Institution: | (1) Department of Pure Mathematics, School of General Studies, Australian National University, P.O. Box 4, 2600 Canberra, A.C.T., Australia;(2) Mathematics Institute, University of Warwick, CV4 7AL Coventry, England;(3) Fachbereich Mathematik der Universität, Saarstraße 21, D-6500 Mainz, Federal Republic of Germany |