@article{GDZPPN002044560,
title = {The recursive sets in certain monadic second order fragments of arithmetic.},
journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
volume = {17},
year = {1975},
pages = {71-80},
zbl = {0325.02033},
url = {http://dml.mathdoc.fr/item/GDZPPN002044560}
}
Siefkes, Dirk. The recursive sets in certain monadic second order fragments of arithmetic.. Archiv für mathematische Logik und Grundlagenforschung, Tome 17 (1975) pp. 71-80. http://gdmltest.u-ga.fr/item/GDZPPN002044560/