@article{PORMA_1989__46_S_115833,
     author = {Carvalho e Silva, Jaime},
     title = {On the hyperbolicity of a third order operator and the generalized {Goursat-Darboux} problem},
     journal = {Portugaliae mathematica},
     pages = {567--577},
     publisher = {mathdoc},
     volume = {46},
     number = {S},
     year = {1989},
     mrnumber = {1080774},
     zbl = {0768.35056},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/PORMA_1989__46_S_115833/}
}