Secret Correlation in Repeated Games with Imperfect Monitoring: The Need for Nonstationary Strategies

The minmax in repeated games with imperfect monitoring can differ from the minmax of those games with perfect monitoring when two or more players are able to gain common information known only to themselves, and utilize this information at a later stage. Gossner and Tomala showed that in a class of such games, the minmax is given by a weighted average of the payoffs of two main strategies: one in which the information is gained, and the other in which the information is utilized. However, all examples analyzed to date require only one main strategy in which information is created and utilized simultaneously. We show that two strategies are indeed needed by providing and solving a concrete example of a three-player game.