∀ {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) {X Y : C} (f : X ⟶ Y)
  (i : Fin (1 + 1)),
  (G.mapComposableArrowsObjMk₁Iso f).inv.app i =
    match i with
    | ⟨0, isLt⟩ => CategoryTheory.CategoryStruct.id (G.obj X)
    | ⟨1, isLt⟩ => CategoryTheory.CategoryStruct.id (G.obj Y)