On continuous convex or concave functions with respect to the logarithmic mean T. Zgraja — 2005 Acta Universitatis Carolinae. Mathematica et Physica
Convex functions with respect to logarithmic mean and ѕandwich theorem Zygfryd Kominek; T. Zgraja — 1999 Acta Universitatis Carolinae. Mathematica et Physica