ZHYHALLO, K. M.; KHARKEVYCH, Yu. I. Approximation of functions from the classes $C^{\psi}_{\beta, \infty}$ by biharmonic Poisson integrals. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 63, n. 7, p. 939–959, 2011. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2776. Acesso em: 5 dec. 2025.