RomanyukV. S. “Weighted Approximation in Mean of Classes of Analytic Functions by Algebraic Polynomials and Finite-Dimensional Subspaces”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 51, no. 5, May 1999, pp. 645–662, https://umj.imath.kiev.ua/index.php/umj/article/view/4651.