A. A. Bondar and Y. M. Dymarskii, “Submanifolds of compact operators with fixed multiplicities of eigenvalues”, Ukr. Mat. Zhurn., vol. 63, no. 9, pp. 1179–1189, Sep. 2011, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/2796