In the Possible Winner problem in computational social choice theory, we are given a set of partial preferences and the question is whether a distinguished candidate could be made winner by extending the partial preferences to linear preferences. Previous work has provided, for many common voting rules, fixed parameter tractable algorithms for the Possible Winner problem, with number of candida...

Persuasion is a common social and economic activity. It usually arises when conflicting interests among agents exist, and one of the agents wishes to sway the opinions of others. This paper considers the problem of an automated agent that needs to influence the decision of a group of self-interested agents that must reach an agreement on a joint action. For example, consider an automated agent ...

A strict ranking of n items may profitably be viewed as a permutation of the objects. In particular, social preference functions may be viewed as having both input and output be such rankings (or possibly ties among several such rankings). A natural combinatorial object for studying such functions is the permutahedron, because pairwise comparisons are viewed as particularly important. In this p...

The election of 1860 was one of the most important and contentious elections in US history. It was also one of the most interesting. Four candidates from three different parties battled for the presidency and all four received a significant number of votes. We ask whether Lincoln’s victory was sound, or was it due to a fluke in the electoral system? Did a Lincoln win plausibly represent the wil...

résumé – Les caractérisations axiomatiques du vote majoritaire et des classements par points. Le cadre arrowien de la théorie des choix collectifs est suffisament flexible pour entreprendre une étude axiomatique précise des règles de vote qui sont communément utilisées dans des élections politiques, lors de compétitions sportives ou par des comités d’experts etc. comme le vote à la majorité ou ...

In the Shift Bribery problem, we are given an election (based on preference orders), a preferred candidate p, and a budget. The goal is to ensure p’s victory by shifting p higher in some voters’ preference orders. However, each such shift request comes at a price (depending on the voter and on the extent of the shift) and we must not exceed the given budget. We study the parameterized computati...

We consider the scenario of a parliament that is going to vote on a specific important issue. The voters are grouped in parties, and all voters of a party vote in the same way. The expected winner decision is known, because parties declare their intentions to vote, but before the actual vote takes place some voters may leave the leading party to join other parties. We investigate the computatio...