ChaichenkoS. O. “Approximations by Fourier Sums on the Sets $L^{ψ} L^{P(∙)}$”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 6, June 2014, pp. 835–846, https://umj.imath.kiev.ua/index.php/umj/article/view/2181.