ALLERGRETTO, W.; PAPINI, D. Periodic solutions to nonlinear equations with oblique boundary conditions. Topological Methods in Nonlinear Analysis, [S. l.], v. 40, n. 2, p. 225–243, 2012. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.2012.030. Acesso em: 25 jan. 2022.