Serdyuk, A. S. 2001. “Approximation of Infinitely Differentiable Periodic Functions by Interpolation Trigonometric Polynomials in Integral Metric”. Ukrains’kyi Matematychnyi Zhurnal 53 (12), 1654-63. https://umj.imath.kiev.ua/index.php/umj/article/view/4385.