@article{GDZPPN002329492, title = {Nonstrictly Hyperbolic Nonlinear Systems.}, journal = {Mathematische Annalen}, volume = {277}, year = {1987}, pages = {213-232}, zbl = {0614.35060}, url = {http://dml.mathdoc.fr/item/GDZPPN002329492} }
Craig, Walter. Nonstrictly Hyperbolic Nonlinear Systems.. Mathematische Annalen, Tome 277 (1987) pp. 213-232. http://gdmltest.u-ga.fr/item/GDZPPN002329492/