@article{AMLG_1971__9_137786,
     author = {D.L. Kreider and R.W. Ritchie},
     title = {A universal two-way automation.},
     journal = {Archiv f\"ur mathematische Logik und Grundlagenforschung},
     pages = {49--58},
     publisher = {mathdoc},
     volume = {9},
     year = {1971},
     zbl = {0173.01407},
     url = {http://geodesic.mathdoc.fr/item/AMLG_1971__9_137786/}
}