BABENKO, V. F. One inequality of the Landau – Kolmogorov type for periodic functions of two variable. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 71, n. 2, p. 158–167, 2019. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/1428. Acesso em: 5 dec. 2025.