EL OUADIH, S. Direct and inverse approximation theorems for functions defined in Damek–Ricci spaces. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 76, n. 8, p. 1132–1146, 2024. DOI: 10.3842/umzh.v76i8.7549. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/7549. Acesso em: 5 dec. 2025.