Proceedings Abstracts of the Twenty-Fourth International Joint Conference on Artificial Intelligence

Gibbard–Satterthwaite Games / 533
Edith Elkind, Umberto Grandi, Francesca Rossi, Arkadii Slinko

The Gibbard-Satterthwaite theorem implies the ubiquity of manipulators — voters who could change the election outcome in their favor by unilaterally modifying their vote. In this paper, we ask what happens if a given profile admits several such voters. We model strategic interactions among Gibbard–Satterthwaite manipulators as a normal-form game. We classify the 2-by-2 games that can arise in this setting for two simple voting rules, namely Plurality and Borda, and study the complexity of determining whether a given manipulative vote weakly dominates truth-telling, as well as existence of Nash equilibria.