1. Resource Economics, West Virginia University, Morgantown, WV, USA
2. Department of Mathematics, University of Montpellier 2, Montpellier, France
3. Department of Economics, University of Laval, Quebec City, Qc, Canada
4. Department of Economics, University Felix Houphouet Boigny (FHB), Abidjan – Cocody, Cote d'Ivoire