@article{DAN_1968_180_2_a2,
     author = {A. L. Verner},
     title = {The structure of certain complete surfaces of non-positive curvature},
     journal = {Doklady Akademii Nauk},
     pages = {269--272},
     publisher = {mathdoc},
     volume = {180},
     number = {2},
     year = {1968},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1968_180_2_a2/}
}