NOWAKOWSKI, A.; ROGOWSKI, A. Periodic solutions of Lagrange equations. Topological Methods in Nonlinear Analysis, [S. l.], v. 22, n. 1, p. 167–180, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.034. Acesso em: 22 jul. 2024.