f6m)=l2网 f(n)=2f(n-1) 2m={S E [n]|n年S}U{Scm|n∈S} 2川=2-川+}2-川=20m-1） Sum rule: finite disjoint sets S and T SUT=S+T f(n)=2f(n ￾ 1) ￾ Sum rule: finite disjoint sets S and T |S ￾ T| = |S| + |T| = 2f(n ￾ 1) f(n) = ￾ ￾ ￾ 2[n] ￾ ￾ ￾ ￾ ￾ ￾ 2[n] ￾ ￾ ￾ = 2[n] = ￾ ￾ ￾ 2[n￾1] ￾ ￾ ￾ ￾ ￾ ￾ 2[n￾1] ￾ ￾ + ￾ {S ✓ [n] | n 62 S} {S ✓ [n] | n 2 S}