LAMIH ROAD, Universite de Valenciennes, UMR CNRS 8530 Le Mont Houy-BP311, F-59304 Valenciennes Cedex, FRANCE. gandibleux@univ-valenciennes.fr;Institute of Computing Sciences, Poznan University of Technology ul. Piotrowo 3a, 60-965 Poznan, POLAND. jaszkiewicz@cs.put.poznan.pl;LAMIH ROAD, Universite de Valenciennes, UMR CNRS 8530 Le Mont Houy-BP311, F-59304 Valenciennes Cedex, FRANCE. freville@univ-valenciennes.fr;Institute of Computing Sciences, Poznan University of Technology ul. Piotrowo 3a, 60-965 Poznan, POLAND. Slowinski@cs.put.poznan.pl