Author: Joachim Rang
Date: 06:04:39 02/11/06
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On February 11, 2006 at 08:53:11, Tord Romstad wrote: >Hi Andre, > >Thanks for your help! Thanks also to H.G. Muller for the interesting >comments. > >On February 11, 2006 at 08:21:22, Andre Reffhaug wrote: > >>Rybka settles down with mate in 16 after a couple of minutes. Fruit gives Rxh7+ >>+21.5 after 10 minutes of thinking, and Hiarcs 10 has a mate in 20 after 13 >>minutes. > >Good to know that there is a forced mate, at least. Nevertheless, after some >more testing, I am convinced that I have a bug. In the following position (also >from LCT2), Glaurung announces mate in just 7 moves after only a second >of thought: > >[D]2b1r1k1/r4ppp/p7/2pNP3/4Q3/q6P/2P2PP1/3RR1K1 w - - > >The search output: > >2 +34 26 134 Rd3 Qb2 >3 +40 26 605 Rd3 Qb2 Rg3 >4 +43 26 1404 Rd3 Qb2 Rg3 a5 >5 +54 27 5601 Rd3 Qa5 Rg3 Bf5 Nf6+ Kh8 >5 +68 28 11070 Re3 Qb2 Rg3 Qxe5 Nf6+ Kf8 Nxh7+ Kg8 >6 +51 29 14451 Re3 Qb2 Rg3 Kh8 Rg5 g6 >7 +40 33 33900 Re3 Qb2 Rg3 Kh8 Rg5 f6 Rh5 >7 +223 34 40308 Nf6+ gxf6 exf6 Rf8 Rd8 c4 Rxc8 Kh8 Qxc4 >8 +232 39 63318 Nf6+ gxf6 exf6 Rf8 Rd8 c4 Rxc8 Kh8 Qxc4 a5 >9 +864 52 142958 Nf6+ gxf6 exf6 Rf8 Qh4 Qd3 Rxd3 Bf5 Qg5+ Bg6 Qxc5 Bxd3 Qxa7 >Bxc2 Qxa6 >10 +864 58 175843 Nf6+ gxf6 exf6 Rf8 Qh4 Qd3 Rxd3 Bf5 Qg5+ Bg6 Qxc5 Bxd3 Qxa7 >Bxc2 Qxa6 >11 +909 73 289161 Nf6+ gxf6 exf6 Rf8 Qh4 Qe3 Rxe3 Bf5 Qg5+ Bg6 Qxc5 Raa8 Rd7 >Rab8 >12 +1239 103 518008 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Bf5 Qxc5 Raa8 Qxf5 Kh8 Re7 >Rab8 >13 +9987 128 679813 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >14 +9987 161 942794 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >15 +9987 219 1391173 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >16 +9987 333 2314397 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >17 +9987 517 3762627 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >18 +9987 850 6446616 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 Rd8# >19 +9987 1397 11025335 Nf6+ gxf6 exf6 Rf8 Qf4 Qe3 Qxe3 Kh8 Qg5 Rg8 Qxg8+ Kxg8 >Rd8# > >This mate in 7 is obviously incorrect. When I force 1. Nf6+ Kf8, Glaurung >no longer sees a mate. Clearly a bug. > the above mate is indeed incorrect. However as Maarten has pointed out the initial position which you posted is indeed a mate in 14 (checked with a couple of engines in backward analysis). In the second position after Nf6+ gxf6 it is a mate in 6, the question is, why Glaurung prunes away the better answer Kf8? regards Joachim
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