@article{GDZPPN002300052, title = {On the Essential Spectrum of Symmetrizable Operators.}, journal = {Mathematische Annalen}, volume = {179}, year = {1968}, pages = {145-153}, zbl = {0164.16401}, url = {http://dml.mathdoc.fr/item/GDZPPN002300052} }
NIETO, J.I. On the Essential Spectrum of Symmetrizable Operators.. Mathematische Annalen, Tome 179 (1968) pp. 145-153. http://gdmltest.u-ga.fr/item/GDZPPN002300052/