∀ {C : Type u_1} [inst : CategoryTheory.Category.{v_1, u_1} C] {D : Type u_2}
  [inst_1 : CategoryTheory.Category.{v_2, u_2} D] (G : CategoryTheory.Functor C D) (n : ℕ)
  (F : CategoryTheory.Functor (Fin (n + 1)) C) (X : Fin (n + 1)),
  ((G.mapComposableArrows n).obj F).obj X = G.obj (F.obj X)