%0 Journal Article
%A Rainer Hempel
%T Perturbations by Quadratic Forms and Invariance of Essential Spectra.
%J Mathematische Zeitschrift
%D 1984
%P 281-290
%V 185
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MZ_1984__185_173402/
%F MZ_1984__185_173402