a100 0 a00 例A BBB 2 10b1 011b B 0a00 4= B 011b 上页, 321   = BBB   = b b a a A 0 1 1 1 0 1 0 0 0 1 0 0 例   A = a 1 0 0b a 0 1 1 0 0 0 0 1 1 b   = B 1 B 2 B 3 即