∀ (C : Type u_2) [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C] (n₁ n₂ n₁₂ : ℤ)
  (h : n₁ + n₂ = n₁₂) (K : CochainComplex C ℤ) (x x_1 : ℤ),
  CategoryTheory.CategoryStruct.comp ((fun i => K.shiftFunctorObjXIso n₁₂ i (i + n₂ + n₁) ⋯) x).hom
      ((((CochainComplex.shiftFunctor C n₁).comp (CochainComplex.shiftFunctor C n₂)).obj K).d x x_1) =
    CategoryTheory.CategoryStruct.comp (((CochainComplex.shiftFunctor C n₁₂).obj K).d x x_1)
      ((fun i => K.shiftFunctorObjXIso n₁₂ i (i + n₂ + n₁) ⋯) x_1).hom