Answer the following questions with a brief explanation (a couple of sentences is fine).

(a) What is a Grim Trigger Strategy in the infinitely repeated Prisoners' Dilemma? Under such strategies, why is cooperation more likely if players are more patient?

(b) Suppose that you believe the probability of an event, X, occuring is P(X) and you observe some new evidence, E, about the likelihood of X. Explain how Bayes' Rule allows you to figure out new beliefs P(X|E) over the probability of X conditional on your new evidence.