Originally posted by David113
What was the first move of the black queen?
8 White pieces on board + 7 necessary bP captures + 1 Bc1 dead @ home = 16.
14 Black pieces on board + 0 necessary P caps = 14.
The only possible place wBf1 could have died is g6 - the only light square on which a bP could have captured.
To get bNc1 out of there, I need a wNb1 to shield. No other piece can get in [bNc3 is illegal check to wK].
Retraction starts -1...Re2 -2.h6 Rb1 freeing wR. Now, how do I get my wN back on the board? Pf2 is stuck until Pe3 steps back. Pg5 is reserved for uncapturing on g6. It must be g7xNf6. But I can't retract that until Bf8 is home, and he can't retract home until Pb7 is back, which can't step back until Bc8 is home. And all of that can't be retracted with bK outside the pawn chain. Bc8, Bf8, and Ke8 must all go home before a wN can appear
The resulting intermediate position is:
From here, it could go -1.Nd5 Kd8 -2.Nc3 Ke8 -3.Ra2 Ra1 -4.Nb1 Nd3 -5.Kc1 Nc6 -6.Kd1 Na4 -7.Kc1 Nc3 -8.h4 Nd1 -9.h3 Re1 -10.e2 fe3[+P] -11.h2 ed4[Q or R both work fine].
The new piece on d4 unpromotes on h8 and uncaptures on g5 to fix the pawn structure. The rest of the pieces can easily leave the first rank. The position is unwound.
It's important to note that White must save his h-pawn tempos, thus making it impossible to even think about uncapturing a Q earlier [later?!] on.
bQ never moved.