Ivan, D. M., and I. Rașa. “A Popoviciu-Type Mean Value Theorem”. Rev. Anal. Numér. Théor. Approx., vol. 26, no. 1, Aug. 1997, pp. 95-98, https://ictp.acad.ro/jnaat/journal/article/view/1997-vol26-nos1-2-art13.