@article{bwmeta1.element.bwnjournal-article-aav33i3p261bwm,
author = {Britto, Juliet},
title = {On the construction of non-congruence subgroups},
journal = {Acta Arithmetica},
volume = {32},
year = {1977},
pages = {261-267},
zbl = {0361.20048},
language = {en},
url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-aav33i3p261bwm}
}
Britto, Juliet. On the construction of non-congruence subgroups. Acta Arithmetica, Tome 32 (1977) pp. 261-267. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-aav33i3p261bwm/