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Mathlib.CategoryTheory.Monoidal.Action.End

Actions as monoidal functors to endofunctor categories #

In this file, we show that given a right action of a monoidal category C on a category D, the curried action functor C ⥤ D ⥤ D is monoidal. Conversely, given a monoidal functor C ⥤ D ⥤ D, we can define a right action of C on D.

The corresponding results are also available for left actions: given a left action of C on D, composing CategoryTheory.MonoidalCategory.MonoidalLeftAction.curriedAction C D with CategoryTheory.MonoidalCategory.MonoidalOpposite.mopFunctor (D ⥤ D) is monoidal, and conversely one can define a left action of C on D from a monoidal functor C ⥤ (D ⥤ D)ᴹᵒᵖ.

When C acts on the left on D, the functor curriedActionMop : C ⥤ (D ⥤ D)ᴹᵒᵖ is monoidal, where D ⥤ D has the composition monoidal structure.

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    A monoidal functor F : C ⥤ (D ⥤ D)ᴹᵒᵖ can be thought of as a left action of C on D.

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        If the (left) action of C on D comes from a monoidal functor C ⥤ (D ⥤ D)ᴹᵒᵖ, then curriedActionMop C D is naturally isomorphic to that functor.

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            When C acts on the right on D, the functor curriedAction : C ⥤ (D ⥤ D) is monoidal, where D ⥤ D has the composition monoidal structure.

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              A monoidal functor F : C ⥤ D ⥤ D can be thought of as a right action of C on D.

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                  If the action of C on D comes from a monoidal functor C ⥤ (D ⥤ D), then curriedActionMop C D is naturally isomorphic to that functor.

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                      Functor evaluation gives a right action of C ⥤ C.

                      Note that in the literature, this is defined as a left action, but mathlib's monoidal structure on C ⥤ C is the monoidal opposite of the one usually considered in the literature.

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