StepanetsO. I. (1998). Approximation of $\bar {\psi} - \text{Integrals}$ of periodic functions by Fourier sums (small smoothness). IIof periodic functions by Fourier sums (small smoothness). II. Ukrains’kyi Matematychnyi Zhurnal, 50(3), 388-400. Retrieved from https://umj.imath.kiev.ua/index.php/umj/article/view/4938