Precup, Radu. “Convex Functions of Order \(n\) and \(P_n\)-Simple Functionals”. Anal. Numér. Théor. Approx. 18, no. 2 (August 1, 1989): 161–170. Accessed May 9, 2024. https://ictp.acad.ro/jnaat/journal/article/view/1989-vol18-no2-art7.