(C : Type u) →
  [inst : CategoryTheory.Category.{v, u} C] →
    [inst_1 : CategoryTheory.Preadditive C] →
      (n₁ n₂ n₁₂ : ℤ) →
        n₁ + n₂ = n₁₂ →
          (CochainComplex.shiftFunctor C n₁₂ ≅
            (CochainComplex.shiftFunctor C n₁).comp (CochainComplex.shiftFunctor C n₂))