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I fed @HaukeReddmann's "hack" to this scenario

[FEN "8/p7/rp6/rp6/pP6/R7/8/K6k w - - 0 1"]

to Lichess Stockfish 14, white to move. Up to Depth 77 (after which I gave up waiting), it declares draw, and suggests Ka2 as best move. Yet, the moment I play Kb1, it immediately realizes mate in 11 for white.

Shouldn't 10 pieces be easy? Surely, eventually, it realizes M11 - but why not already with 38 (77/2) moves? And why doesn't Stockfish consider Kb1 for itself (since it instantly realizes M11 when I play it)?

Clarifying, this explains my second question, but not quite the first and last. I get that ultimately it's heuristics, but is there something to specifically explain how it fails to find mate with just 10 pieces, and that me making the right move makes it see mate? Yes, longer wait (or better hardware, it runs on cloud) would help, so it's a question on efficiency (which moves it chooses to discard).

OverLordGoldDragon
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    Stockfish isn't designed to solve endgame puzzles, but play realistic games well. – qwr Jul 23 '23 at 02:12
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    This https://chess.stackexchange.com/questions/37333/why-does-it-take-stockfish-depth-35-to-find-mate-in-7?rq=1 should answer your question (observed the same in the position, initially was as flabbergasted as you). – Hauke Reddmann Jul 23 '23 at 06:17
  • @Allure Hmm sort of, though I'd prefer an answer to this more focused question. – OverLordGoldDragon Jul 24 '23 at 02:18
  • What about this, does it answer your question? https://chess.stackexchange.com/questions/29417/why-are-world-class-engines-playing-like-this/39722#39722 – Allure Jul 24 '23 at 03:12
  • @Allure Well, an idea with Stack Exchange is direct answers to questions as-asked. If I have to dig much to find relevance, it's not a duplicate. An answer that merely cites an excerpt from another answer would count (likely along brief commentary). – OverLordGoldDragon Jul 24 '23 at 03:27

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My instance of Stockfish 16 saw M11 after about 7 seconds, so I think you just didn't wait long enough, although Stockfish 16 is stronger than 14 so that could also be why.

George Bland
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What version of Stockfish are you using? I am using Stockfish 15.1, with Chessis Pro GUI on Android 13, Snapdragon 8 Gen 1, and it found the mate in few seconds with depth around 70.

Edit: sorry, I missed the part where you say the version of the engine.

Giulio Severini
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