On the construction of non-congruence subgroups
On the Cuspidal Cohomology of the Bianchi Modular Groups.
On the Homology and Cohomology of Congruence Subgroups.
On the Margulis constant for Kleinian groups. I.
On the number of facets of three-dimensional Dirichlet stereohedra. II: Non-cubic groups.
On the number of subgroups of given index in the modular group.
On the principal congruence subgroups of the Hecke-group .
On the representations of GL (2). II. ...-factors of the representations of GL(2) x GL(2).
On the subgroups of the Picard group.
On the Top Betti Number of Subgroups of SL(n,Z).
On three-dimensional space groups.
Operator k-theory for the group SU(n, 1).
Orders of some modular linear groups.
Outer automorphism groups of Bieberbach groups.