1. Sloan School of Management, Computer Science and Artificial Intelligence Laboratory, and Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA;
2. Laboratory for Financial Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
3. National Bureau of Economic Research, Cambridge, Massachusetts, USA
4. Santa Fe Institute, Santa Fe, New Mexico, USA
5. Carlson School of Management, University of Minnesota, Minneapolis, Minnesota, USA