@article{SM_1967_2_2_a4,
     author = {\`E. R. Rozendorn},
     title = {The influence of the intrinsic metric on the regularity of a surface of negative curvature},
     journal = {Sbornik. Mathematics},
     pages = {207--223},
     year = {1967},
     volume = {2},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_2_2_a4/}
}