@article{1255632506, author = {Newman, Morris}, title = {The structure of some subgroups of the modular group}, journal = {Illinois J. Math.}, volume = {6}, number = {1}, year = {1962}, pages = { 480-487}, language = {en}, url = {http://dml.mathdoc.fr/item/1255632506} }
Newman, Morris. The structure of some subgroups of the modular group. Illinois J. Math., Tome 6 (1962) no. 1, pp. 480-487. http://gdmltest.u-ga.fr/item/1255632506/