∀ {C : Type u_1} [inst : CategoryTheory.Category.{v, u_1} C] [inst_1 : CategoryTheory.Preadditive C]
  {F G : CochainComplex C ℤ} (φ : F ⟶ G) [inst_2 : HomologicalComplex.HasHomotopyCofiber φ] (i j k : ℤ)
  (hij : i + -1 = j) (hik : k + -1 = i) {Z : C} (h : (CochainComplex.mappingCone φ).X i ⟶ Z),
  CategoryTheory.CategoryStruct.comp ((CochainComplex.mappingCone.inl φ).v i j hij)
      (CategoryTheory.CategoryStruct.comp ((CochainComplex.mappingCone φ).d j i) h) =
    CategoryTheory.CategoryStruct.comp
      (CategoryTheory.CategoryStruct.comp (φ.f i) ((CochainComplex.mappingCone.inr φ).f i) -
        CategoryTheory.CategoryStruct.comp (F.d i k) ((CochainComplex.mappingCone.inl φ).v k i hik))
      h