∀ {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] (p q : ℤ) (hpq : p + -1 = q)
  {Z : C} (h : G.X q ⟶ Z),
  CategoryTheory.CategoryStruct.comp ((CochainComplex.mappingCone.inl φ).v p q hpq)
      (CategoryTheory.CategoryStruct.comp ((CochainComplex.mappingCone.snd φ).v q q ⋯) h) =
    CategoryTheory.CategoryStruct.comp 0 h