∀ {C : Type u_3} [inst : CategoryTheory.Category.{u_1, u_3} C] {D : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_2, u_4} D] {F : CategoryTheory.Functor C D} (G : CategoryTheory.Functor D C)
  (η : CategoryTheory.Functor.id C ≅ F.comp G) (ε : G.comp F ≅ CategoryTheory.Functor.id D), F.IsEquivalence