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Mathlib.Algebra.Homology.Embedding.Connect

Connecting a chain complex and a cochain complex #

Given a chain complex K: ... ⟶ K.X 2 ⟶ K.X 1 ⟶ K.X 0, a cochain complex L: L.X 0 ⟶ L.X 1 ⟶ L.X 2 ⟶ ..., a morphism d₀: K.X 0 ⟶ L.X 0 satisfying the identifies K.d 1 0 ≫ d₀ = 0 and d₀ ≫ L.d 0 1 = 0, we construct a cochain complex indexed by of the form ... ⟶ K.X 2 ⟶ K.X 1 ⟶ K.X 0 ⟶ L.X 0 ⟶ L.X 1 ⟶ L.X 2 ⟶ ..., where K.X 0 lies in degree -1 and L.X 0 in degree 0.

Given K : ChainComplex C ℕ and L : CochainComplex C ℕ, this data allows to connect K and L in order to get a cochain complex indexed by , see ConnectData.cochainComplex.

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    Auxiliary definition for ConnectData.cochainComplex.

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      Given h : ConnectData K L where K : ChainComplex C ℕ and L : CochainComplex C ℕ, this is the cochain complex indexed by obtained by connecting K and L: ... ⟶ K.X 2 ⟶ K.X 1 ⟶ K.X 0 ⟶ L.X 0 ⟶ L.X 1 ⟶ L.X 2 ⟶ ....

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