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Subject: Re: Howard's positional sacrifice test

Author: Ed Schröder

Date: 02:12:19 12/02/99

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>rnbq1rk1/p3nppp/1p2p3/2ppP3/3P4/P1PB1N2/2P2PPP/R1BQK2R w KQ - bm Bxh7+;

Aha, a standard Bxh7+ case, it made the Novag Constellation world famous :)

Another nice positional sacrifice later proven right by search. On ply 5 Rebel
sacs the bishop in return for a strong king attack, no material gain is involved
sofar, see Rebel's main-line. On ply 7 the sac is proven right as the score goes
up to 2.15.

Bob, sofar Rebel's king safety is doing well, no errors seen yet :)

Please recover soon BTW.

00:00:00  4.00  0.34   1.Ng5 g6 2.O-O c4 3.Be2 h6 4.Nf3
00:00:00  5.00  0.40   1.Ng5 g6 2.O-O c4 3.Be2 Ba6
00:00:01  5.26  0.40   1.Bxh7+
00:00:01  5.26  0.63   1.Bxh7+ Kxh7 2.Ng5+ Kg6 3.h4 Qe8
                       4.Qg4  (1)

00:00:01  6.00  0.72   1.Bxh7+ Kxh7 2.Ng5+ Kg6 3.h4 Qe8
                       4.Qd3+ f5 5.h5+ Kh6 6.Nxe6+ Kh7
                       7.Nxf8+ Qxf8  (1)

00:00:03  7.00  2.15   1.Bxh7+ Kxh7 2.Ng5+ Kg8 3.Qh5 Re8
                       4.Qh7+ Kf8 5.Qh8+ Ng8 6.Nh7+ Ke7
                       7.Bg5+ Nf6 8.exf6+ Kd7 9.Qxg7  (1)

00:00:05  8.00  2.57   1.Bxh7+ Kxh7 2.Ng5+ Kg6 3.h4 Qe8
                       4.Qg4 Nf5 5.Nxe6+ Kh7 6.Qxf5+ Kg8  (3)

00:00:49  9.00  2.22   1.Bxh7+ Kxh7 2.Ng5+ Kg6 3.h4 Qe8
                       4.Qg4 Nf5 5.dxc5 bxc5 6.Nxe6+ Kh7
                       7.Qxf5+ Kh8 8.exf6+  (10)


>3r3k/p1b3p1/2R1pr1p/3q4/3PQ3/5p2/P4PPP/B3R1K1 b - - bm Bxh2+;

No positional sacrifice here. Bxh2+ is found by normal search at ply 7.

00:00:04  7.00  0.04   1..Bd6 2.Qxd5 exd5 3.g3 Rb8 4.Bc3
                       Kh7 5.Ba5  (3)

00:00:09  7.16  0.04   1..Bxh2+
00:00:18  7.16  1.60   1..Bxh2+ 2.Kxh2 Qh5+ 3.Kg1 fxg2
                       4.Kxg2 Rg6 5.Kf1 Rg4 6.Qf3 Rg1+
                       7.Kxg1 Qxf3 8.Rcxe6  (9)

Thanks John for the positions. It allows me to waterproof an important part
of my chess program. I will try to extract some positional sacrifices from
my own databases and post them.

Ed




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