@article{ZNSL_1977_71_a16,
     author = {V. G. Khalin and A. V. Yakovlev},
     title = {Universal norms in $\Gamma$-extensions},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {251--255},
     publisher = {mathdoc},
     volume = {71},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1977_71_a16/}
}