1. Mathematical Institute, University of Koblenz, 56070 Koblenz, Germany
2. Faculty of Information and Communication Technology, Wrocław University of Science and Technology, 50-372 Wrocław, Poland
3. Interdisciplinary Centre for Mathematical and Computational Modelling (ICM), University of Warsaw, 00-927 Warsaw, Poland
4. Faculty of Management, Wroclaw University of Science and Technology, 50-371 Wrocław, Poland