@article{MZM_1997_61_4_a4,
     author = {S. I. Dudov},
     title = {Subdifferentiability and superdifferentiability of distance functions},
     journal = {Matemati\v{c}eskie zametki},
     pages = {530--542},
     year = {1997},
     volume = {61},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1997_61_4_a4/}
}