@article{AM2_1980__20_182385,
     author = {Peter Kardos},
     title = {Belman's functional equation generalized {I.} {(Short} {Communication).}},
     journal = {Aequationes mathematicae},
     pages = {113--114},
     publisher = {mathdoc},
     volume = {20},
     year = {1980},
     url = {http://geodesic.mathdoc.fr/item/AM2_1980__20_182385/}
}