1. Department of Mathematics, Quaid-i-Azam University, Islamabad, IS, Pakistan
2. School of Mathematics & Actuarial Science, Univerisity of Leicester, Leicester, Leicestershire, UK
3. Department of Mathematics, College of Science, King Khalid University, Abha, Asir, Saudi Arabia
4. Al-Farabi Kazakh National University, Faculty of mechanics and mathematics, Almaty, Kazakhstan