MotornayaO. V., and MotornyiV. P. 2000. “On Asymptotically Exact Estimates for the Approximation of Certain Classes of Functions by Algebraic Polynomials”. Ukrains’kyi Matematychnyi Zhurnal 52 (1), 85-99. https://umj.imath.kiev.ua/index.php/umj/article/view/4399.