@article{AMLG_1983__23_138007,
     author = {J.C. Shepherdson and J.P. Jones},
     title = {Variants of {Robinson's} essentially undecidable theory {R.}},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {61--64},
     publisher = {mathdoc},
     volume = {23},
     year = {1983},
     zbl = {0511.03015},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1983__23_138007/}
}