Shortest-proof-game challenge

White can mate in one, but the position does not qualify--too many units.

White could also mate in one without the rook and with the bishop at c1, since the black king can't leave the first rank. That one also has too many units.

That feels like it has to be the right solution, but if the rook has to be confined to the first rank, it has to already have moved...

This position meets the requirement, provided White has castling rights. What's left is to see how short a proof game you can make to reach the position.

Since only pieces that move to the first rank are confined, this means that white can move the starting pieces off of the first rank, correct?

Is it required that all pieces have to be confined to the first rank?

Read the problem statement. There's a special condition that a piece moving to the first rank can't leave it. There's a separate condition that at the end, all remaining pieces have to be on the first rank. There's another separate condition that at the end, the remaining pieces on the first rank are confined to the first rank.

Is it that at the end of the checkmate, all pieces have to be confined to the first rank or that at the end of the proof game where White has the opportunity to deliver mate in one all pieces have to be confined to the first rank?

If it's the latter, then that position would not work, because the rook and the king would have to be confined to the first rank and that means that neither could be used in castling.

It means the latter. A piece confined to the first rank has to be on the first rank at the beginning and end of any move it makes.

But how could a rook be confined to the first rank and also be able to participate in castling?

You should be able to figure that out. Maybe it would help if you made a proof game that included castling and played through it, to see if you could pause your game at a time when the rook is not on the first rank.

I call this checkmate position "Rook rage" lol

@5799
First attempt:

@5801 One move faster:

Correct, and currently shortest.

The king and the rook are not confined to the first rank, however, since they never moved at all, and therefore never moved to the first rank.

Those who think they can explain the problem to amrugg are welcome to try. Their chances may not be good.

Wow this is a really fun idea! But I'm not nearly big brained enough to figure any of these out haha

Challenge: find the fastest game that ends with (white/black) playing Kxe1#.

Here's the first idea that came to me.