@article{DE_1977_13_9_a13,
     author = {O. N. Naida and A. G. Prudkovskii},
     title = {The {WKB} method for the system $(-{}ih\partial /\partial t+{\cal A}(x,t,-{}ih\partial /\partial x))U=0$ in the case of characteristics of variable multiplicity},
     journal = {Differencialʹnye uravneni\^a},
     pages = {1678--1691},
     publisher = {mathdoc},
     volume = {13},
     number = {9},
     year = {1977},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1977_13_9_a13/}
}