LI, Y. On Nirenberg’s problem and related topics. Topological Methods in Nonlinear Analysis, [S. l.], v. 3, n. 2, p. 221–233, 1994. Disponível em: https://apcz.umk.pl/TMNA/article/view/TMNA.1994.012. Acesso em: 22 jul. 2024.