1. Department of Mathematics, Kyungpook National University, Daegu 41566, Republic of Korea
2. Department of Mathematics Education and RINS, Gyeongsang National University, Jinju 52828, Republic of Korea
3. University of Bucharest, Faculty of Mathematics and Computer Science, Research Center in Geometry, Topology and Algebra, Str. Academiei, Nr. 14, Sector 1, Bucureşti 70109, Romania
4. Petroleum-Gas University of Ploieşti, Department of Cybernetics, Economic Informatics, Finance and Accountancy, Bd. Bucureşti, Nr. 39, Ploieşti 100680, Romania