∀ {C : Type u_2} [inst : CategoryTheory.Category.{u_1, u_2} C] (M : CategoryTheory.Mon (CategoryTheory.Functor C C))
  (X : C),
  CategoryTheory.CategoryStruct.comp (CategoryTheory.MonObj.one.app (M.X.obj X)) (CategoryTheory.MonObj.mul.app X) =
    CategoryTheory.CategoryStruct.id ((CategoryTheory.Functor.id C).obj (M.X.obj X))