@article{MZ_1952__56_169300,
     author = {G\"unter Hellwig},
     title = {Das {Randwertproblem} eines linearen elliptischen {Systems.}},
     journal = {Mathematische Zeitschrift},
     pages = {388--408},
     publisher = {mathdoc},
     volume = {56},
     year = {1952},
     zbl = {0047.34001},
     url = {http://geodesic.mathdoc.fr/item/MZ_1952__56_169300/}
}