@article{MZ_1921__10_167639,
     author = {C., Siegel},
     title = {Approximation algebraischer {Zahlen}},
     journal = {Mathematische Zeitschrift},
     pages = {173--213},
     year = {1921},
     volume = {10},
     zbl = {48.0163.07},
     url = {http://geodesic.mathdoc.fr/item/MZ_1921__10_167639/}
}