Alomari, M. W. “New Sharp Ostrowski-Type Inequalities and Generalized Trapezoid-Type Inequalities for Riemann–Stieltjes Integrals and Their Applications”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 65, no. 7, July 2013, pp. 894–916, https://umj.imath.kiev.ua/index.php/umj/article/view/2476.