Proof Game in 13.0

White is missing three pawns; Black, four. Were they all captured, or did some slip through and promote? A seasoned solver knows the golden rule: a proof game unfolds in one precise, transposition-proof sequence. WRd8 all but shouts promotion—no rook from the first rank could have reached d8 by a unique route. But if a pawn promoted there by capturing Black’s original queen, then BQh1 must be promoted too. With WRd8 and BQh1 likely promotions, it’s only natural to suspect WNh7 and BBg1 are as well—completing the full AUW.

Now to unravel the sequence. Starting with 1.b4 falls flat: after 1.b4 g5 2.b5 g4 3.b6 g3 4.bxc7 gxh2 5.cxd8=R+, the check comes too soon—e7’s blocked, and Black’s king can’t escape. The correct launch is 1.d4 g5 2.d5 g4 3.d6 g3 4.dxe7 gxh2 5.exf8=N hxg1=B. By now, it’s clear that WRh1 was the piece captured on a6, since WPb2 needs to reach d8 via c7. So: 6.Rh6 Ke7 7.Ra6. The pawns then march up the board from opposite wings: 7...h5 8.b4 h4 9.b5 h3 10.b6 h2 11.bxc7 h1=Q 12.cxd8=R, and it all culminates with 12...Rh2 13.Nh7 bxa6. Voilà!

It’s crucial to hold off on bxa6 until the very end. Capture too early, and the h7 pawn’s queening is delayed—disrupting the pas de deux of Rh2 and Nh7. For example: 7...bxa6 8.b4 h5 9.b5 h4 10.b6 h3 11.bxc7 h2 12.cxd8=R h1=Q—and now 13.Nh7 gets in Rh8's way. Timing, as ever, is everything.