%0 Journal Article
%A Mason, A. W.
%T Lattice subgroups of free congruence groups
%J Glasgow mathematical journal
%D 1969
%P 106-115
%V 10
%N 2
%U http://geodesic.mathdoc.fr/articles/10.1017/S0017089500000641/
%R 10.1017/S0017089500000641
%F 10_1017_S0017089500000641