Y. Algom-Kfir, and M. Bestvina. (2009)cite arxiv:0910.5408
Comment: 15 pages, accepted to Geometriae Dedicata, omitted the comment about
the potential function in rank 2 being equal to injrad (because it was false).
M. Bridson, and K. Vogtmann. (2010)cite arxiv:1007.2598
Comment: Incorrect Lemma (2.5) replaced by new Proposition 2.5. Typos
corrected, references updated.