1. Department of Mathematics , Thai Nguyen University of Education , Luong Ngoc Quyen street , Thai Nguyen city , Thai Nguyen; and Thang Long Institute of Mathematics and Applied Sciences, Thang Long University, Nghiem Xuan Yem, Hoang Mai, Hanoi , Vietnam
2. Faculty of Applied Mathematics , AGH University of Kraków , Kraków 30-059 , Poland ; and Brno University of Technology, Faculty of Electrical Engineering and Communication, Technická 3058/10, Brno 61600, Czech Republic; and Simion Stoilow Institute of Mathematics of the Romanian Academy, 21 Calea Griviţei Street, 010702 Bucharest, Romania; and Department of Mathematics, University of Craiova, Street A.I. Cuza 13, 200585 Craiova, Romania; and School of Mathematics, Zhejiang Normal University, Jinhua, Zhejian