Affiliation: | 1. Institute of Mathematics, University of P.J. Šafárik, Jesenná 5, 041 54 Košice, Slovak Republic;2. Faculty of Mathematics and Physics, DIMATIA and Institute for Theoretical Computer Science (ITI), Charles University, Malostranské nám. 2/25, 118 00 Prague, Czech Republic;3. Department of Mathematics, University of Ljubljana, Jadranska 19, 1111 Ljubljana, Slovenia;4. Department of Mathematics, Technical University of Dresden, D-01062 Dresden, Germany;1. Cracow,Poland;2. Cracow,Poland |