VAKARCHUK, S. B.; ZABUTNAYA, V. I. On the best polynomial approximation in the space L2 and widths of some classes of functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 64, n. 8, p. 1025–1032, 2012. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2637. Acesso em: 5 dec. 2025.