@article{SM_1996_187_2_a4,
     author = {Yu. V. Kuz'min},
     title = {The groups of knotted compact surfaces, and central extensions},
     journal = {Sbornik. Mathematics},
     pages = {237--257},
     publisher = {mathdoc},
     volume = {187},
     number = {2},
     year = {1996},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1996_187_2_a4/}
}