Lupşa, L., D. I. Duca, and E. Duca. “Equivalence Classes in the Set of Efficient Solutions”. Rev. Anal. Numér. Théor. Approx., vol. 25, no. 1, Aug. 1996, pp. 127-36, https://ictp.acad.ro/jnaat/journal/article/view/1996-vol25-nos1-2-art14.