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  1. 30 Jan '12 19:35
    A queen's ending from 1972, find white's winning move:



    will post if someone gets it right
  2. 30 Jan '12 19:43
    the obvious move is a8 queening which is winning if there are no stalemate tricks available for black. Unfortunately there is. If you figure out this stalemate trick you almost have the solution
    /hint
  3. 30 Jan '12 21:48
    The only way that I can see of getting mate is by promoting the pawn to a bishop, but I needed the hint.
  4. 31 Jan '12 01:03
    yes this is correct 🙂 funny thing is also that i analyzed this with an engine, and it doesnt find the correct move even with depth 26
  5. Subscriber sonhouse
    Fast and Curious
    31 Jan '12 03:29
    Originally posted by tolleh
    yes this is correct 🙂 funny thing is also that i analyzed this with an engine, and it doesnt find the correct move even with depth 26
    First thing I thought of was promoting to a knight. That seems also enough to win, no stalemate from the check with the black queen.
  6. 31 Jan '12 03:56
    why would someone who has never moved and only joined the day before post this ??

    not suggesting anything just interested in how they would and how they would know how to etc etc etc
  7. 31 Jan '12 08:31 / 1 edit
    Originally posted by tolleh
    yes this is correct 🙂 funny thing is also that i analyzed this with an engine, and it doesnt find the correct move even with depth 26
    I'm guessing you used Rybka which doesn't support underpromotion to bishop (an optimisation in the code). Other top engines find it immediately.

    I solved it myself through a process of elimination... can't do that... can't do that... so that only leaves...
  8. 31 Jan '12 11:49
    Originally posted by Varenka
    I'm guessing you used Rybka which doesn't support underpromotion to bishop (an optimisation in the code). Other top engines find it immediately.

    I solved it myself through a process of elimination... can't do that... can't do that... so that only leaves...
    Out of interest, why doesn't Rybka support this? Why is eliminating a rule that may be your only way to win a game (as demonstrated above) an 'optimisation'?
  9. 31 Jan '12 12:12
    Originally posted by Rank outsider
    Out of interest, why doesn't Rybka support this? Why is eliminating a rule that may be your only way to win a game (as demonstrated above) an 'optimisation'?
    http://rybkaforum.net/cgi-bin/rybkaforum/topic_show.pl?tid=1042

    Vasik Rajlich is the Rybka author so you can see his posts there.
  10. 31 Jan '12 12:30
    Originally posted by Varenka
    http://rybkaforum.net/cgi-bin/rybkaforum/topic_show.pl?tid=1042

    Vasik Rajlich is the Rybka author so you can see his posts there.
    Funny attitude he has. Why disable some rules, because generally they are rare? En Passants are also rare...

    A few of my games here on RHP I have underpromoted, because of the stalemate risque. So I don't see them as sooo rare after all.
  11. 31 Jan '12 12:49
    Hi V.

    I read that link. Quite funny. I like this bit.

    "You must understand that Rybka will lose chess strength if Vas adds that option."
    (adding under promotion to a Bishop as a valid option.)

    OK coaches. New Rule No.103.
    Do not teach your students how to under promote.
    Doing so will make them weaker.

    Is Rybka not a clone of another program? I know Rybka was stripped of all
    it awards. Does the program it copied have the same trouble?

    I know the earlier programs of Fritz had trouble finding simple mates in two
    in certain positions.

    This one stumps Fritz 6 (I think I have the mark correct.)

    White to Play Mate in Two.

    The solution is 1.Re1 Kxe1 2.Qd2 mate. Simply enough but Fritz failed.

    Yet here. White to Play Mate in Two.

    The same program finds the mate in 2 in a second. (it's the same solution 1.Re1 and Qd2 mate.)
  12. 31 Jan '12 16:19
    Originally posted by FabianFnas
    Funny attitude he has. Why disable some rules, because generally they are rare? En Passants are also rare...

    A few of my games here on RHP I have underpromoted, because of the stalemate risque. So I don't see them as sooo rare after all.
    I think it is only bishop underpromotion that is not covered. And in the above example, would not underpromotion to knight work?

    In fact, is there any real-life example of a game that anyone is aware of where underpromotion to a bishop is the only way to win?

    One for Greenpawn I think.

    (Loving the Kindle, by the way 😉)
  13. 31 Jan '12 16:37
    Originally posted by Rank outsider
    I think it is only bishop underpromotion that is not covered. And in the above example, would not underpromotion to knight work?

    In fact, is there any real-life example of a game that anyone is aware of where underpromotion to a bishop is the only way to win?

    One for Greenpawn I think.

    (Loving the Kindle, by the way 😉)
    Err....winning with the knight does not look easy. But then again, I would have probably struggled with the bishop.
  14. 31 Jan '12 17:38
    Originally posted by greenpawn34
    Is Rybka not a clone of another program? I know Rybka was stripped of all
    it awards. Does the program it copied have the same trouble?
    There's a big debate that I'm not clued up on. I think the claim is that an early version of Rybka used some - not all - code from another engine called Fruit. I don't think Fruit has this bishop underpromotion issue but that doesn't settle the clone claim.
  15. 31 Jan '12 20:43 / 1 edit
    Valid under promotions to a Bishop are very rare.

    Here is a nice example. Tomic -v- Winzbeck, Dortmund 1993



    Tim Krabbe has gathered together quite a few examples of under promotions.

    http://timkr.home.xs4all.nl/chess2/minor.htm