@article{MZM_2002_72_6_a2,
     author = {V. S. Balaganskii},
     title = {Necessary {Conditions} for {Differentiability} of {Distance} {Functions}},
     journal = {Matemati\v{c}eskie zametki},
     pages = {815--820},
     publisher = {mathdoc},
     volume = {72},
     number = {6},
     year = {2002},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_2002_72_6_a2/}
}