@article{JRAM_1984__351_152647,
     author = {David A. Cox and Walter R. Parry},
     title = {Genera of congruence subgroups in {Q-quaternion} algebras.},
     journal = {Journal f\"ur die reine und angewandte Mathematik},
     pages = {66--112},
     publisher = {mathdoc},
     volume = {351},
     year = {1984},
     zbl = {0531.10028},
     url = {http://geodesic.mathdoc.fr/item/JRAM_1984__351_152647/}
}