LI, Y.; LIU, Z.; ZHAO, C. Nodal solutions of perturbed elliptic problem. Topological Methods in Nonlinear Analysis, [S. l.], v. 32, n. 1, p. 49–68, 2008. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2008.035. Acesso em: 17 jan. 2022.