Affiliation: | Department of Computer Science, Columbia University, New York, NY 10027, USA;Fakultaet fuer Informatik und Mathematik, Universitaet Passau Innstrasse 33, 94032 Passau, Germany;Department of Mathematics, Informatics, and Mechanics, University of Warsaw, Ul. Banacha 2, Warsaw 02-097, Poland;Department of Mathematics, University of Salzburg, Hellbrunnerstr.34, A-5020 Salzburg, Austria |