1. Faculty of Computer Science, "Al.I. Cuza" University, 16 Berthelot St., 6600 Iaşi, Romania
2. CentER and Department of Econometrics, Tilburg University, P.O. Box 90153, 5000 LE Tilburg, The Netherlands
3. Faculty of Mathematical Sciences, University of Twente, P. O. Box 217, 7500 AE Enschede, The Netherlands