@article{MZ_1964__86_170326,
     author = {Burghart Giesecke},
     title = {Zur {Dirchletschen} {Prinzip} f\"ur selbstadjungierte elliptische {Differentialoperatoren.}},
     journal = {Mathematische Zeitschrift},
     pages = {54--62},
     publisher = {mathdoc},
     volume = {86},
     year = {1964},
     zbl = {0173.39103},
     url = {http://geodesic.mathdoc.fr/item/MZ_1964__86_170326/}
}