SERDYUK, A. S.; STEPANETS, O. I.; SHYDLICH, A. L. On some new criteria for infinite differentiability of periodic functions. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 59, n. 10, p. 1399–1409, 2007. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/3398. Acesso em: 5 dec. 2025.