1. Aix-Marseille School of Economics, Aix-Marseille University, CNRS & EHESS, France
2. IRES-CORE, Université Catholique de Louvain, Belgium
3. Department of Mathematics, Prairie View A&M University, P. O. Box 519-MS 2225, Prairie View, Texas 77446-0519, USA
4. School of Business, Houston Baptist University, 7502 Fondren, Houston, TX 77074, USA