Affiliation: | (1) Mathematisches Institut, Bismarckstrasse 1 1/2, D-8520 Erlangen, Federal Republic of Germany;(2) Mathematisches Institut, Postfach 101251, D-8580 Bayreuth, Federal Republic of Germany;(3) School of Mathematics and Physics, Macquarie University, 2113 North Ryde, New South Wales, Australia |