@article{JRAM_1932__168_149836,
     author = {J. Popken and J.F. Koksma},
     title = {Zur {Transzendenz} von e... .},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {211--230},
     publisher = {mathdoc},
     volume = {168},
     year = {1932},
     zbl = {0005.34902},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1932__168_149836/}
}