Serdyuk, A. S. “Approximation of Infinitely Differentiable Periodic Functions by Interpolation Trigonometric Polynomials in Integral Metric”. Ukrains’kyi Matematychnyi Zhurnal 53, no. 12 (December 25, 2001): 1654–1663. Accessed February 17, 2026. https://umj.imath.kiev.ua/index.php/umj/article/view/4385.