Abstract

We show that a non-elementary finitely generated torsion-free func-tion group is uniquely determined by its commutator subgroup. In this way, we obtain a generalization of the results obtained in [2], [3] and [8]. This is well related to Torelli?s theorem for closed Riemann sur-faces.For a general non-elementary torsion-free Kleinian group the above rigidity property still unknown