Robust Predictions in Infinite-Horizon Games--an Unrefinable Folk Theorem

Abstract

We show that in any game that is continuous at infinity, if a plan of action ai is played by a type ti in a Bayesian Nash equilibrium, then there are perturbations of ti for which ai is the only rationalizable plan and whose unique rationalizable belief regarding the play of the game is arbitrarily close to the equilibrium belief of ti. As an application to repeated games, we prove an unrefinable folk theorem: any individually rational and feasible payoff is the unique rationalizable payoff vector for some perturbed type profile. This is true even if perturbed types are restricted to believe that the repeated-game payoff structure and the discount factor are common knowledge.