1. Department of Mathematics, COMSATS Institute of Information Technology, Attock, Pakistan.
2. Department of Mathematical Sciences, United Arab Emirates University, P.O. Box 15551, Al Ain, United Arab Emirates.
3. School of Natural Sciences (SNS), National University of Sciences and Technology (NUST), Sector H-12, Islamabad, Pakistan.
4. Department of Mathematics, COMSATS Institute of Information Technology, Sahiwal, Pakistan.