MIKAYELYAN, H.; SHAHGHOLIAN, H. Hopf’s lemma for a class of singular/degenerate PDE-s. Annales Fennici Mathematici, [S. l.], v. 40, n. 1, p. 475–484, 2015. DOI: 10.5186/aasfm.2015.4033. Disponível em: https://afm.journal.fi/article/view/135555. Acesso em: 30 oct. 2024.