@article{JRAM_1952__190_150224,
     author = {Bodo Volkmann},
     title = {\"Uber {Klassen} von {Mengen} nat\"urlicher {Zahlen.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {199--230},
     publisher = {mathdoc},
     volume = {190},
     year = {1952},
     language = {de},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1952__190_150224/}
}