Both players have an (identical) time discount factor of 0 < < 1. Suppose R and PM decide each period whether to Advertise or Not Advertise and this game is repeated infinitely many times. Consider the grim-trigger strategy: (a) If neither firm has played A in the past, then play NA (b) If some firm has played A in the past, then play A (forever) Show that both players playing this strategy is a subgame perfect Nash equilibrium (i.e., that cooperation can be sustained) for some value of 0 < < 1. What is the (cutoff) value of for which cooperation can be sustained? Interpret your