FABRICANT, Alexander; KUTEV, Nikolai; RANGELOV, Tsviatko. On the first eigenvalue for linear second order elliptic equations in divergence form. CUBO, A Mathematical Journal, [S. l.], v. 9, n. 3, p. 47–64, 2007. Disponível em: https://cubo.ufro.cl/index.php/cubo/article/view/1587. Acesso em: 12 oct. 2025.