sub inc36 {
  my ($left, $right) = shift =~ /^(.*?)(z*)$/i;
  $left = "0" unless length $left;
  substr($left, -1) =~ tr/0-9a-yA-Y/1-9ab-zB-Z/;
  $right =~ tr/zZ/00/;
  $left . $right;
}