Affiliation: | (1) Computer Science Department, University of Ioannina, GR-451 10 Ioannina, Greece; e-mail: akrivis@cs.uoi.gr , GR;(2) IRMAR, Université de Rennes I, Campus de Beaulieu, F-35042 Rennes, France; e-mail: michel.crouzeix@univ-rennes1.fr , FR;(3) Department of Mathematics, University of Crete, GR-714 09 Heraklion, Greece; e-mail: makr@math.uch.gr , GR;(4) IACM, Foundation of Research and Technology-Hellas, GR-711 00 Heraklion, Greece , GR |