BURSKII, V. P.; LESINA, E. V. Neumann problem and one oblique-derivative problem for an improperly elliptic equation. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 4, p. 451–462, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2589. Acesso em: 6 dec. 2025.