Functions count the of functions f:[nl→[m one-one correspondence [n] [m] [ml→[m]÷[m" l[m→[mll=l[mr|=m “Combinatorial proof. Functions [n] [m] f : [n] ￾ [m] count the # of functions one-one correspondence [n] ￾ [m] ⇥ [m] n |[n] ￾ [m]| = |[m] n| = mn “Combinatorial proof