decide on your course of action. Due to this there is a possibility that an equilibrium will not be reached. Voluntary standards In social sciences, a voluntary standard (when characterized also as de facto standard) is a typical solution to a coordination problem. The choice of a voluntary standard tends to be stable in situations in which all parties can realize mutual gains, but only by making mutually consistent decisions. In contrast, an obligation standard (enforced by law as "de jure standard") is a solution to the prisoner's problem. Mixed strategy Nash equilibrium Coordination games also have mixed strategy Nash equilibria. In the generic coordination game above, a mixed Nash equilibrium is given by probabilities p = (d-b)/(a+d-b-c) to play Up and 1-p to play Down for player 1, and q = (D-C)/(A+D-B-C) to play Left and 1-q to play Right for player 2. Since d > b and d-b < a+d-b-c, p is always between zero and one, so existence is assured (similarly for q). In the generic coordination game in Fig. 6, a mixed Nash equilibrium is given by the probabilities: p = (d-b)/(a+d-b-c), to play Option A and 1-p to play Option B for player 1, and q = (D-C)/(A+D-B-C), to play A and 1-q to play B for player 2. If we look at Fig 1. and apply the same probability equations we obtain the following results: p = (4-3) / (4+4-3-3) = ½ and, q = (2-1) / (2+2-1-1) = ½ The reaction correspondences for 2×2 coordination games are shown in Fig. 7. The pure Nash equilibria are the points in the bottom left and top right corners of the strategy space, while the mixed Nash equilibrium lies in the middle, at the intersection of the dashed lines. Unlike the pure Nash equilibria, the mixed equilibrium is not an evolutionarily stable strategy (ESS). The mixed Nash equilibrium is also Pareto dominated by the two pure Nash equilibria (since the players will fail to coordinate with non-zero probability), a quandary that led Robert Aumann to propose the refinement of a correlated equilibrium. Coordination and equilibrium selection Games like the driving example above have illustrated the need for solution to coordination problems. Often we are confronted with circumstances where we must solve coordination problems without the ability to communicate with our partner. Many authors have suggested that particular equilibria are focal for one reason or another. For