BALANOV, Zolman; FARZAMIRAD, Meymanat; KRAWCEWICZ, Wiesław. Symmetric systems of Van Der Pol equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 27, n. 1, p. 29–90, 2006. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2006.002. Acesso em: 3 jul. 2025.