4. Consider the following simultaneous-move 2X2 game. Left Right Top 0,10 b,0 Bottom lO,a X,y a) Dene prisoner's dilemma. What conditions do a,b,x,y have to satisfy for this game to be a prisoner's dilemma? [Hintz See the slides on ISD from earlier in the semester.] For parts b and c, assume that the above game is indeed a prisoner's dilemma (so that the conditions from part a hold) and is repeated innitely many times. b) State player l's grim trigger strategy. 0) Suppose both players have discount factor 0.8. Find and explain the conditions on a,b,x,y (in addition to those from part a) so that both players playing their grim trigger strategy is a subgameperfect equilibrium