Serdyuk AS, Stepanets OI, Shydlich AL. On some new criteria for infinite differentiability of periodic functions. Ukr. Mat. Zhurn. [Internet]. 2007Oct.25 [cited 2024Apr.19];59(10):1399–1409. Available from: https://umj.imath.kiev.ua/index.php/umj/article/view/3398