S. . Vakarchuk 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”, Ukr. Mat. Zhurn., vol. 76, no. 2, pp. 198–223, Feb. 2024, doi: 10.3842/umzh.v76i2.7763.