O. I. Stepanets, “Approximation of $\bar {\psi} - integrals$−integrals of periodic functions by Fourier sums (small smoothness). Iof periodic functions by Fourier sums (small smoothness). I”, Ukr. Mat. Zhurn., vol. 50, no. 2, pp. 274–291, Feb. 1998, Accessed: Dec. 05, 2025. [Online]. Available: https://umj.imath.kiev.ua/index.php/umj/article/view/4961