LIANG, S. Existence of non-collision periodic solutions for second order singular dynamical systems. Topological Methods in Nonlinear Analysis, [S. l.], v. 35, n. 1, p. 127–137, 2010. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2010.008. Acesso em: 14 oct. 2024.