@article{MZ_1964__86_170338,
     author = {Birgitta Hellwig},
     title = {Ein {Kriterium} f\"ur die {Selbstadjungiertheit} elliptischer {Differentialoperatoren} im {Rn.}},
     journal = {Mathematische Zeitschrift},
     pages = {255--262},
     publisher = {mathdoc},
     volume = {86},
     year = {1964},
     zbl = {0134.31204},
     url = {http://geodesic.mathdoc.fr/item/MZ_1964__86_170338/}
}