Negatively curved groups have the convergence property. I. Freden, Eric M. — 1995 Annales Academiae Scientiarum Fennicae. Series A I. Mathematica
Negatively curved groups and the convergence property. II: Transitivity in negatively curved groups. Freden, Eric M. — 1996 Annales Academiae Scientiarum Fennicae. Series A I. Mathematica