RADZIEVSKII, G. V. Asymptotics of eigenvalues of A regular boundary-value problem. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 48, n. 4, p. 483–519, 1996. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/5313. Acesso em: 27 apr. 2025.