@article{DE_1968_4_4_a15,
     author = {A. G. Ramm},
     title = {The principle of the limit amplitude},
     journal = {Differencialʹnye uravneni\^a},
     pages = {714--720},
     year = {1968},
     volume = {4},
     number = {4},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1968_4_4_a15/}
}