@article{SM_1971_13_4_a6,
     author = {I. S. Gudovich and S. G. Krein},
     title = {Some boundary value problems elliptic in a~subspace},
     journal = {Sbornik. Mathematics},
     pages = {589--601},
     publisher = {mathdoc},
     volume = {13},
     number = {4},
     year = {1971},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/SM_1971_13_4_a6/}
}