@article{ZNSL_1973_36_a1,
     author = {O. Ya. Viro},
     title = {Two-sheeted branched coverings of the three-dimensional sphere},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {6--39},
     publisher = {mathdoc},
     volume = {36},
     year = {1973},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1973_36_a1/}
}