SavchukV. V., SavchukM. V., and ChaichenkoS. O. “Approximation of Bounded holomorphic and Harmonic Functions by Fejér Means”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 4, Apr. 2019, pp. 516-42, http://umj.imath.kiev.ua/index.php/umj/article/view/1455.