s a b  indicates  that  an  input point at coordinates a b
              was seen.
       l a b c
              indicates a line with equation ax + by = c.
       v a b  indicates a vertex at a b.
       e l v1 v2
              indicates a Voronoi segment which is  a  subsegment
              of line number l with endpoints numbered v1 and v2.
              If v1 or v2 is -1, the line extends to infinity.
       The other options are:
       s      The input is sorted by  y  coordinate  (the  second
              number  in  the pair).  The first input line should
              be npoints xmin xmax ymin ymax.  This describes the
              number of points and the range of the points.  This
              line is used to determine internal hash table size;
              it  need not be exact but performance suffers if it
              is grossly wrong.
       p      Produce output suitable  for  input  to  plot  (1),
              rather than the forms described above.
       On unsorted data uniformly distributed in the unit square,
       s.sweep uses about 20n+140/n bytes of storage.  On sorted
       data, s.sweep uses about 160/n bytes.
Last changed: $Date: 2002/01/25 05:45:35 $