@article{SM_1967_1_4_a7,
     author = {A. G. Ramm},
     title = {Letter to the {Editor}},
     journal = {Sbornik. Mathematics},
     pages = {570},
     year = {1967},
     volume = {1},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_1_4_a7/}
}