ZHYHALLO, K. M.; KHARKEVYCH, Yu. I. Approximation of (ψ, β)-differentiable functions of low smoothness by biharmonic Poisson integrals. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 63, n. 12, p. 1602–1622, 2011. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2829. Acesso em: 5 dec. 2025.