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Mathlib.Algebra.Homology.ShortComplex.HomologicalComplex

The short complexes attached to homological complexes #

In this file, we define a functor shortComplexFunctor C c i : HomologicalComplex C c ⥤ ShortComplex C. By definition, the image of a homological complex K by this functor is the short complex K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i).

The homology K.homology i of a homological complex K in degree i is defined as the homology of the short complex (shortComplexFunctor C c i).obj K, which can be abbreviated as K.sc i.

@[simp]
theorem HomologicalComplex.shortComplexFunctor'_map_τ₁ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) :
∀ {X Y : HomologicalComplex C c} (f : X Y), ((HomologicalComplex.shortComplexFunctor' C c i j k).map f).τ₁ = f.f i
@[simp]
theorem HomologicalComplex.shortComplexFunctor'_map_τ₃ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) :
∀ {X Y : HomologicalComplex C c} (f : X Y), ((HomologicalComplex.shortComplexFunctor' C c i j k).map f).τ₃ = f.f k
@[simp]
theorem HomologicalComplex.shortComplexFunctor'_map_τ₂ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) :
∀ {X Y : HomologicalComplex C c} (f : X Y), ((HomologicalComplex.shortComplexFunctor' C c i j k).map f).τ₂ = f.f j

The functor HomologicalComplex C c ⥤ ShortComplex C which sends a homological complex K to the short complex K.X i ⟶ K.X j ⟶ K.X k for arbitrary indices i, j and k.

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    The functor HomologicalComplex C c ⥤ ShortComplex C which sends a homological complex K to the short complex K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i).

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      theorem HomologicalComplex.natIsoSc'_hom_app_τ₁ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).hom.app X).τ₁ = (HomologicalComplex.XIsoOfEq X hi).hom
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      theorem HomologicalComplex.natIsoSc'_inv_app_τ₃ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).inv.app X).τ₃ = (HomologicalComplex.XIsoOfEq X hk).inv
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      theorem HomologicalComplex.natIsoSc'_inv_app_τ₂ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).inv.app X).τ₂ = CategoryTheory.CategoryStruct.id (X.X j)
      @[simp]
      theorem HomologicalComplex.natIsoSc'_inv_app_τ₁ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).inv.app X).τ₁ = (HomologicalComplex.XIsoOfEq X hi).inv
      @[simp]
      theorem HomologicalComplex.natIsoSc'_hom_app_τ₂ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).hom.app X).τ₂ = CategoryTheory.CategoryStruct.id (X.X j)
      @[simp]
      theorem HomologicalComplex.natIsoSc'_hom_app_τ₃ (C : Type u_1) [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} (c : ComplexShape ι) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) (X : HomologicalComplex C c) :
      ((HomologicalComplex.natIsoSc' C c i j k hi hk).hom.app X).τ₃ = (HomologicalComplex.XIsoOfEq X hk).hom

      The natural isomorphism shortComplexFunctor C c j ≅ shortComplexFunctor' C c i j k when c.prev j = i and c.next j = k.

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        The short complex K.X i ⟶ K.X j ⟶ K.X k for arbitrary indices i, j and k.

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          The short complex K.X (c.prev i) ⟶ K.X i ⟶ K.X (c.next i).

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            noncomputable abbrev HomologicalComplex.isoSc' {C : Type u_1} [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} {c : ComplexShape ι} (K : HomologicalComplex C c) (i : ι) (j : ι) (k : ι) (hi : ComplexShape.prev c j = i) (hk : ComplexShape.next c j = k) :

            The canonical isomorphism K.sc j ≅ K.sc' i j k when c.prev j = i and c.next j = k.

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              A homological complex K has homology in degree i if the associated short complex K.sc i has.

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                The homology in degree i of a homological complex.

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                  The cycles in degree i of a homological complex.

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                    The inclusion of the cycles of a homological complex.

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                      The morphism to K.cycles i that is induced by a "cycle", i.e. a morphism to K.X i whose postcomposition with the differential is zero.

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                        noncomputable def HomologicalComplex.liftCycles' {C : Type u_1} [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} {c : ComplexShape ι} (K : HomologicalComplex C c) {i : ι} [HomologicalComplex.HasHomology K i] {A : C} (k : A K.X i) (j : ι) (hj : c.Rel i j) (hk : CategoryTheory.CategoryStruct.comp k (K.d i j) = 0) :

                        The morphism to K.cycles i that is induced by a "cycle", i.e. a morphism to K.X i whose postcomposition with the differential is zero.

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                          The map K.X i ⟶ K.cycles j induced by the differential K.d i j.

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                            K.homology j is the cokernel of K.toCycles i j : K.X i ⟶ K.cycles j when c.prev j = i.

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                              The opcycles in degree i of a homological complex.

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                                The morphism from K.opcycles i that is induced by an "opcycle", i.e. a morphism from K.X i whose precomposition with the differential is zero.

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                                  noncomputable def HomologicalComplex.descOpcycles' {C : Type u_1} [CategoryTheory.Category.{u_3, u_1} C] [CategoryTheory.Limits.HasZeroMorphisms C] {ι : Type u_2} {c : ComplexShape ι} (K : HomologicalComplex C c) {i : ι} [HomologicalComplex.HasHomology K i] {A : C} (k : K.X i A) (j : ι) (hj : c.Rel j i) (hk : CategoryTheory.CategoryStruct.comp (K.d j i) k = 0) :

                                  The morphism from K.opcycles i that is induced by an "opcycle", i.e. a morphism from K.X i whose precomposition with the differential is zero.

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                                    The map K.opcycles i ⟶ K.X j induced by the differential K.d i j.

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                                      K.opcycles j is the cokernel of K.d i j when c.prev j = i.

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                                        The ith homology functor HomologicalComplex C c ⥤ C.

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                                          The homology functor to graded objects.

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                                            The ith cycles functor HomologicalComplex C c ⥤ C.

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                                              The ith opcycles functor HomologicalComplex C c ⥤ C.

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                                                The natural isomorphism K.homology j ≅ (K.sc' i j k).homology for all homological complexes K when c.prev j = i and c.next j = k.

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                                                  The canonical isomorphism K.cycles i ≅ K.X i when the differential from i is zero.

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                                                    The canonical isomorphism K.homology i ≅ K.opcycles i when the differential from i is zero.

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                                                      The canonical isomorphism K.X j ≅ K.opCycles j when the differential to j is zero.

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                                                        The canonical isomorphism K.cycles j ≅ K.homology j when the differential to j is zero.

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                                                          A homological complex K is exact at i if the short complex K.sc i is exact.

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                                                            The cycles of a homological complex in degree j can be computed by specifying a choice of c.prev j and c.next j.

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                                                              The homology of a homological complex in degree j can be computed by specifying a choice of c.prev j and c.next j.

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                                                                The opcycles of a homological complex in degree j can be computed by specifying a choice of c.prev j and c.next j.

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