Affiliation: | (1) Department Wiskunde en Informatica, University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium;(2) Department of Mathematics, University of Washington, 98195 Seattle, WA, USA;(3) I.H.E.S., 35 Route de Chartres, F-91440 Bures-sur-Yvette, France;(4) Present address: Department WNI, Limburgs Universitaire Centrum, B-3590 D?penbeek, Belgium |