Chess-playing programs continue to improve with every new release, and Rebel 10 is no exception. Schröder BV, the makers of Rebel, generally introduces a new version approximately every year. Previous versions of Rebel have been very strong and contained numerous features for both the serious and casual user. The latest version continues this trend with significant improvements in features and a modest increase in playing strength. Since the program offers numerous features that are impossible to cover fully in a short review, I will concentrate on the key features and highlights.

System requirements

Rebel 10 is a DOS-based program, and it also runs under Windows 95/98. Windows NT, Mac OS and OS/2 are not supported. I ran Rebel 10 under Windows 98 on a Pentium 2/266 computer for this review.

Chess engines

Apart from Rebel 10, the program includes the Rebel 7, 8, 9 and Decade engines. Computer-computer matches of any length and under any time controls can be played by these engines to compare their relative strengths

User-Interface

The program is designed to be used using a very extensive menu interface. Keyboard entry is supported, but I believe a mouse is essential for ease of use. The available options can be overwhelming for new users. However, the menu system can be tailored to different levels ranging from novice to expert, so that all levels of users can feel conformable with the interface. The novice level is ideal for new and casual users who simply want to play against the program without using its more advanced features. The menu system can also be fully edited by users if required.

Rebel 10 includes more short-cut screen icons than the previous version. The layout of the screen can be changed, and many interesting alternative screen layouts are included. The colours of the menus, board and piece sets can also be changed. Hence, with the new features, users should be able to design a layout that they are comfortable with.

Manual and help system

Rebel comes with a brief printed manual that describes the installation process, the on-line help system and some general operating principles. The full manual is available as a standard text file on the CD-ROM. This manual also forms the basis of the on-line help system that is very useful for consulting the details of less-used features. Hence, there never should be any need to print out the manual.

Strength

Rebel provides an estimate of its strength based on the computer it is running on. On my computer, the strength of Rebel 10 is given as 2679 compared to a strength of 2659 for Rebel 9. I ran a 20-game match between these two engines at a blitz time limit of 5 minutes for the entire game, with Rebel 10 winning by a margin of 9.5 to 7.5 with 3 doubles. This score is consistent with their respective ratings.

While these ratings are probably too high relative to human ratings, it is safe to say that Rebel 10 is simply too strong for most players. Indeed, Rebel has impressive wins over world-class grandmasters such as Yusupov and, more recently, Anand. This latter victory over the number two player in the world clearly shows the advances programs have made in recent times, especially at fast time levels.

Thankfully, for the rest of us, Rebel offers several ways to decrease its strength so that we can enjoy an appropriate challenge without being thrashed in every game. Probably the simplest way to do this is to set an ELO rating for the strength you require. Alternatively, you can specify a strength in the range "novice" to "strong", or restrict Rebel's depth of search. Different strengths can also be achieved by using the other engines provided.

Playing levels and styles

Rebel offers the usual playing levels including fixed time, blitz and tournament levels, and time increments have been included in this version. It also offers handicap levels where the user gets more time than the program. Other options include a blindfold mode and the ability to play four games against Rebel simultaneously if you're feeling particularly masochistic. The program has an autoplay feature for computer-computer games, which is useful to see how to play any given position. Finally, Rebel includes several options for displaying its search information including a very extensive "super" option that I normally use.

The program's style can be varied within five levels ranging from "aggressive" to "defensive". Rebel is noted for its human-like play, and generally favours knowledge over search speed. An interesting new feature in the "anti-GM" playing style option. The basic idea is for the program to steer for positions that human players would generally feel uncomfortable with, and results in the program playing in a riskier manner. It's too soon to know how successful this idea will prove in the long-term, but the option was used with success in the match with Anand.

Opening books

Rebel includes a large opening book that includes an optional book-learning feature, and numerous specialised books are available on the Rebel web site. The opening books are editable from within Rebel, and they can also be analysed. In addition, it is possible to generate an opening book from a database. Using this option, it is easy to generate an opening book for your favourite opening and then use it to play against Rebel.

A very useful new feature in Rebel 10 is the Encyclopedia of Chess (EOC), which is a tree of 16 million chess positions that was derived from the main Rebel database. A larger EOC of 50 million positions is available as a separate product. However, it is not possible for the user to generate an EOC from an existing database. The EOC can be used as a separate opening book or as an option to influence the choice of moves from the main book. When in use, the program automatically generates statistics, including the number of games that contain this position, the moves played by top grandmasters in this position, and the outcome of games resulting from this position. This information can be used to judge the effectiveness of your opening repertoire based on grandmaster praxis. Thus, the combination of the standard opening book and the EOC should satisfy most users who require extensive opening coverage in their programs.

Analysis options

The analysis options in Rebel are excellent. As a first step, Rebel can be used to offer continuous analysis as you play through a game. The analysis can be refined by specifying moves to be either included or excluded, leading to a considerable speedup of the analysis. Rebel's game analysis option is simple and elegant. The program reports on the score and principal variation for both the move played and the move it considers best. Moreover, it provides analysis for every move played. The user only needs to specify the time to spent per move and which side (white or black, or both) to analyse. The complete analysis is stored as text comments within the game, and it can also be exported to a text file. Rebel can analyse either single games or several games from a database in one step. Rebel can also analyse problem sets including those stored in EPD format and provide estimated ELO ratings for a variety of standard test sets that are included with the program.

Database and search features

Rebel includes a large database of over 300,000 games, and registered users can obtain updates from the web site. Of course, the database can also be augmented with the numerous games available from the Pitt and TWIC sites, for example. The program supports PGN files directly without requiring an initial conversion to its own format. In addition, conversions between PGN and EPD formats and Rebel's format are in-built. Separate programs are included to convert ChessBase (old cbf format) and NicBase databases to Rebel's format, and to manipulate Rebel databases.

The database and search options have been extended in Rebel 10, and the current options should be sufficient for most practical purposes. A useful feature in the database window is the game overview option that includes a facility for Rebel to evaluate any position from a game directly. The user can search a database for a variety of items, including names, moves, ECO categories, score, tournament, positions, and material or material patterns. The material option can be used to search for particular piece distributions, for example, two pawns versus one pawn. The material pattern option can be used to search for features such as isolated pawns, or particular pawn chains. In addition, a new searchable "free index" has been introduced. As the name implies, this field can be used to hold other items that are of interest, such as tags for best games, opening novelties, etc. The search options can be combined using the new search mask, with particular options being able to be either included or excluded from the search. The one major feature that I still miss is the ability to store variations within the game, and this would be my first choice for a new feature in the next version.

Conclusion

Rebel 10 is a significant and worthwhile upgrade of an already excellent program. The program is easy to use, and has a clean and visually-pleasing display. Its features and strength make it an excellent choice for all players, and it is highly recommended.