(?:(?{local $q [0] = $nodes [0]})|
   (?{local $q [0] = $nodes [1]})|
   (?{local $q [0] = $nodes [2]})|
   (?{local $q [0] = $nodes [3]})|
   (?{local $q [0] = $nodes [4]})|
   (?{local $q [0] = $nodes [5]})|
   (?{local $q [0] = $nodes [6]})|
   (?{local $q [0] = $nodes [7]}))
(?:(?{local $q [1] = $nodes [0]})|
   (?{local $q [1] = $nodes [1]})|
   (?{local $q [1] = $nodes [2]})|
   (?{local $q [1] = $nodes [3]})|
   (?{local $q [1] = $nodes [4]})|
   (?{local $q [1] = $nodes [5]})|
   (?{local $q [1] = $nodes [6]})|
   (?{local $q [1] = $nodes [7]}))
(?(?{$q [1] eq $q [0] ||
     !$graph {$q [0]} {$q [1]}})x|)
(?:(?{local $q [2] = $nodes [0]})|
   (?{local $q [2] = $nodes [1]})|
   (?{local $q [2] = $nodes [2]})|
   (?{local $q [2] = $nodes [3]})|
   (?{local $q [2] = $nodes [4]})|
   (?{local $q [2] = $nodes [5]})|
   (?{local $q [2] = $nodes [6]})|
   (?{local $q [2] = $nodes [7]}))
(?(?{$q [2] eq $q [0] ||
     $q [2] eq $q [1] ||
     !$graph {$q [1]} {$q [2]}})x|)
(?:(?{local $q [3] = $nodes [0]})|
   (?{local $q [3] = $nodes [1]})|
   (?{local $q [3] = $nodes [2]})|
   (?{local $q [3] = $nodes [3]})|
   (?{local $q [3] = $nodes [4]})|
   (?{local $q [3] = $nodes [5]})|
   (?{local $q [3] = $nodes [6]})|
   (?{local $q [3] = $nodes [7]}))
(?(?{$q [3] eq $q [0] ||
     $q [3] eq $q [1] ||
     $q [3] eq $q [2] ||
     !$graph {$q [2]} {$q [3]}})x|)
(?:(?{local $q [4] = $nodes [0]})|
   (?{local $q [4] = $nodes [1]})|
   (?{local $q [4] = $nodes [2]})|
   (?{local $q [4] = $nodes [3]})|
   (?{local $q [4] = $nodes [4]})|
   (?{local $q [4] = $nodes [5]})|
   (?{local $q [4] = $nodes [6]})|
   (?{local $q [4] = $nodes [7]}))
(?(?{$q [4] eq $q [0] ||
     $q [4] eq $q [1] ||
     $q [4] eq $q [2] ||
     $q [4] eq $q [3] ||
     !$graph {$q [3]} {$q [4]}})x|)
(?:(?{local $q [5] = $nodes [0]})|
   (?{local $q [5] = $nodes [1]})|
   (?{local $q [5] = $nodes [2]})|
   (?{local $q [5] = $nodes [3]})|
   (?{local $q [5] = $nodes [4]})|
   (?{local $q [5] = $nodes [5]})|
   (?{local $q [5] = $nodes [6]})|
   (?{local $q [5] = $nodes [7]}))
(?(?{$q [5] eq $q [0] ||
     $q [5] eq $q [1] ||
     $q [5] eq $q [2] ||
     $q [5] eq $q [3] ||
     $q [5] eq $q [4] ||
     !$graph {$q [4]} {$q [5]}})x|)
(?:(?{local $q [6] = $nodes [0]})|
   (?{local $q [6] = $nodes [1]})|
   (?{local $q [6] = $nodes [2]})|
   (?{local $q [6] = $nodes [3]})|
   (?{local $q [6] = $nodes [4]})|
   (?{local $q [6] = $nodes [5]})|
   (?{local $q [6] = $nodes [6]})|
   (?{local $q [6] = $nodes [7]}))
(?(?{$q [6] eq $q [0] ||
     $q [6] eq $q [1] ||
     $q [6] eq $q [2] ||
     $q [6] eq $q [3] ||
     $q [6] eq $q [4] ||
     $q [6] eq $q [5] ||
     !$graph {$q [5]} {$q [6]}})x|)
(?:(?{local $q [7] = $nodes [0]})|
   (?{local $q [7] = $nodes [1]})|
   (?{local $q [7] = $nodes [2]})|
   (?{local $q [7] = $nodes [3]})|
   (?{local $q [7] = $nodes [4]})|
   (?{local $q [7] = $nodes [5]})|
   (?{local $q [7] = $nodes [6]})|
   (?{local $q [7] = $nodes [7]}))
(?(?{$q [7] eq $q [0] ||
     $q [7] eq $q [1] ||
     $q [7] eq $q [2] ||
     $q [7] eq $q [3] ||
     $q [7] eq $q [4] ||
     $q [7] eq $q [5] ||
     $q [7] eq $q [6] ||
     !$graph {$q [6]} {$q [7]}})x|)
(?{ @path = @q })

##</code><code>##

(?:(?{local $q [0] = $nodes [0]})|
   (?{local $q [0] = $nodes [1]})|
   (?{local $q [0] = $nodes [2]})|
   (?{local $q [0] = $nodes [3]})|
   (?{local $q [0] = $nodes [4]})|
   (?{local $q [0] = $nodes [5]})|
   (?{local $q [0] = $nodes [6]})|
   (?{local $q [0] = $nodes [7]}))
(?:(?{local $q [1] = $nodes [0]})|
   (?{local $q [1] = $nodes [1]})|
   (?{local $q [1] = $nodes [2]})|
   (?{local $q [1] = $nodes [3]})|
   (?{local $q [1] = $nodes [4]})|
   (?{local $q [1] = $nodes [5]})|
   (?{local $q [1] = $nodes [6]})|
   (?{local $q [1] = $nodes [7]}))
(?(?{$q [1] eq $q [0] ||
     !$graph {$q [0]} {$q [1]}})x|)

##</code><code>##

(?:(?{local $q [2] = $nodes [0]})|
   (?{local $q [2] = $nodes [1]})|
   (?{local $q [2] = $nodes [2]})|
   (?{local $q [2] = $nodes [3]})|
   (?{local $q [2] = $nodes [4]})|
   (?{local $q [2] = $nodes [5]})|
   (?{local $q [2] = $nodes [6]})|
   (?{local $q [2] = $nodes [7]}))
(?(?{$q [2] eq $q [0] ||
     $q [2] eq $q [1] ||
     !$graph {$q [1]} {$q [2]}})x|)

##</code><code>##

(?:(?{local $q [0] = $nodes [0]})|   (?:(?{local $q [1] = $nodes [0]})|    (?:(?{local $q [2] = $nodes [0]})|
   (?{local $q [0] = $nodes [1]})|      (?{local $q [1] = $nodes [1]})|       (?{local $q [2] = $nodes [1]})|
   (?{local $q [0] = $nodes [2]})|      (?{local $q [1] = $nodes [2]})|       (?{local $q [2] = $nodes [2]})|
   (?{local $q [0] = $nodes [3]})|      (?{local $q [1] = $nodes [3]})|       (?{local $q [2] = $nodes [3]})|
   (?{local $q [0] = $nodes [4]})|      (?{local $q [1] = $nodes [4]})|       (?{local $q [2] = $nodes [4]})|
   (?{local $q [0] = $nodes [5]})|      (?{local $q [1] = $nodes [5]})|       (?{local $q [2] = $nodes [5]})|
   (?{local $q [0] = $nodes [6]})|      (?{local $q [1] = $nodes [6]})|       (?{local $q [2] = $nodes [6]})|
   (?{local $q [0] = $nodes [7]}))      (?{local $q [1] = $nodes [7]}))       (?{local $q [2] = $nodes [7]}))
                                     (?(?{$q [1] eq $q [0] ||              (?(?{$q [2] eq $q [0] ||
                                          !$graph {$q [0]} {$q [1]}})x|)         $q [2] eq $q [1] ||
                                                                                !$graph {$q [1]} {$q [2]}})x|)


##</code><code>##

(?:(?{local $q [2] = $nodes [0]})|
   (?{local $q [2] = $nodes [1]})|
   (?{local $q [2] = $nodes [2]})|
   (?{local $q [2] = $nodes [3]})|
   (?{local $q [2] = $nodes [4]})|
   (?{local $q [2] = $nodes [5]})|
   (?{local $q [2] = $nodes [6]})|
   (?{local $q [2] = $nodes [7]}))

(?(?{$q [2] eq $q [0] ||
     $q [2] eq $q [1] ||
     !$graph {$q [1]} {$q [2]}})x|)

##</code><code>##

(?: exp1 | exp2 | exp3 ... )

##</code><code>##

# The second element was missing from the first group.
(? (?{ $q[1] eq $q[0] ||                                     !$graph{$q [0]}{$q [1]} } ) x | )
(? (?{ $q[2] eq $q[0] || $q[2] eq $q[1] ||                   !$graph{$q [1]}{$q [2]} } ) x | )
(? (?{ $q[3] eq $q[0] || $q[3] eq $q[1] || $q[3] eq $q[2] || !$graph{$q [2]}{$q [3]} } ) x | )

##</code><code>##

if(cond)
   re_1
else
   re_2

##</code><code>##

if ("" =~ /$regex/x) {

##</code><code>##

# null.
$q[1] eq $q[0] ||                                     !$graph{$q [0]}{$q [1]}
$q[2] eq $q[0] || $q[2] eq $q[1] ||                   !$graph{$q [1]}{$q [2]}
$q[3] eq $q[0] || $q[3] eq $q[1] || $q[3] eq $q[2] || !$graph{$q [2]}{$q [3]}