T. N. Popovicheva and V. V. Khlobystov, “On interpolation approximation of differentiable operators in a Hilbert space”, Ukr. Mat. Zhurn., vol. 58, no. 4, pp. 554–563, Apr. 2006, Accessed: Feb. 17, 2026. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/3473