The point that I didn't see made yet is that it's only Iterated Prisoner's Dilemma for the first N-1 times. After that it's simply singe PD.
It is not correct to say that the last round is simple PD, because each player has additional information at that point. Consequentially, while the decision for round N is the same as in PD, N-1 does not actually become the new N.
Each player has additional information about how the other player has played in the past. I wasn't trying to say that iterated PD for N=100 rounds becomes N=0, I was saying it becomes N=99, followed by one straight game.
Also, new information about how a player has behaved in radically different circumstances is different from being able to rationally update what they will do in the future. You have never encountered the agent before you in circumstances where they are interacting with you for the last time, ever.
Today's post, The Truly Iterated Prisoner's Dilemma was originally published on 04 September 2008. A summary (taken from the LW wiki):
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