Öziş, Turgut, and Ahmet Yildirim. “Determination of Limit Cycles by Iterated Homotopy Perturbation Method for Nonlinear Oscillators With Strong Nonlinearity”. Topological Methods in Nonlinear Analysis 31, no. 2 (June 1, 2008): 349–357. Accessed January 25, 2022. https://apcz.umk.pl/TMNA/article/view/TMNA.2008.026.