Muhiuddin, G., S. Aldhafeeri, and K. P. Shum. “\((\varepsilon,\delta)\)-Characteristic Fuzzy Sets Approach to the Ideal Theory of \(BCK/BCI\)-Algebras”. Journal of Informatics and Mathematical Sciences, vol. 10, no. 4, Dec. 2018, pp. 573-81, doi:10.26713/jims.v10i4.1130.