@article{SM_1970_12_2_a9,
     author = {I. S. Brandt},
     title = {Some properties of surfaces with slowly varying negative extrinsic curvature in {a~Riemannian} space},
     journal = {Sbornik. Mathematics},
     pages = {313--324},
     publisher = {mathdoc},
     volume = {12},
     number = {2},
     year = {1970},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1970_12_2_a9/}
}