ZHYHALLO, K. M.; KHARKEVYCH, Yu. I. On the Approximation of Functions of the Hölder Class by Biharmonic Poisson Integrals. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 7, p. 971–974, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4496. Acesso em: 27 apr. 2025.