@article{JRAM_1986__367_152832,
     author = {Egbert Harzheim and Paul Erd\"os},
     title = {Congruent subsets of infinite sets of natural numbers.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {207--214},
     publisher = {mathdoc},
     volume = {367},
     year = {1986},
     zbl = {0575.10041},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1986__367_152832/}
}