1. Department of Mathematics, University of Rhode Island, Kingston, RI, USA
2. Mathematisches Seminar, Christian-Albrechts-Universität zu Kiel, Kiel, Germany
3. Department of Mathematical Sciences, Ball State University, Muncie, IN, USA
4. Course of Mathematical Science, Department of Human Coexistence, Graduate School of Human and Environmental Studies, Kyoto University, Yoshida-nihonmatsu-cho, Sakyo-ku, Kyoto, Japan