∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] {U X : C} (m : U ⟶ X),
  CategoryTheory.CategoryStruct.comp m (CategoryTheory.Iso.refl X).hom =
    CategoryTheory.CategoryStruct.comp (CategoryTheory.Iso.refl U).hom m