∀ (C : Type u_4) [inst : CategoryTheory.Category.{u_3, u_4} C] (D : Type u_6)
  [inst_1 : CategoryTheory.Category.{u_5, u_6} D] (E : Type u_2) [inst_2 : CategoryTheory.Category.{u_1, u_2} E]
  (X : CategoryTheory.Functor C (CategoryTheory.Functor D E)) (x : D) (x_1 : C),
  ({ app := fun Y => { app := fun X_1 => ((CategoryTheory.CategoryStruct.id X).app X_1).app Y, naturality := ⋯ },
              naturality := ⋯ }.app
          x).app
      x_1 =
    ((CategoryTheory.CategoryStruct.id X.flip).app x).app x_1