@article{ZNSL_1975_51_a6,
     author = {A. P. Kiselev},
     title = {Focusing of the {WKB-solutions} of the equation $[\Delta+k^2n^2(x)]u=0$, $k\to\infty$},
     journal = {Zapiski Nauchnykh Seminarov POMI},
     pages = {123--128},
     publisher = {mathdoc},
     volume = {51},
     year = {1975},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/ZNSL_1975_51_a6/}
}