Affiliation: | (1) Mathematisches Institut, Universität München, Theresienstrasse 39, W-8000 München 2, Federal Republic of Germany;(2) Department of Mathematics, University of California, 405 Hilgard Ave., 90024 Los Angeles, CA, USA;(3) Present address: Fachbereich Mathematik, Universität Frankfurt, Robert-Mayer-Strass 6-10, W-6000 Frankfurt am Main, Federal Republic of Germany |