∀ {C : Type u} [inst : CategoryTheory.Category.{v, u} C] [inst_1 : CategoryTheory.Preadditive C]
  {F G : CochainComplex C ℤ} {φ₁ φ₂ : F ⟶ G} (h : φ₁ = φ₂),
  CochainComplex.HomComplex.Cochain.ofHomotopy (Homotopy.ofEq h) = 0