迭代法设 $f(x): M \to M$. 记
$$f^0(x) = x, f^1(x) = f(x), f^2(x) = f(f(x)), \cdots, f^{n+1}(x) = f(f^n(x))$$
其中的 $n$ 叫做 $f^n
2020-01-31