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  3. Lichess considers time out in position with no legal way to mate a win

There is no way for white to win, but when black timed out, white won.

Uh. Nice.

Rules say a draw if time runs out but there is no way to checkmate by any possible series of legal moves.

Here, there is no way to *force* a win but there is still a possible series of (terribly blundering) moves for black to lose. So, I guess, that's why black loses when it timed out.

Such things are hard to implement, you have to install complicated and time-consuming tests, one can even add some useless bishops or further pawns.

A pragmatic approach: not nice, but fairly rare and no easy way out. It‘s ok - it‘s stricter than FIDE in this regard.

How does Black lose exactly? Maybe you can give an example :P
(hint: the kings can never cross the central ranks)

Interesting phenomenon in any case. It's exactly the type of position that engines are notoriously bad with.
We humans can solve it trivially by doing a "bottom-up" search, but engines currently don't have that option outside of tablebases.. and their regular "top-down" search cannot nearly go deep enough so far..

There is work in progress to cure this, but it is not as easy to implement as it seems. This kind of position seems unnatural, i.e. unlikely to occur in a real game.

I'm working both on addressing helpmate solving in Stockfish and in Lichess, although it is universally acknowledged that fortress detection is one of the most challenging problems in chess.

Here is my latest progress:

and some helpmate positions (the last of which should be a helpmate in 5 but SF only finds it in 6):
position fen 2k5/8/K7/8/8/8/8/7R b - - 0 1
position fen k7/8/2K5/8/8/8/8/6bB b - - 0 1
position fen bk6/8/K7/8/8/8/8/B7 b - - 0 1
position fen 8/8/8/8/k7/2R5/p5N1/7K b - - 0 1

@ProfDrHack you're right. Very cool stuff.

Sometimes I can't even post on here because of the chess CAPTCHA. :P

lol, I once had to redo the CAPTCHA because I blundered my queen in it :( Followed by a long period of wondering whether I deserve the right to post or not.

Ive always liked the idea that on "REPORT"; if you fail the Captcha on your first try the Report automatically gets discarded.


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