????:1????????????:???????

2??????????????

3???sn

4??????

5?????

??11??????????????26?? (?? ???)11??????25?????,????????????????????,????????????????????????????????????????????,??????11?25?27??3??

????? ?

?????“?+N”??????????????,?????,?????;????????,?????????????,??,????????;??“???????????????????????????????????????????”???????????,?;??????????,????(?????????)?????(?)

????????????????????:???