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A classic theorem of Euclidean geometry,often attributed as a De Bruijn-Erd?s theorem,asserts that any noncollinear set of n points in the plane determines at least n distinct lines.Chen and Chvátal conjectured that this holds for an arbitrary finite metric space,with a certain natural definition of lines in a metric space.The form has special cases in restricted metric spaces,spaces generated by graphs,as well as more general situations in hypergraphs.We will survey the most recent results and their proof techniques.