Author: blass uri
Date: 12:47:03 05/13/00
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On May 13, 2000 at 15:25:21, blass uri wrote: >>It may not have to generate _all_ the ply=1 moves to find the mate. It >>certainly has to try them _all_ before it can prove there isn't a mate. >>And that is the problem.. 99% of null-move positions cause no problems at >>all... it is the <1% that is the issue. But the test has to be done for >>_all_ positions. > >I understood that the idea behind chest is that it has not to try all the ply=1 >moves to find that there is no mate in 2(it is obvious for mate in 1 when you >need to generate only threat king moves but I understood that it is also >possible to do it for mate in 2). > >Chest knows for every piece the squares that it controls so it knows the squares >need to be controled in order to do mate. > >If it is obvious from the starting position of the pieces that they cannot >control the relevant squares in 2 moves then you can discover that there is no >mate in 2 without generating moves. > >Uri Here is a better explanation from the file mate2.c of chest. The basic idea is to detect impossibilities for a mate in 2 moves * not by detecting aggressive defender moves (that is done by fac), * but rather by missing activity of the attacker. * * We assume that the defender will do a K-move (defender strategy). * We must guarantee the legality of the defender move. * * Then for all the legal attacker moves (move list, 2-mate candidates), * we try to verify, without really executing the move, that after this * move, * - the indended defender move is legal, and * - no further attacker move can complete the mate net around defK. * You can see from the explanation that chest try to verify without really executing that after the move there is no mate. Uri
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