@article{1183740114, author = {Simpson, Stephen G.}, title = {Sets Which Do Not Have Subsets of Every Higher Degree}, journal = {J. Symbolic Logic}, volume = {43}, number = {1}, year = {1978}, pages = { 135-138}, language = {en}, url = {http://dml.mathdoc.fr/item/1183740114} }
Simpson, Stephen G. Sets Which Do Not Have Subsets of Every Higher Degree. J. Symbolic Logic, Tome 43 (1978) no. 1, pp. 135-138. http://gdmltest.u-ga.fr/item/1183740114/