∀ (C : Type u) [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C] (n₁ n₂ n₁₂ : ℤ)
  (h : n₁ + n₂ = n₁₂) (X : CochainComplex C ℤ) (i : ℤ),
  ((CochainComplex.shiftFunctorAdd' C n₁ n₂ n₁₂ h).hom.app X).f i = (HomologicalComplex.XIsoOfEq X ⋯).hom