@article{GDZPPN00220228X,
title = {The bottom of the spectrum of a Riemannian covering.},
journal = {Journal f\"ur die reine und angewandte Mathematik},
volume = {358},
year = {1985},
pages = {101-114},
zbl = {0553.53027},
url = {http://dml.mathdoc.fr/item/GDZPPN00220228X}
}
Brooks, Robert. The bottom of the spectrum of a Riemannian covering.. Journal für die reine und angewandte Mathematik, Tome 358 (1985) pp. 101-114. http://gdmltest.u-ga.fr/item/GDZPPN00220228X/