@article{1077311951, author = {Ephraim, Robert}, title = {$C^1$ preservation of multiplicity}, journal = {Duke Math. J.}, volume = {43}, number = {1}, year = {1976}, pages = { 797-803}, language = {en}, url = {http://dml.mathdoc.fr/item/1077311951} }
Ephraim, Robert. $C^1$ preservation of multiplicity. Duke Math. J., Tome 43 (1976) no. 1, pp. 797-803. http://gdmltest.u-ga.fr/item/1077311951/