M. M. . Malamud, “Certain classes for expansions of the Hermitian operator with gaps”, Ukr. Mat. Zhurn., vol. 44, no. 2, pp. 215–233, Feb. 1992, Accessed: Apr. 09, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/7836