Affiliation: | a INRIA, 2004 Route des Lucioles, 06902, Sophia Antipolis, France b CESIMO, Facultad de Ingeneria, Universidad de Los Andes, Merida, Venezuela c CWI, P.O. Box 94079, 1090 GB, Amsterdam, Netherlands d Department of Mathematics and Computer Science, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, Netherlands |