my @superset = split /\s+/, 'convert python to perl';
my $N = scalar @superset;
for my $combo (0..((2**$N) - 1)) {   # a combo is also a bit mask
    print "selection:";
    for my $selector (0..($N-1)) {  # a selector is also a bit
	(2**$selector) & $combo and print ' ' . $superset[$selector];
    }
    print "\n";
}