Título: Comparing Voting by Committees According to their Manipulability
Expositor: Dr. Pablo Arribillaga
Abstract: We consider the class of voting by committees used by a society to collectively choose a subset from a given set of objects. We offer a simple criterion to compare voting by committees without dummy agents according to their manipulability. This criterion is based on the set-inclusion relationships of the decisive and vetoer sets. We show that the binary relation "to be as manipulable as" endows the set of equivalence classes of anonymous voting by committees (i.e., voting by quotas) with a complete upper semilattice structure, whose supremum is the equivalence class containing all voting by quotas whose quota of each object is strictly larger than one and strictly lower than the number of agents. Finally, we extend the comparability criterion to the full class of all voting by committees.