@article{MZ_1968__103_170888,
     author = {Herbert Beckert},
     title = {\"Uber eine bemerkenswerte {Klasse} gemischtfreier {Variationsprobleme} h\"oherer {Ordnung.}},
     journal = {Mathematische Zeitschrift},
     pages = {8--29},
     publisher = {mathdoc},
     volume = {103},
     year = {1968},
     zbl = {0153.43401},
     url = {http://geodesic.mathdoc.fr/item/MZ_1968__103_170888/}
}