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