Zelinskii, Y.B. and Momot, I.V. (2001) “On $(n, m)$-Convex Sets”, Ukrains’kyi Matematychnyi Zhurnal, 53(3), pp. 422–427. Available at: https://umj.imath.kiev.ua/index.php/umj/article/view/4263 (Accessed: 6 December 2025).