@article{DAN_1969_188_5_a13,
     author = {E. V. Shikin},
     title = {The regular realization in the large in $E^3$ of two-dimensional metrics of class $C^2$ with negative curvature of class $C^1$},
     journal = {Doklady Akademii Nauk},
     pages = {1014--1016},
     year = {1969},
     volume = {188},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1969_188_5_a13/}
}