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In the below position, how many moves will it take for Black to be stalemated? Black moves first, and both sides are working together. Black's pawns are moving down. Have fun solving!

Zdravko Maslar, Problem 1958, Special Prize

enter image description here

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  • $\begingroup$ What do you mean by "both sides are working together"? $\endgroup$ – new QOpenGLWidget Dec 29 '20 at 22:47
  • $\begingroup$ Cooperative chess, I assume. en.wikipedia.org/wiki/Cooperative_chess $\endgroup$ – Timothy Chen Dec 29 '20 at 22:48
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    $\begingroup$ @hexomino - chess.stackexchange.com/questions/8/… $\endgroup$ – marsnebulasoup Dec 29 '20 at 22:49
  • $\begingroup$ @marsnebulasoup As far as I understand though, a draw is not the same as "black being stalemated". It's okay, I think I can envisage a scenario now at least. $\endgroup$ – hexomino Dec 29 '20 at 22:51
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    $\begingroup$ @hexomino - Yes, you're right. A stalemate occurs when a player has to move but can't legally do so. The stalemate results in a draw, and the game is over. Draws, however can be caused by other chess rules/situations (e.g. the Fifty-Move Rule/Dead Position) besides a stalemate...more here $\endgroup$ – marsnebulasoup Dec 29 '20 at 23:17
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I believe the solution is the following

[FEN "K1b2rk1/4pr2/1b1n1p2/5q2/3p1p2/1p5n/8/8"]\n1.... f4-f3 2.Ka8-b8 f3-f2 3.Kb8-a8 f2-f1B 4.Ka8-b8 Bf1-d3 5.Kb8-a8 Bd3-b1 6.Ka8-b8 Bb1-a2 7.Kb8-a8 Qf5-b1 8.Ka8-b8 f6-f5 9.Kb8-a8 f5-f4 10.Ka8-b8 f4-f3 11.Kb8-a8 f3-f2 12.Ka8-b8 f2-f1B 13.Kb8-a8 Rf7-f2 14.Ka8-b8 Kg8-f7 15.Kb8-a8 Kf7-e6 16.Ka8-b8 Ke6-d5 17.Kb8-a8 Kd5-c4 18.Ka8-b8 Kc4-c3 19.Kb8-a8 Kc3-b2 20.Ka8-b8 Kb2-a1 21.Kb8-a8 Rf2-b2 22.Ka8-b8 Rf8-f2 23.Kb8-a8 Bc8-f5 24.Ka8-b8 Bf5-c2 25.Kb8-a8 d4-d3 26.Ka8-b8 Bb6-e3 27.Kb8-c7 e7-e5 28.Kc7xd6 Be3-c1 29.Kd6-e6 Rf2-d2 30.Ke6-f5 e5-e4 31.Kf5-g4 Bf1-e2+ 32.Kg4xh3 e4-e3 33.Kh3-g2 Be2-d1+ 34.Kg2-f1 e3-e2+ 35.Kf1-e1 stalemate

What gives me confidence in this one is that it appears carefully crafted to only admit a single line of play.

Replay scroll down to second game. Thanks @Rewan for help with the FEN.

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  • $\begingroup$ So, how did you manage to solve it? Just wondering! $\endgroup$ – Rewan Demontay Dec 30 '20 at 8:50
  • $\begingroup$ @RewanDemontay Well, with white being down to K only, the only way for black to get stalemated is somthing involving pawns and the far end of the board. The two light-squared B's together with the P structure were suggestive and after some trying to find any stalemate at all with the given material I started suspecting that that a promotion to another light-squared B might be needed and also the the white K might play a part in plugging the right half of the choke. Once I had one working layout of the final position (with K positioned slightly differently and IIRC a N instead of the Q) ... $\endgroup$ – Paul Panzer Dec 30 '20 at 9:15
  • $\begingroup$ ... I started trying to get there as quickly as possible, and doing so couldn't help noticing how purposefully everything was constructed. $\endgroup$ – Paul Panzer Dec 30 '20 at 9:17

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