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        riddles >> easy >> Black's Last Move?
        
(Message started by: THUDandBLUNDER on Sep 3rd, 2003, 9:59pm)
Title: Black's Last Move?
Post by THUDandBLUNDER on Sep 3rd, 2003, 9:59pm
What was Black's last move?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 3:40am
Let me ask a question to clarify the rules of your reconstruction problems:
You're looking for a unique solution, right? I mean one where the moves are forced. Otherwise, -1. ... Kg1-h2 would be too obvious a possibility, but that wouldn't be forced as Black could also have captured on g2.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 7:53am
Wowbagger, GIVEN the above board position, there is only ONE possible last move by Black.

That's NOT the same as saying that the move was forced.
Title: Re: Black's Last Move?
Post by Sir Col on Sep 4th, 2003, 8:27am
I don't know how you use the chess notation, but... [hide]after white castled with the king, the black king was in check, so it was forced to move from G1 to H2. But, as wowbagger said, I don't know why the king didn't capture the pawn[/hide]?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 8:29am

on 09/04/03 at 07:53:28, THUDandBLUNDER wrote:
Wowbagger, GIVEN the above board position, there is only ONE possible last move by Black.

I dont think so. How about [hide]-2. ... Qh4xQd1+ -1. Rg1xd1 with Black to move - you didn't say the last move played was a Black move[/hide]!
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 8:32am

on 09/04/03 at 08:27:57, Sir Col wrote:
I don't know how you use the chess notation

Castling  to the Kingside is 0-0, to the Queenside (Queen's side?), 0-0-0.


Quote:
[the black king] was forced to move from G1 to H2.

As you say yourself, he could have captured on g2, so the move wasn't forced.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 8:34am

Quote:
you didn't say the last move played was a Black move!

OK, what move did Black JUST play??

Given the above board position, his last move was forced.
Given the previous board position, his next move is NOT forced.

I don't think many solvers here have the hang of these retro puzzles yet.
They are not about 'best' moves, but about possible moves.
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 8:39am

on 09/04/03 at 08:34:49, THUDandBLUNDER wrote:
OK, what move did Black JUST play??

What are you aiming at?
The original question was " What was Black's last move?".
My answer: I don't know. There are too many possibilities, becase I don't know whether it's White to move now, which would imply that the immediately preceding move would have been made by Black... [hide]...and would have been Kg1-h2[/hide]
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 8:41am
BLACK played last.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 8:41am
The last move was by BLACK.
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 8:45am

on 09/04/03 at 08:34:49, THUDandBLUNDER wrote:
I don't think many solvers here have the hang of these retro puzzles yet.

That's definitely true! :D
Maybe you should expound on the rules to this sort of puzzle in a separate thread in the FAQ section. You could then link to this thread to help beginners.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 8:54am

Quote:
Maybe you should expound on the rules to this sort of puzzle in a separate thread in the FAQ section that you could link to.

Retrograde Analysis is a genre of chess problems where the legality of the position is a key element.
A position is legal if it can be reached through a legal chess game (no matter how weird).

Retros may ask (for example) for a mate in two, but the main content is in analysing the history of the position.
This is essentially a matter of logical reasoning.

For complete beginners, the Sherlock Holmes book by Raymond Smullyan is a good start.

Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 8:57am

on 09/04/03 at 08:41:09, THUDandBLUNDER wrote:
BLACK played last.


on 09/04/03 at 08:41:50, THUDandBLUNDER wrote:
The last move was by BLACK.

You think I would have found only one of these formulations not clear-cut enough? ;)

So the correct answer is Kg1-h2?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 9:04am

on 09/04/03 at 08:54:18, THUDandBLUNDER wrote:
For complete beginners, the Sherlock Holmes book by Raymond Smullyan is a very good start.

Thanks for the recommendation, I put it on my list of books to buy.
Title: Re: Black's Last Move?
Post by Kitty on Sep 4th, 2003, 9:05am
Yeah but would not the tower have eaten it, i mean look at where the tower is now, how did it get there? If you get what i'm saying :-/
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 9:05am

Quote:
You think I would have found only one of these formulations not clear-cut enough?

Why did I post two? Because I couldn't think of anymore.  :D


Quote:
So the correct answer is Kg1-h2?

No. (Hehe.) There is a good reason why not.
Consider what White must have played before that move (Kg1-h2), and study the position.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 9:10am

Quote:
Yeah but would not the tower have eaten it, i mean look at where the tower is now, how did it get there?

Kitty, [hide]there exists a 'double move' in chess called 'castling'.   :)[/hide]
Title: Re: Black's Last Move?
Post by Kitty on Sep 4th, 2003, 9:24am
Fine, I don't play chess, i just guessing.  :P
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 9:52am

on 09/04/03 at 09:05:45, THUDandBLUNDER wrote:
Consider what White must have played before that move (Kg1-h2), and study the position.

Okay, I think I'm starting to really appreciate this one.  :D
Here's what I have arrived at by now, using my retro-notation - if there is some other, standard way, let me know:
[hide]
-1. ... Kg1-h2
-2. 0-0-0 Kh2-g1  (forced)
The only White pieces allowed to have moved further back in the past are the Knight and the former f- or h-Pawn (otherwise White would have lost the right to castle).
I claim that this is not a legal position, as the Black King could not have arrived at h2: Ke1 and Pg2 block all squares but g3. This last one was controlled by the f- or h-Pawn, unless the capture on g3 took place before the Black King got through. In this case, however, the Black King is also blocked from arriving at h2 (without contradicting the final position).[/hide]
Boy, this is really cumbersome to explain! - Or is it just me?
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 10:03am
Yes, wowbagger, you are on the right track!

Your conclusion?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 4th, 2003, 10:12am

on 09/04/03 at 10:03:13, THUDandBLUNDER wrote:
Your conclusion?

That [hide]the position isn't legal[/hide]?
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 10:29am

Quote:
That the position isn't legal?

Now that wouldn't be much of a chess puzzle, would it?

The above board position is a legal one and Black has JUST played a legal move.
Title: Re: Black's Last Move?
Post by visitor on Sep 4th, 2003, 1:41pm
I assume his last move was g1 to h2. But the only way for the black king to get to g1 is if the castling move occurred early. Then there must have been a white piece between him and the rook. It must have been a knight that moved to h2, and the black king knocked it off on his final turn.
Title: Re: Black's Last Move?
Post by visitor on Sep 4th, 2003, 1:56pm
Sorry, my solution doesn't work. It doesn't leave black with any valid move on its turn right before the knight moved to h2. Back to the drawing board.
Title: Re: Black's Last Move?
Post by visitor on Sep 4th, 2003, 2:09pm
Let's say there was a bishop on e1 when the black king moved in (d3,e2,f1,g1). Bf2...Kh2.
Be3 where it was knocked off by some black piece. Nxe3
Black moved its only other piece somewhere. white Nf1. Black moves that other piece to c1, where it's knocked off by the white king. Then black Kg1, Nh2, Kxg2.
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 4th, 2003, 8:32pm

Quote:
Then there must have been a white piece between him and the rook. It must have been a knight that moved to h2, and the black king knocked it off on his final turn.

You are getting there, visitor.

Wowbagger proved that if Black's last move was Kg1-h2, White's previous move must have been 0-0-0
(that is, castles queenside). However, the resulting position is illegal as the Black king is now in a cage
formed by the White king at e1 (which hasn't moved) and the pawns on g2 and g3. He wrongly concluded
that the original board position is illegal. All we can conclude from his analysis is that Kg1-h2 was NOT
Black's last move, and that we do not need to retract 0-0-0 for White. Now, with no White king at e1,
there is no cage.
Title: Re: Black's Last Move?
Post by BNC on Sep 5th, 2003, 4:27am
IS the game based on "current" chess rules? That is, when a black pawn reaches row 1, can it change to a white piece, or just a black piece?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 5th, 2003, 5:05am

on 09/04/03 at 14:09:30, visitor wrote:
Let's say there was a bishop on e1 when the black king moved in (d3,e2,f1,g1). Bf2...Kh2.
Be3 where it was knocked off by some black piece. Nxe3
Black moved its only other piece somewhere. white Nf1.

Check!


on 09/04/03 at 20:32:39, THUDandBLUNDER wrote:
You are getting there, visitor.

Wowbagger proved that if Black's last move was Kg1-h2, White's previous move must have been 0-0-0
(that is, castles queenside). However, the resulting position is illegal as the Black king is now in a cage
formed by the White king at e1 (which hasn't moved) and the pawns on g2 and g3. He wrongly concluded
that the original board position is illegal. All we can conclude from his analysis is that Kg1-h2 was NOT
Black's last move, and that we do not need to retract 0-0-0 for White. Now, with no White king at e1,
there is no cage.

So the last move by Black was not Kg1-h2, which implies that his last move was not by his King - or am I mistaken here once again? Anyway, any other pieces he might have moved would still be on the board, as there is no legal move off of the board.


on 09/05/03 at 04:27:14, BNC wrote:
IS the game based on "current" chess rules? That is, when a black pawn reaches row 1, can it change to a white piece, or just a black piece?

Oh, c'mon! Not again!? :o
Please spare me from having to rant about the difference between history-of-the-rules riddles and chess riddles. >:(
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 5:05am
BNC, all retro puzzles are based on standard chess rules. Here, promotion is not an issue. But castling is.

Title: Re: Black's Last Move?
Post by wowbagger on Sep 5th, 2003, 5:14am

on 09/05/03 at 05:05:41, THUDandBLUNDER wrote:
BNC, all retro puzzles are based on standard chess rules.

That's reassuring. :)
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 6:23am

Quote:
So the last move by Black was not Kg1-h2, which implies that his last move was not by his King - or am I mistaken here once again?

What is the notation for capturing?
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 7:13am

Quote:
Let's say there was a bishop on e1 when the black king moved in (d3,e2,f1,g1). Bf2...Kh2.
Be3 where it was knocked off by some black piece. Nxe3
Black moved its only other piece somewhere. white Nf1. Black moves that other piece to c1, where it's knocked off by the white king. Then black Kg1, Nh2, Kxg2.

I will just say that this is.......wrong.
I won't say anymore as I don't want to upset Icarus - especially now that he is a moderator.  ;)
Title: Re: Black's Last Move?
Post by visitor on Sep 5th, 2003, 7:18am
I really should give up on these chess puzzles, but I'll take one more stab at it
The castling took place earlier. Black moved a rook to e1 (or a white bishop sat there, which the black rook knocked off after the king moved into position). He safely moves his king in to g1. From that point it's rook to f1, white Ne3, Kh2, Nxf1, Kg1, Nh2, Kxg2. (doesn't make much sense, but it's legal, I think)
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 7:19am

Quote:
Then there must have been a white piece between him and the rook. It must have been a knight that moved to h2, and the black king knocked it off on his final turn.

This analysis seems OK to me.


Quote:
Sorry, my solution doesn't work. It doesn't leave black with any valid move on its turn right before the knight moved to h2. Back to the drawing board.

But here you seem to overlook the fact that the White knight may, indeed must, have captured something.
Title: Re: Black's Last Move?
Post by wowbagger on Sep 5th, 2003, 7:43am

on 09/05/03 at 06:23:34, THUDandBLUNDER wrote:
What is the notation for capturing?

Boy, do I feel stupid!
Next try:
[hide]-1. ... Kg1xh2
-2. Nf1xh2+ Rh8xQh2 (or -2. ... Ng4xQh2)[/hide]
How's that?
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 8:21am
Eureka! You got it, wowbagger. And I thought that this puzzle was Easy.
(It is not necessary for the Black piece to capture anything on h2.)

I wonder how visitor is getting on with his bishops.  ;D
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 8:40am
If we started with the position below, the game would go:
[hide]
1. Nh1  Rh2
2. Nxh2+ Kxh2
[/hide]
In order to arrive at the original puzzle position, all the moves are forced.
Title: Re: Black's Last Move?
Post by Sir Col on Sep 5th, 2003, 9:07am
But surely after white knight moves to h1, the rook or king would take it?
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 9:18am

Quote:
But surely after white knight moves to h1, the rook or king would take it?

AAAARRGH!!!   >:(  

Aren't threads meant to be read from the beginning rather than from the end?
Title: Re: Black's Last Move?
Post by wowbagger on Sep 5th, 2003, 9:22am
;D ;D
Title: Re: Black's Last Move?
Post by Sir Col on Sep 5th, 2003, 10:06am

on 09/05/03 at 09:18:46, THUDandBLUNDER wrote:
AAAARRGH!!!   >:(  

Temper, temper!

I wasn't serious about suggesting that the king or rook should have taken the knight, after all it would have been much better for the rook to have put the white king in check by moving to c8.  So why didn't black do that?   ;D
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 10:53am

Quote:
I wasn't serious about suggesting that the king or rook should have taken the knight, after all it would have been much better for the rook to have put the white king in check by moving to c8.  So why didn't black do that?    

Yes, I have to hand it to you, Sir Col, that's very subtle.

After the fingerfehlur Nh1, rather than immediately capture the errant knight on h1, you would calmly play the zweischenzug Rc8+, while defying anybody to utter the old adage "Patzer sees a check, gives a check."  :D
Title: Re: Black's Last Move?
Post by wowbagger on Sep 5th, 2003, 11:58am
T&B, I suppose you mean fingerfehler and zwischenzug. :)
Title: Re: Black's Last Move?
Post by THUDandBLUNDER on Sep 5th, 2003, 12:10pm

Quote:
T&B, I suppose you mean fingerfehler and zwischenzug.

Yes. Thanks, wowbagger.

Trust me to check my spelling by choosing the ONLY site on the Web which spells them both wrongly!

www.theopenfile.com/articles/lingo.htm
Title: Re: Black's Last Move?
Post by towr on Sep 6th, 2003, 5:19am
how did the king ever get to g1 in the first place?
Title: Re: Black's Last Move?
Post by Sir Col on Sep 6th, 2003, 6:17am
That was my initial reaction when I saw the problem, but as T&B has said since, and highlighting my ignorance over these types of problem, "Retrograde Analysis is a genre of chess problems where the legality of the position is a key element.  
A position is legal if it can be reached through a legal chess game (no matter how weird)."

It is possible IF... the black king was on d3 and moved diagonally to f1, but this would depend of two things: (i) there was a white piece, like a bishop, on e1 (blocking the rooks line of attack on row 1, and, (ii) the white pieces sit back and do nothing troublesome whilst the black king moves into position.


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