@article{10_1090_S1079_6762_03_00112_4,
     author = {Babson, Eric and Kozlov, Dmitry},
     title = {Topological obstructions to graph colorings},
     journal = {Electronic research announcements of the American Mathematical Society},
     pages = {61--68},
     year = {2003},
     volume = {09},
     doi = {10.1090/S1079-6762-03-00112-4},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S1079-6762-03-00112-4/}
}