Kejun Zhuang,  Periodicity for a Semi–Ratio–Dependent Predator–Prey System with Delays on Time Scales.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    July 2010, vol. 43(7). 780 - 783
    [viewed 16 April 2021]. Available from: https://publications.waset.org/pdf/9158.