Shortest-proof-game challenge

First position, non-unique SPG in 23.0.

Took me a while to make a position with this "theme", if you will

Should be a unique 17.5 PG. All white pawns on the 3rd rank, very nice.

Unique SPG, confirmed by Stelvio.

Why stop at the 3rd rank? Here's one with the pawns on the 5th.

Solution is unique, verified by Jacobi

20.0 moves

What is the fastest unique SPG that can accomplish this theme (in general)?

E. Minerva, 2005

Leither, does the theme require a double check by an en passant capture? If so, you're looking for something shorter than your position's unique SPG in 15.5.

Theme is Valladao task; the double check is only to force an en passant

So it needs castling, en passant, and promotion. The 8.5 move game at #6799 should be the winner.

I'd like to see if I can find a unique SPG shorter than yours that ends with double check by en passant capture, even if it's not a known task. Do you have any ideas?

I've located a position by Gerd Wilts and Norbert Geissler, 1996, that does the trick.

Proof game in 7.0.

@6803

Good job.

thanks for the challenge : )

#6799

Very neat solution! Forced to ep without using any double checks or trapped bishops

Possibly unique extension:

18.0 moves.

Interestingly, each side can theoretically reach their own position in 17 moves, but all the interferences between the pieces make this practically impossible. And if only white wastes a move for 17.5, there’s still problems with pieces clashing (at least what I think), so black must waste a move too.

The extension is cooked though. The bQ can go directly to a5, allowing for several SPGs in 23.5.