1. School of Mathematics and Informatics Henan Polytechnic University Jiaozuo City Henan Province 454010 CHINA
2. College of Mathematics Inner Mongolia University for Nationalities Tongliao City Inner Mongolia Autonomous Region 028043 CHINA
3. Department of Mathematics and Informatics Weinan Teachers University Weinan City Shaanxi Province 714000 CHINA
4. Department of Mathematics Chongqing Normal University Chongqing City 401331 CHINA