@article{MZM_1990_47_4_a5,
     author = {S. B. Kadomtsev},
     title = {Surfaces with constant extrinsic geometry of negative curvature},
     journal = {Matemati\v{c}eskie zametki},
     pages = {41--45},
     year = {1990},
     volume = {47},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1990_47_4_a5/}
}