1. Department of Algorithms and Their Applications, Faculty of Informatics, Eötvös Loránd University, Pázmány Péter sétány 1/c, 1117 Budapest, Hungary. csuhaj@inf.elte.hu
2. Department of Computer Science, Faculty of Informatics, University of Debrecen, Kassai út 26, 4028 Debrecen, Hungary. vaszil.gyorgy@inf.unideb.hu