%0 Journal Article
%A L. HÖRMANDER
%T Differential Operators of Principal Type.
%J Mathematische Annalen
%D 1960
%P 124-146
%V 140
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MAN_1960__140_160767/
%F MAN_1960__140_160767