TY  - JOUR
AU  - Tretkoff, Carol
TI  - Nonparabolic subgroups of the modular group
JO  - Glasgow mathematical journal
PY  - 1975
SP  - 91
EP  - 102
VL  - 16
IS  - 2
UR  - http://geodesic.mathdoc.fr/articles/10.1017/S0017089500002573/
DO  - 10.1017/S0017089500002573
ID  - 10_1017_S0017089500002573
ER  -