@article{10_4064_fm_127_1_67_76,
     author = {J. Paris and A. Wilkie},
     title = {Counting $\ensuremath{\Delta}_0$ sets},
     journal = {Fundamenta Mathematicae},
     pages = {67--76},
     publisher = {mathdoc},
     volume = {127},
     number = {1},
     year = {1987},
     doi = {10.4064/fm-127-1-67-76},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/fm-127-1-67-76/}
}