5

I'm going through the 100 endgames you must know book on Chessable and stumbled upon something I don't understand. This position with white to move is described as a draw starting with 1. Kh1. I figured well why wouldn't 1. Kf1 be a draw and I put the exercise into Lichess analyses, which evaluates the position as -2,5, no matter which move white plays.

Why isn't Stockfish able to evaluate this position as 0.0? It says 'depth 64'. Wouldn't it only need to calculate 50 moves to establish that this is a fortress and thereby a draw?

[FEN "8/8/1n6/8/8/5k1p/7P/6K1 w - - 0 1"]

enter image description here

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  • 1
    by the way stockfish does not get it wrong - it gives you evaluation - as it can't count till 50 move rule - it evaluates chances - even black is piece up - it does not give eval of +3.0; it gives less that means black does not have clear win but has chances due to extra piece
    – Drako
    Nov 5 '20 at 7:32
  • You can check this position with 7-men tablebases in: tb7.chessok.com/probe
    – djnavas
    Nov 10 '20 at 4:29
15

Depth 64 means 64 half moves, it includes moves both by white and black. It isn't close to being able detect draws by means of the 50 move rule (100 plies). Especially since that is only the depth of the deepest line in the search, and to conclude it was certainly a draw, Stockfish would have to look at a huge number of lines that all eventually draw by the 50 move rule.

Endgame draws like this are notoriously difficult for engines, they have no good way to judge "progress" in their calculations. There are some attempts being tried out but they aren't at the level of Stockfish yet.

This is why tablebases were invented -- huge databases of all positions with up to some number of pieces (7 at the moment I think). They give an immediate answer. This is a five-piece position and a Stockfish configured to use tablebases would immediately know it is a draw.

3
  • Are there any open source engines available that use tablebases?
    – Maxim
    Nov 4 '20 at 15:39
  • 8
    @Maxim Chassable has tablebase integrated into their analysis board: i.stack.imgur.com/Xel55.png
    – Sleafar
    Nov 4 '20 at 16:45
  • @Maxim any engine worth it's salt can, it just needs to be set up! Seemingly, SF in chessable hasn't been linked up. You can use the tablebase in the lichess analysis board (the same button as for the opening DB) or via syzygy-tables.info
    – pulsar512b
    Nov 6 '20 at 4:37
5

This is an easy position for Stockfish with tablebase, but very hard without it. The only way Stockfish can work out it's a draw is search all the way through 50-move draw. Otherwise, it'd think the position is winning for Black because Black has a knight up.

Your browser may not have the capability to search such high depth. That's exactly the reason why we need tablebase in high quality analysis.

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