Balanov, Zolman, Meymanat Farzamirad, and Wiesław Krawcewicz. “Symmetric Systems of Van Der Pol Equations”. Topological Methods in Nonlinear Analysis 27, no. 1 (March 1, 2006): 29–90. Accessed April 20, 2024. https://apcz.umk.pl/TMNA/article/view/TMNA.2006.002.