1. School of Mathematics and Physics, Hulunbuir University, Inner Mongolia, Hulunbuir 021008, China
2. School of Mathematics and Informatics, Henan Polytechnic University, Jiaozuo 454010, China
3. Independent Researcher, Dallas, TX 75252-8024, USA
4. Department of Mathematics, National Kaohsiung Normal University, Kaohsiung 82444, Taiwan