@article{GDZPPN002030357,
title = {On the functional equation f(...(x) + g(y)) = ...(x) * h(x+y).},
journal = {Aequationes mathematicae},
volume = {15},
year = {1977},
pages = {21-30},
zbl = {0433.39011},
url = {http://dml.mathdoc.fr/item/GDZPPN002030357}
}
Lundberg, A. On the functional equation f(...(x) + g(y)) = ...(x) * h(x+y).. Aequationes mathematicae, Tome 15 (1977) pp. 21-30. http://gdmltest.u-ga.fr/item/GDZPPN002030357/