On July 4th this yr, after plenty of ready, Stockfish and Chessbase lastly bought their first day in court docket. The battle between the 2 software program makers started when ChessBase launched a chess engine referred to as “Fats Fritz 2” that was allegedly a repackaged model of Stockfish. This led to some important recrimination, together with on this very web site. The case was of curiosity to free software program advocates and chess gamers all over the place, so we despatched a Lichess developer to the courtroom in Munich to witness occasions firsthand and report on them. We additionally spoke with ChessBase CEO Matthias Wüllenweber. (Full textual content of the interview)

The character of this dispute may be tough to clarify to people who are usually not accustomed to the Free Software program design course of. This course of not solely produced Stockfish and Lichess, however different fashionable software program like VLC, Firefox, and the Linux OS that in all probability runs the servers of all of your favourite web sites.

In contrast to proprietary software program, the code from free software program can be utilized freed from cost in another undertaking, however you have to fulfill different non-financial necessities of the license. Within the case of the “GPLv3” license that Stockfish makes use of, meaning you have to inform customers clearly that the software program they’re utilizing is free software program, and make the supply code, with any modifications you’ve made, publicly out there to make use of in the identical means that the unique is. On this case, neither the Fats Fritz 2 code nor the license textual content was  made out there. 

Shortly after Fats Fritz 2 was launched, the Stockfish workforce despatched a stop and desist letter to ChessBase asking that they fulfill the necessities of their license for Fats Fritz 2, and, very importantly, additionally fulfill the license for another ChessBase merchandise which may comprise Stockfish code. After receiving the letter, Chessbase launched a brand new product “Fats Fritz 2 SE”, packaged with a duplicate of the GPLv3 license and a duplicate of the supply code with what seems to be a distinct, and weaker, neural web. The code for the unique Fats Fritz 2 has but to be launched.

ChessBase admits they violated the license, though by mistake, and solely briefly. In line with Wüllenweber: “With Stockfish we didn’t fulfill the GPLv3 necessities and frantically scrambled to repair this inside days of the primary publication. The fault that almost all irritated me was that the unique model someway entangled the brand new neural community in a means with the engine that made it unusable in another context. A transparent violation. We mounted it instantly, however it was [in]appropriately perceived as unhealthy intention. As soon as in your life, you have got this undertaking the place all the pieces that may go improper goes improper.”

Along with the lacking authorized necessities, ChessBase additionally didn’t give Stockfish a lot public recognition for his or her contribution both. The ChessBase homepage referred to as Fats Fritz 2 “the brand new #1” engine.” Presumably, supplanting the now “inferior” Stockfish. Fats Fritz 2 creator Albert Silver did interviews the place he mentioned what it was prefer to “begin virtually fully from scratch.” This stuff triggered important resentment among the many Stockfish workforce. In line with Wüllenweber; “Within the publication technique of Fats Fritz 2, I made a number of errors. Consequently, the Stockfish authors are actually fairly indignant at us, and I can absolutely perceive this. Essentially the most critical error was to not describe the undertaking to them beforehand. If they’d objected, we might have canceled it. One other error was to do overzealous boasting about Fats Fritz on our website. Whereas we believed that the brand new neural web was unique and beneficial, this advertising downplayed Stockfish in an unacceptable method. These articles had been naturally learn and quoted broadly, whereas no one noticed the official promoting and packaging which at all times mentioned “Based mostly on the open-source engine Stockfish” because the very first declare.

The again of the packaging of a bodily copy of Fats Fritz 2

The Stockfish workforce was equally unflattering of their communication in regards to the challenge. On the official Stockfish weblog Joost VandeVondele wrote: “ChessBase’s communication on Fats Fritz 2, claiming originality the place there’s none, has shocked our group. Moreover, the engine Fats Fritz 2 fails to persuade on unbiased score lists, casting doubt on the usefulness of these modifications. Certainly, we really feel that prospects shopping for Fats Fritz 2 get little or no added worth for cash. Claims on the contrary seem deceptive.”

The stop and desist letter wouldn’t be the top of the authorized wrangling. Whereas some steps had been taken to convey Fats Fritz 2 into compliance, there was nonetheless an issue with one other ChessBase product. “Houdini 6” is one other older engine that ChessBase has been promoting since 2017. What was claimed to be supply code for Houdini, acquired by unclear strategies, was posted anonymously on GitHub, and it bore a hanging resemblance to Stockfish code. Six weeks after the primary stop and desist letter, the Stockfish workforce ready one other for Houdini, and this one would carry a distinct demand that will change into the important thing challenge within the upcoming lawsuit; GPLv3 license termination.

Any license has to have some tooth; a particular penalty for not following its necessities. The GPLv3 wouldn’t be price a lot if the one penalty for violating it was to shrug, apologize, and do the identical factor once more later. To this finish, the second Stockfish stop and desist letter didn’t demand success of the license necessities for Houdini, it knowledgeable ChessBase that as a consequence of repeated violations, their license to make use of Stockfish code had been revoked they usually should stop distributing any Stockfish derived software program completely. When ChessBase refused, the Stockfish workforce determined to implement their license termination with a lawsuit.

We requested a Lichess dev to examine the alleged Houdini code that the Stockfish workforce submitted to the German court docket and his opinion was clear. In line with him: “It isn’t an entire 1-to-1 copy. He (Robert Houdart, The Houdini developer) added customized elements, and modified some elements, however massive and important elements of the code, positively greater than 1000 strains, are plainly and clearly the identical as Stockfish code. It additionally incorporates 1-to-1 copied and really particular feedback which in elements even reference Stockfish (e.g. “To compile stockfish…” within the Makefile) and Glaurung (the Stockfish predecessor)”

Nonetheless, Wüllenweber insists that there’s something unique in Houdini “A few weeks in the past, I regarded on the code samples demonstrated by the plaintiffs. I assume that from Stockfish’s viewpoint they supplied the stuff that involved them most. To me it appeared clear that each packages use the identical concepts in these code snippets. Concepts of originality and worth. To me it additionally appeared clear that Houdart expressed these concepts in his personal phrases, the place his implementation was typically fairly environment friendly or at the very least completely different from the Stockfish pattern.”

A code comparability between Stockfish and alleged Houdini from the Stockfish workforce’s court docket submissions. Additionally they included proof that the compiled program behaves in observe just like the commercially launched Houdini binary.

A German civil court docket is a much more informal affair than you could anticipate, there aren’t any hovering Hollywood speeches, or witnesses cracking below a shrewd lawyer’s interrogation. As a substitute, the 2 events in a lawsuit meet with the choose in a quiet room to debate the case. She asks inquiries to each events, and after the assembly is over she’s going to both make a ruling or request additional proof. Though the choose on this case made no formal ruling, she did clearly state her opinion on sure particular questions. It’s additionally attainable to make extremely educated guesses on her view of issues from the strains of questioning she chooses and the topics she finds probably the most related. In line with our on-site reporter, the choose on this case is satisfied that Houdini comes from Stockfish and explicitly put the duty to show in any other case on ChessBase. She additionally appeared to agree that a number of license violations happened, and that revocation was not solely legitimate on the whole, however an inexpensive end result on this explicit case as nicely.

A German civil courtroom seems extra like a classroom.

Her major concern appears to be the precise scope of any potential revocation. A German court docket ruling must be outlined in a means {that a} bailiff can perceive nicely sufficient to implement, and with a Stockfish codebase that’s continually rising and altering this may very well be tough to do. The Stockfish workforce appeared pleased with the results of the primary listening to. In line with VandeVondele on the Stockfish Discord: “I believe typically we’re fairly completely happy about the way it went. The choose was very educated and understood our arguments and proof fairly nicely. The burden of proof has been reversed for Houdini, and we perceive that termination by few copyright holders is feasible. The scope of termination is one thing that wants additional work (which variations, which code, and so forth). The choice can be to settle, with phrases that we have to replicate on, and specifically additionally talk about with Tord. (Romstad, a Stockfish Developer)“

German civil courts strongly encourage the events to discover a settlement, and the choose on this case was no exception. She spoke to each events to push them in that route. Nevertheless, evidently a settlement won’t be straightforward to rearrange. When requested why not merely comply with not promote Stockfish-derived software program if he regrets doing it within the first place, Wüllenweber admitted that there was some unhealthy blood on his facet too: “Stockfish’s public response to Fats Fritz 2 was fairly painful and damage us. Perhaps we deserved some punishment. Nevertheless, now singling us out whereas opponents drive many monetization schemes based mostly on Stockfish seems like one thing one ought to stand as much as.”

The court docket will meet once more on March twentieth, 2023 except a settlement is reached first. If a ruling is made there may very well be appeals afterwards. Altogether, this case may take years to resolve. Keep tuned to all the usual Lichess communication channels for updates on this case because it develops additional.