1. Department of Mathematics, University of Padova, Via Trieste 63, Padova, Italy
2. Léonard de Vinci Pôle Universitaire, Research Center, 92916 Paris La Défense, France
3. IESEG School of Management, 3 rue de la Digue, 59000 Lille, France
4. LEM-CNRS 9221, 3 rue de la Digue, 59000 Lille, France