my ($only_a, $only_b, $only_c, $all, $any) = listy(\@a, \@b, \@c);

sub listy {
  my %tmp1;
  my @keys;
  for (0..$#_) {
    my $key = pop @keys;
    push @keys, $_, (defined $key ? $key : '') . $_;
    for my $k (@{$_[$_]}) {
      $tmp1{$k} .= $_;
    }
  }
  my %tmp2;
  while (my($k, $v) = each %tmp1) {
    push @{$tmp2{$v}}, $k;
  }
  return @tmp2{@keys}, [keys %tmp1];
}