This paper proposes an equilibrium concept for a class of games in which players make irreversible costly decisions; these games have been widely used in the recent I.O. literature. The equilibrium concept is defined, not in the space of strategies, but in the space of (observable) outcomes. It...

Models of (horizontal) product differentiation generally admit many equilibria. These include concentrated equilibria, in which few firms each offer many products, and fragmented equilibria, in which many firms each offer one product. Since these outcomes depend in a delicate way on features of...