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Retrograde analysis is a technique employed to determine which events occurred leading up to a given situation.

5 votes
Accepted

That Ain’t Right.... #3

Here is a solution, or more precisely a family of solutions.
Gareth McCaughan's user avatar
2 votes
Accepted

Where is the White King?

The white king is on and the last few moves were Proof: Let's consider these possibilities in order. Therefore Now, This is no good yet, because
Gareth McCaughan's user avatar
3 votes

Can White Castle? #3

Wrong answer (I made a boneheaded mistake, kindly pointed out in comments by @RShields, to which I have drawn attention below.)
Gareth McCaughan's user avatar
15 votes
Accepted

White's last move?

In the position shown, Now, Before that Black White So we have the following sequence of events. Now, We still haven't figured out Suppose that Now So let's consider W …
Gareth McCaughan's user avatar
3 votes

Smallest number of moves to get to a chess position

Certainly not an optimal solution Here is a way to get to that position, as a baseline for others' improvements. I bet it can be reduced quite a lot: 1. b3 d6 2. Ba3 Nc6 3. Bc5 dxc5 4. Qc1 g5 5. Qa3 …
Gareth McCaughan's user avatar
20 votes

Only one square for the white king

HTM's answer is very nice and must be what's intended here. But I'm not quite seeing why the puzzle isn't cooked as follows:
Gareth McCaughan's user avatar
0 votes

Which piece moved last?

Grossly incomplete answer (I misread the question; having had this kindly pointed out in comments I spent a short while seeing whether I could finish the job before needing to go to bed tonight, but i …
Gareth McCaughan's user avatar
7 votes
Accepted

Introducing: Sudoku-Janpu

Alice's last move must have been because Clearly Bob's previous move was Now consider We can't
Gareth McCaughan's user avatar
1 vote

The master programmer and the mystical reversal

This is an at-most-half-baked answer, but I begin to suspect that the trouble lies For a (ridiculous) example, This sort of possibility is maybe made more plausible by
Gareth McCaughan's user avatar
1 vote

The master programmer and the mystical reversal

I hope this is not the correct answer, but perhaps In which case,
Gareth McCaughan's user avatar
9 votes
Accepted

Paper, pencil and a bunch of bars

This game is So in this case If we take "rational" to mean that when either player had a winning move they took it then Now So
Gareth McCaughan's user avatar