∀ {C : Type u_3} [inst : CategoryTheory.Category.{u_1, u_3} C] {D : Type u_5}
  [inst_1 : CategoryTheory.Category.{u_2, u_5} D] {E : Type u_6} [inst_2 : CategoryTheory.Category.{u_4, u_6} E]
  (F : CategoryTheory.Functor C D) {G : CategoryTheory.Functor D E} {e : E} (f : CategoryTheory.CostructuredArrow G e)
  {X Y Z : CategoryTheory.CostructuredArrow (CategoryTheory.CostructuredArrow.pre F G e) f} (f_1 : X ⟶ Y) (g : Y ⟶ Z),
  CategoryTheory.CostructuredArrow.homMk (CategoryTheory.CategoryStruct.comp f_1 g).left.left ⋯ =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.CostructuredArrow.homMk f_1.left.left ⋯)
      (CategoryTheory.CostructuredArrow.homMk g.left.left ⋯)