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In a 2001 book by Karsten Muller and Frank Lampart FUNDAMENTAL chess ending the following position WHITE King on a4 Bishop on d5 pawns on a5 c6 e2 BLACK King on c7 Bishop on d4 pawn on f4 WHITE to move is given as a draw. Stockfish 14.1 NNUE disagree and found a very complicated way to win for White. The position appeared in the game Alexandrov vs Gleizerov in 1993 . What do you think?

[Title "Alexandrov-Gleizerov 1993, White to move: is it really a draw?"]
[FEN "8/2k5/2P5/P2B4/K2b1p2/8/4P3/8 w - - 0 0"]

Here's a continuation Stockfish gave :

[FEN "8/2k5/2P5/P2B4/K2b1p2/8/4P3/8 w - - 0 1"]

1. Kb4 Kd6 2. Kc4 Bf2 3. Kb5 Bg1 4. Bb3 Be3 5. Ba4 Bd4 6. Kc4 Bg1 7. Bb5 Ba7 8. a6 Bb8 9. Kd4 Kc7 10. Ke5 Kb6+ 11. Kf5 Bd6 12. Ke6 Bb8 13. Kd7 Kxb5 14. a7 Bxa7 15. c7 f3 16. exf3 Kc5 17. Ke6 Kd4 18. f4 Bb6 19. c8=Q Bc5 20. f5 Ba3 *
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    chess.com analysis at first gave +2 advantage but as I played out the moves the advantage dropped to 0.00. But when I ran the position on "downloaded Stockfish" it gave a beautiful continuation share.chessbase.com/SharedGames/share/… Since It was opposite color bishop I also thought it as draw.
    – Billy Istiak
    Jan 14 at 10:00
  • It seems like the computer is making a critical strategic error as black on move 8 by moving their bishop off the g1-a7 diagonal. As long as Black's bishop stays on that diagonal I see absolutely no way for white to force a zugzwang, as the only winning configuration for white is to trade their c-pawn for black's f-pawn. But this is impossible if black just keeps blocking the c-pawn with their king and lets their bishop handle the a-pawn (see Pit's answer below).
    – Scounged
    Jan 16 at 4:29
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    Hi Scounged. A passive black is hopeless as well. Say Ke4 and Be3, protecting f4. But now say Kf5. You either move your bishop off of the diag, or you move the king, right? What's next is Kd6, a handshake and a see you soon.
    – Pit
    Jan 16 at 11:24
  • @Pit yeah, that's a nice triangulation that I missed initially. You should definitely edit this point into your answer and emphasize that there is a clear conclusion: white actually wins with best play.
    – Scounged
    Jan 17 at 15:46

1 Answer 1

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There are quite a number of lines here, and it's not obvious how White can force concessions. In sum, White must either win f4, win a bishop for a pawn, or trade their c- for Black's f-pawn. I'll elaborate on the non-obvious latter.

Tablebase observation: First, note that your position without e+f is a tablebase draw:

[fen "8/2k5/2P5/P2B4/K2b4/8/8/8 w - - 0 1"]

Your position without a+f is also a tablebase draw:

[fen "8/2k5/2P5/3B4/K2b4/8/4P3/8 w - - 0 1"]

But your position without c+f is a tablebase win:

[fen "8/2k5/8/P2B4/K2b4/8/4P3/8 w - - 0 1"]

Summary: Black can defend against a+c as well as against c+e, but is lost against a+e.

Conclusion: White's general plan is thus to trade their c- for Black's f-pawn. They seek to send Black's bishop to b8, from where it eyes both f4 and the critical a7, but remains moveless. Then the manoevre c7+-Kxc7-Kxf4 can be prepared and exerted as shown, leading into a known tablebase win.

[fen "1bk5/8/2P5/P2B1K2/5p2/8/4P3/8 w - - 0 1"]

1. Be4 Bc7 2. a6 Bb8 3. Bd3 Kd8 4. c7+ Kxc7 5. Kxf4

TLDR: Keep your outside pawns and seek to trade c- and f-pawn.

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    While there is some useful analysis here, I feel like this answer is incomplete at the moment. For instance, White's winning strategy hinges on pushing black's bishop off the g1-a7 diagonal, but how exactly is this achieved? Black's bishop can sit on e3 and guard the pawn on f4 if it were attacked by white's king, and then black's king could move between c7 and d6 with no way for white to force zugzwang. With this in mind the position seems like a draw to me.
    – Scounged
    Jan 16 at 4:24
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    Restricting Be3 makes exactly for Zugzwang. If your Kd6, then Kf5, Kc7, Ke5 and no more Kd6 for black. If Kd6 and white's king is on f5 already, tempoloss with f.e. Bb5, same outcome: Zugzwang. Either you win f4, or d6, or force the bishop off g1-a7.
    – Pit
    Jan 16 at 11:35
  • @Pit I think your important last comment should be edited into the answer, to make it complete.
    – Evargalo
    Jan 17 at 9:00
  • I agree with Evargalo, your response to my comment should definitely be edited into the main answer, as it was not obvious to me initially how to break black's setup and force a zugzwang. So, white's king goes to e5 to tie black's bishop and king, after which white can play a6 at some point. Then it's just a matter of going back and forth with the bishop and black will be forced to move either their king or their bishop, both of which would be fatal.
    – Scounged
    Jan 17 at 15:43

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