1. Department of Mathematics Zhejiang Normal University Zhejiang Jinhua China
2. Department of Mathematics King Abdulaziz University Jeddah Saudi Arabia
3. Department of Mathematics and Statistics University of South Florida Tampa Florida USA
4. School of Mathematics South China University of Technology Guangzhou China
5. Department of Mathematical Sciences North‐West University Mafikeng Campus Mmabatho South Africa
6. School of Mathematics and Physics North China Electric Power University Beijing China