Komarenkо A. N. “Problem of Eigenvalues With a Parameter under Boundary Value Conditions for Elliptical Equations Degenerating on Part of the Region Boundary ”. Ukrains’kyi Matematychnyi Zhurnal 18, no. 6 (October 27, 1966): 3–11. Accessed April 11, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/8455.