%0 Journal Article %A Stothers, W. W. %T Subgroups of infinite index in the modular group II %J Glasgow mathematical journal %D 1981 %P 101-118 %V 22 %N 1 %U http://geodesic.mathdoc.fr/articles/10.1017/S0017089500004523/ %R 10.1017/S0017089500004523 %F 10_1017_S0017089500004523