Jianguo Tang and  Kun She and  William Zhu,  Covering-based Rough sets Based on the Refinement of Covering-element.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    August 2011, vol. 56(8). 1340 - 1350
    [viewed 26 April 2024]. Available from: https://publications.waset.org/pdf/8682.