Affiliation: | 1.Department of Mathematics and Computer Science, University of Perugia, via L. Vanvitelli 1, 06123, Perugia, Italy ;2.Department of Economics, University of Perugia, via A. Pascoli 20, 06123, Perugia, Italy ;3.Léonard de Vinci P?le Universitaire, Research Center, 92916, Paris, La Défense Cedex, France ; |