Under a k-approval scoring rule each agent attaches a score of one to his k most preferred alternatives and zero to the other alternatives. The rule assigns the set of alternatives with maximal score. Agents may extend preferences to sets in several ways: they may compare the worst alternatives,...

In a model with finitely many agents who have single-dipped Euclidean preferences on a disc in theEuclidean plane, a rule assigns to each profile of reported dips a point of the disc. It is provedthat any strategy-proof and Pareto optimal rule is a dictatorial. This framework models...

In a model with finitely many agents who have single-dipped Euclidean preferences on a polytope inthe Euclidean plane, a rule assigns to each profile of reported dips a point of the polytope. Asingle-best point is a point which is the unique point at maximal distance from some other pointof the...

We characterize all preference profiles at which the approval (voting) rule is manipulable, under three extensions of preferences to sets of alternatives: by comparison of worstalternatives, best alternatives, or by comparison based on stochastic dominance. We perform a similar exercise for...

We consider voting rules on a multidimensional policy space for a continuum of voters with elliptic preferences. Assuming continuity, y-strategy-proofness - meaning that coalitions of size smaller or equal to a small number y cannot manipulate - and unanimity, we show that such rules are...

We consider voting rules on a multidimensional policy space for a continuum of voters with elliptic preferences. Assuming continuity, y-strategy-proofness - meaning that coalitions of size smaller or equal to a small number y cannot manipulate - and unanimity, we show that such rules are...

We characterize all preference profiles at which the approval (voting) rule is manipulable, under three extensions of preferences to sets of alternatives: by comparison of worstalternatives, best alternatives, or by comparison based on stochastic dominance. We perform a similar exercise for...

In this note we extend Jackson and WattsJET2002''s result on the coincidence of S-stochastically stable and core stable networks from the marriage problem to the solvable roommate problem. In particular, we show that the polarization structure of the marriage problem on which the proof of...

We consider one-to-one matching markets in which agents can either be matched as pairs or remain single. In these so-called roommate markets agents are consumers and resources at the same time. We investigate two new properties that capture the effect a newcomer has on incumbent agents....

We study efficient and individually rational exchange rules for markets with heterogeneous indivisible goods that exclude the possibility that an agent benefits by bundling goods in her endowment. Even if agents'' preferences are additive, no such rule exists.