@article{MZ_1967__96_170663,
     author = {Rolf Leis},
     title = {Zur {Monotonie} der {Eigenwerte} selbstadjungierter elliptischer {Differentialgleichungen.}},
     journal = {Mathematische Zeitschrift},
     pages = {26--32},
     publisher = {mathdoc},
     volume = {96},
     year = {1967},
     zbl = {0143.14501},
     url = {http://geodesic.mathdoc.fr/item/MZ_1967__96_170663/}
}