Documentation

Mathlib.CategoryTheory.WithTerminal

WithInitial and WithTerminal #

Given a category C, this file constructs two objects:

  1. WithTerminal C, the category built from C by formally adjoining a terminal object.
  2. WithInitial C, the category built from C by formally adjoining an initial object.

The terminal resp. initial object is WithTerminal.star resp. WithInitial.star, and the proofs that these are terminal resp. initial are in WithTerminal.star_terminal and WithInitial.star_initial.

The inclusion from C into WithTerminal C resp. WithInitial C is denoted WithTerminal.incl resp. WithInitial.incl.

The relevant constructions needed for the universal properties of these constructions are:

  1. lift, which lifts F : C ⥤ D to a functor from WithTerminal C resp. WithInitial C in the case where an object Z : D is provided satisfying some additional conditions.
  2. inclLift shows that the composition of lift with incl is isomorphic to the functor which was lifted.
  3. liftUnique provides the uniqueness property of lift.

In addition to this, we provide WithTerminal.map and WithInitial.map providing the functoriality of these constructions with respect to functors on the base categories.

We define corresponding pseudofunctors WithTerminal.pseudofunctor and WithInitial.pseudofunctor from Cat to Cat.

Formally adjoin a terminal object to a category.

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    inductive CategoryTheory.WithInitial (C : Type u) :

    Formally adjoin an initial object to a category.

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      def CategoryTheory.WithTerminal.down {C : Type u} [Category.{v, u} C] {X Y : C} (f : of X of Y) :
      X Y

      Helper function for typechecking.

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        theorem CategoryTheory.WithTerminal.down_comp {C : Type u} [Category.{v, u} C] {X Y Z : C} (f : of X of Y) (g : of Y of Z) :

        The inclusion from C into WithTerminal C.

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          Map WithTerminal with respect to a functor F : C ⥤ D.

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            theorem CategoryTheory.WithTerminal.map_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor C D) {X Y : WithTerminal C} (f : X Y) :
            (map F).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | of a, star, x => PUnit.unit | star, star, x => PUnit.unit
            @[simp]
            theorem CategoryTheory.WithTerminal.map_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor C D) (X : WithTerminal C) :
            (map F).obj X = match X with | of x => of (F.obj x) | star => star

            A natural isomorphism between the functor map (𝟭 C) and 𝟭 (WithTerminal C).

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              theorem CategoryTheory.WithTerminal.mapId_hom_app (C : Type u_1) [Category.{u_2, u_1} C] (X : WithTerminal C) :
              (mapId C).hom.app X = (match X with | of a => Iso.refl (of a) | star => Iso.refl star).hom
              @[simp]
              theorem CategoryTheory.WithTerminal.mapId_inv_app (C : Type u_1) [Category.{u_2, u_1} C] (X : WithTerminal C) :
              (mapId C).inv.app X = (match X with | of a => Iso.refl (of a) | star => Iso.refl star).inv
              def CategoryTheory.WithTerminal.mapComp {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) :
              map (F.comp G) (map F).comp (map G)

              A natural isomorphism between the functor map (F ⋙ G) and map F ⋙ map G .

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                theorem CategoryTheory.WithTerminal.mapComp_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) (X : WithTerminal C) :
                (mapComp F G).inv.app X = (match X with | of a => Iso.refl (of (G.obj (F.obj a))) | star => Iso.refl star).inv
                @[simp]
                theorem CategoryTheory.WithTerminal.mapComp_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) (X : WithTerminal C) :
                (mapComp F G).hom.app X = (match X with | of a => Iso.refl (of (G.obj (F.obj a))) | star => Iso.refl star).hom
                def CategoryTheory.WithTerminal.map₂ {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {F G : Functor C D} (η : F G) :
                map F map G

                From a natural transformation of functors C ⥤ D, the induced natural transformation of functors WithTerminal C ⥤ WithTerminal D.

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                  theorem CategoryTheory.WithTerminal.map₂_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {F G : Functor C D} (η : F G) (X : WithTerminal C) :
                  (map₂ η).app X = match X with | of x => η.app x | star => CategoryStruct.id star

                  The prelax functor from Cat to Cat defined with WithTerminal.

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                    theorem CategoryTheory.WithTerminal.prelaxfunctor_toPrelaxFunctorStruct_map₂ {a✝ b✝ : Cat} {f✝ g✝ : a✝ b✝} (η : f✝ g✝) :

                    The pseudofunctor from Cat to Cat defined with WithTerminal.

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                      theorem CategoryTheory.WithTerminal.pseudofunctor_mapComp {a✝ b✝ c✝ : Cat} (F : Functor a✝ b✝) (G : Functor b✝ c✝) :
                      def CategoryTheory.WithTerminal.lift {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) :

                      Lift a functor F : C ⥤ D to WithTerminal C ⥤ D.

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                        theorem CategoryTheory.WithTerminal.lift_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) {X Y : WithTerminal C} (f : X Y) :
                        (lift F M hM).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | of x, star, x_1 => M x | star, star, x => CategoryStruct.id Z
                        @[simp]
                        theorem CategoryTheory.WithTerminal.lift_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) (X : WithTerminal C) :
                        (lift F M hM).obj X = match X with | of x => F.obj x | star => Z
                        def CategoryTheory.WithTerminal.inclLift {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) :
                        incl.comp (lift F M hM) F

                        The isomorphism between incllift F _ _ with F.

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                          theorem CategoryTheory.WithTerminal.inclLift_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) (x✝ : C) :
                          (inclLift F M hM).hom.app x✝ = CategoryStruct.id (match incl.obj x✝ with | of x => F.obj x | star => Z)
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                          theorem CategoryTheory.WithTerminal.inclLift_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) (x✝ : C) :
                          (inclLift F M hM).inv.app x✝ = CategoryStruct.id (F.obj x✝)
                          def CategoryTheory.WithTerminal.liftStar {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) :
                          (lift F M hM).obj star Z

                          The isomorphism between (lift F _ _).obj WithTerminal.star with Z.

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                            theorem CategoryTheory.WithTerminal.liftStar_inv {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) :
                            @[simp]
                            theorem CategoryTheory.WithTerminal.liftStar_hom {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) :
                            theorem CategoryTheory.WithTerminal.lift_map_liftStar {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) (x : C) :
                            def CategoryTheory.WithTerminal.liftUnique {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → F.obj x Z) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (F.map f) (M y) = M x) (G : Functor (WithTerminal C) D) (h : incl.comp G F) (hG : G.obj star Z) (hh : ∀ (x : C), CategoryStruct.comp (G.map (starTerminal.from (incl.obj x))) hG.hom = CategoryStruct.comp (h.hom.app x) (M x)) :
                            G lift F M hM

                            The uniqueness of lift.

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                              A variant of lift with Z a terminal object.

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                                theorem CategoryTheory.WithTerminal.liftToTerminal_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) (X : WithTerminal C) :
                                (liftToTerminal F hZ).obj X = match X with | of x => F.obj x | star => Z
                                @[simp]
                                theorem CategoryTheory.WithTerminal.liftToTerminal_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) {X Y : WithTerminal C} (f : X Y) :
                                (liftToTerminal F hZ).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | of x, star, x_1 => hZ.from (F.obj x) | star, star, x => CategoryStruct.id Z

                                A variant of incl_lift with Z a terminal object.

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                                  theorem CategoryTheory.WithTerminal.inclLiftToTerminal_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) (x✝ : C) :
                                  (inclLiftToTerminal F hZ).hom.app x✝ = CategoryStruct.id (match incl.obj x✝ with | of x => F.obj x | star => Z)
                                  def CategoryTheory.WithTerminal.liftToTerminalUnique {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) (G : Functor (WithTerminal C) D) (h : incl.comp G F) (hG : G.obj star Z) :

                                  A variant of lift_unique with Z a terminal object.

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                                    theorem CategoryTheory.WithTerminal.liftToTerminalUnique_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) (G : Functor (WithTerminal C) D) (h : incl.comp G F) (hG : G.obj star Z) (X : WithTerminal C) :
                                    (liftToTerminalUnique F hZ G h hG).inv.app X = (match X with | of x => h.app x | star => hG).inv
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                                    theorem CategoryTheory.WithTerminal.liftToTerminalUnique_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsTerminal Z) (G : Functor (WithTerminal C) D) (h : incl.comp G F) (hG : G.obj star Z) (X : WithTerminal C) :
                                    (liftToTerminalUnique F hZ G h hG).hom.app X = (match X with | of x => h.app x | star => hG).hom

                                    A functor WithTerminal C ⥤ D can be seen as an element of the comma category Comma (𝟭 (C ⥤ D)) (const C).

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                                      theorem CategoryTheory.WithTerminal.mkCommaObject_left_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor (WithTerminal C) D) {X✝ Y✝ : C} (f : X✝ Y✝) :

                                      A morphism of functors WithTerminal C ⥤ D gives a morphism between the associated comma objects.

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                                        An element of the comma category Comma (𝟭 (C ⥤ D)) (Functor.const C) can be seen as a functor WithTerminal C ⥤ D.

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                                          theorem CategoryTheory.WithTerminal.ofCommaObject_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.id (Functor C D)) (Functor.const C)) {X Y : WithTerminal C} (f : X Y) :
                                          (ofCommaObject c).map f = match X, Y, f with | of a, of a_1, f => c.left.map (down f) | of x, star, x_1 => c.hom.app x | star, star, x => CategoryStruct.id c.right
                                          @[simp]
                                          theorem CategoryTheory.WithTerminal.ofCommaObject_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.id (Functor C D)) (Functor.const C)) (X : WithTerminal C) :
                                          (ofCommaObject c).obj X = match X with | of x => c.left.obj x | star => c.right

                                          A morphism in Comma (𝟭 (C ⥤ D)) (Functor.const C) gives a morphism between the associated functors WithTerminal C ⥤ D.

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                                            theorem CategoryTheory.WithTerminal.ofCommaMorphism_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {c c' : Comma (Functor.id (Functor C D)) (Functor.const C)} (φ : c c') (x : WithTerminal C) :
                                            (ofCommaMorphism φ).app x = match x with | of x => φ.left.app x | star => φ.right

                                            The category of functors WithTerminal C ⥤ D is equivalent to the category Comma (𝟭 (C ⥤ D)) (const C) .

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                                              theorem CategoryTheory.WithTerminal.equivComma_functor_map_left_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {X✝ Y✝ : Functor (WithTerminal C) D} (η : X✝ Y✝) (X : C) :
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                                              theorem CategoryTheory.WithTerminal.equivComma_inverse_obj_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.id (Functor C D)) (Functor.const C)) {X Y : WithTerminal C} (f : X Y) :
                                              (equivComma.inverse.obj c).map f = match X, Y, f with | of a, of a_1, f => c.left.map (down f) | of x, star, x_1 => c.hom.app x | star, star, x => CategoryStruct.id c.right
                                              @[simp]
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                                              theorem CategoryTheory.WithTerminal.equivComma_inverse_map_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {X✝ Y✝ : Comma (Functor.id (Functor C D)) (Functor.const C)} (φ : X✝ Y✝) (x : WithTerminal C) :
                                              (equivComma.inverse.map φ).app x = match x with | of x => φ.left.app x | star => φ.right
                                              def CategoryTheory.WithInitial.down {C : Type u} [Category.{v, u} C] {X Y : C} (f : of X of Y) :
                                              X Y

                                              Helper function for typechecking.

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                                                theorem CategoryTheory.WithInitial.down_comp {C : Type u} [Category.{v, u} C] {X Y Z : C} (f : of X of Y) (g : of Y of Z) :

                                                The inclusion of C into WithInitial C.

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                                                  Map WithInitial with respect to a functor F : C ⥤ D.

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                                                    theorem CategoryTheory.WithInitial.map_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor C D) {X Y : WithInitial C} (f : X Y) :
                                                    (map F).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | star, of a, x => PUnit.unit | star, star, x => PUnit.unit
                                                    @[simp]
                                                    theorem CategoryTheory.WithInitial.map_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor C D) (X : WithInitial C) :
                                                    (map F).obj X = match X with | of x => of (F.obj x) | star => star

                                                    A natural isomorphism between the functor map (𝟭 C) and 𝟭 (WithInitial C).

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                                                      theorem CategoryTheory.WithInitial.mapId_inv_app (C : Type u_1) [Category.{u_2, u_1} C] (X : WithInitial C) :
                                                      (mapId C).inv.app X = (match X with | of a => Iso.refl (of a) | star => Iso.refl star).inv
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                                                      theorem CategoryTheory.WithInitial.mapId_hom_app (C : Type u_1) [Category.{u_2, u_1} C] (X : WithInitial C) :
                                                      (mapId C).hom.app X = (match X with | of a => Iso.refl (of a) | star => Iso.refl star).hom
                                                      def CategoryTheory.WithInitial.mapComp {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) :
                                                      map (F.comp G) (map F).comp (map G)

                                                      A natural isomorphism between the functor map (F ⋙ G) and map F ⋙ map G .

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                                                        theorem CategoryTheory.WithInitial.mapComp_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) (X : WithInitial C) :
                                                        (mapComp F G).inv.app X = (match X with | of a => Iso.refl (of (G.obj (F.obj a))) | star => Iso.refl star).inv
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                                                        theorem CategoryTheory.WithInitial.mapComp_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} {E : Type u_2} [Category.{u_3, u_1} D] [Category.{u_4, u_2} E] (F : Functor C D) (G : Functor D E) (X : WithInitial C) :
                                                        (mapComp F G).hom.app X = (match X with | of a => Iso.refl (of (G.obj (F.obj a))) | star => Iso.refl star).hom
                                                        def CategoryTheory.WithInitial.map₂ {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {F G : Functor C D} (η : F G) :
                                                        map F map G

                                                        From a natural transformation of functors C ⥤ D, the induced natural transformation of functors WithInitial C ⥤ WithInitial D.

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                                                          theorem CategoryTheory.WithInitial.map₂_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {F G : Functor C D} (η : F G) (X : WithInitial C) :
                                                          (map₂ η).app X = match X with | of x => η.app x | star => CategoryStruct.id star

                                                          The prelax functor from Cat to Cat defined with WithInitial.

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                                                            theorem CategoryTheory.WithInitial.prelaxfunctor_toPrelaxFunctorStruct_map₂ {a✝ b✝ : Cat} {f✝ g✝ : a✝ b✝} (η : f✝ g✝) :

                                                            The pseudofunctor from Cat to Cat defined with WithInitial.

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                                                              theorem CategoryTheory.WithInitial.pseudofunctor_mapComp {a✝ b✝ c✝ : Cat} (F : Functor a✝ b✝) (G : Functor b✝ c✝) :
                                                              def CategoryTheory.WithInitial.lift {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) :

                                                              Lift a functor F : C ⥤ D to WithInitial C ⥤ D.

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                                                                theorem CategoryTheory.WithInitial.lift_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) (X : WithInitial C) :
                                                                (lift F M hM).obj X = match X with | of x => F.obj x | star => Z
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                                                                theorem CategoryTheory.WithInitial.lift_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) {X Y : WithInitial C} (f : X Y) :
                                                                (lift F M hM).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | star, of a, x => M a | star, star, x => CategoryStruct.id ((fun (X : WithInitial C) => match X with | of x => F.obj x | star => Z) star)
                                                                def CategoryTheory.WithInitial.inclLift {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) :
                                                                incl.comp (lift F M hM) F

                                                                The isomorphism between incllift F _ _ with F.

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                                                                  theorem CategoryTheory.WithInitial.inclLift_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) (x✝ : C) :
                                                                  (inclLift F M hM).inv.app x✝ = CategoryStruct.id (F.obj x✝)
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                                                                  theorem CategoryTheory.WithInitial.inclLift_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) (x✝ : C) :
                                                                  (inclLift F M hM).hom.app x✝ = CategoryStruct.id (match incl.obj x✝ with | of x => F.obj x | star => Z)
                                                                  def CategoryTheory.WithInitial.liftStar {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) :
                                                                  (lift F M hM).obj star Z

                                                                  The isomorphism between (lift F _ _).obj WithInitial.star with Z.

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                                                                    theorem CategoryTheory.WithInitial.liftStar_inv {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) :
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                                                                    theorem CategoryTheory.WithInitial.liftStar_hom {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) :
                                                                    theorem CategoryTheory.WithInitial.liftStar_lift_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) (x : C) :
                                                                    def CategoryTheory.WithInitial.liftUnique {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (M : (x : C) → Z F.obj x) (hM : ∀ (x y : C) (f : x y), CategoryStruct.comp (M x) (F.map f) = M y) (G : Functor (WithInitial C) D) (h : incl.comp G F) (hG : G.obj star Z) (hh : ∀ (x : C), CategoryStruct.comp hG.symm.hom (G.map (starInitial.to (incl.obj x))) = CategoryStruct.comp (M x) (h.symm.hom.app x)) :
                                                                    G lift F M hM

                                                                    The uniqueness of lift.

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                                                                      A variant of lift with Z an initial object.

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                                                                        theorem CategoryTheory.WithInitial.liftToInitial_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) (X : WithInitial C) :
                                                                        (liftToInitial F hZ).obj X = match X with | of x => F.obj x | star => Z
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                                                                        theorem CategoryTheory.WithInitial.liftToInitial_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) {X Y : WithInitial C} (f : X Y) :
                                                                        (liftToInitial F hZ).map f = match X, Y, f with | of a, of a_1, f => F.map (down f) | star, of a, x => hZ.to (F.obj a) | star, star, x => CategoryStruct.id Z

                                                                        A variant of incl_lift with Z an initial object.

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                                                                          theorem CategoryTheory.WithInitial.inclLiftToInitial_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) (x✝ : C) :
                                                                          (inclLiftToInitial F hZ).hom.app x✝ = CategoryStruct.id (match incl.obj x✝ with | of x => F.obj x | star => Z)
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                                                                          def CategoryTheory.WithInitial.liftToInitialUnique {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) (G : Functor (WithInitial C) D) (h : incl.comp G F) (hG : G.obj star Z) :

                                                                          A variant of lift_unique with Z an initial object.

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                                                                            theorem CategoryTheory.WithInitial.liftToInitialUnique_inv_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) (G : Functor (WithInitial C) D) (h : incl.comp G F) (hG : G.obj star Z) (X : WithInitial C) :
                                                                            (liftToInitialUnique F hZ G h hG).inv.app X = (match X with | of x => h.app x | star => hG).inv
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                                                                            theorem CategoryTheory.WithInitial.liftToInitialUnique_hom_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {Z : D} (F : Functor C D) (hZ : Limits.IsInitial Z) (G : Functor (WithInitial C) D) (h : incl.comp G F) (hG : G.obj star Z) (X : WithInitial C) :
                                                                            (liftToInitialUnique F hZ G h hG).hom.app X = (match X with | of x => h.app x | star => hG).hom

                                                                            A functor WithInitial C ⥤ D can be seen as an element of the comma category Comma (const C) (𝟭 (C ⥤ D)).

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                                                                              theorem CategoryTheory.WithInitial.mkCommaObject_right_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (F : Functor (WithInitial C) D) {X✝ Y✝ : C} (f : X✝ Y✝) :

                                                                              A morphism of functors WithInitial C ⥤ D gives a morphism between the associated comma objects.

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                                                                                An element of the comma category Comma (Functor.const C) (𝟭 (C ⥤ D)) can be seen as a functor WithInitial C ⥤ D.

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                                                                                  theorem CategoryTheory.WithInitial.ofCommaObject_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.const C) (Functor.id (Functor C D))) {X Y : WithInitial C} (f : X Y) :
                                                                                  (ofCommaObject c).map f = match X, Y, f with | of a, of a_1, f => c.right.map (down f) | star, of a, x => c.hom.app a | star, star, x => CategoryStruct.id c.left
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                                                                                  theorem CategoryTheory.WithInitial.ofCommaObject_obj {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.const C) (Functor.id (Functor C D))) (X : WithInitial C) :
                                                                                  (ofCommaObject c).obj X = match X with | of x => c.right.obj x | star => c.left

                                                                                  A morphism in Comma (Functor.const C) (𝟭 (C ⥤ D)) gives a morphism between the associated functors WithInitial C ⥤ D.

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                                                                                    theorem CategoryTheory.WithInitial.ofCommaMorphism_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {c c' : Comma (Functor.const C) (Functor.id (Functor C D))} (φ : c c') (x : WithInitial C) :
                                                                                    (ofCommaMorphism φ).app x = match x with | of x => φ.right.app x | star => φ.left

                                                                                    The category of functors WithInitial C ⥤ D is equivalent to the category Comma (const C) (𝟭 (C ⥤ D)).

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                                                                                      theorem CategoryTheory.WithInitial.equivComma_unitIso_inv_app_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (X : Functor (WithInitial C) D) (X✝ : WithInitial C) :
                                                                                      (equivComma.unitIso.inv.app X).app X✝ = (match X✝ with | of x => (Iso.refl (incl.comp X)).app x | star => Iso.refl (X.obj star)).inv
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                                                                                      theorem CategoryTheory.WithInitial.equivComma_inverse_obj_map {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (c : Comma (Functor.const C) (Functor.id (Functor C D))) {X Y : WithInitial C} (f : X Y) :
                                                                                      (equivComma.inverse.obj c).map f = match X, Y, f with | of a, of a_1, f => c.right.map (down f) | star, of a, x => c.hom.app a | star, star, x => CategoryStruct.id c.left
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                                                                                      theorem CategoryTheory.WithInitial.equivComma_functor_map_right_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {X✝ Y✝ : Functor (WithInitial C) D} (η : X✝ Y✝) (X : C) :
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                                                                                      theorem CategoryTheory.WithInitial.equivComma_unitIso_hom_app_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] (X : Functor (WithInitial C) D) (X✝ : WithInitial C) :
                                                                                      (equivComma.unitIso.hom.app X).app X✝ = (match X✝ with | of x => (Iso.refl (incl.comp X)).app x | star => Iso.refl (X.obj star)).hom
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                                                                                      theorem CategoryTheory.WithInitial.equivComma_inverse_map_app {C : Type u} [Category.{v, u} C] {D : Type u_1} [Category.{u_2, u_1} D] {X✝ Y✝ : Comma (Functor.const C) (Functor.id (Functor C D))} (φ : X✝ Y✝) (x : WithInitial C) :
                                                                                      (equivComma.inverse.map φ).app x = match x with | of x => φ.right.app x | star => φ.left
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                                                                                      The opposite category of WithTerminal C is equivalent to WithInitial Cᵒᵖ.

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                                                                                        The opposite category of WithInitial C is equivalent to WithTerminal Cᵒᵖ.

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