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Mathlib.CategoryTheory.Triangulated.Functor

Triangulated functors #

In this file, when C and D are categories equipped with a shift by and F : C ⥤ D is a functor which commutes with the shift, we define the induced functor F.mapTriangle : Triangle C ⥤ Triangle D on the categories of triangles. When C and D are pretriangulated, a triangulated functor is such a functor F which also sends distinguished triangles to distinguished triangles: this defines the typeclass Functor.IsTriangulated.

The functor Triangle C ⥤ Triangle D that is induced by a functor F : C ⥤ D which commutes with shift by .

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    The functor F.mapTriangle commutes with the shift.

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      F.mapTriangle commutes with the rotation of triangles.

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        F.mapTriangle commutes with the inverse of the rotation of triangles.

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          The canonical isomorphism (𝟭 C).mapTriangle ≅ 𝟭 (Triangle C).

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            The canonical isomorphism (F ⋙ G).mapTriangle ≅ F.mapTriangle ⋙ G.mapTriangle.

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              Two isomorphic functors F₁ and F₂ induce isomorphic functors F₁.mapTriangle and F₂.mapTriangle if the isomorphism F₁ ≅ F₂ is compatible with the shifts.

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                A functor which commutes with the shift by is triangulated if it sends distinguished triangles to distinguished triangles.

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                  def CategoryTheory.Triangulated.Octahedron.map {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [HasShift C ] [HasShift D ] [Limits.HasZeroObject C] [Limits.HasZeroObject D] [Preadditive C] [Preadditive D] [∀ (n : ), (shiftFunctor C n).Additive] [∀ (n : ), (shiftFunctor D n).Additive] [Pretriangulated C] [Pretriangulated D] {X₁ X₂ X₃ Z₁₂ Z₂₃ Z₁₃ : C} {u₁₂ : X₁ X₂} {u₂₃ : X₂ X₃} {u₁₃ : X₁ X₃} {comm : CategoryStruct.comp u₁₂ u₂₃ = u₁₃} {v₁₂ : X₂ Z₁₂} {w₁₂ : Z₁₂ (shiftFunctor C 1).obj X₁} {h₁₂ : Pretriangulated.Triangle.mk u₁₂ v₁₂ w₁₂ Pretriangulated.distinguishedTriangles} {v₂₃ : X₃ Z₂₃} {w₂₃ : Z₂₃ (shiftFunctor C 1).obj X₂} {h₂₃ : Pretriangulated.Triangle.mk u₂₃ v₂₃ w₂₃ Pretriangulated.distinguishedTriangles} {v₁₃ : X₃ Z₁₃} {w₁₃ : Z₁₃ (shiftFunctor C 1).obj X₁} {h₁₃ : Pretriangulated.Triangle.mk u₁₃ v₁₃ w₁₃ Pretriangulated.distinguishedTriangles} (h : Octahedron comm h₁₂ h₂₃ h₁₃) (F : Functor C D) [F.CommShift ] [F.IsTriangulated] :
                  Octahedron

                  The image of an octahedron by a triangulated functor.

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                  • h.map F = { m₁ := F.map h.m₁, m₃ := F.map h.m₃, comm₁ := , comm₂ := , comm₃ := , comm₄ := , mem := }
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                    @[simp]
                    theorem CategoryTheory.Triangulated.Octahedron.map_m₁ {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [HasShift C ] [HasShift D ] [Limits.HasZeroObject C] [Limits.HasZeroObject D] [Preadditive C] [Preadditive D] [∀ (n : ), (shiftFunctor C n).Additive] [∀ (n : ), (shiftFunctor D n).Additive] [Pretriangulated C] [Pretriangulated D] {X₁ X₂ X₃ Z₁₂ Z₂₃ Z₁₃ : C} {u₁₂ : X₁ X₂} {u₂₃ : X₂ X₃} {u₁₃ : X₁ X₃} {comm : CategoryStruct.comp u₁₂ u₂₃ = u₁₃} {v₁₂ : X₂ Z₁₂} {w₁₂ : Z₁₂ (shiftFunctor C 1).obj X₁} {h₁₂ : Pretriangulated.Triangle.mk u₁₂ v₁₂ w₁₂ Pretriangulated.distinguishedTriangles} {v₂₃ : X₃ Z₂₃} {w₂₃ : Z₂₃ (shiftFunctor C 1).obj X₂} {h₂₃ : Pretriangulated.Triangle.mk u₂₃ v₂₃ w₂₃ Pretriangulated.distinguishedTriangles} {v₁₃ : X₃ Z₁₃} {w₁₃ : Z₁₃ (shiftFunctor C 1).obj X₁} {h₁₃ : Pretriangulated.Triangle.mk u₁₃ v₁₃ w₁₃ Pretriangulated.distinguishedTriangles} (h : Octahedron comm h₁₂ h₂₃ h₁₃) (F : Functor C D) [F.CommShift ] [F.IsTriangulated] :
                    (h.map F).m₁ = F.map h.m₁
                    @[simp]
                    theorem CategoryTheory.Triangulated.Octahedron.map_m₃ {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [HasShift C ] [HasShift D ] [Limits.HasZeroObject C] [Limits.HasZeroObject D] [Preadditive C] [Preadditive D] [∀ (n : ), (shiftFunctor C n).Additive] [∀ (n : ), (shiftFunctor D n).Additive] [Pretriangulated C] [Pretriangulated D] {X₁ X₂ X₃ Z₁₂ Z₂₃ Z₁₃ : C} {u₁₂ : X₁ X₂} {u₂₃ : X₂ X₃} {u₁₃ : X₁ X₃} {comm : CategoryStruct.comp u₁₂ u₂₃ = u₁₃} {v₁₂ : X₂ Z₁₂} {w₁₂ : Z₁₂ (shiftFunctor C 1).obj X₁} {h₁₂ : Pretriangulated.Triangle.mk u₁₂ v₁₂ w₁₂ Pretriangulated.distinguishedTriangles} {v₂₃ : X₃ Z₂₃} {w₂₃ : Z₂₃ (shiftFunctor C 1).obj X₂} {h₂₃ : Pretriangulated.Triangle.mk u₂₃ v₂₃ w₂₃ Pretriangulated.distinguishedTriangles} {v₁₃ : X₃ Z₁₃} {w₁₃ : Z₁₃ (shiftFunctor C 1).obj X₁} {h₁₃ : Pretriangulated.Triangle.mk u₁₃ v₁₃ w₁₃ Pretriangulated.distinguishedTriangles} (h : Octahedron comm h₁₂ h₂₃ h₁₃) (F : Functor C D) [F.CommShift ] [F.IsTriangulated] :
                    (h.map F).m₃ = F.map h.m₃

                    If F : C ⥤ D is a triangulated functor from a triangulated category, then D is also triangulated if tuples of composables arrows in D can be lifted to C.