A scheme for studying the spectrum of a family of perturbed operators, and its application to spectral problems in thick junctions. Neliniini Kolyvannya, [S. l.], v. 6, n. 2, p. 233–251, 2003. Disponível em: https://twinhead.imath.kiev.ua/index.php/nosc/article/view/263. Acesso em: 22 jan. 2026.