@article{SM_2004_195_4_a1,
     author = {A. V. Borovskikh},
     title = {Group classification of the eikonal equation for},
     journal = {Sbornik. Mathematics},
     pages = {479--520},
     year = {2004},
     volume = {195},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_2004_195_4_a1/}
}