Apetrii, M. “A Dual Generalization of Convex Functions”. Rev. Anal. Numér. Théor. Approx. 36, no. 1 (February 1, 2007): 25–38. Accessed April 14, 2025. https://ictp.acad.ro/jnaat/journal/article/view/2007-vol36-no1-art3.