Institution: | (1) SPb Institute for Economics and Mathematics Russian Academy of Sciences, 1 Tchaikovsky St., 191187 St. Petersburg, Russia (e-mail: anna@AK3141.spb.edu), RU;(2) Faculty of Mathematical Sciences, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands (e-mail: t.s.h.driessen@math.utwente.nl), NL |