# What were the last three single moves?

Puzzle by Niels Høeg:

White just moved. What were the last three single moves? In other words, what was White’s last move and Black’s move before that and White’s move before that?

• Thank you for bringing up this puzzle. It seems famous (or perhaps this idea is used in lots of puzzles). Commented Jul 16 at 7:53
• Classics of the genre Commented Jul 16 at 12:45

This is the first time I'm answering a chess retrograde analysis puzzle. Let's hope I'm doing things right :)

The bishop on a1 is stuck on the diagonal with the black king, so a piece must have been there to block the check. It was either the white pawn or a black piece (the white king is too far away).

However, if the white pawn was blocking the check from the bishop, it would have put himself the black king in check. Hence, a black piece was blocking the check.

The only way the black piece could disappear from the diagonal is by being taken by a white piece. But the white king is too far away and the white bishop could only reach a1 by going backwards on the diagonal (so it did not capture a blocking black piece). Therefore, the pawn captured the black piece.

That means the white pawn captured en passant a black pawn that went from e7 to e5. And we know it must be from column d, because the black king must have been put in check before the black pawn could block it, which is only possible if the white pawn was in d4 and went to d5.