A half-point ko is the common term for a ko in which nothing is at stake beyond the fate of the stone inside the ko.
Often go games end with a fight over such a ko. (These fights are not shown in professional game records, as a rule. Instead the winner is indicated.) It is rare to have a play smaller than this but larger than a Japanese dame.
Bob Myers: What play could be smaller?
Bill: Depending upon komaster, there are kos worth 1/4 and 1/5 point. I constructed the 1/5 point ko; 1/4 point kos show up occasionally in real games but are unrecognized as such.
Bob Myers: Where are these documented?
Bill: I misspoke. There are 1/4 point ko positions. (By the time a ko has appeared, the ko is hotter.) Here is an example, with Black komaster.
-
= threat and reply
elsewhere
takes ko
-
= threat and reply
takes ko
elsewhere
fills ko (
)
elsewhere
Black has gained 1 point with 4 net local plays, each worth, on average 1/4 point.
Despite the name, the miai value of connecting or capturing in a half-point ko is only one third of a point. But if we do not know the winner of the ko fight, who gets the point at stake is a 50-50 proposition, and the term makes sense.
See /Calculation? for determining the value of this ko.
See /Name? for suggestions for naming this ko.
See also Real Half Point Ko