@article{DAN_1971_196_1_a1,
     author = {Yu. G. Borisovich and Yu. I. Sapronov},
     title = {On some topological invariants of nonlinear {Fredholm} mappings},
     journal = {Doklady Akademii Nauk},
     pages = {12--15},
     publisher = {mathdoc},
     volume = {196},
     number = {1},
     year = {1971},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DAN_1971_196_1_a1/}
}