The majority decision function for trees with 3 leaves

Kenneth May in 1952 proved a classical theorem characterizing simple majority rule for two alternatives. The present paper generalizes May’s theorem to the case of three alternatives, but where the voters’ preference relations are required to be trees with alternatives at the leaves. This paper with title “May’s Theorem for Trees” was presented at the joint DIMACS-LAMSADE workshop on Computer Science and Decision Theory, Université Paris-Dauphine, Paris 27–29 October 2004. It appeared in the proceedings Annales du LAMSADE 3 (2004), 259–266.