On the universally beneficial manipulation conjecture

摘要

The universally beneficial manipulation conjecture of Campbell and Kelly states that for a social choice rule, if everyone gains as a result of any optimal manipulation, then the rule satisfies universally beneficial manipulation, i.e., everyone gains as a result of any manipulation, optimal or not. We prove the conjecture for three alternatives and any number of individuals. We also construct a counterexample in a general form with more than three alternatives and at least two individuals.