11 lk k1 bu 如=DD 2 In 0 naul lk 1 k1 akk=(1)D, D 2 11 0 nI 上页n nn n k k n n k k k k b b b b c c c c a a a a             1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 1 1 n nn n k k k k k k n n b b b b a a a a c c c c             = D1 D2 1 2 ( 1) D D nk = −