@article{MZ_1964__85_170297,
     author = {Peter Werner},
     title = {\"Uber die {Randwertprobleme} der {Helmholtzschen} {Schwingungsgleichung.}},
     journal = {Mathematische Zeitschrift},
     pages = {226--240},
     publisher = {mathdoc},
     volume = {85},
     year = {1964},
     zbl = {0151.16001},
     url = {http://geodesic.mathdoc.fr/item/MZ_1964__85_170297/}
}