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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:

In the lemma CochainComplex.mapBifunctorShift₁Iso_trans_mapBifunctorShift₂Iso, we obtain that the two ways to deduce an isomorphism mapBifunctor (K₁⟦x⟧) (K₂⟦y⟧) F ≅ (mapBifunctor K₁ K₂ F)⟦x + y⟧ differ by the sign (x * y).negOnePow.

@[reducible, inline]

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

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    @[reducible, inline]

    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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      @[reducible, inline]
      noncomputable abbrev CochainComplex.ιMapBifunctor {C₁ : Type u_1} {C₂ : Type u_2} {D : Type u_3} [CategoryTheory.Category.{u_4, u_1} C₁] [CategoryTheory.Category.{u_5, u_2} C₂] [CategoryTheory.Category.{u_6, u_3} D] [CategoryTheory.Limits.HasZeroMorphisms C₁] [CategoryTheory.Limits.HasZeroMorphisms C₂] (K₁ : CochainComplex C₁ ) (K₂ : CochainComplex C₂ ) [CategoryTheory.Preadditive D] (F : CategoryTheory.Functor C₁ (CategoryTheory.Functor C₂ D)) [F.PreservesZeroMorphisms] [∀ (X₁ : C₁), (F.obj X₁).PreservesZeroMorphisms] [K₁.HasMapBifunctor K₂ F] (n₁ n₂ n : ) (h : n₁ + n₂ = n) :
      (F.obj (K₁.X n₁)).obj (K₂.X n₂) (K₁.mapBifunctor K₂ F).X n

      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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