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Mathlib.Algebra.Homology.DerivedCategory.HomologySequence

The homology sequence #

In this file, we construct homologyFunctor C n : DerivedCategory C ⥤ C for all n : ℤ, show that they are homological functors which form a shift sequence, and construct the long exact homology sequences associated to distinguished triangles in the derived category.

The homology functor DerivedCategory C ⥤ C in degree n : ℤ.

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    The homology functor on the derived category is induced by the homology functor on the category of cochain complexes.

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      The homology functor on the derived category is induced by the homology functor on the homotopy category of cochain complexes.

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        @[implicit_reducible]

        The functors homologyFunctor C n : DerivedCategory C ⥤ C for all n : ℤ are part of a "shift sequence", i.e. they satisfy compatibilities with shifts.

        The connecting homomorphism on the homology sequence attached to a distinguished triangle in the derived category.

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          theorem DerivedCategory.HomologySequence.exact₃ {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Abelian C] [HasDerivedCategory C] (T : CategoryTheory.Pretriangulated.Triangle (DerivedCategory C)) (hT : T CategoryTheory.Pretriangulated.distinguishedTriangles) (n₀ n₁ : ) (h : n₀ + 1 = n₁ := by lia) :
          { X₁ := (homologyFunctor C n₀).obj T.obj₂, X₂ := (homologyFunctor C n₀).obj T.obj₃, X₃ := (homologyFunctor C n₁).obj T.obj₁, f := (homologyFunctor C n₀).map T.mor₂, g := δ T n₀ n₁ h, zero := }.Exact
          theorem DerivedCategory.HomologySequence.exact₁ {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Abelian C] [HasDerivedCategory C] (T : CategoryTheory.Pretriangulated.Triangle (DerivedCategory C)) (hT : T CategoryTheory.Pretriangulated.distinguishedTriangles) (n₀ n₁ : ) (h : n₀ + 1 = n₁ := by lia) :
          { X₁ := (homologyFunctor C n₀).obj T.obj₃, X₂ := (homologyFunctor C n₁).obj T.obj₁, X₃ := (homologyFunctor C n₁).obj T.obj₂, f := δ T n₀ n₁ h, g := (homologyFunctor C n₁).map T.mor₁, zero := }.Exact

          If T is a triangle in CochainComplex C ℤ, this is the connecting homomorphism T.obj₃.homology n₀ ⟶ T.obj₁.homology n₁ in homology when n₀ + 1 = n₁.

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