1. Department of Mathematics and Statistics, The University of Lahore, Lahore Campus, Lahore, Pakistan
2. Department of Mathematics, King Saud University, P.O.Box 22452, Riyadh 11495, Saudi Arabia
3. Faculty of Science and Technology, University of the Faroe Islands, Vestarabryggja 15, FO 100 Torshavn, Denmark
4. Bangabandhu Sheikh Mujibur Rahman Science and Technology University, Gopalganj, Bangladesh