Takeshi Yamazaki Niigata University   8050 Ikarashi 2-no-cho Nishi-ku Niigata-shi, Niigata-ken 950-2181 Japan   tyamazak@econ.niigata-u.ac.jp             JEL Areas: L1 : Market Structure, Firm Strategy, and Market Performance: General C7 : Game Theory and Bargaining Theory:General