(1,2,3,5)(1,2,3,6)(1,2,4,5)
(1,2,4,6)(1,2,5,6)(1,3,4,5)
(1,3,4,6) (1,3,5,6) (1,4,5,6)
(2,3,4,6)(2,3,5,6)(2,4,5,6)
总数12种