Institution: | (1) Department of Mathematics, Fukuoka University of Education, Munakata, Fukuoka 811-4192, Japan;(2) Department of Mathematics, Hokkaido University, Sapporo 060-0810, Japan;(3) Department of Mathematics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan;(4) Faculty of Mathematics, Kyushu University, Higashi-ku, Fukuoka 812-8581, Japan |