ROMANYUK, A. S. Approximative characteristics of the isotropic classes of periodic functions of many variables. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 61, n. 4, p. 513–523, 2009. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3036. Acesso em: 9 dec. 2025.