Value of a Ko Threat
Several possible meanings.
- Black makes a ko threat, White ignores it, Black follows up his threat and White feels obliged to answer that play, leading to a settled position. Count the swing that makes, based on comparison with the ordinary plays in that part of the board. That number is the value to Black of the threat.
- Valuation, probably approximate, in the same context as 1 but open-ended (no assumption that White answers Black's follow-up so that Black emerges with sente).
- Black makes a ko threat, White ignores it, Black follows up on the threat. (So to say, a dead end threat).
- Valuation of a 'ko threat not intended as a threat', plus a second such, ie of Black making two plays in a row while White captures and finishes the ko.
One can also speak of the value of a ko threat that is answered. If the move played as a threat was for example a one-sided sente endgame play, its value isn't normally of serious importance (it was anyway the prerogative of the player). If the value is negative - the threat is loss-making - that's something to be taken very seriously before playing it.
This topic is further discussed mathematically at Ko Threat - Rule of Thumb.
tapir: Confusing - is it really good to distinguish these cases systematically as different meanings of value?
Bill: If this page is confusing, it is at least in part because there is no single way of thinking about the value of a ko threat. It is an essay by Charles Matthews briefly exploring different ideas. As for the ko threat evaluation page, it is not really about ko threat evaluation, either. ;)