1. Preparatory Year Deanship, King Faisal University, 31982 Hofuf, Al Ahsa, Saudi Arabia
2. Department of Mathematics, University of Lahore, Gujrat Campus, Gujrat, Pakistan
3. Department of Mathematics, COMSATS, University Islamabad Lahore Campus, Pakistan
4. Faculty of Mathematics, University of Dortmund, 44221 Dortmund, Germany
5. Romanian Academy, Bucharest, Romania