抛光纸 发表于 2011-11-10 07:50 
好吧 我又看了下 你确定题目是对的么?
Nash eq.是for the whole game的
不可能是在each stage里的
The quetion is about PD game, which is repeated twice.
Then this game can have strategies such that are NE but are not SPNE.
WE both know that SPNE is play D in each stage.
However, consider this strategy:
PLay D in the first period, play D in the second period if opponent play D in the first period and play C (cooperate) in the second period if opponent play C in the first period. Then this is NE but not SPNE.
Note that strategies in game theory are a full plan. eg. decisions for each node.
Apologies for the mess, my Chinese input is not working..