1. College of Computer Science and Technology, Jilin University, Changchun, Jilin 130012, China
2. Key Laboratory of Symbolic Computation and Knowledge Engineering of Ministry of Education, Jilin University, Changchun, Jilin 130012, China
3. School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30302, USA
4. Department of Information Technology, Changchun Vocational Institute of Technology, Changchun 130033, China