Retrograde Analysis

[faelanstevie]

HI,
I'm working through 'The Chess Mysteries of Sherlock Holmes' by Raymond Smullyan and have come acrosss a problem for which I can see no solution although the book, whilst explaining most steps, offers the solution including the part-sentence 'It must have been from a4'. The problem is a question of whether Black can castle, and the problem is entitled 'You really can't, you know!'. If anyone has the book, can they please explain why pawn a3 MUST have come from a4 NOT b4. With this understanding the solution is clear, however I can't see why the pawn couldn't have come from b4 taking a black piece on a3 which would mean that the solution to the problem is different from as published.any idea.?
Thanks

I did not find the right solution from the internet.
References:
http://www.chessexchange.com/forum/view ... =29&t=4210
Animated Explainer Video

[Otto]

Please tell me the number of the problem in this list:
https://www.janko.at/Schach/Smullyan-SH/index.htm

[wan the man]

Indeed "You really can't, you know!" in Smullyan's chess mysteries of Sherlock Holmes is flawed, because the black pawn on a3 could have come from b4. A game can be constructed that reaches the given position while black can still castle.

An easy fix is to require that the last move from white was with the bishop (instead of the knight).

[Octav]

Hallo,

Ich hatte diese Passage, die ich damals nicht erklären konnte, völlig vergessen. Jetzt ist es etwas klarer mit diesen Erläuterungen von Ihnen.