ZHYHALLO, K. M.; KHARKEVYCH, Yu. I. Approximation of Differentiable Periodic Functions by Their Biharmonic Poisson Integrals. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 54, n. 9, p. 1213–1219, 2002. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4160. Acesso em: 6 dec. 2025.