SerdyukA. S., and StepanetsO. I. “Approximation of Periodic Analytic Functions by Interpolation Trigonometric Polynomials”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 52, no. 12, Dec. 2000, pp. 1689-01, https://umj.imath.kiev.ua/index.php/umj/article/view/4572.