@article{MS2_1955__3_165574,
     author = {VIDAR THOM\'EE},
     title = {Estimates of the {Friedrichs} {-Lewy} type for a hyperbolic equation with three characteristics},
     journal = {Mathematica Scandinavica},
     pages = {115--123},
     publisher = {mathdoc},
     volume = {3},
     year = {1955},
     zbl = {0064.34405},
     url = {http://geodesic.mathdoc.fr/item/MS2_1955__3_165574/}
}