 
 
 
 
 
 
 
  
 
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