Institution: | (1) Department of Mathematics, College of Natural Sciences, Hanyang University, Sungdong-gu, Seoul, 133-791, Korea;(2) Department of Mathematics, Pohang University of Science & technology, Pohang, Kyoungbuk, 790-784, Korea;(3) Department of Mathematics Education, Hongik University, Mapo-gu, Seoul, 121-791, Korea;(4) Science and Liberal Arts-Mathematics Division, Youngdong University, Youngdong, Chungbuk, 370-701, Korea |