# Computer Chess Club Archives

## Messages

### Subject: Re: The Limits of Positional Knowledge

Author: Bella

Date: 12:25:40 11/19/99

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```On November 18, 1999 at 17:46:36, KarinsDad wrote:

>On November 18, 1999 at 16:38:41, Bella Freud wrote:
>
>[snip]
>>
>>
>>I agree that with a sequence
>>
>>a x b y c z d
>>
>>that if d is a bad move that only manifests itself over the horizon, then it is
>>dangerous to have backed that best line and score back to the root.
>>
>>If d loses then there is a danger that a loses.
>>
>>The shorter the line the greater the danger and the longer the line the less the
>>danger, since side 'a' can deviate from b,c,d,e,f,g,h in the move sequence.
>>
>>Or, that the deeper the line, the less chance there is that the position at d is
>>so important, thus causing a to lose.
>>
>>Depth therefore helps bad evaluation functions to play better chess, in the
>>sense that search applied at the next few moves allows for escapes from the
>>consequent trouble. Such a system is just playing obstructionist chess.
>>
>>
>>Bella
>>
>
>Yes, but wouldn't that imply that all programs play obstructionist chess until
>we get to the level that chess is solved (or up to the point that they hit the
>tablebases)?

Au naturelle. I imply just that. Well spotted.

>
>In other words, trouble for most programs can come in one of three basic ways:
>loss of game, loss of material, loss of positional factor (regardless of whether
>the program is able to determine that). So, no matter how far you search and no
>matter how good your evaluation is, there will always be a horizon effect. This
>in turn implies that any program within any given game could always be walking
>towards a cliff and not know it,

Exactament.

just due to the peculiarities of the given
>game/position and although a program (just like a human) might be capable of
>avoiding a given cliff once it comes within view, even the act of avoiding it
>may and most likely will be sending the game towards another cliff (i.e. the
>positional/material factors of the game may have a great likelihood of resulting
>in many cliffs or landmines in a given direction, not just one).

My words exactly.

Except I would not have used "most likely" because the deeper the search the
"less likely".

>