KORNEICHUK, N. P. On the best approximation of periodic functions of two variables by polynomial splines. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 52, n. 1, p. 52–57, 2000. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/4396. Acesso em: 5 dec. 2025.