VakarchukS., and VakarchukM. “Approximation in the Mean of the Classes of Functions in the Space $L_2[(0,1);X]$ by the Fourier–Bessel Sums and Estimates of the Values of Their $n$-Widths”. Ukrains’kyi Matematychnyi Zhurnal 76, no. 2 (February 28, 2024): 198-223. Accessed November 13, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/7763.