my @superset = split /\s+/, 'convert python to perl';
my $N = $#superset; # one less element than in the previous example
for my $combo (0..((2**$N) - 1)) { # a combo is a bit mask
    for my $selector (0..$N) {  # a selector is also a bit position
        print $superset[$selector];
        if ($selector == $N) {
            print "\n";
	    next;
        }
	if ((2**$selector) & $combo) {
            print ' ';
        }
        else {
            print '-';
        }
    }
}