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Mathlib.CategoryTheory.ChosenFiniteProducts

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 #

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.

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    The unique map to the terminal object.

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      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.

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        Construct an instance of ChosenFiniteProducts C given an instance of HasFiniteProducts C.

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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 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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                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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                    Any functor between categories with chosen finite products induces an oplax monoial functor.

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