KOLESNIK, L. I.; Andrashkо M. I. Inverse theorems of approximation on the average in regions with angles. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 23, n. 1, p. 97–104, 1970. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/8487. Acesso em: 6 dec. 2025.