@article{10_1017_S0017089500006157,
     author = {Newman, Morris},
     title = {The classical modular group as a subgroup of {GL(2,} {Z){\textdagger}}},
     journal = {Glasgow mathematical journal},
     pages = {161--164},
     year = {1985},
     volume = {26},
     doi = {10.1017/S0017089500006157},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500006157/}
}