First Author:   Sophie Pommet University Côte d''Azur - GREDEG-CNRS sophie.pommet@unice.fr   250 rue Albert Einstein Valbonne, 06560, France   (+33) 4 93 95 43 96(Phone) (+33) 4 93 95 43 96(Fax) Second Author: Jean-François Sattin University Paris 1 Panthéon-Sorbonne, PRISM Jean-Francois.Sattin@univ-paris1.fr   17, rue de la Sorbonne Paris, 75005, France   (+33) 1 44 07 83 21(Phone)