@article{MAN_1922__85_158905,
     author = {J. Sommer},
     title = {\"Uber die {Bezeichnung} {Grad} einer {Differentialgleichung}},
     journal = {Mathematische Annalen},
     pages = {65--73},
     publisher = {mathdoc},
     volume = {85},
     year = {1922},
     zbl = {48.0513.03},
     url = {http://geodesic.mathdoc.fr/item/MAN_1922__85_158905/}
}