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Subject: Re: Mate that every program will solve...

Author: Heiner Marxen

Date: 14:46:51 04/17/01

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On April 17, 2001 at 14:45:49, Tim Foden wrote:

>On April 17, 2001 at 11:13:02, Heiner Marxen wrote:
>
>>On April 17, 2001 at 07:43:30, leonid wrote:
>>
>>>Hello!
>>>
>>>If you like to solve very "regular" mate position, then you have one.
>>>
>>>[D]R7/4P1Pq/1rR5/2pb1rnk/1Q3B2/4Nn2/1PB2Np1/2K1b1Q1 w - -
>>>
>>>Please, indicate your result.
>>>
>>>Thanks,
>>>Leonid.
>>
>>According to Chest there are two key moves for mate in 7 moves:
>>
>>Qxg2 Bd2+ Qxd2   Bxc6 g8=Q   Qxg8  Rxg8   Bd5  e8=Q+  Bf7  Nxf5   Nd4  Rxg5#
>>Rh8  Bd2+ Qxd2   Be4  e8=Q+  Rf7   Qxf7+  Nxf7 Qd5+   Bf5  Rxh7+  Nh6  Rhxh6#
>
>This is worrying to me, as Green Light thinks it finds another mate in 7, which
>begins with e8=Q+

That should worry you or me, since one program has a bug, but we do not yet
know which program really has the bug.

>As I understand it Chest finds all the mates, doesn't it?

It is supposed to do so.  That is its purpose, yes.


>Here is a snippet of GLC's analysis (v2.14-pr7, hash 48M, Duron 880MHz):
>
>  8  26.25 320.983  16660k  Bd1 Bd2+ Qxd2 Rxc6 Qh2+ Kg6 e8=Q+ Bf7 Qxh7+ Kxh7
>                              g8=Q+ Bxg8 Qxg8+ Kh6 Nxf5+ Kh5 Qxg5#
>  8  51.62 320.987  38611k  e8=Q+ Bf7 Qxg2 Rxc6 Qg4+ Kg6 Qxf5+ Kh5 Qexf7+ Rg6
>                              Qg4+ Kh6 Nf5# <ht>
>  8  55.91 320.987  42689k  e8=Q+ Bf7 Qxg2 Rxc6 Qg4+ Kg6 Qxf5+ Kh5 Qexf7+ Rg6
>                              Qg4+ Kh6 Nf5# <ht>
>  9   1:00 320.987  47464k  e8=Q+ Bf7 Qxg2 Rxc6 Qg4+ Kg6 Qxf5+ Kh5 Qexf7+ Rg6
>                              Qg4+ Kh6 Nf5# <ht>
>  9   1:31 320.987  77248k  e8=Q+ Bf7 Qxg2 Rxc6 Qg4+ Kg6 Qxf5+ Kh5 Qexf7+ Rg6
>                              Qg4+ Kh6 Nf5# <ht>
> 10   1:51 320.987  96843k  e8=Q+ Bf7 Qxg2 Rxc6 Qg4+ Kg6 Qxf5+ Kh5 Qexf7+ Rg6
>                              Qg4+ Kh6 Nf5# <ht>
>
>Cheers, Tim.

Ok, I looked into this variant.
After 1.e8=Q+ Bf7 2.Qxg2 Rxc6 we have
[D]R3Q3/5bPq/2r5/2p2rnk/1Q3B2/4Nn2/1PB2NQ1/2K1b3 w - -
which according to Chest indeed leaves a mate in 5, with this PV:
 Qg4+ Kg6 Qxf5+ Kh5  Qexf7+ Rg6 Qg4+  Kh6 Nf5#
That is exactly your variant.

But Chest chooses another second black move: Bd2+.
After 1.e8=Q+ Bf7 2.Qxg2 Bd2+ we have
[D]R3Q3/5bPq/1rR5/2p2rnk/1Q3B2/4Nn2/1PBb1NQ1/2K5 w - -
and Chest does not find a mate in 5, here.  Here is its refutation table:
refu  1: Qxd2    Rxc6    [  4-]
solu          1: Bxe8    [  1+]
solu          2: Nxd2    [  1+]
solu         11: Nd4     [  1+]
solu         12: Ne5     [  2+]
solu         13: Ne1     [  1+]
solu         14: Ng1     [  1+]
solu         15: Qxg7    [  1+]
solu         16: Ra6     [  1+]
refu  2: Kd1     Rxc6    [  4-]
solu          3: Bxe8    [  1+]
solu          4: cxb4    [  1+]
solu          5: Bxb4    [  1+]
solu          6: Rxb4    [  1+]
solu         17: Ne4     [  1+]
solu         18: Rd5     [  1+]
solu         19: Nh3     [  1+]
solu         20: Ra6     [  1+]
refu  3: Kb1     Rxc6    [  4-]
solu          7: Bxe8    [  1+]
solu          8: cxb4    [  1+]
solu          9: Bxb4    [  1+]
solu         10: Rxb4    [  1+]
solu         21: Ne4     [  1+]
solu         22: Ra6     [  1+]
solu         23: Qxg7    [  1+]

Hope this helps you to pin this down further.

If you still find a short enough mate, here, please post it, and I will
answer with the variant Chest uses to refute it.  In the end we will see
who errs, when the mates become short enough that we poor humans see it
ourselves.

Heiner



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