@article{MZ_1929__30_168130,
     author = {E. Hopf},
     title = {Zum analytischen {Charakter} der {L\"osungen} regul\"arer zweidimensionaler {Variationsprobleme}},
     journal = {Mathematische Zeitschrift},
     pages = {404--413},
     publisher = {mathdoc},
     volume = {30},
     year = {1929},
     zbl = {55.0898.03},
     url = {http://geodesic.mathdoc.fr/item/MZ_1929__30_168130/}
}