Distinct Distances on Curves Via Rigidity

It is shown that N points on a real algebraic curve of degree n in R always determine &n,d N 1+ 1 4 distinct distances, unless the curve is a straight line or the closed geodesic of a flat torus. In the latter case, there are arrangements of N points which determine . N distinct distances. The method may be applied to other quantities of interest to obtain analogous exponent gaps. An important step in the proof involves understanding the structural rigidity of certain frameworks on curves.