Voir la notice de l'article provenant de la source European Digital Mathematics Library
@article{MAN_1960__140_160767, author = {L. H\"ORMANDER}, title = {Differential {Operators} of {Principal} {Type.}}, journal = {Mathematische Annalen}, pages = {124--146}, publisher = {mathdoc}, volume = {140}, year = {1960}, zbl = {0090.08101}, url = {http://geodesic.mathdoc.fr/item/MAN_1960__140_160767/} }
L. HÖRMANDER. Differential Operators of Principal Type.. Mathematische Annalen, Tome 140 (1960), pp. 124-146. http://geodesic.mathdoc.fr/item/MAN_1960__140_160767/