Rybka a Clone?

The German magazine Spiegel recently published an article (Google translation) about the ongoing Rybka controversy. In the computer chess world people are discussing if Rybka 1.0 by Vasik Raijlich is a clone of the engine Fruit 2.1 by Fabien Letouzey. Fruit is an open source programm and the code was published under the GNU license in 2005. The license allows everybody to use the code for their own programs, but only if the resulting program is being published under the GNU license as well. Rybka is not open source. The Internatioal Computer Games Association (ICGA) is investigating in this case.

Some famous people in the computer chess world have written an open letter to the ICGA. They claim that Rybka 1.0 is indeed a cone of Fruit 2.1. The fact that a lot of famous chess engine programmers have signed the letter gives it some relevance. Read the letter in the full article.

Open letter to the ICGA about the Rybka-Fruit issue

Dear David Levy, Jaap van den Herik and the ICGA Board,

Recently the author of Fruit, Fabien Letouzey, wrote an open letter to the computer chess community where he raised the concern that Rybka 1.0 beta may be a derivative of Fruit 2.1 in this public post.

Since then it has emerged from highly respected sources like Zach Wegner, Bob Hyatt and others that there is a lot of evidence that has been accumulated over the last few years that Rybka 1.0 beta is a derivative of Fruit 2.1.

Zach Wegner has presented evidence of alleged significant copied/derived Fruit evaluations in Rybka 1.0 beta here.

A collection of evidence of the many cases of alleged copied/derived Fruit structure, code & data appearing in Rybka 1.0 beta has been put together in this PDF by Mark Watkins.

It is also worth considering that prior to Rybka 1.0 beta, previous Rybka versions were many hundreds of Elo points weaker than the Rybka 1.0 beta version that suddenly emerged in public in December 2005, just a few months after the open source public release of Fruit 2.1 under the GPL license. That same month Rybka beta entered and won the International Paderborn Computer Chess tournament.

The evidence alleges that by using and deriving code, data and structure from Fruit 2.1, Vasik Rajlich was able to make dramatic and huge progress with “his” program Rybka to the detriment of his fellow competitors. In our view this has made competitions involving Rybka grossly unfair.

As chess programmers we find this overwhelming evidence compelling. We believe Rybka is a Fruit derivative albeit an advanced one.

It is very likely that later Rybka versions have derived and benefited from Rybka 1.0 beta and hence in the circumstances our view is they should also be considered derivatives of Fruit 2.1 until proven otherwise.

We wish to make an official complaint to the ICGA that Rybka is a Fruit 2.1 derivative. Furthermore we believe it is a breach of the GPL license under which Fruit 2.1 was released.

We believe as an unauthorized Fruit derivative Rybka’s entry into ICGA events has been contrary to the ICGA rules and the rules of fair play.

We ask the ICGA to carefully review the evidence, assess its validity, and act accordingly.

We note that the ICGA is intending on setting up a tribunal to assess such allegations and we believe this evidence should be strongly considered in that process.

In addition, we think the ICGA should in future insist that all authors of entries to ICGA events must submit to the ICGA the same executable(s), that is taking part in the ICGA event, where they can be stored for future analysis of potential derivative claims should they arise. Each author should also make a full and clear statement as to the originality of the entry, its contributors and any acknowledgements. Should justified suspicions exist authors must be willing to submit source code on a private and confidential basis to a select group of impartial programmers to privately determine source code origin.

Co-signed by the following chess programmers,
Fabien Letouzey, Zach Wegner, Mark Uniacke, Stefan Meyer-Kahlen, Ed Schröder, Don Dailey, Christophe Theron, Richard Pijl, Amir Ban, Anthony Cozzie, Tord Romstad, Ralf Schäfer, Gerd Isenberg, Johannes Zwanzger.