@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/