[1]
StepanetsO.I. 1998. Approximation of $\bar {\psi} - integrals$−integrals of periodic functions by Fourier sums (small smoothness). Iof periodic functions by Fourier sums (small smoothness). I. Ukrains’kyi Matematychnyi Zhurnal. 50, 2 (Feb. 1998), 274-291.