(1) Department of Mathematics and Statistics, McGill University, 805, Sherbrooke Street West, Montreal, Que., Canada H3A 2K6; e-mail:
Abstract:
A group is said to be Hopfian if every surjective endomorphism of the group is injective. We show that finitely generated subgroups of torsion-free hyperbolic groups are Hopfian. Our proof generalizes a theorem of Sela (Topology35 (2) 1999, 301–321).