1. Department of Mathematics, Michigan State University, 619 Red Cedar Road, East Lansing, MI 48824-1027, USA
2. Basic Science Department, Modern Academy for Engineering and Technology, Maadi, Cairo 11571, Egypt
3. Department of Pure Mathematics, University of Calcutta, Ballygaunge Circular Road Kolkata, Kolkata 700019, West Bengal, India
4. Department of Mathematics, Faculty of Science, Fayoum University, Faiyum 63514, Egypt
5. Department of Mathematics, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia