1. Extensions of uniformly continuous transformations and hyperconvex metric spaces;Aronszajn;Pacific J. Math.,1956
2. Nonexpansive mappings and hyperconvex spaces;Baillon,1986
3. R-trees in topology, geometry, and group theory;Bestivina,2002
4. Metric Spaces of Non-Positive Curvature;Bridson,1999
5. Gated sets in metric spaces;Dress;Aequationes Math.,1987