@article{GDZPPN002429101,
title = {Positive Operators and Elliptic Eigenvalue Problems.},
journal = {Mathematische Zeitschrift},
volume = {185},
year = {1984},
pages = {247-264},
zbl = {0549.47026},
url = {http://dml.mathdoc.fr/item/GDZPPN002429101}
}
Nussbaum, Roger D. Positive Operators and Elliptic Eigenvalue Problems.. Mathematische Zeitschrift, Tome 185 (1984) pp. 247-264. http://gdmltest.u-ga.fr/item/GDZPPN002429101/