1. Department of Mathematics and Statistics, Texas Tech University, 1108 Memorial Circle, Lubbock, TX 79409-1042, USA
2. Charles Schwab Corporation, 101 Montgomery St., San Francisco, CA 94104, USA
3. College of Business, Stony Brook University, 100 John S. Toll Drive, Stony Brook, NY 11794, USA
4. EDHEC Business School, 393, Promenade des Anglais, BP3116, 06202 Nice Cedex 3, France