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> Stockfish argues that ChessBase isn’t compliant because they refuse to release the weights.

No. The first license violation was that ChessBase released FF2 without source code for their modified Stockfish, and without the GPL license. This was later fixed after we reported it. The second license violation was Houdini, which contains Stockfish code, and even today is not a available under the GPL.

> But this makes no sense; the weights are distributed with every copy of Fat Fritz 2. (Otherwise, how would the program run?

This reasoning isn’t correct.

The weights may be as object code not as source. Simply saying the program runs doesn’t mean you’ve distributed the weights anymore than it means your distributed the code.

Last time this came up people pointed at the installation information clause

> “Installation Information” for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of a covered work in that User Product from a modified version of its Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code is in no case prevented or interfered with solely because modification has been made.

> Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.

While it seems plausible that the network weights would fall under the "installation information" clause - the intention seems to be to limit this clause to consumer products (e.g. a Digital Video Recorder) and it's not clear that it can apply to Fat Fritz 2.

https://github.com/official-stockfish/Stockfish/blob/sf_14/C...

Good eye. It’ll be interesting if more formal legal debate on this gets published

They probably intend to apply this clause (under Termination) to terminate ChessBase's license: "Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11)."

They also allege that ChessBase didn’t inform users of their rights under the GPL, which would definitely be a license violation.

> Note that it’s legal to sell stockfish as long as you’re compliant with GPLv3. ChessBase seems to be compliant.

Unless your license has been terminated by the copyright holders, in which case you cannot be compliant with the license because don't have a license to distribute the material at all.

> Stockfish argues that ChessBase isn’t compliant because they refuse to release the weights.

I haven't seen them argue this anywhere. You've linked to their previous statement in which they only say that they "condemn" the fact that the weights are not being released.

The announcement says that they've filed the lawsuit "to enforce the consequences of the license termination" because "ChessBase is ignoring the fact that they no longer have the right to distribute Stockfish, modified or unmodified, as part of their products."

> But GPLv3 doesn’t give you the ability to terminate a license arbitrarily; it requires you meet some specific criteria, and it’s unclear that ChessBase meets it.

You seem to be talking about this paragraph in the GPLv3 (https://github.com/official-stockfish/Stockfish/blob/sf_14/C...) :

"Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice."

However, this is not ChessBase's first violation. They've also tried to pass off Houdini as original work: https://shop.chessbase.com/en/products/houdini_6_pro_multipr...

Houdini 6 is also a stockfish clone. https://chess.stackexchange.com/questions/29181/is-houdini-6...

I have no clue about all these copyright litigations and most make no sense to me anyway, but when you put it that way, yeah, that sounds like a weak claim. Again, no idea if a court would see it that way, but if you take it a step further you can almost claim that software is not GPL-3 compliant, because it's being developed using non open-source IDE. Oh, we cannot prove it? But then, we also cannot prove these NN weights are not crafted by hand, I guess.

That’s actually been an issue for some non-GPL Smalltalk systems. What does it mean to distribute the “preferred form for modification” when that’s an image file for a closed-source interpreter? Same deal with GPL’d Mathematica code.

    > I think it’s lame that ChessBase sold stockfish for $80.

I’m interested to know how ChessBase was able to charge $80. If their software were licensed under GPL then couldn’t anyone have asked for its source code and compiled it themselves, for free?

Lots of people (Red Hat, Richard Stallman...) charge money for open-source software, so this seems a moot question.

This case is a bit different though: Chessbase (unlike RH and RMS) didn't tell anyone their product was open source, but pretended it was their own proprietary work and that it was better than the leading open source engine that it was stolen from.

I don't think so. Red Hat Linux - the software - is free under GPL. Red Hat the company charges for support, training, and documentation. ChessBase charges for the software, which means they're either not compliant with the terms of GPL, or there's some other aspect of the software they're not obligated to share. I'm particularly interested if it's the latter.

But I'm just wading into this subject matter, so others chime in if I'm missing something :)

As far as I know, Red Hat does not provide compiled binaries without a (typically paid) Red Hat license.

The point is, Red Hat is not a comparison because users can build, understand, and redistribute their version of Linux for free (in accordance with GPLv2). Not so with ChessBase.

The point being made is that the "for free" part of that sentence doesn't actually exist in the GPL. You can modify GPL code, then charge for access if you want (which, IIUC, Red Hat does). You just have to give it to whoever you sell it to under the terms of the GPL, which means your customers could give it away for free if they so choose.

    > which means your customers could give it away for free if they so choose

If you’re only guaranteed one sale before your first customer undercuts you, then it is free “in the limit”. That is why Red Hat sells everything ancillary to the software itself (quality assurance, training, documentation, support, etc.)

ChessBase is selling the software, and they aren’t getting undercut because they are not redistributing everything the customer needs to rebuild it from source. It will be interesting to find out what that is (neural net weights, or whatever) and whether the court upholds that this is not copylefted under the GPL.

> ChessBase charges for the software, which means they're either not compliant with the terms of GPL, or there's some other aspect of the software they're not obligated to share.

It's very clear from the story that it's the first one: they're not compliant with the GPL. At least that's what the Stockfish authors are claiming. They're pretty obviously acting in good faith and appear to be correct in their claim. ChessBase haven't laid out their side of the story other than their marketing materials saying "we developed the software in house and it's better than that open source stuff" and I wouldn't expect them to have a defence based on anything other than technicalities. You won't be seeing a blog post from them, because their lawyers have told them to say nothing.

It’s very clear that Stockfish _claims_ ChessBase violated the terms of the license (and by corollary, ChessBase claims they didn’t) but it’s not at all clear who’s right until the litigation process plays out. One thing I will say is the perceived superiority of ChessBase’s fork (“better than the open source stuff” as you say) has no bearing on either claim.