@article{CMUC_1974__15_3_a10,
     author = {Durdil, Ji\v{r}{\'\i}},
     title = {On the geometric characterization of differentiability. {I.}},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {521--540},
     publisher = {mathdoc},
     volume = {15},
     number = {3},
     year = {1974},
     mrnumber = {0426019},
     zbl = {0289.58004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1974__15_3_a10/}
}