1) An extreme form of one-sided (hanami) ko fight. The capture by one of the players, Black say, has such a large potential follow-up that White must treat it as a sente play.
Such a ko position, at a given stage of the game so that it really is a sente ko, will not give rise to an extended ko fight. But it is possible sometimes for White to capture once, even in such a fight. The reason is that Black must find some ko threat. White therefore has a chance to make Black use one threat.
2) A ko such that taking the ko is sente for one player. Here is a small example.
(N. B. By convention, stones adjacent to empty space are alive.)
If White takes the ko she raises the local temperature (from 1/3 to 7/9) by threatening to take again.
But see Ambiguous Ko.
Another example:
If White takes the ko she raises the local temperature from 1 2/3 to 2 1/3.
This kind of sente ko is fairly common. They do favor the player with sente, but the sente threat is not so large that they are unfightable, as a rule.
3) A ko such that winning it is sente for one player. Here is an example.
If Black fills, the White group dies. But if White takes and wins the ko,
White threatens to kill the Black group with White 1. This is worth 16 1/3 points, miai, hotter than the original ko position, in which a play is worth only 12 2/3 points.
If White wins the ko in sente, later Black 1 is a 1 2/3 point sente ko, where taking the ko is sente.
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