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Subject: Re: ECM errata (151 thru 200)

Author: Ernst A. Heinz

Date: 10:06:35 01/20/98

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On January 20, 1998 at 10:49:03, Amir Ban wrote:

>No. 153 (Qd8):
>
>Right, but Qd6 is equally good.
>
>Recommend: Add Qd6 as side solution.

Yes, at high depths both score > +11.

>No. 162 (Rd7+):
>
>I find Rb8 which also wins, though Rd7+ analysis proves it's correct.
>
>Recommend: No change, or add Rb8 as side solution.

Maybe Rb8 also wins but "DarkThought" sticks to Rd7+ from iteration #9
(score = +1.8) and fails high on it in iteration #11 with a score of
+3.4.

PV = 1. Rd7+ Bxd7 2. Nd5+ Ke8 3. Qf6 Ng7 4. Be5 Qxe5+ 5. Qxe5+ Be6 ...

>No. 180 (Bd4):
>
>This must be a typo. Correct is Bc4.
>
>Recommend: Change key to Bc4.

"DarkThought" agrees (score = +3.1 after iteration #14).

>No. 186 (Nxh6):
>
>Nxh6 is crushing. I find Qe8 which is good for only +4.
>
>Recommend: Add Qe8 as side solution.

R1b7 seems to be good as well -- actually, there seem to be
many good moves in this position. If none of them clearly
stands out, I would drop the position.

>No. 187 (Nxe7):
>
>A hard one for me. The object of Nxe7 was not clear but after Nxe7 Nxe7
>Rb3 it turns out that it's correct, and is meant to decoy the knight so
>as to trap the black queen.
>
>Recommend: No change.

Yes, this position is very difficult and it is solved correctly only if
the program scores the resulting position > +1.5 -- otherwise
alternative
moves like e.g. Bb5 seem to score equally well (around +1).

>No. 190 (Nd7):
>
>I can't attach any meaning to the key move. I find Ne7+ so this may be
>another typo. Ne7+ Kh8 Rd8! looks correct but doesn't do more than win a
>pawn.
>
>Recommend: Change key to Ne7+.

"DarkThought" agrees.

>No. 191 (Bd3):
>
>I have difficulty in finding the key move, but Bd3 Qxd3 Rg1+ is indeed
>crushing. I do find Qd4 for a score of 3.5.
>
>Recommend: No change.

"DarkThought" scores both Qd4 and Bd3 > +5 in iteration #13 but finally
sticks to Bd3 with a score of +6.9 after iteration #14.

I would add Qd4 as a side solution.

>No. 193 (Nb6):
>
>Correct, but a tough one, because there's an apparent defense that
>ultimately fails. The idea is 1.Nb6 Nxb6 2.Rc7 Qxc7 3.Qxe6+ wins.
>Apparently black has 2...e5, which closes out the bishop and holds, but
>further analysis shows that 3.Rxd7 Rxd7 4.Qe6+ Kh8 5.Nf7+ Kg7 6.Bc1
>wins.
>
>Recommend: No change.

This position seems to be prone to "right" solutions due to wrong
reasons again or 2.. h5 is a refutation of the winning plan.

"DarkThought" finds Nb6 in iteration #10 after 28 sec with a draw score
(PV = 1. Nb6 Nxb6 2. Rc7 h5 3. Qe4 Qe8 4. Qxe6+ Kg7 5. Bb2+ Kh6 ...) and
does not see a win within 10 min after finishing iteration #14.

>No. 198 (Ba6):
>
>I find Nc5 immediately. It's easy and wins a whole rook. Don't know what
>the point of Ba6 was, but looks like they overlooked the simpler and
>better possibility.
>
>Recommend: Change key to Nc5.

"DarkThought" agrees, Ba6 scores only +3.4 whereas Nc5 gets > +5.

=Ernst=



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