We show that all the fundamental properties of competitive equilibrium in Marshall's theory of value, as presented in Note XXI of the mathematical appendix to his Principles of Economics (1890), derive from the Strong Law of Demand. This is, existence, uniqueness, optimality, global stability of...

The actions of different agents sometimes reinforce each other. Examples are network effects and the threshold models used by sociologists as well as Harvey Leibensteins's "bandwagon effects." We model such situations as a game with increasing differences, and show that tipping of equilibria,...

Social distancing via shelter-in-place strategies, and wearing masks, have emerged as the most effective non-pharmaceutical ways of combatting COVID-19. In the United States, choices about these policies are made by individual states. We develop a game-theoretic model and then test it...