Swapnoneel Roy and  Ashok Kumar Thakur and  Minhazur Rahman,  Block Sorting: A New Characterization and a New Heuristic.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    February 2008, vol. 14(2). 133 - 139
    [viewed 14 December 2019]. Available from: https://publications.waset.org/pdf/3557.