Serdyuk, A. S. “Approximation of Infinitely Differentiable Periodic Functions by Interpolation Trigonometric Polynomials”. Ukrains’kyi Matematychnyi Zhurnal 56, no. 4 (April 25, 2004): 495–505. Accessed May 28, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3771.