Institution: | a Department of Mathematics, University of West Bohemia, P.O. Box 314, 306 14 Pilsen, Czech Republicb Institute of Theoretical Computer Science (ITI), Charles University, P.O. Box 314, 306 14 Pilsen, Czech Republicc Department of Math. and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlandsd Department of Mathematics, Beijing Institute of Technology, Beijing, 100081, PR Chinae Department of Mathematics, Qinghai University for Nationalities, PR Chinaf Department of Mathematics, Jiangxi Normal University, PR China |