The Stockfish project, distributed under the GPLv3 license, has filed a lawsuit against ChessBase, revoking its GPL license for the use of its code. Stockfish is the strongest chess engine utilized on chess services lichess.org and chess.com. The lawsuit is based on the incorporation of Stockfish code into a proprietary product without providing the source text of the derivative work.
ChessBase, known for its chess program Fritz since the 1990s, released the Fat Fritz engine in 2019, based on the open-source neural network engine Leela Chess Zero, which was originally developed from the work of the AlphaZero project by Google. This did not constitute a violation of any legislation, although the developers of Leela were displeased that ChessBase marketed Fat Fritz as an independent development without acknowledging the contributions of the AlphaZero and LeelaZero teams.
In 2020, ChessBase launched the product Fat Fritz 2.0, which is based on the Stockfish 12 engine that has its own NNUE (Efficiently Updatable Neural Networks) architecture. The Stockfish team, with the help of lawyers, managed to remove Fat Fritz 2.0 from DVD retailers in Germany, but, dissatisfied with the outcome, announced the revocation of ChessBase's GPL license for Stockfish and filed a lawsuit.
This is not the first season of drama surrounding the Stockfish code, which commercial engines borrow while ignoring the GPL. For instance, there was an incident with the leak of the source code of the proprietary engine Houdini 6, which revealed that it was based on Stockfish code. Houdini 5 participated in the TCEC competition and reached the superfinal of the ninth season but ultimately lost to Stockfish. In 2017, the subsequent version Houdini 6 managed to win against Komodo in the superfinal of the tenth season of TCEC. The leaked source texts in 2020 exposed this unscrupulous deception, undermining one of the cornerstones of FOSS — the GPL.
It is important to remember that the GPL license allows for the revocation of the license from the infringer and the termination of all rights granted to the licensee by this license. According to the rules established in GPLv3 regarding license termination, if violations are first identified and rectified within 30 days of notification, the license rights are restored, and the license is not revoked in full (the contract remains unviolated). Rights are also restored immediately in the case of rectifying violations if the rights holder did not notify about the violation within 60 days. If the deadlines have passed, the violation of the license can be interpreted as a breach of contract, for which the court may award financial penalties.
Source: opennet.ru
