Mate in 2

Obviously not mine:



White to move

Originally posted by Peakite
Obviously not mine:

[fen]4k2r/p1p1p1p1/1p2P3/8/3R4/6P1/5P1P/R3K3[/fen]

White to move

1. 0-0-0!! with the inevitable threat of Rd8#

I can't see a reason why that move couldn't be played.

I don't see how you can prove that black can't castle

Originally posted by Mephisto2
I don't see how you can prove that black can't castle

Easy. If White may play 0-0-0, then Rd4 isn't the original Rh1 (which must have died in the SE corner), but a promoted Rook. The promoted Rook can only exit the 8th rank via d8, f8 or h8, all of which displace Black's K or R.

I might not have the hang of this yet.

I get:
If black may not caslte and white can not castle, there is 1 solution. (Rad1)
If black may not castle but white may, there are 2 solutions. (Rad1 and 0-0-0)
If black may castle, there is no solution.
Assuming this is supposed to have 1 solution only, the solution must be Rad1.

Where is the flaw in this logic?

Originally posted by jfkjmh
I might not have the hang of this yet.

I get:
If black may not caslte and white can not castle, there is 1 solution. (Rad1)
If black may not castle but white may, there are 2 solutions. (Rad1 and 0-0-0)
If black may castle, there is no solution.
Assuming this is supposed to have 1 solution only, the solution must be Rad1.

Where is the flaw in this logic?

Also - doesn't Ra7 followed by Ra8 do the job (assuming that black can't castle)? I still don't get how to deal with the threat of castling, though!

Originally posted by jfkjmh
I might not have the hang of this yet.

I get:
If black may not caslte and white can not castle, there is 1 solution. (Rad1)
If black may not castle but white may, there are 2 solutions. (Rad1 and 0-0-0)
If black may castle, there is no solution.
Assuming this is supposed to have 1 solution only, the solution must be Rad1.

Where is the flaw in this logic?

Your problem is with the case:

"Black may castle".

In this position, you can't disprove this case, unless you are allowed proof A Posteriori, or proof after the fact. From retrograde analysis, we know that only one side may castle. By castling first, White deprives Black of the right to do so.

Not everyone is comfortable with the idea of AP proof, but that is how the logic of this problem is meant to work.

Originally posted by Diapason
Also - doesn't Ra7 followed by Ra8 do the job (assuming that black can't castle)? I still don't get how to deal with the threat of castling, though!

1.Rxa7? does not prove that Black can't castle. 1.0-0-0! does.

Edit: Perhaps this will help people understand AP proof. Imagine that you are a third-party observer to the game. You just walked in the room, and the players were at the position in the diagram. You are allowed to assume the position is legal. Once White plays 1.0-0-0, you know for certain that he has a forced mate the next move. If he had played 1.Rad1, you still would not know for sure.

Originally posted by BigDoggProblem
Your problem is with the case:

"Black may castle".

In this position, you can't disprove this case, unless you are allowed proof A Posteriori, or proof after the fact. From retrograde analysis, we know that only one side may castle. By castling first, White deprives Black of the right to do so.

Not everyone is comfortable with the idea of AP proof, but that is how the logic of this problem is meant to work.

Thank you, I understand now. Is AP common knowledge on "mate in ..."problems or should it be stated explicitly beforehand?

Originally posted by jfkjmh
Thank you, I understand now. Is AP common knowledge on "mate in ..."problems or should it be stated explicitly beforehand?

Article 16, section 2 of the FIDE codex of composition states:

"(2) In case of mutual dependency of castling rights of each party, the party exercising this right first is entitled to do so."

http://www.saunalahti.fi/~stniekat/pccc/codex.htm

Edit: But it also states:

"Other conventions (which also affect other rights to move) should be expressly stipulated, for example:

(a) If an en-passant capture in the course of the solution has to be legalized by a subsequent castling (for example AP)."

So, the answer is: sometimes it is understood, sometimes it should be expressly stipulated. 😛

Originally posted by kbaumen
1. 0-0-0!! with the inevitable threat of Rd8#

I can't see a reason why that move couldn't be played.

first of all, 0-0-0 can simplely be just move the rook. also, rxa7 can threat. there is no # in 2 if black can castle.

Originally posted by jfkjmh
I might not have the hang of this yet.

I get:
If black may not caslte and white can not castle, there is 1 solution. (Rad1)
If black may not castle but white may, there are 2 solutions. (Rad1 and 0-0-0)
If black may castle, there is no solution.
Assuming this is supposed to have 1 solution only, the solution must be Rad1.

Where is the flaw in this logic?

no no, rxa7 alsoworks

Originally posted by Ason Pigg2
first of all, 0-0-0 can simplely be just move the rook. also, rxa7 can threat. there is no # in 2 if black can castle.

First of all, read the thread.