Shortest-proof-game challenge

17.5 is my best attempt so far:

Shorter is possible.

Unique SPG in 16.5.

Non-unique SPG in 14.0.

6660 test

I'm not sure what that means. EvinSung would have given a move count if wanting to have #6660 computer-tested.

I'm guessing 45.5 moves is the intention, but if it is, it's cooked.

Non-unique SPG in 21.0.

Will this work?

Another one. I’m fairly confident that these SPGs are unique this time, although that’s what I thought with my previous positions.

Unique SPG in 19.0.

Unique SPG in 25.0.

Finally! I was right about these SPGs being unique. The idea for both positions was the oscillation of the queen, although I was unsure about the 2nd one. I’ve seen this oscillation idea before with knights, rooks, kings, and even bishops in other proof games, but never with queens.

One last position from me. Made slight changes to extend the proof game a bit:

Unique SPG in 27.0.

I remember when you were struggling to find a 22-move unique SPG and when you made it, said you would probably stop there. But you're on a roll now and I wonder if you're thinking about challenging EvinSung's current 41.0 record.

My proof games are merely exploring different themes (e.g. Schnoebelen, Pronkin) rather than going for length. I currently don't have any ideas for an SPG longer than 41.0 moves, nor do I have any plans of doing so. Even if I did try to go for the longest SPG, I would probably end up failing because I would not have enough moves for either side, so I'll leave EvinSung's record alone. However, I do enjoy making these shorter proof games with some thematic play.