1. Y. B. Jun, C. S. Kim and M. S. Kang, Far East Journal of Mathematical Sciences, 2 (44) (2010) 239–250.
2. Y. B. Jun, C. S. Kim, and J. G. Kang, Ann. Fuzzy Math.Inform. 1 (1) (2011) 25–34.
3. Y. B. Jun, C. S.Kim, and K. O. Yang, Ann. Fuzzy Math. Inform. 4 (1) (2012) 83–98.
4. F.F. Kareem and E. R. Hasan, International Journal of Science and Nature 9(1) (2018), 79–84.
5. F.F. Kareem and E. R. Hasan, Journal of New Theory, 9 (2019) 71–78.