@article{1153494227,
author = {Colombini, Ferruccio and Nishitani, Tatsuo},
title = {On finitely degenerate hyperbolic operators of second order},
journal = {Osaka J. Math.},
volume = {41},
number = {1},
year = {2004},
pages = { 933-947},
language = {en},
url = {http://dml.mathdoc.fr/item/1153494227}
}
Colombini, Ferruccio; Nishitani, Tatsuo. On finitely degenerate hyperbolic operators of second order. Osaka J. Math., Tome 41 (2004) no. 1, pp. 933-947. http://gdmltest.u-ga.fr/item/1153494227/