Mond, B., and J. E. Pečarić. “Converses of Jensen’s Inequality for Several Operators”.
Rev. Anal. Numér. Théor. Approx.
, vol. 23, no. 2, Aug. 1994, pp. 179-83,
https://ictp.acad.ro/jnaat/journal/article/view/1994-vol23-no2-art7
.