Affiliation: | Department of Computer Science, University of Veszprém, 8200 Veszprém, Egyetem u. 10, Hungary Tel.: +36 88 422022; fax: +36 88 428275; Department of Computer Science, Queen Mary University of London, London E1 4NS, England, UK; Department of Computing Science, University of Glasgow, Glasgow G12 8QQ, Scotland, UK |