#!/usr/bin/perl -l

use strict;
use warnings;

{
    my $state;
    sub fail () { $state++ }
    sub failed () { $state ? $state-- : $state }
}

LINE: while (<>) {
    chomp;
    my @chunks=split /_/;
    fail, next if @chunks < 2;

    my $oldch='';
    for (@chunks) {
        /^([a-z])([a-z])\d*$/ or
          fail, next LINE;
        my $diff=(ord $2) - (ord $1);
        fail, next LINE unless 
          ($diff == 0 or $diff == 1) and
          $oldch lt $_;
        $oldch=$_;
    }
} continue {
    print "`$_': ",
      failed ? 'fails!' : 'succeeds!';
}

__END__