1. Department of Mathematics, COMSATS Institute of Information Technology, Abbottabad, 22060 Khyber Pakhtunkhwa, Pakistan
2. Department of Mathematics, King Abdul Aziz University, Jeddah 21589, KSA
3. Department of Mathematics, University of Malakand, Chakdara (18800) Dir (Lower), Khyber Pakhtunkhawa, Pakistan