Affiliation: | (1) School of Mathematics, Korea Institute for Advanced Study, 207-43 CheongNyangNi 2-Dong, DongDaeMun-Gu, Seoul, 130-722, Republic of Korea;(2) Division of Digital Media, SangMyung University, 7 HongJi-Dong, JongRo-Gu, Seoul, 110-743, Republic of Korea |