SHKAPA, V. V. Best trigonometric and bilinear approximations for the classes of $(ψ, β)$ -differentiable periodic functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 68, n. 3, p. 386–399, 2016. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1846. Acesso em: 5 dec. 2025.