1. Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia
2. Department of Mathematics, Faculty of Natural Sciences, Jamia Millia Islamia, New Delhi 110025, India
3. Department of Mathematics, Michigan State University, East Lansing, Michigan 48824-1027, USA
4. Department of Mathematics, Art and Science Faculty, Uludag University, Bursa 16059, Turkey