1. Institute of Mathematics, Henan Polytechnic University, Jiaozuo, Henan, China + School of Mathematics and Physics, Hulunbuir University, Inner Mongolia, China
2. Mathematical Institute, Serbian Academy of Sciences and Arts, Belgrade, Serbia + Univerity of Niš, Faculty of Sciences and Mathematics, Niš, Serbia
3. Department of Mathematics Education, Andong National University, Andong, Republic of Korea