Categories with chosen finite products #
We introduce a class, ChosenFiniteProducts
, which bundles explicit choices
for a terminal object and binary products in a category C
.
This is primarily useful for categories which have finite products with good
definitional properties, such as the category of types.
Given a category with such an instance, we also provide the associated
symmetric monoidal structure so that one can write X ⊗ Y
for the explicit
binary product and 𝟙_ C
for the explicit terminal object.
Projects #
- Construct an instance of chosen finite products in the category of affine scheme, using the tensor product.
- Construct chosen finite products in other categories appearing "in nature".
An instance of ChosenFiniteProducts C
bundles an explicit choice of a binary
product of two objects of C
, and a terminal object in C
.
Users should use the monoidal notation: X ⊗ Y
for the product and 𝟙_ C
for
the terminal object.
- product : (X Y : C) → CategoryTheory.Limits.LimitCone (CategoryTheory.Limits.pair X Y)
A choice of a limit binary fan for any two objects of the category.
- terminal : CategoryTheory.Limits.LimitCone (CategoryTheory.Functor.empty C)
A choice of a terminal object.
Instances
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The unique map to the terminal object.
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- CategoryTheory.ChosenFiniteProducts.instUniqueHomTensorUnit X = { default := CategoryTheory.ChosenFiniteProducts.toUnit X, uniq := ⋯ }
This lemma follows from the preexisting Unique
instance, but
it is often convenient to use it directly as apply toUnit_unique
forcing
lean to do the necessary elaboration.
Construct a morphism to the product given its two components.
Equations
- CategoryTheory.ChosenFiniteProducts.lift f g = (CategoryTheory.ChosenFiniteProducts.product X Y).isLimit.lift (CategoryTheory.Limits.BinaryFan.mk f g)
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The first projection from the product.
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The second projection from the product.
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- ⋯ = ⋯
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- ⋯ = ⋯
Construct an instance of ChosenFiniteProducts C
given an instance of HasFiniteProducts C
.
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Instances For
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- ⋯ = ⋯
When C
and D
have chosen finite products and F : C ⥤ D
is any functor,
terminalComparison F
is the unique map F (𝟙_ C) ⟶ 𝟙_ D
.
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If terminalComparison F
is an Iso, then F
preserves terminal objects.
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If F
preserves terminal objects, then terminalComparison F
is an isomorphism.
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- ⋯ = ⋯
When C
and D
have chosen finite products and F : C ⥤ D
is any functor,
prodComparison F A B
is the canonical comparison morphism from F (A ⊗ B)
to F(A) ⊗ F(B)
.
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Naturality of the prodComparison
morphism in both arguments.
Naturality of the prodComparison
morphism in the right argument.
Naturality of the prodComparison
morphism in the left argument.
If the product comparison morphism is an iso, its inverse is natural in both argument.
If the product comparison morphism is an iso, its inverse is natural in the right argument.
If the product comparison morphism is an iso, its inverse is natural in the left argument.
The product comparison morphism from F(A ⊗ -)
to FA ⊗ F-
, whose components are given by
prodComparison
.
Equations
- CategoryTheory.ChosenFiniteProducts.prodComparisonNatTrans F A = { app := fun (B : C) => CategoryTheory.ChosenFiniteProducts.prodComparison F A B, naturality := ⋯ }
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The product comparison morphism from F(- ⊗ -)
to F- ⊗ F-
, whose components are given by
prodComparison
.
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- CategoryTheory.ChosenFiniteProducts.prodComparisonBifunctorNatTrans F = { app := fun (A : C) => CategoryTheory.ChosenFiniteProducts.prodComparisonNatTrans F A, naturality := ⋯ }
Instances For
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- ⋯ = ⋯
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- ⋯ = ⋯
If F
preserves the limit of the pair (A, B)
, then the binary fan given by
(F.map fst A B, F.map (snd A B))
is a limit cone.
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If F
preserves the limit of the pair (A, B)
, then prodComparison F A B
is an isomorphism.
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- ⋯ = ⋯
The natural isomorphism F(A ⊗ -) ≅ FA ⊗ F-
, provided each prodComparison F A B
is an
isomorphism (as B
changes).
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The natural isomorphism of bifunctors F(- ⊗ -) ≅ F- ⊗ F-
, provided each
prodComparison F A B
is an isomorphism.
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If prodComparison F A B
is an isomorphism, then F
preserves the limit of pair A B
.
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If prodComparison F A B
is an isomorphism for all A B
then F
preserves limits of shape
Discrete (WalkingPair)
.
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Any functor between categories with chosen finite products induces an oplax monoial functor.
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- ⋯ = ⋯
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- ⋯ = ⋯
If F
preserves finite products, the oplax monoidal functor
F.toOplaxMonoidalFunctorOfChosenFiniteProducts
can be promoted to a strong monoidal functor.
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- F.toMonoidalFunctorOfChosenFiniteProducts = CategoryTheory.MonoidalFunctor.fromOplaxMonoidalFunctor F.toOplaxMonoidalFunctorOfChosenFiniteProducts
Instances For
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- ⋯ = inst