PG in 26.0 moves (Baier)

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BigDoggProblem

Here's another tough PG with lots of pawn captures.


Find a legal game that reaches the diagram after Black's 26th move.

Remellion

This one was surprisingly very easy, and very fun.

Looking at the board, we see black has made at least 4 captures, and white has lost 5 pawns, 4 of which (a, b, c, e) are useless for helping black's pawn structure. Therefore white has promoted at least 3 of those pawns (f-pawn could have been captured by bPe3xf2.)

Now counting ply, white has made 2N, 1R, 5K and at least (3 x 6)P ply, which adds up to 26 ply exactly. So we have established that white has promoted exactly 3 pawns, and sacced each of them on a square within one ply range of their promotions.

Counting black's moves, he has made at least 2K and 4 (e-pawn) + 5 (the other kingside pawns) = 11 ply. That leaves him 15 ply to do what? Seeing as black's a-, b- and c- pawns are absent, they could have promoted.

A little mental plotting of pawn trajectories suggests the black a- and b- pawns promoted on a1, the white c- and d-pawns on d8 (sac to h4 and g5) and the e-pawn on e8 (sac to h5). This means that the black pawn moves must've been Pe7-e5-e4-e3xf2, Pf7-f6xg5xh4, Pg7-g6xh5 and Ph7-h6. (...Pf6 after wBh4 and g5, ...Pg6 after wBh5.) So black has made 2K ply, 10 kingside pawn ply and 14P promote-and-return-to-d8 ply. 26 total.

Construction is now easy, bearing in mind the choreographed dancing of the kings to avoid checks.



BigDoggProblem

SOLV'D

This one won 1st Honorable Mention in StrateGems 2012.