@article{INTD_1989_35_a3,
     author = {A. A. Agrachev and R. V. Gamkrelidze},
     title = {Quadratic mappings and smooth vector functions: {Euler} characteristics of level sets},
     journal = {Itogi Nauki i Tekhniki. Seriya Sovremennye Problemy Matematiki. Noveishie Dostizheniya},
     pages = {179--239},
     publisher = {mathdoc},
     volume = {35},
     year = {1989},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/INTD_1989_35_a3/}
}