@article{MAN_1980__251_163433,
     author = {William E. Lang and Niels O. Nygaard},
     title = {A {Short} {Proof} of the {Rydakov-Safarevic} {Theorem.}},
     journal = {Mathematische Annalen},
     pages = {171--174},
     publisher = {mathdoc},
     volume = {251},
     year = {1980},
     zbl = {0457.14018},
     url = {http://geodesic.mathdoc.fr/item/MAN_1980__251_163433/}
}