1. J. Aczél, The General Solution of Two Functional Equations by Reduction to Functions Additive in Two Variables and With the Aid of Hamel Bases, Glasnik Mat.-Fiz. Astr. Ser. II20 (1965), 65–73.
2. B.R. Ebanks, Factoring Multiadditive Mappings, (submitted).
3. C. Hammer andP. Volkmann, Die multiplikativen Lósungen der Parallelogrammgleichung, Abh. Math. Sem. Univ. Hamburg61 (1991), 197–201.
4. M. Kuczma, An Introduction to the Theory of Functional Equations and Inequalities, Polish Scientific Publishers and Silesian University Press, Warszawa-Kraków-Katowice, 1985.