@article{CMUC_1970__11_4_a12,
     author = {Preiss, David},
     title = {On the first derivative of real functions {(Preliminary} communication)},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {817--822},
     publisher = {mathdoc},
     volume = {11},
     number = {4},
     year = {1970},
     mrnumber = {0274669},
     zbl = {0206.06602},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1970__11_4_a12/}
}