1. Department of Mathematical Sciences, Ritsumeikan University, 1-1-1 Nojihigashi, Kusatsu 52-8577, Shiga, Japan
2. Department of Mathematics, King's College London, London WC2R 2LS, United Kingdom
3. Institute of Economic Research, Kyoto University, Yoshida-Honmachi, Sakyo-Ku, Kyoto 606-8501, Japan