@article{DAN_1963_150_6_a4,
     author = {N. V. Efimov},
     title = {The impossibility in {Euclidean} $3$-space of a complete regular surface with a negative upper bound of the {Gaussian} curvature},
     journal = {Doklady Akademii Nauk},
     pages = {1206--1209},
     publisher = {mathdoc},
     volume = {150},
     number = {6},
     year = {1963},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1963_150_6_a4/}
}