sub tilly_UCS {
  my $str = shift;
  # Try all cuts.  Those that don't fall in 2 are repeats
  foreach my $char (split //, $str) {
    my @cut = split /\Q$char\E/, $str, -1;
    if (2 != @cut) {
      my @rejoined = map "$cut[$_-1]$char$cut[$_]", 1..$#cut;
      @rejoined = sort {length $b <=> $a} @rejoined;
      my @unique = tilly_UCS(shift @rejoined);
      foreach my $str (@rejoined) {
        if (length($str) < length($unique[0])) {
          last; # Avoid useless work, cannot improve
        }
        my @found = tilly_UCS($str);
        if (length($found[0]) > length($unique[0])) {
          @unique = @found;
        }
        elsif (length($found[0]) == length($unique[0])) {
          push @unique, @found;
        }
      }
      return @unique;
    }
  }
  # No repeats
  return $str;
}