Vakarchuk, S., and M. Vakarchuk. “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, vol. 76, no. 2, Feb. 2024, pp. 198-23, https://doi.org/10.3842/umzh.v76i2.7763.