∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Preadditive C]
  {S₁ S₂ S₃ : CategoryTheory.ShortComplex C} {φ₁ φ₂ : S₁ ⟶ S₂} (h : CategoryTheory.ShortComplex.Homotopy φ₁ φ₂)
  {ψ₁ ψ₂ : S₂ ⟶ S₃} (h' : CategoryTheory.ShortComplex.Homotopy ψ₁ ψ₂),
  (h.comp h').h₃ = CategoryTheory.CategoryStruct.comp h.h₃ ψ₁.τ₃ + CategoryTheory.CategoryStruct.comp φ₂.τ₃ h'.h₃