@article{MZM_1997_62_6_a0,
     author = {S. M. Ageev and S. A. Bogatyi},
     title = {Obstructions to the extension of partial maps},
     journal = {Matemati\v{c}eskie zametki},
     pages = {803--812},
     publisher = {mathdoc},
     volume = {62},
     number = {6},
     year = {1997},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1997_62_6_a0/}
}