19

In this position, the black move 1. ... Qc3 results in two consecutive forced moves, Kxc3 and Ke7:

2rkr3/2p5/2q5/8/8/8/3KP3/3R4 b - - 0 1

1... Qc3 2. Kxc3 Ke7

What is the longest sequence of mutually forced moves that can be constructed on a standard chessboard?

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14

Inspired by Ed Dean's answer, here is another "infinite loop":

[FEN "8/6p1/1p3pPk/1P3Pp1/1Pp3p1/KpP3P1/1P6/8 - - - 0 0 "]
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  • 1
    There we go! (And I deleted my answer, since it was flawed, as its infinite loop wasn't fully forced.) – ETD Mar 9 '14 at 19:18
  • 11
    Although technically, since neither side can possibly checkmate the other here, it's an immediate draw (just like stalemate). So there aren't any legal moves at all here, the game is over. – RemcoGerlich Mar 9 '14 at 20:01
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    Yes. It's in Article 1 of the rules, even ( fide.com/fide/handbook.html?id=124&view=article ). Infinite loops aren't really compatible with the laws of chess. – RemcoGerlich Mar 9 '14 at 20:08
  • 11
    No, this has nothing to do with the 50 moves rule. See rules 1.3 or 5.2.b in the rules (my link). Or even rule 9.6 -- the rules describe this situation three times! It's an immediate draw, no claims. – RemcoGerlich Mar 9 '14 at 21:44
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    Since the longest sequence of legal moves from this position is 0, perhaps it should not be the accepted answer! – M.M Aug 31 '16 at 5:09
21

Assuming you allow promoted material (since you didn't say anything :-), this (on Page 13 of the PDF is the (unfortunately, extremely unknown) finite record since ages. It shows the record for the longest sequence of only 1 legal move for each side, with use of promoted material.

[Title "Karl Scherer, Feenshach 1980, Page 13"]
[FEN "BQ4R1/2Q5/3Q4/4Q1pp/5B1P/6QK/Rrrrrrrq/R4nk1 w - - 0 1"]

1. Qxh2+ Rxh2+ 2. Bxh2+ Rxh2+ 3. Qxh2+ Rxh2+ 4. Qxh2+ Rxh2+ 5. Qxh2+ Rxh2+ 6. Qxh2+ Rxh2+ 7. Rxh2 g4+ 8. Rxg4+ hxg4+ 9. Kxg4 Kxh2
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  • Wow, that's quite a "machine". – supercat Sep 25 '17 at 0:17
  • To make that position reachable, black must previously have had the queen on h1 and just captured a white pawn, knight or rook on h2, which then starts the forced sequence. – Silas S. Brown Dec 31 '18 at 13:10
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    Can we get attribution in the answer? – hkBst Jan 18 '19 at 9:57
  • Hey @Reddmannm now that the link is dead, do you still know who composed this? – Rewan Demontay May 8 '19 at 11:42
  • Well, Karl Scherer himself :-) See: "feenschach" 51, 07-09/1980, S. 424 for a dead wood source. (Props to "apf" from schachfeld.de!) – Hauke Reddmann May 9 '19 at 8:41
8

You mean like this?

[FEN "K1k5/P1Pp4/p2P4/Pp6/P1p5/2P5/8/8 - - - 0 0 "]

1. axb5 axb5 a6 b4 cxb4 c3 b5 c2 b6 c1=Q b7# 1-0

White mates in 6.

I guess that's 9 consecutive forced moves. It would be eleven except for black's choice of promotion piece on his fifth move. I don't know if it's a record, and I don't know who composed this classic chess problem.

P.S. Thanks to Rosie F. for sourcing the problem. Quoting Rosie F.'s comment:

This problem is by Vilhelm Röpke. PDB cites it as Skakbladet, 1942.

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  • I'm not sure c1=Q can be considered forced, you had other promotions – Alan May 21 '14 at 18:33
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    @Alan That's why I said "I guess that's 9 consecutive forced moves. It would be eleven except for black's choice of promotion piece on his fifth move." – bof May 21 '14 at 19:52
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    This problem is by Vilhelm Röpke. PDB cites it as Skakbladet, 1942. – Rosie F May 26 '16 at 5:37
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    @RosieF Thank you. I edited your comment into my answer. – bof May 26 '16 at 5:57
5

A simpler infinite-loop setting:

[FEN "1kb5/1p1p4/1P1P4/8/8/4p1p1/4P1P1/5BK1 w - - 0 1"]
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  • One can [put white pawns on a7 and f3, put black pawns on c6 and h2, and move black's king to a8] to get 9 consecutive only-legal moves. ​ (without an immediate draw by dead reckoning; see Remco's comments to the other answer) ​ ​ ​ ​ – user2668 Feb 22 '16 at 4:39
  • True, and then wBf1 and the e2/e3 pawns are not needed. – Noam D. Elkies Feb 22 '16 at 6:29
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    It would be the Bc8 and the d pawns that aren't needed, rather than the Bf1 and e pawns. ​ ​ – user2668 Feb 22 '16 at 7:46
  • Sorry, you're right. – Noam D. Elkies Feb 22 '16 at 14:30
0

There are a few categories for mutually forced moves-they either end in checkmate, stalemate, or neither. Either almost/all (almost would apply to neither and stalemate) moves are checks or not. Either multiple legal moves are available or just one is. Promoted pieces are allowed and not.

I shall refer to games where not all of the moves have to be check as No-Checkers” for simplicity’s sake. Another thing to know is that since promotion choice is not forced, it and all moves afterward are not counted.

I shall do by best to cover each category. The sections for neither and stalemated are currently in the works. I have done lots of research and spent time to bring this all to you, for our mutual benefit.

Each game shall be recorded in length by plies, or half-moves.

If you can /create or know of a better, already known composition for a category, feel free to share it. If you create it yourself, I shall credit you. Additionally. I would be more than happy if you could find out who the unknown composers are for the unknown ones.

This is the section for checkmates.

All Checker With Promoted Pieces-22 Ply

[Title "Alexey Khanyan, 2008"]
[FEN "4Q2Q/4r3/4n1n1/1bbK1krn/RR1RR1RR/2qn1R1n/4n1nN/Q3Q3 b - - 0 1"]

1... Ng2f4+ 2. Rfxf4+ N2xf4+ 3. Rgxf4+ Nh3xf4+ 4. Rhxf4+ Ndxf4+ 5. Rxf4+ Nhxf4+ 6. Rxf4+ Ngxf4+ 7. Rxf4+ Nxf4+ 8. Rxf4+ Kxf4+ 9. Qee5+ Qxe5+ 10. Qaxe5+ Rgxe5+ 11. Qxe5+ Rxe5+ 12. Qxe5#

Source: Tim Krabbe’s Website, Journal Entry #267

All Checker With Promoted Pieces & Only One Legal Move-14 Plies

[Title "Noam D. Elkies, 2017"]
[FEN "3b3k/qqqqq3/rr4NK/7R/5N1Q/7Q/B6Q/7R b - - 0 1"]

1... Rxg6+ 2. Nxg6+ Rxg6+ 3. Kxg6+ Qh7+ 4. Rxh7+ Qxh7+ 5. Qxh7+ Qxh7+ 6. Qxh7+ Qxh7+ 7. Qxh7+ Qxh7+ 8. Rxh7#

Source

All Checker Without Promoted Pieces-8 Ply (Based On Alexey Khanyan’s 22 Ply Game:)

[Title "Rewan Demontay, 2019"]
[FEN "8/8/nRb5/1R2PP2/Brk1KP2/1n4r1/8/Q1N5 w - - 0 1"]

1. Rxc6+ Nac5+ 2. Rcxc5+ Nxc5+ 3. Rxc5+ Kxc5+ 4. Qd4+ Rxd4#

All Checker Without Promoted Pieces & Only One Legal Move-6 Ply

[Title "Rewan Demontay, 2019"]
[FEN "8/qB3R2/1b4R1/2p1k3/3P4/2P1K3/1B4r1/Qb3r2 b - - 0 1"]

1... cxd4+ 2. cxd4+ Bxd4+ 3. Bxd4+ Qxd4+ 4. Qxd4#

No Checker Without Promoted Pieces-11 Ply

[Title "Noam D. Elkies, 2004"]
[FEN "KBk5/P1P4p/2Pp3P/P6p/2p3rP/2P3pB/6P1/8 w - - 0 1"]

1. Bxg4+ hxg4 2. a6 d5 3. h5 d4 4. cxd4 c3 5. d5 c2 6. d6 c1=Q 7. d7#

Source: Tim Krabbe’s Website, Journal Entry #267

No Checker Without Promoted Pieces & Only One Legal Move-10 Ply

[Title "Composer Unknown"]
[FEN "7k/q5Q1/p4PPK/6PP/8/5P2/8/8 b - - 0 1"]

1... Qxg7+ 2. fxg7+ Kg8 3. f4 a5 4. f5 a4 5. f6 a3 6. f7#

Source

Here is an honorable mention of 9 half-moves. Since promotion choice is not forced, that is not counted nor any afterward moves.

    [Title "Vilhelm Röpke, Skakbladet 1942"]
    [FEN "K1k5/P1Pp4/p2P4/Pp6/P1p5/2P5/8/8 - - - 0 0 "]

1. axb5 axb5 a6 b4 cxb4 c3 b5 c2 b6 c1=Q b7# 1-0

Interestingly, Tim Krabbe gives a variation of the puzzle by the composer, up above this sentence. The source is the same one for the 22 half-mover. This is also 9-half moves.

[Title "Vilhelm Röpke, Skakbladet 1942"]
[FEN "K1k5/P1Pp4/1p1P4/8/p7/P2P4/8/8 w - - 0 1"]

1. d4 b5 2. d5 b4 3. axb4 a3 4. b5 a2 5. b6 a1=Q 6. b7#

Source

This is the section for neither.

The only thing of worth to put here, at least to me, is this game, of whom I don’t know the composer here, that was originally provided by Hauke Reddmann in his answer.

All Checker With Promoted Pieces & Only One Legal Move

[Title "Unknown"]
[FEN "BQ4R1/2Q5/3Q4/4Q1pp/5B1P/6QK/Rrrrrrrq/R4nk1 w - - 0 1"]

1. Qxh2+ Rxh2+ 2. Bxh2+ Rxh2+ 3. Qxh2+ Rxh2+ 4. Qxh2+ Rxh2+ 5. Qxh2+ Rxh2+ 6. Qxh2+ Rxh2+ 7. Rxh2 g4+ 8. Rxg4+ hxg4+ 9. Kxg4 Kxh2

This is the section for stalemate.

This is what I have so far. This is based of course on the 18 ply game in the nether section, of course.

All Checker With Promoted Pieces & Only One Legal Move

[Title "Rewan Demontay, 2019"]
[FEN "BQ6/2Q5/3Q4/4Q2p/5B1P/6QK/Rrrrrrrq/R4nk1 w - - 0 1"]

1. Qxh2+ Rxh2+ 2. Bxh2+ Rxh2+ 3. Qxh2+ Rxh2+ 4. Qxh2+ Rxh2+ 5. Qxh2+ Rxh2+ 6. Qxh2+ Rxh2+ 7. Rxh2
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  • 2
    I do feel obligated to point out that there is a choice of queens on some of the moves, – D M Apr 8 '19 at 21:53
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    My understanding of a forced move is that the player doesn't have a choice. – Evargalo May 6 '19 at 14:19
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    Can you explicit what would be "the second type, where the move is forced, but there are choices." It seems self-contradictory to me. – Evargalo May 7 '19 at 12:35
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    I am still not sure what you mean, but I am certain this is not the usual definition of a forced move in chess. – Evargalo May 9 '19 at 12:14
  • There are multiple definitions of forced. Every example I give shows a definition. – Rewan Demontay May 9 '19 at 12:15

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