Victor Chepoi Feodor F. Dragan Bertrand Estellon Michel Habib Yann Vaxès Diameters, centers, and approximating trees of delta-hyperbolicgeodesic spaces and graphs. 59-68 2008 Symposium on Computational Geometry http://doi.acm.org/10.1145/1377676.1377687 conf/compgeom/2008 db/conf/compgeom/compgeom2008.html#ChepoiDEHV08