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Mathlib.CategoryTheory.Monoidal.Cartesian.Mon_

Yoneda embedding of Mon C #

We show that monoid objects in Cartesian monoidal categories are exactly those whose yoneda presheaf is a presheaf of monoids, by constructing the yoneda embedding Mon C ⥤ Cᵒᵖ ⥤ MonCat.{v} and showing that it is fully faithful and its (essential) image is the representable functors.

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If X represents a presheaf of monoids, then X is a monoid object.

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    @[deprecated CategoryTheory.MonObj.ofRepresentableBy (since := "2025-09-09")]

    Alias of CategoryTheory.MonObj.ofRepresentableBy.


    If X represents a presheaf of monoids, then X is a monoid object.

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      @[deprecated CategoryTheory.MonObj.ofRepresentableBy (since := "2025-09-09")]

      Alias of CategoryTheory.MonObj.ofRepresentableBy.


      If X represents a presheaf of monoids, then X is a monoid object.

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        @[reducible, inline]

        If M is a monoid object, then Hom(X, M) has a monoid structure.

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          theorem CategoryTheory.Functor.map_mul {C : Type u_1} {D : Type u_2} [Category.{v, u_1} C] [CartesianMonoidalCategory C] [Category.{w, u_2} D] [CartesianMonoidalCategory D] {M X : C} [MonObj M] (F : Functor C D) [F.Monoidal] (f g : X M) :
          F.map (f * g) = F.map f * F.map g

          Functor.map of a monoidal functor as a MonoidHom.

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            @[simp]

            Functor.map of a fully faithful monoidal functor as a MulEquiv.

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              @[simp]
              @[reducible, inline]

              If M is a commutative monoid object, then Hom(X, M) has a commutative monoid structure.

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                If M is a monoid object, then Hom(-, M) is a presheaf of monoids.

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                  @[simp]
                  theorem CategoryTheory.yonedaMonObj_map {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] (M : C) [MonObj M] {X Y₂ : Cᵒᵖ} (φ : X Y₂) :
                  (yonedaMonObj M).map φ = MonCat.ofHom { toFun := fun (x : Opposite.unop X M) => CategoryStruct.comp φ.unop x, map_one' := , map_mul' := }

                  If X represents a presheaf of monoids F, then Hom(-, X) is isomorphic to F as a presheaf of monoids.

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                    The yoneda embedding of Mon_C into presheaves of monoids.

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                      @[simp]
                      theorem CategoryTheory.yonedaMon_map_app {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N : Mon C} (ψ : M N) (Y : Cᵒᵖ) :
                      (yonedaMon.map ψ).app Y = MonCat.ofHom { toFun := fun (x : Opposite.unop Y M.X) => CategoryStruct.comp x ψ.hom, map_one' := , map_mul' := }
                      @[deprecated CategoryTheory.MonObj.ofRepresentableBy_yonedaMonObjRepresentableBy (since := "2025-09-09")]

                      Alias of CategoryTheory.MonObj.ofRepresentableBy_yonedaMonObjRepresentableBy.

                      @[deprecated CategoryTheory.MonObj.ofRepresentableBy_yonedaMonObjRepresentableBy (since := "2025-09-09")]

                      Alias of CategoryTheory.MonObj.ofRepresentableBy_yonedaMonObjRepresentableBy.

                      The yoneda embedding for Mon_C is fully faithful.

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                        @[simp]
                        @[deprecated CategoryTheory.MonObj.one_comp (since := "2025-09-09")]

                        Alias of CategoryTheory.MonObj.one_comp.

                        theorem CategoryTheory.MonObj.mul_comp {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f₁ f₂ : X M) (g : M N) [IsMonHom g] :
                        theorem CategoryTheory.MonObj.mul_comp_assoc {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f₁ f₂ : X M) (g : M N) [IsMonHom g] {Z : C} (h : N Z) :
                        @[deprecated CategoryTheory.MonObj.mul_comp (since := "2025-09-09")]
                        theorem CategoryTheory.Mon_Class.mul_comp {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f₁ f₂ : X M) (g : M N) [IsMonHom g] :

                        Alias of CategoryTheory.MonObj.mul_comp.

                        theorem CategoryTheory.MonObj.pow_comp {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f : X M) (n : ) (g : M N) [IsMonHom g] :
                        theorem CategoryTheory.MonObj.pow_comp_assoc {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f : X M) (n : ) (g : M N) [IsMonHom g] {Z : C} (h : N Z) :
                        @[deprecated CategoryTheory.MonObj.pow_comp (since := "2025-09-09")]
                        theorem CategoryTheory.Mon_Class.pow_comp {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N X : C} [MonObj M] [MonObj N] (f : X M) (n : ) (g : M N) [IsMonHom g] :

                        Alias of CategoryTheory.MonObj.pow_comp.

                        @[simp]
                        @[deprecated CategoryTheory.MonObj.comp_one (since := "2025-09-09")]

                        Alias of CategoryTheory.MonObj.comp_one.

                        theorem CategoryTheory.MonObj.comp_mul {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X Y) (g₁ g₂ : Y M) :
                        theorem CategoryTheory.MonObj.comp_mul_assoc {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X Y) (g₁ g₂ : Y M) {Z : C} (h : M Z) :
                        @[deprecated CategoryTheory.MonObj.comp_mul (since := "2025-09-09")]
                        theorem CategoryTheory.Mon_Class.comp_mul {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X Y) (g₁ g₂ : Y M) :

                        Alias of CategoryTheory.MonObj.comp_mul.

                        theorem CategoryTheory.MonObj.comp_pow {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X M) (n : ) (h : Y X) :
                        theorem CategoryTheory.MonObj.comp_pow_assoc {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X M) (n : ) (h : Y X) {Z : C} (h✝ : M Z) :
                        @[deprecated CategoryTheory.MonObj.comp_pow (since := "2025-09-09")]
                        theorem CategoryTheory.Mon_Class.comp_pow {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M X Y : C} [MonObj M] (f : X M) (n : ) (h : Y X) :

                        Alias of CategoryTheory.MonObj.comp_pow.

                        @[deprecated CategoryTheory.MonObj.one_eq_one (since := "2025-09-09")]

                        Alias of CategoryTheory.MonObj.one_eq_one.

                        @[deprecated CategoryTheory.MonObj.mul_eq_mul (since := "2025-09-09")]

                        Alias of CategoryTheory.MonObj.mul_eq_mul.

                        def CategoryTheory.Hom.mulEquivCongrRight {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N : C} [MonObj M] [MonObj N] (e : M N) [IsMonHom e.hom] (X : C) :
                        (X M) ≃* (X N)

                        If M and N are isomorphic as monoid objects, then X ⟶ M and X ⟶ N are isomorphic monoids.

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                          theorem CategoryTheory.Hom.mulEquivCongrRight_symm_apply {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N : C} [MonObj M] [MonObj N] (e : M N) [IsMonHom e.hom] (X : C) (a : ((yonedaMon.obj { X := N, mon := inst✝ }).obj (Opposite.op X))) :
                          @[simp]
                          theorem CategoryTheory.Hom.mulEquivCongrRight_apply {C : Type u_1} [Category.{v, u_1} C] [CartesianMonoidalCategory C] {M N : C} [MonObj M] [MonObj N] (e : M N) [IsMonHom e.hom] (X : C) (a : ((yonedaMon.obj { X := M, mon := inst✝ }).obj (Opposite.op X))) :