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Mathlib.CategoryTheory.Monoidal.Internal.FunctorCategory

Mon_ (C ⥤ D) ≌ C ⥤ Mon_ D #

When D is a monoidal category, monoid objects in C ⥤ D are the same thing as functors from C into the monoid objects of D.

This is formalised as:

The intended application is that as Ring ≌ Mon_ Ab (not yet constructed!), we have presheaf Ring X ≌ presheaf (Mon_ Ab) X ≌ Mon_ (presheaf Ab X), and we can model a module over a presheaf of rings as a module object in presheaf Ab X.

Future work #

Presumably this statement is not specific to monoids, and could be generalised to any internal algebraic objects, if the appropriate framework was available.

A monoid object in a functor category induces a functor to the category of monoid objects.

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    Functor translating a monoid object in a functor category to a functor into the category of monoid objects.

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      A functor to the category of monoid objects can be translated as a monoid object in the functor category.

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        Functor translating a functor into the category of monoid objects to a monoid object in the functor category

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          @[simp]

          The unit for the equivalence Mon_ (C ⥤ D) ≌ C ⥤ Mon_ D.

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            The counit for the equivalence Mon_ (C ⥤ D) ≌ C ⥤ Mon_ D.

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              When D is a monoidal category, monoid objects in C ⥤ D are the same thing as functors from C into the monoid objects of D.

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                A comonoid object in a functor category induces a functor to the category of comonoid objects.

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                  Functor translating a comonoid object in a functor category to a functor into the category of comonoid objects.

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                    A functor to the category of comonoid objects can be translated as a comonoid object in the functor category.

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                      The counit for the equivalence Mon_ (C ⥤ D) ≌ C ⥤ Mon_ D.

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                        When D is a monoidal category, comonoid objects in C ⥤ D are the same thing as functors from C into the comonoid objects of D.

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                          Functor translating a commutative monoid object in a functor category to a functor into the category of commutative monoid objects.

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                            Functor translating a functor into the category of commutative monoid objects to a commutative monoid object in the functor category

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                              The unit for the equivalence CommMon_ (C ⥤ D) ≌ C ⥤ CommMon_ D.

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                                The counit for the equivalence CommMon_ (C ⥤ D) ≌ C ⥤ CommMon_ D.

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                                  When D is a braided monoidal category, commutative monoid objects in C ⥤ D are the same thing as functors from C into the commutative monoid objects of D.

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