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Prisoner's Dilemma Variant
There are a few tweaks to the Iterated Prisoner's Dilemma which can affect which strategies tend to be successful. A very common one is to randomize how long the round is, so predicting the end-game doesn't overwhelm all other strategy factors. A less common one is adding noise, so that what each program tries to do isn't necessarily what happens.
Does anyone know of any tourneys that have been run where, in addition to Cooperation or Defection, each program also has the choice to End The Game, simulating quitting a business relationship, moving away, shunning, or otherwise ceasing to interact with another program?
Not aware of any tourneys with this tweak, but I use a similar example when I teach.
If the payoff from exiting is zero and the mutual defection payoff is negative, then the game doesn't change much. Exit on the first round becomes the unique subgame-perfect equilibrium of any finite repetition, and with a random end date, trigger strategies to support cooperation work similarly to the original game.
Life is a more interesting if the mutual defection payoff is sufficiently better than exit. Cooperation can happen in equilibrium even when the end date is known (except on the last round) since exit is a viable threat to punish defection.