f_0(n)=n+1
f_k+1(n)=sup{f_k^m(n)｜m∈n}
f_k(n)=sup{f_m(n)｜m∈k}
f_f(g(n))(n)=sup{f_f(m)(n)｜m∈n}
g(x)=min{Ω_n｜Ω_n＞x}