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@article{EXMA_2004__13_3_52776, author = {Cummins, C.J.}, title = {Congruence subgroups of groups commensurable with of genus 0 and 1.}, journal = {Experimental mathematics}, pages = {361--382}, publisher = {mathdoc}, volume = {13}, number = {3}, year = {2004}, zbl = {1099.11022}, language = {en}, url = {http://geodesic.mathdoc.fr/item/EXMA_2004__13_3_52776/} }
Cummins, C.J. Congruence subgroups of groups commensurable with of genus 0 and 1.. Experimental mathematics, Tome 13 (2004) no. 3, pp. 361-382. http://geodesic.mathdoc.fr/item/EXMA_2004__13_3_52776/