@article{SM_1969_7_3_a9,
     author = {Ya. A. Roitberg and Z. G. Sheftel},
     title = {A~theorem on homeomorphisms for elliptic systems and its applications},
     journal = {Sbornik. Mathematics},
     pages = {439--465},
     publisher = {mathdoc},
     volume = {7},
     number = {3},
     year = {1969},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1969_7_3_a9/}
}