RASULOV, T. H. On the finiteness of the discrete spectrum of a 3x3 operator matrix. Methods of Functional Analysis and Topology, [S. l.], v. 22, n. 1, p. 48–61, 2016. Disponível em: https://zen.imath.kiev.ua/index.php/mfat/article/view/626. Acesso em: 16 dec. 2025.