1. Department of Mathematics, Williams College, Williamstown, MA 01267, USA
2. Department of Economics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3. Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA
4. Mahidol University, Bangkok, Thailand
5. College of the Holy Cross, 1 College St., Worcester, MA 01610, USA
6. Departments of Computer Science and Engineering, Stanford University, Stanford, CA 94304, USA