Ţigan, Ştefan. “Optimality Conditions for Multiobjective Symmetric Convex Programming”. Rev. Anal. Numér. Théor. Approx., vol. 25, no. 1, Aug. 1996, pp. 235-4, https://ictp.acad.ro/jnaat/journal/article/view/1996-vol25-nos1-2-art24.