Affiliation: | 1. Department of Mathematics Education, Research Institute of Natural Sciences, College of Education, Gyeongsang National University, Chinju 660-701, Republic of Korea;2. School of Mathematics and Information, China West Normal University, Nanchong, Sichuan 637002, PR China;3. Department of Mathematics, Sichuan University, Chengdu, Sichuan 610064, PR China |