ZHYHALLO, T. V.; KHARKEVYCH, Yu. I. Approximation of functions from the class $\hat{C}^{\psi}_{\beta, \infty}$ by Poisson biharmonic operators in the uniform metric. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 5, p. 669 – 693, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3185. Acesso em: 5 dec. 2025.