@article{SM_1996_187_6_a7,
     author = {Z. D. Usmanov},
     title = {On {Efimov} surfaces that are rigid 'in the~small'},
     journal = {Sbornik. Mathematics},
     pages = {903--915},
     year = {1996},
     volume = {187},
     number = {6},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1996_187_6_a7/}
}