Motornaya, O. V., and V. P. Motornyi. “Comparison Theorems for Some Nonsymmetric Classes of Functions”. Ukrains’kyi Matematychnyi Zhurnal, vol. 60, no. 7, July 2008, pp. 969–975, https://umj.imath.kiev.ua/index.php/umj/article/view/3212.