∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] [inst_1 : CategoryTheory.HasShift C ℤ]
  {X Y Z : CategoryTheory.Pretriangulated.Triangle C} (f : X ⟶ Y) (g : Y ⟶ Z),
  (CategoryTheory.CategoryStruct.comp f g).hom₃ = CategoryTheory.CategoryStruct.comp f.hom₃ g.hom₃