An original retro problem #10

"A question of promotion"

There are three promoted pieces in this position. Where?

Black's last move was Nb2# or O-O#. White is missing a rook and two bishops; black is missing three pawns (which must have promoted) and a rook (and of course three other pieces were captured at some point). The most obvious possibility is that the white bishops were captured on b2 and g2 and the rook was captured on d2 (which would mean white's last move was Nb2#).

Assuming I haven't accidentally captured a promoted piece, that would be a way to do it, and the queen and both knights are promoted pieces. This doesn't prove other methods (such as involving bxa3 and axb3, or at least one of black's existing pawns having captured) don't work.

Hi Bentley, good analyse!

This is a clear mistake in the position... 49. Nb2# shouldn't be possible 

I fixed the original post. Feel free to comment!

White just played 0-0+. White's missing 3 pieces. The promoting pawns did not pass through d2, checking wK, nor did any promote on h1, since white's Rook has always been there.

This leaves a scheme of e7xfxg, hxg, and a7-a1. White's a-, b-, g-, and h-pawns all captured, allowing wRa1 to be sacrificed to a pawn on the kingside. (The g- and h-pawns did not move straight up because that requires two sacrifices on g2 and white can't get Ra1 or Bc1 there.)

The promotion squares are g1 (twice) and a1. N's can't escape from either one (there is a pawn on b3 before a1=X and a pawn on h3 before g1=X and Ng1-f3 is illegal check to wK) and a Bishop can't escape from g1 (there has always been a wP on h2 or g3).

This means that Qe8 and Rd8 promoted on g1, and Bf8 promoted on a1, because that is the only square which allows a promoted minor piece to escape.

Good job, of course. I may need to compose harder puzzles for you! :P