Ko fight Example 2
Lets have a look at an example.
White has played . This starts a ko for the life and death of the black group.
How much is the ko worth? In this case the ko is worth 20 + 3 = 23. What is the score, ignoring the ko? Black has 29 points, white has about 26. So black can't afford to ignore , and must fight the ko.
In simple terms, if the value of the ko is greater than the value of your opponent's ko threat plus your next ko threat, you should ignore the threat and win the ko.
N. B.: This advice is inaccurate because it ignores the value of sente.
Black has ko threats at a, b, g, h and e.
White has ko threats at f, c and d.
How much is each threat worth? To calculate the value of a threat, working out how many points the player gains if the threat is ignored.
a is worth 8 points
b is worth 6 points
c is worth 24 points
d is worth 24 points
e is worth 2 points
f is worth 18 points
g is worth 6 points
h is worth about 4 points
Arranged in pairs in descending order, we get:
So, play should go as follows:
White plays c. 24 + 8 > 23, so black answers the ko threat, and white retakes the ko.
Black plays a. 8 + 24 > 23, so white answers the ko threat, and black retakes the ko.
White plays d. 24 + 6 > 23, so black answers the ko threat, and white retakes the ko.
Black plays g. 6 + 18 > 23, so white answers the ko threat, and black retakes the ko.
White plays f. 18 + 4 < 23, so black ignores the ko threat.
Black plays some forcing moves, and in this game, Black loses by 6 points. What would have happened if black had answered that last ko threat?
In that case white should ignore black's next threat and win the ko. Black loses this game by 13 points
tapir: The point here is that White is what Bill would probably call ko-monster in so far as it can answer even to too small ko threats because that decreases the compensation for Black further. But why if you win the game anyway?