R. Pušenjak, M. Oblak, and M. Lipičnik, “Competitive Predator-Prey Systems with Time-Dependent Coefficients: A Multistage Homotopy Perturbation Analysis”, analipazu, vol. 2, no. 1, pp. 22–31, May 2022, doi: 10.18690/analipazu.2.1.22-31.2012.