@article{JRAM_1931__165_149779,
     author = {Leon Lichtenstein},
     title = {Zur {Variationsrechnung.} {Zweite} {Mitteilung.} {Das} isoperimetrische {Problem.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {194--216},
     publisher = {mathdoc},
     volume = {165},
     year = {1931},
     zbl = {0002.14202},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1931__165_149779/}
}