@article{AMLG_1975__17_137900,
     author = {Donald A. Alton},
     title = {A characterization of r-maximal sets.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {35--36},
     publisher = {mathdoc},
     volume = {17},
     year = {1975},
     zbl = {0315.02039},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1975__17_137900/}
}