A Unified Theory of Implementation

This paper unifies the theories of Nash implementation and Bayesian implementation. Environments considered are such that each agent's characteristics include, in addition to a specification of his private information, a commonly known type parameter, while both attributes are unknown to the designer. Each social choice correspondence (SCC) assigns a commonly known type vector to a social choice set. Conditions that fully characterize an implementable SCC in economic environments where agents are not satiated generalize and merge respective conditions in the complete information model of Danilov (1992) and the incomplete information model of Jackson (1991).Bayesian implementation

A Note on Jackson's Theorems in Bayesian Implementation

This note shows that in an incomplete information situation the closure condition will be satisfied by all social choice sets if and only if the set of states of the society which all agents believeoccur with positive probability satisfies the `connection' condition.It then follows from Jackson''s [1] fundamental theorems that whenever `connection'' is satisfied and there are at least three agents in the society, for the implementability of social choice sets in Bayesian equilibrium the incentive compatibility and Bayesian monotonicity conditions are both necessary and sufficient in economic environments. It also follows that the incentive compatibility and monotonicity-no-veto conditions are sufficient in noneconomic environments.Bayesian implementation incomplete information

A Unified Implementation Theory

This paper unifies the theories of Nash implementation and Bayesian implementation in a single framework. Environments considered are such that each agent's characteristics include, in addition to a specification of his private information, a commonly known type parameter, while both attributes are unknown to the designer. Each social choice correspondence (SCC) assigns a commonly known type vector to a social choice set, a collection of functions mapping private type vectors to allocations. Conditions that fully characterize an implementable SCC in economic environments where agents are not satiated generalize and merge respective conditions in the complete information model of Danilov (1992) and the incomplete information model of Jackson (1991). In noneconomic environments there remains to exist a gap between the necessary and sufficient conditions, like in Jackson (1991). In order to narrow down this gap, we employ Danilov's notion of essential elements and develop a stronger necessary condition, termed essential-generalized-Bayesian monotonicity (EGBM).Bayesian implementation; Nash implementation; mechanism; complete information; incomplete information; social choice correspondence

One-to-One Matching with Interdependent Preferences

In this paper, we introduce interdependent preferences to a classical one-to-one matching problem that allows for the prospect of being single, and study the existence and properties of stable matchings. We obtain the relationship between the stable set, the core, and the Pareto set, and give a sufficiency result for the existence of the stable set and the core. We also present several findings on the issues of gender optimality, lattices, strategy-proofness, and rationalizability.One-to-one matching; externalities

College Admissions under Early Decision

In this paper, we model college admissions under early decision in a many-to-one matching framework with two periods. We show that there exists no stable matching system, involving an early decision matching rule and a regular decision matching rule, which is nonmanipulable via early decision quotas by colleges or via early decision preferences by colleges or students. We then analyze the Nash equilibria of the game, in which the preferences of colleges and students in each period are common knowledge and every college determines a quota for the early decision period given its total capacity for the two periods. Under college-optimal and student-optimal matching systems, we show that a pure strategy equilibrium may not exist. However, when colleges or students have common preferences over the other set of agents, 'terminating early decision program' becomes a weakly dominant strategy for each college if every student, choosing to act early, always applies early to his or her top choice college.Many-to-one matching; college admissions; early decision