@article{AM2_1977__15_136666,
     author = {A. Lundberg},
     title = {On the functional equation f(...(x) + g(y)) = ..(x) * h(x+y). {(Short} {Communication).}},
     journal = {Aequationes mathematicae},
     pages = {309--310},
     publisher = {mathdoc},
     volume = {15},
     year = {1977},
     zbl = {0433.39011},
     url = {http://geodesic.mathdoc.fr/item/AM2_1977__15_136666/}
}