就是：有 f(n)=∑(in)g(i)f(n)=\sum \binom i n g(i)f(n)=∑(ni)g(i) 是否有 g(n)=∑(in)(−1)i−nf(i)g(n)=\sum \binom i n (-1)^{i-n}f(i)g(n)=∑(ni)(−1)i−nf(i)
