Retroanalysis.

[massimilianogoi]

This topic was suggested more than one and half year ago from a Member of my site, who is registered in this forum as Nepo17. The content is really interesting as it cannot be solved by chess engines, as far as I know.

We are talking about retroanalysis, that is guessing the last move a player made to reach a certain position and the color of the last player, a nice variation in an era where computer chess became so flat because of the very high rate of draw games.



In this specific case we have to guess what was the last move made and what color had the player. I tried to figure out the solution but looks like impossible to me. Any hint?

[FritzUser]

Six of Black's pawns haven't moved yet, and neither has the Bishop. So the White King walked in, followed by two pawns, which promoted to rooks. To do all of that, the c-pawn must already have been out, and thus can't have been the last piece moved. That leaves only White's Rook.

The only other moveable piece is the Black King, I guess, and there's no room for its move to have been the last one. The White King must have already moved in there, and the two promoted pawns moved in behind that.

[massimilianogoi]

Well done. I guess the last piece that moved was the rook in b8, capturing some piece after the pawns promotion.

Six of Black's pawns haven't moved yet, and neither has the Bishop. So the White King walked in, followed by two pawns, which promoted to rooks. To do all of that, the c-pawn must already have been out, and thus can't have been the last piece moved. That leaves only White's Rook.

The only other moveable piece is the Black King, I guess, and there's no room for its move to have been the last one. The White King must have already moved in there, and the two promoted pawns moved in behind that.