On single-peakedness and strategy-proofness: ties between adjacent alternatives

Abstract

We extend the classical characterizations of social choice rules that satisfy strategy-proofness in the single-peaked domain of preferences by Moulin (Public Choice, 1980) and Barberà, Gul, and Stacchetti (Journal of Economic Theory, 1993) to multivalued social choice rules that admit either the selection of single alternatives or the selection of pairs of adjacent alternatives.