ZHANG, X.; LIU, C.; LU, X. Minimal periodic problem for brake orbits of first-order Hamiltonian systems. Topological Methods in Nonlinear Analysis, [S. l.], v. 57, n. 1, p. 73–87, 2021. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2020.032. Acesso em: 22 lip. 2024.