@article{MAN_1922__87_158969,
     author = {A. Hammerstein},
     title = {Elementarer {Beitrag} zur {Variationsrechnung}},
     journal = {Mathematische Annalen},
     pages = {229--237},
     publisher = {mathdoc},
     volume = {87},
     year = {1922},
     zbl = {48.0590.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1922__87_158969/}
}