my $iter = combinations( $k => \@vertices );

SUBSET:
while ( my @subset = $iter->() ) {
    my $pairs = combinations( 2 => \@subset );
    while ( my @pair = $pairs->() ) {
        next SUBSET unless @pair is an edge in the graph;
    }
    print "@subset is a $k-clique\n";
}

##</code><code>##

        if ($string =~ /$regex/x) {
            print join(" ", map $$_, 1..$k), "\n";
        }

##</code><code>##

$regex .= '(?{ print join(" ", map $$_, 1..$k), "\\n" })(?!)';
$string =~ /$regex/x;

##</code><code>##

5 6 9
2 3 4
1 3 4
1 2 4
1 2 3