Remove double threats before you first capture the ko

  Difficulty: Intermediate   Keywords: Ko

The 'double threat' concept is defined at Mutual ko threat, and depicted at ko threat playing order. Another particular example is given at an example of removing a local threat.

As preparation for making first capture in a ko fight, one ought to remove the double threats by playing out each of these situations.

The logic is this: if you leave any double threats on the board when you first capture in the ko, your opponent can immediately play all of them as one 'long ko threat', and then retake in the ko. This has an unfavourable effect on your stock of ko threats, equivalent to losing one threat (for nothing at all).

That is, suppose before the ko fight starts there are identifiable double threat pairs P(B), P(W), Q(B), Q(W) and so on (where P(B) for example is Black's local play in one such situation). Then if Black has first capture in the ko fight, Black before capturing ought to play out the whole sequence

  1. Black P(B)
  2. White answers P(W)
  3. Black Q(B)
  4. White answers Q(W)

in some order, until no double threats remain. All significant double threats should be removed, in one pass, by Black, before the ko starts.

This theoretical idea is important for any algorithmic approach to ko fights, and for any serious discussion of preparation ahead of ko fights. It should of course be qualified in some ways:

  • if it isn't quite clear that Black's play P(B) will be sente, that might make it very doubtful;
  • if the potential ko threats are loss-making, that may also change the decision.

The points here are that what matters most is that one shouldn't give the opponent a large, good threat for nothing; and that ko fights are supposed to be a source of profit, so that loss-making threats are rigorously avoided (and welcomed if the opponent plays them).

See also Ko Threat in Seki Example for a complex case.


Remove double threats before you first capture the ko last edited by Dieter on January 9, 2013 - 18:52
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