  In a recent paper Chatterji and Niblo proved that a geodesic metric space is
Gromov hyperbolic if and only if the intersection of any two closed balls has
uniformly bounded eccentricity. In their paper, the authors raise the question
whether a geodesic metric space with the property that the intersection of any
two closed balls has eccentricity 0, is necessarily a real tree. The purpose of
this note is to answer this question affirmatively. We also partially improve
the main result of Chatterji and Niblo by showing that already sublinear
eccentricity implies Gromov hyperbolicity.
