Institution: | a D.M.A., Ecole Normale Supérieure, 45 rue d'Ulm, 75005 Paris, France b Institutul de Matematic? al Academiei Române, P.O. Box 1-764, RO-014700 Bucharest, Romania c Scoala Normal? Superioar? Bucharest, calea Grivitei 21, Bucharest, Romania d School of Mathematics, Korea Institute for Advanced Study, Hoegiro 87, Dongdaemun-gu, Seoul 130-722, Republic of Korea |