Composed by Tim Krabbe in 1972. White to play and mate in three. This is not legal under current FIDE rules, but it was technically allowed before this problem was composed. The other lines are in the movelist and the last move is missing because the board doesn't accept it.

what the?

Moving your King to d3 via o-o-o-o would be putting him in check. And having a rook on d2 would not be putting the opponent in check.

Am I missing something?

Remember, I couldn't show the last move, so if I showed Kg2 it would mess the puzzle up (it won't show a response to your move if you don't make another move afterwards). I put it in the caption after the last move- he plays Kg2, you play 0-0-0-0. The Rook on e2 (I mistyped, it's e2, not d2) puts the King in check.

hahahah! i get it! it used to be that the rook didnt have to move to castle... and it didnt! now they have to be on the same rank though.... haha

thank god they changed the rules :)

I see - white is castling upwards, and after Kg2, white plays o-o-o-o, which is the king moving two squares up, to e3, and the e8 rook castles down to e2.

Crazy.

They should let that rule come back, it would make games more interesting.

it would be very hard to actually use that kind of castling because your king cant move and the e pawn would have to be underpromoted and usually, promotions come towards the end of the game and by then, king shouldve moved. there also cant be any pieces on the e file nor can the king pass through check when castling. it would be quite difficult to use it.