@article{bwmeta1.element.bwnjournal-article-fmv127i1p7bwm,
author = {J. Paris and A. Wilkie},
title = {Counting $$\Delta$\_0$ sets},
journal = {Fundamenta Mathematicae},
volume = {128},
year = {1987},
pages = {67-76},
zbl = {0627.03018},
language = {en},
url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-fmv127i1p7bwm}
}
Paris, J.; Wilkie, A. Counting $Δ_0$ sets. Fundamenta Mathematicae, Tome 128 (1987) pp. 67-76. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-fmv127i1p7bwm/