@article{JRAM_1978__302_152041,
     author = {John V. Ryff},
     title = {The functional equation {F(ax)} + {F(bx+a)} = {F(bx)} + {F(ax+b),} entire and almost periodic solutions.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {116--136},
     publisher = {mathdoc},
     volume = {302},
     year = {1978},
     zbl = {0376.39003},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1978__302_152041/}
}