∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] [inst_1 : CategoryTheory.Limits.HasZeroMorphisms C]
  {S₁ S₂ S₃ : CategoryTheory.ShortComplex C} (φ₁₂ : S₁ ⟶ S₂) (φ₂₃ : S₂ ⟶ S₃) {Z : C} (h : S₃.X₂ ⟶ Z),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.CategoryStruct.comp φ₁₂ φ₂₃).τ₂ h =
    CategoryTheory.CategoryStruct.comp φ₁₂.τ₂ (CategoryTheory.CategoryStruct.comp φ₂₃.τ₂ h)