1. On the different characterizations of entropies;Aczél,1969
2. Forte, B. and Ng, C. T. (unpublished data).
3. Methods in Classical and Functional Analysis;Hille,1972
4. Some functional equations in groups and rings;Jessen;Math. Scand.,1968
5. A general functional equation;Kemperman;Trans. Amer. Math. Soc.,1957