Radzievskii, G.V. (1996) “Asymptotics of eigenvalues of A regular boundary-value problem”, Ukrains’kyi Matematychnyi Zhurnal, 48(4), pp. 483–519. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/5313 (Accessed: 26 April 2025).