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Mathlib.Algebra.Homology.BifunctorShift

Behavior of the action of a bifunctor on cochain complexes with respect to shifts #

In this file, given cochain complexes K₁ : CochainComplex C₁ ℤ, K₂ : CochainComplex C₂ ℤ and a functor F : C₁ ⥤ C₂ ⥤ D, we define an isomorphism of cochain complexes in D:

TODO #

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The condition that ((F.mapBifunctorHomologicalComplex _ _).obj K₁).obj K₂ has a total cochain complex.

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    Given K₁ : CochainComplex C₁ ℤ, K₂ : CochainComplex C₂ ℤ, a bifunctor F : C₁ ⥤ C₂ ⥤ D, this mapBifunctor K₁ K₂ F : CochainComplex D ℤ is the total complex of the bicomplex obtained by applying F to K₁ and K₂.

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      The inclusion of a summand (F.obj (K₁.X n₁)).obj (K₂.X n₂) ⟶ (mapBifunctor K₁ K₂ F).X n of the total cochain complex when n₁ + n₂ = n.

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        The canonical isomorphism mapBifunctor (K₁⟦x⟧) K₂ F ≅ (mapBifunctor K₁ K₂ F)⟦x⟧. This isomorphism does not involve signs.

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          The canonical isomorphism mapBifunctor K₁ (K₂⟦y⟧) F ≅ (mapBifunctor K₁ K₂ F)⟦y⟧. This isomorphism involves signs: on the summand (F.obj (K₁.X p)).obj (K₂.X q), it is given by the multiplication by (p * y).negOnePow.

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