KopotunK. A., LeviatanD., and ShevchukI. A. “Are the Degrees of the Best (co)convex and Unconstrained Polynomial Approximations the Same? II”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 62, no. 3, Mar. 2010, pp. 369–386, https://umj.imath.kiev.ua/index.php/umj/article/view/2873.