@article{10_1090_S0894_0347_1992_1127079_X,
     author = {Phillips, R. and Sarnak, P.},
     title = {Perturbation theory for the {Laplacian} on automorphic functions},
     journal = {Journal of the American Mathematical Society},
     pages = {1--32},
     publisher = {mathdoc},
     volume = {05},
     number = {1},
     year = {1992},
     doi = {10.1090/S0894-0347-1992-1127079-X},
     url = {http://geodesic.mathdoc.fr/articles/10.1090/S0894-0347-1992-1127079-X/}
}