GROSSI, M.; PACELLA, F.; YADAVA, S. L. Symmetry results for perturbed problems and related questions. Topological Methods in Nonlinear Analysis, [S. l.], v. 21, n. 2, p. 211–226, 2003. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2003.013. Acesso em: 8 dec. 2021.