Popovicheva, T. N., and V. V. Khlobystov. “On Interpolation Approximation of Differentiable Operators in a Hilbert Space”. Ukrains’kyi Matematychnyi Zhurnal 58, no. 4 (April 25, 2006): 554–563. Accessed April 28, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3473.