(New) 5 November 2026, Computational Social Choice Seminar, Federico Fioravanti

Abstract

We extend obvious manipulability to coalitional deviations in voting. Conditional on a report being a group manipulation, we show that it is obvious if and only if every coalition member can benefit from it under every rule with the same coalitional option sets. This gives a robustness interpretation of obviousness in terms of option-set indistinguishability. On the universal domain with at least three alternatives, we show that an onto tops-only rule is not obviously manipulable by groups (NOMG) if and only if it is group strategy-proof. For the case of only two alternatives, being NOMG is less demanding. We then turn to non-tops-only rules, where we present some NOMG rules and we obtain a general impossibility result for rules satisfying the majority criterion.
This is joint work with Pablo Arribillaga and Agustin Bonifacio.

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