@article{SM_1970_10_2_a4,
     author = {L. A. Sakhnovich},
     title = {Generalized wave operators},
     journal = {Sbornik. Mathematics},
     pages = {197--216},
     year = {1970},
     volume = {10},
     number = {2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1970_10_2_a4/}
}