Retrograde analysis is the method of deducing information by working backwards from a given position or outcome. This information can be about past positions of the same game, or may contain forward content, such as optimal play.

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### A mysterious mate in one

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 ...
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### Are there any illegal positions that are difficult to spot?

I have a question and I'm sorry if it sounds very uninformed, I'm not a professional chess player so my interest is mere curiosity. I was wondering if there are examples of illegal positions that ...
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### Legal positions with one color to move only?

Most positions in chess can be reached with both black or white to move. Some positions are only legal with one color to move. One such position is the starting position, which famously can't be ...
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### Problem: reconstruct the game

In the following position, each side has made exactly 4 moves (8 in total). [fen "rnbqkbnr/pp3ppp/2p1p3/8/4P3/8/PPPP1PPP/RNBQK1NR w KQkq - 0 1"] I need to find what these moves were.
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### Searching for a "where is the black king" problem

Sometime ago, a friend showed me a position where he had the Black king removed. The goal was to find where is the Black king using some pretty weird reasoning. There were only a few pieces on the ...
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### Given a legal chess position, is there an algorithm that generates a series of moves that lead to it?

Given a FEN board position, is there an algorithm that can return a PGN move list that evaluates to it from the standard initial position?
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### Can it be proven that 11. 0-0-0+ is legal in this position?

Because the chess site this was on takes its puzzles from real games and gives the move numbers, potential solvers knew that the following position was reached after exactly 10 moves by each player. [...
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### Which methods can be used to prove that a position is illegal?

Given a board position, there are programs that try to find a series of legal moves that lead to it. Are there algorithms that can do the opposite - prove that the position is not reachable by a ...
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### Beautiful retrograde analysis problem by Alexsey A. Troitsky

I saw this beautiful, subtle & accessible problem a couple of days ago, and wanted to share it with you folks. (It's by the ground-breaking endgame theorist who e.g. invented the "Troitsky line" ...
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### What is the result? (Rules + puzzle)

[EDITED to include followup - EDIT 2 to include definition of position] This is in part a genuine question on the FIDE Laws of Chess, and in part a small puzzle to solve. Suppose that during a long ...
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### Identify a problem where a potentially winning move draws because of the 50 move rule

I'm trying to recall a particular chess problem. It's related to retrograde analysis. All what I can remember is this: it's an endgame where there is only one way to reach the position, and during ...
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### Mate in One the Missing King

The post "A mysterious mate in one" made me think of one of my last problems which is also a Mate-in-One with no black King: [Title "White to move and mate in one"] [FEN &...
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### How is this retrograde analysis position legal?

On his page on Harry Goldsteen's "Horse Concoction,", Tim Krabbé gives this position by "N. Höeg, 1935." [FEN "4k3/1p4pp/p1pQ1p2/1q1pp3/8/8/1K6/8 b - - 0 1"] [...
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Raymond Smullyan wrote some great books with Retrograde Analysis chess puzzles. I know of two, are there others?
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