1. Professor, Dept. of Mathematics, Quaid-I-Azam Univ., 45320, Islamabad 44000, Pakistan.
2. Dept. of Mathematics, COMSATS Institute of Information Technology, WAH Campus, GT Rd., Quaid Ave., Wah Cantt, Pakistan (corresponding author).
3. Professor, Nonlinear Analysis and Applied Mathematics (NAAM) Research Group, Dept. of Mathematics, Faculty of Sciences, King Abdulaziz Univ., P.O. Box 80203, Jeddah 21589, Saudi Arabia.