When the members of a voting body exhibit single peaked preferences, majority winners exist. Moreover, the median(s) of the preferred alternatives of voters is (are) indeed the majority (Condorcet) winner(s). This important result of Duncan Black (1958) has been crucial in the development of...

We explore to what extent we can propose fixed negotiation rules as well as simple mechanisms (or protocols) that guarantee that political parties can form stable coalition-governments. We analyze the case where three parties can hold office in the form of two-party coalitions. We define the...

A group of agents has to decide whether to accept or reject a proposal. Agents vote in favor or against the proposal and, if the number of agents in favor is greater to certain quota, the proposal is accepted. The \textit{socially optimal decision} is the one adopted when all agents vote...

A high court has to decide whether a law is constitutional, un- constitutional, or interpretable. The voting system is runoff. Runoff voting systems can be interpreted both, as social choice functions or as mechanisms. It is known that, for universal domains of preferences, runoff voting systems...

A jury has to choose the winner of a contest. There exists a deserving winner, whose identity is common knowledge among the jurors, but not known by the planner. Jurors may be biased in favor (friend) or against (enemy) some contestants. We study conditions on the confi?guration of the jury so...

A jury has to decide the winner of a competition among a group of contestants. All members of the jury know who the deserving winner is, but this contestant is unknown to the planner. The social optimum is that the jury select the deserving winner. Each individual juror may be biased in favor...

We analyze the problem of choosing the w contestants who will win a competition within a group of n w competitors when all jurors commonly observe who the w best contestants are, but they may be biased. We study conditions on the configuration of the jury so that it is possible to induce the...

We analyze the problem of a jury choosing the winner from a set of agents when the identity of the deserving winner is common knowledge amongst the jurors but each juror is biased in favor of one di¤erent agent. We propose a simple and natural mechanism that implements the socially optimal rule...

We analyze the problem of choosing the w contestants who will win a competition within a group of nw competitors when all jurors commonly observe who are the w best contestants but may be biased. We study conditions on the configuration of the jury so that it is possible to induce the jurors to...

We concentrate on the problem of the provision of one pure public good whenever agents that form the society have either single-plateaued preferences or single-peaked preferences over the set of alternatives. We are interested in comparing the relationships between different nonmanipulability...