Yuli Hu and  Shaoquan Sun,  Generalized Fuzzy Subalgebras and Fuzzy Ideals of BCI-Algebras with Operators .   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    November 2017, vol. 130(10). 475 - 480
    [viewed 25 May 2022]. Available from: https://publications.waset.org/pdf/10008379.