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Subject: Two WAC positions

Author: Tord Romstad

Date: 08:53:02 10/21/03


I don't run my engine through WAC very often, but before releasing a new
version (which I will do within a couple of days) I run the whole suite as
a sanity test.  This time, the following position made me worried:

[D]8/8/2Kp4/3P1B2/2P2k2/5p2/8/8 w - - bm Bc8; id "WAC146";

Previously, my program had no problems with this position.  The new
version, which is the first one to include tablebase support, prefers
Bd3 instead of Bc8.  At ply 21, the score is +12 for white.  When I
disable tablebases, the program plays Bc8.

Does Bd3 also win, or should I look for yet another bug?

One of the hardest positions in WAC for my engine is number 163:

[D]5rk1/2p4p/2p4r/3P4/4p1b1/1Q2NqPp/PP3P1K/R4R2 b - - bm Qg2+; id "WAC163";

On a Pentium IV 2.4 GHz, I need 11 plies and 1m53s to find the winning move.
The problem is to find the line 1... Qg2+ 2. Nxg2 hxg2+ 3. Kxg2 Bf3+ 4. Qxf3
exf3+ 5. Kg1 Rf5! followed by Rfh5.  Without nullmove pruning, this position
is solved within a few seconds.

This is rather annoying, as I have lost more games than I would like on
the ICC because of missing similar tactics.  Are there any inexpensive
tricks to help me solve this kind of positions more quickly?

Tord



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