Institution: | (1) Institut für Algebra und Diskrete Mathematik, Technische Universität Wien, E118.2, A-1040 Vienna, Austria;(2) Institute of Computer Science Academy of Sciences, Pod vodárenskou ví 2, 182 07 Prague, Czech Republic;(3) Mathematical Institute and Institute of Computer Science Academy of Sciences, itná 25, 115 67 Prague, Czech Republic |