1. Key Laboratory of High Confidence Software Technologies (Ministry of Education), school of Computer Science, Peking University, Beijing, China
2. University at Buffalo, Buffalo, New York, United States
3. Institute of Software, Chinese Academy of Sciences and University of Chinese Academy of Sciences, Beijing, China
4. Key Laboratory of High Confidence Software Technologies (Ministry of Education), school of Computer Science, Peking University, Beijing, China, Telecom SudParis and Institut Polytechnique de Paris, Paris, France