@article{10_21136_MB_2009_140656,
     author = {Bedna\v{r}{\'\i}k, Du\v{s}an and Pastor, Karel},
     title = {A characterization of $C^{1,1}$ functions via lower directional derivatives},
     journal = {Mathematica Bohemica},
     pages = {217--221},
     publisher = {mathdoc},
     volume = {134},
     number = {2},
     year = {2009},
     doi = {10.21136/MB.2009.140656},
     mrnumber = {2535149},
     zbl = {1212.49043},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.21136/MB.2009.140656/}
}