Smooth Monotone Contribution Games

A monotone game is a multistage game in which no player can lower her action in any period below its previous level. A motivation for the monotone games of this paper is dynamic voluntary contribution to a public project. Each player's utility is a strictly concave function of the public good, and quasilinear in the private good. The main result is a description of the limit points of (subgame perfect) equilibrium paths as the period length shrinks. The limiting set of such profiles is equal to the undercore of the underlying static game - the set of profiles that cannot be blocked by a coalition using a smaller profile. A corollary is that the limiting set of achievable profiles does not depend on whether the players can move simultaneously or only in a round-robin fashion. The familiar core is the efficient subset of the undercore; hence, some but not all profiles that are efficient and individually rational can be nearly achieved when the period length is small. As the period length shrinks, any core profile can be achieved in a “twinkling of the eye” - neither real-time gradualism nor inefficiency are necessary.