1. Centre for Advanced Mathematics and Physics, National University of Sciences and Technology, Islamabad 44000, Pakistan
2. Department of Mathematics and Statistics, Missouri University of Science and Technology, Rolla, MI 65409-0020, USA
3. Abdus Salam School of Mathematical Sciences, GC University, Lahore 54000, Pakistan
4. Faculty of Textile Technology, University of Zagreb, Pierottijeva 6, 10000 Zagreb, Croatia