LAMBERTI, P.; PROVENZANO, L. A Maximum Principle in Spectral Optimization Problems for Elliptic Operators Subject to Mass Density Perturbations. Eurasian Mathematical Journal, [S. l.], v. 4, n. 3, p. 70–83, 2013. Disponível em: https://emj.enu.kz/index.php/main/article/view/538. Acesso em: 31 oct. 2025.