@article{EXMA_2004__13_3_52775,
     author = {Chua, Kok Seng and Lang, Mong Lung},
     title = {Congruence subgroups associated to the {Monster.}},
     journal = {Experimental mathematics},
     pages = {343--360},
     publisher = {mathdoc},
     volume = {13},
     number = {3},
     year = {2004},
     zbl = {1099.11021},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/EXMA_2004__13_3_52775/}
}