Differentials of a spectral object #
Let X be a spectral object in an abelian category C indexed by a category ι.
In this file, we construct the differentials d : E^{n}(f₃, f₄, f₅) ⟶ E^{n+1}(f₁, f₂, f₃)
that are attached to families of five composable morphisms f₁, f₂, f₃, f₄, f₅
in ι. We show that d ≫ d = 0. The homology of these differentials is computed in the
file Mathlib/Algebra/Homology/SpectralObject/Homology.lean (TODO).
References #
The differential E^{n}(f₃, f₄, f₅) ⟶ E^{n+1}(f₁, f₂, f₃) that is
attached to a family of five composable morphisms f₁, f₂, f₃, f₄, f₅.
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Instances For
When f₁, f₂ and f₃ are composable morphisms, this is the canonical
morphism Z^n(f₂, f₃) ⟶ opZ^{n+1}(f₁, f₂) that is induced both
by δ : H^n(f₂ ≫ f₃) ⟶ H^{n+1}(f₁) (see toCycles_Ψ) and
by δ : H^n(f₃) ⟶ H^{n+1}(f₁ ≫ f₂) (see Ψ_fromOpcycles).
See the lemma πE_d_ιE for the relation between this definition
and the differentials d.
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When f₁, f₂ and f₃ are composable morphisms, this is the exact sequence
Z^n(f₁ ≫ f₂, f₃) ⟶ Z^n(f₂, f₃) ⟶ opZ^{n+1}(f₁, f₂) ⟶ opZ^{n+1}(f₁, f₂ ≫ f₃).
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