1. College of Information Science and Engineering, Ritsumeikan University, Kusatsu, Gunma, Japan
2. College of Computer Science and Technology, Zhejiang University, Zhejiang, P. R. China
3. School of Education, Soochow University, Suzhou, Jiangsu, P. R. China
4. Artificial Intelligence Research Center, Yamaguchi University, Yamaguchi, Japan