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Not exactly a traditional chess puzzle, and I won't offer much of an explanation for fear of giving away the answer.

White must mate in 0 moves, meaning he must deliver a check mate without touching any of his pieces. How can he do that?

enter image description here

Courtesy of: Chess Fruits, 1884

JGibbers
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5 Answers5

122

White must

Remove the black pawn on c5 that she has just taken en passant.

Indeed

One move ago, wPc6 was on b5 and bPc5 was on c7. Black played c7-c5 and White took b5xc6 e.p. It just remains to remove the black pawn.

Note that

e7-e5 for Black followed by f5xe6 e.p. for White is not an option, because then you cannot explain how black pawns arrived on g6 and h4.

Evargalo
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  • I did think it would be quick, but I didn't expect that quick! nice job! – JGibbers Oct 18 '18 at 15:39
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    If this is correct, then technically the image of the chess board is not in a legal state. – forest Oct 19 '18 at 10:43
  • @forest - why not? – Justin Oct 19 '18 at 12:49
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    @forest It's in a legal state, but white's next action must be as specified to remain legal. After all, it's possible that this state was achieved because a fire alarm sounded right before that exact moment. – Michael Oct 19 '18 at 16:03
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    The last few moves you assert aren't necessarily true right? – greenturtle3141 Oct 19 '18 at 19:08
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    @greenturtle3141 : unless we know that a 'mate in 0' is possible, we cannot prove that this is how the position was reached. – Evargalo Oct 19 '18 at 21:05
  • @Evargalo : maybe we could redesign this puzzle so that the only legal move of black before this image was to move that pawn. – vsz Oct 20 '18 at 20:49
  • @vsz : sure. This has already been done. Usually it requires bK on the 7th rank and wK facing it on the 5th. – Evargalo Oct 21 '18 at 13:28
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    @Evargalo: All such chess puzzles are critically defective because chess puzzles exist that originate from impossible positions. – Joshua Oct 21 '18 at 19:47
  • I don't think that it is a legal state. In the rules of chess, moves are transitions from one legal state to another. Capturing en passant is a single move, just like castling is a single move. They don't "pass through" intermediate legal positions but are direct transitions from one position to the next. The fact that it involves two physical actions is irrelevant. It is a clever puzzle, but based on a dubious premise. – John Coleman Oct 23 '18 at 11:45
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    It is in a legal state, it's just a state that is not recorded when you write down a game. Just like castling, you move one figure, then you move another or take it away. It's a state that will happen every time when a pawn is taken en-passent. – gnasher729 Oct 23 '18 at 11:47
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    It becomes a question of definition. Is it a legal state to have the king not on the board? Physically you remove the king from the board in the act of castling, only to redeposit it on the board somewhere else. I don't see any use (beyond clever puzzles perhaps) for calling physical configurations of the chess board "states" if those physical configurations don't correspond to a position which is reached after a legal move. – John Coleman Oct 23 '18 at 11:51
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I see Evargalo has found the right answer, but the first thing that occurred to me was

rotate the board 180 degrees. This will cause White's pawns which are currently on c6 and e6 to be attacking Black's king, and Black has no way to get out of check.

Tanner Swett
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Especially Lime
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    I thought someone might try that, that's why I made sure to include the letters/numbers in the picture :) – JGibbers Oct 18 '18 at 16:44
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    Well, obviously the part with numbers and letters wouldn't be included in the rotation. – Acccumulation Oct 18 '18 at 17:03
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    That's double-check with two pawns, which is not possible (and the post is tagged retrograde-analysis so it's assumed there was a previous move) – BlueRaja - Danny Pflughoeft Oct 18 '18 at 21:30
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    I like this answer much more than the correct one. – Surb Oct 19 '18 at 08:44
  • Yeah, that one occurred to me as well because I already saw a problem with that solution in a book that has a lot of fun with chess. E.g. there was another problem where black had 9 pawns so you had to remove any one of them to checkmate black. :-) Also I believe the board-rotating solution in that book was obligatory because the game was not in a legal state the other way round. – Alex Oct 19 '18 at 14:38
  • great, now i'm imagining a variation of chess (I'm going to say invented by somebody like Bobby Fischer) where there are a few once in a game legal moves like this added. we could call it "space chess" and this could be called the "kessel maneuver". – Michael Oct 19 '18 at 16:06
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    How does rotating the board change anything? – Fabian Röling Oct 20 '18 at 23:56
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    @FabianRöling Pawns have directions. – Abhimanyu Pallavi Sudhir Oct 22 '18 at 09:27
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    Could this answer be updated with an explanation of what rotating the board accomplishes, and how that translates into a check? – doppelgreener Oct 22 '18 at 12:35
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Not exactly a checkmate, but there is an option with a similar effect that can be performed in zero moves:

Resign.

Ray
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    Welcome to Puzzling SE. Make sure when you answer questions you fully explain your thoughts behind it and approach. – gabbo1092 Oct 19 '18 at 16:52
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    @gabbo1092 Thanks. I'd be happy to elaborate, but I'm not sure what else there is to say. I suppose I could explicitly state that a resignation, like a checkmate, ends the game with a loss (and does so in zero moves), but I assumed anyone reading chess problems knows that already. Is there anything in particular that I should explain more clearly? – Ray Oct 19 '18 at 17:00
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    Sorry entirely my bad somehow I had misread the answer and misunderstood. hope you enjoy your time her on PSE – gabbo1092 Oct 19 '18 at 17:04
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    I wouldn't call winning and losing "similar effects" – buzjwa Oct 21 '18 at 06:33
  • @buzjwa Fortunately, both winning and losing happen, just to the opposite players they usually happen to in chess puzzles. It's definitely a stretch, but there doesn't exist a traditional solution to this one. – Ray Oct 21 '18 at 14:19
  • Have White player give his sit to Chewbacca. – Cœur Oct 22 '18 at 05:54
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    Since white is the one who is doing the action, I believe your answer should really say Force black to resign. Maybe even list a few methods to do so :P – thesilican Aug 20 '21 at 15:52
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I don't think this is within the rules of the game, but rotating the board 180 degrees would mate the black king. Obviously, the board would be setup incorrectly at that point, but doing anything in 0 moves in chess is illegal, so I would say this is the best answer.

technoplato
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    Welcome to Puzzling.SE, @lustig! Innovative twist (no pun intended)! – SteveV Oct 21 '18 at 19:37
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    Thank you! Just realized the answer was already posted but didn't read through them all. Apologies, but will leave unless deleted by mods. – technoplato Oct 21 '18 at 20:13
  • Turns out my answer was NOT correct and had been debunked by the puzzle "host"; and yet here I was grumpily checking why my answer didn't have more votes. How silly I was ... https://puzzling.stackexchange.com/questions/74086/mate-in-0-moves/74195#comment221138_74093 – technoplato Apr 02 '22 at 08:28
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[...] check mate without touching any of his pieces?

So therefore white should be able to:

Move the black king to d8.

Evargalo
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Viktor Mellgren
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