BhatiD., and SinghP. 2017. “Multi-Objective Nonlinear Sum of Fractional Optimization problems with Non-Convex Constraints Using Duality Based Branch and Bound Algorithm”. Ukrains’kyi Matematychnyi Zhurnal 69 (11), 1455-71. https://umj.imath.kiev.ua/index.php/umj/article/view/1795.