1. Institute of Mathematics, University of Silesia in Katowice, Bankowa 14, 40-007 Katowice, Poland
2. Institute of Theoretical and Applied Informatics, Polish Academy of Sciences, Bałtycka 5, 44-100 Gliwice, Poland
3. Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian University, 30-348 Kraków, Poland