∀ {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] (X : CategoryTheory.Functor (CategoryTheory.WithTerminal C) D),
  CategoryTheory.WithTerminal.mkCommaMorphism (CategoryTheory.CategoryStruct.id X) =
    CategoryTheory.CategoryStruct.id (CategoryTheory.WithTerminal.mkCommaObject X)