TOSHEVA, N. LOWER BOUND OF THE ESSENTIAL SPECTRUM OF A FAMILY OF 3X3 OPERATOR MATRICES. Центр Научных Публикаций (buxdu.uz), [S. l.], v. 33, n. 33, 2023. Disponível em: https://journal.buxdu.uz/index.php/journals_buxdu/article/view/9610. Acesso em: 19 апр. 2025.