@article{MAN_1897__48_157823,
     author = {Otto Bierbaum},
     title = {Ueber {Functionen} zweier reeller {Variablen}},
     journal = {Mathematische Annalen},
     pages = {393--400},
     year = {1897},
     volume = {48},
     url = {http://geodesic.mathdoc.fr/item/MAN_1897__48_157823/}
}