@article{GDZPPN00241502X, title = {Finiteness of the Lower Spectrum of Schr\"odinger Operators.}, journal = {Mathematische Zeitschrift}, volume = {136}, year = {1974}, pages = {29-40}, zbl = {0305.35076}, url = {http://dml.mathdoc.fr/item/GDZPPN00241502X} }
Piepenbrink, John. Finiteness of the Lower Spectrum of Schrödinger Operators.. Mathematische Zeitschrift, Tome 136 (1974) pp. 29-40. http://gdmltest.u-ga.fr/item/GDZPPN00241502X/