@article{GDZPPN002231360, title = {A lower bound for the least eigenvalue of ... + V.}, journal = {Manuscripta mathematica}, volume = {67}, year = {1990}, pages = {255-260}, zbl = {0717.58056}, url = {http://dml.mathdoc.fr/item/GDZPPN002231360} }
Bérard, Pierre. A lower bound for the least eigenvalue of ... + V.. Manuscripta mathematica, Tome 67 (1990) pp. 255-260. http://gdmltest.u-ga.fr/item/GDZPPN002231360/