@article{10_4064_aa110_4_2,
     author = {Umberto Zannier},
     title = {Parametrizing ${\rm SL}_2({\Bbb Z})$ and a question of {Skolem}},
     journal = {Acta Arithmetica},
     pages = {331--337},
     publisher = {mathdoc},
     volume = {110},
     number = {4},
     year = {2003},
     doi = {10.4064/aa110-4-2},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa110-4-2/}
}