MOTREANU, Dumitru; MOTREANU, Viorica V.; PAPAGEORGIOU, Nikolaos S. Periodic solutions for nonautonomous systems with nonsmooth quadratic or superquadratic potential. Topological Methods in Nonlinear Analysis, [S. l.], v. 24, n. 2, p. 269–296, 2004. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2004.028. Acesso em: 1 jul. 2025.