@article{GDZPPN002320533,
title = {Universal Families of C$^\circ$$^\circ$-Functions on D2.},
journal = {Mathematische Annalen},
volume = {255},
year = {1981},
pages = {67-84},
zbl = {0442.58006},
url = {http://dml.mathdoc.fr/item/GDZPPN002320533}
}
Jänich, Klaus. Universal Families of C°°-Functions on D2.. Mathematische Annalen, Tome 255 (1981) pp. 67-84. http://gdmltest.u-ga.fr/item/GDZPPN002320533/