Shortest-proof-game challenge

#901
This seems illegal: Ba1 must be a promotion, so it must be pawn f7 in disguise, but then it must have captured 5 white men on its path, while only 2 white men are missing.

#901

This position belongs in the Illegal Position thread, not the Shortest Proof Game thread.

#899
Down to 20

That's impressive. Have you made any progress with #893?

#894
Shortened to 60

I'm surprised to see a game that short, although I felt pretty sure you would be able to improve on the 65-move game posted by browni3141 at #70. I would be curious to know if there is anything systematic you do when you work on shortening a proof game.

#907
It is mainly trial and error and some imagination, just like making a plan in a chess game.
#904 is about minimising the non capture moves and finding double duty moves that are both a capture and useful to reach the final positions, like Bxh7, ...Rxb4.
#906 is about the bottleneck b2, where 10 pieces must pass. So it is a matter of finding which pieces get priority on b2.
I guess a systematic approach would be to define all moves to reach the final position and declare these as 'tasks' in MS Project and then for each of them determine which other move has to precede it e.g. Ba3 after b4, O-O-O after Ba3 and Nc3 and Qb4 etc.
The priority for square b2 would be: Bc1, Qd1, Ke1, Ra1, Rh1, Qd8, Ke8, Ra8, Rh8, Bf8.

Thanks.

#911
14 seems the shortest
alternative proof game:

Qf3#

#911
And another one

find the shortest proof game when the 2 knight are switched for white!

10 moves

#904
Down to 19

#919
Another one at 19