@article{IM2_1973_7_6_a2,
     author = {O. Ya. Viro},
     title = {Branched coverings of manifolds with boundary and link {invariants.~I}},
     journal = {Izvestiya. Mathematics },
     pages = {1239--1256},
     publisher = {mathdoc},
     volume = {7},
     number = {6},
     year = {1973},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1973_7_6_a2/}
}