HRABOVA, U. Z.; KALCHUK, I. V.; STEPANYUK, T. A. On the approximation of the classes $W_{β}^rH^{α}$ by biharmonic Poisson integrals. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 70, n. 5, p. 625–634, 2018. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1582. Acesso em: 5 dec. 2025.