Serdyuk, A. S. 2002. “Approximation of Periodic Analytic Functions by Interpolation Trigonometric Polynomials in the Metric of the Space $L$”.
Ukrains’kyi Matematychnyi Zhurnal 54 (5): 692-99.
https://umj.imath.kiev.ua/index.php/umj/article/view/4108.