| Institution: | (1) ZiF, Universität Bielefeld, D-4800 Bielefeld, Federal Republic of Germany;(2) Present address: Research Institute for Mathematical Sciences, Kyoto University, 606 Kyoto, Japan;(3) Present address: UER scientifique de Marseille-Luminy, Route Léon Lachamp, F-13008 Marseille, France;(4) Present address: Department of Mathematics, University of California, Los Angeles, California, USA;(5) II. Institut für Theoretische Physik, Universität Hamburg, D-2000 Hamburg, Federal Republic of Germany |
