@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/