@article{CMUC_1974_15_4_a12,
     author = {Durdil, Ji\v{r}{\'\i}},
     title = {On the geometric characterization of differentiability. {II}},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {727--744},
     year = {1974},
     volume = {15},
     number = {4},
     mrnumber = {0426019},
     zbl = {0294.58003},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1974_15_4_a12/}
}