generate ©umerate all subsets of {O,●，Q} (x0+x21)(x0+x1)(x0+2) z0aOx0 +x0xOx1+z0x1x0+x0x1z1 x1x0x0+x1x0x1+x1x1x0+x1x1x1 (1+x)3=1+3x+3x2+x3 coefficient of:of k-subsets{ , , } enumerate all subsets of generate (x0 + x1)(x0 + x1)(x0 + x1) = + + + + + + + x1 x0x0x0 x0x0x1 x0 x0 x1 x0 x1 x1 x0 x0 x1 x0 x1 x1 x0 x1 x1 x1 x1 (1 + x) 3 =1+3x + 3x2 + x3 coefficient of xk : # of k-subsets