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Mathlib.Algebra.Homology.ShortComplex.LeftHomology

Left Homology of short complexes #

Given a short complex S : ShortComplex C, which consists of two composable maps f : X₁ ⟶ X₂ and g : X₂ ⟶ X₃ such that f ≫ g = 0, we shall define here the "left homology" S.leftHomology of S. For this, we introduce the notion of "left homology data". Such an h : S.LeftHomologyData consists of the data of morphisms i : K ⟶ X₂ and π : KH such that i identifies K with the kernel of g : X₂ ⟶ X₃, and that π identifies H with the cokernel of the induced map f' : X₁ ⟶ K.

When such a S.LeftHomologyData exists, we shall say that [S.HasLeftHomology] and we define S.leftHomology to be the H field of a chosen left homology data. Similarly, we define S.cycles to be the K field.

The dual notion is defined in RightHomologyData.lean. In Homology.lean, when S has two compatible left and right homology data (i.e. they give the same H up to a canonical isomorphism), we shall define [S.HasHomology] and S.homology.

A left homology data for a short complex S consists of morphisms i : K ⟶ S.X₂ and π : KH such that i identifies K to the kernel of g : S.X₂ ⟶ S.X₃, and that π identifies H to the cokernel of the induced map f' : S.X₁ ⟶ K

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    The chosen kernels and cokernels of the limits API give a LeftHomologyData

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        Any morphism k : A ⟶ S.X₂ that is a cycle (i.e. k ≫ S.g = 0) lifts to a morphism A ⟶ K

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            The (left) homology class A ⟶ H attached to a cycle k : A ⟶ S.X₂

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                Given h : LeftHomologyData S, this is morphism S.X₁ ⟶ h.K induced by S.f : S.X₁ ⟶ S.X₂ and the fact that h.K is a kernel of S.g : S.X₂ ⟶ S.X₃.

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                    For h : S.LeftHomologyData, this is a restatement of h., saying that π : h.K ⟶ h.H is a cokernel of h.f' : S.X₁ ⟶ h.K.

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                        The morphism H ⟶ A induced by a morphism k : K ⟶ A such that f' ≫ k = 0

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                            When the second map S.g is zero, this is the left homology data on S given by any colimit cokernel cofork of S.f

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                                When the second map S.g is zero, this is the left homology data on S given by the chosen cokernel S.f

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                                    When the first map S.f is zero, this is the left homology data on S given by any limit kernel fork of S.g

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                                        When the first map S.f is zero, this is the left homology data on S given by the chosen kernel S.g

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                                            When both S.f and S.g are zero, the middle object S.X₂ gives a left homology data on S

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                                                Given a left homology data h of a short complex S, we can construct another left homology data by choosing another kernel and cokernel that are isomorphic to the ones in h.

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                                                    theorem CategoryTheory.ShortComplex.LeftHomologyData.copy_H {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S : ShortComplex C} (h : S.LeftHomologyData) {K' H' : C} (eK : K' h.K) (eH : H' h.H) :
                                                    (h.copy eK eH).H = H'
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                                                    theorem CategoryTheory.ShortComplex.LeftHomologyData.copy_K {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S : ShortComplex C} (h : S.LeftHomologyData) {K' H' : C} (eK : K' h.K) (eH : H' h.H) :
                                                    (h.copy eK eH).K = K'

                                                    A short complex S has left homology when there exists a S.LeftHomologyData

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                                                      A chosen S.LeftHomologyData for a short complex S that has left homology

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                                                          instance CategoryTheory.ShortComplex.HasLeftHomology.of_hasCokernel {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {X Y : C} (f : X Y) (Z : C) [Limits.HasCokernel f] :
                                                          { X₁ := X, X₂ := Y, X₃ := Z, f := f, g := 0, zero := }.HasLeftHomology
                                                          instance CategoryTheory.ShortComplex.HasLeftHomology.of_hasKernel {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {Y Z : C} (g : Y Z) (X : C) [Limits.HasKernel g] :
                                                          { X₁ := X, X₂ := Y, X₃ := Z, f := 0, g := g, zero := }.HasLeftHomology
                                                          instance CategoryTheory.ShortComplex.HasLeftHomology.of_zeros {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] (X Y Z : C) :
                                                          { X₁ := X, X₂ := Y, X₃ := Z, f := 0, g := 0, zero := }.HasLeftHomology
                                                          structure CategoryTheory.ShortComplex.LeftHomologyMapData {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                          Type v_1

                                                          Given left homology data h₁ and h₂ for two short complexes S₁ and S₂, a LeftHomologyMapData for a morphism φ : S₁ ⟶ S₂ consists of a description of the induced morphisms on the K (cycles) and H (left homology) fields of h₁ and h₂.

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                                                            commutation with i

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                                                            commutation with f'

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                                                            theorem CategoryTheory.ShortComplex.LeftHomologyMapData.commπ_assoc {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} (self : LeftHomologyMapData φ h₁ h₂) {Z : C} (h : h₂.H Z) :

                                                            commutation with π

                                                            The left homology map data associated to the zero morphism between two short complexes.

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                                                                The left homology map data associated to the identity morphism of a short complex.

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                                                                    def CategoryTheory.ShortComplex.LeftHomologyMapData.comp {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} {φ : S₁ S₂} {φ' : S₂ S₃} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {h₃ : S₃.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (ψ' : LeftHomologyMapData φ' h₂ h₃) :

                                                                    The composition of left homology map data.

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                                                                        theorem CategoryTheory.ShortComplex.LeftHomologyMapData.comp_φK {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} {φ : S₁ S₂} {φ' : S₂ S₃} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {h₃ : S₃.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (ψ' : LeftHomologyMapData φ' h₂ h₃) :
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                                                                        theorem CategoryTheory.ShortComplex.LeftHomologyMapData.comp_φH {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} {φ : S₁ S₂} {φ' : S₂ S₃} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {h₃ : S₃.LeftHomologyData} (ψ : LeftHomologyMapData φ h₁ h₂) (ψ' : LeftHomologyMapData φ' h₂ h₃) :
                                                                        theorem CategoryTheory.ShortComplex.LeftHomologyMapData.congr_φH {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {γ₁ γ₂ : LeftHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) :
                                                                        γ₁.φH = γ₂.φH
                                                                        theorem CategoryTheory.ShortComplex.LeftHomologyMapData.congr_φK {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} {φ : S₁ S₂} {h₁ : S₁.LeftHomologyData} {h₂ : S₂.LeftHomologyData} {γ₁ γ₂ : LeftHomologyMapData φ h₁ h₂} (eq : γ₁ = γ₂) :
                                                                        γ₁.φK = γ₂.φK
                                                                        def CategoryTheory.ShortComplex.LeftHomologyMapData.ofZeros {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (hg₁ : S₁.g = 0) (hf₂ : S₂.f = 0) (hg₂ : S₂.g = 0) :

                                                                        When S₁.f, S₁.g, S₂.f and S₂.g are all zero, the action on left homology of a morphism φ : S₁ ⟶ S₂ is given by the action φ.τ₂ on the middle objects.

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                                                                            theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofZeros_φK {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (hg₁ : S₁.g = 0) (hf₂ : S₂.f = 0) (hg₂ : S₂.g = 0) :
                                                                            (ofZeros φ hf₁ hg₁ hf₂ hg₂).φK = φ.τ₂
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                                                                            theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofZeros_φH {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (hg₁ : S₁.g = 0) (hf₂ : S₂.f = 0) (hg₂ : S₂.g = 0) :
                                                                            (ofZeros φ hf₁ hg₁ hf₂ hg₂).φH = φ.τ₂
                                                                            def CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsColimitCokernelCofork {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hg₁ : S₁.g = 0) (c₁ : Limits.CokernelCofork S₁.f) (hc₁ : Limits.IsColimit c₁) (hg₂ : S₂.g = 0) (c₂ : Limits.CokernelCofork S₂.f) (hc₂ : Limits.IsColimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp φ.τ₂ (Limits.Cofork.π c₂) = CategoryStruct.comp (Limits.Cofork.π c₁) f) :

                                                                            When S₁.g and S₂.g are zero and we have chosen colimit cokernel coforks c₁ and c₂ for S₁.f and S₂.f respectively, the action on left homology of a morphism φ : S₁ ⟶ S₂ of short complexes is given by the unique morphism f : c₁.pt ⟶ c₂.pt such that φ.τ₂ ≫ c₂.π = c₁.π ≫ f.

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                                                                                theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsColimitCokernelCofork_φH {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hg₁ : S₁.g = 0) (c₁ : Limits.CokernelCofork S₁.f) (hc₁ : Limits.IsColimit c₁) (hg₂ : S₂.g = 0) (c₂ : Limits.CokernelCofork S₂.f) (hc₂ : Limits.IsColimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp φ.τ₂ (Limits.Cofork.π c₂) = CategoryStruct.comp (Limits.Cofork.π c₁) f) :
                                                                                (ofIsColimitCokernelCofork φ hg₁ c₁ hc₁ hg₂ c₂ hc₂ f comm).φH = f
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                                                                                theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsColimitCokernelCofork_φK {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hg₁ : S₁.g = 0) (c₁ : Limits.CokernelCofork S₁.f) (hc₁ : Limits.IsColimit c₁) (hg₂ : S₂.g = 0) (c₂ : Limits.CokernelCofork S₂.f) (hc₂ : Limits.IsColimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp φ.τ₂ (Limits.Cofork.π c₂) = CategoryStruct.comp (Limits.Cofork.π c₁) f) :
                                                                                (ofIsColimitCokernelCofork φ hg₁ c₁ hc₁ hg₂ c₂ hc₂ f comm).φK = φ.τ₂
                                                                                def CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsLimitKernelFork {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (c₁ : Limits.KernelFork S₁.g) (hc₁ : Limits.IsLimit c₁) (hf₂ : S₂.f = 0) (c₂ : Limits.KernelFork S₂.g) (hc₂ : Limits.IsLimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp (Limits.Fork.ι c₁) φ.τ₂ = CategoryStruct.comp f (Limits.Fork.ι c₂)) :

                                                                                When S₁.f and S₂.f are zero and we have chosen limit kernel forks c₁ and c₂ for S₁.g and S₂.g respectively, the action on left homology of a morphism φ : S₁ ⟶ S₂ of short complexes is given by the unique morphism f : c₁.pt ⟶ c₂.pt such that c₁.ι ≫ φ.τ₂ = f ≫ c₂.ι.

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                                                                                    theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsLimitKernelFork_φH {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (c₁ : Limits.KernelFork S₁.g) (hc₁ : Limits.IsLimit c₁) (hf₂ : S₂.f = 0) (c₂ : Limits.KernelFork S₂.g) (hc₂ : Limits.IsLimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp (Limits.Fork.ι c₁) φ.τ₂ = CategoryStruct.comp f (Limits.Fork.ι c₂)) :
                                                                                    (ofIsLimitKernelFork φ hf₁ c₁ hc₁ hf₂ c₂ hc₂ f comm).φH = f
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                                                                                    theorem CategoryTheory.ShortComplex.LeftHomologyMapData.ofIsLimitKernelFork_φK {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (hf₁ : S₁.f = 0) (c₁ : Limits.KernelFork S₁.g) (hc₁ : Limits.IsLimit c₁) (hf₂ : S₂.f = 0) (c₂ : Limits.KernelFork S₂.g) (hc₂ : Limits.IsLimit c₂) (f : c₁.pt c₂.pt) (comm : CategoryStruct.comp (Limits.Fork.ι c₁) φ.τ₂ = CategoryStruct.comp f (Limits.Fork.ι c₂)) :
                                                                                    (ofIsLimitKernelFork φ hf₁ c₁ hc₁ hf₂ c₂ hc₂ f comm).φK = f

                                                                                    When both maps S.f and S.g of a short complex S are zero, this is the left homology map data (for the identity of S) which relates the left homology data ofZeros and ofIsColimitCokernelCofork.

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                                                                                        When both maps S.f and S.g of a short complex S are zero, this is the left homology map data (for the identity of S) which relates the left homology data LeftHomologyData.ofIsLimitKernelFork and ofZeros .

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                                                                                            The left homology of a short complex, given by the H field of a chosen left homology data.

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                                                                                                The cycles of a short complex, given by the K field of a chosen left homology data.

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                                                                                                    The "homology class" map S.cycles ⟶ S.leftHomology.

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                                                                                                        The inclusion S.cycles ⟶ S.X₂.

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                                                                                                            The "boundaries" map S.X₁ ⟶ S.cycles. (Note that in this homology API, we make no use of the "image" of this morphism, which under some categorical assumptions would be a subobject of S.X₂ contained in S.cycles.)

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                                                                                                                When S.g = 0, this is the canonical isomorphism S.cycles ≅ S.X₂ induced by S.iCycles.

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                                                                                                                    When S.f = 0, this is the canonical isomorphism S.cycles ≅ S.leftHomology induced by S.leftHomologyπ.

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                                                                                                                        The (unique) left homology map data associated to a morphism of short complexes that are both equipped with left homology data.

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                                                                                                                            def CategoryTheory.ShortComplex.leftHomologyMap' {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                            h₁.H h₂.H

                                                                                                                            Given a morphism φ : S₁ ⟶ S₂ of short complexes and left homology data h₁ and h₂ for S₁ and S₂ respectively, this is the induced left homology map h₁.H ⟶ h₁.H.

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                                                                                                                                def CategoryTheory.ShortComplex.cyclesMap' {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                                h₁.K h₂.K

                                                                                                                                Given a morphism φ : S₁ ⟶ S₂ of short complexes and left homology data h₁ and h₂ for S₁ and S₂ respectively, this is the induced morphism h₁.K ⟶ h₁.K on cycles.

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                                                                                                                                    theorem CategoryTheory.ShortComplex.cyclesMap'_i {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
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                                                                                                                                    theorem CategoryTheory.ShortComplex.cyclesMap'_i_assoc {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) {Z : C} (h : S₂.X₂ Z) :
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                                                                                                                                    theorem CategoryTheory.ShortComplex.f'_cyclesMap'_assoc {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) {Z : C} (h : h₂.K Z) :

                                                                                                                                    The (left) homology map S₁.leftHomology ⟶ S₂.leftHomology induced by a morphism S₁ ⟶ S₂ of short complexes.

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                                                                                                                                        noncomputable def CategoryTheory.ShortComplex.cyclesMap {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} [S₁.HasLeftHomology] [S₂.HasLeftHomology] (φ : S₁ S₂) :
                                                                                                                                        S₁.cycles S₂.cycles

                                                                                                                                        The morphism S₁.cycles ⟶ S₂.cycles induced by a morphism S₁ ⟶ S₂ of short complexes.

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                                                                                                                                            theorem CategoryTheory.ShortComplex.leftHomologyMap'_comp {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} (φ₁ : S₁ S₂) (φ₂ : S₂ S₃) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) (h₃ : S₃.LeftHomologyData) :
                                                                                                                                            leftHomologyMap' (CategoryStruct.comp φ₁ φ₂) h₁ h₃ = CategoryStruct.comp (leftHomologyMap' φ₁ h₁ h₂) (leftHomologyMap' φ₂ h₂ h₃)
                                                                                                                                            theorem CategoryTheory.ShortComplex.leftHomologyMap'_comp_assoc {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} (φ₁ : S₁ S₂) (φ₂ : S₂ S₃) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) (h₃ : S₃.LeftHomologyData) {Z : C} (h : h₃.H Z) :
                                                                                                                                            theorem CategoryTheory.ShortComplex.cyclesMap'_comp {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} (φ₁ : S₁ S₂) (φ₂ : S₂ S₃) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) (h₃ : S₃.LeftHomologyData) :
                                                                                                                                            cyclesMap' (CategoryStruct.comp φ₁ φ₂) h₁ h₃ = CategoryStruct.comp (cyclesMap' φ₁ h₁ h₂) (cyclesMap' φ₂ h₂ h₃)
                                                                                                                                            theorem CategoryTheory.ShortComplex.cyclesMap'_comp_assoc {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} (φ₁ : S₁ S₂) (φ₂ : S₂ S₃) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) (h₃ : S₃.LeftHomologyData) {Z : C} (h : h₃.K Z) :
                                                                                                                                            CategoryStruct.comp (cyclesMap' (CategoryStruct.comp φ₁ φ₂) h₁ h₃) h = CategoryStruct.comp (cyclesMap' φ₁ h₁ h₂) (CategoryStruct.comp (cyclesMap' φ₂ h₂ h₃) h)
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                                                                                                                                            theorem CategoryTheory.ShortComplex.cyclesMap_comp {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ S₃ : ShortComplex C} [S₁.HasLeftHomology] [S₂.HasLeftHomology] [S₃.HasLeftHomology] (φ₁ : S₁ S₂) (φ₂ : S₂ S₃) :
                                                                                                                                            def CategoryTheory.ShortComplex.leftHomologyMapIso' {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (e : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                                            h₁.H h₂.H

                                                                                                                                            An isomorphism of short complexes S₁ ≅ S₂ induces an isomorphism on the H fields of left homology data of S₁ and S₂.

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                                                                                                                                                def CategoryTheory.ShortComplex.cyclesMapIso' {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (e : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                                                h₁.K h₂.K

                                                                                                                                                An isomorphism of short complexes S₁ ≅ S₂ induces an isomorphism on the K fields of left homology data of S₁ and S₂.

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                                                                                                                                                    theorem CategoryTheory.ShortComplex.cyclesMapIso'_hom {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (e : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                                                    (cyclesMapIso' e h₁ h₂).hom = cyclesMap' e.hom h₁ h₂
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                                                                                                                                                    theorem CategoryTheory.ShortComplex.cyclesMapIso'_inv {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (e : S₁ S₂) (h₁ : S₁.LeftHomologyData) (h₂ : S₂.LeftHomologyData) :
                                                                                                                                                    (cyclesMapIso' e h₁ h₂).inv = cyclesMap' e.inv h₂ h₁

                                                                                                                                                    The isomorphism S₁.leftHomology ≅ S₂.leftHomology induced by an isomorphism of short complexes S₁ ≅ S₂.

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                                                                                                                                                        noncomputable def CategoryTheory.ShortComplex.cyclesMapIso {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (e : S₁ S₂) [S₁.HasLeftHomology] [S₂.HasLeftHomology] :
                                                                                                                                                        S₁.cycles S₂.cycles

                                                                                                                                                        The isomorphism S₁.cycles ≅ S₂.cycles induced by an isomorphism of short complexes S₁ ≅ S₂.

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                                                                                                                                                            The isomorphism S.leftHomology ≅ h.H induced by a left homology data h for a short complex S.

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                                                                                                                                                                The isomorphism S.cycles ≅ h.K induced by a left homology data h for a short complex S.

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                                                                                                                                                                    The left homology functor ShortComplex C ⥤ C, where the left homology of a short complex S is understood as a cokernel of the obvious map S.toCycles : S.X₁ ⟶ S.cycles where S.cycles is a kernel of S.g : S.X₂ ⟶ S.X₃.

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                                                                                                                                                                        The cycles functor ShortComplex C ⥤ C which sends a short complex S to S.cycles which is a kernel of S.g : S.X₂ ⟶ S.X₃.

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                                                                                                                                                                            The natural transformation S.cycles ⟶ S.leftHomology for all short complexes S.

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                                                                                                                                                                                The natural transformation S.cycles ⟶ S.X₂ for all short complexes S.

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                                                                                                                                                                                    The natural transformation S.X₁ ⟶ S.cycles for all short complexes S.

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                                                                                                                                                                                        If φ : S₁ ⟶ S₂ is a morphism of short complexes such that φ.τ₁ is epi, φ.τ₂ is an iso and φ.τ₃ is mono, then a left homology data for S₁ induces a left homology data for S₂ with the same K and H fields. The inverse construction is ofEpiOfIsIsoOfMono'.

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                                                                                                                                                                                            If φ : S₁ ⟶ S₂ is a morphism of short complexes such that φ.τ₁ is epi, φ.τ₂ is an iso and φ.τ₃ is mono, then a left homology data for S₂ induces a left homology data for S₁ with the same K and H fields. The inverse construction is ofEpiOfIsIsoOfMono.

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                                                                                                                                                                                                If e : S₁ ≅ S₂ is an isomorphism of short complexes and h₁ : LeftHomologyData S₁, this is the left homology data for S₂ deduced from the isomorphism.

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                                                                                                                                                                                                    This left homology map data expresses compatibilities of the left homology data constructed by LeftHomologyData.ofEpiOfIsIsoOfMono

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                                                                                                                                                                                                        This left homology map data expresses compatibilities of the left homology data constructed by LeftHomologyData.ofEpiOfIsIsoOfMono'

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                                                                                                                                                                                                            If a morphism of short complexes φ : S₁ ⟶ S₂ is such that φ.τ₁ is epi, φ.τ₂ is an iso, and φ.τ₃ is mono, then the induced morphism on left homology is an isomorphism.

                                                                                                                                                                                                            A morphism k : A ⟶ S.X₂ such that k ≫ S.g = 0 lifts to a morphism A ⟶ S.cycles.

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                                                                                                                                                                                                                Via S.iCycles : S.cycles ⟶ S.X₂, the object S.cycles identifies to the kernel of S.g : S.X₂ ⟶ S.X₃.

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                                                                                                                                                                                                                    The canonical isomorphism S.cycles ≅ kernel S.g.

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                                                                                                                                                                                                                        The isomorphism from the point of a limit kernel fork of S.g to S.cycles.

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                                                                                                                                                                                                                            The morphism A ⟶ S.leftHomology obtained from a morphism k : A ⟶ S.X₂ such that k ≫ S.g = 0.

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                                                                                                                                                                                                                                Via S.leftHomologyπ : S.cycles ⟶ S.leftHomology, the object S.leftHomology identifies to the cokernel of S.toCycles : S.X₁ ⟶ S.cycles.

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                                                                                                                                                                                                                                    The left homology of a short complex S identifies to the cokernel of the canonical morphism S.X₁ ⟶ kernel S.g.

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                                                                                                                                                                                                                                        The following lemmas and instance gives a sufficient condition for a morphism of short complexes to induce an isomorphism on cycles.

                                                                                                                                                                                                                                        theorem CategoryTheory.ShortComplex.isIso_cyclesMap'_of_isIso_of_mono {C : Type u_1} [Category.{v_1, u_1} C] [Limits.HasZeroMorphisms C] {S₁ S₂ : ShortComplex C} (φ : S₁ S₂) (h₂ : IsIso φ.τ₂) (h₃ : Mono φ.τ₃) (h₁ : S₁.LeftHomologyData) (h₂✝ : S₂.LeftHomologyData) :
                                                                                                                                                                                                                                        IsIso (cyclesMap' φ h₁ h₂✝)