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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 sends any object to a monoid object.

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      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]
                      theorem CategoryTheory.Monoidal.MonFunctorCategoryEquivalence.inverse_map_hom_app {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] [MonoidalCategory D] {X✝ Y✝ : Functor C (Mon D)} (α : X✝ Y✝) (X : C) :
                      (inverse.map α).hom.app X = (α.app X).hom

                      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 sends any object to a comonoid object.

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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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                                                  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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