If a prisoners' dilemma game is played repeatedly, what punishment strategies might the players employ and how does playing the game repeatedly change the equilibrium?

What will be an ideal response?

Two strategies for motivating compliance in a repeated prisoner's dilemma game are: i) a tit-for-tat strategy, where cheating by one firm in the current period is punished by the other firm cheating in the next period, but compliance by one firm in the current period is rewarded by compliance in the next period, ii) a trigger strategy, where cheating by one firm in the current period is punished by cheating by the other firm in all subsequent periods. Both strategies may create a cooperative equilibrium where all players share in the maximum possible benefit.