@article{10_4064_sm_36_1_1_76,
     author = {N. Aronszajn and R. Brown},
     title = {Finite-dimensional perturbations of spectral problems and variational approximation methods for eigenvalue problems. {Part} {I.} {Finite-dimensional} perturbations},
     journal = {Studia Mathematica},
     pages = {1--76},
     year = {1970},
     volume = {36},
     number = {1},
     doi = {10.4064/sm-36-1-1-76},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/sm-36-1-1-76/}
}