User blog comment:Ikosarakt1/Fast-growing hierarchy/@comment-7484840-20130620190007/@comment-5150073-20130622120023

z_0^(e_0^(w+Omega)) is illegal since any proper expression of ordinals must be a_1+a_2+...+a_m (where a_1>a_2>...>a_m). So, w+Omega is illegal.