@article{1183736953,
author = {Jones, J. P.},
title = {Effectively Retractable Theories and Degrees of Undecidability},
journal = {J. Symbolic Logic},
volume = {34},
number = {1},
year = {1969},
pages = { 597-604},
language = {en},
url = {http://dml.mathdoc.fr/item/1183736953}
}
Jones, J. P. Effectively Retractable Theories and Degrees of Undecidability. J. Symbolic Logic, Tome 34 (1969) no. 1, pp. 597-604. http://gdmltest.u-ga.fr/item/1183736953/