Affiliation: | (1) Mathematisches Seminar, Universität Hamburg, Bundesstraße 55, D-2000 Hamburg, Germany;(2) Department of Mathematics and Statistics, University of Massachusetts, 01003 Amherst, MA, U.S.A.;(3) Faculty of Agricultural Technology, T.E.I./M. at Arta, P.O. Box 110, GR-47100 Arta, Greece |