By Samuel Katagi

In keeping with Mick‘s lecture theme of endgames for this month and what he presented as far as Retrograde Analysis, I wanted to give a Happy New Year 2010 chess puzzle. This puzzle is derived from a puzzle that Dr. Neils Hoeg orignially came up with and had published in Skakbladet in 1916**. It comes from a class of chess problems called Retrograde Analysis.

** Dr. Neils Hoeg‘s puzzle was printed in Burt Hochberg‘s "Outrageous Chess Problems" book as puzzle #40 in his chapter "Remembrance of Things Past." The derived problem you see in this article keeps the original flavor of the orignal puzzle. What Hochberg says about solving these "retro" problems is that "Castling is always legal unless proven illegal" and "en passant captures are always illegal unless proven legal."

What was the Last Move by Black or White and Why?

Enjoy! Try not to look at the solution until you have given a serious try at it!

Scroll for solution below

Since Black is in check, obviously it is White‘s move. Since, the white pawn on a2 is in its original square, it‘s not the white a2-pawn that moved. Since the white bishop is in the corner at a1, it is not the bishop that moved last either giving check. Since the white king could not have moved so as to give check, that leaves only the white pawn on e6 as the only possible candidate. How could it have moved to give a discovered check? It was not from moving from e5 because then the black king would have already been in check. Thus, Black would have to move his king out of check. As Hochberg describes it...the only answer left is that there was a black pawn on e5! There had to have been a black pawn or piece that blocked White‘s bishop check. And it to be a piece that the white pawn could take while the black piece was on e5. Obviously, it was not a black queen, rook, bishop or knight because then how could a white pawn then capture it? This leaves the only answer as being a black pawn on e5. So then how could have that white pawn taken that black pawn on e5? Because the white pawn was on d5 and the black pawn was on e5 after having moved 2 squares forward from e7. The white pawn on d5 then took the black pawn by en passant. They call this type of solving as Retrograde Analysis.