Abstract (EN)

Sequential voting rules and correspondences provide a way for agents to make group decisionswhen the set of available options has a multi-issuestructure. One important question about sequentialvoting rules (correspondences) is whether they satisfy two crucial criteria, namely neutrality and efficiency. Recently, Benoit and Kornhauser estab-lished an important result about seat-by-seat votingrules (which are a special case of sequential votingrules): they proved that if the multi-issue domainsatisfies some properties, then the only seat-by-seatrules being either efficient or neutral are dictatorships. However, there are still some cases not covered by their results, including a very importantand interesting case—voting correspondences. Inthis paper, we extend the impossibility theorems byBenoit and Kornhauser to voting correspondences,and obtain a dichotomy theoremon the existence ofefficient or neutral sequential (seat-by-seat) votingrules and correspondences. Therefore, the questionof whether sequential (seat-by-seat) voting rules(correspondences) can be efficient or neutral is nowcompletely answered.