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Subject: Re: Mate in 46

Author: Heiner Marxen

Date: 15:18:55 01/31/01

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On January 31, 2001 at 17:54:13, Dann Corbit wrote:

>On January 31, 2001 at 10:25:50, Heiner Marxen wrote:
>
>>On January 30, 2001 at 17:15:45, Olaf Jenkner wrote:
>>
>>>Perhaps I had in mind this problem what is easily to prove that there is
>>>no shorter mate.
>>>
>>>Pervakow/Sum.  #46
>>>[D]2N5/p4P2/p4RqP/P2krb2/5RNK/2PPBnP1/3P1pP1/5Q2 w - - 1 0
>>
>>Yes, that can be.  Much to my own surprise Chest really proves this
>>as a mate in 46 moves, and needs just 8.2 seconds (K7/600) for it.
>>It gives the following PV:
>>
>> 1. gxf3  Qh5+
>> 2. Kxh5  Bg6+
>> 3. Kxg6  Rg5+
>> 4. Kh7   Rg7+
>> 5. Kh8   Rh7+
>> 6. Kg8   Rh8+
>> 7. Kg7   Rh7+
>> 8. Kf8   Rh8+
>> 9. Ke7   Re8+
>>10. Kd7   Rd8+
>>11. Kc7   Rd7+
>>12. Kb8   Rb7+
>>13. Ka8   Rb8+
>>14. Kxa7  Rb7+
>>15. Kxa6  Ra7+
>>16. Kb5   Rxa5+
>>17. Kb4   Rb5+
>>18. Ka3   Rb3+
>>19. Ka2   Rb2+
>>20. Ka1   Ra2+
>>21. Kb1   Rb2+
>>22. Kc1   Rb1+
>>23. Kc2   Rb2+
>>24. Kd1   Rb1+
>>25. Ke2   Re1+
>>26. Kxf2  Re2+
>>27. Kg1   Rg2+
>>28. Kh1   Rg1+
>>29. Kh2   Rh1+
>>30. Kg2   Rg1+
>>31. Kh3   Rxg3+
>>32. Kh4   Rh3+
>>33. Kg5   Rh5+
>>34. Kg6   Rg5+
>>35. Kh7   Rg7+
>>36. Kh8   Rh7+
>>37. Kg8   Rh8+
>>38. Kg7   Rh7+
>>39. Kg6   Rg7+
>>40. Kh5   Rg5+
>>41. Kh4   Rh5+
>>42. Kg3   Rh3+
>>43. Kf2   Rxf3+
>>44. Ke2   Rf2+
>>45. Nxf2  Ke5
>>46. R4f5#
>>
>>I even had to increase the maximal allowed depth in Chest (formerly 30).
>>Quite an exceptional position!
>>
>>Can the playing programs solve this, also?  I suspect so.
>
>4 seconds on my machine.  I made this change:
>
>#ifndef MAX_ANA_DEPTH
># define MAX_ANA_DEPTH  ((255 >> 2)-1)      /* CF: maximum depth (a 2 moves) of
>analysis */
>#endif

Perfect!

>can MAX_ANA_DEPTH be increased further without major surgery?

I don't know, offhand.  I have to look deeper.  There could be problems...

Just now it would not compile, because ANA_MANY should be at least as large,
which together with two more bits shall fit into a single byte in the TT...
well, "major surgery" will be needed.

>2N5/p4P2/p4RqP/P2krb2/5RNK/2PPBnP1/3P1pP1/5Q2 w - - acn 571764; acs 4; bm gxf3;
>ce 32676; dm 46; pv gxf3 Qh5+ Kxh5 Bg6+ Kxg6 Rg5+ Kh7 Rg7+ Kh8 Rh7+ Kg8 Rh8+ Kg7
>Rh7+ Kf8 Rh8+ Ke7 Re8+ Kd7 Rd8+ Kc7 Rd7+ Kb8 Rb7+ Ka8 Rb8+ Kxa7 Rb7+ Kxa6 Ra7+
>Kb5 Rxa5+ Kb4 Rb5+ Ka3 Rb3+ Ka2 Rb2+ Ka1 Ra2+ Kb1 Rb2+ Kc1 Rb1+ Kc2 Rb2+ Kd1
>Rb1+ Ke2 Re1+ Kxf2 Re2+ Kg1 Rg2+ Kh1 Rg1+ Kh2 Rh1+ Kg2 Rg1+ Kh3 Rxg3+ Kh4 Rh3+
>Kg5 Rh5+ Kg6 Rg5+ Kh7 Rg7+ Kh8 Rh7+ Kg8 Rh8+ Kg7 Rh7+ Kg6 Rg7+ Kh5 Rg5+ Kh4 Rh5+
>Kg3 Rh3+ Kf2 Rxf3+ Ke2 Rxe3+ Nxe3+ Ke5 d4#;

Amazing!  :-O

Heiner



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