Dynamics of the continued fraction map and the spectral theory of SL (2, Z). Isaac Efrat — 1993 Inventiones mathematicae
On the existence of cusp forms over function fields. Isaac Efrat — 1989 Journal für die reine und angewandte Mathematik
Spectral deformations of automorphic functions over graphs of groups. Isaac Efrat — 1990 Inventiones mathematicae