Tetsuo Yamamori Graduate School of Economics, University of Tokyo   3-26-20-405 Raionzu-manshon-Nishidai-dai2 Hasune Itabashi-ku Tokyo, Tokyo 174-0046 Japan   ee27004@mail.ecc.u-tokyo.ac.jp   http://homepage3.nifty.com/tetsu-ym           JEL Areas: