Affiliation: | 1.Diskrete Mathematik, Technische Universit?t Braunschweig, D-38023 Braunschweig, Germany,DE;2.Computer and Automation Research Institute, Hungarian Academy of Sciences, Lágymányosi u. 11, H-1111 Budapest, Hungary,HU;3.Department of Geometry, E?tv?s University, Kecskeméti utca 10-12, H-1053 Budapest, Hungary,HU |