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References
- ↑ Gersten, S. M. (1994). "The automorphism group of a free group is not a CAT(0) group". Proceedings of the American Mathematical Society. 121 (4): 999–1002. doi:10.2307/2161207. MR 1195719.
- ↑ Bridson, Martin R.; Haefliger, André (1999). "Chapter III.Γ Non-Positive Curvature and Group Theory, Section 1. Isometries of CAT(0) Spaces". Metric spaces of non-positive curvature. Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences] 319. Berlin: Springer-Verlag. pp. 439–448. ISBN 3-540-64324-9. MR 1744486.
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