@article{MZM_1976_20_5_a15,
     author = {Yu. V. Pokornyi and S. V. Smitskikh},
     title = {Inversion of the oscillatory property of focusing operators},
     journal = {Matemati\v{c}eskie zametki},
     pages = {753--760},
     year = {1976},
     volume = {20},
     number = {5},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1976_20_5_a15/}
}