SERDYUK, A. S.; SOKOLENKO, I. V. Linear approximation methods and the best approximations of the Poisson integrals of functions from the classes $H_{ω_p}$ in the metrics of the spaces $L_p$. Ukrains’kyi Matematychnyi Zhurnal, v. 62, n. 7, p. 979–996, 25 Jul. 2010.