Landau’s Inequality for Semigroups

Kraljevič and Kurepa in 1970 [14] proved a nice Landau type inequality for semigroups by making use of Taylor’s formula with integral remainder for semigroups, which has been a traditional method for proving such inequalities. The author offers another method in the semigroups and reproves the above result by using his earlier result about Ostrowski inequalities for semigroups, see [1], Chap. 16, pp. 259–289