@article{10_4064_aa_33_3_261_267,
     author = {Juliet Britto},
     title = {On the construction of non-congruence subgroups},
     journal = {Acta Arithmetica},
     pages = {261--267},
     publisher = {mathdoc},
     volume = {33},
     number = {3},
     year = {1977},
     doi = {10.4064/aa-33-3-261-267},
     language = {en},
     url = {http://geodesic.mathdoc.fr/articles/10.4064/aa-33-3-261-267/}
}