KARPIŃSKA, W. A note on bounded solutions of second order differential equations at resonance. Topological Methods in Nonlinear Analysis, [S. l.], v. 14, n. 2, p. 371–384, 1999. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1999.040. Acesso em: 19 apr. 2024.