@article{INTA_1974_12_a3,
     author = {\`E. G. Poznyak and E. V. Shikin},
     title = {Surfaces of negative curvature},
     journal = {Itogi Nauki i Tekhniki. Seriya Algebra. Geometriya. Topologiya},
     pages = {171--207},
     year = {1974},
     volume = {12},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTA_1974_12_a3/}
}