K. Ratan Singh and  P. K. Das,  Induced Acyclic Graphoidal Covers in a Graph.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    August 2010, vol. 44(8). 1078 - 1084
    [viewed 29 January 2020]. Available from: https://publications.waset.org/pdf/11912.