TY  - JOUR
AU  - A.W. Mason
TI  - Free quotients of congruence subgroups of Bianchi groups.
JO  - Mathematische Annalen
PY  - 1992
SP  - 65
EP  - 76
VL  - 293
IS  - 4
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MAN_1992__293_4_164945/
ID  - MAN_1992__293_4_164945
ER  -