Affiliation: | 1. Mathematics Research Unit, University of Luxembourg, 6, rue Richard Coudenhove-Kalergi, L–1359 Luxembourg, Luxembourg;2. Computer Science and Communications Research Unit, University of Luxembourg, 6, rue Richard Coudenhove-Kalergi, L–1359 Luxembourg, Luxembourg;3. Bolyai Institute, University of Szeged, Aradi vértanúk tere 1, H–6720 Szeged, Hungary |