@article{GDZPPN002045567,
title = {Variants of Robinson's essentially undecidable theory R.},
journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
volume = {23},
year = {1983},
pages = {61-64},
zbl = {0511.03015},
url = {http://dml.mathdoc.fr/item/GDZPPN002045567}
}
Shepherdson, J.C.; Jones, J.P. Variants of Robinson's essentially undecidable theory R.. Archiv für mathematische Logik und Grundlagenforschung, Tome 23 (1983) pp. 61-64. http://gdmltest.u-ga.fr/item/GDZPPN002045567/