BOYKO, O. P.; MARTYNYUK, O. M.; PIVOVARCHIK, V. N. On maximal multiplicity of eigenvalues of finite-dimensional spectral problem on a graph. Methods of Functional Analysis and Topology, [S. l.], v. 25, n. 2, p. 104–117, 2019. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/715. Acesso em: 15 dec. 2025.