LUPO, D. Existence and multiplicity of solutions for superquadratic noncooperative variational elliptic systems. Topological Methods in Nonlinear Analysis, [S. l.], v. 12, n. 1, p. 27–46, 1998. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1998.026. Acesso em: 26 apr. 2024.