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Chess

cinelli
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Chess

#440789

Postby cinelli » September 8th, 2021, 9:14 pm

We haven't had a chess problem for some time:

.  --- --- --- --- --- --- --- ---
8 | | | | | | | | k |
--- --- --- --- --- --- --- ---
7 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
6 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
5 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
4 | | | | | | | | |
--- --- --- --- --- --- --- ---
3 | | | | | | | | |
--- --- --- --- --- --- --- ---
2 | | | | | | | | |
--- --- --- --- --- --- --- ---
1 | | | | | | | | K |
--- --- --- --- --- --- --- ---
a b c d e f g h

White to move has three queens against a lone black king at h8. Checkmate in seven moves, but there’s a catch. The three queens are allowed to move only on the extreme left hand file from a1 to a8. You have a choice of two alternatives at white’s first move. All the other moves have to be precise, and all black’s replies are forced.

Cinelli

UncleEbenezer
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Re: Chess

#440825

Postby UncleEbenezer » September 8th, 2021, 11:49 pm

cinelli wrote:We haven't had a chess problem for some time:

Might I humbly suggest it's a stretch calling this "a chess problem"?

Looks far too easy. What am I missing?

1. Five moves of the white king bring it to your choice of g6 or h6.
2. A queen on a3, together with the one on a7, trivially ensure all black moves are forced. It can move there on the first or second move.
3. That's six moves. Mate in 7 is the queen moving to a8, now that the white king (in the corner after six moves) blocks escape to row 7.

UncleEbenezer
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Re: Chess

#440828

Postby UncleEbenezer » September 9th, 2021, 12:09 am

UncleEbenezer wrote:
cinelli wrote:We haven't had a chess problem for some time:

Might I humbly suggest it's a stretch calling this "a chess problem"?

Looks far too easy. What am I missing?

1. Five moves of the white king bring it to your choice of g6 or h6.
2. A queen on a3, together with the one on a7, trivially ensure all black moves are forced. It can move there on the first or second move.
3. That's six moves. Mate in 7 is the queen moving to a8, now that the white king (in the corner after six moves) blocks escape to row 7.

Bah. Edited that to add the parentheses "(in the corner ...)" without reading what I was updating. Wrong king! But it's obvious enough what I meant.

9873210
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Re: Chess

#440850

Postby 9873210 » September 9th, 2021, 7:32 am

UncleEbenezer wrote:Might I humbly suggest it's a stretch calling this "a chess problem"?

Looks far too easy. What am I missing?


Perhaps this:
cinelli wrote: You have a choice of two alternatives at white’s first move. All the other moves have to be precise


1. Five moves of the white king bring it to your choice of g6 or h6.
The white king's moves seem very imprecise, it can meander up the board in many different ways.

Gengulphus
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Re: Chess

#440909

Postby Gengulphus » September 9th, 2021, 11:09 am

cinelli wrote:We haven't had a chess problem for some time:

.  --- --- --- --- --- --- --- ---
8 | | | | | | | | k |
--- --- --- --- --- --- --- ---
7 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
6 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
5 | Q | | | | | | | |
--- --- --- --- --- --- --- ---
4 | | | | | | | | |
--- --- --- --- --- --- --- ---
3 | | | | | | | | |
--- --- --- --- --- --- --- ---
2 | | | | | | | | |
--- --- --- --- --- --- --- ---
1 | | | | | | | | K |
--- --- --- --- --- --- --- ---
a b c d e f g h

White to move has three queens against a lone black king at h8. Checkmate in seven moves, but there’s a catch. The three queens are allowed to move only on the extreme left hand file from a1 to a8. You have a choice of two alternatives at white’s first move. All the other moves have to be precise, and all black’s replies are forced.

I have to admit to not being at all certain what the word "precise" means in the context of chess problems.

It's clear that there are multiple sequences of moves that force all of black's responses, keep the queens on the a file, and lead to mate in 7. Basically, any sequence that matches the template:

1. Qa3 Kg8
2. K(g|h)2 Kh8
3. K(f|g|h)3 Kg8
4. K(e|f|g|h)4 Kh8
5. K(f|g|h)5 Kg8
6. K(g|h)6 Kh8
7. Qa8 mate

matches those conditions. As UncleEbenezer indicates, that's far too easy, and since it meets every condition in the problem posed except the one about every move other than the first one being "precise", it seems pretty clear that it doesn't meet that condition - probably because there are multiple sequences of moves that fit that template.

My best guess is that the problem's statement about moves being "precise" means that white's first move is required to be one that, once played, only allows mate to be achieved in 7 (while forcing every black move and keeping the queens on the a file) with a unique sequence of moves, and that there are two available first moves for white that meet that condition. Is this correct?

If so, an immediate consequence of the above template producing multiple move sequences that 'solve' the problem is that neither of those first moves is Qa3, and the trivial extra observation that its first two moves Qa3 and K(g|h)2 can be swapped without altering the fact that it produces multiple such move sequences means that neither of those first moves can be either Kg2 or Kh2.

Alternatively, if not, I really need to be told exactly what the "precise" condition means to be able to understand the problem, let alone solve it!

Gengulphus

cinelli
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Re: Chess

#440913

Postby cinelli » September 9th, 2021, 11:15 am

UncleEbenezer wrote:Looks far too easy. What am I missing?


Very sorry. I agree with your analysis. I should have added an extra condition - the white king plays no part in the solution.

Cinelli

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Re: Chess

#440953

Postby mc2fool » September 9th, 2021, 12:50 pm


Gengulphus
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Re: Chess

#440972

Postby Gengulphus » September 9th, 2021, 2:40 pm

Got it!

1. Qa3 or Qa4; Kg8 (forced)
2. Qa1; Kf8 (forced)
3. Qa1-a2; Ke8 (forced)
4. Qa2-a3; Kd8 (forced)
5. Qa6-a4; Kc8 (forced)
6. Qa8; Kc7 (forced)
7. Qa4-a7 mate

Not all that difficult once one realises that one needs to bring the black king over to the left side of the board, so that the queens' diagonal attacks can make as effective a contribution as possible to the mating net.

Gengulphus

cinelli
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Re: Chess

#441213

Postby cinelli » September 10th, 2021, 11:03 am

Very well solved, Gengulphus. This is a problem by Florencio de Mordes. I especially like move 5 as the black king is shepherded towards the corner. Again, sorry about the confusion of the white king.

Cinelli


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