VakarchukS.; 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, v. 76, n. 2, p. 198-223, 28 Feb. 2024.