Qi, F., B.-Y. Xi, and T.-Y. Zhang. “Hermite–Hadamard-Type Integral Inequalities for Functions Whose First Derivatives Are Convex”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 67, no. 4, Apr. 2015, pp. 555-67, https://umj.imath.kiev.ua/index.php/umj/article/view/2002.