Tikhonov, S. Yu. “On the Equivalence of Some Conditions for Convex Functions”. Ukrains’kyi Matematychnyi Zhurnal 57, no. 3 (March 25, 2005): 427–431. Accessed May 5, 2024. https://umj.imath.kiev.ua/index.php/umj/article/view/3610.