AMSTER, P.; HADDAD, J. On existence of periodic solutions for Kepler type problems. Topological Methods in Nonlinear Analysis, [S. l.], v. 48, n. 2, p. 465–476, 2016. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2016.053. Acesso em: 22 jul. 2024.