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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.

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

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

    Alias of MonObj.ofRepresentableBy.


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

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      @[deprecated MonObj.ofRepresentableBy (since := "2025-03-07")]

      Alias of MonObj.ofRepresentableBy.


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

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        @[deprecated MonObjOfRepresentableBy (since := "2025-09-09")]

        Alias of MonObj.ofRepresentableBy.


        Alias of 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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            @[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 yonedaMonObj_map {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.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) => CategoryTheory.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 yonedaMon_map_app {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.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) => CategoryTheory.CategoryStruct.comp x ψ.hom, map_one' := , map_mul' := }

                    The yoneda embedding for Mon_C is fully faithful.

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

                      Alias of MonObj.one_comp.

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

                      Alias of MonObj.mul_comp.

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

                      Alias of MonObj.pow_comp.

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

                      Alias of MonObj.comp_one.

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

                      Alias of MonObj.comp_mul.

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

                      Alias of MonObj.comp_pow.

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

                      Alias of MonObj.one_eq_one.