Su, T., and D. Hang. “Closedness of the Optimal Solution Sets for General Vector Alpha Optimization Problems”. *Journal of Nonlinear Analysis and Optimization: Theory & Applications* 11, no. 1 (April 6, 2020): 1-14. Accessed October 25, 2021. http://www.math.sci.nu.ac.th/ojs302/index.php/jnao/article/view/518.