Institution: | aDepartment of Mathematics, Kyoto Prefectural University of Medicine, 13 Nishitakatsukasa-cho, Taishogun Kita-ku, Kyoto 603-8334, Japan bDepartment of Mathematics, Faculty of Science, Kyoto Sangyo University, Kamigamo Motoyama, Kita-ku, Kyoto 603-8555, Japan |