1. (BKOS ex.7.1) Prove that for any n > 3 there is a set of n point
   sites in the plane such that one of the cells of the Voronoi diagram
   has n-1 vertices.

2. (BKOS ex.7.5) Give an example where the parabola defined by some site
   contributes n-1 different arcs to the beach line.

3. (BKOS ex.7.10) Describe an O(n log n) time algorithm to find the
   closest pair of points among a given set of n points in the
   plane. (You may assume the existence of an O(n log n) time algorithm
   for constructing either Voronoi diagrams or Delaunay triangulations.)

4. (BKOS ex.9.17) Describe a set of points such that the Delaunay
   triangulation of the points has greater total edge length than some
   other triangulation. (Hint: you should need only four points.)