The Iterated Prisoner’s Dilemma: Press-Dyson Interactive

The Game

In each round, each of us can choose to cooperate or to defect. We play repeated rounds. In each round:

  1. Fixed score
  2. Extortion
  3. Generous

In this game, I’ve decided I want your average score to be 2. You’ll see that, however you play, after a few hundred moves your average score will be approximately 2.

Your move:
Your average score:
My average score:

History new game

How does it work?

I am playing a very simple strategy in the game above. My play is based purely on how both of us played in the previous move:

These probabilities were obtained by deciding I wanted your average score to be 2, and solving equations [8] and [9] in Press and Dyson’s paper for a target score of 2.


Although this strategy does belong to the new and interesting class of Press-Dyson strategies, it turns out that this particular type of Press-Dyson strategy (ones that force your opponent to have a particular fixed score, on average, however they play) was described earlier by Maarten C Boerlijst, Martin A Nowak and Karl Sigmund in their 1997 paper Equal Pay for All Prisoners.