1Department of Appl. Mathematics, Technical University, Letnd 9, 04200 Kosice, Slovakia
2Abdus Salam School of Mathematical Sciences, GC University, 68-B, New Muslim Town, Lahore, Pakistan
3Facultat de Ciéncies Polttiques i Juridiques, Universitat Internacional de Catalunia, C/Immaculada 22, 08017 Barcelona, Spain
4 Abdus Salam School of Mathematical Sciences, GC University, 68-B, New Muslim Town, Lahore, Pakistan