HLADYSH, B. I.; PRISHLYAK, O. O. Functions with nondegenerate critical points on the boundary of the surface. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 68, n. 1, p. 28–37, 2016. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1819. Acesso em: 17 apr. 2025.