@article{MZ_1980__171_172936,
     author = {Dieter Lutz},
     title = {\"Uber operatorwetige {L\"osungen} der {Funktionalgleichung} des {Cosinus.}},
     journal = {Mathematische Zeitschrift},
     pages = {233--246},
     publisher = {mathdoc},
     volume = {171},
     year = {1980},
     zbl = {0414.47021},
     url = {http://geodesic.mathdoc.fr/item/MZ_1980__171_172936/}
}