The Copeland choice function. An axiomatic characterization (Q1082226)

Consider a social choice problem with a finite number of voters and alternatives. Let P be the majority preference relation and I, the majority indifference relation. The Copeland score for alternative x is the sum of the scores of x against all other alternatives y (xPy is worth two points, xIy is worth one point, yPx is worth zero points for x). The Copeland choice rule picks the alternatives with maximum Copeland scores. This paper gives an axiomatic characterization of the Copeland choice rule. It is the only choice rule satisfying independence of irrelevant alternatives, strong monotonicity, neutrality, and independence of cycles.