@article{AM2_1983__26_136996,
     author = {Luigi Paganoni and Daniela Rusconi},
     title = {A characterization of some classes of functions {F} of the form {F(x,} y) = g(...f(x) + {\ss}f(y) + ...) or {F(x,} y) = ...(h(x) + k(y)).},
     journal = {Aequationes mathematicae},
     pages = {138--162},
     publisher = {mathdoc},
     volume = {26},
     year = {1983},
     zbl = {0563.39006},
     url = {http://geodesic.mathdoc.fr/item/AM2_1983__26_136996/}
}