# an arbitrary permutation
  @o = @permutation = (1,2,0);
  # position of 0 is in $o[2], so $p[0]=2.
  # This leads to
  @p = @positions   = (2,0,1); 
  # And then 
  print " o[p] = (@o[@p]) = p[o] = (@p[@o]) \n";