Raşa, I. “Sets on Which Concave Functions Are Affine and Korovkin Closures”. Anal. Numér. Théor. Approx. 15, no. 2 (August 1, 1986): 163–165. Accessed April 14, 2025. https://ictp.acad.ro/jnaat/journal/article/view/1986-vol15-no2-art11.