@article{JRAM_1968__232_150875,
     author = {Erich H\"artter},
     title = {Differenzen von {Mengen} nichtnegativer ganzer {Zahlen.}},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {112--117},
     publisher = {mathdoc},
     volume = {232},
     year = {1968},
     zbl = {0165.06102},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1968__232_150875/}
}