -].DayFunctor.monoidalClosed: theMonoidalClosedinstance onC ⊛⥤ V.
Main statements #
DayFunctor.η_app_comp_ev_natTrans_app: the evaluationF ⊗ [F, G] ⟶ G, restricted along the Day convolution unit, is the uncurried end projection.DayFunctor.coev_natTrans_app_comp_π: the coevaluationG ⟶ [F, F ⊗ G], followed by an end projection, is the curried Day convolution unit.
References #
- B. Day, On closed categories of functors, Reports of the Midwest Category Seminar IV, Lecture Notes in Math. 137 (1970), 1–38.
The internal hom functor [F, -] for the Day convolution product: the functor G ↦ [F, G]
with [F, G].obj c = ∫_j [F j, G (j ⊗ c)].
Instances For
The value of [F, G] at c is the end ∫_j [F j, G (j ⊗ c)].
The projection [F, G].obj c ⟶ [F j, G (j ⊗ c)] from the end.
Instances For
Morphisms into [F, G].obj c are determined by their composites with the projections.
The projections out of [F, G].obj c form a wedge.
The projections out of [F, G].obj c form a wedge.
The functoriality of [F, G] in the variable c, along the projections.
The functoriality of [F, G] in the variable c, along the projections.
The functoriality of [F, -], along the projections.
The functoriality of [F, -], along the projections.
[F, G] is an internal hom of F and G for Day convolution in the sense of Mathlib's
DayConvolutionInternalHom: its values are ends, with the projections π.
Instances For
The projections of dayConvolutionInternalHom F G are the end projections π.
The morphism of internal homs that Mathlib's DayConvolutionInternalHom.map induces from a
morphism g : G ⟶ G' is the image of g under the functor [F, -].
The evaluation F ⊗ [F, G] ⟶ G of the Day convolution internal hom.
Instances For
The coevaluation G ⟶ [F, F ⊗ G] of the Day convolution internal hom.
Instances For
The evaluation F ⊗ [F, G] ⟶ G, restricted along the Day convolution unit, is the uncurried
projection from the end.
The evaluation F ⊗ [F, G] ⟶ G, restricted along the Day convolution unit, is the uncurried
projection from the end.
The coevaluation G ⟶ [F, F ⊗ G], followed by a projection from the end, is the curried
Day convolution unit.
The coevaluation G ⟶ [F, F ⊗ G], followed by a projection from the end, is the curried
Day convolution unit.
The coevaluation G ⟶ [F, F ⊗ G] is natural in G.
The coevaluation G ⟶ [F, F ⊗ G] is natural in G.
The evaluation F ⊗ [F, G] ⟶ G is natural in G.
The evaluation F ⊗ [F, G] ⟶ G is natural in G.
The first triangle identity: F ⊗ G ⟶ F ⊗ [F, F ⊗ G] ⟶ F ⊗ G is the identity.
The first triangle identity: F ⊗ G ⟶ F ⊗ [F, F ⊗ G] ⟶ F ⊗ G is the identity.
The second triangle identity: [F, G] ⟶ [F, F ⊗ [F, G]] ⟶ [F, G] is the identity.
The second triangle identity: [F, G] ⟶ [F, F ⊗ [F, G]] ⟶ [F, G] is the identity.
The Day convolution product with F is left adjoint to the internal hom functor [F, -].
Instances For
Day convolution with values in a monoidal closed category with ends is monoidal closed, with
internal hom [F, G].obj c = ∫_j [F j, G (j ⊗ c)].
The internal hom of C ⊛⥤ V is internalHom.
The evaluation of the monoidal closed structure on C ⊛⥤ V is ev.
The coevaluation of the monoidal closed structure on C ⊛⥤ V is coev.
The curried morphism G ⟶ [F, H] of f : F ⊗ G ⟶ H, followed by a projection from the end,
is the curried restriction of f along the Day convolution unit.
The curried morphism G ⟶ [F, H] of f : F ⊗ G ⟶ H, followed by a projection from the end,
is the curried restriction of f along the Day convolution unit.
The uncurried morphism F ⊗ G ⟶ H of g : G ⟶ [F, H], restricted along the Day convolution
unit, is the uncurried composite of g with a projection from the end.
The uncurried morphism F ⊗ G ⟶ H of g : G ⟶ [F, H], restricted along the Day convolution
unit, is the uncurried composite of g with a projection from the end.