@article{1103043343,
author = {Kramer, Henry P.},
title = {Perturbation of differential operators.},
journal = {Pacific J. Math.},
volume = {7},
number = {4},
year = {1957},
pages = { 1405-1435},
language = {en},
url = {http://dml.mathdoc.fr/item/1103043343}
}
Kramer, Henry P. Perturbation of differential operators.. Pacific J. Math., Tome 7 (1957) no. 4, pp. 1405-1435. http://gdmltest.u-ga.fr/item/1103043343/