Kazuyoshi Mori,  Number of Parametrization of Discrete-Time Systems without Unit-Delay Element: Single-Input Single-Output Case.   journal   = {International Journal of Electrical and Information Engineering}, [online]. World Academy of Science, Engineering and Technology.
    June 2017, vol. 126(6). 778 - 782
    [viewed 05 April 2020]. Available from: https://publications.waset.org/pdf/10007548.