Institution: | Fachbereich Mathematik, TU Darmstadt, Schlossgartenstraße 7, 64289 Darmstadt, Germany ; Institute of Mathematics, Clausthal University of Technology, Erzstraße 1, 38678 Clausthal-Zellerfeld, Germany ; Institute of Computer Science, Academy of Sciences of the Czech Republic, Pod Vodárenskou vezí 2, 18207 Prague 8, Czech Republic |