@article{CMUC_1982__23_4_a6,
     author = {Preiss, David and Zaj{\'\i}\v{c}ek, Lud\v{e}k},
     title = {On the symmetry of approximate {Dini} derivates of arbitrary functions},
     journal = {Commentationes Mathematicae Universitatis Carolinae},
     pages = {691--697},
     publisher = {mathdoc},
     volume = {23},
     number = {4},
     year = {1982},
     mrnumber = {687564},
     zbl = {0513.26004},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/CMUC_1982__23_4_a6/}
}