∀ {C : Type u_4} [inst : CategoryTheory.Category.{u_5, u_4} C] {D : Type u_6}
  [inst_1 : CategoryTheory.Category.{u_3, u_6} D] {E : Type u_1} [inst_2 : CategoryTheory.Category.{u_2, u_1} E]
  (L : CategoryTheory.Functor C D) (R : CategoryTheory.Functor E D)
  {X Y Z : CategoryTheory.Grothendieck (R.comp (CategoryTheory.CostructuredArrow.functor L))} (f : X ⟶ Y) (g : Y ⟶ Z),
  { left := (CategoryTheory.CategoryStruct.comp f g).fiber.left, right := (CategoryTheory.CategoryStruct.comp f g).base,
      w := ⋯ } =
    CategoryTheory.CategoryStruct.comp { left := f.fiber.left, right := f.base, w := ⋯ }
      { left := g.fiber.left, right := g.base, w := ⋯ }