Komaster
Professor Elwyn Berlekamp coined the term, komaster, for the person who can win a ko (or superko) fight without having to ignore a ko threat. The opponent is the koloser. It is possible, of course, that a ko has neither komaster nor koloser.
(The above is an informal explanation. For Berlekamp's original treatment, see http://www.msri.org/publications/books/Book29/files/ber.pdf.)
For certain kos, such as approach kos and ten thousand year kos, the count depends on who is komaster. Such kos, and similar ko positions, are called hyperactive. In some ko positions, who is komaster does not affect the count, but does affect the miai value; Bill Spight coined the term active for such positions. Other ko positions are called ''placid''.
Example of how who is komaster affects the count of an approach ko:
elsewhere.
-
= ko threat and response.
takes the ko.
elsewhere.
If Black is komaster, White has nothing better than to make the approach move and convert this to a regular ko. Assuming that a is White's territory, the local score is 14. Since this is, in effect, White's sente, that is the count of the original position.
elsewhere.
takes ko.
-
= ko threat and reply.
takes the ko.
,
elsewhere.
If White is komaster she can win the ko in three net plays, for a local score of -12. Black can win the ko in 1 play at a, for a local score of 15. (Black 3 will be Black sente later. four plays make a difference of 27 points, so the miai value of the ko is 6 3/4, and this position has a count of 8 1/4. Who is komaster makes a difference of 5 3/4 points.
Note that the komaster won the ko after using only one ko threat. That threat was enough to make her komaster. If a komaster can gain from using additional ko threats to delay winning the ko, she is ko monster.
For more, see the Forum and /Discussion.
When Bill talks about "ko threats" here, I believe he is basically referring to sufficiently big sente moves. If a gote move is big enough to distract your opponent from finishing a ko, then it suggests that the ko was probably too small to be worth fighting yet. If big gote moves are the best "ko threats" you can find, then by this usage, you have no ko threats.
Some ko fights, including many ordinary direct kos, don't require ko threats, because the alternative to winning the ko is just as good -- this is often true, since kos become interesting when they have roughly the same miai value as the biggest plays elsewhere. If losing the ko is as good as winning it, then why waste ko threats you might need later?
Ko threats become important when ordinary moves elsewhere are worth less than winning the ko. When you're fighting that last tiny ko that ends the game, the ambient temperature is zero. When a complex situation turns into an all-or-nothing ko, that ko may be very hot. And as Bill discussed, turning an approach ko into a direct ko can raise the local temperature.
-- EricB
Also see virtual-force.