Illegal Position Contest!

By "corner configuration" I was referring to either the top left, bottom left, and bottom right corners. I had chosen to refer to it as a "configuration" in an attempt to mislead people into focusing on the bottom right corner specifically >:-)

What I think is very nice is that depending on what move order is played, one out of three of the corners will always be impossible. In fact, the three most optimal methods used to reach the position each have two of the corners reached, but not the final one.

btw is my answer correct?

You are correct that the position is illegal because white is too slow, which is true for when each individual corner is illegal. But can you give an explanation on how the game would play out when each individual corner (top left, bottom left, bottom right) is illegal?

You proved the position is legal with the f7 pawn shifted but didn't completely explain why the original is illegal. Here's how I would explain it. The doubled g-pawns use one of Black's two captures, so the a7 pawn couldn't leave and return to the a-file, meaning the a2 pawn made three captures in promoting on b8. With the one capture by the h2 pawn in promoting on g8, all Black's missing pieces will be gone by the time both bishop promotions occur, and Black will have only four moves left (by pawns on the a and g files) before running out of moves. That's not enough tempo moves to let the promoted bishops and other White pieces get to their final places.

With the f7 pawn moved to f6, the black king can supply the needed tempo moves. Here's a 48-move game for that position.

Black can actually have either 5 or 6 moves remaining after the last white bishop promotes, which would be enough for white to set up the position if those moves didn't interfere with white's movement.

I'm sure that you already know, or if not, are very close to finding it, but can you explain how the interference occurs?

That's right, and it makes the explanation a little trickier than what I had given.

I tried to improve my illegality explanation and concluded that the best White can do is come up just one tempo short. At the end of the game below, the problem position could be reached legally if it were White's move, but Black is out of moves to give White another move.

Cool, this is like that other one where blacks pieces are all crammed up in the upper right corner and black runs out of pawn moves for the position to be legal. What page was that one on? One of the best ones!

I remember that position; the concept of running out of moves was a large inspiration behind the position I made.

Something that I think is really nice is that depending on the moves you choose, one out of three corners is impossible. If white promotes the dark squared bishop last, white can only set up the top left and bottom left corners, but not the bottom right corner. If black tries to get an extra pawn move by keeping the pawn on a6, white's rooks in the top left corner will be one move late. If black allows white to set up the rooks ahead of time, black would have enough moves if white's bishop did not block the last pawn.

The person making mad faces stop

Kxe8#

Kyobir, that's funny, but I'm thinking the best way to get spammers to leave us alone is not to respond to anything they post.

wait that was a spam post???

This position is illegal with white to move.

Then I must have done something illegal when I reached it with White to move.

Dang it. I forgot about a knight going to f8. The idea was supposed to be that if it was white to move, then what was blacks last move. It couldn't have been with the pawns still on the 7th rank or the locked in bishop, so it had to be with the king or the pawn. I thought I had set up a position where blacks king couldn't have been in check the last move as a double check or discovered check would have been impossible (I was wrong lol), so the only possible last move had to be with the b pawn. But then how could White's king have gotten to a8 if the pawn was on b7, as a king can never reach the 8th rank with b,c,f, and g pawns still on the board. Let me try to correct it.

white to move