@article{ZNSL_2005_325_a12,
     author = {P. V. Yagodovskii},
     title = {$\sigma${-Extensions} of discrete multivalued groups},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {225--242},
     publisher = {mathdoc},
     volume = {325},
     year = {2005},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_2005_325_a12/}
}