@article{GDZPPN00253939X, title = {Symmetric perturbation of a self-adjoint operator}, journal = {Revista colombiana de matematicas}, volume = {7}, year = {1973}, pages = {81-84}, zbl = {0295.47020}, url = {http://dml.mathdoc.fr/item/GDZPPN00253939X} }
Rao, D. K. Symmetric perturbation of a self-adjoint operator. Revista colombiana de matematicas, Tome 7 (1973) pp. 81-84. http://gdmltest.u-ga.fr/item/GDZPPN00253939X/