Shaoquan Sun and  Chunxiang Liu,   (λ,μ)-fuzzy Subrings and (λ,μ)-fuzzy Quotient Subrings with Operators.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    October 2016, vol. 116(8). 413 - 416
    [viewed 27 May 2022]. Available from: https://publications.waset.org/pdf/10005827.