DU, Y.; GUO, Y. Mountain pass solutions and an indefinite superlinear elliptic problem on $\mathbb R^{\mathbb N}$. Topological Methods in Nonlinear Analysis, [S. l.], v. 22, n. 1, p. 69–92, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.028. Acesso em: 22 jul. 2024.