1. School of Mathematics, Wenzhou University, Wenzhou 325000, China
2. Chengdu Institute of Computer Application, Chinese Academy of Sciences, Chengdu 610041, China
3. School of Mathematics and Statistics, Chongqing University of Technology, Chongqing 400054, China
4. Department of Mathematics, Hubei Minzu University, Enshi, Hubei 445000, China