此程序为一个用链表实现集合的各种运算，包括求并集，求交集，求补集，求笛卡儿集等，是本人刚学完数据结构是写的-the procedure used for a pool List in the operation, including the demand and to gather, seek common ground, seeking fill sets, Set for Descartes, I was just learning to End data structure is written! !