1. Department of Mathematics, School of Sciences, University of Management and Technology, C-II, Johar Town, Lahore 54770, Pakistan
2. Department of Mathematics, Government College University, Lahore 54000, Pakistan
3. Institute of Research and Development of Processes, University of the Basque Country, Campus of Leioa (Bizkaia), P.O. Box 644- Bilbao, Barrio Sarriena, Leioa 48940, Spain