(The non-repeated, one-shot prisoner's dilemma never results in cooperation. As the game theorist Ken Binmore explains in several of his books, among them Natural Justice, defection strongly dominates cooperation in the one-shot PD and it inexorably follows that a rational player never cooperates.)
Can you be more precise? Always cooperating in the prisoner's dilemma is not going to be optimal. Are you thinking of something like where each side is allowed to simulate the other? In that case, see here.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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