1. School of Mathematics and Physics, Anhui Jianzhu University, Hefei 230601, China
2. Department of Mathematics, University of Engineering and Technology, Lahore, Pakistan
3. Department of Mathematics, Quaid-i-Azam University, Islamabad-45320, Pakistan
4. Department of Mathematics, Khawaja Fareed University of Engineering and Information Technology, Rahim Yar Kahn, Pakistan
5. Department of Mathematics, University of Punjab, New Campus, Lahore, Pakistan