1. Department of Computer Science and Engineering, and the MoE Key Laboratory of Artificial Intelligence, AI Institute, Shanghai Jiao Tong University, Shanghai 200240, China.
2. Department of Computer Science and Engineering, and the MoE Key Laboratory of Artificial Intelligence, AI Institute, Shanghai Jiao Tong University, Shanghai 200240, China (e-mail: yanjunchi@sjtu.edu.cn)
3. Microsoft Research Laboratory, Redmond, WA 98052 USA.