Answers.Body: <p>That's a nice archaeological find. However, I'm not so sure there is in fact a checkmate in just one &quot;move&quot;. Of course, there is a (unique!) checkmate for both colors in all orientations considered by @Brian Towers, which makes this a very nice problem indeed. But what about the <em>other</em> orientations?</p>
  <p>You may protest that <a href="https://chess.stackexchange.com/a/32045/">there's a rule that the bottom right corner must be a light square</a>, but I think you're going to have to consult a historian to determine whether this rule was in effect in this particular  late 19th century London chess club, and in particular whether the game could have continued without rotating the board if the players noticed their error during the game. You likely also need to consult a medium in order to determine whether one of the players noticed it. So, I think this rule doesn't mean we can exclude other orientations.</p>
  <p>You may argue that the other orientations are excluded because there's a pawn on the side of the board. Not quite. First, a pawn can never legally be put on the first rank, so that excludes one orientation (white being to the left of our current view). But this is not true for the eighth rank. Promotion of a pawn is done by first moving the pawn to the promotion square on the eighth rank, and then replacing it with another piece. So, it is possible for a pawn to be on the eighth rank in a legal game.  Of course, in the current state of the board the move is not yet completed, but that doesn't matter. We already know that in the other orientations the game was ended before the checkmate (as we still have to make one move), so the same could happen in the middle of the promotion move. I certainly have seen the board being left abandoned in such a state at my own chess club.</p>
  <p>It could be possible that we can show the position is unreachable via retrograde analysis, but that seems very difficult, so I'm just going to leave that to others and just say that I don't know how to prove this one way or the other.</p>
  <p>Ok. So, let's assume the pawn on the side from our orientation is mid-promotion. Now suppose white wanted to promote into a knight. This is check, but not checkmate, as black can take the knight with the bishop. However, black cannot give mate here while getting out of check at the same time. So, neither player can give checkmate in one move. (technically, I have shown this is not possible in one half-move, but I believe the technical term &quot;Mate in <em>one</em>&quot; is generally understood to refer to <em>one half-move</em>)</p>
  <p>In conclusion, I believe I have made a decent argument for why there exists a scenario where this position has been reached from a perfectly legal game (under the rules in this particular chess club), yet there exists no mate in one. Hence, however unlikely my scenario may be, I must conclude that I cannot be certain that there is checkmate in one move.</p>
  <hr />
  <p>That said, I don't think my problem hurts the essence of your <s>archaeological find</s> clever composition. As long as the promoted piece can deliver checkmate as well, we can be certain that there is a mate <em>within</em> one move.</p>
  <p>I think just placing a pawn between the bishop and the pedantic promotion square would do:</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;3b4/R3P3/1pkPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w - - 0 1&quot;] 
  </code></pre>
  <p>I believe this does not change the checkmate moves in the other orientations, or even their uniqueness. It does make the checkmate for white easier to find in the other orientations, but I think the new orientation you get in return is more than worth it. Maybe there are retrograde arguments against this position, I'm not sure.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T11:59:14.453Z
Answers.Text: Interesting argument... Why "archeological find" ? tks.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T12:46:40.123Z
Answers.Text: Or add another useless pawn (for either colour) that would be on row 1 or 8 with the wrong-coloured orientations
Answers.UserDisplayName: Hagen von Eitzen
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T14:23:13.040Z
Answers.Text: @XavierLabouze Well, the 19th century was a while ago. I'd guess that you weren't there personally over 120 years ago, so you somehow learnt about an abandoned chessboard from a long time ago. Perhaps it is more likely that a historian told you. In any case, you made a good puzzle, I just thought it would be even better with a minor alteration. I do admit that the argument for why I think this alteration leads to a better puzzle is rather complicated, and may be of little interest of others. Still, I enjoyed your puzzle, although perhaps in a strange way.
Answers.UserDisplayName: Discrete lizard
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T14:24:23.013Z
Answers.Text: @HagenvonEitzen That removes the extra orientations from the puzzle. There are ways to do that without changing the position, such as remarking that you actually saw how the players had their chairs arranged during the game, but did not manage to speak the players, somehow. My goal here was to add the orientation to the puzzle, mostly because I expected more than 2 orientations to be relevant. Perhaps I should design a puzzle myself where multiple orientations are relevant...
Answers.UserDisplayName: Discrete lizard
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T16:17:37.893Z
Answers.Text: @Discretelizard The 19th century is just an element of narration nothing more.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T16:22:37.563Z
Answers.Text: @XavierLabouze Yes, I understand that is _your intention_. However, for _my interpretation_ of your puzzle, it becomes relevant. One of the hardest parts of making a puzzle is often making sure there is only one interpretation that leads to a meaningful solution.
Answers.UserDisplayName: Discrete lizard
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T16:26:28.973Z
Answers.Text: @Discretelizard You are right, I thought it was clear enough, but not. I will post another problem soon, I hope it will be clearer.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-22T00:30:14.573Z
Answers.Text: @XavierLabouze: It’s a lovely puzzle as it is; but I had the same reaction as @ Discretelizard, and was misled by the framing to think that the “sideways” orientations would play a role.  So on the one hand, be careful with extraneous narrative elements… but on the other hand, the “sideways” orientations could make a nice idea for a twist in a future puzzle!
Answers.UserDisplayName: Peter LeFanu Lumsdaine
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-22T00:54:30.230Z
Answers.Text: @PeterLeFanuLumsdaine Thank you for your comment. Next time, I shouldn't use sideways elements of speech and should be more direct. Thanks again.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-22T00:58:38.503Z
Answers.Text: @Discretelizard. I edited the question to take into account your comments - and Peter's. Hope it is clearer now.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T11:04:21.850Z
Answers.LastActivityDate: 2020-11-21T11:04:21.850Z
Answers.UserDisplayName: Discrete lizard
Answers.Body: <p>It looks like</p>
  <blockquote class="spoiler">
  <p> e7xd8=N (by White)</p>
  </blockquote>
  <p>is checkmate, but so is</p>
  <blockquote class="spoiler">
  <p> Rd3xc3 (by Black)</p>
  </blockquote>
  <p>So perhaps there's more to this puzzle than meets the eye ...</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T18:06:04.440Z
Answers.Text: Nearly... two more left...
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T17:21:35.090Z
Answers.LastActivityDate: 2020-11-19T17:21:35.090Z
Answers.UserDisplayName: Glorfindel
Answers.Body: <p>If we assume that the players were not bad at chess, then the move before this move, that player had to have something more important to do than checkmate their opponent.</p>
  <p>If we take the board orientation as black moving upwards, with the white king at e5 and black rook at (e.g.) a6, then black moves rook to e6, check, white moves king to d5, black moves pawn to c6, mate.</p>
  <p>If it was white's turn, for either orientation, there is no move that black would have made on the previous turn besides checkmate.  Likewise if black is moving down, white would have mated black on the previous turn.</p>
  <p>I think the only solution is black moving up, pawn to c6.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T17:53:14.250Z
Answers.Text: Interesting comment. But if White is at the bottom, White to move, black king could have come from d7 with white rook at a6 (e.g.). no Mate in 1 for White. So Ra7+, ...Kc6, exd8=N#
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-21T16:51:19.430Z
Answers.LastActivityDate: 2020-11-21T16:51:19.430Z
Answers.UserDisplayName: drawnonward
Answers.Body: <p>Looks more like black plays rd4++  and mates white.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T17:48:02.793Z
Answers.Text: Ke3 or K x R (depends on where is white). Thanks for your answer anyway.
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T17:45:15.817Z
Answers.LastActivityDate: 2020-11-19T17:45:15.817Z
Answers.UserDisplayName: yobmamama
Answers.Body: <p>There are two checkmates per orientation:</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w KQkq - 0 1&quot;] 
  
  1. exd8=N#
  </code></pre>
  <p>and</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 b KQkq - 0 1&quot;] 
  
  1... Rxc3#
  </code></pre>
  <p>and</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;6b1/2p5/4rN2/1p1K4/3n1p1P/1n1RPk2/3P3R/4b3 b KQkq - 0 1&quot;] 
  
  1...c6#
  </code></pre>
  <p>and</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;6b1/2p5/4rN2/1p1K4/3n1p1P/1n1RPk2/3P3R/4b3 w KQkq - 0 1&quot;] 
  
  1. e4#
  </code></pre>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T18:05:33.323Z
Answers.Text: Thank you for the boards!
Answers.UserDisplayName: Xavier Labouze
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2022-12-30T21:30:50.677Z
Answers.Text: Also e8=B# or e8=Q# as well as exd8=N#?
Answers.UserDisplayName: studog
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-19T17:40:20.343Z
Answers.LastActivityDate: 2020-11-19T18:01:29.483Z
Answers.LastEditDate: 2020-11-19T18:01:29.483Z
Answers.UserDisplayName: Brian Towers
Body: <p>Here is another mate-in-one of my own i.e. a not quite usual one...</p>
  <pre><code>    [title &quot;Mate in one&quot;]
      [FEN &quot;3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w KQkq - 0 1&quot;] 
  </code></pre>
  <p>Imagine, you walk into a chess club, an abandoned chessboard hangs out on a table. You take a look at the position. You don't know where white or black is, who to play, yet one thing is certain: there is checkmate in one move...</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-11-20T10:45:27.547Z
Comments.Text: Nice, very original :-)
Comments.UserDisplayName: RemcoGerlich
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-11-20T12:43:36.253Z
Comments.Text: Enjoyed it! Very ingenious.
Comments.UserDisplayName: James Martin
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2020-11-20T15:12:07.273Z
Comments.Text: @RemcoGerlich and James. Tks !
Comments.UserDisplayName: Xavier Labouze
Tags: <checkmate><problems><puzzles>
Title: Another Unusual Mate in One
ThreadText: # Another Unusual Mate in One
  
  (Asked by: username_0 on 2020-11-19)
  
  Here is another mate-in-one of my own i.e. a not quite usual one...
  
  ```
      [title "Mate in one"]
      [FEN "3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w KQkq - 0 1"] 
  
  ```
  
  Imagine, you walk into a chess club, an abandoned chessboard hangs out on a table. You take a look at the position. You don't know where white or black is, who to play, yet one thing is certain: there is checkmate in one move...
  
  **Tags:** checkmate, problems, puzzles
  
  > **Comments:**
  > **username_1**: Nice, very original :-)  
  > **username_2**: Enjoyed it! Very ingenious.  
  > **username_0**: @username_1 and username_2. Tks !  
  
  ---
  
  ## 5 answers
  
  ### Answer by username_9 on 2020-11-19. Score: 22 | Accepted answer
  
  There are two checkmates per orientation:
  
  ```
      [title "Mate in one"]
      [FEN "3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w KQkq - 0 1"] 
  
  1. exd8=N#
  
  ```
  
  and
  
  ```
      [title "Mate in one"]
      [FEN "3b4/R3P3/2kPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 b KQkq - 0 1"] 
  
  1... Rxc3#
  
  ```
  
  and
  
  ```
      [title "Mate in one"]
      [FEN "6b1/2p5/4rN2/1p1K4/3n1p1P/1n1RPk2/3P3R/4b3 b KQkq - 0 1"] 
  
  1...c6#
  
  ```
  
  and
  
  ```
      [title "Mate in one"]
      [FEN "6b1/2p5/4rN2/1p1K4/3n1p1P/1n1RPk2/3P3R/4b3 w KQkq - 0 1"] 
  
  1. e4#
  
  ```
  
  > **Comments:**
  > **username_0**: Thank you for the boards!  
  > **username_10**: Also e8=B# or e8=Q# as well as exd8=N#?  
  
  ---
  
  ### Answer by username_6 on 2020-11-19. Score: 5
  
  It looks like
  
  > e7xd8=N (by White)
  
  is checkmate, but so is
  
  > Rd3xc3 (by Black)
  
  So perhaps there's more to this puzzle than meets the eye ...
  
  > **Comments:**
  > **username_0**: Nearly... two more left...  
  
  ---
  
  ### Answer by username_3 on 2020-11-21. Score: 4
  
  That's a nice archaeological find. However, I'm not so sure there is in fact a checkmate in just one "move". Of course, there is a (unique!) checkmate for both colors in all orientations considered by @username_9, which makes this a very nice problem indeed. But what about the *other* orientations?
  
  You may protest that [there's a rule that the bottom right corner must be a light square](https://chess.stackexchange.com/a/32045/), but I think you're going to have to consult a historian to determine whether this rule was in effect in this particular late 19th century London chess club, and in particular whether the game could have continued without rotating the board if the players noticed their error during the game. You likely also need to consult a medium in order to determine whether one of the players noticed it. So, I think this rule doesn't mean we can exclude other orientations.
  
  You may argue that the other orientations are excluded because there's a pawn on the side of the board. Not quite. First, a pawn can never legally be put on the first rank, so that excludes one orientation (white being to the left of our current view). But this is not true for the eighth rank. Promotion of a pawn is done by first moving the pawn to the promotion square on the eighth rank, and then replacing it with another piece. So, it is possible for a pawn to be on the eighth rank in a legal game. Of course, in the current state of the board the move is not yet completed, but that doesn't matter. We already know that in the other orientations the game was ended before the checkmate (as we still have to make one move), so the same could happen in the middle of the promotion move. I certainly have seen the board being left abandoned in such a state at my own chess club.
  
  It could be possible that we can show the position is unreachable via retrograde analysis, but that seems very difficult, so I'm just going to leave that to others and just say that I don't know how to prove this one way or the other.
  
  Ok. So, let's assume the pawn on the side from our orientation is mid-promotion. Now suppose white wanted to promote into a knight. This is check, but not checkmate, as black can take the knight with the bishop. However, black cannot give mate here while getting out of check at the same time. So, neither player can give checkmate in one move. (technically, I have shown this is not possible in one half-move, but I believe the technical term "Mate in *one*" is generally understood to refer to *one half-move*)
  
  In conclusion, I believe I have made a decent argument for why there exists a scenario where this position has been reached from a perfectly legal game (under the rules in this particular chess club), yet there exists no mate in one. Hence, however unlikely my scenario may be, I must conclude that I cannot be certain that there is checkmate in one move.
  
  ---
  
  That said, I don't think my problem hurts the essence of your ~~archaeological find~~ clever composition. As long as the promoted piece can deliver checkmate as well, we can be certain that there is a mate *within* one move.
  
  I think just placing a pawn between the bishop and the pedantic promotion square would do:
  
  ```
      [title "Mate in one"]
      [FEN "3b4/R3P3/1pkPR1n1/P1p1n3/4K1p1/2Nr4/5p2/1b6 w - - 0 1"] 
  
  ```
  
  I believe this does not change the checkmate moves in the other orientations, or even their uniqueness. It does make the checkmate for white easier to find in the other orientations, but I think the new orientation you get in return is more than worth it. Maybe there are retrograde arguments against this position, I'm not sure.
  
  > **Comments:**
  > **username_0**: Interesting argument... Why "archeological find" ? tks.  
  > **username_4**: Or add another useless pawn (for either colour) that would be on row 1 or 8 with the wrong-coloured orientations  
  > **username_3**: @username_0 Well, the 19th century was a while ago. I'd guess that you weren't there personally over 120 years ago, so you somehow learnt about an abandoned chessboard from a long time ago. Perhaps it is more likely that a historian told you. In any case, you made a good puzzle, I just thought it would be even better with a minor alteration. I do admit that the argument for why I think this alteration leads to a better puzzle is rather complicated, and may be of little interest of others. Still, I enjoyed your puzzle, although perhaps in a strange way.  
  > **username_3**: @username_4 That removes the extra orientations from the puzzle. There are ways to do that without changing the position, such as remarking that you actually saw how the players had their chairs arranged during the game, but did not manage to speak the players, somehow. My goal here was to add the orientation to the puzzle, mostly because I expected more than 2 orientations to be relevant. Perhaps I should design a puzzle myself where multiple orientations are relevant...  
  > **username_0**: @username_3 The 19th century is just an element of narration nothing more.  
  > **username_3**: @username_0 Yes, I understand that is _your intention_. However, for _my interpretation_ of your puzzle, it becomes relevant. One of the hardest parts of making a puzzle is often making sure there is only one interpretation that leads to a meaningful solution.  
  > **username_0**: @username_3 You are right, I thought it was clear enough, but not. I will post another problem soon, I hope it will be clearer.  
  > **username_5**: @username_0: It’s a lovely puzzle as it is; but I had the same reaction as @ username_3, and was misled by the framing to think that the “sideways” orientations would play a role.  So on the one hand, be careful with extraneous narrative elements… but on the other hand, the “sideways” orientations could make a nice idea for a twist in a future puzzle!  
  > **username_0**: @username_5 Thank you for your comment. Next time, I shouldn't use sideways elements of speech and should be more direct. Thanks again.  
  > **username_0**: @username_3. I edited the question to take into account your comments - and username_5's. Hope it is clearer now.  
  
  ---
  
  ### Answer by username_7 on 2020-11-21. Score: 1
  
  If we assume that the players were not bad at chess, then the move before this move, that player had to have something more important to do than checkmate their opponent.
  
  If we take the board orientation as black moving upwards, with the white king at e5 and black rook at (e.g.) a6, then black moves rook to e6, check, white moves king to d5, black moves pawn to c6, mate.
  
  If it was white's turn, for either orientation, there is no move that black would have made on the previous turn besides checkmate. Likewise if black is moving down, white would have mated black on the previous turn.
  
  I think the only solution is black moving up, pawn to c6.
  
  > **Comments:**
  > **username_0**: Interesting comment. But if White is at the bottom, White to move, black king could have come from d7 with white rook at a6 (e.g.). no Mate in 1 for White. So Ra7+, ...Kc6, exd8=N#  
  
  ---
  
  ### Answer by username_8 on 2020-11-19. Score: 0
  
  Looks more like black plays rd4++ and mates white.
  
  > **Comments:**
  > **username_0**: Ke3 or K x R (depends on where is white). Thanks for your answer anyway.  
  
  ---
  
  