@article{CMUC_1968_9_2_a10,
     author = {Preiss, David},
     title = {Limits of derivatives {(Preliminary} communication)},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {307--309},
     year = {1968},
     volume = {9},
     number = {2},
     mrnumber = {0235078},
     zbl = {0165.37701},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1968_9_2_a10/}
}