Victor Chepoi Feodor F. Dragan Bertrand Estellon Michel Habib Yann Vaxès Notes on diameters, centers, and approximating trees of delta-hyperbolic geodesic spaces and graphs. 231-234 2008 31 Electronic Notes in Discrete Mathematics http://dx.doi.org/10.1016/j.endm.2008.06.046 db/journals/endm/endm31.html#ChepoiDEHV08