A retrograde chess problem
Problem statement
White to play and mate in two moves
First hint: show
Second hint: show
Third hint: show
Solution to metapuzzle: show
Solution to puzzle: show
O-O-O
Where did the two white rooks start the game? There are two possibilities:
- They both started as rooks. One of them escaped from the lower right
corner of the board by the white king moving. Therefore White can't castle.
- At least one of them is a promoted pawn. It must have left the eighth
rank via one of d8, f8, or h8. Any of these would involve either the black
king or the black rook moving. In all these cases, Black can't castle.
So it's possible that White can castle, and it's possible that Black can
castle, but it's not possible that both can castle.
White can play O-O-O, and does. Now Black can't play O-O. Whatever else he does,
White plays Rd8#.
Comment: show
This puzzle is from the site linked below. Also on that site are
this document
and
this
one, which both support the view "a player can castle if and only
if there's no proof that they can't". Both documents were created 50
years after the puzzle was composed.
Source: janko.at,
puzzle no. 11
This is one of several pages on puzzles and metapuzzles
.