I OB B AB 12 CI八B 21 B 22 IB 1B12 CBM+1B21 CBi2+ 1B22 B B I CBu+ B21 CB12+ B22 1032 120 2411 1153              − − − =         + + =         + + =                 = 1 1 5 3 2 4 1 1 1 2 0 1 1 0 3 2 1 1 2 1 1 2 2 2 1 1 1 2 1 1 2 1 1 2 2 2 1 1 1 2 2 1 2 2 1 1 1 2 CB B CB B B B CB IB CB IB IB IB B B B B C I I O AB