1. Institute of Systems Science, Academy of Mathematics and Systems Sciences, Chinese Academy of Sciences, Beijing 100080, People's Republic of China
2. School of Knowledge Science, Japan Advanced Institute of Science and Technology, 1-1, Asahidai, Ishikawa 923-1292, Japan
3. Department of Management Sciences, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China