@article{10_21136_CMJ_1967_100764,
     author = {Matyska, Ji\v{r}{\'\i}},
     title = {Approximate differential and {Federer} normal},
     journal = {Czechoslovak Mathematical Journal},
     pages = {97--107},
     year = {1967},
     volume = {17},
     number = {1},
     doi = {10.21136/CMJ.1967.100764},
     mrnumber = {0207926},
     zbl = {0162.07601},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/CMJ.1967.100764/}
}