@article{SM_1967_1_4_a4,
     author = {B. R. Vainberg and V. V. Grushin},
     title = {Uniformly nonelliptic problems. {I}},
     journal = {Sbornik. Mathematics},
     pages = {543--568},
     year = {1967},
     volume = {1},
     number = {4},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1967_1_4_a4/}
}