In game theory

Game theory

Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...

, a trigger strategy is any of a class of strategies employed in a repeated non-cooperative game

Game theory

Game theory is a mathematical method for analyzing calculated circumstances, such as in games, where a person’s success is based upon the choices of others...

. A player using 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
  Tit for tat
  Tit for tat is an English saying meaning "equivalent retaliation". It is also a highly effective strategy in game theory for the iterated prisoner's dilemma. It was first introduced by Anatol Rapoport in Robert Axelrod's two tournaments, held around 1980. An agent using this strategy will initially...
  
   (the punishment continues as long as the other player defects)
• Tit for two tats (a more forgiving variant of tit for tat)
• Grim trigger
  Grim trigger
  In game theory, grim trigger is a trigger strategy for a repeated game, such as an iterated prisoner's dilemma. Initially, a player using grim trigger will cooperate, but as soon as the opponent defects , the player using grim trigger will defect for the remainder of the iterated game...
  
  (the punishment continues indefinitely after the other player defects just once, until death of the player playing it, causing massive damage to any players who are juveniles in the population, since indefinitely applies more to them as a punishment. Life expectancy calculations are sometimes done in the insurance industry about this problem. After grim trigger, was he insured?)