1. Department of Mathematics and Computer Science, University of Marburg, Hans-Meerwein-Straße 6, D-35032 Marburg, Germany ()
2. Faculty of Business, Economics and Statistics, University of Vienna and Center for Financial Studies, Frankfurt, Oskar-Morgenstern-Platz 1, A-1090 Vienna, Austria ()
3. Faculty of Economics, University of Cambridge, Sidgwick Avenue, Cambridge CB3 9DD, United Kingdom ()
4. Institute of Mathematics, Humboldt-Universität zu Berlin, Unter den Linden 6, D-10099 Berlin, Germany ()