Kaihong Zhao,  Existence of Multiple Positive Periodic Solutions to n Species Nonautonomous Lotka-Volterra Cooperative Systems with Harvesting Terms.   journal   = {International Journal of Mathematical and Computational Sciences}, [online]. World Academy of Science, Engineering and Technology.
    August 2012, vol. 68(8). 819 - 824
    [viewed 24 April 2024]. Available from: https://publications.waset.org/pdf/12665.