Ken-ichi Akao School of Social Sciences, Waseda University   1-6-1 Nishiwaseda Shijuku Tokyo, 169-8050 Japan   akao@waseda.jp   http://www.f.waseda.jp/akao/KA/Kenichi_Akao.htm           JEL Areas: Q5 : Environmental Economics: General D9 : Intertemporal Choice and Growth: General