@article{SM_1971_14_1_a7,
     author = {V. I. Voitinskii},
     title = {Density of {Cauchy} initial data for solutions of elliptic equations},
     journal = {Sbornik. Mathematics},
     pages = {131--139},
     year = {1971},
     volume = {14},
     number = {1},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1971_14_1_a7/}
}