Bondar, A. A., and Ya. M. Dymarskii. “Submanifolds of Compact Operators With Fixed Multiplicities of Eigenvalues”. Ukrains’kyi Matematychnyi Zhurnal 63, no. 9 (September 25, 2011): 1179–1189. Accessed December 5, 2025. https://umj.imath.kiev.ua/index.php/umj/article/view/2796.