@article{AM2_1981__22_136879,
     author = {K. Niino},
     title = {On the functional equation.},
     journal = {Aequationes mathematicae},
     pages = {293--301},
     year = {1981},
     volume = {22},
     zbl = {0484.30019},
     url = {http://geodesic.mathdoc.fr/item/AM2_1981__22_136879/}
}