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I was looking at this game on Lichess, where it says "Checkmate is now unavoidable. Best move was Kc4." As far as I can tell, checkmate was already unavoidable, including after Kc4. Namely, Black can move Ke3,Ke2,Rf3,Kf1,Kg2,g3 and then either gxh2 or Rxg3 according to White's next move, leading to a won end-game. Am I missing something?

  • I cannot check LI since they forked their interface and declared that chrome is not supported so I need to get chrome. Don't they explain their symbol usage somewhere? – edwina oliver Jan 21 at 16:57
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    @edwinaoliver: Not that I am aware of. – user21820 Jan 21 at 16:59
  • Might want to try to ask in their forum andor email the owners of the site. – edwina oliver Jan 21 at 17:03
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There is no valid human reason. The difference between Kc4 (mate in 12), and Kc2 (mate in 10) is fairly irrelevant. It simply appended the "?!" based on the algorithm that 10 is slightly worse than 12. Either way, it is, indeed, a simple win from there.

By the way, my plan would be Rd7, then bring the king to h1/g1, and only then, bring the rook over via the f-file to take on h2. The longer you can keep the white king out, the less you have to calculate.

In general though, if the situation were different, and the material were more even, you might not want to box your king into the smaller area.

 [FEN "1B6/8/8/8/4k1p1/2Kr3p/7P/8 w - - 0 0"]

 1. Kc2 (1.Kc4)
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    Usually, I observed that Lichess does not mark a move as "?!" unless it is significantly worse, and it does not distinguish between "mate in 12" and "mate in 10". In the case I linked, it evaluates Kc2 as #-14 and Kc4 as #-22. Maybe that's why. – user21820 Jan 21 at 11:44
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    I'll accept your answer in a few days if nobody gives any other reason for this unusual annotation. – user21820 Jan 21 at 11:45
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On Lichess, inaccuracies are denoted ?!, mistakes by ? and blunders by ??. You can click on the `x inaccuracies/x mistakes/ x blunders' to move between these.

The move was inaccurate since it reduced a forced mate from 16 moves (Kc3) to 13 moves. Lichess marks inaccuracies for large checkmate sequences, since humans aren't expected to find these.

  • I see thanks for that information! – user21820 Jan 22 at 10:00

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