%0 Journal Article
%A Gerd Grubb
%A Giuseppe Geymonat
%T The Essential Spectrum of Elliptic Systems of Mixed Order.
%J Mathematische Annalen
%D 1977
%P 247-276
%V 227
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MAN_1977__227_162979/
%F MAN_1977__227_162979