Surjections f:[n]ont [ml ∀i∈[m f-1()≠0 (f-1(1),f-1(2),.,f-1(m) ordered m-partition of [n mrSurjections f : [n] on-to ￾￾ [m] ￾i ￾ [m] f ￾1(i) ￾= ￾ (f ￾1(1), f ￾1(2),...,f ￾1(m)) ordered m-partition of [n] ! n m " m!