Affiliation: | 1. Department of Mathematics Education and the RINS, Gyeongsang National University, Chinju 660-701, South Korea;2. Department of Mathematics, Science & Research Branch, Islamic Azad University, Post Code 14778, Ashrafi Esfahani Ave, Tehran, Islamic Republic of Iran;3. Department of Mathematics and Physics, North China Electric Power University, Baoding 071003, China;4. Department of Mathematics, Gyeongsang National University, Chinju 660-701, South Korea |