HRABOVA, U.Z.; KAL’CHUK, I.V. Approximation of the classes $W^{r}_{\beta,\infty}$ by three-harmonic Poisson integrals: Array. Carpathian Mathematical Publications, [S. l.], v. 11, n. 2, p. 321–334, 2019. DOI: 10.15330/cmp.11.2.321-334. Disponível em: https://journals.pnu.edu.ua/index.php/cmp/article/view/2111. Acesso em: 29 mar. 2024.