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Mathlib.Algebra.Homology.ShortComplex.PreservesHomology

Functors which preserves homology #

If F : C ⥤ D is a functor between categories with zero morphisms, we shall say that F preserves homology when F preserves both kernels and cokernels. This typeclass is named [F.PreservesHomology], and is automatically satisfied when F preserves both finite limits and finite colimits.

If S : ShortComplex C and [F.PreservesHomology], then there is an isomorphism S.mapHomologyIso F : (S.map F).homology ≅ F.obj S.homology, which is part of the natural isomorphism homologyFunctorIso F between the functors F.mapShortComplex ⋙ homologyFunctor D and homologyFunctor C ⋙ F.

A functor preserves homology when it preserves both kernels and cokernels.

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    A left homology data h of a short complex S is preserved by a functor F is F preserves the kernel of S.g : S.X₂ ⟶ S.X₃ and the cokernel of h.f' : S.X₁ ⟶ h.K.

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      When a left homology data is preserved by a functor F, this functor preserves the kernel of S.g : S.X₂ ⟶ S.X₃.

      When a left homology data h is preserved by a functor F, this functor preserves the cokernel of h.f' : S.X₁ ⟶ h.K.

      When a left homology data h of a short complex S is preserved by a functor F, this is the induced left homology data h.map F for the short complex S.map F.

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          noncomputable def CategoryTheory.ShortComplex.LeftHomologyMapData.map {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
          LeftHomologyMapData (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F)

          Given a left homology map data ψ : LeftHomologyMapData φ h₁ h₂ such that both left homology data h₁ and h₂ are preserved by a functor F, this is the induced left homology map data for the morphism F.mapShortComplex.map φ.

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              theorem CategoryTheory.ShortComplex.LeftHomologyMapData.map_φH {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
              (ψ.map F).φH = F.map ψ.φH
              @[simp]
              theorem CategoryTheory.ShortComplex.LeftHomologyMapData.map_φK {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
              (ψ.map F).φK = F.map ψ.φK

              A right homology data h of a short complex S is preserved by a functor F is F preserves the cokernel of S.f : S.X₁ ⟶ S.X₂ and the kernel of h.g' : h.Q ⟶ S.X₃.

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                When a right homology data is preserved by a functor F, this functor preserves the cokernel of S.f : S.X₁ ⟶ S.X₂.

                When a right homology data h is preserved by a functor F, this functor preserves the kernel of h.g' : h.Q ⟶ S.X₃.

                When a right homology data h of a short complex S is preserved by a functor F, this is the induced right homology data h.map F for the short complex S.map F.

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                    noncomputable def CategoryTheory.ShortComplex.RightHomologyMapData.map {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData} (ψ : RightHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :

                    Given a right homology map data ψ : RightHomologyMapData φ h₁ h₂ such that both right homology data h₁ and h₂ are preserved by a functor F, this is the induced right homology map data for the morphism F.mapShortComplex.map φ.

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                        theorem CategoryTheory.ShortComplex.RightHomologyMapData.map_φQ {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData} (ψ : RightHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
                        (ψ.map F).φQ = F.map ψ.φQ
                        @[simp]
                        theorem CategoryTheory.ShortComplex.RightHomologyMapData.map_φH {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.RightHomologyData} {h₂ : S₂.RightHomologyData} (ψ : RightHomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.IsPreservedBy F] [h₂.IsPreservedBy F] :
                        (ψ.map F).φH = F.map ψ.φH

                        When a homology data h of a short complex S is such that both h.left and h.right are preserved by a functor F, this is the induced homology data h.map F for the short complex S.map F.

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                            noncomputable def CategoryTheory.ShortComplex.HomologyMapData.map {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.HomologyData} {h₂ : S₂.HomologyData} (ψ : HomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.left.IsPreservedBy F] [h₁.right.IsPreservedBy F] [h₂.left.IsPreservedBy F] [h₂.right.IsPreservedBy F] :
                            HomologyMapData (F.mapShortComplex.map φ) (h₁.map F) (h₂.map F)

                            Given a homology map data ψ : HomologyMapData φ h₁ h₂ such that h₁.left, h₁.right, h₂.left and h₂.right are all preserved by a functor F, this is the induced homology map data for the morphism F.mapShortComplex.map φ.

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                                theorem CategoryTheory.ShortComplex.HomologyMapData.map_left {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.HomologyData} {h₂ : S₂.HomologyData} (ψ : HomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.left.IsPreservedBy F] [h₁.right.IsPreservedBy F] [h₂.left.IsPreservedBy F] [h₂.right.IsPreservedBy F] :
                                (ψ.map F).left = ψ.left.map F
                                @[simp]
                                theorem CategoryTheory.ShortComplex.HomologyMapData.map_right {C : Type u_1} {D : Type u_2} [Category.{u_3, u_1} C] [Category.{u_4, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.HomologyData} {h₂ : S₂.HomologyData} (ψ : HomologyMapData φ h₁ h₂) (F : Functor C D) [F.PreservesZeroMorphisms] [h₁.left.IsPreservedBy F] [h₁.right.IsPreservedBy F] [h₂.left.IsPreservedBy F] [h₂.right.IsPreservedBy F] :
                                (ψ.map F).right = ψ.right.map F

                                A functor preserves the left homology of a short complex S if it preserves all the left homology data of S.

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                                  A functor preserves the right homology of a short complex S if it preserves all the right homology data of S.

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                                    If a functor preserves a certain left homology data of a short complex S, then it preserves the left homology of S.

                                    If a functor preserves a certain right homology data of a short complex S, then it preserves the right homology of S.

                                    theorem CategoryTheory.ShortComplex.LeftHomologyData.map_cyclesMap' {C : Type u_1} {D : Type u_2} [Category.{u_4, u_1} C] [Category.{u_3, u_2} D] [Limits.HasZeroMorphisms C] [Limits.HasZeroMorphisms D] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hl₁ : S₁.LeftHomologyData) (hl₂ : S₂.LeftHomologyData) (F : Functor C D) [F.PreservesZeroMorphisms] [hl₁.IsPreservedBy F] [hl₂.IsPreservedBy F] :
                                    F.map (cyclesMap' φ hl₁ hl₂) = cyclesMap' (F.mapShortComplex.map φ) (hl₁.map F) (hl₂.map F)

                                    When a functor F preserves the left homology of a short complex S, this is the canonical isomorphism (S.map F).cycles ≅ F.obj S.cycles.

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                                        When a functor F preserves the left homology of a short complex S, this is the canonical isomorphism (S.map F).leftHomology ≅ F.obj S.leftHomology.

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                                            When a functor F preserves the right homology of a short complex S, this is the canonical isomorphism (S.map F).opcycles ≅ F.obj S.opcycles.

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                                                When a functor F preserves the right homology of a short complex S, this is the canonical isomorphism (S.map F).rightHomology ≅ F.obj S.rightHomology.

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                                                    When a functor F preserves the left homology of a short complex S, this is the canonical isomorphism (S.map F).homology ≅ F.obj S.homology.

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                                                        When a functor F preserves the right homology of a short complex S, this is the canonical isomorphism (S.map F).homology ≅ F.obj S.homology.

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                                                            Given a natural transformation τ : F ⟶ G between functors C ⥤ D which preserve the left homology of a short complex S, and a left homology data for S, this is the left homology map data for the morphism S.mapNatTrans τ obtained by evaluating τ.

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                                                                Given a natural transformation τ : F ⟶ G between functors C ⥤ D which preserve the right homology of a short complex S, and a right homology data for S, this is the right homology map data for the morphism S.mapNatTrans τ obtained by evaluating τ.

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                                                                    Given a natural transformation τ : F ⟶ G between functors C ⥤ D which preserve the homology of a short complex S, and a homology data for S, this is the homology map data for the morphism S.mapNatTrans τ obtained by evaluating τ.

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                                                                        The natural isomorphism F.mapShortComplex ⋙ cyclesFunctor D ≅ cyclesFunctor C ⋙ F for a functor F : C ⥤ D which preserves homology.

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                                                                            The natural isomorphism F.mapShortComplex ⋙ leftHomologyFunctor D ≅ leftHomologyFunctor C ⋙ F for a functor F : C ⥤ D which preserves homology.

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                                                                                The natural isomorphism F.mapShortComplex ⋙ opcyclesFunctor D ≅ opcyclesFunctor C ⋙ F for a functor F : C ⥤ D which preserves homology.

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                                                                                    The natural isomorphism F.mapShortComplex ⋙ rightHomologyFunctor D ≅ rightHomologyFunctor C ⋙ F for a functor F : C ⥤ D which preserves homology.

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                                                                                        The natural isomorphism F.mapShortComplex ⋙ homologyFunctor D ≅ homologyFunctor C ⋙ F for a functor F : C ⥤ D which preserves homology.

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                                                                                            If a short complex S is such that S.f = 0 and that the kernel of S.g is preserved by a functor F, then F preserves the left homology of S.

                                                                                            If a short complex S is such that S.g = 0 and that the cokernel of S.f is preserved by a functor F, then F preserves the right homology of S.

                                                                                            If a short complex S is such that S.g = 0 and that the cokernel of S.f is preserved by a functor F, then F preserves the left homology of S.

                                                                                            If a short complex S is such that S.f = 0 and that the kernel of S.g is preserved by a functor F, then F preserves the right homology of S.