First Author:   Gilles Lafforgue INRA-LERNA, University of Toulouse glafforg@toulouse.inra.fr   21 Allée de Brienne Toulouse, 31000, France   +33.(0)5.61.12.88.76(Phone) +33.(0)5.61.12.88.76(Fax) Second Author: Walid Oueslati INH walid.oueslati@inh.fr