@article{GDZPPN002283298, title = {Perturbation Theory of Semi-Bounded Operators.}, journal = {Mathematische Annalen}, volume = {125}, year = {1952}, pages = {435-447}, zbl = {0050.34502}, url = {http://dml.mathdoc.fr/item/GDZPPN002283298} }
Kato, T. Perturbation Theory of Semi-Bounded Operators.. Mathematische Annalen, Tome 125 (1952) pp. 435-447. http://gdmltest.u-ga.fr/item/GDZPPN002283298/