1. Faculty of Mathematics, Computer Science, and Econometrics, University of Zielona Góra, 65-516 Zielona Góra, Poland
2. Algorithmics Research Group, Faculty of Mathematics and Computer Science, Jagiellonian University, 30-387 Krakow, Poland
3. Department of Mathematics and Statistics, Arizona State University, Tempe, Arizona 85287, U.S.A.
4. Department of Applied Mathematics, National Sun Yat-sen University, Taiwan, National Center for Theoretical Sciences