A graph model of unanimous decision systems

A graph model of unanimous decision systems is proposed and some properties of unanimous decision systems are clarified. In particular, with regard to Nash stability, general metarationality, symmetric metarationality and sequential stability, the conditions for a state in the graph model of unanimous decision systems to be an equilibrium are specified, respectively. These properties imply that unanimous decision systems are efficient in the sense that they achieve Pareto optimal states under some realistic conditions.