Real Half Point Ko
This article demonstrates a ko whose miai value really is ½, unlike a so-called “½-point ko”, whose miai value is ⅓.
So-called half point ko
This ko, commonly known as a half point ko, has a miai value of only ⅓.
As a rule, there will be no smaller plays between this ko and dame, so that the only question is who wins the ko, and it will behave as though it were a half point ko. When there are many of them, however, with one player leading in most of them, that player can expect ⅓ of a point for all that remain after cancelling those where their opponent leads with ones where they lead; see the section Half-point-ko § Playing order of third-point kos for details.
Real half point ko
elsewhere
Black wins the ko with
, unless that is ko-banned in which case Black wins the ko with
. Either play is sente and White responds at
.
In the end White will net only 2 points of territory locally.
A net difference of two plays in the ko makes a net difference of one point. Each play has a miai value of 1/2.
Real half point ko, komaster dependent
Result: 0.
A difference of two moves makes a difference of one point, so the miai value of the ko is 1/2.
elsewhere.
-
= ko threat and reply.
takes ko back.
elsewhere.
at
.
Result: 0.
Again, a difference of two plays makes a difference of one point. Miai value of ko = 1/2.
When Black is komaster the ko has a miai value of 7/12.
elsewhere.
takes ko.
-
= ko threat and reply.
takes ko.
Result: +2/3. (Black has taken one stone for one point, minus 1/3 point for the black stone in ko.)
After
the local temperature drops to 1/3. Black has a sente sequence with
-
.
Two plays make a difference of 1/2 + 2/3 = 7/6 points. The miai value of the ko is 7/12.
-- Bill Spight
See also:
![[Diagram]](../../diagrams/8/752691690da27ddf58862a351d267dab.png)
![[Diagram]](../../diagrams/1/aa49079b3adadb893bb50ff54315a25c.png)
![[Diagram]](../../diagrams/34/0fd24c40c46ca4e1ffb29860e0b57390.png)
![[Diagram]](../../diagrams/39/e56c001af8095024948d461c87958122.png)
![[Diagram]](../../diagrams/30/0d40b201b0820066f5008a4f408c9b0c.png)
![[Diagram]](../../diagrams/26/35ec6aac8cc403f892bfb60b22762ce9.png)
![[Diagram]](../../diagrams/14/a260d5ff204d036d0898e5d0374f5328.png)
.
![[Diagram]](../../diagrams/1/8ecbf224fc26a2ca92047abefedb46b8.png)
![[Diagram]](../../diagrams/0/6a1114628df81c357a2572175b3cb731.png)
-
(ko threat) and reply.
takes the ko back.
elsewhere.
at ![[Diagram]](../../diagrams/37/3960681490d00976ec56f11619376ad3.png)
![[Diagram]](../../diagrams/27/f9206815c6d1805efc77685337c1a065.png)
fills, leaving a 1/2 point play at a.
![[Diagram]](../../diagrams/41/bb31a6b9abe728c7f080fd5b8e85db60.png)
2024 the Authors,
published under the ![Sensei's Library [Welcome to Sensei's Library!]](../../images/stone-hello.png)