Answers.Body: <p>A solution may be that it used to be possible to</p>
  <blockquote class="spoiler">
  <p> promote to an enemy piece, as mentioned e.g. <a href="https://en.chessbase.com/post/study-of-the-month-2018-07" rel="noreferrer">here</a>. This loophole has long been fixed in the official rules, but under old rules it was allowed to do <code>1. g7xf8=(black)K</code> which would be mate.</p>
  </blockquote>
  <p>Would that really explain</p>
  <blockquote class="spoiler">
  <p> the <a href="/questions/tagged/retrograde-analysis" class="post-tag" title="show questions tagged &#39;retrograde-analysis&#39;" rel="tag">retrograde-analysis</a> tag?</p>
  </blockquote>
  <p>Perhaps, in the sense that</p>
  <blockquote class="spoiler">
  <p> we <em>do</em> need to go back in time.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-06T08:19:48.917Z
Answers.LastActivityDate: 2020-11-06T08:19:48.917Z
Answers.UserDisplayName: Glorfindel
Answers.Body: <p>This is easy.</p>
  <blockquote class="spoiler">
  <p> The Black king is somewhere on the 8th rank. It is checkmated in one move by pawn x knight on f8, queening. Now the new queen is giving check, and the rook on h7 prevents the king from going anywhere, resulting in checkmate.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-07T04:26:44.987Z
Answers.LastActivityDate: 2020-11-08T09:42:33.773Z
Answers.LastEditDate: 2020-11-08T09:42:33.773Z
Answers.UserDisplayName: Michael Bartlett
Answers.Body: <p>Looking at the problem as if the black King is currently invisible...</p>
  <blockquote class="spoiler">
  <p>gxf8=Q#
  All squares are now covered. So where ever the black King is hiding, the game is over.</p>
  </blockquote>
  
Answers.ContentLicense: CC BY-SA 4.0
Answers.CreationDate: 2020-11-06T14:39:43.133Z
Answers.LastActivityDate: 2020-11-06T14:39:43.133Z
Answers.UserDisplayName: Jesper Nielsen
Body: <p>Here's a question that's a little off the usual format, but problem questions like this have been done before and are on topic, so here we go!</p>
  <p>Question: Can you find the mysterious mate in one? The trick is not board rotation, removing a piece, retracting any moves, completing a move, or an illegal move-there is but one solution. Have fun solving!</p>
  <pre><code> [Title &quot;White checkmates Black in one move&quot;]
   [FEN &quot;5nRQ/6PR/1p6/p2P4/p1B5/3Pp3/8/1b1K4 w - - 0 1&quot;]
  </code></pre>
  
Tags: <problems><checkmate><retrograde-analysis>
Title: A mysterious mate in one
ThreadText: # A mysterious mate in one
  
  (Asked by: username_0 on 2020-11-06)
  
  Here's a question that's a little off the usual format, but problem questions like this have been done before and are on topic, so here we go!
  
  Question: Can you find the mysterious mate in one? The trick is not board rotation, removing a piece, retracting any moves, completing a move, or an illegal move-there is but one solution. Have fun solving!
  
  ```
   [Title "White checkmates Black in one move"]
   [FEN "5nRQ/6PR/1p6/p2P4/p1B5/3Pp3/8/1b1K4 w - - 0 1"]
  
  ```
  
  **Tags:** problems, checkmate, retrograde-analysis
  
  
  ---
  
  ## 3 answers
  
  ### Answer by username_3 on 2020-11-06. Score: 48 | Accepted answer
  
  Looking at the problem as if the black King is currently invisible...
  
  > gxf8=Q#
  > All squares are now covered. So where ever the black King is hiding, the game is over.
  
  
  ---
  
  ### Answer by username_1 on 2020-11-06. Score: 15
  
  A solution may be that it used to be possible to
  
  > promote to an enemy piece, as mentioned e.g. [here](https://en.chessbase.com/post/study-of-the-month-2018-07). This loophole has long been fixed in the official rules, but under old rules it was allowed to do `1. g7xf8=(black)K` which would be mate.
  
  Would that really explain
  
  > the [retrograde-analysis](/questions/tagged/retrograde-analysis "show questions tagged 'retrograde-analysis'") tag?
  
  Perhaps, in the sense that
  
  > we *do* need to go back in time.
  
  
  ---
  
  ### Answer by username_2 on 2020-11-07. Score: 0
  
  This is easy.
  
  > The Black king is somewhere on the 8th rank. It is checkmated in one move by pawn x knight on f8, queening. Now the new queen is giving check, and the rook on h7 prevents the king from going anywhere, resulting in checkmate.
  
  
  ---
  
  