The distinction between nonatomicity and thick markets as the source of perfect competition is examined. The authors construct a model of an imperfectly competitive economy with a nonatomic continuum of traders and a continuum of differentiated commodities for which Walrasian equilibria exist....

The first theorem of welfare economics rests on the assumption that individuals have neither price-making nor market-making capacities. The authors offer a revision in which individuals have such capacities. The revision emphasizes two keys for market efficiency: the need to align private...

Two of the most important refinements of the Nash equilibrium concept for extensive form games are (trembling hand) perfect equilibrium and sequential equilibrium. It is shown here that, for almost all assignments of payoffs to outcomes, the sets of sequential and perfect equilibrium strategy...