@article{AMLG_1975__17_137907,
     author = {Dirk Siefkes},
     title = {The recursive sets in certain monadic second order fragments of arithmetic.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {71--80},
     publisher = {mathdoc},
     volume = {17},
     year = {1975},
     zbl = {0325.02033},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1975__17_137907/}
}