Institution: | a Mathematical Sciences Department, Hail Community College, King Fahd University of Petroleum and Minerals, P.O. Box 2440, 44 Avenue Bartholdi, 72000 le Mans, Hail, Saudi Arabia b Equipe de Mathématiques de Besançon, Université de Franche-Comté, CNRS-UMR 6623, 16, route de Gray, 25030, Besançon Cedex, France |