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Mathlib.CategoryTheory.Monoidal.Functor

(Lax) monoidal functors #

A lax monoidal functor F between monoidal categories C and D is a functor between the underlying categories equipped with morphisms

Similarly, we define the typeclass F.OplaxMonoidal. For these oplax monoidal functors, we have similar data η and δ, but with morphisms in the opposite direction.

A monoidal functor (F.Monoidal) is defined here as the combination of F.LaxMonoidal and F.OplaxMonoidal, with the additional conditions that ε/η and μ/δ are inverse isomorphisms.

We show that the composition of (lax) monoidal functors gives a (lax) monoidal functor.

See CategoryTheory.Monoidal.NaturalTransformation for monoidal natural transformations.

We show in CategoryTheory.Monoidal.Mon_ that lax monoidal functors take monoid objects to monoid objects.

References #

See https://stacks.math.columbia.edu/tag/0FFL.

A functor F : C ⥤ D between monoidal categories is lax monoidal if it is equipped with morphisms ε : 𝟙 _D ⟶ F.obj (𝟙_ C) and μ X Y : F.obj X ⊗ F.obj Y ⟶ F.obj (X ⊗ Y), satisfying the appropriate coherences.

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    the unit morphism of a lax monoidal functor

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    def CategoryTheory.Functor.LaxMonoidal.ofTensorHom {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] {F : CategoryTheory.Functor C D} (ε' : 𝟙_ D F.obj (𝟙_ C)) (μ' : (X Y : C) → CategoryTheory.MonoidalCategory.tensorObj (F.obj X) (F.obj Y) F.obj (CategoryTheory.MonoidalCategory.tensorObj X Y)) (μ'_natural : ∀ {X Y X' Y' : C} (f : X Y) (g : X' Y'), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (F.map f) (F.map g)) (μ' Y Y') = CategoryTheory.CategoryStruct.comp (μ' X X') (F.map (CategoryTheory.MonoidalCategory.tensorHom f g)) := by aesop_cat) (associativity' : ∀ (X Y Z : C), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (μ' X Y) (CategoryTheory.CategoryStruct.id (F.obj Z))) (CategoryTheory.CategoryStruct.comp (μ' (CategoryTheory.MonoidalCategory.tensorObj X Y) Z) (F.map (CategoryTheory.MonoidalCategory.associator X Y Z).hom)) = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.associator (F.obj X) (F.obj Y) (F.obj Z)).hom (CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) (μ' Y Z)) (μ' X (CategoryTheory.MonoidalCategory.tensorObj Y Z))) := by aesop_cat) (left_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.leftUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom ε' (CategoryTheory.CategoryStruct.id (F.obj X))) (CategoryTheory.CategoryStruct.comp (μ' (𝟙_ C) X) (F.map (CategoryTheory.MonoidalCategory.leftUnitor X).hom)) := by aesop_cat) (right_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.rightUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) ε') (CategoryTheory.CategoryStruct.comp (μ' X (𝟙_ C)) (F.map (CategoryTheory.MonoidalCategory.rightUnitor X).hom)) := by aesop_cat) :
    F.LaxMonoidal

    A constructor for lax monoidal functors whose axioms are described by tensorHom instead of whiskerLeft and whiskerRight.

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    theorem CategoryTheory.Functor.LaxMonoidal.ofTensorHom_ε {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] {F : CategoryTheory.Functor C D} (ε' : 𝟙_ D F.obj (𝟙_ C)) (μ' : (X Y : C) → CategoryTheory.MonoidalCategory.tensorObj (F.obj X) (F.obj Y) F.obj (CategoryTheory.MonoidalCategory.tensorObj X Y)) (μ'_natural : ∀ {X Y X' Y' : C} (f : X Y) (g : X' Y'), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (F.map f) (F.map g)) (μ' Y Y') = CategoryTheory.CategoryStruct.comp (μ' X X') (F.map (CategoryTheory.MonoidalCategory.tensorHom f g)) := by aesop_cat) (associativity' : ∀ (X Y Z : C), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (μ' X Y) (CategoryTheory.CategoryStruct.id (F.obj Z))) (CategoryTheory.CategoryStruct.comp (μ' (CategoryTheory.MonoidalCategory.tensorObj X Y) Z) (F.map (CategoryTheory.MonoidalCategory.associator X Y Z).hom)) = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.associator (F.obj X) (F.obj Y) (F.obj Z)).hom (CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) (μ' Y Z)) (μ' X (CategoryTheory.MonoidalCategory.tensorObj Y Z))) := by aesop_cat) (left_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.leftUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom ε' (CategoryTheory.CategoryStruct.id (F.obj X))) (CategoryTheory.CategoryStruct.comp (μ' (𝟙_ C) X) (F.map (CategoryTheory.MonoidalCategory.leftUnitor X).hom)) := by aesop_cat) (right_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.rightUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) ε') (CategoryTheory.CategoryStruct.comp (μ' X (𝟙_ C)) (F.map (CategoryTheory.MonoidalCategory.rightUnitor X).hom)) := by aesop_cat) :
    theorem CategoryTheory.Functor.LaxMonoidal.ofTensorHom_μ {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] {F : CategoryTheory.Functor C D} (ε' : 𝟙_ D F.obj (𝟙_ C)) (μ' : (X Y : C) → CategoryTheory.MonoidalCategory.tensorObj (F.obj X) (F.obj Y) F.obj (CategoryTheory.MonoidalCategory.tensorObj X Y)) (μ'_natural : ∀ {X Y X' Y' : C} (f : X Y) (g : X' Y'), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (F.map f) (F.map g)) (μ' Y Y') = CategoryTheory.CategoryStruct.comp (μ' X X') (F.map (CategoryTheory.MonoidalCategory.tensorHom f g)) := by aesop_cat) (associativity' : ∀ (X Y Z : C), CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (μ' X Y) (CategoryTheory.CategoryStruct.id (F.obj Z))) (CategoryTheory.CategoryStruct.comp (μ' (CategoryTheory.MonoidalCategory.tensorObj X Y) Z) (F.map (CategoryTheory.MonoidalCategory.associator X Y Z).hom)) = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.associator (F.obj X) (F.obj Y) (F.obj Z)).hom (CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) (μ' Y Z)) (μ' X (CategoryTheory.MonoidalCategory.tensorObj Y Z))) := by aesop_cat) (left_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.leftUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom ε' (CategoryTheory.CategoryStruct.id (F.obj X))) (CategoryTheory.CategoryStruct.comp (μ' (𝟙_ C) X) (F.map (CategoryTheory.MonoidalCategory.leftUnitor X).hom)) := by aesop_cat) (right_unitality' : ∀ (X : C), (CategoryTheory.MonoidalCategory.rightUnitor (F.obj X)).hom = CategoryTheory.CategoryStruct.comp (CategoryTheory.MonoidalCategory.tensorHom (CategoryTheory.CategoryStruct.id (F.obj X)) ε') (CategoryTheory.CategoryStruct.comp (μ' X (𝟙_ C)) (F.map (CategoryTheory.MonoidalCategory.rightUnitor X).hom)) := by aesop_cat) :
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    A functor F : C ⥤ D between monoidal categories is oplax monoidal if it is equipped with morphisms η : F.obj (𝟙_ C) ⟶ 𝟙 _D and δ X Y : F.obj (X ⊗ Y) ⟶ F.obj X ⊗ F.obj Y, satisfying the appropriate coherences.

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      the counit morphism of a lax monoidal functor

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      A functor between monoidal categories is monoidal if it is lax and oplax monoidals, and both data give inverse isomorphisms.

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        The isomorphism 𝟙_ D ≅ F.obj (𝟙_ C) when F is a monoidal functor.

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        The isomorphism F.obj X ⊗ F.obj Y ≅ F.obj (X ⊗ Y) when F is a monoidal functor.

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        Structure which is a helper in order to show that a functor is monoidal. It consists of isomorphisms εIso and μIso such that the morphisms .hom induced by these isomorphisms satisfy the axioms of lax monoidal functors.

        The lax monoidal functor structure induced by a Functor.CoreMonoidal structure.

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        • h.toLaxMonoidal = { ε' := h.εIso.hom, μ' := fun (X Y : C) => (h.μIso X Y).hom, μ'_natural_left := , μ'_natural_right := , associativity' := , left_unitality' := , right_unitality' := }

        The oplax monoidal functor structure induced by a Functor.CoreMonoidal structure.

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        The monoidal functor structure induced by a Functor.CoreMonoidal structure.

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        @[simp]
        theorem CategoryTheory.Functor.CoreMonoidal.toMonoidal_toOplaxMonoidal {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] {F : CategoryTheory.Functor C D} (h : F.CoreMonoidal) :
        CategoryTheory.Functor.Monoidal.toOplaxMonoidal = h.toOplaxMonoidal
        @[simp]

        The Functor.CoreMonoidal structure given by a lax monoidal functor such that ε and μ are isomorphisms.

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        The Functor.CoreMonoidal structure given by an oplax monoidal functor such that η and δ are isomorphisms.

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        The functor C ⥤ D × E obtained from two lax monoidal functors is lax monoidal.

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        The functor C ⥤ D × E obtained from two oplax monoidal functors is oplax monoidal.

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        The functor C ⥤ D × E obtained from two monoidal functors is monoidal.

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        The right adjoint of an oplax monoidal functor is lax monoidal.

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        When adj : F ⊣ G is an adjunction, with F oplax monoidal and G monoidal, this typeclass expresses compatibilities between the adjunction and the (op)lax monoidal structures.

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          If a monoidal functor F is an equivalence of categories then its inverse is also monoidal.

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          @[reducible, inline]

          An equivalence of categories involving monoidal functors is monoidal if the underlying adjunction satisfies certain compatibilities with respect to the monoidal funtor data.

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          • e.IsMonoidal = e.toAdjunction.IsMonoidal
          theorem CategoryTheory.Equivalence.counitIso_inv_app_tensor_comp_functor_map_δ_inverse {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] (e : C D) [e.functor.Monoidal] [e.inverse.Monoidal] [e.IsMonoidal] (X Y : C) :
          CategoryTheory.CategoryStruct.comp (e.counitIso.inv.app (CategoryTheory.MonoidalCategory.tensorObj (e.functor.obj X) (e.functor.obj Y))) (e.functor.map (CategoryTheory.Functor.OplaxMonoidal.δ e.inverse (e.functor.obj X) (e.functor.obj Y))) = CategoryTheory.CategoryStruct.comp (CategoryTheory.Functor.LaxMonoidal.μ e.functor X Y) (e.functor.map (CategoryTheory.MonoidalCategory.tensorHom (e.unitIso.hom.app X) (e.unitIso.hom.app Y)))
          theorem CategoryTheory.Equivalence.counitIso_inv_app_tensor_comp_functor_map_δ_inverse_assoc {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] (e : C D) [e.functor.Monoidal] [e.inverse.Monoidal] [e.IsMonoidal] (X Y : C) {Z : D} (h : e.functor.obj (CategoryTheory.MonoidalCategory.tensorObj (e.inverse.obj (e.functor.obj X)) (e.inverse.obj (e.functor.obj Y))) Z) :
          CategoryTheory.CategoryStruct.comp (e.counitIso.inv.app (CategoryTheory.MonoidalCategory.tensorObj (e.functor.obj X) (e.functor.obj Y))) (CategoryTheory.CategoryStruct.comp (e.functor.map (CategoryTheory.Functor.OplaxMonoidal.δ e.inverse (e.functor.obj X) (e.functor.obj Y))) h) = CategoryTheory.CategoryStruct.comp (CategoryTheory.Functor.LaxMonoidal.μ e.functor X Y) (CategoryTheory.CategoryStruct.comp (e.functor.map (CategoryTheory.MonoidalCategory.tensorHom (e.unitIso.hom.app X) (e.unitIso.hom.app Y))) h)
          instance CategoryTheory.Equivalence.isMonoidal_symm {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {D : Type u₂} [CategoryTheory.Category.{v₂, u₂} D] [CategoryTheory.MonoidalCategory D] (e : C D) [e.functor.Monoidal] [e.inverse.Monoidal] [e.IsMonoidal] :
          e.symm.IsMonoidal

          The inverse of a monoidal category equivalence is also a monoidal category equivalence.

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          Bundled version of lax monoidal functors. This type is equipped with a category structure in CategoryTheory.Monoidal.NaturalTransformation.