Institution: | 1. Department of Mathematics, Korea University, 136-701 Seoul, Republic of Korea;2. Département GEA, IUT Bobigny, Université Paris 13, 1, rue de Chablis, 93000 Bobigny, France;3. Department of Mathematics Education, Korea University, 136-701 Seoul, Republic of Korea;4. Institut de Mathématiques de Luminy, UMR 6206, 163, avenue de Luminy, Case 907, 13288 Marseille Cedex 9, France |