@article{GDZPPN002436973,
title = {An Elementary Proof of Harnack's Inequality for Schr\"odinger Operators and Related Topics.},
journal = {Mathematische Zeitschrift},
volume = {205},
year = {1990},
pages = {129-152},
zbl = {0697.35017},
url = {http://dml.mathdoc.fr/item/GDZPPN002436973}
}
Simader, Christian G. An Elementary Proof of Harnack's Inequality for Schrödinger Operators and Related Topics.. Mathematische Zeitschrift, Tome 205 (1990) pp. 129-152. http://gdmltest.u-ga.fr/item/GDZPPN002436973/