Author: Robert Hyatt
Date: 16:42:03 02/14/06
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On February 14, 2006 at 19:04:52, David B Weller wrote: >I was just thinking about knight forks, and thought of yet another way an engine >can 'delude itself' > >Lets say, white can fork black, but it is at the horizon. 0 depth remaining > >Now if black _HAS_ any captures, they will allow white to play its capture and >the gain of the fork will be realized > >But all black has to do, to make the position seem better, is retract any >threats it has, and poof! the fork disappears [search ends with white's knight >move, and it never gets to play the capture] > >I suspect there are a ton more rediculous things going on at the horizon that I >havent even thought of...what else is lost at the horizon!?!?! > >Delay type threats, capture/recaptures, hiding double attacks, .... > >I wonder, if there are so many different types of these things, and it isnt >really worth trying to catch the few I have found by, eg., recap extension, >threat extensions, etc... > >Thoughts? There are dozens of ways this show up. Pawn pushes to 6th, but not 7th and then promotes. Mate threat on g7 with Ph6 and Qf6, but the losing side does enough things to use up all the depth before Qg7# is found and the q-search probably won't find it (non-capture). The list goes on and on for simply pushing the bad thing away via checks and captures. It gets worse when you start tossing pawns to save a knight that can't be saved. That's the point of search extensions, extend checks not because you think they lead to mate, but because you want to make sure they are not delaying moves that push something bad beyond the horizon. Ditto for recaptures. What better delaying tactic than to capture a rook, requring your opponent to burn a ply and recapture, so that he won't then see that he can later capture that trapped knight that your capture just "saved"..
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