1. Non-free projective modules for torsion-free groups;Berridge;J. London Math. Soc.,1979
2. The homotopy type of a two-dimensional complex;Dunwoody;Bull. London Math. Soc.,1976
3. Trees of homotopy types of (π, m)-complexes;Dyer,1979
4. Relator identifies in groups and stably free modules;Lustig,1992
5. Combinatorial Group Theory;Lyndon,1977