Functions count the of functions f:[ml→[m] one-one correspondence [n] [m] [nl→[ml台[m" Bijection rule: finite sets S and T 0:S1-1T →S1=T on-toFunctions [n] [m] f : [n] ￾ [m] count the # of functions one-one correspondence [n] ￾ [m] ⇥ [m] n Bijection rule: finite sets S and T ⇤￾ : S 1￾1 ￾￾￾￾⇥ on￾to T =￾ |S| = |T|