Documentation

Mathlib.CategoryTheory.Monoidal.Comon_

The category of comonoids in a monoidal category. #

We define comonoids in a monoidal category C, and show that they are equivalently monoid objects in the opposite category.

We construct the monoidal structure on Comon_ C, when C is braided.

An oplax monoidal functor takes comonoid objects to comonoid objects. That is, a oplax monoidal functor F : C ⥤ D induces a functor Comon_ C ⥤ Comon_ D.

TODO #

The comultiplication morphism of a comonoid object.

Equations
Instances For

    The comultiplication morphism of a comonoid object.

    Equations
    • One or more equations did not get rendered due to their size.
    Instances For

      The counit morphism of a comonoid object.

      Equations
      Instances For

        The counit morphism of a comonoid object.

        Equations
        • One or more equations did not get rendered due to their size.
        Instances For
          Equations
          • One or more equations did not get rendered due to their size.

          A comonoid object internal to a monoidal category.

          When the monoidal category is preadditive, this is also sometimes called a "coalgebra object".

          • X : C

            The underlying object of a comonoid object.

          • comon : Comon_Class self.X
          Instances For

            The trivial comonoid object. We later show this is terminal in Comon_ C.

            Equations
            Instances For
              theorem Comon_.Hom.ext_iff {C : Type u₁} {inst✝ : CategoryTheory.Category.{v₁, u₁} C} {inst✝¹ : CategoryTheory.MonoidalCategory C} {M N : Comon_ C} {x y : M.Hom N} :
              x = y x.hom = y.hom
              theorem Comon_.Hom.ext {C : Type u₁} {inst✝ : CategoryTheory.Category.{v₁, u₁} C} {inst✝¹ : CategoryTheory.MonoidalCategory C} {M N : Comon_ C} {x y : M.Hom N} (hom : x.hom = y.hom) :
              x = y
              @[reducible, inline]
              abbrev Comon_.Hom.mk' {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {M N : C} [Comon_Class M] [Comon_Class N] (f : M N) [IsComon_Hom f] :
              { X := M, comon := inst✝ }.Hom { X := N, comon := inst✝¹ }

              Construct a morphism M ⟶ N of Comon_ C from a map f : M ⟶ N and a IsComon_Hom f instance.

              Equations
              Instances For

                The identity morphism on a comonoid object.

                Equations
                Instances For
                  def Comon_.comp {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {M N O : Comon_ C} (f : M.Hom N) (g : N.Hom O) :
                  M.Hom O

                  Composition of morphisms of monoid objects.

                  Equations
                  Instances For
                    Equations
                    • One or more equations did not get rendered due to their size.
                    theorem Comon_.ext {C : Type u₁} [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {X Y : Comon_ C} {f g : X Y} (w : f.hom = g.hom) :
                    f = g

                    The forgetful functor from comonoid objects to the ambient category.

                    Equations
                    Instances For
                      @[simp]
                      theorem Comon_.forget_map (C : Type u₁) [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {X✝ Y✝ : Comon_ C} (f : X✝ Y✝) :
                      (forget C).map f = f.hom

                      The forgetful functor from comonoid objects to the ambient category reflects isomorphisms.

                      Construct an isomorphism of comonoids by giving an isomorphism between the underlying objects and checking compatibility with counit and comultiplication only in the forward direction.

                      Equations
                      Instances For

                        Construct an isomorphism of comonoids by giving an isomorphism between the underlying objects and checking compatibility with counit and comultiplication only in the forward direction.

                        Equations
                        • One or more equations did not get rendered due to their size.
                        Instances For
                          Equations
                          @[reducible, inline]

                          Auxiliary definition for Comon_ToMon_OpOpObj.

                          Equations
                          Instances For

                            Turn a comonoid object into a monoid object in the opposite category.

                            Equations
                            Instances For

                              The contravariant functor turning comonoid objects into monoid objects in the opposite category.

                              Equations
                              • One or more equations did not get rendered due to their size.
                              Instances For
                                @[simp]
                                theorem Comon_.Comon_ToMon_OpOp_map (C : Type u₁) [CategoryTheory.Category.{v₁, u₁} C] [CategoryTheory.MonoidalCategory C] {X✝ Y✝ : Comon_ C} (f : X✝ Y✝) :
                                (Comon_ToMon_OpOp C).map f = Opposite.op { hom := f.hom.op, one_hom := , mul_hom := }
                                @[reducible, inline]

                                Auxiliary definition for Mon_OpOpToComonObj.

                                Equations
                                Instances For

                                  Turn a monoid object in the opposite category into a comonoid object.

                                  Equations
                                  Instances For

                                    The contravariant functor turning monoid objects in the opposite category into comonoid objects.

                                    Equations
                                    • One or more equations did not get rendered due to their size.
                                    Instances For

                                      Comonoid objects are contravariantly equivalent to monoid objects in the opposite category.

                                      Equations
                                      • One or more equations did not get rendered due to their size.
                                      Instances For

                                        Comonoid objects in a braided category form a monoidal category.

                                        This definition is via transporting back and forth to monoids in the opposite category.

                                        Equations

                                        Preliminary statement of the comultiplication for a tensor product of comonoids. This version is the definitional equality provided by transport, and not quite as good as the version provided in tensorObj_comul below.

                                        @[simp]

                                        The comultiplication on the tensor product of two comonoids is the tensor product of the comultiplications followed by the tensor strength (to shuffle the factors back into order).

                                        The forgetful functor from Comon_ C to C is monoidal when C is monoidal.

                                        Equations
                                        • One or more equations did not get rendered due to their size.

                                        A oplax monoidal functor takes comonoid objects to comonoid objects.

                                        That is, a oplax monoidal functor F : C ⥤ D induces a functor Comon_ C ⥤ Comon_ D.

                                        Equations
                                        • One or more equations did not get rendered due to their size.
                                        Instances For
                                          @[simp]
                                          theorem CategoryTheory.Functor.mapComon_map_hom {C : Type u₁} [Category.{v₁, u₁} C] [MonoidalCategory C] {D : Type u₂} [Category.{v₂, u₂} D] [MonoidalCategory D] (F : Functor C D) [F.OplaxMonoidal] {X✝ Y✝ : Comon_ C} (f : X✝ Y✝) :
                                          (F.mapComon.map f).hom = F.map f.hom