Affiliation: | 1. Yonago National College of Technology, Yonago 683-8502, Japan;2. Department of Mathematics, Faculty of Science, Niigata University, Niigata 950-2181, Japan;3. Department of Mathematical Sciences, Faculty of Science, Shinshu University, Matsumoto 390-8621, Japan;4. Toho University, Chiba 273-0866, Japan |