Yukio Koriyama Ecole Polytechnique   Ecole Polytechnique Departement d'Economie Palaiseau, 91128 France   yukio.koriyama@polytechnique.edu   http://www.yatsuke.gr.jp/~korbie/           JEL Areas: D7 : Analysis of Collective Decision-Making: General C7 : Game Theory and Bargaining Theory:General