Keiichiro Honda Graduate School of Economics, Osaka University   1-7 Machikaneyama-machi Toyonaka, Osaka 560-0043 Japan   kgp802hk@mail2.econ.osaka-u.ac.jp   http://sites.google.com/site/khondaweb/           JEL Areas: F1 : Trade: General Q0 : Agricultural and Natural Resource Economics; Environmental and Ecological Economics: General