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Subject: Re: Mate in 38.

Author: Heiner Marxen

Date: 18:48:06 01/25/01

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On January 25, 2001 at 20:41:50, Paul wrote:

>On January 25, 2001 at 20:31:55, Heiner Marxen wrote:
>
>>On January 25, 2001 at 19:40:58, Paul wrote:
>>
>>>On January 24, 2001 at 19:39:52, Dan Andersson wrote:
>>>
>>>>[D]1R6/6pK/5p2/4p3/1B1p3n/8/p1p1pp2/1k3b2 w - - 0 1
>>>>Krabbé (1985)
>>>
>>>I just tried this position with my program Pretz, after having unsuccesfully
>>>grappled with the mate in 16/20 positions by José Antônio Fabiano Mendes
>>>(I ran out of patience :) and indeed get a mate in 38! It's amazing!
>>>
>>>02:17 WM38 09 1. Ba3+ Ka1 2. Bb2+ Kb1 3. Bxd4+ Kc1 4. Be3+ Kd1 5. Rd8+ Ke1 6.
>>>Bd2+ Kd1 7. Bb4+ Kc1 8. Ba3+ Kb1 9. Rb8+ Ka1 10. Bb2+ Kb1 11. Bxe5+ Kc1 12. Bf4+
>>>Kd1 13. Rd8+ Ke1 14. Bd2+ Kd1 15. Bb4+ Kc1 16. Ba3+ Kb1 17. Rb8+ Ka1 18. Bb2+
>>>Kb1 19. Bxf6+ Kc1 20. Bg5+ Kd1 21. Rd8+ Ke1 22. Bd2+ Kd1 23. Bb4+ Kc1 24. Ba3+
>>>Kb1 25. Rb8+ Ka1 26. Bb2+ Kb1 27. Bxg7+ Kc1 28. Bh6+ Kd1 29. Rd8+ Ke1 30. Bd2+
>>>Kd1 31. Bb4+ Kc1 32. Ba3+ Kb1 33. Rb8+ Ka1 34. Be7 c1=Q 35. Bf6+ Qb2 36. Rxb2
>>>e1=Q 37. Rb8+ Qe5 38. Bxe5x
>>>
>>>I used 96MB hash and full ply extensions on check and one-rep, and some
>>>other tricks :) Does this look ok? Has anyone else tried this position?
>>>
>>>Groetjes,
>>>Paul
>>
>>That looks ok to me.
>>From a 1993 posting of Dennis Breuker:
>>
>>An implementation of proof-number search (a kind of conspiracy-number
>>search) finds the intended solution in 225752 nodes (86 seconds)
>>on a SPARC-2.
>>
>>He gives the exact same solution as you do.
>>
>>Heiner
>
>Thanks for checking that for me. I couldn't believe it at first!!
>
>I really hope some other programmer will also try this, coz I don't use
>proofnumber search, just 'plain' alpha-beta. Didn't know it was possible.

Since the solution line is nearly completely forced, that does not
look so impossible to me.  I would expect that some programs do find this one,
depending on the nature of extensions they do.

>Heiner, is it out of reach for Chest? What do you think?
>
>Paul

Yes, that is absolutely out of reach for Chest.  The problem is not to find
the solution, but to prove all the non-solutions up to a depth of 38.
For depth 9 Chest needs 111 seconds, and increasing the depth by one,
multiplies the search time by 4.  Do the math and be shocked.  ;-)

Heiner



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