1. Length functions of group actions on ∧-trees;Alperin,1987
2. Uniform tree lattices;Bass;J. Amer. Math. Soc.,1990
3. Finiteness theorems for Fuchsian and Kleinian groups;Greenberg,1977
4. Finite and infinite cyclic extensions of free groups;Karass;J. Austral. Math. Soc.,1973