Value of a Ko Threat

  Difficulty: Introductory   Keywords: Ko

Several possible meanings.

  1. Black makes a ko threat, White ignores it, Black follows up the 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.
  2. 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).
  3. Black makes a ko threat, White ignores it, Black follows up on the threat. (So to say, a dead end threat).
  4. 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 systemically 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 Cherles Matthews briefly exploring different ideas. As for the ko threat evaluation page, it is not really about ko threat evaluation, either. ;)

See also


Value of a Ko Threat last edited by tapir on December 15, 2012 - 01:49
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