1. Department of Mathematics, Faculty of Sciences, University of Algiers, Algeria
2. Section of Mathematics, International Telematic University Uninettuno, Corso Vittorio Emanuele Ⅱ, 39, 00186 Roma, Italy
3. Department of Mathematics, Faculty of Science, Yarmouk University, Irbid 211-63, Jordan
4. Department of Mathematics, Faculty of Sciences, University of Djilali Bounaama, Khemise Miliana, Algeria