SERDYUK, A. S.; STEPANETS, O. I.; SHYDLICH, A. L. Classification of infinitely differentiable periodic functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 60, n. 12, p. 1686–1708, 2008. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3282. Acesso em: 5 dec. 2025.