MotornayaO. V., and MotornyiV. P. “On Asymptotically Exact Estimates for the Approximation of Certain Classes of Functions by Algebraic Polynomials”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 52, no. 1, Jan. 2000, pp. 85-99, https://umj.imath.kiev.ua/index.php/umj/article/view/4399.