# If piece is efficiently placed, try the next pentomino
  #   (tend to cluster them towards origin)
  if (!exceeds_hole_count($index)) { solve ($index+1); }

##</code><code>##

  ($x, $y) = next_position_accross ( $x, $y ); 
  # if the pentomino has run off the board, backup
  #   and try again. (n_p_a returns (-1,-1) in this case
  if ($x < 0) { return } 

  $SOLVE_COUNT++;    

  # Start the piece well out onto the board 
  if (($x+$y) < $index)     { next };

##</code><code>##

            
  # Optimization by which piece never starts too far out on board.
  if (($x+$y) > (2*$index)) { print 'b'; next };
  if ($y > $index)          { print 'y'; return };
  last;