Xiaoquan Ding and  Jianmin Hao and  Changwen Liu,  Multiple Periodic Solutions for a Delayed Predator-prey System on Time Scales.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    December 2011, vol. 60(12). 1921 - 1926
    [viewed 29 February 2020]. Available from: https://publications.waset.org/pdf/3268.