1. Department of Knowledge-Based Mathematical Systems, Johannes Kepler University, 4040 Linz, Austria
2. Institute of Information Engineering, Automation and Mathematics, Slovak University of Technology, 812 37 Bratislava, Slovakia
3. Department of Mathematics and Descriptive Geometry, SvF, Slovak University of Technology, 813 68 Bratislava, Slovakia
4. Institute of Information and Automation, Czech Academy of Sciences, 182 08 Prague, Czech Republic
5. Dipartimento di Matematica "Ennio De Giorgi", Università del Salento, 73100 Lecce, Italy