A De Bruijn-Erdos theorem for chordal graphs
  A special case of a combinatorial theorem of De Bruijn and Erdos asserts that every noncollinear set of n points in the plane determines at least n distinct lines. Chen and Chvatal suggested a possible generalization of this assertion in metric spaces with appropriately defined lines. We prove this generalization in all metric spaces induced by connected chordal graphs. 
Laurent Beaudou, Adrian Bondy, Xiaomin Chen, Ehsan Chiniforooshan,   Maria Chudnovsky, Vasek Chvatal, Nicolas Fraiman, Yori ...
math.CO