1. School of Mathematical Sciences, Nanjing Normal University, Nanjing 210023, China
2. School of Mathematics and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044, China
3. Business School, Nanjing Normal University, Nanjing 210023, China
4. Stern School of Business, New York University, 44 West Fourth Street, New York, NY 10012, USA