Institution: | a Department of Mathematics and Computer Science, Graduate School of Science and Engineering, Kagoshima University, 1-21-35 Korimoto, Kagoshima 890-0065, Japanb Kushiro Campus, Hokkaido University of Education, Kushiro 085-8580, Japanc Division of Computer Science, Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan |