%0 Journal Article
%A Mason, A.W.
%T Non-Standard, Normal Subgroups and Non-Normal, Standard Subgroups of the Modular Group
%J Canadian mathematical bulletin
%D 1989
%P 109-113
%V 32
%N 1
%U http://geodesic.mathdoc.fr/articles/10.4153/CMB-1989-016-5/
%R 10.4153/CMB-1989-016-5
%F 10_4153_CMB_1989_016_5