@article{DAN_1970_195_5_a13,
     author = {S. Z. Shefel'},
     title = {Isometric imbeddings of class $C^1$},
     journal = {Doklady Akademii Nauk},
     pages = {1052--1054},
     publisher = {mathdoc},
     volume = {195},
     number = {5},
     year = {1970},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1970_195_5_a13/}
}