1. College of Computer Science and Technology Jilin University Changchun Jilin China
2. Key Laboratory of Symbolic Computation and Knowledge Engineering of Ministry of Education Jilin University Changchun Jilin China
3. Center for Computer Fundamental Education Jilin University Changchun Jilin China
4. School of Computer Science and Engineering Nanjing University of Science and Technology Nanjing Jiangsu China
5. School of Computing National University of Singapore Singapore Singapore