@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/}
}