tion. 16. Use the inclusion-exclusion principle (Question 4) to prove the number of surjections N7 Nn is given by 21 n- 1)m For each i E Nn, let Ai = { f: N,n Nn | i is not a value offW Deduce that -8)(n-1)" + (2)(n-2)"-... +(-1)"-1C1)1"=