TY  - JOUR
AU  - Rainer Hempel
TI  - Perturbations by Quadratic Forms and Invariance of Essential Spectra.
JO  - Mathematische Zeitschrift
PY  - 1984
SP  - 281
EP  - 290
VL  - 185
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MZ_1984__185_173402/
ID  - MZ_1984__185_173402
ER  -