1. Institute of Statistical Science & Institute of Information Science, Academia Sinica, Taipei 115, Taiwan
2. Institut für Diskrete Mathematik und Geometrie, Technische Universität Wien, Wiedner Hauptstraße 8-10/104, 1040 Wien, Austria
3. LIPN, Institut Galilée, Université Paris 13, 93430, Villetaneuse, France
4. Institute of Statistical Science, Academia Sinica, Taipei 115, Taiwan
5. Department of Electronic and Computer Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan