1. Institut für Mathematische Stochastik Technische Universität Dresden Zellescher Weg 12–14, 01069 Dresden Germany
2. Instytut Matematyczny Uniwersytet Wrocławski pl. Grunwaldzki 2/4, 50‐384 Wrocław Poland
3. Department of Applied Mathematics Faculty of Electrical Engineering and Computing University of Zagreb Unska 3, 10000 Zagreb Croatia
4. Institute of Discrete Mathematics Graz University of Technology Steyrergasse 30, 8010 Graz Austria