@article{MAN_1913__73_158595,
     author = {D. Hilbert},
     title = {\"Uber den {Begriff} der {Klasse} von {Differentialgleichungen}},
     journal = {Mathematische Annalen},
     pages = {95--108},
     year = {1913},
     volume = {73},
     zbl = {43.0378.01},
     url = {http://geodesic.mathdoc.fr/item/MAN_1913__73_158595/}
}