1. Department of Mathematics and Statistics, The University of Lahore, Lahore Campus, Pakistan
2. Department of Mathematics, Punjab Tianjin University of Technology, Lahore, Pakistan
3. Faculty of Science and Technology, University of the Faroe Islands, Faroe Islands, Denmark
4. Department of Mathematics, College of Sciences, King Saud University, P.O. Box 2455 Riyadh 11451, Saudi Arabia