Originally posted by greenpawn34
It's 2pm. this is taking me longer than I thought it would.
SG: looks like you will have to show us (and then show us an easy retro).
The main goal of retros like this is to take back moves until a King is free. Taking back moves seems weird at first. The 3 weirdest things to watch for are:
1) Checks. You're allowed to walk a King into a check (!), so long as you remove the check with the next retraction. You're NOT allowed to expose the enemy King to check with a retracted move [because that would mean, going forward, that the King could have simply been captured].
2) Special moves. Castling, promotion, and en passant look really weird when played in reverse. Composers love to use them to fool solvers. Be on the lookout for these three things.
3) Un-captures. Don't forget that you can place pieces back on the board by un-capturing them.
Now, to the actual solving. The first thing to do is figure out the pawn captures.
Black is missing 3 units [NNP] and White pawns must have captured 3 units [to reach c3 and c4].
White is missing 3 units [PPP] and Black pawns must have captured 2 units [two sets of doubled pawns showing].
The missing pawns are on the Kingside, and thus could not have been directly captured by other pawns. Instead, many promotions must have taken place, with the promoted pieces either a) sacrificing themselves to pawns or b) replacing other pieces that did.
White is missing Pf2/g2/h2 and Black is missing Pg7. Black must have played ...gxh to get his promotion in. White promoted the f- and g-pawns on f8 and g8 respectively. This supplies the necessary captures.
Promotion paths are important. Note that Black cannot immediately take back the move ...f6xe5, because then wPf2 never could have promoted.
The other pawns cannot immediately uncapture either. Pc4 came from a2, not e2 [because White already has an e-pawn on e6]. Pc3 cannot step back to d2 until Bc1 is home [or else how did he get out?].
So, this is a maddening type of sliding-block problem, like Loyd's 14-15 puzzle. The only way to solve it is to figure out how to shift the pieces around until something frees up [maybe a piece leaves the block].
Next, I'll work on getting a PGN of the solution....