Authors
Huimei Wang
Department of Mathematics, Kunming University, Yunnan
Xiaofang Meng
Department of Mathematics, Yunnan University, Yunnan
© 2019 Yongkun Li, Huimei Wang, Xiaofang Meng, published by University of Zielona Góra
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.