31
91
100
()23
()16.6
ABABPAPB180APB
33
(73)
(1)→(13) (2)→(43) (3)→(47) (4)→(67)
(5)→(85) (6)→(58) (7)→(117)(8)→(73)
34
lA3lmnA60lmn3(图1)
ACAB(69)CBCnBBnmABABCA60Cmn
490
2PQRSABCD3PQRS904
APQ∩SPBQR∩PQ
CRS∩QRDSP∩RS
PQRSABCD
图4
35
