@article{SM_1967_2_1_a5,
     author = {A. I. Achil'diev and Z. D. Usmanov},
     title = {Rigidity of a surface with a point of flattening},
     journal = {Sbornik. Mathematics},
     pages = {77--83},
     publisher = {mathdoc},
     volume = {2},
     number = {1},
     year = {1967},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_2_1_a5/}
}