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Public exports of all rated games, puzzles, and computer evaluations.
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Invalid FENs in 2023-11 dump of Chess 960 games #54

Closed jlherren closed 1 month ago

jlherren commented 5 months ago

The file lichess_db_chess960_rated_2023-11.pgn.zst contains a whole series of invalid starting FEN positions. For example, the 89569th game contains the follow FEN header:

[FEN "rkrnnbbq/pppppppp/8/8/8/8/PPPPPPPP/RKRNNBBQ w HEhe - 0 1"]

Chess 960 start positions usually have the castling availability specified as "KQkq" and not using the files where the rooks are, which is odd. But in this case the specification "HEhe" is entirely invalid, because the rooks are on files A and C. On the website that same game (https://lichess.org/osfJ5OM2) shows no castling availability at all in the initial position, which is also wrong.

The file has many other start positions with invalid initial castling availability, some are even just "-".

I didn't find this error in any other files from January 2023 to May 2024 for Chess 960.

lenguyenthanh commented 5 months ago

We had a bug around that time: https://github.com/lichess-org/lila/pull/13967.

How would We fix this? Maybe removing those games from database 🤔

niklasf commented 5 months ago

So far, for irrecoverable mistakes, we just noted them down under "Known issues".