{
  # in the same block as the previous code

  sub rx_inc_b36 {
    my $n = shift;
    $n =~ s/([^Z])(Z*)$/$to_b36[$to_num{$1}+1] . 0 x length $2/e
      or $n = 1 . 0 x length $n;
    return $n;
  }
}