@article{MZ_1930__31_168206,
     author = {Oskar Perron},
     title = {Die {Ordnungszahlen} linearer {Differentialgleichungssysteme}},
     journal = {Mathematische Zeitschrift},
     pages = {748--766},
     publisher = {mathdoc},
     volume = {31},
     year = {1930},
     zbl = {56.1038.03},
     url = {http://geodesic.mathdoc.fr/item/MZ_1930__31_168206/}
}