1. J. Dhombres -R. Ger,Conditional Cauchy equations, Glasnik Mat.,13 (33) (1978), pp. 39–62.
2. G. L.Forti,On an alternative functional equation related to the Cauchy equation, Aequationes Math. (submitted to the Editorial Board).
3. L. Fuchs,Infinite Abelian Groups, Academic Press, New York (1970).
4. R. Ger,On a method of solving of conditional Cauchy equations, Univ. Beograd. Publ. Elektrotehn. Fak., Ser. Mat. Fiz., No. 544–576 (1976), pp. 159–165.
5. M. Kuczma,Functional equations on restricted domains, Aequationes Math.,18 (1978), pp. 1–34.