Trigger strategy

A trigger strategy is a class of strategies employed in a repeated non-cooperative game. A player utilizing a trigger strategy initially cooperates but punishes the opponent if a certain level of defection (i.e., the trigger) is observed. The level of punishment and the sensitivity of the trigger vary with different trigger strategies.

Trigger strategies

 * Tit for Tat (the punishment continues as long as the other player defects)
 * Tit for Two Tats (a more forgiving variant of tit for tat)
 * Grim trigger (the punishment continues indefinitely after the other player defects just once)


 * Textbooks and general reference texts


 * Vives, X. (1999) Oligopoly pricing, MIT Press, Cambridge MA (readable; suitable for advanced undergraduates.)
 * Tirole, J. (1988) The Theory of Industrial Organization, MIT Press, Cambridge MA (An organized introduction to industrial organization)


 * Classical paper on this subject


 * Friedman, J. (1971). A non-cooperative equilibrium for supergames, Review of Economic Studies 38, 1-12. (The first formal proof of the Folk theorem (game theory)).