Address Research Center for Mathematical Economics, Director Prof. Toru Maruyama Department of Economics, Keio University, 2-15-45, Mita, Minato-ku, Tokyo, 108-8345, JAPAN

E-mail maruyama@econ.keio.ac.jp Tel +81-3-3453-4511 (ex. 23271) Fax +81-3-5427-1578