Toader, Gh. “On the Hierarchy of Convexity of Functions”. Anal. Numér. Théor. Approx. 15, no. 2 (August 1, 1986): 167–172. Accessed November 24, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1986-vol15-no2-art12.