∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {D : Type u_4}
  [inst_1 : CategoryTheory.Category.{u_3, u_4} D] {F : CategoryTheory.Functor C D} (hF : F.FullyFaithful) {X Y : C}
  (e : F.obj X ≅ F.obj Y),
  CategoryTheory.CategoryStruct.comp (hF.preimage e.hom) (hF.preimage e.inv) = CategoryTheory.CategoryStruct.id X