∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.Preadditive C]
  {S₁ S₂ : CategoryTheory.ShortComplex C} (φ φ' : S₁ ⟶ S₂),
  CategoryTheory.CategoryStruct.comp (φ.τ₁ + φ'.τ₁) S₂.f = CategoryTheory.CategoryStruct.comp S₁.f (φ.τ₂ + φ'.τ₂)