On one minimal hyperbolic Gellerstedt operator with internal degeneracy. Kazakh Mathematical Journal, [S. l.], v. 22, n. 3, p. 21–32, 2024. DOI: 10.70474/kam6z559. Disponível em: https://mathjournal.kz/index.php/kmj/article/view/19. Acesso em: 31 jan. 2025.