Flip Distance Between Two Triangulations of a Point-Set is NP-complete
  Given two triangulations of a convex polygon, computing the minimum number of flips required to transform one to the other is a long-standing open problem. It is not known whether the problem is in P or NP-complete. We prove that two natural generalizations of the problem are NP-complete, namely computing the minimum number of flips between two triangulations of (1) a polygon with holes; (2) a set of points in the plane. 
Anna Lubiw and Vinayak Pathak
cs.CG