First Author:   Lina Mallozzi University of Naples Federico II mallozzi@unina.it   Department of Mathematics and, Applications, V. Claudio 21 Naples, 80125, Italy       Second Author: Stef Tijs University of Tilburg S.H.Tijs@uvt.nl   Econometrics and Operations, Econometrics and Operations, Research Tilburg, 5000 LE, The Netherlands