1. Department of Mathematics, University of Nigeria, Nsukka, Nigeria
2. Department of Mathematics, Zhejiang Normal University, Jinhua, People's Republic of China; Institute of Science and Technology (IST), Klosterneuburg, Austria; Institute of Science and Technology (IST), Klosterneuburg, Austria
3. Research Center for Interneural Computing, China Medical University Hospital, China Medical University, Tiachung, Taiwan
4. Department of Applied Mathematics, National Sun Yat-sen University, Kaohsiung, Taiwan