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Mathlib.CategoryTheory.Limits.ExactFunctor

Bundled exact functors #

We say that a functor F is left exact if it preserves finite limits, it is right exact if it preserves finite colimits, and it is exact if it is both left exact and right exact.

In this file, we define the categories of bundled left exact, right exact and exact functors.

Left-exactness, as a property of objects in C ⥤ D.

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    @[reducible, inline]
    abbrev CategoryTheory.LeftExactFunctor (C : Type u₁) [Category.{v₁, u₁} C] (D : Type u₂) [Category.{v₂, u₂} D] :
    Type (max (max (max u₁ u₂) v₁) v₂)

    Bundled left-exact functors.

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      C ⥤ₗ D denotes left exact functors C ⥤ D

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        @[reducible, inline]

        A left exact functor is in particular a functor.

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          The inclusion of left exact functors into functors is fully faithful.

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            Right-exactness, as a property of objects in C ⥤ D.

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              @[reducible, inline]
              abbrev CategoryTheory.RightExactFunctor (C : Type u₁) [Category.{v₁, u₁} C] (D : Type u₂) [Category.{v₂, u₂} D] :
              Type (max (max (max u₁ u₂) v₁) v₂)

              Bundled right-exact functors.

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                C ⥤ᵣ D denotes right exact functors C ⥤ D

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                  @[reducible, inline]

                  A right exact functor is in particular a functor.

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                    @[reducible, inline]

                    The inclusion of right exact functors into functors is fully faithful.

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                      Rxactness, as a property of objects in C ⥤ D.

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                        @[reducible, inline]
                        abbrev CategoryTheory.ExactFunctor (C : Type u₁) [Category.{v₁, u₁} C] (D : Type u₂) [Category.{v₂, u₂} D] :
                        Type (max (max (max u₁ u₂) v₁) v₂)

                        Bundled exact functors.

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                          C ⥤ₑ D denotes exact functors C ⥤ D

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                            @[reducible, inline]

                            An exact functor is in particular a functor.

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                              Turn an exact functor into a left exact functor.

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                                Turn an exact functor into a left exact functor.

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                                  @[simp]
                                  theorem CategoryTheory.LeftExactFunctor.ofExact_obj {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] (F : C ⥤ₑ D) :
                                  (ofExact C D).obj F = { obj := F.obj, property := }
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                                  theorem CategoryTheory.RightExactFunctor.ofExact_obj {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] (F : C ⥤ₑ D) :
                                  (ofExact C D).obj F = { obj := F.obj, property := }
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                                  theorem CategoryTheory.LeftExactFunctor.ofExact_map_hom {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₑ D} (α : F G) :
                                  ((ofExact C D).map α).hom = α.hom
                                  @[simp]
                                  theorem CategoryTheory.RightExactFunctor.ofExact_map_hom {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₑ D} (α : F G) :
                                  ((ofExact C D).map α).hom = α.hom
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                                  @[simp]
                                  theorem CategoryTheory.LeftExactFunctor.forget_map {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₗ D} (α : F G) :
                                  (forget C D).map α = α.hom
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                                  theorem CategoryTheory.RightExactFunctor.forget_map {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ᵣ D} (α : F G) :
                                  (forget C D).map α = α.hom
                                  @[simp]
                                  theorem CategoryTheory.ExactFunctor.forget_map {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₑ D} (α : F G) :
                                  (forget C D).map α = α.hom

                                  Turn a left exact functor into an object of the category LeftExactFunctor C D.

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                                    Turn a right exact functor into an object of the category RightExactFunctor C D.

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                                      Turn an exact functor into an object of the category ExactFunctor C D.

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                                        Whiskering a left exact functor by a left exact functor yields a left exact functor.

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                                          @[simp]
                                          theorem CategoryTheory.LeftExactFunctor.whiskeringLeft_obj_map (C : Type u₁) [Category.{v₁, u₁} C] (D : Type u₂) [Category.{v₂, u₂} D] (E : Type u₃) [Category.{v₃, u₃} E] (F : C ⥤ₗ D) {X✝ Y✝ : D ⥤ₗ E} (f : X✝ Y✝) :

                                          Whiskering a left exact functor by a left exact functor yields a left exact functor.

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                                            Whiskering a right exact functor by a right exact functor yields a right exact functor.

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                                              @[simp]

                                              Whiskering a right exact functor by a right exact functor yields a right exact functor.

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                                                Whiskering an exact functor by an exact functor yields an exact functor.

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                                                  @[simp]
                                                  theorem CategoryTheory.ExactFunctor.whiskeringLeft_obj_map (C : Type u₁) [Category.{v₁, u₁} C] (D : Type u₂) [Category.{v₂, u₂} D] (E : Type u₃) [Category.{v₃, u₃} E] (F : C ⥤ₑ D) {X✝ Y✝ : D ⥤ₑ E} (f : X✝ Y✝) :

                                                  Whiskering an exact functor by an exact functor yields an exact functor.

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                                                    @[deprecated CategoryTheory.LeftExactFunctor.ofExact_map_hom (since := "2025-12-18")]
                                                    theorem CategoryTheory.LeftExactFunctor.ofExact_map {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₑ D} (α : F G) :
                                                    ((ofExact C D).map α).hom = α.hom

                                                    Alias of CategoryTheory.LeftExactFunctor.ofExact_map_hom.

                                                    @[deprecated CategoryTheory.RightExactFunctor.ofExact_map_hom (since := "2025-12-18")]
                                                    theorem CategoryTheory.RightExactFunctor.ofExact_map {C : Type u₁} [Category.{v₁, u₁} C] {D : Type u₂} [Category.{v₂, u₂} D] {F G : C ⥤ₑ D} (α : F G) :
                                                    ((ofExact C D).map α).hom = α.hom

                                                    Alias of CategoryTheory.RightExactFunctor.ofExact_map_hom.