1. College of Computer Science and Technology, Jilin University, Changchun 130012, China
2. Key Laboratory of Symbolic Computation and Knowledge Engineering of Ministry of Education, Jilin University, Changchun, China
3. School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA
4. Center for Computer Fundamental Education, Jilin University, Changchun, Jilin 130012, China
5. College of Communication Engineering, Jilin University, Changchun, Jilin 130012, China
6. Department of Information Technology, Changchun Vocational Institute of Technology, Changchun 130033, China