Incidences of lines in $P^3$ and the arithmetic genus of curves
  Guth and Katz proved that, as conjectured by Elekes and Sharir, $m$ lines in 3-space have at most constant times $ m^{3/2}$ intersection points, aside from some obvious counter examples. We give an explicit bound for the constant, using the arithmetic genus of the union of the lines. 
J\'anos Koll\'ar (Princeton Univ)
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