Alt, Johannes
Section of Mathematics, University of Geneva, 2-4 Rue du Lièvre, CH-1211 Genève 4, Switzerland
Erdős, László
IST Austria, Am Campus 1, A-3400 Klosterneuburg, Austria
Krüger, Torben
Department of Mathematical Sciences, University of Copenhagen, Universitetsparken 5, DK-2100 København, Denmark