NAME: 
  intrsect
 PURPOSE: 
  Find the intersection or its inverse between two arrays.
 DESCRIPTION:
 CATEGORY:
  Set Manipulation
 CALLING SEQUENCE:
  intrsect,a,b,c,nfound, [NNOT]
 INPUTS:
     a - First set.
     b - Second set.
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
     NNOT - Flag, if true will invert the intersection operations, that is,
            the entries that do NOT appear in both sets will be returned.
 OUTPUTS:
     c      - Intersection (or NOT) of sets A and B.
     nfound - Number of items in the intersectoin (or NOT).
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
  93/12/16 - Marc W. Buie, Lowell Observatory, original version.