Answers.Body: <p>As the tags suggests, the problem is a retrograde problem. If Black may no longer castle, there is an easy solution-1. Qc7 and mate on the second move.</p>
  <p>The Black pawns on a6-a2 must have taken 10 white pieces or pawns. White has 3 pieces left, so the pawns could have taken 5 pieces and the pawns from a2 to d2. So one of the other pawns (e2-h2) must have been taken too. That only could have happened if one of those pawns promoted. But with the Black king on e8 and the black rook on h8, this is impossible, taking in account that the Black pawns are on f6, g7 and h5.</p>
  <p>Conclusion: the Black king and/or rook must have moved, so castling is illegal and 1. Qc7 wins.</p>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-11T18:25:32.357Z
Answers.LastActivityDate: 2020-09-11T18:33:23.510Z
Answers.LastEditDate: 2020-09-11T18:33:23.510Z
Answers.UserDisplayName: marcel wubben
Answers.Body: <p>The solution is</p>
  
  <blockquote class="spoiler">
    <p> 1. Qc7 followed by Qe7, Qf7 or Qc8 mate (depending on Black's second move).</p>
  </blockquote>
  
  <p>This works because</p>
  
  <blockquote class="spoiler">
    <p> Black can't castle because either his king or rook on h8 have moved already. As Brian Towers notes, the black a-pawns need to have captured 10 white pieces and/or pawns; there are enough pieces missing, <em>but</em> capturing the white e-pawn (or to the right) doesn't bring you any closer to the a-file. So, one white pawn on the queenside must have been captured on another file; this is possible via promotion, but since there's just one black piece missing (a white-squared bishop) the promotion could have happened on the d-, e-, f-, or h-file. The pawn has either attacked the black king at f7 or d7, or it promoted on e8, forcing the black King to move in all cases. Or it promoted on h8, forcing the black rook to move. Another possibility, as @Laska noted, is that the e-pawn captures the black bishop on the d-file and is captured itself before promotion; however, we only need a single capture on the d-file, and the original white d-pawn must be captured too.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-07T03:01:26.860Z
Answers.Text: did you switch black and white in your answer?
Answers.UserDisplayName: Ant
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-07T06:24:28.857Z
Answers.Text: @Ant I edited my question and switched the colors. The answer here is now corrected (after your comment).
Answers.UserDisplayName: Albert Hendriks
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2018-05-06T13:47:10.820Z
Answers.LastActivityDate: 2018-05-17T06:29:31.973Z
Answers.LastEditDate: 2018-05-17T06:29:31.973Z
Answers.UserDisplayName: Glorfindel
Body: <p>It's White to move-can they force a win?. The left bottom is a1 as usual.</p>
  <pre><code>[FEN &quot;4k2r/6p1/p4pKb/p2N3p/p7/p5Q1/p1n5/qrn5 w - - 9 9&quot;]
  </code></pre>
  <p>Note for people who saw an earlier version: the position was edited (including a swap of the colors) for a more beautiful puzzle by Laska's suggestions. The answer has now been fixed accordingly.</p>
  <p>History: I came up with this puzzle when I was a student, almost 20 years ago. It was published in the magazine of my local chess club, but nobody found the answer. A friend popularized it with his new chess-friends after he emigrated to Canada.</p>
  
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T12:30:40.540Z
Comments.Text: You do know that the position on the board is illegal and therefore it does not comprise a proper chess problem? You have 5 pawns on the a file requiring 10 captures of which at most 4 can be pawn captures. That leaves 6 black pieces which must have been captured out of a total of 7 leaving just one. However black has two pieces remaining.
Comments.UserDisplayName: Brian Towers
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T12:49:43.757Z
Comments.Text: @BrianTowers if you've looked at the FEN source code, please don't. I don't know how that works. Other than that, the position is perfectly legal and it's a proper chess problem. Basically your analysis is wrong.
Comments.UserDisplayName: Albert Hendriks
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T14:40:11.833Z
Comments.Text: Ah, OK, so either the black queen or knight is the result of a pawn promotion and probably the e pawn.
Comments.UserDisplayName: Brian Towers
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T14:52:04.370Z
Comments.Text: @Laska if you move the black king to g3, castling kingside won't help anymore for white.
Comments.UserDisplayName: Glorfindel
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T14:52:21.383Z
Comments.Text: @BrianTowers: there was certainly at least one black promotion, but the promoted unit might have been captured itself to fuel the white pawns' eastward lurch. wQ & wN can both be original.
Comments.UserDisplayName: Laska
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T15:00:16.090Z
Comments.Text: Are we meant to deduce retroanalytically that White is at the top of the board? Or can we assume that because Black to move? If the latter, we can delete all three Black pawns, pushing bK to g3 and wQ to a8, Also need  wPh3 on h4, wBc8 on h3 & wNc5 on c8. Now 0-0 is an escape again, thanks @Glorfindel for spotting hole. Quite nice reasoning why bPg3 can be taken away.
Comments.UserDisplayName: Laska
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T16:08:54.553Z
Comments.Text: @Laska I like your suggestion very much: https://lichess.org/editor/Q1N5/PRN5/P5q1/P7/P2n3P/P4PkB/6P1/4K2R_w_-_- but I'm not sure if white can then still get away after 1,... Qd3?
Comments.UserDisplayName: Albert Hendriks
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T17:19:20.200Z
Comments.Text: No worries: Qd3 is what they call a "try". That means it's nearly a solution but there is a single defence which defeats it: Rb2. You can safely start this rook off on b8 by the way: don't need to block bQ so much. If I  were you, I would swap the roles of Black & White in this problem, as it's more normal for White to be the mating party in these problems, and then people can check your problem is sound on special problem software e.g. Popeye, Problemist etc.
Comments.UserDisplayName: Laska
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T21:41:28.670Z
Comments.Text: (I'm thoroughly confused as to which direction the sides are going, and it's complicated by the fact that the sides were swapped.)
Comments.UserDisplayName: geometrian
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T21:45:50.493Z
Comments.Text: @imallett left bottom is now a1, as it should be. I've now clarified it in the question.
Comments.UserDisplayName: Albert Hendriks
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-06T22:55:35.147Z
Comments.Text: @AlbertHendriks I hope you also edited Glorfindel's answer accordingly and it just waits to be reviewed? Please never edit questions on StackExchange in a a way that invalidates existing answers!
Comments.UserDisplayName: leftaroundabout
Comments.ContentLicense: CC BY-SA 4.0
Comments.CreationDate: 2018-05-07T06:27:00.880Z
Comments.Text: The answer is now fixed according to the changed question.
Comments.UserDisplayName: Albert Hendriks
Tags: <problems><retrograde-analysis>
Title: Can white win in this almost 20 year old puzzle?
ThreadText: # Can white win in this almost 20 year old puzzle?
  
  (Asked by: username_0 on 2018-05-06)
  
  It's White to move-can they force a win?. The left bottom is a1 as usual.
  
  ```
  [FEN "4k2r/6p1/p4pKb/p2N3p/p7/p5Q1/p1n5/qrn5 w - - 9 9"]
  
  ```
  
  Note for people who saw an earlier version: the position was edited (including a swap of the colors) for a more beautiful puzzle by username_3's suggestions. The answer has now been fixed accordingly.
  
  History: I came up with this puzzle when I was a student, almost 20 years ago. It was published in the magazine of my local chess club, but nobody found the answer. A friend popularized it with his new chess-friends after he emigrated to Canada.
  
  **Tags:** problems, retrograde-analysis
  
  > **Comments:**
  > **username_1**: You do know that the position on the board is illegal and therefore it does not comprise a proper chess problem? You have 5 pawns on the a file requiring 10 captures of which at most 4 can be pawn captures. That leaves 6 black pieces which must have been captured out of a total of 7 leaving just one. However black has two pieces remaining.  
  > **username_0**: @username_1 if you've looked at the FEN source code, please don't. I don't know how that works. Other than that, the position is perfectly legal and it's a proper chess problem. Basically your analysis is wrong.  
  > **username_1**: Ah, OK, so either the black queen or knight is the result of a pawn promotion and probably the e pawn.  
  > **username_2**: @username_3 if you move the black king to g3, castling kingside won't help anymore for white.  
  > **username_3**: @username_1: there was certainly at least one black promotion, but the promoted unit might have been captured itself to fuel the white pawns' eastward lurch. wQ & wN can both be original.  
  > **username_3**: Are we meant to deduce retroanalytically that White is at the top of the board? Or can we assume that because Black to move? If the latter, we can delete all three Black pawns, pushing bK to g3 and wQ to a8, Also need  wPh3 on h4, wBc8 on h3 & wNc5 on c8. Now 0-0 is an escape again, thanks @username_2 for spotting hole. Quite nice reasoning why bPg3 can be taken away.  
  > **username_0**: @username_3 I like your suggestion very much: https://lichess.org/editor/Q1N5/PRN5/P5q1/P7/P2n3P/P4PkB/6P1/4K2R_w_-_- but I'm not sure if white can then still get away after 1,... Qd3?  
  > **username_3**: No worries: Qd3 is what they call a "try". That means it's nearly a solution but there is a single defence which defeats it: Rb2. You can safely start this rook off on b8 by the way: don't need to block bQ so much. If I  were you, I would swap the roles of Black & White in this problem, as it's more normal for White to be the mating party in these problems, and then people can check your problem is sound on special problem software e.g. Popeye, Problemist etc.  
  > **username_4**: (I'm thoroughly confused as to which direction the sides are going, and it's complicated by the fact that the sides were swapped.)  
  > **username_0**: @imallett left bottom is now a1, as it should be. I've now clarified it in the question.  
  > **username_5**: @username_0 I hope you also edited username_2's answer accordingly and it just waits to be reviewed? Please never edit questions on StackExchange in a a way that invalidates existing answers!  
  > **username_0**: The answer is now fixed according to the changed question.  
  
  ---
  
  ## 2 answers
  
  ### Answer by username_2 on 2018-05-06. Score: 14 | Accepted answer
  
  The solution is
  
  > 1. Qc7 followed by Qe7, Qf7 or Qc8 mate (depending on Black's second move).
  
  This works because
  
  > Black can't castle because either his king or rook on h8 have moved already. As username_1 username_1 notes, the black a-pawns need to have captured 10 white pieces and/or pawns; there are enough pieces missing, *but* capturing the white e-pawn (or to the right) doesn't bring you any closer to the a-file. So, one white pawn on the queenside must have been captured on another file; this is possible via promotion, but since there's just one black piece missing (a white-squared bishop) the promotion could have happened on the d-, e-, f-, or h-file. The pawn has either attacked the black king at f7 or d7, or it promoted on e8, forcing the black King to move in all cases. Or it promoted on h8, forcing the black rook to move. Another possibility, as @username_3 noted, is that the e-pawn captures the black bishop on the d-file and is captured itself before promotion; however, we only need a single capture on the d-file, and the original white d-pawn must be captured too.
  
  > **Comments:**
  > **username_7**: did you switch black and white in your answer?  
  > **username_0**: @username_7 I edited my question and switched the colors. The answer here is now corrected (after your comment).  
  
  ---
  
  ### Answer by username_6 on 2018-05-11. Score: 3
  
  As the tags suggests, the problem is a retrograde problem. If Black may no longer castle, there is an easy solution-1. Qc7 and mate on the second move.
  
  The Black pawns on a6-a2 must have taken 10 white pieces or pawns. White has 3 pieces left, so the pawns could have taken 5 pieces and the pawns from a2 to d2. So one of the other pawns (e2-h2) must have been taken too. That only could have happened if one of those pawns promoted. But with the Black king on e8 and the black rook on h8, this is impossible, taking in account that the Black pawns are on f6, g7 and h5.
  
  Conclusion: the Black king and/or rook must have moved, so castling is illegal and 1. Qc7 wins.
  
  
  ---
  
  