@article{MAN_1981__256_163499,
     author = {Klaus J\"anich},
     title = {Universal {Families} of {C{\textdegree}{\textdegree}-Functions} on {D2.}},
     journal = {Mathematische Annalen},
     pages = {67--84},
     publisher = {mathdoc},
     volume = {256},
     year = {1981},
     zbl = {0442.58006},
     url = {http://geodesic.mathdoc.fr/item/MAN_1981__256_163499/}
}