<n,m>=∑k=0m(n+1k)(m+1−k)n(−1)k<n,m>=\sum_{k=0}^m \binom{n+1}{k}(m+1-k)^n(-1)^k<n,m>=∑k=0m(kn+1)(m+1−k)n(−1)k
答案是 <n,k><n,k><n,k>
求助这个怎么证明的？
