@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/