Voir la notice de l'article provenant de la source Math-Net.Ru
@article{MZM_1991_50_6_a13, author = {V. L. Selivanov}, title = {Jumps of certain classes of $\Delta^0_2$-sets}, journal = {Matemati\v{c}eskie zametki}, pages = {122--125}, publisher = {mathdoc}, volume = {50}, number = {6}, year = {1991}, language = {ru}, url = {http://geodesic.mathdoc.fr/item/MZM_1991_50_6_a13/} }
V. L. Selivanov. Jumps of certain classes of $\Delta^0_2$-sets. Matematičeskie zametki, Tome 50 (1991) no. 6, pp. 122-125. http://geodesic.mathdoc.fr/item/MZM_1991_50_6_a13/