1. Department of Mathematics, College of Science, University of Ha'il, Ha'il 2440, Saudi Arabia
2. School of Mathematical Sciences, Anhui University, Anhui 230601, China
3. University of Massachusetts Medical School, Worcester, MA 01655, USA
4. Department of Mathematics, Abdul Wali Khan University, Mardan 23200, Pakistan
5. Department of Mathematics, Faculty of Science, Khon Kaen University, Khon Kaen 40002, Thailand