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PG in 26.0 moves (Baier)


  • 3 months ago · Quote · #1

    BigDoggProblem

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


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

  • 3 months ago · Quote · #2

    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.



  • 3 months ago · Quote · #3

    BigDoggProblem

    SOLV'D

    This one won 1st Honorable Mention in StrateGems 2012.


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