Frank Dehne Henk R. van de Zandschulp
Division of Mathematics and Computer Science Department of Computer Science
Faculty of Sciences, Vrije Universiteit University of Twente
De Boelelaan 1081a, 1081 HV Amsterdam P.O. Box 217, 7500 AE Enschede
The Netherlands The Netherlands
frank@cs.vu.nl henkz@cs.utwente.nl
February 12, 2001