@article{SM_1972_18_3_a1,
     author = {A. I. Shnirel'man},
     title = {The degree of a~quasi-ruled mapping and a~nonlinear {Hilbert} problem},
     journal = {Sbornik. Mathematics},
     pages = {373--396},
     publisher = {mathdoc},
     volume = {18},
     number = {3},
     year = {1972},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1972_18_3_a1/}
}