Vakarchuk SB, Zabutnaya VI. On the best polynomial approximation in the space L2 and widths of some classes of functions. Ukr. Mat. Zhurn. [Internet]. 2012Aug.25 [cited 2024Apr.25];64(8):1025-32. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/2637