1. Korea Research Institute of Arts and Mathematics, Asan-si, Chungcheongnam-do, 31551, Korea
2. Major in Mathematics Education, Graduate School of Education, Hankuk University of Foreign Studies, Seoul 02450, Korea
3. Department of Mathematics, Sungshin Women’s University, Seoul 02844, Korea
4. School of Mathematics, Korea Institute for Advanced Study, Seoul 02455, Korea