@article{MAN_1921__84_158884,
     author = {Schauffler. R.},
     title = {\"Uber wiederholbare {Funktionen}},
     journal = {Mathematische Annalen},
     pages = {137--142},
     year = {1921},
     volume = {84},
     zbl = {48.1204.04},
     url = {http://geodesic.mathdoc.fr/item/MAN_1921__84_158884/}
}