BREZIS, Haïm; LI, YanYan; MIRONESCU, Petru; NIRENBERG, Louis. Degree and Sobolev spaces. Topological Methods in Nonlinear Analysis, [S. l.], v. 13, n. 2, p. 181–190, 1999. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1999.009. Acesso em: 1 jul. 2025.