@article{AM2_1981__22_136853,
     author = {E.T. Ljubenova},
     title = {On {D'Alembert's} functional equation on a {Abelian} group.},
     journal = {Aequationes mathematicae},
     pages = {54--55},
     year = {1981},
     volume = {22},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/AM2_1981__22_136853/}
}