@article{RM_1971_26_6_a4,
     author = {B. M. Levitan},
     title = {Asymptotic behaviour of the spectral function of an elliptic equat},
     journal = {Trudy Matematicheskogo Instituta imeni V.A. Steklova},
     pages = {165--232},
     publisher = {mathdoc},
     volume = {26},
     number = {6},
     year = {1971},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/RM_1971_26_6_a4/}
}