For the game in Figure 12.4, the coarse correlated equilibrium \(z\) on the right has only two probabilities \(a=z_{32}\) for the strategy pair \((B, M)\) and \(b=z_{23}\) for the strategy pair \((M, B)\) that are positive; all other components \(z_{i j}\) are zero. Find all possible values of \(a\) and \(b=1-a\) so that the correlation devices \(z\) that are defined in this way define a coarse correlated equilibrium of the game.