1. J. P. Aubin, H. Frankowska, Set-Valued Analysis, Birkhäuser, Boston-Basel-Berlin, 1990.
2. J. Diestel, J. J. Uhl, Jr., Vector Measures, Amer. Math. Soc., Providence, RI., 1977.
3. W. Feller, An Introduction to Probability Theory and its Applications, Vol. 2, John Wiley and Sons, Inc. New York, 1966.
4. M. Kuczma, An Introduction to the Theory of Functional Equations and Inequalities. Cauchy’s equation and Jensen’s inequality, Państwowe Wydawnictwo Naukowe &; Uniwersytet Ślcaski, 1985.
5. J. Matkowski, Integrable solutions of functional equations, Dissertationes Math. 127(1975).