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Mathlib.Algebra.Homology.HomotopyCategory.HomComplexShift

Shifting cochains

Let C be a preadditive category. Given two cochain complexes (indexed by ), the type of cochains HomComplex.Cochain K L n of degree n was introduced in Mathlib.Algebra.Homology.HomotopyCategory.HomComplex. In this file, we study how these cochains behave with respect to the shift on the complexes K and L.

When n, a, n' are integers such that h : n' + a = n, we obtain rightShiftAddEquiv K L n a n' h : Cochain K L n ≃+ Cochain K (L⟦a⟧) n'. This definition does not involve signs, but the analogous definition of leftShiftAddEquiv K L n a n' h' : Cochain K L n ≃+ Cochain (K⟦a⟧) L n' when h' : n + a = n' does involve signs, as we follow the conventions appearing in the introduction of [Brian Conrad's book Grothendieck duality and base change][conrad2000].

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The map Cochain K L n → Cochain K (L⟦a⟧) n' when n' + a = n.

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    theorem CochainComplex.HomComplex.Cochain.rightShift_v {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Preadditive C] {K : CochainComplex C } {L : CochainComplex C } {n : } (γ : CochainComplex.HomComplex.Cochain K L n) (a : ) (n' : ) (hn' : n' + a = n) (p : ) (q : ) (hpq : p + n' = q) (p' : ) (hp' : p + n = p') :

    The map Cochain K L n → Cochain (K⟦a⟧) L n' when n + a = n'.

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      theorem CochainComplex.HomComplex.Cochain.leftShift_v {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Preadditive C] {K : CochainComplex C } {L : CochainComplex C } {n : } (γ : CochainComplex.HomComplex.Cochain K L n) (a : ) (n' : ) (hn' : n + a = n') (p : ) (q : ) (hpq : p + n' = q) (p' : ) (hp' : p' + n = q) :
      (CochainComplex.HomComplex.Cochain.leftShift γ a n' hn').v p q hpq = (a * n' + a * (a - 1) / 2).negOnePow CategoryTheory.CategoryStruct.comp (CochainComplex.shiftFunctorObjXIso K a p p' ).hom (γ.v p' q hp')

      The map Cochain K (L⟦a⟧) n' → Cochain K L n when n' + a = n.

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        The map Cochain (K⟦a⟧) L n' → Cochain K L n when n + a = n'.

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          theorem CochainComplex.HomComplex.Cochain.leftUnshift_v {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Preadditive C] {K : CochainComplex C } {L : CochainComplex C } {n' : } {a : } (γ : CochainComplex.HomComplex.Cochain ((CategoryTheory.shiftFunctor (CochainComplex C ) a).obj K) L n') (n : ) (hn : n + a = n') (p : ) (q : ) (hpq : p + n = q) (p' : ) (hp' : p' + n' = q) :
          (CochainComplex.HomComplex.Cochain.leftUnshift γ n hn).v p q hpq = (a * n' + a * (a - 1) / 2).negOnePow CategoryTheory.CategoryStruct.comp (CochainComplex.shiftFunctorObjXIso K a p' p ).inv (γ.v p' q )

          The map Cochain K L n → Cochain (K⟦a⟧) (L⟦a⟧) n.

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            The additive equivalence Cochain K L n ≃+ Cochain K L⟦a⟧ n' when n' + a = n.

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              The additive equivalence Cochain K L n ≃+ Cochain (K⟦a⟧) L n' when n + a = n'.

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                The linear equivalence Cochain K L n ≃+ Cochain K L⟦a⟧ n' when n' + a = n and the category is R-linear.

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                  The additive equivalence Cochain K L n ≃+ Cochain (K⟦a⟧) L n' when n + a = n' and the category is R-linear.

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                    The linear map Cochain K L n ≃+ Cochain (K⟦a⟧) (L⟦a⟧) n when the category is R-linear.

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                      theorem CochainComplex.HomComplex.Cochain.leftShift_comp {C : Type u} [CategoryTheory.Category.{v, u} C] [CategoryTheory.Preadditive C] {K : CochainComplex C } {L : CochainComplex C } {M : CochainComplex C } {n : } (γ : CochainComplex.HomComplex.Cochain K L n) (a : ) (n' : ) (hn' : n + a = n') {m : } {t : } {t' : } (γ' : CochainComplex.HomComplex.Cochain L M m) (h : n + m = t) (ht' : t + a = t') :
                      CochainComplex.HomComplex.Cochain.leftShift (γ.comp γ' h) a t' ht' = (a * m).negOnePow (CochainComplex.HomComplex.Cochain.leftShift γ a n' hn').comp γ'

                      The map Cocycle K L n → Cocycle (K⟦a⟧) L n' when n + a = n'.

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